JP2005071678A - Battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery which can improve charging/discharging cycle characteristics in the battery which contains the capacity component of the capacity of a negative electrode due to the occlusion and separation of a light metal and a capacity component due to analysis and dissolution of the light metal. <P>SOLUTION: The battery includes a positive electrode 21 and a negative electrode 22 having a winding electrode 20 wound through a separator 23. The capacity of the negative electrode 22 contains a capacity component of Li due to occlusion/separation and a capacity component of Li metal due to the analysis/dissolution, and is displayed by its sum. The separator 23 impregnates an electrolyte in which an electrolyte salt is dissolved in a solvent. As the solvent, a fluoroethylene carbonate is used, and as the electrolyte salt, LiN[SO<SB>2</SB>(C<SB>2</SB>F<SB>5</SB>)]<SB>2</SB>is used. Thus, a stable and uniform film is formed on the negative electrode 22, and the decomposition reaction of the electrolyte and the reaction of the analyzed Li metal with the electrolyte are suppressed. Also, the deposition state of the Li metal is improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a battery provided with an electrolyte together with a positive electrode and a negative electrode, and in particular, the capacity of the negative electrode includes a capacity component due to insertion and extraction of light metals and a capacity component due to precipitation and dissolution of light metals, and is expressed by the sum thereof. Related to the battery.

  With the downsizing of electronic equipment, development of a battery capable of obtaining a high energy density is required. As a secondary battery capable of obtaining a high energy density, there is a lithium metal secondary battery that uses lithium metal for the negative electrode and uses precipitation and dissolution reactions of lithium metal for the negative electrode reaction. However, the lithium metal secondary battery has a large deterioration in discharge capacity when repeated charging and discharging, and its practical use is very difficult at present. This capacity deterioration is based on the fact that the lithium metal secondary battery uses the precipitation / dissolution reaction of lithium metal in the negative electrode. The cause is thought to be deactivated by the reaction.

Therefore, the present applicant has newly developed a secondary battery in which the capacity of the negative electrode includes a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium metal, and is represented by the sum thereof ( For example, see Patent Document 1.) In this method, a carbon material capable of inserting and extracting lithium ions is used for the negative electrode, and lithium metal is deposited on the surface of the carbon material during charging. According to this secondary battery, it can be expected to improve the charge / discharge cycle characteristics while achieving a high energy density.
International Publication No. 01/22519 Pamphlet

  However, in this secondary battery as well as the lithium metal secondary battery, the lithium precipitation / dissolution reaction is used, so that the lithium metal drop-off from the electrode and the reaction with the electrolyte are completely suppressed. Is extremely difficult, and the charge / discharge cycle characteristics are not sufficient.

  This invention is made | formed in view of this problem, The objective is to provide the battery which can improve charging / discharging cycling characteristics.

A battery according to the present invention includes an electrolyte solution together with a positive electrode and a negative electrode, and the capacity of the negative electrode includes a capacity component due to insertion and extraction of light metals and a capacity component due to precipitation and dissolution of light metals, and the sum thereof. The electrolytic solution contains fluoroethylene carbonate and lithium bis (pentafluoroethanesulfonyl) imide (LiN [SO ₂ (C ₂ F ₅ )] ₂ ).

  According to the battery of the present invention, since the electrolytic solution contains fluoroethylene carbonate and lithium bis (pentafluoroethanesulfonyl) imide, a stable and uniform film is formed on the surface of the negative electrode. Therefore, side reactions such as decomposition of the electrolytic solution on the negative electrode during charging can be suppressed. In addition, the current concentration on the negative electrode is alleviated and the precipitation and dissolution of the light metal is performed under this coating, so that the light metal precipitation form on the surface of the negative electrode can be improved, and the light metal and the electrolyte This reaction can also be suppressed. Therefore, the initial discharge capacity and the charge / discharge cycle characteristics can be improved. Furthermore, since both fluoroethylene carbonate and lithium bis (pentafluoroethanesulfonyl) imide are contained, a greater effect can be obtained than when they are contained alone.

  In particular, the content of fluoroethylene carbonate in the electrolytic solution is in the range of 0.5% by mass or more and 20% by mass or less, or the content of lithium bis (pentafluoroethanesulfonyl) imide in the electrolytic solution is set to 0.00. A higher effect can be obtained by setting it within the range of 5 mol / kg or more and 2.0 mol / kg or less.

  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 is a wound electrode in which a strip-like positive electrode 21 and a strip-like negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. It has a body 20. 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 winding 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 wound 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 wound electrode body 20. A positive electrode lead 25 made of aluminum (Al) or the like is connected to the positive electrode 21 of the spirally wound 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 part of the spirally wound 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, a positive electrode material capable of inserting and extracting lithium, which is a light metal, as a positive electrode active material.

As the positive electrode material capable of inserting and extracting lithium, for example, lithium-containing compounds such as lithium oxide, lithium sulfide, or an intercalation compound containing lithium are suitable, and a mixture of two or more of these is used. May be. In particular, in order to increase the energy density, a lithium composite oxide represented by the general formula Li _x MO ₂ or an intercalation compound containing lithium is preferable. Note that M is preferably one or more transition metals, specifically, at least one of cobalt (Co), nickel, manganese (Mn), iron, aluminum, vanadium (V), and titanium (Ti). preferable. x varies depending on the charge / discharge state of the battery, and is usually a value in the range of 0.05 ≦ x ≦ 1.10. In addition, manganese spinel (LiMn ₂ O ₄ ) having a spinel type crystal structure or lithium iron phosphate (LiFePO ₄ ) having an olivine type crystal structure is preferable because a high energy density can be obtained.

  Examples of the positive electrode material capable of inserting and extracting lithium include other metal compounds or polymer materials. Examples of the other metal compounds include oxides such as titanium oxide, vanadium oxide, and manganese dioxide, and disulfides such as titanium sulfide and molybdenum sulfide. Examples of the polymer material include polyaniline and polythiophene. It is done.

  The positive electrode mixture layer 21B also contains, for example, a conductive agent, and may further contain a binder as necessary. Examples of the conductive agent include carbon materials such as graphite, carbon black, and ketjen black. In addition to the carbon material, a metal material or a conductive polymer material may be used as long as it is a conductive material. Any one kind of conductive agent may be used, or two or more kinds may be mixed and used. Examples of the binder include synthetic rubber such as styrene butadiene rubber, fluorine rubber or ethylene propylene diene rubber, or a polymer material such as polyvinylidene fluoride. Any one kind of binder may be used, or two or more kinds may be mixed and used.

  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 (Cu) foil, a nickel foil, or a stainless steel foil.

  The negative electrode mixture layer 22B includes one or more negative electrode materials capable of inserting and extracting lithium, which is a light metal, as a negative electrode active material. The binder similar to the mixture layer 21B may be included.

  In this specification, light metal occlusion / release means that light metal ions are electrochemically occluded / released without losing their ionicity. This includes not only the case where the occluded light metal exists in a complete ionic state but also the case where it exists in a state that cannot be said to be a complete ionic state. As a case corresponding to these, for example, occlusion by an electrochemical intercalation reaction of light metal ions to graphite can be mentioned. Further, light metal occlusion in an alloy containing an intermetallic compound or light metal occlusion by formation of an alloy can also be mentioned.

  Examples of the negative electrode material capable of inserting and extracting lithium include carbon materials such as graphite, non-graphitizable carbon, and graphitizable carbon. These carbon materials are preferable because the change in crystal structure that occurs during charge / discharge is very small, a high charge / discharge capacity can be obtained, and good charge / discharge cycle characteristics can be obtained. In particular, graphite is preferable because it has a high electrochemical equivalent and can provide a high energy density.

As the graphite, for example, the true density is preferably 2.10 g / cm ³ or more, and more preferably 2.18 g / cm ³ or more. In order to obtain such a true density, it is necessary that the (002) plane C-axis crystallite thickness is 14.0 nm or more. The (002) plane spacing is preferably less than 0.340 nm, and more preferably in the range of 0.335 nm to 0.337 nm. The graphite may be natural graphite or artificial graphite.

As non-graphitizable carbon, (002) plane spacing is 0.37 nm or more, true density is less than 1.70 g / cm ³ , and in differential thermal analysis (DTA) in air What does not show an exothermic peak at 700 ° C. or higher is preferable.

  Examples of the negative electrode material capable of inserting and extracting lithium include a single element, an alloy, or a compound of a metal element or a metalloid element capable of forming an alloy with lithium. These are preferable because a high energy density can be obtained. In particular, when used together with a carbon material, a high energy density can be obtained and excellent charge / discharge cycle characteristics can be obtained. 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 capable of forming an alloy with lithium include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth ( Bi), cadmium (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y) or hafnium ( Hf). These alloys or compounds, such as 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 capable of forming an alloy 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, alloy or compound of a group 14 metal element or metalloid element in the long-period periodic table is preferable, and silicon or tin, or an alloy or compound thereof is particularly preferable. These may be crystalline or amorphous.

Specific examples of such alloys or compounds include LiAl, AlSb, CuMgSb, 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, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 < _{v ≦ 2), SnO w (} 0 <w ≦ 2), there is such SnSiO _3, LiSiO or LiSnO.

Examples of the negative electrode material capable of inserting and extracting lithium further include other metal compounds or polymer materials. Examples of other metal compounds include oxides such as iron oxide, ruthenium oxide, and molybdenum oxide, and LiN _3. Examples of polymer materials include polyacetylene, polyaniline, and polypyrrole.

  Further, in this secondary battery, lithium metal starts to deposit on the negative electrode 22 when the open circuit voltage (that is, the battery voltage) is lower than the overcharge voltage during the charging process. That is, lithium metal is deposited on the negative electrode 22 in a state where the open circuit voltage is lower than the overcharge voltage, and the capacity of the negative electrode 22 includes a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium metal. And is represented by the sum. Therefore, in this secondary battery, both the negative electrode material capable of inserting and extracting lithium and lithium metal function as a negative electrode active material, and the negative electrode material capable of inserting and extracting lithium is lithium metal. It is a base material for precipitation.

  The overcharge voltage refers to the open circuit voltage when the battery is overcharged. For example, the “lithium secondary battery” is one of the guidelines established by the Japan Storage Battery Industry Association (Battery Industry Association). Refers to a voltage that is higher than the open circuit voltage of a “fully charged” battery as defined and defined in the “Safety Evaluation Criteria Guidelines” (SBA G1101). In other words, it refers to a voltage higher than the open circuit voltage after charging using the charging method, standard charging method, or recommended charging method used when determining the nominal capacity of each battery. Specifically, this secondary battery is fully charged when, for example, the open circuit voltage is 4.2 V, and lithium can be occluded and released in a part of the open circuit voltage in the range of 0 V to 4.2 V. Lithium metal is deposited on the surface of the possible negative electrode material.

  Thereby, in this secondary battery, while being able to obtain a high energy density, it is possible to improve charge / discharge cycle characteristics and quick charge characteristics. This is the same as a conventional lithium metal secondary battery using lithium metal or a lithium alloy as a negative electrode in that lithium metal is deposited on the negative electrode 22, but a negative electrode material capable of inserting and extracting lithium. It is considered that this is because the following advantages are caused by depositing lithium metal.

  First, in a conventional lithium metal secondary battery, it is difficult to deposit lithium metal uniformly, which causes deterioration of charge / discharge cycle characteristics, but a negative electrode capable of inserting and extracting lithium. Since the material generally has a large surface area, this secondary battery can deposit lithium metal uniformly. Secondly, in the conventional lithium metal secondary battery, the volume change accompanying the precipitation and dissolution of lithium metal is large, which also causes deterioration of the charge / discharge cycle characteristics. Lithium metal is also deposited in the gaps between the particles of the negative electrode material that can be detached, so that the volume change is small. Thirdly, the larger the amount of lithium metal deposited / dissolved in the conventional lithium metal secondary battery, the greater the above-mentioned problem. In this secondary battery, however, it depends on the negative electrode material capable of inserting and extracting lithium. Since insertion and extraction of lithium also contributes to the charge / discharge capacity, the amount of lithium metal deposited and dissolved is small although the battery capacity is large. Fourthly, in a conventional lithium metal secondary battery, when rapid charging is performed, lithium metal is deposited more unevenly, so that the charge / discharge cycle characteristics are further deteriorated. Since lithium is occluded in the negative electrode material capable of inserting and extracting lithium, rapid charging becomes possible.

  In order to obtain these advantages more effectively, for example, the maximum deposition capacity of the lithium metal deposited on the negative electrode 22 at the maximum voltage before the open circuit voltage becomes the overcharge voltage is to insert and extract lithium. It is preferable that it is 0.05 times or more and 3.0 times or less of the charge capacity capacity of the negative electrode material which can carry out. This is because if the amount of deposited lithium metal is too large, the same problem as in the conventional lithium metal secondary battery occurs, and if the amount is too small, the charge / discharge capacity cannot be sufficiently increased. For example, the discharge capacity capability of the negative electrode material capable of inserting and extracting lithium is preferably 150 mAh / g or more. This is because the larger the lithium occlusion / release ability, the smaller the amount of lithium metal deposited. The charge capacity capability of the negative electrode material can be obtained, for example, from the amount of electricity when a negative electrode using lithium metal as a counter electrode and the negative electrode material as a negative electrode active material is charged to 0 V by a constant current / constant voltage method. The discharge capacity capability of the negative electrode material is obtained, for example, from the amount of electricity when the current is discharged to 2.5 V over 10 hours or more by the constant current method.

  The separator 23 separates the positive electrode 21 and the negative electrode 22 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. The separator 23 is made of, for example, a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramic, and has a structure in which two or more kinds of porous films are laminated. It may be said. Among these, a porous film made of polyolefin is preferable because it is excellent in short-circuit preventing effect and can improve the safety of the battery due to the shutdown effect. In particular, polyethylene is preferable as a material constituting the separator 23 because a shutdown effect can be obtained within a range of 100 ° C. or higher and 160 ° C. or lower and the electrochemical stability is excellent. Polypropylene is also preferable, and any other resin having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.

  The electrolytic solution impregnated in the separator 23 includes a liquid solvent, for example, a nonaqueous solvent such as an organic solvent, an electrolyte salt dissolved in the nonaqueous solvent, and an additive as necessary. The liquid non-aqueous solvent is made of, for example, a non-aqueous compound and has an intrinsic viscosity at 25 ° C. of 10.0 mPa · s or less. In addition, the intrinsic viscosity in a state where the electrolyte salt is dissolved may be 10.0 mPa · s or less. When a solvent is formed by mixing a plurality of types of nonaqueous compounds, the intrinsic viscosity in the mixed state is What is necessary is just 10.0 mPa * s or less.

  Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4 -Methyl-1,3-dioxolane, methyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropyronitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide or And trimethyl phosphate.

  Especially, in order to implement | achieve the outstanding charging / discharging capacity | capacitance characteristic and charging / discharging cycling characteristics, it is preferable that at least 1 sort (s) of ethylene carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is included.

  The nonaqueous solvent contains fluoroethylene carbonate. This fluoroethylene carbonate forms a stable and uniform film on the surface of the negative electrode 22, specifically, the negative electrode material capable of inserting and extracting lithium. By this coating, side reactions such as decomposition of the electrolytic solution on the negative electrode 22 during charging are suppressed. Further, current concentration on the negative electrode 22 is alleviated, and precipitation and dissolution of lithium metal are performed under this coating, so that generation of dendrites by lithium metal on the surface of the negative electrode 22 is suppressed. It is considered that the precipitation form of is improved and the reaction between the lithium metal and the electrolytic solution is also suppressed.

  The content of fluoroethylene carbonate in the electrolytic solution is preferably in the range of 0.5% by mass or more and 20% by mass or less. This is because a higher effect can be obtained within this range.

  The electrolyte salt contains lithium bis (pentafluoroethanesulfonyl) imide. This lithium bis (pentafluoroethanesulfonyl) imide, like fluoroethylene carbonate, forms a stable and uniform film on the surface of the negative electrode 22, specifically, the negative electrode material capable of inserting and extracting lithium. It is. In this secondary battery, by including both fluoroethylene carbonate and lithium bis (pentafluoroethanesulfonyl) imide, they act synergistically, and the initial capacity and charge / discharge cycle characteristics are higher than when they are included alone. Can be improved.

  The content of lithium bis (pentafluoroethanesulfonyl) imide in the electrolytic solution is preferably in the range of 0.5 mol / kg to 2.0 mol / kg. If the content of lithium bis (pentafluoroethanesulfonyl) imide is too small, the coating is not sufficiently formed, the formation of dendrites by lithium metal is not sufficiently suppressed, and the charge / discharge cycle characteristics may be deteriorated. This is because if the amount is too large, the viscosity of the electrolytic solution increases and the ionic conductivity decreases, so that the initial capacity and charge / discharge cycle characteristics may decrease.

The electrolyte salt may also contain any one or more of other lithium salts in order to obtain characteristics according to the purpose. Examples of other lithium salts include lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), and lithium tetrafluoroborate (LiBF ₄ ). , Lithium trifluoromethanesulfonate (LiSO ₃ CF ₃ ), bis (trifluoromethanesulfonyl) imido lithium (LiN [SO ₂ (CF ₃ )] ₂ ), tris (trifluoromethanesulfonyl) methyl lithium (LiC [SO ₂ (CF _{3 3} ), lithium chloride (LiCl) or lithium bromide (LiBr).

  Instead of the electrolytic solution, a gel electrolyte in which an electrolytic solution is held in a polymer compound may be used. The electrolyte solution (that is, liquid solvent and electrolyte salt) is as described above. Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and polyhexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, poly Examples thereof include siloxane, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene, and polycarbonate. In particular, from the viewpoint of electrochemical stability, it is desirable to use a polymer compound having a polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene or polyethylene oxide structure. Although the amount of the polymer compound added to the electrolytic solution varies depending on the compatibility between the two, it is usually preferable to add a polymer compound corresponding to 5% by mass to 50% by mass of the electrolytic solution.

  In this secondary battery, when charged, lithium ions are released from the positive electrode mixture layer 21B, and first, the lithium contained in the negative electrode mixture layer 22B is occluded and released through the electrolyte impregnated in the separator 23. Can be occluded by the negative electrode material. If the battery is further charged, the charge capacity exceeds the charge capacity of the negative electrode material that can occlude and desorb lithium when the open circuit voltage is lower than the overcharge voltage, and lithium can be occluded and desorbed. Lithium metal begins to deposit on the surface of the negative electrode material. Thereafter, lithium metal continues to deposit on the negative electrode 22 until charging is completed. As a result, the appearance of the negative electrode mixture layer 22B changes from black to golden or even silvery when graphite is used as a negative electrode material capable of inserting and extracting lithium, for example.

  Next, when discharging is performed, first, lithium metal deposited on the negative electrode 22 is eluted as ions, and is inserted into the positive electrode mixture layer 21 </ b> B through the electrolyte impregnated in the separator 23. When the discharge is further continued, lithium ions occluded in the negative electrode material capable of inserting and extracting lithium in the negative electrode mixture layer 22B are released and inserted into the positive electrode mixture layer 21B through the electrolyte. Therefore, in this secondary battery, the characteristics of both conventional so-called lithium metal secondary batteries and lithium ion secondary batteries, that is, high energy density and good charge / discharge cycle characteristics can be obtained.

  In particular, in the present embodiment, since the electrolytic solution contains fluoroethylene carbonate and lithium bis (pentafluoroethanesulfonyl) imide, the surface of the negative electrode material capable of inserting and extracting lithium is stable and A uniform film is formed. Therefore, side reactions such as decomposition of the electrolytic solution on the negative electrode 22 during charging are suppressed. Further, current concentration on the negative electrode 22 is alleviated, and lithium deposition and dissolution are performed under this coating, so that the lithium metal deposition form on the surface of the negative electrode 22 is improved, and lithium metal and electrolysis are obtained. Reaction with the liquid is also suppressed. Furthermore, since both fluoroethylene carbonate and lithium bis (pentafluoroethanesulfonyl) imide are contained, they have a synergistic effect, and the above action is expressed more strongly than when they are contained alone.

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

  First, for example, a positive electrode material capable of inserting and extracting lithium is mixed with a conductive agent and a binder to prepare a positive electrode mixture, and the positive electrode mixture is mixed with a solvent such as N-methyl-2-pyrrolidone. To make a positive electrode mixture slurry. 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.

  Further, for example, a negative electrode material capable of inserting and extracting lithium and a binder are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone. To make 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.

  Subsequently, the positive electrode lead 25 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector 22A by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are wound through the separator 23, and 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. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11. After the positive electrode 21 and the negative electrode 22 are accommodated in the battery can 11, an electrolyte 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 shown in FIG. 1 is completed.

  As described above, in the present embodiment, since the electrolytic solution contains fluoroethylene carbonate and lithium bis (pentafluoroethanesulfonyl) imide, the surface of the negative electrode material capable of inserting and extracting lithium is stable and A uniform film is formed. Therefore, side reactions such as decomposition of the electrolytic solution on the negative electrode 22 during charging can be suppressed. In addition, current concentration on the negative electrode 22 is alleviated, and precipitation and dissolution of lithium are performed under this coating, so that the lithium precipitation form on the surface of the negative electrode 22 can be improved, and lithium and electrolysis can be achieved. Reaction with the liquid can also be suppressed. Therefore, the initial discharge capacity and the charge / discharge cycle characteristics can be improved. Furthermore, since both fluoroethylene carbonate and lithium bis (pentafluoroethanesulfonyl) imide are contained, a greater effect can be obtained than when they are contained alone.

In particular, the content of fluoroethylene carbonate in the electrolytic solution is in the range of 0.5% by mass to 20% by mass, or the content of LiN [SO ₂ (C ₂ F ₅ )] _{2 in} the electrolytic solution. A higher effect can be obtained by setting the value in the range of 0.5 mol / kg to 2.0 mol / kg.

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

As Examples 1 to 12 and Comparative Examples 1 to 6 for Examples 1 to 12, secondary batteries were manufactured as follows. First, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed at a ratio of Li ₂ CO ₃ : CoCO ₃ = 0.5: 1 (molar ratio), and 5 ° C. at 900 ° C. in the air. The lithium-cobalt composite oxide was obtained by firing for a period of time. When the obtained lithium / cobalt composite oxide was subjected to X-ray diffraction measurement, it was in good agreement with the LiCoO ₂ peak registered in the JCPDS file. Next, the lithium-cobalt composite oxide was pulverized to form a powder having a cumulative 50% particle size of 15 μm obtained by a laser diffraction method, and used as a positive electrode active material.

  Subsequently, 95% by mass of this lithium / cobalt composite oxide powder and 5% by mass of lithium carbonate powder are mixed, and 94% by mass of this mixture, 3% by mass of ketjen black as a conductive agent, and a binder. A positive electrode mixture was prepared by mixing 3% by mass of polyvinylidene fluoride. Next, this positive electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a paste-like positive electrode mixture slurry, which is uniformly applied to both surfaces of a positive electrode current collector 21A made of a strip-shaped aluminum foil having a thickness of 20 μm. And dried and compression molded to form the positive electrode mixture layer 21B, and the positive electrode 21 having a total thickness of 150 μm was produced.

  Further, a granular graphite powder having an average particle diameter of 25 μm was prepared as a negative electrode active material, and 90% by mass of the granular graphite powder and 10% by mass of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture. Next, this negative electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a paste-like negative electrode mixture slurry, which is uniformly applied to both surfaces of a negative electrode current collector 22A made of a strip-shaped copper foil having a thickness of 15 μm. The negative electrode mixture layer 22B was formed by compression molding and the negative electrode 22 having a total thickness of 160 μm was produced. The capacity ratio of the opposing surfaces of the positive electrode 21 and the negative electrode 22 is expressed by the sum of the capacity of the negative electrode 22 including the capacity component due to insertion and extraction of lithium and the capacity component due to precipitation and dissolution of lithium. Thus, positive electrode capacity: negative electrode capacity = 130: 100.

  After producing the positive electrode 21 and the negative electrode 22, respectively, the positive electrode 21 and the negative electrode 22 are laminated in the order of the negative electrode 22, the separator 23, the positive electrode 21, and the separator 23 with a separator 23 made of a microporous polyethylene stretched film having a thickness of 25 μm. After that, it was wound many times to produce a jelly roll type wound electrode body 20 having an outer diameter of 14 mm.

  Next, the wound electrode body 20 was housed inside an iron battery can 11 on which nickel plating was applied. At that time, the insulating plates 12 and 13 are arranged on the upper and lower surfaces of the wound electrode body 20, the positive electrode lead 25 made of aluminum is led out from the positive electrode current collector 21A and welded to the safety valve mechanism 15, and the negative electrode made of nickel The lead 26 was led out from the negative electrode current collector 22A and welded to the battery can 11. Subsequently, an electrolytic solution was injected into the battery can 11. The electrolytic solution used was an electrolyte salt dissolved in a solvent.

  At that time, in Examples 1 to 12 and Comparative Examples 1 to 6, the types of solvents and electrolyte salts and their contents were changed as shown in Table 1 or Table 2. In Tables 1 and 2, EC represents ethylene carbonate, PC represents propylene carbonate, FEC represents fluoroethylene carbonate, TFPC represents trifluoropropylene carbonate, and BTFEC represents butyl trifluoroethylene carbonate.

  A charge / discharge test was performed on the fabricated secondary batteries of Examples 1 to 12 and Comparative Examples 1 to 6 to determine an initial discharge capacity and a discharge capacity retention rate. At that time, charging was performed at a constant current of 1200 mA until the battery voltage reached 4.2 V, and then at a constant voltage of 4.2 V until the total charging time reached 4 hours. Discharging was performed at a constant current of 1200 mA until the battery voltage reached 2.75V. The initial discharge capacity is the discharge capacity at the first cycle, and the discharge capacity maintenance ratio is the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle, that is, (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × Calculated as 100. The results are shown in Table 1 or Table 2.

  As can be seen from Table 1, according to Examples 1 to 7 using fluoroethylene carbonate, both the initial discharge capacity and the discharge capacity retention rate can be improved as compared with Comparative Examples 1 to 3 which were not used. It was. On the other hand, in Comparative Example 4 using trifluoropropylene carbonate and Comparative Example 5 using butyl trifluoroethylene carbonate, both the initial discharge capacity and the discharge capacity retention rate were lower than those of Comparative Examples 1 to 3. Further, as can be seen from Table 2, according to Examples 8 to 12, both the initial discharge capacity and the discharge capacity retention rate could be improved as compared with Comparative Examples 1, 2, and 6.

  That is, it has been found that if the electrolytic solution contains fluoroethylene carbonate and lithium bis (pentafluoroethanesulfonyl) imide, the initial discharge capacity and charge / discharge cycle characteristics can be improved.

  Furthermore, as can be seen from a comparison of Examples 1 to 7, the discharge capacity retention rate improved as the content of fluoroethylene carbonate in the electrolyte increased, and showed a tendency to decrease after showing a maximum value. That is, it has been found that if the content of fluoroethylene carbonate in the electrolytic solution is 0.5% by mass or more and 20% by mass or less, the charge / discharge cycle characteristics can be further improved.

  In addition, as can be seen by comparing Examples 8 to 12, the discharge capacity retention ratio is improved when the content of lithium bis (pentafluoroethanesulfonyl) imide in the electrolytic solution is increased, and then decreased after showing the maximum value. There was also a trend. That is, it is understood that even when the content of lithium bis (pentafluoroethanesulfonyl) imide in the electrolytic solution is 0.5 mol / kg or more and 2.0 mol / kg or less, the charge / discharge cycle characteristics can be further improved. It was.

  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 embodiments and examples, the case where lithium is used as a light metal has been described. However, other group 1 elements in a long-period periodic table such as sodium (Na) or potassium (K), or magnesium or calcium The present invention can also be applied to the case of using a Group 2 element in the long-period periodic table such as (Ca), other light metals such as aluminum, lithium, or an alloy thereof, and obtain the same effect. be able to. At that time, a negative electrode material, a positive electrode material, a non-aqueous solvent, or the like capable of inserting and extracting a light metal is selected according to the light metal.

  However, it is preferable to use lithium or an alloy containing lithium as a light metal because voltage compatibility with a lithium ion secondary battery currently in practical use is high. In addition, when using an alloy containing lithium as a light metal, there is a substance that can form an alloy with lithium in the electrolyte, and the alloy may be formed at the time of precipitation, or an alloy with lithium is formed on the negative electrode. Possible materials are present and may form an alloy during precipitation.

  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. Examples of other electrolytes include, for example, a mixture of an ion conductive inorganic compound made of ion conductive ceramics, ion conductive glass, ionic crystal, or the like and an electrolyte solution, or these ion conductive inorganic compound and a gel-like one. What mixed the polymer solid electrolyte which disperse | distributed electrolyte salt to the electrolyte or the polymer compound which has ion conductivity is mentioned.

  Further, in the above-described embodiments and examples, the cylindrical secondary battery having a winding structure has been described. However, the present invention can be applied to an elliptical or polygonal secondary battery having a winding structure, or a positive electrode and The present invention can be similarly applied to a secondary battery having a structure in which the negative electrode is folded or stacked. In addition, the present invention can also be applied to a so-called coin type, button type, or square type secondary battery. Furthermore, not only the secondary battery but also the primary battery can be applied.

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 winding electrode body shown in FIG.

Explanation of symbols

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

Claims (5)

A battery comprising an electrolyte solution together with a positive electrode and a negative electrode,
The capacity of the negative electrode includes a capacity component due to insertion and extraction of light metal, and a capacity component due to precipitation and dissolution of light metal, and is represented by the sum thereof.
The battery, wherein the electrolytic solution contains fluoroethylene carbonate and lithium bis (pentafluoroethanesulfonyl) imide (LiN [SO ₂ (C ₂ F ₅ )] ₂ ).   2. The battery according to claim 1, wherein the content of fluoroethylene carbonate in the electrolytic solution is in a range of 0.5 mass% to 20 mass%.   2. The battery according to claim 1, wherein a content of lithium bis (pentafluoroethanesulfonyl) imide in the electrolytic solution is in a range of 0.5 mol / kg to 2.0 mol / kg.   The battery according to claim 1, wherein the negative electrode includes a negative electrode material capable of inserting and extracting light metals. The battery according to claim 4, wherein the negative electrode includes at least one selected from the group consisting of graphite, graphitizable carbon, and non-graphitizable carbon.

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