Negative electrode sheet, battery, and electric device

Abstract

The application provides a negative electrode sheet, a battery and an electric device. The negative electrode sheet comprises a current collector and a negative active material layer coated on at least one side of the current collector; the negative active material layer comprises a negative active material, a silica aerogel and a binder; the silica aerogel is filled between the negative active materials; and the silica aerogel accounts for 0.1% to 5% of the total mass of the negative active material layer. The addition of 0.1% to 5% of the silica aerogel in the negative electrode sheet can improve the ionic conductivity of the negative electrode sheet, shorten the carrier ion conduction path and improve the polarization of the electrode sheet and the battery, thereby effectively improving the cycle performance and rate performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a negative electrode sheet, a battery and an electric device. BACKGROUND

[0002] Secondary batteries (for example: lithium ion batteries) are widely used in new energy vehicles, portable electronic products and large-scale energy storage devices due to their high working voltage, large energy density, long cycle life and small self-discharge. With the continuous pursuit of high energy density and fast charging technology by the downstream application end, the compaction density and thickness of the battery electrode sheet are continuously improved, which leads to serious problems such as low porosity and poor electrolyte wettability of the negative electrode sheet. In the prior art, the content of the conductive agent in the negative electrode sheet is increased to improve the electrical conductivity of the negative electrode sheet, thereby promoting the conduction ability of the charge carriers (for example: lithium ions) in the negative electrode sheet. However, too much conductive agent will increase the electrical contact interface between the negative electrode sheet and the electrolyte, leading to an increase in the side reaction of the negative electrode sheet and a decrease in the cycle life of the secondary battery.

[0003] Therefore, it is necessary to provide a new negative electrode sheet to meet the application requirements of fast charging performance and long cycle life of the secondary battery (for example: lithium ion battery). SUMMARY

[0004] In view of this, the present application provides a negative electrode sheet, which can improve the liquid retention capacity and the transmission ability of the charge carrier ions of the negative electrode sheet, thereby effectively increasing the cycle performance and the fast charging performance of the battery.

[0005] The first aspect of the present application provides a negative electrode sheet, which comprises a current collector and a negative active material layer coated on at least one side of the current collector; the negative active material layer comprises a negative active material, a silica aerogel and a binder; the silica aerogel is filled between the negative active materials; the silica aerogel accounts for 0.1% to 5% of the total mass of the negative active material layer.

[0006] In the present application, the negative electrode sheet contains 0.1% to 5% of the silica aerogel, which improves the rate performance and cycle life of the negative electrode sheet and the battery. First, the porous structure of the silica aerogel is beneficial to enhancing the electrolyte absorption effect of the negative electrode sheet, making the electrolyte permeate from the pores of the silica aerogel to the negative active material, shortening the carrier ion (lithium ion) conduction path, and promoting the electrochemical kinetic performance of the negative electrode sheet and the battery; second, filling 0.1% to 5% of the silica aerogel between the negative active materials is beneficial to improving the pore structure of the negative electrode sheet, relieving the non-uniformity of the electrode sheet pores caused by the disordered expansion and shrinkage of the negative active material during the charging and discharging process of the battery, further improving the polarization phenomenon, and improving the rate performance of the battery; third, the silica aerogel has a low dielectric constant, which can reduce the side reaction of the exposed conductive interface of the negative electrode sheet and the electrolyte, and increase the cycle life of the battery.

[0007] The second aspect of the present application provides a battery, which comprises a positive electrode sheet, an electrolyte, a diaphragm and the negative electrode sheet provided in the first aspect of the present application.

[0008] Since the above-mentioned battery comprises the negative electrode sheet provided in the first aspect of the present application, the battery has high rate performance and cycle life, and meets more application requirements.

[0009] The third aspect of the present application provides a power consumption device, which comprises the battery provided in the second aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 The SEM picture of the cross section of the negative electrode sheet vertical current collector provided in Example 1 in the present application.

[0011] Figure 2 The SEM picture provided in the present application Figure 1 The EDS element distribution picture of C, O, Si and Cu in the SEM picture. IMPLEMENTATION

[0012] The present application will be further described below by examples and comparative examples, which are only used to illustrate the present application, and the present application is not limited to the following examples. Any modification or equivalent replacement to the technical solutions of the present application without departing from the scope of the technical solutions of the present application shall be covered in the protection scope of the present application.

[0013] The negative electrode sheet provided in the present application comprises a current collector and a negative active material layer coated on at least one side of the current collector; the negative active material layer comprises a negative active material, a silica aerogel and a binder; the silica aerogel accounts for 0.1% to 5% of the total mass of the negative active material layer.

[0014] In the present application, the negative electrode sheet contains 0.1% to 5% of silica aerogel, which improves the rate performance and cycle life of the negative electrode sheet and the battery. First, the porous structure of the silica aerogel is beneficial to enhancing the electrolyte absorption effect of the negative electrode sheet, making the electrolyte permeate from the pores of the silica aerogel to the negative active material, shortening the carrier ion (lithium ion) conduction path, and promoting the electrochemical kinetic performance of the negative electrode sheet and the battery; second, filling 0.1% to 5% of silica aerogel between the negative active materials is beneficial to improving the pore structure of the negative electrode sheet, relieving the unevenness of the electrode sheet pores caused by the disordered expansion and shrinkage of the negative active material during the charging and discharging process of the battery, further improving the polarization phenomenon, and improving the rate performance of the battery; third, the silica aerogel has a low dielectric constant, which can reduce the side reaction of the exposed conductive interface of the negative electrode sheet and the electrolyte, and increase the cycle life of the battery.

[0015] In addition, the silica aerogel has stable chemical properties and will not destroy the electrochemical reaction system inside the battery; has good thermal insulation property, can also increase the safety performance of the battery; and has a low price to meet the application requirements of industrial grade.

[0016] Exemplarily, the total mass of the negative active material layer can be 0.1%, 0.5%, 1%, 2%, 3%, or 5%, etc.

[0017] In the present application, the negative active material layer can be coated on one side of the current collector. The negative active material layer can also be coated on both sides of the current collector. When the negative active material layer is coated on both sides of the current collector, the thickness, surface density, component content, etc. of the negative active material layer located on both sides of the current collector can be independently designed according to the application requirements, which can be the same or different.

[0018] In the present application, the negative active material can be a carbon-based material.

[0019] In the present application, the negative active material can also be a combination of one or more of a silicon-based material, a tin-based material, and a lithium titanate material and a carbon-based material, wherein the carbon-based material accounts for 80% to 97% of the total mass of the negative active material.

[0020] The carbon-based material can be a combination of one or more of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, and carbon fiber.

[0021] The silicon-based material can be a combination of one or more of elemental silicon, silicon oxide (SiO x , 0 < x < 2), and silicon alloy. The tin-based material can be a combination of one or more of elemental tin, tin oxide (SnO x , 0 < x ≤ 2), and tin alloy.

[0022] In the present application, the current collector can be any one of copper foil, carbon-coated copper foil, polymer-coated copper foil, carbon cloth, carbon nanotube film or carbon paper.

[0023] In the present application, the current collector can also be any one of aluminum foil, carbon-coated aluminum foil, polymer-coated aluminum foil (for example, used for sodium ion battery negative electrode current collector).

[0024] In the present application, the binder includes one or a combination of several of styrene butadiene rubber (SBR), carboxymethyl cellulose sodium (CMC), polyacrylic acid (PAA), polyacrylic ethylene acrylic acid (PEAA), sodium alginate, carboxymethyl chitosan, polyacrylonitrile (PAN) and polyvinyl alcohol (PVA).

[0025] In some embodiments of the present application, the porosity of the negative electrode sheet is 20% to 80%.

[0026] In the present application, the negative electrode sheet contains silica aerogel. Understandably, the pores of the negative electrode sheet include the pores of the silica aerogel itself, the gaps between the silica aerogel and the negative electrode active material, and the gaps between the negative electrode active materials after disordered stacking. The porosity of the negative electrode sheet is in the range of 20% to 80%, the carrier (lithium ion) shuttle efficiency of the negative electrode sheet is better, and the negative electrode sheet and the battery have higher rate performance; at the same time, the negative electrode sheet has a higher liquid storage capacity, which can provide more sufficient electrolyte during battery cycling, thereby increasing the cycle life of the battery. Exemplarily, the porosity of the negative electrode sheet can be 20%, 30%, 50%, 60% or 80%, etc.

[0027] In the present application, the porosity of the negative electrode sheet is further preferably 30% to 60%. The porosity of the negative electrode sheet in this range can also ensure higher mechanical properties of the negative electrode sheet, further improving the cycle stability of the battery.

[0028] The porosity of the negative electrode sheet is measured as follows: the negative electrode sheet is cut into a film of a certain area, the film is dried in a 120°C vacuum drying oven for 12h, and then tested after being cooled in a desiccator. First, the thickness of the sample (excluding the thickness of the current collector foil) is measured using a micrometer, and the apparent volume (V1) of the sample is calculated according to the surface area and thickness of the sample. Then, the true volume (V2) of the sample (excluding the volume of the current collector foil) is measured using a true density instrument. The porosity of the negative electrode sheet is calculated as follows: porosity of the negative electrode sheet = true volume (V2) / apparent volume (V1) * 100%.

[0029] In some embodiments of the present application, the dielectric constant of the silica aerogel is ε, and 0 < ε ≤ 10. That is, the silica aerogel has the property of not conducting electricity under the action of an external electric field, so as to stabilize the contact interface between the negative electrode sheet and the electrolyte, alleviate the side reaction with the electrolyte, and thus improve the coulomb efficiency of the battery; at the same time, it can also reduce the excessive consumption of electrolyte and increase the cycle life of the battery.

[0030] In some embodiments of the present application, the bulk density of the silica aerogel is 0.003-0.500 g / cm 3 .

[0031] Understandably, in the charging and discharging process of the negative electrode sheet, the pore structure of the negative electrode sheet changes randomly with the expansion and contraction of the negative active material, resulting in uneven distribution of pores in the negative electrode sheet, causing significant differences in electrolyte diffusion and carrier ion transfer flux, and the rate of the battery cannot be fully utilized. Therefore, the bulk density of the silica aerogel is in the range of 0.003-0.500 g / cm 3 , the electrolyte ions in the negative electrode sheet have a suitable storage capacity and diffusion path, which can further increase the rate performance of the battery. When the bulk density of the silica aerogel is too low (less than 0.003 g / cm 3 , it affects its dispersibility in the negative electrode sheet; when the bulk density of the silica aerogel in the negative electrode sheet is too high (greater than 0.5 g / cm 3 , the buffering effect on the expansion and contraction of the negative active material is not obvious.

[0032] In addition, the silica aerogel with a volume density of 0.1%-5% in the range of 0.003-0.500 g / cm 3 can also act as an effective buffer medium to prevent irreversible damage to the negative electrode sheet caused by excessive pressure during the rolling of the negative electrode sheet, resulting in the inability of the electrolyte to infiltrate the negative electrode sheet.

[0033] In some embodiments of the present application, the specific surface area of the silica aerogel is 100-1500 m 2 / g.

[0034] Understandably, the silica aerogel has a high specific surface area and can adsorb more electrolyte to improve the liquid storage capacity of the negative electrode sheet. Therefore, the specific surface area of the silica aerogel is in the range of 100-1500 m 2 / g, which can further increase the cycle life of the battery.

[0035] In some embodiments of the present application, the silica aerogel comprises mesopores and macropores, and the volume of the mesopores and the macropores accounts for 60%-99.99% of the total pore volume of the silica aerogel.

[0036] Internationally, pores are generally divided into three categories according to size: micropores, mesopores (i.e. medium pores), and macropores. Among them, micropores have a pore size of less than 2 nm, mesopores have a pore size in the range of 2-50 nm, and macropores have a pore size of greater than 50 nm. The silica aerogel contains mesopores, which is conducive to the storage of electrolyte and can provide a buffer pool for the electrolyte, which is released when necessary, increasing the storage capacity of the negative electrode sheet and being conducive to increasing the cycle stability and rate performance of the negative electrode sheet; the silica aerogel also contains macropores, which provide a channel for the transmission of electrolyte, and the electrolyte ions stored in the mesopores diffuse to the surface of the negative electrode active material through the macropore channel, reducing the diffusion path of the electrolyte in the negative electrode sheet and increasing the rate performance of the battery. In this way, when the volume of the mesopores and macropores of the silica aerogel and the proportion of the total pore volume of the silica aerogel are 60% to 99.99%, the battery has better cycle performance and rate performance.

[0037] Among them, the volume of the mesopores and macropores of the silica aerogel is based on the ratio of the pore volume of the mesopores and macropores to the total cumulative pore volume in the BET test results of the silica aerogel.

[0038] In some embodiments of the present application, the average particle size of the silica aerogel is 0.05-100 μm.

[0039] The average particle size of the silica aerogel in the present application is in the range of 0.05-100 μm, which can meet the use requirements of negative electrode active materials in different particle size ranges, achieve better filling effect, and thus help the absorption and diffusion of electrolyte. For example, the particle size of the silica aerogel can be 0.05 μm, 0.1 μm, 0.5 μm, 1.0 μm, 2.0 μm, 3.0 μm, 10 μm, 20 μm, 50 μm, or 100 μm, etc.

[0040] In the present application, the average particle size of the silica aerogel is further preferably 0.5-50 μm. If the average particle size of the silica aerogel is too small, the surface energy is too large, which will affect its dispersibility in the negative electrode sheet; if the average particle size of the silica aerogel is too large, it will affect its contact effect with the negative electrode active material.

[0041] Among them, the determination method of the average particle size of the silica aerogel is: the silica aerogel is ultrasonically dispersed in anhydrous ethanol for 5 minutes, and a laser particle size analyzer is used for testing. Among them, D50 is the particle size of the silica aerogel, that is, the particle size corresponding to a volume percentage of less than 50% of the total volume on the particle size distribution curve.

[0042] In some embodiments of the present application, the negative electrode active material layer further comprises a conductive agent.

[0043] In the present application, the negative electrode sheet contains both the silica aerogel and the conductive agent, and the synergistic effect of the two can further improve the electrochemical performance of the battery.

[0044] In some embodiments of the present application, the conductive agent accounts for 0.1% to 5% of the total content of the active material layer.

[0045] It can be understood that the conductive agent in the negative electrode sheet fills between the negative electrode active materials, and can play a certain role in liquid storage and electrical conduction, but the exposed conductive interface will increase the side reactions of the electrolyte. Therefore, the content of the conductive agent in the above range can ensure the electrical conductivity and liquid storage capacity of the negative electrode sheet, and can also inhibit the side reactions of the electrode sheet to ensure the rate performance and cycle life of the battery.

[0046] In some embodiments of the present application, the mass ratio of the silica aerogel to the conductive agent is (0.2-10):1. In this way, when the mass ratio of the silica aerogel to the conductive agent is within the range of (0.2-10):1, the synergistic effect of the silica aerogel and the conductive agent is stronger, and the comprehensive performance of the battery is better.

[0047] In the present application, the conductive agent can be one or a combination of several of conductive carbon black, carbon nanotubes, graphene, and carbon fibers. Among them, the conductive carbon black material can be one or a combination of several of acetylene black, furnace black, channel black, pyrolytic black, lamp black, and ketjen black; the carbon nanotubes can be one or a combination of several carbon nanotubes with different tube diameters (1-100 nm) and different tube lengths (0.05-100 μm); and the graphene can be one or a combination of several graphene with different layers (1-1000 layers).

[0048] Correspondingly, the present application also provides a battery, which includes a positive electrode sheet, an electrolyte, a diaphragm, and the negative electrode sheet provided in the first aspect. Since the above-mentioned battery includes the negative electrode sheet provided in the first aspect of the present application, the battery has higher rate performance and cycle life, and meets more application requirements.

[0049] In the present application, the above-mentioned battery can be any one of a lithium ion battery or a sodium ion battery.

[0050] In the present application, the positive electrode sheet includes a current collector and a positive electrode active material layer coated on at least one side of the current collector; and the active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0051] In the present application, the positive electrode active material layer can be coated on one side of the current collector; or can be coated on both sides of the current collector. When the positive electrode active material layer is coated on both sides of the current collector, the thickness, surface density, and component content of the positive electrode active material layer on both sides of the current collector can be independently designed according to application requirements, and can be the same or different.

[0052] In the present application, the positive current collector can be any one of an aluminum foil, a carbon-coated aluminum foil, a polymer-coated aluminum foil, a carbon cloth, a carbon nanotube film, or a carbon paper.

[0053] In the present application, the separator can be a composite film of one or more of polyethylene, polypropylene, and polyvinylidene fluoride.

[0054] In the present application, the positive active material can be one or a combination of several of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-containing phosphate with an olivine structure. The above positive active material is suitable for a lithium ion battery.

[0055] In the present application, the positive active material can also be one or a combination of several of a transition metal oxide, a polyanion compound, an organic polymer, and a Prussian blue / white material. The above positive active material is suitable for a sodium ion battery.

[0056] In the present application, the electrolyte is an organic solvent in which a carrier ion is dissolved. The electrolyte is not limited in the present application and can be self-adjusted according to actual conditions.

[0057] The present application also provides a power-consuming device. The power-consuming device can have higher market competitiveness by using the battery provided in the present application.

[0058] In some embodiments of the present application, the power-consuming device includes, but is not limited to, a mobile phone, a notebook computer, a tablet computer, a wearable electronic device such as a smart watch, an electronic cigarette, and a new energy vehicle, an electric moped, and an energy storage base station.

[0059] The technical solutions of the present application are further described in the following embodiments. Embodiment 1

[0060] The negative active material (artificial graphite), the conductive agent (conductive carbon black), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and silica aerogel are mixed in a ratio of 96:0.5:1:2:0.5, and the powder and deionized water are stirred into a negative electrode slurry by using a homogenizer and uniformly coated on a copper foil. The dielectric constant of the silica aerogel is 2.1, the average particle size (D50) is 3 μm, the mesopore and macropore volume sum is 65%, the bulk density is 0.4 g / cm 3 , and the specific surface area is 500 m 2 / g.

[0061] The positive active material lithium iron phosphate (LiFePO4), conductive agent (CNT), and binder (PVDF) are mixed in a ratio of 97:1:2, and the powder and NMP are stirred in a homogenizer to form a positive electrode slurry and uniformly coated on an aluminum foil.

[0062] Ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) are mixed in a volume ratio of 1:1:1 to prepare an electrolyte containing 1M LiPF6.

[0063] A polypropylene separator is selected to prepare a 1.5 Ah laminated battery. Example 2

[0064] The difference from Example 1 is that the mass ratio of the negative active material (artificial graphite), conductive agent (conductive carbon black), carboxymethyl cellulose sodium (CMC), styrene butadiene rubber (SBR), and silica aerogel is 96:0.9:1:2:0.1. Example 3

[0065] The difference from Example 1 is that the mass ratio of the negative active material (artificial graphite), conductive agent (conductive carbon black), carboxymethyl cellulose sodium (CMC), styrene butadiene rubber (SBR), and silica aerogel is 96:0.1:1:2:0.9. Example 4

[0066] The difference from Example 1 is that the mixing ratio of the negative active material (artificial graphite), conductive agent (conductive carbon black SP), thickening agent (CMC), binder (SBR), and silica aerogel is 94.55:2.0:1:2:0.45. Example 5

[0067] The difference from Example 1 is that the mixing ratio of the negative active material (artificial graphite), conductive agent (conductive carbon black SP), thickening agent (CMC), binder (SBR), and silica aerogel is 94.8:0.2:1:2:2.0. Example 6

[0068] The difference from Example 1 is that the mixing ratio of the negative active material (artificial graphite), conductive agent (conductive carbon black SP), thickening agent (CMC), binder (SBR), and silica aerogel is 96:0:1:2:1. Example 7

[0069] The difference from Example 1 is that the mixing ratio of the negative active material (artificial graphite), conductive agent (conductive carbon black SP), thickening agent (CMC), binder (SBR), and silica aerogel is 95:0:1:2:2. Example 8

[0070] The difference from Example 1 is only that the mixing ratio of the negative active material (artificial graphite), the conductive agent (conductive carbon black SP), the thickening agent (CMC), the binder (SBR), and the silica aerogel is 94:0:1:2:3. Example 9

[0071] The difference from Example 1 is only that the mixing ratio of the negative active material (artificial graphite), the conductive agent (conductive carbon black SP), the thickening agent (CMC), the binder (SBR), and the silica aerogel is 93:0:1:2:4. Example 10

[0072] The difference from Example 1 is only that the mixing ratio of the negative active material (artificial graphite), the conductive agent (conductive carbon black SP), the thickening agent (CMC), the binder (SBR), and the silica aerogel is 92:0:1:2:5. Example 11

[0073] The difference from Example 10 is only that the mesopore and macropore volume of the silica aerogel is 42%. Example 12

[0074] The difference from Example 10 is only that the mesopore and macropore volume of the silica aerogel is 99%. Example 13

[0075] The difference from Example 10 is only that the bulk density of the silica aerogel is: 0.8 g / cm 3 . Example 14

[0076] The difference from Example 10 is only that the bulk density of the silica aerogel is: 0.02 g / cm 3 . Example 15

[0077] The difference from Example 10 is only that the specific surface area of the silica aerogel is: 1450 m 2 / g. Example 16

[0078] The difference from Example 10 is only that the particle size of the silica aerogel is 20 μm; the specific surface area is: 250 m 2 / g. Example 17

[0079] The difference from Example 10 is only that the particle size of the silica aerogel is 20 μm; the specific surface area is: 1000 m 2 / g.

[0080] To highlight the beneficial effects of the embodiments of the present application, the following comparative examples are provided.

[0081] Comparative Example 1

[0082] The difference from Example 1 is only that the mass ratio of the negative active material (artificial graphite), the conductive agent (conductive carbon black), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and silica aerogel is 91.99:5:1:2:0.01.

[0083] Comparative Example 2

[0084] The difference from Example 5 is only that the mass ratio of the negative active material (artificial graphite), the conductive agent (conductive carbon black), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and silica aerogel is 90:0:1:2:7.

[0085] The content of silica aerogel, the content of conductive agent, and the porosity parameters in the negative electrode sheet of the present application are shown in Table 1; the battery performance test results are shown in Table 2.

[0086] Table 1

[0087] Test No. Silica aerogel (%) Conductive agent content (%) Negative electrode sheet porosity (%) Example 1 0.5 0.5 35.2 Example 2 0.1 0.9 25.8 Example 3 0.9 0.1 44.0 Example 4 0.45 2.0 36.3 Example 5 2.0 0.2 58 Example 6 1 0 48.6 Example 7 2 0 55.4 Example 8 3 0 63.5 Example 9 4 0 69.0 Example 10 5 0 74.5 Example 11 5 0 71.0 Example 12 5 0 79.5 Example 13 5 0 72.0 Example 14 5 0 81.4 Example 15 5 0 79.5 Example 16 5 0 71.0 Example 17 5 0 77 Comparative Example 1 0.01 5 23.1 Comparative Example 2 7 0 86.3

[0088] Electrochemical performance test

[0089] The above prepared batteries (including comparative example batteries) were tested at room temperature using a blue CT3002A battery test system, and the test results are summarized in Table 2.

[0090] Battery discharge capacity test: The battery was tested at 25°C under 0.1C / 0.1C cycle test, the voltage range was 2.0V-3.8V (charged to a voltage of 3.8V at a rate of 0.1C, rested for 30 min, then discharged to a voltage of 2.0V at a rate of 0.1C, i.e. 1 cycle), cycled 3 times, and the third discharge capacity of the battery was recorded as the discharge capacity of the battery.

[0091] First charge-discharge test:

[0092] The battery was tested at 25°C under 0.1C / 0.1C cycle test, the voltage range was 2.0V-3.8V (charged to a voltage of 3.8V at a rate of 0.1C, rested for 10 min, then discharged to a voltage of 2.0V at a rate of 0.1C, i.e. 1 cycle), and the first charge specific capacity and the first discharge specific capacity of the battery were recorded, and the first charge-discharge efficiency of the battery was calculated therefrom; the first discharge efficiency of the battery (%) = first charge specific capacity / first discharge specific capacity*100%.

[0093] Discharge rate test:

[0094] The battery was charged at 25℃ at 0.1C to a voltage of 3.8V, rested for 30 min, and then discharged at a discharge rate of 3C to a voltage of 2.0V, sequentially cycled 3 times, and the discharge efficiency of the battery was calculated using the charge and discharge data of the third cycle to evaluate the rate performance of the battery; battery discharge rate (%) = third cycle discharge specific capacity (3C) / third cycle charge specific capacity (0.1C) * 100%.

[0095] Charge ratio test:

[0096] The battery was charged at 25℃ at 3C to a voltage of 3.8V, rested for 30 min, and then discharged at a discharge rate of 0.1C to a voltage of 2.0V, sequentially cycled 3 times, and the charge efficiency of the battery was calculated using the charge and discharge data of the third cycle; battery charge rate (%) = third cycle discharge specific capacity (0.1C) / third cycle charge specific capacity (3C) * 100%.

[0097] Cycle life test: The battery was charged at 25℃ at 1C to a voltage of 3.8V, rested for 10 min, and then discharged at a discharge rate of 1C to a voltage of 2.0V, sequentially cycled 1000 times, and the capacity retention rate was recorded; capacity retention rate (%) after 1000 cycles = discharge specific capacity after 1000 cycles / discharge specific capacity after the third cycle * 100%.

[0098] Table 2

[0099] Test No. Battery discharge capacity (Ah) Capacity retention rate at 1000 cycles (%) Discharge rate (%) Charge rate (%) First charge-discharge efficiency (%) Example 1 1.44 92.5 94.6 91.7 89.7 Example 2 1.43 91.4 91.2 89.6 88.6 Example 3 1.46 92.7 93.7 91.6 90.2 Example 4 1.42 91.9 91.6 90.4 87.8 Example 5 1.42 92.9 94.1 91.9 90.8 Example 6 1.41 92.1 93.1 91.2 90.1 Example 7 1.39 92.4 93.8 91.6 90.3 Example 8 1.36 91.8 93.0 90.8 90.0 Example 9 1.35 89.9 92.0 89.3 89.4 Example 10 1.33 89.2 91.5 88.9 88.7 Example 11 1.31 88.5 89.8 88.0 88.5 Example 12 1.39 89.4 91.3 88.7 88.6 Example 13 1.34 89.1 90.5 88.0 88.9 Example 14 1.37 89.6 91.3 88.6 88.4 Example 15 1.32 88.5 90.8 88.0 88.3 Example 16 1.35 89.3 91.4 88.7 88.6 Example 17 1.36 89.5 91.6 88.9 88.7 Comparative Example 1 1.29 83.8 86.9 85.2 85.1 Comparative Example 2 1.23 86.4 87.5 86.9 88.4

[0100] As can be seen from the data in Tables 1-2, compared with Comparative Example 1 and Comparative Example 2, the negative electrode sheet provided in the embodiments of the present application contains a suitable mass percentage of silica aerogel, which partially or completely replaces the conductive agent and is filled in the negative electrode active material, thereby regulating the porosity of the negative electrode sheet and significantly improving the rate performance (discharge ratio and charge ratio) and cycle performance of the battery. Figure 1 And Figure 2 The SEM image of the vertical current collector cross-section of the negative electrode sheet in Example 1 of the present application and its corresponding EDS image are shown in the figure, from which it can be seen that the silicon element (silica aerogel) is uniformly dispersed in the negative electrode material. In Comparative Example 1, a small amount of silica aerogel is added to the negative electrode sheet, the porosity of the electrode sheet is low, the diffusion path of the electrolyte is long, resulting in high lithium ion transmission impedance and poor battery rate performance. It can be seen that by adding silica aerogel to the negative electrode sheet, the pore structure in the negative electrode sheet is optimized, the porosity and liquid absorption rate of the negative electrode sheet are increased, which is of great benefit to promoting the adsorption and migration of the electrolyte.

[0101] In addition, the data of embodiments 1-6 can find that the addition of a suitable conductive agent and silica aerogel in the negative electrode sheet at the same time, through the synergistic effect between the two, can further improve the conductivity and ion conductivity of the negative electrode sheet, which is beneficial to further improve the rate performance and cycle performance of the battery.

[0102] From the data of embodiments 10-12, it can be found that changing the mesopore and macropore volume of the silica aerogel in the negative electrode sheet affects the porosity and cycle performance of the electrode sheet.

[0103] From the data of embodiments 10 and embodiments 13, 14, it can be found that the density of the silica aerogel affects the rate performance of the battery.

[0104] From the data of embodiments 10 and embodiments 15-17, it can be found that the specific surface area of the silica aerogel affects the cycle of the battery.

[0105] The above is an exemplary embodiment of the present application, it should be pointed out that for those skilled in the art, without departing from the principles of the present application, can make a number of improvements and refinements, these improvements and refinements also regarded as the protection scope of the present application.

Claims

1. A negative electrode sheet characterized by comprising: The negative electrode sheet comprises a current collector and a negative electrode active material layer coated on at least one side of the current collector; the negative electrode active material layer comprises a negative electrode active material, a silica aerogel and a binder; the silica aerogel is filled between the negative electrode active materials; the silica aerogel accounts for 0.1% to 5% of the total mass of the negative electrode active material layer; and the negative electrode sheet has a porosity of 20% to 80%.

2. The negative electrode sheet according to claim 1, wherein The volume density of the silica aerogel is 0.003 to 0.500 g / cm 3 .

3. The negative electrode sheet according to claim 1, wherein the negative electrode sheet is a negative electrode sheet for a lithium-ion secondary battery. The specific surface area of the silica aerogel is 100 to 1500 m 2 / g.

4. The negative electrode sheet according to claim 1, wherein The silica aerogel comprises mesopores and macropores, and the volume of the mesopores and the macropores accounts for 60% to 99.99% of the total pore volume of the silica aerogel.

5. The negative electrode sheet according to claim 1, wherein The average particle size of the silica aerogel is 0.05 to 100 μm.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein The negative electrode active material layer further comprises a conductive agent.

7. The negative electrode sheet according to claim 6, characterized by The conductive agent accounts for 0.1% to 5% of the total mass of the negative electrode active material layer.

8. The negative electrode sheet according to claim 7, wherein The mass ratio of the silica aerogel to the conductive agent is (0.2-10):

1.

9. A battery, characterized by The battery comprises a positive electrode sheet, an electrolyte, a diaphragm and the negative electrode sheet as claimed in any one of claims 1 to 8.

10. An electric device, characterized by The electric device comprises the battery as claimed in claim 9.

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