JP6443675B2 - Positive electrode and Li-ion secondary battery containing LiaMxMnyO4 powder having a spinel crystal structure, and methods for producing the same - Google Patents

Description

The present invention relates to a positive electrode including _a Li _a M _x Mn _y O ₄ powder having _a spinel crystal structure, _a lithium ion secondary battery, and a method for producing the same.

Spinel-type crystal structure compounds include metal oxides such as nickel, manganese, cobalt, and iron, and these compounds are used as electronic materials. In particular, Li _a M _x Mn _y O _{4 having a} spinel crystal structure (M is a metal, 0.8 ≦ a ≦ 1.1, 0 ≦ x ≦ 1, 1 ≦ y ≦ 2.2, 1.8 ≦ x + y ≦ 2.2) is known to be used as a positive electrode active material of a lithium ion secondary battery, and its manufacturing method is also known.

For example, Patent Document 1 describes LiNi _0.5 Mn _1.5 O ₄ having an average particle diameter of 11 μm, which is calcined in air at 600 ° C. using lithium carbonate, manganese carbonate and nickel hydroxide as raw materials. Moreover, LiMn ₂ O ₄ having an average particle size of 9 μm, which is fired at 600 ° C. in air using lithium carbonate and manganese carbonate as raw materials, is also described. In the same document, a secondary battery including these metal oxides as a positive electrode active material is described.

Patent Document 2 describes LiMn ₂ O ₄ baked in air at 1000 ° C. using lithium carbonate and manganese oxide as raw materials, and further includes a secondary battery comprising LiMn ₂ O ₄ as a positive electrode active material. Is described.

  Patent Document 3 describes spinel type lithium manganese nickel oxide having an average particle size of about 10 μm, which is obtained by using lithium carbonate, manganese dioxide or the like as a raw material and calcined at 950 ° C. in the air. A secondary battery provided as a substance is described.

As described in Patent Documents _{1~3, Li a M x Mn y} O 4 of the spinel crystal structure, firing the _M x Mn _y source, such as a Li source and a manganese carbonate such as lithium carbonate in an oxygen atmosphere It is manufactured by doing. _{Then, Li a M x Mn y O} 4 obtained by this production method is generally average about particle size 10 to 30 [mu] m.

JP 2014-241229 A JP 2013-214489 A Japanese Patent No. 5572268

As described above, the conventional spinel crystal structure Li _a M _x Mn _y O ₄ has an average particle diameter of about 10 to 30 μm. And even if it grind | pulverized further in order to obtain the thing of a finer average particle diameter, the average particle diameter remained at the level of about 0.6-1 micrometer. Therefore, in order to obtain a finer powder, it was necessary to drastically change the production method itself, not the pulverization method.

The present invention has been made in view of such circumstances, aims to provide a positive electrode and a lithium ion secondary battery comprising the Li _a M _x Mn _y O ₄ powder manufactured by a new manufacturing process And

The present inventor has conceived that Li _a M _x Mn _y O ₄ powder is obtained under completely different conditions from the conventional production method. Specifically, _a raw material or raw material mixture that can be a raw material of desired Li _a M _x Mn _y O ₄ is introduced into a plasma at a temperature of about 10,000 ° C., and the raw material or raw material mixture is reacted in a gas or liquid state. It was recalled that the product was quenched by using an extreme temperature difference between the inside and outside of the plasma to obtain a fine powder. Then, the present inventors found was examined intensively by repeated trial and error, in the manufacturing method, very that Li _a M _x Mn _y O ₄ powder of fine particle size spinel crystalline structure was obtained confirmed. Then, the present inventors based on the above findings, ensure that to prepare a positive electrode having a Li _a M _x Mn _y O ₄ powder manufactured by a new manufacturing method, which is operating normally, the present invention Was completed.

That is, the positive electrode of the present invention has a spinel crystal structure Li _a M _x Mn _y O ₄ (M is a metal, 0.8 ≦ a ≦ 1.1, 0 ≦) with an average particle diameter in the range of 10 nm to 400 nm. x ≦ 1, 1 ≦ y ≦ 2.2, 1.8 ≦ x + y ≦ 2.2).

The positive electrode manufacturing method of the present _invention, Li _a M x _Mn y at _{O 4} source and oxygen gas introducing flow, a spinel crystal structure comprising introducing into the plasma _Li a _M x _Mn y _{O 4} (M is a metal, 0.8 ≦ a ≦ 1.1, 0 ≦ x ≦ 1, 1 ≦ y ≦ 2.2, 1.8 ≦ x + y ≦ 2.2) Powder manufacturing process, Li _a M _x Mn _a step of using _y O ₄ powder.

The present invention can provide a positive electrode and a lithium ion secondary battery comprising a LiM _x Mn _2-x O ₄ produced by the new production method.

It is a schematic diagram of a plasma generator. 6 is an X-ray diffraction chart of powders of Production Example 1, Production Example 3, and Production Example 6. 2 is a transmission electron microscope image of the powder of Production Example 1. 6 is a transmission electron microscope image of the powder of Production Example 3. 7 is a transmission electron microscope image of the powder of Production Example 6. 2 is a scanning electron microscope image of the powder of Production Example 1. 7 is a scanning electron microscope image of the powder of Production Example 6. Is a scanning electron micrograph of LiMn ₂ O ₄ powder of a commercially available spinel-type crystal structure. 10 is a transmission electron microscope image of the powder of Production Example 10.

  The best mode for carrying out the present invention will be described below. Unless otherwise specified, the numerical range “x to y” described in this specification includes the lower limit x and the upper limit y. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.

  Hereinafter, the present invention will be described along the method for producing a positive electrode of the present invention.

The method for producing a positive electrode of the present invention includes a Li _a M _x Mn _y O ₄ source and an oxygen gas introduced into a plasma by an introduction flow, and a spinel crystal structure of Li _a M _x Mn _y O ₄ (M Is a metal, 0.8 ≦ a ≦ 1.1, 0 ≦ x ≦ 1, 1 ≦ y ≦ 2.2, 1.8 ≦ x + y ≦ 2.2) Powder production process, Li _a M _x Mn _y O _A step of using _four powders.

First, a Li _a M _x Mn _y O ₄ source and an oxygen gas are introduced into the plasma by an introduction flow, and the spinel type crystal structure Li _a M _x Mn _y O ₄ (M is a metal, 0.8 ≦ a ≦ 1.1, 0 ≦ x ≦ 1, 1 ≦ y ≦ 2.2, 1.8 ≦ x + y ≦ 2.2) Powder manufacturing process (hereinafter referred to as “powder manufacturing process”) The spinel type crystal structure Li _a M _x Mn _y O ₄ powder produced in the production process is sometimes referred to as “the powder of the present invention”).

M in Li _a M _x Mn _y O ₄ (M is metal, 0.8 ≦ a ≦ 1.1, 0 ≦ x ≦ 1, 1 ≦ y ≦ 2.2, 1.8 ≦ x + y ≦ 2.2) , A metal element capable of taking valences 2-4. Preferred examples of M include Mg, Al, Ti, Cr, Fe, Co, Ni, Cu, and La. a may be in the above range, and may be in a range of 0.9 ≦ a ≦ 1.1. x should just be in said range, and may be in the range of 0 <= x <= 0.6. y should just be in said range, and may be in the range of 1 <= y <= 2.1. x + y should just be in said range, and may be in the range of 1.9 <= x + y <= 2.1. Specific examples of Li _a M _x Mn _y O ₄ include LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiAl _0.1 Mn _1.9 O ₄ , LiCrMnO ₄ , LiCoMnO ₄ , LiFe _{0. 5} Mn _1.5 O ₄ , LiLa _0.05 Mn _1.95 O ₄ , Li _0.91 Mn _2.09 O ₄ (same as (Li _0.91 Mn _0.09 ) Mn ₂ O ₄ ) Can be illustrated.

The Li _a M _x Mn _y O ₄ source may be a raw material substance or a raw material mixture that can be a raw material of the powder of the present invention. For example, Li _a M _x Mn _y O ₄ itself may be used. and M _x Mn _y source may be used in combination. The Li _a M _x Mn _y O ₄ source is preferably in a powder state.

  The Li source may be metallic lithium or a lithium compound. Examples of the lithium compound include lithium carbonate, lithium hydroxide, lithium nitrate, lithium oxide, lithium acetate, lithium oxalate, and lithium halide. One type of Li source may be used, or two or more types may be used.

The M _x Mn _y source, M, Mn, M compound, a Mn compound, such that the ratio of _M x Mn _y to desired, may be adopted. Examples of the M compound or Mn compound include oxides, hydroxides, carbonates, nitrates, sulfates, acetates, oxalates, and halogenates.

The ratio of the Li source to the M _x Mn _y source may be such that the molar ratio of the elements of lithium and M _x Mn _y is a: x + y and the vicinity thereof. The molar ratio is preferably in the range of 1.5 to 1: 2.5, and particularly a molar ratio of around 1: 2.

  The powder production process is performed using a plasma generator. The plasma may be generated by arc discharge, high frequency electromagnetic induction, microwave heating discharge, or the like.

  In the case of a high frequency electromagnetic induction type plasma generator, the frequency may be, for example, in the range of 0.5 to 400 MHz, preferably in the range of 1 to 80 MHz. The plasma output may be, for example, in the range of 3 to 300 kW, preferably in the range of 5 to 100 kW. What is necessary is just to set the pressure in a plasma generator suitably, for example, the inside of the range of 10 kPa-atmospheric pressure can be illustrated. The average particle size of the powder of the present invention can be changed by changing the plasma output or the pressure in the plasma generator. For example, the average particle diameter of the powder of the present invention can be reduced by increasing the plasma output.

  As the introduction flow, in consideration of the stability of the plasma, a gas that can be used under the plasma is preferably used as the main flow. As the gas, a rare gas such as helium or argon is preferable. The introduced gas flow rate is 20 to 120 L / min. Can be illustrated.

Depending on the type of plasma generator, in the powder production process, as an introduction flow, a carrier gas carrying a Li _a M _x Mn _y O ₄ source, an inner gas introduced into the coil separately from the carrier gas, and a plasma It is preferable to employ a process gas for bringing the generation site into an inert atmosphere.

  The flow rate of the carrier gas is 1 to 10 L / min. Can be illustrated. The flow rate of the inner gas is 1 to 10 L / min. Can be illustrated. The flow rate of the process gas is 15 to 100 L / min. Can be illustrated.

The oxygen gas may be introduced as a part of the carrier gas, the inner gas and / or the process gas, for example, in an amount of 0.4 to 20% by volume of the entire introduced gas. Considering the stability of the gas piping of the plasma generator, the Li _a M _x Mn _y O ₄ source and the uniformity of the reaction of oxygen in the plasma, oxygen gas is introduced as part of the process gas. This is preferable because the gas can be diluted most suitably. The amount of oxygen gas introduced is, for example, 0.5 to 10 L / min. Can be illustrated. The average particle size of the powder of the present invention can be changed by changing the amount of oxygen gas, and the average particle size of the powder of the present invention can be increased by increasing the amount of oxygen gas.

_Here, consider the powder generation mechanism of the present invention using a Li source and _M x Mn _y source as Li _a M x _Mn y _{O 4} source. The temperature in plasma is about 8000-20000 degreeC. Li source and the _M x Mn _y source will be vaporized or decomposed state in the plasma. By introducing the Li source and _M x Mn _y source together with oxygen gas into plasma, Li source lithium oxides such as Li _{2 O,} M x Mn _y source of manganese oxide or manganese -M complex, such as MnO It can be converted to an oxide. Since Li ₂ O has a higher melting point than Li alone, and MnO has the highest melting point among Mn alone and manganese oxides such as MnO ₂ , Mn ₂ O ₃ , Mn ₃ O _4, etc. It can be said that Li ₂ O and MnO are compounds that are easily nucleated in the initial stage of cooling in the process of being discharged from the inside and cooled. Then, when the melting points of Li ₂ O and MnO are compared, the melting point of MnO is higher, so it is considered that nucleation of MnO occurs first.

Here, for example, Li ₂ O having a melting point of 1705K and a boiling point of 2873K and MnO having a melting point of 2113K and a boiling point of 3400K both have a temperature range between the melting point and the boiling point of about 2200 to 2800K. Duplicate in range. Therefore, it is presumed that Li ₂ O and MnO in the liquid state are cooled in the presence of oxygen to generate nuclei, and these aggregate to form LiMn ₂ O ₄ . This reaction is represented by the following reaction formula.
2Li ₂ O (liq.) + 8MnO (liq.) + 3O ₂ (gas) → 4LiMn ₂ O ₄

Furthermore, it is estimated that the resulting LiMn ₂ O ₄ crystal nucleus is controlled in crystal structure and crystal growth by further rapid cooling, and as a result, fine LiMn ₂ O ₄ particles are obtained.

Since Li _a M _x Mn _y O ₄ particles (hereinafter referred to as particles of the present invention) obtained in the powder production process are rapidly cooled from a high temperature state to near room temperature, there is almost no period for crystal growth. For this reason, the particles of the present invention are prevented from becoming needle-like crystals having a specific axis grown as obtained by a general production method. As a result, the particles of the present invention contained in the powder of the present invention have a shape with no unevenness in the crystal growth rate of each axis. And as an aspect of the particles of the present invention, a polyhedral shape composed of a large number of planes was observed. Specific examples of the polyhedron include those including triangular and quadrangular planes, those including quadrangular and hexagonal planes, and those including triangular, quadrangular and hexagonal planes. Further, as a specific example of the polyhedron, a truncated octahedron obtained by removing six quadrangular pyramids having the apex of the octahedron as the head apex from an octahedron consisting of eight triangles can be exemplified.

  The average particle size of the powder of the present invention is preferably in the range of 10 nm to 400 nm, more preferably in the range of 30 nm to 150 nm. The average particle diameter here means the arithmetic average value of the diameter of the circumscribed circle of the observed particle image when the powder of the present invention is observed with an electron microscope such as a scanning electron microscope or a transmission electron microscope. . For example, when a hexagonal particle image is observed, a circumscribed circle is created and the diameter of the circumscribed circle is measured. Thus, for example, for 200 particles, the diameter of each circumscribed circle is measured, and the arithmetic average value is calculated. This value is the average particle size.

In the powder manufacturing process, if the cooling rate of the gas flow containing Li _a M _x Mn _y O ₄ is increased, the crystal growth of the Li _a M _x Mn _y O ₄ crystal nucleus is interrupted in the initial stage, so It can be said that Li _a M _x Mn _y O ₄ particles having _a uniform shape are obtained.

Therefore, in the powder production process, when the introduction flow has a step of cooling the passage flow after passing through the plasma with a cooling gas flow facing the passage flow, finer Li _a M _x Mn _y O ₄ particles are formed. Since it is obtained, it is more preferable.

  As the gas of the cooling gas flow, a rare gas such as helium and argon, oxygen, and air are preferable, and these may be mixed and used. The temperature of the cooling gas flow may be room temperature or may be below room temperature. The flow rate of the cooling gas may be a flow rate smaller than the introduction flow, for example, 1 to 30 L / min. This can be illustrated as an example.

When the fine Li _a M _x Mn _y O ₄ powder is used as the positive electrode active material of the battery, for example, it is possible to reduce the reaction resistance of the battery, and to exhibit a sufficient capacity even at high speed charge / discharge. Played.

Next, the process using the powder of the present invention will be described. Specifically, the step is a step of mixing a Li _a M _x Mn _y O ₄ powder functioning as a positive electrode active material with a solvent to obtain _a composition for a positive electrode active material layer.

  Examples of the solvent include N-methyl-2-pyrrolidone, methanol, and methyl isobutyl ketone. The amount of the solvent used is preferably such an amount that the composition for the positive electrode active material layer becomes a slurry.

In addition to the Li _a M _x Mn _y O ₄ powder and the solvent, other known positive electrode active materials, binders, and conductive assistants may be added to the positive electrode active material layer composition.

  The binder plays a role of securing the active material to the surface of the current collector and maintaining a conductive network in the electrode. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, poly ( Examples thereof include acrylic resins such as (meth) acrylic acid, styrene-butadiene rubber, and carboxymethyl cellulose. These binders may be used singly or in plural.

  The blending ratio of the binder to the composition for the positive electrode active material layer is preferably a mass ratio in the range of positive electrode active material: binder = 1: 0.001 to 1: 0.3. More preferably, it is within the range of 0.005 to 1: 0.2, and even more preferably within the range of 1: 0.01 to 1: 0.15. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  The conductive assistant is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent. The conductive auxiliary agent may be any chemically inert electronic high conductor, such as carbon black, graphite, acetylene black, ketjen black (registered trademark), vapor grown carbon fiber (Vapor Grown Carbon). Fiber: VGCF) and various metal particles are exemplified. These conductive assistants can be added to the positive electrode active material layer alone or in combination of two or more.

  The blending ratio of the conductive additive to the positive electrode active material layer composition is, by mass ratio, preferably within the range of positive electrode active material: conductive additive = 1: 0.005 to 1: 0.5. A range of 0.01 to 1: 0.2 is more preferable, and a range of 1: 0.02 to 1: 0.1 is even more preferable. This is because if the amount of the conductive auxiliary is too small, an efficient conductive path cannot be formed, and if the amount of the conductive auxiliary is too large, the formability of the positive electrode active material layer is deteriorated and the energy density of the electrode is lowered.

  The positive electrode of the present invention is manufactured through a step of applying the composition for a positive electrode active material layer to a current collector, a drying step, and a compression step as necessary.

  The current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel, etc. Metal materials can be exemplified. The current collector may be covered with a known protective layer. What collected the surface of the electrical power collector by the well-known method may be used as an electrical power collector.

  The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.

  In order to apply the composition for the positive electrode active material layer to the current collector, a conventionally known method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method may be used. .

  The positive electrode of the present invention can be used as a positive electrode of a lithium ion secondary battery. Hereinafter, the lithium ion secondary battery provided with the positive electrode of the present invention is referred to as the lithium ion secondary battery of the present invention. One aspect of the lithium ion secondary battery of the present invention includes the positive electrode, the negative electrode, the electrolytic solution, and the separator of the present invention.

  The negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector. What is necessary is just to employ | adopt suitably what was demonstrated with the positive electrode about a collector. The negative electrode active material layer includes a negative electrode active material and, if necessary, a conductive additive and / or a binder.

  Examples of the negative electrode active material include a carbon-based material capable of inserting and extracting lithium, an element that can be alloyed with lithium, a compound having an element that can be alloyed with lithium, a polymer material, and the like.

  Examples of the carbon-based material include non-graphitizable carbon, graphite, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon, and carbon blacks. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.

  Specifically, elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si. , Ge, Sn, Pb, Sb, Bi can be exemplified, and Si or Sn is particularly preferable.

Specific examples of the compound having an element that can be alloyed with lithium include ZnLiAl, AlSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , _{CaSi 2, CrSi 2, Cu 5} Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO 2 or LiSnO, particularly SiO _x (0.3 ≦ x ≦ 1.6, or 0.5 ≦ x ≦ 1.5) Is preferred.

  Among these, the negative electrode active material preferably includes a Si-based material having Si. The Si-based material may be made of silicon or / and a silicon compound capable of occluding / releasing lithium ions, for example, SiOx (0.5 ≦ x ≦ 1.5). Although silicon has a large theoretical charge / discharge capacity, silicon has a large volume change during charge / discharge. Therefore, the volume change of silicon can be mitigated by using SiOx containing silicon as the negative electrode active material.

The Si-based material preferably has a Si phase and a SiO ₂ phase. The Si phase is composed of simple silicon, and is a phase that can occlude and release Li ions, and expands and contracts as Li ions are occluded and released. The SiO ₂ phase is made of SiO ₂ and serves as a buffer phase that absorbs the expansion and contraction of the Si phase. A Si-based material in which the Si phase is covered with the SiO ₂ phase is preferable. Furthermore, it is preferable that a plurality of micronized Si phases are covered with a SiO ₂ phase to form particles integrally. In this case, the volume change of the entire Si-based material can be effectively suppressed.

The mass ratio of the SiO ₂ phase to the Si phase in the Si-based material is preferably 1 to 3. When the mass ratio is less than 1, the expansion and contraction of the Si-based material increases, and the negative electrode active material layer containing the Si-based material may be cracked. On the other hand, when the mass ratio exceeds 3, the amount of occlusion and release of Li ions of the negative electrode active material decreases, and the electric capacity per unit negative electrode mass of the battery decreases. Moreover, tin compounds, such as a tin alloy (Cu-Sn alloy, Co-Sn alloy, etc.), can be illustrated as a compound which has an element which can be alloyed with lithium.

  Specific examples of the polymer material include polyacetylene and polypyrrole.

As the negative electrode active material, a Si material obtained by heating a layered polysilane obtained by treating CaSi ₂ with an acid such as hydrochloric acid or hydrofluoric acid at 300 to 1000 ° C. may be employed. Furthermore, the Si material heated with a carbon source and carbon coated may be adopted as the negative electrode active material.

  As the negative electrode active material, one or more of the above can be used.

  About the conductive support agent used for a negative electrode, what was demonstrated with the positive electrode should just be employ | adopted suitably suitably with the same mixture ratio.

  What is necessary is just to employ | adopt suitably suitably about the binder used for a negative electrode with the same mixture ratio as what was demonstrated with the positive electrode.

  The electrolytic solution includes a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent.

  As the non-aqueous solvent, cyclic esters, chain esters, ethers and the like can be used. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, ethyl methyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. As the non-aqueous solvent, a compound in which part or all of hydrogen in the chemical structure of the specific solvent is substituted with fluorine may be employed.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ .

As an electrolytic solution, 0.5 mol / L to 1.7 mol of a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 in} a nonaqueous solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and diethyl carbonate. A solution dissolved at a concentration of about / L can be exemplified.

  The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit of current due to contact between the two electrodes. As separators, natural resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polymer), polyester, polyacrylonitrile, and other polysaccharides, cellulose, amylose and other polysaccharides, fibroin, keratin, lignin, suberin, etc. Examples thereof include porous bodies, nonwoven fabrics, and woven fabrics using one or more electrically insulating materials such as polymers and ceramics. The separator may have a multilayer structure.

  Next, the manufacturing method of the lithium ion secondary battery of this invention is demonstrated. The manufacturing method of the lithium ion secondary battery of this invention includes the process of arrange | positioning the positive electrode obtained by the manufacturing method of the positive electrode of this invention. Specifically, it is as follows.

  A separator is sandwiched between the positive electrode and the negative electrode as necessary to form an electrode body. The electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched. After connecting between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal connected to the outside using a current collecting lead or the like, an electrolytic solution is added to the electrode body to form a lithium ion secondary battery. It is good to do. Moreover, the lithium ion secondary battery of this invention should just be charged / discharged in the voltage range suitable for the kind of active material contained in an electrode.

  The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.

  The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a lithium ion secondary battery for all or a part of its power source, and may be, for example, an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form an assembled battery. Examples of devices equipped with lithium ion secondary batteries include various home appliances driven by batteries such as personal computers and portable communication devices, office devices, and industrial devices in addition to vehicles. Furthermore, the lithium ion secondary battery of the present invention includes wind power generation, solar power generation, hydroelectric power generation and other power system power storage devices and power smoothing devices, power supplies for ships and / or auxiliary power supply sources, aircraft, Power supply for spacecraft and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as a power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charging station for electric vehicles.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art. Some powders of the present invention contain impurities.

  Hereinafter, the present invention will be described more specifically with reference to production examples, examples and comparative examples. In addition, this invention is not limited by these Examples.

(Production Example 1)
The powder of Production Example 1 was produced using the plasma generator shown in FIG. In the plasma generator shown in FIG. 1, black arrows represent cooling water.

Lithium carbonate as a Li source, to prepare manganese dioxide as M _x Mn _y source, these molar ratio of 1: obtain a mixed powder were mixed at 4. Then, the mixed powder was placed in a powder feeder. The element molar ratio of lithium and manganese in the mixed powder is 1: 2.

  In the plasma generator, a mixed gas having a volume ratio of 59: 1 of argon and oxygen of 60 L / min. And argon as the inner gas at 5 L / min. At a flow rate of 3 L / min. Supplied with. Electric power was supplied from the power supply device, and a magnetic field with a frequency of 4 MHz was applied to the coil to generate plasma with an output of 20 kW. The pressure in the plasma generator was atmospheric pressure.

  After the plasma was stabilized, the powder feeder was operated, and the mixed powder was charged at 400 mg / min. Was introduced into the plasma together with the carrier gas. The powder discharged together with the flow after passing through the plasma was collected and used as the powder of Production Example 1.

  In Production Example 1, no cooling gas was used.

(Production Example 2)
As a process gas, a mixed gas having a volume ratio of 57.5: 2.5 of argon and oxygen was 60 L / min. The powder of Production Example 2 was produced in the same manner as in Production Example 1, except that it was supplied in the above.

(Production Example 3)
As a process gas, a mixed gas of 55: 5 by volume of argon and oxygen was used at 60 L / min. The powder of Production Example 3 was produced in the same manner as in Production Example 1 except that the powder was supplied in the above.

(Production Example 4)
As a process gas, a mixed gas having a volume ratio of 52.5: 7.5 of argon and oxygen was 60 L / min. The powder of Production Example 4 was produced in the same manner as in Production Example 1, except that the powder was supplied in the above.

(Production Example 5)
In order to perform the step of cooling the flow after the introduction flow has passed through the plasma with the cooling gas flow facing the flow, argon at room temperature is used as the cooling gas at 10 L / min. The powder of Production Example 5 was produced in the same manner as in Production Example 3, except that the powder was supplied in (5).

(Production Example 6)
Argon at room temperature was used as a cooling gas at 20 L / min. The powder of Production Example 6 was produced in the same manner as in Production Example 5, except that the powder was supplied in the above.

(Production Example 7)
The powder of Production Example 7 was produced in the same manner as in Production Example 3, except that the plasma output was 25 kW.

(Production Example 8)
The powder of Production Example 8 was produced in the same manner as in Production Example 3, except that the plasma output was 30 kW.

(Comparative Production Example 1)
Argon is used as a process gas at 60 L / min. The powder of Comparative Production Example 1 was produced in the same manner as in Production Example 1 except that the powder was supplied in Step 1.

  Table 1 shows a list of production methods of the powders of Production Examples 1 to 8 and Comparative Production Example 1.

(Evaluation example 1)
X-ray diffraction of the powders of Production Examples 1 to 8 and Comparative Example 1 was measured with a powder X-ray diffractometer. In the X-ray diffraction charts obtained from the powders of Production Examples 1 to 8, diffraction patterns peculiar to LiMn ₂ O ₄ and (Li _0.91 Mn _0.09 ) Mn ₂ O ₄ having a spinel crystal structure are present. Observed. In addition, in the X-ray diffraction charts obtained from the powders of Production Examples 1 to 8, diffraction peaks corresponding to Mn ₃ O ₄ as an impurity were also observed. Here, it was confirmed from the comparison of the respective X-ray diffraction charts that Mn ₃ O ₄ decreased as the amount of oxygen in the process gas increased. Furthermore, it was also confirmed that Mn ₃ O ₄ was reduced due to the presence of the cooling gas. The X-ray diffraction charts of the powders of Production Example 1, Production Example 3 and Production Example 6 are shown in FIG. 2, and the mass% of the components contained in each powder calculated from these X-ray diffraction charts is shown in Table 2.

On the other hand, in the X-ray diffraction chart obtained from the powder of Comparative Production Example 1, diffraction patterns peculiar to Mn ₃ O ₄ and LiMnO ₂ which is not a spinel crystal structure were observed.

In the powder production process, Li _a M _x Mn _y O ₄ (M is a metal, 0.8 ≦ a ≦ 1.1, 0 ≦ x ≦ 1, 1 due to the presence of oxygen gas is preferable. ≦ y ≦ 2.2, 1.8 ≦ x + y ≦ 2.2) It was confirmed that the powder was produced.

(Evaluation example 2)
The powders of Production Examples 1 to 8 were observed with a transmission electron microscope (TEM). In each of the obtained TEM images, the diameter of the circumscribed circle of each particle image was measured for 200 particles, and the average particle diameter that was the arithmetic average value was calculated. The results are shown in Table 3. Moreover, the TEM image of the powder of the manufacture example 1, the manufacture example 3, and the manufacture example 6 is shown to FIGS.

  From the results of Production Examples 1 to 4, it can be said that the average particle diameter of the powder of the present invention tends to increase by increasing the amount of oxygen gas. From the results of Production Example 3 and Production Examples 5 to 6, it can be said that the average particle size of the powder of the present invention is reduced by increasing the cooling gas amount. Moreover, it can be said from the results of Production Example 3 and Production Examples 7 to 8 that the average particle size of the powder of the present invention is reduced by increasing the plasma output.

  Further, the powders of Production Example 1 and Production Example 6 were observed with a scanning electron microscope (SEM). SEM images of the powders of Production Example 1 and Production Example 6 are shown in FIGS. From the SEM images of FIGS. 6 to 7, it can be seen that the powder of the present invention contains polyhedral particles rather than needles. In the SEM images of FIGS. 6 to 7, truncated octahedral particles were also observed. The observed truncated octahedron is composed of a hexagonal {111 plane} × 8 plane and a square {100 plane} × 6 plane. Presence of {100 face} can alleviate stress concentration at the top of the octahedron (Yarn-Teller effect), facilitate Li entry and exit, and improve the input / output characteristics of the secondary battery. For truncated octahedron shaped particles, the side length a shared by the square and the hexagon and the side length b shared by the hexagon and the other hexagon were measured. Table 4 shows the arithmetic average values of a and b measured for 200 parts of the truncated octahedron-shaped particles for the powders of Production Example 1 and Production Example 6. Note that the relation between a and b in each hexagon satisfied b ≦ 1.5a.

As a reference, FIG. 8 shows an SEM image of a commercially available spinel crystal structure LiMn ₂ O ₄ powder (Toshima Seisakusho Co., Ltd.) observed with a scanning electron microscope.

(Production Example 9)
The powder of Production Example 9 was produced using the plasma generator shown in FIG.

Lithium carbonate as a Li source, to prepare the manganese dioxide and Ni powder as M _x Mn _y source, these molar ratio of 1: 3: was mixed powder was mixed with 1. Then, the mixed powder was placed in a powder feeder. In addition, the element molar ratio of lithium, manganese, and nickel in the mixed powder is 2: 3: 1, and the element molar ratio of lithium, manganese, and nickel is 1: 2.

  In the plasma generator, a mixed gas having a volume ratio of 57.5: 2.5 of argon and oxygen as a process gas was 60 L / min. And argon as the inner gas at 5 L / min. At a flow rate of 3 L / min. Supplied with. Electric power was supplied from the power supply device, and a magnetic field with a frequency of 4 MHz was applied to the coil to generate plasma with an output of 20 kW. The pressure in the plasma generator was atmospheric pressure.

  After the plasma was stabilized, the powder feeder was operated, and the mixed powder was charged at 400 mg / min. Was introduced into the plasma together with the carrier gas. The powder discharged together with the flow after passing through the plasma was collected and used as the powder of Production Example 9.

  In Production Example 9, no cooling gas was used.

(Production Example 10)
As a process gas, a mixed gas of 55: 5 by volume of argon and oxygen was used at 60 L / min. The powder of Production Example 10 was produced in the same manner as in Production Example 9, except that the powder was supplied in the above.

(Production Example 11)
In order to perform the step of cooling the flow after the introduction flow has passed through the plasma with the cooling gas flow facing the flow, argon at room temperature is used as the cooling gas at 10 L / min. The powder of Production Example 11 was produced in the same manner as in Production Example 9, except that the powder was supplied in the above.

(Production Example 12)
Argon at room temperature was used as a cooling gas at 20 L / min. The powder of Production Example 12 was produced in the same manner as in Production Example 11, except that the powder was supplied in the above.

(Evaluation example 3)
The X-ray diffraction of the powders of Production Examples 9 to 12 was measured with a powder X-ray diffractometer. In the X-ray diffraction charts obtained from the powders of Production Examples 9 to 12, a diffraction pattern specific to LiNi _0.5 Mn _1.5 O ₄ having a spinel crystal structure was observed.

(Evaluation example 4)
The powder of Production Example 10 was observed with TEM. A TEM image of the powder of Production Example 10 is shown in FIG. From the TEM image, fine particles were observed.

Example 1
The positive electrode and lithium ion secondary battery of Example 1 were manufactured as follows.

  90 parts by mass of the powder of Production Example 1 as a positive electrode active material, 5 parts by mass of acetylene black as a conductive additive, and 5 parts by mass of polyvinylidene fluoride as a binder were mixed. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry-like composition for a positive electrode active material layer.

  An aluminum foil having a thickness of 20 μm was prepared as a current collector. The composition for positive electrode active material layer was placed on the surface of the aluminum foil, and applied so that the composition for positive electrode active material layer became a film using a doctor blade. The aluminum foil coated with the positive electrode active material layer composition was dried at 80 ° C. for 20 minutes to remove N-methyl-2-pyrrolidone by volatilization, thereby forming a positive electrode active material layer on the aluminum foil surface. The aluminum foil having the positive electrode active material layer formed on the surface was compressed using a roll press machine, and the aluminum foil and the positive electrode active material layer were firmly bonded. The joined product was heated with a vacuum dryer at 120 ° C. for 6 hours and cut into a predetermined shape to obtain a positive electrode of Example 1.

  A lithium ion secondary battery (half cell) was produced using the positive electrode of Example 1 produced by the above procedure as a working electrode. The counter electrode was a metal lithium foil.

A working electrode and a counter electrode, and a separator (Hoechst Celanese glass filter and Celgard “Celgard 2400”) interposed between the two electrodes were disposed to form an electrode body. This electrode body was accommodated in a battery case (CR2032-type coin battery member, manufactured by Hosen Co., Ltd.). Into the battery case, a nonaqueous electrolyte solution in which LiPF ₆ was dissolved at a concentration of 1M was poured into a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1, the battery case was sealed, and A lithium ion secondary battery was obtained.

(Example 2)
A positive electrode and a lithium ion secondary battery of Example 2 were obtained in the same manner as in Example 1, except that the powder of Production Example 6 was used as the positive electrode active material.

(Comparative Example 1)
Example 1 except that a commercially available LiMn ₂ O ₄ powder having a spinel crystal structure (Toshima Seisakusho, average particle size of 6 μm (value of D50 in laser diffraction particle size distribution measurement)) was used as the positive electrode active material. In the same manner, a positive electrode and a lithium ion secondary battery of Comparative Example 1 were obtained.

(Evaluation example A)
Each lithium ion secondary battery was adjusted to 3.5 V after being adjusted to 4.2 V at a constant current of 25 ° C. and a 0.1 C rate, and then discharged at a constant C rate for 60 seconds. The direct current resistance of each lithium ion secondary battery during discharge was calculated from the voltage change amount and current value before and after discharge according to Ohm's law. The results are shown in Table 5.

It was confirmed that the resistances of the lithium ion secondary batteries of Example 1 and Example 2 were lower than the resistance of the lithium ion secondary battery of Comparative Example 1. It was confirmed that the positive electrode and the lithium ion secondary battery including the powder of the present invention exhibit lower resistance than the positive electrode and the secondary battery including the conventional LiMn ₂ O ₄ powder.

(Evaluation Example B)
For each lithium ion secondary battery, charging from 3.5 V to 4.2 V and discharging from 4.2 V to 3.5 V at room temperature was performed at a rate of 0.1 C, 0.2 C, 0.5 C, and 1 C. A charge / discharge cycle test was performed in order. Table 6 shows the result of calculating the ratio of the discharge capacity at the 1C rate to the discharge capacity at the 0.1C rate. In this description, the counter electrode is regarded as a negative electrode and the working electrode is regarded as a positive electrode. 1C means a current value required to fully charge or discharge a battery in one hour at a constant current.

  From the results shown in Table 6, the lithium ion secondary batteries of Example 1 and Example 2 are suppressed from decreasing the discharge capacity at a high rate as compared with the lithium ion secondary battery of Comparative Example 1. Excellent rate characteristics. It was confirmed that the positive electrode and the lithium ion secondary battery including the powder of the present invention exhibit excellent rate characteristics.

Claims (10)

A step of introducing a Li _a M _x Mn _y O ₄ source and an oxygen gas into the plasma in an introduced flow, and a cooling gas that opposes the passing flow after the introduced flow has passed through the plasma. _{Li a M x Mn y O 4} (M is a metal of the spinel type crystal structure comprising the step, of cooling the flow, 0.8 ≦ a ≦ 1.1,0 ≦ x ≦ 1,1 ≦ y ≦ 2.2, 1.8 ≦ x + y ≦ 2.2) production process of powder,
Using the Li _a M _x Mn _y O ₄ powder,
The manufacturing method of the positive electrode containing this. Powdered Li _a M _x Mn _y O ₄ source and oxygen gas are introduced into the plasma in an introduced flow, and the spinel type crystal structure Li _a M _x Mn _y O ₄ (M is a metal, 0.8 ≦ a ≦ 1.1, 0 ≦ x ≦ 1, 1 ≦ y ≦ 2.2, 1.8 ≦ x + y ≦ 2.2) powder manufacturing process,
Using the Li _a M _x Mn _y O ₄ powder,
The manufacturing method of the positive electrode containing this. Cooling the flow after the introduced flow has passed through the plasma with a cooling gas flow facing the flow;
The _Li a _M x _Mn y _{O 4} powder positive electrode manufacturing method according to claim 2, including the manufacturing process of the. 4. The method for producing a positive electrode according to claim 1, wherein an average particle diameter of the Li _a M _x Mn _y O ₄ powder is in a range of 10 nm to 400 nm. The _Li a _M x _Mn y _{O 4} powder, the positive electrode manufacturing method according to claim 1, comprising particles of polyhedral shape. The _Li a _M x _Mn y _{O 4} processes using powders is at the _Li a _M x _Mn y _{O 4} steps of a powder was mixed with a solvent positive electrode active material layer composition,
Furthermore, the process of apply | coating the said composition for positive electrode active material layers to a collector,
The manufacturing method of the positive electrode of any one of Claims 1-5 containing these. Step of disposing a positive electrode obtained by the manufacturing method according to any one of claim 1 to 6
The manufacturing method of the lithium ion secondary battery containing this. The method for producing a lithium ion secondary battery according to claim 7, wherein the lithium ion secondary battery is a lithium ion secondary battery including an electrolytic solution. Li _a M _x Mn _y O ₄ (M is a metal, 0.8 ≦ a ≦ 1.1, 0 ≦ x ≦ 1, 1 ≦ y ≦) having a spinel crystal structure with an average particle diameter in the range of 10 nm to 400 nm 2.2, 1.8 ≦ x + y ≦ 2.2) positive electrode comprising powder ,
And a lithium ion secondary battery comprising an electrolytic solution,
The Li _a M _x Mn _y O ₄ powder is a lithium ion containing truncated octahedral particles in which hexagonal {111 face} is composed of 8 faces and square {100 face} is composed of 6 faces. Secondary battery. In the truncated octahedron shape of the particle, the side length a shared by the square and the hexagon and the side length b shared by the hexagon and the other hexagon satisfy b ≦ 1.5a. Claim 9 satisfied
Lithium ion secondary battery.