Graphite negative electrode particles, preparation method thereof, battery and energy storage device

Abstract

The present application provides graphite anode particles, a preparation method thereof, a battery, and an energy storage device. The graphite anode particles of the embodiments of the present application comprise multiple layers stacked sequentially, each of which has a plurality of openings, each of which extends through a portion of the layers, and the size of each opening gradually decreases from the opening of the opening toward the bottom wall of the opening.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and specifically to a graphite negative electrode particle, a preparation method thereof, a battery and an energy storage device. Background Art

[0002] Lithium-ion batteries for energy storage are increasingly demanding in terms of energy efficiency. Improving this performance primarily relies on enhancing the kinetics of the electrochemical system. Graphite is commonly used as the negative electrode material for lithium-ion batteries, but the cycling performance of existing graphite materials still needs improvement. Summary of the Invention

[0003] The embodiments of the present application provide a graphite negative electrode particle having high cycle performance.

[0004] In a first aspect, an embodiment of the present application provides a graphite negative electrode particle, which includes a plurality of layers stacked in sequence, and the graphite negative electrode particle also has a plurality of openings, each of the openings passes through a portion of the layers in the plurality of layers, and the size of the opening gradually decreases from the opening of the opening to the bottom wall of the opening.

[0005] Furthermore, an average value w of the maximum dimensions of the plurality of openings is in the range of 0.05 μm≤w≤2 μm.

[0006] Furthermore, the depth h of the opening is in the range of 1 nm ≤ h ≤ 800 nm.

[0007] Furthermore, the ratio A of the total area of ​​the openings penetrating three or more sheets to the total area of ​​the plurality of openings on the surface of the graphite negative electrode particles is in the range of 5%≤A≤50%.

[0008] Furthermore, the range of the surface defectivity ID / IG of the graphite negative electrode particles is: 0.62≤ID / IG≤1.71, wherein ID is the intensity of the D peak in the Raman spectrum of the graphite negative electrode particles, and IG is the intensity of the G peak in the Raman spectrum of the graphite negative electrode particles.

[0009] Furthermore, the particle size distribution of the graphite negative electrode particles satisfies: 1.1≤(Dv90-Dv10) / Dv50≤1.5, wherein Dv10 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the graphite negative electrode particles reaches 10%, Dv50 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the graphite negative electrode particles reaches 50%, and Dv90 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the graphite negative electrode particles reaches 90%.

[0010] In a second aspect, an embodiment of the present application further provides a method for preparing graphite negative electrode particles, the preparation method comprising:

[0011] providing graphite matrix particles; and

[0012] Carboxymethyl cellulose salt is added to the graphite matrix particles and heat treated to obtain the graphite negative electrode particles, wherein the graphite negative electrode particles include multiple layers stacked in sequence, and the graphite negative electrode particles also have multiple openings, each of the openings penetrates a portion of the multiple layers, and the size of the openings gradually decreases from the opening of the opening to the bottom wall of the opening.

[0013] Furthermore, providing graphite matrix particles comprises:

[0014] Providing a carbon source, wherein the mass fraction of volatile matter in the carbon source ranges from 5% to 15%;

[0015] Pre-treating at a first temperature T1 in the range of 25° C. ≤ T1 ≤ 800° C. to obtain intermediate particles; and

[0016] The intermediate particles are graphitized at a second temperature T2 in the range of 2800° C. ≤ T2 ≤ 3500° C. to obtain the graphite matrix particles.

[0017] Furthermore, before the pretreatment, the providing of graphite matrix particles further comprises:

[0018] The carbon source is sieving to obtain precursor particles, wherein the particle size distribution of the precursor particles satisfies: 1.1≤(Dv'90-Dv'10) / Dv'50≤1.5, wherein Dv'10 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the precursor particles reaches 10%, Dv'50 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the precursor particles reaches 50%, and Dv'90 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the precursor particles reaches 90%.

[0019] Furthermore, the carboxymethyl cellulose salt includes at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and potassium carboxymethyl cellulose, and the mass of the carboxymethyl cellulose salt is 0.1% to 5% of the mass of the graphite matrix particles.

[0020] Furthermore, the heat treatment comprises:

[0021] The temperature T3 of the heat treatment is in the range of 200° C. ≤ T3 ≤ 650° C., and the heat treatment is performed in an oxygen atmosphere.

[0022] In a third aspect, an embodiment of the present application further provides a battery, comprising:

[0023] electrolyte;

[0024] Positive electrode;

[0025] a diaphragm located on one side of the positive electrode plate, and

[0026] A negative electrode plate is provided on a side of the diaphragm facing away from the positive electrode plate. The negative electrode plate includes a negative electrode active layer, and the negative electrode active layer includes the graphite negative electrode particles described in the embodiment of the present application.

[0027] In a fourth aspect, an embodiment of the present application further provides an energy storage device, comprising:

[0028] cabinet; and

[0029] A plurality of batteries according to the embodiments of the present application are housed in the box.

[0030] The graphite negative electrode particles of the present invention include multiple layers stacked in sequence, and the graphite negative electrode particles further have multiple openings, each of which penetrates a portion of the multiple layers, and the size of the opening gradually decreases from the opening of the opening to the bottom wall of the opening. The multi-layer stepped pore structure of the graphite negative electrode particles of the present invention is small inside and widens outside. The large openings in the outer layer are conducive to the infiltration of electrolyte, forming small "reservoirs". Even in the negative electrode plates of a high compaction density system, because the graphite negative electrode particles themselves have a certain function of storing electrolyte, when used in a battery, in the middle and late stages of the battery cycle, under the reverse extrusion force of the battery shell caused by the expansion of the negative electrode plate, the electrolyte "reservoirs" formed on the graphite negative electrode particles are not affected by the extrusion force, thereby improving the cycle performance of the graphite negative electrode particles. The openings do not excessively affect the specific capacity of the graphite negative electrode particles, thereby enabling the graphite negative electrode particles to have a higher specific capacity. In addition, the openings running through multiple layers can increase the active sites of the graphite negative electrode particles, and the number of entrances for active lithium to be embedded in the graphite layers increases, which can significantly increase the insertion and extraction rate of lithium ions, shorten the insertion and extraction path of lithium ions, reduce the electrochemical polarization phenomenon of the graphite negative electrode particles, and improve the kinetic performance and cycle performance of the graphite negative electrode particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 This is a scanning electron microscope image of the graphite negative electrode particles according to an embodiment of the present application, wherein the magnification is 5000 times.

[0033] Figure 2 This is a scanning electron microscope image of the graphite negative electrode particles according to one embodiment of the present application, wherein the magnification is 20,000 times.

[0034] Figure 3 Schematic diagram of a process for preparing graphite negative electrode particles according to an embodiment of the present application.

[0035] Figure 4 Schematic diagram of a process for preparing graphite matrix particles according to an embodiment of the present application.

[0036] Figure 5 Schematic diagram of the structure of a battery according to an embodiment of the present application.

[0037] Figure 6 The battery of one embodiment of the present application is Figure 5 Schematic diagram of the cross-sectional structure in the AA direction.

[0038] Figure 7 Schematic diagram of the structure of the negative electrode sheet of one embodiment of the present application.

[0039] Figure 8 It is a structural schematic diagram of the positive electrode plate of an embodiment of the present application.

[0040] Figure 9 This is a scanning electron microscope image of the graphite negative electrode particles of Comparative Example 3 of the present application.

[0041] Figure 10 It is a structural diagram of an energy storage device according to an embodiment of the present application.

[0042] Description of reference numerals:

[0043] 100-graphite negative electrode particles, 10-sheet, 20-opening, 300-battery, 310-positive electrode sheet, 311-positive electrode current collector, 312-positive electrode active layer, 320-diaphragm, 330-negative electrode sheet, 331-negative electrode current collector, 332-negative electrode active layer, 340-shell, 350-end cover assembly, 400-energy storage device, 410-case. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0045] The terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0046] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings.

[0047] It should be noted that, for the convenience of explanation, in the embodiments of the present application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0048] Lithium-ion batteries for energy storage are increasingly demanding in terms of energy efficiency. Improving this performance primarily relies on enhancing the kinetics of the electrochemical system. Graphite is commonly used as the negative electrode material for lithium-ion batteries, but the cycling performance of existing graphite materials still needs improvement.

[0049] See Figure 1 and Figure 2 An embodiment of the present application provides a graphite negative electrode particle 100, which includes a multilayer layer 10 stacked in sequence. The graphite negative electrode particle 100 also has a plurality of openings 20, each of the openings 20 passes through a portion of the multilayer layer 10, and the size of the opening 20 gradually decreases from the opening of the opening 20 to the bottom wall of the opening 20.

[0050] The graphite negative electrode particles 100 of the embodiment of the present application can be used as, but not limited to, negative electrode active materials for negative electrode plates of lithium-ion batteries. The battery also includes an electrolyte, and the negative electrode plates are immersed in the electrolyte.

[0051] It should be noted that the "openings 20" refer to pores that penetrate the surface of the graphite negative electrode particles 100 or are located on the surface of the graphite negative electrode particles 100. The "openings 20" are in contrast to the pores (i.e., closed pores) located within the graphite negative electrode particles 100. The "opening" refers to the portion of the opening 20 that is close to the surface of the graphite negative electrode particles 100.

[0052] It can be understood that each of the openings 20 is formed by enclosing multiple layers of sheet 10. From the opening of the opening 20 toward the bottom wall of the opening 20, the multiple layers of sheet 10 enclosing the opening 20 gradually expand outward toward the direction close to the opening 20, so that each opening 20 forms an inverted "tower-like" structure.

[0053] It can also be understood that the pore diameters of the openings 20 gradually increase from the inside of the graphite negative electrode particles 100 to the outside of the graphite negative electrode particles 100 .

[0054] It can also be understood that the multiple layers 10 surrounding the opening 20 form a step-like structure, that is, the opening 20 is a stepped hole structure.

[0055] The graphite negative electrode particles 100 of the embodiment of the present application include a plurality of layers 10 stacked in sequence, and the graphite negative electrode particles 100 also have a plurality of openings 20, each of the openings 20 passes through a portion of the layers 10 in the multi-layer layers 10, and the size of the openings 20 gradually decreases from the opening of the opening 20 to the bottom wall of the opening 20. The multi-layer 10-step pore structure of the graphite negative electrode particles 100 of the present application is small inside and expanded outside. The large openings in the outer layer are conducive to the infiltration of the electrolyte, forming small "water reservoirs". Even in the negative electrode plates of the high-density system, since the graphite negative electrode particles 100 themselves have a certain function of storing electrolyte, when used in the battery, in the middle and late stages of the battery cycle, under the reverse extrusion force of the battery shell caused by the expansion of the negative electrode plates, the electrolyte "water reservoir" formed on the graphite negative electrode particles 100 will not be affected by the extrusion force, thereby improving the cycle performance of the graphite negative electrode particles 100. The openings 20 will not excessively affect the performance of the gram capacity of the graphite negative electrode particles 100, thereby making the graphite negative electrode particles 100 have a higher gram capacity. In addition, the openings 20 that penetrate the multiple layers 10 can increase the active sites of the graphite negative electrode particles 100, increase the entrances for active lithium to be embedded in the graphite layers, significantly increase the insertion and extraction rate of lithium ions, shorten the insertion and extraction path of lithium ions, reduce the electrochemical polarization phenomenon of the graphite negative electrode particles 100, and improve the kinetic performance and cycle performance of the graphite negative electrode particles 100.

[0056] In some embodiments, the average maximum size of the plurality of openings 20 is in the range of 0.05 μm ≤ w ≤ 2 μm. It is understood that the average maximum size w of the plurality of openings 20 near the surface of the graphite negative electrode particles 100 is in the range of 0.05 μm ≤ w ≤ 2 μm. It is also understood that the average pore size w of the outermost layer of the plurality of openings 20 (the layer 10 closest to the surface of the graphite negative electrode particles 100) is in the range of 0.05 μm ≤ w ≤ 2 μm.

[0057] Specifically, the average value w of the maximum size of the plurality of openings 20 may be, but is not limited to, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, etc.

[0058] In this embodiment, if the average value w of the maximum dimensions of the plurality of openings 20 is too small, the electrolyte storage capacity of the openings 20 decreases, thereby limiting the improvement in the cycling performance of the graphite negative electrode particles 100. As the average value w of the maximum dimensions of the plurality of openings 20 increases, the number of end surface sites located at the openings 20 on the surface of the graphite negative electrode particles 100 increases, and the basal surface area excluding the openings 20 decreases. Since lithium ions are primarily intercalated into the graphite negative electrode particles 100 as interlayer lithium on the basal surface, the amount of lithium intercalation decreases, reducing the specific capacity of the graphite negative electrode particles 100. However, the increased electrolyte storage capacity in the openings 20 improves the cycling performance of the graphite negative electrode particles 100. In addition, the number of active sites on the surface of the graphite negative electrode particles 100 increases, improving the kinetic performance of the graphite negative electrode particles 100. If the maximum dimension w of the openings 20 is too large, the specific capacity of the graphite negative electrode particles 100 decreases significantly, which is not conducive to improving the specific capacity of the graphite negative electrode particles 100.

[0059] Furthermore, the average value w of the maximum dimensions of the plurality of openings 20 is in the range of 0.4 μm ≤ w ≤ 1 μm. This allows the graphite negative electrode particles 100 to have a greater storage capacity for electrolyte when used in a battery, thereby better improving the cycle capacity retention rate of the graphite negative electrode particles 100. At the same time, the graphite negative electrode particles 100 can have a more appropriate basal area ratio, thereby having a higher specific capacity.

[0060] In some embodiments, the depth h of the opening 20 is in the range of 1 nm≤h≤800 nm.

[0061] Specifically, the depth h of the opening 20 can be, but is not limited to, 1 nm, 3 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, etc.

[0062] In this embodiment, if the depth h of the openings 20 is too shallow, the electrolyte storage capacity of the openings 20 is reduced, thereby limiting the improvement in the cycling performance of the graphite negative electrode particles 100. As the depth h of the openings 20 increases, the electrolyte storage capacity of the openings 20 gradually increases, thereby improving the cycling performance of the graphite negative electrode particles 100. In addition, the lithium ion transmission path is shortened, allowing lithium ions to enter the graphite interlayers of the graphite negative electrode particles 100 more quickly, thereby improving the kinetic performance of the graphite negative electrode particles 100. When the depth h of the openings 20 is within the range of 1 nm ≤ h ≤ 800 nm, the graphite negative electrode particles 100 can have a greater electrolyte storage capacity when used in a battery, thereby better improving the cycling capacity retention rate of the graphite negative electrode particles 100, while also having a higher specific capacity and higher kinetic performance.

[0063] In some embodiments, the ratio A of the total area of ​​the openings 20 penetrating three or more sheets 10 to the total area of ​​the plurality of openings 20 on the surface of the graphite negative electrode particles 100 is in the range of 5%≤A≤50%.

[0064] Specifically, the ratio A of the total area of ​​the openings 20 passing through three or more layers 10 to the total area of ​​the multiple openings 20 on the surface of the graphite negative electrode particles 100 can be, but is not limited to, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.

[0065] In this embodiment, if the ratio A of the total area of ​​the openings 20 passing through more than three layers of sheets 10 to the total area of ​​the multiple openings 20 on the surface of the graphite negative electrode particles 100 is too small, the graphite negative electrode can store too little electrolyte, and the improvement of the cycle performance of the graphite negative electrode particles 100 is limited; as the ratio A of the total area of ​​the openings 20 passing through more than three layers of sheets 10 to the total area of ​​the multiple openings 20 on the surface of the graphite negative electrode particles 100 increases, the area of ​​the openings 20 increases, the lithium insertion and extraction polarization phenomenon is reduced, and the cycle performance of the graphite negative electrode particles 100 using the graphite negative electrode particles 100 is improved. However, if the ratio A of the total area of ​​the openings 20 extending through three or more layers 10 to the total area of ​​the plurality of openings 20 on the surface of the graphite negative electrode particles 100 is too large, the basal area ratio is reduced, thereby reducing the specific capacity of the graphite negative electrode particles 100. Furthermore, side reactions of the graphite negative electrode particles 100 are increased, and the cycle capacity retention rate of the graphite negative electrode particles 100 is also reduced. When the ratio A of the total area of ​​the openings 20 extending through three or more layers 10 to the total area of ​​the plurality of openings 20 on the surface of the graphite negative electrode particles 100 is within the range of 5% ≤ A ≤ 50%, the graphite negative electrode particles 100 can have both a high cycle capacity retention rate and a high specific capacity.

[0066] Furthermore, the ratio A of the total area of ​​the openings 20 extending through three or more layers 10 to the total area of ​​the plurality of openings 20 on the surface of the graphite negative electrode particles 100 is in the range of 10% ≤ A ≤ 30%. This allows the graphite negative electrode particles 100 to have both a high cycle capacity retention rate and a high specific capacity.

[0067] In some embodiments, the range of the surface defect ID / IG of the graphite negative electrode particle 100 is: 0.62≤ID / IG≤1.71, wherein ID is the intensity of the D peak in the Raman spectrum of the graphite negative electrode particle 100, and IG is the intensity of the G peak in the Raman spectrum of the graphite negative electrode particle 100.

[0068] Specifically, the surface defectivity ID / IG of the graphite negative electrode particles 100 may be, but is not limited to, 0.62, 0.65, 0.68, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.71, etc.

[0069] In this embodiment, if the surface defectivity ID / IG of the graphite negative electrode particles 100 is too low, the number of active sites on the surface of the graphite negative electrode particles 100 is too small, reducing the kinetic performance of the graphite negative electrode particles 100. As the surface defectivity ID / IG of the graphite negative electrode particles 100 increases, the specific capacity of the graphite negative electrode particles 100 slightly increases. This is due to the lithium insertion mechanism of the defects, which helps to store lithium, thereby increasing the specific capacity of the graphite negative electrode particles 100. However, the increase in defects also increases side reactions in the graphite negative electrode particles 100, thereby consuming more film-forming additives in the electrolyte, thereby deteriorating the cycle life and reducing the cycle capacity retention rate of the graphite negative electrode particles 100. Therefore, when the surface defectivity ID / IG of the graphite negative electrode particles 100 is within the range of 0.62≤ID / IG≤1.71, the graphite negative electrode particles 100 can have both high cyclability and high specific capacity and kinetic performance.

[0070] In some embodiments, the particle size distribution of the graphite negative electrode particles 100 satisfies: 1.1≤(Dv90-Dv10) / Dv50≤1.5, wherein Dv10 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the graphite negative electrode particles 100 reaches 10%, Dv50 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the graphite negative electrode particles 100 reaches 50%, and Dv90 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the graphite negative electrode particles 100 reaches 90%.

[0071] Specifically, (Dv90-Dv10) / Dv50 of the graphite negative electrode particles 100 may be, but is not limited to, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, etc.

[0072] It should be noted that, the smaller (Dv90-Dv10) / Dv50 is, the narrower the particle size distribution of the graphite negative electrode particles 100 is, and the larger (Dv90-Dv10) / Dv50 is, the wider the particle size distribution of the graphite negative electrode particles 100 is.

[0073] Optionally, the Dv50 of the graphite negative electrode particles 100 is in the range of 9 μm≤Dv50≤18 μm. Specifically, the Dv50 of the graphite negative electrode particles 100 may be, but is not limited to, 9 μm, 10 μm, 12 μm, 14 μm, 16 μm, 17 μm, 18 μm, etc.

[0074] In this embodiment, the narrower the particle size distribution of the graphite negative electrode particles 100, the more uniform the pores in the negative electrode active layer after the graphite negative electrode particles 100 are made into the negative electrode active layer of the negative electrode sheet, which is conducive to the infiltration of the electrolyte into the negative electrode active layer, thereby improving the cycle performance of the negative electrode sheet using the graphite negative electrode particles 100. However, when the graphite negative electrode particles 100 are made into the negative electrode active layer of the negative electrode sheet, the porosity of the negative electrode sheet is increased, and the energy density of the negative electrode sheet is reduced. If the particle size distribution of the graphite negative electrode particles 100 is wider, the gram capacity of the graphite negative electrode particles 100 is slightly increased. However, when the graphite negative electrode particles 100 are made into the negative electrode active layer of the negative electrode sheet, the pores between the graphite negative electrode particles 100 are too small, which easily causes insufficient infiltration of the electrolyte and reduces the cycle capacity retention rate of the negative electrode sheet. Therefore, when the particle size distribution of the graphite negative electrode particles 100 satisfies: 1.1≤(Dv90-Dv10) / Dv50≤1.5, the graphite negative electrode particles 100 can have a higher cycle capacity retention rate, better wettability and higher specific capacity.

[0075] The gram capacity of the graphite negative electrode particles 100 of the present application embodiment ranges from 330 mAh / g to 345 mAh / g. Specifically, the gram capacity of the graphite negative electrode particles 100 can be, but is not limited to, 330 mAh / g, 333 mAh / g, 335 mAh / g, 338 mAh / g, 340 mAh / g, 343 mAh / g, 345 mAh / g, 348 mAh / g, 342 mAh / g, 345 mAh / g, etc. The graphite negative electrode particles 100 of the present application have a relatively high gram capacity.

[0076] The graphite anode particles 100 of the embodiment of the present application have a relatively high compaction density. The compaction density of 5 tons (5t) of the powder is 1.8 g / cm 3Up to 1.95g / cm 3 Specifically, it can be but not limited to 1.8 g / cm 3 , 1.82g / cm 3 、1.84g / cm 3 , 1.86g / cm 3 , 1.88g / cm 3 、1.90g / cm 3 、1.93g / cm 3 , 1.95g / cm 3 wait.

[0077] The graphite negative electrode particles 100 of the embodiments of the present application can be prepared by the methods described in the following embodiments of the present application. In addition, they can also be prepared by other methods. The preparation methods of the embodiments of the present application are merely one or more preparation methods of the graphite negative electrode particles 100 of the present application and should not be understood as limiting the graphite negative electrode particles 100 provided in the embodiments of the present application.

[0078] See Figure 3 The present invention also provides a method for preparing graphite negative electrode particles 100, the method comprising:

[0079] S201, providing graphite matrix particles; and

[0080] S202, adding carboxymethyl cellulose salt to the graphite matrix particles and performing heat treatment to obtain the graphite negative electrode particles 100, wherein the graphite negative electrode particles 100 include a plurality of layers 10 stacked in sequence, and the graphite negative electrode particles 100 also have a plurality of openings 20, each of the openings 20 penetrates a portion of the layers 10 in the multilayer layers 10, and the size of the openings 20 gradually decreases from the opening of the opening 20 to the bottom wall of the opening 20.

[0081] It can be understood that after the graphite matrix particles and carboxymethyl cellulose salt are uniformly mixed according to a preset mass ratio, heat treatment is performed to obtain the graphite negative electrode particles 100.

[0082] For detailed descriptions of other aspects such as the graphite negative electrode particles 100 , the sheet layer 10 , and the openings 20 , please refer to the descriptions of the corresponding parts of the above embodiments, which will not be repeated here.

[0083] In the preparation method of the graphite negative electrode particles 100 of the embodiment of the present application, carboxymethyl cellulose salt is added to the graphite matrix particles and heat treated, so that the prepared graphite negative electrode particles 100 have a multi-layered sheet 10 structure and a stepped pore structure with a pore diameter gradually decreasing from the outside to the inside. The multi-layer 10-step pore structure of the graphite negative electrode particles 100 of the present application is small inside and expanded outside. The large openings in the outer layer are conducive to the infiltration of the electrolyte, forming small "water reservoirs". Even in the negative electrode plates of the high-density system, since the graphite negative electrode particles 100 themselves have a certain function of storing electrolyte, when used in the battery, in the middle and late stages of the battery cycle, under the reverse extrusion force of the battery shell caused by the expansion of the negative electrode plates, the electrolyte "water reservoir" formed on the graphite negative electrode particles 100 will not be affected by the extrusion force, thereby improving the cycle performance of the graphite negative electrode particles 100. The openings 20 will not excessively affect the performance of the gram capacity of the graphite negative electrode particles 100, thereby making the graphite negative electrode particles 100 have a higher gram capacity. In addition, the openings 20 that penetrate the multiple layers 10 can increase the active sites of the graphite negative electrode particles 100, increase the entrances for active lithium to be embedded in the graphite layers, significantly increase the insertion and extraction rate of lithium ions, shorten the insertion and extraction path of lithium ions, reduce the electrochemical polarization phenomenon of the graphite negative electrode particles 100, and improve the kinetic performance and cycle performance of the graphite negative electrode particles 100.

[0084] See Figure 4 In some embodiments, in S201, providing graphite matrix particles includes:

[0085] S2011, providing a carbon source, wherein the mass fraction of volatile matter in the carbon source is in a range of 5% to 15%;

[0086] Optionally, the carbon source may be, but is not limited to, at least one of petroleum coke, pitch coke, needle coke, and the like.

[0087] Specifically, the mass fraction of the volatile matter in the carbon source may be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc. If the mass fraction of the volatile matter in the carbon source is too low, the proportion of the open pores 20 in the prepared graphite negative electrode particles 100 is too low, which increases the impedance of the graphite negative electrode particles 100, reduces the dynamic performance of the graphite negative electrode particles 100, and increases the expansion force of the graphite negative electrode particles 100 during the lithium insertion process, thereby reducing the cycle performance of the graphite negative electrode particles 100. As the mass fraction of volatile matter in the carbon source increases, the number of pores 20 extending through the sheets 10 increases, which helps improve the electrolyte storage capacity of the graphite negative electrode particles 100, thereby improving the cycling performance of the graphite negative electrode particles 100. However, if the mass fraction of volatile matter in the carbon source is too high, the resulting graphite negative electrode particles 100 will have too many pores 20, reducing the gram capacity of the graphite negative electrode particles 100. In addition, it will increase side reactions in the graphite negative electrode particles 100 and also reduce the cycling capacity retention rate of the graphite negative electrode particles 100. When the mass fraction of volatile matter in the carbon source is within the range of 5% to 15%, the resulting graphite negative electrode particles 100 can have a relatively suitable number and depth of pores 20, thereby enabling the graphite negative electrode particles 100 to have both high cycling performance and high kinetic performance.

[0088] S2012, performing pretreatment at a first temperature T1 in the range of 25°C ≤ T1 ≤ 800°C to obtain intermediate particles; and

[0089] Alternatively, pretreatment can be performed in a horizontal tank.

[0090] It can be understood that when the first temperature T1 is room temperature or normal temperature, it is equivalent to no pretreatment process; in other words, the pretreatment process may also be unnecessary.

[0091] Specifically, the temperature of the pretreatment may be, but is not limited to, 25°C, 30°C, 40°C, 50°C, 100°C, 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, etc.

[0092] Furthermore, the range of the first temperature T1 is 200° C. ≤ T1 ≤ 800° C., which can increase the pores inside the prepared graphite negative electrode particles 100 , thereby reducing the expansion rate of the graphite negative electrode particles 100 during the potentialization process.

[0093] Optionally, stirring is performed during the pretreatment, and the stirring speed is 30 r / min to 50 r / min. Specifically, the stirring speed can be, but is not limited to, 30 r / min, 32 r / min, 34 r / min, 36 r / min, 38 r / min, 40 r / min, 42 r / min, 44 r / min, 46 r / min, 48 r / min, 50 r / min, etc. Stirring can make the particle size of the intermediate particles more uniform, which is beneficial to the infiltration of the electrolyte into the negative electrode active layer, thereby improving the cycle performance of the negative electrode sheet using the graphite negative electrode particles 100; if the stirring speed is too low, the intermediate particle size distribution is still large. When the graphite negative electrode particles 100 are made into the negative electrode active layer of the negative electrode sheet, it is not conducive to the infiltration of the electrolyte into the negative electrode active layer, and the improvement of the cycle performance is limited; if the stirring speed is too high, the particle size distribution of the intermediate particles is too small, so that the particle size distribution of the obtained graphite negative electrode particles 100 is too small. When the graphite negative electrode particles 100 are made into the negative electrode active layer of the negative electrode sheet, the porosity of the negative electrode sheet is increased and the energy density of the negative electrode sheet is reduced.

[0094] S2013, graphitizing the intermediate particles at a second temperature T2 in the range of 2800° C. ≤ T2 ≤ 3500° C. to obtain the graphite matrix particles.

[0095] Specifically, the second temperature T2 may be, but is not limited to, 2800° C., 2900° C., 3000° C., 3050° C., 3100° C., 3150° C., 3200° C., 3250° C., 3300° C., 3350° C., 3400° C., 3450° C., 3500° C., etc. If the temperature of the graphitization treatment is too low, the degree of graphitization of the graphite negative electrode particles 100 is reduced, the conductivity of the graphite negative electrode particles 100 is reduced, and thus the dynamic performance of the graphite negative electrode particles 100 is reduced; if the temperature of the graphitization treatment is too high, the preparation cost of the graphite negative electrode particles 100 is increased.

[0096] In some embodiments, before the pretreatment, providing graphite matrix particles further comprises:

[0097] The carbon source is sieving to obtain precursor particles, wherein the particle size distribution of the precursor particles satisfies: 1.1≤(Dv'90-Dv'10) / Dv'50≤1.5, wherein Dv'10 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the precursor particles reaches 10%, Dv'50 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the precursor particles reaches 50%, and Dv'90 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the precursor particles reaches 90%.

[0098] Optionally, the carbon source is coarsely crushed in a jaw crusher, ground into fine powder in a fluidized bed mill, and then sieved to obtain precursor particles with a particle size distribution of 1.1≤(Dv'90-Dv'10) / Dv'50≤1.5.

[0099] Specifically, (Dv'90-Dv'10) / Dv'50 of the precursor particles may be, but is not limited to, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, etc.

[0100] The smaller the (Dv'90-Dv'10) / Dv'50 of the precursor particles, the narrower the particle size distribution of the prepared graphite negative electrode particles 100. After the graphite negative electrode particles 100 are made into the negative electrode active layer of the negative electrode sheet, the pores in the negative electrode active layer tend to be more uniform, which is conducive to the infiltration of the electrolyte into the negative electrode active layer, thereby improving the cycle performance of the negative electrode sheet using the graphite negative electrode particles 100. However, when the graphite negative electrode particles 100 are made into the negative electrode active layer of the negative electrode sheet, the increase The porosity of the negative electrode sheet is reduced, thereby reducing the energy density of the negative electrode sheet. The larger the (Dv'90-Dv'10) / Dv'50 of the precursor particles, the wider the particle size distribution of the obtained graphite negative electrode particles 100, and the slightly increased gram capacity of the graphite negative electrode particles 100. However, after the graphite negative electrode particles 100 are made into the negative electrode active layer of the negative electrode sheet, the pores between the graphite negative electrode particles 100 are too small, which easily causes insufficient electrolyte infiltration and reduces the cycle capacity retention rate of the negative electrode sheet. Therefore, in the embodiment of the present application, the carbon source is ground into fine particles and then sieved to obtain precursor particles with a particle size distribution of 1.1≤(Dv'90-Dv'10) / Dv'50≤1.5. In this way, the particle size distribution of the obtained graphite negative electrode particles 100 can be within an appropriate range, thereby making the graphite negative electrode particles 100 have a high cycle capacity retention rate, good wettability and high gram capacity.

[0101] In some embodiments, the carboxymethyl cellulose salt includes at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and potassium carboxymethyl cellulose, and the mass of the carboxymethyl cellulose salt is 0.1% to 5% of the mass of the graphite matrix particles.

[0102] Specifically, the mass of the carboxymethyl cellulose salt is 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc., of the mass of the graphite matrix particles.

[0103] In this embodiment, if the amount of carboxymethyl cellulose salt added is too little, the structure of the porous sheet layer 10 on the surface of the prepared graphite negative electrode particles 100 is not obvious, and the improvement of the cycle capacity retention rate of the battery using the graphite negative electrode particles 100 is limited; as the amount of carboxymethyl cellulose salt added increases, the number of openings 20 formed that penetrate the sheet layer 10 increases, and the number of openings 20 also increases, thereby increasing the "water reservoir" capacity of the prepared graphite negative electrode particles 100 for the electrolyte, and gradually increasing the cycle capacity retention rate of the battery using the graphite negative electrode particles 100; however, when the amount of carboxymethyl cellulose salt added is too much, the defects of the prepared graphite negative electrode particles 100 are too many, excessive side reactions will occur, and excessive active lithium will be consumed, which will deteriorate the cycle capacity retention rate of the battery using the graphite negative electrode particles 100. When the mass of the carboxymethyl cellulose salt is 0.1% to 5% of the mass of the graphite matrix particles, the surface of the prepared graphite negative electrode particles 100 can have more openings 20 and lamellae 10, and the number of lamellae 10 penetrated by the openings 20 is relatively large, so that the openings 20 have a better ability to store electrolyte. In addition, the prepared graphite negative electrode particles 100 can also have a more appropriate defective degree and will not have excessive side reactions, so that the battery using the graphite negative electrode particles 100 has a higher cycle capacity retention rate.

[0104] In some embodiments, in S202 , the heat treatment includes: performing the heat treatment in an oxygen atmosphere at a temperature T3 in a range of 200° C. ≤ T3 ≤ 650° C.

[0105] Specifically, the temperature T3 of the heat treatment may be, but is not limited to, 200°C, 230°C, 250°C, 280°C, 300°C, 330°C, 350°C, 380°C, 400°C, 420°C, 440°C, 460°C, 480°C, 500°C, 520°C, 540°C, 560°C, 580°C, 600°C, 630°C, 650°C, etc.

[0106] In this embodiment, if the heat treatment temperature T3 is too low, the surface of the graphite negative electrode particles 100 produced will have too few open pores 20, and the number of layers penetrated by the open pores 20 will be too small, resulting in limited improvement in the cycle capacity retention rate of batteries using the graphite negative electrode particles 100. If the heat treatment temperature T3 is too high, too many open pores 20 will be formed, and the number of open pores 20 penetrating too many layers 10 will increase side reactions in the graphite negative electrode particles 100, consuming too much active lithium, and ultimately reducing the cycle capacity retention rate of batteries using the graphite negative electrode particles 100. When the heat treatment temperature T3 is within the range of 200°C ≤ T3 ≤ 650°C, the surface of the graphite negative electrode particles 100 produced can have an appropriate number of open pores 20, and the proportion of three or more layers penetrated by the open pores 20 is within a relatively appropriate range, thereby enabling batteries using the graphite negative electrode particles 100 to have a higher cycle capacity retention rate.

[0107] Furthermore, the range of the heat treatment temperature T3 is 300° C. ≤ T3 ≤ 600° C. This allows the surface of the prepared graphite negative electrode particles 100 to have an appropriate number of openings 20, and the proportion of the number of layers 10 penetrated by the openings 20 being three or more is within a more appropriate range, thereby allowing the battery using the graphite negative electrode particles 100 to have a higher cycle capacity retention rate.

[0108] Furthermore, the range of the heat treatment temperature T3 is 400° C. ≤ T3 ≤ 550° C. This allows the surface of the prepared graphite negative electrode particles 100 to have an appropriate number of openings 20, and the proportion of the number of layers 10 penetrated by the openings 20 being three or more is within a more appropriate range, thereby allowing the battery using the graphite negative electrode particles 100 to have a higher cycle capacity retention rate.

[0109] See Figures 5 to 7 The embodiment of the present application also provides a battery 300, which includes an electrolyte, a positive electrode plate 310, a separator 320 and a negative electrode plate 330, wherein the separator 320 is located on one side of the positive electrode plate 310, and the negative electrode plate 330 is arranged on the side of the separator 320 away from the positive electrode plate 310, and the negative electrode plate 330 includes a negative electrode active layer 332, and the negative electrode active layer 332 includes the graphite negative electrode particles 100 described in the embodiment of the present application.

[0110] It can be understood that the positive electrode plate 310 , the separator 320 , and the negative electrode plate 330 are at least partially immersed in the electrolyte.

[0111] It is understood that the positive electrode sheet 310, the separator 320 and the negative electrode sheet 330 are stacked in sequence to form an electrode assembly. The electrode assembly can be, but is not limited to, a wound structure, a laminated structure, etc., which is not specifically limited in this application.

[0112] Optionally, the negative electrode sheet 330 further includes a negative current collector 331 , and the negative active layer 332 is disposed on the surface of the negative current collector 331 . It is understood that the negative active layer 332 may cover one surface or two opposite surfaces of the negative current collector 331 .

[0113] Optionally, the negative electrode current collector 331 may be, but is not limited to, a copper sheet.

[0114] Optionally, the negative electrode active layer 332 further includes a negative electrode conductor, a negative electrode binder, and a negative electrode thickener.

[0115] See Figure 8 Optionally, the positive electrode sheet 310 includes a positive electrode current collector 311 and a positive electrode active layer 312, wherein the positive electrode active layer 312 is disposed on the surface of the positive electrode current collector 311. It is understood that the positive electrode active layer 312 may cover one surface or two opposite surfaces of the positive electrode current collector 311.

[0116] Optionally, the positive electrode current collector 311 may be, but is not limited to, an aluminum sheet.

[0117] Optionally, the positive electrode active layer 312 includes a positive electrode active material, a positive electrode conductor, a positive electrode binder, and a positive electrode thickener.

[0118] Optionally, the positive electrode active material may be, but is not limited to, lithium iron phosphate.

[0119] Optionally, the diaphragm 320 may be, but is not limited to, at least one of a polypropylene film (PP film for short), a polyethylene film (PE film for short), a ceramic diaphragm 320 , and the like.

[0120] Optionally, the battery 300 further includes a housing 340 and an end cap assembly 350. The housing 340 and the end cap assembly 350 enclose a closed receiving chamber for accommodating the electrolyte, the positive electrode sheet 310, the separator 320, and the negative electrode sheet 330. It is understood that the end cap assembly 350 is electrically connected to the positive electrode sheet 310 and the negative electrode sheet 330, respectively, and leads the positive electrode sheet 310 and the negative electrode sheet 330 out for electrical connection to external devices or other batteries 300.

[0121] After the battery of the present application has been used for a period of time, the graphite negative electrode particles 100 can be recycled by the following steps: (1) disassembling the battery after it is fully discharged and removing the negative electrode plate; (2) soaking it in dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) or other organic solvents for 24 hours; (3) placing it in a drying oven and drying it at 80°C to 100°C for 24 to 48 hours; (4) taking it out and placing it in a muffle furnace and heating it for 6 to 10 hours, thereby recovering the graphite negative electrode particles 100.

[0122] The graphite negative electrode particles 100 and the battery 300 according to the embodiment of the present application are further described below through specific examples.

[0123] Examples 1 to 19, Comparative Examples 1 to 9

[0124] The graphite negative electrode particles 100 of this embodiment are prepared by the following steps:

[0125] (1) Petroleum coke was provided as a carbon source, and the petroleum coke was coarsely crushed by a jaw crusher and ground into fine powder by a jet mill. The volatile matter content of the petroleum coke of each embodiment and comparative example is shown in Table 1 below;

[0126] (2) The carbon source particles ground into fine powder were sieved to obtain precursor particles. The particle size distribution of the precursor particles of each embodiment and comparative example is shown in Table 1 below;

[0127] (3) performing a graphitization treatment in a graphite furnace at a temperature of 3100° C. to obtain graphite matrix particles; and

[0128] (4) Sodium carboxymethyl cellulose was added to the graphite matrix particles, mixed evenly, and heat treated in an oxygen atmosphere to obtain graphite negative electrode particles 100. The amount of sodium carboxymethyl cellulose added and the heat treatment temperature of each embodiment and comparative example are shown in Table 1 below. The scanning electron microscope image of the graphite negative electrode particles 100 obtained in Example 3 is shown in FIG. Figure 1 and Figure 2 shown.

[0129] Example 20

[0130] The difference between this embodiment and embodiment 3 is that the carboxymethyl cellulose salt of the present application is lithium carboxymethyl cellulose.

[0131] Example 21

[0132] The difference between this embodiment and embodiment 3 is that the carboxymethyl cellulose salt in this application is potassium carboxymethyl cellulose.

[0133] Example 22

[0134] The difference between this embodiment and embodiment 3 is that the precursor particles of the present application are heat-treated at a first temperature T1 of 600° C. before graphitization, and the stirring speed is 40 r / min.

[0135] Example 23

[0136] The difference between this embodiment and embodiment 3 is that the precursor particles of the present application are heat-treated at a first temperature T1 of 200° C. before graphitization, and the stirring speed is 40 r / min.

[0137] Example 24

[0138] The difference between this embodiment and embodiment 3 is that the precursor particles of the present application are heat-treated at a first temperature T1 of 100° C. before graphitization, and the stirring speed is 40 r / min.

[0139] The graphite negative electrode particles 100 of each embodiment and comparative example are assembled into a battery 300: the graphite negative electrode particles 100 prepared in each embodiment and comparative example are used to prepare negative electrode sheets 330, and the negative electrode sheets 330, the polypropylene separator 320, the lithium iron phosphate positive electrode sheet 310 and the lithium hexafluorophosphate electrolyte with a concentration of 1 mol / L are assembled into a square shell battery 300.

[0140] Various performance tests were performed on the graphite negative electrode particles 100 of the embodiments and comparative examples and the batteries 300 assembled therefrom. The test results are shown in Table 2 below.

[0141] (1) Scanning electron microscope (SEM) test: used to measure the average value w of the maximum size of the openings 20 and the ratio A of the total area of ​​the openings 20 that penetrate three or more layers 10 to the total area of ​​the multiple openings 20 on the surface of the graphite negative electrode particles 100.

[0142] (2) ID / IG test: Raman spectroscopy is used for measurement.

[0143] (3) Gram capacity test: 10 wt% sodium carboxymethyl cellulose binder was fully dissolved in water, 10 wt% carbon black conductive agent and 80 wt% of the above-prepared graphite negative electrode particles 100 were added and stirred to obtain a uniformly dispersed slurry. The slurry was evenly coated on the surface of the copper foil, and then transferred to a vacuum drying oven for complete drying to obtain a negative electrode plate 330. The obtained negative electrode plate 330 was roller-pressed, then punched, and then weighed. The negative electrode plate 330 was assembled with the electrolyte, polypropylene separator 320, and metal lithium plate into a button battery.

[0144] The button battery was left to stand for 4 hours, then discharged at a rate of 0.05C to a voltage of 0.005V, left to stand for 10 minutes, discharged at a constant current of 0.05mA to a voltage of 0.005V, left to stand for 10 minutes, discharged at a constant current of 0.01mA to a voltage of 0.005V, left to stand for 10 minutes, and charged at a rate of 0.1C to a voltage of 2V. The above charge and discharge steps were performed 3 times, and the total capacity during the third discharge process was recorded. The gram capacity of the graphite negative electrode particles 100 = the total capacity during the third discharge process / the weight of the graphite negative electrode particles 100.

[0145] (4) Cycle capacity retention rate test after 500 cycles: The battery 300 was subjected to a charge and discharge cycle test on a charge and discharge instrument (Nebula Charge and Discharge Test System - BAT-NEEFLCT-05300-V010). The test temperature was 25°C. The battery 300 was charged at a constant power of 0.5P to a charge cut-off voltage of 3.65V. The initial charge capacity was recorded. The battery 300 was left to stand for 10 minutes. The battery 300 was discharged at a constant power of 0.5P to a discharge cut-off voltage of 2.5V. The discharge capacity of the battery 300 was recorded. Wherein, P refers to the rated charge or discharge power of the battery, and its value is the nominal voltage U of the battery multiplied by the current density of 1C. The nominal voltage of the iron phosphate battery is 3.2V, and 0.5P refers to 0.5 times the rated power.

[0146] The capacity retention rate after 25°C cycling is calculated as follows: capacity retention rate after the nth cycle = (discharge capacity after the nth cycle / discharge capacity of the first cycle) × 100%.

[0147] Table 1 Process parameters of graphite negative electrode particles 100 of various embodiments and comparative examples

[0148]

[0149] Table 2 Performance parameters of graphite negative electrode particles 100 and batteries prepared in various embodiments and comparative examples

[0150]

[0151] The test results of Comparative Example 1 show that when sodium carboxymethyl cellulose is not added and heat treatment is performed directly, the surface of the resulting graphite negative electrode particles 100 does not have openings 20 formed by the lamellae 10, the surface defectivity ID / IG of the graphite negative electrode particles 100 is small, the specific capacity is relatively low, and the cycle capacity retention rate of the battery 300 made from the graphite negative electrode particles 100 is low. The test results of Examples 1 to 6 show that when sodium carboxymethyl cellulose is added and heat treated, openings 20 penetrating multiple lamellae 10 are formed on the surface of the resulting graphite negative electrode particles 100. As the amount of sodium carboxymethyl cellulose added increases, the area ratio of the openings 20 penetrating more than three lamellae 10 in the resulting graphite negative electrode particles 100 gradually increases, the size of the openings 20 on the surface of the graphite negative electrode particles 100 gradually increases, and the surface defectivity ID / IG also gradually increases. Compared to Comparative Example 1, in which sodium carboxymethyl cellulose was not added, the gram capacity of the graphite negative electrode particles 100 and the 500-cycle capacity retention rate of the resulting batteries 300 in Examples 1 to 6 increased. However, as the amount of sodium carboxymethyl cellulose added gradually increased, the gram capacity of the graphite negative electrode particles 100 gradually decreased, while the cycle capacity retention rate gradually increased. The test results of Comparative Example 2 show that when the amount of sodium carboxymethyl cellulose added was too high, the openings 20 of the resulting graphite negative electrode particles 100 were too large and the surface defects were too large, resulting in a decrease in the gram capacity of the graphite negative electrode particles 100 and a decrease in the 500-cycle capacity retention rate of the resulting batteries 300.

[0152] Figure 9 3 is a scanning electron microscope image of the graphite negative electrode particles 100 prepared in Comparative Example 3. It can be seen from the test results of Example 3 and Comparative Example 3 in Tables 1 and 2 that when other conditions are the same and only the atmosphere of the heat treatment is changed, when the heat treatment is carried out in an oxygen atmosphere (Example 3), the graphite negative electrode particles 100 of the present application having openings 20 penetrating multiple layers 10 can be obtained; however, when the heat treatment is carried out in a nitrogen atmosphere, the surface of the obtained graphite negative electrode particles 100 has no pores, as shown in FIG. Figure 9 The surface defect degree and gram capacity of the graphite negative electrode particles 100 of Comparative Example 3 are relatively low, and the capacity retention rate after 500 cycles of the battery 300 is low.

[0153] The test results of Examples 7 to 11, Comparative Examples 4 and 5 show that when the heat treatment temperature is low (such as Comparative Example 4), the graphite negative electrode particles 100 obtained do not have the openings 20 described in this application, have low surface defects, and have a relatively low specific capacity. After the battery 300 is made, the cycle capacity retention rate after 500 cycles is also low. When the heat treatment temperature is between 200°C and 650°C, the proportion of openings 20 in the graphite negative electrode particles 100 that penetrate more than three layers 10 gradually increases, the size of the openings 20 gradually increases, the surface defects and specific capacity of the graphite negative electrode particles 100 also gradually increase. After the battery 300 is made, the 500 cycle capacity retention rate of the battery 300 remains in a high range. When the heat treatment temperature increases, the cycle capacity retention rate decreases. When the heat treatment temperature is too high, the cycle capacity retention rate is low.

[0154] It can be seen from the test results of Examples 12 to 15, Comparative Examples 6 and 7 that when the particle size distribution of the precursor particles is small (such as Comparative Example 6), the gram capacity of the obtained graphite negative electrode particles 100 is higher, and the 500-cycle capacity retention rate of the battery 300 prepared from the graphite negative electrode particles 100 is relatively low; as the particle size distribution of the precursor particles gradually increases, the proportion of openings 20 that penetrate three or more layers 10 of the obtained graphite negative electrode particles 100, the size of the openings 20, the surface defects of the graphite negative electrode particles 100 and the gram capacity all gradually increase, and the 500-cycle capacity retention rate of the battery 300 decreases slightly; when the particle size distribution of the precursor particles is too wide (such as Comparative Example 7), the 500-cycle capacity retention rate of the obtained graphite negative electrode particles 100 decreases significantly.

[0155] From the test results of Examples 16 to 19, Comparative Examples 8 and 9, it can be seen that when the mass fraction of volatile matter in the carbon source is too small (such as Comparative Example 8), the proportion of the openings 20 on the obtained graphite negative electrode particles 100 that penetrate more than three layers of sheets 10 is very small, the size and surface defectivity of the openings 20 are very small, and the 500-cycle capacity retention rate of the battery 300 is low; as the mass fraction of volatile matter in the carbon source gradually increases, the proportion of the openings 20 on the obtained graphite negative electrode particles 100 that penetrate more than three layers of sheets 10 gradually increases, the size and surface defectivity of the openings 20 gradually increase, and the gram capacity of the graphite negative electrode particles 100 gradually decreases, but the 500-cycle capacity retention rate of the battery 300 gradually increases. When the mass fraction of volatile matter in the carbon source is too large (such as in Comparative Example 9), the proportion of the openings 20 that penetrate three or more layers 10 on the prepared graphite negative electrode particles 100 is too large, and the surface defects are too large, which greatly reduces the 500-cycle capacity retention rate of the battery 300.

[0156] It can be seen from the test results of Example 3, Example 20 and Example 21 that during the preparation process of the graphite negative electrode particles 100, adding different carboxymethyl cellulose salts for heat treatment can make the surface of the prepared graphite negative electrode particles 100 have openings 20 that penetrate multiple layers 10, and the proportion of the openings 20 that penetrate more than three layers 10 and the surface defectivity are both within an appropriate range, and the 500-cycle capacity retention rate of the battery 300 is relatively high.

[0157] It can be seen from the test results of Examples 22 to 24 that stirring during pretreatment can enable the prepared graphite negative electrode particles 100 to have a higher gram capacity and a higher cycle capacity retention rate.

[0158] See Figure 10 The embodiment of the present application further provides an energy storage device 400 , which includes a box 410 and the battery 300 described in the embodiment of the present application, wherein the multiple batteries 300 are accommodated in the box 410 .

[0159] The energy storage device 400 of the present application can be applied to, but is not limited to, energy storage on the power generation side, energy storage on the grid side, and energy storage on the power consumption side.

[0160] The term "plurality" means greater than or equal to two.

[0161] It can be understood that the multiple batteries 300 of the energy storage device 400 can be connected in parallel with each other; or in series with each other; or partially in parallel and partially in series (in other words, mixed connection). This application does not specifically limit the connection method of the multiple batteries 300 of the same energy storage device 400.

[0162] It is understood that the housing 410 has a receiving cavity, and multiple batteries 300 are received in the receiving cavity. In some embodiments, each receiving cavity receives one battery 300. In other embodiments, each receiving cavity receives multiple batteries 300.

[0163] Optionally, the energy storage device 400 may include, but is not limited to, a battery module, a battery pack, a battery system, and the like. The actual application form of the energy storage device 400 provided in the embodiments of the present application may be, but is not limited to, the products listed, and may also be other application forms. The embodiments of the present application do not impose strict restrictions on the application form of the energy storage device 400. The embodiments of the present application only illustrate the energy storage device 400 as a multi-core battery 300. When the energy storage device 400 is a single cell 300, the energy storage device 400 may be at least one of a cylindrical battery 300, a square battery 300, and the like.

[0164] Mentioning "embodiments" and "implementation methods" in this application means that the specific features, structures or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrases in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is understood explicitly and implicitly by those skilled in the art that the embodiments described in this application can be combined with other embodiments. In addition, it should be understood that the features, structures or characteristics described in the various embodiments of this application can be arbitrarily combined to form another embodiment that does not deviate from the spirit and scope of the technical solution of this application, unless there is a contradiction between them.

[0165] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solutions of the present application and are not intended to limit them. Although the present application has been described in detail with reference to the above preferred implementation modes, those skilled in the art should understand that modifications or equivalent replacements of the technical solutions of the present application should not depart from the spirit and scope of the technical solutions of the present application.

Claims

1. A graphite negative electrode particle, characterized in that: The graphite negative electrode particles include multiple layers stacked in sequence, and the graphite negative electrode particles also have multiple openings, each of which penetrates part of the multiple layers, and the size of the opening gradually decreases from the opening of the opening to the bottom wall of the opening. The opening has a stepped hole structure, and the ratio A of the total area of ​​the openings penetrating three or more layers to the total area of ​​the multiple openings on the surface of the graphite negative electrode particles is in the range of: 5%≤A≤50%.

2. The graphite negative electrode particle according to claim 1, characterized in that An average value w of maximum dimensions of the plurality of openings is in the range of 0.05 μm ≤ w ≤ 2 μm.

3. The graphite negative electrode particle according to claim 1, characterized in that The depth h of the opening is in the range of 1 nm ≤ h ≤ 800 nm.

4. The graphite negative electrode particle according to claim 1, characterized in that The range of the surface defectivity ID / IG of the graphite negative electrode particles is: 0.62≤ID / IG≤1.71, wherein ID is the intensity of the D peak in the Raman spectrum of the graphite negative electrode particles, and IG is the intensity of the G peak in the Raman spectrum of the graphite negative electrode particles.

5. The graphite negative electrode particle according to any one of claims 1 to 4, characterized in that The particle size distribution of the graphite negative electrode particles satisfies: 1.1≤(Dv90-Dv10) / Dv50≤1.5, wherein Dv10 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the graphite negative electrode particles reaches 10%, Dv50 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the graphite negative electrode particles reaches 50%, and Dv90 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the graphite negative electrode particles reaches 90%.

6. A method for preparing graphite negative electrode particles, characterized in that: The preparation method comprises: providing graphite matrix particles; and Carboxymethyl cellulose salt is added to the graphite matrix particles and heat treated to obtain the graphite negative electrode particles, wherein the graphite negative electrode particles include multiple layers stacked in sequence, and the graphite negative electrode particles also have multiple openings, each of the openings penetrates part of the multiple layers, the size of the openings gradually decreases from the opening of the opening to the bottom wall of the opening, the openings have a stepped pore structure, and the ratio A of the total area of ​​the openings penetrating three or more layers to the total area of ​​the multiple openings on the surface of the graphite negative electrode particles is in the range of: 5%≤A≤50%.

7. The method for preparing graphite negative electrode particles according to claim 6, characterized in that: The providing of graphite matrix particles comprises: Providing a carbon source, wherein the mass fraction of volatile matter in the carbon source ranges from 5% to 15%; Pre-treating at a first temperature T1 in the range of 25° C. ≤ T1 ≤ 800° C. to obtain intermediate particles; and The intermediate particles are graphitized at a second temperature T2 in the range of 2800° C. ≤ T2 ≤ 3500° C. to obtain the graphite matrix particles.

8. The method for preparing graphite negative electrode particles according to claim 7, wherein: Before the pretreatment, the providing of graphite matrix particles further comprises: The carbon source is sieving to obtain precursor particles, wherein the particle size distribution of the precursor particles satisfies: 1.1≤(Dv'90-Dv'10) / Dv'50≤1.5, wherein Dv'10 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the precursor particles reaches 10%, Dv'50 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the precursor particles reaches 50%, and Dv'90 is the particle size corresponding to when the cumulative particle size distribution percentage in the volume distribution of the precursor particles reaches 90%.

9. The method for preparing graphite negative electrode particles according to claim 6, wherein: The carboxymethyl cellulose salt includes at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and potassium carboxymethyl cellulose. The mass of the carboxymethyl cellulose salt is 0.1% to 5% of the mass of the graphite matrix particles.

10. The method for preparing graphite negative electrode particles according to claim 9, characterized in that: The heat treatment comprises: The temperature T3 of the heat treatment is in the range of 200° C. ≤ T3 ≤ 650° C., and the heat treatment is performed in an oxygen atmosphere.

11. A battery, characterized in that: include: electrolyte; Positive electrode; a diaphragm located on one side of the positive electrode plate, and A negative electrode plate, the negative electrode plate is arranged on the side of the diaphragm away from the positive electrode plate, the negative electrode plate includes a negative electrode active layer, and the negative electrode active layer includes the graphite negative electrode particles according to any one of claims 1 to 5 or the graphite negative electrode particles prepared by the preparation method of the graphite negative electrode particles according to any one of claims 6 to 10.

12. An energy storage device, characterized in that: include: Box; as well as A plurality of batteries according to claim 11, wherein the plurality of batteries are housed in the casing.

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