Negative electrode and battery

Abstract

A negative electrode 10 is used in an electrode group having a wound structure. The negative electrode 10 comprises: a negative electrode current collector 11 having a first surface 11a located on the winding inner circumferential side and a second surface 11b located on the winding outer circumferential side; a first negative electrode mixture layer 12 disposed on the first surface 11a; and a second negative electrode mixture layer 13 disposed on the second surface 11b. Each of the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 contains a silicon-containing material and graphite as negative electrode active materials. In at least a portion of the negative electrode 10, A1 and A2 satisfy relational expression (1), where A1 is an expansion ratio of the first negative electrode mixture layer 12 during charging, and A2 is an expansion ratio of the second negative electrode mixture layer 13 during charging.　(1): A1>A2

Description

Negative electrode and battery

[0001] This disclosure relates to a negative electrode and a battery.

[0002] In recent years, secondary batteries have been widely used as high-power, high-energy-density batteries. These batteries feature an electrode group with a wound structure in which the positive and negative electrodes are wound around each other via a separator, and charge and discharge are performed by moving lithium ions between the positive and negative electrodes.

[0003] It is known that silicon (Si)-containing negative electrode active materials are effective in increasing the capacity of batteries. However, negative electrode active materials containing Si undergo large volume changes during charging and discharging, so repeated charging and discharging can break the conductive path with surrounding active materials, resulting in capacity degradation with each charge-discharge cycle. For example, Patent Document 1 proposes a technique to improve the charge-discharge cycle characteristics of lithium secondary batteries that use a material containing Si and O as the negative electrode active material.

[0004] Japanese Patent Publication No. 2011-233245

[0005] In an electrode group having the winding structure described above, different stresses are applied to the inner and outer sides of the winding. Therefore, in the negative electrode constituting the electrode group having a winding structure, the density increases on the inner side of the winding and decreases on the outer side.

[0006] As described above, negative electrode active materials containing Si undergo significant volume changes during charging and discharging. Therefore, when a negative electrode active material containing Si is included in a negative electrode constituting an electrode group having the winding structure described above, degradation occurs during charge-discharge cycles on the inner and outer sides of the winding for different reasons. For example, on the denser inner side of the winding, liquid unevenness is likely to occur due to the movement of electrolyte caused by the expansion and contraction of Si during repeated charging and discharging, while on the less dense outer side of the winding, the conductive path is easily broken due to the expansion and contraction of Si. Therefore, for negative electrodes used in electrode groups having a winding structure, it is difficult to simultaneously reduce degradation during charge-discharge cycles on both the inner and outer sides of the winding and improve the battery's charge-discharge cycle characteristics.

[0007] Therefore, this disclosure provides a technology that can improve the charge-discharge cycle characteristics of a battery for a negative electrode used in an electrode group having a wound structure.

[0008] The negative electrode of the present disclosure is a negative electrode used in an electrode group having a wound structure, the negative electrode comprises: a negative electrode current collector having a first surface on the inner circumference side of the winding and a second surface on the outer circumference side of the winding; a first negative electrode mixture layer disposed on the first surface of the negative electrode current collector; and a second negative electrode mixture layer disposed on the second surface of the negative electrode current collector, wherein the first negative electrode mixture layer and the second negative electrode mixture layer contain a silicon-containing material and graphite as negative electrode active materials, and when the expansion rate of the first negative electrode mixture layer during charging is A1 and the expansion rate of the second negative electrode mixture layer during charging is A2, then in at least a part of the negative electrode, A1 and A2 satisfy the following relational expression (1). A1 > A2 ... (1) Here, the charging expansion rate of the first negative electrode mixture layer is the rate of increase in thickness of the first negative electrode mixture layer in the charging state relative to the thickness of the first negative electrode mixture layer in the discharge state, and the charging expansion rate of the second negative electrode mixture layer is the rate of increase in thickness of the second negative electrode mixture layer in the charging state relative to the thickness of the second negative electrode mixture layer in the discharge state.

[0009] The technology of this disclosure makes it possible to improve the charge-discharge cycle characteristics of a battery equipped with an electrode group having a wound structure.

[0010] Figure 1 is a partial cross-sectional view of the negative electrode according to Embodiment 1, as seen from the winding axis direction, when the negative electrode is wound. Figure 2 is a schematic longitudinal cross-sectional view showing an example of a battery according to Embodiment 2.

[0011] The embodiments of this disclosure will be described in detail below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0012] (Embodiment 1) The negative electrode according to Embodiment 1 is a negative electrode used in an electrode group having a winding structure. Figure 1 is a partial cross-sectional view of the negative electrode according to Embodiment 1 when it is wound, as seen from the winding axis direction. The negative electrode 10 according to Embodiment 1 comprises a negative electrode current collector 11, a first negative electrode mixture layer 12, and a second negative electrode mixture layer 13. The negative electrode current collector 11 has a first surface 11a on the inner circumference side of the winding and a second surface 11b on the outer circumference side of the winding. The first negative electrode mixture layer 12 is disposed on the first surface 11a of the negative electrode current collector 11. The second negative electrode mixture layer 13 is disposed on the second surface 11b of the negative electrode current collector 11. That is, the first negative electrode mixture layer 12 is a mixture layer located on the inner circumference side of the winding (inner mixture layer), and the second negative electrode mixture layer 13 is a mixture layer located on the outer circumference side of the winding (outer mixture layer).

[0013] The first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 contain a silicon-containing material and graphite as negative electrode active materials.

[0014] If the expansion rate of the first negative electrode mixture layer 12 during charging is A1, and the expansion rate of the second negative electrode mixture layer 13 during charging is A2, then in at least a portion of the negative electrode 10, A1 and A2 satisfy the following relationship (1): A1 > A2 ... (1)

[0015] Here, the expansion rate of the first negative electrode mixture layer 12 during charging is the rate of increase in thickness of the first negative electrode mixture layer 12 in the charged state relative to the thickness of the first negative electrode mixture layer 12 in the discharged state. The expansion rate of the second negative electrode mixture layer 13 during charging is the rate of increase in thickness of the second negative electrode mixture layer 13 in the charged state relative to the thickness of the second negative electrode mixture layer 13 in the discharged state.

[0016] In this specification, the expansion rate of the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 during charging is measured by the following method: (1) The battery to be evaluated is disassembled and the negative electrode is cut out, and a unipolar cell is made using metallic Li as the counter electrode and an ionic liquid as the electrolyte. (2) The unipolar cell is charged at 0.1C in a temperature environment of 25°C until the cell voltage reaches 5mV, and then discharged at 0.1C until the cell voltage reaches 1.0V, and the thickness of the first negative electrode mixture layer 12 (T1a) and the thickness of the second negative electrode mixture layer 13 (T2a) in the charged state (fully charged state) and the thickness of the first negative electrode mixture layer 12 (T1b) and the thickness of the second negative electrode mixture layer 13 (T2b) in the discharged state (fully discharged state) are determined. (3) Calculate the rate of increase in thickness of the first negative electrode mixture layer 12 in the charged state relative to the thickness of the first negative electrode mixture layer 12 in the discharged state (T1a × 100 / T1b - 100), and use this as the expansion rate (%) of the first negative electrode mixture layer 12 during charging. Calculate the rate of increase in thickness of the second negative electrode mixture layer 13 in the charged state relative to the thickness of the second negative electrode mixture layer 13 in the discharged state (T2a × 100 / T2b - 100), and use this as the expansion rate (%) of the second negative electrode mixture layer 13 during charging.

[0017] Here, the thickness of the first anode mixture layer 12 and the thickness of the second anode mixture layer 13 are determined from the cross-sectional SEM images of each layer, obtained by observing the cross-section of each layer with a scanning electron microscope (SEM). Specifically, the thickness of the first anode mixture layer 12 and the second anode mixture layer 13 is measured at five arbitrary locations, and the average value calculated from the five obtained measurements is taken as the thickness.

[0018] As described above, in the negative electrode 10 according to the first embodiment that satisfies the above relational expression (1), the first negative electrode mixture layer 12, which is the in-winding mixture layer, has a larger expansion rate during charging than the second negative electrode mixture layer 13, which is the out-winding mixture layer. With this configuration, the first negative electrode mixture layer 12, which becomes denser when wound, improves the unevenness of the electrolyte caused by the expansion and contraction of the silicon-containing material during repeated charging and discharging (i.e., the non-uniformity of the electrolyte due to repeated charging and discharging), thereby improving degradation and durability. On the other hand, the second negative electrode mixture layer 13, which becomes less dense when wound, has a reduced expansion rate during charging, which suppresses the isolation of the silicon-containing material associated with repeated charging and discharging, making it less likely for the conductive path to break, and thus improving degradation. In this way, the negative electrode 10 according to the first embodiment having the above configuration can improve the degradation that occurs specifically in the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13, respectively, and thus improve the charge-discharge cycle characteristics of the battery.

[0019] Furthermore, the expansion rates of the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 during charging satisfy the above relational expression (1) only if they are at least a portion of the negative electrode 10. That is, in a portion of the negative electrode 10, the first negative electrode mixture layer 12 may have a larger expansion rate during charging than the second negative electrode mixture layer 13. In this case, for example, it is desirable that the negative electrode 10 satisfies the above relational expression (1) in the portion closer to the center when the electrode group having a winding structure is viewed from the winding axis direction. The central portion of the electrode group having a winding structure is prone to deterioration of the negative electrode. Therefore, by having the portion of the negative electrode 10 closer to the center of the winding structure satisfy the above relational expression (1), the charge-discharge cycle characteristics of the battery can be effectively improved. Alternatively, the expansion rates of the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 during charging may satisfy the above relational expression (1) throughout the entire negative electrode 10.

[0020] The configurations of the negative electrode 10 in Embodiment 1 will be described in detail below.

[0021] [Negative Electrode Current Collector] A sheet or film made of a metallic material such as stainless steel, nickel, copper, or alloys thereof may be used as the negative electrode current collector 11. The sheet or film may be porous or non-porous. Metal foil, metal mesh, etc., may be used as the sheet or film. A carbon material such as carbon may be coated on the surface of the negative electrode current collector 11 as a conductive auxiliary material.

[0022] The thickness of the negative electrode current collector 11 is not particularly limited, but from the viewpoint of balancing the strength and weight reduction of the negative electrode 10, it may be, for example, 1 μm or more and 50 μm or less, or 5 μm or more and 20 μm or less.

[0023] [Negative Electrode Compound Layer] The negative electrode 10 according to Embodiment 1 comprises a first negative electrode compound layer 12 and a second negative electrode compound layer 13 as negative electrode compound layers. As described above, the expansion rates of the first negative electrode compound layer 12 and the second negative electrode compound layer 13 during charging satisfy relational expression (1).

[0024] The configurations of the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 that satisfy relational equation (1) are not particularly limited. For example, the expansion rate during charging of the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 may be controlled by using multiple types of silicon-containing materials with different particle volume expansion rates for the silicon-containing material used as the negative electrode active material.

[0025] As the silicon-containing material, for example, a first silicon-containing material and a second silicon-containing material having a smaller particle volume expansion coefficient than the first silicon-containing material may be used. In this case, the silicon-containing material in the first negative electrode mixture layer 12 may include the first silicon-containing material, and the silicon-containing material in the second negative electrode mixture layer 13 may include the second silicon-containing material having a smaller particle volume expansion coefficient than the first silicon-containing material. With such a configuration, a first negative electrode mixture layer 12 and a second negative electrode mixture layer 13 that satisfy relational equation (1) can be easily realized.

[0026] Here, the particle volume expansion coefficient of the first silicon-containing material is the ratio of the particle volume of the first silicon-containing material in the charged state to the particle volume of the first silicon-containing material in the discharged state, and the particle volume expansion coefficient of the second silicon-containing material is the ratio of the particle volume of the second silicon-containing material in the charged state to the particle volume of the second silicon-containing material in the discharged state.

[0027] When the negative electrode active material contained in the first negative electrode mixture layer 12 is designated as the first negative electrode active material, and the negative electrode active material contained in the second negative electrode mixture layer 13 is designated as the second negative electrode active material, the mass ratio of the first silicon-containing material in the first negative electrode active material may be greater than the mass ratio of the first silicon-containing material in the second negative electrode active material, and the mass ratio of the second silicon-containing material in the second negative electrode active material may be greater than the mass ratio of the second silicon-containing material in the first negative electrode active material. With this configuration, the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 that satisfy relational equation (1) can be realized more easily.

[0028] When two silicon-containing materials, a first silicon-containing material and a second silicon-containing material, have different particle volume expansion rates, are used as silicon-containing materials, the particle volume expansion rate of the silicon-containing material can be controlled by changing, for example, the proportion of silicon contained, the density of the silicon-containing material, the particle size of the silicon-containing material, the particle shape of the silicon-containing material, etc. For example, if the silicon-containing material is a composite material containing Si as described later, the particle volume expansion rate can be controlled to a desired range by adjusting the size of the Si phase contained in the composite material, the proportion of the Si phase, the pore diameter and pore volume of the ion-conducting phase, etc.

[0029] In this specification, the particle volume expansion coefficients of the first silicon-containing material and the second silicon-containing material are measured by the following method: (1) The battery to be evaluated is disassembled and the negative electrode is cut out. A monoelectrode cell is prepared in which the particle cross-section of the silicon-containing material is exposed by using metallic Li as the counter electrode and an ionic liquid as the electrolyte. (2) The monoelectrode cell is charged at 0.002C in a temperature environment of 25°C until the cell voltage reaches 5mV, then discharged at 0.05C until the cell voltage reaches 1.0V, and the particle cross-section of the silicon-containing material is observed in situ using a SEM. (3) For the particle volume expansion coefficient of the silicon-containing material, the particle volume (Va) of the silicon-containing material in the charged state (fully charged state) and the particle volume (Vb) of the silicon-containing material in the discharged state (fully discharged state) are determined from the particle cross-sectional area of ​​the silicon-containing material, and the particle volume expansion coefficient (Va / Vb) is calculated. The particle volume is obtained by raising the particle cross-sectional area of ​​the silicon-containing material obtained from the SEM image of the particle cross-section to the power of 3 / 2. (4) For the silicon-containing material contained in the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13, the above measurement (2) and the above calculation of the particle volume expansion rate (3) are performed on 50 particles each to obtain a particle volume expansion rate distribution based on the particle area. The particle area in the particle volume expansion rate distribution obtained here is the area of ​​the particle in a complete discharge state. (5) The area-based particle volume expansion rate distribution obtained in (4) above is separated into two peaks using a Gaussian function for each layer, and the group of particles corresponding to the first peak on the side with a large particle expansion rate is designated as the first silicon-containing material, and the group of particles corresponding to the second peak on the side with a small particle expansion rate is designated as the second silicon-containing material. Here, in each layer, the particle volume expansion coefficient of the first silicon-containing material is the particle volume expansion coefficient at the peak of the first peak, and the particle volume expansion coefficient of the second silicon-containing material is the particle volume expansion coefficient at the peak of the second peak.

[0030] Furthermore, the fact that the mass proportion of the first silicon-containing material in the first negative electrode active material is greater than the mass proportion of the first silicon-containing material in the second negative electrode active material, and that the mass proportion of the second silicon-containing material in the second negative electrode active material is greater than the mass proportion of the second silicon-containing material in the first negative electrode active material, can be confirmed by the following method.

[0031] This can be confirmed from the area-based particle volume expansion rate distribution obtained by the method described above, specifically by comparing the ratio of the total area originating from the first peak in the first anode mixture layer 12 to the total area of ​​the first anode active material and the ratio of the total area originating from the first peak in the second anode mixture layer 13 to the total area of ​​the second anode active material, as well as the ratio of the total area originating from the second peak in the first anode mixture layer 12 to the total first anode active material and the ratio of the total area originating from the second peak in the second anode mixture layer 13 to the total second anode active material.

[0032] The negative electrode active material in the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 can be determined by elemental mapping of the cross-section along the thickness direction of the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13, in the case of silicon-containing materials. Quantitative analysis of the negative electrode active material by elemental mapping can be performed using an electron beam microanalyzer (EPMA). Graphite included as the negative electrode active material needs to be quantified separately from carbon materials such as carbon black included as a conductive agent. In this case, the two can be distinguished and quantified using the method described later.

[0033] The distinction between graphite, which is included as a negative electrode active material in the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13, and carbon materials such as carbon black, which are included as conductive agents, is made by determining the G / D ratio using the Raman spectrum obtained by micro-Raman spectroscopy analysis of the cross-section of the negative electrode mixture layer. Materials with a G / D ratio of ≤1 are identified as carbon materials such as carbon black included as conductive agents, and materials with a G / D ratio >1 are identified as graphite, which is included as a negative electrode active material. The volume ratio is calculated by raising the area ratio of the negative electrode active material and conductive agent identified in this way to the power of 3 / 2, and the mass ratio is calculated from their respective true densities (graphite: 2.24 g / cc, carbon black: 1.8 g / cc). In this way, graphite included as a negative electrode active material and carbon materials such as carbon black included as conductive agents can be distinguished, and their respective mass ratios can be determined separately.

[0034] When the particle volume expansion rate of the first silicon-containing material is V1 and the particle volume expansion rate of the second silicon-containing material is V2, V1 and V2 may satisfy the following relational expressions (2) and (3). 1.7 ≤ V1 < 3... (2) 1.3 ≤ V2 < 2.2... (3)

[0035] By V1 and V2 satisfying the relational expressions (2) and (3), the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 that satisfy the relational expression (1) can be more easily realized. As described above, since the second silicon-containing material has a smaller particle volume expansion rate than the first silicon-containing material, on the premise that V1 > V2, the above relational expressions (2) and (3) are satisfied. V1 may satisfy 2.0 ≤ V1 < 3, and V2 may satisfy 1.3 ≤ V2 < 2.0.

[0036] The ratio (V2 / V1) of the particle volume expansion rate V2 of the second silicon-containing material to the particle volume expansion rate V1 of the first silicon-containing material satisfies, for example, 0.5 < V2 / V1 < 1, and may be, for example, 0.5 < V2 / V1 < 0.8.

[0037] The method for realizing the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 that satisfy the relational expression (1) is not limited to the above-described method using a plurality of types of silicon-containing materials having different particle volume expansion rates from each other. For example, by using a plurality of types of silicon-containing materials having different particle diameters from each other, the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 that satisfy the relational expression (1) can also be realized. Further, by changing the content ratio of the silicon-containing material in the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13, the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 that satisfy the relational expression (1) may be realized.

[0038] In order to further improve the charge-discharge cycle characteristics, the expansion rate A1 during charging of the first negative electrode mixture layer 12 and the expansion rate A2 during charging of the second negative electrode mixture layer 13 may further satisfy the following relational expression (4). 1 < A1 / A2 ≤ 1.5... (4)

[0039] The first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 may further contain a conductive agent. The conductive agent includes, for example, a carbon material. With such a configuration, the conductivity of the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 can be improved, so that the charge-discharge cycle characteristics can be further improved.

[0040] As the carbon material contained as the conductive agent, for example, carbon black such as acetylene black and ketjen black, carbon nanotubes (CNT), carbon nanofibers, graphene, etc. can be used.

[0041] When the conductive agent contained in the first negative electrode mixture layer 12 is regarded as the first conductive agent and the conductive agent contained in the second negative electrode mixture layer 13 is regarded as the second conductive agent, the mass ratio θ1 of the first conductive agent to the first negative electrode active material and the mass ratio θ2 of the second conductive agent to the second negative electrode active material may satisfy the following relational expression (5). θ1 ≤ θ2 ··· (5)

[0042] As in the above configuration, by making the mass ratio θ2 of the conductive agent contained in the second negative electrode mixture layer 13, which is the outer wound mixture layer, not less than the mass ratio θ1 of the conductive agent contained in the first negative electrode mixture layer 12, which is the inner wound mixture layer, the conductive path of the second negative electrode mixture layer 13, which becomes less dense when wound, can be made more difficult to break. Therefore, according to this configuration, the charge-discharge cycle characteristics of the battery can be further improved.

[0043] As described above, the carbon material such as graphite contained as the negative electrode active material in the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 and the carbon material such as carbon black contained as the conductive agent can be distinguished and their respective mass ratios can be obtained.

[0044] When CNTs are included as a conductive agent, the amount of CNTs relative to the total negative electrode active material in the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 may be determined by the following method. The amount of CNTs relative to the total negative electrode active material can be determined from a sample obtained by removing only the negative electrode mixture layers (the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13, respectively) from a discharged secondary battery. Specifically, first, the discharged secondary battery is disassembled and the negative electrode is removed. Next, the negative electrode is washed with an organic solvent, then vacuum dried, and a sample is obtained by peeling off only the negative electrode mixture layer. The pulverized sample can be dispersed in a dispersion medium such as water and / or alcohol, and the CNTs can be separated by centrifugation. Furthermore, the ratio of binder components and conductive agent components other than the negative electrode active material can be calculated by performing thermal analysis such as TG-DTA on the sample. By performing micro-Raman spectroscopy on a cross-section of the negative electrode mixture layer, the carbon species of carbon nanotubes (CNTs) and carbon black such as acetylene black can be identified, and their proportions can be calculated from thermal analysis such as TG-DTA of the exfoliated sample.

[0045] Furthermore, by performing thermal analysis such as TG-DTA on the above sample obtained by peeling off only the negative electrode mixture layer, the ratio of binder components and conductive agent components other than the negative electrode active material can be calculated.

[0046] As described above, by determining the mass ratio of each component in the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 using an appropriate method for each component, the mass ratio of the first conductive agent to the first negative electrode active material and the mass ratio of the second conductive agent to the second negative electrode active material can be determined.

[0047] As described above, the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 contain a silicon-containing material as the negative electrode active material. In this specification, the silicon-containing material means a material containing Si. Examples of silicon-containing materials include Si, Si alloys, Si compounds, and Si-containing composite materials.

[0048] The average particle size of the silicon-containing material is, for example, 1 μm or more and 20 μm or less, or it may be 1 μm or more and 15 μm or less. The average particle size of the silicon-containing material refers to the particle size at which the volume integrated value in the particle size distribution measured by laser diffraction scattering method becomes 50% (hereinafter referred to as "volume-based D50"). For the measuring device, for example, the "MT3000II" manufactured by Microtrac-Bell Co., Ltd. is used, and the measurement is performed using, for example, water as the dispersion medium.

[0049] Silicon-containing materials are preferably composite materials containing Si. Si-containing composite materials are, for example, composite particles comprising an ionic conductive phase and a Si phase dispersed within the ionic conductive phase. The ionic conductive phase includes, for example, at least one selected from the group consisting of an aluminate phase, a silicate phase, a carbon phase, a silicide phase, and a silicon oxide phase. The ionic conductive phase may consist of one phase or multiple phases. In the Si phase, for example, Si is formed into fine particles and dispersed within the ionic conductive phase.

[0050] The silicate phase may satisfy the following conditions (A) and / or (B): (A) The silicate phase contains at least one element selected from the group consisting of alkali metal elements and Group 2 elements (Group 2 elements of the long-period periodic table). (B) The silicate phase contains element L. Element L is at least one element selected from the group consisting of B, Al, Zr, Nb, Ta, V, lanthanides, Y, Ti, P, Bi, Zn, Sn, Pb, Sb, Co, Er, F, and W. Lanthanides are a collective term for 15 elements from lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71.

[0051] Regarding the above condition (A), examples of alkali metal elements include lithium (Li), potassium (K), and sodium (Na). Examples of group 2 elements include magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). The inclusion of alkali metal elements and / or group 2 elements may reduce the irreversible capacity of the silicate phase. A lithium-containing silicate phase (hereinafter sometimes referred to as the "lithium silicate phase") is preferred, for example, for its low irreversible capacity and high initial charge-discharge efficiency.

[0052] The lithium silicate phase may be any oxide phase containing Li, Si, and O, and may also contain other elements. The atomic ratio of O to Si in the lithium silicate phase, O / Si, is, for example, greater than 2 and less than 4. Preferably, O / Si is greater than 2 and less than 3. The atomic ratio of Li to Si in the lithium silicate phase, Li / Si, is, for example, greater than 0 and less than 4.

[0053] The lithium silicate phase is given by formula: Li 2z SiO (2+z) The material may contain a lithium silicate phase represented by (0 < z < 2), or may be composed of such lithium silicate phase. It is preferable that z satisfies the relationship 0 < z < 1, and more preferably z = 1 / 2 (i.e., Li2Si2O5).

[0054] The carbon phase may be composed of, for example, amorphous carbon. Examples of amorphous carbon constituting the carbon phase include hard carbon, soft carbon, and other amorphous carbons. Amorphous carbon is a carbon material in which the average interplanar spacing d002 of the (002) planes, as measured by Kα diffraction, exceeds 0.34 nm.

[0055] The silicide phase is a compound phase consisting of Si and an element that is more electrically positive than Si, and examples include NiSi, Mg2Si, and TiSi2.

[0056] The silicon oxide phase is composed of compounds of Si and O. The main component of the silicon oxide phase may be silicon dioxide. The main component of the silicon oxide phase is, for example, a component that accounts for 95% or more and 100% or less by mass of the silicon oxide phase.

[0057] The aluminate phase is, for example, a phase containing alkali aluminate containing at least one alkali metal element, Al, and O. The alkali metal element is, for example, Li. The composition of lithium aluminate is given by the formula: Li u AlO (3+u) / 2 It can be expressed as follows. From the viewpoint of ease of fabrication, stability, and ionic conductivity, etc., u in the formula may be, for example, greater than 0 and less than or equal to 5, or greater than 0 and less than or equal to 1. When u = 1 / 5, it can be expressed as LiAl5O8, and when u = 1 / 2, it can be expressed as Li2Al4O7. When u = 1, it can be expressed as LiAlO2, and when u = 5, it can be expressed as Li5AlO4.

[0058] The average size of the Si phase is, for example, between 1 nm and 200 nm, but may also be between 1 nm and 100 nm, or between 1 nm and 10 nm. The average size of the Si phase is calculated as the average of the diameters of the circumscribed circles of 100 Si phases extracted by image analysis after capturing SEM images of the particle cross-sections of the silicon-containing material.

[0059] The above composite material may have a conductive layer covering the surface of the ion-conducting phase. The conductive layer is composed of a material with higher conductivity than the ion-conducting phase, for example, and forms good conductive paths in the negative electrode composite layer. The conductive layer is, for example, a carbon film composed of a conductive carbon material. The conductive carbon material can be carbon black such as acetylene black or Ketjen black, graphite, or amorphous carbon with low crystallinity. The thickness of the conductive layer is, for example, 1 nm or more and 200 nm or less, or 5 nm or more and 100 nm or less, taking into consideration the securing of conductivity and the diffusion of Li ions into the particle interior. The thickness of the conductive layer can be measured by cross-sectional observation of the composite material using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0060] The composite material may be at least one selected from the group consisting of a first silicon-containing material and a second silicon-containing material. That is, the composite material may be at least one selected from the group consisting of a first silicon-containing material and a second silicon-containing material, comprising an ionic conductive phase and a Si phase dispersed in the ionic conductive phase. Both the first silicon-containing material and the second silicon-containing material may be the composite material.

[0061] As described above, the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 contain graphite as the negative electrode active material. The inclusion of graphite as the negative electrode active material ensures that conductive paths in the negative electrode active material are maintained even when the silicon-containing material expands and contracts with charging and discharging, thereby further suppressing capacity degradation associated with the charge-discharge cycle. Furthermore, the inclusion of graphite makes it easier to control the porosity in the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13, enabling control of porosity while considering the permeability of the electrolyte.

[0062] The graphite included as the negative electrode active material may be natural graphite or artificial graphite. As graphite, for example, artificial graphite such as bulk artificial graphite (MAG) or graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, bulk graphite, or earthy graphite, or mixtures thereof can be used. The volume-based D50 of the graphite is, for example, 1 μm or more and 30 μm or less, and may be 5 μm or more and 25 μm or less.

[0063] In each of the first anode mixture layer 12 and the second anode mixture layer 13, the content of silicon-containing material is, for example, 40% by mass or less of the total mass of the anode active material, may be 35% by mass or less, or 30% by mass or less, from the viewpoint of improving cycle characteristics. In each of the first anode mixture layer 12 and the second anode mixture layer 13, the content of silicon-containing material is, for example, 5% by mass or more of the total mass of the anode active material, from the viewpoint of increasing capacity and improving cycle characteristics. An example of a preferred range for the content of silicon-containing material is, for example, 5% by mass or more and 35% by mass or less of the total mass of the anode active material, may be 10% by mass or more and 30% by mass or less, or 5% by mass or more and 15% by mass or less.

[0064] The negative electrode mixture layer 12 may further contain a binder. Examples of binders include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, and styrene-butadiene rubber (SBR). In addition, these resins may be used in combination with carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc.

[0065] (Method for manufacturing the negative electrode) An example of a method for manufacturing the negative electrode 10 is described below. A first negative electrode slurry for the first negative electrode slurry layer is prepared by adding a negative electrode active material containing silicon-containing material and graphite, along with optional components such as a conductive agent and a binder, to a dispersion medium (e.g., water) in a predetermined ratio. Similarly, a second negative electrode slurry for the second negative electrode slurry layer is prepared by adding a negative electrode active material containing silicon-containing material and graphite, along with optional components such as a conductive agent and a binder, to a dispersion medium (e.g., water) in a predetermined ratio. The first negative electrode slurry is applied to the first surface 11a of the negative electrode current collector 11 and dried to form the first negative electrode active material layer 12. The second negative electrode slurry is applied to the second surface 11b of the negative electrode current collector 11 and dried to form the second negative electrode active material layer 13. The first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 are rolled at a predetermined linear pressure using rolling rollers or the like. In this way, the negative electrode 10 is manufactured. The rolling may be performed after forming the first negative electrode mixture layer 12 on the first surface 11a of the negative electrode current collector 11, and then additional rolling may be performed after forming the second negative electrode mixture layer 13 on the second surface 11b of the negative electrode current collector 11, or the second negative electrode mixture layer 13 may be formed on the second surface 11b of the negative electrode current collector 11, and then additional rolling may be performed after forming the first negative electrode mixture layer 12 on the first surface 11a of the negative electrode current collector 11.

[0066] As described above, the first negative electrode mixture layer 12 and the second negative electrode mixture layer 13 that satisfy relational equation (1) can be formed, for example, by using multiple types of silicon-containing materials with different particle volume expansion coefficients, using multiple types of silicon-containing materials with different particle sizes, adjusting the mixing ratio of these multiple types of silicon-containing materials, or adjusting the content ratio of silicon-containing materials in the first negative electrode mixture slurry and the second negative electrode mixture slurry.

[0067] (Embodiment 2) The battery in Embodiment 2 comprises a positive electrode, a negative electrode, and an electrolyte. The negative electrode is the same as the negative electrode in Embodiment 1. With this configuration, the battery in Embodiment 2 can improve the charge-discharge cycle characteristics.

[0068] Figure 2 is a schematic longitudinal cross-sectional view showing an example of a battery according to Embodiment 2. The battery 100 is a cylindrical battery comprising a cylindrical battery case, a wound electrode group 24, and an electrolyte (not shown). The electrode group 24 is housed within the battery case and is in contact with the electrolyte.

[0069] The battery case consists of a case body 25, which is a bottomed cylindrical metal container, and a sealing body 26 that seals the opening of the case body 25. A gasket 37 is placed between the case body 25 and the sealing body 26. The gasket 37 ensures that the battery case is airtight. Inside the case body 25, insulating plates 27 and 28 are placed at both ends of the electrode group 24 in the winding axis direction.

[0070] The case body 25 has, for example, a stepped portion 31. The stepped portion 31 can be formed by partially pressing the side wall of the case body 25 from the outside. The stepped portion 31 may be formed in an annular shape on the side wall of the case body 25 along the circumferential direction of a virtual circle defined by the case body 25. In this case, the sealing body 26 is supported, for example, by the opening side surface of the stepped portion 31.

[0071] The sealing body 26 comprises a filter 32, a lower valve body 33, an insulating member 34, an upper valve body 35, and a cap 36. In the sealing body 26, these members are stacked in this order. The sealing body 26 is installed in the opening of the case body 25 such that the cap 36 is located on the outside of the case body 25 and the filter 32 is located on the inside of the case body 25.

[0072] Each of the above-mentioned components constituting the sealing body 26 is, for example, disc-shaped or ring-shaped. Except for the insulating member 34, each of the above-mentioned components is electrically connected to one another.

[0073] The electrode group 24 includes a positive electrode 21, a separator 22, and a negative electrode 23. The positive electrode 21, the separator 22, and the negative electrode 23 are all strip-shaped. The width direction of the strip-shaped positive electrode 21 and negative electrode 23 is, for example, parallel to the winding axis of the electrode group 24. The separator 22 is positioned between the positive electrode 21 and the negative electrode 23. The positive electrode 21 and the negative electrode 23 are wound in a spiral shape with the separator 22 interposed between them.

[0074] When observing a cross-section of the battery 100 in a direction perpendicular to the winding axis of the electrode group 24, the positive electrode 21 and the negative electrode 23 are alternately stacked in the radial direction of a virtual circle defined by the case body 25, with a separator 22 interposed between them.

[0075] The positive electrode 21 is electrically connected to the cap 36, which also serves as the positive electrode terminal, via a positive electrode lead 29. One end of the positive electrode lead 29 is connected, for example, near the center of the positive electrode 21 in the longitudinal direction. The positive electrode lead 29 extends from the positive electrode 21 to the filter 32 through a through hole formed in the insulating plate 27. The other end of the positive electrode lead 29 is welded, for example, to the electrode group 24 side of the filter 32.

[0076] The negative electrode 23 is electrically connected to the case body 25, which also serves as the negative electrode terminal, via a negative electrode lead 30. One end of the negative electrode lead 30 is connected, for example, to the end of the negative electrode 23 in the longitudinal direction of the negative electrode 23. The other end of the negative electrode lead 30 is welded, for example, to the inner bottom surface of the case body 25.

[0077] The components of battery 100 will be described in detail below.

[0078] The positive electrode 21 includes a material having the property of intercalating and releasing metal ions (e.g., lithium ions). The positive electrode 21 includes, for example, a positive electrode active material. The positive electrode 21 comprises, for example, a positive electrode current collector and a positive electrode mixture layer supported on the surface of the positive electrode current collector.

[0079] As the positive electrode current collector, a sheet or film made of a metallic material such as aluminum, stainless steel, titanium, or their alloys can be used. Aluminum and its alloys are suitable as materials for positive electrode current collectors because they are inexpensive and easy to make into thin films. The sheet or film may be porous or non-porous. Metal foil, metal mesh, etc., can be used as the sheet or film. A carbon material such as carbon may be coated on the surface of the positive electrode current collector as a conductive auxiliary material.

[0080] The positive electrode mixture layer contains a positive electrode active material. The positive electrode active material may be a material that has the ability to intercept and release metal ions (e.g., lithium ions). As the positive electrode active material, lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, transition metal oxynitrides, etc., can be used. In particular, when lithium-containing transition metal oxides or lithium-containing transition metal phosphates are used as the positive electrode active material, the manufacturing cost of the battery can be reduced and the average discharge voltage can be increased. Examples of lithium-containing transition metal oxides include lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate.

[0081] The positive electrode mixture layer may further contain a binder. As the binder, the material described in Embodiment 1 as a binder usable in the negative electrode mixture layer can also be used in the positive electrode mixture layer.

[0082] The positive electrode mixture layer may further contain a conductive agent. As the conductive agent, the material described in Embodiment 1 as a conductive agent usable in the negative electrode mixture layer can also be used in the positive electrode mixture layer.

[0083] The negative electrode 23 includes a material having the property of intercalating and releasing metal ions (e.g., lithium ions). The negative electrode 23 is the negative electrode 10 according to Embodiment 1.

[0084] The electrolyte solution used as the electrolyte may contain a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolyte solution may be, for example, 0.5 mol / liter or more and 2 mol / liter or less. By controlling the lithium salt concentration within the above range, an electrolyte solution with excellent ionic conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0085] As non-aqueous solvents, cyclic carbonate esters, linear carbonate esters, cyclic ethers, linear ethers, nitriles, amides, etc., may be used. One of these solvents may be used, or two or more may be used in combination.

[0086] Examples of lithium salts that can be used include lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. One of these electrolyte salts may be used, or two or more may be used in combination.

[0087] Typically, it is desirable to interpose a separator between the positive and negative electrodes. The separator 22 has high ion permeability and appropriate mechanical strength and insulating properties. As the separator 22, a microporous thin film, woven fabric, and nonwoven fabric can be used. As the material of the separator 22, for example, a polymer can be used. The polymer may be polyolefin such as polypropylene and polyethylene.

[0088] In the battery according to Embodiment 2, the electrolyte may be impregnated into a polymer provided as a separator, for example. That is, the battery according to Embodiment 2 may have a structure in which both the electrolyte and the polymer are used in combination.

[0089] The battery according to Embodiment 2 may further contain a solid electrolyte as the electrolyte. That is, the battery of this disclosure may have a hybrid structure in which an electrolyte and a solid electrolyte are used in combination. Examples of solid electrolyte materials are halide solid electrolytes, sulfide solid electrolytes, oxide solid electrolytes, or organic polymer solid electrolytes. In this disclosure, "halide solid electrolyte" means a solid electrolyte in which a halogen element is the main component of the anions. "Sulfide solid electrolyte" means a solid electrolyte in which sulfur is the main component of the anions. "Oxide solid electrolyte" means a solid electrolyte in which oxygen is the main component of the anions. The main component of the anions means the anion with the largest amount of substance among all the anions that make up the solid electrolyte.

[0090] As an example of the structure of the battery according to Embodiment 2, Figure 2 describes a configuration example, namely a cylindrical non-aqueous electrolyte secondary battery in which a wound electrode group, in which a positive electrode and a negative electrode are wound around a separator, and an electrolyte are housed in an outer casing. However, the battery according to this disclosure is not limited to this configuration example. The battery according to Embodiment 2 may take any form, such as prismatic, coin-type, button-type, laminate-type, etc. Furthermore, as the electrode group in the battery according to Embodiment 2, other forms of electrode groups may be used instead of the wound electrode group, such as an electrode group in which a positive electrode and a negative electrode are stacked with a separator in between.

[0091] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0092] (Technology 1) A negative electrode used in an electrode group having a wound structure, wherein the negative electrode comprises: a negative electrode current collector having a first surface on the inner circumference side of the winding and a second surface on the outer circumference side of the winding; a first negative electrode mixture layer disposed on the first surface of the negative electrode current collector; and a second negative electrode mixture layer disposed on the second surface of the negative electrode current collector, wherein the first negative electrode mixture layer and the second negative electrode mixture layer contain a silicon-containing material and graphite as negative electrode active materials, and when the expansion rate of the first negative electrode mixture layer during charging is A1 and the expansion rate of the second negative electrode mixture layer during charging is A2, in at least a part of the negative electrode, A1 and A2 satisfy the following relational expression (1). A1 > A2 ... (1) Here, the charging expansion rate of the first negative electrode mixture layer is the rate of increase in thickness of the first negative electrode mixture layer in the charging state relative to the thickness of the first negative electrode mixture layer in the discharge state, and the charging expansion rate of the second negative electrode mixture layer is the rate of increase in thickness of the second negative electrode mixture layer in the charging state relative to the thickness of the second negative electrode mixture layer in the discharge state.

[0093] With this configuration, the negative electrode according to Technology 1 can improve the charge-discharge cycle characteristics of the battery.

[0094] (Technical 2) The negative electrode according to Technical 1, wherein the silicon-containing material in the first negative electrode mixture layer includes a first silicon-containing material, and the silicon-containing material in the second negative electrode mixture layer includes a second silicon-containing material having a smaller particle volume expansion coefficient than the first silicon-containing material. Here, the particle volume expansion coefficient of the first silicon-containing material is the ratio of the particle volume of the first silicon-containing material in the charged state to the particle volume of the first silicon-containing material in the discharged state, and the particle volume expansion coefficient of the second silicon-containing material is the ratio of the particle volume of the second silicon-containing material in the charged state to the particle volume of the second silicon-containing material in the discharged state.

[0095] With this configuration, the negative electrode according to Technology 2 can easily realize a first negative electrode mixture layer and a second negative electrode mixture layer that satisfy relational equation (1). Therefore, the negative electrode according to Technology 2 can easily improve the charge-discharge cycle characteristics of the battery.

[0096] (Technical 3) The negative electrode according to Technical 2, wherein when the negative electrode active material contained in the first negative electrode mixture layer is defined as the first negative electrode active material, and the negative electrode active material contained in the second negative electrode mixture layer is defined as the second negative electrode active material, the mass ratio of the first silicon-containing material in the first negative electrode active material is greater than the mass ratio of the first silicon-containing material in the second negative electrode active material, and the mass ratio of the second silicon-containing material in the second negative electrode active material is greater than the mass ratio of the second silicon-containing material in the first negative electrode active material.

[0097] This configuration allows the negative electrode according to Technology 3 to more easily realize a first negative electrode mixture layer and a second negative electrode mixture layer that satisfy relational equation (1). Therefore, the negative electrode according to Technology 3 makes it easier to improve the charge-discharge cycle characteristics of the battery.

[0098] (Technology 4) When the particle volume expansion coefficient of the first silicon-containing material is V1 and the particle volume expansion coefficient of the second silicon-containing material is V2, V1 and V2 satisfy the following relationships (2) and (3) for the negative electrode described in Technology 2 or 3. 1.7 ≤ V1 < 3 ... (2) 1.3 ≤ V2 < 2.2 ... (3)

[0099] This configuration allows the negative electrode according to Technology 4 to more easily realize a first negative electrode mixture layer and a second negative electrode mixture layer that satisfy relational equation (1). Therefore, the negative electrode according to Technology 4 makes it easier to improve the charge-discharge cycle characteristics of the battery.

[0100] (Technical 5) A1 and A2 are negative electrodes according to any one of Technical 1 to 4, satisfying the following relation (4): 1 < A1 / A2 ≤ 1.5 ... (4)

[0101] This configuration allows the negative electrode related to technology 5 to further improve the charge-discharge cycle characteristics of the battery.

[0102] (Technical 6) The negative electrode according to any one of Technical 1 to 5, wherein the first negative electrode mixture layer and the second negative electrode mixture layer further contain a conductive agent, and the conductive agent contains a carbon material.

[0103] With this configuration, the negative electrode according to Technology 6 can further improve the charge-discharge cycle characteristics of the battery.

[0104] (Technology 7) When the negative electrode active material contained in the first negative electrode mixture layer is used as the first negative electrode active material, the negative electrode active material contained in the second negative electrode mixture layer is used as the second negative electrode active material, the conductive agent contained in the first negative electrode mixture layer is used as the first conductive agent, and the conductive agent contained in the second negative electrode mixture layer is used as the second conductive agent, the mass ratio θ1 of the first conductive agent to the first negative electrode active material and the mass ratio θ2 of the second conductive agent to the second negative electrode active material satisfy the following relational expression (5). The negative electrode according to Technology 6. θ1 ≦ θ2 ··· (5)

[0105] With this configuration, the negative electrode according to Technology 7 can further improve the charge-discharge cycle characteristics of the battery.

[0106] (Technology 8) A battery including the negative electrode according to any one of Technologies 1 to 7, a positive electrode, and an electrolyte.

[0107] With this configuration, the battery according to Technology 8 can improve the charge-discharge cycle characteristics.

[0108] Hereinafter, the present disclosure will be described in more detail using examples. The following examples are merely illustrative and not limited thereto.

[0109] [Example 1] (Production of positive electrode active material) The composite hydroxide represented by [Ni 0.88 Co 0.09 Al 0.03 (OH)2 obtained by the coprecipitation method was calcined at 500 ° C for 8 hours to obtain an oxide (Ni 0.88 Co 0.09 Al 0.03 O2). Next, LiOH and the composite oxide were mixed so that the molar ratio of Li to the total amount of Ni, Co, and Al was 1.03:1 to obtain a mixture. This mixture was under an oxygen stream with an oxygen concentration of 95% (10 cm 3(Flow rate of 2 mL / min per unit area and 5 L / min per 1 kg of mixture), calcined from room temperature to 650°C at a heating rate of 2.0°C / min, then calcined from 650°C to 780°C at a heating rate of 0.5°C / min to LiNi 0.88 Co 0.09 Al 0.03 A lithium-containing composite oxide represented by O2 was obtained.

[0110] (Preparation of the positive electrode) The above positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 95:2.5:2.5, and N-methyl-2-pyrrolidone (NMP) was used as a dispersion medium to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to a positive electrode current collector made of aluminum foil, the coating was dried and compressed, and then the positive electrode current collector was cut to a predetermined electrode size to obtain a positive electrode in which positive electrode mixture layers were arranged on both sides of the positive electrode current collector. An exposed portion was provided on a part of the positive electrode in which the surface of the positive electrode current collector was exposed.

[0111] (Preparation of the first silicon-containing material) Coal pitch (manufactured by JFE Chemical Corporation, MCP250) and raw silicon (3N, average particle size 10 μm) were mixed as carbon raw materials in a mass ratio of coal pitch:raw silicon = 2:1, and the mixture was pulverized into fine particles using a planetary ball mill (manufactured by Fritsch, P-5). Next, the finely pulverized powder mixture was calcined in an inert atmosphere to carbonize the carbon source and obtain a sintered product in which the Si phase was dispersed within the amorphous carbon phase. Subsequently, the sintered product was pulverized using a jet mill to obtain composite particles as the first silicon-containing material with an average particle size of 8 μm.

[0112] (Preparation of the second silicon-containing material) As the second silicon-containing material, a composite described in Japanese Patent No. 6451340 was prepared. That is, a porous body was prepared, and the second silicon-containing material was prepared by introducing vapor of a silicon compound, which is liquid or gaseous at room temperature, or liquid or solution of a silicon compound into the pores of the porous body. Specifically, the composite was prepared in the same manner as in Example 1 described in Japanese Patent No. 6451340, and the prepared composite was used as the second silicon-containing material of this example.

[0113] (Preparation of the negative electrode) Graphite, a first silicon-containing material, and a second silicon-containing material were mixed in a mass ratio of graphite:first silicon-containing material:second silicon-containing material = 91:6:3, and this was used as the negative electrode active material for the first negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material, 1 part by mass of SBR, 1 part by mass of CMC, and 0.05 parts by mass of CNT (conductive agent) were mixed, and an appropriate amount of water was added to prepare the first negative electrode mixture slurry for the first negative electrode mixture layer.

[0114] Graphite, a first silicon-containing material, and a second silicon-containing material were mixed in a mass ratio of graphite:first silicon-containing material:second silicon-containing material = 91:3:6, and this was used as the negative electrode active material for the second negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material, 1 part by mass of SBR, 1 part by mass of CMC, and 0.05 parts by mass of CNT (conductive agent) were mixed, and an appropriate amount of water was added to prepare the second negative electrode mixture slurry for the second negative electrode mixture layer.

[0115] Next, a first negative electrode mixture slurry was applied to one surface (first surface) of a negative electrode current collector made of copper foil, and a first negative electrode mixture slurry was applied to the other surface (second surface) of the negative electrode current collector. These coatings were dried and compressed to form a first negative electrode mixture layer and a second negative electrode mixture layer. The thicknesses of the formed first negative electrode mixture layer (T1) and second negative electrode mixture layer (T2) were 80 μm for T1 and 80 μm for T2. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0116] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for both the first and second anode composite layers. In Table 1, the first silicon-containing material is abbreviated as "First Si" and the second silicon-containing material as "Second Si". Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, determined from the charging ratio, for both the first and second anode composite layers.

[0117] (Preparation of non-aqueous electrolyte) A non-aqueous electrolyte was prepared by dissolving LiPF6 at a concentration of 1.2 mol / liter in a mixed solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC = 3:3:4 (at 25°C).

[0118] (Preparation of test cell (secondary battery)) An aluminum lead was attached to the exposed part of the positive electrode and a nickel lead was attached to the exposed part of the negative electrode. The positive and negative electrodes were wound in a spiral shape via a polyolefin separator to create a wound electrode body. Insulating plates were placed above and below the electrode body, and the electrode body was housed in an outer casing. The negative electrode lead was welded to the bottom of the bottomed cylindrical outer casing, and the positive electrode lead was welded to the sealing body. Electrolyte was injected into the outer casing, and the opening of the outer casing was sealed with the sealing body via a gasket to create a secondary battery as a test cell.

[0119] [Example 2] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0120] (Preparation of the first silicon-containing material and the second silicon-containing material) The first silicon-containing material and the second silicon-containing material were prepared in the same manner as in Example 1.

[0121] (Preparation of the negative electrode) Graphite and a silicon-1 material were mixed in a mass ratio of graphite:silicon-1 material = 91:9, and this was used as the negative electrode active material for the first negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material was mixed with 1 part by mass of SBR, 1 part by mass of CMC, and 0.05 parts by mass of CNT (conductive agent), and an appropriate amount of water was added to prepare the first negative electrode mixture slurry for the first negative electrode mixture layer.

[0122] Graphite and a silicon-containing material were mixed in a mass ratio of graphite:silicon-containing material = 91:9, and this was used as the negative electrode active material for the second negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material, 1 part by mass of SBR, 1 part by mass of CMC, and 0.05 parts by mass of CNT (conductive agent) were mixed, and an appropriate amount of water was added to prepare the second negative electrode mixture slurry for the second negative electrode mixture layer.

[0123] Next, a first negative electrode mixture slurry was applied to one surface (first surface) of a negative electrode current collector made of copper foil, and a first negative electrode mixture slurry was applied to the other surface (second surface) of the negative electrode current collector. These coatings were dried and compressed to form a first negative electrode mixture layer and a second negative electrode mixture layer. The thicknesses of the formed first negative electrode mixture layer (T1) and second negative electrode mixture layer (T2) were 80 μm for T1 and 80 μm for T2. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0124] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0125] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0126] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Example 2 was used.

[0127] [Example 3] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0128] (Preparation of the first silicon-containing material and the second silicon-containing material) The first silicon-containing material and the second silicon-containing material were prepared in the same manner as in Example 1.

[0129] (Preparation of the negative electrode) The negative electrode slurry for the first negative electrode mixture layer was prepared in the same manner as in Example 1.

[0130] Graphite, a first silicon-containing material, and a second silicon-containing material were mixed in a mass ratio of graphite:first silicon-containing material:second silicon-containing material = 91:4.5:4.5, and this was used as the negative electrode active material for the second negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material, 1 part by mass of SBR, 1 part by mass of CMC, and 0.05 parts by mass of CNT (conductive agent) were mixed, and an appropriate amount of water was added to prepare the second negative electrode mixture slurry for the second negative electrode mixture layer.

[0131] Next, a first negative electrode mixture slurry was applied to one surface (first surface) of a negative electrode current collector made of copper foil, and a first negative electrode mixture slurry was applied to the other surface (second surface) of the negative electrode current collector. These coatings were dried and compressed to form a first negative electrode mixture layer and a second negative electrode mixture layer. The thicknesses of the formed first negative electrode mixture layer (T1) and second negative electrode mixture layer (T2) were 80 μm for T1 and 80 μm for T2. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0132] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0133] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0134] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Example 3 was used.

[0135] [Example 4] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0136] (Preparation of the first silicon-containing material and the second silicon-containing material) The first silicon-containing material and the second silicon-containing material were prepared in the same manner as in Example 1.

[0137] (Preparation of the negative electrode) The negative electrode slurry for the first negative electrode mixture layer was prepared in the same manner as in Example 1.

[0138] The anode slurry for the second anode slurry layer was prepared in the same manner as in Example 2.

[0139] Next, a first negative electrode mixture slurry was applied to one surface (first surface) of a negative electrode current collector made of copper foil, and a first negative electrode mixture slurry was applied to the other surface (second surface) of the negative electrode current collector. These coatings were dried and compressed to form a first negative electrode mixture layer and a second negative electrode mixture layer. The thicknesses of the formed first negative electrode mixture layer (T1) and second negative electrode mixture layer (T2) were 80 μm for T1 and 80 μm for T2. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0140] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0141] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0142] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Example 4 was used.

[0143] [Example 5] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0144] (Preparation of the first silicon-containing material and the second silicon-containing material) The first silicon-containing material and the second silicon-containing material were prepared in the same manner as in Example 1.

[0145] (Preparation of the negative electrode) Graphite, a first silicon-containing material, and a second silicon-containing material were mixed in a mass ratio of graphite:first silicon-containing material:second silicon-containing material = 91:3:6, and this was used as the negative electrode active material for the first negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material, 1 part by mass of SBR, 1 part by mass of CMC, and 0.05 parts by mass of CNT (conductive agent) were mixed, and an appropriate amount of water was added to prepare the first negative electrode mixture slurry for the first negative electrode mixture layer.

[0146] The anode slurry for the second anode slurry layer was prepared in the same manner as in Example 2.

[0147] Next, a first negative electrode mixture slurry was applied to one surface (first surface) of a negative electrode current collector made of copper foil, and a first negative electrode mixture slurry was applied to the other surface (second surface) of the negative electrode current collector. These coatings were dried and compressed to form a first negative electrode mixture layer and a second negative electrode mixture layer. The thicknesses of the formed first negative electrode mixture layer (T1) and second negative electrode mixture layer (T2) were 80 μm for T1 and 80 μm for T2. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0148] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0149] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0150] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Example 5 was used.

[0151] [Example 6] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0152] (Preparation of the first silicon-containing material and the second silicon-containing material) The first silicon-containing material and the second silicon-containing material were prepared in the same manner as in Example 1.

[0153] (Preparation of the negative electrode) The negative electrode slurry for the first negative electrode mixture layer was prepared in the same manner as in Example 2.

[0154] The anode slurry for the second anode slurry layer was prepared in the same manner as in Example 1.

[0155] Next, a first negative electrode mixture slurry was applied to one surface (first surface) of a negative electrode current collector made of copper foil, and a first negative electrode mixture slurry was applied to the other surface (second surface) of the negative electrode current collector. These coatings were dried and compressed to form a first negative electrode mixture layer and a second negative electrode mixture layer. The thicknesses of the formed first negative electrode mixture layer (T1) and second negative electrode mixture layer (T2) were 80 μm for T1 and 80 μm for T2. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0156] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0157] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0158] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Example 6 was used.

[0159] [Example 7] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0160] (Preparation of the first silicon-containing material and the second silicon-containing material) The first silicon-containing material and the second silicon-containing material were prepared in the same manner as in Example 1.

[0161] (Preparation of the negative electrode) The negative electrode slurry for the first negative electrode mixture layer was prepared in the same manner as in Example 2.

[0162] Graphite, a first silicon-containing material, and a second silicon-containing material were mixed in a mass ratio of graphite:first silicon-containing material:second silicon-containing material = 91:6:3, and this was used as the negative electrode active material for the second negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material, 1 part by mass of SBR, 1 part by mass of CMC, and 0.05 parts by mass of CNT (conductive agent) were mixed, and an appropriate amount of water was added to prepare the second negative electrode mixture slurry for the second negative electrode mixture layer.

[0163] Next, a first negative electrode mixture slurry was applied to one surface (first surface) of a negative electrode current collector made of copper foil, and a first negative electrode mixture slurry was applied to the other surface (second surface) of the negative electrode current collector. These coatings were dried and compressed to form a first negative electrode mixture layer and a second negative electrode mixture layer. The thicknesses of the formed first negative electrode mixture layer (T1) and second negative electrode mixture layer (T2) were 80 μm for T1 and 80 μm for T2. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0164] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0165] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0166] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Example 7 was used.

[0167] [Example 8] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0168] (Preparation of the first silicon-containing material and the second silicon-containing material) The first silicon-containing material and the second silicon-containing material were prepared in the same manner as in Example 1.

[0169] (Preparation of the negative electrode) Graphite and a silicon-1 material were mixed in a mass ratio of graphite:silicon-1 material = 91:9, and this was used as the negative electrode active material for the first negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material was mixed with 1 part by mass of SBR, 1 part by mass of CMC, and 0.04 parts by mass of CNT (conductive agent), and an appropriate amount of water was added to prepare the first negative electrode mixture slurry for the first negative electrode mixture layer.

[0170] Graphite and a silicon-2 content material were mixed in a mass ratio of graphite:silicon-2 content material = 91:9, and this was used as the negative electrode active material for the second negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material was mixed with 1 part by mass of SBR, 1 part by mass of CMC, and 0.06 parts by mass of CNT (conductive agent), and an appropriate amount of water was added to prepare the second negative electrode mixture slurry for the second negative electrode mixture layer.

[0171] Next, a first negative electrode mixture slurry was applied to one surface (first surface) of a negative electrode current collector made of copper foil, and a first negative electrode mixture slurry was applied to the other surface (second surface) of the negative electrode current collector. These coatings were dried and compressed to form a first negative electrode mixture layer and a second negative electrode mixture layer. The thicknesses of the formed first negative electrode mixture layer (T1) and second negative electrode mixture layer (T2) were 80 μm for T1 and 80 μm for T2. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0172] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0173] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0174] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Example 8 was used.

[0175] [Example 9] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0176] (Preparation of the first silicon-containing material and the second silicon-containing material) The first silicon-containing material and the second silicon-containing material were prepared in the same manner as in Example 1.

[0177] (Preparation of the negative electrode) Graphite and a silicon-1 material were mixed in a mass ratio of graphite:silicon-1 material = 91:9 to form the negative electrode active material for the first negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material was mixed with 1 part by mass of SBR, 1 part by mass of CMC, and 0.02 parts by mass of CNT (conductive agent), and an appropriate amount of water was added to prepare the first negative electrode mixture slurry for the first negative electrode mixture layer.

[0178] Graphite and a silicon-2 content material were mixed in a mass ratio of graphite:silicon-2 content material = 91:9, and this was used as the negative electrode active material for the second negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material was mixed with 1 part by mass of SBR, 1 part by mass of CMC, and 0.08 parts by mass of CNT (conductive agent), and an appropriate amount of water was added to prepare the second negative electrode mixture slurry for the second negative electrode mixture layer.

[0179] Next, a first negative electrode mixture slurry was applied to one surface (first surface) of a negative electrode current collector made of copper foil, and a first negative electrode mixture slurry was applied to the other surface (second surface) of the negative electrode current collector. These coatings were dried and compressed to form a first negative electrode mixture layer and a second negative electrode mixture layer. The thicknesses of the formed first negative electrode mixture layer (T1) and second negative electrode mixture layer (T2) were 80 μm for T1 and 80 μm for T2. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0180] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0181] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0182] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Example 9 was used.

[0183] [Example 10] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0184] (Preparation of the first silicon-containing material and the second silicon-containing material) The first silicon-containing material and the second silicon-containing material were prepared in the same manner as in Example 1.

[0185] (Preparation of the negative electrode) Graphite and a silicon-first material were mixed in a mass ratio of graphite:silicon-first material = 91:9, and this was used as the negative electrode active material for the first negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material, 1 part by mass of SBR, 1 part by mass of CMC, and 0.01 parts by mass of CNT (conductive agent) were mixed, and an appropriate amount of water was added to prepare the first negative electrode mixture slurry for the first negative electrode mixture layer.

[0186] Graphite and a silicon-2 content material were mixed in a mass ratio of graphite:silicon-2 content material = 91:9, and this was used as the negative electrode active material for the second negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material, 1 part by mass of SBR, 1 part by mass of CMC, and 0.09 parts by mass of CNT (conductive agent) were mixed, and an appropriate amount of water was added to prepare the second negative electrode mixture slurry for the second negative electrode mixture layer.

[0187] Next, a first negative electrode mixture slurry was applied to one surface (first surface) of a negative electrode current collector made of copper foil, and a first negative electrode mixture slurry was applied to the other surface (second surface) of the negative electrode current collector. These coatings were dried and compressed to form a first negative electrode mixture layer and a second negative electrode mixture layer. The thicknesses of the formed first negative electrode mixture layer (T1) and second negative electrode mixture layer (T2) were 80 μm for T1 and 80 μm for T2. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0188] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0189] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0190] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Example 10 was used.

[0191] [Example 11] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0192] (Preparation of the first silicon-containing material and the second silicon-containing material) The first silicon-containing material and the second silicon-containing material were prepared in the same manner as in Example 1.

[0193] (Preparation of the negative electrode) Graphite, a first silicon-containing material, and a second silicon-containing material were mixed in a mass ratio of graphite:first silicon-containing material:second silicon-containing material = 91:6:3, and this was used as the negative electrode active material for the first negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material, 1 part by mass of SBR, 1 part by mass of CMC, and 0.06 parts by mass of CNT (conductive agent) were mixed, and an appropriate amount of water was added to prepare the first negative electrode mixture slurry for the first negative electrode mixture layer.

[0194] Graphite, a first silicon-containing material, and a second silicon-containing material were mixed in a mass ratio of graphite:first silicon-containing material:second silicon-containing material = 91:3:6, and this was used as the negative electrode active material for the second negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material, 1 part by mass of SBR, 1 part by mass of CMC, and 0.04 parts by mass of CNT (conductive agent) were mixed, and an appropriate amount of water was added to prepare the second negative electrode mixture slurry for the second negative electrode mixture layer.

[0195] Next, a first negative electrode mixture slurry was applied to one surface (first surface) of a negative electrode current collector made of copper foil, and a first negative electrode mixture slurry was applied to the other surface (second surface) of the negative electrode current collector. These coatings were dried and compressed to form a first negative electrode mixture layer and a second negative electrode mixture layer. The thicknesses of the formed first negative electrode mixture layer (T1) and second negative electrode mixture layer (T2) were 80 μm for T1 and 80 μm for T2. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0196] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0197] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0198] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Example 11 was used.

[0199] [Comparative Example 1] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0200] (Preparation of the first silicon-containing material and the second silicon-containing material) The first silicon-containing material and the second silicon-containing material were prepared in the same manner as in Example 1.

[0201] (Preparation of the negative electrode) Graphite, a first silicon-containing material, and a second silicon-containing material were mixed in a mass ratio of graphite:first silicon-containing material:second silicon-containing material = 91:4.5:4.5 to form the negative electrode active material. Then, 100 parts by mass of the negative electrode active material was mixed with 1 part by mass of SBR, 1 part by mass of CMC, and 0.05 parts by mass of CNT (conductive agent), and an appropriate amount of water was added to prepare the negative electrode mixture slurry.

[0202] Next, the prepared negative electrode mixture slurry was applied to both sides of a negative electrode current collector made of copper foil, and the coating was dried and compressed to form a negative electrode mixture layer. The thickness of the negative electrode mixture layer was 80 μm on each side. In addition, an exposed portion of the negative electrode was provided where the surface of the negative electrode current collector was exposed.

[0203] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0204] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0205] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Comparative Example 1 was used.

[0206] [Comparative Example 2] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0207] (Preparation of the second silicon-containing material) The second silicon-containing material was prepared in the same manner as in Example 1. In Comparative Example 2, only the second silicon-containing material was used, and the first silicon-containing material was not used.

[0208] (Preparation of the negative electrode) Graphite and silicon-2 content material were mixed in a mass ratio of graphite:silicon-2 content material = 91:9 to form the negative electrode active material. Then, 100 parts by mass of the negative electrode active material was mixed with 1 part by mass of SBR, 1 part by mass of CMC, and 0.05 parts by mass of CNT (conductive agent), and an appropriate amount of water was added to prepare the negative electrode mixture slurry.

[0209] Next, the prepared negative electrode mixture slurry was applied to both sides of a negative electrode current collector made of copper foil, and the coating was dried and compressed to form a negative electrode mixture layer. The thickness of the negative electrode mixture layer was 80 μm on each side. In addition, an exposed portion of the negative electrode was provided where the surface of the negative electrode current collector was exposed.

[0210] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0211] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0212] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Comparative Example 2 was used.

[0213] [Comparative Example 3] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0214] (Preparation of the first silicon-containing material) The first silicon-containing material was prepared in the same manner as in Example 1. In Comparative Example 2, only the first silicon-containing material was used, and the second silicon-containing material was not used.

[0215] (Preparation of the negative electrode) Graphite and a silicon-1 content material were mixed in a mass ratio of graphite:silicon-1 content material = 91:9 to form the negative electrode active material. Then, 100 parts by mass of the negative electrode active material was mixed with 1 part by mass of SBR, 1 part by mass of CMC, and 0.05 parts by mass of CNT (conductive agent), and an appropriate amount of water was added to prepare the negative electrode mixture slurry.

[0216] Next, the prepared negative electrode mixture slurry was applied to both sides of a negative electrode current collector made of copper foil, and the coating was dried and compressed to form a negative electrode mixture layer. The thickness of the negative electrode mixture layer was 80 μm on each side. In addition, an exposed portion of the negative electrode was provided where the surface of the negative electrode current collector was exposed.

[0217] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0218] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0219] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Comparative Example 3 was used.

[0220] [Reference Example 1] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0221] (Preparation of the first silicon-containing material and the second silicon-containing material) The first silicon-containing material and the second silicon-containing material were prepared in the same manner as in Example 1.

[0222] (Preparation of the negative electrode) Graphite, a first silicon-containing material, and a second silicon-containing material were mixed in a mass ratio of graphite:first silicon-containing material:second silicon-containing material = 91:3:6, and this was used as the negative electrode active material for the first negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material, 1 part by mass of SBR, 1 part by mass of CMC, and 0.05 parts by mass of CNT (conductive agent) were mixed, and an appropriate amount of water was added to prepare the first negative electrode mixture slurry for the first negative electrode mixture layer.

[0223] Graphite, a first silicon-containing material, and a second silicon-containing material were mixed in a mass ratio of graphite:first silicon-containing material:second silicon-containing material = 91:6:3, and this was used as the negative electrode active material for the second negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material, 1 part by mass of SBR, 1 part by mass of CMC, and 0.05 parts by mass of CNT (conductive agent) were mixed, and an appropriate amount of water was added to prepare the second negative electrode mixture slurry for the second negative electrode mixture layer.

[0224] Next, a first negative electrode mixture slurry was applied to one surface (first surface) of a negative electrode current collector made of copper foil, and a first negative electrode mixture slurry was applied to the other surface (second surface) of the negative electrode current collector. These coatings were dried and compressed to form a first negative electrode mixture layer and a second negative electrode mixture layer. The thicknesses of the formed first negative electrode mixture layer (T1) and second negative electrode mixture layer (T2) were 80 μm for T1 and 80 μm for T2. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0225] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0226] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0227] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Reference Example 1 was used.

[0228] [Reference Example 2] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0229] (Preparation of the first silicon-containing material and the second silicon-containing material) The first silicon-containing material and the second silicon-containing material were prepared in the same manner as in Example 1.

[0230] (Preparation of the negative electrode) The negative electrode slurry for the first negative electrode mixture layer was prepared in the same manner as in Example 1.

[0231] Graphite and a silicon-containing material were mixed in a mass ratio of graphite:silicon-containing material = 91:9, and this was used as the negative electrode active material for the second negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material, 1 part by mass of SBR, 1 part by mass of CMC, and 0.05 parts by mass of CNT (conductive agent) were mixed, and an appropriate amount of water was added to prepare the second negative electrode mixture slurry for the second negative electrode mixture layer.

[0232] Next, a first negative electrode mixture slurry was applied to one surface (first surface) of a negative electrode current collector made of copper foil, and a first negative electrode mixture slurry was applied to the other surface (second surface) of the negative electrode current collector. These coatings were dried and compressed to form a first negative electrode mixture layer and a second negative electrode mixture layer. The thicknesses of the formed first negative electrode mixture layer (T1) and second negative electrode mixture layer (T2) were 80 μm for T1 and 80 μm for T2. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0233] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0234] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0235] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Reference Example 2 was used.

[0236] [Reference Example 3] (Preparation of positive electrode active material and positive electrode) The positive electrode active material and positive electrode were prepared in the same manner as in Example 1.

[0237] (Preparation of the first silicon-containing material and the second silicon-containing material) The first silicon-containing material and the second silicon-containing material were prepared in the same manner as in Example 1.

[0238] (Preparation of the negative electrode) Graphite and a silicon-2 content material were mixed in a mass ratio of graphite:silicon-2 content material = 91:9, and this was used as the negative electrode active material for the first negative electrode mixture layer. Then, 100 parts by mass of the negative electrode active material was mixed with 1 part by mass of SBR, 1 part by mass of CMC, and 0.05 parts by mass of CNT (conductive agent), and an appropriate amount of water was added to prepare the first negative electrode mixture slurry for the first negative electrode mixture layer.

[0239] The anode slurry for the second anode slurry layer was prepared in the same manner as in Example 1.

[0240] Next, a first negative electrode mixture slurry was applied to one surface (first surface) of a negative electrode current collector made of copper foil, and a first negative electrode mixture slurry was applied to the other surface (second surface) of the negative electrode current collector. These coatings were dried and compressed to form a first negative electrode mixture layer and a second negative electrode mixture layer. The thicknesses of the formed first negative electrode mixture layer (T1) and second negative electrode mixture layer (T2) were 80 μm for T1 and 80 μm for T2. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0241] Table 1 shows the mass percentages of the first silicon-containing material and the second silicon-containing material in the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer. Table 2 also shows the mass ratio (%) of the conductive agent to the anode active material, respectively, determined from the charging ratio, for the first anode mixture layer and the second anode mixture layer.

[0242] (Preparation of non-aqueous electrolyte) The non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0243] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Reference Example 3 was used.

[0244] [Measurement of Particle Volume Expansion Rate of First and Second Silicon-Containing Materials] For the negative electrodes of each example, comparative example, and reference example, the particle volume expansion rates of the first and second silicon-containing materials were determined using the method described in Embodiment 1. However, instead of disassembling the battery and cutting out the negative electrode, a single-electrode cell was made using the fabricated negative electrode, and the particle volume expansion rates of the first and second silicon-containing materials were determined using that single-electrode cell. The results are shown in Table 1. However, for silicon-containing materials fabricated using the same method, the particle volume expansion rate of one representative silicon-containing material was measured, and that measurement value was used.

[0245] [Measurement of the expansion rate of the first and second negative electrode mixture layers during charging] For each example, comparative example, and reference example of the negative electrode, the expansion rate of the first and second negative electrode mixture layers during charging was determined using the method described in Embodiment 1. However, instead of disassembling the battery and cutting out the negative electrode, a single-electrode cell was made using the fabricated negative electrode, and the expansion rate of the first and second negative electrode mixture layers during charging was determined using that single-electrode cell. The results are shown in Table 2.

[0246] [Evaluation of Charge / Discharge Cycle Characteristics] The test cells of each example, comparative example, and reference example were charged at a constant current of 0.3C at a temperature of 25°C until the battery voltage reached 4.2V, and then charged at a constant voltage of 4.2V until the current value was 0.02C. After that, the batteries were discharged at a constant current of 0.5C until the battery voltage reached 2.5V, and the discharge capacity at this time was defined as the initial discharge capacity. This charge / discharge cycle was considered one cycle, and 100 cycles were performed. The initial discharge capacity and the discharge capacity at the 100th cycle were determined, and the capacity retention rate was calculated using the following formula: Capacity retention rate (%) = Discharge capacity at the 100th cycle / Initial discharge capacity × 100

[0247] The obtained capacity retention rate was defined as the cycle retention rate. The results are shown in Table 2. Table 1 shows the relative values ​​when the cycle retention rate of Comparative Example 1 is set as the baseline (100%).

[0248]

[0249]

[0250] (Discussion) As shown in Table 1, the test cells of the embodiment equipped with a first negative electrode mixture layer and a second negative electrode mixture layer satisfying relational equation (1), that is, the test cells in which the first negative electrode mixture layer on the inner circumference of the winding has a larger expansion rate during charging than the second negative electrode mixture layer on the outer circumference of the winding, all showed improved charge-discharge cycle characteristics compared to the test cells of the comparative example and reference example in which the first and second negative electrode mixture layers did not satisfy relational equation (1).

[0251] Furthermore, comparing Examples 8 to 11, the test cells in Examples 8 to 10, where the mass ratio of the conductive agent satisfies relation (5), i.e., the second negative electrode mixture layer on the outer circumference of the winding has a larger mass ratio of conductive agent than the first negative electrode mixture layer on the inner circumference of the winding, exhibited more improved charge-discharge cycle characteristics than the test cell in Example 11, where the second negative electrode mixture layer on the outer circumference of the winding has a smaller mass ratio of conductive agent than the first negative electrode mixture layer on the inner circumference of the winding.

[0252] The technology disclosed herein is useful for batteries such as lithium-ion secondary batteries that require excellent charge-discharge cycle characteristics.

Claims

1. A negative electrode used in an electrode group having a wound structure, wherein the negative electrode comprises: a negative electrode current collector having a first surface on the inner circumference side of the winding and a second surface on the outer circumference side of the winding; a first negative electrode mixture layer disposed on the first surface of the negative electrode current collector; and a second negative electrode mixture layer disposed on the second surface of the negative electrode current collector, wherein the first negative electrode mixture layer and the second negative electrode mixture layer contain a silicon-containing material and graphite as negative electrode active materials, and when the expansion rate of the first negative electrode mixture layer during charging is A1 and the expansion rate of the second negative electrode mixture layer during charging is A2, in at least a part of the negative electrode, A1 and A2 satisfy the following relational expression (1). A1 > A2 ... (1) Here, the charging expansion rate of the first negative electrode mixture layer is the rate of increase in thickness of the first negative electrode mixture layer in the charging state relative to the thickness of the first negative electrode mixture layer in the discharge state, and the charging expansion rate of the second negative electrode mixture layer is the rate of increase in thickness of the second negative electrode mixture layer in the charging state relative to the thickness of the second negative electrode mixture layer in the discharge state.

2. The negative electrode according to claim 1, wherein the silicon-containing material in the first negative electrode mixture layer comprises a first silicon-containing material, and the silicon-containing material in the second negative electrode mixture layer comprises a second silicon-containing material having a smaller particle volume expansion coefficient than the first silicon-containing material. Here, the particle volume expansion coefficient of the first silicon-containing material is the ratio of the particle volume of the first silicon-containing material in the charged state to the particle volume of the first silicon-containing material in the discharged state, and the particle volume expansion coefficient of the second silicon-containing material is the ratio of the particle volume of the second silicon-containing material in the charged state to the particle volume of the second silicon-containing material in the discharged state.

3. The negative electrode according to claim 2, wherein when the negative electrode active material contained in the first negative electrode mixture layer is defined as the first negative electrode active material, and the negative electrode active material contained in the second negative electrode mixture layer is defined as the second negative electrode active material, the mass ratio of the first silicon-containing material in the first negative electrode active material is greater than the mass ratio of the first silicon-containing material in the second negative electrode active material, and the mass ratio of the second silicon-containing material in the second negative electrode active material is greater than the mass ratio of the second silicon-containing material in the first negative electrode active material.

4. The negative electrode according to claim 2, wherein, when the particle volume expansion coefficient of the first silicon-containing material is V1 and the particle volume expansion coefficient of the second silicon-containing material is V2, V1 and V2 satisfy the following relationships (2) and (3): 1.7 ≤ V1 < 3 ... (2) 1.3 ≤ V2 < 2.2 ... (3) 5. The negative electrode according to claim 1, wherein A1 and A2 satisfy the following relation (4): 1 < A1 / A2 ≤ 1.5 ... (4) 6. The negative electrode according to claim 1, wherein the first negative electrode mixture layer and the second negative electrode mixture layer further contain a conductive agent, the conductive agent containing a carbon material.

7. The negative electrode according to claim 6, wherein when the negative electrode active material contained in the first negative electrode mixture layer is designated as the first negative electrode active material, the negative electrode active material contained in the second negative electrode mixture layer is designated as the second negative electrode active material, the conductive agent contained in the first negative electrode mixture layer is designated as the first conductive agent, and the conductive agent contained in the second negative electrode mixture layer is designated as the second conductive agent, the mass ratio θ1 of the first conductive agent to the first negative electrode active material and the mass ratio θ2 of the second conductive agent to the second negative electrode active material satisfy the following relationship (5). θ1 ≤ θ2 ... (5) 8. A battery comprising a negative electrode, a positive electrode, and an electrolyte, as described in any one of claims 1 to 7.

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