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

Abstract

Provided are: a battery reaction auxiliary material capable of favorably assisting in battery reaction and extending the life of a lithium ion battery; a positive electrode or a negative electrode including the same; a lithium ion battery including said positive electrode or negative electrode; and an electrode manufacturing method. The battery reaction auxiliary material according to the present invention comprises a plurality of primary particles which each include carbonaceous matter and have a three-dimensional skeleton including a space therein. A portion of the plurality of primary particles is fixed to form secondary particles, and the secondary particles undergo plastic deformation in an extremely small load-unload test while a portion of which is not restored. The carbonaceous matter may contain graphene.

Description

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

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

[0002] Since their birth, lithium-ion batteries have been widely used in a wide range of everyday applications, including smartphones and electric vehicles (EVs). As a result, the manufacturing of lithium-ion batteries has been subject to cost competition and the market demand for higher performance. In order to protect the global environment, carbon dioxide (CO ２ For low-emission EVs to replace gasoline-powered vehicles, extending the driving range of EVs is one of the prerequisites. To extend the driving range of EVs, the lithium-ion batteries they use must have a longer lifespan, higher performance, and a more efficient battery reaction.

[0003] Used lithium-ion batteries are usually discarded at the end of their lifespan. However, in recent years, there has been a growing movement to secure resources and materials on a global scale in order to manufacture and ensure a stable supply of lithium-ion batteries. For this reason, there has been a strong call for the need to recycle used lithium-ion batteries and utilize their materials like urban mines, a concept known as resource recycling.

[0004] Recycling and remanufacturing lithium-ion batteries requires the same amount of energy as manufacturing new batteries from raw materials. ２ Since lithium-ion batteries are also discharged at the same rate, it is not easy to stop the destruction of the global environment even if they are recycled or remanufactured. For this reason, there is a strong demand for higher performance and longer lifespan lithium-ion batteries.

[0005] Patent Document 1 discloses a positive electrode powder that contains an active material containing Ni, Mn, and Fe, which enables application to non-aqueous electrolyte secondary batteries and is capable of exhibiting excellent discharge characteristics at higher current rates. Patent Document 2 discloses a non-aqueous electrolyte secondary battery having 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.

[0006] Non-Patent Document 1 describes electrolyte movement in cylindrical lithium-ion batteries. During charging, lithium ions are inserted into a negative electrode material such as graphite, causing the negative electrode material particles to expand. When lithium ions are inserted and removed during the next discharge, the negative electrode material particles contract, causing the voids within the electrode to change. In response to this change in voids, the electrolyte present in the voids within the electrode moves, being pushed out and re-impregnated. This unevenness in the amount and location of electrolyte within the electrode is thought to be one of the causes of charge-discharge cycle deterioration.

[0007] JP 2011-216472 A JP 2005-317509 A

[0008] C. P. Aiken, et. al. , Journal of The Electrochemical Society, 2023, 170, 040529

[0009] However, the secondary battery described in Patent Document 1 adds too much conductive additive to achieve sufficient characteristics, resulting in a low battery energy density. It also lacks binder, reducing electrode strength and shortening its lifespan. The secondary battery described in Patent Document 2 maintains a constant voltage for a long time, but has a low voltage and low energy density. Therefore, it must be said that the technologies described in Patent Documents 1 and 2 are unsuitable for applications such as EVs. The development of a high-performance secondary battery that can be used for a longer period of time is an urgent issue.

[0010] In order to improve the performance of lithium-ion batteries and achieve true environmental conservation, extending the lifespan of lithium-ion batteries is an essential theme. The mechanisms of performance degradation of lithium-ion battery products have been extensively studied. The degradation reaction phenomena of lithium-ion batteries are diverse, including alteration of active materials, poor contact between electrode materials, alteration of electrolyte components and loss of ions due to side reactions during degradation, blockage of separator pores by side reaction products, and corrosion of current collector metal parts, all of which contribute to increased resistance in the battery reaction. In addition, Non-Patent Document 1 reports that the expansion and contraction of electrode active materials during the battery reaction increases or decreases the voids within the electrode, which in turn increases or decreases the amount of electrolyte in the electrode within the battery (electrolyte motion), resulting in uneven amounts of electrolyte present, increased resistance, and the generation of overvoltage, all of which contribute to the degradation reaction of the battery.

[0011] Among these, the increase in electrode resistance, which is the root cause of degradation and can be said to be a collection of degradation reaction phenomena, is caused by a disruption of the electron supply network to the active material necessary for the insertion and extraction of lithium ions within the electrode, a delay in the supply of lithium ions due to a decrease in the amount of electrolyte, etc. This is a major issue that prevents the extension of the lifespan of lithium-ion batteries.

[0012] The present invention has been made in view of the above circumstances, and aims to provide a battery reaction auxiliary material that can favorably assist battery reactions and enable the extension of the life of lithium ion batteries, a positive electrode or negative electrode containing the battery reaction auxiliary material, a lithium ion battery including the positive electrode or negative electrode, and a method for manufacturing the battery reaction auxiliary material.

[0013] In order to solve the above problems, the battery reaction assisting material of the present invention employs the following means.

[0014] A first aspect of the present invention provides a battery reaction assisting material comprising a plurality of primary particles that contain carbonaceous matter and have a three-dimensional skeleton with an internal space, wherein some of the primary particles are adhered to each other to form secondary particles, and the secondary particles undergo plastic deformation in an extremely small load / unload test, with some of the secondary particles not recovering.

[0015] In the first aspect, the carbonaceous material may include graphene.

[0016] In the first aspect, the plastic deformation power may be 5% or more and 92% or less.

[0017] In the first aspect, the battery reaction assisting function may have an electron transfer function and an electrolyte retention function.

[0018] In the first aspect, the pore volume measured by gas adsorption may be 1 cc / g or more and 6 cc / g or less.

[0019] In the first aspect, the carbon layer stacking index may be 0.4 or more and 5 or less.

[0020] In the first aspect, the secondary particles may be hollow, and solid particles may be mixed with the secondary particles.

[0021] 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.

[0022] In the above embodiment, the solid particles may be ceramic particles coated with a carbonaceous material.

[0023] In the first aspect, the secondary particles may have an average particle size of 0.1 μm or more and 6 μm or less.

[0024] A 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.

[0025] In the second aspect, the positive electrode or negative electrode for a lithium ion battery may have a permanently deformed portion in which the secondary particles are permanently deformed in part of the structure.

[0026] In the above aspect, the permanently deformed portion may contain multilayer graphene.

[0027] A third aspect of the present invention provides a positive electrode or a negative electrode for a lithium ion battery, which comprises only solid particles as a battery reaction supporting material.

[0028] A fourth aspect of the present invention provides a lithium ion battery comprising at least one of the positive electrode and the negative electrode for the lithium ion battery according to the second or third aspect.

[0029] A fifth aspect of the present invention provides a method for manufacturing a positive electrode or a negative electrode for a lithium ion battery, the method comprising the steps of: mixing a battery reaction auxiliary material containing carbonaceous material, the battery reaction auxiliary material including primary particles having a three-dimensional skeleton with internal spaces and secondary particles formed by fixing a plurality of the primary particles together, a binder resin, and a solvent to prepare a slurry; and applying the slurry to a current collector, drying the current collector, and pressing the current collector to obtain a positive electrode or a negative electrode, wherein during the pressing, the shapes of some of the primary particles and the secondary particles remain deformed, while the shapes of another part of the primary particles and the secondary particles are restored.

[0030] The battery reaction assisting material according to the present invention can favorably assist the battery reaction. A lithium ion battery having a positive electrode or a negative electrode containing the battery reaction assisting material according to the present invention can have an extended life and high performance.

[0031] FIG. 1 is a schematic diagram showing an enlarged 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. FIG. 3 is an SEM photograph (20 μm scale) of the electrode surface before pressing in the production of a positive electrode of Example 1. FIG. 4 is an SEM photograph (1 μm scale) of the electrode surface before pressing in the production of a positive electrode of Example 1. FIG. 5 is an SEM photograph (20 μm scale) of the electrode surface after pressing in the production of a positive electrode of Example 1. FIG. 6 is an SEM photograph (1 μm scale) of the electrode surface after pressing in the production of a positive electrode of Example 1. FIG. 7 is a diagram showing the results of an ultra-small load unloading test performed on the battery reaction auxiliary material prepared in Example 1. FIG. 8 is a diagram showing an example of the cross-sectional structure of a lithium ion battery according to one embodiment of the present invention. FIG. 9 is a transmission electron microscope (TEM) image of the battery reaction auxiliary material obtained in Example 1. FIG. 10 is a TEM image of the battery reaction auxiliary material obtained in Example 2. FIG. 11 is a diagram showing the pore size distribution curve of the battery reaction auxiliary material obtained in Example 1. FIG. 12 is a diagram showing the particle size distribution of the battery reaction auxiliary material obtained in Example 1. FIG. 1 is a discharge curve using a test battery of Example 1 according to one embodiment of the present invention, showing the difference in current during discharge. FIG. 2 is a TEM photograph of a battery reaction auxiliary material obtained in Example 6. FIG. 3 is a graph showing the relationship between plastic deformation power and 2C rate discharge retention rate for a test battery according to an Example and a test battery according to a Comparative Example. FIG. 4 is a graph showing the relationship between carbon layering index and 2C rate discharge retention rate for a test battery according to an Example and a test battery according to a Comparative Example. FIG. 5 is a graph showing the relationship between pore volume and 2C rate discharge retention rate for a test battery according to an Example and a test battery according to a Comparative Example. FIG. 6 is a graph showing the relationship between secondary particle diameter in the auxiliary material and 2C rate discharge retention rate for a test battery according to an Example and a test battery according to a Comparative Example. FIG. 7 is a graph showing the relationship between the amount of auxiliary material added and charge / discharge capacity for a test battery according to an Example and a test battery according to a Comparative Example.

[0032] Hereinafter, an embodiment of a battery reaction auxiliary material according to the present invention, a positive electrode or a negative electrode for a lithium ion battery containing the battery reaction auxiliary material, and a lithium ion battery including the positive electrode or the negative electrode will be described with reference to the drawings. First, the battery reaction auxiliary material according to this embodiment will be described.

[0033] Fig. 1 shows a schematic diagram enlarging a portion of the structure of an electrode containing the battery reaction auxiliary material (hereinafter also referred to as "auxiliary material") of this embodiment. The battery reaction auxiliary material of this embodiment is contained in, for example, the negative electrode or positive electrode of a lithium ion battery. Fig. 1 shows an example in which the battery reaction auxiliary material of this embodiment is applied to a positive electrode.

[0034] As shown in Figure 1, the auxiliary material of this embodiment includes primary particles 1 and secondary particles 2 formed by bonding a plurality of primary particles together. The primary particles 1 contain carbonaceous material, and the carbonaceous material includes thin-layer graphene, which will be described later. The primary particles 1 are hollow particles having a three-dimensional skeleton and an internal space. Reference numeral 3 in Figure 1 denotes a positive electrode material.

[0035] The auxiliary material of this embodiment includes a thin-layer graphene material. Graphene has a sheet-like structure in which hexagonal carbon network planes bonded to benzene rings grow planarly. Graphite is a structure in which many graphenes are stacked. On the other hand, a structure in which hexagonal carbon network planes grow planarly but the number of stacks is small, and therefore the structure has elastic deformability, is defined as a thin-layer graphene material in this specification. The thin-layer graphene material is the main structure of the auxiliary material of this embodiment.

[0036] When stress is applied to the primary particles and secondary particles of this embodiment, the three-dimensional shape of the thin graphene portion of the particle is mainly deformed and compressed. On the other hand, when the applied stress is released, the deformed portion recovers to a certain extent due to its elastic deformability. The portion that does not recover upon release of the stress is a portion with low elasticity. When the thin graphene portion contains many structural defects or many amorphous bonds, the shape does not recover, i.e., it has plastic deformability against stress. Such a structural portion that has plastic deformability against stress exhibits high strength against stress or has the property of easily deforming and not being able to recover afterwards.

[0037] As described above, in the auxiliary material of this embodiment, the thin graphene portion has elastic deformability, and the portion other than the thin graphene portion is amorphous carbon and has plastic deformability. The primary particles of the auxiliary material of this embodiment deform when stress is applied. Depending on the magnitude of the applied stress, some of the multiple primary particles restore their shape when the stress is released, while other parts of the multiple primary particles maintain a permanently deformed 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 loading and unloading test described below.

[0038] When the thin graphene material is relatively thick, the thin graphene material maintains elastic deformability within a certain stress range, but undergoes sudden plastic deformation when a certain threshold is exceeded. General carbon materials may be deformed by a relatively large stress, resulting in particle destruction. 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 in the extremely small load / unload test performed in this embodiment, i.e., the property of a large amount of work required for elastic deformation.

[0039] Graphene can be said to be a carbonaceous material with high electronic conductivity due to its highly regular hexagonal planar structure.

[0040] Here, the state of the thin graphene microcrystalline structure can be analyzed by Raman spectroscopy.

[0041] An example of the Raman spectrum measured for the auxiliary material of Example 1 described later is shown in Figure 2. This spectrum includes the G band (aromatic ring C=C stretching motion, 1593 cm) derived from the skeletal vibration of the graphite sheet. －１ ), the D band (C-H stretching motion, 1356 cm) derived from defects such as non-hexagonal sites including edge sites －１ ), and the 2D band due to second-order phonon scattering (C–H stretching motion, 2680 cm －１ ) is present. These findings suggest that the auxiliary material of Example 1 has a structure containing graphene. Ｇ ) and the intensity of the 2D band (I ２Ｄ ) is the ratio of I Ｇ　 / I ２Ｄ　is said to be an index indicating the stacking state of graphene layers (D. Graf, et al., NANO LETTERS, 7, 238-242; (2007)). In this embodiment, I Ｇ　 / I ２Ｄ　 The index expressed by the formula is called the "carbon stacking index." Based on the above paper, the value per layer was set to 0.2.

[0042] I Ｇ　 / I ２Ｄ　 The smaller the value of , 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 suggests that it has a structure that exhibits elastic deformability. 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.

[0043] The auxiliary material of this embodiment contains graphene and therefore has excellent electron transport properties. 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. Furthermore, 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 skeletons of the primary particles and secondary particles.

[0044] Therefore, the auxiliary material of this embodiment can utilize elastic deformation and plastic deformation in a balanced manner under the conditions of use of a lithium-ion battery. That is, high electronic conductivity is ensured 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 source of ions, can be stored in the space within the particles. Therefore, the auxiliary material of this embodiment can favorably support the battery reaction.

[0045] 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 referred to as T-CVD). This is a technique in which an organic gas is passed through ceramics that has CVD activity and is heated in an inert gas atmosphere, and carbon atoms of the organic matter in the gas are condensed to form a carbonaceous film.

[0046] Next, to create spaces within the primary particles, the ceramic particles coated with the carbonaceous film are treated with a reagent (e.g., an acidic solution) that can dissolve ceramics. This treatment dissolves and removes the ceramic portion of the ceramic particles coated with the carbonaceous film. After dissolution, the interior of the primary particles formed from the carbonaceous material is washed to remove any remaining material in the spaces. By dissolving and removing the ceramic particles, spaces are created within the primary particles formed from the carbonaceous material.

[0047] Next, the primary particles are heat-treated at 3000°C or less to adjust structural defects in the thin graphene portion and the portion other than the thin graphene portion that constitutes the particles. These structural defects include spaces formed within the particles due to dissolution of the template and infiltration holes formed in the three-dimensional framework formed from the carbonaceous material. The degree of these structural defects can be adjusted by adjusting reaction conditions such as the heat treatment temperature and heat treatment time, i.e., the size of the spaces present inside the particles and the size of the infiltration holes that allow the electrolyte to penetrate into the particles can be adjusted.

[0048] Functional groups (mainly oxygen-containing functional groups) that bond to carbon and carbon chains that do not form six-membered rings are detached at temperatures above approximately 1000°C, forming dangling bonds. When the dangling bonds that are formed bond with other nearby carbons, the surface of the carbon material becomes a state in which functional groups are less likely to bond. By heat-treating at 1500°C or higher, preferably 1600°C or higher, the auxiliary material of this embodiment can exhibit favorable functions such as electron conductivity and maintaining internal space.

[0049] The auxiliary material of this embodiment has a pore volume of 1 cc / g or more and 4 cc / g or less, as measured by gas adsorption, specifically, nitrogen adsorption / desorption measurement. Pore volume refers to the volume of the space present inside the particle. A larger pore volume value means that more electrolyte is retained within the particle, resulting in higher reaction efficiency. On the other hand, a larger pore volume value means a larger space, which weakens the skeletal strength and makes it difficult to maintain the particle shape under pressure during loading. In the auxiliary material of this embodiment, the pore volume is 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. Having such an appropriate pore volume provides the particles with appropriate strength, contributing to the stability of the particle shape and maintaining the shape. This allows a good balance between electronic conductivity and the supply of ions retained in the pores.

[0050] The positive electrode material for lithium-ion batteries is a powder of lithium-containing transition metal oxide with a particle size distribution and low electronic conductivity. Conventionally, a conductive additive made of a carbon material that aids in electronic conduction for the battery reaction is mixed with a binder resin, which is then pressed and fixed to a current collector, establishing an electronic conduction route. Because all materials except the binder resin are powder particles, the electrolyte is only present incidentally in the spaces between the particles. For this reason, it has been difficult with conventional technology to actively position the electrolyte, or in other words, lithium ions, near the positive electrode material.

[0051] In contrast, in this embodiment, a battery reaction auxiliary material is used instead of the conventionally used conductive auxiliary. The battery reaction auxiliary material of this embodiment is formed from particles mainly composed of thin-layer graphene, and has spaces inside the particles that can hold an electrolyte. The auxiliary material exhibits high electronic conductivity derived from graphene, although it permanently deforms when pressurized between particles such as the positive electrode material in the positive electrode, while maintaining spaces that hold 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 more effectively achieve a rapid battery reaction.

[0052] The three-dimensional skeleton of the auxiliary material of this embodiment is deformed by pressure. When the soft graphene portion is crushed, the single-layer graphene changes to a multi-layered state, which improves electron conduction.

[0053] In an actual electrode, for example, when a positive electrode mixture slurry is applied to a current collector, dried, and then pressed, the mixture layer is crushed. When an electrode includes the auxiliary material of this embodiment, particles sandwiched between positive electrode material particles are directly subjected to stress, undergoing plastic deformation and exhibiting electronic conductivity. Meanwhile, particles present in the gaps between the positive electrode material and not subjected to stress remain as particles with internal spaces maintained, thereby exhibiting the function of retaining the electrolyte. As an example, SEM photographs of the electrode surface before press-forming in this embodiment are shown in FIGS. 3A and 3B, and SEM photographs of the electrode surface after press-forming are shown in FIGS. 3C and 3D, respectively. Comparisons between FIGS. 3A and 3C and between FIGS. 3B and 3D confirm that a structure in which some primary and secondary particles are crushed by pressing is produced. The crushed portions correspond to the permanently deformed portions described above.

[0054] The auxiliary material of this embodiment includes primary particles that are hollow particles with internal spaces. On the other hand, solid particles can be mixed with the hollow particles when selecting the composition of the electrode or when adjusting the electrode porosity without increasing the electrode density. The solid particles are the template particles that remain without being dissolved in the T-CVD method described above.

[0055] The solid particles are preferably carbonaceous from the viewpoint of electron conductivity, and carbon black, acetylene black, single-walled carbon nanotubes, and multi-walled carbon nanotubes are preferably used.

[0056] In the auxiliary material according to this embodiment, the solid particles are preferably ceramic particles coated with carbonaceous material. When fabricating 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 material.

[0057] When ceramic particles are selected as the solid particles, they can be used as they are without being eluted with the above-mentioned reagents.

[0058] As the ceramic particles, a compound inactive to the battery reaction can be appropriately selected. For example, Al ２ O3, MgO, SiO ２ , ZrO ２ Other examples include those that have CVD activity and can be used as a template in the T-CVD method.

[0059] In addition to strength, ceramic particles can also be used to their advantage due to their various properties, such as chemical reactivity, catalytic properties, and physical properties.

[0060] The proportion of solid particles mixed into the auxiliary material varies depending on the purpose of use, but is preferably 10% by weight or more, more preferably 30% by weight or more, and most preferably 50% by weight or more to clearly exert efficacy.

[0061] When solid particles are mixed into the auxiliary material, carbon-based solid particles can be appropriately mixed in to fine-tune the electrode specifications. By adding carbon-based solid particles, the electronic conductivity can be adjusted.

[0062] 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 solid particles in which ceramic particles are coated with carbonaceous material are used, there is no significant difference in the battery reaction compared to 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 developing new functional properties.

[0063] As the electrode active material, lithium-containing oxides and lithium transition metal phosphates can be used for the positive electrode, and graphite, carbons, alloys containing Si, Sn, and intermetallic compounds can be used for the negative electrode.

[0064] The auxiliary material of this embodiment is a primary particle or at least a secondary particle formed by adhering a plurality of primary particles. Although it depends on the type of electrode active material, it is preferable that the length of the primary particle or secondary particle is not more than twice the particle diameter of the electrode active material.

[0065] Although it depends on whether the functionality of the primary particles or the secondary particles is desired to be dominant in the auxiliary material, secondary particles having an average particle size of 0.05 μm to 6 μm are preferably used, and the average particle size of the secondary particles is more preferably 0.1 μm to 5 μm.

[0066] Furthermore, the auxiliary material of this embodiment cannot supply lithium ions, which are the source of battery capacity, from the outside. Therefore, the additive ratio of the auxiliary material to the electrode should be kept to the minimum necessary. To obtain good characteristics, the auxiliary material is preferably added in an amount of 0.1 wt % to 5 wt % of the electrode mixture.

[0067] If it is smaller than this range, the functionality cannot be utilized, whereas if it is too large, the bulk density of the electrode mixture becomes too large, which is undesirable as it reduces the electrode strength.

[0068] Next, the measurement of the ultra-small load unloading test for confirming the physical properties of the battery reaction auxiliary material according to this embodiment will be described.

[0069] As an example of an ultra-small load unloading test, a load-displacement curve obtained by performing the test on the battery reaction auxiliary material prepared in Example 1 described below is shown in FIG. 4. In the ultra-small load unloading test used in this embodiment, a load is applied to the test particle by pressing an indenter against the sample particle and pressing it in. Measurement begins when the indenter contacts the particle and the sensor detects the pressure. Then, as the pressing depth increases, the load on the particle increases. In the ultra-small load unloading test of this embodiment, the load is removed when the load reaches 0.1 mN.

[0070] If the particle were to completely recover its shape without any deformation, the indentation depth would return to 0, i.e., return to the origin of the horizontal axis in the graph of Figure 3. Conversely, if the particle were to completely deform due to the load, i.e., be crushed in the direction of the load, the indentation depth would remain at 300 nm. This means that the space that existed within the particle has disappeared, and the layers that formed the skeleton have become two overlapping layers.

[0071] In the battery reaction assisting material of this embodiment, the indentation depth does not return to 0 even when the load is removed. For example, in FIG. 4, the particles to which the load was applied had an indentation depth of about 230 nm. This indicates that the particles were partially deformed by the load, but some space remained within the particles. In FIG. 3, the part corresponding to the work required to restore the shape in response to the applied load is the elastic deformation work W Ｅ (the shaded area in Figure 3) corresponds to the amount of work required to deform the material under a given load. Ｐ (portions surrounded by vertical lines in FIG. 3) are shown.

[0072] 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. The particles are more likely to be destroyed by the pressure applied during electrode fabrication, which reduces the amount of electrolyte held and reduces the properties. If the carbon layer stacking index is too small, the particles are more likely to collapse when loaded. This means that the space within the particles is smaller, making it more difficult to hold the electrolyte within the particles.

[0073] Next, a lithium ion secondary battery including an electrode containing the auxiliary material of this embodiment will be described.

[0074] 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 metal exterior part 211 and a disk-shaped negative electrode 214 housed in a metal exterior part 113 with a separator 215 interposed therebetween. A metal spring 218 and a spacer 219 are disposed between the exterior part 213 and the negative electrode 214. The interiors of the exterior parts 211 and 213 are filled with a liquid electrolyte, and the peripheral edges of the exterior parts 211 and 213 are sealed by being crimped with a seal gasket 217 interposed therebetween.

[0075] The positive electrode 212 is generally obtained by applying a slurry containing a metal oxide material, a conductive additive that enhances electronic conductivity, a binder, and a solvent to a current collecting metal foil such as rolled aluminum foil to form a coating film, which is then heated and dried to remove the solvent, and then formed to a predetermined size and density. In this embodiment, the above-mentioned battery reaction auxiliary material is used instead of a commonly used conductive additive such as acetylene black.

[0076] A metal compound material that can be used as a positive electrode active material is one that can release electrons to the external circuit of the battery and simultaneously release Li ions to the electrolyte. The amount of Li ions contained varies depending on the chemical composition, crystalline structure, etc., but a material that can reversibly absorb and release many Li ions is preferred.

[0077] Examples of such materials include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides. Examples of transition metals that can be used include Fe, Co, Ni, and Mn. Specific examples include MnO, V, and the like. ２ O ５ , V ６ O １３ , TiO ２ transition metal oxides such as LiNiO ２ , LiCoO ２ , LiMn ２ O ４ etc., TiS ２ , FeS, MoS ２In order to improve the properties of these inorganic compounds, specific elements may be partially substituted with other elements.

[0078] In addition to the inorganic compounds listed above, there are also positive electrode materials made of organic compounds, such as polyaniline, polypyrrole, polyacene, disulfide-based compounds, polysulfide-based compounds, and N-fluoropyridinium salts. The positive electrode material may also be a mixture of the inorganic and organic compounds listed above.

[0079] The physical properties of cathode materials are determined by the requirements of the battery design and manufacturing process, which are based on constraints such as the type of use of lithium-ion batteries. In manufacturing cathode materials, the process is designed to achieve the desired physical properties. Physical properties include powder particle size and distribution, specific surface area, and density.

[0080] As an example, the powder particle size is appropriately selected in consideration of other constituent requirements of the lithium ion battery, but from the viewpoint of improving battery characteristics such as rate characteristics and cycle characteristics, an average particle size of 1 to 30 μm is usually preferred, and an average particle size of 1 to 10 μm is more preferred.

[0081] Since the above-mentioned positive electrode materials generally have low electronic conductivity, it is preferable to have a battery reaction auxiliary material that assists electronic conductivity coexist in the positive electrode. 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 preferred.

[0082] The amount of coexisting battery reaction auxiliary materials should be kept to a minimum, and the content of the positive electrode material, which determines the capacity of the lithium-ion battery, should be maximized.

[0083] Examples of conventional carbon-based materials include soot, acetylene black, ketjen black, lamp black, furnace black, carbon black, graphite, carbon fiber, graphite fiber, nanofiber, nanotube, coke, hard carbon, and amorphous carbon.

[0084] In comparison, the auxiliary material of this embodiment has a significant feature not found in conventional materials. That is, because the auxiliary material of this embodiment contains a graphene portion with a relatively large area in its structure, it has few defects other than carbon-carbon bonds, such as oxygen-containing functional groups at the end of carbon bonds in a six-membered ring. Therefore, it is less likely to deteriorate and decompose in the electrochemical oxidative environment to which it is exposed inside a battery.

[0085] Furthermore, if necessary, further effects can be obtained by combining the above-mentioned conventional materials. For example, flake graphite and highly linear carbon nanotubes have high electronic conductivity but low ion storage capacity. By combining these properties with the auxiliary material of this embodiment, it is possible to construct a good battery reaction auxiliary system that adds ion storage capacity to electronic conductivity.

[0086] Carbon blacks, such as acetylene black, are composed of interconnected structural particles with diameters of several tens of nanometers. However, the crystallinity of carbon is not particularly high, the structural length is short, and the carbon is easily broken down, making it difficult to transmit electrons over long distances. By combining this with the auxiliary material of this embodiment, it is possible to realize a system that maintains electronic conductivity and also has ion supply capability, even when the three-dimensional structure is maintained or when the three-dimensional structure is crushed and flattened like flake graphite.

[0087] The preferred 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 ratio 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 the battery reaction auxiliary material in this range, good characteristics can be obtained.

[0088] The positive electrode material and the battery reaction auxiliary material are often in powder form, and in order to fix them together and on the current collecting metal foil, it is preferable to mix them with a small amount of a binder. The binder is required to be chemically and electrochemically inert and to have some elastic deformability and affinity, and a plastic resin material is preferably used.

[0089] Another application of the battery reaction assisting material is in the form of a coating material in which the powder is dispersed in a liquid solvent at a certain ratio. In this case, the solvent can be an organic or inorganic compound applicable to the production of lithium-ion batteries. To maintain a good dispersion state of the powder in the solvent, an organic or inorganic dispersant (e.g., a monomolecular or plastic resin material) can be suitably used.

[0090] Examples of the plastic resin material include fluorine-based resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene, CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide, polyvinyl alcohol-based polymers such as polyvinyl acetate and polyvinyl alcohol, halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride, conductive polymers such as polyaniline, alkane-based polymers such as polyethylene, polypropylene, and poly-1,1-dimethylethylene, unsaturated polymers such as polybutadiene and polyisoprene, ring-containing polymers such as polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N-vinylpyrrolidone, and acrylic polymers such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide. The resin materials may also be mixtures, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, or block copolymers. The weight average molecular weight of these resins is usually 10,000 to 3,000,000, and preferably 100,000 to 1,000,000. If the molecular weight is too small, the strength of the coating film decreases, and if it is too large, the viscosity increases, making it difficult to form an electrode.

[0091] In order to distribute the binder sufficiently uniformly and to form a coating film of the slurry with the predetermined dimensions, an appropriate 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 the solvent can be selected appropriately depending on the conditions of the manufacturing process.

[0092] The current collecting metal foil is preferably made of a material that is inexpensive and durable for industrial use, and is preferably made of a material that has electrochemical resistance to the potential developed by the positive electrode. Examples of the current collecting metal foil include aluminum foil, nickel foil, titanium foil, and stainless steel foil, and more preferably rolled aluminum foil, which is commonly available.

[0093] A commonly used printing technique can be used to form a coating film of the slurry on the current collecting metal foil. When the coating thickness is small, gravure printing or the like is preferably used, and when the coating thickness is large, doctor blade printing, die printing or the like is preferably used.

[0094] Thereafter, the coating film is dried by heating. Any drying method can be used, and a method that can achieve the desired binding strength by the binder is preferably used.

[0095] Thereafter, when forming the cathode into a predetermined size, an industrially available cutting blade and the like and the method thereof are preferably used. In addition, to achieve a predetermined density, an industrially available pressing device and the like and the method thereof are preferably used as needed.

[0096] Next, the negative electrode 214 will be described. The negative electrode 214 can be obtained by coating a current collecting metal foil such as rolled copper foil with a slurry made by mixing a carbon-based material, a binder, and a solvent, and then heating and drying the coating to remove the solvent, followed by forming the coating into a predetermined size and density.

[0097] As a carbonaceous material that can be used for the negative electrode, it is preferable that the material has many stabilizing sites inside, and can bond and stabilize Li ions with electrons flowing from an external circuit.

[0098] For example, any material of organic origin, whether high or low in crystallinity, can be used, 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 bond with electrons to stabilize them.

[0099] As another stabilization mechanism, a method of electrochemically forming an intermetallic compound can also be used, and silicon, tin, zinc, bismuth, antimony, cadmium, lead, germanium, etc. can be suitably used.

[0100] In addition, other materials that exhibit low electrochemical reaction potentials and are used for the negative electrode of lithium-ion batteries can also be used, such as compounds of metals with oxygen, sulfur, halogens, nitrogen, phosphorus, etc.

[0101] Depending on the application of the lithium ion battery, a plurality of the above negative electrode materials can be mixed in a predetermined ratio and used to obtain a desired discharge profile.

[0102] The physical properties of anode materials are determined by the requirements of the device (e.g., storage battery) design and manufacturing process, which are based on constraints such as the usage of lithium-ion batteries. The manufacturing process is designed to achieve the desired physical properties. Physical properties include powder particle size and distribution, specific surface area, and density.

[0103] As an example, the powder particle size is appropriately selected in consideration of other constituent requirements of the lithium ion battery, but from the viewpoint of improving battery characteristics such as rate characteristics and cycle characteristics, an average particle size of 1 to 70 μm is usually preferred, and 3 to 30 μm is more preferred.

[0104] The above-mentioned negative electrode materials generally have high electronic conductivity, but some materials have smooth surfaces and insufficient contact between particles, so it is preferable to add a conductive additive to enhance electronic conductivity. Carbon-based materials, metal-based materials, and other materials with high electronic conductivity can also be used as materials, with carbon-based materials being preferred. The battery reaction auxiliary material of this embodiment described above may also be used as a conductive additive.

[0105] 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.

[0106] Examples of conventional carbon-based materials include soot, acetylene black, ketjen black, lamp black, furnace black, carbon black, graphite, carbon fiber, graphite fiber, nanofiber, nanotube, coke, hard carbon, and amorphous carbon.

[0107] In comparison, the battery reaction assisting material of this embodiment has significant features not found in conventional materials, and can achieve even greater effectiveness by combining it with conventional materials as needed. For example, flake graphite and highly linear carbon nanotubes have high electronic conductivity but low ion storage capacity. Therefore, by combining them with the auxiliary material of the present invention, it is possible to construct an excellent battery reaction assisting system that combines electronic conductivity with ion storage capacity.

[0108] Carbon blacks, such as acetylene black, are composed of interconnected structural particles with diameters of several tens of nanometers. However, the crystallinity of carbon is not particularly high, the structural length is short, and they are prone to collapse, making them difficult to transport electrons over long distances. Despite these properties, by combining them with the auxiliary material of the present invention, it is possible to realize a system that maintains electronic conductivity and also has ion supply ability, even when the three-dimensional structure is maintained or when the three-dimensional structure is crushed and flattened like flake graphite.

[0109] The preferred ratio of the battery reaction auxiliary material of this embodiment to be contained in the negative electrode varies depending on the type of positive electrode material, the type and amount of binder, the battery capacity design, etc. In this embodiment, as described above, the addition ratio 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 the material in this range, good characteristics can be obtained.

[0110] The current collecting metal foil is preferably made of a material that is inexpensive and durable for industrial use, and is preferably a material that does not electrochemically react with the potential developed by the negative electrode. For example, copper foil, nickel foil, titanium foil, and stainless steel foil are preferred as the current collecting metal foil, and electrolytic copper foil and rolled copper foil, which are generally readily available, are more preferred.

[0111] The method for forming the coating film of the above-mentioned slurry can be a commonly used printing technique. When the thickness is small, gravure printing or the like is preferably used, and when the thickness is large, printing techniques such as doctor blade printing or die printing are preferably used.

[0112] Thereafter, the coating film is dried by heating. Any drying method can be used, and a method that can achieve the desired binding strength by the binder is preferably used.

[0113] Thereafter, when forming the negative electrode into a predetermined size, an industrially available cutting blade and the like and the method thereof are preferably used. In addition, to achieve a predetermined density, an industrially available pressing device and the like and the method thereof are preferably used as needed.

[0114] The negative electrode material and conductive additive 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 binder. The binder is required to be chemically and electrochemically inert and to have some degree of elastic deformability and affinity, and a plastic resin material is preferably used.

[0115] Another application of the battery reaction assisting material is in the form of a coating material in which the powder is dispersed in a liquid solvent at a certain ratio. In this case, the solvent can be an organic or inorganic compound applicable to the production of lithium-ion batteries. To maintain a good dispersion state of the powder in the solvent, an organic or inorganic dispersant (e.g., a monomolecular or plastic resin material) can be suitably used.

[0116] Examples of the plastic resin material include fluorine-based resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; polyvinyl alcohol-based polymers such as polyvinyl acetate and polyvinyl alcohol; halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride; conductive polymers such as polyaniline; alkane-based polymers such as polyethylene, polypropylene, and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; ring-containing polymers such as polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N-vinylpyrrolidone; acrylic polymers such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide; carboxymethyl cellulose; and styrene-butadiene rubber. The resin materials may also be mixtures, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, or block copolymers. The weight average molecular weight of these resins is usually 10,000 to 3,000,000, and preferably 100,000 to 1,000,000. If the molecular weight is too small, the strength of the coating film decreases, and if it is too large, the viscosity increases, making it difficult to form an electrode.

[0117] In order to distribute the binder sufficiently uniformly and to form a coating film of the slurry with the predetermined dimensions, an appropriate 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 the solvent can be selected appropriately depending on the conditions of the manufacturing process.

[0118] In this embodiment, a battery electrolyte applied to a lithium ion battery will be described.

[0119] An electrolyte is a solute dissolved in an organic solvent, and is usually the main component.

[0120] One of the components of the electrolyte is a solute that is the source of ions, that is, a Li salt.

[0121] The type of solute is not particularly limited, and any solute known to be used in this lithium ion battery can be used. Specific examples include the following:

[0122] An example of the solute is LiPF ６ and LiBF ４ inorganic salts such as LiCF ３ SO ３ , LiN(CF ３ SO ２ ) ２ , LiN(C ２ F ５ SO ２ ) ２ , Li cyclic 1,2-perfluoroethane disulfonylimide, Li cyclic 1,3-perfluoropropane disulfonylimide, LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ ), LiC(CF ３ SO ２ ) ３ , LiPF ４ (CF ３ ) ２ , LiPF ４ (C ２ F ５ ) ２ , LiPF ４ (CF ３ SO ２ ) ２ , LiPF ４ (C ２ F ５ SO ２ ) ２ , LiBF ２ (CF ３ ) ２ , LiBF ２ (C ２ F ５ ) ２ , LiBF ２ (CF ３ SO ２ ) ２ , LiBF ２(C ２ F ５ SO ２ ) ２ and Li bis(oxalate)borate.

[0123] Of these, LiPF ６ , LiBF ４ , LiN(CF ３ SO ２ ) ２ and LiN(C ２ F ５ SO ２ ) ２ is preferred in terms of exhibiting battery performance, and LiPF ６ and LiBF ４ is preferred.

[0124] These Li salts may be used alone or in combination of two or more.

[0125] The content of the Li salt in the electrolyte varies depending on the type of solvent in which the Li salt is dissolved and the mixed composition, but the content of the Li salt in the electrolyte is preferably 7 to 190 wt %, more preferably 10 to 180 wt %, and even more preferably 13 to 150 wt %.

[0126] Next, the organic solvent used in the electrolyte will be described.

[0127] The type of solvent is not particularly limited, and can be appropriately selected from those conventionally known as solvents, such as cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, cyclic carboxylic acid esters, chain carboxylic acid esters, phosphorus-containing organic solvents, and the like, which have no unsaturated bond.

[0128] In addition to viscosity, factors that affect the migration of Li ions include the viscosity and solvating power of the organic solvent. Solvating power is the force that dissociates dissolved ions, and if it is too strong, it will inhibit the migration of ions, so there is an optimum value.

[0129] Furthermore, practical lithium-ion batteries can be used under a wide range of environmental conditions, and physical properties such as the melting and boiling points of organic solvents must also be kept within certain ranges.

[0130] A practical solution to the above requirements is to use a mixture of multiple organic solvents. The mixture composition is determined by taking into consideration practical properties, such as the combination of organic solvents with high and low melting points, or organic solvents with high and low solvating power.

[0131] 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.

[0132] Examples of cyclic carbonates include alkylene carbonates having an alkylene group having 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.

[0133] 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.

[0134] However, because dimethyl carbonate has a slightly low boiling point, more suitable properties can be obtained by further mixing it with a chain carbonate having a higher boiling point. Diethyl carbonate is the preferred chain carbonate to be mixed, but other chain carbonates can also be used without any problems.

[0135] The mixing ratio also varies depending on the desired practical properties. There is an optimum ratio of the chain carbonate to the cyclic carbonate, taking into account the ratio of the Li salt.

[0136] The content of the cyclic carbonate in the electrolyte is preferably 1 to 35% by weight, more preferably 3 to 30% by weight, and even more preferably 4 to 25% by weight. A mixture of multiple cyclic carbonates can be used.

[0137] On the other hand, the content of the chain carbonate in the electrolyte is preferably 40 to 70% by weight, more preferably 43 to 68% by weight. A plurality of chain carbonates can be used in combination.

[0138] The following combinations are suitable as overall compositions. Among combinations of ethylene carbonate and dialkyl carbonates, ethylene carbonate and dimethyl carbonate are preferred, and a symmetric chain dialkyl carbonate and / or an asymmetric chain dialkyl carbonate may also be included. For example, combinations containing ethylene carbonate, a symmetric chain dialkyl carbonate, and an asymmetric chain dialkyl carbonate, such as ethylene carbonate, dimethyl carbonate, and diethyl carbonate; ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate; or ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, are preferred because they provide a good balance between cycle characteristics and high-power discharge characteristics. Among these, ethyl methyl carbonate is preferred as the asymmetric chain dialkyl carbonate, and the alkyl group of the alkyl carbonate preferably has 1 to 2 carbon atoms.

[0139] Furthermore, as a solvent that aids in the dissociation and migration of ions, cyclic ethers, chain ethers, cyclic carboxylic acid esters, chain carboxylic acid esters, etc. may be added in addition to the above-mentioned main organic solvents.

[0140] Examples of cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran, and examples of chain ethers include dimethoxyethane and dimethoxymethane.

[0141] Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone, and examples of chain carboxylic acid esters include methyl acetate, methyl propionate, ethyl propionate, and methyl butyrate.

[0142] Among these, chain carboxylic acid esters are particularly preferred.

[0143] Furthermore, it is also preferable that the electrolyte of this embodiment contains a fluorine-containing cyclic carbonate having two or more fluorine atoms.

[0144] The number of fluorine atoms in a fluorinated 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.

[0145] 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.

[0146] 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.

[0147] The fluorine-containing cyclic carbonate having two or more fluorine atoms may be used alone or in combination of two or more. The proportion of the fluorine-containing cyclic carbonate compound having two or more fluorine atoms in the nonaqueous electrolyte solution 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.

[0148] Furthermore, cyclic carbonates having unsaturated bonds or aromatic compounds having a total carbon number of 7 or more and 18 or less may be mixed into the electrolyte.

[0149] Among cyclic carbonates having an unsaturated bond, vinylene carbonate, vinylethylene carbonate, 4-methyl-4-vinylethylene carbonate, and 4,5-divinylethylene carbonate are preferred from the viewpoint of improving cycle characteristics, and among these, vinylene carbonate and vinylethylene carbonate are more preferred. These may be used alone or in combination of two or more kinds.

[0150] Preferred aromatic compounds having a total carbon number of 7 or more and 18 or less include biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, and the like.

[0151] It is believed that by suppressing the side reaction between the aromatic compound having a total carbon number of 7 to 18 and the negative and positive electrodes in this way, a significant decrease in discharge characteristics after high-temperature storage can be suppressed.

[0152] 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 wt% or more, preferably 0.1 wt% or more, particularly preferably 0.3 wt% or more, and most preferably 0.5 wt% or more, with the upper limit being usually 5 wt% or less, preferably 3 wt% or less, and particularly preferably 2 wt% or less. At a concentration lower than this lower limit, the effect of improving safety during overcharge may be difficult to achieve. Conversely, if the concentration is too high, battery characteristics such as high-temperature storage characteristics may be deteriorated.

[0153] The separator 215 separates the positive electrode 212 and the negative electrode 214, prevents short circuits of 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.

[0154] Suitable membrane forms include stretched membranes in which pores are formed by stretching bulk resin, and nonwoven fabrics in which a large number of fibrous resin fibers are laminated to form a porous structure like a porous membrane.

[0155] Examples of resin materials include polyolefins, with polyethylene being particularly suitable. Polyethylene has a relatively low melting temperature, and when the battery temperature rises for some reason (e.g., an unsafe condition such as a short circuit), the pores in the membrane are blocked by thermal melting, preventing the movement of driving ions, thereby stopping the reaction and ensuring safety.

[0156] Porous membranes formed by the stretching method are usually prepared 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.

[0157] In producing a stretched membrane, stretching is usually carried out in both the longitudinal and transverse directions. A suitable stretched membrane can be obtained by appropriately combining any atmospheric medium, temperature, speed, stress, number of process repetitions, etc., together with the removal of the plasticizer, etc.

[0158] Although the above manufacturing process produces high-quality stretched membranes, it is a multi-step process, which makes it difficult to reduce manufacturing costs, such as process costs, and may be a negative factor in the widespread use of lithium-ion batteries.

[0159] On the other hand, by simplifying the process so that stretching is performed only in the longitudinal direction without using plasticizers, etc., it is possible to obtain a porous membrane that can be produced on an industrial level and whose production cost can be reduced. In this case, the applicable resin is polyolefin, and polypropylene is preferably used.

[0160] The separator interposed between the positive electrode and the negative electrode may be formed from an electrically insulating porous material. Examples of the separator include films made of polymers such as polyolefins (e.g., polyethylene and polypropylene), polyesters, polyethylene terephthalate, and polyimides, or fibrous nonwoven fabrics. The separator may be made of one material alone or multiple materials. The separator may be a single layer or a multilayer (composite film). The separator may contain inorganic nanoparticles such as ceramic. The separator may also be coated on both sides with a polymer compound (e.g., polyvinylidene fluoride).

[0161] In the nonaqueous electrolyte battery according to this embodiment, a gelled electrolyte containing a polymer compound that swells in an organic solvent to serve as a support for the nonaqueous electrolyte may be used. This is because the inclusion of a polymer compound that swells in an organic solvent can provide high ionic conductivity, leading to excellent charge / discharge efficiency and preventing leakage of the battery. 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.

[0162] When a polymer compound such as polyvinylidene fluoride is applied to both sides of the separator, the mass ratio of the non-aqueous electrolyte to the polymer compound is preferably within a range of 50:1 to 10:1. By setting the mass ratio within this range, higher charge / discharge efficiency can be obtained.

[0163] Examples of the polymer compound include ether-based polymer compounds such as polyvinyl formal, polyethylene oxide, and crosslinked polyethylene oxide-containing polymer compounds, 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. One type of polymer compound may be used alone, or multiple types may be used in combination. In particular, from the viewpoint of the effect of preventing swelling during high-temperature storage, it is desirable to use a fluorine-based polymer compound such as polyvinylidene fluoride.

[0164] A lithium-ion battery having the above-described 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 return to the positive electrode 212 through the separator 215. This series of actions causes the battery reaction to proceed.

[0165] 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 changes are possible within the scope of the gist of the present invention described in the claims.

[0166] In the above embodiment, a coin-type lithium ion battery has been described as an example of the lithium ion battery, but the lithium ion battery of this embodiment can be similarly applied to batteries of other shapes such as a button type, a paper type, a square type, or a cylindrical type having a spiral structure. Furthermore, the lithium ion battery of this embodiment can be made into various sizes such as a thin type or a large type.

[0167] Furthermore, although the above description describes an embodiment in which a lithium ion battery according to the present embodiment has a liquid electrolyte, any other electrolytes can be used. For example, gel electrolytes and solid electrolytes can also be suitably used.

[0168] Experiment 1: Confirmation of basic performance of battery reaction auxiliary material Example 1 (Production of battery reaction auxiliary material) Magnesium oxide nanopowder (primary particle size 0.4 μm, SSA 130 m) was used as a template for the carbonaceous film. ２ The mixture was filled in a heat treatment vessel and then placed in a tube furnace. The inside of the vessel was replaced with Ar gas, and then the temperature was raised to 920°C. If necessary, a preliminary heat treatment was performed for the purpose of dehydration, etc. Then, the mixture was heated in a gas atmosphere of Ar gas and CH ４ A mixed gas of 20% by volume of carbon dioxide gas was flowed for 2.3 hours, and a carbonaceous film containing a graphene structure was formed on the template by T-CVD. After cooling, the template was taken out and subjected to a crushing and classification treatment.

[0169] Next, the template was dissolved from this treated product with hydrochloric acid, washed and dried while maintaining the intraparticle space, to obtain a precursor of the auxiliary material, which was then heat-treated at 1700°C in an inert atmosphere to optimize the carbon structure, thereby obtaining the battery reaction auxiliary material of Example 1.

[0170] The shape of the obtained auxiliary material was observed by TEM using a transmission electron microscope (JEM-2010, JEOL Ltd.). Observation of the porous carbon material using a transmission electron microscope was carried out 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 ( FIG. 6 ) that a skeletal structure mainly composed of layered graphene was formed.

[0171] (Ultra-small Loading / Unloading Test) A small amount of the auxiliary material dispersed in ethanol was spread on a sample stage and dried. The sample was then introduced into an SEM, and the measurement particles were observed. Particles measuring 1-5 μm in height and 1-5 μm in width were placed directly under the indenter as the measurement target. A nanoindenter (Toyo Corporation) incorporated into the SEM was then used to perform a loading / unloading test under the following conditions: InForce 50 indenter head, 10 μm indenter diameter, 0.1 mN maximum load, 5 seconds time to maximum load, and 5 seconds maximum load holding time. A sample shape that was stably fixed to the sample stage was selected, and if the position easily changed during the initial pressure application, remeasurement was performed. The plastic deformation power shown in Figure 3 can be calculated using the following formula:

[0172] (Preparation of Positive Electrode) A ternary positive electrode material NCM (LiNi) with an average particle size of 8 μm was prepared. ０．５ Co ０．２ Mn ０．３ O ２ 96% by weight of PVDF powder, 1% by weight of the battery reaction auxiliary material of Example 1 as a conductive additive, and 3% by weight of PVDF were added to N-methyl-pyrrolidone (NMP) as a solvent. The resulting mixture was stirred and mixed to make a homogeneous solution, producing a positive electrode agent paste. This was applied to a 15 μm thick Al current collector, dried at 110°C, and then punched to a diameter of 15 mm and pressed at 45 kN to form a positive electrode.

[0173] (Preparation of a Test Battery for a Positive Electrode) The obtained positive electrode was dried in a vacuum at 120°C, and then dissolved in 1M LiPF in a glove box in an argon gas atmosphere. ６ A 2032 size coin-type test battery with a metal Li counter electrode was fabricated using a solution (a 1:1 mixed solvent of ethylene carbonate (EC):diethyl carbonate (DEC)) as an electrolyte and a polypropylene separator.

[0174] (Positive Electrode Evaluation Method) Each test battery was energized to 4.2 V at a constant current of 1.25 mA (equivalent to 0.2 C). After reaching 4.2 V, it was charged at a constant voltage and continued until it reached 0.31 mA (0.05 C). It was then discharged to 3 V at a constant current of 1.25 mA. The discharge capacity and average voltage at this time were determined. Next, using the same test battery, it was energized to 4.2 V at a constant current of 1.25 mA (equivalent to 0.2 C). After reaching 4.2 V, it was charged at a constant voltage and continued until it reached 0.31 mA (0.05 C). It was then discharged to 3 V at a high rate of 12.5 mA (equivalent to 2 C). The 2 C retention rate (2 C capacity / 0.2 C capacity) of each test battery was calculated from the discharge capacity of the obtained test battery.

[0175] 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 m / 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.

[0176] The formation of a skeletal structure of mainly layered graphene was confirmed in the obtained auxiliary material of Example 2 by a transmission electron microscope (TEM) (FIG. 7), and the average secondary particle size was 2.1 μm.

[0177] Test cells of Example 2 were fabricated under conditions similar to those of Example 1.

[0178] 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.

[0179] 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, trade name: EC300) was used instead of the auxiliary material.

[0180] Comparative Example 3 Instead of the auxiliary material, single-walled carbon nanotubes (SSA: 600 m ２ A test battery was manufactured under the same conditions as in Example 1, except that the amount of the positive electrode added in the battery production was 97.95 wt % and the amount of the single-walled carbon nanotubes added was 0.05 wt %.

[0181] In addition to the above-mentioned ultra-small load / unload test, nitrogen adsorption / desorption measurements and Raman spectroscopy measurements were performed on the battery reaction auxiliary materials produced in Examples 1 and 2, the acetylene black used in Comparative Example 1, the ketjen black used in Comparative Example 2, and the single-walled carbon nanotubes used in Comparative Example 3, and the plastic deformation power, pore volume, and carbon layer stacking index were determined.

[0182] The pore volume of the auxiliary materials in the examples was measured by nitrogen adsorption / desorption using a specific surface area / pore distribution analyzer (BELSORP MAX, manufactured by BEL Japan) at -196°C. Prior to the measurement, the samples were 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.

[0183] The obtained nitrogen adsorption / desorption isotherm data was analyzed using the software Autosorb 1 (manufactured by Anton Paar Japan). In the case of a type I adsorption isotherm, the distribution of the electrolyte conducting pore diameters was analyzed with reference to a kernel calculated by density functional theory (DFT method) assuming slit-type pores. For samples showing a type IV adsorption isotherm, 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 FIG. 8.

[0184] The particle size distribution of the auxiliary materials of the examples was measured using a laser diffraction particle size distribution analyzer (MT3300EXII-SDC, manufactured by Microtrac-Bell Corporation). Specifically, each auxiliary material was added to water, and ethanol was further mixed therewith before measurement. After ultrasonic treatment for 5 minutes using a triple-frequency ultrasonic cleaner (VS-100III, manufactured by AS ONE Corporation), the particle size distribution was measured using the same device. The particle size distribution of the auxiliary material of Example 1 is shown in Figure 9.

[0185] The Raman spectrum of the auxiliary material of the example was measured using a micro-Raman spectrometer (DXR3 Micro Laser Raman | Thermo Fisher Scientific). The measurement was performed using a 532 nm (2 mW) laser with a grating of 900 lines / mm, a spectrometer aperture of 50 μmφ, an exposure time of 0.500 sec (2 Hz), and an accumulation count of 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.

[0186] Next, from the values ​​of the G band and 2D band obtained by measurement, I Ｇ　 / I ２Ｄ　 The carbon layer stacking index, expressed as

[0187] The 2C retention rate was determined as the battery discharge rate characteristics using the above-described positive electrode evaluation method for the test batteries of Examples 1 and 2 and Comparative Examples 1 to 3. The results are shown in Table 1. Furthermore, discharge curves for different currents during discharge using the test battery of Example 1 are shown in Figure 10.

[0188]

[0189] <Discussion> It was confirmed that the auxiliary material of this example had a higher high-rate discharge maintenance rate than the conductive auxiliary of the comparative example. Ｇ　 / I ２Ｄ　 The value of the carbon layer stacking index represented by the formula (1) suggests that the auxiliary material of the example has a graphene structure in at least a part of its structure.

[0190] The auxiliary material of this example has appropriate mechanical properties, i.e., plastic deformation, i.e., plastic deformation when subjected to a force above a certain level and elastic deformation when subjected to a force below a certain level. The auxiliary material of this example is formed from a three-dimensional framework made of graphene with a small number of layers. Therefore, between particles of the positive electrode material in the electrode, the elasticity allows the pore volume in the auxiliary material to remain and retain the electrolyte, while the high-quality graphene maintains electronic conductivity even when permanently deformed by plasticity. This property can be said to be one of the features of the auxiliary material of this example.

[0191] Experiment 2: Comparison of Battery Reaction Auxiliary Material and Existing Conductive Auxiliary Material Example 3 The amount of the auxiliary material of Example 1 added to the positive electrode was 0.5 wt %, and acetylene black (SSA: 65 m ２ Test batteries were manufactured under the same conditions as in Example 1, except that the amount of the ion-exchange polymer (DENKA BLACK, manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: Denka Black) added was 0.5 wt %, and battery evaluation was carried out.

[0192] Example 4 The amount of the auxiliary material of Example 1 added to the positive electrode was 0.5 wt %, and Ketjen Black (SSA: 800 ml) ２ Test batteries were manufactured under the same conditions as in Example 1, except that the amount of the ethylenediamine diamine nitrate (product name: EC300, manufactured by Lion Specialty Chemicals) added was 0.5 wt %, and battery evaluation was carried out.

[0193] Example 5: The amount of the cathode material added was 96.45 wt %, the amount of the auxiliary material added to the cathode in Example 1 was 0.5 wt %, and single-walled carbon nanotubes (SSA: 700 m ２ A test battery was manufactured under the same conditions as in Example 1, except that the amount of added 0.05 wt % of ZnO (CuO / g, outer diameter: 2 nm, length: 2-5 μm; manufactured by Guangzhou Hongwu Material Technology Co., Ltd.) was changed to 0.05 wt %, and battery evaluation was carried out.

[0194] Example 6 A battery reaction assisting material of Example 6 was obtained in the same manner as in Example 2, except that the template was not eluted (i.e., ceramic particles remained).

[0195] With respect to the obtained auxiliary material of Example 6, it was confirmed by a transmission electron microscope (TEM) that a layered graphene structure was mainly formed on the template particles and that the template was present inside ( FIG. 11 ).

[0196] 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 the auxiliary material of Example 6 added was 0.5 wt %, and battery evaluation was carried out.

[0197] The results of the battery evaluation for the test batteries of Examples 3 to 6 are shown in Table 2.

[0198]

[0199] <Discussion> When the auxiliary material of this example was mixed with the conductive additive used in the comparative examples and used in an electrode, the high-rate discharge maintenance rate was higher than when the conductive additive of the comparative examples was used alone (Comparative Examples 1 to 3). The size and shape vary depending on the type of conductive additive, but among the types of carbon black formed by agglomeration of nanoparticles, which are primary particles, ketjen black, which has micropores inside and a larger specific surface area than acetylene black, showed greater effectiveness. This is thought to be because ketjen black has many oxygen functional groups and is less likely to agglomerate with the auxiliary material of the present invention.

[0200] 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 a relatively large amount of electrolyte was present, resulting in good results.

[0201] Experiment 3: Investigation of synthesis conditions for the battery reaction auxiliary material of Example 1 For the auxiliary material of this example, a carbonaceous film is formed on ceramic by the T-CVD method, but auxiliary materials with carbonaceous film thicknesses and properties that differ are produced by varying the gas flow time while keeping the organic gas concentration in the mixed gas constant, as in Examples 1, 7 to 10 and Comparative Example 4. <Example 7> The battery reaction auxiliary material of Example 7 was obtained by the same operation as in Example 1, except that the mixed gas was flowed for 0.5 hours by the T-CVD method.

[0202] Example 8 A battery reaction auxiliary material of Example 8 was obtained in the same manner as in Example 1, except that the mixed gas was flowed for 1.0 hour by T-CVD.

[0203] Example 9 A battery reaction auxiliary material of Example 9 was obtained in the same manner as in Example 1, except that the mixed gas was flowed for 1.6 hours by T-CVD.

[0204] 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.

[0205] Example 11 A battery reaction auxiliary material of Example 11 was obtained in the same manner as in Example 1, except that the mixed gas was flowed for 5.0 hours by T-CVD.

[0206] Example 12 A carbonaceous film including a graphene structure was formed on a template by the T-CVD method of Example 2, and then cooled. After removal, the same procedure as in Example 2 was carried out except that the film was not crushed or classified, and was not heat-treated in an inert atmosphere, to obtain a battery reaction assisting material of Example 12.

[0207] Similar to Example 1, test batteries were fabricated using the battery reaction-promoting materials of Examples 7 to 12. Various tests and battery evaluations were performed on these batteries, and the results are shown in Table 3 and FIGS. 12, 13, and 14. Evaluations of Comparative Examples 1 to 3 are also shown in Table 3. FIG. 12 shows the relationship between the plastic deformation power and the 2C rate discharge retention ratio for the test batteries of Examples 1, 2, and 7 to 12 and the test batteries of Comparative Examples 1 to 3. The vertical axis of FIG. 12 represents the 2C rate discharge retention ratio, and the horizontal axis represents the plastic deformation power. FIG. 13 shows the relationship between the carbon layering index and the 2C rate discharge retention ratio for the test batteries of Examples 1, 2, and 7 to 12 and the test batteries of Comparative Examples 1 and 2. The vertical axis of FIG. 13 represents the 2C rate discharge retention ratio, and the horizontal axis represents the carbon layering index. FIG. 14 shows the relationship between the pore volume and the 2C rate discharge retention ratio for the test batteries of Examples 1, 2, and 7 to 12 and the test battery of Comparative Example 1. In FIG. 14, the vertical axis represents the 2C rate discharge maintenance ratio, and the horizontal axis represents the pore volume.

[0208]

[0209] 12 to 14, the high-rate characteristics remained favorable within the range of the evaluation test of the examples. This is thought to be because the range is one in which the balance between elastic deformation and plastic deformation is favorable, in other words, the balance between electronic conductivity and ionic conductivity is favorable.

[0210] Regarding the relationship between the carbon layering index and the 2C rate discharge retention ratio ( FIG. 13 ), it was confirmed that the carbon layering index in the test batteries of the examples was in the range of 0.3 to 5.8, and that all of them exhibited higher rate characteristics than the test batteries of Comparative Examples 1 and 2. This is thought to be due to the fact that the electrodes of the test batteries according to the examples contain graphene, which provides excellent electron transport.

[0211] Regarding the relationship between pore volume and 2C rate discharge retention ratio (FIG. 14), it was confirmed that all of the test batteries according to the examples exhibited higher rate characteristics compared to the test battery of Comparative Example 1. This is thought to be due to the fact that the larger the pore volume, the more the electrolyte solution containing dissolved lithium ions penetrates and the larger the retention amount, resulting in an excellent supply of ions during the battery reaction.

[0212] Experiment 4: Investigation of secondary particle size of battery reaction auxiliary material Example 13 A battery reaction auxiliary material of Example 13 was obtained in the same manner as in Example 1, except that the pulverization and classification treatment conditions were changed. The average particle size of the secondary particles of the obtained auxiliary material was 0.4 μm.

[0213] Example 14 A battery reaction auxiliary material of Example 14 was obtained in the same manner as in Example 1, except that the pulverization and classification treatment conditions were changed. The average particle size of the secondary particles of the obtained auxiliary material was 1.3 μm.

[0214] Example 15 A battery reaction auxiliary material of Example 15 was obtained in the same manner as in Example 1, except that the pulverization and classification treatment conditions were changed. The average particle size of the secondary particles of the obtained auxiliary material was 4.9 μm.

[0215] Example 16 A battery reaction auxiliary material of Example 16 was obtained in the same manner as in Example 1, except that the pulverization and classification treatment conditions were changed. The average particle size of the secondary particles of the obtained auxiliary material was 0.1 μm.

[0216] Example 17 A battery reaction auxiliary material of Example 17 was obtained in the same manner as in Example 1, except that the pulverization and classification treatment conditions were changed. The average particle size of the secondary particles of the obtained auxiliary material was 6.0 μm.

[0217] 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 pulverization and classification treatment conditions were changed. The average particle size of the secondary particles of the obtained auxiliary material was 6.8 μm.

[0218] As in Example 1, test batteries were manufactured using the battery reaction auxiliary materials of Examples 13 to 17 and Comparative Example 4. Various tests and battery evaluations were performed on the batteries, and the results are shown in Table 4 and FIG. 15. FIG. 15 is a graph showing the relationship between the average particle size of secondary particles in the auxiliary material and the 2C rate discharge retention rate for the test batteries of Examples 1 and 13 to 17 and the test battery of Comparative Example 4. The vertical axis of FIG. 15 represents the 2C rate discharge retention rate, and the horizontal axis represents the average particle size of secondary particles.

[0219]

[0220] <Discussion> From the results of Table 4 and Figure 15, it was confirmed that the high-rate characteristics remained favorable within the particle size range of the auxiliary material in Examples 1, 13 to 17, but that 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 intra-particle space responsible for ion retention became smaller, adversely affecting 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 performance could not be fully demonstrated.

[0221] Experiment 5: Investigation of the amount of added battery reaction auxiliary material of Example 1 Example 18 The test battery was fabricated in the same manner as in Example 1, except that the amount of added positive electrode material was 96.9 wt %, and the amount of added auxiliary material of Example 1 to the positive electrode was 0.1 wt %.

[0222] Example 19 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 wt %, and the amount of the auxiliary material of Example 1 added to the positive electrode was 0.5 wt %.

[0223] Example 20 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 wt % and the amount of the auxiliary material of Example 1 added to the positive electrode was 2.0 wt %.

[0224] Example 21 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 wt % and the amount of the auxiliary material of Example 1 added to the positive electrode was 4.0 wt %.

[0225] Comparative Example 5 The test battery was fabricated in the same manner as in Example 1, except that the amount of the positive electrode material added was 96.95 wt % and the amount of the auxiliary material of Example 1 added to the positive electrode was 0.05 wt %.

[0226] Comparative Example 6 The test battery was fabricated in the same manner as in Example 1, except that the amount of the positive electrode material added was 90.0 wt % and the amount of the auxiliary material of Example 1 added to the positive electrode was 7.0 wt %.

[0227] Charge-discharge tests were conducted on the test batteries of Examples 18 to 21 and Comparative Examples 5 and 6. Each test battery was charged at a constant current of 1.25 mA (equivalent to 0.2 C) up to 4.2 V. After reaching 4.2 V, it was charged at a constant voltage and continued to charge to 0.31 mA (0.05 C). It was then discharged at a constant current of 1.25 mA down to 3 V. The charge and discharge capacities were determined. The results are shown in Table 5 and Figure 16. Figure 16 is a graph showing the relationship between the amount of auxiliary material added and the charge-discharge capacity for the test batteries of Examples and Comparative Examples. The vertical axis of Figure 16 represents capacity, the horizontal axis represents the amount added, and the open circles (◯) represent charge capacity and the closed circles (●) represent discharge capacity.

[0228]

[0229] 16, it was confirmed that the high-rate characteristics of the test batteries remained favorable within the ranges of the amounts of auxiliary material added in Examples 1, and 18 to 21. Comparison with the results of the comparative examples showed that if the amount of auxiliary material added was too large, the content of the active material decreased, resulting in a decrease in the charge / discharge capacity of the electrode, and if the amount was too small, the auxiliary material was less likely to exhibit its function.

[0230] Experiment 6: Study of anode containing the battery reaction auxiliary material of Example 1 Example 22 Anode test batteries were manufactured using 1.0 wt% of the auxiliary material of Example 1 added to the anode. 97 wt% artificial graphite, 1 wt% of the auxiliary material of Example 1, 1 wt% carboxymethyl cellulose, and 1 wt% styrene butadiene rubber (SBR) were mixed and stirred uniformly using distilled water as the solvent to prepare an anode additive paste. The resulting paste was applied to a 20 μm thick copper foil, dried at 110°C, and then punched to a diameter of 15 mm and pressed at 30 kN to form a cathode.

[0231] The resulting negative electrode was dried in vacuum at 120°C, and then reconstituted in a glove box under an argon gas atmosphere with 1M LiPF ６ A 2032 size coin-type test battery with a metal Li counter electrode was fabricated using a solution (a 1:1 mixed solvent of ethylene carbonate (EC):diethyl carbonate (DEC)) as an electrolyte and a polypropylene separator.

[0232] Each test battery was energized to 0 V at a constant current of 1.23 mA (equivalent to 0.2 C). After reaching 0 V, it was charged at a constant voltage and continued until it reached 0.31 mA (0.05 C). It was then discharged to 1.5 V at a constant current of 1.23 mA. The discharge capacity at this time was determined. Next, using the same test battery, it was energized to 0 V at a constant current of 1.23 mA (equivalent to 0.2 C). After reaching 0 V, it was charged at a constant voltage and continued until it reached 0.31 mA (0.05 C). It was then discharged to 1.5 V at a high rate of 12.3 mA (equivalent to 2 C). The 2 C retention rate (2 C capacity ÷ 0.2 C capacity) was calculated from the discharge capacity of the test battery obtained in the above evaluation test. Evaluation of the resulting negative electrode battery revealed a retention rate of 0.45 at 2 C discharge.

[0233] Comparative Example 7 A negative electrode test battery was produced in the same manner as in Example 22, except that acetylene black (trade name: Denka Black, manufactured by Denki Kagaku Kogyo Kogyo Co., Ltd.) was used as a conductive additive instead of the auxiliary material used in Example 1, and the amount of this conductive additive added to the negative electrode was 1.0 wt %. Evaluation of the resulting negative electrode battery revealed that the retention rate during 2 C discharge was 0.23.

[0234] <Consideration> From the above results, it was confirmed that the auxiliary material of the present invention effectively acts in the negative electrode.

[0235] 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. This is due to the high electronic conductivity of the auxiliary material of this embodiment. That is, compared to the conductive additive used in the comparative example, the auxiliary material of this embodiment has a highly conductive carbonaceous structure containing graphene as its skeleton and has spaces within the particles that can hold an electrolyte. The discharge reaction is a reaction in which lithium ions released during charging return to the positive electrode material. When discharge begins, electrons flow from the external circuit to the positive electrode, and the electrons and lithium ions bond with each other and return to the crystalline structure sites of the positive electrode, restoring the bonding state before charging. In other words, the bonding between lithium ions and electrons and the phase change in the crystalline structure of the positive electrode occur simultaneously. The phase change can be observed from a change in voltage. The "simultaneity" of this phase change is important for the high high-rate discharge retention rate, and it was confirmed that the auxiliary material of this example can achieve this "simultaneity."

[0236] Furthermore, the auxiliary material of the present embodiment present in the electrode is thought to be able to suppress leakage of the electrolyte present inside the particles (electrolyte motion) due to the highly flexible carbonaceous skeleton containing graphene in response to the expansion pressure of the electrode that occurs during charging, thereby maintaining a state in which the ions necessary for the next discharge can be smoothly supplied. The auxiliary material of the present embodiment is a material that can uniformly retain and maintain the electrolyte in the electrode, and is expected to have a high potential for mitigating the effects of electrolyte movement due to internal electrode stress in larger practical batteries (cylindrical, prismatic, pouch, CTP, blade, etc.), thereby suppressing cycle degradation.

[0237] The present invention is not limited to the above-described embodiments and examples, and various design modifications within the scope of the present invention are included in the present invention.

[0238] REFERENCE SIGNS LIST 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

1. A battery reaction auxiliary material comprising a plurality of primary particles containing carbonaceous matter and having a three-dimensional skeleton including an internal space, wherein a portion of the plurality of primary particles are adhered to each other to form secondary particles, and the secondary particles are plastically deformed in an extremely small load / unload test, and a portion of the secondary particles does not return to their original shape.

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

3. The battery reaction auxiliary material according to claim 1, having a plastic deformation power of 5% or more and 92% or less.

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

5. The battery reaction auxiliary material according to claim 1, having a pore volume measured by a gas adsorption method of 1 cc / g or more and 6 cc / g or less.

6. The battery reaction auxiliary material according to claim 1, having a carbon layer stacking index of 0.4 or more and 5 or less.

7. The battery reaction assisting material according to claim 1, wherein the secondary particles are hollow and solid particles are mixed with the secondary particles.

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

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

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

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

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

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

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

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

16. A method for producing a positive electrode or a negative electrode for a lithium ion battery, comprising: a step of mixing a battery reaction auxiliary material containing carbonaceous primary particles having a three-dimensional skeleton including an internal space and secondary particles formed by fixing a plurality of the primary particles together, with a binder resin and a solvent to prepare a slurry; and a step of applying the slurry onto a current collector, drying the current collector, and performing a press process to obtain a positive electrode or a negative electrode, wherein, during the press process, the shapes of some of the primary particles and the secondary particles are left deformed, and the shapes of another part of the primary particles and the secondary particles are restored.

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