JP6851647B2 - Manufacturing method of positive electrode for non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a method for producing a positive electrode for a non-aqueous electrolyte secondary battery.

In recent years, the use of non-aqueous electrolyte secondary batteries as batteries having a high energy density has been promoted in small consumer devices such as mobile phones and notebook computers. Examples of the non-aqueous electrolyte secondary battery include a lithium ion secondary battery. In recent years, lithium-ion secondary batteries have been studied for use in large devices such as stationary power storage systems, hybrid vehicles, and electric vehicles. Application to large equipment requires higher capacity and larger current than small equipment.

The capacity of the lithium ion secondary battery changes depending on the composition of the positive electrode active material in which lithium ions (Li ions) are electrochemically removed and inserted. As the positive electrode active material, a composite oxide such as _{LiCoO 2} , LiMn ₂ O ₄ , or LiFePO _{4 is used.}

In a lithium ion secondary battery, a positive electrode having a positive electrode active material layer having a positive electrode active material formed on the surface of a positive electrode current collector and a negative electrode active material layer having a negative electrode active material formed on the surface of the negative electrode current collector are generally formed. The negative electrode is connected via a non-aqueous electrolyte and is housed in a battery case. The electrode active material layer (positive electrode active material layer, negative electrode active material layer) is formed by applying a mixture of electrode active material powder together with a binder and a conductive material to the surface of the current collector.
Lithium-ion secondary batteries are required to improve battery performance such as battery capacity.

For example, in Patent Document 1, a non-aqueous electrolyte secondary battery is provided between a positive electrode and a resin layer (separator), contains aluminum fluoride as a main component, and has an insulating layer having a thickness of 10 nm or more and 1 μm or less. Is disclosed.

Japanese Unexamined Patent Publication No. 2013-127883

In the secondary battery described in Patent Document 1, not only the positive electrode and the resin layer but also the insulating layer is configured to come into contact with the electrolytic solution. Further, the insulating layer is provided with fine pores having a size such that the surface of the positive electrode and the surface of the separator do not come into contact with each other. In this configuration, electrons are transferred between the positive electrode and the electrolytic solution, so that a current leaking to the outside of the system (so-called leakage current) is generated. Therefore, it is difficult to raise the battery potential to 4.5 V or higher.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a positive electrode for a non-aqueous electrolyte secondary battery capable of increasing the battery potential.

As a result of repeated studies on the structure of the positive electrode in order to solve the above problems, the present inventors have completed the present invention.

That is, in the method for producing a positive electrode for a non-aqueous electrolyte secondary battery of the present invention, _{a raw material for a thin film composed of K 2} CO ₃ and Nb ₂ O ₅ and a flux composed of K Cl are mixed, heated, cooled, and then warm water is used. To produce a thin film compound by washing with, and to prepare a solution of the thin film compound, and apply it to the surface of a positive electrode active material layer having a positive electrode active material by a method for producing a positive electrode for a non-aqueous electrolyte secondary battery. The positive electrode active material has a layered structure of LiNi _α Mn _β Co _γ M _δ O ₂ (α + β + γ + δ = 1,0 <α, 0 <β, 0 <γ, 0 ≦ δ, M: transition metal element and aluminum. It is characterized by consisting of one or more selected from the above.

In the method for producing a positive electrode for a non-aqueous electrolyte secondary battery of the present invention, the thin film compound is immersed in an HCl solution, washed with water, immersed in an aqueous solution of tetrabutylammonium hydroxide (TBAOH), and then the thin film compound is produced. It is preferable to prepare a solution.

It is a block diagram which shows the structure of the lithium ion secondary battery of an embodiment. It is a block diagram which shows the structure of the coin-type lithium ion secondary battery of embodiment. It is a figure which shows the XRD peak of the thin film compound of an Example. It is an SEM photograph of the thin film compound of an Example. It is a figure which shows the charge / discharge characteristic of the secondary battery of the sample 1 of an Example. It is a figure which shows the charge / discharge characteristic of the secondary battery of the sample 2 of an Example. It is a figure which shows the charge / discharge characteristic of the secondary battery of the sample 3 of an Example. It is a figure which shows the charge / discharge characteristic of the secondary battery of the sample 4 of an Example. It is a figure which shows the discharge capacity in the rate test of the secondary battery of each sample of an Example. It is a figure which shows the discharge capacity in the cycle test of the secondary battery of each sample of an Example.

Hereinafter, the present invention will be specifically described with reference to embodiments.
The method for producing a positive electrode for a non-aqueous electrolyte secondary battery of the present invention will be specifically described with reference to a form applied to the production of a positive electrode and a lithium ion secondary battery.

[Embodiment]
The lithium ion secondary battery 1 of the present embodiment is a battery whose schematic configuration is shown in FIG. The secondary battery 1 of this embodiment has a positive electrode 2, a negative electrode 3, a non-aqueous electrolyte 4, and a separator 5.

(Positive electrode)
The positive electrode 2 has a positive electrode current collector 20, a positive electrode active material layer 21 formed on the surface thereof, and a thin film 22 formed on the surface of the positive electrode active material layer 21. The positive electrode active material layer 21 is formed by applying and drying a positive electrode mixture formed by mixing a positive electrode active material with a binder and a conductive material on the surface of the positive electrode current collector 20. The positive electrode active material layer 21 may be compressed after drying.
The thin film 22 is formed by preparing a solution containing a material for forming the thin film 22 and applying and drying it on the surface of the positive electrode active material layer 21.

(Positive electrode active material)
The positive electrode active material is selected from a layered structure of LiNi _α Mn _β Co _γ M _δ O ₂ (α + β + γ + δ = 1,0 <α, 0 <β, 0 <γ, 0 ≦ δ, M: transition metal element and aluminum 1). (More than seeds). The positive electrode active material having this composition can occlude and release ^{alkali metal ions (Li +} ) with a potential difference of 4.2 V or more with the alkali metal (Li) as a reference potential. From this, when the positive electrode active material has the above composition, the secondary battery 1 has a high battery voltage.

In addition, M in the composition formula is one or more selected from the transition metal element and aluminum. Transition metal elements are elements included in Group 3 to Group 12 in the periodic table. Preferred transition metals include elements such as Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo and Ta.

The production method of the positive electrode active material is not limited, and the positive electrode active material can be produced by mixing and firing a compound containing each metal element (for example, an oxide or a nitrate). Further, like the thin film 22, it may be produced by the flux method.

(Conductive material)
The conductive material ensures the electrical conductivity of the positive electrode 2. As the conductive material, fine particles of graphite, acetylene black, Ketjen black, carbon black such as carbon nanofibers, and fine particles of amorphous carbon such as needle coke can be used, but the conductive material is not limited thereto.

(Bundling material)
The binder binds positive electrode active material particles and a conductive material. As the binder, for example, PVDF, EPDM, SBR, NBR, fluororubber and the like can be used, but the binder is not limited thereto.

(Positive electrode mixture)
The positive electrode mixture is dispersed in a solvent and applied to the positive electrode current collector 20. As the solvent, an organic solvent that dissolves the binder is usually used. For example, NMP, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and the like can be mentioned, but are not limited thereto. In some cases, a dispersant, a thickener, or the like is added to water to slurry the positive electrode active material with PTFE or the like.

As the positive electrode current collector 20, for example, a processed metal such as aluminum or stainless steel, for example, a plate-shaped foil, a net, a punched metal, a foam metal, or the like can be used, but the positive electrode current collector 20 is not limited thereto.

(Thin film)
The thin film 22 is formed on the surface of the positive electrode active material layer 21.

In this embodiment, the thin film indicates a substance formed thinner than the positive electrode active material layer 21 when formed on the surface of the positive electrode active material layer 21, and even if it is a film-like compound, it is a positive electrode. It may be a layered compound laminated on the surface of the active material layer 21 or any of them.

Here, since the thin film 22 does not exhibit the battery capacity, it is preferable that the thin film 22 has a thin thickness. Preferably, it is a monolayer compound.

The material of the thin film 22 is not limited. The thin film 22 does not inhibit the insertion and desorption of Li ions from the non-aqueous electrolyte 4 into the positive electrode active material. Examples of the material for forming the thin film 22 satisfying such conditions include compounds such _{as NbO x-} based oxides, TiO _x- based oxides, VO _x- based oxides, and WO _{x-based oxides.} ..

The thin film 22 is preferably thin, and is preferably formed from a single-layer compound. The method for forming the single-layer compound is not limited, but the flux method is used to precipitate crystals of the layered compound, and each layer is peeled off to produce the compound. In the method of exfoliating a monolayer compound from a layered compound, for example, a bulky compound (for example, an ion) can be inserted between each layer of a crystal of the layered compound to exfoliate the monolayer from the produced layered compound.

The method of forming the thin film 22 on the surface of the positive electrode active material layer 21 is not limited. For example, a solution in which the compound forming the thin film 22 is dispersed (or dissolved) is applied by a spin coating method, a spray method, or the like. -Can be formed by drying. Further, the thin film 22 may be formed by a method in which the crystal formation reaction proceeds directly on the surface of the positive electrode active material layer 21.

When the thin film 22 is formed by the spin coating method, the solution in which the compound forming the thin film 22 is dispersed (or dissolved) preferably contains the compound in an amount of 0.1 mass% or more, and preferably contains the compound in an amount of 0.5 mass% or more. It is more preferable to do so. By forming the thin film 22 from the solution containing a large amount of the compounds forming the thin film 22, the compounds forming the thin film 22 are arranged without forming a gap, and the positive electrode active material layer 21 and the non-water formed by the thin film 22 are arranged. The effect of suppressing the transfer of electrons to and from the electrolyte 4 can be more reliably exhibited.

(Negative electrode)
Like the positive electrode 2, the negative electrode 3 has a negative electrode current collector 30 and a negative electrode active material layer 31 formed on the surface thereof. Even if the negative electrode active material layer 31 is formed only from the negative electrode active material, a negative electrode mixture formed by mixing the negative electrode active material with a binder and a conductive material is applied and dried on the surface of the negative electrode current collector 30. It may be formed by the above method. The negative electrode active material layer 31 formed from the negative electrode mixture may be compressed after drying.

(Negative electrode active material)
The negative electrode active material is not limited as long as it is a material that can occlude and release Li ions. For example, metallic lithium, lithium alloy, metal oxide, metal sulfide, metal nitride, carbon material, silicon material and the like can be mentioned.

Examples of the carbon material include graphite-based materials such as graphite, coke, carbon fiber, spherical carbon, and granular carbon, or carbon-based materials. The carbon material is a graphite-based material or carbon-based material obtained by heat-treating thermosetting resin, isotropic pitch, mesophase pitch, mesophase pitch-based carbon fiber, gas phase growth-based carbon fiber, mesophase globules, etc. It may be a material. Examples of the silicon material include amorphous silicon, microcrystalline silicon, and polycrystalline silicon, and two or more of these may be used in combination. It is known that the higher the crystallinity of a silicon material, the higher the electrical conductivity.

(Conductive material)
The conductive material ensures the electrical conductivity of the negative electrode 3. As the conductive material, similar to the conductive material of the positive electrode 2, graphite fine particles, acetylene black, Ketjen black, carbon black such as carbon nanofibers, and amorphous carbon fine particles such as needle coke can be used. Not limited. Further, conductive plastics such as the conductive polymer polyaniline, polypyrrole, polythiophene, polyacetylene, and polyacene may be used.

(Bundling material)
The binder binds the negative electrode active material particles and the conductive material. As the binder, for example, PVDF, EPDM, SBR, NBR, fluororubber and the like can be used as in the binder of the positive electrode 2, but the binder is not limited thereto.

(Negative electrode mixture)
The negative electrode mixture is dispersed in a solvent and applied to the negative electrode current collector 30. As the solvent, a solvent such as water or NMP that dissolves the binder is usually used. In some cases, a dispersant, a thickener, or the like is added to water to slurry the negative electrode active material with PTFE or the like.

As the negative electrode current collector 30, a conventional current collector can be used, and a metal such as copper, stainless steel, titanium or nickel is processed, for example, a plate-shaped foil, net, punched metal or foam metal. Etc. can be used, but the present invention is not limited to these.

(Non-aqueous electrolyte)
The non-aqueous electrolyte 4 transports Li ions (charge carriers) between the positive electrode 2 and the negative electrode 3. The non-aqueous electrolyte 4 is not particularly limited. A liquid that can physically, chemically, and electrically stably exist in the atmosphere in which the secondary battery 1 is used and is generally used as the secondary battery 1 is preferable. It is preferably a non-aqueous electrolyte (also referred to as a non-aqueous electrolyte solution) in which a supporting salt is dissolved in an organic solvent.

(solvent)
As the organic solvent, a general solvent solvating the alkali metal may be used. For example, cyclic carbonates, cyclic esters, chain esters, cyclic ethers, chain ethers, nitriles and the like can be mentioned.

Examples of the cyclic carbonate include propylene carbonate (PC), ethylene carbonate (EC), dimethyl sulfoxide (DMSO) and the like. Examples of the cyclic ester include γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-hexanolactone, and δ-octanolactone. Examples of the chain ester include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and the like. Examples of the cyclic ether include oxetane, tetrahydrofuran (THF), tetrahydropyran (THP) and the like. Examples of the chain ether include dimethoxyethane (DME), ethoxymethoxyethane (EME), and diethoxyethane (DEE). Examples of nitriles include acetonitrile, propionitrile, glutaronitrile, methoxynitrile, 3-methoxypropionitrile and the like. In addition, hexamethylsulfoltriamide (HMPA), acetone (AC), N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMA), pyridine, dimethylformamide (DMF), ethanol, formamide (FA), methanol, Water or the like may be used as the solvent.

By using an electrolytic solution containing a carbonate-based solvent among these solvents, stability at high temperatures is improved. Solid polymer electrolytes containing the above electrolytes in solid polymers such as polyethylene oxide, and solid electrolytes such as ceramics and glass having lithium ion conductivity can also be used.

As the organic solvent, a mixed solvent in which two or more of the above solvents are mixed may be used. For example, a mixed solution of a cyclic ester having a high dielectric constant and a chain ester for the purpose of reducing the viscosity can be mentioned. An unsaturated compound having an unsaturated bond, such as vinylene carbonate (VC) or fluoroethylene carbonate (FEC), may be added for the purpose of improving the cycle characteristics.

(Supporting salt)
As the supporting salt, any salt suitable for supporting can be used. For example, when the alkali metal is lithium, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiSbF ₆ , LiSCN, LiClO ₄ , Examples thereof include LiAlCl ₄ , NaClO ₄ , NaBF ₄ , NaI, and salt compounds such as derivatives thereof. From the viewpoint of improving electrical characteristics, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiN (FSO ₂ ) ₂ , Selected from the group consisting of LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiCF ₃ SO ₃ derivative, LiN (CF ₃ SO ₂ ) ₂ derivative, and LiC (CF ₃ SO ₂ ) _{3 derivative.} It is preferable to use one or more kinds of salts.

Further, in order to obtain high load discharge characteristics, it is preferable to include a substance having a large relative permittivity such as ethylene carbonate (EC) and propylene carbonate (PC).

Further, as the supporting salt, an oxalate complex or an oxalate derivative complex may be used instead of (or in addition to) the above-mentioned supporting salt. Examples of the oxalate complex and the oxalate derivative complex include lithium bis (oxalate) borate (LiBOB), lithium difluoro (oxalate) borate (LiFOB), lithium difluorobis (oxalate) phosphate, and lithium bis (oxalate) silane. The same supporting salt may be used for alkali metals other than lithium (for example, sodium and potassium).

Instead of (or in addition to) the organic solvent and supporting salt described above, an ionic liquid that can be used for a non-aqueous electrolyte secondary battery may be used. Examples of the cation component of the ionic liquid include N-methyl-N-propylpiperidinium and dimethylethylmethoxyammonium cation. The anionic component, BF ₄ ^- or _N (SO ^₂ CF ^{3) 2-,} and the like. Further, the non-aqueous electrolyte may be gelled by containing a gelling agent.

(Separator 5)
The separator 5 is interposed between the positive electrode 2 and the negative electrode 3 to insulate the positive electrode 2 and the negative electrode 3 from contact with each other, and to provide the non-aqueous electrolyte 4 (non-aqueous electrolyte solution) in a state where the movement of Li ions is not hindered. Hold. As the separator 5, a general porous resin, silicon oxide, silicon nitride, or the like can be used. For example, those made of a porous polypropylene resin can be mentioned.

The separator 5 preferably has a shape larger than at least one of the positive electrode 2 and the negative electrode 3 in order to ensure insulation between the positive electrode 2 and the negative electrode 3. The thickness of the separator 5 is not limited and can be set arbitrarily. For example, the thickness can be 1 μm or more and 30 μm or less. In this case, if it is molded thinner than 1 μm, the insulation becomes insufficient, and if it is molded thicker than 30 μm, the volume occupied by the separator 5 in the secondary battery increases, and the proportion occupied by the positive electrode 2 and the negative electrode 3 decreases. As a result, the battery capacity per volume of the secondary battery 1 becomes small.

[Other configurations]
The specific shape of the secondary battery 1 of the present embodiment is not limited as long as it has the above-mentioned configuration having the positive electrode 2, the negative electrode 3, and the non-aqueous electrolyte 4. For example, a coin-type secondary battery 1 whose configuration is shown in FIG. 2 can be mentioned. In FIG. 2, members having the same configuration as the above are given the same reference numerals.
The secondary battery 1 shown in FIG. 2 is formed by enclosing a positive electrode 2, a negative electrode 3, a non-aqueous electrolyte 4, and a separator 5 in a battery case 6.
The positive electrode 2, the negative electrode 3, the non-aqueous electrolyte 4 and the separator 5 have the same configuration as described above.
The battery case 6 is formed of a lower case 60 and an upper case 61, and seals between the cases 60 and 61 with a sealing member 62.

[Modified form of secondary battery]
In the above-described form, the coin-type secondary battery 1 has been illustrated, but the non-aqueous electrolyte secondary battery of the present invention is not limited to this form.
The shape of the secondary battery 1 is not particularly limited, and the secondary battery 1 may be a battery having various shapes such as a cylindrical shape or a square shape, or a battery having an indefinite shape enclosed in a laminated outer body.

Hereinafter, the present invention will be described with reference to examples.
As an example of the present invention, a positive electrode and a lithium ion secondary battery were manufactured.

(Example)
The lithium ion secondary battery 1 of this example has the same configuration as the coin-type lithium ion secondary battery 1 whose configuration is shown in FIG. The positive electrode 2 of this example has the configuration of FIG. 1 described in the above embodiment. The positive electrode 2 of this example has a positive electrode current collector 20, a positive electrode active material layer 21, and a thin film 22.

(Formation of thin film)
_{K 2} CO ₃ (0.928 g) and Nb ₂ O ₅ (5.353 g) are prepared as raw materials for forming the thin film 22. These compounds are thoroughly mixed with a flux consisting of 5.353 g of KCl.

The mixed powder was put into an alumina crucible and heated in a heating furnace. The heating in the heating furnace was performed by heating and raising the temperature to a preset temperature (800 ° C.) at a heating rate of 1000 (° C./hour). Then, after holding at this heating temperature for 5 hours, the temperature was lowered and cooled to 300 ° C. at a temperature lowering rate of 250 (° C./hour).
Then, it was allowed to cool to room temperature and washed with warm water to remove the flux.
As described above, the compound (thin film compound) forming the thin film of this example was produced.
The thin film compound was observed by XRD and SEM. The XRD measurement results are shown in FIG. 3, and the SEM photographs are shown in FIG. 4, respectively.
As shown in FIG. 3, it was confirmed that the thin film compound had a composition of _{KNb 3} O _8. Further, as shown in FIG. 4, it was confirmed that the thin film compound had a thin layer shape.

The obtained thin film compound was stirred and immersed in a 1 mol / L HCl solution for 72 hours for proton exchange. Then, washing with distilled water was repeated until the pH of the solution reached 7. Then, the thin film compound is immersed in Tetrabutylamnium Hydroxide (40 wt% aqueous solution) (TBAOH) and shaken for 72 hours in a light-shielded state.
Then, a centrifugation operation is performed to remove the colloidal precipitate. Further, a centrifugation operation was performed to extract a dispersion solution of a thin film compound having a single-layer nanosheet structure.

Three types of extracted dispersion solutions were prepared, when the total mass of the dispersion solution was 100 mass%, and the thin film compound was contained in 0.1 mass%, 0.5 mass%, and 1 mass%.

(Formation of positive electrode)
The extracted dispersion solution is used as a positive electrode (commercially available product, manufactured by Hosen Co., Ltd., trade name: HS-LIB-P-NMC-001, positive electrode activity) in which a positive electrode active material layer 21 is formed on the surface of the positive electrode current collector 20. Material: LiNi _0.33 Mn _0.33 Co _0.33 O ₂ ) was added dropwise to the surface, and the mixture was rotated at 2000 rpm for 60 seconds (spin coating method).
A drying step was performed to produce the positive electrode 2 of this example.
The manufactured positive electrode 2 of this example has a positive electrode current collector 20 and a thin film 22 formed on the surface of a positive electrode active material layer 21 formed on the surface thereof.

(Other secondary battery configurations)
Metallic lithium was used for the negative electrode (counter electrode). Corresponds to the negative electrode active material layer 31 in FIG.
_{The non-aqueous electrolyte 4 was prepared by dissolving LiPF 6} in a mixed solvent of 30% by volume of ethylene carbonate (EC) and 70% by volume of diethyl carbonate (DEC) so as to be 1 mol / liter. ..
After the test cell was assembled, it was activated by charging / discharging in 1/3 C × 2 cycles.
From the above, a test cell (half cell) was manufactured.

In the test cell, the secondary battery 1 manufactured from a dispersion solution containing a thin film compound at 1 mass% was sample 1, and the secondary battery 1 manufactured from a dispersion solution containing 0.5 mass% was sample 2, 0.1 mass% dispersed. The secondary battery 1 manufactured from the solution was used as sample 3, and the secondary battery that did not form the thin film 22 was used as sample 4.

(Charge / discharge test)
For the secondary battery 1 of each sample produced, charging / discharging of 4.6V-2.8V was repeated for 3 cycles at a charging / discharging rate of 0.25C. The battery capacity at this time is shown in FIGS. 5 to 8. FIG. 5 shows the measurement result of the secondary battery 1 of the sample 1, FIG. 6 shows the measurement result of the secondary battery 1 of the sample 2, FIG. 7 shows the measurement result of the secondary battery 1 of the sample 3, and FIG. 8 shows the measurement result of the secondary battery 1. The measurement results of the secondary battery 1 of the above are shown respectively.

As shown in FIGS. 5 to 7, the secondary batteries 1 of the samples 1 to 3 in which the thin film 22 is formed on the surface of the positive electrode 2 has a larger battery capacity than the sample 4 in which the thin film 22 is not formed. It can be confirmed that it has.

Further, the characteristics of the charge / discharge capacity of the secondary batteries 1 of the samples 1 to 3 have little change in each cycle. On the other hand, in the sample 4 in which the thin film 22 is not formed, it can be confirmed that the difference in charge / discharge capacity for each cycle is large.

On top of that, as shown in FIGS. 5 to 7, it can be confirmed that the larger the amount of the thin film 22 formed (the larger the dispersion amount of the thin film compound), the more the effect of increasing the battery capacity can be exhibited.

Further, it can be confirmed that as the amount of thin film 22 formed increases (the amount of dispersion of the thin film compound increases), the characteristics of the charge / discharge capacity do not deviate, and the effect of suppressing the decrease in battery capacity can be exhibited.

(Rate test)
For each of the produced secondary batteries 1 of the sample, charging / discharging of 4.6V-2.8V at a predetermined charging / discharging rate was repeated for a predetermined number of cycles. The discharge capacity at this time is shown in FIG. Charging and discharging were performed at each rate of 0.25C, 0.5C, 1C, 2C, 4C, and 10C. Then, in FIG. 9, the discharge capacity at 1,2,3,19,20,21 cycles at 0.25C, the discharge capacity at 4,5,6 cycles at 0.5C, and 7, at 1C. Discharge capacity at 8, 9 cycles, discharge capacity at 10, 11, 12 cycles at 2C, discharge capacity at 13, 14, 15 cycles at 4C, discharge capacity at 16, 17, 18 cycles at 10C Are shown respectively.

As shown in FIG. 9, in any of the secondary batteries 1, when the charge / discharge rate is 0.25C, it can be seen that the discharge capacity hardly changes (decreases) even if the charge / discharge is repeated.

The higher the charge / discharge rate, the larger the difference between the discharge capacities of Samples 1 to 3 and the discharge capacities of Sample 4. On top of that, it can be confirmed that the discharge capacity of the sample 4 is greatly reduced by charging / discharging at a high rate of 4C, whereas the samples 1 to 3 have a practically usable discharge capacity.

(Cycle test)
For the secondary batteries 1 of the manufactured samples 1, 2 and 4, charging / discharging of 4.6V-2.8V was repeated for 100 cycles at a charging / discharging rate of 1C. The discharge capacity at this time is shown in FIG.

As shown in FIG. 10, from around 70 cycles, it can be confirmed that the discharge capacity of the sample 4 in which the thin film 22 is not formed is significantly reduced. On the other hand, in the samples 1 and 2 having the thin film 22, such a large decrease in the discharge capacity cannot be confirmed, and it can be confirmed that the cycle characteristics are excellent.

As shown above, the positive electrode 2 and the secondary battery 1 of each sample having the thin film 22 made _{of KNb 3} O ₈ on the surface of the positive electrode active material layer 21 are repeatedly charged and discharged at a high potential of 4.6 V. However, the deterioration of battery characteristics is suppressed.

This may mean that the thin film 22 regulates the movement of the oxygen to the non-aqueous electrolyte 5 even if the valence of Ni contained in the positive electrode active material changes and oxygen is desorbed. This regulation of oxygen movement suppresses the generation of irreversible capacity of the positive electrode active material. As a result, it is also considered that deterioration of battery characteristics can be suppressed.

Further, as a result of analyzing the positive electrode active material layer 21 on which the thin film 22 is formed, the thin film 22 does not exist only on the surface of the positive electrode active material layer 21, but is an internal positive electrode along the voids of the positive electrode active material layer 21. It was confirmed that the active material, the conductive material, and the binder surface were covered.

That is, the secondary batteries 1 of the samples 1 to 3 according to the present invention exhibit the effect of having excellent battery characteristics.

1: Lithium ion secondary battery 2: Positive electrode 20: Positive electrode current collector 21: Positive electrode active material layer 3: Negative electrode 30: Negative electrode current collector 31: Negative electrode active material layer 4: Non-aqueous electrolyte 5: Separator 6: Battery case

Claims (2)

The raw material of the thin film composed of K ₂ CO ₃ and Nb ₂ O ₅ and the flux composed of KCl are mixed, heated, cooled, and then washed with warm water to remove the flux to produce a thin film compound.
A method for producing a positive electrode for a non-aqueous electrolyte secondary battery, wherein a solution of the thin film compound is prepared and applied to the surface of a positive electrode active material layer having a positive electrode active material.
The positive electrode active material is selected from a layered structure of LiNi _α Mn _β Co _γ M _δ O ₂ (α + β + γ + δ = 1,0 <α, 0 <β, 0 <γ, 0 ≦ δ, M: transition metal element and aluminum. A method for producing a positive electrode for a non-aqueous electrolyte secondary battery, which comprises one or more types). The non-aqueous electrolyte secondary battery according to claim 1, wherein the thin film compound is immersed in an HCl solution, washed with water, immersed in an aqueous solution of tetrabutylammonium hydroxide (TBAOH), and then a solution of the thin film compound is prepared. Method for manufacturing a positive electrode for use.

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