JP6270771B2 - Synthesis method of polyanionic compound - Google Patents

Description

The present invention relates to a method for synthesizing Li ₂ MSiO _{4 that} can be used as a positive electrode material of a lithium ion secondary battery.

As one of positive electrode materials for lithium ion secondary batteries, phosphate-based LiMPO ₄ having an olivine-type crystal structure, olivine-type polyanion-type LiMSiO ₄ (Non-patent Document 1), polyanion-type similar to olivine Li ₂ MSiO ₄ has been proposed (Non-Patent Document 2, where M represents a transition metal element such as Mn or Fe). In particular, Li ₂ MSiO _{4, which} is a polyanionic compound having a composition formula capable of two-electron reaction, is abundant in the earth's crust because Fe or Mn, which is a main constituent element, and Si, are put into practical use. Is considered to be highly useful.

As an example of a method for producing this compound, for example, synthetic methods such as Patent Document 1 and Non-Patent Document 2 have been proposed. However, Li ₂ MSiO ₄ has lower electronic conductivity and lithium ion diffusivity than LiCoO ₂ , and it has been proposed to use it as a positive electrode material by mixing with a carbon material such as carbon black in order to obtain high battery characteristics. (Patent Document 2 [0027]).

Further, Patent Document 3 describes a method for producing Li ₂ MSiO ₄ in which a carbon colloid solution such as ink is mixed and fired together with a Li source, a transition metal source, and a Si source. Uniformity of the obtained particles can be improved by once drying the dispersion liquid in which these materials are mixed, followed by calcination and then baking. In addition, the obtained Li ₂ MSiO ₄ is in a state of being complexed with carbon derived from a carbon colloid dispersed in water, thereby ensuring an electron path in the entire particle and making the battery capacity close to the ideal value. it can.

JP 2013-14499 A JP 2011-216272 A JP 2014-68490 A

Is it possible to prepare olivine-type LiFeSiO4? A joint computational and experimental investigation (SOLID STATE IONICS 179 (2008) 1758-1762) Microwave-Solvothermal Synthesis of Nanostructured Li2MSiO4 / C (M = Mn and Fe) Cathodes for Lithium-Ion Batteries (Chem. Mater., 2010, 22 (20), pp 5754-5761)

However, even if the above method is used, it is difficult to bring it close to the theoretical capacity of Li ₂ MSiO ₄ . This is because, even if any one of the above methods is used, the provision of electron conductivity is insufficient, and it is insufficient to bring out the high battery characteristics possessed by Li ₂ MSiO ₄ .

Accordingly, an object of the present invention is to obtain Li ₂ MSiO ₄ composited with carbon more effectively and to improve the battery capacity of a lithium ion battery using the same.

In this invention, a Li source, a transition metal source, a Si source, and a carbon source are dispersed and mixed in a liquid, and an oxygen inflow per unit furnace volume is 0.052 ml / (min · m ³ ) or less. The above-mentioned problem was solved by firing in the inside.

Li ₂ MSiO ₄ cannot be produced sufficiently under an oxidizing atmosphere such as in the air. On the other hand, under a completely reducing atmosphere, the transition metal precipitates and high purity Li ₂ MSiO ₄ cannot be generated. For this reason, precise atmosphere control is required, and an example of firing in an atmosphere in which hydrogen or carbon monoxide is mixed with carbon dioxide has been attempted. In addition, an example in which nitrogen or argon gas, which is a general inert gas, is introduced during firing has been attempted. This is because the oxidizing power due to a small amount of oxygen mixed in a commercially available inert gas such as argon is negligible and it is considered that a certain amount of mixing is allowed. However, in practice, it was found that this small amount of oxygen causes reduction to inhibit single-phase formation of Li ₂ MSiO ₄ . In the present invention, focusing on this discovery, the amount of oxygen supplied into the system is reduced to an accuracy far from the conventional common sense, thereby overcoming the inhibition of single-phase generation due to trace amounts of oxygen.

  As described above, a carbon source is included in the material used in the present invention in order to increase electrical conductivity. If there is even a small amount of oxygen during firing, the oxygen will combine with the carbon in the material to generate carbon monoxide. Since it is basically an oxygen-deficient environment, it does not become carbon dioxide as it is. It was found that when this carbon monoxide is generated, the transition metal source is reduced, which causes the generation of impurities. That is, the present invention is achieved by deliberately reducing the oxygen mixing rate in order to suppress a reduction reaction that occurs in a complex manner under conditions unique to an oxygen-poor environment.

In this invention, since generation | occurrence | production of the carbon monoxide derived from a carbon source is suppressed, the range of the material which can be utilized as a carbon source spreads. For example, water-soluble carbon-containing molecules can be used instead of the carbon colloid solution or as a carbon source used in combination with the carbon colloid solution. If the liquid used to disperse and mix the material is water, the water-soluble carbon-containing molecules will dissolve in the water, and will disperse more than the water-insoluble carbon-containing molecules and carbon. A thin carbon film can be formed on the surface of the Li ₂ MSiO ₄ particles. Since this carbon film acts as a conductive path with high coverage to individual Li ₂ MSiO ₄ particles, when used as a positive electrode material, the area without the conductive path can be reduced and the battery capacity can be improved. it can.

  As the water-soluble carbon-containing molecule, for example, water-soluble saccharides such as glucose and fructose are preferably used. However, since it must be a molecule that can remain in a certain amount of material without being vaporized at least during firing, it is preferably non-volatile. For example, low molecular weight alcohols such as methanol and ethanol evaporate during firing, and it is difficult to control the amount remaining in the material. Specifically, it is desirable that the boiling point is less than 800 ° C. or a molecule that does not vaporize in the first place.

The total amount of carbon atoms of these carbon sources that may contain carbon colloid is preferably 8% by mass or more and 15% by mass or less of Li ₂ MSiO ₄ to be synthesized. If the amount is too small, the effect of carbon that contributes to conductivity cannot be sufficiently exerted. If the amount is too large, other side reactions may occur and the formation of a single phase may be hindered. In addition, a decrease in battery capacity per unit mass may not be negligible.

  According to the present invention, it is possible to obtain a positive electrode material with higher uniformity and improved battery capacity than before.

Comparison graph of XRD analysis results due to difference in oxygen passage amount in Examples Comparison graph of XRD analysis results by difference in carbon content in Examples (A) Charging / discharging curve using the positive electrode material of Example 1, (b) Charging / discharging curve using the positive electrode material of Example 2

Hereinafter, embodiments according to the present invention will be described in detail.
The present invention, in the production of Li ₂ MSiO _4, the raw material and a carbon source and a liquid mixture obtained by mixing and dispersing in, calcined after drying in an inert gas flow, method of manufacturing the Li ₂ MSiO ₄ It is. Here, M represents a transition metal in the fourth period of the periodic table. Li ₂ MSiO ₄ is a polyanionic silicate compound having a crystal structure similar to olivine.

  The said raw material is a compound which is each of Li source, a transition metal source, and Si source. In addition, although it can be implemented even if a compound containing a plurality of Li, transition metal, and Si is included, each element uses a different compound as a raw material for the uniformity of reaction and ease of blending. Better.

  As the Li source used in the present invention, a lithium salt compound can be used. In particular, in order to facilitate the mixing with the carbon colloid solution and colloidal silica described later, it is preferably water-soluble that can be used as an aqueous solution, and more preferably easily soluble. Specifically, the solubility in water at room temperature is preferably 10 g / 100 ml or more. Examples of such lithium salt compounds include lithium acetate dihydrate and lithium nitrate trihydrate. In particular, lithium acetate dihydrate is the most preferable because of the ease of mixing and the uniformity of the obtained substance. preferable.

On the other hand, as the transition metal source, a salt compound of a transition metal can be used as well, which is preferably water-soluble and more preferably easily soluble. Specifically, the solubility in water at room temperature is preferably 10 g / 100 ml or more. Examples of the transition metal element M that can suitably generate a Li ₂ MSiO ₄ compound in the present invention include Fe and Mn among the transition metal elements in the fourth period. Examples of the Fe source include iron (II) acetate, iron (II) nitrate, and iron (III) nitrate nonahydrate. Examples of the Mn source include manganese (II) nitrate tetrahydrate and manganese acetate (II) tetrahydrate. However, it is necessary that it does not generate an insoluble salt when mixed with a lithium salt compound used as a lithium source, and is preferably the same acid salt as the above lithium salt compound.

  These lithium source and transition metal source may be dispersed and dissolved in water and then mixed, or may be mixed from the beginning with a carbon molecule solution or dispersion or colloidal silica described later. However, if it is too thin, it takes too much time for drying after mixing, so that each concentration is preferably 0.1 mol / l or more.

Further, as the Si source, it is preferable to use SiO ₂ particles, and it is more preferable to use particles in the form of colloidal silica. The colloidal silica is a dispersion in which SiO ₂ particles are dispersed in a colloidal form. The weight average particle diameter of SiO ₂ in the colloidal silica liquid used in the present invention is preferably 1 nm or more, and more preferably 4 nm or more. It is not realistic for the weight average particle diameter to be less than 1 nm, and it is difficult to obtain such a material itself. On the other hand, it is preferably 10 nm or less, and more preferably 6 nm or less. In colloidal silica exceeding 10 nm, the contained SiO ₂ particles are not sufficiently mixed with solutes of other components, and it becomes difficult to obtain a uniform phase.

The content of SiO ₂ contained in the colloidal silica is preferably 2% by mass or more, and more preferably 5% by mass or more. If it is too little, it takes too much time to dry. On the other hand, 30 mass% or less is preferable, and it is more preferable in it being 20 mass% or less. If it exceeds 30% by mass, the colloid may be agglomerated without being sufficiently dispersed, and the mixing with the lithium source and the transition metal source is difficult to proceed, and the uniformity of the phase may be lowered due to insufficient mixing. There is.

  The colloidal silica preferably has a pH of 2.0 or more and 4.0 or less. If it is out of this range, the colloid may not be stable, and aggregation may occur, or other components may be mixed, and mixing may not proceed sufficiently. In order to adjust the pH within this range, a pH adjuster such as citric acid may be added.

The higher the purity, the more preferable is the SiO ₂ contained in the colloidal silica. Colloidal silica is usually produced from sodium silicate as a raw material, so Na often remains. Moreover, in other manufacturing methods, there is a possibility that alkali metal or alkaline earth metal is mixed. Since these remaining alkali metals and alkaline earth metals cause the uniformity of Li ₂ MSiO ₄ to be obtained to deteriorate, the lower the content, the better. Specifically, the content in SiO ₂ contained in the colloidal silica is preferably 200 ppm or less and more preferably 100 ppm or less in terms of mass ratio.

  The carbon source is dispersed in the fired product as carbon after sintering, and can increase electrical conductivity when used as a positive electrode material. As this carbon source, a water-soluble carbon-containing molecule or a carbon colloid solution can be used.

It is preferable that the water-soluble carbon-containing molecules do not evaporate during firing. Moreover, it is desirable not to contain a metal salt even if it is water-soluble. If a metal element is mixed, the production of Li ₂ MSiO ₄ may be hindered. For this reason, it is preferable that the said water-soluble carbon containing molecule | numerator does not contain elements other than carbon, hydrogen, oxygen, and nitrogen, and it is more preferable in it being a carbohydrate. Among these, water-soluble saccharides are more preferable. Examples of such water-soluble saccharides include glucose, fructose, trehalose and the like. However, sugars having a solubility in water at room temperature of less than 5 g / mL, such as maltose and lactose, cannot be used as a carbon source, but cannot sufficiently realize the high dispersibility exhibited by becoming a solute. For this reason, the solubility in water at room temperature is preferably 5 g / mL or more, and more preferably 10 g / mL or more. These saccharides may be used alone or in combination of two or more.

When fired using the water-soluble carbon-containing molecules, a thin carbon film covering the surface of the fired Li ₂ MSiO ₄ particles is formed. Since the thickness of this film is smaller than the particle size of the carbon colloid, it is possible to ensure the conductivity by the carbon film even to the part where the carbon colloid-derived carbon alone could not ensure the conductivity, and to improve the battery capacity Greatly contribute to In addition, since the film is thin, the occupied volume necessary to ensure conductivity can be made smaller than when carbon particles are used.

  The carbon colloid solution is a solution in which carbon particles are dispersed in water as a colloid. Specific examples of the carbon include carbon black such as Ketjen Black (registered trademark), acetylene black, and the like.

  Since the carbon is a carbon particle and is difficult to disperse as a colloid by itself, the carbon colloid solution preferably contains a water-soluble polymer for assisting dispersion. The water-soluble polymer is adsorbed on the surface of the carbon particles to make the carbon particles hydrophilic, so that they are more uniformly dispersed in the solution. As the water-soluble polymer, starch, agar, gelatin, glue, sodium polyacrylate, polyacrylic acid, and other acrylic acid copolymers can be used. Examples of the carbon colloid solution having such a water-soluble polymer include ink.

When the carbon colloid solution is used for firing, a carbon region can be secured in the form of coexisting with the fired Li ₂ MSiO ₄ particles. This becomes a thick conductive path in the particle as compared with the carbon film.

  As the carbon source dispersion containing the carbon source, the water-soluble carbon-containing molecule solution may be used, the carbon colloid solution may be used, or the carbon colloid is dispersed in the carbon-containing molecule solution. A solution may be used. In particular, by using both together, the current collected from the individual particles through the carbon film can be bundled with a thick conductive path made of carbon derived from carbon colloid, and can be charged and discharged with a large current. .

The amount of carbon atoms derived from the carbon colloid, the water-soluble carbon-containing molecule, or both of them remaining in the product during the firing is 8% by mass or more based on Li ₂ MSiO ₄ to be synthesized. Preferably, it is more preferable that it is 9 mass% or more. If the amount is less than 8% by mass, the conductive path may be insufficient, and the battery capacity may not be sufficiently secured. On the other hand, the amount of carbon atoms is preferably 15% by mass or less and more preferably 13% by mass or less with respect to Li ₂ MSiO ₄ to be synthesized. If the amount is too large, not only the battery capacity as a whole product may be slightly lowered, but also the reducing power derived from carbon becomes too strong, which may interfere with obtaining a single phase during firing.

The lithium source, transition metal source, and Si source are mixed with the carbon source dispersion basically according to the stoichiometric ratio. That is, it is preferable to mix so that the lithium source is 2 equivalents, the transition metal source is 1 equivalent, and the colloidal silica is 1 equivalent. However, if the amount of lithium contained in the obtained compound is 1 equivalent or more and 2 equivalents or less, a practical amount of Li _2-x MSiO ₄ can be produced by the following procedure. Moreover, even if the equivalent ratio of the transition metal source and the Si source is somewhat deviated from 1: 1, the compound Li _2-x M _1-y Si _{1 + y} O ₄ belonging to the same crystal point group can be produced. Here, 0 ≦ x ≦ 1, and −0.5 ≦ y ≦ + 0.5.

  The order of mixing is not particularly limited. The raw material consisting of solid particles may be dropped directly into the carbon source dispersion and dissolved or mixed, or once dissolved to form an aqueous solution. Even when a non-water-soluble raw material is used, a dispersion liquid dispersed in water may be used. Further, when colloidal silica is used as the Si source, they can be mixed as they are.

  After mixing, it is necessary to dry to remove water. The drying method can be simply drying by standing, but in order to shorten the time, heating at around 100 ° C. or instantaneous drying by freeze-drying method or the like is preferable. In particular, the spray freeze-drying method is desirable because the powder of the mixed raw material after drying is less likely to agglomerate and a uniform powder is easily obtained during the main firing.

  Regardless of the method, if the mixed raw material obtained after drying is subjected to a calcining treatment in which acetate or nitrate is decomposed and a water-soluble polymer is burned in advance before the main firing. preferable. By this calcining process, carbon monoxide, nitrogen oxides and other gases are not generated during the main firing, so it is possible to suppress a reduction in the production rate due to reduction of part of the raw material, forming a single phase It becomes easy to let you. In addition, since the adverse effect on the main firing due to the generation of gas accompanying the combustion of the water-soluble polymer can be avoided, the reproducibility of the electrode material obtained by firing is improved.

  The above-mentioned effect is obtained when the temperature of the calcining treatment is equal to or higher than a temperature at which a compound used as a lithium source and a transition metal source among the raw materials is thermally decomposed to generate gas and is equal to or higher than a combustion temperature of the water-soluble polymer Can be obtained. Although it depends on the type of lithium source and transition metal source to be used, when it is any of acetate, nitrate and sulfate, it is preferably 300 ° C. or higher, more preferably 350 ° C. or higher. On the other hand, it is preferably 550 ° C. or lower, and more preferably 520 ° C. or lower. If the calcination treatment is performed within this range, the above effect can be obtained. In addition, the water-soluble polymer derived from a living organism can be combusted in the same temperature range, and the acrylic polymer can be combusted at 400 ° C. or higher. On the other hand, if the temperature is too close to the firing temperature, the firing proceeds with gas generation, and thus it is preferably 50 ° C. or more lower than the firing temperature, and more preferably 100 ° C. or more lower.

The calcination treatment is performed during the supply (flow) of an inert gas such as an argon atmosphere, a nitrogen atmosphere, or a mixed atmosphere thereof, and the inflow amount of oxygen contained in the supplied inert gas is determined as a unit furnace. per inner volume, must be 0.052ml / (min · m ³⁾ or less, preferably to 0.017ml / (min · m ³⁾ or less. If it exceeds 0.052 ml / (min · m ³ ), the reducing power due to carbon monoxide generated by the combination of the carbon source and oxygen becomes too strong, and high purity Li ₂ MSiO ₄ cannot be obtained. Capacity will drop.

  The time for maintaining the temperature of the calcining treatment is preferably 3 minutes or more, and preferably 5 minutes or more. If it is less than 3 minutes, the gas may not be sufficiently removed. On the other hand, if the temperature of the calcination treatment is maintained for more than 1 hour, the firing reaction may be partially started, and therefore it is preferably 1 hour or less.

Thereafter, the main calcination is performed in an argon atmosphere or an argon / hydrogen atmosphere. This firing is also performed during the supply (flow) of the inert gas, and the inflow of oxygen contained in the supplied inert gas is set to 0.052 ml / (min · m ³ ) or less per unit furnace volume. Therefore, it is preferable that the amount be 0.017 ml / (min · m ³ ) or less. If it exceeds 0.052 ml / (min · m ³ ), the reducing power due to carbon monoxide generated by the combination of the carbon source and oxygen becomes too strong, and high purity Li ₂ MSiO ₄ cannot be obtained. Capacity will drop.

  The temperature for the main firing is preferably 600 ° C. or higher, and more preferably 700 ° C. or higher. Below 600 ° C., non-uniform transition metals tend to remain. On the other hand, 900 ° C. or lower is preferable, and 800 ° C. or lower is more preferable. If the temperature is too high, the particles become coarse, which is not preferable.

  The firing time is preferably 3 hours or longer. If it is less than 3 hours, the risk of insufficient phase change increases. On the other hand, it is preferably 20 hours or shorter, and more preferably 15 hours or shorter. If the length is too long, not only the load is increased, but also the particles become coarse, which is not preferable.

By performing the main firing in an environment in which the oxygen concentration is sufficiently reduced as described above, it is possible to obtain a positive electrode material in which Li ₂ MSiO ₄ is not reduced by carbon monoxide and has a small amount of byproducts and a high battery capacity. I can do it.

  In addition, when the water-soluble carbon-containing molecule is used as the carbon source, by securing a film-like conductive path reaching individual particles of the positive electrode material obtained with high purity, The battery capacity can be used without wasting it more than ever.

  Further, when the carbon colloid solution is used in combination, a large current collected from the film-like conductive path can be collected by the main conductive path by the carbon colloid. With such a configuration, when a battery is manufactured as the positive electrode active material, a sufficient battery capacity can be secured without the need to add an additional conductive additive. In addition, the presence of a carbon film formed so as to cover individual particles and a main conductive path that collects current from the conductive path on the film makes it possible to achieve current collection more efficiently than a conductive additive added later. .

In the production of specific electrodes and batteries, suitable electrodes and batteries can be produced without adding additional conductive aids. For example, an electrode and a battery can be manufactured by the following procedure. Li ₂ MSiO ₄ particles fired by the production method according to the present invention are used. When it is a lump, it is once pulverized into particles. An additional conductive auxiliary agent is not added to the particles, but mixed with a resin binder for forming an electrode to obtain a synthetic slurry dispersed in an organic solvent. As the resin binder, a nonionic polymer such as polytetrafluoroethylene may be used. Moreover, it is good to use nonpolar organic solvents, such as hexane, as an organic solvent. This synthetic slurry is formed and hardened by applying pressure. In order to evaporate the organic solvent from the solidified material, the electrode is manufactured by drying. At this time, drying is preferably performed at less than 300 ° C. so that the Li ₂ MSiO _{4 that} has already been generated does not deteriorate. The electrode obtained in this way has a conductive path stretched so that current can be suitably collected inside, and can exhibit high battery capacity when used as a battery.

Next, the present invention will be described more specifically with reference to examples.
First, the materials used will be described.
Lithium acetate dihydrate (Nacalai Tesque, Inc .: 20604-35, purity> 98%, molecular weight 102.02)
Iron (II) acetate (manufactured by Wako Chemical Co., Ltd .: 351-10952, molecular weight 173.93)
Iron nitrate (III) 9 hydrate (Nacalai Tesque, Inc .: 19514-55, purity> 99%, formula weight 404.0)
Colloidal silica (manufactured by Nissan Chemical Industries, Ltd .: Snowtex OXS (20 mass%: weight average particle size 4-6 nm, pH 3.0, Na content: 83 μg / g)
・ Glucose (Nacalai Tesque, Inc .: D-(+)-glucose)
・ Carbon colloid solution (manufactured by Kuretake Co., Ltd .: BA4 (black ink), carbon concentration of about 6% by mass, containing a small amount of water-soluble polymer (glue))
・ Polytetrafluoroethylene (Daikin Industries, Ltd .: Polyflon F104)
・ Hexane (Kishida Chemical Co., Ltd .: special grade)

<Examination of oxygen flow>
Example 1
Lithium acetate dihydrate as a lithium source, iron acetate and iron (III) nitrate nonahydrate as an Fe source as a transition metal source, colloidal silica as a silica source, and a molar ratio of iron acetate: iron nitrate is 26 : 74, and the molar ratio of Li: Fe: Si was 2: 1: 1. The mass ratio of these raw materials, glucose and carbon colloid solution (total of raw material elements Li, Fe, Si in the raw materials) :( carbon in glucose) :( carbon in carbon colloid solution) is 100: 15: It was weighed to 10 and poured into distilled water and stirred and dispersed until glucose was dissolved.

  The obtained mixed solution was freeze-dried by a spray-freeze-drying method (SFD method) using FD-50 manufactured by Tokyo Rika Kikai Co., Ltd. to obtain a dried mixed powder. .

Argon flow (8.67 L / (min · m ³ ) per unit furnace volume in which oxygen partial pressure was reduced, and 0.5 to 1.0 g of the powder after spray freeze-drying of the above mixed solution: oxygen inflow 0.052 ml / (min · m ³ )) at 450 ° C. for 30 minutes to perform a calcination treatment.

Argon gas flow per unit furnace volume in which oxygen partial pressure is reduced (8.67 L / (min · m ³ ): of oxygen inflow amount 0.052 ml / (min · m ³ ) ) Was heated at 700 ° C. for 5 hours and fired to obtain a mixed powder. About this mixed powder, the XRD analysis of the obtained data was performed using the XRD analyzer (Rigaku Co., Ltd. product: Sample horizontal type multipurpose X-ray-diffraction apparatus UltimaIV). The result is shown in FIG.

(Comparative Examples 1-3)
In Example 1, the argon flow per unit furnace volume was doubled to 17.34 L / (min · m ³ ) (oxygen inflow 0.104 ml / (min · m ³ )), Comparative Example 1, argon Comparative Example 2 in which the flow rate was tripled to 26.01 L / (min · m ³ ) (oxygen inflow rate 0.156 ml / (min · m ³ )), and the argon flow rate was tripled to 43.35 L / (min · ^m 3) (oxygen inflow ^{0.260ml / (min · m 3)} ) and the the article according to Comparative example 3 were respectively obtained. The XRD analysis results of those obtained samples are also shown in FIG.

The bottom row in FIG. 1 is a theoretical XRD of Li ₂ FeSiO ₄ . In Comparative Examples 1 to 3 in which the amount of argon gas flow is large and the oxygen supply amount is not sufficiently reduced, sufficient Li ₂ FeSiO ₄ is not obtained, but in Example 1, Li ₂ FeSiO with a clearly high purity is obtained. It was confirmed that ₄ was obtained.

<Examination of carbon content>
(Example 2)
In Example 1, a carbon colloid solution is not used as a carbon source, but only glucose is used, and the mass ratio of (total of raw material elements Li, Fe, Si in the raw material) :( carbon in glucose) is 100: 15. The mixture was weighed and calcined and fired in the same manner to obtain a mixed powder. The XRD analysis result of this obtained sample is shown in FIG.

(Example 3, Reference Examples 1-3)
In Example 2, the mass ratio of (carbon in glucose) to the total of 100 parts by mass of the raw material elements is 8 parts by mass (Example 3), 20 parts by mass (Reference Example 1), 35 parts by mass (Reference Example 2), It weighed so that it might become 50 mass parts (reference example 3), and the calcination process and the main calcination were performed similarly, respectively, and mixed powder was obtained. The XRD analysis results of the obtained sample are also shown in FIG.
By-products were not confirmed when the carbon content relative to the raw material element of Li ₂ MSiO ₄ was in the range of 8 to 15% by mass, but in Reference Example 1 of 20% by mass, impurities became mixed, and a reference of 35% by mass or more In Examples 2 and 3, almost no Li ₂ MSiO ₄ was detected. From this, it was found that when too much carbon was added, single-phase Li ₂ MSiO ₄ could not be obtained, and it was necessary to be 15% by mass or less.

<Examination of charge / discharge capacity>
Example 1
The battery material of Example 1 obtained by the main firing described above and polytetrafluoroethylene (PTFE) were weighed so as to have a mass mixing ratio of (Li + Fe + Si): carbon: PTFE = 73: 20: 7, After adding hexane, the mixture was formed into a sheet, pressed onto a 12 mm aluminum mesh and pressed at 40 MPa, then placed in an oven, held at 220 ° C. for 10 hours and dried to obtain a positive electrode material. This positive electrode material, a glass separator (manufactured by Advantech, φ16 mm), and a cathode Li foil (0.5 mm, φ12 mm) are enclosed in a coin cell (CR2032) together with an electrolytic solution (1M LiPF ₆ EC-DEC) for a test battery. Was made. Charging / discharging repeated CCCV charge and CC discharge in the range of 1.5 to 4.8V, and confirmed the battery capacity after 11 cycles. The result is shown in FIG. A battery capacity of 200 mAh / g could be secured without adding a conductive aid.

(Example 2)
The battery material of Example 2 obtained by the above main firing and polytetrafluoroethylene (PTFE) were weighed so as to have a mass mixing ratio of (Li + Fe + Si): carbon: PTFE = 79: 14: 7. Except for mixing, a test battery was prepared by the same procedure as in Example 1, and the battery capacity was confirmed by the same cycle. The result is shown in FIG. A battery capacity of 180 mAh / g could be secured without adding a conductive aid.

Claims (6)

In a production method of obtaining a Li ₂ MSiO ₄ by drying a mixed liquid in which a lithium source, a transition metal source, a Si source, and a carbon source are dispersed and mixed in a liquid and then firing in an inert gas flow.
A method for producing Li ₂ MSiO ₄ , wherein an oxygen supply amount during firing is 0.052 ml / (min · m ³ ) or less per unit furnace volume.
(However, M represents Fe or Mn.) The method for producing Li ₂ MSiO _{4 according} to claim 1, wherein the carbon source contains a water-soluble carbon-containing molecule that is nonvolatile, and is dissolved and dispersed in the mixed solution. The method for producing Li ₂ MSiO _{4 according} to claim 2, wherein the water-soluble carbon-containing molecule is a saccharide having a water solubility of 5 g / mL or more. The method for producing Li ₂ MSiO _{4 according} to claim 2 or 3, wherein a carbon colloid solution is further used as the carbon source, and the mixture is dispersed and mixed in the mixed solution in which the water-soluble carbon-containing molecules are dissolved and the carbon colloid is dispersed. . The method for producing Li ₂ MSiO _{4 according} to any one of claims 1 to 4, wherein a carbon amount of the carbon source to be mixed is 8% by mass or more and 15% by mass or less of Li ₂ MSiO ₄ to be synthesized. Using Li ₂ MSiO ₄ produced by the production method according to claim 1, a synthetic slurry dispersed in an organic solvent without adding an additional conductive auxiliary agent, and using this synthetic slurry The manufacturing method of the lithium ion secondary battery positive electrode which shape | molds an electrode and dries.

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