JP2017188344A - Lithium-containing silicon oxide powder and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the worsening of a battery performance owing to lithium elution in a slurry forming step for electrode coating without impairing a battery performance-improving effect by Li doping in Li-containing silicon oxide powder which is to be used for a negative electrode material of a lithium ion secondary battery.SOLUTION: Li-containing silicon oxide powder is manufactured by reacting Li ion-doped doped silicon oxide powder with a P-containing material, of which the composition is expressed by the following general formula: SiLiOP, where the element ratios satisfy the relation given by 0.01<z/x<0.25 and 0.1<x-3z<y-4z<1.5. With the Li-containing silicon oxide powder thus manufactured, low reactive, water-insoluble LiPOis produced in the powder, and the substance coexists with a lithium silicate resulting from Li doping, which lowers the reactivity of the powder, and increases the stability of the powder to water.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a Li-containing silicon oxide powder used for a negative electrode material of a lithium ion secondary battery and a method for producing the same.

  Among negative electrode materials for lithium ion secondary batteries, silicon oxide negative electrode materials are known for their large electric capacity. There is silicon oxide powder as the negative electrode material, and a slurry obtained by mixing a conductive additive and a binder is applied onto a current collector made of copper foil or the like and dried to form a thin film-like working electrode. . The silicon oxide powder here is obtained by cooling and precipitating silicon monoxide gas produced by heating a mixture of silicon dioxide and silicon, and then finely crushing. The silicon oxide powder produced by such a precipitation method is advantageous in that it contains a lot of amorphous parts, reduces expansion and contraction due to charge and discharge, and improves cycle characteristics.

  As a problem of such a silicon oxide negative electrode material, there is a low initial efficiency, and lithium ion doping (Li doping) is known as a technique for solving this problem. Li doping is carried out by electrochemical reaction with a substance containing lithium, mixing silicon oxide powder and powdered lithium source, and firing (Patent Documents 1 to 4). By performing Li doping on the silicon oxide powder particles, the generation of a lithium compound that does not contribute to charge / discharge is suppressed during the initial charge, and the initial efficiency is improved.

  In addition to Li doping, the surface of particles (powder particles) constituting silicon oxide is subjected to carbon coating treatment (C coating) to improve cycle characteristics. C coating is performed after Li doping, and in Patent Document 4, Li doping is performed after C coating.

However, the Li doping has the following problems related to lithium silicate. That is, lithium silicate such as Li ₂ Si ₂ O ₅ , Li ₂ SiO ₃ , and Li ₄ SiO ₄ is generated by Li doping with respect to the silicon oxide powder. Moreover, a LiSi alloy may be produced. These lithium silicates, LiSi alloys, and residual lithium in the powder are highly reactive and have low stability against water, so they react with binders and solvents when preparing a slurry for electrode coating. As a result, the battery performance deteriorates, and it becomes a cause of problems during electrode coating. In particular, since lithium eluted in the slurrying process raises the pH, silicon oxide reacts with water to generate hydrogen, so that the problem in producing a slurry with an aqueous binder is particularly great.

  In order to solve this problem, Patent Document 5 proposes pickling treatment of Li-doped silicon oxide powder subjected to Li doping. By dissolving and removing the lithium silicate in the Li-containing silicon oxide powder by the pickling treatment, various problems due to the elution of lithium in the slurrying process are solved, but on the other hand, Since the amount of lithium decreases, there is a concern that the performance improvement effect due to the addition of Li is hindered.

Japanese Patent No. 2999741 Japanese Patent No. 4702510 Japanese Patent No. 4985949 Japanese Patent No. 54117781 JP2015-153520A

  An object of the present invention is to provide a Li-containing silicon oxide powder capable of solving various problems caused by lithium elution in a slurrying process for electrode coating without impairing the performance improvement effect by adding Li, and a method for producing the same. There is.

In order to achieve the above object, the present inventor considered that it is effective to reduce the reactivity of the Li-containing silicon oxide powder, and studied various measures. As a result, it has been found that it is effective to produce a phosphorus compound, particularly lithium phosphate, in the Li-containing silicon oxide powder. That is, when Li-containing silicon oxide powder is reacted with a phosphorus compound, Li ₃ PO ₄ that is lithium phosphate is generated in the Li-containing silicon oxide powder. Li ₃ PO ₄ has low reactivity unlike lithium silicate and is poorly water-soluble. As a result, even if it is contained in a small amount in the powder, the reactivity of the powder is lowered, and as a result, the stability to water is improved. Thus, elution of lithium in the slurrying process and various problems caused by this are solved.

The Li-containing silicon oxide powder of the present invention is based on such knowledge, and is a Li-containing silicon oxide powder used for a negative electrode material of a lithium ion secondary battery, the composition of which is a general formula SiLi _x O _y P _z. The elemental ratio here is 0.01 <z / x <0.25 and 0.1 <x-3z <y-4z <1.5 is satisfied.

  Moreover, the manufacturing method of the Li-containing silicon oxide powder according to the present invention includes, firstly, a Li doping step of doping a raw material silicon oxide powder with Li ions and a silicon oxide powder doped with Li ions dispersed in an organic solvent. And a P treatment step in which the P-containing material is mixed and reacted. Second, it includes a Li doping step of doping the raw silicon oxide powder with Li ions, and a P treatment step of contacting and reacting the silicon oxide powder doped with Li ions with a P-containing material in a liquid state or a gaseous state. Is the method.

In the Li-containing silicon oxide powder of the present invention, at least part of P present in the powder is present as low-reactivity and poorly water-soluble Li ₃ PO ₄ , so that lithium silicate in the powder is not removed. In both cases, the reactivity of the powder is reduced, and the stability of the powder to water is improved. Thus, without impairing the performance improvement effect due to the addition of Li, lithium elution in the slurrying process for electrode coating, that is, lithium elution when preparing a slurry with an aqueous binder, further increasing the pH, resulting in hydrogen Is prevented, and deterioration of battery performance due to these is prevented.

  As an index representing the composition of the Li-containing silicon oxide powder of the present invention, “z / x” representing the amount of P, “x-3z” representing the amount of Li, and “y-4z” representing the amount of O are important. .

z / x, that is, the ratio of the P amount to the Si amount needs to be more than 0.01 and less than 0.25. In the case of 0.01 or less, the abundance of P is small, and Li ₃ PO ₄ is reduced, so that the reactivity of the powder is increased and the stability of the powder to water is reduced, so that the desired effect can be obtained. I can't. In the case of 0.25 or more, most of Li is present as Li ₃ PO ₄ , and lithium silicate such as Li ₂ SiO is reduced, so that the effect of improving battery characteristics due to the inclusion of Li cannot be obtained.

As can be seen from this, in the Li-containing silicon oxide powder of the present invention, the contained Li is consumed in a balanced manner between Li ₃ PO ₄ that is lithium phosphate and lithium silicate such as Li ₂ SiO _3. Battery performance due to lithium elution in the slurrying process for electrode coating, while maintaining the effect of improving battery characteristics by inclusion, ensuring low powder reactivity and high stability to water Decline is prevented.

x-3z represents the amount of Li contained in the powder in a form other than Li amount, particularly Li ₃ PO ₄ , and needs to be more than 0.1 and less than y-4z. Incidentally, y-4z represents the amount of O, particularly the amount of O contained in the powder in a form other than Li ₃ PO ₄ . When x-3z is 0.1 or less, since the amount of Li is insufficient, improvement in battery performance due to the inclusion of Li cannot be expected. When x-3z is equal to or greater than y-4z, the Li amount is excessive, thereby producing a Li-Si alloy, and the reactivity of the powder is extremely increased, making handling difficult. By controlling x-3z to be more than 0.1 and less than y-4z, the amount of Li in the powder is optimized, and the Li is present in the form of an oxide-based lithium compound. Become.

  The y-4z needs to be less than 1.5. When y-4z is 1.5 or more, since the O content in the powder becomes excessive, battery performance, in particular, charge / discharge efficiency and conductivity are deteriorated. On the other hand, when the O content is small, the effect of suppressing volume expansion by the oxide is lowered, and the life characteristics are deteriorated. From this viewpoint, it is desirable that y-4z exceeds 0.4, that is, 0.4 <y-4z.

The presence of Li ₃ PO ₄ in the Li-containing silicon oxide powder of the present invention is the presence of a diffraction peak derived from Li ₃ PO ₄ that appears in the vicinity of a diffraction angle 2θ = 23.3 ° in powder X-ray diffraction using CuKα rays. Confirmation is possible by examining. Specifically, the minimum diffraction intensity from 2θ = 22.8 ° to 2θ = 23.3 ° and the minimum diffraction intensity from 2θ = 23.3 ° to 2θ = 23.8 ° are connected by a straight line, and the line The intensity at 2θ = 23.3 ° is the background intensity B1. Then, minus the background intensity B1 from the maximum diffraction intensity at 2θ = 23.3 ± 0.2 ° as the peak intensity P1 of _Li 3 PO _{4, Li} 3 when satisfying P1 / B1> 0.03 PO It can be assumed that ₄ exists.

  When calculating the peak intensity by powder X-ray diffraction, data obtained by powder X-ray diffraction using CuKα rays and having a diffraction angle interval of 0.02 ° are specified as a data specific number 11. It is desirable to use data converted to a moving average approximate curve as By using the moving average approximate curve, errors in the measured value due to fluctuations in diffraction intensity are reduced.

  In the Li-containing silicon oxide powder of the present invention, it is also desirable that the Si crystallinity is low. When Si is crystallized, the structure becomes non-uniform, the internal resistance increases, and the cycle characteristics may deteriorate due to cracking of the Si crystal.

  The low crystallinity of Si can be confirmed by examining the presence or absence of a Si-derived diffraction peak appearing at a diffraction angle of 2θ = 47.4 ° by powder X-ray diffraction using CuKα rays. Specifically, the diffraction intensity at 2θ = 46.4 ° and the diffraction intensity at 2θ = 48.4 ° are connected by a straight line, and the intensity at 2θ = 47.4 ° on the straight line is set as the background intensity B2. . Further, when the peak intensity P2 of Si is obtained by subtracting the background intensity B2 from the maximum diffraction intensity at 2θ = 47.4 ± 0.3 °, the crystallinity of Si is low when P2 / B2 ≦ 0.3 is satisfied. Can be considered. With such a powder, the negative electrode material has low internal resistance and excellent cycle characteristics.

The Li-containing silicon oxide powder of the present invention can be produced by reacting a Li-containing silicon oxide powder as a base material, that is, a Li-containing silicon oxide powder before P treatment, with a P-containing material. The P-containing material may be any element or compound that reacts with Li-containing silicon oxide powder before P treatment to produce Li ₃ PO ₄ , and specifically, phosphorus alone, phosphorus oxide, phosphoric acid, phosphoric acid compound However, either phosphorus oxide or phosphoric acid is desirable from the viewpoint of preventing the impurity elements from being mixed and handling.

  As a reaction method, a P-containing material is dissolved and dispersed in a non-aqueous solvent such as an organic solvent, and mixed with Li-containing silicon oxide powder before P treatment and reacted, or a P-containing material in a liquid state or a gaseous state There is a method of contacting and reacting with Li-containing silicon oxide powder before P treatment. The former is the first production method of the present invention, and the latter is the second production method of the present invention.

  In the first production method in which a P-containing material is dissolved and decomposed in an organic solvent and mixed with Li-containing silicon oxide powder before P treatment and reacted, a uniform surface reaction can be expected by using an organic solvent as the solvent. The reaction between the Li-containing silicon oxide powder before the P treatment, which is the base material, and the solvent is suppressed, and a powder with higher battery performance can be obtained. The organic solvent is not limited as long as the P-containing material dissolves and decomposes. After the reaction, the residual P-containing material in the solvent can be removed by filtering the solvent and drying. If the amount of P-containing material added is adjusted so that no residue is generated, a filtration process is not necessarily required.

  As a second production method for contacting and reacting a P-containing material in a liquid state or a gas state with a Li-containing silicon oxide powder before P treatment which is a base material, a solid P-containing material and a Li-containing oxidation before P treatment are used. A method of heating to a temperature at which the P-containing material is liquefied or vaporized by mixing with silicon powder, or a P-containing material in a liquid or gaseous state is introduced into a container in which the Li-containing silicon oxide powder before P treatment exists. There are methods. The reaction temperature is preferably 900 ° C. or lower, and more preferably 600 ° C. or lower. When the reaction temperature exceeds 900 ° C., crystallization of Si proceeds.

Li _A SiO _B (0 <A <B ≦ 2) can be used as the Li-containing silicon oxide powder before P treatment, which is the base material, and in particular, 0.1 <A, 0.4 <B <1 .5 is particularly desirable. When A is small, a sufficient initial efficiency improvement effect cannot be obtained. When A is large, the reactivity is high and handling becomes difficult. When B is small, the cycle characteristics are deteriorated. When B is large, initial efficiency and capacity are reduced. As a method for producing the Li-containing silicon oxide powder before the P treatment, mechanical mixing or thermochemical reaction between the silicon oxide powder and lithium metal or a lithium compound, lithium addition by an electrochemical method for silicon oxide, during the silicon oxide production process There is a technique such as lithium addition by gas or the like, and there is no particular limitation.

  In the Li-containing silicon oxide powder of the present invention, a part or all of the surface of the powder particles may be coated with a conductive carbon film. By covering a part or all of the surface of the powder particle with the conductive carbon film, the surface resistance is lowered, the battery characteristics are improved, and the effect of suppressing the reactivity of the particle surface can be expected. This conductive carbon film can be coated by a thermal CVD reaction of hydrocarbon gas. When the thermal CVD reaction is performed with a hydrocarbon gas after the reaction with lithium, it is desirable to control the reaction temperature between 400 ° C. and 900 ° C. When the reaction temperature is lower than 400 ° C., the thermal CVD reaction does not proceed sufficiently. When the reaction temperature exceeds 900 ° C., crystallization of Si proceeds.

  In addition, about the order of Li dope and P process, as above-mentioned, Li dope is performed first and it is based on performing P process after that. This is because if the P treatment is performed first and then Li doping is performed, unreacted Li compounds remain, and the effect of reducing the reactivity by the P treatment cannot be obtained sufficiently.

The Li-containing silicon oxide powder of the present invention contains an appropriate amount of P, and at least a part of the P is present as low-reactivity and poorly water-soluble Li ₃ PO ₄ and coexists with Li-doped lithium silicate. Thus, without impairing the performance improvement effect due to the addition of Li, the lithium elution in the slurrying process for electrode coating, further the increase in pH, thereby preventing the generation of hydrogen, the battery performance resulting from these Decline can be prevented.

The method for producing Li-containing silicon oxide powder according to the present invention generates a large amount of Li ₃ PO ₄ near the surface of the powder particles by reacting the P-containing material from the surface of the powder particles with respect to the Li-doped silicon oxide powder. Therefore, it is more effective in reducing the reactivity of the powder and improving the stability to water, and exerts a greater effect in improving the battery performance.

3 is an X-ray diffraction chart of Li-containing silicon oxide powder of the present invention. It is an X-ray diffraction chart of conventional Li-containing silicon oxide powder.

  Embodiments of the present invention will be described below. The Li-containing silicon oxide powder of this embodiment is typically produced by the following method.

First, a Li-containing silicon oxide powder as a base material, that is, a Li-containing silicon oxide powder before P treatment is prepared. That is, the lower silicon oxide powder represented by a composition formula _{SiO C (0.5 <C <1.5} ) as a raw material silicon oxide powder, to which is doped with Li-ion (Li doping step).

Specifically, SiO _C powder (0.5 <C <1.5), which is a raw silicon oxide powder, is mixed with a powder lithium source and fired in an inert gas atmosphere. The SiO _C powder (0.5 <C <1.5), using the produced amorphous _SiO C (C = 1), for example, by deposition. As the powder lithium source, lithium hydride (LiH), lithium oxide (Li ₂ O), lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ) and the like can be used. Here, lithium hydride (LiH) is used. ) Is used.

By Li doping, a lithium compound such as Li ₂ SiO ₃ that does not contribute to charging / discharging is generated in advance, and the generation of the lithium compound during initial charging is suppressed, thereby improving the initial efficiency.

  If necessary, C coating treatment for forming a conductive carbon film is performed on the lower silicon oxide powder before or after Li doping.

When Li-containing silicon oxide powder before P treatment, which is a base material, is prepared, it is mixed with phosphoric acid or phosphorus oxide, which is a P-containing material, and reacted, so that the powder particles have low reactivity and are difficult to react. Water-soluble Li ₃ PO ₄ is generated (P treatment step).

When the P-containing material is phosphoric acid, the Li-containing silicon oxide powder before P treatment is stirred and mixed with a phosphoric acid solution in an organic solvent, reacted, and then dried. When the P-containing material is phosphorus oxide (P ₂ O ₅ ), it is mixed with the Li-containing silicon oxide powder before P treatment and heated to a temperature above the sublimation point. As a result, the Li-containing silicon oxide powder before P treatment reacts with gaseous phosphorus oxide to produce Li ₃ PO ₄ .

In any case, since the reaction proceeds from the surface of the powder particle of the Li-containing silicon oxide powder, Li ₃ PO ₄ tends to be generated near the surface of the powder particle. Thereby, the reactivity of the powder is particularly effectively reduced, and the stability to water is particularly effectively improved.

  The produced Li-containing silicon oxide powder is used as a negative electrode material for a lithium ion secondary battery. Specifically, Li-containing silicon oxide powder is mixed with a conductive additive for improving conductivity, a binder, etc., and slurried, applied onto a current collector made of copper foil, etc., and dried to form a thin film. The negative electrode.

Since the Li-containing silicon oxide powder contains not only lithium silicate such as Li ₂ SiO ₃ as a lithium compound but also Li ₃ PO ₄ that is lithium phosphate, Li ₃ PO ₄ has low reactivity and high stability to water. Without removing the lithium silicate, the reactivity of the powder is lowered and the stability to water is improved. Thereby, the fall of the battery performance resulting from the lithium elution in the slurrying process for electrode coating is prevented. In addition, a decrease in battery performance associated with lithium silicate removal treatment (pickling treatment) is also avoided.

  Moreover, since the crystallization of Si in the powder is suppressed, the internal resistance of the negative electrode material is small, and the cycle characteristics are also excellent from this point.

Example 1
Li doping was performed on silicon oxide powder, which is a raw material for producing Li-containing silicon oxide powder. The raw material silicon oxide powder was an amorphous SiO 2 _C powder (C = 1) produced by a precipitation method, and the average particle size was 4.9 μm. LiH powder was selected as the powder lithium source to be mixed with the raw silicon oxide powder.

  The raw material silicon oxide powder and the LiH powder as the powder lithium source were mixed at a molar ratio of 1: 0.4 and heat-treated. The heat treatment conditions were an argon atmosphere, a pressure of 1 atm, a reaction temperature of 600 ° C., and a reaction time of 1440 min.

  Next, the Li-containing silicon oxide powder after Li doping, that is, the Li-containing silicon oxide powder before P treatment was reacted with the P-containing material. Specifically, 10 g of the produced Li-containing silicon oxide powder is put in a glass beaker as a base material, and mixed with 1 g of phosphoric acid (85 wt%) as a P-containing material and 50 ml of ethanol as a solvent in the beaker, The mixture was stirred for 2 hours with a magnetic stirrer, reacted, filtered and dried.

The composition (SiLi _x O _y P _z ) of the Li-containing silicon oxide powder after P treatment was examined by ICP emission spectroscopy and infrared absorption. x = 0.37, y = 1.08, z = 0.04, z / x = 0.11, x-3z = 0.25, y-4z = 0.92, so 0.01 <Z / x <0.25 and 0.1 <x-3z <y-4z <1.5 were satisfied.

The Li-containing silicon oxide powder is subjected to X-ray diffraction measurement using CuKα rays, and the ratio P1 / D1 of the diffraction peak intensity P1 derived from Li ₃ PO ₄ appearing at a diffraction angle of 2θ = 23.3 ° to the background intensity B1. B1 was examined. P1 / B1 = 0.4 (> 0.03), and it was confirmed that Li ₃ PO ₄ was present in the powder.

  Further, the ratio P2 / B2 of the Si-derived diffraction peak intensity P2 appearing near the diffraction angle 2θ = 47.4 to the background intensity B2 was examined. P2 / B2 = 0.07 (≦ 0.3), and it was confirmed that the crystallinity of Si was low in the powder.

The X-ray diffraction chart at this time is shown in FIG. A peak derived from Li ₂ SiO ₃ that appears in the vicinity of the diffraction angle 2θ = 18.9 ° or the like is also clearly recognized.

(Example 2)
The same Li-containing silicon oxide powder before P treatment as that used in Example 1 was reacted with phosphorus oxide (P ₂ O ₅ ), which is a P-containing material. Specifically, 10 g of Li-containing silicon oxide powder before P treatment was mixed with 0.5 g of P ₂ O ₅ and heat-treated at 400 ° C. higher than the sublimation point of P ₂ O ₅ for 120 min. P ₂ O _{5 has} a melting point of 340 ° C. and a sublimation point of 360 ° C.

The composition of the Li-containing silicon oxide powder after the P processing (SiLi _X O _Y P _Z) was examined similarly. x = 0.40, y = 1.07, z = 0.03, z / x = 0.08, x-3z = 0.31, y-4z = 0.95, 0.01 <z /X<0.25 and 0.1 <x-3z <y-4z <1.5 were satisfied.

The Li-containing silicon oxide powder is subjected to X-ray diffraction measurement using CuKα rays, and the ratio P1 / D1 of the diffraction peak intensity P1 derived from Li ₃ PO ₄ appearing at a diffraction angle of 2θ = 23.3 ° to the background intensity B1. B1 was examined. P1 / B1 = 0.3 (> 0.03), and it was confirmed that Li ₃ PO ₄ was present in the powder. Further, a diffraction peak derived from Li ₂ SiO ₃ appearing in the vicinity of a diffraction angle 2θ = 18.9 ° or the like was also clearly recognized.

  Further, the ratio P2 / B2 of the Si-derived diffraction peak intensity P2 appearing near the diffraction angle 2θ = 47.4 to the background intensity B2 was examined. P2 / B2 = 0.08 (≦ 0.3), and it was also confirmed that the crystallinity of Si was low in the powder.

(Example 3)
The raw material silicon oxide powder used in Example 1, that is, the amorphous SiO 2 _C powder (C = 1, average particle size 4.9 μm) produced by the precipitation method, was preliminarily subjected to C coating. When the raw material silicon oxide powder after the C coating treatment was subjected to a combustion infrared absorption method, it was confirmed that a conductive carbon film of 1.1% by weight was formed.

  The raw material silicon oxide powder after the C coating treatment and the LiH powder as the powder lithium source were mixed and heat-treated at a molar ratio of 1: 0.6. The heat treatment conditions were the same argon atmosphere as in Example 1, a pressure of 1 atm, a reaction temperature of 600 ° C., and a reaction time of 1440 min.

The produced Li-containing silicon oxide powder before P treatment was reacted with phosphoric acid as a P-containing material in the same manner and under the same conditions as in Example 1. The composition of the Li-containing silicon oxide powder after the P processing (SiLi _X O _Y P _Z) was examined similarly. x = 0.40, y = 1.07, z = 0.03, z / x = 0.08, x-3z = 0.31, y-4z = 0.95, so 0.01 <Z / x <0.25 and 0.1 <x-3z <y-4z <1.5 were satisfied.

The Li-containing silicon oxide powder is subjected to X-ray diffraction measurement using CuKα rays, and the ratio P1 / D1 of the diffraction peak intensity P1 derived from Li ₃ PO ₄ appearing at a diffraction angle of 2θ = 23.3 ° to the background intensity B1. B1 was examined. P1 / B1 = 0.3 (> 0.03), and it was confirmed that Li ₃ PO ₄ was present in the powder. Further, a diffraction peak derived from Li ₂ SiO ₃ appearing in the vicinity of a diffraction angle 2θ = 18.9 ° or the like was also clearly recognized.

  Further, the ratio P2 / B2 of the Si-derived diffraction peak intensity P2 appearing near the diffraction angle 2θ = 47.4 to the background intensity B2 was examined. P2 / B2 = 0.08 (≦ 0.3), and it was also confirmed that the crystallinity of Si was low in the powder.

(Comparative Example 1)
The composition (SiLi _X O _Y P _Z ) of the Li-containing silicon oxide powder before P treatment obtained in Example 1 was similarly examined. Since x = 0.39, y = 0.98, z = 0, z / x = 0, x-3z = 0.39, y-4z = 0.98, 0.01 <z / x <0.25 and 0.1 <x-3z <y-4z <1.5 are not satisfied. That is, z / x corresponding to the P amount is too small as 0.

The Li-containing silicon oxide powder is subjected to X-ray diffraction measurement using CuKα rays, and the ratio P1 / D1 of the diffraction peak intensity P1 derived from Li ₃ PO ₄ appearing at a diffraction angle of 2θ = 23.3 ° to the background intensity B1. B1 was examined. Since it did not receive P treatment, P1 / B1 = 0 (> 0.03), and Li ₃ PO ₄ was not confirmed in the powder.

The X-ray diffraction chart at this time is shown in FIG. 2, and a diffraction peak derived from Li ₂ SiO ₃ appearing in the vicinity of a diffraction angle 2θ = 18.9 ° or the like was clearly recognized. _The diffraction peaks derived from Li 2 _Si 2 _{O 5} was also clearly observed.

  When the ratio P2 / B2 of the diffraction peak intensity P2 derived from Si appearing in the vicinity of the diffraction angle 2θ = 47.4 to the background intensity B2 was examined, it was P2 / B2 = 0.07 (≦ 0.3). Also, it was confirmed that the Si crystallinity was low in the powder.

(Comparative Example 2)
The composition (SiLi _x O _y P _z ) of the Li-containing silicon oxide powder before P treatment obtained in Example 3 was similarly examined. Since x = 0.58, y = 1.02, z = 0, z / x = 0, x-3z = 0.58, y-4z = 1.02, 0.01 <z / x <0.25 and 0.1 <x-3z <y-4z <1.5 are not satisfied. That is, z / x corresponding to the P amount is too small as 0.

The Li-containing silicon oxide powder is subjected to X-ray diffraction measurement using CuKα rays, and the ratio P1 / D1 of the diffraction peak intensity P1 derived from Li ₃ PO ₄ appearing at a diffraction angle of 2θ = 23.3 ° to the background intensity B1. B1 was examined. Since it did not receive P treatment, P1 / B1 = 0 (> 0.03), and Li ₃ PO ₄ was not confirmed in the powder. On the other hand, a diffraction peak derived from Li ₂ SiO ₃ that appears at a diffraction angle of 2θ = 18.9 ° or the like was clearly recognized. _The diffraction peaks derived from Li 2 _Si 2 _{O 5} was also clearly observed.

  The ratio P2 / B2 of the diffraction peak intensity P2 derived from Si appearing near the diffraction angle 2θ = 47.4 to the background intensity B2 is P2 / B2 = 0.07 (≦ 0.3). It was confirmed that the crystallinity of Si was low.

(Comparative Example 3)
In Example 1, 50 ml of ethanol used for the P treatment was changed to 50 ml of water. That is, 10 g of Li-containing silicon oxide powder before P treatment was placed in a glass beaker as a base material, mixed with 1 g of phosphoric acid (85 wt%) and 50 ml of water in the beaker, and stirred for 2 hours with a magnetic stirrer to react. And then filtered and dried. P treatment also serves as pickling treatment. Other conditions were the same as in Example 1.

The composition (SiLi _x O _y P _z ) of the Li-containing silicon oxide powder after the P treatment that also serves as the pickling treatment was similarly examined. x = 0.15, y = 1.12, z = 0.04, z / x = 0.27, x-3z = 0.03, y-4z = 0.96, so 0.01 <Z / x <0.25 and 0.1 <x-3z <y-4z <1.5 are not satisfied. That is, z / x corresponding to the P amount is excessively large as 0.27 (≧ 0.25), and x−3z corresponding to the Li amount is excessively small as 0.03 (≦ 0.1).

The Li-containing silicon oxide powder is subjected to X-ray diffraction measurement using CuKα rays, and the ratio P1 / D1 of the diffraction peak intensity P1 derived from Li ₃ PO ₄ appearing at a diffraction angle of 2θ = 23.3 ° to the background intensity B1. B1 was examined. P1 / B1 = 0.7 (> 0.03), and a diffraction peak derived from Li ₃ PO ₄ was confirmed. However, the diffraction peak derived from Li ₂ SiO ₃ appearing in the vicinity of the diffraction angle 2θ = 18.9 ° or the like has almost disappeared.

  The ratio P2 / B2 of the diffraction peak intensity P2 derived from Si appearing near the diffraction angle 2θ = 47.4 to the background intensity B2 is P2 / B2 = 0.07 (≦ 0.3). It was confirmed that the crystallinity of Si was low.

(Comparative Example 4)
In Example 1, the P treatment was changed to a pickling treatment. That is, 10 g of Li-containing silicon oxide powder before P treatment was placed in a glass beaker as a base material, mixed with 2 g of citric acid and 50 ml of water in the beaker, stirred for 2 hours with a magnetic stirrer, reacted, and then filtered. And dried. Other conditions were the same as in Example 1.

The composition (SiLi _x O _y P _z ) of the Li-containing silicon oxide powder after the pickling treatment instead of the P treatment was similarly examined. Since x = 0.07, y = 1.00, z = 0, z / x = 0, x-3z = 0.07, and y-4z = 1.00, 0.01 <z / x <0.25 and 0.1 <x-3z <y-4z <1.5 are not satisfied. That is, z / x corresponding to the P amount is too small as 0, and x-3z corresponding to the Li amount is too small as 0.07 (≦ 0.1).

The Li-containing silicon oxide powder is subjected to X-ray diffraction measurement using CuKα rays, and the ratio P1 / D1 of the diffraction peak intensity P1 derived from Li ₃ PO ₄ appearing at a diffraction angle of 2θ = 23.3 ° to the background intensity B1. B1 was examined. P1 / B1 = 0 (> 0.03), and no diffraction peak derived from Li ₃ PO ₄ was confirmed. The diffraction peak derived from Li ₂ SiO ₃ that appears in the vicinity of the diffraction angle 2θ = 18.9 ° or the like almost disappeared.

  The ratio P2 / B2 of the diffraction peak intensity P2 derived from Si appearing near the diffraction angle 2θ = 47.4 to the background intensity B2 is P2 / B2 = 0.07 (≦ 0.3). It was confirmed that the crystallinity of Si was low.

(Battery performance test)
A battery performance test was performed on the Li-containing silicon oxide powders produced in Examples 1 to 3 and Comparative Examples 1 to 4 by the following procedure.

The produced Li-containing silicon oxide powder, a PI binder that is a non-aqueous (organic) binder, and KB that is a conductive aid are mixed at a weight ratio of 80: 15: 5, and organic NMP is used as a solvent. A kneaded slurry was obtained. The prepared slurry was coated on a copper foil and vacuum heat-treated at 350 ° C. for 30 minutes to obtain a negative electrode. A coin cell battery was produced using this negative electrode, a counter electrode (Li foil), an electrolytic solution (EC: DEC = 1: 1), an electrolyte (LiPF ₆ 1 mol / L), and a separator (polyethylene porous film 30 μm thick).

  A charge / discharge test was performed on the manufactured coin cell battery. Charging was performed at a constant current of 0.5 C until the voltage between both electrodes of the battery reached 0.05 V, and after a voltage reached 0.05 V, charging was performed at a constant potential until the current reached 0.01 C. . Discharging was performed at a constant current of 0.1 C until the voltage between both electrodes of the battery reached 1.5V. The above charge / discharge test was performed 50 cycles.

By this charge / discharge test, the initial charge capacity and the initial discharge capacity were measured to determine the initial efficiency. Further, as the cycle characteristics, this charge / discharge test was performed 50 cycles, and the discharge capacity retention rate after 50 cycles was obtained. The test results are the specifications of the silicon oxide powder for the negative electrode material (Li amount, presence / absence of C coating, treatment method before Li doping, presence / absence of Li ₃ PO ₄ , presence / absence of Li ₂ SiO ₃ , and each value of x, y and z , Z / x, x-3z, and y-4z) are shown in Table 1 and Table 2.

In any of Examples 1 to 3, the silicon oxide powder for negative electrode material was SiLi _x O _y P _z (0.01 <z / x <0.25 and 0.1 <x−3z <y−4z <1. By satisfying 5), Li ₃ PO ₄ is present in the powder and coexists with Li ₂ SiO ₃ . Since an organic binder is sometimes used, the initial efficiency, which is one of battery performances, exceeds 70%. Also, the cycle characteristics exceed 60% in capacity retention after 50 cycles.

On the other hand, in Comparative Example 1, since the powder was not subjected to the P treatment, z / x corresponding to the amount of P becomes too small as 0, and Li ₃ PO ₄ does not exist. Despite the organic binder, the powder reacts with the binder and the like, the initial efficiency is very low at 29.7%, and the capacity retention after 50 cycles is very poor at 1.6%. This is because the powder does not function as a negative electrode material.

  In Comparative Example 2, since the powder was not subjected to the P treatment, z / x corresponding to the amount of P was too low as 0, but the battery performance was improved by the C coating, and the initial efficiency was high. However, the capacity retention rate after 50 cycles is still very low at 11.1%. This is presumably because the powder reacts with the binder and the like as in Comparative Example 1.

  In Comparative Examples 3 and 4, since the powder after Li doping was treated with water, Li in the powder was greatly reduced by reaction and elution with water, and x-3z corresponding to the amount of Li was 0.03, 0, respectively. .07 was too low. As a result, the initial efficiency is as low as less than 70%.

The treatment with water after Li doping is a pickling treatment (pickling treatment with phosphoric acid) also serving as a P treatment in Comparative Example 3, and a pure pickling treatment (pickling treatment with citric acid) in Comparative Example 4. . In Comparative Example 3, z / x corresponding to the amount of P is excessively increased to 0.27 (≧ 0.25) due to P treatment, and a large amount of Li ₃ PO ₄ is present, but Li ₃ PO ₄ is segregated in an aqueous solution. Therefore, the battery performance, particularly the cycle characteristics, is 3.6%, which is extremely lower than that of Comparative Example 4. The pure pickling treatment in Comparative Example 4 shows an initial efficiency of 69.7% and a cycle characteristic of 60.4%, respectively, and is relatively effective in improving battery performance.

Claims (6)

Li-containing silicon oxide powder used for a negative electrode material of a lithium ion secondary battery, the composition of which is represented by the general formula SiLi _x O _y P _z , where the element ratio is 0.01 <z / x <0. 25, and Li-containing silicon oxide powder satisfying 0.1 <x-3z <y-4z <1.5. The Li-containing silicon oxide powder according to claim 1, wherein at least part of P contained in the powder is present as Li ₃ PO ₄ .   3. The Li-containing silicon oxide powder according to claim 1, wherein the powder is a reaction product generated by a reaction between a Li-doped silicon oxide powder and a P-containing material.   The Li-containing silicon oxide powder according to any one of claims 1 to 3, wherein the particles constituting the powder further have a conductive carbon film on at least a part of the surface.   A method for producing a Li-containing silicon oxide powder used for a negative electrode material of a lithium ion secondary battery, wherein a raw silicon oxide powder is doped with Li ions, a Li oxide doped silicon oxide powder, A method for producing Li-containing silicon oxide powder, comprising a P treatment step of mixing and reacting with a P-containing material dispersed in an organic solvent.   A method for producing a Li-containing silicon oxide powder used for a negative electrode material of a lithium ion secondary battery, wherein a raw silicon oxide powder is doped with Li ions, a Li oxide doped silicon oxide powder, A method for producing a Li-containing silicon oxide powder, comprising a P treatment step for contacting and reacting with a P-containing material in a liquid state or a gas state.

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