JP2010108603A - Manufacturing method of anode active material for lithium-ion battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of an anode active material stable at storage etc., made of a composite oxide of lithium and transition metal, and capable of reacting under a safe inert atmosphere. <P>SOLUTION: The manufacturing method of the anode active material for lithium-ion battery is such that by adding and calcinating a carbon material during a manufacturing process of a compound, having the composition formula (1): Li<SB>a</SB>V<SB>b</SB>M<SB>c</SB>O<SB>2+d</SB>.... In the formula (1), the values of a, b, c showing the composition ratios should respectively be in the range of: 1≤a≤2.5, 0.5≤b≤1.5, 0≤c≤0.5, 0≤d≤0.5, and M should at least be one selected from among a group consisting of Mg, Al, Cr, Mo, Ti, W and Zr. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a negative electrode active material for a lithium ion battery, and includes adding a specific amount of a specific material such as a carbon material as a material hardly remaining in the finally obtained negative electrode active material, and firing the material. Relates to a method for producing a negative electrode active material of Li-VM composite oxide which can be reacted in an economical and safe inert atmosphere and has a uniform particle size distribution in which abnormal particle growth is suppressed. .

  With the spread of portable small electronic devices in recent years, lithium ion batteries having a higher energy density than other batteries have been actively developed as power sources for such electronic devices.

This lithium ion battery generally uses a carbon material as a negative electrode material, and allows Li ions (Li ⁺ ) to enter and exit between carbon (graphite) layers during charge and discharge. That is, at the time of charging, electrons are sent to the carbon material of the negative electrode, the carbon is negatively charged, and Li ions stored in the positive electrode are desorbed and inserted (intercalated) into the negatively charged carbon material of the negative electrode. . On the other hand, during discharge, Li ions stored in the carbon material of the negative electrode are desorbed (deintercalated) and stored in the positive electrode.

  In recent years, when a carbon material is used for the negative electrode, lithium such as Li—V composite oxide or Li—Ti composite oxide is used instead of the carbon material in order to overcome the disadvantage that the discharge capacity of the lithium ion battery is small. There has been proposed a method of using a composite oxide of a metal and a transition metal as a negative electrode active material (see Patent Document 1).

  However, for example, when Li-V composite oxide is used for the negative electrode, in general, the conventional manufacturing method is synthesized using an inert atmosphere such as argon or nitrogen, or a reducing atmosphere such as nitrogen / hydrogen or argon / hydrogen. Therefore, it is not necessarily a preferable production method from the viewpoint of adjusting the reducing atmosphere in the firing furnace and safety, and is not suitable for mass production of the negative electrode active material (see Patent Document 2-5).

  Furthermore, since it is necessary to set the firing temperature to 1000 ° C. or higher for synthesis, abnormal particle growth is likely to occur, and a broad and broad particle size distribution is obtained, thereby obtaining a lithium ion active material having good characteristics. There was also a problem that it was not possible.

JP-A-6-60867 JP 2006-128115 A JP 2003-68305 A JP 2005-216855 A JP 2002-216753 A

  Therefore, in view of the above problems, the present invention can produce a negative electrode active material comprising a composite oxide of lithium and a transition metal that can be reacted in a safe inert atmosphere and has a uniform particle size distribution. It aims to provide a method.

  As a result of intensive studies, the present inventors, for example, add a specific amount of a substance released outside the system during firing, such as a carbon material, and the additive substance remains in the finally obtained negative electrode active material. Li-VM composite oxide negative electrode active material that can be reacted in a safe inert atmosphere without using a reducing gas atmosphere such as hydrogen. It came to complete invention concerning the manufacturing method of this.

Specifically, the present invention is a method for producing a negative electrode active material for a lithium ion battery, wherein a carbon material is added and calcined in a production process of a compound having the following composition formula (1).
_{Li a V b M c O 2} + d ··· composition formula (1)
(However, in the composition formula (1), the values of a, b, and c indicating the composition ratio are 1 ≦ a ≦ 2.5, 0.5 ≦ b ≦ 1.5, and 0 ≦ c ≦ 0. 5, 0 ≦ d ≦ 0.5, and M is at least one selected from the group consisting of Mg, Al, Cr, Mo, Ti, W, Zr)

Among the raw materials that can be used to produce the compound of the composition formula (1), the raw materials that can be used as the vanadium source are vanadium metal, VO, V ₂ O ₃ , V ₂ O ₄ , V ₂ O ₅ , NH. ₄ VO ₃ etc. Among these, it is desirable to use NH ₄ VO ₃ from the viewpoints of economy, stability, and safety.

Similarly, raw materials that can be used as a lithium source include Li ₂ O, LiCl, LiOH, lithium carbonate (Li ₂ CO ₃ ), lithium acetate, and the like. Among these, it is desirable to use Li ₂ CO ₃ from the viewpoint of economy.

Moreover, as a raw material which can use M element, the oxide containing the metal selected from the group which consists of Mg, Al, Cr, Mo, Ti, W, Zr, or the metal selected from the said group is included. Hydroxides and carbonates can be used. Examples include MgO, MgCO ₃ , Al (OH) ₃ , Al ₂ O ₃ , Cr ₂ O ₃ , MoO ₃ , TiO ₂ , WO ₃ and ZrO ₂ .

  Examples of the carbon material added in the production process of the present invention include carbon black, petroleum pitch, natural graphite, artificial graphite, and flake graphite. However, the carbon material works as a reducing agent during firing, and is released outside the system. For example, it is desirable to use carbon black because it does not remain in the objective compound obtained.

The amount of the carbon material to be added is preferably 0.1 to 5.0 wt% as carbon with respect to the Li-VM composite oxide to be generated. If the amount added is too large, the particle size becomes small and the discharge capacity decreases, which is not preferable. On the contrary, if the addition amount is too small, a large amount of impurities such as Li ₃ VO ₄ presumed to be caused by insufficient reduction action, and ultimately the target crystal structure cannot be sufficiently constituted. The electrical characteristics of the negative electrode active material are not improved.

  Next, details of producing the Li-VM composite oxide in the present invention will be described.

As each constituent metal raw material compound to be used, lithium carbonate (Li ₂ CO ₃ ) is selected as the lithium source, ammonium metavanadate (NH ₄ VO ₃ ) is selected as the vanadium source, titanium is selected as the M metal source, and titanium oxide (TiO ₂ ) is selected. It will be described as being used.

  The raw material compounds are weighed so as to have a predetermined molar ratio, that is, Li: V: Ti = 1.10: 0.89: 0.01, and then mixed. Mixing may be performed by a general dry mixing method, and can be performed using a Henschel mixer, a Proshear mixer, or the like.

  The carbon material that is considered to work as a reducing agent may be mixed at the same time as the lithium source, vanadium source, and titanium source as raw materials, but only the raw materials are mixed first with emphasis on the reaction between the raw metal compounds. After that, it is more preferable to adopt a mixing method divided into two stages in which a carbon material is added and mixed again.

  The amount of carbon material added is in the range of 0.1 to 5.0 wt% as carbon, but considering the balance between reducing properties and the amount of carbon remaining, it is more preferably 0.1 to 2.0 wt%. preferable.

  Next, the mixed powder described above is fired. An atmosphere furnace is used for firing. The type of the furnace may be either a continuous type or a batch type, but in order to avoid the influence of the atmosphere, it is necessary to use a furnace that can be filled or circulated with a specific gas during firing.

The atmosphere gas to be filled in the furnace during firing is He (helium), Ar (argon), N ₂ (nitrogen), inert gas, H ₂ (hydrogen), CO (carbon monoxide), N ₂ / H. reducing gas, such as ₂ mixed gas may be used. When the reducing gas is used, since the reducing power is too strong, each raw material is easily reduced in valence, it is difficult to obtain a target product, and it is difficult to adjust and maintain an optimal reducing atmosphere. In particular, a gas mixed with H ₂ (hydrogen) and CO (carbon monoxide) tends to stay by performing continuous firing, and particle growth is suppressed, so that the target particle size does not grow. It is desirable to use an active N ₂ gas.

  The firing method is preferably a one-step firing method in which firing is completed in one step at a firing temperature of 700 to 1300 ° C., more preferably 1000 to 1300 ° C. First, preliminary firing is performed at 700 to 1300 ° C., and then cooled once Preferably, after crushing using an automatic mortar or the like, there is a two-stage baking method in which the second stage baking is further performed at 1000 to 1300 ° C., and any baking method can be applied in the present invention. .

  The target product can be obtained by only one-step firing, but firing in two steps is more preferable because of excellent uniformity of particles after firing. The reason why the properties of the particles are improved by firing in two stages is not clear, but from direct observation of the particles with an electron microscope of the powder obtained under various conditions, the shape in one firing Although it is non-uniform and there are many variations in powder particles, it is considered that the uniformity of the particles is maintained by performing the second baking, and as a result, the battery performance is improved.

As for the firing temperature, if the temperature is too high, Li scattering is likely to occur, the target crystal structure cannot be obtained, and impurities are also likely to occur. On the other hand, if the temperature is too low, a product having a non-target structure such as Li ₃ VO ₄ is formed, and a product having a target crystal structure cannot be obtained.

  Therefore, the firing temperature when firing is completed in one stage or the second stage firing temperature in the two-stage firing method is preferably in the range of 700 to 1300 ° C, more preferably 1100 to 1200 ° C. The holding time at the firing temperature is suitably 2 to 5 hours. However, the firing temperature in the first stage when firing in two stages is about the generation of impurities, the removal of carbon dioxide gas from the raw material that is thought to affect the particle growth, the particle diameter after the second stage firing, In consideration of the uniformity of the particles, it is preferably in the range of 700 to 1000 ° C.

  The product obtained after firing is then adjusted to a negative electrode active material for a lithium ion battery comprising a Li—V—Ti composite oxide having a desired size by pulverization and classification. In addition, it is preferable that the particle diameter of the powder obtained through the above manufacturing process is generally adjusted to a range of 5 to 50 μm. When filling a battery as a negative electrode material for a lithium ion battery, 10 to 30 μm. It is more preferable to have a uniform particle size distribution.

  Moreover, the lattice constant ratio (c / a) between the a-axis and the c-axis of the powder made of the Li—V—Ti composite oxide obtained through the above manufacturing process is 5.1 to 5.2. preferable.

  If the production method according to the present invention is used, it is possible to increase the reducibility by adding and firing a carbon material, and it is possible to ensure high safety on the production process and to cause abnormal particle growth. A lithium ion negative electrode active material having a suppressed uniform particle size distribution can be produced. In addition, particle control can be performed by increasing or decreasing the amount of carbon material added. Furthermore, since the uniformity of the particles can be further improved by dividing the firing into two stages and introducing a pulverization process after the first stage firing, the performance of the battery to which the negative electrode active material according to the present invention is applied Can be improved.

  Hereinafter, the present invention will be described with reference to examples. In addition, this invention is not limited to the Example shown below, A various change is possible within the range which does not deviate from the technical idea of this invention.

[Example 1]
Production method Ammonium metavanadate (NH ₄ VO ₃ ) (manufactured by STRATCOR), lithium carbonate (Li ₂ CO ₃ ) (manufactured by FMC), titanium oxide (TiO ₂ ) (manufactured by Teika), acetylene black [electricity] Chemical Industries, Ltd.] was mixed with a Henschel mixer to prepare a mixed powder. The mixing molar ratio of the metal compound at the time of mixing is adjusted to be Li: V: Ti = 1.1: 0.89: 0.01, and the amount of the carbon material to be added is based on the expected weight of the final product. 2.0 wt%.

  The mixed powder was fired under a nitrogen atmosphere at a temperature of 800 ° C. and a holding time of 3 hours (first stage firing). Subsequently, the fired product was cooled to room temperature, pulverized in an automatic mortar, and then fired in a nitrogen atmosphere at a temperature of 1200 ° C. and a holding time of 2 hours (second stage firing). The obtained fired product was pulverized and classified to obtain a negative electrode active material.

Measurement Method Physical properties of the obtained substance (negative electrode active material) powder were measured using the following measuring apparatus. Further, in the following examples and comparative examples, the obtained powders were measured, and the results are shown in Table 1.
-X-ray diffractometer: After measuring under the following measurement conditions using X'Pert PRO-MRD PW3040 / 60 manufactured by Panaritical, the c-axis and a-axis lattice constants were calculated.
(45 kV, 40 mA (Cu), angle: 5 to 110 °, scan speed: 0.104446 ° / S, Step size: 0.0083556 °)
-Particle size and particle size distribution: Measured with Microtrac MT-3000 (manufactured by Nikkiso Co., Ltd.). Regarding the particle size, the 50% average particle size (D50) was evaluated, and the variation in particle size was evaluated by the ratio of 90% particle size (D90) and 10% particle size (D10).
Specific surface area: A fully automatic surface area measuring device manufactured by Yuasa Ionics Co., Ltd. Multisorb 12 was used to measure the specific surface area by BET.

[Example 2]
The negative electrode active material was obtained by operating under the same conditions as in Example 1 except that the second stage baking temperature was changed to 1100 ° C.

Example 3
The negative electrode active material was obtained by operating under the same conditions as in Example 1 except that the first stage baking temperature was changed to 1200 ° C. and no pulverization was performed after the first stage baking.

Example 4
The negative electrode active material was obtained by operating under the same conditions as in Example 3 except that the first stage baking temperature was changed to 1000 ° C.

Example 5
The negative electrode active material was obtained by operating under the same conditions as in Example 3 except that the first stage baking temperature was changed to 800 ° C.

Example 17
The negative electrode active material was obtained by operating under the same conditions as in Example 3 except that the first stage baking temperature was changed to 600 ° C.

Example 6
The negative electrode active material was obtained by operating under the same conditions as in Example 3 except that the first stage baking temperature was changed to 1000 ° C.

Example 18
The operation was performed under the same conditions as in Example 5 except that the firing temperature was changed to 1400 ° C. Since the product adhered to the mortar after firing was large and could not be taken out as a powder, the powder physical properties and battery performance were not measured. Note that the fused material was forcibly taken out, pulverized, and analyzed with an X-ray diffractometer. As a result, the crystal structure of the Li—V—Ti composite oxide (which was the target substance) was not constituted.

Example 7
Except changing the calcination temperature to 1100 degreeC, it operated on the conditions similar to Example 5, and obtained the negative electrode active material.

Example 8
The negative electrode active material was obtained by operating under the same conditions as in Example 7 except that the amount of carbon material to be mixed was changed to 5.0 wt%.

Example 9
The negative electrode active material was obtained by operating under the same conditions as in Example 8 except that the amount of carbon material to be mixed was changed to 0.8 wt%.

Example 10
Ammonium metavanadate (NH ₄ VO ₃ ) (manufactured by STRATCOR), lithium carbonate (Li ₂ CO ₃ ) (manufactured by FMC), titanium oxide (TiO ₂ ) (manufactured by Teika), acetylene black [Electrochemical Industry Co., Ltd.] Were mixed with a Henschel mixer to prepare a mixed powder. The mixing molar ratio of the metal compound at the time of mixing was adjusted to be Li: V: Ti = 1.1: 0.87: 0.03, and the amount of the carbon material to be added was based on the expected weight of the final product. 2.0 wt%.

  The mixed powder was fired under a nitrogen atmosphere at a temperature of 800 ° C. and a holding time of 3 hours (first stage firing). Subsequently, the fired product was cooled to room temperature, pulverized in an automatic mortar, and then fired in a nitrogen atmosphere at a temperature of 1200 ° C. and a holding time of 2 hours (second stage firing). The obtained fired product was pulverized and classified to obtain a negative electrode active material.

Example 11
The negative electrode active material was obtained by changing from titanium oxide, which is an M metal source, to basic magnesium carbonate, and performing other operations under the same conditions as in Example 10.

Example 12
The M metal source was changed from titanium oxide to aluminum oxide, and other operations were performed under the same conditions as in Example 10 to obtain a negative electrode active material.

Example 13
The titanium oxide as the M metal source was changed to molybdenum oxide, and other operations were performed under the same conditions as in Example 10 to obtain a negative electrode active material.

Example 14
Chromium oxide was changed from titanium oxide as the M metal source, and the other operations were performed under the same conditions as in Example 10 to obtain a negative electrode active material.

Example 15
The titanium oxide as the M metal source was changed to zirconium oxide, and other operations were performed under the same conditions as in Example 10 to obtain a negative electrode active material.

Example 16
The titanium oxide as the M metal source was changed to tungsten oxide, and other operations were performed under the same conditions as in Example 10 to obtain a negative electrode active material.

Example 20
The negative electrode active material was obtained by operating under the same conditions as in Example 3 except that the second stage baking temperature was changed to 1300 ° C.

Example 21
The negative electrode active material was obtained by operating under the same conditions as in Example 19 except that the firing temperature was 1000 ° C.

[Example 22]
The negative electrode active material was obtained by operating under the same conditions as in Example 19 except that the firing temperature was 1100 ° C.

Example 23
The negative electrode active material was obtained by operating under the same conditions as in Example 19 except that the firing temperature was 1300 ° C.

Example 24
The negative electrode active material was obtained by operating under the same conditions as in Example 19 except that the firing temperature was 900 ° C.

[Comparative Example 1]
An operation was performed under the same conditions as in Example 8 without adding any carbon compound to obtain a negative electrode active material.

Example 19
Ammonium metavanadate (NH ₄ VO ₃ ) (manufactured by STRATCOR), lithium carbonate (Li ₂ CO ₃ ) (manufactured by FMC), titanium oxide (TiO ₂ ) (manufactured by Teika), acetylene black [Electrochemical Industry Co., Ltd.] Were mixed with a Henschel mixer to prepare a mixed powder. The mixing molar ratio of the metal compound at the time of mixing is adjusted to be Li: V: Ti = 1.1: 0.89: 0.01, and the amount of the carbon material to be added is based on the expected weight of the final product. 2.0 wt%.

  The mixed powder was fired under a nitrogen atmosphere under conditions of a temperature of 1200 ° C. and a holding time of 2 hours. The obtained fired product was pulverized and classified to obtain a negative electrode active material.

Electrochemical Evaluation of Negative Electrode Active Material N-methyl is 80% by weight of the negative electrode active material of Example 1, 10% by weight of carbon black as a conductive additive, and 10% by weight of polyvinylidene fluoride (PVDF) as a binder. A slurry was prepared by dissolving in pyrrolidone. This slurry was applied to Cu foil and dried. An evaluation electrode was produced by punching the dried sheet with a punching machine. As the counter electrode, metallic lithium was used, and a Li metal foil punched out was used.

An electrode was formed by sandwiching a polypropylene separator between the evaluation electrode and the counter electrode, and placed in a coin-type battery container. Then, an electrolytic solution in which 1.3 M LiPF ₆ was dissolved was injected into a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of EC: DMC = 3: 7. Then, the coin-type battery for negative electrode active material evaluation of Example 1 was manufactured by sealing a battery container.

  The negative electrode active material obtained in Examples 2 to 17, 19 to 24 and Comparative Example 1 was also subjected to the same operation as described above to produce a negative electrode active material evaluation coin-type battery.

  For each of the batteries configured using the negative electrode active materials of the examples and comparative examples, constant current charging is performed at a charging current of 0.2 C until the end-of-charge voltage is 0 V, and then constant voltage charging is performed for 3 hours. The battery was charged. Thereafter, discharge was performed at a discharge current of 0.2 C until the voltage reached 2.0V. The discharge capacity of each battery at this time is shown in Table 1 together with the production conditions and powder physical properties.

According to the present invention, in the production process of the compound having the following composition formula (1), it is possible to increase the reducibility by adding and baking a carbon material, and as a result, the reaction is performed in a safe inert atmosphere It is possible to provide a method for producing a negative electrode active material of a Li-VM composite oxide that can be produced.
_{Li a V b M c O 2} + d ··· composition formula (1)
(However, in the above composition formula (1), the values of a, b, c indicating the composition ratio are 1 ≦ a ≦ 2.5, 0.5 ≦ b ≦ 1.5, 0 ≦ c ≦ 0. Within the range of 5, 0 ≦ d ≦ 0.5, M is at least one selected from the group consisting of Mg, Al, Cr, Mo, Ti, W, and Zr.)

  Further, as shown in Table 1 above, the properties of the negative electrode active materials of Examples 1 to 17 and 19 to 24 produced by the production method of the present invention are homogenized, and this negative electrode active material is applied. It is understood that the lithium ion battery exhibits extremely excellent battery characteristics (discharge capacity).

Claims (9)

In the manufacturing process of the compound which has the following compositional formula (1), a carbon material is added and baked, The manufacturing method of the negative electrode active material for lithium ion batteries characterized by the above-mentioned.
_{Li a V b M c O 2} + d ··· composition formula (1)
(However, in the composition formula (1), the values of a, b, and c indicating the composition ratio are 1 ≦ a ≦ 2.5, 0.5 ≦ b ≦ 1.5, and 0 ≦ c ≦ 0. 5, 0 ≦ d ≦ 0.5, and M is at least one selected from the group consisting of Mg, Al, Cr, Mo, Ti, W, and Zr.)   The method for producing a negative electrode active material for a lithium ion battery according to claim 1, wherein the amount of the carbon material to be added is 0.1 to 5.0 wt% as carbon with respect to the compound of the composition formula (1).   The method for producing a negative electrode active material for a lithium ion battery according to claim 1, wherein the firing step is one stage, and the firing temperature is 700 to 1300 ° C.   The method for producing a negative electrode active material for a lithium ion battery according to claim 3, wherein the firing temperature is 1000 to 1300 ° C.   4. The negative electrode active material for a lithium ion battery according to claim 3, wherein the firing step is divided into two stages, at least the first stage firing temperature is 700 to 1000 ° C., and the grinding process is performed after the first stage firing. 5. Production method.   The method for producing a negative electrode active material for a lithium ion battery according to claim 5, wherein the firing temperature in the second stage is 1000 to 1300 ° C.   2. The method for producing a negative electrode active material for a lithium ion battery according to claim 1, wherein the obtained compound of the composition formula (1) has a powder particle diameter of 5 to 50 μm. The vanadium raw material for producing the compound of the composition formula (1) is at least one selected from the group consisting of vanadium metal, VO, V ₂ O ₃ , V ₂ O ₄ , V ₂ O ₅ , and NH ₄ VO _3. The manufacturing method of the negative electrode active material for lithium ion batteries of Claim 1 characterized by the above-mentioned. The lithium raw material for producing the compound of the composition formula (1) is at least one selected from the group consisting of Li ₂ O, LiCl, LiOH, and Li ₂ CO _3. Manufacturing method of negative electrode active material for lithium ion battery.