Negative electrode and non-aqueous electrolyte secondary battery having the same

Abstract

This invention provides a negative electrode that improves both the cycle life of a non-aqueous electrolyte secondary battery and the capacity retention after rapid charge-discharge cycles. The disclosed negative electrode comprises a negative current collector and a negative active material layer formed on the surface of the negative current collector. The negative active material layer contains silicon oxide containing at least one alkaline earth metal. The negative active material layer comprises at least a first layer and a second layer. The first layer is disposed between the second layer and the negative current collector. The alkaline earth metal content of the second layer, calculated based on energy dispersive X-ray analysis using scanning electron microscopy images, is higher than that of the first layer.

Description

Technical Field

[0001] This invention relates to a negative electrode. This invention also relates to a non-aqueous electrolyte secondary battery having the negative electrode. Background Technology

[0002] In recent years, non-aqueous electrolyte secondary batteries such as lithium-ion batteries have become suitable for use as portable power sources for personal computers, portable terminals, electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] The negative electrode of a non-aqueous electrolyte secondary battery generally has a structure in which a layer of negative electrode active material containing negative electrode active material is supported on a negative electrode current collector. In recent years, with the aim of increasing the capacity of the negative electrode, silicon (Si)-based negative electrode active materials such as silicon and silicon compounds that can absorb and release chemical species (such as lithium ions) that can serve as charge carriers have been studied (for example, Patent Documents 1 and 2).

[0004] Furthermore, while the aforementioned Si-based anode active materials are known to have high theoretical capacity, the expansion and contraction (volume change) of the anode active materials during charge-discharge cycles is significant, resulting in a decrease in capacity retention after charge-discharge cycles. In contrast, Patent Document 3 discloses a silicon composite oxide anode material comprising MgSiO3 crystals, a carbon coating on its surface, and an anode using this oxide. This discloses improvements in the charge-discharge capacity, initial charge-discharge efficiency, and capacity retention of the secondary battery.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2015-18663

[0008] Patent Document 2: Japanese Patent Application Publication No. 2016-181331

[0009] Patent Document 3: Japanese Patent Application Publication No. 2018-156922 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] However, the inventors conducted in-depth research and found that, for secondary batteries using Si-based negative electrode active materials containing MgSiO3 crystals, although the capacity retention rate (cycle life) of charge-discharge cycles is improved, the capacity retention rate is significantly reduced when performing rapid charge-discharge cycles.

[0012] The present invention was made in view of the above circumstances, and its main objective is to provide a negative electrode that balances the improvement of cycle life of a secondary battery and the improvement of capacity retention after rapid charge-discharge cycles. Another objective is to provide a non-aqueous electrolyte secondary battery having this negative electrode.

[0013] Methods for solving problems

[0014] The disclosed negative electrode comprises a negative current collector and a negative active material layer formed on the surface of the negative current collector. The negative active material layer comprises silicon oxide containing at least one alkaline earth metal. The negative active material layer comprises at least a first layer and a second layer. The first layer is disposed between the second layer and the negative current collector. The amount of alkaline earth metal in the second layer, calculated based on energy-dispersive X-ray analysis using scanning electron microscopy images, is higher than the amount of alkaline earth metal in the first layer.

[0015] According to this configuration, by placing the alkaline earth metal-containing silicon oxide, which contributes to improved cycle life, in a second layer disposed on the surface side of the negative electrode active material layer, the reaction is suppressed from concentrating only near the surface of the negative electrode active material layer during rapid charge-discharge cycling. Thus, a negative electrode that achieves improved cycle life of a secondary battery and improved capacity retention after rapid charge-discharge cycling can be provided.

[0016] In a preferred embodiment of the negative electrode disclosed herein, when the negative electrode active material of the second layer is set to 100% by mass, the second layer contains at least 2% by mass of the aforementioned alkaline earth metal-containing silicon oxide. According to this configuration, the cycle life of the secondary battery can be further improved.

[0017] In a preferred embodiment of the negative electrode disclosed herein, when the negative electrode active material of the first layer is set to 100% by mass, the silicon oxide containing alkaline earth metal contained in the first layer is less than 2% by mass. Based on this configuration, a negative electrode can be provided that can more appropriately achieve both improved cycle life of the secondary battery and improved capacity retention after rapid charge-discharge cycles.

[0018] In a preferred embodiment of the disclosed negative electrode, the average thickness of the second layer is 20% or more and 70% or less relative to the average thickness of the negative electrode active material layer. According to this configuration, the capacity retention rate of the secondary battery after rapid charge-discharge cycles can be further improved.

[0019] In a preferred embodiment of the disclosed negative electrode, the aforementioned alkaline earth metal-containing silicon oxide comprises magnesium-containing silicon oxide and / or calcium-containing silicon oxide. According to this configuration, a negative electrode can be provided that more appropriately achieves both improved cycle life of the secondary battery and improved capacity retention after rapid charge-discharge cycles.

[0020] In a preferred embodiment of the disclosed negative electrode, the aforementioned negative electrode active material layer comprises a carbon material. Based on this configuration, a negative electrode can be provided that more appropriately achieves both improved cycle life of the secondary battery and improved capacity retention after rapid charge-discharge cycles.

[0021] In a preferred embodiment of the disclosed negative electrode, the first layer, in addition to the aforementioned silicon oxide containing alkaline earth metals, also comprises silicon containing alkali metals. Furthermore, in another preferred embodiment, the second layer, in addition to the aforementioned silicon oxide containing alkaline earth metals, also comprises silicon containing alkali metals. According to this configuration, a negative electrode can be provided that more appropriately achieves both improved cycle life of the secondary battery and improved capacity retention after rapid charge-discharge cycles.

[0022] In a preferred embodiment of the disclosed negative electrode, the aforementioned alkali metal-containing silicon oxide includes lithium-containing silicon oxide. According to this configuration, by using alkaline earth metal-containing silicon oxide that appropriately improves cycle life and lithium-containing silicon oxide with high Li diffusivity, the overall active material layer of the negative electrode can efficiently contribute to the battery reaction. Therefore, it is possible to more appropriately achieve both improved cycle life of the secondary battery and improved capacity retention after rapid charge-discharge cycles.

[0023] From another perspective, the non-aqueous electrolyte secondary battery disclosed herein includes a positive electrode, the negative electrode described above, and a non-aqueous electrolyte. Based on this configuration, a non-aqueous electrolyte secondary battery with excellent cycle life and excellent capacity retention during rapid charge-discharge cycles can be provided. Attached Figure Description

[0024] Figure 1 An explanatory diagram illustrating the structure of the negative electrode in one embodiment.

[0025] Figure 2 A cross-sectional view of a lithium-ion secondary battery according to one embodiment is shown schematically.

[0026] Figure 3 This is a schematic exploded view illustrating the configuration of the wound electrode body of a lithium-ion secondary battery according to one embodiment.

[0027] Explanation of reference numerals in the attached figures

[0028] 20. Winded electrode body

[0029] 30 Battery casing

[0030] 32 Safety valve

[0031] 42 Positive extremes

[0032] 42a Positive Current Collector

[0033] 44 Negative extremes

[0034] 44a Negative Current Collector

[0035] 50 Positive electrode sheet (positive electrode)

[0036] 52 Positive current collector

[0037] 54 Positive electrode active material layer

[0038] 56. Non-forming portion of the positive electrode active material layer

[0039] 60 Negative electrode sheet (negative electrode)

[0040] 62 Negative current collector

[0041] 64 Negative Electrode Active Material Layer

[0042] 66. Non-forming portion of the negative electrode active material layer

[0043] 64A First Floor

[0044] 64B Second Layer

[0045] 70 Separator

[0046] 100 Lithium-ion Secondary Battery Detailed Implementation

[0047] The following is a reference to the appendix. Figure 1 The embodiments of the present invention will be described below. It should be noted that matters not mentioned in this specification but necessary for the implementation of the present invention can be understood by those skilled in the art based on prior art in this field. The present invention can be implemented based on the content disclosed in this specification and common technical knowledge in this field. Furthermore, in the following drawings, components and parts that perform the same function are labeled with the same reference numerals. Also, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect actual dimensional relationships.

[0048] It should be noted that in this specification, "secondary battery" refers to an energy storage device capable of repeated charging and discharging, encompassing energy storage components such as batteries and double-layer capacitors. Furthermore, in this specification, "lithium-ion secondary battery" refers to a secondary battery that utilizes lithium ions as charge carriers, achieving charging and discharging through the movement of lithium ions between the positive and negative electrodes.

[0049] Figure 1 A diagram of the negative electrode disclosed herein is shown schematically. As shown, the negative electrode 60 includes a negative electrode current collector 62 and a negative electrode active material layer 64 supported on the negative electrode current collector 62. Figure 1In the example shown, the negative electrode active material layer 64 is disposed on one side of the negative electrode current collector 62, but it can also be disposed on both sides. Preferably, the negative electrode active material layer 64 is disposed on both sides of the negative electrode current collector 62.

[0050] As the negative current collector 62, sheets or foils made of metals such as copper, nickel, titanium, and stainless steel can be used, with copper foil being preferred. When using copper foil as the negative current collector 62, there is no particular limitation on its thickness, for example, it can be 5 μm or more and 35 μm or less, preferably 7 μm or more and 20 μm or less.

[0051] like Figure 1 As shown, the negative electrode active material layer 64 includes at least a first layer 64A and a second layer 64B. The first layer 64A is formed between the second layer 64B and the negative electrode current collector 62. The first layer 64A is located on the side of the negative electrode current collector 62, and the second layer 64B is located on the surface side of the negative electrode active material layer 64. The first layer 64A is typically formed on the surface of the negative electrode current collector 62. The negative electrode active material layer 64 can be a multilayer structure with at least two layers, or it can be a multilayer structure with three or more layers.

[0052] The negative electrode active material layer 64 comprises silicon oxide containing at least one alkaline earth metal as the negative electrode active material. In the negative electrode 60 disclosed herein, the second layer 64B, based on energy dispersive X-ray analysis using scanning electron microscopy images, contains more alkaline earth metal than the first layer 64A.

[0053] The "alkaline earth metal content (mass%)" in this specification can be determined using energy-dispersive X-ray analysis (SEM-EDS) of scanning electron microscope images. Specifically, first, a SEM image of a cross-section along the thickness direction of the negative electrode active material layer is taken. Then, EDS analysis is performed on the SEM image to calculate the proportion (mass%) of each constituent element contained in the negative electrode active material layer. The proportion of alkaline earth metal elements (Mg, Ca, etc.) calculated at this time (i.e., the proportion of alkaline earth metal elements relative to all constituent elements of the negative electrode active material layer) is set as the "alkaline earth metal content (mass%)" in this specification.

[0054] The alkaline earth metal content (mass%) of the first and second layers can be calculated, for example, as follows. In a cross-section along the thickness direction of the negative electrode active material layer, the thickness of 20% from the current collector toward the interior of the active material layer is defined as the first layer, and the thickness of 20% from the surface layer toward the interior of the active material layer is defined as the second layer. Then, following the same procedure as above, EDS analysis is performed on the first and second layers respectively to calculate the proportion (mass%) of each constituent element in each layer. The proportion of alkaline earth metal elements relative to all constituent elements of the first layer is defined as the "alkaline earth metal content (mass%) of the first layer" in this specification, and the proportion of alkaline earth metal elements relative to all constituent elements of the second layer is defined as the "alkaline earth metal content (mass%) of the second layer" in this specification.

[0055] The amount of alkaline earth metal in the second layer 64B is typically preferred to be 0.5% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 8% by mass or less. Furthermore, the amount of alkaline earth metal in the first layer 64A can be less than 2% by mass or less than 1% by mass. It should be noted that, typically, the region containing an alkaline earth metal content of 0.5% by mass or more as calculated using SEM-EDS is defined as the second layer 64B. Furthermore, the amount of alkaline earth metal in the first layer 64A is not limited to the technology disclosed herein. That is, the amount of alkaline earth metal in the first layer 64A can also be 0% by mass. By ensuring that the amounts of alkaline earth metal in the first layer 64A and the second layer 64B are within the aforementioned ranges, it is possible to appropriately balance the improvement in cycle life of the secondary battery and the improvement in capacity retention after rapid charge-discharge cycles.

[0056] The average thickness of the negative electrode active material layer 64 is, for example, 10 μm or more and 300 μm or less, preferably 20 μm or more and 200 μm or less. In a preferred embodiment, the average thickness of the second layer 64B is preferably 15% to 75% of the average thickness of the negative electrode active material layer 64, more preferably 20% to 70%.

[0057] The negative electrode active material layer 64 contains at least a negative electrode active material capable of reversibly adsorbing and releasing chemical species (lithium ions in a lithium-ion secondary battery) that serve as charge carriers. In the disclosed technology, the negative electrode active material layer 64 comprises silicon oxide containing at least one alkaline earth metal as the negative electrode active material. The alkaline earth metal-containing silicon oxide is typically silicon oxide (SiO₂) doped with an alkaline earth metal (Mg, Ca, etc.) and containing silicon (Si) and oxygen (O) as essential components. y The state in ) is preferred. For example, it preferably has the general formula: M x SiO y(In the formula, x and y each satisfy 0 < x ≦ 0.25 and 0 < y ≦ 2. M is at least one element selected from Mg, Ca, Be, Sr, Ba and Ra) represents the composition. Preferably, it is silicon dioxide containing Mg and / or silicon dioxide containing Ca.

[0058] There is no particular limitation on the average particle size (median particle size D50) of silica containing alkaline earth metals; for example, it can be greater than 0.5 μm and less than 15 μm. It should be noted that in this specification, "average particle size (median particle size D50)" refers to the particle size in a particle size distribution based on a general laser diffraction / light scattering method, which corresponds to a cumulative frequency of 50% by volume from the side of the smallest particle.

[0059] As a Mg-containing silicon dioxide, it is typically a Mg-Si-O compound, which is silicon dioxide (SiO₂) doped with Mg, an alkaline earth metal. y ). In Mg doped SiO y In this case, as a crystal structure, Si phase and SiO can be formed. y Mg-containing silicon oxide typically contains the MgSiO3 phase. In the disclosed technology, Mg-containing silicon oxide preferably has a phase composed of the general formula: Mg α SiO y (In the formula, α and y satisfy 0<α≦0.25 and 0<y≦2 respectively) represents the composition.

[0060] Similarly, as a Ca-containing silicon dioxide, typically a Ca-Si-O compound, it is silicon dioxide (SiO₂) doped with Ca, an alkaline earth metal. y In the disclosed technology, silicon dioxide containing Ca is preferably composed of the general formula: Ca β SiO y (In the formula, β and y satisfy 0<β≦0.25 and 0<y≦2 respectively) represents the composition.

[0061] When the negative electrode active material of the second layer 64B is set to 100% by mass, the mass proportion of silicon oxide containing alkaline earth metals contained in the second layer 64B is preferably 1% to 20% by mass, more preferably 1.5% to 20% by mass, and particularly preferably 2% to 20% by mass. When the negative electrode active material of the first layer 64A is set to 100% by mass, the mass proportion of silicon oxide containing alkaline earth metals contained in the first layer 64A is preferably less than 2% by mass, more preferably 1.5% by mass or less, and particularly preferably 1% by mass or less. It should be noted that whether or not the first layer 64A contains silicon oxide containing alkaline earth metals is not a limitation of the technology disclosed herein. That is, the silicon oxide containing alkaline earth metals contained in the first layer 64A may also be 0% by mass.

[0062] It should be noted that the mass ratio of alkaline earth metal-containing silicon dioxide in each layer can be determined, for example, by setting the first and second layers as described above and performing ICP analysis.

[0063] By biasing the alkaline earth metal-containing silicon oxide into the second layer, it is possible to appropriately balance the improvement in cycle life of the secondary battery and the improvement in capacity retention after rapid charge-discharge cycles. Although not specifically limited, it is speculated that the above-mentioned effects can be obtained for the following reasons.

[0064] By incorporating alkaline earth metals into silicon oxide through doping, the diffusion of the charge-carrying chemical species (lithium ions in lithium-ion secondary batteries) tends to slow down. When the negative electrode active material layer is formed solely from silicon oxide containing alkaline earth metals, the capacity retention after cycling is improved. However, during repeated rapid charge-discharge cycles, excess lithium that has not fully diffused is deposited, leading to a decrease in capacity retention after rapid charge-discharge cycles. In contrast, in the disclosed technology, the alkaline earth metal-containing silicon oxide is positioned as a second layer on the surface side of the negative electrode active material layer. This results in better lithium ion diffusion on the current collector side compared to the surface side, thus enabling the entire negative electrode active material layer to efficiently facilitate charge-discharge, thereby improving the cycle life of the secondary battery and the capacity retention during rapid charge-discharge cycles.

[0065] Silicon oxide containing alkaline earth metals can be prepared, for example, by the following method. First, prepare SiO₂... y The powder and raw material powder of alkaline earth metals (such as Mg, Ca, etc.). The raw material powder of alkaline earth metals can be, for example, Mg powder or Ca powder. SiO2 is processed using a ball mill or similar equipment. y The powder of SiO2 is mixed with the raw material powder of alkaline earth metals to obtain a mixed powder. This mixed powder is then heated at approximately 1000°C for about 1 hour under an argon (Ar) atmosphere. This process allows for the production of SiO2. y It is doped with alkaline earth metals.

[0066] The negative electrode active material contained in the negative electrode active material layer 64, in addition to the aforementioned silicon oxide containing alkaline earth metals, also includes carbon materials such as graphite, hard carbon, and soft carbon. The graphite can be natural graphite, artificial graphite, or graphite coated with amorphous carbon materials in the form of amorphous carbon-coated graphite.

[0067] There are no particular limitations on the morphology (average particle size, BET specific surface area, etc.) of carbon materials. Carbon materials are typically in particulate form. The average particle size D50 of particulate carbon materials is typically 1 μm or more and 20 μm or less, for example, 5 μm or more and 15 μm or less. Furthermore, the BET specific surface area obtained using the BET method is typically preferably 0.5 cm². 2 / g or more and 3cm 2 BET specific surface area below / g.

[0068] In addition to the materials mentioned above, the negative electrode active material layer 64 may further contain silicon oxide containing an alkali metal. Typically, the silicon oxide containing an alkali metal (Li, Na, etc.) is doped with silicon oxide (SiO₂) containing silicon (Si) and oxygen (O) as essential components. y The state in ) . For example, it is preferable to have the general formula: Q γ SiO y (In the formula, γ and y satisfy 0 < γ ≦ 2 and 0 < y ≦ 2, respectively. Q is at least one element selected from Li, Na, K, Rb, Cs, and Fr.) Preferably, it is silicon oxide containing Li.

[0069] It should be noted that silicon dioxide containing alkali metals can be produced using the same method as silicon dioxide containing alkaline earth metals.

[0070] When the negative electrode active material of the first layer 64A is set to 100% by mass, the mass proportion of alkali metal-containing silicon oxide contained in the first layer 64A can be 18% by mass or less, 9% by mass or less, or 8% by mass or less. Similarly, when the negative electrode active material of the second layer 64B is set to 100% by mass, the mass proportion of alkali metal-containing silicon oxide contained in the second layer 64B can be 20% by mass or less, 18% by mass or less, or 16% by mass or less. It should be noted that in the technology disclosed herein, the mass proportion of alkali metal-containing silicon oxide in the first layer 64A and the second layer 64B (in other words, the negative electrode active material layer 64) is not limited to the technology disclosed herein. That is, the mass proportion of alkali metal-containing silicon oxide in the negative electrode active material layer 64 can also be 0% by mass.

[0071] It should be noted that the mass ratio of alkali metal-containing silicon dioxide in each layer can be determined, for example, through the aforementioned ICP analysis.

[0072] In addition to the materials described above, the negative electrode active material layer 64 may also contain other negative electrode active materials without impairing the technical effects disclosed herein. Examples of other negative electrode active materials include, for example, Si-based negative electrode active materials. Examples of Si-based negative electrode active materials include metallic Si and oxides with Si as a constituent element (e.g., SiO₂). y Alloys with Si as a constituent element, etc.

[0073] While not specifically limited, the content of the negative electrode active material in the negative electrode active material layer 64 (i.e., the ratio of the negative electrode active material to the total mass of the negative electrode active material layer) can be 80% to 99% by mass, or 85% to 98% by mass. When the negative electrode active material in the negative electrode active material layer 64 is set to 100% by mass, the mass ratio of the Si-based negative electrode active material (including silicon oxide containing alkaline earth metals and silicon oxide containing alkali metals) is preferably 1% to 30% by mass, more preferably 2% to 30% by mass. Furthermore, when the negative electrode active material in the negative electrode active material layer 64 is set to 100% by mass, the mass ratio of the carbon material is preferably 70% to 99% by mass, more preferably 80% to 98% by mass.

[0074] Although not specifically limited, the content of the negative electrode active material in the first layer 64A can be 80% to 99% by mass, or 85% to 98% by mass. When the negative electrode active material of the first layer 64A is set to 100% by mass, the mass ratio of the Si-based negative electrode active material (including silicon oxide containing alkaline earth metals and silicon oxide containing alkali metals) is typically 0% to 20% by mass, 0% to 10% by mass, or 1% to 10% by mass. Furthermore, when the negative electrode active material of the first layer 64A is set to 100% by mass, the mass ratio of the carbon material is typically 80% to 100% by mass, 90% to 100% by mass, or 90% to 99% by mass.

[0075] Although not specifically limited, the content of the negative electrode active material in the second layer 64B can be 80% to 99% by mass, or 85% to 98% by mass. When the negative electrode active material of the second layer 64B is set to 100% by mass, the mass ratio of the Si-based negative electrode active material (including silicon oxide containing alkaline earth metals and silicon oxide containing alkali metals) is preferably 1% to 20% by mass, more preferably 2% to 20% by mass. Furthermore, when the negative electrode active material of the second layer 64B is set to 100% by mass, the mass ratio of the carbon material is preferably 80% to 99% by mass, more preferably 80% to 98% by mass.

[0076] The negative electrode active material layer 64 may contain components other than the aforementioned negative electrode active material, such as adhesives and tackifiers. As adhesives, examples include styrene-butadiene rubber (SBR) and its modifiers, acrylonitrile-butadiene rubber and its modifiers, acrylic rubber and its modifiers, and fluororubber. SBR is preferred. The content of the adhesive in the negative electrode active material layer 64 is not particularly limited, but is preferably 0.1% by mass or more and 8% by mass or less, more preferably 0.2% by mass or more and 3% by mass or less.

[0077] As a thickener, cellulose-based polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropyl methyl cellulose (HPMC) can be used; polyvinyl alcohol (PVA) is also acceptable. CMC is preferred. The content of the thickener in the negative electrode active material layer 64 is not particularly limited, but is preferably 0.3% by mass or more and 3% by mass or less, more preferably 0.4% by mass or more and 2% by mass or less.

[0078] The negative electrode constructed as described above can improve the cycle life of the secondary battery and enhance the capacity retention during rapid charge-discharge cycles. The negative electrode constructed as described above can be used as the negative electrode of a secondary battery according to known methods. Therefore, the negative electrode disclosed herein is suitable for use in secondary batteries. This secondary battery is suitable as a non-aqueous electrolyte secondary battery.

[0079] <Non-aqueous electrolyte secondary battery>

[0080] Therefore, from another perspective, the non-aqueous electrolyte secondary battery disclosed herein has the aforementioned negative electrode, positive electrode, and non-aqueous electrolyte.

[0081] The following describes in detail one embodiment of the non-aqueous electrolyte secondary battery disclosed herein, using a flat square lithium-ion secondary battery having a flat-shaped wound electrode body and a flat-shaped battery casing as an example. However, it is not intended to limit the non-aqueous electrolyte secondary battery disclosed herein to the contents described in this embodiment.

[0082] Figure 2 The lithium-ion secondary battery 100 shown is a sealed battery constructed by housing a flat, wound electrode body 20 and a non-aqueous electrolyte (not shown) within a flat, square battery casing (i.e., outer packaging container) 30. The battery casing 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, and a thin-walled safety valve 32 configured to release internal pressure when the internal pressure of the battery casing 30 rises above a predetermined level. Additionally, the battery casing 30 is provided with an injection port (not shown) for injecting non-aqueous electrolyte. The positive terminal 42 is electrically connected to a positive current collector 42a. The negative terminal 44 is electrically connected to a negative current collector 44a. The battery casing 30 is made of a lightweight and thermally conductive metal material, such as aluminum.

[0083] like Figure 2 and Figure 3As shown, the wound electrode body 20 has a configuration in which a positive electrode sheet 50 and a negative electrode sheet 60 are overlapped and wound along the length direction, separated by two elongated separators 70. The positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed on one or both (in this case, both) sides of the elongated positive electrode current collector 52 along the length direction. The negative electrode sheet 60 has a configuration in which a negative electrode active material layer 64 is formed on one or both (in this case, both) sides of the elongated negative electrode current collector 62 along the length direction. The non-formed portions 56 of the positive electrode active material layer (i.e., the portions where the positive electrode active material layer 54 is not formed and thus the positive electrode current collector 52 is exposed) and the non-formed portions 66 of the negative electrode active material layer (i.e., the portions where the negative electrode active material layer 64 is not formed and thus the negative electrode current collector 62 is exposed) are formed to extend outward from both ends in the winding axis direction of the wound electrode body 20 (i.e., the sheet width direction orthogonal to the aforementioned length direction). The non-forming portion 56 of the positive electrode active material layer and the non-forming portion 66 of the negative electrode active material layer are respectively bonded with a positive electrode current collector 42a and a negative electrode current collector 44a.

[0084] The negative electrode sheet 60 uses the above-mentioned negative electrode.

[0085] The positive current collector 52 constituting the positive electrode sheet 50 can be made of sheet or foil material of metals such as aluminum, nickel, titanium, or stainless steel, with aluminum foil being suitable. When using aluminum foil as the positive current collector 52, there is no particular limitation on its thickness, for example, it can be 5 μm or more and 35 μm or less, preferably 7 μm or more and 20 μm or less.

[0086] There are no particular limitations on the positive electrode active material included in the positive electrode active material layer 54. One or more positive electrode active materials that have been conventionally used as positive electrode active materials in non-aqueous electrolyte secondary batteries, particularly as positive electrode active materials in lithium-ion secondary batteries, may be used. Examples of preferred positive electrode active materials include lithium composite oxides and lithium transition metal phosphate compounds (e.g., LiFePO4). Examples of lithium composite oxides include lithium nickel composite oxides, lithium cobalt composite oxides, lithium manganese composite oxides, and lithium nickel manganese composite oxides (e.g., LiNi). 0.5 Mn 1.5 O4), lithium nickel manganese cobalt composite oxides (e.g., LiNi) 1 / 3 Co 1 / 3 Mn 1 / 3 O2), etc.

[0087] There is no particular limitation on the average particle size of the positive electrode active material; it can be approximately 0.5 μm or larger and 50 μm or smaller, typically 1 μm or larger and 20 μm or smaller.

[0088] The positive electrode active material layer 54 may contain substances other than the positive electrode active material, such as conductive materials and adhesives. As conductive materials, carbon black such as acetylene black (AB) and other carbon materials (such as graphite) are preferred. As adhesives, fluorine-based adhesives such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE), and rubber-based adhesives such as styrene-butadiene rubber (SBR) are preferred. Furthermore, the positive electrode active material layer 54 may also contain materials other than those mentioned above (such as various additives) as long as it does not impair the effects of the present invention.

[0089] From the viewpoint of energy density, the content of the positive electrode active material in the positive electrode active material layer 54 (i.e., the ratio of the positive electrode active material to the total mass of the positive electrode active material layer) is preferably approximately 70% by mass or more. More preferably, it is 75% to 99% by mass, and even more preferably 80% to 97% by mass. Furthermore, the content of the conductive material in the positive electrode active material layer 54 is preferably 0.1% to 20% by mass, and more preferably 1% to 15% by mass. The content of the binder in the positive electrode active material layer 54 is preferably 0.5% to 15% by mass, and more preferably 1% to 10% by mass. Additionally, when various additives such as thickeners are included, the content of additives in the positive electrode active material layer 54 is preferably 7% by mass or less, and more preferably 5% by mass or less.

[0090] Examples of separators 70 include porous sheets (membranes) made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. These porous sheets can be single-layered or multi-layered (e.g., a three-layered structure with PP layers laminated on both sides of a PE layer). A heat-resistant layer (HRL) can be provided on the surface of the separator 70.

[0091] There is no particular limitation on the thickness of the separator 70, for example, it is 5 μm or more and 50 μm or less, preferably 10 μm or more and 30 μm or less.

[0092] Non-aqueous electrolytes are typically liquids in which electrolyte salts (in other words, supporting salts) are dissolved or dispersed in a non-aqueous solvent (non-aqueous electrolyte solutions). Alternatively, polymers can be added to the non-aqueous electrolyte to form a solid (typically so-called gel) non-aqueous electrolyte.

[0093] As a non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones commonly used in the electrolytes of lithium-ion secondary batteries can be used without particular limitation. Among them, carbonates are preferred, and specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene monofluorocarbonate (MFEC), ethylene difluorocarbonate (DFEC), difluoromethyl difluoromethyl carbonate (F-DMC), and dimethyl trifluorocarbonate (TFDMC). Such non-aqueous solvents can be used alone or in appropriate combinations of two or more.

[0094] As the electrolyte salt, lithium salts such as LiPF6, LiBF4, and lithium bis(fluorosulfonyl)imide (LiFSI) can be used, with LiPF6 being preferred. The concentration of the electrolyte salt is not particularly limited, but is preferably 0.7 mol / L or higher and 1.3 mol / L or lower. It should be noted that, provided it does not significantly impair the effects of the present invention, the above-mentioned non-aqueous electrolyte may also contain components other than those described above, such as film-forming agents like oxalic acid complexes, gas generators like biphenyl (BP) and cyclohexylbenzene (CHB), and various additives such as thickeners.

[0095] The lithium-ion secondary battery 100 configured as described above can improve cycle life and capacity retention after rapid charge-discharge cycles. The lithium-ion secondary battery 100 can be used for various applications. Suitable applications include power supplies for driving electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). Among these, power supplies for driving electric vehicles (BEVs) require rapid charging (fast charging) and frequent rapid discharging during vehicle acceleration, thus the negative electrode and secondary battery equipped with the negative electrode disclosed herein are more suitable. Furthermore, the lithium-ion secondary battery 100 can typically be used in the form of a battery pack consisting of multiple batteries connected in series and / or in parallel.

[0096] Furthermore, as an example, a square lithium-ion secondary battery 100 having a flat, wound electrode body 20 has been described. However, the lithium-ion secondary battery disclosed herein can be configured as a lithium-ion secondary battery having a stacked electrode body (i.e., an electrode body formed by alternating stacking of multiple positive electrodes and multiple negative electrodes). In addition, the non-aqueous electrolyte secondary battery disclosed herein can also be configured as a cylindrical lithium-ion secondary battery, a laminated shell type lithium-ion secondary battery, a coin-shaped lithium-ion secondary battery, etc.

[0097] In addition, according to known methods, the above-mentioned negative electrode can be used to construct all-solid-state batteries, sodium-ion secondary batteries, etc., which include a solid electrolyte layer, a gel electrolyte to replace the non-aqueous electrolyte and a separator.

[0098] The following describes experimental examples related to the present invention, but it is not intended to limit the present invention to the contents shown in these experimental examples.

[0099] <Example 1>

[0100] 100 parts by mass of graphite (C) as the negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as the binder, and 1 part by mass of carboxymethyl cellulose (CMC) as the tackifier are mixed in ion-exchanged water to prepare the first negative electrode composite slurry.

[0101] In addition, as a negative electrode active material, 10 parts by mass of silica containing magnesium (Mg) and 90 parts by mass of graphite (C) are mixed to prepare a mixed negative electrode active material containing Mg silica and graphite. 100 parts by mass of this mixed negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as a binder, and 1 part by mass of carboxymethyl cellulose (CMC) as a tackifier are mixed in ion-exchanged water to prepare a second negative electrode composite slurry.

[0102] A first negative electrode composite slurry is coated on both sides of a copper foil negative electrode current collector and dried. The coating is then pressed and calendered using calendering rollers. Next, a second negative electrode composite slurry is coated on the dried coating of the first negative electrode composite slurry, and dried and calendered in the same manner. This yields the negative electrode sheet of Example 1, comprising a first layer formed of the first negative electrode composite slurry and a second layer formed of the second negative electrode composite slurry supported on the negative electrode current collector. It is noted that the second negative electrode composite slurry is coated such that the average thickness of the second layer is 50% of the average thickness of the negative electrode active material layer.

[0103] In addition, LiNi will be used as the positive electrode active material. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM), acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are mixed in N-methylpyrrolidone (NMP) at a mass ratio of NCM:AB:PVdF = 97:2:1 to prepare a positive electrode composite slurry. This positive electrode composite slurry is then coated onto aluminum foil. After drying, it is rolled to a specified thickness to produce a positive electrode sheet.

[0104] A porous polyolefin sheet with a three-layer structure of PP / PE / PE is prepared as a separator. The positive and negative electrode sheets are overlapped with the separator in between and wound together to obtain a wound body. This wound body is then pressed to create a flat wound electrode body.

[0105] The electrode terminals were installed on the electrode body, inserted into the aluminum laminated film housing, and fused together. Then, a non-aqueous electrolyte was injected. The non-aqueous electrolyte used was a solution prepared by dissolving LiPF6 at a concentration of 1.0 mol / L in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a 3:4:3 volume ratio. The laminated housing was then sealed, thus obtaining the lithium-ion secondary battery for evaluation in Example 1.

[0106] <Example 2 and Example 3>

[0107] As shown in Table 1, the mass ratio (mass%) of Mg-containing silicon dioxide in the second layer was changed. Otherwise, the same procedure as in Example 1 was followed to produce the evaluation lithium-ion secondary batteries for Examples 2 and 3.

[0108] <Example 4>

[0109] As the negative electrode active material, 10 parts by mass of Mg-containing silicon dioxide and 90 parts by mass of graphite (C) were mixed to prepare a mixed negative electrode active material containing Mg-containing silicon dioxide and graphite. 100 parts by mass of this mixed negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as a binder, and 1 part by mass of carboxymethyl cellulose (CMC) as a tackifier were mixed in ion-exchanged water to prepare a first negative electrode composite slurry. Except for the first negative electrode composite slurry, the same procedure as in Example 1 was followed to prepare the evaluation lithium-ion secondary battery of Example 4.

[0110] <Example 5~Example 7>

[0111] As the negative electrode active material, 10 parts by mass of lithium (Li)-containing silicon dioxide and 90 parts by mass of graphite (C) were mixed to prepare a mixed negative electrode active material containing Li-containing silicon dioxide and graphite. 100 parts by mass of this mixed negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as a binder, and 1 part by mass of carboxymethyl cellulose (CMC) as a tackifier were mixed in ion-exchanged water to prepare a first negative electrode slurry. Furthermore, the mass ratio (mass %) of Mg-containing silicon dioxide in the second layer was varied as shown in Table 1. Otherwise, the same procedures as in Example 1 were followed to prepare evaluation lithium-ion secondary batteries for Examples 5 to 7.

[0112] <Example 8 and Example 9>

[0113] As shown in Table 1, the mass ratio (mass%) of Mg-containing silicon oxide and Li-containing silicon oxide in the first layer was changed. Otherwise, the same procedure as in Example 1 was followed to produce the evaluation lithium-ion secondary batteries of Examples 8 and 9.

[0114] <Example 10~Example 12>

[0115] The second negative electrode composite slurry was coated in such a way that the average thickness of the second layer was relative to the average thickness of the negative electrode active material layer as shown in Table 1. Otherwise, the same procedure as in Example 6 was followed to produce the evaluation lithium-ion secondary batteries of Examples 10 to 12.

[0116] <Evaluation of activation of lithium-ion secondary batteries>

[0117] The evaluation lithium-ion secondary batteries prepared in Examples 1 to 12 were placed in an environment at 25°C. For activation (initial charging), a constant current-constant voltage method was used. Each evaluation lithium-ion secondary battery was charged at a constant current value of 1 / 3C to 4.1V, and then charged at a constant voltage value until the current value reached 1 / 50C, achieving a fully charged state. Then, each evaluation lithium-ion secondary battery was discharged at a constant current value of 1 / 3C until 3.0V.

[0118] <Charge-Discharge Cycle Test>

[0119] The activated lithium-ion secondary batteries for evaluation were placed in an environment of 25°C. One cycle consisted of constant current charging at 0.5C to 4.1V and constant current discharging at 0.5C to 3.0V, repeated for 500 cycles. The discharge capacity of the first and 500th cycles was measured, and the ratio of the discharge capacity of the 500th cycle to the discharge capacity of the first cycle was calculated as the capacity retention rate (%). If the capacity retention rate after 500 cycles was 90% or higher, it was rated "◎"; if it was 80% or higher but less than 90%, it was rated "○"; and if it was less than 80%, it was rated "×". The results are shown in Table 1. It is noted that a good capacity retention rate after 500 cycles indicates a high cycle life for the secondary battery.

[0120] <Fast Charge-Discharge Cycle Test>

[0121] The activated lithium-ion secondary batteries for evaluation were placed in an environment of 25°C. One cycle consisted of constant current charging at 2C to 4.1V and constant current discharging at 2C to 3.0V, repeated for 100 cycles. The discharge capacity of the first and 100th cycles was measured, and the ratio of the discharge capacity of the 100th cycle to the discharge capacity of the first cycle was calculated as the capacity retention rate (%). If the capacity retention rate after rapid charge-discharge cycles was 90% or higher, it was rated "◎"; if it was 80% or higher but less than 90%, it was rated "○"; and if it was less than 80%, it was rated "×". The results are shown in Table 1.

[0122] [Table 1]

[0123] Table 1

[0124]

[0125] As shown in Table 1, it can be seen that when the negative electrode active material layer contains silicon oxide containing at least one alkaline earth metal, and the amount of alkaline earth metal in the second layer is higher than that in the first layer, the capacity retention rate after 500 cycles and after fast charge-discharge cycles is more than 80%. On the other hand, according to the results of Example 4, when the amount of alkaline earth metal in the first and second layers is the same, the capacity retention rate after fast charge-discharge cycles is less than 80%.

[0126] Furthermore, as shown in Example 3, it can be seen that when the negative electrode active material of the second layer is set to 100% by mass, and when it contains at least 2% by mass of silicon oxide containing alkaline earth metals, the capacity retention rate after 500 cycles and after fast charge-discharge cycles is 90% or more.

[0127] As shown in Example 8, it can be seen that when the negative electrode active material of the first layer is set to 100% by mass, and the silicon oxide containing alkaline earth metal is less than 2% by mass, the capacity retention rate after 500 cycles and after rapid charge-discharge cycles is both above 90%.

[0128] As shown in Examples 10 and 11, it can be seen that when the average thickness of the second layer is more than 20% and less than 70% of the average thickness of the negative electrode active material layer, the capacity retention rate after 500 cycles and after fast charge-discharge cycles is more than 90%.

[0129] <Example 13>

[0130] As the negative electrode active material, 1 part by mass of silicon dioxide containing Mg, 9 parts by mass of silicon dioxide containing Li, and 90 parts by mass of graphite (C) are mixed to prepare a mixed negative electrode active material containing Mg silicon dioxide and a mixed negative electrode active material containing Li silicon dioxide and graphite. 100 parts by mass of this mixed negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as a binder, and 1 part by mass of carboxymethyl cellulose (CMC) as a tackifier are mixed in ion-exchanged water to prepare a first negative electrode composite slurry.

[0131] In addition, as the negative electrode active material, 2 parts by mass of Mg-containing silicon dioxide, 8 parts by mass of Li-containing silicon dioxide, and 90 parts by mass of graphite (C) are mixed to prepare a mixed negative electrode active material containing Mg-containing silicon dioxide, Li-containing silicon dioxide, and graphite. 100 parts by mass of this mixed negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as a binder, and 1 part by mass of carboxymethyl cellulose (CMC) as a tackifier are mixed in ion-exchanged water to prepare a second negative electrode composite slurry.

[0132] The first negative electrode composite slurry and the second negative electrode composite slurry are coated onto the negative electrode current collector as described above, and then dried and pressed to produce the negative electrode sheet of Example 13.

[0133] In addition to the above, the same procedure as in Example 1 was followed to produce the evaluation lithium-ion secondary battery for Example 13.

[0134] <Example 14 and Example 15>

[0135] As shown in Table 2, the mass ratio (mass%) of Mg-containing silicon oxide and Li-containing silicon oxide in the first and second layers were changed. Otherwise, the same procedure as in Example 13 was followed to produce the evaluation lithium-ion secondary batteries of Examples 14 and 15.

[0136] <Example 16>

[0137] As the negative electrode active material, 10 parts by mass of Mg-containing silicon dioxide and 90 parts by mass of graphite (C) are mixed to prepare a mixed negative electrode active material containing Mg-containing silicon dioxide and graphite. 100 parts by mass of this mixed negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as a binder, and 1 part by mass of carboxymethyl cellulose (CMC) as a tackifier are mixed in ion-exchanged water to prepare a first negative electrode composite slurry.

[0138] In addition, as the negative electrode active material, 10 parts by mass of Li-containing silicon dioxide and 90 parts by mass of graphite (C) were mixed to prepare a mixed negative electrode active material containing Li-containing silicon dioxide and graphite. 100 parts by mass of this mixed negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as a binder, and 1 part by mass of carboxymethyl cellulose (CMC) as a tackifier were mixed in deionized water to prepare a second negative electrode slurry. Otherwise, the same procedure as in Example 1 was followed to prepare the evaluation lithium-ion secondary battery of Example 16.

[0139] <Reference Example>

[0140] As a reference example, a negative electrode active material layer without containing Mg-containing silicon oxide was formed. Specifically, as the negative electrode active material, 10 parts by mass of Li-containing silicon oxide and 90 parts by mass of graphite (C) were mixed to prepare a mixed negative electrode active material containing Li-containing silicon oxide and graphite. 100 parts by mass of this mixed negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as a binder, and 1 part by mass of carboxymethyl cellulose (CMC) as a tackifier were mixed in ion-exchanged water to prepare a first negative electrode composite slurry and a second negative electrode composite slurry. Otherwise, the same procedure as in Example 1 was followed to prepare an evaluation lithium-ion secondary battery of the reference example.

[0141] As described above, the lithium-ion secondary batteries used for evaluation in Examples 13 to 16 and the reference example were activated (initial charge). Following the same procedure as described above, charge-discharge cycle tests and fast charge-discharge cycle tests were performed on the activated lithium-ion secondary batteries. If the capacity retention rate after 500 cycles and after fast charge-discharge cycles was 90% or more, it was rated as "◎"; if it was 80% or more but less than 90%, it was rated as "○"; and if it was less than 80%, it was rated as "×". The results are shown in Table 2.

[0142] [Table 2]

[0143] Table 2

[0144]

[0145] As shown in Table 2, it can be seen that even when the second layer contains silicon oxide containing Li, the amount of alkaline earth metal in the second layer is higher than that in the first layer. When the negative electrode active material of the second layer is set to 100% by mass and the amount of silicon oxide containing alkaline earth metal is more than 2% by mass, the capacity retention rate after 500 cycles and after fast charge-discharge cycles is also more than 90%. The cycle life and fast charge-discharge cycle characteristics of the secondary battery are particularly good.

[0146] <Example 21>

[0147] Ten parts by mass of Li-containing silicon dioxide and 90 parts by mass of graphite (C) were mixed to prepare a mixed negative electrode active material containing Li-containing silicon dioxide and graphite. One hundred parts by mass of this mixed negative electrode active material, one part by mass of styrene-butadiene rubber (SBR) as a binder, and one part by mass of carboxymethyl cellulose (CMC) as a tackifier were mixed in ion-exchanged water to prepare a first negative electrode composite slurry.

[0148] In addition, 20 parts by mass of Ca-containing silica and 80 parts by mass of graphite (C) are mixed to prepare a mixed negative electrode active material containing Ca and silica. 100 parts by mass of this mixed negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as a binder, and 1 part by mass of carboxymethyl cellulose (CMC) as a tackifier are mixed in ion-exchanged water to prepare a second negative electrode slurry.

[0149] A first negative electrode composite slurry is coated on both sides of a copper foil negative electrode current collector and dried. The coating is then pressed using calendering rollers. Next, a second negative electrode composite slurry is coated on the dried coating of the first negative electrode composite slurry, and dried and calendered in the same manner. This yields a negative electrode sheet of Example 21, comprising a first layer formed of the first negative electrode composite slurry and a second layer formed of the second negative electrode composite slurry, supported on a negative electrode current collector. It is noted that the second negative electrode composite slurry is coated such that the average thickness of the second layer is 50% of the average thickness of the negative electrode active material layer.

[0150] In addition to the negative electrode sheet mentioned above, the same procedure as in Example 1 was followed to produce the evaluation lithium-ion secondary battery of Example 21.

[0151] <Example 22 and Example 23>

[0152] As shown in Table 3, the mass ratio (mass%) of Ca-containing silicon oxide in the second layer was changed. Otherwise, the same procedure as in Example 1 was followed to produce the evaluation lithium-ion secondary batteries of Examples 22 and 23.

[0153] <Example 24>

[0154] As the negative electrode active material, 10 parts by mass of silica containing Ca and 90 parts by mass of graphite (C) are mixed to prepare a mixed negative electrode active material containing Mg, which is composed of silica and graphite. 100 parts by mass of this mixed negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as a binder, and 1 part by mass of carboxymethyl cellulose (CMC) as a tackifier are mixed in ion-exchanged water to prepare a first negative electrode composite slurry.

[0155] In addition, as the negative electrode active material, 10 parts by mass of Li-containing silicon dioxide and 90 parts by mass of graphite (C) were mixed to prepare a mixed negative electrode active material containing Li-containing silicon dioxide and graphite. 100 parts by mass of this mixed negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as a binder, and 1 part by mass of carboxymethyl cellulose (CMC) as a tackifier were mixed in ion-exchanged water to prepare a second negative electrode slurry. Otherwise, the same procedure as in Example 1 was followed to prepare the evaluation lithium-ion secondary battery of Example 24.

[0156] The lithium-ion secondary batteries used for evaluation in Examples 21 to 24, prepared as described above, were activated (initial charge). Following the same procedure as described above, charge-discharge cycle tests and rapid charge-discharge cycle tests were performed on the activated lithium-ion secondary batteries. If the capacity retention rate after 500 cycles and after rapid charge-discharge cycles was 90% or more, it was rated "◎"; if it was 80% or more but less than 90%, it was rated "○"; and if it was less than 80%, it was rated "×". The results are shown in Table 3.

[0157] [Table 3]

[0158] Table 3

[0159]

[0160] As shown in Table 3, even when the type of silicon oxide containing alkaline earth metals is changed, the same trend as in Examples 5 to 7 of Table 1 is observed. Therefore, regardless of the type of silicon oxide containing alkaline earth metals, it is possible to provide a negative electrode for secondary batteries with excellent cycle life and capacity retention after rapid charge-discharge cycles.

[0161] The specific examples of the present invention have been described in detail above, but these are merely illustrative and do not limit the scope of the claims. The technology described within the scope of the claims includes technologies obtained by various modifications and alterations to the specific examples described above.

Claims

1. A negative electrode for a secondary battery, comprising a negative electrode current collector and a layer of negative electrode active material formed on the surface of the negative electrode current collector. The negative electrode active material layer comprises carbon material, silicon oxide containing at least one alkaline earth metal, and silicon oxide containing an alkali metal. The negative electrode active material layer comprises at least a first layer and a second layer. The first layer is disposed between the second layer and the negative current collector. in, The alkaline earth metal content in the second layer, calculated using energy-dispersive X-ray diffraction analysis of scanning electron microscopy images, is higher than that in the first layer. The second layer comprises carbon materials and silicon dioxide containing alkaline earth metals, but does not contain silicon dioxide containing alkali metals. The first layer comprises carbon material and silicon dioxide containing alkali metals, but does not contain silicon dioxide containing alkaline earth metals. When the negative electrode active material of the second layer is set to 100% by mass, the mass proportion of the alkaline earth metal-containing silicon oxide in the second layer is 2% to 20% by mass. When the negative electrode active material of the first layer is set to 100% by mass, the mass percentage of the alkali metal-containing silicon oxide contained in the first layer is less than 10% by mass.

2. The negative electrode for a secondary battery according to claim 1, wherein, The average thickness of the second layer is more than 20% and less than 70% relative to the average thickness of the negative electrode active material layer.

3. The negative electrode for a secondary battery according to claim 1 or 2, wherein, The alkaline earth metal-containing silicon oxide includes magnesium-containing silicon oxide and / or calcium-containing silicon oxide.

4. The negative electrode for a secondary battery according to claim 1 or 2, wherein, The alkali metal-containing silicon oxide includes lithium-containing silicon oxide.

5. Non-aqueous electrolyte secondary batteries, which possess the following characteristics: The negative electrode according to any one of claims 1 to 4, Positive electrode, and Non-aqueous electrolyte.

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