JP3081291B2 - Non-aqueous electrolyte battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonaqueous electrolyte battery using lithium as an active material, and more particularly to improvement of a carbon material as a conductive material of a positive electrode.

[0002]

2. Description of the Related Art In a nonaqueous electrolyte battery of this type, when a positive electrode is produced, manganese dioxide as a positive electrode material and a carbon material as a conductive material are mixed and pressed to form a pellet-shaped or band-shaped positive electrode. When such a battery is overdischarged, the conductive material reacts with the electrolytic solution to decompose the electrolytic solution and generate gas. Then, since the battery swells or leaks, and particularly the secondary battery is in an overdischarged state, adverse effects such as deterioration of subsequent cycle characteristics occur.

[0003] The reason is that a carbon material generally has a crystal structure in which carbon atoms are mainly bonded in a hexagonal form, but the hexagonal structure cannot be maintained at the end of the bond.
The carbon atoms at the ends easily bond with oxygen and moisture in the air,
They are hydroxyl groups (OH) and carboxyl groups (COOH). Since these functional groups have high activity, when the potential of the positive electrode decreases as in the case of overdischarge, the electrolytic solution is easily affected by the functional groups.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and eliminates the influence of the functional groups of the carbon powder added as a conductive material to form a reaction between the conductive material and the electrolyte. Is to suppress. As a result, battery swelling,
An object of the present invention is to provide a battery in which no liquid leakage occurs, and in particular, even if the secondary battery is in an overdischarged state, the subsequent cycle characteristics do not deteriorate.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a non-aqueous electrolyte battery having a positive electrode, a non-aqueous electrolyte, and a lithium, lithium alloy or a compound of lithium and carbon as a negative electrode. , Characterized by using a carbon material from which the influence of the functional group has been removed.

Here, as the carbon material, it is necessary to use a carbon material which has been subjected to a neutralization treatment, an alkali treatment or an esterification treatment to remove the influence of the functional groups .

[0007]

According to the present invention, if a carbon material obtained by removing a functional group in a carbon material by a chemical treatment is used as a conductive material of a positive electrode, a battery with high resistance to overdischarge and high reliability can be provided. . The reason is that carbon, which is a carbon material, generally has a crystal structure in which carbon atoms are mainly bonded in a hexagon,
The hexagonal structure cannot be maintained at the end of the bond, and the carbon atom at the end is easily bonded to oxygen or moisture in the air to form a hydroxyl group (OH) or a carboxyl group (COOH). Since these functional groups have high activity, when the potential of the positive electrode decreases as in the case of overdischarge, it reacts with the electrolytic solution to decompose the electrolytic solution and generate gas and the like. As a result, swelling or leakage of the battery occurs, and in particular, the secondary battery is in an over-discharged state, so that the subsequent cycle characteristics are degraded. Therefore, it is necessary to reduce the activity of these functional groups in advance and use them as a conductive material for the positive electrode. That is, according to the present invention, by removing the influence of the functional group by performing a chemical treatment such as an esterification, a neutralization treatment or an alkali treatment, it is possible to suppress the decomposition of the electrolytic solution at the time of overdischarge by the carbon material. Thus, it is possible to suppress battery swelling due to gas generation during overdischarge, liquid leakage, and deterioration of cycle characteristics of the secondary battery in an overdischarged state.

[0008]

FIG. 1 is a longitudinal sectional view of a battery according to an embodiment of the present invention. Here, reference numeral 1 denotes a negative electrode made of a lithium-aluminum alloy, which is pressure-bonded to a negative electrode current collector 3 fixed to the inner bottom surface of the negative electrode can 2. Reference numeral 4 denotes a positive electrode, which is composed of a manganese oxide as an active material and a conductive material of a carbon material, which is the gist of the present invention (a specific manufacturing method will be described later), and a fluororesin binder 80:10:10 (weight). The mixture is molded at a ratio of (ratio), and is pressed against the inner bottom surface of the positive electrode can 5 via a positive electrode current collector 6.

Reference numeral 7 denotes a separator made of a polypropylene non-woven fabric. The separator 7 contains a non-aqueous electrolyte obtained by dissolving lithium perchlorate at 1 mol / L in an equal volume mixed solvent of propylene carbonate and 1,2-dimethoxyethane. Impregnated. Reference numeral 8 denotes an insulating packing for electrically insulating the positive electrode can and the negative electrode can. The battery has a diameter of 25 mm and a thickness of 3.
0 mm.

Next, an example of producing a carbon material as a conductive material of the positive electrode will be described in detail. [Preparation Example-1] 300 g of graphite powder as a carbon material was dispersed in a liquid obtained by adding 300 g of concentrated sulfuric acid to 1 liter of ethyl alcohol, mixed well, and left at room temperature for 3 days. Then, the carbon material is washed with acetone, dried sufficiently, dispersed in a solution of 300 g of concentrated sulfuric acid added to 1 liter of acetone in which 50 g of acetic acid is dissolved, mixed well, and left at room temperature for 3 days. Then, a treatment for removing the functional group was performed. Then, it was washed with acetone and dried.

The carbon material thus obtained was measured by infrared spectroscopy. As a result, it was found that the hydroxyl groups and carboxyl groups in the carbon material had disappeared. This is considered to be due to esterification of a hydroxyl group or a carboxyl group in the carbon material by the above treatment.

A battery was prepared using the carbon material thus treated as a conductive material for a positive electrode, and was referred to as Battery A of the present invention. [Preparation Example-2] A carbon material was treated in the same manner as in Preparation Example 1, except that methyl alcohol was used instead of ethyl alcohol and propionic acid was used instead of acetic acid. A battery using the carbon material thus obtained as a conductive material for a positive electrode was designated as Battery B of the present invention. [Preparation Example-3] A carbon material was treated in the same manner as in Preparation Example 1, except that propyl alcohol was used instead of ethyl alcohol and benzoic acid was used instead of acetic acid. The carbon material obtained in this manner was used as a conductive material for a positive electrode, to thereby prepare a battery C of the present invention. [Production Example-4] Acetylene black 30 as a carbon material
0 g was dispersed in 1 liter of benzene in which 100 g of phenol was dissolved, and 200 g of molecular sieve 5A was dispersed in the treatment liquid. The mixture was thoroughly mixed, allowed to stand at room temperature for one week, washed with acetone, and dried. The carbon material thus obtained was further mixed with 200 g of molecular sieve 5A in 1 liter of benzene in which 50 g of benzoic acid was dissolved.
g was dispersed in the treatment liquid to which g had been added, mixed well, left at room temperature for one week, washed with acetone, and dried. The carbon material thus obtained was also measured by infrared spectroscopy, and it was found that the hydroxyl group and carboxyl group in the carbon material had disappeared. This is considered to be because the hydroxyl groups and carboxyl groups in the carbon material were esterified by the treatment. A battery using the carbon material thus obtained as a conductive material for a positive electrode was designated as Battery D of the present invention.
And [Preparation Example-5] Lithium hydroxide and acetylene black were mixed at a weight ratio of 2:98, and this was mixed at 800 ° C.
To produce a composite powder of carbon and a lithium salt. The carbon material powder produced in this way was measured by infrared spectroscopy. As a result, it was found that hydrogen of a hydroxyl group and a carboxyl group in carbon was replaced with lithium. Also, when the ratio of carbon, hydrogen and lithium in these carbon materials was measured, it was found that most of the hydrogen in the carbon was replaced by lithium. The battery E of the present invention was manufactured using the carbon material manufactured as described above as a conductive material of the positive electrode. [Preparation Example-6] A graphite material was dispersed in water, treated with lithium hydroxide until the pH reached 9, filtered, dried sufficiently, and a carbon material in which hydrogen of a hydroxyl group or a carboxyl group was replaced with lithium. Obtained. The battery F of the present invention was manufactured using the carbon material manufactured as described above as a conductive material of the positive electrode. [Preparation Example-7] Graphite powder was dispersed in water, treated with potassium hydroxide until the pH reached 9, filtered, and then sufficiently dried to obtain a carbon material in which hydrogen of a hydroxyl group or a carboxyl group was replaced with potassium. Was. Using the carbon material thus obtained as a conductive material for a positive electrode, a battery G of the present invention was produced. Comparative Example 1 A battery was manufactured using untreated graphite powder as a conductive material of the positive electrode as it was, and a comparative battery X was obtained. Comparative Example 2 A battery was produced using untreated acetylene black powder as a conductive material for the positive electrode as it was, and a comparative battery Y was obtained.

Using these batteries A to G, X and Y, the rate of occurrence of liquid leakage of the batteries was examined. The experimental conditions at this time were as follows: 100 batteries under each condition were prepared and discharged until the voltage reached 0 V. After that, the number of leaks after leaving the battery voltage at 0 V for one month was measured. A check was made and the rate of occurrence of liquid leakage was determined.
Table 1 shows the results.

[0014]

[Table 1]

Thus, it is understood that the batteries A to G of the present invention have a smaller number of leaks and a lower leak rate than the comparative batteries X and Y.

Next, the cycle characteristics after overdischarge of the batteries A to G, X and Y were compared. The experimental conditions at this time were as follows: each battery was discharged until it reached 0 V, and then maintained at 0 V for one week, then charged, and the cycle life was measured. The cycle test conditions were a discharge capacity of 12 mAh, and a charge test. 3.2 V was terminated at a current of 3 mA. The result is shown in FIG. In FIG. 2, the horizontal axis represents the number of cycles, and the vertical axis represents the discharge end voltage in each cycle of each battery.

From this, it is understood that the batteries A to G of the present invention have a longer cycle life even after overdischarge and are superior in cycle characteristics as compared with the comparative batteries X and Y.

Next, here, the influence of the pH value when the carbon material was subjected to alkali treatment as in the battery F of the present invention and the battery G of the present invention was examined.

Here, graphite as a carbon material is dispersed in water, treated with lithium hydroxide to adjust each pH value, filtered and dried sufficiently, and one of hydroxyl and carboxyl groups in carbon is removed. Parts were replaced with lithium. Thus, a carbon material from which the influence of the functional group was removed was obtained, and 100 batteries each using the carbon material as a conductive material were prepared. Then, after discharging each battery to 0 V, the battery voltage was kept at 0 V and left for one month, and the number of leaks of these batteries was defined as the leak occurrence rate (%) of each battery. Table 2 shows the results.

[0020]

[Table 2]

From these results, it is understood that the rate of occurrence of liquid leakage is significantly reduced when the pH value is 7 or more. The reason for this is presumed to be that many hydrogen (H) in the hydroxyl group and carboxyl group in the carbon material were replaced with lithium (Li), and the activity of these functional groups was reduced, thereby eliminating the effect. .

The alkali-treated carbon material used here shows a value almost coincident with the pH value of the treatment liquid when dispersed in water, but the pH value becomes high (pH value).
= 10), the value is slightly shifted.

Next, acetylene black as a carbon material is dispersed in water, which is treated with potassium hydroxide to adjust each pH value, filtered and sufficiently dried, and then the hydroxyl group or carboxyl group in carbon is removed. Some were replaced with potassium. Thus, a carbon material from which the influence of the functional group in carbon was removed was obtained, and batteries were produced in the same manner as described above, and the rate of occurrence of liquid leakage (%) of these batteries was examined. Table 3 shows the results.

[0024]

[Table 3]

From the results shown in Table 3, it is understood that the rate of occurrence of liquid leakage is significantly reduced when the pH value is 7 or more.
The reason for this is that, similarly to the above, many hydrogens (H) in the hydroxyl groups and carboxyl groups in the carbon material were replaced by potassium (K), and the activity of these functional groups was reduced, thereby eliminating the effect. Presumed.

From the results shown in Tables 2 and 3, it is considered that a carbon material which has been treated at a pH value of 7 or more is particularly suitable as a conductive material for a battery.

[0027]

As described above in detail, according to the nonaqueous electrolyte battery of the present invention, the influence of the functional groups of the carbon powder added as the conductive material of the positive electrode is determined by the carbon neutralization treatment and the alkali treatment.
Or remove the effect of functional groups by esterification
This suppresses the reaction between the conductive material and the electrolyte,
Since the battery can be prevented from swelling and leaking, and a secondary battery can provide a battery having excellent cycle characteristics in which the subsequent cycle characteristics are not deteriorated even in an overdischarged state, the industrial value thereof is extremely large.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a battery of the present invention.

FIG. 2 is a comparison diagram of cycle characteristics of a battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Negative electrode 2 Negative electrode can 3 Negative electrode current collector 4 Positive electrode 5 Positive electrode can 6 Positive electrode current collector 7 Separator 8 Insulating packing A, B, C, D, E, F, G Battery X, Y Comparative battery

Continuation of the front page (56) References JP-A-4-215252 (JP, A) JP-A-3-22357 (JP, A) JP-A-63-279573 (JP, A) JP-A-62-117313 (JP) JP-A-59-149674 (JP, A) JP-A-59-149654 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/62 H01M 4/02 H01M 10/40

Claims (1)

(57) [Claims] (1) A positive electrode containing a carbon material as a conductive material;
Water electrolyte and lithium, lithium alloy or lithium
Non-aqueous electrolyte battery using a compound of
Wherein the carbon material is a carbon neutralization treatment, an alkali treatment,
Alternatively, the effect of functional groups was removed by esterification
A non-aqueous electrolyte battery, characterized in that: