JP7003006B2 - Manufacturing method of negative electrode active material for non-aqueous electrolyte secondary battery - Google Patents

Description

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 such as mobile terminals have become widespread, and further miniaturization, weight reduction, and long life are strongly required. In response to such market demands, the development of a secondary battery that is particularly compact, lightweight, and capable of obtaining a high energy density is underway. This secondary battery is being considered for application not only to small electronic devices but also to large electronic devices such as automobiles and power storage systems such as houses.

Among them, lithium-ion secondary batteries are highly expected because they are compact and easy to increase in capacity, and can obtain higher energy density than lead-acid batteries and nickel-cadmium batteries.

The above-mentioned lithium ion secondary battery includes 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.

While carbon materials are widely used as the negative electrode active material, further improvement in battery capacity is required due to recent market demands. In order to improve the battery capacity, it is being studied to use silicon as a negative electrode active material. This is because the theoretical capacity of silicon (4199 mAh / g) is more than 10 times larger than the theoretical capacity of graphite (372 mAh / g), so that a significant improvement in battery capacity can be expected. The development of Kay material as a negative electrode active material is being studied not only for silicon alone, but also for alloys and compounds typified by oxides. In addition, the shape of the active material has been studied from the standard coating type for carbon materials to the integrated type that deposits directly on the 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 charging and discharging, so that it is easily cracked mainly in the vicinity of 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 fragile substance. When the surface layer of the negative electrode active material is cracked, a new surface is created, which increases the reaction area of the active material. At this time, the decomposition reaction of the electrolytic solution occurs on the new surface, and the electrolytic solution is consumed because a film which is a decomposition product of the electrolytic solution is formed on the new surface. Therefore, the cycle characteristics tend to deteriorate.

So far, in order to improve the initial efficiency of the battery and the cycle characteristics, various studies have been made on the negative electrode material for lithium ion secondary batteries and the electrode configuration, which are mainly made of Kay material.

Specifically, silicon and amorphous silicon dioxide are simultaneously deposited using the vapor phase method for the purpose of obtaining good cycle characteristics and high safety (see, for example, 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 (see, for example, Patent Document 2). Further, in order to improve the cycle characteristics and obtain high input / output characteristics, an active material containing silicon and oxygen is prepared, and an active material layer having a high oxygen ratio is formed in the vicinity of the current collector (). For example, see Patent Document 3). Further, in order to improve the cycle characteristics, oxygen is contained in the silicon active material, and the average oxygen content is 40 at% or less, and the oxygen content is increased in a place close to the current collector. (See, for example, Patent Document 4).

Further, in order to improve the initial charge / discharge efficiency, a _{nanocomposite} containing a Si phase, SiO ₂ , and My O metal oxide is used (see, for example, Patent Document 5). Further, in order to improve the 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 (see, for example, Patent Document 6). In addition, 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 and minimum molar ratios near the interface between the active material and the current collector is set. The active material is controlled within the range of 0.4 or less (see, for example, Patent Document 7). Further, in order to improve the battery load characteristics, a metal oxide containing lithium is used (see, for example, 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 Kay material (see, for example, Patent Document 9).

Further, in order to improve the cycle characteristics, silicon oxide is used and a graphite film is formed on the surface layer thereof to impart conductivity (see, for example, Patent Document 10). In Patent Document 10, broad peaks appear at 1330 cm ^-1 and 1580 cm ^-1 with respect to the shift value obtained from the Raman spectrum for the graphite coating, and their intensity ratios I ₁₃₃₀ / I ₁₅₈₀ are 1.5 <I ₁₃₃₀ / I. ₁₅₈₀ <3. Further, in order to improve the battery capacity and cycle characteristics, particles having a silicon microcrystalline phase dispersed in silicon dioxide are used (see, for example, Patent Document 11). Further, in order to improve the overcharge and overdischarge characteristics, a silicon oxide in which the atomic number ratio of silicon and oxygen is controlled to 1: y (0 <y <2) is used (see, for example, Patent Document 12). Further, in order to improve the high battery capacity and 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 (see, for example, Patent Document 13).

Japanese Unexamined Patent Publication No. 2001-185127 Japanese Unexamined Patent Publication No. 2002-042806 Japanese Unexamined Patent Publication No. 2006-164954 Japanese Unexamined Patent Publication No. 2006-114454 Japanese Unexamined Patent Publication No. 2009-070825 Japanese Unexamined Patent Publication No. 2008-282819 Japanese Unexamined Patent Publication No. 2008-251369 Japanese Unexamined Patent Publication No. 2008-177346 JP-A-2007-234255 Japanese Unexamined Patent Publication No. 2009-21204 Japanese Unexamined Patent Publication No. 2009-205950 Japanese Patent No. 2997741 Japanese Unexamined Patent Publication No. 2010-922830

As mentioned above, in recent years, small electronic devices such as mobile terminals have been promoted to have higher performance and higher functionality, and the lithium ion secondary battery, which is the main power source thereof, is required to have an increased battery capacity. ing. As one method for solving this problem, it is desired to develop a lithium ion secondary battery made of a negative electrode using a Kay material as a main material.

Silicon oxide is used as the negative electrode active material for lithium-ion secondary batteries to obtain high-capacity electrodes, but the irreversible capacity at the time of initial charging and discharging is still large, and there is room for improvement. It is still insufficient as a substance. In Patent Document 5, a _{nanocomposite} containing a Si phase, SiO ₂ , and My O metal oxide is used in order to improve the initial charge / discharge efficiency, but a good negative electrode active material capable of sufficiently improving battery characteristics. (Negative electrode material) was not obtained.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery having good initial efficiency.

In order to solve the above problems, the present invention is a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, which comprises negative electrode active material particles containing silicon compound particles containing lithium, wherein the silicon compound (SiO _x ) is used. : 0.5 ≦ x ≦ 1.6) The step of producing silicon compound particles, the step of mixing the silicon compound particles with a lithium compound to make a mixed raw material, and the step of mixing the mixed raw material with 1000 ppm of oxygen. For a non-aqueous electrolyte secondary battery, which comprises a step of firing in the presence of an inert gas containing the following, and comprises producing a negative electrode active material for a non-aqueous electrolyte secondary battery containing the 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 atmosphere inside the furnace, so that the produced negative electrode active material has a surface state in which lithium ions are easily charged and discharged. Will be. As a result, the effect of increasing the charge / discharge efficiency is likely to be exhibited, so that a negative electrode active material for a non-aqueous electrolyte secondary battery having a good initial efficiency can be manufactured.

At this time, it is preferable to include a step of forming a carbon film 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.

By forming a carbon film 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 covered with the carbon film, and the conductivity is excellent. Therefore, if the negative electrode active material produced by the method for producing the negative electrode active material of the present invention is used, it has a high battery capacity and a good cycle maintenance rate utilizing the original characteristics of the silicon compound modified with Li. It will be possible to manufacture non-aqueous electrolyte secondary batteries in an advantageous manner in industrial production.

Further, 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 the lithium source, oxidation of the silicon compound by oxygen can be suppressed, and a negative electrode active material for a non-aqueous electrolyte secondary battery having good initial efficiency can be obtained. It can be manufactured.

Further, in the firing step, it is preferable to keep the temperature of the mixed raw material at 300 ° C. or higher and 700 ° C. or lower for 30 minutes or longer.

By keeping the temperature of the mixed raw material at 300 ° C. or higher and 700 ° C. or lower for 30 minutes or longer and then raising the temperature to the maximum temperature, the heat generation behavior becomes mild and safe firing becomes possible.

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

When the manufactured negative electrode active material has a composite layer, the cycleability is high. Further, if the complex is amorphous, Li can be easily exchanged. As described above, when the composite layer is excellent in conductivity and contains a complex composed of an amorphous metal oxide and a metal hydroxide, the cycle characteristics are good. Therefore, a non-aqueous electrolyte secondary battery having a high battery capacity and a good cycle maintenance rate, which makes the best use of the original characteristics of the silicon compound, can be manufactured advantageously in industrial production. In addition, metal oxides and metal hydroxides show the same performance.

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

Since the metal oxide and the metal hydroxide contain the above-mentioned metal elements, the slurry at the time of electrode production becomes more stable.

Further, in the firing step, it is preferable that the inert gas is a gas containing nitrogen gas so that the surface of the negative electrode active material particles contains 1 mass ppm or more and 50 mass ppm or less of NO ₃ ions.

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 with respect to the mass of the negative electrode active material particles, The dispersion liquid of the negative electrode active material particles takes a value close to neutral, and the stability of the slurry at the time of forming the electrode can be improved. Further, the secondary battery manufactured by using such negative electrode active material particles has a high battery capacity and good initial efficiency, and can be manufactured industrially superiorly.

The method for producing a negative electrode active material of the present invention can produce a negative electrode active material that can improve the charge / discharge efficiency and substantially improve the initial charge / discharge characteristics. Further, the secondary battery containing the negative electrode active material can be industrially produced in an advantageous manner, and the battery capacity, cycle characteristics, and initial charge / discharge characteristics are good. Further, the same effect can be obtained in electronic devices, electric tools, electric vehicles, power storage systems, etc. using the secondary battery.

It is sectional drawing which shows the structure of the negative electrode containing the negative electrode active material produced by the manufacturing method of the negative electrode active material of this invention. It is an X-ray diffraction spectrum measured from the negative electrode active material particle in Example 1-1. It is an exploded view which shows the structural example (laminate film type) of the lithium ion secondary battery which contains the negative electrode active material produced by the manufacturing method of the negative electrode active material of this invention.

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

As described above, as one method for increasing the battery capacity of a lithium ion secondary battery, it has been studied to use a negative electrode using a silicon-based active material as a main material as a negative electrode of a lithium ion secondary battery. A lithium-ion secondary battery using a silicon-based active material as a main material is desired to have cycle characteristics and initial efficiency close to those of a lithium-ion secondary battery using a carbon material, but irreversible lithium during initial charging and discharging. Since silicates were generated, it was difficult to obtain initial efficiency close to that of a lithium-ion secondary battery using a carbon material.

Therefore, the present inventors have made extensive studies in order to obtain a negative electrode active material capable of easily producing a non-aqueous electrolyte secondary battery having a high battery capacity and good initial efficiency, and have made the present invention. I arrived.

The present invention is a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, and in order to improve charge / discharge efficiency, a silicon compound and a lithium compound are mixed at the time of synthesizing the negative electrode active material to have a constant oxygen concentration. Provided is a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, which comprises reforming by inserting and partially removing Li by firing under an inert gas containing. Conventionally, there was a concern that oxygen in an inert atmosphere would have an adverse effect during firing, but it was found that the effect of improving the initial efficiency can be obtained when oxygen is contained in a certain range.

A method for producing a 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 produced. Next, a lithium compound is mixed with the silicon compound particles to obtain a mixed raw material. Next, the mixed raw material is fired in the presence of an inert gas containing 1000 ppm or less of oxygen to insert and desorb Li into the silicon compound particles, thereby modifying the silicon compound particles. At this time, the Li compound can be generated inside or on the surface of the silicon compound particles at the same time. Then, the negative electrode active material particles (silicon-based active material particles) produced in this manner can be mixed with a conductive auxiliary agent or a binder to produce a negative electrode material and a negative electrode.

Further, it is preferable to include a step of forming a carbon film 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. By forming a carbon film on at least a part of the surface of the silicon compound particles in this way, at least a part of the surface of the silicon compound is covered with the carbon film, and the conductivity is excellent. Therefore, if the negative electrode active material produced by the method for producing the negative electrode active material of the present invention is used, it has a high battery capacity and a good cycle maintenance rate utilizing the original characteristics of the silicon compound modified with Li. It will be possible to manufacture non-aqueous electrolyte secondary batteries in an advantageous manner 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 film formed on the surface) of the mixed raw material are used. ), If oxygen is contained in the lithium compound for lithium doping, the silicon compound particles may be excessively oxidized by the oxygen. Therefore, as the lithium compound, lithium hydride and lithium nitride that do not contain oxygen are used. It is preferable to use at least one of them.

Further, in the firing step, it is preferable to keep the temperature of the mixed raw material at 300 ° C. or higher and 700 ° C. or lower for 30 minutes or longer. By keeping the temperature of the mixed raw material at 300 ° C. or higher and 700 ° C. or lower for 30 minutes or longer and then raising the temperature to the maximum temperature, the heat generation behavior becomes mild and safe firing becomes possible.

The reaction between lithium hydride and lithium nitride and SiO _x is an exothermic reaction. It is preferable to make the reaction milder 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. By holding the temperature at 300 ° C. or higher and 700 ° C. or lower for 30 minutes or longer and then raising the temperature to the maximum temperature, the heat generation behavior becomes mild and safe firing becomes possible. Further, in order to synthesize more safely, it is preferable to keep the temperature in the range of 400 to 600 ° C. The final temperature is preferably 500 ° C. or higher and 750 ° C. or lower, and the optimum temperature is about 720 ° C.

Further, after the step of firing, a composite in which the surface of the silicon compound particles, the surface of the carbon film, or both all or at least a part thereof contains a composite composed of an amorphous metal oxide and a metal hydroxide. It is preferable to include a step of forming a layer. As a method for forming the composite layer, any one of a surface coating by a liquid phase, a mechanochemical coating by a dry method, a wet coating by a spray, and a sol-gel reaction treatment of aluminum isopropoxide can be used.

In particular, a composite composed of a metal oxide and a metal hydroxide is desirable because wet coating by spraying and mechanochemical coating by a dry method are simpler methods and cost competitive.

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

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

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

First, the raw material that generates silicon oxide gas is heated in the presence of an inert gas or under reduced pressure in a temperature range of 900 ° C. to 1600 ° C. to generate silicon oxide gas. In this case, the raw material is a mixture of metallic silicon powder and silicon dioxide powder, and considering the presence of surface oxygen of the metallic silicon powder and trace oxygen in the reaction furnace, the mixed molar ratio is 0.8 <metal silicon powder /. It is desirable that the silicon dioxide powder is in the range of <1.3. The Si crystallites in the particles are controlled by changing the charging range and vaporization temperature, and by heat treatment after formation. The generated gas is deposited on the adsorption plate. The deposit is taken out in a state where the temperature in the reaction furnace is lowered to 100 ° C. or less, and pulverized and pulverized by 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 film is effective for further improving the battery characteristics of the negative electrode active material.

Pyrolysis CVD is desirable as a method for forming a carbon film on the surface layer of a powder material. In pyrolysis CVD, silicon oxide powder is set in a furnace, and the furnace is filled with a hydrocarbon gas to raise the temperature in the furnace. The decomposition temperature is not particularly limited, but is particularly preferably 1200 ° C. or lower. More preferably, the temperature is 950 ° C. or lower, and it is possible to suppress unintended disproportionation of silicon compounds. The hydrocarbon gas is not particularly limited, but it is desirable that 3 ≧ _n in the Cn _Hm composition. This is because the manufacturing cost is low and the physical characteristics of the decomposition product are good.

Modification is performed using the heat doping method. In this case, for example, the powder material can be reformed by mixing it with lithium hydride (LiH) powder and heating it in an oxidizing atmosphere containing oxygen in a certain range. As the oxidizing atmosphere, for example, a gas containing oxygen in the argon atmosphere or oxygen in the nitrogen atmosphere can be used. It is also possible to mix oxygen for a certain period of time while using argon or nitrogen gas. More specifically, first, LiH powder and silicon oxide powder are sufficiently mixed under a nitrogen atmosphere, sealed, and the sealed container is stirred together to make the powder uniform. Then, it is reformed by heating in an oxidizing atmosphere containing oxygen in a certain range in the range of 500 ° C. to 750 ° C. More preferably, oxygen is contained in the nitrogen atmosphere, which is superior in terms of cost. It is considered that the inflow and outflow of Li becomes smooth by including oxygen in a certain range, and the effect is exhibited if oxygen is within a certain range for 10 minutes or more at a temperature of 300 ° C. or higher.

Further, in order to desorb Li from the silicon compound, a method of sufficiently cooling the heated powder and then washing with alcohol, alkaline water, a weak acid or pure water can be used.

When the silicon compound is modified by the heat doping method, the negative electrode active material can be modified at low cost and the battery characteristics are improved. Further, this further improves the stability of the negative electrode active material 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 should have a composite layer containing a composite composed of an amorphous metal oxide and a metal hydroxide on the surface of the silicon compound particles or the surface of the carbon film. preferable. Examples of the method for synthesizing the composite layer include a surface coating by a liquid phase, a mechanochemical coating by a dry method, a wet coating by a spray, and a sol-gel reaction treatment of aluminum isopropoxide.

The produced negative electrode active material particles are mixed with a carbon-based active material as necessary, and these negative electrode active materials are mixed with other materials such as a binder and a conductive auxiliary agent to form a negative electrode mixture, and then an organic solvent is used. Alternatively, water or the like is added to make 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 if necessary. As described above, the negative electrode can be manufactured.

As described above, the negative electrode active material can be produced by the method for producing the negative electrode active material of the present invention. The negative electrode active material produced in this manner can be configured as described below.

The negative electrode active material produced by the method for producing a negative electrode active material of the present invention contains negative electrode active material particles, and the negative electrode active material particles are silicon compound particles having a silicon compound (SiOx: 0.5≤x≤1.6). include. Further, 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, it is preferable that the negative electrode active material contains NO ₃ ions on the surface of the negative electrode active material particles, 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. .. This ratio is the mass ratio of _NO3 ions to the mass of the entire negative electrode active material particles.

Since Li silicates such as Li ₂ SiO ₃ and Li ₂ Si ₂ O ₅ are relatively more stable than other Li compounds, the 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. Further, 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 activity. The dispersion liquid of the substance particles takes a value close to neutral, and the stability of the slurry at the time of forming the electrode can be improved.

The _NO3 ion content on the surface of the negative electrode active material particles is determined by weighing 1 g of lithium-doped silicon compound particles, adding them to 50 g of ultrapure water, stirring for 5 minutes to disperse them, and then using a membrane filter. The filtered material was measured by ion chromatography.

Further, it is desirable that a carbon film is formed on at least a part of the surface of the silicon compound particles. Here, in the negative electrode active material produced by the method for producing a negative electrode active material of the present invention, a carbon film is formed on at least a part of the surface of the silicon compound particles, but the carbon film is formed on the entire surface of the silicon compound particles. It may have been done.

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 by using, for example, AXS D2 PHASER manufactured by Bruker.

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 27.5 to 29 as diffraction peaks (2θ) obtained from the X-ray diffraction spectrum using Cu—Kα rays. Peak intensity A from the Si region given at 0.0 ° and peak intensity B from the Li ₂ SiO ₃ given at 26.5 to 27.5 ° and 24.5 to 25.5 °. It is preferable that the intensity C of the peak derived from the given Li ₂ Si ₂ O ₅ satisfies the relationship of A> B and A> C. Further, it is more preferable to satisfy the relationship of B> C. The reason is not clear, but if A, B, and C satisfy these relationships, the battery characteristics can be improved.

Further, 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 rays. It is preferable to have a broad peak derived from the SiO ₂ region given in. As described above, if the negative electrode active material particles contain an appropriate amount of the SiO ₂ component and the Li ₂ SiO ₃ is larger than the Li ₂ Si ₂ O ₅ , the effect of improving the battery characteristics can be sufficiently obtained. It becomes the negative electrode active material to be used.

Further, if the amount of Li ₂ SiO ₃ is relatively large in the negative electrode active material particles when the SiO ₂ component is used as a reference, the effect of improving the battery characteristics by inserting Li can be sufficiently obtained.

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

The median diameter of the silicon compound particles is not particularly limited, but is preferably 0.5 μm or more and 15 μm or less. This is because within this range, lithium ions are easily occluded and released during charging and discharging, and the silicon-based active material particles are less likely to be cracked. When the median diameter is 0.5 μm or more, the surface area is not too large, so that side reactions are unlikely to occur during charging and discharging, 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.

Further, in the negative electrode active material produced by the method for producing a negative electrode active material of the present invention, the surface of the silicon compound particles, the surface of the carbon film, or at least a part of both of them is an amorphous metal oxide and a metal. It is preferable to include a composite layer containing a composite composed of hydroxide. As the composite layer, for example, a composite layer including a composite composed of an amorphous aluminum oxide and an 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 a crystalline phase. Further, the complex is not limited to aluminum and may contain 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 thereof, the water resistance to the aqueous slurry is high. Become. However, since the negative electrode active material particles have the above-mentioned composite layer, it becomes difficult for gas to be generated due to the change of the slurry with time, a stable coating film can be obtained, and the binding property is sufficiently ensured. be able to. Further, if the complex is amorphous, Li can be easily exchanged.

Further, the amorphous metal oxide and the metal hydroxide preferably contain at least one element among aluminum, magnesium, titanium, and zirconium.

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

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

At this time, a test cell composed of a negative electrode containing a mixture of the negative electrode active material produced by the method for producing the negative electrode active material of the present invention and a carbon-based active material and counterpolar lithium was prepared, and the test cell was used. Charging / discharging consisting of charging in which a current is passed so as to insert lithium into the negative electrode active material and discharging in which a current is passed so as to desorb lithium from the negative electrode active material is carried out, and the discharge capacity Q in the charging / discharging is based on the counter electrode lithium. 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 0.40V to 0.55V. Is preferable. The above-mentioned peak in the V-dQ / dV curve is similar to the peak of the Kay material, and the discharge curve on the higher potential side rises sharply, so that the capacity is easily expressed when designing the battery.

As described above, the negative electrode active material produced by the method for producing a negative electrode active material of the present invention contains silicon compound particles composed 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. The composition of the silica oxide material in the present invention does not necessarily mean 100% purity, and may contain a trace amount of impurity elements and Li.

Subsequently, the configuration of the negative electrode including the negative electrode active material produced by the method for producing the negative electrode active material of the present invention will be described.

[Construction of negative electrode]
FIG. 1 shows a cross-sectional view of a negative electrode containing a negative electrode active material produced by the method for producing a negative electrode active material of the present invention. As shown in FIG. 1, the negative electrode 10 has a negative electrode active material layer 12 on the negative electrode current collector 11. The negative electrode active material layer 12 may be provided on both sides or only one side of the negative electrode current collector 11. Further, in the negative electrode of the non-aqueous electrolyte secondary battery, the negative electrode current collector 11 may not be present.

[Negative electrode current collector]
The negative electrode current collector 11 is made of an excellent conductive material and has 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). The 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) or 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 the current collector has an active material layer that expands during charging, if the current collector contains the above elements, there is an effect of suppressing deformation of the electrode including the current collector. The content of the above-mentioned contained elements is not particularly limited, but is preferably 100 ppm or less. This is because a higher deformation suppressing effect can be obtained.

The surface of the negative electrode current collector 11 may or may not be roughened. The roughened negative electrode current collector is, for example, an electrolytic treatment, an embossing treatment, or a chemically etched metal foil. The unroughened negative electrode current collector is, for example, a rolled metal foil.

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

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

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

The positive and negative electrode leads 32 and 33 are led out in one direction from the inside of the exterior member 35 toward the outside, for example. 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 or copper.

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

A close contact 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, polyolefin resin.

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

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

The positive electrode active material layer contains any one or more of the positive electrode materials capable of occluding and releasing 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 include. In this case, the details regarding the positive electrode binder and the positive electrode conductive auxiliary agent are the same as those of the negative electrode binder and the negative electrode conductive auxiliary agent already described, for example.

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, or a phosphoric acid compound having lithium and a transition metal element. Among these positive electrode materials, a compound having at least one of nickel, iron, manganese, and cobalt is preferable. These chemical formulas are represented by, for example, 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 transition metal element. The values of x and y show different values depending on the battery charge / discharge state, but are generally shown by 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

Examples of the composite oxide having lithium and a transition metal element include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), lithium nickel cobalt composite oxide, and the like. .. 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 phosphoric acid compound having lithium and a transition metal element include a lithium iron phosphoric acid compound (LiFePO ₄ ) and a lithium iron manganese phosphoric acid compound (LiFe _1-u Mn _u PO ₄ (0 <u <1)). Can be mentioned. By using these positive electrode materials, a high battery capacity can be obtained and also excellent cycle characteristics can be obtained.

[Negative electrode]
The negative electrode has the same configuration as the negative electrode 10 for the lithium ion secondary battery of FIG. 1 described above, and has, for example, negative electrode active material layers on both sides of the current collector. It is preferable that the negative electrode has a larger negative electrode charge capacity than the electric capacity (charge capacity as a battery) obtained from the positive electrode active material. This makes it possible to suppress the precipitation of lithium metal on the negative electrode.

The positive electrode active material layer is provided on a part of both sides of the positive electrode current collector, and similarly, the negative electrode active material layer is also provided on a part of both sides 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 in which the opposite positive electrode active material layer does not exist. This is for stable battery design.

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 charge / discharge. 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 and the like can be accurately investigated with good reproducibility regardless of 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 through while preventing a current short circuit due to contact between the two electrodes. This separator is formed of, for example, a porous film made of synthetic resin or ceramic, and may have a laminated structure in which two or more kinds of porous films are laminated. Examples of the synthetic resin include polytetrafluoroethylene, polypropylene, polyethylene and the like.

[Electrolytic solution]
At least a part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolyte solution). The electrolyte salt has an electrolyte salt dissolved in the 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 of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate. This is because better characteristics can be obtained. Further, in this case, more advantageous 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, ethylmethyl carbonate and diethyl carbonate. This is because the dissociability and ion mobility of the electrolyte salt are improved.

It is preferable to contain unsaturated carbon-bonded cyclic carbonate as a solvent additive. This is because a stable film is formed on the surface of the negative electrode during charging and discharging, and the decomposition reaction of the electrolytic solution can be suppressed. Examples of unsaturated carbon-bonded cyclic carbonates include vinylene carbonate and vinylethylene carbonate.

Further, it is preferable to contain sultone (cyclic sulfonic acid ester) 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.

Further, the solvent preferably contains acid anhydride. This is because the chemical stability of the electrolytic solution is improved. Examples of the acid anhydride include propanedisulfonic acid anhydride.

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

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 can be obtained.

[Manufacturing method of laminated film type secondary battery]
First, a positive electrode is manufactured using the above-mentioned positive electrode material. First, the positive electrode active material is mixed with a positive electrode binder, a positive electrode conductive auxiliary agent, and the like as necessary to form a positive electrode mixture, and then dispersed in an organic solvent to form a positive electrode mixture slurry. Subsequently, the mixture slurry is applied to the positive electrode current collector with 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 with a roll press or the like. At this time, heating may be performed, or compression may be repeated a plurality of times.

Next, the negative electrode active material layer is formed on the negative electrode current collector to prepare the negative electrode by using the same work procedure as the manufacturing of the negative electrode 10 for the lithium ion secondary battery described above.

When the positive electrode and the negative electrode are manufactured, the active material layers are formed on both sides of the positive electrode and the negative electrode current collector. At this time, the active material coating lengths on both sides of either electrode may be different (see FIG. 1).

Subsequently, the electrolytic solution is prepared. Subsequently, the positive electrode lead 32 is attached to the positive electrode current collector by ultrasonic welding or the like, and the negative electrode lead 33 is attached to the negative electrode current collector. Subsequently, the positive electrode and the negative electrode are laminated or wound via a separator to produce a wound electrode body 31, and a protective tape is adhered to the outermost peripheral portion thereof. Next, the winding body is molded so as to have 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 adhered to each other by a heat fusion method, and the wound electrode body is opened in only one direction. Is enclosed. Subsequently, the positive electrode lead and the adhesive film are inserted between the negative electrode lead and the exterior member. Subsequently, a predetermined amount of the electrolytic solution prepared above is charged from the open portion, and vacuum impregnation is performed. After impregnation, the open portion is bonded by the vacuum heat fusion method. As described above, the laminated film type secondary battery 30 can be manufactured.

In the non-aqueous electrolyte secondary battery such as the laminated film type secondary battery 30 produced above, the negative electrode utilization rate at the time of charging / discharging is preferably 93% or more and 99% or less. If the negative electrode utilization rate is in the range of 93% or more, the initial charge efficiency does not decrease and the battery capacity can be greatly improved. Further, if the negative electrode utilization rate is in the range of 99% or less, Li does not precipitate and safety can be ensured.

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

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

A raw material (vaporization starting material), which is a mixture of metallic silicon and silicon dioxide, is installed in a reactor, vaporized in an atmosphere with a vacuum degree of 10 Pa, deposited on an adsorption plate, cooled sufficiently, and then the deposit is deposited. It was crushed with a take-out ball mill. After adjusting the particle size, the carbon film was coated by performing thermal CVD. Subsequently, lithium hydride having a mass corresponding 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. Then, in an atmosphere control furnace, the stirred powder was reformed by firing at 740 ° C. while flowing a mixed gas obtained by adding 1000 ppm of oxygen to argon 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 film at a flow rate of 5 L / min during firing to generate _NO3 ions on the surface of the negative electrode active material particles. For _NO3 ions on the surface of the negative electrode active material particles, the raw material is held in an inert gas, the initial gas replacement in the furnace is performed with nitrogen gas, and then a mixed gas in which 1000 ppm of oxygen is added to argon is used. It can also be produced by firing at 740 ° C. while flowing into the furnace. Modification was performed and no holding temperature zone was provided before firing. The _NO3 ion content on the surface of the negative electrode active material particles was 40 mass ppm.

Next, the prepared negative electrode active material, conductive auxiliary agent 1 (Denka Black), conductive auxiliary agent 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. The above SBR and CMC are negative electrode binders (negative electrode binders).

An electrolytic copper foil (thickness 15 μm) was used as the 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. After drying, the deposited amount (also referred to as area density) of the negative electrode active material layer per unit area on one side of the negative electrode was 2.0 mg / cm ² . The negative electrode mixture slurry was applied to only one side of the negative electrode current collector, and the negative electrode active material layer was provided to only one side.

In order to investigate the initial charge / discharge characteristics, a 2032 type coin battery was assembled as a test cell.

As the negative electrode, one manufactured by the same procedure as the electrode containing the negative electrode active material of the above-mentioned laminated film type secondary battery was used. As the electrolytic solution, a solution prepared by dissolving ₁ mol of LiPF in 1 liter of a 2: 7: 1 kneaded solution 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. Further, as a separator, polyethylene having a thickness of 20 μm was used. Subsequently, the bottom cover, lithium foil, and separator of the 2032 type coin battery are overlaid and 150 mL of the electrolytic solution is injected, and then the negative electrode and the spacer (thickness 1.0 mm) are overlaid and 150 mL of the electrolytic solution is injected. Then, the spring and the upper pig of the coin battery were pumped up in this order and crimped 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 produced by the method for producing the negative electrode active material of the present invention, the laminated film type secondary battery as shown in FIG. 3 is subsequently evaluated. 30 was produced as follows.

First, a positive electrode used for a laminated film type secondary battery was prepared. 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 conductive auxiliary agent (acetylene black), and 2.5 parts by mass of a positive electrode binder (polyfluorinated vinylidene: Pvdf). Was mixed to obtain a positive electrode mixture. Subsequently, the positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) to obtain a paste-like slurry. Subsequently, the slurry was applied to both sides of the positive electrode current collector with a coating device having a die head, and dried with a hot air type drying device. At this time, a positive electrode current collector having a thickness of 15 μm was used. Finally, compression molding was performed with a roll press.

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

As the electrolytic solution, one prepared by the same procedure as the electrolytic solution of the above 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, the positive electrode, the separator, the negative electrode, and the separator were laminated in this order and wound in the longitudinal direction to obtain a wound electrode body. The winding end portion was fixed with PET protective tape. As the separator, a laminated film of 12 μm in which a film containing porous polyethylene as a main component was sandwiched between films containing porous polypropylene as a main component was used. Subsequently, after sandwiching the electrode body between the exterior members, the outer peripheral edges except one side were heat-sealed, and the electrode body was housed inside. As the exterior member, a nylon film, an aluminum foil, and an aluminum laminated film in which a polypropylene film was laminated were used. Subsequently, the electrolytic solution prepared from the opening was injected, impregnated in a vacuum atmosphere, and then heat-sealed and sealed.

The cycle characteristics (maintenance rate%) of the laminated film type lithium ion secondary battery thus produced were investigated.

(Example 1-2)
In Example 1-2, the lithium compound at the time of firing was changed to lithium nitride (Li 3N), the NO ₃ ion content _on the surface of the negative electrode active material particles was changed, and nitrogen gas was blown at the time of firing. The procedure was the same as in Example 1-1, except that there was no such thing. The _NO3 ion content on the surface of the negative electrode active material particles was 47 mass ppm.

(Example 1-3)
Examples 1-3 were carried out in the same manner as in Example 1-1 except that the _NO3 ion content on the surface of the negative electrode active material particles was changed and the atmosphere at the time of firing was changed. The _NO3 ion content on the surface of the negative electrode active material particles was 32 mass ppm. Further, the atmosphere at the time of firing was a mixed gas in which 200 ppm of oxygen was added to argon, and the gas was fired while flowing into the furnace.

(Example 1-4)
Example 1-4 was carried out in the same manner as in Example 1-2 except that the _NO3 ion content on the surface of the negative electrode active material particles was changed and the atmosphere at the time of firing was changed. The _NO3 ion content on the surface of the negative electrode active material particles was 42 mass ppm. Further, the atmosphere at the time of firing was a mixed gas in which 200 ppm of oxygen was added to argon, and the gas was fired while flowing into the furnace.

(Example 1-5)
In Example 1-5, the _NO3 ion content on the surface of the negative electrode active material particles was changed, the atmosphere at the time of firing was changed, and nitrogen gas was not blown at the time of firing. It was done in the same manner as -1. The _NO3 ion content on the surface of the negative electrode active material particles was 37 mass ppm. Further, the atmosphere at the time of firing was a mixed gas in which 100 ppm of oxygen was added to nitrogen, and the gas was fired while flowing into the furnace.

(Example 1-6)
Examples 1-6 were carried out in the same manner as in Example 1-2 except that the _NO3 ion content on the surface of the negative electrode active material particles was changed and the atmosphere at the time of firing was changed. The _NO3 ion content on the surface of the negative electrode active material particles was 26 mass ppm. Further, the atmosphere at the time of firing was a mixed gas in which 100 ppm of oxygen was added to nitrogen, and the gas was fired while flowing into the furnace.

(Example 1-7)
Examples 1-7 were carried out in the same manner as in Examples 1-5, except that a holding temperature zone was provided before firing and the _NO3 ion content on the surface of the negative electrode active material particles was changed. The _NO3 ion content on the surface of the negative electrode active material particles was 15 mass ppm.

(Example 1-8)
Examples 1-8 were carried out in the same manner as in Examples 1-7 except that the lithium compound at the time of firing was changed to lithium nitride and the _NO3 ion content on the surface of the negative electrode active material particles was changed. The _NO3 ion content on the surface of the negative electrode active material particles was 5 mass ppm.

(Example 1-9)
Examples 1-9 were carried out in the same manner as in Examples 1-8 except that the _NO3 ion content on the surface of the negative electrode active material particles was changed and a composite layer was formed. The _NO3 ion content on the surface of the negative electrode active material particles was 8 mass ppm. In particular, with respect to Example 1-9, the modified silicon compound particles were put into a mixed solution of dehydrated ethanol and aluminum isopropoxide, and the mixture was stirred, filtered and dried to remove ethanol. As a result, a composite layer containing a composite of aluminum oxide and aluminum hydroxide was formed. The film 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 reforming by firing was longer than that in Example 1-1. In Example 1-10, crystallization was promoted by raising the temperature of reforming in firing higher than that in Examples 1-1 to 1-11. That is, the half width (2θ) of the diffraction peak caused by the Si (111) crystal plane was made smaller. The _NO3 ion content on the surface of the negative electrode active material particles was 42 mass ppm.

(Comparative Example 1-1)
In Comparative Example 1-1, Examples were obtained except that the _NO3 ion content on the surface of the negative electrode active material particles was changed, the atmosphere during firing was changed, and nitrogen gas was not blown during firing. It was done in the same manner as 1-1. The _NO3 ion content on the surface of the negative electrode active material particles was lower than 1 mass ppm. The atmosphere at the time of firing was argon.

(Comparative Example 1-2)
In Comparative Example 1-2, the same procedure as in Comparative Example 1-1 was carried out except that the lithium compound was changed to lithium nitride. The _NO3 ion content on the surface of the negative electrode active material particles was lower than 1 mass ppm.

(Comparative Example 1-3)
In Comparative Example 1-3, the same procedure as in Comparative Example 1-1 was performed except that the atmosphere at the time of firing was changed. The atmosphere at the time of firing was nitrogen. In addition, the _NO3 ion content on the surface of the negative electrode active material particles was lower than 1 mass ppm.

(Comparative Example 1-4)
In Comparative Example 1-4, the same procedure as in Comparative Example 1-3 was carried out except that the lithium compound was changed to lithium nitride. In addition, the _NO3 ion content on the surface of the negative electrode active material particles was lower than 1 mass ppm.

(Comparative Example 1-5)
In Comparative Example 1-5, the same procedure as in Comparative Example 1-1 was carried out except that the 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 the gas was fired while flowing into the furnace. In addition, the _NO3 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 set to 0.4. The _NO3 ion content on the surface of the negative electrode active material particles was 20 mass ppm.

(Comparative Example 1-7)
Comparative Example 1-7 was carried out in the same manner as in Example 1-1 except that x of the silicon compound (SiO _x ) was larger than 1.6. The _NO3 ion content on the surface of the negative electrode active material particles was 45 mass ppm.

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

The physical characteristics of the silicon compound in the above Examples and Comparative Examples are as follows. In all 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 1. It was 5.2 μm. Further, in Examples 1-1 to 1-9, the half width (2θ) of the diffraction peak due to the Si (111) crystal plane obtained by the X-ray diffraction of the modified silicon compound was 2.257 °. rice field. Further, in Example 1-10, the half width (2θ) of the diffraction peak caused by the Si (111) crystal plane obtained by the 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 .

Further, the intensity A of the peak derived from the Si region given at 27.5 to 29.0 ° as the diffraction peak (2θ) obtained from the X-ray diffraction spectrum using the Cu—Kα ray of the negative electrode active material particles, and 26. Relationship between the intensity B of the peak derived from Li ₂ SiO ₃ given at .5 to 27.5 ° and the intensity C of the peak derived from Li ₂ Si ₂ O ₅ given at 24.5 to 25.5 °. In Examples 1-1 and 1-2, A> B, A> C, and C> B. Further, in Examples 1-3 to 1-4 and Comparative Example 1-2, A> B, A> C, and B> C. Further, in Comparative Example 1-1, B> A, C> A, and C> B. Further, 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 the 2θ had a broad peak derived from the SiO ₂ region given in the vicinity of 22 °. The X-ray diffraction spectrum obtained in Example 1-1 is shown in FIG.

Further, 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 thereof was evaluated. More specifically, first, constant current and constant voltage charging was performed up to 0 V with counter electrode Li, and charging was terminated when the current density reached 0.05 mA / cm ² . Then, 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 charging and discharging, a graph is drawn with the vertical axis as the rate of change in capacitance (dQ / dV) and the horizontal axis as the voltage (V), and V is 0.4 to 0.55 (V). It was confirmed whether a peak could be obtained in the range. As a result, peaks were confirmed in all Examples and Comparative Examples other than Examples 1-6.

When investigating the initial charge / discharge characteristics, the initial efficiency (initial efficiency) was calculated. The initial efficiency was calculated from the formula represented by the initial efficiency (%) = (initial discharge capacity / initial charge capacity) × 100.

The cycle characteristics were investigated as follows. First, in order to stabilize the battery, charging and discharging were performed for two cycles in an atmosphere of 25 ° C., and the discharge capacity of 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 of the 100th cycle was divided by the discharge capacity of the second cycle (× 100 for% display) to calculate the capacity retention rate. As a cycle condition, the battery is charged at a constant current density of 2.5 mA / cm ² until it reaches 4.3 V, and when the voltage reaches 4.3 V, the current density reaches 0.25 mA / cm ² at a constant voltage of 4.3 V. Charged up to. At the time of discharge, 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 produced by the method for producing the negative electrode active material of the present invention, oxygen is constant in the atmosphere in the furnace. By firing under the condition that 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 oxygen is not contained in the atmosphere in the furnace at the time of firing (Comparative Examples 1-1 to 1-4) and when oxygen is contained in an amount of more than 1000 ppm (Comparative Example 1-5), it is sufficient. Initial efficiency was not obtained.

Further, 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 better initial efficiency was shown.

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

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

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

The present invention is not limited to the above embodiment. The above-described embodiment is an example, and the present invention can be anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same function and effect. Is included in the technical scope of.

10 ... Negative electrode, 11 ... Negative electrode current collector, 12 ... Negative electrode active material layer,
30 ... Laminating film type secondary battery, 31 ... Winding electrode body,
32 ... Positive electrode lead (positive electrode aluminum lead),
33 ... Negative electrode lead (negative electrode nickel lead),
34 ... Adhesive film, 35 ... Exterior member.

Claims (7)

A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, which comprises negative electrode active material particles containing silicon compound particles containing lithium.
A step of producing silicon compound particles containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6) and
A step of mixing a lithium compound with the silicon compound particles to obtain a mixed raw material,
A step of firing the mixed raw material in the presence of an inert gas containing 100 ppm or more and 1000 ppm or less of oxygen is included, and a negative electrode active material for a non-aqueous electrolyte secondary battery containing the silicon compound particles containing lithium is produced. A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery. The first aspect of claim 1 comprises a step of forming a carbon film 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 non-aqueous electrolyte secondary battery according to the above method. The method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the lithium compound contains at least one of lithium hydride and lithium nitride. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein in the firing step, the temperature of the mixed raw material is maintained at 300 ° C. or higher and 700 ° C. or lower for 30 minutes or longer. A method for manufacturing a negative electrode active material for use. After the calcination step, the surface of the silicon compound particles, the surface of the carbon film, or both all or at least a part thereof contains 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, which comprises a step of forming a composite layer. The non-aqueous electrolyte secondary battery according to claim 5, wherein the amorphous metal oxide and the metal hydroxide contain at least one element among aluminum, magnesium, titanium, and zirconium. Method for manufacturing negative electrode active material. The claim is characterized in that, in the firing step, the inert gas is a gas containing a nitrogen gas, so that the surface of the negative electrode active material particles contains 1 mass ppm or more and 50 mass ppm or less of NO ₃ ions. 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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