JP3021892B2 - Non-aqueous electrolyte secondary 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 non-aqueous electrolyte secondary battery, and more particularly to the selection of an optimal pre-charge time for a non-aqueous electrolyte secondary battery which requires pre-charging after electrolyte injection.

[0002]

2. Description of the Related Art Recently,
A carbon material capable of inserting and extracting lithium has been proposed as a negative electrode material for nonaqueous electrolyte secondary batteries because, for example, there is no generation of electrodeposited lithium during charging, and the battery shape is not limited due to its excellent flexibility. It is in the spotlight.

[0003] This type of secondary battery is charged (this charging is referred to as "preliminary charging" in the present specification) after assembling the battery by injecting an electrolyte, and lithium is used as a negative electrode material. After being absorbed (intercalated), it is put to practical use.

[0004] However, the potential of the negative electrode at a stage where the carbon material does not occlude lithium is about 3.2 V. This potential depends on Cu used in the core (negative electrode current collector),
Since the metal material such as Ni or stainless steel has a minimum electric potential at which the electrolytic solution dissolves in the electrolytic solution (this electric potential is referred to as “dissolution potential” in this specification, usually about 3 V), the electrolytic solution is introduced into the battery. If the time required for pre-charging after assembling the battery by injecting it is long, these metal materials gradually elute into the electrolyte, causing clogging of the separator during repeated charge and discharge cycles. It has been found that there is a problem that the metal material eluted in the electrolytic solution is deposited on the negative electrode and the battery characteristics are hindered.

[0005] This problem is not limited to the case where a carbon material is used, but is common to non-aqueous electrolyte secondary batteries provided with a negative electrode material whose potential after injecting the electrolyte is higher than or equal to the dissolution potential of the metal material serving as the core. For example, a non-aqueous electrolyte secondary battery using a metal oxide capable of inserting and extracting lithium as a negative electrode material may also occur.

[0006] This problem is not only a problem relating to the core, but also for a negative electrode can having the same electric potential as the core, the electric potential of the negative electrode can after the injection of the electrolytic solution dissolves the metal material constituting the negative electrode can. In the case where the potential is higher than the potential, there is a similar problem.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a non-aqueous electrolyte solution which exhibits excellent cycle characteristics by selecting an optimal pre-charging time. Next is to provide batteries.

[0008]

According to a first aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery (hereinafter referred to as a "first battery") for achieving the above object. A negative electrode in which a body and a material capable of inserting and extracting lithium are bound, and a potential after injecting a non-aqueous electrolyte into the battery is equal to or higher than the dissolution potential of the metal material, and lithium can be inserted and extracted. A non-aqueous electrolyte secondary battery comprising a positive electrode using a metal oxide as an active material and a separator interposed between the two electrodes, wherein the potential of the negative electrode is lower than the dissolution potential of the metal material. For this purpose, the battery is precharged within 24 hours after the non-aqueous electrolyte is injected into the battery.

A non-aqueous electrolyte secondary battery (hereinafter, referred to as a "second battery") according to the invention of claim 4 is a battery of the negative electrode can after the non-aqueous electrolyte is injected into the battery. A non-aqueous electrolyte secondary battery whose potential is equal to or higher than the dissolution potential of the metal material forming the negative electrode can, wherein the non-aqueous electrolyte is reduced so that the potential of the negative electrode can is lower than the dissolution potential of the metal material. The battery is precharged within 24 hours after being injected into the battery. Hereinafter, the first battery and the second battery are collectively referred to as a battery according to the present invention.

The negative electrode of the first battery is obtained by binding a material capable of inserting and extracting lithium to a core (anode current collector) made of a metal material via a binder, and further comprising an electrolyte. The potential after injection is equal to or higher than the dissolution potential of the metal material.

The reason why the potential after the injection of the electrolytic solution is limited to the potential higher than the dissolution potential of the metal material constituting the core body is that the potential is lower than the dissolution potential of the metal material. This is because there is no problem to be solved by the present invention, that is, no problem that the metal material elutes into the electrolytic solution.

As a metal material (core) having such a problem, a foil or lath plate made of Cu, Ni or stainless steel (SUS) is exemplified.

Examples of the material capable of occluding and releasing lithium bound to the metal material include carbon materials such as graphite and coke, and metal oxides such as WO ₃ , Fe ₂ O ₅ and Nb ₂ O _5. Is exemplified.

The above-mentioned metal material has a dissolution potential of about 3 V with respect to Li / Li ⁺ unipolar potential, and this potential is equal to the Li / Li ⁺ after the injection of the electrolytic solution of the negative electrode using the above-mentioned carbon material or metal oxide as the negative electrode material. 3.2 which is the potential with respect to the Li ⁺ unipolar potential
Since it is lower than about V, it gradually elutes into the electrolytic solution.

The negative electrode of the first battery is prepared by kneading the above carbon material or the like with a binder such as PTFE (polytetrafluoroethylene) or PVdF (polyvinylidene difluoride) to obtain a negative electrode mixture. The negative electrode mixture is rolled into the above-described core, and is subjected to a vacuum heat treatment at a temperature of about 250 ° C. for about 2 hours.

The negative electrode can of the second battery is one in which the potential of the negative electrode can after the injection of the electrolytic solution is equal to or higher than the melting potential of the metal material constituting the negative electrode can. The reason why the potential after the injection of the electrolytic solution is limited to a value equal to or higher than the dissolution potential of the metal material constituting the negative electrode can is also the same as the reason for the core described above.

Metal material (anode can material) for the second battery
Examples include stainless steel and Fe.

The cathode material (cathode active material) in the battery according to the present invention is not particularly limited as long as it is a metal oxide capable of inserting and extracting lithium for use in a secondary battery. For example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO _{2 and the} like.

The positive electrode of the battery according to the present invention is obtained by kneading the above-mentioned positive electrode material with a conductive agent such as acetylene black and carbon black and a binder such as PTFE and PVdF to form a positive electrode mixture. The agent is rolled into an aluminum lath plate as a core (positive electrode current collector),
It is manufactured by performing a vacuum heat treatment at a temperature of about 250 ° C. for about 2 hours.

The separator in the battery according to the present invention also includes
There is no particular limitation, and various separators conventionally used for non-aqueous electrolyte secondary batteries, such as a microporous thin film made of polypropylene, polyethylene, or the like, can be used.

The non-aqueous electrolyte in the battery according to the present invention is not particularly limited, either, and the solvent such as propylene carbonate, ethylene carbonate, 1,2-butylene carbonate, dimethyl carbonate, diethyl carbonate, etc.
Various non-aqueous electrolytes conventionally proposed for non-aqueous electrolyte secondary batteries, such as a solution in which a solute such as iPF ₆ is dissolved, can be used.

The battery according to the present invention provides a non-aqueous electrolyte secondary battery comprising the above-described members so that the potential of the negative electrode is lower than the dissolution potential of the metal material constituting the core or the negative electrode can. Pre-charging is performed within 24 hours after the injection into the battery.

In the present invention, the reason why the pre-charging is performed within 24 hours after the injection of the non-aqueous electrolyte is that if the charging / discharging cycle is repeated within 24 hours after the injection of the electrolyte. However, the reduction in battery capacity due to material degradation is somewhat to some extent, and the reduction in battery capacity due to the elution of the metal material constituting the core and the negative electrode can into the electrolytic solution is almost nonexistent. This fact will be clarified by examples described later.

[0024]

In the non-aqueous electrolyte secondary battery according to the present invention, the negative electrode of the negative electrode material is converted into a negative electrode by pre-charging within 24 hours after the injection of the non-aqueous electrolyte. Of the metal material to be dissolved into the non-aqueous electrolyte is small.
For this reason, even when charge / discharge cycles are repeated, clogging of the separator and electrodeposition of the metal material from the non-aqueous electrolyte hardly occur. Below, the principle (action) of the present invention
Will be described with reference to the drawings for further clarification.

FIG. 1 is a diagram illustrating the principle of the present invention. The vertical axis represents the potential (V) of a negative electrode using a carbon material as a negative electrode material (the same applies to the following potentials) with respect to the Li / Li ⁺ unipolar potential. The time (h) after the start of the preliminary charging is plotted on the axis, and is shown in the graph.

As shown in the figure, the potential of the negative electrode, which was about 3.2 V (point a) before the preliminary charge was performed, gradually decreased as the preliminary charge progressed and the amount of lithium absorbed by the negative electrode material increased. Falls and indicates 0 V when pre-charging is completed.
To the point. Next, when an external resistor is connected and discharge is performed,
The potential of the negative electrode gradually rises to reach a point c (about 1 V) indicating a discharge termination potential. The reason why the potential of the negative electrode does not return to the same potential as the original point a by the discharge is that a part of the occluded lithium metal is captured by the negative electrode material. When the battery is charged for further reuse, the potential of the negative electrode becomes c
D, indicating 0 V when charging is completed
To the point. In the subsequent repetition of the charge / discharge cycle, the potential of the negative electrode repeats a potential cycle of b → c → d.

By the way, as shown in FIG. 1, the potential of the negative electrode core and the negative electrode can before the pre-charging is performed after the electrolyte is injected.
Generally, it is around 3.2V. For this reason, when a metal material such as Cu, Ni, stainless steel, or Fe having a dissolution potential of about 3 V lower than the above 3.2 V is used as the material of the negative electrode core or the negative electrode can, it has a high potential before the preliminary charge. In the meantime, those metal materials are eluted in the electrolytic solution.

According to the present invention, such a metal material is preliminarily charged by elution within 24 hours after the injection of the electrolytic solution.
By making the potential of the negative electrode lower than the melting potential of the metal material, the potential is reduced as much as possible.

[0029]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples, and may be carried out by appropriately changing the scope of the present invention. Is possible.

Example 1 [Preparation of Positive Electrode] LiCoO ₂ was kneaded with acetylene black as a conductive agent and a fluororesin dispersion as a binder in a weight ratio of 90: 6: 4 to form a positive electrode. Agent was obtained. Next, this positive electrode mixture was rolled into an aluminum lath plate as a current collector, and subjected to vacuum heat treatment at 250 ° C. for 2 hours to produce a positive electrode.

[Preparation of Negative Electrode] A 400 mesh pass graphite powder was mixed with a fluororesin dispersion as a binder at a weight ratio of 95: 5 to obtain a negative electrode mixture.
This negative electrode mixture was rolled into a copper lath plate as a current collector (core), and heat-treated under vacuum at 250 ° C. for 2 hours to produce a negative electrode.

[Preparation of Non-Aqueous Electrolyte] LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 1 at 1 mol / L to prepare a non-aqueous electrolyte.

[Preparation of Non-Aqueous Electrolyte Secondary Battery] A cylindrical secondary battery is composed of the above-mentioned positive and negative electrodes, a separator, a negative electrode can, etc., and a non-aqueous electrolyte is injected into the secondary battery to assemble the battery. The battery BA1 of the present invention (battery size: diameter 14.2 mm, height:
50.0 mm). Note that an iron material was used as the negative electrode can, and a polypropylene microporous thin film was used as the separator.

FIG. 2 is a cross-sectional view of the produced battery BA1 of the present invention. The battery BA1 shown in FIG.
Separator 3, positive electrode lead 4, separating these two electrodes,
It comprises a negative electrode lead 5, a positive electrode external terminal 6, a negative electrode can 7, and the like. The positive electrode 1 and the negative electrode 2 are wound in a spiral shape through a separator 3 into which a non-aqueous electrolyte is injected.
The positive electrode 1 is connected to a positive electrode external terminal 6 via a positive electrode lead 4, and the negative electrode 2 is connected to a negative electrode can 7 via a negative electrode lead 5. It can be taken out to the outside.

(Example 2) Pre-charging was performed 24 hours after the electrolyte was injected.
A battery BA2 of the present invention was produced in the same manner as in Example 1, except that the battery BA2 was left standing for a while.

(Comparative Example 1) A preliminary charge was performed 48 hours after the electrolyte was injected.
A comparative battery BC1 was produced in the same manner as in Example 1 except that the operation was performed after standing for a period of time.

FIG. 3 is a cycle characteristic diagram of these batteries, in which the vertical axis represents the battery capacity (mAh) and the horizontal axis represents the number of cycles (times). As shown in the figure, the batteries BA1 and BA2 of the present invention having a standing time of 24 hours or less.
Is that, even after 500 cycles, the cycle deterioration of the battery capacity is about the capacity decrease due to the fatigue of the material, whereas the decrease in the battery capacity of the comparative battery BC1 in which the leaving time is 48 hours becomes more severe as the number of cycles increases, Initially 500mAh
It can be seen that the weak battery capacity is reduced to about 200 mAh, which is less than half the initial capacity, after 500 cycles.

(Examples 3 and 4 and Comparative Examples 2 and 3) Preliminary charging was performed for 10 hours, 20 hours,
The battery BA of the present invention was prepared in the same manner as in Example 1 except that the test was performed after leaving each battery at 25 ° C. for 0 hour, 36 hours, and
3, BA4, and comparative batteries BC2 and BC3.

FIG. 4 is a graph showing the relationship between the cycle time and the standing time after injecting the electrolyte into these batteries.
It is the graph which showed the discharge capacity (mAh) after the passage of the cycle, and the abscissa plotted the standing time (h) after the electrolyte injection.
FIG. 4 also transcribes data on the batteries BA1 and BA2 of the present invention and the comparative battery BC1.

It can be seen from the figure that the batteries BA1 to BA4 of the present invention having a leaving time of less than 24 hours have a large discharge capacity after 500 cycles of just over 400 mAh, while the comparative batteries BC1 to BC4 having a leaving time of more than 24 hours. It can be seen that BC3 has a smaller discharge capacity after 500 cycles than the batteries of the present invention, BA1 to BA4.

(Examples 5 to 8 and Comparative Examples 4 and 6) Preliminary charging was performed for 1 hour, 10 hours, and 20 hours after the electrolyte solution was injected.
Hours, 24 hours, 30 hours, 36 hours, 48 hours, 40
Example 1 except that each battery was left standing at
Batteries BA5 to BA8 of the present invention and comparative battery B
C4 to BC6 were produced.

FIG. 5 is a graph showing the relationship between the cycle time and the standing time after injection of the electrolyte in these batteries.
It is the graph which showed the discharge capacity (mAh) after the passage of the cycle, and the abscissa plotted the standing time (h) after the electrolyte injection.

As can be seen from the figure, the batteries BA5 to BA8 of the present invention having a standing time of 24 hours or less when the standing temperature is 40 ° C. are similar to the case where the standing temperature is 25 ° C.
A comparative battery BC having a discharge capacity after 500 cycles of as little as 400 mAh or more and a standing time of more than 24 hours
4 to BC6 are 50 times smaller than the batteries BA5 to BA8 of the present invention.
It can be seen that the discharge capacities after 0 cycles are all small.

(Examples 9 to 12 and Comparative Examples 7 and 8)
Pre-charging was performed for 1 hour, 10 hours, 20 hours, 24 hours, 30 hours, 36 hours, and 60 ° after electrolyte injection.
Inventive batteries BA9 to BA12 and comparative batteries BC7 and BC8 were prepared in the same manner as in Example 1 except that the battery was left at C.

FIG. 6 is a graph showing the relationship between the cycle time and the standing time after injection of the electrolyte in these batteries.
It is the graph which showed the discharge capacity (mAh) after the passage of the cycle, and the abscissa plotted the standing time (h) after the electrolyte injection.

As can be seen from the figure, even when the storage temperature is 60 ° C., the battery BA of the present invention in which the storage time is within 24 hours.
9 to BA12 show that the discharge capacity after 500 cycles is larger than those of the comparative batteries BC7 and BC8 in which the leaving time exceeds 24 hours. By comparing the three figures of FIGS. 4 to 6, it was found that the leaving temperature was 25 ° C. to 40 ° C.
It is understood that the cycle deterioration of the discharge capacity increases as the temperature increases to 0 ° C.

In the above embodiment, a specific example in which the present invention is applied to a cylindrical battery has been described. However, the shape of the battery is not particularly limited, and the present invention is applicable to various shapes such as a flat type and a square type. It can be applied to a non-aqueous electrolyte secondary battery.

[0048]

The non-aqueous electrolyte secondary battery according to the present invention comprises:
Since the pre-charging is performed within 24 hours after the injection of the non-aqueous electrolyte, the elution of the metal material forming the core or the negative electrode can into the non-aqueous electrolyte is small. The present invention has excellent unique effects, such as little clogging of the separator and little electrodeposition of the metal material on the negative electrode, and excellent cycle characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a sectional view of the battery of the present invention.

FIG. 3 is a cycle characteristic diagram of a battery of the present invention and a comparative battery.

FIG. 4 is a graph showing a relationship between a standing time at 25 ° C. after injection of an electrolytic solution and cycle characteristics.

FIG. 5 is a graph showing a relationship between a standing time at 40 ° C. after injection of an electrolytic solution and cycle characteristics.

FIG. 6 is a diagram showing the relationship between the standing time at 60 ° C. after the electrolyte injection and the cycle characteristics.

[Explanation of Signs] BA1 Battery 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode lead 5 Negative electrode lead 6 Positive external terminal 7 Negative electrode can

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ryuji Oshita 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Norihiro Furukawa 2--18 Keihanhondori, Moriguchi-shi, Osaka (56) References JP-A-1-294372 (JP, A) JP-A-5-41249 (JP, A) JP-A-59-128779 (JP, A) JP-A-59-128780 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 10/40

Claims (5)

(57) [Claims] A battery comprising a core made of a metal material and a material capable of inserting and extracting lithium, wherein a potential after injecting a non-aqueous electrolyte into a battery is higher than a dissolution potential of the metal material. A non-aqueous electrolyte secondary battery comprising a certain negative electrode, a positive electrode using a metal oxide capable of inserting and extracting lithium as an active material, and a separator interposed between these two electrodes, wherein the potential of the negative electrode is To be lower than the melting potential of the metal material,
A non-aqueous electrolyte secondary battery, wherein pre-charging is performed within 24 hours after the non-aqueous electrolyte is injected into the battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein said metal material is Cu, Ni or stainless steel. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the material capable of inserting and extracting lithium is a carbon material or a metal oxide. 4. A non-aqueous electrolyte secondary battery in which the potential of the negative electrode can after injecting the non-aqueous electrolyte into the battery is equal to or higher than the dissolution potential of the metal material forming the negative electrode can. Non-aqueous electrolyte secondary battery characterized in that pre-charging is performed within 24 hours after injecting the non-aqueous electrolyte into the battery so that the potential of the can is lower than the dissolution potential of the metal material. . 5. The non-aqueous electrolyte secondary battery according to claim 4, wherein said metal material is stainless steel or Fe.