JPH087886A - Nonaquoeus electrolytic secondary battery and manufacture thereof - Google Patents

Abstract

PURPOSE:To make voltage change in the final stage of discharge gently to easily detect the remaining capacity by using a mixture of graphite and a lithium-containing metal oxide in a negative electrode capable of absorbing/ desorbing lithium. CONSTITUTION:By adding a lithium-containing metal oxide to graphite, deintercalation (release) of lithium from the metal oxide is generated in the final stage of discharge and sharp rising in negative potential, or sharp drop in battery voltage is retarded. As a result, since battery voltage gently drops in the final stage of discharge while battery capacity and potential flatness are maintained, by detecting voltage in this part, the remaining capacity is easily detected. By controlling the mixing ratio of the lithium-containing metal oxide to 0.1-30wt.%, discharge capacity at 2.75-3.5V is increased, and the remaining capacity is easily detected. In addition, by limiting to 1-10wt.%, battery performance obtained by the complete discharge is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous secondary battery using graphite as a negative electrode material, and more particularly to improvement of a battery using graphite as a negative electrode.

[0002]

2. Description of the Related Art Recently, graphite such as natural graphite and artificial graphite has been
It has attracted attention as a negative electrode material for non-aqueous electrolyte secondary batteries because of its high capacity, potential flatness, and excellent cycle characteristics.

It can be said that the use of this graphite in the negative electrode makes it possible to provide a battery excellent in flatness of potential as compared with known coke, non-graphitizable carbon and the like. That is, the battery having the graphite negative electrode has a small change in battery voltage. However, at the end of discharge, the negative electrode potential sharply rises and the battery voltage sharply drops, making it difficult to detect the remaining battery capacity. As a result, there is a problem that the battery capacity suddenly runs out during use of the battery device, and the device is stopped.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to maintain the flatness of the battery capacity and the potential while maintaining the voltage change at the end of discharge. (EN) It is intended to provide a non-aqueous electrolyte secondary battery which is caused gently and whose remaining capacity is easily detected.

Further, another object of the present invention is to provide a secondary battery having improved cycle characteristics.

[0006]

In the present invention, the non-aqueous electrolyte secondary battery according to claim 1 stores a lithium mixture containing graphite and a lithium-containing metal oxide.
It is characterized in that it is used as a dischargeable negative electrode.

Further, in the method for producing a non-aqueous electrolyte secondary battery according to claim 8, a lithium-containing metal oxide in a state of occluding lithium and graphite are mixed to obtain a mixture,
It is characterized in that the negative electrode capable of absorbing and desorbing lithium is subjected to a heat treatment for removing the water content of this mixture.

Here, the mixture contains the above-mentioned lithium-containing metal oxide in the range of 0.1% by weight to 30% by weight, particularly 1% by weight.
It is preferable to add and contain it in the range of not less than 10% by weight.

Then, as the lithium-containing metal oxide,
LiNbO₃, LiVO₃, LiTi₂O_Four, Li ₂TiO₃, Li₂WO_FourFrom
At least one selected from the group consisting of
It

Further, LiCo is used as the positive electrode material (active material).
Compounds represented by O ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO ₂ , and LiM _1X M _2Y O _Z ( _X , _Y , and _Z are arbitrary real numbers, M ₁ and M ₂ are transition metals) are preferable. It is mentioned as a thing.

Further, usable solvents include, for example, ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), γ-butyrolactone (γ-BL), dimethyl carbonate (DM).
C), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), dimethoxyethane (DM)
E), tetrahydrofuran (THF), dioxolane (DOXL), 1,2-diethoxyethane (DEE) and the like can be used, and a mixed solvent thereof can be appropriately used depending on the battery design. Particularly preferred is, as shown in the examples,
Ethylene carbonate (EC) and dimethoxyethane (D
ME) is a mixed solvent.

Also, as a solute that can be used, LiPF₆, L
iCF₃SO₃, LiBF_Four, LiAsF₆, LiClO_FourCan mention
However, considering the cycle characteristics of the secondary battery, LiPF₆, LiC
F₃SO ₃Is particularly preferable. This solute is added to 0.7-1.5M
The solution dissolved at a ratio of about 1M
Optimal. Moreover, you may use a solid electrolyte.

Further, the non-water of the present invention according to claim 5
-Based electrolyte secondary battery is LiNbO₃, LiVO ₃, LiTi₂O_Four, Li₂TiO
₃, Li₂WO_FourAt least one selected from the group consisting of
Negative consisting of a mixture of lithium-containing metal oxide and graphite
Pole and LiCoO₂, LiNiO₂, LiMn ₂O_Four, LiFeO₂, LiM_1XM_2YO_Z
The compound represented by_X,_Y,_ZIs any real number and M₁,
M₂Is at least a transition metal)
A positive electrode made of one material and ethylene carbonate (E
C), butylene carbonate (BC), vinylene carbo
Nate (VC), γ-butyrolactone (γ-BL), di
Methyl carbonate (DMC), diethyl carbonate
(DEC), methyl ethyl carbonate (MEC), di
Methoxyethane (DME), tetrahydrofuran (TH
F), dioxolane (DOXL), 1,2-diethoxyethane
At least one selected from the group consisting of
Non-aqueous electrolyte solvent and LiPF₆, LiCF₃SO₃, LiBF_Four, LiAs
F₆, LiClO_FourAnd a solute selected from the group consisting of
And are characterized.

Here, ethylene carbonate (E
A mixed solvent of C) and dimethoxyethane (DME) is preferred.

As the solute, at least one selected from the group consisting of LiPF ₆ and LiCF ₃ SO ₃ is suitable. The optimum concentration is 0.7 to 1.5 M (mol / liter), especially about 1 M.

Further, as the graphite used here, powder obtained by pulverizing graphite may be used as it is, and it may be subjected to purification treatment, heat treatment (500 to 3700 ° C.), acid treatment, alkali treatment, expansion treatment and the like. You may use what performed the pretreatment.

For other members constituting the battery such as a separator (when a liquid electrolyte is used), various materials that have been practically used or proposed as conventional non-aqueous batteries are used without particular limitation. Is possible.

[0018]

In the present invention, by adding a lithium-containing metal oxide to graphite of the negative electrode, deintercalation (release) of lithium from the metal oxide occurs at the end of discharge, resulting in a rapid increase in the negative electrode potential. That is, it is possible to suppress a rapid decrease in battery voltage. As a result, the battery voltage gradually decreases at the end of discharge while maintaining the battery capacity and potential flatness. Therefore, the remaining capacity can be easily detected by detecting this portion.

Further, the mixing ratio of the lithium-containing metal oxide is set to 0.1% by weight or more and 30% by weight or less, because in this range, the discharge capacity of the battery at 2.75 V or more and 3.5 V or less becomes large, and the remaining capacity becomes This is because it can be easily detected.

In addition to the above characteristics, especially 1% by weight
By setting the content to 10% by weight or less, the battery capacity until the battery is almost completely discharged can be improved.

In the battery of the present invention, since the lithium-containing metal oxide is mixed and used at the time of manufacturing the negative electrode, there is no lithium occlusion in the oxide during the initial charge and it can be involved only in the discharge. Therefore, there is no decrease in initial charge / discharge efficiency, and almost no decrease in capacity is observed as compared with the case of no addition.

[0022]

EXAMPLES The present invention will be described below in detail based on examples. However, the present invention is not limited to the following examples, and various modifications may be made without departing from the scope of the invention. It is possible. (Example 1) [Production of negative electrode] Carbon lump (d ₀₀₂ = 3.356Å, Lc> 1)
Graphite powder obtained by jetting and crushing (1000 Å) an air stream and jetting it as a lithium-containing metal oxide.
LiNbO ₃ was mixed at a weight ratio of 95: 5 to prepare a negative electrode mixture. Here, as the lithium-containing metal oxide, a compound represented by a composition formula of LiNbO ₃ is added and mixed, and a state in which lithium is occluded in this way can be used in the present invention.

Next, polyvinylidene fluoride as a binder was added to N-methyl-2-pyrrolidone (NMP) in an amount of 5% by weight.
It was made to melt | dissolve and the NMP solution was prepared. So that the weight ratio of the negative electrode mixture and polyvinylidene fluoride is 95: 5,
The negative electrode mixture and the NMP solution were kneaded to prepare a slurry. This slurry on both sides of the copper foil as a negative electrode current collector,
Apply by doctor blade method, 150 ℃ for 2 hours,
It was vacuum dried to prepare a negative electrode.

The vacuum drying is a heat treatment for removing water and NMP. This heat treatment is from 80 ℃ to 1
It should be set in the temperature range of 80 ° C. for about 30 minutes to 5 hours, appropriately considering the removal state of water and NMP. [Production of Positive Electrode] LiCoO ₂ as a positive electrode active material and artificial graphite as a conductive agent were mixed at a weight ratio of 9: 1 to produce a positive electrode mixture. Further, polyvinylidene fluoride, which is a binder, was dissolved in 5% by weight in NMP to prepare an NMP solution. Then, the positive electrode mixture and the NMP solution were kneaded to prepare a slurry so that the weight ratio of the positive electrode mixture and polyvinylidene fluoride was 95: 5. This slurry was applied on both sides of an aluminum foil as a positive electrode current collector by the doctor blade method and vacuum dried at 150 ° C. for 2 hours to produce a positive electrode. [Preparation of Electrolyte Solution] Ethylene carbonate (EC) and 1,2-
In an equal volume mixed solvent with dimethoxyethane (DME), Li
PF ₆ (lithium hexafluorophosphate) was dissolved at a concentration of 1 mol / liter to prepare a non-aqueous electrolyte solution. [Battery assembly] Using the above positive and negative electrodes and electrolyte solution,
A size A battery (AA type) of the present invention A was manufactured. As the separator, an ion-permeable polypropylene microporous film is used.

FIG. 1 is a sectional view schematically showing the manufactured battery A of the present invention. As shown in FIG. 1, the battery A of the present invention is
It is composed of a positive electrode 1 and a negative electrode 2, a separator 3 separating these two electrodes, a negative electrode can 4, a negative electrode lead 5, a positive electrode lead 6, a positive electrode external terminal 7, an insulating packing 8, and the like. Positive electrode 1
The negative electrode 2 and the negative electrode 2 form a spiral electrode body in a state of being spirally wound via the separator 3 in which the nonaqueous electrolytic solution is injected and held. The electrode body is housed in the negative electrode can 4. The positive electrode 1 is connected to the positive electrode external terminal 7 via the positive electrode lead 6.
In addition, the negative electrode 2 is connected to the negative electrode can 4 via the negative electrode lead 5 so that the chemical energy generated inside the battery A can be taken out as electric energy to the outside. The insulating packing 8 insulates the positive electrode external terminal 7 from the negative electrode can 4,
It is sealed. As a main material (Example 2) the negative electrode, and a graphite powder and a lithium-containing metal oxide LiVO _3, a weight ratio of 95: except prepared were mixed in 5 negative electrode mixture in the same manner as in Example 1, the Invention battery A2 was assembled. (Example 3) As in Example 1, except that graphite powder and lithium-containing metal oxide LiTi ₂ O ₄ were mixed at a weight ratio of 95: 5 as a main material of the negative electrode to prepare a negative electrode mixture. ,
The present invention battery A3 was assembled. (Example 4) As in Example 1, except that graphite powder and lithium-containing metal oxide Li ₂ TiO ₃ were mixed at a weight ratio of 95: 5 as a main material of the negative electrode to prepare a negative electrode mixture. ,
The present invention battery A4 was assembled. As a main material (Example 5) anode, a graphite powder and a lithium-containing metal oxides Li ₂ WO _4, the weight ratio of 95: except were mixed in a 5 to form anode mixture in the same manner as in Example 1 The present invention battery A5 was assembled. (Comparative Example) Comparative battery X was prepared in the same manner as in Example 1 except that graphite powder was directly used as the negative electrode mixture without adding and mixing the lithium-containing metal oxide as the main material of the negative electrode.
Assembled. [Charge / Discharge Characteristics] The present invention batteries A1 to A thus obtained
Using 5 and Comparative Battery X, the relationship between charge / discharge capacity and battery voltage was investigated. The experimental conditions at this time are as follows:
After charging at a final voltage of 4.2V at 200mA, 2
This is to discharge to a discharge end voltage of 2.75 V at 00 mA and investigate the charge / discharge characteristics at this time. The result is shown in FIG.

FIG. 2 is a graph showing the charge / discharge characteristics of each battery, with the horizontal axis representing the battery capacity (mAh) and the vertical axis representing the battery voltage (V). From FIG. 2, the batteries A1 to A5 of the present invention to which the lithium-containing metal oxide is added maintain the potential flatness and have a gradual voltage drop at the end of discharge as compared with the conventional comparative battery X, and detect the remaining amount. You can see that it has become easier.

Further, in the batteries A1 to A5 of the present invention, since the initial charge / discharge efficiency of the negative electrode does not decrease, it can be said that the capacity is larger than the battery using a metal oxide containing no lithium in the negative electrode. [Cycle characteristics] Next, using the present batteries A1 to A5 and the comparative battery X, the relationship between the number of cycles and the discharge capacity of the battery was examined. Regarding the experimental conditions at this time, each battery was charged at 200 mA to a charge end voltage of 4.2 V, then discharged at 200 mA to a discharge end voltage of 2.75 V, and the cycle characteristics were examined. The result is shown in FIG.

FIG. 3 is a graph showing the cycle characteristics of each battery by plotting the number of cycles (times) on the horizontal axis and the battery capacity (mAh) on the vertical axis. From FIG. 3, the battery A of the present invention
It can be understood that 1 to A5 have excellent cycle characteristics as compared with the comparative battery X. [Discharge Characteristics] In particular, based on the battery A1 of the present invention, the addition and mixing ratio of the lithium-containing metal oxide LiNbO _{3 in} the negative electrode mixture were changed, and the change in the characteristics of each battery was investigated. The experimental conditions at this time are the same as the charge / discharge conditions of the cycle characteristics described above.
The battery capacity (mAh) at the 00th cycle is plotted on the left axis, and the battery capacity (mAh) at the 400th cycle, particularly between 2.75 and 3.5V, is plotted on the right axis. This result is shown in FIG.
Shown in

From the above, by setting the mixing ratio of the lithium-containing metal oxide to 0.1% by weight or more and 30% by weight or less, the battery capacity at 2.75 V or more and 3.5 V or less can be improved.

The battery capacity at 2.75 V or more and 3.5 V or less is a capacity that is hardly observed at the end of discharge of a battery using only graphite for the negative electrode, but discharge by adding a lithium-containing metal oxide. It is the volume that is significantly increased and observed at the end stage.

In particular, the mixing ratio is 1% by weight or more and 10
It can be understood that by setting the content to be less than or equal to wt%, in addition to the above effects, the battery capacity until the battery is almost completely discharged is improved.

In this experimental example, LiNbO ₃ was used as the lithium-containing metal oxide, but other LiVO ₃ and LiTi ₂ were used.
Even when O ₄ , Li ₂ TiO ₃ , and Li ₂ WO ₄ were used, the same tendency was observed in the discharge characteristics and the addition ratio.

As described above, the cylindrical type is illustrated in the examples, but the battery of the present invention is not particularly limited in its shape, and is applied to various other types of non-aqueous electrolyte batteries such as flat type and rectangular type. It is possible.

[0034]

In the battery of the present invention, carbon powder mixed with a lithium-containing metal oxide is used as a negative electrode material, so that a rapid increase in the negative electrode potential at the end of discharge can be suppressed. That is, when observed as a battery, a rapid voltage drop is suppressed. That is, it becomes easy to detect the remaining capacity at the end of discharge. Furthermore, the cycle characteristics of this type of battery can be improved, and its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a battery of the present invention manufactured in an example.

FIG. 2 is a diagram showing the relationship between the battery capacity and the battery voltage of the battery of the present invention and the comparative battery.

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

FIG. 4 is a diagram showing the relationship between the addition ratio of a lithium-containing metal oxide in a negative electrode mixture, the battery capacity, and the battery capacity between 2.75 and 3.5V.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode 3 Separator 4 Negative electrode can 5 Negative electrode lead 6 Positive electrode lead 7 Positive electrode external terminal 8 Insulation packing A1 to A5 Inventive battery X Comparative battery

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiko Saito 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (11)

[Claims] 1. A non-aqueous electrolyte secondary battery characterized by using a mixture of graphite and a lithium-containing metal oxide as a negative electrode capable of inserting and extracting lithium. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the mixture contains the lithium-containing metal oxide in a range of 0.1% by weight or more and 30% by weight or less. 3. The non-aqueous electrolyte secondary battery according to claim 2, wherein the mixture contains the lithium-containing metal oxide in a range of 1% by weight or more and 10% by weight or less. 4. The lithium-containing metal oxide is LiNb
The non-aqueous electrolyte secondary battery according to claim 1, which is at least one selected from the group consisting of O ₃ , LiVO ₃ , LiTi ₂ O ₄ , Li ₂ TiO ₃ , and Li ₂ WO _4. . 5. LiNbO ₃ , LiVO ₃ , LiTi ₂ O ₄ , Li ₂ TiO ₃ , Li ₂
At least one lithium-containing metal oxide selected from the group consisting of WO ₄ , and a negative electrode composed of a mixture of graphite, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO ₂ , LiM _1X M _2Y O _Z A positive electrode made of at least one material selected from the group consisting of compounds ( _X , _Y , and _Z are arbitrary real numbers and M ₁ and M ₂ are transition metals), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), γ-butyrolactone (γ-BL), dimethyl carbonate (DM
C), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), dimethoxyethane (DM)
E), tetrahydrofuran (THF), dioxolane (DOXL), at least one non-aqueous electrolyte solvent selected from the group consisting of 1,2-diethoxyethane (DEE), LiPF ₆ , LiCF ₃ SO ₃ , and LiBF ₄ , LiAsF ₆ , and LiClO ₄ and at least one solute selected from the group consisting of LiClO ₄ and a non-aqueous electrolyte secondary battery. 6. The solvent is ethylene carbonate (E
The non-aqueous electrolyte secondary battery according to claim 5, which is a mixed solvent of C) and dimethoxyethane (DME). 7. The non-aqueous electrolyte secondary battery according to claim 5, wherein the solute is at least one selected from the group consisting of LiPF ₆ and LiCF ₃ SO ₃ . 8. A negative electrode capable of occluding / releasing lithium is obtained by mixing a lithium-containing metal oxide in a state of occluding lithium with graphite to obtain a mixture, and heat-treating the mixture. And a method for manufacturing a non-aqueous electrolyte secondary battery. 9. The method for producing a non-aqueous electrolyte secondary battery according to claim 8, wherein the mixture contains the lithium-containing metal oxide in a range of 0.1% by weight or more and 30% by weight or less. 10. The method for producing a non-aqueous electrolyte secondary battery according to claim 9, wherein the mixture contains the lithium-containing metal oxide in a range of 1% by weight or more and 10% by weight or less. 11. The lithium-containing metal oxide is LiNb
The non-aqueous electrolyte secondary battery according to claim 8, which is at least one selected from the group consisting of O ₃ , LiVO ₃ , LiTi ₂ O ₄ , Li ₂ TiO ₃ , and Li ₂ WO _4. Manufacturing method.