JPH07105978A - Non-aqueous electrolyte secondary battery and its manufacture - Google Patents

Abstract

PURPOSE:To provide a non-aqueous electrolyte secondary battery, which has a high energy density and is excellent in the charge/discharge lifetime characteristics, and to offer a method of manufacturing such batteries. CONSTITUTION:In the vessel 10 of a battery cell for measuring the characteristics, a positive electrode 12 and a negative electrode 14 are installed opposingly while positioned on the oversurface of a lower can 10a made of stainless steel and on the bottom surface of an upper lid 10b made of stainless steel, respectively, and a separator 16 and a glass fiber filtrating paper 18 impregnated with electrolytic solution are installed between these positive and negative electrodes 12, 14. Because the positive electrode 12 is made of mesophase carbon and various oxygen-including functional radicals existing at the surface of the mesophase carbon are removed through a reductive treatment as immersing in a solution consisting of LiAlH4 and diethyl ether, intercalation of Li ions can be done smoothly, and a good discharge characteristic is obtained. Accordingly the resultant non-aqueous electrolyte secondary battery is equipped with a good charge/discharge lifetime characteristic owing to the reductive treatment of the surface of mesophase carbon which is used to t,he negative electrode.

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 a manufacturing method thereof, and more particularly to a non-aqueous electrolyte secondary battery having a high energy density and an excellent charge / discharge life and a manufacturing method thereof. .

[0002]

_2. Description of the Related Art Conventionally, various intercalation compounds such as MoS ₂ (molybdenum disulfide) and conductive polymer substances such as polyaniline have been used as secondary batteries having an alkali metal such as Li (lithium) as a negative electrode. Is used as a positive electrode active material, and an electrolyte solution in which LiPF ₆ (lithium hexafluorophosphate) or the like is dissolved in an organic solvent such as propylene carbonate has been actively developed.

In such a secondary battery, Li or Li is used for the negative electrode.
An alloy is used, and the electrolyte is L such as LiPF ₆ described above.
The use of a compound containing i ions has a feature that the battery voltage is high and a secondary battery with high energy density can be obtained.

[0004]

However, there are very few examples of secondary batteries using this kind of Li or Li alloy as a negative electrode, which have been put to practical use until now. The main reason for this is that when applied to secondary batteries used in automobiles, portable devices, audio devices, etc., safety problems associated with charge / discharge cycles have not been solved.

For example, when Li is used for the negative electrode, Li ions in the electrolytic solution are deposited on the Li negative electrode plate during charging, but it is difficult to deposit uniformly at that time, and therefore dendrite (dendritic) Li is used. Occurs, and a phenomenon such as penetrating the separator between the positive electrode and the negative electrode to cause a short circuit, or causing Li to be finely precipitated and falling off occurs. Then, due to such a short circuit or the like, the metal Li may be ignited. In addition, when these batteries are arranged in series or in parallel, and if some of them are defective, current may be concentrated there and the batteries may be destroyed, resulting in a safety problem.

For this reason, various methods have been proposed which mainly improve the above-mentioned drawbacks of the negative electrode. For example, Li and A
It has been proposed to use an alloy with l (aluminum), silver, lead or the like for the negative electrode. However, in the case of a Li-Al alloy as an example, although dendrite is not generated, atomization and collapse of the electrode (negative electrode) occur when charging and discharging are repeated, and the Li diffusion rate of the alloy phase is small. Therefore, it has drawbacks such as unsatisfactory Coulombic efficiency. Further, when a roll type battery is produced, there is a drawback that the winding machine cannot be used due to insufficient mechanical strength.

In recent years, it has been proposed to use carbon as the negative electrode. This is because the use of carbons as the negative electrode has the drawback of causing a large amount of self-discharge, but can overcome the safety problem. However, when carbon is used as the negative electrode, the intercalation and deintercalation of Li ions into the carbon is 1.2 V to
Since it is performed at 0 V (vs. Li voltage), LiCoO ₂ and L
When a 4 V positive electrode material made of iNiO ₂ is used, the voltage required for intercalation, that is, the voltage of 3 V obtained by subtracting about 1 V from the above is the battery voltage, so that the energy density of the battery is considerably reduced.

On the other hand, when graphite (graphite) is used among carbons, intercalation and deintercalation into graphite is 0.3 V to 0 V (vs. L).
i voltage), the battery voltage increases and Li-
It is possible to create a high energy battery that is no different from an Al alloy. However, graphite often decomposes the solvent due to its catalytic action. Especially propylene carbonate is easily decomposed. For this reason, it has been pointed out that a solvent mainly composed of EC (ethylene carbonate) is suitable, but when a solvent mainly composed of EC is used when graphite is used as the negative electrode, the solvent is partially decomposed. There is a drawback that the battery is easily deteriorated.

That is, graphite was used for the positive electrode, metallic Li was used for the negative electrode, and 1M / l LiPF was used for a 50% equal volume mixture of EC and DEC (diethyl carbonate) as the electrolytic solution.
_{When a} solution of ₆ was used and a current was passed to intercalate Li ions in graphite, the cell voltage was 0.8 V to 0.4 V (as indicated by the broken line in the graph of FIG. A flat potential is seen in (Li voltage), and it can be seen that the solvent is decomposed here.

In view of the above circumstances, the present invention provides a non-aqueous electrolyte containing an alkali metal ion, a rechargeable positive electrode, and a negative electrode that occludes the alkali metal ion during charging and releases the alkali metal ion during discharging. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery including the above and a method for producing the same, which has a high energy density and an excellent charge / discharge life, and a method for producing the same.

[0011]

The inventors of the present invention repeatedly conducted experiments on the decomposition phenomenon of a solvent that occurs when graphite is used for the positive electrode and metallic Li is used for the negative electrode. It was found to be promoted under various functional groups with oxygen present in.

[0012] Therefore, the above-mentioned problem is solved by a non-aqueous electrolytic solution containing an alkali metal ion, a rechargeable positive electrode provided in contact with the non-aqueous electrolytic solution, and a positive electrode facing the positive electrode via the non-aqueous electrolytic solution. In a non-aqueous electrolyte secondary battery provided with a negative electrode that occludes alkali metal ions during charging and releases alkali metal ions during discharging, carbon whose surface is subjected to reduction treatment is used as the negative electrode. And a non-aqueous electrolyte secondary battery.

In the above non-aqueous electrolyte secondary battery, the carbon is graphite, and the non-aqueous electrolyte secondary battery is achieved. Further, the above problem is a non-aqueous electrolytic solution containing an alkali metal ion, a positive electrode that is provided in contact with the non-aqueous electrolytic solution and is rechargeable,
Provided opposite to the positive electrode via the non-aqueous electrolyte,
In a method for producing a non-aqueous electrolyte secondary battery comprising a negative electrode that occludes alkali metal ions during charging and releases alkali metal ions during discharging, a reduction treatment step of treating the carbon surface used as the negative electrode with a reducing agent. And a non-aqueous electrolyte secondary battery manufacturing method.

Further, in the above-mentioned method for producing a non-aqueous electrolyte secondary battery, in the reduction treatment step, the negative electrode made of carbon is immersed in a non-aqueous solution in which a hydride is dissolved to form an oxide layer on the surface of the negative electrode. Is achieved by a method of manufacturing a non-aqueous electrolyte secondary battery. Furthermore, in the method for producing a non-aqueous electrolyte secondary battery, the reduction treatment step involves immersing the negative electrode made of carbon in an aqueous solution in which a borohydride is dissolved to reduce the oxide layer on the negative electrode surface. It is achieved by a method for manufacturing a non-aqueous electrolyte secondary battery, which is characterized by being a step.

[0015]

The present invention treats the surface of carbon used as the negative electrode of a non-aqueous electrolyte secondary battery with a reducing agent to reduce and remove various functional groups having oxygen present on the surface of the carbon to reduce the negative electrode of the negative electrode. It suppresses deterioration and decomposition of electrolytes and organic solvents on the surface of the negative electrode, and enables intercalation of alkali metal ions at low potential. Therefore, it is possible to realize a secondary battery having a good charge / discharge life and a high energy density even when charge / discharge is repeated at a high charge / discharge capacity.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on illustrated embodiments. FIG. 1 is a schematic sectional view showing a coin-type battery cell for measuring characteristics of a non-aqueous electrolyte secondary battery according to a first embodiment of the present invention. The battery container 10 includes a stainless steel lower can 10a, a stainless steel upper lid 10b, and a Teflon cover 10c that insulates the both. In the container 10, the positive electrode 12 installed on the upper surface of the stainless steel lower can 10a and the negative electrode 14 installed on the bottom surface of the stainless steel upper lid 10b face each other. Between the positive electrode 12 and the negative electrode 14, a separator 1 made of a porous separator for preventing current short circuit due to contact of both electrodes.
6 and a glass fiber filter paper 18 impregnated with the electrolytic solution are installed.

Further, a stainless steel lower can 10a of the container 10
The stainless steel upper lid 10b is connected to a battery charging / discharging device 20 that measures the potential of the positive electrode 12 with respect to the negative electrode 14 at a predetermined current density. Further, the battery charging / discharging device 20 has a recorder 22 for recording the measurement result.
Are connected. Here, the positive electrode 12 was prepared by mixing 50 mg of mesophase carbon heat-treated at 2800 ° C. and 30 mg of a conductive binder made of a composite of Teflon and acetylene black, and using a stainless steel collector having a size of 2.5 cm ^2. 1 ton / 1c on scale mesh
What was crimped at a pressure of m ² or more was used.

The present embodiment is characterized in that the positive electrode 12 made of mesophase carbon is impregnated twice in a solution of 1M / 1 LiAlH ₄ and diethyl ether for one day or more for two times. By this reduction treatment, various functional groups having oxygen existing on the surface of the mesophase carbon are reduced and removed. As the negative electrode 14, a 200 μm-thick Li was pressure-bonded to a stainless scale mesh current collector.

The electrolytic solution impregnated in the glass fiber filter paper 18 is 1M in a mixed solution of EC and DEC having a volume ratio of 1: 1.
A non-aqueous electrolytic solution in which LiPF ₆ was dissolved was used. Next, the result of a characteristic test using the coin type battery cell configured as described above will be described with reference to FIG. FIG. 2 is a graph showing discharge characteristics of the non-aqueous electrolyte secondary battery according to the first embodiment of the present invention.

In this characteristic test, the current density was 0.4 mA.
/ Cm ² Li ions were intercalated into the positive electrode 12 made of mesophase carbon to evaluate the potential based on the negative electrode 14 made of Li. In the graph of FIG. 2, the solid line shows the case where the surface of the positive electrode 12 made of mesophase carbon according to this example was subjected to the reduction treatment twice, and the broken line shows the case where the reduction treatment was not carried out for comparison. .

As indicated by the broken line in the graph of FIG.
When the reduction process is not performed, the cell voltage is about 0.8V
There is a flat part at 0.2 V (to Li electrode), and the electrolyte is decomposed at this potential. On the other hand, when the reduction treatment is performed, as shown by the solid line in the graph, it is found that the discharge is smooth and Li ions are intercalated into the positive electrode 12 made of mesophase carbon.

Further, according to the analysis of the negative electrode 14 made of Li, when the cell voltage was discharged to near 0 V, the untreated one had a current efficiency of 75%, while the one subjected to the reduction treatment was almost the same. It was found that the intercalation was performed with 100% efficiency. Thus, according to this embodiment,
Mesophase carbon is used for the positive electrode 12 and L is used for the negative electrode 14.
In the coin-type battery cell using i, the positive electrode 12 made of this mesophase carbon was used as a 1M / 1 LiAlH ₄
By performing the reduction treatment of impregnating with a solution of diethyl ether and diethyl ether for one day or more twice, various functional groups having oxygen existing on the surface of the mesophase carbon are reduced and removed, so that the intercalation of Li ions is smooth. Then, good discharge characteristics could be obtained.

Therefore, in the non-aqueous electrolyte secondary battery using mesophase carbon as the negative electrode, the mesophase carbon surface of the negative electrode is subjected to a reduction treatment and used to prevent repeated charge / discharge at a high charge / discharge capacity. It is possible to realize a good charge and discharge life. Next, a non-aqueous electrolyte secondary battery according to a second embodiment of the present invention will be described.

Since the structure of the coin type battery cell for measuring the characteristic used in the experiment is the same as that of the first embodiment shown in FIG. 1, its illustration is omitted. In this example, as the positive electrode 12, a kind of mesophase carbon different from that of the first example was used. Then, 50 mg of this mesophase carbon was heat-treated at 2800 ° C., and then mixed with 30 mg of a conductive binder made of a composite of Teflon and acetylene black to obtain a size of 2.
1 on a stainless steel scale mesh of 5 cm ^{2 current} collector
A pressure of at least 1 ton / cm ² was applied to obtain a positive electrode 12.

Then, the positive electrode 12 made of this mesophase carbon is impregnated with a solution of 0.33M / 1 LiAlH ₄ and diethyl ether for one day or more for one reduction treatment once to obtain oxygen existing on the surface of the mesophase carbon. This embodiment is characterized in that various functional groups are removed by reduction. As in the case of the first embodiment, as the negative electrode 14, a 200 μm-thick Li crimped onto a current collector of a stainless scale mesh was used, and the glass fiber filter paper 18 was impregnated with electrolysis. As the liquid, as in the case of the first embodiment, a nonaqueous electrolytic solution in which 1M / 1 LiPF ₆ was dissolved in a mixed liquid of EC and DEC with a volume ratio of 1: 1 was used.

Next, the result of a characteristic test using the coin type battery cell configured as described above will be described with reference to FIG. FIG. 3 is a graph showing discharge characteristics of the non-aqueous electrolyte secondary battery according to the second embodiment of the present invention. Also in this characteristic test, the potential based on the negative electrode 14 made of Li when Li ions were intercalated into the positive electrode 12 made of mesophase carbon at a current density of 0.4 mA / cm ² was evaluated. Incidentally, in the graph of FIG. 3, 1 is formed on the surface of the positive electrode 12 made of mesophase carbon according to the present embodiment.
The case where the reduction process is performed twice is shown by a solid line, and for comparison,
The case where no reduction treatment was performed is shown by a broken line.

As indicated by the broken line in the graph of FIG.
Without reduction treatment, cell voltage is about 0.75V
Suddenly flattened in the vicinity of (to Li electrode), and then gradually discharged. On the other hand, when the reduction process is performed,
As shown by the solid line in the graph, Li ions are smoothly intercalated into the positive electrode 12 made of mesophase carbon, so that good discharge characteristics can be obtained.

As described above, according to the present embodiment, in the coin type battery cell in which the positive electrode 12 uses a different type of mesophase carbon from the case of the first embodiment and the negative electrode 14 uses Li, the mesophase carbon is used. Become positive electrode 1
By performing a reduction treatment in which 2 is impregnated in a solution of 0.33 M / 1 LiAlH ₄ and diethyl ether for one day or more, various functional groups having oxygen existing on the surface of the mesophase carbon are reduced and removed. , Li ions were smoothly intercalated, and good discharge characteristics could be obtained.

Therefore, as in the case of the first embodiment, in the secondary battery using mesophase carbon as the negative electrode, the mesophase carbon surface of the negative electrode is subjected to a reduction treatment and used to obtain a high charge / discharge capacity. It is possible to realize a good charge and discharge life even when the charge and discharge are repeated. As the electrode material used for the negative electrode of the non-aqueous electrolyte secondary battery of the present invention, it is possible to widely use carbons other than the reduction-treated mesophase carbon used in the first and second examples. Is. Particularly when high energy density is required, it is desirable to use various reduced graphites.

The positive electrode material for the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and may be TiO ₂ , Cr ₂ O ₃ or Cr _{3.
O 8, V 2 O 5,} V 6 O 18, MnO 2, CuO, MoO
₈ , metal oxides such as Cu ₅ V ₂ O ₁₀ , TiS ₂ and Fe
S, CuCoS ₄ , MoS ₃ , MoS _{2 and} other metal sulfides, NbSe ₃ , VSe _{2 and} other metal selenides, Li
_{VO 2, LiCrO 2, LiFeO 2} , LiNiO 2,
Examples thereof include complex oxides such as LiCoO ₂ . Furthermore, organic conductive polymer materials such as polymers such as polyaniline, polythiophene and polypyrrole can also be used as the positive electrode material.

Further, as the reducing agent for reducing the surface of the negative electrode of the non-aqueous electrolyte secondary battery of the present invention, the above first and second reducing agents can be used.
In addition to LiAlH ₄ used in the examples of
_A hydride such as ₄ may be used as the reducing agent. Also,
As the non-polar solvent capable of dissolving these hydrides, in addition to the diethyl ether used in the first and second embodiments, there are mainly ether solvents such as ethyl ether, tetrahydrofuran and anisole. Then, an aromatic hydrocarbon solvent such as non-polar benzene, toluene or xylene may be added to these solvents to enhance the safety of this solution.

In addition to the method of using an organic solvent containing such a hydride as a reducing agent, a method of reducing the surface of the negative electrode with a solution of borohydride such as NaBH ₄ dissolved in an alkaline aqueous solution is also available. is there. However, comparing the two, the former method using an organic solvent containing a hydride is superior in terms of removing the functional group on the carbon surface.

As the polar solvent used in the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery, in addition to the EC and DEC used in the first and second embodiments, carbonates such as vinylene carbonate and , One or more of cyclic esters such as γ-butyrolactone and ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, diethylene glycol dimethyl ether, dioxolane, dioxane, anisole, and diethyl ether can be used. However, it is not limited to these solvents. A non-polar solvent such as benzene may be added to a non-aqueous electrolytic solution containing one or more of these solvents in a volume fraction of 50% or less.

Further, by adding to such a non-aqueous solvent,
As the electrolyte that constitutes the lysate, the first and second
LiPF used in the examples₆In addition to non-aqueous electrolyte
Any substance that forms an alkali metal ion may be used, and
As an example, LiSbF₆, LiAsF₆, LiClO
_Four, NaPF₆, NaSbF₆, NaAsF₆, NaC
10_Four, NaI, KPF₆, KSbF₆, KAsF₆,
KClO_Four, LiBF _Four, LiAlCl_Four, And LiS
O₈CF₃Etc. Among these, non-hydroelectric
LiClO forming Li ions in the solution_Four, LiBF
_Four, LiAsF ₆, And LiPF₆Etc. are suitable.

Further, the non-aqueous electrolyte secondary battery of the present invention is constructed by interposing the above-mentioned electrolyte solution between the positive and negative electrodes. In this case, a short circuit of current due to contact between the positive and negative electrodes is caused. A preventive separator can be interposed. As the separator, for example, a non-woven fabric, a woven fabric, a film, a net, or the like of a synthetic resin microporous film such as polytetrafluoroethylene, polypropylene, or polyethylene can be used.

[0036]

As described above, according to the present invention,
In a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte solution containing an alkali metal ion, a rechargeable positive electrode, and a negative electrode that occludes the alkali metal ion during charging and releases the alkali metal ion during discharging, By using carbon whose surface has been subjected to a reduction treatment as the negative electrode, various functional groups having oxygen existing on the carbon surface are reduced and removed, resulting in deterioration of the negative electrode, deterioration of the electrolyte or organic solvent on the negative electrode surface. It suppresses decomposition and enables intercalation of alkali metal ions at low potential. This allows
It has a good charge / discharge life even after repeated charge / discharge with a high charge / discharge capacity, and enables the practical application of a secondary battery with a high energy density.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a battery cell for measuring characteristics of a non-aqueous electrolyte secondary battery according to a first embodiment of the present invention.

FIG. 2 is a graph showing discharge characteristics of the non-aqueous electrolyte secondary battery according to the first exemplary embodiment of the present invention.

FIG. 3 is a graph showing discharge characteristics of a non-aqueous electrolyte secondary battery according to a second exemplary embodiment of the present invention.

[Explanation of symbols]

 10: Container 10a: Stainless steel lower can 10b: Stainless steel upper lid 10c: Teflon cover 12: Positive electrode 14: Negative electrode 16: Separator 18: Glass fiber filter 20: Battery charging / discharging device 22: Recorder

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masami Tsutsumi, 1015 Kamiodanaka, Nakahara-ku, Kawasaki, Kanagawa, Kanagawa Prefecture, 1015, Fujitsu Limited (72) Inventor, Isao Watanabe, 1015, Kamedota, Nakahara-ku, Kawasaki, Kanagawa, Fujitsu Limited

Claims (5)

[Claims] 1. A non-aqueous electrolytic solution containing an alkali metal ion, a positive electrode that is provided in contact with the non-aqueous electrolytic solution and is rechargeable, and a positive electrode that faces the positive electrode via the non-aqueous electrolytic solution. A non-aqueous electrolyte secondary battery including a negative electrode that occludes alkali metal ions during charging and releases alkali metal ions during discharging, wherein carbon whose surface is subjected to reduction treatment is used as the negative electrode. And a non-aqueous electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the carbon is graphite. 3. A non-aqueous electrolytic solution containing an alkali metal ion, a rechargeable positive electrode provided in contact with the non-aqueous electrolytic solution, and a rechargeable positive electrode facing the positive electrode via the non-aqueous electrolytic solution. A method for producing a non-aqueous electrolyte secondary battery comprising a negative electrode that occludes alkali metal ions during charging and releases alkali metal ions during discharging, wherein a reduction treatment of treating a carbon surface used as the negative electrode with a reducing agent A method for manufacturing a non-aqueous electrolyte secondary battery, which comprises steps. 4. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 3, wherein the reduction treatment step involves immersing the negative electrode made of carbon in a non-aqueous solution in which a hydride is dissolved, A method for manufacturing a non-aqueous electrolyte secondary battery, which is a step of reducing an oxide layer. 5. The method for producing a non-aqueous electrolyte secondary battery according to claim 3, wherein the reduction treatment step involves immersing the negative electrode made of carbon in an aqueous solution in which a borohydride is dissolved, A method for manufacturing a non-aqueous electrolyte secondary battery, which is a step of reducing an oxide layer.