JP3906944B2 - Non-aqueous solid electrolyte battery - Google Patents

Description

【００３６】
表１に示した如く、各電池について１サイクル目の放電容量を同じにし、サイクル特性を調査した。１００サイクル後のサイクル劣化率を比べると明らかにサイクル特性に差が有ることがわかる。理由は定かではないが、非水固体電解質電池の場合、充放電に伴う活物質の膨張、収縮が、活物質と非水固体電解質との界面に隙間を生じさせ、活物質の孤立化を起こし、サイクル劣化が生じているものと考えられる。特にこの現象は、フィルム状のような外部からの緊圧をかけにくいセル構造に生じることが考えられる。つまり、充放電の際に膨張収縮の大きなグラファイトを用いた場合、この現象が顕著に現れたものと考えられる。
【００３７】
なお、本発明は上記実施例に記載された活物質の出発原料、製造方法、正極、負極、電解質、セパレータ及び電池形状などに限定されるものではない。また、上記実施例においては、リン酸化合物を負極活物質として用いているが、正極活物質としても使用可能であることは言うまでもない。さらに、電池の形状についてもフィルム状に限定されるものではない。
【００３８】
【発明の効果】
本発明は上述の如く構成されているので、軽量で優れたサイクル特性を示し、かつ液漏れのない安全な非水固体電解質電池を提供できる。
【図面の簡単な説明】
【図１】本発明非水固体電解質電池の断面図である。
【符号の説明】
１ 正極
２ 負極
３ 非水固体電解質層
４ 正極缶
５ 負極缶
６ 正極集電体
７ 負極集電体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a safe non-aqueous solid electrolyte battery that is lightweight, exhibits excellent cycle characteristics, and does not leak.
[0002]
[Prior art]
A nonaqueous electrolyte battery using a solid electrolyte is an excellent battery that is small and lightweight and has no liquid leakage. In this type of battery, it has been typical to use lithium metal for the negative electrode and an oxide such as V, Co, Mn or the like for the positive electrode, but due to dendritic precipitation of lithium (dendrite) generated during charging, There was a problem in terms of cycle life. In addition, this dendrite penetrates through the separator and causes an internal short circuit or causes ignition.
[0003]
Further, lithium alloys are also used for the negative electrode for the purpose of preventing dendrite generated during charging as described above. However, when the charge amount is increased, there are problems such as fine powdering of the negative electrode and dropping of the negative electrode active material.
[0004]
On the other hand, a battery using a carbon material for the negative electrode has been attracting attention for the purpose of extending its life and safety. However, in the carbon material used for the negative electrode, the lattice constant changes with lithium doping and undoping, and the active material expands and contracts. Therefore, when a solid electrolyte is used, the active material is ionized and the cycle characteristics are insufficient.
[0005]
[Problems to be solved by the invention]
Therefore, in order to improve the cycle characteristics of a battery using a solid electrolyte, it is desired to develop a battery material having excellent cycle characteristics with little change in crystal system and volume during the insertion and extraction of lithium during charge and discharge. ing.
[0006]
The present invention solves the above-described problems. By preventing the active material crystals from expanding and contracting during charging / discharging and increasing the impedance inside the particles, the charging / discharging cycle characteristics are excellent, and the liquid weight is low. The object is to provide a safe non-aqueous solid electrolyte battery without leakage.
[0007]
[Means for Solving the Problems]
Nonaqueous electrolyte batteries using solid electrolytes are attracting attention as light batteries and safe batteries that do not leak. In other words, since a battery using a solid electrolyte is a solid electrolyte, the electrolyte has almost no fluidity compared to a battery system using only an electrolytic solution, and it is less likely to ignite. Provision is possible. On the other hand, since the active material to be a positive electrode or a negative electrode includes movement of a substance such as lithium, a change in crystal structure accompanying charge / discharge, and volume expansion and contraction of the crystal are observed. In other words, in a battery using a solid electrolyte, if an active material having a large change in crystal structure due to charging / discharging and a large volume expansion or contraction of the crystal is used, the solid electrolyte cannot follow the change, and the active material is ionically isolated. This is one of the causes of cycle deterioration. That is, in a battery using a solid electrolyte, it was found that it is important to improve the cycle characteristics by using an active material having a small change in crystal structure accompanying charge / discharge, and a small volume expansion and contraction of the crystal. .
[0008]
This invention is made | formed in view of the said problem, Comprising: It uses for a non-aqueous solid electrolyte battery, It is characterized by using a phosphoric acid compound for the main component of the active material which occludes and discharge | releases lithium.
[0009]
The solid electrolyte according to the present invention is preferably an organic solid electrolyte in order to achieve a high energy density. Furthermore, in order to obtain good charge / discharge characteristics, the organic solid electrolyte is preferably a gel electrolyte. Moreover, it is desirable that the phosphoric acid compound which is the main component of the active material contains iron, and it is most desirable that the phosphoric acid compound is represented by the chemical formula Li _x FePO ₄ . The battery shape is desirably a film shape in order to achieve a high energy density.
[0010]
The present invention uses a solid electrolyte in which a supporting electrolyte is dissolved, and by using a phosphoric acid compound as a main component of an active material that occludes and releases lithium, the reason why the above excellent charge / discharge cycle characteristics are obtained is as follows. Although it is not necessarily clear, it is considered as follows. In other words, conventional positive and negative electrode materials using a solid electrolyte undergo a volume change due to a change in crystal accompanying charge / discharge, resulting in a gap at the interface with the solid electrolyte, and cycle deterioration due to isolation of the active material. It is thought. However, the phosphoric acid compound used in the present invention shows almost no change in crystal accompanying charging / discharging, and therefore does not cause isolation of the active material accompanying the cycle, so that sufficient ion conduction can be obtained forever. Thus, excellent charge / discharge cycle characteristics can be obtained, and a safe non-aqueous solid electrolyte battery that is lightweight and does not leak can be realized. Further, for the purpose of weight reduction, the shape of the non-aqueous solid electrolyte battery is preferably a film.
[0011]
Examples of the phosphoric acid compound represented by the chemical formula _{Li x M y (PO 4)} z. M is preferably a transition metal, and among the transition metals, Ti and Fe are preferable, and Fe is more preferable because it is rich in resources. X, y, and z in the formula are determined by the valence of M. For example, when M is Fe, the chemical formulas Li _{3 + x} Fe ₂ (PO ₄ ) ₃ , Li _x FePO _{4 and the} like can be mentioned. Among these, Li _x FePO ₄ is most preferable because the crystal structure hardly changes during insertion and extraction of lithium.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
As the solid electrolyte of the present invention, for example, an inorganic solid electrolyte, an organic solid electrolyte, an inorganic organic solid electrolyte, a molten salt, or the like can be used. As the inorganic solid electrolyte, lithium nitride, halide, oxyacid salt, phosphorus sulfide compound, and the like are well known, and one or more of these can be used in combination. Among _{them, Li 3 N, LiI, Li} 5 NI 2, Li 3 N-LiI-LiOH, Li 4 SiO 4, Li 4 SiO 4 -LiI-LiOH, xLi 3 PO 4- (1-x) Li 4 SiO 4 Li ₂ SiS _{3 and the} like are effective. On the other hand, for organic solid electrolytes, polyethylene oxide derivatives or polymers containing at least the derivatives, polypropylene oxide derivatives or polymers containing at least the derivatives, polyphosphazenes and derivatives thereof, polymers containing ionic dissociation groups, phosphate ester polymer derivatives, and polyvinyl A polymer matrix material (gel electrolyte) in which a nonaqueous electrolytic solution is contained in a pyridine derivative, a bisphenol A derivative, polyacrylonitrile, polyvinylidene fluoride, fluorine rubber or the like is effective. Examples of organic solvents for this non-aqueous electrolyte include esters such as propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and γ-butyrolactone, substituted tetrahydrofuran such as tetrahydrofuran and 2-methyltetrahydrofuran, and dioxolane. , Ethers such as diethyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, dimethyl sulfoxide, sulfolane, methyl sulfolane, acetonitrile, methyl formate, methyl acetate, N-methylpyrrolidone, dimethylformamide, etc. It can be used alone or as a mixed solvent. In addition, a method of using these inorganic and organic solid electrolytes together is also effective. Examples of the supporting electrolyte salt used for the solid electrolyte as described above include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) _{2 and the} like.
[0013]
In the non-aqueous solid electrolyte battery of the present invention, a conductive agent, a binder, a filler, or the like can be added as an electrode mixture. As the conductive agent, any electronic conductive material that does not adversely affect battery performance may be used. Usually, natural graphite (flaky graphite, earthy graphite, etc.), artificial graphite, carbon black, acetylene black, ketjen black, carbon whisker, carbon fiber and metal (copper, nickel, iron, silver, gold, etc.) powder, metal Conductive materials such as fibers, metal vapor deposition, and conductive ceramic materials can be included as one type or a mixture thereof. The addition amount is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight.
[0014]
As the binder, thermoplastics such as tetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, ethylene-propylene diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoro rubber, carboxymethyl cellulose, etc. are usually used. Resins, polymers having rubber elasticity, polysaccharides, and the like can be used as one or a mixture of two or more. In addition, it is desirable that a binder having a functional group that reacts with lithium, such as a polysaccharide, be deactivated by, for example, methylation. The addition amount is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight.
[0015]
As the filler, any material that does not adversely affect the battery performance may be used. Usually, olefin polymers such as polypropylene and polyethylene, aerosil, alumina, carbon and the like are used. The amount of filler added is preferably 0 to 30% by weight.
[0016]
When the phosphoric acid compound of the present invention is used as a negative electrode active material, examples of the positive electrode active material include MnO ₂ , MoO ₃ , V ₂ O ₅ , Li _x CoO ₂ , Li _x NiO ₂ , and Li _x Mn ₂ O ₄ . Absorbs and releases metal oxides, metal chalcogenides such as TiS ₂ , MoS ₂ , NbSe ₃ , graphite intercalation compounds such as polyacene, polyparaphenylene, polypyrrole, polyaniline, and alkali metal ions such as conductive polymers, and anions A variety of possible materials can be utilized.
[0017]
In particular, in the case of the nonaqueous solid electrolyte battery of the present invention, an electrode potential of 3 to ₄ V such as V ₂ O ₅ , MnO ₂ , Li _x CoO ₂ , Li _x NiO ₂ , or Li _x Mn ₂ O ₄ from the viewpoint of high energy density. It is desirable to have Particularly preferred are lithium-containing transition metal oxides such as Li _x CoO ₂ , Li _x NiO ₂ , and Li _x Mn ₂ O ₄ . Especially, since the volume change accompanying charging / discharging is small, the main component of the positive electrode active material of the non-aqueous solid electrolyte battery is Li _a Co _b Ni _1-b O ₂ (a ≧ 0, 0 ≦ b ≦ 1). It is desirable to be. In addition, when b = 0.5, it is further desirable because the volume change accompanying charge / discharge is the smallest.
[0018]
On the other hand, when the phosphoric acid compound of the present invention is used as a positive electrode active material, examples of the negative electrode active material include lithium metals, lithium alloys, foreign semiconductors doped with impurities in silicon and germanium, tin oxide, lithium spinel oxide, etc. Examples thereof include metal oxides, metal chalcogenides, phosphoric acid compounds used in the present invention, graphite intercalation compounds, carbon materials such as non-graphitizable materials, and the like. In particular, in the case of the non-aqueous solid electrolyte battery of the present invention, those having an electrode potential of 0 to 1 V such as lithium metal and lithium alloy are desirable from the viewpoint of high energy density. In addition, some titanium-based spinel oxides, such as Li ₄ Ti ₅ O ₁₂ , do not show a change in crystal system due to charge / discharge, and such characteristics are particularly preferable in the case of a solid electrolyte battery.
[0019]
A separator can be used in combination with a solid electrolyte. As the separator, an insulating thin film having excellent ion permeability and mechanical strength can be used. Sheets, microporous membranes, and nonwoven fabrics made from olefin polymers such as polypropylene and polyethylene, glass fibers, polyvinylidene fluoride, polytetrafluoroethylene, etc. are used because of their organic solvent resistance and hydrophobicity. The pore diameter of the separator is in a range generally used for batteries, and is, for example, 0.01 to 10 μm. Moreover, it is the same also about the thickness, and is a thing of the range generally used for a battery, for example, is 5-300 micrometers.
[0020]
The positive and negative electrode active materials used in the present invention are preferably powders having an average particle size of 0.1 to 100 μm. In obtaining a predetermined shape, a pulverizer, a classifier, or a granulator is used to obtain a powder. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as hexane may be used. The classification method is not particularly limited, and a sieve, an air classifier, or the like is used as necessary for both dry and wet methods.
[0021]
Examples of the negative electrode material that can be used in conjunction with the present invention include lithium metal, lithium alloy, and the like, alloys capable of occluding and releasing lithium ions or lithium metal, fired carbonaceous compounds, chalcogen compounds, and organic compounds containing lithium such as methyllithium. Compounds and the like. In addition, by using a lithium metal, a lithium alloy, or an organic compound containing lithium, the negative electrode active material used in the present invention can be set to a low (base) potential in advance, or the initial efficiency can be improved.
[0022]
The current collector for the electrode active material may be any electronic conductor as long as it does not adversely affect the constructed battery. For example, the positive electrode material includes aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymer, conductive glass, etc., and aluminum, copper, etc. for the purpose of improving adhesion, conductivity, and oxidation resistance. A material obtained by treating the surface with carbon, nickel, titanium, silver or the like can be used. In addition to copper, stainless steel, nickel, aluminum, titanium, baked carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., the negative electrode material is used for the purpose of improving adhesion, conductivity, and oxidation resistance. A material obtained by treating the surface of copper or the like with carbon, nickel, titanium, silver or the like can be used. The surface of these materials can be oxidized. As for these shapes, a film shape, a sheet shape, a net shape, a punch, an expanded shape, a lath body, a porous body, a foamed body, a formed body of fiber groups, and the like are used in addition to the foil shape. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used.
[0024]
Examples of the battery shape using the solid electrolyte include a cylindrical shape, a square shape, a coin shape, a button shape, a flat shape, and a film shape. Among these, in order to achieve a high energy density, the battery shape of the non-aqueous solid electrolyte battery is preferably a film shape.
[0025]
【Example】
Examples of the present invention will be described below.
[0026]
(Invention)
Iron phosphate (FePO ₄ .2H ₂ O) manufactured by High Purity Chemical Co., Ltd. was vacuum-dried at 200 ° C., and anhydrous iron phosphate (FePO ₄ ) was used as the negative electrode active material. As the positive electrode active material, cobalt hydroxide (Co (OH) ₂ ) and nickel hydroxide (Ni (OH) ₂ ) are mixed in an equimolar amount, and further mixed with LiOH · H ₂ O. The lithium nickel cobaltate (LiNi _0.5 Co _0.5 O ₂ ) obtained by heat treatment at 750 ° C. for 20 hours was used as the positive electrode active material.
[0027]
An acrylated adduct of bisphenol A with ethylene oxide was used as a polymer matrix material monomer (monomer). The average molecular weight was about 500. As an electrolytic solution to be contained here, a solution obtained by dissolving LiBF ₄ in γ-butyrolactone so as to be 1 mol / liter was used.
[0028]
As a method for adjusting the negative electrode, 10 g and 0.2 g of the negative electrode active material FePO ₄ and Ketjen black on the copper foil 35 μm as the current collector, 1.2 g of the monomer and 4.8 g of the electrolytic solution, respectively, The mixture was applied and irradiated with an electron beam for polymerization.
[0029]
As a method for preparing the positive electrode, a carbon film was applied and dried as an undercoat on 50 μm of an aluminum foil as a current collector, and LiNi _0.5 Co _0.5 O ₂ and Ketjen Black were applied thereon to 10 g and 0.2 g, respectively. A mixture of 1.2 g of the monomer and 4.8 g of the above-described electrolyte solution was applied and irradiated with an electron beam for polymerization.
[0030]
A copolymer of polyethylene oxide and polypropylene oxide in which a trifunctional acrylic ester and the above-described electrolyte solution were mixed at a ratio of 3: 7 was applied and cured on the positive electrode and the negative electrode to provide a non-aqueous solid electrolyte layer of 45 μm.
[0031]
The prepared positive electrode / electrolyte and electrolyte / negative electrode were bonded to each other, and a hot melt adhesive was set around the electrode. Then, three sides of the quadrilateral were heat sealed, and the remaining one side was heat sealed under vacuum.
[0032]
FIG. 1 shows a cross section of the nonaqueous solid electrolyte battery of the present invention. In FIG. 1, 1 is a positive electrode , 2 is a negative electrode , 3 is a non-aqueous solid electrolyte layer , 6 is a positive electrode current collector, and 7 is a negative electrode current collector .
[0033]
(Comparative example)
A nonaqueous solid electrolyte battery was produced in the same manner as in the present invention except that graphite was used as the negative electrode active material.
[0034]
A charge / discharge test was performed using these cells. The charge / discharge test was performed at room temperature. Charging / discharging was performed at a rate of 10 hours, and in the battery of the present invention, the charge end voltage was 3.0 V and the discharge end voltage was 2.0 V. On the other hand, in the comparative battery, the end-of-charge voltage was 4.2V, and the end-of-discharge voltage was 3.0V. Table 1 shows the results of a cycle test performed on the present invention and comparative examples.
[0035]
[Table 1]

[0036]
As shown in Table 1, the discharge capacity in the first cycle for each battery the same west were investigated cycle characteristics. When the cycle deterioration rate after 100 cycles is compared, it is clear that there is a difference in cycle characteristics. The reason is not clear, but in the case of a non-aqueous solid electrolyte battery, the expansion and contraction of the active material that accompanies charging / discharging creates a gap at the interface between the active material and the non-aqueous solid electrolyte, causing isolation of the active material. It is considered that cycle deterioration has occurred. In particular, this phenomenon is considered to occur in a cell structure that is difficult to apply external pressure such as a film. That is, it is considered that this phenomenon appears remarkably when graphite having a large expansion and contraction is used during charging and discharging.
[0037]
In addition, this invention is not limited to the starting material of the active material described in the said Example, the manufacturing method, a positive electrode, a negative electrode, an electrolyte, a separator, a battery shape, etc. Moreover, in the said Example, although the phosphoric acid compound is used as a negative electrode active material, it cannot be overemphasized that it can be used also as a positive electrode active material. Furthermore, the shape of the battery is not limited to a film shape.
[0038]
【The invention's effect】
Since the present invention is configured as described above, it is possible to provide a safe non-aqueous solid electrolyte battery that is lightweight, exhibits excellent cycle characteristics, and does not leak.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a nonaqueous solid electrolyte battery of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Non-aqueous solid electrolyte layer 4 Positive electrode can 5 Negative electrode can 6 Positive electrode collector 7 Negative electrode collector

Claims (1)

  A non-aqueous solid electrolyte battery using a gel electrolyte in which a supporting electrolyte is dissolved and using a phosphoric acid compound containing iron as a main component of a negative electrode active material that absorbs and releases lithium.

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