JP4909466B2 - Polymer secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polymer secondary battery comprising a negative electrode having a carbonaceous material as an active material, a lithium ion conductive polymer electrolyte layer, and a positive electrode having at least a metal oxide containing lithium as an active material. Lithium ion conductive polymer electrolyte layer was crosslinked with terminal polyol (meth) acrylate ester of polyether polyol containing EO unit alone or both EO unit and PO unit in at least two kinds of thermal polymerization initiators. Regarding the polymer secondary battery, the electrolyte layer further contains an organic solvent and a lithium salt.
[0002]
[Prior art and its problems]
Lithium secondary batteries have an extremely high theoretical energy density compared to other batteries, and can be reduced in size and weight. Therefore, lithium secondary batteries have been actively researched and developed as power sources for portable electronic devices and the like. However, with the improvement in performance of portable electronic devices, further reduction in weight and thickness has been demanded. In addition, devices such as mobile phones are required to have reliability and safety with respect to a large number of repeated charge / discharge cycles.
[0003]
Until now, in lithium secondary batteries, an electrolyte solution in which a lithium salt is dissolved in an organic solvent is used as the electrolyte between the positive electrode and the negative electrode. Therefore, in order to maintain reliability against liquid leakage, etc., an iron or aluminum can is used. Used as an exterior material. Therefore, the weight and thickness of the lithium secondary battery are limited to the weight and thickness of the metal can which is the exterior material.
[0004]
Therefore, development of lithium polymer secondary batteries that do not use a liquid as an electrolyte is being actively conducted. Since this battery has a solid electrolyte, it is easy to seal the battery, and it is possible to use a very light and thin material such as an aluminum laminate film for the exterior material, which can further reduce the weight and thickness of the battery. It has become. The lithium polymer secondary battery is a battery using a lithium ion conductive polymer or a lithium ion conductive gel as an electrolyte. For example, in Japanese Patent Application Laid-Open No. 4-206156, a thermal polymerization initiator and a photopolymerization initiator are used in combination. First, a surface film on the surface of each battery element is selectively cured by a photopolymerization method, and then a gel is formed by a thermal polymerization method. A technique of facilitating sealing of a sheet-like battery by curing the whole is disclosed. However, two steps of photopolymerization and thermal polymerization are required to cure the ion conductive gel, and there remains a problem in productivity. Moreover, the technique of producing an ion conductive gel only by thermal polymerization is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 11-121035, 11-265616, 2000-6740, and 2000-100246. Although disclosed in publications and the like, it was invented from the viewpoint of improving the productivity of polymer batteries, and there remains a problem with respect to the problem of cycle deterioration of polymer secondary batteries due to the thermal polymerization initiator itself. .
[0005]
[Means for Solving the Problems]
The polymer secondary battery of the present invention is a polymer secondary battery comprising a negative electrode using a carbonaceous material as an active material, a lithium ion conductive polymer electrolyte layer, and a positive electrode using at least a metal oxide containing lithium as an active material. In which a terminal polyol (meth) acrylate ester of a polyether polyol containing EO units alone or both EO units and PO units in the polymer chain is crosslinked with at least two different half-life temperature thermal polymerization initiators Is used for the electrolyte layer to solve the above problems.
[0006]
According to the present invention, at least two different half-life temperature thermal polymerization initiators are added to the terminal polyol (meth) acrylate ester of polyether polyol containing EO unit alone or both EO unit and PO unit in the polymer chain. By using it for thermal polymerization (thermal crosslinking), first, an interface between the electrolyte layer and the positive electrode active material and the negative electrode active material and the skeleton of the polymer electrolyte layer itself are formed by an initiator having a lower half-life temperature, and then the half-life temperature. Of the electrolyte layer / electrode active material interface by thermally polymerizing (thermal crosslinking) unreacted (meth) acrylate other than the skeleton of the electrolyte layer / electrode active material interface and polymer electrolyte layer with a high initiator Has been found to significantly reduce the long-term cycle characteristics of the polymer secondary battery. Furthermore, according to the present invention, since the skeleton of the polymer electrolyte layer itself at the electrolyte layer / electrode active material interface is formed first, variation in the performance of the polymer secondary battery can be suppressed, and the yield in battery production can be improved. is there.
[0007]
The thermal polymerization initiator used in the polymer secondary battery of the present invention is an organic peroxide, and has a 10-hour half-life temperature as low as about 30 to 50 ° C., for example, isobutyryl peroxide, α, α′- Bis (neodecanoylperoxy) diisopropylbenzene, α-cumylperoxyneodecanoate, di-n-propylperoxydicarbonate, diisopropylperoxydicarbonate, 1,1,3,3-tetramethylbutylperoxy Neodecanoate, bis (4-T-butylcyclohexyl) peroxydicarbonate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, di-2-ethoxyethyl peroxydicarbonate, di (2-ethylhexyl) Peroxy) dicarbonate, t-hexylperoxyneodecanoate Dimethoxybutyl peroxydicarbonate, di (3-methyl-3-methoxybutyl peroxy) dicarbonate, t- butyl peroxyneodecanoate, and the like. Further, as a high 10-hour half-life temperature of 50 to 80 ° C., for example, 3,5,5-trimethylhexanoyl peroxide, m-toluoxyl-benzoyl peroxide, t-hexyl peroxypivalate, lauroyl peroxide, Stearoyl peroxide and the like can be mentioned, and at least two types having a low 10-hour half-life temperature and a high one can be used. The combination is not limited to the above initiator.
[0008]
The polymer electrolyte used in the polymer secondary battery of the present invention is the above thermal polymerization initiator comprising a terminal polyol (meth) acrylate ester of a polyether polyol containing EO units alone or both EO units and PO units in a polymer chain. Crosslinks using bis are preferable because they exhibit high ionic conductivity over a wide temperature range.
[0009]
The monomer component of the polymer electrolyte used in the polymer secondary battery of the present invention preferably has a polyether segment and is polyfunctional with respect to the polymerization site so that the polymer forms a three-dimensional cross-linked structure. . The typical monomer is one obtained by esterifying the terminal hydroxyl group of a polyether polyol with acrylic acid or methacrylic acid (collectively referred to as “(meth) acrylic acid”). As is well known, a polyether polyol can be obtained by subjecting a polyhydric alcohol such as ethylene glycol, glycerin or trimethylolpropane as a starting material to addition polymerization of ethylene oxide alone or propylene oxide. Polyfunctional polyether polyol poly (meth) acrylic acid ester can be copolymerized alone or in combination with monofunctional polyether polyol poly (meth) acrylate. In particular, when the polymer electrolyte is a gel electrolyte containing an organic electrolytic solution, a trifunctional polyether polyol poly (meth) acrylic acid ester is preferable because it easily takes a three-dimensional cross-linked structure and is excellent in liquid retention of the electrolytic solution.
[0010]
Examples of the organic solvent that can be used for the gel electrolyte in the polymer secondary battery of the present invention include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC); dimethyl carbonate (DMC), diethyl carbonate (DEC), Chain carbonates such as ethyl methyl carbonate (EMC); Lactones such as γ-butyrolactone (GBL); Esters such as methyl propionate and ethyl propionate; Tetrahydrofuran and its derivatives, 1,4-dimethoxybutane, 1 Ethers such as 1,3-dimethoxybutane, 1,3-dioxane, 1,2-dimethoxyethane and methyldiglyme; nitriles such as acetonitrile and benzonitrile; dioxolane and derivatives thereof; sulfolane and derivatives thereof; Mixtures of al and the like.
[0011]
In particular, when a carbonaceous material is used as the negative electrode active material, it is preferable to contain at least EC because the decomposition of the electrolytic solution is small, and it is preferable to contain at least GBL in order to improve low temperature characteristics. . In addition, it is possible to produce a uniform gel electrolyte with good compatibility with the polyether polyol (meth) acrylic acid ester, and further to improve the permeability of the gel electrolyte to the inside of the pores of the porous electrode. It is preferable to add 2 to 5% by weight of butane and / or 1,3-dimethoxybutane with respect to the whole organic solvent.
[0012]
The lithium salt used as the solute used in the polymer secondary battery of the present invention is LiClO._Four, LiBF_Four, LiPF₆, LiCF_ThreeSO_Three, LiN (SO₂CF_Three)₂, LiN (COCF_Three)₂, LiC (SO₂CF_Three)_Three, And combinations thereof can be used. Moreover, it is preferable that lithium salt concentration is 0.8-2.5 mol / l with respect to the whole organic solvent. If the salt concentration is lower than 0.8 mol / l, sufficient ion conductivity cannot be obtained to obtain high-load discharge characteristics of the battery, and if the salt concentration is higher than 2.5 mol / l, the cost of the lithium salt is high. In addition, it takes a very long time to dissolve it, which is not preferable because it is industrially unsuitable.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In the embodiment of the polymer secondary battery of the present invention, the blending ratio of the polyether polyol (meth) acrylic acid ester and the organic electrolyte obtained by dissolving a lithium salt in the organic solvent is such that the mixture after polymerization is an ion conductive gel electrolyte. The organic electrolyte is sufficient to form a layer and form a continuous phase therein, but it must not be so excessive that the electrolyte separates and exudes over time. This can generally be achieved by setting the monomer / electrolyte weight ratio in the range of 20/80 to 2/98. Furthermore, in order to obtain sufficient ionic conductivity, the range of 5/95 to 2/98 is preferable.
[0014]
In the polymer electrolyte of the present invention, a thermal polymerization initiator having a low 10-hour half-life temperature of 50 to 1000 ppm is added to a precursor solution obtained by dissolving the monomer component in an organic electrolytic solution in which a lithium salt is dissolved in an organic solvent. It can be obtained by adding a thermal polymerization initiator having a high time half-life temperature in the range of 50 to 1000 ppm and polymerizing (crosslinking) at a temperature of 30 to 80 ° C. for 2 to 80 hours. In this case, the half-life temperature of the initiator having a low 10-hour half-life temperature is 30 to 50 ° C., the half-life temperature of the initiator having a high 10-hour half-life temperature is in the range of 50 to 80 ° C., and its activation energy is It is preferably 30 Kcal / mol or less. When the activation energy is higher than 30 Kcal / mol and the 10-hour half-life temperature is higher than 80 ° C., the influence of heat on other battery components is increased, and the reliability of the battery itself is lowered. On the other hand, a 10-hour half-life temperature lower than 30 ° C. is not preferable because the storage stability of the thermal polymerization initiator is lowered. When the activation energy is 25 Kcal / mol or less, storage stability is lowered and battery performance varies, which is not preferable.
[0015]
In the battery of the present invention, an ion conductive gel electrolyte layer is formed on each of a negative electrode and a positive electrode prepared in advance, and the both are overlapped, or a separator base material is previously placed between the negative electrode and the positive electrode, and then the monomer and the organic It can be produced by injecting a solution in which a solvent, a lithium salt, and a thermal polymerization initiator are mixed and polymerizing (crosslinking), but is not limited thereto.
[0016]
When using a separator substrate, the substrate is a microporous membrane of a polymer that is chemically stable in an organic electrolyte such as polypropylene, polyethylene, or polyester, or a sheet (paper, nonwoven fabric, etc.) of these polymer fibers. preferable. These substrates have an air permeability of 1 to 500 sec / cm.^ThreeIt is preferable because it has a strength sufficient to prevent a battery internal short circuit while maintaining a low battery internal resistance.
[0017]
The carbonaceous material that is a negative electrode active material that can be used in the present invention is preferably a material that can electrochemically insert and desorb lithium. Since the lithium insertion / extraction potential is close to the deposition / dissolution potential of metallic lithium, a high energy density battery can be constructed, which is particularly preferable. A typical example is natural or artificial graphite in the form of particles (scale-like, lump-like, fibrous, whisker-like, spherical, pulverized particles, etc.). Artificial graphite obtained by graphitizing mesocarbon microbeads, mesophase pitch powder, isotropic pitch powder, and the like may be used.
[0018]
With respect to the negative electrode active material of the present invention, more preferred carbon materials include graphite particles having amorphous carbon attached to the surface. As this adhesion method, graphite particles are immersed in coal-based heavy oil such as tar and pitch, or petroleum heavy oil such as heavy oil, pulled up, heated to above the carbonization temperature, and decomposed heavy oil. The carbon material is obtained by pulverization according to the above. Such a treatment significantly suppresses the decomposition reaction of the organic solvent and lithium salt that occurs at the negative electrode during charging, thereby improving the charge / discharge cycle life and suppressing gas generation due to the decomposition reaction. .
[0019]
In the carbon material of the present invention, the pores related to the specific surface area measured by the BET method are blocked to some extent by the adhesion of amorphous carbon, and the specific surface area is 1 to 5 m.²A range of / g is preferred. If the specific surface area is larger than this range, the contact area with an organic electrolyte solution in which a lithium salt is dissolved in an organic solvent is also increased, and these decomposition reactions are liable to occur. Moreover, since the adsorption amount of the thermal polymerization initiator for forming the polymer electrolyte layer on the negative electrode is increased, it is not preferable because the polymer electrolyte is inhibited from being crosslinked. If the specific surface area is smaller than this range, the contact area with the electrolyte also becomes small, so that the electrochemical reaction rate becomes slow and the load characteristics of the battery become low.
[0020]
In the present invention, a metal oxide containing lithium can be used as the positive electrode active material. In particular, Lia (A) b (B) cO₂(Here, A is one or more elements of transition metal elements. B is a non-metal element and a semi-metal element of group IIIB, IVB and VB of the periodic table, alkaline earth metal, Zn, Cu, One or more elements selected from metal elements such as Ti, a, b, and c are 0 <a ≦ 1.15, 0.85 ≦ b + c ≦ 1.30, and 0 <c, respectively. It is preferably selected from at least one of a composite oxide having a layered structure represented by (1)) or a composite oxide containing a spinel structure. Further, these metal oxides are preferable because they have an effect of promoting the reaction of the organic peroxide thermal polymerization initiator.
[0021]
A typical lithium-containing composite oxide is LiCoO.₂, LiNiO₂, LiMn₂O, LiCo_XNi_1-xO₂(0 <x <1)_FourAnd LiNi_1-xM_xO₂(Where M is a transition metal element) and the like, and when a carbonaceous material is used for the negative electrode active material using these, a voltage change (about 1 V vs. Li) associated with charging / discharging of the carbonaceous material itself. / Li⁺) Occurs in a sufficiently practical operating voltage, and Li ions necessary for battery charging / discharging reactions are assembled before the battery is assembled.₂, LiNiO₂Etc. already have the benefit of being contained within the battery.
[0022]
The positive electrode and the negative electrode are basically formed by forming respective active material layers in which a positive electrode and a negative electrode active material are fixed with a binder on a metal foil serving as a current collector. The material of the metal foil used as the current collector is aluminum, stainless steel, titanium, copper, nickel, etc., but considering the electrochemical stability, stretchability and economy, the aluminum foil and the negative electrode are used for the positive electrode. Copper foil is preferred for use.
[0023]
In the present invention, the form of the positive electrode and negative electrode current collector is mainly a metal foil, but other forms include a mesh, an expanded metal, a lath body, a porous body or a resin film coated with an electron conductive material, etc. However, it is not limited to this.
[0024]
If necessary for the production of the positive and negative electrodes, use a chemically stable conductive material such as graphite, carbon black, acetylene black, ketjen black, carbon fiber, and conductive metal oxide in combination with the active material to conduct electronic conduction. Can be improved.
[0025]
In preparing the positive electrode and the negative electrode, the binder is selected from thermoplastic resins that are chemically stable and soluble in an appropriate solvent but not affected by the organic electrolyte. Many resins are known, but for example, polyvinylidene fluoride (PVDF) which is selectively soluble in organic solvent N-methyl-2-pyrrolidone (NMP) but is stable in organic electrolytes is preferably used. .
[0026]
Other thermoplastic resins that can be used include, for example, acrylonitrile, methacrylonitrile, vinyl fluoride, chloroprene, vinyl pyridine and derivatives thereof, vinylidene chloride, ethylene, propylene, cyclic dienes (eg, cyclopentadiene, 1,3-cyclohexadiene). And the like. Instead of the solution, a dispersion of a binder resin may be used.
[0027]
For the electrode, paste the active material and, if necessary, the conductive material with a binder resin solution to make a paste, apply this to the metal foil with a uniform coater, dry, and press It is produced by. The ratio of the binder in the active material layer should be the minimum necessary, and generally 1 to 15 parts by weight is sufficient. When a conductive material is used, the amount of the conductive material is generally 2 to 15 parts by weight of the active material layer.
[0028]
In the electrode thus fabricated, an ion conductive gel electrolyte layer and an electrode active material layer are integrally formed, and the ion conductive gel layer is impregnated with an organic electrolyte containing a lithium salt in an ion conductive polymer matrix. Or it is something held. Such a layer is macroscopically in a solid state, but microscopically, a lithium salt solution forms a continuous phase and exhibits higher ionic conductivity than an ion conductive polymer electrolyte without using a solvent. The ion conductive gel electrolyte layer is prepared by polymerizing monomers of a polymer matrix in the form of a mixture with a lithium salt-containing organic electrolyte solution by a method such as thermal polymerization or photopolymerization.
[0029]
The manufactured battery can be used as an outer packaging material made of nickel plated iron, cylindrical cans made of aluminum, rectangular cans, or films laminated with resin on aluminum foil, but are not limited to these. Absent.
[0030]
(Example)
The following examples are for illustrative purposes and are not intended to limit the invention.
[0031]
Example 1
The battery of Example 1 was produced through the following steps.
[0032]
a) Preparation of negative electrode
Carbon material powder in which amorphous carbon is adhered to the surface of graphite particles (average particle size 12 μm, specific surface area 2 m²/ G) 100 parts by weight and PVDF as a binder were mixed at a weight ratio of 100: 9, and an appropriate amount of NMP was added as a solvent and kneaded to obtain a negative electrode material paste. This was coated on 18 μm Cu foil, dried and pressed to obtain a negative electrode sheet. The negative electrode was cut into 30 × 30 mm, and a Ni collector tab was welded to obtain a negative electrode.
[0033]
b) Preparation of positive electrode
LiCoO with an average particle size of 7 μm₂100 parts by weight, 5 parts by weight of conductive material acetylene black and 5 parts by weight of PVDF binder were mixed, and an appropriate amount of NMP was added as a solvent and kneaded to obtain a positive electrode material paste. This was coated on a 20 μm Al foil, dried and pressed to obtain a positive electrode sheet. This positive electrode was cut into 30 × 30 mm, and an AL current collecting tab was welded to obtain a positive electrode.
[0034]
c) Preparation of precursor solution of polymer electrolyte
LiBF in a 50:50 volume ratio mixed solvent of EC and GBL_FourWas dissolved to a concentration of 2 mol / l to obtain an organic electrolyte.
[0035]
To this organic electrolytic solution 95% by weight, 3.5% by weight of a trifunctional polyether polyol acrylate ester having a molecular weight of 7500 to 9000 and 1.5% by weight of a monofunctional polyether polyol acrylate ester having a molecular weight of 220 to 300 are mixed. Furthermore, t-butyl peroxyneodecanoate (10 hours half-life temperature 47 ° C., activation energy 29 Kcal / mol) 50 ppm and t-butyl peroxypivalate (10 hours half-life temperature 53 ° C.) which are thermal polymerization initiators. , Activation energy 28 Kcal / mol) 100 ppm was added to the above solution to obtain a precursor solution.
[0036]
d) Battery assembly
A polyester nonwoven fabric (thickness 20 μm, air permeability 180 sec / cm) as a separator substrate between the negative electrode and the positive electrode obtained above.^Three) Were inserted into a bag made of an Al laminate resin film as an exterior material, and the precursor solution obtained in c) was injected to seal the bag. It was heat-treated at 60 ° C. for 24 hours to complete the battery.
[0037]
(Example 2)
The battery of Example 2 was produced through the following steps.
[0038]
a) Preparation of negative electrode
Artificial graphite powder (average particle size 12μm, specific surface area 8m²/ G) 100 parts by weight and PVDF as a binder were mixed at a weight ratio of 100: 9, and an appropriate amount of NMP was added as a solvent and kneaded to obtain a negative electrode material paste. This was coated on 18 μm Cu foil, dried and pressed to obtain a negative electrode sheet. The negative electrode was cut into 30 × 30 mm, and a Ni collector tab was welded to obtain a negative electrode.
[0039]
b) Preparation of positive electrode
LiNi with an average particle size of 7 μm_0.2Co_0.8O₂100 parts by weight, 5 parts by weight of conductive material acetylene black and 5 parts by weight of PVDF binder were mixed, and an appropriate amount of NMP was added as a solvent and kneaded to obtain a positive electrode material paste. This was coated on a 20 μm Al foil, dried and pressed to obtain a positive electrode sheet. This positive electrode was cut into 30 × 30 mm, and an Al current collecting tab was welded to obtain a positive electrode.
[0040]
c) Preparation of precursor solution of polymer electrolyte
LiPF6 was dissolved in a 20:60:20 volume ratio mixed solvent of EC, GBL, and EMC to a concentration of 1.5 mol / l to obtain an organic electrolyte.
To 97 wt% of the organic electrolyte, 2.5 wt% of a trifunctional polyether polyol acrylate ester having a molecular weight of 7500 to 9000 and 0.5 wt% of a monofunctional polyether polyol acrylate ester having a molecular weight of 2500 to 3000 are mixed. Furthermore, α-cumylperoxyneodecanoate (10-hour half-life temperature 38 ° C., activation energy 27 Kcal / mol) 250 ppm which is a thermal polymerization initiator and m-toluoxyl-benzoyl peroxide (10-hour half-life temperature 73 ° C.) , Activation energy 30 Kcal / mol) 500 ppm was added to the above solution to obtain a precursor solution.
[0041]
d) Battery assembly
A polyethylene microporous membrane (thickness 25 μm, air permeability 380 sec / cm) as a separator substrate between the negative electrode and the positive electrode obtained above.^Three) Were inserted into a bag made of an Al laminate resin film as an exterior material, and the precursor solution obtained in c) was injected to seal the bag. It was heat-treated at 40 ° C. for 80 hours to complete the battery.
[0042]
(Example 3)
A battery of Example 3 was fabricated through the following steps.
[0043]
a) Preparation of negative electrode
Artificial graphite powder (average particle size 12μm, specific surface area 5m²/ G) 100 parts by weight and PVDF as a binder were mixed at a weight ratio of 100: 9, and an appropriate amount of NMP was added as a solvent and kneaded to obtain a negative electrode material paste. This was coated on 18 μm Cu foil, dried and pressed to obtain a negative electrode sheet. The negative electrode was cut into 30 × 30 mm, and a Ni collector tab was welded to obtain a negative electrode.
[0044]
b) Preparation of positive electrode
LiMn with an average particle size of 9 μm₂O_Four100 parts by weight, 7 parts by weight of conductive material acetylene black and 3 parts by weight of PVDF binder were mixed, and an appropriate amount of NMP was added as a solvent and kneaded to obtain a positive electrode material paste. This was coated on a 20 μm Al foil, dried and pressed to obtain a positive electrode sheet. This positive electrode was cut into 30 × 30 mm, and an Al current collecting tab was welded to obtain a positive electrode.
[0045]
c) Preparation of precursor solution of polymer electrolyte
In a 50:30:20 volume ratio mixed solvent of EC, PC and DEC, LiN (COCF_Three)₂Was dissolved to a concentration of 1.0 mol / l to obtain an organic electrolyte.
[0046]
90% by weight of the organic electrolyte is mixed with 7% by weight of a trifunctional polyether polyol acrylate ester having a molecular weight of 7500 to 9000 and 3% by weight of a monofunctional polyether polyol acrylate ester having a molecular weight of 7500 to 9000, and is further thermally polymerized. Α-cumylperoxyneodecanoate as an initiator (10-hour half-life temperature 38 ° C., activation energy 27 Kcal / mol) 100 ppm and 3,5,5-trimethylhexanoyl peroxide (10-hour half-life temperature 59 ° C.) , Activation energy 30 Kcal / mol) 1000 ppm was added to the above solution to obtain a precursor solution.
[0047]
d) Battery assembly
A polypropylene microporous membrane (thickness 25 μm, air permeability 480 sec / cm) as a separator substrate between the negative electrode and the positive electrode obtained above.^Three) Were inserted into a bag made of an Al laminate resin film as an exterior material, and the precursor solution obtained in c) was injected to seal the bag. It was heat-treated at 80 ° C. for 2 hours to complete the battery.
[0048]
(Comparative Example 1)
The battery of Comparative Example 1 was produced through the following steps.
[0049]
a) Preparation of negative electrode
The same operation as in Example 1 was repeated to obtain a negative electrode.
[0050]
b) Preparation of positive electrode
The same operation as in Example 1 was repeated to obtain a positive electrode.
[0051]
c) Preparation of precursor solution of polymer electrolyte
Thermal polymerization initiator is t-butyl peroxyneodecanoate (10 hour half-life temperature 47 ° C., activation energy 29 Kcal / mol) 50 ppm and benzoyl peroxide (10 hour half-life temperature 74 ° C., activation energy 32 Kcal / mol). ) A precursor solution was obtained by repeating the same operation as in Example 1 except that 100 ppm was added.
[0052]
d) Battery assembly
The same operation as in Example 1 was repeated to complete the battery.
[0053]
(Comparative Example 2)
The battery of Comparative Example 2 was produced through the following steps.
[0054]
a) Preparation of negative electrode
The same operation as in Example 2 was repeated to obtain a negative electrode.
[0055]
b) Preparation of positive electrode
The same operation as in Example 2 was repeated to obtain a positive electrode.
[0056]
c) Preparation of precursor solution of polymer electrolyte
The same procedure as in Example 2 was repeated except that only one thermopolymerization initiator, 750 ppm of m-toluoxyl-benzoyl peroxide (10-hour half-life temperature 73 ° C., activation energy 30 Kcal / mol), was added to the precursor. A solution was obtained.
[0057]
d) Battery assembly
The same operation as in Example 2 was repeated to complete the battery.
[0058]
Example 4Reference example
A battery of Example 4 was produced through the following steps.
[0059]
a) Preparation of negative electrode
The same operation as in Example 3 was repeated to obtain a negative electrode.
[0060]
b) Preparation of positive electrode
The same operation as in Example 3 was repeated to obtain a positive electrode.
[0061]
c) Preparation of precursor solution of polymer electrolyte
The same operation as in Example 3 was performed except that the monomer used was 8% by weight of a bifunctional polyether polyol acrylate ester having a molecular weight of 7500 to 9000 and 2% by weight of a monofunctional polyether polyol acrylate ester having a molecular weight of 7500 to 9000. Repeatedly, a precursor solution was obtained.
[0062]
d) Battery assembly
The same operation as in Example 3 was repeated to complete the battery.
[0063]
The batteries of Examples 1 to 4 and Comparative Examples 1 and 2 were charged with a positive electrode active material and a negative electrode active material so that the battery capacity was 20 mAh. These batteries were charged at a constant current value of 2.5 mA until the battery voltage reached 4.1 V, and after reaching 4.1 V, the batteries were charged at a constant voltage until the total charging time reached 12 hours. Discharging was performed at a constant current value of 5 mA until the battery voltage reached 2.75V. FIG. 1 shows the transition of the discharge capacity when charging / discharging was repeated up to 300 cycles.
[0064]
As can be seen from FIG. 1, the cycle characteristic of the battery of Comparative Example 1 was lower than that of Example 1. This is because, even when two types of thermal polymerization initiators are used, benzoyl peroxide having a high activation energy of 32 Kcal / mol is used as one initiator, so that the crosslinking reaction inside the polymer electrolyte layer becomes insufficient. Further, the strength of the electrolyte layer itself is low, and the unreacted monomer remains in the battery, so that the cycle characteristics of the polymer secondary battery are deteriorated.
[0065]
Also, the cycle characteristics of the battery of Comparative Example 2 were lower than those of Example 2. This is because a thermal polymerization initiator having a low 10-hour half-life temperature was not used, so that the skeleton formation between the electrode active material / polymer electrolyte layer interface and the polymer electrolyte layer itself was insufficient, and the cycle characteristics of the polymer secondary battery were It has deteriorated.
[0066]
Next, when Example 1 and Example 2 were compared, the polymer secondary battery of Example 1 showed better cycle characteristics. This is because a carbon material powder in which amorphous carbon is adhered to the surface of graphite particles is used as the negative electrode active material, so that the adsorption amount of the thermal polymerization initiator is reduced because the specific surface area is low, and the electrode active material / polymer This is because the skeleton formation between the interface of the electrolyte layer and the polymer electrolyte layer itself is sufficient, and no unreacted monomer remains in the battery.
[0067]
Finally, from the results of Example 3 and Example 4, it is easier to form a three-dimensional skeleton of the polymer electrolyte layer itself when the trifunctional polyether polyol acrylate is used, the strength of the electrolyte layer itself is high, and the unreacted Since the monomer did not remain in the battery, cycle deterioration was reduced.
[0068]
【The invention's effect】
According to the present invention, a negative electrode using a carbonaceous material as an active material, a lithium ion conductive polymer electrolyte layer, and a positive electrode using at least a metal oxide containing lithium as an active material, the polymer electrolyte layer is high. Polyether polyol terminal (meth) acrylic acid ester containing EO unit alone or both EO unit and PO unit in the molecular chain, at least two kinds of 10-hour half-life temperature and activation energy of 30 Kcal / mol or less Thus, a lithium polymer secondary battery with improved cycle characteristics can be provided.
[0069]
In addition, by using a carbon material with amorphous carbon attached to the surface of the graphite particles as the negative electrode active material, adsorption of the thermal polymerization initiator is suppressed, and a lithium polymer secondary battery with excellent cycle characteristics and reliability is provided. it can.
[Brief description of the drawings]
FIG. 1 is a graph showing changes in charge / discharge cycles and discharge capacities of Examples 1 to 4 and Comparative Examples 1 and 2. FIG.

Claims (4)

A negative electrode using a carbonaceous material as an active material, a lithium ion conductive polymer electrolyte layer, and a positive electrode using at least a metal oxide containing lithium as an active material, and the polymer electrolyte layer contains ethylene oxide ( EO) unit alone or a polyether polyol terminal (meth) acrylic ester containing both EO units and propylene oxide (PO) units crosslinked with two different 10 hour half-life temperature thermal polymerization initiators. Oh it is,
The thermal polymerization initiator has an activation energy of 30 Kcal / mol or less,
The end of the polyether polyol (meth) acrylic acid ester, trifunctional polyether polyol (meth) polymer secondary battery, characterized Rukoto include acrylic acid ester. The polymer 2 according to claim 1 , which is an organic peroxide selected from at least two types of 10-hour half-life temperatures in the range of 30 to 50 ° C and those in the range of 50 to 80 ° C. Next battery. The polymer secondary battery according to claim 1 or 2 , wherein the polymer electrolyte layer is a gel electrolyte layer containing at least ethylene carbonate (EC) and γ-butyrolactone (GBL). The polymer secondary battery according to any one of claims 1 to 3 , wherein the carbonaceous material includes at least a carbon material in which amorphous carbon is adhered to the surface of graphite particles.

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