Secondary batteries

Abstract

Provided is a secondary battery capable of achieving excellent battery characteristics. This secondary battery is provided with a positive electrode, a negative electrode containing a lithium metal, and an electrolyte solution containing a solvent. The solvent contains an ortho-carbonate ester compound represented by formula (1), and the content of the ortho-carbonate ester compound in the solvent is 40 wt% or more.

Description

[Technical Field]

[0001] This technology relates to secondary batteries. [Background technology]

[0002] With the widespread use of various electronic devices such as mobile phones, development of rechargeable batteries is progressing as a power source that is small, lightweight, and provides high energy density. These rechargeable batteries contain an electrolyte along with a positive electrode and a negative electrode, and various studies are being conducted on the configuration of these batteries.

[0003] Specifically, the positive electrode active material contains manganese oxide, the negative electrode active material contains lithium metal, and the electrolyte solvent contains linear tetraether, with the linear tetraether content in the solvent being 1% to 20% by volume (see, for example, Patent Document 1). In addition, the non-aqueous electrolyte contains orthocarbonate, with the orthocarbonate content in the non-aqueous electrolyte being 0.001 mmol / g to 0.18 mmol / g (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 09-045339 [Patent Document 2] Japanese Patent Publication No. 2002-270222 [Overview of the project] [Problems that the invention aims to solve]

[0005] Although various studies have been conducted on the configuration of secondary batteries, their battery characteristics are still not satisfactory, and there is room for improvement.

[0006] There is a need for a secondary battery that can achieve excellent battery characteristics. [Means for solving the problem]

[0007] A secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode containing lithium metal, and an electrolytic solution containing a solvent. The solvent contains an orthocarbonate ester compound represented by formula (1), and the content of the orthocarbonate ester compound in the solvent is 40% by weight or more.

[0008]

Chemical Formula

Effects of the Invention

[0009] According to the secondary battery of an embodiment of the present technology, the negative electrode contains lithium metal, the solvent of the electrolytic solution contains the orthocarbonate ester compound represented by formula (1), and the content of the orthocarbonate ester compound in the solvent is 40% by weight or more, so excellent battery characteristics can be obtained.

[0010] It should be noted that the effects of the present technology are not necessarily limited to the effects described herein, and may be any of a series of effects related to the present technology described below.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a perspective view showing the configuration of a secondary battery according to an embodiment of the present technology. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing the configuration of the battery element illustrated in FIG. 1. [Figure 3] FIG. 3 is a block diagram showing the configuration of an application example of the secondary battery.

Mode for Carrying Out the Invention

[0012] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The order of description is as follows. 1. Secondary Battery 1-1. Overall Structure 1-2. Detailed composition of the electrolyte 1-3.Operation 1-4. Manufacturing method 1-5. Action and Effects 2. Variations 3. Applications of rechargeable batteries

[0013] <1. Secondary battery> First, we will describe a secondary battery according to one embodiment of this technology.

[0014] The secondary battery described here is a so-called lithium metal secondary battery, as it obtains its capacity by utilizing the deposition and dissolution of lithium.

[0015] <1-1. Overall Structure> Figure 1 shows a perspective view of the secondary battery. Figure 2 shows a magnified view of the cross-sectional configuration of the battery element 20 shown in Figure 1.

[0016] However, Figure 1 shows the outer film 10 and the battery element 20 separated from each other. Also, in Figure 1, the cross-section of the battery element 20 along the XZ plane is shown with a dashed line. In Figure 2, only a portion of the battery element 20 is shown.

[0017] As shown in Figures 1 and 2, this secondary battery comprises an outer film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and 42.

[0018] As described above, the secondary battery described here uses a flexible or pliable outer film 10 as an outer material for housing the battery element 20. Therefore, the secondary battery shown in Figures 1 and 2 is a so-called laminate film type secondary battery.

[0019] [Exterior film] As shown in Figure 1, the outer film 10 has a sealed bag-like structure in which the battery element 20 is housed. Thus, the outer film 10 houses the positive electrode 21, negative electrode 22, and separator 23, which will be described later.

[0020] Here, the outer film 10 is a single film-like component that is folded in the folding direction F. The outer film 10 is provided with a recessed portion 10U (a so-called deep-drawn portion) for housing the battery element 20.

[0021] Specifically, the outer film 10 is a three-layer laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside out. When the outer film 10 is folded, the outer edges of the opposing fusion layers are fused together. The fusion layer contains a polymer compound such as polypropylene. The metal layer contains a metallic material such as aluminum. The surface protection layer contains a polymer compound such as nylon.

[0022] However, the number of layers of the outer film 10 is not particularly limited; it may be one layer, two layers, or four or more layers.

[0023] [Battery element] The battery element 20 is housed in the outer film 10. This battery element 20 is a so-called power generation element and, as shown in Figures 1 and 2, includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown).

[0024] Here, the battery element 20 is a so-called wound electrode body, and the positive electrode 21 and negative electrode 22 are wound around a winding axis P, facing each other via a separator 23. This winding axis P is a virtual axis extending in the Y-axis direction, as shown in Figure 1.

[0025] The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the battery element 20 has a flattened three-dimensional shape, the shape of the cross-section of the battery element 20 intersecting the winding axis P (cross-section along the XZ plane) is a flattened shape defined by the major axis J1 and the minor axis J2.

[0026] The major axis J1 is a virtual axis extending in the X-axis direction and has a length greater than the length of the minor axis J2. The minor axis J2 is a virtual axis extending in the Z-axis direction intersecting the X-axis direction and has a length less than the length of the major axis J1. Here, since the three-dimensional shape of the battery element 20 is a flattened cylinder, the cross-sectional shape of the battery element 20 is a flattened, approximately elliptical shape.

[0027] (positive electrode) The positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B, as shown in Figure 2. However, the positive electrode current collector 21A may be omitted.

[0028] The positive electrode current collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is provided. This positive electrode current collector 21A contains a conductive material such as a metal material, a specific example of which is aluminum.

[0029] The positive electrode active material layer 21B contains one or more types of positive electrode active materials that intercalate and deintercalate lithium. However, the positive electrode active material layer 21B may further contain one or more types of other materials such as positive electrode binders and positive electrode conductive agents. The method for forming the positive electrode active material layer 21B is not particularly limited, but specifically includes methods such as coating.

[0030] Here, the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A. However, the positive electrode active material layer 21B may be provided on only one side of the positive electrode current collector 21A on the side where the positive electrode 21 faces the negative electrode 22.

[0031] The type of the positive electrode active material is not particularly limited, and specifically, it is a lithium-containing compound or the like. This lithium-containing compound is a compound containing lithium and one or more transition metal elements as constituent elements, and may further contain one or more other elements as constituent elements. The type of the other element is not particularly limited as long as it is an element other than lithium and the transition metal element, and specifically, it is an element belonging to Groups 2 to 15 in the long-form periodic table. The type of the lithium-containing compound is not particularly limited, and specifically, it is an oxide, a phosphate compound, a silicate compound, a borate compound, or the like.

[0032] Specific examples of oxides include LiNiO2, LiCoO2, LiCo 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2, Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O2 and LiMn2O4. Specific examples of phosphate compounds include LiFePO4, LiMnPO4, LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4 and the like.

[0033] The positive electrode binder contains any one or two or more of materials such as synthetic rubber and polymer compounds. Specific examples of the synthetic rubber include styrene-butadiene rubber, fluorine rubber, and ethylene propylene diene rubber. Specific examples of the polymer compound include polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

[0034] The positive electrode conductive agent contains one or more conductive materials, such as carbon materials, metallic materials, and conductive polymer compounds. Specific examples of carbon materials include graphite, carbon black, acetylene black, and Ketjen black.

[0035] (Negative electrode) As shown in Figure 2, the negative electrode 22 faces the positive electrode 21 via a separator 23 and contains lithium metal.

[0036] This lithium metal is what is known as elemental lithium. However, the purity of lithium metal is not necessarily limited to 100%. Therefore, lithium metal may unintentionally contain any amount of impurities, or may intentionally contain any amount of additives.

[0037] (Separator) As shown in Figure 2, the separator 23 is an insulating porous membrane interposed between the positive electrode 21 and the negative electrode 22. The separator 23 allows lithium to pass through in an ionic state while preventing short circuits caused by contact between the positive electrode 21 and the negative electrode 22. This separator 23 contains one or more types of insulating polymer compounds, the like being polyethylene.

[0038] (electrolyte) The electrolyte is a liquid electrolyte impregnated into the positive electrode 21 and the separator 23, respectively. This electrolyte contains a solvent and an electrolyte salt, the solvent being an orthocarbonate compound. The detailed composition of the electrolyte will be described later.

[0039] [Positive lead] As shown in Figures 1 and 2, the positive electrode lead 31 is a positive electrode wiring connected to the positive electrode current collector 21A of the positive electrode 21, and is led out to the outside of the outer film 10. This positive electrode lead 31 contains one or more types of conductive materials, such as metal materials, and a specific example of such conductive material is aluminum. The shape of the positive electrode lead 31 can be a thin plate or a mesh.

[0040] [Negative lead] The negative electrode lead 32 is a negative electrode wire connected to the negative electrode 22, as shown in Figures 1 and 2, and is led out to the outside of the outer film 10. Here, the direction of lead generation of the negative electrode lead 32 is the same as the direction of lead generation of the positive electrode lead 31. This negative electrode lead 32 contains one or more types of conductive materials, such as metal materials, and a specific example of such conductive material is copper. Details regarding the shape of the negative electrode lead 32 are the same as details regarding the shape of the positive electrode lead 31.

[0041] [Sealing film] As shown in Figure 1, the sealing film 41 is inserted between the outer film 10 and the positive lead 31. Similarly, as shown in Figure 1, the sealing film 42 is inserted between the outer film 10 and the negative lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

[0042] The sealing film 41 is a sealing member that prevents outside air and other elements from entering the interior of the outer film 10. This sealing film 41 contains a polymer compound such as polyolefin that has good adhesion to the positive electrode lead 31, and a specific example of such a polymer compound is polypropylene.

[0043] The structure of the sealing film 42 is the same as that of the sealing film 41, except that it is a sealing member that adheres to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as a polyolefin that adheres to the negative electrode lead 32.

[0044] <1-2. Detailed composition of the electrolyte> Details regarding the composition of the electrolyte are as follows.

[0045] [solvent] As mentioned above, this electrolyte contains a solvent. This solvent is a medium for dissolving and ionizing the electrolyte salt.

[0046] (Orthocarbonate compounds) The solvent contains one or more of the orthocarbonate compounds represented by formula (1). Therefore, an electrolyte containing an orthocarbonate compound whose solvent is a non-aqueous solvent is a so-called non-aqueous electrolyte.

[0047] [ka] (R1, R2, R3, and R4 are each hydrocarbon groups.)

[0048] As is clear from formula (1), this ortho-carbonate compound is a compound in which four oxygen-containing groups (-OR1, -OR2, -OR3, and -OR4) are bonded to a carbon atom. Each of R1 to R4 is a hydrocarbon group, as described above, and each of the R1 to R4 types may be the same as or different from each other. Of course, any two of the R1 to R4 types may be the same as each other, or any three of the R1 to R4 types may be the same as each other.

[0049] A hydrocarbon group is a general term for a group that contains carbon and hydrogen as constituent elements, and the number of carbon atoms in the hydrocarbon group is not particularly limited. This hydrocarbon group may be a chain-like group, a cyclic group, or a group in which a chain-like group and a cyclic group are bonded to each other. The chain-like group may be a straight chain or a branched group having one or more side chains.

[0050] Specifically, hydrocarbon groups include alkyl groups, alkenyl groups, alkynyl groups, aryl groups, cycloalkyl groups, and bonding groups. Details regarding bonding groups will be discussed later.

[0051] Specific examples of alkyl groups include methyl, ethyl, propyl, and butyl groups. Specific examples of alkenyl groups include vinyl and allyl groups. Specific examples of alkynyl groups include ethynyl groups. Specific examples of aryl groups include phenyl and naphthyl groups. Specific examples of cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl groups.

[0052] A bonding group is a general term for a monovalent group formed by the bonding of two or more groups from among alkyl groups, alkenyl groups, alkynyl groups, aryl groups, and cycloalkyl groups. A specific example of a bonding group is the benzyl group, which is a monovalent group formed by the bonding of an aryl group (phenyl group) and an alkyl group (methyl group).

[0053] In particular, the hydrocarbon group preferably contains an alkyl group, and the number of carbon atoms in that alkyl group is 3 or less. This is because it improves the solubility and compatibility of the orthocarbonate compound and makes the orthocarbonate compound easier to synthesize.

[0054] Specific examples of ortho-carbonate compounds include ortho-tetramethyl carbonate (R1=R2=R3=R4=methyl group), ortho-tetraethyl carbonate (R1=R2=R3=R4=ethyl group), ortho-tetrapropyl carbonate (R1=R2=R3=R4=propyl group), and ortho-tetraisopropyl carbonate (R1=R2=R3=R4=isopropyl group).

[0055] However, the content of the orthocarbonate compound in the solvent is set to a predetermined amount. Specifically, the content of the orthocarbonate compound in the solvent is 40% by weight or more.

[0056] The reason the solvent contains an orthocarbonate compound, and that the orthocarbonate compound content in the solvent is 40% by weight or more, is that even if the negative electrode 22 contains lithium metal, the decomposition reaction of the electrolyte on the surface of the negative electrode 22 is suppressed during charging and discharging.

[0057] In detail, ortho-carbonate compounds possess the property of being able to sufficiently dissolve and ionize electrolyte salts even when used alone, making them excellent solvents for electrolytes. Therefore, the electrolyte can function effectively even when using only ortho-carbonate compounds as the solvent.

[0058] Furthermore, ortho-carbonate compounds have a high lowest emptying level (LUMO), giving them excellent resistance to reduction. Therefore, the ortho-carbonate compounds contained in the solvent are less likely to decompose during charging and discharging, while the electrolyte salt and other compounds described later are preferentially decomposed over the ortho-carbonate compounds. As a result, a film derived from the electrolyte salt and other solvents is easily formed on the surface of the negative electrode 22, and this film is used to electrochemically protect the surface of the negative electrode 22.

[0059] Based on these findings, even if the negative electrode 22 contains a highly reactive lithium metal, the decomposition reaction of the electrolyte on the surface of the negative electrode 22 is suppressed during charging and discharging.

[0060] In this case, in particular, because the content of the orthocarbonate compound in the solvent is optimized, the protective function of the orthocarbonate compound that protects the surface of the negative electrode 22 is fully exerted. As a result, the surface of the negative electrode 22 is sufficiently and stably protected by the film derived from the electrolyte salt and other solvents, and the decomposition reaction of the electrolyte is sufficiently and stably suppressed.

[0061] In particular, the content of the orthocarbonate compound in the solvent is preferably 60% by weight or more, and more preferably 80% by weight or more. This is because the protective function of the orthocarbonate compound is more effectively exerted, thereby further suppressing the decomposition reaction of the electrolyte.

[0062] Furthermore, it is preferable that the orthocarbonate compound contains orthotetramethyl carbonate. This is because the protective function of the orthocarbonate compound is fully exhibited, and the decomposition reaction of the electrolyte is sufficiently suppressed.

[0063] Furthermore, in order to confirm that the solvent contains ortho-carbonate compounds and to measure the content of ortho-carbonate compounds in that solvent, the electrolyte is analyzed. The method for analyzing this electrolyte is not particularly limited, but specifically, it may be one or more of the following: inductively coupled plasma (ICP) emission spectroscopy, nuclear magnetic resonance spectroscopy (NMR), and gas chromatography-mass spectroscopy (GC-MS).

[0064] When analyzing the electrolyte, the rechargeable battery is disassembled, the electrolyte is recovered, and then analyzed. This allows for the identification of the types of components (ortho-carbonate compounds) contained in the electrolyte, as well as the amount of each component present.

[0065] (Other compounds) Furthermore, the solvent may contain one or more of the other compounds. As is clear from the range of ortho-carbonate compound content in the solvent described above, the solvent may contain other compounds together with the ortho-carbonate compound.

[0066] Other compounds are non-aqueous solvents (organic solvents). However, the ortho-carbonate compounds mentioned above are excluded from the other compounds described here.

[0067] Non-aqueous solvents include esters and ethers, and more specifically, carbonate ester compounds, carboxylic acid ester compounds, and lactone compounds. This is because they improve the dissociation of the electrolyte salt and also improve the mobility of ions.

[0068] Carbonate ester compounds include cyclic carbonate esters and linear carbonate esters. Specific examples of cyclic carbonate esters include ethylene carbonate and propylene carbonate, while specific examples of linear carbonate esters include dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate.

[0069] Carboxylic acid ester compounds include linear carboxylic acid esters. Specific examples of linear carboxylic acid esters include ethyl acetate, ethyl propionate, propyl propionate, and trimethylethyl acetate.

[0070] Lactone compounds include lactones, among others. Specific examples of lactones include γ-butyrolactone and γ-valerolactone.

[0071] The ethers may also be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane.

[0072] Non-aqueous solvents include unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonic acid esters, phosphate esters, acid anhydrides, nitrile compounds, and isocyanate compounds. Using these compounds can improve the electrochemical stability of the electrolyte.

[0073] Specific examples of unsaturated cyclic carbonate esters include vinylene carbonate, vinylethylene carbonate, and methyleneethylene carbonate. Specific examples of fluorinated cyclic carbonate esters include monofluoroethylene carbonate and difluoroethylene carbonate. Specific examples of sulfonic acid esters include propanesultone and propensultone. Specific examples of phosphate esters include trimethyl phosphate and triethyl phosphate. Specific examples of acid anhydrides include succinic anhydride, 1,2-ethanedisulfonic anhydride, and 2-sulfobenzoic anhydride. Specific examples of nitrile compounds include succinonitrile. Specific examples of isocyanate compounds include hexamethylene diisocyanate.

[0074] (Electrolyte salts) The electrolyte salt contains one or more types of light metal salts, such as lithium salts.

[0075] Specific examples of lithium salts include lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF3SO2)3), lithium bis(oxalato)borate (LiB(C2O4)2), lithium monofluorophosphate (Li2PFO3), and lithium difluorophosphate (LiPF2O2). High ionic conductivity can be obtained with these concentrations.

[0076] The electrolyte salt content is not particularly limited, but specifically, it is between 0.3 mol / kg and 5.0 mol / kg relative to the solvent. This is because it allows for high ionic conductivity.

[0077] <1-3. Operation> This secondary battery operates as follows in the battery element 20.

[0078] During charging, lithium is released from the positive electrode 21 in an ionic state. As a result, lithium moves to the negative electrode 22 via the electrolyte, causing lithium metal to deposit on the surface of the negative electrode 22.

[0079] During discharge, lithium metal dissolves at the negative electrode 22. As a result, lithium moves to the positive electrode 21 in an ionic state through the electrolyte, and lithium is intercalated at the positive electrode 21.

[0080] <1-4. Manufacturing method> When manufacturing a secondary battery, the positive electrode 21 and the negative electrode 22 are prepared according to the example procedure described below, the electrolyte is prepared, the secondary battery is assembled, and the assembled secondary battery is subjected to stabilization treatment.

[0081] [Fabrication of the positive electrode] First, a positive electrode mixture is prepared by mixing the positive electrode active material, positive electrode binder, and positive electrode conductive agent together. Next, a paste-like positive electrode mixture slurry is prepared by adding the positive electrode mixture to a solvent. This solvent may be an aqueous solvent or an organic solvent. Finally, a positive electrode active material layer 21B is formed by applying the positive electrode mixture slurry to both sides of the positive electrode current collector 21A. After this, the positive electrode active material layer 21B may be compressed and molded using a compression device such as a roll press. In this case, the positive electrode active material layer 21B may be heated, or the compression molding may be repeated multiple times. As a result, a positive electrode 21 is produced by forming a positive electrode active material layer 21B on both sides of the positive electrode current collector 21A.

[0082] [Fabrication of the negative electrode] A negative electrode 22 containing lithium metal is prepared as the negative electrode active material. In this case, the negative electrode 22 may be manufactured by attaching lithium metal foil or the like to the negative electrode current collector.

[0083] [Preparation of electrolyte solution] After adding the electrolyte salt to a solvent containing an ortho-carbonate compound, the solvent is stirred. In this case, the amount of ortho-carbonate compound added is adjusted so that its content in the solvent falls within the range described above. As a result, the electrolyte salt dissolves in the solvent, and the electrolyte solution is prepared.

[0084] [Assembly of rechargeable batteries] First, the positive electrode lead 31 is connected to the positive electrode current collector 21A of the positive electrode 21 using a joining method such as welding. Then, the negative electrode lead 32 is connected to the negative electrode 22 using a joining method such as welding.

[0085] Next, a laminate (not shown) is formed by stacking the positive electrode 21 and the negative electrode 22 on top of each other via a separator 23. Subsequently, a wound body (not shown) is produced by winding the laminate, and then the wound body is molded into a flattened shape by pressing it with a compression device such as a press. The molded wound body has the same configuration as the battery element 20, except that the positive electrode 21 and the separator 23 are not impregnated with electrolyte.

[0086] Next, after the winding body is placed in the recessed portion 10U, the outer film 10 (fusion layer / metal layer / surface protection layer) is folded so that the outer films 10 face each other. Subsequently, using an adhesive method such as heat fusion, the outer edges of two sides of the opposing fusion layers are joined together to house the winding body in the bag-shaped outer film 10.

[0087] Finally, after injecting the electrolyte into the bag-shaped outer film 10, the outer edges of the remaining sides of the opposing fused layers are joined together using an adhesive method such as heat fusion. In this case, a sealing film 41 is inserted between the outer film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the outer film 10 and the negative electrode lead 32.

[0088] As a result, the winding material is impregnated with electrolyte, and the winding material is sealed in the bag-shaped outer film 10, thus assembling the secondary battery.

[0089] [Stabilization treatment for rechargeable batteries after assembly] The assembled secondary battery is charged and discharged. Stabilization conditions such as ambient temperature, number of charge / discharge cycles, and charge / discharge conditions can be set arbitrarily.

[0090] As a result, a coating is formed on the surfaces of the positive electrode 21 and the negative electrode 22. In this case, as described above, a coating derived from the electrolyte salt and other compounds is formed on the surface of the negative electrode 22.

[0091] Therefore, the state of the battery element 20 is electrochemically stabilized, and the secondary battery is completed.

[0092] <1-5. Mechanism and Effects> According to this secondary battery, the negative electrode 22 contains lithium metal, the electrolyte solvent contains an orthocarbonate compound, and the orthocarbonate compound content in the solvent is 40% by weight or more.

[0093] In this case, as described above, by utilizing the properties of the ortho-carbonate compound, the solubility of the electrolyte salt in the solvent is improved, and a good film derived from the electrolyte salt and other compounds is easily formed on the surface of the negative electrode 22 during charging and discharging. As a result, the surface of the negative electrode 22 is electrochemically protected by the film, and even if the negative electrode 22 contains a highly reactive lithium metal, the decomposition reaction of the electrolyte on the surface of the negative electrode 22 is suppressed during charging and discharging. Therefore, excellent battery characteristics can be obtained.

[0094] In particular, if the ortho-carbonate compound content in the solvent is 60% by weight or more, the decomposition reaction of the electrolyte is further suppressed by utilizing the protective function of the ortho-carbonate compound, thereby achieving a higher effect. In this case, if the ortho-carbonate compound content in the solvent is 80% by weight or more, the decomposition reaction of the electrolyte is further suppressed, resulting in an even higher effect.

[0095] Furthermore, if the hydrocarbon group in formula (1) relating to the orthocarbonate compound contains an alkyl group, and the number of carbon atoms in that alkyl group is 3 or less, the solubility and compatibility of the orthocarbonate compound will improve, thus achieving a higher effect.

[0096] Furthermore, if the orthocarbonate compound contains orthotetramethyl carbonate, the protective function of the orthocarbonate compound is fully exercised. Therefore, the decomposition reaction of the electrolyte is sufficiently suppressed, resulting in a higher effect.

[0097] <2. Variant> The configuration of the secondary battery can be modified as appropriate, as described below. However, the variations described below may be combined with each other.

[0098] [Example 1] A porous membrane separator 23 was used. However, although not specifically shown in the diagram, a laminated separator containing a polymer compound layer may also be used.

[0099] Specifically, the laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer provided on one or both sides of the porous membrane. This improves the adhesion of the separator to the positive electrode 21 and the negative electrode 22, thereby suppressing misalignment of the battery element 20. As a result, misalignment of the windings of the positive electrode 21, the negative electrode 22, and the separator 23 is suppressed, and swelling of the secondary battery is suppressed even if a decomposition reaction of the electrolyte occurs. The polymer compound layer includes polyvinylidene fluoride, etc. Polyvinylidene fluoride is chosen because it has excellent physical strength and is electrochemically stable.

[0100] Furthermore, one or both of the porous membrane and the polymer compound layer may contain one or more types of insulating particles from a selection of multiple insulating particles. This is because the multiple insulating particles dissipate heat when the secondary battery generates heat, thereby improving the safety (heat resistance) of the secondary battery. The multiple insulating particles include one or more types of insulating materials, such as inorganic materials and resin materials. Specific examples of inorganic materials include aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of resin materials include acrylic resin and styrene resin.

[0101] When fabricating a laminated separator, a precursor solution containing a polymer compound and an organic solvent is prepared, and then the precursor solution is applied to one or both sides of a porous membrane. In this case, the precursor solution may contain multiple insulating particles.

[0102] Even when using this stacked separator, lithium can move in an ionic state between the positive electrode 21 and the negative electrode 22, thus achieving a similar effect. In this case, in particular, as mentioned above, swelling of the secondary battery is further suppressed, resulting in an even greater effect.

[0103] [Differentiation 2] A liquid electrolyte solution was used. However, although not specifically illustrated here, a gel-like electrolyte layer may also be used.

[0104] In the battery element 20 using an electrolyte layer, the positive electrode 21 and the negative electrode 22 are wound facing each other via a separator 23 and the electrolyte layer. This electrolyte layer is interposed between the positive electrode 21 and the separator 23, and also between the negative electrode 22 and the separator 23.

[0105] Specifically, the electrolyte layer contains a polymer compound along with the electrolyte, and the electrolyte is held in place by the polymer compound. This prevents leakage of the electrolyte. The composition of the electrolyte is as described above. The polymer compound includes polyvinylidene fluoride, etc. When forming the electrolyte layer, a precursor solution containing the electrolyte, polymer compound, and solvent is prepared, and then the precursor solution is applied to one or both sides of the positive electrode 21 and the negative electrode 22, respectively.

[0106] Even when this electrolyte layer is used, lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer, thus achieving a similar effect. In this case, in particular, as mentioned above, leakage of the electrolyte is prevented, resulting in an even greater effect.

[0107] <3. Applications of rechargeable batteries> Finally, I will explain the applications (examples of use) of secondary batteries.

[0108] The uses of secondary batteries are not particularly limited. Secondary batteries used as power sources may be the primary power source or the auxiliary power source in electronic devices and electric vehicles, etc. A primary power source is a power source that is used preferentially regardless of the presence or absence of other power sources. An auxiliary power source may be a power source used in place of the primary power source, or a power source that can be switched from the primary power source.

[0109] Specific examples of secondary battery applications are described below: Electronic devices such as video cameras, digital still cameras, mobile phones, notebook computers, headphone stereos, portable radios, and portable information terminals; backup power supplies and storage devices such as memory cards; power tools such as electric drills and electric saws; battery packs installed in electronic devices; medical electronic devices such as pacemakers and hearing aids; electric vehicles (including hybrid vehicles); and power storage systems such as household or industrial battery systems that store power in preparation for emergencies. In these applications, one secondary battery may be used, or multiple secondary batteries may be used.

[0110] A battery pack may consist of individual cells or a battery pack. An electric vehicle is a vehicle that runs using a secondary battery as a power source, and may also be a hybrid vehicle that has a power source other than the secondary battery. In a household power storage system, household electrical appliances can be used by utilizing the electricity stored in the secondary battery, which is the power storage source.

[0111] Here, we will specifically explain one example of a secondary battery application. The configuration described below is merely an example and can be modified as needed.

[0112] Figure 3 shows the block configuration of a battery pack, which is an example of a rechargeable battery application. The battery pack described here is a single rechargeable battery pack (a so-called soft pack) and is installed in electronic devices such as smartphones.

[0113] As shown in Figure 3, this battery pack comprises a power supply 51 and a circuit board 52. The circuit board 52 is connected to the power supply 51 and includes a positive terminal 53, a negative terminal 54, and a temperature detection terminal 55.

[0114] The power supply 51 includes one rechargeable battery. In this rechargeable battery, the positive lead is connected to the positive terminal 53, and the negative lead is connected to the negative terminal 54. Since the power supply 51 is connected to the outside via the positive terminal 53 and the negative terminal 54, it is rechargeable and dischargeable. The circuit board 52 includes a control unit 56, a switch 57, a PTC element 58 which is a thermal resistance element, and a temperature detection unit 59. However, the PTC element 58 may be omitted.

[0115] The control unit 56 includes a central processing unit (CPU) and memory, and controls the operation of the entire battery pack. This control unit 56 also detects and controls the usage status of the power supply 51.

[0116] Furthermore, when the voltage of the power supply 51 (secondary battery) reaches the overcharge detection voltage or over-discharge detection voltage, the control unit 56 disconnects the switch 57 to prevent charging current from flowing through the current path of the power supply 51. The overcharge detection voltage is not particularly limited, but specifically it is 4.20V ± 0.05V, and the over-discharge detection voltage is not particularly limited, but specifically it is 2.40V ± 0.10V.

[0117] Switch 57 includes a charge control switch, a discharge control switch, a charging diode, and a discharge diode, and switches the connection between the power supply 51 and external equipment according to the instructions of the control unit 56. This switch 57 includes a field-effect transistor (MOSFET) using a metal oxide semiconductor, and the charging current and discharge current are detected based on the ON resistance of the switch 57.

[0118] The temperature detection unit 59 includes a temperature detection element such as a thermistor. This temperature detection unit 59 measures the temperature of the power supply 51 using the temperature detection terminal 55 and outputs the temperature measurement result to the control unit 56. The temperature measurement result measured by the temperature detection unit 59 is used when the control unit 56 performs charge / discharge control in the event of abnormal heat generation and when the control unit 56 performs correction processing when calculating the remaining capacity. [Examples]

[0119] An example of this technology will be described below.

[0120] <Examples 1-4 and Comparative Examples 1, 2> As explained below, after manufacturing the rechargeable batteries, their battery characteristics were evaluated.

[0121] [Manufacturing of secondary batteries] Here, to easily evaluate the battery characteristics, a test secondary battery was prepared using the following procedure. This test secondary battery is a simple lithium metal secondary battery.

[0122] First, the electrolyte solution was prepared by adding the electrolyte salt (bis(trifluoromethanesulfonyl)imide lithium) to the solvent and then stirring the solvent.

[0123] As solvents, ortho-tetramethyl ortho-carbonate (OTTM), an ortho-carbonate ester compound, and another compound, 1,2-dimethoxyethane (DME), were used. In this case, the mixing ratio of the ortho-carbonate ester compound and the other compound was adjusted. The electrolyte salt content was 1 mol / l (= 1 mol / dm³) relative to the solvent. 3 )

[0124] The content (by weight) of orthocarbonate compounds in the solvent and the content (by weight) of other compounds in the solvent are shown in Table 1.

[0125] Next, a test electrode was fabricated by pressing a lithium metal foil (thickness = 0.1 mm) onto a copper foil (thickness = 0.01 mm) using a press machine.

[0126] Next, the electrolyte was impregnated into a separator (microporous polyethylene film, thickness = 10 μm) by dropping the electrolyte onto it. The amount of electrolyte dropped was 0.01 ml (= 0.01 cm). 3 )

[0127] Next, a copper foil (thickness = 0.012 mm) was prepared as the counter electrode, and the test electrode and the counter electrode were stacked on top of each other via a separator impregnated with electrolyte. As a result, the test electrode and the counter electrode faced each other via the electrolyte-impregnated separator, completing the test secondary battery.

[0128] [Evaluation of battery characteristics] The charge-discharge characteristics of the battery were evaluated using the procedure described below, and the results shown in Table 1 were obtained.

[0129] When evaluating the charge and discharge characteristics, the charging capacity was first measured by charging the secondary battery in a normal temperature environment (temperature = 23°C), and then the discharge capacity was measured by discharging the same secondary battery.

[0130] During charging, the current is 0.22mA / cm². 2 The battery was charged at a current density until the total charging time reached 3 hours. During discharge, it was discharged until the voltage reached 0.1V.

[0131] Next, the Coulomb efficiency was calculated based on the formula: Coulomb efficiency (%) = (discharge capacity / charge capacity) × 100.

[0132] Next, under the same conditions, the secondary battery was repeatedly charged and discharged, calculating the Coulomb efficiency after each cycle, until the total number of cycles reached 25. The charge and discharge conditions were as described above.

[0133] Finally, the average Coulomb efficiency, an index for evaluating charge-discharge characteristics, was calculated by averaging the 16 Coulomb efficiencies obtained for each of the 10th to 25th cycles. This average Coulomb efficiency value is rounded to two decimal places.

[0134] Furthermore, the nine Coulomb efficiencies calculated during the initial charge-discharge cycles (cycles 1-9) were not used to calculate the average Coulomb efficiency. This is because the Coulomb efficiency tends to vary during the initial charge-discharge cycles. By using only the Coulomb efficiencies calculated during later charge-discharge cycles (cycles 10-25) and excluding those from the initial cycles, the variation in Coulomb efficiency becomes less pronounced. This ensures the accuracy and reproducibility of the average Coulomb efficiency calculation.

[0135] [Table 1]

[0136] [Consideration] As shown in Table 1, the average Coulomb efficiency varied depending on the solvent composition.

[0137] Specifically, when the content of the orthocarbonate compound in the solvent was less than 40% by weight (Comparative Examples 1 and 2), the average Coulomb efficiency decreased.

[0138] In contrast, when the content of the orthocarbonate compound in the solvent was 40% by weight or more (Examples 1-4), the average Coulomb efficiency increased. In this case, the average Coulomb efficiency increased even more when the content of the orthocarbonate compound in the solvent was 60% by weight or more (Examples 2-4). Furthermore, when the content of the orthocarbonate compound in the solvent was 80% by weight or more (Examples 3,4), the average Coulomb efficiency increased even further.

[0139] Furthermore, Patent Document 2 (Japanese Patent Publication No. 2002-270222) mentioned above contains an orthocarbonate similar to the orthocarbonate compound.

[0140] However, the secondary battery disclosed in Patent Document 2 is a lithium-ion secondary battery, and not a lithium metal secondary battery. Furthermore, in the secondary battery disclosed in Patent Document 2, the orthocarbonate compound in the non-aqueous electrolyte is 0.001 mmol / g to 0.18 mmol / g, so the orthocarbonate content in the non-aqueous electrolyte should be less than 40% by weight when converted to the orthocarbonate compound content in the solvent.

[0141] Therefore, the appropriate range of orthocarbonate content necessary to increase the average Coulomb growth rate in lithium metal secondary batteries is not disclosed in Patent Document 2.

[0142] [summary] As shown in Table 1, when the test electrode contained lithium metal, the electrolyte solvent contained an orthocarbonate compound, and the orthocarbonate compound content in the solvent was 40% by weight or more, a high average Coulomb efficiency was obtained. Therefore, the charge and discharge characteristics were improved, resulting in excellent battery characteristics and superior safety.

[0143] Although the present technology has been described above with reference to one embodiment and one example, the configuration of the present technology is not limited to the configuration described in the one embodiment and one example, and can be modified in various ways.

[0144] Specifically, the explanation described the case where the battery structure of the rechargeable battery is of the laminated film type. However, the battery structure of the rechargeable battery is not particularly limited, and may be cylindrical, prismatic, coin-shaped, or button-shaped, etc.

[0145] Furthermore, the case where the element structure of the battery element is of the wound type has been described. However, the element structure of the battery element is not particularly limited, and may also be of the stacked type or the zigzag type. In the stacked type, the positive electrode and negative electrode are stacked alternately with a separator in between, while in the zigzag type, the positive electrode and negative electrode are folded in a zigzag pattern with a separator in between, facing each other.

[0146] The effects described herein are illustrative only, and therefore the effects of this technology are not limited to those described herein. Accordingly, other effects may be obtained with respect to this technology.

[0147] Furthermore, this technology can also be configured as follows: <1> Positive electrode and, A negative electrode containing lithium metal, Electrolyte containing solvent and Equipped with, The solvent comprises an orthocarbonate compound represented by formula (1), The content of the orthocarbonate compound in the solvent is 40% by weight or more. Secondary battery. [ka] (R1, R2, R3, and R4 are each hydrocarbon groups.) <2> The content of the orthocarbonate compound in the solvent is 60% by weight or more. <1> The secondary battery described above. <3> The content of the orthocarbonate compound in the solvent is 80% by weight or more. <2> The secondary battery described above. <4> The hydrocarbon group includes an alkyl group, The number of carbon atoms in the alkyl group is 3 or less. <1> or <3> A rechargeable battery as described in one of the following. <5> The orthocarbonate ester compound includes orthocarbonate tetramethyl. <1> or <4> A rechargeable battery as described in one of the following. [Explanation of Symbols]

[0148] 21...Positive electrode, 22...Negative electrode

Claims

1. Positive electrode and, A negative electrode containing lithium metal, Electrolyte containing solvent and Equipped with, The solvent comprises an orthocarbonate compound represented by formula (1), The content of the orthocarbonate compound in the solvent is 40% by weight or more. Secondary battery. 【Chemistry 1】 (R1, R2, R3, and R4 are each hydrocarbon groups.)

2. The content of the orthocarbonate compound in the solvent is 60% by weight or more. The secondary battery according to claim 1.

3. The content of the orthocarbonate compound in the solvent is 80% by weight or more. The secondary battery according to claim 2.

4. The hydrocarbon group includes an alkyl group, The number of carbon atoms in the alkyl group is 3 or less. A secondary battery according to any one of claims 1 to 3.

5. The orthocarbonate ester compound includes orthocarbonate tetramethyl. A secondary battery according to any one of claims 1 to 3.

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