Battery monomer, negative pole piece, preparation method, battery device and power utilization device

Abstract

The invention relates to a battery monomer, a negative pole piece, a preparation method, a battery device and a power utilization device. The battery monomer comprises a positive pole piece, a separator and a negative pole piece, the negative pole piece is provided with a negative current collector and a negative active layer located on the negative current collector, an active material of the negative active layer comprises graphite, the graphite comprises primary particle graphite, the electrochemical activity specific surface area of the graphite is 0.5 m < 2 > / g-1 m < 2 > / g, and the specific surface area of the primary particle graphite is 0.5 m < 2 > / g-1 m < 2 > / g. The gram capacity of the negative electrode active material under 0.05 C is 340 mAh / g-350 mAh / g, and the ratio of the thickness H1 of the negative electrode active layer in a complete charging state to the thickness H2 of the negative electrode active layer in a complete discharging state is 1.05-1.2. The battery monomer has relatively good cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a battery monomer, a negative electrode sheet, a preparation method, a battery device and a power utilization device. BACKGROUND

[0002] With the development of new energy technology, the performance of battery monomers such as lithium ion batteries has also been significantly improved. Based on the upgrading of graphite-based technology and the increasing market demand, the performance of graphite, such as cycle performance, is becoming more and more demanding, and it is required that the graphite and other negative active materials can further improve the cycle performance while maintaining a certain gram capacity.

[0003] However, the current battery monomer, negative electrode sheet, preparation method, battery device and power utilization device still need to be improved. SUMMARY

[0004] In view of the above problems, the purpose of the present application is to provide a battery monomer, a negative electrode sheet, a preparation method, a battery device and a power utilization device. The negative active material of the battery monomer includes primary particle graphite. By controlling the active specific surface area of the graphite, particles with a low electrochemical active specific surface area are obtained. The battery monomer can reduce the loss of active lithium caused by the need to repeatedly repair the interface film of the negative active layer surface rupture during the cycle process, thereby reducing the loss of active lithium and improving the cycle performance of the battery monomer. The primary particle graphite has moderate gram capacity, low active specific surface area and low expansion, thereby comprehensively improving the performance of the battery monomer, so that the battery monomer can balance good cycle performance and initial efficiency. And the primary particle graphite is beneficial to alleviate the adverse effects of the reduction of the active specific surface on the rate performance of the negative active material and the wettability of the electrolyte, and compared with the secondary particles which need to be granulated to form, the preparation process of the primary particles is simpler and does not need granulation treatment, so the production cost can be reduced.

[0005] Therefore, the first aspect of the present application provides a battery monomer. The battery monomer includes a positive electrode sheet, a separator and a negative electrode sheet, the negative electrode sheet has a negative current collector and a negative active layer on the negative current collector, the active material of the negative active layer includes graphite, the graphite includes primary particle graphite, the electrochemical active specific surface area of the graphite is 0.5 m 2 / g~1 m 2 / g, and the gram capacity of the negative active material at 0.05C is 340mAh / g~350mAh / g. The battery monomer has good cycle performance and initial charging efficiency.

[0006] According to embodiments of the present application, the ratio of the thickness H1 of the negative active layer in the fully charged state to the thickness H2 in the fully discharged state is 1.05-1.2. Thus, the expansion of the negative electrode sheet can be reduced.

[0007] According to embodiments of the present application, the specific surface area of the graphite is 0.8 m 2 / g-1 m 2 / g. Thus, the performance of the battery cell can be further improved. According to embodiments of the present application, the Dv50 of the graphite is 10-22 μm. Thus, the performance of the negative electrode sheet can be improved.

[0008] According to embodiments of the present application, the Dv1 of the graphite is 1.5-4 μm.

[0009] According to embodiments of the present application, the Dv90 of the graphite is 30-40 μm.

[0010] According to embodiments of the present application, the graphitization degree of the graphite is 92%-94%. Thus, the expansion of the negative electrode sheet can be further reduced.

[0011] According to embodiments of the present application, the negative active material further comprises secondary particle graphite.

[0012] According to embodiments of the present application, the powder compaction density of the active material of the negative active layer at 5T is 1.73-1.9 g / cc. Thus, the energy density of the battery cell can be further improved.

[0013] In another aspect of the present application, a negative electrode sheet is provided. The negative electrode sheet comprises a negative current collector and a negative active layer on the negative current collector, wherein the active material of the negative active layer comprises graphite, the graphite comprises primary particle graphite, the specific surface area of the graphite is 0.5 m 2 / g-1 m 2 / g, and the gravimetric capacity of the negative active material at 0.05C is 340 mAh / g-350 mAh / g. Thus, the performance of the negative electrode sheet can be improved.

[0014] According to embodiments of the present application, the ratio of the thickness H1 of the negative active layer in the fully charged state to the thickness H2 in the fully discharged state is 1.05-1.2; and / or the average particle size of the graphite is 12-22 μm; the Dv1 of the graphite is 1.5-4 μm; and / or the Dv90 of the graphite is 30-40 μm; and / or the graphitization degree of the graphite is 92%-94%. Thus, the performance of the negative electrode sheet can be further improved.

[0015] According to an embodiment of the present application, the negative active layer further comprises a second graphite, and the second graphite comprises graphite secondary particles.

[0016] In another aspect of the present application, the present application provides a method for preparing a negative active material. The method comprises: grinding, shaping and removing fine powder of a coke material to obtain a raw material with a Dv50 of 15-20 μm; and sintering the raw material, wherein the sintering comprises sequentially increasing the temperature from a first sintering temperature to a third sintering temperature by gradient heating, the first sintering temperature is lower than the second sintering temperature, and the second sintering temperature is lower than the third sintering temperature, the temperature increasing rate from the first sintering temperature to the second sintering temperature is greater than the temperature increasing rate from the second sintering temperature to the third sintering temperature, and after the sintering is completed, the sintered product is naturally cooled to a temperature below 400 degrees Celsius before being taken out of the sintering equipment. Thus, a negative active material with a low electrochemical active specific surface area and low expansion can be easily obtained.

[0017] According to an embodiment of the present application, the removing fine powder comprises removing 10%-30% of fine powder by mass percentage. The coke material comprises at least one of petroleum coke, coal-based coke and needle coke. Thus, the performance of the negative active material can be further improved.

[0018] According to an embodiment of the present application, the sintering satisfies at least one of the following conditions: the first sintering temperature is 1100-1200 degrees Celsius, the second sintering temperature is 2000-2300 degrees Celsius, and the third sintering temperature is 2500-3000 degrees Celsius; the temperature increasing rate from the first sintering temperature to the second sintering temperature is 10-20 degrees Celsius per minute; the temperature increasing rate from the second sintering temperature to the third sintering temperature is 3-10 degrees Celsius per minute; and after the sintering temperature is increased to the third sintering temperature, a heat preservation operation is further included for 1-4 hours. Thus, the performance of the negative active material can be further improved.

[0019] In another aspect of the present application, the present application provides a battery device comprising the battery cell, the negative electrode sheet, or the negative active material prepared by the method as described above.

[0020] In another aspect of the present application, the present application provides an electric device, which comprises the battery device as described above.

[0021] The above description is only a summary of the technical solutions of the present application. In order to make the technical solutions of the present application more clearly understood, the specific embodiments of the present application are described below according to the contents of the description, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Various other advantages and benefits will become apparent to those skilled in the art by reading the detailed description of the preferred embodiment below. The accompanying drawings are only for the purpose of illustrating the preferred embodiment and are not to be considered as limiting the present application. In the accompanying drawings: Figure 1 is a schematic diagram of a battery cell according to one embodiment of the present application; Figure 2 yes Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown; Figure 3 is a schematic diagram of a battery module according to one embodiment of the present application; Figure 4 is a schematic diagram of a battery pack according to one embodiment of the present application; Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown; Figure 6 is a schematic diagram of an electrical device using a battery cell as a power source according to one embodiment of the present application; Figure 7 This is a scanning electron microscope photograph of the negative electrode active material of Example 1 of the present application.

[0023] Description of reference numerals: 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 end cover. DETAILED DESCRIPTION

[0024] The exemplary embodiments of the present disclosure will be described in more detail below. It should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Instead, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0025] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are listed, then the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, wherein a and b are both 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, stating that a parameter is an integer ≥ 2 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.

[0026] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0027] 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.

[0028] 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), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, it is mentioned that the method may also include step (c), which means 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.

[0029] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0030] As mentioned above, with the upgrading of technology and the increasing market demand, the performance of the battery cell needs to be further improved to meet such demand. Among them, the cycle performance is one of the more important performances of the battery cell. The negative active material has a relatively important influence on the cycle performance of the battery cell: compared with the positive active material, the negative active material is more prone to volume expansion during the cycle process. When the toughness of the solid-state electrolyte film (SEI film) on the surface of the negative electrode cannot withstand such expansion during the cycle process, the interface film is prone to damage and rupture, and thus during the cycle process, the SEI film repair process will occur, which will cause the loss of active lithium and lead to a decrease in cycle performance.

[0031] The present application mainly includes a primary particle graphite negative active material with a relatively low electrochemical active specific surface area in the battery cell. The primary particle has a relatively low electrochemical active specific surface area, which can reduce the surface reaction active sites of the negative active material and thus reduce the film formation area of the SEI film and reduce the consumption of active lithium. At the same time, the graphite with a relatively low electrochemical active specific surface area also has a relatively low expansion, thereby reducing the probability of rupture of the negative SEI film and thus improving the cycle performance and life of the battery cell. However, the reduction of the electrochemical specific surface area also affects the rate performance and electrolyte infiltration to some extent, thereby reducing the cycle performance. Therefore, the primary particle graphite also has a moderate capacity, which reduces the serious cycle decay caused by excessively high capacity, thereby further improving the cycle retention rate. Through the dual adjustment of capacity and electrochemical specific surface area, the cycle is improved, and the aforementioned problems caused by simply reducing the electrochemical active specific surface area are alleviated. Moreover, the morphology of the primary particle can also balance the negative effects caused by the low electrochemical active specific surface area to some extent. In addition, the primary particle can also simplify the production process and reduce the cost: the primary particle does not need to be granulated to form a secondary particle, and can be obtained through a relatively simple preparation process.

[0032] The scheme described in the embodiments of the present application is applicable to a battery cell, a battery device using the battery cell, and a power consumption device using at least one of the battery cell and the battery device.

[0033] Battery cell In the embodiments of the present application, the battery cell can be a secondary battery, which refers to a battery cell that can be activated by charging after discharging. In some embodiments, the battery cell can be a lithium ion secondary battery.

[0034] Electrode assembly The battery cell generally comprises an electrode assembly. The electrode assembly comprises a positive electrode sheet, a negative electrode sheet, and a separator disposed between the negative electrode sheet and the positive electrode sheet. During the charging and discharging of the battery cell, active ions (e.g., lithium ions) are reversibly intercalated and deintercalated between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and can prevent the positive and negative electrodes from shorting while allowing the active ions to pass through.

[0035] In some embodiments of the present application, the battery cell comprises a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. The separator is disposed between the positive electrode sheet and the negative electrode sheet to insulate and separate the two. The negative electrode sheet has a negative current collector and a negative active layer disposed on the negative current collector. The active material of the negative active layer comprises graphite. The graphite comprises primary particle graphite, and the electrochemically active specific surface area of the graphite is 0.5 m 2 / g~1 m 2 / g, and the gram capacity of the negative active material at 0.05C is 330 mAh / g~350 mAh / g. The battery cell has good cycle performance.

[0036] The primary particle graphite has relatively high mechanical strength, so it is not easy to crack during the cycle of the battery cell, and this characteristic is more pronounced in high-temperature cycles, which can reduce the loss of active lithium due to graphite cracking. Moreover, the graphite with the above characteristics can have a smaller electrochemically active specific surface area, so the reaction active sites of the graphite particles are fewer, which can reduce the area, especially the microscopic area, of SEI film formation on one hand, and on the other hand, due to its relatively low graphitization degree, the degree of expansion of the graphite during the cycle of the battery cell is relatively low, thereby reducing the probability of damage to the SEI film during the cycle, thereby reducing the loss of active lithium from both the formation and repair of the SEI film, and thus the cycle performance of the battery cell can be improved.

[0037] [The negative electrode sheet] In some embodiments, the negative electrode sheet comprises a negative current collector and a negative active layer disposed on at least one surface of the negative current collector.

[0038] In the present application, the negative active layer should be understood in a broad sense. For a secondary battery, the negative active layer contains a negative active material.

[0039] According to an embodiment of the present application, the negative active material of the negative active layer comprises graphite. Specifically, it comprises primary particle graphite. More specifically, the graphite in the negative active layer can be primarily primary particle graphite, which can account for more than 50% of the total number of graphite particles, or more than 60%, 70%, or even 80%, 90%.

[0040] Primary particle graphite has complete particle boundaries, and there is no significant agglomeration or bonding between the particles. The single particles can be relatively independently dispersed in the negative active layer. There can be small pores and point or linear defects on the particle surface or at the boundaries, which are different from the structures of accumulation and agglomeration, and are the smallest structural units of the negative active material. Unlike secondary particle graphite, primary particle graphite generally has a larger particle size, a more complete crystal structure inside, and fewer bulk defects. The state and proportion of primary particle graphite in the negative active layer can be determined by, for example, scanning electron microscope observation of the surface or cross-section of the negative active layer along the thickness direction.

[0041] As described above, the primary particle graphite has a more compact crystal structure and no interfacial gaps between the secondary particles, and thus can reduce the volume expansion caused by the insertion of lithium ions to a certain extent, and the destruction of the graphite structure caused by the insertion and extraction of lithium ions is also less. Therefore, the negative active layer with a high content of primary particle graphite can reduce the expansion of the negative active layer to a certain extent.

[0042] In some embodiments, the ratio of the thickness H1 of the negative active layer in the fully charged state and the thickness H2 of the negative active layer in the fully discharged state is 1.05-1.2. In this application, the thickness of the negative active layer has the meaning known in the art, and can be detected by the known meaning and equipment in the art. For example, a freshly prepared negative electrode sheet can be taken as a sample, or a negative electrode sheet can be obtained from a battery cell that has been fully discharged (discharged to the lower limit cutoff voltage so that the charged state of the battery cell is about 0% SOC), cleaned to remove the surface electrolyte and dried, and the thickness of the negative electrode sheet is measured by a micrometer and recorded as H2. The thickness of the negative active layer in the fully charged state can be obtained by full charging and disassembly. The thickness is recorded as H1. The closer the ratio of H1 and H2 is to 1, the smaller the expansion of the negative active layer during actual cycling.

[0043] According to the embodiments of the present application, the specific surface area of the graphite in the battery cell is 0.5 m 2 / g-1 m 2 / g, and the gram capacity of the negative active material is 340 mAh / g-350 mAh / g. Since the primary particle graphite accounts for a relatively large proportion in the graphite, the specific surface area of the graphite is relatively low. In particular, by controlling the raw materials and sintering process for preparing the graphite, the specific surface area of the obtained primary particle graphite can be further reduced. Specifically, the specific surface area of the graphite can be 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 0.72 m2 / g, 0.75 m 2 / g, 0.78 m 2 / g, 0.8 m 2 / g, 0.82 m 2 / g, 0.85 m 2 / g, 0.86 m 2 / g, 0.88 m 2 / g, 0.9 m 2 / g, 0.95 m 2 / g, or 1 m 2 / g.

[0044] The electrochemical active specific surface area can better reflect the content of active sites on the surface of graphite, and thus can more accurately measure the sites on the surface of the graphite particles that can provide lithium ion deintercalation and the content of reactive sites. A lower electrochemical active specific surface area has fewer electrochemically active sites, and thus fewer sites for side reactions with the electrolyte, thereby reducing the area of the solid electrolyte interface (SEI) film formed on the surface of the negative active material at the micro level. As a result, the loss of active lithium can be reduced to some extent, thereby improving the cycle performance of the battery cell.

[0045] According to embodiments of the present application, the electrochemical active specific surface area can be obtained by performing electrochemical cyclic voltammetry curve scanning on a half-cell composed of the negative electrode sheet, and calculating the active peak area in the scanning curve.

[0046] According to embodiments of the present application, the Dv50 of the graphite in the negative active layer can be 10-22 μm, and more specifically, 16-20 μm. Since the graphite has a certain proportion of primary particle graphite, the Dv50 particle size of the graphite is relatively large. As a result, the area of the interface between the graphite in the negative active layer can also be reduced, thereby reducing the area of the solid electrolyte interface (SEI) film formed on the surface of the negative active material and reducing the loss of active lithium ions during the formation of the interface film.

[0047] According to embodiments of the present application, the Dv1 of the graphite in the negative active layer can be 1.5-4 μm, and the Dv90 can be 30-40 μm. As a result, the performance of the negative active layer can be further improved.

[0048] According to embodiments of the present application, the graphitization degree of the graphite can be 92%-94%, and specifically, 93%. Graphite with a moderate graphitization degree can also reduce the expansion of graphite particles during the cycle, thereby reducing the probability of damage to the SEI film.

[0049] According to embodiments of the present application, the gram capacity of the active material of the negative active layer at 0.05C is 330-350 mAh / g, specifically 340-350 mAh / g, and more specifically 340 mAh / g, 342 mAh / g, 345 mAh / g, etc. The gram capacity is moderate, which can meet the capacity requirement of the battery cell for the negative electrode, and can also alleviate the substantial increase in the volume expansion rate after lithium intercalation corresponding to the increase in the gram capacity, and improve the cycle capacity retention rate. Thus, the cycle performance can be improved while the energy density of the battery cell is taken into account.

[0050] In some embodiments, the powder compaction density of the active material of the negative active layer at 5T is 1.73-1.9 g / cc. Since the negative active layer contains a certain amount of primary particle graphite, the powder compaction density of the active material of the negative active layer is improved, which is conducive to further improving the energy density of the battery cell. In some specific embodiments, the powder compaction density of the active material of the negative active layer at 5T can be 1.73 g / cc, 1.75 g / cc, 1.78 g / cc, 1.80 g / cc, 1.82 g / cc, 1.83 g / cc, 1.85 g / cc, 1.86 g / cc, 1.87 g / cc, 1.88 g / cc, 1.90 g / cc, etc.

[0051] In general, the primary particle graphite meeting the foregoing requirements can be prepared by a relatively simple process, avoiding secondary granulation and thus being conducive to reducing production costs. The negative active layer using the primary particle graphite described above can have a low expansion rate, a high initial efficiency, and good cycle performance, especially high-temperature cycle performance. The capacity retention rate of the battery cell at 45°C after 1000 cycles can reach more than 86%, or even more than 90%. Due to the characteristics of the primary particles, the storage capacity retention rate of the battery cell can also be maintained at a high level.

[0052] In some embodiments, the negative current collector can be a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0053] In some embodiments, the negative active layer can also optionally include a binder. For example, the binder can include one or more than two combinations of the following group: styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS).

[0054] In some embodiments, the negative active layer can also optionally include a conductive agent. For example, the conductive agent can include one or more than two combinations of the following group: Super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers.

[0055] In some embodiments, the negative active layer can also optionally include other auxiliary agents. For example, the other auxiliary agent can be a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)).

[0056] In some embodiments, the negative electrode sheet can be prepared by the following method (dry mixing): mixing the components of the negative active layer described above, such as the negative active material, the additive, the optional conductive agent, the optional binder, and any other components, uniformly, then adding an appropriate amount of solvent (such as deionized water), stirring uniformly to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after drying, cold pressing, etc. processes, the negative electrode sheet can be obtained.

[0057] Electrolyte In some embodiments, the battery cell includes an electrolyte. The electrolyte is a medium having the ability to transport active ions, such as lithium ions, such as can include an electrolyte, a solid-state electrolyte, or a semi-solid electrolyte. In some embodiments, the battery cell also includes an electrolyte. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. In some embodiments, the electrolyte includes an electrolyte, a lithium salt, and a solvent.

[0058] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0059] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butyl sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent can also be selected from an ether solvent. The ether solvent can include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and a crown ether.

[0060] In some embodiments, other functional additives can also be optionally included in the electrolyte. The functional additives can include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve overcharge / fast charge properties of the battery cell, additives that improve high-temperature properties of the battery cell, additives that improve low-temperature properties of the battery cell, and the like.

[0061] Positive electrode sheet In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, the positive electrode material layer including a positive electrode active material.

[0062] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0063] As an example, when the battery assembly is a secondary battery, the positive active material can include at least one of a lithium-containing phosphate, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive active material of a battery can also be used. These positive active materials can be used alone only one or two or more in combination. Among them, examples of the lithium-containing phosphate can include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFeP04 (which can also be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnP04), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon. Examples of the lithium transition metal oxide can include, but are not limited to, at least one of lithium cobalt oxide (e.g., LiCo02), lithium nickel oxide (e.g., LiNi02), lithium manganese oxide (e.g., LiMn02, LiMn204), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.8 Co 0.15 Al 0.05 O2), and a modified compound thereof. The modified compound refers to a substance obtained by a modification method such as doping or coating on the basis of the above-mentioned substance.

[0064] In some embodiments, the positive active material layer can also optionally include a binder. For example, the binder can include one or a combination of two or more of the following group: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene-fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene-fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, a fluorine-containing acrylate resin.

[0065] In some embodiments, the positive electrode material layer can also optionally include a conductive agent. For example, the conductive agent can include one or more than two combinations of the following group: Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers.

[0066] In some embodiments, the positive electrode sheet can be prepared by the following method (dry mixing): mixing the components of the positive electrode material layer described above, such as the positive electrode active material, the additive, the optional conductive agent, the optional binder, and any other components, uniformly, then adding an appropriate amount of solvent (for example, N-methyl pyrrolidone), stirring uniformly to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying, cold pressing, etc., the positive electrode sheet can be obtained.

[0067] Separator In some embodiments, the electrode assembly further includes a separator, which is disposed between the positive electrode sheet and the negative electrode sheet.

[0068] In some embodiments, the separator is a separator film. As an example, the main material of the separator film base film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, ceramic. The separator film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited. The separator film can be a separate component located between the positive and negative electrodes, or can be attached to the surface of the positive and negative electrodes.

[0069] Structure of the electrode assembly The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of winding and stacking. In some embodiments, the electrode assembly is a wound structure. The positive electrode sheet and the negative electrode sheet are wound into a wound structure.

[0070] In some embodiments, the electrode assembly is a stacked structure. As an example, a plurality of positive electrode sheets and a plurality of negative electrode sheets can be provided, and the plurality of positive electrode sheets and the plurality of negative electrode sheets are alternately stacked. As an example, a plurality of positive electrode sheets can be provided, and the negative electrode sheet is folded to form a plurality of folded segments which are stacked. As an example, both the positive electrode sheet and the negative electrode sheet are folded to form a plurality of folded segments which are stacked.

[0071] As an example, a plurality of separators can be provided, and each of the plurality of separators is disposed between any adjacent positive electrode sheet or negative electrode sheet. As an example, the separators can be continuously provided, and are disposed between any adjacent positive electrode sheet or negative electrode sheet by folding or winding.

[0072] In some embodiments, the shape of the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0073] In some embodiments, the electrode assembly is provided with tabs, which can conduct current out of the electrode assembly. The tabs include positive tabs and negative tabs.

[0074] The housing In some embodiments, the battery cell can include a housing. The housing can be a steel housing, an aluminum housing, a plastic housing (such as polypropylene), a composite metal housing (such as a copper-aluminum composite housing), or an aluminum-plastic film, etc. In some embodiments, the housing can be a sealed structure, or a non-sealed structure. As an example, when the housing is a non-sealed structure, the housing serves to protect the electrode assembly, and a sealing bag is further included between the housing and the electrode assembly, which is used to encapsulate the electrode assembly and the electrolyte. Specifically, the sealing bag can be a bag-shaped insulating member or an aluminum-plastic film. When the housing is a sealed structure, it is used to encapsulate the electrode assembly and the electrolyte, etc.

[0075] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes, including a square battery cell, a blade battery cell, a multi-prismatic battery cell (such as a hexagonal battery cell), etc., without specific limitation in the present application. For example, Figure 1 is a square battery cell 5 as an example.

[0076] In some embodiments, referring to Figure 2 , the housing includes an end cap 53 and a housing body 51, the housing body 51 is provided with an opening, and the end cap 53 is provided on the opening. The housing body 51 can be provided with one or more openings. The end cap 53 can also be provided with one or more. The positive electrode sheet, the negative electrode sheet, and the separator can form the electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the accommodation cavity enclosed by the housing body 51 and the end cap 53. The electrolyte is impregnated in the electrode assembly 52.

[0077] The electrode terminal In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected with the tab. The electrode terminal can be directly connected with the tab, or indirectly connected with the tab through a current collecting member. The electrode terminal can be provided on the end cap, or provided on the housing body.

[0078] The pressure relief mechanism In some embodiments, a pressure relief mechanism is provided on the housing. The pressure relief mechanism is used to discharge the internal gas of the battery cell.

[0079] As an example, the battery cell is actuated to release internal pressure or temperature when the internal pressure or temperature reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism performs an action or a weak structure provided in the pressure relief mechanism is broken, thereby forming an opening or a passage for the internal pressure or temperature to be released. The threshold is designed differently according to design requirements. The threshold can depend on the material of one or more of the positive electrode tab, the negative electrode tab, the electrolyte, and the separator in the battery cell.

[0080] As an example, the pressure relief mechanism can be integrally formed with the housing.

[0081] As an example, the pressure relief mechanism can also be provided separately from the housing and connected to the housing.

[0082] As used herein, "actuation" refers to the pressure relief mechanism performing an action or being activated to a certain state, thereby allowing the internal pressure and temperature of the battery cell to be released. The action performed by the pressure relief mechanism can include, but is not limited to, a component in the pressure relief mechanism moving to form an exhaust passage, at least a portion of the pressure relief mechanism breaking, shattering, being torn or opened, etc. When the pressure relief mechanism is actuated, the high-temperature and high-pressure substances inside the battery cell are discharged as exhaust from the actuated part. In this way, the battery cell can be released in a controllable pressure or temperature, thereby avoiding potential more serious accidents.

[0083] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be provided as a through hole for discharging the gas inside the battery cell.

[0084] As used herein, the exhaust from the battery cell includes, but is not limited to, electrolyte, dissolved or split positive and negative electrode tabs, fragments of the separator, high-temperature and high-pressure gas generated by reaction, flame, etc.

[0085] In another aspect of the present application, a negative electrode tab is provided. The negative electrode tab includes a negative current collector and a negative active layer on the negative current collector. The active material of the negative active layer includes graphite, the graphite including primary particle graphite, the graphite having an electrochemical active specific surface area of 0.5 m 2 / g~1 m 2 / g, and the negative active material having a gravimetric capacity of 340 mAh / g~350 mAh / g at 0.05C. In this way, the performance of the negative electrode tab is improved.

[0086] According to embodiments of the present application, the negative electrode tab can have all the features and advantages of the negative electrode tab in the battery cell as described above, which will not be repeated here. In general, the negative electrode tab has a certain energy density and a low expansion rate, so that the battery cell using the negative electrode tab has good cycle performance.

[0087] According to embodiments of the present application, the ratio of the thickness H1 of the negative active layer in the fully charged state and the thickness H2 of the negative active layer in the fully discharged state is 1.05-1.2. The gram capacity of the active material of the negative active layer at 0.05C is 340mAh / g-350mAh / g. The negative active layer can have graphite, the average particle size of the graphite is 12-22μm, Dv1 is 2.5-4μm, and Dv90 is 30-40μm. The graphitization degree of the graphite is 92%-94%. Thus, the performance of the negative electrode sheet can be further improved.

[0088] In yet another aspect of the present application, the present application provides a method for preparing a negative active material. According to embodiments of the present application, the method comprises grinding and shaping a coke material to obtain a raw material with a Dv50 of 15-20μm. The raw material is subjected to a sintering treatment, which comprises sequentially increasing the temperature from a first sintering temperature to a third sintering temperature by gradient heating, the first sintering temperature being lower than the second sintering temperature, and the second sintering temperature being lower than the third sintering temperature, the heating rate from the first sintering temperature to the second sintering temperature being greater than the heating rate from the second sintering temperature to the third sintering temperature, and after the sintering treatment is completed, the sintering product is naturally cooled to a temperature of less than 400 degrees Celsius before being removed from the sintering equipment. Thus, a negative active material with a low electrochemical active specific surface area and low expansion can be conveniently obtained.

[0089] The present application obtains a granular aggregate with a moderate particle size by selecting and processing the raw material, and obtains a primary particle graphite with a low electrochemical active specific surface area by regulating the gradient heating parameters of the sintering treatment.

[0090] Specifically, the coke material can be selected as the raw material for preparing the graphite particles, and the coke material can include at least one of petroleum coke, coal-based coke, and needle coke. Thus, the performance of the negative active material can be further improved. In order to further improve the performance of the negative active material obtained by the method, the coke material can be pretreated before the sintering treatment. Specifically, the pretreatment can include grinding the coke material. For example, the coke material can be treated using a crusher, and then subjected to a shaping treatment to obtain a raw material with a particle size of 15-20μm. The shaping treatment can be performed using a shaper to remove the obvious corners on the surface of the raw material and reduce the roughness of the surface of the raw material. The raw material can be further subjected to an operation for removing fine powder at the same time or after the crusher or shaper treatment. For example, the raw material can be treated using a classification device to remove a part of the fine powder generated during grinding. Specifically, the amount of removed fine powder can be controlled to be between 10%-30%. The fine powder can be the powdery substance in the treated raw material.

[0091] In some embodiments, the raw material for the sintering process can be mainly or only the aforementioned treated coke material. Thus, the primary particle graphite can be formed.

[0092] According to embodiments of the present application, the sintering temperature of the sintering process can be high, for example, can be 2500-3000℃. Those skilled in the art can understand that the sintering process can be carried out in an inert atmosphere. Therefore, the high sintering temperature is beneficial to obtain the primary particle graphite with less defects and small electrochemically active specific surface area. In order to optimize the temperature control of the sintering process and improve the sintering efficiency, the temperature can be raised to the predetermined sintering temperature by gradient heating. Specifically, the sintering process can include gradient heating of three temperature nodes, that is, the temperature is sequentially raised from the first sintering temperature to the third sintering temperature. The first sintering temperature is 1100-1200℃, the second sintering temperature is 2000-2300℃, and the third sintering temperature is 2500-3000℃. Thus, the temperature rising process of the sintering process can be more reasonably controlled, and the substantial increase in equipment cost caused by rapidly raising the temperature to a high temperature can be reduced.

[0093] According to the embodiments of the present application, the temperature can be first raised to the first sintering temperature by using gradient heating. Specifically, the first sintering temperature can be 1100-1200°C. The first sintering temperature is relatively low, and thus the temperature can be raised to the temperature range relatively quickly. The second sintering temperature can be 2000-2300°C, and the temperature raising rate when the temperature is raised from the first sintering temperature to the second sintering temperature can be 10-20°C / min. In this way, the temperature can be raised from the first sintering temperature to the second sintering temperature at a moderate temperature raising rate. The temperature raising rate is relatively fast, and thus the second sintering temperature can be reached quickly. The second sintering temperature is set to 2000-2300°C, which is on one hand conducive to reaching the second sintering temperature quickly at the aforementioned temperature raising rate, and on the other hand is also closer to the third sintering temperature, i.e., the predetermined sintering temperature, and thus the temperature can be kept at the second sintering temperature to obtain the primary particle graphite with a small electrochemically active specific surface area. The third sintering temperature can be 2500-3000°C, such as 2500-2900°C. Since the third sintering temperature is relatively high, the temperature raising rate when the temperature is raised from the second sintering temperature to the third sintering temperature can be relatively low, which on one hand can reduce the performance requirement of the sintering equipment, and on the other hand can also be conducive to the raw materials to fully react at a relatively high temperature. The second sintering temperature is set to 2000-2300°C, and thus the substances such as floating carbon on the surface of the raw materials can have been fully reacted, and thus the temperature raising rate can be controlled to be relatively slow when the temperature is raised from the second sintering temperature to the third sintering temperature, which can also make the raw materials fully react. Specifically, the temperature raising rate when the temperature is raised from the second sintering temperature to the third sintering temperature can be 3-10°C / min. After the temperature reaches the third sintering temperature, the temperature can be kept at the third sintering temperature for a certain period of time. The time for keeping the temperature at the third sintering temperature can be 1-4h.

[0094] According to the embodiments of the present application, after the temperature keeping is completed, the temperature can be naturally cooled to below 400°C, such as to below 200°C, and then the raw materials can be taken out of the sintering equipment. In this way, the performance of the negative electrode active material can be further improved. When the temperature is lowered to a relatively low temperature, the temperature difference between the surface of the graphite particles obtained when taken out and the ambient temperature is small, and thus the graphite particles are not easy to be oxidized due to the high temperature of the surface of the graphite particles when taken out. In this way, the electrochemically active specific surface area of the material can be kept small.

[0095] In another aspect of the present application, a battery device is provided. The battery device comprises the battery cell, the negative electrode sheet, the negative electrode sheet prepared according to the aforementioned method, or the battery cell prepared according to the aforementioned method.

[0096] Battery device The battery apparatus mentioned in the embodiments of the present application can include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly can include a plurality of battery cells connected in series, in parallel, or in a mixed connection through a busbar component.

[0097] In some embodiments, the battery cell assembly is generally formed by arranging a plurality of battery cells.

[0098] As an example, the battery cell assembly can be a battery module formed by arranging and fixing a plurality of battery cells into a separate module. As an example, the battery module can be formed by bundling a plurality of battery cells with a cable tie. Figure 3 is a battery module 4 as an example. Refer to Figure 3 In the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements are also possible.

[0099] In some embodiments, the battery apparatus can be a battery pack including a case and one or more battery cell assemblies housed in the case.

[0100] As an example, the battery cell assembly can be a battery module, which can be housed in the case by fixing the battery module in the case. Figure 4 and Figure 5 is a battery pack 1 as an example. Refer to Figure 4 and Figure 5 In the battery pack 1, a case and a plurality of battery modules 4 disposed in the case can be included. The case includes an upper case 2 and a lower case 3, and the upper case 2 is capable of being disposed on the lower case 3 to form an enclosed space for housing the battery modules 4. The plurality of battery modules 4 can be arranged in the battery case in any manner.

[0101] As an example, the battery cell assembly can also be housed in the case by directly fixing a plurality of battery cells in the case.

[0102] As an example, the case can include a first case and a second case. The first case and the second case are coupled so that an enclosed space is formed inside the case to accommodate the battery cell assembly. The enclosed here means covered or closed, which can be sealed or unsealed. The first case can be a top cover or a bottom plate.

[0103] As an example, the box may include a top cover, a frame, and a bottom plate, wherein the top cover and the bottom plate are respectively connected to the frame to form a closed space inside the box to accommodate the battery cell assembly.

[0104] In some embodiments, the box body can be used as a part of the chassis structure of the vehicle. For example, part of the box body can become at least a part of the floor of the vehicle, or part of the box body can become at least a part of the cross beam and longitudinal beam of the vehicle.

[0105] In another aspect of the present application, an electrical device is provided, which includes the aforementioned battery cell, negative electrode sheet, negative electrode sheet prepared according to the aforementioned method, or battery cell and battery device prepared according to the aforementioned method.

[0106] Electrical devices The technical solutions described in the embodiments of the present application are applicable to various electrical devices that use battery cells, such as mobile phones, portable devices, laptop computers, electric vehicles, electric toys, electric tools, vehicles, ships and spacecraft, for example, spacecraft include airplanes, rockets, space shuttles and spacecraft, etc. Figure 6 The power consumption device is taken as an example, and the power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

[0107] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0108] Example 1 Preparation of primary graphite particles Needle coke is selected as the raw material. A crusher is used for grinding, controlling the Dv50 to approximately 15±5μm. Classification equipment is also used to remove 20% of fine powder. The raw material is then shaped: a shaping machine is used to modify the surface of the particles, removing significant surface edges and reducing surface roughness. Aggregates with a Dv50 of approximately 15μm are obtained. The aggregates are sintered by heating to 1100°C, then increasing the temperature at a rate of 10°C / min to 2000°C, then at a rate of 3°C / min to 2800°C, and maintaining this temperature for 4 hours. Finally, the temperature is naturally cooled to 100°C before being removed from the furnace.

[0109] The scanning electron microscope photos of the prepared negative electrode active material are shown in the attached Figure 7 , the obtained negative electrode active material is mainly primary particles.

[0110] Example 2 Example 2 is the same as Example 1, except that the third temperature node of high-temperature graphitization is at 3000°C.

[0111] Example 3 Example 3 is the same as Example 1, except that the product is taken out after natural cooling to 400°C after high-temperature graphitization.

[0112] Example 4 Example 4 is the same as Example 1, except that after the second-stage program temperature rise to 2300°C, the temperature is raised to 2800°C at a temperature rise rate of 5°C / min and held for 4h.

[0113] Example 5 Example 5 is the same as Example 1, except that the temperature rise rate when the temperature is raised from the first sintering temperature to the second sintering temperature can be 20°C / min.

[0114] Comparative Example 1 The same as Example 1, except that no classifier is used to remove fine powder.

[0115] Comparative Example 2 The same as Example 1, except that a two-stage program temperature rise is used, and the temperature is raised to 3200°C at a temperature rise rate of 10°C / min after being raised to 1100°C.

[0116] Comparative Example 3 The same as Example 1, except that after the holding is completed, the product is taken out directly without cooling.

[0117] Secondary batteries are assembled using the negative electrode active materials prepared in the examples and comparative examples, and the secondary batteries are prepared as follows: Preparation of positive electrode sheet: Lithium iron phosphate: conductive carbon black: PVDF = 96:2:2 by mass ratio, after mixing, add solvent N-methyl pyrrolidone, stir uniformly, obtain positive electrode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil, after drying, cold pressing, the positive electrode sheet is obtained.

[0118] Preparation of negative electrode sheet: The graphite material, conductive agent carbon black (Super P), thickening agent carboxymethyl cellulose sodium, and binder styrene-butadiene rubber prepared in each example and comparative example are mixed in a weight ratio of 96.4:1:1.2:1.4 in an appropriate amount of solvent deionized water to form a negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector copper foil by extrusion coating, and after drying and cold pressing, the negative electrode sheet is obtained.

[0119] Preparation of separator: A 12μm polyethylene film is used as the separator.

[0120] Preparation of electrolyte: Ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 was dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0121] Assembly of button half-cell: The prepared slurry was coated on the surface of the negative current collector copper foil and placed in a vacuum drying oven for drying; a lithium metal sheet was used as the counter electrode, a 12 μm polyethylene (PE) film was used as the separator film, and the above-prepared electrolyte was assembled into a CR2430 type button cell in an argon glove box.

[0122] Assembly of secondary full cell: The above-prepared positive and negative electrode sheets were placed in order with the separator film in the middle of the positive and negative electrode sheets to play a separating role, and then wound to obtain an electrode assembly; the electrode assembly was placed in an outer package, dried, and then injected with electrolyte, and then subjected to vacuum packaging, standing, formation, shaping, and other processes to obtain a secondary battery.

[0123] The negative electrode materials and secondary batteries obtained in the above examples and comparative examples were subjected to performance tests.

[0124] Active specific surface area test: (1) The electrode sheet to be tested, a metal sheet, and electrolyte were assembled into a button half-cell, wherein the electrolyte contained an electrochemical redox probe molecule with a concentration of c, the redox potential of the probe molecule was 1 V-4 V, and the probe molecule was dissolved in the electrolyte; (2) a series of cyclic voltammetry curves of the button half-cell at different scan rates v were obtained on an electrochemical workstation, and the peak current ip was obtained from the cyclic voltammetry curves; the peak current ip of the series of button half-cells obtained and the square root of the scan rate v were plotted to obtain the slope K; according to the Randles-Sevick equation ip represents the peak current, n represents the number of electron transfer of the electrode reaction, A represents the active surface area of the electrode sheet, c represents the concentration of the probe molecule, D represents the diffusion coefficient of the probe molecule, v represents the scan rate, and the ratio of the active surface area A of the electrode sheet to the weight m of the electrode sheet is the active specific surface area of the electrode sheet.

[0125] Dv50 test: Referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, it is conveniently measured by using a laser particle size analyzer. The test instrument can be a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0126] Powder compaction density test under 50000N: According to GB / T 24533-2009, the test is performed by an electronic pressure testing machine (for example, UTM7305 type electronic pressure testing machine). The exemplary test method is as follows: 1 g of carbon material powder is weighed and added to a mold with a bottom area of 1.327 cm2, and is pressed to 2000 kg (equivalent to 20000 N), and is kept for 30 s, and then is unloaded, and is kept for 10 s, and then the carbon material powder compaction density under a pressure of 50000 N is recorded and calculated. Gram capacity test: At 25°C, the above prepared button cell is first discharged at a current of 0.15 mA to 0.005 V, and is kept for 5 minutes, and then is discharged at a current of 10 μA to 0.005 V, and the first circle discharge capacity of the button cell is recorded; then the button cell is charged at a current of 0.3 mA to 2.0 V, and the first circle charge capacity of the button cell is recorded, and the ratio of the charge capacity to the sample mass is the gram capacity of the material.

[0127] Negative electrode sheet expansion rate test: 1) Determination of fully discharged electrode sheet thickness: before assembling the secondary battery, the thickness of the negative electrode sheet is measured by a micrometer, and the thickness average of five points at the periphery and the middle of the negative electrode sheet is taken as the fully discharged electrode sheet thickness H2.

[0128] 2) Fully charged electrode sheet thickness: after the secondary battery is fully charged, the secondary battery is disassembled in a dry room, the surface electrolyte is removed after cleaning and drying, and the thickness average of five points at the periphery and the middle of the negative electrode sheet is taken as the fully charged electrode sheet thickness H1.

[0129] 3) The expansion rate of the negative electrode sheet is (fully charged electrode sheet thickness / fully discharged electrode sheet thickness-1) x 100%.

[0130] Secondary battery first coulomb efficiency test: At 45°C, the above prepared secondary battery is formed, and is charged at a current of 0.02 C to 10 h (the charge capacity C0 at this time is recorded). At 25°C, the secondary battery is discharged at a current of 0.2 C to 2.0 V, and the discharge capacity D0 at this time is recorded. Then it is charged at a current of 0.33 C to 3.8 V, and then charged at a constant voltage to a current of 0.05 C, and the charge capacity C1 at this time is recorded. It is discharged at a current of 0.33 C to 2.5 V, and is kept for 5 min, and then discharged at a current of 0.33 C to 2.0 V, and then discharged at a current of 0.1 C to 2.0 V, and the discharge capacity D1 at this time is recorded. The first coulomb efficiency of the secondary battery (%) = D1 / (C0 -D0+C1) Secondary battery cycle performance test: 45℃, the battery is charged at 0.33C constant current to the charge cut-off voltage 3.65V, then charged at constant voltage to the current is 0.05C, stand for 5min, then discharged at 0.33C constant current to the discharge cut-off voltage 2.5V, record its initial capacity as C0. Then charge at 1C0 rate, discharge at 1C0, record the discharge capacity Cn of each cycle (n is the cycle number, n = 1 1000), until after 1000 cycles, calculate the cycle capacity retention rate (i.e. C1000 / C0x100%).

[0131] The above test results are shown in Table 1 below: Table 1

[0132] Table 1 (continued)

[0133] From the above Table 1 and Table 1 (continued), when the capacity and the electrochemical active specific surface area meet the requirements of the present application, the battery monomer obtained has good performance, the negative electrode expansion rate is low, and the full-electricity initial efficiency, cycle capacity retention rate and storage retention rate can be well balanced.

[0134] The above description is only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any changes or replacements within the technical range disclosed by the present application can be easily thought by those skilled in the art, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A battery cell, characterized by, The cathode electrode sheet, the separator, and the anode electrode sheet, The anode electrode sheet has an anode current collector and an anode active layer on the anode current collector, and the anode active material of the anode active layer comprises graphite, The graphite includes primary particle graphite, the electrochemical activity specific surface area of the graphite is 0.5 m 2 / g~1 m 2 / g, the gram capacity of the negative electrode active material at 0.05C is 340mAh / g~350mAh / g, The ratio of the thickness H1 of the anode active layer in the fully charged state to the thickness H2 of the anode active layer in the fully discharged state is 1.05-1.

2.

2. The battery cell of claim 1, wherein, The graphite has an electrochemically active specific surface area of 0.8 m 2 / g~1 m 2 / g.

3. The battery cell of claim 1, wherein, The Dv50 of the graphite is 10-22 μm; and / or The Dv1 of the graphite is 1.5-4 μm; and / or The Dv90 of the graphite is 30-40 μm.

4. The battery cell of claim 1, wherein, The graphitization degree of the graphite is 92%-94%.

5. The battery cell of claim 1, wherein, The anode active material further comprises secondary particle graphite.

6. The battery cell of claim 1, wherein, The powder compaction density of the active material of the anode active layer at 5T is 1.73-1.9 g / cc.

7. A negative electrode sheet characterized by comprising: The cathode electrode sheet, the separator, and the anode electrode sheet, The graphite includes primary particle graphite, the electrochemical activity specific surface area of the graphite is 0.5 m 2 / g~1 m 2 / g, the gram capacity of the negative electrode active material at 0.05C is 340 mAh / g~350 mAh / g, The ratio of the thickness H1 of the anode active layer in the fully charged state to the thickness H2 of the anode active layer in the fully discharged state is 1.05-1.

2.

8. The negative electrode sheet according to claim 7, wherein The average particle size of the graphite is 12-22 μm; and / or The Dv1 of the graphite is 2.5-4 μm; and / or The Dv90 of the graphite is 30-40 μm; and / or The graphitization degree of the graphite is 92%-94%.

9. The negative electrode sheet according to claim 7 or 8, wherein The anode active layer further comprises second graphite, and the second graphite comprises secondary particle graphite.

10. A method for producing a negative electrode active material, characterized by, The method comprises: Grinding, shaping, and removing fine powder of the coking material to obtain raw material with Dv50 of 15-20 μm; Sintering treatment of the raw material, the sintering treatment comprising sequentially increasing the temperature from a first sintering temperature to a third sintering temperature by gradient heating, the first sintering temperature being lower than the second sintering temperature, and the second sintering temperature being lower than the third sintering temperature, the heating rate from the first sintering temperature to the second sintering temperature being greater than the heating rate from the second sintering temperature to the third sintering temperature, and after the sintering treatment is completed, the sintering product is naturally cooled to a temperature below 400 degrees Celsius before being taken out of the sintering equipment, The negative active material includes graphite, the graphite includes primary particle graphite, the electrochemical active specific surface area of the graphite is 0.5 m 2 / g~1 m 2 / g, the gram capacity of the negative active material at 0.05C is 340 mAh / g~350 mAh / g, The ratio of the thickness H1 of the anode active layer in the fully charged state to the thickness H2 of the anode active layer in the fully discharged state based on the anode active material is 1.05-1.

2.

11. The method of claim 10, wherein, The method comprises: The removing fine powder comprises removing 10%-30% of the fine powder by mass percentage; The coking material comprises at least one of petroleum coke, coal-based coke, and needle coke, The sintering treatment satisfies at least one of the following conditions: The first sintering temperature is 1100-1200 degrees Celsius, the second sintering temperature is 2000-2300 degrees Celsius, and the third sintering temperature is 2500-3000 degrees Celsius; The heating rate from the first sintering temperature to the second sintering temperature is 10-20 degrees Celsius per minute; The heating rate from the second sintering temperature to the third sintering temperature is 3-10 degrees Celsius per minute; After the sintering temperature is increased to the third sintering temperature, further comprising the operation of heat preservation for 1-4 hours.

12. A battery device characterized by comprising: The battery cell according to any one of claims 1 to 6, the negative electrode sheet according to any one of claims 7 to 9, or the negative electrode active material prepared according to the method of claim 10 or 11.

13. An electrical device, characterized by The battery device according to claim 12.

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