JP5910652B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery having a negative electrode active material layer containing silicon (Si) as a constituent element.

  In recent years, as mobile devices have higher performance and more functions, there is a demand for higher capacities of secondary batteries serving as power sources thereof. Secondary batteries that meet this requirement include lithium ion secondary batteries, but those currently in practical use use graphite for the negative electrode, so the battery capacity is saturated and it is difficult to achieve significant increases in capacity. . Therefore, it has been studied to use silicon or the like for the negative electrode, and recently, it has been reported that a negative electrode active material layer is formed on the negative electrode current collector by a vapor phase method or the like (see, for example, Patent Documents 1 to 3). ). Since silicon and the like have a large expansion / contraction due to charging / discharging, deterioration of cycle characteristics due to pulverization has been a problem. However, according to a vapor phase method or the like, miniaturization can be suppressed and a negative electrode current collector and Since the negative electrode active material layer can be integrated, the electron conductivity in the negative electrode becomes extremely good, and high performance is expected in terms of capacity and cycle life.

JP-A-8-50922 Japanese Patent No. 2948205 Japanese Patent Laid-Open No. 11-135115

  However, even this negative electrode has a problem that charge and discharge efficiency is lowered due to expansion and contraction of silicon accompanying charge and discharge, and it is difficult to obtain sufficient cycle characteristics.

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

A lithium ion secondary battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode. The negative electrode includes a negative electrode current collector having a surface roughness Ra value of 0.2 μm or more, and the negative electrode current collector. An anode active material layer which is alloyed at least at a part of the interface and contains silicon as a constituent element. Here, when the amount of occlusion of lithium per unit area in the fully charged state of the negative electrode is A and the amount of lithium that can be occluded electrochemically per unit area of the negative electrode is B, (A / B) × 100 The maximum utilization rate C% defined is 40% or more and 60% or less .

According to the lithium ion secondary battery of the present invention, since the maximum utilization rate C% of the negative electrode is set to 60% or less , the expansion and contraction of the negative electrode active material layer can be suppressed, and the negative electrode active material layer is detached. Can be suppressed. In addition, since the maximum utilization C% of the negative electrode is set to 40% or more, side reactions caused by silicon that is not used can be suppressed, and a high-quality film can be formed on the surface by lowering the potential of the negative electrode in a charged state. Can be formed. Therefore, charge / discharge efficiency can be improved.

  In particular, if the oxygen content in the negative electrode active material layer is 3 atomic% or more, the second layer having a higher oxygen content than the first layer is at least one layer between the first layers. If it has it above, charging / discharging efficiency can be improved more.

It is sectional drawing showing the structure of the secondary battery which concerns on the 1st Embodiment of this invention. It is sectional drawing showing the structure of the secondary battery which concerns on the 2nd Embodiment of this invention. It is sectional drawing showing the structure along the II line | wire of the electrode winding body shown in FIG.

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

(First embodiment)
FIG. 1 shows the configuration of the secondary battery according to the first embodiment of the present invention. This secondary battery is a so-called coin-type battery, and is a separator in which a negative electrode 12 accommodated in an exterior cup 11 and a positive electrode 14 accommodated in an exterior can 13 are impregnated with an electrolytic solution that is a liquid electrolyte. 15 are stacked.

  The peripheral portions of the outer cup 11 and the outer can 13 are sealed by caulking through an insulating gasket 16. The exterior cup 11 and the exterior can 13 are made of, for example, a metal such as stainless steel or aluminum.

  The negative electrode 12 includes, for example, a negative electrode current collector 12A and a negative electrode active material layer 12B provided on the negative electrode current collector 12A. The anode current collector 12A is preferably made of a metal material containing at least one metal element that does not form an intermetallic compound with lithium. When lithium and an intermetallic compound are formed, they expand and contract with charge / discharge, structural breakdown occurs, current collection performance decreases, and the ability to support the negative electrode active material layer 12B decreases, so that the negative electrode active material layer 12B becomes a negative electrode. This is because it is easy to drop off from the current collector 12A. Examples of the metal element that does not form an intermetallic compound with lithium include copper (Cu), nickel (Ni), titanium (Ti), iron (Fe), and chromium (Cr).

  As the metal material constituting the negative electrode current collector 12A, a material containing a metal element that forms an alloy with the negative electrode active material layer 12B is preferable. This is because the adhesion between the negative electrode active material layer 12B and the negative electrode current collector 12A can be improved, and the loss of the negative electrode active material layer 12B can be suppressed. As will be described later, when the negative electrode active material layer 12B contains silicon as a constituent element, copper, nickel, and iron are used as metal elements that do not form an intermetallic compound with lithium and alloy with the negative electrode active material layer 12B. Can be mentioned. Among these, copper is preferable because sufficient strength and conductivity can be obtained.

  The negative electrode current collector 12A may be composed of a single layer, but may be composed of a plurality of layers. In that case, the layer in contact with the negative electrode active material layer 12B may be made of a metal material alloyed with silicon, and the other layers may be made of another metal material.

  The surface roughness Ra value of the negative electrode current collector 12A is preferably 0.2 μm or more. This is because the adhesion between the negative electrode active material layer 12B and the negative electrode current collector 12A can be further improved. Further, the surface roughness Ra value of the negative electrode current collector 12A is preferably 5 μm or less. This is because if the surface roughness Ra value is too high, the negative electrode current collector 12A is likely to be cracked as the negative electrode active material layer 12B expands. The surface roughness Ra value is the arithmetic average roughness Ra defined in JIS B0601, and the surface roughness Ra of the region where at least the negative electrode active material layer 12B is provided in the negative electrode current collector 12A. May be within the above-described range.

  The negative electrode active material layer 12B contains silicon as a constituent element. This is because the ability to occlude and release lithium is large, and a high energy density can be obtained. Silicon may be contained as a simple substance, may be contained as an alloy, or may be contained as a compound.

  The negative electrode active material layer 12B is preferably formed by at least one method selected from the group consisting of, for example, a vapor phase method, a plating method, a firing method, and a thermal spray method. Breakage due to expansion / contraction of the negative electrode active material layer 12 due to charge / discharge can be suppressed, the negative electrode current collector 11 and the negative electrode active material layer 12 can be integrated, and electrons in the negative electrode active material layer 12 can be integrated. This is because the conductivity can be improved. Note that the “firing method” means that a layer formed by mixing a powder containing an active material and a binder is heat-treated in a non-oxidizing atmosphere or the like, so that the volume density is higher than that before the heat treatment and the denser. It means the method of forming a layer.

  The negative electrode active material layer 12B is preferably alloyed with the negative electrode current collector 12A at least at a part of the interface with the negative electrode current collector 12A. This is because the adhesion between the negative electrode active material layer 12B and the negative electrode current collector 12A can be improved as described above. Specifically, the constituent elements of the negative electrode current collector 12A are diffused into the negative electrode active material layer 12B, the constituent elements of the negative electrode active material layer 12B are diffused into the negative electrode current collector 12A, or they are mutually diffused at the interface. preferable. In the present application, the above-described element diffusion is included in one form of alloying.

  The negative electrode active material layer 12B further preferably contains oxygen as a constituent element. This is because the expansion / contraction of the negative electrode active material layer 12B can be suppressed. It is preferable that at least a part of oxygen contained in the negative electrode active material layer 12B is bonded to silicon, and the bonding state may be silicon monoxide, silicon dioxide, or other metastable state. The oxygen content in the negative electrode active material layer 12B is preferably 3 atomic% or more. This is because a higher effect can be obtained. The oxygen content in the negative electrode active material layer 12B is preferably 40 atomic% or less. This is because if the oxygen content is excessively high, the resistance of the negative electrode 12 increases and the load characteristics decrease, or the battery capacity decreases. Note that the negative electrode active material layer 12B does not include a coating film that is formed on the surface of the negative electrode active material layer 12B due to decomposition of the electrolytic solution by charge and discharge. Therefore, when the oxygen content in the negative electrode active material layer 12B is calculated, oxygen contained in the coating is not included.

  In addition, the negative electrode active material layer 12B preferably has alternately stacked first layers having a low oxygen content and second layers having a higher oxygen content than the first layer. It is preferable that at least one second layer exists between at least the first layer. This is because expansion / contraction associated with charge / discharge can be more effectively suppressed. For example, the silicon content in the first layer is preferably 90 atomic% or more, and oxygen may or may not be contained, but the oxygen content is preferably as low as possible, More preferably, it does not contain oxygen and its content is zero. This is because a higher capacity can be obtained. On the other hand, the silicon content in the second layer is preferably 90 atomic% or less, and the oxygen content is preferably 10 atomic% or more. This is because structural destruction due to expansion / contraction can be more effectively suppressed. The first layer and the second layer may be laminated in the order of the first layer and the second layer from the negative electrode current collector 12A side, but are laminated in the order of the second layer and the first layer. The surface may be the first layer or the second layer. Moreover, it is preferable that the oxygen content changes stepwise or continuously between the first layer and the second layer. This is because, if the oxygen content changes abruptly, the diffusibility of lithium ions decreases and the resistance may increase.

  In this secondary battery, the maximum utilization ratio C% of the negative electrode 12 is set in the range of 35% to 85% by adjusting the ratio between the capacity of the negative electrode 12 and the capacity of the positive electrode 14. By setting the maximum utilization rate C% of the negative electrode 12 to 85% or less, expansion / contraction of the negative electrode active material layer 12B accompanying charge / discharge can be suppressed, and dropping of the negative electrode active material layer 12B can be suppressed. Because. Further, if the maximum utilization ratio C% of the negative electrode 12 is smaller than 35%, side reaction due to unused silicon increases, and the initial charge / discharge efficiency decreases, and the potential of the negative electrode 12 in the charged state increases. This is because a good-quality film due to the decomposition of the electrolytic solution is hardly formed on the surface of the negative electrode 12, and the side reaction cannot be sufficiently suppressed. The maximum utilization C% of the negative electrode 12 is more preferably 40% or more and 80% or less. This is because a higher effect can be obtained.

  Note that the maximum utilization ratio C% of the negative electrode 12 is the amount of lithium occluded per unit area when the negative electrode 12 is fully charged, and the amount of lithium that can be electrochemically occluded per unit area of the negative electrode 12. When B is defined, C = (A / B) × 100.

Among these, the lithium storage amount A per unit area in the fully charged state of the negative electrode 12 is, for example, a part of the negative electrode facing the positive electrode 14 by disassembling a battery charged until it is fully charged by a corresponding charger. After a part of 12 is cut out as an inspection negative electrode and an evaluation battery is assembled using metallic lithium as a counter electrode, the evaluation battery is discharged, and the capacity value in the initial discharge is divided by the area of the inspection negative electrode. In this case, discharging means energizing in the direction in which lithium ions are released from the inspection negative electrode. Further, the amount B of electrochemically occluded lithium per unit area of the negative electrode 12 is, for example, after discharging the evaluation battery described above, performing constant current constant voltage charging until the battery voltage becomes 0 V, It can be obtained by dividing the obtained capacitance value by the area of the inspection negative electrode. In this case, charging means energizing in the direction in which lithium ions are occluded in the inspection negative electrode. In such an evaluation, normally, the energization current value is about 1 mA / cm ² , discharging is performed until the battery voltage of the evaluation battery reaches 1.5V, and charging is performed at a constant voltage charge at a battery voltage of 0V. Continue until 0.05 mA or less.

  The positive electrode 14 includes, for example, a positive electrode current collector 14A and a positive electrode active material layer 14B provided on the positive electrode current collector 14A so that the positive electrode active material layer 14B side faces the negative electrode active material layer 12B. Is arranged. The positive electrode current collector 14A is made of, for example, aluminum, nickel, stainless steel, or the like.

The positive electrode active material layer 14B includes, for example, any one or more of positive electrode materials capable of inserting and extracting lithium as a positive electrode active material, and a conductive material such as a carbon material and the like as necessary. A binder such as polyvinylidene fluoride may be included. Examples of the positive electrode material capable of inserting and extracting lithium include chalcogenides that do not contain lithium, or lithium composite oxides that contain lithium. As the lithium composite oxide, for example, one represented by the general formula Li _x MO ₂ is preferable. This is because a high voltage can be generated and a high energy density can be obtained. Note that M preferably contains one or more transition metal elements, and preferably contains at least one of cobalt and nickel, for example. x varies depending on the charge / discharge state of the battery and is usually a value in the range of 0.05 ≦ x ≦ 1.10. Specific examples of such a lithium-containing metal composite oxide include LiCoO _{2 and} LiNiO ₂ .

  The separator 15 separates the negative electrode 12 and the positive electrode 14 and allows lithium ions to pass while preventing a short circuit of current due to contact between both electrodes, and is made of, for example, polyethylene or polypropylene.

  The electrolytic solution impregnated in the separator 15 includes, for example, a solvent and an electrolyte salt dissolved in the solvent, and may include an additive as necessary. Examples of the solvent include nonaqueous solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Any one of the solvents may be used alone, or two or more of them may be mixed and used. For example, it is preferable to use a high boiling point solvent such as ethylene carbonate or propylene carbonate and a low boiling point solvent such as dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate because high ionic conductivity can be obtained. .

  Examples of the solvent also include a carbonic acid ester derivative having a halogen atom, and it is preferable to use this because the charge / discharge efficiency can be further improved. In that case, it may be used by mixing with other solvents as described above, or may be used alone. The carbonic acid ester derivative having a halogen atom may be either a cyclic compound or a chain compound, but the cyclic compound is preferable because a higher effect can be obtained. Such cyclic compounds include 4-fluoro-1,3-dioxolan-2-one, 4-chloro-1,3-dioxolan-2-one, 4-bromo-1,3-dioxolan-2-one Or 4,5-difluoro-1,3-dioxolan-2-one, among which 4-fluoro-1,3-dioxolan-2-one is preferred. This is because a higher effect can be obtained.

  Examples of the solvent further include a cyclic carbonate having an unsaturated bond, and it is preferable to use a mixture with another solvent. This is because the charge / discharge efficiency can be further improved. Examples of the cyclic carbonate having an unsaturated bond include 1,3-dioxol-2-one and 4-vinyl-1,3-dioxolan-2-one.

Examples of the electrolyte salt include lithium salts such as LiPF ₆ , LiCF ₃ SO _{3, and} LiClO ₄ . Any one electrolyte salt may be used alone, or two or more electrolyte salts may be mixed and used.

  This battery can be manufactured, for example, as follows.

  First, the negative electrode 12 is fabricated by forming the negative electrode active material layer 12B on the negative electrode current collector 12A by a vapor phase method, a plating method, a firing method, or a thermal spraying method. Further, the negative electrode active material layer 12B may be formed by combining these two or more methods. Examples of the vapor phase method include a physical deposition method or a chemical deposition method. Specifically, a vacuum deposition method, a sputtering method, an ion plating method, a laser ablation method, or a CVD (Chemical Vapor Deposition; chemical vapor phase). (Growth) method. Examples of the liquid phase method include plating.

  The oxygen content in the negative electrode active material layer 12B is, for example, that oxygen is contained in the atmosphere when the negative electrode active material layer 12B is formed, or that oxygen is contained or used in the atmosphere during firing or heat treatment. It adjusts with the oxygen concentration of a negative electrode active material particle. Further, as described above, when the negative electrode active material layer 12B is formed by alternately stacking the first layer having a low oxygen content and the second layer having a higher oxygen content than the first layer. The oxygen concentration in the atmosphere may be changed, or the first layer may be formed and then the surface may be oxidized to form the second layer.

  In addition, after forming the negative electrode active material layer 12B, heat treatment may be performed in a vacuum atmosphere or a non-oxidizing atmosphere to further alloy the interface between the negative electrode current collector 12A and the negative electrode active material layer 12B. Good.

  Next, for example, a positive electrode active material, a conductive material, and a binder are mixed to prepare a mixture, and this is dispersed in a dispersion medium such as N-methyl-2-pyrrolidone to form a mixture slurry on the positive electrode current collector 14A. After coating, the positive electrode 14 is produced by compression molding to form the positive electrode active material layer 14B. At that time, the amount of the negative electrode active material and the amount of the positive electrode active material are adjusted so that the maximum utilization ratio C% of the negative electrode 12 falls within the above-described range.

  Subsequently, for example, the positive electrode 14, the separator 15 impregnated with the electrolytic solution, and the negative electrode 12 are stacked, put into the outer can 13 and the outer cup 11, and caulked. Thereby, the secondary battery shown in FIG. 1 is obtained.

  In the secondary battery, when charged, for example, lithium ions are released from the positive electrode 14 and inserted in the negative electrode 12 through the electrolytic solution. When the discharge is performed, for example, lithium ions are released from the negative electrode 12 and inserted in the positive electrode 14 through the electrolytic solution. At that time, since the maximum utilization rate C% of the negative electrode 12 is 85% or less, the expansion / contraction of the negative electrode active material layer 12B is suppressed, and the falling off of the negative electrode active material layer 12B is suppressed. Further, since the maximum utilization C% of the negative electrode 12 is 35% or more, side reactions due to unused silicon are suppressed, and the potential of the negative electrode 12 in a charged state is lowered, and the surface of the negative electrode 12 is favorable. A film is formed. Therefore, the charge / discharge efficiency is improved.

  Thus, according to the present embodiment, the surface roughness Ra value of the negative electrode current collector 12A is set to 0.2 μm or more, and the maximum utilization rate C% of the negative electrode 12 is set to 35% or more and 85% or less. Therefore, expansion and contraction of the negative electrode active material layer 12B can be suppressed, and side reactions in the negative electrode 12 can be suppressed. Therefore, charge / discharge efficiency can be improved and cycle characteristics can be improved.

  Further, if the oxygen content in the negative electrode active material layer 12B is set to 3 atomic% or more, or the second layer having a higher oxygen content than the first layer is at least 1 between the first layers. If it is made to have more than one layer, the charge / discharge efficiency can be further improved.

  Furthermore, if the electrolytic solution contains a carbonic acid ester derivative having a halogen atom, the charge / discharge efficiency can be further improved.

(Second Embodiment)
FIG. 2 shows a configuration of a secondary battery according to the second embodiment of the present invention. In this secondary battery, the wound electrode body 20 to which the leads 21 and 22 are attached is housed in a film-like exterior member 31 and can be reduced in size, weight, and thickness.

  The leads 21 and 22 are led out from the inside of the exterior member 31 to the outside, for example, in the same direction. The leads 21 and 22 are made of a metal material such as aluminum, copper, nickel, or stainless steel, respectively, and have a thin plate shape or a mesh shape, respectively.

  The exterior member 31 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. The exterior member 31 is disposed, for example, so that the polyethylene film side and the electrode winding body 20 face each other, and the outer edge portions are in close contact with each other by fusion bonding or an adhesive. An adhesion film 32 for preventing the entry of outside air is inserted between the exterior member 31 and the leads 21 and 22. The adhesion film 32 is made of a material having adhesion to the leads 21 and 22, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 31 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminated film.

  FIG. 3 shows a cross-sectional structure taken along line II of the electrode winding body 20 shown in FIG. The electrode winding body 20 is obtained by laminating a negative electrode 23 and a positive electrode 24 via a separator 25 and an electrolyte 26 and winding them, and the outermost periphery is protected by a protective tape 27.

  The negative electrode 23 has a structure in which a negative electrode active material layer 23B is provided on both surfaces of a negative electrode current collector 23A. The positive electrode 24 also has a structure in which the positive electrode active material layer 24B is provided on both surfaces of the positive electrode current collector 24A, and the positive electrode active material layer 24B is disposed so as to face the negative electrode active material layer 23B. The configuration of the negative electrode current collector 23A, the negative electrode active material layer 24B, the positive electrode current collector 24A, the positive electrode active material layer 24B, and the separator 25 is the same as that of the negative electrode current collector 12A, the negative electrode active material layer 12B, and the positive electrode in the first embodiment. The same as the current collector 14A, the positive electrode active material layer 14B, and the separator 15.

  The electrolyte 26 is constituted by a so-called gel electrolyte in which an electrolytic solution is held in a polymer compound. The configuration of the electrolytic solution (that is, the solvent, the electrolyte salt, and the like) is the same as that in the first embodiment. As the polymer material, for example, a polymer containing vinylidene fluoride is preferably exemplified. This is because the redox stability is high. Examples of the polymer compound include those formed by polymerizing a polymerizable compound. Examples of the polymerizable compound include those containing a vinyl group or a group obtained by substituting a part of hydrogen with a substituent such as a methyl group. Specifically, monofunctional acrylates such as acrylic acid esters, monofunctional methacrylates such as methacrylic acid esters, polyfunctional acrylates such as diacrylic acid esters or triacrylic acid esters, and polyfunctional acrylates such as dimethacrylic acid esters or trimethacrylic acid esters. There are functional methacrylate, acrylonitrile, methacrylonitrile, and the like. Among them, an ester having an acrylate group or a methacrylate group is preferable. This is because the polymerization proceeds easily and the reaction rate of the polymerizable compound is high.

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

  First, the negative electrode 23 and the positive electrode 24 are produced in the same manner as in the first embodiment, and then the electrolyte 26 in which the electrolytic solution is held in the polymer compound is formed on the negative electrode 23 and the positive electrode 24, respectively. Next, the leads 21 and 22 are attached to the negative electrode current collector 23A and the positive electrode current collector 24A, respectively. Subsequently, the negative electrode 23 and the positive electrode 24 are laminated via the separator 25 to form a laminated body, and then the laminated body is wound in the longitudinal direction, and the protective tape 27 is adhered to the outermost peripheral portion to wrap the electrode wound body. 20 is formed. After that, for example, the electrode winding body 20 is sandwiched between the exterior members 31, and the outer edges of the exterior members 31 are in close contact with each other by thermal fusion or the like and sealed. At that time, an adhesive film 32 is inserted between the leads 21 and 22 and the exterior member 31. Thereby, the secondary battery shown in FIGS. 2 and 3 is completed.

  The electrolyte 26 may be formed as follows. For example, an electrolyte composition containing a polymerizable compound and an electrolytic solution is applied to the negative electrode 23 and the positive electrode 24, wound through a separator 25 and sealed in the exterior member 31, and then the polymerizable compound is polymerized. Alternatively, the negative electrode 23 and the positive electrode 24 may be wound around the separator 25 and sealed in the exterior member 31, and then the polymerizable compound and the electrolyte may be contained in the exterior member 31. You may make it form by inject | pouring the composition for electrolyte containing and polymerizing a polymeric compound.

  The operation and effect of the secondary battery are the same as those in the first embodiment.

  Further, specific embodiments of the present invention will be described in detail with reference to the drawings. In the following examples, the symbols and symbols used in the above embodiment are used in correspondence.

(Examples 1-1 to 1-7)
The laminate film type secondary battery shown in FIGS. First, lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride as a binder are mixed and dispersed in N-methyl-2-pyrrolidone as a dispersion medium, and then aluminum. The positive electrode active material layer 24 </ b> B was formed by applying to a positive electrode current collector 24 </ b> A made of foil and drying to prepare a positive electrode 24. After that, the lead 22 was attached.

  Next, silicon is deposited on the negative electrode current collector 23A made of an electrolytic copper foil having a thickness of 18 μm and a surface roughness Ra value of 0.4 μm by an electron beam deposition method, and then annealed at 280 ° C. for 24 hours. Thereby, the negative electrode active material layer 23B was formed, and the negative electrode 23 was produced. At that time, silicon was deposited while flowing oxygen gas diluted with argon (Ar). Further, when the thickness of the negative electrode active material layer 23B is 6 μm, the maximum utilization factor C of the negative electrode 23 is designed to be 50%, and the desired maximum utilization factor is changed by changing the thickness of the negative electrode active material layer 23B. C. After that, the lead 21 was attached.

Subsequently, 5 parts by mass of the polymerizable compound solution and 0.1 parts by mass of the polymerization initiator were mixed with 100 parts by mass of the electrolytic solution to prepare an electrolyte composition. A polymerizable compound solution is obtained by combining trimethylolpropane triacrylate shown in Chemical Formula 1 and neopentyl glycol diacrylate shown in Chemical Formula 2 with a mass ratio of trimethylolpropane triacrylate: neopentyl glycol diacrylate = 3: 7. Mixed. The polymerization initiator was t-butyl peroxyneodecanoate which is a peroxy ester polymerization initiator. The electrolytic solution was prepared by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) as a solvent in a mass ratio of ethylene carbonate: dimethyl carbonate = 3: 7 and further dissolving LiPF ₆ as an electrolyte salt. . The concentration of LiPF _{6 in} the electrolytic solution was 1 mol / l.

  The produced electrolyte composition was applied to the positive electrode 24 and the negative electrode 23, and these were closely adhered via a separator 25 made of a microporous polyethylene film having a thickness of 25 μm, and wound to be a precursor of the wound electrode body 20. It was a round body.

  Next, after sandwiching the wound body between the exterior members 31 made of a moisture-proof aluminum laminate film, the outer edges of the exterior members 31 were bonded together. At that time, the leads 21 and 22 are led out of the exterior member 31. The aluminum laminate film was formed by laminating a 25 μm thick nylon film, a 40 μm thick aluminum foil, and a 30 μm thick polypropylene in order from the outermost layer. Thereafter, this was sandwiched between glass plates and heated at 75 ° C. for 30 minutes to polymerize the polymerizable compound, whereby the electrolyte composition was gelled to form the electrolyte 26, thereby producing a secondary battery.

  For the fabricated secondary batteries of Examples 1-1 to 1-7, as described in the embodiment, the lithium storage amount A per unit volume in the fully charged state of the negative electrode 23 and the unit volume of the negative electrode 23 The amount B of electrochemically occluded lithium was measured, and the maximum utilization rate C of the negative electrode 23 was determined. The results are shown in Table 1.

  Moreover, about the produced secondary battery, the charge / discharge test was done and the first time charge / discharge efficiency and cycling characteristics were investigated. Charging was performed at a constant current and constant voltage with a current of 500 mA and an upper limit voltage of 4.2 V, and discharging was performed at a constant current of 500 mA until the battery voltage reached 2.7 V. The initial charge / discharge efficiency is obtained from the ratio of the initial discharge capacity (discharge capacity at the first cycle) to the initial charge capacity (charge capacity at the first cycle), that is, (initial discharge capacity / initial charge capacity) × 100 (%). It was. The cycle characteristics were obtained from the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle, that is, (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100 (%). The results are shown in Table 1.

  Further, the fabricated secondary battery was charged and discharged in the first cycle under the above-described conditions, and then disassembled and the negative electrode 23 was taken out. When the cross section of the negative electrode 23 was subjected to SEM (Scanning Electron Microscope) image analysis, it was confirmed that the negative electrode current collector 23A and the negative electrode active material layer 23B were adhered to each other at the interface. Further, when spot analysis of AES (Auger electron spectroscopy) was performed on this interface, it was found that the copper component as the component of the negative electrode current collector 23A was diffused in the negative electrode active material layer 23B. confirmed. That is, it was confirmed that the negative electrode current collector 23A and the negative electrode active material layer 23B were alloyed.

  As Comparative Examples 1-1 to 1-4 for Examples 1-1 to 1-7, the thickness of the negative electrode active material layer was changed so that the maximum utilization rate C of the negative electrode was less than 35% or more than 85%. A secondary battery was fabricated in the same manner as in Examples 1-1 to 1-7, except that a negative electrode was fabricated. Moreover, as Comparative Examples 1-5 to 1-7, an electrolytic copper foil having a surface roughness Ra value of 0.05 μm was used as the negative electrode current collector, and the maximum utilization rate C of the negative electrode was 20% to 90%. A secondary battery was fabricated in the same manner as in Examples 1-1 to 1-7, except that the negative electrode was fabricated by changing the thickness of the negative electrode active material layer.

  For the fabricated secondary batteries of Comparative Examples 1-1 to 1-7, the maximum utilization factor C, the initial charge / discharge efficiency, and the cycle characteristics of the negative electrode were examined in the same manner as in Examples 1-1 to 1-7. The results are shown in Table 1.

  Further, regarding the secondary battery of Comparative Example 1-6, when the SEM image analysis was performed on the cross section of the negative electrode in the same manner as in Examples 1-1 to 1-7, the negative electrode current collector and the negative electrode active material layer Numerous peeling was confirmed at the interface.

  As can be seen from Table 1, Examples 1-1 to 1-7 in which the surface roughness Ra value of the negative electrode current collector 23A was 0.2 μm or more and the maximum utilization rate C of the negative electrode 23 was 35% or more and 85% or less. According to the comparative example 1-1, the maximum capacity utilization C of the negative electrode is more improved than the comparative examples 1-1 and 1-2 in which the maximum utilization ratio C exceeds 85%, and the maximum utilization ratio C of the negative electrode is less than 35% The initial charge / discharge efficiency was improved as compared with 3,1-4. In particular, in Examples 1-2 to 1-6 in which the maximum utilization rate C of the negative electrode was 40% or more and 80% or less, a high value was obtained.

  On the other hand, in Comparative Examples 1-5 to 1-7 in which the surface roughness Ra value of the negative electrode current collector was less than 0.2 μm, even if the maximum utilization rate C of the negative electrode was 35% or more and 85% or less, the discharge capacity maintenance rate No improvement effect was observed.

  That is, if the surface roughness Ra value of the negative electrode current collector 23A is 0.2 μm or more and the maximum utilization rate C of the negative electrode 23 is 35% or more and 85% or less, the initial charge / discharge efficiency and cycle characteristics are improved. I found out that

(Examples 2-1 to 2-4)
Except that the negative electrode current collector 23A made of an electrolytic copper foil having a surface roughness Ra value of 0.2 μm, 1.0 μm, 3.0 μm, or 5.0 μm was used, the others were the same as in Example 1-5 Thus, a secondary battery was produced. At that time, the maximum utilization rate C of the negative electrode 23 was designed to be 50%.

  As Comparative Example 2-1 with respect to Examples 2-1 to 2-4, except that a negative electrode current collector made of an electrolytic copper foil having a surface roughness Ra value of 0.1 μm was used, the others were Example 2- Secondary batteries were produced in the same manner as in 1-2-4. At that time, the maximum utilization factor C of the negative electrode was designed to be 50%.

  For the fabricated secondary batteries of Examples 2-1 to 2-4 and Comparative Example 2-1, the initial charge and discharge efficiency and the cycle characteristics were examined in the same manner as in Examples 1-1 to 1-7. The results are shown in Table 2 together with the results of Example 1-5 and Comparative example 1-6.

  As can be seen from Table 2, in Examples 1-5, 2-1 to 2-4 in which the surface roughness Ra value of the negative electrode current collector 23A was 0.2 μm or more, the initial charge / discharge efficiency and the discharge capacity retention ratio were Dramatically improved.

  That is, it has been found that it is preferable that the surface roughness Ra value of the negative electrode current collector 23A be 0.2 μm or more.

(Examples 3-1 to 3-6)
Except that the oxygen content in the negative electrode active material layer 23B was changed by appropriately changing the flow conditions of oxygen gas diluted with argon when depositing silicon, the others were the same as in Example 1-5. A secondary battery was manufactured. At that time, the maximum utilization rate C of the negative electrode 23 was designed to be 50%.

  As Comparative Example 3-1 with respect to Examples 3-1 to 3-6, a negative electrode current collector made of an electrolytic copper foil having a surface roughness Ra value of 0.05 μm was used, and the flow condition of oxygen gas diluted with argon was changed. A secondary battery was fabricated in the same manner as in Examples 3-1 to 3-6, except for the above.

  For the fabricated secondary batteries of Examples 3-1 to 3-6 and Comparative example 3-1, the initial charge and discharge efficiency and the cycle characteristics were examined in the same manner as in Examples 1-1 to 1-7. The results are shown in Table 3 together with the results of Example 1-5 and Comparative example 1-6.

  In addition, the secondary batteries of Examples 1-5, 3-1 to 3-6 and Comparative Examples 1-6 and 3-1, were charged and discharged in the first cycle under the same conditions as in Examples 1-1 to 1-7. Then, the negative electrode 23 was taken out, and the oxygen content in the negative electrode active material layer 23B was measured with an oxygen concentration analyzer. At that time, the surface of the negative electrode 23 was washed with diethyl carbonate to remove the film formed on the surface. The results are shown in Table 3.

  As can be seen from Table 3, according to Examples 1-5, 3-1 to 3-6, as the oxygen content in the negative electrode active material layer 23B increases, the initial charge / discharge efficiency and the discharge capacity retention rate are Both improved, showed a tendency to decrease after showing the maximum value. On the other hand, according to Comparative Examples 1-6 and 3-1, in which the surface roughness Ra value is less than 0.2 μm, the discharge capacity retention ratio is improved when the oxygen content in the negative electrode active material layer is increased. The discharge efficiency was significantly reduced, and these values were not sufficient.

  That is, when the negative electrode current collector 23A having a surface roughness Ra value of 0.2 μm or more is used, it is more preferable that the oxygen content in the negative electrode active material layer 23B is 3 atomic% or more. I understood.

(Examples 4-1 to 4-4)
Except that the negative electrode active material layer 23B was formed by alternately laminating the first layer with a low oxygen content and the second layer with a high oxygen content, the others were the same as in Example 3-4. A secondary battery was manufactured. At that time, the first layer is formed by electron beam evaporation, and the second layer is formed by interrupting the formation of the first layer and oxidizing the surface of the first layer by flowing an oxygen gas diluted with argon. did. In Example 4-1, the first layer, the second layer, and the first layer are formed in this order. In Example 4-2, the first layer and the second layer are stacked in this order, and the first layer is further stacked. Formed. In Example 4-3, five layers were stacked in the order of the first layer and the second layer, and the first layer was further formed. In Example 4-4, 10 layers were laminated in order of the first layer and the second layer, and the first layer was further formed. The total oxygen content in the negative electrode active material layer 23B was designed to be about 11 atomic% as in Example 3-4, and the maximum utilization rate C of the negative electrode 23 was designed to be 50%. .

  For the fabricated secondary batteries of Examples 4-1 to 4-4, the initial charge and discharge efficiency and the cycle characteristics were examined in the same manner as in Examples 1-1 to 1-7. The results are shown in Table 4 together with the results of Example 3-4.

  As can be seen from Table 4, according to Examples 4-1 to 4-4 in which the first layer and the second layer are provided, the initial charge / discharge efficiency and the discharge capacity are maintained compared to Example 3-4 in which the first layer and the second layer are not provided. The rate has improved. In addition, as the number of layers increased, the initial charge / discharge efficiency and the discharge capacity retention rate tended to improve. That is, it has been found that it is more preferable to provide at least one second layer having a high oxygen content between the first layers having a low oxygen content.

(Example 5-1)
The secondary reaction was carried out in the same manner as in Example 1-5 except that 4-fluoro-1,3-dioxolan-2-one (FEC), which is a carbonate ester derivative having a halogen atom, was used instead of ethylene carbonate. A battery was produced.

  As Comparative Example 5-1 with respect to Example 5-1, except that an electrolytic copper foil having a surface roughness Ra value of 0.05 μm was used as the negative electrode current collector, the others were the same as Example 5-1. A secondary battery was produced. At that time, the maximum utilization factor C of the negative electrode was designed to be 50%.

  For the fabricated secondary batteries of Example 5-1 and Comparative Example 5-1, the initial charge and discharge efficiency and the cycle characteristics were examined in the same manner as in Examples 1-1 to 1-7. The results are shown in Table 5 together with the results of Example 1-5 and Comparative Example 1-6.

  As can be seen from Table 5, according to Example 5-1 using 4-fluoro-1,3-dioxolan-2-one, the discharge capacity retention rate is improved as compared with Example 1-5 not using this. did. On the other hand, in Comparative Example 5-1, in which the surface roughness Ra value of the negative electrode current collector was 0.05, a comparative example in which 4-fluoro-1,3-dioxolan-2-one was used and this was not used Although the discharge capacity retention rate was improved from 1-6, the initial charge / discharge efficiency was lowered.

  That is, when a negative electrode current collector having a surface roughness Ra value of 0.2 μm or more is used, if a cyclic carbonate derivative having a halogen atom is used, cycle characteristics are maintained while maintaining high initial charge / discharge efficiency. It was found that can be further improved.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the case where an electrolyte or a gel electrolyte in which an electrolytic solution is held in a polymer compound is used as the electrolyte has been described, but other electrolytes may be used. Other electrolytes include inorganic conductors containing lithium nitride or lithium phosphate, polymer solid electrolytes in which an electrolyte salt is dispersed in a polymer compound having ionic conductivity, or a mixture of these and an electrolyte. Etc.

  In the above embodiments and examples, a coin type or wound laminate type secondary battery has been described. However, the present invention is not limited to a cylindrical type, a square type, a button type, a thin type, a large type, and a laminated laminate type. The same applies to the secondary battery. Moreover, not only a secondary battery but a primary battery is applicable.

  DESCRIPTION OF SYMBOLS 11 ... Exterior cup, 12, 23 ... Negative electrode, 12A, 23A ... Negative electrode current collector, 12B, 23B ... Negative electrode active material layer, 13 ... Outer can, 14, 24 ... Positive electrode, 14A, 24A ... Positive electrode current collector, 14B , 24B ... positive electrode active material layer, 15, 25 ... separator, 16 ... gasket, 20 ... wound electrode body, 21, 22 ... lead, 26 ... electrolyte, 27 ... protective tape.

Claims (6)

A lithium ion secondary battery comprising an electrolyte together with a positive electrode and a negative electrode,
The negative electrode is
The anode active surface roughness Ra is made of a negative electrode active material comprising as constituent elements and the negative electrode current collector, the alloyed in at least part of the negative electrode current collector and the interface, the silicon (Si) which is 0.2μm or more A material layer,
When the storage amount of lithium (Li) per unit area in the fully charged state of the negative electrode is A, and the amount of lithium that can be stored electrochemically per unit area of the negative electrode is B, (A / B) × A lithium ion secondary battery having a maximum utilization rate C% defined by 100 of 40% or more and 60% or less.
(However, A disassembles the battery that is charged until it is fully charged by the corresponding charger, cuts out a part of the negative electrode facing the positive electrode as the inspection negative electrode, and evaluates the evaluation battery using metallic lithium as the counter electrode. After assembling, this evaluation battery is discharged (by energizing in the direction in which lithium ions are released from the inspection negative electrode), and can be obtained by dividing the capacity value in the initial discharge by the area of the inspection negative electrode, B was discharged for this evaluation battery, and then charged at a constant current and a constant voltage until the battery voltage reached 0 V (energization in the direction in which lithium ions were occluded in the inspection negative electrode). those which can be obtained by dividing the value by the area of the inspection anode. here, the energization current is set to 1 mA / cm ^2, discharge the battery voltage of the evaluation battery is 1.5V Performed until the charging is performed until the current value becomes less 0.05mA battery voltage in the constant voltage charging at 0V.) At an interface between the negative electrode current collector and the negative electrode active material layer, one or more elements constituting the negative electrode current collector are diffused in a part of the negative electrode active material.
The lithium ion secondary battery according to claim 1. The lithium ion secondary battery according to claim 1, wherein the negative electrode active material layer further contains oxygen (O) as a constituent element, and the content of oxygen in the negative electrode active material layer is 3 atomic% or more. . The lithium ion secondary battery according to claim 3, wherein at least a part of oxygen contained in the negative electrode active material layer is bonded to silicon. The negative electrode active material layer has alternately stacked first and second layers having different oxygen contents,
The second layer has a higher oxygen content than the first layer,
5. The lithium ion secondary battery according to claim 3 , wherein one or more of the second layers exist between the two first layers. The lithium ion secondary battery according to any one of claims 1 to 5, wherein the electrolyte includes a carbonate ester derivative having a halogen atom.

Images