Negative electrode sheet, battery, battery pack, and electric device

Abstract

Provided in the present application are a negative electrode sheet, a battery, a battery pack, and an electric device. The negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer, wherein the negative electrode material layer comprises a second active material layer and a first active material layer arranged between the negative electrode current collector and the second active material layer; the material of the first active material layer comprises a first active carbon material; the material of the second active material layer comprises a second active carbon material; d1≥d2, P1<P2, and G1<G2, d1 and d2 being the thicknesses of the first active material layer and the second active material layer, with the unit thereof being μm, P1 and P2 being the porosities of the first active carbon material and the second active carbon material, and 1 / G1 and 1 / G2 being the graphitization degrees of the first active carbon material and the second active carbon material; and the negative electrode sheet meets at least one of the following conditions: (1) 0.18≤100×G1×P1 / d1≤0.68; and (2) 0.82≤100×G2×P2 / d2≤2.96.

Description

Negative electrode sheets, batteries, battery packs and electrical equipment

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 19, 2023, with application number 202311210057X and application name “Negative electrode sheet, battery, battery pack and electrical equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the field of battery technology, and specifically relates to negative electrode sheets, batteries, battery packs and electrical equipment. Background Art

[0003] With the continuous development of batteries, researchers have begun to pursue batteries with higher energy density and better cycle performance. As a key component of batteries, the anode plate plays an important role in improving battery performance. However, related technologies often focus on the selection of anode materials, with less research on the design of the overall structure of the anode plate, which has limited improvement in battery performance.

[0004] Summary of the Invention

[0005] In view of this, the present application provides a negative electrode plate, a battery, a battery pack and an electrical device. The negative electrode plate has good compaction density and dynamic performance, which can improve the energy density and cycle performance of the battery, and facilitate the use of the battery, battery pack and electrical equipment.

[0006] In a first aspect, the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode material layer disposed on the surface of the negative electrode current collector, wherein the negative electrode material layer comprises a first active material layer and a second active material layer stacked, wherein the first active material layer is disposed between the negative electrode current collector and the second active material layer, wherein the material of the first active material layer comprises a first activated carbon material, and the material of the second active material layer comprises a second activated carbon material, wherein the thickness of the first active material layer is d1, and the thickness of the second active material layer is d2, and d1 ≥ The units of d2, d1 and d2 are μm; the porosity of the first activated carbon material is P1, the porosity of the second activated carbon material is P2, and P1<P2; the degree of graphitization of the first activated carbon material is 1 / G1, and the degree of graphitization of the second activated carbon material is 1 / G2, and G1<G2; wherein, calculated based on the numerical values ​​of each parameter, the negative electrode plate satisfies at least one of the following conditions: (1) 0.18≤100×G1×P1 / d1≤0.68; (2) 0.82≤100×G2×P2 / d2≤2.96.

[0007] In a second aspect, the present application provides a battery comprising a positive electrode sheet and the negative electrode sheet described in the first aspect. The battery comprising the negative electrode sheet has excellent energy density, rate performance, and cycle performance, and is highly safe to use.

[0008] In a third aspect, the present application provides a battery pack comprising a housing and at least one battery according to the second aspect, wherein the battery is housed in the housing. The battery pack having the battery has excellent performance and is convenient for use.

[0009] In a fourth aspect, the present application provides an electrical device comprising the battery described in the second aspect or the battery pack described in the third aspect. Such a configuration is conducive to improving the product competitiveness and performance of the electrical device.

[0010] The first active material layer and the second active material layer in the negative electrode plate provided in the present application cooperate with each other, so that the negative electrode plate has excellent compaction density and kinetic performance, and can reduce the precipitation of active ions on the negative electrode surface during high-rate charging, thereby helping to improve the energy density, cycle rate and cycle life of the battery, while ensuring the safety of battery use. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0012] FIG1 is a schematic cross-sectional view of a negative electrode sheet provided in one embodiment of the present application. DETAILED DESCRIPTION

[0013] The following will clearly and completely describe the technical solution of this application in conjunction with the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0014] Please refer to Figure 1, which is a cross-sectional schematic diagram of a negative electrode plate provided in one embodiment of the present application. The negative electrode plate 100 includes a negative electrode current collector 10 and a negative electrode material layer 20 provided on the surface of the negative electrode current collector 10. The negative electrode material layer 20 includes a first active material layer 21 and a second active material layer 22 stacked together. The first active material layer 21 is provided between the negative electrode current collector 10 and the second active material layer 22. The material of the first active material layer 21 includes a first activated carbon material, and the material of the second active material layer 22 includes a second activated carbon material. The thickness of the first active material layer 21 is d1, and the thickness of the second active material layer 22 is d2. The thickness of the active material layer 22 is d2, d1≥d2, and the units of d1 and d2 are μm; the porosity of the first activated carbon material is P1, the porosity of the second activated carbon material is P2, P1<P2; the degree of graphitization of the first activated carbon material is 1 / G1, the degree of graphitization of the second activated carbon material is 1 / G2, G1<G2; wherein, calculated based on the numerical values ​​of each parameter, the negative electrode sheet 100 satisfies at least one of the following conditions: (1) 0.18≤100×G1×P1 / d1≤0.68; (2) 0.82≤100×G2×P2 / d2≤2.96.

[0015] In the negative electrode sheet, the thickness of the second active material layer is less than or equal to the thickness of the first active material layer, which is beneficial for the active ions (lithium ions, sodium ions, potassium ions, etc.) to pass through the second active material layer and enter the first active material layer in a shorter time during the charge and discharge process, thereby avoiding the precipitation of active ions on the surface of the second active material layer and improving the fast charging capability; the porosity of the first activated carbon material is less than that of the second activated carbon material, that is, the pores inside the first activated carbon material are relatively fewer, the internal graphite microcrystalline layers are tightly stacked, and the compaction density is relatively high, while the pores inside the second activated carbon material are relatively more and the compaction density is relatively low; the degree of graphitization of the first activated carbon material is greater than the degree of graphitization of the second activated carbon material, that is, the defects inside the first activated carbon material are relatively fewer, the degree of order of the formed graphite microcrystalline structure is relatively high, and the compaction density is relatively high, while the defects inside the second activated carbon material are relatively more, the degree of disorder of the formed graphite microcrystalline structure is relatively high, and the compaction density is relatively low. That is, the low porosity and high degree of graphitization of the first activated carbon material help to improve the compaction density, and it has fewer defects and low surface activity, which can improve the coulombic efficiency of the first cycle. It is easy to form a stable and dense solid electrolyte membrane (SEI membrane) during the cycle, which is beneficial to the improvement of the cycle performance; the high porosity and low degree of graphitization of the second activated carbon material help to quickly transport active ions in the second active material layer, reduce the transmission impedance, and increase the diffusion rate, so that the second active material layer has better kinetic properties. In the present application, the negative electrode plate satisfies at least one of the following conditions when calculated based on the numerical values ​​of each parameter (that is, calculated based on the numerical values ​​of d1 and d2): (1) 0.18≤100×G1×P1 / d1≤0.68; (2) 0.82≤100×G2×P2 / d2≤2.96; that is, the first active material layer satisfies 0.18≤100×G1×P1 / d1≤0.68, and / or the second active material layer satisfies 0.82≤100×G2×P2 / d2≤2.96. When the value of 100×G1×P1 / d1 is less than 0.18, the degree of graphitization of the first activated carbon material is relatively large, the porosity is relatively low and / or the thickness of the first active material layer is relatively large, which makes it relatively difficult for the negative electrode sheet to be infiltrated with the electrolyte, the ion transfer resistance increases, and the liquid phase transfer path of the active ions increases, resulting in increased polarization, thereby affecting the rate performance and cycle performance of the battery; when the value of 100×G1×P1 / d1 is greater than 0.68, the degree of graphitization of the first activated carbon material is relatively small, the porosity is relatively high and / or the thickness of the first active material layer is relatively small, which reduces the compaction density of the negative electrode sheet, thereby affecting the energy density of the battery; therefore, when the first active material layer satisfies 0.18≤100×G1×P1 / d1≤0.68, it helps to improve the compaction density of the negative electrode sheet, thereby improving the energy density and cycle performance of the battery, which is beneficial to its use.When the value of 100×G2×P2 / d2 is less than 0.82, the degree of graphitization of the second activated carbon material is too large, the porosity is too low and / or the thickness of the second active material layer is too large, which makes it relatively difficult for the negative electrode plate to be infiltrated with the electrolyte, increases the ion transport resistance, and increases the liquid phase transport path of the active ions, resulting in increased polarization, which reduces the kinetic performance of the second active material layer, and the active ions are easily accumulated on the surface of the second active material layer to precipitate dendrites, thereby affecting the rate performance, cycle performance and safety of the battery; when the value of 100×G2×P2 / d2 is greater than 2.96, the graphitization of the second activated carbon material is too large, and the porosity is too low and / or the thickness of the second active material layer is too large, which makes it relatively difficult for the negative electrode plate to be infiltrated with the electrolyte, increases the ion transport resistance, and increases the liquid phase transport path of the active ions, which leads to increased polarization, reduces the kinetic performance of the second active material layer, and easily accumulates on the surface of the second active material layer to precipitate dendrites, thereby affecting the rate performance, cycle performance and safety of the battery. The degree is too small, the porosity is too high, and / or the thickness of the second active material layer is too small, which increases the defects of the second activated carbon material, increases the surface activity, and increases the contact area with the electrolyte, thereby increasing the side reaction between the second activated carbon material and the electrolyte, causing the SEI film to continuously rupture and repair during the cycle, increasing the loss of active ions, and affecting the first-cycle coulomb efficiency and cycle life of the battery; therefore, when the second active material layer satisfies 0.82≤100×G2×P2 / d2≤2.96, it is beneficial to improve the kinetic performance of the negative electrode plate, and at the same time, there are fewer side reactions with the electrolyte, thereby improving the rate performance and cycle life of the battery. Therefore, the negative electrode plate provided by the present application has excellent compaction density and kinetic performance, and can reduce the precipitation of active ions on the negative electrode surface during high-rate charging, thereby helping to improve the energy density, cycle rate and cycle life of the battery, while ensuring the safety of the battery.

[0016] In one embodiment of the present application, the thickness d1 of the first active material layer is 35 μm to 100 μm. Specifically, d1 may be, but is not limited to, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 58 μm, 60 μm, 65 μm, 70 μm, 80 μm, 90 μm, or 100 μm. In one embodiment of the present application, d1 may be 50 μm to 100 μm. In another embodiment of the present application, d1 may be 60 μm to 80 μm. In one embodiment of the present application, the thickness d2 of the second active material layer is 15 μm to 50 μm. Specifically, d2 may be, but is not limited to, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm. In one embodiment of the present application, d2 may be 15 μm to 45 μm. In another embodiment of the present application, d2 can be 20μm to 35μm. In one embodiment of the present application, d1 is 35μm to 100μm, and d2 is 15μm to 50μm. Since d1≥d2, the above setting ensures the content of the first activated carbon material and the second activated carbon material in the negative electrode sheet, which is beneficial to improving the performance of the negative electrode sheet. In one embodiment of the present application, d1 is 50μm to 100μm, and d2 is 15μm to 45μm. In another embodiment of the present application, d1 is 60μm to 80μm, and d2 is 20μm to 35μm.

[0017] In one embodiment of the present application, the ratio of d1 to d2 is 1.4 to 4.5, which can further reduce the transmission time of active ions in the second active material layer, thereby reaching the first active material layer more quickly, avoiding the accumulation of active ions on the surface of the negative electrode sheet and the precipitation of dendrites, and further improving the fast charging performance and safety performance of the negative electrode sheet and the battery. Specifically, the ratio of d1 to d2 can be, but is not limited to, 1.4, 1.5, 1.7, 2, 2.2, 2.5, 2.8, 3, 3.4, 3.5, 3.7, 4, 4.1, 4.3 or 4.5, etc. In one embodiment of the present application, the ratio of d1 to d2 is 1.5 to 4. In another embodiment of the present application, the ratio of d1 to d2 is 2 to 3.5.

[0018] The degree of graphitization can be obtained by Raman spectroscopy. In the Raman spectrum, 1350 cm -1 The peak is D peak, 1585cm -1 The peak is the G peak, and the integrated area intensity ratio of the G peak to the D peak is I G / I D , the degree of graphitization is I G / I D The ratio of I G / I D The larger the value, the higher the degree of graphitization, indicating that the material has fewer internal defects and an increased degree of order, resulting in a higher compaction density. G / I D The smaller the value, the lower the degree of graphitization, indicating that there are a large number of defects in the material, the disordered degree of the graphite microcrystal structure formed is high, and the compaction density of the material is low. In this application, 1 / G1 is the integrated area intensity ratio of the G peak and the D peak of the first activated carbon material (I G / I D ), 1 / G2 is the integrated area intensity ratio of the G peak and the D peak of the second activated carbon material; G1<G2, that is, the degree of graphitization of the first activated carbon material is relatively high, and the degree of graphitization of the second activated carbon material is relatively low, which can improve the compaction density of the first active material layer and improve the kinetic performance of the second active material layer, thereby improving the performance of the negative electrode sheet.

[0019] In one embodiment of the present application, G1 is 0.84 to 1.2. That is, the integrated area intensity ratio of the D peak and the G peak of the first activated carbon material is I D / I Gis 0.84 to 1.2, which is beneficial to improve the compaction density of the first active material layer and the negative electrode sheet, and contributes to the improvement of the battery energy density. Specifically, G1 can be, but is not limited to, 0.84, 0.87, 0.9, 0.93, 0.95, 0.98, 1, 1.05, 1.1, 1.15 or 1.2, etc. In one embodiment of the present application, G1 can be 0.85 to 1.1. In another embodiment of the present application, G1 can be 0.88 to 1. In one embodiment of the present application, G2 is 1.32 to 1.82. That is, the integrated area intensity ratio of the D peak and the G peak of the second activated carbon material is I D / I G It is 1.32 to 1.82, which is beneficial to improving the kinetic performance of the second active material layer, thereby preventing the accumulation of active ions on the surface of the negative electrode and the precipitation of dendrites, and further improving safety. Specifically, G2 can be, but is not limited to, 1.32, 1.35, 1.4, 1.45, 1.5, 1.55, 1.58, 1.62, 1.7, 1.75 or 1.8, etc. In one embodiment of the present application, G2 can be 1.4 to 1.8. In another embodiment of the present application, G2 can be 1.5 to 1.75. In one embodiment of the present application, G1 is 0.84 to 1.2, and G2 is 1.32 to 1.82. Since G1 is less than G2, the above setting is beneficial to further improve the kinetic performance and safety of the negative electrode. In one embodiment of the present application, G1 can be 0.85 to 1.1, and G2 can be 1.4 to 1.8. In another embodiment of the present application, G1 may be 0.88-1, and G2 may be 1.5-1.75.

[0020] In one embodiment of the present application, the ratio of G1 to G2 is 0.52 to 0.80, which helps to further improve the compaction density of the negative electrode sheet, while improving the dynamic performance of the negative electrode sheet, thereby helping to improve the energy density, rate performance and cycle performance of the battery. Specifically, the ratio of G1 to G2 can be, but is not limited to, 0.52, 0.55, 0.6, 0.63, 0.65, 0.68, 0.7, 0.73, 0.75, 0.79, 0.8, 0.83 or 0.85, etc. In one embodiment of the present application, the ratio of G1 to G2 can be 0.55 to 0.83. In another embodiment of the present application, the ratio of G1 to G2 can be 0.6 to 0.78.

[0021] The porosity can be obtained by nitrogen adsorption and desorption method. P1<P2 means that the porosity of the first activated carbon material is relatively low, and the porosity of the second activated carbon material is relatively high, which is beneficial to improve the compaction density of the first active material layer and promote the rapid transmission of active ions in the second active material layer, thereby improving the performance of the negative electrode sheet.

[0022] In one embodiment of the present application, P1 is 10% to 25%. That is, the porosity of the first activated carbon material is 10% to 25%. The first activated carbon material has a low porosity and a high compaction density, which is beneficial to improving the compaction density of the first active material layer and the negative electrode sheet. Specifically, P1 can be, but is not limited to, 10%, 13%, 15%, 18%, 20%, 21%, 23% or 25%, etc. In one embodiment of the present application, P1 can be 10% to 20%. In another embodiment of the present application, P1 can be 13% to 18%.

[0023] In one embodiment of the present application, P2 is 20% to 40%. That is to say, the porosity of the second activated carbon material is 20% to 40%. The high porosity of the second activated carbon material facilitates the infiltration of the electrolyte, thereby facilitating the rapid transmission of active ions and improving the kinetic performance of the negative electrode sheet. Specifically, P2 can be, but is not limited to, 20%, 23%, 25%, 28%, 30%, 32%, 35%, 37% or 40%, etc. In one embodiment of the present application, P2 can be 25% to 38%. In another embodiment of the present application, P2 can be 27% to 35%.

[0024] In one embodiment of the present application, P1 is 10% to 25%, and P2 is 20% to 40%. Since P1 < P2, the above configuration is conducive to further improving the dynamic performance of the negative electrode. In one embodiment of the present application, P1 can be 10% to 20%, and P2 can be 25% to 38%. In another embodiment of the present application, P1 can be 13% to 18%, and P2 can be 27% to 35%.

[0025] In one embodiment of the present application, the ratio of P1 to P2 is 0.36 to 0.84, which helps to further improve the compaction density and dynamic performance of the negative electrode sheet, thereby improving the energy density, rate performance and cycle performance of the battery. Specifically, the ratio of P1 to P2 can be, but is not limited to, 0.36, 0.38, 0.4, 0.42, 0.45, 0.48, 0.5, 0.55, 0.58, 0.6, 0.65, 0.7, 0.75, 0.8 or 0.82, etc. In one embodiment of the present application, the ratio of P1 to P2 can be 0.4 to 0.8. In another embodiment of the present application, the ratio of P1 to P2 can be 0.45 to 0.75.

[0026] In one embodiment of the present application, the values ​​of d1, P1 and G1 satisfy: 0.26≤100×G1×P1 / d1≤0.52, which is conducive to further improving the compaction density of the negative electrode sheet, thereby improving the energy density and cycle performance of the battery. Exemplarily, the value of 100×G1×P1 / d1 can be, but not limited to, in the range of 0.27 to 0.5, 0.28 to 0.49, 0.3 to 0.45 or 0.33 to 0.43. Specifically, the value of 100×G1×P1 / d1 can be, but not limited to, 0.27, 0.29, 0.32, 0.35, 0.39, 0.4, 0.41, 0.44, 0.46, 0.49 or 0.5, etc.

[0027] In one embodiment of the present application, the values ​​of d2, P2 and G2 satisfy: 1.06≤100×G2×P2 / d2≤2.42, which is beneficial to further improve the dynamic performance of the negative electrode sheet, thereby improving the rate performance of the battery. Exemplarily, the value of 100×G2×P2 / d2 can be, but not limited to, in the range of 1.06 to 2.42, 1.1 to 2.5, 1.15 to 2.45, 1.2 to 2.2, 1.3 to 2 or 1.35 to 1.9. Specifically, the value of 100×G2×P2 / d2 can be, but not limited to, 1.06, 1.08, 1.13, 1.15, 1.2, 1.25, 1.3, 1.36, 1.4, 1.5, 1.6, 1.73, 1.86, 1.9, 2, 2.2 or 2.35, etc.

[0028] In one embodiment of the present application, the particle size of the first activated carbon material may be 5 μm to 14 μm, and the appropriate particle size is conducive to further improving the compaction density of the first active material layer. Specifically, the particle size of the first activated carbon material may be, but is not limited to, 5 μm, 6 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm or 14 μm, etc. In one embodiment of the present application, the particle size of the first activated carbon material may be 5 μm to 10 μm. In another embodiment of the present application, the particle size of the first activated carbon material may be 9 μm to 14 μm.

[0029] In one embodiment of the present application, the specific surface area of ​​the first activated carbon material can be 1.5 m 2 / g~5m 2 / g, the specific surface area is suitable, which is conducive to the infiltration of the electrolyte and improves the transmission capacity of active ions. Specifically, the specific surface area of ​​the first activated carbon material can be but is not limited to 1.5m 2 / g, 1.8m 2 / g, 2m 2 / g, 2.2m 2 / g, 2.5m 2 / g, 2.7m 2 / g, 2.9m2 / g、3m 2 / g, 3.1m 2 / g, 3.5m 2 / g, 3.7m 2 / g、4m 2 / g, 4.3m 2 / g, 4.5m 2 / g, 4.8m 2 / g or 5m 2 / g, etc.

[0030] In one embodiment of the present application, the particle size of the second activated carbon material may be 3 μm to 8 μm, which is an appropriate particle size and is conducive to further improving the compaction density of the second active material layer. Specifically, the particle size of the second activated carbon material may be, but is not limited to, 3 μm, 5 μm, 6 μm, 7 μm, or 8 μm. In one embodiment of the present application, the particle size of the second activated carbon material may be 3 μm to 6 μm. In another embodiment of the present application, the particle size of the second activated carbon material may be 5 μm to 8 μm.

[0031] In one embodiment of the present application, the specific surface area of ​​the second activated carbon material can be 2 m 2 / g~8m 2 / g, the specific surface area is suitable, which is conducive to the infiltration of the electrolyte and improves the transmission capacity of active ions. Specifically, the specific surface area of ​​the second activated carbon material can be but is not limited to 2m 2 / g, 2.2m 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g, 3.7m 2 / g、4m 2 / g, 4.3m 2 / g, 4.5m 2 / g、5m 2 / g, 5.5m 2 / g, 5.9m 2 / g、6m 2 / g, 6.5m 2 / g or 7m 2 / g, etc.

[0032] The first active carbon material with a high degree of graphitization and low porosity is used in the first active material layer of the present application, which is beneficial to improving the performance of the negative electrode sheet. In one embodiment of the present application, the first activated carbon material includes at least one of soft carbon, hard carbon, natural graphite and artificial graphite. The second activated carbon material with a low degree of graphitization and high porosity is used in the second active material layer of the present application, which is beneficial to improving the performance of the negative electrode sheet. In one embodiment of the present application, the second activated carbon material includes at least one of soft carbon, hard carbon, natural graphite and artificial graphite. The materials of the first activated carbon material and the second activated carbon material in the present application can be the same or different. In one embodiment of the present application, the first activated carbon material and the second activated carbon material are both hard carbon. In related art, when hard carbon is used as a negative electrode active material in batteries, its use is hampered by low initial charge and discharge efficiency, low capacity, and poor rate characteristics. Furthermore, hard carbon materials have a low compaction density, which affects the processing performance of the negative electrode sheet and the volumetric energy density of the battery. In this application, by combining the first and second active material layers, a negative electrode sheet and battery with excellent electrochemical performance can be achieved, facilitating the widespread use of hard carbon. In another embodiment of this application, the first activated carbon material can be hard carbon, and the second activated carbon material can be soft carbon.

[0033] In one embodiment of the present application, the first active material layer further includes at least one of a first binder and a first conductive agent, and the second active material layer further includes at least one of a second binder and a second conductive agent. In one embodiment of the present application, the first binder and the second binder are independently selected from at least one of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyacrylate, carboxymethyl cellulose (CMC) and sodium alginate. In one embodiment of the present application, the first conductive agent and the second conductive agent are independently selected from at least one of acetylene black, conductive carbon black (such as Super-P, etc.), carbon nanotubes, carbon fibers and graphene. In the present application, the materials of the first binder and the second binder may be the same or different; the materials of the first conductive agent and the second conductive agent may be the same or different.

[0034] In the present application, the negative electrode material layer is disposed on the surface of the negative electrode current collector. That is, the negative electrode material layer can be disposed on a portion of one surface of the negative electrode current collector, the entire surface of one surface of the negative electrode current collector, or two opposing surfaces of the negative electrode current collector. In one embodiment of the present application, the negative electrode current collector is made of at least one of copper, aluminum, or stainless steel. In one embodiment of the present application, the negative electrode current collector can include at least one of copper foil, stainless steel foil, copper alloy foil, carbon-coated copper foil, aluminum foil, and carbon-coated aluminum foil.

[0035] The present application provides a battery comprising a positive electrode sheet and a negative electrode sheet according to any of the above embodiments. The battery having the negative electrode sheet has excellent energy density, rate performance, and cycle performance, and is highly safe to use.

[0036] In the present application, the battery may include at least one of a lithium-ion battery, a sodium-ion battery, and a potassium-ion battery, and the battery type may be specifically set as needed.

[0037] In one embodiment of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on the surface of the positive electrode current collector. The positive electrode material layer includes a positive electrode active material. In one embodiment of the present application, the positive electrode active material may include at least one of a transition metal oxide, a polyanionic compound, an organic polymer, and a Prussian blue-based material, which is advantageous for use in sodium-ion batteries and potassium-ion batteries. In another embodiment of the present application, the positive electrode active material may include at least one of lithium cobalt metal oxide, lithium nickel metal oxide, lithium manganese metal oxide, and a polyanionic battery positive electrode material, which is advantageous for use in lithium-ion batteries. In one embodiment of the present application, the positive electrode material layer also includes at least one of a positive electrode binder and a positive electrode conductive agent. Specifically, the positive electrode binder includes at least one of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacrylonitrile, polyacrylic acid, polyacrylate, carboxymethyl cellulose, and sodium alginate; the positive electrode conductive agent includes at least one of acetylene black, conductive carbon black (such as Super-P), carbon nanotubes, carbon fibers, and graphene.

[0038] In one embodiment of the present application, the battery further includes a separator disposed between the positive electrode plate and the negative electrode plate. The separator can be any separator material used in existing batteries. In one embodiment of the present application, the separator is made of at least one of polypropylene (PP), polyethylene (PE), and ceramic.

[0039] In one embodiment of the present application, the battery further comprises an electrolyte, wherein at least a portion of the positive electrode sheet and at least a portion of the negative electrode sheet are immersed in the electrolyte. In one example of the present application, the electrolyte comprises an electrolyte salt and an organic solvent. The specific types and compositions of the electrolyte salt and organic solvent are conventional in the battery field and can be selected based on actual needs.

[0040] The present application provides a battery pack comprising a housing and at least one battery according to any of the above-described embodiments, the battery being housed within the housing. A battery pack comprising such a battery exhibits excellent performance, facilitating its use. Enclosing the battery within the housing enhances its securement and protection, thereby extending the battery pack's service life. It will be appreciated that a battery pack may comprise one or more batteries. When a battery pack comprises multiple batteries, the multiple batteries may be connected in at least one of parallel and series connection.

[0041] The present application provides an electrical device, including a battery or battery pack in any of the above-mentioned embodiments, which is conducive to improving the product competitiveness and performance of the electrical device. In one embodiment of the present application, the electrical device includes an electrical device body, and the battery or battery pack is used to power the electrical device body. In one embodiment of the present application, the electrical device body includes a positive electrode and a negative electrode, the positive electrode plate of the battery or battery pack is used to electrically connect to the positive electrode of the electrical device body, and the negative electrode plate of the battery or battery pack is used to electrically connect to the negative electrode of the electrical device body to power the electrical device.

[0042] The electrical equipment of the present application may be, but is not limited to, portable electronic devices such as mobile phones, tablet computers, laptop computers, desktop computers, smart toys, smart bracelets, smart watches, e-readers, game consoles, toys, etc.; it may also be large equipment such as electric vehicles, electric vehicles, ships, and spacecraft.

[0043] The effects of the technical solution of this application are further illustrated below through specific examples.

[0044] Examples 1-8

[0045] A hard carbon material with high graphitization strength and low porosity (first activated carbon material), a first conductive agent (conductive carbon black), and a first binder (sodium hydroxymethyl cellulose and styrene-butadiene rubber, CMC+SBR) are mixed in a mass ratio of 95.5:1:1.5:2. The mixed powder is placed in a vacuum mixer, deionized water is added and stirred to obtain a first negative electrode slurry. The first negative electrode slurry is evenly coated on the opposite sides of the negative electrode current collector and transferred to an oven for drying to obtain a first active material layer formed on the surface of the negative electrode current collector.

[0046] A hard carbon material with relatively low graphitization strength and high porosity (second activated carbon material), a second conductive agent (conductive carbon black), and a second binder (sodium hydroxymethyl cellulose and styrene-butadiene rubber, CMC+SBR) are mixed in a mass ratio of 95.5:1:1.5:2. The mixed powder is placed in a vacuum mixer, deionized water is added and stirred to obtain a second negative electrode slurry. The second negative electrode slurry is evenly coated on the surface of the first active material layer and transferred to an oven for drying to obtain a second negative electrode active material layer, and then rolled and cut to obtain a negative electrode sheet.

[0047] The structural parameters of the negative electrode plates in Examples 1 to 8 are different, and the specific information is shown in Table 1.

[0048] Comparative Example 1

[0049] The method is substantially the same as Example 1, except that the second negative electrode active material layer is not provided.

[0050] Comparative Example 2

[0051] The process is substantially the same as Example 1, except that the first negative electrode active material layer is not provided.

[0052] Comparative Example 3

[0053] It is roughly the same as Example 1, except that the second negative electrode slurry is first coated on the surface of the negative electrode current collector to form the first negative electrode active material layer, and then the first negative electrode slurry is coated on the surface of the first negative electrode active material layer to form the second negative electrode active material layer to prepare the negative electrode sheet.

[0054] Negative electrode parameter test:

[0055] The thicknesses d1 and d2 (in μm) of the first active material layer and the second active material layer in the negative electrode sheets prepared in the above embodiments and comparative examples were detected by scanning electron microscope analysis and measurement. The specific test process is as follows: the negative electrode sheet was selected, and the cross section of the negative electrode sheet was analyzed by scanning electron microscope, and the thicknesses of the first active material layer and the second active material layer were measured and calculated respectively. The porosity P1 and P2 of the first activated carbon material and the second activated carbon material in the above embodiments and comparative examples were detected by nitrogen adsorption and desorption test method; the graphitization degree G1 and G2 of the first activated carbon material and the second activated carbon material in the above embodiments and comparative examples were detected by Raman spectroscopy test method; the specific test process is as follows: an argon ion polisher was used to ionize argon gas using a high voltage electric field to generate argon ions. The generated argon ions, under the action of the accelerating voltage, polished and removed the second active material layer of the negative electrode sheet, and then immersed in water. After the sheet dressing fell off, the copper foil was removed, and the aqueous solution was filtered to take the residue and ethanol. The acetylene flame is burned in an oxygen atmosphere at a burning temperature of 600°C to 800°C. The residue after burning is the first activated carbon material powder of the negative electrode plate. The porosity test and Raman spectroscopy test are performed by nitrogen adsorption and desorption method to calculate the degree of graphitization. Similarly, the copper foil and the first active material layer of the negative electrode plate are removed by an argon ion polisher, then immersed in water and filtered, the residue is taken, and burned in an oxygen atmosphere with an acetylene flame at a burning temperature of 600°C to 800°C. The residue after burning is the second activated carbon material powder of the negative electrode plate. The porosity test and Raman spectroscopy test are performed by nitrogen adsorption and desorption method to calculate the degree of graphitization. According to the numerical values ​​of d1, d2, P1, P2, G1, and G2, the values ​​of formula 1 (100×G1×P1 / d1) and formula 2 (100×G2×P2 / d2) are calculated. The comparison of the various parameters of the embodiment and the comparative example is summarized in Table 1.

[0056] Table 1 Negative electrode plate parameters of Examples 1 to 8 and Comparative Examples 1 to 3

[0057] The positive electrode active material (Na3V2(PO4)3), positive electrode conductive agent (Super-P), and positive electrode binder (PVDF) are mixed in a mass ratio of 95:2.5:2.5, the mixed powder is placed in a vacuum mixer, N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the opposite sides of the positive electrode collector aluminum foil, the positive electrode collector coated with the positive electrode slurry is transferred to an oven for drying, and then the positive electrode sheet is obtained after rolling and slitting.

[0058] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed solvent, to which dry sodium salt NaPF6 is added to form an electrolyte with a concentration of 1 mol / L, and 2% fluoroethylene carbonate (FEC) additive is added.

[0059] The negative and positive electrode sheets and polypropylene separators prepared in the above examples and comparative examples were stacked in order, with the separator positioned between the positive and negative electrode sheets. The cells were then wound to obtain bare cells. The bare cells were then placed in an aluminum-plastic film soft package, dried, and filled with electrolyte. The secondary battery was obtained after vacuum packaging, standing, forming, and shaping. The battery performance tests were as follows:

[0060] Energy density test: Each sodium-ion battery was weighed using an electronic balance at 25°C. Each sodium-ion battery was charged and discharged at a 1C rate at 25°C, and the actual discharge energy was recorded. The ratio of the actual discharge energy of the sodium-ion battery to its weight was the actual energy density of the sodium-ion battery.

[0061] Cycle performance test: Each sodium ion battery was charged at a 2C rate and discharged at a 1C rate, and a full charge and discharge cycle test was performed, and the capacity retention rate after 1000 cycles was recorded.

[0062] Test of dynamic performance: At 25°C, each sodium-ion battery was fully charged at nC and fully discharged at 1C. After repeating the charge and discharge cycle 10 times, the battery was charged to a full state at nC rate, and then the negative electrode was disassembled and the sodium precipitation on the surface of the negative electrode was observed. Among them, the area of ​​sodium precipitation on the surface of the negative electrode is less than 2%, which is considered to be no sodium precipitation. The sodium precipitation rate means that if there is no sodium precipitation on the surface of the negative electrode, the charging rate is increased from nC in a gradient of 0.1C, and the test is repeated until sodium precipitation occurs on the negative electrode surface. The charging rate at this time, nC minus 0.1C, is the maximum charging rate of the battery under the condition of no sodium precipitation.

[0063] The battery performance test results of the embodiments and comparative examples are shown in Table 2. It can be seen that compared with comparative examples 1-3, the batteries prepared in Examples 1-8 have a high cycle capacity retention rate and excellent cycle performance. At the same time, the sodium precipitation rate is high, indicating that their kinetic performance is good, and the energy density and the first-week charge and discharge efficiency are maintained at a high level; moreover, compared with Examples 2-8, the battery prepared in Example 1 has high energy density, cycle capacity retention rate, first-week charge and discharge efficiency, and sodium precipitation rate, and has excellent comprehensive performance, which is conducive to the use of the battery.

[0064] Table 2 Battery performance test results of Examples 1 to 8 and Comparative Examples 1 to 3

[0065] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A negative electrode sheet, wherein: The invention comprises a negative electrode current collector and a negative electrode material layer arranged on the surface of the negative electrode current collector, wherein the negative electrode material layer comprises a first active material layer and a second active material layer stacked, wherein the first active material layer is arranged between the negative electrode current collector and the second active material layer, wherein the material of the first active material layer comprises a first activated carbon material, and the material of the second active material layer comprises a second activated carbon material, The thickness of the first active material layer is d1, the thickness of the second active material layer is d2, d1≥d2, and the units of d1 and d2 are μm; The porosity of the first activated carbon material is P1, the porosity of the second activated carbon material is P2, and P1<P2; The graphitization degree of the first activated carbon material is 1 / G1, and the graphitization degree of the second activated carbon material is 1 / G2, G1<G2; Wherein, the negative electrode sheet satisfies at least one of the following conditions when calculated by the values ​​of each parameter: (1) 0.18≤100×G1×P1 / d1≤0.68; (2)0.82≤100×G2×P2 / d2≤2.

96.

2. The negative electrode sheet according to claim 1, wherein: The values ​​of d1, P1 and G1 satisfy: 0.26≤100×G1×P1 / d1≤0.

52.

3. The negative electrode sheet according to claim 1, wherein: The values ​​of d2, P2 and G2 satisfy: 1.06≤100×G2×P2 / d2≤2.

42.

4. The negative electrode sheet according to claim 1, wherein: The ratio of d1 to d2 is 1.4 to 4.

5.

5. The negative electrode sheet according to claim 1, wherein: The d1 is 35 μm to 100 μm, and the d2 is 15 μm to 50 μm.

6. The negative electrode sheet according to claim 1, wherein: The ratio of G1 to G2 is 0.52-0.

80.

7. The negative electrode sheet according to claim 1, wherein: The G1 is 0.84 to 1.2, and the G2 is 1.32 to 1.

82.

8. The negative electrode sheet according to claim 1, wherein: The ratio of P1 to P2 is 0.36 to 0.

84.

9. The negative electrode sheet according to claim 1, wherein: The P1 is 10% to 25%, and the P2 is 20% to 40%.

10. The negative electrode sheet according to claim 1, wherein: The first activated carbon material includes at least one of soft carbon, hard carbon, natural graphite and artificial graphite; The second activated carbon material includes at least one of soft carbon, hard carbon, natural graphite and artificial graphite.

11. A battery, wherein: It comprises a positive electrode sheet and a negative electrode sheet as claimed in any one of claims 1 to 10.

12. A battery pack, wherein: The invention comprises a casing and at least one battery according to claim 11, wherein the battery is accommodated in the casing.

13. An electrical device, wherein: Includes the battery according to claim 11 or the battery pack according to claim 12.

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