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

Abstract

The application provides 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, 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, La1 > La2, Lc1 > Lc2, d1 and d2 are the thicknesses of the first active material layer and the second active material layer, p1 and p2 are the true densities of the first active carbon material and the second active carbon material, La1, La2, Lc1 and Lc2 are the sizes of the graphite crystallites of the first active carbon material and the second active carbon material on the a-axis and the c-axis, 0.64 <= La1 * Lc1 * p1 / d1 <= 3.86 and / or 0.48 <= La2 * Lc2 * p2 / d2 <= 1.92.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to negative electrode sheets, batteries, battery packs, and electrical devices. Background Technology

[0002] As batteries continue to evolve, researchers are constantly pursuing batteries with higher energy density and better cycle performance. The negative electrode, as a key component of a battery, plays a crucial role in improving battery performance. However, related technologies often focus on the selection of negative electrode materials, with less research on the overall structure design of the negative electrode, resulting in limited improvements in battery performance. Summary of the Invention

[0003] In view of this, this application provides a negative electrode sheet, a battery, a battery pack, and an electrical device. The negative electrode sheet has good compaction density and kinetic performance, which can improve the energy density and cycle performance of the battery and facilitate the use of the battery, battery pack, and electrical device.

[0004] In a first aspect, this application provides a negative electrode sheet, including a negative current collector and a negative electrode material layer disposed on the surface of the negative current collector. The negative electrode material layer includes a first active material layer and a second active material layer stacked together. The first active material layer is disposed between the negative current collector and the second active material layer. The material of the first active material layer includes a first activated carbon material, and the material of the second active material layer includes a second activated carbon material. The thickness of the first active material layer is d1, and the thickness of the second active material layer is d2, where d1 ≥ d2, and the units of d1 and d2 are μm. The true density of the first activated carbon material is ρ1, and the true density of the second activated carbon material is ρ2, where ρ1 > ρ2, and the units of ρ1 and ρ2 are g / cm³. 3 The first activated carbon material has a graphite crystallite size of La1 along the a-axis direction, and the second activated carbon material has a graphite crystallite size of La2 along the a-axis direction, where La1 > La2 and the units of La1 and La2 are nm; the first activated carbon material has a graphite crystallite size of Lc1 along the c-axis direction, and the second activated carbon material has a graphite crystallite size of Lc2 along the c-axis direction, where Lc1 > Lc2 and the units of Lc1 and Lc2 are nm; wherein, calculated by the values ​​of each parameter, the negative electrode sheet satisfies at least one of the following conditions: (1) 0.64 ≤ La1 × Lc1 × ρ1 / d1 ≤ 3.86; (2) 0.48 ≤ La2 × Lc2 × ρ2 / d2 ≤ 1.92.

[0005] Optionally, the values ​​of d1, ρ1, La1, and Lc1 satisfy: 1.18 ≤ La1 × Lc1 × ρ1 / d1 ≤ 2.82. This setting helps to further increase the compaction density of the negative electrode sheet, thereby improving the energy density of the battery.

[0006] Optionally, the values ​​of d2, ρ2, La2, and Lc2 satisfy: 0.72 ≤ La2 × Lc2 × ρ2 / d2 ≤ 1.62. This setting is beneficial for further improving the kinetic performance of the negative electrode, thereby improving the rate performance and cycle performance of the battery.

[0007] Optionally, the ratio of d1 to d2 is 1.4 to 4.5. This configuration can further reduce the transport time of active ions in the second active material layer, thereby allowing them to reach the first active material layer more quickly. This prevents active ions from accumulating on the electrode surface and forming dendrites, further improving the fast-charging performance and safety performance of the negative electrode and the battery.

[0008] Optionally, d1 is 35μm to 100μm, and d2 is 15μm to 45μm. This configuration ensures the content of the first and second activated carbon materials in the negative electrode sheet, which is beneficial to improving the performance of the negative electrode sheet.

[0009] Optionally, La1 has a wavelength of 5.2 nm to 11.6 nm, Lc1 has a wavelength of 3.2 nm to 7.6 nm, La2 has a wavelength of 3.2 nm to 5.8 nm, and Lc2 has a wavelength of 2.1 nm to 3.8 nm. This configuration helps to further improve the compaction density and kinetic performance of the negative electrode, thereby improving the energy density, rate performance, and cycle performance of the battery.

[0010] Optionally, the ρ1 is 1.92 g / cm³. 3 ~2.12g / cm 3 The ρ2 is 1.56 g / cm³. 3 ~1.86g / cm 3 The above settings help to further improve the compaction density and kinetic performance of the negative electrode sheet, thereby improving the energy density, rate performance, and cycle performance of the battery.

[0011] Optionally, 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.

[0012] Secondly, this application provides a battery including a positive electrode and the negative electrode as described in the first aspect. The battery having this negative electrode exhibits excellent energy density, rate performance, and cycle performance, and also boasts high safety in use.

[0013] Thirdly, this application provides a battery pack, including a housing and at least one battery as described in the second aspect, the battery being housed within the housing. The battery pack with this battery exhibits excellent performance, which is beneficial for the use of the battery pack.

[0014] Fourthly, this application provides an electrical device including the battery described in the second aspect or the battery pack described in the third aspect. This configuration is beneficial for improving the product competitiveness and performance of the electrical device. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a cross-sectional schematic diagram of the negative electrode sheet provided in one embodiment of this application. Detailed Implementation

[0017] The technical solution of this application will be clearly and completely described below with reference to its embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] Please see Figure 1 This is a cross-sectional schematic diagram of a negative electrode sheet provided in one embodiment of this application. The negative electrode sheet 100 includes a negative current collector 10 and a negative electrode material layer 20 disposed on the surface of the negative 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 disposed between the negative 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 is d1, and the thickness of the second active material layer is d2, where d1 ≥ d2, and the units of d1 and d2 are μm. The true density of the first activated carbon material is ρ1, and the true density of the second activated carbon material is ρ2, where ρ1 > ρ2, and the units of ρ1 and ρ2 are g / cm³. 3The grain size of the graphite microcrystals of the first activated carbon material in the a-axis direction is La1, and the grain size of the graphite microcrystals of the second activated carbon material in the a-axis direction is La2, La1 > La2, and the units of La1 and La2 are nm; the grain size of the graphite microcrystals of the first activated carbon material in the c-axis direction is Lc1, and the grain size of the graphite microcrystals of the second activated carbon material in the c-axis direction is Lc2, Lc1 > Lc2, and the units of Lc1 and Lc2 are nm; among them, based on the values ​​of each parameter, the negative electrode sheet satisfies at least one of the following conditions: (1) 0.64 ≤ La1 × Lc1 × ρ1 / d1 ≤ 3.86; (2) 0.48 ≤ La2 × Lc2 × ρ2 / d2 ≤ 1.92.

[0019] In the negative electrode sheet, a thickness of the second active material layer that is less than or equal to the thickness of the first active material layer facilitates the rapid passage of active ions (lithium ions, sodium ions, potassium ions, etc.) through the second active material layer and into the first active material layer during charging and discharging, thereby preventing the precipitation of active ions on the surface of the second active material layer and improving fast charging capability. The graphite crystallites of the first activated carbon material have a larger grain size along the a-axis direction than the graphite crystallites of the second activated carbon material along the a-axis direction, and the graphite crystallites of the first activated carbon material have a larger grain size along the c-axis direction than the graphite crystallites of the second activated carbon material along the c-axis direction. This results in a higher degree of graphitization in the first activated carbon material, fewer internal defects, a higher degree of order in the formed graphite crystallite structure, and a higher compaction density. Conversely, the second activated carbon material has a lower degree of graphitization and fewer internal defects. The first activated carbon material has relatively more defects, resulting in a relatively high degree of disorder in the formed graphite microcrystal structure and a relatively low compaction density. Since the true density of the first activated carbon material is greater than that of the second activated carbon material, the graphite microcrystal layers inside the first activated carbon material are tightly stacked, with a high degree of graphitization, few internal pores, and a relatively high compaction density. Conversely, the second activated carbon material has more internal pores and a relatively low compaction density. In other words, the high graphite microcrystal size and high true density of the first activated carbon material help improve the compaction density, and its fewer defects and low surface activity can improve the first-cycle coulombic efficiency. Furthermore, it easily forms a stable and dense solid electrolyte interphase (SEI) membrane during cycling, which is beneficial for improving cycle performance. The low graphite microcrystal size and low true density of the second activated carbon material help improve the kinetic performance of the second active material layer and prevent active ions from accumulating on the surface of the negative electrode and precipitating dendrites, thereby improving safety. In this application, the negative electrode sheet is calculated using the values ​​of each parameter (that is, using the values ​​of d1, ρ1, La1, Lc1, d2, ρ2, La2, Lc2) and satisfies at least one of the following conditions: (1) 0.64≤La1×Lc1×ρ1 / d1≤3.86; (2) 0.48≤La2×Lc2×ρ2 / d2≤1.92; that is, the first active material layer satisfies 0.64≤La1×Lc1×ρ1 / d1≤3.86, and / or the second active material layer satisfies 0.48≤La2×Lc2×ρ2 / d2≤1.92.When the value of La1×Lc1×ρ1 / d1 is less than 0.64, the graphite crystallite size of the first activated carbon material is small, the true density is low, and / or the thickness of the first active material layer is large, resulting in a large number of pores in the first activated carbon material, affecting the compaction density of the negative electrode sheet. At the same time, the liquid phase transport path of active ions increases, leading to increased polarization, thus affecting the energy density and cycle performance of the battery. When the value of La1×Lc1×ρ1 / d1 is greater than 3.86, the graphite crystallite size of the first activated carbon material is large, the true density is high, and / or the thickness of the first active material layer is small, resulting in fewer internal pores in the first activated carbon material, making electrolyte wetting difficult and increasing ion transport resistance, thus affecting the rate performance and cycle performance of the battery. Furthermore, a smaller thickness will reduce the energy density of the battery. Therefore, when the first active material layer satisfies 0.64≤La1×Lc1×ρ1 / d1≤3.86, it helps to improve the compaction density of the negative electrode sheet, thereby increasing the energy density of the battery. When the value of La2×Lc2×ρ2 / d2 is less than 0.48, the graphite crystallite size of the second activated carbon material is smaller, the true density is lower, and / or the thickness of the second active material layer is larger. This results in a lower degree of graphitization of the second activated carbon material, increased defects, enhanced surface activity, and an increased contact area with the electrolyte, leading to increased side reactions with the electrolyte. During cycling, the SEI film will continuously rupture and repair, resulting in the loss of active ions. This, in turn, leads to low coulombic efficiency in the first cycle and low cycle life. Furthermore, the increased liquid-phase transport path of active ions leads to increased polarization, thereby affecting the kinetic performance of the second active material layer and ultimately reducing its effectiveness. Ions accumulate on the surface of the negative electrode, forming dendrites. When the value of La2×Lc2×ρ2 / d2 is greater than 1.92, the graphite crystallite size of the second active carbon material is larger, the true density is higher, and / or the thickness of the second active material layer is smaller. This results in a higher degree of graphitization and fewer internal pores in the second active carbon material, leading to difficulties in electrolyte wetting and increased ion transport resistance, thus affecting the kinetic performance of the second active material layer. Therefore, when the second active material layer satisfies 0.48≤La2×Lc2×ρ2 / d2≤1.92, it is beneficial to improve the kinetic performance of the negative electrode, thereby improving the rate performance and cycle performance of the battery. Therefore, the negative electrode provided in this 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 battery use.

[0020] In one embodiment of this application, the thickness d1 of the first active material layer is 35 μm to 100 μm. Specifically, d1 can 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 this application, d1 can be 50 μm to 100 μm. In another embodiment of this application, d1 can be 60 μm to 80 μm. In one embodiment of this application, the thickness d2 of the second active material layer is 15 μm to 45 μm. Specifically, d2 can be, but is not limited to, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, or 45 μm. In one embodiment of this application, d2 can be 15 μm to 40 μm. In another embodiment of this application, d2 can be 20 μm to 35 μm. In one embodiment of this application, d1 is 35μm to 100μm, and d2 is 15μm to 40μm. Since d1 ≥ d2, the above setting ensures the content of the first and second activated carbon materials in the negative electrode sheet, which is beneficial to improving the performance of the negative electrode sheet. In one embodiment of this application, d1 is 50μm to 100μm, and d2 is 15μm to 40μm. In another embodiment of this application, d1 is 60μm to 80μm, and d2 is 20μm to 35μm.

[0021] In one embodiment of this application, the ratio of d1 to d2 is 1.4 to 4.5. This further reduces the transport time of active ions in the second active material layer, allowing them to reach the first active material layer more quickly. This prevents active ions from accumulating on the surface of the negative electrode and forming dendrites, thereby further improving the fast charging performance and safety performance of the negative electrode 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. In one embodiment of this application, the ratio of d1 to d2 is 1.5 to 4. In another embodiment of this application, the ratio of d1 to d2 is 2 to 3.5.

[0022] In carbon materials, the grain size of graphite crystallites along the a-axis is called the La size, and the grain size along the c-axis is called the Lc size. The La size can also be referred to as the size of the graphite crystallites along the basal plane of the crystal, and the Lc size can also be referred to as the size of the graphite crystallites perpendicular to the basal plane. In this application, La1, Lc1, La2, and Lc2 can be obtained by X-ray diffraction testing and calculation, with units in nm.

[0023] In one embodiment of this application, the grain size La1 of the graphite microcrystals of the first activated carbon material along the a-axis direction is 5.2 nm to 11.6 nm. Specifically, La1 can be, but is not limited to, 5.2 nm, 5.8 nm, 6 nm, 6.5 nm, 7 nm, 8 nm, 9.4 nm, 10.5 nm, 11 nm, or 11.5 nm. In one embodiment of this application, La1 can be 6 nm to 11.5 nm. In another embodiment of this application, La1 can be 7 nm to 10 nm. In one embodiment of this application, the grain size Lc1 of the graphite microcrystals of the first activated carbon material along the c-axis direction is 3.2 nm to 7.6 nm. Specifically, Lc1 can be, but is not limited to, 3.5 nm, 4 nm, 5 nm, 5.5 nm, 5.8 nm, 6 nm, 6.5 nm, 7 nm, or 7.5 nm. In one embodiment of this application, Lc1 can be 4 nm to 7.2 nm. In another embodiment of this application, Lc1 can be 4.5nm to 7nm. This configuration results in a relatively high degree of graphitization of the first activated carbon material, thereby increasing the compaction density of the first active material layer and thus improving the compaction density of the negative electrode sheet. In one embodiment of this application, the grain size La2 of the graphite microcrystals of the second activated carbon material in the a-axis direction is 3.2nm to 5.8nm. Specifically, La2 can be, but is not limited to, 3.5nm, 3.8nm, 4nm, 4.3nm, 4.5nm, 5nm, 5.5nm, or 5.7nm. In one embodiment of this application, La2 can be 3.5nm to 5nm. In another embodiment of this application, La2 can be 3.8nm to 4.8nm. In one embodiment of this application, the grain size Lc2 of the graphite microcrystals of the second activated carbon material in the c-axis direction is 2.1nm to 3.8nm. Specifically, Lc2 can be, but is not limited to, 2.1nm, 2.5nm, 2.7nm, 3nm, 3.3nm, 3.5nm, or 3.7nm. In one embodiment of this application, Lc2 can be 2.2nm to 3.5nm. In another embodiment of this application, Lc2 can be 2.5nm to 3.2nm. The above configuration is beneficial to improving the kinetic performance of the second active material layer, further reducing the accumulation of active ions on the surface of the negative electrode and the precipitation of dendrites, thereby improving the cycle performance and safety performance of the negative electrode. In one embodiment of this application, La1 is 5.2nm to 11.6nm, Lc1 is 3.2nm to 7.6nm, La2 is 3.2nm to 5.8nm, and Lc2 is 2.1nm to 3.8nm. The above configuration helps to further improve the compaction density and kinetic performance of the negative electrode, thereby improving the energy density, cycle performance, and safety of the battery.

[0024] In this application, the true density can be obtained by measuring a true density meter. In one embodiment of this application, the true density ρ1 of the first activated carbon material is 1.92 g / cm³. 3 ~2.12g / cm 3 This is beneficial for further increasing the compaction density of the negative electrode sheet, thereby improving the energy density of the battery. Specifically, ρ1 can be, but is not limited to, 1.95 g / cm³. 3 1.98g / cm 3 2g / cm 3 2.03 g / cm 3 2.05g / cm 3 2.07 g / cm 3 2.1g / cm 3 Or 2.12 g / cm 3 Etc. In one embodiment of this application, ρ1 can be 1.95 g / cm³. 3 ~2.1g / cm 3 In another embodiment of this application, ρ1 can be 1.98 g / cm³. 3 ~2.07g / cm 3 In one embodiment of this application, the true density ρ2 of the second activated carbon material is 1.56 g / cm³. 3 ~1.86g / cm 3 This facilitates the rapid transport of active ions in the second active material layer, further enhancing the kinetic performance of the negative electrode. Specifically, ρ2 can be, but is not limited to, 1.58 g / cm³. 3 1.6g / cm 3 1.64 g / cm 3 1.68g / cm 3 1.7g / cm 3 1.73g / cm 3 1.75g / cm 3 Or 1.82g / cm 3 Etc. In one embodiment of this application, ρ2 can be 1.58 g / cm³. 3 ~1.8g / cm 3 In another embodiment of this application, ρ2 can be 1.6 g / cm³. 3 ~1.77g / cm 3 In one embodiment of this application, ρ1 is 1.92 g / cm³. 3 ~2.12g / cm 3 ρ2 is 1.56 g / cm³ 3 ~1.86g / cm 3 The above settings help to further improve the compaction density and kinetic performance of the negative electrode sheet, thereby improving the battery's energy density, cycle performance, and safety.

[0025] In one embodiment of this application, the values ​​of d1, ρ1, La1, and Lc1 satisfy the condition: 1.18 ≤ La1 × Lc1 × ρ1 / d1 ≤ 2.82. This is beneficial for further increasing the compaction density of the negative electrode sheet, thereby improving the energy density of the battery. For example, the value of La1 × Lc1 × ρ1 / d1 can be, but is not limited to, within the range of 1.2–2.7, 1.5–2.5, 1.75–2.3, or 1.3–1.5. Specifically, the value of La1 × Lc1 × ρ1 / d1 can be, but is not limited to, 1.35, 1.5, 1.8, 1.95, 2, 2.1, 2.35, 2.5, 2.65, 2.7, or 2.8, etc.

[0026] In one embodiment of this application, the values ​​of d2, ρ2, La2, and Lc2 satisfy the condition: 0.72 ≤ La2 × Lc2 × ρ2 / d2 ≤ 1.62. This is beneficial for further improving the kinetic performance of the negative electrode, thereby improving the rate performance and cycle performance of the battery. For example, the value of La2 × Lc2 × ρ2 / d2 can be, but is not limited to, within the range of 0.75–1.5, 0.8–1.47, 0.9–1.45, or 0.95–1.4. Specifically, the value of La2 × Lc2 × ρ2 / d2 can be, but is not limited to, 0.75, 0.8, 0.83, 0.85, 0.9, 1, 1.2, 1.35, 1.5, 1.57, or 1.6, etc.

[0027] In one embodiment of this application, the particle size of the first activated carbon material can be 5μm to 14μm, which is suitable and beneficial for further improving the compaction density of the first activated material layer. Specifically, the particle size of the first activated carbon material can be, but is not limited to, 5μm, 6μm, 9μm, 10μm, 11μm, 12μm, 13μm, or 14μm. In one embodiment of this application, the particle size of the first activated carbon material can be 5μm to 10μm. In another embodiment of this application, the particle size of the first activated carbon material can be 9μm to 14μm.

[0028] In one embodiment of this application, the specific surface area of ​​the first activated carbon material can be 1.5 m². 2 / g~5m 2 The specific surface area is suitable, which is beneficial for electrolyte wetting and enhances the transport capacity of active ions. Specifically, the specific surface area of ​​the first activated carbon material can be, but is not limited to, 1.5 m² / g. 2 / g, 1.8m 2 / g、2m 2 / g, 2.2m 2 / g, 2.5m 2 / g, 2.7m 2 / g, 2.9m 2 / g、3m2 / 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.

[0029] In one embodiment of this application, the particle size of the second activated carbon material can be 3μm to 8μm. This suitable particle size is beneficial for further improving the compaction density of the second activated material layer. Specifically, the particle size of the second activated carbon material can be, but is not limited to, 3μm, 5μm, 6μm, 7μm, or 8μm. In one embodiment of this application, the particle size of the second activated carbon material can be 3μm to 6μm. In another embodiment of this application, the particle size of the second activated carbon material can be 5μm to 8μm.

[0030] In one embodiment of this application, the specific surface area of ​​the second activated carbon material can be 2m². 2 / g~8m 2 The specific surface area is suitable, which is beneficial for electrolyte wetting and enhances the transport capacity of active ions. Specifically, the specific surface area of ​​the second activated carbon material can be, but is not limited to, 2 m² / g. 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.

[0031] The first active material layer of this application uses a first activated carbon material with high graphite crystallite size and high true density, which helps to improve the compaction density of the electrode sheet. It also has a high degree of graphitization, fewer defects, and low surface activity, which can improve the first-cycle coulombic efficiency and facilitate the formation of a stable and dense SEI film during cycling, thus improving the performance of the negative electrode sheet. In one embodiment of this application, the first activated carbon material includes at least one of soft carbon, hard carbon, natural graphite, and artificial graphite. The second active material layer of this application uses a second activated carbon material with low graphite crystallite size and low true density. It has a lower degree of graphitization, which is beneficial for the conduction of active ions within the active material, reduces the active ion transport impedance, and increases the active ion diffusion rate, thus improving the performance of the negative electrode sheet. In one embodiment of this 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 and second activated carbon materials in this application can be the same or different. In one embodiment of this application, both the first and second activated carbon materials are hard carbon. In related technologies, when hard carbon is used as a negative electrode active material in batteries, its low initial charge-discharge efficiency, low capacity, and poor rate performance hinder its use. Furthermore, the low compaction density of hard carbon affects the processing performance of the negative electrode sheet and the volumetric energy density of the battery. In this application, the combination of a first active material layer and a second active material layer can improve the negative electrode sheet and battery with excellent electrochemical performance, thus facilitating the widespread use of hard carbon. In another embodiment of this application, the first active carbon material can be hard carbon, and the second active carbon material can be soft carbon.

[0032] In one embodiment of this application, the first active material layer further includes at least one of a first adhesive and a first conductive agent, and the second active material layer further includes at least one of a second adhesive and a second conductive agent. In one embodiment of this application, the first adhesive and the second adhesive 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 this 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), carbon nanotubes, carbon fibers, and graphene. In this application, the materials of the first adhesive and the second adhesive can be the same or different; the materials of the first conductive agent and the second conductive agent can be the same or different.

[0033] In this application, the negative electrode material layer is disposed on the surface of the negative electrode current collector. Specifically, the negative electrode material layer can be disposed on a portion of one surface of the negative electrode current collector, or on the entire surface of one surface of the negative electrode current collector, or on two opposing surfaces of the negative electrode current collector. In one embodiment of this application, the material of the negative electrode current collector includes at least one of copper and aluminum, or stainless steel. In one embodiment of this application, the negative electrode current collector may include at least one of copper foil, stainless steel foil, copper alloy foil, carbon-coated copper foil, aluminum foil, and carbon-coated aluminum foil.

[0034] This application provides a battery including a positive electrode and a negative electrode as described in any of the above embodiments. The battery having this negative electrode exhibits excellent energy density, rate performance, and cycle performance, and also demonstrates high safety in use.

[0035] In this application, the battery may include at least one of lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries, and the specific battery type can be set as needed.

[0036] In one embodiment of this application, the positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on the surface of the positive current collector, the positive electrode material layer including a positive electrode active material. In one embodiment of this application, the positive electrode active material may include at least one of transition metal oxides, polyanionic compounds, organic polymers, and Prussian blue-based materials, which is beneficial for the use of sodium-ion batteries and potassium-ion batteries. In another embodiment of this 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 polyanionic battery positive electrode materials, which is beneficial for the use of lithium-ion batteries. In one embodiment of this 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.

[0037] In one embodiment of this application, the battery further includes a separator disposed between the positive electrode and the negative electrode. The separator can be any separator material used in existing batteries. In one embodiment of this application, the separator material includes at least one of polypropylene (PP), polyethylene (PE), and ceramic.

[0038] In one embodiment of this application, the battery further includes an electrolyte, in which at least a portion of the positive electrode and at least a portion of the negative electrode are immersed. In one embodiment of this application, the electrolyte includes an electrolyte salt and an organic solvent. The specific types and compositions of the electrolyte salt and organic solvent are conventional choices in the battery field and can be selected according to actual needs.

[0039] This application provides a battery pack, including a housing and at least one battery as described in any of the above embodiments, with the battery housed within the housing. The battery pack with this battery exhibits excellent performance, which is beneficial for its use. Housed within the housing, the battery is secured and protected, thus extending the battery pack's lifespan. It is understood that the battery pack may contain one or more batteries, and when multiple batteries are included, they can be connected in at least one manner, such as in parallel or series.

[0040] This application provides an electrical device including a battery or battery pack as described in any of the above embodiments, which is beneficial for improving the product competitiveness and performance of the electrical device. In one embodiment of this application, the electrical device includes an electrical device body, and a battery or battery pack is used to supply power to the electrical device body. In one embodiment of this application, the electrical device body includes a positive terminal and a negative terminal, the positive terminal of the battery or battery pack is used to electrically connect to the positive terminal of the electrical device body, and the negative terminal of the battery or battery pack is used to electrically connect to the negative terminal of the electrical device body, so as to supply power to the electrical device.

[0041] The electrical equipment covered by this application can be, but is not limited to, portable electronic devices such as mobile phones, tablets, laptops, desktop computers, smart toys, smart bracelets, smartwatches, e-readers, game consoles, and toys; it can also be large equipment such as electric vehicles, electric cars, ships, and spacecraft.

[0042] The effects of the technical solution in this application will be further illustrated below with specific examples.

[0043] Examples 1-8

[0044] High-graphite-crystal-size, high-true-density hard carbon material (first activated carbon material), first conductive agent (conductive carbon black), and 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 uniformly coated on the opposite two 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.

[0045] A hard carbon material with relatively low graphite crystallite size and low true density (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 uniformly coated on the surface of the first active material layer and transferred to an oven to dry to obtain the second negative electrode active material layer. Then, after rolling and slitting, the negative electrode sheet is obtained.

[0046] The structural parameters of the negative electrode plates in Examples 1 to 8 are different, and the specific information is shown in Table 1.

[0047] Comparative Example 1

[0048] It is largely the same as Example 1, except that it does not have a second negative electrode active material layer.

[0049] Comparative Example 2

[0050] It is largely the same as Example 1, except that it does not have a first negative electrode active material layer.

[0051] Comparative Example 3

[0052] Similar to Example 1, except that a second negative electrode slurry is first coated on the surface of the negative electrode current collector to form a first negative electrode active material layer, and then a second negative electrode slurry is coated on the surface of the first negative electrode active material layer to form a second negative electrode active material layer, thus obtaining a negative electrode sheet.

[0053] Performance testing

[0054] The thicknesses d1 and d2 (in μm) of the first and second active material layers in the negative electrode sheets prepared in the above embodiments and comparative examples were measured using scanning electron microscopy. The specific testing process was as follows: A negative electrode sheet was selected, and its cross-section was analyzed using a scanning electron microscope to measure and statistically determine the thicknesses of the first and second active material layers. The first and second activated carbon materials in the above embodiments and comparative examples were analyzed using X-ray diffraction to obtain La1, Lc1, La2, and Lc2 (in nm). The true densities ρ1 and ρ2 (in g / cm³) of the first and second activated carbon materials in the above embodiments and comparative examples were measured using a true density meter. 3The following testing procedures were performed: An argon ion polisher was used to ionize argon gas using a high-voltage electric field. The generated argon ions, under the action of an accelerating voltage, polished and removed the second active material layer of the negative electrode sheet. The sheet was then immersed in water until the electrode coating detached. The copper foil was removed, and the aqueous solution was filtered. The residue was then burned in an oxygen atmosphere with an acetylene flame at a temperature of 600℃~800℃. The residue after burning was the first activated carbon material powder of the negative electrode sheet. X-ray diffraction was used to obtain La1 and Lc1, and the true density was obtained by testing with a true density meter. Similarly, an argon ion polisher was used to remove the copper foil and the first active material layer of the negative electrode sheet. The sheet was then immersed in water and filtered. The residue was burned in an oxygen atmosphere with an acetylene flame at a temperature of 600℃~800℃. The residue after burning was the second activated carbon material powder of the negative electrode sheet. X-ray diffraction was used to obtain La2 and Lc2, and the true density was obtained by testing with a true density meter. The values ​​of Equation 1 (La1×Lc1×ρ1 / d1) and Equation 2 (La2×Lc2×ρ2 / d2) are calculated based on the numerical values ​​of La1, Lc1, La2, Lc2, ρ1, ρ2, d1, and d2. A summary of the parameters in the examples and comparative examples is shown in Table 1.

[0055] Table 1. Negative electrode structure parameters of Examples 1-8 and Comparative Examples 1-3

[0056]

[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 two sides of the positive electrode current collector aluminum foil. The positive electrode current collector coated with the positive electrode slurry is transferred to an oven for drying. After rolling and slitting, the positive electrode sheet is obtained.

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

[0059] The negative electrode sheet and positive electrode sheet prepared in the above embodiments and comparative examples are stacked sequentially with a polypropylene separator, with the separator positioned between the positive and negative electrode sheets. Then, they are wound to obtain a bare battery cell. The bare battery cell is placed in an aluminum-plastic film soft package, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a secondary battery is obtained. The battery performance is tested as follows:

[0060] Energy density test: Weigh each sodium-ion battery using an electronic balance at 25℃; charge and discharge each sodium-ion battery at 1C rate at 25℃ and record the actual discharge energy; the ratio of the actual discharge energy of the sodium-ion battery to the weight of the sodium-ion battery is the actual energy density of the sodium-ion battery.

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

[0062] Dynamic performance testing: At 25℃, each sodium-ion battery was fully charged at nC and fully discharged at 1C for 10 cycles. Then, the battery was fully charged at nC. The negative electrode was then disassembled, and the sodium deposition on its surface was observed. A sodium deposition area of ​​less than 2% on the negative electrode surface was considered non-sodium deposition. The sodium deposition rate refers to the maximum charging rate under non-sodium deposition conditions: if no sodium deposition occurs on the negative electrode surface, the charging rate is increased from nC in 0.1C increments until sodium deposition occurs. The difference between nC and 0.1C is the maximum charging rate under non-sodium deposition conditions.

[0063] The battery performance test results of the examples 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 deposition rate is high, indicating that its kinetic performance is good, and the energy density and first-cycle charge-discharge efficiency remain at a high level. Moreover, compared with examples 2-8, the battery prepared in example 1 has a higher energy density, cycle capacity retention rate, first-cycle charge-discharge efficiency, and sodium deposition rate, and its comprehensive performance is excellent, which is beneficial to the use of the battery.

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

[0065]

[0066] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A negative electrode sheet, characterized in that, The device includes a negative electrode current collector and a negative electrode material layer disposed on the surface of the negative electrode current collector. The negative electrode material layer includes a first active material layer and a second active material layer stacked together. The first active material layer is disposed between the negative electrode current collector and the second active material layer. The first active material layer is made of a first activated carbon material, and the second active material layer is made of 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 true density of the first activated carbon material is ρ1, and the true density of the second activated carbon material is ρ2, where ρ1 > ρ2. The units of ρ1 and ρ2 are g / cm³. 3 ; The grain size of the graphite microcrystals of the first activated carbon material in the a-axis direction is La1, and the grain size of the graphite microcrystals of the second activated carbon material in the a-axis direction is La2, where La1 > La2, and the units of La1 and La2 are nm. The grain size of the graphite microcrystals of the first activated carbon material in the c-axis direction is Lc1, and the grain size of the graphite microcrystals of the second activated carbon material in the c-axis direction is Lc2, where Lc1 > Lc2, and the units of Lc1 and Lc2 are nm. Specifically, based on the values ​​of each parameter, the negative electrode sheet satisfies at least one of the following conditions: (1) 0.64≤La1×Lc1×ρ1 / d1≤3.86; (2)0.48≤La2×Lc2×ρ2 / d2≤1.

92.

2. The negative electrode sheet as described in claim 1, characterized in that, The values ​​of d1, ρ1, La1, and Lc1 satisfy: 1.18 ≤ La1 × Lc1 × ρ1 / d1 ≤ 2.

82.

3. The negative electrode sheet as described in claim 1, characterized in that, The values ​​of d2, ρ2, La2, and Lc2 satisfy: 0.72≤La2×Lc2×ρ2 / d2≤1.

62.

4. The negative electrode sheet as described in claim 1, characterized in that, The ratio of d1 to d2 is 1.4 to 4.

5.

5. The negative electrode sheet as described in claim 1, characterized in that, The d1 is 35μm to 100μm, and the d2 is 15μm to 45μm.

6. The negative electrode sheet as described in claim 1, characterized in that, The La1 is 5.2nm to 11.6nm, the Lc1 is 3.2nm to 7.6nm, the La2 is 3.2nm to 5.8nm, and the Lc2 is 2.1nm to 3.8nm.

7. The negative electrode sheet as described in claim 1, characterized in that, The ρ1 is 1.92 g / cm³. 3 ~2.12g / cm 3 The ρ2 is 1.56 g / cm³. 3 ~1.86g / cm 3 .

8. The negative electrode sheet as described in claim 1, characterized in that, 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.

9. A battery, characterized in that, It includes the positive electrode sheet and the negative electrode sheet as described in any one of claims 1 to 8.

10. A battery pack, characterized in that, It includes a housing and at least one battery as described in claim 9, the battery being housed within the housing.

11. An electrical appliance, characterized in that, Includes the battery of claim 9 or the battery pack of claim 10.

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