JP2012169224A - Positive electrode active material for lithium ion battery, positive electrode for lithium ion battery, and lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a lithium ion battery having excellent battery characteristics.SOLUTION: The positive electrode active material for a lithium ion battery contains a lithium-containing transition metal oxide, and a chlorine component, a silicon component, and a sulfur component, where the content of each component is 100 ppm or less with respect to the content of the lithium-containing transition metal oxide. The total content of the chlorine component, the silicon component, and the sulfur component is 200 ppm or less with respect to the content of the lithium-containing transition metal oxide.

Description

  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.

Lithium-containing transition metal oxides are generally used as positive electrode active materials for lithium ion batteries. Specifically, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), etc., improved characteristics (higher capacity, cycle characteristics, storage characteristics, reduced internal resistance) In order to improve the rate characteristics and safety, it is underway to combine them. Lithium ion batteries for large-scale applications such as in-vehicle use and load leveling are required to have different characteristics from those of conventional mobile phones and personal computers.

Conventionally, various methods have been used to improve battery characteristics. For example, Patent Document 1 _{discloses a} general formula Li [Ni _0.5-0.5 , characterized in that the content of Si element is 200 to _{1000 ppm.} lithium having _{x Mn 0.5-0.5x Li x] O 2} ( where 0.02 ≦ x ≦ 0.11) layered rock-salt structure represented by - nickel - manganese composite oxide is disclosed. And according to this, it describes that the improvement of the charge / discharge cycle characteristic under high temperature is realizable.

  Further, Patent Document 2 discloses that 100 to 1500 ppm of Group 1 and / or Group 2 element component (excluding lithium) with respect to the lithium transition metal composite oxide and 150 with respect to the lithium transition metal composite oxide. A positive electrode material for a lithium secondary battery comprising a lithium transition metal composite oxide having a sulfate ion component of 10000 ppm is disclosed. And according to this, it is described that a lithium secondary battery having a high high-temperature capacity maintenance rate can be provided by coexisting a metal component of Group 1 or Group 2 and a sulfate ion component.

  Further, Patent Document 3 discloses a method for producing lithium manganese oxide, characterized in that electrolytic manganese dioxide having a K content of 500 ppm or less is used as a raw material. And according to this, it is described that it is possible to provide a positive electrode material for a lithium ion secondary battery which is not only high in capacity but also excellent in rate characteristics.

Furthermore, Patent Document 4 discloses a general formula Li _x Co _1-y Me _y O ₂ (wherein x and y represent 0 <x <1.1 and 0 ≦ y <1. Me represents Co, Fe In the lithium composite oxide for a positive electrode active material of a lithium secondary battery represented by :), the impurity silicon (Si) contained in the lithium composite oxide is 500 ppm or less, and the average particle A lithium composite oxide for a lithium secondary battery positive electrode active material, characterized in that the diameter is 0.5 to 50 μm, is disclosed. And according to this, the lithium composite oxide for secondary batteries which can maintain the stable state with a small viscosity change rate of a lithium secondary battery positive electrode composition liquid, and a lithium secondary battery with high discharge capacity are provided. It is described that it can.

Further, Patent Document 5 discloses a positive electrode composite in which a positive electrode current collector made of an aluminum core material and LiM _x Co _1-x O ₂ (M is a metal element and x is 0 or more and less than 1) as a positive electrode active material. A non-aqueous electrolyte secondary battery in which a positive electrode coated with an agent and a negative electrode are sealed together with an electrolyte solution through a separator, and the positive electrode active material contains 5 to 30 ppm of chlorine. A secondary battery is disclosed. And according to this, it is excellent in safety by suppressing the calorific value generated even when the battery causes an internal short circuit, and further, the dropping of the positive electrode mixture from the positive electrode current collector is suppressed in the manufacturing process. It is described that a non-aqueous electrolyte secondary battery can be provided.

JP 2005-325000 A JP 2002-15739 A JP 2004-250270 A Japanese Patent No. 3891458 JP 2004-273200 A

  The lithium composite oxides described in Patent Documents 1 to 5 are intended to regulate the amount of impurities contained in the oxide, thereby improving various battery characteristics. There is room for improvement as a positive electrode active material for ion batteries.

  Then, this invention makes it a subject to provide the positive electrode active material for lithium ion batteries which has a favorable battery characteristic.

  As a result of intensive studies, the present inventor has found that there is a close correlation between the concentration of various impurities in the positive electrode active material and the battery characteristics. That is, it has been found that particularly good battery characteristics can be obtained when the concentration of various impurities in the positive electrode active material is below a predetermined value.

  The present invention completed on the basis of the above knowledge includes, in one aspect, a lithium-containing transition metal oxide and a chlorine component, a silicon component and a sulfur component of 100 ppm or less with respect to the lithium-containing transition metal oxide, The positive electrode active material for a lithium ion battery, wherein the total of the silicon component and the sulfur component is 200 ppm or less with respect to the lithium-containing transition metal oxide.

  In one embodiment, the positive electrode active material for a lithium ion battery according to the present invention has a chlorine component, a silicon component, and a sulfur component of 50 ppm or less with respect to the lithium-containing transition metal oxide, respectively, and a chlorine component, a silicon component, and a sulfur component. Is 100 ppm or less with respect to the lithium-containing transition metal oxide.

In another embodiment of the positive electrode active material for a lithium ion battery according to the present invention, the composition of the lithium-containing transition metal oxide has the composition formula: Li _x (Ni _y M _1-y ) O _z
(In the formula, M is one or more selected from the group consisting of Mn, Co and Al, x is 0.9 to 1.2, and y is 0.3 to 0.9. Yes, z is 1.9 or more.)
And has a layered structure.

  In another aspect, the present invention is a positive electrode for a lithium ion battery using the positive electrode active material for a lithium ion battery according to the present invention.

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

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material for lithium ion batteries which has a favorable battery characteristic can be provided.

(Configuration of positive electrode active material for lithium ion battery)
As a material of the positive electrode active material for lithium ion batteries of the present invention, compounds useful as a positive electrode active material for general positive electrodes for lithium ion batteries can be widely used. In particular, lithium cobaltate (LiCoO ₂ ), It is preferable to use lithium-containing transition metal oxides such as lithium nickelate (LiNiO ₂ ) and lithium manganate (LiMn ₂ O ₄ ). The lithium-containing transition metal oxide is not particularly limited. For example, the composition formula: Li _x (Ni _y M _1-y ) O _z
(In the formula, M is one or more selected from the group consisting of Mn, Co and Al, x is 0.9 to 1.2, and y is 0.3 to 0.9. Yes, z is 1.9 or more.)
And has a layered structure.
The ratio of lithium to all metals in the positive electrode active material for a lithium ion battery is 0.9 to 1.1. This is less than 0.9, and it is difficult to maintain a stable crystal structure. This is because of a low. Moreover, since the positive electrode active material has a layered structure, the discharge capacity is higher than that of a spinel structure or the like.

  The positive electrode active material for a lithium ion battery of the present invention contains oxygen excessively in the composition formula, and when used in a lithium ion battery, battery characteristics such as capacity, rate characteristics, and capacity retention ratio are improved.

The positive electrode active material for a lithium ion battery of the present invention contains a lithium-containing transition metal oxide and a chlorine component, a silicon component, and a sulfur component of 100 ppm or less with respect to the lithium-containing transition metal oxide, respectively. The total of the chlorine component, silicon component and sulfur component is 200 ppm or less with respect to the lithium-containing transition metal oxide.
The positive electrode active material for a lithium ion battery usually contains impurities such as chlorine, silicon and sulfur in the production process. At this time, chlorine is mainly contained in the form of LiCl or NaCl, silicon is mainly contained in the form of SiO ₂ , and sulfur is mainly contained in the form of Li ₂ S. Of these, LiCl, NaCl, and SiO ₂ each have a hygroscopic property, and bringing moisture into the battery causes deterioration of the battery. Li ₂ S becomes a factor that inhibits the battery action of Li ions. Moreover, since these do not dissolve in the crystal, they exist at the grain boundaries between the particles constituting the positive electrode active material, but when they are present on the surface of the positive electrode material, the battery characteristics are particularly adversely affected.
With respect to such problems, the positive electrode active material for lithium ion batteries according to the present invention has a chlorine component, a silicon component, and a sulfur component in impurities that adversely affect the battery characteristics as described above, compared to the lithium-containing transition metal oxide. Each of them is 100 ppm or less, and the influence of impurities on the battery characteristics is well suppressed.
Preferably, the chlorine component, silicon component, and sulfur component are each 50 ppm or less with respect to the lithium-containing transition metal oxide, and the total of the chlorine component, silicon component, and sulfur component is 100 ppm with respect to the lithium-containing transition metal oxide. It is as follows.

(Configuration of positive electrode for lithium ion battery and lithium ion battery using the same)
The positive electrode for a lithium ion battery according to an embodiment of the present invention includes, for example, a positive electrode mixture prepared by mixing a positive electrode active material for a lithium ion battery having the above-described configuration, a conductive additive, and a binder from an aluminum foil or the like. The current collector has a structure provided on one side or both sides. Moreover, the lithium ion battery which concerns on embodiment of this invention is equipped with the positive electrode for lithium ion batteries of such a structure.

(Method for producing positive electrode active material for lithium ion battery)
Next, the manufacturing method of the positive electrode active material for lithium ion batteries which concerns on embodiment of this invention is demonstrated in detail.
First, a metal salt solution is prepared. The metal is composed of, for example, Ni and one or more selected from the group consisting of Mn, Co, and Al. The metal salt is sulfate, chloride, nitrate, acetate, etc., and nitrate is particularly preferable. This is because even if it is mixed in the firing raw material, the nitrate base hardly remains if fired, and the nitrate functions as an oxidant and promotes the oxidation of the metal in the firing raw material. Each metal contained in the metal salt is adjusted so as to have a desired molar ratio. Thereby, the molar ratio of each metal in the positive electrode active material is determined.

Next, for example, lithium carbonate is suspended in pure water as a lithium raw material. The lithium raw material is not limited to lithium carbonate, and may be, for example, lithium nitrate, lithium hydroxide, lithium acetate, alkyl lithium, fatty acid lithium, or halogen lithium. Thereafter, a metal salt solution of the above metal is added to prepare a lithium salt solution slurry. At this time, fine particles of lithium-containing carbonate precipitate in the slurry. The average particle size of the fine particles in the slurry is adjusted to 8 to 16 μm by shearing with stirring for a predetermined time. Thus, by adjusting the particle size of the particles in the slurry, the particles are prevented from becoming too fine. For this reason, the baking condition of the particle | grains in a subsequent baking process becomes favorable. If the lithium compound does not react during heat treatment such as sulfate or chloride as a metal salt, it is washed with a saturated lithium carbonate solution and then filtered off. When the lithium compound reacts as a lithium raw material during the heat treatment, such as nitrate or acetate, it can be used as a calcined precursor by washing and drying as it is without washing.
Next, the lithium-containing carbonate separated by filtration is dried to obtain a lithium salt composite (precursor for lithium ion battery positive electrode material) powder.

In the above-described cleaning step, when sulfate or chloride salt is used as a raw material for the metal salt solution, the following measures are taken. That is, filtration by a filter press or the like is performed following the above-described cleaning. At this time, the air permeability of the filter cloth used for filtration is 0.4 cc / cm ² · sec or more, and the number of washings is 2 or more. Thereby, the residual amount of a chlorine component, a sulfur component, and a silicon component can be reduced from about 1000 mg / L before cleaning to about 300 mg / L. If the residual amounts of the chlorine component, silicon component, and sulfur component are reduced so far, the subsequent firing step is appropriately performed, so that all of chlorine, silicon, and sulfur are 50 ppm relative to the lithium-containing transition metal oxide. It becomes possible to be about.

Next, a mortar (firing container) having a predetermined capacity is prepared, and this calcining container is filled with the precursor powder for the lithium ion battery positive electrode material produced as described above. Next, the firing container filled with the precursor powder for the lithium ion battery positive electrode material is moved to a firing furnace and fired. Firing is performed by heating and holding for a predetermined time in an oxygen-containing atmosphere, preferably in an oxygen atmosphere. Further, it is preferable to perform baking under pressure of 101 to 202 KPa because the amount of oxygen in the composition further increases. The firing temperature is 850 to 1200 ° C. Preferably, it is performed at 850 to 950 ° C. When the firing temperature is in such a range, the crystallinity is improved and a high-performance positive electrode active material is obtained.
Moreover, the device which avoids the contamination from the mortar used is needed at this time. The mortar is a refractory usually made of alumina, mullite, cordierite, etc., but contains Al, Si, Mg, etc. as main components, and may become a contamination source of Si in particular. As a result of examining various types of mortars, it was found that the higher the thermal conductivity, the more contamination by Si. Accordingly, it is preferable that the material of the mortar has a thermal conductivity of 1.2 W / (m · K) or less.
Thereafter, the powder is taken out from the firing container and pulverized to obtain a powder of the positive electrode active material. At this time, it is preferable to use a pulverizer for crushing. When a pulverizer is used, the particles are classified, so that there is an advantage that a uniform particle size can be obtained.

  Examples for better understanding of the present invention and its advantages are provided below, but the present invention is not limited to these examples.

(Examples 1 to 11)
First, after suspending the amount of lithium carbonate described in Table 1 in pure water, a metal salt solution was added at 1.6 L / hr. Here, the metal salt solution was prepared by adjusting the nitrate, sulfate and chloride hydrates of each metal so that each metal had the composition ratio shown in Table 1, and the total number of moles of metal was 14 moles. It adjusted so that it might become.
By this treatment, fine lithium-containing carbonate was precipitated in the solution. When a sulfate or chloride was used as a metal salt, the precipitate was washed twice or more with a saturated lithium carbonate solution, and filtered using a filter press. At this time, the air permeability of the filter cloth was set to 1.2 to 1.5 cc / cm ² · sec.
Subsequently, the precipitate was dried to obtain a lithium-containing carbonate (a precursor for a lithium ion battery positive electrode material).
Next, a mortar having a constitutional component and thermal conductivity shown in Table 2 (alarm mortar A or mortar B) was prepared as a calcination container, and this calcination container was filled with a lithium-containing carbonate. Next, the firing container was put into a firing furnace, and the temperature was raised to the firing temperature shown in Table 1 over 6 hours, followed by heating and holding for 2 hours, followed by cooling to obtain an oxide. Next, the obtained oxide was crushed with a pulverizer to obtain a powder of a positive electrode material for a lithium ion secondary battery.

(Comparative Examples 1-10)
As Comparative Examples 1-10, each metal of the raw material has a composition as shown in Table 1, except that the combination of the precursor cleaning method and the firing container (cooker A to C) is different as shown in Table 1, The same processing as in Examples 1 to 11 was performed.

(Evaluation)
The metal content in each positive electrode material was measured with an inductively coupled plasma optical emission spectrometer (ICP-OES), and the composition ratio (molar ratio) of each metal was calculated. Moreover, each content rate of Si, S, and Cl was measured by ICP method and the pyrolysis potentiometric titration method. The oxygen content was obtained by subtracting the impurity concentration and the residual alkali amount from the total amount of the analytical sample in addition to the analytical values of Li and metal components, and z was calculated thereby. The average particle size of the precipitate (lithium-containing carbonate) in the lithium salt solution slurry was determined by observing 100 particles from SEM (Scanning Electron Microscope) photographs of the powder of each positive electrode material. The diameter was calculated by calculating the average value.
Also, each positive electrode material, conductive material, and binder are weighed at a ratio of 85: 8: 7, and the positive electrode material and the conductive material are mixed with the binder dissolved in an organic solvent (N-methylpyrrolidone). Then, it was made into a slurry, applied onto an Al foil, dried and pressed to obtain a positive electrode. Subsequently, a 2032 type coin cell for evaluation with Li as the counter electrode was prepared, and 1M-LiPF ₆ dissolved in EC-DMC (1: 1) was used as the electrolyte, and the current density was 0.2C. The discharge capacity was measured. Moreover, the ratio of the discharge capacity at the current density of 2C to the battery capacity at the current density of 0.2C was calculated to obtain rate characteristics. Furthermore, the capacity retention was measured by comparing the initial discharge capacity obtained with a 1 C discharge current at room temperature with the discharge capacity after 100 cycles. Table 3 shows the measurement results.

In Examples 1 to 11, good battery characteristics were obtained in all cases.
In Comparative Examples 1 to 3, 5 to 7, and 9, in all of the production process, although sulfides or chlorides remaining after firing such as sulfates or chlorides were precipitated, the precipitation Since the washing method of the object was not appropriate, the battery characteristics were poor.
In Comparative Examples 2, 4 and 8 to 10, the thermal conductivity of the mortar used for firing was large, especially contamination by Si was increased, resulting in poor battery characteristics.
Moreover, it was confirmed by XRD measurement that all of Examples 1-11 and Comparative Examples 1-10 are layered structures.

Claims (5)

  A lithium-containing transition metal oxide and a chlorine component, a silicon component and a sulfur component of 100 ppm or less with respect to the lithium-containing transition metal oxide, respectively, and the total of the chlorine component, silicon component and sulfur component is the lithium-containing transition The positive electrode active material for lithium ion batteries which is 200 ppm or less with respect to a metal oxide.   The chlorine component, silicon component, and sulfur component are each 50 ppm or less with respect to the lithium-containing transition metal oxide, and the total of the chlorine component, silicon component, and sulfur component is 100 ppm with respect to the lithium-containing transition metal oxide. The positive electrode active material for a lithium ion battery according to claim 1, wherein: The composition of the lithium-containing transition metal oxide has the composition formula: Li _x (Ni _y M _1-y ) O _z
(In the formula, M is one or more selected from the group consisting of Mn, Co and Al, x is 0.9 to 1.2, and y is 0.3 to 0.9. Yes, z is 1.9 or more.)
The positive electrode active material for a lithium ion battery according to claim 1 or 2, which has a layered structure.   The positive electrode for lithium ion batteries using the positive electrode active material for lithium ion batteries in any one of Claims 1-3.   The lithium ion battery using the positive electrode for lithium ion batteries of Claim 4.