Negative electrode active material and preparation method therefor, negative electrode sheet, lithium-ion battery, and electric device

Abstract

A negative electrode active material and a preparation method therefor, a negative electrode sheet, a lithium-ion battery, and an electric device. The lithium-ion battery comprises one or more battery cells (5), the battery cell (5) comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, and the negative electrode film layer comprises a negative electrode active material. The negative electrode active material comprises an inner core and a coating layer located on at least part of the surface of the inner core, wherein the inner core comprises graphite, and the coating layer comprises hard carbon; and in the cumulative distribution curve of the R value of the negative electrode active material obtained in the area scanning mode of a laser microscopic confocal Raman spectrometer, from the lower limit, the R value of R50 having a cumulative distribution of 50% is 0.15-0.40. The negative electrode active material can make the battery have both a high energy density, and good dynamic performance and cycle performance.

Description

Negative electrode active material and preparation method thereof, negative electrode sheet, lithium ion battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410129306.0 filed on January 30, 2024, entitled “Negative electrode active material, preparation method thereof, and negative electrode sheet, battery and electrical device containing the same,” and the entire contents of that application are incorporated herein by reference. Technical Field

[0003] The present application relates to a negative electrode active material and a preparation method thereof, a negative electrode plate, a lithium-ion battery and an electrical device. Background Art

[0004] With the continuous expansion of battery application fields, people have higher and higher requirements for the fast charging performance of batteries. As an important component of the battery, the performance of the negative electrode will affect the overall performance of the battery. At present, the commonly used negative electrode active material for the negative electrode is graphite, but the fast charging performance of graphite is usually not excellent enough. Based on this, fast-charging negative electrode active materials have been developed, such as fast-charging hard carbon. The energy density of the battery assembled by fast-charging hard carbon is usually not high, and its cycle life is not excellent enough, which limits its practical application. Therefore, how to make the battery have good fast charging performance and cycle performance while having a higher energy density is still a difficulty in current battery development. The above statements are only used to provide background technical information related to this application, and do not necessarily constitute prior art. Summary of the Invention

[0005] The present application provides a negative electrode active material and a preparation method thereof, a negative electrode plate, a lithium ion battery and an electrical device, which can enable the battery to have high energy density, good dynamic performance and cycle performance.

[0006] In a first aspect, the present application provides a lithium-ion battery comprising one or more battery cells, wherein the battery cells include a negative electrode pole piece, the negative electrode pole piece includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a core and a coating layer located on at least a portion of the surface of the core, the core includes graphite, and the coating layer includes hard carbon; in the R value cumulative distribution curve of the negative electrode active material obtained in the surface scanning mode of a laser microconfocal Raman spectrometer, from the lower limit, the R value R50 with a cumulative distribution of 50% is 0.15-0.40.

[0007] The R value of the negative electrode active material can characterize the degree of defect and disorder in the negative electrode active material. An R value (R50) of 0.15-0.40, representing a cumulative distribution of 50%, can both enhance the charge exchange capacity of ions on the surface of the negative electrode active material and minimize side reactions on the surface of the negative electrode active material particles. Therefore, the negative electrode active materials provided in the embodiments of this application can enable batteries to achieve both high energy density and excellent kinetic and cycling performance.

[0008] In some embodiments, the cumulative distribution of the negative electrode active material has an R value R50 of 0.20-0.30, thereby enabling the battery to better achieve high energy density, good kinetic performance and cycle performance.

[0009] In some embodiments, among all R values ​​obtained for the negative electrode active material, the number of R values ​​R50 less than 50% of the cumulative distribution of the core accounts for less than or equal to 10%. Alternatively, among all R values ​​obtained for the negative electrode active material, the number of R values ​​R50 less than 50% of the cumulative distribution of the core accounts for less than or equal to 6%.

[0010] The smaller the value is, the less the degree of uncoating of the negative electrode active material is, and the isotropy of the negative electrode active material is improved. At this time, the negative electrode active material has more active sites, and thus the charge exchange ability of ions on the surface of the negative electrode active material is better, which can further improve the kinetic performance of the negative electrode active material and the battery; in addition, the less uncoating degree of the negative electrode active material is, the co-embedding phenomenon of the electrolyte solvent during the cycle can be reduced, and the battery can also have better cycle performance.

[0011] In some embodiments, the R-value R50 of the core at 50% of the cumulative distribution is smaller than the R-value R50 of the cladding layer at 50% of the cumulative distribution.

[0012] The cumulative distribution of the coating layer of the negative electrode active material is 50%, and the R value R50 is large and the disorder is large, which can make the negative electrode active material and the battery have good kinetic performance; the cumulative distribution of the core of the negative electrode active material is 50%, and the R value R50 is small and the disorder is small, which can make the negative electrode active material as a whole have a higher gram capacity and the battery have a higher energy density.

[0013] In some embodiments, the coating layer has an R value (R50) of 0.9 to 1.4 at a cumulative distribution of 50%. When the R value (R50) of the coating layer is within this range, the coating layer itself has good kinetic properties, which can improve the kinetic properties of the negative electrode active material and the battery. It can also reduce the specific surface area of ​​the negative electrode active material, thereby reducing battery side reactions and improving the battery's cycling performance.

[0014] In some embodiments, the core has an R value R50 of 0.06-0.13 at a cumulative distribution of 50%. When the R value R50 of 50% of the cumulative distribution of the core is within the above range, the battery can have both high energy density and good kinetic performance.

[0015] In some embodiments, the mass of the coating layer is 0.3%-4.5% of the mass of the core, and optionally 1%-3.2%. The coating layer mass ratio within the above range is conducive to the battery having high energy density, good dynamic performance and long cycle life.

[0016] In some embodiments, the difference between the volume distribution particle size Dv50 of the negative electrode active material and the volume distribution particle size Dv50 of the core is 1 μm-5.5 μm, and optionally 1.5 μm-4.2 μm. The difference between the volume distribution particle size Dv50 of the negative electrode active material and the volume distribution particle size Dv50 of the core being within the above range can not only enhance the charge exchange capacity of ions on the surface of the negative electrode active material, but also reduce side reactions on the surface of the negative electrode active material particles, and also enable the negative electrode active material to have a higher specific capacity, thereby facilitating the battery to have high energy density, good kinetic performance, and long cycle life.

[0017] In some embodiments, the volume distribution particle size Dv50 of the negative electrode active material is 8 μm-25 μm, optionally 12 μm-17 μm. When the volume distribution particle size Dv50 of the negative electrode active material is within the above range, lithium ions can have good solid-phase conductivity within the negative electrode active material particles and a small specific surface area, thereby facilitating both good cycle performance and kinetic performance of the battery. When the volume distribution particle size Dv50 of the negative electrode active material is within the above range, the negative electrode slurry can also have good dispersibility.

[0018] In some embodiments, the graphite is artificial graphite. The core includes artificial graphite, which can make the battery have high energy density and good cycle performance.

[0019] In some embodiments, the graphite has a secondary particle morphology. When the graphite has a secondary particle morphology, the isotropy of the graphite increases, which facilitates rapid lithium ion insertion, thereby facilitating good kinetic performance of the battery and further increasing the specific capacity of the negative electrode active material and the energy density of the battery.

[0020] In some embodiments, the graphite has an intensity ratio C(004) / C(110) of 004 ​​crystal plane diffraction peak to 110 crystal plane diffraction peak measured by X-ray diffraction method of 5.5-6.5.

[0021] In some embodiments, the negative electrode active material has a gram capacity of 354 mAh / g to 361 mAh / g.

[0022] In some embodiments, the powder compaction density of the negative electrode active material under a pressure of 20000N is 1.68g / cm 3 -1.78g / cm 3 .

[0023] In some embodiments, the specific surface area of ​​the negative electrode active material is 1.5 m 2 / g-4.5m 2 / g.

[0024] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer located between the first negative electrode film layer and the negative electrode current collector, the thickness of the first negative electrode film layer is 30%-60% of the thickness of the negative electrode film layer, the first negative electrode film layer includes a first negative electrode active material, the second negative electrode film layer includes a second negative electrode active material, and the first negative electrode active material includes any one of the foregoing negative electrode active materials.

[0025] In some embodiments, the second negative electrode active material comprises any of the aforementioned negative electrode active materials, and the mass content w1 of the first negative electrode active material in the first negative electrode film layer is greater than the mass content w2 of the second negative electrode active material in the second negative electrode film layer. This can reduce the problem of negative electrode binder floating during slurry drying and reduce the negative electrode binder content on the outer surface of the negative electrode film layer, thereby facilitating liquid-phase ion conduction within the negative porous electrode and charge exchange of ions on the surface of the negative electrode active material, thereby further improving the battery's kinetic performance.

[0026] Optionally, the mass content w1 of the first negative electrode active material in the first negative electrode film layer is greater than or equal to 96.9%, and the mass content w2 of the second negative electrode active material in the second negative electrode film layer is less than 96.9%.

[0027] In some embodiments, the second negative electrode active material includes graphite, the graphite has a secondary particle morphology, and a cumulative distribution of 50% of the R value R50 of the graphite is 0.06-0.13.

[0028] Optionally, the mass content w1 of the first negative electrode active material in the first negative electrode film layer is greater than the mass content w2 of the second negative electrode active material in the second negative electrode film layer.

[0029] Optionally, the mass content w1 of the first negative electrode active material in the first negative electrode film layer is greater than or equal to 96.9%, and the mass content w2 of the second negative electrode active material in the second negative electrode film layer is less than 96.9%.

[0030] This can reduce the problem of negative electrode binder floating during the slurry drying process and reduce the negative electrode binder content on the outer surface of the negative electrode film layer, which is beneficial to the liquid phase conduction of ions inside the negative electrode porous electrode and the charge exchange of ions on the surface of the negative electrode active material, thereby further improving the battery's kinetic performance.

[0031] In some embodiments, the compaction density of the negative electrode film layer is 1.62 g / cm 3 -1.80g / cm 3 , optional 1.65g / cm 3 -1.80g / cm 3 .

[0032] In some embodiments, the thickness of the negative electrode film layer is 45 μm-100 μm, and can be 70 μm-100 μm. By adjusting the thickness of the negative electrode film layer within the above range, the battery can have better dynamic performance while having high energy density.

[0033] In a second aspect, the present application provides an electrical device comprising the lithium-ion battery of the first aspect of the present application, wherein the lithium-ion battery is used to provide electrical energy.

[0034] The electric device of the present application includes the lithium-ion battery provided by the present application, and thus has at least the same advantages as the lithium-ion battery.

[0035] In a third aspect, the present application provides a negative electrode active material, comprising a core and a coating layer located on at least a portion of the surface of the core, the core comprising graphite, and the coating layer comprising hard carbon; in the cumulative distribution curve of the R value of the negative electrode active material obtained in the surface scanning mode of a laser microconfocal Raman spectrometer, starting from the lower limit, the R value R50 with a cumulative distribution of 50% is 0.15-0.40.

[0036] In a fourth aspect, the present application provides a method for preparing a negative electrode active material, comprising the following steps: providing a coke raw material; crushing, shaping and grading the coke raw material to obtain aggregate; mixing the obtained aggregate with a binder and sequentially performing granulation and graphitization to obtain graphite; solid-liquid fusion of the obtained graphite and a liquid hard carbon coating agent; carbonizing the product after the solid-liquid fusion under a protective gas atmosphere so that the liquid hard carbon coating agent is carbonized into hard carbon and coated on at least a portion of the surface of the graphite to obtain a negative electrode active material, wherein the negative electrode active material comprises a core and a coating layer located on at least a portion of the surface of the core, the core comprising graphite, and the coating layer comprising hard carbon; in the R value cumulative distribution curve of the negative electrode active material obtained in the surface scanning mode of a laser microconfocal Raman spectrometer, starting from the lower limit, the R value R50 with a cumulative distribution of 50% is 0.15-0.40.

[0037] In the preparation method provided in the embodiment of the present application, a liquid-phase hard carbon coating agent is used to carry out solid-liquid fusion with graphite. Since the liquid-phase hard carbon coating agent has good fluidity, it can be evenly distributed on the surface of the graphite particles, thereby improving the coating effect of the coating layer and reducing the degree of non-coating; and after the liquid-phase hard carbon coating agent is carbonized, the negative electrode active material can have a smaller R50, thereby improving the charge exchange capacity of ions on the surface of the negative electrode active material, and improving the kinetic performance of the negative electrode active material and the battery. The degree of non-coating of the negative electrode active material is reduced, and the side reactions on the surface of the negative electrode active material particles can be kept at a lower level, which is also beneficial for the battery to have good cycle performance. Therefore, the negative electrode active material prepared by the preparation method provided in the embodiment of the present application can enable the battery to have high energy density, good kinetic performance and cycle performance.

[0038] In some embodiments, the coke feedstock includes one or more of petroleum-based needle coke and coal-based needle coke. These coke feedstocks are anisotropic materials that can help reduce the disorder of the core material and increase the gram capacity of the core material and the overall gram capacity of the negative electrode active material.

[0039] In some embodiments, the temperature of the graphitization treatment is 2800° C.-3800° C., and optionally 2850° C.-3300° C. By selecting a suitable graphitization treatment temperature, the battery can have both high energy density and good dynamic performance.

[0040] In some embodiments, the mass of the liquid-phase hard carbon coating agent is 0.7%-10% of the mass of the graphite, and optionally 3%-7%. When the mass ratio of the liquid-phase hard carbon coating agent is within the above range, the degree of uncoating of the negative electrode active material can be kept to a relatively small level. This can not only enhance the charge exchange capacity of ions on the surface of the prepared negative electrode active material, but also reduce the level of side reactions on the surface of the prepared negative electrode active material particles. Furthermore, the prepared negative electrode active material can have a higher specific capacity, thereby facilitating the battery to achieve high energy density, good kinetic performance, and long cycle life.

[0041] In some embodiments, the liquid hard carbon coating agent includes a liquid resin, the viscosity of the liquid resin at 25° C. is 150 mPa·s-2000 mPa·s, and the solid content of the liquid resin is 50%-85%.

[0042] Optionally, the viscosity of the liquid resin at 25° C. is 300 mPa·s-900 mPa·s, and the solid content of the liquid resin is 60%-82%.

[0043] The viscosity of the liquid resin is within the above range, which can make the liquid resin have good fluidity and diffusivity, as well as good curing effect and coating effect. Thus, the liquid resin can be evenly dispersed on the surface of the graphite particles, which is beneficial to improve the coating effect, reduce the degree of uncoating, and improve the coating uniformity of the surface of the graphite particles, which is beneficial to the battery having both good dynamic performance and long cycle life.

[0044] The solid content of the liquid resin is within the above range, which can make the liquid resin have good fluidity and diffusivity, as well as good curing effect and coating effect. Thus, the liquid resin can be evenly dispersed on the surface of the graphite particles, which is beneficial to improve the coating effect and reduce the degree of uncoating. It can also adjust the cumulative distribution of the negative electrode active material to 50% R value R50, increase the disorder of the surface of the negative electrode active material particles, and enhance the charge exchange capacity of ions on the surface of the negative electrode active material, which is beneficial to the battery having both good kinetic performance and long cycle life.

[0045] In some embodiments, the liquid resin includes at least one of liquid phenolic resin, liquid epoxy resin, liquid vinyl ester resin, liquid unsaturated polyester resin, liquid furan resin, and derivatives thereof.

[0046] In some embodiments, the liquid hard carbon coating agent includes liquid phenolic resin, and the liquid phenolic resin has a solid content of 60%-82% and a weight average molecular weight of 300-800.

[0047] Optionally, the liquid phenolic resin has a solid content of 68%-78% and a weight average molecular weight of 450-700.

[0048] Compared with other liquid resins, the hard carbon formed by carbonization and coking of liquid phenolic resin itself has better performance.

[0049] By further adjusting the solid content and weight-average molecular weight of the liquid phenolic resin within the above range, the hard carbon formed by its carbonization can have better kinetic properties, and the coating effect can be improved and the degree of uncoating can be reduced, thereby enhancing the charge exchange capacity of ions on the surface of the negative electrode active material, and further improving the kinetic properties of the negative electrode active material.

[0050] In some embodiments, the device for solid-liquid fusion of the graphite and the liquid-phase hard carbon coating agent is a fusion machine, the stirring speed of the fusion machine is 350r / min-1000r / min, and the stirring time of solid-liquid fusion is 4min-10min. Optionally, the stirring speed of the fusion machine is 450r / min-850r / min, and the stirring time of solid-liquid fusion is 6min-8min. Increasing the stirring speed of the fusion machine is beneficial to improving the coating effect and reducing the degree of non-coating, thereby improving the charge exchange capacity of ions on the surface of the negative electrode active material, and thus improving the kinetic properties of the negative electrode active material. Increasing the stirring time of solid-liquid fusion is beneficial to improving the coating effect and reducing the degree of non-coating, thereby improving the charge exchange capacity of ions on the surface of the negative electrode active material, and thus improving the kinetic properties of the negative electrode active material.

[0051] In some embodiments, the carbonization treatment is carried out at a holding temperature of 900°C to 1500°C.

[0052] In some embodiments, the carbonization treatment is carried out for a holding time of 2 hours to 10 hours.

[0053] In a fifth aspect, the present application provides a negative electrode plate, comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material, the negative electrode active material comprising a core and a coating layer located on at least a portion of the surface of the core, the core comprising graphite, and the coating layer comprising hard carbon; in the cumulative distribution curve of the R value of the negative electrode active material obtained in the surface scanning mode of a laser microconfocal Raman spectrometer, starting from the lower limit, the R value R50 with a cumulative distribution of 50% is 0.15-0.40. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0055] FIG1 is a schematic diagram of a battery cell provided in some embodiments of the present application.

[0056] FIG2 is a schematic diagram of a battery module provided in some embodiments of the present application.

[0057] FIG3 is a schematic diagram of a battery pack provided in some embodiments of the present application.

[0058] FIG4 is an exploded schematic diagram of the battery pack shown in FIG3 .

[0059] FIG5 is an exploded schematic diagram of a battery cell provided in some embodiments of the present application.

[0060] FIG6 is a schematic diagram of an electrical device provided in some embodiments of the present application.

[0061] In the accompanying drawings, the drawings are not necessarily drawn to scale.

[0062] The description of the accompanying figures is as follows: 1. battery pack; 2. upper box; 3. lower box; 4. battery module; 5. battery cell; 51. shell; 52. electrode assembly; 53. cover plate. DETAILED DESCRIPTION

[0063] Below, the embodiments of the negative electrode active material and its preparation method, negative electrode plate, lithium-ion battery and electric device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0064] " 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.

[0065] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0066] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0067] 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.

[0068] In this application, the terms "plurality" and "multiple" refer to two or more.

[0069] Unless otherwise specified, the terms used in this application have the common meanings that are commonly understood by those skilled in the art.

[0070] Unless otherwise stated, the numerical values ​​of the various parameters mentioned in this application can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise stated, the test temperature of each parameter is 25°C.

[0071] The battery mentioned in the embodiments of the present application may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application may include a battery cell, a battery module, or a battery pack.

[0072] A battery cell is the smallest unit of a battery, independently capable of charging and discharging. A battery cell can be cylindrical, rectangular, or have other shapes, though this is not a limitation in the present invention. Figure 1 shows a battery cell 5 with a rectangular structure as an example.

[0073] When there are multiple battery cells, the multiple battery cells are connected in series, in parallel, or in mixed series via a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed in the housing. In some embodiments, the housing may serve as part of the vehicle's chassis structure. For example, a portion of the housing may form at least a portion of the vehicle's floor, or a portion of the housing may form at least a portion of the vehicle's crossbeam or longitudinal beam.

[0074] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0075] In some embodiments, battery cells can be assembled into a battery module. The number of battery cells contained in a battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 2 is a schematic diagram of a battery module 4 as an example. As shown in Figure 2, in the battery module 4, multiple battery cells 5 can be arranged in sequence along the length of the battery module 4. Of course, they can also be arranged in any other manner. The multiple battery cells 5 can further be fixed by fasteners.

[0076] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0077] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0078] Figures 3 and 4 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 3 and 4, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing comprises an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in any manner within the housing.

[0079] The battery provided in the embodiments of the present application may include a lithium-ion battery.

[0080] The battery cell includes an electrode assembly and an electrolyte. The electrode assembly can be a wound structure or a laminated structure, which is not limited in the present embodiment.

[0081] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode assembly and electrolyte. The outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging can also be a soft package, such as a bag-type soft package. The soft package can be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0082] In some embodiments, as shown in Figure 5, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, which together form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening, thereby sealing the receiving cavity. The electrode assembly 52 is enclosed in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and can be adjusted according to needs.

[0083] An electrode assembly typically includes a positive electrode sheet and a negative electrode sheet. The negative electrode is the electrode that absorbs or lithiates lithium ions during charging and releases or delithiates lithium during discharge. The positive electrode is the electrode that releases or delithiates lithium ions during charging and absorbs or lithiates lithium during discharge. The positive electrode sheet contains positive active material, and the negative electrode sheet contains negative active material.

[0084] When the battery is charging, the electrochemical processes occurring at the negative electrode can be roughly divided into the following three steps: (1) the liquid phase conduction process of ions inside the negative electrode porous electrode, including the liquid phase diffusion process and the electromigration process; (2) the charge exchange process of ions on the surface of the negative electrode active material; (3) the solid phase conduction process of ions inside the negative electrode active material particles.

[0085] The charge exchange ability of ions on the surface of the negative electrode active material is very important for achieving fast charging. Fast charging, abbreviated as fast charging, refers to charging the battery to a full or nearly full state in a relatively short period of time. If the battery is charged and the time it takes for the battery to charge from 0% SOC to 100% SOC is recorded, the fast charging performance of the battery can be characterized by this time. The shorter the time, the better the fast charging ability of the battery. For example, if the time is around 20 minutes (the error does not exceed 1 minute), it is generally considered to be a 3C fast charging battery. For another example, if the time is around 15 minutes (the error does not exceed 1 minute), it is generally considered to be a 4C fast charging battery.

[0086] Currently, graphite is the most commonly used negative electrode active material, but its kinetic properties are not very good. Fast-charging hard carbon has good kinetic properties, but the energy density of batteries assembled from it is usually not high, and the cycle life of the battery is also not very good.

[0087] In view of this, an embodiment of the present application provides a negative electrode active material.

[0088] The negative electrode active material includes a core and a coating layer located on at least a portion of the surface of the core, the core includes graphite, and the coating layer includes hard carbon; in the R value cumulative distribution curve of the negative electrode active material obtained in the surface scanning mode of the laser microconfocal Raman spectrometer, from the lower limit, the R value R50 with a cumulative distribution of 50% is 0.15-0.40.

[0089] In this application, the R value of the negative electrode active material, core, and coating layer refers to the ratio of the peak heights of the D peak (D-band) and the G peak (G-band) of its Raman spectrum, with the D peak position being 1350±50cm -1 , the G peak position is 1585±50cm -1 The R value can characterize the degree of defects and disorder of each carbon material. The larger the value, the greater the degree of defects and the higher the disorder of the carbon material.

[0090] Raman spectra of various carbon materials can be obtained using a laser confocal Raman microscope, using a laser wavelength of 532 nm. During testing, a suitable sample is taken and its surface scanned in all directions, with a scanning area of ​​100 μm × 100 μm, a step size of 2 μm, and a total of 2500 scan points. This yields all R values ​​and a cumulative R value distribution curve. R50 is the R value at which the cumulative distribution reaches 50% from the lower limit. Specifically, the 2500 R values ​​obtained are arranged in ascending order, and R50 is the R value corresponding to the 50th percentile in this order. The testing instrument can be a high-precision Renishaw laser confocal Raman microscope.

[0091] The negative electrode active material sample can be obtained by sampling during the preparation of the battery, or by disassembling the sample from the prepared battery. For example, the battery cell can be discharged (for safety reasons, the battery cell is generally in a fully discharged state); after disassembling the battery cell, the negative electrode plate is taken out and soaked in dimethyl carbonate for a certain period of time (for example, 2h-10h); then the negative electrode plate is taken out and dried at a certain temperature and time (for example, 60°C, more than 4h), and the negative electrode plate is taken out after drying; the dried negative electrode plate is baked at a certain temperature and time (for example, 400°C, more than 2h), and a sample of the negative electrode active material is taken from any area of ​​the baked negative electrode plate (a blade can be used for powder scraping); the collected negative electrode active material is ground and sieved (for example, sieved with a 200-mesh sieve) to obtain a negative electrode active material sample that can be used for testing.

[0092] The core material sample can be obtained by sampling during the process of preparing the negative electrode active material.

[0093] The R value and R value concentration of the coating layer refer to the properties of the hard carbon material itself, formed by carbonizing the precursor compound used to prepare the coating layer material. Coating layer material samples can be obtained by taking an appropriate amount of the precursor compound used to prepare the coating layer material (e.g., the liquid hard carbon coating agent described below) and carbonizing it under the same carbonization conditions as those used to prepare the negative electrode active material coating layer. The resulting material is then ground and sieved to obtain the coating layer material sample.

[0094] The R value of a negative electrode active material can characterize the degree of defect and disorder in the material. The R value (R50) at the 50th percentile of the cumulative distribution of the negative electrode active material is related to the R value (R50) at the 50th percentile of the cumulative distribution of the core, the R value (R50) at the 50th percentile of the cumulative distribution of the coating, the thickness of the coating, and the uniformity of the coating. For example, when all other conditions are the same, a higher R value (R50) at the 50th percentile of the cumulative distribution of the core is associated with a higher R value (R50) at the 50th percentile of the cumulative distribution of the negative electrode active material; and a thicker coating is associated with a higher R value (R50) at the 50th percentile of the cumulative distribution of the negative electrode active material.

[0095] The cumulative distribution of the negative electrode active material is 50%, and the R value R50 is large. The defect degree of the negative electrode active material is high, the charge exchange of ions on the surface of the negative electrode active material is fast, the kinetic performance of the negative electrode active material is good, and the negative electrode is not prone to lithium plating problems when the battery is quickly charged; however, due to the high degree of defects in the negative electrode active material, side reactions on the surface of the negative electrode active material, such as side reactions at the negative electrode-electrolyte interface, will increase, thereby increasing irreversible capacity loss and reducing the capacity retention rate after cycling.

[0096] The cumulative distribution of the negative electrode active material, with an R value (R50) of 0.15-0.40 at 50%, can both enhance the charge exchange capacity of ions on the surface of the negative electrode active material and minimize side reactions on the surface of the negative electrode active material particles. Therefore, the negative electrode active material provided in the embodiments of the present application can enable a battery to achieve both high energy density and good kinetic and cycling performance.

[0097] The R value R50 at which the cumulative distribution of the negative electrode active material is 50% can be 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, or a range consisting of any of the above values.

[0098] Alternatively, the R value R50 at a cumulative distribution of 50% of the negative electrode active material may be 0.20-0.39, 0.20-0.38, 0.20-0.37, 0.20-0.36, 0.20-0.35, 0.20-0.34, 0.20-0.33, 0.20-0.32, 0.20-0.31, or 0.20-0.30, thereby enabling the battery to better combine high energy density with good kinetic performance and cycle performance.

[0099] The critical charging rate of the battery of the present application without lithium deposition is greater than or equal to 3C, that is, the battery of the present application is a fast-charging battery above 3C. The time for charging the battery from 0% SOC to 100% SOC is within 20 minutes, which can meet the current demand for fast charging.

[0100] By further defining the R values ​​of the negative electrode active material, the core, and the coating layer, at least one of the energy density, kinetic performance, and cycle performance of the battery can be improved.

[0101] In some embodiments, among all R values ​​obtained by the negative electrode active material, the number of R values ​​R50 less than 50% of the cumulative distribution of the core may account for less than or equal to 10%.

[0102] The percentage of R values ​​(R50) less than 50% of the cumulative distribution of the core within the negative electrode active material, among all R values ​​obtained, more accurately represents the extent of the negative electrode active material's uncoating. The smaller this value, the less uncoated the negative electrode active material, and the more isotropic the negative electrode active material. This increases the number of active sites in the negative electrode active material, thereby enhancing the charge exchange capacity of ions on the surface of the negative electrode active material, further improving the kinetic performance of the negative electrode active material and the battery. Furthermore, a smaller degree of uncoated negative electrode active material can reduce the co-intercalation of electrolyte solvents during cycling, leading to better battery cycling performance.

[0103] Optionally, among all R values ​​obtained by the negative electrode active material, the number of R values ​​R50 less than 50% of the cumulative distribution of the core may account for less than or equal to 8%, and more optionally less than or equal to 6%.

[0104] This can further improve the battery's kinetic performance and cycle performance.

[0105] In some embodiments, the R value R50 of the core of the negative electrode active material at 50% of the cumulative distribution is smaller than the R value R50 of the coating layer at 50% of the cumulative distribution.

[0106] The cumulative distribution of the coating layer of the negative electrode active material is 50%, and the R value R50 is large and the disorder is large, which can make the negative electrode active material and the battery have good kinetic performance; the cumulative distribution of the core of the negative electrode active material is 50%, and the R value R50 is small and the disorder is small, which can make the negative electrode active material as a whole have a higher gram capacity and the battery have a higher energy density.

[0107] In some embodiments, the R value R50 of the coating layer at a cumulative distribution of 50% can be 0.9-1.4, for example, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.4, or a range consisting of any of the above values. Alternatively, the R value R50 of the coating layer at a cumulative distribution of 50% can be 0.95-1.25. When the R value R50 of the coating layer at a cumulative distribution of 50% is within the above range, the coating layer itself has good kinetic properties, which can improve the kinetic properties of the negative electrode active material and the battery; it can also make the negative electrode active material have a smaller specific surface area, thereby reducing battery side reactions and providing the battery with good cycle performance.

[0108] In some embodiments, the R value R50 at which the cumulative distribution of the kernel is 50% can be 0.06-0.13, for example, can be 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, or a range consisting of any of the above values.

[0109] A larger R value (R50) at 50% of the cumulative distribution of the core indicates better kinetic performance of the negative electrode active material; a smaller R value (R50) at 50% of the cumulative distribution of the core indicates a higher gram capacity of the negative electrode active material. When the R value (R50) at 50% of the cumulative distribution of the core is within the above range, the battery can achieve both high energy density and good kinetic performance.

[0110] In some embodiments, the mass of the coating can be 0.3%-4.5% of the mass of the core, for example, 0.3%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.4%, 2.8%, 3.2%, 3.6%, 4%, 4.5%, or a range consisting of any of the above values. Alternatively, the mass of the coating can be 1%-3.2% of the mass of the core.

[0111] The quality of the coating layer affects the thickness of the coating layer, and also affects the R value R50 (50% cumulative distribution of the negative electrode active material) and the degree of uncoating of the coating layer.

[0112] Coating the core surface with a coating layer can reduce the contact between the core and the electrolyte, thereby reducing the co-embedding phenomenon of the electrolyte solvent during the cycle, thereby improving the cycle performance of the battery; when the thickness of the coating layer continues to increase, due to the large number of pores in the coating layer itself, the side reactions at the negative electrode-electrolyte interface increase, thereby increasing the irreversible capacity loss and causing the cycle performance of the battery to decline to a certain extent.

[0113] The coating layer mass percentage within the above range can reduce the degree of uncoated coating, thereby improving the charge exchange capacity of ions on the surface of the negative electrode active material. It can also reduce the level of side reactions on the surface of the negative electrode active material particles, resulting in a higher specific capacity of the negative electrode active material. The coating layer mass percentage within the above range is conducive to the battery having high energy density, good kinetic performance, and long cycle life.

[0114] In some embodiments, the difference between the volume distribution particle size Dv50 of the negative electrode active material and the volume distribution particle size Dv50 of the core can be 1 μm-5.5 μm, for example, 1 μm, 1.4 μm, 1.8 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 5 μm, 5.5 μm, or a range consisting of any of the above values. Alternatively, the difference between the volume distribution particle size Dv50 of the negative electrode active material and the volume distribution particle size Dv50 of the core can be 1.5 μm-4.2 μm, or 2 μm-4 μm.

[0115] The difference between the volume distribution particle size Dv50 of the negative electrode active material and the volume distribution particle size Dv50 of the core is within the above range, which can not only enhance the charge exchange capacity of ions on the surface of the negative electrode active material, but also lower the side reactions on the surface of the negative electrode active material particles, and also make the negative electrode active material have a higher gram capacity, thereby benefiting the battery to have high energy density, good kinetic performance and long cycle life.

[0116] In some embodiments, the volume distribution particle size Dv50 of the negative electrode active material may be 8 μm to 25 μm, optionally 12 μm to 17 μm. When the volume distribution particle size Dv50 of the negative electrode active material is within the above range, lithium ions can have good solid-phase conductivity within the negative electrode active material particles and can also have a small specific surface area, thereby facilitating both good cycle performance and kinetic performance of the battery. When the volume distribution particle size Dv50 of the negative electrode active material is within the above range, the negative electrode slurry can also have good dispersibility.

[0117] The volume distribution particle size Dv50 of a material is well known in the art and represents the particle size corresponding to 50% of the cumulative volume distribution percentage of the material. It can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer, as described in GB / T 19077-2016, "Particle Size Distribution Laser Diffraction Method." The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0118] The graphite is artificial graphite. The core includes artificial graphite, which can make the battery have high energy density and good cycle performance.

[0119] In some embodiments, the graphite may have a secondary particle morphology. When the graphite has a secondary particle morphology, the graphite becomes more isotropic, which facilitates rapid lithium ion insertion, thereby facilitating good battery kinetics and further increasing the specific capacity of the negative electrode active material and the energy density of the battery.

[0120] In some embodiments, the intensity ratio C(004) / C(110) of the diffraction peak of the 004 crystal plane to the diffraction peak of the 110 crystal plane of the graphite measured by X-ray diffraction can be 5.5-6.5.

[0121] The intensity ratio of the diffraction peak at the 004 crystal plane to the diffraction peak at the 110 crystal plane, measured by X-ray diffraction, indicates the degree of graphite isotropy. A lower value indicates high graphite isotropy, with lithium ion insertion openings in all directions of the graphite particles. This facilitates rapid lithium ion insertion and, in turn, contributes to good battery kinetic performance.

[0122] For example, the intensity ratio C(004) / C(110) of the 004 crystal plane diffraction peak and the 110 crystal plane diffraction peak of graphite measured by X-ray diffraction method can be tested using an X-ray diffractometer (such as Bruker D8 Discover). The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the X-ray diffraction spectrum of the powder sample. C(004) / C(110) represents the ratio of the integral area of ​​the 004 crystal plane diffraction peak to the integral area of ​​the 110 crystal plane diffraction peak in the powder sample. In the X-ray diffraction analysis test, a copper target can be used as the anode target, CuKα rays can be used as the radiation source, and the ray wavelength can be 0.1%. The scanning 2θ angle range was 20°-80°, and the scanning rate was 4° / min.

[0123] In some embodiments, the gram capacity of the negative electrode active material can be 354 mAh / g to 361 mAh / g.

[0124] The gram capacity of the negative electrode active material can be obtained by assembling a button cell and performing a charge and discharge test. For example, the negative electrode active material sample can be mixed with the conductive agent Super P, the binder polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6, and the solvent N-methylpyrrolidone (NMP) to form a slurry; the prepared slurry is coated on a copper foil current collector, and then dried in an oven and cold pressed for use. The compaction density is controlled to 1.4g / cm 3 -1.6g / cm 3A lithium metal sheet was then used as the counter electrode, a polyethylene film as the separator, and an electrolyte was injected. The cells were assembled into CR2430 button cells in an argon-protected glove box. The electrolyte formulation used was as follows: ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a 1:1:1 volume ratio. Thoroughly dried lithium salt LiPF6 was then dissolved in the mixed solvent at a ratio of 1 mol / L to prepare the electrolyte. The resulting button cell was allowed to stand for 12 hours at 25°C. The cell was then discharged at a constant current of 0.05C to 0.005V. The cell was allowed to stand for 10 minutes, and then discharged at a constant current of 50μA to 0.005V. The cell was allowed to stand for 10 minutes, and then discharged at a constant current of 10μA to 0.005V. The cell was then discharged at a constant current of 0.1C to 2.0V, and the first charge capacity of the cell was recorded. The ratio of the first cycle charging capacity of the button battery to the mass of the negative electrode active material sample is the gram capacity of the negative electrode active material.

[0125] In some embodiments, the powder compaction density of the negative electrode active material under a pressure of 20,000 N can be 1.68 g / cm 3 -1.78g / cm 3 .

[0126] For example, take an appropriate amount of negative electrode active material powder and place it in a special compaction mold. Place the mold on a compaction density instrument, set different pressures, read the thickness of the powder under different pressures on the instrument (here, the thickness after pressure relief), and calculate the compaction density ρ of the negative electrode active material powder under the corresponding pressure using ρ = m / (s*h). The pressure is set to 20000N. m represents the mass of the negative electrode active material powder sample in g. s is the bottom area of ​​the special compaction mold, which is 1.327cm here. 2 h is the compacted thickness of the negative electrode active material powder sample, in cm.

[0127] In some embodiments, the specific surface area of ​​the negative electrode active material can be 1.5 m 2 / g-4.5m 2 / g.

[0128] When the specific surface area of ​​the negative electrode active material is within the above range, side reactions at the negative electrode-electrolyte interface can be reduced, and the irreversible consumption of lithium ions can be reduced, thereby improving the cycle life of the battery.

[0129] The specific surface area of ​​a material is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis test method in accordance with GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using a Micromeritics Tri-Star 3020 specific surface area pore size analyzer.

[0130] The embodiments of the present application also provide a method for preparing a negative electrode active material, which can prepare the negative electrode active material provided in the embodiments of the present application.

[0131] The preparation method includes the following steps: providing a coke raw material; crushing, shaping, and grading the coke raw material to obtain aggregate; mixing the obtained aggregate with a binder, and sequentially granulating and graphitizing the aggregate to obtain graphite; solid-liquid fusing the obtained graphite with a liquid hard carbon coating agent; and carbonizing the solid-liquid fusion product under a protective gas atmosphere to carbonize the liquid hard carbon coating agent into hard carbon and coat at least a portion of the surface of the graphite to obtain a negative electrode active material. The negative electrode active material includes a core and a coating layer located on at least a portion of the surface of the core, wherein the core includes graphite and the coating layer includes hard carbon. The negative electrode active material, in a cumulative distribution curve of R values ​​obtained in a surface scanning mode of a laser microconfocal Raman spectrometer, has an R value (R50) at a cumulative distribution of 50% from the lower limit of 0.15 to 0.40.

[0132] Coke raw materials are typically large in particle size, and crushing can reduce this size. Crushing can optionally include two steps: coarse crushing and pulverization. Coarse crushing breaks the coke raw material into millimeter-sized lumps. Pulverization can reduce particle sizes from millimeters to tens of microns. After crushing, the coke raw material surface is uneven, and shaping can make the coke raw material particles more rounded. Grading can reduce the content of oversized and undersized particles and further adjust the particle size and distribution of the coke raw material.

[0133] Coke feedstock can include one or more of petroleum-based needle coke and coal-based needle coke. These coke feedstocks are anisotropic materials that help reduce the disorder of the core material, increase the gram capacity of the core material and the gram capacity of the negative electrode active material as a whole, and also help improve the energy density of the battery.

[0134] In the preparation method provided in the embodiment of the present application, a liquid-phase hard carbon coating agent is used to carry out solid-liquid fusion with graphite. Since the liquid-phase hard carbon coating agent has good fluidity, it can be evenly distributed on the surface of the graphite particles, thereby improving the coating effect of the coating layer and reducing the degree of non-coating; and after the liquid-phase hard carbon coating agent is carbonized, the negative electrode active material can have a smaller R50, thereby improving the charge exchange capacity of ions on the surface of the negative electrode active material, and improving the kinetic performance of the negative electrode active material and the battery. The degree of non-coating of the negative electrode active material is reduced, and the side reactions on the surface of the negative electrode active material particles can be kept at a lower level, which is also beneficial for the battery to have good cycle performance. Therefore, the negative electrode active material prepared by the preparation method provided in the embodiment of the present application can enable the battery to have high energy density, good kinetic performance and cycle performance.

[0135] Optionally, the mass of the binder can be 6%-12%, or optionally 8%-10%, of the mass of the aggregate obtained by the classification process, thereby enabling the graphite to have a good secondary particle morphology.

[0136] Alternatively, the binder may comprise asphalt.

[0137] The equipment used for the granulation process may include either a horizontal reactor or a vertical reactor.

[0138] Alternatively, the granulation process may be performed using a stepwise heating and holding process, thereby enabling the graphite to have a good secondary particle morphology and high capacity.

[0139] Optionally, 2-4 programmed temperature rising platforms can be set during the heating process.

[0140] Usually, the surface of coke raw materials from different batches and different raw materials is uneven and has many defects. Graphitization treatment can also significantly repair the surface defects of the material, thereby making the Raman value of the core material in the surface scanning mode more concentrated, and thus making the performance of the finished graphite product more consistent.

[0141] The equipment used for graphitization treatment may include any one of an Acheson graphitization furnace, a box furnace or an internal channeling furnace.

[0142] Optionally, the temperature of the graphitization treatment may be 2800° C.-3800° C., for example, 2800° C., 2850° C., 2900° C., 3000° C., 3100° C., 3200° C., 3300° C., 3400° C., 3500° C., 3600° C., 3700° C., 3800° C., or a range thereof. More preferably, the temperature of the graphitization treatment may be 2850° C.-3300° C. The specific time of the graphitization treatment may be reasonably selected according to the equipment used.

[0143] The graphitization temperature is high, the graphitization treatment time is long, the gram capacity of graphite is high, the disorder degree is small, and the R value R50 of the cumulative distribution of graphite is 50% small.

[0144] By selecting the appropriate graphitization treatment temperature, the battery can have both high energy density and good kinetic performance.

[0145] In some embodiments, the coking value of the liquid-phase hard carbon coating agent may be 35%-50%, and optionally 38%-48%.

[0146] The coking value of a liquid hard carbon coating agent refers to the percentage of the mass of the residual carbon left after a certain amount of the liquid hard carbon coating agent sample is heated under specified conditions to the mass of the liquid hard carbon coating agent sample. The test can be carried out in accordance with GB / T 8727-2008.

[0147] In some embodiments, the mass of the liquid-phase hard carbon coating agent may be 0.7%-10% of the mass of the graphite, for example, 0.7%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any range thereof. Alternatively, the mass of the liquid-phase hard carbon coating agent may be 3%-7% of the mass of the graphite.

[0148] As the mass proportion of the liquid-phase hard carbon coating agent increases, the R value R50 of the cumulative distribution of the negative electrode active material is 50% increases, and the disorder degree of the surface of the negative electrode active material particles increases.

[0149] The mass proportion of the liquid-phase hard carbon coating agent is within the above range, which can keep the degree of uncoating of the negative electrode active material within a smaller range. This can not only improve the charge exchange capacity of ions on the surface of the prepared negative electrode active material, but also keep the side reactions on the surface of the prepared negative electrode active material particles at a lower level, and also make the prepared negative electrode active material have a higher gram capacity, which is beneficial for the battery to have high energy density, good kinetic performance and long cycle life.

[0150] In some embodiments, the liquid hard carbon coating agent includes a liquid resin, which is a hard carbon precursor material. When the coating layer includes hard carbon, the negative electrode active material and the battery can have better dynamic performance.

[0151] The liquid resin can be purchased commercially, or synthesized according to methods known in the art, or can be obtained by mixing resin powder with a solvent and stirring uniformly.

[0152] In some embodiments, the viscosity of the liquid resin at 25° C. may be 150 mPa·s to 2000 mPa·s, for example, 150 mPa·s, 200 mPa·s, 300 mPa·s, 400 mPa·s, 500 mPa·s, 600 mPa·s, 700 mPa·s, 800 mPa·s, 900 mPa·s, 1050 mPa·s, 1200 mPa·s, 1400 mPa·s, 1600 mPa·s, 1800 mPa·s, 2000 mPa·s, or any range thereof. Alternatively, the viscosity of the liquid resin at 25° C. may be 300 mPa·s to 900 mPa·s.

[0153] The viscosity of liquid resin can be tested according to GB / T 14074-2017. The test temperature is 25°C and the test equipment can be NDJ-1 rotational viscometer.

[0154] The viscosity of the liquid resin is within the above range, which can make the liquid resin have good fluidity and diffusivity, as well as good curing effect and coating effect. Thus, the liquid resin can be evenly dispersed on the surface of the graphite particles, which is beneficial to improve the coating effect, reduce the degree of uncoating, and improve the coating uniformity of the surface of the graphite particles, which is beneficial to the battery having both good dynamic performance and long cycle life.

[0155] In some embodiments, the solid content of the liquid resin may be 50%-85%, optionally 60%-82%.

[0156] The solid content of a liquid hard carbon coating can be tested using the drying method according to GB / T 14074-2017. Free components and water in a liquid hard carbon coating evaporate at high temperatures. The solid content of a liquid hard carbon coating is the percentage of the total mass remaining after drying under specified conditions. The oven temperature is set to 150°C and the coating is baked to constant weight.

[0157] The solid content of the liquid resin is within the above range, which can make the liquid resin have good fluidity and diffusivity, as well as good curing effect and coating effect. Thus, the liquid resin can be evenly dispersed on the surface of the graphite particles, which is beneficial to improve the coating effect and reduce the degree of uncoating. It can also adjust the cumulative distribution of the negative electrode active material to 50% R value R50, increase the disorder of the surface of the negative electrode active material particles, and enhance the charge exchange capacity of ions on the surface of the negative electrode active material, which is beneficial to the battery having both good kinetic performance and long cycle life.

[0158] In some embodiments, the liquid resin may include at least one of liquid phenolic resin, liquid epoxy resin, liquid vinyl ester resin, liquid unsaturated polyester resin, liquid furan resin, and derivatives thereof. Derivatives generally refer to products derived from the replacement of hydrogen atoms or atomic groups in a polymer with other atoms or atomic groups.

[0159] The liquid resin is a good hard carbon precursor material. As a liquid hard carbon coating agent, it can better improve the dynamic performance of the battery and also make the battery have good cycle performance.

[0160] In some embodiments, the liquid hard carbon coating agent includes liquid phenolic resin. The solid content of the liquid phenolic resin may be 60%-82% and the weight average molecular weight may be 300-800.

[0161] Optionally, the solid content of the liquid phenolic resin may be 68%-78% and the weight average molecular weight may be 450-700.

[0162] Compared with other liquid resins, the hard carbon formed by carbonization and coking of liquid phenolic resin itself has better performance.

[0163] By further adjusting the solid content and weight-average molecular weight of the liquid phenolic resin within the above range, the hard carbon formed by its carbonization can have better kinetic properties, and the coating effect can be improved and the degree of uncoating can be reduced, thereby enhancing the charge exchange capacity of ions on the surface of the negative electrode active material, and further improving the kinetic properties of the negative electrode active material.

[0164] The weight-average molecular weight of the liquid hard carbon coating agent can be measured using gel permeation chromatography. The testing instrument can be an Agilent 1290 Infinity II GPC system. The eluent can be tetrahydrofuran, and polystyrene standards are used for calibration.

[0165] The liquid phenolic resin can be a phenolic compound, an aldehyde compound, etc., which is formed by condensation in the presence of an alkaline catalyst. The condensation reaction begins to generate a liquid. The liquid phenolic resin mentioned in the embodiment of the present application is a resol phenolic resin.

[0166] The phenolic compound may include one or more of phenol, cresol, xylenol, nonylphenol, bisphenol A, bisphenol F, resorcinol, propylphenol, ethylphenol, and cardanol, and phenol may be selected. The aldehyde compound may include one or more of formaldehyde, acetaldehyde, butyraldehyde, paraformaldehyde, and furfural, and formaldehyde may be selected. The alkaline catalyst may include one or more of sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, magnesium hydroxide, ammoniacal liquor, sodium carbonate, and tertiary amine.

[0167] In some embodiments, the device for performing solid-liquid fusion of graphite and liquid hard carbon coating agent may be a fusion machine.

[0168] Optionally, the stirring speed of the fusion machine can be 350r / min-1000r / min, for example, 350r / min, 400r / min, 450r / min, 500r / min, 550r / min, 600r / min, 650r / min, 700r / min, 750r / min, 800r / min, 850r / min, 900r / min, 1000r / min, or a range consisting of any of the above values. More optionally, the stirring speed of the fusion machine can be 450r / min-850r / min.

[0169] Increasing the stirring speed of the fusion machine is beneficial to improving the coating effect and reducing the degree of uncoating, thereby enhancing the charge exchange capacity of ions on the surface of the negative electrode active material, and further improving the kinetic performance of the negative electrode active material; however, excessive stirring speed of the fusion machine will destroy the outer surface structure of the core, and strong centrifugation will also cause mass loss of the liquid phase hard carbon coating agent.

[0170] Optionally, the stirring time of solid-liquid fusion can be 4 min-10 min, for example, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, or a range consisting of any of the above values. More optionally, the stirring time of solid-liquid fusion can be 6 min-8 min.

[0171] Increasing the stirring time of solid-liquid fusion can improve the coating effect and reduce the degree of uncoated materials, thereby enhancing the charge exchange capacity of ions on the surface of the negative electrode active material, and thus improving the kinetic performance of the negative electrode active material. However, if the stirring time is too long, the improvement in coating effect is not significant and energy consumption is increased.

[0172] In some embodiments, the carbonization treatment equipment may be a rail kiln.

[0173] In some embodiments, the holding temperature of the carbonization treatment may be 900° C.-1500° C., for example, 900° C., 1000° C., 1050° C., 1100° C., 1150° C., 1200° C., 1250° C., 1300° C., 1350° C., 1400° C., 1500° C., or any range thereof. Alternatively, the holding temperature of the carbonization treatment may be 1050° C.-1350° C.

[0174] In some embodiments, the holding time of the carbonization treatment can be 2 hours to 10 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, or a range thereof. Alternatively, the holding time of the carbonization treatment can be 5 hours to 8 hours. The holding time of the carbonization treatment refers to the residence time at the holding temperature.

[0175] In some embodiments, the preparation method may further include the steps of: deagglomerating, screening and demagnetizing the carbonized material.

[0176] Deagglomeration can be performed in a deagglomerator. This eliminates the weak adhesive properties of the coating surface and reduces excessive agglomeration of the finished product particles. Screening can reduce the content of large particles and fine powder in the finished product, thereby facilitating the achievement of the desired particle size and distribution. Demagnetization can also reduce the content of magnetic impurities in the finished product, which can increase battery self-discharge and reduce battery performance.

[0177] [Negative electrode]

[0178] The battery cell includes a negative electrode plate.

[0179] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two surfaces that face each other in the thickness direction of the negative electrode current collector, and the negative electrode film layer is located on either or both of the two facing surfaces of the negative electrode current collector.

[0180] In some embodiments, the negative electrode current collector may include a metal foil, a three-dimensional porous current collector, or a composite current collector. As examples of metal foils, copper foil, copper alloy foil, nickel foil, nickel alloy foil, aluminum foil, and aluminum alloy foil may be used. As examples of three-dimensional porous current collectors, copper mesh, nickel mesh, foam copper, foam nickel, and foam aluminum may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include, but is not limited to, one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, aluminum, aluminum alloy, silver, and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0181] The negative electrode film layer includes the negative electrode active material or the negative electrode active material prepared by the above preparation method, thereby enabling the battery to have high energy density, good kinetic performance and cycle performance.

[0182] In some embodiments, the negative electrode film layer may also include other negative electrode active materials known in the art, for example, other negative electrode active materials include but are not limited to one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

[0183] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. As examples, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0184] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. As examples, the negative electrode binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0185] In some embodiments, the negative electrode film layer may further include other additives. For example, the other additives may include but are not limited to thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0186] In some embodiments, the thickness of the negative electrode film layer can be 45 μm-100 μm, optionally 55 μm-100 μm, or 70 μm-100 μm. The thickness of the negative electrode film layer is the thickness of the negative electrode film layer on a single side of the negative electrode current collector. The thickness of the negative electrode film layer can be measured using a micrometer.

[0187] The thickness of the negative electrode film is related to the ion embedding rate and the magnitude of the negative electrode polarization, and therefore its thickness affects the dynamic performance of the negative electrode sheet. Generally, the thicker the negative electrode film, the more difficult it is for ions to diffuse in the liquid phase within the negative porous electrode under the same conditions.

[0188] By adjusting the thickness of the negative electrode film layer within the above range, the battery can have better dynamic performance while having high energy density.

[0189] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer located between the first negative electrode film layer and the negative electrode current collector, wherein the thickness of the first negative electrode film layer is 30%-60% of the thickness of the negative electrode film layer, and the thickness of the second negative electrode film layer is 70%-40% of the thickness of the negative electrode film layer. Alternatively, the thickness of the first negative electrode film layer is 30%-40% of the thickness of the negative electrode film layer, and the thickness of the second negative electrode film layer is 70%-60% of the thickness of the negative electrode film layer.

[0190] The first negative electrode film layer includes a first negative electrode active material, and the second negative electrode film layer includes a second negative electrode active material. The first negative electrode active material includes the above-mentioned negative electrode active material or a negative electrode active material prepared by the above-mentioned preparation method. This allows the battery to have high energy density, good kinetic performance, and good cycle performance.

[0191] Optionally, in some embodiments, the second negative electrode active material may include the above-mentioned negative electrode active material or the negative electrode active material prepared by the above-mentioned preparation method, the mass content w1 of the first negative electrode active material in the first negative electrode film layer is greater than the mass content w2 of the second negative electrode active material in the second negative electrode film layer, and the mass content of the negative electrode binder in the first negative electrode film layer is less than the mass content of the negative electrode binder in the second negative electrode film layer.

[0192] During the slurry drying process, the negative electrode binder will float up, causing the negative electrode binder content on the outer surface of the negative electrode film layer to increase, which is not conducive to the liquid phase conduction of ions inside the negative electrode porous electrode and the charge exchange of ions on the surface of the negative electrode active material.

[0193] By partitioning the negative electrode film layer and making the mass content w1 of the first negative electrode active material in the first negative electrode film layer greater than the mass content w2 of the second negative electrode active material in the second negative electrode film layer, and the mass content of the negative electrode binder in the first negative electrode film layer is less than the mass content of the negative electrode binder in the second negative electrode film layer, the problem of floating of the negative electrode binder during the slurry drying process can be reduced, and the negative electrode binder content on the outer surface of the negative electrode film layer can be reduced, which is beneficial to the liquid phase conduction of ions inside the negative electrode porous electrode and the charge exchange of ions on the surface of the negative electrode active material, thereby further improving the battery's kinetic performance.

[0194] Optionally, the mass content w1 of the second negative electrode active material in the first negative electrode film layer may be greater than or equal to 96.9%, and may be 96.9%-97.4%.

[0195] Optionally, the mass content w2 of the second negative electrode active material in the second negative electrode film layer may be less than 96.9%, and may be 96.4%-96.8%.

[0196] In some alternative embodiments, the second negative electrode active material may include graphite, having a secondary particle morphology and a cumulative distribution of graphite with a 50% R value (R50) of 0.06-0.13. The second negative electrode active material may be the core of the negative electrode active material provided in the above embodiments of the present application, i.e., graphite. The second negative electrode active material lacks a coating layer, thereby enabling the battery to have a higher energy density.

[0197] Optionally, the mass content w1 of the first negative electrode active material in the first negative electrode film layer is greater than the mass content w2 of the second negative electrode active material in the second negative electrode film layer, and the mass content of the negative electrode binder in the first negative electrode film layer is less than the mass content of the negative electrode binder in the second negative electrode film layer.

[0198] By partitioning the negative electrode film layer and making the mass content w1 of the first negative electrode active material in the first negative electrode film layer greater than the mass content w2 of the second negative electrode active material in the second negative electrode film layer, and the mass content of the negative electrode binder in the first negative electrode film layer is less than the mass content of the negative electrode binder in the second negative electrode film layer, the problem of floating of the negative electrode binder during the slurry drying process can be reduced, and the negative electrode binder content on the outer surface of the negative electrode film layer can be reduced, which is beneficial to the liquid phase conduction of ions inside the negative electrode porous electrode and the charge exchange of ions on the surface of the negative electrode active material, thereby further improving the battery's kinetic performance.

[0199] Optionally, the mass content w1 of the second negative electrode active material in the first negative electrode film layer may be greater than or equal to 96.9%, and may be 96.9%-97.4%.

[0200] Optionally, the mass content w2 of the second negative electrode active material in the second negative electrode film layer may be less than 96.9%, and may be 96.4%-96.8%.

[0201] In some embodiments, the compaction density of the negative electrode film layer can be 1.62 g / cm 3 -1.80g / cm 3 , optional 1.65g / cm 3 -1.80g / cm 3 The negative electrode active material provided in the embodiments of the present application or the negative electrode active material prepared by the preparation method provided in the embodiments of the present application can enable the negative electrode film layer to have a high compaction density.

[0202] The compacted density of the negative electrode film refers to the ratio of the surface density of the negative electrode film to its thickness. The surface density of the negative electrode film refers to the ratio of the weight of the negative electrode film after coating, drying, and rolling to the coating area.

[0203] The negative electrode film layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, negative electrode conductive agent, negative electrode binder, and other optional additives in a solvent and stirring them evenly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0204] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate may further include a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer; in some embodiments, the negative electrode plate may further include a protective layer covering the surface of the negative electrode film layer.

[0205] [Positive electrode]

[0206] The battery cell includes a positive electrode plate.

[0207] The positive electrode sheet includes a positive electrode current collector and a positive electrode film disposed on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two surfaces that face each other in the thickness direction of the positive electrode current collector, and the positive electrode film is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0208] The positive electrode film layer includes a positive electrode active material. For example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, lithium-containing phosphates, and modified compounds thereof.

[0209] As an example, the lithium transition metal oxide may include, but is not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. In some embodiments, the lithium transition metal oxide may include Li a Ni b Co c M d O e A f , wherein 0<a≤1.2; 0.8≤b<1; 0<c<1; 0<d<1; 1≤e≤2; 0≤f≤1; M includes but is not limited to one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B; A includes but is not limited to one or more of N, F, S and Cl. This can further improve the energy density of the battery cell. Optionally, the lithium transition metal oxide may include but is not limited to LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.80 Co 0.15 Al 0.05 O2、LiNi 0.9 Co 0.06 Mn 0.04 O2、LiNi 0.92 Co 0.06 Mn 0.02 O2、LiNi 0.96 Co 0.02 Mn 0.02 One or more of O2.

[0210] The charge and discharge process of a battery cell is accompanied by the intercalation and deintercalation of Li, and the molar content of Li in the battery cell varies at different discharge states. The molar content of Li in the examples of this application regarding the positive electrode active materials refers to the initial state of the material, i.e., the state before the materials are added. The molar content of Li in the positive electrode active materials used in the battery cell may change after charge and discharge cycles.

[0211] In the examples of the present application regarding the positive electrode active materials, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0212] As an example, the lithium-containing phosphate may include, but is not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds.

[0213] The modified compounds of the above-mentioned positive electrode active materials may be used to perform doping modification and / or surface coating modification on the positive electrode active materials.

[0214] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0215] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylic resin, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and one or more of carboxymethyl chitosan (CMCS).

[0216] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include but is not limited to one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include but is not limited to one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0217] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, positive electrode conductive agent, positive electrode binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0218] [Electrolytes]

[0219] The battery cell includes an electrolyte. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected according to needs. For example, the electrolyte can include one or more of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte solution).

[0220] In some embodiments, the electrolyte is an electrolyte solution including an electrolyte salt and a solvent.

[0221] In some embodiments, as examples, the electrolyte salt may include, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).

[0222] In some embodiments, the solvent may include, but is not limited to, one or more of an ester solvent, a sulfone solvent, and an ether solvent. As an example, the solvent may include, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and one or more of diethyl sulfone (ESE).

[0223] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0224] [Isolation film]

[0225] Battery cells using electrolytes, as well as some battery cells using solid electrolytes, also include a separator. The separator is placed between the positive and negative electrode sheets to prevent internal short circuits.

[0226] The present application has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0227] In some embodiments, the material of the isolation membrane may include, but is not limited to, one or more of fiberglass, non-woven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different.

[0228] The preparation method of battery cells is well known. In some embodiments, the positive electrode sheet, separator, negative electrode sheet and electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, dried and injected with the above-mentioned electrolyte, and then subjected to packaging, standing, formation and other processes to obtain a battery cell. Multiple battery cells can also be further connected in series, in parallel or in a mixed connection to form a battery module. Multiple battery modules can also be connected in series, in parallel or in a mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0229] Electrical devices

[0230] The embodiments of the present application also provide an electrical device, which includes a battery provided in the embodiments of the present application, and the battery is used to provide electrical energy. The battery can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0231] The electrical device can select a specific type of battery, such as a battery cell, a battery module, or a battery pack, according to its usage requirements.

[0232] Figure 6 is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module may be used.

[0233] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0234] Example

[0235] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are commercially available.

[0236] Example 1

[0237] (1) Preparation of negative electrode active materials

[0238] The petroleum needle coke is crushed, shaped and graded to obtain aggregate; the obtained aggregate is mixed with binder asphalt in a mass ratio of 100:8 and placed in a horizontal reactor for heating and granulation. A step-by-step heating and insulation process is adopted during heating. The programmed temperature platforms are set to 200°C, 300°C, and 600°C, respectively. The temperature is maintained at 200°C for 1 hour, 300°C for 2 hours, and 600°C for 2 hours. The mixture is cooled for 3 hours and then taken out of the furnace; the granulated material is placed in an Acheson graphitization furnace for graphitization at 3000°C for about 50 hours to obtain graphite.

[0239] A fusion machine is used to fuse graphite and a liquid hard carbon coating agent in a mass ratio of 100:5. The stirring speed of the fusion machine is 600 r / min, and the stirring time is 7 minutes. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 580, a viscosity of 550 mPa·s at 25°C, and a solid content of 70%-71%. The product after solid-liquid fusion is placed in a track kiln, heated to 1150°C under a nitrogen atmosphere for carbonization treatment, and kept warm for 6 hours. The product is then cooled to 50°C and taken out of the kiln. After depolymerization, screening and demagnetization treatment, a negative electrode active material is obtained.

[0240] (2) Preparation of negative electrode sheet

[0241] The above-mentioned negative electrode active material, thickener sodium carboxymethyl cellulose, negative electrode binder styrene-butadiene rubber (SBR), and negative electrode conductive agent Super P were mixed in a mass ratio of 97.3:1.1:0.8:0.8, solvent deionized water was added, and the mixture was stirred evenly under the action of a vacuum mixer to prepare a first negative electrode slurry.

[0242] The above-mentioned negative electrode active material, thickener sodium carboxymethyl cellulose, negative electrode binder styrene-butadiene rubber (SBR), and negative electrode conductive agent Super P were mixed in a mass ratio of 96.5:1.1:2.0:0.4, and deionized water solvent was added. The mixture was stirred evenly under the action of a vacuum mixer to prepare a second negative electrode slurry.

[0243] The second negative electrode slurry was evenly coated on both surfaces of the negative electrode current collector copper foil. The first negative electrode slurry was then applied over the second negative electrode slurry. The negative electrode current collector coated with the slurry was air-dried at room temperature and then transferred to an oven for drying. The negative electrode sheets were then cold-pressed and slit. The thickness of the negative electrode film on one side of the negative electrode current collector was 58 μm. The ratio of the coating thickness of the first negative electrode slurry to the coating thickness of the second negative electrode slurry was 4:6.

[0244] (3) Preparation of positive electrode sheet

[0245] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, positive electrode conductive agent Super P, and positive electrode binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96:2:2, and solvent N-methylpyrrolidone (NMP) is added. The mixture is stirred under the action of a vacuum mixer until the system becomes uniform and transparent to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on both surfaces of the positive electrode current collector aluminum foil; the positive electrode current collector coated with the slurry is dried at room temperature and then transferred to an oven for drying, and then cold pressed and cut to obtain positive electrode sheets.

[0246] (4) Preparation of electrolyte

[0247] 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 lithium salt LiPF6 is dissolved in the mixed solvent at a ratio of 1 mol / L to prepare an electrolyte.

[0248] (5) Preparation of isolation membrane

[0249] Use 12 micron polyethylene film.

[0250] (6) Preparation of batteries (full batteries)

[0251] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried electrode assembly. After vacuum packaging, standing, formation, shaping and other processes, a battery is obtained.

[0252] Comparative Example 1

[0253] The preparation process of the battery is the same as that of Example 1 except that the preparation process of the negative electrode active material is different.

[0254] (1) Preparation of negative electrode active materials

[0255] The petroleum-based needle coke is crushed, shaped and graded to obtain aggregate; the obtained aggregate is mixed with binder asphalt in a mass ratio of 100:8 and placed in a horizontal reactor for heating and granulation. A step-by-step heating and insulation process is adopted during heating. The programmed temperature platforms are set to 200°C, 300°C, and 600°C, respectively. The temperature is maintained at 200°C for 1 hour, 300°C for 2 hours, and 600°C for 2 hours. The material is then taken out of the furnace after cooling for 3 hours. The granulated material is placed in an Acheson graphitization furnace for graphitization at 3000°C for about 50 hours, and then sieving and demagnetizing to obtain a negative electrode active material.

[0256] Comparative Example 2

[0257] The preparation process of the battery is the same as that of Example 1 except that the preparation process of the negative electrode active material is different.

[0258] (1) Preparation of negative electrode active materials

[0259] The petroleum needle coke is crushed, shaped and graded to obtain aggregate; the obtained aggregate is mixed with binder asphalt in a mass ratio of 100:8 and placed in a horizontal reactor for heating and granulation. A step-by-step heating and insulation process is adopted during heating. The programmed temperature platforms are set to 200°C, 300°C, and 600°C, respectively. The temperature is maintained at 200°C for 1 hour, 300°C for 2 hours, and 600°C for 2 hours. The mixture is then cooled for 3 hours and then taken out of the furnace; the granulated material is placed in an Acheson graphitization furnace for graphitization at 2850°C for 45 hours to obtain graphite.

[0260] A VC mixer is used to mix graphite and a solid-phase coating agent in a mass ratio of 100:5. The solid-phase coating agent is asphalt with a softening point of 270°C. The solid-solid mixing product is placed in a track kiln and heated to 1150°C for carbonization treatment under a nitrogen atmosphere for 6 hours. The kiln is then cooled to 50°C and taken out of the kiln. After depolymerization, screening and demagnetization, the negative electrode active material is obtained.

[0261] Performance test of liquid phase hard carbon coating agent

[0262] The viscosity of the liquid hard carbon coating agent was tested according to GB / T 14074-2017. The test temperature was 25°C and the test equipment was an NDJ-1 rotational viscometer.

[0263] The solid content of the liquid hard carbon coating agent was tested using the drying method according to GB / T 14074-2017. The oven temperature was set to 150°C and the coating was baked to constant weight.

[0264] Test section

[0265] (1) Raman spectroscopy test of negative electrode active materials

[0266] The test instrument is a high-precision Renishaw laser microscope confocal Raman spectrometer with a laser wavelength of 532nm.

[0267] During the test, an appropriate amount of negative electrode active material sample was taken and its surface was scanned in all directions. The scanning area was 100μm×100μm, the step length was 2μm, and the total number of scanning points was 2500 points. The R value and the cumulative distribution curve of the R value at different positions were obtained. The R value refers to the ratio of the peak height of the D peak and the G peak of the Raman spectrum. The D peak position is 1350±50cm - 1 , the G peak position is 1585±50cm -1 R50 is the R value at which the cumulative distribution from the lower limit is 50%.

[0268] Raman spectroscopy testing of graphite and coating materials was performed using methods similar to those described above. Coating material samples can be obtained by carbonizing an appropriate amount of a liquid hard carbon coating agent or a solid coating agent using the same carbonization conditions as in the Examples and Comparative Examples. The resulting material is then ground and sieved to obtain a coating material sample.

[0269] The percentage of the R value R50 less than 50% of the cumulative distribution of graphite in all R values ​​of the obtained negative electrode active material is marked as the uncoating degree X of the negative electrode active material.

[0270] (2) Battery mass energy density test

[0271] At 25°C, the batteries prepared in each example and comparative example were fully charged and fully discharged at a 0.33C rate three times. The actual discharge energy (D0) of the battery was recorded. The battery charge and discharge voltage range was 2.5V to 4.25V. The battery was weighed using an electronic balance at 25°C. The ratio of the battery's actual discharge energy (D0) to the battery's mass is the battery's mass energy density.

[0272] (3) Battery cycle performance test

[0273] At 35°C, the batteries prepared in each example and comparative example were fully charged at a 1C rate and fully discharged at a 0.5C rate, and the charge and discharge voltage range of the battery was 2.5V to 4.25V. The battery's cycling performance was characterized by the capacity retention rate after 2000 cycles; a higher value indicates better cycling performance. The capacity retention rate after 2000 cycles = discharge capacity after 2000 cycles / discharge capacity after the first cycle.

[0274] (4) Battery critical charge rate test

[0275] At 25°C, the batteries prepared in each embodiment and comparative example were charged and discharged at an equivalent charge rate of xC for full charge and 1C for full discharge. After 10 cycles, the battery was fully charged at an equivalent charge rate of xC, the negative electrode was disassembled and the lithium deposition on the surface was observed. The battery charge and discharge voltage range is 2.5V to 4.25V. If lithium is not deposited on the negative electrode surface, the equivalent charge rate xC is increased by 0.1C for the above test until lithium is deposited on the negative electrode surface. The test is stopped and the charge rate xC at this time is recorded. (x-0.1)C is recorded as the critical charge rate of the battery.

[0276] Table 1

[0277] It can be seen from the test results of Example 1 and Comparative Example 1 that by providing a coating layer on the graphite surface and making the cumulative distribution of the negative electrode active material after coating 50% R value R50 greater than 0.15, the battery can have a higher critical charge rate, thereby making the battery have better fast charging performance.

[0278] Table 2

[0279] It can be seen from the test results in Table 2 that compared with the negative electrode active material prepared by using a solid phase coating agent in Comparative Example 2, the use of a liquid phase hard carbon coating agent in Example 1 can reduce the R value R50 of the cumulative distribution of the negative electrode active material to 50%, thereby enabling the battery to have better fast charging performance while also having a higher cycle capacity retention rate.

[0280] It can also be seen from the test results in Table 2 that, compared with the negative electrode active material prepared by using a solid-phase coating agent in Comparative Example 2, the use of a liquid-phase hard carbon coating agent in Example 1 can also enable the battery to have a higher energy density.

[0281] Example 2

[0282] The preparation process of the battery is the same as that of Example 1 except that the preparation process of the negative electrode active material is different.

[0283] (1) Preparation of negative electrode active materials

[0284] The petroleum-based needle coke is crushed, shaped and graded to obtain aggregate; the obtained aggregate is mixed with binder asphalt in a mass ratio of 100:8 and placed in a horizontal reactor for heating and granulation. A step-by-step heating and insulation process is adopted during heating. The programmed temperature platforms are set to 200°C, 300°C, and 600°C, respectively. The temperature is maintained at 200°C for 1 hour, 300°C for 2 hours, and 600°C for 2 hours. The material is then taken out of the furnace after cooling for 3 hours. The granulated material is placed in an Acheson graphitization furnace for graphitization at 3200°C for about 55 hours to obtain graphite.

[0285] A fusion machine is used to fuse graphite and a liquid hard carbon coating agent in a mass ratio of 100:5. The stirring speed of the fusion machine is 600 r / min, and the stirring time is 7 minutes. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 580, a viscosity of 550 mPa·s at 25°C, and a solid content of 70%-71%. The product after solid-liquid fusion is placed in a track kiln, heated to 1150°C under a nitrogen atmosphere for carbonization treatment, and kept warm for 6 hours. The product is then cooled to 50°C and taken out of the kiln. After depolymerization, screening and demagnetization treatment, a negative electrode active material is obtained.

[0286] Example 3

[0287] The preparation process of the battery is the same as that of Example 1 except that the preparation process of the negative electrode active material is different.

[0288] (1) Preparation of negative electrode active materials

[0289] The petroleum needle coke is crushed, shaped and graded to obtain aggregate; the obtained aggregate is mixed with binder asphalt in a mass ratio of 100:8 and placed in a horizontal reactor for heating and granulation. A step-by-step heating and insulation process is adopted during heating. The programmed temperature platforms are set to 200°C, 300°C, and 600°C, respectively. The temperature is maintained at 200°C for 1 hour, 300°C for 2 hours, and 600°C for 2 hours. The product is then cooled for 3 hours and then taken out of the furnace; the granulated material is placed in an Acheson graphitization furnace for graphitization at 2850°C for about 45 hours to obtain graphite.

[0290] A fusion machine is used to fuse graphite and a liquid hard carbon coating agent in a mass ratio of 100:5. The stirring speed of the fusion machine is 600 r / min, and the stirring time is 7 minutes. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 580, a viscosity of 550 mPa·s at 25°C, and a solid content of 70%-71%. The product after solid-liquid fusion is placed in a track kiln, heated to 1150°C under a nitrogen atmosphere for carbonization treatment, and kept warm for 6 hours. The product is then cooled to 50°C and taken out of the kiln. After depolymerization, screening and demagnetization treatment, a negative electrode active material is obtained.

[0291] Table 3

[0292] From the test results in Table 3, it can be seen that, under the same conditions, by adjusting the preparation process of the core graphite, the cumulative distribution of the negative electrode active material can be adjusted to an R value R50 of 50%.

[0293] The test results in Table 3 also show that, when the degree of uncoating of the negative electrode active material is the same, the R value R50 at which the cumulative distribution of the negative electrode active material is 50% increases, and the fast charging performance of the battery is improved.

[0294] Example 4

[0295] The preparation process of the battery is the same as that of Example 1 except that the preparation process of the negative electrode active material is different.

[0296] (1) Preparation of negative electrode active materials

[0297] The petroleum needle coke is crushed, shaped and graded to obtain aggregate; the obtained aggregate is mixed with binder asphalt in a mass ratio of 100:8 and placed in a horizontal reactor for heating and granulation. A step-by-step heating and insulation process is adopted during heating. The programmed temperature platforms are set to 200°C, 300°C, and 600°C, respectively. The temperature is maintained at 200°C for 1 hour, 300°C for 2 hours, and 600°C for 2 hours. The mixture is cooled for 3 hours and then taken out of the furnace; the granulated material is placed in an Acheson graphitization furnace for graphitization at 3000°C for about 50 hours to obtain graphite.

[0298] Graphite and a liquid hard carbon coating agent are fused in a solid-liquid mixture at a mass ratio of 100:3 using a fusion machine. The stirring speed of the fusion machine is 600 r / min, and the stirring time is 7 minutes. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 580, a viscosity of 550 mPa·s at 25°C, and a solid content of 70%-71%. The product after solid-liquid fusion is placed in a track kiln, heated to 1150°C under a nitrogen atmosphere for carbonization treatment, and kept warm for 6 hours. The product is then cooled to 50°C and taken out of the kiln. After depolymerization, screening and demagnetization treatment, a negative electrode active material is obtained.

[0299] Example 5

[0300] The preparation process of the battery is the same as that of Example 1 except that the preparation process of the negative electrode active material is different.

[0301] (1) Preparation of negative electrode active materials

[0302] The petroleum needle coke is crushed, shaped and graded to obtain aggregate; the obtained aggregate is mixed with binder asphalt in a mass ratio of 100:8 and placed in a horizontal reactor for heating and granulation. A step-by-step heating and insulation process is adopted during heating. The programmed temperature platforms are set to 200°C, 300°C, and 600°C, respectively. The temperature is maintained at 200°C for 1 hour, 300°C for 2 hours, and 600°C for 2 hours. The mixture is cooled for 3 hours and then taken out of the furnace; the granulated material is placed in an Acheson graphitization furnace for graphitization at 3000°C for about 50 hours to obtain graphite.

[0303] Graphite and a liquid hard carbon coating agent are fused in a solid-liquid mixture in a mass ratio of 100:7 using a fusion machine. The stirring speed of the fusion machine is 600 r / min, and the stirring time is 7 minutes. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 580, a viscosity of 550 mPa·s at 25°C, and a solid content of 70%-71%. The product after solid-liquid fusion is placed in a track kiln, heated to 1150°C for carbonization treatment under a nitrogen atmosphere, and kept warm for 6 hours. The product is then cooled to 50°C and taken out of the kiln. After depolymerization, screening and demagnetization treatment, a negative electrode active material is obtained.

[0304] Example 6

[0305] The preparation process of the battery is the same as that of Example 1 except that the preparation process of the negative electrode active material is different.

[0306] (1) Preparation of negative electrode active materials

[0307] The petroleum needle coke is crushed, shaped and graded to obtain aggregate; the obtained aggregate is mixed with binder asphalt in a mass ratio of 100:8 and placed in a horizontal reactor for heating and granulation. A step-by-step heating and insulation process is adopted during heating. The programmed temperature platforms are set to 200°C, 300°C, and 600°C, respectively. The temperature is maintained at 200°C for 1 hour, 300°C for 2 hours, and 600°C for 2 hours. The mixture is cooled for 3 hours and then taken out of the furnace; the granulated material is placed in an Acheson graphitization furnace for graphitization at 3000°C for about 50 hours to obtain graphite.

[0308] Graphite and a liquid hard carbon coating agent are fused in a solid-liquid mixture at a mass ratio of 100:10 using a fusion machine. The stirring speed of the fusion machine is 600 r / min, and the stirring time is 7 minutes. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 580, a viscosity of 550 mPa·s at 25°C, and a solid content of 70%-71%. The product after solid-liquid fusion is placed in a track kiln, heated to 1150°C under a nitrogen atmosphere for carbonization treatment, and kept warm for 6 hours. The product is then cooled to 50°C and taken out of the kiln. After depolymerization, screening, and demagnetization, a negative electrode active material is obtained.

[0309] Example 7

[0310] The preparation process of the battery is the same as that of Example 1 except that the preparation process of the negative electrode active material is different.

[0311] (1) Preparation of negative electrode active materials

[0312] The petroleum needle coke is crushed, shaped and graded to obtain aggregate; the obtained aggregate is mixed with binder asphalt in a mass ratio of 100:8 and placed in a horizontal reactor for heating and granulation. A step-by-step heating and insulation process is adopted during heating. The programmed temperature platforms are set to 200°C, 300°C, and 600°C, respectively. The temperature is maintained at 200°C for 1 hour, 300°C for 2 hours, and 600°C for 2 hours. The mixture is cooled for 3 hours and then taken out of the furnace; the granulated material is placed in an Acheson graphitization furnace for graphitization at 3000°C for about 50 hours to obtain graphite.

[0313] A fusion machine is used to fuse graphite and a liquid hard carbon coating agent in a mass ratio of 100:0.7. The stirring speed of the fusion machine is 600 r / min, and the stirring time is 7 minutes. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 580, a viscosity of 550 mPa·s at 25°C, and a solid content of 70%-71%. The product after solid-liquid fusion is placed in a track kiln, heated to 1150°C under a nitrogen atmosphere for carbonization treatment, and kept warm for 6 hours. The product is then cooled to 50°C and taken out of the kiln. After depolymerization, screening and demagnetization treatment, a negative electrode active material is obtained.

[0314] Table 4

[0315] From the test results in Table 4, it can be seen that, under the same other conditions, adjusting the mass ratio of graphite to liquid hard carbon coating agent can adjust the R value R50 of 50% of the cumulative distribution of negative electrode active materials and the degree of uncoating of negative electrode active materials.

[0316] The test results in Table 4 also show that when the mass ratio of graphite to liquid hard carbon coating agent is between 100:3 and 100:7, the battery can better combine high energy density, high cycle capacity retention rate and high critical charge rate.

[0317] The test results in Table 4 also show that increasing the mass of the liquid-phase hard carbon coating agent initially improves the battery's cycling performance. However, as the mass of the liquid-phase hard carbon coating agent increases, the battery's cycling performance decreases. This is because when the mass of the liquid-phase hard carbon coating agent is low, the resulting coating layer is thinner, which reduces solvent co-intercalation and thus improves the battery's cycling performance. However, as the mass of the liquid-phase hard carbon coating agent increases, the coating layer becomes thicker. Due to the increased porosity and side reactions in the coating layer, the battery's cycling performance decreases.

[0318] Example 8

[0319] The preparation process of the battery is the same as that of Example 1 except that the preparation process of the negative electrode active material is different.

[0320] (1) Preparation of negative electrode active materials

[0321] The petroleum needle coke is crushed, shaped and graded to obtain aggregate; the obtained aggregate is mixed with binder asphalt in a mass ratio of 100:8 and placed in a horizontal reactor for heating and granulation. A step-by-step heating and insulation process is adopted during heating. The programmed temperature platforms are set to 200°C, 300°C, and 600°C, respectively. The temperature is maintained at 200°C for 1 hour, 300°C for 2 hours, and 600°C for 2 hours. The mixture is cooled for 3 hours and then taken out of the furnace; the granulated material is placed in an Acheson graphitization furnace for graphitization at 3000°C for about 50 hours to obtain graphite.

[0322] A fusion machine is used to fuse graphite and a liquid hard carbon coating agent in a mass ratio of 100:5. The stirring speed of the fusion machine is 600 r / min, and the stirring time is 7 minutes. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 800, a viscosity of 2000 mPa·s at 25°C, and a solid content of 70%-71%. The product after solid-liquid fusion is placed in a track kiln, heated to 1150°C for carbonization treatment under a nitrogen atmosphere, and kept warm for 6 hours. The product is then cooled to 50°C and taken out of the kiln. After depolymerization, screening and demagnetization treatment, a negative electrode active material is obtained.

[0323] Table 5

[0324] The test results in Table 5 demonstrate that, under the same conditions, adjusting the weight-average molecular weight and / or viscosity of the liquid-phase hard carbon coating agent can adjust the R value (R50), at which the cumulative distribution of the negative electrode active material reaches 50%, as well as the extent of the negative electrode active material being uncoated. When the weight-average molecular weight and / or viscosity of the liquid-phase hard carbon coating agent are within an appropriate range, the extent of the negative electrode active material being uncoated can be minimized, resulting in a higher critical charge rate for the battery and, consequently, improved fast-charging performance.

[0325] Example 9

[0326] The preparation process of the battery is the same as that of Example 1 except that the preparation process of the negative electrode active material is different.

[0327] (1) Preparation of negative electrode active materials

[0328] The petroleum needle coke is crushed, shaped and graded to obtain aggregate; the obtained aggregate is mixed with binder asphalt in a mass ratio of 100:8 and placed in a horizontal reactor for heating and granulation. A step-by-step heating and insulation process is adopted during heating. The programmed temperature platforms are set to 200°C, 300°C, and 600°C, respectively. The temperature is maintained at 200°C for 1 hour, 300°C for 2 hours, and 600°C for 2 hours. The mixture is cooled for 3 hours and then taken out of the furnace; the granulated material is placed in an Acheson graphitization furnace for graphitization at 3000°C for about 50 hours to obtain graphite.

[0329] Graphite and a liquid hard carbon coating agent are fused in a solid-liquid ratio of 100:5 using a fusion machine. The stirring speed of the fusion machine is 350 r / min, and the stirring time is 7 minutes. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 580, a viscosity of 550 mPa·s at 25°C, and a solid content of 70%-71%. The product after solid-liquid fusion is placed in a track kiln, heated to 1150°C under a nitrogen atmosphere for carbonization treatment, and kept warm for 6 hours. The product is then cooled to 50°C and taken out of the kiln. After depolymerization, screening and demagnetization treatment, a negative electrode active material is obtained.

[0330] Example 10

[0331] The preparation process of the battery is the same as that of Example 1 except that the preparation process of the negative electrode active material is different.

[0332] (1) Preparation of negative electrode active materials

[0333] The petroleum needle coke is crushed, shaped and graded to obtain aggregate; the obtained aggregate is mixed with binder asphalt in a mass ratio of 100:8 and placed in a horizontal reactor for heating and granulation. A step-by-step heating and insulation process is adopted during heating. The programmed temperature platforms are set to 200°C, 300°C, and 600°C, respectively. The temperature is maintained at 200°C for 1 hour, 300°C for 2 hours, and 600°C for 2 hours. The mixture is cooled for 3 hours and then taken out of the furnace; the granulated material is placed in an Acheson graphitization furnace for graphitization at 3000°C for about 50 hours to obtain graphite.

[0334] A fusion machine is used to fuse graphite and a liquid hard carbon coating agent in a mass ratio of 100:5. The stirring speed of the fusion machine is 600 r / min, and the stirring time is 5 minutes. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 580, a viscosity of 550 mPa·s at 25°C, and a solid content of 70%-71%. The product after solid-liquid fusion is placed in a track kiln, heated to 1150°C under a nitrogen atmosphere for carbonization treatment, and kept warm for 6 hours. The product is then cooled to 50°C and taken out of the kiln. After depolymerization, screening and demagnetization treatment, a negative electrode active material is obtained.

[0335] Table 6

[0336] The test results in Table 6 demonstrate that, under the same conditions, adjusting the solid-liquid fusion parameters of graphite and the liquid-phase hard carbon coating agent can adjust the degree of uncoated negative electrode active material. Within an appropriate range of solid-liquid fusion parameters, the degree of uncoated negative electrode active material can be minimized. Under the same conditions, a reduced degree of uncoated negative electrode active material can result in a higher critical charge rate for the battery, thereby enhancing fast-charging performance.

[0337] Example 11

[0338] The preparation process of the battery is the same as that of Example 1 except that the preparation process of the negative electrode plate is different.

[0339] (2) Preparation of negative electrode sheet

[0340] The negative electrode active material prepared in Example 1, the thickener sodium carboxymethyl cellulose, the negative electrode binder styrene-butadiene rubber (SBR), and the negative electrode conductive agent Super P were mixed in a mass ratio of 96.9:1.1:1.5:0.5, and deionized water was added as a solvent. The mixture was stirred evenly in a vacuum mixer to prepare a negative electrode slurry.

[0341] The negative electrode slurry was evenly coated on both surfaces of the negative electrode current collector copper foil. The negative electrode current collector coated with the slurry was air-dried at room temperature and then transferred to an oven for drying. The negative electrode sheets were then cold-pressed and slit. The thickness of the negative electrode film on one side of the negative electrode current collector was 58 μm.

[0342] Table 7

[0343] The test results in Table 7 show that by partitioning the negative electrode film layer and making the mass content of the first negative electrode active material in the first negative electrode film layer greater than the mass content of the second negative electrode active material in the second negative electrode film layer, and the mass content of the negative electrode binder in the first negative electrode film layer less than the mass content of the negative electrode binder in the second negative electrode film layer, the battery can have a higher critical charge rate, thereby enabling the battery to have better fast charging performance. This is because the above-mentioned arrangement can reduce the problem of the negative electrode binder floating during the slurry drying process, thereby reducing the negative electrode binder content on the outer surface of the negative electrode film layer, thereby facilitating the liquid phase conduction of ions inside the negative porous electrode and the charge exchange of ions on the surface of the negative electrode active material, thereby enabling the battery to have better fast charging performance.

[0344] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A lithium-ion battery comprising one or more battery cells, wherein the battery cells include a negative electrode plate, wherein: The negative electrode plate includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a core and a coating layer located on at least a portion of the surface of the core, the core includes graphite, and the coating layer includes hard carbon; in the R value cumulative distribution curve of the negative electrode active material obtained in the surface scanning mode of the laser microconfocal Raman spectrometer, starting from the lower limit, the R value R50 with a cumulative distribution of 50% is 0.15-0.

40.

2. The lithium-ion battery according to claim 1, wherein The cumulative distribution of the negative electrode active material has an R value R50 of 50% in the range of 0.20 to 0.

30.

3. The lithium-ion battery according to any one of claims 1 to 2, wherein: Among all R values obtained for the negative electrode active material, the number of R values R50 less than 50% of the cumulative distribution of the core accounts for less than or equal to 10%.

4. The lithium ion battery according to claim 3, wherein Among all R values obtained for the negative electrode active material, the number of R values R50 that are less than 50% of the cumulative distribution of the core accounts for less than or equal to 6%.

5. The lithium ion battery according to any one of claims 1 to 4, wherein: The R value R50 of the core at 50% of the cumulative distribution is less than the R value R50 of the coating layer at 50% of the cumulative distribution; and / or, The cumulative distribution of the coating layer is such that the R value R50 of 50% is 0.9-1.4; and / or, The cumulative distribution of the kernels had a 50% R value R50 of 0.06-0.

13.

6. The lithium-ion battery according to any one of claims 1 to 5, wherein: The mass of the coating layer is 0.3%-4.5% of the mass of the core.

7. The lithium-ion battery according to any one of claims 1 to 6, wherein: The mass of the coating layer is 1%-3.2% of the mass of the core.

8. The lithium ion battery according to any one of claims 1 to 7, wherein: The difference between the volume distribution particle size Dv50 of the negative electrode active material and the volume distribution particle size Dv50 of the core is 1 μm-5.5 μm; and / or, The volume distribution particle size Dv50 of the negative electrode active material is 8 μm-25 μm.

9. The lithium ion battery according to claim 8, wherein The difference between the volume distribution particle size Dv50 of the negative electrode active material and the volume distribution particle size Dv50 of the core is 1.5 μm-4.2 μm; and / or, The volume distribution particle size Dv50 of the negative electrode active material is 12 μm-17 μm.

10. The lithium ion battery according to any one of claims 1 to 9, wherein: The graphite is artificial graphite; and / or, The graphite is in the form of secondary particles; and / or, The graphite has an intensity ratio C(004) / C(110) of 004 crystal plane diffraction peak to 110 crystal plane diffraction peak measured by X-ray diffraction method of 5.5-6.5; and / or, The gram capacity of the negative electrode active material is 354 mAh / g-361 mAh / g; and / or, The powder compaction density of the negative electrode active material under a pressure of 20000N is 1.68g / cm 3 -1.78g / cm 3 and / or, The specific surface area of the negative electrode active material is 1.5 m 2 / g-4.5m 2 / g.

11. The lithium ion battery according to any one of claims 1 to 10, wherein: The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer located between the first negative electrode film layer and the negative electrode current collector, the thickness of the first negative electrode film layer is 30%-60% of the thickness of the negative electrode film layer, the first negative electrode film layer includes a first negative electrode active material, the second negative electrode film layer includes a second negative electrode active material, and the first negative electrode active material includes the negative electrode active material according to any one of claims 1 to 10.

12. The lithium ion battery according to claim 11, wherein The second negative electrode active material includes the negative electrode active material according to any one of claims 1 to 10, the mass content w1 of the first negative electrode active material in the first negative electrode film layer is greater than the mass content w2 of the second negative electrode active material in the second negative electrode film layer; and / or the mass content w1 of the first negative electrode active material in the first negative electrode film layer is greater than or equal to 96.9%, and the mass content w2 of the second negative electrode active material in the second negative electrode film layer is less than 96.9%.

13. The lithium ion battery according to claim 11, wherein The second negative electrode active material includes graphite, the graphite has a secondary particle morphology, and a cumulative distribution of 50% of the R value R50 of the graphite is 0.06-0.

13.

14. The lithium ion battery according to claim 13, wherein The mass content w1 of the first negative electrode active material in the first negative electrode film layer is greater than the mass content w2 of the second negative electrode active material in the second negative electrode film layer; and / or the mass content w1 of the first negative electrode active material in the first negative electrode film layer is greater than or equal to 96.9%, and the mass content w2 of the second negative electrode active material in the second negative electrode film layer is less than 96.9%.

15. The lithium ion battery according to any one of claims 1 to 14, wherein: The compaction density of the negative electrode film layer is 1.62 g / cm 3 -1.80g / cm 3 ; and / or, the thickness of the negative electrode film layer is 45μm-100μm.

16. The lithium ion battery according to claim 15, wherein The compaction density of the negative electrode film layer is 1.65 g / cm 3 -1.80g / cm 3 ; and / or, the thickness of the negative electrode film layer is 70μm-100μm.

17. An electrical device comprising the lithium-ion battery according to any one of claims 1 to 16, wherein the lithium-ion battery is used to provide electrical energy.

18. A negative electrode active material, wherein: The negative electrode active material includes a core and a coating layer located on at least a portion of the surface of the core, the core includes graphite, and the coating layer includes hard carbon; in the R value cumulative distribution curve of the negative electrode active material obtained in the surface scanning mode of a laser microconfocal Raman spectrometer, from the lower limit, the R value R50 with a cumulative distribution of 50% is 0.15-0.

40.

19. A method for preparing a negative electrode active material, comprising the following steps: Provide coke raw materials; The coke raw material is crushed, shaped and graded to obtain aggregate; The obtained aggregate is mixed with a binder and subjected to granulation treatment and graphitization treatment in sequence to obtain graphite; solid-liquid fusion of the obtained graphite and a liquid hard carbon coating agent; The solid-liquid fusion product is carbonized under a protective gas atmosphere so that the liquid phase hard carbon coating agent is carbonized into hard carbon and coated on at least a portion of the surface of the graphite to obtain a negative electrode active material. The negative electrode active material includes a core and a coating layer located on at least a portion of the surface of the core, the core includes graphite, and the coating layer includes hard carbon; in the R value cumulative distribution curve of the negative electrode active material obtained in the surface scanning mode of a laser microconfocal Raman spectrometer, from the lower limit, the R value R50 with a cumulative distribution of 50% is 0.15-0.

40.

20. The preparation method according to claim 19, wherein The coke raw material includes one or more of petroleum-based needle coke and coal-based needle coke; and / or, The temperature of the graphitization treatment is 2800° C.-3800° C.; and / or, The mass of the liquid-phase hard carbon coating agent is 0.7%-10% of the mass of the graphite.

21. The preparation method according to claim 20, wherein The temperature of the graphitization treatment is 2850°C-3300°C; and / or, The mass of the liquid-phase hard carbon coating agent is 3%-7% of the mass of the graphite.

22. The preparation method according to any one of claims 19 to 21, wherein: The liquid-phase hard carbon coating agent includes a liquid resin. The viscosity of the liquid resin at 25° C. is 150 mPa·s to 2000 mPa·s. The solid content of the liquid resin is 50% to 85%.

23. The preparation method according to claim 22, wherein The viscosity of the liquid resin at 25° C. is 300 mPa·s to 900 mPa·s, and the solid content of the liquid resin is 60% to 82%.

24. The preparation method according to any one of claims 22 to 23, wherein: The liquid resin includes at least one of liquid phenolic resin, liquid epoxy resin, liquid vinyl ester resin, liquid unsaturated polyester resin, liquid furan resin, and derivatives thereof.

25. The preparation method according to claim 24, wherein The liquid-phase hard carbon coating agent includes liquid phenolic resin, and the liquid phenolic resin has a solid content of 60%-82% and a weight-average molecular weight of 300-800.

26. The preparation method according to claim 25, wherein The liquid phenolic resin has a solid content of 68%-78% and a weight average molecular weight of 450-700.

27. The preparation method according to any one of claims 19 to 26, wherein: The equipment for solid-liquid fusion of the graphite and the liquid hard carbon coating agent is a fusion machine, the stirring speed of the fusion machine is 350r / min-1000r / min, and the stirring time of solid-liquid fusion is 4min-10min; and / or, The holding temperature of the carbonization treatment is 900° C.-1500° C.; and / or, The heat preservation time of the carbonization treatment is 2h-10h.

28. The preparation method according to claim 27, wherein The stirring speed of the fusion machine is 450r / min-850r / min, and the stirring time of solid-liquid fusion is 6min-8min.

29. A negative electrode sheet, wherein: The negative electrode plate includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a core and a coating layer located on at least a portion of the surface of the core, the core includes graphite, and the coating layer includes hard carbon; in the R value cumulative distribution curve of the negative electrode active material obtained in the surface scanning mode of the laser microconfocal Raman spectrometer, starting from the lower limit, the R value R50 with a cumulative distribution of 50% is 0.15-0.40.

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