WO2020003692A1 - Method of manufacturing negative electrode active material for nonaqueous electrolyte secondary battery - Google Patents

Abstract

The present invention is a method of manufacturing a negative electrode active material for a nonaqueous electrolyte secondary battery that comprises silicon compound particles containing lithium, the method being characterized by including a step of preparing silicon compound particles containing a silicon compound (SiO_x:0.5≤x≤1.6), a step of mixing a lithium compound with the silicon compound particles to form a mixed material, and a step of firing the mixed material in the presence of inert gas containing oxygen in an amount of 1000 ppm or less, whereby a negative electrode active material for a nonaqueous electrolyte secondary battery that comprises the silicon compound particles containing lithium is manufactured. Thus, the method of manufacturing a negative electrode active material for a nonaqueous electrolyte secondary battery which has good initial efficiency is provided.

Description

Method for producing negative electrode active material for non-aqueous electrolyte secondary battery

<< The present invention relates to a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery.

In recent years, small electronic devices represented by mobile terminals and the like have become widespread, and there is a strong demand for further miniaturization, lighter weight, and longer life. In response to such market demands, development of a secondary battery that is particularly small and lightweight and that can obtain a high energy density is being promoted. The application of this secondary battery to not only a small electronic device but also a large electronic device such as an automobile and a power storage system such as a house is being studied.

中 で も Among them, lithium-ion secondary batteries are highly expected because they can be easily made smaller and have higher capacities, and can obtain higher energy density than lead batteries and nickel-cadmium batteries.

The above-mentioned lithium ion secondary battery is provided with an electrolytic solution together with a positive electrode, a negative electrode and a separator, and the negative electrode contains a negative electrode active material involved in a charge / discharge reaction.

炭素 While carbon materials are widely used as the negative electrode active material, further improvement in battery capacity is required due to recent market requirements. Use of silicon as a negative electrode active material has been studied to improve battery capacity. This is because the theoretical capacity of silicon (4199 mAh / g) is at least 10 times greater than the theoretical capacity of graphite (372 mAh / g), so that a significant improvement in battery capacity can be expected. Development of a silicon material as a negative electrode active material is being studied not only for silicon alone but also for compounds represented by alloys and oxides. The active material shape is being studied from a standard coating type of carbon material to an integrated type directly deposited on a current collector.

However, when silicon is used as the main raw material as the negative electrode active material, the negative electrode active material expands and contracts during charge and discharge, and thus tends to be cracked mainly near the surface layer of the negative electrode active material. In addition, an ionic substance is generated inside the active material, and the negative electrode active material becomes a substance that is easily broken. When the surface layer of the negative electrode active material is broken, a new surface is generated, and the reaction area of the active material increases. At this time, a decomposition reaction of the electrolytic solution occurs on the new surface, and a film which is a decomposition product of the electrolytic solution is formed on the new surface, so that the electrolytic solution is consumed. For this reason, the cycle characteristics are likely to deteriorate.

Various studies have been made on negative electrode materials for lithium ion secondary batteries, mainly composed of silicon materials, and electrode configurations in order to improve battery initial efficiency and cycle characteristics.

Specifically, for the purpose of obtaining good cycle characteristics and high safety, silicon and amorphous silicon dioxide are simultaneously deposited using a gas phase method (for example, see Patent Document 1). Further, in order to obtain high battery capacity and safety, a carbon material (electron conductive material) is provided on the surface layer of the silicon oxide particles (for example, see Patent Document 2). Further, in order to improve cycle characteristics and obtain high input / output characteristics, an active material containing silicon and oxygen is produced, and an active material layer having a high oxygen ratio in the vicinity of the current collector is formed ( For example, see Patent Document 3). Further, in order to improve the cycle characteristics, oxygen is contained in the silicon active material, and is formed so that the average oxygen content is 40 at% or less and the oxygen content increases near the current collector. (For example, see Patent Document 4).

Further, Si phase, (for example, see Patent Document 5) by using a nanocomposite containing SiO 2, _M y _O metal oxide in order to improve the initial charge and discharge efficiency. Further, in order to improve cycle characteristics, SiO _x (0.8 ≦ x ≦ 1.5, particle size range = 1 μm to 50 μm) and a carbon material are mixed and fired at a high temperature (for example, see Patent Document 6). In order to improve the cycle characteristics, the molar ratio of oxygen to silicon in the negative electrode active material is set to 0.1 to 1.2, and the difference between the maximum value and the minimum value of the molar ratio near the interface between the active material and the current collector is determined. Is controlled to be 0.4 or less (for example, see Patent Document 7). Further, in order to improve battery load characteristics, a metal oxide containing lithium is used (for example, see Patent Document 8). Further, in order to improve the cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface layer of the silicon material (for example, see Patent Document 9).

Further, in order to improve cycle characteristics, silicon oxide is used, and conductivity is imparted by forming a graphite coating on the surface layer thereof (for example, see Patent Document 10). In Patent Document 10, with respect to the shift value obtained from the Raman spectra for graphite coating, with broad peaks appearing at 1330 cm ^-1 and 1580 cm ^-1, their intensity ratio _I 1330 _{/ I 1580} is _{1.5 <I 1330} / _{I 1580} <3. Further, particles having a silicon microcrystalline phase dispersed in silicon dioxide are used for high battery capacity and improvement of cycle characteristics (for example, see Patent Document 11). In order to improve overcharge and overdischarge characteristics, a silicon oxide in which the atomic ratio of silicon and oxygen is controlled to 1: y (0 <y <2) is used (for example, see Patent Document 12). Further, in order to improve the battery capacity and the cycle characteristics, a mixed electrode of silicon and carbon is prepared and the silicon ratio is designed to be 5 wt% or more and 13 wt% or less (for example, see Patent Document 13).

JP 2001-185127 A JP 2002-042806 A JP 2006-164954 A JP 2006-114454 A JP 2009-070825 A JP 2008-282819 A JP 2008-251369 A JP 2008-177346 A JP 2007-234255 A JP 2009-212074 A JP 2009-205950 A Japanese Patent No. 2997741 Japanese Patent Application Laid-Open No. 2010-092830

As described above, in recent years, small electronic devices represented by mobile terminals and the like have been required to have higher performance and more functions, and a lithium-ion secondary battery as a main power source has been required to have an increased battery capacity. ing. As one method of solving this problem, development of a lithium ion secondary battery including a negative electrode using a silicon material as a main material is desired.

Although high-capacity electrodes have been obtained by using silicon oxide as a negative electrode active material for lithium ion secondary batteries, the irreversible capacity at the time of initial charge / discharge is still large, and there is room for improvement. Not enough as a substance. In Patent Document 5, Si phase in order to improve the initial charge-discharge efficiency, is used nanocomposites containing SiO 2, _M y _O metal oxide, good negative electrode active material can be sufficiently improved battery characteristics (Negative electrode material) was not obtained.

The present invention has been made in view of the above-described problems, and has as its object to provide a method for producing a negative electrode active material for a nonaqueous electrolyte secondary battery having good initial efficiency.

In order to solve the above problems, the present invention provides a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery including negative electrode active material particles containing silicon compound particles containing lithium, comprising a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6), a step of mixing the silicon compound particles with a lithium compound to form a mixed raw material, and mixing the mixed raw material with 1000 ppm of oxygen. Baking in the presence of an inert gas containing the following, for a non-aqueous electrolyte secondary battery, characterized by producing a negative electrode active material for a non-aqueous electrolyte secondary battery containing silicon compound particles containing lithium Provided is a method for producing a negative electrode active material.

In such a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, a certain amount of oxygen is present in the furnace atmosphere, so that the produced negative electrode active material has a surface state in which lithium ions are easily charged and discharged. It becomes. As a result, the effect of increasing the charge / discharge efficiency is easily exerted, so that a negative electrode active material for a nonaqueous electrolyte secondary battery having good initial efficiency can be manufactured.

At this time, it is preferable to include a step of forming a carbon coating on at least a part of the surface of the silicon compound particles after the step of preparing the silicon compound particles and before the step of using the mixed raw material.

こ と By forming a carbon coating on at least a part of the surface of the silicon compound particles as described above, at least a part of the surface of the silicon compound is coated with the carbon coating, and the conductive compound is excellent in conductivity. Therefore, if the negative electrode active material manufactured by the method for manufacturing a negative electrode active material of the present invention is used, it has a high battery capacity and a good cycle retention ratio utilizing the intrinsic characteristics of a silicon compound modified using Li. The non-aqueous electrolyte secondary battery can be manufactured to be superior in industrial production.

It is preferable that the lithium compound contains at least one of lithium hydride and lithium nitride.

By using at least one of lithium hydride and lithium nitride as a lithium source, oxidation of a silicon compound by oxygen can be suppressed, and a negative electrode active material for a nonaqueous electrolyte secondary battery having a good initial efficiency can be obtained. It can be manufactured.

In the firing step, it is preferable that the temperature of the mixed raw material is maintained at 300 ° C. or more and 700 ° C. or less for 30 minutes or more.

(4) After the temperature of the mixed raw material is maintained at 300 ° C. or more and 700 ° C. or less for 30 minutes or more and then increased to the maximum temperature, the exothermic behavior becomes mild, and safe firing can be performed.

Further, after the baking step, a complex in which all or at least a part of the surface of the silicon compound particles or the surface of the carbon coating, or both of them comprises an amorphous metal oxide and a metal hydroxide. It is preferable to include a step of forming a composite layer containing

(4) If the manufactured negative electrode active material has a composite layer, the cycle characteristics are high. If the complex is amorphous, transfer of Li is easily performed. As described above, when the composite layer including the composite including the amorphous metal oxide and the metal hydroxide having excellent conductivity is provided, the cycle characteristics are improved. Therefore, a non-aqueous electrolyte secondary battery having a high battery capacity and a good cycle maintenance ratio utilizing the inherent characteristics of the silicon compound can be manufactured to be superior in industrial production. In addition, metal oxides and metal hydroxides show equivalent performance.

At this time, it is preferable that the amorphous metal oxide and the metal hydroxide include at least one element of aluminum, magnesium, titanium, and zirconium.

ス ラ リ ー Since the metal oxide and the metal hydroxide contain the above-mentioned metal element, the slurry at the time of manufacturing the electrode is more stable.

Further, in the firing step, it is preferable that NO ₃ ions be contained in the surface of the negative electrode active material particles in an amount of 1 mass ppm or more and 50 mass ppm or less by using a gas containing nitrogen gas as the inert gas.

If the produced negative electrode active material particles contain NO ₃ ions on the surface thereof and the content of NO ₃ ions is 1 mass ppm or more and 50 mass ppm or less based on the mass of the negative electrode active material particles, The dispersion of the negative electrode active material particles takes a value close to neutrality, and the stability of the slurry at the time of forming the electrode can be improved. In addition, a secondary battery manufactured using such negative electrode active material particles has a high battery capacity and a good initial efficiency, and can be industrially manufactured.

は The method for producing a negative electrode active material of the present invention can improve the charge / discharge efficiency, and can produce a negative electrode active material capable of substantially improving the initial charge / discharge characteristics. Further, a secondary battery containing this negative electrode active material can be produced industrially with superiority, and has good battery capacity, cycle characteristics, and initial charge / discharge characteristics. In addition, the same effect can be obtained in an electronic device, a power tool, an electric vehicle, a power storage system, and the like using the secondary battery.

FIG. 2 is a cross-sectional view illustrating a configuration of a negative electrode including a negative electrode active material manufactured by the method for manufacturing a negative electrode active material of the present invention. 3 is an X-ray diffraction spectrum measured from negative electrode active material particles in Example 1-1. FIG. 2 is an exploded view illustrating a configuration example (laminate film type) of a lithium ion secondary battery including a negative electrode active material manufactured by the method for manufacturing a negative electrode active material of the present invention.

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

As described above, as one method of increasing the battery capacity of a lithium ion secondary battery, the use of a negative electrode using a silicon-based active material as a main material as a negative electrode of a lithium ion secondary battery is being studied. A lithium ion secondary battery using a silicon-based active material as a main material is expected to have cycle characteristics and initial efficiency close to those of a lithium ion secondary battery using a carbon material. Since silicate was generated, it was difficult to obtain an initial efficiency close to that of a lithium ion secondary battery using a carbon material.

Therefore, the present inventors have conducted intensive studies in order to obtain a negative electrode active material capable of easily producing a nonaqueous electrolyte secondary battery having a high initial capacity and a high initial battery efficiency, and developed the present invention. Reached.

The present invention relates to a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, in which a silicon compound and a lithium compound are mixed at the time of synthesis of the negative electrode active material to improve charge and discharge efficiency. The present invention provides a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, wherein the method is calcined under an inert gas containing, thereby reforming by insertion and partial desorption of Li. Conventionally, there has been a concern that oxygen in an inert atmosphere may have an adverse effect upon firing, but it has been found that the effect of improving the initial efficiency can be obtained when oxygen is contained in a certain range.

製造 A method for producing the negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention will be described.

First, silicon compound particles containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6) are prepared. Next, a lithium compound is mixed with the silicon compound particles to obtain a mixed raw material. Next, by firing this mixed raw material in the presence of an inert gas containing 1000 ppm or less of oxygen (more than 0 ppm and 1000 ppm or less), Li is inserted into and desorbed from the silicon compound particles. Is modified. At this time, a Li compound can be simultaneously generated inside or on the surface of the silicon compound particles. Then, the negative electrode material and the negative electrode can be manufactured by mixing the negative electrode active material particles (silicon-based active material particles) thus manufactured with a conductive additive and a binder.

It is preferable to include a step of forming a carbon coating on at least a part of the surface of the silicon compound particles after the step of preparing the silicon compound particles and before the step of using the mixed raw material. By forming a carbon coating on at least a part of the surface of the silicon compound particles as described above, at least a part of the surface of the silicon compound is coated with the carbon coating, and the conductivity is excellent. Therefore, if the negative electrode active material manufactured by the method for manufacturing a negative electrode active material of the present invention is used, it has a high battery capacity and a good cycle retention ratio utilizing the intrinsic characteristics of a silicon compound modified using Li. The non-aqueous electrolyte secondary battery can be manufactured to be superior in industrial production.

The presence of a certain range of oxygen in the inert gas atmosphere during firing is useful for improving the initial efficiency as described above, but the silicon compound particles (or the silicon compound particles having a carbon coating formed on the surface) in the mixed raw material are used. If the lithium compound for lithium doping which comes into direct contact with oxygen contains oxygen, the silicon compound particles may be excessively oxidized by oxygen. Therefore, lithium hydride and lithium nitride containing no oxygen are used as lithium compounds. Preferably, at least one of them is used.

(4) In the firing step, the temperature of the mixed raw material is preferably maintained at 300 ° C. or more and 700 ° C. or less for 30 minutes or more. By keeping the temperature of the mixed raw material at 300 ° C. or more and 700 ° C. or less for 30 minutes or more and then increasing the maximum temperature, the exothermic behavior becomes mild, and safe firing becomes possible.

The reaction of lithium hydride and lithium nitride with SiO _x is an exothermic reaction. In order to prevent the risk of damaging the firing furnace by exceeding the heat-resistant temperature of the furnace due to the temperature rise due to the exothermic reaction, it is preferable to make the reaction more mild. By maintaining the temperature at 300 ° C. or more and 700 ° C. or less for 30 minutes or more and then raising it to the maximum temperature, the exothermic behavior becomes mild and safe firing becomes possible. Further, for safer synthesis, it is preferable to maintain the temperature in the range of 400 to 600 ° C. Further, the final temperature is preferably 500 ° C. or more and 750 ° C. or less, and the optimum temperature is about 720 ° C.

In addition, after the firing step, the surface of the silicon compound particles or the surface of the carbon coating, or both or all or at least a part thereof, includes a composite including a composite including an amorphous metal oxide and a metal hydroxide. Preferably, the method includes a step of forming a layer. As a method for forming the composite layer, any of surface coating by a liquid phase, mechanochemical coating by a dry method, wet coating by spraying, and sol-gel reaction treatment of aluminum isopropoxide can be used.

Particularly, in the case of a composite comprising a metal oxide and a metal hydroxide, wet coating by spraying and mechanochemical coating by dry method are more convenient and cost-competitive.

It is preferable that the amorphous metal oxide and the metal hydroxide include at least one element of aluminum, magnesium, titanium, and zirconium.

In the firing step, the inert gas is a gas containing nitrogen gas, so that the surface of the negative electrode active material particles contains 1 to 50 ppm by mass of NO ₃ ions.

More specifically, the negative electrode active material is produced, for example, by the following procedure.

{Circle around (1)} First, a silicon oxide gas-generating material is heated in the presence of an inert gas or under a reduced pressure in a temperature range of 900 ° C. to 1600 ° C. to generate a silicon oxide gas. In this case, the raw material is a mixture of the metal silicon powder and the silicon dioxide powder, and considering the surface oxygen of the metal silicon powder and the presence of trace oxygen in the reaction furnace, the mixing molar ratio is 0.8 <metal silicon powder / It is desirable that the range of silicon dioxide powder is less than 1.3. The Si crystallites in the particles are controlled by changing the charging range and vaporization temperature, and by heat treatment after generation. The generated gas is deposited on the adsorption plate. The deposit is taken out while the temperature in the reactor is lowered to 100 ° C. or lower, and pulverized and powdered using a ball mill, a jet mill or the like.

Next, a carbon film is formed on the surface layer of the obtained powder material (silicon compound). The carbon coating is effective for further improving the battery characteristics of the negative electrode active material.

As a technique for forming a carbon film on the surface layer of the powder material, thermal decomposition CVD is desirable. In the thermal decomposition CVD, a silicon oxide powder is set in a furnace, a hydrocarbon gas is filled in the furnace, and the furnace temperature is raised. The decomposition temperature is not particularly limited, but is preferably 1200 ° C. or lower. More desirably, the temperature is 950 ° C. or lower, and it is possible to suppress unintended disproportionation of the silicon compound. The hydrocarbon gas is not particularly limited, but preferably 3 ≧ n in the C _n H _m composition. This is because the low production cost and the physical properties of the decomposition product are good.

The reforming is performed using a thermal doping method. In this case, for example, the powder material can be modified by mixing it with lithium hydride (LiH) powder and heating in an oxidizing atmosphere containing oxygen in a certain range. As the oxidizing atmosphere, for example, a gas containing oxygen in an argon atmosphere, or a gas containing oxygen in a nitrogen atmosphere can be used. It is also possible to mix oxygen for a certain period of time while using argon and nitrogen gas. More specifically, first, the LiH powder and the silicon oxide powder are sufficiently mixed in a nitrogen atmosphere, sealed, and uniformized by stirring the sealed container together. Thereafter, reforming is performed by heating in an oxidizing atmosphere containing oxygen in a certain range in a range of 500 ° C. to 750 ° C. More preferably, oxygen is contained in a nitrogen atmosphere in terms of cost. It is considered that the incorporation of oxygen in a certain range facilitates the inflow and outflow of Li. The effect is exhibited when the oxygen is in a certain range at a temperature of 300 ° C. or more for 10 minutes or more.

In order to desorb Li from the silicon compound, a method in which the powder after heating is sufficiently cooled and then washed with alcohol, alkaline water, weak acid or pure water can be used.

(4) When the silicon compound is modified using the heat doping method, the negative electrode active material can be modified at low cost, and the battery characteristics are improved. This also improves the stability of the negative electrode active material with respect to the slurry, such as water resistance.

Subsequently, a composite layer containing a composite composed of an amorphous metal oxide and a metal hydroxide is formed on the surface of the modified silicon compound particles. Further, as described above, the silicon-based active material particles preferably have a composite layer including a composite including an amorphous metal oxide and a metal hydroxide on the surface of the silicon compound particles and the surface of the carbon coating. preferable. Examples of the method for synthesizing the composite layer include surface coating with a liquid phase, mechanochemical coating with a dry method, wet coating with a spray, and sol-gel reaction treatment of aluminum isopropoxide.

The manufactured negative electrode active material particles are mixed with a carbon-based active material as necessary, and then mixed with the negative electrode active material and other materials such as a binder and a conductive additive to form a negative electrode mixture, and then an organic solvent. Alternatively, water or the like is added to form a slurry.

Next, as shown in FIG. 1, the slurry of the negative electrode mixture is applied to the surface of the negative electrode current collector 11 and dried to form the negative electrode active material layer 12. At this time, a heating press or the like may be performed as necessary. As described above, a negative electrode can be manufactured.

負極 As described above, a negative electrode active material can be produced by the method for producing a negative electrode active material of the present invention. The negative electrode active material thus manufactured can have a configuration as described below.

The negative electrode active material produced by the method for producing a negative electrode active material of the present invention includes negative electrode active material particles, and the negative electrode active material particles include silicon compound particles having a silicon compound (SiOx: 0.5 ≦ x ≦ 1.6). Including. The silicon compound particles contained in the negative electrode active material contain at least one of Li ₂ SiO ₃ and Li ₂ Si ₂ O ₅ . Further, the negative electrode active material preferably contains NO ₃ ions on the surface of the negative electrode active material particles, and the content of the NO ₃ ions is preferably 1 mass ppm or more and 50 mass ppm or less based on the mass of the negative electrode active material particles. . This ratio is the mass ratio of NO ₃ ions to the mass of the entire negative electrode active material particles.

Li silicates such as Li ₂ SiO ₃ and Li ₂ Si ₂ O ₅ are relatively more stable than other Li compounds. Therefore, a negative electrode active material containing these Li compounds obtains more stable battery characteristics. be able to. These Li compounds can be obtained by selectively changing a part of the SiO ₂ component generated inside the silicon compound to the Li compound and modifying the silicon compound. If the negative electrode active material particles contain NO ₃ ions on the surface thereof and the content of NO ₃ ions is 1 mass ppm or more and 50 mass ppm or less with respect to the mass of the negative electrode active material particles, the negative electrode active material The dispersion of the substance particles takes a value close to neutrality, and the stability of the slurry at the time of forming the electrode can be improved.

The NO ₃ ion content on the surface of the negative electrode active material particles was determined by weighing 1 g of lithium-doped silicon compound particles, adding them to 50 g of ultrapure water, and stirring for 5 minutes to disperse them. The filtered product was measured by ion chromatography.

It is desirable that a carbon coating is formed on at least a part of the surface of the silicon compound particles. Here, in the negative electrode active material manufactured by the method for manufacturing a negative electrode active material of the present invention, a carbon coating is formed on at least a part of the surface of the silicon compound particles, and the carbon coating is formed on the entire surface of the silicon compound particles. It may be.

Ｌｉ The Li compound inside the negative electrode active material particles can be analyzed by XRD (X-ray diffraction). The measurement of XRD can be performed using, for example, AXS D2 PHASER manufactured by Bruker.

In the negative electrode active material manufactured by the method for manufacturing a negative electrode active material of the present invention, the negative electrode active material particles have a diffraction peak (2θ) obtained from an X-ray diffraction spectrum using Cu—Kα ray of 27.5 to 29. The intensity A of the peak derived from the Si region given at 2.0 °, the intensity B of the peak derived from Li ₂ SiO ₃ given at 26.5 to 27.5 °, and the intensity A at 24.5 to 25.5 ° It is preferable that the given intensity C of the peak derived from Li ₂ Si ₂ O ₅ satisfies the relationship of A> B and A> C. It is more preferable to satisfy the relationship of B> C. Although the reason is not clear, battery characteristics can be improved when A, B, and C satisfy these relationships.

In the negative electrode active material produced by the method for producing a negative electrode active material of the present invention, the negative electrode active material particles have a diffraction peak (2θ) of about 22 ° obtained from an X-ray diffraction spectrum using Cu-Kα radiation. It is preferable to have a broad peak derived from the SiO ₂ region given by As described above, when the anode active material particles contain an appropriate amount of the SiO ₂ component and the amount of Li ₂ SiO ₃ is larger than that of Li ₂ Si ₂ O ₅ , the effect of improving the battery characteristics is sufficiently obtained. Negative electrode active material.

If the amount of Li ₂ SiO ₃ is relatively large in the negative electrode active material particles based on the SiO ₂ component, the effect of improving the battery characteristics by inserting Li can be sufficiently obtained.

The lower the crystallinity of the silicon compound, the better. Specifically, the half width (2θ) of the diffraction peak attributable to the Si (111) crystal plane obtained by X-ray diffraction using Cu—Kα radiation of the negative electrode active material particles is preferably 1.2 ° or more. desirable. As described above, since the crystallinity is low and the amount of Si crystals is small, not only the battery characteristics are improved, but also a stable negative electrode active material is obtained.

メ デ ィ ア Although the median diameter of the silicon compound particles is not particularly limited, it is preferably from 0.5 μm to 15 μm. This is because in this range, lithium ions are easily inserted and discharged during charging and discharging, and the silicon-based active material particles are hardly broken. When the median diameter is 0.5 μm or more, the surface area is not too large, so that a side reaction hardly occurs during charge and discharge, and the irreversible capacity of the battery can be reduced. On the other hand, when the median diameter is 15 μm or less, the silicon-based active material particles are less likely to crack and a new surface is less likely to appear, which is preferable.

In the negative electrode active material manufactured by the method for manufacturing a negative electrode active material of the present invention, the surface of the silicon compound particles or the surface of the carbon coating, or at least a part of both of them, is an amorphous metal oxide and metal. It is preferable to include a composite layer containing a composite made of a hydroxide. As the composite layer, for example, a composite layer including a composite including amorphous aluminum oxide and aluminum hydroxide can be formed. In this case, the composite layer has an aluminum oxide region and an aluminum hydroxide region. Further, a part of the metal oxide of the composite layer may be in a crystalline phase. Further, the composite is not limited to aluminum and may include other metal elements.

When the negative electrode active material particles have a composite layer containing a composite composed of an amorphous metal oxide and a metal hydroxide on the outermost surface, the water resistance to the aqueous slurry is high. Become. However, since the negative electrode active material particles have the above-described composite layer, gas generation due to the aging of the slurry becomes difficult to occur, a stable coating film can be obtained, and the binding property is sufficiently secured. be able to. If the complex is amorphous, transfer of Li is easily performed.

Further, it is preferable that the amorphous metal oxide and the metal hydroxide contain at least one element of aluminum, magnesium, titanium, and zirconium.

最 Also, the outermost layer of the composite layer may contain chlorides, sulfates and phosphates of aluminum, magnesium, titanium and zirconium.

Further, the thickness of the composite layer is preferably 10 nm or less, and more preferably 5 nm or less. When the thickness of the composite layer is 10 nm or less, the battery characteristics are improved because the electric resistance does not become too large depending on the composition of the mixture. Further, when the film thickness is about 2 to 3 nm, the stability to the slurry can be further improved while suppressing an increase in electric resistance. The thickness of the composite layer can be confirmed by a TEM (transmission electron microscope).

Further, at this time, a test cell comprising a negative electrode and a counter electrode lithium containing a mixture of the negative electrode active material and the carbon-based active material produced by the method for producing a negative electrode active material of the present invention was prepared, and in the test cell, Charge / discharge consisting of charging in which a current is inserted to insert lithium into the negative electrode active material and discharging in which a current is applied so as to desorb lithium from the negative electrode active material is performed. When a graph showing the relationship between the differential value dQ / dV differentiated by the potential V of the negative electrode and the potential V is drawn, the potential V of the negative electrode has a peak in the range of 0.40 V to 0.55 V. It is preferable that The above-mentioned peak in the V-dQ / dV curve is similar to the peak of the silicon material, and the discharge curve on the higher potential side rises sharply.

As described above, the negative electrode active material manufactured by the method for manufacturing a negative electrode active material of the present invention includes silicon compound particles made of SiO _x (0.5 ≦ x ≦ 1.6). As the composition of the silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6), it is preferable that x is close to 1. This is because high cycle characteristics can be obtained. Note that the composition of the silicon oxide material in the present invention does not necessarily mean that the purity is 100%, and may include a trace amount of an impurity element or Li.

Next, the configuration of the negative electrode including the negative electrode active material manufactured by the method for manufacturing a negative electrode active material of the present invention will be described.

[Configuration of negative electrode]
FIG. 1 is a cross-sectional view of a negative electrode including a negative electrode active material manufactured by the method for manufacturing a negative electrode active material of the present invention. As shown in FIG. 1, the negative electrode 10 has a configuration in which a negative electrode active material layer 12 is provided on a negative electrode current collector 11. The negative electrode active material layer 12 may be provided on both sides of the negative electrode current collector 11 or only on one side. Further, in the negative electrode of the nonaqueous electrolyte secondary battery, the negative electrode current collector 11 may not be provided.

[Negative electrode current collector]
The negative electrode current collector 11 is an excellent conductive material and is made of a material having excellent mechanical strength. Examples of the conductive material that can be used for the negative electrode current collector 11 include copper (Cu) and nickel (Ni). This conductive material is preferably a material that does not form an intermetallic compound with lithium (Li).

The negative electrode current collector 11 preferably contains carbon (C) and sulfur (S) in addition to the main element. This is because the physical strength of the negative electrode current collector is improved. In particular, when an active material layer which expands at the time of charging is included, if the current collector contains the above element, there is an effect of suppressing deformation of an electrode including the current collector. The content of the above-mentioned contained elements is not particularly limited, but among them, each is preferably 100 ppm or less. This is because a higher deformation suppressing effect can be obtained.

表面 The surface of the negative electrode current collector 11 may or may not be roughened. The roughened negative electrode current collector is, for example, a metal foil that has been subjected to electrolytic treatment, emboss treatment, or chemical etching. The non-roughened negative electrode current collector is, for example, a rolled metal foil.

[Negative electrode active material layer]
The negative electrode active material layer 12 may include a plurality of types of negative electrode active materials such as a carbon-based active material in addition to the silicon compound particles. Further, other materials such as a thickener (also referred to as a “binder” or a “binder”) or a conductive aid may be included in the battery design. Further, the shape of the negative electrode active material may be a particle shape.

<Lithium ion secondary battery>
Next, a non-aqueous electrolyte secondary battery including the negative electrode active material manufactured by the method for manufacturing a negative electrode active material of the present invention will be described. Here, a laminated film type lithium ion secondary battery will be described as a specific example.

[Structure of laminated film type secondary battery]
The laminated film type lithium ion secondary battery 30 shown in FIG. 3 has a wound electrode body 31 housed inside a sheet-shaped exterior member 35. The wound electrode body 31 has a separator between a positive electrode and a negative electrode, and is wound. Further, there is a case where a laminate is housed with a separator between the positive electrode and the negative electrode. In both electrode bodies, a positive electrode lead 32 is attached to the positive electrode, and a negative electrode lead 33 is attached to the negative electrode. The outermost periphery of the electrode body is protected by a protective tape.

The positive and negative electrode leads 32 and 33 are, for example, led in one direction from the inside of the exterior member 35 to the outside. The positive electrode lead 32 is formed of a conductive material such as aluminum, and the negative electrode lead 33 is formed of a conductive material such as nickel and copper.

The package member 35 is, for example, a laminated film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order. The laminate film is formed by two sheets so that the fusion layer faces the wound electrode body 31. The outer peripheral edges of the fusion layer of the film are fused or adhered with an adhesive or the like. The fusion portion is, for example, a film such as polyethylene or polypropylene, and the metal portion is aluminum foil. The protective layer is, for example, nylon.

密 着 An adhesive film 34 is inserted between the exterior member 35 and the positive and negative electrode leads to prevent outside air from entering. This material is, for example, polyethylene, polypropylene, or polyolefin resin.

The positive electrode has a positive electrode active material layer on both surfaces or one surface of the positive electrode current collector, for example, similarly to the negative electrode 10 in FIG.

The positive electrode current collector is formed of, for example, a conductive material such as aluminum.

The positive electrode active material layer contains one or more of positive electrode materials capable of inserting and extracting lithium ions, and other materials such as a positive electrode binder, a positive electrode conductive auxiliary agent, and a dispersant depending on the design. May be included. In this case, the details of the positive electrode binder and the positive electrode conduction aid are the same as, for example, the already described negative electrode binder and the negative electrode conduction aid.

As the positive electrode material, a lithium-containing compound is desirable. Examples of the lithium-containing compound include a composite oxide composed of lithium and a transition metal element, and a phosphate compound having lithium and a transition metal element. Among these cathode materials, compounds having at least one of nickel, iron, manganese and cobalt are preferred. These chemical formulas are represented, for example, by Li _x M ₁ O ₂ or Li _y M ₂ PO ₄ . In the formula, M ₁ and M ₂ represent at least one or more transition metal elements. The values of x and y vary depending on the state of charge and discharge of the battery, but are generally represented by 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

Examples of the composite oxide containing lithium and a transition metal element include a lithium cobalt composite oxide (Li _x CoO ₂ ), a lithium nickel composite oxide (Li _x NiO ₂ ), and a lithium nickel cobalt composite oxide. . Examples of the lithium nickel cobalt composite oxide include lithium nickel cobalt aluminum composite oxide (NCA) and lithium nickel cobalt manganese composite oxide (NCM).

Examples of the phosphate compound having lithium and a transition metal element include a lithium iron phosphate compound (LiFePO ₄ ) and a lithium iron manganese phosphate compound (LiFe _1- uMn _u PO ₄ (0 <u <1)). Is mentioned. By using these positive electrode materials, a high battery capacity can be obtained and excellent cycle characteristics can be obtained.

[Negative electrode]
The negative electrode has the same configuration as the above-described negative electrode 10 for a lithium ion secondary battery in FIG. 1, and has, for example, a negative electrode active material layer on both surfaces of a current collector. It is preferable that the negative electrode has a larger negative charge capacity than the electric capacity (charge capacity as a battery) obtained from the positive electrode active material agent. Thereby, precipitation of lithium metal on the negative electrode can be suppressed.

(4) The positive electrode active material layer is provided on a part of both surfaces of the positive electrode current collector. Similarly, the negative electrode active material layer is provided on a part of both surfaces of the negative electrode current collector. In this case, for example, the negative electrode active material layer provided on the negative electrode current collector is provided with a region where the opposed positive electrode active material layer does not exist. This is for performing stable battery design.

領域 In the region where the negative electrode active material layer and the positive electrode active material layer do not face each other, there is almost no influence of charging and discharging. Therefore, the state of the negative electrode active material layer is maintained as it is immediately after formation, whereby the composition of the negative electrode active material can be accurately and reproducibly examined without depending on the presence or absence of charge and discharge.

[Separator]
The separator separates the positive electrode and the negative electrode, and allows lithium ions to pass therethrough while preventing a current short circuit caused by contact between the two electrodes. This separator is formed of a porous film made of, for example, a synthetic resin or ceramic, and may have a laminated structure in which two or more types of porous films are laminated. Examples of the synthetic resin include polytetrafluoroethylene, polypropylene, and polyethylene.

[Electrolyte]
At least a part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolyte solution). This electrolyte solution has an electrolyte salt dissolved in a solvent, and may contain other materials such as additives.

As the solvent, for example, a non-aqueous solvent can be used. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, 1,2-dimethoxyethane, and tetrahydrofuran. Among these, it is desirable to use at least one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. This is because better characteristics can be obtained. In this case, more excellent characteristics can be obtained by combining a high-viscosity solvent such as ethylene carbonate and propylene carbonate with a low-viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate. This is because the dissociation property and ion mobility of the electrolyte salt are improved.

(4) It is preferable that an unsaturated carbon-bonded cyclic carbonate is contained as a solvent additive. This is because a stable film is formed on the surface of the negative electrode during charge and discharge, and the decomposition reaction of the electrolytic solution can be suppressed. Examples of the unsaturated carbon-bonded cyclic carbonate include vinylene carbonate and vinyl ethylene carbonate.

It is preferable that sultone (cyclic sulfonic acid ester) is contained as a solvent additive. This is because the chemical stability of the battery is improved. Examples of the sultone include propane sultone and propene sultone.

Furthermore, the solvent preferably contains an acid anhydride. This is because the chemical stability of the electrolytic solution is improved. Examples of the acid anhydride include propane disulfonic anhydride.

The electrolyte salt may include, for example, one or more light metal salts such as a lithium salt. Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ).

含有 The content of the electrolyte salt is preferably 0.5 mol / kg or more and 2.5 mol / kg or less with respect to the solvent. This is because high ionic conductivity is obtained.

[Production method of laminated film type secondary battery]
First, a positive electrode is manufactured using the above-described positive electrode material. First, a positive electrode active material and, if necessary, a positive electrode binder and a positive electrode conduction aid are mixed to form a positive electrode mixture, and then dispersed in an organic solvent to obtain a positive electrode mixture slurry. Subsequently, the mixture slurry is applied to the positive electrode current collector by a coating device such as a knife roll or a die coater having a die head, and dried with hot air to obtain a positive electrode active material layer. Finally, the positive electrode active material layer is compression-molded by a roll press or the like. At this time, heating may be performed, and compression may be repeated a plurality of times.

Next, a negative electrode is formed by forming a negative electrode active material layer on a negative electrode current collector by using the same operation procedure as that for manufacturing the negative electrode 10 for a lithium ion secondary battery described above.

(4) When producing a positive electrode and a negative electrode, respective active material layers are formed on both surfaces of the positive electrode and the negative electrode current collector. At this time, in both electrodes, the active material application length on both sides may be shifted (see FIG. 1).

Continue to prepare the electrolyte. Subsequently, the cathode lead 32 is attached to the cathode current collector by ultrasonic welding or the like, and the anode lead 33 is attached to the anode current collector. Subsequently, the positive electrode and the negative electrode are laminated or wound with a separator interposed therebetween to produce a wound electrode body 31, and a protective tape is adhered to the outermost peripheral portion thereof. Next, the wound body is formed into a flat shape. Subsequently, after sandwiching the wound electrode body between the folded film-shaped exterior members 35, the insulating portions of the exterior members are bonded to each other by a heat fusion method, and the wound electrode body is opened in only one direction. Is enclosed. Subsequently, an adhesive film is inserted between the positive electrode lead and the negative electrode lead and the exterior member. Subsequently, a predetermined amount of the above-prepared electrolytic solution is charged from the open portion, and vacuum impregnation is performed. After the impregnation, the opening is bonded by a vacuum heat fusion method. As described above, the laminate film type secondary battery 30 can be manufactured.

に お い て In the non-aqueous electrolyte secondary battery such as the laminated film type secondary battery 30 manufactured as described above, it is preferable that the utilization rate of the negative electrode during charge and discharge is 93% or more and 99% or less. When the negative electrode utilization rate is in the range of 93% or more, the initial charging efficiency does not decrease, and the improvement in battery capacity can be increased. In addition, when the negative electrode utilization rate is in the range of 99% or less, safety can be secured without precipitation of Li.

Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(Example 1-1)
First, negative electrode active material particles were prepared as follows.

A raw material (vaporization starting material) in which metal silicon and silicon dioxide are mixed is set in a reaction furnace, and a material vaporized in an atmosphere of a vacuum of 10 Pa is deposited on an adsorption plate, and after sufficiently cooled, the deposit is removed. It was then crushed by a ball mill. After adjusting the particle size, the carbon film was coated by performing thermal CVD. Subsequently, lithium hydride having a mass equivalent to 4% by mass with respect to the silicon compound coated with the carbon film was stirred and mixed with a shaker under a nitrogen atmosphere. Thereafter, in a controlled atmosphere furnace, reforming was performed by firing at 740 ° C. while flowing a mixed gas obtained by adding 1000 ppm of oxygen to argon to the stirred powder in the furnace to obtain negative electrode active material particles. At the time of firing, nitrogen gas was blown into the silicon compound particles coated with the carbon coating during the firing at a flow rate of 5 L / min to generate NO ₃ ions on the surfaces of the negative electrode active material particles. In addition, NO ₃ ions on the surface of the negative electrode active material particles were obtained by holding the raw material in an inert gas and performing initial gas replacement in the furnace with nitrogen gas, and then adding a mixed gas obtained by adding 1000 ppm of oxygen to argon. It can also be produced by firing at 740 ° C. while flowing in a furnace. The reforming was not performed and a holding temperature zone was not provided before firing. The NO ₃ ion content on the surface of the negative electrode active material particles was 40 mass ppm.

Next, the prepared negative electrode active material, conductive aid 1 (Denka Black), conductive aid 2 (KS6), styrene butadiene rubber (styrene butadiene copolymer, hereinafter referred to as SBR), carboxymethyl cellulose (hereinafter referred to as CMC) Was mixed at a dry mass ratio of 81: 2.7: 11.3: 3.3: 1.7, and then diluted with pure water to obtain a negative electrode mixture slurry. Note that SBR and CMC are negative electrode binders (negative electrode binders).

In addition, an electrolytic copper foil (thickness: 15 μm) was used as a negative electrode current collector. Finally, the negative electrode mixture slurry was applied to the negative electrode current collector, and dried at 100 ° C. for 3 hours in a vacuum atmosphere. The amount of the negative electrode active material layer deposited on one surface of the negative electrode per unit area after drying (also referred to as area density) was 2.0 mg / cm ² . The negative electrode mixture slurry was applied only on one side of the negative electrode current collector, and the negative electrode active material layer was provided on only one side.

(4) A 2032 type coin battery was assembled as a test cell to examine the initial charge / discharge characteristics.

As the negative electrode, a negative electrode prepared by the same procedure as the electrode including the negative electrode active material of the above-mentioned laminated film type secondary battery was used. As the electrolytic solution, a solution obtained by dissolving 1 mol of LiPF _{6 in} 1 liter of a kneading solution of 2: 7: 1 of ethylene carbonate, didiethyl carbonate and fluoroethylene carbonate was used. As the counter electrode, a metal lithium foil having a thickness of 0.5 mm was used. In addition, polyethylene having a thickness of 20 μm was used as a separator. Subsequently, the bottom pig of the 2032 type coin battery, the lithium foil, and the separator are stacked, and 150 mL of the electrolyte is injected. Subsequently, the negative electrode and the spacer (1.0 mm in thickness) are stacked, and 150 mL of the electrolyte is injected. Subsequently, a spring and a coin battery were swaged up in this order, and swaged with an automatic coin cell caulking machine, to produce a 2032 type coin battery.

Subsequently, in order to evaluate the cycle characteristics of the non-aqueous electrolyte secondary battery using the negative electrode active material manufactured by the method for manufacturing a negative electrode active material of the present invention, a laminated film type secondary battery as shown in FIG. No. 30 was produced as follows.

First, a positive electrode used for a laminated film type secondary battery was produced. The positive electrode active material is 95 parts by mass of LiCoO ₂ which is a lithium-cobalt composite oxide, 2.5 parts by mass of a positive electrode conduction aid (acetylene black), and 2.5 parts by mass of a positive electrode binder (polyvinylidene fluoride: Pvdf). Were mixed to form a positive electrode mixture. Subsequently, the positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) to obtain a paste slurry. Subsequently, the slurry was applied to both surfaces of the positive electrode current collector by a coating device having a die head, and dried by a hot-air drying device. At this time, a cathode collector having a thickness of 15 μm was used. Finally, compression molding was performed by a roll press.

As the negative electrode, a negative electrode produced by the same procedure as the electrode containing the silicon-based active material of the test cell was used.

(4) As the electrolytic solution, one prepared by the same procedure as the electrolytic solution of the test cell was used.

Next, a laminated film type lithium ion secondary battery was assembled as follows. First, an aluminum lead was ultrasonically welded to one end of the positive electrode current collector, and a nickel lead was welded to the negative electrode current collector. Subsequently, a positive electrode, a separator, a negative electrode, and a separator were laminated in this order and wound in the longitudinal direction to obtain a wound electrode body. The end of the winding was fixed with PET protective tape. The separator used was a laminated film 12 μm in which a film mainly composed of porous polyethylene was sandwiched between films composed mainly of porous polypropylene. Subsequently, after sandwiching the electrode body between the exterior members, the outer peripheral edges except one side were thermally fused to each other, and the electrode body was housed inside. The exterior member used an aluminum laminated film in which a nylon film, an aluminum foil, and a polypropylene film were laminated. Subsequently, an electrolytic solution prepared from the opening was injected, impregnated in a vacuum atmosphere, and then heat-sealed and sealed.

サ イ ク ル The cycle characteristics (retention rate%) of the laminated film type lithium ion secondary battery produced in this manner were examined.

(Example 1-2)
In Example 1-2, the lithium compound at the time of firing was changed to lithium nitride (Li ₃ N), the NO ₃ ion content on the surface of the negative electrode active material particles was changed, and nitrogen gas was blown during firing. The procedure was the same as in Example 1-1, except that there was none. The NO ₃ ion content on the surface of the negative electrode active material particles was 47 mass ppm.

(Example 1-3)
Example 1-3 was carried out in the same manner as in Example 1-1, except that the NO ₃ ion content on the surface of the negative electrode active material particles was changed, and the atmosphere during firing was changed. The NO ₃ ion content on the surface of the negative electrode active material particles was 32 ppm by mass. In addition, the atmosphere for firing was a mixed gas obtained by adding 200 ppm of oxygen to argon, and firing was performed while flowing into a furnace.

(Example 1-4)
Example 1-4 was carried out in the same manner as in Example 1-2, except that the NO ₃ ion content on the surface of the negative electrode active material particles was changed, and the atmosphere during firing was changed. The NO ₃ ion content on the surface of the negative electrode active material particles was 42 mass ppm. In addition, the atmosphere for firing was a mixed gas obtained by adding 200 ppm of oxygen to argon, and firing was performed while flowing into a furnace.

(Example 1-5)
Example 1-5 was the same as Example 1 except that the NO ₃ ion content on the surface of the negative electrode active material particles was changed, the atmosphere for firing was changed, and no nitrogen gas was blown during firing. Performed similarly to -1. The NO ₃ ion content on the surface of the negative electrode active material particles was 37 mass ppm. Further, the atmosphere for firing was a mixed gas obtained by adding 100 ppm of oxygen to nitrogen, and firing was performed while flowing into a furnace.

(Example 1-6)
Example 1-6 was carried out in the same manner as in Example 1-2, except that the NO ₃ ion content on the surface of the negative electrode active material particles was changed, and the atmosphere for firing was changed. The NO ₃ ion content on the surface of the negative electrode active material particles was 26 ppm by mass. Further, the atmosphere for firing was a mixed gas obtained by adding 100 ppm of oxygen to nitrogen, and firing was performed while flowing into a furnace.

(Example 1-7)
Example 1-7 was performed in the same manner as in Example 1-5, except that a holding temperature zone was provided before firing, and the NO ₃ ion content on the surface of the negative electrode active material particles was changed. The NO ₃ ion content on the surface of the negative electrode active material particles was 15 mass ppm.

(Example 1-8)
Example 1-8 was carried out in the same manner as in Example 1-7, except that the lithium compound at the time of firing was changed to lithium nitride, and the NO ₃ ion content on the surface of the negative electrode active material particles was changed. The NO ₃ ion content on the surface of the negative electrode active material particles was 5 ppm by mass.

(Example 1-9)
Example 1-9 was performed in the same manner as in Example 1-8, except that the NO ₃ ion content on the surface of the negative electrode active material particles was changed, and a composite layer was formed. The NO ₃ ion content on the surface of the negative electrode active material particles was 8 ppm by mass. In particular, in Example 1-9, the modified silicon compound particles were charged into a mixed solution of dehydrated ethanol and aluminum isopropoxide, stirred, filtered, and dried to remove ethanol. Thus, a composite layer containing a composite of aluminum oxide and aluminum hydroxide was formed. The thickness of the composite layer was 3 nm. Here, the film thickness was calculated from the amount of aluminum remaining in the filtrate after filtration.

(Example 1-10)
Example 1-10 was carried out in the same manner as in Example 1-1, except that the time for modification by firing was longer than that in Example 1-1. In Example 1-10, the crystallization was advanced by setting the reforming temperature in firing higher than in Examples 1-1 to 1-11. That is, the half width (2θ) of the diffraction peak due to the Si (111) crystal plane was made smaller. The NO ₃ ion content on the surface of the negative electrode active material particles was 42 mass ppm.

(Comparative Example 1-1)
Comparative Example 1-1 was the same as Example 1 except that the NO ₃ ion content on the surface of the negative electrode active material particles was changed, the atmosphere for firing was changed, and no nitrogen gas was blown during firing. This was performed in the same manner as in 1-1. The NO ₃ ion content on the surface of the negative electrode active material particles was lower than 1 ppm by mass. The atmosphere during firing was argon.

(Comparative Example 1-2)
Comparative Example 1-2 was performed in the same manner as Comparative Example 1-1, except that the lithium compound was changed to lithium nitride. The NO ₃ ion content on the surface of the negative electrode active material particles was lower than 1 ppm by mass.

(Comparative Example 1-3)
Comparative Example 1-3 was carried out in the same manner as in Comparative Example 1-1, except that the firing atmosphere was changed. The atmosphere for firing was nitrogen. The NO ₃ ion content on the surface of the negative electrode active material particles was lower than 1 mass ppm.

(Comparative Example 1-4)
Comparative Example 1-4 was performed in the same manner as Comparative Example 1-3, except that the lithium compound was changed to lithium nitride. The NO ₃ ion content on the surface of the negative electrode active material particles was lower than 1 mass ppm.

(Comparative Example 1-5)
Comparative Example 1-5 was performed in the same manner as Comparative Example 1-1, except that a holding temperature zone was provided before firing and the atmosphere at the time of firing was changed. The atmosphere at the time of firing was a mixed gas in which 2000 ppm of oxygen was added to argon, and firing was performed while flowing into a furnace. The NO ₃ ion content on the surface of the negative electrode active material particles was lower than 1 mass ppm.

(Comparative Example 1-6)
Comparative Example 1-6 was carried out in the same manner as in Example 1-1, except that _{x of the} silicon compound (SiO _x ) was changed to 0.4. The NO ₃ ion content on the surface of the negative electrode active material particles was 20 ppm by mass.

(Comparative Example 1-7)
Comparative Example 1-7 was carried out in the same manner as in Example 1-1, except that _{x in the} silicon compound (SiO _x ) was larger than 1.6. The NO ₃ ion content on the surface of the negative electrode active material particles was 45 ppm by mass.

に お い て In the above Examples and Comparative Examples, when a holding temperature zone was provided before firing, the holding temperature was 400 ° C., and the holding time was 30 minutes.

The physical properties of the silicon compounds in the above Examples and Comparative Examples are as follows. In all of the above Examples and Comparative Examples except Comparative Examples 1-6 and 1-7, the value of x of the silicon compound represented by SiO _x is 1.0, and the median diameter D ₅₀ of the silicon compound is It was 5.2 μm. In Examples 1-1 to 1-9, the half width (2θ) of the diffraction peak attributable to the Si (111) crystal plane obtained by X-ray diffraction of the modified silicon compound was 2.257 °. Was. In Example 1-10, the half value width (2θ) of the diffraction peak attributable to the Si (111) crystal plane obtained by X-ray diffraction of the modified silicon compound was 1.108 °. The modified silicon compound contained Li ₂ SiO ₃ and Li ₂ Si ₂ O ₅ .

The intensity A of a peak derived from a Si region, which is given as a diffraction peak (2θ) obtained from an X-ray diffraction spectrum using Cu—Kα rays of the negative electrode active material particles at 27.5 to 29.0 °, and 26 Relationship between peak intensity B derived from Li ₂ SiO ₃ given at 0.5 to 27.5 ° and intensity C of peak derived from Li ₂ Si ₂ O ₅ given at 24.5 to 25.5 ° Was A> B, A> C and C> B in Examples 1-1 and 1-2. In Examples 1-3 to 1-4 and Comparative Example 1-2, A> B, A> C, and B> C. In Comparative Example 1-1, B> A, C> A, and C> B. In Comparative Examples 1-3 and 1-4, B> A, C> A, and B> C. Further, in Examples 1-5 and 1-6 and Comparative examples 1-5 and 1-6, it was confirmed that there were broad peaks derived from the SiO ₂ region given as 22 around 22 °. FIG. 2 shows the X-ray diffraction spectrum obtained in Example 1-1.

A 2032-size coin battery type test cell was prepared from the negative electrode and the counter electrode lithium prepared as described above, and the discharge behavior was evaluated. More specifically, first, constant-current constant-voltage charging was performed to 0 V at the counter electrode Li, and the charging was stopped when the current density reached 0.05 mA / cm ² . Thereafter, constant current discharge was performed up to 1.2V. The current density at this time was 0.2 mA / cm ² . From the data obtained by such charge and discharge, a graph is drawn with the vertical axis representing the rate of change of capacity (dQ / dV) and the horizontal axis representing voltage (V), where V is 0.4 to 0.55 (V). It was confirmed whether a peak was obtained in the range. As a result, peaks were confirmed in all Examples and Comparative Examples except Example 1-6.

初 回 When examining the initial charge / discharge characteristics, the initial efficiency (initial efficiency) was calculated. The initial efficiency was calculated from an equation represented by initial efficiency (%) = (initial discharge capacity / initial charge capacity) × 100.

The cycle characteristics were examined as follows. First, charge and discharge were performed for two cycles in an atmosphere at 25 ° C. for stabilizing the battery, and the discharge capacity at the second cycle was measured. Subsequently, charging and discharging were performed until the total number of cycles reached 100, and the discharge capacity was measured each time. Finally, the discharge capacity at the 100th cycle was divided by the discharge capacity at the second cycle (× 100 for% display), and the capacity retention rate was calculated. As cycling conditions, a constant current density until reaching 4.3V, and charged at 2.5 mA / cm ^2, current density reached 0.25 mA / cm ² at 4.3V constant voltage at the stage of reaching the voltage 4.3V Charged up to. During discharging, the battery was discharged at a constant current density of ^2.5 mA / cm ² until the voltage reached 3.0 V.

Table 1 shows the evaluation results of Examples 1-1 to 1-10 and Comparative Examples 1-1 to 1-7.

As shown in Examples 1-1 to 1-9 of Table 1, in the secondary battery using the negative electrode active material manufactured by the method for manufacturing a negative electrode active material of the present invention, oxygen is kept constant in the furnace atmosphere. By sintering under the condition where the amount exists, the effect of improving the battery characteristics such as the improvement of the initial efficiency and the improvement of the cycle maintenance rate was obtained.

On the other hand, when the atmosphere in the furnace at the time of firing does not contain oxygen (Comparative Examples 1-1 to 1-4) and when oxygen is contained in more than 1000 ppm (Comparative Example 1-5), sufficient results are obtained. No initial efficiency was obtained.

回 折 In Examples 1-1 and 1-2, the diffraction peak (2θ) obtained from the X-ray diffraction spectrum using Cu-Kα rays satisfied the relationship of A> B and A> C. In particular, in Examples 1-3 and 1-4, the relationship of B> C was satisfied, and a better initial efficiency was exhibited.

Further, the half width (2θ) of the diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction using Cu—Kα ray is 1.108 °, which is more than the half width (Example 1-10). High charge / discharge efficiency was obtained with a low crystalline material having (2θ) of 1.2 ° or more (Examples 1-1 to 1-9).

サ イ ク ル The cycle maintenance rate of Example 1-1 was 80.1, while the cycle maintenance rate of Example 1-9 was 83.1. That is, in Example 1-9 having the composite layer composed of the amorphous metal oxide and the metal hydroxide on the outermost surface of the negative electrode active material particles, a better cycle retention was obtained.

When the amount of oxygen in the silicon compound is reduced, that is, when x <0.5 as in Comparative Example 1-6, Si becomes rich, and the cycle retention rate is significantly reduced. When oxygen was rich, that is, when x> 1.6 as in Comparative Example 1-7, the resistance of the silicon oxide was increased, and the cycle retention rate was significantly reduced.

Note that the present invention is not limited to the above embodiment. The above embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and has the same effect. Within the technical scope.

Claims (7)

1. A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery including negative electrode active material particles containing silicon compound particles containing lithium,
   Producing silicon compound particles containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6);
   A step of mixing the lithium compound with the silicon compound particles to form a mixed raw material;
   Baking the mixed raw material in the presence of an inert gas containing 1000 ppm or less of oxygen, and producing a negative electrode active material for a non-aqueous electrolyte secondary battery including the silicon compound particles containing lithium. Of producing a negative electrode active material for a non-aqueous electrolyte secondary battery.
2. The method according to claim 1, further comprising a step of forming a carbon coating on at least a part of the surface of the silicon compound particles after the step of producing the silicon compound particles and before the step of using the mixed raw material. The method for producing a negative electrode active material for a nonaqueous electrolyte secondary battery according to the above.
3. 3. The method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium compound contains at least one of lithium hydride and lithium nitride.
4. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein in the firing step, the temperature of the mixed raw material is maintained at 300 ° C. or more and 700 ° C. or less for 30 minutes or more. 5. Of producing a negative electrode active material for use.
5. After the calcining step, the surface of the silicon compound particles or the surface of the carbon coating, or all or at least a part of both of them, includes a composite composed of an amorphous metal oxide and a metal hydroxide. The method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, further comprising a step of forming a composite layer.
6. The non-aqueous electrolyte secondary battery according to claim 5, wherein the amorphous metal oxide and metal hydroxide contain at least one element of aluminum, magnesium, titanium, and zirconium. A method for producing a negative electrode active material.
7. The step of baking, wherein the inert gas is a gas containing nitrogen gas, so that NO ₃ ions are contained in the surface of the negative electrode active material particles in an amount of 1 mass ppm or more and 50 mass ppm or less. The method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6.

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