Negative electrode for secondary battery and secondary battery

Abstract

This secondary battery comprises a positive electrode, a negative electrode including a negative electrode active material layer, and an electrolyte, and the negative electrode active material layer includes a negative electrode active material, lithium fluoride (LiF), and lithium ethylene dicarbonate (Li-OC(=O)O-C2H4-OC(=O)O-Li). The weight ratio represented by formula (1) is 0.01-0.2 inclusive, and the weight sum represented by formula (2) is 0.2-2.0 wt% inclusive.　MA = M2 / M1… (1) (MA is the weight ratio. M1 is the ratio (wt%) of the weight of the lithium fluoride with respect to the weight of the negative electrode active material. M2 is the ratio (wt%) of the weight of the lithium ethylene dicarbonate with respect to the weight of the negative electrode active material.)　MB = M1 + M2…(2) (MB is the weight sum (wt%). M1 is the ratio (wt%) of the weight of the lithium fluoride with respect to the weight of the negative electrode active material. M2 is the ratio (wt%) of the weight of the lithium ethylene dicarbonate with respect to the weight of the negative electrode active material.)

Description

Technical Field

[0001] This technology relates to a negative electrode for a secondary battery and a secondary battery.

Background Art

[0002] Due to the widespread use of various electronic devices such as mobile phones, the development of secondary batteries is underway as a power source that is small and lightweight and can obtain a high energy density. This secondary battery includes an electrolytic solution together with a positive electrode and a negative electrode (negative electrode for secondary battery), and various studies have been made on the configuration of the secondary battery.

[0003] Specifically, in a surface-modified carbonaceous particle material containing carbonaceous core particles, the carbonaceous core particles have a hydrophilic non-graphitic carbon coating (see, for example, Patent Document 1). Further, the electrolytic solution contains a lithium salt additive, and the lithium salt additive contains lithium fluoride or the like (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

[0005] Although various studies have been made on the configuration of secondary batteries, the battery characteristics of the secondary batteries are not yet sufficient, so there is room for improvement.

[0006] There is a need for a negative electrode for a secondary battery and a secondary battery that can obtain excellent battery characteristics.

[0007] The negative electrode for a secondary battery according to an embodiment of the present technology includes a negative electrode active material layer, and the negative electrode active material layer contains a negative electrode active material, lithium fluoride (LiF), and lithium ethylene dicarbonate (Li-OC(=O)O-C2H4-OC(=O)O-Li). The weight ratio represented by the formula (1) is 0.01 or more and 0.2 or less, and the weight sum represented by the formula (2) is 0.2% by weight or more and 2.0% by weight or less.

[0008] MA = M2 / M1 ···(1) (MA is the weight ratio. M1 is the ratio (% by weight) of the weight of lithium fluoride to the weight of the negative electrode active material. M2 is the ratio (% by weight) of the weight of lithium ethylene dicarbonate to the weight of the negative electrode active material.)

[0009] MB = M1 + M2 ···(2) (MB is the weight sum (% by weight). M1 is the ratio (% by weight) of the weight of lithium fluoride to the weight of the negative electrode active material. M2 is the ratio (% by weight) of the weight of lithium ethylene dicarbonate to the weight of the negative electrode active material.)

[0010] The secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolytic solution, and the negative electrode has the same configuration as that of the negative electrode for a secondary battery according to an embodiment of the present technology described above.

[0011] According to the negative electrode for a secondary battery or the secondary battery according to an embodiment of the present technology, the negative electrode active material layer of the negative electrode for a secondary battery contains a negative electrode active material, lithium fluoride, and lithium ethylene dicarbonate, the weight ratio shown in the formula (1) is 0.01 or more and 0.2 or less, and the weight sum shown in the formula (2) is 0.2% by weight or more and 2.0% by weight or less, so excellent battery characteristics can be obtained.

[0012] Note that the effects of the present technology are not necessarily limited to the effects described here, and may be any of a series of effects related to the present technology described later.

Brief Description of Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0014] Hereinafter, one embodiment of the present technology will be described in detail with reference to the drawings. The order of description is as follows. 1. Negative electrode for secondary battery 1-1. Configuration 1-2. Operation 1-3. Manufacturing method 1-4. Action and effect 2. Secondary battery 2-1. Configuration 2-2. Operation 2-3. Manufacturing method 2-4. Action and effect 3. Modification example 4. Applications of secondary battery

[0015] <1. Negative electrode for secondary battery> First, the negative electrode for a secondary battery (hereinafter simply referred to as "negative electrode") in one embodiment of the present technology will be described.

[0016] The negative electrode described here is used in a secondary battery, which is an electrochemical device. However, the negative electrode may also be used in other electrochemical devices other than secondary batteries. Specific examples of other electrochemical devices include capacitors and the like.

[0017] This negative electrode occludes and releases electrode reaction substances during the electrode reaction of the electrochemical device. The type of electrode reaction substance is not particularly limited, but specifically, it is a light metal such as an alkali metal and an alkaline earth metal. Specific examples of alkali metals include lithium, sodium, and potassium, and specific examples of alkaline earth metals include beryllium, magnesium, and calcium.

[0018] Hereinafter, the case where the electrode reaction substance is lithium will be taken as an example. That is, in the negative electrode, lithium is occluded and released in an ionic state during the electrode reaction.

[0019] <1-1. Structure> FIG. 1 shows a cross-sectional structure of a negative electrode 100, which is an example of a negative electrode. However, in FIG. 1, only a part of the negative electrode 100 is shown.

[0020] As shown in FIG. 1, this negative electrode 100 includes a negative electrode active material layer 120. Here, the negative electrode 100 further includes a negative electrode current collector 110 that supports the negative electrode active material layer 120.

[0021] [Negative electrode current collector] The negative electrode current collector 110 is a conductive support that supports the negative electrode active material layer 120 and has a pair of surfaces on which the negative electrode active material layer 120 is provided. This negative electrode current collector 110 includes any one or two or more of conductive materials such as metal materials, and specific examples of the conductive materials include copper and the like.

[0022] The surface of the negative electrode current collector 110 is preferably roughened using an electrolysis method or the like. This is because the adhesion of the negative electrode active material layer 120 to the negative electrode current collector 110 is improved by utilizing the so-called anchor effect.

[0023] However, the negative electrode current collector 110 may be omitted. That is, the negative electrode 100 may consist only of the negative electrode active material layer 120.

[0024] [Negative electrode active material layer] The negative electrode active material layer 120 contains a negative electrode active material that occludes and releases lithium, lithium fluoride, and lithium ethylene carbonate. However, the negative electrode active material layer 120 may further contain any one or two or more of other materials such as a negative electrode binder and a negative electrode conductive agent.

[0025] Here, the negative electrode active material layer 120 is provided on both sides of the negative electrode current collector 110. However, the negative electrode active material layer 120 may be provided on only one side of the negative electrode current collector 110.

[0026] The method for forming the negative electrode active material layer 120 is not particularly limited, but specifically, it is any one or two or more of a coating method, a vapor phase method, a liquid phase method, a spraying method, and a firing method (sintering method).

[0027] (Negative electrode active material) The type of the negative electrode active material is not particularly limited, but specifically, it is any one or two or more of materials such as a carbon material and a metal-based material. That is, the negative electrode active material may be only a carbon material, only a metal-based material, or both a carbon material and a metal-based material. This is because a high energy density can be obtained. However, the type of the negative electrode active material may be other materials other than each of the carbon material and the metal-based material.

[0028] The carbon material is a general term for materials containing carbon as a constituent element. Since the crystal structure of the carbon material hardly changes during the occlusion and release of lithium, a high energy density can be stably obtained. In addition, since the carbon material also functions as a negative electrode conductive agent, the conductivity of the negative electrode active material layer 120 is improved.

[0029] Specific examples of the carbon material include graphitizable carbon, non-graphitizable carbon, and graphite. This graphite may be natural graphite, artificial graphite, or both. The interlayer spacing of the (002) plane for non-graphitizable carbon is not particularly limited, but specifically, it is 0.37 nm or more. The interlayer spacing of the (002) plane for graphite is not particularly limited, but specifically, it is 0.34 nm or less.

[0030] In addition, specific examples of the carbon material include pyrolytic carbons, cokes, glassy carbon fibers, fired products of organic polymer compounds, activated carbons, and carbon blacks. These cokes include pitch coke, needle coke, and petroleum coke. The fired product of the organic polymer compound is a fired product obtained by firing (carbonizing) a polymer compound such as a phenol resin and a furan resin at an appropriate temperature. In addition, the carbon material may be low-crystalline carbon heat-treated at a temperature of about 1000 °C or lower, or amorphous carbon. The shape of the carbon material is not particularly limited, but specifically, it is any one or two or more of fibrous, spherical, granular, and flaky shapes.

[0031] The metal-based material is a general term for materials containing any one or two or more of metal elements and metalloid elements that can form an alloy with lithium as constituent elements. A higher energy density can be obtained with the metal-based material.

[0032] This metal-based material may be a single substance, an alloy, a compound, a mixture of two or more of them, or a material containing one or two or more phases of them. The "single substance" described here means only a general single substance, so the single substance may contain trace amounts of impurities. That is, the purity of the single substance is not necessarily limited to 100%.

[0033] However, the "alloy" described herein includes not only materials containing two or more metal elements as constituent elements, but also materials containing one or two or more metal elements and one or two or more metalloid elements as constituent elements. Further, the "alloy" may contain one or two or more non-metal elements as constituent elements. The structure of the metal-based material is not particularly limited, but specifically, it is any one or two or more of a solid solution, eutectic (eutectic mixture), intermetallic compound, and a coexistence of two or more of them.

[0034] Specific examples of the metal element and the metalloid element include magnesium, boron, aluminum, gallium, indium, silicon, germanium, tin, lead, bismuth, cadmium, silver, zinc, hafnium, zirconium, yttrium, palladium, and platinum.

[0035] Among them, the metal-based material is preferably a silicon-containing material. This is because it has excellent lithium storage and release ability, and thus can obtain a significantly high energy density. This silicon-containing material is a general term for materials containing silicon as a constituent element. That is, the silicon-containing material may be a single substance of silicon, an alloy of silicon, a compound of silicon, a mixture of two or more of them, or a material containing one or two or more of these phases.

[0036] The alloy of silicon contains any one or two or more of metal elements such as tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as constituent elements other than silicon. The compound of silicon contains any one or two or more of non-metal elements such as carbon and oxygen as constituent elements other than silicon. However, the compound of silicon may further contain any one or two or more of the series of metal elements described for the alloy of silicon as constituent elements other than silicon.

[0037] Specific examples of silicon alloys include SiB4, SiB6, Mg2Si, Ni2Si, TiSi2, MoSi2, CoSi2, NiSi2, CaSi2, CrSi2, Cu5Si, FeSi2, MnSi2, NbSi2, TaSi2, VSi2, WSi2, ZnSi2, and SiC. However, the composition of the silicon alloy (mixing ratio of silicon and metal elements) can be arbitrarily changed.

[0038] Specific examples of silicon compounds include Si3N4, Si2N2O, SiO x (0 < x ≤ 2) and LiSiO, etc. However, the range of x may also be 0.2 < x < 1.4.

[0039] From these facts, it is preferable that the negative electrode active material contains a silicon-containing material which is a metal-based material. This is because, as described above, an extremely high energy density can be obtained.

[0040] In this case, it is preferable that the negative electrode active material further contains a carbon material. That is, it is preferable that the negative electrode active material contains both a carbon material and a silicon-containing material. This is because, during the electrode reaction (charging and discharging) of the secondary battery provided with the negative electrode 100, damage and dropout of the negative electrode active material layer 120 are prevented while ensuring the battery capacity.

[0041] Specifically, the silicon-containing material which is a metal-based material has the advantage of a high theoretical capacity, but on the other hand, has the concern of being likely to expand and contract violently during charging and discharging. On the other hand, the carbon material has the concern of a low theoretical capacity, but on the other hand, has the advantage of being difficult to expand and contract during charging and discharging. Therefore, by using the carbon material and the silicon-containing material in combination, while obtaining a high theoretical capacity, the expansion and contraction of the negative electrode active material layer 120 during charging and discharging are suppressed. As a result, as described above, damage and dropout of the negative electrode active material layer 120 are prevented while ensuring the battery capacity.

[0042] (lithium fluoride and lithium ethylene carbonate) Lithium fluoride and lithium ethylene carbonate are included in the negative electrode active material layer 120 as described above. As a result, each of the negative electrode active material, lithium fluoride, and lithium ethylene carbonate is dispersed while being mixed with each other in the negative electrode active material layer 120.

[0043] Lithium ethylene carbonate forms a protective film on the surface of the negative electrode active material by decomposing and reacting during the electrode reaction. As a result, since the surface of the reactive negative electrode active material is protected by the protective film, the decomposition reaction of the electrolytic solution on the surface of the negative electrode active material is suppressed during charge and discharge of the secondary battery provided with the negative electrode 100. Hereinafter, the function of protecting the surface of the negative electrode active material by using the film derived from lithium ethylene carbonate is referred to as the "protection function of lithium ethylene carbonate".

[0044] Lithium fluoride preferentially decomposes and reacts more than lithium ethylene carbonate during the electrode reaction, thereby suppressing the decomposition of lithium ethylene carbonate without forming a protective film. That is, lithium fluoride acts self-sacrificially during the electrode reaction, thereby suppressing the disappearance of the protection function of lithium ethylene carbonate.

[0045] (Weight ratio MA and weight sum MB) However, in order to ensure the protection function of lithium ethylene carbonate, predetermined conditions are satisfied regarding the mixing ratio and the mixing amount of lithium fluoride and lithium ethylene carbonate, respectively.

[0046] Specifically, the weight ratio MA represented by the formula (1) is 0.01 to 0.2, and the weight sum MB represented by the formula (2) is 0.2% by weight to 2.0% by weight.

[0047] MA = M2 / M1 ···(1) (MA is a weight ratio. M1 is the ratio (weight %) of the weight of lithium fluoride to the weight of the negative electrode active material. M2 is the ratio (weight %) of the weight of lithium ethylene carbonate to the weight of the negative electrode active material.)

[0048] MB = M1 + M2 ···(2) (MB is the sum of weights (weight %). M1 is the ratio (weight %) of the weight of lithium fluoride to the weight of the negative electrode active material. M2 is the ratio (weight %) of the weight of lithium ethylene carbonate to the weight of the negative electrode active material.)

[0049] As is clear from Equation (1), the weight ratio MA is a parameter representing the mixing ratio of lithium fluoride and lithium ethylene carbonate, and is calculated based on the ratio M1 of lithium fluoride and the ratio M2 of lithium ethylene carbonate.

[0050] As is clear from Equation (2), the sum of weights MB is a parameter representing the mixing amount of lithium fluoride and lithium ethylene carbonate, and is calculated based on the ratios M1 and M2 in the same manner as the weight ratio MA.

[0051] The negative electrode active material layer 120 contains lithium fluoride and lithium ethylene carbonate, and the above-described conditions are satisfied for each of the weight ratio MA and the sum of weights MB because the mixing ratio and the mixing amount of the lithium fluoride and the lithium ethylene carbonate are optimized respectively. Thereby, while suppressing a decrease in the conductivity of the negative electrode active material layer 120 caused by the presence of lithium fluoride and lithium ethylene carbonate, the protective function of the lithium ethylene carbonate is ensured.

[0052] Note that the ratio M1 can be adjusted to a desired value by changing the amounts of the negative electrode active material and lithium fluoride respectively in the manufacturing process of the negative electrode 100 described later. Also, the ratio M2 can be adjusted to a desired value by changing the amounts of the negative electrode active material and lithium ethylene carbonate respectively in the manufacturing process of the negative electrode 100. Therefore, by changing each of the ratios M1 and M2, each of the weight ratio MA and the weight sum MB can be adjusted.

[0053] (Calculation procedure for ratio M1) The procedure for calculating the ratio M1 is as described below. Hereinafter, a case where the negative electrode active material layer 120 contains a negative electrode binder together with a negative electrode active material, lithium fluoride, and lithium ethylene carbonate will be described.

[0054] First, in the negative electrode 100, the negative electrode active material layer 120 is recovered by peeling the negative electrode current collector 110 from the negative electrode active material layer 120. When using a secondary battery provided with the negative electrode 100, the negative electrode 100 is recovered by disassembling the secondary battery.

[0055] Subsequently, after the negative electrode active material layer 120 is put into a solvent for dissolution removal, the solvent is stirred. This solvent is any one or two or more of the solvents capable of dissolving lithium fluoride, lithium ethylene carbonate, and the negative electrode binder, and specifically, an aqueous solvent such as water. Thereby, while lithium fluoride, lithium ethylene carbonate, and the negative electrode binder are dissolved by the solvent, the negative electrode active material is not dissolved by the solvent, so that the negative electrode active material is separated from lithium fluoride, lithium ethylene carbonate, and the negative electrode binder in the solvent.

[0056] Subsequently, after recovering the negative electrode active material by filtering the solvent, the weight G1 of the negative electrode active material is measured.

[0057] On one hand, after washing the negative electrode 100 with a solvent for cleaning, the negative electrode 100 is dried. This solvent is any one or two or more of organic solvents, specifically, acetone or the like. The environment during drying may be an inert gas atmosphere using argon gas or the like, or a dry environment.

[0058] Subsequently, extraction treatment (extraction time = 15 minutes) is performed by putting the negative electrode 100 into a solution for extraction. As this solution, a dimethyl sulfoxide-d6 solution of lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2) (LiTFSI DMSO-d6) is used. Thereby, an extract containing lithium fluoride is obtained.

[0059] Subsequently, the extract is analyzed using fluorine-19 nuclear magnetic resonance method ( 19 19F NMR). Thereby, a peak attributed to lithium fluoride is detected at -203 ppm. Subsequently, by comparing the integral value of the signal with the integral value of the signal of the internal standard substance, the weight G2 of lithium fluoride contained in the extract is specified. As this internal standard substance, sodium 3-(trimethylsilyl)propionate-d4 is used.

[0060] Finally, based on the weights G1 and G2, the ratio M1 (= G2 / G1) is calculated.

[0061] (Procedure for calculating ratio M2) The procedure for calculating the ratio M2 is the same as the procedure for calculating the ratio M1, except that the analysis method is changed.

[0062] When analyzing the extract, proton nuclear magnetic resonance method ( 1 1H NMR) and carbon-13 nuclear magnetic resonance method ( 13The extract is analyzed using 13C NMR. As a result, when proton nuclear magnetic resonance method is used, a peak attributed to lithium ethylene carbonate is detected at 3.63 ppm. Also, when carbon-13 nuclear magnetic resonance method is used, peaks attributed to lithium ethylene carbonate are detected at 62.7 ppm and 166.2 ppm, respectively. Thus, the weight G3 of lithium ethylene carbonate contained in the extract is specified, and the ratio M2 (=G3 / G1) is calculated based on the weights G1 and G3.

[0063] (Procedure for calculating weight ratio MA and weight sum MB) Based on the calculation results of the above ratios M1 and M2, the weight ratio MA (=M2 / M1) is calculated and the weight sum MB (=M1 + M2) is calculated.

[0064] (Negative electrode binder) The negative electrode binder contains any one or two or more of materials such as synthetic rubber and polymer compounds. Specific examples of synthetic rubber are styrene-butadiene rubber, fluorine rubber, and ethylene propylene diene. Specific examples of polymer compounds are polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

[0065] (Negative electrode conductive agent) The negative electrode conductive agent contains any one or two or more of conductive materials such as carbon materials. Specific examples of the conductive materials are graphite, carbon black, acetylene black, and ketjen black. However, the conductive material is not limited to carbon materials and may be metal materials, polymer compounds, etc.

[0066] <1-2. Operation> In this negative electrode 100, in the negative electrode active material layer 120 during the electrode reaction, the negative electrode active material occludes lithium in an ionic state and lithium is released from the negative electrode active material in an ionic state.

[0067] <1-3. Manufacturing method> When manufacturing the negative electrode 100, first, a negative electrode mixture is prepared by mixing a negative electrode active material, lithium fluoride, and lithium ethylene carbonate with each other. In this case, the amounts of the negative electrode active material, lithium fluoride, and lithium ethylene carbonate are adjusted so that the above-described conditions are satisfied for each of the weight ratio MA and the weight sum MB. Incidentally, if necessary, the negative electrode mixture may contain a negative electrode binder, a negative electrode conductive agent, and the like.

[0068] Subsequently, a paste-like negative electrode mixture slurry is prepared by adding the negative electrode mixture to a solvent. This solvent is an aqueous solvent such as water. In this case, the solvent containing the negative electrode mixture may be stirred using a stirring device such as a mixer.

[0069] Here, after preparing a negative electrode mixture containing lithium fluoride and lithium ethylene carbonate, a negative electrode mixture slurry was prepared using the negative electrode mixture. However, after preparing a negative electrode mixture slurry using a negative electrode mixture not containing lithium fluoride and lithium ethylene carbonate, lithium fluoride and lithium ethylene carbonate may be added to the negative electrode mixture slurry.

[0070] Finally, a negative electrode active material layer 120 is formed by applying the negative electrode mixture slurry to both sides of the negative electrode current collector 110. Thereafter, the negative electrode active material layer 120 may be compression molded using a roll press or the like. In this case, the negative electrode active material layer 120 may be heated, or the compression molding may be repeated a plurality of times.

[0071] Thereby, since the negative electrode active material layers 120 are formed on both sides of the negative electrode current collector 110, the negative electrode 100 is completed.

[0072] <1-4. Action and effect> According to this negative electrode 100, the negative electrode active material layer 120 of the negative electrode 100 contains a negative electrode active material, lithium fluoride, and lithium ethylene carbonate, the weight ratio MA is 0.01 to 0.2, and the weight sum MB is 0.2 wt% to 2.0 wt%.

[0073] In this case, as described above, since the mixing ratio and the mixing amount of lithium fluoride and lithium ethylene carbonate are optimized respectively, while suppressing the decrease in the conductivity of the negative electrode active material layer 120 caused by the presence of the lithium fluoride and the lithium ethylene carbonate, the protective function of the lithium ethylene carbonate is ensured.

[0074] Therefore, in a secondary battery including the negative electrode 100, excellent battery characteristics can be obtained.

[0075] In particular, if the negative electrode active material contains a silicon-containing material, a significantly high energy density can be obtained, so that a higher effect can be obtained. In this case, if the negative electrode active material further contains a carbon material, while ensuring the battery capacity, breakage and detachment of the negative electrode active material layer 120 are prevented, so that an even higher effect can be obtained.

[0076] <2. Secondary Battery> Next, a secondary battery according to an embodiment of the present technology to which the negative electrode 100 is applied will be described.

[0077] The secondary battery described here is a secondary battery in which battery capacity is obtained by utilizing the occlusion and release of electrode reactants, and includes an electrolytic solution together with a positive electrode and a negative electrode.

[0078] In this secondary battery, the charging capacity of the negative electrode is larger than the discharging capacity of the positive electrode. That is, the electrochemical capacity per unit area of the negative electrode is set to be larger than the electrochemical capacity per unit area of the positive electrode. This is to prevent the deposition of electrode reactants on the surface of the negative electrode during charging.

[0079] Hereinafter, as described above, the case where the electrode reactant is lithium will be taken as an example. A secondary battery in which battery capacity is obtained by utilizing the occlusion and release of lithium is a so-called lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is occluded and released in an ionic state.

[0080] <2-1. Configuration> FIG. 2 shows a perspective configuration of the secondary battery, and FIG. 3 shows a cross-sectional configuration of the battery element 20 shown in FIG. 2. FIG. 4 shows a planar configuration of the positive electrode 21 shown in FIG. 3, and FIG. 5 shows a planar configuration of the negative electrode 22 shown in FIG. 3. However, in FIG. 2, a state in which the exterior film 10 and the battery element 20 are separated from each other is shown, and in FIG. 3, only a part of the battery element 20 is shown.

[0081] As shown in FIGS. 2 and 3, this secondary battery includes an exterior film 10, a battery element 20, a plurality of positive electrode terminals 31, a plurality of negative electrode terminals 32, a positive electrode lead 41, a negative electrode lead 42, and sealing films 51 and 52.

[0082] As described above, the secondary battery described here uses a flexible or pliable exterior film 10 as an exterior member, so it is a so-called laminate film type secondary battery.

[0083] [Exterior Film] As shown in FIG. 2, the exterior film 10 is an exterior member that houses the battery element 20, and has a bag-like structure that is sealed in a state in which the battery element 20 is housed inside. Thereby, the exterior film 10 houses an electrolytic solution together with the positive electrode 21 and the negative electrode 22 described later.

[0084] Here, the exterior film 10 is a single film-like member and is folded in the folding direction F. The exterior film 10 is provided with a recessed portion 10U (so-called deep drawing portion) for accommodating the battery element 20.

[0085] Specifically, the exterior film 10 is a three-layer laminated film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside. In a state where the exterior film 10 is folded, the outer peripheral edges of the fusion layers facing each other are fused to each other. The fusion layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protection layer contains a polymer compound such as nylon.

[0086] However, the configuration (number of layers) of the exterior film 10 is not particularly limited, so it may be one layer or two layers, or four or more layers.

[0087] [Battery element] As shown in FIGS. 2 to 5, the battery element 20 is a power generation element including a positive electrode 21, a negative electrode 22, a separator 23, and an electrolytic solution (not shown), and is housed inside the exterior film 10.

[0088] Here, since the battery element 20 is a so-called laminated electrode body, the positive electrode 21 and the negative electrode 22 are alternately laminated via the separator 23. The number of each of the positive electrode 21, the negative electrode 22, and the separator 23 is not particularly limited, so it can be arbitrarily set.

[0089] [Positive electrode] As shown in FIGS. 3 and 4, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B. In FIG. 4, the positive electrode active material layer 21B is shaded.

[0090] 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, and specific examples of the conductive material are aluminum and the like.

[0091] The positive electrode active material layer 21B contains any one or two or more kinds of positive electrode active materials capable of occluding and releasing lithium. However, the positive electrode active material layer 21B may further contain any one or two or more kinds of other materials such as a positive electrode binder and a positive electrode conductive agent.

[0092] 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 only on one side of the positive electrode current collector 21A on the side where the positive electrode 21 faces the negative electrode 22. The method for forming the positive electrode active material layer 21B is not particularly limited, but specifically, it is a coating method or the like.

[0093] The type of the positive electrode active material is not particularly limited, but specifically, it is a lithium-containing compound or the like. This lithium-containing compound is a compound containing one or two or more transition metal elements as constituent elements together with lithium, and may further contain one or two 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 each of lithium and the transition metal element, but specifically, it is an element belonging to Groups 2 to 15 in the long-period type periodic table. The type of the lithium-containing compound is not particularly limited, but specifically, it is an oxide, a phosphate compound, a silicate compound, a borate compound, or the like.

[0094] Specific examples of the oxide are 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)Such as O2 and LiMn2O4. Specific examples of the phosphate compound are LiFePO4, LiMnPO4, LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4 and the like.

[0095] Details regarding each of the positive electrode binder and the positive electrode conductive agent are the same as those regarding each of the negative electrode binder and the negative electrode conductive agent described above.

[0096] Here, as shown in FIG. 4, since a part of the positive electrode current collector 21A protrudes, the positive electrode current collector 21A includes a portion protruding outward from the positive electrode active material layer 21B (hereinafter referred to as "the protruding portion of the positive electrode current collector 21A"). Since the positive electrode active material layer 21B is not provided on the protruding portion of the positive electrode current collector 21A, the protruding portion of the positive electrode current collector 21A functions as the positive electrode terminal 31. Details regarding the positive electrode terminal 31 will be described later.

[0097] On both surfaces of the positive electrode current collector 21A (excluding the positive electrode terminal 31), the positive electrode active material layer 21B is provided only on a part of the positive electrode current collector 21A. Therefore, the portion of the positive electrode current collector 21A where the positive electrode active material layer 21B is not provided is not covered by the positive electrode active material layer 21B and is exposed.

[0098] Specifically, as shown in FIG. 4, the positive electrode current collector 21A includes a coated portion 21AX and an uncoated portion 21AY. The coated portion 21AX is located at the central portion of the positive electrode current collector 21A and is the portion where the positive electrode active material layer 21B is formed. The uncoated portion 21AY is located around the coated portion 21AX and is a frame-shaped portion where the positive electrode active material layer 21B is not formed. Thus, the coated portion 21AX is covered by the positive electrode active material layer 21B, while the uncoated portion 21AY is not covered by the positive electrode active material layer 21B and is exposed.

[0099] (Negative electrode) The negative electrode 22 has the same configuration as that of the negative electrode 100. Specifically, as shown in FIGS. 3 and 5, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B. In FIG. 5, the negative electrode active material layer 22B is masked.

[0100] The configuration of the negative electrode current collector 22A is the same as that of the negative electrode current collector 110, and the configuration of the negative electrode active material layer 22B is the same as that of the negative electrode active material layer 120. That is, the negative electrode active material layer 22B contains a negative electrode active material, lithium fluoride, and lithium ethylene carbonate, and the above-described conditions are satisfied with respect to each of the weight ratio MA and the weight sum MB.

[0101] Here, as shown in FIG. 5, since a part of the negative electrode current collector 22A protrudes, the negative electrode current collector 22A includes a portion protruding outward from the negative electrode active material layer 22B (hereinafter referred to as "the protruding portion of the negative electrode current collector 22A").

[0102] The protruding direction of the protruding portion of the negative electrode current collector 22A is the same as the protruding direction of the protruding portion of the positive electrode current collector 21A. Further, the position of the protruding portion of the negative electrode current collector 22A is a position that does not overlap with the protruding portion of the positive electrode current collector 21A in a state where the positive electrode 21 and the negative electrode 22 are alternately laminated via the separator 23.

[0103] Since the negative electrode active material layer 22B is not provided on the protruding portion of the negative electrode current collector 22A, the protruding portion of the negative electrode current collector 22A functions as the negative electrode terminal 32. Details of the negative electrode terminal 32 will be described later.

[0104] On both surfaces of the negative electrode current collector 22A (excluding the negative electrode terminal 32), the negative electrode active material layer 22B is provided over the entire negative electrode current collector 22A. For this reason, the entire negative electrode current collector 22A is not exposed and is covered with the negative electrode active material layer 22B.

[0105] Specifically, as shown in FIG. 5, the negative electrode active material layer 22B includes an opposing portion 22BX and a non-opposing portion 22BY. The opposing portion 22BX is the portion that faces the covering portion 21AX. That is, since the opposing portion 22BX faces the positive electrode active material layer 21B, it is the portion involved in the charge-discharge reaction. The non-opposing portion 22BY is the portion that faces the non-covered portion 21AY. That is, since the non-opposing portion 22BY does not face the positive electrode active material layer 21B but faces the positive electrode current collector 21A, it is the portion not involved in the charge-discharge reaction. In FIG. 5, in order to clearly show the formation range of the covering portion 21AX (positive electrode active material layer 21B), the formation range of the covering portion 21AX (the boundary between the opposing portion 22BX and the non-opposing portion 22BY) is indicated by a dashed line.

[0106] The reason that the negative electrode active material layer 22B is provided on the entire both surfaces of the negative electrode current collector 22A, while the positive electrode active material layer 21B is provided only on a part (covering portion 21AX) of the both surfaces of the positive electrode current collector 21A, is to prevent lithium released from the positive electrode active material layer 21B during charging from depositing on the surface of the negative electrode 22.

[0107] Here, when the weight ratio MA and the weight sum MB are examined retrospectively after the completion of the secondary battery, it is preferable to use the non-opposing portion 22BY of the negative electrode active material layer 22B. This is because the non-opposing portion 22BY is hardly involved in the charge-discharge reaction. In the non-opposing portion 22BY, the mixing ratio and the mixing amount of lithium fluoride and lithium ethylene carbonate are maintained as they are at the time of forming the negative electrode 22 without being affected by the charge-discharge reaction. Thereby, even when the secondary battery has been used, the weight ratio MA and the weight sum MB can be examined stably and reproducibly.

[0108] (Separator) As shown in FIG. 3, the separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, and allows lithium ions to pass through while preventing contact (short circuit) between the positive electrode 21 and the negative electrode 22. This separator 23 contains a polymer compound such as polyethylene.

[0109] (Electrolyte solution) The electrolyte solution is a liquid electrolyte. This electrolyte solution is impregnated in each of the positive electrode 21, the negative electrode 22, and the separator 23, and contains a solvent and an electrolyte salt.

[0110] Here, the solvent contains any one or two or more of non-aqueous solvents (organic solvents), and the electrolyte solution containing the non-aqueous solvent is a so-called non-aqueous electrolyte solution. This non-aqueous solvent contains esters and ethers, etc. More specifically, it contains carbonate-based compounds, carboxylic acid ester-based compounds, and lactone-based compounds, etc. This is because the dissociation property of the electrolyte salt is improved and the mobility of ions is also improved.

[0111] The carbonate-based compounds are cyclic carbonates and chain carbonates, etc. Specific examples of cyclic carbonates are ethylene carbonate and propylene carbonate, etc., and specific examples of chain carbonates are dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, etc.

[0112] The carboxylic acid ester-based compounds are chain carboxylic acid esters, etc. Specific examples of chain carboxylic acid esters are ethyl acetate, ethyl propionate, propyl propionate, and ethyl trimethylacetate, etc.

[0113] The lactone-based compounds are lactones, etc. Specific examples of lactones are γ-butyrolactone and γ-valerolactone, etc.

[0114] In addition, the ethers may be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, etc.

[0115] The electrolyte salt contains any one or two or more of light metal salts such as lithium salts. Specific examples of the lithium salt include lithium hexafluorophosphate (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). This is because a high battery capacity can be obtained.

[0116] The content of the electrolyte salt is not particularly limited, but specifically, it is 0.3 mol / kg to 3.0 mol / kg with respect to the solvent. This is because high ionic conductivity can be obtained.

[0117] In addition, the electrolytic solution may further contain any one or two or more of the additives. The types of additives are not particularly limited, but specifically, they include unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonic acid esters, phosphoric acid esters, acid anhydrides, nitrile compounds, and isocyanate compounds.

[0118] Specific examples of the unsaturated cyclic carbonate include vinylene carbonate, vinyl ethylene carbonate, and methylene ethylene carbonate. Specific examples of the fluorinated cyclic carbonate include ethylene monofluorocarbonate and ethylene difluorocarbonate. Specific examples of the sulfonic acid ester include propane sultone and propene sultone. Specific examples of the phosphoric acid ester include trimethyl phosphate and triethyl phosphate. Specific examples of the acid anhydride include succinic anhydride, 1,2-ethanedisulfonic anhydride, and 2-sulfobenzoic anhydride. Specific examples of the nitrile compound include succinonitrile. Specific examples of the isocyanate compound include hexamethylene diisocyanate.

[0119] [Plurality of positive electrode terminals and plurality of negative electrode terminals] As shown in FIG. 4, the positive electrode terminal 31 is electrically connected to the positive electrode 21, and more specifically, is electrically connected to the positive electrode current collector 21A. In the battery element 20, as described above, since the positive electrode 21 and the negative electrode 22 are alternately laminated via the separator 23, the battery element 20 includes a plurality of positive electrodes 21. Accordingly, the secondary battery includes a plurality of positive electrode terminals 31.

[0120] The positive electrode terminal 31 includes a conductive material such as a metal material, and the type of the conductive material is not particularly limited. Specifically, the positive electrode terminal 31 includes the same material as the material for forming the positive electrode current collector 21A.

[0121] Here, as described above, since the protruding portion of the positive electrode current collector 21A functions as the positive electrode terminal 31, the positive electrode terminal 31 is physically integrated with the positive electrode current collector 21A. This is because the connection resistance between the positive electrode current collector 21A and the positive electrode terminal 31 is reduced, and thus the electrical resistance of the entire secondary battery is reduced.

[0122] As will be described later, the plurality of positive electrode terminals 31 are joined to each other using a joining method such as a welding method, and thus, as shown in FIG. 2, a single lead-shaped joint portion 31Z is formed.

[0123] As shown in FIG. 5, the negative electrode terminal 32 is electrically connected to the negative electrode 22, and more specifically, is electrically connected to the negative electrode current collector 22A. In the battery element 20, as described above, since the positive electrode 21 and the negative electrode 22 are alternately laminated via the separator 23, the battery element 20 includes a plurality of negative electrodes 22. Accordingly, the secondary battery includes a plurality of negative electrode terminals 32.

[0124] The negative electrode terminal 32 includes a conductive material such as a metal material, and the type of the conductive material is not particularly limited. Specifically, the negative electrode terminal 32 includes the same material as the material for forming the negative electrode current collector 22A.

[0125] Here, as described above, since the protruding portion of the negative electrode current collector 22A functions as the negative electrode terminal 32, the negative electrode terminal 32 is physically integrated with the negative electrode current collector 22A. This is because the connection resistance between the negative electrode current collector 22A and the negative electrode terminal 32 decreases, resulting in a decrease in the overall electrical resistance of the secondary battery.

[0126] As will be described later, the plurality of negative electrode terminals 32 are joined to each other using a joining method such as a welding method, and thus, as shown in FIG. 2, a single lead-shaped joint portion 32Z is formed.

[0127] [Positive Electrode Lead and Negative Electrode Lead] As shown in FIG. 2, the positive electrode lead 41 is connected to the joint portion 31Z and is led out from the inside to the outside of the exterior film 10. This positive electrode lead 41 contains a conductive material such as a metal material, and specifically, contains the same material as the material forming the positive electrode current collector 21A. The shape of the positive electrode lead 41 is not particularly limited, but specifically, it is either a thin plate shape or a mesh shape or the like.

[0128] As shown in FIG. 2, the negative electrode lead 42 is connected to the joint portion 32Z and is led out from the inside to the outside of the exterior film 10. This negative electrode lead 42 contains a conductive material such as a metal material, and specifically, contains the same material as the material forming the negative electrode current collector 22A. Note that the leading-out direction of the negative electrode lead 42 is the same as that of the positive electrode lead 41. Also, the details regarding the shape of the negative electrode lead 42 are the same as the details regarding the shape of the positive electrode lead 41.

[0129] [Sealing Film] The sealing film 51 is inserted between the exterior film 10 and the positive electrode lead 41, and the sealing film 52 is inserted between the exterior film 10 and the negative electrode lead 42. However, one or both of the sealing films 51 and 52 may be omitted.

[0130] This sealing film 51 is a sealing member that prevents the intrusion of outside air or the like into the exterior film 10. The sealing film 51 contains a polymer compound such as polyolefin having adhesiveness to the positive electrode lead 41, and specific examples of the polymer compound are polypropylene and the like.

[0131] The configuration of the sealing film 52 is the same as that of the sealing film 51 except that it is a sealing member having adhesiveness to the negative electrode lead 42. That is, the sealing film 52 contains a polymer compound such as polyolefin having adhesiveness to the negative electrode lead 42.

[0132] <2-2. Operation> During charging of the secondary battery, in the battery element 20, lithium is released from the positive electrode 21 and the lithium is occluded in the negative electrode 22 through the electrolyte. On the other hand, during discharging of the secondary battery, in the battery element 20, lithium is released from the negative electrode 22 and the lithium is occluded in the positive electrode 21 through the electrolyte. During these charging and discharging processes, lithium is occluded and released in an ionic state.

[0133] <2-3. Manufacturing Method> FIG. 6 shows a perspective configuration corresponding to FIG. 2 for explaining the manufacturing method of the secondary battery. However, in FIG. 6, instead of the battery element 20, a laminate 20Z used for manufacturing the battery element 20 is shown. Details of the laminate 20Z will be described later.

[0134] When manufacturing a secondary battery, each of the positive electrode 21 and the negative electrode 22 is manufactured according to a procedure of an example described below, and after preparing the electrolyte, the secondary battery is assembled using the positive electrode 21, the negative electrode 22, and the electrolyte, and the secondary battery is subjected to a stabilization process.

[0135] [Manufacture of Positive Electrode] First, a paste-like positive electrode mixture slurry is prepared by introducing a mixture (positive electrode mixture) in which a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent are mixed with each other into a solvent. This solvent may be an aqueous solvent or an organic solvent. Subsequently, a positive electrode active material layer 21B is formed by applying the positive electrode mixture slurry to both surfaces (excluding the positive electrode terminal 31) of the positive electrode current collector 21A integrated with the positive electrode terminal 31. Finally, the positive electrode active material layer 21B is compression-molded using a roll press or the like. In this case, the positive electrode active material layer 21B may be heated, or the compression molding may be repeated a plurality of times. Thereby, since the positive electrode active material layers 21B are formed on both surfaces of the positive electrode current collector 21A, the positive electrode 21 is produced.

[0136] [Fabrication of negative electrode] A negative electrode 22 is formed by the same procedure as the fabrication procedure of the negative electrode 100 described above. Specifically, first, a paste-like negative electrode mixture slurry is prepared by introducing a mixture (negative electrode mixture) in which a negative electrode active material, lithium fluoride, lithium ethylene carbonate, and a negative electrode binder are mixed with each other into a solvent. Subsequently, a negative electrode active material layer 22B is formed by applying the negative electrode mixture slurry to both surfaces (excluding the negative electrode terminal 32) of the negative electrode current collector 22A integrated with the negative electrode terminal 32. Finally, the negative electrode active material layer 22B is compression-molded. Thereby, since the negative electrode active material layers 22B are formed on both surfaces of the negative electrode current collector 22A, the negative electrode 22 is produced.

[0137] [Preparation of electrolyte] An electrolyte salt is introduced into a solvent. Thereby, since the electrolyte salt is dispersed or dissolved in the solvent, an electrolyte is prepared.

[0138] [Assembly of secondary battery] First, a laminate 20Z is produced by alternately laminating the positive electrode 21 and the negative electrode 22 via a separator 23 as shown in FIG. 6. This laminate 20Z has the same configuration as that of the battery element 20 except that each of the positive electrode 21, the negative electrode 22, and the separator 23 is not impregnated with the electrolyte.

[0139] Subsequently, by using a joining method such as a welding method to join a plurality of positive electrode terminals 31 to each other to form a joint portion 31Z, and then using a joining method such as a welding method to connect a positive electrode lead 41 to the joint portion 31Z. Also, by using a joining method such as a welding method to join a plurality of negative electrode terminals 32 to each other to form a joint portion 32Z, and then using a joining method such as a welding method to connect a negative electrode lead 42 to the joint portion 32Z.

[0140] Subsequently, after accommodating the laminate 20Z inside the recessed portion 10U, the outer packaging film 10 (fusion layer / metal layer / surface protection layer) is folded so that the outer packaging films 10 face each other. Subsequently, by using an adhesion method such as a thermal fusion method to adhere the outer peripheral edge portions of two sides of the facing fusion layers to each other, the laminate 20Z is stored inside the bag-shaped outer packaging film 10.

[0141] Finally, after injecting an electrolytic solution inside the bag-shaped outer packaging film 10, by using an adhesion method such as a thermal fusion method to adhere the outer peripheral edge portions of the remaining one side of the facing fusion layers to each other. In this case, a sealing film 51 is inserted between the outer packaging film 10 and the positive electrode lead 41, and a sealing film 52 is inserted between the outer packaging film 10 and the negative electrode lead 42.

[0142] As a result, since the laminate 20Z is impregnated with the electrolytic solution, the battery element 20 which is a laminated electrode body is produced. Therefore, since the battery element 20 is enclosed inside the bag-shaped outer packaging film 10, a secondary battery is assembled.

[0143] [Stabilization of Secondary Battery] The assembled secondary battery is charged and discharged. Various conditions such as the environmental temperature, the number of charge and discharge cycles (cycle number), and the charge and discharge conditions can be arbitrarily set. As a result, a film is formed on the surface of each of the positive electrode 21 and the negative electrode 22, so that the state of the secondary battery is electrochemically stabilized. Therefore, the secondary battery is completed.

[0144] In the stabilization process of this secondary battery, since the negative electrode active material layer 22B of the negative electrode 22 contains lithium fluoride and lithium ethylene carbonate, and the above-described conditions are satisfied with respect to each of the weight ratio MA and the weight sum MB, a film having a plurality of pores is formed and the film is densified.

[0145] <2-4. Action and effect> According to this secondary battery, since it includes the negative electrode 22 and the negative electrode 22 has the same configuration as that of the negative electrode 100, excellent battery characteristics can be obtained for the reasons described above.

[0146] In particular, if the secondary battery is a lithium ion secondary battery, a sufficient battery capacity can be stably obtained by utilizing the intercalation and deintercalation of lithium, so that a higher effect can be obtained.

[0147] <3. Modification example> The configuration of the secondary battery described above can be appropriately changed as described below. However, any two or more of the series of modification examples described below may be combined with each other.

[0148] [Modification example 1] In FIG. 4, since the protruding portion of the positive electrode current collector 21A also serves as the positive electrode terminal 31, the positive electrode terminal 31 is physically integrated with the positive electrode current collector 21A. However, since the positive electrode terminal 31 is physically separated from the positive electrode current collector 21A, it may be separated from the positive electrode current collector 21A. In this case, the positive electrode terminal 31 may be connected to the positive electrode current collector 21A using a joining method such as a welding method.

[0149] Also in this case, since the positive electrode terminal 31 is electrically connected to the positive electrode 21, the same effect can be obtained. However, in order to reduce the electrical resistance of the entire secondary battery in accordance with the reduction of the connection resistance, it is preferable that the positive electrode terminal 31 is physically integrated with the positive electrode current collector 21A.

[0150] Similarly, in FIG. 5, since the protruding portion of the negative electrode current collector 22A also serves as the negative electrode terminal 32, the negative electrode terminal 32 is physically integrated with the negative electrode current collector 22A. However, since the negative electrode terminal 32 is physically separated from the negative electrode current collector 22A, it may be separated from the negative electrode current collector 22A. In this case, the negative electrode terminal 32 may be connected to the negative electrode current collector 22A using a joining method such as a welding method.

[0151] Even in this case, since the negative electrode terminal 32 is electrically connected to the negative electrode 22, the same effects can be obtained. However, in order to reduce the electrical resistance of the entire secondary battery in accordance with the reduction of the connection resistance, it is preferable that the negative electrode terminal 32 is physically integrated with the negative electrode current collector 22A.

[0152] [Modification Example 2] In FIG. 2, the battery element 20 which is a laminated electrode body is used. However, although not specifically shown here, a battery element which is a wound electrode body may be used. In this case, the positive electrode 21 has a strip-like structure, the positive electrode terminal 31 is electrically connected to the positive electrode current collector 21A, the negative electrode 22 has a strip-like structure, and the negative electrode terminal 32 is electrically connected to the negative electrode current collector 22A. Thereby, the positive electrode 21 and the negative electrode 22 are wound while facing each other via the separator 23.

[0153] Even in this case, since the secondary battery can be charged and discharged using the battery element 20, the same effects can be obtained.

[0154] [Modification Example 3] The separator 23 which is a porous membrane is used. However, although not specifically shown here, a laminated separator including a polymer compound layer may be used.

[0155] Specifically, the laminated separator includes a porous membrane having a pair of surfaces, and a polymer compound layer provided on one or both surfaces of the porous membrane. This is because the adhesion of the separator to each of the positive electrode 21 and the negative electrode 22 is improved, suppressing the displacement (warpage) of the battery element 20. As a result, even if side reactions such as the decomposition reaction of the electrolyte occur, the swelling of the secondary battery is suppressed. The polymer compound layer contains a polymer compound such as polyvinylidene fluoride. This is because excellent physical strength and excellent electrochemical stability can be obtained.

[0156] Note that one or both of the porous membrane and the polymer compound layer may contain any one or two or more of a plurality of insulating particles. This is because when the secondary battery generates heat, the plurality of insulating particles promote heat dissipation, improving the safety (heat resistance) of the secondary battery. The insulating particles contain any one or two or more of insulating materials such as inorganic materials and resin materials. Specific examples of the inorganic material include aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of the resin material include acrylic resin and styrene resin.

[0157] When manufacturing the laminated separator, a precursor solution containing a polymer compound, a solvent, etc. is prepared, and then the precursor solution is applied to one or both surfaces of the porous membrane. In this case, if necessary, a plurality of insulating particles may be added to the precursor solution.

[0158] Even when this laminated separator is used, lithium ions can move between the positive electrode 21 and the negative electrode 22, so the same effect can be obtained. In this case, in particular, as described above, since the safety of the secondary battery is improved, a higher effect can be obtained.

[0159] [Modification Example 4] An electrolyte solution that is a liquid electrolyte was used. However, although not specifically illustrated here, an electrolyte layer that is a gel electrolyte may be used.

[0160] In the battery element 20 using an electrolyte layer, the positive electrode 21 and the negative electrode 22 are alternately laminated via the 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.

[0161] Specifically, the electrolyte layer contains a polymer compound together with an electrolytic solution, and the electrolytic solution is retained by the polymer compound. This is because leakage of the electrolytic solution is prevented. The configuration of the electrolytic solution is as described above. The polymer compound includes polyvinylidene fluoride and the like. When forming the electrolyte layer, a precursor solution containing an electrolytic solution, a polymer compound, a solvent, etc. is prepared, and then the precursor solution is applied to one or both sides of each of the positive electrode 21 and the negative electrode 22.

[0162] 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, so the same effect can be obtained. In this case, in particular, as described above, since leakage of the electrolytic solution is prevented, a higher effect can be obtained.

[0163] <4. Applications of Secondary Batteries> The applications (application examples) of the secondary battery are not particularly limited. The secondary battery used as a power source may be a main power source or an auxiliary power source in electronic devices, electric vehicles, etc. The main power source is a power source that is preferentially used regardless of the presence or absence of other power sources. The auxiliary power source may be a power source used instead of the main power source or a power source that can be switched from the main power source.

[0164] Specific examples of the uses of secondary batteries are as follows. They are electronic devices such as video cameras, digital still cameras, mobile phones, notebook computers, headphone stereos, portable radios, and portable information terminals. They are storage devices such as backup power supplies and memory cards. They are power tools such as electric drills and electric saws. They are battery packs mounted on electronic devices and the like. They are medical electronic devices such as pacemakers and hearing aids. They are electric vehicles (including hybrid vehicles). They are power storage systems such as household or industrial battery systems that store power for emergencies and the like. In these uses, one secondary battery may be used, or a plurality of secondary batteries may be used.

[0165] For the battery pack, a single cell or a battery module may be used. An electric vehicle is a vehicle that runs using a secondary battery as a driving power source, and may be a hybrid vehicle that also has other driving sources in addition to the secondary battery. In a household power storage system, household electrical appliances and the like can be used by utilizing the power stored in the secondary battery which is the power storage source.

[0166] Here, a specific example of an application example of a secondary battery will be described. Since the configuration of the application example described below is merely an example, it can be changed as appropriate.

[0167] FIG. 7 shows the block configuration of a battery pack. The battery pack described here is a battery pack (so-called soft pack) using one secondary battery, and is mounted on an electronic device typified by a smartphone.

[0168] As shown in FIG. 7, this battery pack includes a power source 71 and a circuit board 72. This circuit board 72 is connected to the power source 71 and includes a positive electrode terminal 73, a negative electrode terminal 74, and a temperature detection terminal 75.

[0169] Power supply 71 includes one secondary battery. In this secondary battery, the positive electrode lead is connected to the positive electrode terminal 73, and the negative electrode lead is connected to the negative electrode terminal 74. Since this power supply 71 can be connected to the outside via the positive electrode terminal 73 and the negative electrode terminal 74, it can be charged and discharged. Circuit board 72 includes a control unit 76, a switch 77, a thermistor (PTC element) 78, and a temperature detection unit 79. However, the PTC element 78 may be omitted.

[0170] Control unit 76 includes a central processing unit (CPU) and a memory, etc., and controls the operation of the entire battery pack. This control unit 76 detects and controls the usage state of power supply 71 as necessary.

[0171] In addition, when the voltage of power supply 71 (secondary battery) reaches the overcharge detection voltage or the over-discharge detection voltage, control unit 76 disconnects switch 77 so that no charging current flows through the current path of power supply 71. 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 ± 0.1V.

[0172] Switch 77 includes a charge control switch, a discharge control switch, a charging diode, a discharging diode, etc., and switches the connection between power supply 71 and an external device according to an instruction from control unit 76. This switch 77 includes a metal-oxide-semiconductor field-effect transistor (MOSFET), etc., and the charge and discharge current is detected based on the ON resistance of switch 77.

[0173] Temperature detection unit 79 includes a temperature detection element such as a thermistor. This temperature detection unit 79 measures the temperature of power supply 71 using temperature detection terminal 75 and outputs the measurement result of the temperature to control unit 76. The measurement result of the temperature measured by temperature detection unit 79 is used when control unit 76 performs charge and discharge control during abnormal heat generation and when control unit 76 performs correction processing during calculation of the remaining capacity.

Example

[0174] An embodiment of the present technology will be described.

[0175] <Examples 1 to 8 and Comparative Examples 1 to 5> As described below, after manufacturing the secondary battery, the battery characteristics of the secondary battery were evaluated.

[0176] [Manufacture of secondary battery] The secondary batteries (laminated film type lithium ion secondary batteries) shown in FIGS. 2 to 5 were manufactured according to the following procedure.

[0177] [Fabrication of positive electrode] First, 94 parts by mass of a positive electrode active material (LiCoO2, which is a lithium-containing compound (oxide)), 3 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 3 parts by mass of a positive electrode conductive agent (Ketjenblack, which is amorphous carbon powder) were mixed with each other to obtain a positive electrode mixture. Subsequently, after introducing the positive electrode mixture into a solvent (N-methyl-2-pyrrolidone, which is an organic solvent), the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. Subsequently, using a coating device, the positive electrode mixture slurry was applied to both sides (excluding the positive electrode terminal 31) of the positive electrode current collector 21A (aluminum foil with a thickness of 20 μm) integrated with the positive electrode terminal 31, and then the positive electrode mixture slurry was dried to form a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B was compression-molded using a roll press. Thereby, the positive electrode 21 was fabricated.

[0178] [Fabrication of negative electrode] First, 70 parts by mass of a negative electrode active material (artificial graphite, which is a carbon material), 25 parts by mass of a negative electrode active material (SiO x ), 3 parts by mass of a negative electrode binder (styrene-butadiene rubber), and 2 parts by mass of a thickener (carboxymethyl cellulose) were mixed with each other to obtain a negative electrode mixture. Subsequently, after introducing the negative electrode mixture into a solvent (water, which is an aqueous solvent), the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry.

[0179] Subsequently, lithium fluoride and lithium ethylene carbonate were added to the negative electrode mixture slurry, and the negative electrode mixture slurry was stirred. In this case, the addition amounts of lithium fluoride and lithium ethylene carbonate were adjusted so that the weight ratio MA and the weight sum MB (weight %) each became the values shown in Table 1.

[0180] When synthesizing lithium ethylene carbonate, an organic solvent (ethylene carbonate) and a tetrahydrofuran solution of lithium naphthalenide were mixed with each other, and then the mixture was left standing (standing time = 1 day). As a result, since ethylene carbonate and lithium naphthalenide reacted with each other, lithium ethylene carbonate was synthesized.

[0181] Subsequently, using a coating device, after applying the negative electrode mixture slurry to both surfaces (excluding the negative electrode terminal 32) of the negative electrode current collector 22A (copper foil with a thickness of 15 μm) integrated with the negative electrode terminal 32, the negative electrode mixture slurry was dried to form the negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B was compression molded using a roll press machine. Thereby, the negative electrode 22 was produced.

[0182] For comparison, as shown in Table 1, the negative electrode 22 was produced by the same procedure except that lithium fluoride and lithium ethylene carbonate were not used.

[0183] (Preparation of Electrolyte Solution) First, an electrolyte salt (LiPF6) was put into the solvent, and then the solvent was stirred. As this solvent, ethylene carbonate and propylene carbonate which are cyclic carbonates, dimethyl carbonate and ethyl methyl carbonate which are chain carbonates, and ethylene monofluorocarbonate which is a fluorinated cyclic carbonate were used. The composition (mass ratio) of the solvent was ethylene carbonate:propylene carbonate:dimethyl carbonate:ethyl methyl carbonate:ethylene monofluorocarbonate = 29:5:60:5:1. The content of the electrolyte salt was 1.2 mol / kg with respect to the solvent.

[0184] (Assembly of Secondary Battery) First, a laminate 20Z was fabricated by laminating a positive electrode 21 and a negative electrode 22 with each other via a separator 23 (a microporous polyethylene film with a thickness of 15 μm).

[0185] Subsequently, after forming a joint portion 31Z by welding a plurality of positive electrode terminals 31 to each other, a positive electrode lead 41 (aluminum foil) was welded to the joint portion 31Z. Also, after forming a joint portion 32Z by welding a plurality of negative electrode terminals 32 to each other, a negative electrode lead 42 (copper foil) was welded to the joint portion 32Z.

[0186] Subsequently, after folding an exterior film 10 (a fusion layer / metal layer / surface protection layer) so as to sandwich the laminate 20Z accommodated in the recessed portion 10U, the outer peripheral edge portions of two sides of the fusion layer were heat-sealed to each other, thereby storing the laminate 20Z inside the bag-shaped exterior film 10. As the exterior film 10, an aluminum laminate film in which a fusion layer (a polypropylene film with a thickness of 30 μm), a metal layer (an aluminum foil with a thickness of 40 μm), and a surface protection layer (a nylon film with a thickness of 25 μm) were laminated in this order from the inside was used.

[0187] Finally, after injecting an electrolytic solution into the bag-shaped exterior film 10, the outer peripheral edge portions of the remaining one side of the fusion layer were heat-sealed to each other in a reduced-pressure environment. In this case, a sealing film 51 (a polypropylene film with a thickness of 5 μm) was inserted between the exterior film 10 and the positive electrode lead 41, and a sealing film 52 (a polypropylene film with a thickness of 5 μm) was inserted between the exterior film 10 and the negative electrode lead 42. As a result, since the laminate 20Z was impregnated with the electrolytic solution, a battery element 20 which is a laminated electrode body was fabricated.

[0188] Therefore, since the battery element 20 was enclosed inside the exterior film 10, a secondary battery was assembled.

[0189] (Stabilization of Secondary Battery) The secondary battery was charged and discharged once in a normal temperature environment (temperature = 25°C). During charging, it was first charged at a constant current with a current of 0.1C until the voltage reached 4.2V, and then charged at a constant voltage with the voltage of 4.2V until the current reached 0.05C. During discharging, it was discharged at a constant current with a current of 0.1C until the voltage reached 2.5V. 0.1C is the current value that can completely discharge the battery capacity (theoretical capacity) in 10 hours, and 0.05C is the current value that can completely discharge the battery capacity in 20 hours.

[0190] As a result, a film was formed on the surfaces of the positive electrode 21 and the negative electrode 22 respectively, so that the state of the secondary battery was electrochemically stabilized. Thus, a laminated film type secondary battery was completed.

[0191] [Evaluation of Battery Characteristics] When evaluating the cycle characteristics as battery characteristics, the results shown in Table 1 were obtained.

[0192] When evaluating the cycle characteristics, first, the secondary battery was charged and discharged in a normal temperature environment (temperature = 25°C) to measure the discharge capacity (the discharge capacity of the first cycle).

[0193] Subsequently, in the same environment, the secondary battery was repeatedly charged and discharged until the total number of cycles reached 300 cycles to measure the discharge capacity (the discharge capacity of the 300th cycle).

[0194] Finally, based on the calculation formula of capacity retention rate (%) = (discharge capacity of the 300th cycle / discharge capacity of the first cycle) × 100, the capacity retention rate, which is an index for evaluating the cycle characteristics, was calculated.

[0195] During charging, it was charged at a constant current with a current density of 3 mA / cm 2 until the voltage reached 4.45V, and then charged at a constant voltage with the voltage of 4.45V until the current density reached 0.7 mA / cm 2 . During discharging, it was discharged at a constant current with a current density of 100 mA / cm 2 until the voltage reached 3.0V.

[0196] [Table 1]

[0197] [Investigation] As shown in Table 1, the capacity retention rate varied significantly depending on the configuration of the negative electrode 22.

[0198] Hereinafter, when the negative electrode active material layer 22B of the negative electrode 22 does not contain lithium fluoride and lithium ethylene carbonate (Comparative Example 5), the capacity retention rate is used as a comparison reference.

[0199] Specifically, when the negative electrode active material layer 22B of the negative electrode 22 contains lithium fluoride and lithium ethylene carbonate (Examples 1 to 8 and Comparative Examples 1 to 4), the capacity retention rate varied depending on each of the weight ratio MA and the weight sum MB.

[0200] That is, when the proper conditions that the weight ratio MA is 0.01 to 0.2 and the weight sum MB is 0.2 wt% to 2.0 wt% are not satisfied (Comparative Examples 1 to 4), although the capacity retention rate increased in some cases, the capacity retention rate did not increase sufficiently.

[0201] On the other hand, when the above-mentioned proper conditions are satisfied for each of the weight ratios MA and MB (Examples 1 to 8), the capacity retention rate increased significantly.

[0202] In this case, in particular, since the negative electrode active material contains a silicon-containing material, and more specifically, the negative electrode active material contains a carbon material and a silicon-containing material, the capacity retention rate increased sufficiently.

[0203] [Summary] From the results shown in Table 1, when the negative electrode active material layer 22B of the negative electrode 22 contains a negative electrode active material, lithium fluoride, and lithium ethylene carbonate, the weight ratio MA is 0.01 to 0.2, and the weight sum MB is 0.2 wt% to 2.0 wt%, a high capacity retention rate was obtained. Therefore, since the cycle characteristics of the secondary battery were improved, excellent battery characteristics could be obtained.

[0204] As described above, the present technology has been described by giving one embodiment and examples. However, the configuration of the present technology is not limited to the configuration described in one embodiment and examples, and thus can be variously modified.

[0205] Specifically, the element structure of the battery element has been described for the case where it is a laminated type (laminated electrode body) and a wound type (wound electrode body). However, since the element structure of the battery element is not particularly limited, it may be a ninety-fold type or the like. In this ninety-fold type, the positive electrode and the negative electrode are folded in a zigzag while facing each other with a separator interposed therebetween.

[0206] In addition, although the electrode reactant has been described for the case where it is lithium, the electrode reactant is not particularly limited. Specifically, as described above, the electrode reactant may be another alkali metal such as sodium and potassium, or an alkaline earth metal such as beryllium, magnesium, and calcium. In addition, the electrode reactant may be another light metal such as aluminum.

[0207] The effects described in this specification are merely examples, and thus the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present technology.

Claims

1. A positive electrode and a negative electrode including a negative electrode active material layer; Electrolyte and Equipped with The negative electrode active material layer is A negative electrode active material; Lithium fluoride (LiF), Lithium ethylene dicarbonate (Li-OC(=O)O-C 2 H 4 -OC(=O)O-Li) and Including, The weight ratio represented by formula (1) is 0.01 or more and 0.2 or less, The weight sum represented by formula (2) is 0.2% by weight or more and 2.0% by weight or less. Secondary battery. MA=M2 / M1...(1) (MA is a weight ratio. M1 is the ratio (wt%) of the weight of lithium fluoride to the weight of the negative electrode active material. M2 is the ratio (wt%) of the weight of lithium ethylene dicarbonate to the weight of the negative electrode active material.) MB=M1+M2...(2) (MB is the weight sum (wt%). M1 is the ratio (wt%) of the weight of lithium fluoride to the weight of the negative electrode active material. M2 is the ratio (wt%) of the weight of lithium ethylene dicarbonate to the weight of the negative electrode active material.)

2. The negative electrode active material includes a silicon-containing material. The secondary battery according to claim 1 .

3. The negative electrode active material further includes a carbon material. The secondary battery according to claim 2.

4. It is a lithium-ion secondary battery. The secondary battery according to claim 1 .

5. A negative electrode active material layer is provided, The negative electrode active material layer is A negative electrode active material; Lithium fluoride, lithium ethylene carbonate, and includes, the weight ratio represented by the formula (1) is 0.01 or more and 0.2 or less, and the weight sum represented by the formula (2) is 0.2% by weight or more and 2.0% by weight or less, a negative electrode for a secondary battery. MA = M2 / M1... (1) (MA is a weight ratio. M1 is the ratio (% by weight) of the weight of lithium fluoride to the weight of the negative electrode active material. M2 is the ratio (% by weight) of the weight of lithium ethylene carbonate to the weight of the negative electrode active material.) MB = M1 + M2... (2) (MB is the weight sum (% by weight). M1 is the ratio (% by weight) of the weight of lithium fluoride to the weight of the negative electrode active material. M2 is the ratio (% by weight) of the weight of lithium ethylene carbonate to the weight of the negative electrode active material.)

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