JPH11195418A - Quantitating method for elution mn quantity of spinel li/mn system composite oxide and positive electrode active material for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quantitating method for elution Mn quantity of a spinel Li/Mn system composite oxide and a positive electrode active material for lithium secondary battery which is excellent in charging/discharging cycle characteristic and whose quality is stable. SOLUTION: This quantitating method for elution Mn quantity of a spinel Li/Mn system composite oxide comprises the steps of: existing a spinel Li/Mn system composite oxide of about 10<-2> -0.5×10<-2> mol per. 1l of an acidic aqueous solution whose pH is equal or smaller than 2 without dissolving λ-MnO<2> and eluting Mn; and quantitating a quantity of Mn eluted in the acidic aqueous solution in the dissolution equilibrium situation. There is provided, by this method, a positive electrode active material for lithium secondary battery containing a spinel Li/Mn system composite oxide as a main component wherein the eluted Mn quantity rate measured by using an acidic aqueous solution of pH 1±0.2 at 20 deg.C is equal or smaller than 15 wt.%. They are preferable for manufacturing a lithium secondary battery for various electric equipment, in particular, portable equipment having a long life.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a spinel type Li ·
The present invention relates to a method for determining the amount of Mn eluted from a Mn-based composite oxide and a positive electrode active material for a lithium secondary battery containing a spinel-type Li · Mn-based composite oxide as a main component.

[0002]

2. Description of the Related Art Lithium secondary batteries are generally receiving more and more attention because they are superior in terms of electromotive force and energy density. In the art, various improvements have been studied in order to develop more practical products. Has been keen. Improvement research on positive electrode active materials is also one of the important issues. As a positive electrode active material,
Conventional composite oxides of lithium and transition metal elements (LiM
eO ₂ and Me are new transition metal elements of Groups 9 to 10 of the periodic table)
Instead of spinel-type Li that can obtain higher electromotive force
Mn composite oxide (Li _A Mn ₂ O ₄ ) has recently been proposed, and the value of A in the general formula of the composite oxide is 0.0
In the case of 5 to 0.5, 4V class, and the value of A is 0.5 to 0.5
It is known that a 1.1V lithium secondary battery can be obtained in the case of 1.1.

A secondary battery using the Li.Mn composite oxide as a positive electrode active material has a problem in charge / discharge cycle characteristics. That is, when the charge / discharge cycle is repeated, the discharge capacity of the battery gradually decreases.

In order to solve this problem, a part of Mn is replaced by
Co, Cr, Ni, Fe, or various other elements
It has been proposed to substitute one or more of them.
Various Li-Mn based composite oxides obtained from such proposal
Indicates that the charge-discharge cycle characteristics tend to be improved
Of an unsubstituted Li-Mn composite oxide (Li_AMn
_TwoO _FourAs in the case of), charge-discharge cycle characteristics between production lots
There is a problem that large variations exist.

[0005] Spinel-type Li-Mn-based composite oxides are
At the time of electricity, Li is released and λ-MnO _TwoPhase change and discharge
Sometimes λ-MnO_TwoOriginal Li-Mn-based composite oxidation
It is known that a substance changes its phase. Also spinel structure
In theory, Li is theoretically at the 8a site, while M
n is present at each of the 16d sites.

Accordingly, the present inventors have made the following based on the above facts and theory for the purpose of investigating the reason for the above-mentioned variation or deterioration of the charge / discharge cycle characteristics.
Made the hypothesis. In general, the decrease in charge / discharge cycle characteristics is due to partial collapse of the spinel structure due to elution of a part of Mn into the electrolyte. In addition, during the repetition of the above-mentioned alternating phase change in the charge / discharge cycle, the crystal structure is broken due to expansion and contraction of the lattice of the spinel structure, and Mn that is in a state of being easily eluted is eluted into the electrolytic solution. , Mn are theoretically present at the 16d site, but some Mn are present at the 8a site. This Mn is an example of Mn in the above-mentioned easily eluted state, and should be released along with the release of Li during charging.

On the other hand, it is known that the spinel-type Li.Mn-based composite oxide undergoes a phase change to λ-MnO ₂ in an acid aqueous solution while retaining Li and releasing the spinel structure as in the case of charging. . Therefore, focusing on this point, various types of Li
Examination of the relationship between the amount of Mn eluted in an aqueous solution of an Mn-based composite oxide and the charge / discharge cycle characteristics revealed that the use of a material with a large amount of eluted Mn as the positive electrode active material deteriorated the charge / discharge cycle characteristics of the battery. It was found that the above-mentioned hypothesis was somewhat correct, and that it was possible to establish a selection criterion capable of selecting a Li.Mn-based composite oxide having good charge / discharge cycle characteristics.

[0008]

SUMMARY OF THE INVENTION The present invention has been completed on the basis of the above-mentioned new findings, and is directed to a method for quantifying the amount of dissolved Mn of a spinel-type Li.Mn-based composite oxide and a charge / discharge cycle. It is an object to propose a positive electrode active material for a lithium secondary battery having excellent characteristics and stable quality.

[0009]

The above object can be solved by the following quantitative method and a positive electrode active material for a lithium secondary battery. (1) The spinel-type Li · Mn-based composite oxide to be inspected is present in an aqueous acid solution having substantially no solubility of λ-MnO ₂ and a pH of 2 or less to elute Mn. Dissolution M of spinel-type Li · Mn-based composite oxide characterized by quantifying the amount of Mn eluted in an aqueous solution
A method for determining the amount of n. (2) The method for determining the elution Mn amount of a spinel-type Li.Mn-based composite oxide according to (1), wherein the aqueous acid solution is at least one aqueous solution selected from the group consisting of nitric acid, sulfuric acid, and hydrochloric acid. (3) The method according to (1) or (2) above, wherein the pH of the aqueous acid solution is 1 ± 0.2. (4) When the dissolution Mn content rate calculated by the following formula from the dissolution Mn content determined in the dissolution equilibrium state at 20 ° C. by the method according to any of the above (1) to (3) is 15% by weight or less. A positive electrode active material for a lithium secondary battery, comprising a spinel-type Li · Mn-based composite oxide as a main component. Eluted Mn amount rate = ([Eluted Mn amount] / [Total Mn amount contained in spinel-type Li · Mn-based composite oxide of amount to be inspected in the acid aqueous solution]) × 100 (5) Eluted Mn amount ratio Is 13% by weight or less, the positive electrode active material for a lithium secondary battery according to the above (4).

[0010]

In the above invention (1), the spinel-type Li.Mn-based composite oxide to be inspected (hereinafter, the spinel-type Li-Mn-based composite oxide is simply referred to as "SLM composite oxide"). ) Without dissolving λ-MnO ₂ and pH
By introducing the solution into an acid aqueous solution of 2 or less to reach a dissolution equilibrium state, the amount of eluted Mn, which is important in determining the quality of charge / discharge cycle characteristics, can be accurately determined.

In the above invention (4), the SLM composite oxide having an elution Mn content rate of 15% by weight or less calculated based on the elution Mn content determined from the invention of the above (1) is lithium. By using as a positive electrode active material for a secondary battery, a lithium secondary battery having excellent charge-discharge cycle characteristics and stable quality can be manufactured.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION For SLM composite oxide, M
n is not substituted with another element, Mn is partially substituted with another element, Mn is partially substituted with another element, and two or more elements are substituted. However, the variation in the amount of eluted Mn is not essentially affected by the presence or absence of the Mn substitution element and the type of the substitution element, and therefore, in the present invention, these various SLM composite oxides are targeted. It can be. For example, those represented by the following general formula (1) can be exemplified. _{Li A Mn 2-x Me x} O 4 (1) General formula (1), A is from 0.05 to 2.3, preferably 0.5 to 1.5, X is 0 to 0.5 is there. X
Is 0, it means that Mn is not replaced by another element. On the other hand, when X is not 0, it means that Mn is replaced by the element Me, and in this case, X is 0.01 to 0.5,
It is particularly preferably 0.02 to 0.2. Element Me
As elements of Group 3 to 10 of the new periodic table, for example, Zr,
V, Cr, Mo, Fe, Co, Ni, etc., or 13 to
Group 15 element, for example, B, Al, Ge, Pb, Sn, Sb
And so on. In the case of an SLM composite oxide in which Mn is substituted by two or more of these elements, the total amount of the two or more elements may be within the range of X described above.

In the determination of the elution Mn amount of the SLM composite oxide, an aqueous solution of an acid that does not dissolve or substantially dissolves λ-MnO ₂ and has a pH of 2 or less is used as the solution. When a strong acid having a pH of about 0.1 is used as the acid aqueous solution, λ-MnO generated during charging in a normal battery reaction is used.
Since there is a problem of dissolving ₂ in the determination of the amount of eluted Mn, the acid aqueous solution used must be one that does not substantially dissolve λ-MnO ₂ , particularly one that has a solubility of 0.1% by weight or less. It is advisable to confirm this in a preliminary dissolution test. λ
Do not dissolve or substantially dissolve MnO ₂ and
As an example of the acid aqueous solution of H2 or less, dilute nitric acid, dilute sulfuric acid, dilute hydrochloric acid, and the like having a pH of 0.5 to 2, particularly preferably a pH of 0.8 to 2, are preferable. Since the elution of soluble Mn tends to be somewhat insufficient if the pH of the aqueous acid solution is high, an aqueous solution of nitric acid and / or sulfuric acid having a pH of 2 or less, particularly 1 ± 0.2 is preferable as the aqueous acid solution in the present invention. .

When an excessive amount of the SLM composite oxide to be inspected is put into an acid aqueous solution, Li is eluted and the pH of the acid aqueous solution is increased.
To reduce the solubility of soluble Mn for quantitative purposes. For this reason, the input amount of the SLM composite oxide is not more than 10 ^-2 mol per liter of the aqueous acid solution, preferably 1 to ² mol.
The appropriate amount is about 0 ^{-2 to} 0.5 × 10 ^-2 mol.

The SLM composite oxide to be inspected is preferably a fine powder in order to effectively dissolve soluble Mn, particularly a fine powder which passes 100% through a 300 mesh Tyler standard sieve. . A predetermined amount of the SLM complex oxide may be added to an acid aqueous solution whose pH has been adjusted in advance, or the SLM complex oxide may be suspended in distilled water, and about 1 to 5 N of the above acid or the like may be added thereon. Then, the pH may be adjusted to a desired value.

In any case, the soluble Mn in the SLM composite oxide to be inspected is brought to a solution equilibrium state, and the amount of Mn eluted in the acid aqueous solution is determined by, for example, ICP (inductively coupled high frequency plasma emission spectroscopy). And quantify. SL
The elution Mn amount ratio (%) of the M composite oxide can be calculated by the following equation (2). Eluted Mn amount ratio (%) = ([Eluted Mn amount] / [Total Mn amount contained in the SLM composite oxide of the amount to be tested in the acid aqueous solution]) × 100 (2)

Although the amount of eluted Mn slightly varies depending on the temperature in the dissolution equilibrium state, a stable amount of eluted Mn can be obtained when quantified in the range of about 10 to 40 ° C. The amount of eluted Mn thus determined is very useful for selecting an SLM composite oxide exhibiting excellent performance as a positive electrode active material for a lithium secondary battery as described below.

In the present invention, a positive electrode for a lithium secondary battery
As the active material, the elution Mn amount determined by the above method,
In particular, use an acid aqueous solution with a pH of 1 ± 0.2 to reach 20 ° C.
From the amount of eluted Mn determined at equilibrium
The dissolution rate of the released Mn is 15% by weight or less, especially 13 times.
% Or less of SLM composite oxide
Can be Such an SLM composite oxide has, for example, the chemical formula
Is Li_AMn_2-xMe _xO_FourIf the formula is
Oxidation of elements other than oxygen to be formed, ie, Li, Mn, Me
Substances, hydroxides, carbonates, nitrates, etc.
Was mixed so that the ratio represented by the chemical formula was obtained.
The mixture is heated in air at 500-1000 ° C for 1-50 hours.
Thermal firing and then melting out of lots of
In order to select those whose Mn output rate is less than the above value
You can get more.

The positive electrode active material of the present invention is the same as a conventionally known method in the fields of a non-aqueous electrolyte lithium secondary battery and a solid electrolyte lithium secondary battery using a conventional SLM composite oxide as a positive electrode active material. It can be put to practical use by the method.
Hereinafter, some examples of typical or preferable practical methods will be described.

Examples of the binder for the positive electrode active material include polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and ethylene-propylene-diene-based polymers. Examples of the conductive agent include various types of conductive graphite and conductive carbon. Black is exemplified.

The amount of the positive electrode active material used is 80 to 9 per 100 parts by weight of the total amount of the positive electrode active material, the binder, and the conductive agent.
It is about 5 parts by weight, and the amount of the binder used is 10
The amount is about 1 to 10 parts by weight per 0 parts by weight, and the amount of the conductive agent is about 3 to 15 parts by weight per 100 parts by weight of the positive electrode active material.

The positive electrode sheet can be formed by applying a mixed composition comprising a positive electrode active material, a binder, and a conductive agent to one or both surfaces of a positive electrode current collector, sufficiently drying the resultant, and rolling. One having a positive electrode active material layer having a thickness of about 20 to 500 μm, particularly about 50 to 200 μm on one or both sides is exemplified.

Preferred examples of the negative electrode active material used in common with the positive electrode active material of the present invention include various natural graphites and artificial graphites, for example, graphites such as fibrous graphite, flake graphite, and spherical graphite. Examples of the binder include polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and an ethylene-propylene-diene-based polymer. The amount of the negative electrode active material used is about 80 to 96 parts by weight per 100 parts by weight of the total amount of the negative electrode active material and the binder.

As the positive electrode current collector, a conductive metal such as aluminum, an aluminum alloy,
About 100 μm, especially about 15 to 50 μm foil or perforated foil, about 25 to 300 μm thickness, especially about 30 to 150 μm
A certain degree of expanded metal is preferred. As the negative electrode current collector, a conductive metal such as copper, nickel, silver, or SUS, having a thickness of about 5 to 100 μm, particularly about 8 to 50 μm or a perforated foil, and a thickness of about 20 to 300 μm, particularly about 25 to 300 μm,
An expanded metal of about 100 μm is preferable.

Examples of the non-aqueous electrolyte include an electrolyte in which salts are dissolved in an organic solvent. The salts include LiC
10 ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , Li
Examples thereof include AlCl ₄ and Li (CF ₃ SO ₂ ) ₂ N, and one or a mixture of two or more thereof is used.

As the organic solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate,
Diethyl carbonate, ethyl methyl carbonate, dimethyl sulfoxide, sulfolane, γ-butyrolactone, 1,2-dimethoxyethane, N, N-dimethylformamide, tetrahydrofuran, 1,3-dioxolan, 2-methyltetrahydrofuran, diethyl ether, and the like, One or a mixture of two or more thereof is used. The concentration of the above salts in the electrolyte is suitably about 0.1 to 3 mol / l.

[0027]

EXAMPLES The present invention will be described in more detail with reference to the following examples, and comparative examples will also be described to show the remarkable effects of the present invention.

Examples 1 and 2, Comparative Example 1 A mixture of electrolytic MnO ₂ and Li ₂ CO ₃ was calcined at about 750 ° C. for about 15 hours, and then pulverized to obtain a fine powder having the chemical formula of LiMn ₂ O ₄ ( Ten lots of SLM composite oxide (100% passed through a 330 mesh Tyler standard sieve) were produced. Then, the eluted Mn content ratio (pH of the aqueous acid solution: 1 ± 0.2, quantification temperature: 20 ° C.) for each lot was measured, and the lot having a value of 12.5% (% by weight, hereinafter the same) was used in Examples. 1, a lot of 14.5% was taken as Example 2, and a lot with a value of 16.4% was taken as Comparative Example 1.

Examples 3-4, Comparative Example 2 A mixture of electrolytic MnO ₂ , Li ₂ CO ₃ , and Al (OH) ₃ was calcined at about 750 ° C. for about 15 hours and then pulverized to obtain LiMn _1.95 Al _0.05 O Ten lots of SLM composite oxides of fine powder (100% passed through a 330 mesh Tyler standard sieve) having the chemical formula of ₄ were produced. Then, the eluted Mn content rate (pH of the aqueous acid solution: 1 ± 0.2, quantification temperature: 20 ° C.) for each lot was measured, and the lot having the value of 10.6% was determined as Example 3, and 12.2%. Was determined as Example 4 and a lot having a value of 15.3% was determined as Comparative Example 2.

Using each of the positive electrode active materials of Examples 1-4 and Comparative Examples 1-2, 92 parts by weight of the positive electrode active material, 3 parts by weight of acetylene black, 5 parts by weight of polyvinylidene fluoride, and N-methyl-2-pyrrolidone And 70 parts by weight to obtain a slurry. This slurry was applied on an aluminum foil and dried to prepare a positive electrode sheet having a positive electrode active material of 20 mg / cm ² . Each positive electrode sheet thus obtained and Li
A foil is brought into close contact with a porous polyethylene separator therebetween, and a solution obtained by dissolving 1 mol of LiPF ₆ per liter of a mixed solvent of ethylene carbonate and ethyl methyl carbonate (mixing volume ratio is 1: 1) is used as an electrolytic solution. This was impregnated between the positive electrode sheet and the Li foil to produce a sealed coin-type lithium secondary battery.

Each lithium secondary battery was subjected to 20 charge / discharge cycles according to the test method described below. As a result,
The retention rate of the discharge capacity at the 20th cycle (percentage with respect to the discharge capacity at the first cycle) is as shown in Table 1. In each of the examples, the retention rate was 80% or more, and a good discharge capacity was maintained. On the other hand, it can be seen that in both Comparative Examples 1 and 2, the retention was 60% or less, and the discharge capacity was rapidly reduced by the charge / discharge cycle.

Charge / discharge cycle test method: At 60 ° C., the battery was charged for 5 hours under a constant current of 1 mA / cm ² of the positive electrode sheet and a constant voltage of 4.3 V, and then charged at a constant current of 0.5 mA / cm ^{2 of the} positive electrode sheet. Discharge is performed until the terminal voltage becomes 3 V under a constant current, and then charging and discharging are paused for 1 hour. The above-described charging / discharging and pausing are repeated 20 times as one cycle. The discharge capacity in each cycle is calculated by calculating the quantity of electricity (mA · H) from the discharge current value and the discharge time, and calculating the discharge capacity (mA · H) from the weight (g) of the positive electrode active material contained in the lithium secondary battery. / G).

[0033]

[Table 1]

[0034]

Industrial Applicability The method for quantifying the amount of dissolved Mn according to the present invention is an industrial method as a test method for selecting those having good charge / discharge cycle characteristics from SLM composite oxides manufactured or prepared in factories and laboratories. It is useful for research or development research. In addition, the positive electrode active material of the present invention is excellent in charge-discharge cycle characteristics and stable in quality, so that it is suitable for production of a long-life lithium secondary battery for various electric devices, especially portable products.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI // G01N 21/73 G01N 21/73

Claims (5)

[Claims] 1. The method according to claim 1, wherein substantially no λ-MnO ₂ is dissolved and p
Spinel type Li.
Mn eluted in the presence of a Mn-based composite oxide and quantification of the amount of Mn eluted in the spinel-type LiMn-based composite oxide, wherein the amount of Mn eluted in the acid aqueous solution in a solution equilibrium state is determined. Method. 2. The elution M of the spinel-type Li · Mn-based composite oxide according to claim 1, wherein the acid aqueous solution is at least one aqueous solution selected from the group consisting of nitric acid, sulfuric acid and hydrochloric acid.
A method for determining the amount of n. 3. The method according to claim 1, wherein the pH of the aqueous acid solution is 1 ± 0.2. 4. The eluted M quantified in a solution equilibrium state at 20 ° C. by the method according to claim 1.
The elution Mn content rate calculated from the n content by the following formula is 15% by weight.
A positive electrode active material for a lithium secondary battery, comprising the following spinel-type Li · Mn-based composite oxide as a main component. Eluted Mn amount rate = ([Eluted Mn amount] / [Total Mn amount contained in spinel-type Li · Mn-based composite oxide of amount to be inspected in acid aqueous solution]) × 100 5. The positive electrode active material for a lithium secondary battery according to claim 4, wherein the amount ratio of dissolved Mn is 13% by weight or less.