JP4993159B2 - Secondary battery - Google Patents

Description

The present invention relates to a secondary battery containing a halogen compound in an electrolyte.

  In recent years, mobile electronic devices such as mobile phones, PDAs (Personal Digital Assistants) or notebook computers have been energetically reduced in size and weight, and as part of that, driving them Improvement of the energy density of a battery as a power source, particularly a secondary battery is strongly desired. As a secondary battery capable of obtaining a high energy density, a lithium-ion secondary battery using a material capable of inserting and extracting lithium (Li) such as a carbon material into the negative electrode has been commercialized, and the market has expanded. is doing.

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 only precipitation and dissolution reactions of lithium metal for the negative electrode reaction. Lithium metal secondary batteries have a large theoretical electrochemical equivalent of 2054 mAh / cm ^{3 of} lithium metal, which is equivalent to 2.5 times that of graphite used in lithium ion secondary batteries, so it is higher than lithium ion secondary batteries. The energy density is expected to be obtained. Until now, research and development regarding practical application of lithium metal secondary batteries has been made by many researchers and the like (for example, see Non-Patent Document 1).

  Furthermore, recently, a secondary battery has been developed 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, and is represented by the sum thereof (for example, Patent Documents). 1). In this method, a carbon material capable of inserting and extracting lithium is used for the negative electrode, and lithium is deposited on the surface of the carbon material during charging. According to this secondary battery, it can be expected to achieve a high energy density as in the case of the lithium metal secondary battery.

In these lithium secondary batteries, for the purpose of improving battery characteristics such as cycle characteristics, it has been conventionally studied to use a mixture of two or more solvents in the electrolyte, or to use a halogenated compound or the like. (For example, refer to Patent Documents 2 and 3.)
Edited by Jean-Paul Gabano, "Lithium Batteries", London, New York, Academic Press, 1983 International Publication No. 01/22519 Pamphlet JP-A-62-290071 Japanese Patent Laid-Open No. 62-217567

  However, in a secondary battery in which the capacity of a lithium metal secondary battery or a negative electrode includes a capacity component due to insertion and extraction of lithium and a capacity component due to lithium precipitation and dissolution, and is represented by the sum thereof, Since the reactivity is high, the effect is not always sufficient by the conventional means, and further improvement has been desired.

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

A first secondary battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, uses lithium metal as a negative electrode active material, and the electrolyte includes 4-fluoro-1,3-dioxolan-2-one. In addition, a solvent containing a halogenated carbonate represented by Chemical Formula 1 is contained , and the content of the halogenated carbonate in the solvent is in the range of 0.1% by volume to 30% by volume .

（化１において、Ｒ１，Ｒ２，Ｒ３およびＲ４は、それぞれ独立的に、水素，アルキル基，アリール基，ハロゲン化アリール基またはハロゲンであり、Ｒ１，Ｒ２，Ｒ３およびＲ４のうちの１つ以上はハロゲンであり、他の１つ以上はアルキル基またはアリール基である。）

(In Formula 1, R1, R2, R3 and R4 are each independently hydrogen, an alkyl group, an aryl group, a halogenated aryl group or a halogen, and one or more of R1, R2, R3 and R4 are A halogen, one or more of the other being an alkyl group or an aryl group.)

A second secondary 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 the electrolyte contains a solvent containing 4-fluoro-1,3-dioxolan-2-one and the halogenated carbonate shown in Chemical Formula 2, and the electrolyte of the halogenated carbonate in the solvent The content is within the range of 0.1 volume% or more and 30 volume% or less .

（化２において、Ｒ１，Ｒ２，Ｒ３およびＲ４は、それぞれ独立的に、水素，アルキル基，アリール基，ハロゲン化アリール基またはハロゲンであり、Ｒ１，Ｒ２，Ｒ３およびＲ４のうちの１つ以上はハロゲンであり、他の１つ以上はアルキル基またはアリール基である。）

(In Chemical Formula 2, R1, R2, R3 and R4 are each independently hydrogen, an alkyl group, an aryl group, a halogenated aryl group or a halogen, and one or more of R1, R2, R3 and R4 are A halogen, one or more of the other being an alkyl group or an aryl group.)

According to the first or the second secondary battery of the present invention, viewed contains a 4-fluoro-1,3-dioxolan-2-one in the electrolyte, of 1, and a halogenated carbonate represented by Chemical Formula 2, Since the content of the halogenated carbonate in the solvent is in the range of 0.1 volume% or more and 30 volume% or less, the decomposition reaction of the solvent in the negative electrode can be suppressed. Therefore, the charge / discharge efficiency in the negative electrode is improved, and the cycle characteristics can be improved.

  Further, if the content of the halogenated carbonate shown in Chemical Formula 1 and Chemical Formula 2 in the solvent is within the range of 0.1% by volume or more and 20% by volume or less, a higher effect can be obtained.

Further, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiB (OCOCF ₃ ) ₄ , LiB (OCOC ₂ F ₅ ) ₄ , LiN (C _m F _{2m + 1} SO ₂ ) (C _n F _{2n + 1} SO ₂ ) (m and n are integers of 1 or more) and LiC (C _p F _{2p + 1} SO ₂ ) (C _q F _{2q + 1} SO ₂ ) (C _r F _{2r Even} if it includes at least one selected from the group consisting of lithium salts represented by ₊₁ SO ₂ (p, q, r are integers of 1 or more), a higher effect can be obtained.

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

(First embodiment)
FIG. 1 shows a cross-sectional structure of the secondary battery according to the first embodiment. This secondary battery is a so-called lithium metal secondary battery in which the capacity of the negative electrode is represented by a capacity component due to precipitation and dissolution of lithium as an electrode reactant. This secondary battery is a so-called cylindrical type, and is a wound electrode in which a strip-shaped positive electrode 21 and a strip-shaped 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, 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.

  The wound electrode body 20 is wound around a center pin 24, for example. 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 has, for example, a structure in which a positive electrode active material layer 21B is provided on both surfaces of a positive electrode current collector 21A having a pair of opposed surfaces. Although not shown, the positive electrode active material layer 21B may be provided only on one surface of the positive electrode current collector 21A. The positive electrode current collector 21A has, for example, a thickness of about 5 μm to 50 μm and is made of a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode active material layer 21B includes, for example, one or more positive electrode materials capable of inserting and extracting lithium, which is an electrode reactant, as a positive electrode active material. It is configured to contain a binder. The thickness of the positive electrode active material layer 21B is, for example, 60 μm to 250 μm. The thickness of the positive electrode active material layer 21B is the total thickness when the positive electrode active material layer 21B is provided on both surfaces of the positive electrode current collector 21A.

As a positive electrode material capable of inserting and extracting lithium, for example, a lithium-containing compound containing lithium, a transition metal element, and oxygen (O) is preferable in order to increase energy density. It is more preferable if it contains at least one selected from the group consisting of cobalt (Co), nickel, manganese (Mn) and iron. Examples of such a lithium-containing compound include LiCoO ₂ , LiNi _0.5 Co _0.5 O ₂ , LiMn ₂ O _{4, and} LiFePO ₄ .

  Such a positive electrode material is prepared by, for example, mixing lithium carbonate, nitrate, oxide or hydroxide with transition metal carbonate, nitrate, oxide or hydroxide so as to have a desired composition. And then pulverized and then fired at a temperature in the range of 600 ° C. to 1000 ° C. in an oxygen atmosphere.

  Examples of the conductive agent include carbon materials such as graphite, carbon black, and ketjen black, and one or more of them are used in combination. 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 rubbers such as styrene butadiene rubber, fluorine rubber or ethylene propylene diene rubber, or polymer materials such as polyvinylidene fluoride, and one or more of them are mixed. Used. For example, when the positive electrode 21 and the negative electrode 22 are wound as shown in FIG. 1, it is preferable to use a styrene butadiene rubber or a fluorine rubber having high flexibility as the binder.

  The negative electrode 22 has, for example, a structure in which a negative electrode active material layer 22B is provided on both surfaces of a negative electrode current collector 22A having a pair of opposed surfaces. Although not shown, the negative electrode active material layer 22B may be provided only on one surface of the negative electrode current collector 22A. The negative electrode current collector 22A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil having good electrochemical stability, electrical conductivity, and mechanical strength. In particular, copper foil is most preferable because it has high electrical conductivity. The thickness of the anode current collector 22A is preferably about 5 to 40 μm, for example. If the thickness is less than 5 μm, the mechanical strength decreases, and the negative electrode current collector 22A is easily torn in the manufacturing process, resulting in a decrease in production efficiency. If the thickness is larger than 40 μm, the negative electrode current collector 22A in the battery This is because the volume ratio becomes larger than necessary and it is difficult to increase the energy density.

  The negative electrode active material layer 22B is made of, for example, lithium metal that is a negative electrode active material, so that a high energy density can be obtained. The negative electrode active material layer 22B may be configured to be already provided from the time of assembly, but may be configured by lithium metal which is not present at the time of assembly and is deposited during charging. Alternatively, the negative electrode active material layer 22B may be used as a current collector, and the negative electrode current collector 22A may be deleted.

  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. 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 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 separator 23 is impregnated with an electrolytic solution that is a liquid electrolyte. This electrolytic solution contains, for example, a solvent and an electrolyte salt dissolved in this solvent.

  The solvent contains 4-fluoro-1,3-dioxolan-2-one shown in Chemical formula 3 and a halogenated carbonate shown in Chemical formula 4. This is because the decomposition reaction of the electrolyte can be suppressed by forming a good film on the surface of the negative electrode 22. One of the halogenated carbonates shown in Chemical Formula 4 may be used alone, or a plurality of types may be mixed and used.

  In Formula 4, R1, R2, R3 and R4 are each independently hydrogen, an alkyl group, an aryl group, a halogenated aryl group or a halogen, and one or more of R1, R2, R3 and R4 are halogen And the other one or more is an alkyl group or an aryl group. R1, R2, R3, and R4 may be different from each other or may be partially the same.

  Moreover, as an alkyl group, a C1-C6 thing is preferable and may be linear or cyclic. Specifically, methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, t-butyl group, n-pentyl group, i-pentyl group, t-pentyl group , Neopentyl group, n-hexyl group, cyclohexyl group and the like. Examples of the aryl group or the halogenated aryl group include a phenyl group and a halogen-substituted phenyl group. Halogen includes fluorine, chlorine or bromine.

  Therefore, specific examples of the halogenated carbonate represented by Chemical Formula 4 include 4-fluoro-4-methyl-1,3-dioxolan-2-one, cis-4-fluoro-5-methyl-1,3-dioxolane. 2-one, trans-4-fluoro-5-methyl-1,3-dioxolan-2-one, 4-fluoro-4-ethyl-1,3-dioxolan-2-one, cis-4-fluoro-5 -Ethyl-1,3-dioxolan-2-one, trans-4-fluoro-5-ethyl-1,3-dioxolan-2-one, 4-fluoro-4-propyl-1,3-dioxolan-2-one Cis-4-fluoro-5-propyl-1,3-dioxolan-2-one, trans-4-fluoro-5-propyl-1,3-dioxolan-2-one, 4-fluoro-4-butyl-1 , -Dioxolan-2-one, cis-4-fluoro-5-butyl-1,3-dioxolan-2-one, trans-4-fluoro-5-butyl-1,3-dioxolan-2-one, 4-fluoro -4-pentyl-1,3-dioxolan-2-one, cis-4-fluoro-5-pentyl-1,3-dioxolan-2-one, trans-4-fluoro-5-pentyl-1,3-dioxolane 2-one, 4-fluoro-4-hexyl-1,3-dioxolan-2-one, cis-4-fluoro-5-hexyl-1,3-dioxolan-2-one, trans-4-fluoro-5 -Hexyl-1,3-dioxolan-2-one, 4-fluoro-4-phenyl-1,3-dioxolan-2-one, cis-4-fluoro-5-phenyl-1,3-dioxolane 2-one, trans-4-fluoro-5-phenyl-1,3-dioxolan-2-one, or a 4-fluoro-4,5-dimethyl-1,3-dioxolan-2-one and the like.

  The content of the halogenated carbonate shown in Chemical Formula 4 in the solvent is preferably in the range of 0.1% by volume to 20% by volume. This is because a higher effect can be obtained within this range.

  These solvents may also be used by mixing with various conventionally used solvents. Specific examples of such solvents 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-methoxypropironitrile N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N, N′-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide, trimethyl phosphate There are. Among these, in order to realize excellent charge / discharge capacity characteristics and charge / discharge cycle characteristics, it is preferable to use at least one selected from the group consisting of ethylene carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. These solvents may be mixed alone or in combination of two or more.

Examples of the electrolyte salt include LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, LiBr, LiPF ₆ , LiBF ₄ , LiB (OCOCF ₃ ) ₄ , LiB. (OCOC ₂ F ₅ ) ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ or LiN (C ₄ F ₉ SO ₂ ) (CF ₃ SO ₂ ) And the lithium salt shown in Chemical Formula 6 such as LiC (CF ₃ SO ₂ ) ₃ .

（式中、ｍおよびｎは１以上の整数である。ｍおよびｎは同一の値であってもよいし、異なる値であってもよい。）

(In the formula, m and n are integers of 1 or more. M and n may be the same value or different values.)

（式中、ｐ，ｑおよびｒは１以上の整数である。ｐ，ｑおよびｒは同一の値のものがあってもよいし、すべてが異なる値であってもよい。）

(In the formula, p, q and r are integers of 1 or more. P, q and r may have the same value, or all may have different values.)

Among them, among the group consisting of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiB (OCOCF ₃ ) ₄ , LiB (OCOC ₂ F ₅ ) ₄ , the lithium salt shown in Chemical Formula 5 and the lithium salt shown in Chemical Formula 6 If at least one of these is included, battery characteristics such as storage characteristics can be improved, internal resistance can be reduced, heavy load characteristics can be improved, and higher electrical conductivity can be obtained. In particular, from LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiB (OCOCF ₃ ) ₄ , LiB (OCOC ₂ F ₅ ) ₄ , the lithium salt shown in Chemical Formula 5 and the lithium salt shown in Chemical Formula 6 It is more preferable to use a mixture of at least one member of the group.

  The content (concentration) of the electrolyte salt is preferably in the range of 0.3 mol / kg or more and 3.0 mol / kg or less with respect to the solvent. This is because, outside this range, sufficient battery characteristics may not be obtained due to an extreme decrease in ionic conductivity.

  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, and a binder are mixed to prepare a positive electrode mixture, and this positive electrode mixture is mixed with N-methyl-2-pyrrolidone or the like. To make a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry is applied to the positive electrode current collector 21A, and the solvent is dried. Then, the positive electrode active material layer 21B is formed by compression molding using a roll press or the like, and the positive electrode 21 is manufactured.

  For example, a negative electrode current collector 22 </ b> A is prepared as the negative electrode 22. Note that lithium metal may be used as it is for the negative electrode 22, or a negative electrode active material layer 22B may be formed by attaching lithium metal to the negative electrode current collector 22A.

  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, the electrolytic solution is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through a gasket 17. Thereby, the secondary battery shown in FIG. 1 is formed.

  In this secondary battery, when charged, for example, lithium ions are released from the positive electrode 21 and deposited as lithium metal on the surface of the negative electrode current collector 22A via the electrolytic solution, as shown in FIG. Then, the negative electrode active material layer 22B is formed. When the discharge is performed, for example, lithium metal is eluted as lithium ions from the negative electrode active material layer 22B, and is occluded in the positive electrode 21 through the electrolytic solution. As described above, in this secondary battery, the deposition and dissolution of lithium metal are repeated in the negative electrode 22, so that the activity of the negative electrode 22 is very high, but 4-fluoro-1,3-dioxolane-2 is contained in the electrolytic solution. Since -one and the halogenated carbonate shown in Chemical formula 4 are contained, a good film is formed on the surface of the negative electrode 22, and the decomposition reaction of the solvent is suppressed. Therefore, the charge / discharge efficiency of lithium in the negative electrode 22 is improved.

  As described above, in this embodiment, since the electrolytic solution contains 4-fluoro-1,3-dioxolan-2-one and the halogenated carbonate shown in Chemical formula 4, decomposition of the solvent in the negative electrode 22 The reaction can be suppressed. Therefore, the charge / discharge efficiency in the negative electrode 22 is improved, and the cycle characteristics can be improved.

  Further, if the content of the halogenated carbonate shown in Chemical formula 4 in the solvent is in the range of 0.1% by volume or more and 20% by volume or less, a higher effect can be obtained.

Furthermore, LiPF ₆ as an electrolyte salt, LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiB (OCOCF ₃ ) ₄ , LiB (OCOC ₂ F ₅ ) ₄ , lithium salt shown in Chemical Formula 5 and lithium salt shown in Chemical Formula 6 Even if it includes at least one member of the group, higher effects can be obtained.

(Second Embodiment)
The secondary battery according to the second embodiment of the present invention includes a capacity component due to insertion and extraction of lithium, which is an electrode reactant, and a capacity component due to precipitation and dissolution of lithium. It is represented by.

  This secondary battery has the same configuration and effects as those of the secondary battery according to the first embodiment except that the configuration of the negative electrode active material layer is different, and can be manufactured in the same manner. it can. Therefore, here, description will be made with reference to FIGS. 1 and 2 using the same reference numerals. Detailed descriptions of the same parts are omitted.

  The negative electrode active material layer 22B includes, for example, a negative electrode material capable of inserting and extracting lithium as an electrode reactant as a negative electrode active material, and is similar to the positive electrode active material layer 21B as necessary. The binder may be included.

  Examples of the negative electrode material capable of inserting and extracting lithium include carbon materials such as graphite, non-graphitizable carbon, and graphitizable carbon. This is because such a carbon material has very little change in the crystal structure that occurs during charge and discharge, can obtain a high energy density, and can obtain excellent cycle characteristics. 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. Further, 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.

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 also include a material including at least one of a metal element and a metalloid element as a constituent element. If such a negative electrode material is used, it is preferable because a high energy density can be obtained. In particular, if it is used together with the carbon material described above, a high energy density can be obtained and excellent cycle characteristics can be obtained. It is more preferable because it is possible.

  The negative electrode material may be a single element, alloy or compound of a metal element or metalloid element, or may have at least a part of one or more of these phases. In the present invention, alloys include those containing one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. Moreover, the nonmetallic element may be included. 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 constituting the negative electrode material include magnesium (Mg), boron (B), aluminum, gallium (Ga), indium (In), and silicon (Si) that can form an alloy with lithium. , Germanium (Ge), tin (Sn), lead (Pb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y) , Palladium (Pd) or platinum (Pt). These may be crystalline or amorphous.

  Among these, as the negative electrode material, a material containing a 4B group metal element or a semimetal element in the short-period type periodic table as a constituent element is preferable, and at least one of silicon and tin is particularly preferable as a constituent element. This is because silicon and tin have a large ability to occlude and release lithium, and a high energy density can be obtained.

  Examples of tin alloys include silicon, nickel, copper (Cu), iron, cobalt, manganese, zinc, indium, silver, titanium (Ti), germanium, bismuth, and antimony (second constituent elements other than tin). Sb) and those containing at least one selected from the group consisting of chromium (Cr). As an alloy of silicon, for example, as a second constituent element other than silicon, among the group consisting of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony and chromium The thing containing at least 1 sort (s) of these is mentioned.

  Examples of the tin compound or silicon compound include those containing oxygen or carbon (C), and may contain the second constituent element described above in addition to tin or silicon.

  For example, the negative electrode active material layer 22B has an open circuit voltage (that is, a battery voltage) in the charging process by making the charge capacity of the negative electrode material capable of occluding and releasing lithium smaller than the charge capacity of the positive electrode 21. When lithium is lower than the overcharge voltage, lithium metal begins to deposit on the negative electrode 22. 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.

  Accordingly, this secondary battery is the same as the conventional lithium ion secondary battery in that a negative electrode material capable of inserting and extracting lithium is used for the negative electrode 22, and lithium metal is deposited on the negative electrode 22. It is the same as the conventional lithium metal secondary battery in that the lithium metal is deposited on the negative electrode material capable of occluding and releasing lithium, so that a high energy density can be obtained. The cycle characteristics and the quick charge characteristics can be improved.

  In order to obtain these characteristics 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 occlude and release lithium. It is preferable that it is 0.05 times or more and 3.0 times or less the charge capacity capability of the negative electrode material capable of being 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. Further, 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 amount of lithium metal deposited becomes relatively smaller as the ability to occlude and release lithium increases. 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.

  In this secondary battery, when charged, lithium ions are released from the positive electrode 21 and are first inserted into the negative electrode material capable of inserting and extracting lithium contained in the negative electrode 22 through the electrolytic solution. When charging is further continued, lithium metal begins to deposit on the surface of the negative electrode material capable of inserting and extracting lithium in a state where the open circuit voltage is lower than the overcharge voltage. After that, lithium metal continues to deposit on the negative electrode 22 until charging is completed. Next, when discharging is performed, first, lithium metal deposited on the negative electrode 22 is eluted as ions, and is occluded in the positive electrode 21 through the electrolytic solution. When the discharge is further continued, lithium ions occluded in the negative electrode material capable of occluding and releasing lithium in the negative electrode 22 are released and inserted in the positive electrode 21 through the electrolytic solution. Thus, even in this secondary battery, the deposition and dissolution of lithium metal are repeated in the negative electrode 22, so that the activity of the negative electrode 22 is very high, but 4-fluoro-1,3-dioxolane-2 is contained in the electrolyte. Since -one and the halogenated carbonate shown in Chemical formula 4 are contained, a good film is formed on the surface of the negative electrode 22, and the decomposition reaction of the solvent is suppressed. Therefore, the charge / discharge efficiency of lithium in the negative electrode 22 is improved.

(Third embodiment)
FIG. 3 shows the configuration of the secondary battery according to the third embodiment. In this secondary battery, a wound electrode body 30 to which a positive electrode lead 31 and a negative electrode lead 32 are attached is accommodated in a film-like exterior member 40, and can be reduced in size, weight, and thickness. ing.

  The positive electrode lead 31 and the negative electrode lead 32 are led out from the inside of the exterior member 40 to the outside, for example, in the same direction. The positive electrode lead 31 and the negative electrode lead 32 are each made of a metal material such as aluminum, copper, nickel, or stainless steel, and each have a thin plate shape or a mesh shape.

  The exterior member 40 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. For example, the exterior member 40 is disposed so that the polyethylene film side and the wound electrode body 30 face each other, and the outer edge portions are in close contact with each other by fusion bonding or an adhesive. An adhesive film 41 is inserted between the exterior member 40 and the positive electrode lead 31 and the negative electrode lead 32 to prevent intrusion of outside air. The adhesion film 41 is made of a material having adhesion to the positive electrode lead 31 and the negative electrode lead 32, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 40 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminated film.

  FIG. 4 shows a cross-sectional structure taken along line II of the spirally wound electrode body 30 shown in FIG. The wound electrode body 30 is obtained by stacking and winding a positive electrode 33 and a negative electrode 34 with a separator 35 and an electrolyte layer 36 interposed therebetween, and the outermost peripheral portion is protected by a protective tape 37.

  The positive electrode 33 has a structure in which a positive electrode active material layer 33B is provided on one or both surfaces of a positive electrode current collector 33A. The negative electrode 34 has a structure in which a negative electrode active material layer 34B is provided on one surface or both surfaces of a negative electrode current collector 34A, and the negative electrode active material layer 34B side is disposed so as to face the positive electrode active material layer 33B. Yes. The configurations of the positive electrode current collector 33A, the positive electrode active material layer 33B, the negative electrode current collector 34A, the negative electrode active material layer 34B, and the separator 35 are the positive electrode current collector 21A and the positive electrode described in the first or second embodiment, respectively. This is the same as the active material layer 21B, the negative electrode current collector 22A, the negative electrode active material layer 22B, and the separator 23.

  The electrolyte layer 36 includes an electrolytic solution and a polymer compound serving as a holding body that holds the electrolytic solution, and has a so-called gel shape. The gel electrolyte layer 36 is preferable because it can prevent battery leakage. The gel electrolyte is not particularly limited as long as the ion conductivity is 1 mS / cm or more at room temperature, and the composition and the structure of the polymer compound are not particularly limited. The configuration of the electrolytic solution (that is, the solvent, the electrolyte salt, and the like) is the same as that in the first or second embodiment. Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, 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 it is usually preferable to add a polymer compound corresponding to 5% by mass to 50% by mass of the electrolytic solution.

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

  First, a precursor solution containing an electrolytic solution, a polymer compound, and a mixed solvent is applied to each of the positive electrode 33 and the negative electrode 34, and the mixed solvent is volatilized to form the electrolyte layer 36. After that, the positive electrode lead 31 is attached to the end of the positive electrode current collector 33A by welding, and the negative electrode lead 32 is attached to the end of the negative electrode current collector 34A by welding. Next, the positive electrode 33 and the negative electrode 34 on which the electrolyte layer 36 is formed are laminated via a separator 35 to form a laminated body, and then the laminated body is wound in the longitudinal direction, and a protective tape 37 is adhered to the outermost peripheral portion. Thus, the wound electrode body 30 is formed. Finally, for example, the wound electrode body 30 is sandwiched between the exterior members 40, and the outer edges of the exterior members 40 are sealed and sealed by heat fusion or the like. At that time, the adhesion film 41 is inserted between the positive electrode lead 31 and the negative electrode lead 32 and the exterior member 40. Thereby, the secondary battery shown in FIGS. 3 and 4 is completed.

  Further, this secondary battery may be manufactured as follows. First, after attaching the positive electrode lead 31 and the negative electrode lead 32 to the positive electrode 33 and the negative electrode 34, the positive electrode 33 and the negative electrode 34 are laminated and wound via the separator 35, and a protective tape 37 is adhered to the outermost peripheral portion. A wound body that is a precursor of the wound electrode body 30 is formed. Next, the wound body is sandwiched between the exterior members 40, and the outer peripheral edge portion excluding one side is heat-sealed to form a bag shape, and is stored inside the exterior member 40. Subsequently, an electrolyte composition including an electrolytic solution, a monomer that is a raw material of the polymer compound, a polymerization initiator, and other materials such as a polymerization inhibitor as necessary is prepared, and the interior of the exterior member 40 Inject.

  After injecting the electrolyte composition, the opening of the exterior member 40 is heat-sealed and sealed in a vacuum atmosphere. Next, heat is applied to polymerize the monomer to obtain a polymer compound, whereby the gel electrolyte layer 36 is formed, and the secondary battery shown in FIGS. 3 and 4 is completed.

  This secondary battery has the same operations and effects as the secondary battery according to the first or second embodiment.

  Note that an electrolytic solution that is a liquid electrolyte may be used instead of the gel electrolyte. The configuration of the electrolytic solution is as described above. For example, the secondary battery can be manufactured as follows.

  First, after attaching the positive electrode lead 31 and the negative electrode lead 32 to the positive electrode 33 and the negative electrode 34 as described above, the positive electrode 33 and the negative electrode 34 are laminated and wound via the separator 35, and the protective tape 37 is attached to the outermost periphery. By bonding, a wound body that is a precursor of the wound electrode body 30 is formed. Next, the wound body is sandwiched between the exterior members 40, and the outer peripheral edge portion excluding one side is heat-sealed to form a bag shape, and is stored inside the exterior member 40. Subsequently, the electrolytic solution is injected into the exterior member 40. After that, the opening of the exterior member 40 is heat-sealed and sealed in a vacuum atmosphere. Thereby, the secondary battery shown in FIG. 3 is completed.

  Furthermore, specific examples of the present invention will be described in detail.

(Examples 1-1 to 1-28)
A battery in which the capacity of the negative electrode 22 is expressed by a capacity component due to precipitation and dissolution of lithium, a so-called lithium metal secondary battery was produced. At that time, the battery was as shown in FIG.

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. in air at 900 ° C. After firing for a time, lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode material was obtained. Next, 91 parts by mass of this lithium / cobalt composite oxide, 6 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. Subsequently, this positive electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a 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. Then, the cathode active material layer 21B was formed by compression molding with a roll press machine, and the cathode 21 was produced. After that, an aluminum positive electrode lead 25 was attached to one end of the positive electrode current collector 21A.

  Further, a negative electrode active material layer 22B was formed on a negative electrode current collector 22A made of a strip-shaped copper foil having a thickness of 10 μm, and a lithium metal foil having a thickness of 30 μm was formed.

  After preparing the positive electrode 21 and the negative electrode 22, a separator 23 made of a microporous polypropylene film having a thickness of 25 μm is prepared, and the negative electrode 22, the separator 23, the positive electrode 21, and the separator 23 are stacked in this order to form a spiral structure. The wound electrode body 20 was produced by winding a number of times.

  After producing the wound electrode body 20, the wound electrode body 20 is sandwiched between the pair of insulating plates 12 and 13, the negative electrode lead 26 is welded to the battery can 11, and the positive electrode lead 25 is welded to the safety valve mechanism 15. The wound electrode body 20 was housed inside a nickel-plated iron battery can 11. After that, an electrolytic solution was injected into the battery can 11 by a reduced pressure method.

In the electrolytic solution, 4-fluoro-1,3-dioxolan-2-one (FEC), the fluorinated carbonate shown in Chemical Formula 4, and dimethyl carbonate (DMC) were mixed at the volume ratio shown in Table 1. the mixed solvent was used as the LiPF ₆ as an electrolyte salt was dissolved at a 1.0 mol / kg. In Examples 1-1 to 1-7 and 1-21 to 1-28, the fluorinated carbonate shown in Chemical formula 4 is 4-fluoro-4-methyl-1,3- Dioxolan-2-one, cis-4-fluoro-5-methyl-1,3-dioxolan-2-one shown in Chemical Formula 7 (B), and trans-4-fluoro-shown in Chemical Formula 7 (C) An isomer mixture (hereinafter referred to as FPC) containing 5-methyl-1,3-dioxolan-2-one in this order at a molar ratio of 3: 1: 1, and in Examples 1-8 to 1-14, 4-fluoro-4-ethyl-1,3-dioxolan-2-one represented by Chemical Formula 8 (A) and cis-4-fluoro-5-ethyl-1,3- represented by Chemical Formula 8 (B) Dioxolan-2-one and trans-4-fluoro-5-ethyl-1,3-dioxo shown in Chemical Formula 8 (C) Is an isomer mixture (hereinafter referred to as FBC) containing N-2-one in this order at a molar ratio of 5: 1: 1. In Examples 1-15 to 1-20, 4-fluoro-4-phenyl-1,3-dioxolan-2-one and cis-4-fluoro-5-phenyl-1,3-dioxolan-2-one shown in Chemical Formula 9 (B) An isomer mixture (hereinafter referred to as FPhEC) containing trans-4-fluoro-5-phenyl-1,3-dioxolan-2-one shown in 9 (C) in this order at a molar ratio of 3: 1: 1. ).

  After injecting the electrolyte into the battery can 11, the battery lid 14 was caulked to the battery can 11 via the gasket 17 coated with asphalt on the surface. A cylindrical secondary battery having a height of 65 mm was obtained.

  As Comparative Example 1-1 for Examples 1-1 to 1-28, except that 4-fluoro-1,3-dioxolan-2-one and the halogenated carbonate shown in Chemical Formula 4 were not used, The same as in Examples 1-1 to 1-28, except that a solvent obtained by mixing ethylene carbonate (EC) and dimethyl carbonate in a volume ratio of ethylene carbonate: dimethyl carbonate = 30: 70 was used. Thus, a secondary battery was produced. Further, as Comparative Example 1-2, except that the halogenated carbonate shown in Chemical Formula 4 was not used, specifically, 4-fluoro-1,3-dioxolan-2-one and dimethyl carbonate were used. Except that a solvent mixed in a volume ratio of 4-fluoro-1,3-dioxolan-2-one: dimethyl carbonate = 30: 70 was used, the same procedure was followed as in Examples 1-1 to 1-28. A secondary battery was produced. Furthermore, as Comparative Example 1-3, except that 4-fluoro-1,3-dioxolan-2-one was not used, specifically, FPC and dimethyl carbonate were used, and FPC: dimethyl carbonate = 30: A secondary battery was fabricated in the same manner as in Examples 1-1 to 1-28, except that a solvent mixed at a volume ratio of 70 was used.

  Furthermore, as Comparative Examples 1-4 to 1-6, secondary graphite was used in the same manner as in Examples 1-1 to 1-28 except that artificial graphite was used as the negative electrode material and the composition of the electrolytic solution was changed. A battery was produced. At that time, the negative electrode was prepared by mixing 90 parts by mass of artificial graphite powder and 10 parts by mass of polyvinylidene fluoride as a binder, adding N-methyl-2-pyrrolidone as a solvent, and forming a strip-shaped copper foil having a thickness of 15 μm. The negative electrode current collector 22A was uniformly coated on both surfaces, dried, and compression molded with a roll press to form the negative electrode active material layer 22B. The solvent is a solvent in which ethylene carbonate and dimethyl carbonate are mixed in a volume of ethylene carbonate: dimethyl carbonate = 30: 70, or 4-fluoro-1,3-dioxolan-2-one and dimethyl carbonate. 4-fluoro-1,3-dioxolan-2-one: dimethyl carbonate = 30: 70 mixed solvent or 4-fluoro-1,3-dioxolan-2-one, FPC, dimethyl carbonate Were mixed in a volume ratio of 4-fluoro-1,3-dioxolan-2-one: FPC: dimethyl carbonate = 20: 10: 70. In addition, the area density ratio between the positive electrode 21 and the negative electrode 22 was designed so that the capacity of the negative electrode 22 is represented by a capacity component due to insertion and extraction of lithium.

  For the obtained secondary batteries of Examples 1-1 to 1-28 and Comparative examples 1-1 to 1-6, cycle characteristics were measured as follows.

  First, constant current charging was performed at a constant current of 100 mA until the battery voltage reached 4.2 V, then constant voltage charging was performed at a constant voltage of 4.2 V until the current reached 1 mA, and then at a constant current of 300 mA. The constant current discharge was performed until the battery voltage reached 3.0V. This charging / discharging was repeated, and the cycle characteristics were determined as the discharge capacity retention rate at the 100th cycle (discharge capacity at the 100th cycle / initial discharge capacity) × 100 (%) with respect to the initial discharge capacity (discharge capacity at the first cycle). . The results are shown in Tables 1 and 2.

  As can be seen from Table 1, according to Examples 1-1 to 1-28 using 4-fluoro-1,3-dioxolan-2-one and FPC, FBC or FPhEC, both of these were used. Comparative Example 1-1 having no FPC, FBC and FPhEC, or Comparative Example 1-3 having no 4-fluoro-1,3-dioxolan-2-one As a result, the discharge capacity retention rate was improved. On the other hand, according to Comparative Examples 1-4 to 6 using artificial graphite as the negative electrode material, the effect of mixing these was not observed.

  Furthermore, the discharge capacity retention rate increased as the content of FPC, FBC or FPhEC increased, and showed a tendency to decrease after showing a maximum value.

  That is, when lithium metal is used as the negative electrode active material, cycle characteristics can be improved by using 4-fluoro-1,3-dioxolan-2-one and the halogenated carbonate shown in Chemical formula 4. It was found that the content of the halogenated carbonate shown in Chemical formula 4 in the solvent is preferably in the range of 0.1% by volume to 20% by volume.

(Examples 2-1 to 2-4)
A lithium metal secondary battery was fabricated in the same manner as in Examples 1-4 and 1-11 except that LiBF ₄ or LiB (OCOCF ₃ ) ₄ was further used in addition to LiPF ₆ as the electrolyte salt. At that time, in Examples 2-1 and 2-3, the concentrations of LiPF ₆ and LiBF ₄ in the electrolytic solution were 0.8 mol / kg and 0.2 mol / kg, respectively. In Examples 2-2 and 2-4, the concentrations of LiPF ₆ and LiB (OCOCF ₃ ) ₄ in the electrolytic solution were 0.8 mol / kg and 0.2 mol / kg, respectively.

  For the fabricated secondary batteries of Examples 2-1 to 2-4, cycle characteristics were examined in the same manner as in Examples 1-1 to 1-28. The results are shown in Table 3 together with the results of Examples 1-4 and 1-11.

As can be seen from Table 3, according to the LiBF ₄ or LiB (OCOCF _{3) 4} Example 2-1 or Example 2-3 and 2-4 were used in addition to LiPF _6, only LiPF ₆ The discharge capacity retention rate was improved over Examples 1-4 and 1-11, respectively.

That is, it has been found that the cycle characteristics can be further improved by using another electrolyte salt in addition to LiPF ₆ .

(Examples 3-1 to 3-10)
A secondary battery including a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium and represented by the sum thereof was manufactured. At that time, artificial graphite was used as a negative electrode material, and the negative electrode 22 was prepared in the same manner as in Comparative Examples 1-4 to 1-6. A battery was produced. The solvent was a mixture of 4-fluoro-1,3-dioxolan-2-one, FPC, and dimethyl carbonate in a volume ratio shown in Table 4. Furthermore, LiPF ₆ was used as the electrolyte salt, and the concentration in the electrolytic solution was 1.0 mol / kg. The filling amount of the positive electrode material and the negative electrode material is designed so that 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, and is represented by the sum thereof. did.

  As Comparative Example 1-1 with respect to Examples 3-1 to 3-10, except that 4-fluoro-1,3-dioxolan-2-one and the halogenated carbonate shown in Chemical Formula 4 were not used, Specifically, except that a solvent obtained by mixing ethylene carbonate (EC) and dimethyl carbonate at a volume ratio of ethylene carbonate: dimethyl carbonate = 30: 70 was used, the other examples were as in Examples 3-1 to 1-10. Similarly, a secondary battery was produced. Further, as Comparative Example 3-2, except that FPC was not used, specifically, 4-fluoro-1,3-dioxolan-2-one and dimethyl carbonate were combined with 4-fluoro-1,3- A secondary battery was fabricated in the same manner as in Examples 3-1 to 3-10, except that a solvent mixed in a volume ratio of dioxolan-2-one: dimethyl carbonate = 30: 70 was used. Furthermore, as Comparative Example 3-3, except that 4-fluoro-1,3-dioxolan-2-one was not used, specifically, FPC and dimethyl carbonate, FPC: dimethyl carbonate = 30: A secondary battery was fabricated in the same manner as in Examples 3-1 to 3-10, except that a solvent mixed at a volume ratio of 70 was used.

  For the obtained secondary batteries of Examples 3-1 to 3-10 and Comparative examples 3-1 to 3-3, cycle characteristics were measured in the same manner as in Examples 1-1 to 1-28. The results are shown in Table 4.

Further, regarding the secondary batteries of Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-3, whether lithium metal and lithium ions are present on the negative electrode 22 by visual observation and ⁷ Li nuclear magnetic resonance spectroscopy I investigated whether or not.

As a result of ⁷ Li nuclear magnetic resonance spectroscopy, in the secondary batteries of Examples 3-1 to 3-10 and Comparative examples 4-1 to 4-3, a peak attributed to lithium metal is present in the vicinity of 265 ppm in the fully charged state. In addition, a peak attributed to lithium ions was observed around 44 ppm. These peak positions are values relative to external standard lithium chloride. On the other hand, no peak attributed to lithium metal was observed in the fully discharged state. Moreover, the lithium metal was also confirmed by visual inspection only in the fully charged state. That is, it was confirmed that 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, and is expressed by the sum thereof.

  As can be seen from Table 4, in Examples 3-1 to 3-10 using 4-fluoro-1,3-dioxolan-2-one and FPC, as in Examples 1-1 to 1-28. According to this, the discharge capacity maintenance rate was improved.

  That is, in the case of a secondary battery in which the capacity of the negative electrode 22 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 expressed as the sum thereof, 4-fluoro-1 , 3-dioxolan-2-one and the halogenated carbonate shown in Chemical formula 4 were found to improve the cycle characteristics.

(Examples 4-1 to 4-8, 5-1 to 5-8)
A battery in which the capacity of the negative electrode 22 is represented by a capacity component due to precipitation and dissolution of lithium, that is, a lithium metal secondary battery was produced.

  In Examples 4-1 to 4-8, the positive electrode lead 31 and the negative electrode lead 32 were attached to the positive electrode 33 and the negative electrode 34 produced in the same manner as in Examples 1-1 to 1-28, and these were connected via the separator 35. After laminating and winding, a secondary battery was fabricated by sandwiching between outer packaging members 40 made of a laminate film, injecting an electrolyte, and sealing. A laminate film made of nylon-aluminum-unstretched polypropylene from the outside and having a thickness of 30 μm, 40 μm, and 30 μm in total of 100 μm was used. The positive electrode current collector 33A was a strip-shaped aluminum foil having a thickness of 12 μm.

  Moreover, in Examples 5-1 to 5-8, except that a square container having a width of 30 mm, a height of 48 mm, and a thickness of 5 mm was used, other than the secondary, A battery was produced. The positive electrode current collector was a strip-shaped aluminum foil having a thickness of 12 μm.

In these examples, 4-fluoro-1,3-dioxolan-2-one, FPC or FBC as the halogenated carbonate shown in Chemical Formula 4, and dimethyl carbonate in Table 4 A solvent in which LiPF ₆ and LiBF ₄ or LiB (OCOCF ₃ ) ₄ as required were dissolved as an electrolyte salt in a solvent mixed at the indicated volume ratio was used. The concentration of each electrolyte salt in the electrolytic solution was as shown in Tables 4 and 5.

As Comparative Examples 4-1 and 5-1 for Examples 4-1 to 4-8 and 5-1 to 5-8, 4-fluoro-1,3-dioxolan-2-one and the halogenation shown in Chemical Formula 4 Specifically, except that the carbonate was not used, specifically, a solvent in which ethylene carbonate (EC) and dimethyl carbonate were mixed in a volume ratio of ethylene carbonate: dimethyl carbonate = 30: 70 was used. Were fabricated in the same manner as in Examples 4-1 to 4-8 and 5-1 to 5-8. Further, as Comparative Examples 4-2 and 5-2, except that the halogenated carbonate shown in Chemical Formula 4 was not used, specifically, 4-fluoro-1,3-dioxolan-2-one and carbonate Except for using a solvent obtained by mixing dimethyl and 4-fluoro-1,3-dioxolan-2-one: dimethyl carbonate = 30: 70 in a volume ratio, other examples 4-1 to 4-8, Secondary batteries were fabricated in the same manner as in 5-1 to 5-8. At that time, the electrolyte salt was LiPF ₆ and the concentration in the electrolyte was 1 mol / kg.

  Regarding the fabricated secondary batteries of Examples 4-1 to 4-8, 5-1 to 5-8 and Comparative Examples 4-1, 4-2, 5-1, 5-2, Examples 1-1 to 1-1 The discharge capacity retention rate was examined in the same manner as -28. The results are shown in Tables 5 and 6.

  As can be seen from Tables 5 and 6, Examples 4-1 to 4- using 4-fluoro-1,3-dioxolan-2-one and FPC as in Examples 1-1 to 1-28 According to 8,5-1 to 5-8, the discharge capacity retention rate was improved.

  That is, even when other exterior members are used, the cycle characteristics can be improved by using 4-fluoro-1,3-dioxolan-2-one and the halogenated carbonate shown in Chemical formula 4. I found out that I could do it.

  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 embodiments and examples, the case where lithium is used as the electrode reactant has been described. However, other Group 1A elements such as sodium (Na) or potassium (K), or magnesium or calcium (Ca), etc. The present invention can also be applied to the case of using the 2A group element, other light metals such as aluminum, lithium, or alloys thereof, and the same effects can be obtained. At that time, as the negative electrode active material, the negative electrode material described in the above embodiment can be used in the same manner.

  Moreover, in the said embodiment and Example, although 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 electrolyte is mentioned.

  Further, in the above embodiments and examples, the secondary battery having a wound structure has been described, but the present invention is similarly applied to a secondary battery having a structure in which the positive electrode and the negative electrode are folded or stacked. be able to.

Furthermore, in the above-described embodiment or example, a cylindrical type, a laminate film type, a coin type or a square type secondary battery has been specifically described. However, the present invention is not limited to a button type other shape. next batteries, Ru can be similarly applied to a variety of secondary batteries having a size such as a secondary battery or thin, with such other metal container to the exterior member.

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 in the secondary battery shown in FIG. It is a disassembled perspective view showing the structure of the secondary battery which concerns on other embodiment of this invention. It is sectional drawing along the II line | wire of the 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, 30 ... Winding electrode body, 21, 33 ... Positive electrode, 21A, 33A ... Positive electrode current collector, 21B, 33B ... Positive electrode active material layer, 22, 34 ... Negative electrode, 22A, 34A ... Negative electrode current collector, 22B, 34B ... Negative electrode active material layer, 23, 35 ... Separator , 24 ... Center pin, 25, 31 ... Positive electrode lead, 26, 32 ... Negative electrode lead, 36 ... Electrolyte layer, 37 ... Protective tape, 40 ... Exterior member, 41 ... Adhesion film.

Claims (9)

Bei example a cathode, an anode,
Lithium metal is used as the negative electrode active material,
The electrolyte contains a solvent containing 4-fluoro-1,3-dioxolan-2-one and a halogenated carbonate represented by Chemical Formula 1 ,
The secondary battery , wherein the content of the halogenated carbonate in the solvent is in the range of 0.1% by volume to 30% by volume .

(In Formula 1, R1, R2, R3 and R4 are each independently hydrogen, an alkyl group, an aryl group, a halogenated aryl group or a halogen, and one or more of R1, R2, R3 and R4 are A halogen, one or more of the other being an alkyl group or an aryl group.) The secondary battery according to claim 1 , wherein a content of the halogenated carbonate in the solvent is in a range of 0.1 volume% or more and 20 volume% or less. The electrolyte, and _{LiPF 6, LiBF 4, LiClO 4} , LiAsF 6, LiB (OCOCF 3) 4, LiB (OCOC 2 F 5) 4, LiN (C m F 2m + 1 SO 2) (C n F 2n + ₁ SO ₂ ) (m and n are integers of 1 or more) and LiC (C _p F _{2p + 1} SO ₂ ) (C _q F _{2q + 1} SO ₂ ) (C _r F _{2r +1} SO ₂₎ lithium salt represented by (p, q, r comprises a one or more integers.) at least one selected from the group consisting of secondary battery according to claim 1, wherein. The total content of 4-fluoro-1,3-dioxolan-2-one and the halogenated carbonate in the solvent is in the range of 10% by volume to 50% by volume. Next battery. Bei example a cathode, an anode,
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 a solvent containing 4-fluoro-1,3-dioxolan-2-one and a halogenated carbonate represented by Chemical Formula 2 ,
The secondary battery , wherein the content of the halogenated carbonate in the solvent is in the range of 0.1% by volume to 30% by volume .

(In Chemical Formula 2, R1, R2, R3 and R4 are each independently hydrogen, an alkyl group, an aryl group, a halogenated aryl group or a halogen, and one or more of R1, R2, R3 and R4 are A halogen, one or more of the other being an alkyl group or an aryl group.) The secondary battery according to claim 5 , wherein a content of the halogenated carbonate in the solvent is in a range of 0.1% by volume to 20% by volume. The electrolyte, and _{LiPF 6, LiBF 4, LiClO 4} , LiAsF 6, LiB (OCOCF 3) 4, LiB (OCOC 2 F 5) 4, LiN (C m F 2m + 1 SO 2) (C n F 2n + ₁ SO ₂ ) (m and n are integers of 1 or more) and LiC (C _p F _{2p + 1} SO ₂ ) (C _q F _{2q + 1} SO ₂ ) (C _r F _{2r +1} SO ₂₎ in a lithium salt represented (p, q, r comprises at least one kind selected from the group consisting of 1 or more is an integer.) the secondary battery according to claim 5, wherein. The total content of 4-fluoro-1,3-dioxolan-2-one and the halogenated carbonate in the solvent is in the range of 10% by volume to 50% by volume. Next battery. The secondary battery according to claim 5, wherein the light metal is lithium.

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