JP2005093238A - Electrolyte and battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electrolyte which can improve battery characteristics, such as capacity and charge/discharge cycle characteristic, and to provide a battery which uses the same. <P>SOLUTION: The battery has an electrode body 20 in which a positive electrode 21 and a negative electrode 22 are wound, interposing a separator 23. The negative electrode 22 preferably contains at least one type selected among from a group consisting of a single body, an alloy, and a compound of a metal or semi-metal element capable of combining with Li. In the separator 23, the electrolyte in which electrolytic salt is dissolved is impregnated. As the solvent, an organic compound containing active oxygen is used. Hereby, decomposition of the electrolyte, and formation of a film based on the decomposition at the negative electrode 22 can be restrained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a battery including an electrolyte together with a positive electrode and a negative electrode, and an electrolyte used therefor.

  In recent years, many portable electronic devices such as mobile phones, camera-integrated VTRs (video tape recorders), and laptop computers have appeared, and improvements in performance are required for these portable electronic devices. Accordingly, as a power source for portable electronic devices, there is a demand for improvement in energy density and reduction in size and weight for secondary batteries that can be charged and discharged. Among them, the lithium ion secondary battery is superior in that it has higher energy than a lead battery or a nickel cadmium battery and can be used for a long time.

  In the lithium ion secondary battery, a carbonaceous material such as non-graphitizable carbon or graphite is conventionally used as the negative electrode active material. This is because good charge / discharge cycle characteristics can be obtained. With respect to such a negative electrode active material, as described in Patent Document 1, for example, it has been reported that the capacity can be further increased by controlling the starting materials and the production conditions.

  However, since the discharge potential of the negative electrode using this negative electrode active material is as high as 0.8 V to 1.0 V with respect to lithium, when this negative electrode active material is used in a lithium ion secondary battery, the capacity can be further increased. It becomes difficult. There is also a problem that the charge / discharge curve shape has a large hysteresis and the charge / discharge cycle characteristics deteriorate.

As a negative electrode active material for solving such a problem, there is a lithium alloy. A lithium alloy can be charged and discharged by applying a reversible reaction of electrochemical generation and decomposition. As a lithium alloy, for example, a Li—Al alloy, a Li—Si alloy, or the like is known. For example, Patent Document 2 proposes using an alloy with silicon (Si) as a negative electrode active material.
JP-A-8-315825 U.S. Pat. No. 4,950,566

  However, in a lithium ion secondary battery, it is difficult to obtain sufficient capacity and good charge / discharge cycle characteristics when charging / discharging is repeated using a Li-Al alloy or a Li-Si alloy as a negative electrode active material. was there. One of the causes is that the negative electrode and the electrolytic solution react excessively and the electrolytic solution is decomposed. Another example is that the decomposed electrolyte is formed as a film on the surface of the negative electrode, which inhibits occlusion and release of lithium ions.

  The present invention has been made in view of such problems, and an object thereof is to provide an electrolyte capable of improving battery characteristics such as capacity and charge / discharge cycle characteristics, and a battery using the electrolyte.

  The electrolyte according to the present invention contains a solvent containing an organic compound not containing oxygen (O).

  The battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, and the electrolyte contains a solvent containing an organic compound not containing oxygen.

  In the electrolyte and battery according to the present invention, the organic compound is contained, and since the organic compound is electrochemically stable, decomposition of the electrolyte on the surface of the negative electrode accompanying charge / discharge and formation of a coating based thereon are suppressed. . Therefore, the occlusion and release reaction of ions with respect to the positive electrode or the negative electrode is efficiently performed.

  According to the electrolyte and battery of the present invention, since the organic compound is included, decomposition of the electrolyte on the surface of the negative electrode and formation of a coating based thereon are suppressed. As a result, ion storage and release reactions with respect to the positive electrode or the negative electrode are performed efficiently, and battery characteristics such as battery capacity and charge / discharge cycle characteristics can be improved. In particular, when the negative electrode contains at least one member selected from the group consisting of simple elements, alloys, and compounds of metal elements or metalloid elements that can be combined with lithium, battery characteristics are likely to deteriorate when charging and discharging are repeated. A higher effect can be exhibited.

  In particular, if the ratio of the oxygen-free compound in the solvent is in the range of 1% by volume or more and 90% by volume or less, a higher effect can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a cross-sectional structure of a secondary battery according to an embodiment of the present invention. This secondary battery is a so-called cylindrical type, and an electrode body 20 in which a belt-like positive electrode 21 and a belt-like negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. have. The battery can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 11, an electrolytic solution which is a liquid electrolyte is injected and impregnated in the separator 23. In addition, a pair of insulating plates 12 and 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the electrode body 20.

  At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14 and a heat sensitive resistance element (Positive Temperature Coefficient; PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the electrode body 20 is cut off. When the temperature rises, the heat sensitive resistance element 16 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.

  For example, a center pin 24 is inserted in the center of the electrode body 20. A positive electrode lead 25 made of aluminum (Al) or the like is connected to the positive electrode 21 of the electrode body 20, and a negative electrode lead 26 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

FIG. 2 shows an enlarged view of a part of the electrode body 20 shown in FIG. The positive electrode 21 includes, for example, a positive electrode current collector 21A having a pair of opposed surfaces and a positive electrode mixture layer 21B provided on both surfaces or one surface of the positive electrode current collector 21A. The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode mixture layer 21B includes, for example, any one or two or more positive electrode materials capable of inserting and extracting lithium as a positive electrode active material, and polytetrafluoroethylene or polyfluoride as necessary. A binder such as vinylidene fluoride and a conductive agent such as artificial graphite or carbon black may be included. Examples of the positive electrode material capable of inserting and extracting lithium include lithium such as titanium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), niobium selenide (NbSe ₂ ), and vanadium oxide (V ₂ O ₅ ). Metal sulfides or metal oxides containing no lithium, or lithium composite oxides containing lithium.

Among these, lithium composite oxides are preferable because there are those that can obtain a high voltage and a high energy density. Examples of such a lithium composite oxide include those represented by the chemical formula Li _{(1 + x)} MI _y MII _(1-xy) O ₂ . In the formula, MI represents at least one of cobalt and nickel, and MII represents manganese (Mn), magnesium (Mg), aluminum, titanium (Ti), vanadium (V), chromium (Cr), iron (Fe ), Copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). The value of x is −0.1 ≦ x ≦ 0.1, and the value of y is y = 0 or 0.005 ≦ y ≦ 0.5. Specific examples of the lithium composite oxide include a lithium cobalt composite oxide (LiCoO ₂ ), a lithium nickel composite oxide (LiNiO ₂ ) having a hexagonal structure, or a lithium manganese composite oxide (LiMn ₂ O ₄ ) having a spinel structure. ) And the like.

  The negative electrode 22 includes, for example, a negative electrode current collector 22A having a pair of opposed surfaces, and a negative electrode mixture layer 22B provided on both surfaces or one surface of the negative electrode current collector 22A. The negative electrode current collector 22A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. The negative electrode mixture layer 22B includes, for example, any one or more of negative electrode materials capable of inserting and extracting lithium as a negative electrode active material, and polytetrafluoroethylene or polyfluoride as necessary. A binder such as vinylidene chloride may be included.

  As a negative electrode material capable of inserting and extracting lithium, simple elements, alloys and compounds of metal elements or metalloid elements capable of combining with lithium are preferable. This is because the capacity of the battery can be increased. Note that in this specification, alloys include those composed of one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. There are structures in which a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of them coexist.

Examples of metal elements or metalloid elements that can be combined with lithium include zinc (Zn), cadmium (Cd), lead (Pb), tin (Sn), bismuth (Bi), indium (In), and antimony (Sb). , Germanium (Ge), boron (B), silicon (Si), or arsenic (As). These compounds include for example, those represented by the chemical formula Ma _s Mb _t. In this chemical formula, Ma represents at least one of a metal element and a metalloid element that can combine with lithium, and Mb represents at least one of elements other than Ma. The values of s and t are s> 0 and t ≧ 0, respectively.

  Among them, a single element or compound of a group 14 metal element or metalloid element in the long-period periodic table is preferable, and silicon or tin, or a compound thereof is particularly preferable. This is because a higher capacity can be obtained. These may be crystalline or amorphous.

Specific examples of such compounds include SiB ₄ . _{SiB 6, Mg 2 Si, Mg} 2 Sn, Ni 2 Si, TiSi 2, MoSi 2, CoSi 2, NiSi 2, CaSi 2, CrSi 2, Cu 5 Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi ₂ , an alloy or compound represented by McMd _u such as WSi ₂ or ZnSi ₂ (Mc represents silicon or tin, Md represents one or more metal elements, and u ≧ 0), or SiC, Si ₃ N ₄ , Si ₂ N ₂ O, Ge ₂ N ₂ O, SiO _v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), LiSiO, or LiSnO.

  As other compounds, for example, LiAl alloy, LiAlMe alloy (Me represents at least one of the group consisting of elements of group 2-11 and group 14 in the long-period periodic table), AlSb alloy Or a CuMgSb alloy is mentioned.

  A method for producing such a negative electrode active material is not limited. For example, a mixture in which starting materials are mixed is heat-treated in an inert gas atmosphere such as argon or a reducing gas atmosphere, and the heat-treated mixture is pulverized. It can produce by doing. It can also be produced by a mechanical alloying method in which a mechanical force is applied to the starting material.

  Examples of the negative electrode material capable of inserting and extracting lithium include carbonaceous materials. This carbonaceous material is excellent in charge / discharge cycle characteristics, and if used together with any one or more of a single element, alloy, or compound of a metal element or a metalloid element that can be combined with the lithium, It is preferable because capacity can be obtained and charge / discharge cycle characteristics can be improved. Moreover, since it functions also as a electrically conductive agent, it is preferable. Specific examples of carbonaceous materials include non-graphitizable carbon, graphitizable carbon, graphite, pyrolytic carbons, cokes, glassy carbons, organic polymer compounds, fired bodies, carbon fibers or activated carbon. is there. Among these, examples of coke include pitch coke, needle coke, and petroleum coke. An organic polymer compound is a material obtained by firing and carbonizing a polymer material such as phenol resin or furan resin at an appropriate temperature, and is partially classified as non-graphitizable carbon or graphitizable carbon. There are also things.

  The ratio of the simple substance, alloy, and compound of the metal element or metalloid element that can be combined with these lithiums to the carbonaceous material is 0.5 to 5 or less for the simple substance, alloy, and compound, and the carbonaceous material is a weight ratio. It is preferably within the range of 0.2 or more and 2 or less. Further, these ratios in the negative electrode mixture layer 22B are preferably in the range of 30 wt% to 75 wt% for the simple substance, alloy and compound, and 15 wt% to 60 wt% for the carbonaceous material. If the amount of the carbonaceous material that also functions as a conductive agent is too small, the conductivity of the negative electrode 22 decreases, and if it is too large, the amount of the high-capacity single substance, alloy, and compound decreases, and the battery capacity decreases. is there.

  The separator 23 isolates the positive electrode 21 and the negative electrode 22 to prevent an internal short circuit due to contact between the two electrodes and allow ions to pass therethrough. The separator 23 is configured by, for example, a single layer or a stack of microporous films having a large number of micropores having an average particle size of about 5 μm or less. As a constituent material for such microporous film formation, for example, there are olefin polymer, propylene polymer, cellulose polymer, polyimide or nylon, and glass fiber or alumina fiber can also be used. Among these, polypropylene and polyolefin are preferable because they are excellent in short-circuit prevention effect and can improve battery safety by a shutdown effect.

  The electrolytic solution impregnated in the separator 23 contains a solvent such as a non-aqueous solvent and an electrolyte salt dissolved in the solvent. The non-aqueous solvent contains one or more organic compounds that do not contain oxygen (hereinafter referred to as oxygen-free compounds). Since the oxygen-free compound is electrochemically stable, it is difficult to decompose even if charging and discharging are repeated. Therefore, by including this oxygen-free compound, in this secondary battery, decomposition of the electrolytic solution on the surface of the negative electrode 22 and formation of a coating based thereon are suppressed, so that the lithium ion insertion and release reaction is efficient. Thus, battery characteristics such as battery capacity and charge / discharge cycle characteristics can be improved.

  As the oxygen-free compound, for example, compounds shown in Chemical Formula 1 to Chemical Formula 12 are preferable, more preferable are chemical compounds shown in Chemical Formula 1, Chemical Formula 2, Chemical Formula 4, Chemical Formula 6 or Chemical Formula 7, and the most preferable chemical formula is 1 is the compound shown. This is because higher effects can be obtained by using these compounds.

(In the chemical formulas 1 to 13, X1 to X138 represent hydrogen (H), fluorine (F), chlorine (Cl), bromine (Br), amino group (—NH ₂ ) or a group shown in chemical formula 14; And Y2 each represent fluorine, chlorine or bromine, and m, n, a and b are integers satisfying 1 ≦ m ≦ 12, 0 ≦ a ≦ 2m + 1, 6 ≦ n ≦ 12 and 0 ≦ b ≦ 2n + 2, respectively. )

(In Chemical Formula 14, Z represents fluorine, chlorine or bromine, and p and c are integers satisfying 1 ≦ p ≦ 12 and 0 ≦ c ≦ 2p + 1, respectively)

  As the compound shown in Chemical formula 1, the fluorobenzene shown in Chemical formula 15, the benzene shown in Chemical formula 16, the hexafluorobenzene shown in Chemical formula 17, the chlorobenzene shown in Chemical formula 18, the bromobenzene shown in Chemical formula 19, and the chemical formula 20 Aniline shown in the formula 1, 1,3,5-trimethylbenzene shown in the formula 21, 1,4-bis (trifluoromethyl) benzene shown in the formula 22, tert-butylbenzene shown in the formula 23, and shown in the formula 24 And tert-pentylbenzene or dodecylbenzene shown in Chemical Formula 25.

  Further, the compound shown in Chemical formula 2 is diphenyl shown in Chemical formula 26, and the compound shown in Chemical formula 3 is diphenylmethane shown in Chemical formula 27 or 2,2-diphenylpropane shown in Chemical formula 28. 1,3-dimethylnaphthalene shown in Chemical formula 29 as the compound, tetrahydronaphthalene shown in Chemical formula 30 as the compound shown in Chemical formula 5, and orthoterphenyl shown in Chemical formula 31 as the compound shown in Chemical formula 6 The compound shown in Chemical formula 7 is metaterphenyl shown in Chemical formula 32, the compound shown in Chemical formula 8 is cyclohexane shown in Chemical formula 33, and the compound shown in Chemical formula 9 is cyclohexene shown in Chemical formula 34. The compound shown in Chemical formula 10 is decalin shown in Chemical formula 35, and the compound shown in Chemical formula 11 is the cyclopent shown in Chemical formula 36. Emissions, etc., of dodecane shown in the reduction 37 as the compound shown in 12, such as cyclohexylbenzene represented by Chemical Formula 38 as a compound shown in Chemical formula 13 can be mentioned.

  In addition to the oxygen-free compound, the non-aqueous solvent is preferably used by mixing one or more of cyclic carbonates or chain carbonates, and the cyclic carbonate is used in a volume of 50 volumes in the non-aqueous solvent. It is more preferable to mix and use so that it may become in the range of% or less. This is because when the proportion of the cyclic carbonate is larger than this, the viscosity of the electrolytic solution is increased, the electric conductivity is lowered, and the capacity retention rate is lowered. As the cyclic carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate or vinyl ethylene carbonate is preferable, and as the chain carbonate ester, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, dipropyl carbonate, ethyl Propyl carbonate or butyl ethyl carbonate is preferred.

  In addition, for example, 1,2-diethoxyethane, γ-butyrolactone, tetravidrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane Any one or more of other substances such as acetonitrile, propionitrile, anisole, acetate, butyrate or propionate may be used.

  As described above, when using a substance other than the oxygen-free compound in the non-aqueous solvent, the proportion of the oxygen-free compound in the non-aqueous solvent varies depending on the type of the other solvent to be mixed and the like. It is preferably within the range of volume% or less, and more preferably within the range of 20 volume% or more and 60 volume% or less. If the amount of oxygen-free compound is too small, the above-mentioned effects may not be sufficiently exhibited. On the other hand, if the amount is too large, the electrolyte salt is difficult to dissolve sufficiently, resulting in low electrical conductivity and poor battery characteristics. Because there are cases. That is, by making it within this range, a film is sufficiently prevented from being formed on the surface of the negative electrode 22, and sufficient electric conductivity can be obtained, so that the lithium ion occlusion and release reactions can be performed more efficiently. The battery characteristics can be sufficiently improved.

As electrolyte salt, lithium salt is mentioned, for example, 1 type may be used independently, and 2 or more types may be mixed and used for it. The lithium _{salt, LiPF 6, LiN (CF 3} SO 2) 2, LiN (C 2 F 5 SO 2) 2, LiClO 4, LiAsF 6, LiBF 4, LiB (C 6 H 5) 4. CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiCl, LiBr, or the like can be given. Among these, it is preferable to use one or more of LiPF ₆ , LiN (CF ₃ SO ₂ ) ₂ or LiN (C ₂ F ₅ SO ₂ ) ₂ . LiPF ₆ is excellent in oxidation stability and rarely decomposes even after repeated charge and discharge. Therefore, lithium ions can be moved smoothly and the capacity can be increased, and LiN (CF ₃ SO ₂ ) ₂ and Since LiN (C ₂ F ₅ SO ₂ ) ₂ has a larger anion size than LiPF ₆ , the volume occupied by the non-aqueous solvent other than the oxygen-free compound contained in the same volume is reduced, and the surface of the anode 22 This is because it is considered that the decomposition of the electrolyte solution and the formation of the coating film based thereon are suppressed.

The ratio of the electrolyte salt in the electrolytic solution (concentration) is preferably in the range of 0.4 mol / dm ^{3 to} 2.0 mol / dm ³ . This is because when the amount of electrolyte salt is small, the electric conductivity is small, and conversely, when the amount of electrolyte salt is large, the viscosity of the electrolytic solution is high, and ions are difficult to move between the positive electrode 21 and the negative electrode 22. That is, by making it within this range, the occlusion / release amount of ions becomes good, and the deterioration of battery characteristics is suppressed.

A gel electrolyte may be used in place of the electrolytic solution. The gel electrolyte is obtained, for example, by holding an electrolytic solution in a polymer compound. The electrolytic solution (that is, the solvent, the electrolyte salt, etc.) is as described above. As the polymer compound, for example, any polymer that absorbs an electrolytic solution and gelates can be used. Examples of such a polymer compound include polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene. And a fluorine-based polymer compound such as polyethylene oxide or an ether-based polymer compound such as a crosslinked product containing polyethylene oxide, or polyacrylonitrile. In particular, a fluorine-based polymer compound is desirable from the viewpoint of redox stability. The ratio of the electrolyte salt in the gel electrolyte is preferably in the range of 0.4 mol / dm ³ or more and 2.0 mol / dm ³ or less, as in the electrolytic solution.

  In the secondary battery, when charged, for example, lithium ions are released from the positive electrode mixture layer 21B and inserted into the negative electrode mixture layer 22B through the electrolyte. When the discharge is performed, for example, lithium ions are released from the negative electrode mixture layer 22B and inserted into the positive electrode mixture layer 21B through the electrolyte. Here, since the oxygen-free compound contained in the electrolytic solution is electrochemically stable, decomposition of the electrolytic solution on the surface of the negative electrode 22 associated with charge / discharge and formation of a coating based thereon are suppressed. Thus, lithium ion storage and release reactions are efficiently performed.

  For example, the secondary battery can be manufactured as follows.

  First, for example, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a mixed solvent such as N-methyl-2-pyrrolidone to form a positive electrode mixture slurry. And Next, the positive electrode mixture slurry is applied to the positive electrode current collector 21 </ b> A, dried, and then compression-molded to form the positive electrode mixture layer 21 </ b> B, thereby producing the positive electrode 21. After that, the positive electrode lead 25 is joined to the positive electrode current collector 21A by ultrasonic welding or spot welding.

  Further, for example, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a mixed solvent such as N-methyl-2-pyrrolidone to obtain a negative electrode mixture slurry. Next, the negative electrode mixture slurry is applied to the negative electrode current collector 22 </ b> A, dried, and then compression-molded to form the negative electrode mixture layer 22 </ b> B, thereby producing the negative electrode 22. After that, the negative electrode lead 26 is joined to the negative electrode current collector 22A by ultrasonic welding or spot welding.

  Next, the positive electrode 21 and the negative electrode 22 are wound many times through the separator 23 to produce the electrode body 20, and then the electrode body 20 is sandwiched between the pair of insulating plates 12 and 13 and stored in the battery can 11. . Subsequently, the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15 and the tip of the negative electrode lead 26 is welded to the battery can 11.

  In addition, an electrolyte salt is dissolved in a solvent to prepare an electrolytic solution. After that, the electrolytic solution is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through a gasket 17. Thereby, the secondary battery of the present embodiment is completed.

  As described above, in this embodiment, since the solvent contains an oxygen-free compound that is electrochemically stable and difficult to decompose, decomposition of the electrolytic solution on the surface of the negative electrode 22 and formation of a film based thereon are suppressed. The As a result, lithium ion storage and release reactions are efficiently performed, and battery characteristics such as battery capacity and charge / discharge cycle characteristics can be improved. In particular, at least one member selected from the group consisting of simple elements, alloys, and compounds of metal elements or metalloid elements that can be combined with lithium in the negative electrode 22 is highly reactive with an electrolyte, and deteriorates when repeated charge and discharge are performed. Since it is easy to deteriorate, a higher effect can be exhibited when these are included.

  In particular, if the ratio of the oxygen-free compound in the solvent is in the range of 1% by volume or more and 90% by volume or less, a higher effect can be obtained.

  Further, specific embodiments of the present invention will be described in detail.

(Examples 1-1 to 1-24)
First, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are thoroughly mixed at a ratio of 0.5 mol: 1 mol using a mixer, and then fired in air at 900 ° C. for 5 hours in an electric furnace. The powdered lithium cobalt composite oxide was synthesized by grinding after firing. When this lithium cobalt composite oxide was subjected to X-ray diffraction measurement, it was confirmed to be LiCoO ₂ .

  Next, using the synthesized lithium cobalt composite oxide as a positive electrode active material, 91 parts by weight of lithium cobalt composite oxide, 6 parts by weight of graphite as a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder, Using a mixed solvent, N-methyl-2-pyrrolidone, the mixture was kneaded and dispersed by a planetary mixer to prepare a positive electrode mixture coating solution. Subsequently, using a die coater as a coating apparatus, the positive electrode mixture coating liquid was uniformly applied to both surfaces of the positive electrode current collector 21A made of an aluminum foil having a thickness of 20 μm, dried, and then compression molded by a roll press. A positive electrode mixture layer 21B was formed. After that, the positive electrode 21 was manufactured by cutting at intervals of 54 mm in length. Next, a positive electrode lead 25 made of an aluminum piece was joined to the positive electrode current collector 21A so as to protrude from one end in the width direction.

  Also, cobalt powder and tin powder were prepared as raw materials, 28 g of cobalt powder and 72 g of tin powder were mixed, this mixture was put into a quartz board, heated at 1500 ° C. in an argon gas atmosphere, and cooled to room temperature. . The resulting mixture was pulverized by a ball mill in an argon gas atmosphere and classified to synthesize cobalt-tin (Co-Sn) alloy powder. When this cobalt-tin alloy powder was observed with a scanning electron microscope, it was confirmed that the average particle diameter was 10 μm.

  Next, using the synthesized cobalt-tin alloy powder as a negative electrode active material, 45 parts by weight of the cobalt-tin alloy powder and 45 parts by weight of flaky graphite (KS-44 manufactured by Timical) as a negative electrode active material and a conductive agent were combined. A negative electrode mixture coating solution was prepared by kneading and dispersing 10 parts by weight of polyvinylidene fluoride as an adhesive with a planetary mixer using N-methyl-2-pyrrolidone as a mixed solvent. Subsequently, using a die coater as a coating device, the negative electrode mixture coating liquid was uniformly applied to both surfaces of the negative electrode current collector 22A made of a copper foil having a thickness of 10 μm and dried, followed by compression molding with a roll press. A negative electrode mixture layer 22B was formed. Then, it cut | judged by the length 56mm space | interval and the negative electrode 22 was produced. Next, a negative electrode lead 26 made of a nickel piece was joined to the negative electrode current collector 22A so as to protrude from one end in the width direction.

  After that, a separator 23 made of a microporous polypropylene film having a thickness of 25 μm was interposed between the positive electrode 21 and the negative electrode 22, and a plurality of laminated bodies obtained by laminating a plurality of these were wound to produce the electrode body 20. At this time, the positive electrode lead 25 was led out from one end surface of the electrode body 20, and the negative electrode lead 26 was led out from the other end surface. Next, the positive electrode lead 26 was welded to the battery lid 14, and the negative electrode lead 26 was welded to the battery can 11 in which nickel was plated on iron, and the electrode body 20 was housed inside the battery can 11.

Further, LiPF ₆ was dissolved in a solvent obtained by mixing an oxygen-free compound, ethylene carbonate as a cyclic carbonate, and diethyl carbonate as a chain carbonate to prepare an electrolytic solution. The types of the oxygen-free compound and the contents of the oxygen-free compound, ethylene carbonate, and diethyl carbonate in the solvent were changed as shown in Table 1 in Examples 1-1 to 1-24. In Table 1, EC represents ethylene carbonate, and DEC represents diethyl carbonate. The concentration of LiPF _{6 in} the electrolytic solution was 1 mol / dm ^{3 in} any of Examples 1-1 to 1-24.

  Next, an electrolytic solution is injected into the battery can 11, and the battery lid 14 is press-fitted into the opening of the battery can 11 through the insulating gasket 17 coated with asphalt to caulk the opening of the battery can 11. As a result, the battery lid 14 was firmly fixed. As described above, secondary batteries (diameter 18 mm, height 65 mm, inner diameter 17.38 mm, can thickness 0.31 mm) of Examples 1-1 to 1-24 were fabricated.

  Moreover, as Comparative Example 1-1 with respect to Examples 1-1 to 1-24, except that no oxygen-free compound was used and the ratio of ethylene carbonate and diethyl carbonate in the solvent was changed as shown in Table 1. Other than that, secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-24. About the produced secondary battery of Examples 1-1 to 1-24 and Comparative Example 1-1, the capacity | capacitance maintenance factor as an initial stage capacity | capacitance and charging / discharging cycling characteristics was evaluated as follows. First, in a temperature environment of 23 ° C., a constant voltage current charge is performed under a charging condition of a maximum voltage of 4.2 V, a charging current of 1 A, and a charging time of 5 hours, and then a discharging current of 1 A and a final voltage of 2.5 V is set. Current discharge was performed and the initial capacity was determined. Next, charging / discharging is repeated under the same charging / discharging conditions, the discharge capacity at the 100th cycle is obtained, and the capacity is maintained as the initial capacity and the discharge capacity at the 100th cycle (discharge capacity at the 100th cycle / initial capacity) × 100. The rate was determined. The obtained results are shown in Table 1.

  As shown in Table 1, according to Examples 1-1 to 1-24 using an oxygen-free compound, both the initial capacity and the capacity retention rate were higher than those of Comparative Example 1-1 that was not used. A value was obtained. That is, it was found that the battery capacity and charge / discharge cycle characteristics can be improved by including an oxygen-free compound in the solvent.

(Examples 2-1 to 2-14)
As Examples 2-1 to 2-8, except that the proportions of fluorobenzene, ethylene carbonate and diethyl carbonate in the solvent were changed as shown in Table 2, other than that in Example 1-1, the secondary A battery was produced. In addition, as Examples 2-9 to 2-14, except that the types of cyclic carbonates and chain carbonates and the ratios thereof in the solvent were changed as shown in Table 2, the others were the same as Example 1-1. Similarly, a secondary battery was produced. In Table 2, PC is propylene carbonate, BC is butylene carbonate, VC is vinylene carbonate, VEC is vinyl ethylene carbonate, EC is ethylene carbonate, DMC is dimethyl carbonate, MEC is methyl ethyl carbonate, MPC is methyl propyl carbonate, DPC Represents dipropyl carbonate, EPC represents ethyl propyl carbonate, and BEC represents butyl ethyl carbonate. For the secondary batteries of Examples 2-1 to 2-14, the initial capacity and the capacity retention rate were evaluated in the same manner as in Example 1-1. The results are shown in Table 2 together with the results of Example 1-1 and Comparative example 1-1.

  As shown in Table 2, the initial capacity and the capacity retention ratio were high when the amount of fluorobenzene was large, and small when the amount of fluorobenzene was small. That is, it has been found that the proportion of fluorobenzene in the solvent is preferably in the range of 1% by volume to 90% by volume, and more preferably in the range of 20% by volume to 60% by volume.

  Moreover, as shown in Table 2, according to Examples 2-9 to 2-14, both the initial capacity and the capacity retention rate are higher than those of Comparative Example 1-1, as in Example 1-1. A value was obtained. That is, propylene carbonate other than ethylene carbonate, butylene carbonate, vinylene carbonate or vinyl ethylene carbonate may be used as the cyclic carbonate, and dimethyl carbonate other than diethyl carbonate, methyl ethyl carbonate, methyl may be used as the chain carbonate. It has been found that even when propyl carbonate, dipropyl carbonate, ethyl propyl carbonate or butyl ethyl carbonate is used, the battery capacity and charge / discharge cycle characteristics can be improved.

(Examples 3-1 to 3-13)
As Examples 3-1 to 3-5, copper-tin (Cu-Sn) alloy powder was used instead of cobalt-tin alloy powder, and the ratios of fluorobenzene, ethylene carbonate, and diethyl carbonate in the solvent are shown in Table 3. A secondary battery was fabricated in the same manner as in Example 1-1 except that the above was changed. The copper-tin alloy powder was prepared in the same manner as the cobalt-tin alloy powder of Example 1-1 except that 20 wt% copper powder and 80 wt% tin powder were used as raw materials. Further, as Examples 3-6 to 3-10, iron-tin (Fe-Sn) alloy powder was used instead of cobalt-tin alloy powder, and the ratios of fluorobenzene, ethylene carbonate, and diethyl carbonate in the solvent were shown in Table 4. A secondary battery was fabricated in the same manner as in Example 1-1 except that the changes were made as shown in FIG. The iron-tin alloy powder was produced in the same manner as the cobalt-tin alloy powder of Example 1-1 except that 40 wt% iron powder and 60 wt% tin powder were used as raw materials. Further, as Examples 3-11 to 13-13, graphite was used instead of cobalt-tin alloy powder, dimethyl carbonate was used instead of diethyl carbonate, and the ratios of fluorobenzene, ethylene carbonate, and dimethyl carbonate in the solvent were shown. A secondary battery was fabricated in the same manner as in Example 1-1 except for the change as shown in FIG.

  Further, as Comparative Example 3-1 with respect to Examples 3-11 to 3-13, Example 3 was the same as Example 3 except that the ratio of fluorobenzene, ethylene carbonate, and dimethyl carbonate in the solvent was changed as shown in Table 5. Secondary batteries were fabricated in the same manner as in -11 to 3-13. For the secondary batteries of Examples 3-1 to 3-13 and Comparative example 3-1, the initial capacity and charge / discharge cycle characteristics were evaluated in the same manner as in Example 1-1. The results are shown in Tables 3 to 5.

  As shown in Table 3 and Table 4, also in Examples 3-1 to 3-10 using a copper-tin alloy or an iron-tin alloy as the negative electrode active material, Example 2- using a cobalt-tin alloy Similar to 1-2-8, good results were obtained. Moreover, as shown in Table 5, also in Examples 3-11 to 13-13 using the carbonaceous material as the negative electrode active material, the initial capacity was compared with Comparative Example 3-1 in which no fluorobenzene was added. High values were obtained for both the capacity retention rate. That is, it has been found that even when other negative electrode active materials other than the cobalt-tin alloy are used, the battery capacity and charge / discharge cycle characteristics can be improved if the solvent contains an oxygen-free compound.

  Further, as can be seen from a comparison between Table 2 and Table 5, Examples 21 to 2-14 using an alloy as the negative electrode active material are examples of using only a carbonaceous material as the negative electrode active material. Compared with 11 to 13-13, the capacity retention rate could be dramatically improved over the corresponding Comparative Examples 1-1 and 3-1. That is, it has been found that when an alloy is used for the negative electrode 22, a higher effect can be exhibited if the solvent contains an oxygen-free compound.

(Examples 4-1 to 4-10)
As Examples 4-1 to 4-5, Example 1-1 except that the ratio of the cobalt-tin alloy and the flaky graphite in the negative electrode mixture layer 22B was changed as shown in Table 6. A secondary battery was fabricated in the same manner as described above. In addition, as Examples 4-6 to 4-10, except that the ratio of the copper-tin alloy and the flaky graphite in the negative electrode mixture layer 22B was changed as shown in Table 7, Example 3 was otherwise performed. A secondary battery was fabricated in the same manner as in -3. For the secondary batteries of Examples 4-1 to 4-10, the initial capacity and the capacity retention rate were evaluated in the same manner as in Examples 1-1 and 3-3. The results are shown in Table 6 or Table 7 together with the results of Examples 1-1 and 3-3. 3 shows the relationship between the ratio of the cobalt-tin alloy in the negative electrode mixture layer 22B and the initial capacity and the capacity retention rate, and FIG. 4 shows the ratio of the copper-tin alloy in the negative electrode mixture layer 22B and the initial capacity. The relationship with the capacity maintenance rate is shown.

  As can be seen from Tables 6 and 7 and FIGS. 3 and 4, both when the cobalt-tin alloy is used as the negative electrode active material and when the copper-tin alloy is used, the initial capacity ratio is increased when the proportion of the alloy is increased. The capacity retention rate tends to decrease and the ratio of the alloy to the flaky graphite is 0.5 to 5 or less and the flaky graphite is 0.2 to 2 in weight ratio, or When the proportion of the alloy in the negative electrode mixture layer 22B was 30% by weight or more and 75% by weight or less, and the proportion of the flake graphite was 15% by weight or more and 60% by weight or less, higher initial capacity and capacity retention ratio were obtained.

  That is, if the negative electrode mixture layer 22B contains the alloy and the carbonaceous material in a weight ratio of 0.5 to 5 and the carbonaceous material in a proportion of 0.2 to 2 respectively. Alternatively, if the alloy is included in the range of 30 wt% to 75 wt% and the carbonaceous material is included in the range of 15 wt% to 60 wt%, the battery capacity and cycle characteristics can be sufficiently improved. I understood.

(Examples 5-1 to 5-12)
A secondary battery was fabricated in the same manner as in Example 1-1, except that the type of electrolyte salt and the ratio of the electrolyte salt in the electrolytic solution were changed as shown in Table 8. For the secondary batteries of Examples 5-1 to 5-12, the initial capacity and charge / discharge cycle characteristics were evaluated in the same manner as in Example 1-1. The results are shown in Table 8 together with the results of Comparative Example 1-1.

As shown in Table 8, according to Examples 5-1 to 5-12, similarly to Example 1-1, a higher capacity retention rate was obtained as compared with Comparative Example 1-1. That is, even if LiN (CF ₃ SO ₂ ) ₂ or LiN (C ₂ F ₅ SO ₂ ) ₂ is used as the electrolyte salt, the electrolyte solution contains an oxygen-free compound as in the case of using only LiPF _6. It was found that the charge / discharge cycle characteristics can be improved.

Further, as can be seen from Examples 1-1, 5-1 to 5-4, the initial capacity and the capacity retention ratio are improved when the ratio of the electrolyte salt is increased, and tend to decrease after showing the maximum value. It was. That is, it has been found that the ratio of the electrolyte salt in the electrolytic solution is preferably in the range of 0.4 mol / dm ³ or more and 2.0 mol / dm ³ or less.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the oxygen-free compound has been described with a specific example, but the above effect is considered to be due to the structure of the oxygen-free compound. Therefore, the same effect can be obtained even when other oxygen-free compounds are used.

  Moreover, although the said embodiment and Example demonstrated the case where the gel electrolyte which is 1 type of electrolyte solution or solid electrolyte was used, you may make it use another electrolyte. Other electrolytes include, for example, a polymer solid electrolyte in which an electrolyte salt is dispersed in a polymer compound having ion conductivity, an ion conductive inorganic compound made of ion conductive ceramics, ion conductive glass or ionic crystals, Or what mixed these ion conductive inorganic compounds and electrolyte solution, or what mixed these ion conductive inorganic compounds, gel-like electrolyte, or polymer solid electrolyte is mentioned. Examples of the polymer compound of the solid polymer electrolyte include, for example, an ether polymer compound such as polyethylene oxide or a crosslinked product containing polyethylene oxide, an ester polymer compound such as polymethacrylate, and an acrylate polymer compound. Or may be copolymerized. As the inorganic solid electrolyte, lithium nitride, lithium iodide, or the like can be used.

  Furthermore, in the above-described embodiments and examples, the cylindrical secondary battery has been described. However, the shape is not particularly limited, and various shapes such as a so-called square shape, coin shape, button shape, or thin shape can be used. You may make it do.

  In addition, in the above embodiments and examples, the case where lithium is used as the electrode reactive species has been described. However, other group 1 elements in the long-period periodic table such as sodium (Na) or potassium (K), or The present invention can also be applied to the case of using elements of Group 2 in the long-period periodic table such as magnesium or calcium (Ca), other light metals such as aluminum, lithium, or alloys thereof. An effect can be obtained. In that case, the positive electrode active material, the electrolyte salt, and the like are appropriately selected according to the light metal. Others can be configured similarly to the above embodiment.

  Furthermore, in the above embodiments and examples, the case where the electrolyte of the present invention is used for a secondary battery has been described, but the present invention can also be applied to other batteries such as a primary battery. It can also be used for other electrochemical elements such as capacitors, capacitors or electrochromic elements.

It is sectional drawing showing the structure of the secondary battery which concerns on one embodiment of this invention. It is sectional drawing which expands and represents a part of electrode body shown in FIG. It is a characteristic view showing the relationship between the ratio of the cobalt tin alloy in the negative mix layer concerning Examples 1-1, 4-1 to 4-5 of this invention, an initial stage capacity | capacitance, and a capacity | capacitance maintenance factor. It is a characteristic view showing the relationship between the ratio of the copper-tin alloy in the negative mix layer concerning Example 3-3, 4-6 to 4-10 of this invention, an initial stage capacity | capacitance, and a capacity | capacitance maintenance factor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulating plate, 14 ... Battery cover, 15 ... Safety valve mechanism, 15A ... Disc board, 16 ... Heat sensitive resistance element, 17 ... Gasket, 20 ... Electrode body, 21 ... Positive electrode, 21A ... Positive electrode Current collector, 21B ... Positive electrode mixture layer, 22 ... Negative electrode, 22A ... Negative electrode current collector, 22B ... Negative electrode mixture layer, 23 ... Separator, 24 ... Center pin, 25 ... Positive electrode lead, 26 ... Negative electrode lead.

Claims (17)

  An electrolyte comprising a solvent containing an organic compound not containing oxygen (O). The electrolyte according to claim 1, wherein the solvent includes at least one member selected from the group consisting of the compounds represented by Chemical Formulas 1 to 12 as the organic compound.

(In the chemical formulas 1 to 12, X1 to X124 represent hydrogen (H), fluorine (F), chlorine (Cl), bromine (Br), amino group (—NH ₂ ) or the group shown in chemical formula 13; And Y2 each represent fluorine, chlorine or bromine, and m, n, a and b are integers satisfying 1 ≦ m ≦ 12, 0 ≦ a ≦ 2m + 1, 6 ≦ n ≦ 12 and 0 ≦ b ≦ 2n + 2, respectively. )

(In Chemical formula 13, Z represents fluorine, chlorine or bromine, and p and c are integers satisfying 1 ≦ p ≦ 12 and 0 ≦ c ≦ 2p + 1, respectively) The ratio of the said organic compound in the said solvent exists in the range of 1 volume% or more and 90 volume% or less. The electrolyte of Claim 1 characterized by the above-mentioned. The electrolyte according to claim 1, wherein the solvent further includes at least one member selected from the group consisting of cyclic carbonates and chain carbonates. The solvent includes at least one cyclic carbonate selected from the group consisting of propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, and vinyl ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, dipropyl. And at least one chain carbonate selected from the group consisting of carbonate, ethylpropyl carbonate, and butylethyl carbonate, and the ratio of the cyclic carbonate is within a range of 50% by volume or less in total. The electrolyte according to claim 1. 2. The electrolyte according to claim 1, wherein the electrolyte further contains at least one of LiPF ₆ , LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ . The electrolyte according to claim 1, further comprising an electrolyte salt at a rate of 0.4 mol / dm ³ or more and 2.0 mol / dm ³ or less. A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The battery includes a solvent containing an organic compound not containing oxygen (O). The battery according to claim 8, wherein the solvent includes at least one member selected from the group consisting of compounds represented by chemical formulas 14 to 25 as the organic compound.

(In the chemical formulas 14 to 25, X1 to X124 represent hydrogen (H), fluorine (F), chlorine (Cl), bromine (Br), amino group (—NH ₂ ), or a group shown in chemical formula 26; And Y2 each represent fluorine, chlorine or bromine, and m, n, a and b are integers satisfying 1 ≦ m ≦ 12, 0 ≦ a ≦ 2m + 1, 6 ≦ n ≦ 12 and 0 ≦ b ≦ 2n + 2, respectively. )

(In Chemical Formula 26, Z represents fluorine, chlorine or bromine, and p and c are integers satisfying 1 ≦ p ≦ 12 and 0 ≦ c ≦ 2p + 1, respectively) The battery according to claim 8, wherein a ratio of the organic compound in the solvent is in a range of 1% by volume to 90% by volume. The battery according to claim 8, wherein the solvent further includes at least one selected from the group consisting of a cyclic carbonate and a chain carbonate. The solvent includes at least one cyclic carbonate selected from the group consisting of propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, and vinyl ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, dipropyl. And at least one chain carbonate selected from the group consisting of carbonate, ethylpropyl carbonate, and butylethyl carbonate, and the ratio of the cyclic carbonate is within a range of 50% by volume or less in total. The battery according to claim 8. The battery according to claim 8, wherein the electrolyte further contains at least one of LiPF ₆ , LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ . The battery according to claim 8, wherein the electrolyte further contains an electrolyte salt at a rate of 0.4 mol / dm ³ or more and 2.0 mol / dm ³ or less. The battery according to claim 8, wherein the negative electrode includes at least one selected from the group consisting of simple elements, alloys, and compounds of metal elements or metalloid elements that can be combined with lithium (Li).   The battery according to claim 15, wherein the negative electrode includes an alloy of cobalt (Co) and tin (Sn) or an alloy of copper (Cu) and tin (Sn). The negative electrode includes at least one carbonaceous material in addition to at least one selected from the group consisting of the simple substance, an alloy, and a compound, the simple substance, the alloy, and the compound at 30 wt% to 75 wt%, and the carbonaceous material. The battery according to claim 15, further comprising a negative electrode mixture layer containing 15% by weight or more and 60% by weight or less.

Images