JPH09259927A - Manufacture of nomaqueous electrolyte lithium secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a nonaqueous electrolyte lithium secondary cell without decreasing a cell characteristic, by making a cell provided with a positive/ negative electrode and a nonaqueous electrolyte containing a lithium compound oxide, and leaving the cell left as it is at a specific temperature, thereafter performing a charge. SOLUTION: A positive electrode containing a lithium contained compound oxide of LiMO2 (M is Co, Ni, Mn, Fe, V, B, Al, Mg) and a chargeable/ dischargeable negative electrode of carbon material or the like are wound or layered by interposing a separator, inside a cell case is charged with the electrodes together with a nonaqueous electrolyte, a cell is formed. Thereafter, this cell is charged to a charge condition generating cell voltage exceeding 3.6V. In this case, before this charging, the cell is left as it is at a temperature in a 30 to 85 deg.C range. A time of this leaving the cell as it is preferably is 3 hours to 15 days. In this way, a nonaqueous electrolyte lithium secondary cell, infiltrating a nonaqueous organic electrolyte of high viscosity sufficiently uniformly in a cell charged with the electrolyte in high density and improving a charge/discharge cycle characteristic in a charge process, is obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte lithium secondary battery, and more particularly to an improvement in a battery using a lithium composite oxide as an active material for a positive electrode.

[0002]

2. Description of the Related Art In recent years, portable and cordless AV devices or electronic devices such as personal computers have been rapidly developed, and there is a great demand for secondary batteries having a small size, a light weight and a high energy density as a power source for driving these devices. From such a viewpoint, non-aqueous secondary batteries, particularly lithium secondary batteries, are expected to have high voltage and high energy density. As a positive electrode active material for a high energy density non-aqueous electrolyte lithium secondary battery as described above, a lithium-transition metal-based composite oxide (hereinafter referred to as lithium-intercalation capable of intercalating and deintercalating lithium) , Lithium composite oxide) is used. In particular, the general formulas LiNi _1-X Co _X O ₂ (0 ≦ x ≦ 1) and Li
The lithium composite oxide represented by Mn _2-2X Co _2X 0 ₄ (0 ≦ x ≦ 0.5) has been actively developed because it can obtain a high energy density. Further, as the negative electrode active material, a material capable of reversible intercalation and deintercalation of lithium at a low potential has been studied, and particularly, a carbon material has been developed.

At present, as a high energy density lithium secondary battery, a battery system in which the above lithium composite oxide positive electrode and a carbon material negative electrode are combined is at the center of development, and batteries of cylindrical shape, prismatic shape and the like are available. Being developed. These batteries use a powdered active material for both the positive electrode and the negative electrode, and mix a mixture of carbon powder as a conductive agent and resin as a binder, and a metal foil as a current collector. A sheet-shaped electrode plate is formed and used. In order for such a combination of the positive electrode plate and the negative electrode plate to function as a battery, an electrolytic solution is required. In a lithium secondary battery, lithium has a high reactivity with water and an aqueous solution type electrolytic solution cannot be used. Therefore, an electrolytic solution using a non-aqueous organic solvent is used.

As for the internal structure of the battery, the cylindrical structure has a spiral structure in which a positive electrode sheet and a negative electrode sheet are wound with a separator sandwiched between them, and the prismatic structure has a laminated structure or a cylindrical structure in which a positive electrode sheet and a negative electrode sheet are superposed with a separator in between. The spiral structure is similar to that of the mold. The sheet-like large-area electrode plate structure can reduce the current density per unit area, and is therefore advantageous in performing rapid charging / discharging with a large current. This is a nickel cadmium battery,
It is an indispensable element in non-aqueous electrolyte battery systems that are inferior in rapid charge / discharge characteristics as compared to batteries using nickel-hydrogen storage batteries and other aqueous electrolytes. Further, in order to obtain a higher energy density, it is necessary to fill the battery case with high density.

A non-aqueous electrolyte lithium secondary battery is manufactured by sealing and sealing materials such as a positive electrode, a negative electrode, a separator and an organic electrolytic solution in a battery case with the above-mentioned battery structure. Further, the manufactured battery is put to practical use as a high energy density non-aqueous electrolyte lithium secondary battery after preliminary charging and discharging to finish before use.

[0006]

The non-aqueous electrolyte of the lithium secondary battery has a high viscosity and is densely packed in a spiral structure or a laminated structure. It is difficult to uniformly penetrate into. In particular, in the central portion of the electrode plate, the electrolytic solution does not sufficiently permeate, and the electrolytic solution is likely to partially run short. If charging / discharging is performed in this state, a minute amount of lithium metal will be deposited on the negative electrode and the utilization factor will be decreased on the positive electrode in the portion where the electrolytic solution is insufficient, resulting in deterioration of battery characteristics.

[0007]

In order to solve the above problems, the present invention provides at least a positive electrode containing a lithium-containing composite oxide and a negative electrode containing a carbon material powder capable of reversibly inserting and extracting lithium. After the non-aqueous electrolyte battery having one of them is prepared, a step of leaving it at a temperature within the range of 30 ° C. to 85 ° C. is provided before charging to a charged state where the battery voltage exceeds 3.6 V. Is. As a result, the viscosity of the electrolytic solution in the battery can be reduced and the electrolytic solution can be made to uniformly permeate into the electrode plate. The lithium-containing composite oxide used here is LiMO ₂ (M is Co, N, which is known as an active material for providing a 4 V class lithium battery.
A compound represented by at least one element selected from the group consisting of i, Mn, Fe, V, B, Al, and Mg) is used.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention improves the cycle characteristics of a battery by leaving it at a predetermined temperature for a certain period of time after the battery is manufactured. The temperature condition for leaving this for a certain period of time is preferably in the range of 30 ° C to 85 ° C. Also, the leaving time is 3 days to 15 at 30 ° C.
It is preferable that the time at 85 ° C. is 1 hour to 24 hours. Since the treatment time depends on the treatment temperature, it is preferable to leave the treatment at a high temperature for a short time and the treatment at a low temperature for a long time. In a battery having a spiral structure or a laminated structure, penetration of the electrolytic solution into the battery, particularly in the central portion of the electrode plate, tends to be insufficient. In such a state, the battery characteristics will deteriorate. In particular, the cycle characteristics may be significantly deteriorated. This is because charging and discharging can be partially performed because the liquid spillage progresses in the part where the electrolyte is insufficient by repeating the charge and discharge cycle, the minute amount of lithium metal deposits in the negative electrode, and the utilization factor decreases in the positive electrode. This is because the total capacity decreases, and the capacity of the entire battery decreases.

In order to prevent such characteristic deterioration due to insufficient permeation of the electrolytic solution, it is necessary to sufficiently permeate the electrolytic solution into the entire electrode plate before charging / discharging. is there. As a means for this, in the present invention, heat treatment is performed after the battery is manufactured and before charging and discharging. The organic electrolyte used in the lithium secondary battery has a high viscosity at room temperature and hardly penetrates into the mixture, but if the whole battery is kept at a temperature in the range of 30 ° C to 85 ° C for a certain period of time, the organic electrolyte in the battery is The viscosity of is reduced, and it can be permeated uniformly throughout the electrode plate. However, it is preferable that the standing time at the predetermined temperature is within the range indicated by the diagonal lines in FIG. As a result, it is possible to prevent liquid dripping inside the battery due to charge and discharge, and suppress deterioration of charge and discharge cycle characteristics of the battery.

[0010]

EXAMPLES Specific examples will be shown below, but the present invention is not limited to the contents of these examples. << Example 1 >> In this example, LiNiO was used as the positive electrode active material.
₂ , and a cylindrical battery having a spiral structure using a carbon material as the negative electrode active material will be described. First, positive electrode active material powder, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder were mixed in a weight ratio of 100: 4: 4, and N, N-dimethylformamide was further added to sufficiently mix them. The positive electrode mixture paste was mixed. This was applied to an aluminum foil current collector and rolled, and an aluminum lead for current collection was attached to obtain a positive electrode plate. The weight of the positive electrode active material contained in one positive electrode plate was adjusted to be 5 g. next,
The weight ratio of the solid content of the aqueous dispersion of the negative electrode active material powder and styrene-butadiene rubber (SBR) as the binder is 100: 7.
To obtain a negative electrode mixture paste. This was coated on a copper foil current collector and rolled, and a nickel lead for current collection was attached to obtain a negative electrode plate. The amount of the negative electrode active material contained in one negative electrode plate was adjusted according to the capacity of the positive electrode.

After the positive electrode and the negative electrode produced as described above were sufficiently dried, they were superposed with a separator made of a polypropylene porous film interposed therebetween and wound in a spiral shape.
This was inserted into a battery case, and after pouring a predetermined amount of electrolyte solution, the battery was sealed to produce a battery. The current collecting leads of the positive electrode plate and the negative electrode plate are welded to the sealing plate and the battery case, respectively, to make electrical contact. As the electrolytic solution, an organic electrolytic solution prepared by dissolving lithium hexafluorophosphate at a concentration of 1M in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 was used. Further, the produced battery was left for 15 days, 3 days, and 10 hours in a constant temperature bath set at 30 ° C., 45 ° C., and 85 ° C., respectively, and then taken out to perform a charge / discharge test. A battery treated at 30 ° C. is referred to as battery A1, a battery subjected to 45 ° C. is referred to as battery B1, and a battery subjected to 85 ° C. is referred to as battery C1.

As a comparative example, a battery produced in the same manner was not treated in a constant temperature bath, and another battery was operated at 90 ° C.
After leaving it in the constant temperature bath for 8 hours, it was taken out and subjected to a charge-discharge test. Batteries that are not treated are batteries D1 and 9
The battery subjected to 0 ° C. treatment is referred to as battery E1. Furthermore, without processing, only for one cycle, charging to a voltage of 4.2 V and 2.
After discharging up to 5 V, a charge / discharge test was similarly performed on the battery left in a discharged state at 45 ° C. for 3 days. This battery is referred to as battery F1. The charge / discharge conditions were a charge / discharge current of 1 A and a voltage range of 3.0 V to 4.2 V, and the test was performed at room temperature. Table 1 shows the initial capacity of each battery and the capacity retention rate at the 50th cycle. In addition, A1 and B in FIG.
The cycle characteristics of 1, C1, D1, E1, and F1 up to the 50th cycle are shown.

[0013]

[Table 1]

As shown in Table 1 and FIG. 2, 5 of each battery is used.
The capacity retention ratio at the 0th cycle was 80% to 82% in the battery D1 which was subjected to the charge / discharge cycle without being left at high temperature. On the other hand, the batteries A1, B1, C1 of this example
In both cases, the cycle characteristics are 95% or more, showing a significant improvement in cycle characteristics. Even when the same treatment as that of the battery B1 of this example was performed, the battery F1 that was treated after one cycle of untreated charging / discharging had a capacity retention rate of 87% to 89%, and the degree was small. However, the characteristics are deteriorated. It is speculated that this is because one cycle of charge and discharge when untreated damaged the part of the electrode plate where the electrolyte solution was insufficient. Then, the battery E treated at 90 ° C.
In Nos. 1 to E3, the capacity retention rate was 89% to 90%, and deterioration was observed due to the treatment temperature being too high.

Example 2 Using the battery produced in the same manner as in Example 1, the battery was charged to the upper limit voltage of 3.6 V and 3.8 V, and these two types of batteries in the charged state were stored at 30 ° C.
Put in a constant temperature bath set to the temperature of 45 ℃ and 85 ℃,
It was left for 15 days, 3 days and 10 hours, respectively. After standing, the same charge / discharge test as in Example 1 was performed. 3.6V
Batteries A2 and
The battery treated at 5 ° C. is referred to as battery B2, and the battery treated at 85 ° C. is referred to as battery C2. Further, a battery treated at 30 ° C. in a charged state of 3.8 V is referred to as battery A3, a battery subjected to treatment at 45 ° C. is referred to as battery B3, and a battery subjected to treatment at 85 ° C. is referred to as battery C3. Table 2 shows the initial capacity of each battery and 5
The capacity retention rate at the 0th cycle is shown.

[0016]

[Table 2]

As shown in Table 2, in the battery in the charged state of 3.6 V, the effect of improving the cycle characteristics is obtained in any battery left at any temperature. However, in the battery charged to 3.8 V, the deterioration was large and the effect of improving the characteristics was not observed at any temperature.

Example 3 A battery prepared in the same manner as in Example 1 was used and left at 30 ° C., 45 ° C. and 85 ° C. Batteries left at 30 ° C for 2 days (Battery A4), 3 days (Battery A5),
15 days (battery A6) and 16 days (battery A7), 45 ° C
45 hours (battery B4), 50 hours (battery B5), 2
70 hours (battery B6) and 280 hours (battery B7),
At 85 ° C, 1 hour (battery C4), 2 hours (battery C5),
After 24 hours (battery C6) and 25 hours (battery C7), each battery was taken out and the same charge / discharge test as in Example 1 was performed. Table 3 shows the initial capacity of each battery and 50
The capacity retention rate at the cycle is shown.

[0019]

[Table 3]

As shown in Table 3, at 30 ° C., 3 days to 15 days
Preferably, the standing time is in the range of 50 hours to 270 hours at 45 ° C and 2 hours to 24 hours at 85 ° C.

In this example, L was used as the positive electrode active material.
iNiO ₂ was used, but other LiMO ₂ (M is Co, N
lithium composite oxidation capable of reversible lithium intercalation and deintercalation represented by at least one element selected from the group consisting of i, Mn, Fe, V, B, Al, and Mg). The same effect can be obtained by using a product. In addition to the carbon material as the negative electrode active material, the same effect can be obtained by using a carbon analog compound in which carbon is doped with a different element, aluminum, or an alloy containing a metal capable of alloying with lithium such as lead. To be That is, in a battery system in which at least one of the positive electrode and the negative electrode is manufactured by using a powder material as an active material, the same effect can be obtained in any case.

Further, in the examples, as the organic electrolytic solution, an organic electrolytic solution prepared by dissolving LiPF ₆ at a concentration of 1M in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 was used. Propylene carbonate, diethyl carbonate,
One or a mixture of two or more of methylethyl carbonate, dimethyl carbonate, dimethoxyethane, γ-butyrolactone, tetrahydrofuran, methyltetrahydrofuran, LiClO ₄ , LiB as an electrolyte salt
The same effect can be obtained when F ₄ , LiPF ₆ , LiAsF _6, or the like, which is known as an electrolyte solution for lithium secondary batteries, is used. As for the structure of the battery, the cylindrical battery having the spiral structure has been described, but the same effect can be obtained not only in the spiral structure but also in the battery having a structure in which the electrolyte solution hardly penetrates such as a laminated structure.

[0023]

As described above, according to the present invention, a non-aqueous electrolyte lithium secondary battery having improved charge / discharge cycle characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a preferable relationship between a time for leaving a battery and temperature.

FIG. 2 is a diagram showing cycle characteristics of a battery that has undergone various treatments.

Claims (4)

[Claims] 1. A battery including a positive electrode containing a lithium-containing composite oxide powder, a chargeable / dischargeable negative electrode, and a non-aqueous electrolyte is prepared, and then charged to a charged state in which the battery voltage exceeds 3.6 V. A method for producing a non-aqueous electrolyte lithium secondary battery, which comprises a step of leaving at a temperature in the range of 30 ° C. to 85 ° C. inclusive. 2. A chargeable / dischargeable positive electrode, a negative electrode containing a carbon material powder capable of reversibly occluding and releasing lithium.
And after charging the battery including the non-aqueous electrolyte solution and before charging to a charged state where the battery voltage exceeds 3.6 V,
A method for producing a non-aqueous electrolyte lithium secondary battery, comprising a step of leaving the temperature of the non-aqueous electrolyte lithium battery at a temperature in the range of 30 ° C to 85 ° C. 3. The method for producing a non-aqueous electrolyte lithium secondary battery according to claim 1, wherein the leaving time is 3 hours or more and 15 days or less. 4. The lithium-containing composite oxide is LiMO ₂
(M is at least one element selected from the group consisting of Co, Ni, Mn, Fe, V, B, Al, and Mg)
The method for producing a non-aqueous electrolyte lithium secondary battery according to claim 1, which is a compound represented by: