Graphite material, preparation method therefor, negative electrode piece containing graphite material, battery, and electrical apparatus

Abstract

A graphite material, a preparation method therefor, a negative electrode piece containing graphite material, a battery, and an electrical apparatus. The graphite material satisfies (Lc100%SOC-Lc0%SOC) / Lc50%SOC≤0.0750, and Lc0%SOC is less than or equal to 50 nm. The graphite material enables the battery to have a long cycle life.

Description

Graphite material and preparation method thereof, as well as negative electrode sheet, battery and electrical device containing the same

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202311677312.1 filed on December 7, 2023, entitled “Graphite 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 graphite material and a preparation method thereof, as well as a negative electrode sheet, a battery and an electrical device containing the same. Background Art

[0004] In recent years, batteries have been widely used in the energy storage field, leading to increasingly higher requirements for battery cycle life. However, how to achieve a longer cycle life while maintaining a high energy density remains a challenge in current battery development.

[0005] Summary of the Invention

[0006] The present application provides a graphite material and a preparation method thereof, as well as a negative electrode plate, a battery and an electrical device containing the same, which can enable the battery to have a long cycle life.

[0007] In a first aspect, the present application provides a graphite material, wherein the graphite material satisfies (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, and Lc 0％SOC Less than or equal to 50nm.

[0008] Lc 0％SOC Indicates the grain size of the graphite material along the c-axis direction in the lithium-intercalated 0% SOC state, in nm; Lc 50％SOC Indicates the grain size of the graphite material along the c-axis direction in the state of 50% lithium insertion SOC, in nm; Lc 100％SOC It represents the grain size of the graphite material along the c-axis direction in the lithium-intercalated 100% SOC state, in nm.

[0009] The graphite material provided in the embodiment of the present application satisfies (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, and Lc 0％SOCThe graphite material has a small grain size along the c-axis in the lithium insertion 0% SOC state, and the volume change of the graphite material during the entire lithium insertion process is small, thereby reducing the lattice expansion of the graphite material during battery charging and reducing the thickness expansion of the negative electrode sheet, thereby reducing the negative electrode-electrolyte interface side reaction and reducing the irreversible consumption of lithium ions, thereby improving the cycle life of the battery and meeting the needs of long-life energy storage batteries.

[0010] In some embodiments, 0.0100≤(Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, optionally, 0.0100≤(Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0500. This helps the battery better achieve both higher energy density and longer cycle life.

[0011] In some embodiments, 15 nm ≤ Lc 0％SOC ≤47nm, optionally, 25nm≤Lc 0％SOC ≤45nm. The grain size Lc of graphite material along the c-axis direction in the lithium-intercalated 0% SOC state 0％SOC When within the above range, the lattice expansion of the graphite material during battery charging can be further reduced, and the thickness expansion of the negative electrode plate can be reduced, thereby further reducing the side reactions at the negative electrode-electrolyte interface and reducing the irreversible consumption of lithium ions, thereby further improving the cycle life of the battery.

[0012] In some embodiments, 20 nm ≤ Lc 100％SOC ≤60nm, optionally, 28nm≤Lc 100％SOC ≤50nm. The grain size Lc of graphite material along the c-axis direction in the state of 100% lithium insertion 100％SOC When within the above range, the lattice expansion of the graphite material during battery charging can be further reduced, and the thickness expansion of the negative electrode plate can be reduced, thereby further reducing the side reactions at the negative electrode-electrolyte interface and reducing the irreversible consumption of lithium ions, thereby further improving the cycle life of the battery.

[0013] In some embodiments, the gram capacity of the graphite material is 280 mAh / g-340 mAh / g, optionally 290 mAh / g-335 mAh / g. When the gram capacity of the graphite material is within the above range, it is beneficial for the battery to have both high energy density and long cycle life.

[0014] In some embodiments, the volume distribution particle size Dv1 of the graphite material is 0.5 μm-3.1 μm, and can be optionally 1 μm-2.5 μm.

[0015] In some embodiments, the volume distribution particle size Dv10 of the graphite material is 3 μm-6.2 μm, and can be optionally 3.2 μm-5 μm.

[0016] In some embodiments, the volume distribution particle size Dv50 of the graphite material is 5 μm-15 μm, optionally 8 μm-12 μm.

[0017] By adjusting the volume distribution particle size of the graphite material, the grain size along the c-axis direction during the lithium insertion process of the graphite material can be reduced, thereby reducing the lattice expansion of the graphite material during battery charging and the thickness expansion of the negative electrode plate, thereby reducing the side reactions at the negative electrode-electrolyte interface and reducing the irreversible consumption of lithium ions, thereby improving the cycle life of the battery; it can also increase the lithium insertion channel of the graphite material and reduce lithium deposition.

[0018] In some embodiments, the particle size distribution of the graphite material (Dv90-Dv10) / Dv50 is 1.02-1.57, and optionally 1.11-1.49.

[0019] When the particle size distribution (Dv90-Dv10) / Dv50 of the graphite material is within the above range, the thickness expansion of the negative electrode plate during battery charging can be reduced, thereby reducing the side reactions at the negative electrode-electrolyte interface, reducing the irreversible consumption of lithium ions, and thus improving the cycle life of the battery.

[0020] In some embodiments, the graphite material has a grain size La along the a-axis in a lithium-intercalated 0% SOC state. 0％SOC Less than or equal to 140nm. The grain size La along the a-axis direction of the graphite material in the lithium-intercalated 0% SOC state 0％SOC Within the above range, the graphite material has the characteristics of high isotropy and small grain size, which can make the graphite material have more lithium insertion channels, thereby reducing lithium deposition, and further helping to improve the cycle life of the battery.

[0021] In some embodiments, the graphite material has a degree of graphitization of 70%-88%, optionally 75%-85%. When the graphitization degree of the graphite material is within the above range, on the one hand, the graphite material can have a higher capacity, resulting in a higher energy density for the battery; on the other hand, the grain size along the c-axis of the graphite material during lithium insertion can be reduced, thereby reducing the lattice expansion of the graphite material during battery charging and reducing the thickness expansion of the negative electrode plate, thereby reducing negative electrode-electrolyte interface side reactions, reducing irreversible consumption of lithium ions, and thereby improving the cycle life of the battery.

[0022] In some embodiments, the tap density of the graphite material is 1.0 m3 / g-1.3m 3 When the tap density of the graphite material is within the above range, the compaction density of the negative electrode film layer can be increased, thereby facilitating the battery to have a higher energy density.

[0023] In some embodiments, the specific surface area of ​​the graphite material is 0.6 m 2 / g-2m 2 When the specific surface area of ​​the graphite material is within the above range, the negative electrode-electrolyte interface side reaction can be reduced, the irreversible consumption of lithium ions can be reduced, and thus the cycle life of the battery can be improved.

[0024] In some embodiments, the surface of the graphite material further includes a carbon layer.

[0025] In a second aspect, the present application provides a method for preparing a graphite material, comprising the following steps: providing a coke raw material; crushing, shaping, and grading the coke raw material to obtain a graphite precursor; placing the obtained graphite precursor in a graphitization furnace for graphitization at a preset temperature and a preset time, and cooling the furnace to obtain a graphite material, wherein the preset temperature is less than 3000°C and the preset time is less than 24 hours, wherein the graphite material satisfies (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, and Lc 0％SOC Less than or equal to 50nm; Lc 0％SOC Indicates the grain size of the graphite material along the c-axis direction in the lithium-intercalated 0% SOC state, in nm; Lc 50％SOC Indicates the grain size of the graphite material along the c-axis direction in the state of 50% lithium insertion SOC, in nm; Lc 100％SOC It represents the grain size of the graphite material along the c-axis direction in the lithium-intercalated 100% SOC state, in nm.

[0026] The graphite material prepared by the preparation method provided in the embodiment of the present application has a smaller grain size along the c-axis direction, and the volume change of the graphite material during the entire lithium insertion process is small, thereby reducing the lattice expansion of the graphite material during battery charging and reducing the thickness expansion of the negative electrode plate, thereby reducing the negative electrode-electrolyte interface side reactions, reducing the irreversible consumption of lithium ions, and thus improving the cycle life of the battery.

[0027] In some embodiments, the graphitization furnace is a continuous graphitization furnace.

[0028] In some embodiments, the preset temperature is 2500°C-2800°C, optionally 2500°C-2750°C.

[0029] In some embodiments, the preset time is 6 hours to 18 hours, and can be optionally 8 hours to 15 hours.

[0030] By further adjusting the preset temperature and / or preset time during the graphitization treatment, on the one hand, the lattice expansion of the graphite material during battery charging can be reduced, the thickness expansion of the negative electrode plate can be reduced, the side reactions at the negative electrode-electrolyte interface can be reduced, the irreversible consumption of lithium ions can be reduced, and the cycle life of the battery can be improved; on the other hand, the graphite material can also have a higher gram capacity, so that the battery can have both a long cycle life and a higher energy density.

[0031] In some embodiments, the coke feedstock includes at least one of petroleum coke and needle coke.

[0032] In some embodiments, the coke raw material is petroleum coke, and based on the total volume of the coke raw material structure, the volume proportion of the mosaic and regional structures in the petroleum coke is greater than or equal to 60%, and can be optionally 65%-80%.

[0033] In some embodiments, the coke raw material is needle coke, and based on the total volume of the coke raw material structure, the volume proportion of the fibrous structure in the needle coke is 40%-60%, and optionally 45%-55%.

[0034] By selecting the above-mentioned specific type of coke raw material, under the same graphitization treatment conditions, the degree of grain development is slower, which is beneficial to regulating the degree of grain development during the graphitization process and can also reduce the volume change of the graphite particles prepared thereby during the battery charging and discharging process.

[0035] In some embodiments, the coke raw material further satisfies the following requirements: volatile matter content is less than or equal to 10 wt %, ash content is less than or equal to 0.3 wt %, and sulfur content is less than or equal to 2 wt %.

[0036] In some embodiments, in the step of crushing, shaping and grading the coke raw material to obtain a graphite precursor, the volume distribution particle size Dv1 of the obtained graphite precursor is greater than or equal to 0.3 μm, and can be optionally 0.3 μm-1.4 μm; and / or, the volume distribution particle size Dv10 of the obtained graphite precursor is greater than or equal to 2.0 μm, and can be optionally 2.1 μm-4.0 μm; and / or, the volume distribution particle size Dv50 of the obtained graphite precursor is 5 μm-16 μm, and can be optionally 8 μm-11 μm; and / or, the particle size distribution of the obtained graphite precursor (Dv90-Dv10) / Dv50 is 1.05-1.61, and can be optionally 1.18-1.52.

[0037] By adjusting the volume particle size distribution of the graphite precursor within the above range, the grain size of the graphite material crystal along the c-axis direction can be reduced, the volume expansion of the graphite material during battery charging can be reduced, and the graphite material can also have good dynamic properties.

[0038] In some embodiments, before placing the obtained graphite precursor in a graphitization furnace for graphitization at a preset temperature and for a preset time, the method further includes the step of pre-carbonizing the obtained graphite precursor. Optionally, the obtained graphite precursor is heated to 600°C-1100°C at a heating rate of 1°C / min-5°C / min and maintained at this temperature for 18-24 hours for pre-carbonization.

[0039] In some embodiments, the preparation method further includes the steps of placing the obtained graphite precursor in a graphitization furnace for graphitization treatment at a preset temperature and a preset time, and then screening and demagnetizing to obtain a graphite material.

[0040] In some embodiments, the preparation method further comprises the step of: mixing the obtained graphite material with a coating agent and placing the mixture in a carbonization furnace for carbonization treatment to form a carbon layer on the surface of the graphite material.

[0041] Optionally, the coating agent includes asphalt, and more optionally, the softening point temperature of the asphalt is 150°C-300°C, optionally 200°C-250°C.

[0042] Optionally, the temperature of the carbonization treatment is 950°C-1300°C, optionally 1100°C-1200°C.

[0043] Optionally, the carbonization treatment time is 1 hour to 5 hours, optionally 2 hours to 3 hours.

[0044] In a third 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, wherein the negative electrode film layer comprises the graphite material of the first aspect of the present application or the graphite material prepared by the preparation method of the second aspect of the present application.

[0045] In some embodiments, the compaction density of the negative electrode film layer is 1.15 g / cm 3 -1.55g / cm 3 .

[0046] In some embodiments, the surface density of the negative electrode film layer is 7 mg / cm 2 -15mg / cm 2 .

[0047] In a fourth aspect, the present application provides a battery comprising the negative electrode sheet according to the third aspect of the present application.

[0048] In a fifth aspect, the present application provides an electrical device comprising the battery according to the fourth aspect of the present application, wherein the battery is used to provide electrical energy.

[0049] The electric device of the present application includes the battery provided by the present application, and thus has at least the same advantages as the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] 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.

[0051] FIG1 is a schematic diagram of a battery cell provided in some embodiments of the present application.

[0052] FIG2 is an exploded schematic diagram of a battery cell provided in some embodiments of the present application.

[0053] FIG3 is a schematic diagram of a battery module provided in some embodiments of the present application.

[0054] FIG4 is a schematic diagram of a battery pack provided in some embodiments of the present application.

[0055] FIG5 is an exploded schematic diagram of the battery pack shown in FIG4 .

[0056] FIG6 is a schematic diagram of an electrical device provided in some embodiments of the present application.

[0057] In the accompanying drawings, which are not necessarily drawn to scale, reference numerals are as follows: 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 battery cell, 51 housing, 52 electrode assembly, 53 cover plate. DETAILED DESCRIPTION

[0058] Below, the graphite material and its preparation method, as well as the embodiments of the negative electrode sheet, battery and electrical device containing the same are described in detail with appropriate reference to the accompanying 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.

[0059] " 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] In this application, the terms "plurality" and "multiple" refer to two or more.

[0064] Unless otherwise specified, the terms used in this application have the common meanings that are commonly understood by those skilled in the art.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0070] A battery cell generally includes an electrode assembly and an electrolyte. The electrode assembly typically includes a positive electrode sheet and a negative electrode sheet. The electrode assembly can be a wound structure or a stacked structure, which is not limited in the present application.

[0071] 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).

[0072] In some embodiments, as shown in Figure 2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom 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.

[0073] 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 3 is a schematic diagram of a battery module 4 as an example. As shown in Figure 3, 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.

[0074] 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.

[0075] 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.

[0076] Figures 4 and 5 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 4 and 5, 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.

[0077] The battery provided in the embodiments of the present application may include a lithium-ion battery.

[0078] The graphite material provided in the embodiment of the present application satisfies (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, and Lc 0％SOC Less than or equal to 50nm.

[0079] Lc 0％SOC Indicates the grain size of graphite material along the c-axis direction in the state of lithium insertion 0% SOC, in nm; Lc 50％SOC Indicates the grain size of graphite material along the c-axis direction in the state of 50% lithium insertion SOC, in nm; Lc 100％SOC It indicates the grain size of graphite material along the c-axis direction in the state of 100% lithium insertion SOC, in nm.

[0080] As the battery charge level deepens, lithium ions continue to embed into the lattice of the graphite material, which causes the lattice of the graphite material to expand. And as the number of battery cycles increases, the graphite material will experience a larger lattice expansion, which will cause the graphite material particles to experience a larger volume change, which will in turn cause the solid electrolyte interface (SEI) film on the surface of the graphite material particles to repeatedly break and form, thereby increasing the negative electrode-electrolyte interface side reactions, increasing the irreversible consumption of lithium ions, and affecting the cycle life of the battery. In addition, the larger lattice expansion of the graphite material will also deteriorate the electronic contact between the graphite material particles and the negative electrode current collector, causing some graphite material particles to lose electronic contact and electrochemical activity, thereby causing uneven local current at the negative electrode, which in turn leads to accelerated lithium precipitation and battery capacity decay, reducing the battery's cycle performance.

[0081] The graphite material provided in the embodiment of the present application satisfies (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC Greater than 0 and less than or equal to 0.0750, and Lc 0％SOC The graphite material has a small grain size along the c-axis in the lithium insertion 0% SOC state, and the volume change of the graphite material during the entire lithium insertion process is small, thereby reducing the lattice expansion of the graphite material during battery charging and reducing the thickness expansion of the negative electrode sheet, thereby reducing the negative electrode-electrolyte interface side reaction and reducing the irreversible consumption of lithium ions, thereby improving the cycle life of the battery and meeting the needs of long-life energy storage batteries.

[0082] Optionally, (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC The amount may be 0.0100, 0.0120, 0.0140, 0.0155, 0.0169, 0.0185, 0.0200, 0.0250, 0.0300, 0.0350, 0.0400, 0.0440, 0.0500, 0.0550, 0.0600, 0.0650, 0.0700, 0.0750, or a range consisting of any of the above values.

[0083] Optionally, in some embodiments, 0.0100≤(Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750,0.0100≤(Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0500. This helps the battery better achieve both higher energy density and longer cycle life.

[0084] In some embodiments, 15 nm ≤ Lc 0％SOC ≤47nm, optionally, 25nm≤Lc 0％SOC ≤45nm.

[0085] The grain size Lc of graphite material along the c-axis in the lithium-intercalated 0% SOC state 0％SOC When within the above range, the lattice expansion of the graphite material during battery charging can be further reduced, and the thickness expansion of the negative electrode plate can be reduced, thereby further reducing the side reactions at the negative electrode-electrolyte interface and reducing the irreversible consumption of lithium ions, thereby further improving the cycle life of the battery.

[0086] In some embodiments, 20 nm ≤ Lc 100％SOC ≤60nm, optionally, 28nm≤Lc 100％SOC ≤50nm.

[0087] The grain size Lc of graphite material along the c-axis direction in the state of 100% lithium insertion SOC 100％SOC When within the above range, the lattice expansion of the graphite material during battery charging can be further reduced, and the thickness expansion of the negative electrode plate can be reduced, thereby further reducing the side reactions at the negative electrode-electrolyte interface and reducing the irreversible consumption of lithium ions, thereby further improving the cycle life of the battery.

[0088] In some embodiments, the grain size La of the graphite material along the a-axis direction in the lithium-intercalated 0% SOC state is 0％SOC It can be greater than 0 and less than or equal to 140nm.

[0089] The grain size La of graphite material along the a-axis in the lithium-intercalated 0% SOC state 0％SOC Within the above range, the graphite material has the characteristics of high isotropy and small grain size, which can make the graphite material have more lithium insertion channels, thereby reducing lithium deposition, and further helping to improve the cycle life of the battery.

[0090] In some embodiments, the gram capacity of the graphite material may be 280 mAh / g to 340 mAh / g, and optionally 290 mAh / g to 335 mAh / g.

[0091] When the gram capacity of the graphite material is within the above range, it is beneficial for the battery to have both higher energy density and long cycle life.

[0092] In some embodiments, the graphite material may have a degree of graphitization of 70%-88%, and optionally 75%-85%.

[0093] When the graphitization degree of the graphite material is within the above range, on the one hand, the graphite material can have a higher capacity and the battery can have a higher energy density; on the other hand, the grain size along the c-axis direction during the lithium insertion process of the graphite material can be reduced, thereby reducing the lattice expansion of the graphite material during battery charging and reducing the thickness expansion of the negative electrode sheet, thereby reducing the side reactions at the negative electrode-electrolyte interface and reducing the irreversible consumption of lithium ions, thereby improving the cycle life of the battery.

[0094] In some embodiments, the graphite material is in the form of primary particles.

[0095] In some embodiments, the volume distribution particle size Dv1 of the graphite material may be 0.5 μm-3.1 μm, and optionally 1 μm-2.5 μm.

[0096] In some embodiments, the volume distribution particle size Dv10 of the graphite material may be 3 μm-6.2 μm, and optionally 3.2 μm-5 μm.

[0097] In some embodiments, the volume distribution particle size Dv50 of the graphite material may be 5 μm-15 μm, optionally 8 μm-12 μm.

[0098] By adjusting the volume distribution particle size of the graphite material, the grain size along the c-axis direction during the lithium insertion process of the graphite material can be reduced, thereby reducing the lattice expansion of the graphite material during battery charging and the thickness expansion of the negative electrode plate, thereby reducing the side reactions at the negative electrode-electrolyte interface and reducing the irreversible consumption of lithium ions, thereby improving the cycle life of the battery; it can also increase the lithium insertion channel of the graphite material and reduce lithium deposition.

[0099] In some embodiments, the particle size distribution of the graphite material (Dv90-Dv10) / Dv50 may be 1.02-1.57, and optionally 1.11-1.49.

[0100] When the graphite material's particle size distribution (Dv90-Dv10) / Dv50 is within the above range, the thickness expansion of the negative electrode sheet during battery charging can be reduced, thereby reducing side reactions at the negative electrode-electrolyte interface, reducing irreversible consumption of lithium ions, and thereby improving the battery's cycle life. When the graphite material's particle size distribution (Dv90-Dv10) / Dv50 is large, the fine powder content in the graphite material is high, thereby increasing irreversible capacity loss during battery cycling and reducing the battery's cycle life. When the particle size distribution (Dv90-Dv10) / Dv50 of the graphite material is small, the repeated charging and discharging of the graphite particles during the battery cycle causes the graphite particles to repeatedly expand and contract, and then some graphite particles may be displaced, resulting in an increase in the gaps between the graphite particles; in addition, when the particle size distribution (Dv90-Dv10) / Dv50 of the graphite material is small, the fine powder content in the graphite material is small, and the graphite particles may be out of electrical contact due to the lack of small fine powder to fill the gaps between the graphite particles, thereby causing the battery cycle capacity to rapidly decay in the later stages of use.

[0101] In some embodiments, the tap density of the graphite material may be 1.0 m 3 / g-1.3m 3 / g.

[0102] When the tap density of the graphite material is within the above range, the compaction density of the negative electrode film layer can be improved, which is conducive to the battery having a higher energy density.

[0103] In some embodiments, the specific surface area of ​​the graphite material can be 0.6 m 2 / g-2m 2 / g.

[0104] When the specific surface area of ​​the graphite 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.

[0105] In some embodiments, the surface of the graphite material may further include a carbon layer. Optionally, the carbon layer may include one or more of soft carbon and hard carbon.

[0106] The grain size Lc of the graphite material along the c-axis direction or the grain size La along the a-axis direction are both well known in the art and can be tested using instruments and methods known in the art. For example, an X-ray diffractometer (such as a Bruker D8 Discover) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the half-maximum width FWHM (002) and FWHM (110) of the 002 and 110 crystal planes in the crystal structure of the graphite material and the crystal plane diffraction peaks Pos (002) and Pos (100). The crystal Lc and La values ​​are then calculated using the Scherrer formula, where π represents the circumference constant.

[0107] Lc=0.89*0.15405*180 / FWHM(002) / π / Cos[Pos(002)*π*2 / 180].

[0108] La=1.84*0.15405*180 / FWHM(110) / π / Cos[Pos(110)*π*2 / 180].

[0109] Lc 0％SOC 、Lc 50％SOC 、Lc 100％SOC They represent the grain size of graphite material along the c-axis direction under different lithium insertion states, that is, the height along the c-axis direction. 0％SOC 、Lc 50％SOC 、Lc 100％SOC All of these can be obtained by testing graphite materials in different lithium insertion states using the above-mentioned test method.

[0110] La 0％SOC Indicates the grain size of graphite material along the a-axis in the state of lithium insertion 0% SOC. 0％SOC It can be obtained by the above test method.

[0111] During testing, the negative electrode sheet containing the graphite material provided in the embodiments of the present application can be made into a button battery. For example, the negative electrode sheet containing the graphite material provided in the embodiments of the present application can be assembled with a lithium metal sheet (as the counter electrode) into a button battery.

[0112] The electrolyte of the button battery can be prepared as follows: in an argon atmosphere glove box with a water content of less than 10 ppm, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a mass ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L.

[0113] The isolation film of the button cell can be a polypropylene (PP) film with a thickness of 12 μm.

[0114] The assembly process of the button cell can adopt techniques known in the art, for example, it can be assembled from the positive electrode shell and from the bottom up, or it can be assembled from the negative electrode shell and from the bottom up, and the entire assembly process is carried out in an argon atmosphere glove box with a water content of less than 10 ppm.

[0115] At 25°C, the prepared button battery was left standing for 6 hours, then discharged at a constant current of 0.15 mA to 5.0 mV; left standing for 5 minutes, and then continued to discharge at a constant current of 50 μA to 5.0 mV; then charged at a constant current of 0.30 mA to 2 V, at which point the charge capacity was recorded as C0; then the negative electrode was disassembled from the button battery and tested by X-ray diffractometer to obtain Lc 0％SOC and La 0％SOC .

[0116] At 25°C, the prepared button battery was left standing for 6 hours, then discharged at a constant current of 0.15 mA to 5.0 mV; left standing for 5 minutes, and then continued to discharge at a constant current of 50 μA to 5.0 mV; then charged at a constant current of 0.30 mA to 2 V, at which point the charge capacity was recorded as C0; then discharged at a constant current of 0.05 C0 for 10 hours; then the negative electrode was disassembled from the button battery and tested by X-ray diffractometer to obtain Lc 50％SOC .

[0117] At 25°C, the prepared button battery was left standing for 6 hours, then discharged at a constant current of 0.15 mA to 5.0 mV; left standing for 5 minutes, and then continued to discharge at a constant current of 50 μA to 5.0 mV; then charged at a constant current of 0.30 mA to 2 V, at which point the charge capacity was recorded as C0; then discharged at a constant current of 0.05 C0 for 20 hours; then the negative electrode was disassembled from the button battery and tested by X-ray diffractometer to obtain Lc 100％SOC .

[0118] For example, a graphite material sample can be mixed with a conductive agent, carbon black, and a binder, polyvinylidene fluoride (PVDF), in a mass ratio of 91.6:1.8:6.6 in an appropriate amount of solvent, N-methylpyrrolidone (NMP), and stirred to form a uniform negative electrode slurry; the negative electrode slurry is evenly coated on the surface of the negative electrode current collector copper foil and dried and cold pressed; then a metal lithium sheet is used as a counter electrode, a polypropylene (PP) film is used as an isolation membrane, an electrolyte is injected, and a CR2430 button battery is assembled in an argon-protected glove box. The electrolyte formula used is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a mass ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. The compacted density of the negative electrode sheet can be 1.3 g / cm 3 -1.5g / cm3 .

[0119] At 25°C, the prepared button cell was first discharged at a constant current of 0.05C to 0.005V, then discharged at a constant current of 10μA to 0.005V. The cell was allowed to rest for 5 minutes, and the first-cycle discharge capacity was recorded. The cell was then charged at a constant current of 0.1C to 2.0V, and the first-cycle charge capacity was recorded. The ratio of the first-cycle charge capacity of the button cell to the mass of the graphite sample is the gram capacity of the graphite material.

[0120] The degree of graphitization of graphite materials is well known in the art and can be measured using instruments and methods known in the art. For example, an X-ray diffractometer (such as Bruker D8 Discover) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the average interlayer spacing d of the (002) crystal plane in the crystal structure of the graphite material. 002 Then according to the formula g=(0.344-d 002 ) / (0.344-0.3354)×100% to calculate the degree of graphitization. In the above formula, d 002 It is the average interlayer spacing of the (002) crystal planes in the crystal structure of graphite material expressed in nanometers (nm).

[0121] In X-ray diffraction analysis, a copper target can be used as the anode target, and CuKα rays can be used as the radiation source. The scanning 2θ angle range may be 15°-75°, and the scanning rate may be 4° / min.

[0122] The volume distribution particle sizes Dv1, Dv10, Dv50, and Dv90 of materials (e.g., graphite materials, graphite precursors hereinafter, etc.) are well known in the art and represent the particle sizes corresponding to the cumulative volume distribution percentages of the materials reaching 1%, 10%, 50%, and 90%, respectively. They can be measured using instruments and methods known in the art. For example, the particle size distribution laser diffraction method according to GB / T19077-2016 can be conveniently measured using a laser particle size analyzer. The test instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0123] The tap density of graphite materials 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 a powder tap density tester, as per GB / T 5162-2006. A suitable tester is the Dandong Better BT-301.

[0124] The specific surface area of ​​a graphite 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 according to 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.

[0125] The present application also provides a method for preparing the graphite material.

[0126] The preparation method comprises the following steps: providing coke raw material; crushing, shaping and grading the coke raw material to obtain a graphite precursor; placing the obtained graphite precursor in a graphitization furnace for graphitization at a preset temperature and a preset time, cooling the furnace and removing the graphite material from the furnace, wherein the preset temperature is less than 3000°C and the preset time is less than 24 hours. The graphite material satisfies (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, and Lc 0％SOC Less than or equal to 50nm; Lc 0％SOC Indicates the grain size of graphite material along the c-axis direction in the state of lithium insertion 0% SOC, in nm; Lc 50％SOC Indicates the grain size of graphite material along the c-axis direction in the state of 50% lithium insertion SOC, in nm; Lc 100％SOC It indicates the grain size of graphite material along the c-axis direction in the state of 100% lithium insertion SOC, in nm.

[0127] By selecting the preset temperature and preset time during the graphitization treatment within the above range, the grain size of the graphite material crystal along the c-axis direction can be reduced, the volume expansion of the graphite material during battery charging can be reduced, and the graphite material can also have a higher gram capacity.

[0128] When the preset temperature during graphitization treatment is high and / or the preset time is long, the degree of grain development is better, the grain size of the graphite material crystal along the c-axis direction is larger, and the lattice expansion and volume expansion of the graphite material during the battery charging process are large, which will cause repeated breakage and generation of the SEI film, which is not conducive to improving the cycle life of the battery.

[0129] Therefore, the graphite material prepared by the preparation method provided in the embodiment of the present application has a smaller grain size along the c-axis direction, and the volume change of the graphite material during the entire lithium insertion process is small, thereby reducing the lattice expansion of the graphite material during battery charging and reducing the thickness expansion of the negative electrode plate, thereby reducing the side reactions at the negative electrode-electrolyte interface, reducing the irreversible consumption of lithium ions, and thus improving the cycle life of the battery.

[0130] In some embodiments, when the obtained graphite precursor is placed in a graphitization furnace and graphitized at a preset temperature and a preset time, the preset temperature may be 2500°C-2800°C, and may be optionally 2500°C-2750°C.

[0131] In some embodiments, when the obtained graphite precursor is placed in a graphitization furnace and graphitized at a preset temperature and a preset time, the preset time may be 6 hours to 18 hours, and may be optionally 8 hours to 15 hours.

[0132] By further adjusting the preset temperature and / or preset time during the graphitization treatment, on the one hand, the lattice expansion of the graphite material during battery charging can be reduced, the thickness expansion of the negative electrode plate can be reduced, the side reactions at the negative electrode-electrolyte interface can be reduced, the irreversible consumption of lithium ions can be reduced, and the cycle life of the battery can be improved; on the other hand, the graphite material can also have a higher gram capacity, so that the battery can have both a long cycle life and a higher energy density.

[0133] In some embodiments, the cooling time may be less than or equal to 5 hours, thereby reducing the surface oxidation problem of the graphite material and improving the performance of the graphite material.

[0134] In some embodiments, the furnace temperature may be less than or equal to 250° C. This can reduce the surface oxidation problem of the graphite material during the furnace transfer process, thereby improving the performance of the graphite material.

[0135] In some embodiments, the coke feedstock may include at least one of petroleum coke and needle coke.

[0136] In this application, the term "petroleum coke" refers to coke formed by high-temperature carbonization of petroleum residue or petroleum asphalt.

[0137] In this application, the term "needle coke" refers to coal tar pitch or petroleum pitch, which is carbonized in the liquid phase to form an anisotropic mesophase and then subjected to high-temperature carbonization and other processes to produce coke with a needle-like texture.

[0138] In some embodiments, the raw material may include petroleum coke. Petroleum coke has excellent anisotropy, which facilitates the preparation of graphite materials with low volume expansion and contributes to a long cycle life for batteries. Furthermore, petroleum coke has a high compacted density and high gram capacity, which helps improve the energy density of batteries. Furthermore, petroleum coke is widely available, facilitating industrial production.

[0139] The coke raw material typically includes at least one of a mosaic, areal, and fibrous structure. Typically, based on the morphological characteristics and isochromatic zone size of the coke raw material under a polarizing microscope, isochromatic zones smaller than 30 μm are classified as mosaic, those larger than 30 μm are classified as areal, and anisotropic banded isochromatic zones are classified as fibrous.

[0140] In some embodiments, the coke raw material may be petroleum coke, and based on the total volume of the coke raw material structure, the volume proportion of the mosaic and regional structures in the petroleum coke may be greater than or equal to 60%, and may be optionally 65%-80%.

[0141] In some embodiments, the coke raw material may be needle coke, and based on the total volume of the coke raw material structure, the volume proportion of the fibrous structure in the needle coke may be 40%-60%, optionally 45%-55%.

[0142] By selecting the above-mentioned specific type of coke raw material, under the same graphitization treatment conditions, the degree of grain development is slower, which is beneficial to regulating the degree of grain development during the graphitization process and can also reduce the volume change of the graphite particles prepared thereby during the battery charging and discharging process.

[0143] In this application, the volume proportion of mosaic, regional and fibrous structures in the coke raw material can be tested by methods known in the art. As an example, the raw materials can be taken according to GB 1997-89, the raw materials crushed to 1mm are mixed, and 40g-50g are separated. A square hole sieve is used to take 4g-5g of 0.07mm-1.0mm grade samples for film making; powder coke and block coke optical slices are prepared according to MT 116.1-86. The diameter of the powder coke optical slice shall not be less than 22mm, and the volume occupied by the cement shall be less than 1 / 3; the sample is placed on a slide with clay, flattened, and then placed on the stage for focusing. After calibrating the microscope, the polarizer and analyzer are adjusted to make them orthogonal. Insert the azurite inspection plate (1λ) so that the field of view shows the interference color of the first-order red; determine the step length of the moving ruler to ensure that more than 400 effective measuring points are evenly distributed, with a point spacing of 0.3mm-0.5mm and a line spacing of 0.5mm-0.8mm. Starting from one end of the sample, determine the type of microstructure at the intersection of the crosshairs, and divide the number of effective measurement points of the mosaic-type, regional-type, or fiber-type optical structure by the total number of test points as the volume proportion of each structure in the raw material.

[0144] In some embodiments, the coke raw material may further satisfy the following requirements: volatile matter content is less than or equal to 10 wt %, ash content is less than or equal to 0.3 wt %, and sulfur content is less than or equal to 2 wt %.

[0145] In some embodiments, during the step of crushing the coke raw material, a crusher, such as a jaw crusher, can be used to crush the coke raw material. For example, the coke raw material can be crushed to 2 mm to 5 mm and then sieved, such as through a 3-20 mesh screen.

[0146] By crushing the coke raw materials, the grain size of the graphite material crystals along the c-axis direction can be reduced, and the volume expansion of the graphite material during battery charging can be reduced.

[0147] In some embodiments, in the step of shaping the coke raw material, a shaping machine can be used to shape the crushed coke raw material. The shaping process can reduce burrs on the surface of the crushed coke raw material.

[0148] In some embodiments, during the step of classifying the coke raw material, an air classifier can be used to classify the shaped coke raw material. Optionally, the induced air frequency can be greater than or equal to 20 Hz, and the classification frequency can be greater than or equal to 60 Hz. Classification can reduce the content of large particles and fine powder in the resulting graphite precursor.

[0149] In some embodiments, in the step of crushing, shaping and grading the coke raw material to obtain a graphite precursor, the volume distribution particle size Dv1 of the obtained graphite precursor can be greater than or equal to 0.3 μm, the volume distribution particle size Dv10 can be greater than or equal to 2.0 μm, the volume distribution particle size Dv50 can be 5 μm-16 μm, and the particle size distribution (Dv90-Dv10) / Dv50 can be 1.05-1.61.

[0150] Optionally, the volume distribution particle size Dv1 of the obtained graphite precursor may be 0.3 μm-1.7 μm, optionally 0.3 μm-1.4 μm.

[0151] Optionally, the volume distribution particle size Dv10 of the obtained graphite precursor may be 2.1 μm-4.5 μm, optionally 2.1 μm-4.0 μm.

[0152] Optionally, the volume distribution particle size Dv50 of the obtained graphite precursor may be 8 μm-11 μm.

[0153] Optionally, the particle size distribution of the obtained graphite precursor (Dv90-Dv10) / Dv50 may be 1.18-1.52.

[0154] By adjusting the volume particle size distribution of the graphite precursor within the above range, the grain size of the graphite material crystal along the c-axis direction can be reduced, the volume expansion of the graphite material during battery charging can be reduced, and the graphite material can also have good dynamic properties.

[0155] In some embodiments, the graphitization furnace may be a continuous graphitization furnace.

[0156] In some embodiments, before placing the obtained graphite precursor in a graphitization furnace for graphitization treatment at a preset temperature and a preset time, the preparation method further includes the step of: pre-carbonizing the obtained graphite precursor.

[0157] Optionally, the obtained graphite precursor may be heated to 600° C.-1100° C. at a heating rate of 1° C. / min-5° C. / min and kept at this temperature for 18 h-24 h for pre-carbonization treatment.

[0158] In some embodiments, the preparation method further includes the steps of placing the obtained graphite precursor in a graphitization furnace for graphitization treatment at a preset temperature and a preset time, and then screening and demagnetizing to obtain a graphite material.

[0159] Screening can reduce the content of large particles and fine powder in the finished graphite material, thereby helping to adjust the particle size and volume particle size distribution of the resulting graphite material. This can further reduce the grain size of the graphite material crystals along the c-axis and reduce the volume expansion of the graphite material during battery charging. Demagnetization can also reduce the content of magnetic impurities in the finished graphite material. Magnetic impurities can increase battery self-discharge and reduce battery performance.

[0160] In some embodiments, the preparation method may further include the steps of: adding the graphite material obtained after graphitization treatment and the coating agent into a high-speed fusion machine for fusion treatment to obtain an intermediate; then placing the intermediate in a carbonization furnace for carbonization treatment to carbonize the coating agent and form a carbon layer on the surface of the graphite material.

[0161] Optionally, the frequency of the fusion processing may be 20 Hz-40 Hz, or optionally 30 Hz-38 Hz.

[0162] Optionally, the fusion treatment time may be 5 min-15 min, optionally 8 min-12 min.

[0163] Alternatively, the coating agent may include asphalt.

[0164] Optionally, the softening point temperature of the asphalt may be 150°C-300°C, optionally 200°C-250°C.

[0165] Optionally, the temperature of the carbonization treatment may be 950°C-1300°C, optionally 1100°C-1200°C.

[0166] Optionally, the carbonization treatment time may be 1 hour to 5 hours, optionally 2 hours to 3 hours.

[0167] Optionally, the fusion process can be performed twice: in the first fusion process, no coating agent is added to the high-speed fusion machine; in the second fusion process, the coating agent is added to the high-speed fusion machine.

[0168] In some embodiments, the preparation method includes the following steps: providing a coke raw material, the coke raw material includes petroleum coke, and based on the total volume of the coke raw material structure, the volume proportion of the mosaic and regional structures in the petroleum coke is greater than or equal to 60%, and can be selected from 65% to 80%; crushing, shaping and grading the coke raw material to obtain a graphite precursor, wherein the volume distribution particle size Dv1 of the obtained graphite precursor is greater than or equal to 0.3 μm, and can be selected from 0.3 μm to 1.4 μm, and the obtained graphite precursor is The volume distribution particle size Dv10 of the graphite precursor is greater than or equal to 2.0 μm, and can be selected from 2.1 μm to 4.0 μm. The volume distribution particle size Dv50 of the obtained graphite precursor is 5 μm to 16 μm, and can be selected from 8 μm to 11 μm. The particle size distribution (Dv90-Dv10) / Dv50 of the obtained graphite precursor is 1.05-1.61, and can be selected from 1.40-1.52. The obtained graphite precursor is heated to 600°C to 11 00℃ and keep it warm for 18h-24h for pre-carbonization treatment; the pre-carbonized material is graphitized in a continuous graphitization furnace at a preset temperature and preset time, and after cooling, it is taken out of the furnace to obtain a graphitized product. The preset temperature is 2500℃-2800℃, which can be optionally 2500℃-2750℃, and the preset time is 6h-18h, which can be optionally 8h-15h; the obtained graphitized product is sieved and demagnetized to obtain an intermediate product; the sieved and demagnetized intermediate product and the coating agent are added to a high-speed fusion machine for fusion The intermediate is obtained by fusion treatment, the fusion treatment time is 5min-15min, optionally 8min-12min, the fusion treatment frequency is 20Hz-40Hz, optionally 30Hz-38Hz; the intermediate after fusion treatment is placed in a carbonization furnace for carbonization treatment, the carbonization temperature is 950℃-1300℃, optionally 1100℃-1200℃, the carbonization time is 1h-5h, optionally 2h-3h; and the final graphite material is obtained after the finished product screening, demagnetization and mixed batch process. The graphite material meets (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, and Lc 0％SOC Less than or equal to 50nm.

[0169] In some embodiments, the preparation method includes the following steps: providing a coke raw material, the coke raw material includes needle coke, and based on the total volume of the coke raw material structure, the volume proportion of the fiber structure in the needle coke is 40%-60%, and can be optionally 45%-55%; crushing, shaping and grading the coke raw material to obtain a graphite precursor, and the volume distribution particle size Dv1 of the obtained graphite precursor is greater than or equal to 0.3 μm, and can be optionally 0.3 μm-1.4 μm, and the volume distribution particle size of the obtained graphite precursor is greater than or equal to 0.3 μm, and can be optionally 0.3 μm-1.4 μm. The volume distribution particle size Dv10 is greater than or equal to 2.0 μm, and can be selected from 2.1 μm to 4.0 μm. The volume distribution particle size Dv50 of the obtained graphite precursor is 5 μm to 16 μm, and can be selected from 8 μm to 11 μm. The particle size distribution (Dv90-Dv10) / Dv50 of the obtained graphite precursor is 1.05-1.61, and can be selected from 1.18-1.40. The obtained graphite precursor is heated to 600°C to 1100°C at a heating rate of 1°C / min to 5°C / min. ℃ and keep warm for 18h-24h for pre-carbonization treatment; the pre-carbonized material is graphitized in a continuous graphitization furnace at a preset temperature and preset time, and after cooling, it is taken out of the furnace to obtain a graphitized product. The preset temperature is 2500℃-2800℃, and can be optionally 2500℃-2750℃. The preset time is 6h-18h, and can be optionally 8h-15h; the obtained graphitized product is sieved and demagnetized to obtain an intermediate product; the sieved and demagnetized intermediate product and the coating agent are added to a high-speed fusion machine for fusion The intermediate is obtained by fusion treatment, the fusion treatment time is 5min-15min, optionally 8min-12min, and the fusion treatment frequency is 20Hz-40Hz, optionally 30Hz-38Hz; the intermediate after fusion treatment is placed in a carbonization furnace for carbonization treatment, the carbonization temperature is 950℃-1300℃, optionally 1100℃-1200℃, and the carbonization time can be 1h-5h, optionally 2h-3h; after the finished product screening, demagnetization and mixed batch process, the final graphite material is obtained. The graphite material meets (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, and Lc 0％SOC Less than or equal to 50nm.

[0170] [Negative electrode]

[0171] The battery cell includes a negative electrode plate.

[0172] The negative electrode sheet includes a negative electrode current collector and a negative electrode film disposed on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two surfaces that are opposite to each other in the thickness direction of the negative electrode current collector, and the negative electrode film is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0173] The negative electrode film layer includes a negative electrode active material, which includes the above-mentioned graphite material or the graphite material prepared by the above-mentioned method.

[0174] In some embodiments, the negative electrode active material may further include other materials known in the art, for example, other materials include but are not limited to one or more of natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

[0175] 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.

[0176] 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).

[0177] 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.

[0178] In some embodiments, the compaction density of the negative electrode film layer can be 1.15 g / cm 3 -1.55g / cm 3 The compaction density of the negative electrode film layer refers to the compaction density of the negative electrode film layer on one side of the negative electrode current collector.

[0179] In some embodiments, the surface density of the negative electrode film layer can be 7 mg / cm 2 -15mg / cm 2 The surface density of the negative electrode film layer refers to the surface density of the negative electrode film layer on one side of the negative electrode current collector.

[0180] The areal density of the negative electrode film is well known in the art and can be measured using methods known in the art. For example, a negative electrode sheet coated on one side and cold-pressed can be taken (if it is a double-sided coated negative electrode sheet, the negative electrode film layer on one side can be wiped off first), punched into small discs with an area of ​​S1, and the mass of each disc is measured and recorded as M1. The negative electrode film layer of the weighed negative electrode sheet is then wiped off, and the mass of the negative electrode current collector is weighed and recorded as M0. The areal density of the negative electrode film layer = (M1-M0) / S1.

[0181] The compacted density of the negative electrode film layer is well known in the art and can be measured using methods known in the art. The compacted density of the negative electrode film layer = the surface density of the negative electrode film layer / the thickness of the negative electrode film layer. The thickness of the negative electrode film layer is well known in the art and can be measured using methods known in the art, such as using a micrometer.

[0182] 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, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0183] 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.

[0184] 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).

[0185] [Positive electrode]

[0186] The battery cell includes a positive electrode plate.

[0187] 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.

[0188] 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.

[0189] In some embodiments, the positive electrode active material may include one or more of lithium-containing phosphates and modified compounds thereof, thereby further improving the cycle life of the battery.

[0190] 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.

[0191] 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. In the present application, the modified compound of each of the above-mentioned positive electrode active materials may be a doping modification and / or surface coating modification of the positive electrode active material.

[0192] 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.

[0193] 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).

[0194] 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).

[0195] 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, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0196] [Electrolytes]

[0197] 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 selected from solid electrolytes and liquid electrolytes (i.e., electrolytes).

[0198] In some embodiments, the electrolyte is an electrolyte solution including an electrolyte salt and a solvent.

[0199] 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).

[0200] 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, 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).

[0201] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and 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. Optionally, the additives may include one or more of vinylene carbonate and fluoroethylene carbonate (FEC). Optionally, the mass of the additives does not exceed 5% of the total mass of the electrolyte.

[0202] [Isolation film]

[0203] 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.

[0204] 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.

[0205] 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.

[0206] 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.

[0207] Electrical devices

[0208] 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.

[0209] 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.

[0210] 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.

[0211] 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.

[0212] Example

[0213] 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.

[0214] Example 1

[0215] (1) Preparation of negative electrode active materials

[0216] A petroleum coke raw material is provided, wherein the volatile matter mass content is less than or equal to 10wt%, the ash mass content is less than or equal to 0.3wt%, the sulfur mass content is less than or equal to 2wt%, and the following conditions are met: the volume proportion of the mosaic and regional structures is 69%.

[0217] The above petroleum coke raw materials are coarsely crushed, and then the coarsely crushed materials are crushed and sieved. The sieved materials are shaped and graded. A certain amount of fine powder is removed during the grading process to obtain a precursor. The grading frequency of the air flow classifier is 60Hz, and the induced draft frequency is 20Hz. The volume distribution particle size Dv1 of the obtained precursor is controlled at 0.3μm, the volume distribution particle size Dv10 is controlled at 2.1μm, the volume distribution particle size Dv50 is controlled at 8.5μm, and the particle size distribution (Dv90-Dv10) / Dv50 is controlled at 1.52. Then, a pre-carbonization treatment is carried out. During the pre-carbonization treatment, the temperature is increased at a heating rate of 5℃ / min. Heat to 950℃ and keep warm for 20h; then the pre-carbonized material is continuously graphitized at 2500℃ for 12h to obtain a graphitized product; the obtained graphitized product is screened and demagnetized to obtain an intermediate product; the intermediate product is fused for the first time in a high-speed fusion machine, and then asphalt is added for a second fusion process. The frequency of the fusion process is 34Hz, the time of each fusion process is 8min, and the mass ratio of the intermediate product to the asphalt is 98:2; the fused material is transferred to a carbonization furnace for carbonization at 1150℃ for 2h; finally, after the finished product screening, demagnetization and mixed batch process, a graphite material is obtained. The volume distribution particle size Dv1 of the graphite material is 1.1μm, the volume distribution particle size Dv10 is 4.3μm, the volume distribution particle size Dv50 is 9.5μm, the particle size distribution (Dv90-Dv10) / Dv50 is 1.49, and the graphite material meets (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC It is 0.0169.

[0218] (2) Preparation of negative electrode sheet

[0219] The above graphite material, conductive agent Super P, thickener CMC, and binder SBR were mixed in a mass ratio of 96:1:1.2:1.8, and deionized water was added as a solvent. Then, the mixture was stirred in a vacuum mixer until the system became uniform to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on the negative electrode current collector copper foil, and the negative electrode sheets were obtained after drying, cold pressing, and slitting. The compacted density of the negative electrode film layer is 1.30g / cm 3 , the surface density is 10.22 mg / cm 2 .

[0220] (3) Preparation of positive electrode sheet

[0221] The positive electrode active material lithium iron phosphate, conductive agent Super P, and binder PVDF were mixed in a mass ratio of 97:1:2, and the solvent N-methylpyrrolidone (NMP) was added. Then, the mixture was stirred in a vacuum mixer until the system became uniform to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil, and the positive electrode sheets were obtained after drying, cold pressing, and slitting. The compacted density of the positive electrode film layer is 2.50g / cm 3 , the surface density is 19.51 mg / cm 2 .

[0222] (4) Preparation of electrolyte

[0223] In an argon atmosphere glove box with a water content of less than 10 ppm, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a mass ratio of 1:1:1 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare a solution with a concentration of 1.0 mol / L. Finally, vinylene carbonate was added to the solution at a mass content of 2 wt%, based on the total mass of the electrolyte.

[0224] (5) Preparation of isolation membrane

[0225] Polypropylene film is used as the isolation film.

[0226] (6) Preparation of batteries (full batteries)

[0227] 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, dried, and then injected with electrolyte, and after vacuum packaging, standing, formation, shaping and other processes, a battery is obtained.

[0228] (7) Preparation of button cells

[0229] A lithium metal sheet is used as a counter electrode and assembled into a button battery with the negative electrode sheet, separator and electrolyte prepared above.

[0230] Examples 2 to 5 and Comparative Examples 1 to 3

[0231] Except for the preparation process of the negative electrode active material, the preparation process of the battery is the same as that of Example 1. The specific parameters are shown in Table 1.

[0232] Table 1

[0233] Example 6

[0234] 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.

[0235] (1) Preparation of negative electrode active materials

[0236] A needle coke raw material is provided, wherein the volatile matter mass content is less than or equal to 10wt%, the ash mass content is less than or equal to 0.3wt%, the sulfur mass content is less than or equal to 2wt%, and the volume proportion of the fiber structure is 53%.

[0237] The needle coke raw material is crushed into 2mm-5mm by a crusher and passed through a 3-20 mesh screen; the small particles after coarse crushing are dried to a moisture content of less than 0.5%, and then the small particles of needle coke are crushed, shaped and classified by a ball mill. A certain amount of fine powder is removed during the classification process to obtain a precursor. The classification frequency of the air flow classifier is 60Hz and the induced draft frequency is 20Hz; the volume distribution particle size Dv1 of the obtained precursor is controlled to be 0.4μm, the volume distribution particle size Dv10 is controlled to be 2.8μm, the volume distribution particle size Dv50 is controlled to be 8.2μm, and the particle size distribution (Dv90-Dv10) / Dv50 is controlled to be 1.34, and then pre-carbonization treatment is carried out. During the carbonization treatment, the temperature is raised to 950°C at a heating rate of 5°C / min and kept warm for 2 hours; the pre-carbonized material is then continuously graphitized at 2650°C for 12 hours to obtain a graphitized product; the obtained graphitized product is screened and demagnetized to obtain an intermediate product; the intermediate product is subjected to a first fusion treatment in a high-speed fusion machine, and then asphalt is added for a second fusion treatment, the frequency of the fusion treatment is 34Hz, the time for each fusion treatment is 8 minutes, and the mass ratio of the intermediate product to the asphalt is 98:2; the fused material is transferred to a carbonization furnace for carbonization treatment at 1150°C for 2 hours; finally, after the finished product screening, demagnetization and mixed batching process, the graphite material is obtained. The graphite material has a volume distribution particle size Dv1 of 1.5 μm, a volume distribution particle size Dv10 of 4.0 μm, a volume distribution particle size Dv50 of 9.2 μm, and a primary particle graphite material with a particle size distribution (Dv90-Dv10) / Dv50 of 1.27, and the graphite material satisfies (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC It is 0.0195.

[0238] Example 7 and Comparative Example 4

[0239] Except for the preparation process of the negative electrode active material, the preparation process of the battery is the same as that of Example 6. The specific parameters are shown in Table 2.

[0240] Table 2

[0241] Test section

[0242] (1) Gram capacity test of graphite material

[0243] The negative electrode active material samples prepared in each embodiment and comparative example were thoroughly stirred and mixed with the conductive agent carbon black and the binder polyvinylidene fluoride (PVDF) in a suitable amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 91.6:1.8:6.6 to form a uniform negative electrode slurry; the negative electrode slurry was evenly coated on the surface of the negative electrode current collector copper foil, dried in an oven, and then pressed to 1.3 g / cm using a double-roll cold press. 3 -1.5g / cm 3 The compaction density is set aside; dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a mass ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L; thereafter, a metal lithium sheet is used as a counter electrode and a polypropylene film is used as an isolation membrane to assemble a CR2430 button battery in an argon-protected glove box.

[0244] At 25°C, the prepared button cell was first discharged at a constant current of 0.05C to 0.005V, then discharged at a constant current of 10μA to 0.005V. The cell was allowed to rest for 5 minutes, and the first-cycle discharge capacity was recorded. The cell was then charged at a constant current of 0.1C to 2.0V, and the first-cycle charge capacity was recorded. The ratio of the first-cycle charge capacity of the button cell to the mass of the negative electrode active material sample is the gram capacity of the negative electrode active material (i.e., graphite material).

[0245] (2)Lc 0％SOC 、Lc 50％SOC 、Lc 100％SOC 、La 0％SOC Test

[0246] At 25°C, the button cell prepared in the above test was left to stand for 6 hours, then discharged at a constant current of 0.15 mA to 5.0 mV; left to stand for 5 minutes, and then continued to discharge at a constant current of 50 μA to 5.0 mV; then charged at a constant current of 0.30 mA to 2 V, at which point the charge capacity was recorded as C0; the negative electrode was then disassembled from the button cell, tested using an X-ray diffractometer, and Lc was calculated using the Scherrer formula. 0％SOC and La 0％SOC .

[0247] At 25°C, the button cell prepared in the above test was left to stand for 6 hours, then discharged at a constant current of 0.15 mA to 5.0 mV; left to stand for 5 minutes, and then continued to discharge at a constant current of 50 μA to 5.0 mV; then charged at a constant current of 0.30 mA to 2 V, at which point the charge capacity was recorded as C0; then discharged at a constant current of 0.05 C0 for 10 hours; then the negative electrode was disassembled from the button cell, tested by X-ray diffractometer, and Lc was calculated using the Scherrer formula. 50％SOC .

[0248] At 25°C, the button cell prepared in the above test was left to stand for 6 hours, then discharged at a constant current of 0.15 mA to 5.0 mV; left to stand for 5 minutes, and then continued to discharge at a constant current of 50 μA to 5.0 mV; then charged at a constant current of 0.30 mA to 2 V, at which point the charge capacity was recorded as C0; then discharged at a constant current of 0.05 C0 for 20 hours; then the negative electrode was disassembled from the button cell, tested by X-ray diffractometer, and Lc was calculated using the Scherrer formula. 100％SOC .

[0249] (3) Battery cycle performance test

[0250] At 60°C, the prepared full battery was charged at a constant current of 1C to 3.65V and discharged at a constant current of 1C to 2.5V for cyclic charge and discharge testing. The test was stopped until the discharge capacity of the full battery decayed to 80% of the initial discharge capacity. The number of cycles of the full battery was recorded. The greater the number of cycles of the full battery, the better the cycling stability of the full battery.

[0251] The test results are shown in Tables 3 and 4.

[0252] Table 3

[0253] Table 4

[0254] From the test results in Table 3 and Table 4, it can be seen that (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, and Lc 0％SOC Graphite materials with a thickness of 50nm or less have excellent cycling performance. This is because the volume change of the graphite material is small during the entire lithium insertion process, which can reduce the lattice expansion of the graphite material during battery charging and reduce the thickness expansion of the negative electrode plate. This can reduce side reactions at the negative electrode-electrolyte interface and reduce the irreversible consumption of lithium ions, thereby improving the cycle life of the battery and meeting the demand for long-life energy storage batteries.

[0255] 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 graphite material, wherein: The graphite material satisfies (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, and Lc 0％SOC Less than or equal to 50nm; Lc 0％SOC It indicates the grain size of the graphite material along the c-axis direction in the lithium-embedded 0% SOC state, in nm; Lc 50％SOC It indicates the grain size of the graphite material along the c-axis direction when the lithium is inserted into the 50% SOC state, in nm; Lc 100％SOC It represents the grain size of the graphite material along the c-axis direction in the lithium-intercalated 100% SOC state, in nm.

2. The graphite material according to claim 1, wherein 0.0100≤(Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, optionally, 0.0100≤(Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0500; and / or, 15nm≤Lc 0％SOC ≤47nm, optionally, 25nm≤Lc 0％SOC ≤45nm.

3. The graphite material according to any one of claims 1 to 2, wherein: 20nm≤Lc 100％SOC ≤60nm, optionally, 28nm≤Lc 100％SOC ≤50nm.

4. The graphite material according to any one of claims 1 to 3, wherein: The gram capacity of the graphite material is 280 mAh / g-340 mAh / g, and can be optionally 290 mAh / g-335 mAh / g.

5. The graphite material according to any one of claims 1 to 4, wherein: The volume distribution particle size Dv1 of the graphite material is 0.5 μm-3.1 μm, and can be 1 μm-2.5 μm; and / or, The volume distribution particle size Dv10 of the graphite material is 3 μm-6.2 μm, and can be 3.2 μm-5 μm; and / or, The volume distribution particle size Dv50 of the graphite material is 5 μm-15 μm, and can be 8 μm-12 μm; and / or, The particle size distribution (Dv90-Dv10) / Dv50 of the graphite material is 1.02-1.57, and can be optionally 1.11-1.

49.

6. The graphite material according to any one of claims 1 to 5, wherein: The grain size La of the graphite material along the a-axis direction in the lithium-intercalated 0% SOC state is 0％SOC Less than or equal to 140nm.

7. The graphite material according to any one of claims 1 to 6, wherein: The graphitization degree of the graphite material is 70%-88%, and can be optionally 75%-85%.

8. The graphite material according to any one of claims 1 to 7, wherein: The tap density of the graphite material is 1.0 m 3 / g-1.3m 3 / g; and / or, The specific surface area of ​​the graphite material is 0.6 m 2 / g-2m 2 / g.

9. The graphite material according to any one of claims 1 to 8, wherein: The surface of the graphite material also includes a carbon layer.

10. A method for preparing a graphite material, comprising the following steps: Providing coke raw materials; The coke raw material is crushed, shaped and graded to obtain a graphite precursor; The obtained graphite precursor is placed in a graphitization furnace for graphitization treatment at a preset temperature and a preset time, and then taken out of the furnace after cooling to obtain a graphite material, wherein the preset temperature is less than 3000° C. and the preset time is less than 24 hours. in, The graphite material satisfies (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, and Lc 0％SOC Less than or equal to 50nm; Lc 0％SOC It indicates the grain size of the graphite material along the c-axis direction in the lithium-embedded 0% SOC state, in nm; Lc 50％SOC It indicates the grain size of the graphite material along the c-axis direction when the lithium is inserted into the 50% SOC state, in nm; Lc 100％SOC It represents the grain size of the graphite material along the c-axis direction in the lithium-intercalated 100% SOC state, in nm.

11. The preparation method according to claim 10, wherein: The graphitization furnace is a continuous graphitization furnace; and / or, The preset temperature is 2500°C-2800°C, and can be optionally 2500°C-2750°C; and / or, The preset time is 6h-18h, and can be optionally 8h-15h.

12. The preparation method according to any one of claims 10 to 11, wherein: The coke raw material includes at least one of petroleum coke and needle coke; Optionally, the coke raw material also meets the following requirements: the mass content of volatile matter is less than or equal to 10wt%, the mass content of ash is less than or equal to 0.3wt%, and the mass content of sulfur is less than or equal to 2wt%.

13. The preparation method according to claim 12, wherein: The coke raw material is petroleum coke, and based on the total volume of the coke raw material structure, the volume proportion of the mosaic and regional structures in the petroleum coke is greater than or equal to 60%, and can be optionally 65%-80%; or, The coke raw material is needle coke, and based on the total volume of the coke raw material structure, the volume proportion of the fiber-type structure in the needle coke is 40%-60%, and can be optionally 45%-55%.

14. The preparation method according to any one of claims 10 to 13, wherein: In the step of crushing, shaping and classifying the coke raw material to obtain a graphite precursor, The volume distribution particle size Dv1 of the obtained graphite precursor is greater than or equal to 0.3 μm, and can be selected to be 0.3 μm-1.4 μm; and / or, The volume distribution particle size Dv10 of the obtained graphite precursor is greater than or equal to 2.0 μm, and can be selected to be 2.1 μm-4.0 μm; and / or, The volume distribution particle size Dv50 of the obtained graphite precursor is 5 μm-16 μm, and can be 8 μm-11 μm; and / or, The particle size distribution (Dv90-Dv10) / Dv50 of the obtained graphite precursor is 1.05-1.61, and can be optionally 1.18-1.

52.

15. The preparation method according to any one of claims 10 to 14, wherein: Before placing the obtained graphite precursor in a graphitization furnace for graphitization treatment at a preset temperature and a preset time, the method further includes the steps of: pre-carbonizing the obtained graphite precursor; Optionally, the obtained graphite precursor is heated to 600° C.-1100° C. at a heating rate of 1° C. / min-5° C. / min and kept at this temperature for 18 h-24 h for pre-carbonization treatment.

16. The preparation method according to any one of claims 10 to 15, wherein: The preparation method further comprises the steps of placing the obtained graphite precursor in a graphitization furnace for graphitization treatment at a preset temperature and a preset time, and then screening and removing magnetism to obtain a graphite material.

17. The preparation method according to any one of claims 10 to 16, wherein: The preparation method further comprises the steps of: mixing the obtained graphite material with the coating agent and placing the mixture in a carbonization furnace for carbonization treatment to form a carbon layer on the surface of the graphite material; Optionally, the coating agent includes asphalt, and more preferably, the softening point temperature of the asphalt is 150°C-300°C, and optionally 200°C-250°C; and / or, Optionally, the temperature of the carbonization treatment is 950°C-1300°C, optionally 1100°C-1200°C; and / or, Optionally, the carbonization treatment time is 1h-5h, optionally 2h-3h.

18. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, wherein: The negative electrode film layer comprises the graphite material according to any one of claims 1 to 9 or the graphite material prepared by the preparation method according to any one of claims 10 to 17.

19. The negative electrode sheet according to claim 18, wherein: The compaction density of the negative electrode film layer is 1.15 g / cm 3 -1.55g / cm 3 and / or, The surface density of the negative electrode film layer is 7 mg / cm 2 -15mg / cm 2 .

20. A battery comprising the negative electrode sheet according to any one of claims 18 to 19.

21. An electrical device comprising the battery according to claim 20, wherein the battery is used to provide electrical energy.

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