Battery reaction auxiliary material, positive electrode or negative electrode including the same, lithium-ion battery including the positive electrode or negative electrode, and manufacturing method for electrode

Abstract

To provide: a battery reaction auxiliary material that can suitably assist battery reactions and capable of extending the life of a lithium-ion battery; a positive electrode or negative electrode including the same; a lithium-ion battery including the positive electrode or negative electrode; and a manufacturing method for the electrode.SOLUTION: The battery reaction auxiliary material includes a plurality of primary particles which each include carbonaceous matter and have a three-dimensional skeleton including a space therein. A portion of the primary particles is agglomerated to form secondary particles. The secondary particles undergo plastic deformation in an extremely small load-unload test while a portion of which is not restored. The carbonaceous matter may include graphene.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a battery reaction auxiliary material, a positive electrode or a negative electrode containing the battery reaction auxiliary material, a lithium ion battery including the positive electrode or the negative electrode, and a method for producing the electrode. [Background technology]

[0002] Since their birth, lithium-ion batteries have been widely used in everyday life, including smartphones and electric vehicles (EVs). As a result, the manufacturing of lithium-ion batteries is subject to cost competition and ongoing market demand for higher performance. In order for EVs, which emit less carbon dioxide (CO2), to replace gasoline-powered vehicles in order to protect the global environment, extending the driving range of EVs is one of the necessary conditions. To extend the driving range of EVs, the lithium-ion batteries they are equipped with must have a longer life, higher performance, and more efficient battery reactions.

[0003] Used lithium-ion batteries are usually discarded when their lifespan is over. In recent years, however, there has been a growing movement to secure resources and materials on a global scale in order to manufacture and stably supply lithium-ion batteries. For this reason, there has been a loud call for the need to utilize materials like urban mines by recycling used lithium-ion batteries, a practice known as resource recycling.

[0004] Recycling and remanufacturing lithium-ion batteries requires the same amount of energy as manufacturing new batteries from raw materials. In addition, the same amount of CO2 is re-emitted, so it is not easy to stop the destruction of the global environment even if we recycle and remanufacture them. For this reason, there is a strong demand for lithium-ion batteries to have higher performance and longer life.

[0005] Patent Document 1 discloses a powder for a positive electrode that contains an active material containing Ni, Mn, and Fe, and that can exhibit excellent discharge characteristics at a higher current rate, making it possible to apply the powder to a nonaqueous electrolyte secondary battery. Patent Document 2 discloses a nonaqueous electrolyte secondary battery having a negative electrode that uses a negative electrode active material made of lithium titanate, making it possible to prevent deterioration of battery characteristics even when charging is performed with a minute current of about 1 to 5 μA while maintaining a constant voltage state of about 3.0 V for a long period of time. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2011-216472 A [Patent Document 2] JP 2005-317509 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the secondary battery described in Patent Document 1 has a low battery energy density because too much conductive additive is added to obtain sufficient characteristics. In addition, the binder is insufficient, which reduces the electrode strength and shortens the life. The secondary battery described in Patent Document 2 has a long maintenance time in a constant voltage state, but has a low voltage and low energy density. Therefore, it must be said that the technologies shown in Patent Document 1 and Patent Document 2 are unsuitable for use in EVs and the like. One of the urgent issues is the development of a secondary battery that can be used for a longer period of time and has high performance.

[0008] In order to improve the performance of lithium-ion batteries and to aim for true environmental conservation, it is essential to extend the lifespan of lithium-ion batteries. Various studies have been conducted on the mechanism of performance degradation of lithium-ion battery products. The degradation reaction phenomena of lithium-ion batteries are diverse, including the change in the active material, poor contact of electrode materials, the change in the electrolyte components and the loss of ions due to side reactions during degradation, the blockage of pores in the separator by side reaction products, and the corrosion of metal current collector parts, all of which are factors that increase the resistance of the battery reaction.

[0009] Among these, the increase in electrode resistance, which is the root cause of degradation and can be said to be a concentration of degradation reaction phenomena, causes the disruption of the electron supply network to the active material necessary for the insertion and removal of lithium ions in the electrode, and delays in the supply of lithium ions due to a decrease in the amount of electrolyte, etc. This is a major issue that prevents the extension of the lifespan of lithium-ion batteries.

[0010] The present invention has been made in consideration of the above circumstances, and has an object to provide a battery reaction auxiliary material that can favorably assist battery reactions and enable the extension of the life of lithium-ion batteries, a positive electrode or negative electrode containing the battery reaction auxiliary material, a lithium-ion battery including the positive electrode or negative electrode, and a method for producing the battery reaction auxiliary material. [Means for solving the problem]

[0011] In order to solve the above problems, the battery reaction auxiliary material of the present invention employs the following measures.

[0012] A first aspect of the present invention provides a battery reaction auxiliary material comprising a plurality of primary particles which contain carbonaceous matter and have a three-dimensional skeleton with an internal space, and some of the primary particles are fixed to each other to form secondary particles, and the secondary particles are plastically deformed in an extremely small load / unload test, and some of the secondary particles do not recover.

[0013] In the first aspect, the carbonaceous material may include graphene.

[0014] In the first aspect, the plastic deformation power may be 5% or more and 92% or less.

[0015] In the first embodiment, the battery reaction assisting function may have an electron transfer function and an electrolyte retention function.

[0016] In the first embodiment, the pore volume measured by a gas adsorption method may be 1 cc / g or more and 4 cc / g or less.

[0017] In the first embodiment, the carbon layer stacking index may be 0.4 or more and 5 or less.

[0018] In the first embodiment, solid particles may be contained among the plurality of primary particles.

[0019] In the above embodiment, the solid particles may be at least one of carbon black, acetylene black, single-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0020] In the above embodiment, the solid particles may be ceramic particles coated with a carbonaceous material.

[0021] In the first aspect, the secondary particles may have an average particle size of 0.1 μm or more and 6 μm or less.

[0022] A second aspect of the present invention provides a positive electrode or a negative electrode for a lithium ion battery, the content of the battery reaction auxiliary material of the first aspect being 0.1 wt % or more and 5 wt % or less.

[0023] In the second embodiment, the positive electrode or negative electrode for a lithium ion battery may have a permanently deformed portion in which the secondary particles are permanently deformed in part of the structure.

[0024] In the above embodiment, the permanently deformed portion may contain multi-layer graphene.

[0025] A third aspect of the present invention provides a positive or negative electrode for a lithium-ion battery, comprising only solid particles as a battery reaction auxiliary material.

[0026] A fourth aspect of the present invention provides a lithium ion battery comprising at least one of the positive electrode and the negative electrode for a lithium ion battery according to the second or third aspect.

[0027] A fifth aspect of the present invention provides a method for manufacturing a positive electrode or a negative electrode for a lithium ion battery, the method comprising the steps of: mixing a battery reaction auxiliary material containing carbonaceous primary particles having a three-dimensional skeleton including an internal space and secondary particles formed by fixing a plurality of the primary particles together, a binder resin, and a solvent to prepare a slurry; and applying the slurry onto a current collector, drying the current collector, and pressing the current collector to obtain a positive electrode or a negative electrode, wherein during the pressing, some of the primary particles and the secondary particles remain deformed in shape, and another part of the primary particles and the secondary particles are restored in shape. Effect of the Invention

[0028] The battery reaction auxiliary material according to the present invention can favorably assist the battery reaction. A lithium ion battery having a positive electrode or a negative electrode containing the battery reaction auxiliary material according to the present invention can have an extended life and high performance. [Brief description of the drawings]

[0029] [Figure 1] 1 is a schematic diagram showing an enlarged view of a portion of the structure of an electrode containing a battery reaction auxiliary material according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a Raman spectrum measured for the auxiliary material of Example 1. [Figure 3A] 1 is a SEM photograph (20 μm scale) of the electrode surface before pressing in the production of the positive electrode in Example 1. [Figure 3B] 1 is a SEM photograph (1 μm scale) of the electrode surface before pressing in the production of the positive electrode in Example 1. [Figure 3C] 1 is a SEM photograph (20 μm scale) of the electrode surface after pressing in the production of the positive electrode in Example 1. [Figure 3D] 1 is a SEM photograph (1 μm scale) of the electrode surface after pressing in the production of the positive electrode in Example 1. [Figure 4] FIG. 2 is a diagram showing the results of an extremely small load unloading test performed on the battery reaction auxiliary material prepared in Example 1. [Diagram 5] 1 is a diagram showing an example of a cross-sectional structure of a lithium-ion battery according to an embodiment of the present invention. [Figure 6] 1 is a transmission electron microscope (TEM) image of the battery reaction auxiliary material obtained in Example 1. [Figure 7] 1 is a TEM image of the battery reaction auxiliary material obtained in Example 2. [Figure 8] FIG. 2 is a diagram showing a pore size distribution curve of the battery reaction auxiliary material obtained in Example 1. [Figure 9] FIG. 2 is a graph showing the particle size distribution of the battery reaction auxiliary material obtained in Example 1. [Figure 10] FIG. 2 is a discharge curve of the test battery of Example 1 according to one embodiment of the present invention, showing a difference in current during discharge. [Figure 11] 1 is a TEM photograph of the battery reaction auxiliary material obtained in Example 6. [Figure 12] FIG. 1 is a graph showing the relationship between the plastic deformation power and the 2C rate discharge maintenance rate for the test battery according to the embodiment and the test battery according to the comparative example. [Figure 13] FIG. 1 is a graph showing the relationship between the carbon layering index and the 2C rate discharge retention rate for a test battery according to an embodiment and a test battery according to a comparative example. [Figure 14] FIG. 2 is a graph showing the relationship between pore volume and 2C rate discharge retention rate for a test battery according to an embodiment and a test battery according to a comparative example. [Figure 15] FIG. 1 is a graph showing the relationship between the secondary particle diameter in the auxiliary material and the 2C rate discharge retention rate for the test battery according to the example and the test battery according to the comparative example. [Figure 16]FIG. 1 is a diagram showing the relationship between the amount of auxiliary material added and the charge / discharge capacity for a test battery according to an example and a test battery according to a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Hereinafter, an embodiment of the battery reaction auxiliary material according to the present invention, a positive electrode or negative electrode for a lithium ion battery containing the battery reaction auxiliary material, and a lithium ion battery including the positive electrode or negative electrode will be described with reference to the drawings. First, the battery reaction auxiliary material according to this embodiment will be described.

[0031] Fig. 1 shows a schematic diagram in which a part of the structure of an electrode containing the battery reaction auxiliary material (hereinafter also referred to as "auxiliary material") of this embodiment is enlarged. The battery reaction auxiliary material of this embodiment is contained in, for example, the negative electrode or positive electrode of a lithium ion battery. Fig. 1 shows an example in which the battery reaction auxiliary material of this embodiment is applied to a positive electrode.

[0032] As shown in Fig. 1, the auxiliary material of this embodiment includes a primary particle 1 and a secondary particle 2 formed by adhering a plurality of primary particles. The primary particle 1 contains carbonaceous matter, and the carbonaceous matter includes a thin-layer graphene material described below. The primary particle 1 is a hollow particle having a three-dimensional skeleton and an internal space. Reference numeral 3 in Fig. 1 denotes a positive electrode material.

[0033] The auxiliary material of the present embodiment includes a thin graphene material. Graphene has a structure in which a hexagonal carbon network plane to which benzene rings are bonded grows planarly to form a sheet. Graphite is a structure in which many graphenes are stacked. On the other hand, a structure in which the hexagonal carbon network planes grow planarly but the number of stacks is small, and therefore the structure has elastic deformation, is defined as a thin graphene material in this specification. The thin graphene material is the main structure of the auxiliary material of the present embodiment.

[0034] When stress is applied to the primary particles and secondary particles of this embodiment, the three-dimensional shape of the thin graphene portion of the particle is mainly deformed and compressed. On the other hand, when the applied stress is released, the deformed portion is restored to a certain extent due to its elastic deformability. The portion that does not restore upon release of the stress is a portion with low elasticity. When the thin graphene portion contains many structural defects or many amorphous bonds, the shape does not restore, that is, it has plastic deformability against stress. Such a structural portion that has plastic deformability against stress has a property of exhibiting high strength against stress or being easily deformed and not being able to restore afterwards.

[0035] As described above, in the auxiliary material of this embodiment, the thin graphene portion has elastic deformation properties, and the portion other than the thin graphene portion is amorphous carbon and has plastic deformation properties. The primary particles of the auxiliary material of this embodiment deform when stress is applied. Depending on the magnitude of the applied stress, some of the multiple primary particles restore their shape when the load is removed, while another part of the multiple primary particles maintains a permanent deformation state. This mechanical property is caused by the influence of the carbonaceous microstructure. The degree of elastic deformation and the degree of plastic deformation of the auxiliary material can be measured by a very small loading and unloading test described later.

[0036] When the thin graphene layer is relatively thick, the thin graphene layer maintains elastic deformation within a certain stress range, but when a certain threshold is exceeded, it undergoes plastic deformation all at once. In general carbon materials, they may be deformed by a relatively large stress, and the particles may be destroyed. In other words, the auxiliary material of this embodiment has a property of returning to its original shape with almost no deformation under weak stress, such as the extremely small load unloading test performed in this embodiment, that is, a property of a large amount of work for elastic deformation.

[0037] Graphene is a carbonaceous material with high electronic conductivity due to its highly regular hexagonal planar structure.

[0038] Here, the state in the microcrystalline structure of thin graphene can be analyzed by Raman spectroscopy.

[0039] An example of the Raman spectrum measured for the auxiliary material of Example 1 described later is shown in FIG. 2. In this spectrum, the G band (aromatic ring C=C stretching motion, 1593 cm) derived from the skeletal vibration of the graphite sheet is observed. -1 ), and the D band (CH stretching motion, 1356 cm ) derived from defects such as non-hexagonal sites including edge sites. -1 ), and the 2D band due to second-order phonon scattering (CH stretching motion, 2680 cm -1 ) is present. These findings suggest that the auxiliary material of Example 1 has a structure containing graphene. G ) and 2D band intensity (I 2D ) is the ratio of I G / I 2D is said to be an index indicating the stacking state of graphene layers. (D. Graf, et al., NANO LETTERS, 7, 238-242; (2007)) In this embodiment, I G / I 2D The index expressed by is called the "carbon layering index." Based on the above paper, the value per layer was set to 0.4.

[0040] I G / I 2D The smaller the value, i.e., the smaller the carbon stacking index, the fewer the number of layers, and the closer it is to single-layer graphene. In other words, it is suggested that it has a structure that exhibits elastic deformation. In this specification, "when the thin-layer graphene material is relatively thick" refers to the case where the carbon stacking index of the particles in the auxiliary material is greater than 6.

[0041] The auxiliary material of the present embodiment is excellent in electron transfer because it contains graphene. Therefore, the auxiliary material of the present embodiment can exhibit a function of assisting the battery reaction in the lithium ion battery by being contained in the electrode of the lithium ion battery. In addition, the auxiliary material of the present embodiment is excellent in ion supply during the reaction because an electrolyte solution containing dissolved lithium ions penetrates and is retained in the space provided in the three-dimensional skeleton of the primary particles and the secondary particles.

[0042] Therefore, the auxiliary material of this embodiment can utilize elastic deformation and plastic deformation in a well-balanced manner under the conditions of use of a lithium-ion battery. That is, even if the primary particles and / or secondary particles in the auxiliary material undergo plastic deformation, high electronic conductivity is guaranteed, while if they do not undergo plastic deformation, the electrolyte, which is the storage source of ions, can be stored in the space within the particles. Therefore, the auxiliary material of this embodiment can favorably assist the battery reaction.

[0043] A method for producing the auxiliary material of this embodiment will be described. The auxiliary material of this embodiment can be produced by template chemical vapor deposition (hereinafter, T-CVD). This is a technique in which an organic gas is passed through ceramics that have CVD activity and are heated in an inert gas atmosphere, and carbon atoms of the organic matter in the gas are condensed to form a carbonaceous film.

[0044] Next, in order to create spaces within the primary particles, the ceramic particles coated with the carbonaceous film are treated with a reagent capable of dissolving ceramics (e.g., an acidic solution). This treatment dissolves and removes the ceramic portion of the ceramic particles coated with the carbonaceous film. After dissolution, the interior of the primary particles formed from carbonaceous material is washed so that no material remains in the spaces. By dissolving and removing the ceramic particles, spaces are created within the primary particles formed from carbonaceous material.

[0045] Next, the primary particles are heat-treated at 3000°C or less to adjust structural defects in the thin graphene portion constituting the particle and in the portion other than the thin graphene portion. These structural defects include spaces generated within the particle due to dissolution of the template and intrusion holes generated in the three-dimensional framework formed from the carbonaceous material. By adjusting reaction conditions such as the heat treatment temperature and heat treatment time, the degree of these structural defects can be adjusted, that is, the size of the spaces present inside the particle and the size of the intrusion holes for infiltrating the electrolyte into the particle can be adjusted.

[0046] Functional groups (mainly oxygen-containing functional groups) that are bonded to carbon and carbon chains that do not form six-membered rings are detached at temperatures above about 1000°C, forming dangling bonds. When the dangling bonds that are formed bond with other nearby carbons, the surface of the carbon material becomes in a state in which functional groups are less likely to bond. By subjecting the auxiliary material of this embodiment to heat treatment at 1500°C or higher, preferably 1600°C or higher, the auxiliary material can exhibit suitable functions such as electronic conductivity and maintaining internal space.

[0047] The auxiliary material of this embodiment has a pore volume of 1 cc / g or more and 4 cc / g or less, measured by a gas adsorption method, specifically, nitrogen adsorption / desorption measurement. The pore volume is the volume of the space present inside the particle. If the pore volume value is large, the electrolyte held in the particle increases, and the reaction efficiency increases. On the other hand, a large pore volume value means a large space, so that the skeleton strength is weakened and it becomes difficult to maintain the shape of the particle due to the pressure under load. In the auxiliary material of this embodiment, the pore volume is more preferably greater than 1 cc / g and less than 4 cc / g, and more preferably greater than 1.5 cc / g and less than 4 cc / g. By having such a moderate pore volume, the particle has a moderate strength, which contributes to the stability of the particle shape and maintains the shape. As a result, it is possible to maintain a good balance between electronic conductivity and the supply of ions held in the pores.

[0048] The positive electrode material of a lithium-ion battery is a powder of lithium-containing transition metal oxide with a particle size distribution and low electronic conductivity. In the conventional method, a conductive assistant made of a carbon material that helps with electronic conduction for the battery reaction is mixed with a binder resin and pressed and fixed to a current collector, establishing an electronic conduction route. Since the materials other than the binder resin are powder particles, the electrolyte is only accidentally present in the space between the particles. For this reason, it was difficult with conventional technology to actively place the electrolyte, in other words, lithium ions, near the positive electrode material.

[0049] In contrast, in place of the conductive assistant that has been used conventionally, a battery reaction assistant material is used in this embodiment. The battery reaction assistant material of this embodiment is mainly formed of particles made of thin graphene, and has a space inside the particle that can hold an electrolyte. The assistant material exhibits high electronic conductivity derived from graphene, although it is permanently deformed when pressurized between particles of the positive electrode material in the positive electrode, while it can maintain the space that holds lithium ions if it does not deform. Therefore, the battery reaction assistant material of this embodiment can be said to be a material that simultaneously assists in the supply of electrons and ions necessary for the battery reaction and can better realize a rapid battery reaction.

[0050] In the auxiliary material of the present embodiment, the three-dimensional skeleton is deformed by pressure. When the soft graphene part is crushed, the single-layer graphene changes to a multi-layered state, which improves electronic conduction.

[0051] In an actual electrode, for example, when a positive electrode mixture slurry is applied to a current collector and dried, and then pressed, the mixture layer is crushed. When an electrode contains the auxiliary material of this embodiment, the particles sandwiched between the positive electrode material particles are directly stressed and plastically deformed, thereby exhibiting electronic conductivity. At the same time, the particles that are present in the gaps of the positive electrode material and are not subjected to stress exist as particles that maintain space inside, and exhibit the function of retaining the electrolyte. As an example, SEM photographs of the electrode surface before the press processing of this embodiment are shown in Figures 3A and 3B, and SEM photographs of the electrode surface after the press processing are shown in Figures 3C and 3D, respectively. From a comparison between Figures 3A and 3C, and a comparison between Figures 3B and 3D, it can be confirmed that a structure in which some primary particles and secondary particles are crushed by pressing has been generated. The crushed parts correspond to the permanently deformed parts described above.

[0052] The auxiliary material of this embodiment includes primary particles that are hollow particles having a space inside. On the other hand, solid particles can be mixed with the hollow particles when selecting the composition in the electrode or adjusting the electrode porosity without increasing the electrode density. The solid particles are the ones that remain without dissolving the template in the above-mentioned T-CVD method.

[0053] The solid particles are preferably carbonaceous from the viewpoint of electronic conductivity, and carbon black, acetylene black, single-walled carbon nanotubes, and multi-walled carbon nanotubes are preferably used.

[0054] In the auxiliary material according to the present embodiment, the solid particles are preferably ceramic particles coated with carbonaceous matter. In producing a high-density electrode, ceramic particles have a higher strength than carbon-based particles. This reinforces the structure of the electrode containing the auxiliary material, and improves electronic conductivity by adding the electrical conductivity of the carbonaceous matter.

[0055] When ceramic particles are selected as the solid particles, they can be used as they are without being eluted with the above-mentioned reagents.

[0056] As the ceramic particles, a compound that is inactive in the battery reaction can be appropriately selected. Examples include Al2O3, MgO, SiO2, ZrO2, etc. In addition, a compound that has CVD activity and can be used as a template in the T-CVD method can also be used.

[0057] In addition to strength, ceramic particles can also have other properties that can be utilized, such as chemical reactivity, catalytic properties, and physical properties.

[0058] The proportion of solid particles mixed into the auxiliary material varies depending on the purpose of use, but is preferably 10% by weight or more, more preferably 30% by weight or more, and most preferably 50% by weight or more in order to clearly exert the effect.

[0059] When solid particles are mixed into the auxiliary material, carbon-based solid particles can be appropriately mixed in to fine-tune the electrode specifications. By adding carbon-based solid particles, the electronic conductivity can be adjusted.

[0060] In some cases, a lithium ion battery can be provided with an electrode in which all of the hollow particles described above are replaced with solid particles in which ceramic particles are coated with carbonaceous matter. From the viewpoint of battery reaction, even if a lithium ion battery is used with an electrode containing an auxiliary material in which ceramic particles are replaced with solid particles in which carbonaceous matter is coated, there is no significant difference in the battery reaction from a lithium ion battery containing an auxiliary material using hollow particles. Replacing hollow particles with solid particles in which ceramic particles are coated with carbonaceous matter is suitable for expressing other new functional properties.

[0061] As the electrode active material, lithium-containing oxides and lithium transition metal phosphates can be used for the positive electrode, and graphite, carbons, alloys containing Si, Sn, and intermetallic compounds can be used for the negative electrode.

[0062] The auxiliary material of this embodiment is a primary particle or at least a secondary particle formed by adhering a plurality of primary particles. Although it depends on the type of electrode active material, it is preferable that the length of the primary particle or secondary particle is not more than twice the particle diameter of the electrode active material.

[0063] Although it depends on whether the functionality of the primary particles or the secondary particles is desired to be predominant in the auxiliary material, secondary particles having an average particle size of 0.05 μm to 6 μm are preferably used, and the average particle size of the secondary particles is preferably 0.1 μm to 5 μm.

[0064] In addition, the auxiliary material of this embodiment cannot supply lithium ions, which are the source of battery capacity, from the outside. Therefore, the additive ratio of the auxiliary material to the electrode should be kept to the minimum necessary. In order to obtain good characteristics, the auxiliary material is preferably 0.1 wt% or more and 5 wt% or less of the electrode mixture.

[0065] If it is smaller than this range, the functionality cannot be utilized, whereas if it is too large, the bulk density of the electrode mixture becomes too large, undesirably decreasing the electrode strength.

[0066] Next, the measurement of the extremely small load unloading test for confirming the physical properties of the battery reaction auxiliary material according to this embodiment will be described.

[0067] As an example of the ultra-small load-unloading test, a load-displacement curve obtained by performing the test on the battery reaction auxiliary material prepared in Example 1 described later is shown in FIG. 4. In the ultra-small load-unloading test used in this embodiment, a load is applied to the test particle by pressing an indenter against the sample particle and pressing it in. Measurement begins when the indenter comes into contact with the particle and the sensor detects the pressure. Then, as the pressing depth increases, the load on the particle increases. In the ultra-small load-unloading test in this embodiment, the load is removed when the load reaches 0.1 mN.

[0068] If the particle were to completely recover its shape without any deformation, the indentation depth would return to 0, i.e., it would return to the origin of the horizontal axis in the graph of Figure 3. Conversely, if the particle were to completely deform due to the load, i.e., if the particle were to be crushed in the direction in which the load was applied, the indentation depth would remain at 300 nm. This means that the space that existed within the particle has disappeared, and the layers that formed the skeleton have become two overlapping layers.

[0069] In the battery reaction assistant material of this embodiment, the indentation depth does not return to 0 even when the load is removed. For example, in FIG. 4, the particle to which the load was applied had an indentation depth of about 230 nm. This indicates that while the particle was partially deformed by the load, a space remained within the particle. In FIG. 3, the part corresponding to the work required to restore the shape in response to the applied load is the elastic deformation work W E (The shaded area in Figure 3) corresponds to the amount of work required to deform the material under a given load. P (The vertically lined parts in FIG. 3) are shown.

[0070] The carbon layer stacking index in the auxiliary material of this embodiment is preferably 5 or less. If the carbon layer stacking index is larger than this, the skeleton of the particle becomes harder, which reduces the elastic deformability of the particle structure. It is easily broken by the pressure during electrode production, and the amount of electrolyte held is reduced, resulting in a deterioration of the properties. If the carbon layer stacking index is too small, it is easily crushed when loaded. This means that the space within the particle becomes smaller, which makes it difficult to hold the electrolyte within the particle.

[0071] Next, a lithium ion secondary battery including an electrode containing the auxiliary material of this embodiment will be described.

[0072] 5 shows an example of a cross-sectional structure of a coin-type lithium-ion battery 200 according to an embodiment of the present invention. This lithium-ion battery 200 is formed by stacking a disk-shaped positive electrode 212 housed in a metal exterior part 211 and a disk-shaped negative electrode 214 housed in a metal exterior part 113 with a separator 215 interposed therebetween. A metal spring 218 and a spacer 219 are disposed between the exterior part 213 and the negative electrode 214. The interiors of the exterior parts 211 and 213 are filled with a liquid electrolyte, and the peripheries of the exterior parts 211 and 213 are sealed by being crimped via a seal gasket 217.

[0073] The positive electrode will now be described. The positive electrode 212 is generally obtained by applying a slurry of a metal oxide material, a conductive assistant that assists electronic conductivity, a binder, and a solvent onto a current collecting metal foil such as rolled aluminum foil to form a coating film, heating and drying to remove the solvent, and then forming the coating into a predetermined size and density. In this embodiment, the above-mentioned battery reaction auxiliary material is used instead of a commonly used conductive assistant such as acetylene black.

[0074] Metal compound materials that can be used as positive electrode active materials are those that can release electrons to the external circuit of the battery and simultaneously release Li ions to the electrolyte. The amount of Li ions contained varies depending on the chemical composition, crystal structure, etc., but materials that can reversibly release and absorb many Li ions are preferable.

[0075] Examples of such materials include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides. Examples of transition metals include Fe, Co, Ni, and Mn. Specific examples include MnO, V2O5, and V6O 13 Examples of such materials include transition metal oxides such as TiO2, LiNiO2, LiCoO2, LiMn2O4, and inorganic compounds such as TiS2, FeS, and MoS2. In order to improve the properties of these materials, certain elements may be partially substituted with other elements.

[0076] In addition to the above inorganic compounds, there are also organic compounds that can be used as cathode materials. For example, polyaniline, polypyrrole, polyacene, disulfide compounds, polysulfide compounds, N-fluoropyridinium salts, etc. The cathode material can be a mixture of the above inorganic compounds and organic compounds.

[0077] The physical properties of the positive electrode material are determined by the requirements in the battery design and manufacturing process, which are caused by constraints such as the usage form of the lithium-ion battery. In the manufacturing of the positive electrode material, the process is designed so that the physical properties can be realized. The physical properties include the powder particle size and distribution, specific surface area, density, etc.

[0078] As an example, the powder particle size is appropriately selected taking into account other constituent requirements of the lithium ion battery, but from the viewpoint of improving battery characteristics such as rate characteristics and cycle characteristics, the average particle size is usually preferably 1 to 30 μm, and more preferably 1 to 10 μm.

[0079] Since the above-mentioned positive electrode materials generally have low electronic conductivity, it is preferable to have a battery reaction auxiliary material that assists electronic conductivity coexist in the positive electrode. Carbon-based materials and metal-based materials are commonly used as conductive auxiliary materials, and other materials with high electronic conductivity can also be used, among which carbon-based materials are preferable.

[0080] The amount of battery reaction auxiliary materials used should be kept to a minimum, while the content of the positive electrode material, which determines the capacity of the lithium-ion battery, should be maximized.

[0081] Examples of conventional carbon-based materials include soot, acetylene black, ketjen black, lamp black, furnace black, carbon black, graphite, carbon fiber, graphite fiber, nanofiber, nanotube, coke, hard carbon, and amorphous carbon.

[0082] In comparison, the auxiliary material of the present embodiment has a significant feature not found in conventional materials. That is, since the auxiliary material of the present embodiment contains a graphene portion with a relatively large area in its structure, there are few defects other than carbon-carbon bonds, such as oxygen-containing functional groups at the ends of carbon bonds in a six-membered ring. Therefore, it is less likely to deteriorate and decompose in the electrochemical oxidation environment to which it is exposed inside a battery.

[0083] In addition, further effects can be obtained by combining it with the conventional materials as necessary. For example, flake graphite and highly linear carbon nanotubes have high electronic conductivity but low ion storage. By combining such properties with the auxiliary material of the present embodiment, it is possible to construct a good battery reaction auxiliary system that adds ion storage to electronic conductivity.

[0084] Carbon blacks such as acetylene black are composed of structural particles with a diameter of several tens of nanometers. On the other hand, the crystallinity of carbon is not so high, the structural length is short, and it is easy to collapse, so it is difficult to transmit electrons over long distances. By combining with the auxiliary material of this embodiment, it is possible to realize a system that maintains electronic conductivity and also has ion supply ability even when the three-dimensional structure is maintained or when the three-dimensional structure is crushed and flattened like flake graphite.

[0085] The suitable ratio of the battery reaction auxiliary material made of the carbon material of this embodiment to be contained in the positive electrode varies depending on the type of positive electrode material, the type and amount of binder, the battery capacity design, etc. In this embodiment, as described above, the addition rate of the battery reaction auxiliary material to the positive electrode is preferably 0.1 wt% or more and 5 wt% or less per electrode mixture. By adding it in such a range, good characteristics can be obtained.

[0086] The positive electrode material and the battery reaction auxiliary material are often in powder form, and in order to fix them together and on the current collecting metal foil, it is preferable to mix them with a small amount of a binder. The binder is required to be chemically and electrochemically inactive and to have some elasticity and affinity, and a plastic resin material is preferably used.

[0087] Another mode of use of the battery reaction auxiliary material is to use it in the form of a paint in which the powder is dispersed in a liquid solvent at a certain ratio. In this case, the solvent can be an organic or inorganic compound applicable to the manufacture of lithium-ion batteries. In order to keep the powder well dispersed in the solvent, an organic or inorganic dispersant (e.g., a monomolecular or plastic resin material) can be suitably used.

[0088] Examples of the plastic resin material include fluorine-based resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene, CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide, polyvinyl alcohol-based polymers such as polyvinyl acetate and polyvinyl alcohol, halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride, conductive polymers such as polyaniline, alkane-based polymers such as polyethylene, polypropylene, and poly-1,1-dimethylethylene, unsaturated polymers such as polybutadiene and polyisoprene, polymers having rings such as polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N-vinylpyrrolidone, acrylic polymers such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide, etc. Also, the resin material may be a mixture, modified product, derivative, random copolymer, alternating copolymer, graft copolymer, block copolymer, etc. The weight average molecular weight of these resins is usually 10,000 to 3,000,000, and preferably 100,000 to 1,000,000. If the molecular weight is too small, the strength of the coating film decreases, and if it is too large, the viscosity increases, making it difficult to form an electrode.

[0089] In order to distribute the binder sufficiently uniformly and form a coating film of the slurry with a predetermined size, a suitable slurry solvent that dissolves only the binder resin and does not dissolve other materials can be used. For example, when polyvinylidene fluoride is used, dimethylformamide is preferably used as the solvent. Alternatively, N-methylpyrrolidone may be used as the solvent, and it can be appropriately selected and used depending on the conditions of the manufacturing process.

[0090] The current collecting metal foil is preferably made of a material that is inexpensive and can withstand industrial use, and is preferably made of a material that has electrochemical resistance to the potential generated by the positive electrode. Examples of the current collecting metal foil include aluminum foil, nickel foil, titanium foil, and stainless steel foil, and rolled aluminum foil, which is generally available, is more preferable.

[0091] The method for forming a coating film of the slurry on the current collecting metal foil can be a commonly used printing technique. When the thickness of the coating film is small, gravure printing or the like is preferably used, and when the thickness is large, printing techniques such as doctor blade printing or die printing are preferably used.

[0092] Thereafter, the coating film is dried by heating. Any drying method can be used, and a method that can achieve the desired binding strength by the binder is preferably used.

[0093] Thereafter, when forming the positive electrode into a predetermined size, an industrially available cutting blade and the like and the method thereof are preferably used. In addition, in order to achieve a predetermined density, an industrially available pressurizing device and the like and the method thereof are preferably used as necessary.

[0094] Next, the negative electrode will be described. The negative electrode 214 is obtained by coating a slurry made of, for example, a carbon-based material, a binder, and a solvent onto a current-collecting metal foil such as rolled copper foil, heating and drying to remove the solvent, and then forming the resulting product into a predetermined size and density.

[0095] As a carbon-based material that can be used for the negative electrode, it is preferable that the material has many stabilization sites inside, and can bond and stabilize Li ions with electrons flowing from an external circuit.

[0096] For example, any material of organic origin can be used regardless of whether it has high or low crystallinity, and graphite, coke, amorphous carbon, hard carbon, polymer carbon, etc. can be suitably used. In this case, the principle is that Li ions are sandwiched between graphene layers, etc., and are stabilized by bonding with electrons.

[0097] As another stabilization mechanism, a method of electrochemically forming an intermetallic compound can also be used, and silicon, tin, zinc, bismuth, antimony, cadmium, lead, germanium, etc. can be suitably used.

[0098] In addition, other materials that exhibit low electrochemical reaction potentials and serve as the negative electrode of a lithium-ion battery can also be used, such as metals and compounds of oxygen, sulfur, halogens, nitrogen, phosphorus, etc.

[0099] Depending on the application of the lithium ion battery, a plurality of the above negative electrode materials can be mixed in a predetermined ratio and used to obtain a desired discharge profile.

[0100] The physical properties of the negative electrode material are determined by the requirements in the device (e.g. storage battery) design and manufacturing process, which are caused by constraints such as the usage form of the lithium-ion battery. In the manufacturing of the material, the process is designed so that the physical properties can be realized. Physical property values ​​include powder particle size and distribution, specific surface area, density, etc.

[0101] As an example, the powder particle size is appropriately selected taking into account other constituent requirements of the lithium ion battery, but from the viewpoint of improving battery characteristics such as rate characteristics and cycle characteristics, the average particle size is usually preferably 1 to 70 μm, and more preferably 3 to 30 μm.

[0102] The above-mentioned negative electrode materials generally have high electronic conductivity, but some materials have a smooth surface, and when the contact between particles is insufficient, it is also preferable to coexist a conductive assistant that assists in electronic conductivity. Carbon-based materials, metal-based materials, and other materials with high electronic conductivity can also be used as materials, and among them, carbon-based materials are preferable. The battery reaction assistant material of the present embodiment described above may be used as a conductive assistant.

[0103] The amount of conductive additive used should be kept to a minimum, while the content of the negative electrode material, which determines the capacity of the lithium-ion battery, should be maximized.

[0104] Examples of conventional carbon-based materials include soot, acetylene black, ketjen black, lamp black, furnace black, carbon black, graphite, carbon fiber, graphite fiber, nanofiber, nanotube, coke, hard carbon, and amorphous carbon.

[0105] In comparison, the battery reaction auxiliary material of the present embodiment has a significant feature not found in conventional materials, and furthermore, by using it in combination with conventional materials as necessary, further efficacy can be obtained. For example, flaky graphite and highly linear carbon nanotubes have high electronic conductivity but low ion storage. Therefore, by combining it with the auxiliary material of the present invention, it is possible to construct a good battery reaction auxiliary system that adds ion storage to electronic conductivity.

[0106] Carbon blacks such as acetylene black are composed of structural particles with a diameter of several tens of nanometers. On the other hand, the crystallinity of carbon is not so high, the structural length is short, and it is easy to collapse, so it is difficult to transmit electrons over long distances. Although it has such properties, by combining it with the auxiliary material of the present invention, it is possible to realize a system that maintains electronic conductivity and also has ion supply ability even in a state where the three-dimensional structure is maintained or in a state where the three-dimensional structure is crushed and flattened like flake graphite.

[0107] The preferred ratio of the battery reaction auxiliary material of this embodiment to be contained in the negative electrode varies depending on the type of the positive electrode material, the type and amount of the binder, the battery capacity design, etc. In this embodiment, as described above, the addition rate of the battery reaction auxiliary material to the positive electrode is preferably 0.1 wt% or more and 5 wt% or less per electrode mixture. By adding it in such a range, good characteristics can be obtained.

[0108] The current collecting metal foil is preferably made of a material that is inexpensive and can withstand industrial use, and is preferably made of a material that does not have electrochemical reactivity to the potential generated by the negative electrode. For example, the current collecting metal foil is preferably made of copper foil, nickel foil, titanium foil, or stainless steel foil, and more preferably made of electrolytic copper foil or rolled copper foil, which are generally readily available.

[0109] The method for forming the coating film of the above-mentioned slurry can be a commonly used printing technique. When the thickness dimension is small, gravure printing or the like is preferably used, and when the thickness dimension is large, printing techniques such as doctor blade printing and die printing are preferably used.

[0110] Thereafter, the coating film is dried by heating. Any drying method can be used, and a method that can achieve the desired binding strength by the binder is preferably used.

[0111] Thereafter, when forming the negative electrode into a predetermined size, an industrially available cutting blade and the like and the method are preferably used. In addition, in order to achieve a predetermined density, an industrially available pressing device and the like and the method are preferably used as necessary.

[0112] The negative electrode material and the conductive assistant are often in powder form, and in order to fix them together and on the current collecting metal foil, it is preferable to mix them with a small amount of a binder. The binder is required to be chemically and electrochemically inactive and to have some degree of elasticity and affinity, and a plastic resin material is preferably used.

[0113] Another mode of use of the battery reaction auxiliary material is to use it in the form of a paint in which the powder is dispersed in a liquid solvent at a certain ratio. In this case, the solvent can be an organic or inorganic compound applicable to the manufacture of lithium-ion batteries. In order to keep the powder well dispersed in the solvent, an organic or inorganic dispersant (e.g., a monomolecular or plastic resin material) can be suitably used.

[0114] Examples of the plastic resin material include fluorine-based resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene, CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide, polyvinyl alcohol-based polymers such as polyvinyl acetate and polyvinyl alcohol, halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride, conductive polymers such as polyaniline, alkane-based polymers such as polyethylene, polypropylene, and poly-1,1-dimethylethylene, unsaturated polymers such as polybutadiene and polyisoprene, ring-containing polymers such as polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N-vinylpyrrolidone, acrylic polymers such as polymethylmethacrylate, polyethylmethacrylate, polybutylmethacrylate, polymethylacrylate, polyethylacrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide, carboxymethylcellulose, and styrene-butadiene rubber. The resin material may also be a mixture, modified product, derivative, random copolymer, alternating copolymer, graft copolymer, or block copolymer. The weight average molecular weight of these resins is usually 10,000 to 3,000,000, and preferably 100,000 to 1,000,000. If the molecular weight is too small, the strength of the coating film decreases, and if it is too large, the viscosity increases, making it difficult to form an electrode.

[0115] In order to distribute the binder sufficiently uniformly and form a coating film of the slurry with a predetermined size, a suitable slurry solvent that dissolves only the binder resin and does not dissolve other materials can be used. For example, when polyvinylidene fluoride is used, dimethylformamide is preferably used as the solvent. Alternatively, N-methylpyrrolidone may be used as the solvent, and it can be appropriately selected and used depending on the conditions of the manufacturing process.

[0116] In this embodiment, a battery electrolyte applied to a lithium ion battery will be described.

[0117] An electrolyte is a solute dissolved in an organic solvent, and is usually the main component.

[0118] One of the components of an electrolyte is a solute that is the source of ions, namely a Li salt.

[0119] The type of solute is not particularly limited, and any solute known to be used in the application of this lithium ion battery can be used. Specific examples include the following:

[0120] Examples of solutes include inorganic salts such as LiPF6 and LiBF4, fluorine-containing organic Li salts such as LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, Li cyclic 1,2-perfluoroethane disulfonylimide, Li cyclic 1,3-perfluoropropane disulfonylimide, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, and LiBF2(C2F5SO2)2, and Li bis(oxalate)borate.

[0121] Among these, LiPF6, LiBF4, LiN(CF3SO2)2 and LiN(C2F5SO2)2 are preferred in terms of exerting battery performance, and LiPF6 and LiBF4 are particularly preferred.

[0122] These Li salts may be used alone or in combination of two or more.

[0123] The content of the Li salt in the electrolyte varies depending on the type of solvent in which the Li salt is dissolved and the mixed composition, but the content of the Li salt in the electrolyte is preferably 7 to 190% by weight, more preferably 10 to 180% by weight, and even more preferably 13 to 150% by weight.

[0124] Next, the organic solvent used in the electrolyte will be described.

[0125] The type of the solvent is not particularly limited, and may be appropriately selected from those conventionally known as solvents. For example, cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, cyclic carboxylates, chain carboxylates, phosphorus-containing organic solvents, etc., each of which does not have an unsaturated bond may be used.

[0126] In addition to viscosity, factors that affect the movement of Li ions include the viscosity and solvation power of the organic solvent. Solvation power is the force that dissociates dissolved ions, and if it is too strong, it will hinder the movement of ions, so there is an optimal value.

[0127] In addition, practical lithium-ion batteries can be used in a wide range of environmental conditions, and physical properties such as the melting point and boiling point of the organic solvent must also fall within certain ranges.

[0128] A practical solution to the above requirements is to use a mixture of multiple organic solvents. The mixture composition is determined by taking into consideration practical properties and combinations of organic solvents with high and low melting points, high and low solvating power, etc.

[0129] In the electrolyte of this embodiment, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate, neither of which has a carbon-carbon unsaturated bond.

[0130] Examples of the cyclic carbonate include alkylene carbonates having an alkylene group having 2 to 4 carbon atoms, such as ethylene carbonate, propylene carbonate, butylene carbonate, etc. Among these, ethylene carbonate and propylene carbonate are preferred from the viewpoint of improving battery characteristics, and ethylene carbonate is particularly preferred.

[0131] As the chain carbonates, dialkyl carbonates are preferred, and the number of carbon atoms in the constituent alkyl groups is preferably 1 to 5, and particularly preferably 1 to 4. Specific examples include dialkyl carbonates such as symmetric chain alkyl carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate, and asymmetric chain alkyl carbonates such as ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate. Among them, dimethyl carbonate is the most preferred in terms of viscosity because it has the lowest viscosity.

[0132] However, since dimethyl carbonate has a rather low boiling point, more suitable properties can be obtained by further mixing it with a chain carbonate having a higher boiling point. Diethyl carbonate is suitable as the chain carbonate to be mixed, but other chain carbonates can also be used without problems.

[0133] The mixing ratio also varies depending on the desired practical properties. There is an optimal composition for the ratio of the chain carbonate to the cyclic carbonate, including the ratio of the Li salt.

[0134] The content of the cyclic carbonate in the electrolyte is preferably 1 to 35% by weight, more preferably 3 to 30% by weight, and even more preferably 4 to 25% by weight. A mixture of multiple cyclic carbonates can be used.

[0135] On the other hand, the content of the chain carbonate in the electrolyte is preferably 40 to 70% by weight, more preferably 43 to 68% by weight. A mixture of multiple chain carbonates can be used.

[0136] As a comprehensive composition, the following combination is preferable. Among the combinations of ethylene carbonate and dialkyl carbonates, ethylene carbonate and dimethyl carbonate are preferred, and may further contain symmetric chain dialkyl carbonate and / or asymmetric chain dialkyl carbonate. For example, those containing ethylene carbonate, symmetric chain dialkyl carbonate and asymmetric chain dialkyl carbonate, such as ethylene carbonate, dimethyl carbonate and diethyl carbonate, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, are preferred because they have a good balance between cycle characteristics and high-power discharge characteristics. Among them, it is preferred that the asymmetric chain dialkyl carbonate is ethyl methyl carbonate, and the alkyl group of the alkyl carbonate has 1 to 2 carbon atoms.

[0137] Furthermore, as a solvent that aids in the dissociation and movement of ions, cyclic ethers, chain ethers, cyclic carboxylate esters, chain carboxylate esters, etc. may be added in addition to the above-mentioned main organic solvents.

[0138] Examples of cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran, and examples of chain ethers include dimethoxyethane and dimethoxymethane.

[0139] Examples of cyclic carboxylates include γ-butyrolactone and γ-valerolactone, and examples of chain carboxylates include methyl acetate, methyl propionate, ethyl propionate, and methyl butyrate.

[0140] Among these, chain carboxylates are particularly preferred.

[0141] Furthermore, it is also preferable that the electrolyte of this embodiment contains a fluorine-containing cyclic carbonate having two or more fluorine atoms.

[0142] The number of fluorine atoms in a fluorine-containing cyclic carbonate having two or more fluorine atoms is not particularly limited, but in the case of fluorinated ethylene carbonate, the lower limit is usually two or more and the upper limit is usually four or less, preferably three or less.

[0143] In the case of fluorinated propylene carbonate, the lower limit is usually 2 or more, and the upper limit is usually 6 or less, preferably 5 or less. In particular, those in which two or more fluorine atoms are bonded to carbons forming a ring structure are preferred from the viewpoint of improving cycle characteristics and storage characteristics.

[0144] Among these, fluorinated ethylene carbonates having two or more fluorine atoms are preferred from the viewpoint of improving battery characteristics, and among these, cis-4,5-difluoro-1,3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, and 4,4-difluoro-1,3-dioxolan-2-one are particularly preferred.

[0145] The fluorine-containing cyclic carbonate having two or more fluorine atoms may be used alone or in combination of two or more. The ratio of the fluorine-containing cyclic carbonate compound having two or more fluorine atoms in the non-aqueous electrolyte is not particularly limited in order to exhibit the effects of this embodiment, but is usually 0.001% by weight or more, preferably 0.01% by weight or more, more preferably 0.1% by weight or more, particularly preferably 0.2% by weight or more, and most preferably 0.25% by weight or more. At a concentration lower than this, the effects of this embodiment may be difficult to exhibit. On the other hand, if the concentration is too high, the battery internal pressure may increase during high-temperature storage, so the upper limit is usually 10% by weight or less, preferably 4% by weight or less, more preferably 2% by weight or less, particularly preferably 1% by weight or less, and most preferably 0.5% by weight or less.

[0146] Furthermore, cyclic carbonates having unsaturated bonds and aromatic compounds having a total carbon number of 7 or more and 18 or less may be mixed into the electrolyte.

[0147] Among the cyclic carbonates having unsaturated bonds, vinylene carbonate, vinylethylene carbonate, 4-methyl-4-vinylethylene carbonate, and 4,5-divinylethylene carbonate are preferred from the viewpoint of improving cycle characteristics, and among these, vinylene carbonate and vinylethylene carbonate are more preferred. These may be used alone or in combination of two or more kinds.

[0148] Preferred aromatic compounds having a total carbon number of 7 to 18 include biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, and the like.

[0149] It is believed that by suppressing the side reaction between the aromatic compound having a total carbon number of 7 to 18 and the negative and positive electrodes in this way, a significant decrease in discharge characteristics after high-temperature storage can be suppressed.

[0150] In order to achieve the effects of this embodiment, the proportion of aromatic compounds having a total carbon number of 7 to 18 in the electrolyte is usually 0.001% by weight or more, preferably 0.1% by weight or more, particularly preferably 0.3% by weight or more, and most preferably 0.5% by weight or more, and the upper limit is usually 5% by weight or less, preferably 3% by weight or less, and particularly preferably 2% by weight or less. If the concentration is lower than this lower limit, it may be difficult to achieve the effect of improving safety during overcharging. Conversely, if the concentration is too high, battery characteristics such as high-temperature storage characteristics may be reduced.

[0151] The separator 215 separates the positive electrode 212 and the negative electrode 214, prevents a short circuit of current due to contact between the two electrodes, and allows lithium ions to pass through. A porous film made of a resin is preferably used for the separator 215.

[0152] As the form of the membrane, a stretched membrane in which pores are formed by stretching a bulk resin, or a nonwoven fabric in which a large number of fibrous resin fibers are laminated to form a porous structure like a porous membrane, etc. are preferably used.

[0153] Examples of resin materials include polyolefins, and polyethylene is particularly suitable. Polyethylene has a relatively low melting temperature, and when the temperature of the battery rises for some reason (e.g., an unsafe condition such as a short circuit), the pores in the membrane are blocked by thermal melting, preventing the movement of the driving ions, thereby stopping the reaction and ensuring safety.

[0154] A porous film formed by the stretching method is usually prepared by adding a plasticizer to a polyolefin, and the plasticizer is removed before and after stretching. The areas where the plasticizer was present become the starting points, resulting in a relatively uniform microporous structure.

[0155] In producing a stretched film, stretching is usually performed in both the longitudinal and transverse directions. In addition to the removal of the plasticizer, etc., any atmosphere, temperature, speed, stress, number of process repetitions, etc. can be appropriately combined to obtain a suitable stretched film.

[0156] Although the above manufacturing process can produce a high-quality stretched membrane, it is a multi-step process, which makes it difficult to reduce manufacturing costs such as process costs, and may be a negative factor in the spread of lithium-ion batteries.

[0157] On the other hand, by simplifying the process so that the stretching is performed only in the longitudinal direction without using plasticizers, it is possible to obtain a porous membrane that can be manufactured on an industrial level and can reduce the manufacturing cost. In this case, the applicable resin is polyolefin, and polypropylene is preferably used.

[0158] The separator interposed between the positive electrode and the negative electrode may be formed from an electrically insulating porous body. For example, a polymer film or a fiber nonwoven fabric made of polyolefin such as polyethylene or polypropylene, polyester, polyethylene terephthalate, or polyimide can be used as the separator. The separator may be made of one material alone or a plurality of materials. The separator may be a single layer or a multilayer (composite film). The separator may contain inorganic material nanoparticles such as ceramic. The separator may be used by coating both sides with a polymer compound such as polyvinylidene fluoride.

[0159] In the nonaqueous electrolyte battery according to the present embodiment, a gelled electrolyte may be used by including a polymer compound that swells with an organic solvent to serve as a support for holding the nonaqueous electrolyte. By including a polymer compound that swells with an organic solvent, high ionic conductivity can be obtained, excellent charge / discharge efficiency can be obtained, and leakage of the battery can be prevented. When the nonaqueous electrolyte includes a polymer compound, the content of the polymer compound is preferably within a range of 0.1% by mass to 10% by mass of the nonaqueous electrolyte.

[0160] In addition, when a polymer compound such as polyvinylidene fluoride is applied to both sides of the separator, the mass ratio of the non-aqueous electrolyte to the polymer compound is preferably within a range of 50: 1 to 10: 1. By setting the mass ratio within this range, higher charge / discharge efficiency can be obtained.

[0161] Examples of the polymeric compound include ether-based polymeric compounds such as polyvinyl formal, polyethylene oxide, and crosslinked products containing polyethylene oxide, ester-based polymeric compounds such as polymethacrylate, acrylate-based polymeric compounds, and vinylidene fluoride polymers such as polyvinylidene fluoride and copolymers of vinylidene fluoride and hexafluoropropylene. The polymeric compound may be used alone or in combination. In particular, from the viewpoint of the swelling prevention effect during high-temperature storage, it is desirable to use a fluorine-based polymeric compound such as polyvinylidene fluoride.

[0162] The lithium ion battery having the above configuration operates as follows. When the lithium ion battery is charged, Li ions contained in the positive electrode 212 pass through the separator 215 and are inserted between the layers of the layered structure of graphite contained in the negative electrode 214. When the battery is subsequently discharged, Li ions are released from between the layers of the layered structure contained in the negative electrode 214 and pass through the separator 215 back to the positive electrode 212. The battery reaction proceeds through this series of actions.

[0163] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims.

[0164] In the above embodiment, a coin-type lithium ion battery has been described as an example of the lithium ion battery, but the lithium ion battery of this embodiment can be similarly applied to other shapes such as a button type, a paper type, a square type, or a cylindrical type having a spiral structure. The lithium ion battery of this embodiment can also be made in various sizes such as a thin type or a large type.

[0165] Furthermore, in the above description, the lithium ion battery according to the present embodiment is described assuming a lithium ion battery having a liquid electrolyte, but any other electrolytes can be used. For example, a gel electrolyte or a solid electrolyte can be suitably used. EXAMPLES

[0166] Experiment 1: Confirmation of the basic performance of battery reaction auxiliary materials <Example 1> (Manufacture of battery reaction auxiliary materials) Magnesium oxide nanopowder (primary particle size 0.4 μm, SSA 130 μm) was used as a template for the carbonaceous membrane. 2 A heat treatment vessel was filled with 100% ZnO (100% ZnO / g; manufactured by Guangzhou Hongwu Material Technology Co., Ltd.) and then loaded into a tube furnace. The inside was replaced with Ar gas, and then the temperature was raised to 920°C. If necessary, preliminary heat treatment was performed for the purpose of dehydration, etc. Then, a mixed gas of Ar gas and CH4 gas (concentration 20 vol%) was flowed for 2.3 hours, and a carbonaceous film containing a graphene structure was formed on the template by the T-CVD method. After cooling, the mixture was removed and crushed and classified.

[0167] Next, the template was dissolved from this treated material with hydrochloric acid, washed and dried while maintaining the intraparticle space, to obtain a precursor of the auxiliary material. This was then heat-treated at 1700°C in an inert atmosphere to optimize the carbon structure, to obtain the battery reaction auxiliary material of Example 1.

[0168] The shape of the obtained auxiliary material was observed by TEM using a transmission electron microscope (JEM-2010, JEOL). Observation of the porous carbon material using a transmission electron microscope was performed at an acceleration voltage of 200 kV. The average particle size of the secondary particles of the obtained auxiliary material was 3.2 μm, and it was confirmed from the transmission electron microscope (TEM) image (Figure 6) that a skeletal structure mainly composed of layered graphene was formed.

[0169] (Very small load / unload test) A small amount of the auxiliary material dispersed in ethanol was spread on the sample stage and dried. It was then introduced into the SEM, and the measurement particles were observed. Particles with a height of 1 to 5 μm and a width of 1 to 5 μm were placed directly under the indenter as the measurement target. Then, using a nanoindenter: Nanoflip (Toyo Technica) built into the SEM, a load-unloading test was performed under the following conditions: indentation head: InForce50, indenter diameter: 10 μm, maximum load: 0.1 mN, time to maximum load: 5 sec, maximum load holding time: 5 sec. The sample shape was selected to be stably fixed on the sample stage, and if the position easily changed during the initial pressure application, remeasurement was performed. The plastic deformation power shown in Figure 3 can be calculated from the following formula.

number

[0170] (Preparation of positive electrode) Ternary positive electrode material NCM (LiNi 0.5 Co 0.2 Mn 0.3 96% by weight of O2) powder, 1% by weight of the battery reaction auxiliary material of Example 1 as a conductive assistant, and 3% by weight of PVdF were added to the solvent N-methyl-pyrrolidone (NMP). The resulting mixture was stirred and mixed to make a homogeneous positive electrode paste. This was applied to an Al current collector with a thickness of 15 μm, dried at 110 ° C, and then punched to φ 15 mm and pressed at 45 kN to make a positive electrode.

[0171] (Preparation of positive electrode test battery) The obtained positive electrode was vacuum-dried at 120°C, and then in a glove box with an argon gas atmosphere, a 2032 size coin-type test battery with a metallic Li counter electrode was fabricated using a 1M LiPF6 solution (a 1:1 mixed solvent of ethylene carbonate (EC):diethyl carbonate (DEC)) as the electrolyte and a polypropylene separator.

[0172] (Positive electrode evaluation method) A constant current of 1.25mA (equivalent to 0.2C) was applied to each test battery up to 4.2V, and after reaching 4.2V, constant voltage charging was continued until it reached 0.31mA (0.05C). Then, the battery was discharged to 3V at a constant current of 1.25mA. The discharge capacity and average voltage at this time were determined. Next, the same test battery was used to apply a constant current of 1.25mA (equivalent to 0.2C) up to 4.2V, and after reaching 4.2V, constant voltage charging was continued until it reached 0.31mA (0.05C). Then, the battery was discharged to 3V at a high rate of 12.5mA (equivalent to 2C). From the discharge capacity of the test battery obtained, the 2C retention rate (2C capacity ÷ 0.2C capacity) of each test battery was determined.

[0173] <Example 2> A battery reaction auxiliary material of Example 2 was obtained in the same manner as in Example 1, except that aluminum oxide nanopowder (primary particle size 0.015 μm, SSA 157 m2 / g; manufactured by TECNAN Corporation) was used as a carbonaceous film template, the heat treatment temperature was 890°C, the T-CVD method time was 2.1 hours, and hydrofluoric acid was used to dissolve the template.

[0174] The formation of a skeletal structure mainly composed of layered graphene was confirmed in the obtained auxiliary material of Example 2 by a transmission electron microscope (TEM) (FIG. 7), and the average secondary particle size was 2.1 μm.

[0175] Test cells of Example 2 were prepared under conditions similar to those of Example 1.

[0176] <Comparative Example 1> A test battery was produced under the same conditions as in Example 1, except that acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., product name: Denka Black) was used instead of the auxiliary material.

[0177] <Comparative Example 2> A test battery was produced under the same conditions as in Example 1, except that Ketjen Black (manufactured by Lion Specialty Chemicals, product name: EC300) was used instead of the auxiliary material.

[0178] <Comparative Example 3> Instead of auxiliary materials, single-walled carbon nanotubes (SSA: 600m 2 A test battery was manufactured under the same conditions as in Example 1, except that a positive electrode additive amount of 97.95 wt % and a single-walled carbon nanotube additive amount of 0.05 wt % were used (Guangzhou Hongwu Material Technology Co., Ltd., outer diameter: 2 nm, length: 2 to 5 μm).

[0179] In addition to the ultra-small load / unload test described above, nitrogen adsorption / desorption measurements and Raman spectroscopy measurements were also performed on the battery reaction auxiliary materials produced in Examples 1 and 2, the acetylene black used in Comparative Example 1, the ketjen black used in Comparative Example 2, and the single-walled carbon nanotubes used in Comparative Example 3, to determine the plastic deformation power, pore volume, and carbon layer stacking index, respectively.

[0180] The pore volume of the auxiliary material of the example was measured by nitrogen adsorption and desorption at -196°C using a specific surface area / pore distribution measuring device (BELSORP MAX, manufactured by BEL Japan). Before the measurement, the material was degassed by vacuum drying at 150°C for 6 hours. The equilibrium judgment condition for measuring the pressure inside the sample tube was 300 seconds.

[0181] The obtained nitrogen adsorption and desorption isotherm data was analyzed using the software Autosorb 1 (manufactured by Anton Paar Japan). In the case of type I adsorption isotherm, the distribution of the diameter of the electrolyte conducting pores was analyzed with reference to the kernel calculated by density functional theory (DFT method) assuming slit-type pores. In addition, for samples showing type IV adsorption isotherm, the pore size distribution was analyzed by applying the Barrett-Joyner-Halenda method (BJH method) to each adsorption isotherm to obtain the pore volume. The pore size distribution curve of the auxiliary material of Example 1 is shown in FIG. 8.

[0182] The particle size distribution of the auxiliary materials in the examples was measured using a laser diffraction particle size distribution measuring device (MT3300EXII-SDC, manufactured by Microtrack Bell Co., Ltd.). Specifically, each auxiliary material was added to water, and ethanol was further mixed before measurement. After ultrasonic treatment for 5 minutes using a three-frequency ultrasonic cleaner (VS-100III, manufactured by AS ONE Co., Ltd.), the particle size distribution was measured using the above device. The particle size distribution of the auxiliary material in Example 1 is shown in FIG. 9.

[0183] The Raman spectrum of the auxiliary material of the example was measured using a micro-Raman spectrometer (DXR3 Micro Laser Raman | Thermo Fisher Scientific). The measurement was performed using a 532 nm (2 mW) laser with the following settings: grating: 900 lines / mm, spectrometer aperture: 50 μmφ, exposure time: 0.500 sec (2 Hz), and accumulation count: 10 (5 min). The measurement range was 300 to 3500 cm. -1 The Raman spectrum measured for the auxiliary material of Example 1 is shown in FIG.

[0184] Next, from the measured values ​​of G band and 2D band, I G / I 2D The carbon layer stacking index, expressed as

[0185] The 2C retention rate was determined as the battery discharge rate characteristic by the above-mentioned positive electrode evaluation method for the test batteries of Examples 1 and 2 and Comparative Examples 1 to 3. The results are shown in Table 1. Furthermore, the discharge curves of the test battery of Example 1 at different currents during discharge are shown in FIG.

[0186] [Table 1]

[0187] <Consideration> It was confirmed that the auxiliary material of this example had a higher high-rate discharge maintenance rate than the conductive assistant of the comparative example. G / I 2DThe carbon layer stacking index value represented by the formula (1) indicates that the auxiliary material of the example has a graphene structure in at least a part of its structure.

[0188] The auxiliary material of this embodiment has moderate mechanical properties, that is, plastic deformation properties in which it undergoes plastic deformation when subjected to a force above a certain level, and elastic deformation when subjected to a force below a certain level. The auxiliary material of this embodiment is formed from a three-dimensional framework made of graphene with a small number of layers. Therefore, it has the property that, even if it is permanently deformed by plasticity, the high-quality graphene can maintain electronic conduction between the particles of the positive electrode material in the electrode while retaining the pore volume in the auxiliary material by elasticity to hold the electrolyte. This property can be said to be one of the features of the auxiliary material of this embodiment.

[0189] Experiment 2: Comparison of battery reaction auxiliary materials and existing conductive additives <Example 3> The amount of the auxiliary material of Example 1 added to the positive electrode was 0.5% by weight, and acetylene black (SSA: 65 ml 2 A test battery was produced under the same conditions as in Example 1, except that the amount of the electrolyte used was 0.5 wt % (trade name: Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) and a battery evaluation was carried out.

[0190] <Example 4> The amount of the auxiliary material of Example 1 added to the positive electrode was 0.5% by weight, and Ketjen Black (SSA: 800 ml) was added. 2 Test batteries were manufactured under the same conditions as in Example 1, except that the amount of 0.5 wt % of ethylenediaminetetraacetate (Eu200 / g, product name: EC300, manufactured by Lion Specialty Chemicals) was changed to 0.5 wt %, and battery evaluation was performed.

[0191] <Example 5> The amount of the positive electrode material added was 96.45% by weight, the amount of the auxiliary material of Example 1 added to the positive electrode was 0.5% by weight, and single-walled carbon nanotubes (SSA: 700 mm 2 Test batteries were manufactured under the same conditions as in Example 1, except that the amount of added 0.05 wt % of ZnO (ZnO / g, outer diameter: 2 nm, length: 2-5 μm; manufactured by Guangzhou Hongwu Material Technology Co., Ltd.) was changed to 0.05 wt %, and battery evaluation was performed.

[0192] <Example 6> The same procedure as in Example 2 was carried out except that the template was not eluted (=ceramic particles remained), to obtain a battery reaction auxiliary material of Example 6.

[0193] With respect to the obtained auxiliary material of Example 6, it was confirmed by a transmission electron microscope (TEM) that a layered graphene structure was mainly formed on the template particles and that the template was present inside ( FIG. 11 ).

[0194] Test batteries were produced under the same conditions as in Example 1, except that the amount of the auxiliary material of Example 1 added to the positive electrode was 0.5 wt %, and the amount of the auxiliary material of Example 6 added was 0.5 wt %, and battery evaluation was performed.

[0195] The results of the battery evaluation for the test batteries of Examples 3 to 6 are shown in Table 2.

[0196] [Table 2]

[0197] <Consideration> When the auxiliary material of this example was mixed with the conductive assistant used in the comparative examples and used in an electrode, the high rate discharge retention rate was higher than when the conductive assistant of the comparative examples was used alone (Comparative Examples 1 to 3). The size and shape differ depending on the type of conductive assistant, but for carbon black in which nanoparticles, which are primary particles, are aggregated, Ketjen Black, which has fine pores inside and a larger specific surface area than Denka Black, was more effective. This is thought to be because Ketjen Black has many oxygen functional groups and is less likely to aggregate with the auxiliary material of the present invention.

[0198] On the other hand, in Example 6 using ceramic solid particles, a 2C retention rate similar to that of Example 4 was obtained. This is thought to be because the relatively large voids in the electrode were not easily crushed and a relatively large amount of electrolyte was present, resulting in good results.

[0199] Experiment 3: Study of synthesis conditions for the battery reaction auxiliary material of Example 1 The auxiliary material of this example is prepared by forming a carbonaceous film on ceramics by the T-CVD method. However, as in Examples 1, 7 to 10 and Comparative Example 4, the organic gas concentration in the mixed gas was kept constant and the gas flow time was varied to produce auxiliary materials with carbonaceous film having different thicknesses and properties. <Example 7> The battery reaction auxiliary material of Example 7 was obtained in the same manner as in Example 1, except that the mixed gas was allowed to flow for 0.5 hours by the T-CVD method.

[0200] <Example 8> The same procedure as in Example 1 was carried out by the T-CVD method, except that the mixed gas was allowed to flow for 1.0 hour, to obtain a battery reaction auxiliary material of Example 8.

[0201] <Example 9> The same procedure as in Example 1 was carried out by the T-CVD method, except that the mixed gas was allowed to flow for 1.6 hours, to obtain a battery reaction auxiliary material of Example 9.

[0202] <Example 10> The same procedure as in Example 1 was carried out by the T-CVD method, except that the mixed gas was allowed to flow for 3.0 hours, to obtain a battery reaction auxiliary material of Example 10.

[0203] <Comparative Example 4> A battery reaction auxiliary material of Comparative Example 4 was obtained in the same manner as in Example 1, except that the mixed gas was flowed for 5.0 hours by the T-CVD method.

[0204] Similarly to Example 1, test batteries were manufactured using the battery reaction auxiliary materials of Examples 7 to 10 and Comparative Example 4. Various tests and battery evaluations were performed on them, and the results are shown in Table 3 and Figs. 12, 13, and 14. Evaluations of Comparative Examples 1 to 3 are also shown in Table 3. Fig. 12 is a diagram showing the relationship between the plastic deformation power and the 2C rate discharge retention rate of the test batteries according to Examples 1, 2, 7 to 10 and the test batteries according to Comparative Examples 1 to 4. The vertical axis of Fig. 12 indicates the 2C rate discharge retention rate, and the horizontal axis indicates the plastic deformation power. Fig. 13 is a diagram showing the relationship between the carbon layering index and the 2C rate discharge retention rate of the test batteries according to Examples 1, 2, 7 to 10 and the test batteries according to Comparative Examples 1, 2, and 4. The vertical axis of Fig. 13 indicates the 2C rate discharge retention rate, and the horizontal axis indicates the carbon layering index. Fig. 14 is a diagram showing the relationship between the pore volume and the 2C rate discharge retention rate of the test batteries according to the examples and the test batteries according to the comparative examples. In FIG. 14, the vertical axis represents the 2C rate discharge maintenance ratio, and the horizontal axis represents the pore volume.

[0205] [Table 3]

[0206] <Consideration> 12 to 14, the high-rate characteristics are good within the range of the evaluation test of the embodiment. This is thought to be because the range is well balanced between elastic deformation and plastic deformation, in other words, the balance between electronic conductivity and ionic conductivity is good.

[0207] Regarding the relationship between the carbon layering index and the 2C rate discharge retention rate, it was confirmed that the carbon layering index in the test batteries of the examples was in the range of 0.3 to 4.2, and all of them exhibited high rate characteristics compared to the test batteries of Comparative Examples 1, 2, and 4. This is considered to be due to the fact that the electrodes of the test batteries according to the examples contain graphene, and therefore have excellent electron transport.

[0208] Regarding the relationship between the pore volume and the 2C rate discharge retention rate, it was confirmed that all of the test batteries according to the examples exhibited high rate characteristics compared to the test batteries of Comparative Examples 1, 2, and 4. This is believed to be due to the fact that the larger the pore volume, the more the electrolyte solution containing dissolved lithium ions penetrates and the larger the retention amount, resulting in excellent ion supply during the battery reaction.

[0209] Experiment 4: Secondary particle size study of battery reaction auxiliary materials <Example 11> Except for changing the pulverization and classification treatment conditions, the same procedure as in Example 1 was carried out to obtain a battery reaction auxiliary material of Example 11. The average particle size of the secondary particles of the obtained auxiliary material was 0.4 μm.

[0210] <Example 12> Except for changing the pulverization and classification treatment conditions, the same procedure as in Example 1 was carried out to obtain a battery reaction auxiliary material of Example 12. The average particle size of the secondary particles of the obtained auxiliary material was 1.3 μm.

[0211] <Example 13> Except for changing the pulverization and classification treatment conditions, the same procedure as in Example 1 was carried out to obtain a battery reaction auxiliary material of Example 13. The average particle size of the secondary particles of the obtained auxiliary material was 4.9 μm.

[0212] <Example 14> Except for changing the pulverization and classification treatment conditions, the same procedure as in Example 1 was carried out to obtain a battery reaction auxiliary material of Comparative Example 5. The average particle size of the secondary particles of the obtained auxiliary material was 0.1 μm.

[0213] <Comparative Example 5> Except for changing the pulverization and classification treatment conditions, the same procedure as in Example 1 was carried out to obtain a battery reaction auxiliary material of Comparative Example 6. The average particle size of the secondary particles of the obtained auxiliary material was 6.8 μm.

[0214] As in Example 1, test batteries were produced using the battery reaction auxiliary materials of Examples 11 to 14 and Comparative Example 5. Various tests and battery evaluations were carried out on the batteries, and the results are shown in Table 4 and Fig. 15. Fig. 15 is a diagram showing the relationship between the secondary particle diameter in the auxiliary material and the 2C rate discharge retention rate for the test batteries of Examples 1, 11 to 14 and the test battery of Comparative Example 5.

[0215] [Table 4]

[0216] <Consideration> From the results of Table 4 and FIG. 15, it was confirmed that the high rate characteristics were good within the particle size range of the auxiliary material in the present Examples 1, 11 to 13, but the characteristics deteriorated if the particle size was too small or too large. If the particle size was too small, the auxiliary material was destroyed by pulverization, the graphene surface responsible for electronic conduction became smaller, and the intraparticle space responsible for ion retention became smaller, which adversely affected the characteristics. On the other hand, if the particle size was too large, the dispersion of the auxiliary material in the electrode became poor, the electron conduction path did not develop sufficiently, and the performance could not be fully demonstrated.

[0217] Experiment 5: Examination of the amount of battery reaction auxiliary material added in Example 1 <Example 15> The test battery was fabricated in the same manner as in Example 1, except that the amount of the positive electrode material added was 96.9% by weight, and the amount of the auxiliary material of Example 1 added to the positive electrode was 0.1% by weight.

[0218] <Example 16> The test battery was fabricated in the same manner as in Example 1, except that the amount of the positive electrode material added was 96.5% by weight, and the amount of the auxiliary material of Example 1 added to the positive electrode was 0.5% by weight.

[0219] <Example 17> The test battery was prepared in the same manner as in Example 1, except that the amount of the positive electrode material added was 95.0% by weight, and the amount of the auxiliary material of Example 1 added to the positive electrode was 2.0% by weight.

[0220] <Comparative Example 6> The test battery was prepared in the same manner as in Example 1, except that the amount of the positive electrode material added was 96.95% by weight, and the amount of the auxiliary material of Example 1 added to the positive electrode was 0.05% by weight.

[0221] <Comparative Example 7> The test battery was prepared in the same manner as in Example 1, except that the amount of the positive electrode material added was 90.0 wt %, and the amount of the auxiliary material of Example 1 added to the positive electrode was 7.0 wt %.

[0222] Charge and discharge tests were carried out on the test batteries of Examples 15 to 17 and Comparative Examples 6 and 7. A constant current of 1.25 mA (equivalent to 0.2 C) was applied to each test battery up to 4.2 V, and constant voltage charging was continued after reaching 4.2 V until the current reached 0.31 mA (0.05 C). The battery was then discharged to 3 V at a constant current of 1.25 mA. The charge capacity and discharge capacity at this time were determined. The results are shown in Table 5 and FIG. 16. FIG. 16 is a diagram showing the relationship between the amount of auxiliary material added and the charge and discharge capacity for the test batteries according to the examples and the test batteries according to the comparative examples.

[0223] [Table 5]

[0224] <Consideration> From the results of Table 5 and Figure 16, it was confirmed that the high rate characteristics of the test batteries remained good within the range of the amount of the auxiliary material added in Examples 1, 15, 16, and 17. It was shown that if the amount of the auxiliary material added is too large, the content of the active material decreases, and the charge / discharge capacity of the electrode decreases, and if the amount is too small, the auxiliary material does not easily exhibit its function.

[0225] Experiment 6: Study of negative electrodes containing the battery reaction auxiliary material of Example 1 <Example 18> The amount of the auxiliary material of Example 1 added to the negative electrode was 1.0 wt %, and a negative electrode test battery was manufactured. 97 wt % of artificial graphite, 1 wt % of the auxiliary material of Example 1, 1 wt % of carboxymethyl cellulose, and 1 wt % of styrene butadiene rubber (SBR) were stirred and mixed uniformly using distilled water as a solvent to prepare a negative electrode paste. The obtained paste was applied to a copper foil with a thickness of 20 μm, dried at 110° C., and then punched to φ15 mm and pressed at 30 kN to form a negative electrode.

[0226] The obtained negative electrode was vacuum dried at 120°C, and then in a glove box with an argon gas atmosphere, a 2032 size coin type test battery with a metallic Li counter electrode was fabricated using a 1M LiPF6 solution (a 1:1 mixed solvent of ethylene carbonate (EC):diethyl carbonate (DEC)) as the electrolyte and a polypropylene separator.

[0227] A constant current of 1.23 mA (equivalent to 0.2 C) was applied to each test battery to 0 V, and constant voltage charging was continued until 0 V was reached and the charge reached 0.31 mA (0.05 C). After that, the battery was discharged to 1.5 V at a constant current of 1.23 mA. The discharge capacity at this time was determined. Next, the same test battery was used to apply a constant current of 1.23 mA (equivalent to 0.2 C) to 0 V, and after 0 V was reached, constant voltage charging was continued until 0.31 mA (0.05 C). After that, the battery was discharged to 1.5 V at a high rate of 12.3 mA (equivalent to 2 C). The 2C retention rate (2C capacity ÷ 0.2C capacity) was determined from the discharge capacity of the test battery obtained in the above evaluation test. As a result of evaluation of the obtained negative electrode battery, the retention rate at 2C discharge was 0.45.

[0228] <Comparative Example 8> A negative electrode test battery was produced in the same manner as in Example 18, except that acetylene black (manufactured by Denki Kagaku Kogyo, product name: Denka Black) was used as a conductive assistant instead of the auxiliary material of Example 1, and the amount of this conductive assistant added to the negative electrode was 1.0 wt %. Evaluation of the obtained negative electrode battery revealed that the retention rate during 2C discharge was 0.23.

[0229] <Consideration> From the above results, it was confirmed that the auxiliary material of the present invention effectively acts in the negative electrode.

[0230] As is clear from the above examples, the high-rate discharge retention rate of the battery using the auxiliary material of this embodiment is higher than that of the battery of the comparative example. The reason for this is that the electronic conductivity of the auxiliary material of this embodiment is high. That is, compared to the conductive assistant used in the comparative example, the auxiliary material of this embodiment has a highly conductive carbonaceous material including graphene as a skeleton, and has a space capable of holding an electrolyte inside the particle. The discharge reaction is a reaction in which lithium ions desorbed during charging return to the positive electrode material, and when discharge begins, electrons flow from the external circuit to the positive electrode, and the electrons and lithium ions are combined to return to the crystal structure site of the positive electrode, restoring the combined state before charging. That is, the combination of lithium ions and electrons and the phase change of the crystal structure of the positive electrode occur simultaneously. The phase change can be observed from the change in voltage. With regard to the high retention rate of high-rate discharge, the "simultaneity" of this phase change is important, and it was confirmed that the auxiliary material of this example can achieve this "simultaneity".

[0231] The present invention is not limited to the above-described embodiment and examples, and various design modifications are included within the scope of the present invention. [Explanation of symbols]

[0232] 1 primary particle 2 Secondary particles 3. Cathode materials 200 Lithium-ion battery 211 Exterior parts 212 Positive electrode 213 Exterior parts 214 Negative electrode 215 Separator 217 Sealing gasket 218 Spring 219 Spacer

Claims

1. The carbonaceous material includes a plurality of primary particles having a three-dimensional skeleton including a space therein, a part of the plurality of primary particles is adhered to each other to form a plurality of secondary particles; The secondary particles are plastically deformed in an extremely small load-unloading test, and some of the secondary particles do not return to their original shape.

2. The battery reaction assist material according to claim 1 , wherein the carbonaceous material comprises graphene.

3. The battery reaction auxiliary material according to claim 1 , wherein the plastic deformation power is 5% or more and 92% or less.

4. The battery reaction assisting material according to claim 1 , wherein the battery reaction assisting function has an electron transfer function and an electrolyte retention function.

5. 2. The battery reaction auxiliary material according to claim 1, which has a pore volume measured by a gas adsorption method of 1 cc / g or more and 4 cc / g or less.

6. The battery reaction auxiliary material according to claim 1 , wherein the carbon layer stacking index is 0.4 or more and 5 or less.

7. The battery reaction assisting material according to claim 1 , comprising solid particles in the space inside the primary particles.

8. The battery reaction assisting material according to claim 7 , wherein the solid particles are at least one of carbon black, acetylene black, single-walled carbon nanotubes, and multi-walled carbon nanotubes.

9. 8. The battery reaction assisting material according to claim 7, wherein the solid particles are ceramic particles coated with a carbonaceous material.

10. The battery reaction assisting material according to claim 1 , wherein the secondary particles have an average particle size of 0.05 μm or more and 6 μm or less.

11. A positive electrode or a negative electrode for a lithium ion battery, comprising the battery reaction auxiliary material according to claim 1 in an amount of 0.1 wt % or more and 5 wt % or less.

12. The positive electrode or negative electrode for a lithium ion battery according to claim 11, wherein a part of the structure has a permanently deformed portion where the secondary particles in the battery reaction auxiliary material are permanently deformed.

13. 13. The positive or negative electrode for a lithium ion battery according to claim 12, comprising multi-layer graphene in the permanently deformed portion.

14. A positive electrode or negative electrode for a lithium ion battery, comprising only the solid particles according to claim 9 as a battery reaction auxiliary material.

15. A lithium ion battery comprising at least one of the positive electrode and the negative electrode according to claim 13 or 14.

16. A step of preparing a slurry by mixing a battery reaction auxiliary material including primary particles having a three-dimensional skeleton including a space therein and secondary particles formed by bonding a plurality of the primary particles, a binder resin, and a solvent; a step of applying the slurry onto a current collector, drying the resulting mixture, and pressing the resulting mixture to obtain a positive electrode or a negative electrode; A method for producing a positive electrode or a negative electrode for a lithium ion battery, comprising: In the press working, the shapes of some of the primary particles and the secondary particles are kept deformed, and the shapes of another part of the primary particles and the secondary particles are restored. A method for producing positive or negative electrodes for lithium-ion batteries.

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