Method for producing lithium vanadium oxide and negative electrode active material for lithium ion battery

Abstract

The present invention addresses the problem of providing a method with which it is possible to easily produce a lithium vanadium oxide at a large quantity. This method for producing a lithium vanadium oxide comprises: a first step for generating a lithium vanadium precursor by reacting a vanadium compound, a lithium compound, and a reducing agent in water; and a second step for generating a lithium vanadium oxide by firing the lithium vanadium precursor in an inert atmosphere. As the reducing agent, a substance having a standard electrode potential of 0.375 V / SHE or less is used. Preferably, the vanadium oxide is vanadium pentoxide and the lithium compound is a water-soluble lithium compound.

Description

Method for producing lithium vanadium oxide and negative electrode active material for lithium ion battery

[0001] The present invention relates to a method for producing lithium vanadium oxide. The present invention also relates to a negative electrode active material for a lithium ion battery obtained by said production method.

[0002] Lithium ion batteries are characterized by higher energy efficiency compared to other types of batteries. Lithium ion batteries also have the advantages of less energy loss during charging and discharging, and can efficiently supply power. Therefore, compared with other types of batteries, lithium ion batteries can suppress energy consumption and greatly contribute to the prevention of global warming through carbon dioxide reduction. Since lithium ion batteries do not use harmful substances such as cadmium, lead, and mercury in their materials, they are also advantageous in terms of low environmental impact.

[0003] Graphite is a typical representative of negative electrode active materials for lithium ion batteries. In addition, silicon, Li ４ Ti ５ O １２ and SiO, and the like are also known as negative electrode active materials. In particular, lithium vanadium oxide Li ３ V ２ O ５ has a higher operating potential than graphite, so it can suppress the formation of lithium dendrites that cause short circuits, and has attracted attention as a promising negative electrode active material for realizing lithium ion batteries that enable high-rate charging and discharging.

[0004] Conventionally, Li ３ V ２ O ５ has been produced by electrochemically reducing vanadium pentoxide to insert lithium ions. However, this method is not suitable for industrial mass production. Accordingly, Patent Document 1 proposes a method for producing lithium vanadium oxide by reacting metallic vanadium or a vanadium oxide, lithium hydroxide, and hydrogen peroxide.

[0005] Japanese Patent Application Laid-Open No. 2004-010445

[0006] However, upon examining the contents of Patent Document 1, the inventors found that the method described in that document either does not yield the desired lithium vanadium oxide, or even if it does, the amount is not sufficient for industrial mass production. Therefore, the object of the present invention is to provide a method for easily and in large quantities producing lithium vanadium oxide, which is useful as a negative electrode active material for lithium-ion batteries.

[0007] The present invention provides a method for producing lithium vanadium oxide, comprising: a first step of reacting a vanadium compound, a lithium compound, and a reducing agent in water to produce a lithium vanadium precursor; and a second step of calcining the lithium vanadium precursor in an inert atmosphere to produce lithium vanadium oxide, wherein the reducing agent is a substance having a standard electrode potential of 0.375 V / SHE or less.

[0008] Furthermore, the present invention comprises lithium vanadium oxide and the element carbon, wherein the lithium vanadium oxide has the compositional formula Li ３±ｘ V ２±ｙ O ５±ｚ The present invention provides a negative electrode active material for a lithium-ion battery, which is expressed as (wherein x is a number between 0 and 2, y is a number between 0 and 1, and z is a number greater than 0) and has a carbon element content of 3% by mass or more and 20% by mass or less.

[0009] Figure 1 is the X-ray diffraction pattern of lithium vanadium oxide obtained in Example 1.

[0010] The present invention will be described below based on its preferred embodiments. The present invention relates to a method for producing lithium vanadium oxide, which is useful as an active material for batteries. This lithium vanadium oxide is typically composed of Li ３±ｘ V ２±ｙ O ５±ｚ It is expressed as follows: In the formula, x is a number between 0 and 2 (inclusive), y is a number between 0 and 1 (inclusive), z is a number greater than 0, and [Li ３±ｘ V ２±ｙ This is a number determined by the charge of [the element].

[0011] As described in the section on prior art, lithium vanadium oxide has traditionally been produced by electrochemically reducing vanadium pentoxide and inserting lithium ions. However, this method is not suitable for industrial mass production. Therefore, in this invention, instead of the electrochemical method, a wet process, which is suitable for mass production, is adopted. Along with the wet process, another method suitable for mass production is the solid-phase process, in which a vanadium source compound powder and a lithium source compound powder are mixed and the mixed powder is calcined. However, the solid-phase process requires calcination at high temperatures, for example, 700°C or higher, which has the disadvantage of causing thermal decomposition of the generated lithium vanadium oxide. Although this decomposition product has charge-discharge characteristics, it is unsuitable as a negative electrode material because of its high reaction potential. As will be described later, a calcination process is also performed in the wet process, but the calcination temperature in the wet process can be lower than that in the solid-phase process, thus suppressing the occurrence of thermal decomposition of lithium vanadium oxide.

[0012] In this manufacturing method, the first step involves reacting a vanadium compound, a lithium compound, and a reducing agent in water to produce a lithium vanadium precursor. Examples of vanadium compounds include vanadium oxides and ammonium vanadium salts. Examples of vanadium oxides include pentavalent vanadium oxides. ２ O ５ (Vanadium pentoxide), a tetravalent vanadium oxide VO ２ , and V, which is a trivalent vanadium oxide. ２ O ３ These are some examples. Of these vanadium oxides, V ２ O ５ This is preferably used. Ammonium vanadate is an example of an ammonium salt of vanadium.

[0013] V as vanadium oxide ２ O ５ When using V ２ O ５ It can be used in powder form. ２ O ５The particle size of the powder is determined by the cumulative volume particle size D at 50% of the cumulative volume, as measured by laser diffraction scattering particle size distribution analysis. ５０ Expressed as such, for example, a size of 20 μm or less is preferable from the viewpoint of high reactivity, a size of 10 μm or less is more preferable, and a size of 5 μm or less is even more preferable. Also, V ２ O ５ The powder has a particle size D ５０ However, from the standpoint of ease of handling and cost-effectiveness, it is preferable that the particle size be, for example, 1 μm or larger.

[0014] As the lithium compound, it is preferable to use a water-soluble compound because it facilitates the insertion of lithium ions into the vanadium oxide mentioned above. Examples of water-soluble lithium compounds include lithium hydroxide, lithium halides (e.g., lithium chloride, lithium bromide, lithium fluoride, and lithium iodide), lithium nitrate, and lithium sulfate. These lithium compounds may be used individually or in combination of two or more. Of these lithium compounds, lithium hydroxide is preferred because it can also adjust the pH simultaneously. When lithium hydroxide is used as the lithium compound, it may be in an anhydrous form or a hydrated form. From the viewpoint of handling, lithium hydroxide monohydrate is preferably used industrially.

[0015] The reducing agent is used for the purpose of reducing the vanadium in the vanadium compound described above. From this viewpoint, it is preferable to use a substance that has the reducing ability to reduce the vanadium in the vanadium compound as the reducing agent. In particular, it is preferable to use a substance that has the reducing ability to reduce vanadium (V) in a pentavalent vanadium compound. As a result of the inventors' diligent research on such reducing agents, it was found that it is effective to use a substance having a standard electrode potential of 0.375 V / SHE or less. When the inventors investigated various reducing agents, it was found that when a reducing agent with a high standard electrode potential, such as hydrogen peroxide (0.68 V / SHE), was used, the reduction of the vanadium compound did not proceed successfully, and the target lithium vanadium oxide could not be obtained. Further research by the inventors revealed that by using a reducing agent with a standard electrode potential of 0.375 V / SHE or less, the reduction of the vanadium compound proceeded successfully, and the insertion of lithium ions into the reduced vanadium oxide also proceeded successfully. "SHE" refers to the standard hydrogen electrode potential, which is measured under the conditions of supplying hydrogen gas at 1 atm (101.3 kPa) and having a hydrogen ion concentration of 1 mol / L in an aqueous solution at 25°C. ＋ +2e － ⇔H ２ This refers to the reaction potential.

[0016] As described above, the standard electrode potential of the reducing agent used in the present invention is 0.375 V / SHE or less. The lower limit of the standard electrode potential is preferably -3.045 V / SHE or higher, more preferably -2.500 V / SHE or higher, and even more preferably greater than -1.000 V / SHE.

[0017] Examples of reducing agents having the standard electrode potential described above include ascorbic acid and its salts, hydrazine, and oxalic acid and its salts. These reducing agents may be used individually or in combination of two or more. Examples of ascorbic acid salts include sodium salt and potassium salt. Examples of oxalic acid salts include sodium salt and potassium salt.

[0018] In the present invention, in addition to the reducing agent having the standard electrode potential described above (hereinafter referred to as the "main reducing agent"), a reducing agent that does not have the standard electrode potential described above (hereinafter referred to as the "additional reducing agent") may also be used. Examples of such reducing agents include hydrogen peroxide (0.68 V / SHE) and citric acid (0.571 V / SHE).

[0019] When an additional reducing agent is used in addition to the main reducing agent, the ratio of the number of moles of the main reducing agent to the total number of moles of both is preferably 0.1 or higher, more preferably 0.2 or higher, and even more preferably 0.27 or higher. Furthermore, the ratio of the number of moles of the main reducing agent to the total number of moles of the main reducing agent and the additional reducing agent is preferably 0.9 or lower, more preferably 0.75 or lower, and even more preferably 0.6 or lower. Note that the additional reducing agent may be omitted, and only the main reducing agent may be used.

[0020] In this manufacturing method, there are four main methods for producing a lithium vanadium precursor by reacting a vanadium compound, a lithium compound, and a reducing agent in water. The desired lithium vanadium oxide can be successfully obtained by any of these methods. <Method 1> A reducing agent is added to a vanadium dispersion or aqueous solution obtained by dispersing or dissolving a vanadium compound in water, and a lithium compound is added to the resulting dispersion or aqueous solution. <Method 2> A lithium compound is added to a vanadium dispersion or aqueous solution obtained by dispersing or dissolving vanadium oxide in water, and a reducing agent is added to the resulting dispersion or aqueous solution. <Method 3> A vanadium compound, a lithium compound, and a reducing agent are added together to water. <Method 4> A vanadium compound is added to a lithium dispersion or aqueous solution obtained by dispersing or dissolving a lithium compound in water, and a reducing agent is added to the resulting dispersion or aqueous solution.

[0021] In Method 1, the vanadium compound is dispersed or dissolved in water (this step is referred to as "Step A"). At this time, the water may be in an unheated state (e.g., room temperature) or in a heated state. If the water is heated, the temperature can be set to, for example, 60°C to 100°C. From the viewpoint of efficiently carrying out the reaction, the amount of vanadium compound added is preferably, for example, 0.5% by mass or more relative to the water, more preferably 1% by mass or more, and even more preferably 1.5% by mass or more. From a similar viewpoint, the amount of vanadium compound added is preferably, for example, 20% by mass or less relative to the water.

[0022] Next, while maintaining the temperature of the vanadium compound dispersion or aqueous solution in step A, a reducing agent is added to the dispersion or aqueous solution (this step is referred to as "step B"). From the viewpoint of successfully reducing vanadium, the amount of reducing agent added is preferably 1.0 or more in molar ratio with respect to the vanadium compound, more preferably 1.4 or more, and even more preferably 1.7 or more. Furthermore, from the viewpoint of suppressing excessive reduction of vanadium, the amount of reducing agent added is preferably 4.0 or less in molar ratio with respect to the vanadium compound, more preferably 3.0 or less, and even more preferably 2.3 or less. However, when hydrazine is used as a reducing agent, it may be added in excess of the above molar ratio because hydrazine is oxidized by oxygen in water and decomposed into nitrogen and water. When two or more of the above-mentioned main reducing agents are used as reducing agents, it is preferable that the ratio of the total number of moles of all main reducing agents to the vanadium compound is within the above range. However, hydrazine is not included in the calculation of the molar ratio for the reasons mentioned above. Furthermore, when using the above-mentioned primary reducing agent and additional reducing agent as reducing agents, it is preferable that the ratio of the total number of moles of all primary and additional reducing agents to the vanadium compound is within the range described above.

[0023] In step B, a reducing agent is added to the dispersion or aqueous solution of the vanadium compound, and the dispersion or aqueous solution is stirred for a predetermined time to allow the reduction reaction to proceed. After that, a lithium compound is added to the dispersion or aqueous solution (this step is called "step C"). This inserts lithium ions into the reduced vanadium compound to produce a lithium vanadium precursor. The temperature of the dispersion or aqueous solution in step C can be set to the same temperature as the dispersion or aqueous solution in step A. Preferably, the amount of lithium compound added in step C is adjusted so that the composition ratio of lithium element to vanadium element in the target lithium vanadium oxide is Li ３ V ２ O ５ In this case, it is preferable to add the lithium compound such that the molar ratio of lithium to vanadium is 3:2. Furthermore, since lithium may volatilize and decrease during calcination, the lithium compound may be added in excess of the stoichiometric ratio. For example, it is preferable to add the lithium compound such that the molar ratio of lithium to vanadium is 2:1.

[0024] In Method 1, after adding the lithium compound in step C, that is, during the reaction in which the lithium vanadium precursor is formed, it is preferable to select the type of reducing agent and / or adjust the pH of the reaction solution so that the standard electrode potential of the reaction solution (i.e., the aqueous dispersion) is 0.5 V / SHE or less. For this purpose, it is preferable to select an appropriate reducing agent and / or to select and use an appropriate pH adjusting agent. When lithium hydroxide is used as the lithium compound, the lithium hydroxide also acts as a pH adjusting agent.

[0025] In step C, the standard electrode potential of the reaction solution during the reaction is more preferably 0.4 V / SHE or less, even more preferably 0.3 V / SHE or less, and even more preferably 0.1 V / SHE or less. The lower limit of the standard electrode potential of the reaction solution during the reaction in step C can be -1.0 V / SHE or higher, may be -0.6 V / SHE or higher, or may be -0.3 V / SHE or higher. The standard electrode potential of the reaction solution during the reaction in step C can be measured, for example, using ORP-11 manufactured by Horiba Advanced Techno Co., Ltd.

[0026] The pH of the reaction solution during the reaction in step C is preferably set to 7 or higher, more preferably to 8 or higher, and even more preferably to 10 or higher. Furthermore, the pH of the reaction solution during the reaction in step C is preferably set to 14 or lower.

[0027] In this way, a precipitate of lithium vanadium precursor is obtained. Although the details of this lithium vanadium precursor are not clear, the inventors believe it is an amorphous material containing lithium and vanadium elements.

[0028] In Method 2, the vanadium compound is dispersed or dissolved in water, similar to step A of Method 1. This operation is the same as in Method 1, and the explanation for Method 1 also applies to Method 2.

[0029] Next, while maintaining the temperature of the vanadium compound dispersion or aqueous solution, the lithium compound is added to the dispersion or aqueous solution. This operation corresponds to step C of Method 1. The amount of lithium compound added is the same as in step C of Method 1, and the explanation for step C of Method 1 also applies to Method 2. When lithium hydroxide is used as the lithium compound, the pH of the dispersion or aqueous solution increases (for example, to about 9 to 12), and the vanadium oxide dissolves and VO ４ ３－ Ions may be generated.

[0030] After a predetermined time has elapsed since the addition of the lithium compound, a reducing agent is added to generate a lithium vanadium precursor. This operation corresponds to step B of Method 1. The amount of reducing agent added is the same as in step B of Method 1, and the explanation for step B of Method 1 also applies to Method 2. In Method 2, after the addition of the reducing agent, i.e., during the reaction in which the lithium vanadium precursor is generated, it is preferable to select the type of reducing agent and / or adjust the pH of the reaction solution so that the standard electrode potential of the reaction solution falls within the range described above. For this purpose, it is preferable to select an appropriate reducing agent and / or to select and use an appropriate pH adjusting agent. When ascorbic acid is used as the reducing agent, the ascorbic acid also acts as a pH adjusting agent.

[0031] The preferred range of the standard electrode potential of the reaction solution during the reaction, and the preferred range of the pH of the reaction solution during the reaction, are the same as in Method 1, and the description for Method 1 also applies to Method 2.

[0032] In Method 3, water is placed in a container, similar to Methods 1 and 2, and the vanadium compound, lithium compound, and reducing agent are added together. The amount of vanadium compound used relative to the water, as well as the amounts of lithium compound and reducing agent added, are the same as in Method 1, and the explanation for Method 1 also applies to Method 3.

[0033] In Method 3, after adding the vanadium compound, lithium compound, and reducing agent together, it is preferable to select the type of reducing agent and / or adjust the pH of the reaction solution so that the standard electrode potential of the reaction solution during the reaction in which the lithium vanadium precursor is generated falls within the range described above. For this purpose, it is preferable to select an appropriate reducing agent and / or to select and use an appropriate pH adjusting agent. When ascorbic acid is used as the reducing agent and / or lithium hydroxide is used as the lithium compound, the ascorbic acid and lithium hydroxide also act as pH adjusting agents.

[0034] In Method 4, water is placed in a container and the lithium compound is dispersed or dissolved in the water, similar to Methods 1 to 3. At this time, the water may be unheated (e.g., at room temperature) or heated. If the water is heated, the temperature can be set to, for example, 60°C to 100°C. The amount of lithium compound added is preferably adjusted based on the amount of vanadium compound to be added later, so that the composition ratio of lithium and vanadium elements in the target lithium vanadium oxide is achieved. The amount of lithium compound added is the same as in Method 1, and the explanation for Method 1 also applies to Method 4. Next, while maintaining the temperature of the dispersion or aqueous solution of the lithium compound, the vanadium compound is added to the dispersion or aqueous solution. The amount of vanadium compound used relative to the water is the same as in Method 1, and the explanation for Method 1 also applies to Method 4. After a predetermined time has elapsed since the addition of the vanadium compound, a reducing agent is added to generate a lithium vanadium precursor. The amount of reducing agent added is the same as in Method 1, and the explanation for Method 1 also applies to Method 4. In Method 4, after adding the reducing agent, i.e., during the reaction in which the lithium vanadium precursor is formed, it is preferable to select the type of reducing agent and / or adjust the pH of the reaction solution so that the standard electrode potential of the reaction solution falls within the range described above. For this purpose, it is preferable to select an appropriate reducing agent and / or to select and use an appropriate pH adjuster. When ascorbic acid is used as the reducing agent, the ascorbic acid also acts as a pH adjuster.

[0035] A lithium vanadium precursor is obtained by any of the above methods 1 to 4. Next, the second step is carried out. In the second step, the obtained lithium vanadium precursor is recovered by evaporation to dryness or solid-liquid separation and subjected to a calcination step. The calcination of the lithium vanadium precursor is preferably carried out in an inert atmosphere, such as an argon atmosphere, from the viewpoint of successfully obtaining the target lithium vanadium oxide. The calcination temperature is preferably 200°C or higher from the viewpoint of reliably obtaining the target lithium vanadium oxide, and more preferably 330°C or higher. Furthermore, the calcination temperature is preferably 650°C or lower from the viewpoint of suppressing thermal decomposition of lithium vanadium oxide, more preferably 600°C or lower, and even more preferably 550°C or lower. The calcination time is preferably 30 minutes or more from the viewpoint of reliably obtaining the target lithium vanadium oxide, more preferably 60 minutes or more, and even more preferably 90 minutes or more.

[0036] In this way, the desired lithium vanadium oxide is obtained. As mentioned earlier, this oxide is Li ３±ｘ V ２±ｙ O ５±ｚ It is preferable that it be represented by the following formula. The values ​​of x, y, and z in the formula are as described above. When this lithium vanadium oxide is used as the negative electrode active material of a lithium-ion secondary battery, it has the advantage of enabling rapid charging of the battery and improving its long lifespan. Furthermore, it also has the advantage of having little volume change when lithium ions are intercalated and released.

[0037] The negative electrode active material may contain lithium vanadium oxide and carbon. This is because the lithium vanadium oxide produced by the method of the present invention uses a reducing agent in its production process, and if the reducing agent contains carbon, some of the carbon may be contained in the negative electrode active material together with the lithium vanadium oxide. For example, if an organic acid such as ascorbic acid or oxalic acid is used as the reducing agent, carbon may be contained in the negative electrode active material. Conductive carbon may be added to the negative electrode active material in addition to, or instead of, the carbon derived from the reducing agent. When the negative electrode active material contains carbon, the carbon content relative to the negative electrode active material may be, for example, 3% by mass or more, 5% by mass or more, or 10% by mass or more. On the other hand, the carbon content is preferably, for example, 20% by mass or less, preferably 17% by mass or less, and preferably 15% by mass or less. When an amount of carbon within this range is included in the negative electrode active material, the carbon acts as a reducing agent and can reduce vanadium.

[0038] In a battery using lithium vanadium oxide produced by the method of the present invention as the negative electrode active material, for example, LiFePO4 is used as the positive electrode active material. ４ LiMn ２ O ４ LiNi ０．５ Mn １．５ O ４ LiNi ｘ Co ｙ Mn ｚ O ２ (x+y+z=1), LiCoO ２ LiNi ｘ Co ｙ Al ｚ O ２ (x+y+z=1), LiFe ｘ Mn ｙ PO ４ (x+y=1) and aLiNi ｘ Co ｙ Mn ｚ O2・(1-a)Li ２ MnO ３One or more can be selected from the group consisting of (a = 0 to 1 and x + y + z = 1), and combinations thereof. The electrolyte of the battery may be selected from, for example, solid electrolytes, liquid electrolytes (e.g., non-aqueous electrolytes), polymer gel electrolytes, and ionic liquids, and combinations thereof.

[0039] With respect to the embodiments described above, the present invention further discloses the following methods for producing lithium vanadium oxide and negative electrode active materials for lithium-ion batteries. [1] A method for producing lithium vanadium oxide, comprising: a first step of reacting a vanadium compound, a lithium compound, and a reducing agent in water to produce a lithium vanadium precursor; and a second step of calcining the lithium vanadium precursor in an inert atmosphere to produce lithium vanadium oxide, wherein the reducing agent is a substance having a standard electrode potential of 0.375 V / SHE or less. [2] The method according to [1], wherein the reducing agent is selected such that the standard electrode potential of the reaction solution during the reaction to produce the lithium vanadium precursor is 0.5 V / SHE or less, and the pH of the reaction solution is adjusted. [3] The method according to [1] or [2], wherein the vanadium compound is vanadium oxide, the vanadium oxide is vanadium pentoxide, and the lithium compound is a water-soluble lithium compound. [4] The manufacturing method according to any one of [1] to [3], wherein the reducing agent is selected from the group consisting of ascorbic acid and its salts, oxalic acid and its salts, and hydrazine. [5] The manufacturing method according to any one of [1] to [4], wherein the first step is to add the reducing agent to a vanadium dispersion or aqueous solution obtained by dispersing or dissolving the vanadium compound in water, and to add the lithium compound to the obtained dispersion or aqueous solution. [6] The manufacturing method according to any one of [1] to [5], wherein the first step is to add the lithium compound to a vanadium dispersion or aqueous solution obtained by dispersing or dissolving the vanadium compound in water, and to add the reducing agent to the obtained dispersion or aqueous solution. [7] The manufacturing method according to any one of [1] to [6], wherein the first step is to add the vanadium compound, the lithium compound and the reducing agent together to water. [8] A material comprising lithium vanadium oxide and carbon, wherein the lithium vanadium oxide has the compositional formula Li ３±ｘ V ２±ｙ O ５±ｚA negative electrode active material for a lithium-ion battery, expressed as (wherein x is a number between 0 and 2, y is a number between 0 and 1, and z is a number greater than 0), having a carbon content of 3% by mass or more and 20% by mass or less.

[0040] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0041] [Example 1] 100g of water is placed in a container, and then 1g of V is added to the container. ２ O ５ A dispersion was obtained by adding the powder. ２ O ５ Particle size D ５０ The particle size was 3.9 μm. This dispersion was heated to 60°C, and reducing agent 1, as shown in Table 1, was added. The amount of reducing agent added was V ２ O ５ The amounts shown in Table 1 were used. The pH of the dispersion at this time was approximately 3. After continuing heating for 10 minutes while maintaining the liquid temperature at 60°C, lithium hydroxide monohydrate was added. The amount added was such that there were 3 moles of lithium atoms for every 2 moles of vanadium atoms. The pH of the dispersion rose to approximately 8 after the addition of lithium hydroxide monohydrate. The standard electrode potential of the dispersion at this point was the value shown in Table 1. Heating was continued for another 10 minutes while maintaining the liquid temperature at 60°C to obtain a lithium vanadium precursor. After washing the lithium vanadium precursor recovered by solid-liquid separation with water, it was calcined in a tubular furnace under an argon atmosphere. The calcination conditions were 380°C for 2 hours. In this way, the target lithium vanadium oxide was obtained.

[0042] [Examples 2 to 6] Reducing agent 1 used in Example 1 was replaced with reducing agent 1 and reducing agent 2 shown in Table 1 in the amounts shown in the same table. In addition, the calcination temperature of the lithium vanadium precursor was changed to the temperature shown in the same table. Except for these changes, the same procedure as in Example 1 was followed to obtain the target lithium vanadium oxide.

[0043] [Example 7] Instead of the reducing agent 1 used in Example 1, the amount of reducing agent 1 shown in Table 1 was used as specified in the same table. Except for this, the target lithium vanadium oxide was obtained in the same manner as in Example 1.

[0044] [Example 8] Instead of the reducing agent 1 used in Example 1, the reducing agent 1 shown in Table 1 was used. The amount of reducing agent 1 used was V ２ O ５ , and an excess amount (40 mL) was used relative to said component. Except for this, the target lithium vanadium oxide was obtained in the same manner as in Example 1.

[0045] [Example 9] Instead of the reducing agent 1 used in Example 1, reducing agent 1 and reducing agent 2 shown in Table 1 were used. The amount of reducing agent 1 used was V ２ O ５ , and an excess amount (40 mL) was used relative to said component. Further, the amount of reducing agent 2 shown in the same table was used as specified in the same table. Except for these, the target lithium vanadium oxide was obtained in the same manner as in Example 1.

[0046] [Comparative Example 1] Instead of the reducing agent 1 used in Example 1, the amount of reducing agent 1 shown in Table 1 was used as specified in the same table. Except for this, lithium vanadium oxide was obtained in the same manner as in Example 1.

[0047] [Example 10] 100 g of water was charged into a container, and lithium hydroxide monohydrate was further added into the container to obtain an aqueous solution. The addition amount was such that the amount of lithium atoms was 3 moles per 2 moles of vanadium atoms in 1 g of V ２ O ５ . This aqueous solution was heated to 60°C. The pH of the aqueous solution at this time was about 11. After continuing heating for 10 minutes while maintaining the liquid temperature at 60°C, 1 g of V ２ O ５ powder was added. V ２ O ５ addition lowered the pH of the dispersion to about 10. Reducing agent 1 shown in Table 2 was added to the solution that became colorless and transparent after continuous stirring. The addition amount of the reducing agent was based on V ２ O ５The amounts shown in Table 2 were used therefor. The pH of the dispersion at this time was approximately 7. The standard electrode potential of the dispersion at this point was the value shown in Table 2. Heating was continued for 30 minutes while maintaining the liquid temperature at 60°C, to obtain a lithium vanadium precursor. The lithium vanadium precursor recovered by solid-liquid separation was washed with water, and then fired in a tube furnace under an Ar atmosphere. Firing was performed at 500°C for 2 hours. In this way, the target lithium vanadium oxide was obtained.

[0048] [Examples 11 to 24] Instead of the reducing agent 1 used in Example 1, reducing agent 1 and reducing agent 2 shown in Table 2 were used in the amounts shown in the same table. Further, the firing temperature of the lithium vanadium precursor was changed to the temperature shown in the same table. Except for these, the same procedure as in Example 1 was carried out to obtain the target lithium vanadium oxide.

[0049] [Example 25] 100 g of water was charged into a container, and 1 g of V ２ O ５ powder was added to obtain a dispersion. V ２ O ５ had a particle diameter D ５０ of 3.9 µm. This dispersion was heated to 60°C. The pH of the dispersion at this time was approximately 3. After heating was continued for 10 minutes while maintaining the liquid temperature at 60°C, lithium hydroxide monohydrate was added. The addition amount was an amount such that the amount of lithium atoms was 3 moles per 2 moles of vanadium atoms. The addition of lithium hydroxide monohydrate increased the pH of the dispersion to approximately 9. The standard electrode potential of the dispersion at this point was the value shown in Table 2. While continuing stirring, the reducing agent 1 shown in Table 2 was added to the yellow transparent solution. The addition amount of the reducing agent was the amount shown in Table 2 with respect to V ２ O ５ , and the pH of the dispersion at this time was approximately 11. Heating was continued for 10 minutes while maintaining the liquid temperature at 60°C, to obtain a lithium vanadium precursor. The lithium vanadium precursor recovered by solid-liquid separation was washed with water, and then fired in a tube furnace under an argon atmosphere. Firing was performed at 380°C for 2 hours. In this way, the target lithium vanadium oxide was obtained.

[0050] [Evaluation 1] X-ray diffraction measurements were performed on the lithium vanadium oxide obtained in the examples and comparative examples, and Li ３ V ２ O ５ We checked whether or not diffraction peaks were observed. The results are shown in Tables 1 and 2. Figure 1 shows the X-ray diffraction pattern of lithium vanadium oxide obtained in Example 1.

[0051] [Evaluation 2] Solid-state battery cells were fabricated using lithium vanadium oxide obtained in the examples and comparative examples as the negative electrode active material. The reversible capacity of these solid-state battery cells was measured. The results are shown in Tables 1 and 2. The procedure for fabricating the solid-state battery cells and measuring the reversible capacity is described below.

[0052] (Preparation of negative electrode mixture) The negative electrode active material powder, solid electrolyte powder, and conductive additive were mixed in a mortar in a mass ratio of 60:37:3. (Fabrication of solid battery cell) The lower opening of a polypropylene cylinder (opening diameter 10.5 mm, height 18 mm) with open top and bottom was closed with a working electrode (made of SUS), solid electrolyte powder was placed on top of it, and then closed with a counter electrode (made of SUS), and a solid electrolyte layer was formed by uniaxial pressing at 80 MPa. Next, the working electrode was removed, the negative electrode mixture was placed on top of the solid electrolyte layer and closed again with the working electrode, and then uniaxial pressing at 250 MPa was performed to laminate the negative electrode active material layer and the solid electrolyte layer. After that, the cylinder was inverted, the counter electrode was removed, In-Li foil was placed on top of the solid electrolyte layer and closed again with the counter electrode. Finally, a solid-state battery cell was fabricated by clamping the two electrodes together with a C-clamp, resulting in a stacked negative electrode active material layer, a solid electrolyte layer, and an In-Li layer. The thicknesses of each layer were approximately 40 μm for the negative electrode active material layer, 600 μm for the solid electrolyte layer, and 400 μm for the In-Li layer. All of the above operations were performed in a glove box purged with argon gas at a dew point of -60°C.

[0053] <Measurement of Reversible Capacity> The obtained solid-state battery cell was discharged at 25°C with a constant current of 0.1 mA to -0.61 V, with the termination point being when the voltage reached -0.61 V. Next, it was charged with a constant current of 0.1 mA to 1.38 V. The reversible capacity was determined from this charging capacity.

[0054] [Evaluation 3] The amount of carbon atoms contained in the lithium vanadium oxide obtained in the examples and comparative examples was measured by gas analysis. The results are shown in Tables 1 and 2.

[0055]

[0056] As is clear from the results shown in Tables 1 and 2, according to the method of each example, Li, which is lithium vanadium oxide ３ V ２ O ５ This allows for the successful manufacture of Li obtained in this manner. ３ V ２ O ５ Li was found by X-ray diffraction measurement. ３ V ２ O ５ Since diffraction peaks were observed, or reversible charging and discharging was confirmed, it can be concluded that it is useful as a negative electrode active material for lithium-ion batteries.

[0057] The present invention provides a method for easily and in large quantities producing lithium vanadium oxide. The lithium vanadium oxide obtained by this method is useful as a negative electrode active material for lithium-ion batteries.

Claims

1. A method for producing lithium vanadium oxide, comprising: a first step of reacting a vanadium compound, a lithium compound, and a reducing agent in water to produce a lithium vanadium precursor; and a second step of calcining the lithium vanadium precursor in an inert atmosphere to produce lithium vanadium oxide, wherein the reducing agent is a substance having a standard electrode potential of 0.375 V / SHE or less.

2. The manufacturing method according to claim 1, wherein the reducing agent is selected such that the standard electrode potential of the reaction solution during the reaction to produce the lithium vanadium precursor is 0.5 V / SHE or less, and the pH of the reaction solution is adjusted.

3. The manufacturing method according to claim 1 or 2, wherein the vanadium compound is a vanadium oxide, the vanadium oxide is vanadium pentoxide, and the lithium compound is a water-soluble lithium compound.

4. The manufacturing method according to claim 1 or 2, wherein the reducing agent is selected from the group consisting of ascorbic acid and its salts, oxalic acid and its salts, and hydrazine.

5. The manufacturing method according to claim 1 or 2, wherein the first step is to add the reducing agent to a vanadium dispersion or aqueous solution obtained by dispersing or dissolving the vanadium compound in water, and then add the lithium compound to the resulting dispersion or aqueous solution.

6. The manufacturing method according to claim 1 or 2, wherein the first step is to add the lithium compound to a vanadium dispersion or aqueous solution obtained by dispersing or dissolving the vanadium compound in water, and to add the reducing agent to the resulting dispersion or aqueous solution.

7. The manufacturing method according to claim 1 or 2, wherein the first step is a step of adding the vanadium compound, the lithium compound, and the reducing agent to water all at once.

8. A material comprising lithium vanadium oxide and carbon, wherein the lithium vanadium oxide has the compositional formula Li ３±ｘ V ２±ｙ O ５±ｚ A negative electrode active material for a lithium-ion battery, expressed as (wherein x is a number between 0 and 2, y is a number between 0 and 1, and z is a number greater than 0), having a carbon content of 3% by mass or more and 20% by mass or less.

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