JP2016146261A - Nonaqueous electrolyte power storage element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte power storage element excellent in cycle characteristics and maintaining a high energy density.SOLUTION: (1) A nonaqueous electrolyte power storage element having a positive electrode containing a positive electrode active material capable of inserting and detaching anion, a negative electrode containing a negative electrode active material capable of inserting and detaching cation, and a nonaqueous electrolyte, where the positive electrode active material contains carbon as a core material, and the edge on the surface thereof is coated with particulate amorphous carbon. (2) When the Rh(1360 cm/1580 cm) of the core material is Rh, and the Rh(1360 cm/1580 cm) of the positive electrode active material is Rh, 0.08≤Rh/Rh≤0.70 is satisfied, in the nonaqueous electrolyte power storage element described in (1).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a nonaqueous electrolyte storage element capable of inserting and removing an anion in a positive electrode and a cation in a negative electrode.

In recent years, the characteristics of non-aqueous electrolyte storage elements with high energy density have improved and become widespread with the downsizing and higher performance of portable devices. Development is also underway, and installation in electric vehicles has begun.
Such a non-aqueous electrolyte storage element comprises a positive electrode such as a lithium cobalt composite oxide, a carbon negative electrode, and a non-aqueous electrolyte obtained by dissolving a lithium salt in a non-aqueous solvent. Lithium ion secondary batteries are often used that are charged and discharged by lithium being desorbed and inserted into carbon of the negative electrode, and lithium inserted into the negative electrode being desorbed and returning to the composite oxide of the positive electrode during discharge.
On the other hand, when a power storage element is used in a hybrid vehicle or the like, it is essential to be able to output a large current instantaneously, and it is desirable that it can be charged with regenerative energy. Becomes important. Therefore, an electric double layer capacitor that can be charged and discharged at high speed without requiring a chemical reaction is used. However, the energy density is a few tenths compared with a lithium ion power storage element, and a heavy power storage element is required to secure a sufficient capacity, and hindering improvement in fuel consumption when mounted on an automobile.

As an energy storage device having a high energy density and suitable for high-speed charge / discharge, a conductive polymer, a carbon material or the like is used as a positive electrode, a negative electrode such as carbon, and a nonaqueous electrolytic solution in which a lithium salt is dissolved in a nonaqueous solvent, At the time of charging, the anion in the non-aqueous electrolyte is inserted into the positive electrode and the cation is inserted into the negative electrode, and at the time of discharging, the anion and cation inserted into the positive electrode and the negative electrode are desorbed into the electrolytic solution to perform charging / discharging. The so-called dual intercalation type non-aqueous electrolyte storage element (dual carbon battery) is expected to be put to practical use.
When LiPF ₆ is used as the lithium salt, charging is performed by inserting PF ₆ ⁻ into the positive electrode from the non-aqueous electrolyte and inserting Li ⁺ into the negative electrode as shown in the following reaction formula. To PF ₆ ⁻ and Li ⁺ from the negative electrode are desorbed to the non-aqueous electrolyte, thereby discharging.

The discharge capacity of the dual carbon battery is determined by the anion storage amount of the positive electrode, the anion release amount of the positive electrode, the cation storage amount of the negative electrode, the cation release amount of the negative electrode, the anion amount and the cation amount in the non-aqueous electrolyte. For this reason, in order to increase the discharge capacity of the dual carbon battery, in addition to the positive electrode active material and the negative electrode active material, it is necessary to increase the amount of the non-aqueous electrolyte containing a lithium salt (see Patent Document 1).
As described above, the electric quantity of the battery in the dual carbon battery is proportional to the total amount of anions and cations in the non-aqueous electrolyte. Therefore, the energy stored in the battery is proportional to the total mass of the non-aqueous electrolyte in addition to the positive electrode active material and the negative electrode active material. For this reason, it is difficult to increase the weight energy density of the battery. When a non-aqueous electrolyte solution having a lithium salt concentration of about 1 mol / L, which is usually used for lithium ion secondary batteries, is used, a larger amount of non-aqueous electrolyte solution is required than lithium ion secondary batteries. On the other hand, when a non-aqueous electrolyte having a high lithium salt concentration of about 3 mol / L is used, there is a problem that the battery capacity is greatly reduced due to repeated charge and discharge of the battery.

The dual carbon battery has an operating voltage range of about 2.5 V to 5.4 V, and the highest voltage is about 1 V higher than about 4.2 V of the lithium ion secondary battery, so that the non-aqueous electrolyte is easily decomposed. Decomposition of the non-aqueous electrolyte causes deterioration such as reduction in battery capacity due to generation of gas and formation of an excessive film of fluoride on the surface of the negative electrode. Therefore, it is necessary to take measures against fluoride by decomposition of the non-aqueous electrolyte.
Further, in a non-aqueous electrolyte secondary battery as a non-aqueous electrolyte storage element, a non-conductive film called SEI (Solid Electrolyte Interface) is formed at the time of initial charge and discharge. It prevents gas generation due to degradation and degradation of the non-aqueous electrolyte. However, if the electrolyte salt concentration is increased to increase the discharge capacity, the formation of SEI will not be successful, the storage capacity will decrease as the number of charge / discharge cycles increases, the capacity maintenance rate per cycle will decrease, and the service life will decrease. There is a problem that it ends up.

Patent Document 2 proposes a power storage system that uses graphite uniformly coated with amorphous carbon as a positive electrode active material and has a durable life and safety at high temperatures. However, the upper limit of the studied voltage is as low as 3 V, and expansion / contraction during anion intercalation with a large ion diameter is not taken into consideration. When carbon is expanded and contracted, the possibility that the uniformly coated film is broken is considered to be sufficient, and as a result, the durable life is considered to deteriorate.
In Patent Document 3, the graphite powder and the coated solid material are agitated in advance, carbonized by heat, and preferentially adheres carbon to the edge of the graphite particles, so that the charge / discharge efficiency and cycle characteristics are not impaired. Capacitive electrodes are presented. However, since the heat treatment is performed by standing after pre-stirring as an adhesion processing method, it is considered that the entire edge portion is always carbonized while continuously in contact with the coating material, and carbon is adhered to the edge portion in a planar shape. It is considered that such a planar adhesion film may break due to expansion / contraction during anion intercalation, and as a result, the durability life is considered to deteriorate.

  An object of the present invention is to provide a nonaqueous electrolyte storage element that can solve the above-described problems of the prior art, maintains a high energy density, and has excellent cycle characteristics.

The above problem is solved by the following invention 1).
1) A non-aqueous electrolyte storage element having a positive electrode containing a positive electrode active material capable of inserting and removing anions, a negative electrode containing a negative electrode active material capable of inserting and removing cations, and a non-aqueous electrolyte. The non-aqueous electrolyte storage element is characterized in that the positive electrode active material has carbon as a core material, and an edge portion of the surface thereof is coated with particulate amorphous carbon.

  ADVANTAGE OF THE INVENTION According to this invention, the non-aqueous-electrolyte electrical storage element excellent in cycling characteristics while maintaining a high energy density can be provided.

The figure which shows a graphite particle model. The figure which shows the capacity | capacitance maintenance factor in the reference current value in Example 1 and Comparative Examples 1-2.

Hereinafter, the present invention 1) will be described in detail, but the following 2) to 3) are also included in the embodiment, and these will also be described together.
2) ^Rh and (1360cm ^-1 / 1580cm -1) and Rh ₁ of the core material, when the positive electrode active material ^Rh and (1360cm ^-1 / 1580cm -1) was Rh _2, 0.08 ≦ _Rh 1 / The nonaqueous electrolyte storage element according to 1), wherein Rh ₂ ≦ 0.70.
3) The nonaqueous electrolyte storage element according to 1) or 2), wherein a particle diameter of the particulate amorphous carbon is 8 to 300 nm.

[Configuration of nonaqueous electrolyte storage element]
1. The positive electrode is not particularly limited as long as it contains a positive electrode active material according to the present invention described later, and can be appropriately selected according to the purpose. For example, a positive electrode material having a positive electrode active material on a positive electrode current collector is used. And a positive electrode provided.
There is no restriction | limiting in particular in the shape of a positive electrode, According to the objective, it can select suitably, For example, flat form etc. are mentioned.

1-1. Positive electrode material The positive electrode material needs to contain the positive electrode active material which concerns on this invention mentioned later at least. There is no restriction | limiting in particular in materials other than this positive electrode active material, According to the objective, it can select suitably, For example, a conductive support agent, a binder, a thickener, etc. are mentioned.

(1) Positive electrode active material The positive electrode active material used in the present invention is a non-aqueous solvent system in which anions can be inserted and desorbed, carbon is used as a core material, and the edge portion of the surface is particulate amorphous carbon. Must be covered.
A general structure of carbon as a core material is shown in FIG. 1, and the carbon primary particles 1 are composed of graphene 2, edge portions 3, and basal portions 4.
Examples of the carbon of the core material include graphite (graphite) such as coke, artificial graphite and natural graphite, and organic pyrolysis products under various pyrolysis conditions.

(2) Coating agent There is no restriction | limiting in particular in the coating agent used as the raw material of the said particulate amorphous carbon.
As a method for coating the surface of the core material with particulate amorphous carbon, chemical vapor deposition using a fluidized bed reactor is excellent. The organic substance used as the carbon source for chemical vapor deposition is not particularly limited as long as it is a compound containing carbon. Examples include aromatic hydrocarbons such as benzene, toluene, xylene and styrene, aliphatic hydrocarbons such as methane, ethane and propane, alcohols such as methanol, ethanol, propanol and butanol, dimethyl ether, ethyl methyl ether and diethyl ether. And ethers.
When performing the coating treatment, these organic substances are mixed with an inert gas such as nitrogen or argon and introduced. The chemical vapor deposition temperature is preferably 700 to 1200 ° C, more preferably 850 to 1150 ° C, and still more preferably 950 to 1100 ° C. Moreover, when performing a chemical vapor deposition process, it is preferable to process a core material, stirring, and by this, the edge part of the surface of a core material can be coat | covered with a particulate amorphous carbon successfully.

The degree of graphitization of the positive electrode active material (ratio of particulate amorphous carbon in the positive electrode active material) can be measured, for example, by Raman spectroscopy.
The positive electrode active material of the ratio of the peak intensity of the peak intensity and 1580 cm ^-1 in 1360 cm ^-1 in the Raman spectrum (hereinafter referred to as "Rh"), the Rh of the core material Rh _1, the positive electrode active material after coating the Rh as Rh _2, Rh 1 / Rh ₂ is preferably has from 0.08 to 0.70, more preferably 0.08 to 0.50. If it is 0.08 or more, the ratio of the core material in the positive electrode active material is sufficient, there is no inconvenience such as capacity reduction, and the manufacturing cost does not increase. Moreover, if it is 0.70 or less, the sufficient coating effect by a coating agent will be acquired.
The particle diameter of the particulate amorphous carbon coated with the core material is preferably 8 to 300 nm, more preferably 20 to 250 nm. If it is 8 nm or more, coating occurs so as to spread on the surface of the carbon of the core material, so that the coated particles are not broken and the cycle characteristics are not deteriorated during insertion and desorption of anions. Moreover, if it is 300 nm or less, since the reaction site can be sufficiently covered, the cycle characteristics are not deteriorated.

(3) Binder and thickener The binder and thickener are not particularly limited as long as they are materials that are stable with respect to the solvent and electrolyte used for electrode preparation and the applied potential, and are appropriately selected according to the purpose. can do.
Examples thereof include fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), ethylene-propylene-butadiene rubber (EPBR), styrene-butadiene rubber (SBR), isoprene rubber, acrylate latex, Examples thereof include carboxymethylcellulose (CMC), methylcellulose, hydroxymethylcellulose, ethylcellulose, polyacrylic acid, polyvinyl alcohol, alginic acid, oxidized starch, phosphate starch, and casein. These may be used individually by 1 type and may use 2 or more types together. Among these, fluorine-based binders such as PVDF and PTFE, acrylate latex, and CMC are preferable.

(4) Conductive aid Examples of the conductive aid include metal materials such as copper and aluminum, and carbonaceous materials such as carbon black, acetylene black, and carbon nanotube. These may be used individually by 1 type and may use 2 or more types together.

1-2. Positive electrode current collector The material, shape, size, and structure of the positive electrode current collector are not particularly limited, and can be appropriately selected according to the purpose.
The material of the positive electrode current collector may be formed of a conductive material and stable with respect to the applied potential. Examples thereof include stainless steel, nickel, aluminum, titanium, and tantalum. Among these, stainless steel and aluminum are particularly preferable.
The magnitude | size of a positive electrode electrical power collector should just be a magnitude | size which can be used for a nonaqueous electrolyte storage element.

1-3. Method for Producing Positive Electrode The positive electrode is obtained by applying a positive electrode material made into a slurry form by adding a binder, a thickener, a conductive agent, a solvent, etc. to the positive electrode active material as necessary, and drying it. Can be made.
There is no restriction | limiting in particular as said solvent, According to the objective, it can select suitably, For example, an aqueous solvent, an organic solvent, etc. are mentioned. Examples of the aqueous solvent include water, alcohol, and the like. Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP), toluene, and the like.
In addition, the positive electrode active material can be roll-formed as it is to obtain a sheet electrode, or a pellet electrode can be obtained by compression molding.

2. The negative electrode is not particularly limited as long as it contains a negative electrode active material, and can be appropriately selected according to the purpose. For example, a negative electrode including a negative electrode material having a negative electrode active material on a negative electrode current collector, and the like. Can be mentioned.
There is no restriction | limiting in particular in the shape of a negative electrode, According to the objective, it can select suitably, For example, flat form etc. are mentioned.

2-1. Negative electrode material The negative electrode material includes at least a negative electrode active material, and includes a conductive additive, a binder, a thickener, and the like as necessary.

(1) Negative electrode active material The negative electrode active material is not particularly limited as long as it is a non-aqueous solvent material capable of inserting and removing cations such as lithium ions. Examples of substances related to lithium ions include carbonaceous materials, antimony tin oxide, metal oxides capable of occluding and releasing lithium such as silicon monoxide, metals capable of being alloyed with lithium such as aluminum, tin, silicon and zinc Alternatively, a metal alloy, a metal alloyable with lithium, a composite alloy compound of lithium and an alloy containing the metal, lithium metal nitride such as cobalt lithium nitride, and the like can be given. These may be used individually by 1 type and may use 2 or more types together. Among these, carbonaceous materials are particularly preferable from the viewpoint of safety and cost.
Examples of the carbonaceous material include graphite (graphite) such as coke, artificial graphite and natural graphite, and organic pyrolysis products under various pyrolysis conditions. Among these, artificial graphite and natural graphite are particularly preferable.

(2) Binder and thickener The binder and thickener are not particularly limited as long as they are materials that are stable with respect to the solvent and electrolyte used in electrode preparation and the applied potential, and are appropriately selected according to the purpose. can do.
Examples thereof include those similar to the positive electrode binder and thickener. These may be used individually by 1 type and may use 2 or more types together. Among these, fluorine-based binders such as PVDF and PTFE, SBR, and CMC are preferable.

(3) Conductive aid The conductive aid may be the same as the conductive aid for the positive electrode. These may be used individually by 1 type and may use 2 or more types together.

2-2. Negative electrode current collector The material, shape, size, and structure of the negative electrode current collector are not particularly limited, and can be appropriately selected according to the purpose.
The material of the negative electrode current collector may be formed of a conductive material and stable with respect to the applied potential, and examples thereof include stainless steel, nickel, aluminum, and copper. Among these, stainless steel, copper, and aluminum are particularly preferable.
The magnitude | size of a negative electrode collector should just be a magnitude | size which can be used for a non-aqueous-electrolyte electrical storage element.

2-3. Method for producing negative electrode A negative electrode is obtained by applying a negative electrode material in a slurry form by adding a binder, a thickener, a conductive agent, a solvent, etc. to a negative electrode active material as necessary, and then drying the negative electrode current collector. Can be made.
As the solvent, the same solvent as in the method for producing the positive electrode can be used.
In addition, a negative electrode active material added with a binder, a thickener, a conductive agent, etc. is roll-formed as it is to form a sheet electrode, a pellet electrode is formed by compression molding, and negative electrode current collection is performed by techniques such as vapor deposition, sputtering, and plating. A thin film of a negative electrode active material can also be formed on the body.

3. Nonaqueous Electrolytic Solution The nonaqueous electrolytic solution is an electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent.

3-1. Nonaqueous solvent There is no restriction | limiting in particular as a nonaqueous solvent, Although it can select suitably according to the objective, An aprotic organic solvent is suitable.
As the aprotic organic solvent, carbonate-based organic solvents such as chain carbonates and cyclic carbonates are used, and low viscosity solvents are preferred. Among these, a chain carbonate is preferable from the viewpoint that the dissolving power of the electrolyte salt is high.
Examples of the chain carbonate include dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). Among these, DMC is preferable.
There is no restriction | limiting in particular in content of DMC, Although it can select suitably according to the objective, 70 mass% or more of the whole nonaqueous solvent is preferable, and 83 mass% or more is more preferable. If the content is 70% by mass or more, a cyclic substance (cyclic carbonate, cyclic ester, etc.) having a high dielectric constant is used as the remaining solvent, and the viscosity is high even when a non-aqueous electrolyte solution having a high concentration of 3M or more is prepared. It does not become too high, and there is no problem in terms of penetration of the non-aqueous electrolyte into the electrode and ion diffusion.

Examples of the cyclic carbonate include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), and the like.
The mixing ratio in the case of using a mixed solvent in which EC of the cyclic carbonate and DMC of the chain carbonate are used is not particularly limited and can be appropriately selected according to the purpose. However, the mass ratio (EC: DMC) 3:10 to 1:99 are preferable, and 3:10 to 1:20 are more preferable.

As the non-aqueous solvent, an ester organic solvent such as a cyclic ester or a chain ester, an ether organic solvent such as a cyclic ether or a chain ether, or the like can be used as necessary.
Examples of the cyclic ester include γ-butyrolactone (γBL), 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, and γ-valerolactone.
Examples of the chain ester include propionic acid alkyl ester, malonic acid dialkyl ester, acetic acid alkyl ester [methyl acetate (MA), ethyl acetate, etc.], formic acid alkyl ester [methyl formate (MF), ethyl formate, etc.], etc. Is mentioned.
Examples of the cyclic ether include tetrahydrofuran, alkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane, and the like.
Examples of the chain ether include 1,2-dimethoxyethane (DME), diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, and tetraethylene glycol dialkyl ether.

3-2. Electrolyte salt The electrolyte salt is preferably a lithium salt, but is not particularly limited as long as it is dissolved in a non-aqueous solvent and exhibits high ionic conductivity. Examples of lithium salts include lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium chloride (LiCl), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ). , Lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide [LiN (CF ₃ SO ₂ ) ₂ ], lithium bisfurfluoroethylsulfonylimide [LiN (C ₂ F ₅ SO ₂ ) ₂ ] , Etc. These may be used individually by 1 type and may use 2 or more types together. Among these, LiPF ₆ is particularly preferable from the viewpoint of the amount of occlusion of anions in the carbon electrode.
There is no restriction | limiting in particular in the density | concentration of electrolyte salt, Although it can select suitably according to the objective, 0.5-6 mol / L is preferable in a nonaqueous solvent, and the point of coexistence of battery capacity and output is 2 -4 mol / L is more preferable.

4). Separator The separator is provided between the positive electrode and the negative electrode in order to prevent a short circuit between the positive electrode and the negative electrode.
There is no restriction | limiting in particular in the material of a separator, a shape, a magnitude | size, and a structure, According to the objective, it can select suitably.
Examples of the material of the separator include paper such as kraft paper, vinylon mixed paper, synthetic pulp mixed paper, cellophane, polyethylene graft membrane, polyolefin nonwoven fabric such as polypropylene melt blown nonwoven fabric, polyamide nonwoven fabric, glass fiber nonwoven fabric, and micropore membrane. It is done. Among these, those having a porosity of 50% or more are preferable from the viewpoint of electrolyte solution retention.
As for the shape of the separator, the nonwoven fabric type is preferable because it has a higher porosity than the thin film type having micropores. The thickness of the separator is preferably 20 μm or more from the viewpoint of short circuit prevention and electrolyte solution retention.
The magnitude | size of a separator should just be a magnitude | size which can be used for a non-aqueous-electrolyte electrical storage element.
The structure of the separator may be a single layer structure or a laminated structure.

5. Production method and shape of non-aqueous electrolyte storage element The non-aqueous electrolyte storage element of the present invention is produced by assembling a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator used as necessary into an appropriate shape. it can. Furthermore, other constituent members such as a battery outer can can be used as necessary.
There is no restriction | limiting in particular in the method of assembling a non-aqueous electrolyte electrical storage element, It can select suitably from the method employ | adopted normally.
There is no restriction | limiting in particular in the shape of the nonaqueous electrolyte electrical storage element of this invention, According to a use, it can select suitably from the various shapes generally employ | adopted. Examples thereof include a cylinder type in which the sheet electrode and the separator are spiral, a cylinder type having an inside-out structure in which the pellet electrode and the separator are combined, a coin type in which the pellet electrode and the separator are stacked, and the like.

6). Applications The non-aqueous electrolyte storage element of the present invention can be used for various applications. Examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. Electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting equipment, toys, game machines, watches, strobes, cameras, etc.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated further more concretely, this invention is not limited at all by these Examples. In the examples, “%” is “mass%”.

[Example 1]
<Preparation of positive electrode active material (coating treatment)>
Carbon powder (manufactured by TIMCAL, KS-6) is used as a core material, the carbon powder is added to a quartz cuvette in a fluidized bed furnace, the interior of the cuvette is filled with Ar gas, and a coating treatment is performed. A carbon powder (positive electrode active material) in which the edge portion was coated with particulate amorphous carbon was produced.
Table 1 shows the coating agent, the processing temperature, the processing time, and the presence or absence of stirring during the coating process.

<Preparation of positive electrode>
Using the positive electrode active material, acetylene black (Denka black powder: manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, acrylate latex of a binder (TRD202A: manufactured by JSR), carboxymethyl cellulose as a thickener (Daicel 2200: Daicel) Chemical Industry Co., Ltd.) was mixed so that the mass ratio of the solid content was 100: 7.5: 3.0: 3.8, and water was added to adjust the viscosity to an appropriate viscosity to obtain a slurry. This slurry was applied to one side of an aluminum foil having a thickness of 20 μm using a doctor blade. The average weight per unit area (mass of carbon active material powder in the coated positive electrode) after drying was 10 mg / cm ² . This was punched out to φ16 mm to obtain a positive electrode.

<Preparation of nonaqueous electrolyte storage element>
After the above positive electrode and separator (ADVANTEC GA-100) were vacuum-dried at 150 ° C. for 4 hours, a lithium metal foil having a diameter of 16 mm was used as the negative electrode in a dry argon glove box, and “2 mol / L as a non-aqueous electrolyte solution was used. A 2032 type coin cell (non-aqueous electrolyte storage element) was assembled using “an EC / DMC / FEC solution of LiPF ₆ ” (manufactured by Kishida Chemical Co., Ltd.).

<Measurement of non-aqueous electrolyte storage element>
The non-aqueous electrolyte storage element was held in a constant temperature bath at 25 ° C., and a charge / discharge test was performed under the following conditions using an automatic battery evaluation device (1024B-7V0.1A-4: manufactured by Electrofield). .
That is, the reference current value was set to 2.0 mA, and the battery was charged to a charge end voltage of 5.2V. After the first charge, the battery was discharged to 3.0V. There was a 5-minute pause between charging and discharging and between discharging and charging. The discharge capacity (discharge capacity after 10 cycles) when this charge / discharge was repeated 10 times was measured, and the number of cycles until the capacity retention rate fell below 80% was measured using this discharge capacity as a reference.

[Comparative Example 1]
A positive electrode and a power storage device were produced in the same manner as in Example 1 except that the same carbon powder as in Example 1 was used as the positive electrode active material without coating, and a charge / discharge test was performed.

[Comparative Example 2]
The same carbon powder as in Example 1 was coated as a core material to produce a carbon powder (positive electrode active material) whose surface was uniformly coated with amorphous carbon. Table 1 shows the coating agent, the processing temperature, the processing time, and the presence or absence of stirring during the coating process.
A positive electrode and a storage element were produced in the same manner as in Example 1 except that the positive electrode active material was used, and a charge / discharge test was performed.

[Comparative Example 3]
Except for using lithium cobalt oxide powder (manufactured by Nichia Chemical Co., Ltd.) as a core material, a coating active was performed in the same manner as in Example 1 to prepare a positive electrode active material having amorphous carbon attached to the surface. Table 1 shows the coating agent, the processing temperature, the processing time, and the presence or absence of stirring during the coating process.
A positive electrode and a storage element were produced in the same manner as in Example 1 except that the positive electrode active material was used, and a charge / discharge test was performed.

Table 2 shows the discharge capacity after 10 cycles of Example 1 and Comparative Examples 1 to 3, and the number of cycles when the capacity retention rate was less than 80%. The physical property values of the positive electrode active material are also shown. Further, FIG. 2 shows the capacity retention ratio at the reference current value in Example 1 and Comparative Examples 1 and 2.
Rh ₁ and Rh ₂ are determined by Raman spectroscopy (NRS-1000, manufactured by JASCO Corporation), and the shape of amorphous carbon was observed with a scanning electron microscope (SU8230, manufactured by Hitachi High-Tech). The particle diameter of amorphous carbon is an analysis value obtained by image analysis from an observation image of the scanning electron microscope.

As can be seen from Table 2 and FIG. 2, the non-aqueous electrolyte storage element of Example 1 has a sufficiently high discharge capacity after 10 cycles due to the coating of particulate amorphous carbon, and the cycle characteristics are also very good. Met.
On the other hand, in Comparative Example 1 in which the coating with amorphous carbon was not performed, the reaction with the electrolytic solution for each cycle could not be suppressed, and thus the cycle characteristics were significantly deteriorated.
Further, in Comparative Example 2 in which the amorphous carbon coating shape was made uniform, the uniform coating broke without enduring the expansion and contraction of the active material for each cycle, and the cycle characteristics were remarkably deteriorated.
Further, in Comparative Example 3 in which lithium cobalt oxide was used as the core material, the discharge capacity was remarkably reduced and the cycle characteristics were remarkably deteriorated due to the increase in internal resistance due to amorphous carbon.

[Examples 2 to 15]
The same carbon powder as in Example 1 was used as the core material, and the coating treatment similar to that in Example 1 was performed except that a part of the coating agent and / or coating treatment conditions were changed, and the edge portion of the surface was particulate. Each carbon powder (positive electrode active material) of Examples 2 to 15 coated with amorphous carbon was produced. Table 3 shows the coating agent, treatment temperature, treatment time, and presence / absence of stirring.

Except for the use of each positive electrode active material, each positive electrode and power storage device of Examples 2 to 15 were produced in the same manner as in Example 1, and a charge / discharge test was performed.
Table 4 shows the discharge capacity after 10 cycles, the number of cycles when the capacity retention rate was less than 80%, and the physical properties of the positive electrode active material measured in the same manner as in Example 1. In Table 4, the data of Comparative Examples 1 and 2 are also shown for reference.
As can be seen from Table 4, the nonaqueous electrolyte electricity storage devices of Examples 2 to 15 have sufficiently high discharge capacity after 10 cycles, and the cycle characteristics are improved as compared with Comparative Examples 1 and 2.

[Example 16]
<Production of negative electrode>
Carbon powder of negative electrode active material (manufactured by Hitachi Chemical Co., Ltd., MAGD), acetylene black of conductive additive (DENKA black powder: manufactured by Denki Kagaku Kogyo Co., Ltd.), styrene butadiene rubber of binder (EX-1215: manufactured by Denki Kagaku Kogyo Co., Ltd.) ), Carboxymethyl cellulose (Daicel 2200: manufactured by Daicel Chemical Industries, Ltd.), a thickener, is mixed so that the weight ratio of the solid content is 100: 5: 3: 2, and water is added to adjust the viscosity appropriately. A slurry was obtained. This slurry was applied to one side of a 18 μm thick copper foil using a doctor blade. The average basis weight after drying was 10.0 mg / cm ² . This was punched out to φ16 mm to form a negative electrode.

<Preparation and measurement of nonaqueous electrolyte storage element>
A power storage device was produced in the same manner as in Example 1 except that the negative electrode in Example 1 was changed to the negative electrode, and a charge / discharge test was performed.

[Example 17]
A power storage device was produced in the same manner as in Example 1 except that the positive electrode and negative electrode in Example 1 were changed to the positive electrode produced in Example 2 and the negative electrode produced in Example 16, and a charge / discharge test was performed. .

[Example 18]
<Preparation of positive electrode>
A positive electrode was produced in the same manner as in Example 1 except that the average weight per unit area after drying in producing the positive electrode of Example 1 was changed to 3.0 mg / cm ² .

<Production of negative electrode>
Lithium titanate as a negative electrode active material (Li ₄ Ti ₅ O ₁₂ : manufactured by Titanium Industry Co., Ltd.), acetylene black as a conductive additive (Denka Black powder: manufactured by Denki Kagaku Kogyo Co., Ltd.), acrylate latex of a binder (TRD202A: JSR Corporation) ), A thickener carboxymethylcellulose (Daicel 2200: manufactured by Daicel Chemical Industries) was mixed so that the weight ratio of the solid content was 100: 7: 3: 1, and water was added to adjust the viscosity to an appropriate level. Thus, a slurry was obtained. This slurry was applied to one side of a 18 μm thick copper foil using a doctor blade. The average basis weight after drying was 3.0 mg / cm ² . This was punched out to φ16 mm to form a negative electrode.

<Preparation and measurement of nonaqueous electrolyte storage element>
A power storage device was produced in the same manner as in Example 1 except that the positive electrode and the negative electrode in Example 1 were changed to the positive electrode and the negative electrode, and a charge / discharge test was performed.

[Example 19]
<Preparation of positive electrode>
A positive electrode was produced in the same manner as in Example 2 except that the average weight per unit area after drying in producing the positive electrode of Example 2 was changed to 3.0 mg / cm ² .

<Preparation and measurement of nonaqueous electrolyte storage element>
A power storage device was produced in the same manner as in Example 1 except that the positive electrode and the negative electrode in Example 1 were changed to the positive electrode and the negative electrode produced in Example 18, and a charge / discharge test was performed.

[Comparative Example 4]
A power storage device was produced in the same manner as in Comparative Example 1 except that the negative electrode of Comparative Example 1 was changed to the negative electrode produced in Example 16, and a charge / discharge test was performed.

[Comparative Example 5]
A power storage device was produced in the same manner as in Comparative Example 1 except that the negative electrode of Comparative Example 1 was changed to the negative electrode produced in Example 18, and a charge / discharge test was performed.

In Examples 16 to 19 and Comparative Examples 4 to 5, the discharge capacity after 10 cycles, the number of cycles when the capacity retention rate was less than 80%, and the positive electrode active material measured in the same manner as in Example 1 Table 6 shows the physical property values.
As can be seen from Table 6, the non-aqueous electrolyte storage elements of Examples 16 to 17 had a sufficiently high discharge capacity after 10 cycles, and the cycle characteristics were significantly improved as compared with Comparative Example 4.
Moreover, the non-aqueous electrolyte storage elements of Examples 18 to 19 had sufficiently high discharge capacity after 10 cycles, and the cycle characteristics were improved as compared with Comparative Example 5.

1 carbon primary particle 2 graphene 3 edge part 4 basal part

Japanese Patent No. 4569126 JP 2007-305625 A International Publication 2008/093724 Pamphlet

Claims (3)

  A non-aqueous electrolyte storage element comprising a positive electrode containing a positive electrode active material capable of inserting and removing anions, a negative electrode containing a negative electrode active material capable of inserting and removing cations, and a non-aqueous electrolyte solution, A non-aqueous electrolyte storage element, wherein the positive electrode active material has carbon as a core material, and an edge portion of the surface thereof is coated with particulate amorphous carbon. ^Rh and (1360cm ^-1 / 1580cm -1) and Rh ₁ of the core material, when the positive electrode active material ^Rh and (1360cm ^-1 / 1580cm -1) was _{Rh 2, 0.08 ≦ Rh 1 /} Rh 2 The nonaqueous electrolyte storage element according to claim 1, wherein ≦ 0.70.   3. The nonaqueous electrolyte storage element according to claim 1, wherein the particulate amorphous carbon has a particle diameter of 8 to 300 nm.