JP7548627B1 - Battery reaction auxiliary material, positive electrode or negative electrode containing the same, lithium ion battery including the positive electrode or negative electrode, and method for manufacturing the electrode - Google Patents

Abstract

[Problem] The object is to provide a battery reaction auxiliary material capable of favorably assisting a battery reaction and enabling the lifespan of a lithium ion battery to be extended, a positive electrode or negative electrode containing the same, a lithium ion battery equipped with the positive electrode or negative electrode, and a method for manufacturing the electrode. [Solution] The battery reaction auxiliary material of the present invention includes a plurality of primary particles that contain carbonaceous matter and have a three-dimensional skeleton containing internal spaces, some of the plurality of primary particles being fixed together to form secondary particles, and the secondary particles are plastically deformed in an extremely small load/unload test, with some not being able to restore their original shape. The carbonaceous matter may contain graphene. [Selected Figure] Figure 1

Description

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 a negative electrode, and a method for manufacturing the electrode.

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 the demand for higher performance in the market. In order to protect the global environment, one of the necessary conditions for EVs, which emit less carbon dioxide (CO ₂ ), to replace gasoline-powered vehicles is to extend the driving range of EVs. To extend the driving range of EVs, the lithium-ion batteries installed in them must have a longer life, higher performance, and a more efficient battery reaction.

Used lithium-ion batteries are usually discarded when they reach the end of their lifespan. However, in recent years, there has been a growing movement to secure resources and materials on a global scale, with the aim of manufacturing and ensuring a stable supply of lithium-ion batteries. For this reason, there has been a loud call for the need to recycle used lithium-ion batteries and utilize the materials like urban mines, a process known as resource recycling.

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 also re-emitted, so it is not easy to stop the destruction of the global environment even if recycling and remanufacturing are carried out. For this reason, there is a strong demand for lithium-ion batteries to have higher performance and longer life.

Patent Document 1 discloses a positive electrode powder that contains an active material containing Ni, Mn, and Fe, enabling application to non-aqueous electrolyte secondary batteries, and that is capable of exhibiting excellent discharge characteristics at a higher current rate. Patent Document 2 discloses a non-aqueous electrolyte secondary battery with a negative electrode that uses a negative electrode active material made of lithium titanate, which makes 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.

JP 2011-216472 A JP 2005-317509 A

However, the secondary battery described in Patent Document 1 has a low battery energy density because too much conductive additive is added in order to obtain sufficient characteristics. In addition, the binder is insufficient, which reduces electrode strength and shortens the battery 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 Documents 1 and 2 are unsuitable for applications such as EVs. One of the most urgent issues is the development of a secondary battery that can be used for a longer period of time and has high performance.

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

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

The present invention has been made in view of these circumstances, and aims to provide a battery reaction auxiliary material that can favorably assist battery reactions and enable the life extension of lithium-ion batteries, a positive electrode or negative electrode that includes the battery reaction auxiliary material, a lithium-ion battery that includes the positive electrode or negative electrode, and a method for manufacturing the battery reaction auxiliary material.

To solve the above problems, the battery reaction auxiliary material of the present invention employs the following measures.

The first aspect of the present invention provides a battery reaction auxiliary material that includes a plurality of primary particles having a three-dimensional skeleton containing carbonaceous matter and having an internal space, and a portion of the plurality of primary particles are adhered to each other to form secondary particles, which undergo plastic deformation in an extremely small load/unload test, and some of the secondary particles do not recover.

In the first aspect, the carbonaceous material may include graphene.

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

In the first aspect, the battery reaction assisting function may have an electron transfer function and an electrolyte retention function.

In the first aspect, the pore volume measured by gas adsorption may be 1 cc/g or more and 4 cc/g or less.

In the first aspect, the carbon layer stacking index may be 0.4 or more and 5 or less.

In the first embodiment, solid particles may be included between the primary particles.

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.

In the above embodiment, the solid particles may be ceramic particles coated with carbonaceous material.

In the first aspect, the average particle size of the secondary particles may be 0.1 μm or more and 6 μm or less.

The second aspect of the present invention provides a positive electrode or a negative electrode for a lithium ion battery, in which the content of the battery reaction auxiliary material of the first aspect is 0.1 wt % or more and 5 wt % or less.

In the second aspect, the structure of the positive or negative electrode for the lithium ion battery may include a permanently deformed portion in which the secondary particles are permanently deformed.

In the above embodiment, the permanent deformation portion may contain multi-layer graphene.

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.

The fourth aspect of the present invention provides a lithium-ion battery comprising at least one of the positive electrode and the negative electrode for the lithium-ion battery of the second or third aspect.

The fifth aspect of the present invention provides a method for manufacturing a positive electrode or a negative electrode for a lithium ion battery, comprising the steps of: mixing a battery reaction auxiliary material containing carbonaceous material and containing primary particles having a three-dimensional skeleton containing internal spaces and secondary particles formed by bonding a plurality of the primary particles together with 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, in which the shapes of some of the primary particles and the secondary particles remain deformed during the pressing process, while the shapes of another part of the primary particles and the secondary particles are restored.

The battery reaction auxiliary material according to the present invention can effectively assist the battery reaction. A lithium-ion battery equipped with a positive electrode or a negative electrode containing the battery reaction auxiliary material according to the present invention can extend the life and improve the performance.

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. FIG. 2 is a diagram showing a Raman spectrum measured for the auxiliary material of Example 1. 1 is a SEM photograph (20 μm scale) of the electrode surface before pressing in the production of the positive electrode in Example 1. 1 is a SEM photograph (1 μm scale) of an electrode surface before pressing in the production of a positive electrode in Example 1. 1 is a SEM photograph (20 μm scale) of the electrode surface after pressing in the production of the positive electrode in Example 1. 1 is a SEM photograph (1 μm scale) of the electrode surface after pressing in the production of the positive electrode in Example 1. 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. 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; 1 is a transmission electron microscope (TEM) image of the battery reaction auxiliary material obtained in Example 1. 1 is a TEM image of the battery reaction auxiliary material obtained in Example 2. FIG. 2 is a diagram showing a pore size distribution curve of the battery reaction auxiliary material obtained in Example 1. FIG. 2 is a diagram showing the particle size distribution of the battery reaction auxiliary material obtained in Example 1. 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. 4 is a TEM photograph of the battery reaction auxiliary material obtained in Example 6. 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. FIG. 1 is a graph showing the relationship between the carbon layering index and the 2C rate discharge retention rate for the test battery according to the embodiment and the test battery according to the comparative example. FIG. 1 is a graph showing the relationship between pore volume and 2C rate discharge retention rate for test batteries according to examples and comparative examples. FIG. 1 is a diagram showing the relationship between the secondary particle diameter in the auxiliary material and the 2C rate discharge maintenance ratio for the test battery according to the example and the test battery according to the comparative example. 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.

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.

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

As shown in FIG. 1, the auxiliary material of this embodiment includes primary particles 1 and secondary particles 2 formed by bonding multiple primary particles together. The primary particles 1 contain carbonaceous matter, and the carbonaceous matter includes thin-layer graphene, which will be described later. The primary particles 1 are hollow particles that have a three-dimensional skeleton and have space inside. The reference numeral 3 in FIG. 1 indicates the positive electrode material.

The auxiliary material of this embodiment includes a thin-layer graphene material. Graphene has a structure in which hexagonal carbon mesh planes bonded to benzene rings grow planarly into a sheet shape. Graphite is a multi-layer of graphene. On the other hand, a structure in which hexagonal carbon mesh planes grow planarly but have a small number of layers, and therefore have elastic deformation, is defined in this specification as a thin-layer graphene material. The thin-layer graphene material is the main structure of the auxiliary material of this embodiment.

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

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 will restore their shape when the load is removed, while another portion of the multiple primary particles will maintain 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 the ultra-small load-unload test described later.

When the thin graphene layer is relatively thick, the thin graphene layer maintains elastic deformation within a certain stress range, but undergoes sudden plastic deformation when a certain threshold is exceeded. In general carbon materials, they may deform under a relatively large stress, resulting in the destruction of particles. In other words, the auxiliary material of this embodiment has the property of returning to its original shape with almost no deformation under weak stress, such as the extremely small load and unload test performed in this embodiment, i.e., the property of a large amount of work required for elastic deformation.

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

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

FIG. 2 shows an example of the Raman spectrum measured for the auxiliary material of Example 1 described later. In this spectrum, there are a G band (aromatic ring C═C stretching motion, 1593 cm ⁻¹ ) derived from the skeletal vibration of the graphite sheet, a D band (C—H stretching motion, 1356 cm ⁻¹ ) derived from defects such as non-hexagonal sites including edge sites, and a 2D band (C—H stretching motion, 2680 cm ⁻¹ ) due to secondary phonon scattering. These results suggest that the auxiliary material of Example 1 has a structure containing graphene. I _G /I _2D, which is the ratio of the intensity of the G band (I _G ) to the intensity of the 2D band (I _2D ), is said to be an index indicating the stacking state of the graphene layers. (D. Graf, et al., NANO LETTERS, 7, 238-242; (2007)). In this embodiment, the index expressed by I _G /I _2D is called the "carbon stacking index". Based on the above paper, the value per layer was set to 0.4.

The smaller the value of I _G /I _2D , 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 the graphene has a structure that exhibits elastic deformation. In this specification, the term "when the thin-layer graphene is relatively thick" refers to a case where the carbon stacking index of the particles in the auxiliary material is greater than 6.

The auxiliary material of this embodiment is excellent in electron transfer because it contains graphene. Therefore, when the auxiliary material of this embodiment is contained in an electrode of a lithium ion battery, it can function to assist the battery reaction in the lithium ion battery. In addition, the auxiliary material of this embodiment is excellent in supplying ions during the reaction because an electrolyte solution containing dissolved lithium ions penetrates and is retained in the spaces provided in the three-dimensional skeleton of the primary particles and secondary particles.

Therefore, the auxiliary material of this embodiment is capable of utilizing elastic deformation and plastic deformation in a well-balanced manner under the operating conditions of a lithium-ion battery. In other words, high electronic conductivity is guaranteed even when the primary particles and/or secondary particles in the auxiliary material undergo plastic deformation, while when they do not undergo plastic deformation, the electrolyte, which is the storage source of ions, is stored in the space within the particles. For this reason, the auxiliary material of this embodiment can favorably assist the battery reaction.

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.

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 inside 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.

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 created within the particle due to dissolution of the template and intrusion holes created in the three-dimensional framework formed from the carbonaceous material. By adjusting reaction conditions such as the heat treatment temperature and heat treatment time, it is possible to adjust the degree of these structural defects, i.e., the size of the space present inside the particle and the size of the intrusion holes for allowing the electrolyte to infiltrate into the particle can be adjusted.

When the temperature exceeds approximately 1000°C, functional groups (mainly oxygen-containing functional groups) that are bonded to carbon and carbon chains that do not form six-membered rings are detached, 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 where 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, it is possible for the material to exhibit favorable functions such as electronic conductivity and maintaining internal space.

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, more electrolyte is held in the particle, and the reaction efficiency is high. 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 an appropriate pore volume, the particle has an appropriate 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.

The positive electrode material of a lithium-ion battery is a powder with a particle size distribution made of lithium-containing transition metal oxide with low electronic conductivity. In conventional methods, an electronic conduction route is established by mixing a conductive assistant made of a carbon material that assists in electronic conduction for the battery reaction with a binder resin and pressing it into a current collector. 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.

In contrast, in this embodiment, a battery reaction auxiliary material is used instead of the conductive auxiliary agent that has been used conventionally. The battery reaction auxiliary material of this embodiment is formed mainly from particles made of thin graphene, and has a space inside the particle that can hold an electrolyte. The auxiliary material exhibits high electronic conductivity derived from graphene, although it is permanently deformed when pressurized between particles such as 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 auxiliary 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.

In the auxiliary material of this 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. This improves electronic conduction.

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 the electrode contains the auxiliary material of this embodiment, the particles sandwiched between the positive electrode material particles are directly subjected to stress and plastically deformed, thereby exhibiting electronic conductivity. At the same time, the particles that are present in the gaps between the positive electrode materials 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 pressing in this embodiment are shown in Figures 3A and 3B, and SEM photographs of the electrode surface after pressing 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 created. The crushed parts correspond to the permanently deformed parts described above.

The auxiliary material of this embodiment includes primary particles that are hollow particles with spaces 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 template that is not dissolved and remains in the above-mentioned T-CVD method.

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.

In the auxiliary material according to this embodiment, the solid particles are preferably ceramic particles coated with carbonaceous matter. When producing a high-density electrode, ceramic particles have higher strength than carbon-based particles. This not only reinforces the structure of the electrode containing the auxiliary material, but also improves electronic conductivity by adding the electrical conductivity of the carbonaceous matter.

If ceramic particles are selected as the solid particles, they can be used as is without dissolving with the above-mentioned reagents.

As the ceramic particles, a compound inactive to the battery reaction can be appropriately selected. Examples include Al ₂ O 3 , MgO, SiO ₂ , ZrO ₂ , etc. In addition, a compound having CVD activity and usable as a template in the T-CVD method may also be used.

In addition to strength, the various properties of ceramic particles can be utilized. Examples of properties include chemical reactivity, catalytic properties, and physical properties.

The ratio of solid particles mixed into the auxiliary material depends 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 to clearly exert its effect.

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

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 material. 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 material 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 material is suitable for expressing other new functional properties.

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

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

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 with an average particle size of 0.05 μm or more and 6 μm or less are preferably used. The average particle size of the secondary particles is more preferably 0.1 μm or more and 5 μm or less.

In addition, the auxiliary material of this embodiment cannot supply lithium ions, which are the source of battery capacity, from the outside. For this reason, the addition rate of the auxiliary material to the electrode should be kept to the minimum necessary. To obtain good characteristics, the auxiliary material is preferably 0.1 wt % or more and 5 wt % or less of the electrode mixture.

If it is smaller than this range, its functionality cannot be utilized, and if it is too large, the bulk density of the electrode mixture becomes too large, which is undesirable as it reduces the electrode strength.

Next, we will explain the measurement of the ultra-small load/unload test to confirm the physical properties of the battery reaction auxiliary material according to this embodiment.

As an example of an ultra-small load-unloading test, FIG. 4 shows a load-displacement curve obtained by performing the test on the battery reaction auxiliary material prepared in Example 1 described below. 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. 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.

If the particle does not deform at all and completely restores its shape, the indentation depth returns to 0, i.e., returns to the origin of the horizontal axis in the graph of Figure 3. Conversely, if the particle is completely deformed by the load, i.e., if the particle is crushed in the direction of the load, the indentation depth remains 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.

In the battery reaction auxiliary 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 the particle was partially deformed by the load, while a space remained within the particle. In FIG. 3, the part corresponding to the work of restoring the shape to the applied load indicates the elastic deformation work W _E (the hatched part in FIG. 3), and the part corresponding to the work of deformation to the applied load indicates the plastic deformation work W _P (the vertical line part in FIG. 3).

The carbon layer stacking index in the auxiliary material of this embodiment is preferably 5 or less. If the carbon layer stacking index is greater than this, the particle skeleton becomes harder, which reduces the elastic deformability of the particle structure. It becomes more susceptible to destruction by the pressure applied during electrode fabrication, which reduces the amount of electrolyte retained and reduces the properties. If the carbon layer stacking index is too small, it becomes more susceptible to crushing when loaded. This means that the space within the particle becomes smaller, which makes it difficult to retain electrolyte within the particle.

Next, we will explain a lithium-ion secondary battery equipped with an electrode containing the auxiliary material of this embodiment.

Figure 5 shows an example of the cross-sectional structure of a coin-type lithium-ion battery 200 according to one embodiment of the present invention. This lithium-ion battery 200 is formed by stacking a disk-shaped positive electrode 212 housed in a metallic exterior part 211 and a disk-shaped negative electrode 214 housed in a metallic exterior part 113 with a separator 215 between them. A metallic 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 crimping them with a seal gasket 217.

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.

Metal compound materials that can be used as positive electrode active materials are materials that can release electrons to the battery's external circuit 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 preferred.

Examples of the material include transition metal oxides, composite oxides of lithium and transition metals, transition metal sulfides, etc. Examples of transition metals include Fe, Co, Ni, Mn, etc. Specific examples include transition metal oxides such as MnO, _V2O5 , _V6O13 , _{and TiO2, and inorganic compounds such as LiNiO2, LiCoO2, and LiMn2O4 , TiS2 , FeS , and MoS2} , but these may be used _in which a specific element is partially substituted with another element in order to improve the characteristics.

In addition to the above inorganic compounds, there are also positive electrode materials made of organic compounds. Examples include polyaniline, polypyrrole, polyacene, disulfide-based compounds, polysulfide-based compounds, and N-fluoropyridinium salts. The positive electrode material may be a mixture of the above inorganic compounds and organic compounds.

The physical properties of the positive electrode material are determined by the requirements in the battery design and manufacturing process, which stem from constraints such as the way the lithium-ion battery is used. In manufacturing the positive electrode 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.

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

The above positive electrode materials generally have low electronic conductivity, so it is preferable to have a battery reaction auxiliary material that assists in electronic conductivity coexist in the positive electrode. Commonly used conductive auxiliary materials include carbon-based materials and metal-based materials, and other materials with high electronic conductivity can also be used, with carbon-based materials being the most suitable.

The amount of battery reaction auxiliary materials that are used should be kept to a minimum, and the content of the positive electrode material that determines the capacity of the lithium-ion battery should be maximized.

Conventional carbon-based materials include soot, acetylene black, ketjen black, lamp black, furnace black, carbon black, graphite, carbon fiber, graphite fiber, nanofiber, nanotubes, coke, hard carbon, and amorphous carbon.

In comparison, the auxiliary material of this embodiment has a significant feature not found in conventional materials. That is, since the auxiliary material of this 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 six-membered ring carbon bonds. For this reason, it is less susceptible to degradation and decomposition in the electrochemical oxidation environment to which it is exposed inside the battery.

If necessary, further benefits can be obtained by combining it with the conventional materials. For example, flake graphite and highly linear carbon nanotubes have high electronic conductivity but low ion storage. By combining these properties with the auxiliary material of this embodiment, it is possible to construct an excellent battery reaction auxiliary system that adds ion storage to electronic conductivity.

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

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.

The above-mentioned positive electrode material and 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 must be chemically and electrochemically inactive and have some degree of elastic deformability and affinity, and a plastic resin material is preferably used.

As another mode of use of the battery reaction auxiliary material, the powder can be dispersed in a liquid solvent at a certain ratio to form a paint. 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.

Examples of the plastic resin materials 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 polymethylmethacrylate, polyethylmethacrylate, polybutylmethacrylate, polymethylacrylate, polyethylacrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide, etc. The resin materials may also be mixtures, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, 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 the electrode.

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

The metal foil for current collection 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 metal foil for current collection are aluminum foil, nickel foil, titanium foil, and stainless steel foil, and rolled aluminum foil, which is generally readily available, is more preferable.

Commonly used printing techniques can be used to form a coating of the slurry on the metal foil for current collection. When the coating thickness is small, gravure printing is suitable, and when it is large, printing techniques such as doctor blade printing and die printing are suitable.

The coating is then dried by heating. Any drying method can be used, and the method that can achieve the desired binding strength with the binder is preferably used.

Then, when forming the positive electrode to the specified dimensions, an industrially available cutting blade and the like and the method are preferably used. In addition, to achieve the specified density, an industrially available pressure device and the like and the method are preferably used as necessary.

Next, the negative electrode will be described.
The negative electrode 214 is obtained by, for example, coating a slurry made of a mixture of 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.

Carbon-based materials that can be used for the negative electrode are preferably those that can bond and stabilize Li ions with electrons flowing from an external circuit and have many stabilization sites inside.

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.

Another stabilization mechanism is the electrochemical formation of intermetallic compounds, and suitable elements include silicon, tin, zinc, bismuth, antimony, cadmium, lead, and germanium.

In addition, other materials that exhibit low electrochemical reaction potentials that serve as the negative electrode of lithium-ion batteries can also be used. Suitable examples include compounds of metals with oxygen, sulfur, halogens, nitrogen, phosphorus, etc.

Depending on the application of the lithium-ion battery, multiple negative electrode materials listed above can be mixed in a given ratio and used to obtain the desired discharge profile.

The physical properties of negative electrode materials are determined by the requirements in the device (e.g. storage battery) design and manufacturing process, which stem from constraints such as the usage pattern of lithium-ion batteries. In the manufacture of materials, processes are designed to realize the physical properties. Physical property values include powder particle size and distribution, specific surface area, density, etc.

As an example, the powder particle size is appropriately selected taking into account other constituent elements of the lithium ion battery, but from the perspective of improving battery characteristics such as rate characteristics and cycle characteristics, an average value of 1 to 70 μm is usually preferred, and 3 to 30 μm is more preferred.

The above negative electrode materials generally have high electronic conductivity, but some materials have smooth surfaces and in cases where the contact between particles is insufficient, it is also preferable to use a conductive assistant to assist in electronic conductivity. Carbon-based materials, metal-based materials, and other materials with high electronic conductivity can also be used as materials, and among these, carbon-based materials are preferable. The battery reaction assistant material of this embodiment described above may be used as a conductive assistant.

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

Conventional carbon-based materials include soot, acetylene black, ketjen black, lamp black, furnace black, carbon black, graphite, carbon fiber, graphite fiber, nanofiber, nanotubes, coke, hard carbon, and amorphous carbon.

In comparison, the battery reaction auxiliary material of this embodiment has significant features not found in conventional materials, and can be used in combination with conventional materials as necessary to obtain even greater effectiveness. For example, flaky graphite and highly linear carbon nanotubes have high electronic conductivity but low ion storage. For this reason, by combining them with the auxiliary material of the present invention, it is possible to construct an excellent battery reaction auxiliary system that combines electronic conductivity with ion storage.

Carbon blacks such as acetylene black are composed of linked structural particles with diameters of several tens of nanometers. However, the crystallinity of carbon is not very high, the structural length is short, and it is prone to collapse, making it difficult to transmit electrons over long distances. Despite these properties, by combining it with the auxiliary material of the present invention, it is possible to realize a system that retains electronic conductivity and also has ion supply capabilities, even when the three-dimensional structure is maintained or when the three-dimensional structure is crushed and flattened like flake graphite.

The suitable ratio of the battery reaction auxiliary material of this embodiment to be contained in the negative 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.

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

The above-mentioned slurry can be applied to a coating of a commonly used printing technique. When the thickness is small, gravure printing is suitable, and when the thickness is large, doctor blade printing, die printing, or other printing techniques are suitable.

The coating is then dried by heating. Any drying method can be used, and the method that can achieve the desired binding strength with the binder is preferably used.

Then, when forming the negative electrode to the specified dimensions, an industrially available cutting blade and the like and the method are preferably used. In addition, to achieve the specified density, an industrially available pressure device and the like and the method are preferably used as necessary.

The above-mentioned negative electrode material and 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 must be chemically and electrochemically inactive and have some degree of elastic deformability and affinity, and a plastic resin material is preferably used.

As another mode of use of the battery reaction auxiliary material, the powder can be dispersed in a liquid solvent at a certain ratio to form a paint. 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.

Examples of the plastic resin materials 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 polymethylmethacrylate, polyethylmethacrylate, polybutylmethacrylate, polymethylacrylate, polyethylacrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide, carboxymethylcellulose, and styrene butadiene rubber. The resin materials may also be mixtures, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, and the like. 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 the electrode.

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

In this embodiment, we will explain the battery electrolyte that is applied to lithium-ion batteries.

Electrolytes are solutes dissolved in organic solvents, and these are usually the main components.

One of the components of an electrolyte is a solute that is the source of ions, i.e. Li salt.

There are no particular limitations on the type of solute, but any solute known to be used in this lithium-ion battery can be used. Specific examples include the following:

Examples of solutes include _inorganic salts such as _LiPF6 and _LiBF4 , _{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} Fluorine-containing organic Li salts such as ( _CF3 ) _{2 , LiBF2} ( _C2F5 ) ₂ , _LiBF2 ( _CF3SO2 ) ₂ , and _LiBF2 ( _C2F5SO2 ) _{2 ,} and Li bis( _oxalate ) _borate are exemplified.

Among these, LiPF ₆ , LiBF ₄ , LiN(CF ₃ SO ₂ ) ₂ and LiN(C ₂ F ₅ SO ₂ ) ₂ are preferred in terms of exerting battery performance, with LiPF ₆ and LiBF ₄ being particularly preferred.

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

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 mixture 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.

Next, we will explain the organic solvent used in the electrolyte.

The type of solvent is not particularly limited, but may be appropriately selected from those conventionally known as solvents. Examples include cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, cyclic carboxylate esters, chain carboxylate esters, phosphorus-containing organic solvents, etc. that do not have unsaturated bonds.

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.

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

A realistic solution to the above requirements is to use a mixture of multiple organic solvents. The mixture composition is determined by taking into account practical properties and combining organic solvents with high and low melting points, high and low solvation abilities, etc.

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.

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

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 these, dimethyl carbonate is the most preferred in terms of viscosity because it has the lowest viscosity.

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

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

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. Multiple cyclic carbonates can be mixed and used.

On the other hand, the content of the chain carbonate in the electrolyte is preferably 40 to 70% by weight, and more preferably 43 to 68% by weight. Multiple chain carbonates can be mixed and used.

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-output 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.

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

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

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.

Among these, chain carboxylic acid esters are particularly suitable.

Furthermore, it is also preferable to incorporate a fluorine-containing cyclic carbonate having two or more fluorine atoms into the electrolyte of this embodiment.

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.

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.

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-dioxolane-2-one, trans-4,5-difluoro-1,3-dioxolane-2-one, and 4,4-difluoro-1,3-dioxolane-2-one are particularly preferred.

The fluorine-containing cyclic carbonate having two or more fluorine atoms may be used alone or in combination of two or more kinds. 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 wt% or more, preferably 0.01 wt% or more, more preferably 0.1 wt% or more, particularly preferably 0.2 wt% or more, and most preferably 0.25 wt% or more. At a concentration lower than this, the effects of this embodiment may be difficult to exhibit. Conversely, if the concentration is too high, the internal pressure of the battery may increase during high-temperature storage, so the upper limit is usually 10 wt% or less, preferably 4 wt% or less, more preferably 2 wt% or less, particularly preferably 1 wt% or less, and most preferably 0.5 wt% or less.

Furthermore, cyclic carbonates having unsaturated bonds and aromatic compounds having a total carbon number of 7 to 18 may be mixed into the electrolyte.

Of the cyclic carbonates having unsaturated bonds, vinylene carbonate, vinyl ethylene carbonate, 4-methyl-4-vinyl ethylene carbonate, and 4,5-divinyl ethylene carbonate are preferred from the viewpoint of improving cycle characteristics, and among these, vinylene carbonate and vinyl ethylene carbonate are more preferred. These may be used alone or in combination of two or more kinds.

Preferred aromatic compounds having a total carbon number of 7 to 18 are biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, and other aromatic compounds.

In this way, it is believed that by suppressing the side reactions between the aromatic compounds with a total carbon number of 7 to 18 and the negative and positive electrodes, a significant decrease in discharge characteristics after high-temperature storage can be suppressed.

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, with the upper limit usually being 5% by weight or less, preferably 3% by weight or less, and particularly preferably 2% by weight or less. At a concentration 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.

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

As for the form of the membrane, a stretched membrane in which pores are created by stretching the bulk resin, or a nonwoven fabric in which a large number of fibrous resin fibers are layered to create a porous structure like a porous membrane, are preferably used.

Polyolefins are suitable as resin materials, with polyethylene being particularly suitable. Polyethylene has a relatively low melting temperature, and when the temperature of the battery rises for some reason (for example, an unsafe condition such as a short circuit), the thermal melting causes the pores in the membrane to close, inhibiting the movement of the driving ions, thereby stopping the reaction and ensuring safety.

Porous membranes formed by the stretching method are usually made by adding a plasticizer to polyolefin, and the plasticizer is removed before and after stretching, resulting in a relatively uniform microporous structure with the areas where the plasticizer was present as the starting points.

When producing a stretched film, stretching is usually performed in both the longitudinal and transverse directions. In addition to removing the above-mentioned plasticizers, a suitable stretched film can be obtained by appropriately combining any atmospheric medium, temperature, speed, stress, number of process repetitions, etc.

Although the above manufacturing process produces high-quality stretched membranes, it is a multi-step process. This makes it difficult to reduce manufacturing costs, such as process costs, and can be a negative factor in the widespread use of lithium-ion batteries.

On the other hand, by simplifying the process so that the stretching is done 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 at low manufacturing costs. In this case, the applicable resin is polyolefin, and polypropylene is preferably used.

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 polyolefins such as polyethylene and polypropylene, polyester, polyethylene terephthalate, polyimide, etc. may be used as the separator. The separator may be made of one type alone or multiple types. 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.

In the nonaqueous electrolyte battery according to this embodiment, an electrolyte that is gelled by containing a polymer compound that swells with an organic solvent and serves as a support for holding the nonaqueous electrolyte may be used. By containing 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 contains 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.

When a polymeric compound such as polyvinylidene fluoride is applied to both sides of the separator, it is preferable to set the mass ratio of the non-aqueous electrolyte to the polymeric compound within the range of 50:1 to 10:1. By setting the ratio within this range, higher charge/discharge efficiency can be obtained.

The above-mentioned polymer compounds include, for example, ether-based polymer compounds such as polyvinyl formal, polyethylene oxide, and crosslinked products containing polyethylene oxide, ester-based polymer compounds such as polymethacrylate, acrylate-based polymer compounds, and vinylidene fluoride polymers such as polyvinylidene fluoride and copolymers of vinylidene fluoride and hexafluoropropylene. The polymer compounds may be used alone or in combination. In particular, from the viewpoint of the effect of preventing swelling during high-temperature storage, it is desirable to use fluorine-based polymer compounds such as polyvinylidene fluoride.

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 to return to the positive electrode 212. The battery reaction proceeds through this series of actions.

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 as described in the claims.

In the above embodiment, a coin-type lithium ion battery has been described as an example of a 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 with a spiral structure. In addition, the lithium ion battery of this embodiment can be made in various sizes such as a thin type or a large type.

In addition, in the above description, the electrolyte used in the lithium ion battery according to this embodiment is a liquid electrolyte, but any other electrolyte can be used. For example, a gel electrolyte or a solid electrolyte can be used.

Experiment 1: Confirmation of basic performance of battery reaction auxiliary material <Example 1>
(Production of battery reaction auxiliary materials)
Magnesium oxide nanopowder (primary particle size 0.4 μm, SSA 130 m ² /g; manufactured by Guangzhou Hongwu Material Technology Co., Ltd.) was filled into a heat treatment container as a carbonaceous film template, 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, a preliminary heat treatment was added for the purpose of dehydration, etc. Then, a mixed gas of Ar gas and CH ₄ 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, it was taken out and crushed and classified.

Next, the template was dissolved from this processed material using hydrochloric acid, and the material was 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, yielding the battery reaction auxiliary material of Example 1.

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 consisting of layered graphene had been formed.

(Very small load/unload test)
A small amount of the auxiliary material dispersed in ethanol was spread on the sample stage and dried. Then, it was introduced into the SEM, and the measurement particles were observed, and 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) incorporated in the SEM, a load-unloading test was performed under the conditions of an indentation head: InForce50, an indenter diameter: 10 μm, a maximum load of 0.1 mN, a time to maximum load: 5 sec, and a 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 FIG. 3 can be calculated from the following formula.

(Preparation of Positive Electrode)
96% by weight _of ternary positive electrode material NCM ( _{LiNi0.5Co0.2Mn0.3O2} ) powder with an average particle size of 8 _{μm ,} 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 be uniform, and a positive electrode paste was prepared. This was applied to an Al current collector with a thickness of 15 μm and dried at 110° C., and then punched to φ15 mm and pressed at 45 kN to form a positive electrode.

(Preparation of Positive Electrode Test Battery)
The obtained positive electrode was vacuum dried at 120°C, and then in a glove box in an argon gas atmosphere, a 1M _LiPF46 solution (a 1:1 mixed solvent of ethylene carbonate (EC):diethyl carbonate (DEC)) was used as an electrolyte, and a polypropylene separator was used to prepare a 2032 size coin type test battery with a metallic Li counter electrode.

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

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.

The auxiliary material of Example 2 obtained was confirmed to have a skeletal structure mainly composed of layered graphene using a transmission electron microscope (TEM) (Figure 7), and the average secondary particle size was 2.1 μm.

The test battery of Example 2 was manufactured under the same conditions as Example 1.

<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., trade name: Denka Black) was used instead of the auxiliary material.

<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.

<Comparative Example 3>
A test battery was manufactured under the same conditions as in Example 1, except that single-walled carbon nanotubes (SSA: 600 m ² /g, outer diameter: 2 nm, length: 2-5 μm; manufactured by Guangzhou Hongwu Material Technology Co., Ltd.) were used instead of the auxiliary material, and the amount of the positive electrode added in the battery preparation was 97.95 wt %, and the amount of the single-walled carbon nanotubes added was 0.05 wt %.

For 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, in addition to the ultra-small load/unload test described above, nitrogen adsorption/desorption measurements and Raman spectroscopy measurements were performed to determine the plastic deformation power, pore volume, and carbon layer stacking index.

The pore volume of the auxiliary material in 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.

The obtained nitrogen adsorption/desorption isotherm data was analyzed using the software Autosorb 1 (manufactured by Anton Paar Japan). In the case of type I adsorption isotherms, the distribution of electrolyte conduction pore diameters 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 isotherms, the pore size distribution was analyzed and the pore volume was determined by applying the Barrett-Joyner-Halenda method (BJH method) to each adsorption isotherm. The pore size distribution curve of the auxiliary material of Example 1 is shown in Figure 8.

Particle size distribution measurements were performed on the auxiliary materials of the examples using a laser diffraction particle size distribution measurement device (MT3300EXII-SDC, manufactured by Microtrac-Bell Co., Ltd.). Specifically, each auxiliary material was added to water, and ethanol was further mixed before measurement. Ultrasonic treatment was performed for 5 minutes using a triple frequency ultrasonic cleaner (VS-100III, manufactured by AS ONE Co., Ltd.), and then particle size distribution measurements were performed using the above device. The particle size distribution of the auxiliary materials of Example 1 is shown in Figure 9.

The Raman spectrum of the auxiliary material of the example was measured using a micro-Raman spectrometer (DXR3 Micro Laser Raman | Thermo Fisher Scientific). For the measurement, a 532 nm (2 mW) laser was used, and the following settings were set: grating: 900 lines/mm, spectrometer aperture: 50 μmφ, exposure time: 0.500 sec (2 Hz), and number of accumulations: 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. 2.

Next, from the values of the G band and the 2D band obtained by the measurement, a carbon layer stacking index expressed as I _G /I _2D was calculated.

The 2C retention rate was determined as the battery discharge rate characteristics for the test batteries of Examples 1 and 2 and Comparative Examples 1 to 3 using the above-mentioned positive electrode evaluation method. These results are shown in Table 1. Figure 10 shows the discharge curves for different currents during discharge using the test battery of Example 1.

<Considerations>
It was confirmed that the auxiliary material of this example had a higher high-rate discharge retention rate than the conductive assistant of the comparative example. In addition, the carbon layer stacking index value expressed as I _G /I _2D suggested that the auxiliary material of the example had a graphene structure in at least a part of its structure.

The auxiliary material of this embodiment has moderate mechanical properties, that is, it has the plasticity to deform plastically when subjected to a force above a certain level, and elastically deforms 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 conductivity between the particles of the positive electrode material in the electrode, while the pore volume in the auxiliary material remains due to elasticity to hold the electrolyte. This property can be said to be one of the features of the auxiliary material of this embodiment.

Experiment 2: Comparison of battery reaction auxiliary material and existing conductive assistant <Example 3>
Test batteries were manufactured 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 acetylene black (SSA: 65 ^m2 /g, manufactured by Denki Kagaku Kogyo, product name: Denka Black) added to the positive electrode was 0.5 wt %, and battery evaluation was performed.

Example 4
Test batteries were manufactured 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 Ketjen Black (SSA: 800 m ² /g, manufactured by Lion Specialty Chemicals, product name: EC300) added to the positive electrode was 0.5 wt %, and battery evaluation was performed.

Example 5
Test batteries were manufactured under the same conditions as in Example 1, except that 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 the amount of single-walled carbon nanotubes (SSA: 700 m ² /g, outer diameter: 2 nm, length: 2-5 μm; manufactured by Guangzhou Hongwu Material Technology Co., Ltd.) added was 0.05% by weight, and battery evaluation was performed.

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

A transmission electron microscope (TEM) confirmed that the auxiliary material of Example 6 obtained had a layered graphene structure formed on the template particles and that the template was present inside (Figure 11).

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

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

<Considerations>
When the auxiliary material of this example was mixed with the conductive assistant used in the comparative examples and used in the electrodes, 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). Although the size and shape differ depending on the type of conductive assistant, Ketjen Black, which has fine holes inside and a larger specific surface area than Denka Black, was more effective in carbon black, which is agglomerated nanoparticles that are primary particles. 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.

On the other hand, in Example 6, which used solid ceramic 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 less likely to collapse and there was a relatively large amount of electrolyte, resulting in good results.

Experiment 3: Study on synthesis conditions for battery reaction auxiliary material of Example 1 For the auxiliary material of this example, a carbonaceous film was formed on ceramics by the T-CVD method, but as in Examples 1, 7 to 10 and Comparative Example 4, auxiliary materials with carbonaceous film having different thicknesses and properties were produced by varying the gas flow time while keeping the organic gas concentration in the mixed gas constant.
Example 7
The same procedure as in Example 1 was carried out by T-CVD except that the mixed gas was flowed for 0.5 hours, to obtain a battery reaction auxiliary material of Example 7.

Example 8
The same procedure as in Example 1 was carried out by T-CVD except that the mixed gas was flowed for 1.0 hour, to obtain a battery reaction auxiliary material of Example 8.

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

Example 10
A battery reaction auxiliary material of Example 10 was obtained in the same manner as in Example 1, except that the mixed gas was flowed for 3.0 hours by T-CVD.

<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 T-CVD.

As in 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 Figures 12, 13, and 14. The evaluations of Comparative Examples 1 to 3 are also shown in Table 3. Figure 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, and 7 to 10 and the test batteries according to Comparative Examples 1 to 4. The vertical axis of Figure 12 indicates the 2C rate discharge retention rate, and the horizontal axis indicates the plastic deformation power. Figure 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 Figure 13 indicates the 2C rate discharge retention rate, and the horizontal axis indicates the carbon layering index. Figure 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 Figure 14, the vertical axis shows the 2C rate discharge maintenance rate, and the horizontal axis shows the pore volume.

<Considerations>
12 to 14, the high rate characteristics are good within the range of the evaluation test of the examples. 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.

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 that all of them 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 electrodes of the test batteries of the examples contain graphene, which provides excellent electron transport.

In addition, regarding the relationship between pore volume and 2C rate discharge retention rate, it was confirmed that all of the test batteries according to the embodiment exhibited high rate characteristics compared to the test batteries of Comparative Examples 1, 2, and 4. This is thought to be due to the fact that the larger the pore volume, the more the electrolyte containing dissolved lithium ions penetrates and the greater the amount retained, resulting in excellent ion supply during the battery reaction.

Experiment 4: Investigation of secondary particle size of battery reaction auxiliary material <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.

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.

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.

<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.

<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.

As in Example 1, test batteries were manufactured 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 Figure 15. Figure 15 is a diagram showing the relationship between the secondary particle size in the auxiliary material and the 2C rate discharge retention rate for the test batteries of Examples 1 and 11 to 14 and the test battery of Comparative Example 5.

<Considerations>
From the results of Table 4 and Figure 15, it was confirmed that the high rate characteristics were good within the particle size range of the auxiliary material in 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. Conversely, 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.

Experiment 5: Study on the amount of the 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.

<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.

<Example 17>
The test battery was fabricated 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.

<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.

<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% by weight, and the amount of the auxiliary material of Example 1 added to the positive electrode was 7.0% by weight.

Charge and discharge tests were conducted 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 and discharge capacities at this time were determined. The results are shown in Table 5 and Figure 16. Figure 16 is a diagram showing the relationship between the amount of auxiliary material added and the charge and discharge capacity for the test batteries of the Examples and Comparative Examples.

<Considerations>
From the results of Table 5 and Fig. 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.

Experiment 6: Study of negative electrode 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 having a thickness of 20 μm, dried at 110 ° C, and then punched to φ 15 mm and pressed at 30 kN to form a negative electrode.

The obtained negative electrode was vacuum dried at 120°C, and then in a glove box in an argon gas atmosphere, a 1M _LiPF46 solution (a 1:1 mixed solvent of ethylene carbonate (EC):diethyl carbonate (DEC)) was used as an electrolyte, and a polypropylene separator was used to prepare a 2032 size coin type test battery with a metallic Li counter electrode.

A constant current of 1.23 mA (equivalent to 0.2 C) was applied to each test battery until it reached 0 V, and constant voltage charging was continued until it 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 calculated. Next, the same test battery was used to apply a constant current of 1.23 mA (equivalent to 0.2 C) until it reached 0 V, and constant voltage charging was continued until it reached 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 calculated from the discharge capacity of the test battery calculated 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.

<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 %. As a result of evaluation of the obtained negative electrode battery, the retention rate during 2C discharge was 0.23.

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

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 particles. The discharge reaction is a reaction in which lithium ions that have been 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 return to the crystal structure site of the positive electrode in a form that combines with them, restoring the bonded state before charging. That is, the bond between the 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".

The present invention is not limited to the above-mentioned embodiments and examples. Various design modifications that do not deviate from the scope of the present invention are included in the present invention.

1 Primary particle 2 Secondary particle 3 Positive electrode material 200 Lithium ion battery 211 Exterior part 212 Positive electrode 213 Exterior part 214 Negative electrode 215 Separator 217 Seal gasket 218 Spring 219 Spacer

Claims (13)

The porous 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 a very small load-unload test, and some of them do not recover.
The plastic deformation power is 5% or more and 92% or less,
The pore volume measured by a gas adsorption method is 1 cc/g or more and 4 cc/g or less,
The secondary particles have an average particle size of 0.05 μm or more and 6 μm or less. The battery reaction auxiliary material according to claim 1, wherein the carbonaceous material comprises graphene. 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. The battery reaction auxiliary material according to claim 1, wherein the carbon layer stacking index is 0.4 or more and 5 or less. The battery reaction assisting material according to claim 1 , comprising solid particles between a plurality of the primary particles. The battery reaction assisting material according to claim 5 , wherein the solid particles are at least one of carbon black, acetylene black, single-walled carbon nanotubes, and multi-walled carbon nanotubes. 6. The battery reaction assisting material according to claim 5 , wherein the solid particles are ceramic particles coated with a carbonaceous material. A positive electrode or negative electrode for a lithium ion battery, the content of the battery reaction auxiliary material according to claim 1 being 0.1 wt% or more and 5 wt% or less. 9. The positive electrode or negative electrode for a lithium ion battery according to claim 8 , wherein the secondary particles in the battery reaction auxiliary material have a permanently deformed portion in a part of their structure. 10. The positive or negative electrode for a lithium ion battery according to claim 9 , comprising a multi-layer graphene in the permanently deformed portion. A positive electrode or negative electrode for a lithium ion battery, comprising only the solid particles according to claim 7 as a battery reaction auxiliary material. A lithium ion battery comprising at least one of the positive electrode and the negative electrode according to claim 10 or 11 . A step of preparing a slurry by mixing the battery reaction auxiliary material according to claim 1 , a binder resin, and a solvent;
a step of applying the slurry onto a current collector, drying the same, and pressing the same 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 a part 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.