Electrode for lithium ion secondary battery and lithium ion secondary battery

Abstract

Provided herein is an electrode for a lithium-ion secondary battery and a lithium-ion secondary battery using the electrode, which can realize a battery in which the reduction in output due to repeated charge and discharge is still small even when the volume energy density is high and the amount of electrolyte retained by the electrode is small. A high dielectric oxide solid and a high-concentration electrolyte coexist in the gap between the active material particles inside the electrode. Specifically, an electrode for a lithium-ion secondary battery comprises an electrode active material, a high dielectric oxide solid, and an electrolyte, wherein the high dielectric oxide solid and the electrolyte are arranged in the gap formed between the particles of the electrode active material, and the concentration of the lithium salt in the electrolyte is set to a range of 0.5 to 3.0 mol / L.

Description

Technical Field

[0001] The present invention relates to an electrode for a lithium ion secondary battery and a lithium ion secondary battery using the electrode. Background Art

[0002] Currently, lithium ion secondary batteries are widely used as secondary batteries with high energy density. A lithium ion secondary battery using a liquid as an electrolyte has a structure in which a separator is present between a positive electrode and a negative electrode and is filled with a liquid electrolyte (electrolyte).

[0003] Since the electrolyte of a lithium ion secondary battery is generally a flammable organic solvent, safety against heat is particularly problematic. Therefore, a solid battery using a flame-retardant solid electrolyte instead of an organic liquid electrolyte has been proposed.

[0004] Such lithium ion secondary batteries have various requirements depending on their use. For example, when used in automobiles, it is desired to have a battery that has a high energy density and has little reduction in output characteristics even after repeated charge and discharge.

[0005] However, the output characteristics of lithium-ion secondary batteries generally tend to decrease due to repeated charge and discharge. This is because the electrolyte decomposes due to repeated charge and discharge, forming a passivation film on the electrode, and the internal resistance gradually increases.

[0006] In this regard, a method has been proposed in which at least one metal element selected from Ni, Co and Mn and W are used as a positive electrode active material, and at least one of a difluorophosphate and a monofluorophosphate is mixed in an electrolyte solution (see Patent Document 1).

[0007] In addition, a method has been proposed in which at least one metal element among Ni, Co and Mn and W are used as a positive electrode active material, and difluorobisoxalylphosphate is mixed in an electrolyte solution (see Patent Document 2).

[0008] According to the techniques described in Patent Documents 1 and 2, excellent output characteristics can be maintained within a usage range of a low temperature of about 0°C to a high temperature of about 60°C.

[0009] In addition, in order to further improve the volume energy density of lithium-ion secondary batteries, which is one of the required characteristics, a method of increasing the packing density of electrode active materials is listed. However, if the packing density of electrode active materials is increased, the gap between the active material particles inside the electrode will be reduced, and the amount of electrolyte retained by the electrode will be relatively reduced.

[0010] Furthermore, in an electrode having a high packing density of the electrode active material, the electrode surface pressure increases due to expansion of the negative electrode active material during charge and discharge, and thus the electrolyte present between the electrode active materials is squeezed out, which tends to cause the electrolyte to dry up.

[0011] Moreover, if charging and discharging are repeated when the amount of electrolyte retained by the electrode is insufficient or unevenly distributed, the resistance increases and potential deviation occurs due to the lack of lithium ions. As a result, the solvent constituting the electrolyte is easily decomposed, and a non-conductive film is easily formed on the electrode.

[0012] In the above-mentioned case, even when the amount of electrolyte retained by the electrode is small, the lithium ion secondary battery has not been able to fully realize a small decrease in output due to repeated charge and discharge.

[0013] [Prior art literature]

[0014] (Patent Document)

[0015] Patent Document 1: Japanese Patent Application Publication No. 2013-069580

[0016] Patent Document 2: Japanese Patent Application Publication No. 2014-183031 Summary of the invention

[0017] [Problems to be solved by the invention]

[0018] The present invention is completed in view of the above situation, and its purpose is to provide an electrode for a lithium ion secondary battery, and a lithium ion secondary battery using the electrode, which can realize a battery that can suppress the reduction in output caused by repeated charge and discharge even when the volume energy density is high and the amount of electrolyte retained by the electrode is small.

[0019] [Technical means to solve the problem]

[0020] The inventors of the present invention considered that if the electrolyte and the high dielectric solid particles coexist, the electrolyte can be prevented from being unevenly distributed in the electrode, and the ionic conductivity can also be improved, so that the increase in the resistance inside the battery during repeated charge and discharge can be suppressed, and they have conducted serious research and discussion on this. Then, they found that if the high dielectric oxide and the high-concentration electrolyte are dispersed in the gaps between the active material particles inside the electrode, the above-mentioned problems can be solved, and thus the present invention was completed.

[0021] That is, the present invention provides an electrode for a lithium-ion secondary battery, comprising an electrode active material, a high dielectric solid oxide, and an electrolyte, wherein the high dielectric solid oxide and the electrolyte are arranged in the gaps formed between particles of the electrode active material, and the concentration of the lithium salt in the electrolyte is 0.5 to 3.0 mol / L.

[0022] In cross-sectional observation of the lithium ion secondary battery electrode, the ratio of the cross-sectional area of ​​the high dielectric oxide solid to the total cross-sectional area of ​​the gaps may be 1 to 22%.

[0023] The aforementioned high dielectric oxide solid may be an oxide solid electrolyte.

[0024] The aforementioned oxide solid electrolyte may be selected from Li7La3Zr2O 12 (LLZO), Li 6.75 Ln3Z 1.75 Ta 0.25 O 12 (LLZTO), Li 0.33 La 0.56 TiO3(LLTO), Li 1.3 Al 0.3 Ti 1.7 (PO4)3(LATP), and Li 1.6 Al 0.6 Ge 1.4 At least one of the group consisting of (PO4)3(LAGP).

[0025] The volume filling rate of the electrode active material may be 60% or more relative to the total volume of the electrode composite material constituting the electrode.

[0026] The thickness of the lithium ion secondary battery electrode may be 40 μm or more.

[0027] The aforementioned electrode for lithium ion secondary battery may be a positive electrode.

[0028] The aforementioned electrode for lithium ion secondary battery may be a negative electrode.

[0029] The present invention also provides a lithium ion secondary battery comprising the above-mentioned lithium ion secondary battery electrode and an electrolyte.

[0030] (Effects of the Invention)

[0031] According to the lithium ion secondary battery electrode of the present invention, even when the thickness of the electrode is large and the packing density of the electrode active material is large, the diffusion of lithium ions inside the electrode can be suppressed and the increase of resistance can be suppressed. As a result, a lithium ion secondary battery can be realized: even when the volume energy density is high and the amount of electrolyte retained by the electrode is small, the reduction of output caused by repeated charge and discharge can be suppressed.

[0032] In addition, usually, when the concentration of lithium salts in the electrolyte is high, due to the increase in viscosity of the electrolyte, the permeability of the electrolyte to the electrode is reduced. However, the electrode for lithium ion secondary battery of the present invention has not only electrolyte but also high dielectric oxide solid in the gap formed between the particles of the electrode active material, so the permeability of the electrolyte is improved. As a result, the uniformity of the electrolyte maintained in the electrode is improved. And then, the immersion time of the electrolyte in the electrode can be shortened, and productivity can be improved.

[0033] In addition, usually, when the concentration of lithium salt in the electrolyte is high, since the meeting of lithium ions and anions will occur, the ionic conductivity tends to decrease in the electrolyte with a high concentration of lithium salt and increased viscosity. However, the electrode for lithium ion secondary battery of the present invention has not only electrolyte but also high dielectric oxide solid in the gap formed between the particles of the electrode active material, therefore, the meeting of lithium ions and anions can be suppressed by the dielectric effect. As a result, even when using an electrolyte containing a high concentration of lithium salt, a low resistance battery can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A diagram showing one embodiment of the lithium ion secondary battery of the present invention is shown.

[0035] Figure 2 The graph shows the relationship between the lithium salt concentration and the resistance value of the lithium ion secondary batteries of Examples 1 to 4 of the present invention.

[0036] Figure 3 The graph shows the relationship between the lithium salt concentration and the resistance value of the lithium ion secondary batteries of Comparative Examples 1 to 4 of the present invention.

[0037] Figure 4 The graph shows the capacity retention rates of the lithium ion secondary batteries of Examples 1 to 4 of the present invention and Comparative Examples 1 to 4. DETAILED DESCRIPTION

[0038] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments.

[0039] <Electrodes for lithium-ion secondary batteries>

[0040] The lithium ion secondary battery electrode of the present invention comprises an electrode active material, a high dielectric solid oxide, and an electrolyte. The high dielectric solid oxide and the electrolyte are disposed in gaps formed between particles of the electrode active material, and the concentration of the lithium salt in the electrolyte is 0.5 to 3.0 mol / L.

[0041] The electrode for lithium ion secondary battery of the present invention can be a positive electrode for lithium ion secondary battery or a negative electrode for lithium ion secondary battery. In either case, the structure of the present invention can be applied to obtain the effect of the present invention.

[0042] In addition, the composition of the electrode for lithium ion secondary battery of the present invention is not particularly limited, and the following composition can be cited, for example: an electrode composite material layer composed of an electrode composite material containing an electrode active material is stacked on an electrode current collector, and an electrolyte is impregnated in the electrode composite material layer. The constituent elements of the present invention, namely, the electrode active material and the high dielectric oxide solid are included in the electrode composite material layer as necessary components, and known components such as a conductive aid and a binder may also be optionally included.

[0043] [Current Collector]

[0044] The electrode current collector in the electrode for lithium ion secondary batteries of the present invention is not particularly limited, and a known current collector used in lithium ion secondary batteries can be used.

[0045] Examples of the positive electrode current collector material include metal materials such as SUS, Ni, Cr, Au, Pt, Al, Fe, Ti, Zn, and Cu. Examples of the negative electrode current collector material include SUS, Ni, Cu, Ti, Al, calcined carbon, conductive polymers, conductive glass, and Al-Cd alloys.

[0046] The shape of the electrode current collector may be, for example, a foil, a plate, a mesh, etc. The thickness thereof is not particularly limited and may be, for example, 1 to 20 μm, and may be appropriately selected as required.

[0047] [Electrode active material]

[0048] The electrode active material contained in the electrode for lithium ion secondary battery of the present invention is not particularly limited as long as it is a material that can absorb and release lithium ions, and a known substance as an electrode active material for lithium ion secondary batteries can be used.

[0049] (Positive electrode active material)

[0050] When the electrode for lithium ion secondary battery of the present invention is a positive electrode for lithium ion secondary battery, as the positive electrode active material layer, for example, LiCoO2, LiCoO4, LiMn2O4, LiNiO2, LiFePO4, lithium sulfide, sulfur, etc. can be listed. As the positive electrode active material, a material that exhibits a higher potential than the negative electrode can be selected from the materials that can constitute the electrode.

[0051] When the electrode for lithium ion secondary battery of the present invention is a negative electrode for lithium ion secondary battery, as the negative electrode active material, for example, metal lithium, lithium alloy, metal oxide, metal sulfide, metal nitride, silicon oxide, carbon materials such as silicon and graphite, etc. can be listed. As the negative electrode active material, a material that exhibits a lower potential than the positive electrode can be selected from the materials that can constitute the electrode.

[0052] (Electrode composite material layer)

[0053] In the lithium ion secondary battery electrode of the present invention, the electrode composite material layer containing the electrode active material as an essential component may be formed on at least one side of the current collector or may be formed on both sides, and may be appropriately selected according to the type and structure of the target lithium ion secondary battery.

[0054] In addition, the electrode composite material layer comprises the electrode active material and the high dielectric oxide solid as the constituent elements of the present invention as necessary components, and may also comprise known components such as conductive aids, adhesives as arbitrary components. By first allocating the high dielectric oxide solid in the gap between the particles of the electrode active material to the electrode composite material, it is possible to easily configure between the particles of the electrode active material in the formed electrode composite material layer. In addition, if the high dielectric oxide solid is attached to the conductive aid, adhesive, etc. in advance, and then mixed with the electrode active material to make the paste forming the electrode composite material, the dielectric solid powder can be more evenly configured in the gap between the particles of the electrode active material.

[0055] [Volume filling rate of electrode active material]

[0056] Preferably, the volume filling rate of the electrode active material in the electrode for lithium ion secondary battery of the present invention is more than 60% relative to the total volume of the electrode composite material constituting the electrode. If the volume filling rate of the electrode active material is more than 60%, the gap rate formed between the particles of the electrode active material will be less than 40%. Therefore, since the electrode for lithium ion secondary battery with a smaller gap rate is formed, an electrode with a larger volume energy density can be formed. When the volume filling rate of the electrode active material is more than 60%, a high volume energy density of, for example, a monomer of more than 500Wh / L can be achieved.

[0057] Furthermore, in the present invention, it is further preferred that the volume filling rate of the electrode active material is 65% or more, and most preferably 70% or more, relative to the total volume of the electrode composite material constituting the electrode.

[0058] [gap]

[0059] The electrode for lithium ion secondary battery of the present invention has a gap between the particles of the electrode active material. The gap formed between the particles of the electrode active material can be controlled by the filling rate of the electrode active material and is related to the density of the electrode composite material layer. In the present invention, it is characterized in that a high dielectric oxide solid and an electrolyte are arranged in the gap between the particles of the electrode active material. In addition, a resin adhesive forming an adhesive, a carbon material for imparting electronic conductivity, etc. can also be arranged in the gap.

[0060] By configuring a high dielectric oxide solid and an electrolyte in the gaps between the particles of the electrode active material, the lithium ion secondary battery electrode of the present invention can suppress the reduction of the diffusion of lithium ions in the electrode and the increase of the resistance, and can realize an electrode with a high packing density of the electrode active material. As a result, a lithium ion secondary battery can be realized as follows: even when the volume energy density is high and the amount of electrolyte retained by the electrode is small, the reduction of the output caused by repeated charge and discharge can be suppressed.

[0061] In addition, since the lithium ion secondary battery electrode of the present invention has not only electrolyte but also high dielectric oxide solid in the gap between the particles of the electrode active material, the permeability of the electrolyte is improved. As a result, the uniformity of the electrolyte in the electrode is improved. In addition, the immersion time of the electrolyte in the electrode can be shortened, and productivity can be improved.

[0062] Furthermore, since the lithium ion secondary battery electrode of the present invention contains not only electrolyte but also high dielectric oxide solid in the gaps between the particles of the electrode active material, the dielectric effect can suppress the convergence of lithium ions and anions. As a result, even when using an electrolyte containing a high concentration of lithium salt, the resistance can be reduced.

[0063] (Cross-sectional area occupancy of high dielectric oxide solid in gap)

[0064] In the lithium ion secondary battery electrode of the present invention, regarding the occupancy rate of the high dielectric oxide solid in the gap between the particles of the electrode active material, in the cross-sectional observation of the lithium ion secondary battery electrode, the ratio of the cross-sectional area of ​​the high dielectric oxide solid relative to the total cross-sectional area of ​​the gap is preferably in the range of 1 to 22%. If it is within this range, the effects of reducing resistance and improving durability can be obtained at the same time.

[0065] Here, the gap in the present invention refers to the region outside the region occupied by active material in the electrode composite material layer as mentioned above, and can also be configured in the gap: a resin adhesive forming an adhesive, a carbon material for imparting electronic conductivity, etc. When calculating the occupancy rate of the high dielectric oxide solid in the gap portion, the cross-section observation of the lithium ion secondary battery electrode is implemented. The cross-section observation is carried out in the following steps.

[0066] (Method of cross-sectional observation)

[0067] - The cross section of the electrode composite material layer was prepared by ion milling and observed by SEM.

[0068] - The imaging range of the cross-sectional SEM is selected to be approximately 80% or more of the thickness direction (vertical direction) of the electrode with respect to the electrode composite material layer.

[0069] - Set the shooting magnification to about 5000x to 10000x and shoot it in multiple images.

[0070] -Images in the planar direction (left-right direction) are captured in the same manner as in the up-down direction.

[0071] - Combined with the obtained images, the brightness of the reflected electron image is binarized, and the area occupancy of each component constituting the electrode composite material is derived from the brightness distribution curve.

[0072] - Regarding the area occupancy, the active material region and the oxide solid region are set, and the dark area other than that is set as the residual space. The residual space contains resin binders, conductive additives, etc., and also includes pores impregnated with electrolyte.

[0073] The reason why the cross-sectional area occupancy rate of the high dielectric oxide solid in the gap is preferably in the above range is due to the dielectric constant of the high dielectric oxide solid itself. Specifically, if the dielectric constant of the high dielectric oxide solid increases, the influence on the electrolyte increases, and therefore, the cross-sectional area occupancy rate of the high dielectric oxide solid is preferably close to 1%. On the contrary, when the dielectric constant of the high dielectric oxide solid is small, the cross-sectional area occupancy rate of the high dielectric oxide solid is preferably close to 22%.

[0074] If the cross-sectional area occupancy rate of the high dielectric oxide solid is less than 1%, the dielectric effect of the high dielectric oxide solid is reduced, and only the same effect as the ordinary electrolyte can be obtained. On the other hand, if the cross-sectional area occupancy rate of the high dielectric oxide solid is greater than 22%, the electrolyte in the gap is relatively reduced, the liquid is insufficient, resulting in a reduction in the lithium ion movement path, and the internal resistance is increased, making it difficult to obtain the effect of reducing resistance.

[0075] [High dielectric oxide solids]

[0076] In the lithium ion secondary battery electrode of the present invention, the high dielectric oxide solid disposed in the gap between the particles of the electrode active material is not particularly limited if it is an oxide with a high dielectric constant, and preferably an oxide solid electrolyte. If it is an oxide solid electrolyte, cheap crystals can be made, and the electrochemical oxidation resistance and reduction resistance are excellent. In particular, the true specific gravity of the Li-based oxide is small, and the battery weight will not be increased even if it is deployed in the electrode, so it is preferred.

[0077] As the oxide solid electrolyte, for example, Li7La3Zr2O 12 (LLZO), Li 6.75 LqCy 1.75 Ta 0.25 O 12 (LLZTO), Li 0.33 La 0.56 TiO3(LLTO), Li 1.3 Al 0.3 Ti 1.7 (PO4)3(LATP), and Li 1.6 Al 0.6 Ge 1.4 (PO4)3(LAGP), in the present invention, it is preferred to use at least one selected from the group consisting of these materials.

[0078] (Particle size)

[0079] As a preferred particle size of a high dielectric oxide solid, there is no particular limitation, preferably above 0.1 μm, and below about 10 μm below the particle size of the active material. If the particle size is too small, it will adhere to the surface of the electrode active material, hindering the electronic conductivity and causing the battery resistance to increase. Furthermore, since the anisotropy of the crystal structure of the oxide particles is reduced and the dielectric constant is reduced, it is difficult to obtain a sufficient effect. On the other hand, if the particle size is too large, it will not be configured in the gap, therefore, it will hinder the improvement of the filling rate of the active material in the electrode body.

[0080] [Electrolyte]

[0081] In the electrode for lithium ion secondary battery of the present invention, the electrolyte disposed in the gap between the particles of the electrode active material is not particularly limited, and a known electrolyte can be used as the electrolyte of the lithium ion secondary battery. In addition, the electrolyte used when forming a secondary battery using the electrode for lithium ion secondary battery of the present invention may be the same as or different from the electrolyte disposed in the electrode for lithium ion secondary battery of the present invention.

[0082] (Solvent)

[0083] As the solvent used in the electrolyte, a solvent that forms a general non-aqueous electrolyte can be used. For example, solvents with cyclic structures such as ethylene carbonate (EC) and propylene carbonate (PC) and solvents consisting of chain structures such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) can be listed. In addition, partially fluorinated fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC) etc. can also be used.

[0084] Furthermore, a known additive may be mixed into the electrolyte solution. Examples of the additive include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), propane sultone (PS), and fluoroethylene carbonate (FEC).

[0085] The electrolyte may also contain an ionic liquid. Examples of the ionic liquid include pyrrolidinium, piperidinium, and imidazolium ions composed of quaternary ammonium cations.

[0086] In the present invention, it is expected that a solvent with a high relative dielectric constant such as EC or PC and a solvent with a low viscosity such as DMC or EMC are used in combination. By using a solvent with a high relative dielectric constant, the dissociation degree of the lithium salt is improved, and a high concentration of lithium salt can be used. In addition, if only a solvent with a high relative dielectric constant is used, the viscosity increases and the ion conductivity decreases. Therefore, it is necessary to appropriately mix a solvent with a low viscosity to adjust the viscosity. As a composition of the electrolyte, the amount of a solvent with a high relative dielectric constant such as EC or PC is preferably more than 20 volume % and less than 40 volume %. It is more expected to be more than 25 volume % and less than 35 volume %.

[0087] (Lithium Salt)

[0088] In the electrode for lithium ion secondary battery of the present invention, the lithium salt contained in the electrolyte disposed in the gap between the particles of the electrode active material is not particularly limited, and examples thereof include LiPF6, LiBF4, LiClO4, LiN(SO2CF3), LiN(SO2C2F5)2, LiCF3SO3, etc. Among them, LiPF6, LiBF4, or a mixture thereof having high ion conductivity and high dissociation degree is preferred.

[0089] In addition, the concentration of the lithium salt contained in the electrolyte disposed in the gaps between the particles of the electrode active material is in the range of 0.5 to 3.0 mol / L. When it is less than 0.5 mol / L, the ion conductivity decreases, while when it exceeds 3.0 mol / L, the ion conductivity also decreases due to the increase in viscosity, so it is difficult to fully obtain the effect of the solid oxide.

[0090] Furthermore, in the present invention, the concentration of the lithium salt contained in the electrolyte disposed in the gaps between the particles of the electrode active material is preferably in the range of 1.0 to 3.0 mol / L, and most preferably in the range of 1.2 to 2.2 mol / L in order to improve the output performance after the endurance test.

[0091] Generally, when the lithium salt concentration in the electrolyte is high, the viscosity of the electrolyte increases, and therefore, the permeability of the electrolyte into the electrode decreases. However, since the electrode for lithium ion secondary battery of the present invention contains not only the electrolyte but also the high dielectric oxide solid in the gap formed between the particles of the electrode active material, the permeability of the electrolyte increases.

[0092] In addition, generally, when the concentration of lithium salt in the electrolyte is high, lithium ions and anions will converge, so the ionic conductivity tends to decrease. However, it is considered that since the electrode for lithium ion secondary battery of the present invention has not only electrolyte but also high dielectric oxide solid in the gap formed between the particles of the electrode active material, the ionic conductivity is improved.

[0093] Therefore, in the lithium ion secondary battery electrode of the present invention, the electrolyte disposed in the gaps between the particles of the electrode active material can use an electrolyte having a higher concentration than the lithium salt concentration in the electrolyte used in a common lithium ion secondary battery. Even when a high concentration electrolyte is used, the productivity can be improved due to the shortened immersion time of the electrolyte in the electrode, and a battery with a high initial capacity can be obtained.

[0094] Therefore, in the electrode for lithium ion secondary batteries of the present invention, the effect of the present invention can be more effectively exerted in the case of an electrolyte solution containing a high concentration of lithium salt.

[0095] (Solvent)

[0096] The solvent contained in the electrolyte disposed in the gap between the particles of the electrode active material is not particularly limited, and the solvent used in the electrolyte of the lithium ion secondary battery can be appropriately used. Examples of aprotic solvents include carbonates, esters, ethers, nitriles, sulfones and lactones. Specifically, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), tetrahydrofuran (THF), 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile (AN), propionitrile, nitromethane, N,N-dimethylformamide (DMF), dimethyl sulfoxide, cyclopentane, γ-butyrolactone, etc.

[0097] In addition, the lithium ion secondary battery electrode of the present invention is as mentioned above, because in the gap formed between the particles of the electrode active material, not only there is electrolyte but also there is high dielectric oxide solid, therefore, by dielectric effect, the meeting of lithium ion and negative ion is suppressed.Therefore, the ratio of cyclic carbonates such as ethylene carbonate (EC) can also be reduced, the ratio of low-viscosity linear carbonates is increased, and a low-viscosity electrolyte is used.

[0098] [thickness]

[0099] The thickness of the electrode for lithium ion secondary battery of the present invention is not particularly limited, for example, preferably above 40 μm. When the thickness is above 40 μm and the volume filling rate of the electrode active material is above 60%, the obtained electrode for lithium ion secondary battery forms a high-density electrode. Moreover, the volume energy density of the manufactured battery cell can also reach above 500Wh / L.

[0100] <Method for producing electrode for lithium ion secondary battery>

[0101] The manufacturing method of the electrode for the lithium ion secondary battery of the present invention is not particularly limited, and the usual method in the art can be used. For example, the following method can be cited: an electrode paste is applied to an electrode collector, the electrode paste is used as an electrode composite material, and contains an electrode active material and a high dielectric oxide solid as essential components; after drying, it is rolled and then immersed in an electrolyte. At this time, by changing the pressing pressure during rolling, the volume filling rate of the electrode active material (that is, the gap rate of the gap formed between the particles of the electrode active material) can be controlled.

[0102] As a method for applying the electrode paste to the electrode current collector, a known method may be used, such as roll coating with a coating roll, screen coating, doctor blade coating, spin coating, bar coating, and the like.

[0103] <Lithium-ion secondary battery>

[0104] The lithium ion secondary battery of the present invention comprises the lithium ion secondary battery electrode of the present invention and an electrolyte. The lithium ion secondary battery electrode of the present invention may be a positive electrode or a negative electrode, or both the positive electrode and the negative electrode may be used as the lithium ion secondary battery electrode of the present invention.

[0105] Figure 1 One embodiment of the lithium ion secondary battery of the present invention is shown. Figure 1The lithium-ion secondary battery 10 shown comprises: a positive electrode 4, comprising a positive electrode composite material layer 3 formed on a positive electrode collector 2; a negative electrode 7, comprising a negative electrode composite material layer 6 formed on a negative electrode collector 5; a separator 8, electrically insulating the positive electrode 4 and the negative electrode 7; an electrolyte 9; and a container 1, accommodating the positive electrode 4, the negative electrode 7, the separator 8, and the electrolyte 9.

[0106] In the container 1, the positive electrode composite material layer 3 and the negative electrode composite material layer 6 are opposite to each other in a manner of sandwiching a separator 8, and an electrolyte 9 is stored below the positive electrode composite material layer 3 and the negative electrode composite material layer 6. Moreover, the end of the separator 8 is immersed in the electrolyte 9. The positive electrode 4 or the negative electrode 7, or both, is an electrode for a lithium ion secondary battery of the present invention, comprising an electrode active material, a high dielectric oxide solid, and an electrolyte, and the high dielectric oxide solid and the electrolyte are arranged in the gap formed between the particles of the electrode active material.

[0107] [Positive and negative electrodes]

[0108] In the lithium ion secondary battery of the present invention, the positive electrode or the negative electrode, or both the positive electrode and the negative electrode are set as the electrode for the lithium ion secondary battery of the present invention. In addition, when only the positive electrode is set as the electrode for the lithium ion secondary battery of the present invention, as the negative electrode, a metal, a carbon material, etc. used as a negative electrode active material can be directly used as a sheet material.

[0109] [Electrolyte]

[0110] The electrolyte used in the lithium ion secondary battery of the present invention is not particularly limited, and a known electrolyte can be used as the electrolyte of the lithium ion secondary battery. In addition, the electrolyte used when forming the secondary battery and the electrolyte configured on the lithium ion secondary battery electrode of the present invention can be the same or different.

[0111] <Method for producing lithium-ion secondary battery>

[0112] The method for producing the lithium ion secondary battery of the present invention is not particularly limited, and a common method in the technical field can be used.

[0113] Example

[0114] Next, the present invention will be described in further detail based on Examples, but the present invention is not limited thereto.

[0115] <Example 1>

[0116] [Production of positive electrode]

[0117] Acetylene black as a conductive additive and Lithium ion as an oxide solid electrolyte 1.3 Al 0.3 Ti 1.7(PO4)3(LATP) was mixed and dispersed using a rotation / revolution mixer to obtain a mixture. Then, polyvinylidene fluoride (PVDF) as a binder and LiNi as a positive electrode active material were added to the obtained mixture. 0.6 Co 0.2 Mn 0.2 O2 (NCM622, D50 = 12 μm), using a planetary mixer for dispersion treatment, to obtain a positive electrode composite material mixture. In addition, the ratio of each component in the positive electrode composite material mixture is calculated by mass ratio, positive electrode active material: LATP: conductive aid: resin binder (PVDF) = 92.1:2:4.1:1.8, that is, the amount of LATP added to 100 parts by mass of the positive electrode composite material mixture is 2 parts by mass. Next, the obtained positive electrode composite material mixture is dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode composite material paste.

[0118] A 12 μm thick aluminum foil was prepared as a current collector, and the prepared positive electrode composite material paste was applied to one side of the current collector, dried at 120° C. for 10 minutes, pressed with a roller press at a line pressure of 1 t / cm, and then dried in a vacuum at 120° C. to prepare a positive electrode for a lithium ion secondary battery. In addition, the prepared positive electrode was punched to 30 mm×40 mm for use.

[0119] The thickness of the electrode composite material layer in the obtained positive electrode for lithium ion secondary battery was 68 μm. In addition, the volume filling rate of the electrode active material relative to the total volume of the electrode composite material was 65.9%. The measurement method is described below.

[0120] (Method for measuring thickness of electrode composite material layer)

[0121] The obtained positive electrode for lithium ion secondary battery is a current collector foil and an electrode composite material layer formed integrally. These thicknesses are combined and measured with a thickness gauge, and the thickness of the electrode composite material layer is obtained by subtracting the thickness of the current collector foil.

[0122] (Method for calculating the volume filling rate of the electrode active material relative to the total volume of the electrode composite material)

[0123] After making the positive electrode for lithium-ion secondary batteries, the dry weight (grain weight) of the electrode composite material layer is measured in advance, and the density of the electrode composite material is calculated from the thickness of the electrode after pressing. 3 ), find the occupied volume of each component in the electrode composite material, and calculate the volume filling rate of the electrode active material relative to all of these components. In addition, the true specific gravity of the positive electrode active material used in this embodiment is 4.73g / cm3 .

[0124] [Production of negative electrode]

[0125] Sodium carboxymethyl cellulose (CMC) as a binder and acetylene black as a conductive aid are mixed and dispersed using a planetary mixer to obtain a mixture. Artificial graphite (AG, D50 = 12 μm) as a negative electrode active material is mixed into the obtained mixture, and a planetary mixer is used to perform dispersion treatment again to obtain a mixture for a negative electrode composite material. Next, the obtained mixture for a negative electrode composite material is dispersed in N-methyl-2-pyrrolidone (NMP), and styrene butadiene rubber (SBR) as a binder is added to prepare a negative electrode composite material paste in a mass ratio of negative electrode active material: conductive aid: styrene butadiene rubber (SBR): binder (CMC) = 96.5:1:1.5:1.

[0126] A copper foil with a thickness of 12 μm was prepared as a current collector, and the prepared negative electrode composite material paste was applied to one side of the current collector, dried at 100° C. for 10 minutes, pressed with a roller press at a line pressure of 1 t / cm, and then dried in a vacuum at 120° C. to prepare a negative electrode for a lithium ion secondary battery. In addition, the prepared negative electrode was punched to 34 mm×44 mm for use.

[0127] The thickness of the electrode composite material layer of the obtained negative electrode for lithium ion secondary battery was determined by the same method as that of the positive electrode. The result was 77 μm.

[0128] [Manufacturing of lithium-ion secondary batteries]

[0129] A nonwoven fabric (thickness 20 μm) of a three-layer laminate of polypropylene / polyethylene / polypropylene was prepared as a separator. An aluminum laminate for secondary batteries (manufactured by Dai Nippon Printing Co., Ltd.) was heat-sealed and processed into a bag, and the positive electrode, separator, and negative electrode prepared above were laminated and inserted into the bag. As an electrolyte, a solution of 1.0 mol / L of LiPF6 was dissolved in a solvent in which ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate were mixed in a volume ratio of 30:30:40 to prepare a lithium ion secondary battery.

[0130] The ratio of the cross-sectional area of ​​the high dielectric oxide solid to the total cross-sectional area of ​​the gaps in the obtained lithium ion secondary battery electrode was determined by the following method and the result was 11.6%.

[0131] (Solution method for calculating the occupancy rate of the cross-sectional area of ​​the high dielectric oxide solid relative to the total cross-sectional area of ​​the gap)

[0132] (1) For the composite material layer of the positive electrode or the negative electrode, the cross section of the electrode is cut and processed using an ion milling device to prepare a cross-sectional sample of the electrode composite material layer.

[0133] (2) Using a field emission scanning electron microscope (FE-SEM), images were taken at an accelerating voltage of 3 kV, a magnification of 5000 to 10000 times, and an image size of 1280 × 960. The element distribution state of the cross-sectional sample was confirmed by backscattered electron imaging and EDX.

[0134] (3) Binarizing the backscattered electron image of the cross-sectional sample to create a graph of the brightness distribution curve, differentiating the obtained curve to obtain the inflection point, thereby dividing the electrode active material particles, high dielectric oxide solid particles, and areas other than the above particles.

[0135] (4) Based on the above-set division conditions, the cross-sectional area occupancy of the electrode active material particles, the cross-sectional area occupancy of the high dielectric oxide solid particles, and the cross-sectional area occupancy of the region other than the above particles (remaining space) are derived.

[0136] (5) Perform operations (1) to (4) on a total of 8 locations of the cross-sectional sample, namely 3 locations in the vertical direction and 5 locations in the horizontal direction, and set the average value of the cross-sectional area occupancy of the high dielectric oxide solid particles as the occupancy of the cross-sectional area of ​​the high dielectric oxide solid relative to the total cross-sectional area of ​​the gap.

[0137] When calculating the cross-sectional area occupancy, the cross-sectional area occupancy A of the electrode active material particles, the cross-sectional area occupancy B of the high dielectric oxide solid particles, and the cross-sectional area occupancy C of the remaining space as the region outside the above particles are obtained. The occupancy of the cross-sectional area of ​​the high dielectric oxide solid to the total cross-sectional area of ​​the gap is set as the ratio of the cross-sectional area occupancy B of the high dielectric oxide solid particles to the sum of the cross-sectional area occupancy B of the high dielectric oxide solid particles and the cross-sectional area occupancy C of the remaining space (% (B / (B+C)×100)).

[0138] <Examples 2 to 4>

[0139] A lithium ion secondary battery was produced in the same manner as in Example 1 except that the lithium salt concentration of the electrolyte solution disposed in the gaps formed between particles of the positive electrode active material in the positive electrode was changed as shown in Table 1.

[0140] <Comparative Examples 1 to 4>

[0141] A lithium ion secondary battery was produced in the same manner as in Example 1 except that LATP as an oxide solid electrolyte was not added to the positive electrode and the lithium salt concentration of the electrolyte arranged in the gaps formed between the particles of the positive electrode active material was changed as shown in Table 1.

[0142] <Example 5>

[0143] [Production of positive electrode]

[0144] A positive electrode for a lithium ion secondary battery was produced in the same manner as in Example 1 except that LATP as an oxide solid electrolyte was not added to the positive electrode.

[0145] [Production of negative electrode]

[0146] Artificial graphite (AG, D50 = 12 μm) as the negative electrode active material and Li7La3Zr2O as the lithium ion conductive solid electrolyte as the strong dielectric component were mixed. 12 (LLZO, D50 = 0.5 μm), acetylene black as a conductive aid, and mixed and dispersed using a rotation / revolution mixer to obtain a mixture. Next, the obtained mixture is dispersed in distilled water, carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) as a binder are added, and a planetary mixer is used for dispersion treatment to obtain a negative electrode composite material paste. In addition, the ratio of each component in the negative electrode composite material is calculated by mass ratio, and the negative electrode active material: LLZO: conductive aid: SBR: CMC is mixed in a manner of 94.5:2:1:1.5:1, that is, the amount of LLZO added to 100 parts by mass of the mixture for the negative electrode composite material is 2 parts by mass.

[0147] Using the obtained negative electrode composite material paste, a negative electrode for a lithium ion secondary battery was produced in the same manner as in Example 1, and punching was performed to a size of 34 mm×44 mm.

[0148] The thickness of the obtained negative electrode for lithium ion secondary battery was 77 μm. The volume filling rate of the electrode active material relative to the total volume of the electrode composite material was 64.2%.

[0149] [Manufacturing of lithium-ion secondary batteries]

[0150] A lithium ion secondary battery was produced in the same manner as in Example 1 except that an electrolyte solution in which LiPF6 was dissolved at a concentration of 2.0 mol / L was used.

[0151] <Evaluation>

[0152] The lithium ion secondary batteries obtained in Examples and Comparative Examples were evaluated as follows.

[0153] [Initial discharge capacity]

[0154] The prepared lithium ion secondary battery was placed at the measurement temperature (25°C) for 1 hour, charged to 4.2V at a constant current of 0.33C, then charged to 4.2V at a constant voltage of 4.2V for 1 hour, and after being placed for 30 minutes, discharged to 2.5V at a discharge rate of 0.2C, and the initial discharge capacity was measured. The results are shown in Tables 1 and 2.

[0155] [Initial battery resistance]

[0156] The charge level (SOC (State of Charge)) of the lithium-ion secondary battery after the initial discharge capacity measurement is adjusted to 50%. Next, set the C rate to 0.2C, perform pulse discharge for 10 seconds, and measure the voltage during the 10-second discharge. Then, set the horizontal axis to the current value and the vertical axis to the voltage, and plot the voltage during the 10-second discharge relative to the current at 0.2C. Next, after leaving it for 5 minutes, perform supplementary charging to restore the SOC to 50%, and then leave it for another 5 minutes.

[0157] Next, the above operation was performed for each C rate of 0.5C, 1C, 2C, 5C, and 10C, and the voltage at 10 seconds of discharge relative to the current at each C rate was plotted. Then, the slope of the approximate straight line obtained from each plot was set as the initial battery resistance of the lithium ion secondary battery obtained in this example. The results are shown in Tables 1 and 2.

[0158] [Discharge capacity after endurance test]

[0159] As a charge and discharge cycle durability test, one cycle is to charge to 4.2V at a constant current of 1C in a constant temperature bath at 45°C, and then discharge to 2.5V at a constant current of 2C, and repeat this operation for 500 cycles. After 500 cycles, the constant temperature bath is set to 25°C and placed in a state after discharge at 2.5V for 24 hours, and then the discharge capacity after the durability test is measured in the same way as the initial discharge capacity. The results are shown in Tables 1 and 2.

[0160] [Battery resistance after endurance test]

[0161] In the same manner as the measurement of the initial battery resistance, the lithium ion secondary battery after the discharge capacity measurement after the endurance test was charged and adjusted to (SOC (State of Charge)) 50%, and the battery resistance after the endurance test was measured by the same method as the measurement of the initial battery resistance. The results are shown in Tables 1 and 2.

[0162] [Battery resistance increase rate]

[0163] The battery resistance after the endurance test relative to the initial battery resistance was determined and defined as the battery resistance increase rate.

[0164] The relationship between the lithium salt concentration and the resistance value of the lithium ion batteries obtained in Examples 1 to 4 is shown in FIG. Figure 2 In addition, for the lithium ion batteries obtained in Comparative Examples 1 to 4, the relationship between the lithium salt concentration and the resistance value is shown in Figure 3 .

[0165] [Capacity retention rate]

[0166] The discharge capacity after the endurance test relative to the initial discharge capacity was determined and defined as the capacity retention rate. The results are shown in Tables 1 and 2.

[0167] In addition, the capacity retention rates of the lithium ion batteries obtained in Examples 1 to 4 and Comparative Examples 1 to 4 are shown in FIG. Figure 4 .

[0168] Table 1

[0169]

[0170]

[0171] Table 2

[0172]

[0173] Reference numerals

[0174] 10: Lithium-ion secondary battery

[0175] 1: Container

[0176] 2: Positive electrode collector

[0177] 3: Positive electrode composite material layer

[0178] 4: Positive electrode

[0179] 5: Negative electrode collector

[0180] 6: Negative electrode composite material layer

[0181] 7: Negative electrode

[0182] 8: Diaphragm

[0183] 9: Electrolyte

Claims

1. An electrode for a lithium ion secondary battery, comprising an electrode active material, an oxide solid electrolyte, and an electrolyte, The oxide solid electrolyte and the electrolyte are arranged in the gaps formed between the particles of the electrode active material. The aforementioned oxide solid electrolyte is selected from Li7La3Zr2O 12 (LLZO), Li 6.75 LqCy 1.75 Ta 0.25 O 12 (LLZTO), Li 0.33 La 0.56 TiO3(LLTO), Li 1.3 Al 0.3 Ti 1.7 (PO4)3(LATP), and Li 1.6 Al 0.6 Ge 1.4 At least one of the group consisting of (PO4)3(LAGP), The concentration of lithium salt in the above electrolyte is 0.5 to 3.0 mol / L. In cross-sectional observation of the electrode for a lithium ion secondary battery, the ratio of the cross-sectional area of ​​the oxide solid electrolyte to the total cross-sectional area of ​​the gap is 11.6 to 22%. The cross-sectional observation is performed by observing the cross-section of the electrode composite material layer including the electrode active material and the oxide solid electrolyte by SEM, and the SEM imaging range is 80% or more of the electrode composite material layer in the electrode thickness direction.

2. The lithium ion secondary battery electrode according to claim 1, wherein The volume filling rate of the electrode active material is 60% or more relative to the total volume of the electrode composite material constituting the electrode.

3. The lithium ion secondary battery electrode according to claim 1, wherein The thickness of the lithium ion secondary battery electrode is 40 μm or more.

4. The lithium ion secondary battery electrode according to claim 1, wherein The aforementioned electrode for lithium ion secondary batteries is a positive electrode.

5. The lithium ion secondary battery electrode according to claim 1, wherein The aforementioned electrode for lithium ion secondary batteries is a negative electrode. 6 . A lithium ion secondary battery comprising: the lithium ion secondary battery electrode according to claim 1 , and an electrolyte solution.

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