JP4016712B2 - Lithium ion conductive polymer electrolyte and polymer electrolyte battery using the same - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a lithium ion conductive polymer electrolyte and a polymer electrolyte battery using the same .
[0002]
[Prior art]
In recent years, with the development of electronic devices, the appearance of new high-performance batteries is expected. Currently, the main power sources of electronic devices are manganese dioxide / zinc batteries for primary batteries, and nickel-based batteries such as nickel / cadmium batteries, nickel / zinc batteries, nickel / hydride batteries, and lead batteries for secondary batteries. Is used.
[0003]
An alkaline aqueous solution such as potassium hydroxide or an aqueous solution such as sulfuric acid is used for the electrolyte of these batteries. The theoretical decomposition voltage of water is 1.23V. If the battery system exceeds that value, water will be easily decomposed, and it will be difficult to stably store it as electric energy. Therefore, only those having an electromotive force of about 2 V have been put into practical use. Therefore, a non-aqueous electrolyte solution is used as an electrolyte solution for a high voltage battery of 3 V or higher. As a typical battery, there is a so-called lithium battery using lithium for the negative electrode.
[0004]
Examples of lithium primary batteries include manganese dioxide / lithium batteries and carbon fluoride / lithium batteries, and examples of lithium secondary batteries include manganese dioxide / lithium batteries and vanadium oxide / lithium batteries.
[0005]
Secondary batteries that use metallic lithium for the negative electrode have the disadvantages of short-circuiting due to the deposition of metallic lithium dendrite, the short lifetime, and the high reactivity of metallic lithium to ensure safety. Is difficult. Therefore, a so-called lithium ion battery using graphite or carbon instead of metallic lithium and using lithium cobaltate or nickel nickelate as a positive electrode has been devised and used as a high energy density battery. Recently, with the expansion of applications, higher performance batteries have been demanded. In particular, the organic electrolyte battery has a problem that the discharge performance at a high rate is inferior to that of the aqueous battery.
[0006]
[Problems to be solved by the invention]
The organic electrolyte has a problem that the conductivity of ions is extremely low as compared with the aqueous solution and the diffusion rate is slow, so that discharge at a high rate cannot be performed particularly at a low temperature. The present invention has been made in view of the above problems, and provides a lithium ion conductive polymer electrolyte used for a non-aqueous polymer electrolyte battery capable of discharging at a high rate even at a low temperature.
[0007]
[Means for Solving the Problems]
Therefore, the present invention is based on a completely new principle as an electrolyte of a non-aqueous polymer battery, unlike the principle of an insulating film through which lithium ions cannot pass and a lithium ion conductive polymer film in which the diffusion rate of ions is slow. The present invention provides a lithium ion conductive polymer electrolyte having pores and being porous, and a polymer electrolyte battery using the lithium ion conductive polymer electrolyte .
[0008]
The present invention is a lithium ion conductive polymer electrolyte , wherein the polymer material exhibits lithium ion conductivity, and the polymer has a large number of pores, and by holding an organic electrolyte in the pores, A path through which ions diffuse is secured.
[0009]
The present invention specifically provides a lithium ion conductive polymer electrolyte having a porosity of 10% to 80%.
Furthermore, the present invention is a polymer electrolyte battery comprising the porous lithium ion conductive polymer electrolyte and a free lithium ion conductive organic electrolyte.
[0011]
[Action]
In a conventional liquid electrolyte lithium battery, a porous polymer film such as polypropylene or polyethylene is used as a separator, and a lithium ion conduction path is secured by holding an electrolytic solution in the hole. In this case, the separator is an insulator in ionic conduction, and becomes an obstacle when charging and discharging at a high rate.
[0012]
In addition, in a lithium battery using a conventional polymer electrolyte without pores as an electrolyte, the transport number of lithium ions in the electrolyte is 1 because diffusion of cations and anions in the electrolyte is extremely slow. However, unless it is close to 1, discharge at a high rate cannot be performed, but a polymer electrolyte satisfying this condition has not been obtained.
[0013]
In the polymer electrolyte battery using the porous lithium ion conductive polymer electrolyte according to the present invention, lithium ions can pass not only in the electrolytic solution but also in the polymer electrolyte, which is higher than the conventional liquid electrolyte lithium battery. Discharge is possible. Further, in the polymer electrolyte battery using the porous lithium ion conductive polymer electrolyte according to the present invention, a passage through which ions diffuse quickly is secured by the electrolyte in the pores of the porous lithium ion conductive polymer electrolyte. Therefore, the discharge can be performed at a higher rate than the conventional polymer electrolyte lithium battery.
[0014]
【Example】
[Example 1]
First, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1: 1, and 1 mol / l LiPF ₆ was added to obtain an electrolytic solution. A mixture of this electrolytic solution and polyacrylonitrile (PAN) having a molecular weight of about 100,000 in a weight ratio of 7: 1 is applied on a stainless steel plate, heated at 100 ° C. for 30 minutes, and then cooled at −20 ° C. for 15 hours. As a result, it became a gel and its thickness was 30 μm. In this gel polymer electrolyte, a large number of holes are physically opened in the above-mentioned electrolyte solution using a stainless fine needle, and the electrolyte solution is contained in the inside of the hole, so that the porosity is 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% porous lithium ion conducting polymer electrolytes were fabricated.
[0015]
In the above embodiment, to prepare a pre-gel lithium ion conductive polymer electrolyte, and then, in a non-aqueous electrolyte solution containing a lithium salt, by the porous processing performed on the gel-like lithium ion conductive polymer electrolyte The non-aqueous electrolyte containing the lithium salt was held in the pores of the porous lithium ion conductive polymer electrolyte , but the porous lithium ion conductive polymer electrolyte was manufactured in advance, and then this porous lithium ion conductive By immersing the polymer electrolyte in a non-aqueous electrolyte containing a lithium salt, the non-aqueous electrolyte containing a lithium salt can be held in the pores of the porous lithium ion conductive polymer electrolyte .
[0016]
Next, production of the positive electrode will be described. First, a mixture of lithium cobaltate 70 wt%, acetylene black 6 wt%, polyvinylidene fluoride (PVdF) 9 wt% , and n-methylpyrrolidone (NMP) 15 wt% was obtained. It was applied on a foil and dried at 150 ° C. to evaporate NMP. After performing the above operation on both surfaces of the aluminum foil, it was pressed to obtain a positive electrode. The thickness of the positive electrode after pressing was 170 μm, and the weight of the active material, the conductive agent and the binder filled per unit area was 23 mg / cm ² .
[0017]
The negative electrode was manufactured as follows. A mixture of 81 wt% graphite, 9 wt% PVdF, and 10 wt% NMP was applied onto a 14 μm thick copper foil and dried at 150 ° C. to evaporate NMP. After the above operation was performed on both sides of the copper foil, pressing was performed to obtain a negative electrode. The thickness of the negative electrode after pressing was 190 μm.
[0018]
The porous lithium ion conductive polymer electrolyte prepared in this way, the positive electrode and the negative electrode are rolled up and inserted into a stainless steel case having a height of 47.0 mm, a width of 22.2 mm, and a thickness of 6.4 mm. I assembled the battery. Inside the battery, 2.5 g of the electrolyte solution was added to manufacture a battery (A) having a nominal capacity of 400 mAh.
[0019]
[Comparative Example 1]
Instead of using a porous lithium ion conductive electrolyte , a polypropylene film having a thickness of 26 μm, a porosity of 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% was used. A conventionally known battery (B) having the same configuration as described above and having a nominal capacity of 400 mAh was manufactured.
[0020]
[Comparative Example 2]
A conventionally known battery (C) having a nominal capacity of 400 mAh having the same configuration as that described above except that the lithium ion conductive polymer electrolyte was not perforated was manufactured.
[0021]
Using these batteries (A), (B), and (C), charging at -10 ° C. with a current of 1 CA for 1 hour, followed by charging at a constant voltage of 4.1 V for 2 hours, and then a current of 1 CA Was discharged to 2.5V.
[0022]
FIG. 1 is a diagram showing test results of these batteries, in which the horizontal axis indicates the porosity of the separator used and the vertical axis indicates the discharge capacity. From the figure, a battery using the porous lithium ion conductive polymer electrolyte according to the present invention (A), between the porosity of the lithium ion conducting polymer electrolyte is 80% to 10%, the porous lithium ion conductive polymer It is understood that the discharge capacity is superior to that of the conventional battery (B) using a polypropylene film instead of the electrolyte .
[0023]
Further, in the polymer electrolyte and the separator, when the porosity becomes large, internal short circuit and dropping of the active material become a problem. Therefore, there is a battery in which the porosity of the porous lithium ion conductive polymer electrolyte according to the present invention is 10%. The importance of the present invention can be understood by showing the discharge capacity superior to that of the battery having the separator porosity of 80% using the polypropylene of Comparative Example 1.
[0024]
FIG. 2 shows a battery using the porous lithium ion conductive polymer electrolyte of the example having a porosity of 40%, a battery using the polypropylene of the comparative example 1 having a porosity of 40%, and the thin film of the comparative example 2. FIG. 1 shows the results of an experiment similar to that shown in FIG. 1 using a battery using a lithium ion conductive polymer electrolyte that does not open a hole. The vertical axis represents discharge voltage (V), and the horizontal axis represents discharge capacity (mAh). ). According to this figure, a battery (A) using a porous lithium ion conductive polymer electrolyte according to the present invention includes a battery (B) using a conventional polypropylene and a battery using an ion conductive polymer electrolyte having no holes ( It can be seen that it exhibits superior low temperature discharge characteristics compared to C).
[0025]
In the above embodiment, polyacrylonitrile is used as the polymer in the polymer electrolyte. However, the polymer electrolyte is not limited thereto, but is not limited to polyethers such as polyethylene oxide and polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride, polychlorinated. Vinylidene, polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinyl pyrrolidone, polyethyleneimine, polybutadiene, polystyrene, polyisoprene, or derivatives thereof may be used alone or in combination. Good. Further, a polymer obtained by copolymerizing various monomers constituting the polymer may be used.
[0026]
Moreover, in the lithium ion conductive polymer electrolyte in the said Example, in order to improve lithium ion conductivity, it contains as an organic solvent of the organic electrolyte solution contained in a polymer | macromolecule, and in the hole of a lithium ion conductive polymer electrolyte. A mixed solution of EC and DEC is used as an organic solvent for the electrolytic solution to be used, but is not limited to this, and is not limited to this. Polar solvents such as acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, methyl acetate, or the like The mixture may be used. Further, in the lithium ion conductive polymer electrolyte , the organic solvent of the electrolytic solution contained in the polymer may be different from the organic solvent of the electrolytic solution contained in the pores.
[0027]
Further, in the above embodiment, the use of the LiPF ₆ as the lithium salt to be incorporated in and organic solvent a lithium ion conducting polymer electrolyte, the _{other, LiBF 4, LiAsF 6, LiClO} 4, LiSCN, LiI, LiCF ₃ SO _3, LiCl, LiBr, lithium salts such as LiCF ₃ CO ₂ or may be a mixture thereof. Different salts may be used in the ion conductive polymer electrolyte and in the organic electrolyte.
[0028]
Furthermore, in the polymer electrolyte battery using the porous lithium ion conductive polymer electrolyte of the above example, LiCoO ₂ is used as a compound capable of occluding and releasing lithium as the positive electrode material. However, the present invention is not limited to this. Absent. In addition to this, as the inorganic compound, a compound represented by a composition formula Li _x MO ₂ or Li _y M ₂ O ₄ (where M is a transition metal, 0 ≦ x ≦ 1, 0 ≦ y ≦ 2) is used. An oxide, an oxide having a tunnel-like hole, or a metal chalcogenide having a layered structure can be used. Specific examples thereof include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , MnO ₂ , FeO ₂ , V ₂ 0 ₅ , V ₆ O ₁₃ , TiO ₂ and TiS ₂ . Examples of the organic compound include conductive polymers such as polyaniline. Furthermore, the above various active materials may be mixed and used regardless of whether they are inorganic compounds or organic compounds.
[0029]
Further, in the polymer electrolyte battery using the porous lithium ion conductive polymer electrolyte of the above example, graphite is used as the compound as the negative electrode material. In addition, Al, Si, Pb, Sn, Zn, Cd Alloys of lithium and the like, transition metal composite oxides such as LiFe ₂ O ₃ , transition metal oxides such as WO ₂ and MoO ₂ , carbonaceous materials such as graphite and carbon, nitriding such as Li ₅ (Li ₃ N) Lithium, metal lithium foil, or a mixture thereof may be used.
[0030]
【The invention's effect】
As described above, in the lithium ion conductive polymer electrolyte according to the present invention, the polymer material contains an organic electrolyte, and the polymer material has a large number of pores, and the organic electrolyte is held in the pores. Thus, a passage through which ions diffuse is secured.
[0031]
The present invention specifically provides a lithium ion conductive polymer electrolyte having a porosity of 10% to 80%. The lithium ion conductive polymer electrolyte of the present invention allows lithium ions to pass through the polymer electrolyte, and further, a passage through which ions are diffused is ensured by the electrolytic solution in the numerous pores of the porous polymer electrolyte. .
[0032]
Furthermore, the present invention is a polymer electrolyte battery comprising the porous lithium ion conductive polymer electrolyte and a free lithium ion conductive organic electrolyte.
[0033]
As a result, the battery using the porous ion conductive polymer electrolyte of the present invention has a high rate discharge performance at a low temperature and less self-discharge at a high temperature than a conventional non-aqueous electrolyte battery, and can be left for a long time. A polymer battery having excellent characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between porosity and discharge capacity in a battery using the porous ion conductive polymer electrolyte of the present invention and a battery using a known substance of a comparative example.
FIG. 2 is a diagram showing discharge characteristics of a battery using the porous ion conductive polymer electrolyte of the present invention and a battery using a known substance of a comparative example.

Claims (2)

A lithium ion conductive polymer electrolyte , wherein the polymer material contains an organic electrolyte and exhibits lithium ion conductivity, and the polymer material has a large number of holes, and the organic electrolyte is placed in the holes. A porous lithium ion conductive polymer electrolyte characterized in that a passage through which ions diffuse is secured by holding. The positive electrode, the negative electrode, the porous lithium ion conductive polymer electrolyte according to claim 1, the organic electrolyte contained in the polymer material of the porous lithium ion conductive polymer electrolyte, and the organic electrolyte retained in the pores In addition, a polymer electrolyte battery comprising a free lithium ion conductive organic electrolyte.

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