JP5207589B2 - Method for producing negative electrode active material for lithium secondary battery - Google Patents

Description

  The present invention relates to a method for producing a negative electrode active material for a lithium secondary battery, and more particularly to a method for producing a negative electrode active material for a lithium secondary battery using a wet mixing method.

2. Description of the Related Art Lithium (Li) secondary batteries having a high energy density that is small and light and has a low environmental impact have been developed as power sources for driving portable electronic devices. This lithium secondary battery has a structure in which a positive electrode active material and a negative electrode active material sandwich a separator having an electrolytic solution, and lithium ions (Li ⁺ ) are intercalated (intercalated) into the negative electrode active material. It is discharged when it is deintercalated (interlayer desorption) from the negative electrode active material, and can be reused by repeating this charge / discharge.

However, when the charge / discharge cycle is increased, acicular lithium (Li) crystals (dendrites) are deposited on the surface of the negative electrode active material, or the dendrites are peeled off from the current collector to cause a short circuit inside the battery, There may be a problem that the life of the battery is shortened or the cycle characteristics are deteriorated.
For this reason, the carbon material which does not have the above problems is used as a negative electrode active material in a practical battery. Among these, a typical one is a graphite-based carbon material, but since the capacity per volume is small, it is difficult to improve the performance particularly as a portable electronic device.

  Further, although alloy systems such as silicon (Si) and tin (Sn) have been studied, there are problems that expansion during charging is large and cycle deterioration is large. In addition, this alloy-based negative electrode active material has a higher potential compared to Li than carbon, and as a battery, it may be difficult to increase the capacity and voltage.

In addition, Li _X V _Y O ₂ synthesized from an oxide raw material as a negative electrode active material different from these has been reported, but there are problems in cycle characteristics, rate characteristics, and the like.

  This invention is made | formed based on recognition of this subject, The objective is to provide the manufacturing method of the negative electrode active material for lithium secondary batteries with a more uniform composition.

According to one embodiment of the present invention, each organic salt of Li, V, and Me (Me is one of transition metals other than V, alkali metal, alkaline earth metal, or a mixture thereof) is added to a: b. A step of forming an organic acid salt mixture at a molar ratio of: c, a step of forming a mixed aqueous solution in which a reducing agent is added to the organic acid salt mixture, and a step of drying the mixed aqueous solution to form an organic acid salt precursor And Li _a V _b Me _C O ₂ (1.0 ≦ a ≦ 1.25, 0.75 ≦ b ≦ 1,0 ≦) by firing the organic acid salt precursor in a nitrogen or inert gas atmosphere. and a step of forming a composite oxide represented by the composition formula c ≦ 0.1). A method for producing a negative electrode active material for a lithium ion secondary battery is provided.

In the present invention, a step of forming an organic acid salt mixture of each organic acid salt of Li, V, and Me at a molar ratio of a: b: c, and a mixed aqueous solution in which a reducing agent is added to the organic acid salt mixture. The step of forming and the step of drying the mixed aqueous solution to form the organic acid salt precursor enable uniform mixing, and a mixed powder having a uniform composition can be prepared. Li _a V _b Me _c O ₂ (1.0 ≦ a ≦ 1.25, 0.75 ≦ b ≦ 1, 0 ≦ c ≦ 0.1) by firing in a nitrogen or inert gas atmosphere The method of manufacturing the homogenized negative electrode active material for secondary batteries is obtained by performing the process of forming complex oxide represented by these.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the negative electrode active material for lithium secondary batteries with a more uniform composition by the wet mixing system using an organic acid is provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a flowchart showing a method for manufacturing a negative electrode active material of a lithium secondary battery according to this embodiment.

FIG. 2 is a partial cross-sectional view illustrating the main part of the lithium secondary battery 5 using the negative electrode active material obtained by the manufacturing method of the present embodiment of FIG.
First, a lithium secondary battery using the negative electrode active material obtained by the present embodiment will be described with reference to FIG. The lithium secondary battery 5 has a spiral cylindrical shape, and a positive electrode 26 in which a positive electrode current collector 25 is sandwiched between two layers of a positive electrode active material 20 and a negative electrode current collector 15 is sandwiched between two layers of a negative electrode active material 10. A laminate having a cylindrical structure in which a laminate in which a thin film separator 30 is sandwiched between the negative electrode 16 and a center pin 7 is wound in multiple layers is formed. Insulating plates 13a and 13b are provided above and below the laminate, respectively. This cylindrical laminated body is housed in a positive electrode terminal 28 having a hollow cylindrical shape with a bottom formed at one end. The positive electrode current collector 25 of the laminate passes through the insulating plate 13 a and is connected to the positive electrode terminal 28 by the positive electrode lead 27. Further, on the insulating plate 13b on the opening side facing the bottom, a safety valve 31 having a convex shape in the direction of the insulating plate 13b, and a cap-shaped negative electrode terminal 18 having a convex shape in the opposite direction to the safety valve 31, Are formed in this order. The edge surfaces of the safety valve 31 and the negative electrode terminal 18 are sealed by the gasket 32 and are separated from the positive electrode terminal 28. Further, the negative electrode current collector 15 of the laminate passes through the insulating plate 13 b and is connected to the negative electrode terminal 18 by the negative electrode lead 17.

  The negative electrode active material 10 and the positive electrode active material 20 have a crystal structure having an interstitial distance capable of intercalating or deintercalating lithium ions. Further, the negative electrode current collector 15 and the positive electrode current collector 25 play a role of extracting an electromotive force generated by the movement of lithium ions. The separator 30 plays the role which prevents the short circuit with the negative electrode 16 and the positive electrode 26, and also has a role which hold | maintains electrolyte solution and moves lithium ion between both electrodes. The separator 30 is porous and has pores formed on its surface.

Here, according to the present embodiment, Li _a V _b Me _c O ₂ (1.0 ≦ a ≦ 1.25, 0.75 ≦ b ≦ 1.0, 0 ≦ c ≦ 0) is used as the negative electrode active material 10. .10) can be used. This Me is, for example, one or more kinds of elements composed of transition metals, alkali metals, and alkaline earth metals. For example, as transition metals, Sc, Ti, Cr, Mn, Fe, Co excluding V , Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, alkali metals are Li, Na, K, Rb, Cs, Fr, alkaline earths Examples of the metal include Mg, Ca, Sr, Ba, and Ra, and in the ionic state, MeX + (X is a valence). When Me is added in this manner, the crystal structure of the negative electrode active material is stabilized, so that desired battery characteristics can be obtained. Further, such a compound is advantageous in that it retains reversibility even after repeated charge and discharge and is a long-life electrode.

On the other hand, for the positive electrode active material 20, for example, LiCoO ₂ , lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), or the like can be used. For the negative electrode current collector 15 and the positive electrode current collector 25, for example, a metal having high electrical conductivity such as copper (Cu) or aluminum (Al) can be used. Moreover, it is suitable that the electrical conductivity of the electrolytic solution held in the separator is 1 × 10 ⁻³ S / centimeter or more.

  Next, the charge / discharge operation of the lithium secondary battery 5 that can be used in this embodiment will be described. When charging, the lithium ions released from the crystal lattice of the positive electrode active material 20 by applying a voltage from the outside of the battery penetrate into the crystal lattice of the negative electrode active material 10 via the separator 30 holding the electrolyte and are dissolved. And stored in the negative electrode active material 10. In the case of discharging, the lithium ions stored in the negative electrode active material 10 penetrate into the crystal lattice lattice in the positive electrode active material 20 through the separator 30 and are dissolved and stored in the positive electrode active material 20.

  Here, if the composition of the negative electrode active material 10 is not uniform, the uniformity of the surface is also impaired. Therefore, as the charge / discharge cycle frequency increases, the dendrite tends to be locally deposited on the surface of the negative electrode active material 10. There arises a problem that the variation in capacity increases.

  On the other hand, according to the manufacturing method of this embodiment, the negative electrode active material 10 with a more uniform composition is obtained by wet-mixing using an organic acid. Thereby, battery characteristics can be improved.

Hereinafter, a method for manufacturing the lithium secondary battery 5 according to the present embodiment will be described with reference to a comparative example.
FIG. 3 is a flowchart showing a manufacturing method for comparison with the present embodiment.

First, a comparative manufacturing method will be described.
As shown in FIG. 3, lithium carbonate powder (Li ₂ CO ₃ ), vanadium oxide powder, and Me powder are a: b: c (1.0 ≦ a ≦ 1) in a molar ratio of lithium, vanadium, and Me. .25, 0.75 ≦ b ≦ 1.0, 0 ≦ c ≦ 0.10) (step S200). And these raw materials are dry-mixed and a raw material mixture is prepared (step S210). The dry mixing method can be performed using, for example, a ball mill. Thereafter, the prepared powder thus obtained was calcined in a nitrogen or inert gas atmosphere and Li _a V _b Me _C O ₂ (1.0 ≦ a ≦ 1.25, 0.75 ≦ b ≦ 1, 0 ≦ c ≦ 0.1) is formed (step S220).

  Thus, the raw material mixture prepared using dry mixing has a non-uniform particle size distribution and is in a non-uniform mixed state, as will be described later with reference to examples. For this reason, since the segregated composition is formed in the negative electrode active material 10 obtained by firing this raw material mixture, the battery capacity varies greatly.

In contrast, in the manufacturing method of the present embodiment, as shown in FIG. 1, a raw material made of each organic acid salt containing lithium, vanadium, and Me is used as a: b: c (1.0 ≦ a ≦ 1.25, 0.75 ≦ b ≦ 1, 0 ≦ c ≦ 0.1) (step S100). Here, as for each raw material, for example, the raw material containing lithium is Li ₂ CO ₃ , the raw material containing vanadium is V ₂ O ₅ , V ₂ O ₄ , V ₂ O _3, etc., and the raw material containing Me is organic Acid Ti or the like can be used.

  Then, these raw materials are added to an organic acid to form an organic acid salt mixture, and this organic acid salt mixture is mixed by a wet mixing method to form a mixed aqueous solution (step S110). As the organic acid, those having a reducing action are desirable, and examples thereof include those having 1 to 4 COOH groups, those having 1 to 3 OH groups, and those having 1 to 4 N (nitrogen) elements. be able to. This can reduce the raw material supplied in the form of an oxide or the like and can stably form a compound of lithium, vanadium, and Me.

In this wet mixing method, the ratio of the organic acid to each metal of the organic acid salt is about 1 to 6 times equivalent, and the Li _a V _b Me _c O ₂ concentration in the mixed aqueous solution is 0.1 to ₂ mol / liter. It is good to. Thereby, in the mixed aqueous solution, for example, a reaction represented by Chemical Formula 1 occurs.

Thus, when wet mixing is performed using an organic acid, each element is dissolved and mixed in an ionic state, and can be mixed extremely uniformly. Here, if an inorganic acid is used instead of an organic acid, each raw material may not be sufficiently dissolved, and a desired mixed aqueous solution may not be obtained. Subsequently, this mixed aqueous solution is dried at 60 ° C. to 150 ° C. to form a powdery organic acid salt precursor (step S120).

Then, the organic acid salt precursor is calcined in a nitrogen or other inert gas atmosphere to obtain Li _a V _b Me _c O ₂ (1.25 ≧ a ≧ 1.0, 1.0 ≧ b ≧ 0.75). , 0.1 ≧ c ≧ 0) (step S130). Here, the firing can be carried out in two stages. That is, for example, after “pre-baking” the organic acid salt precursor in a nitrogen gas or inert gas atmosphere at a temperature of 600 ° C. or lower, the “main baking” is further performed in the same atmosphere at a temperature of 600 to 1300 ° C. "can do. By pre-baking, the organic acid component in the organic acid salt precursor is gasified and removed by thermal decomposition and can be highly purified. Moreover, the organic acid salt precursor highly purified by the main firing can be grown and crystallized.

The Li _{a Vb} Me _c O ₂ thus obtained has an average primary particle size of 0.01 to 20 micrometers and an average secondary particle size of 0.5 to 30.0 micrometers. The specific surface area according to the nitrogen adsorption method is, for example, 0.2 to 2.0 square meters / gram. The shape of the particles is close to a rounded shape or isotropic polyhedron, and relatively uniform fine particles can be obtained. The primary particles are, for example, the microstructure of Li _a V _{b Me} O ₂ observed using an electron microscope such as SEM (Scanning Electron Microscopy), and the average particle diameter is obtained by microstructure observation. It is a particle size when the two-dimensional particle size is calculated as a three-dimensional particle size. Secondary particles mean, for example, a particle size obtained by a particle size measuring instrument such as laser diffraction particle size distribution measurement. In the production method of the present embodiment, a desired particle size, shape, and particle size distribution can be obtained by controlling the amount of organic acid added and the firing conditions.

And according to the manufacturing method of this embodiment, the organic acid salt precursor which has a uniform mixed state is formed by wet-mixing using an organic acid, and a lithium secondary battery with a more uniform composition by baking. Negative electrode active material 10 for use is obtained. That is, the negative electrode active material 10 in which lithium, vanadium, and Me are coordinated at ideal lattice positions is obtained. Further, when a small amount of Me is contained in the negative electrode active material 10 for a lithium secondary ion battery, this Me is substituted by the lattice position of vanadium, the crystal structure is further stabilized, and the battery characteristics are further improved.
However, in the case of using the dry mixing method as a comparison in FIG. 3, since the mixed state becomes inhomogeneous, the additive element Me does not substitute for the lattice position of vanadium, and the compound of lithium and vanadium is not replaced. The surface often segregated, and the crystal structure was not stabilized, resulting in large variations in battery capacity.
Next, the sinterability of the raw material powder constituting the negative electrode will be described.

FIG. 4 is a high-temperature behavior of an organic acid salt precursor composed of Li _a V _b Me _c O (C ₂ O ₄ ) prepared by the method for manufacturing the negative electrode active material 10 for a secondary battery according to the present embodiment of FIG. .
FIG. 5 is a graph showing the high-temperature behavior of the raw material mixture obtained by the comparative manufacturing method of FIG. 3, and (a) the lines are Li ₂ CO ₃ and trioxide 2 vanadium (V ₂ O ₃ ). (B) Line is a raw material mixture of Li ₂ CO ₃ and tetroxide 2 vanadium (V ₂ O ₄ ), and (c) Line is Li ₂ CO ₃ and pentoxide 2 vanadium (V ₂ O ₅ ).
Here, in FIG.4 and FIG.5, a horizontal axis is temperature (degreeC) and a vertical axis | shaft is a weight change rate (percent). Each measurement condition was raised from room temperature to 1200 ° C. in a nitrogen atmosphere at 2.5 ° C. per minute. The temperature at which the rate of weight change is maximum is the temperature at which the reaction starts, and the lower the temperature, the higher the reactivity.

First, FIG. 5 for comparison will be described.
As shown in FIG. 5, it can be seen that the raw material mixture obtained by the powder manufacturing method of FIG. 3 has the maximum weight change rate at about 700 ° C. regardless of the composition of the vanadium oxide. Moreover, it turns out that a difference is not looked at by the reactivity with respect to the kind of each raw material mixture.

  On the other hand, as shown in FIG. 4, it can be confirmed that the organic acid salt precursor according to the manufacturing method of FIG. 1 has the maximum weight change rate at about 400 ° C. and the reactivity is improved. . By using such a precursor, low-temperature firing can be performed, and the negative electrode active material 10 having a more uniform composition can be formed.

  Next, the embodiment of the present invention will be described in more detail with reference to the embodiment performed by the present inventor and the comparative manufacturing method.

Table 1 is a list showing the experimental results of Examples 1-9 and Comparative Examples 1-3.

As the evaluation items, initial capacity (mAh / g), efficiency (percent), and 35 cycle maintenance ratio (percent) were adopted. Here, if the initial capacity (mAh / g) is, for example, 260 (mAh / g) or more, it can be said that it is satisfactory. On the other hand, the efficiency is the charging efficiency. For example, if it is 80 (percent) or more, it can be said that the efficiency is good. The 35 cycle maintenance rate (percentage) represents the capacity maintenance rate after 35 charge / discharge cycles. For example, it can be said to be good if it is 80 (percent) or more.
Here, an Example and a comparative example can be evaluated using the following apparatuses. The uniformity of the negative electrode active material component obtained by firing can be evaluated by X-ray diffraction analysis. X-ray diffraction analysis was performed under the following conditions using, for example, a MULTIFLEX analyzer manufactured by Rigaku Corporation. The X-ray source is Cu, the output is 40 kilovolts x 40 milliamps, and in the optical system, the divergence slit is 1 °, the scattering slit is 1 °, the light receiving slit is 0.15 millimeters, and the monochrome light receiving slit is 0.8 millimeters The SCAN speed is 4.000 ° / min, the sampling width is 0.020 °, and the scanning range is 10 ° to 80 °.

  The obtained negative electrode active material 10 has a particle size distribution of, for example, a refractive index of 2.40-0.20i using a laser diffraction particle size distribution analyzer (model SALD-2000J) manufactured by Shimadzu Corporation. Measured under conditions. The BET specific surface area value can be measured with a specific surface area measuring machine (model Flowsorb II type 2300) manufactured by Shimadzu Corporation.

  6 is a microstructure photograph of the negative electrode active material 10 synthesized according to Examples 1 to 9 and Comparative Examples 1 to 3. FIGS. 6 (a) to 6 (i) are examples of Examples 1 to 9, respectively. 6 (j) is Comparative Example 1. FIG.

Here, the microstructure observation can be performed using, for example, an Elionix scanning electron microscope (model ERAX-8000S type).
First, the detail of the manufacturing method of a present Example and a comparative example is demonstrated.
Examples 1 to 9 used the manufacturing method described above with reference to FIG. 1, and Comparative Examples 1 to 3 used the comparative manufacturing method described above with reference to FIG. Details will be described below.

That is, in Example 1, 20.8 grams of lithium carbonate (40.23 percent as Li ₂ O) powder, 42.5 grams of vanadium pentoxide (98.0 percent as V ₂ O ₅ ) powder, and oxalic acid 2 A mixed aqueous solution is prepared by adding 121.8 grams of water salt ((COOH) ₂ · 2H ₂ O) to 500 grams of pure water (H ₂ O) and mixing them. Here, the molar ratio of Li / V / (COOH) ₂ · 2H ₂ O is 1.1 / 0.9 / 1.9, respectively, and the molar ratio of the amount of organic acid added to Li / V is 1.9. It is. This aqueous solution is placed in a fluororesin vat and dried at 120 ° C. to form 99.8 grams of Li _1.1 V _0.9 oxalate precursor. This precursor is put in an alumina container and fired by holding at 700 ° C. for 18 hours in a nitrogen gas atmosphere to form 43.0 grams of Li _1.1 V _0.9 O ₂ . The fired product is pulverized and then classified to obtain a lithium vanadium composite oxide negative electrode active material 10. This powder characteristic has an average particle size (d ₅₀ ) of secondary particles obtained from a particle size distribution measuring instrument of 11.5 micrometers, a particle size distribution of d ₁₀ = 1.5 micrometers, d ₉₀ = 34. 1 micrometer. The BET specific surface area value is 5.8 square meters / gram, and it can be confirmed from X-ray diffraction analysis that it is homogenized.

In Example 2, 99.8 grams of an oxalate precursor obtained by the same process as in Example 1 was placed in an alumina container and calcined by maintaining at 900 ° C. for 18 hours in a nitrogen gas atmosphere. Form grams of Li _1.1 V _0.9 O ₂ . Here, the molar ratio of the amount of organic acid added to Li / V was 1.9. The fired product is pulverized and classified to form a negative electrode active material 10 of a lithium vanadium composite oxide. As for the powder characteristics, the average particle size (d ₅₀ ) of secondary particles obtained from the particle size distribution measuring instrument is 4.1 micrometers, the particle size distribution is d ₁₀ = 1.9 micrometers, and d ₉₀ = 12. 3 micrometers. The BET specific surface area value is 1.4 square meters / gram, which can be confirmed to be homogenized by X-ray diffraction analysis.

In Example 3, 99.8 grams of an oxalate precursor obtained by the same process as in Example 1 was placed in an alumina container, and calcined at 1100 ° C. for 18 hours in a nitrogen gas atmosphere. Form grams of Li _1.1 V _0.9 O ₂ . Here, the molar ratio of the amount of organic acid added to Li / V was 1.9. The fired product is pulverized and classified to form a negative electrode active material 10 of a lithium vanadium composite oxide. In this powder characteristic, the average particle size (d ₅₀ ) of the secondary particles obtained from the particle size distribution measuring instrument is 26.2 micrometers, the particle size distribution is d ₁₀ = 12.2 micrometers, d ₉₀ = 40. 3 micrometers. The BET specific surface area value is 0.2 square meter / gram, and it can be confirmed from the X-ray diffraction analysis that it is homogenized.

In Example 4, 20.8 grams of lithium carbonate powder (40.23 percent as Li ₂ O), 42.5 grams of vanadium pentoxide powder (98.0 percent as V ₂ O ₅ ), oxalic acid 2 96.2 grams of water salt and 500 grams of pure water are added and mixed to prepare a mixed aqueous solution. Here, the molar ratio of Li / V / (COOH) ₂ · 2H ₂ O of each element is 1.1 / 0.9 / 1.5, respectively, and the molar ratio of the amount of organic acid added to Li / V is 1.5. This aqueous solution is placed in a fluororesin vat and dried at 120 ° C. to form 90.2 grams of Li _1.1 V _0.9 oxalate precursor. This precursor is put into an alumina container and calcined at 700 ° C. for 18 hours under a nitrogen gas atmosphere to form 42.8 grams of Li _1.1 V _0.9 O ₂ . The fired product is pulverized and classified to form a negative electrode active material 10 of a lithium vanadium composite oxide. As for the powder characteristics, the average particle diameter (d ₅₀ ) of secondary particles obtained from the particle size distribution measuring instrument is 1.9 micrometers, and the particle size distribution is d ₁₀ = 0.5 micrometers, d ₉₀ = 13.4 micrometers. The BET specific surface area value is 3.5 square meters / gram, and it can be confirmed from X-ray diffraction analysis that it is homogenized.

In Example 5, 90.3 grams of an oxalate precursor obtained by the same process as in Example 4 was placed in an alumina container, and calcined by maintaining at 900 ° C. for 18 hours in a nitrogen gas atmosphere. Form grams of Li _1.1 V _0.9 O ₂ . Here, the molar ratio of the amount of organic acid added to Li / V is 1.5. The fired product is pulverized and classified to form a negative electrode active material 10 of a lithium vanadium composite oxide. In this powder characteristic, the average particle size (d ₅₀ ) of the secondary particles obtained from the particle size distribution analyzer is 7.8 micrometers, the particle size distribution is d ₁₀ = 3.1 micrometers, and d ₉₀ = 21.9. It is a micrometer. The BET specific surface area value is 0.2 square meters / gram, and it can be confirmed from the X-ray diffraction analysis that it is homogenized.

In Example 6, 20.8 grams of lithium carbonate powder (40.23 percent as LiO ₂ ), 42.5 grams of vanadium pentoxide powder (98.0 percent as V ₂ O ₅ ), 2 water oxalic acid 185.9 grams of salt is added to 500 grams of pure water and mixed to prepare a mixed aqueous solution. Here, the molar ratio of Li / V / (COOH) ₂ .2H ₂ O of each element is 1.1 / 0.9 / 2.85, respectively, and the molar ratio of the amount of organic acid added to Li / V is 2.85. The This aqueous solution is placed in a fluororesin vat and dried at 120 ° C. to form 145.6 grams of Li _1.1 V _0.9 oxalate precursor. This precursor is put into an alumina container and calcined by holding at 700 ° C. for 18 hours under a nitrogen gas atmosphere to form 129.3 grams of Li _1.1 V _0.9 O ₂ . The fired product is pulverized and classified to form a negative electrode active material 10 of a lithium vanadium composite oxide. The powder characteristics are as follows. The average particle size (d ₅₀ ) of secondary particles obtained from the particle size distribution analyzer is 14.4 micrometers, the particle size distribution is d ₁₀ = 0.7 micrometers, and d ₉₀ = 54.8. It is a micrometer. The BET specific surface area value is 1.9 square meters / gram, and it can be confirmed from the X-ray diffraction analysis that it is homogenized.

In Example 7, 129.3 grams of the oxalate precursor obtained from the same process as in Example 6 was placed in an alumina container and calcined by holding at 900 ° C. for 18 hours in a nitrogen gas atmosphere. Grams of Li _1.1 V _0.9 O ₂ are obtained. Here, the molar ratio of the amount of organic acid added to Li / V is 2.85. The fired product is pulverized and classified to form a negative electrode active material 10 of a lithium vanadium composite oxide. In this powder characteristic, the average particle size (d ₅₀ ) of the secondary particles obtained from the particle size distribution analyzer is 7.0 micrometers, the particle size distribution is d ₁₀ = 2.6 micrometers, d ₉₀ = 18. 6 micrometers. The BET specific surface area value is 0.2 square meter / gram, and it can be confirmed from the X-ray diffraction analysis that it is homogenized.

In Example 8, 20.8 grams of lithium carbonate powder (40.23 percent as LiO ₂ ), 42.1 grams of vanadium pentoxide powder (98.0 percent as V ₂ O ₅ ), Ti oxalate aqueous solution (10.8 grams as TiO ₂ ) and 121.0 grams of oxalic acid dihydrate are added to 500 grams of pure water and mixed to prepare a mixed aqueous solution. Here, the molar ratio of Li / V / Ti / (COOH) ₂ · 2H ₂ O of each element is 1.1 / 0.89 / 0.01 / 1.9, respectively, and the organic acid with respect to Li / V The molar ratio of the addition amount is 1.9. This aqueous solution is placed in a fluororesin and dried at 120 ° C. to form 99.8 grams of Li _1.1 V _0.89 Ti _0.01 oxalate precursor. This precursor is put in an alumina container and fired by holding at 700 ° C. for 18 hours in a nitrogen gas atmosphere to form 43.0 grams of Li _1.1 V _0.89 Ti _0.01 O ₂ . The fired product is pulverized and classified to form a negative electrode active material 10 of lithium vanadium titanium composite oxide. The powder characteristics are as follows. The average particle size (d ₅₀ ) of secondary particles obtained from the particle size distribution analyzer is 3.9 micrometers, the particle size distribution is d ₁₀ = 1.7 micrometers, and d ₉₀ = 11.5. It is a micrometer. The BET specific surface area value is 1.5 square meters / gram, and it can be confirmed from the X-ray diffraction analysis that it is homogenized.

In Example 9, 20.9 grams of lithium carbonate powder (40.23 percent as LiO ₂ ), 41.2 grams of vanadium pentoxide powder (98.0 percent as V ₂ O ₅ ), Ti oxalate aqueous solution (3.78 percent as TiO ₂ ) 32.4 grams and 119.4 grams of oxalic acid dihydrate are added to and mixed with 500 grams of pure water to prepare a mixed aqueous solution. Here, the molar ratio of Li / V / Ti / (COOH) ₂ · 2H ₂ O of each element is 1.1 / 0.87 / 0.03 / 1.9, respectively, and the organic acid relative to Li / V The molar ratio of the addition amount is 1.9. This aqueous solution is placed in a fluororesin vat and dried at 120 ° C. to form 99.8 grams of Li _1.1 V _0.87 Ti _0.03 oxalate precursor. This precursor is put in an alumina container and fired by holding at 700 ° C. for 18 hours in a nitrogen gas atmosphere to form 43.0 grams of Li _1.1 V _0.87 Ti _0.03 O ₂ . The fired product is pulverized and classified to form a negative electrode active material 10 of lithium vanadium titanium composite oxide. The powder characteristics are as follows. The average particle size (d ₅₀ ) of secondary particles obtained from the particle size distribution analyzer is 3.8 micrometers, the particle size distribution is d ₁₀ = 1.7 micrometers, and d ₉₀ = 11.7. It is a micrometer. The BET specific surface area value is 1.4 square meters / gram, and it can be confirmed from the X-ray diffraction analysis that it is homogenized.

Then, the manufacturing method of Comparative Examples 1 thru | or 3 is demonstrated.
In Comparative Example 1, lithium carbonate powder and vanadium trioxide (V ₂ O ₃ ) powder were weighed and mixed in an alumina mortar. This mixture is put into an alumina container, and calcined at 700 ° C. for 18 hours under a nitrogen gas atmosphere to form Li _1.1 V _0.9 O ₂ . The fired product is pulverized and then classified to form a lithium vanadium composite oxide. This powder characteristic has an average particle size (d ₅₀ ) of secondary particles obtained from a particle size distribution measuring instrument of 30.5 micrometers, a particle size distribution of d ₁₀ = 3.5 micrometers, and d ₉₀ = 52. 3 micrometers. The BET specific surface area was 0.2 square meter / gram, and X-ray diffraction analysis revealed that it was inhomogeneous.

In Comparative Example 2, a sample is synthesized in the same process as Comparative Example 1, and the negative electrode active material 10 made of a lithium vanadium composite oxide is formed at a firing temperature of 1100 ° C. In this powder characteristic, the average particle size (d ₅₀ ) of the secondary particles obtained from the particle size distribution measuring device is 38.7 micrometers, the particle size distribution is d ₁₀ = 6.7 micrometers, d ₉₀ = 61. 3 micrometers. The BET specific surface area was 0.15 square meter / gram, and X-ray diffraction analysis revealed that it was heterogeneous.

In Comparative Example 3, a sample is synthesized in the same process as Comparative Example 1, and the negative electrode active material 10 made of a lithium vanadium composite oxide is formed at a firing temperature of 1200 ° C. In this powder characteristic, the average particle diameter (d ₅₀ ) of the secondary particles obtained from the particle size distribution measuring device is 38.2 micrometers, the particle size distribution is d ₁₀ = 7.1 micrometers, d ₉₀ = 65. 1 micrometer. The BET specific surface area was 0.12 square meter / gram, and X-ray diffraction analysis revealed that it was heterogeneous.

Next, the result of evaluating the negative electrode active material 10 for a lithium secondary battery thus obtained will be described.
First, Comparative Examples 1 to 3 will be described.
As a result, the initial capacity (mAh / g), the efficiency (percent), and the 35 cycle maintenance ratio (percent) tended to increase as the firing temperature increased, but all were below the target values. For example, in Comparative Example 1 with the lowest firing temperature, the initial capacity is 95 (mAh / g), the efficiency is 63 (percent), and the 35 cycle maintenance efficiency is 60 (percent). It can be seen that the initial capacity is 189 (mAh / g), the efficiency is 76 (percent), and the 35 cycle maintenance efficiency is 64 (percent).

FIG. 6D is a structural photograph of the negative electrode active material 10 of Comparative Example 1. Since the mixing of the raw materials is insufficient, the average particle size of the secondary particles is larger than 30 micrometers, and the particle size and particle shape are not uniform.
Thus, according to the dry mixing method, in any of the comparative examples, since the average particle diameter of the secondary particles is larger than 30 micrometers and the raw material mixing is insufficient, the homogenized negative electrode active material 10 is obtained. It cannot be obtained, and it is presumed that the crystal structure becomes unstable and the characteristics of the battery become insufficient.

  On the other hand, according to the production method of this example, the particle size of the secondary particles can be 30 micrometers or less regardless of the amount of organic acid added, and even at the lowest firing temperature, the target value is reached. Can be satisfied. That is, Example 1 in which the molar ratio of the amount of organic acid added is 1.9 has an initial capacity of 262 (mAh / g), an efficiency of 80 (percent), and a 35 cycle maintenance efficiency of 84 (percent). In Example 5 where the molar ratio of the acid addition amount is 1.5, the initial capacity is 254 (mAh / g), the efficiency is 90 (percent), the 35 cycle maintenance efficiency is 87 (percent), and the organic acid addition amount is In Example 7 having a molar ratio of 2.85, the initial capacity is 267 (mAh / g), the efficiency is 80 (percent), and the 35 cycle maintenance efficiency is 88 (percent). In addition, it can be confirmed that the initial capacity (mAh / g), efficiency (percent), and 35 cycle maintenance ratio (percent) increase as the firing temperature increases.

  Further, even when the firing temperature was 700 ° C., it was confirmed that the battery characteristics were further improved by adding Me as in Examples 8 and 9. For example, in Example 8, the initial capacity is 285 (mAh / g), the efficiency is 94 (percent), and the 35 cycle maintenance ratio is 94 (percent). In Example 9, the initial capacity is 287 (mAh / g). The efficiency is 93 (percent) and the 35 cycle maintenance ratio is 93 (percent), and it can be seen that battery characteristics superior to those of Examples 1 to 7 can be obtained.

  FIGS. 6A to 6I are tissue photographs corresponding to Examples 1 to 9, respectively. In Example 1 in FIG. 6 (a), Example 4 in FIG. 6 (d), and Example 6 in FIG. 6 (f) in which the firing temperature is 700 ° C., the shape of the particles is somewhat irregular and the surface irregularities However, compared with the comparative example shown in FIG. 6J, it can be seen that the particle size is much smaller and the uniformity is higher. Then, Example 2 in FIG. 6 (b), Example 3 in FIG. 6 (c), Example 5 in FIG. 6 (e) and Example 7 in FIG. 6 (i) and FIG. 6 (j) with Me added, the particle size and particle shape are very uniform, and no segregation is observed.

  Thus, according to the manufacturing method of this embodiment, the negative electrode active material 10 for lithium secondary batteries with a uniform composition is obtained by performing a wet mixing system using an organic acid salt.

The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples.
For example, the lithium secondary battery using the negative electrode active material 10 of the present embodiment is not limited to the spiral cylindrical lithium secondary battery illustrated in FIG. 1, but the coin-type lithium secondary battery illustrated in FIG. A square lithium secondary battery (not shown) can achieve the same effect as long as it has the features of the present invention.
Regarding the composition of the negative electrode active material of the present embodiment, the type of Me element contained therein, the type of organic acid, the material, shape, manufacturing process, manufacturing conditions, shape of the lithium secondary battery, etc. Even if a trader makes various design changes, as long as it has the characteristics of the present invention, it is included in the scope of the present invention.

It is a flowchart showing the manufacturing method of the negative electrode active material of the lithium secondary battery which concerns on this embodiment. It is a partial cross section which illustrates the principal part of the lithium secondary battery 5 using the negative electrode active material obtained by the manufacturing method of this embodiment. It is a flowchart showing the manufacturing method used as the comparison of this embodiment. It is a high temperature behavior of the organic acid salt precursor consisting of _Li a _V b _Me c _O prepared _(C 2 _{O 4)} by the method of manufacturing a secondary battery negative electrode active material 10 according to the present embodiment of FIG. FIG. 4 is a graph showing high-temperature behavior of a raw material mixture obtained by the comparative manufacturing method of FIG. 3, wherein (a) line is a raw material mixture of Li ₂ CO ₃ and trioxide 2 vanadium (V ₂ O ₃ ). , (B) line is a raw material mixture of Li ₂ CO ₃ and divanadium tetroxide (V ₂ O ₄ ), and (c) line of Li ₂ CO ₃ and pentoxide 2 vanadium (V ₂ O ₅ ) It is a raw material mixture. It is a microstructure photograph of negative electrode active material 10 synthesize | combined by Examples 1-9 and Comparative Examples 1-3, FIG.6 (a)-FIG.6 (i) respond | correspond to each of Examples 1-9, FIG. 6 (j) is Comparative Example 1. It is a schematic diagram showing the principal part of the coin-type lithium secondary battery 5 which can be used for the lithium secondary battery which concerns on this embodiment.

Explanation of symbols

5 lithium secondary battery 7 center pin 10 negative electrode active layer 15 negative electrode current collector 16 negative electrode 18 negative electrode terminal 20 positive electrode active layer 30 separator 35 coin-type lithium secondary battery

Claims (7)

Each of Li, V, and Me (Me is a transition metal other than V, an alkali metal, an alkaline earth metal, or a mixture thereof) is prepared at a molar ratio of a: b: c and has a reducing action. Adding an organic acid to form an organic acid salt mixture;
Mixing the organic acid salt mixture with water to form a mixed aqueous solution;
Drying the mixed aqueous solution to form an organic acid salt precursor;
Li _a V _b Me _c O ₂ (1.0 ≦ a ≦ 1.25, 0.75 ≦ b ≦ 1, 0 ≦ c ≦) is obtained by firing the organic acid salt precursor in a nitrogen or inert gas atmosphere. And a step of forming a composite oxide represented by the composition formula: 0.1). A method for producing a negative electrode active material for a lithium ion secondary battery. The ratio of the organic acid to each metal of the organic acid salt mixture is about 1 to 6 times equivalent,
2. The production of a negative electrode active material for a lithium ion secondary battery according to claim 1, wherein the concentration of Li _a V _b Me _c O _{2 in} the mixed aqueous solution is 0.1 to 2.0 mol / liter. Method.   The organic acid used to form the organic acid mixture includes at least one of 1 to 4 COOH groups, 1 to 3 OH groups, and 1 to 4 N elements. The manufacturing method of the negative electrode active material for lithium ion secondary batteries in any one of Claim 1 or 2.   The method for producing a negative electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the temperature for drying the mixed solution is 60 to 150 ° C. The firing of the organic acid salt precursor comprises a first firing and a second firing,
5. The negative electrode active material for a lithium ion secondary battery according to claim 1, wherein the temperature of the first baking is lower than 600 ° C., and the temperature of the second baking is 600 to 1300 ° C. 6. Method.   The composite oxide is characterized in that the average particle diameter of primary particles is 0.01 to 20.0 micrometers and the average particle diameter of secondary particles is 0.5 to 30.0 micrometers. The manufacturing method of the negative electrode active material for lithium ion secondary batteries in any one of Claims 1-5.   7. The lithium ion secondary battery according to claim 1, wherein the composite oxide has a specific surface area measured by a nitrogen adsorption method of 0.2 to 2.0 square meters / gram. A method for producing a negative electrode active material.