JPH0696800A - Lithium secondary battery - Google Patents

Abstract

(57) [Abstract] [Purpose] The electrolyte layer is a composition containing at least a polyether polyol polymer compound and a lithium salt,
And by using a lithium secondary battery in which the negative electrode is a cured composition containing at least the electrolyte and graphite,
A lithium secondary battery with a small capacity deterioration even after repeated charge and discharge cycles. [Structure] A stock solution of a polymer electrolyte 3 is prepared by stirring and mixing a base polymer in which a terminal group of a polyether polyol polymer compound is acrylated, LiBF ₄ and propylene carbonate. Next, graphite particles and acetylene black were added to the polymer electrolyte stock solution, and mixed with an alumina ball mill to prepare a stock solution for the negative electrode.
This is electron beam crosslinked to form the negative electrode 4. The positive electrode 2 is also preferably a cured composition containing the electrolyte and a compound containing lithium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery. More specifically, it relates to a lithium secondary battery containing a specific polyether polyol polymer compound.

[0002]

2. Description of the Related Art Recently, a lithium secondary battery using a polymer electrolyte prepared by dissolving a lithium salt in a polymer compound has been proposed (Battery Handbook, P331, 1).
Published by Maruzen in 990).

A typical constitution of such a battery is one in which a conductive polymer such as polyaniline or an oxide such as V ₂ O ₅ is kneaded into a polymer electrolyte together with a conductive agent such as acetylene black as a positive electrode. This is done by sticking this and the metallic lithium foil used as the negative electrode to the front and back of the polymer solid electrolyte sheet. Metal lithium is used as the negative electrode material, and in a lithium secondary battery made by pressure-bonding this to a solid polymer electrolyte, a dissolution / deposition reaction of metallic lithium occurs at the negative electrode / electrolyte interface during charge / discharge cycles. ing. Such a solid electrolyte and the dissolution and precipitation reaction of the metal are poor in reversibility, and particularly in the part where the metal is dissolved in the electrolyte, the electrical connection between the metal electrode and the electrolyte is locally deteriorated, and this is used as a battery. In this case, it has been a problem that the battery capacity gradually decreases when the charge / discharge cycle is repeated (Proceedings of the 31st Battery Symposium, P35-38).

As a means for solving such a problem, it is conceivable that graphite is used as a negative electrode material and an intercalation reaction of lithium ions between the layers of graphite is used in charging / discharging a battery.

Generally, the intercalation reaction at the electrode / electrolyte interface is highly reversible and has been proposed at present.
Most of the negative electrode materials for electrolyte-based lithium secondary batteries use graphite (31st battery discussion meeting proceedings).

[0006]

However, a secondary battery constructed by using graphite and a polymer electrolyte as a negative electrode has not yet been put to practical use. The reason for this is the development of a polymer electrolyte material that has sufficient electrical conductivity comparable to that of an electrolytic solution, has good bondability with graphite, and does not cause characteristic deterioration associated with battery charge / discharge cycles. There is a point that is not done.

In order to solve the above-mentioned problems of the prior art, it is an object of the present invention to provide a lithium secondary battery with less capacity deterioration due to charge / discharge cycles.

[0008]

In order to achieve the above object, the lithium secondary battery of the present invention is a lithium secondary battery comprising at least a positive electrode, a negative electrode and an electrolyte layer, wherein the electrolyte layer is a polyether polyol. It is a composition containing at least a polymer compound and a lithium salt, and the negative electrode is a cured composition containing at least an electrolyte composed of a polyether polyol polymer compound and a lithium salt and graphite.

In the above constitution, it is preferable that the positive electrode is a cured composition containing at least an electrolyte consisting of a polyether polyol polymer compound and a lithium salt, and a compound containing lithium.

Further, in the above-mentioned constitution, the polyether polyol polymer compound is a random copolymer of oxyethylene and oxypropylene [the above-mentioned formula (Formula 1)] having a polyether skeleton as a basic skeleton. preferable.

Further, in the above constitution, it is preferable that the terminal of the above formula (Formula 1) of the polymer compound is crosslinked. Further, in the above-mentioned constitution, as a material constituting the electrolyte, at least one kind of plasticizer selected from propylene carbonate, ethylene carbonate, sulfolane, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol and polyalkylene glycol dimethyl ether is contained. It is preferable.

Further, in the above-mentioned constitution, the relation between the weight Z of the above-mentioned formula (Formula 1) of the polymer compound constituting the electrolyte and the weight X of the plasticizer is 1 ≦ (X / Z) ≦ 5. Is preferred.

Further, in the above-mentioned constitution, the relation between the weight Z of the above-mentioned formula (Formula 1) of the polymer compound constituting the electrolyte and the weight W of graphite is 0.5 ≦ (W / Z) ≦ 1.5.
Is preferred.

[0014]

According to the above-mentioned constitution of the present invention, the electrolyte layer is a composition containing at least a polyether polyol polymer compound and a lithium salt, and the negative electrode is composed of a polyether polyol polymer compound and a lithium salt. By using a cured composition containing at least an electrolyte and graphite, it is possible to obtain a lithium secondary battery with less capacity deterioration due to charge / discharge cycles.

Further, a lithium secondary battery can be effectively constructed by using a material such as LiCoO ₂ containing lithium ions in the composition and a positive electrode composed of the polymer electrolyte of the above-mentioned specific composition. I can.

[0016]

EXAMPLES The present invention will be described in more detail with reference to the following examples. Example 1 FIG. 1 is a sectional view of the configuration of a lithium secondary battery of this example. Reference numeral 1 is a positive electrode terminal made of nickel having a thickness of 0.1 mm, 2 is a positive electrode made of LiCoO ₂ , acetylene black and a polymer electrolyte, 3 is a polymer electrolyte layer, 4 is graphite, acetylene black and a polymer electrolyte Negative electrode made of nickel, 5 is a negative electrode terminal made of nickel having a thickness of 0.1 mm as in the case of 1, 6 is a sealant made of polypropylene having a thickness of 1 mm, and 7 is a casing. The manufacturing method of each component will be described below.

In the above formula (Formula 1), (j + m) × n =
100 g of a base polymer in which the terminal group of the polyether polyol polymer compound represented by 50 is acrylated,
LiBF ₄ 9.4g, propylene carbonate 10
0 ml was weighed in dry nitrogen and then mixed with stirring to prepare a polymer electrolyte stock solution.

Continuing, 10 g of the above polymer electrolyte stock solution
To the above, 4 g of graphite having an average particle diameter of 5 μm was added, and the mixture was stirred and mixed by an alumina ball mill for 24 hours to prepare a negative electrode stock solution.

Further, 4 g of LiCoO ₂ powder having an average particle size of 5 μm and 0.2 g of acetylene black were added to 10 g of the above polymer electrolyte stock solution, and the mixture was mixed with an alumina ball mill to obtain 24
A stock solution for positive electrode was prepared by stirring and mixing for a period of time.
However, the LiCoO ₂ powder was prepared using commercially available Li ₂ CO ₃
After mixing a predetermined amount of Co ₃ O ₄ and 600 ° C. for 10 hours,
Further, the reaction was performed by heating at 850 ° C. for 5 hours.

The polyelectrolyte, positive electrode and negative electrode stock solutions prepared by the above method were each added to a titanium flat plate vat of 0.2.
It was cast in a thickness of 0.2 mm, 0.2 mm, and 0.5 mm, and cured by irradiating it with an electron beam to obtain an electrolyte, positive electrode, and negative electrode sheet.

The electron beam irradiation is performed by accelerating voltage of 750 keV,
Irradiation dose was 2 Mrad in a nitrogen atmosphere. Next,
The size of the positive and negative electrode sheets is 4.5 x 7.5 cm,
After cutting the electrolyte sheet into a size of 5 x 8 cm,
These sheets were pressure-bonded with their centers aligned in the order of positive electrode terminal 1 / positive electrode / electrolyte / negative electrode / negative electrode terminal 5. The pressure bonding was performed by applying a pressure of 1 kg / cm ² evenly for 1 minute.

Finally, the battery portion was housed in two sheets of polypropylene having a thickness of 1 mm, and the end faces of the polypropylene sheets were fusion-sealed at a temperature of 180 ° C. Battery A was made.

Next, as a comparative example, a battery B prepared by using a metallic lithium sheet having a thickness of 0.5 mm instead of the negative electrode sheet was prepared. In Battery B,
Except for the negative electrode, the same components and construction method as in Battery A were used.

For the batteries A and B prepared by the above method,
A charge / discharge cycle test was performed at 20 ° C. in a constant current mode of 8 mA at an upper limit voltage of 4.3 V and a lower limit voltage of 3 V, and the results are shown in FIG.

In FIG. 2, the horizontal axis represents the number of charge / discharge cycles,
The vertical axis represents the discharge capacity. In this figure, in comparison with the battery B in which only a metallic lithium foil is pressed under pressure as the negative electrode causes a deterioration in characteristics early, the battery A of the embodiment has a discharge capacity comparable to that of the conventional solution system. It was found that the capacity hardly deteriorates even after exceeding 200 cycles.

Example 2 In Example 1, a battery was prepared by using a negative electrode in which graphite was mixed with a base polymer at a weight ratio of 5: 4. In this Example, a battery was prepared by changing this ratio. The effect of the requirement of claim 7 was verified, and the results are shown in Table 1.

In this embodiment, the same constituent members and construction method as in the battery A of Embodiment 1 were used except that the mixing ratio W / Z of the base polymer and graphite was changed. In Table 1, if the mixing ratio of graphite is less than 0.5,
It was found that the discharge capacity was remarkably reduced, and conversely, when the discharge capacity was more than 1.5, the material stock solution was not cured even when irradiated with an electron beam.

[0028]

[Table 1]

Example 3 In Example 1, propylene carbonate was used as the plasticizer in the same weight as the base polymer, but in this Example, a battery was constructed using the plasticizers shown below. In this embodiment,
Except for the type and addition amount of the plasticizer used, the same constituent members and construction method as in Battery A of Example 1 were used.

Table 2 shows the plasticizer used, the mixing weight ratio to the base polymer, and the discharge capacity at the 200th cycle.

[0031]

[Table 2]

In the above examples, the polymer compound was used as the base polymer of the electrolyte, but it goes without saying that it can be used as a binder for physically adhering graphite to each other.

[0033]

As described above, according to the present invention, it is possible to produce a lithium secondary battery with a small capacity deterioration due to charge / discharge cycles.

[Brief description of drawings]

FIG. 1 is a sectional view showing the configuration of a lithium secondary battery according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram of a lithium secondary battery according to an embodiment of the present invention.

[Explanation of symbols]

 1 Terminal for Positive Electrode 2 Positive Electrode 3 Electrolyte Layer 4 Negative Electrode 5 Terminal for Negative Electrode 6 Sealant 7 Casing

Claims (7)

[Claims] 1. A lithium secondary battery comprising at least a positive electrode, a negative electrode and an electrolyte layer, wherein the electrolyte layer is a composition containing at least a polyether polyol polymer compound and a lithium salt, and the negative electrode is A lithium secondary battery, which is a curable composition containing at least graphite and an electrolyte composed of a polyether polyol polymer compound and a lithium salt. 2. The lithium secondary battery according to claim 1, wherein the positive electrode is a curable composition containing at least an electrolyte composed of a polyether polyol polymer compound and a lithium salt, and a compound containing lithium. 3. The polyether polyol-based polymer compound according to claim 1 or 2, wherein the polyether skeleton has a polyether skeleton as a basic skeleton, and the polyether moiety is a random copolymer of oxyethylene and oxypropylene [the following formula (Formula 1)]. The lithium secondary battery described. [Chemical 1] 4. The lithium secondary battery according to claim 1, wherein the terminal of the formula (Formula 1) of the polymer compound is crosslinked. 5. The material constituting the electrolyte contains at least one plasticizer selected from propylene carbonate, ethylene carbonate, sulfolane, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol and polyalkylene glycol dimethyl ether. Item 3. A lithium secondary battery according to item 1 or 2. 6. The relationship between the weight Z of the above-mentioned formula (Formula 1) of the polymer compound constituting the electrolyte and the weight X of the plasticizer is 1 ≦.
The lithium secondary battery according to claim 1, wherein (X / Z) ≦ 5. 7. The relationship between the weight Z of the polymer compound constituting the electrolyte in the formula (Formula 1) and the weight W of graphite is 0.5 ≦ (W / Z) ≦ 1.5. 1. The lithium secondary battery according to 1 or 2.