A negative electrode sheet and its application

Abstract

The present invention provides a negative electrode sheet and its application. The negative electrode sheet includes a negative electrode sheet substrate and a porous capacitor layer arranged on at least a portion of the surface of the negative electrode sheet substrate. The fast charging parameter K value is comprehensively limited by the specific capacitance and resistivity of the negative electrode sheet and the specific surface area, average pore size and thickness of the porous capacitor layer. When K ≥ 1, better fast charging capability can be achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a negative electrode sheet and applications thereof. Background Art

[0002] The electric vehicle industry is rapidly emerging and growing, and related companies are also experiencing increasing demand for lithium-ion power batteries. This demand has stimulated creative energy and led to the rapid development of the lithium battery industry. However, lithium-ion batteries still lag behind consumer demand in terms of battery energy density and charging speed.

[0003] Currently, charging times for lithium-ion batteries in pure electric vehicles generally exceed one hour, making a full charge approximately 20 times longer than refueling a conventional fuel-powered vehicle. Consequently, electric vehicle charging speed has become a major concern for consumers. Therefore, improving lithium-ion battery charging speed is crucial to further boosting the market share of electric vehicles.

[0004] Currently, in order to improve the fast charging capacity of graphite negative electrodes, methods such as reducing the graphite particle size, reducing the electrode thickness, and increasing the carbon coating on the surface of the graphite material can be used, but it is impossible to take into account both energy density and fast charging performance.

[0005] Since the current fast-charging capabilities of negative electrodes are still limited, greater innovation is still needed to make the charging time of power battery vehicles comparable to the refueling time of fuel vehicles. Summary of the Invention

[0006] The present invention provides a negative electrode sheet capable of comprehensively improving the charging speed of a lithium ion battery.

[0007] The present invention provides an application of a negative electrode sheet, which is used in batteries and electronic equipment and can reduce charging time.

[0008] In a first aspect, the present invention provides a negative electrode sheet, comprising a negative electrode sheet substrate and a porous capacitor layer disposed on at least a portion of the surface of the negative electrode sheet substrate; the negative electrode sheet has a fast charging parameter K ≥ 1; the fast charging parameter K is calculated by formula (1):

[0009]

[0010] In formula (1), SC is the specific capacitance of the negative electrode sheet, in F / g; R is the resistivity of the negative electrode sheet, in Ω·cm; S is the specific surface area of ​​the porous capacitor layer, in m 2 / g; D is the average pore size of the porous capacitor layer, in nm; d is the thickness of the porous capacitor layer, in nm.

[0011] Further, 50F / g≤SC≤500F / g; and / or,

[0012] 5Ω·cm≤R≤30Ω·cm.

[0013] Furthermore, the porous capacitor layer comprises a carbon-based material, and the specific surface area of ​​the carbon-based material is not less than 200m 2 / g, and the average pore size is 2 to 50 nm.

[0014] Furthermore, the specific surface area of ​​the carbon-based material is 300 to 1000 m 2 / g.

[0015] Furthermore, the thickness d of the porous capacitor layer is not greater than 1000 nm.

[0016] Furthermore, the thickness d of the porous capacitor layer is 50-500 nm.

[0017] Furthermore, the porous capacitor layer further comprises a binder and a dispersant, and the mass ratio of the carbon-based material to the binder and the dispersant in the porous capacitor layer is (95-99): (0.5-3): (0.5-3).

[0018] Furthermore, the carbon-based material includes at least one of activated carbon, carbon aerogel, graphene, carbon nanotubes and carbon nanofibers.

[0019] Furthermore, the negative electrode sheet substrate includes: a current collector and n negative electrode active layers stacked in sequence on at least a portion of the surface of the current collector, where 1≤n≤5.

[0020] Furthermore, in a direction gradually away from the current collector, the D50 of the negative electrode active material in each of the negative electrode active layers gradually decreases, and the compaction density of each of the negative electrode active layers gradually decreases.

[0021] In a second aspect, the present invention provides a battery comprising the negative electrode sheet described in the first aspect.

[0022] In a third aspect, the present invention provides an electronic device comprising the battery according to the second aspect.

[0023] The present invention provides a negative electrode sheet, comprising a negative electrode sheet substrate and a porous capacitor layer arranged on at least a portion of the surface of the negative electrode sheet substrate; the fast charging parameter K value is comprehensively limited by the specific capacitance and resistivity of the negative electrode sheet and the specific surface area, average pore size and thickness of the porous capacitor layer. When K ≥ 1, better fast charging capability can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the negative electrode sheet provided by the present invention;

[0025] Figure 2 This is a schematic diagram of the fast charging test in Experimental Example 2;

[0026] Figure 3 This is a normal temperature fast charging test curve diagram of Example 1.

[0027] Description of reference numerals:

[0028] 01: porous capacitor layer;

[0029] 02: Negative electrode substrate. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0031] In one aspect, the present invention provides a negative electrode sheet, such as Figure 1 As shown, Figure 1 Schematic diagram of the negative electrode sheet provided by the present invention, including a negative electrode sheet substrate 02 and a porous capacitor layer 01 provided on at least a portion of the surface of the negative electrode sheet substrate 02; the fast charging parameter K of the negative electrode sheet is ≥ 1; the fast charging parameter K is calculated by formula (1):

[0032]

[0033] In formula (1), SC is the specific capacitance of the negative electrode sheet, in F / g; R is the resistivity of the negative electrode sheet, in Ω·cm; S is the specific surface area of ​​the porous capacitor layer, in m 2 / g; D is the average pore size of the porous capacitor layer, in nm; d is the thickness of the porous capacitor layer, in nm.

[0034] The various parameters in formula (1) are obtained by processing and testing the negative electrode sheet using the following methods; wherein, the negative electrode sheet to be tested can be newly prepared, or can be disassembled from a finished battery after capacity conversion or a finished battery with a charge and discharge cycle of less than 100 cls and a SOC state of 0%; the negative electrode sheet obtained from the disassembled finished battery can also be cleaned and dried with DMC before testing.

[0035] Specifically, the specific capacitance SC is measured by the following method: the negative electrode sheet is sampled into a sample with a diameter of 1.5 cm and a lithium button cell (model CR2016) is prepared; the electrolyte uses a conventional lithium-ion battery electrolyte, optionally, the electrolyte includes 1 mol / L LiPF6, wherein the solvent includes at least one of EC, EMC, DMC, and DEC; the negative electrode lithium button cell is subjected to a cyclic voltammetry scan (CV test) at 0-1 V at a scan rate of 1 mV / s;

[0036] The specific capacitance SC is calculated according to the following formula:

[0037] Specific capacitance SC = charge Q / (voltage difference ΔV * electrode mass m)

[0038] Among them, the mass of the electrode is obtained by weighing, the voltage difference is the set value (0~1V), and the electric quantity Q is obtained by integrating the voltage and current.

[0039] The resistivity R was measured by the following method: the negative electrode sheet was cut into a 3*4 cm rectangle and then placed in a Yuanneng Technology two-probe resistivity meter (model BER1300). The test pressure was set to 5 MPa. The resistivity of the negative electrode sheet was tested. The average value was taken to obtain the resistivity after six times of testing.

[0040] The specific surface area S and the average pore size D are measured by the following method: the porous capacitor layer coated on the surface of the negative electrode is scraped off with a utility knife and dispersed in water. The residual additives are removed by centrifugation at 6000 rpm. The precipitate is removed, washed 6 times and baked to obtain the porous capacitor layer material; a certain mass of the porous capacitor layer material is weighed and placed in a specific surface area tester (model TristarII3020). The specific surface area S and the average pore size D of the porous capacitor layer material are tested according to the national standard GB / T 19587-2017 "Determination of the specific surface area of ​​solid substances by gas adsorption BET method".

[0041] The thickness d of the porous capacitor layer is measured by the following method: the cross-section of the negative electrode sheet is obtained by CP testing (Cross-Sectional Polishing) and Ar ion thinning, and the thickness of the porous capacitor layer is measured by SEM to obtain the thickness of the porous capacitor layer.

[0042] In a specific embodiment, the fast charging parameter of the negative electrode sheet can be adjusted and controlled by adjusting and controlling factors such as the specific material composition and ratio, specific surface area, pore size and thickness of the porous capacitor layer, as well as the structure and material composition of the negative electrode sheet substrate, so as to achieve a fast charging parameter K≥1 of the negative electrode sheet.

[0043] The present invention does not limit the structure of the negative electrode substrate, and conventional negative electrode substrates in the art may be used.

[0044] The negative electrode sheet provided by the present invention includes a negative electrode sheet substrate and a porous capacitor layer arranged on at least a portion of the surface of the negative electrode sheet substrate. The negative electrode sheet substrate can be any conventional negative electrode sheet in the art. By further coating a porous capacitor layer on its surface, and the fast charging parameter K of the negative electrode sheet is ≥1, the energy density of the battery can be improved and better fast charging performance can be achieved.

[0045] The inventor speculates that by providing a porous capacitor layer on the negative electrode substrate, a large amount of lithium ions can be adsorbed in a short period of time, thereby quickly storing a large amount of lithium ion materials, which has an energy storage effect. Unlike the intercalation reaction of lithium-ion batteries, the mechanism of the porous capacitor layer is through adsorption. There is no redox reaction of gaining or losing electrons. It is only through the distribution of positive and negative charges on the positive and negative electrodes that the potential difference between the positive and negative electrodes is increased to store energy. Therefore, its charging rate will not be affected by the limitations of reaction kinetics. The porous capacitor layer has an extremely high power density, and the capacitor reaction is not like the redox reaction of lithium ion intercalation and deintercalation, so there will be no significant reduction in fast charging performance. Especially in the case of large polarization such as high current or low temperature, it still has better fast charging performance. In addition, during the charging process, Li+ will gradually migrate to the active material in the inner layer, playing a slow-release effect, thereby getting rid of the problem of insufficient lithium intercalation capacity of the surface graphite.

[0046] The present invention provides a negative electrode sheet, comprising a negative electrode sheet substrate and a porous capacitor layer arranged on at least a portion of the surface of the negative electrode sheet substrate; the fast charging parameter K value is comprehensively limited by the specific capacitance and resistivity of the negative electrode sheet and the specific surface area, average pore size and thickness of the porous capacitor layer. When K ≥ 1, better fast charging capability can be achieved.

[0047] Further, 50F / g≤SC≤500F / g;

[0048] Since the surface of the negative electrode substrate is provided with a porous capacitor layer, it has a certain capacitance effect. Therefore, by further limiting the specific capacitance of the negative electrode, it is helpful to achieve the fast charging parameter K value, increase the energy density of the negative electrode, and increase the charging speed.

[0049] Specifically, the specific capacitance of the negative electrode sheet can be controlled by adjusting factors such as the material composition, specific surface area, pore size and thickness of the porous capacitor layer, and the structure of the negative electrode sheet substrate.

[0050] Furthermore, 5Ω·cm≤R≤30Ω·cm;

[0051] Similarly, since the surface of the negative electrode substrate is provided with a porous capacitor layer, it has a certain capacitance effect, which helps to reduce the resistance of the negative electrode sheet. By further limiting the resistivity of the negative electrode sheet, it helps to achieve the fast charging parameter K value, increase the energy density of the negative electrode sheet, and increase the charging speed.

[0052] Specifically, the resistivity of the negative electrode sheet can be controlled by adjusting factors such as the material composition, specific surface area, pore size and thickness of the porous capacitor layer, and the structure of the negative electrode sheet substrate.

[0053] In one embodiment, the porous capacitor layer comprises a carbon-based material having a specific surface area of ​​not less than 200 m 2 / g, and the average pore size is 2 to 50 nm.

[0054] The present invention does not limit the specific type of carbon-based materials, as long as the specific surface area is not less than 200m 2 / g, and any carbon-based material with an average pore diameter of 2 to 50 nm can be used.

[0055] When the porous capacitor layer is selected with a specific surface area of ​​not less than 200m 2 / g, when the carbon-based material has an average pore size of 2 to 50 nm, it has better conductivity. Through a larger specific surface area, and at the same time, the average pore size of the carbon-based material meets the pore size range of the mesoporous material, it can provide more adsorption sites, improve the adsorption effect of the capacitor layer on lithium ions, and further improve the fast charging performance.

[0056] Furthermore, the specific surface area of ​​the carbon-based material is 300 to 1000 m 2 / g.

[0057] By further limiting the comparative area of ​​the carbon-based material, more adsorption sites can be provided, thereby improving the adsorption effect of the capacitor layer on lithium ions, and reducing the agglomeration of the carbon-based material on the surface of the electrode, thereby further improving the fast charging performance.

[0058] In one embodiment, the thickness d of the porous capacitor layer is no greater than 1000 nm.

[0059] The inventors found that when the thickness d of the porous capacitor layer is no more than 1000nm, the energy density of the battery cell can be further improved, so that the adsorbed lithium ions can be able to migrate from the porous capacitor layer to the active material surface layer of the negative electrode substrate in a short time, which is conducive to the embedding of electrons between the graphite layers, and is conducive to the internal lattice of the porous capacitor layer material to be more orderly, which can further improve the fast charging performance of the negative electrode sheet.

[0060] Furthermore, the thickness d of the porous capacitor layer is 50 to 500 nm. By further limiting the thickness of the porous capacitor layer, the energy density of the battery cell can be further increased, which is conducive to the embedding of lithium ions into graphite and further improves the fast charging performance of the negative electrode sheet.

[0061] Optionally, the porous capacitor layer further includes a binder and a dispersant, and the mass ratio of the carbon-based material in the porous capacitor layer to the binder and the dispersant is (95-99): (0.5-3): (0.5-3).

[0062] It can be understood that the porous capacitor layer also includes a binder and a dispersant. By further limiting the proportion of each component, the carbon-based material can be effectively dispersed in the porous capacitor layer, preventing particle agglomeration, improving the uniformity of the porous capacitor layer and the bonding strength with the negative electrode substrate, and thus improving the electrochemical properties of the negative electrode sheet and further improving the fast charging performance of the negative electrode sheet.

[0063] Optionally, the binder in the porous capacitor layer includes at least one of SBR, PVDF, and PVP;

[0064] The dispersant in the porous capacitor layer includes at least one of CMC and PEG.

[0065] Specifically, the carbon-based material includes at least one of activated carbon, carbon aerogel, graphene, carbon nanotubes and carbon nanofibers.

[0066] When the carbon-based material includes the above materials, the conductivity of the porous capacitor layer can be further improved, and a larger specific surface area can be provided, with better lithium adsorption and lithium storage effects, which can significantly improve the fast charging performance.

[0067] In a specific embodiment, the negative electrode substrate includes: a current collector and n negative electrode active layers stacked in sequence on at least a portion of the surface of the current collector, where 1≤n≤5.

[0068] The present invention does not limit the types of current collector and negative electrode active layer; optionally, each negative electrode active layer independently comprises a negative electrode active material, a dispersant, a binder and a conductive agent, and the mass ratio of the negative electrode active material, the dispersant, the binder and the conductive agent in the negative electrode active layer is (95-99): (0.5-3): (0.5-3);

[0069] The negative electrode active material may include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microbeads, silicon oxygen, silicon carbon and silicon single crystal;

[0070] The dispersant includes at least one of CMC, PVDF, and PVP;

[0071] The binder includes at least one of SBR and PEG;

[0072] The conductive agent includes at least one of carbon black, superconducting carbon, graphene, and acetylene black;

[0073] The current collector includes at least one of copper foil and nickel foil.

[0074] The present invention does not limit the preparation method of the negative electrode substrate. Optionally, it can be obtained by conventional wet slurry mixing and coating, specifically by the following method:

[0075] (1) Adding a dispersant to water and performing a first dispersion treatment to obtain a first adhesive solution; adding a binder to the first adhesive solution and performing a second dispersion treatment to obtain a second adhesive solution; adding a conductive agent to the second adhesive solution and performing a third dispersion treatment to obtain a third adhesive solution; adding a negative electrode active material to the third adhesive solution and performing a fourth dispersion treatment to obtain a fourth adhesive solution.

[0076] (2) The fourth glue solution is coated on both sides of the current collector by a belt-type coating machine and baked to obtain a single-layer coated negative electrode substrate; the double-sided negative electrode is obtained by double-coating the single-sided negative electrode.

[0077] In the above-mentioned method for preparing the negative electrode substrate, the mass ratio of the negative electrode active material, the dispersant, the binder, the conductive agent and water is (92-97): (0.5-2): (1-2): (0.5-3): (90-110);

[0078] The present invention does not specifically limit the relevant process parameters in the preparation process. In one embodiment, the stirring speed of the first dispersion treatment is 1000-1500 rpm, and the dispersion time is 1-3 hours; the stirring speed of the second dispersion treatment is 1500-2000 rpm, and the dispersion time is 1-3 hours; the stirring speed of the third dispersion treatment is 1500-2000 rpm, and the dispersion time is 1-3 hours; the stirring speed of the fourth dispersion treatment is 2000-2400 rpm, and the dispersion time is 2-4 hours; the surface density of the negative electrode active layer is 140-250 m 2 / g.

[0079] Furthermore, in a direction gradually away from the current collector, the D50 of the negative electrode active material in each negative electrode active layer gradually decreases, and the compaction density of each negative electrode active layer gradually decreases.

[0080] By further limiting the D50 of the negative electrode active material in each negative electrode active layer and the compaction density of the negative electrode active layer, the migration path of lithium ions inside the particles and in the thickness direction of the electrode can be further reduced. Combined with the porous capacitor layer coated on the surface of the negative electrode sheet substrate, it is possible to take into account the energy density and further improve the fast charging performance of the upper porous capacitor layer.

[0081] The present invention does not limit the preparation method of the porous carbon layer. Optionally, the porous carbon layer can be prepared by conventional wet slurry mixing-coating, specifically by the following method:

[0082] adding a dispersant and a binder to water, performing a fifth dispersion process to obtain a fifth glue solution; adding a carbon-based material to the fifth glue solution, performing a sixth dispersion process to obtain a carbon solution;

[0083] The carbon solution is coated on the surface of the negative electrode substrate and baked to obtain the negative electrode.

[0084] In the above-mentioned method for preparing the negative electrode sheet, the mass ratio of the carbon-based material to the binder, the dispersant, and the water is (95-99): (0.5-3): (0.5-3): (900-1000);

[0085] The present invention does not specifically limit the relevant process parameters in the preparation process. In one embodiment, the stirring speed of the fifth dispersion treatment is 1000-1500 rpm, and the dispersion time is 2-4 hours; the stirring speed of the sixth dispersion treatment is 2000-2400 rpm, and the dispersion time is 5-8 hours.

[0086] In a second aspect, the present invention provides a battery comprising the negative electrode sheet according to the first aspect.

[0087] The present invention does not limit the specific selection of the positive electrode sheet and the electrolyte in the battery. Optionally, the positive electrode sheet includes at least one of LFP, LMFP, NCM, LCO, and LMO.

[0088] The electrolyte includes lithium salt, solvent and additives; wherein the lithium salt is at least one of LiPF6, LiPF2O2, and LiFSI; the solvent is at least one of EC, EMC, DEC, and DMC; and the additive is VC or other film-forming additives.

[0089] The present invention is not limited to the specific model and capacity of the battery; optionally, the battery is a square shell or cylindrical battery.

[0090] The battery provided by the present invention includes a negative electrode sheet, which includes a negative electrode sheet substrate and a porous capacitor layer arranged on at least a portion of the surface of the negative electrode sheet substrate; the fast charging parameter K value is comprehensively limited by the specific capacitance and resistivity of the negative electrode sheet and the specific surface area, average pore size and thickness of the porous capacitor layer. When K ≥ 1, the battery can achieve better fast charging capability.

[0091] In a third aspect, the present invention further provides an electronic device comprising the battery according to the second aspect.

[0092] The present invention is not limited to the specific type of electronic equipment and can include electric vehicles, mobile phones, smart homes, robots, drones, electronic cigarettes, speakers, and any other device that requires battery power.

[0093] The electronic device provided by the present invention includes the battery of the second aspect, which can enable the electronic device provided by the present invention to have excellent fast charging capability.

[0094] Hereinafter, a negative electrode sheet provided by the present invention is described in detail through specific embodiments.

[0095] Example 1

[0096] The method for preparing the negative electrode sheet of this embodiment includes the following steps:

[0097] (1) adding 10 g of dispersant (CMC) to 1 kg of water and stirring at 1000 rpm for 2 h to perform a first dispersion treatment to obtain a first glue solution;

[0098] (2) adding 10 g of binder (SBR) to the first glue solution and stirring at 1500 rpm for 2 h to perform a second dispersion treatment to obtain a second glue solution;

[0099] (3) adding 30 g of conductive agent (carbon black) to the second glue solution and stirring at 1500 rpm for 2 h to perform a third dispersion treatment to obtain a third glue solution;

[0100] (4) adding 1 kg of the negative electrode active material (artificial graphite) to the third glue solution and stirring at 2000 rpm for 4 h to perform a fourth dispersion treatment to obtain a fourth glue solution;

[0101] (5) The fourth glue solution is coated on one side of the copper foil current collector by a belt-type coating machine, and then baked at 120°C to obtain a single-side surface density of 100g / m 2 The negative electrode substrate;

[0102] (6) Add 1 g of dispersant (CMC) and 1 g of conductive agent (SBR) to 1 kg of water, and stir at 1000 rpm for 2 h to perform the fifth dispersion treatment to obtain the fifth adhesive solution.

[0103] (7) adding 100 g of the carbon-based material to the fifth glue solution and stirring at 2000 rpm for 5 h to perform the sixth dispersion treatment to obtain a carbon solution;

[0104] Among them, the carbon-based material is porous graphene with a specific surface area of ​​S = 580m 2 / g, average pore diameter D = 5.1nm;

[0105] (8) The carbon solution was coated on the surface of the negative electrode substrate and baked to form a porous capacitor layer with a thickness of 100 nm. The above coating of the negative electrode substrate and the porous carbon layer was repeated to obtain a surface density of 200 g / m 2 Double-sided negative electrode sheet.

[0106] Example 2

[0107] The difference between this embodiment and embodiment 1 is that in step (7), the specific surface area of ​​the porous graphene material is changed to S=155m 2 / g, average pore diameter D = 0.3nm.

[0108] Example 3

[0109] The difference between this embodiment and embodiment 1 is that in step (7), the specific surface area of ​​the porous graphene material is changed to S=350m 2 / g, average pore diameter D = 2.7nm.

[0110] Example 4

[0111] The difference between this embodiment and embodiment 1 is that in step (7), the specific surface area of ​​the porous graphene is S=190m 2 / g.

[0112] Example 5

[0113] The difference between this embodiment and embodiment 1 is that in step (7), the average pore diameter D of the porous graphene is 1.9 nm.

[0114] Example 6

[0115] The difference between this embodiment and embodiment 1 is that in step (7), the specific surface area of ​​the porous graphene is S=250m 2 / g.

[0116] Example 7

[0117] The difference between this embodiment and embodiment 1 is that in step (8), the thickness of the porous carbon layer is changed to 1200 nm.

[0118] Example 8

[0119] The difference between this embodiment and embodiment 1 is that in step (8), the thickness of the porous carbon layer is changed to 750 nm.

[0120] Example 9

[0121] The difference between this embodiment and embodiment 1 is that in steps (6) and (7), the mass ratio of the added carbon-based material to the binder and dispersant is 100:3:3.

[0122] Example 10

[0123] The difference between this embodiment and embodiment 1 is that in step (7), the carbon-based material is carbon nanotubes with a diameter of 10 to 30 nm and a specific surface area of ​​S = 420 m 2 / g, average pore diameter D = 3.2nm.

[0124] Example 11

[0125] The difference between this embodiment and embodiment 1 is that in step (7), the carbon-based material is a carbon nanotube with a diameter of 100 to 500 nm and a specific surface area of ​​S = 310 m 2 / g, average pore diameter D = 6.1 nm.

[0126] Example 12

[0127] The difference between this embodiment and embodiment 1 is that in step (7), the specific surface area of ​​the porous graphene is S=450m 2 / g, average pore diameter D = 5.8nm.

[0128] Example 13

[0129] The difference between this embodiment and embodiment 1 is that in step (8), the thickness of the porous carbon layer is changed to 50 nm.

[0130] Example 14

[0131] The difference between this embodiment and embodiment 1 is that in step (8), the thickness of the porous carbon layer is changed to 200 nm.

[0132] Example 15

[0133] The difference between this embodiment and embodiment 1 is that in step (8), the thickness of the porous carbon layer is changed to 500 nm.

[0134] Example 16

[0135] The difference between this embodiment and embodiment 1 is that in step (8), the thickness of the porous carbon layer is changed to 1000 nm.

[0136] Comparative Example 1

[0137] The difference between this comparative example and Example 1 is that steps (6) to (8) are not performed, that is, a porous capacitor layer is not provided.

[0138] Test Example 1

[0139] The negative electrode sheets obtained in the above embodiments and comparative examples were tested.

[0140] The specific capacitance SC is measured by the following method: the negative electrode sheet is sampled into a sample with a diameter of 1.5 cm and a lithium button cell (model CR2016) is prepared; the electrolyte is a conventional lithium-ion battery electrolyte, optionally including 1 mol / L LiPF6; the negative electrode lithium button cell is subjected to a cyclic voltammetry scan (CV test) from 0 to 1 V at a scan rate of 1 mV / s;

[0141] The specific capacitance SC is calculated according to the following formula:

[0142] Specific capacitance SC = charge Q / (voltage difference êV * electrode mass m)

[0143] Among them, the mass of the electrode is obtained by weighing, the voltage difference is the set value (0~1V), and the electric quantity Q is obtained by integrating the voltage and current.

[0144] The resistivity R was measured by the following method: the negative electrode sheet was cut into a 3*4 cm rectangle and then placed in a Yuanneng Technology two-probe resistivity meter (model BER1300). The test pressure was set to 5 MPa. The resistivity of the negative electrode sheet was tested. The average value was taken to obtain the resistivity after six times of testing.

[0145] The specific surface area S and the average pore size D are measured by the following method: after obtaining the finished battery, a clean negative electrode sheet is obtained by disassembly-DMC cleaning; the porous capacitor layer coated on the surface is scraped off with a utility knife and dispersed in water, and the residual CMC and SBR are removed by centrifugation at 6000 rpm. The lower layer of precipitate is removed, washed 6 times and baked to obtain the porous capacitor layer material; a certain mass of the porous capacitor layer material is weighed and placed in a specific surface area tester (model TristarII3020), and the specific surface area S and the average pore size D of the porous capacitor layer material are tested according to the national standard GB / T19587-2017 "Determination of the specific surface area of ​​solid substances by gas adsorption BET method".

[0146] The thickness d of the porous capacitor layer is measured by the following method: the cross-section of the negative electrode sheet is obtained by CP testing (Cross-Sectional Polishing) and Ar ion thinning, and the thickness of the porous capacitor layer is measured by SEM to obtain the thickness of the porous capacitor layer.

[0147] The fast charging parameter K is calculated by formula (1):

[0148]

[0149] In formula (1), SC is the specific capacitance of the negative electrode sheet, in F / g; R is the resistivity of the negative electrode sheet, in Ω·cm; S is the specific surface area of ​​the porous capacitor layer, in m 2 / g; D is the average pore size of the porous capacitor layer, in nm; d is the thickness of the porous capacitor layer, in nm.

[0150] The above test results are shown in Table 1.

[0151] Table 1

[0152]

[0153]

[0154] Test Example 2

[0155] The LFP positive electrode sheet was stacked with the negative electrode sheet obtained in each of the above examples and comparative examples to assemble a soft-pack full battery. A 2 μm copper wire was placed on the negative electrode and separator sides as a reference electrode. The battery was formed and then capacitated at room temperature.

[0156] The formation process is as follows: charge at 0.05C for 2h, charge at 0.1C constant current and constant voltage until 3.8V, and then cut off at 0.05C. Aging at 45℃ for 24h further stabilizes the negative electrode SEI.

[0157] The capacity division process is: 0.33C constant current and constant voltage charging to 3.8V, cutting off 0.05C, leaving it for 10 minutes, 0.33C discharge to 2.0V, cycle three times, and use the discharge capacity of the last cycle as the nominal capacity of the battery for subsequent testing.

[0158] After the battery is charged to capacity, the copper wire is plated with lithium (charging at 50 μA for 4 h). The potential of the lithium-plated copper wire is 0 mV vs. Li. Therefore, the potential of the negative electrode charge can be calibrated by using the lithium-plated copper wire as a reference electrode.

[0159] (1) Fast charging test at room temperature (25°C)

[0160] During the fast charge test, Figure 2 As shown, Figure 2 This is a schematic diagram of the fast charging test in Experiment 2. Figure 2 The connection method shown is used to record the positive and negative voltage changes V respectively through the data acquisition instrument. 正负 , positive electrode and reference electrode voltage changes V 正参 , negative electrode and reference electrode voltage changes V 负参 The change in the negative electrode during charging determines whether the lithium deposition boundary has been reached. When the negative electrode potential drops to 0mV, the lithium deposition boundary is considered to have been reached. To evaluate the fast charging performance of different schemes, 5C charging until the negative electrode potential reaches 0mV is uniformly selected as the evaluation standard. The higher the SOC, the better the fast charging performance of the scheme.

[0161] Figure 3 This is a normal temperature fast charging test curve diagram of Example 1.

[0162] The above test results are shown in Table 2.

[0163] Table 2

[0164] 25℃ fast charging test Charge SOC / % Example 1 60.5 Example 2 39.5 Example 3 40.1 Example 4 36.0 Example 5 47.0 Example 6 44.0 Example 7 36.6 Example 8 40.8 Example 9 45.4 Example 10 54.6 Example 11 39.2 Example 12 46.8 Example 13 40.4 Example 14 49.1 Example 15 42.3 Example 16 37.5 Comparative Example 1 31.2

[0165] (2) Low temperature (0℃) fast charging test

[0166] The low-temperature fast charging test method is consistent with the normal-temperature fast charging method. The test results are shown in Table 3.

[0167] Table 3

[0168]

[0169]

[0170] It can be seen from Tables 1-3 that the negative electrode sheets provided in this application can all meet the fast charging parameter K≥1, so that the battery has better fast charging performance; it can be seen that the specific capacitance, resistivity of the negative electrode sheet and the specific surface area, pore size and thickness of the porous capacitor layer affect the adsorption of lithium ions by the negative electrode material during the fast charging process, and affect the fast charging performance of the negative electrode sheet; among them, the larger the specific capacitance and specific surface area, the more significant the improvement in fast charging; and the larger the pore size of the carbon-based material, the lower the specific surface area of ​​the carbon-based material; the resistivity of the negative electrode sheet reflects the conductivity of the electrode sheet, the lower the resistivity, the better the conductivity; the thickness of the porous capacitor layer needs to be set within an appropriate range to have a more obvious improvement effect and be more conducive to the migration of lithium ions.

[0171] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode sheet, characterized in that: The invention comprises a negative electrode substrate and a porous capacitor layer provided on at least a portion of the surface of the negative electrode substrate; the fast charging parameter K of the negative electrode substrate is greater than or equal to 1; the fast charging parameter K is calculated by formula (1): Formula (1) In formula (1), SC is the specific capacitance of the negative electrode sheet, in F / g; R is the resistivity of the negative electrode sheet, in Ω·cm; S is the specific surface area of ​​the porous capacitor layer, in m 2 / g; D is the average pore size of the porous capacitor layer, in nm; d is the thickness of the porous capacitor layer, in nm; The negative electrode sheet is a lithium-ion battery negative electrode sheet. The negative electrode sheet substrate includes a current collector and a negative electrode active layer stacked in sequence on at least a portion of the surface of the current collector. The active material in the negative electrode active layer is artificial graphite, and the porous capacitor layer includes a carbon-based material.

2. The negative electrode sheet according to claim 1, characterized in that: 50F / g≤SC≤500F / g; and / or, 5Ω•cm≤R≤30Ω•cm.

3. The negative electrode sheet according to claim 1 or 2, characterized in that: The specific surface area of ​​the carbon-based material is not less than 200 m 2 / g, and the average pore size is 2~50nm.

4. The negative electrode sheet according to claim 3, characterized in that: The specific surface area of ​​the carbon-based material is 300-1000 m 2 / g.

5. The negative electrode sheet according to claim 1 or 2, characterized in that: The thickness d of the porous capacitor layer is not greater than 1000 nm.

6. The negative electrode sheet according to claim 5, characterized in that: The thickness d of the porous capacitor layer is 50-500 nm.

7. The negative electrode sheet according to claim 1 or 2, characterized in that: The porous capacitor layer further includes a binder and a dispersant, and the mass ratio of the carbon-based material to the binder and the dispersant in the porous capacitor layer is (95-99): (0.5-3): (0.5-3).

8. The negative electrode sheet according to claim 1 or 2, characterized in that: The carbon-based material includes at least one of activated carbon, carbon aerogel, graphene, carbon nanotubes and carbon nanofibers.

9. The negative electrode sheet according to claim 1 or 2, characterized in that: The negative electrode sheet substrate includes: a current collector and n negative electrode active layers stacked in sequence on at least a portion of the surface of the current collector, where 1≤n≤5.

10. The negative electrode sheet according to claim 9, characterized in that: In a direction gradually away from the current collector, the D50 of the negative electrode active material in each of the negative electrode active layers gradually decreases, and the compaction density of each of the negative electrode active layers gradually decreases.

11. A battery, characterized in that: The negative electrode sheet comprises the negative electrode sheet according to any one of claims 1 to 10.

12. An electronic device, characterized in that: Including the battery according to claim 11.

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