Negative electrode sheet, battery and electric device

Abstract

A negative electrode sheet, a battery and an electric device. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a first negative electrode film layer and a second negative electrode film layer, and the second negative electrode film layer is located between the first negative electrode film layer and the negative electrode current collector; the first negative electrode film layer comprises a first active material, the first active material comprising first artificial graphite; the second negative electrode film layer comprises a second active material, the second active material comprising natural graphite and second artificial graphite; and the Dv50 of the first artificial graphite is D1, the Dv50 of the second artificial graphite is D2, and the Dv50 of natural graphite is D3, where D2>D3≥D1. The fast charging performance of a lithium-ion battery at a low temperature can be improved, and the energy density can be maintained; in addition, the pressure of excessive intercalation of lithium into graphite at the upper layer can be relieved, and the precipitation of lithium from the graphite at the upper layer can be inhibited.

Description

Negative electrode, battery and electrical device

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 202410264899.1 filed on March 7, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a negative electrode sheet, a battery, and an electrical device. Background Art

[0004] The average winter temperature in Northeast my country is -20℃. In low temperature environments, the battery life of new energy vehicle batteries, especially lithium-ion batteries, becomes weaker and the charging time becomes longer, causing new energy vehicles to consume electricity quickly and charge slowly. Therefore, the application of new energy vehicles in winter is restricted, which is not conducive to the promotion of new energy vehicles.

[0005] Summary of the Invention

[0006] The present application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode material to improve the charging rate of lithium-ion batteries at low temperatures.

[0007] In order to achieve the above-mentioned objectives, the embodiments of the present application provide a negative electrode sheet, a battery, and an electrical device.

[0008] In a first aspect, an embodiment of the present application provides a negative electrode sheet, comprising:

[0009] a negative electrode current collector; and

[0010] A negative electrode film layer, located on at least one side of the negative electrode current collector;

[0011] Wherein, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer, and the second negative electrode film layer is located between the first negative electrode film layer and the negative electrode current collector;

[0012] The first negative electrode film layer includes a first active material, and the first active material includes a first artificial graphite;

[0013] The second negative electrode film layer includes a second active material, and the second active material includes natural graphite and a second artificial graphite;

[0014] The Dv50 of the first artificial graphite is D1, the Dv50 of the second artificial graphite is D2, and the Dv50 of the natural graphite is D3, wherein: D2>D3≥D1.

[0015] Therefore, in the technical solution of the embodiment of the present application, the negative electrode film layer includes a first negative electrode film layer, i.e., an upper layer, and a second negative electrode film layer, i.e., a lower layer. The second negative electrode film layer is located between the first negative electrode film layer and the negative electrode current collector. The first negative electrode film layer includes a first artificial graphite Dv50 of D1, the second active material includes a natural graphite Dv50 of D3, and a second artificial graphite Dv50 of D2. D2>D3≥D1 is set, so that graphites with different properties in the upper and lower layers are matched. The upper first artificial graphite Dv50 is small, which can improve the dynamic performance, provide more lithium insertion channels, and quickly insert lithium. The lower second artificial graphite Dv50 is greater than the first artificial graphite Dv50, and can withstand greater pressure, reducing the influence of pressure on the porosity of the graphite of the lower layer, i.e., the second negative electrode film layer, during cold pressing. The uniformity of the overall pore distribution of the electrode plate is improved, so that the electrolyte is quickly transported to the lower layer, alleviating the pressure of excessive lithium insertion of lithium ions in the upper layer, and improving the fast charging performance. By adding some natural graphite to the lower layer of graphite, the particle size of natural graphite is smaller than that of the second artificial graphite in the lower layer, and it has abundant internal pores. Therefore, compared with the second artificial graphite in the lower layer, its specific surface area is larger, which can improve the dynamic performance, thereby giving full play to the advantages of natural graphite at low temperatures, maintaining energy density, and at the same time alleviating the pressure of excessive lithium insertion in the upper layer of graphite, inhibiting lithium precipitation in the upper layer of graphite, and improving low-temperature fast charging performance. By arranging natural graphite and the second artificial graphite in the lower layer, and D2>D3, the second artificial graphite absorbs more pressure, reducing the impact of cold pressing pressure on natural graphite, reducing the degradation of the dynamic performance of natural graphite caused by pressure extrusion, and at the same time improving the life of the second negative electrode film layer, and improving the fast charging performance of lithium-ion batteries at low temperatures. By setting the particle size of natural graphite D3≥D1, while providing sufficient lithium insertion channels in the first artificial graphite, the cold pressing pressure during molding can be further reduced, which is transferred from the upper first artificial graphite to the lower graphite layer, thereby squeezing the lower natural graphite. This reduces the impact on the specific surface area and porosity of the lower natural graphite, thereby improving the kinetic performance of the negative electrode sheet at low temperatures, improving the fast charging performance of the lithium-ion battery at low temperatures, and maintaining energy density. By setting D2>D3≥D1, the cold pressing pressure can be absorbed as much as possible by the upper first artificial graphite, and the remaining pressure transferred to the lower layer can be absorbed as much as possible by the second artificial graphite, thereby minimizing the impact on the internal porosity and specific surface area of ​​the natural graphite, allowing the natural graphite to retain good kinetic performance, improving the fast charging performance of the lithium-ion battery at low temperatures, and transferring the lithium inserted in the upper first artificial graphite to the lower layer as quickly as possible, maintaining energy density, and reducing lithium plating.

[0016] It should be noted that Dv50 refers to the particle size corresponding to when the cumulative volume percentage of the negative electrode active material reaches 50%, which can be measured using methods known in the art. For example, it can be directly measured using a laser diffraction particle size distribution analyzer (such as the Malvern Mastersizer 3000 laser particle size analyzer) in accordance with the standard GB / T 19077.1-2016.

[0017] In any embodiment, the value range of D1 is 3 to 15 μm, and the value of Dv50 of the first artificial graphite is within this range, which can make the gap between the particles within a suitable range, the tortuosity of the pole piece reasonable, improve the transmission performance of the electrolyte, and thus improve the low-temperature fast charging capability. Optionally, the value range of D1 is 8 to 12 μm, which can further make the gap between the particles within a suitable range, the tortuosity of the pole piece reasonable, provide a suitable lithium insertion channel, improve the transmission performance of the electrolyte, and thus improve the low-temperature fast charging capability and reduce the occurrence of lithium plating.

[0018] In any embodiment, the value range of D2 is 10 to 30 μm, and the second artificial graphite Dv50 is within this range, which can reduce the degree of compaction of the second negative electrode film layer, reduce the probability of deterioration of the interface contact between graphite particles due to compaction, and thus improve the transmission capacity of the electrolyte and improve the low-temperature fast charging performance; optionally, the value range of D2 is 15 to 25 μm, which can further reduce the degree of compaction of the second negative electrode film layer, reduce the probability of deterioration of the interface contact between graphite particles due to compaction, and thus improve the transmission capacity of the electrolyte and improve the low-temperature fast charging performance.

[0019] In any embodiment, the D3 value ranges from 5 to 20 μm. Natural graphite Dv50 within this range can reduce the probability of natural graphite compaction, preserve the rich pore structure of natural graphite, and thus improve low-temperature performance. Alternatively, the D3 value ranges from 10 to 18 μm, which can further reduce the probability of natural graphite compaction, preserve the rich pore structure of natural graphite, and thus improve low-temperature performance.

[0020] In any embodiment, the first active material includes secondary particles of the first artificial graphite. The secondary particles can reduce the lithium ion diffusion path and increase the lithium ion embedding channel, thereby improving the kinetic performance of the first negative electrode film layer and improving the low-temperature fast charging performance.

[0021] It should be noted that the second artificial graphite particles in the second active material may be primary particles or secondary particles, and the natural graphite is a primary particle.

[0022] In this application, primary particles and secondary particles have meanings commonly known in the art. Primary particles refer to particles that have not formed an agglomerated state. Secondary particles refer to particles that are agglomerated by two or more primary particles. Primary particles and secondary particles can be easily distinguished by taking SEM images using a scanning electron microscope.

[0023] The number ratio of primary particles or secondary particles in the negative electrode active material can be measured using instruments and methods known in the art, for example, it can be measured using a scanning electron microscope. As an example, the test method for the number ratio of secondary particles can be: laying the negative electrode active material and sticking it on a conductive adhesive to make a sample to be tested with a length x width of -6cmx1.1cm; using a scanning electron microscope (such as ZEISS Sigma300) to test the particle morphology. The test can refer to JV / T010-1996. In order to ensure the accuracy of the test results, a plurality of (for example, 20) different areas can be randomly selected from the sample to be tested for scanning testing, and at a certain magnification (for example, 1000 times), the percentage of the number of secondary particles in each test area to the total number of particles is calculated, that is, the number ratio of secondary particles in the area, and the average value of the test results of multiple test areas is taken as the number ratio of secondary particles in the negative electrode active material. Similarly, the number ratio of the primary particles in the negative electrode active material can also be tested.

[0024] Natural graphite and artificial graphite can also be coated with soft carbon or hard carbon to form a coating structure, providing more lithium insertion channels and reducing the probability of side reactions of graphite, thereby improving dynamic performance and further improving low-temperature fast charging capabilities.

[0025] In any embodiment, the natural graphite accounts for 20% to 80% by mass of the second active material. Within this range, the natural graphite content in the second active material can improve kinetic performance and low-temperature fast charging performance while reducing the impact on the service life of the negative electrode sheet. Alternatively, the natural graphite content in the second active material can be 40% to 60% by mass, further improving kinetic performance and low-temperature fast charging performance while reducing the impact on the service life of the negative electrode sheet.

[0026] It should be noted that the above-mentioned various parameter tests on the negative electrode active material can be conducted by sampling and testing before coating, or by sampling and testing from the negative electrode film layer after cold pressing.

[0027] When the above test sample is sampled from the negative electrode film layer after cold pressing, as an example, the sampling can be carried out according to the following steps:

[0028] First, randomly select a cold-pressed negative electrode film layer and sample the second negative electrode active material (scraping with a blade can be used for sampling). The scraping depth does not exceed the boundary between the first negative electrode film layer and the second negative electrode film layer.

[0029] Secondly, the first negative electrode active material is sampled. During the cold pressing process of the negative electrode film layer, an interfused layer may exist at the boundary between the first negative electrode film layer and the second negative electrode film layer (i.e., the first active material and the second active material are both present in the interfused layer). To ensure the accuracy of the test, when sampling the first negative electrode active material, the interfused layer can be scraped off first, and then the first negative electrode active material powder can be scraped off and sampled.

[0030] The collected first and second negative electrode active materials are placed in deionized water, filtered, and dried. The dried negative electrode active materials are then sintered at a specific temperature and time (e.g., 400°C for 2 hours) to remove the binder and conductive carbon, thereby obtaining test samples of the first and second negative electrode active materials. During the sampling process, an optical microscope or a scanning electron microscope can be used to assist in determining the location of the boundary between the first and second negative electrode film layers.

[0031] The natural graphite and artificial graphite used as the negative electrode active material in this application can be obtained through commercial channels. In the negative electrode sheet of this application, the negative electrode film layer can be arranged on one surface of the negative electrode current collector, or can be arranged on both surfaces of the negative electrode current collector.

[0032] In a second aspect, an embodiment of the present application provides a battery comprising the negative electrode sheet of the first aspect of the present application.

[0033] In a third aspect, an embodiment of the present application provides an electrical device comprising the battery of the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0035] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0036] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0037] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0038] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0039] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0040] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0041] The following specifically discloses embodiments of the negative electrode sheet, battery, and electrical device of the present application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0042] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0044] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0045] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0046] The average winter temperature in Northeast my country is -20°C. In low-temperature environments, the battery life of new energy vehicle batteries, especially lithium-ion batteries, is weakened, and charging times are prolonged. This results in new energy vehicles using electricity quickly but charging slowly. Consequently, the application of new energy vehicles in winter is limited, hindering their promotion. The charging dynamics of lithium-ion batteries are primarily limited by interfacial reaction impedance and liquid phase impedance, with resistance values ​​at low temperatures increasing by several hundred times compared to those at room temperature. This is due to the low reactivity of lithium ions with the negative electrode at low temperatures, as well as the poor conductivity and fluidity of the electrolyte at low temperatures.

[0047] Therefore, research on improving low-temperature charging performance is constantly emerging. For example, a lithium-ion battery with improved low-temperature charging performance has been developed. By reducing the battery's internal resistance, the battery can be charged at low temperatures without lithium plating, improving the low-temperature charging and discharging performance. However, this method cannot guarantee the fast charging performance of lithium-ion batteries at even lower temperatures.

[0048] Unexpectedly, by setting up two different negative electrode active layers and controlling their DV50, fast charging performance at lower temperatures can be achieved while reducing the occurrence of lithium plating.

[0049] Based on this, the present application provides a negative electrode sheet, a battery and an electrical device.

[0050] In a first aspect, an embodiment of the present application proposes a negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer, wherein the negative electrode film layer is located on at least one side of the negative electrode current collector; wherein the negative electrode film layer comprises a first negative electrode film layer and a second negative electrode film layer, wherein the second negative electrode film layer is located between the first negative electrode film layer and the negative electrode current collector; the first negative electrode film layer comprises a first active material, wherein the first active material comprises a first artificial graphite; the second negative electrode film layer comprises a second active material, wherein the second active material comprises natural graphite and a second artificial graphite; the Dv50 of the first artificial graphite is D1, the Dv50 of the second artificial graphite is D2, and the Dv50 of the natural graphite is D3, wherein: D2>D3≥D1.

[0051] At room temperature, liquid-phase diffusion dominates. Because lithium insertion in the upper layer is typically faster than in the lower layer, the utilization rate of the active material in the lower layer is lower than that in the upper layer. If the kinetics of the upper active material are insufficient, there are too few lithium insertion channels, or the liquid-phase transport is too slow, lithium ions cannot be inserted quickly enough and will precipitate out. Therefore, the upper layer of the anode electrode must possess excellent active material kinetics, ample lithium insertion channels, and a high porosity to facilitate the transport of lithium ions from the electrolyte to the lower layer. The lower layer's active material, however, has a low lithium insertion rate, so its kinetics are less affected, allowing the use of high-density active materials to increase energy density. Traditional double-layer electrode coatings utilize this principle, sacrificing the kinetics of the lower film to ensure excellent kinetics in the upper film, thereby achieving both energy density and improved room-temperature charging capability. However, at low temperatures, lithium ion transport is significantly reduced, and interfacial reactions dominate. While the upper layer still preferentially inserts lithium, the utilization rate of the active material in the lower layer is higher at low temperatures than at room temperature, so the lower layer also needs to possess excellent kinetics.

[0052] The bottleneck of low-temperature charging capability lies in the interface reaction impedance and liquid phase impedance, including the electrolyte and graphite interface reaction impedance, the lithium ion diffusion impedance in the SEI membrane, and the electrolyte liquid phase transmission impedance. At low temperatures, the rate of graphite lithium insertion is very slow, but the upper graphite has a higher priority in lithium insertion than the lower graphite. Therefore, the upper graphite should provide as many rapid lithium insertion channels as possible for lithium ions. During the cold pressing process of the electrode, the pressure will be continuously transmitted from top to bottom, causing the lower graphite to bear greater pressure than the upper graphite, which makes the lower graphite easy to be compacted. The upper graphite has large pores and the lower pores are small, which further makes it impossible for the lithium insertion of the upper graphite to be transferred to the lower graphite in time, resulting in lithium precipitation in the upper graphite.

[0053] Natural graphite's excellent kinetic performance stems from its rich internal pore structure, large surface area, abundant lithium insertion active sites, and numerous lithium insertion channels. However, natural graphite is soft, and its pores are easily compacted, thus losing its kinetic advantages. Furthermore, its large contact area with the electrolyte increases the probability of side reactions and gas generation, which shortens battery life and limits its fast-charging capabilities at low temperatures.

[0054] Therefore, in the technical solution of the embodiment of the present application, the negative electrode film layer includes a first negative electrode film layer, i.e., an upper layer, and a second negative electrode film layer, i.e., a lower layer. The second negative electrode film layer is located between the first negative electrode film layer and the negative electrode current collector. The first negative electrode film layer includes a first artificial graphite Dv50 of D1, the second active material includes a natural graphite Dv50 of D3, and the second artificial graphite Dv50 of D2. The smaller the particle size, the shorter the lithium ion transmission path and the better the kinetics, but the less pressure-resistant it is. The smaller the pores between the graphite particles, the larger the contact area, the fewer lithium intercalation active sites, the greater the probability of side reactions, the greater the impact on life, and the easier it is to produce gas. Therefore, D2>D3≥D1 is set so that graphites with different properties in the upper and lower layers are matched. The Dv50 of the first artificial graphite in the upper layer is small, which can improve the kinetic performance, provide more lithium insertion channels, and quickly insert lithium. The Dv50 of the second artificial graphite in the lower layer is greater than the Dv50 of the first artificial graphite, which can withstand greater pressure, reduce the impact of pressure on the porosity of the lower graphite during cold pressing, improve the uniformity of the overall pore distribution of the electrode, and enable rapid transport of the electrolyte to the lower layer, thereby alleviating the pressure of excessive lithium insertion of lithium ions in the upper layer, and thus improving the low-temperature fast charging performance. Some natural graphite is added to the lower layer of graphite. The particle size of natural graphite is smaller than that of the second artificial graphite in the lower layer, and it has abundant internal pores. Therefore, it has a larger specific surface area than the second artificial graphite in the lower layer, which can improve the kinetic performance, thereby giving full play to the advantages of natural graphite at low temperatures, improving the fast charging performance of lithium-ion batteries at low temperatures, maintaining energy density, and at the same time alleviating the pressure of excessive lithium insertion of the upper graphite and inhibiting lithium precipitation of the upper graphite. By arranging natural graphite and a second artificial graphite in the lower layer, with D2>D3, the second artificial graphite absorbs more pressure, reducing the impact of cold pressing pressure on natural graphite, reducing the degradation of the dynamic performance of natural graphite due to pressure extrusion, and at the same time improving the life of the second negative electrode film layer. By setting the particle size of natural graphite D3≥D1, while providing sufficient lithium insertion channels in the first artificial graphite, it is possible to further reduce the molding cold pressing pressure transmitted through the upper first artificial graphite to the lower graphite, thereby squeezing the lower natural graphite, reducing the impact on the specific surface area and porosity of the lower natural graphite, thereby improving the dynamic performance of the negative electrode sheet at low temperatures, improving the fast charging performance of lithium-ion batteries at low temperatures, and maintaining energy density. By satisfying D2>D3≥D1, the pressure of cold pressing can be absorbed as much as possible by the upper first artificial graphite, and the remaining pressure transmitted to the lower layer can be absorbed as much as possible by the second artificial graphite, thereby minimizing the impact on the internal porosity and specific surface area of ​​natural graphite, allowing natural graphite to retain good dynamic properties, thereby improving the fast charging performance of lithium-ion batteries at low temperatures, and transferring the lithium embedded in the upper first artificial graphite to the lower layer as quickly as possible, maintaining energy density, and reducing lithium plating.

[0055] It should be noted that Dv50 refers to the particle size corresponding to when the cumulative volume percentage of the negative electrode active material reaches 50%, which can be measured using methods known in the art. For example, it can be directly measured using a laser diffraction particle size distribution analyzer (such as the Malvern Mastersizer 3000 laser particle size analyzer) in accordance with the standard GB / T 19077.1-2016.

[0056] In any embodiment, the value range of D1 is 3 to 15 μm, and the value of Dv50 of the first artificial graphite is within this range, which can make the gap between the particles in a suitable range, the tortuosity of the pole piece reasonable, improve the transmission performance of the electrolyte, and thus improve the low-temperature fast charging capability. The value of D1 can be 3 μm, 5 μm, 8 μm, 10 μm, 12 μm or 15 μm. Optionally, the value range of D1 is 8 to 12 μm, which can further make the gap between the particles in a suitable range, the tortuosity of the pole piece reasonable, provide a suitable lithium insertion channel, improve the transmission performance of the electrolyte, and thus improve the low-temperature fast charging capability and reduce the occurrence of lithium plating.

[0057] In any embodiment, the value range of D2 is 10 to 30 μm. The second artificial graphite Dv50 is within this range, which can reduce the degree of compaction of the second negative electrode film layer and reduce the probability of deterioration of the interface contact between the graphite particles due to compaction, thereby improving the transmission capacity of the electrolyte and improving the low-temperature fast charging performance. The value of D2 can be 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 23 μm, 25 μm, 28 μm or 30 μm. Optionally, the value range of D2 is 15 to 25 μm, which can further reduce the degree of compaction of the second negative electrode film layer and reduce the probability of deterioration of the interface contact between the graphite particles due to compaction, thereby improving the transmission capacity of the electrolyte and improving the low-temperature fast charging performance.

[0058] In any embodiment, D3 is in the range of 5 to 20 μm. Natural graphite Dv50 within this range can reduce the probability of natural graphite being compacted, retain the rich pore structure of natural graphite, and thus improve low-temperature performance. The value of D3 can be 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, or 20 μm. Optionally, D3 is in the range of 10 to 18 μm, which can further reduce the probability of natural graphite being compacted, retain the rich pore structure of natural graphite, and thus improve low-temperature performance.

[0059] In any embodiment, the first active material includes secondary particles of the first artificial graphite. The secondary particles can reduce the lithium ion diffusion path and increase the lithium ion embedding channel, thereby improving the kinetic performance of the first negative electrode film layer and improving the low-temperature fast charging performance.

[0060] It should be noted that the second artificial graphite particles in the second active material can be primary particles or secondary particles, and the natural graphite is a primary particle.

[0061] In this application, primary particles and secondary particles have meanings commonly known in the art. Primary particles refer to particles that have not formed an agglomerated state. Secondary particles refer to particles that are agglomerated by two or more primary particles. Primary particles and secondary particles can be easily distinguished by taking SEM images using a scanning electron microscope.

[0062] The number ratio of primary particles or secondary particles in the negative electrode active material can be measured using instruments and methods known in the art, for example, it can be measured using a scanning electron microscope. As an example, the test method for the number ratio of secondary particles can be: laying the negative electrode active material and sticking it on a conductive adhesive to make a sample to be tested with a length x width of -6cmx1.1cm; using a scanning electron microscope (such as ZEISS Sigma300) to test the particle morphology. The test can refer to JV / T010-1996. In order to ensure the accuracy of the test results, a plurality of (for example, 20) different areas can be randomly selected from the sample to be tested for scanning testing, and at a certain magnification (for example, 1000 times), the percentage of the number of secondary particles in each test area to the total number of particles is calculated, which is the number ratio of secondary particles in the area, and the average value of the test results of multiple test areas is taken as the number ratio of secondary particles in the negative electrode active material. Similarly, the number ratio of primary particles in the negative electrode active material can also be tested.

[0063] Natural graphite and artificial graphite can also be coated with soft carbon or hard carbon to form a coating structure, providing more lithium insertion channels and reducing the probability of side reactions of graphite, thereby improving dynamic performance and further improving low-temperature fast charging capabilities.

[0064] In any embodiment, the mass proportion of natural graphite in the second active material is 20% to 80%. The mass proportion of natural graphite in the second active material within this range can improve the kinetic performance and low-temperature fast charging performance while reducing the impact on the service life of the negative electrode sheet. The mass proportion of natural graphite in the second active material can be 20%, 30%, 40%, 50%, 60%, 70% or 80%. Optionally, the mass proportion of natural graphite in the second active material is 40% to 60%, which can further improve the kinetic performance and low-temperature fast charging performance while reducing the impact on the service life of the negative electrode sheet.

[0065] It should be noted that the above-mentioned various parameter tests on the negative electrode active material can be conducted by sampling and testing before coating, or by sampling and testing from the negative electrode film layer after cold pressing.

[0066] When the above test sample is sampled from the negative electrode film layer after cold pressing, as an example, the sampling can be carried out according to the following steps:

[0067] First, a cold-pressed negative electrode film layer is randomly selected, and the second negative electrode active material is sampled (scraping with a blade can be used for sampling), and the scraping depth does not exceed the boundary area between the first negative electrode film layer and the second negative electrode film layer.

[0068] Secondly, the first negative electrode active material is sampled. During the cold pressing process of the negative electrode film layer, there may be an interfusion layer in the boundary area between the first negative electrode film layer and the second negative electrode film layer (that is, the first active material and the second active material exist in the interfusion layer at the same time). For the accuracy of the test, when sampling the first negative electrode active material, the interfusion layer can be scraped off first, and then the first negative electrode active material can be sampled by scraping powder.

[0069] The collected first and second negative electrode active materials are placed in deionized water, filtered, and dried. The dried negative electrode active materials are then sintered at a specific temperature and time (e.g., 400°C for 2 hours) to remove the binder and conductive carbon, thereby obtaining test samples of the first and second negative electrode active materials. During the sampling process, an optical microscope or a scanning electron microscope can be used to assist in determining the location of the boundary between the first and second negative electrode film layers.

[0070] Both natural graphite and artificial graphite used as the negative electrode active material in this application are commercially available. In the negative electrode sheet of this application, the negative electrode film layer can be disposed on one surface of the negative electrode current collector or on both surfaces of the negative electrode current collector.

[0071] It should be noted that the negative electrode film parameters (e.g., porosity, compaction density, etc.) given in this application refer to the parameter ranges for a single-sided film. When the negative electrode film is disposed on both surfaces of the negative electrode current collector, the film parameters on either surface that meet the requirements of this application are considered to fall within the scope of protection of this application. Furthermore, the ranges for film thickness, porosity, etc., given in this application refer to the parameters of the film after cold pressing and for battery assembly.

[0072] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0073] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0074] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0075] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0076] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0077] In some embodiments, the negative electrode film layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0078] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0079] In a second aspect, an embodiment of the present application provides a battery comprising the negative electrode sheet of the first aspect of the present application.

[0080] In any embodiment, the battery comprises a primary battery or a secondary battery.

[0081] In one embodiment of the present application, a secondary battery is provided. Typically, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are intercalated and released between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator is positioned between the positive and negative electrodes, primarily preventing a short circuit between the positive and negative electrodes while allowing ions to pass through.

[0082] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0083] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0084] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0085] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may adopt the positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0086] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this application for cathode materials refer to the initial state of the material, i.e., the state before addition of the materials. When the cathode material is used in a battery system, the molar Li content will change after charge and discharge cycles.

[0087] In the list of positive electrode materials in this application, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0088] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0089] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0090] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0091] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0092] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0093] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0094] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0095] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0096] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 having a square structure as an example.

[0097] In some embodiments, referring to FIG2 , the outer package may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0098] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0099] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0100] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0101] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0102] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0103] In a third aspect, an embodiment of the present application provides an electrical device comprising the battery of the second aspect of the present application.

[0104] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module or battery pack provided in the present application. The secondary battery, battery module or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0105] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0106] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0107] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0108] The technical solution of the present application is further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to explain the present application and are not used to limit the present application.

[0109] The parameters of the negative electrode sheets of Examples 1 to 18 and Comparative Examples 1 to 7 of the present application are as shown in Table 1. The first active material is described using secondary particles as an example.

[0110] The negative electrode sheet of Example 1 is prepared into a battery, which can be prepared by the following method:

[0111] 1) Preparation of positive electrode

[0112] The lithium nickel cobalt manganese ternary active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive carbon black SuperP, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in N-methylpyrrolidone at a weight ratio of 94:3:3. The slurry was then coated on an aluminum foil substrate and dried, cold pressed, slit, and cut to obtain a positive electrode sheet. The surface density of the positive electrode film layer was 19.0 mg / cm 2 The compaction density of the positive electrode film is 3.4g / cm 3

[0113] 2) Preparation of negative electrode sheet

[0114] The first step is to prepare negative electrode slurry 1: weigh the first negative electrode active material artificial graphite, binder SBR, thickener sodium carboxymethyl cellulose (CMC-Na) and conductive carbon black (Super P) in a weight ratio of 96.2:1.8:1.2:0.8 and deionized water, add them into a stirring tank in a certain order and mix them to prepare negative electrode slurry 1.

[0115] The second step is to prepare negative electrode slurry 2: the second negative electrode active material artificial graphite and natural graphite (mass ratio 5:5), binder SBR, thickener sodium carboxymethyl cellulose (CMC-Na) and conductive carbon black (Super P) are weighed in a weight ratio of 96.2:1.8:1.2:0.8 and deionized water, and added into a stirring tank in a certain order for mixing to prepare negative electrode slurry 2.

[0116] In the third step, negative electrode slurry 1 and negative electrode slurry 2 are extruded simultaneously through a dual-chamber coating device. Negative electrode slurry 1 is coated on the current collector to form the first negative electrode film layer, and negative electrode slurry 2 is coated on the first negative electrode film layer to form the second negative electrode film layer. The thickness ratio of the first negative electrode film layer to the second negative electrode film layer is 1:1; the surface density of the negative electrode film layer is 12 mg / cm 2 The compaction density of the negative electrode film is 1.67g / cm 3 .

[0117] In the fourth step, the coated wet film is baked in an oven through different temperature zones to obtain a dry electrode sheet, which is then cold pressed to obtain the required negative electrode film layer, and then subjected to processes such as striping and cutting to obtain the negative electrode sheet.

[0118] 3) Isolation film

[0119] PE film is selected as the isolation membrane.

[0120] 4) Preparation of electrolyte

[0121] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then fully dried carp salt LiPF6 is dissolved in a mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.

[0122] 5) Battery Preparation

[0123] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are stacked in order, and a reference electrode is added between the separator and the negative electrode sheet (the reference electrode is used for subsequent performance testing of the battery sample, and carp sheet, carp metal wire, etc. can be selected, and the reference electrode should be separated by a separator to prevent contact with either side of the positive and negative electrodes). After winding, an electrode assembly is obtained, and the electrode assembly is placed in an outer package. The above-mentioned electrolyte is added, and after packaging, standing, formation, aging and other processes, a secondary battery is obtained.

[0124] The secondary batteries of Examples 2 to 18 and the secondary batteries of Comparative Examples 1 to 7 were prepared in a similar manner to the secondary battery of Example 1, but the composition of the battery electrodes and product parameters were adjusted. The different product parameters are detailed in Table 1.

[0125] Performance Testing

[0126] 1) Charging DCR

[0127] Take the battery cell and calibrate the initial capacity C0 at room temperature. Discharge the cell to 50% SOC with 0.33C0. Then place it in a high-low temperature chamber, adjust it to 25°C, and charge it with 4C0 for 30s. Measure the voltage values ​​V0 and V1 before and after discharge. The DCR corresponding to 50% SOC is calculated using the formula R = (V1-V0) / I0, where I0 is the corresponding charging current. Then adjust the temperature to -20°C and repeat the above steps using 0.36C0.

[0128] 2) Lithium deposition rate

[0129] The battery cell was calibrated with an initial capacity C0 at room temperature, and then the SOC was adjusted to 10% SOC. The cell was placed in a -10°C incubator and allowed to stand for 2 hours. The cell was then charged to 50% SOC using different rates X1, X2, ..., Xn, and then discharged to 20% SOC using 0.33C0. This cycle was repeated for 20cls. The interface was disassembled and the minimum rate corresponding to lithium deposition was observed, which was defined as the lithium deposition rate.

[0130] 3) Cycle retention rate

[0131] The cell was calibrated at room temperature for its initial capacity (C0). It was then fully discharged to 0% SOC and placed in a -20°C incubator for 2 hours. The cell was then charged at a rate of 0.2C0 to a voltage limit of 3.8V and discharged at a rate of 0.33C0 to a voltage limit of 2.0V. This cycle was repeated for 200 cls. After returning to room temperature, the post-cycle capacity (C1) was recalibrated. The corresponding cycle retention ratio is C1 / C0. The results are summarized in Table 1.

[0132] As can be seen from Table 1, by setting two layers of negative electrode active layers, the second negative electrode active layer includes natural graphite and artificial graphite, and the first negative electrode active layer includes artificial graphite, D2>D3≥D1, so that the upper and lower layers of graphite with different properties are matched, and the upper and lower layers of graphite with different properties are matched. The Dv50 of the first artificial graphite in the upper layer is small, which can improve the kinetic performance, provide more lithium insertion channels, and quickly insert lithium. The Dv50 of the second artificial graphite in the lower layer is greater than the Dv50 of the first artificial graphite, and can withstand greater pressure, reducing the effect of pressure on the porosity of the graphite in the lower layer, i.e., the second negative electrode film layer, during cold pressing, and improving the uniformity of the overall pore distribution of the pole piece, so that the electrolyte is quickly transported to the lower layer, alleviating the pressure of excessive lithium insertion of lithium ions in the upper layer, and improving the fast charging performance. By adding some natural graphite to the lower layer of graphite, the particle size of natural graphite is smaller than that of the second artificial graphite in the lower layer, and it has abundant internal pores. Therefore, compared with the second artificial graphite in the lower layer, its specific surface area is larger, which can improve the dynamic performance, thereby giving full play to the advantages of natural graphite at low temperatures, maintaining energy density, and at the same time alleviating the pressure of excessive lithium insertion in the upper layer of graphite, inhibiting lithium precipitation in the upper layer of graphite, and improving low-temperature fast charging performance. By arranging natural graphite and the second artificial graphite in the lower layer, and D2>D3, the second artificial graphite absorbs more pressure, reducing the impact of cold pressing pressure on natural graphite, reducing the degradation of the dynamic performance of natural graphite caused by pressure extrusion, and at the same time improving the life of the second negative electrode film layer, and improving the fast charging performance of lithium-ion batteries at low temperatures. By setting the particle size of natural graphite D3≥D1, while providing sufficient lithium insertion channels in the first artificial graphite, the cold pressing pressure during molding can be further reduced, which is transferred from the upper first artificial graphite to the lower graphite layer, thereby squeezing the lower natural graphite. This reduces the impact on the specific surface area and porosity of the lower natural graphite, thereby improving the kinetic performance of the negative electrode sheet at low temperatures, improving the fast charging performance of the lithium-ion battery at low temperatures, and maintaining energy density. By setting D2>D3≥D1, the cold pressing pressure can be absorbed as much as possible by the upper first artificial graphite, and the remaining pressure transferred to the lower layer can be absorbed as much as possible by the second artificial graphite, thereby minimizing the impact on the internal porosity and specific surface area of ​​the natural graphite, allowing the natural graphite to retain good kinetic performance, improving the fast charging performance of the lithium-ion battery at low temperatures, and transferring the lithium inserted in the upper first artificial graphite to the lower layer as quickly as possible, maintaining energy density, and reducing lithium plating.

[0133] Since Comparative Example 1 contains only one layer of artificial graphite, the lower layer has poor dynamic performance and poor low-temperature fast charging capability.

[0134] In Comparative Example 2, since the second negative electrode active layer does not contain artificial graphite, the porosity of the lower layer deteriorates seriously, and the low temperature causes the fast charging performance to decrease.

[0135] In Comparative Example 3, since the second negative electrode active layer does not contain natural graphite, the lower layer has poor kinetic performance and poor low-temperature fast charging capability.

[0136] In Comparative Example 4, the positions of the first negative electrode active layer and the second negative electrode active layer are interchanged, resulting in compaction of the natural graphite and deterioration of the low-temperature fast charging performance.

[0137] In comparative examples 5 and 7, since the relationship between D1, D2, and D3 does not satisfy D2>D3≥D1, the second artificial graphite fails to provide pressure-bearing effect, resulting in the compaction of natural graphite, the reduction of lithium insertion channels, the reduction of dynamic performance, and poor low-temperature fast charging performance.

[0138] In comparative example 6, since D1>D3, there are too few lithium insertion channels in the upper layer, and the upper layer has poor kinetic performance, which easily leads to lithium deposition and affects the low-temperature fast charging performance.

[0139] The above are only preferred embodiments of the present application and are not intended to limit the scope of the present application. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of the present application.

Claims

1. A negative electrode sheet, wherein: include: Negative electrode current collector: and A negative electrode film layer, located on at least one side of the negative electrode current collector; Wherein, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer, and the second negative electrode film layer is located between the first negative electrode film layer and the negative electrode current collector; The first negative electrode film layer includes a first active material, and the first active material includes a first artificial graphite; The second negative electrode film layer includes a second active material, and the second active material includes natural graphite and a second artificial graphite; The Dv50 of the first artificial graphite is D1, the Dv50 of the second artificial graphite is D2, and the Dv50 of the natural graphite is D3, wherein: D2>D3≥D1.

2. The negative electrode sheet according to claim 1, wherein: The value range of D1 is 3 to 15 μm.

3. The negative electrode sheet according to claim 2, wherein: The value range of D1 is 8 to 12 μm.

4. The negative electrode sheet according to any one of claims 1 to 3, wherein: The value range of D2 is 10 to 30 μm.

5. The negative electrode sheet according to claim 4, wherein: The value range of D2 is 15 to 25 μm.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein: The value range of D3 is 5 to 20 μm.

7. The negative electrode sheet according to claim 6, wherein: The value range of D3 is 10 to 18 μm.

8. The negative electrode sheet according to any one of claims 1 to 7, wherein: The first active material includes secondary particles of a first artificial graphite.

9. The negative electrode sheet according to any one of claims 1 to 8, wherein: The mass proportion of the natural graphite in the second active material is 20% to 80%.

10. The negative electrode sheet according to claim 9, wherein: The mass proportion of the natural graphite in the second active material is 40% to 60%.

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

12. An electrical device, wherein: Comprising the battery of claim 11.

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