CN117254117B

CN117254117B - Secondary battery and electricity utilization device

Info

Publication number: CN117254117B
Application number: CN202311533994.9A
Authority: CN
Inventors: 郭洁; 韩昌隆; 王冠
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2023-11-17
Filing date: 2023-11-17
Publication date: 2024-07-12
Anticipated expiration: 2043-11-17
Also published as: CN117254117A

Abstract

The present application relates to a secondary battery and an electric device. The secondary battery comprises a positive pole piece, a negative pole piece and electrolyte arranged between the positive pole piece and the negative pole piece; the electrolyte comprises LiFSI with the mass content of a; the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer contains a positive electrode active material, and the positive electrode active material comprises a nickel-cobalt-manganese ternary positive electrode material; the molar ratio of Co element in the total molar amount of nickel element, cobalt element and manganese element of the nickel-cobalt-manganese ternary positive electrode material is b; the coating density of the positive electrode film layer is w g/1540.25mm ²; the secondary battery satisfies the following conditions: 0.0003.ltoreq.a.ltoreq.b/w.ltoreq.0.05. The application can give consideration to both power performance and cycle performance by controlling the mass content a of the fluorine-containing sulfonamide lithium salt in the electrolyte, the molar ratio b of Co element and the coating density w of the positive electrode film.

Description

Secondary battery and electricity utilization device

Technical Field

The application relates to the technical field of new energy, in particular to a secondary battery and an electric device.

Background

The statements herein merely provide background information related to the present disclosure and may not necessarily constitute prior art.

In recent years, secondary batteries such as lithium ion batteries have been widely used in various fields such as energy storage power systems for hydraulic power, thermal power, wind power, and solar power stations, electric tools, electric bicycles, electric motorcycles, electric automobiles, military equipment, and aerospace. With the tremendous development of lithium ion batteries, higher demands are also being placed on the power performance and energy density of the lithium ion batteries.

Disclosure of Invention

The application provides a secondary battery and an electric device capable of improving power performance on the basis of considering better energy density.

In order to achieve the above object, a first aspect of the present application provides a secondary battery, including a positive electrode tab, a negative electrode tab, and an electrolyte disposed between the positive electrode tab and the negative electrode tab;

The electrolyte comprises fluorine-containing sulfonamide lithium salt with the mass content of a; the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer contains a positive electrode active material, and the positive electrode active material comprises a nickel-cobalt-manganese ternary positive electrode material; the molar ratio of Co element in the total molar amount of nickel element, cobalt element and manganese element of the nickel-cobalt-manganese ternary positive electrode material is b; the coating density of the positive electrode film layer is w g/1540.25mm ²;

The secondary battery satisfies the following conditions: 0.0003.ltoreq.a.ltoreq.b/w.ltoreq.0.05.

Without wishing to be bound by any theory, the secondary battery of the present application has a mass content a of the fluorine-containing sulfonamide lithium salt in the electrolyte that is too small, and the power performance of the secondary battery is deteriorated; the mass content a of the fluorine-containing sulfonamide lithium salt in the electrolyte is too large, so that aluminum foil of the positive electrode plate is easy to corrode, and the cycle performance of the battery is influenced. The lithium salt can be prevented from diffusing to the surface of the aluminum foil by improving the coating density w of the positive electrode film layer, so that the corrosion of the aluminum foil is relieved, and the cycle performance of the battery is improved. However, a larger coating density w of the positive electrode film layer deteriorates power performance; and by improving the mole ratio b of Co in the total mole of nickel element, cobalt element and manganese element in the nickel-cobalt-manganese ternary positive electrode material, the electron conductivity of the positive electrode material can be improved, and the power performance is improved, but too large mole ratio of Co element can catalyze and oxidize the electrolyte, so that the cycle performance is reduced. In summary, the application can give consideration to both the power performance and the cycle performance by controlling the mass content a of the fluorine-containing sulfonamide lithium salt in the electrolyte, the molar ratio b of Co element and the coating density w of the positive electrode film.

The inventor of the application designs different a, b and w experiment groups, firstly adopts a single variable mode to explore optimal a, b and w values, then combines and adjusts the optimal values, tests the power performance and the cycle performance of the batteries of each experiment group, and finds that the power performance and the cycle performance of the batteries are better when the above formula is satisfied.

In any embodiment of the present application, the secondary battery satisfies at least one of the following conditions:

（1）0.1%≤a≤5%；

（2）5%≤b≤15%；

（3）0.15≤w≤0.35；

（4）0.0005≤a*b/ w≤0.02；

(5) The fluorine-containing sulfonamide lithium salt comprises at least one of LiFSI and LiTFSI.

（1）0.2%≤a≤4%；

（2）7%≤b≤12%；

（3）0.15≤w≤0.2；

（4）0.001≤a*b/ w≤0.02。

in any embodiment of the application, 1.ltoreq.b/a.ltoreq.70.

In any embodiment of the application, 2.ltoreq.b/a.ltoreq.50.

The ratio (b/a) of the molar ratio b of Co element in the molar total of nickel element, cobalt element and manganese element of the nickel-cobalt-manganese ternary positive electrode material to the mass content a of fluorine-containing sulfonamide lithium salt in the electrolyte is controlled, so that the power performance and the cycle performance of the secondary battery can be further improved. The power performance of the battery can be improved by properly increasing the Co content, so that the use amount of the fluorine-containing sulfonamide lithium salt can be reduced, and the cycle performance of the battery can be improved, but too much Co content can catalyze and oxidize electrolyte to reduce the cycle performance, so that the lithium ion battery has better power performance and cycle performance by controlling the Co content and the mass content a of the fluorine-containing sulfonamide lithium salt.

In any embodiment of the present application, the ratio of the mass of the electrolyte to the capacity of the secondary battery is c g/Ah, and the secondary battery satisfies the following conditions: a/c is more than or equal to 0.04% and less than or equal to 2.3%.

According to the secondary battery disclosed by the application, the fluorine-containing sulfonamide lithium salt in the electrolyte can improve the power performance of the battery, and the lower liquid injection coefficient c can reduce the power performance, so that when the content of the lithium salt is relatively high, the lower liquid injection coefficient can be adopted, so that the energy density can be improved, but the content of the lithium salt cannot be too high, corrosion can be caused, and therefore the corrosion is required to be controlled in a reasonable range, and the ratio (a/c) between the mass content a of the fluorine-containing sulfonamide lithium salt in the electrolyte and the liquid injection coefficient c (the ratio of the mass of the electrolyte to the capacity of the secondary battery) can be controlled, so that the synergistic effect can be exerted, and the battery has better power performance, circulation performance and energy density.

（1）0.08%≤a/c≤1.5%；

（2）2.1≤c≤2.5g/Ah。

In any embodiment of the present application, in the molar total of nickel element, cobalt element and manganese element in the nickel-cobalt-manganese ternary cathode material, the molar ratio of Ni element is d, and the secondary battery satisfies the following condition: d/a is more than or equal to 10 and less than or equal to 650.

The safety performance of the cathode active material can be improved by controlling the ratio (d/a) of the molar ratio d of Ni element in the cathode active material to the mass content a of fluorine-containing sulfonamide lithium salt in the electrolyte, so that excellent dynamic performance and safety performance are realized at the same time. The Ni content is high, the oxidizing property of the ternary material is strong, the ternary material has a plurality of side reactions with electrolyte, the heat generation is serious, and the safety performance is low. The fluorine-containing sulfonamide lithium salt has higher stability in a high-nickel system, the safety performance of the battery can be improved by increasing the content of the fluorine-containing sulfonamide lithium salt, but the content of the fluorine-containing sulfonamide lithium salt cannot be too high, and otherwise, the problem of corrosion can be caused. In different Ni content systems, proper content of fluorine-containing sulfonamide lithium salt is added, so that the battery has higher safety and better cycle performance.

（1）20≤d/a≤400；

(2) d is 50% -80%.

The second aspect of the application also provides an electric device comprising the secondary battery of the first aspect of the application.

The power consumption device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

The details of one or more embodiments of the application are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the application will be apparent from the description and drawings, and from the claims.

Drawings

For a better description and illustration of embodiments or examples provided by the present application, reference may be made to one or more of the accompanying drawings. Additional details or examples used to describe the drawings should not be construed as limiting the scope of any of the disclosed applications, the presently described embodiments or examples, and the presently understood best mode of carrying out these applications. Also, like reference numerals are used to designate like parts throughout the accompanying drawings. In the drawings:

fig. 1 is a schematic view of a battery cell according to an embodiment of the present application.

Fig. 2 is an exploded view of the battery cell according to an embodiment of the present application shown in fig. 1.

Fig. 3 is a schematic view of a battery module according to an embodiment of the present application.

Fig. 4 is a schematic view of a battery pack according to an embodiment of the present application.

Fig. 5 is an exploded view of the battery pack of the embodiment of the present application shown in fig. 4.

Fig. 6 is a schematic view of an electric device in which a secondary battery according to an embodiment of the present application is used as a power source.

Reference numerals illustrate:

1, a battery pack; 2, upper box body; 3, lower box body; 4, a battery module; 5, a battery cell; 51 a housing; 52 electrode assembly; 53 cover plates; and 6, an electric device.

Detailed Description

Hereinafter, some embodiments of the secondary battery and the power consumption device of the present application are described in detail with reference to the accompanying drawings as appropriate. However, unnecessary detailed description may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of the actual same structure may be omitted. This is to avoid that the following description becomes unnecessarily lengthy, facilitating the understanding of those skilled in the art. Furthermore, the drawings and the following description are provided for a full understanding of the present application by those skilled in the art, and are not intended to limit the subject matter recited in the claims.

The "range" disclosed herein may be defined in terms of lower and upper limits, with a given range being defined by the selection of a lower limit and an upper limit, the selected lower and upper limits defining the boundaries of the particular range. Ranges may be defined in this way as either inclusive or exclusive of the endpoints, any of which may be independently inclusive or exclusive, and any combination may be made, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if minimum range values 1 and 2 are listed, and if maximum range values 3,4 and 5 are also listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise indicated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed throughout, and "0-5" is simply a shorthand representation of a combination of these values. When a certain parameter is expressed as an integer of 2 or more, it is equivalent to the list of the parameter as, for example, integers of 2,3,4, 5,6,7,8, 9,10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", the integers 2,3,4, 5,6,7,8, 9 and 10 are listed.

In the present application, "plural", etc., refer to, unless otherwise specified, an index of 2 or more in number. For example, "one or more" means one kind or two or more kinds.

All embodiments of the application and alternative embodiments may be combined with each other to form new solutions, unless otherwise specified.

Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment or implementation of the application. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Those of skill in the art will explicitly and implicitly appreciate that the embodiments described herein may be combined with other embodiments. Reference herein to "embodiments" is intended to have a similar understanding.

It will be appreciated by those skilled in the art that in the methods of the embodiments or examples, the order of writing the steps is not meant to be a strict order of execution and the detailed order of execution of the steps should be determined by their functions and possible inherent logic. All the steps of the present application may be performed sequentially or randomly, preferably sequentially, unless otherwise specified. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), and the like.

In the present application, the open technical features or technical solutions described by words such as "contain", "include" and the like are considered to provide both closed features or solutions composed of the listed members and open features or solutions including additional members in addition to the listed members unless otherwise stated. For example, a includes a1, a2, and a3, and may include other members or no additional members, unless otherwise stated, and may be considered as providing features or aspects of "a consists of a1, a2, and a 3" as well as features or aspects of "a includes not only a1, a2, and a3, but also other members". In the present application, a (e.g., B), where B is one non-limiting example of a, is understood not to be limited to B, unless otherwise stated.

In the present application, "optional" refers to the presence or absence of the possibility, i.e., to any one of the two parallel schemes selected from "with" or "without". If multiple "alternatives" occur in a technical solution, if no particular description exists and there is no contradiction or mutual constraint, then each "alternative" is independent.

The secondary battery and the power consumption device according to the present application will be described below with reference to the drawings.

In general, a secondary battery includes a positive electrode tab, a negative electrode tab, and an electrolyte. The electrolyte is positioned between the positive pole piece and the negative pole piece. During the charge and discharge of the battery, active ions are inserted and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in ion conduction between the positive electrode plate and the negative electrode plate. Typically, the electrolyte is in a liquid state, i.e., an electrolyte solution.

In addition, in general, the secondary battery further includes a separator. The isolating film is arranged between the positive pole piece and the negative pole piece, and mainly plays a role in preventing the positive pole piece and the negative pole piece from being short-circuited, and meanwhile ions can pass through the isolating film.

An embodiment of the application provides a secondary battery, which comprises a positive electrode plate, a negative electrode plate and electrolyte arranged between the positive electrode plate and the negative electrode plate.

The electrolyte comprises fluorine-containing sulfonamide lithium salt with the mass content of a. The positive pole piece comprises a positive current collector and a positive film layer arranged on at least one surface of the positive current collector. The positive electrode film layer contains a positive electrode active material, and the positive electrode active material comprises a nickel-cobalt-manganese ternary positive electrode material. The molar ratio of Co element in the total of nickel element, cobalt element and manganese element in the nickel-cobalt-manganese ternary positive electrode material is b; the coating density of the positive electrode film layer is w g/1540.25m m ²; the secondary battery satisfies the following conditions: 0.0003 a/w is less than or equal to 0.05; optionally, 0.0005. Ltoreq.a.b/w.ltoreq.0.02, more optionally, 0.001. Ltoreq.a.b/w.ltoreq.0.02, 0.01. Ltoreq.a.b/w.ltoreq.0.02.

As an example, a x b/w may have a value of 0.0003, 0.0005, 0.001, 0.005, 0.0075, 0.01, 0.02, 0.03, 0.04, 0.05; in some examples, any two of these point values may also be used as ranges of end values, and similar is described below.

In the present application, the fluorosulfonamide lithium salt and its content can be measured according to a method known in the art. For example, measurement can be performed by gas chromatography-mass spectrometry (GC-MS), ion Chromatography (IC), liquid Chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), inductively coupled plasma emission spectroscopy (ICP-OES). For example, by nuclear magnetic resonance spectroscopy, specific test procedures are as follows: in a glove box filled with nitrogen, 500. Mu.L of deuterated reagent was added to the nuclear magnetic tube, 100. Mu.L of non-aqueous electrolyte was sampled and added to the nuclear magnetic tube, and the nuclear magnetic tube was shaken to dissolve the non-aqueous electrolyte into the deuterated reagent, and the test was performed using a bench nuclear magnetic resonance spectrometer X-Pulse from Oxford instruments. Since the nonaqueous electrolyte is very sensitive to moisture, it is carried out in a nitrogen atmosphere (H ₂ O content is less than 0.1 ppm, O2 content is less than 0.1 ppm) at the time of performing the nuclear magnetic test and at the time of preparing the sample, and the instrument related to the test needs to be washed with pure water in advance and dried in a vacuum environment at 60 ℃ for more than 48 hours.

The deuterated reagent is prepared according to the following steps: deuterated dimethyl sulfoxide (DMSO-d 6), deuterated acetonitrile and trifluoromethyl benzene are dried by a 4A molecular sieve for more than 3 days at the temperature of more than 25 ℃ to ensure that the water content of all reagents is less than 3 ppm, and a type 831 KF coulomb water tester of Swiss Wanton Co., ltd. And then uniformly mixing 10 ml dried DMSO-d6 and 300 mu L dried internal standard trifluoromethyl benzene in a glove box filled with nitrogen to obtain a first solution, uniformly mixing 10 ml dried deuterated acetonitrile and 300 mu L dried internal standard trifluoromethyl benzene to obtain a second solution, and uniformly mixing the first solution and the second solution to obtain the deuterated reagent.

Optionally, the fluorine-containing sulfonamide lithium salt includes at least one of LiFSI (lithium bis-fluorosulfonyl imide) and LiTFSI (lithium bis-trifluoromethanesulfonyl imide).

The coating density of the positive electrode film layer means the coating unit area density based on the dry weight of the positive electrode slurry (minus the solvent) when the positive electrode slurry is coated. The coating density of the positive electrode film layer can be obtained by the ratio of the solid content in the coated positive electrode slurry to the coating area; the ratio of the mass of the dried positive electrode film layer to the coating area can also be obtained.

For example, the coating density w g/1540.25mm ² of the positive electrode film layer can be measured by the following method: taking a positive pole piece with a positive pole film layer formed on one side, cutting the positive pole piece into a wafer with the thickness of 1540.25mm ², weighing, and subtracting the mass of the positive current collector to obtain the mass w g of the positive pole film layer, wherein the coating density of the positive pole film layer is w g/1540.25mm ².

In some embodiments, 0.15.ltoreq.w.ltoreq.0.35. That is, the coating density w of the positive electrode film layer is (0.15 g to 0.35 g)/1540.25 mm ².

As examples, w may be 0.15, 0.18, 0.2, 0.3, 0.35. Further, w is more than or equal to 0.15 and less than or equal to 0.2.

Positive electrode plate

The positive pole piece comprises a positive current collector and a positive film layer arranged on at least one surface of the positive current collector, and the positive film layer comprises the positive active material.

As a non-limiting example, the positive electrode current collector has two surfaces opposing in the thickness direction thereof, and the positive electrode film layer is provided on either one or both of the two surfaces opposing the positive electrode current collector.

In some of these embodiments, the positive current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base layer. The composite current collector may be obtained by forming a metal material on a polymeric material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, and the like. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

In some embodiments, the thickness of the single-sided positive electrode film layer is 26-68 μm.

In some embodiments, the cathode active material has a Dv99 of 6 to 11 μm, alternatively 8 to 11 μm, and more alternatively 9 to 10 μm. As examples, dv99 of the positive electrode active material may be 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm. The side reaction of the positive electrode active material is suppressed compared to a positive electrode active material having too small Dv99, and the life deterioration of the positive electrode active material is alleviated compared to a positive electrode active material having too large Dv 99. And the positive electrode active material with specific Dv99 is adopted, so that the transmission path of Li ⁺ is reduced, and the lithium ion battery has good dynamic performance, thereby being beneficial to improving the cycle performance and the power performance of the secondary battery.

In some of these embodiments, the positive electrode active material may be a positive electrode active material for a battery, which is well known in the art. As non-limiting examples, the positive electrode active material may include one or more of the following materials: olivine structured lithium-containing phosphates, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material may be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (e.g., liCoO ₂), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, nickel cobalt manganese ternary positive electrode material (or referred to as lithium nickel cobalt manganese oxide), lithium nickel cobalt aluminum oxide, modified compounds thereof, and the like.

Non-limiting examples of olivine structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese phosphate, a composite of lithium manganese phosphate and carbon.

Non-limiting examples of lithium cobalt oxide may include LiCoO ₂; non-limiting examples of lithium nickel oxide may include LiNiO ₂; non-limiting examples of lithium manganese oxide may include LiMnO ₂、LiMn₂O₄, etc.; non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi _0.85Co_0.15Al_0.05O₂.

Non-limiting examples of nickel cobalt manganese ternary cathode materials (or lithium nickel cobalt manganese oxides) may include LiNi_0.68Co_0.10Mn_0.22O₂、LiNi_0.64Co_0.09Mn_0.27O₂、LiNi_0.5Co_0.15Mn_0.35O₂、LiNi_0.8Co_0.1Mn_0.1O₂（, which may also be referred to simply as NCM ₈₁₁）、LiNi_0.85Co_0.05Mn_0.1O₂, and the like. It is understood that the nickel-cobalt-manganese ternary cathode material may also be doped with other metallic elements.

It is understood that the battery is accompanied by deintercalation and consumption of lithium (Li) during charge and discharge, and the content of Li in the positive electrode active material varies when the battery is discharged to different states. In the present application, the Li content is the initial state of the material unless otherwise specified in the list of the positive electrode active materials. The positive electrode active material is applied to a positive electrode plate in a battery system, and the content of Li in the positive electrode active material contained in the plate is generally changed after charge and discharge cycles. The content of Li may be measured by a molar ratio, but is not limited thereto. The "Li content is the initial state of the material", which refers to the state before the positive electrode slurry is fed. It is understood that new materials obtained by suitable modification based on the listed positive electrode active materials are also within the category of positive electrode active materials, the foregoing suitable modification being indicative of acceptable modification modes for the positive electrode active materials, non-limiting examples being coating modification.

In the present application, the content of oxygen (O) is only a theoretical state value, and the lattice oxygen release causes a change in the molar ratio of oxygen, and the actual O content is floating. The content of O may be measured by a molar ratio, but is not limited thereto.

In some of these embodiments, the positive electrode active material comprises a nickel cobalt manganese ternary positive electrode material.

In some embodiments, 1.ltoreq.b/a.ltoreq.70. Further, controlling the ratio of b/a to 50 to 2; as an example, b/a may have a value of 1, 1.5, 2, 2.5, 3,4, 5, 7, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70; or a range formed by any two of the above-mentioned point values.

The molar content of each element (for example, nickel cobalt manganese element) in the positive electrode active material can be tested and analyzed by using an inductively coupled plasma emission spectrometer iCAP 7400 by using an ICP method (microelement analysis-inductively coupled plasma emission spectrometry) which is known in the art. The molar ratio b of Co element in the total molar amount of nickel element, cobalt element and manganese element of the nickel-cobalt-manganese ternary positive electrode material, and the subsequent molar ratio b of Ni element can be obtained by the molar content of nickel-cobalt-manganese element in the positive electrode active material.

In some embodiments, the molar ratio b of Co element in the total of nickel element, cobalt element and manganese element in the nickel-cobalt-manganese ternary cathode material is 5% -15%, and further may be 7% -12%. The higher Co content can improve the electron conductivity of the positive electrode active material, thereby improving the dynamic performance of the positive electrode plate and reducing the temperature rise in the fast charging process.

As an example, the molar ratio b of Co element may be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% in the molar total of nickel element, cobalt element, and manganese element in the nickel-cobalt-manganese ternary cathode material.

Optionally, the mole ratio of the Co element on the surface layer of the nickel-cobalt-manganese ternary cathode material is larger than the mole ratio of the Co element on the inner layer. In other words, the composition of the inner part and the surface layer of the nickel-cobalt-manganese ternary positive electrode material are different, the molar ratio of Co element in the inner layer is smaller, and the molar ratio of Co element in the surface layer is larger. The gradient arrangement of the nickel-cobalt-manganese ternary anode material Co can effectively stabilize the structure of the anode active material and improve the dynamic performance of the anode plate.

It is appreciated that in some examples, differentiation of the molar ratios of the inner and outer Co elements may be achieved by multiple coating with precursors of different compositions. It is to be understood that the specific implementation is not so limited.

In some embodiments, in the molar total of nickel element, cobalt element and manganese element of the nickel-cobalt-manganese ternary cathode material, the molar ratio of the Ni element is d, and the secondary battery satisfies the following condition: 10.ltoreq.d/a.ltoreq.650, further 20.ltoreq.d/a.ltoreq.400.

Alternatively, 10.ltoreq.d/a.ltoreq.500; more preferably, the ratio of d/a is 20-200.

As an example, d/a may take the values of 10, 14, 17, 20, 21, 23, 27, 30, 40, 50, 60, 68, 70, 90, 100, 200, 300, 400, 500, 600, 650.

Further, d is 50% -80%. Optionally, d is 60% -70%. As an example, d may take the values of 50%, 55%, 60%, 65%, 68%, 70%, 75%, 80%.

The secondary battery can be used for a high nickel positive electrode system.

In some of these embodiments, the positive electrode film layer further optionally includes a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymers, tetrafluoroethylene-hexafluoropropylene copolymers, and fluoroacrylate resins.

In some of these embodiments, the positive electrode film layer may further optionally include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the mass content of the positive electrode active material in the positive electrode film layer is 75% -98%.

In some embodiments, the mass content of the conductive agent in the positive electrode film layer is 0.1% -15%.

In some embodiments, the mass content of the binder in the positive electrode film layer is 0.5% -15%.

In some of these embodiments, the positive electrode sheet may be prepared by: dispersing the above components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, in a solvent to form a positive electrode slurry; and coating the positive electrode slurry on at least one side surface of the positive electrode current collector, and obtaining the positive electrode plate after the procedures of drying, cold pressing and the like.

The type of solvent may be selected from, but is not limited to, any of the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or two surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or two surfaces of the positive electrode current collector. The solid content of the positive electrode slurry may be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000-25000 mPa.s.

Negative pole piece

Typically, the negative electrode tab includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

As a non-limiting example, the anode current collector has two surfaces opposing in its own thickness direction, and the anode active material layer is provided on either or both of the two surfaces opposing the anode current collector.

In some of these embodiments, the negative current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base material. The composite current collector may be obtained by forming a metal material on a polymeric material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel alloy, titanium alloy, silver alloy, and the like. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

Further, the anode film layer may include an anode active material layer including an anode active material.

In some embodiments, the thickness of the single-sided negative electrode film layer is 22-110 μm.

In some of these embodiments, the negative active material may employ a negative active material for a battery, which is well known in the art. As non-limiting examples, the anode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like. The silicon-based material may include one or more of elemental silicon, silicon oxygen compounds, silicon carbon composites, silicon nitrogen composites, and silicon alloys. The tin-based material may include one or more of elemental tin, tin oxide, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery anode active material may be used. These negative electrode active materials may be used alone or in combination of two or more.

In some of these embodiments, the negative electrode active material layer may further optionally include a binder. The binder may include one or more of Styrene Butadiene Rubber (SBR), polyacrylic acid (PAA), sodium Polyacrylate (PAAs), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium Alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

In some of these embodiments, the anode active material layer may further optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some of these embodiments, the anode active material layer may optionally further include other adjuvants, such as a thickener (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

In some embodiments, the mass content of the positive electrode active material in the negative electrode film layer is 75% -98%.

In some embodiments, the mass content of the conductive agent in the negative electrode film layer is 0.1% -15%.

In some embodiments, the mass content of the binder in the negative electrode film layer is 0.5% -15%.

In some of these embodiments, the negative pole piece has a compacted density of 1.7g/cm ³ or less; the concentration of the active ingredients is less than or equal to 1.6g/cm ³ or 1.2-1.5 g/cm ³. The arrangement of the small compaction density of the negative electrode plate is controlled, so that larger pores are formed in the negative electrode plate, the infiltration of electrolyte is improved, the transmission of Li ⁺ is improved, the overall dynamic performance of the secondary battery is improved, and the improvement of the power performance is facilitated. It is understood that the compacted density of the negative electrode tab refers to the compacted density of the negative electrode film layer on the negative electrode tab. Compaction density testing: the method comprises the steps of disassembling an electric core, taking a pole piece, punching the pole piece into small disks with the area of S, measuring the weight M and the thickness L of the small disks, taking another layer of pole piece, erasing a film layer on the surface to obtain a residual empty current collector foil, punching the small disks into S, weighing the empty aluminum foil, and compacting the mass M0 of the empty aluminum foil, wherein the compaction density PD= (M-M0)/(S n is L), and n is the number of film layers coated on the current collector, namely 1 or 2, and single-sided coating or double-sided coating. In a specific example, S is 1540.25mm ².

In some of these embodiments, the negative electrode sheet may be prepared by: dispersing the above components for preparing a negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; and coating the negative electrode slurry on at least one side surface of a negative electrode current collector, and obtaining a negative electrode plate after the procedures of drying, cold pressing and the like.

The surface of the negative electrode current collector coated with the negative electrode slurry may be a single surface of the negative electrode current collector or may be two surfaces of the negative electrode current collector. The solid content of the negative electrode slurry may be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature may be adjusted to 2000 to 10000mpa·s.

Electrolyte composition

The electrolyte has the function of conducting ions between the positive pole piece and the negative pole piece. The electrolyte of the application adopts electrolyte. The electrolyte includes an electrolyte salt and a solvent. As described above, the electrolyte includes the fluorine-containing sulfonamide lithium salt with a mass content of a. Further, the fluorine-containing sulfonamide lithium salt includes, but is not limited to, at least one of LiFSI (lithium bis-fluorosulfonyl imide) and LiTFSI (lithium bis-trifluoromethanesulfonyl imide). Wherein the fluorine-containing sulfonamide lithium salt is electrolyte salt.

In some embodiments, 0.1 < a.ltoreq.5%; as an example, a may take the value of 0.1%, 0.15%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%. Alternatively, a is more than or equal to 0.15% and less than or equal to 4%, and the range can be formed by any two points.

In some of these embodiments, the ratio of the mass of the electrolyte to the capacity of the secondary battery is a fill factor c g/Ah, and the secondary battery satisfies the following conditions: a/c is more than or equal to 0.04% and less than or equal to 2.3%, and further, a/c is more than or equal to 0.08% and less than or equal to 1.5%. As an example, a/c may take on values of 0.04%, 0.07%, 0.08%, 0.09%, 0.1%, 0.5%, 1%, 1.2%, 1.3%, 1.5%, 2%, 2.2%, 2.3%.

Further, c is more than or equal to 2.1 and less than or equal to 2.5g/Ah. By way of example, c may be 2.1g/Ah, 2.3g/Ah, 2.5g/Ah.

Battery capacity: referring to the nominal capacity of the battery, the nominal capacity of the battery is generally noted on the label of the battery product or in the specification.

If the nominal capacity is not noted, the battery capacity can be obtained by the following test method: the battery was charged to an upper limit voltage (6 is generally 4.4V,8 is 4.25V) at 25 ℃ with a constant current of 0.33C, then charged to a current falling to 0.05C at an upper limit voltage at a constant voltage, left to stand for 5min, then discharged to 2.5V at a constant current of 0.33C, left to stand for 5min, and the above charge and discharge flow was cycled 3 times, and the discharge capacity of the last time was recorded as the capacity of the battery. In order to accurately test the capacity of the battery, the battery just shipped or the battery within 1W kilometer of the vehicle may be taken for testing.

The quality of the electrolyte in the battery can be obtained by testing the method: taking the battery cell, wiping the battery cell cleanly, testing the weight of the battery cell to be x, fully putting the battery cell, disassembling the battery cell, soaking all parts of the battery cell, cathode and anode, isolating film materials and the like in dimethyl carbonate for 12h, cleaning, putting the soaked materials into a vacuum oven, baking for 14h, weighing the total weight of the baked materials to be y, and then weighing the mass of electrolyte in the battery to be x-y. The injection coefficient c can be obtained by calculating the ratio of the mass (x-y) of the electrolyte to the battery capacity.

In some of these embodiments, the electrolyte salt may further include one or more of lithium hexafluorophosphate (LiPF ₆), lithium tetrafluoroborate (LiBF ₄), lithium perchlorate (LiClO ₄), lithium hexafluoroarsenate (LiAsF ₆), lithium trifluoromethane sulfonate (LiTFS), lithium difluorophosphate (LiPO ₂F₂), lithium difluorooxalato borate (lidaob), lithium dioxaoxalato borate (LiBOB), lithium difluorodioxaato phosphate (LiDFOP), and lithium tetrafluorooxalato phosphate (LiTFOP).

In some of these embodiments, the solvent may include one or more of Ethylene Carbonate (EC), propylene Carbonate (PC), ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl Propyl Carbonate (MPC), ethyl Propyl Carbonate (EPC), fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1, 4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

In some of these embodiments, the electrolyte further optionally includes an additive. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives capable of improving certain properties of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, and the like.

In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of difluoroethylene carbonate (DFEC), trifluoromethylcarbonate (TFPC), and the like.

Isolation film

The isolating film is arranged between the positive pole piece and the negative pole piece, and mainly plays a role in preventing the positive pole piece and the negative pole piece from being short-circuited, and meanwhile ions can pass through the isolating film.

In some embodiments, the barrier film has a Gurley value of 100s to 600s.

Optionally, the Gurley value of the isolation film is 150 s-600 s;

more optionally, the isolation film has a Gurley value of 400s to 600 s; or 400 s-500 s, or 440 s-570 s.

The Gurley value of the control isolating film is in the smaller range, the impedance is smaller, the dynamic performance is better, and the control isolating film can realize more excellent quick charging capability when being matched with electrolyte containing LiFSI.

The Gurley of the release film can be tested as follows: the barrier film was placed in an air permeability tester and the time required for 100mL of air to pass through a1 square inch barrier film, in seconds, s, was tested at a pressure of 1.22 kPa.

In some embodiments, the material of the isolation film may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.

In some embodiments, the thickness of the separator is 6 μm to 40 μm, optionally 12 μm to 20 μm.

In some of these embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.

In some of these embodiments, the secondary battery may include an outer package. The outer package may be used to encapsulate the electrode assembly and electrolyte described above.

In some of these embodiments, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. The exterior package of the secondary battery may also be a pouch type pouch, for example. The material of the soft bag can be plastic, and further, non-limiting examples of the plastic can comprise one or more of polypropylene, polybutylene terephthalate, polybutylene succinate and the like.

The secondary battery includes at least one battery cell therein. The secondary battery may include 1 or more battery cells. In one example, the secondary battery may also be a battery cell.

In the present application, unless otherwise indicated, "battery cell" refers to a basic unit capable of achieving mutual conversion of chemical energy and electric energy, and further, generally includes at least a positive electrode sheet, a negative electrode sheet, and an electrolyte. During the charge and discharge of the battery, active ions are inserted and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate.

The shape of the battery cell is not particularly limited in the present application, and may be cylindrical, square or any other shape. For example, fig. 1 is a square-structured battery cell 5 as one example.

In some of these embodiments, referring to fig. 2, the overpack may include a housing 51 and a cover 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, where the bottom plate and the side plate enclose a receiving chamber. The housing 51 has an opening communicating with the accommodation chamber, and the cover plate 53 can be provided to cover the opening to close the accommodation chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the receiving chamber. The electrolyte is impregnated in the electrode assembly 52. The number of the electrode assemblies 52 included in the battery cell 5 may be one or more, and one skilled in the art may select according to actual needs.

The secondary battery may be the battery module 4 or the battery pack 1.

The battery module includes at least one battery cell. The number of battery cells included in the battery module may be one or more, and one skilled in the art may select an appropriate number according to the application and capacity of the battery module.

Fig. 3 is a battery module 4 as an example. Referring to fig. 3, in the battery module 4, a plurality of battery cells 5 may be sequentially arranged in the longitudinal direction of the battery module 4. Of course, the arrangement may be performed in any other way. The plurality of battery cells 5 may be further fixed by fasteners.

Alternatively, the battery module 4 may further include a housing having an accommodating space in which the plurality of battery cells 5 are accommodated.

In some embodiments, the battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, and one skilled in the art may select an appropriate number according to the application and capacity of the battery pack.

Fig. 4 and 5 are battery packs 1 as an example. Referring to fig. 4 and 5, a battery case and a plurality of battery modules 4 disposed in the battery case may be included in the battery pack 1. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

In addition, the application also provides an electric device, which comprises the secondary battery provided by the application. The secondary battery may be used as a power source of an electric device, or may be used as an energy storage unit of an electric device. The powered devices may include, but are not limited to, mobile devices, electric vehicles, electric trains, boats and ships, and satellites, energy storage systems, and the like. The mobile device may be, for example, a mobile phone, a notebook computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf car, an electric truck, or the like, but is not limited thereto.

As the electric device, a secondary battery may be selected according to its use requirement.

Fig. 6 is an electric device 6 as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle or the like. In order to meet the high power and high energy density requirements of the secondary battery by the power consumption device, a battery pack or a battery module may be employed.

As another example, the device may be a cell phone, tablet computer, notebook computer, or the like. The device is generally required to be light and thin, and a secondary battery can be used as a power source.

The following are specific examples.

Hereinafter, embodiments of the present application are described. The following examples are illustrative only and are not to be construed as limiting the application. The examples are not to be construed as limiting the scope of the application in any way, as defined in the art or as defined in the specification. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

Example 1

1) Preparation of positive electrode plate

Uniformly mixing an anode active material (nickel cobalt manganese ternary anode material), conductive agent carbon black (Super P) and binder polyvinylidene fluoride (PVDF) in a mass ratio of 96.2:2.7:1.1 in a proper amount of solvent N-methylpyrrolidone (NMP) to obtain anode slurry; and (3) coating the positive electrode slurry on a positive electrode current collector aluminum foil, and forming a positive electrode film layer with a single-sided thickness of 38 mu m through the procedures of drying, cold pressing, slitting, cutting and the like to obtain a positive electrode plate. Specific compositions of the nickel-cobalt-manganese ternary positive electrode material, mole ratio b of Co element, mole ratio d of Ni element and coating density w g/11540.25 mm ² of the positive electrode film layer in the total mole amount of nickel element, cobalt element and manganese element of the nickel-cobalt-manganese ternary positive electrode material are shown in table 1.

2) Preparation of negative electrode plate

Uniformly mixing negative electrode active material artificial graphite, conductive agent carbon black (Super P), binder styrene-butadiene rubber (SBR) and sodium carboxymethylcellulose (CMC-Na) in a mass ratio of 96.4:0.7:1.8:1.1 in a proper amount of solvent deionized water to obtain negative electrode slurry; and (3) coating the negative electrode slurry on a negative electrode current collector copper foil, and forming a negative electrode film layer with a single-sided thickness of 54 mu m through the procedures of drying, cold pressing, slitting and cutting to obtain a negative electrode plate.

3) Isolation film

A polypropylene separator film of 12 μm thickness was selected.

4) Preparation of electrolyte

Ethylene Carbonate (EC) and ethylmethyl carbonate (EMC) were mixed according to mass 30:70, and dissolving LiFSI accounting for 3wt% of the whole electrolyte in the mixed solvent, and dissolving fully dried LiPF ₆ in the organic solvent to prepare the electrolyte with the concentration of 1 mol/L.

5) Preparation of secondary battery

Sequentially stacking and winding the positive electrode plate, the isolating film and the negative electrode plate to obtain an electrode assembly; placing the electrode assembly in an outer package, drying, injecting electrolyte, and performing vacuum packaging, standing, formation, shaping and other procedures to obtain a secondary battery; the ratio of the mass of the electrolyte to the capacity of the secondary battery was c g/Ah, and specific parameter values are shown in table 1.

Examples 2 to 4

The secondary batteries of examples 2 to 4 were similar to the secondary battery of example 1 except that the mass content a of LiFSI in the electrolyte was different, and specific parameter values are shown in table 1.

Examples 5 to 9

The secondary batteries of examples 5 to 9 were similar to the secondary battery of example 1 except that at least one of the mass content a of LiFSI in the electrolyte and the specific composition of the nickel-cobalt-manganese ternary cathode material was different, and specific parameter values are shown in table 1.

The secondary batteries of examples 10 to 11 were similar to the secondary battery of example 1 in that the ratio c g/Ah of the capacities of the secondary batteries was different, and specific parameter values are shown in table 1.

The secondary batteries of examples 12 to 13 were similar to the secondary battery of example 1 except that the coating density w g/1540.25mm ² of the positive electrode film layer was different, and specific parameter values are shown in table 1.

The secondary battery of example 14 was similar to the secondary battery of example 1 except that the mass content a of LiFSI in the electrolyte, the specific composition of the nickel-cobalt-manganese ternary positive electrode material, and the coating density w g/1540.25mm ² of the positive electrode film layer were different, and specific parameter values are shown in table 1.

Comparative examples 1 to 2

The secondary batteries of comparative examples 1 to 2 were similar to the secondary battery preparation method of example 1, except that at least one of the mass content a of LiFSI in the electrolyte, the specific composition of the nickel-cobalt-manganese ternary positive electrode material, and the coating density w g/1540.25mm ² of the positive electrode film layer was different, and specific parameter values are shown in table 1.

TABLE 1

The foregoing description of various embodiments is intended to highlight differences between the various embodiments, which may be the same or similar to each other by reference, and is not repeated herein for the sake of brevity.

The following is a performance test.

(1) Quick charge cycle life test:

First, a fast charge window is obtained: the batteries of the above examples and comparative examples were charged and discharged for the first time at a current of 1C (i.e., a current value at which the theoretical capacity was completely discharged within 1 h), specifically including: at 35 ℃, the battery is charged to 4.4V with constant current at 1C multiplying power, then is charged to current less than or equal to 0.05C with constant voltage, is kept stand for 5min, is discharged to 2.5V with constant current at 0.33C multiplying power, and the actual capacity is recorded as C0. Then, the battery is charged to the full battery Charge cut-off voltage of 4.4V or the full battery Charge cut-off voltage of 0V (based on the previous achievement) by constant current sequentially according to 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0 and 5C0, after each charging is completed, the battery is required to be discharged to the full battery discharge cut-off voltage of 2.5V by 1C0, the charging is recorded to 10%, 20%, 30%, … … and 80% SOC (State of Charge) under different charging rates, the battery discharging is completely represented when 'SOC=0', the charging rate-negative electrode potential curve under different SOC states is drawn, the charging rate corresponding to the charging rate under the different SOC states is the charging window under the 0V, and the charging rates are respectively recorded as C (10% SOC), C (20% SOC), C (30% SOC), C (40% SOC), C (50% SOC), C (60% C) and the maximum charging rate (80% SOC), and the maximum charging rate is obtained under the State of Charge window.

Fast charge cycle life: the obtained quick charge window is adopted for step charging, the charging rate of C (10%SOC) is used for constant current charging to 10%SOC, the charging rate of C (20%SOC) is used for constant current charging to 20%SOC, the charging rate of C (30%SOC) is used for constant current charging to 30%SOC, the charging rate of C (40%SOC) is used for constant current charging to 40%SOC, the charging rate of C (50%SOC) is used for constant current charging to 50%SOC, the charging rate of C (60%SOC) is used for constant current charging to 60%SOC, the charging rate of C (70%SOC) is used for constant current charging to 70%SOC, the charging rate of C (80%SOC) is used for constant current charging to 80%SOC, the charging rate of C (0.33C) is used for constant current charging to 100%SOC, the rest is carried out for 10min, the charging rate of 0.33C is used for discharging to 2.5V, and the cycle number when the cycle is attenuated to 80%SOH is recorded according to the flow.

Wherein the number of cycles at decay to 80% SOH is calculated by: dividing the discharge capacity of the nth turn by the discharge capacity of the first turn from small to large, and recording the ratio respectively; when the ratio is equal to or less than 80% SOH for the first time, the number of cycles is the number of cycles that decays to 80% SOH.

(2) And (3) quick temperature rise test: the method comprises the steps of adopting a charge-discharge flow as a quick charge cycle life test to charge and discharge 1 cycle, specifically, charging to 10% SOC at a charge rate of C (10% SOC), charging to 20% SOC at a charge rate of C (20% SOC), charging to 30% SOC at a charge rate of C (30% SOC), charging to 40% SOC at a charge rate of C (40% SOC), charging to 50% SOC at a charge rate of C (50% SOC), charging to 60% SOC at a charge rate of C (60% SOC), charging to 70% SOC at a charge rate of C (70% SOC), charging to 80% SOC at a charge rate of C (80% SOC), charging to 100% SOC at a charge rate of 0.33C at a constant current, resting for 10min, discharging to 2.5V at a charge rate of 0.33C, testing and recording the temperature rise of a large surface of a battery cell in the process, wherein the maximum temperature rise is the quick charge temperature rise in the process.

(3) And (3) testing the safety of the hot box: the battery cell is fully charged to the corresponding designed upper limit voltage, the battery cell is provided with a clamp, the temperature of the incubator is raised from normal temperature, the temperature is raised to 100 ℃ according to the temperature of 2 ℃/min, the temperature is maintained for 1 hour, the temperature is raised by 5 ℃/min, the temperature is maintained for 30 minutes every 5 ℃ until the battery cell fails (the valve is opened to smoke or fire), the test is stopped, the upper limit temperature is set to 250 ℃, and the furnace temperature when the battery cell fails is recorded.

(4) Energy density: at 25 ℃, the battery is charged to the designed upper limit voltage at constant current and constant voltage of 0.33 ℃, the cut-off current is 0.05 ℃, the battery is discharged to the designed lower limit voltage at 0.33 after standing for 30min, the discharge energy P (Wh) is recorded, the weight of the battery core is recorded as m (kg), and then the energy density (Wh/kg) =P/m.

The test results are shown in Table 2.

TABLE 2

The fast charge cycle life (80% soh cycle number) in table 2 can characterize the power performance of the secondary battery. The larger the fast charge cycle life (number of cycles of 80% soh) is, the more excellent the fast charge cycle performance is.

The rapid charge temperature rise and hot box safety test in table 2 can characterize the thermal runaway condition caused by too rapid a temperature rise during rapid charge. The quick charge Wen Shengyue is small, which indicates that the risk of thermal runaway caused by too quick temperature rise in the quick charge process is smaller; the higher the furnace temperature is when the thermal box safety test cell fails, the smaller the thermal runaway risk caused by the too fast temperature rise in the quick charging process is.

Wherein "/" in the table indicates that the example or comparative example was not subjected to the hot box safety performance test.

As can be seen from examples 1 to 14 and comparative examples 1 to 2, the secondary battery has better power performance and cycle performance when the value of ab/w is in the range of 0.0003 to 0.05, particularly in the range of 0.0005 to 0.02, and further when ab/w is 0.001 or less and 0.02 or less. The a/b/w value of the secondary battery is too small or too large, meaning that the mass content a of LiFSI in the electrolyte and the molar ratio b of cobalt element of the positive electrode active material, and the coating density w g/1540.25mm ² of the positive electrode film layer are not well matched, resulting in impaired power performance or cycle performance.

Analysis of examples 1-9 shows that the secondary battery has a b/a value in the range of 1-70, particularly in the range of 2-50, and has excellent power performance and cycle performance. It is explained that the mass content a of LiFSI in the electrolyte and the Co content b in the positive electrode active material need to be maintained at a proper ratio.

Analysis of example 3 and examples 5 to 9 revealed that the secondary battery d/a was in the range of 10 to 650, and in particular, in the range of 20 to 400, and that the secondary battery had superior safety performance and cycle performance. It is indicated that when the Ni content of the positive electrode material is different, the LiFSI mass content a in the electrolyte needs to be controlled, so that the safety performance can be improved, and the cycle performance cannot be deteriorated too much.

By analyzing examples 1 to 6 and examples 10 to 11, it can be seen that the secondary battery has a/c in the range of 0.04% to 2.3%, particularly in the range of 0.08% to 1.5%, and has superior power performance, cycle performance and energy density. It is described that in order to maintain the overall performance of the battery, the lithium salt content cannot be increased infinitely when different energy densities are achieved by adjusting the injection coefficient, so that the power performance of the battery is improved, and it is required to be controlled within a reasonable range.

According to analysis of examples 1-5, it can be seen that the secondary battery has better power performance and cycle performance when the mass content of LiFSI in the electrolyte is 0.1% -5%, especially 0.2% -4%, and further 1% -3%.

The present application is not limited to the above embodiment. The above embodiments are merely examples, and embodiments having substantially the same configuration and the same effects as those of the technical idea within the scope of the present application are included in the technical scope of the present application. Further, various modifications that can be made to the embodiments and other modes of combining some of the constituent elements in the embodiments, which are conceivable to those skilled in the art, are also included in the scope of the present application within the scope not departing from the gist of the present application.

Claims

1. The secondary battery is characterized by comprising a positive pole piece, a negative pole piece and electrolyte arranged between the positive pole piece and the negative pole piece;

The electrolyte comprises 0.2% or more and 5% or less of fluorine-containing sulfonamide lithium salt with the mass content of a; the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer contains a positive electrode active material, and the positive electrode active material comprises a nickel-cobalt-manganese ternary positive electrode material; in the molar total of nickel element, cobalt element and manganese element of the nickel-cobalt-manganese ternary positive electrode material, the molar ratio of Co element is b, and b is more than or equal to 7% and less than or equal to 15%; the coating density of the positive electrode film layer is w g/1540.25mm ², w is more than or equal to 0.15 and less than or equal to 0.2, the ratio of the mass of the electrolyte to the capacity of the secondary battery is c g/Ah, c is more than or equal to 2.1 and less than or equal to 2.5, and the secondary battery meets the following conditions: 0.00389 a, b/w is less than or equal to 0.03.

2. The secondary battery according to claim 1, wherein the secondary battery satisfies at least one of the following conditions:

（1）0.5%≤a≤5%；

（2）7%≤b≤12%；

（3）0.18≤w≤0.2；

（4）0.005≤a*b/ w≤0.03；

3. The secondary battery according to claim 2, wherein the secondary battery satisfies at least one of the following conditions:

（1）1%≤a≤5%；

（2）7%≤b≤10%；

（3）0.01≤a*b/ w≤0.02。

4. The secondary battery according to claim 1, wherein 1.ltoreq.b/a.ltoreq.70.

5. The secondary battery according to claim 4, wherein 2.ltoreq.b/a.ltoreq.50.

6. The secondary battery according to any one of claims 1 to 5, wherein a ratio of a mass of the electrolytic solution to a capacity of the secondary battery is c g/Ah, the secondary battery satisfying the following condition: a/c is more than or equal to 0.04% and less than or equal to 2.3%.

7. The secondary battery according to claim 6, wherein the secondary battery satisfies at least one of the following conditions:

（1）0.08%≤a/c≤1.5%；

（2）2.3≤c≤2.5。

8. The secondary battery according to any one of claims 1 to 5, 7, wherein in the molar total of nickel element, cobalt element and manganese element of the nickel-cobalt-manganese ternary cathode material, the molar ratio of Ni element is d, the secondary battery satisfies the following condition: d/a is more than or equal to 10 and less than or equal to 650.

9. The secondary battery according to claim 8, wherein the secondary battery satisfies at least one of the following conditions:

（1）20≤d/a≤400；

(2) d is 50% -80%.

10. An electric device comprising the secondary battery according to any one of claims 1 to 9.