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 amorphous 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, the concentration degree of the R value is less than or equal to 2.0.

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. 202410129832.7 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, which limits its practical application. Therefore, how to make the battery have good fast charging 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 both high energy density and good kinetic 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 amorphous carbon; in an R value cumulative distribution curve of the negative electrode active material obtained in a surface scanning mode of a laser microconfocal Raman spectrometer, the concentration of R values ​​is less than or equal to 2.0.

[0007] The core of the negative electrode active material includes graphite, the coating layer includes amorphous carbon, and the concentration of the R value of the negative electrode active material is less than or equal to 2.0. The negative electrode active material meets this condition, which means that the coating layer has better consistency and can be more evenly coated on the surface of the core, so that lithium ions can be quickly embedded in all directions of the negative electrode active material, thereby better improving 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 and the battery. Therefore, the negative electrode active material provided in the embodiment of the present application is used in a battery, which can enable the battery to have both high energy density and good kinetic performance.

[0008] In some embodiments, the concentration of the R value of the negative electrode active material is less than or equal to 1.7, thereby further improving the kinetic performance of the negative electrode active material and the battery.

[0009] In some embodiments, the coating layer comprises hard carbon.

[0010] In some embodiments, the negative electrode active material has an R value (R50) of 0.15-0.42, optionally 0.20-0.30. The R value of the negative electrode active material can characterize the degree of defect and disorder in the negative electrode active material. When the R value (R50) of the negative electrode active material is within the above range, the charge exchange capacity of ions on the surface of the negative electrode active material is enhanced while also minimizing side reactions on the surface of the negative electrode active material particles. This contributes to the battery having high energy density, good kinetic performance, and long cycle life.

[0011] In some embodiments, the R value R50 at 50% of the cumulative distribution of the core is less than the R value R50 at 50% of the cumulative distribution of the coating layer. A large R value R50 at 50% of the cumulative distribution of the negative electrode active material coating layer and a high degree of disorder can make the negative electrode active material and the battery have good kinetic performance; a small R value R50 at 50% of the cumulative distribution of the core of the negative electrode active material and a low degree of disorder can make the negative electrode active material as a whole have a higher gram capacity and the battery have a higher energy density.

[0012] In some embodiments, the coating layer has an R value (R50) of 0.55-1.6, optionally 1.0-1.4, at a cumulative distribution of 50%. When the R value (R50) of the coating layer is within this range, the coating layer itself can have good kinetic properties, thereby improving the kinetic properties of the negative electrode active material and the battery. Furthermore, the negative electrode active material can have fewer battery side reactions, resulting in good battery cycling performance.

[0013] In some embodiments, the coating layer has an R value concentration of 0.06-0.33, optionally 0.13-0.25. The coating layer having an R value concentration within the above range can reduce the R value concentration of the negative electrode active material, thereby improving the consistency of the coating layer and the charge exchange capacity of ions on the surface of the negative electrode active material, thereby improving the kinetic performance of the battery.

[0014] In some embodiments, the core has an R value R50 of 0.06-0.14, optionally 0.07-0.11. When the core has an R value R50 of 50% in the cumulative distribution within the above range, the battery can have both high energy density and good kinetic performance.

[0015] 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.

[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 1.2 μm-6 μm, and optionally 1.8 μm-4.5 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 mass of the coating layer is 0.3%-5%, and optionally 1%-3.5% of the mass of the core. A coating layer mass ratio within the above range is beneficial for the battery to have high energy density, good dynamic performance, and long cycle life.

[0018] In some embodiments, the core has a coating layer on 90% to 100% of its surface, and optionally, on 92% to 100% of its surface. This allows the coating layer to be more evenly coated on the core surface, thereby improving the charge exchange capacity of ions on the surface of the negative electrode active material, thereby further improving the kinetic performance of the negative electrode active material and the battery.

[0019] 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.

[0020] 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.

[0021] In some embodiments, the graphite has an intensity ratio of the 004 crystal plane diffraction peak to the 110 crystal plane diffraction peak, as measured by X-ray diffraction, of 2-6.5. When this ratio is relatively low, the graphite is highly isotropic, and graphite particles have lithium ion insertion openings in all directions, thereby facilitating rapid lithium ion insertion and, in turn, improving battery kinetic performance.

[0022] In some embodiments, the negative electrode active material has a gram capacity of 354 mAh / g to 360 mAh / g.

[0023] In some embodiments, the powder compaction density of the negative electrode active material under a pressure of 20000N is 1.63g / cm 3 -1.77g / cm 3 .

[0024] In some embodiments, the specific surface area of ​​the negative electrode active material is 1.5 m 2 / g-5m 2 / g.

[0025] 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.

[0026] 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.

[0027] 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%, thereby enabling the battery to have a higher energy density.

[0028] In some embodiments, the second negative electrode active material includes graphite, the graphite has a secondary particle morphology, and a cumulative distribution of 50% R value R50 of the graphite is 0.06-0.14.

[0029] 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.

[0030] 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%.

[0031] 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.

[0032] In some embodiments, the compaction density of the negative electrode film layer is 1.60 g / cm 3 -1.80g / cm 3 , optional 1.65g / cm 3 -1.80g / cm 3 .

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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 amorphous carbon; in a cumulative distribution curve of R values ​​obtained by the negative electrode active material in a surface scanning mode of a laser microconfocal Raman spectrometer, the concentration of R values ​​is less than or equal to 2.0.

[0037] In a fourth aspect, the present application provides a method for preparing a negative electrode active material, comprising the following steps: providing graphite; solid-liquid fusion of the graphite and a liquid-phase coating agent; carbonizing the product after the solid-liquid fusion under a protective gas atmosphere so that the liquid-phase coating agent is carbonized into amorphous 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 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 amorphous 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, the concentration of the R value is less than or equal to 2.0.

[0038] In the preparation method provided in the embodiments of the present application, a liquid-phase coating agent is used to form a solid-liquid fusion with graphite. Due to the good fluidity of the liquid-phase coating agent, it can be evenly distributed on the surface of the graphite particles, improving the consistency of the coating layer. At the same time, the concentration of the R value of the negative electrode active material can be reduced, 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. Therefore, the negative electrode active material prepared by the preparation method provided in the embodiments of the present application can enable the battery to have both high energy density and good kinetic performance.

[0039] In some embodiments, the liquid coating agent is a liquid hard carbon coating agent.

[0040] 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 to 2500 mPa·s, and the solid content of the liquid resin is 50% to 88%.

[0041] Optionally, the viscosity of the liquid resin at 25° C. is 300 mPa·s-950 mPa·s, and the solid content of the liquid resin is 60%-85%.

[0042] 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. As a result, the liquid resin can be evenly dispersed on the surface of the graphite particles, thereby making the consistency of the coating layer better and the concentration of the R value of the negative electrode active material smaller, thereby better improving the kinetic performance of the negative electrode active material and the battery.

[0043] 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. As a result, the liquid resin can be evenly dispersed on the surface of the graphite particles, thereby making the consistency of the coating layer better and the concentration of the R value of the negative electrode active material smaller, thereby better improving the kinetic performance of the negative electrode active material and the battery.

[0044] 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.

[0045] In some embodiments, the liquid hard carbon coating agent includes liquid phenolic resin, the liquid phenolic resin has a weight average molecular weight of 300-900, a solid content of 60%-85%, a free phenol mass content of less than or equal to 9%, and a free aldehyde mass content of less than or equal to 0.5%.

[0046] Optionally, the liquid phenolic resin has a weight average molecular weight of 500-700, a solid content of 70%-78%, a free phenol content of less than or equal to 6.5%, and a free aldehyde content of 0.

[0047] Compared with other liquid resins, the hard carbon formed by the carbonization and coking of liquid phenolic resin itself has better performance, which can reduce the concentration of the R value of the negative electrode active material, and thus better improve the kinetic performance of the negative electrode active material and the battery.

[0048] The weight-average molecular weight of the liquid phenolic resin is within the above range, which can make the liquid phenolic resin have good fluidity and diffusibility, as well as good curing effect and coating effect. As a result, the liquid phenolic resin can be evenly dispersed on the surface of the graphite particles, thereby making the consistency of the coating layer better and the concentration of the R value of the negative electrode active material smaller, thereby better improving the kinetic performance of the negative electrode active material and the battery.

[0049] The mass content of free phenol in the liquid phenolic resin is within the above range, which can reduce the escape of free phenol during the carbonization treatment, reduce local defects on the surface of the coating layer, and reduce the specific surface area of ​​the negative electrode active material. This can improve the consistency of the coating layer, improve the particle consistency of the negative electrode active material, and reduce the concentration of the R value of the negative electrode active material, thereby better improving the kinetic performance of the negative electrode active material and the battery.

[0050] In some embodiments, the carbonization treatment includes a heating stage, a heat holding stage, and a cooling stage. The heating rate of the carbonization heating stage is 1.3°C / min-3°C / min, and may be 1.5°C / min-2.5°C / min. A slow heating rate during the carbonization treatment allows the liquid hard carbon coating to fully solidify and evenly distribute the coating on the surface of the graphite particles. This improves the consistency of the coating layer and reduces the concentration of the R value of the negative electrode active material, thereby improving the kinetic performance of the negative electrode active material and the battery.

[0051] In some embodiments, the cooling rate of the carbonization cooling stage is 1.2°C / min-3.7°C / min, and optionally 1.5°C / min-2.7°C / min. Using a slow cooling rate during the carbonization treatment can reduce the problem of excessive agglomeration of the finished particles.

[0052] In some embodiments, the insulation temperature of the carbonization treatment insulation section is 900° C.-1500° C.; and / or the insulation time of the carbonization treatment insulation section is 2 h-10 h.

[0053] In some embodiments, the device for solid-liquid fusion of the graphite and the liquid hard carbon coating agent is a fusion machine, and the stirring speed of the fusion machine is 300r / min-1000r / min; and / or the stirring time of solid-liquid fusion is 3min-8min.

[0054] As the stirring speed of the fusion machine increases, the distribution uniformity of the liquid hard carbon coating agent on the surface of the graphite particles is improved.

[0055] As the stirring time of solid-liquid fusion increases, the distribution uniformity of the liquid hard carbon coating agent on the surface of the graphite particles is improved.

[0056] 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 amorphous carbon; in the cumulative distribution curve of R values ​​of the negative electrode active material obtained in the surface scanning mode of a laser microconfocal Raman spectrometer, the concentration of R values ​​is less than or equal to 2.0. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] 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.

[0058] FIG1 is a schematic diagram of a battery cell provided in some embodiments of the present application.

[0059] FIG2 is a schematic diagram of a battery module provided in some embodiments of the present application.

[0060] FIG3 is a schematic diagram of a battery pack provided in some embodiments of the present application.

[0061] FIG4 is an exploded schematic diagram of the battery pack shown in FIG3 .

[0062] FIG5 is an exploded schematic diagram of a battery cell provided in some embodiments of the present application.

[0063] FIG6 is a schematic diagram of an electrical device provided in some embodiments of the present application.

[0064] In the accompanying drawings, the drawings are not necessarily drawn to scale.

[0065] 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

[0066] 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.

[0067] " 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] In this application, the terms "plurality" and "multiple" refer to two or more.

[0072] Unless otherwise specified, the terms used in this application have the common meanings that are commonly understood by those skilled in the art.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] The battery provided in the embodiments of the present application may include a lithium-ion battery.

[0083] 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.

[0084] 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).

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] Graphite is currently the most commonly used negative electrode active material, but its kinetic properties are not very good. By coating the graphite surface with a layer of amorphous carbon material, the high degree of disorder of amorphous carbon facilitates the intercalation and deintercalation of lithium ions, thereby improving the kinetic properties of the negative electrode active material to a certain extent. However, the kinetic properties of the negative electrode active materials currently prepared still cannot meet the current demand for high-rate and fast-charging batteries, and further improvement is needed.

[0090] In view of this, an embodiment of the present application provides a negative electrode active material, which can improve the kinetic performance of the negative electrode active material by optimizing the performance of the core and the coating layer.

[0091] 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, the coating layer includes amorphous carbon, and the concentration of the R value in the R value cumulative distribution curve obtained by the laser microconfocal Raman spectrometer surface scanning mode is less than or equal to 2.0.

[0092] 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.

[0093] Raman spectra of various carbon materials can be obtained using a laser microconfocal Raman spectrometer with a laser wavelength of 532 nm. During testing, an appropriate amount of sample is taken and its surface is scanned in all directions. The scanning area is 100 μm × 100 μm, the step size is 2 μm, and the total number of scanning points is 2500. This allows the R value and R value cumulative distribution curve to be obtained at different locations.

[0094] The concentration of R values ​​is expressed as (R90 - R10) / R50, where R90 is the R value that represents the 90th percentile of the cumulative distribution from the lower limit, R10 is the R value that represents the 10th percentile of the cumulative distribution from the lower limit, and R50 is the R value that represents the 50th percentile of the cumulative distribution from the lower limit. Specifically, the 2500 R values ​​obtained are arranged in ascending order: R10 is the R value corresponding to the 10th percentile, R50 is the R value corresponding to the 50th percentile, and R90 is the R value corresponding to the 90th percentile. The test instrument can be a high-precision Renishaw laser confocal Raman microscope.

[0095] 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.

[0096] The core material sample can be obtained by sampling during the process of preparing the negative electrode active material.

[0097] The R value and R value concentration of the coating layer refer to the properties of the amorphous carbon material itself, formed by carbonizing the precursor compound used to prepare the coating layer material. A coating layer material sample can be obtained by taking an appropriate amount of the precursor compound used to prepare the coating layer material (e.g., the liquid 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 a coating layer material sample.

[0098] The R value concentration of the negative electrode active material is small, the R value distribution width is narrow, and the concentration is good.

[0099] The core of the negative electrode active material includes graphite, the coating layer includes amorphous carbon, and the concentration of the R value of the negative electrode active material is less than or equal to 2.0. The negative electrode active material meets this condition, which means that the consistency of the coating layer is better, and the coating layer can be more evenly coated on the surface of the core, so that the negative electrode active material can be quickly embedded with lithium ions in all directions, thereby better improving the charge exchange capacity of ions on the surface of the negative electrode active material, and then further improving the kinetic performance of the negative electrode active material and the battery. The kinetic performance of the negative electrode active material is good, and when the battery is quickly charged, the negative electrode is not prone to lithium plating problems. Therefore, the negative electrode active material provided in the embodiment of the present application is used in a battery, which can make the battery have both high energy density and good kinetic performance.

[0100] Alternatively, the concentration of R values ​​of the negative electrode active material may be less than or equal to 1.8, less than or equal to 1.7, less than or equal to 1.6, less than or equal to 1.5, or less than or equal to 1.4.

[0101] This can further improve the kinetic performance of negative electrode active materials and batteries.

[0102] The critical charging rate of the battery of the present application without lithium deposition is greater than or equal to 3.4C, that is, the battery of the present application is a fast-charging battery above 3.4C. The time for charging the battery from 0% SOC to 100% SOC is within 17.65 minutes, which can better meet the current demand for fast charging.

[0103] 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.

[0104] In some embodiments, the coating layer comprises hard carbon.

[0105] In some embodiments, the R value R50 at which the cumulative distribution of the negative electrode active material is 50% can be 0.15-0.42, for example, 0.15, 0.18, 0.20, 0.22, 0.24, 0.26, 0.28, 0.30, 0.32, 0.34, 0.36, 0.38, 0.40, 0.42, or any range thereof. Alternatively, the R value R50 at which the cumulative distribution of the negative electrode active material is 50% can be 0.20-0.42, 0.20-0.4, 0.20-0.38, 0.20-0.36, 0.20-0.34, 0.20-0.32, or 0.20-0.30.

[0106] 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.

[0107] It can be understood that when the concentration of the R value 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% 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, and the kinetic performance of the negative electrode active material and the battery is good. However, due to the high degree of defect of 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.

[0108] The cumulative distribution of the negative electrode active material is 50% of the R value R50 within the above range, which can not only improve the charge exchange capacity of ions on the surface of the negative electrode active material, but also keep the side reactions on the surface of the negative electrode active material particles at a lower level, thereby benefiting the battery to have high energy density, good kinetic performance and long cycle life.

[0109] In some embodiments, the R-value R50 at 50% of the cumulative distribution of the core is less than the R-value R50 at 50% of the cumulative distribution of the cladding.

[0110] 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.

[0111] The R value R50 at which the cumulative distribution of the coating layer is 50% and the concentration of the R values ​​refer to the properties of the amorphous carbon material, such as the hard carbon material itself, formed by carbonizing the precursor compound used to prepare the coating layer material.

[0112] In certain embodiments, the cumulative distribution of coating is that 50% R value R50 can be 0.55-1.6, for example, can be 0.55, 0.7, 0.8, 0.9, 1.0, 1.04, 1.08, 1.11, 1.14, 1.17, 1.22, 1.25, 1.29, 1.32, 1.35, 1.4, 1.5, 1.6 or the scope of above-mentioned arbitrary numerical value composition. Alternatively, the cumulative distribution of coating is that 50% R value R50 can be 0.8-1.4, 1.0-1.4.

[0113] The cumulative distribution of the coating layer is 50% of the R value R50 within the above range. The coating layer itself can have 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 fewer battery side reactions, so that the battery has good cycle performance.

[0114] In some embodiments, the concentration of the R value of the coating layer can be 0.06-0.33, for example, 0.06, 0.08, 0.10, 0.13, 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, 0.28, 0.30, 0.33 or the range of any of the above values. Alternatively, the concentration of the R value of the coating layer can be 0.06-0.30, 0.10-0.25, 0.13-0.25.

[0115] The concentration of the R value of the coating layer is within the above range, which can make the concentration of the R value of the negative electrode active material smaller, thereby improving the consistency of the coating layer and the charge exchange capacity of ions on the surface of the negative electrode active material, thereby improving the kinetic performance of the battery.

[0116] In some embodiments, the R value R50 at which the cumulative distribution of the kernel is 50% can be 0.06-0.14, for example, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, or a range consisting of any of the above values. Alternatively, the R value R50 at which the cumulative distribution of the kernel is 50% can be 0.07-0.11.

[0117] 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.

[0118] In some embodiments, the mass of the coating layer can be 0.3%-5% of the mass of the core, for example, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range thereof. Alternatively, the mass of the coating layer can be 1%-3.5% of the mass of the core.

[0119] The quality of the coating layer affects the thickness of the coating layer, and also affects the R value R50 (50% cumulative distribution) and the concentration of the R value of the negative electrode active material.

[0120] 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.

[0121] A coating layer mass percentage within the above range can improve the consistency of the coating layer, thereby enhancing the charge exchange capacity of ions on the surface of the negative electrode active material. It can also reduce side reactions on the surface of the negative electrode active material particles, resulting in a higher specific capacity of the negative electrode active material. Therefore, a coating layer mass percentage within the above range is conducive to batteries with high energy density, good kinetic performance, and long cycle life.

[0122] 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 1.2 μm-6 μm, for example, 1.2 μm, 1.5 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, 6 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 1.8 μm-4.5 μm, or 2.2 μm-4 μm.

[0123] 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.

[0124] In some embodiments, the coating layer covers 90% to 100% of the surface of the core, optionally 92% to 100% of the surface of the core, and more optionally 94% to 100% of the surface of the core. Thus, the coating layer can be more evenly coated on the surface of the core, thereby improving the charge exchange capacity of ions on the surface of the negative electrode active material, thereby further improving the kinetic performance of the negative electrode active material and the battery.

[0125] 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.

[0126] 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.

[0127] The graphite is artificial graphite. The core includes artificial graphite, which can make the battery have high energy density and good cycle performance.

[0128] 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.

[0129] In some embodiments, the intensity ratio of the 004 crystal plane diffraction peak to the 110 crystal plane diffraction peak of the graphite measured by X-ray diffraction may be 2-6.5.

[0130] 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.

[0131] 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 D8Discover). 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.

[0132] In some embodiments, the gram capacity of the negative electrode active material can be 354 mAh / g to 360 mAh / g.

[0133] 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 3 A 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.

[0134] In some embodiments, the powder compaction density of the negative electrode active material under a pressure of 20,000 N can be 1.63 g / cm 3 -1.77g / cm3 , optional 1.73g / cm 3 -1.77g / cm 3 .

[0135] 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 through ρ = m / (s*h). During the test, the pressure was 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.

[0136] In some embodiments, the specific surface area of ​​the negative electrode active material can be 1.5 m 2 / g-5m 2 / g.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] The preparation method includes the following steps: providing graphite; performing solid-liquid fusion of the graphite and a liquid-phase coating agent; and carbonizing the solid-liquid fusion product under a protective gas atmosphere so that the liquid-phase coating agent is carbonized into amorphous carbon and coated on at least a portion of the surface of the graphite, thereby obtaining 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 amorphous carbon. The negative electrode active material has an R value cumulative distribution curve obtained in a surface scanning mode of a laser microconfocal Raman spectrometer, and the concentration of the R value is less than or equal to 2.0.

[0141] In the preparation method provided in the embodiment of the present application, a liquid-phase coating agent is used to perform solid-liquid fusion with graphite. Since the liquid-phase coating agent has good fluidity, it can be evenly distributed on the surface of the graphite particles, thereby improving the consistency of the coating layer. At the same time, the concentration of the R value of the negative electrode active material can be made smaller, 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.

[0142] 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 both high energy density and good kinetic performance.

[0143] In some embodiments, the liquid-phase capping agent is a liquid-phase hard carbon capping agent.

[0144] Graphite and a liquid-phase hard carbon coating agent are subjected to a solid-liquid fusion process; 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, thereby obtaining a negative electrode active material. The negative electrode active material comprises a core and a coating layer located on at least a portion of the surface of the core, wherein the core comprises graphite and the coating layer comprises hard carbon. The negative electrode active material has an R value concentration of less than or equal to 2.0 in a cumulative distribution curve of R values ​​obtained using a laser microconfocal Raman spectrometer in a surface scanning mode.

[0145] 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.

[0146] 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.

[0147] In some embodiments, the viscosity of the liquid resin at 25° C. may be 150 mPa·s to 2500 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, 850 mPa·s, 950 mPa·s, 1050 mPa·s, 1200 mPa·s, 1400 mPa·s, 1600 mPa·s, 1800 mPa·s, 2000 mPa·s, 2250 mPa·s, 2500 mPa·s, or a range consisting of any of the foregoing values. Alternatively, the viscosity of the liquid resin at 25° C. may be 300 mPa·s to 950 mPa·s.

[0148] 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.

[0149] 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. As a result, the liquid resin can be evenly dispersed on the surface of the graphite particles, thereby making the consistency of the coating layer better and the concentration of the R value of the negative electrode active material smaller, thereby better improving the kinetic performance of the negative electrode active material and the battery.

[0150] In some embodiments, the solid content of the liquid resin may be 50%-88%, optionally 60%-85%.

[0151] 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.

[0152] 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. As a result, the liquid resin can be evenly dispersed on the surface of the graphite particles, thereby making the consistency of the coating layer better and the concentration of the R value of the negative electrode active material smaller, thereby better improving the kinetic performance of the negative electrode active material and the battery.

[0153] 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.

[0154] 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.

[0155] In some embodiments, the liquid hard carbon coating agent includes liquid phenolic resin, the weight average molecular weight of the liquid phenolic resin can be 300-900, the solid content can be 60%-85%, the mass content of free phenol can be less than or equal to 9%, and the mass content of free aldehyde can be less than or equal to 0.5%.

[0156] Optionally, the weight average molecular weight of the liquid phenolic resin may be 500-700, the solid content may be 70%-78%, the mass content of free phenol may be less than or equal to 6.5%, and the mass content of free aldehyde may be less than or equal to 0.2%.

[0157] Optionally, the weight average molecular weight of the liquid phenolic resin may be 500-700, the solid content may be 70%-78%, the mass content of free phenol may be less than or equal to 6.5%, and the mass content of free aldehyde may be 0.

[0158] The weight-average molecular weight of the liquid phenolic resin can be measured using gel permeation chromatography (GPC). The instrument used may be an Agilent 1290 Infinity II GPC system. The eluent may be tetrahydrofuran (THF), and polystyrene standards may be used for calibration.

[0159] The content of free phenol in liquid phenolic resin can be tested with reference to GB / T 30773-2014.

[0160] The free formaldehyde content in liquid phenolic resin can be tested by potentiometric titration with reference to GB / T 32684-2016.

[0161] Compared with other liquid resins, the hard carbon formed by the carbonization and coking of liquid phenolic resin itself has better performance, which can reduce the concentration of the R value of the negative electrode active material, and thus better improve the kinetic performance of the negative electrode active material and the battery.

[0162] The weight-average molecular weight of the liquid phenolic resin is within the above range, which can make the liquid phenolic resin have good fluidity and diffusibility, as well as good curing effect and coating effect. As a result, the liquid phenolic resin can be evenly dispersed on the surface of the graphite particles, thereby making the consistency of the coating layer better and the concentration of the R value of the negative electrode active material smaller, thereby better improving the kinetic performance of the negative electrode active material and the battery.

[0163] Free phenol is a small molecule, which can easily escape during the carbonization process and form local defects on the surface of the coating layer.

[0164] The mass content of free phenol in the liquid phenolic resin is within the above range, which can reduce the escape of free phenol during the carbonization treatment, reduce local defects on the surface of the coating layer, and reduce the specific surface area of ​​the negative electrode active material. This can improve the consistency of the coating layer, improve the particle consistency of the negative electrode active material, and reduce the concentration of the R value of the negative electrode active material, thereby better improving the kinetic performance of the negative electrode active material and the battery.

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

[0168] The coking value of the liquid-phase hard carbon coating agent is within the above range, and a larger amount of liquid-phase hard carbon coating agent can be used for solid-liquid fusion, thereby making the liquid-phase hard carbon coating agent uniformly dispersed on the surface of the graphite particles, thereby making the consistency of the coating layer better and the concentration of the R value of the negative electrode active material smaller, thereby improving the kinetic performance of the negative electrode active material and the battery.

[0169] 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.

[0170] In some embodiments, the mass of the liquid-phase hard carbon coating agent may be 1% to 10% of the mass of the graphite, for example, 1%, 1.8%, 2.5%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any range thereof. Alternatively, the mass of the liquid-phase hard carbon coating agent may be 3.5% to 7% of the mass of the graphite.

[0171] 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.

[0172] The mass proportion of the liquid-phase hard carbon coating agent is within the above range, which can make more surfaces of the inner core have a coating layer, improve the consistency of the coating layer, and improve the charge exchange ability of ions on the surface of the prepared negative electrode active material. It can also make the side reactions on the surface of the prepared negative electrode active material particles at a lower level, so that the prepared negative electrode active material has a higher gram capacity, which is beneficial for the battery to have high energy density, good kinetic performance and long cycle life.

[0173] In some embodiments, the device for performing solid-liquid fusion of graphite and liquid coating agent may be a fusion machine.

[0174] Optionally, the stirring speed of the fusion machine can be 300r / min-1000r / min, for example, it can be 300r / min, 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.

[0175] As the stirring speed of the fusion machine increases, the distribution uniformity of the liquid-phase coating agent, such as the liquid-phase hard carbon coating agent, on the surface of the graphite particles is improved, and the consistency of the coating layer is improved; however, an excessively fast stirring speed may break the structure of the graphite and may also cause the loss of the liquid-phase coating agent, such as the liquid-phase hard carbon coating agent. For example, part of the liquid-phase hard carbon coating agent may adhere to the inner wall of the fusion machine.

[0176] Optionally, the stirring time for solid-liquid fusion can be 3 min-8 min, for example, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, or a range consisting of any of the above values.

[0177] As the stirring time of solid-liquid fusion increases, the distribution uniformity of liquid coating agents, such as liquid hard carbon coating agents, on the surface of graphite particles is improved, and the consistency of the coating layer is improved; however, if the stirring time is too long, the gain in improvement effect is not obvious, and energy consumption will also increase.

[0178] In some embodiments, the carbonization treatment equipment may be a rail kiln.

[0179] The carbonization treatment includes a temperature rising section, a temperature holding section and a temperature falling section.

[0180] In some embodiments, the holding temperature of the carbonization treatment holding section 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 holding section may be 1050° C.-1350° C.

[0181] In some embodiments, the holding time of the carbonization treatment holding section 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 any range thereof. Alternatively, the holding time of the carbonization treatment holding section can be 5 hours to 8 hours. The holding time of the carbonization treatment refers to the residence time at the holding temperature.

[0182] In some embodiments, the heating rate of the carbonization heating stage may be 1.3° C. / min-3° C. / min, or optionally 1.5° C. / min-2.5° C. / min.

[0183] Using a slow heating rate during carbonization allows the liquid-phase coating agent, such as a liquid-phase hard carbon coating agent, to fully solidify and evenly distribute the coating agent, such as a liquid-phase hard carbon coating agent, on the graphite particle surface. This improves the consistency of the coating layer, reduces the concentration of R values ​​in the negative electrode active material, and thus enhances the kinetic performance of the negative electrode active material and the battery. However, if the carbonization heating rate is too slow, the improvement in the uniformity of the distribution of the liquid-phase coating agent, such as a liquid-phase hard carbon coating agent, on the graphite surface is not significant, and energy consumption may also increase.

[0184] In some embodiments, the cooling rate of the carbonization cooling stage may be 1.2° C. / min-3.7° C. / min, and may be optionally 1.5° C. / min-2.7° C. / min.

[0185] Using a slow cooling rate during carbonization can reduce the problem of excessive agglomeration of the finished particles. If the cooling rate of carbonization is too slow, it will increase energy consumption.

[0186] In some embodiments, the preparation method may further include the steps of: deagglomerating, screening and demagnetizing the carbonized material.

[0187] 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.

[0188] In some embodiments, the method for preparing graphite may include the following steps: providing 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.

[0189] Coke raw materials are typically large in particle size, and crushing can reduce this size. Crushing leaves the raw materials with uneven surfaces, and shaping can make the particles more rounded. Classification can reduce the content of oversized and undersized particles and further adjust the particle size and distribution of the raw materials.

[0190] Alternatively, the coke raw material may include one or more of petroleum-based non-needle coke, petroleum-based needle coke, coal-based non-needle coke, and coal-based needle coke. Needle coke is an anisotropic material that helps 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. Non-needle coke can reduce the C(004) / C(110) ratio of the core material and improve the kinetic performance of the negative electrode active material.

[0191] 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.

[0192] Alternatively, the binder may comprise asphalt.

[0193] The equipment used for the granulation process may include either a horizontal reactor or a vertical reactor.

[0194] 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.

[0195] Optionally, 2-4 programmed temperature rising platforms can be set during the heating process.

[0196] The equipment used for graphitization treatment may include any one of an Acheson graphitization furnace, a box furnace or an internal channeling furnace.

[0197] Optionally, the temperature of the graphitization treatment may be 2800°C-3600°C, for example, 2800°C, 2900°C, 3000°C, 3100°C, 3200°C, 3300°C, 3400°C, 3500°C, 3600°C, or any range thereof. More preferably, the temperature of the graphitization treatment may be 2800°C-3200°C. The specific time of the graphitization treatment may be reasonably selected according to the equipment used.

[0198] High graphitization temperature and long graphitization treatment time result in high specific capacity of graphite, low disorder, and small R value (R50) of 50% cumulative distribution of graphite. By selecting the appropriate graphitization treatment temperature, the battery can achieve both high energy density and good kinetic performance.

[0199] [Negative electrode]

[0200] The battery cell includes a negative electrode plate.

[0201] 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.

[0202] 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).

[0203] 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 both high energy density and good kinetic performance.

[0204] 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.

[0205] 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.

[0206] 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).

[0207] 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.

[0208] 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.

[0209] 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.

[0210] 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.

[0211] 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.

[0212] 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 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 both high energy density and good kinetic performance.

[0213] 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.

[0214] 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.

[0215] 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.

[0216] Optionally, the mass content w1 of the first 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%.

[0217] 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%.

[0218] In some alternative embodiments, the second negative electrode active material may include graphite, which has a secondary particle morphology and a cumulative distribution of 50% R value (R50) of 0.06-0.14. 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 does not have a coating layer, thereby enabling the battery to have a higher energy density.

[0219] 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.

[0220] 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.

[0221] 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%.

[0222] 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%.

[0223] In some embodiments, the compaction density of the negative electrode film layer can be 1.60 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.

[0224] 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.

[0225] 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.

[0226] 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.

[0227] [Positive electrode]

[0228] The battery cell includes a positive electrode plate.

[0229] 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.

[0230] 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.

[0231] 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.

[0232] 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.

[0233] 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.

[0234] 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.

[0235] 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.

[0236] 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.

[0237] 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).

[0238] 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).

[0239] 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).

[0240] [Electrolytes]

[0241] 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).

[0242] In some embodiments, the electrolyte is an electrolyte solution including an electrolyte salt and a solvent.

[0243] 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).

[0244] 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).

[0245] 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.

[0246] [Isolation film]

[0247] 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.

[0248] 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.

[0249] 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.

[0250] 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.

[0251] Electrical devices

[0252] 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.

[0253] 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.

[0254] 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.

[0255] 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.

[0256] Example

[0257] 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.

[0258] Example 1

[0259] (1) Preparation of negative electrode active materials

[0260] 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 2900°C to obtain graphite.

[0261] Graphite and a liquid hard carbon coating agent are fused in a fusion machine at a mass ratio of 100:5. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 600, a viscosity of 680 mPa·s at 25°C, a solid content of 73%-74%, a free phenol content of 6.5%, and a free aldehyde content of 0. The product after solid-liquid fusion is placed in a track kiln and carbonized at a rate of 2.18°C / min to 1150°C under a nitrogen atmosphere for 370 minutes. After carbonization, the product is cooled to 50°C at a rate of 2.04°C / min and removed from the kiln. The product is then depolymerized, sieved, and demagnetized to obtain a negative electrode active material.

[0262] (2) Preparation of negative electrode sheet

[0263] 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.

[0264] 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.

[0265] 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.

[0266] (3) Preparation of positive electrode sheet

[0267] 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.

[0268] (4) Preparation of electrolyte

[0269] 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.

[0270] (5) Preparation of isolation membrane

[0271] Use 12 micron polyethylene film.

[0272] (6) Preparation of batteries (full batteries)

[0273] 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.

[0274] Comparative Example 1

[0275] 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.

[0276] (1) Preparation of negative electrode active materials

[0277] 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 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 2900°C, and then sieving and demagnetizing to obtain graphite as a negative electrode active material.

[0278] Comparative Example 2

[0279] 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.

[0280] (1) Preparation of negative electrode active materials

[0281] 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 2900°C to obtain graphite.

[0282] A fusion machine is used to mix graphite and a solid-phase coating agent in a mass ratio of 100:4.5. The solid-phase coating agent is asphalt with a softening point between 200°C and 300°C. The product after solid-solid fusion is placed in a track kiln and heated to 1150°C at a rate of 2.85°C / min under a nitrogen atmosphere for carbonization treatment. The heat preservation time is 370 minutes. After the end, the temperature is lowered to 50°C at a rate of 2.04°C / min and then taken out of the kiln. Then, it is depolymerized, screened and demagnetized to obtain the negative electrode active material.

[0283] Comparative Example 3

[0284] 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.

[0285] (1) Preparation of negative electrode active materials

[0286] 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 2900°C to obtain graphite.

[0287] Graphite and a liquid hard carbon coating agent are fused in a fusion machine at a mass ratio of 100:5. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 950, a viscosity of 3050 mPa·s at 25°C, a solid content of 73%-74%, a free phenol content of 6.5%, and a free aldehyde content of 0. The product after solid-liquid fusion is placed in a track kiln and carbonized at a temperature of 3.2°C / min to 1150°C under a nitrogen atmosphere for 370 minutes. After carbonization, the product is cooled to 50°C at a temperature of 2.04°C / min and removed from the kiln. The product is then depolymerized, sieved, and demagnetized to obtain a negative electrode active material.

[0288] Performance test of liquid phase hard carbon coating agent

[0289] 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.

[0290] 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.

[0291] The weight-average molecular weight of liquid phenolic resin was determined using gel permeation chromatography (GPC) using an Agilent 1290 Infinity II GPC system. Tetrahydrofuran was used as the eluent, and polystyrene standards were used for calibration.

[0292] The content of free phenol in liquid phenolic resin is tested with reference to GB / T 30773-2014.

[0293] The free formaldehyde content in liquid phenolic resin was tested by potentiometric titration with reference to GB / T 32684-2016.

[0294] Performance testing of negative electrode active materials and batteries

[0295] (1) Raman spectroscopy test of negative electrode active materials

[0296] The test instrument is a high-precision Renishaw laser microscope confocal Raman spectrometer with a laser wavelength of 532nm.

[0297] 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 wavelength of the D peak is 1350±50cm - 1 , the G peak wavelength is 1585±50cm -1 R90 is the R value at which the cumulative distribution from the lower limit reaches 90%, R10 is the R value at which the cumulative distribution from the lower limit reaches 10%, and R50 is the R value at which the cumulative distribution from the lower limit reaches 50%. The concentration of R values ​​is expressed as (R90-R10) / R50.

[0298] The Raman spectroscopy tests of graphite and coating materials were carried out in a similar manner as described above.

[0299] The coating material sample can be obtained as follows: take an appropriate amount of liquid hard carbon coating agent or solid coating agent, carbonize it according to the same carbonization treatment conditions as the embodiments and comparative examples, and then grind and sieve the obtained material to obtain the coating material sample.

[0300] (2) Gram capacity test of negative electrode active material

[0301] The negative electrode active material sample was 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 prepare a slurry. The prepared slurry was coated on the copper foil current collector, dried in an oven, and then cold pressed for use. The compaction density was controlled to 1.4 g / 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.

[0302] (3) Powder compaction density test of negative electrode active material

[0303] 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 and set different pressures. Read the thickness of the powder under different pressures on the instrument (here, the thickness after pressure relief). Calculate the compaction density ρ of the negative electrode active material powder under the corresponding pressure using ρ = m / (s*h). During the test, the pressure is set to 20,000 N. 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 1.327 cm in this case. 2 h is the compacted thickness of the negative electrode active material powder sample, in cm.

[0304] (4) Battery mass energy density test

[0305] 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 volumetric energy density.

[0306] (5) Battery critical charge rate test

[0307] 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.

[0308] (6) Battery cycle performance test

[0309] 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.

[0310] Table 1

[0311] In Comparative Example 1, no coating layer is provided on the graphite surface, and the battery can have a high energy density, but the fast charging performance of the battery is very poor.

[0312] Comparative Examples 2 and 3 set a coating layer on the graphite surface, but the concentration of the R value of the prepared negative electrode active material was greater than 2.0, the coating uniformity of the coating layer on the graphite surface was poor, and the effect of improving the fast charging performance of the battery was not obvious. At the same time, the energy density of the battery was lower than that of Comparative Example 1.

[0313] The negative electrode active material prepared in Example 1 can improve the fast charging performance of the battery without significantly reducing the battery energy density. Therefore, the negative electrode active material prepared in the examples of the present application can enable the battery to have both high energy density and good kinetic performance.

[0314] Example 2

[0315] 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.

[0316] (1) Preparation of negative electrode active materials

[0317] 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 2900°C to obtain graphite.

[0318] Graphite and a liquid hard carbon coating agent are fused in a fusion machine at a mass ratio of 100:5. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 680, a viscosity of 930 mPa·s at 25°C, a solid content of 73%-74%, a free phenol content of 6.5%, and a free aldehyde content of 0. The product after solid-liquid fusion is placed in a track kiln and carbonized at a rate of 2.18°C / min to 1150°C under a nitrogen atmosphere for 370 minutes. After carbonization, the product is cooled to 50°C at a rate of 2.04°C / min and removed from the kiln. The product is then depolymerized, sieved, and demagnetized to obtain a negative electrode active material.

[0319] Example 3

[0320] 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.

[0321] (1) Preparation of negative electrode active materials

[0322] 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 2900°C to obtain graphite.

[0323] Graphite and a liquid hard carbon coating agent are solid-liquid fused in a fusion machine at a mass ratio of 100:5. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 550, a viscosity of 330 mPa·s at 25°C, a solid content of 73%-74%, a free phenol content of 6.5%, and a free aldehyde content of 0. The product after solid-liquid fusion is placed in a track kiln and carbonized at a rate of 2.18°C / min to 1150°C under a nitrogen atmosphere for 370 minutes. After carbonization, the product is cooled to 50°C at a rate of 2.04°C / min and removed from the kiln. The product is then depolymerized, sieved, and demagnetized to obtain a negative electrode active material.

[0324] Example 4

[0325] 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.

[0326] (1) Preparation of negative electrode active materials

[0327] 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 2900°C to obtain graphite.

[0328] Graphite and a liquid hard carbon coating agent are fused in a fusion machine at a mass ratio of 100:5. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 880, a viscosity of 2450 mPa·s at 25°C, a solid content of 73%-74%, a free phenol content of 6.5%, and a free aldehyde content of 0. The product after solid-liquid fusion is placed in a track kiln and carbonized at a rate of 2.18°C / min to 1150°C under a nitrogen atmosphere for 370 minutes. After carbonization, the product is cooled to 50°C at a rate of 2.04°C / min and removed from the kiln. The product is then depolymerized, sieved, and demagnetized to obtain a negative electrode active material.

[0329] Example 5

[0330] 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.

[0331] (1) Preparation of negative electrode active materials

[0332] 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 2900°C to obtain graphite.

[0333] Graphite and a liquid hard carbon coating agent are fused in a fusion machine at a mass ratio of 100:5. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 410, a viscosity of 155 mPa·s at 25°C, a solid content of 73%-74%, a free phenol content of 6.5%, and a free aldehyde content of 0. The product after solid-liquid fusion is placed in a track kiln and heated to 1150°C at a rate of 2.18°C / min under a nitrogen atmosphere for carbonization treatment. The heat preservation time is 370 minutes. After the carbonization, the product is cooled to 50°C at a rate of 2.04°C / min and taken out of the kiln. The product is then depolymerized, screened, and demagnetized to obtain a negative electrode active material.

[0334] Table 2

[0335] The test results of Examples 1 to 5 show that a reduction in the (R90-R10) / R50 ratio of the negative electrode active material improves the battery's rapid charging performance. The test results of Examples 1 to 5 show that adjusting the weight-average molecular weight and / or viscosity of the liquid phenolic resin can adjust the (R90-R10) / R50 ratio of the negative electrode active material.

[0336] Example 6

[0337] 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.

[0338] (1) Preparation of negative electrode active materials

[0339] 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 2900°C to obtain graphite.

[0340] Graphite and a liquid hard carbon coating agent are fused in a fusion machine at a mass ratio of 100:5. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 300, a viscosity of 680 mPa·s at 25°C, a solid content of 73%-74%, a free phenol content of 6.5%, and a free aldehyde content of 0. The product after solid-liquid fusion is placed in a track kiln and heated to 1150°C at a rate of 2.18°C / min under a nitrogen atmosphere for carbonization treatment. The heat preservation time is 370 minutes. After the carbonization, the product is cooled to 50°C at a rate of 2.04°C / min and taken out of the kiln. The product is then depolymerized, sieved, and demagnetized to obtain a negative electrode active material.

[0341] Table 3

[0342] From the test results in Table 3, it can be seen that by further adjusting the (R90-R10) / R50 of the negative electrode active material, the battery can also have good cycle performance.

[0343] Example 7

[0344] The preparation process of the battery is the same as that of Example 2 except that the preparation process of the negative electrode active material is different.

[0345] (1) Preparation of negative electrode active materials

[0346] 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 2900°C to obtain graphite.

[0347] Graphite and a liquid hard carbon coating agent are fused in a fusion machine at a mass ratio of 100:5. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 680, a viscosity of 930 mPa·s at 25°C, a solid content of 73%-74%, a free phenol content of 7.5%, and a free aldehyde content of 0. The product after solid-liquid fusion is placed in a track kiln and carbonized at a temperature of 2.85°C / min to 1150°C under a nitrogen atmosphere for 370 minutes. After carbonization, the product is cooled at a temperature of 2.04°C / min to 50°C and then removed from the kiln. The product is then depolymerized, sieved, and demagnetized to obtain a negative electrode active material.

[0348] Table 4

[0349] The test results in Table 4 show that by adjusting the free phenol content of the liquid phenolic resin and / or the heating rate of the carbonization treatment heating stage, the (R90-R10) / R50 of the negative electrode active material can be adjusted, and the fast charging performance of the battery can also be improved.

[0350] Example 8

[0351] 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.

[0352] (1) Preparation of negative electrode active materials

[0353] 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 3200°C to obtain graphite.

[0354] Graphite and a liquid hard carbon coating agent are fused in a fusion machine at a mass ratio of 100:5. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 600, a viscosity of 680 mPa·s at 25°C, a solid content of 73%-74%, a free phenol content of 6.5%, and a free aldehyde content of 0. The product after solid-liquid fusion is placed in a track kiln and carbonized at a rate of 2.18°C / min to 1150°C under a nitrogen atmosphere for 370 minutes. After carbonization, the product is cooled to 50°C at a rate of 2.04°C / min and removed from the kiln. The product is then depolymerized, sieved, and demagnetized to obtain a negative electrode active material.

[0355] Table 5

[0356] It can be seen from the test results in Table 5 that, when other conditions are the same, as the R value R50 of the cumulative distribution of graphite increases to 50%, the fast charging performance of the battery is improved.

[0357] Example 9

[0358] 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.

[0359] (1) Preparation of negative electrode active materials

[0360] 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 2900°C to obtain graphite.

[0361] Graphite and a liquid hard carbon coating agent are solid-liquid fused in a mass ratio of 100:1.1 using a fusion machine. The liquid hard carbon coating agent is a commercially available liquid phenolic resin with a weight-average molecular weight of 600, a viscosity of 680 mPa·s at 25°C, a solid content of 73%-74%, a free phenol content of 6.5%, and a free aldehyde content of 0. The product after solid-liquid fusion is placed in a track kiln and carbonized at a rate of 2.18°C / min to 1150°C under a nitrogen atmosphere for 370 minutes. After carbonization, the product is cooled to 50°C at a rate of 2.04°C / min and removed from the kiln. The product is then depolymerized, sieved, and demagnetized to obtain a negative electrode active material.

[0362] Table 6

[0363] From the test results in Table 6, it can be seen that adjusting the ratio of the mass of the liquid hard carbon coating agent to the mass of graphite can adjust the (R90-R10) / R50 of the negative electrode active material.

[0364] Example 10

[0365] The preparation process of the battery is the same as that of Example 1 except that the preparation process of the negative electrode sheet is different.

[0366] (2) Preparation of negative electrode sheet

[0367] 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 96.9:1.1:1.5:0.5, and deionized water solvent was added. The mixture was stirred evenly under the action of a vacuum mixer to prepare a negative electrode slurry.

[0368] 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.

[0369] Table 7

[0370] 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.

[0371] 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 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, 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 amorphous carbon; In the cumulative distribution curve of R values of the negative electrode active material obtained under the surface scanning mode of a laser microconfocal Raman spectrometer, the concentration of R values is less than or equal to 2.

0.

2. The lithium-ion battery according to claim 1, wherein The concentration of R values of the negative electrode active material is less than or equal to 1.

7.

3. The lithium-ion battery according to any one of claims 1 to 2, wherein: The coating layer includes hard carbon.

4. The lithium-ion battery according to any one of claims 1 to 3, wherein: The cumulative distribution of the negative electrode active material has an R value R50 of 50% in the range of 0.15-0.

42.

5. The lithium ion battery according to claim 4, 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.

6. The lithium-ion battery according to any one of claims 1 to 5, 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 0.55-1.6; and / or, The kernel has a cumulative distribution with a 50% R value R50 of 0.06-0.14; and / or The concentration of the R value of the coating layer is 0.06-0.

33.

7. The lithium ion battery according to claim 6, wherein The cumulative distribution of the coating layer is such that the R value R50 of 50% is 1.0-1.4; and / or, The kernel has a cumulative distribution with a 50% R value R50 of 0.07-0.11; and / or, The concentration of the R value of the coating layer is 0.13-0.

25.

8. The lithium ion battery according to any one of claims 1 to 7, wherein: The volume distribution particle size Dv50 of the negative electrode active material is 8 μm-25 μm; and / or, 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 1.2 μm-6 μm; and / or, The mass of the coating layer is 0.3%-5% of the mass of the core; and / or, The core has a coating layer on 90%-100% of its surface.

9. The lithium ion battery according to claim 8, wherein The volume distribution particle size Dv50 of the negative electrode active material is 12 μm-17 μm; and / or, 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 1.8 μm-4.5 μm; and / or, The mass of the coating layer is 1%-3.5% of the mass of the core; and / or, The core has a coating layer on 92%-100% of its surface.

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 of 004 crystal plane diffraction peak to 110 crystal plane diffraction peak measured by X-ray diffraction method of 2-6.5; and / or, The gram capacity of the negative electrode active material is 354 mAh / g-360 mAh / g; and / or, The powder compaction density of the negative electrode active material under a pressure of 20000N is 1.63g / cm 3 -1.77g / cm 3 and / or, The specific surface area of the negative electrode active material is 1.5 m 2 / g-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.

14.

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 1.60 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, wherein the core includes graphite and the coating layer includes amorphous carbon; In the cumulative distribution curve of R values of the negative electrode active material obtained under the surface scanning mode of a laser microconfocal Raman spectrometer, the concentration of R values is less than or equal to 2.

0.

19. A method for preparing a negative electrode active material, comprising the following steps: Provide graphite; Performing solid-liquid fusion of the graphite and the liquid coating agent; The solid-liquid fusion product is carbonized under a protective gas atmosphere so that the liquid coating agent is carbonized into amorphous 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 amorphous carbon; In the cumulative distribution curve of R values of the negative electrode active material obtained under the surface scanning mode of a laser microconfocal Raman spectrometer, the concentration of R values is less than or equal to 2.

0.

20. The preparation method according to claim 19, wherein The liquid-phase coating agent is a liquid-phase hard carbon coating agent.

21. The preparation method according to claim 20, 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 2500 mPa·s. The solid content of the liquid resin is 50% to 88%.

22. The preparation method according to claim 21, wherein The viscosity of the liquid resin at 25° C. is 300 mPa·s-950 mPa·s, and the solid content of the liquid resin is 60%-85%.

23. The preparation method according to any one of claims 21 to 22, 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.

24. The preparation method according to claim 23, wherein The liquid hard carbon coating agent includes liquid phenolic resin, which has a weight average molecular weight of 300-900, a solid content of 60%-85%, a free phenol content of less than or equal to 9%, and a free aldehyde content of less than or equal to 0.5%.

25. The preparation method according to claim 24, wherein The liquid phenolic resin has a weight average molecular weight of 500-700, a solid content of 70%-78%, a free phenol content of less than or equal to 6.5%, and a free aldehyde content of 0.

26. The preparation method according to any one of claims 19 to 25, wherein: The carbonization process includes a temperature rising section, a temperature holding section and a temperature falling section. The heating rate of the carbonization heating stage is 1.3°C / min-3°C / min; and / or, The cooling rate of the carbonization treatment cooling stage is 1.2°C / min-3.7°C / min; and / or, The heat preservation temperature of the carbonization treatment heat preservation section is 900° C.-1500° C.; and / or, The heat preservation time of the carbonization treatment heat preservation section is 2h-10h.

27. The preparation method according to claim 26, wherein The heating rate of the carbonization heating stage is 1.5°C / min-2.5°C / min; and / or, The cooling rate of the carbonization treatment cooling section is 1.5°C / min-2.7°C / min.

28. The preparation method according to any one of claims 19 to 27, wherein: The equipment for solid-liquid fusion of the graphite and the liquid coating agent is a fusion machine, the stirring speed of the fusion machine is 300r / min-1000r / min; and / or the stirring time of solid-liquid fusion is 3min-8min.

29. A negative electrode sheet, wherein: 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, 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 amorphous carbon; In the cumulative distribution curve of R values of the negative electrode active material obtained under the surface scanning mode of a laser microconfocal Raman spectrometer, the concentration of R values is less than or equal to 2.0.

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