JP2005197174A - Battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery capable of preventing capacity deterioration in charge preservation. <P>SOLUTION: A positive electrode 12 and a negative electrode 14 are stacked by interlaying a separator 15 with an electrolyte impregnated. The capacity of the negative electrode 14 includes a capacity component by storage/separation of Li and a capacity component by deposition/dissolution of Li, and is expressed by the sum of them. Carbonate is added to the positive electrode 12 in addition to a positive electrode active material, and the carbonate is dissolved in the electrolyte to form a coating film 14C on a surface of the negative electrode 14. Therefore, Li deposited on the surface of the negative electrode 14 reacts with the electrolyte or the like to prevent the capacity from being deteriorated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a battery in which the capacity of a 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 represented by the sum thereof.

  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, and the deposited lithium metal falls off the electrode or reacts with the electrolyte during charge / discharge. This is considered to be caused by inactivation.

Therefore, the present applicant has newly recharged a secondary battery in which the capacity of the negative electrode includes a capacity component due to insertion and extraction of lithium (Li) and a capacity component due to precipitation and dissolution of lithium metal, and is represented by the sum thereof. Developed (see, for example, 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, since this secondary battery also utilizes a lithium precipitation / dissolution reaction, when stored in a charged state, that is, with lithium metal deposited on the surface of the negative electrode, the lithium metal on the surface becomes the electrolyte. There was a problem that the capacity was deteriorated due to reaction and inactivation.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a battery capable of suppressing capacity deterioration during charge storage.

  A first battery according to the present invention includes an electrolyte 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 is represented by the sum thereof. The positive electrode includes a positive electrode active material and a carbonate.

  The second battery according to the present invention includes an electrolyte 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 is expressed by the sum thereof. The negative electrode has a film containing carbonate on the surface.

  A third battery according to the present invention includes an electrolyte 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 metal and a capacity component due to precipitation and dissolution of light metal, and is represented by the sum thereof. The electrolyte contains carbonate ions.

  According to the first battery of the present invention, since the positive electrode contains carbonate, the carbonate can be dissolved in the electrolyte and a film can be formed on the surface of the negative electrode. Therefore, even if it preserve | saves in the charged state, the side reaction with the lithium metal and electrolyte which precipitated on the negative electrode can be suppressed, and capacity | capacitance degradation at the time of charge preservation | save can be suppressed.

  According to the second battery of the present invention, since a film containing carbonate is formed on the surface of the negative electrode, even if stored in a charged state, side reactions between lithium metal deposited on the negative electrode and the electrolyte are suppressed. It is possible to suppress the capacity deterioration during charge storage.

  According to the third battery of the present invention, since the electrolyte contains carbonate ions, a film containing carbonate ions can be formed on the surface of the negative electrode. Therefore, even if it preserve | saves in the charged state, the side reaction with the lithium metal and electrolyte which precipitated on the negative electrode can be suppressed, and capacity | capacitance degradation at the time of charge preservation | save can be suppressed.

  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 coin-type battery. A disc-shaped positive electrode 12 accommodated in the outer can 11 and a disc-shaped negative electrode 14 accommodated in the outer cup 13 are used as an electrolyte. Is laminated through a separator 15 impregnated with. The peripheral portions of the outer can 11 and the outer cup 13 are sealed by caulking through an insulating gasket 16.

  The outer can 11 is made of, for example, a stainless steel base material coated with aluminum (Al) on the inside. The exterior cup 13 is made of stainless steel, for example.

  The positive electrode 12 has, for example, a configuration in which a positive electrode active material layer 12B is provided on one surface of a positive electrode current collector 12A having a pair of opposed surfaces. The positive electrode current collector 12A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode active material layer 12B includes, for example, a positive electrode material capable of inserting and extracting lithium, which is a light metal.

As a positive electrode material capable of inserting and extracting lithium, for example, lithium-containing compounds such as lithium oxide, lithium phosphorus oxide, lithium sulfide, or an intercalation compound containing lithium are suitable, and two or more kinds are mixed. May be used. 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, cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), aluminum, vanadium (V), and titanium (Ti). At least one of them is preferred. 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, LiMn ₂ O ₄ having a spinel type crystal structure, LiFePO ₄ having an olivine type crystal structure, and the like are also preferable because a high energy density can be obtained.

  The positive electrode active material layer 12B also includes, for example, a conductive agent, and may further include a binder as necessary. Examples of the conductive agent include carbon materials such as graphite, carbon black, and ketjen black, and one kind or a mixture of two or more kinds is used. 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. 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, and one or two or more kinds are used in combination. It is done.

The positive electrode active material layer 12B preferably further contains a carbonate. This is because the side reaction in the negative electrode 14 can be suppressed by dissolving the carbonate in the electrolyte and forming a film on the surface of the negative electrode 14. Although the kind of carbonate is not limited, it is preferable to use a light metal carbonate related to the electrode reaction in the positive electrode 12 and the negative electrode 14. For example, in the secondary battery according to this embodiment, lithium carbonate (Li ₂ CO ₃ ) is preferable because lithium is used for the electrode reaction. Lithium ions generated by dissolution can also be used for electrode reactions, and in the case of other light metal ions, other light metal ions are trapped in the negative electrode material that absorbs and desorbs lithium and cannot be released. This is because there is no possibility of adversely affecting the battery reaction such as a decrease in sites where lithium ions are inserted and extracted. However, potassium carbonate (K ₂ CO ₃ ) or sodium carbonate (Na ₂ CO ₃ ) may be used.

  The negative electrode 14 has, for example, a configuration in which a negative electrode active material layer 14B is provided on one surface of a negative electrode current collector 14A having a pair of opposed surfaces. The negative electrode current collector 14A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.

  The negative electrode active material layer 14B is configured to include any one or two or more negative electrode materials capable of inserting and extracting lithium, which is a light metal. A binder similar to that described above 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. If it is artificial graphite, for example, it can be obtained by carbonizing an organic material, subjecting it to high-temperature heat treatment, and pulverizing and classifying it. In the high temperature heat treatment, for example, carbonization is performed at 300 ° C. to 700 ° C. in an inert gas stream such as nitrogen (N ₂ ) as necessary, and the temperature is increased to 900 ° C. to 1500 ° C. at a rate of 1 ° C. to 100 ° C. per minute. This temperature is maintained for about 0 to 30 hours and calcined, and heated to 2000 ° C. or higher, preferably 2500 ° C. or higher, and this temperature is maintained for an appropriate time.

  As the organic material to be a starting material, coal or pitch can be used. For pitch, for example, tars obtained by thermally decomposing coal tar, ethylene bottom oil or crude oil at high temperature, asphalt, etc. (vacuum distillation, atmospheric distillation or steam distillation), thermal polycondensation, extraction, There are those obtained by chemical polycondensation, those produced when wood is refluxed, polyvinyl chloride resins, polyvinyl acetate, polyvinyl butyrate or 3,5-dimethylphenol resins. These coals or pitches exist as liquids at a maximum temperature of about 400 ° C. during carbonization, and the aromatic rings are condensed and polycyclic by being held at that temperature, and are in a stacked orientation state. It becomes a solid carbon precursor, that is, semi-coke (liquid phase carbonization process).

  Examples of organic materials include condensed polycyclic hydrocarbon compounds such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, perylene, pentaphen, and pentacene, or derivatives thereof (for example, carboxylic acids, carboxylic anhydrides, and carboxylic acids of the above-described compounds). Imide), or mixtures thereof. Furthermore, condensed heterocyclic compounds such as acenaphthylene, indole, isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine, phenanthridine, or a derivative thereof, or a mixture thereof can also be used.

  The pulverization may be performed either before or after carbonization, calcination, or during the temperature raising process before graphitization. In these cases, heat treatment for graphitization is finally performed in a powder state. However, in order to obtain a graphite powder having a high bulk density and high fracture strength, it is preferable to form a raw material and then perform a heat treatment, and pulverize and classify the obtained graphitized molded body.

  For example, when producing a graphitized molded body, coke as a filler and a binder pitch as a molding agent or a sintering agent are mixed and molded, and then the molded body is heat-treated at a low temperature of 1000 ° C. or lower. After repeating the firing step and the pitch impregnation step of impregnating the binder pitch melted in the fired body several times, heat treatment is performed at a high temperature. The impregnated binder pitch is carbonized and graphitized in the above heat treatment process. Incidentally, in this case, since filler (coke) and binder pitch are used as raw materials, they are graphitized as polycrystals, and sulfur and nitrogen contained in the raw materials are generated as a gas during heat treatment. A minute hole is formed in the path. Therefore, the vacancy makes it easy for the occlusion / release reaction of lithium to proceed, and there is also an advantage that the treatment efficiency is industrially high. In addition, as a raw material of a molded object, you may use the filler which has a moldability and sintering property in itself. In this case, it is not necessary to use a binder pitch.

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.

  Such non-graphitizable carbon can be obtained, for example, by heat-treating an organic material at about 1200 ° C., and pulverizing and classifying it. In the heat treatment, for example, carbonization is performed at 300 ° C. to 700 ° C. as necessary (solid-phase carbonization process), and then the temperature is raised to 900 ° C. to 1300 ° C. at a rate of 1 ° C. to 100 ° C. per minute. It is performed by holding for about 30 hours. The pulverization may be performed before or after carbonization or during the temperature raising process.

  As the organic material to be the starting material, for example, furfuryl alcohol or furfural polymer, copolymer, or furan resin that is a copolymer of these polymers and other resins can be used. Crustaceans including phenolic resins, acrylic resins, halogenated vinyl resins, polyimide resins, polyamideimide resins, polyamide resins, conjugated resins such as polyacetylene or polyparaphenylene, cellulose or derivatives thereof, coffee beans, bamboos, and chitosan Also, biocellulose using bacteria can be used. Furthermore, a functional group containing oxygen (O) is introduced into petroleum pitch having a hydrogen atom (H) to carbon atom (C) ratio H / C of, for example, 0.6 to 0.8 (so-called oxygen crosslinking). The compound prepared can also be used.

  The oxygen content in this compound is preferably 3% or more, more preferably 5% or more. This is because the oxygen content affects the crystal structure of the carbon material, and the physical properties of the non-graphitizable carbon can be increased at a content higher than this, and the capacity of the negative electrode 14 can be improved. Incidentally, petroleum pitch, for example, tar (obtained by pyrolyzing coal tar, ethylene bottom oil or crude oil, etc.) at high temperature, or asphalt is distilled (vacuum distillation, atmospheric distillation or steam distillation), It can be obtained by condensation, extraction or chemical polycondensation. Examples of the method for forming an oxidative bridge include a wet method in which an aqueous solution such as nitric acid, sulfuric acid, hypochlorous acid, or a mixed acid thereof is reacted with petroleum pitch, or an oxidizing gas such as air or oxygen is reacted with petroleum pitch. Or a dry method in which a solid reagent such as sulfur, ammonium nitrate, ammonia persulfate, or ferric chloride is reacted with petroleum pitch.

  Note that the organic material that is a starting material is not limited to these, and any other organic material may be used as long as it is an organic material that can be converted into non-graphitizable carbon through a solid-phase carbonization process by oxygen crosslinking treatment or the like.

  As the non-graphitizable carbon, in addition to those produced using the above-mentioned organic materials as starting materials, there are also compounds mainly composed of phosphorus (P), oxygen and carbon described in JP-A-3-137010. Since the physical property parameters described above are shown, it 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 such metal elements or metalloid elements include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), and cadmium. (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y) or hafnium (Hf). It is done. These alloys or compounds, for example, those represented by the chemical formula Ma _s Mb _t Li _u or a chemical formula Ma _p Mc _q Md _r,. In these chemical formulas, Ma represents at least one of a metal element and a metalloid element capable of forming an alloy with lithium, Mb represents at least one of a metal element and a metalloid element other than lithium and Ma, Mc represents at least one of nonmetallic elements, and Md represents at least one of metallic elements and metalloid elements other than Ma. The values of s, t, u, p, q, and r are s> 0, t ≧ 0, u ≧ 0, p> 0, q> 0, and r ≧ 0, respectively.

  Among these, a simple substance, alloy or compound of the group 4B metal element or metalloid element in the short 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, during the charging process, lithium metal starts to deposit on the negative electrode 14 when the open circuit voltage (that is, the battery voltage) is lower than the overcharge voltage. That is, lithium metal is deposited on the negative electrode 14 in a state where the open circuit voltage is lower than the overcharge voltage, and the capacity of the negative electrode 14 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 expressed as its 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 a base material on which lithium metal is deposited. It has become.

  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, in this secondary battery, for example, the battery is fully charged when the open circuit voltage is 4.2 V, and the negative electrode is capable of inserting and extracting lithium 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 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 the conventional lithium secondary battery using lithium metal or a lithium alloy for the negative electrode in that lithium metal is deposited on the negative electrode 14, but the lithium metal is deposited on the negative electrode material capable of inserting and extracting lithium. It is considered that this is because the following advantages arise.

  First, it is difficult to deposit lithium metal uniformly in the conventional lithium secondary battery, which causes deterioration of charge / discharge cycle characteristics. However, negative electrode materials capable of inserting and extracting lithium are generally used. The secondary battery has a large surface area, so that lithium metal can be uniformly deposited in this secondary battery. Secondly, in the conventional lithium secondary battery, the volume change accompanying the precipitation and dissolution of lithium metal was large, which also caused deterioration of the charge / discharge cycle characteristics, but in this secondary battery, lithium was occluded / released. Lithium metal also deposits in the gaps between possible negative electrode material particles, so there is little volume change. Thirdly, in the conventional lithium secondary battery, the larger the amount of lithium metal deposited / dissolved, the greater the above problem. However, in this secondary battery, the insertion / extraction of lithium by an anode material capable of occluding and releasing lithium. Since detachment also contributes to the charge / discharge capacity, the amount of lithium metal deposited / dissolved is small when the battery capacity is large. Fourthly, in the conventional lithium secondary battery, when rapid charging is performed, lithium metal is deposited more unevenly, so that the charge / discharge cycle characteristics are further deteriorated. Lithium is occluded in the negative electrode material capable of occluding and releasing lithium, so that rapid charging becomes possible.

  In order to obtain these advantages more effectively, for example, the maximum deposition capacity of lithium metal deposited on the negative electrode 14 at the maximum voltage before the open circuit voltage becomes the overcharge voltage can absorb and desorb lithium. It is preferably 0.05 times or more and 3.0 times or less of the charge capacity capacity of the negative electrode material. This is because when the amount of deposited lithium metal is too large, the same problem as that of the conventional lithium secondary battery occurs, and when 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.

  Further, for example, a coating 14C containing carbonate is formed on the surface of the negative electrode active material layer 14B. This coating 14C is formed by, for example, the carbonate contained in the positive electrode 12 being dissolved in the electrolyte and reacting on the surface of the negative electrode 14, or the carbonate ions contained in the electrolyte reacting on the surface of the negative electrode 14 as described later. Is formed. In this secondary battery, since lithium is used for the electrode reaction, the coating 14C contains, for example, lithium carbonate generated by a reaction between lithium and carbonate ions.

  The separator 15 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. May be. 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 15 because a shutdown effect can be obtained within a range of 100 ° C. or more and 160 ° C. or less and excellent in electrochemical stability. Polypropylene is also preferable, and any other resin having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.

  This polyolefin porous film is prepared by, for example, kneading a molten low-volatile solvent in a molten polyolefin composition into a high-concentration solution of a uniform polyolefin composition, and molding this with a die. It is obtained by cooling to a gel-like sheet and stretching.

  As the low volatility solvent, for example, low volatility aliphatic or cyclic hydrocarbon such as nonane, decane, decalin, p-xylene, undecane or liquid paraffin can be used. The blending ratio of the polyolefin composition and the low-volatile solvent may be 10% by mass or more and 80% by mass or less, and further 15% by mass or more and 70% by mass or less, with the total of both being 100% by mass. preferable. This is because if the polyolefin composition is too small, swelling or neck-in becomes large at the die outlet during molding, and sheet molding becomes difficult. On the other hand, when there are too many polyolefin compositions, it is difficult to prepare a uniform solution.

  When molding a high-concentration solution of a polyolefin composition with a die, in the case of a sheet die, the gap is preferably, for example, 0.1 mm or more and 5 mm or less. The extrusion temperature is preferably 140 ° C. or more and 250 ° C. or less, and the extrusion rate is preferably 2 cm / min or more and 30 cm / min or less.

  Cooling is performed to at least the gelation temperature or lower. As a cooling method, a method of directly contacting cold air, cooling water, or another cooling medium, a method of contacting a roll cooled by a refrigerant, or the like can be used. Note that the high-concentration solution of the polyolefin composition extruded from the die may be taken up at a take-up ratio of 1 to 10 and preferably 1 to 5 before cooling or during cooling. If the take-up ratio is too large, the neck-in becomes large, and breakage tends to occur during stretching, which is not preferable.

  The gel-like sheet is preferably stretched by biaxial stretching, for example, by heating the gel-like sheet and using a tenter method, a roll method, a rolling method, or a method combining these. At that time, either longitudinal or transverse simultaneous stretching or sequential stretching may be used, but simultaneous secondary stretching is particularly preferable. The stretching temperature is preferably not more than the temperature obtained by adding 10 ° C. to the melting point of the polyolefin composition, and more preferably not less than the crystal dispersion temperature and less than the melting point. If the stretching temperature is too high, effective molecular chain orientation due to stretching cannot be achieved due to melting of the resin, which is not preferable. If the stretching temperature is too low, the resin becomes insufficiently softened and breaks during stretching. This is because it is easy to stretch at a high magnification.

  In addition, after extending | stretching a gel-like sheet | seat, it is preferable to wash | clean the extended film | membrane with a volatile solvent, and to remove the remaining low-volatile solvent. After washing, the stretched film is dried by heating or blowing to volatilize the washing solvent. Examples of the cleaning solvent include hydrocarbons such as pentane, hexane, and hebutane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, fluorocarbons such as ethane trifluoride, and ethers such as diethyl ether and dioxane. Easily volatile materials are used. The cleaning solvent is selected according to the low-volatile solvent used, and is used alone or in combination. Washing can be performed by a method of extracting by immersing in a volatile solvent, a method of sprinkling a volatile solvent, or a method combining these. This washing is performed until the residual low-volatile solvent in the stretched film is less than 1 part by mass with respect to 100 parts by mass of the polyolefin composition.

  The electrolyte impregnated in the separator 15 contains a so-called liquid electrolyte including a nonaqueous solvent such as an organic solvent and a lithium salt that is an electrolyte salt dissolved in the nonaqueous solvent. As the non-aqueous solvent, for example, a mixture of one or more compounds represented by cyclic carbonates or chain carbonates is preferable. Specifically, tylene 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-methoxypropironitrile, N, N-dimethyl Formamide, N-methylpyrrolidinone, N-methyloxazolidinone, N, N'-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, dimethyls Examples thereof include sulfoxide, trimethyl phosphate, and compounds in which some or all of the hydroxyl groups of these compounds are substituted with fluorine groups. In particular, in order to realize excellent charge / discharge capacity characteristics and charge / discharge cycle characteristics, it is preferable to use at least one of ethylene carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

Examples of the lithium salt include LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C _{2 F 5 SO 2) 2,} LiN (C 4 F 9 SO 2) (CF 3 SO 2), LiC (CF 3 SO 2) 3, include LiAlCl _4, LiSiF _6, LiCl or LiBr, any one Alternatively, two or more kinds may be mixed and used.

Among them, LiPF ₆ is preferable because it can obtain high electrical conductivity and is excellent in oxidation stability, and LiBF ₄ is preferable because it is excellent in thermal stability and oxidation stability. LiCF ₃ SO ₃ is preferable because it has high thermal stability, and LiClO ₄ is preferable because high conductivity can be obtained. Furthermore, LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ and LiN (C ₄ F ₉ SO ₂ ) (CF ₃ SO ₂ ) are relatively High electrical conductivity can be obtained, and thermal stability is also high, which is preferable. Furthermore, it is more preferable to use a mixture of at least two of these because these effects can be obtained together.

  The content (concentration) of these lithium salts is preferably in the range of 0.5 mol / kg or more and 3.0 mol / kg or less with respect to the solvent. Outside this range, there is a risk that sufficient battery characteristics may not be obtained due to an extreme decrease in ionic conductivity.

  This electrolyte preferably further contains carbonate ions. This carbonate ion may be generated, for example, by dissolving a carbonate contained in the positive electrode 12, or may be added to the electrolyte separately from the positive electrode 12. This is because the coating 14C can be formed on the surface of the negative electrode 14 as described above.

  In addition, although this electrolyte may be comprised only by electrolyte solution, it may be gelatinized by containing the high molecular compound which hold | maintains electrolyte solution further. Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and polyhexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, and polysiloxane. , Polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene or 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. The amount of the polymer compound added to the electrolytic solution varies depending on the compatibility between the two, but is usually preferably about 5% by mass to 50% by mass of the electrolytic solution.

  In addition, the electrolyte contains an inorganic solution such as lithium nitride, lithium iodide or lithium hydroxide polycrystal, a mixture of lithium iodide and dichromium trioxide, or a mixture of lithium iodide, thilium sulfide, and phosphorous disulfide. You may make it hold | maintain on a conductor, and may make it hold | maintain in the mixture of a polymeric material and an inorganic conductor.

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

  First, for example, a positive electrode material capable of inserting and extracting lithium, a conductive agent, a binder, and a carbonate are mixed to prepare a positive electrode mixture, and this positive electrode mixture is mixed with N-methyl-2-pyrrolidone. It is made to disperse | distribute to solvents, such as, and it is set as a paste-form positive mix slurry. Subsequently, the positive electrode mixture slurry is applied to the positive electrode current collector 12A, and the solvent is dried. Then, the positive electrode current collector 12A on which the positive electrode active material layer 12B is formed is compressed by a roll press machine or the like. The positive electrode 12 is produced by punching into a shape.

  Next, 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 and pasted. A negative electrode mixture slurry. Subsequently, the negative electrode mixture slurry is applied to the negative electrode current collector 14A, and the solvent is dried. Then, the negative electrode active material layer 14B is formed by compression molding using a roll press or the like, and the negative electrode 14 is manufactured. At that time, the ratio of the capacity of the positive electrode active material layer 12B and the negative electrode active material layer 14B is adjusted so that lithium metal is deposited on the negative electrode 14 during charging as described above.

  After producing the positive electrode 12 and the negative electrode 14, for example, the negative electrode 14, the separator 15 impregnated with the electrolyte, and the positive electrode 12 are laminated, put into the outer cup 13 and the outer can 11, and caulked. At that time, carbonate ions may be added to the electrolyte. Thereby, the secondary battery shown in FIG. 1 is completed.

  This secondary battery operates as follows.

  In this secondary battery, when charged, lithium ions are released from the positive electrode active material layer 12B, and first, the lithium contained in the negative electrode active material layer 14B is occluded / released through the electrolytic solution impregnated in the separator 15. Occluded in possible negative electrode materials. If the battery is further charged, the charge capacity exceeds the charge capacity of the negative electrode material capable of inserting and extracting lithium when the open circuit voltage is lower than the overcharge voltage. Lithium metal begins to precipitate. After that, lithium metal continues to deposit on the negative electrode 14 until charging is completed. As a result, the appearance of the negative electrode active material layer 14B changes from black to golden, and further to white silver 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 14 is eluted as ions, and is inserted in the positive electrode active material layer 12 </ b> B through the electrolytic solution impregnated in the separator 15. When the discharge is further continued, lithium ions occluded in the negative electrode material capable of occluding and desorbing lithium in the negative electrode active material layer 14B are desorbed and occluded in the positive electrode active material layer 12B through the electrolytic solution. Therefore, in this secondary battery, the characteristics of both the conventional so-called lithium secondary battery and lithium ion secondary battery, that is, high energy density and good charge / discharge cycle characteristics can be obtained.

  In particular, in the present embodiment, carbonate ions generated by dissolving carbonate contained in the positive electrode 12 in the electrolyte, or carbonate ions added to the electrolyte, such as lithium on the surface of the negative electrode 14 during charging. By reacting, a film 14 </ b> C containing carbonate is formed on the surface of the negative electrode 14. Therefore, even if it preserve | saves in the state which precipitated lithium metal on the negative electrode 14, it will suppress that the lithium metal deposited on the negative electrode 14 reacts with electrolyte etc. and deactivates.

  As described above, according to the present embodiment, since the positive electrode 12 contains carbonate or because the electrolyte contains carbonate ions, the coating 14C containing carbonate is formed on the surface of the negative electrode 14. It is possible to suppress the lithium metal deposited on the negative electrode 14 from reacting with the electrolyte and being deactivated. Therefore, capacity deterioration during charge storage can be suppressed.

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

(Examples 1-1 and 1-2)
A secondary battery in which the capacity of the negative electrode includes a capacity component due to insertion / extraction of lithium and a capacity component due to precipitation / dissolution of lithium, and is represented by the sum thereof, was produced. Here, it demonstrates using the code | symbol shown in FIG. 1 with reference to FIG.

First, lithium-cobalt composite oxide (LiCoO ₂ ) having an average particle diameter of 5 μm is used as the positive electrode material, 97 parts by mass of this lithium-cobalt composite oxide, and 1 part by mass of graphite having an average particle diameter of 1 μm as a conductive agent, A positive electrode mixture was prepared by mixing 2 parts by mass of polyvinylidene fluoride as a binder and 5 parts by mass of carbonate. At that time, lithium carbonate was used in Example 1-1 as the carbonate, and potassium carbonate was used in Example 1-2. Next, this positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, and then uniformly applied to one side of the positive electrode current collector 12A made of aluminum foil and dried. The positive electrode active material layer 12B was formed by compression molding with a press, and the positive electrode 12 was produced. At that time, the thickness or coating density of the positive electrode active material layer 12B was adjusted, and the capacity of the positive electrode active material layer 12B was set to 2.0 mAh / cm ² .

Further, 92 parts by mass of graphite having an average particle diameter of 25 μm as a negative electrode material and 8 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture. Next, the negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a negative electrode mixture slurry, and then uniformly applied to one side of the negative electrode current collector 14A made of copper foil and dried. The negative electrode mixture layer 14 </ b> B was formed by compression molding with a press, and the negative electrode 14 was produced. At that time, the thickness or coating density of the negative electrode active material layer 14B was adjusted, and the capacity of the negative electrode active material layer 14B was set to 1.1 mAh / cm ² . That is, the capacity of the negative electrode active material layer 14B is made smaller than the capacity of the positive electrode active material layer 12B, lithium metal is deposited on the negative electrode 14 in the middle of charging, and the capacity of the negative electrode 14 is a capacity component due to insertion and extraction of lithium. And a capacity component due to precipitation / dissolution of lithium, and expressed as a sum thereof.

After preparing the positive electrode 12 and the negative electrode 14, the negative electrode 14 and the separator 15 are placed in this order on the outer cup 13, the electrolyte is injected from above, and the outer can 11 containing the positive electrode 12 is placed thereon, and then the outer cup 13 And the peripheral part of the armored can 11 was caulked through the gasket 16 to produce a coin-type secondary battery. The electrolyte used was a solution in which LiPF ₆ was dissolved in an amount of 1.0 mol / dm ³ as an electrolyte salt in a solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1: 1. It was. The separator 15 was made of polyethylene having a thickness of 25 μm.

  Further, as Comparative Example 1-1 with respect to Examples 1-1 and 1-2, a secondary battery was fabricated in the same manner as in Examples 1-1 and 1-2, except that carbonate was not added to the positive electrode. did.

  The obtained secondary batteries of Examples 1-1 and 1-2 and Comparative Example 1-1 were subjected to a charge / discharge test to obtain an initial discharge capacity. In the charge / discharge test, a constant current / constant voltage charge with a load of 0.1 C was performed at 23 ° C. for 15 hours up to an upper limit of 4.2 V, and after standing for 12 hours after charging, a constant current discharge with a load of 0.1 C was performed with a final voltage of 3.0 V. Evaluation was performed using the process of performing up to. That is, a larger initial discharge capacity means less capacity deterioration during storage after charging. In addition, 0.1 C means a current value at which the initial capacity can be discharged in 10 hours.

  Table 1 shows the results obtained. The initial discharge capacity shown in Table 1 is a relative representation of the discharge capacities of Examples 1-1 and 1-2, with the initial discharge capacity of Comparative Example 1-1 being 100.

Moreover, about the secondary battery of Examples 1-1 and 1-2 and Comparative Example 1-1, what was fully charged again after performing 1 cycle charge / discharge on the conditions mentioned above was disassembled visually, and ⁷ Li nucleus It was examined by magnetic resonance spectroscopy whether lithium metal was deposited on the negative electrode active material layer 14B. Furthermore, two cycles of charge and discharge were performed under the conditions described above, and the completely discharged one was disassembled, and similarly, it was examined whether lithium metal was deposited on the negative electrode active material layer 14B.

  As a result, in the secondary batteries of Examples 1-1 and 1-2 and Comparative Examples 1-1 and 1-2, the presence of lithium metal was observed in the negative electrode active material layer 14B in the fully charged state, and the fully discharged state The presence of lithium metal was not observed in. That is, it was confirmed that the capacity of the negative electrode 14 includes a capacity component due to insertion / extraction of lithium and a capacity component due to precipitation / dissolution of lithium metal, and is expressed by the sum thereof.

  As shown in Table 1, according to Examples 1-1 and 1-2, it was possible to increase the initial discharge capacity as compared with Comparative Example 1-1.

  That is, in the secondary battery in which the capacity of the negative electrode 14 includes a capacity component due to light metal occlusion / release and a capacity component due to light metal precipitation / dissolution, and the sum thereof, the positive electrode 12 includes carbonate. It was found that capacity deterioration during storage after charging can be suppressed.

(Examples 2-1 and 2-2)
As an electrolytic solution, a solution obtained by dissolving LiPF ₆ as an electrolyte salt at a content of 1.0 mol / dm ³ in a solvent in which ethylene carbonate (EC) and propylene carbonate (PC) are mixed at a volume ratio of 1: 1 is used. A secondary battery was fabricated in the same manner as in Examples 1-1 and 1-2 except for the above. Moreover, as Comparative Example 2-1 with respect to Examples 2-1 and 2-2, a secondary battery was produced in the same manner as in Examples 2-1 and 2-2, except that carbonate was not added to the positive electrode. did.

  The obtained secondary batteries of Examples 2-1 and 2-2 and Comparative Example 2-1 were subjected to a charge / discharge test in the same manner as in Examples 1-1 and 2-2, and the initial discharge capacity was obtained. Table 2 shows the results obtained. The initial discharge capacity shown in Table 2 is a relative representation of the discharge capacities of Examples 2-1 and 2-2, with the initial discharge capacity of Comparative Example 2-1 being 100.

  As shown in Table 2, according to Examples 2-1 and 2-2, the initial discharge capacity is improved as compared with Comparative Example 2-1, similarly to Examples 1-1 and 1-2. I was able to.

  That is, even when the composition of the electrolytic solution was changed, it was found that capacity deterioration during storage after charging can be suppressed if carbonate is included in the positive electrode 12.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiment and examples, the case where the positive electrode 12 includes carbonate has been described. However, the positive electrode 12 may include carbonate, the electrolyte may include carbonate ions, and the positive electrode 12 may include carbonate. The electrolyte may contain no carbonate ions, and conversely, the positive electrode 12 may contain no carbonate and the electrolyte may contain carbonate ions. For example, even when carbonate is added to the positive electrode 12, all is dissolved and no carbonate remains in the positive electrode 12, or part is dissolved and part remains on the positive electrode 12, and all the carbonate ions of the electrolyte are present. This is because there is a case where carbonate ions are not left in the electrolyte used for forming the coating 14C.

  In addition, the carbonate added to the positive electrode 12 or the carbonate ions dissolved or added to the electrolyte are all used for forming the coating 14C, and may not remain in the positive electrode 12 and the electrolyte.

  Furthermore, in the above-described embodiments and examples, the case where the coating 14C contains carbonate has been described. However, the composition of the coating 14C to be formed may vary depending on the composition of the electrolyte, and therefore the coating 14C is carbonated. It may not contain salt.

  In addition, in the embodiments and examples described above, the case where carbonate is added to the positive electrode 12 has been described. However, carbonate may be added to the positive electrode 12 and carbonate ions may be added to the electrolyte. Carbonate may be added only to the positive electrode 12, or carbonate ions may be added only to the electrolyte.

  In addition, in the above-described embodiments and examples, the case where lithium is used as the light metal has been described. However, other alkali metals such as sodium (Na) or potassium (K), or magnesium or calcium (Ca) are used. The present invention can be applied to the case of using alkaline earth metal, other light metal such as aluminum, lithium, or an alloy thereof, and the same effect can be obtained. At that time, a negative electrode material, a positive electrode material, a non-aqueous solvent, an electrolyte salt, 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.

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

It is sectional drawing showing the structure of the secondary battery which concerns on one embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Outer can, 12 ... Positive electrode, 12A ... Positive electrode collector, 12B ... Positive electrode active material layer, 13 ... Outer cup, 14 ... Negative electrode, 14A ... Negative electrode collector, 14B ... Negative electrode active material layer, 14C ... Coating 15 ... separator, 16 ... gasket.

Claims (5)

A battery comprising an electrolyte together with a positive electrode and a negative electrode, wherein 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 positive electrode includes a positive electrode active material and a carbonate.   2. The battery according to claim 1, wherein the carbonate includes at least one selected from the group consisting of lithium carbonate, potassium carbonate, and sodium carbonate. A battery comprising an electrolyte together with a positive electrode and a negative electrode, wherein 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 negative electrode has a coating film containing carbonate on the surface.   The battery according to claim 3, wherein the coating contains lithium carbonate. A battery comprising an electrolyte together with a positive electrode and a negative electrode, wherein 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 electrolyte contains carbonate ions.

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