JP3206836B2 - Lithium 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 lithium secondary battery. More specifically, the present invention relates to a lithium secondary battery containing a specific polyether polyol-based polymer compound.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries using a polymer electrolyte produced by dissolving a lithium salt in a polymer compound have been proposed (Battery Handbook, P331, 1).
990, published by Maruzen).

A typical configuration of such a battery is a battery 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 performed by attaching a metal lithium foil used as a negative electrode to the front and back of a solid polymer electrolyte sheet. Lithium metal is used as the negative electrode material, and the lithium secondary battery created by pressing this onto a solid polymer electrolyte undergoes a dissolution and deposition reaction of metal lithium at the negative electrode / electrolyte interface during the charge / discharge cycle. ing. The dissolution and precipitation reaction of such a solid electrolyte and a metal is poor in reversibility, and particularly where the metal is dissolved in the electrolyte, the electrical connection between the metal electrode and the electrolyte is poor locally, and this was used as a battery. In this case, it has been a problem that the battery capacity gradually decreases when charge / discharge cycles are repeated (the 31st Battery Symposium Proceedings, pp. 35-38).

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 graphite layers is used in charging and discharging of a battery.

In general, the intercalation reaction at the electrode / electrolyte interface has excellent reversibility, and is currently proposed.
Many of the negative electrode materials for electrolyte-based lithium secondary batteries use graphite (Preliminary Proceedings of the 31st Battery Symposium).

[0006]

However, a secondary battery using graphite and a polymer electrolyte as a negative electrode has not yet been put to practical use. The reason for this was the development of a polymer electrolyte material that has sufficient electrical conductivity comparable to the electrolytic solution, has good bonding properties with graphite, and does not cause deterioration in characteristics due to battery charge / discharge cycles. The point is not.

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium secondary battery in which the capacity deterioration due to charge / discharge cycles is small in order to improve the problems of the prior art.

[0008]

To achieve the above object, a 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. Wherein the negative electrode is a cured composition containing at least an electrolyte comprising a polyether polyol-based polymer compound and a lithium salt and graphite.

In the above structure, the positive electrode is preferably a cured composition containing at least an electrolyte comprising a polyether polyol polymer compound and a lithium salt and a compound containing lithium.

In the above structure, the polyether polyol-based polymer compound may be a random copolymer of oxyethylene and oxypropylene [formula (1)] having a polyether polyol basic skeleton and a polyether portion. preferable.

In the above structure, it is preferable that the terminal of the formula (Formula 1) of the polymer compound is cross-linked. Further, in the above configuration, as a material constituting the electrolyte, at least one plasticizer selected from propylene carbonate, ethylene carbonate, sulfolane, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, and polyalkylene glycol dimethyl ether is contained. Is preferred.

In the above structure, the relationship between the weight Z of the polymer compound constituting the electrolyte in the above formula (Formula 1) and the weight X of the plasticizer is 1 ≦ (X / Z) ≦ 5. Is preferred.

In the above structure, the relationship between the weight Z of the polymer compound constituting the electrolyte in the above formula (Formula 1) and the weight W of the graphite is 0.5 ≦ (W / Z) ≦ 1.5.
It is preferred that

[0014]

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

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

[0016]

The present invention will be described more specifically with reference to the following examples. Embodiment 1 FIG. 1 is a cross-sectional view of the configuration of a lithium secondary battery of the present embodiment. 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 polymer electrolyte, 3 is a polymer electrolyte layer, 4 is graphite, acetylene black, and polymer electrolyte A negative electrode 5 made of nickel having a thickness of 0.1 mm as in the case of 1, a sealing agent 6 made of polypropylene having a thickness of 1 mm, and a casing 7 formed. Hereinafter, a method of manufacturing each component will be described.

In the above formula (1), (j + m) × n =
100 g of a base polymer in which terminal groups of the polyether polyol-based polymer compound represented by 50 are acrylated,
9.4 g of LiBF ₄ and 10 of propylene carbonate
After weighing 0 ml in dry nitrogen, the mixture was stirred and mixed to prepare a stock solution of a polymer electrolyte.

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

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-mentioned stock polymer electrolyte solution, and the mixture was subjected to alumina ball milling.
By stirring and mixing for a period of time, a stock solution for the positive electrode was prepared.
In addition, the production of LiCoO ₂ powder is performed using commercially available Li ₂ CO ₃
And a predetermined amount of Co ₃ O ₄ were mixed at 600 ° C. for 10 hours,
Further, the reaction was carried out by heating at 850 ° C. for 5 hours.

Each of the polymer electrolyte, the positive electrode solution, and the negative electrode solution prepared by the above-described method was placed in a titanium flat vat in an amount of 0.2%.
It was cast to a thickness of 0.2 mm, 0.2 mm, and 0.5 mm, and was cured by irradiating it with an electron beam to obtain an electrolyte, a positive electrode, and a negative electrode sheet.

The electron beam is irradiated at an acceleration voltage of 750 keV,
The irradiation was performed in a nitrogen atmosphere at an irradiation dose of 2 Mrad. Next,
The size of the positive and negative electrode sheets is 4.5 × 7.5 cm,
Also, after cutting the electrolyte sheet into a size of 5 x 8 cm,
These sheets were crimped by aligning their centers in the order of positive electrode terminal 1 / positive electrode / electrolyte / negative electrode / negative electrode terminal 5. Crimping was performed by uniformly applying a pressure of 1 kg / cm ² for 1 minute.

Finally, the battery portion is accommodated in two sheets of polypropylene having a thickness of 1 mm, and the end face of the polypropylene sheet is fusion-sealed at a temperature of 180 ° C. Battery A was prepared.

Next, as a comparative example, a battery B was prepared using a metal lithium sheet having a thickness of 0.5 mm instead of the negative electrode sheet. In battery B,
Except for the negative electrode, the same components and configuration method as 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. The results are shown in FIG.

In FIG. 2, the horizontal axis is the number of charge / discharge cycles,
The vertical axis shows the discharge capacity. In this figure, the battery A of the embodiment has a discharge capacity comparable to that of the conventional solution-based battery, as compared with the case where the battery B in which only the metal lithium foil is pressed as the negative electrode causes the deterioration of characteristics early. It was also found that the capacity was hardly deteriorated even after 200 cycles.

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

In the present embodiment, the same components and the same method as the battery A of the embodiment 1 were used except that the mixing ratio W / Z of the base polymer and graphite was changed. In Table 1, when the mixing ratio of graphite is smaller than 0.5,
It was found that the discharge capacity was significantly reduced, and conversely, if the discharge capacity was more than 1.5, the material 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 following plasticizer. In this embodiment,
Except for the type and amount of the plasticizer used, the same components and the same configuration method as those of the battery A of Example 1 were used.

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

[0031]

[Table 2]

In the above embodiments, the high molecular compound is used as the base polymer of the electrolyte. However, it is needless to say that the high molecular compound can be used as a binder for physically bonding 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 a charge / discharge cycle.

[Brief description of the drawings]

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

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 positive electrode terminal 2 positive electrode 3 electrolyte layer 4 negative electrode 5 negative electrode terminal 6 sealant 7 casing

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-34660 (JP, A) JP-A-5-62514 (JP, A) JP-A-5-326021 (JP, A) JP-A-5-32621 205778 (JP, A) JP-A-4-171676 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/02-4/04 H01M 4/62

Claims (7)

(57) [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-based polymer compound and a lithium salt, and the negative electrode is A lithium secondary battery comprising a curable composition containing at least graphite and an electrolyte comprising a polyether polyol-based 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 comprising a polyether polyol-based polymer compound and a lithium salt and a compound containing lithium. 3. The polyether polyol-based polymer compound according to claim 1, wherein the polyether polyol has a basic skeleton and the polyether portion is a random copolymer of oxyethylene and oxypropylene [formula (1)]. The lithium secondary battery according to the above. Embedded image 4. The lithium secondary battery according to claim 3 , wherein the terminal of the formula (Formula 1) of the polymer compound is cross-linked. 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. The lithium secondary battery according to item 1 or 2. 6. The relationship between the weight Z of the polymer compound constituting the electrolyte in the above formula (Formula 1) and the weight X of the plasticizer is 1 ≦
4. The lithium secondary battery according to claim 3 , wherein (X / Z) ≦ 5. 7. The relation 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. lithium secondary battery according to 3.