Negative electrode material, lithium ion secondary battery, method for manufacturing negative electrode material, and method for manufacturing lithium ion secondary battery

Abstract

To appropriately place tungsten trioxide on the surface of a carbon.SOLUTION: A negative electrode material is a negative electrode material for a battery and includes amorphous carbon and tungsten trioxide provided on the surface of the amorphous carbon.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a negative electrode material, a lithium ion secondary battery, a method for producing a negative electrode material, and a method for producing a lithium ion secondary battery. [Background technology]

[0002] Carbon is sometimes used as the negative electrode material for lithium-ion secondary batteries. For example, Patent Document 1 describes a negative electrode in which tungsten trioxide is disposed on the surface of graphite. By disposing tungsten trioxide on the surface of graphite, it is possible to improve the diffusibility of lithium ions, thereby improving battery characteristics such as capacity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-45904 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in such negative electrode materials, there is room for improvement in terms of properly disposing tungsten trioxide on the surface of carbon.

[0005] The present invention has been made in view of the above, and has an object to provide an anode material, a battery, a method for manufacturing an anode material, and a method for manufacturing a battery, which are capable of properly disposing tungsten trioxide on the surface of carbon. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the negative electrode material according to the present disclosure is a negative electrode material for a battery, and includes amorphous carbon and tungsten trioxide provided on a surface of the amorphous carbon.

[0007] It is preferable that the tungsten trioxide has a hexagonal crystal structure.

[0008] It is preferable that the tungsten trioxide contains at least one of a monoclinic and a triclinic crystal structure.

[0009] It is preferable that it does not contain graphite.

[0010] To solve the above problems and achieve the objectives, the battery according to the present disclosure includes the above-described negative electrode material and a positive electrode material.

[0011] In order to solve the above-mentioned problems and achieve the object, the method for producing a negative electrode material according to the present disclosure is a method for producing a negative electrode material for a battery, and includes: a dissolving step of adding tungsten trioxide to a dissolving solution to dissolve the tungsten trioxide; an adding step of adding amorphous carbon to the dissolving solution in which the tungsten trioxide has been dissolved to produce an additive solution; and a negative electrode material producing step of producing a negative electrode material by removing a liquid component from the additive solution.

[0012] It is preferable that the ratio of the amount of tungsten trioxide added to the total amount of the amount of tungsten trioxide added and the amount of amorphous carbon added is more than 2 wt % and not more than 8 wt %.

[0013] It is preferable to add the tungsten trioxide having an average particle size of 100 nm or more and 20 μm or less.

[0014] The negative electrode material producing step preferably includes a drying step of drying the additive solution to produce a negative electrode intermediate, and a heating step of heating the negative electrode intermediate.

[0015] In the dissolving step, an alkaline solution is preferably used as the dissolving solution.

[0016] In order to solve the above-mentioned problems and achieve the objectives, the method for manufacturing a battery according to the present disclosure includes the method for manufacturing the negative electrode material and a step of manufacturing a positive electrode material. [Effects of the Invention]

[0017] According to the present invention, tungsten trioxide can be appropriately disposed on the surface of carbon. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic partial cross-sectional view of a battery according to this embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of the negative electrode according to this embodiment. [Figure 3] FIG. 3 is a flowchart illustrating the method for manufacturing the battery of this embodiment. [Figure 4] FIG. 4 is a photograph of the negative electrode material in this example. [Figure 5] FIG. 5 is a photograph of the negative electrode material in this example. [Figure 6] FIG. 6 is a photograph of the negative electrode material in the comparative example. [Figure 7] FIG. 7 is a diagram showing the measurement results of the capacity of the negative electrode using the negative electrode material of this embodiment. [Figure 8] FIG. 8 is a diagram showing the measurement results of the capacity of the negative electrode using the negative electrode material of this embodiment. [Figure 9] FIG. 9 is a diagram showing the measurement results of the capacity of the negative electrode using the negative electrode material of this embodiment. [Figure 10] FIG. 10 is a diagram showing the measurement results of the capacity of the negative electrode using the negative electrode material of this embodiment. [Figure 11] FIG. 11 is a diagram showing the measurement results of the capacity of the negative electrode using the negative electrode material of this embodiment. [Figure 12] FIG. 12 is a diagram showing the measurement results of the capacity of the negative electrode using the negative electrode material of this embodiment. [Figure 13] FIG. 13 is a diagram showing the measurement results of the capacity of the negative electrode using the negative electrode material of this embodiment. [Figure 14] FIG. 14 is a diagram showing the measurement results of the capacity of the negative electrode using the negative electrode material of this embodiment. [Figure 15] FIG. 15 is a diagram showing the measurement results of the capacity of a negative electrode using a negative electrode material of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the following modes for carrying out the invention (hereinafter referred to as embodiments). Furthermore, the components in the following embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

[0020] (battery) FIG. 1 is a schematic partial cross-sectional view of a battery according to this embodiment. The battery 1 according to this embodiment is a lithium-ion secondary battery. The battery 1 includes a casing 10, an electrode group 12, and an electrolyte (not shown). The casing 10 is a case that houses the electrode group 12 and the electrolyte. In addition to the electrode group 12, the casing 10 may also include wiring and terminals connected to the electrode group 12.

[0021] The electrode group 12 includes a negative electrode 14, a positive electrode 16, and a separator 18. The electrode group 12 is configured such that the separator 18 is disposed between the negative electrode 14 and the positive electrode 16. In the example of FIG. 1 , the electrode group 12 has a so-called stacked electrode group structure in which rectangular negative electrodes 14 and rectangular positive electrodes 16 are alternately stacked with a rectangular separator 18 sandwiched therebetween. However, the electrode group 12 is not limited to a stacked electrode group structure. For example, the electrode group 12 may have a wound electrode group structure in which strip-shaped negative electrodes 14 and strip-shaped positive electrodes 16 are stacked with a strip-shaped separator 18 sandwiched therebetween and then wound.

[0022] (Negative electrode) FIG. 2 is a schematic cross-sectional view of a negative electrode according to this embodiment. As shown in FIG. 2, the negative electrode 14 includes a current collecting layer 20 and a negative electrode material layer 22. The current collecting layer 20 is a layer made of a conductive material. An example of the conductive material of the current collecting layer 20 is copper. The negative electrode material layer 22 is a layer containing the negative electrode material according to this embodiment. The negative electrode material layer 22 is provided on the surface of the current collecting layer 20. The thickness of the current collecting layer 20 may be, for example, approximately 15 μm to 40 μm, and the thickness of the negative electrode material layer 22 may be, for example, approximately 20 μm to 200 μm.

[0023] The negative electrode material layer 22 includes a negative electrode material. The negative electrode material includes amorphous carbon and tungsten trioxide provided on the surface of the amorphous carbon. More specifically, the negative electrode material of the negative electrode material layer 22 includes amorphous carbon particles 30, which are particles of amorphous carbon, and WO3 (tungsten trioxide) particles 32, which are particles of tungsten trioxide. Note that the shape of the particles here is not limited to spherical shapes, and may be any shape, such as linear or sheet-like.

[0024] The negative electrode material of the negative electrode material layer 22 includes a plurality of amorphous carbon particles 30. Amorphous carbon is non-crystalline carbon that does not have a crystalline structure, and is carbon that does not have a planar crystalline structure such as graphite or a crystalline structure such as diamond. Amorphous carbon is also called amorphous carbon or diamond-like carbon, and can be said to be carbon with a mixture of sp2 bonds and sp3 bonds.

[0025] The amorphous carbon particles 30 are preferably composed entirely of amorphous carbon and contain no components other than amorphous carbon, except for unavoidable impurities. Specifically, the amorphous carbon particles 30 preferably do not contain graphite.

[0026] The amorphous carbon particles 30 preferably have an average particle size of 1 μm or more and 50 μm or less, and more preferably 1 μm or more and 20 μm or less. When the average particle size is in this range, the strength of the electrode film can be maintained.

[0027] The negative electrode material of the negative electrode material layer 22 includes a plurality of WO3 particles 32. The WO3 particles 32 are provided on the surfaces of amorphous carbon particles 30. More specifically, a plurality of WO3 particles 32 are provided for each amorphous carbon particle 30. The WO3 particles 32 are in close contact with (in contact with) the surfaces of the amorphous carbon particles 30, and more specifically, the WO3 particles 32 and the amorphous carbon particles 30 are composited together. Here, "composite" refers to a state in which the WO3 particles 32 cannot be separated from the amorphous carbon particles 30, at least in the absence of an external force.

[0028] The WO3 particles 32 include those with a hexagonal crystal structure and those with monoclinic and triclinic crystal structures. That is, the negative electrode material includes tungsten trioxide with a hexagonal crystal structure and tungsten trioxide with monoclinic and triclinic crystal structures. However, the negative electrode material may include at least one of tungsten trioxide with a hexagonal crystal structure, tungsten trioxide with a monoclinic crystal structure, and tungsten trioxide with a triclinic crystal structure. In summary, the negative electrode material preferably includes at least one of hexagonal, monoclinic, and triclinic tungsten trioxide, more preferably hexagonal tungsten trioxide and monoclinic or triclinic tungsten trioxide, and even more preferably hexagonal, monoclinic, and triclinic tungsten trioxide. In addition, when the negative electrode material contains tungsten trioxide of other crystal structures, such as monoclinic or triclinic, in addition to hexagonal tungsten trioxide, it is preferable that the content of hexagonal tungsten trioxide be the largest among the tungsten trioxide of each crystal structure. However, the crystal structure of the tungsten trioxide contained in the negative electrode material is not limited to this, and for example, tungsten trioxide of other crystal structures may be contained. Furthermore, the negative electrode material may also contain amorphous tungsten trioxide.

[0029] The average particle size of the WO3 particles 32 is smaller than the average particle size of the amorphous carbon particles 30. The average particle size of the WO3 particles 32 is preferably 100 nm or more and 20 μm or less, and more preferably 100 nm or more and 1 μm or less.

[0030] In this way, the negative electrode material has a structure in which particulate tungsten trioxide (WO3 particles 32) is provided on the surface of amorphous carbon particles 30, but is not limited to this. The negative electrode material may have a structure in which tungsten trioxide is provided on the surface of amorphous carbon, and the shape of the tungsten trioxide provided on the surface of the amorphous carbon may be arbitrary.

[0031] The negative electrode material layer 22 may contain a substance other than the negative electrode material (amorphous carbon particles 30 and WO3 particles 32). The negative electrode material layer 22 may contain, for example, a binder. Any binder material may be used, and examples thereof include polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), and polyacrylic acid (PAA). Only one type of binder may be used, or two or more types may be used in combination. However, it is preferable that the negative electrode material layer 22, in other words, the negative electrode material, does not contain graphite.

[0032] Amorphous carbon and tungsten trioxide can be identified by X-ray diffraction. For example, if the peak waveform in the X-ray diffraction analysis of the object to be analyzed shows the peak waveform of carbon, but the (002) peak waveform in a known graphite structure is broad, the object can be determined to be amorphous carbon. Also, for example, if the position (angle) of the peak in the X-ray diffraction analysis of the object to be analyzed matches the position of the peak in a known tungsten trioxide, the object to be analyzed can be determined to contain tungsten trioxide.

[0033] In addition, the fact that WO3 particles 32 are arranged on the surface of amorphous carbon particles 30 can be confirmed by observing with an electron microscope such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0034] In addition, the average particle size in the present embodiment refers to the average of the primary particle sizes (the diameters of individual particles). The method for measuring the average particle size is arbitrary. For example, it may be measured using SEM photographs.

[0035] (Positive electrode) The positive electrode 16 includes a current collector layer and a positive electrode material layer. The current collector layer of the positive electrode 16 is a layer composed of a conductive member. Examples of the conductive member here include aluminum. The positive electrode material layer is a layer of a positive electrode material and is provided on the surface of the current collector layer of the positive electrode 16. The thickness of the current collector layer of the positive electrode may be, for example, about 10 μm or more and 30 μm or less, and the thickness of the positive electrode material layer may be, for example, about 10 μm or more and 100 μm or less.

[0036] The positive electrode material layer contains a positive electrode material. The positive electrode material contains particles of a lithium compound which is a compound containing lithium. Examples of the lithium compound may include lithium-containing metal oxides and lithium-containing phosphates. More specifically, the lithium compound may be LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi a Co b Mn c O2 (where 0 < a < 1, 0 < b < 1, 0 < c < 1, and a + b + c = 1), LiFePO4, etc. The lithium compound may contain only one type of material or may contain two or more types of materials. In addition, the positive electrode material layer may contain substances other than the positive electrode material. For example, it may contain a binder. The material of the binder may be arbitrary. Examples include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PAA, etc. The binder may be used alone or in combination of two or more.

[0037] (separator) The separator 18 is an insulating member. In this embodiment, the separator 18 is, for example, a porous film made of resin, and examples of the resin include polyethylene (PE) and polypropylene (PP). The separator 18 may also have a structure in which films of different materials are laminated. The separator 18 and the separator 13 may also have a heat-resistant layer. The heat-resistant layer is a layer containing a substance with a high melting point. The heat-resistant layer may contain particles of an inorganic material such as alumina.

[0038] (electrolyte) The electrolyte provided in the battery 1 is a nonaqueous electrolyte. The electrolyte is impregnated into the voids in the electrode group 12. The electrolyte contains, for example, a lithium salt and an aprotic solvent. The lithium salt is dispersed or dissolved in the aprotic solvent. Examples of the lithium salt include LiPF6, LiBF4, Li[N(FSO2)2], Li[N(CF3SO2)2], Li[B(C2O4)2], and LiPO2F2. The aprotic solvent may be, for example, a mixture of a cyclic carbonate and a chain carbonate. Examples of the cyclic carbonate include EC, PC, and butylene carbonate. Examples of the chain carbonate include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

[0039] (Battery manufacturing method) Next, a method for manufacturing the battery 1 according to this embodiment will be described. Fig. 3 is a flowchart illustrating the method for manufacturing the battery according to this embodiment. As shown in Fig. 3, in this manufacturing method, the negative electrode 14 is formed in steps S10 to S16.

[0040] Specifically, the WO3 raw material is added to the dissolving solution, and the WO3 raw material is dissolved in the dissolving solution (step S10; dissolving step). The WO3 raw material is tungsten trioxide, which is used as a raw material for negative electrode materials. The WO3 raw material preferably has an average particle size of, for example, 100 nm or more and 20 μm or less, and more preferably 100 nm or more and 1 μm or less. The dissolving solution is a solution in which the WO3 raw material, i.e., tungsten trioxide, can be dissolved. For example, an alkaline solution is used as the dissolving solution, and in this embodiment, an aqueous ammonia solution is used. The dissolving solution preferably has an ammonia concentration of 5% or more and 30% or less by weight relative to the total dissolving solution.

[0041] The WO3 raw material is produced, for example, by reacting CaWO4 with hydrochloric acid, dissolving it in ammonia, and calcining the crystallized ammonium paratungstate, but may be produced by any method.

[0042] In step S10, the ratio of the amount of WO3 raw material added to the amount of ammonia contained in the dissolving solution is preferably set to 1% or more and 10% or less in mole percent. By setting the ratio of the WO3 raw material added to 1% or more, the amount of tungsten trioxide in the dissolving solution can be sufficient, and by setting the ratio of the WO3 raw material added to 10% or less, the amount of tungsten trioxide remaining undissolved can be prevented. Furthermore, in step S10, the WO3 raw material is added to the dissolving solution and stirred for a predetermined time, thereby dissolving the WO3 raw material in the dissolving solution. Here, the predetermined time is preferably set to 6 hours or more and 24 hours or less. Setting the predetermined time to 6 hours or more allows the WO3 raw material to be appropriately dissolved in the dissolving solution, and setting the predetermined time to 24 hours or less prevents the production time from being too long.

[0043] Next, an amorphous carbon raw material is added to the dissolving solution (here, an ammonium tungstate solution) in which the WO3 raw material has been dissolved, to generate an additive solution (step S12; adding step). The amorphous carbon raw material is amorphous carbon used as a raw material. The amorphous carbon raw material preferably has an average particle size of 1 μm or more and 50 μm or less, and more preferably 1 μm or more and 20 μm or less. By setting the average particle size of the amorphous carbon raw material within this range, it is possible to increase the capacity of the battery.

[0044] The amorphous carbon raw material may be produced, for example, by an oil furnace method. In the oil furnace method, for example, a raw material oil is sprayed into a high-temperature atmosphere to cause thermal decomposition, and then the mixture is rapidly cooled to produce a particulate amorphous carbon raw material. However, the method for producing the amorphous carbon raw material is not limited to this and may be any method.

[0045] Here, the ratio of the amount of WO3 raw material added to the total amount of the WO3 raw material and the amorphous carbon raw material added when adding the WO3 raw material and the amorphous carbon raw material to the dissolution solution is referred to as the WO3 raw material addition ratio. In this manufacturing method, the WO3 raw material addition ratio is preferably greater than 2% and less than or equal to 8%, and more preferably greater than or equal to 5% and less than or equal to 8%, by weight. By setting the WO3 raw material addition ratio within this range, WO3 particles 32 can be appropriately formed on the surfaces of the amorphous carbon particles 30, and the resulting negative electrode can increase the battery capacity.

[0046] In step S12, the dissolving solution in which the WO3 raw material is dissolved and the amorphous carbon raw material is added, i.e., the additive solution, is stirred to disperse the amorphous carbon raw material in the additive solution. In step S12, a surfactant may be added to the additive solution to improve the affinity between the amorphous carbon raw material and WO3. Sodium dodecyl sulfate (SDS) may be used as the surfactant. The amount of surfactant added is preferably greater than 2% and less than or equal to 8% by weight of the amount of WO3 raw material added to the dissolving solution. By setting the amount within this range, the affinity between the amorphous carbon raw material and WO3 is appropriately improved.

[0047] Next, the liquid component of the additive solution is removed to produce a negative electrode material (negative electrode material production step). In this embodiment, steps S14 and S16 are executed as the negative electrode material production step. Specifically, the additive solution is dried to produce a negative electrode intermediate (step S14; drying step). In step S14, the additive solution is dried in the atmosphere at 80°C for 12 hours to remove, i.e., evaporate, the liquid component contained in the additive solution. It can be said that the negative electrode intermediate contains the solid component remaining after the liquid component of the additive solution has been removed.

[0048] Next, the negative electrode intermediate is heated to produce a negative electrode material (step S16; heating step). By heating the negative electrode intermediate, a negative electrode material is formed in which WO3 particles 32 are provided on the surfaces of amorphous carbon particles 30. The temperature to which the negative electrode intermediate is heated is preferably 500°C or higher and 900°C or lower. By setting the temperature to which the negative electrode intermediate is heated within this range, the negative electrode material can be properly formed. Furthermore, the time to which the negative electrode intermediate is heated is preferably 1 hour or higher and 10 hours or lower. By setting the heating time of the negative electrode intermediate within this range, the negative electrode material can be properly formed.

[0049] Next, the negative electrode 14 is formed using the formed negative electrode material (step S18). That is, the negative electrode 14 is formed by forming a negative electrode material layer 22 containing the negative electrode material on the surface of the current collecting layer 20.

[0050] This manufacturing method also includes forming the positive electrode 16 (step S20). In step S20, the positive electrode material is formed in the same manner as steps S10 to S16, except that a lithium compound raw material, which is a lithium compound, is used instead of the amorphous carbon raw material. Then, a positive electrode material layer containing the positive electrode material is formed on the surface of the current collecting layer for the positive electrode 16, thereby forming the positive electrode 16.

[0051] After the negative electrode 14 and the positive electrode 16 are formed, the negative electrode 14 and the positive electrode 16 are used to manufacture the battery 1 (step S22). Specifically, the negative electrode 14, the separator 18, and the positive electrode 16 are stacked together to form the electrode group 12, and the electrode group 12 and the electrolyte are housed in the casing 10 to manufacture the battery 1.

[0052] As described above, in this embodiment, as shown in steps S10 to S16, the negative electrode material is produced by adding amorphous carbon to a dissolving solution containing dissolved tungsten trioxide and then removing the liquid component. Hereinafter, this method of producing a negative electrode material will be referred to as a solution method where appropriate. However, the method of producing a negative electrode material in this embodiment is not limited to the solution method. For example, instead of the solution method, the negative electrode material may be produced using a ball mill method, a spray drying method, a CVD method, or the like. The ball mill method is a method of producing a negative electrode material by adding amorphous carbon and tungsten trioxide to a ball mill and rotating the ball mill at a predetermined rotation speed for a predetermined time. The spray drying method is a method of producing a negative electrode material by adding amorphous carbon to a dissolving solution containing dissolved tungsten trioxide and spraying and drying the dissolving solution. The CVD method is a method of producing a negative electrode material by drying the dissolving solution containing dissolved tungsten trioxide, placing it in a CVD furnace together with amorphous carbon, and performing chemical vapor deposition at a predetermined temperature. Similarly, the method for producing the positive electrode material is not limited to the solution method, and any method such as a method using a ball mill, a spray drying method, or a CVD method may be used.

[0053] As described above, the negative electrode material of the battery according to this embodiment includes amorphous carbon and tungsten trioxide provided on the surface of the amorphous carbon. The negative electrode material according to this embodiment can improve battery characteristics such as capacity by providing tungsten trioxide on the carbon surface. Furthermore, in a negative electrode material having tungsten trioxide provided on the carbon surface, it is necessary to appropriately dispose the tungsten trioxide on the carbon surface. If the tungsten trioxide cannot be appropriately disposed on the carbon surface, i.e., if tungsten trioxide is not provided on the carbon surface or if tungsten trioxide is detached from the carbon surface, the battery characteristics cannot be appropriately improved. In contrast, the negative electrode material according to this embodiment uses amorphous carbon as the carbon and provides tungsten trioxide on the amorphous carbon surface. The amorphous carbon can contain functional groups on its surface during the process of disposing tungsten trioxide on its surface. Therefore, these functional groups enable tungsten trioxide to be appropriately trapped on the amorphous carbon surface, ensuring appropriate disposition of tungsten trioxide on the surface. Furthermore, this functional group can increase the adhesion of tungsten trioxide to the amorphous carbon surface, thereby preventing tungsten oxide from being separated from the carbon surface. Therefore, the negative electrode material according to this embodiment can appropriately arrange tungsten trioxide on the carbon surface. Furthermore, by using a negative electrode material in which tungsten trioxide is provided on the amorphous carbon surface as in this embodiment, it is possible to improve the capacity, particularly during high current charging and discharging, and thus improve the battery characteristics. In particular, because amorphous carbon raw materials are produced at lower temperatures than, for example, graphite, the functional groups are more likely to remain without being removed, allowing tungsten trioxide to be appropriately arranged on the surface.

[0054] Furthermore, the negative electrode material according to this embodiment preferably contains tungsten trioxide having a hexagonal crystal structure, and more preferably contains tungsten trioxide having at least one of a monoclinic and a triclinic crystal structure. By providing hexagonal, monoclinic, or triclinic tungsten trioxide on the surface of amorphous carbon, it is possible to appropriately arrange tungsten trioxide on the surface of the carbon.

[0055] Furthermore, the negative electrode material according to this embodiment preferably does not contain graphite. By using amorphous carbon without graphite, tungsten trioxide can be appropriately arranged on the surface of the carbon.

[0056] The method for producing a negative electrode material according to this embodiment includes a dissolving step, an adding step, and a negative electrode material producing step. In the dissolving step, tungsten trioxide (tungsten trioxide raw material) is added to a dissolving solution to dissolve the tungsten trioxide raw material. In the adding step, amorphous carbon (amorphous carbon raw material) is added to the dissolving solution in which tungsten trioxide has been dissolved to produce an additive solution. In the negative electrode material producing step, the liquid component of the additive solution is removed to produce the negative electrode material. In this way, the method for producing a negative electrode according to this embodiment adds amorphous carbon to the dissolving solution in which tungsten trioxide has been dissolved to produce the negative electrode material, thereby making it possible to appropriately arrange tungsten trioxide on the surface of the carbon.

[0057] In the method for producing a negative electrode material according to this embodiment, the ratio of the amount of tungsten trioxide added to the total amount of tungsten trioxide and amorphous carbon added is preferably more than 2 wt % and not more than 8 wt %. By setting the amount of tungsten trioxide added within this range, tungsten trioxide can be appropriately formed on the surface of the amorphous carbon, and the battery characteristics can be improved as a negative electrode.

[0058] In the method for producing a negative electrode material according to this embodiment, it is preferable to add tungsten trioxide having an average particle size of 100 nm to 20 μm. By using tungsten trioxide with such a particle size, tungsten trioxide can be appropriately formed on the surface of the amorphous carbon, and the battery characteristics can be improved when used as a negative electrode.

[0059] Furthermore, the negative electrode material producing step preferably includes a drying step of drying the additive solution to produce a negative electrode intermediate, and a heating step of heating the negative electrode intermediate. By producing the negative electrode material by heating the negative electrode intermediate formed by drying the additive solution, tungsten trioxide is appropriately formed on the surface of the amorphous carbon, and the negative electrode can be used as a negative electrode to improve battery characteristics.

[0060] In the dissolving step, it is preferable to use an alkaline solution as the dissolving solution, since the alkaline solution can dissolve tungsten trioxide appropriately.

[0061] (Example) (Manufacturing conditions) Next, examples will be described. In Examples 1 and 2, anode materials were produced using amorphous carbon and tungsten trioxide by the solution method described in the embodiment. Specifically, 5 ml of a 28% ammonia solution and WO3 raw material were added to a 50 ml beaker and stirred for 12 hours to dissolve the WO3 raw material in the ammonia solution. Then, amorphous carbon raw material and 5 ml of pure water were added to the ammonia solution. Furthermore, SDS was also added to the ammonia solution so that the weight ratio of SDS to the WO3 raw material was 1:1. Then, the ammonia solution was stirred and then dried to produce anode intermediates. Then, the anode intermediates were introduced into a tubular furnace and heated at 700°C for 2 hours under an argon atmosphere to produce anode materials.

[0062] In Example 1, the WO3 raw material ratio, i.e., the amount of WO3 raw material added relative to the total amount of the amorphous carbon raw material and the WO3 raw material added, was 5% by weight. In Example 1, the amount of WO3 raw material added was 0.05 g, and the amount of amorphous carbon raw material added was 0.95 g. In Example 2, the WO3 raw material ratio was 8% by weight. In Example 2, the amount of WO3 raw material added was 0.08 g, and the amount of amorphous carbon raw material added was 0.92 g.

[0063] In Example 3, an anode material was produced using amorphous carbon and tungsten trioxide by a method using a ball mill. In Example 3, the WO3 raw material ratio was 5% by weight. Specifically, in Example 3, 0.05 g of WO3 raw material and 0.95 g of amorphous carbon raw material were added to a ball mill (PULVERISETTE 7 manufactured by Fritsch) and rotated at 500 rpm for 8 hours to produce the anode material.

[0064] In Example 4, an anode material was produced by spray drying using amorphous carbon and tungsten trioxide. In Example 4, the WO3 raw material ratio was 5% by weight. Specifically, 0.05 g of WO3 raw material was dissolved in a 28% ammonia solution, and 0.95 g of amorphous carbon raw material was added. SDS was added to the ammonia solution so that the weight ratio of SDS to the WO3 raw material was 1:1, and 95 ml of pure water was also added. The ammonia solution was stirred and spray-dried using a Buchi B-290 spray dryer. The spray-drying temperature was 180°C, and the ammonia solution spray-drying rate was 1 ml / min. The spray-dried sample was then heated at 700°C for 2 hours to produce an anode material.

[0065] In Example 5, an anode material was produced by CVD using amorphous carbon and tungsten trioxide. Specifically, in Example 5, a WO3 raw material was dissolved in a 28% ammonia solution, and the ammonia solution was evaporated to dryness. 1 g of the evaporated and dried sample and 50 mg of the amorphous carbon raw material were placed in a CVD furnace, and the temperatures were set to 850°C and 600°C, respectively, to perform chemical vapor deposition for 2 hours to produce the anode material.

[0066] In the comparative example, a negative electrode material was produced by a solution method using graphite and tungsten trioxide. In the comparative example, the amount of WO3 raw material added was 5% by weight relative to the total amount of graphite and WO3 raw material added. In the comparative example, a negative electrode material was produced by the same method as in Example 1, except that graphite was used instead of the amorphous carbon raw material.

[0067] (Anode material evaluation results) The negative electrode materials produced by the methods of Examples 1 to 5 and the Comparative Example were evaluated. For the evaluation, the negative electrode materials were imaged using an SEM to observe whether a WO3 material was provided on the surface of the carbon. Furthermore, XRD was used to confirm whether peaks corresponding to carbon and tungsten trioxide were present. Furthermore, negative electrodes were produced using the negative electrode materials, and the capacity was measured after repeated charging and discharging.

[0068] FIG. 4 is a diagram of an image of the negative electrode material in this example. FIG. 4 shows photographs of the negative electrode materials of Examples 1 and 2 taken with an SEM. As shown in FIG. 4, the SEM photograph confirmed that WO3 particles 32 were provided on the surfaces of amorphous carbon particles 30 in the negative electrode material of Example 1. The SEM photograph confirmed that WO3 particles 32 were provided on the surfaces of amorphous carbon particles 30 in the negative electrode material of Example 2. In XRD, peaks of amorphous carbon and tungsten trioxide were confirmed in Examples 1 and 2.

[0069] FIG. 5 is a diagram of an image of the negative electrode material in this example. FIG. 5 shows photographs of the negative electrode materials of Examples 3 to 5 taken with an SEM. As shown in FIG. 5, the SEM photograph confirmed that WO particles 32 were provided on the surface of the amorphous carbon particles 30 in the negative electrode material of Example 3. The SEM photograph confirmed that WO particles 32 were provided on the surface of the amorphous carbon particles 30 in the negative electrode material of Example 4. The SEM photograph confirmed that WO particles 32 were provided on the surface of the amorphous carbon particles 30 in the negative electrode material of Example 5. In XRD, amorphous carbon peaks and tungsten trioxide peaks were confirmed in Examples 3 and 5, while in Example 4, an amorphous carbon peak was confirmed, but no clear tungsten trioxide peak was confirmed. However, the TEM photograph confirmed that an amorphous tungsten trioxide layer was provided on the surface of the amorphous carbon particles 30 in the negative electrode material of Example 4.

[0070] Fig. 6 is an image of the negative electrode material of the comparative example. Fig. 6 shows a photograph of the negative electrode material of the comparative example taken with an SEM. As shown in Fig. 6, the SEM photograph confirmed that the negative electrode material of the comparative example had relatively large WO3 particles 32 provided on the surface of the graphite.

[0071] Next, we will explain the results of measuring the capacity of a negative electrode using the negative electrode materials of the examples and comparative examples when they were repeatedly charged and discharged. Figures 7 to 14 are diagrams showing the results of measuring the capacity of a negative electrode using the negative electrode material of this embodiment. Figure 7 is a graph showing the results of measuring the capacity of the negative electrode for each cycle when the C-rate was changed for each predetermined number of cycles for Examples 1 and 2. The C-rate is the ratio of the discharge (charge) current value to the battery capacity (here, the capacity of the negative electrode). For example, if a negative electrode with a capacity of 10 Ah at the zeroth cycle is discharged at a C-rate of 1 C, this means that the current is discharged at 10 A. Here, one cycle refers to discharging to zero capacity at the set C-rate, followed by charging to the maximum capacity. The horizontal axis of Figure 7 represents the number of cycles (number of charge / discharge cycles), and the vertical axis represents the capacity (mAh / g) of the negative electrode per gram when discharged and then charged to the maximum capacity. FIG. 7 shows the capacity for each cycle when discharge and charge were repeated 30 times at 0.2C, discharge and charge were repeated 5 times at 0.4C, discharge and charge were repeated 5 times at 0.8C, discharge and charge were repeated 5 times at 1.6C, discharge and charge were repeated 5 times at 3.2C, and discharge and charge were repeated 5 times at 0.2C.

[0072] Figure 7 also shows test results for the negative electrode materials of Examples 1 and 2, as well as test results for the negative electrode material containing only amorphous carbon, i.e., no tungsten trioxide. As shown in Figure 7, when tungsten trioxide is provided on the surface of amorphous carbon, as in Examples 1 and 2, it is clear that the capacity tends to be maintained higher than when no tungsten trioxide is provided. Furthermore, when charging and discharging at a high current of 3.2 C, it is clear that the capacity can be maintained highest when using Example 1, i.e., when the WO3 raw material ratio is 5%.

[0073] Figure 8 is a graph showing the capacity per cycle when charging and discharging were repeated at a fixed C rate of 0.8 C for Examples 1 and 2. As shown in Figure 8, it can be seen that Example 1, in which the WO3 raw material ratio was 5%, was able to maintain the highest capacity even after repeated cycles.

[0074] 9 is a graph showing the results of measuring the capacity of the negative electrode for each cycle when the C rate was changed every predetermined number of cycles when the negative electrode material of Example 3 was used. The conditions for changing the C rate were the same as those in FIG. 7. As shown in FIGS. 7 and 9, it can be seen that Example 3 can maintain a higher capacity at 3.2 C than the case where tungsten trioxide is not included.

[0075] Fig. 10 is a graph showing the capacity per cycle when the negative electrode material of Example 3 was used and charging and discharging were repeated at a fixed C rate of 0.8 C. As shown in Figs. 8 and 10, in Example 3, the capacity with repeated cycles was not lower than that in the case where tungsten trioxide was not included.

[0076] Fig. 11 is a graph showing the measurement results of the negative electrode capacity for each cycle when the C rate was changed every predetermined number of cycles when the negative electrode material of Example 4 was used. The conditions for changing the C rate were the same as those in Fig. 7. As shown in Figs. 7 and 11, it can be seen that in Example 4, the capacity at 3.2 C can be maintained higher than when tungsten trioxide is not included.

[0077] Fig. 12 is a graph showing the capacity per cycle when the negative electrode material of Example 4 was used and charging and discharging were repeated at a fixed C rate of 0.8 C. As shown in Figs. 8 and 12, in Example 4, the capacity with repeated cycles was not lower than that in the case where tungsten trioxide was not included.

[0078] Fig. 13 is a graph showing the measurement results of the negative electrode capacity for each cycle when the C rate was changed every predetermined number of cycles when the negative electrode material of Example 5 was used. The conditions for changing the C rate were the same as those in Fig. 7. As shown in Figs. 7 and 13, in Example 5, the capacity at 3.2 C was not lower than when tungsten trioxide was not included.

[0079] Fig. 14 is a graph showing the capacity per cycle when the negative electrode material of Example 5 was used and charging and discharging were repeated at a fixed C rate of 0.8 C. As shown in Figs. 8 and 14, in Example 5, the capacity with repeated cycles was not lower than that in the case where tungsten trioxide was not included.

[0080] FIG. 15 is a graph showing the measurement results of the negative electrode capacity for each cycle when the C rate was changed every predetermined number of cycles when a comparative negative electrode material was used. The conditions for changing the C rate were the same as those in FIG. 7. As shown in FIG. 15, the capacity at 3.2 C in the comparative example is lower than that in the case where graphite was included but tungsten trioxide was not. Furthermore, as shown in FIGS. 7, 9, 11, 13, and 15, the capacity at 3.2 C in the comparative example is lower than that in each example. Therefore, it can be seen that the comparative example is unable to properly retain tungsten trioxide on the carbon surface compared to this embodiment, and therefore is unable to increase the capacity during high-current charge / discharge. In other words, it can be seen that using amorphous carbon as in this embodiment allows tungsten trioxide to be properly retained on the amorphous carbon surface, thereby increasing the capacity, especially during high-current charge / discharge.

[0081] Although the embodiments of the present invention have been described above, the embodiments are not limited to the contents of these embodiments. Furthermore, the above-described components include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the scope of what is called equivalents. Furthermore, the above-described components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the above-described embodiments. [Explanation of symbols]

[0082] 1 battery 14 Negative electrode 22 Negative electrode material layer 30 amorphous carbon particles 32 WO3 particles

Claims

1. A battery negative electrode material, It is produced by drying and heating an additive solution in which amorphous carbon raw material is dispersed in a dissolving solution in which tungsten trioxide raw material is dissolved. The amorphous carbon particle includes a tungsten trioxide particle provided on the surface of the amorphous carbon particle, The amorphous carbon particles and the tungsten trioxide particles are composited together. Anode material.

2. 2. The negative electrode material according to claim 1, wherein a ratio of the amount of the tungsten trioxide raw material added to the total amount of the tungsten trioxide raw material added and the amorphous carbon raw material added is more than 2 wt % and not more than 8 wt %.

3. 10. The negative electrode material of claim 1, which is graphite-free.

4. 10. The negative electrode material of claim 1, comprising the tungsten trioxide particles in a hexagonal crystal structure.

5. 2. The negative electrode material according to claim 1, comprising tungsten trioxide particles having at least one of a monoclinic and a triclinic crystal structure.

6. A lithium ion secondary battery comprising the negative electrode material according to any one of claims 1 to 5 and a positive electrode material.

7. A method for producing a negative electrode material for a battery, comprising: an adding step of adding an amorphous carbon raw material to an ammonium tungstate solution to form an additive solution; a drying step of drying the additive solution to obtain a negative electrode intermediate; a heating step of heating the negative electrode intermediate to produce a negative electrode material including amorphous carbon particles and tungsten trioxide particles provided on the surfaces of the amorphous carbon particles; Including, A method for producing anode materials.

8. A method for producing a lithium ion secondary battery, comprising the method for producing a negative electrode material according to claim 7 and a step of producing a positive electrode material.

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