TWI460912B - A positive electrode active material for a lithium ion battery, a positive electrode for a lithium ion battery, and a lithium ion battery - Google Patents

Description

Positive electrode active material for lithium ion battery, positive electrode for lithium ion battery, and lithium ion battery

The present invention relates to a positive electrode active material for a lithium ion battery, a positive electrode for a lithium ion battery, and a lithium ion battery.

For the positive electrode active material of a lithium ion battery, a lithium-containing transition metal oxide is usually used. Specifically, it is lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), etc., in order to improve characteristics (high capacity, cycle characteristics, storage characteristics, internal resistance reduction, Rate characteristics) or improve security, and constantly compositing them. For lithium-ion batteries in large-scale applications such as vehicles or load leveling, they are designed to have different characteristics from those used in mobile phones or personal computers.

In order to improve the battery characteristics, various methods have been previously used. For example, Patent Document 1 discloses a method for producing a positive electrode material for a lithium secondary battery, which is characterized in that Li _x Ni _1-y M _y O _2-δ

(0.8≦x≦1.3,0<y≦0.5, M means selected from Co, Mn, Fe, Cr, V, Ti, Cu, Al, Ga, Bi, Sn, Zn, Mg, Ge, Nb, Ta, Be At least one element selected from the group consisting of B, Ca, Sc, and Zr, δ corresponds to an oxygen deficiency or an excess amount of oxygen, and the lithium nickel composite oxide represented by the composition of -0.1 < δ < 0.1) passes through a classifier. The equilibrium separation particle diameter Dh=1~10μm is separated into smaller and smaller particles, and the weight ratio is 0:100~100:0, and the smaller the particle size is smaller and smaller. Further, it is described that, according to the method, lithium secondary having a balance between the ratio characteristics and the capacity can be easily produced. Positive electrode material for battery.

[Patent Document 1] Japanese Patent No. 4175526

The lithium-nickel composite oxide described in Patent Document 1 is one in which the amount of oxygen in the composition formula is excessive. However, there is still room for improvement in the high-quality positive electrode active material for lithium ion batteries.

Therefore, an object of the present invention is to provide a positive electrode active material for a lithium ion battery having good battery characteristics.

As a result of intensive research, the present inventors have found that there is a close correlation between the amount of oxygen of the positive electrode active material and the particle size of the primary particles and the battery characteristics. In other words, it has been found that the amount of oxygen of the positive electrode active material is equal to or greater than a certain value, and the particle diameter of the primary particles of the positive electrode active material is controlled to an appropriate range, whereby good battery characteristics can be obtained.

Further, among the alkali content of the surface of the particle of the positive electrode active material and the alkali amount on the surface of the particle, the ratio of the amount of lithium hydroxide A to the amount of lithium carbonate B was found to have a close correlation with the battery characteristics. In other words, when the alkali content of the surface of the particle of the positive electrode active material is below a certain value, the ratio A/B of the amount of lithium hydroxide A to the amount of lithium carbonate B is below a certain value among the alkali amount on the surface of the particle. Particularly good battery characteristics are obtained.

The present invention based on the above findings is, in one aspect, a positive electrode active material for a lithium ion battery, which is represented by the following composition formula: Li(Li _x Ni _1-xy M _y )O _2+α

(In the above formula, M is one selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Ga, Ge, Bi, Sn, Mg, Ca, B, and Zr. Upper, 0≦x≦0.1, 0<y≦0.7, α>0), the primary particle has a particle diameter of 1.6 to 2.3 μm, and the amount of alkali on the surface of the particle obtained by the two-stage neutralization titration measurement is 1.2% by mass or less. When lithium hydroxide in the amount of alkali on the surface of the particle is A mass%, and lithium carbonate is B mass%, A/B is 1 or less.

In the positive electrode active material for a lithium ion battery of the present invention, in one embodiment, the amount of alkali on the surface of the particles obtained by two-stage neutralization titration measurement is 0.8% by mass or less.

In another embodiment, the positive electrode active material for a lithium ion battery of the present invention has A/B of 0.7 or less.

In still another embodiment, the positive electrode active material for a lithium ion battery of the present invention is one or more selected from the group consisting of Mn and Co.

In still another embodiment of the positive electrode active material for a lithium ion battery of the present invention, α>0.05 in the composition formula.

In still another embodiment of the positive electrode active material for a lithium ion battery of the present invention, α>0.1 in the composition formula.

In another aspect, the present invention provides a positive electrode for a lithium ion battery using the positive electrode active material for a lithium ion battery of the present invention.

In still another aspect, the present invention is a lithium ion battery using the positive electrode for a lithium ion battery of the present invention.

According to the present invention, a positive electrode active material for a lithium ion battery having good battery characteristics can be provided.

(Composition of positive active material for lithium ion battery)

The material of the positive electrode active material for a lithium ion battery of the present invention can be widely used as a compound for a positive electrode active material for a positive electrode for a general lithium ion battery, and particularly preferably lithium cobaltate (LiCoO ₂ ) or lithium nickelate (LiNiO ₂ ). A lithium-containing transition metal oxide such as lithium manganate (LiMn ₂ O ₄ ). The positive electrode active material for a lithium ion battery of the present invention produced by using the above materials is represented by the following composition formula: Li(Li _x Ni _1-xy M _y )O _2+α

(In the above formula, M is at least one selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Ga, Ge, Bi, Sn, Mg, Ca, B, and Zr, 0≦ x≦0.1,0<y≦0.7, α>0).

The oxygen of the positive electrode active material for a lithium ion battery of the present invention is expressed as O _{2+ α} (α>0) as described above in the composition formula, and is excessively contained. When used in a lithium ion battery, the capacity and ratio are used. Battery characteristics such as characteristics and capacity retention rate are good. Here, with respect to α, it is preferably α>0.05, more preferably α>0.1.

A positive electrode active material for a lithium ion battery is formed by a primary particle or a secondary particle obtained by aggregating primary particles, or a mixture of primary particles and secondary particles (refer to FIG. 1). Among them, the primary particles have a particle diameter of 1.6 to 2.3 μm. If the particle diameter of the primary particles is less than 1.6 μm, there arises a problem of causing particle breakage due to pressurization at the time of battery production or deterioration due to particle cracking when the battery is circulated. Further, when the particle diameter of the primary particles exceeds 2.3 μm, there is a problem that the battery is deteriorated due to dryness of the electrolytic solution or an increase in the amount of the electrolytic solution. The particle diameter of the primary particles is preferably from 1.8 to 2.1 μm.

The positive electrode active material for a lithium ion battery of the present invention is utilized in two stages The amount of alkali on the surface of the particles measured by titration was 1.2% by mass or less. When the amount of the alkali on the surface of the particles in the positive electrode active material for a lithium ion battery exceeds 1.2% by mass, the lithium ion battery using the positive electrode active material reacts with the electrolytic solution when the charge and discharge are repeated. Moreover, if the amount of alkali is large, gas is generated. Therefore, deterioration of the battery is caused, and battery characteristics, particularly cycle characteristics, of the lithium ion battery may become poor. The amount of the alkali measured by the two-stage neutralization titration is preferably 0.8% by mass or less, more preferably 0.6% by mass or less.

In the positive electrode active material for a lithium ion battery of the present invention, when lithium hydroxide in the amount of alkali on the surface of the particles is A mass% and lithium carbonate is B mass%, A/B is 1 or less. Among the bases contained in the positive electrode active material for lithium ion batteries, there are lithium hydroxide and lithium carbonate. Among them, if the ratio of the amount of lithium hydroxide to the amount of lithium carbonate, that is, the above A/B exceeds 1, the lithium hydroxide of a strong base is used. Since the ratio becomes higher than that of the weak base lithium carbonate, the pH value becomes high, and the battery characteristics of the lithium ion battery using the positive electrode active material, particularly the cycle characteristics, may become poor. A/B is preferably 0.7 or less, more preferably 0.4 or less.

The two-stage neutralization titration of the positive electrode active material for a lithium ion battery can be carried out by a general method, and is also defined, for example, in JIS K1201-3-1 (neutralization titration). Specifically, the titration method is based on the reaction of the following base with an acid.

LiOH+HCl → LiCl+H ₂ O (1)

Li ₂ CO ₃ +HCl → LiCl+LiHCO ₃ (2)

LiHCO ₃ +HCl → LiCl+CO ₂ +H ₂ O (3)

In the titration method using the conventional indicator drug, pH 7.8 was detected in the reaction of (1) and (2), and this measurement point was made into the 1st end point. Further, pH 3.9 was detected in the reaction of (3), and the measurement point was set as the second end point. Further, in the predetermined titration method according to JIS K1201-3-2 (potential difference titration), the inflection points of the two positions are detected, and the first end point and the second end point are respectively set. Then, the mass % of lithium hydroxide and lithium carbonate was calculated from the amount of HCl used to the respective end points.

(Construction of a positive electrode for a lithium ion battery and a lithium ion battery using the same)

The positive electrode for a lithium ion battery according to the embodiment of the present invention has a structure in which a positive electrode mixture prepared by mixing a positive electrode active material for a lithium ion battery, a conductive auxiliary agent, and a binder, which are configured as described above, is provided in an aluminum foil or the like. One or both sides of the current collector. Moreover, the lithium ion battery according to the embodiment of the present invention includes the positive electrode for a lithium ion battery having the above configuration.

(Method for producing positive electrode active material for lithium ion battery)

Next, a method for producing a positive electrode active material for a lithium ion battery according to an embodiment of the present invention will be described in detail.

First, a metal salt solution is prepared. The metal is Ni and one or more selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Ga, Ge, Bi, Sn, Mg, Ca, B, and Zr. Further, the metal salt is a sulfate, a chloride, a nitrate, an acetate or the like, and particularly preferably a nitrate. The reason for this is that even if it is mixed into the calcined raw material in the form of impurities, it can be directly calcined, so that the washing step can be omitted, and the nitrate functions as an oxidizing agent, and the oxidation of the metal in the calcining raw material is promoted. effect. The metal contained in the metal salt is adjusted in advance to have a desired molar ratio. Thereby, the molar ratio of each metal in the positive electrode active material is determined.

Next, lithium carbonate was suspended in pure water, and then a metal salt solution of the above metal was introduced to prepare a metal carbonate solution slurry. At this point, the slurry will be analyzed A lithium carbonate containing fine particles. In the case where the lithium compound is not reacted during heat treatment such as a sulfate or a chloride of a metal salt, it is washed with a saturated lithium carbonate solution and then subjected to filtration separation. For example, in the case of a nitrate or an acetate, when a lithium compound is reacted as a lithium raw material during heat treatment, it may be directly used as a firing precursor without being washed and directly separated by filtration and dried.

Next, a powder of a lithium salt composite (precursor for a lithium ion battery positive electrode material) is obtained by drying the filtered lithium-containing carbonate.

Next, a firing vessel having a capacity of a specific size is prepared, and the firing vessel is filled with a powder of a precursor for a positive electrode material for a lithium ion battery. Next, the firing container filled with the powder of the precursor for the positive electrode material for a lithium ion battery is transferred to a baking furnace and fired. The firing is carried out by heating in an oxygen atmosphere for a specific period of time. Further, if the firing is carried out under a pressure of 101 to 202 KPa, the amount of oxygen in the composition is further increased, which is preferable.

The heating and holding temperature in the firing step affects the particle size of the primary particles of the positive electrode material of the lithium ion battery. In the present invention, since lithium carbonate is used as a raw material, reactivity is weaker than when lithium hydroxide is used as a raw material. Therefore, it is necessary to perform baking for a long time at a high temperature, and by the high temperature and long-time baking, the crystallinity of the particles increases and the particle diameter of the primary particles of the positive electrode material increases. In the present invention, lithium carbonate is used as a raw material, and firing is performed at 750 ° C or higher for 12 hours or longer, whereby the particle diameter of the primary particles is controlled to be 1.6 μm to 2.3 μm. On the other hand, in the case of using lithium hydroxide as a raw material, the firing temperature is usually lowered because of high reactivity, and burning is performed. Since the formation time is small, the particle diameter of the generated primary particles is reduced to about 0.5 μm.

Then, the powder is taken out from the firing container, and pulverized using a commercially available pulverizing apparatus or the like to obtain a powder of the positive electrode active material. The pulverization at this time is carried out by appropriately adjusting the pulverization strength and the pulverization time so as not to form fine powder as much as possible. Specifically, by this pulverization, the volume % of the fine powder having a particle diameter of 6 μm or less after the pulverization is adjusted to 4.0 to 7.0%, preferably adjusted to 4.3 to 6.9%.

By controlling the occurrence of the fine powder at the time of pulverization as described above, the surface area per volume of the powder can be reduced, so that the amount of lithium hydroxide on the surface of the particles can be suppressed.

Further, since lithium carbonate becomes lithium hydroxide in a place where moisture is present, it is controlled so as not to take in moisture by pulverization in a dry air atmosphere.

[Examples]

The following examples are provided to better understand the present invention and its advantages, but the invention is not limited to the embodiments.

(Examples 1 to 15)

First, the amount of lithium carbonate described in Table 1 was suspended in 3.2 liters of pure water, and then 4.8 liters of the metal salt solution was charged. Here, the metal salt solution adjusts the hydrate of the nitrate of each metal, and each metal has the composition ratio shown in Table 1, and is adjusted so that the total metal mole number is 14 mol.

Further, the amount of lithium carbonate suspended is a product represented by Li(Li _x Ni _1-xy M _y )O _2+α (a positive electrode material of a lithium ion secondary battery, that is, a positive electrode active material) and x is a value of Table 1. , which are calculated by the following formulas.

W(g)=73.9×14×(1+0.5{(1+X)/(1-X)}×A

In the above formula, "A" is a value obtained by multiplying the amount of lithium of the lithium compound other than the lithium carbonate remaining in the filtered raw material from the amount of suspension in addition to the amount necessary for the precipitation reaction. "A" is 0.9 when the nitrate or acetate is reacted as a raw material of the lithium salt, and is 1.0 when the sulfate or chloride is not reacted as a raw material for the calcination.

By this treatment, lithium carbonate containing fine particles was precipitated in the solution, and the precipitate was separated by filtration using a filter press.

Then, the precipitate was dried to obtain a lithium-containing carbonate (precursor for a positive electrode material for a lithium ion battery).

Next, a baking container is prepared, and a lithium-containing carbonate is filled in the baking container. Next, the baking container was placed in an oxygen atmosphere furnace under atmospheric pressure, and heated and held at the baking temperature shown in Table 1 for 10 hours, and then cooled to obtain an oxide.

Next, a small pulverizer (hosokawamicron ACM-2EC) was used to pulverize the obtained oxide into a specific particle size distribution powder to obtain a distribution of a specific particle size distribution, thereby obtaining a powder of a lithium ion secondary battery positive electrode material.

(Embodiment 16)

In Example 16, the metal of the raw material was a composition shown in Table 1, and the metal salt was a chloride. After the lithium carbonate was precipitated, it was washed and filtered with a saturated lithium carbonate solution, and all were carried out and carried out. The same processing as in Examples 1-15.

(Example 17)

In Example 17, the metal of the raw material was a composition shown in Table 1, and the metal salt was a sulfate. After the lithium carbonate was precipitated, it was washed and filtered with a saturated lithium carbonate solution, and the same was carried out. The same treatments as in Examples 1 to 15 were carried out.

(Embodiment 18)

In Example 18, the respective metals of the raw materials were the compositions shown in Table 1, and the same treatments as in Examples 1 to 15 were carried out except that the firing was carried out under the pressure of 120 KPa under atmospheric pressure.

(Embodiment 19)

In Example 19, each metal of the raw material was a composition shown in Table 1, and the metal salt was a nitrate. After the lithium carbonate was precipitated, it was washed and filtered with a saturated lithium carbonate solution, and all were carried out and carried out. The same processing as in Examples 1-15.

(Comparative examples 1 to 3)

In Comparative Examples 1 to 3, the respective metals of the raw materials were the compositions shown in Table 1, and the pulverization of the last oxide was not adjusted as in Examples 1 to 15, except for the other examples. The same processing as 1~15.

(Comparative examples 4 to 6)

In Comparative Examples 4 to 6, the respective metals of the raw materials were the compositions shown in Table 1, and were not subjected to a firing step in an air atmosphere furnace but in an air atmosphere furnace, and were subjected to Comparative Example 1 except The same process.

(Evaluation) - Evaluation of the composition of the positive electrode material -

The metal content in each positive electrode material is emitted by inductively coupled plasma The composition ratio (mol ratio) of each metal was measured by a spectrum analyzer (ICP-OES). Further, the oxygen content was measured by the LECO method and α was calculated. The results are confirmed as shown in Table 1.

- Evaluation of the particle size of primary particles -

The powder of each positive electrode material was collected, and the particle diameter of the primary particles was measured by a laser diffraction type particle size distribution measuring apparatus (Microtrack MT3300EX II).

- Evaluation of the amount of alkali -

The amount of alkali in the positive electrode material was measured by a two-stage neutralization titration method. Specifically, 1 g of each positive electrode material powder was collected, added to 50 mL of pure water, and stirred for 10 minutes, followed by filtration. Next, 10 mL of the filtrate and 15 mL of pure water were placed in a 50 mL high beaker using a micropipette. Next, the stirrer was placed in a beaker to which phenolphthalein was added as an indicator, and placed in a stirrer to place the electrode in the beaker. Next, 0.01 N HCl was added dropwise while stirring the solution in the beaker.

Here, the two-stage neutralization titration method is based on the reaction of the following base with an acid.

LiOH+HCl → LiCl+H ₂ O (1)

Li ₂ CO ₃ +HCl → LiCl+LiHCO ₃ (2)

LiHCO ₃ +HCl → LiCl+CO ₂ +H ₂ O (3)

In the reaction of (1) and (2), pH 7.8 was detected, and the measurement point was set as the first end point. Further, pH 3.9 was detected in the reaction of (3), and the measurement point was set as the second end point. Then, the amount of HCl used to the first end point was x (mL), the amount of HCl used to the second end point was y (mL), and Li ₂ CO was determined by (yx) × 0.369 mass%. _The amount of LiOH was determined by (2x-y) × 0.12% by mass.

Further, the amount calculated by the amount of LiOH and Li ₂ CO _3, the ratio of these (the amount of LiOH / Li ₂ CO ₃ amount) is obtained.

Further, the calculation formula of the amount of Li ₂ CO ₃ is: (yx) × 0.369 mass%, and the calculation formula of the amount of LiOH: (2x-y) × 0.12 mass%, which is derived from the following formula.

. The molar number of the above formula (3) HCl is determined by the following formula.

(yx) × 1/1000 × 0.01 mol / L = 10 ^-5 × (yx) mol

. Since the molar number of Li ₂ CO ₃ of the above (2) is the same as the molar number of the above HCl, the molecular weight of Li ₂ CO ₃ is 73.89, 10 mL of 50 mL is used at the time of titration, and the input amount of the original positive electrode material is used. Since it is 1 g, the amount of Li ₂ CO ₃ is obtained by the following formula.

73.89 g/mol × 10 ^-5 × (yx) mol × (50 mL/10 mL) ÷ 1 g × 100% = (yx) × 0.369% by mass

. The molar number of LiOH of the above formula (1) is obtained by the following formula.

x×1/1000×0.01mol/L-10 ^-5 ×(yx)mol=10 ^-5 ×(2x-y)mol

. Since the molecular weight of LiOH was 23.95, 10 mL of 50 mL was used for the titration, and the input amount of the original positive electrode material was 1 g, the amount of LiOH was determined by the following formula.

23.95 g/mol × 10 ^-5 × (2x-y) mol × (50 mL/10 mL) ÷ 1 g × 100% = (2x - y) × 0.12% by mass

- Evaluation of battery characteristics -

The positive electrode material, the conductive material and the binder are weighed in a ratio of 85:8:7, and the binder is dissolved in an organic solvent (N-methylpyrrolidone), and then the positive electrode material is mixed with the conductive material. The slurry was applied thereto, coated on an Al foil, dried, and pressed to prepare a positive electrode. Then, a 2032 coin cell for evaluation of Li as a counter electrode was prepared, and 1 M-LiPF _{6 was} dissolved in EC-DMC (1:1) as an electrolyte solution, and a discharge capacity at a current density of 0.2 C was measured. . Moreover, the ratio of the discharge capacity of the battery capacity with respect to the current density of 0.2 C at the current density 2C was calculated, and the ratio characteristic was obtained. Further, the capacity retention ratio was measured by comparing the initial discharge capacity obtained by discharging a current of 1 C at room temperature with the discharge capacity after 100 cycles.

The results of these are shown in Tables 1 and 2.

(Evaluation)

The battery characteristics of Examples 1 to 19 were all good. Further, Examples 1 to 15 and 18 in which the metal salt of the raw material was a nitrate were particularly excellent in battery characteristics. Further, in Example 18, which was not fired under atmospheric pressure but was fired under pressure, the battery characteristics were the best.

Although the composition of the metal as the raw material of Comparative Examples 1 to 3 excessively contained oxygen as in the present invention, the battery characteristics were poor due to the pulverization conditions. In Comparative Examples 4 to 6, the composition of the metal as a raw material was outside the range of the present invention, and battery characteristics were further deteriorated due to the pulverization conditions.

Fig. 1 is a photograph showing the appearance of primary particles and secondary particles of a positive electrode active material.

Claims (8)

A positive electrode active material for a lithium ion battery, which is represented by the following composition formula: Li(Li _x Ni _1-xy M _y )O _2+α (wherein M is selected from the group consisting of Sc, Ti, V, Cr, Mn , one or more of Fe, Co, Cu, Zn, Ga, Ge, Bi, Sn, Mg, Ca, B, and Zr, 0≦x≦0.1, 0<y≦0.7, α>0), primary particles The particle size is 1.6 to 2.3 μm; the amount of alkali on the surface of the particle obtained by the two-stage neutralization titration measurement is 1.2% by mass or less, and if the amount of lithium hydroxide in the amount of the surface of the particle is A% by mass, carbonic acid is used. When lithium is set to B% by mass, A/B is 1 or less. The positive electrode active material for a lithium ion battery according to the first aspect of the invention, wherein the amount of alkali on the surface of the particles is 0.8% by mass or less. The positive electrode active material for a lithium ion battery according to claim 1 or 2, wherein the A/B is 0.7 or less. The positive electrode active material for a lithium ion battery according to the first or second aspect of the invention, wherein the M is one or more selected from the group consisting of Mn and Co. The positive electrode active material for a lithium ion battery according to claim 1 or 2, wherein α>0.05 in the composition formula. The positive electrode active material for a lithium ion battery according to claim 5, wherein α>0.1 in the composition formula. A positive electrode for a lithium ion battery using the positive electrode active material for a lithium ion battery according to claim 1 or 2. A lithium ion battery using lithium as claimed in claim 7 Positive electrode for ion batteries.