JP6448510B2 - Method for producing negative electrode active material for nonaqueous electrolyte secondary battery and method for producing nonaqueous 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 and a method for producing a non-aqueous electrolyte secondary battery.

  In recent years, small electronic devices typified by mobile terminals have been widely used, and further downsizing, weight reduction, and long life have been strongly demanded. In response to such market demands, development of secondary batteries capable of obtaining a high energy density, in particular, being small and light is underway. This secondary battery is not limited to a small electronic device, but is also considered to be applied to a large-sized electronic device represented by an automobile or the like, or an electric power storage system represented by a house.

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

  A lithium ion secondary battery includes an electrolyte solution together with a positive electrode, a negative electrode, and a separator. This negative electrode contains a negative electrode active material involved in the charge / discharge reaction.

  As a negative electrode active material, while carbon materials are widely used, further improvement in battery capacity is required due to recent market demand. As an element for improving battery capacity, the use of silicon as a negative electrode active material has been studied. This is because the theoretical capacity of silicon (4199 mAh / g) is 10 times or more larger than the theoretical capacity of graphite (372 mAh / g), so that significant improvement in battery capacity can be expected. The development of a siliceous material as a negative electrode active material has been examined not only for silicon alone but also for compounds represented by alloys and oxides. The shape of the active material is 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 particles expand and contract during charge and discharge, so that the vicinity of the surface layer of the negative electrode active material particles tends to break. Further, an ionic material is generated inside the active material, and the negative electrode active material particles are easily broken. When the surface layer of the negative electrode active material particles breaks, a new surface is generated, and the reaction area of the negative electrode active material particles increases. At this time, a decomposition reaction of the electrolytic solution occurs on the new surface, and a coating film that 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 of the battery are likely to deteriorate.

  To date, various studies have been made on negative electrode materials and electrode configurations for lithium ion secondary batteries mainly composed of a siliceous material in order to improve the initial efficiency and cycle characteristics of the battery.

  Specifically, for the purpose of obtaining good cycle characteristics and high safety, silicon and amorphous silicon dioxide are deposited simultaneously using a vapor phase method (see, for example, Patent Document 1). Moreover, 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). Furthermore, 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, And Patent Document 3). Further, in order to improve the cycle characteristics, oxygen is contained in the silicon active material, the average oxygen content is 40 at% or less, and the oxygen content is increased at a location close to the current collector. (For example, see Patent Document 4).

Moreover, in order to improve the initial charge / discharge efficiency, a nanocomposite containing a Si phase, SiO ₂ , or _MyO metal oxide is used (see, for example, Patent Document 5). In order to improve the initial charge / discharge efficiency, a Li-containing material is added to the negative electrode, and pre-doping is performed to decompose Li and return Li to the positive electrode when the negative electrode potential is high (see, for example, Patent Document 6).

  In order to improve cycle characteristics, SiOx (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 7). Further, in order to improve cycle characteristics, the molar ratio of oxygen to silicon in the negative electrode active material is 0.1 to 1.2, and the molar ratio of oxygen amount to silicon amount in the vicinity of the interface between the active material and the current collector The active material is controlled in a range where the difference between the maximum value and the minimum value is 0.4 or less (see, for example, Patent Document 8). Moreover, in order to improve battery load characteristics, a metal oxide containing lithium is used (see, for example, Patent Document 9). In addition, in order to improve cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface of the siliceous material (see, for example, Patent Document 10).

In order to improve cycle characteristics, silicon oxide is used and conductivity is imparted by forming a graphite film on the surface layer (see, for example, Patent Document 11). In this case, in Patent Document 11, 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.

  Moreover, in order to improve high battery capacity and cycle characteristics, particles having a silicon microcrystalline phase dispersed in silicon dioxide are used (see, for example, Patent Document 12). Further, in order to improve overcharge and overdischarge characteristics, 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 13). .

  In addition, for improving battery capacity and initial efficiency, there is a method in which an alloy-based material is brought into contact with a solution containing an alkali metal and a polycyclic aromatic compound, and further immersed in a liquid from which the alkali metal element is eliminated (for example, (See Patent Document 14).

JP 2001-185127 A JP 2002-042806 A JP 2006-164955 A JP 2006-114454 A JP 2009-070825 A Special table 2013-513206 gazette 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. 2999741 JP 2005-235439 A

  As described above, in recent years, small electronic devices typified by mobile terminals and the like have been improved in performance and functionality, and secondary batteries, particularly lithium ion secondary batteries, which are the main power source, have a battery capacity. Increase is demanded. As one method for solving this problem, development of a non-aqueous electrolyte secondary battery including a negative electrode using a siliceous material as a main material is desired. In addition, non-aqueous electrolyte secondary batteries using a siliceous material are desired to have cycle characteristics close to those of a non-aqueous electrolyte secondary battery using a carbon material.

  In view of this, the cycle retention rate and the initial efficiency of the battery have been improved by using a thermal Li insertion reaction, an electrical Li insertion reaction, and the like alone. However, since the modified silicon oxide has been modified using Li, its water resistance is relatively low. Therefore, there has been a problem that the slurry containing the modified silicon oxide, which is produced at the time of manufacturing the negative electrode, tends to be insufficiently stabilized.

  The present invention has been made in view of the above problems, and provides a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery capable of increasing battery capacity and improving initial efficiency and cycle characteristics. For the purpose. Moreover, it aims at providing the manufacturing method of the nonaqueous electrolyte secondary battery using such a negative electrode active material for nonaqueous electrolyte secondary batteries.

In order to achieve the above object, the present invention provides a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery comprising silicon compound particles containing lithium,
Preparing silicon compound particles containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6);
The silicon compound particles are mixed with at least one of lithium alone and a lithium compound as a first lithium source and heated to obtain first lithium-containing silicon compound particles;
Using the second lithium source in the first lithium-containing silicon compound particles and inserting lithium by an electrochemical method to obtain second lithium-containing silicon compound particles. A method for producing a negative electrode active material for an electrolyte secondary battery is provided.

Since the negative electrode active material containing silicon compound particles containing lithium produced by the method for producing a negative electrode active material of the present invention is a silicon-based active material mainly composed of a silicon compound, the battery capacity can be increased. it can. Further, since this silicon compound is represented by the general formula SiO _x (where 0.5 ≦ x ≦ 1.6) and the silicon compound particles contain lithium, the cycle characteristics can be improved. it can.

  In the method for producing a negative electrode active material of the present invention, as the step of inserting lithium (Li), a step of obtaining first lithium-containing silicon compound particles (hereinafter also referred to as a thermal Li insertion step) and a second lithium It is possible to selectively modify the irreversible capacity of different sites in the silicon compound particles by passing through two types of steps of obtaining the silicon compound particles (hereinafter also referred to as electrochemical Li insertion step). . As a result, the initial efficiency of the non-aqueous electrolyte secondary battery using the negative electrode active material can be improved, and further, growth of silicon crystallites due to insertion of Li and gelation during slurrying can be prevented. Furthermore, the thermal Li insertion step is performed first, and then the electrochemical Li insertion step is performed, so that the heat-sensitive Li-containing chemical species generated in the electrochemical Li insertion step are destroyed by heating. Can be prevented.

  Moreover, it is preferable to have a step of forming a carbon film on the silicon compound particles before the step of obtaining the first lithium-containing silicon compound particles.

  Thus, when a silicon compound particle has a carbon film, it can be stopped to some extent to the electroconductive fall by Li insertion.

  In the step of preparing the silicon compound particles, it is preferable to prepare the silicon compound particles having a silicon crystallite size of 3 nm to 10 nm.

  Thus, by adjusting the Si crystallite size in the silicon compound particles appropriately, the initial efficiency can be increased and the cycle characteristics can be maintained.

  The lithium content of the second lithium-containing silicon compound particles is preferably 8% by mass or more and 30% by mass or less.

  Thus, by appropriately adjusting the lithium content of the second lithium-containing silicon compound particles, it is possible to adjust the discharge capacity appropriately while increasing the initial efficiency.

  In the step of obtaining the first lithium-containing silicon compound particles, the heating temperature is preferably 400 ° C. or higher. The heating temperature at this time is more preferably 400 ° C. or higher and 800 ° C. or lower, particularly preferably 600 ° C. or higher and 800 ° C. or lower.

  By setting the heating temperature within the above range, it is possible to suppress the crystal growth of silicon in the silicon compound particles and prevent the cycle maintenance rate from deteriorating. Moreover, lithium can be sufficiently inserted, and the initial efficiency can be sufficiently improved.

  In the step of obtaining the first lithium-containing silicon compound particles, it is preferable to use at least one of metallic lithium, lithium hydride, and lithium nitride as the first lithium source.

  The above lithium source is preferably used as the first lithium source because the above lithium source has high activity and facilitates the lithium insertion reaction.

  Further, in the step of obtaining the second lithium-containing silicon compound particles, the second lithium source includes metal lithium, transition metal lithium phosphate, (Ni, Co, Mn) lithium oxide, lithium nitrate, and lithium halide. It is preferable to use at least one of them.

  Thus, by using said lithium source in an electrochemical Li insertion process, a big overvoltage is not applied at the time of electrochemical reforming, and a side reaction is suppressed.

  Furthermore, in the present invention, a negative electrode active material for a nonaqueous electrolyte secondary battery is produced by the method for producing a negative electrode active material for a nonaqueous electrolyte secondary battery of the present invention, and the electrode containing the negative electrode active material for the nonaqueous electrolyte secondary battery A method for producing a non-aqueous electrolyte secondary battery, characterized by producing a non-aqueous electrolyte secondary battery using

  As described above, in the method for producing a negative electrode active material of the present invention, it is possible to selectively modify the irreversible capacity of different sites in the silicon compound particles. As a result, the initial efficiency of the non-aqueous electrolyte secondary battery using the negative electrode active material can be improved, and further, growth of silicon crystallites due to insertion of Li and gelation during slurrying can be prevented. Therefore, the non-aqueous electrolyte secondary battery manufactured using the electrode (negative electrode) containing the said negative electrode active material has a favorable battery characteristic.

  The method for producing a negative electrode active material of the present invention can produce a negative electrode active material capable of obtaining good cycle characteristics and initial charge / discharge characteristics with a high capacity when used in a non-aqueous electrolyte secondary battery.

  Moreover, the same characteristic can be acquired also in the secondary battery containing the negative electrode active material manufactured by the manufacturing method of the negative electrode active material of this invention. Moreover, the same effect can be acquired also in the electronic device, electric tool, electric vehicle, electric power storage system, etc. using this secondary battery.

It is a flowchart which shows an example of the manufacturing method of the negative electrode active material for nonaqueous electrolyte secondary batteries of this invention. It is a schematic sectional drawing which shows an example of a structure of the negative electrode using the negative electrode active material for nonaqueous electrolyte secondary batteries manufactured with the manufacturing method of the negative electrode active material of this invention. It is the schematic which shows an example of the electrochemical Li dope reforming apparatus used in the electrochemical Li insertion process of the manufacturing method of the negative electrode active material of this invention. It is an exploded view which shows an example of a structure of the nonaqueous electrolyte secondary battery (laminated film type lithium ion secondary battery) manufactured using the manufacturing method of the secondary battery of this invention.

  Hereinafter, the present invention will be described in more detail.

  As described above, as one method for increasing the battery capacity of a non-aqueous electrolyte secondary battery, it has been studied to use a negative electrode using a siliceous material as a main material as a negative electrode of a non-aqueous electrolyte secondary battery.

  The non-aqueous electrolyte secondary battery using this siliceous material is expected to have cycle characteristics similar to those of the non-aqueous electrolyte secondary battery using the carbon material, but the non-aqueous electrolyte secondary battery using the carbon material and A negative electrode material exhibiting equivalent cycle stability has not been proposed. In particular, the silicon compound containing oxygen has a lower initial efficiency than the carbon material, so that the battery capacity has been limited to that extent.

  Thus, the use of silicon oxide modified by insertion and partial desorption of Li as the negative electrode active material has improved the cycle retention rate and initial efficiency of the battery. However, when Li insertion is performed using only thermal Li insertion reaction, silicon crystallites in the silicon compound grow with the insertion of Li, cycle characteristics deteriorate, and only electrical Li insertion reaction occurs. When Li is inserted using Li, the Li-containing chemical species generated in the silicon compound particles due to the insertion of Li increase the alkalinity during the preparation of the negative electrode slurry, cut the molecular chain of the binder (binder), and reduce the slurry There is a problem in that it is difficult to form a slurry because it causes viscosity increase or reacts with the binder and solvent molecules of the negative electrode slurry.

  Therefore, the present inventors have conducted intensive studies on a method for producing a negative electrode active material that, when used in a non-aqueous electrolyte secondary battery, provides a high battery capacity and provides good cycle characteristics and initial efficiency. Invented.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings, but the present invention is not limited thereto.

  FIG. 1 is a flowchart showing an example of a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention.

First, the overall flow of the implementation procedure will be described. In the method for producing a negative electrode active material for a nonaqueous electrolyte secondary battery of the present invention, as shown in FIG. 1, first, silicon compound particles containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6) are prepared. (Step 1).

  Next, as shown in FIG. 1, the silicon compound particles prepared in step 1 and the carbon material can be combined (step 2). However, this step is not essential.

  Subsequently, as shown in FIG. 1, the silicon compound particles prepared in Step 1 or the silicon compound particles obtained by compounding the carbon material in Step 2 are either lithium simple substance (metallic lithium) or lithium compound as the first lithium source. One or more kinds are mixed and heated to obtain first lithium-containing silicon compound particles (step 3: thermal Li insertion step).

  Subsequently, as shown in FIG. 1, the silicon compound particles into which lithium is thermally inserted are inserted into the silicon compound particles by an electrochemical method using a second lithium source, and second lithium-containing silicon compound particles are obtained. (Step 4: electrochemical Li insertion step).

Since the negative electrode active material containing silicon compound particles containing lithium produced by the method for producing a negative electrode active material of the present invention is a silicon-based active material mainly composed of a silicon compound, the battery capacity can be increased. it can. Further, since this silicon compound is represented by the general formula SiO _x (where 0.5 ≦ x ≦ 1.6) and the silicon compound particles contain lithium, the cycle characteristics can be improved. it can. Moreover, the irreversible capacity | capacitance is reduced in the case of the first charge / discharge of the battery containing a silicon type active material by including Li in a silicon compound particle.

  In the method for producing a negative electrode active material of the present invention, Li is inserted at different sites in the thermal Li insertion step and the electrochemical Li insertion step. It is possible to selectively modify the irreversible capacity of different sites in the silicon compound particles. Thereby, the initial efficiency of the nonaqueous electrolyte secondary battery using the negative electrode active material can be improved.

  Moreover, the manufacturing method of the negative electrode active material of the present invention performs the initial step while reducing the activity of the Li-containing chemical species generated in the silicon compound particles by performing the electrochemical Li insertion step after the thermal Li insertion step. Increases efficiency. Thus, by passing through two types of Li insertion processes, the disadvantages can be reduced while taking advantage of the respective Li insertion processes. For example, the negative electrode active material has a reduced growth of silicon crystallites compared to a negative electrode active material obtained by performing only a thermal Li insertion step as the Li insertion step. In addition, the negative electrode active material is a Li compound (Li-containing chemical species) that is thermodynamically stable in the silicon compound particles as compared with the negative electrode active material obtained by performing only the electrochemical Li insertion step as the Li insertion step. ). As a result, when the negative electrode active material is mixed with a binder, a solvent, etc. to produce a negative electrode slurry, this Li compound increases the alkalinity of the slurry, cuts the molecular chain of the binder, and lowers the viscosity of the slurry. Li compounds can be prevented from reacting with these binders, solvent molecules, and the like, and the slurry is gelled or overheated by reaction heat. Note that if the thermal Li insertion step is performed after the electrochemical Li insertion step, the initial efficiency cannot be sufficiently improved. This is because when Li is inserted by an electrochemical method, Li-containing chemical species that are deactivated by heat are generated in the silicon compound particles.

  Then, the manufacturing method of the negative electrode active material of this invention is demonstrated more concretely.

<1. Method for producing negative electrode active material>
First, silicon compound particles containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6) are prepared (step 1). Such a silicon compound represented by the general formula SiO _x (where 0.5 ≦ x ≦ 1.6) can be produced, for example, by the following method. First, a raw material that generates silicon oxide gas is heated in a temperature range of 900 ° C. to 1600 ° C. in the presence of an inert gas or under reduced pressure to generate silicon oxide gas. In this case, a mixture of metal silicon powder and silicon dioxide powder can be used as the raw material, and considering the surface oxygen of the metal silicon powder and the presence of trace amounts of oxygen in the reactor, the mixing molar ratio is 0.8 <metal. It is desirable that silicon powder / silicon dioxide powder <1.3. The gas generated from the raw material is deposited on the adsorption plate. Subsequently, the deposit is taken out with the temperature in the reactor lowered to 100 ° C. or lower, and pulverized and powdered using a ball mill, a jet mill, or the like. The crystallinity such as the size of the Si crystallite in the silicon compound particles can be controlled by adjusting the preparation range (mixing molar ratio) and the heating temperature of the raw material. Crystallinity can also be controlled by heat treatment after the formation of silicon compound particles.

  In this step 1, it is preferable to prepare silicon compound particles having a silicon crystallite size of 3 nm to 10 nm. When the crystallite size is 10 nm or less, the expansion and contraction of the silicon compound particles accompanying charge / discharge is reduced, and the capacity retention rate is increased. When the crystallite size is 3 nm or more, the improvement rate of the initial efficiency due to insertion of Li is sufficient. Therefore, by keeping the crystallite size within this range, the capacity retention ratio and the initial efficiency can be improved. This crystallite size can be calculated from the half-value width (half-value width) of the diffraction peak caused by the Si (111) crystal plane obtained by X-ray diffraction.

  Further, as the composition of the silicon compound to be produced, it is preferable that x is close to 1. This is because high cycle characteristics can be obtained. In addition, the composition of the silicon compound in the present invention does not necessarily mean 100% purity, and may contain a trace amount of impurity elements.

  The silicon compound particles may be combined with a carbon material (Step 2). Examples of the composite method include a method of producing a carbon film on the surface of silicon compound particles by a thermal CVD (Chemical Vapor Deposition) method, and a method of physically mixing silicon compound particles and a carbon material. High conductivity can be imparted by combining a carbon material with silicon compound particles. In particular, when the silicon compound particles have a carbon coating, the reduction in conductivity due to insertion of Li can be stopped to some extent.

  In particular, a thermal CVD method is desirable as a method for generating a carbon film on the surface of silicon compound particles. In the thermal CVD method, first, silicon compound particles are set in a furnace. Subsequently, the furnace is filled with hydrocarbon gas and the furnace temperature is raised. By raising the furnace temperature, the hydrocarbon gas is decomposed and a carbon film is formed on the surface of the silicon compound particles. The decomposition temperature of the hydrocarbon gas is not particularly limited, but is preferably 1200 ° C. or lower, and particularly preferably 1050 ° C. or lower. This is because unintended disproportionation of the silicon compound particles can be suppressed.

  When producing a carbon film by the thermal CVD method, for example, by adjusting the pressure and temperature in the furnace, the carbon film can be formed on the surface layer of the powder material while adjusting the coverage and thickness of the carbon film. .

The hydrocarbon gas used in the thermal CVD method is not particularly limited, but 3 ≧ n is desirable in the C _n H _m composition. This is because the manufacturing cost can be lowered and the physical properties of the decomposition product are good.

  Subsequently, the silicon compound particles prepared in Step 1 or the silicon compound particles obtained by combining the carbon material in Step 2 are mixed with one or more of lithium alone and a lithium compound as a first lithium source, heated, One lithium-containing silicon compound particle is obtained (step 3).

  Thus, by mixing and heating the silicon compound particles and the first lithium source, Li can be inserted into the silicon compound particles and Li can be diffused to the inside. This is because the heating imparts sufficient energy for Li atoms to diffuse in the silicon compound particles. As a result, the Li compound is generated in the silicon compound particles, and the Li compound becomes a thermodynamically stable chemical species to some extent. Therefore, the first lithium-containing silicon compound particles thus obtained can be handled safely in the previous process.

  The thermal Li insertion step can be performed, for example, by mixing silicon compound particles with a first lithium source under an inert atmosphere, and charging the resulting mixture in a crucible and heating.

  In the thermal Li insertion step, the heating temperature is preferably 400 ° C. or higher. The heating temperature at this time is more preferably 400 ° C. or higher and 800 ° C. or lower, particularly preferably 600 ° C. or higher and 800 ° C. or lower. If heating temperature is 800 degrees C or less, the crystal growth of the silicon in a silicon compound particle can be suppressed, and it can prevent that a cycle maintenance factor deteriorates. When the heating temperature is 400 ° C. or higher, a thermally stable Li compound is generated, and the initial efficiency can be sufficiently improved even when applied to an aqueous slurry.

  Further, in the thermal Li insertion step, as the substance to be mixed with the silicon compound particles, that is, the first lithium source, lithium alone, a lithium compound (for example, lithium salt) or a mixture thereof is used. Specific examples include lithium metal, lithium hydride, lithium nitride, lithium carbonate, lithium oxide, lithium peroxide, lithium nitrate, lithium sulfate, and lithium aluminum hydride. These can be used singly or in combination of two or more. Among these, it is preferable to use at least one of metallic lithium, lithium hydride, and lithium nitride as the first lithium source. This is because the above lithium source has high activity and facilitates the lithium insertion reaction. In the present invention, any lithium compound or the like can be used as the first lithium source if it contains at least a part thereof.

  These substances are preferably in the form of powder, and preferably have an average particle size of 100 times or less that of the silicon compound particles. This is because the mixed state with the silicon compound particles is thereby improved.

  The first lithium source is preferably used in an amount of 3% by mass or more and 20% by mass or less in terms of lithium with respect to the silicon compound particles. If the amount is 3% by mass or more, sufficient improvement in the initial efficiency can be expected, and if it is 20% by mass or less, the heating temperature is excessively increased or the heating time is excessively lengthened in the thermal Li insertion step. Therefore, the growth of silicon crystallites in the silicon compound particles can be prevented from progressing, and the deterioration of the cycle maintenance rate can be prevented.

  Next, lithium is inserted into the first lithium-containing silicon compound particles obtained by mixing and heating using the second lithium source by an electrochemical method to obtain second lithium-containing silicon compound particles (step) 4). By inserting Li by the electrochemical method in this way, Li is inserted at a site different from Li inserted by the thermal method, so that it is possible to further improve the initial efficiency, and the thermal method. It is possible to mitigate the growth of silicon crystallites.

  The method of inserting Li in the step 4 may be an electrochemical method. For example, Li can be inserted using the electrochemical Li doping reformer 20 shown in FIG. The electrochemical Li doping reformer 20 includes a bathtub 27 filled with a solvent 23, a positive electrode 21 disposed in the bathtub 27 and connected to one side of the power source 26, and disposed in the bathtub 27. And a separator 24 provided between the positive electrode 21 and the powder storage container 25. The powder storage container 25 stores the first lithium-containing silicon compound particles 22.

  Examples of the second lithium source used at this time include lithium alone and lithium compounds. Specifically, metal lithium, transition metal lithium phosphate, (Ni, Co, Mn) lithium oxide (lithium oxide containing at least one of Ni, Co, and Mn), lithium nitrate, lithium halide, etc. Is mentioned. More specifically, metal lithium, lithium cobaltate, lithium iron phosphate, lithium cobalt phosphate, lithium vanadium phosphate, lithium nickel cobaltate, nickel cobalt lithium manganate, lithium manganate, lithium nitrate, lithium chloride, etc. Can be mentioned. Thus, by using said lithium source in an electrochemical Li insertion process, a big overvoltage is not applied at the time of electrochemical reforming, and a side reaction is suppressed. These can be used singly or in combination of two or more. In addition, the form of these 2nd lithium sources is not ask | required. For example, it may be used as a counter electrode (positive electrode 21) or as an electrolyte. Further, the first lithium source and the second lithium source may be the same or different.

At this time, examples of the solvent 23 used for the electrochemical reforming include dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, dioxane, diglyme, triglyme, tetraglyme, and mixtures thereof. In addition, as the electrolyte contained in the solvent 23, LiNO ₃ , LiCl, or the like can be used as an electrolyte that also serves as a Li source, such as LiBF ₄ , LiPF ₆ , LiClO _4, and derivatives thereof.

  In this case, the electrochemical reforming may include a desorption process after insertion of Li. This makes it possible to adjust the amount of Li to be inserted. The amount of Li to be inserted is not particularly limited, but the lithium content of the second lithium-containing silicon compound particles (the total amount of Li insertion in the thermal Li insertion step and the electrochemical Li insertion step) is determined with respect to the silicon compound particles. In addition, it is preferably 8% by mass to 30% by mass in terms of lithium. When the lithium content is 8% or more, the initial efficiency is sufficiently improved. In addition, when the lithium content is 30% or less, a nonaqueous electrolyte secondary battery having a high initial discharge capacity of 1000 mAh / g or more can be produced. Therefore, in order to balance the initial efficiency and the initial discharge capacity, it is preferable to adjust the lithium content therebetween.

  Further, the obtained second lithium-containing silicon compound particles may be washed with water to remove excess Li.

  As described above, the 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 produced can constitute a negative electrode as described below.

<2. Method for producing negative electrode for nonaqueous electrolyte secondary battery>
[Configuration of negative electrode]
As shown in FIG. 2, the negative electrode 10 is configured to have a negative electrode active material layer 12 on a negative electrode current collector 11. The negative electrode active material layer 12 may be provided on both surfaces or only one surface of the negative electrode current collector 11.

[Negative electrode current collector]
The negative electrode current collector 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) or sulfur (S) in addition to the main element. This is because the physical strength of the negative electrode current collector 11 is improved. In particular, when an active material layer that expands during charging is included, if the negative electrode current collector contains the above-described element, there is an effect of suppressing deformation of the electrode including the negative electrode current collector. Although content of said content element is not specifically limited, Especially, it is preferable that it is 100 ppm or less, respectively. This is because a higher deformation suppressing effect can be obtained.

  The surface of the negative electrode current collector 11 may be roughened or not roughened. The negative electrode current collector whose surface is roughened is, for example, a metal foil subjected to electrolytic treatment, embossing treatment, or chemical etching. The negative electrode current collector whose surface is not roughened is, for example, a rolled metal foil.

[Negative electrode active material layer]
The silicon-based active material manufactured by the negative electrode active material manufacturing method of the present invention is a material constituting the negative electrode active material layer 12. The negative electrode active material layer 12 includes a silicon-based active material, and may further include other materials such as a negative electrode binder and a negative electrode conductive additive in terms of battery design. As the negative electrode active material, a carbon-based active material may be included in addition to the silicon-based active material.

  Such a negative electrode can be produced by a coating method using a silicon-based active material produced by the above-described method for producing a negative electrode active material of the present invention. The coating method is a method in which silicon-based active material particles and the following binder are mixed, and if necessary, the following conductive assistant and carbon-based active material are mixed and then dispersed and applied in an organic solvent or water. .

  In this case, first, a silicon-based active material manufactured by the method for manufacturing a negative electrode active material of the present invention, a conductive additive, a binder, and a solvent such as water are mixed to obtain an aqueous slurry. At this time, a carbon-based active material may be mixed as necessary. Next, an aqueous slurry is applied to the surface of the negative electrode current collector 11 and dried to form the negative electrode active material layer 12 of FIG.

  As the conductive assistant, for example, one or more of carbon black, acetylene black, graphite such as flaky graphite, ketjen black, carbon nanotube, carbon nanofiber, and the like can be used. These conductive assistants are preferably in the form of particles having a median diameter smaller than that of silicon compound particles containing lithium. In that case, for example, acetylene black can be selected as the conductive assistant.

  Moreover, as a binder, carboxymethylcellulose, styrene butadiene rubber, polyacrylic acid, etc. can be used, for example.

  Examples of the carbon-based active material include pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound fired bodies, and carbon blacks. As a result, the electrical resistance of the negative electrode active material layer 12 can be reduced, and the expansion stress associated with charging can be reduced.

<3. Manufacturing method of non-aqueous electrolyte secondary battery>
Next, the manufacturing method of the nonaqueous electrolyte secondary battery of this invention is demonstrated. The method for producing a non-aqueous electrolyte secondary battery of the present invention comprises producing a negative electrode active material for a non-aqueous electrolyte secondary battery by the method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery according to the present invention. This is a method for producing a non-aqueous electrolyte secondary battery using an electrode containing a negative electrode active material for a secondary battery. Hereinafter, the production method of the non-aqueous electrolyte secondary battery of the present invention will be more specifically described by taking as an example the case of producing a laminate film type lithium ion secondary battery (hereinafter also referred to as a laminate film type secondary battery). I will explain it.

[Configuration of laminated film type secondary battery]
A laminated film type secondary battery 30 shown in FIG. 4 is one in which a wound electrode body 31 is accommodated mainly in a sheet-like exterior member 35. The wound electrode body 31 has a separator between a positive electrode and a negative electrode, and is wound. There is also a case in which a separator is provided between the positive electrode and the negative electrode and a laminate is accommodated. 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 part of the electrode body is protected by a protective tape.

  The positive and negative electrode leads are led out in one direction from the inside of the exterior member 35 to 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 a laminate film in which, for example, a fusion layer, a metal layer, and a surface protective layer are laminated in this order. This laminate film is composed of two films so that the fusion layer faces the wound electrode body 31. The outer peripheral edge portions of the fused layer are bonded together with an adhesive or the like. The fused part is, for example, a film such as polyethylene or polypropylene, and the metal part is aluminum foil or the like. The protective layer is, for example, nylon.

  An adhesion film 34 is inserted between the exterior member 35 and the positive and negative electrode leads to prevent intrusion of outside air. This material is, for example, polyethylene, polypropylene, or polyolefin resin.

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

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

  The positive electrode active material layer includes one or more positive electrode materials capable of occluding and releasing lithium ions, and includes other materials such as a binder, a conductive additive, and a dispersant depending on the design. You can leave. In this case, details regarding the binder and the conductive additive are the same as, for example, the negative electrode binder and the negative electrode conductive additive already described.

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 phosphate compound having lithium and a transition metal element. Among these positive electrode materials, compounds having at least one of nickel, iron, manganese and cobalt are 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 vary depending on the battery charge / discharge state, but are generally expressed as 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 ), and phosphoric acid having lithium and a transition metal element. Examples of the compound include a lithium iron phosphate compound (LiFePO ₄ ) and a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (0 <u <1)). This is because, when these positive electrode materials are used, a high battery capacity can be obtained and excellent cycle characteristics can be obtained.

[Negative electrode]
The negative electrode has a configuration similar to that of the negative electrode 10 in FIG. 2 described above. For example, the negative electrode has negative electrode active material layers 12 on both surfaces of the negative electrode current collector 11. This negative electrode preferably has a negative electrode charge capacity larger than the electric capacity (charge capacity as a battery) obtained from the positive electrode active material agent. This is because lithium metal deposition on the negative electrode can be suppressed.

  The positive electrode active material layer is provided on part of both surfaces of the positive electrode current collector, and the negative electrode active material layer is also provided on 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 there is no opposing positive electrode active material layer. This is to perform a stable battery design.

  In the non-opposing region, that is, 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. This makes it possible to accurately examine the composition with good reproducibility without depending on the presence or absence of charge / discharge, such as the composition of the negative electrode active material.

[Separator]
The separator separates the positive electrode and the negative electrode, and allows lithium ions to pass through while preventing a 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, and polyethylene.

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

  For example, a non-aqueous solvent can be used as the solvent. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl 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 ethyl methyl carbonate. This is because better characteristics can be obtained. In this case, more advantageous characteristics can be obtained by combining a high viscosity solvent such as ethylene carbonate or propylene carbonate and a low viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate. This is because the dissociation property and ion mobility of the electrolyte salt are improved.

  The solvent additive preferably contains an unsaturated carbon bond cyclic carbonate. 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 the unsaturated carbon bond cyclic ester carbonate include vinylene carbonate and vinyl ethylene carbonate.

  Moreover, it is preferable that sultone (cyclic sulfonate ester) is included as a solvent additive. This is because the chemical stability of the battery is improved. Examples of sultone include propane sultone and propene sultone.

  Furthermore, it is preferable that the solvent contains an 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 can contain, for example, any one or more of light metal salts such as lithium salts. Examples of the lithium salt include the following materials. Examples thereof 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 is obtained.

[Production method of laminated film type secondary battery]
First, a positive electrode is manufactured using the positive electrode material described above. First, a positive electrode active material and, if necessary, a binder, a conductive additive and the like are mixed 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 apparatus such as a die coater having a knife roll or 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. Further, compression and heating may be repeated a plurality of times.

  Next, the negative electrode is produced by forming a negative electrode active material layer on the negative electrode current collector by using the same operation procedure as that for producing the negative electrode 10 described above (see FIG. 2).

  The positive electrode and the negative electrode are manufactured by the same manufacturing procedure as described above. In this case, each active material layer can be formed on both surfaces of the positive electrode and the negative electrode current collector. At this time, as shown in FIG. 2, the active material application lengths of both surface portions may be shifted in either electrode.

  Subsequently, an electrolytic solution is prepared. Subsequently, the positive electrode lead 32 of FIG. 4 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. Then, a positive electrode and a negative electrode are laminated | stacked or wound through a separator, a wound electrode body is produced, and a protective tape is adhere | attached on the outermost periphery part. Next, the wound body is molded so as to have a flat shape. Subsequently, after sandwiching the wound electrode body between the folded film-shaped exterior member 35, the insulating portions of the exterior member are bonded to each other by a thermal fusion method, and the wound electrode body is opened in only one direction. Enclose. The adhesion film 34 is inserted between the positive electrode lead 32 and the negative electrode lead 33 and the exterior member 35. A predetermined amount of the prepared electrolytic solution is introduced from the open portion, and vacuum impregnation is performed. After impregnation, the open part is bonded by a vacuum heat fusion method.

  The laminated film type secondary battery 30 can be manufactured as described above.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these examples.

(Example 1-1)
First, a silicon-based active material was produced as follows.

First, a raw material (vaporization starting material) mixed with metallic silicon and silicon dioxide is placed in a reaction furnace, and vaporized in a vacuum atmosphere of 10 Pa is deposited on an adsorption plate, cooled sufficiently, and then deposited. The product (SiO _x : x = 0.5) was taken out and pulverized with a jet mill. Then, the carbon film was coat | covered on the surface of the particle | grains of the silicon compound by performing thermal CVD using methane gas.

  In addition, as shown also in the following Table 1, in the silicon compound particles after the carbon coating, it is calculated from the half width (half width) of the diffraction peak caused by the Si (111) crystal plane obtained by X-ray diffraction. The crystallite size of silicon was 7.21 nm. The coating amount of carbon was 5% by mass with respect to the silicon compound particles.

  Subsequently, a metal Li powder (average particle size of less than 200 μm) is mixed with the silicon compound particles coated with the carbon film in an inert atmosphere by 4.5 mass% with respect to the silicon compound particles, and the resulting mixture is mixed. The crucible was charged and fired at 700 ° C.

  Next, the obtained first lithium-containing silicon compound particles were subjected to electrochemical modification using an electrochemical Li-doped reformer 20 shown in FIG. At this time, the first lithium-containing silicon compound particles stored in the powder storage container 25 were applied to a current collector after being slurried and processed into an electrode shape. In addition, electrochemical modification was performed using lithium as a counter electrode (positive electrode 21). As a result, the first lithium-containing silicon compound particles stored in the powder container 25 were modified to the second lithium-containing silicon compound particles. Thereafter, the second lithium-containing silicon compound particles obtained from the powder storage container 25 were taken out, dried and crushed.

  Next, the second lithium-containing silicon compound particles were washed, and the second lithium-containing silicon compound particles after the washing treatment were dried under reduced pressure. As described above, a silicon-based active material (silicon-based active material particles) was produced.

  Then, the test cell which consists of an electrode containing the silicon type active material manufactured as mentioned above and counter electrode lithium was produced, and the first time charge / discharge characteristic in first time charge / discharge was investigated. In this case, a 2032 type coin battery was assembled as a test cell.

  An electrode containing silicon-based active material particles was produced as follows. First, silicon-based active material particles and a binder (polyacrylic acid (hereinafter also referred to as PAA)), conductive auxiliary agent 1 (flaky graphite), and conductive auxiliary agent 2 (acetylene black) are 76.5: 10. After mixing at a dry mass ratio of 00: 10.80: 2.70, the mixture was diluted with water to obtain a paste mixture slurry. Water was used as the solvent for the polyacrylic acid used as the binder. Subsequently, the mixture slurry was applied to both sides of the current collector with a coating apparatus and then dried. As this current collector, an electrolytic copper foil (thickness = 20 μm) was used. Finally, it was baked at 90 ° C. for 1 hour in a vacuum atmosphere. Thereby, the negative electrode active material layer was formed.

The electrolyte solution of the test cell was prepared as follows. After mixing a solvent (4-fluoro-1,3-dioxolan-2-one (FEC), ethylene carbonate (EC) and dimethyl carbonate (DMC)), an electrolyte salt (lithium hexafluorophosphate: LiPF ₆ ) is added. The electrolyte was prepared by dissolving. In this case, the composition of the solvent was FEC: EC: DMC = 10: 20: 70 by volume ratio, and the content of the electrolyte salt was 1.0 mol / kg with respect to the solvent.

  A metal lithium foil having a thickness of 0.5 mm was used as the counter electrode. Further, 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 electrolytic solution is injected, and subsequently, the negative electrode and the spacer (thickness: 1.0 mm) are stacked, and 150 mL of the electrolytic solution is injected. Then, a 2032 type coin battery was manufactured by lifting up the spring and the upper lid of the coin battery in this order and caulking with an automatic coin cell caulking machine.

Subsequently, the produced 2032 type coin battery was charged at a constant current density of 0.2 mA / cm ² until reaching 0.0 V, and when the voltage reached 0.0 V, the current density was at 0.0 V constant voltage. It was charged to reach 0.02 mA / cm ^2, when the discharge was discharged until the voltage reached 1.2V at a constant current density of 0.2 mA / cm ^2. And the first time charge / discharge characteristic in this first time charge / discharge was investigated.

  Subsequently, in order to evaluate the cycle characteristics of the non-aqueous electrolyte secondary battery using the negative electrode active material manufactured by the negative electrode active material manufacturing method of the present invention, a laminate film type secondary battery as shown in FIG. 30 was made as follows.

First, a positive electrode used for a laminate 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 conductive additive (acetylene black), and 2.5 parts by mass of a positive electrode binder (polyvinylidene fluoride: Pvdf). Were 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 slurry. Subsequently, the slurry was applied to both surfaces of the positive electrode current collector with a coating apparatus having a die head, and dried with a hot air drying apparatus. 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, a negative electrode produced in the same procedure as the electrode containing the silicon-based active material in the test cell was used.

  As the electrolytic solution, one prepared in 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, 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 portion was fixed with PET protective tape. As the separator, a laminated film of 12 μm sandwiched between a film mainly composed of porous polyethylene and a film mainly composed of porous polypropylene was used. Subsequently, after sandwiching the electrode body between the exterior members, the outer peripheral edges except for 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 laminate film in which a polypropylene film was laminated were used. Subsequently, an electrolyte prepared from the opening was injected, impregnated in a vacuum atmosphere, and then heat-sealed and sealed.

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

The cycle characteristics were examined as follows. First, in order to stabilize the battery, charge / discharge was performed for 2 cycles in an atmosphere at 25 ° C., and the discharge capacity at the second cycle was measured. Subsequently, charge and discharge 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 2nd cycle (because it is expressed in% × 100), and the capacity maintenance 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 Until charged. During discharging, discharging was performed at a constant current density of ^2.5 mA / cm ² until the voltage reached 3.0V.

(Examples 1-2 to 1-5, Comparative Examples 1-1 and 1-2)
A negative electrode active material (silicon-based active material) was produced in the same manner as in Example 1-1 except that x in SiO _x was changed. And the battery characteristic was evaluated similarly to Example 1-1.

  When the initial charge / discharge characteristics of the test cells (coin batteries) produced in Examples 1-1 to 1-5 and Comparative Examples 1-1 and 1-2 and the capacity retention rate of the laminate film type secondary battery were examined, a table was obtained. The result shown in 1 was obtained.

  As shown in Table 1, in the silicon compound represented by SiOx, when the value of x was outside the range of 0.5 ≦ x ≦ 1.6, the battery characteristics deteriorated. For example, as shown in Comparative Example 1-1, when there is not enough oxygen (x = 0.3), the capacity retention rate of the secondary battery is significantly deteriorated. On the other hand, as shown in Comparative Example 1-2, when the amount of oxygen was large (x = 1.8), the conductivity of the silicon compound was lowered, and the capacity retention rate of the secondary battery was lowered.

(Example 2-1 and Comparative Examples 2-1 to 2-5)
A negative electrode active material was produced in the same manner as in Example 1-3 except that the Li insertion method and the presence or absence of the carbon coating of the silicon compound particles were changed. And the battery characteristic was evaluated similarly to Example 1-3. In Comparative Example 2-1, Li insertion was not performed.

  When the initial charge / discharge characteristics of the test cells of Example 2-1 and Comparative Examples 2-1 to 2-5 and the capacity retention rate of the laminate film type secondary battery were examined, the results shown in Table 2 were obtained. In Tables 2 to 6 below, the results of Example 1-3 above are also shown.

  As can be seen from Table 2, when the contact method is used as the Li insertion method, or when the heating doping method and the electrochemical doping method are used alone, the initial efficiency (initial efficiency) is not sufficiently improved. As a result. This is because the amount of sites in the silicon compound particles that can be modified by these methods is determined, and there is a limit to improving the initial efficiency. In addition, when the heat doping method was performed after the electrochemical doping method first, the initial efficiency improvement was insufficient. This is presumably because the Li-containing chemical species generated by the electrochemical doping method are weak against heat and destroyed during the heating dope. Moreover, when the carbon coating was included, both the capacity retention rate and the initial efficiency were better. This is because an increase in powder resistivity due to insertion of Li is suppressed by the carbon coating.

(Examples 3-1 to 3-8)
A negative electrode active material was produced in the same manner as in Example 1-3, except that the crystallinity of the silicon compound particles prepared before the thermal Li insertion step and the electrochemical Li insertion step was changed. And the battery characteristic was evaluated similarly to Example 1-3.

  When the initial charge / discharge characteristics of the test cells (coin batteries) prepared in Examples 3-1 to 3-8 and the capacity retention rate of the laminate film type secondary battery were examined, the results shown in Table 3 were obtained.

  As can be seen from Table 3, when the crystallinity of the silicon compound particles was changed, good battery characteristics were obtained when the Si (111) crystallite size ranged from 3 nm to 10 nm. When the crystallite size is 10 nm or less, the expansion and contraction of the silicon compound particles accompanying charge / discharge is reduced, and the capacity retention rate is increased. When the crystallite size is 3 nm or more, the improvement rate of the initial efficiency due to insertion of Li is sufficient. Therefore, by keeping the crystallite size within this range, the capacity retention ratio and the initial efficiency can be improved. In Example 3-8, the peak of the Si (111) plane was broad, and the silicon microregion was substantially amorphous.

(Examples 4-1 to 4-4)
A negative electrode active material was produced in the same manner as in Example 1-3, except that the amount of Li insertion into the silicon compound particles was changed. And the battery characteristic was evaluated similarly to Example 1-3.

  When the initial charge / discharge characteristics of the test cells (coin batteries) produced in Examples 4-1 to 4-4 and the capacity retention rate of the laminate film type secondary battery were examined, the results shown in Table 4 were obtained.

  As can be seen from Table 4, the initial efficiency is sufficiently improved when the lithium content is 8% or more. In addition, when the lithium content is 30% or less, a nonaqueous electrolyte secondary battery having a high initial discharge capacity of 1000 mAh / g or more can be produced. Therefore, in order to balance the initial efficiency and the initial discharge capacity, it is preferable to adjust the lithium content therebetween.

(Examples 5-1 to 5-9)
A negative electrode active material was produced in the same manner as in Example 1-3, except that in the thermal Li insertion step, the type and blending mass ratio of Li alone or Li compound and the heating temperature were changed. And the battery characteristic was evaluated similarly to Example 1-3.

  When the initial charge / discharge characteristics of the test cells (coin batteries) produced in Examples 5-1 to 5-9 and the capacity retention rate of the laminate film type secondary battery were examined, the results shown in Table 5 were obtained.

As can be seen from Table 5, as the first lithium source, battery characteristics are better when one of the metals Li, LiH, and Li ₃ N is used. Since these Li sources are highly active and Li insertion occurs smoothly to the inside, they react uniformly to the inside of the silicon compound particles and suppress the growth of silicon crystallites. Therefore, both high initial efficiency and capacity maintenance ratio can be achieved, and battery characteristics are improved. The heating temperature is preferably 400 ° C. or higher and 800 ° C. or lower, and preferably 600 ° C. or higher and 800 ° C. or lower. If heating temperature is 800 degrees C or less, the crystal growth of the silicon in a silicon compound particle can be suppressed, and it can prevent that a cycle maintenance factor deteriorates. When the heating temperature is 400 ° C. or higher, a thermally stable Li compound is generated, and the initial efficiency can be sufficiently improved even when applied to an aqueous slurry.

(Examples 6-1 to 6-5, Comparative Example 6-1)
A negative electrode active material was prepared in the same manner as in Example 1-3, except that the type of the second lithium source was changed in the electrochemical Li insertion step. In Examples 1-3, 6-1, and 6-2, the second lithium source is used as a counter electrode, and in Examples 6-3, 6-4, and 6-5, the second lithium source is used as an electrolyte. Used. And the battery characteristic was evaluated similarly to Example 1-3.

  When the initial charge / discharge characteristics of the test cells (coin batteries) produced in Examples 6-1 to 6-5 and the capacity retention rate of the laminate film type secondary battery were examined, the results shown in Table 6 were obtained.

As can be seen from Table 6, it is better to use one of metallic lithium, transition metal lithium phosphate, (Ni, Co, Mn) lithium oxide, lithium nitrate and lithium halide as the second lithium source. Battery characteristics are good. Metallic lithium, transition metal lithium phosphate, and (Ni, Co, Mn) lithium oxide are excellent in lithium conductivity and electrical conductivity inside the substance, so that a large overvoltage is not applied during electrochemical reforming. This is because side reactions are suppressed. In addition, lithium nitrate and lithium halide are highly soluble in organic solvents, so when these compounds are used as electrolytes, large overvoltages are not applied during electrochemical reforming, and side reactions are suppressed. is there. In Comparative Example 6-1, Li ₂ SO ₄ was used for the electrochemical reforming, but this was not dissolved in the organic solvent, and the electrochemical reforming could not be performed substantially. That is, substantially only the thermal Li insertion step is performed.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

10 ... negative electrode, 11 ... negative electrode current collector, 12 ... negative electrode active material layer,
20 ... Electrochemical Li doping reformer, 21 ... Positive electrode,
22: first lithium-containing silicon compound particles,
23 ... Solvent, 24 ... Separator,
25 ... Powder container, 26 ... Power supply, 27 ... Bathtub,
30 ... Laminated 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 ... adhesion film,
35 ... exterior member.

Claims (11)

A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery comprising silicon compound particles containing lithium,
Preparing silicon compound particles containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6);
The silicon compound particles are mixed with at least one of lithium alone and a lithium compound as a first lithium source and heated to obtain first lithium-containing silicon compound particles;
The said first of the lithium-containing silicon compound particles, using a second source of lithium, it inserts the lithium electrochemical methods, see contains the step of obtaining a second lithium-containing silicon compound particles, the first lithium In the method for producing the negative electrode active material for a non-aqueous electrolyte secondary battery, including a step of forming a carbon film on the silicon compound particles before the step of obtaining the containing silicon compound particles,
Each of the above steps is performed before producing a negative electrode slurry for producing a negative electrode using the produced negative electrode active material for a non-aqueous electrolyte secondary battery, and manufacturing a negative electrode active material for a non-aqueous electrolyte secondary battery Method. In the step of preparing the silicon compound particles, as the silicon compound particles, for a non-aqueous electrolyte secondary battery according to claim 1, characterized in that to prepare those crystallite size of the silicon is 3nm or more 10nm or less A method for producing a negative electrode active material. A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery comprising silicon compound particles containing lithium,
Silicon compound _{(SiO x: 0.5 ≦ x ≦} 1.6) only contains the steps of providing a silicon compound particles crystallite size of the silicon is 3nm or more 10nm or less,
The silicon compound particles are mixed with at least one of lithium alone and a lithium compound as a first lithium source and heated to obtain first lithium-containing silicon compound particles;
The said first of the lithium-containing silicon compound particles, using a second source of lithium, it inserts the lithium electrochemical method, the nonaqueous electrolyte secondary battery and a step of obtaining a second lithium-containing silicon compound particles In a method for producing a negative electrode active material,
Each of the above steps is performed before producing a negative electrode slurry for producing a negative electrode using the produced negative electrode active material for a non-aqueous electrolyte secondary battery, and manufacturing a negative electrode active material for a non-aqueous electrolyte secondary battery Method.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein a lithium content of the second lithium-containing silicon compound particles is 8 mass% or more and 30 mass% or less. For producing a negative electrode active material. A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery comprising silicon compound particles containing lithium,
Preparing silicon compound particles containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6);
The silicon compound particles are mixed with at least one of lithium alone and a lithium compound as a first lithium source and heated to obtain first lithium-containing silicon compound particles;
A second lithium-containing silicon compound in which lithium is inserted into the first lithium-containing silicon compound particles by an electrochemical method using a second lithium source, and the lithium content is 8% by mass or more and 30% by mass or less . In the method for producing the negative electrode active material for a non-aqueous electrolyte secondary battery comprising a step of obtaining particles ,
Each of the above steps is performed before producing a negative electrode slurry for producing a negative electrode using the produced negative electrode active material for a non-aqueous electrolyte secondary battery, and manufacturing a negative electrode active material for a non-aqueous electrolyte secondary battery Method. In the step of obtaining the first lithium-containing silicon compound particles, non-aqueous electrolyte secondary battery negative electrode according to the heating temperature from claim 1, characterized in that a 400 ° C. or higher in any of claims 5 A method for producing an active material. The method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 6 , wherein in the step of obtaining the first lithium-containing silicon compound particles, the heating temperature is 400 ° C. or higher and 800 ° C. or lower. The method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 7 , wherein in the step of obtaining the first lithium-containing silicon compound particles, the heating temperature is set to 600 ° C or higher and 800 ° C or lower. In the step of obtaining the first lithium-containing silicon compound particles, the first metallic lithium as a lithium source, claim from claim 1, which comprises using at least one of lithium hydride and lithium nitride 8 The manufacturing method of the negative electrode active material for nonaqueous electrolyte secondary batteries of any one of these. In the step of obtaining the second lithium-containing silicon compound particles, the second lithium source includes metal lithium, transition metal lithium phosphate, (Ni, Co, Mn) lithium oxide, lithium nitrate, and lithium halide. method of manufacturing a nonaqueous electrolyte negative active material for a secondary battery as claimed in any one of claims 9, characterized by using at least one. A negative electrode active material for a nonaqueous electrolyte secondary battery is produced by the method for producing a negative electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 10 , and the nonaqueous electrolyte secondary battery is used. A method for producing a nonaqueous electrolyte secondary battery, comprising producing a nonaqueous electrolyte secondary battery using an electrode containing a negative electrode active material.

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