A negative electrode sheet, a secondary battery, and an electric device

Abstract

This invention provides a negative electrode sheet, a secondary battery, and an electrical device. The negative electrode sheet includes a current collector and a negative electrode active material layer disposed on at least one surface of the current collector. The negative electrode active material layer includes an A negative electrode active material layer near the edge region of the current collector and a B negative electrode active material layer in the middle region of the current collector, satisfying the following relationship: 0.89 ≤ (PD) a ×Q a ×V OIa ) / (PD b ×Q b ×V OIb ≤8.25; PD a PD b These correspond to the compaction densities of the A and B negative electrode active material layers, respectively; Q a Q b These correspond to the specific capacity of the negative electrode active material in layers A and B, respectively; V OIa V OIb These correspond to the OI values ​​of the negative electrode sheets in the regions corresponding to the A and B negative electrode active material layers, respectively. This invention, through the design of the negative electrode sheet, can improve the liquid absorption capacity in the middle of the negative electrode sheet, reduce the risk of lithium plating, and improve the cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode sheet and the secondary battery and electrical device made therefrom. Background Technology

[0002] Due to their advantages such as low cost, high energy density, good safety, and fast charging performance, large cylindrical batteries have attracted many battery manufacturers and car companies to enter the market.

[0003] However, in large cylindrical batteries, the electrolyte wetting path is along the sides of the core towards the center. Because the gas inside the core cannot be completely extracted during electrolyte injection, the electrolyte gradually wets from the sides of the core towards the center of the electrode. The resistance generated by the residual gas inside the core increases the difficulty for the electrolyte to reach the center, resulting in poor wetting in the center of the electrode. This leads to black lines in the center of the electrode after formation, and poses a risk of lithium plating during long-term cycling. Simultaneously, during battery charge-discharge cycles, the expansion of the negative electrode generates significant internal stress. This causes the electrolyte in the center of the cell to be squeezed to the sides of the electrode, resulting in uneven electrolyte distribution within the core and a lack of electrolyte in the center of the electrode. These problems affect the lithium-ion migration rate on the sides and in the center of the electrode, and in severe cases, can lead to lithium plating in the center of the electrode.

[0004] Therefore, it is necessary to improve the lithium plating problem in the middle of large cylindrical secondary batteries and provide a new type of secondary battery. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of lithium plating in the middle of large cylindrical secondary batteries by providing a negative electrode sheet. By designing the active material layer on the surface of the negative electrode sheet, coating different active material layers, and reasonably setting the relevant parameters of different active layers, the liquid absorption capacity in the middle of the negative electrode sheet can be increased, the internal stress in the middle of the negative electrode sheet can be improved, the risk of lithium plating can be reduced, and the cycle performance of the battery can be improved.

[0006] Another object of the present invention is to provide a secondary battery comprising the negative electrode plate.

[0007] Another object of the present invention is to provide an electrical device comprising the secondary battery.

[0008] To achieve the above objectives, a first aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active material layer disposed on at least one surface of the current collector, the negative electrode active material layer comprising an A negative electrode active material layer in a region near the edge of the current collector and a B negative electrode active material layer in a region in the middle of the current collector, and the negative electrode active material layers satisfy the following relationship:

[0009] 0.89≤(PD a ×Q a ×VOIa ) / (PD b ×Q b ×V OIb ≤8.25;

[0010] In the formula, PD a g / cm 3 This indicates the compaction density of the A negative electrode active material layer;

[0011] PD b g / cm 3 This indicates the compaction density of the B negative electrode active material layer;

[0012] Q a mAh / g represents the specific capacity of the negative electrode active material in the A negative electrode active material layer;

[0013] Q b mAh / g represents the specific capacity of the negative electrode active material in the B negative electrode active material layer;

[0014] V OIa This represents the OI value of the negative electrode sheet in the region corresponding to the A negative electrode active material layer;

[0015] V OIb This represents the OI value of the negative electrode sheet in the region corresponding to the B negative electrode active material layer.

[0016] In this invention, PD a and PD b Q a and Q b V OIa and V OIb They are not equal at the same time.

[0017] As an embodiment of the present invention, the negative electrode sheet satisfies: PD a ≥PD b .

[0018] As an embodiment of the present invention, the negative electrode sheet satisfies: Q a ≤Q b .

[0019] As an embodiment of the present invention, the negative electrode sheet satisfies: V OIa ≥V OIb .

[0020] As an embodiment of the present invention, the negative electrode sheet satisfies: PD a =1~2g / cm 3 .

[0021] As an embodiment of the present invention, the negative electrode sheet satisfies: PD b =1~2g / cm3 .

[0022] As an embodiment of the present invention, the negative electrode sheet satisfies: Q a =330~370mAh / g.

[0023] As an embodiment of the present invention, the negative electrode sheet satisfies: Q b =330~370mAh / g.

[0024] As an embodiment of the present invention, the negative electrode sheet satisfies: V OIa =2~15.

[0025] As an embodiment of the present invention, the negative electrode sheet satisfies: V OIb =2~15.

[0026] As an embodiment of the present invention, in the negative electrode sheet, the width H of the region corresponding to the A negative electrode active material layer is... A The width H of the region corresponding to the B negative electrode active material layer B The ratio of H satisfies A H B =0.66~4.

[0027] As an embodiment of the present invention, the active materials in the A negative electrode active material layer and the B negative electrode active material layer independently include at least one of artificial graphite and natural graphite.

[0028] As an embodiment of the present invention, the negative electrode sheet satisfies: G OIa ≥G OIb Among them, G OIa G represents the OI value of the negative electrode active material powder in the A negative electrode active material layer. OIb This indicates the OI value of the negative electrode active material powder in the B negative electrode active material layer.

[0029] As an embodiment of the present invention, the negative electrode sheet satisfies: G OIa =1 to 6.

[0030] As an embodiment of the present invention, the negative electrode sheet satisfies: G OIb =1 to 6.

[0031] As an embodiment of the present invention, the negative electrode sheet satisfies: D v50a ≥D v50b , where D v50a μm represents the particle size corresponding to when the cumulative volume percentage of the negative electrode active material in layer A reaches 50%; D v50b μm represents the particle size corresponding to when the cumulative volume percentage of the negative electrode active material in the B negative electrode active material layer reaches 50%.

[0032] As an embodiment of the present invention, the negative electrode sheet satisfies: D v50a =6~20μm.

[0033] As an embodiment of the present invention, the negative electrode sheet satisfies: D v50b =6~20μm.

[0034] As an embodiment of the present invention, the negative electrode sheet satisfies: BET a ≤BET b Among them, BET a m 2 / g represents the specific surface area of ​​the negative electrode active material in the A negative electrode active material layer, BET b m 2 / g represents the specific surface area of ​​the negative electrode active material in the B negative electrode active material layer.

[0035] As an embodiment of the present invention, the negative electrode sheet satisfies: BET a =0.6~1.8m 2 / g.

[0036] As an embodiment of the present invention, the negative electrode sheet satisfies: BET b =0.6~1.8m 2 / g.

[0037] As an embodiment of the present invention, the negative electrode sheet satisfies: α A ≤α B , where α A % represents the porosity of the A negative electrode active material layer, α B % represents the porosity of the B negative electrode active material layer.

[0038] As an embodiment of the present invention, the negative electrode sheet satisfies: ρ A ≥ρ B , where ρ A g / 1540.25cm 2 ρ represents the surface density of the A negative electrode active material layer. B g / 1540.25cm 2 This represents the areal density of the B negative electrode active material layer.

[0039] In a second aspect, the present invention provides a secondary battery comprising the negative electrode sheet described in the first aspect of the present invention.

[0040] A third aspect of the present invention provides an electrical device comprising the secondary battery described in the second aspect of the present invention.

[0041] Compared with the prior art, the beneficial effects of the present invention are:

[0042] This invention designs the active material layer on the surface of the negative electrode sheet, coats different active material layers, and reasonably sets the relevant parameters of different active layers. This can increase the liquid absorption capacity in the middle of the negative electrode sheet, improve the internal stress in the middle of the negative electrode sheet, reduce the risk of lithium plating, and improve the cycle performance of the battery. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the negative electrode sheet in an embodiment of the present invention. In the figure, regions A1 and A2 are the A negative electrode active material layers disposed near the edge of the current collector surface. The parameters of the active material layers in regions A1 and A2 are consistent, and the coating width is also the same. Region B is the B negative electrode active material layer disposed in the middle of the current collector surface. Detailed Implementation

[0044] To better illustrate the purpose, technical solution, and advantages of this invention, specific embodiments will be used to further describe the invention below. However, these embodiments do not limit the invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this invention are commercially available.

[0045] An embodiment of the present invention provides a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active material layer disposed on at least one surface of the current collector, the negative electrode active material layer comprising an A negative electrode active material layer near the edge region of the current collector and a B negative electrode active material layer in the middle region of the current collector, and the negative electrode active material layers satisfy the following relationship:

[0046] 0.89≤(PD a ×Q a ×V OIa ) / (PD b ×Q b ×V OIb ≤8.25;

[0047] In the formula, PD a g / cm 3 This indicates the compaction density of the A negative electrode active material layer;

[0048] PD b g / cm 3 This indicates the compaction density of the B negative electrode active material layer;

[0049] Q a mAh / g represents the specific capacity of the negative electrode active material in the A negative electrode active material layer;

[0050] Qb mAh / g represents the specific capacity of the negative electrode active material in the B negative electrode active material layer;

[0051] V OIa This represents the OI value of the negative electrode sheet in the region corresponding to the A negative electrode active material layer;

[0052] V OIb This represents the OI value of the negative electrode sheet in the region corresponding to the B negative electrode active material layer.

[0053] This invention designs the active coating layers in the middle and on both sides of the electrode, setting different active material layers in the middle of the electrode and specifically designing and matching the parameters of the two active material layers. This can significantly increase the porosity of the coating layer in the middle of the electrode, increase the liquid absorption capacity in the middle of the electrode, and improve the wettability of the active material in the middle of the electrode; reduce the compaction density in the middle of the electrode, improve the internal stress in the middle of the electrode, and improve the problem of liquid shortage in the middle of the electrode caused by electrolyte compression after the electrode expands; thereby reducing the risk of lithium plating in the cell, improving the cycle performance of the cell, and extending the life of the cell; at the same time, it can also reduce the amount of high-cost active material used, which is conducive to reducing production costs.

[0054] It should be noted that in this invention, the A negative electrode active material layer and the B negative electrode active material layer in the negative electrode sheet are not the same, specifically in that: PD a and PD b Q a and Q b V OIa and V OIb They are not equal at the same time.

[0055] In some embodiments, the negative electrode sheet satisfies: PD a ≥PD b The negative electrode active material coating on the negative electrode sheet has a higher compaction density in the edge region (A negative electrode active material layer) to ensure the strength of the electrode sheet; the middle region (B negative electrode active material layer) has a lower compaction density, which provides a certain buffer for the volume expansion of the negative electrode active material during cycling, and has a larger porosity, which is beneficial to electrolyte wetting and ion exchange.

[0056] In some embodiments, the negative electrode plate satisfies: Q a ≤Q b .

[0057] In some embodiments, the negative electrode plate satisfies: V OIa ≥V OIb .

[0058] Generally, using active materials with relatively small specific capacity in areas with lower compaction density can reduce lithium plating on the electrode. However, this leads to lower energy density in the secondary battery, or limited improvement in energy density. Therefore, the inventors of this invention further adjust the compaction of the negative electrode by setting the OI value of the two electrode regions, which is more conducive to the design of a lower compaction density in the middle of the negative electrode, while ensuring that the secondary battery has a higher energy density.

[0059] In this invention, the OI value V of the negative electrode is... OI =C 004 / C 110 , where C 004 C represents the peak area of ​​the characteristic diffraction peak 004 in the X-ray diffraction pattern of the negative electrode. 110 V represents the peak area of ​​the characteristic diffraction peak 110 in the X-ray diffraction pattern of the negative electrode. OIa The X-ray diffraction pattern of region A, the negative electrode active material layer on the surface of the negative electrode sheet, V OIb X-ray diffraction pattern of the region of the B-type active material layer on the surface of the corresponding negative electrode sheet.

[0060] In some embodiments, the negative electrode sheet satisfies: PD a =1~2g / cm 3 Specifically, it could be 1.55 g / cm³. 3 1.60g / cm 3 1.70g / cm 3 , and the range formed by any two of the above values.

[0061] In some embodiments, the negative electrode sheet satisfies: PD b =1~2g / cm 3 Specifically, it could be 1.56 g / cm³. 3 1.57g / cm 3 1.60g / cm 3 , and the range formed by any two of the above values.

[0062] In some embodiments, the negative electrode plate satisfies: Q a =330~370mAh / g. Specifically, it can be 335mAh / g, 348mAh / g, 350mAh / g, or any range of two of the above values.

[0063] In some embodiments, the negative electrode plate satisfies: Q b =330~370mAh / g. Specifically, it can be 335mAh / g, 348mAh / g, 354mAh / g, 356mAh / g, or any range of two of the above values.

[0064] In some embodiments, the negative electrode plate satisfies: V OIa =2 to 15. Specifically, it can be 2.23, 6.87, 14.50, or any two of the above values.

[0065] In some embodiments, the negative electrode plate satisfies: V OIb =2 to 15. Specifically, it can be 2.03, 2.86, 3.27, 3.65, or any range of two of the above values.

[0066] In the negative electrode sheet, if the compaction density, specific capacity, and electrode OI value are within the above-mentioned appropriate ranges, the energy density and cycle performance of the secondary battery can be further improved.

[0067] In some embodiments, the width H of the region corresponding to the A negative electrode active material layer in the negative electrode sheet. A The width H of the region corresponding to the B negative electrode active material layer B The ratio of H satisfies A H B =0.66~4. When the proportions of the two coating regions are within the above-mentioned suitable range, lithium plating on the negative electrode can be significantly reduced and the expansion of the electrode during cycling can be alleviated, thereby further improving the cycle life of the secondary battery prepared from it.

[0068] In some embodiments, the negative electrode sheet satisfies: G OIa ≥G OIb Among them, G OIa G represents the OI value of the negative electrode active material powder in the A negative electrode active material layer. OIb This represents the OI value of the negative electrode active material powder in the B negative electrode active material layer. The OI value G of the negative electrode active material powder. OI =C′ 004 / C′ 110 , where C′ 004 The peak area of ​​the characteristic diffraction peak 004 in the X-ray diffraction pattern of the negative electrode active material powder, C′ 110 The peak area of ​​the 110 characteristic diffraction peak in the X-ray diffraction pattern of the powder used as the negative electrode active material.

[0069] In some embodiments, the G OIa =1 to 6.

[0070] In some embodiments, the G OIb =1 to 6.

[0071] In some embodiments, the negative electrode sheet satisfies: D v50a ≥D v50b , where Dv50a μm represents the particle size corresponding to when the cumulative volume percentage of the negative electrode active material in layer A reaches 50%; D v50b μm represents the particle size corresponding to the cumulative volume percentage of the negative electrode active material in the B negative electrode active material layer reaching 50%. A particle size of the negative electrode active material powder within the aforementioned suitable range is beneficial for controlling the OI value of different active coating regions on the electrode surface; it also ensures the electrode surface has a suitable specific surface area and porosity, improving the electrode's wettability to the electrolyte and enhancing the battery's cycle performance.

[0072] In some embodiments, the negative electrode sheet satisfies: BET a ≤BET b Among them, BET a m 2 / g represents the specific surface area of ​​the negative electrode active material in the A negative electrode active material layer, BET b m 2 / g represents the specific surface area of ​​the negative electrode active material in the B negative electrode active material layer. a =0.6~1.8m 2 / g; and / or, BET b =0.6~1.8m 2 / g. The specific surface area of ​​the negative electrode can be obtained by measuring the specific surface area.

[0073] In some embodiments, the negative electrode plate satisfies: α A ≤α B , where α A % represents the porosity of the A negative electrode active material layer, α B The percentage (%) represents the porosity of the B-type negative electrode active material layer. The porosity of the corresponding negative electrode active material layer can be controlled by adjusting the density of the negative electrode active material and the compaction density of different coatings on the electrode sheet. α A and α B Within the range of 20-40%.

[0074] In some embodiments, the negative electrode plate satisfies: ρ A ≥ρ B , where ρ A g / 1540.25cm 2 ρ represents the surface density of the A negative electrode active material layer. B g / 1540.25cm 2 ρ represents the areal density of the B-type negative electrode active material layer. A and ρ B Within 0.1-0.35g / 1540.25cm 2Within the aforementioned suitable range, setting the areal density of the active material coating can further improve the battery's energy density and cycle performance.

[0075] Commonly used negative electrode active materials in this field can be used in this invention. The active materials in the A negative electrode active material layer and the B negative electrode active material layer are independently including, but not limited to, at least one of artificial graphite and natural graphite.

[0076] In addition to the negative electrode active material, the negative electrode active material layer may also include a certain amount of conductive agent, binder, thickener, and solvent required to form a slurry. The conductive agent, binder, thickener, and solvent commonly used in secondary batteries in the art can be used to prepare the negative electrode sheet in this invention.

[0077] In some embodiments, the slurry of the negative electrode active material layer comprises the following components in parts by weight: 90-99 wt% negative electrode active material, 0.01-3 wt% thickener, 0.01-3 wt% binder, and 0.01-3 wt% conductive agent.

[0078] The conductive agent includes, but is not limited to, at least one of acetylene black, Ketjen black, CNT, SWCNT, Superp, VGCF, and graphene; the thickener includes, but is not limited to, carboxymethyl cellulose or its inorganic salt; and the binder includes, but is not limited to, styrene-butadiene rubber (SBR).

[0079] Embodiments of the present invention also provide a secondary battery comprising the aforementioned negative electrode, positive electrode, electrolyte, and separator. In this invention, the types of positive electrode, electrolyte, and separator are not specifically limited.

[0080] The present invention also protects electrical devices that include the aforementioned secondary batteries.

[0081] The following are specific embodiments of the present invention, and the technical solution of the present invention will be further described in conjunction with the embodiments. However, the present invention is not limited to these embodiments. Unless otherwise specified, the reagents, methods and equipment used in the present invention are all conventional reagents, methods and equipment in this technical field.

[0082] Examples 1-7, Comparative Examples 1-4

[0083] A series of secondary batteries are provided, and the preparation method of the secondary batteries includes the following steps:

[0084] Preparation of positive electrode sheet

[0085] The positive electrode active material NCM523, conductive agent acetylene black, and binder PVDF are mixed at a mass ratio of 96:2:2. The solvent NMP is added, and the mixture is stirred under vacuum until the system is homogeneous to obtain the positive electrode slurry. The positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to an oven for further drying. After cold pressing, slitting, and cutting, the positive electrode sheet is obtained.

[0086] Preparation of negative electrode sheet

[0087] The negative electrode active material graphite, conductive agent acetylene black, thickener CMC, and binder SBR were mixed in a mass ratio of 96.4:1:1.2:1.4. Deionized water was added as a solvent, and the mixture was stirred under vacuum until homogeneous, yielding negative electrode slurry A and negative electrode slurry B. Negative electrode slurry A and negative electrode slurry B were uniformly coated onto the negative electrode current collector copper foil to form negative electrode active material layer A and negative electrode active material layer B, respectively. After air drying at room temperature, they were transferred to an oven for further drying. Then, after cold pressing, slitting, and cutting, the final product was obtained as shown below. Figure 1 The negative electrode sheet of the structure shown has the same width in regions A1 and A2 on the electrode sheet.

[0088] The specific parameters of the A negative electrode active material layer and the B negative electrode active material layer are shown in Table 1 and Table 2.

[0089] Preparation of electrolyte

[0090] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0091] Preparation of secondary batteries

[0092] The positive electrode, separator (polyethylene film), and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The cells are then wound to obtain a bare cell with a core area margin of 97.5%. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0093] Table 1. Relevant parameters of the negative electrode sheet (Part 1)

[0094]

[0095] Note: In Table 1, Comparative Example 3 shows that the active material layer on the surface of the negative electrode does not contain negative electrode active material layer B, but instead uses negative electrode slurry A to coat the entire surface of the negative electrode; similarly, Comparative Example 4 shows that the active material layer on the surface of the negative electrode does not contain negative electrode active material layer A, but instead uses negative electrode slurry B to coat the entire surface of the negative electrode; the same applies below.

[0096] Table 2. Relevant parameters of the negative electrode sheet (II)

[0097]

[0098]

[0099] The performance of the secondary batteries obtained in the above embodiments and comparative examples was tested. The specific test items, test methods, and results are as follows:

[0100] 1) Test of liquid absorption rate (mg / s) of negative electrode: a. Cut electrode samples with the same area of ​​coating region A1 or A2 and coating region B, and weigh them M0; b. Put the weighed electrode samples into a container; c. Pour electrolyte into the container to immerse the electrode samples; d. Place the container in a constant temperature / low humidity environment for a time t; e. Take out the electrode, wipe the free wetting liquid on the surface of the electrode sample with filter paper, and weigh it M1; f. Calculate: Electrode liquid absorption amount = M1 - M0; Electrode liquid absorption rate = (M1 - M0) / t.

[0101] 2) Test the battery's DCR: At room temperature (25℃), charge the battery to full charge (100% SOC) using a 1 / 3C charging current, and cut off the current at 0.05C. After resting for 15 minutes, discharge the battery to 30%, 50%, and 70% SOC at a 1 / 3C current, followed by 10 seconds of 3C discharge / charge. The battery's DCR can predict its lifespan. The lower the DCR, the greater the battery's output power and the longer its lifespan.

[0102] 3) Lithium plating: At room temperature (25℃), the battery was charged to full capacity (100% SOC) using a 1 / 3C charging current, and the cutoff current was 0.05C. After resting for 15 minutes, the battery was discharged to 0% SOC at a 1 / 3C current, and the discharge capacity was recorded as C0. Then, a stepped charging cycle strategy was executed: rest for 15 minutes, charge at 1C for 6 minutes to 10% SOC, and then perform a stepped (2C, 2.4C, 2.6C, 2.8C) charging strategy from 10% to 80% SOC. Then, charge at 0.5C for 1008 seconds and at 0.2C for 540 seconds to 97% SOC. After resting for 30 minutes, the battery was discharged to 0% SOC at 1C0 and then rested for 120 minutes.

[0103] 10%–80% SOC tiered charging strategy:

[0104] 2.0C 10~80% SOC charging strategy: 2.8C charging 386s, 2.4C charging 150s, 2C charging 180s, 1.55C charging 232s, 1.15C charging 313s;

[0105] 2.4C 10~80% SOC charging strategy: 3.2C charging for 338s, 2.8C charging for 128s, 2.3C charging for 156s, 1.9C charging for 190s, and 1.5C charging for 240s;

[0106] 2.6C 10~80% SOC charging strategy: 3.4C charging 318s, 2.9C charging 124s, 2.5C charging 144s, 2.1C charging 171s, 1.7C charging 212s;

[0107] 2.8C 10~80% SOC charging strategy: 3.7C charging 292s, 3.2C charging 112s, 2.7C charging 133s, 2.2C charging 164s, 1.8C charging 200s.

[0108] After 50 cycles, the fully charged disassembly and analysis interface defines the following: when the lithium plating area on the negative electrode is >40%, it is defined as "severe lithium plating"; when the lithium plating area on the negative electrode is 10% < X ≤ 40%, it is defined as "moderate lithium plating"; when the lithium plating area on the negative electrode is 0% < X ≤ 10%, it is defined as "slight lithium plating"; and when the lithium plating area on the negative electrode is X ≤ 0%, it is considered "no lithium plating".

[0109] 4) Battery energy density (Wh / kg) test: At room temperature of 25℃, charge to full charge (100% SOC) using a 1 / 3C charging current, and cut off current of 0.05C; after resting for 15 minutes, discharge to 0% SOC at a 1 / 3C current, record the cell discharge energy, and calculate using the formula: Energy density = Discharge energy / Cell weight.

[0110] Table 3

[0111]

[0112] Table 4. Lithium deposition results of the negative electrode sheet.

[0113]

[0114] The results above show that:

[0115] This invention designs the active material layer on the surface of the negative electrode sheet, coats different active material layers, and reasonably sets the relevant parameters of different active layers to meet the specific relationship formula of this invention within a certain range. This can increase the liquid absorption capacity in the middle of the negative electrode sheet, improve the internal stress in the middle of the negative electrode sheet, reduce the risk of lithium plating, and improve the cycle performance of the battery.

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A negative electrode sheet, comprising a current collector and a negative electrode active material layer disposed on at least one surface of the current collector, characterized in that, The negative electrode active material layer includes a negative electrode active material layer A near the edge region of the current collector and a negative electrode active material layer B in the middle region of the current collector, and the negative electrode active material layers satisfy the following relationship: 0.89≤(PD a ×Q a ×V OIa ) / (PD b ×Q b ×V OIb )≤2.41; In the formula, PD a g / cm 3 This indicates the compaction density of the A negative electrode active material layer; PD b g / cm 3 This indicates the compaction density of the B negative electrode active material layer; Q a mAh / g represents the specific capacity of the negative electrode active material in the A negative electrode active material layer; Q b mAh / g represents the specific capacity of the negative electrode active material in the B negative electrode active material layer; V OIa V represents the OI value of the negative electrode sheet in the region corresponding to the A negative electrode active material layer. OIa =2~6.87; V OIb V represents the OI value of the negative electrode sheet in the region corresponding to the B negative electrode active material layer. OIb =2~3.

65.

2. The negative electrode sheet according to claim 1, characterized in that, PD a and PD b Q a and Q b V OIa and V OIb They are not simultaneously equal if at least one of the following conditions is met: (1)PD a ≥PD b ; (2)Q a ≤Q b ; (3)In OIa ≥V OIb 。 3. The negative electrode sheet according to claim 2, characterized in that, At least one of the following conditions must be met: (1)PD a =1~2 g / cm 3 ; (2)PD b =1~2 g / cm 3 ; (3)Q a =330~370 mAh / g; (4)Q b =330~370 mAh / g。 4. The negative electrode sheet according to claim 1, characterized in that, In the negative electrode sheet, the width H of the region corresponding to the A negative electrode active material layer is... A The width H of the region corresponding to the B negative electrode active material layer B The ratio of H satisfies A H B =0.66~4.

5. The negative electrode sheet according to claim 1, characterized in that, The active materials in the A negative electrode active material layer and the B negative electrode active material layer independently include at least one of artificial graphite and natural graphite.

6. The negative electrode sheet according to claim 5, characterized in that, The active material satisfies at least one of the following conditions: 1) G OIa ≥G OIb Among them, G OIa G represents the OI value of the negative electrode active material powder in the A negative electrode active material layer. OIb This indicates the OI value of the negative electrode active material powder in the B negative electrode active material layer; 2) D v50a ≥D v50b , where D v50a μm represents the particle size corresponding to when the cumulative volume percentage of the negative electrode active material in layer A reaches 50%; D v50b μm represents the particle size when the cumulative volume percentage of the negative electrode active material in the B negative electrode active material layer reaches 50%. 3) BET a ≤BET b Among them, BET a m 2 / g represents the specific surface area of ​​the negative electrode active material in the A negative electrode active material layer, BET b m 2 / g represents the specific surface area of ​​the negative electrode active material in the B negative electrode active material layer.

7. The negative electrode sheet according to claim 1, characterized in that, The negative electrode plate satisfies: α A ≤α B , where α A % represents the porosity of the A negative electrode active material layer, α B % represents the porosity of the B negative electrode active material layer.

8. The negative electrode sheet according to claim 1, characterized in that, The negative electrode plate satisfies: ρ A ≥ρ B , where ρ A g / 1540.25cm 2 ρ represents the surface density of the A negative electrode active material layer. B g / 1540.25cm 2 This represents the areal density of the B negative electrode active material layer.

9. A secondary battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1 to 8.

10. An electrical device, characterized in that, Includes the secondary battery as described in claim 9.

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