Negative electrode and battery

Abstract

A negative electrode 10 according to the present disclosure comprises: a negative electrode current collector 11; and a negative electrode mixture layer 12 disposed on the negative electrode current collector 11. The negative electrode mixture layer 12 includes a first negative electrode mixture layer 13 including the surface of the negative electrode 10, and a second negative electrode mixture layer 14 located between the first negative electrode mixture layer 13 and the negative electrode current collector 11. When a negative electrode active material contained in the first negative electrode mixture layer 13 is defined as a first negative electrode active material and a negative electrode active material contained in the second negative electrode mixture layer 14 is defined as a second negative electrode active material, the second negative electrode active material contains a carbon material in which the average surface interval d002 of a (002) plane measured by an X-ray diffraction method is 0.34 nm or more. The mass ratio of the carbon material in the second negative electrode active material is larger than the mass ratio of the carbon material in the first negative electrode active material. At least one active material selected from the group consisting of the first negative electrode active material and the second negative electrode active material includes the carbon material and graphite.

Description

Anodes and Batteries

[0001] The present disclosure relates to anodes and batteries.

[0002] In recent years, secondary batteries such as lithium-ion batteries have been widely used in applications requiring high capacity, such as in-vehicle applications and power storage applications. The electrodes that constitute such batteries have a significant impact on battery performance. For this reason, various studies have been conducted on electrodes.

[0003] Conventionally, lithium-ion secondary batteries have used, for example, carbon materials as the negative electrode active material. However, such lithium-ion secondary batteries have a problem in that lithium deposition occurs on the negative electrode surface when repeatedly charged at a high load rate to shorten the charging time. Therefore, Patent Document 1 proposes a negative electrode that does not cause lithium deposition even when repeatedly charged at a high load rate. The negative electrode comprises a first layer provided on a conductive substrate and a second layer provided on the first layer, the first layer containing a graphite material as the negative electrode active material, and the second layer containing non-graphitizable carbon as the negative electrode active material.

[0004] Japanese Patent Application Laid-Open No. 2008-59999

[0005] The negative electrode proposed in Patent Document 1 can suppress lithium deposition due to charging at a high load rate, but has the problem of a deterioration in the rapid charging time to a specified capacity, i.e., an increase in charging time.

[0006] The present disclosure provides a negative electrode that can improve the charge capacity per unit time during rapid charging.

[0007] The negative electrode of the present disclosure is a negative electrode including: a negative electrode current collector; and a negative electrode mixture layer disposed on the negative electrode current collector, wherein the negative electrode mixture layer includes a first negative electrode mixture layer including a surface of the negative electrode, and a second negative electrode mixture layer located between the first negative electrode mixture layer and the negative electrode current collector, and when the negative electrode active material contained in the first negative electrode mixture layer is defined as a first negative electrode active material and the negative electrode active material contained in the second negative electrode mixture layer is defined as a second negative electrode active material, the second negative electrode active material has an average interplanar spacing d of (002) planes measured by X-ray diffraction. 002a mass ratio of the carbon material in the second negative electrode active material is greater than a mass ratio of the carbon material in the first negative electrode active material, and at least one selected from the group consisting of the first negative electrode active material and the second negative electrode active material includes the carbon material and graphite.

[0008] According to the present disclosure, it is possible to provide a negative electrode that can improve the charge capacity per unit time during rapid charging.

[0009] Fig. 1 is a cross-sectional view showing a schematic configuration of a negative electrode according to embodiment 1. Fig. 2 is a longitudinal cross-sectional view showing a schematic example of a battery according to embodiment 2.

[0010] [Findings that Form the Basis of the Present Disclosure] The present inventors have investigated anodes containing a carbon material as an active material. The anode disclosed in Patent Document 1 uses a non-graphitizable carbon, which has high lithium ion acceptability, as the anode active material in the second layer located on the surface side of the anode. This configuration allows the anode disclosed in Patent Document 1 to suppress lithium deposition during high-load rate charging. However, the inventors' investigations have revealed that the anode disclosed in Patent Document 1 has issues during rapid charging. Because rapid charging involves charging the battery to its specified capacity, increasing the internal resistance of the battery reduces the current that can be passed. As a result, the rapid charging time to the specified capacity deteriorates, i.e., the charging time during rapid charging increases. According to the inventors' investigations, the anode disclosed in Patent Document 1 preferentially charges the non-graphitizable carbon in the second layer during charging, and current concentrates in the graphite in the first layer during the latter half of charging. This increases the resistance of the anode during the latter half of charging, preventing it from passing a large current. As a result, the negative electrode disclosed in Patent Document 1 has a poor rapid charge time up to a specified capacity, that is, the charging time during rapid charge increases.

[0011] Therefore, the present inventors have conducted further intensive research based on the above findings, and have reconsidered the configuration of the negative electrode, thereby discovering a new negative electrode that can improve the charge capacity per unit time during fast charging. Below, we will describe the negative electrode of the present disclosure that can improve the charge capacity per unit time during fast charging.

[0012] [Embodiments of the Present Disclosure] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0013] 1 is a cross-sectional view showing a schematic configuration of a negative electrode according to Embodiment 1. The negative electrode 10 according to Embodiment 1 includes a negative electrode current collector 11 and a negative electrode mixture layer 12 disposed on the negative electrode current collector 11. The negative electrode mixture layer 12 includes a first negative electrode mixture layer 13 including the surface of the negative electrode 10, and a second negative electrode mixture layer 14 located between the first negative electrode mixture layer 13 and the negative electrode current collector 11. When the negative electrode active material contained in the first negative electrode mixture layer 13 is defined as the first negative electrode active material and the negative electrode active material contained in the second negative electrode mixture layer 14 is defined as the second negative electrode active material, the second negative electrode active material has an average interplanar spacing d 002 a mass ratio of the carbon material in the second negative electrode active material is greater than a mass ratio of the carbon material in the first negative electrode active material. Furthermore, at least one selected from the group consisting of the first negative electrode active material and the second negative electrode active material contains the carbon material and graphite.

[0014] Here, the average interplanar spacing d of the (002) plane in the carbon material 002 can be determined using a peak derived from the (002) plane of carbon in an X-ray diffraction pattern obtained by X-ray diffraction measurement of the negative electrode active material using Cu—Kα rays.

[0015] Hereinafter, the average interplanar spacing d of the (002) plane measured by X-ray diffraction method will be referred to as 002 For convenience of explanation, a carbon material having a particle size of 0.34 nm or more will be referred to as the "carbon material of embodiment 1."

[0016] Here, whether the mass proportion of the carbon material of Embodiment 1 in the second negative electrode active material is greater than the mass proportion of the carbon material of Embodiment 1 in the first negative electrode active material can be confirmed by the following method.

[0017] The non-aqueous electrolyte secondary battery in the final discharge state is disassembled, the negative electrode is removed, washed with dimethyl carbonate, and then vacuum dried. A cross section of the negative electrode is cut out using a cross section polisher or the like, and the Raman scattering spectrum is measured. -1 Nearby G band and 1360 cm -1 The peak intensity ratio of the D band near the G band is mapped. Particles with an R value (R = I1360 / I1580) expressed as the peak intensity ratio of the G band to the D band of less than 0.8 are considered to be graphite, and particles with an R value of 0.8 or more are considered to be the carbon material of embodiment 1, and the area ratio of the regions of each carbon material in the first negative electrode mixture layer 13 and the second negative electrode mixture layer 14 is calculated. At this time, the area ratio of the carbon material of embodiment 1 is large in a negative electrode mixture layer with a large mass proportion of the carbon material of embodiment 1.

[0018] The mass proportion of the carbon material of Embodiment 1 in each negative electrode mixture layer can be determined by multiplying the area ratio of the carbon material of Embodiment 1 determined by the above-described method by the value of the true density of the carbon material of Embodiment 1. The mass proportion of graphite in each negative electrode mixture layer can also be determined by multiplying the area ratio of the graphite of Embodiment 1 by the value of the true density of the graphite. For example, in the second negative electrode active material, the mass proportion of the carbon material of Embodiment 1 relative to the total mass of the carbon material of Embodiment 1 and graphite can be determined by determining the mass proportion of the carbon material of Embodiment 1 and the mass proportion of graphite in the second negative electrode mixture layer 14 by the above-described method, and using the values ​​of these mass proportions.

[0019] Note that a carbon material may be contained in the negative electrode mixture layer 12 for purposes other than as an active material. In such cases, in this specification, the active material is defined as a carbon material that includes a peak derived from the (002) plane of carbon in an X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu—Kα radiation.

[0020] Furthermore, it can be confirmed by the above-mentioned method that at least one selected from the group consisting of the first negative electrode active material and the second negative electrode active material contains the carbon material and graphite of embodiment 1. That is, a nonaqueous electrolyte secondary battery in an end-of-discharge state is disassembled, the negative electrode is removed, washed with dimethyl carbonate, and then vacuum dried. A cross section of the negative electrode is cut out using a cross-section polisher or the like, and the Raman scattering spectrum is measured to determine whether the peak at 1580 cm -1 Nearby G band and 1360 cm -1 The peak intensity ratio of the D band near the peak intensity ratio of the G band to the D band is mapped. Particles with an R value (R = I1360 / I1580) of less than 0.8 are considered to be graphite, and particles with an R value of 0.8 or more are considered to be the carbon material of embodiment 1, and the presence of the carbon material and graphite of embodiment 1 in the first negative electrode mixture layer 13 and the second negative electrode mixture layer 14 is confirmed. This makes it possible to confirm the presence of the carbon material and graphite of embodiment 1 in the first negative electrode active material and the presence of the carbon material and graphite of embodiment 1 in the second negative electrode active material.

[0021] During rapid charging, due to the rate-limiting effect of lithium ion diffusion, the surface side of the negative electrode 10, i.e., the first negative electrode mixture layer 13, has a lower potential than the current collector side, i.e., the second negative electrode mixture layer 14. In the negative electrode 10 according to embodiment 1, as described above, the mass proportion of the carbon material of embodiment 1 in the negative electrode active material is higher in the second negative electrode mixture layer 14 than in the first negative electrode mixture layer 13. The carbon material of embodiment 1 allows charging to proceed even at a low potential. Therefore, in a negative electrode 10 in which the mass proportion of the carbon material of embodiment 1 in the second negative electrode active material of the second negative electrode mixture layer 14 is higher than the mass proportion of the carbon material of embodiment 1 in the first negative electrode active material of the first negative electrode mixture layer 13, charging of the first negative electrode mixture layer 13 and the second negative electrode mixture layer 14 proceeds in a balanced manner during rapid charging. As a result, the negative electrode 10 according to embodiment 1 can suppress an increase in the internal resistance of the battery due to current concentration in the second negative electrode mixture layer 14 in the latter half of charging.

[0022] Furthermore, in the negative electrode 10 according to embodiment 1, at least one selected from the group consisting of the first negative electrode active material and the second negative electrode active material contains the carbon material of embodiment 1 and graphite. Therefore, the negative electrode 10 according to embodiment 1 does not include a configuration in which the second negative electrode active material is composed solely of the carbon material of embodiment 1 and the first negative electrode active material does not contain the carbon material of embodiment 1, for example, is composed solely of graphite. The carbon material of embodiment 1 is more difficult to fill than graphite, i.e., it is a material in which it is relatively difficult to reduce voids. Therefore, when the second negative electrode active material is composed solely of the carbon material of embodiment 1 and the first negative electrode active material is composed solely of graphite, the voids are adjusted by reducing the voids on the graphite side of the first negative electrode active material, i.e., in the first negative electrode mixture layer 13. In this case, the lithium ion acceptance in the negative electrode 10 is deteriorated, and the internal resistance of the battery increases. However, in the negative electrode 10 according to the first embodiment, at least one selected from the group consisting of the first negative electrode active material and the second negative electrode active material contains both the carbon material of the first embodiment and graphite, and therefore, it is possible to suppress an increase in the internal resistance of the battery due to a deterioration in the lithium ion acceptability of the first negative electrode mixture layer 13. Furthermore, since the inclusion of graphite as the negative electrode active material can suppress a significant decrease in capacity, the negative electrode 10 according to the first embodiment can also maintain the capacity to a certain extent.

[0023] As described above, the anode 10 according to the first embodiment can suppress an increase in the internal resistance of the battery during rapid charging, thereby improving the charge capacity per unit time during rapid charging. Furthermore, the anode 10 according to the first embodiment can maintain the capacity.

[0024] The carbon material of the first embodiment may include, for example, non-graphitizable carbon. This makes it possible to more effectively improve the charge capacity per unit time during rapid charging. The carbon material of the first embodiment may be non-graphitizable carbon.

[0025] 1 is configured of two layers, the first anode mixture layer 13 and the second anode mixture layer 14, but is not limited to this and may be configured of three or more layers. The anode mixture layer 12 may further include a layer located between the first anode mixture layer 13 and the second anode mixture layer 14, or between the second anode mixture layer 14 and the anode current collector 11.

[0026] The first anode mixture layer 13 and the second anode mixture layer 14 can be distinguished by differences in constituent components, composition ratios, etc. The first anode mixture layer 13 can be identified, for example, by identifying a region having similar constituent components and similar composition ratios from the surface of the anode 10 to the depth direction of the anode mixture layer 12. The second anode mixture layer 14 can be identified by identifying a region that exists between the identified first anode mixture layer 13 and the anode current collector 11 and has the above-mentioned structural relationship with the first anode mixture layer 13.

[0027] In addition, in the anode mixture layer 12, if it is difficult to identify the first anode mixture layer 13 and the second anode mixture layer 14 due to differences in the constituent components and composition ratios, for example, the anode mixture layer 12 is divided into two equal parts in the thickness direction, and the divided layer located on the surface side of the anode mixture layer 12 may be identified as the first anode mixture layer 13, and the divided layer located on the anode current collector 11 side may be identified as the second anode mixture layer 14.

[0028] Each component of the negative electrode 10 of the first embodiment will be specifically described below.

[0029] [Negative Electrode Current Collector] The negative electrode current collector 11 may be a sheet or film made of a metal material such as stainless steel, nickel, copper, or an alloy thereof. The sheet or film may be porous or non-porous. Examples of the sheet or film include metal foil and metal mesh. A carbon material such as carbon may be applied to the surface of the negative electrode current collector 11 as a conductive auxiliary material.

[0030] The thickness of the negative electrode current collector 11 is not particularly limited, but may be, for example, 1 μm or more and 50 μm or less, or 5 μm or more and 20 μm or less, from the viewpoint of balancing the strength and weight reduction of the negative electrode 10.

[0031] [Negative Electrode Mixture Layer] As described above, the negative electrode mixture layer 12 includes the first negative electrode mixture layer 13 and the second negative electrode mixture layer 14 .

[0032] When the thickness of the first anode mixture layer 13 is X and the thickness of the anode mixture layer 12 is Y, X and Y may satisfy, for example, 0.5Y≦X. That is, the thickness of the first anode mixture layer 13 may account for half or more of the thickness of the entire anode mixture layer. With this configuration, the anode 10 of embodiment 1 can further suppress an increase in the internal resistance of the battery during rapid charging, thereby further improving the charge capacity per unit time during rapid charging. Furthermore, with this configuration, the anode 10 of embodiment 1 can also improve capacity.

[0033] Furthermore, X and Y may satisfy 0.5Y≦X≦0.9Y. According to this configuration, the negative electrode 10 of Embodiment 1 can more effectively improve the charge capacity per unit time and can also improve the capacity.

[0034] Here, in this specification, the thickness (Y) of the anode mixture layer 12 and the thickness (X) of the first anode mixture layer 13 are measured by the following method. (1) A battery to be evaluated is disassembled, and the anode is cut out. A single-electrode cell is fabricated using metallic Li as a counter electrode and an ionic liquid as an electrolyte. (2) The single-electrode cell is charged at 0.1 C in a temperature environment of 25°C until the cell voltage reaches 5 mV, and then discharged at 0.1 C until the cell voltage reaches 1.0 V, and the thickness (Y) of the anode mixture layer 12 and the thickness (X) of the first anode mixture layer 13 in a charged state (fully charged state) are determined. Here, the thickness (Y) of the anode mixture layer 12 and the thickness (X) of the first anode mixture layer 13 are determined from cross-sectional scanning electron microscope (SEM) images of each layer. Specifically, the thickness of each of the negative electrode mixture layer 12 and the first negative electrode mixture layer 13 is measured at any five locations, and the average value calculated from the five measured values ​​is defined as the thickness.

[0035] The first negative electrode active material may not contain the carbon material of embodiment 1. That is, the first negative electrode mixture layer 13 including the surface of the negative electrode 10, in other words, the first negative electrode mixture layer 13 located on the surface side of the negative electrode 10, may not contain the carbon material of embodiment 1, such as non-graphitizable carbon, as the negative electrode active material. According to this configuration, the negative electrode 10 of embodiment 1 can further suppress an increase in the internal resistance of the battery during rapid charging, thereby further improving the charge capacity per unit time during rapid charging. Furthermore, according to this configuration, the negative electrode 10 of embodiment 1 can also improve capacity.

[0036] In the second negative electrode active material, the mass ratio of the carbon material of Embodiment 1 to the total mass of the carbon material of Embodiment 1 and graphite may be more than 0 mass % and less than 80 mass %. With this configuration, the negative electrode 10 of Embodiment 1 can further suppress an increase in the internal resistance of the battery during rapid charging, thereby further improving the charge capacity per unit time during rapid charging.

[0037] In the second negative electrode active material, the mass ratio of the carbon material of Embodiment 1 to the total mass of the carbon material of Embodiment 1 and graphite may be 20 mass % or more and 60 mass % or less. With this configuration, the negative electrode 10 of Embodiment 1 can further suppress an increase in the internal resistance of the battery during rapid charging, thereby further improving the charge capacity per unit time during rapid charging.

[0038] The method for determining the mass ratio of the carbon material of embodiment 1 to the total mass of the carbon material of embodiment 1 and graphite in the second negative electrode active material is as described above.

[0039] Although the carbon material and graphite in the first embodiment have been described as the negative electrode active material that can be contained in the negative electrode mixture layer 12, i.e., the materials that can be contained in the first and second negative electrode active materials, the negative electrode mixture layer 12 may also contain a silicon-containing material as the negative electrode active material. That is, the first negative electrode active material may contain a silicon-containing material. Furthermore, the second negative electrode active material may contain a silicon-containing material. By including a silicon-containing material as the negative electrode active material, a battery with a higher capacity can be realized.

[0040] In this specification, the term "silicon-containing material" refers to a material containing Si. Examples of silicon-containing materials include Si, Si alloys, Si compounds, and composite materials containing Si.

[0041] The average particle size of the silicon-containing material is, for example, 1 μm or more and 20 μm or less, or may be 1 μm or more and 15 μm or less. The average particle size of the silicon-containing material means the particle size at which the volume integrated value is 50% in the particle size distribution measured by a laser diffraction scattering method (hereinafter referred to as "volume-based D50"). For example, an "MT3000II" manufactured by Microtrac Bell Co., Ltd. is used as a measuring device, and the measurement is performed using, for example, water as a dispersion medium.

[0042] The silicon-containing material is preferably a composite material containing Si. The composite material containing Si is, for example, a composite particle containing an ion-conducting phase and a Si phase dispersed in the ion-conducting phase. The ion-conducting 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 ion-conducting phase may be composed of a single phase or multiple phases. The Si phase is, for example, formed of fine Si particles dispersed within the ion-conducting phase. In the Si-containing composite material, the ion-conducting phase alleviates stress associated with the expansion and contraction of the Si phase during charge and discharge, thereby suppressing cracking and fracture of the composite material. Therefore, the Si-containing composite material can achieve both high capacity due to the inclusion of Si and improved charge and discharge cycle characteristics.

[0043] The particle volume expansion coefficient V1 of the silicon-containing material may satisfy, for example, 1.3≦V1<2.2. When the particle volume expansion coefficient V1 of the silicon-containing material satisfies this range, capacity degradation in the negative electrode mixture layer 12 due to isolation of the negative electrode active material caused by volume changes of the silicon-containing material accompanying charge and discharge can be effectively suppressed.

[0044] Here, the particle volume expansion coefficient of the silicon-containing material is the ratio of the particle volume of the silicon-containing material in a charged state to the particle volume of the silicon-containing material in a discharged state.

[0045] In this specification, the particle volume expansion coefficient of the silicon-containing material is measured by the following method. (1) A battery to be evaluated is disassembled, and the negative electrode is cut out. A single-electrode cell is prepared in which the particle cross-section of the silicon-containing material is exposed using metallic Li as the counter electrode and an ionic liquid as the electrolyte. (2) The single-electrode cell is charged at 0.002 C in a 25°C environment until the cell voltage reaches 5 mV, and then discharged at 0.05 C until the cell voltage reaches 1.0 V, and the particle cross-section of the silicon-containing material is observed in situ using an SEM. (3) The particle volume expansion coefficient of the silicon-containing material is determined by determining the particle volume (Va) of the silicon-containing material in a charged state (fully charged state) and the particle volume (Vb) of the silicon-containing material in a discharged state (fully discharged state) from the particle cross-sectional area of ​​the silicon-containing material, and then calculating the particle volume expansion coefficient (Va / Vb). The particle volume is obtained by raising the particle cross-sectional area of ​​the silicon-containing material obtained from an SEM image of the particle cross-section to the 3 / 2 power. (4) The measurement (2) and calculation (3) of the particle volume expansion coefficients of 50 particles of the silicon-containing material contained in the negative electrode mixture layer 12 are performed to obtain a particle area-based particle volume expansion coefficient distribution. Note that the particle area in the particle volume expansion coefficient distribution obtained here is the area of ​​the particle in a fully discharged state. (5) The particle volume expansion coefficient at the apex of the peak of the area-based particle volume expansion coefficient distribution obtained in (4) above is designated as the particle volume expansion coefficient V1 of the silicon-containing material.

[0046] In each of the first negative electrode mixture layer 13 and the second negative electrode mixture layer 14, the content of the silicon-containing material is, for example, 40 mass% or less, or may be 35 mass% or less, or 30 mass% or less, of the total mass of the negative electrode active material, from the viewpoint of improving cycle characteristics. In each of the first negative electrode mixture layer 13 and the second negative electrode mixture layer 14, the content of the silicon-containing material is, for example, 5 mass% or more, of the total mass of the negative electrode active material, from the viewpoint of increasing capacity and improving cycle characteristics. An example of a suitable range of the content of the silicon-containing material is, for example, 5 mass% or more and 35 mass% or less, or 10 mass% or more and 30 mass% or less, or 5 mass% or more and 15 mass% or less, of the total mass of the negative electrode active material.

[0047] The negative electrode mixture layer 12 may further contain a binder. Examples of binders include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, and styrene-butadiene rubber (SBR). These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like.

[0048] The negative electrode mixture layer 12 may further contain a conductive agent. Examples of the conductive agent include carbon materials such as carbon black, such as acetylene black or ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, and graphene.

[0049] (Embodiment 2) A battery according to embodiment 2 includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode is the negative electrode according to embodiment 1. With this configuration, the battery according to embodiment 2 can improve the charge capacity per unit time during rapid charging.

[0050] 2 is a longitudinal cross-sectional view schematically illustrating an example of a battery according to embodiment 2. The battery 100 is a cylindrical battery including a cylindrical battery case, a wound electrode group 24, and an electrolyte (not shown). The electrode group 24 is housed in the battery case and is in contact with the electrolyte.

[0051] The battery case is composed of a case body 25, which is a cylindrical metal container with a bottom, and a sealing body 26 that seals the opening of the case body 25. A gasket 37 is disposed between the case body 25 and the sealing body 26. The gasket 37 ensures the airtightness of the battery case. Within the case body 25, insulating plates 27 and 28 are disposed on both ends of the electrode group 24 in the direction of the winding axis of the electrode group 24, respectively.

[0052] Case body 25 has, for example, a step portion 31. Step portion 31 can be formed by partially pressing the side wall of case body 25 from the outside. Step portion 31 may be formed in an annular shape on the side wall of case body 25 along the circumferential direction of an imaginary circle defined by case body 25. In this case, sealing body 26 is supported by, for example, the surface of step portion 31 on the opening side.

[0053] Sealing body 26 includes a filter 32, a lower valve body 33, an insulating member 34, an upper valve body 35, and a cap 36. These components are stacked in this order in sealing body 26. Sealing body 26 is attached to the opening of case body 25 so that cap 36 is located on the outside of case body 25 and filter 32 is located on the inside of case body 25.

[0054] Each of the above-mentioned members constituting the sealing body 26 has, for example, a disk or ring shape. The above-mentioned members, except for the insulating member 34, are electrically connected to one another.

[0055] The electrode group 24 has 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 the negative electrode 23 is, for example, parallel to the winding axis of the electrode group 24. The separator 22 is disposed between the positive electrode 21 and the negative electrode 23. The positive electrode 21 and the negative electrode 23 are spirally wound with the separator 22 interposed between these electrodes.

[0056] When observing the cross section of the battery 100 in a direction perpendicular to the winding axis of the electrode group 24, the positive electrodes 21 and negative electrodes 23 are stacked alternately in the radial direction of an imaginary circle defined by the case body 25, with a separator 22 interposed between these electrodes.

[0057] The positive electrode 21 is electrically connected to a cap 36, which also serves as a positive electrode terminal, via a positive electrode lead 29. One end of the positive electrode lead 29 is connected, for example, to near the center of the positive electrode 21 in the longitudinal direction of the positive electrode 21. The positive electrode lead 29 passes through a through-hole formed in the insulating plate 27 and extends from the positive electrode 21 to the filter 32. The other end of the positive electrode lead 29 is welded, for example, to the surface of the filter 32 on the electrode group 24 side.

[0058] The negative electrode 23 is electrically connected to the case body 25, which also serves as a negative electrode terminal, via a negative electrode lead 30. One end of the negative electrode lead 30 is connected to, for example, an 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 to, for example, the inner bottom surface of the case body 25.

[0059] Each component of the battery 100 will be specifically described below.

[0060] The positive electrode 21 includes a material having the property of absorbing and releasing metal ions (e.g., lithium ions). The positive electrode 21 includes, for example, a positive electrode active material. The positive electrode 21 includes, for example, a positive electrode current collector and a positive electrode mixture layer supported on the surface of the positive electrode current collector.

[0061] The positive electrode current collector can be, for example, a sheet or film made of a metal material such as aluminum, stainless steel, titanium, or an alloy thereof. Aluminum and its alloys are suitable as materials for the positive electrode current collector because they are inexpensive and easy to form into thin films. The sheet or film may be porous or non-porous. Metal foil, metal mesh, or the like may be used as the sheet or film. A carbon material such as carbon may be applied to the surface of the positive electrode current collector as a conductive auxiliary material.

[0062] The positive electrode mixture layer includes a positive electrode active material. The positive electrode active material can be a material capable of absorbing and releasing metal ions (e.g., lithium ions). Examples of the positive electrode active material include lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, using a lithium-containing transition metal oxide or a lithium-containing transition metal phosphate as the positive electrode active material can reduce battery manufacturing costs and increase average discharge voltage. 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.

[0063] The positive electrode mixture layer may further contain a binder. As the binder, the materials described in the first embodiment as binders that can be used in the negative electrode mixture layer can also be used in the positive electrode mixture layer.

[0064] The positive electrode material mixture layer may further contain a conductive agent. As the conductive agent, the materials described in the first embodiment as conductive agents usable in the negative electrode material mixture layer can also be used in the positive electrode material mixture layer.

[0065] The negative electrode 23 includes a material having the property of absorbing and releasing metal ions (for example, lithium ions). The negative electrode 23 is the negative electrode 10 according to the first embodiment.

[0066] 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 / L or more and 2 mol / L or less. By controlling the lithium salt concentration within the above range, an electrolyte solution having excellent ionic conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0067] The non-aqueous solvent may be a cyclic carbonate, a chain carbonate, a cyclic ether, a chain ether, a nitrile, an amide, etc. One selected from these solvents may be used, or two or more may be used in combination.

[0068] Examples of lithium salts that can be used include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. One selected from these electrolyte salts may be used, or two or more may be used in combination.

[0069] It is usually desirable to interpose a separator between the positive electrode and the negative electrode. The separator 22 has high ion permeability and adequate mechanical strength and insulating properties. The separator 22 can be made of a microporous thin film, a woven fabric, a nonwoven fabric, or the like. The separator 22 can be made of a polymer, for example. The polymer can be a polyolefin such as polypropylene or polyethylene.

[0070] In the battery according to the second embodiment, the electrolyte may be impregnated into a polymer provided as a separator, for example, i.e., the battery according to the second embodiment may have a structure in which the electrolyte and the polymer are used in combination.

[0071] The battery according to the second embodiment may further include a solid electrolyte as the electrolyte. That is, the battery according to the present disclosure may have a hybrid structure in which an electrolytic solution and a solid electrolyte are used in combination. Examples of solid electrolyte materials include halide solid electrolytes, sulfide solid electrolytes, oxide solid electrolytes, and organic polymer solid electrolytes. In the present disclosure, the term "halide solid electrolyte" refers to a solid electrolyte containing a halogen element as the main component of the anions. The term "sulfide solid electrolyte" refers to a solid electrolyte containing sulfur as the main component of the anions. The term "oxide solid electrolyte" refers to a solid electrolyte containing oxygen as the main component of the anions. The term "main component of the anions" refers to the anion with the largest mass among all the anions constituting the solid electrolyte.

[0072] As an example of the structure of the battery according to the second embodiment, the configuration example shown in FIG. 2 is described, i.e., a cylindrical nonaqueous electrolyte secondary battery in which a wound electrode group formed by winding a positive electrode and a negative electrode with a separator interposed therebetween and an electrolyte solution are housed in an outer casing. However, the battery according to the present disclosure is not limited to this configuration example. The battery according to the second embodiment may have any shape, such as a prismatic shape, a coin shape, a button shape, or a laminate shape. Furthermore, instead of the wound electrode group in the battery according to the second embodiment, an electrode group of another shape, such as an electrode group formed by stacking a positive electrode and a negative electrode with a separator interposed therebetween, may be used.

[0073] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0074] (Technology 1) A negative electrode including a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, wherein the negative electrode mixture layer includes a first negative electrode mixture layer including a surface of the negative electrode, and a second negative electrode mixture layer located between the first negative electrode mixture layer and the negative electrode current collector, and when the negative electrode active material contained in the first negative electrode mixture layer is defined as a first negative electrode active material and the negative electrode active material contained in the second negative electrode mixture layer is defined as a second negative electrode active material, the second negative electrode active material has an average interplanar spacing d of (002) planes measured by X-ray diffraction. 002a mass ratio of the carbon material in the second negative electrode active material is greater than a mass ratio of the carbon material in the first negative electrode active material, and at least one selected from the group consisting of the first negative electrode active material and the second negative electrode active material contains the carbon material and graphite.

[0075] With this configuration, the negative electrode according to Technology 1 can improve the charge capacity per unit time during rapid charging.

[0076] (Technology 2) The negative electrode according to Technology 1, wherein the carbon material contains non-graphitizable carbon.

[0077] With this configuration, the negative electrode according to Technology 2 can more effectively improve the charge capacity per unit time during rapid charging.

[0078] (Technology 3) The negative electrode according to Technology 1 or 2, wherein the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material.

[0079] By including a silicon-containing material as the negative electrode active material, the negative electrode according to Technology 3 can realize a further increase in the capacity of the battery.

[0080] (Technology 4) The negative electrode according to Technology 3, wherein the particle volume expansion coefficient V1 of the silicon-containing material satisfies 1.3≦V1<2.2. Here, the particle volume expansion coefficient V1 of the silicon-containing material is the ratio of the particle volume of the silicon-containing material in a charged state to the particle volume of the silicon-containing material in a discharged state.

[0081] This configuration effectively prevents capacity degradation caused by isolation of the negative electrode active material due to volume changes of the silicon-containing material accompanying charge and discharge.

[0082] (Technology 5) The negative electrode according to any one of Technologies 1 to 4, wherein, when a thickness of the first negative electrode mixture layer is X and a thickness of the negative electrode mixture layer is Y, X and Y satisfy 0.5Y≦X.

[0083] With this configuration, the negative electrode according to Technique 5 can further improve the charge capacity per unit time during rapid charging.

[0084] (Technology 6) The negative electrode according to Technology 5, wherein the X and the Y satisfy 0.5Y≦X≦0.9Y.

[0085] With this configuration, the negative electrode according to Technique 6 can further improve the charge capacity per unit time during rapid charging.

[0086] (Technology 7) The negative electrode according to any one of Technologies 1 to 6, wherein the first negative electrode active material does not contain the carbon material.

[0087] With this configuration, the negative electrode according to Technique 7 can further improve the charge capacity per unit time during rapid charging.

[0088] (Technology 8) The negative electrode according to any one of Technologies 1 to 7, wherein in the second negative electrode active material, a mass ratio of the carbon material to a total mass of the carbon material and graphite is more than 0 mass% and less than 80 mass%.

[0089] With this configuration, the negative electrode according to Technology 8 can further improve the charge capacity per unit time during rapid charging.

[0090] (Technology 9) The negative electrode according to Technology 8, wherein the mass ratio of the carbon material is 20 mass % or more and 60 mass % or less.

[0091] With this configuration, the negative electrode according to Technology 9 can further improve the charge capacity per unit time during rapid charging.

[0092] (Technology 10) A battery comprising: the negative electrode according to any one of Technologies 1 to 9; a positive electrode; and an electrolyte.

[0093] With this configuration, the battery according to Technique 10 can improve the charge capacity per unit time during rapid charging.

[0094] The present disclosure will be described in more detail below using examples. The following examples are merely examples of embodiments, and are not intended to limit the scope of the present disclosure.

[0095] [Examples 1 to 11, Comparative Examples 1 to 6] (Preparation of Positive Electrode Active Material) [Ni 0.88Co 0.09 Al 0.03 ] (OH)2 was calcined at 500°C for 8 hours to form an oxide (Ni 0.88 Co 0.09 Al 0.03 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 placed under an oxygen stream (10 cm) with an oxygen concentration of 95%. 3 The mixture was heated from room temperature to 650°C at a rate of 2.0°C / min, and then heated from 650°C to 780°C at a rate of 0.5°C / min to obtain LiNi. 0.88 Co 0.09 Al 0.03 A lithium-containing composite oxide represented by O2 was obtained.

[0096] (Preparation of Positive Electrode) The 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, and the coating was dried and compressed. The positive electrode current collector was then cut to a predetermined electrode size to obtain a positive electrode in which a positive electrode mixture layer was disposed on both sides of the positive electrode current collector. An exposed portion was provided in part of the positive electrode, exposing the surface of the positive electrode current collector.

[0097] (Preparation of negative electrode active material) A carbon active material and a silicon-containing material were prepared as negative electrode active materials. Non-graphitizable carbon and graphite were prepared as carbon active materials. The non-graphitizable carbon had an average interplanar spacing d of (002) plane measured by X-ray diffraction. 002 The silicon-containing material was prepared as a carbon material having a particle size of 0.34 nm or more.

[0098] (Preparation of Silicon-Containing Material) Tetraethylorthosilicate (TEOS) and cetyltrimethylammonium bromide (CTAB) were mixed in an ethanol / water / ammonia mixed solution to prepare CTAB-modified SiO nanoparticles. Resorcinol, formaldehyde, and a surfactant (Pluronic F-127) were added to the mixture and polymerized to obtain polymer particles encapsulating the aforementioned SiO nanoparticles. The molar ratio of surfactant to resorcinol (surfactant / resorcinol) was set to 0.005, and the mass ratio of resorcinol to TEOS (resorcinol / TEOS) was set to approximately 0.5 / 1. After drying, the polymer particles were carbonized at 800°C in a nitrogen atmosphere, mixed with magnesium powder, and heated at 650°C in an argon atmosphere to undergo a magnesium thermal reduction reaction. MgO was dissolved from the particles after the reaction in a mixed solution of HCl / H2O / ethanol, and the particles were washed with ethanol and then dried to produce a mesoporous silicon-containing material containing Si and C and having an average particle size of 8 μm.

[0099] (Preparation of first negative electrode active material) A carbon active material and a silicon-containing material were mixed in a mass ratio of carbon active material:silicon-containing material = 95:5, and this was used as the first negative electrode active material of the first negative electrode mixture layer. The carbon active material was a mixture of non-graphitizable carbon and graphite in the mass ratio shown in Table 1. In Table 1, non-graphitizable carbon is represented as "HC".

[0100] (Preparation of second negative electrode active material) A carbon active material and a silicon-containing material were mixed in a mass ratio of carbon active material:silicon-containing material = 95:5, and this was used as the first negative electrode active material of the first negative electrode mixture layer. The carbon active material was a mixture of non-graphitizable carbon and graphite in the mass ratio shown in Table 1.

[0101] (Preparation of Negative Electrode) 100 parts by mass of the first negative electrode active material, 1 part by mass of styrene butadiene rubber (SBR), and 1 part by mass of carboxymethyl cellulose (CMC) were mixed, and an appropriate amount of water was added to prepare a negative electrode mixture slurry for the first negative electrode mixture layer.

[0102] A negative electrode mixture slurry for the second negative electrode mixture layer was prepared by mixing 100 parts by mass of the second negative electrode active material, 1 part by mass of styrene butadiene rubber (SBR), and 1 part by mass of carboxymethyl cellulose (CMC), and adding an appropriate amount of water.

[0103] Next, the prepared anode mixture slurry for the second anode mixture layer was applied to both sides of a copper foil anode current collector, and the coating was dried and compressed to form a second anode mixture layer. Furthermore, the prepared anode mixture slurry for the first anode mixture layer was applied to the second anode mixture layer, and the coating was dried to form a first anode mixture layer. At this time, the coating mass ratio of the slurry for the first anode mixture layer to the slurry for the second anode mixture layer was such that, when the total coating mass of the slurry for the first anode mixture layer and the slurry for the second anode mixture layer was taken as 1, the slurry for the first anode mixture layer was applied to the coating mass ratio shown in Table 1. The prepared anode had a two-layer structure including a lower layer (second anode mixture layer) and an upper layer (first anode mixture layer) on both sides of the anode current collector, and the thickness of the anode mixture layer was 100 μm on each side. An exposed portion in which the surface of the negative electrode current collector was exposed was provided in a part of the negative electrode. The coating mass ratio of the slurry for the first negative electrode mixture layer to the slurry for the second negative electrode mixture layer represents the thickness ratio between the first negative electrode mixture layer and the second negative electrode mixture layer. That is, for example, in Example 1, the coating mass ratio of the slurry for the first negative electrode mixture layer was 0.5, so the thickness ratio between the first negative electrode mixture layer and the second negative electrode mixture layer was 1:1. That is, in Example 1, the thickness X of the first negative electrode mixture layer was X = 0.5Y.

[0104] (Preparation of non-aqueous electrolyte (electrolyte solution)) A non-aqueous electrolyte solution was prepared by dissolving LiPF at a concentration of 1.2 mol / L in a mixed solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio (25°C) of EC:EMC:DMC = 3:3:4.

[0105] (Preparation of Test Cell (Secondary Battery)) An aluminum lead was attached to the exposed portion of the positive electrode, and a nickel lead was attached to the exposed portion of the negative electrode. The positive and negative electrodes were spirally wound with a polyolefin separator between them to prepare a wound electrode body. Insulating plates were placed on the top and bottom of the electrode body, and the electrode body was housed in an outer can. The negative electrode lead was welded to the bottom of a cylindrical outer can with a bottom, and the positive electrode lead was welded to a sealing member. An electrolyte was poured into the outer can, and the opening of the outer can was sealed with a sealing member via a gasket to prepare a secondary battery as a test cell.

[0106] [Evaluation of Rapid Charging] The test cells of each example and comparative example were charged at a constant current of 5 C in a temperature environment of 25°C until the battery voltage reached 4.2 V, and then switched to constant voltage charging and charged until the specified capacity was reached, i.e., until the fully charged state (SOC (State of Charge) 100%) was reached. The charge capacity per unit time was calculated using the charge time and charge capacity from SOC 10 to 90%. Table 1 shows the charge time, charge capacity, and charge capacity per unit time. Note that Table 1 shows the relative values ​​for the charge time, charge capacity, and charge capacity per unit time, with the result of Comparative Example 1 set as the reference (100%).

[0107] [Measurement of particle volume expansion coefficient of silicon-containing material] For the negative electrode of Example 1, the particle volume expansion coefficient of the silicon-containing material 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 produced using the produced negative electrode, and the particle volume expansion coefficient of the silicon-containing material was determined using this single-electrode cell. The particle volume expansion coefficient of the silicon-containing material was 1.8. Note that the silicon-containing materials used in Examples 2 to 10 and Comparative Examples 1 to 6 were produced using the same method as the silicon-containing material of Example 1, and are therefore considered to have the same particle volume expansion coefficient.

[0108]

[0109] (Discussion) As shown in Table 1, the test cells of Examples 1 to 11 all had improved charge capacities per unit time during fast charging compared to the test cells of Comparative Examples 1 to 6. That is, the average interplanar spacing d 002 a negative electrode satisfying a configuration in which the negative electrode contains a carbon material having a particle size of 0.34 nm or more, the mass proportion of the carbon material in the second negative electrode active material is greater than the mass proportion of the carbon material in the first negative electrode active material, and at least one selected from the group consisting of the first negative electrode active material and the second negative electrode active material contains the carbon material and graphite, was able to improve the charge capacity per unit time during fast charging compared to conventional negative electrodes that did not satisfy this configuration.

[0110] From the results of Examples 1 and 5-7, it was confirmed that when the thickness of the first negative electrode mixture layer is X and the thickness of the negative electrode mixture layer is Y, if X and Y satisfy 0.5Y≦X≦0.9Y, the charge capacity per unit time in rapid charging is further improved, and the capacity is also improved.

[0111] From the results of Examples 1 and 3, it was confirmed that the charge capacity per unit time during rapid charging was further improved and the capacity was also improved when the first negative electrode active material did not contain the carbon material.

[0112] From the results of Examples 3, 8-11 and Comparative Example 6, it was confirmed that when the mass ratio of the carbon material to the total mass of the carbon material and graphite in the second negative electrode active material is less than 80 mass%, particularly when it is 20 mass% or more and 60 mass% or less, the charge capacity per unit time during rapid charging is further improved.

[0113] The technology of the present disclosure is useful for batteries such as lithium-ion secondary batteries that require rapid charging.

Claims

1. A negative electrode comprising: a negative electrode current collector; and a negative electrode mixture layer disposed on the negative electrode current collector, wherein the negative electrode mixture layer includes a first negative electrode mixture layer including a surface of the negative electrode, and a second negative electrode mixture layer located between the first negative electrode mixture layer and the negative electrode current collector, and when the negative electrode active material contained in the first negative electrode mixture layer is defined as a first negative electrode active material and the negative electrode active material contained in the second negative electrode mixture layer is defined as a second negative electrode active material, the second negative electrode active material has an average interplanar spacing d of (002) planes measured by X-ray diffraction. 002 a mass ratio of the carbon material in the second negative electrode active material is greater than a mass ratio of the carbon material in the first negative electrode active material, and at least one selected from the group consisting of the first negative electrode active material and the second negative electrode active material contains the carbon material and graphite.

2. The negative electrode according to claim 1, wherein the carbon material includes non-graphitizable carbon.

3. The negative electrode according to claim 1, wherein the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material.

4. The negative electrode according to claim 3, wherein the particle volume expansion coefficient V1 of the silicon-containing material satisfies 1.3≦V1<2.2, wherein the particle volume expansion coefficient V1 of the silicon-containing material is the ratio of the particle volume of the silicon-containing material in a charged state to the particle volume of the silicon-containing material in a discharged state.

5. The negative electrode according to claim 1, wherein when the thickness of the first negative electrode mixture layer is X and the thickness of the negative electrode mixture layer is Y, X and Y satisfy 0.5Y≦X.

6. The negative electrode according to claim 5, wherein X and Y satisfy the relationship 0.5Y≦X≦0.9Y.

7. The negative electrode according to claim 1, wherein the first negative electrode active material does not include the carbon material.

8. The negative electrode according to claim 1, wherein in the second negative electrode active material, the mass ratio of the carbon material to the total mass of the carbon material and graphite is greater than 0 mass % and less than 80 mass %.

9. The negative electrode according to claim 8, wherein the mass ratio of the carbon material is 20 mass % or more and 60 mass % or less.

10. A battery comprising: a negative electrode according to any one of claims 1 to 9; a positive electrode; and an electrolyte.

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