JP2000048862A - Charging method for nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging method for sufficiently exhibiting performance of an electrode by setting a constant voltage value in initial charging, producing suitable amount of protective films on a negative electrode, and preventing reduction of electrolyte. SOLUTION: In a charging method for a nonaqueous secondary battery, using carbonaceous material as a negative electrode active material capable of doping and de-doping lithium ion, when initial charging of the nonaqueous secondary battery is performed, a constant current value is set in the range of 0.02 to 1.0 CmA, a constant voltage value is set in the range of 1.0 to 3.8 V, and the constant-current and constant-voltage charge is performed. Moreover, a constant current value is set in the range of 0.02 to 0.5 mA/cm, a constant voltage value is so set that negative electrode potential is in the range of 0.5 to 1.5 Vvs. Carbon dioxide atmosphere of Li/Li+ is made, and the constant- current and constant-voltage charge is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for charging a non-aqueous secondary battery using a carbonaceous material which can be doped and dedoped with lithium ions as a negative electrode active material.

[0002]

2. Description of the Related Art Conventionally, as a method for charging a non-aqueous secondary battery using a carbon material which can be doped and dedoped with lithium ions as a negative electrode active material, a charging current value is kept constant (current value Is). Charging in a constant current region Zi and a constant voltage region Zv in which the magnitude of the charging pressure value E is constant (current value Es), and the charging current I in the low voltage region Zv.
There is disclosed a method of detecting the magnitude of the current, and terminating charging when the detected current value reaches a preset current setting value (Japanese Patent Laid-Open No. 5-111184).

This method is effective as a rapid charging method for non-aqueous secondary batteries, especially lithium ion secondary batteries. However, at the time of the first charge in which the electrode in the battery is not used at all, the electrode characteristics of the battery cannot be sufficiently obtained unless the current value and the voltage value during the constant current and constant voltage charging are optimized. It can be expected that charging 100% of the theoretical capacity of the electrode from the first time with the above method will have a considerable adverse effect on the electrode. Specifically, when the electrode is oxidized and reduced before the electrolyte is sufficiently impregnated into the inside of the electrode, the electrolyte is notably reduced and oxidized in parallel with the oxidation and reduction of the active material. Can be expected. Originally, non-uniform electrode reactions and redox of the electrolyte should not occur.

Japanese Patent Application Laid-Open No. 5-144472 discloses that in order to suppress capacity deterioration after overdischarge, lithium metal is pasted to a carbon material of a negative electrode in advance and lithium is supplied to the carbon material by a potential difference or the like. There is a disclosure that lithium can be charged. However, this method has a problem that management and the like are troublesome because active and unstable metal lithium is used.

On the other hand, the electrode active material used in non-aqueous secondary batteries, particularly lithium ion secondary batteries, has a different lattice constant (positive electrode) and a different interlayer distance due to the difference between charge and discharge states. (Negative electrode). Therefore,
The entire electrode of the secondary battery expands and contracts. Until the first charge, the electrolyte is impregnating the pores of the electrode only depending on physical properties. Rather than charging from the physical impregnation state to 100% of the theoretical capacity of the electrode, first perform shallow charge / discharge, expand and contract the electrode, allow the electrolyte to adapt to the electrode active material, It is anticipated that a deeper charge than that will give less burden on the active material.

On the other hand, in a lithium secondary battery using metallic lithium as a negative electrode, the first charge is 1.2 to 0.8.
Vvs. At the negative electrode potential of Li / Li ⁺ , it has been reported that a protective film serving as a passivation film is formed on the negative electrode surface due to reduction of the electrolytic solution (D. Aurbach, Y. Ein Eli, O. Ch.
usid, Y. Carmerli, M. Babai and H. Yamin, J. Electrochem.
Soc., 141.603 (1994)).

The passivation film can be expected to suppress a further reaction between the carbon material on the negative electrode surface and the electrolytic solution and stabilize the reaction on the negative electrode. However, as described above, this passivation film is generated at the time of the first charge at 1.2 to 0.8 Vvs. Since it is the negative electrode potential of Li / Li ⁺ , it is presumed that it is effective to set a constant voltage value at the time of the first charge and generate an appropriate amount of the passivation film.

In the method proposed in the prior art, when the upper limit voltage value of a lithium ion secondary battery is set to a constant voltage charge value of 4.2 V and the first charge is performed, a passivation film is generated with the negative electrode potential. 1.2-0.8Vvs. Li /
The condition of Li ⁺ can be used for a very short time, and it cannot be said that the passivation film is sufficiently formed on the negative electrode.

[0009] Further, in a lithium secondary battery also using metallic lithium as a negative electrode, there is a report that the cycle life is improved when carbon dioxide gas is blown into an electrolytic solution (Tetsuya Osaka et al., Electrochemistry, 62, 451 ( 199
4)).

[0010]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and sets a constant voltage value at the time of initial charging, and forms the appropriate amount of the protective coating on the negative electrode,
It is an object of the present invention to provide a charging method for preventing reduction of an electrolyte solution and sufficiently exhibiting the performance of an electrode.

[0011]

The method for charging a non-aqueous secondary battery according to the present invention is a method for charging a non-aqueous secondary battery using a carbonaceous material which can be doped and de-doped with lithium ions as a negative electrode active material. When the non-aqueous secondary battery is charged for the first time, the constant current value is regulated to 0.02 to 1.0 CmA, the constant voltage value is regulated to 1.0 to 3.8 V, and the constant current constant is regulated. It is characterized by performing voltage charging.

When the non-aqueous secondary battery is charged for the first time, the constant current value is 0.02 to 0.5 mA / cm ² , and the constant voltage value is 0.5 to 1.5 V vs. negative electrode potential. It is characterized in that it is regulated to be in the range of Li / Li ⁺ and that constant-current constant-voltage charging is performed using carbon dioxide as the atmosphere in the battery.
The method for charging a non-aqueous secondary battery of the present invention uses the charging conditions shown in FIG. 3 when first charging a non-aqueous secondary battery using a carbon material capable of doping or undoping lithium ions as a negative electrode active material. The constant current value is 0.02 to 1.0 CmA and the constant voltage value is 1.0 to
The constant current charging is performed in a range of 3.8 V, and then the constant voltage charging is performed. Here, CmA means a current value at which the nominal capacity of the battery is fully charged in one hour.

[0013] By charging the battery manufactured by this method for the first time, the electrodes constituting the battery are charged and discharged shallowly, and the electrode active material is not exposed to a remarkable oxidation or reduction state. Due to the expansion and contraction of the electrode active material accompanying the above, the electrolyte solution can be sufficiently mixed with the electrode active material. By charging by this method, at the time of initial charging, the negative electrode is charged with a very small current value while maintaining the above potential range, and a denser protective film is formed on the surface of the negative electrode than before. At the time of the first charge, if the inside of the battery system is filled with carbon dioxide gas, the film is formed with more lithium carbonate (Li ₂ CO ₃ ) components than before. Since this coating is dense with components different from those of the related art, deterioration of the negative electrode due to mixed moisture and the like can be suppressed, and the negative electrode voltage can be kept stable for a long time.

[0014] Therefore, it is preferable to perform the first charge in the battery, particularly in an atmosphere in which the electrolytic solution contains a sufficient amount of carbon dioxide gas. The battery treated by this initial charging method has an increased battery capacity, an improved capacity retention rate during a charge / discharge cycle test, and high reliability. In addition, the battery treated by the first charging method of the present invention has a small capacity deterioration after storage and can ensure high reliability.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The secondary battery of the present invention is non-aqueous and has a positive electrode active material and a negative electrode active material via a separator in principle, and the current collector in the positive electrode active material is a positive electrode and a negative electrode active material. The current collector in the substance becomes the negative electrode. The positive electrode active material may be any material capable of dedoping lithium ions. For example, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium chromium oxide, lithium molybdenum oxide, lithium titanium oxide, etc. are used. it can. Particularly preferred are lithium manganese oxide and lithium cobalt oxide.

The negative electrode active material is a carbonaceous material capable of doping or undoping lithium ions, for example, graphite,
Pyrolytic carbon, pitch coke, needle coke, petroleum coke, and baked organic polymers can be used. Each of the positive electrode active material and the negative electrode active material is made into a particle shape, and is applied to a current collector using a metal foil. Then, it is spirally wound through a separator, further housed in a battery can, attached with a lead wire, and impregnated with an electrolyte solution and sealed.

As the electrolyte of the non-aqueous electrolyte solution, for example, LiClO ₄ , LiAsF ₆ , LiBF ₄ , CH ₃ SO ₃
Any one or more of lithium salts such as Li, CF ₃ SO ₃ Li, and (CF ₃ SO ₂ ) ₂ NLi are used in combination. The solvent of the electrolyte solution is, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, Any one or a mixture of two or more of 3-dioxolan, sulfolane, methylsulfolane, acetonitrile, propionitrile, methyl formate, ethyl formate, methyl acetate, ethyl acetate and the like can be used.

The separator may be a laminated film of one or more of microporous films of polyethylene, polypropylene, etc., a single film of nonwoven fabric of polyolefin, polyester, polyamide, cellulose or the like, or a laminated film of the above-mentioned microporous film. use. Particularly preferred is a polyethylene microporous membrane.

[0019]

The present invention will be specifically described below with reference to examples. It goes without saying that the present invention is not limited to this. FIG. 1 shows a cross-sectional perspective view of a cylindrical lithium secondary battery used in this example. The positive electrode plate 1 of the battery includes lithium manganese spinel (LiMn ₂ O ₄ , average particle diameter 7 μm, 90 parts by weight) as an active material, ketjen black (7 parts by weight) as a conductive additive, and polyvinylidene fluoride powder as a binder. (7 parts by weight) in N-methylpyrrolidone to form a paste and form a 20 μm rolled aluminum foil (positive electrode current collector)
The coating was rolled so that one side after drying was 70 μm.

The negative electrode 2 is made of artificial graphite (having an average particle size of 25) as an active material.
μm, 90 parts by weight) and polyvinylidene fluoride powder (10 parts by weight) as a binder are mixed in N-methylpyrrolidone to form a paste, which is coated on a 20 μm-thick copper foil (negative electrode current collector) and dried. Then, it was rolled to a thickness of 40 μm on one side. These band-shaped electrodes and a polyethylene porous separator 3 (25 μm in thickness) were wound in a circle to form an electrode group.

The electrolytic solution was prepared by dissolving lithium hexafluorophosphate in a mixture of ethylene carbonate and diethyl carbonate at a water content of 50 pp or less at a volume ratio of 1: 1. As shown in FIG. 1, the above-mentioned electrode group was loaded in a nickel-plated iron negative electrode can 4. At this time, the lead wire 7b connected to the copper in the negative electrode plate 2 is connected to the negative electrode can 4
The lead wire 7a connected to the aluminum foil in the positive electrode plate 1 was welded to the nickel-plated iron positive electrode cap 5 at the bottom of the positive electrode plate 1, respectively. Next, this negative electrode can 4
The inside is covered with the positive electrode cap 5 and the insulator 6 is sealed and caulked,
A cylindrical lithium secondary battery was manufactured. The nominal capacity of this battery is 130 mAh.

Example 1 A battery formed by the above method was
The following initial charge / discharge was performed. As the charge and discharge conditions, a battery was charged at a constant current of constant voltage of 3.8 V, constant current of 3.8 V for 4 hours at a constant current of 1/3 CmA, and discharged at a constant current of 1/3 CmA to 3.0 V at 1/3 CmA. Example.

Similarly, the battery formed by the above method was charged at a constant current and constant voltage for 4 hours at an ambient temperature of 20 ° C., a constant current of ３ CmA, a constant voltage of 4.2 V for 4 hours as initial charging and discharging conditions. A battery discharged at a constant current of 3.0 CmA to 3.0 V was used as a comparative example. After the first charge / discharge for the example and the comparative example, an ambient temperature of 20 ° C., a constant current of ３ CmA,
After charging at a constant voltage of 4.2 V for 4 hours at a constant current and a constant voltage,
One cycle of constant current discharge to 3.0 V at 1/3 CmA (the second time in total), and then an ambient temperature of 20 ° C. and 1 Cm
When the battery voltage reaches 4.2 V at the constant current of A, charging is completed,
The effect of the discharge was confirmed by a cycle evaluation in which a constant current discharge cycle of 3.0 V at 1 CmA was performed 80 times (82 times from the first time).

Table 1 shows the first and second discharge capacities of the example and the comparative example. FIG. 2 shows that the second discharge capacity is 100
The vertical axis shows the capacity change for each cycle when
The number of charge / discharge cycles is plotted on the horizontal axis, and the capacity retention rate of the battery as the cycle increases is shown in a graph. As shown in Table 1, in the example, the second discharge capacity is 124.6, which is larger than 118.7 of the comparative example. Further, as is clear from FIG. 2, the capacity retention rate of the battery of the example shows a higher retention rate at each cycle number than that of the comparative example.

[0025]

[Table 1] Discharge capacity (Example 2) The battery obtained by the above method was used as an initial charging condition at an ambient temperature of 20 ° C, a constant current of 0.05 mA / cm ² ,
After charging at a constant voltage of 3.0 V for 4 hours at a constant current and constant voltage, the current value was set to 0.5 mA / cm ^2, and charging was performed at a constant current and constant voltage of 4.2 V for 6 hours. After that, it is set to 0.
A battery discharged at a constant current of 5 mA / cm ² is referred to as Example 2. FIG. 4 shows the result of observing the potential of the negative electrode at the time of the first charge in Example 2 using metallic lithium as the reference electrode. According to FIG. 4, in the case of a constant current and constant voltage state of 0.05 mA / cm ² and 3.0 V, the potential of the negative electrode is 1 V with respect to lithium.
It can be seen that it is held near.

Example 3 A battery manufactured in exactly the same procedure as in Example 3 except that carbon dioxide was bubbled through the non-aqueous electrolyte solution to be used, and the operation of impregnating the electrolyte and sealing the battery was performed in a carbon dioxide atmosphere. In Comparative Example 2, the battery obtained by the above method was used as an initial charge / discharge condition at an environmental temperature of 20 ° C.
6 hours at a constant current of 5 mA / cm ^{2 and} a constant voltage of 4.2 V
After charging at a constant current and a constant voltage, 3.0 at 0.5 mA / cm ² .
A battery discharged at a constant current up to V was used.

Similarly to Example 2, Comparative Example 2
FIG. 5 shows the result of observing the potential of the negative electrode at the time of the first charge using metallic lithium as the reference electrode. Unlike Example 2, it can be seen that the potential of the negative electrode drops to about 0.5 V with respect to lithium from about one hour after the start of charging. After the first charge / discharge of Examples 2 and 3 and Comparative Example 2, the reference capacity of the battery was measured. The charging and discharging conditions are as follows: an ambient temperature of 20 ° C.
Constant current of 1 mA / cm ² , constant voltage of 4.2 V for 4 hours,
After charging at a constant current and a constant voltage, 3.0 at 0.5 mA / cm ² .
The cycle of constant current discharge to V was performed five times. Part 5
The discharge capacity at the sixth time (a total of six times) was defined as a reference capacity before storage.

After measuring the reference capacity, the ambient temperature is 20 ° C., 1 m
The battery was charged at a constant voltage of A / cm ² for 4 hours at a constant current and a constant voltage, and then stored in a thermostat at 60 ° C. for 21 days. After storage, the battery was discharged at a constant current of 3.0 V at an environmental temperature of 20 ° C. and 0.5 mA / cm ² , and the capacity retention rate during the storage period was measured. Thereafter, charge and discharge were repeated five times again under the conditions for measuring the reference capacity previously, and the fifth discharge capacity was defined as the capacity after storage. Table 2 below
Shows the capacity retention rates of Examples 2 and 3 and Comparative Example 2, and the rate of change in capacity before and after storage. The capacity retention rate and the change rate are represented by relative ratios with reference capacity being 100.

As is clear from Table 2, the present invention can provide a battery having a small change in characteristics due to storage.

[0030]

[Table 2]

[0031]

As described above, in the method for charging a non-aqueous secondary battery according to the present invention, the negative electrode potential is 1.2 to 0.
8Vvs. The electrolyte solution solvent is reduced by Li to form a protective film on the surface of the negative electrode. This protective film has lithium ion conductivity but has no electron conductivity and can suppress reduction of the electrolyte solution.

According to the charging method of the present invention, the charge / discharge is initially performed at a shallower voltage of 3.8 V or less than the conventional upper limit voltage of 4.2 V, so that the above protective film can be appropriately formed. In addition, the negative electrode active material can adapt the electrolyte to the electrode by swelling and shrinking of the active material without being exposed to a remarkable oxidation / reduction state. Therefore, the battery of the present invention can increase the battery capacity, improve the capacity retention rate of the discharge / charge cycle test, and obtain a highly reliable secondary battery.

The charging method according to the second aspect of the present invention has a small capacity deterioration after high-temperature storage and has high reliability. This means that the negative electrode is charged in a specific potential range with a very small current value at the time of the initial charging, so that a denser protective film is formed on the negative electrode surface than before. Since the battery system is filled with carbon dioxide at the time of the first charge, the lithium carbonate component of the protective film is increased compared to the conventional case, and the deterioration of the negative electrode due to mixed water and the like can be suppressed.
It is possible to keep the negative electrode voltage stable for a long time.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a secondary battery used in a charging test in this example.

FIG. 2 is a graph showing the relationship between the number of charge / discharge cycles and the battery capacity retention rate in Examples and Comparative Examples.

FIG. 3 is a graph illustrating the progress of voltage and current under charging conditions of the present battery.

FIG. 4 is a graph showing the progress of the negative electrode potential at the time of initial charging of the battery of Example 2.

FIG. 5 is a graph showing the progress of the negative electrode potential when the battery of Comparative Example 2 is initially charged.

[Explanation of symbols]

1. 1. positive electrode plate; 2. negative electrode plate; Separator, 4. Negative electrode can, 5. 5. positive electrode cap, Insulator, 7a. Positive electrode lead, 7b. Negative electrode lead

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masao Kanzaki 41-Cho, Yokomichi, Nagakute-machi, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Institute, Inc. 41, Yokomichi, Toyota Central Research Institute, Inc.

Claims (2)

[Claims] 1. A method for charging a non-aqueous secondary battery using a carbonaceous material which can be doped with lithium ions and de-doped as a negative electrode active material, wherein the non-aqueous secondary battery is charged for the first time. The constant current value is set to 0.02 to 1.0 CmA, and the constant voltage value is set to 1.0 to 3.8.
A method for charging a non-aqueous secondary battery, wherein the charging is performed at a constant current and a constant voltage specified in a range of V. 2. A method for charging a non-aqueous secondary battery using a carbonaceous material which can be doped and de-doped with lithium ions as a negative electrode active material, comprising: The current value is 0.02 to 0.5 mA / cm ² , and the constant voltage value is 0.5 to 1.5 V vs. negative electrode potential. A method for charging a non-aqueous secondary battery, wherein the charging is performed so as to be in the range of Li / Li ⁺ , and the battery is charged with a constant current and a constant voltage in a carbon dioxide atmosphere.