JP2021106113A - Positive electrode, lithium ion secondary battery, positive electrode manufacturing method, and lithium ion secondary battery manufacturing method - Google Patents

Abstract

To provide a positive electrode active material for a lithium ion secondary battery, a positive electrode, and a lithium ion secondary battery capable of achieving both excellent slurry stability and excellent cycle characteristics.SOLUTION: In a positive electrode according to an embodiment of the present invention, a positive electrode active material layer including a positive electrode active material containing a lithium transition metal oxide and an oxide solid electrolyte and a phosphonic acid compound as additives is formed on a positive electrode current collector.SELECTED DRAWING: None

Description

Embodiments of the present invention relate to a positive electrode, a lithium ion secondary battery, a method for manufacturing a positive electrode, and a method for manufacturing a lithium ion secondary battery.

With the increase in technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, lithium ion secondary batteries having a high energy density and voltage, a long cycle life, and a low self-discharge rate are commonly used and widely used. Currently, research is being vigorously pursued to increase the capacity and energy density of such lithium-ion secondary batteries.

However, in order to increase the capacity of such a lithium ion secondary battery, the slurry stability of the positive electrode active material slurry may be lowered or sufficient life characteristics may not be obtained, and improvement of these characteristics is desired. There is.

Japanese Unexamined Patent Publication No. 2000-034134

JP-A-2017-010923

An object to be solved by the present invention is to provide a positive electrode active material for a lithium ion secondary battery, a positive electrode, and a lithium ion secondary battery capable of achieving both excellent slurry stability and excellent cycle characteristics. Is.

According to one aspect of the present invention, a positive electrode active material layer containing a positive electrode active material containing a lithium transition metal oxide and an oxide solid electrolyte and a phosphonic acid compound as additives was formed on the positive electrode current collector. , Positive electrode is provided. As used herein, the term "lithium transition metal oxide" means a compound containing lithium and a transition metal and having a transition metal-oxygen bond, and contains a typical metal element such as aluminum and a non-metal element other than oxygen. Including things. Further, the "oxide solid electrolyte" means a compound in which electricity flows by moving ions in the solid and contains oxygen. The "phosphonic acid compound" is an inorganic phosphonic acid represented by the demonstrative formula HP (= O) (OH) ₂ (hereinafter, simply referred to as "phosphonic acid") and the demonstrative formula RP (=). It is a general term for organic phosphonic acids represented by O) (OH) ₂ (R: any organic group), and salts, esters and other derivatives thereof.

In the positive electrode according to the above aspect, the lithium transition metal oxide may contain 50 mol% or more of nickel based on the total amount of transition metals.

In the positive electrode according to the above aspect, the lithium transition metal oxide may contain 80 mol% or more of nickel based on the total amount of transition metals.

In the positive electrode according to the above aspect, the oxide solid electrolyte may have lithium ion conductivity.

In the positive electrode according to the above aspect, the content of the oxide solid electrolyte in the positive electrode active material layer can be 0.01% by weight or more and 5% by weight or less.

In the positive electrode according to the above aspect, the phosphonic acid compound can form a coating on the surface of the particles of the lithium transition metal oxide.

The amount of the phosphonic acid compound added may be 0.01% by weight or more and 5% by weight or less based on the weight of the positive electrode active material layer.

The phosphonic acid compound can be a phosphonic acid or an organic phosphonic acid.

According to another aspect of the present invention, a lithium ion comprising a positive electrode according to the above aspect and a negative electrode having a negative electrode active material layer containing a negative electrode active material containing silicon or a silicon compound formed on a negative electrode current collector. Secondary batteries are provided.

The lithium ion secondary battery according to the above aspect may further include an electrolytic solution containing at least one of fluoroethylene carbonate and difluoroethylene carbonate.

According to another aspect of the present invention, it is a method for manufacturing a positive electrode for a lithium ion secondary battery.
A step of obtaining a positive electrode active material slurry by mixing a lithium transition metal oxide, an oxide solid electrolyte, a phosphonic acid compound, and a solvent.
A step of obtaining a positive electrode by forming a positive electrode active material layer on a positive electrode current collector by drying the positive electrode active material slurry.
A method for manufacturing a positive electrode is provided.

According to another aspect of the present invention, it is a method for manufacturing a lithium ion secondary battery.
The step of obtaining a positive electrode by the method for manufacturing a positive electrode according to the above aspect, and
A step of obtaining a negative electrode by forming a negative electrode active material layer containing a negative electrode active material containing silicon or a silicon compound on a negative electrode current collector, and
A step of interposing a separator and an electrolytic solution between the positive electrode and the negative electrode,
A method for manufacturing a lithium ion secondary battery including the above is provided.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited thereto.

As used herein, the "average particle size" means the particle size at an integrated value of 50% in the particle size distribution measured by the laser diffraction / scattering method, that is, the median diameter (D ₅₀ ).

Regarding the problems of slurry stability and life characteristics at high temperatures that may occur with the increase in capacity of lithium ion secondary batteries, as an example, a lithium ion secondary battery that uses a lithium transition metal oxide having a high nickel content as a positive electrode material. Will be taken up and explained.

As the positive electrode material of a lithium ion secondary battery, in Li _a Ni _x Co _y Mn _z lithium-nickel-cobalt-manganese ternary positive electrode active material, such as O _2, increase the capacity by increasing the amount of nickel in the composition It is known that it can be done. However, in the lithium nickel cobalt manganese ternary positive electrode active material, the alkalinity increases as the amount of nickel increases. When such an alkaline positive electrode active material is used, the reaction with polyvinylidene fluoride (PVdF), which is generally used as a binder, and moisture in the atmosphere causes gelation and viscosity increase of the positive electrode active material slurry, resulting in slurry stability. May be difficult to apply to the electrode current collector.

On the other hand, as for the negative electrode material _{, silicon-based materials such as silicon (Si) and silicon oxide (SiO x} ) have a higher theoretical capacity density than carbon-based materials such as graphite, which are currently mainstream, and therefore lithium ions. It is expected as a negative electrode active material that improves the energy density of secondary batteries. However, in carbon-based materials that are widely used as negative electrode materials at present, an SEI (Solid Electrolyte Interface) film is formed at the electrode-electrolyte solution interface at the time of initial charging, and this SEI film is maintained even after repeated charging and discharging. In contrast to the suppression of side reactions with the electrolytic solution, silicon-based materials have large expansion and contraction during charging and contraction during discharge. Therefore, this expansion and contraction causes cracks on the particle surface and inside the particles, and the SEI coating. It may be damaged or fall off, which may adversely affect the cycle characteristics (that is, the life characteristics) of the battery. Therefore, when a silicon-based material is used as the negative electrode material, fluoroethylene carbonate (FEC) or difluoroethylene carbonate (DFEC), which are SEI forming agents, are added to the electrolytic solution to form a good film for each charge and discharge. Is effective. However, when a highly alkaline positive electrode material is used as described above, FEC and DFEC in the electrolytic solution react with the alkaline component of the positive electrode active material, and carbon dioxide gas, carbon monoxide, etc. are particularly generated at a high temperature of 45 ° C. or higher. Gas can be generated. Accumulation of these gases between the electrodes and the separator may deteriorate the life characteristics of the battery.

When a positive electrode active material containing a lithium transition metal oxide is used in a lithium ion secondary battery, the present inventor adds an oxide solid electrolyte and a phosphonic acid compound to the slurry stability of the positive electrode active material slurry. We have found that the cycle characteristics of a lithium ion secondary battery can be improved, and have completed the present invention.

In addition, the present inventor has remarkable problems with the slurry stability of the positive electrode active material slurry and the life characteristics at high temperatures, especially when the positive electrode active material is alkaline, such as when the nickel content of the lithium transition metal oxide is high. It has been found that the present invention may be particularly effective because it may be found in.

[Lithium-ion secondary battery]
The lithium ion secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. Further, the lithium ion secondary battery may selectively include a battery case for accommodating an electrode assembly composed of a positive electrode, a negative electrode, and a separator, and a sealing member for sealing the battery case.

[Positive electrode]
In the lithium ion secondary battery according to the embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on one surface or both surfaces of the positive electrode current collector. The positive electrode active material layer may be formed on the entire surface of the positive electrode current collector, or may be formed only on a part of the surface of the positive electrode current collector. For example, the positive electrode according to the embodiment is a positive electrode for a lithium ion secondary battery containing an electrolytic solution.

(Positive current collector)
The positive electrode current collector used for the positive electrode is not particularly limited as long as it can be used electrochemically stably and has conductivity. For example, the positive electrode current collector may be stainless steel; aluminum; nickel; titanium; or an alloy thereof, or may be one kind or a mixture of two or more kinds composed of a combination thereof. Further, the surface of calcined carbon or aluminum or stainless steel may be surface-treated with carbon, nickel, titanium, silver or the like.

The positive electrode current collector can have a thickness of 3 μm or more and 500 μm or less. It is also possible to form fine irregularities on the surface of the positive electrode current collector to enhance the adhesive force with the positive electrode active material. The positive electrode current collector can have various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric.

(Positive electrode active material layer)
The positive electrode active material layer is formed by applying a positive electrode active material slurry in which a mixture of a positive electrode active material, a positive electrode additive, a conductive agent, and a binder is dissolved and dispersed in a solvent to a positive electrode current collector, and then drying and rolling. can do.

(Positive electrode active material)
As the positive electrode active material, a lithium transition metal oxide capable of occluding and releasing lithium can be used. The positive electrode active material may contain, for example, a nickel-containing lithium transition metal oxide, preferably a lithium transition metal oxide having a high nickel content. Here, "high nickel content" means that 50 mol% or more of nickel is contained based on the total amount of transition metals.

The content of the positive electrode active material can be 80% by weight or more and 99.5% by weight or less with respect to the total weight of the positive electrode active material layer. The content of the positive electrode active material can be preferably 85% by weight or more and 98.5% by weight or less. When the content of the positive electrode active material is within the above range, excellent capacitance characteristics can be realized. On the other hand, when the content of the positive electrode active material is less than the above range, the coating amount of the positive electrode increases, the thickness increases, and a sufficient volumetric energy density may not be achieved. There is a possibility that the binder and the conductive material are insufficient, and as a result, the conductivity and the adhesive force of the electrodes are insufficient, and the performance of the battery is deteriorated.

(Lithium transition metal oxide)
Examples of the lithium metal composite oxide, lithium - manganese oxide _(e.g., such as _{LiMnO 2, LiMnO 3, LiMn 2} O 3, LiMn 2 O 4); lithium - cobalt oxide (e.g., LiCoO ₂₎ ; lithium - nickel based oxide (e.g., LiNiO _2); lithium - copper oxide _(e.g., Li 2 CuO _2); lithium - vanadium oxides (e.g., such as _LiV 3 _{O 8);} lithium - nickel -Mangane oxides (eg LiNi _1-z Mn _z O ₂ (0 <z <1), LiMn _2-z Ni _z O ₄ (0 <z <2), etc.); Lithium-nickel-cobalt oxide (for _{example, LiNi 1-y Co y O 2} (0 <y <1)); lithium - manganese - cobalt oxide _{(e.g., LiCo 1-z Mn z O} 2 (0 <z <1), LiMn 2 _{-y Co y O 4 (0 <} y <2) , etc.); lithium - nickel - manganese - cobalt oxide _{(e.g., Li (Ni x Co y Mn} z) O 2 (0 <x <1,0 <y _{<1,0 <z <1, x} + y + z = 1), Li (Ni x Co y Mn z) O 4 (0 <x <2,0 <y <2,0 <z <2, x + y + z = 2) , etc.) ; lithium - nickel - cobalt - metal (M) oxide (for _example, a _{Li (Ni x Co y Mn z} M w) O 2 (M is Al, Fe, V, Cr, Ti, Ta, Mg, and Mo Selected from the group, 0 <x <1, 0 <y <1, 0 <z <1, 0 <w <1, x + y + z + w = 1), etc.); Li
Excess solid solution positive electrode _{(e.g., pLi 2 MnO 3 - (1} -p) Li (Ni x Co y Mn z) O 2 (0 <x <1,0 <y <1,0 <z <1, x + y + z = 1, 0 <p <1); Examples thereof include compounds in which the transition metal element in these compounds is partially replaced with another one or more metal elements. The positive electrode active material layer is any of these. Can include, but is not limited to, one or more compounds.

In particular, examples of the content of active nickel high capacity high lithium transition metal oxide _{cell, Li a NiO 2 (0.5 ≦} a ≦ 1.5); Li a (Ni x Co y Mn z ) O ₂ (0.5 ≦ a ≦ 1.5, 0.5 ≦ x <1, 0 <y <0.5, 0 <z <0.5, x + y + z = 1); Li _a Ni _1-y Co _y O ₂ (0.5 ≦ a ≦ 1.5, 0 <y ≦ 0.5); Li _a Ni _1-z Mn _z O ₂ (0.5 ≦ a ≦ 1.5, 0 <z ≦ 0. _{5); Li a (Ni x} Co y Mn z) O 4 (0.5 ≦ a ≦ 1.5,1 ≦ x <2,0 <y <1,0 <z <1, x + y + z = 2); Li _{a (Ni x Co y M w} ) O 2 (M is, Al, Fe, V, Cr , Ti, Ta, Mg, Mo, Zr, Zn, 1 kind selected from the group consisting of Ga, and in or 2 Elements of more than one species, 0.5 ≦ a ≦ 1.5, 0.5 ≦ x <1, 0 <y <0.5, 0 <w <0.5, x + y + w = 1); Li _a (Ni) _{x Co y Mn z M w)} O 2 (M is, Al, Fe, V, Cr , Ti, Ta, Mg, Mo, Zr, Zn, 1 kind or two kinds selected from the group consisting of Ga, and in These elements are 0.5 ≦ a ≦ 1.5, 0.5 ≦ x <1, 0 <y <0.5, 0 <z <0.5, 0 <w <0.5, x + y + z + w = 1); Transition metal atoms in these compounds are at least partially other metal elements of one or more (eg, Al, Fe, V, Cr, Ti, Ta, Mg, Mo, Zr, Zn, Compounds substituted with one or more of Ga and In; oxygen atoms in these compounds are partially other one or more non-metallic elements (eg, P, F, S). , And a compound substituted with one or more of N). The positive electrode active material can include, but is not limited to, one or more of these. Further, even within the same particle, there may be a distribution in the concentration substituted between the inside and the surface layer. Further, the surface of the particles may be coated. For example, a surface coated with a metal oxide, a lithium transition metal oxide, a polymer, or the like can be mentioned, but the present invention is not limited thereto.

In particular, in terms of improving the capacity characteristics and stability of the battery, Li _a NiO ₂ , Li _a (Ni _0.5 Mn _y Co _z ) O ₂ (y + z = 0.5), Li _a (Ni _0.6 Mn) _y Co _z ) O ₂ (y + z = 0.4), Li _a (Ni _0.7 Mn _y Co _z ) O ₂ (y + z = 0.3), Li _a (Ni _0.8 Mn _y Co _z ) O _{2 (y + z = 0.2),} Li a (Ni 0.8 Co y Mn z Al w) O 2 (y + z + w = 0.2), Li a (Ni 0.85 Co y Mn z) O 2 (y + z = 0 .15), Li _a (Ni _0.85 Co _y Mn _z Al _w ) O ₂ (y + z + w = 0.15), Li _a (Ni _0.9 Co _y Mn _z ) O ₂ (y + z = 0.1), _{Li a (Ni 0.9 Co y Mn} z Al w) O 2 (y + z + w = 0.1), Li a (Ni 0.9 Co y Mn z) O 2 (y + z = 0.1), Li a (Ni _0.95 Co _y Mn _z Al _w), such as _{O 2 (y + z + w} = 0.05) is preferred. Here, the value of a can be, for example, 0.5 ≦ a ≦ 1.5, preferably 1.0 ≦ a ≦ 1.5.

More specifically, LiNiO ₂ , Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ , Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ , Li (Ni _{0. 7} Mn _0.15 Co _0.15 ) O ₂ , Li (Ni _0.8 Mn _0.1 Co _0.1 ) O ₂ , Li (Ni _0.8 Co _0.15 Al _0.05 ) O ₂ , Li (Ni _0.8 Co _0.1 Mn _0.05 Al _0.05 ) O ₂ , Li (Ni _0.85 Co _0.10 Mn _0.05 ) O ₂ , Li (Ni _0.85 Co _0.10 Mn) _0.03 Al _0.02 ) O ₂ , Li (Ni _0.9 Co _0.05 Mn _0.05 ) O _2, Li (Ni _0.9 Co _0.05 Al _0.05 ) O ₂ , Li (Ni) _0.95 Co _0.03 Mn _0.02 ) O ₂ and Li (Ni _0.95 Co _0.03 Al _0.02 ) O ₂ are preferable.

The average particle size of the particles of the lithium transition metal oxide can be, for example, 1 μm or more and 50 μm or less, preferably 1 μm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less.

(Positive electrode additive)
As the positive electrode additive, an additive containing one or more kinds of oxide solid electrolytes and one or more kinds of phosphonic acid compounds can be used. In addition to the above, a dispersant, a filler, and other additives for improving the dispersion of the conductive material may be contained.

The amount of the positive electrode additive may be, for example, 0.01% by weight or more and 5% by weight or less, preferably 1% by weight or more and 3% by weight or less, based on the total weight of the positive electrode active material layer. When the amount of the positive electrode additive added is within the range, excellent capacitance characteristics can be realized.

(Oxide solid electrolyte)
The oxide solid electrolyte is not particularly limited as long as it is a solid oxide having ionic conductivity, and may be a crystalline solid electrolyte, an amorphous solid electrolyte, a glass ceramic solid electrolyte, or the like. The conduction ion is also not particularly limited, and may be an alkali metal ion such as lithium or sodium, a proton, an ammonium ion, an oxygen ion, or the like.

In particular, it is preferable to use an oxide solid electrolyte having lithium ion conductivity because it is considered that lithium ions can easily enter and exit the positive electrode active material during charging and discharging. Examples of solid oxide electrolytes having lithium ion conductivity include LLTO compounds ((La, Li) TiO ₃ ), Li ₆ La ₂ CaTa ₂ O ₁₂ , Li ₆ La ₂ ANb ₂ O ₁₂ (A: alkaline soil). Metals), Li ₂ Nd ₃ TeSbO ₁₂ , Li ₃ BO _2.5 N _0.5 , Li ₉ SiAlO ₈ , LAGP-based compounds (Li _{1 + x} Al _x Ge _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 1) , 0 ≤ y ≤ 1)), LATP-based compounds such as _{Li 2} O-Al ₂ O _3- TiO _2- P ₂ O _{5 (Li 1 + x} Al _x Ti _2-x (PO ₄ ) ₃ (0 ≤ x ≤) 1, 0 ≤ y ≤ 1)), Li _{1 + x} Ti _2-x Al _{x S y} (PO ₄ ) _3-y (0 ≤ x ≤ 1, 0 ≤ y ≤ 1), Li _{1 + y} Al _x M _2-x ( PO ₄ ) ₃ (M is one or more elements selected from the group consisting of Ti, Ge, Sr, Sn, Zr, and Ca, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) , LiTi _x Zr _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1), LISION (Li _{4-2 x} Zn _x GeO ₄ (0 ≦ x ≦ 1)), LIPON-based compounds (Li) _{3 + y} PO _4-x N _x (0 ≦ x ≦ 1, 0 ≦ y ≦ 1)), NASICON-based compounds (LiTi ₂ (PO ₄ ) _3, etc.), garnet-based compounds (Li ₇ La ₃ Zr ₂ O ₁₂ , Li _7-x La ₃ Zr _1-x Nb _x O ₁₂ (0≤x≤1), etc.) and the like.

Examples of the oxide solid electrolyte having ionic conductivity other than lithium ion include tungsten bronze (Na _x WO ₃ ), β-alumina, stabilized zirconia and the like.

The positive electrode additive, and thus the positive electrode active material layer, may contain, but is not limited to, one or more of the above-mentioned solid oxide electrolytes.

It is presumed that the oxide solid electrolyte suppresses the heterogeneous reaction of the electrode reaction by suppressing the generation of gas generated during the cycle, and improves the capacity retention rate of 50 cycles or less. In particular, the oxide solid electrolyte can exert an effect of improving the capacity retention rate in a state of being scattered in the positive electrode active material layer rather than on the surface of the particles of the positive electrode active material. Therefore, the surface of the particles of the positive electrode active material is not covered to suppress the reaction between the electrolytic solution and the surface of the positive electrode active material, but the gas is absorbed or acts on the electrolytic solution. It is presumed that the cycle deterioration of the battery can be suppressed by suppressing the reaction. However, this is merely an exemplary speculation to aid in the understanding of the present application and does not limit the present invention in any way.

The content of the oxide solid electrolyte is, for example, 0.01% by weight or more and 5% by weight or less, preferably 0.1% by weight or more and 4% by weight or less, based on the total weight of the positive electrode active material layer. More preferably, it may be 0.1% by weight or more and 3% by weight or less. When the content of the oxide solid electrolyte is within the above range, deterioration of the positive electrode can be suppressed, and a good capacity retention rate can be realized. On the other hand, if the content of the oxide solid electrolyte is less than the above range, the deterioration of the battery may not be sufficiently suppressed, and if the content of the oxide solid electrolyte exceeds the above range, it is sufficient. Energy density may not be obtained.

The average particle size of the particles of the oxide solid electrolyte can be, for example, 0.1 μm or more and 10 μm or less, preferably 0.2 μm or more and 5 μm or less, and more preferably 0.2 μm or more and 2 μm or less. For example, the average particle size of the particles of the oxide solid electrolyte is smaller than the average particle size of the particles of the lithium transition metal oxide.

(Phosphonate compound)
Examples of the phosphonic acid compound used as the positive electrode additive include phosphonic acid, organic phosphonic acid, phosphonate, organic phosphonate, phosphonic acid ester, organic phosphonic acid ester and the like. Examples of the organic phosphonic acid include methylphosphonic acid, ethylphosphonic acid, propylphosphonic acid, butylphosphonic acid, phenylphosphonic acid and the like, and may have a substituent. However, it is not limited to these. By adding the phosphonic acid compound together with the oxide solid electrolyte, the positive electrode active material layer may contain a compound derived from the added phosphonic acid compound. In the present specification, for example, even when the lithium transition metal oxide and the compound derived from the phosphonic acid compound are chemically bonded in the positive electrode active material layer, "the positive electrode active material layer is a compound derived from the phosphonic acid compound. Express as "include".

For example, the phosphonic acid compound added as a positive electrode additive is phosphonic acid or organic phosphonic acid. Further, the positive electrode additive may contain, but is not limited to, one or more of the above phosphonic acid compounds.

It is presumed that the phosphonic acid compound can suppress the cycle deterioration of the battery and the deterioration of the slurry stability by the following mechanism. However, this is merely an exemplary speculation to aid in the understanding of the present application and does not limit the present invention in any way.

When the lithium transition metal oxide is alkaline due to the hydroxyl group on the particle surface, or when lithium hydroxide, lithium carbonate, etc. are present on the particle surface of the lithium transition metal oxide, the lithium transition metal oxide is present. When the phosphonic acid compound is mixed with the phosphonic acid compound, the phosphonic acid compound reacts with these alkaline components, and although the details are unknown, the particle surface of the lithium transition metal oxide and the phosphonic acid compound are bonded to each other, resulting in the compound. It is thought that can form. It is considered that the compound thus produced can form a coating on the surface of the particles of the lithium transition metal oxide. It is presumed that this coating suppresses the chemical reaction between the positive electrode material and the electrolytic solution, so that the cycle deterioration of the battery and the generation of gas can be suppressed. As described in Patent Document 2, it is considered that the phosphonic acid compound can form such a coating. Further, it is presumed that the neutralization reaction between the phosphonic acid compound and the alkaline component can suppress the gelation of the positive electrode active material slurry and improve the slurry stability.

(binder)
The binder is added as a component that promotes the bond between the active material and the conductive agent, the bond with the current collector, and the like. Examples of binders include polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene- Examples thereof include propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, various copolymers thereof, and one or a mixture of two or more of these can be used. , Not limited to these.

The content of the binder can be 0.1% by weight or more and 30% by weight or less based on the total weight of the positive electrode active material layer. The content of the binder is preferably 0.5% by weight or more and 15% by weight or less, and more preferably 0.5% by weight or more and 5% by weight or less. When the content of the binder polymer satisfies the above range, sufficient adhesive force in the electrode can be imparted while preventing deterioration of the capacity characteristics of the battery.

(Conducting agent)
The conductive agent is not particularly limited as long as it is an electrically conductive material that does not induce a chemical change. Examples of conductive agents are carbon-based materials such as artificial graphite, natural graphite, carbon black, acetylene black, ketjen black, denca black, thermal black, channel black, furnace black, lamp black, carbon nanotubes, and carbon fiber; aluminum. , Tin, bismuth, silicon, antimony, nickel, copper, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, gold, lantern, ruthenium, platinum, iridium and other metal powders and fibers; Conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive polymers such as polyaniline, polythiophene, polyacetylene, polypyrrole and polyphenylene derivatives, and one or two of these. Mixtures of more than one species can be used, but are not limited thereto.

The content of the conductive agent can be 0.1% by weight or more and 30% by weight or less based on the total weight of the positive electrode active material layer. The content of the conductive agent is preferably 0.5% by weight or more and 15% by weight or less, and more preferably 0.5% by weight or more and 5% by weight or less. When the content of the conductive agent satisfies the above range, it is advantageous in that sufficient conductivity can be imparted and the battery capacity can be secured because the amount of the positive electrode active material is not reduced.

(solvent)
The solvent used in the positive electrode active material slurry is not particularly limited as long as it is generally used for producing a positive electrode. Examples of the solvent include amine solvents such as N, N-dimethylaminopropylamine, diethylenetriamine, N, N-dimethylformamide (DMF), ether solvents such as tetrahydrofuran, ketone solvents such as methyl ethyl ketone, methyl acetate and the like. Examples of the ester solvent, dimethylacetamide, amide solvent such as 1-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), water, etc., and one or a mixture of two or more of these are used. Obtain, but are not limited to these.

The amount of the solvent used is such that the positive electrode active material, the conductive material, and the binder are dissolved or dispersed in consideration of the coating thickness of the slurry and the production yield, and excellent thickness uniformity is obtained when the slurry is coated on the positive electrode current collector. It is sufficient if it has a viscosity that can be shown.

[Manufacturing method of positive electrode]
The method for producing a positive electrode for a lithium ion secondary battery according to an embodiment may include (1) obtaining a positive electrode active material slurry from a positive electrode active material; and (2) obtaining a positive electrode from a positive electrode active material slurry.

(1) Step to obtain a positive electrode active material slurry At least one kind of lithium transition metal oxide which is a positive electrode active material is mixed with an oxide solid electrolyte and a phosphonic acid compound which are positive electrode additives, a solvent, a conductive agent, a binder and the like. Added. At this time, other additives such as a dispersant may be added as needed. Then, by dispersing these in a solvent, a positive electrode active material slurry is obtained. The oxide solid electrolyte may be added as a powder or may be added in the state of a dispersion liquid. The form of the phosphonic acid compound is not particularly limited, and it may be added in the powder state, in the dispersion state, or in the solution state, but in the solution state. It is preferable to add it. Further, as for the timing of addition, any of the additives may be mixed with the positive electrode active material first, or may be mixed at once.

The amount of the lithium transition metal oxide added is, for example, 85 parts by weight or more and 99.5 parts by weight or less, preferably 90 parts by weight or more and 99 parts by weight or less, when the total weight of the positive electrode active material layer is 100 parts by weight. Can be. The amount of the oxide solid electrolyte added is, for example, 0.01 parts by weight or more and 5 parts by weight or less, preferably 0.1 parts by weight or more and 4 parts by weight or less, and more preferably 0.1 parts by weight or more. It can be 3 parts by weight or less. The amount of the phosphonic acid compound added is, for example, 0.01 parts by weight or more and 5 parts by weight or less, preferably 0.1 parts by weight or more and 4 parts by weight or less, and more preferably 0.1 parts by weight or more and 3 parts by weight. It can be less than a part by weight.

During the mixing of (1), a reaction between an alkaline component such as a hydroxyl group or lithium hydroxide on the particle surface of the lithium transition metal oxide and a phosphonic acid compound may occur. As a result, it is considered that a coating derived from the phosphonic acid compound can be formed on the particle surface of the lithium transition metal oxide.

Here, in the present invention, the reason why an excellent effect can be obtained by using the phosphonic acid compound and the oxide solid electrolyte in combination is presumed as follows. The phosphonic acid compound is located on the particle surface of the positive electrode active material and reacts with the alkaline component on the particle surface to reduce the gas generation area on the surface, so that it is presumed to have an effect such as improvement of cycle characteristics. However, it is considered that the effect of coating decreases as the amount of the phosphonic acid compound added increases. On the other hand, the oxide solid electrolyte is not necessarily on the surface of the active material and can be sparsely distributed in the positive electrode active material layer. Further, since the main effect of the oxide solid electrolyte is presumed to be due to gas absorption, the effect per weight added is inferior to that of the phosphonic acid compound when added in a small amount, but the effect is effective on the amount added. It is thought that it is hard to fall off. By keeping the addition amount optimal, it is considered that a higher gas suppression effect can be obtained as compared with the case where the phosphonic acid compound or the oxide solid electrolyte is added alone. In addition to the synergistic effect of gas suppression as described above, it is presumed that the use of the oxide solid electrolyte also has the effect of further reducing the impedance.

(2) Step of obtaining a positive electrode from a positive electrode active material slurry By applying a positive electrode active material slurry to a positive electrode current collector, drying and rolling the positive electrode, a positive electrode having a positive electrode active material layer formed on the positive electrode current collector is manufactured. Can be done.

As another method, for example, a positive electrode is manufactured by casting the above-mentioned positive electrode active material slurry on another support and then laminating a film obtained by peeling from the support on a positive electrode current collector. You may. Further, the positive electrode active material layer may be formed on the positive electrode current collector by using any other method.

[Negative electrode]
In the lithium ion secondary battery according to the embodiment, the negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on one surface or both surfaces of the negative electrode current collector. The negative electrode active material layer may be formed on the entire surface of the negative electrode current collector, or may be formed only on a part of the surface of the negative electrode current collector.

(Negative electrode current collector)
The negative electrode current collector used for the negative electrode is not particularly limited as long as it can be used electrochemically stably and has conductivity. For example, as the negative electrode current collector, copper; stainless steel; aluminum; nickel; titanium; calcined carbon; copper or stainless steel whose surface is surface-treated with carbon, nickel, titanium, silver, etc .; aluminum-cadmium alloy, etc. are used. Can be done.

The negative electrode current collector can have a thickness of 3 μm or more and 500 μm or less. It is also possible to form fine irregularities on the surface of the negative electrode current collector to enhance the adhesive force with the negative electrode active material. The negative electrode current collector can have various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric.

(Negative electrode active material layer)
The negative electrode active material layer can be formed, for example, by applying a negative electrode active material slurry in which a mixture of a negative electrode active material, a binder, and a conductive agent is dissolved or dispersed in a solvent to a negative electrode current collector, and then drying and rolling. .. The mixture may further contain dispersants, fillers and any other additives, if desired.

(Negative electrode active material)
As the negative electrode active material, a compound capable of reversible insertion (intercalation) and deintercalation (deintercalation) of lithium can be used. Examples of negative electrode active materials include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; siliconic materials such as silicon powder, amorphous silicon, silicon nanofibers, and silicon nanowires; silicon alloys. , Silicon compounds such as silicon oxides doped with silicon oxides, alkali metals or alkaline earth metals (such as lithium and magnesium); Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Sn alloys. , Al alloys and other metallic materials that can be alloyed with lithium; SnO ₂ , vanadium oxides, lithium vanadium oxides and other metallic oxides that can be doped and dedoped with lithium; Examples thereof include a complex, a complex such as a Sn—C complex, and one or a mixture of two or more of these may be used, but the present invention is not limited thereto. As the carbonaceous material, either low crystalline carbon or high crystalline carbon may be used. Soft carbon and hard carbon are typical as low crystalline carbon, and amorphous, plate-shaped, fragment-shaped, spherical, or fibrous natural graphite or artificial graphite, kissed graphite, etc. as high crystalline carbon. Typical examples are high-temperature calcined carbon such as thermally decomposed carbon, mesophase pitch carbon fiber, mesocarbon microbeads, mesophase pitch, and petroleum / coal coke.

In particular, when the negative electrode active material contains silicon or a silicon compound (silicon alloy, silicon oxide, etc.), it is effective in increasing the charge / discharge capacity of the negative electrode.

The silicon alloy is an alloy whose main component is silicon. The silicon alloy can be, for example, an alloy of silicon Si and one or more metal elements of Sn, In, Al, and Ti. The content of silicon in the silicon alloy can be, for example, 50 mol% or more, preferably 70 mol% or more, and more preferably 90 mol% or more.

Silicon oxide is, for example, _{a compound represented by SiO x} (0 <x <2). SiO _x may have, for example, a structure in which Si fine particles are dispersed in a matrix of amorphous silicon oxide in the form of microcrystals or amorphous. The ratio x of oxygen to silicon can be 0 <x <2, preferably 0.5 ≦ x ≦ 1.6, and more preferably 0.8 ≦ x ≦ 1.5. For example, silicon oxide can be SiO (x = 1).

The negative electrode active material may preferably include a silicon material and a carbon material. For example, the negative electrode active material may include the above SiO _x (0 <x <2) and the above carbonaceous material (natural graphite or the like). The weight ratio of the silicon material to the carbon material in the negative electrode active material is, for example, 1:99 to 30:70, preferably 5:95 to 20:80, and more preferably 8:92 to 15 : Can be 85. In addition to the carbonaceous material mixed on the surface of the siliconous material, the carbonaceous material may be coated on the surface in advance.

The average particle size of the particles of the siliconaceous material can be, for example, 1 μm or more and 15 μm or less, preferably 2 μm or more and 10 μm or less. The average particle size of the particles of the carbonaceous material may be, for example, 1 μm or more and 50 μm or less, preferably 10 μm or more and 20 μm or less.

The negative electrode active material may be contained in an amount of 80% by weight or more and 99% by weight or less based on the total weight of the negative electrode active material layer.

(Binder and conductive agent)
The types and contents of the binder and the conductive agent used in the negative electrode active material slurry can be the same as those described for the positive electrode.

(Thickener)
The negative electrode active material slurry can further contain a thickener. Specifically, the thickener can be a cellulosic compound such as carboxymethyl cellulose (CMC). The thickener may be contained in an amount of, for example, 0.5% by mass or more and 10% by mass or less based on the total weight of the negative electrode active material layer.

(solvent)
The solvent used in the negative electrode active material slurry is not particularly limited as long as it is generally used for producing a negative electrode. Examples of the solvent include N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, acetone, water and the like, and one or a mixture of two or more of these can be used. , Not limited to these.

[Manufacturing method of negative electrode]
In the method for manufacturing a negative electrode for a lithium ion secondary battery according to the embodiment, a negative electrode active material slurry is obtained by dissolving or dispersing the negative electrode active material in a solvent together with a binder, a conductive agent, a thickener and the like, if necessary. The steps may include a step of obtaining a negative electrode by forming a negative electrode active material layer on the negative electrode current collector by applying a negative electrode active material slurry on the negative electrode current collector as in the method of manufacturing a positive electrode. ..

[Separator]
In the lithium ion secondary battery according to the embodiment, the separator is one that separates the negative electrode and the positive electrode to provide a movement passage for lithium ions, and is usually used as a separator in the lithium ion secondary battery. It can be used without any particular restrictions. In particular, those having a small resistance to ion transfer of the electrolyte and having an excellent moisture-containing capacity of the electrolyte are preferable. For example, a porous polymer film produced from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or these. A laminated structure of two or more layers can be used as a separator. Further, ordinary porous non-woven fabrics, for example, non-woven fabrics made from high melting point glass fibers, polyethylene terephthalate fibers, etc., can also be used. Further, a separator coated with a ceramic component or a polymer substance may be used to ensure heat resistance or mechanical strength.

[Non-aqueous electrolyte]
In the lithium ion secondary battery according to the embodiment, examples of the non-aqueous electrolyte include, but are not limited to, an organic liquid electrolyte and an inorganic liquid electrolyte that can be used in the production of the lithium ion secondary battery. ..

The non-aqueous electrolyte can contain an organic solvent and a lithium salt, and can further contain an electrolyte additive if necessary. Hereinafter, the liquid electrolyte is also referred to as "electrolyte solution".

The organic solvent can be used without particular limitation as long as it can serve as a medium in which ions involved in the electrochemical reaction of the battery can move. Examples of organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatics such as benzene and fluorobenzene. Group hydrocarbon solvent; carbonate solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC); ethyl Alcohol-based solvents such as alcohol and isopropyl alcohol; R-CN (R is a linear, branched or cyclic hydrocarbon group of C2 to C20 and may contain a double-bonded aromatic ring or an ether bond) and the like. Nitrile-based solvent; amide-based solvent such as dimethylformamide; dioxolane-based solvent such as 1,3-dioxolane; sulfolane-based solvent and the like, and one or a mixture of two or more of these can be used. It is not limited to. In particular, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate and propylene carbonate) that can enhance the charging / discharging performance of the battery and low-viscosity linear carbonates. A mixture of the system compounds (for example, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of 1: 1 to 1: 9, excellent electrolyte performance can be exhibited.

The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium ion secondary battery. _Examples of the lithium _{salt, LiPF 6, LiClO 4, LiAsF} 6, LiBF 4, LiSbF 6, LiAlO 4, LiAlCl 4, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiN (C 2 F 5 SO 3) 2 , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiCl, LiI or LiB (C ₂ O ₄ ) _2, etc., and one or a mixture of two or more of these can be mentioned. It can be used, but is not limited to these. The lithium salt can be contained in the electrolyte at a concentration of 0.1 mol / L or more and 2 mol / L or less, for example. When the concentration of the lithium salt is included in the range, the electrolyte has appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited and lithium ions can move effectively.

The electrolyte additive can be used as needed for the purpose of improving the battery life characteristics, suppressing the decrease in battery capacity, improving the battery discharge capacity, and the like. Examples of electrolyte additives include haloalkylene carbonate compounds such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC), pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylenediamine, n-grim, hexaphosphate. Examples thereof include triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, and the like. Species or mixtures of two or more species may be used, but are not limited thereto. The electrolyte additive may be contained, for example, in an amount of 0.1% by weight or more and 15% by weight or less based on the total weight of the electrolyte.

In particular, fluoroethylene carbonate and difluoroethylene carbonate can act as a film-forming agent that forms a film at the interface between the electrode and the electrolyte. For example, when at least one of fluoroethylene carbonate and difluoroethylene carbonate is contained, a good SEI film is formed in the process of alloying the silicon-based material and lithium in the negative electrode using the negative electrode active material containing the silicon-based material. As a result, stable charging and discharging can be performed. On the other hand, the positive electrode reacts with the positive electrode active material at a high temperature and may cause gas generation. Therefore, for the negative electrode containing a silicon-based material, the electrolytic solution may contain a film-forming agent, but for the positive electrode, it is preferably in a small amount, and the content of the film-forming agent is, for example, Based on the total weight of the electrolytic solution, it is 0.1% by weight or more and 15% by weight or less, preferably 0.5% by weight or more and 10% by weight or less, and more preferably 0.5% by weight or more and 7% by weight or less. Can be. The film-forming agent may contain at least one of fluoroethylene carbonate and difluoroethylene carbonate.

[Manufacturing method of lithium ion secondary battery]
The lithium ion secondary battery according to the embodiment can be manufactured by interposing a separator (for example, a separation membrane) and an electrolytic solution between the positive electrode manufactured as described above and the negative electrode manufactured as described above. More specifically, a separator is arranged between the positive electrode and the negative electrode to form an electrode assembly, the electrode assembly is placed in a battery case such as a cylindrical battery case or a square battery case, and then an electrolyte is injected. Can be manufactured. Alternatively, after laminating the electrode assembly, the resulting product obtained by impregnating the electrolyte with an electrolyte can be placed in a battery case and sealed for production.

As the above battery case, those commonly used in the art can be adopted. The shape of the battery case can be, for example, a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

The lithium ion secondary battery according to the embodiment can be used not only as a power source for a small device but also as a unit battery of a medium-sized and large-sized battery module including a large number of battery cells and the like. Preferred examples of such medium- and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, and the like.

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Moreover, the mechanism described below is merely an exemplary speculation for assisting the understanding of the present application, and does not limit the present invention in any way.

[Example 1]
(Manufacturing of positive electrode)
For 92 parts by weight of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder, 2 parts by weight of Li ₂ O-Al ₂ O _3- SiO _2- P ₂ O _5- TiO _{2 as a positive electrode additive.} -GeO ₂ Lithium ion conductive glass-ceramic solid electrolyte (LICGC (registered trademark) PW-01 manufactured by O'Hara); 2 parts by weight of phosphonic acid, hereinafter simply referred to as "LICGC") and 2 parts by weight as a conductive agent. Carbon black and 2 parts by weight of polyvinylidene fluoride (PVdF) as a binder are added together with the solvent N-methyl-2-pyrrolidone (NMP) and mixed with a mixer (Thinky's Awatori Rentaro). A positive electrode active material slurry was obtained. Here, the average particle size of _{the LiNi 0.8} Co _0.1 Mn _0.1 O _{2 powder used was about 5 μm.} The alkaline component (total assuming lithium carbonate and lithium hydroxide) _{in the LiNi 0.8} Co _0.1 Mn _0.1 O ₂ powder measured by neutralization titration _{is LiNi 0.8} Co _0.1 Mn _0. It corresponded to 0.45% by weight of the whole ₁ O _{2 powder.}

Next, the obtained positive electrode active material slurry was applied to an aluminum foil, vacuum dried at 120 ° C., and pressed with a roll press to a predetermined density to obtain a positive electrode.

(Manufacturing of negative electrode)
SiO powder having an average particle size of 6 μm and natural graphite having an average particle size of 15 μm were mixed so as to have a weight ratio of 1: 9 to obtain a negative electrode active material powder. Next, with respect to 96 parts by weight of the negative electrode active material powder, 1 part by weight of carbon black as a conductive agent, 1.5 parts by weight of styrene butadiene rubber (SBR) as a binder, and 1.5 parts by weight of carboxy as a thickener. Methyl cellulose (CMC; thickener) was added, pure water was added as a solvent, and the mixture was mixed with a mixer in the same manner as the positive electrode material to obtain a negative electrode active material slurry. This negative electrode active material slurry was applied to a copper foil, vacuum dried at 110 ° C., and pressed to a predetermined density to obtain a negative electrode.

(Manufacturing of electrolyte)
Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 3: 7, and fluoroethylene carbonate (FEC) was added so as to be 5% by weight based on the total weight of the electrolytic solution. .. _{LiPF 6} was dissolved here at a concentration of 1 mol / L to obtain an electrolytic solution.

(Battery manufacturing)
The positive electrode and the negative electrode manufactured as described above were opposed to each other so ^{that the facing area was 12 cm 2.} Here, the coating amounts of the positive electrode active material and the negative electrode active material were set so that the charge capacity ratio between the positive electrode and the negative electrode was 1: 1.05 in terms of the capacity of one side (each facing surface). A polyolefin film was sandwiched between the positive electrode and the negative electrode as a separator, and the positive electrode, the separator, and the negative electrode were sealed in an aluminum laminate. Then, 300 μL of the above-mentioned electrolytic solution was vacuum-injected, and the electrolytic solution injection port of the aluminum laminate was sealed to manufacture a cell.

[Example 2]
Except that the amount of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder was 94 parts by weight, the amount of phosphonic acid was 1 part by weight, and the amount of LICGC was 1 part by weight. Similarly, a positive electrode and a cell cell using the positive electrode were manufactured.

[Comparative Example 1]
_{Positive electrode as in Example 1 except that the amount of LiNi 0.8} Co _0.1 Mn _0.1 O ₂ powder was 91 parts by weight and the amount of LICGC was 5 parts by weight without adding phosphonic acid. And a cell cell using the positive electrode was manufactured.

[Comparative Example 2]
_{Positive electrode as in Example 1 except that the amount of LiNi 0.8} Co _0.1 Mn _0.1 O ₂ powder was 91 parts by weight and the amount of phosphonic acid was 5 parts by weight without adding LICGC. And a cell cell using the positive electrode was manufactured.

[Comparative Example 3]
_{Positive electrode as in Example 1 except that the amount of LiNi 0.8} Co _0.1 Mn _0.1 O ₂ powder was 94 parts by weight and the amount of LICGC was 2 parts by weight without adding phosphonic acid. And a cell cell using the positive electrode was manufactured.

[Comparative Example 4]
_{Positive electrode as in Example 1 except that the amount of LiNi 0.8} Co _0.1 Mn _0.1 O ₂ powder was 94 parts by weight and the amount of phosphonic acid was 2 parts by weight without adding LICGC. And a cell cell using the positive electrode was manufactured.

[Comparative Example 5]
The positive electrode and the positive electrode were used in the same manner as in Example 1 except that the amount of _{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ powder was 96 parts by weight without adding phosphonic acid and LICGC. Manufactured a battery.

[Evaluation Example 1: Fluidity of Positive Electrode Active Material Slurry]
The fluidity of the positive electrode active material slurry in each Example and each Comparative Example was examined. Gelation was observed in the positive electrode active material slurry, which had low fluidity, and it was difficult to apply it to the aluminum foil.

[Evaluation example 2: Capacity retention rate at high temperature]
The cells manufactured according to each Example and each Comparative Example were charged and discharged once at 25 ° C., and then the inside of the battery was once degassed and resealed. Next, charging / discharging was repeated 50 times at 45 ° C. with the upper limit voltage of charging set to 4.25 V and the lower limit voltage of discharge set to 2.50 V. The capacity retention rate in the 50 times of repeated charging and discharging is defined by the following equation.

[Evaluation example 3: Impedance measurement]
With the cells manufactured by each Example and each Comparative Example fully charged, the impedance of the entire cells at a frequency of 1 kHz was measured using an impedance analyzer.

[Evaluation example 4: Battery volume change]
The volume was measured by the Archimedes method with the cells manufactured by each Example and each Comparative Example fully charged, and compared with one cycle at 45 ° C., the table below shows how much the volume has increased at 50 cycles. Described in.

The fluidity of the positive electrode active material slurry, the capacity retention rate, and the impedance of the cell in each Example and each Comparative Example were as follows. The amount of phosphonic acid and LICGC added (indicated by weight) is also shown in the table below.

In Example 1, Example 2, Comparative Example 2, and Comparative Example 4 to which phosphonic acid was added, the positive electrode active material slurry exhibited good fluidity regardless of the presence or absence of LICGC. On the other hand, in Comparative Example 1, Comparative Example 3, and Comparative Example 5 in which phosphonic acid was not added, gelation of the positive electrode active material slurry was observed, and the fluidity was low. This is because in the presence of phosphonic acid _{, alkaline functional groups on the particle surface of LiNi 0.8} Co _0.1 Mn _0.1 O ₂ powder and alkaline components such as lithium hydroxide remaining on the particle surface are neutralized. Alternatively, gelation is suppressed by forming a film of a compound derived from phosphonic acid on the particle surface of _{LiNi 0.8} Co _0.1 Mn _0.1 O _{2 powder and suppressing the gelation reaction.} It is presumed that this is because when phosphonic acid is not added, the gelation of the slurry is promoted without neutralization reaction or coating.

Comparing the capacity retention rates in 50 times of repeated charging and discharging at 45 ° C., in Examples 1, 2, and Comparative Examples 1 to 3, an excellent capacity retention rate of 90% or more was obtained. On the other hand, in Comparative Example 4 in which only 2 parts by weight of phosphonic acid was added and Comparative Example 5 in which neither phosphonic acid nor LICGC was added, the volume retention rate was less than 90%. That is, when LICGC was not added, a sufficient volume retention rate could not be obtained by adding only a small amount of phosphonic acid.

Comparing the impedances at a frequency of 1 kHz, the single batteries according to Comparative Example 2 and Comparative Example 5 showed higher impedance than the other examples. When the amount of phosphonic acid added is large as in Comparative Example 2, _{the surface of the LiNi 0.8} Co _0.1 Mn _0.1 O ₂ powder is excessively coated with phosphonic acid, which causes impedance. Is expected to increase. If the impedance is high, there is a problem that sufficient output characteristics cannot be obtained and the energy that can be actually used decreases.

Thus, only in Examples 1 and 2 to which both the phosphonic acid and the oxide solid electrolyte (LICGC) are added, excellent slurry fluidity, high capacity retention, and good impedance characteristics are all realized. Was made.

In addition, a synergistic effect was also observed due to the mixture of phosphonic acid and LICGC. Compared with the case where only 2 parts by weight of LICGC was added (Comparative Example 3: volume change 0.16 cc) and the case where neither phosphonic acid nor LICGC was added (Comparative Example 5: volume change 0.31 cc), it depends on the gas. The presumed volume change decreased by 0.15 cc, whereas when only 2 parts by weight of phosphonic acid was added (Comparative Example 4: Volume change 0.12 cc), when it was not added (Comparative Example 5: Volume change 0). The volume change compared to .31 cc) was reduced by 0.19 cc. That is, the effect of suppressing the volume change was higher when the phosphonic acid was added than when the LICGC was added. On the other hand, in Example 2 (volume change 0.06 cc), when 1 part by weight of LICGC and 1 part by weight of phosphonic acid were added (the total amount of the positive electrode additive was the same as in Comparative Example 3 and Comparative Example 4 above). The volume change was −0.25 cc as compared with the case where the additive was not added (Comparative Example 5: Volume change 0.31 cc). As described above, when two types of positive electrode additives are added, compared with the case where only one type of positive electrode additive is added (Comparative Example 3 and Comparative Example 4), the volume change considered to be caused by gas generation is caused by the synergistic effect. It is considerably suppressed. The difference in the results when 5 parts by weight of one type of positive electrode additive is added is that when 5 parts by weight of phosphonic acid is added, the amount is excessive and actually remains on the particle surface of the positive electrode active material. This is probably because the rate of reaction with alkali is small. The presumed mechanism is shown below. Phosphonate is located on the particle surface of the positive electrode active material, and is presumed to have an effect of improving cycle characteristics in order to reduce the gas generation area on the surface by reacting with the alkaline component on the particle surface. However, it is considered that the effect of coating decreases as the amount of phosphonic acid added increases. On the other hand, since it is presumed that the main effect of LICGC is due to gas absorption, the effect per weight added is inferior to that of phosphonic acid when a small amount is added, but the effect is less likely to decrease with respect to the amount added. it is conceivable that. By keeping the addition amount optimal, it is considered that a higher gas suppressing effect can be obtained as compared with the case where the phosphonic acid or the oxide solid electrolyte is added alone. Further, by using LICGC, which is a conductive solid electrolyte, in addition to the effect of not coating, the effect of reducing impedance is also obtained, and it is presumed that this contributes to the result of impedance measurement.

As described above, the addition of the phosphonic acid compound (here, phosphonic acid) improved the slurry stability of the positive electrode active material slurry and also showed a certain improvement in the capacity retention rate. However, when the phosphonic acid compound is added alone, if the amount added is too large, the impedance of the battery increases, and a sufficient capacity retention rate cannot be obtained. On the other hand, the addition of the oxide solid electrolyte also showed a certain improvement in the capacity retention rate, and by adding both the phosphonic acid compound and the oxide solid electrolyte, a sufficient capacity retention rate was achieved while suppressing the increase in impedance. We were able to. Furthermore, by adding both the phosphonic acid compound and the oxide solid electrolyte, the gas suppression effect was improved more than expected. Moreover, since it can be improved with a small amount of additives, the energy density can also be improved.

In particular, when a lithium transition metal oxide having a high nickel content is used as the positive electrode material and a silicon-based material is used as the negative electrode material with the aim of increasing the capacity of the battery, the alkali component of the lithium transition metal oxide or Due to the influence of fluoroethylene carbonate and difluoroethylene carbonate added to the electrolytic solution to prevent deterioration of the silicon material, slurry stability and cycle characteristics tend to become major problems. Therefore, the positive electrode active material to which both the phosphonic acid compound and the oxide solid electrolyte as described above are added is particularly effective.

Claims (12)

A positive electrode in which a positive electrode active material layer containing a positive electrode active material containing a lithium transition metal oxide and an oxide solid electrolyte and a phosphonic acid compound as additives is formed on a positive electrode current collector. The positive electrode according to claim 1, wherein the lithium transition metal oxide contains 50 mol% or more of nickel based on the total amount of transition metals. The positive electrode according to claim 2, wherein the lithium transition metal oxide contains 80 mol% or more of nickel based on the total amount of transition metals. The positive electrode according to any one of claims 1 to 3, wherein the oxide solid electrolyte has lithium ion conductivity. The positive electrode according to any one of claims 1 to 4, wherein the content of the oxide solid electrolyte in the positive electrode active material layer is 0.01% by weight or more and 5% by weight or less. The positive electrode according to any one of claims 1 to 5, wherein the phosphonic acid compound forms a coating on the surface of the particles of the lithium transition metal oxide. The positive electrode according to any one of claims 1 to 6, wherein the amount of the phosphonic acid compound added is 0.01% by weight or more and 5% by weight or less based on the weight of the positive electrode active material layer. The positive electrode according to any one of claims 1 to 7, wherein the phosphonic acid compound is a phosphonic acid or an organic phosphonic acid. The positive electrode according to any one of claims 1 to 8.
A negative electrode in which a negative electrode active material layer containing a negative electrode active material containing silicon or a silicon compound is formed on a negative electrode current collector, and a negative electrode.
Lithium-ion secondary battery. The lithium ion secondary battery according to claim 9, further comprising an electrolytic solution containing at least one of fluoroethylene carbonate and difluoroethylene carbonate. A method for manufacturing a positive electrode for a lithium ion secondary battery.
A step of obtaining a positive electrode active material slurry by mixing a lithium transition metal oxide, an oxide solid electrolyte, a phosphonic acid compound, and a solvent.
A step of obtaining a positive electrode by forming a positive electrode active material layer on a positive electrode current collector by drying the positive electrode active material slurry.
A method for manufacturing a positive electrode, including. A method for manufacturing lithium-ion secondary batteries.
The step of obtaining a positive electrode by the method according to claim 11 and
A step of obtaining a negative electrode by forming a negative electrode active material layer containing a negative electrode active material containing silicon or a silicon compound on a negative electrode current collector, and
A step of interposing a separator and an electrolytic solution between the positive electrode and the negative electrode,
A method for manufacturing a lithium ion secondary battery, including.