JPH0536438A - Gelled electrolyte for lithium battery and battery using the same - Google Patents

Abstract

PURPOSE:To prevent the deterioration of polyurethane by a positive electrode and improve cycle characteristic by using a polyurethane having saturated fatty group or/and alicyclic diisocyanates as starting materials for a gelled electrolyte. CONSTITUTION:A battery is formed by interposing a gelled electrolyte 3 in which a nonaqueous solvent containing an electrolyte is contained in a sheet polymer cross-linked body consisting of a polyurethane between a lithium alloy negative electrode 2 and a positive active material 4 such as vanadium pentoxide, and nipping it by stainless plates 1 used as both a collector and a case followed by sealing with a nipping seal material 5. The gelled electrolyte is obtained by impregnating a polyurethane having a saturated fatty group diisocyanate with mixed solution of a propylene carbonate containing LiClO4 and a dimethoxyethane to swell the polyurethane. Thus, no unsaturated bond is contained in the polyurethane, the oxidative deterioration by the positive electrode is moderated, and cycle characteristic is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gel electrolyte for a lithium battery and a battery using the same.

[0002]

2. Description of the Related Art Conventional lithium batteries include, for example, a sheet-shaped positive and negative electrode with a separator and an electrolyte solution interposed therebetween, and a solid electrolyte such as a complex of polyethylene oxide and a lithium salt interposed therebetween. Alternatively, as an electrolyte for an electrochromic display, there is known an electrolyte obtained by swelling a crosslinkable elastomer film with a nonaqueous solvent solution of a lithium salt. Further, as the above-mentioned improvement, there has been known one using polyurethane as a crosslinkable elastomer.

[0003]

However, in the above case, the device is thin and has a large area (for example, the unit cell has a size of 1 mm).
There is a problem that the process of injecting the electrolyte solution becomes difficult when manufacturing a laminated battery of about 30 cm × 30 cm or more in area, and the cycle life is shortened due to the loss of the active material and the deposition of dendrites. ing. In the above case, the conductivity of the solid electrolyte is 10 ⁻⁴ S · cm ^−1.
In addition to being smaller than the following, it is difficult to maintain the adhesiveness between the electrode and the solid electrolyte, so that there is a problem that the interface impedance increases and polarization increases. Furthermore, in the above electrolyte, the polarization of the positive electrode is large and a large amount of electric power cannot be taken out. Further, although the above-mentioned disadvantages are improved, when the diisocyanate of the polyurethane manufacturing material contains a double bond, the polyurethane is oxidatively deteriorated when combined with a positive electrode having a strong oxidation catalytic ability such as vanadium pentoxide. However, it has a drawback that the cycle performance as a battery becomes poor. The present invention has been made against the background of the conventional technical problems as described above, and facilitates the production of a thin and large-area stacked lithium battery, and prevents the active material from falling off and dendrites from being deposited. A gel electrolyte for lithium batteries, which can improve the cycle life by preventing oxidative deterioration of polyurethane, improve the adhesion between the electrode and the electrolyte, and obtain an interface impedance similar to that of an electrolyte solution, and a gel electrolyte for the lithium battery. The purpose of the present invention is to provide a battery.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides (a) a polyurethane prepared from a saturated aliphatic and / or alicyclic diisocyanate derivative as a raw material, (b) an electrolyte, and (c) a non-aqueous solution capable of dissolving the electrolyte. A gel electrolyte for a lithium battery, which contains a solvent as a main component.

The present invention also provides a lithium battery using the gel electrolyte as an electrolyte, wherein the negative electrode active material is lithium or an alkali metal mainly containing lithium, and the positive electrode active material is an oxide of a transition metal. It is a thing.

The polyurethane (a) constituting the gel electrolyte of the present invention has a polar group having an affinity for a non-aqueous solvent capable of dissolving an electrolyte having a relatively large polarity described later and swelling with the solvent. It is important that the raw material is a saturated aliphatic and / or alicyclic diisocyanate derivative. The reason is that when an aromatic diisocyanate or one having an unsaturated bond is used as the diisocyanate, when it is combined with a positive electrode having a strong oxidation catalytic ability such as vanadium pentoxide, the polyurethane deteriorates and the cycle performance as a battery is improved. Because it becomes worse.

Such diisocyanate derivatives include HDI (hexamethylene diisocyanate, TMH
Examples thereof include saturated aliphatic diisocyanate derivatives such as DI (trimethylhexamethylene diisocyanate) and alicyclic diisocyanate derivatives such as isophorone diisocyanate. By reacting such a diisocyanate derivative with a polyfunctional polyol having a molecular weight of about 1,500 to 4,000 using a catalyst if necessary, the (a) polyurethane used in the present invention can be produced.

Examples of polyfunctional polyols include trifunctional polyethylene glycol, trifunctional polypropylene glycol, and trifunctional (ethylene glycol-propylene glycol) copolymer.
You may use these in mixture of 2 or more types. As the urethane synthesis catalyst, tin compounds such as tin octylate and dibutyltin dilaurate, amine-based catalysts such as 1,4-diazabicyclo [2.2.2] octane] (DABCO), triethylamine and tetramethylbutanediamine are used. Can be used.

In the present invention, the (b) electrolyte used in the gel electrolyte is chemically stable with respect to the positive electrode active material and the negative electrode active material, and lithium ions cause an electrochemical reaction with the positive electrode active material. Any non-aqueous substance that can move in order to be used can be used, in particular, a compound composed of a combination of a cation and an anion,
Li ⁺ as the cation, and P as the anion
A halide anion of a Vb group element such as F ₆ ⁻ , AsF ₆ ⁻ , and SbF ₆ ⁻ with a halogen group element, I ⁻ (I ₃
^-), Br ^-, Cl ^- halogen anion, such as, Cl
O ₄ ^- perchlorate anions such as, HF ₂ ^-, CF ₃ S
O ₃ ^-, SCN ^- and the like can be mentioned compounds having an anion such as, but not necessarily limited to these anions.

Specific examples of the lithium salt having such a cation and anion include LiPF ₆ , LiAsF ₆ ,
LiSbF ₆ , LiBF ₄ , LiClO ₄ , LiI, L
iBr, LiCl, LiAlCl ₄ , LiHF ₂ , Li
Examples thereof include SCN and LiSO ₃ CF ₃ . Of these, especially LiPF _6, LiAsF _6, LiB
F ₄ , LiClO ₄ , LiSbF ₆ , LiSO ₃ CF ₃
Is preferred.

Next, (c) the non-aqueous solvent capable of dissolving the electrolyte is not particularly limited, but a solvent having a relatively large polarity is favorably used. Specifically, propylene carbonate, ethylene carbonate, tetrahydrofuran, 2
-Glymes such as methyltetrahydrofuran, dioxolane, dioxane, dimethoxyethane, diethylene glycol dimethyl ether, lactones such as r-butyrolactone, phosphoric acid esters such as triethyl phosphate, borate esters such as triethyl borate, sulfolane, dimethyl sulfoxide, etc. And sulfur compounds, nitriles such as acetonitrile, amides such as dimethylformamide and dimethylacetamide, and one or a mixture of two or more such as dimethyl sulfate, nitromethane, nitrobenzene and dichloroethane. Of these, one or a mixture of two or more selected from ethylene carbonate, propylene carbonate, butylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, dioxolane and γ-butyrolactone is particularly preferable.

The gel electrolyte of the present invention comprises a polyurethane prepared from the above (a) saturated aliphatic and / or alicyclic diisocyanate derivative, (b) electrolyte, and (c) non-aqueous solution capable of dissolving the electrolyte. Composed of solvent,
The composition ratio of these is 1 to 90/1 to 9/9 by weight.
81, preferably 30 to 70/3 to 7/27 to 63 [(a) + (b) + (c) = 100% by weight].

Thus, by impregnating the above-mentioned sheet-like cross-linked polymer of polyurethane (a) with (b) a nonaqueous solvent containing an electrolyte (c), the cross-linked polymer swells and gels. Becomes a solid electrolyte, and a lithium battery is constituted by interposing the gel electrolyte between the positive and negative electrodes.

Here, the negative electrode active material used in the battery of the present invention is lithium or an alkali metal mainly containing lithium, and specifically lithium or a lithium alloy capable of absorbing and releasing lithium is used. in this case,
Lithium alloys include lithium containing IIa, IIb, II
A group Ia, IVa, or Va metal or an alloy of two or more kinds thereof can be used, and particularly Al, In, and S containing lithium.
Preference is given to n, Pb, Bi, Cd, Zn or alloys of two or more of these.

The transition metal oxides used for the positive electrode active material include vanadium pentoxide, manganese dioxide,
Examples thereof include cobalt dioxide, and of these, vanadium pentoxide is preferable.

An example of a lithium battery using the gel electrolyte of the present invention will be described in detail below with reference to the drawings. That is, as shown in FIG. 1, this lithium battery is obtained by impregnating a sheet-like polymer cross-linked body made of polyurethane with a non-aqueous solvent containing an electrolyte between a lithium alloy negative electrode 2 and a positive electrode active material 4. The gel electrolyte 3 is interposed and sandwiched by the stainless steel plate 1 which also serves as a collector and a case, and a sealing material 5
It is sealed with.

As described above, in the lithium battery using the gel electrolyte of the present invention, the gel electrolyte is a molded product, so that even if a thin lithium battery having a large area is produced. Assembling is easy, and since the gel electrolyte is an elastic body, it has a compression effect to improve the adhesion between the electrode and the electrolyte, and prevents the active material from falling off and dendrites from being deposited, and it is also possible to use a specific polyurethane. Improves the cycle life, and because it is in the form of gel, the surface of the electrolyte is in a wet state, so the contact between the electrode and the electrolyte is as good as a solution, and the interface impedance is similar to that of an electrolyte solution. Can be obtained.

[0018]

In the lithium battery using the gel electrolyte of the present invention, the polyurethane constituting the gel electrolyte uses a saturated aliphatic and / or alicyclic diisocyanate derivative as a raw material. It is considered that there is no unsaturated bond, oxidation deterioration due to the positive electrode is alleviated, and cycle characteristics are improved.

[0019]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Example 1 50 g of a trifunctional (propylene glycol-ethylene glycol) random copolymer (Mw = 3,050),
DABCO (1,4-diazabicyclo [2.
2.2] -Octane) 0.2 g was added and stirred, and HDI
(Hexamethylene diisocyanate) (4.91 g) was further added, and the mixture was stirred, degassed in vacuum, and then coated on a glass with a bar coder and left in an oven at 80 ° C. for 5 hours to obtain a polyurethane film (thickness 100 μm).

This polyurethane film was swollen with a solution of LiClO ₄ dissolved at 1 mol / l in a mixed solvent of propylene carbonate and dimethoxyethane at a volume ratio of 1: 1 to obtain a gel electrolyte. Using this gel electrolyte, vanadium pentoxide was used for the positive electrode and metallic lithium was used for the negative electrode, and a battery as shown in FIG. 1 was produced. The electrode area was 16 cm ² each. The battery was repeatedly charged and discharged under the conditions of 25 mA discharge (up to 2.5 V) and 10 mA charge (up to 4 V) (rest for 1 hour). FIG. 2 shows a plot of the discharge capacity per positive electrode active material weight against the cycle.

Comparative Example 1 The HDI of Example 1 was mixed with tolylene diisocyanate (TD
A battery was prepared in the same manner as in Example 1 except that the battery was replaced with I), and the cycle stability was examined. The results are shown in Fig. 3. By comparing FIG. 2 and FIG. 3, it can be seen that the cycle stability of the lithium secondary battery is improved by using the saturated aliphatic diisocyanate as the diisocyanate derivative.

Example 2 A battery was prepared in the same manner as in Example 1 except that HDI of Example 1 was replaced with trimethylhexamethylene diisocyanate (TMHDI), and the cycle stability was examined. The results are shown in Fig. 4. From FIG. 4, it can be seen that the cycle stability of the battery of the present invention is excellent.

Example 3 (Evaluation of Stability for Positive Electrode) The gel electrolyte obtained in Example 2 was sandwiched between a fully charged vanadium pentoxide positive electrode and a completely discharged vanadium pentoxide positive electrode to form a cell. Configured. The electrode area is 16 cm ²
Met. Using lithium metal as a reference electrode, a discharge current of 25 mA, a discharge end voltage of 2.5 V, and a charge current of 10
The cycle of charging at a cutoff voltage of 4 V (1 hour pause) was repeated at mA to examine the discharge capacity per weight of the positive electrode active material. Results are shown in FIG. From FIG. 5, it can be seen that no deterioration is observed even after 125 cycles. With respect to the cells having the same structure, the discharge end potential was examined when charging and discharging were repeated at a discharge depth of 50%. Results are shown in FIG. It can be seen that no deterioration is observed even after 180 cycles.

[0024]

EFFECTS OF THE INVENTION According to the present invention, by using a polyurethane containing a saturated aliphatic type and / or an alicyclic diisocyanate as a raw material in the gel electrolyte, it is possible to prevent the deterioration of the polyurethane due to the positive electrode and to improve the cycle characteristics. A good battery can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a lithium battery using a gel electrolyte of the present invention.

FIG. 2 is a graph showing the relationship between the discharge capacity and the number of cycles when the battery obtained in Example 1 was repeatedly charged and discharged.

FIG. 3 is a graph showing the relationship between the discharge capacity and the number of cycles when the battery obtained in Comparative Example 1 was repeatedly charged and discharged.

FIG. 4 is a graph showing the relationship between the discharge capacity and the number of cycles when the battery obtained in Example 2 was repeatedly charged and discharged.

FIG. 5 is a graph showing the relationship between the discharge capacity and the number of cycles when charging and discharging are repeated in the stability evaluation for the positive electrode performed in Example 3.

FIG. 6 is a graph showing the relationship between the discharge capacity and the number of cycles when charging / discharging at a depth of 50% is repeated in the stability evaluation for the positive electrode performed in Example 3.

[Explanation of symbols]

1 stainless steel plate 2 Negative electrode 3 gel electrolyte 4 Positive electrode active material 5 Sealant

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naohiko Oki             1-4-1 Chuo 1-4-1 Wako City, Saitama Prefecture             Inside Honda Research Laboratory (72) Inventor Koichi Miyashita             1-4-1 Chuo 1-4-1 Wako City, Saitama Prefecture             Inside Honda Research Laboratory

Claims (3)

[Claims] 1. A polyurethane comprising (a) a saturated aliphatic and / or alicyclic diisocyanate derivative as a raw material,
(B) An electrolyte, and (c) a gel electrolyte for a lithium battery containing a non-aqueous solvent capable of dissolving the electrolyte as a main component. 2. A lithium battery in which the gel electrolyte according to claim 1 is used as an electrolyte, the negative electrode active material is lithium or an alkali metal mainly containing lithium, and the positive electrode active material is an oxide of a transition metal. 3. The lithium battery according to claim 2, wherein the positive electrode active material is vanadium pentoxide.