JP2002008724A - Nano-particle composite polymer electrolyte and lithium secondary battery using this - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gel polymer battery with excellent high-temperature characteristics and excellent low-temperature characteristics by increasing high temperature resistance and suppressing decreased content of an electrolyte solution caused by contraction at low temperature in a lithium gel polymer battery. SOLUTION: Inorganic, metal nano-particles having a particle size of 100 nm or less is mixed to a polymer to form a composite, and the particles are taken into a polymer network to spread the volume, to strengthen, to suppress contraction caused by temperature drop, and to impregnate a large volume of electrolyte solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium polymer battery, and more particularly to a lithium polymer battery having improved battery performance at high and low temperatures by improving a polymer electrolyte.

[0002]

2. Description of the Related Art In order to ensure the safety of a non-aqueous lithium secondary battery, it has been attempted to use a solid polymer electrolyte without using an organic electrolyte. However, with the application of completely solid polymers (intrinsic polymers), compared to liquid systems,
Sufficient lithium ion conductivity has not been obtained, and it has not reached practical use.

[0003] In recent years, a gel polymer has been developed which is intermediate between a solution system and a solid polymer, and its practical use has been spotlighted. This gel polymer is roughly divided into two.
One type is called a physical gel, and examples of the polymer include a PAN-based (polyacrylonitrile), PVDF-based (polyfukkavinyldene), and PEO-based (polyethylene oxide). The other is a so-called chemical gel which is further strengthened by further intermolecular cross-linking. Polymers include PMMA (polymethyl methacrylate).

[0004] The physical gel is characterized by containing many pores, so that it can contain a large amount of electrolyte.
The structure is apt to change, which tends to cause liquid leakage and the like. On the other hand, chemical gels are unlikely to undergo a structural change, but contain a large amount of electrolytic solution, which is not sufficient compared to physical gels, and it is difficult to obtain high ionic conductivity.

[0005]

In order to prevent liquid leakage of the conventional gel polymer, there was a contradictory relationship that when the strength of the resin at a high temperature was increased, the ionic conductivity was reduced. Further, even at a low temperature, there is a problem that the magnetic content of the electrolytic solution is reduced due to the shrinkage of the resin, and the battery performance is significantly impaired.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to be stable in temperature and low in temperature. An object of the present invention is to provide a lithium polymer battery having good high-temperature characteristics.

[0007]

Means for Solving the Problems The present inventor has conducted intensive studies to solve the above-mentioned problems. As a result, the present inventors have developed a gel having excellent high-temperature characteristics and low-temperature characteristics by combining a normal gel electrolyte with inorganic nanoparticles. The inventors have found that an electrolyte is obtained and completed the present invention.

[0008] The polymer forming the gel electrolyte includes:
As described above, there are a PVDF type, a PEO type, a PAN type and a PMMA type. These polymers are already in the practical stage. The nanoparticles to be composited with these polymers are selected from inorganic oxides such as AL ₂ O ₃ , SiO ₂ , MgO, and TiO ₂ and metal powders that do not form a compound with Li such as Ni, Cu, and Si. The average particle size of these nanoparticles is preferably 100 nm or less, and more preferably 50 nm or less.

In order to prepare a nanoparticle composite gel polymer, 5
〜１０10% of nanoparticles are mixed with the above-mentioned momer or oligomer and polymerized to obtain a powder polymer. The resulting polymer can be infiltrated with an organic electrolyte to obtain a polygelmer, or the nanoparticles can be mixed with a liquid monomer, dried and singulated after polymerization, then penetrated into the organic electrolyte, and further crosslinked to obtain a gel polymer. Can also.

[0010] In the above nanoparticle composite gel polymer, the nanoparticles enter the polymer network and expand the local free space of the polymer. FIG. Refer to the schematic diagram. Therefore, the amount of the electrolytic solution entering the free space increases, and contraction at a low temperature is suppressed, so that a decrease in capacity at a low temperature is reduced.

[0011] The effect of the nanoparticles to suppress the shrinkage at low temperature is that when the particles reach a size close to 1 µm, they act as independent particles and cannot be incorporated into the polymer net.
It is known that it has little effect. As the amount of the nanoparticles increases, the amount of permeation of the electrolyte decreases correspondingly, so that there is an optimum value between the effect of expanding the free space and the volume of the nanoparticles. The amount of the nanoparticles is preferably 5 to 10% by volume. It is desirable that the volume of the electrolyte solution to penetrate is 60% or more by volume ratio. Even if the electrolyte solution is sufficiently penetrated at a high temperature (at a room temperature or more), the excess solution is separated due to shrinkage of the polymer at a low temperature, and the whole does not work effectively.

[0012] Even at high temperatures, crosslinking due to thermal expansion of the polymer is lost, the polymer and the liquid are separated, and only the performance is reduced or the liquid is leaked. In the nanoparticle composite polymer, the interaction between the nanoparticles and the resin network increases the strength of the polymer at a high temperature, so that the performance at a high temperature can be maintained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION As a preferred embodiment of the invention, a nanoparticle composite gel polymer is prepared by adding an electrolyte solution and nanoparticles to a powdered polymer prepared by ordinary polymerization, forming a slurry, and then heating and dissolving. And a polymer solution,
A gel polymer can be obtained by adding a cross-linking agent and a catalyst and further polymerizing (polymerization is thermal polymerization, UV polymerization, EV polymerization). Alternatively, a monomer, nanoparticles, and a catalyst are mixed with an electrolyte solution and polymerized to form a polymer solution. None, and can be obtained by the same procedure.

Another embodiment is applied to a polymer battery. This is a method in which a thin gel film is used instead of a separator impregnated with an organic solvent electrolyte. After setting the pre-reaction solution to a certain thickness using a spacer,
The polymerization / gelation reaction is performed to produce a gel film of 50 to 100 μm. A method of assembling a battery by attaching sheets of a positive electrode plate and a negative electrode plate to each surface of the gel film is adopted.

Further, in order to increase the efficiency of the battery (reduction of irreversible capacity), the metal oxide powder and carbon powder constituting the positive electrode and the negative electrode are kneaded with a gel polymer, and each particle is covered with the gel polymer. It is effective to form a slurry in a state, form a positive electrode plate and a negative electrode plate into a sheet shape, and attach them to both sides of a gel film instead of a separator to assemble a battery.

Also, it is possible to use a thin plate of Li metal or alloy as it is for the negative electrode. This is because the generation and growth of dendrites are prevented by physical constraint because the electrolyte salt in contact is a gel polymer. By using Li metal, the anode capacity can be approached to the highest theoretical capacity obtained.

The positive electrode active material used in the polymer battery is L
iCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ or a composite material thereof is used, and a carbon material, Sn oxide, Li metal or Li alloy is used as a negative electrode material. Other than that, the use of a positive electrode material and a negative electrode material that can be used in a solvent is all possible.

[0018]

The present invention will be described more specifically with reference to examples and comparative examples. [Preparation of gel polymer] PAN (polyacrylonitrile) was subjected to dispersion treatment with a polymer dispersant, and had an average particle size of about 5
Dissolving 5% _Al 2 _{O 3} particles of 0nm with MNP (N-methylpyrrolidone) was slurried. After applying the slurry to a thickness of about 100 μm on a glass plate, the slurry was vacuum-dried at 80 to 100 ° C. for about 12 hours to extract a solvent to form a thin film.

Next, this film is made of PC (polycarbonate):
A solution prepared by dissolving 1 M LiBF ₄ in a solvent of EC (ethylene carbonate): DMC (dimethyl carbonate) 1: 1: 1 was impregnated at −10 ° C. until equilibrium swelling was obtained to obtain a gel polymer electrolyte. The content of the electrolyte solution in the gel polymer membrane was 40% at -10 ° C, and the polymer and the electrolytic solution did not separate until heated at 120 ° C.

[Measurement of Ionic Conductivity] Conductivity of the gel polymer film was measured at −10 ° C. by an alternating current impedance method. As a result, the conductivity was 10-4 S / cm at -10C.

[Comparative Example] In the examples, the nanoparticles A
A gel thin film was obtained in exactly the same manner as in the example except that l ₂ O ₃ was not added, and the measurement was performed in the same manner. -10 ° C
Was 30%, and the polymer and the solution were separated by heating at 100 ° C. In the measurement of ionic conductivity, it was 10-5 S / cm at -10 degreeC.

[0022]

As described above, by using a gel polymer obtained by impregnating an electrolyte solution with a polymer in which nanoparticles are composited, shrinkage at a low temperature can be suppressed, and the low-temperature properties can be obtained without reducing the amount of solution impregnation. And a gel polymer battery excellent in the above.

[0023]

[Brief description of the drawings]

Fig. 1 Schematic drawing

[Explanation of symbols]

 1 ‥ Nanoparticles 2 ‥ Polymer net

Claims (2)

[Claims] 1. A lithium polymer battery comprising: a polymer electrolyte battery provided with a positive electrode, a negative electrode, and a polymer electrolyte, wherein a polymer electrolyte in which inorganic nanoparticle powder is compounded is used as a polymer electrolyte substrate. 2. A composite gel polymer comprising a polymer obtained by uniformly mixing inorganic nanoparticles having a particle size of 100 nm or less with a powdery or liquid electrolyte monomer or oligomer, and then polymerizing or cross-linking the polymer to contain an electrolyte solution. The lithium polymer battery according to claim 1, wherein