JP2002075462A - Charge-discharge control method of nonaqueous secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charge-discharge control method enabling a nonaqueous secondary cell to improve cycle property and preservation property. SOLUTION: For the charge-discharge control method of the nonaqueous secondary cell, comprising a positive pole using lithium-manganese double oxide expressed by the general formula; Li1+aMn2-a-yMyO4 (M represents one or more kinds of elements chosen from metal elements excluding manganese, or transition metal elements, 0<=a<=0.5, 0<=y<=y<=0.5) as an activator, and a negative pole using lithium, lithium alloy, or carbon material reversibly occluding and releasing lithium as an activator, the charge-discharge control is carried out so that the range of x in the general formula; Lix+aMn2-a-yMyO4, using the coefficient x (0<=x<=1) determined by adding or removing Li, becomes 0<x<=0.6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge / discharge control method for a non-aqueous electrolyte secondary battery using a lithium manganese composite oxide as a positive electrode active material.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become more portable and cordless, there is a demand for the development of a small, lightweight, and high energy density secondary battery as a power supply for driving the electronic devices. As a positive electrode material used for a nonaqueous electrolyte secondary battery, a composite oxide of lithium and a transition metal having an electron in a 3d orbit, such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ , is known. In particular, lithium manganese composite oxides have the advantages of low pollution, low cost, and high safety compared to other oxides, and research and development have been active from this viewpoint.

In this research and development, in addition to the study to improve the battery capacity and the safety, the following issues have been studied. In non-aqueous electrolyte secondary batteries for electric vehicles, severe environmental tests are indispensable elements compared to small consumer devices.For example, use in high temperature and high humidity, storage, and use in low temperature environment are assumed. Required tests and the like. In particular, in a non-aqueous electrolyte secondary battery using a lithium manganese composite oxide as a positive electrode active material, it is serious that a non-aqueous electrolyte secondary battery stored in a high-temperature environment deteriorates its battery characteristics. It is a problem.

One of the causes of deterioration is the elution of manganese ions. From this viewpoint, materials that can suppress the elution of manganese from the positive electrode active material have been studied. For example,
In Japanese Patent Application Laid-Open No. 9-82360, means for suppressing the elution of manganese ions by forming a lithium ion conductive solid electrolyte layer on the surface of a positive electrode active material has been studied. Also, in Japanese Unexamined Patent Application Publication No. 11-332115, a state of charge (SOC) is described.
Since the amount of manganese ions eluted in a high region of (ge) is large and the deterioration rate is high, a method of controlling the SOC at a SOC of 50% or less has also been proposed.

[0005]

However, these conventional techniques have a problem that the impedance of the battery increases when the battery is left in the low SOC state. In particular, the rate of increase in the impedance of the battery at the depth of charge SOC where the range of the x value of Li _{x + a} Mn _{2- ay My} O _{4 satisfies} x> 0.6 becomes high. Therefore, there is a problem that long-term reliability cannot be ensured especially for a power supply for high output.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a non-aqueous electrolyte secondary battery capable of preventing an increase in impedance even when used in a high-temperature environment or stored for a long period of time. It is an object to provide a control method.

[0007]

The non-aqueous electrolyte secondary of the present invention
The charge / discharge control method of the battery is represented by the general formula Li_{1 + a}Mn_2-ayM
_yO_Four(M is a metal element other than manganese or a transition metal element
One or two or more elements selected from the group consisting of 0 ≦ a ≦
0.5, 0 ≦ y ≦ 0.5) lithium manganese
Using a composite oxide as the positive electrode active material, lithium, lithium alloy
Or negatively impact carbon materials that occlude and release lithium reversibly.
This is a method for charging and discharging non-aqueous electrolyte
The coefficient x (0 ≦ x ≦ 1) by insertion and extraction of Li was used.
General formula Li _{x + a}Mn_2-ayM_yO_FourIs in the range of 0
The charge / discharge control is performed so that <x ≦ 0.6.
You.

Accordingly, the x value x> in the above general formula
It is possible to prevent an increase in the impedance of the battery which occurs when the battery is stored in the range of 0.6, particularly when the x value is around 0.75. That is, the lithium manganese composite oxide has an unstable crystal structure when the range of the x value is x> 0.6, and the crystal structure is destroyed by charge / discharge or storage. It is estimated to rise.

More specifically, the lithium manganese composite oxide according to the present invention has the general formula Li _{1 + a} Mn _2-ay M
_y O ₄ (M is one or more elements selected from metal elements or transition metal elements other than manganese, 0 ≦ a ≦
0.5, 0 ≦ y ≦ 0.5). Compounds in which a part of manganese in the crystal structure is substituted with a metal element or a transition metal element, for example, sodium (Na), magnesium (Mg), chromium (Cr), cobalt (C
o) In the substituted body substituted by one or more elements selected from iron (Fe) and the like, the range of the coefficient x by the insertion and extraction of Li is 0 <x ≦ 0, as compared with the unsubstituted body. .6
If so, the rate of increase in the impedance of the battery can be reduced.

When the coefficient x due to the insertion / removal of Li is 0 <x ≦ 0.
In order to control the charge / discharge to be 6, the relationship between the x value and the SOC of the battery is determined from the irreversible capacity by the first charge / discharge and the charge capacity up to a predetermined full charge according to the design of the battery. Then, the required SOC range may be obtained. Furthermore, S
A method of grasping the relationship between the OC and the battery voltage and the current value and controlling the SOC based on the detection of the voltage and the current, and a method of controlling the SOC based on the calculated value of the current capacity flowing into and out of the battery are possible.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a cylindrical non-aqueous electrolyte secondary battery used in an embodiment of the present invention will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes a negative electrode, which is made of artificial graphite as a main material, and which has a weight ratio of 100: 9 with a binder PVDF.
The mixture in the ratio of is applied to both sides of the copper foil and dried,
After rolling, it is cut into a predetermined size. Reference numeral 2 denotes a nickel negative electrode lead spot-welded to the negative electrode 1. Reference numeral 3 denotes a positive electrode, in which Li _1.1 Mn ₂ O _{4 as} an active material is mixed with a conductive agent carbon black and a binder PVDF in a weight ratio of 10%.
A mixture mixed at a ratio of 0: 3: 4 was applied to both sides of an aluminum foil, dried, rolled, and cut into a predetermined size. Reference numeral 4 denotes an aluminum positive electrode lead ultrasonically welded to the positive electrode 3. Reference numeral 5 denotes a separator made of a microporous film made of polyethylene. The separator 5 is interposed between the negative electrode 1 and the positive electrode 3 and is swirled to form an electrode plate group.
6 is an upper insulating plate made of propylene disposed above the electrode plate group,
Reference numeral 7 denotes a lower insulating plate disposed below the electrode group. Reference numeral 8 denotes a case in which an electrode group is housed, which is obtained by plating nickel on iron.

After the positive electrode lead 4 is spot-welded to the aluminum sealing plate and the negative electrode lead 2 is spot-welded to the bottom of the case 8, a predetermined amount of non-aqueous electrolyte is injected into the electrode plate group in the case 8, and the gasket is 9 to the opening of the case 8 with the sealing plate 1
0 to complete the battery. In addition, 11 is a positive electrode terminal of the battery, and the negative electrode terminal is also the case 8 of the battery.

As an electrolytic solution, lithium hexafluorophosphate (1 mol / mol) was used as a supporting electrolyte in an organic solvent obtained by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 1: 3.
Use a non-aqueous electrolyte dissolved at a concentration of 1 liter.

(Experiment 1) The cylindrical non-aqueous electrolyte secondary battery produced as described above was used as an evaluation battery. The test conditions were a charge current of 130 mA, a charge end voltage of 4.3 V, and a discharge current of 1.
Charge and discharge were repeated four times at 30 mA, a discharge end voltage of 3 V, and an environmental temperature of 25 ° C. Using an AC impedance measuring device, the actual value of the impedance was measured when the measurement frequency was 0.1 Hz. Hereinafter, the measured value by this method is referred to as an impedance measured value. Next, the depth of charge and discharge was adjusted under the following conditions (Comparative Examples 1 to 3 and Examples 1 to 4). After storage at an ambient temperature of 60 ° C. for 30 days, charge and discharge were performed, and the impedance of the battery was measured. Comparative Example 1 Lithium manganese composite oxide, general formula L
ix _{+ 0.1} Mn ₂ O ₄ : Adjusted so that x = 0.9 (SOC 0% in this experiment) and preserved. Comparative Example 2 Lithium manganese composite oxide, general formula L
ix _{+ 0.1} Mn ₂ O ₄ : Adjusted so that x = 0.85 (SOC 5% in this experiment) and preserved. [Comparative Example 3] Lithium manganese composite oxide, general formula L
ix _{+ 0.1} Mn ₂ O ₄ : Adjusted so that x = 0.75 (SOC 20% in this experiment) and preserved. [Example 1] Lithium manganese composite oxide, general formula L
ix _{+ 0.1} Mn ₂ O ₄ : Adjusted so that x = 0.6 (SOC 40% in this experiment) and preserved. [Example 2] Lithium manganese composite oxide, general formula L
ix _{+ 0.1} Mn ₂ O ₄ : Adjusted so that x = 0.45 (SOC 60% in this experiment) and preserved. [Example 3] Lithium manganese composite oxide, general formula L
ix _{+ 0.1} Mn ₂ O ₄ : Adjusted so that x = 0.3 (SOC 80% in this experiment) and preserved. [Example 4] Lithium manganese composite oxide, general formula L
ix _{+ 0.1} Mn ₂ O ₄ : Adjusted so that x = 0.15 (SOC 100% in this experiment) and preserved.

(Experiment 2) The cathode active material was Li _1.1 Mn _1.9
A battery was fabricated in the same manner as in Experiment 1 except that the battery was changed to Cr _0.1 O ₄ . Under the following conditions (Comparative Examples 4 to 6, Example 5)
The charge / discharge depth was adjusted in 8), and the battery was stored at an ambient temperature of 60 ° C. for 30 days, charged / discharged, and the impedance of the battery was measured. [Comparative Example 4] Lithium manganese composite oxide, general formula L
_{i x Mn 1.9 Cr 0. 1 O} 4: Adjusted so that x = 0.9 (SOC0% in this experiment) Save. [Comparative Example 5] Lithium manganese composite oxide, general formula L
_{i x Mn 1.9 Cr 0. 1 O} 4: Adjusted so that x = 0.85 (SOC5% in this experiment) Save. [Comparative Example 6] Lithium manganese composite oxide, general formula L
_{i x Mn 1.9 Cr 0. 1 O} 4: Adjusted so that x = 0.75 (SOC20% in this experiment) Save. Example 5 Lithium-manganese composite oxide, general formula L
_{i x Mn 1.9 Cr 0. 1 O} 4: Adjusted so that x = 0.6 (SOC40% in this experiment) Save. Example 6 Lithium-manganese composite oxide, general formula L
_{i x Mn 1.9 Cr 0. 1 O} 4: Adjusted so that x = 0.45 (SOC60% in this experiment) Save. Example 7 Lithium manganese composite oxide, general formula L
_{i x Mn 1.9 Cr 0. 1 O} 4: Adjusted so that x = 0.3 (SOC80% in this experiment) Save. Example 8 Lithium-manganese composite oxide, general formula L
_{i x Mn 1.9 Cr 0. 1 O} 4: Adjusted so that x = 0.15 (SOC100% in this experiment) Save.

Examples 1 to 4 of Experiment 1 and Comparative Examples 1 to
For the non-aqueous electrolyte secondary batteries of Examples 3 to 8 and Comparative Examples 4 and 6 of Experiment 2 and Experiment 2, the rate of change obtained by comparing the impedance measured under the above measurement conditions with the impedance before storage as 100 (hereinafter, referred to as the impedance). , Impedance rise rate).

FIG. 2 shows the relationship between the impedance increase rate in Experiments 1 and 2 and the x value (hereinafter referred to as x value) in the general formula of the lithium manganese composite oxide.

As can be seen from FIG. 2, in the range of x value, 0 ≦ x ≦ 0.6 (Examples 1 to 8)
It can be seen that the rate of increase in impedance after storage in a high-temperature environment is lower than that of (Comparative Examples 1 to 6). x> 0.
The reason why the impedance increase rate is high in the range of 6 is that the lithium manganese composite compound is unstable in the above range,
It is presumed that the crystal structure collapsed due to high-temperature storage.

As described above, in the nonaqueous electrolyte secondary battery using the lithium manganese composite oxide as a positive electrode, the general formula Li
range of _{x + a Mn 2-ay M} y O 4 of x is, by controlling the non-aqueous electrolyte secondary battery so as not to be stored in x> 0.6, to prevent an increase in impedance be able to.

In Experiment 1, the lithium manganese composite acid was used.
General formula Li_{x + a}Mn_2-ayM _yO_FourIn a
= 0.1, y = 0, but 0 ≦ a ≦ 0.5, 0
The same effect can be obtained when ≦ y ≦ 0.5. Also,
In Experiment 2, chromium (Cr) was used as a typical example of M in the general formula.
Was selected, for example, sodium (Na), magnesium
Gold such as aluminum (Mg), cobalt (Co), iron (Fe)
One or two selected from the group elements or transition metal elements
A similar effect can be obtained with the combined element.

The relationship between the x value and the SOC or the battery voltage with respect to the battery capacity is determined by the battery material, design, and charging / discharging method. In the non-aqueous electrolyte secondary batteries used in Examples 1 to 8 and Comparative Examples 1 to 6, since artificial graphite was used for the negative electrode, the negative electrode has an irreversible capacity for several cycles after the battery was manufactured. Therefore, the SOC0 of the nonaqueous electrolyte secondary battery
X value of the general formula _{Li x + a Mn 2-ay} M y O 4 , which corresponds to percentages of 0.9, which calculates the difference irreversible capacity equivalent terms Li amount from 1. The x value corresponding to 100% SOC is 0.15, which is the difference between the converted Li equivalent to the charging capacity and the calculated Li from 0.9. X value and SOC between SOC0 and 100%
Are in a proportional relationship. These values can be more accurately confirmed by taking out the positive electrode for each SOC from an experiment and performing chemical analysis. As described above, for the nonaqueous electrolyte secondary battery under the battery design and charge / discharge conditions, the SOC corresponding to the above-mentioned x value is found, and by controlling this to a predetermined value, the x value is set to 0 <x ≦ 0.6. Can be controlled within the range. As the SOC control method, a conventional method such as voltage detection or management of the calculated value of the current capacity flowing into and out of the nonaqueous electrolyte secondary battery can be used.

[0022]

According to the charge / discharge control method for a nonaqueous electrolyte secondary battery of the present invention, the storage characteristics are excellent as described above, and the charge / discharge cycle characteristics are also improved, so that long-term reliability can be obtained. Becomes

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

FIG. 2 illustrates a non-aqueous electrolyte secondary battery 6 according to the same embodiment.
It is explanatory drawing of the relationship between SOC at the time of storage at 0 degreeC for 20 days, and an impedance maintenance rate.

[Explanation of symbols]

 1 negative electrode 3 positive electrode 5 separator 8 case

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeshi Hatanaka 1-1, Matsushita-cho, Moriguchi-shi, Osaka Matsushita Battery Industry Co., Ltd. (72) Takaya Saito 1-1-1, Matsushita-cho, Moriguchi-shi, Osaka Matsushita Battery F-term in Industrial Co., Ltd. (reference) 5H029 AJ04 AK03 AL06 AM03 AM05 AM07 BJ02 BJ14 CJ16 HJ02 5H030 AA10 AS20 BB01 BB21 5H050 AA05 AA09 BA16 BA17 CA09 CB07 CB12 GA18 HA02

Claims (1)

[Claims] 1. A general formula _{Li 1 + a Mn 2-ay} M y O 4 (M
Is one or more elements selected from metal elements or transition metal elements other than manganese, 0 ≦ a ≦ 0.5, 0 ≦
y ≦ 0.5) of a non-aqueous electrolyte secondary battery in which a lithium manganese composite oxide represented by the following formula is used as a positive electrode active material, and a lithium, lithium alloy or a carbon material that reversibly stores and releases lithium is a negative electrode active material. A charge / discharge method using a general formula Li using a coefficient x (0 ≦ x ≦ 1) by insertion / removal of Li
_x + a Mn range of _2-ay M x value of _y O ₄ is, 0 <x ≦ 0.
6. A charge / discharge control method for a non-aqueous electrolyte secondary battery, wherein charge / discharge control is performed so as to be 6.