Graphite material and method for manufacturing the same, and negative electrode sheet, battery, and electric device comprising the same

Abstract

The application discloses a graphite material and a preparation method thereof, a negative electrode sheet containing the graphite material, a battery and an electric device, and the graphite material meets Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, and Lc 0％SOC is less than or equal to 50 nm. The application can enable the battery to have a long cycle life.

Description

Technical Field

[0001] This application relates to a graphite material and its preparation method, as well as a negative electrode sheet, battery and electrical device containing the same. Background Technology

[0002] In recent years, batteries have been widely used in energy storage, leading to increasingly higher requirements for battery cycle life. However, achieving longer cycle life while maintaining high energy density remains a challenge in current battery development. Summary of the Invention

[0003] This application provides a graphite material and a method for preparing the same, as well as a negative electrode sheet, a battery, and an electrical device containing the same, which enables the battery to have a long cycle life.

[0004] In a first aspect, this 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.

[0005] Lc 0％SOC Lc represents the grain size of the graphite material along the c-axis in the 0% SOC state after lithium intercalation, in nm. 50％SOC Lc represents the grain size of the graphite material along the c-axis in the 50% SOC state after lithium intercalation, in nm. 100％SOC The value represents the grain size of the graphite material along the c-axis in the 100% SOC state after lithium intercalation, expressed in nm.

[0006] The graphite material provided in this application embodiment satisfies (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, and Lc 0％SOC With a particle size of 50 nm or less, graphite materials have a smaller grain size along the c-axis in the 0% SOC state of lithium intercalation, and the volume change of graphite materials during the entire lithium intercalation process is small. This can reduce the lattice expansion of graphite materials during battery charging, reduce the thickness expansion of the negative electrode sheet, 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, which is conducive to meeting the needs of long-life energy storage batteries.

[0007] In some embodiments, 0.0100 ≤ (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, optionally, 0.0100≤(Lc 100％SOC -Lc0％SOC ) / Lc 50％SOC ≤0.0500. This helps the battery to better balance higher energy density and longer cycle life.

[0008] In some embodiments, 15nm≤Lc 0％SOC ≤47nm, optionally, 25nm≤Lc 0％SOC ≤45nm. Grain size Lc of graphite material along the c-axis in the 0% SOC state after lithium intercalation. 0％SOC Within the aforementioned range, the lattice expansion of graphite materials during battery charging can be further reduced, as can the thickness expansion of the negative electrode sheet. This can further reduce the side reactions at the negative electrode-electrolyte interface, reduce the irreversible consumption of lithium ions, and thus further improve the cycle life of the battery.

[0009] In some embodiments, 20nm≤Lc 100％SOC ≤60nm, optionally, 28nm≤Lc 100％SOC ≤50nm. Grain size Lc of graphite material along the c-axis in the 100% SOC state after lithium intercalation. 100％SOC Within the aforementioned range, the lattice expansion of graphite materials during battery charging can be further reduced, as can the thickness expansion of the negative electrode sheet. This can further reduce the side reactions at the negative electrode-electrolyte interface, reduce the irreversible consumption of lithium ions, and thus further improve the cycle life of the battery.

[0010] In some embodiments, the specific capacity of the graphite material is 280 mAh / g-340 mAh / g, optionally 290 mAh / g-335 mAh / g. When the specific 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.

[0011] In some embodiments, the volume distribution particle size Dv1 of the graphite material is 0.5 μm-3.1 μm, and can be selected as 1 μm-2.5 μm.

[0012] In some embodiments, the volume distribution particle size Dv10 of the graphite material is 3μm-6.2μm, and can be optionally 3.2μm-5μm.

[0013] In some embodiments, the volume distribution particle size Dv50 of the graphite material is 5μm-15μm, and can be selected as 8μm-12μm.

[0014] By adjusting the volume distribution and particle size of graphite materials, the grain size along the c-axis during lithium intercalation can be reduced. This reduces the lattice expansion of graphite materials during battery charging, decreases the thickness expansion of the negative electrode sheet, thereby reducing side reactions at the negative electrode-electrolyte interface, reducing irreversible lithium-ion consumption, and ultimately improving the cycle life of the battery. It can also increase the lithium intercalation channels in graphite materials and reduce lithium deposition.

[0015] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the graphite material is 1.02-1.57, and optionally 1.11-1.49.

[0016] When the particle size distribution (Dv90-Dv10) / Dv50 of graphite material is within the above range, the thickness expansion of the negative electrode sheet 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.

[0017] In some embodiments, the grain size La of the graphite material along the a-axis in the lithium-intercalated 0% SOC state is... 0％SOC Less than or equal to 140 nm. The grain size La along the a-axis of graphite material in a lithium-intercalated 0% SOC state. 0％SOC Within the aforementioned range, graphite materials exhibit high isotropy and small grain size, which allows them to have more lithium intercalation channels, thereby reducing lithium deposition and improving battery cycle life.

[0018] In some embodiments, the graphitization degree of the graphite material is 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 in the battery; on the other hand, it can reduce the grain size along the c-axis direction during lithium intercalation, thereby reducing the lattice expansion of the graphite material during battery charging, reducing the thickness expansion of the negative electrode sheet, thus reducing the side reactions at the negative electrode-electrolyte interface, reducing irreversible lithium-ion consumption, and ultimately improving the cycle life of the battery.

[0019] In some embodiments, the tap density of the graphite material is 1.0 m³. 3 / g-1.3m 3 / g. When the tap density of graphite material is within the above range, the compaction density of the negative electrode film can be increased, which is beneficial for the battery to have a higher energy density.

[0020] In some embodiments, the specific surface area of ​​the graphite material is 0.6 m². 2 / g-2m 2 / g. When the specific surface area of ​​graphite materials is within the above range, side reactions at the negative electrode-electrolyte interface can be reduced, and irreversible lithium-ion consumption can be decreased, thereby improving the cycle life of the battery.

[0021] In some embodiments, the surface of the graphite material further includes a carbon layer.

[0022] Secondly, this application provides a method for preparing graphite material, comprising the following steps: providing coke raw material; crushing, shaping, and classifying the coke raw material to obtain a graphite precursor; placing the obtained graphite precursor in a graphitization furnace for graphitization treatment at a preset temperature and a preset time, and then removing it from the furnace after cooling to obtain graphite material, wherein the preset temperature is less than 3000℃ and the preset time is less than 24h, 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 Lc represents the grain size of the graphite material along the c-axis in the 0% SOC state after lithium intercalation, in nm. 50％SOC Lc represents the grain size of the graphite material along the c-axis in the 50% SOC state after lithium intercalation, in nm. 100％SOC The value represents the grain size of the graphite material along the c-axis in the 100% SOC state after lithium intercalation, expressed in nm.

[0023] The graphite material prepared by the preparation method provided in this application has a small grain size along the c-axis direction, and the volume change of the graphite material is small throughout the lithium intercalation process. This can reduce the lattice expansion of the graphite material during battery charging, reduce the thickness expansion of the negative electrode sheet, 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.

[0024] In some embodiments, the graphitization furnace is a continuous graphitization furnace.

[0025] In some embodiments, the preset temperature is 2500℃-2800℃, and can be selected as 2500℃-2750℃.

[0026] In some embodiments, the preset time is 6h-18h, and can be selected as 8h-15h.

[0027] By further adjusting the preset temperature and / or preset time during graphitization, on the one hand, the lattice expansion of graphite materials during battery charging can be reduced, the thickness expansion of the negative electrode sheet 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 specific capacity, so that the battery can have both a long cycle life and a high energy density.

[0028] In some embodiments, the coke raw material includes at least one of petroleum coke and needle coke.

[0029] In some embodiments, the coke raw material is petroleum coke, and based on the total volume of the coke raw material structure, the volume ratio of the embedded and regional structures in the petroleum coke is greater than or equal to 60%, and can be selected as 65%-80%.

[0030] In some embodiments, the coke feedstock is needle coke, and based on the total volume of the coke feedstock structure, the volume percentage of the fibrous structure in the needle coke is 40%-60%, optionally 45%-55%.

[0031] By selecting the specific types of coke raw materials mentioned above, under the same graphitization treatment conditions, the degree of grain development is slower, which is beneficial to regulate the degree of grain development during the graphitization process and can also reduce the volume change of the graphite particles prepared in this way during the battery charging and discharging process.

[0032] In some embodiments, the coke raw material further satisfies the following conditions: volatile matter content ≤ 10 wt%, ash content ≤ 0.3 wt%, and sulfur content ≤ 2 wt%.

[0033] In some embodiments, 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, 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, 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, optionally 8 μm-11 μm; and / or, the particle size distribution (Dv90-Dv10) / Dv50 of the obtained graphite precursor is 1.05-1.61, optionally 1.18-1.52.

[0034] By adjusting the volumetric particle size distribution of the graphite precursor within the aforementioned range, the grain size of the graphite material along the c-axis can be reduced, the volume expansion of the graphite material during battery charging can be reduced, and the graphite material can also have good kinetic properties.

[0035] In some embodiments, before placing the obtained graphite precursor in a graphitization furnace for graphitization at a preset temperature and time, the method further includes a step of pre-carbonizing the obtained graphite precursor. Optionally, the obtained graphite precursor is heated to 600℃-1100℃ at a heating rate of 1℃ / min-5℃ / min and held at that temperature for 18h-24h for pre-carbonization.

[0036] 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, followed by sieving and demagnetization to obtain graphite material.

[0037] In some embodiments, the preparation method further includes the step of: mixing the obtained graphite material with a coating agent and placing it in a carbonization furnace for carbonization treatment to form a carbon layer on the surface of the graphite material.

[0038] Optionally, the coating agent includes asphalt, and more preferably, the softening point temperature of the asphalt is 150℃-300℃, or optionally 200℃-250℃.

[0039] Optionally, the carbonization temperature is 950℃-1300℃, or optionally 1100℃-1200℃.

[0040] Optionally, the carbonization treatment time is 1h-5h, or 2h-3h.

[0041] Thirdly, this application provides a negative electrode sheet, including a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector, wherein the negative electrode film layer includes the graphite material of the first aspect of this application or the graphite material prepared by the preparation method of the second aspect of this application.

[0042] In some embodiments, the compaction density of the negative electrode film is 1.15 g / cm³. 3 -1.55g / cm 3 .

[0043] In some embodiments, the areal density of the negative electrode film is 7 mg / cm³. 2 -15mg / cm 2 .

[0044] Fourthly, this application provides a battery including the negative electrode sheet of the third aspect of this application.

[0045] Fifthly, this application provides an electrical device including the battery of the fourth aspect of this application, said battery being used to provide electrical energy.

[0046] The electrical device of this application includes the battery provided in this application, and therefore has at least the same advantages as the battery. Attached Figure Description

[0047] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of a battery cell provided in some embodiments of this application.

[0049] Figure 2 This is an exploded view of a battery cell provided in some embodiments of this application.

[0050] Figure 3 This is a schematic diagram of a battery module provided in some embodiments of this application.

[0051] Figure 4 This is a schematic diagram of a battery pack provided in some embodiments of this application.

[0052] Figure 5 yes Figure 4 The diagram shown is an exploded view of the battery pack.

[0053] Figure 6 This is a schematic diagram of an electrical device provided in some embodiments of this application.

[0054] The accompanying drawings are not necessarily drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Individual battery cell, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0055] The following detailed description, with appropriate reference to the accompanying drawings, discloses the graphite material and its preparation method, as well as embodiments of the negative electrode sheet, battery, and electrical device comprising the graphite material. However, unnecessary details may be omitted. For example, detailed descriptions of well-known facts and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0056] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0057] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0058] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0059] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the method may also 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 it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0060] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0061] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0062] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0063] The battery mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0064] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. A battery cell can be cylindrical, cuboid, or other shapes, etc., and the embodiments of this application are not limited in this respect. Figure 1 The example shown is a rectangular battery cell 5.

[0065] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed within the housing. In some embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least part of the vehicle's floor, or a portion of the housing can be at least part of the vehicle's crossbeams and longitudinal beams.

[0066] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0067] A single battery cell generally includes an electrode assembly and an electrolyte. The electrode assembly typically includes a positive electrode and a negative electrode. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited in this regard.

[0068] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode components and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0069] In some embodiments, such as Figure 2As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted according to requirements.

[0070] In some embodiments, individual battery cells can be assembled into a battery module, and the number of individual battery cells contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module. Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0071] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0072] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0073] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0074] The battery provided in this application embodiment may include a lithium-ion battery.

[0075] The graphite material provided in this application embodiment satisfies (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, and Lc 0％SOC Less than or equal to 50nm.

[0076] Lc 0％SOC Lc represents the grain size of graphite material along the c-axis in the 0% SOC state after lithium intercalation, in nm. 50％SOC Lc represents the grain size of graphite material along the c-axis in the 50% SOC state after lithium intercalation, in nm.100％SOC This indicates the grain size of graphite material along the c-axis in the 100% SOC state after lithium intercalation, expressed in nm.

[0077] As the battery is charged, lithium ions continuously embed into the graphite lattice, causing the lattice to expand. Furthermore, with increasing battery cycle count, significant lattice expansion occurs in the graphite, leading to substantial volume changes in the graphite particles. This results in repeated breakage and formation of the solid electrolyte interphase (SEI) film on the surface of the graphite particles, increasing side reactions at the negative electrode-electrolyte interface, accelerating irreversible lithium ion consumption, and impacting battery cycle life. In addition, the significant lattice expansion of graphite also worsens the electronic contact between the graphite particles and the negative electrode current collector, causing some graphite particles to lose electronic contact and electrochemical activity. This leads to uneven local current at the negative electrode, accelerating lithium plating, accelerating battery capacity decay, and reducing battery cycle performance.

[0078] The graphite material provided in this application embodiment 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 With a size greater than 0 and less than or equal to 50 nm, the grain size of graphite material in the c-axis direction is small when lithium is inserted at 0% SOC, and the volume change of graphite material is small throughout the lithium insertion process. This can reduce the lattice expansion of graphite material during battery charging, reduce the thickness expansion of the negative electrode sheet, 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, which is conducive to meeting the needs of long-life energy storage batteries.

[0079] Optionally, (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC It can 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 any range of the above values.

[0080] 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 to better balance higher energy density and longer cycle life.

[0081] In some embodiments, 15nm≤Lc 0％SOC ≤47nm, optionally, 25nm≤Lc 0％SOC ≤45nm.

[0082] Grain size Lc of graphite material along the c-axis in the lithium-intercalated 0% SOC state 0％SOC Within the aforementioned range, the lattice expansion of graphite materials during battery charging can be further reduced, as can the thickness expansion of the negative electrode sheet. This can further reduce the side reactions at the negative electrode-electrolyte interface, reduce the irreversible consumption of lithium ions, and thus further improve the cycle life of the battery.

[0083] In some embodiments, 20nm≤Lc 100％SOC ≤60nm, optionally, 28nm≤Lc 100％SOC ≤50nm.

[0084] The grain size Lc of graphite material along the c-axis in the 100% SOC state after lithium intercalation 100％SOC Within the aforementioned range, the lattice expansion of graphite materials during battery charging can be further reduced, as can the thickness expansion of the negative electrode sheet. This can further reduce the side reactions at the negative electrode-electrolyte interface, reduce the irreversible consumption of lithium ions, and thus further improve the cycle life of the battery.

[0085] In some embodiments, the grain size La along the a-axis direction of the graphite material in the lithium-intercalated 0% SOC state is... 0％SOC It can be greater than 0 and less than or equal to 140nm.

[0086] The grain size La along the a-axis of graphite material in the lithium-intercalated 0% SOC state. 0％SOC Within the aforementioned range, graphite materials exhibit high isotropy and small grain size, which allows them to have more lithium intercalation channels, thereby reducing lithium deposition and improving battery cycle life.

[0087] In some embodiments, the specific capacity of the graphite material can be 280mAh / g-340mAh / g, and optionally 290mAh / g-335mAh / g.

[0088] When the specific capacity of graphite materials is within the above range, it is beneficial for the battery to have both high energy density and long cycle life.

[0089] In some embodiments, the graphitization degree of the graphite material can be 70%-88%, optionally 75%-85%.

[0090] When the degree of graphitization of graphite materials is within the above range, on the one hand, the graphite materials can have a higher capacity, enabling the battery to have a higher energy density; on the other hand, it can reduce the grain size along the c-axis direction during the lithium intercalation process of graphite materials, thereby reducing the lattice expansion of graphite materials during battery charging, reducing the thickness expansion of the negative electrode sheet, thus reducing the side reactions at the negative electrode-electrolyte interface, reducing the irreversible consumption of lithium ions, and further improving the cycle life of the battery.

[0091] In some embodiments, the graphite material has a primary particle morphology.

[0092] In some embodiments, the volumetric particle size Dv1 of the graphite material can be 0.5 μm-3.1 μm, and can be selected as 1 μm-2.5 μm.

[0093] In some embodiments, the volumetric particle size Dv10 of the graphite material can be 3μm-6.2μm, and optionally 3.2μm-5μm.

[0094] In some embodiments, the volumetric particle size Dv50 of the graphite material can be 5μm-15μm, and optionally 8μm-12μm.

[0095] By adjusting the volume distribution and particle size of graphite materials, the grain size along the c-axis during lithium intercalation can be reduced. This reduces the lattice expansion of graphite materials during battery charging, decreases the thickness expansion of the negative electrode sheet, thereby reducing side reactions at the negative electrode-electrolyte interface, reducing irreversible lithium-ion consumption, and ultimately improving the cycle life of the battery. It can also increase the lithium intercalation channels in graphite materials and reduce lithium deposition.

[0096] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the graphite material can be 1.02-1.57, and optionally 1.11-1.49.

[0097] When the particle size distribution (Dv90-Dv10) / Dv50 of the graphite material 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 lithium-ion consumption, and thus improving the battery's cycle life. When the particle size distribution (Dv90-Dv10) / Dv50 of the graphite material is large, the content of fine powder in the graphite material is high, which increases the irreversible capacity loss during battery cycling, thereby 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 battery cycling causes repeated expansion and contraction of the graphite particles, which may lead to displacement of some graphite particles and increase the gap between the graphite particles. In addition, when the particle size distribution (Dv90-Dv10) / Dv50 of the graphite material is small, the content of fine powder in the graphite material is low, and the lack of small fine powder to fill the gap between the graphite particles may cause the graphite particles to lose electrical contact, which in turn leads to rapid decay of the cycle capacity in the later stage of battery use.

[0098] In some embodiments, the tap density of the graphite material can be 1.0 m³. 3 / g-1.3m 3 / g.

[0099] When the tap density of graphite material is within the above range, the compaction density of the negative electrode film can be increased, which is beneficial for the battery to have a higher energy density.

[0100] In some embodiments, the specific surface area of ​​the graphite material can be 0.6 m². 2 / g-2m 2 / g.

[0101] When the specific surface area of ​​graphite materials is within the above range, side reactions at the negative electrode-electrolyte interface can be reduced, and irreversible consumption of lithium ions can be decreased, thereby improving the cycle life of the battery.

[0102] In some embodiments, the surface of the graphite material may also include a carbon layer, which may optionally include one or more of soft carbon and hard carbon.

[0103] The grain size Lc along the c-axis or La along the a-axis of graphite materials are 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 testing can be performed with reference to JIS K 0131-1996 and JB / T 4220-2011 to obtain the full width at half maximum (FWHM) of the 002 and 110 crystal planes in the graphite material crystal structure, FWHM(002) and FWHM(110), as well as the diffraction peaks Pos(002) and Pos(100). Then, the values ​​of Lc and La are calculated using the Scherrer formula, where π represents the constant of pi.

[0104] Lc=0.89*0.15405*180 / FWHM(002) / π / Cos [Pos(002) * π * 2 / 180] .

[0105] La=1.84*0.15405*180 / FWHM(110) / π / Cos [Pos(110) * π * 2 / 180] .

[0106] Lc 0％SOC Lc 50％SOC Lc 100％SOC Lc represents the grain size along the c-axis of graphite material in different lithium-intercalation states, i.e., the height along the c-axis. 0％SOC Lc 50％SOC Lc 100％SOC All of these can be obtained by testing graphite materials in different lithium-intercalation states using the above-mentioned testing methods.

[0107] La 0％SOC This represents the grain size of graphite material along the a-axis in the 0% SOC state after lithium intercalation. 0％SOC This can be obtained through the testing methods described above.

[0108] During testing, the negative electrode sheet containing the graphite material provided in the embodiments of this application can be made into a coin cell. For example, the negative electrode sheet containing the graphite material provided in the embodiments of this application can be assembled with a lithium metal sheet (as the counter electrode) to form a coin cell.

[0109] The electrolyte for a coin cell 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. Then, LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L.

[0110] The separator for button cells can be made of polypropylene (PP) film; the thickness can be 12μm.

[0111] The assembly process of button cells can employ techniques known in the art. For example, assembly can be carried out from the bottom up, starting with the positive electrode case, or from the bottom up, starting with the negative electrode case. The entire assembly process is carried out in an argon atmosphere glove box with a water content of less than 10 ppm.

[0112] After the prepared coin cell was left to stand at 25℃ for 6 hours, it was discharged at a constant current of 0.15mA to 5.0mV; after standing for 5 minutes, it was discharged again at a constant current of 50μA to 5.0mV; then it was charged at a constant current of 0.30mA to 2V, and the charging capacity at this point was recorded as C0; then the negative electrode was removed from the coin cell and tested by X-ray diffraction to obtain Lc. 0％SOC and La 0％SOC .

[0113] After the prepared coin cell was left to stand at 25℃ for 6 hours, it was discharged at a constant current of 0.15mA to 5.0mV; left to stand for 5 minutes, and then discharged at a constant current of 50μA to 5.0mV; then it was charged at a constant current of 0.30mA to 2V, and the charging capacity at this point was recorded as C0; then it was discharged at a constant current of 0.05C0 for 10 hours; then the negative electrode was removed from the coin cell and tested by X-ray diffraction to obtain Lc 50％SOC .

[0114] After the prepared coin cell was left to stand at 25℃ for 6 hours, it was discharged at a constant current of 0.15mA to 5.0mV; left to stand for 5 minutes, and then discharged at a constant current of 50μA to 5.0mV; then it was charged at a constant current of 0.30mA to 2V, and the charging capacity at this point was recorded as C0; then it was discharged at a constant current of 0.05C0 for 20 hours; then the negative electrode was removed from the coin cell and tested by X-ray diffraction to obtain Lc 100％SOC .

[0115] For example, a graphite material sample can be thoroughly mixed with conductive agent carbon black and binder polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 in an appropriate amount of solvent N-methylpyrrolidone (NMP) to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the surface of a copper foil current collector and dried and cold-pressed. Subsequently, using a lithium metal sheet as the counter electrode and a polypropylene (PP) film as the separator, electrolyte is injected, and the cells are assembled into a CR2430 coin cell in an argon-protected glove box. The electrolyte formulation 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. LiPF6 is then dissolved in this organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. The compaction density of the negative electrode sheet can be 1.3 g / cm³. 3 -1.5g / cm 3 .

[0116] At 25°C, the prepared coin 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, and allowed to stand for 5 minutes. The first discharge capacity of the coin cell was recorded. Subsequently, it was charged at a constant current of 0.1C to 2.0V, and the first charge capacity of the coin cell was recorded. The ratio of the first charge capacity of the coin cell to the mass of the graphite sample is the specific capacity of the graphite material.

[0117] The degree of graphitization of graphite materials is a well-known concept in the art and can be tested using instruments and methods known in the field. For example, it can be tested using an X-ray diffractometer (such as a Bruker D8 Discover), and the testing can be referenced in JIS K0131-1996 and JB / T 4220-2011 to obtain the average interlayer spacing d of the (002) crystal plane in the graphite material crystal structure. 002 Then, according to the formula g = (0.344 - d) 002 The degree of graphitization is calculated as d / (0.344-0.3354)×100%. In the above formula, d... 002 The average interlayer spacing of the (002) crystal plane in the crystal structure of graphite material is expressed in nanometers (nm).

[0118] In X-ray diffraction analysis, a copper target can be used as the anode target, with CuKα rays as the radiation source, and the ray wavelength... The scanning 2θ angle range can be 15°-75°, and the scanning rate can be 4° / min.

[0119] The volumetric distribution particle sizes Dv1, Dv10, Dv50, and Dv90 of materials (e.g., graphite materials, graphite precursors, etc., hereinafter) have well-known meanings in the art, representing the particle sizes corresponding to a cumulative volume distribution percentage of 1%, 10%, 50%, and 90%, respectively. These sizes can be determined using instruments and methods known in the art. For example, they can be conveniently determined using a laser particle size analyzer, referring to GB / T19077-2016 Particle Size Distribution Laser Diffraction Method. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0120] The tap density of graphite materials is a well-known concept in the art and can be determined using instruments and methods known in the field. For example, it can be determined using a powder tap density tester, referring to GB / T 5162-2006. The testing instrument can be the Dandong Baite BT-301.

[0121] The specific surface area of ​​graphite materials is a well-known concept 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 method according to GB / T 19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc., USA.

[0122] This application also provides a method for preparing the above-mentioned graphite material.

[0123] The preparation method includes 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 treatment at a preset temperature and time, and then cooling it off to obtain graphite material. The preset temperature is less than 3000℃, 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 Lc represents the grain size of graphite material along the c-axis in the 0% SOC state after lithium intercalation, in nm. 50％SOC Lc represents the grain size of graphite material along the c-axis in the 50% SOC state after lithium intercalation, in nm. 100％SOC This indicates the grain size of graphite material along the c-axis in the 100% SOC state after lithium intercalation, expressed in nm.

[0124] By selecting a preset temperature and preset time within the above range during graphitization treatment, the grain size of graphite material along the c-axis can be reduced, the volume expansion of graphite material during battery charging can be reduced, and the graphite material can also have a higher specific capacity.

[0125] When the preset temperature and / or preset time during graphitization are high, the grain development is better, the grain size of the graphite material along the c-axis is larger, and the lattice expansion and volume expansion of the graphite material during battery charging are larger. This will cause repeated breakage and formation of the SEI film, which is detrimental to improving the cycle life of the battery.

[0126] Therefore, the graphite material prepared by the preparation method provided in this application has a small grain size along the c-axis direction, and the volume change of the graphite material during the entire lithium intercalation process is small. This can reduce the lattice expansion of the graphite material during battery charging, reduce the thickness expansion of the negative electrode sheet, 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.

[0127] In some embodiments, when the obtained graphite precursor is placed in a graphitization furnace for graphitization treatment at a preset temperature and a preset time, the preset temperature can be 2500℃-2800℃, or optionally 2500℃-2750℃.

[0128] In some embodiments, when the obtained graphite precursor is placed in a graphitization furnace for graphitization treatment at a preset temperature and a preset time, the preset time can be 6h-18h, or optionally 8h-15h.

[0129] By further adjusting the preset temperature and / or preset time during graphitization, on the one hand, the lattice expansion of graphite materials during battery charging can be reduced, the thickness expansion of the negative electrode sheet 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 specific capacity, so that the battery can have both a long cycle life and a high energy density.

[0130] In some embodiments, the cooling time can be less than or equal to 5 hours. This can reduce surface oxidation of graphite materials and improve their performance.

[0131] In some embodiments, the furnace exit temperature can be less than or equal to 250°C. This can reduce surface oxidation during the transfer of graphite materials from the furnace, thereby improving the performance of the graphite materials.

[0132] In some embodiments, the coke feedstock may include at least one of petroleum coke and needle coke.

[0133] In this application, the term "petroleum coke" refers to coke formed after petroleum residue or petroleum asphalt has undergone high-temperature carbonization.

[0134] In this application, the term "needle coke" refers to coke with needle-like textures generated by coal tar pitch or petroleum pitch through liquid-phase carbonization to generate anisotropic mesophase, followed by high-temperature carbonization and other processes.

[0135] In some embodiments, the raw material may include petroleum coke. Petroleum coke exhibits excellent anisotropy, which is beneficial for preparing graphite materials with low volume expansion, thus contributing to a long cycle life in batteries. Simultaneously, petroleum coke possesses high compaction density and high specific capacity, which is beneficial for improving the energy density of batteries. Furthermore, petroleum coke is more widely available, which is conducive to industrial production.

[0136] The aforementioned coke raw materials typically include at least one of the following structures: mosaic, regional, and fibrous. Generally, based on the morphological characteristics and isochromatic region size of the coke raw materials under a polarizing microscope, isochromatic microstructures with a size less than 30 μm are classified as mosaic structures, isochromatic microstructures with a size greater than 30 μm are classified as regional structures, and anisotropic strip-shaped isochromatic regions are classified as fibrous structures.

[0137] In some embodiments, the coke feedstock may be petroleum coke, and based on the total volume of the coke feedstock structure, the volume ratio of the embedded and regional structures in the petroleum coke may be greater than or equal to 60%, and may be selected as 65%-80%.

[0138] In some embodiments, the coke feedstock may be needle coke, and based on the total volume of the coke feedstock structure, the volume percentage of the fibrous structure in the needle coke may be 40%-60%, optionally 45%-55%.

[0139] By selecting the specific types of coke raw materials mentioned above, under the same graphitization treatment conditions, the degree of grain development is slower, which is beneficial to regulate the degree of grain development during the graphitization process and can also reduce the volume change of the graphite particles prepared in this way during the battery charging and discharging process.

[0140] In this application, the volume percentage of embedded, regional, and fibrous structures in the coke raw material can be tested using methods known in the art. As an example, raw materials can be taken according to GB 1997-89. Raw materials crushed to 1mm are mixed and reduced to 40g-50g. 4g-5g of 0.07mm-1.0mm grade samples are taken using a square-hole sieve for sample preparation. Powdered coke and lump coke sheets are prepared according to MT 116.1-86. The diameter of the powdered coke sheet should not be less than 22mm, and the volume occupied by the cementing material should be less than 1 / 3. The sample is placed on a slide with cement, flattened, and then placed on the stage for focusing. After calibrating the microscope, the polarizer and analyzer are adjusted to ensure orthogonality. A lapis lazuli test plate (1λ) is inserted to produce a first-order red interference color in the field of view. The step size of the moving scale is determined to ensure that more than 400 effective measuring points are evenly distributed, with a point spacing of 0.3mm-0.5mm and a row spacing of 0.5mm-0.8mm. Starting from one end of the sample, determine the type of microstructure under the intersection of the crosshairs, and divide the effective number of measurement points of the optical structure of the mosaic, regional, or fiber structure by the total number of measurement points to obtain the volume ratio of each structure in the raw material.

[0141] In some embodiments, the coke raw material may also meet the following requirements: volatile matter content ≤ 10 wt%, ash content ≤ 0.3 wt%, and sulfur content ≤ 2 wt%.

[0142] In some embodiments, the step of crushing the coke raw material can be performed using a crusher, such as a jaw crusher. For example, the coke raw material can be crushed to 2mm-5mm before being sieved, such as through a 3-20 mesh screen.

[0143] By crushing the coke raw material, the grain size of graphite material along the c-axis can be reduced, thereby reducing the volume expansion of graphite material during battery charging.

[0144] In some embodiments, during the step of shaping the coke raw material, a shaping machine can be used to shape the crushed coke raw material. This shaping process can reduce burrs on the surface of the crushed coke raw material.

[0145] 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 draft 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 obtained graphite precursor.

[0146] In some embodiments, in the step of crushing, shaping and classifying coke raw materials to obtain graphite precursor, the obtained graphite precursor may have a volume distribution particle size Dv1 greater than or equal to 0.3 μm, a volume distribution particle size Dv10 greater than or equal to 2.0 μm, a volume distribution particle size Dv50 of 5 μm-16 μm, and a particle size distribution (Dv90-Dv10) / Dv50 of 1.05-1.61.

[0147] Optionally, the volumetric particle size Dv1 of the obtained graphite precursor can be 0.3 μm-1.7 μm, or optionally 0.3 μm-1.4 μm.

[0148] Optionally, the volumetric particle size Dv10 of the obtained graphite precursor can be 2.1 μm-4.5 μm, or optionally 2.1 μm-4.0 μm.

[0149] Optionally, the volumetric particle size Dv50 of the obtained graphite precursor can be 8 μm-11 μm.

[0150] Optionally, the particle size distribution (Dv90-Dv10) / Dv50 of the obtained graphite precursor can be 1.18-1.52.

[0151] By adjusting the volumetric particle size distribution of the graphite precursor within the aforementioned range, the grain size of the graphite material along the c-axis can be reduced, the volume expansion of the graphite material during battery charging can be reduced, and the graphite material can also have good kinetic properties.

[0152] In some embodiments, the graphitization furnace may be a continuous graphitization furnace.

[0153] 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.

[0154] Optionally, the obtained graphite precursor can be pre-carbonized by heating it to 600℃-1100℃ at a heating rate of 1℃ / min-5℃ / min and holding it at that temperature for 18h-24h.

[0155] 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, followed by sieving and demagnetization to obtain graphite material.

[0156] Sieving can reduce the content of large particles and fine powder in the finished graphite material, which helps to adjust the particle size and volumetric particle size distribution of the finished graphite material. This, in turn, can reduce the grain size of the graphite material along the c-axis, thus reducing the volume expansion of the graphite material during battery charging. Demagnetization can reduce the content of magnetic impurities in the finished graphite material. Magnetic impurities increase battery self-discharge and reduce battery performance.

[0157] 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; and 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.

[0158] Optionally, the frequency of the fusion processing can be 20Hz-40Hz, or optionally 30Hz-38Hz.

[0159] Optionally, the fusion processing time can be 5 min-15 min, or optionally 8 min-12 min.

[0160] Alternatively, the coating agent may include bitumen.

[0161] Optionally, the softening point temperature of the asphalt can be 150℃-300℃, or optionally 200℃-250℃.

[0162] Optionally, the carbonization temperature can be 950℃-1300℃, or optionally 1100℃-1200℃.

[0163] Optionally, the carbonization treatment time can be 1h-5h, or 2h-3h.

[0164] 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.

[0165] In some embodiments, the preparation method includes the following steps: providing coke raw material, the coke raw material including petroleum coke, and based on the total volume of the coke raw material structure, the volume ratio of embedded and regional structures in the petroleum coke is greater than or equal to 60%, optionally 65%-80%; crushing, shaping and classifying 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, optionally 0.3 μm-1.4 μm, and the obtained graphite precursor... The volumetric particle size distribution Dv10 of the obtained graphite precursor is greater than or equal to 2.0 μm, and can be selected from 2.1 μm to 4.0 μm. The volumetric particle size distribution 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℃-11℃ at a heating rate of 1℃ / min-5℃ / min. The material is pre-carbonized at 00℃ for 18-24 hours; the pre-carbonized material is then graphitized in a continuous graphitization furnace at a preset temperature and time, and cooled to obtain the graphitized product. The preset temperature is 2500℃-2800℃, optionally 2500℃-2750℃, and the preset time is 6-18 hours, optionally 8-15 hours. The obtained graphitized product is then screened and demagnetized to obtain an intermediate product. The screened and demagnetized intermediate product and a coating agent are then added to a high-speed fusion machine for melting. The intermediate is obtained through a fusion process. The fusion processing time is 5-15 minutes, optionally 8-12 minutes, and the fusion processing frequency is 20Hz-40Hz, optionally 30Hz-38Hz. The fused intermediate is then placed in a carbonization furnace for carbonization at a temperature of 950℃-1300℃, optionally 1100℃-1200℃, for a time of 1-5 hours, optionally 2-3 hours. After further processing, including finished product sieving, demagnetization, and batch mixing, the final graphite material is obtained. 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.

[0166] In some embodiments, the preparation method includes the following steps: providing coke raw material, the coke raw material comprising needle coke, and based on the total volume of the coke raw material structure, the volume percentage of fibrous structure in the needle coke is 40%-60%, optionally 45%-55%; subjecting the coke raw material to crushing, shaping, and grading 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, optionally 0.3 μm-1.4 μm, and the volume distribution particle size Dv1 of the obtained graphite precursor is... The integral 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 resulting graphite precursor has a volume distribution particle size Dv50 of 5 μm to 16 μm, and can be selected from 8 μm to 11 μm. The resulting graphite precursor has a particle size distribution (Dv90-Dv10) / Dv50 of 1.05-1.61, and can be selected from 1.18-1.40. The resulting graphite precursor is heated to 600℃-1100℃ at a heating rate of 1℃ / min-5℃ / min. The material is pre-carbonized at ℃ and held at that temperature for 18-24 hours. The pre-carbonized material is then graphitized in a continuous graphitization furnace at a preset temperature and time. After cooling, the graphitized product is obtained. The preset temperature is 2500℃-2800℃, optionally 2500℃-2750℃, and the preset time is 6-18 hours, optionally 8-15 hours. The obtained graphitized product is then screened and demagnetized to obtain an intermediate product. The screened and demagnetized intermediate product is then added to a high-speed fusion machine with a coating agent for fusion. The intermediate is obtained by fusion treatment, with a fusion time of 5-15 minutes (optional 8-12 minutes) and a fusion frequency of 20Hz-40Hz (optional 30Hz-38Hz). The fused intermediate is then placed in a carbonization furnace for carbonization at a temperature of 950℃-1300℃ (optional 1100℃-1200℃) for 1-5 hours (optional 2-3 hours). After screening, demagnetization, and batch mixing, the final graphite material is obtained. 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.

[0167] [Negative electrode plate]

[0168] A single battery cell includes a negative electrode plate.

[0169] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0170] The negative electrode film layer includes a negative electrode active material. The negative electrode active material includes the above-mentioned graphite material or a graphite material prepared by the above method.

[0171] In some embodiments, the negative electrode active material may also include other materials known in the art, such as, but not limited to, one or more of natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

[0172] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. As an example, 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.

[0173] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. As an example, 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, waterborne 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).

[0174] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include, but are not limited to, thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0175] In some embodiments, the compaction density of the negative electrode film can be 1.15 g / cm³. 3 -1.55g / cm 3 The compaction density of the negative electrode film refers to the compaction density of the negative electrode film on one side of the negative electrode current collector.

[0176] In some embodiments, the areal density of the negative electrode film can be 7 mg / cm³. 2 -15mg / cm 2 The areal density of the negative electrode film refers to the areal density of the negative electrode film on one side of the negative electrode current collector.

[0177] The areal density of the negative electrode film is a term known in the art and can be tested using methods known in the art. For example, a negative electrode sheet coated on one side and cold-pressed (if it is a double-sided coated negative electrode sheet, the negative electrode film on one side can be wiped off first) can be cut into small circular pieces with an area of ​​S1, and its mass can be weighed and recorded as M1. Then, the negative electrode film on the weighed negative electrode sheet can be wiped off, and the mass of the negative electrode current collector can be weighed and recorded as M0. The areal density of the negative electrode film = (M1-M0) / S1.

[0178] The compaction density of the negative electrode film is a term known in the art and can be tested using methods known in the art. The compaction density of the negative electrode film = areal density of the negative electrode film / thickness of the negative electrode film. The thickness of the negative electrode film is a term known in the art and can be tested using methods known in the art, such as a micrometer.

[0179] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0180] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet may also include a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet may also include a protective layer covering the surface of the negative electrode film layer.

[0181] In some embodiments, the negative electrode current collector may include a metal foil, a three-dimensional porous current collector, or a composite current collector. Examples of metal foils include copper foil, copper alloy foil, nickel foil, nickel alloy foil, aluminum foil, and aluminum alloy foil. Examples of three-dimensional porous current collectors include copper mesh, nickel mesh, copper foam, nickel foam, and aluminum foam. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. Examples of metal materials include, but are not limited to, one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, aluminum, aluminum alloys, silver, and silver alloys. Examples of polymer material substrates include, but are not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0182] [Positive electrode plate]

[0183] A single battery cell includes a positive electrode plate.

[0184] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0185] The positive electrode film includes a positive electrode active material, which may include, but is not limited to, one or more of lithium transition metal oxides, lithium phosphates, and their respective modified compounds.

[0186] In some embodiments, the positive electrode active material may include one or more lithium phosphates and their modified compounds. This can further improve the cycle life of the battery.

[0187] As an example, lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their respective modified compounds.

[0188] As an example, lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. In this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0189] In some embodiments, the positive electrode film may 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.

[0190] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resins, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne 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).

[0191] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0192] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0193] [Electrolytes]

[0194] A single battery cell includes an electrolyte. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte may include one or more selected from solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0195] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0196] In some embodiments, as an example, 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 bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0197] In some embodiments, the solvent may include, but is not limited to, one or more of ester solvents, sulfone solvents, and ether solvents. For 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), butyl ester 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), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0198] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives capable of improving certain battery performance, such as additives improving battery overcharge performance, battery high-temperature performance, and battery low-temperature power performance. Optionally, 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.

[0199] [Isolation membrane]

[0200] 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 electrodes, primarily to prevent internal short circuits.

[0201] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0202] In some embodiments, the material of the separator may include, but is not limited to, one or more of glass fiber, nonwoven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0203] The methods for preparing a single battery cell are well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a single battery cell. As an example, the positive electrode, separator, and negative electrode can be wound and / or stacked to form an electrode assembly. The electrode assembly is then placed in an outer package, dried, and injected with the electrolyte. After encapsulation, settling, and formation processes, a single battery cell is obtained. Multiple single battery cells can be further connected in series, parallel, or a combination thereof to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination thereof to form a battery pack. In some embodiments, multiple single battery cells can also be directly assembled into a battery pack.

[0204] Electrical appliances

[0205] This application also provides an electrical device, which includes a battery provided in this application embodiment. The battery is used to provide electrical energy. The battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (such as mobile phones, tablets, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0206] Electrical devices can choose the specific type of battery according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0207] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0208] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0209] Example

[0210] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0211] Example 1

[0212] (1) Preparation of negative electrode active materials

[0213] Provide petroleum coke feedstock with a volatile matter content of less than or equal to 10 wt%, an ash content of less than or equal to 0.3 wt%, and a sulfur content of less than or equal to 2 wt%, and satisfy the following: the volume ratio of the mosaic and regional structures is 69%.

[0214] The above petroleum coke raw materials were coarsely crushed, then crushed and sieved. The sieved material was then shaped and classified. During the classification process, a certain amount of fine powder was removed to obtain the precursor. The classification frequency of the air classifier was 60Hz, and the induced draft frequency was 20Hz. The obtained precursor was controlled with a volumetric particle size distribution (Dv1) of 0.3μm, a volumetric particle size distribution (Dv10) of 2.1μm, a volumetric particle size distribution (Dv50) of 8.5μm, and a particle size distribution (Dv90-Dv10) / Dv50 of 1.52. Then, it underwent pre-carbonization treatment with a heating rate of 5℃ / min. The material is heated to 950℃ and held for 20 hours; then, the pre-carbonized material is continuously graphitized at 2500℃ for 12 hours to obtain graphitized product; the obtained graphitized product is screened and demagnetized to obtain intermediate product; the intermediate product is first fused in a high-speed fusion machine, and then asphalt is added for a second fusion treatment. The fusion treatment frequency is 34Hz, and the time of each fusion treatment is 8 minutes. The mass ratio of intermediate product to asphalt is 98:2; the fused material is transferred to a carbonization furnace for carbonization treatment at 1150℃ for 2 hours; finally, after finished product screening, demagnetization, and batch mixing, graphite material is obtained. The graphite material is a primary particle size distribution with a particle size distribution Dv1 of 1.1μm, a particle size distribution Dv10 of 4.3μm, a particle size distribution Dv50 of 9.5μm, and a particle size distribution (Dv90-Dv10) / Dv50 of 1.49, and the graphite material satisfies (Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC It is 0.0169.

[0215] (2) Preparation of negative electrode sheet

[0216] The above-mentioned 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. The mixture was then stirred under vacuum until the system was homogeneous to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto the negative electrode current collector copper foil, and after drying, cold pressing, and slitting, the negative electrode sheet was obtained. The compaction density of the negative electrode film was 1.30 g / cm³. 3 Its surface density is 10.22 mg / cm³. 2 .

[0217] (3) Preparation of positive electrode sheet

[0218] Lithium iron phosphate (LiFePO4), a conductive agent (Super P), and a binder (PVDF) were mixed at a mass ratio of 97:1:2. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred under vacuum until homogeneous to obtain a positive electrode slurry. This slurry was then uniformly coated onto an aluminum foil current collector, and after drying, cold pressing, and slitting, positive electrode sheets were obtained. The compaction density of the positive electrode film was 2.50 g / cm³. 3 Its surface density is 19.51 mg / cm³. 2 .

[0219] (4) Preparation of electrolyte

[0220] 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, ethylene carbonate was added to the solution at a mass content of 2 wt%, based on the total mass of the electrolyte.

[0221] (5) Preparation of the separating membrane

[0222] Polypropylene film is used as the separator.

[0223] (6) Preparation of batteries (full cells)

[0224] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound up. The electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, the battery is obtained.

[0225] (7) Preparation of button cells

[0226] A coin cell is assembled using a lithium metal sheet as the counter electrode, along with the negative electrode sheet, separator, and electrolyte prepared above.

[0227] Examples 2 to 5 and Comparative Examples 1 to 3

[0228] Except for the different preparation process of the negative electrode active material, the battery preparation process is the same as that in Example 1. For specific parameters, please refer to Table 1.

[0229] Table 1

[0230]

[0231] Example 6

[0232] Except for the different preparation process of the negative electrode active material, the battery preparation process is the same as that in Example 1.

[0233] (1) Preparation of negative electrode active materials

[0234] Provide needle coke raw materials with a volatile matter content of less than or equal to 10 wt%, an ash content of less than or equal to 0.3 wt%, and a sulfur content of less than or equal to 2 wt%, and satisfy the following condition: the volume percentage of fibrous structure is 53%.

[0235] The above needle coke raw materials are coarsely crushed to 2mm-5mm using a crusher and passed through a 3-20 mesh sieve. The coarsely crushed particles are dried until the moisture content is less than 0.5%, and then subjected to ball mill crushing, shaping, and grading. During the grading process, a certain amount of fine powder is removed to obtain the precursor. The air classifier has a grading frequency of 60Hz and an induced draft frequency of 20Hz. The obtained precursor has its volumetric particle size distribution (Dv1) controlled at 0.4μm, volumetric particle size distribution (Dv10) controlled at 2.8μm, volumetric particle size distribution (Dv50) controlled at 8.2μm, and particle size distribution (Dv90-Dv10) / Dv50 controlled at 1.34. It then undergoes pre-carbonization treatment. During carbonization, the temperature is increased to 950℃ at a rate of 5℃ / min and held for 2 hours. The pre-carbonized material is then continuously graphitized at 2650℃ for 12 hours to obtain a graphitized product. The obtained graphitized product is then screened and demagnetized to obtain an intermediate product. This intermediate product undergoes a first fusion treatment in a high-speed fusion machine, followed by the addition of asphalt for a second fusion treatment. The fusion frequency is 34Hz, and each fusion treatment lasts for 8 minutes, with a mass ratio of intermediate product to asphalt of 98:2. The fused material is then transferred to a carbonization furnace for carbonization at 1150℃ for 2 hours. Finally, after finished product screening, demagnetization, and batch mixing, graphite material is obtained. The graphite material is a primary graphite material with 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 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.

[0236] Example 7 and Comparative Example 4

[0237] Except for the different preparation process of the negative electrode active material, the battery preparation process is the same as that in Example 6. For specific parameters, please refer to Table 2.

[0238] Table 2

[0239]

[0240] Test section

[0241] (1) Specific capacity testing of graphite materials

[0242] The negative electrode active material samples prepared in each embodiment and comparative example were thoroughly mixed with conductive agent carbon black and binder polyvinylidene fluoride (PVDF) in an appropriate 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 uniformly coated onto the surface of the negative electrode current collector copper foil, dried in an oven, and then pressed to 1.3 g / cm³ using a roller 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; then, using a lithium metal sheet as the counter electrode and a polypropylene film as the separator, a CR2430 coin cell is assembled in an argon-protected glove box.

[0243] At 25°C, the prepared coin 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, and allowed to stand for 5 minutes. The first discharge capacity of the coin cell was recorded. Afterward, it was charged at a constant current of 0.1C to 2.0V, and the first charge capacity of the coin cell was recorded. The ratio of the first charge capacity of the coin cell to the mass of the negative electrode active material sample is the specific capacity of the negative electrode active material (i.e., graphite material).

[0244] (2)Lc 0％SOC Lc 50％SOC Lc 100％SOC La 0％SOC Test

[0245] At 25°C, the coin cells prepared in the above test were left to stand for 6 hours, then discharged at a constant current of 0.15mA to 5.0mV; left to stand for 5 minutes, and then discharged at a constant current of 50μA to 5.0mV; then charged at a constant current of 0.30mA to 2V, and the charging capacity at this point was recorded as C0; then the negative electrode was removed from the coin cells, tested by an X-ray diffractometer, and Lc was calculated using the Scherrer formula. 0％SOC and La 0％SOC .

[0246] At 25°C, the coin cells prepared in the above test were left to stand for 6 hours, then discharged at a constant current of 0.15mA to 5.0mV; left to stand for 5 minutes, then discharged at a constant current of 50μA to 5.0mV; then charged at a constant current of 0.30mA to 2V, the charging capacity at this point being recorded as C0; then discharged at a constant current of 0.05C0 for 10 hours; then the negative electrode was removed from the coin cells, tested using an X-ray diffractometer, and Lc was calculated using the Scherrer formula. 50％SOC .

[0247] At 25°C, the coin cells prepared in the above test were left to stand for 6 hours, then discharged at a constant current of 0.15mA to 5.0mV; left to stand for 5 minutes, then discharged at a constant current of 50μA to 5.0mV; then charged at a constant current of 0.30mA to 2V, the charging capacity at this point being recorded as C0; then discharged at a constant current of 0.05C0 for 20 hours; then the negative electrode was removed from the coin cells, tested using an X-ray diffractometer, and Lc was calculated using the Scherrer equation. 100％SOC .

[0248] (3) Battery cycle performance test

[0249] The prepared full cell was charged at 1C constant current to 3.65V and discharged at 1C constant current to 2.5V for cyclic charge-discharge testing until the discharge capacity of the full cell decreased to 80% of the first discharge capacity. The test was then stopped, and the number of cycles was recorded. A higher number of cycles indicates better cycle stability of the full cell.

[0250] The test results are shown in Tables 3 and 4.

[0251] Table 3

[0252]

[0253] Table 4

[0254]

[0255] The test results in Tables 3 and 4 show that (Lc) is satisfied. 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750, and Lc 0％SOC Graphite materials with a diameter of 50 nm or less exhibit excellent cycle performance. This is because the volume change of graphite materials is small throughout the lithium intercalation process, which reduces lattice expansion of graphite materials during battery charging, reduces the thickness expansion of the negative electrode sheet, thereby reducing side reactions at the negative electrode-electrolyte interface, reducing irreversible lithium-ion consumption, and thus improving the cycle life of the battery, which is beneficial to meeting the needs of long-life energy storage batteries.

[0256] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A graphite material, characterized in that, 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 Lc represents the grain size of the graphite material along the c-axis in the 0% SOC state after lithium intercalation, in nm. 50％SOC Lc represents the grain size of the graphite material along the c-axis in the 50% SOC state after lithium intercalation, in nm. 100％SOC The value represents the grain size of the graphite material along the c-axis in the 100% SOC state after lithium intercalation, expressed in nm.

2. The graphite material according to claim 1, characterized in that: 0.0100≤(Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0750; and / or, 15nm≤Lc 0％SOC ≤47nm。 3. The graphite material according to claim 2, characterized in that: 0.0100≤(Lc 100％SOC -Lc 0％SOC ) / Lc 50％SOC ≤0.0500; and / or, 25nm≤Lc 0％SOC ≤45nm。 4. The graphite material according to claim 1, characterized in that, 20nm≤Lc 100％SOC ≤60nm。 5. The graphite material according to claim 4, characterized in that, 28nm≤Lc 100％SOC ≤50nm。 6. The graphite material according to claim 1, characterized in that, The specific capacity of the graphite material is 280mAh / g-340mAh / g.

7. The graphite material according to claim 6, characterized in that, The specific capacity of the graphite material is 290mAh / g-335mAh / g.

8. The graphite material according to any one of claims 1-7, characterized in that, The volumetric particle size distribution Dv1 of the graphite material is 0.5 μm-3.1 μm; and / or, The volumetric particle size distribution Dv10 of the graphite material is 3 μm-6.2 μm; and / or, The volumetric particle size distribution Dv50 of the graphite material is 5μm-15μm; and / or, The particle size distribution (Dv90-Dv10) / Dv50 of the graphite material is 1.02-1.

57.

9. The graphite material according to claim 8, characterized in that, The volumetric particle size distribution Dv1 of the graphite material is 1 μm-2.5 μm; and / or, The volumetric particle size distribution Dv10 of the graphite material is 3.2 μm-5 μm; and / or, The volumetric particle size distribution Dv50 of the graphite material is 8μm-12μm; and / or, The particle size distribution (Dv90-Dv10) / Dv50 of the graphite material is 1.11-1.

49.

10. The graphite material according to any one of claims 1-7, characterized in that, The grain size La of the graphite material along the a-axis in the lithium-intercalated 0% SOC state is... 0％SOC Less than or equal to 140nm.

11. The graphite material according to any one of claims 1-7, characterized in that, The graphitization degree of the graphite material is 70%-88%.

12. The graphite material according to claim 11, characterized in that, The graphitization degree of the graphite material is 75%-85%.

13. The graphite material according to any one of claims 1-7, characterized in that, The tap density of the graphite material is 1.0 m³. 3 / g-1.3m 3 / g; and / or, The specific surface area of ​​the graphite material is 0.6 m². 2 / g-2m 2 / g.

14. The graphite material according to any one of claims 1-7, characterized in that, The surface of the graphite material also includes a carbon layer.

15. A method for preparing a graphite material, characterized in that, Includes the following steps: Provide coke raw materials, wherein the coke raw materials meet the following conditions: the coke raw materials are petroleum coke, and based on the total volume of the coke raw materials structure, the volume ratio of the petroleum coke with embedded and regional structures is greater than or equal to 60%; or, the coke raw materials are needle coke, and based on the total volume of the coke raw materials structure, the volume ratio of the needle coke with fibrous structures is 40%-60%. The coke raw material is subjected to crushing, shaping and grading processes to obtain a graphite precursor. The obtained graphite precursor was placed in a graphitization furnace and graphitized at a preset temperature and time. After cooling, the graphite material was obtained. The preset temperature was greater than or equal to 2500℃ and less than 3000℃, and the preset time was 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 Lc represents the grain size of the graphite material along the c-axis in the 0% SOC state after lithium intercalation, in nm. 50％SOC Lc represents the grain size of the graphite material along the c-axis in the 50% SOC state after lithium intercalation, in nm. 100％SOC The value represents the grain size of the graphite material along the c-axis in the 100% SOC state after lithium intercalation, expressed in nm.

16. The preparation method according to claim 15, characterized in that, The graphitization furnace is a continuous graphitization furnace; and / or, The preset temperature is 2500℃-2800℃; and / or, The preset time is 6h-18h.

17. The preparation method according to claim 16, characterized in that, The preset temperature is 2500℃-2750℃; and / or, The preset time is 8h-15h.

18. The preparation method according to claim 15, characterized in that, The coke raw material also meets the following requirements: volatile matter content ≤ 10 wt%, ash content ≤ 0.3 wt%, and sulfur content ≤ 2 wt%.

19. The preparation method according to claim 15, characterized in that, The coke feedstock is petroleum coke, and based on the total volume of the coke feedstock structure, the volume ratio of embedded and regional structures in the petroleum coke is 65%-80%; or, The coke raw material is needle coke, and based on the total volume of the coke raw material structure, the volume ratio of the fibrous structure in the needle coke is 45%-55%.

20. The preparation method according to claim 15, characterized in that, In the step of crushing, shaping, and classifying the coke raw material to obtain the graphite precursor... The obtained graphite precursor has a volumetric particle size Dv1 greater than or equal to 0.3 μm; and / or, The obtained graphite precursor has a volumetric particle size Dv10 greater than or equal to 2.0 μm; and / or, The obtained graphite precursors have a volumetric particle size distribution (Dv50) of 5 μm–16 μm; and / or, The particle size distribution (Dv90-Dv10) / Dv50 of the obtained graphite precursor is 1.05-1.

61.

21. The preparation method according to claim 20, characterized in that, In the step of crushing, shaping, and classifying the coke raw material to obtain the graphite precursor... The obtained graphite precursor has a volumetric particle size distribution Dv1 of 0.3 μm–1.4 μm; and / or, The obtained graphite precursors have a volumetric particle size distribution Dv10 of 2.1 μm–4.0 μm; and / or, The obtained graphite precursors have a volumetric particle size distribution (Dv50) of 8 μm–11 μm; and / or, The particle size distribution (Dv90-Dv10) / Dv50 of the obtained graphite precursor is 1.18-1.

52.

22. The preparation method according to claim 15, characterized in that, Before placing the obtained graphite precursor in a graphitization furnace for graphitization at a preset temperature and time, the process further includes the step of pre-carbonizing the obtained graphite precursor.

23. The preparation method according to claim 22, characterized in that, The obtained graphite precursor was heated to 600℃-1100℃ at a heating rate of 1℃ / min-5℃ / min and held at that temperature for 18h-24h for pre-carbonization treatment.

24. The preparation method according to claim 15, characterized in that, The preparation method further includes the following steps: placing the obtained graphite precursor in a graphitization furnace for graphitization treatment at a preset temperature and time, followed by sieving and demagnetization to obtain graphite material.

25. The preparation method according to claim 15, characterized in that, The preparation method further includes the step of mixing the obtained graphite material with a coating agent and placing it in a carbonization furnace for carbonization treatment to form a carbon layer on the surface of the graphite material.

26. The preparation method according to claim 25, characterized in that, The coating agent includes asphalt.

27. The preparation method according to claim 26, characterized in that, The softening point temperature of the asphalt is 150℃-300℃.

28. The preparation method according to claim 27, characterized in that, The softening point temperature of the asphalt is 200℃-250℃.

29. The preparation method according to claim 25, characterized in that, The carbonization treatment temperature is 950℃-1300℃; and / or, The carbonization process takes 1-5 hours.

30. The preparation method according to claim 29, characterized in that, The carbonization treatment temperature is 1100℃-1200℃; and / or, The carbonization process takes 2-3 hours.

31. 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, characterized in that, The negative electrode film layer comprises the graphite material according to any one of claims 1-14 or the graphite material prepared by the preparation method according to any one of claims 15-30.

32. The negative electrode sheet according to claim 31, characterized in that, The compaction density of the negative electrode film is 1.15 g / cm³. 3 -1.55g / cm 3 ; and / or, The areal density of the negative electrode film is 7 mg / cm³. 2 -15mg / cm 2 .

33. A battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 31-32.

34. An electrical appliance, characterized in that, Includes the battery of claim 33, the battery being used to provide electrical energy.

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