CN115172749A

CN115172749A - Electrochemical device and electronic device

Info

Publication number: CN115172749A
Application number: CN202210644961.0A
Authority: CN
Inventors: 王可飞; 韩冬冬; 郭俊; 刘胜奇
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2020-10-15
Filing date: 2020-10-15
Publication date: 2022-10-11
Also published as: CN112151855B; CN115101802A; CN112151855A

Abstract

The present application relates to an electrochemical device and an electronic device. Specifically, the present application provides an electrochemical device comprising: an electrode including a current collector, an intermediate layer on the current collector, and an active material layer on the intermediate layer, wherein the intermediate layer and the active material layer have a specific area ratio, and an electrolyte including a compound containing a sulfur-oxygen double bond. The electrochemical device of the present application has improved direct current internal resistance and safety performance.

Description

Electrochemical device and electronic device

The present application is a divisional application of an invention patent application having an application date of 2020, 10/15, and an application number of "202011101160.7" entitled "electrochemical device and electronic device".

Technical Field

The present application relates to the field of energy storage, and in particular to an electrochemical device and an electronic device, in particular a lithium ion battery.

Background

As technology advances and the demand for mobile devices increases, various demands for electrochemical devices (e.g., lithium ion batteries) are also increasing. While pursuing high endurance time, higher requirements are put forward on the performance of the lithium ion battery, especially the safety performance of the lithium ion battery.

Lithium ion batteries generally suffer from the following deficiencies or problems: the internal resistance of the battery is large, allowing a small current to be charged and discharged, resulting in a charge time that is too long (e.g., at least 3.5 hours for slow charge and at least 30 minutes for fast charge). When a lithium ion battery is charged and discharged at a high rate, a large amount of heat is generated due to the internal resistance of the battery. Due to the lack of effective means for uniformly radiating the heat of the lithium ion battery, the inside of the lithium ion battery is locally overheated, which not only accelerates the aging of the lithium ion battery, leads to the decline of the battery capacity and power performance, but also leads to the potential safety hazards of expansion, deformation and even explosion of the lithium ion battery.

In view of the above, there is a need for an electrochemical device and an electronic device having improved performance.

Disclosure of Invention

Embodiments of the present application address at least one of the problems occurring in the related art to at least some extent by providing an electrochemical device and an electronic device having improved direct current internal resistance and safety performance.

In one aspect of the present application, there is provided an electrochemical device comprising: an electrode and an electrolyte, the electrode comprising a current collector, an intermediate layer on the current collector, and an active material layer on the intermediate layer, wherein: the area ratio of the intermediate layer to the active material layer is A, and A is in the range of 0.9 to 1.1; the electrolyte includes a compound containing a sulfur-oxygen double bond.

According to an embodiment of the present application, the intermediate layer includes a conductive material having an average particle diameter of 1 μm or less.

According to an embodiment of the application, the electrically conductive material comprises at least one of carbon black, carbon fibers, graphene or carbon nanotubes.

According to an embodiment of the present application, the conductive material has a specific surface area of X m ² In the range of 20 to 300,/g, X.

According to an embodiment of the present application, the content of the compound containing a sulfur-oxygen double bond is Y% based on the weight of the electrolytic solution, and Y is in the range of 0.01 to 10.

According to the embodiment of the application, A and Y satisfy: 0.009A multiplied by Y is less than or equal to 6.

According to embodiments of the present application, X and Y satisfy: x is more than or equal to 0.2 and less than or equal to 200.

According to an embodiment of the application, the compound containing a thiooxy-double bond comprises at least one of the following compounds: cyclic sulfate ester, chain sulfonate ester, cyclic sulfonate ester, chain sulfite ester, or cyclic sulfite ester.

According to embodiments of the present application, the sulfur oxy-double bond containing compound includes a compound of formula 1:

wherein:

w is selected from

L is selected from a single bond or methylene, and two L in the same ring structure are not the single bond at the same time;

m is 1,2,3 or 4;

n is 0, 1 or 2; and is

p is 0, 1,2,3, 4, 5 or 6.

According to embodiments of the application, the compound of formula 1 comprises at least one of:

according to an embodiment of the application, the electrolyte further comprises at least one of the following compounds:

(a) Propionate esters;

(b) An organic compound having a cyano group;

(c) Lithium difluorophosphate;

(d) A compound of formula 2:

wherein:

R ¹ 、R ² 、R ³ 、R ⁴ 、R ⁵ and R ⁶ Each independently is hydrogen or C ₁ -C ₁₀ An alkyl group;

L ₁ and L ₂ Each independently is- (CR) ⁷ R ⁸ ) _n -；

R ⁷ And R ⁸ Each independently is hydrogen or C ₁ -C ₁₀ An alkyl group; and

n is 1,2 or 3.

According to an embodiment of the application, the compound of formula 2 comprises at least one of the following compounds:

according to an embodiment of the present application, the propionate is contained in an amount of a% based on the weight of the electrolyte, and a is in the range of 10 to 60.

According to an embodiment of the present application, the lithium difluorophosphate is present in an amount b% based on the weight of the electrolyte, b being in the range of 0.01 to 2.

According to embodiments of the present application, Y and b are satisfied; y/b is more than or equal to 0.01 and less than or equal to 100.

In another aspect of the present application, an electronic device is provided comprising an electrochemical device according to the present application.

Additional aspects and advantages of embodiments of the present application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the present application.

Detailed Description

Embodiments of the present application will be described in detail below. The embodiments of the present application should not be construed as limiting the present application.

The following terms used herein have the meanings indicated below, unless explicitly indicated otherwise.

In the detailed description and claims, a list of items connected by the term "at least one of can mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means a only; only B; or A and B. In another example, if items A, B and C are listed, the phrase "at least one of A, B and C" means a only; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and all of C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements. At least one of the terms has the same meaning as at least one of the terms.

As used herein, the term "alkyl" is intended to be a straight chain saturated hydrocarbon structure having from 1 to 20 carbon atoms. "alkyl" is also contemplated to be a branched or cyclic hydrocarbon structure having from 3 to 20 carbon atoms. When an alkyl group having a particular carbon number is specified, all geometric isomers having that carbon number are intended to be encompassed; thus, for example, "butyl" is meant to include n-butyl, sec-butyl, isobutyl, tert-butyl, and cyclobutyl; "propyl" includes n-propyl, isopropyl and cyclopropyl. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, and the like.

As used herein, the term "halo" refers to a partial or complete replacement of a hydrogen atom in a group by a halogen atom (e.g., fluorine, chlorine, bromine, or iodine).

With the widespread use of electrochemical devices, such as lithium ion batteries, their safety performance is receiving increasing attention. The safety hazard of the electrochemical device is mainly caused by internal overheating. When the lithium ion battery is charged and discharged with a large multiplying power, a large amount of heat generated inside the lithium ion battery cannot be uniformly dissipated, so that the aging of the lithium ion battery can be accelerated, and the lithium ion battery can generate potential safety hazards such as expansion, deformation and even explosion.

The present application aims to solve the above-mentioned problems by providing an intermediate layer having a specific area ratio to an active material layer between an electrode current collector and the active material layer while using an electrolyte solution including a compound having a sulfur-oxygen double bond in combination.

In one embodiment, the present application provides an electrochemical device comprising an electrode and an electrolyte as described below.

I. Electrode for electrochemical cell

One feature of the electrochemical device of the present application is that the electrode includes a current collector, an intermediate layer located on the current collector, and an active material layer located on the intermediate layer, an area ratio of the intermediate layer to the active material layer being a, a being in a range of 0.9 to 1.1. In some embodiments, a is 0.9, 1.0, 1.1, or within a range consisting of any two of the foregoing values. The intermediate layer can remarkably reduce the direct-current internal resistance and the thickness expansion rate of the electrochemical device and improve the safety of the electrochemical device.

In some embodiments, the intermediate layer comprises a conductive material having an average particle size of 1 μm or less. In some embodiments, the conductive material has an average particle size of 0.8 μm or less. In some embodiments, the conductive material has an average particle size of 0.7 μm or less. In some embodiments, the conductive material has an average particle size of 0.5 μm or less. In some embodiments, the conductive material has an average particle size of 0.2 μm or less. In some embodiments, the conductive material has an average particle size of 0.1 μm or less. When the average particle diameter of the conductive material is within the above range, it may not only improve the conductivity at the interface of the negative electrode current collector and the negative electrode active material layer, but also the interface thereof may become blurred, thereby improving the adhesion between the two. The conductive material is generally accumulated in a direction parallel to the surface of the negative electrode current collector, and is hardly stacked in a direction perpendicular to the negative electrode current collector. In this case, when the average particle diameter of the conductive material is smaller than that of the anode active material, the interface between the anode current collector and the anode active material layer containing the conductive material is very thin, which can significantly reduce the direct current internal resistance and the thickness expansion rate of the electrochemical device, improving the safety of the electrochemical device.

In some embodiments, the electrically conductive material comprises at least one of carbon black, carbon fibers, graphene, or carbon nanotubes. In some embodiments, the carbon black comprises at least one of acetylene black, furnace black, or ketjen black.

In some embodiments, the conductive material has a specific surface area of X m ² In the range of 20 to 300,/g, X. In some embodiments, X is in the range of 50 to 250. In some embodiments, X is in the range of 80 to 200. In some embodiments, X is in the range of 100 to 150. In some embodiments, X is 20, 50, 80, 100, 120, 150, 180, 200, 250, 280, 300, or within a range consisting of any two of the foregoing values. When the specific surface area of the conductive material is within the above range, it is helpful to further reduce the direct current internal resistance and the thickness expansion rate of the electrochemical device, improving the safety of the electrochemical device.

The specific surface area (BET) of the conductive material can be measured by the following method: the measurement was performed by a nitrogen adsorption BET single point method using a gas flow method using a nitrogen helium mixed gas in which a sample was pre-dried at 150 ℃ for 30 minutes under a nitrogen gas flow using a surface area meter (for example, a full-automatic surface area measuring apparatus manufactured by large-scale research), and then a relative pressure value of nitrogen gas with respect to atmospheric pressure was accurately adjusted to 0.3.

The electrode described herein can be either a positive electrode or a negative electrode.

Positive electrode

The positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on one or both surfaces of the positive electrode current collector.

1. Positive electrode active material layer

The positive electrode active material layer contains a positive electrode active material, and the positive electrode active material layer may be one layer or a plurality of layers. Each of the multiple layers of the positive electrode active material may contain the same or different positive electrode active material. The positive electrode active material is any material capable of reversibly intercalating and deintercalating metal ions such as lithium ions.

The kind of the positive electrode active material is not particularly limited as long as it can electrochemically occlude and release metal ions (for example, lithium ions). In some embodiments, the positive active material is a material containing lithium and at least one transition metal. Examples of the positive active material may include, but are not limited to, lithium transition metal composite oxides and lithium transition metal phosphate compounds.

In some embodiments, the transition metal in the lithium transition metal composite oxide includes V, ti, cr, mn, fe, co, ni, cu, and the like. In some embodiments, the lithium transition metal composite oxide comprises LiCoO ₂ Lithium cobalt composite oxide, liNiO, etc ₂ Lithium nickel composite oxide and LiMnO ₂ 、LiMn ₂ O ₄ 、Li ₂ MnO ₄ Lithium manganese composite oxide, liNi _1/3 Mn _1/3 Co _1/3 O ₂ 、LiNi _0.5 Mn _0.3 Co _0.2 O ₂ And lithium nickel manganese cobalt composite oxides in which a part of transition metal atoms that are the main components of these lithium transition metal composite oxides is replaced with another element such as Na, K, B, F, al, ti, V, cr, mn, fe, co, li, ni, cu, zn, mg, ga, zr, si, nb, mo, sn, W, and the like. Examples of the lithium transition metal composite oxide may include, but are not limited to, liNi _0.5 Mn _0.5 O ₂ 、LiNi _0.85 Co _0.10 Al _0.05 O ₂ 、LiNi _0.33 C0 _0.33 Mn _0.33 O ₂ 、LiNi _0.45 Co _0.10 Al _0.45 O ₂ 、LiMn _1.8 Al _0.2 O ₄ And LiMn _1.5 Ni _0.5 O ₄ And so on. Examples of the combination of lithium transition metal composite oxides include, but are not limited to, liCoO ₂ With LiMn ₂ O ₄ In which LiMn is ₂ O ₄ A part of Mn in (b) may be substituted with a transition metal (e.g., liNi) _0.33 Co _0.33 Mn _0.33 O ₂ )，LiCoO ₂ A part of Co in (a) may be substituted with a transition metal.

In some embodiments, the transition metal in the lithium-containing transition metal phosphate compound includes V, ti, cr, mn, fe, co, ni, cu, and the like. In some embodiments, the lithium-containing transition metal phosphate compound comprises LiFePO ₄ 、Li ₃ Fe ₂ (PO ₄ ) ₃ 、LiFeP ₂ O ₇ Iso-phosphates, liCoPO ₄ And cobalt phosphates in which a part of the transition metal atoms as the main component of the lithium transition metal phosphate compound is replaced with another element such as Al, ti, V, cr, mn, fe, co, li, ni, cu, zn, mg, ga, zr, nb, or Si.

In some embodiments, lithium phosphate is included in the positive active material, which may improve continuous charging characteristics of the electrochemical device. The use of lithium phosphate is not limited. In some embodiments, the positive electrode active material and lithium phosphate are used in mixture. In some embodiments, the lithium phosphate is present in an amount greater than 0.1%, greater than 0.3%, or greater than 0.5% relative to the weight of the positive electrode active material and lithium phosphate described above. In some embodiments, the lithium phosphate is present in an amount less than 10%, less than 8%, or less than 5% by weight of the positive electrode active material and lithium phosphate. In some embodiments, the lithium phosphate is present in an amount within the range of any two of the above recited values.

Surface coating

A material having a different composition from the positive electrode active material may be attached to the surface of the positive electrode active material. Examples of surface attachment substances may include, but are not limited to: oxides such as alumina, silica, titania, zirconia, magnesia, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; carbon, and the like.

These surface-adhering substances can be adhered to the surface of the positive electrode active material by the following method: a method of dissolving or suspending a surface adhesion substance in a solvent, infiltrating the surface adhesion substance into the positive electrode active material, and drying the positive electrode active material; a method in which a precursor of a surface-adhering substance is dissolved or suspended in a solvent, and the solution is added to the positive electrode active material after being impregnated with the precursor, and then the precursor is reacted by heating or the like; and a method of adding to a positive electrode active material precursor while firing, and the like. In the case of carbon attachment, a method of mechanically attaching a carbon material (for example, activated carbon or the like) may also be used.

In some embodiments, the content of the surface attachment substance is more than 0.1ppm, more than 1ppm, or more than 10ppm based on the weight of the positive electrode active material layer. In some embodiments, the content of the surface attachment substance is less than 10%, less than 5%, or less than 2% based on the weight of the positive electrode active material layer. In some embodiments, the content of the surface-adhering substance is within a range consisting of any two of the above-described values, based on the weight of the positive electrode active material layer.

By adhering a substance to the surface of the positive electrode active material, the oxidation reaction of the electrolyte on the surface of the positive electrode active material can be suppressed, and the life of the electrochemical device can be improved. When the amount of the surface-adhering substance is too small, the effect cannot be sufficiently exhibited; when the amount of the surface-adhering substance is too large, the entry and exit of lithium ions are inhibited, and the electric resistance may increase.

In the present application, a positive electrode active material having a composition different from that of the positive electrode active material deposited on the surface thereof is also referred to as a "positive electrode active material".

Shape of

In some embodiments, the shape of the positive electrode active material particles includes, but is not limited to, a block shape, a polyhedral shape, a spherical shape, an elliptical spherical shape, a plate shape, a needle shape, a columnar shape, and the like. In some embodiments, the positive active material particles include primary particles, secondary particles, or a combination thereof. In some embodiments, the primary particles may agglomerate to form secondary particles.

Tap density

In some embodiments, the tap density of the positive electrode active material is greater than 0.5g/cm ³ More than 0.8g/cm ³ Or more than 1.0g/cm ³ . When the tap density of the positive electrode active material is within the above range, the amount of the dispersion medium and the required amounts of the conductive material and the positive electrode binder required for forming the positive electrode active material layer can be suppressed, whereby the filling ratio of the positive electrode active material and the capacity of the electrochemical device can be ensured. By using the composite oxide powder having a high tap density, a high-density positive electrode active material layer can be formed. The higher the tap density is, the more preferable the tap density is, and there is no particular upper limit. In some embodiments, the tap density of the positive electrode active material is less than 4.0g/cm ³ Less than 3.7g/cm ³ Or less than 3.5g/cm ³ . When the tap density of the positive electrode active material has the above-described upper limit, the reduction in load characteristics can be suppressed.

The tap density of the positive electrode active material can be calculated by: the positive electrode active material powder of 5g to 10g was put into a 10mL glass measuring cylinder and vibrated by 20mm strokes 200 times to obtain a powder packing density (tap density).

Median particle diameter (D50)

When the positive electrode active material particles are primary particles, the median particle diameter (D50) of the positive electrode active material particles refers to the primary particle diameter of the positive electrode active material particles. When the primary particles of the positive electrode active material particles aggregate to form secondary particles, the median particle diameter (D50) of the positive electrode active material particles refers to the positive electrode active material particle secondary particle diameter.

In some embodiments, the median particle diameter (D50) of the positive electrode active material particles is greater than 0.3 μm, greater than 0.5 μm, greater than 0.8 μm, or greater than 1.0 μm. In some embodiments, the median particle diameter (D50) of the positive electrode active material particles is less than 30 μm, less than 27 μm, less than 25 μm, or less than 22 μm. In some embodiments, the median particle diameter (D50) of the positive electrode active material particles is within a range consisting of any two of the above values. When the median diameter (D50) of the positive electrode active material particles is within the above range, a positive electrode active material having a high tap density can be obtained, and a decrease in the performance of the electrochemical device can be suppressed. On the other hand, in the process of manufacturing a positive electrode for an electrochemical device (that is, when a positive electrode active material, a conductive material, a binder, and the like are slurried in a solvent and applied in a film form), problems such as occurrence of streaks can be prevented. Here, by mixing two or more positive electrode active materials having different median particle diameters, the filling property at the time of producing the positive electrode can be further improved.

The median particle diameter (D50) of the positive electrode active material particles can be measured using a laser diffraction/scattering particle size distribution measuring apparatus: when LA-920 manufactured by HORIBA corporation was used as a particle size distribution meter, a 0.1% aqueous solution of sodium hexametaphosphate was used as a dispersion medium used for measurement, and the dispersion was subjected to ultrasonic dispersion for 5 minutes and then measured with the refractive index of 1.24.

Average primary particle diameter

In the case where the primary particles of the positive electrode active material particles are aggregated to form the secondary particles, in some embodiments, the average primary particle diameter of the positive electrode active material is greater than 0.05 μm, greater than 0.1 μm, or greater than 0.5 μm. In some embodiments, the average primary particle size of the positive electrode active material is less than 5 μm, less than 4 μm, less than 3 μm, or less than 2 μm. In some embodiments, the average primary particle size of the positive electrode active material is within a range of any two of the above values. When the average primary particle diameter of the positive electrode active material is within the above range, the reversibility of charge and discharge of the electrochemical device can be ensured by ensuring powder-filling property and specific surface area, suppressing a decrease in battery performance, and obtaining appropriate crystallinity.

The average primary particle diameter of the positive electrode active material can be obtained by observing an image obtained by a Scanning Electron Microscope (SEM): in the SEM image having a magnification of 10000 times, the longest value of a slice obtained from left and right boundary lines of the primary particles with respect to a horizontal straight line is obtained for any 50 primary particles, and the average primary particle diameter is obtained by obtaining the average value thereof.

Specific surface area (BET)

In some embodiments, the specific surface area (BET) of the positive electrode active material is greater than 0.1m ² A ratio of the water to the water of more than 0.2m ² A/g or more than 0.3m ² (ii) in terms of/g. In some embodiments, the specific surface area (BET) of the positive electrode active material is less than 50m ² A ratio of/g to less than 40m ² A/g or less than 30m ² (ii) in terms of/g. In some embodiments, the specific surface area (BET) of the positive electrode active material is within a range consisting of any two of the above values. When the specific surface area (BET) of the positive electrode active material is within the above range, the performance of the electrochemical device can be ensured while the positive electrode active material can be provided with good coatability.

The specific surface area (BET) of the positive electrode active material can be measured by the following method: the measurement is carried out by a nitrogen adsorption BET single point method using a gas flow method using a nitrogen helium mixed gas in which a sample is pre-dried at 150 ℃ for 30 minutes under a nitrogen flow using a surface area meter (for example, a full-automatic surface area measuring apparatus manufactured by the university of japan).

Positive electrode conductive material

The kind of the positive electrode conductive material is not limited, and any known conductive material may be used. Examples of the positive electrode conductive material may include, but are not limited to, natural graphite, artificial graphite, and the like; carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke; a carbon nanotube; graphene, and the like. The above-mentioned positive electrode conductive materials may be used alone or in any combination.

In some embodiments, the positive electrode conductive material is present in an amount greater than 0.01%, greater than 0.1%, or greater than 1%, based on the weight of the positive electrode active material layer. In some embodiments, the content of the positive electrode conductive material is less than 10%, less than 8%, or less than 5% based on the weight of the positive electrode active material layer. When the content of the positive electrode conductive material is within the above range, sufficient conductivity and capacity of the electrochemical device may be ensured.

Positive electrode binder

The type of the positive electrode binder used for producing the positive electrode active material layer is not particularly limited, and in the case of the coating method, it is sufficient if it is a material that can be dissolved or dispersed in a liquid medium used for producing the electrode. Examples of the positive electrode binder may include, but are not limited to, one or more of the following: resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and cellulose nitrate; rubber-like polymers such as Styrene Butadiene Rubber (SBR), nitrile Butadiene Rubber (NBR), fluororubber, isoprene rubber, butadiene rubber, and ethylene-propylene rubber; thermoplastic elastomer polymers such as styrene-butadiene-styrene block copolymers or hydrogenated products thereof, ethylene-propylene-diene terpolymers (EPDM), styrene-ethylene-butadiene-ethylene copolymers, styrene-isoprene-styrene block copolymers or hydrogenated products thereof; syndiotactic 1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, propylene- α -olefin copolymer, and other soft resinous polymers; fluorine-based polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer; and a polymer composition having ion conductivity of alkali metal ions (particularly lithium ions). The positive electrode binder may be used alone or in any combination thereof.

In some embodiments, the positive electrode binder is present in an amount greater than 0.1%, greater than 1%, or greater than 1.5% based on the weight of the positive electrode active material layer. In some embodiments, the positive electrode binder is present in an amount of less than 10%, less than 5%, less than 4%, or less than 3% based on the weight of the positive electrode active material layer. When the content of the positive electrode binder is within the above range, it is possible to provide the positive electrode with good electrical conductivity and sufficient mechanical strength, and to secure the capacity of the electrochemical device.

Solvent(s)

The type of solvent used for forming the positive electrode slurry is not limited as long as it can dissolve or disperse the positive electrode active material, the conductive material, the positive electrode binder, and the thickener used as needed. Examples of the solvent used for forming the positive electrode slurry may include any one of an aqueous solvent and an organic solvent. Examples of the aqueous medium may include, but are not limited to, water and a mixed medium of alcohol and water, and the like. Examples of the organic medium may include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N, N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and Tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; aprotic polar solvents such as hexamethylphosphoramide and dimethylsulfoxide.

Thickening agent

Thickeners are commonly used to adjust the viscosity of the slurry. In the case of using an aqueous medium, slurrying may be performed using a thickener and a Styrene Butadiene Rubber (SBR) emulsion. The kind of the thickener is not particularly limited, and examples thereof may include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof, and the like. The above thickeners may be used alone or in any combination.

In some embodiments, the thickener is present in an amount greater than 0.1%, greater than 0.2%, or greater than 0.3% based on the weight of the positive electrode active material layer. In some embodiments, the content of the thickener is less than 5%, less than 3%, or less than 2% based on the weight of the positive electrode active material layer. In some embodiments, the content of the thickener is within a range consisting of any two of the above-described values, based on the weight of the positive electrode active material layer. When the content of the thickener is within the above range, the positive electrode slurry can have good coatability, and the decrease in capacity and the increase in resistance of the electrochemical device can be suppressed.

Content of positive electrode active material

In some embodiments, the content of the positive electrode active material is greater than 80%, greater than 82%, or greater than 84% based on the weight of the positive electrode active material layer. In some embodiments, the content of the positive electrode active material is less than 99% or less than 98% based on the weight of the positive electrode active material layer. In some embodiments, the content of the positive electrode active material is within a range consisting of any two of the above-described groups, based on the weight of the positive electrode active material layer. When the content of the positive electrode active material is within the above range, the capacity of the positive electrode active material in the positive electrode active material layer can be secured, and the strength of the positive electrode can be maintained.

Density of positive electrode active material layer

The positive electrode active material layer obtained by coating and drying may be subjected to a compacting treatment by a hand press, a roll press, or the like in order to increase the packing density of the positive electrode active material. In some embodiments, the density of the positive electrode active material layer is greater than 1.5g/cm ³ More than 2g/cm ³ Or more than 2.2g/cm ³ . In some embodiments, the density of the positive electrode active material layer is less than 5g/cm ³ Less than 4.5g/cm ³ Or less than 4g/cm ³ . In some embodiments, the density of the positive electrode active material layer is within a range consisting of any two of the above values. When the density of the positive electrode active material layer is within the above range, the electrochemical device can have good charge and discharge characteristics while suppressing an increase in resistance.

Thickness of positive electrode active material layer

The thickness of the positive electrode active material layer refers to the thickness of the positive electrode active material layer on either side of the positive electrode current collector. In some embodiments, the thickness of the positive electrode active material layer is greater than 10 μm or greater than 20 μm. In some embodiments, the thickness of the positive electrode active material layer is less than 500 μm or less than 450 μm.

Method for producing positive electrode active material

The positive electrode active material can be produced by a method commonly used for producing inorganic compounds. In order to produce a spherical or ellipsoidal positive electrode active material, the following production method can be used: dissolving or pulverizing transition metal raw material, dispersing in solvent such as water, adjusting pH under stirring to obtain spherical precursor, recovering, drying if necessary, adding LiOH and Li ₂ CO ₃ 、LiNO ₃ And firing the Li source at a high temperature to obtain the positive electrode active material.

2. Positive current collector

The kind of the positive electrode current collector is not particularly limited, and it may be any material known to be suitable for use as a positive electrode current collector. Examples of the positive electrode current collector may include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, etc.; carbon cloth, carbon paper, and the like. In some embodiments, the positive current collector is a metallic material. In some embodiments, the positive current collector is aluminum.

The form of the positive electrode current collector is not particularly limited. When the positive electrode collector is a metal material, the form of the positive electrode collector may include, but is not limited to, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal foil, a metal lath, a stamped metal, a foamed metal, and the like. When the positive electrode collector is a carbon material, the form of the positive electrode collector may include, but is not limited to, a carbon plate, a carbon thin film, a carbon cylinder, and the like. In some embodiments, the positive current collector is a metal foil. In some embodiments, the metal foil is mesh-shaped. The thickness of the metal foil is not particularly limited. In some embodiments, the metal foil has a thickness of greater than 1 μm, greater than 3 μm, or greater than 5 μm. In some embodiments, the metal foil has a thickness of less than 1mm, less than 100 μm, or less than 50 μm. In some embodiments, the metal foil has a thickness within a range consisting of any two of the above values.

In order to reduce the electron contact resistance of the positive electrode current collector and the positive electrode active material layer, the surface of the positive electrode current collector may include a conductive assistant. Examples of the conductive aid may include, but are not limited to, carbon and noble metals such as gold, platinum, silver, and the like.

The thickness ratio of the positive electrode active material layer to the positive electrode current collector is the thickness of the positive electrode active material layer on one side divided by the thickness of the positive electrode current collector, and the numerical value is not particularly limited. In some embodiments, the thickness ratio is less than 50, less than 30, or less than 20. In some embodiments, the thickness ratio is greater than 0.5, greater than 0.8, or greater than 1. In some embodiments, the thickness ratio is within a range consisting of any two of the above values. When the thickness ratio is within the above range, heat generation of the positive electrode current collector during high current density charge and discharge can be suppressed, and the capacity of the electrochemical device can be ensured.

3. Method for producing positive electrode

The positive electrode can be produced by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector. The positive electrode using the positive electrode active material can be produced by a conventional method in which the positive electrode active material and the binder, and if necessary, the conductive material and the thickener, etc. are dry-mixed and formed into a sheet, and the obtained sheet is pressure-bonded to the positive electrode current collector; alternatively, these materials are dissolved or dispersed in a liquid medium to prepare a slurry, and the slurry is applied onto a positive electrode current collector and dried to form a positive electrode active material layer on the current collector, thereby obtaining a positive electrode.

Negative electrode

The negative electrode includes a negative electrode current collector and a positive electrode active material layer disposed on one or both surfaces of the negative electrode current collector, the negative electrode active material layer containing a negative electrode active material. The anode active material layer may be one layer or a plurality of layers, and each layer of the plurality of layers may contain the same or different anode active materials. The negative electrode active material is any material capable of reversibly intercalating and deintercalating metal ions such as lithium ions. In some embodiments, the chargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material to prevent unintentional precipitation of lithium metal on the negative electrode during charging.

As the current collector for holding the negative electrode active material, a known current collector may be used arbitrarily. Examples of the negative electrode current collector include, but are not limited to, metal materials such as aluminum, copper, nickel, stainless steel, nickel-plated steel, and the like. In some embodiments, the negative current collector is copper.

In the case where the negative electrode current collector is a metal material, the form of the negative electrode current collector may include, but is not limited to, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal film, a metal lath, a stamped metal, a foamed metal, and the like. In some embodiments, the negative electrode current collector is a metal thin film. In some embodiments, the negative current collector is a copper foil. In some embodiments, the negative electrode current collector is a rolled copper foil based on a rolling process or an electrolytic copper foil based on an electrolytic process.

In some embodiments, the thickness of the negative electrode current collector is greater than 1 μm or greater than 5 μm. In some embodiments, the thickness of the negative electrode current collector is less than 100 μm or less than 50 μm. In some embodiments, the thickness of the negative electrode current collector is within a range consisting of any two of the above values.

The negative electrode active material is not particularly limited as long as it can reversibly store and release lithium ions. Examples of the negative electrode active material may include, but are not limited to, carbon materials such as natural graphite, artificial graphite, and the like; metals such as silicon (Si) and tin (Sn); and oxides of metal elements such as Si and Sn. The negative electrode active materials may be used alone or in combination.

The anode active material layer may further include an anode binder. The negative electrode binder may improve the binding of the negative electrode active material particles to each other and the binding of the negative electrode active material to the current collector. The kind of the negative electrode binder is not particularly limited as long as it is a material that is stable to the electrolyte solution or the solvent used in the production of the electrode. In some embodiments, the negative electrode binder comprises a resin binder. Examples of the resin binder include, but are not limited to, fluororesins, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, and the like. When the negative electrode mix slurry is prepared using an aqueous solvent, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or a salt thereof, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, and the like.

The negative electrode can be prepared by the following method: a negative electrode can be obtained by applying a negative electrode mixture slurry containing a negative electrode active material, a resin binder, and the like onto a negative electrode current collector, drying the slurry, and then rolling the dried slurry to form negative electrode active material layers on both surfaces of the negative electrode current collector.

II. Electrolyte solution

The electrolyte used in the electrochemical device of the present application includes an electrolyte and a solvent dissolving the electrolyte. In some embodiments, the electrolyte used in the electrochemical device of the present application further comprises an additive.

Another feature of the electrochemical device of the present application is that the electrolytic solution includes a compound containing a sulfur-oxygen double bond.

In some embodiments, the compound containing a thiooxy double bond comprises at least one of the following compounds: cyclic sulfate ester, chain sulfonate ester, cyclic sulfonate ester, chain sulfite ester, or cyclic sulfite ester.

In some embodiments, the cyclic sulfate includes, but is not limited to, one or more of the following: 1,2-ethylene glycol sulfate, 1,2-propylene glycol sulfate, 1,3-propylene glycol sulfate, 1,2-butanediol sulfate, 1,3-butanediol sulfate, 1,4-butanediol sulfate, 1,2-pentanediol sulfate, 1,3-pentanediol sulfate, 1,4-pentanediol sulfate, and 1,5-pentanediol sulfate, and the like.

In some embodiments, the chain sulfates include, but are not limited to, one or more of the following: dimethyl sulfate, ethyl methyl sulfate, diethyl sulfate, and the like.

In some embodiments, the chain sulfonates include, but are not limited to, one or more of the following: fluorosulfonate esters such as methyl fluorosulfonate and ethyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, butyl methanesulfonate, methyl 2- (methylsulfonyloxy) propionate, and ethyl 2- (methylsulfonyloxy) propionate.

In some embodiments, the cyclic sulfonate includes, but is not limited to, one or more of the following: 1,3-propane sultone, 1-fluoro-1,3-propane sultone, 2-fluoro-1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 2-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1-propylene-1,3-sultone, 2-propylene-1,3-sultone, 1-fluoro-1-propylene-1,3-sultone, 2-fluoro-1-propylene-1,3-sultone 3-fluoro-1-propene-1,3-sultone, 1-fluoro-2-propene-1,3-sultone, 2-fluoro-2-propene-1,3-sultone, 3-fluoro-2-propene-1,3-sultone, 1-methyl-1-propene-1,3-sultone, 2-methyl-1-propene-1,3-sultone, 3-methyl-1-propene-1,3-sultone, 1-methyl-2-propene-1,3-sultone, 2-methyl-2-propene-1,3-sultone, 3-methyl-2-propene-1,3-sultone, 1,4-butanesultone, 1,5-pentasultone, methylene methanedisulfonate, and ethylene methanedisulfonate, among others.

In some embodiments, the chain sulfites include, but are not limited to, one or more of the following: dimethyl sulfite, ethyl methyl sulfite, diethyl sulfite, and the like.

In some embodiments, the cyclic sulfites include, but are not limited to, one or more of the following: 1,2-ethylene glycol sulfite, 1,2-propylene glycol sulfite, 1,3-propylene glycol sulfite, 1,2-butanediol sulfite, 1,3-butanediol sulfite, 1,4-butanediol sulfite, 1,2-pentanediol sulfite, 1,3-pentanediol sulfite, 1,4-pentanediol sulfite, and 1,5-pentanediol sulfite, among others.

In some embodiments, the compound containing a thiooxy double bond comprises a compound of formula 1:

wherein:

w is selected from

m is 1,2,3 or 4;

n is 0, 1 or 2; and is provided with

p is 0, 1,2,3, 4, 5 or 6.

In some embodiments, the compound of formula 1 comprises at least one of:

in some embodiments, the sulfur oxygen double bond containing compound is present in an amount Y% based on the weight of the electrolyte, with Y being in the range of 0.01 to 10. In some embodiments, Y is in the range of 0.1 to 8. In some embodiments, Y is in the range of 0.5 to 5. In some embodiments, Y is in the range of 1 to 3. In some embodiments, Y is 0.01, 0.05, 0.1, 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or within a range consisting of any two of the foregoing values. When the content of the compound containing a sulfur-oxygen double bond in the electrolyte is within the above range, it is helpful to further reduce the direct-current internal resistance and the thickness expansion rate of the electrochemical device, and to improve the safety of the electrochemical device.

In some embodiments, the content Y% of the compound containing a thiooxy double bond in the electrolyte and the area ratio a of the intermediate layer to the active material layer satisfy: 0.009 ≤ A × Y ≤ 6. In some embodiments, 0.01 real A Y ≦ 5. In some embodiments, 0.05 real A Y ≦ 3. In some embodiments, 0.1A Y ≦ 2. In some embodiments, 0.5 of A Y ≦ 1. In some embodiments, axy is 0.009, 0.01, 0.05, 0.1, 0.5, 1,2,3, 4, 5, 6, or within a range consisting of any two of the foregoing values. When the content Y% of the compound containing a sulfur-oxygen double bond in the electrolyte and the area ratio a of the intermediate layer to the active material layer satisfy the above-described relationship, the direct-current internal resistance and the thickness expansion rate of the electrochemical device can be further reduced, and the safety of the electrochemical device can be improved.

In some embodiments, the electrolyte contains Y% of the compound containing a sulfur-oxygen double bond and X m is the specific surface area of the conductive material ² Per g is full ofFoot: x is more than or equal to 0.2 and less than or equal to 200. In some embodiments, 0.5 ≦ X Y ≦ 50. In some embodiments, 1 is at X Y ≦ 0. In some embodiments, 5 is 0 at X Y ≦. In some embodiments, 10-X Y ≦ 00. In some embodiments, X by Y is 0.2, 0.5, 1,5, 10, 20, 50, 80, 100, 120, 150, 180, 200, or within a range consisting of any two of the foregoing values. When the content of the compound containing the sulfur-oxygen double bond in the electrolyte is Y percent and the specific surface area of the conductive material is X m ² When the ratio/g satisfies the above relationship, the direct current internal resistance and the thickness expansion ratio of the electrochemical device can be further reduced, and the safety of the electrochemical device can be improved.

In some embodiments, the electrolyte further comprises at least one of the following compounds:

(a) Propionate esters;

(b) An organic compound having a cyano group;

(c) Lithium difluorophosphate;

(d) A compound of formula 2:

wherein:

L ₁ and L ₂ Each independently is- (CR) ⁷ R ⁸ ) _n -；

n is 1,2 or 3.

(a) Propionic acid ester

In some embodiments, the propionate includes a compound of formula 3:

wherein:

R ¹ is selected from the group consisting of ethyl or haloethyl,

R ² is selected from C ₁ -C ₆ Alkyl or C ₁ -C ₆ A haloalkyl group.

In some embodiments, the propionic acid esters include, but are not limited to, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, methyl halopropionate, ethyl halopropionate, propyl halopropionate, butyl halopropionate, and pentyl halopropionate. In some embodiments, the propionate is selected from at least one of methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and pentyl propionate. In some embodiments, the halogen group of the methyl, ethyl, propyl, butyl and pentyl halopropionates is selected from one or more of a fluoro group (-F), a chloro group (-C1), a bromo group (-Br) and an iodo group (-I). In some embodiments, the halogen group is a fluorine group (-F), which may achieve more excellent effects.

In some embodiments, the propionate is present in an amount of 10% to 60% based on the weight of the electrolyte. In some embodiments, the propionate is present in an amount of 15% to 55% based on the weight of the electrolyte. In some embodiments, the propionate is present in an amount of 30% to 50% based on the weight of the electrolyte. In some embodiments, the propionate is present in an amount of 30% to 40% based on the weight of the electrolyte. The use of the propionate having the above content can achieve more excellent effects.

(b) Compound having cyano group

In some embodiments, compounds having a cyano group include, but are not limited to, one or more of the following: succinonitrile, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, tetramethylsuccinonitrile, 2-methylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, ethylene glycol bis (propionitrile) ether, 3,5-dioxa-pimelonitrile, 1,4-bis (cyanoethoxy) butane, diethylene glycol bis (2-cyanoethyl) ether, triethylene glycol bis (2-cyanoethyl) ether, tetraethylene glycol bis (2-cyanoethyl) ether 1,3-bis (2-cyanoethoxy) propane, 1,4-bis (2-cyanoethoxy) butane, 1,5-bis (2-cyanoethoxy) pentane, ethylene glycol di (4-cyanobutyl) ether, 1,4-dicyano-2-butene, 1,4-dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, 1,4-dicyano-2,3-diethyl-2-butene, 1,6-dicyano-3-hexene, 1,6-dicyano-2-methyl-3-hexene, and mixtures thereof, 1,3,5-pentanetrimethylnitrile, 1,2,3-propanetrimethylnitrile, 1,3,6-hexantrimethylnitrile, 1,2,6-hexantrimethylnitrile, 1,2,3-tris (2-cyanoethoxy) propane, 1,2,4-tris (2-cyanoethoxy) butane, 1,1,1-tris (cyanoethoxymethylene) ethane, 1,1,1-tris (cyanoethoxymethylene) propane, 3-methyl-1,3,5-tris (cyanoethoxy) pentane, 1,2,7-tris (cyanoethoxy) heptane, 1,2,6-tris (cyanoethoxy) hexane, and 1,2,5-tris (cyanoethoxy) pentane.

The above-mentioned compounds having a cyano group may be used alone or in any combination. When the electrolyte contains two or more compounds having a cyano group, the content of the compounds having a cyano group means the total content of the two or more compounds having a cyano group. In some embodiments, the compound having a cyano group is contained in an amount of 0.1 to 15% based on the weight of the electrolyte. In some embodiments, the compound having a cyano group is contained in an amount of 0.5 to 10% based on the weight of the electrolyte. In some embodiments, the content of the compound having a cyano group is 1% to 8% based on the weight of the electrolyte. In some embodiments, the compound having a cyano group is contained in an amount of 3% to 5% based on the weight of the electrolyte.

₂ ₂ (c) Lithium difluorophosphate (LiPOF)

In some embodiments, the lithium difluorophosphate is present in an amount b%, b being in the range of 0.01 to 2, based on the weight of the electrolyte. In some embodiments, b is in the range of 0.05 to 1.5. In some embodiments, b is in the range of 0.1 to 1. In some embodiments, b is in the range of 0.3 to 0.5. In some embodiments, b is 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, or within a range consisting of any two of the foregoing values. When the content of lithium difluorophosphate in the electrolyte is within the above range, the direct-current internal resistance and the thickness expansion rate of the electrochemical device can be further reduced, and the safety of the electrochemical device is improved.

In some embodiments, the content Y% of the compound containing a thiooxy double bond in the electrolyte and the content b% of the lithium difluorophosphate satisfy 0.01. Ltoreq. Y/b. Ltoreq.100. In some embodiments, 0.05 ≦ Y/b ≦ 80. In some embodiments, 0.1 ≦ Y/b ≦ 50. In some embodiments, 0.5 ≦ Y/b ≦ 20. In some embodiments, 1 is at Y/b ≦ 10. In some embodiments, Y/b is 0.01, 0.05, 0.1, 0.5, 1,5, 10, 20, 50, 80, 100, or within a range consisting of any two of the foregoing values. When the content Y% of the compound containing the sulfur-oxygen double bond in the electrolyte and the content b% of the lithium difluorophosphate satisfy the above relationship, the direct-current internal resistance and the thickness expansion rate of the electrochemical device can be further reduced, and the safety of the electrochemical device is improved.

(d) A compound of formula 2

In some embodiments, the compound of formula 2 comprises at least one of the following compounds:

in some embodiments, the compound of formula 2 is present in an amount of 0.01% to 5% based on the weight of the electrolyte. In some embodiments, the compound of formula 2 is present in an amount of 0.05% to 3% based on the weight of the electrolyte. In some embodiments, the compound of formula 2 is present in an amount of 0.1% to 2% based on the weight of the electrolyte. In some embodiments, the compound of formula 2 is present in an amount of 0.5% to 1% based on the weight of the electrolyte. In some embodiments, the compound of formula 2 is present in an amount of 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or in a range consisting of any two of the foregoing, based on the weight of the electrolyte.

Solvent(s)

In some embodiments, the electrolyte further comprises any non-aqueous solvent known in the art that can act as a solvent for the electrolyte.

In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of: cyclic carbonate, chain carbonate, cyclic carboxylate, chain carboxylate, cyclic ether, chain ether, phosphorus-containing organic solvent, sulfur-containing organic solvent, and aromatic fluorine-containing solvent.

In some embodiments, examples of the cyclic carbonate may include, but are not limited to, one or more of the following: ethylene Carbonate (EC), propylene Carbonate (PC) and butylene carbonate. In some embodiments, the cyclic carbonate has 3 to 6 carbon atoms.

In some embodiments, examples of the chain carbonates can include, but are not limited to, one or more of the following: and chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate (DEC), methyl-n-propyl carbonate, ethyl-n-propyl carbonate, and di-n-propyl carbonate. Examples of chain carbonates substituted with fluorine may include, but are not limited to, one or more of the following: bis (fluoromethyl) carbonate, bis (difluoromethyl) carbonate, bis (trifluoromethyl) carbonate, bis (2-fluoroethyl) carbonate, bis (2,2-difluoroethyl) carbonate, bis (2,2,2-trifluoroethyl) carbonate, 2-fluoroethyl methyl carbonate, 2,2-difluoroethyl methyl carbonate and 2,2,2-trifluoroethyl methyl carbonate, and the like.

In some embodiments, examples of the cyclic carboxylic acid ester may include, but are not limited to, one or more of the following: one or more of gamma-butyrolactone and gamma-valerolactone. In some embodiments, a portion of the hydrogen atoms of the cyclic carboxylic acid ester may be replaced with fluorine.

In some embodiments, examples of the chain carboxylic acid ester may include, but are not limited to, one or more of the following: methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate, and ethyl pivalate, and the like. In some embodiments, a part of hydrogen atoms of the chain carboxylic acid ester may be substituted with fluorine. In some embodiments, examples of the fluorine-substituted chain carboxylic acid ester may include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, 2,2,2-trifluoroethyl trifluoroacetate, and the like.

In some embodiments, examples of the cyclic ether may include, but are not limited to, one or more of the following: tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl 1,3-dioxolane, 4-methyl 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, and dimethoxypropane.

In some embodiments, examples of the chain ethers may include, but are not limited to, one or more of the following: dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane, 1,2-ethoxymethoxyethane, and the like.

In some embodiments, examples of the phosphorus-containing organic solvent may include, but are not limited to, one or more of the following: trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylene methyl phosphate, ethylene ethyl phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphate, tris (2,2,2-trifluoroethyl) phosphate, tris (2,2,3,3,3-pentafluoropropyl) phosphate, and the like.

In some embodiments, examples of the sulfur-containing organic solvent may include, but are not limited to, one or more of the following: sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethylsulfone, diethylsulfone, ethylmethylsulfone, methylpropylsulfone, dimethylsulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate and dibutyl sulfate. In some embodiments, a portion of the hydrogen atoms of the sulfur-containing organic solvent may be substituted with fluorine.

In some embodiments, the aromatic fluorine-containing solvent includes, but is not limited to, one or more of: fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene and trifluoromethylbenzene.

In some embodiments, the solvent used in the electrolyte of the present application includes cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, and combinations thereof. In some embodiments, the solvent used in the electrolytes of the present application comprises an organic solvent selected from the group consisting of: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, n-propyl acetate, ethyl acetate, and combinations thereof. In some embodiments, the solvent used in the electrolyte of the present application comprises: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, gamma-butyrolactone, and combinations thereof.

Additive agent

In some embodiments, examples of the additive may include, but are not limited to, one or more of the following: fluoro carbonate, ethylene carbonate containing carbon-carbon double bond and acid anhydride.

In some embodiments, the additive is present in an amount of 0.01% to 15%, 0.1% to 10%, or 1% to 5%, based on the weight of the electrolyte.

According to an embodiment of the present application, the propionate is contained in an amount of 1.5 to 30 times, 1.5 to 20 times, 2 to 20 times, or 5 to 20 times the additive, based on the weight of the electrolyte.

In some embodiments, the additive comprises one or more ethylene carbonates containing carbon-carbon double bonds. Examples of the ethylene carbonate containing a carbon-carbon double bond may include, but are not limited to, one or more of the following: vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 1,2-dimethyl vinylene carbonate, 1,2-diethyl vinylene carbonate, fluoroethylene carbonate and trifluoromethyl vinylene carbonate; vinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, 1-ethyl-2-vinyl ethylene carbonate, 1-n-propyl-2-vinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, 1,1-divinyl ethylene carbonate, 1,2-divinyl ethylene carbonate, 1,1-dimethyl-2-methylene ethylene carbonate, and 1,1-diethyl-2-methylene ethylene carbonate, and the like. In some embodiments, the ethylene carbonate containing a carbon-carbon double bond includes vinylene carbonate, which is easily available and can achieve more excellent effects.

In some embodiments, the additive is a combination of a fluoro carbonate and ethylene carbonate containing a carbon-carbon double bond. In some embodiments, the additive is a combination of a fluoro carbonate and a compound containing a thiooxy double bond. In some embodiments, the additive is a combination of a fluoro carbonate and a compound having 2-4 cyano groups. In some embodiments, the additive is a combination of a fluorocarbonate and a cyclic carboxylic acid ester. In some embodiments, the additive is a combination of a fluoro carbonate and a cyclic phosphoric anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a carboxylic acid anhydride. In some embodiments, the additive is a combination of a fluoro carbonate and a sulfonic anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a carboxylic acid sulfonic anhydride.

Electrolyte

The electrolyte is not particularly limited, and any known electrolyte can be used. In the case of a lithium secondary battery, a lithium salt is generally used. Examples of the electrolyte may include, but are not limited to, liPF ₆ 、LiBF ₄ 、LiClO ₄ 、LiAlF ₄ 、LiSbF ₆ 、LiWF ₇ Inorganic lithium salts; liWOF ₅ Lithium tungstate species; HCO ₂ Li、CH ₃ CO ₂ Li、CH ₂ FCO ₂ Li、CHF ₂ CO ₂ Li、CF ₃ CO ₂ Li、CF ₃ CH ₂ CO ₂ Li、CF ₃ CF ₂ CO ₂ Li、CF ₃ CF ₂ CF ₂ CO ₂ Li、CF ₃ CF ₂ CF ₂ CF ₂ CO ₂ Lithium carboxylates such as Li; FSO ₃ Li、CH ₃ SO ₃ Li、CH ₂ FSO ₃ Li、CHF ₂ SO ₃ Li、CF ₃ SO ₃ Li、CF ₃ CF ₂ SO ₃ Li、CF ₃ CF ₂ CF ₂ SO ₃ Li、CF ₃ CF ₂ CF ₂ CF ₂ So ₃ Lithium sulfonates such as Li; liN (FCO) ₂ 、LiN(FCO)(FSO ₂ )、LiN(FSO ₂ ) ₂ 、LiN(FSO ₂ )(CF ₃ SO ₂ )、LiN(CF ₃ SO ₂ ) ₂ 、LiN(C ₂ F ₅ SO ₂ ) ₂ Cyclic 1,2-perfluoroethane bis-sulfonyl imide lithium, cyclic 1,3-perfluoropropane bis-sulfonyl imide lithium, liN (CF) ₃ SO ₂ )(C ₄ F ₉ SO ₂ ) Lithium imide salts; liC (FSO) ₂ ) ₃ 、LiC(CF ₃ SO ₂ ) ₃ 、LiC(C ₂ F ₅ SO ₂ ) ₃ Lithium methide salts; lithium (malonate) borate salts such as lithium bis (malonate) borate, lithium difluoro (malonate) borate, and the like; lithium (malonate) phosphates such as lithium tris (malonate) phosphate, lithium difluorobis (malonate) phosphate, and lithium tetrafluoro (malonate) phosphate; and LiPF ₄ (CF ₃ ) ₂ 、LiPF ₄ (C ₂ F ₅ ) ₂ 、LiPF ₄ (CF ₃ SO ₂ ) ₂ 、LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ 、LiBF ₃ CF ₃ 、LiBF ₃ C ₂ F ₅ 、LiBF ₃ C ₃ F ₇ 、LiBF ₂ (CF ₃ ) ₂ 、LiBF ₂ (C ₂ F ₅ ) ₂ 、LiBF ₂ (CF ₃ SO ₂ ) ₂ 、LiBF ₂ (C ₂ F ₅ SO ₂ ) ₂ Isofluorine-containing organic lithium salts(ii) a Lithium oxalato borates such as lithium difluorooxalato borate and lithium bis (oxalato) borate; lithium oxalate phosphates such as lithium tetrafluorooxalate phosphate, lithium difluorobis (oxalate) phosphate, and lithium tris (oxalate) phosphate.

In some embodiments, the electrolyte is selected from LiPF ₆ 、LiSbF ₆ 、FSO ₃ Li、CF ₃ SO ₃ Li、LiN(FSO ₂ ) ₂ 、LiN(FSO ₂ )(CF ₃ SO ₂ )、LiN(CF ₃ SO ₂ ) ₂ 、LiN(C ₂ F ₅ SO ₂ ) ₂ Cyclic 1,2-perfluoroethane bis-sulfonyl imide lithium, cyclic 1,3-perfluoropropane bis-sulfonyl imide lithium, liC (FSO) ₂ ) ₃ 、LiC(CF ₃ SO ₂ ) ₃ 、LiC(C ₂ F ₅ SO ₂ ) ₃ 、LiBF ₃ CF ₃ 、LiBF ₃ C ₂ F ₅ 、LiPF ₃ (CF ₃ ) ₃ 、LiPF ₃ (C ₂ F ₅ ) ₃ Lithium difluorooxalato borate, lithium bis (oxalato) borate, or lithium difluorobis (oxalato) phosphate, which contribute to improvement in output characteristics, high-rate charge-discharge characteristics, high-temperature storage characteristics, cycle characteristics, and the like of an electrochemical device.

The content of the electrolyte is not particularly limited as long as the effects of the present application are not impaired. In some embodiments, the total molar concentration of lithium in the electrolyte is greater than 0.3mol/L or greater, greater than 0.4mol/L, or greater than 0.5mol/L. In some embodiments, the total molar concentration of lithium in the electrolyte is less than 3mol/L, less than 2.5mol/L, or less than 2.0 mol/L. In some embodiments, the total molar concentration of lithium in the electrolyte is within a range consisting of any two of the above values. When the electrolyte concentration is within the above range, lithium as charged particles is not excessively small, and the viscosity can be made to be in an appropriate range, so that good conductivity is easily ensured.

In the case where two or more electrolytes are used, the electrolyte includes at least one salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte comprises a salt selected from the group consisting of a monofluorophosphate, an oxalate, and a fluorosulfonate. In some embodiments, the electrolyte comprises a lithium salt. In some embodiments, the salt selected from the group consisting of monofluorophosphates, borates, oxalates, and fluorosulfonates is present in an amount of greater than 0.01% or greater than 0.1%, based on the weight of the electrolyte. In some embodiments, the salt selected from the group consisting of monofluorophosphates, borates, oxalates, and fluorosulfonates is present in an amount of less than 20% or less than 10% by weight of the electrolyte. In some embodiments, the amount of a salt selected from the group consisting of monofluorophosphates, borates, oxalates, and fluorosulfonates is within a range consisting of any two of the foregoing values.

In some embodiments, the electrolyte comprises one or more substances selected from the group consisting of monofluorophosphates, borates, oxalates, and fluorosulfonates, and one or more salts in addition thereto. As other salts, there may be mentioned the lithium salts exemplified hereinabove, and LiPF in some examples ₆ 、LiN(FSO ₂ )(CF ₃ SO ₂ )、LiN(CF ₃ SO ₂ ) ₂ 、LiN(C ₂ F ₅ SO ₂ ) ₂ Cyclic 1,2-perfluoroethane bis-sulfonyl imide lithium, cyclic 1,3-perfluoropropane bis-sulfonyl imide lithium, liC (FSO) ₂ ) ₃ 、LiC(CF ₃ SO ₂ ) ₃ 、LiC(C ₂ F ₅ SO ₂ ) ₃ 、LiBF ₃ CF ₃ 、LiBF ₃ C ₂ F ₅ 、LiPF ₃ (CF ₃ ) ₃ 、LiPF ₃ (C ₂ F ₅ ) ₃ . In some embodiments, the additional salt is LiPF ₆ 。

In some embodiments, the amount of the additional salt is greater than 0.01% or greater than 0.1% based on the weight of the electrolyte. In some embodiments, the content of the salt other than this is less than 20%, less than 15%, or less than 10% based on the weight of the electrolyte. In some embodiments, the amount of other salts is within a range consisting of any two of the above values. The other salts having the above contents help to balance the conductivity and viscosity of the electrolyte.

The electrolyte solution may contain, in addition to the above-mentioned solvent, additive and electrolyte salt, additional additives such as a negative electrode coating film forming agent, a positive electrode protecting agent, and an overcharge preventing agent, as required. As the additive, additives generally used in nonaqueous electrolyte secondary batteries may be used, and examples thereof may include, but are not limited to, vinylene carbonate, succinic anhydride, biphenyl, cyclohexylbenzene, 2,4-difluoroanisole, and the like. These additives may be used alone or in any combination thereof. The content of these additives in the electrolyte solution is not particularly limited, and may be appropriately set according to the kind of the additives. In some embodiments, the additive is present in an amount less than 5%, in the range of 0.01% to 5%, or in the range of 0.2% to 5%, based on the weight of the electrolyte.

III, isolation film

In order to prevent short-circuiting, a separator is generally provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application is generally used by penetrating the separator.

The material and shape of the separator are not particularly limited as long as the effects of the present application are not significantly impaired. The separator may be a resin, glass fiber, inorganic substance, or the like formed of a material stable to the electrolyte solution of the present application. In some embodiments, the separator includes a porous sheet having excellent liquid retention properties, a nonwoven fabric-like material, or the like. Examples of materials for the resin or glass fiber separator film may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, and the like. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above-mentioned separator may be used alone or in any combination.

The separator may also be a material laminated with the above materials, and examples thereof include, but are not limited to, a three-layer separator laminated in the order of polypropylene, polyethylene, polypropylene, and the like.

Examples of the material of the inorganic substance may include, but are not limited to, oxides such as alumina, silica, nitrides such as aluminum nitride, silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, and the like). Forms of inorganic matter may include, but are not limited to, particulate or fibrous.

The form of the separator may be a film form, and examples thereof include, but are not limited to, a nonwoven fabric, a woven fabric, a microporous film, and the like. In the form of a thin film, the separator has a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm. In addition to the above-mentioned separate film-like separator, the following separators may be used: the separator is formed by forming a composite porous layer containing the inorganic particles on the surface of the positive electrode and/or the negative electrode using a resin-based binder, and is formed by forming porous layers on both surfaces of the positive electrode using, for example, a fluororesin as a binder and alumina particles having a particle size of 90% less than 1 μm.

The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the release film has a thickness of less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the thickness of the barrier film is within a range consisting of any two of the above values. When the thickness of the separator is within the above range, the insulating property and the mechanical strength can be secured, and the rate characteristic and the energy density of the electrochemical device can be secured.

When a porous material such as a porous sheet or nonwoven fabric is used as the separator, the porosity of the separator is arbitrary. In some embodiments, the separator has a porosity of greater than 10%, greater than 15%, or greater than 20%. In some embodiments, the separator has a porosity of less than 60%, less than 50%, or less than 45%. In some embodiments, the porosity of the separator is within a range consisting of any two of the above values. When the porosity of the separator is within the above range, insulation and mechanical strength can be secured, and membrane resistance can be suppressed, resulting in an electrochemical device having good safety characteristics.

The average pore diameter of the separator is also arbitrary. In some embodiments, the mean pore size of the separator is less than 0.5 μm or less than 0.2 μm. In some embodiments, the separator membrane has an average pore size greater than 0.05 μm. In some embodiments, the mean pore size of the separator is within a range consisting of any two of the above values. If the average pore diameter of the separator exceeds the above range, short circuits are likely to occur. When the average pore diameter of the separation membrane is within the above range, the electrochemical device has good safety characteristics.

IV, electrochemical device Assembly

The electrochemical device assembly includes an electrode assembly, a current collecting structure, an outer case, and a protection member.

Electrode group

The electrode group may have any of a laminated structure in which the positive electrode and the negative electrode are laminated with the separator interposed therebetween, and a structure in which the positive electrode and the negative electrode are spirally wound with the separator interposed therebetween. In some embodiments, the electrode group has a mass occupying a proportion (electrode group occupying ratio) in the battery internal volume of greater than 40% or greater than 50%. In some embodiments, the electrode set occupancy is less than 90% or less than 80%. In some embodiments, the electrode set occupancy is within a range consisting of any two of the values recited above. When the electrode group occupancy is within the above range, the capacity of the electrochemical device can be secured, and the deterioration of the characteristics such as repeated charge/discharge performance and high-temperature storage due to the increase in internal pressure can be suppressed.

Current collecting structure

The current collecting structure is not particularly limited. In some embodiments, the current collecting structure is a structure that reduces the resistance of the wiring portion and the bonding portion. When the electrode group has the above-described laminated structure, a structure in which the metal core portions of the respective electrode layers are bundled and welded to the terminals is suitably used. Since the internal resistance increases when the area of one electrode is increased, it is also preferable to provide 2 or more terminals in the electrode to reduce the resistance. When the electrode group has the above-described wound structure, 2 or more lead structures are provided for the positive electrode and the negative electrode, respectively, and the terminals are bundled together, whereby the internal resistance can be reduced.

External casing

The material of the outer case is not particularly limited as long as it is stable to the electrolyte used. The outer case may be made of, but not limited to, a metal such as nickel-plated steel plate, stainless steel, aluminum, an aluminum alloy, or a magnesium alloy, or a laminated film of a resin and an aluminum foil. In some embodiments, the outer case is a metal or laminated film of aluminum or aluminum alloy.

The metal outer case includes, but is not limited to, a hermetically sealed structure formed by welding metals to each other by laser welding, resistance welding, or ultrasonic welding; or a caulking structure formed by using the metal through a resin spacer. The outer case using the laminated film includes, but is not limited to, a sealed structure formed by thermally bonding resin layers to each other. In order to improve the sealing property, a resin different from the resin used for the laminate film may be interposed between the resin layers. When the resin layer is thermally adhered to the current collecting terminal to form a sealed structure, a resin having a polar group or a modified resin into which a polar group has been introduced may be used as the resin to be interposed, because of the bonding between the metal and the resin. The shape of the outer package is also arbitrary, and may be any of a cylindrical shape, a square shape, a laminated shape, a button shape, a large size, and the like.

Protective element

The protection element may be a Positive Temperature Coefficient (PTC) element whose resistance increases when abnormal heat radiation or an excessive current flows, a temperature fuse, a thermistor, a valve (current cutoff valve) that cuts off a current flowing through a circuit by rapidly increasing the internal pressure or internal temperature of the battery when abnormal heat radiation occurs, or the like. The protective element may be selected from elements that do not operate under normal use of high current, and may be designed so that abnormal heat release or thermal runaway does not occur even if the protective element is not present.

V, applications

The electrochemical device of the present application includes any device in which electrochemical reactions occur, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery or a lithium ion secondary battery.

The present application further provides an electronic device comprising an electrochemical device according to the present application.

The use of the electrochemical device of the present application is not particularly limited, and it can be used for any electronic device known in the art. In some embodiments, the electrochemical device of the present application can be used in, but is not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, cellular phones, portable facsimile machines, portable copiers, portable printers, headphones, video recorders, liquid crystal televisions, portable cleaners, portable CDs, mini-discs, transceivers, electronic organizers, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large batteries, lithium ion capacitors, and the like.

Taking a lithium ion battery as an example and describing the preparation of the lithium ion battery with reference to specific examples, those skilled in the art will understand that the preparation method described in the present application is only an example, and any other suitable preparation method is within the scope of the present application.

Examples

The following describes performance evaluation according to examples and comparative examples of lithium ion batteries of the present application.

1. Preparation of lithium ion battery

1. Preparation of the intermediate layer

Mixing the conductive material and Styrene Butadiene Rubber (SBR) with deionized water according to the mass ratio of 64.5 to 35.5 percent, and uniformly stirring to obtain the intermediate layer slurry. The slurry is coated on a positive or negative current collector.

2. Preparation of the negative electrode

Mixing the artificial graphite, the styrene-butadiene rubber and the sodium carboxymethylcellulose with deionized water according to the mass ratio of 96% to 2%, and uniformly stirring to obtain the cathode slurry. The negative electrode slurry was coated on a current collector of 12 μm or on an intermediate layer. Drying, cold pressing, cutting into pieces, and welding tabs to obtain the cathode.

3. Preparation of the Positive electrode

Mixing lithium cobaltate (LiCoO) ₂ ) Conductive material (Super-P) and polyvinylidene fluoride (PVDF) according to a 95%:2%:3 percent of the mixture is mixed with N-methyl pyrrolidone (NMP) and stirred evenly to obtain the anode slurry. The anode slurry is coated on an aluminum foil with the thickness of 12 mu m or an intermediate layer, dried, cold-pressed, cut into pieces and welded with lugs to obtain the anode.

4. Preparation of the electrolyte

EC, PC and DEC (weight ratio 1: 1) were mixed under dry argon atmosphere, and LiPF was added ₆ Mixing uniformly to form a basic electrolyte, wherein LiPF ₆ The concentration of (2) is 1.15mol/L. The electrolytes of different examples and comparative examples were obtained by adding additives of different contents to the base electrolyte.

The abbreviations and names of the components in the electrolyte are shown in the following table:

5. preparation of the separator

Polyethylene (PE) porous polymer films were used as separators.

6. Preparation of lithium ion battery

The obtained positive electrode, separator and negative electrode were wound in order and placed in an outer packaging foil, leaving a liquid inlet. And (4) pouring electrolyte from the electrolyte injection port, packaging, and performing formation, capacity and other processes to obtain the lithium ion battery.

2. Test method

1. Method for testing direct current internal resistance of lithium ion battery

Charging the lithium ion battery to 4.45V at a constant current of 1C (nominal capacity), charging to a current of less than 0.05C at a constant voltage of 4.45V, standing for 5 minutes, then discharging to a cut-off voltage of 3V at a constant current of 1C, then charging to 4.45V at a constant current of 1C (nominal capacity), charging to a current of less than 0.05C at a constant voltage of 4.45V, standing for 5 minutes, then discharging to a cut-off voltage of 3V at a constant current of 1C, repeating the steps for 400 times, recording the discharge capacity of 400 times, adjusting the lithium ion battery to 20% of the required full charge capacity at the actual discharge capacity of 400 times, and continuously discharging for 10 seconds at a current of 0.3C. Calculating the direct current internal resistance of the lithium ion battery by the following formula:

dc internal resistance = (voltage before discharge-voltage at end of discharge)/current

15 samples were tested per example or comparative example and averaged.

2. Method for testing thickness expansion rate of lithium ion battery

The lithium ion battery is allowed to stand at 25 ℃ for 30 minutes, the thickness T1 of the lithium ion battery is measured, then the temperature rise is started at the temperature rise speed of 5 ℃/min, when the temperature rises to 130 ℃, the temperature is kept for 30 minutes, and the thickness T2 of the lithium ion battery is measured. The thickness expansion ratio of the lithium ion battery was calculated by the following formula:

thickness expansion rate = [ (T2-T1)/T1 ] × 100%.

3. Test results

Table 1 shows the influence of the area ratio of the intermediate layer to the active material layer and the sulfur-oxygen double bond-containing compound in the electrolyte on the direct-current internal resistance and the thickness expansion rate of the lithium ion battery.

TABLE 1

"/" indicates that the feature is not added or present

The results show that when the area ratio of the intermediate layer to the active material layer is in the range of 0.9 to 1.1 and the electrolyte includes a compound containing a thiooxy double bond, the expansion/shrinkage of the pole piece caused during the charge and discharge process can be suppressed, and the compound containing a thiooxy double bond helps to stabilize the surface structure of the electrode, the interface between the active material layer and the current collector, and the interface between the active material layer and the electrolyte, so that the direct current internal resistance and the thickness expansion rate of the lithium ion battery can be significantly reduced, and the safety thereof can be improved.

The intermediate layer may be present at the positive or negative electrode, which may achieve substantially equivalent effects.

When the content of the compound containing the sulfur-oxygen double bond in the electrolyte is in the range of 0.01-10%, the direct current internal resistance and the thickness expansion rate of the lithium ion battery can be further reduced, and the safety of the lithium ion battery is improved.

When the area ratio A of the intermediate layer to the active material layer and the content of the compound containing the sulfur-oxygen double bond in the electrolyte are Y%, and the content is more than or equal to 0.009 and less than or equal to AxY and less than or equal to 6, the direct current internal resistance and the thickness expansion rate of the lithium ion battery can be further reduced, and the safety of the lithium ion battery can be improved.

Table 2 shows the average particle diameter and specific surface area X m of the conductive material ² The influence of the concentration of the sulfur-oxygen double bond-containing compound in the electrolyte on the direct current internal resistance and the thickness expansion rate of the lithium ion battery is Y percent. Examples 2-1 to 2-12 differ from example 1-1 only in the parameters listed in Table 2.

TABLE 2

The results indicate that the conductive material may have the following characteristics: has an average particle diameter of 1 μm or less and a specific surface area of 20m ² G to 300m ² In the range of/g and specific surface area X m ² The content of the compound/g and the compound containing the sulfur-oxygen double bond in the electrolyte Y% meets the condition that X is more than or equal to 0.2 and Y is less than or equal to 200. When the conductive material has at least one of the above characteristics, the direct-current internal resistance and the thickness expansion rate of the lithium ion battery can be further reduced, and the safety thereof is improved.

Table 3 further demonstrates the effect of the negative active material on the dc internal resistance and thickness expansion rate of the lithium ion battery performance. Examples 3-1 to 3-5 differ from example 1-1 only in the parameters listed in Table 3.

TABLE 3

The result shows that the direct current internal resistance and the thickness expansion rate of the lithium ion battery can be further reduced by adjusting the negative active material, and the safety of the lithium ion battery is improved. When the negative active material contains a silicon material or hard carbon, the reduction of the direct current internal resistance and the thickness expansion rate of the lithium ion battery is particularly significant.

Table 4 further demonstrates the effect of the positive active material on the dc internal resistance and thickness expansion rate of the lithium ion battery. Examples 4-1 to 4-5 differ from example 1-1 only in the parameters listed in Table 4.

TABLE 4

	Positive electrode active material	DC internal resistance (m omega)	Rate of thickness expansion
				Example 1-1	Lithium cobaltate	185	135％
Example 4-1	80% lithium cobaltate +20% NCM (532)	135	95％
				Example 4 to 2	NCM(532)	113	89％
Examples 4 to 3	80% NCM (532) +20% lithium manganate	106	91％
				Examples 4 to 4	Lithium iron phosphate	117	95％
Examples 4 to 5	80% lithium iron phosphate +20% lithium manganese iron phosphate	112	84％

The result shows that the direct current internal resistance and the thickness expansion rate of the lithium ion battery can be further reduced by adjusting the positive electrode active substance, and the safety of the lithium ion battery is improved.

Table 5 shows the effect of electrolyte composition on the dc internal resistance and thickness swell ratio of the lithium ion battery. Examples 5-1 to 5-31 differ from example 1-1 only in the parameters listed in Table 5.

TABLE 5

"/" indicates that the feature is not added or not present

The results show that, on the basis that the area ratio of the intermediate layer to the active material layer is in the range of 0.9 to 1.1 and the electrolytic solution includes a compound containing a sulfur-oxygen double bond, when the electrolytic solution contains a propionic acid ester, an organic compound having a cyano group, lithium difluorophosphate and/or a compound of formula 2, the direct-current internal resistance and the thickness expansion rate of the lithium ion battery can be further reduced, improving the safety thereof.

Table 6 shows the influence of the relationship between the content Y% of the compound containing a sulfur-oxygen double bond in the electrolyte and the content b% of lithium difluorophosphate on the direct current internal resistance and the thickness expansion rate of the lithium ion battery. Examples 6-1 to 6-11 differ from example 1-1 only in the parameters listed in Table 6

TABLE 6

The result shows that when the content of the lithium difluorophosphate in the electrolyte is 0.01-2%, the direct current internal resistance and the thickness expansion rate of the lithium ion battery can be further reduced, and the safety of the lithium ion battery is improved.

When the content Y percent of the compound containing the sulfur-oxygen double bond and the content b percent of the lithium difluorophosphate in the electrolyte further meet the condition that Y/b is more than or equal to 0.01 and less than or equal to 100, the direct current internal resistance and the thickness expansion rate of the lithium ion battery can be further reduced, and the safety of the lithium ion battery is improved.

Reference throughout this specification to "an embodiment," "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "some examples" means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. Thus, throughout the specification, descriptions appear, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "by example," which do not necessarily refer to the same embodiment or example in this application. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Although illustrative embodiments have been illustrated and described, it will be appreciated by those skilled in the art that the above embodiments are not to be construed as limiting the application and that changes, substitutions and alterations can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. An electrochemical device, comprising: an electrode and an electrolyte, the electrode comprising a current collector, an intermediate layer on the current collector, and an active material layer on the intermediate layer, the intermediate layer comprising a conductive material, wherein:

the area ratio of the intermediate layer to the active material layer is A, A is in the range of 0.9 to 1.1;

the electrolyte includes a compound containing a double sulfur-oxygen bond and an organic compound having a cyano group; the organic compound having a cyano group includes at least one of succinonitrile, adiponitrile, ethylene glycol bis (propionitrile) ether, 1,3,6-hexanetricarbonitrile, or 1,2,3-tris (2-cyanoethoxy) propane.

2. The electrochemical device of claim 1, wherein the compound containing a thiooxy double bond comprises at least one of the following compounds: cyclic sulfate ester, chain sulfonate ester, cyclic sulfonate ester, chain sulfite ester, or cyclic sulfite ester.

3. The electrochemical device of claim 2, wherein the compound containing a thiooxy double bond comprises at least one of 1,3-propane sultone, 1,2-ethylene glycol sulfate, 1-propene-1,3-sultone, or methylene methanedisulfonate.

4. The electrochemical device of claim 1, wherein a is in a range of 0.9 to 1.0, or a is in a range of 1.0 to 1.1.

5. The electrochemical device according to claim 1, wherein the content of the compound containing a sulfur-oxygen double bond is Y%, based on the weight of the electrolytic solution, Y is in the range of 0.01 to 10, and satisfies: 0.009 ≤ A × Y ≤ 6.

6. The electrochemical device according to claim 1, wherein the content of the compound containing a sulfur-oxygen double bond is Y%, based on the weight of the electrolytic solution, Y is in the range of 0.01 to 5, and satisfies: 0.01 is less than or equal to A multiplied by Y is less than or equal to 5.

7. The electrochemical device according to claim 1, wherein the content of the compound containing a sulfur-oxygen double bond is Y% based on the weight of the electrolytic solution, Y being in a range of 0.01 to 10.

8. The electrochemical device according to claim 1, wherein the content of the compound containing a sulfur-oxygen double bond is Y%, Y is in a range of 0.1 to 3, or Y is in a range of 3 to 5, based on the weight of the electrolyte.

9. The electrochemical device according to claim 1, wherein the content of the organic compound having a cyano group is 0.1 to 15% based on the weight of the electrolyte.

10. The electrochemical device according to claim 1, wherein the content of the organic compound having a cyano group is 3 to 5%, or 1 to 8%, based on the weight of the electrolyte.

11. The electrochemical device of claim 1, wherein the electrolyte comprises lithium difluorophosphate and/or propionate based on the weight of the electrolyte.

12. The electrochemical device according to claim 11, wherein the lithium difluorophosphate has a content b% based on the weight of the electrolyte, b being in the range of 0.01 to 2.

13. The electrochemical device of claim 11, wherein the lithium difluorophosphate is present in an amount of b%, b is in the range of 0.01 to 1, or b is in the range of 1 to 2, based on the weight of the electrolyte.

14. The electrochemical device according to claim 11, wherein the propionate is contained in a range of 10 to 60% based on the weight of the electrolyte.

15. The electrochemical device of claim 11, wherein the propionate is in a range of 15% to 55%, or 30% to 50%, based on the weight of the electrolyte.

16. The electrochemical device of claim 11, wherein the propionate comprises at least one of propyl propionate and ethyl propionate.

17. The electrochemical device according to claim 1, wherein the sulfur-oxygen double bond-containing compound is contained in an amount of Y%, the lithium difluorophosphate is contained in an amount of b%, Y is in a range of 0.01 to 5, and 0.1. Ltoreq. Y/b. Ltoreq.100, based on the weight of the electrolyte.

18. The electrochemical device according to claim 1, wherein the content of the compound containing a sulfur-oxygen double bond is Y%, the content of the lithium difluorophosphate is b%, b is in the range of 0.01 to 1, and 1. Ltoreq. Y/b. Ltoreq.50, based on the weight of the electrolyte.

19. The electrochemical device according to claim 1, wherein the conductive material has an average particle diameter of 1 μm or less.

20. The electrochemical device of claim 1, wherein the electrically conductive material comprises at least one of carbon black, carbon fibers, graphene, or carbon nanotubes.

21. The electrochemical device of claim 1, wherein the conductive material has a specific surface area of X m ² In the range of 20 to 300,/g, X.

22. The electrochemical device of claim 21, wherein X is in the range of 80 to 200.

23. The electrochemical device according to claim 21, wherein the content of the compound containing a sulfur-oxygen double bond is Y%, based on the weight of the electrolytic solution, Y is in a range of 0.01 to 10, and satisfies: x is more than or equal to 0.2 and Y is less than or equal to 200.

24. The electrochemical device according to claim 21, wherein the content of the compound containing a sulfur-oxygen double bond is Y%, based on the weight of the electrolytic solution, Y is in a range of 0.01 to 3, and satisfies: x is more than or equal to 0.5 and less than or equal to 150.

25. The electrochemical device of claim 1, wherein the compound containing a thiooxy double bond comprises a compound of formula 1:

wherein:

w is selected from

m is 1,2,3 or 4;

n is 0, 1 or 2; and is

p is 0, 1,2,3, 4, 5 or 6.

26. The electrochemical device of claim 25, wherein the compound of formula 1 comprises at least one of:

，

wherein p is 1.

27. The electrochemical device of claim 1, wherein the electrolyte further comprises at least one of the compounds of formula 2:

wherein:

L ₁ and L ₂ Each independently is- (CR) ⁷ R ⁸ ) _n -；

n is 1,2 or 3.

28. The electrochemical device of claim 27, wherein the compound of formula 2 comprises at least one of the following compounds:

29. an electronic device comprising the electrochemical device of any one of claims 1-28.