Negative electrode sheets, batteries and electrical devices

Abstract

A negative electrode sheet, a battery, and an electrical device. The negative electrode sheet comprises a current collector and a negative electrode active material layer coating at least one surface of the current collector, wherein the negative electrode active material layer comprises a negative electrode active material, an inorganic porous material, and a binder, and the inorganic porous material accounts for 0.1% to 5% of the total mass of the negative electrode active material layer.

Description

Technical Field

[0001] Priority Information This disclosure claims the priority and benefits of Patent Application No. 202310338119.9 filed with the China National Intellectual Property Administration on March 31, 2023, the entire content of which is incorporated herein by reference.

[0002] Technical Field This disclosure relates to the field of battery technology, particularly to a negative electrode sheet, a battery, and an electrical device.

Background Art

[0003] Secondary batteries (such as lithium-ion batteries) are widely used in new energy vehicles, portable electronic products, and large-scale energy storage devices due to advantages such as high operating voltage, high energy density, long cycle life, and low self-discharge. The performance of a secondary battery mainly depends on the physicochemical properties of the positive and negative electrode sheets. Carriers (such as lithium ions) in the negative electrode sheet have high migration impedance and severe polarization, which limit the rate performance of secondary batteries (such as lithium-ion batteries).

[0004] In the prior art, by modifying the negative electrode active material, the mobility of carriers (such as lithium ions) in the negative electrode sheet is increased, thereby improving the rate performance of the battery. However, the modification of the negative electrode active material causes a relatively high cost and only improves the diffusion of carriers (such as lithium ions) in the negative electrode active material, and does not significantly improve the diffusion of carriers between the negative electrode active materials in the electrode sheet.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, there is a need to provide a new negative electrode sheet that meets the requirements for high rate performance applications in secondary batteries (such as lithium-ion batteries).

Means for Solving the Problems

[0006] Summary of the Invention In view of this, this disclosure provides a negative electrode sheet that can satisfy the high rate performance requirements of a secondary battery.

[0007] A first aspect of the present disclosure provides a negative electrode sheet comprising a current collector and a negative electrode active material layer coated on at least one surface of the current collector, wherein the negative electrode active material layer comprises a negative electrode active material, an inorganic porous material, and a first binder, and the inorganic porous material accounts for 0.1% to 5% of the total mass of the negative electrode active material layer.

[0008] The negative electrode sheet of this disclosure contains 0.1% to 5% inorganic porous material, which effectively improves the ionic conductivity of the negative electrode sheet and the rate performance of the negative electrode sheet and the corresponding battery. The pores in the inorganic porous material can absorb electrolyte. Adding inorganic porous material to the negative electrode sheet not only serves as a buffer pool for the electrolyte within the negative electrode sheet but also improves the pore structure of the negative electrode sheet. During charging and discharging of the battery, the electrolyte permeates from the pores of the inorganic porous material into the negative electrode active material, shortening the conduction path of carriers (lithium ions), thereby reducing or mitigating polarization in the negative electrode sheet. If the content of inorganic porous material in the negative electrode sheet is excessively high, it adversely affects the conductivity of the negative electrode sheet, and if the content of inorganic porous material in the negative electrode sheet is excessively low, the improvement in the ionic conductivity of the negative electrode sheet is minimal. Thus, in this disclosure, when the inorganic porous material accounts for 0.1% to 5% of the total mass of the negative electrode active material layer, the rate performance of the negative electrode sheet and the battery can be effectively improved.

[0009] A second aspect of this disclosure provides a battery comprising a positive electrode sheet, an electrolyte, a separator, and a negative electrode sheet provided in the first aspect.

[0010] Since the battery includes a negative electrode sheet provided in a first embodiment of this disclosure, the battery has high rate performance and meets the requirements of a wider range of applications.

[0011] A third aspect of this disclosure provides an electrical device including a battery as provided in the second aspect of this disclosure. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 shows the distribution curve of the pore structure of the inorganic porous material (mesoporous silica) in this disclosure. [Modes for carrying out the invention]

[0013] Description of the Embodiment This disclosure is further described below with reference to embodiments and comparative examples, which are used solely for illustrative purposes and are not limited to the embodiments described below. Any modification or equivalent substitution of the technical solutions of this disclosure, which does not deviate from the scope of the technical solutions of this disclosure, shall be within the scope of protection of this disclosure.

[0014] A first embodiment of the present disclosure provides a negative electrode sheet comprising a current collector and a negative electrode active material layer coated on at least one surface of the current collector, wherein the negative electrode active material layer comprises a negative electrode active material, an inorganic porous material, and a first binder, and the inorganic porous material accounts for 0.1% to 5% of the total mass of the negative electrode active material layer.

[0015] The negative electrode sheet of this disclosure contains 0.1% to 5% inorganic porous material, which effectively improves the ionic conductivity of the negative electrode sheet and can improve the rate performance of the negative electrode sheet and the corresponding battery. The pores in the inorganic porous material can absorb the electrolyte. Adding the inorganic porous material to the negative electrode sheet not only serves as a buffer pool for the electrolyte within the negative electrode sheet, but also improves the porous structure of the negative electrode sheet. During charging and discharging of the battery, the electrolyte permeates from the pores of the inorganic porous material into the negative electrode active material, shortening the conduction path of the carrier (lithium ions), thereby reducing or mitigating polarization phenomena in the negative electrode sheet and improving the rate performance of the negative electrode sheet and the battery. Furthermore, the inorganic porous material has stable chemical properties and does not impair the electrochemical reaction system of the battery.

[0016] Inorganic porous materials themselves have relatively poor conductivity and energy storage properties (i.e., the ability to convert chemical energy into electrical energy during lithium ion storage / release). If the content of inorganic porous material in the negative electrode sheet is excessively high (above 5%), it affects the conductivity of the negative electrode sheet and indirectly reduces the content of the negative electrode active material, thereby affecting the energy density of the negative electrode sheet. If the content of inorganic porous material is excessively low (less than 0.1%), the improvement in the battery's rate performance is minimal. Therefore, the content of inorganic porous material in the negative electrode sheet is important to this disclosure.

[0017] In some embodiments of this disclosure, the inorganic porous material accounts for 0.2% to 3% of the total mass of the negative electrode active material layer.

[0018] When inorganic porous material accounts for 0.2% to 3% of the total mass of the negative electrode active material layer, uniform dispersion of the inorganic porous material within the negative electrode sheet can be ensured, achieving the function of homogenizing the pore structure of the electrode sheet, further shortening the diffusion pathway of the electrolyte, reducing the lithium ion migration impedance, and thereby improving the polarization of the electrode sheet.

[0019] The content of inorganic porous material in the negative electrode sheet can be measured using a thermogravimetric analysis method. The test method includes the following: scraping off a first solid material containing carriers (e.g., lithium ions) removed from the current collector, subjecting it to acid cleaning with dilute hydrochloric acid, and then drying it at 120°C for 2 hours; weighing a specific mass (m1) of the first solid material and placing it in the sample pan of a TA TGA 2050 thermogravimetric analyzer; thermal decomposition by heating to 800°C in an air atmosphere, and taking the residual mass as m2. The percentage content of inorganic porous material = (residual mass (m2) / first solid material (m1)) × 100%.

[0020] In the present disclosure, the negative electrode active material layer may be coated on one surface of the current collector. Alternatively, the negative electrode active material layer may be coated on both surfaces of the current collector. When the negative electrode active material layer is coated on both surfaces of the current collector, the thickness, surface density, component content ratio, etc. of the negative electrode active material layers respectively located on both surfaces of the current collector can be independently designed according to the requirements of the application, and may be the same or different.

[0021] In the present disclosure, the negative electrode active material may be a carbon-based material.

[0022] The carbon-based material may be one or a combination of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microbeads, and carbon fiber.

[0023] In the present disclosure, the current collector may be any one of copper foil, carbon-coated copper foil, polymer-coated copper foil, carbon cloth, carbon nanotube film, or carbon paper.

[0024] In the present disclosure, alternatively, the current collector may be any one of aluminum foil, carbon-coated aluminum foil, and polymer-coated aluminum foil (for example, used for the negative electrode current collector of a sodium ion battery).

[0025] In the present disclosure, the binder includes one or a combination of styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyacrylic ethylene acrylic acid (PEAA), sodium alginate, carboxymethyl chitosan, polyacrylonitrile (PAN), and polyvinyl alcohol (PVA).

[0026] In some embodiments of this disclosure, the porosity of the negative electrode sheet is 20% to 60%.

[0027] In this disclosure, the negative electrode sheet comprises an inorganic porous material. It can be understood that the pores of the negative electrode sheet include pores in the inorganic porous material, gaps formed by the disorderly deposition of the inorganic porous material and the negative electrode active material, and gaps formed after the disorderly deposition of the negative electrode active material. When the porosity of the negative electrode sheet is in the range of 20% to 60%, the transport (shuttle) efficiency of carriers (lithium ions) within the negative electrode sheet is good, and the negative electrode sheet and battery have high rate performance. Furthermore, the negative electrode sheet has a high liquid storage capacity, which can provide a more sufficient electrolyte in the battery cycle process and can increase the battery cycle life. For example, the porosity of the negative electrode sheet may be 20%, 30%, 40%, 50%, 60%, etc.

[0028] In this disclosure, the porosity of the negative electrode sheet is more preferably 30% to 50%. When the porosity of the negative electrode sheet is within this range, higher mechanical performance of the negative electrode sheet can be ensured, and the cycle stability of the battery can be further improved.

[0029] The method for determining the porosity of a negative electrode sheet is as follows: The negative electrode sheet is cut into pieces of a specific area, the pieces are dried in a vacuum drying oven at 120°C for 12 hours, removed and cooled in a dryer, and then the porosity is tested. First, the thickness of the sample is measured using a 1 / 1000 gauge (subtracting the thickness of the current collector foil), and the apparent volume (V1) of the sample is calculated according to the surface area and thickness of the sample; the true volume (V2) of the sample is measured using a true density analyzer (subtracting the volume of the current collector foil). The porosity of the negative electrode sheet is obtained as follows: (True volume (V2) / Apparent volume (V1)) × 100%.

[0030] In some embodiments of this disclosure, the liquid absorption rate of the negative electrode sheet is 2 to 8 mg / min.

[0031] The inorganic porous material filled within the negative electrode sheet alters the pore structure within the sheet, resulting in a liquid absorption rate of 2-8 mg / min. This explains why a battery of this type exhibits relatively high rate performance.

[0032] The liquid absorption rate of a negative electrode sheet relates to the amount of electrolyte absorbed by the negative electrode sheet per unit time. The method for measuring the liquid absorption rate of a negative electrode sheet is as follows: Cut the negative electrode sheet into a film piece of a specific area, dry the film piece in a vacuum drying oven at 120°C for 12 hours, remove it and cool it in a dryer, then test its porosity; Take a 2cm × 5cm negative electrode sheet and fix it on the stage of an SDC-2000S contact angle tester; Drop a specific mass (m) of electrolyte onto the negative electrode sheet vertically via a syringe; Record the time (t) required for complete absorption of the electrolyte using a camera: Liquid absorption rate of negative electrode sheet = Mass of electrolyte dropped (m) / Time for complete absorption (t); Repeat the test five times at different locations on the electrode sheet and obtain the average value. The electrolyte used in this disclosure is as follows: an electrolyte containing 1 M LiPF6 is prepared by mixing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1; the test temperature was 25°C. Note: Test results may vary slightly depending on the type of electrolyte and the test environment.

[0033] In some embodiments of this disclosure, the dielectric constant of the inorganic porous material is ε, where 0 < ε ≤ 50.

[0034] In this disclosure, by having the dielectric constant of the inorganic porous material in the negative electrode sheet within the above range, the contact interface between the negative electrode sheet and the electrolyte can be stabilized, side reactions between the negative electrode sheet and the electrolyte can be reduced or mitigated, the Coulomb efficiency of the battery can be improved, and the cycle life of the battery can be further increased.

[0035] In this disclosure, the dielectric constant ε of the inorganic porous material is more preferably 0 < ε ≤ 10. That is, the lower the dielectric constant of the inorganic porous material, the better the effect when the requirements of the application are met. Circumstantially, the dielectric constant of the inorganic porous material may be, without limitation, 0.5, 1, 1.56, 3, 3.6, 6, 6.5, 8.8, or 10.

[0036] The method for measuring the dielectric constant of an inorganic porous material is as follows: The dielectric constant of the sample is measured using an Agilent Technologies E8362B vector network analyzer, and the measurement is performed at a frequency in the range of 8.2 to 12.4 GHz. The powder to be tested (mass M1) and paraffin (mass M2) are heated and uniformly mixed in a ratio of M1:M2 = 1:4, and then poured into a standard copper flange. After solidification in air, a rectangular sample with dimensions of 22.86 mm (length) × 10.16 mm (width) × 2.52 mm (thickness) is obtained for testing. The real part of the dielectric constant in the test result is the dielectric constant ε of the first inorganic porous material.

[0037] In some embodiments of this disclosure, the inorganic porous material includes at least one of the following: porous oxide of Si, porous nitride of Si, porous fluoride of Si, porous oxide of Ti, porous nitride of Ti, porous fluoride of Ti, porous oxide of Zn, porous nitride of Zn, porous fluoride of Zn, porous oxide of Mg, porous nitride of Mg, porous fluoride of Mg, porous oxide of Zr, porous nitride of Zr, porous fluoride of Zr, porous oxide of Ca, porous nitride of Ca, porous fluoride of Ca, porous oxide of Zn, porous nitride of Zn, porous fluoride of Zn, porous oxide of Ba, porous nitride of Ba, or porous fluoride of Ba.

[0038] In some embodiments of this disclosure, the inorganic porous material is more preferably at least one of porous silica, porous titanium oxide, porous alumina, or porous boehmite. Some of the above types of inorganic porous materials have relatively good dielectric properties. When filled between negative electrode active materials, the inorganic porous material helps reduce side reactions at the negative electrode sheet interface, exhibits a certain degree of mechanical strength, allows for the effective mitigation of non-uniformity of the pore structure within the negative electrode sheet caused by the expansion and contraction of the negative electrode active material during battery charging and discharging, exhibits stable chemical properties without impairing the electrochemical reaction system inside the battery, provides excellent thermal insulation to improve the safety performance of the battery, and offers a low cost to meet the requirements of industrial-grade applications. Furthermore, the preparation processes for some of the above types of inorganic porous materials are relatively mature and allow for tunable pore structures and surface activity according to requirements. Thus, when some of the above types of inorganic porous materials are filled between negative electrode active materials, the specific capacity, rate performance, cycle life, and safety performance of the battery can be effectively improved.

[0039] In some embodiments of this disclosure, the inorganic porous material includes mesopores, and the volume of the mesopores accounts for 10% to 95% of the total volume of pores in the inorganic porous material.

[0040] Internationally, pores are generally classified into three categories according to their size: micropores, mesopores (i.e., intermediate pores), and macropores. Micropores have a diameter of less than 2 nm, mesopores have a diameter in the range of 2 to 50 nm, and macropores have a diameter greater than 50 nm. Mesopores in inorganic porous materials have high electrolyte adsorption capacity and can be used as a buffer pool for the electrolyte in the negative electrode sheet, providing continuous carriers during battery cycles and increasing the battery's cycle life. Furthermore, during the battery's charge-discharge process, the pore structure in the negative electrode sheet changes dynamically, which affects electrolyte diffusion and carrier transport, resulting in a non-uniform carrier ion flux. By adding inorganic porous material with a mesopore content of 10% to 95% to the negative electrode sheet, the flux during the negative electrode change process can be homogenized, the diffusion distance of carriers to the negative electrode active material layer can be shortened, and the battery's rate performance can be improved.

[0041] When the volume of mesopores accounts for 10% to 95% of the total volume of pores in the inorganic porous material, the cycle life and rate performance of the negative electrode sheet and the corresponding battery are better.

[0042] The volume of mesopores in inorganic porous materials is obtained based on the ratio of the pore volume of mesopores (pore size 2-50 nm) to the total cumulative pore volume in BET test results for inorganic porous materials.

[0043] In some specific embodiments of this disclosure, more preferably, the volume of mesopores accounts for 40% to 95% of the total volume of pores in the inorganic porous material. Therefore, when the volume of mesopores in the inorganic porous material in this disclosure is within the above range, the battery cycle life and rate performance are better.

[0044] In some embodiments of this disclosure, the inorganic porous material further includes macropores, the volume of which accounts for 5% to 40% of the total volume of pores in the inorganic porous material. The macropores in the inorganic porous material provide channels for the transport of electrolytes, and electrolyte ions stored in the mesopores diffuse through the channels of the macropores to the surface of the negative electrode active material, thereby shortening the diffusion pathway of carriers within the negative electrode sheet and further improving the rate performance of the battery.

[0045] The volume of macropores in inorganic porous materials is obtained based on the ratio of the pore volume of macropores (pore size > 50 nm) to the total cumulative pore volume in BET test results for inorganic porous materials.

[0046] In some embodiments of this disclosure, the inorganic porous material has an average particle size of 10 to 1000 nm.

[0047] The average particle size of the inorganic porous material disclosed in this invention is in the range of 10 to 1000 nm, which can satisfy the requirements for using negative electrode active materials in a range of particle sizes, achieve a better packing effect, and further promote the absorption and diffusion of electrolytes. For example, the particle size of the inorganic porous material may be 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 600 nm, 800 nm, 900 nm, or 1000 nm.

[0048] In this disclosure, the average particle size of the inorganic porous material is more preferably 200 to 1000 nm. If the average particle size of the inorganic porous material is too small and the surface energy is too large, this will affect the dispersibility of the inorganic porous material in the negative electrode sheet. If the average particle size of the inorganic porous material is too large, this will affect the contact effect between the inorganic porous material and the negative electrode active material.

[0049] The method for measuring the average particle size of inorganic porous materials is as follows: The inorganic porous material is dispersed in absolute ethanol by ultrasound for 5 minutes and tested using a laser particle size analyzer. D50 is the average particle size of the inorganic porous material, i.e., the particle size corresponding to less than 50% of the total volume in the particle size distribution curve.

[0050] In some embodiments of this disclosure, the negative electrode active material layer further comprises a conductive agent.

[0051] In this disclosure, the negative electrode sheet comprises both an inorganic porous material and a conductive agent, and the electrochemical performance of the battery can be further improved through the synergistic effect of the inorganic porous material and the conductive agent.

[0052] In some embodiments of this disclosure, the conductive agent accounts for 0.1% to 5% of the total content of the active material layer.

[0053] The conductive agent within the negative electrode sheet is filled between the negative electrode active materials and can store some liquid and conduct electricity; however, it can be understood that its exposed conductive interface increases side reactions of the electrolyte. Therefore, the conductive agent content within the above range can ensure the conductivity and liquid storage capacity of the negative electrode sheet, suppress side reactions of the electrode sheet, and ensure the battery's rate performance and cycle life.

[0054] In some specific embodiments of this disclosure, the conductive agent accounts for 0.1% to 2% of the total content of the active material layer.

[0055] When the conductive agent content is in the range of 0.1% to 2%, the synergistic effect between the inorganic porous material and the conductive agent is stronger, resulting in better overall battery performance.

[0056] In this disclosure, the conductive agent may be one or a combination of conductive carbon black, carbon nanotubes, graphene, and carbon fibers. The conductive carbon black material may be one or a combination of acetylene black, furnace black, channel black, thermal black, lamp black, and Ketjen black. The carbon nanotubes may be one or a combination of carbon nanotubes having various tube diameters (1 to 100 nm) and various tube lengths (0.05 to 100 μm). The graphene may be one or a combination of graphene having various number of layers (1 to 1000 layers).

[0057] Accordingly, embodiments of the present disclosure further provide a battery comprising a positive electrode sheet, an electrolyte, a separator, and a negative electrode sheet provided in the first embodiment. Since the battery comprises the negative electrode sheet provided in the first embodiment of the present disclosure, the battery has high specific capacity, rate performance, and cycle life, and meets the requirements of a wider range of applications.

[0058] In this disclosure, the battery may be either a lithium-ion battery or a sodium-ion battery.

[0059] In this disclosure, the positive electrode sheet includes a current collector and a positive electrode active material layer coated on at least one surface of the current collector. The active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0060] In this disclosure, the positive electrode active material layer may be coated on one side of the current collector or on both sides of the current collector. When the positive electrode active material layer is coated on both surfaces of the current collector, the thickness, surface density, and component content of the positive electrode active material layer located on each surface of the current collector can be designed independently according to the requirements of the application and may be the same or different.

[0061] In this disclosure, the positive electrode current collector may be any one of the following: aluminum foil, carbon-coated aluminum foil, polymer-coated aluminum foil, carbon cloth, carbon nanotube film, or carbon paper.

[0062] In this disclosure, the separator may be one or a composite separator of polyethylene, polypropylene, and polyvinylidene fluoride.

[0063] In this disclosure, the positive electrode active material may be one or a combination 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 phosphates with an olivine structure. The positive electrode active material is suitable for lithium-ion batteries.

[0064] In this disclosure, the positive electrode active material may alternatively be one or a combination of a transition metal oxide, a polyanionic compound, an organic polymer, and a Prussian blue / white analog. The positive electrode active material is suitable for sodium-ion batteries.

[0065] In this disclosure, the electrolyte is an organic solvent in which the carrier is dissolved. This disclosure does not impose any limitations on the electrolyte, and it can be formulated according to the actual circumstances.

[0066] Embodiments of the present disclosure further provide an electrical device, which uses a battery provided in an embodiment of the present disclosure, and which may have a higher market competitiveness.

[0067] In some embodiments of this disclosure, electrical devices include, but are not limited to, wearable electronic devices such as mobile phones, notebook computers, tablet computers, or smartwatches, e-cigarettes, new energy vehicles, electric mopeds, and energy storage base stations.

[0068] The technical solutions of this disclosure are further described below in several examples. [Examples]

[0069] Example 1 A negative electrode active material (artificial graphite), a conductive agent (conductive carbon black), sodium carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), and an inorganic porous material (porous silica) were mixed in a ratio of 96:0.9:1:2:0.1. The powder materials and deionized water were stirred using a homogenizer to form a negative electrode slurry, which was then uniformly coated onto a copper foil. For the silica, the dielectric constant was 1.6, the average particle size was 500 nm, the volume of mesopores was 80%, and the volume of macropores was 15%. Figure 1 shows the pore structure distribution curve of porous silica according to an embodiment of this disclosure, from which it can be seen that the porous silica contains both mesopores and macropores.

[0070] The positive electrode active material, lithium iron phosphate (LiFePO4), a conductive agent (CNT), and a second binder (PVDF) were mixed in a ratio of 97:1:2. The powder materials and NMP were stirred using a homogenizer to form a positive electrode slurry, which was then uniformly coated onto aluminum foil.

[0071] An electrolyte containing 1M LiPF6 was prepared by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1.

[0072] A 2.0Ah stacked battery was manufactured using a polypropylene separator.

[0073] Example 2 The only difference from Example 1 was that the mixing ratio of the negative electrode active material (artificial graphite), conductive agent (conductive carbon black), carboxymethylcellulose sodium (CMC), styrene-butadiene rubber (SBR), and inorganic porous material (porous silica) was 95:1.8:1:2:0.2.

[0074] Example 3 The only difference from Example 1 was that the mixing ratio of the negative electrode active material (artificial graphite), conductive agent (conductive carbon black), carboxymethylcellulose sodium (CMC), styrene-butadiene rubber (SBR), and inorganic porous material (porous silica) was 93.75:3:1:2:0.25.

[0075] Example 4 The only difference from Example 1 was that the mass ratio of the negative electrode active material (artificial graphite), conductive agent (conductive carbon black), carboxymethylcellulose sodium (CMC), styrene-butadiene rubber (SBR), and inorganic porous material (porous silica) was 96:0.5:1:2:0.5.

[0076] Example 5 The only difference from Example 1 is that the mass ratio of the negative electrode active material (artificial graphite), conductive agent (conductive carbon black), carboxymethylcellulose sodium (CMC), styrene-butadiene rubber (SBR), and inorganic porous material (porous silica) was 96:0.25:2:1:0.75.

[0077] Example 6 The only difference from Example 1 was that the mass ratio of the negative electrode active material (artificial graphite), conductive agent (conductive carbon black), carboxymethylcellulose sodium (CMC), styrene-butadiene rubber (SBR), and inorganic porous material (porous silica) was 95:0.5:1:2:1.5.

[0078] Example 7 The only difference from Example 1 was that the mixing ratio of the negative electrode active material (artificial graphite), conductive agent (conductive carbon black), carboxymethylcellulose sodium (CMC), styrene-butadiene rubber (SBR), and inorganic porous material (porous silica) was 95:0.2:1:2:1.8.

[0079] Example 8 The only difference from Example 1 is that the mixing ratio of the negative electrode active material (artificial graphite), conductive agent (conductive carbon black), carboxymethylcellulose sodium (CMC), styrene-butadiene rubber (SBR), and inorganic porous material (porous silica) was 96:0:1:2:1.

[0080] Example 9 The only difference from Example 1 is that the mixing ratio of the negative electrode active material (artificial graphite), conductive agent (conductive carbon black), carboxymethylcellulose sodium (CMC), styrene-butadiene rubber (SBR), and inorganic porous material (porous silica) was 95:0:1:2:2.

[0081] Example 10 The only difference from Example 1 is that the mixing ratio of the negative electrode active material (artificial graphite), conductive agent (conductive carbon black), carboxymethylcellulose sodium (CMC), styrene-butadiene rubber (SBR), and inorganic porous material (porous silica) was 94:0:1:2:3.

[0082] Example 11 The only difference from Example 1 was that the mixing ratio of the negative electrode active material (artificial graphite), conductive agent (conductive carbon black), carboxymethylcellulose sodium (CMC), styrene-butadiene rubber (SBR), and inorganic porous material (porous silica) was 93:0:1:2:4.

[0083] Example 12 The only difference from Example 1 is that the mixing ratio of the negative electrode active material (artificial graphite), conductive agent (conductive carbon black), carboxymethylcellulose sodium (CMC), styrene-butadiene rubber (SBR), and inorganic porous material (porous silica) was 92:0:1:2:5.

[0084] Example 13 The only difference from Example 12 is that the inorganic porous material is porous alumina, its dielectric constant is 6.5, its average particle size is 400 nm, the volume of mesopores is 76%, and the volume of macropores is 20%.

[0085] Example 14 The only difference from Example 12 is that the inorganic porous material is porous boehmite, its dielectric constant is 10, its average particle size is 800 nm, the volume of mesopores is 60%, and the volume of macropores is 18%.

[0086] Example 15 The only difference from Example 12 is that the inorganic porous material is porous titanium oxide, its dielectric constant is 48, its average particle size is 1000 nm, the volume of mesopores is 92%, and the volume of macropores is 5%.

[0087] Example 16 The only difference from Example 15 is that the inorganic porous material is porous titanium oxide, its dielectric constant is 48, its average particle size is 1000 nm, the volume of mesopores is 42%, and the volume of macropores is 21%.

[0088] Example 17 The only difference from Example 15 is that the inorganic porous material is porous titanium oxide, its dielectric constant is 48, its average particle size is 1000 nm, the volume of mesopores is 25%, and the volume of macropores is 26%.

[0089] To highlight the beneficial effects of the embodiments of this disclosure, the following comparative examples are provided.

[0090] Comparative Example 1 The only difference from Example 1 is that the mass ratio of the negative electrode active material (artificial graphite), conductive agent (conductive carbon black), carboxymethylcellulose sodium (CMC), styrene-butadiene rubber (SBR), and inorganic porous material (porous silica) was 91.99:5:1:2:0.01.

[0091] Comparative Example 2 The only difference from Example 1 is that the mass ratio of the negative electrode active material (artificial graphite), conductive agent (conductive carbon black), carboxymethylcellulose sodium (CMC), styrene-butadiene rubber (SBR), and inorganic porous material (porous silica) was 90:0:1:2:7.

[0092] Table 1 shows the parameters of the inorganic porous material content, conductive agent content, porosity, and liquid absorption rate in the negative electrode sheet of this disclosure. Table 2 shows the performance test results of the battery.

[0093] [Table 1]

[0094] Electrochemical performance test The batteries manufactured as described above (including the batteries in the comparative example) were subjected to room temperature testing using the Land Electronics CT3002A battery test system, and the test results are summarized in Table 2.

[0095] Battery discharge capacity test: A 0.1C / 0.1C cycle test was performed on the battery at 25°C within the voltage range of 2.0V to 3.8V (charging was performed at 0.1C to a voltage of 3.8V, followed by a 30-minute rest, and then discharging was performed at 0.1C to a voltage of 2.0V; this sequence constituted one cycle). After three cycles, the discharge capacity of the battery in the third cycle was recorded and used as the battery's discharge capacity.

[0096] Initial charge / discharge test: A 0.1C / 0.1C cycle test was performed on the battery at 25°C within a voltage range of 2.0V to 3.8V (charging was performed at 0.1C to a voltage of 3.8V, followed by a 10-minute rest, and then discharging was performed at 0.1C to a voltage of 2.0V; this sequence constituted one cycle). The charge ratio capacity and discharge ratio capacity of the battery in its first cycle were recorded, and the charge / discharge efficiency of the first cycle was calculated from these values. The discharge efficiency of the battery in its first cycle (%) was calculated as follows: Charge ratio capacity of the first cycle / Discharge ratio capacity of the first cycle × 100%.

[0097] Discharge rate test: At 25°C, the battery was charged to 3.8V at 0.1C, followed by a 30-minute rest period, and then discharged to 2.0V at a rate of 3C. This cycle was repeated three times consecutively. The charge-discharge data from the third cycle onward was used to calculate the battery's discharge efficiency for rate performance evaluation. The discharge rate (%) was calculated as: Discharge ratio capacity of the third cycle (3C) / Charge ratio capacity of the third cycle (0.1C) × 100%.

[0098] Charge level test: At 25°C, the battery was charged to 3.8V at 3C, followed by a 30-minute rest period, and then discharged to 2.0V at 0.1C. This cycle was repeated three times consecutively. The charge-discharge data from the third cycle onward was used to calculate the battery's charging efficiency. The charge rate (%) was calculated as (discharge ratio capacity in the third cycle (0.1C) / charge ratio capacity in the third cycle (3C)) × 100%.

[0099] Cycle life test: At 25°C, the battery was charged to 3.8V at 1C, followed by a 10-minute rest period, and then discharged to 2.0V at 1C. This cycle was repeated 1000 times consecutively. The capacity retention rate was recorded, and the capacity retention rate (%) after 1000 cycles was calculated as (discharge ratio capacity after 1000 cycles / discharge ratio capacity after the 3rd cycle) × 100%.

[0100] [Table 2]

[0101] As can be seen from the data in Tables 1 and 2, the negative electrode sheets provided in the embodiments of this disclosure contain an appropriate mass percentage of inorganic porous material compared to Comparative Examples 1 and 2. The inorganic porous material fills the spaces between the negative electrode active materials, partially or completely replacing the conductive agent, thereby regulating the porosity and liquid absorption rate of the negative electrode sheet and significantly improving the battery's rate performance (discharge rate and charge rate). In Comparative Example 1, a very small amount of inorganic porous material was added to the negative electrode sheet, resulting in low porosity and liquid absorption rate of the electrode sheet, and a winding diffusion path for the electrolyte, which in turn leads to high lithium ion migration impedance and poor battery rate performance. It can be seen that adding inorganic porous material to the negative electrode sheet alters the pore structure within the negative electrode sheet, increasing the porosity and liquid absorption rate of the negative electrode sheet, which is significantly beneficial in promoting electrolyte adsorption and migration.

[0102] The foregoing description is an exemplary embodiment of the present disclosure. Those skilled in the art should note that several further improvements and refinements can be made in this application without departing from the principles of the present disclosure. These improvements and refinements are also within the scope of protection of the present disclosure.

Claims

1. A negative electrode sheet comprising a current collector and a negative electrode active material layer coated on at least one surface of the current collector, wherein the negative electrode active material layer comprises a negative electrode active material, an inorganic porous material, and a first binder, and the inorganic porous material accounts for 0.1% to 5% of the total mass of the negative electrode active material layer.

2. The negative electrode sheet according to claim 1, wherein the inorganic porous material accounts for 0.2% to 3% of the total mass of the negative electrode active material layer.

3. The negative electrode sheet according to claim 1 or 2, wherein the porosity of the negative electrode sheet is 20% to 60%.

4. The negative electrode sheet according to any one of claims 1 to 3, wherein the liquid absorption rate of the negative electrode sheet is 2 to 8 mg / min.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein the dielectric constant of the inorganic porous material is ε, and 0 < ε ≤ 50 or 0 < ε ≤ 10.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein the inorganic porous material contains mesopores, and the volume of the mesopores accounts for 10% to 95% of the total volume of pores in the inorganic porous material.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein the average particle size of the inorganic porous material is 10 to 1000 nm.

8. The negative electrode sheet according to any one of claims 1 to 7, wherein the inorganic porous material comprises at least one of porous silica, porous titanium oxide, porous alumina, or porous boehmite.

9. The negative electrode sheet according to any one of claims 1 to 8, wherein the negative electrode active material is a carbon-based material.

10. The negative electrode sheet according to any one of claims 1 to 9, wherein the negative electrode active material layer further comprises a conductive agent.

11. The negative electrode sheet according to claim 10, wherein the conductive agent accounts for 0.1% to 5% of the total mass of the negative electrode active material layer.

12. The negative electrode sheet according to claim 11, wherein the conductive agent accounts for 0.1% to 2% of the total mass of the negative electrode active material layer.

13. A battery comprising a positive electrode sheet, an electrolyte, a separator, and a negative electrode sheet according to any one of claims 1 to 12.

14. An electrical device including a battery as described in claim 13.

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