JP2023111498A - Method for manufacturing positive electrode for lithium ion secondary battery - Google Patents

Abstract

To provide a method for manufacturing a positive electrode for a lithium ion secondary battery, by which gas generation as a result of oxidation decomposition of a nonaqueous electrolyte can be suppressed further in comparison to a prior method.SOLUTION: A method for manufacturing a positive electrode for a lithium ion secondary battery according to the present invention, in which the positive electrode includes a positive electrode active substance with its surface coated with a coating layer made of a coating material containing a lithium ion-conducting metal oxide and/or phosphorus oxide, comprises: an electrolyte dispersion-forming step of performing a ball-mill treatment on the coating material in an organic solvent to obtain a slurry in which a concentration of the coating material in the organic solvent is 2 mass% or more and 25 mass% or less; an electrolyte-applied material-forming step of applying the slurry to the positive electrode active substance by spraying means to obtain a spray-coated positive electrode active substance; and a crushed product forming step of applying an external force to the spray-coated positive electrode active substance, thereby gaining a mechanical coated positive electrode active substance.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a positive electrode for lithium ion secondary batteries.

Research and development of lithium-ion secondary batteries are actively carried out for a wide range of applications such as mobile devices, hybrid vehicles, electric vehicles, and household power storage. Lithium ion secondary batteries used in these fields are required to have high safety, long-term cycle stability, high energy density, and the like.

In recent years, lithium ion secondary batteries using lithium titanate (LTO) as a negative electrode active material have been proposed from the viewpoint of high safety and long-term cycle stability. Since the operating potential of lithium titanate is higher than that of graphite, which is a common negative electrode active material, lithium deposition is less likely to occur, improving safety, but it is disadvantageous from the viewpoint of energy density.

On the other hand, as a positive electrode active material, a material that operates at a high potential of 4.5 V or more relative to the deposition potential of Li has been proposed (for example, Patent Document 1).

The reduction in energy density due to the high operating potential of lithium titanate is expected to be improved by combining a positive electrode active material that operates at a high potential as shown in Patent Document 1.

On the other hand, in a conventional lithium ion secondary battery using graphite as a negative electrode active material, gas is generated due to oxidative decomposition of the liquid non-aqueous electrolyte on the surface of the positive electrode active material. In the case of a secondary battery in which the operating potential of the active material is high, the problem of gas generation becomes more pronounced.

Further, in conventional lithium ion secondary batteries, an additive is added to the non-aqueous electrolyte to form a film on the surface of the positive electrode, thereby suppressing gas generation.

However, although the same principle can be applied to the formation of a film on the surface of the positive electrode even for high-potential positive electrode active materials, the film is required to have higher oxidation resistance, so the effect is considered to be insufficient.

In addition, there is Patent Document 2 as a related document.

On the other hand, in a lithium ion secondary battery using a positive electrode active material that operates at a high potential, a manufacturing method has also been disclosed in which the positive electrode material is coated with a solid electrolyte in order to suppress the generation of gas due to oxidative decomposition of the non-aqueous electrolyte ( Patent document 3).

Japanese Patent Application Laid-Open No. 2001-185148 WO2020/049843 Patent application 2020-184772

As a method of forming such a coated positive electrode material, that is, a method of surface-coating a positive electrode active material with a solid electrolyte, a spray coating method and a mechanical coating method have been implemented. In the spray coating method, the oxidative decomposition of the non-aqueous electrolyte cannot be completely suppressed due to the presence of voids in the coating layer, and in the mechanical coating method, there is a problem that the solid electrolyte cannot be dispersed unless a large amount of energy is applied. I found

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for manufacturing a positive electrode for a lithium ion secondary battery, which can suppress gas generation due to oxidative decomposition of a non-aqueous electrolyte more than conventionally.

In view of the above-described problems, the present inventors conducted extensive studies and found that when the positive electrode active material is coated with the oxide-based solid electrolyte and/or the lithium ion conductive phosphorus compound, the mechanical coating method is performed after the spray coating method is performed. Thus, the inventors have found that the coating state of the positive electrode active material is improved, and gas generation can be suppressed in a lithium ion secondary battery using the above positive electrode active material.

The present invention derived from the above findings includes a positive electrode active material whose surface is coated with a coating layer made of a coating material containing a lithium ion conductive metal oxide and/or phosphorous oxide. A method for manufacturing a positive electrode for a lithium ion secondary battery, comprising:
an electrolyte dispersion forming step of ball milling the coating material in an organic solvent to obtain a slurry having a concentration of the coating material nanoparticles in the organic solvent of 2% by mass or more and 25% by mass or less;
a step of forming an electrolyte deposit to obtain a spray-applied positive electrode active material by spray-coating the slurry onto the positive electrode active material;
The present invention relates to a method for producing a positive electrode for a lithium-ion secondary battery, including a ground material forming step for obtaining a mechanically applied positive electrode active material by applying an external force to the spray-applied positive electrode active material.

More specifically, the method for producing a positive electrode for a lithium ion secondary battery of the present invention is a method for producing a positive electrode composite active material related to the insertion and extraction of lithium ions, which are the main parts constituting the electrode. and the coating material constituting the coating layer is the above-mentioned lithium ion conductive metal oxide and / or phosphor oxide, in other words, the oxide-based solid electrolyte and / or the lithium ion conductive phosphorus compound is the main material , for example, 90% by mass or more, preferably 95% by mass or more, more preferably 98% by mass or more, and still more preferably approximately 100% by mass except for a trace amount of impurities.

Such a method for manufacturing a positive electrode for a lithium ion secondary battery of the present invention is characterized by including, in order, an electrolyte dispersion formation step, an electrolyte adhering body formation step, and a ground material formation step.

One of the features of the present invention is that it includes an electrolyte dispersion forming step of forming an electrolyte dispersion dispersed in an organic solvent. It is required that the concentration of the raw material is 2% by mass or more and 25% by mass or less.

The manufacturing method of the present invention includes an electrolyte deposit forming step of forming an electrolyte deposit by adhering such an electrolyte dispersion to a positive electrode active material, and grinding the electrolyte deposit to form a ground material. Furthermore, preferably, the triturated material forming step includes a removal operation of removing the dispersion solvent from the system containing the positive electrode active material to which the triturated material and the dispersion are attached. include.

According to the production method of the present invention, a high-performance positive electrode for a lithium ion secondary battery can be produced, because the surface of the positive electrode active material can be easily coated with the coating layer according to the present invention. is.

A preferred aspect is that the removing operation includes heat treatment at 300° C. or higher to remove the dispersing solvent.

A preferred aspect is the manufacturing method of the present invention, in which the positive electrode mixture, which is the positive electrode active material whose surface is covered with the coating layer according to the present invention and which contains the positive electrode composite active material described above, is applied to the positive electrode current collector. A method for manufacturing a positive electrode for a lithium ion secondary battery, including a positive electrode coating step.

One aspect of the present invention is that the electrolyte dispersion forming step includes a pulverizing step of pulverizing the raw material according to the present invention to an average particle size of 80 nm or less. When the material is a metal oxide, for example, LATP, which will be described later, the thickness should be 20 nm or less.

That is, the preferred BET specific surface area conversion diameter of the raw material of the coating material is 20 nm or less in the case of the raw material of the oxide-based solid electrolyte, which is a lithium ion conductive metal oxide, and the lithium ion conductive metal phosphate. is 80 nm or less in the case of the raw material.

Methods for pulverizing such coating material raw materials include wet pulverization and dry pulverization, and wet pulverization has the advantage of being able to pulverize to a smaller particle size than dry pulverization.

On the other hand, in the case of wet pulverization, it is necessary to pulverize the raw material of the coating material dispersed in a volatile solvent into powder, and then evaporate the volatile solvent to take out the powder. When heated and volatilized in order to promote .

Therefore, a preferred mode is to disperse the raw material particles in the dispersion solvent while pulverizing them in the electrolyte dispersion forming step, and more preferably to pulverize and disperse them so as to obtain the preferred particle size described above.

According to this aspect, in the electrolyte dispersion forming step, the raw material particles are pulverized and dispersed in the dispersion solution at the same time. It is difficult for variations to occur within

One aspect of the present invention is a lithium ion secondary battery having a positive electrode containing the positive electrode composite active material described above, a negative electrode, and a non-aqueous electrolyte.

According to this aspect, even when a non-aqueous electrolyte is used, the generation of gas in the non-aqueous electrolyte can be suppressed.

In a preferred aspect, the negative electrode has a negative active material comprising lithium titanate.

One aspect of the present invention is a method for manufacturing a lithium ion secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode mixture containing the above-described positive electrode composite active material is applied to a positive electrode current collector. A method for manufacturing a lithium ion secondary battery, including a coating step.

According to this aspect, it is easy to manufacture a lithium ion secondary battery.

One aspect of the present invention is that the average potential of lithium desorption and insertion of the positive electrode active material coated with such a coating layer is 4.5 V or more and 5.0 V or less with respect to Li + /Li, Basically, the positive electrode active material has an operating potential of 4.5 V (vs. Li/Li ⁺ ) or more, and according to this aspect, the generation of gas due to oxidative decomposition of the non-aqueous electrolyte is suppressed more than before. can.

According to the present invention, even when a positive electrode active material that operates at a high potential is used, generation of gas due to oxidative decomposition of the non-aqueous electrolyte can be suppressed more than before.

1 is a cross-sectional view schematically showing a lithium ion secondary battery according to an embodiment of the invention; FIG.

A lithium ion secondary battery 1 according to one embodiment of the present invention will be described below, but the present invention is not limited thereto.

A lithium ion secondary battery 1 includes a positive electrode 2 , a negative electrode 3 , a non-aqueous electrolyte 5 , and a separator 6 , as shown in FIG. 1 .

The positive electrode 2 is obtained by laminating a positive electrode composite active material layer 11 containing a positive electrode composite active material 20 on a positive electrode current collector 10 .

The negative electrode 3 is obtained by stacking a negative electrode active material layer 13 containing a negative electrode active material 21 on a negative electrode current collector 12 .

(Positive electrode composite active material 20)
The positive electrode composite active material 20 is the positive electrode active material 30 whose surface is covered with the coating layer according to the present invention, that is, the surface of the positive electrode active material 30 is covered with the coating layer according to the present invention. is.

The coating material, which is the main material of the coating layer, is a lithium ion conductive metal oxide 31 and/or a phosphor oxide 32, such as an oxide-based solid electrolyte 31 and/or a lithium ion conductive phosphor compound. 32 (hereinafter also simply referred to as solid electrolyte 31 and/or phosphorus compound 32).

(Positive electrode active material 30)
The positive electrode active material 30 has an average potential for lithium desorption and insertion relative to Li ⁺ /Li, that is, relative to the deposition potential of Li (also indicated as vs. Li ⁺ /Li) of 4.5 V or more and 5.0 V The following lithium ion conductive active material is preferable.

The positive electrode active material 30 preferably has an operating potential of 4.5 V or higher and 5.0 V or lower based on lithium metal.

The potential of lithium ion insertion/extraction reaction (hereinafter also referred to as voltage) (vs. Li ⁺ /Li) is, for example, the charge/discharge characteristics of a half-cell with a working electrode using the positive electrode active material 30 and a lithium metal as a counter electrode. can be obtained by measuring and reading the voltage values at the start and end of the plateau. When there are two or more plateaus, the plateau with the lowest voltage value may be 4.5 V (vs. Li ⁺ /Li) or more, and the plateau with the highest voltage value is 5.0 V (vs. Li ⁺ / Li) or less.

The positive electrode active material 30 is not particularly limited as long as the insertion/extraction reaction of lithium ions proceeds at 4.5 V or more and 5.0 V or less with respect to the deposition potential of Li, but is preferably Li _1+x M _y Mn _2-xy O ₄ (x and y respectively satisfy 0≦x≦0.2 and 0<y≦0.8; M is Al, Mg, Zn, Ni, Co, Fe, Ti, Cu is at least one selected from the group consisting of and Cr.). LiNi _0.5 Mn _1.5 O ₄ where y=0.5 and M=Ni is particularly preferred because it has a high stability effect during charge-discharge cycles.

The particle size of the positive electrode active material 30 is not particularly limited, but if the particle size is too small, the difference from the particle size of the coating material nanoparticles becomes small, making coating difficult. Therefore, the median diameter d50 is preferably 5 μm or more, more preferably 10 μm or more, still more preferably 20 μm or more, and is preferably 100 μm or less, more preferably 80 μm or less, further preferably 50 μm or less, and 30 μm or less. is particularly preferred.

Considering the thickness range when processing into an electrode, the median diameter d50 of the positive electrode active material 30 is preferably 10 μm or more, more preferably 20 μm or more.

(Covering materials 31, 32)
In order to uniformly coat the surface of the positive electrode active material 30, the coating material nanoparticles preferably have a BET specific surface area conversion diameter (dBET) of 20 nm or less, and preferably 10 nm or less. It is more preferable that the particles are finely divided to 6 nm or less, and the average particle diameter calculated using the X-ray small angle scattering method is preferably 20 nm or less.

Known means such as a ball mill and a bead mill can be used as a method of microparticulation treatment. In addition, the BET specific surface area conversion diameter (dBET) is determined by the nitrogen adsorption BET specific surface area by the nitrogen adsorption method according to the method specified in JIS Z8830 (2013), dBET = 6 / (density × BET specific surface area) is the particle size obtained by the formula of

The ratio of the median diameter d50 of the positive electrode active material 30 to the BET specific surface area conversion diameter dBET of the coating material nanoparticles is preferably 10000:1 to 50:1, more preferably 5000:1 to 100:1. , more preferably 2000:1 to 500:1, particularly preferably 1000:1 to 100:1.

The difference between the median diameter d50 of the positive electrode active material 30 and the BET specific surface area equivalent diameter (dBET) of the coating material nanoparticles should be as large as possible.

When the above difference is small, the aggregation of the coating material nanoparticles and the formation of aggregates of the positive electrode active material 30 and the coating material nanoparticles are dominant over the coating of the positive electrode active material 30 with the coating material nanoparticles. , the intended effect may not be exhibited.

In addition, the ratio of the coating material nanoparticles (solid content when used in slurry) to 100 parts by mass of the positive electrode active material 30 is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably It is 2 parts by mass or more, preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and still more preferably 4 parts by mass or less.

The ratio is preferably 1 part by mass or more and 5 parts by mass or less (that is, the mass ratio of the positive electrode active material 30 and the solid electrolyte 31 is 100:1 to 20:1), and is 2 parts by mass or more and 4 parts by mass or less. (That is, the mass ratio of the positive electrode active material 30 and the coating material nanoparticles is preferably 50:1 to 25:1).

The coating material is a metal oxide 31 and/or phosphorous oxide 32 which is lithium-ion conductive.

Lithium ion conductive metal oxide 31, in other words, the oxide-based solid electrolyte is preferably Li _1+p+q+r Al _p Ga _q (Ti, Ge) _2-p-q Si _r P _3-r O ₁₂ (p , q, and r satisfy 0<p≦1, 0≦q<1, and 0≦r≦1, respectively.), more preferably LATP.

That is, the solid electrolyte 31 preferably contains aluminum as an element, and an oxide-based solid electrolyte is used in consideration of chemical stability.

The oxide-based solid electrolyte used for the solid electrolyte 31 includes an inverse fluorite type, a NASICON type, a perovskite type, a garnet type, and the like depending on the crystal structure, but is not particularly limited.

Examples of the oxide-based solid electrolyte used for the solid electrolyte 31 include solid electrolyte Li _1+p+q+r Al _p Ga _q (Ti, Ge) _2-pq Si _r P _3-r O ₁₂ (0<p≦1, 0 ≦q<1, 0≦r≦1) (hereinafter also referred to as LATP) can be used, and Li _1+p Al _p Ti _2-p P ₃ O ₁₂ (0≦p≦1) is particularly preferred.

The lithium ion conductive metal phosphate 32, in other words, said lithium ion conductive phosphorus compound is Li _{a Ab} D _c PO4 (where a, b, c are 0.9<a<1.1, 0< satisfies b ≤ 1, 0 ≤ c < 1, 0.9 < b + c < 1.1, A is at least one selected from the group consisting of Co, Mn, Ni, Fe, Cu and Cr, and D is is at least one selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, and Y).

The phosphorus compound 32 is preferably composed of a lithium ion conductive oxide containing phosphorus as an element, and more preferably composed of an intercalation material that functions alone as a positive electrode active material.

The lithium ion conductive oxide used in the phosphorus compound 32 of this embodiment is preferably LiaAbDcPO4 (where a, b, c are 0.9<a<1.1, 0<b≤1, 0≤c< 1, 0.9<b+c<1.1 is satisfied, A is at least one selected from the group consisting of Co, Mn, Ni, Fe, Cu and Cr, and D is Mg, Ca, Sr, Ba, At least one selected from the group consisting of Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, and Y.) A lithium phosphate-based lithium ion conductive oxide represented by be.

(Manufacturing method of positive electrode for lithium ion secondary battery)
The production method of the present invention is characterized by carrying out a pulverization step (nanoparticulation step) for pulverizing raw material particles, which will be described later.

In the electrolyte dispersion forming step, raw material particles and a dispersion solvent (preferably an alcohol solution) are mixed to prepare a mixed solution. As the alcohol, ethanol is preferable from the viewpoint of volatility and safety, but a mixture of multiple alcohol solutions may also be used.

The mixed solution is ball-milled to prepare a slurry according to the present invention in which the coating material nanoparticles are dispersed in the organic solvent so that the concentration of the raw material in the organic solvent is 2% by mass or more and 25% by mass or less. .

The coating method according to the manufacturing method of the present invention is characterized by carrying out mechanical coating after carrying out spray coating, making it possible to coat more uniformly than in the past.

The specific surface area of the particles is reduced by performing mechanical coating after spray coating. That is, preferably, the BET value BET _M of the mechanically applied positive electrode active material is equal to or less than the BET value BET _S of the spray applied positive electrode active material.

Although it is possible to use the sample after spray coating and mechanical coating as it is, it is preferable to perform heat treatment.

As a result, the adhesion of the coating layer according to the present invention to the positive electrode active material 30 is improved, the peeling of the coating layer from the positive electrode active material 30 is suppressed even after repeated charging and discharging, and the long-term reliability of the battery is improved. do.

<Spray coating method>
In the spray coating, the base material corresponding to the positive electrode active material 30 is wetted by the mist of the spray liquid containing the coating material nanoparticles sprayed from the spray nozzle, and at the same time, the solid coating material nanoparticles contained in the spray liquid are wetted. The component adheres to the surface of the base material and dries and solidifies to form a layer of coating material nanoparticles on the surface of the base material. A dynamic coating apparatus and a tumbling fluidized bed coating apparatus are suitable.

In the spray coating method treatment, the solvent to be used is not particularly limited as long as it is an organic solvent, and for example, an alcohol such as ethanol can be preferably used. Mixing a polymer material such as polyethylene glycol or polyvinyl alcohol with the solvent is preferable because aggregation of the coating material nanoparticles is suppressed and uniform coating is facilitated. The concentration of the coating material nanoparticles in the slurry during spray coating is, for example, 2 to 25 mass %.

The treatment temperature for spray coating is preferably 5 to 100°C, more preferably 8 to 80°C, still more preferably 10 to 50°C. Although the treatment time depends on the size of the apparatus, it is preferably 5 to 90 minutes, more preferably 10 to 60 minutes. The treatment atmosphere is not particularly limited, and is preferably an inert gas atmosphere or an air atmosphere.

<Mechanical coating method>
The mechanical coating method applies at least one or more external forces selected from the group consisting of shear force, compression force, impact force, and centrifugal force to a mixture containing coating material nanoparticles and a base material, thereby mechanically While in contact with the base material surface based on the energy derived from the contact of the external force (energy based on shear force and compression force is preferable, energy based on shear force, compression force and collision force is more preferable) It is a means for firmly fixing and covering the material, and the device to be used is not particularly limited. Among them, the operation is simple, there is no need to separate the balls after treatment as in a ball mill, coating proceeds preferentially over particle aggregation, and surface smoothness can be easily obtained. From the point of view of above, it is more preferable to use an attrition mill, more preferably a device comprising a bottomed cylindrical container and a rotor having tip blades, in which case the tip blades and the inner circumference of the container By providing a predetermined clearance between and rotating the rotor, it is preferable to apply a compressive force and a shear force to the mixture containing the coating material nanoparticles and the base material to perform mechanical coating.

The treatment by the mechanical coating method may be either dry or wet, and in the case of the wet method, an alcohol such as ethanol can be used as the organic solvent. In the wet method, the timing of adding the solvent is not particularly limited, but it is preferable to mechanically coat the slurry of the spray-applied positive electrode active material, which is obtained by mixing the spray-applied positive electrode active material with the solvent. The raw material particle concentration in the inside is preferably 80 to 99% by weight, more preferably 90 to 99% by weight, even more preferably 95 to 99% by weight.

The treatment temperature for mechanical coating is preferably 5 to 100°C, more preferably 8 to 80°C, still more preferably 10 to 50°C.

The treatment time for mechanical coating is preferably 5 to 90 minutes, more preferably 10 to 60 minutes.

The treatment atmosphere for mechanical coating is not particularly limited, but is preferably an inert gas atmosphere or an air atmosphere.

<Lithium ion secondary battery 1>
A lithium ion secondary battery 1 is composed of a positive electrode 2, a negative electrode 3, and a non-aqueous electrolyte 5 as shown in FIG.

The positive electrode 2 is produced by coating the positive electrode current collector 10 with a positive electrode mixture containing a positive electrode composite active material 20 (coated positive electrode active material), a conductive aid, a binder, and the like.

The positive electrode composite active material 20 is suitably used as an active material for the positive electrode 2 of the lithium ion secondary battery 1 .

The negative electrode 3 is produced by coating the negative electrode current collector 12 with a negative electrode mixture containing the negative electrode active material 21 , a conductive aid, a binder, and the like.

The positive electrode 2 can be formed by coating the positive electrode mixture on the positive electrode current collector 10 and then drying it at about 100 to 200.degree.

The negative electrode 3 can be formed by applying a negative electrode mixture to the negative electrode current collector 12 and then drying it at about 100 to 200.degree.

The configuration of the lithium ion secondary battery 1 using the positive electrode composite active material 20, the materials used other than the positive electrode composite active material 20, the manufacturing apparatus and conditions of the lithium ion secondary battery 1 can be applied to conventionally known ones, It is not particularly limited.

<Negative electrode active material 21>
As described above, it is preferable to use lithium titanate as the negative electrode active material 21 from the viewpoint that lithium deposition is less likely to occur and safety is improved. Among the lithium titanates, lithium titanate having a spinel structure is particularly preferable because the expansion and contraction of the active material in the lithium ion insertion/extraction reaction is small. Lithium titanate may contain trace amounts of elements other than lithium and titanium, such as Nb.

<Conductivity aid>
The conductive aid is not particularly limited, but a carbon material is preferable. Carbon materials include, for example, natural graphite, artificial graphite, vapor-grown carbon fiber, carbon nanotube, acetylene black, ketjen black, and furnace black.

One type of these carbon materials may be used, or two or more types may be used.

The amount of the conductive aid contained in the positive electrode 2 is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the positive electrode composite active material 20 .

If it is the said range, the electroconductivity of the positive electrode 2 can be ensured. Moreover, the adhesiveness with the binder is maintained, and sufficient adhesiveness with the positive electrode current collector 10 can be obtained.

The amount of the conductive aid contained in the negative electrode 3 is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the negative electrode active material 21 .

<Binder>
The binder is not particularly limited, but for both the positive electrode 2 and the negative electrode 3, for example, from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber, polyimide, and derivatives thereof At least one selected can be used.

The binder is preferably dissolved or dispersed in a non-aqueous solvent or water for ease of production of the positive electrode 2 and the negative electrode 3 .

Non-aqueous solvents include, but are not limited to, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, ethyl acetate, and tetrahydrofuran. A dispersant and a thickener may be added to these.

The amount of the binder contained in the positive electrode 2 is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the positive electrode composite active material 20 .

Within the above range, the adhesiveness between the positive electrode composite active material 20 and the conductive aid is maintained, and sufficient adhesiveness with the positive electrode current collector 10 can be obtained.

The amount of the binder contained in the negative electrode 3 is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the negative electrode active material 21 .

<Current collectors 10, 12>
Both the positive electrode current collector 10 and the negative electrode current collector 12 are preferably made of aluminum or an aluminum alloy. Aluminum or an aluminum alloy is not particularly limited because it is stable under the positive electrode reaction atmosphere and the negative electrode reaction atmosphere, but it is preferably high-purity aluminum represented by JIS standards 1030, 1050, 1085, 1N90, 1N99, etc. preferable.

Although the thickness of the current collectors 10 and 12 is not particularly limited, it is preferably 10 μm or more and 100 μm or less. Within this range, it is easy to achieve a good balance in terms of handleability in battery production, cost, and obtained battery characteristics. The current collectors 10 and 12 may be made of a metal other than aluminum (copper, SUS, nickel, titanium, and alloys thereof) coated with a metal that does not react with the potential of the positive electrode 2 and the negative electrode 3. can.

<Nonaqueous electrolyte 5>
The non-aqueous electrolyte 5 is not particularly limited, but a non-aqueous electrolytic solution in which a solute is dissolved in a non-aqueous solvent, a gel electrolyte in which a polymer is impregnated with a non-aqueous electrolytic solution in which a solute is dissolved in a non-aqueous solvent, or the like is used. be able to.

The non-aqueous solvent preferably contains a cyclic aprotic solvent and/or a chain aprotic solvent. Examples of cyclic aprotic solvents include cyclic carbonates, cyclic esters, cyclic sulfones and cyclic ethers. As the chain aprotic solvent, a chain carbonate, a chain carboxylic acid ester, a chain ether, a solvent generally used as a solvent for non-aqueous electrolytes, such as acetonitrile, may be used. More specifically, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyl lactone, 1,2-dimethoxyethane, sulfolane, dioxolane, propion Methyl acid and the like can be used. These solvents may be used alone, or two or more of them may be used in combination. is preferably used.

Chains exemplified by dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, and methyl propyl carbonate, when two or more types are mixed, have high stability at high temperatures and high lithium conductivity at low temperatures. It is preferable to mix one or more of cyclic carbonates, and one or more of cyclic compounds exemplified by ethylene carbonate, propylene carbonate, butylene carbonate, and γ-butyl lactone, and dimethyl carbonate, methylethyl carbonate, and diethyl carbonate. It is particularly preferable to mix one or more chain carbonates exemplified by carbonate with one or more cyclic carbonates exemplified by ethylene carbonate, propylene carbonate and butylene carbonate.

The solute used in the non-aqueous electrolyte 5 is not particularly limited, but examples include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiBOB (Lithium Bis (Oxalato) Borate), LiN (SO ₂ CF ₃ ) ₂ and the like are preferable because they are easily dissolved in a solvent. The concentration of the solute contained in the non-aqueous electrolyte 5 is preferably 0.5 mol/L or more and 2.0 mol/L or less. If the solute concentration is less than 0.5 mol/L, the desired lithium ion conductivity may not be exhibited, while if the solute concentration is higher than 2.0 mol/L, the solute may not dissolve any more.

Although the amount of the non-aqueous electrolyte 5 is not particularly limited, it is preferably 0.1 mL or more and 10 mL or less per 1 Ah of battery capacity. With this amount, the conduction of lithium ions accompanying the electrode reaction can be ensured, and the desired battery performance is exhibited.

The non-aqueous electrolyte 5 may be included in the positive electrode 2, the negative electrode 3, and the separator 6 in advance if it has fluidity, or the separator 6 may be placed between the positive electrode 2 side and the negative electrode 3 side. It may be added once or after lamination.

The lithium ion secondary battery 1 normally further includes a separator 6 and an exterior material in addition to the above-described configuration.

(Separator 6)
The separator 6 is placed between the positive electrode 2 and the negative electrode 3, and may have any structure as long as it is insulating and can contain the non-aqueous electrolyte 5. Examples thereof include nylon, cellulose, polysulfone, polyethylene, polypropylene, polybutene, and polyacrylonitrile. , polyimide, polyamide, polyethylene terephthalate, and woven fabrics, non-woven fabrics, and microporous membranes of composites of two or more thereof.

The separator 6 is a nonwoven fabric of nylon, cellulose, polysulfone, polyethylene, polypropylene, polybutene, polyacrylonitrile, polyimide, polyamide, polyethylene terephthalate, or a composite of two or more of these, because of its excellent stability of cycle characteristics. is preferred.

The separator 6 may contain various plasticizers, antioxidants, and flame retardants, or may be coated with metal oxide or the like. Although the thickness of the separator 6 is not particularly limited, it is preferably 10 μm or more and 100 μm or less. Within this range, it is possible to prevent the positive electrode 2 and the negative electrode 3 from being short-circuited while suppressing an increase in battery resistance. From the viewpoint of economy and handling, it is more preferable that the thickness is 15 μm or more and 50 μm or less.

The porosity of the separator 6 is preferably 30% or more and 90% or less. When it is 30% or more, the diffusibility of lithium ions is less likely to decrease, so that the cycle characteristics can be easily maintained. be able to.

The porosity of the separator 6 is more preferably 35% or more and 85% or less from the viewpoint of the balance between ensuring lithium ion diffusibility and short circuit prevention. % or less is particularly preferred.

(Exterior material)
The exterior material is a member that encloses a laminate obtained by alternately laminating or winding the positive electrode 2, the negative electrode 3, and the separator 6, and a terminal that electrically connects the laminate. As the exterior material, a composite film in which a thermoplastic resin layer for heat sealing is provided on a metal foil, or a metal layer formed by vapor deposition or sputtering can be used. Also, square, elliptical, cylindrical, coin-shaped, button-shaped or sheet-shaped metal cans are preferably used.

(Manufacturing method of lithium ion secondary battery 1)
Next, a method for manufacturing the lithium ion secondary battery 1 of this embodiment will be described.

The lithium ion secondary battery 1 of the present embodiment mainly includes a positive electrode forming process for forming the positive electrode 2, a negative electrode forming process for forming the negative electrode 3, and a secondary battery in which the positive electrode 2, the negative electrode 3, and the non-aqueous electrolyte 5 are assembled. It is configured by an assembly process.

(Positive electrode forming step)
In the positive electrode forming step, first, the coating material particles are first pulverized by a pulverizing device such as a ball mill so that the average particle size is, for example, 20 nm or less, and the coating material nanoparticles are dispersed in an organic solvent that is a dispersion solvent, thereby dispersing the electrolyte. An electrolyte dispersion forming step is performed to form a slurry that is a body. Here, this electrolytic dispersion forming step also includes an operation of setting the concentration of the raw material in the organic solvent to 2% by mass or more and 25% by mass or less.

The electrolyte dispersion formed at this time is a transparent sol in a sol state, and is an electrolyte sol having fluidity. Also, the solid electrolyte 31 in the electrolyte dispersion is partially amorphous because the crystal structure is partially destroyed by the pulverization process.

Subsequently, the electrolyte dispersion is adhered to the positive electrode active material 30 by a spray coating device such as a fluidized bed coating device to form an electrolyte adhered body (electrolyte adhered body forming step).

Subsequently, the electrolyte dispersion is ground into the positive electrode active material 30 by a grinding device such as a grinding mill to form a ground material (ground material forming step).

Subsequently, the pulverized material is heat-treated to remove the dispersion solvent from the pulverized material to form the positive electrode composite active material 20 (removal step).

The heat treatment temperature at this time is preferably 300° C. or higher, more preferably 350° C. or higher.

If the heat treatment temperature is lower than 300° C., the adhesion between the positive electrode active material 30 and the solid electrolyte 31 is insufficient, so the solid electrolyte 31 may separate during charging and discharging of the battery, leading to a decrease in long-term reliability of the battery. .

On the other hand, if the heat treatment temperature is too high, the crystal structure of the solid electrolyte 31 will change, the Li ion conductivity will decrease, and charging and discharging of the battery may not be performed normally. It is preferably 500° C. or less, more preferably 500° C. or less. The heat treatment time is preferably 30 minutes or longer, more preferably 1 hour or longer, and the upper limit is not particularly limited, but is, for example, 3 hours or shorter.

The positive electrode composite active material 20 obtained by the above steps is mixed with a conductive aid and a binder to prepare a positive electrode mixture, which is applied to the positive electrode current collector 10 (positive electrode application step).

Subsequently, the positive electrode current collector 10 coated with the positive electrode mixture is dried to form the positive electrode 2 (positive electrode drying step).

The positive electrode 2 formed by the above steps is assembled together with the negative electrode 3 formed by the negative electrode forming step and the non-aqueous electrolyte 5 in the same manner as in the prior art to complete the lithium ion secondary battery 1 .

In the above-described embodiment, the pulverization step of pulverizing the solid electrolyte 31 to an average particle size of 20 nm or less was performed before the electrolyte dispersion forming step. Since the solid electrolyte 31 is pulverized and dispersed in the dispersion solvent at the same time, the positive electrode forming process can be simplified, and the solid electrolyte 31 is less likely to aggregate in the pulverized product forming process. It is difficult to cause variations in the coating of

In this case, the electrolyte dispersion preferably has a solid content concentration of the solid electrolyte 31 in the dispersion solvent of 2% or more and 7% or less.

In the application example described above, the positive electrode composite active material 20 is formed by covering the positive electrode active material 30 with the solid electrolyte 31, but the negative electrode active material 21 may be covered with the solid electrolyte 31 to form the negative electrode composite active material. In this case, the negative electrode active material 21 is preferably titanium oxide such as lithium titanate (for example, Li ₄ Ti ₅ O ₁₂ ).

As long as the above-described embodiments are within the technical scope of the present invention, each component can be freely replaced or added between the embodiments.

Hereinafter, the present invention will be described more specifically with reference to experimental examples.

The present invention is not limited by the following experimental examples, and it is of course possible to make appropriate modifications within the scope that can be adapted to the spirit of the above and later descriptions, and all of them are technical aspects of the present invention. Included in scope.

Batteries obtained in the following experimental examples were evaluated by the following methods.

(Gas generation amount)
The amount of gas generated by the lithium ion secondary battery before and after the cycle characteristics evaluation in each experimental example was evaluated using the Archimedes method, that is, the buoyancy of the lithium ion secondary battery. Evaluation was performed as follows.

First, the weight of the lithium ion secondary battery was measured with an electronic balance. Next, the weight in water was measured using a hydrometer (manufactured by Alpha Mirage Co., Ltd., product number: MDS-3000), and the buoyancy was calculated by taking the difference between these weights. The volume of the lithium ion secondary battery was calculated by dividing this buoyancy by the density of water (1.0 g/cm ³ ). The amount of generated gas was calculated by comparing the volume after aging and the volume after the following cycle characteristic evaluation. Those with a gas generation amount of less than 20 ml were judged to be good.

(Evaluation of cycle characteristics of lithium-ion secondary battery)
The lithium-ion secondary battery produced in the experimental example was connected to a charge/discharge device (HJ1005SD8, manufactured by Hokuto Denko Co., Ltd.) and subjected to cycle operation. Under an environment of 60° C., constant current charging was performed at a current value corresponding to 1.0 C until the battery voltage reached the final voltage of 3.4 V, and charging was stopped. Subsequently, constant current discharge was performed at a current value corresponding to 1.0 C, and discharge was stopped when the battery voltage reached 2.5V. This cycle was defined as one cycle, and charging and discharging were repeated. The stability of the cycle characteristics was evaluated by taking the discharge capacity at the 500th time assuming that the discharge capacity at the first time was 100, as a discharge capacity retention rate (%). A discharge capacity retention rate of 80% or more at the 500th cycle was judged as good, and a discharge capacity retention rate of less than 80% was judged as unsatisfactory.

(Synthesis Example 1: Preparation of ethanol dispersion slurry of LATP fine powder)
Using Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ (hereinafter also referred to as LATP) as a solid electrolyte, an ethanol dispersion slurry of LATP fine powder was prepared.

A predetermined amount of Li ₂ CO ₃ , AlPO ₄ , TiO ₂ , NH ₄ H ₂ PO ₄ and ethanol as a solvent were mixed as starting materials, and subjected to planetary ball mill treatment at 150 G for 1 hour using zirconia balls with a diameter of 3 mm. . After removing the zirconia balls from the treated mixture with a sieve, the mixture was dried at 120° C. to remove the ethanol. Thereafter, treatment was performed at 800° C. for 2 hours to obtain LATP powder.

The obtained LATP powder was mixed with a predetermined amount of ethanol as a solvent, and subjected to planetary ball mill treatment using zirconia balls having a diameter of 0.5 mm for 1 to 3 hours. After removing the zirconia spheres from the treated mixture with a sieve, an ethanol-dispersed slurry containing 5.6% by weight of LATP fine powder was obtained.

A portion of the resulting slurry was concentrated and dried at 120° C. to remove ethanol, confirming that the d _BET of the LATP fine powder was 3 to 25 nm.

(Synthesis Example 2: Preparation of ethanol dispersion slurry of LFP fine powder)
As the phosphorus compound, lithium iron phosphate (LiFePO4, hereinafter also referred to as LFP) powder having a surface area of 9.5 m / g and a median diameter of 1.5 μm is used. Planetary ball milling was performed for 3 hours using 0.5 mm zirconia balls.

After removing the zirconia spheres from the treated mixture with a sieve, an ethanol-dispersed slurry containing 5.6% by weight of LFP fine powder was obtained.

A portion of the resulting slurry was dried at 120° C. to remove ethanol, confirming that the LFP fine powder had a d _BET of 20 to 80 nm.

(Example 1)
(i Preparation of positive electrode)
Spinel-type lithium nickel manganate (LiNi _0.5 Mn _1.5 O ₄ , hereinafter also referred to as LNMO) with a median diameter of 20 μm was used as the active material for the positive electrode, and 400 g of this LNMO was placed in a tumbling flow apparatus (Powrex Co., Ltd.). (product name: Multiplex), and pulverized by planetary ball milling for 1 hour in Synthesis Example 1 at an air supply temperature of 80°C. /min. Spray coating was performed to obtain LNMO with LATP attached to the surface.

The BET value of this LNMO powder with LATP adhered to the surface was 4.1 m 2 /g.

40 g of LNMO with this LATP attached to the surface is put into a grinding mill (manufactured by Hosokawa Micron Corporation, product name: Nobilta), and the clearance is 0.6 mm, the rotor load power is 0.8 kW, and the rotor rotation speed is in the range of 2600 rpm to 3000 rpm. After mechanical coating was performed by processing at room temperature for 10 minutes in an air atmosphere to obtain an LNMO whose surface was coated with LATP, this surface-coated LNMO was heat-treated at 350 ° C. for 1 hour to obtain a positive electrode composite active material. got the substance.

The BET value of this positive electrode composite active material was 1.3 m ² /g.

N - A slurry dispersed in methyl-2-pyrrolidone (NMP) was prepared. The binder used was prepared in an N-methyl-2-pyrrolidone (NMP) solution having a solid concentration of 5% by weight, and NMP was further added to adjust the viscosity so as to facilitate the later-described coating.

After coating the slurry on a 20 μm aluminum foil, it was dried in an oven at 120°C. After this operation was performed on both sides of the aluminum foil, the positive electrode was produced by vacuum drying at 170°C.

(ii Preparation of negative electrode)
Spinel-type lithium titanate (Li ₄ Ti ₅ O ₁₂ , hereinafter also referred to as LTO) is used as the negative electrode active material, and this LTO, acetylene black as a conductive aid, and polyvinylidene fluoride (PVdF) as a binder are used. , 100 parts by weight, 5 parts by weight, and 5 parts by weight in terms of solid concentration, respectively, was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a slurry. The binder was prepared as an NMP solution having a solid concentration of 5% by weight, and NMP was further added to adjust the viscosity so as to facilitate the later-described coating.

After coating the slurry on a 20 μm aluminum foil, it was dried in an oven at 120°C. After this operation was performed on both sides of the aluminum foil, the negative electrode was produced by vacuum-drying at 170°C.

(iii Production of lithium ion secondary battery)
Using the positive and negative electrodes produced in (i) and (ii) above and a polypropylene separator having a thickness of 20 μm, a battery was produced in the following procedure.

First, the positive and negative electrodes were dried under reduced pressure at 80° C. for 12 hours. Next, 15 positive electrodes and 16 negative electrodes were laminated in the order of negative electrode/separator/positive electrode. Both of the outermost layers were made to serve as separators. Next, aluminum tabs were vibration-welded to the positive and negative electrodes at both ends.

Two sheets of aluminum laminate films were prepared as exterior materials, and after forming a recess for the battery portion and a recess for the gas trapping portion by pressing, the electrode laminate was put therein.

The outer periphery leaving a space for non-aqueous electrolyte injection is heat-sealed at 180 ° C. for 7 seconds, and ethylene carbonate, propylene carbonate, and ethyl methyl carbonate are removed from the unsealed portion on a volume basis, ethylene carbonate/propylene carbonate/ After adding a non-aqueous electrolyte prepared by dissolving LiPF ₆ at a ratio of 1 mol/L in a solvent mixed with ethyl methyl carbonate at a ratio of 15/15/70, the unsealed portion was heated to 180° C. for 7 seconds while reducing the pressure. It was heat sealed with

The obtained battery was subjected to constant current charging at a current value corresponding to 0.2 C until the battery voltage reached the final voltage of 3.4 V, and charging was stopped. Then, after standing in an environment of 60° C. for 24 hours, constant current discharge was performed at a current value corresponding to 0.2 C, and discharge was stopped when the battery voltage reached 2.5V. After the discharge was stopped, the gas collected in the gas collecting portion was extracted, and the sealing was performed again. A lithium ion secondary battery for evaluation was produced by the above operation.

(Example 2)
A lithium ion secondary battery for evaluation was produced in the same manner as in Experimental Example 1, except that the LFP produced in Synthesis Example 2 was used to produce a surface-coated LNMO in the production of the positive electrode.

(Example 3)
A lithium-ion secondary battery for evaluation was produced in the same manner as in Experimental Example 1, except that 1.2 g of ethanol was added during the mechanical coating in the production of the positive electrode.

(Comparative example 1)
A lithium ion secondary battery for evaluation was produced by performing the same operation as in Experimental Example 1, except that only mechanical coating was performed without spray coating in the preparation of the positive electrode to prepare a surface-coated LNMO. .

(Comparative example 2)
A lithium-ion secondary battery for evaluation was produced in the same manner as in Experimental Example 1, except that a surface-coated LNMO was produced without performing mechanical coating after spray coating in the production of the positive electrode.

(Comparative Example 3)
A lithium ion secondary battery for evaluation was produced by performing the same operation as in Experimental Example 2, except that only mechanical coating was performed without spray coating in the preparation of the positive electrode to prepare a surface-coated LNMO. .

(Evaluation results of Examples and Comparative Examples)
Table 1 shows the evaluation results of Examples 1 to 3 and Comparative Examples 1 to 7.

In the lithium ion secondary batteries of Examples 1 and 2, the amount of gas generated was remarkably smaller than that of the prior art in the cycle characteristic evaluation, and the capacity retention rate was also high. That is, in Examples 1 and 2, the amount of gas generated was less than 5 ml, and the capacity retention rate was 94% or more. Also, in Example 3 in which ethanol was added during mechanical coating, the amount of gas generated was reduced.

On the other hand, Comparative Examples 1 and 2 use the same LATP as the coating material as in Example 1, and Comparative Example 3 uses the same LFP as the coating material as in Example 2, but only mechanical coating or spray coating was performed as the coating method. A large amount of gas was generated, and the capacity retention rate also decreased.

From the above results, it is speculated that the nanoparticles of the solid electrolyte and the lithium ion conductive phosphorus compound can be coated more densely by performing mechanical coating after performing spray coating as a coating method. It was suggested that the

The composite active material of the present invention is suitably used as an electrode active material for lithium ion secondary batteries.

REFERENCE SIGNS LIST 1 lithium ion secondary battery 2 positive electrode 3 negative electrode 5 non-aqueous electrolyte 10 positive electrode current collector 21 negative electrode active material 30 positive electrode active material 31 oxide-based solid electrolyte 32 phosphorous oxide-based solid electrolyte 40 amorphous portion 41 crystalline portion

Claims (4)

A method for producing a positive electrode for a lithium ion secondary battery comprising a positive electrode active material coated on the surface with a coating layer made of a coating material containing a lithium ion conductive metal oxide and/or phosphorous oxide, comprising: ,
an electrolyte dispersion forming step of ball milling the coating material in an organic solvent to obtain a slurry having a concentration of the coating material nanoparticles in the organic solvent of 2% by mass or more and 25% by mass or less;
a step of forming an electrolyte deposit to obtain a spray-applied positive electrode active material by spray-coating the slurry onto the positive electrode active material;
a grinding product forming step for obtaining a mechanically applied positive electrode active material by applying an external force to the spray applied positive electrode active material,
A method for producing a positive electrode for a lithium ion secondary battery, wherein the BET value BET _M of the mechanically applied positive electrode active material is equal to or lower than the BET value BET _S of the spray applied positive electrode active material. 2. The method for producing a positive electrode for a lithium ion secondary battery according to claim 1, wherein the ground material forming step is carried out in the state of a spray-applied positive electrode active material slurry, which is obtained by mixing the spray-applied positive electrode active material and an organic solvent. . 3. The lithium according to claim 1, wherein the positive electrode active material coated with the coating layer has an average lithium desorption and insertion potential of 4.5 V or more and 5.0 V or less with respect to Li+/Li. A manufacturing method for an ion secondary battery. The lithium ion conductive metal oxide is LATP, which is an oxide-based solid electrolyte,
The lithium ion conductive metal phosphate is LFP, and
The method for producing a lithium ion secondary battery according to any one of claims 1 to 3, wherein the positive electrode active material is LNMO.