WO2025225584A1 - Negative electrode and battery - Google Patents

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

This disclosure relates to negative electrodes and batteries.

In recent years, secondary batteries such as lithium-ion batteries have been widely used in applications requiring high capacity, such as automotive and power storage. The electrodes that make up such batteries have a significant impact on their performance. For this reason, various studies have been conducted on electrodes.

Conventionally, lithium-ion secondary batteries have used carbon materials, for example, as the negative electrode active material. However, with such lithium-ion secondary batteries, repeated charging at a high load rate to shorten charging time can cause lithium to precipitate on the negative electrode surface. Therefore, Patent Document 1 proposes a negative electrode that does not undergo lithium precipitation even when repeatedly charged at a high load rate. The negative electrode consists of a first layer provided on a conductive substrate and a second layer provided on the first layer, with 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.

Japanese Patent Application Laid-Open No. 2008-59999

The negative electrode proposed in Patent Document 1 can suppress lithium deposition during charging at a high load rate, but it has the problem of slowing down the rapid charge time to the specified capacity, i.e., increasing the charge time.

This disclosure provides a negative electrode that can improve charge capacity per unit time during rapid charging.

The negative electrode of the present disclosure comprises:
a negative electrode current collector;
a negative electrode mixture layer disposed on the negative electrode current collector;
A negative electrode comprising:
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,
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 includes a carbon material having an average interplanar spacing d ₀₀₂ of (002) planes of 0.34 nm or more as measured by X-ray diffraction;
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,
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.

This disclosure makes it possible to provide a negative electrode that can improve the charge capacity per unit time during rapid charging.

FIG. 1 is a cross-sectional view showing a schematic configuration of a negative electrode according to the first embodiment. FIG. 2 is a longitudinal sectional view schematically illustrating an example of a battery according to the second embodiment.

[Findings that form the basis of this disclosure]
The present inventors have investigated a negative electrode containing a carbon material as an active material. The negative electrode disclosed in Patent Document 1 uses a non-graphitizable carbon, which has high lithium ion acceptability, as the negative electrode active material in the second layer located on the surface side of the negative electrode. This configuration allows the negative electrode disclosed in Patent Document 1 to suppress lithium deposition during high-load rate charging. However, the inventors' investigations have revealed that the negative electrode 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, resulting in a deterioration in the rapid charge time to the specified capacity, i.e., an increase in the charging time during rapid charging. According to the inventors' investigations, the negative electrode 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 negative electrode during the latter half of charging, preventing the passage of large currents. 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.

Based on the above findings, the inventors conducted further intensive research and reconsidered the configuration of the negative electrode, discovering a new negative electrode that can improve the charge capacity per unit time during fast charging. Below, we will explain the negative electrode of the present disclosure that can improve the charge capacity per unit time during fast charging.

[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.

(Embodiment 1)
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 includes a carbon material having an average interplanar spacing d ₀₀₂ of (002) planes of 0.34 nm or more as measured by X-ray diffraction, and 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. 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 above carbon material and graphite.

Here, the average interplanar spacing d ₀₀₂ of the (002) plane in the carbon material 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 radiation.

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

Here, the fact that 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.

The nonaqueous electrolyte secondary battery at the end of discharge 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 map the peak intensity ratio between the G band near 1580 cm ⁻¹ and the D band near 1360 cm ⁻¹ . Particles with an R value (R = I1360/I1580) represented by 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. 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. In this case, the area ratio of the carbon material of embodiment 1 is larger in negative electrode mixture layers with a larger mass proportion of the carbon material of embodiment 1.

Furthermore, the mass proportion of the carbon material of embodiment 1 in each negative electrode mixture layer can be determined by multiplying the above-mentioned area ratio of the carbon material of embodiment 1 determined by the above-mentioned method by the value of the true density of the carbon material of embodiment 1. Similarly, the mass proportion of graphite in each negative electrode mixture layer can be determined by multiplying the above-mentioned 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 second negative electrode mixture layer 14 by the above-mentioned method, and using these mass proportions.

Note that the negative electrode mixture layer 12 may contain a carbon material 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.

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 of embodiment 1 and graphite. That is, a nonaqueous electrolyte secondary battery in an end-of-discharge state is disassembled to remove the negative electrode, which is then washed with dimethyl carbonate and vacuum dried. A cross section of the negative electrode is cut out using a cross-section polisher or the like, and a Raman scattering spectrum is measured to map the peak intensity ratio between the G band near 1580 cm ⁻¹ and the D band near 1360 cm ⁻¹ . Particles with an R value (R=I1360/I1580), expressed as the peak intensity ratio between the G band and the D band, of less than 0.8 are considered to be graphite, and particles with an R value of 0.8 or greater are considered to be the carbon material of embodiment 1, and the presence of the carbon material of embodiment 1 and graphite 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.

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

Furthermore, in the negative electrode 10 of 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 of embodiment 1 does not include a configuration in which the second negative electrode active material consists 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, consists 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 consists solely of the carbon material of embodiment 1 and the first negative electrode active material consists 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 deteriorates, and the internal resistance of the battery increases. However, 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 both the carbon material of embodiment 1 and graphite, thereby preventing a deterioration in the lithium ion acceptability of the first negative electrode mixture layer 13 and an increase in the internal resistance of the battery. Furthermore, since the inclusion of graphite as a negative electrode active material prevents a significant decrease in capacity, the negative electrode 10 according to embodiment 1 can also maintain a certain level of capacity.

As described above, the anode 10 according to embodiment 1 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 embodiment 1 can maintain the capacity.

The carbon material of embodiment 1 includes, 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 embodiment 1 may be non-graphitizable carbon.

Note that while the negative electrode mixture layer 12 shown in FIG. 1 is composed of two layers, a first negative electrode mixture layer 13 and a second negative electrode mixture layer 14, it is not limited to this and may be composed of three or more layers. The negative electrode mixture layer 12 may further include a layer located between the first negative electrode mixture layer 13 and the second negative electrode mixture layer 14, or between the second negative electrode mixture layer 14 and the negative electrode current collector 11.

The first anode mixture layer 13 and the second anode mixture layer 14 can be distinguished by differences in their constituent components and composition ratios. 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 that has the above-described structural relationship with the first anode mixture layer 13.

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

The following describes in detail each component of the negative electrode 10 of embodiment 1.

[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.

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 of the negative electrode 10.

[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 .

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, for example, satisfy the relationship 0.5Y≦X. In other words, the thickness of the first anode mixture layer 13 may account for half or more of the overall thickness of the anode mixture layers. 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 its capacity.

Furthermore, X and Y may satisfy the relationship 0.5Y≦X≦0.9Y. With this configuration, the negative electrode 10 of embodiment 1 can more effectively improve the charge capacity per unit time and also improve the capacity.

In this specification, the thickness (Y) of the negative electrode mixture layer 12 and the thickness (X) of the first negative electrode mixture layer 13 are measured by the following method.
(1) The battery to be evaluated is disassembled, and the negative electrode is cut out. A single-electrode cell is fabricated using metallic Li as the counter electrode and an ionic liquid as the 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 the 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 thicknesses of the anode mixture layer 12 and the first anode mixture layer 13 are measured at five arbitrary locations, and the thickness is calculated as the average value of the five measured values.

The first negative electrode active material does not have to 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, does not have to contain the carbon material of embodiment 1, such as non-graphitizable carbon, as the negative electrode active material. 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. Furthermore, with this configuration, the negative electrode 10 of embodiment 1 can also improve its capacity.

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 greater 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.

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.

Note that 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.

In the first embodiment, carbon material and graphite were 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. However, 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, it is possible to achieve even higher battery capacity.

In this specification, silicon-containing materials refer to materials that contain Si. Examples of silicon-containing materials include Si, Si alloys, Si compounds, and composite materials containing Si.

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 refers to the particle size at which the volume cumulative value is 50% in the particle size distribution measured by laser diffraction scattering (hereinafter referred to as "volume-based D50"). The measurement is performed using, for example, an "MT3000II" manufactured by Microtrac Bell Co., Ltd. as a measuring device, and using, for example, water as the dispersion medium.

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 phase 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 particles of Si dispersed within the ion-conducting phase. In a composite material containing Si, the stress associated with the expansion and contraction of the Si phase during charge and discharge is alleviated by the ion-conducting phase, thereby suppressing cracking and fracture in the composite material. Therefore, a composite material containing Si can achieve both high capacity due to the inclusion of Si and improved charge and discharge cycle characteristics.

The particle volume expansion coefficient V1 of the silicon-containing material may, for example, satisfy the relationship 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 associated with charging and discharging can be effectively suppressed.

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.

In this specification, the particle volume expansion coefficient of the silicon-containing material is measured by the following method.
(1) The battery to be evaluated is disassembled, and the negative electrode is cut out. A single-electrode cell is fabricated using metallic Li as the counter electrode and an ionic liquid as the electrolyte, with the particle cross-section of the silicon-containing material exposed.
(2) The monopolar cell is charged at 0.002 C in a temperature environment of 25°C 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) Regarding the particle volume expansion coefficient of the silicon-containing material, 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) 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 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 particles 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 defined as the particle volume expansion coefficient V1 of the silicon-containing material.

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 alternatively 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 for the content of the silicon-containing material is, for example, 5 mass% or more and 35 mass% or less, or alternatively 10 mass% or more and 30 mass% or less, or alternatively 5 mass% or more and 15 mass% or less, of the total mass of the negative electrode active material.

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), etc.

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

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

Figure 2 is a longitudinal cross-sectional view schematically illustrating an example of a battery according to embodiment 2. 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.

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 that the battery case is airtight. Inside 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.

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

The 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 the sealing body 26. The sealing body 26 is attached to the opening of the case body 25 so 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.

Each of the above components constituting the sealing body 26 is, for example, disk-shaped or ring-shaped. The above components are electrically connected to each other, except for the insulating member 34.

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 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.

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.

The positive electrode 21 is electrically connected to the cap 36, which also serves as the positive electrode terminal, via the 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 of the positive electrode 21. 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 surface of the filter 32 facing the electrode group 24.

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

The following describes each component of the battery 100 in detail.

The positive electrode 21 contains a material capable of absorbing and releasing metal ions (e.g., lithium ions). The positive electrode 21 contains, 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.

The positive electrode current collector can be a sheet or film made of a metal material such as aluminum, stainless steel, titanium, or an alloy of these. Aluminum and its alloys are inexpensive and easy to form into thin films, making them suitable materials for the positive electrode current collector. 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 applied to the surface of the positive electrode current collector as an auxiliary conductive material.

The positive electrode mixture layer contains 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). Possible positive electrode active materials 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 lithium-containing transition metal phosphate as the positive electrode active material can reduce battery manufacturing costs and increase the 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.

The positive electrode mixture layer may further contain a binder. The materials described in embodiment 1 as binders that can be used in the negative electrode mixture layer can also be used in the positive electrode mixture layer.

The positive electrode mixture layer may further contain a conductive agent. The materials described in embodiment 1 as conductive agents that can be used in the negative electrode mixture layer can also be used in the positive electrode mixture layer.

The negative electrode 23 contains a material capable of absorbing and releasing metal ions (e.g., lithium ions). The negative electrode 23 is the negative electrode 10 according to embodiment 1.

The electrolytic 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 electrolytic 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 electrolytic solution with excellent ionic conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

Cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, nitriles, amides, etc. may be used as non-aqueous solvents. One of these solvents may be used, or two or more may be used in combination.

Examples of lithium salts that can be used include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO ₂ C ₂ F ₅ ) ₂ ), LiAsF ₆ , LiCF ₃ SO ₃ , and lithium difluoro(oxalato)borate. One or more of these electrolyte salts may be used alone or in combination.

It is usually desirable to interpose a separator between the positive electrode and negative electrode. The separator 22 has high ion permeability and adequate mechanical strength and insulation properties. The separator 22 can be made of a microporous thin film, woven fabric, 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.

In the battery according to embodiment 2, the electrolyte may be impregnated into a polymer provided as a separator, for example. In other words, the battery according to embodiment 2 may have a structure in which both the electrolyte and the polymer are used.

The battery according to embodiment 2 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 this disclosure, "halide solid electrolyte" refers to a solid electrolyte containing a halogen element as the main anion component. "sulfide solid electrolyte" refers to a solid electrolyte containing sulfur as the main anion component. "Oxide solid electrolyte" refers to a solid electrolyte containing oxygen as the main anion component. The "main anion component" refers to the anion with the largest mass among all the anions constituting the solid electrolyte.

As an example of the structure of the battery according to embodiment 2, the configuration example shown in FIG. 2 is described, namely, a cylindrical non-aqueous 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 embodiment 2 may be in any form, such as a prismatic, coin, button, or laminate type. Furthermore, instead of a wound electrode group in the battery according to embodiment 2, an electrode group of another form, such as an electrode group formed by stacking a positive electrode and a negative electrode with a separator interposed therebetween, may be used.

(Other embodiments)
(Additional Note)
The above description of the embodiments discloses the following techniques.

(Technology 1)
a negative electrode current collector;
a negative electrode mixture layer disposed on the negative electrode current collector;
A negative electrode comprising:
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,
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 includes a carbon material having an average interplanar spacing d ₀₀₂ of (002) planes of 0.34 nm or more as measured by X-ray diffraction;
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,
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.
Negative electrode.

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

(Technology 2)
The carbon material includes non-graphitizable carbon.
The negative electrode according to Technology 1.

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

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

By including a silicon-containing material as the negative electrode active material, the negative electrode according to Technology 3 can achieve even higher battery capacity.

(Technology 4)
The particle volume expansion coefficient V1 of the silicon-containing material satisfies 1.3≦V1<2.2;
The negative electrode according to technology 3.
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.

This configuration effectively prevents capacity degradation caused by isolation of the negative electrode active material due to volume changes that occur during charging and discharging of the silicon-containing material.

(Technique 5)
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.
The negative electrode according to any one of techniques 1 to 4.

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

(Technology 6)
The X and Y satisfy 0.5Y≦X≦0.9Y.
The negative electrode according to technology 5.

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

(Technology 7)
the first negative electrode active material does not contain the carbon material;
The negative electrode according to any one of techniques 1 to 6.

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

(Technology 8)
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 greater than 0 mass% and less than 80 mass%.
The negative electrode according to any one of techniques 1 to 7.

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

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

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

(Technology 10)
The negative electrode according to any one of techniques 1 to 9,
A positive electrode and
Electrolytes,
A battery equipped with

This configuration enables the battery according to Technology 10 to improve the charge capacity per unit time during rapid charging.

The present disclosure will now be described in more detail using examples. The following examples are merely examples of one embodiment and are not intended to be limiting.

[Examples 1 to 11, Comparative Examples 1 to 6]
(Preparation of Positive Electrode Active Material)
The composite _hydroxide represented by [ _{Ni0.88Co0.09Al0.03 ]} (OH) ₂ obtained by the _{coprecipitation} method was calcined _at 500°C for 8 hours to obtain an oxide ( _{Ni0.88Co0.09Al0.03O2 )} . 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 calcined from room temperature to 650°C at a heating rate of 2.0°C/min under an oxygen stream with an oxygen concentration of 95% (flow rate of 2 mL/min per ¹⁰ cm3 and 5 L/min per kg of the mixture), and then calcined at a heating rate of 0.5°C/min from 650°C to ₇₈₀ °C to obtain a lithium _- containing composite oxide represented by _{LiNi0.88Co0.09Al0.03O2 .}

(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, 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 a positive electrode mixture layer was disposed on both sides of the positive electrode current collector. Note that an exposed portion was provided in part of the positive electrode, exposing the surface of the positive electrode current collector.

(Preparation of negative electrode active material)
As the negative electrode active materials, a carbon active material and a silicon-containing material were prepared. As the carbon active materials, non-graphitizable carbon and graphite were prepared. The non-graphitizable carbon was prepared as a carbon material having an average interplanar spacing d ₀₀₂ of the (002) plane of 0.34 nm or more as measured by X-ray diffraction. The silicon-containing material was produced by the following method.

(Preparation of silicon-containing materials)
Tetraethylorthosilane (TEOS) and cetyltrimethylammonium bromide (CTAB) were mixed in an ethanol/water/ammonia mixture 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 0.005, and the mass ratio of resorcinol to TEOS (resorcinol/TEOS) was approximately 0.5/1. The polymer particles were dried and then carbonized at 800°C in a nitrogen atmosphere. They were then 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/H ₂ O/ethanol, and the particles were washed with ethanol and then dried to prepare a mesoporous silicon-containing material containing Si and C and having an average particle size of 8 μm.

(Preparation of First Negative Electrode Active Material)
The carbon active material and the 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."

(Preparation of Second Negative Electrode Active Material)
The carbon active material and the 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.

(Preparation of negative electrode)
A negative electrode mixture slurry for the first negative electrode mixture layer was prepared by mixing 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), and adding an appropriate amount of water.

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) were mixed, and an appropriate amount of water was added to prepare a negative electrode mixture slurry for the second negative electrode mixture layer.

Next, the prepared anode mix slurry for the second anode mix 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 mix layer. Furthermore, the prepared anode mix slurry for the first anode mix layer was applied onto the second anode mix layer, and the coating was dried to form a first anode mix layer. The coating mass ratio of the slurry for the first anode mix layer to the slurry for the second anode mix layer was set to 1, with the slurry for the first anode mix layer being applied at the coating mass ratio shown in Table 1. The prepared anode had a two-layer structure including a lower layer (second anode mix layer) and an upper layer (first anode mix layer) on both sides of the anode current collector, and the thickness of the anode mix layer was 100 μm on each side. An exposed portion was provided on a portion of the negative electrode, exposing the surface of the negative electrode current collector. 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. 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. In Example 1, the thickness X of the first negative electrode mixture layer was X = 0.5Y.

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

(Preparation of test cells (secondary batteries))
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 then spirally wound with a polyolefin separator between them to produce a wound electrode assembly. Insulating plates were placed on the top and bottom of the electrode assembly, and the electrode assembly 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 produce a secondary battery as a test cell.

[Evaluation of fast 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 charge time, charge capacity, and charge capacity per unit time relative to the result of Comparative Example 1 (100%).

[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 fabricated using the fabricated negative electrode, and the particle volume expansion coefficient of the silicon-containing material was determined using the 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 fabricated using the same method as the silicon-containing material of Example 1, and are therefore considered to have the same particle volume expansion coefficient.

(Consideration)
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, a negative electrode satisfying a configuration in which the second negative electrode active material contains a carbon material having an average interplanar spacing d ₀₀₂ of the (002) plane of 0.34 nm or more as measured by X-ray diffraction, 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 a conventional negative electrode that did not satisfy this configuration.

The results of Examples 1 and 5-7 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 the relationship 0.5Y≦X≦0.9Y, the charge capacity per unit time during rapid charging is further improved, and the capacity is also improved.

The results of Examples 1 and 3 confirmed that when the first negative electrode active material does not contain the above-mentioned carbon material, the charge capacity per unit time during rapid charging is further improved, and the capacity is also improved.

The results of Examples 3, 8-11, and Comparative Example 6 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.

The technology disclosed herein is useful for batteries such as lithium-ion secondary batteries that require rapid charging.

Claims (10)

a negative electrode current collector;
a negative electrode mixture layer disposed on the negative electrode current collector;
A negative electrode comprising:
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,
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 includes a carbon material having an average interplanar spacing d ₀₀₂ of (002) planes of 0.34 nm or more as measured by X-ray diffraction;
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,
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.
Negative electrode. The carbon material includes non-graphitizable carbon.
The negative electrode according to claim 1 . the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material,
The negative electrode according to claim 1 . The particle volume expansion coefficient V1 of the silicon-containing material satisfies 1.3≦V1<2.2;
The negative electrode according to claim 3 .
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. 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.
The negative electrode according to claim 1 . The X and Y satisfy 0.5Y≦X≦0.9Y.
The negative electrode according to claim 5 . the first negative electrode active material does not contain the carbon material;
The negative electrode according to claim 1 . 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 greater than 0 mass% and less than 80 mass%.
The negative electrode according to claim 1 . The mass ratio of the carbon material is 20 mass% or more and 60 mass% or less.
The negative electrode according to claim 8 . The negative electrode according to any one of claims 1 to 9,
A positive electrode and
Electrolytes,
A battery equipped with