Graphite particles, their preparation methods, batteries and energy storage devices

Abstract

This application provides graphite particles, a method for preparing the same, a battery, and an energy storage device. The graphite particles in this application satisfy the relationship: 0.8 ≤ La / Lc ≤ 1.6, where La is the average crystallite length of the graphite particles, and Lc is the average crystallite height of the graphite particles. The graphite particles in this application exhibit high cycle performance.

Description

Technical Field

[0001] This application relates to the field of energy storage, specifically to a graphite particle, its preparation method, a battery, and an energy storage device. Background Technology

[0002] The energy efficiency requirements for lithium-ion batteries are becoming increasingly stringent, and improving energy efficiency mainly relies on enhancing the kinetics of the electrochemical system. Graphite is commonly used as the anode material in lithium-ion batteries; however, in related technologies, graphite materials have relatively low cycle life and still require improvement. Summary of the Invention

[0003] This application provides a graphite particle with high cycling performance.

[0004] In a first aspect, embodiments of this application provide a graphite particle that satisfies the relationship: 0.8≤La / Lc≤1.6, where La is the average crystallite length of the graphite particle and Lc is the average crystallite height of the graphite particle.

[0005] Furthermore, the average crystallite length La of the graphite particles is in the range of 35nm≤La≤55nm.

[0006] Furthermore, the average crystallite height Lc of the graphite particles is in the range of 30nm≤Lc≤45nm.

[0007] Furthermore, the orientation degree OI of the graphite particles is in the range of 2.1 ≤ OI ≤ 4.0.

[0008] Furthermore, the graphite particles satisfy the relationship: 0.05≤ID / IG≤0.1, where ID is the intensity of the D peak in the Raman spectrum of the graphite particles, and IG is the intensity of the G peak in the Raman spectrum of the graphite particles.

[0009] Furthermore, the graphite particles are obtained by pre-carbonizing and graphitizing a carbon source, wherein the carbon source includes at least one of petroleum coke and pitch coke.

[0010] Furthermore, the polarization structure of the carbon source includes an inlaid structure, a block structure, and a linear structure, wherein the volume fraction x of the inlaid structure in the polarization structure of the carbon source ranges from 40% to x ≤ 80%.

[0011] Furthermore, the polarization structure of the carbon source satisfies the following relationship: 1≤(x+y) / z≤4, where x+y+z=1, x is the volume fraction of the mosaic structure in the polarization structure of the carbon source, y is the volume fraction of the block structure in the polarization structure of the carbon source, and z is the volume fraction of the linear structure in the polarization structure of the carbon source.

[0012] Furthermore, the volume fraction y of the bulk structure in the polarization structure of the carbon source ranges from 4% to 16%.

[0013] Furthermore, the volume fraction z of the linear structure in the polarization structure of the carbon source ranges from 15% to z ≤ 50%.

[0014] Secondly, embodiments of this application also provide a method for preparing graphite particles, the method comprising:

[0015] Provide carbon source; and

[0016] The carbon source is pretreated and graphitized to obtain the graphite particles, wherein the graphite particles satisfy the relationship: 0.8≤La / Lc≤1.6, where La is the average crystallite length of the graphite particles and Lc is the average crystallite height of the graphite particles.

[0017] Furthermore, the polarization structure of the carbon source includes an inlaid structure, a block structure, and a linear structure, wherein the volume fraction x of the inlaid structure in the polarization structure of the carbon source ranges from 40% to x ≤ 80%.

[0018] Furthermore, the polarization structure of the carbon source satisfies the following relationship: 1≤(x+y) / z≤4, where x+y+z=1, x is the volume fraction of the mosaic structure in the polarization structure of the carbon source, y is the volume fraction of the block structure in the polarization structure of the carbon source, and z is the volume fraction of the linear structure in the polarization structure of the carbon source.

[0019] Furthermore, the volume fraction y of the bulk structure in the carbon source is in the range of 4% ≤ y ≤ 16%.

[0020] Furthermore, the volume fraction z of the linear structure in the polarization structure of the carbon source ranges from 15% to z ≤ 50%.

[0021] Furthermore, the carbon source satisfies at least one of the following conditions:

[0022] The mass fraction of sulfur in the carbon source ranges from 0.2% to 2%.

[0023] The mass fraction of volatiles in the carbon source ranges from 5% to 15%.

[0024] The mass fraction of ash in the carbon source ranges from 0.1% to 1%; and

[0025] The mass fraction of water in the carbon source ranges from 3% to 9%.

[0026] Thirdly, embodiments of this application also provide a battery comprising: an electrolyte, a positive electrode, a separator, and a negative electrode, wherein the negative electrode includes a negative active layer, and the negative active layer includes the graphite particles described in embodiments of this application.

[0027] Fourthly, embodiments of this application also provide an energy storage device, which includes:

[0028] Box; and

[0029] The battery described in this application embodiment is housed within the casing.

[0030] In this embodiment, the ratio of the average crystallite length La to the average crystallite height Lc of the graphite particles, La / Lc, is between 0.8 and 1.6. This results in a smaller orientation degree (OI) value for the graphite particles, and a greater degree of orientation (i.e., more orientation directions) within the particles. When applied to a battery, these graphite particles can better release lithium insertion stress during lithium intercalation, reducing the expansion of the negative electrode along the z-axis. This reduces the battery's expansion rate during charge-discharge cycles, improving the initial efficiency and cycle capacity retention. Furthermore, when the ratio of the average crystallite length La to the average crystallite height Lc is between 0.8 and 1.6, the battery using these graphite particles consumes less material during the initial film formation stage. This reduces the breakage and recombination of the solid electrolyte interface film (SEI film) and the consumption of active lithium during cycling, improving the cycle capacity retention and resulting in a higher cycle life and longer cycle life. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced 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 these drawings without creative effort.

[0032] Figure 1 A schematic flowchart of a method for preparing graphite particles according to an embodiment of this application.

[0033] Figure 2 A schematic diagram of the process for pretreatment and graphitization of carbon source according to an embodiment of this application.

[0034] Figure 3 This is a schematic diagram of the structure of a battery according to an embodiment of this application.

[0035] Figure 4 This is a battery edge according to an embodiment of the present application. Figure 3 A schematic diagram of the cross-sectional structure along the AA direction.

[0036] Figure 5 This is a cross-sectional structural schematic diagram of the negative electrode sheet according to an embodiment of this application.

[0037] Figure 6 This is a cross-sectional structural schematic diagram of the positive electrode sheet according to an embodiment of this application.

[0038] Figure 7 These are XRD patterns of graphite particles from Embodiment 2 and Comparative Example 1 of this application.

[0039] Figure 8 This is a graph showing the change in capacity of a pouch cell made from graphite particles in Example 2 and Comparative Example 1 of this application during the formation stage, as a function of voltage (dQ / dV-V).

[0040] Figure 9 These are the Raman spectra of the graphite particles in Example 2 and Comparative Example 1 of this application.

[0041] Figure 10 This is a graph showing the cycle capacity retention rate versus the number of cycles of the batteries made from graphite particles in Example 2 and Comparative Example 1 of this application, after constant power charge-discharge cycles at 25°C and 0.5P.

[0042] Figure 11 This is a graph showing the cycle capacity retention rate versus the number of cycles of the batteries made from graphite particles in Example 2 and Comparative Example 1 of this application, after constant power charge-discharge cycles at 45°C with 1P.

[0043] Figure 12 This is a scanning electron microscope image of the graphite particles in Embodiment 2 of this application, wherein the magnification is 1000x.

[0044] Figure 13 This is a scanning electron microscope image of the graphite particles in Embodiment 2 of this application, wherein the magnification is 5000x.

[0045] Figure 14 This is a scanning electron microscope image of the graphite particles in Comparative Example 1 of this application, with a magnification of 1000x.

[0046] Figure 15 This is a scanning electron microscope image of the graphite particles in Comparative Example 1 of this application, with a magnification of 3000x.

[0047] Figure 16 This is a schematic diagram of the structure of an energy storage device according to an embodiment of this application.

[0048] Explanation of reference numerals in the attached figures:

[0049] 300 - Battery, 310 - Positive electrode sheet, 311 - Positive current collector, 312 - Positive active layer, 320 - Separator, 330 - Negative electrode sheet, 331 - Negative current collector, 332 - Negative active layer, 340 - Housing, 350 - End cap assembly, 400 - Energy storage device, 410 - Housing. Detailed Implementation

[0050] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0051] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0052] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0053] It should be noted that, for ease of explanation, the same reference numerals denote the same components in the embodiments of this application, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0054] The energy efficiency requirements for lithium-ion batteries are becoming increasingly stringent, and improving energy efficiency mainly relies on enhancing the kinetics of the electrochemical system. Graphite is commonly used as the anode material in lithium-ion batteries; however, in related technologies, graphite materials have relatively low cycle life and still require improvement.

[0055] Therefore, this application provides a graphite particle.

[0056] This application provides a graphite particle that satisfies the following relationship: 0.8≤La / Lc≤1.6, where La is the average crystallite length of the graphite particle and Lc is the average crystallite height of the graphite particle.

[0057] The graphite particles in this application embodiment can be used as, but are not limited to, as the negative electrode active material of the negative electrode sheet of a lithium-ion battery.

[0058] The average crystallite length La and the average crystallite height Lc of graphite particles can be calculated using the X-ray diffraction (XRD) pattern of the graphite particles.

[0059] The formula for calculating the average crystallite length La of graphite particles is: La=k1λ / β1cosθ1, where k1=1.84, λ=0.154nm, β1 is the diffraction peak of the 110 crystal plane of the graphite particles, θ1 is the half diffraction angle of the diffraction peak of the 110 crystal plane in the XRD pattern of the graphite particles, k1 is a constant, and λ is the wavelength of the X-ray.

[0060] The formula for calculating the average crystallite height Lc of graphite particles is: Lc=k2λ / β2cosθ1, where k2=0.94, λ=0.154nm, β2 is the diffraction peak of the 002 crystal plane packing of graphite particles, θ2 is the half diffraction angle of the diffraction peak of the 002 crystal plane packing in the XRD pattern of graphite particles, k2 is a constant, and λ is the wavelength of X-rays.

[0061] Understandably, the ratio of the average crystallite length La to the average crystallite height Lc of graphite particles, La / Lc, ranges from 0.8 to 1.6. In other words, the ratio La / Lc can be any value between 0.8 and 1.6.

[0062] Specifically, the ratio La / Lc of the average crystallite length La to the average crystallite height Lc of the graphite particles can be, but is not limited to, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, etc. As the ratio La / Lc increases, the orientation degree of the graphite particles gradually increases (i.e., the OI value gradually increases), and the initial efficiency (first efficiency) of the battery using these graphite particles gradually decreases, as does the cycle capacity retention rate. Therefore, when the ratio La / Lc is too large, the initial efficiency and cycle capacity retention rate of the battery using these graphite particles are reduced.

[0063] In this embodiment, the ratio of the average crystallite length La to the average crystallite height Lc of the graphite particles, La / Lc, is between 0.8 and 1.6. This results in a smaller orientation degree (OI) value for the graphite particles, and a greater degree of orientation (i.e., more orientation directions) within the particles. When applied to a battery, these graphite particles can better release lithium insertion stress during lithium intercalation, reducing the expansion of the negative electrode along the z-axis. This reduces the battery's expansion rate during charge-discharge cycles, improving the initial efficiency and cycle capacity retention. Furthermore, when the ratio of the average crystallite length La to the average crystallite height Lc is between 0.8 and 1.6, the battery using these graphite particles consumes less material during the initial film formation stage. This reduces the breakage and recombination of the solid electrolyte interface film (SEI film) and the consumption of active lithium during cycling, improving the cycle capacity retention and resulting in a higher cycle life and longer cycle life.

[0064] It should be noted that the negative electrode sheet includes a negative current collector and a negative active layer. The negative active layer is wrapped around the surface of the negative current collector. The z-axis direction of the negative electrode sheet refers to the stacking direction of the negative current collector and the negative active layer.

[0065] In some embodiments, the average crystallite length La of the graphite particles ranges from 35nm to 55nm.

[0066] Specifically, the average crystallite length La of the graphite particles can be, but is not limited to, 35nm, 36nm, 37nm, 38nm, 39nm, 40nm, 41nm, 42nm, 43nm, 44nm, 45nm, 46nm, 47nm, 48nm, 49nm, 50nm, 51nm, 52nm, 53nm, 54nm, 55nm, etc.

[0067] In this embodiment, as the average crystallite length La of the graphite particles increases, the initial efficiency, room temperature (25°C) cycle capacity retention, and high temperature (45°C) cycle capacity retention of the battery using these graphite particles show a decreasing trend. When the average crystallite length La of the graphite particles is too large, the initial efficiency and cycle capacity retention of the battery using these graphite particles are both low. When the average crystallite length La of the graphite particles is in the range of 35nm≤La≤55nm, the orientation degree OI value of the graphite particles is smaller, and the internal orientation of the graphite particles is more oriented. When graphite particles are used in batteries, during the lithium intercalation process, the lithium intercalation stress can be better released, and the expansion of the negative electrode sheet in the z-axis direction can be reduced, thereby reducing the expansion rate of the battery during charge and discharge cycles and improving the cycle capacity retention of the battery. Furthermore, when the average crystallite length La of the graphite particles is in the range of 35nm≤La≤55nm, the battery using the graphite particles can consume less during the initial film formation stage, thereby reducing the rupture and recombination of the solid electrolyte interphase (SEI) film and the consumption of active lithium during cycling, and improving the cycle capacity retention rate of the battery.

[0068] In some embodiments, the average crystallite height Lc of the graphite particles ranges from 30nm to 45nm.

[0069] Specifically, the average crystallite height Lc of the graphite particles can be, but is not limited to, 30nm, 31nm, 32nm, 33nm, 34nm, 35nm, 36nm, 37nm, 38nm, 39nm, 40nm, 41nm, 42nm, 43nm, 44nm, 45nm, etc.

[0070] In this embodiment, when the average crystallite height Lc of the graphite particles is in the range of 30nm≤Lc≤45nm, the orientation degree OI value of the graphite particles is relatively small, and the internal orientation of the graphite particles is more pronounced. When graphite particles are used in batteries, during the lithium intercalation process, lithium intercalation stress can be better released, reducing the expansion of the negative electrode sheet in the z-axis direction, thereby reducing the expansion rate of the battery during charge-discharge cycles and improving the initial efficiency and cycle capacity retention rate of the battery. Furthermore, when the average crystallite height Lc of the graphite particles is in the range of 30nm≤Lc≤45nm, the battery using these graphite particles consumes less material during the initial film formation stage, reducing the rupture and recombination of the solid electrolyte interphase (SEI) film and the consumption of active lithium during cycling, thus improving the cycle capacity retention rate of the battery.

[0071] In some embodiments, the orientation degree OI of the graphite particles is in the range of 2.1 ≤ OI ≤ 4.0.

[0072] Specifically, the orientation degree OI of the graphite particles can be, but is not limited to, 2.1, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, etc.

[0073] In this embodiment, the smaller the orientation degree (OI) of the graphite particles, the smaller the expansion rate of the negative electrode sheet during lithium intercalation, which is beneficial to improving the initial efficiency and cycle capacity retention of the battery. However, if the orientation degree (OI) of the graphite particles is too small, it increases the difficulty of graphite particle preparation. As the orientation degree (OI) of the graphite particles increases, the initial efficiency and cycle capacity retention of the battery using these graphite particles gradually decrease. Therefore, when the orientation degree (OI) of the graphite particles is in the range of 2.1 ≤ OI ≤ 4.0, the battery using these graphite particles can have a higher initial efficiency and cycle capacity retention.

[0074] In some embodiments, the graphite particles satisfy the relationship: 0.05≤ID / IG≤0.1, where ID is the intensity of the D peak in the Raman spectrum of the graphite particles, and IG is the intensity of the G peak in the Raman spectrum of the graphite particles.

[0075] Understandably, the ratio of the intensity of the D peak in the Raman spectrum of the graphite particles to the intensity of the G peak in the Raman spectrum of the graphite particles ranges from 0.05 to 0.1.

[0076] Specifically, the ratio of the intensity of the D peak in the Raman spectrum of the graphite particles to the intensity of the G peak in the Raman spectrum of the graphite particles can be, but is not limited to, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc.

[0077] In this embodiment, if the ratio of the intensity of the D peak in the Raman spectrum of the graphite particles to the intensity of the G peak in the Raman spectrum of the graphite particles is too low or too high, it will reduce the initial efficiency and cycle capacity retention of the battery using the graphite particles.

[0078] In some embodiments, the graphite particles are obtained by pre-carbonizing and graphitizing a carbon source, wherein the carbon source includes at least one of petroleum coke and pitch coke.

[0079] In this embodiment, petroleum coke and pitch coke are used to prepare graphite particles. This ensures that the ratio of the average crystallite length La to the average crystallite height Lc of the graphite particles, La / Lc, falls within the range of 0.8 to 1.6. Consequently, the orientation degree OI of the graphite particles is lower, and the internal orientation of the graphite particles is more pronounced. When applied to batteries, these graphite particles can better release lithium intercalation stress during lithium intercalation, reducing the expansion of the negative electrode in the z-axis direction. This lowers the expansion rate of the battery during charge-discharge cycles, improving the initial efficiency and cycle capacity retention. Furthermore, when the ratio of the average crystallite length La to the average crystallite height Lc of the graphite particles, La / Lc, is between 0.8 and 1.6, the batteries using these graphite particles consume less material during the initial film formation stage, reducing the breakage and recombination of the solid electrolyte interphase (SEI) film and the consumption of active lithium during cycling, thus improving the cycle capacity retention.

[0080] In some embodiments, the polarization structure of the carbon source includes a mosaic structure (also known as a mosaic-type structure), a block structure (also known as a blocky structure or a regional structure), and a linear structure (also known as a linear structure or a fiber structure), wherein the volume fraction (i.e., volume percentage) x of the mosaic structure in the polarization structure of the carbon source ranges from 40% to x ≤ 80%.

[0081] Understandably, x = 100% × volume of mosaic structure / (volume of mosaic structure + volume of block structure + volume of linear structure).

[0082] Specifically, the volume fraction x of the embedded structure in the polarization structure of the carbon source can be, but is not limited to, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, etc.

[0083] In this embodiment, if the volume fraction of the embedded structure in the polarizing structure of the carbon source is too small, the orientation of the resulting graphite particles will be too large, leading to excessive expansion during lithium intercalation in the battery using these graphite particles, thus reducing the initial efficiency and cycle capacity retention rate of the battery. As the volume fraction of the embedded structure in the polarizing structure of the carbon source increases, the initial efficiency and cycle capacity retention rate of the battery using these graphite particles gradually increase. If the volume fraction of the embedded structure in the polarizing structure of the carbon source is too large, the requirements for the carbon source increase, increasing the manufacturing cost of the graphite particles. When the volume fraction x of the embedded structure in the polarizing structure of the carbon source is in the range of 40% ≤ x ≤ 80%, the battery using these graphite particles can achieve both high initial efficiency and cycle capacity retention rate while maintaining low manufacturing cost.

[0084] In some embodiments, the polarization structure of the carbon source satisfies the relationship: 1≤(x+y) / z≤4, where x+y+z=1, x is the volume fraction of the mosaic structure in the polarization structure of the carbon source, y is the volume fraction of the block structure in the polarization structure of the carbon source, and z is the volume fraction of the linear structure in the polarization structure of the carbon source.

[0085] Specifically, the value of (x+y) / z can be, but is not limited to, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, etc.

[0086] In this embodiment, if (x+y) / z is too small, the orientation of the graphite particles will be too large, resulting in excessive expansion of the battery during lithium intercalation, thus reducing the initial efficiency and cycle capacity retention. If (x+y) / z is too large, the requirements for the carbon source will increase, raising the manufacturing cost of the graphite particles. When the polarization structure of the carbon source satisfies the relationship 1≤(x+y) / z≤4, the battery using the graphite particles can achieve high initial efficiency and cycle capacity retention while maintaining low manufacturing cost.

[0087] In some embodiments, the volume fraction y of the bulk structure in the polarization structure of the carbon source ranges from 4% to 16%.

[0088] Specifically, the volume fraction y of the block structure in the polarization structure of the carbon source can be, but is not limited to, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, etc.

[0089] In this embodiment, when the volume fraction y of the block structure in the polarization structure of the carbon source is small, it is beneficial to reduce the orientation degree of the graphite particles, reduce the expansion rate of the battery using the graphite particles during the lithium intercalation process, and improve the initial efficiency and cycle capacity retention rate of the battery using the graphite particles. If the volume fraction y of the block structure in the polarization structure of the carbon source is too high, it will reduce the initial efficiency and cycle capacity retention rate of the battery using the graphite particles.

[0090] In some embodiments, the volume fraction z of the linear structure in the polarization structure of the carbon source ranges from 15% to z ≤ 50%.

[0091] Specifically, the linear volume fraction z in the polarization structure of the carbon source can be, but is not limited to, 15%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, etc.

[0092] In this embodiment, when the volume fraction z of the linear structure in the polarization structure of the carbon source is small, it is beneficial to reduce the orientation degree of the graphite particles, reduce the expansion rate of the battery using the graphite particles during the lithium intercalation process, and improve the initial efficiency and cycle capacity retention rate of the battery using the graphite particles. If the volume fraction z of the linear structure in the polarization structure of the carbon source is too high, it will reduce the initial efficiency and cycle capacity retention rate of the battery using the graphite particles.

[0093] In some embodiments, the carbon source satisfies at least one of the following conditions:

[0094] The mass fraction of sulfur in the carbon source ranges from 0.2% to 2%.

[0095] The mass fraction of volatiles in the carbon source ranges from 5% to 15%.

[0096] The mass fraction of ash in the carbon source ranges from 0.1% to 1%; and

[0097] The mass fraction of water in the carbon source ranges from 3% to 9%.

[0098] Specifically, the mass fraction of sulfur in the carbon source can be, but is not limited to, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, etc. Too low or too high a mass fraction of sulfur in the carbon source will reduce the mass of the resulting graphite particles and decrease the cycle performance of the battery using these graphite particles.

[0099] Specifically, the mass fraction of volatiles in the carbon source can be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc. If the mass fraction of volatiles in the carbon source is too low, the porosity of the resulting graphite particles will be too low, increasing the impedance of the graphite particles, reducing their kinetic properties, and increasing the expansion force during lithium intercalation, thus reducing their cycling performance. If the mass fraction of volatiles in the carbon source is too high, the compaction density of the resulting graphite particles will be reduced, thus reducing their specific capacity and energy density.

[0100] Specifically, the mass fraction of ash in the carbon source can be, but is not limited to, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, etc. Too low or too high a mass fraction of ash in the carbon source will reduce the mass of the obtained graphite particles and decrease the cycle performance of the battery using these graphite particles.

[0101] Specifically, the mass fraction of water in the carbon source can be, but is not limited to, 3%, 4%, 5%, 6%, 7%, 8%, 9%, etc. Too low or too high a mass fraction of water in the carbon source will reduce the mass of the resulting graphite particles and decrease the cycle performance of the battery using these graphite particles.

[0102] Optionally, the graphite particles satisfy the following relationship: 3μm≤Dv90-Dv10≤18.5μm, where Dv90 is the particle size corresponding to the cumulative particle size distribution percentage in the volume distribution of the graphite particles reaching 90%, and Dv10 is the particle size corresponding to the cumulative particle size distribution percentage in the volume distribution of the graphite particles reaching 10%.

[0103] It should be noted that the smaller the Dv90-Dv10, the narrower the particle size distribution of the graphite particles; the larger the Dv90-Dv10, the wider the particle size distribution of the graphite particles.

[0104] Specifically, the values ​​of Dv90-Dv10 can be, but are not limited to, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 18.5μm, etc.

[0105] In this embodiment, the smaller the values ​​of Dv90-Dv10, the narrower the particle size distribution of the graphite particles. When the graphite particles are used to form the negative electrode active layer of the negative electrode sheet, the pores within the active layer tend to be more uniform, which is beneficial for the electrolyte to wet the active layer and thus improves the cycle performance of the negative electrode sheet using these graphite particles. However, when graphite particles are used to form the negative electrode active layer, the porosity of the negative electrode sheet increases, reducing its energy density. A wider particle size distribution of graphite particles slightly increases the specific capacity. However, when graphite particles are used to form the negative electrode active layer, the pores between the graphite particles are too small, which can easily lead to insufficient electrolyte wetting and reduce the battery's cycle capacity retention rate.

[0106] Optionally, the specific surface area (BET) of the graphite particles ranges from 1.0 m² / g to 1.8 m² / g. Specifically, the specific surface area (BET) of the graphite particles can be, but is not limited to, 1.0 m² / g, 1.1 m² / g, 1.2 m² / g, 1.3 m² / g, 1.4 m² / g, 1.5 m² / g, 1.6 m² / g, 1.7 m² / g, 1.8 m² / g, etc. In this embodiment, if the specific surface area (BET) of the graphite particles is too small, the kinetic performance of the battery using the graphite particles is reduced; if the specific surface area (BET) of the graphite particles is too large, the side reactions between the graphite particles and the electrolyte are increased, reducing the cycle capacity retention rate of the battery using the graphite particles.

[0107] Optionally, the specific capacity of the graphite particles ranges from 340 mAh / g to 350 mAh / g. Specifically, the specific capacity of the graphite particles can be, but is not limited to, 340 mAh / g, 342 mAh / g, 344 mAh / g, 345 mAh / g, 346 mAh / g, 348 mAh / g, 350 mAh / g, etc. The graphite particles of this application have a high specific capacity.

[0108] Optionally, the tap density of the graphite particles ranges from 1.1 g / cm³. 3 Up to 1.4 g / cm 3 Specifically, the tap density of the graphite particles can be, but is not limited to, 1.1 g / cm³. 3 1.15g / cm 3 1.2g / cm 3 1.25g / cm 3 1.3g / cm 3 1.335g / cm 3 1.4g / cm 3 wait.

[0109] Optionally, the oil absorption value (OAV) of the graphite particles ranges from 25 cm⁻¹. 3 / g≤OAV≤40cm 3 / g. Specifically, the oil absorption value (OAV) of graphite particles can be, but is not limited to, 25 cm⁻¹. 3 / g、26cm 3 / g、28cm 3 / g, 30cm 3 / g、32cm 3 / g、34cm 3 / g、36cm 3 / g, 38cm 3 / g、40cm 3 / g、42cm 3 / g、44cm 3 / g、45cm 3 / g etc. If the oil absorption value (OAV) of graphite particles is too low, the cycle performance of the battery using the graphite particles will be reduced; if the oil absorption value (OAV) of graphite particles is too high, the cost of the graphite particles will increase, or even make them impossible to produce.

[0110] The graphite particles of this application embodiment can be prepared by the methods described in the following embodiments of this application. In addition, they can also be prepared by other methods. The preparation methods of this application embodiment are merely one or more preparation methods of the graphite particles of this application and should not be construed as limiting the graphite particles provided in the embodiments of this application.

[0111] Please see Figure 1This application also improves a method for preparing graphite particles, the method comprising:

[0112] S201 provides a carbon source; and

[0113] S202, the carbon source is pretreated and graphitized to obtain the graphite particles, wherein the graphite particles satisfy the relationship: 0.8≤La / Lc≤1.6, where La is the average crystallite length of the graphite particles and Lc is the average crystallite height of the graphite particles.

[0114] The graphite particle preparation method of this application produces graphite particles with an average crystallite length La to average crystallite height Lc ratio La / Lc of 0.8 to 1.6, resulting in a lower orientation degree OI value and greater internal orientation of the graphite particles. When applied to batteries, these graphite particles can better release lithium insertion stress during lithium intercalation, reducing the expansion of the negative electrode in the z-axis direction, thereby lowering the battery's expansion rate during charge-discharge cycles and improving the battery's initial efficiency and cycle capacity retention. Furthermore, when the ratio La / Lc of the average crystallite length La to average crystallite height Lc is 0.8 to 1.6, batteries using these graphite particles consume less material during the initial film formation stage, reducing the rupture and recombination of the solid electrolyte interface film and the consumption of active lithium during cycling, thus improving the battery's cycle capacity retention.

[0115] In some embodiments, the polarization structure of the carbon source includes an inlaid structure, a block structure, and a linear structure, wherein the volume fraction x of the inlaid structure in the polarization structure of the carbon source ranges from 40% to x ≤ 80%.

[0116] Specifically, the volume fraction x of the embedded structure in the polarization structure of the carbon source can be, but is not limited to, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, etc.

[0117] In this embodiment, if the volume fraction of the embedded structure in the polarizing structure of the carbon source is too small, the orientation of the resulting graphite particles will be too large, leading to excessive expansion during lithium intercalation in the battery using these graphite particles, thus reducing the initial efficiency and cycle capacity retention rate of the battery. As the volume fraction of the embedded structure in the polarizing structure of the carbon source increases, the initial efficiency and cycle capacity retention rate of the battery using these graphite particles gradually increase. If the volume fraction of the embedded structure in the polarizing structure of the carbon source is too large, the requirements for the carbon source increase, increasing the manufacturing cost of the graphite particles. When the volume fraction x of the embedded structure in the polarizing structure of the carbon source is in the range of 40% ≤ x ≤ 80%, the battery using these graphite particles can achieve both high initial efficiency and cycle capacity retention rate while maintaining low manufacturing cost.

[0118] In some embodiments, the polarization structure of the carbon source satisfies the relationship: 1≤(x+y) / z≤4, where x+y+z=1, x is the volume fraction of the mosaic structure in the polarization structure of the carbon source, y is the volume fraction of the block structure in the polarization structure of the carbon source, and z is the volume fraction of the linear structure in the polarization structure of the carbon source.

[0119] Specifically, the value of (x+y) / z can be, but is not limited to, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, etc.

[0120] In this embodiment, if (x+y) / z is too small, the orientation of the graphite particles will be too large, resulting in excessive expansion of the battery during lithium intercalation, thus reducing the initial efficiency and cycle capacity retention. If (x+y) / z is too large, the requirements for the carbon source will increase, raising the manufacturing cost of the graphite particles. When the polarization structure of the carbon source satisfies the relationship 1≤(x+y) / z≤4, the battery using the graphite particles can achieve high initial efficiency and cycle capacity retention while maintaining low manufacturing cost.

[0121] In some embodiments, the volume fraction y of the bulk structure in the polarization structure of the carbon source ranges from 4% to 16%.

[0122] Specifically, the volume fraction y of the block structure in the polarization structure of the carbon source can be, but is not limited to, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, etc.

[0123] In this embodiment, when the volume fraction y of the block structure in the polarization structure of the carbon source is small, it is beneficial to reduce the orientation degree of the graphite particles, reduce the expansion rate of the battery using the graphite particles during the lithium intercalation process, and improve the initial efficiency and cycle capacity retention rate of the battery using the graphite particles. If the volume fraction y of the block structure in the polarization structure of the carbon source is too high, it will reduce the initial efficiency and cycle capacity retention rate of the battery using the graphite particles.

[0124] In some embodiments, the volume fraction z of the linear structure in the polarization structure of the carbon source ranges from 15% to z ≤ 50%.

[0125] Specifically, the linear volume fraction z in the polarization structure of the carbon source can be, but is not limited to, 15%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, etc.

[0126] In this embodiment, when the volume fraction z of the linear structure in the polarization structure of the carbon source is small, it is beneficial to reduce the orientation degree of the graphite particles, reduce the expansion rate of the battery using the graphite particles during the lithium intercalation process, and improve the initial efficiency and cycle capacity retention rate of the battery using the graphite particles. If the volume fraction z of the linear structure in the polarization structure of the carbon source is too high, it will reduce the initial efficiency and cycle capacity retention rate of the battery using the graphite particles.

[0127] In some embodiments, the carbon source satisfies at least one of the following conditions:

[0128] The mass fraction of sulfur in the carbon source ranges from 0.2% to 2%.

[0129] The mass fraction of volatiles in the carbon source ranges from 5% to 15%.

[0130] The mass fraction of ash in the carbon source ranges from 0.1% to 1%; and

[0131] The mass fraction of water in the carbon source ranges from 3% to 9%.

[0132] Specifically, the mass fraction of sulfur in the carbon source can be, but is not limited to, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, etc. Too low or too high a mass fraction of sulfur in the carbon source will reduce the mass of the resulting graphite particles and decrease the cycle performance of the battery using these graphite particles.

[0133] Specifically, the mass fraction of volatiles in the carbon source can be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc. If the mass fraction of volatiles in the carbon source is too low, the porosity of the resulting graphite particles will be too low, increasing the impedance of the graphite particles, reducing their kinetic properties, and increasing the expansion force during lithium intercalation, thus reducing their cycling performance. If the mass fraction of volatiles in the carbon source is too high, the compaction density of the resulting graphite particles will be reduced, thus reducing their specific capacity and energy density.

[0134] Specifically, the mass fraction of ash in the carbon source can be, but is not limited to, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, etc. Too low or too high a mass fraction of ash in the carbon source will reduce the mass of the obtained graphite particles and decrease the cycle performance of the battery using these graphite particles.

[0135] Specifically, the mass fraction of water in the carbon source can be, but is not limited to, 3%, 4%, 5%, 6%, 7%, 8%, 9%, etc. Too low or too high a mass fraction of water in the carbon source will reduce the mass of the resulting graphite particles and decrease the cycle performance of the battery using these graphite particles.

[0136] Please see Figure 2 In some embodiments, in step S202, the carbon source is pretreated and graphitized to obtain the graphite particles, including:

[0137] S2021, The carbon source is crushed to obtain precursor particles;

[0138] Optionally, the carbon source is coarsely crushed using a jaw crusher, and then ground into fine powder using an air jet mill to obtain precursor particles. These particles are then sieved to ensure that the precursor particle size meets the following requirement: Dv90-Dv10≤18.5μm.

[0139] S2022, the precursor particles are pretreated at a first temperature T1 within the range of 900℃≤T1≤1300℃ to obtain intermediate particles; and

[0140] Specifically, the first temperature T1 can be, but is not limited to, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, etc. In this embodiment, if the pretreatment temperature is too low, it will not have a significant effect on the volatilization of volatiles, and will not play a role in creating internal pores, thus reducing the porosity of the obtained graphite particles and increasing the expansion force of the graphite particles during the lithium intercalation process; if the pretreatment temperature is too high, it will increase the preparation cost of graphite particles, and will also increase the size of the internal pores of the obtained graphite particles, reducing the compaction density of the graphite particles.

[0141] Optionally, the pretreatment time can range from 2 hours to 4 hours. Specifically, the pretreatment time can be, but is not limited to, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, etc. If the pretreatment time is too short, too little volatile matter will be removed; if the pretreatment time is too long, the preparation cost of graphite particles will increase.

[0142] S2023, the intermediate particles are placed at a second temperature T2 within the range of 2800℃≤T2≤3100℃ for graphitization treatment to obtain graphite particles.

[0143] Specifically, the second temperature T2 can be, but is not limited to, 2800℃, 2850℃, 2900℃, 2950℃, 3000℃, 3050℃, 3100℃, etc. If the graphitization temperature is too low, the degree of graphitization of the graphite particles will be reduced, the specific capacity of the graphite particles will be reduced, and the defects of the graphite particles will be further increased; if the graphitization temperature is too high, the preparation cost of the graphite particles will be increased.

[0144] Optionally, the holding time for the graphitization treatment ranges from 12 hours to 96 hours. Specifically, the holding time for the graphitization treatment can be, but is not limited to, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 28 hours, 32 hours, 36 hours, 44 hours, 48 ​​hours, 52 hours, 56 hours, 60 hours, 64 hours, 68 hours, 72 hours, 76 hours, 80 hours, 84 hours, 88 hours, 92 hours, and 96 hours. If the graphitization treatment time is too short, it reduces the degree of graphitization of the graphite particles, decreases the conductivity and specific capacity of the graphite particles, and further reduces the kinetic properties of the graphite particles; if the graphitization treatment time is too long, it increases the preparation cost of the graphite particles.

[0145] Please see Figure 3 , Figure 4 and Figure 5This application also provides a battery 300, which includes: an electrolyte, a positive electrode 310, a separator 320, and a negative electrode 330. The negative electrode 330 includes a negative electrode active layer 332, which includes the graphite particles (not shown) described in this application embodiment.

[0146] The battery 300 in this application embodiment can be, but is not limited to, at least one of lithium battery, sodium battery, lithium-sodium hybrid battery, etc.

[0147] Optionally, the battery 300 can be, but is not limited to, a square battery, a round battery, etc.

[0148] Understandably, the positive electrode 310, the separator 320, and the negative electrode 330 are all at least partially immersed in the electrolyte.

[0149] Understandably, the positive electrode 310 and the negative electrode 330 are located on opposite sides of the separator 320, which is used to separate the positive electrode 310 and the negative electrode 330.

[0150] It should be noted that graphite particles are used as the negative electrode active material in the negative electrode active layer 332.

[0151] Understandably, the positive electrode 310, the separator 320, and the negative electrode 330 are sequentially stacked to form an electrode assembly (not shown in the figure). The electrode assembly can be, but is not limited to, a wound structure, a stacked structure, etc., and this application does not make specific limitations in this regard.

[0152] Please see Figure 5 Optionally, the negative electrode 330 further includes a negative electrode current collector 331, and the negative electrode active layer 332 is disposed on the surface of the negative electrode current collector 331. It is understood that the negative electrode active layer 332 may cover one surface or both opposite surfaces of the negative electrode current collector 331.

[0153] Optionally, the negative electrode current collector 331 can be, but is not limited to, a copper sheet.

[0154] Optionally, the negative electrode active layer 332 further includes a negative electrode conductive agent, a negative electrode binder, and a negative electrode thickener.

[0155] Optionally, the negative electrode conductive agent may be, but is not limited to, at least one of conductive carbon black (SP), acetylene black, carbon nanotubes, carbon fibers, graphene, etc.

[0156] Optionally, the negative electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), polyhexanefluoropropylene, and polymerized styrene-butadiene rubber (SBR).

[0157] Optionally, the negative electrode thickener may be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), and polymethyl methacrylate (PMA).

[0158] Please see Figure 6 Optionally, the positive electrode 310 includes a positive current collector 311 and a positive active layer 312, wherein the positive active layer 312 is disposed on the surface of the positive current collector 311. It is understood that the positive active layer 312 may cover one surface or both opposite surfaces of the positive current collector 311.

[0159] Optionally, the positive current collector 311 can be, but is not limited to, an aluminum sheet.

[0160] Optionally, the positive electrode active layer 312 includes a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, and a positive electrode thickener.

[0161] Optionally, the positive electrode active material can be, but is not limited to, lithium iron phosphate.

[0162] Optionally, the positive electrode conductive agent can be, but is not limited to, at least one of conductive carbon black, acetylene black, carbon nanotubes, carbon fibers, graphene, etc.

[0163] Optionally, the positive electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), polyhexanefluoropropylene, and polymerized styrene-butadiene rubber (SBR).

[0164] Optionally, the positive electrode thickener may be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), and polymethyl methacrylate (PMA).

[0165] Optionally, the diaphragm 320 can be, but is not limited to, at least one of polypropylene membrane (PP membrane), polyethylene membrane (PE membrane), ceramic diaphragm 320, etc.

[0166] Optionally, the electrolyte includes an electrolyte salt, an organic solvent, and a film-forming additive.

[0167] Optionally, the electrolyte salt is a lithium salt, which includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalateborate)borate (LiBOB), lithium difluorodioxalate phosphate (LOIDFP), lithium difluorooxalate borate (LOIDFB), lithium difluorophosphate (LiPO2F2), and lithium trifluoromethanesulfonate (CF3SO3Li).

[0168] Optionally, the organic solvent includes at least one of cyclic carbonates and chain carbonates. Cyclic carbonates have high dielectric constants and high ionic conductivity, enabling the formation of a stable SEI film on the surface of the negative electrode 330, but they have a relatively high viscosity. Chain carbonates have lower viscosity than cyclic carbonates, better electrochemical stability, and can improve the low-temperature performance of the electrolyte. Therefore, using a mixed solvent of cyclic and chain carbonates can achieve both suitable viscosity and low-temperature stability in the electrolyte, and also allow for better film formation in the battery 300 using this electrolyte.

[0169] Optionally, the cyclic carbonate may include, but is not limited to, at least one of ethylene carbonate (EC) and propylene carbonate (PC). Ethylene carbonate has a much higher dielectric constant than propylene carbonate, and therefore can better promote the formation of the SEI film.

[0170] Optionally, the chain carbonate may include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0171] Optionally, the organic solvent further includes at least one of ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, γ-butyrolactone, and 2,2-difluoroethyl acetate.

[0172] Optionally, the electrolyte further includes a film-forming additive. When the electrolyte is applied to the lithium-ion battery 300, the film-forming additive can be used to promote the formation of an interface film of at least one of the positive electrode 310 and the negative electrode 330 and maintain the stability of the interface film.

[0173] Optionally, the film-forming additive includes at least one selected from fluoroethylene carbonate (FEC), ethylene sulfate (DTD), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, adiponitrile, succinate, and 1,3,6-hexanetrionitrile.

[0174] Optionally, the battery 300 further includes a housing 340 and an end cap assembly 350, the housing 340 and the end cap assembly 350 forming a closed receiving cavity for housing the electrolyte, the positive electrode 310, the separator 320, and the negative electrode 330. Understandably, the end cap assembly 350 electrically connects the positive electrode 310 and the negative electrode 330, respectively, leading out the positive electrode 310 and the negative electrode 330 for electrical connection to external devices or other batteries 300.

[0175] The graphite particles and battery 300 of this application will be further described below through specific embodiments.

[0176] Examples 1 to 5, Comparative Examples 1 to 2

[0177] The graphite particles of each embodiment and comparative example were prepared by the following steps:

[0178] (1) Petroleum coke is provided as a carbon source, wherein the mass fraction of sulfur in the carbon source is 0.3%; the mass fraction of volatile matter in the carbon source is 10%; the mass fraction of ash in the carbon source is 0.2%; and the mass fraction of moisture in the carbon source is 6%. In each embodiment and comparative example, the volume fraction x of the mosaic structure, the volume fraction y of the block structure, and the volume fraction z of the linear structure in the polarization structure of the carbon source are shown in Table 1 below.

[0179] (2) The petroleum coke is coarsely crushed by a jaw crusher and then ground into fine powder by an air jet mill; the carbon source particles ground into fine powder are screened to obtain precursor particles.

[0180] (3) The precursor particles are pretreated at 1000°C to obtain intermediate particles; and

[0181] (4) The intermediate particles were placed in a graphite furnace at 3100℃ for graphitization treatment to obtain graphite particles.

[0182] The graphite particles of each embodiment and comparative example were assembled into a pouch cell 300 according to the following steps:

[0183] (1) 97.4% lithium iron phosphate (positive electrode active material), 0.7% conductive carbon black (positive electrode conductive agent), 1.8% polyvinylidene fluoride (positive electrode binder), and 0.1% polyvinylpyrrolidone (PVP, additive) are dispersed in methylpyrrolidone (NMP) according to the mass ratio to prepare a positive electrode slurry; the positive electrode slurry is coated on aluminum foil (positive electrode current collector 311), and then dried, rolled, and cut to obtain a positive electrode sheet 310;

[0184] (2) 96.7% graphite particles (negative electrode active material), 2.5% aqueous carboxymethyl cellulose binder (negative electrode binder) and 0.8% conductive carbon black (negative electrode conductive agent) are dispersed in deionized water according to the mass ratio to prepare a negative electrode slurry; the negative electrode slurry is uniformly coated on the surface of copper foil (negative electrode current collector 331), and then dried, rolled and cut to obtain negative electrode sheet 330.

[0185] (3) Preparation of electrolyte: Ethyl carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed solvent; then, fully dried lithium salt LiPF6 is dissolved in the mixed solvent to prepare an electrolyte with a LiPF6 molar concentration of 1 mol / L.

[0186] (4) Preparation of diaphragm 320: A polyethylene film with a thickness of 16 micrometers was selected as diaphragm 320; and

[0187] (5) Assembly of soft-pack battery 300: The positive electrode 310, separator 320 and negative electrode 330 are stacked in sequence, so that the separator 320 is placed between the positive electrode 310 and the negative electrode 330 to play a role in isolation. The battery cell is obtained by winding. The battery cell is then subjected to hot pressing, welding, casing, electrolyte injection and capacity testing to obtain soft-pack battery 300.

[0188] Various performance tests were conducted on the graphite particles of each embodiment and comparative example and the soft-pack battery 300 assembled therefrom. The test results are shown in Table 2 below.

[0189] (1) Average crystallite length La and average crystallite height Lc of graphite particles: XRD patterns were measured using an X-ray diffractometer. A wide-angle test mode was used for phase analysis, with a test range of 5° to 85° and a scan rate of 10° / min. The formula for calculating the average crystallite length La of graphite particles is: La = k1λ / β1cosθ1, where k1 = 1.84, λ = 0.154 nm, β1 is the diffraction peak of the 110 crystal plane of the graphite particles, and θ1 is the half-diffraction angle of the diffraction peak of the 110 crystal plane in the XRD pattern of the graphite particles. The formula for calculating the average crystallite height Lc of graphite particles is: Lc = k2λ / β2cosθ1, where k2 = 0.94, λ = 0.154 nm, β2 is the diffraction peak of the 002 crystal plane of the graphite particles, and θ2 is the half-diffraction angle of the diffraction peak of the 002 crystal plane in the XRD pattern of the graphite particles. The XRD patterns of the graphite particles in Embodiment 2 and Comparative Example 1 of this application are shown below. Figure 7 As shown.

[0190] (2) Measurement of the volume fraction of mosaic, massive, and linear structures in the carbon source: Polarized light photographs were taken using a polarizing microscope at a magnification of 100x. The volume fraction of mosaic, massive, and linear structures in the carbon source was calculated based on the area ratio of the mosaic, massive, and linear structures in the polarized light photographs.

[0191] (3) ID / IG Measurement: Measurements were performed using a Raman spectrometer with a 535nm laser wavelength and a test range of 1000cm. -1 Up to 3500cm -1 .

[0192] (4) Measurement of orientation degree OI of graphite particles: XRD pattern was measured using an X-ray diffractometer. Wide-angle test mode was used for phase analysis, with a test range of 5° to 85° and a scanning rate of 10° / min. The OI of graphite particles was calculated according to the formula OI=I(004) / I(110), where I(004) is the intensity of the 004 diffraction peak on the XRD and I(110) is the intensity of the 110 diffraction peak on the XRD.

[0193] (5) First-time performance test of battery 300: Battery 300 was subjected to its first charge-discharge test on a charge-discharge tester (Nebula Charge-Discharge Test System-BAT-NEEFLCT-05-V010) at a test temperature of 25℃. Battery 300 was charged at a constant power of 0.33C to its charging cutoff voltage of 3.65V, and the initial charging capacity was recorded. Battery 300 was then left to stand for 10 minutes and discharged at a constant power of 0.33C to its discharge cutoff voltage of 2V, and the first discharge capacity was recorded. Where C refers to the charging or discharging current rate of battery 300. First-time charge-discharge capacity retention rate (i.e., first-time performance) = (first-time discharge capacity / first-time discharge capacity) × 100%.

[0194] (6) Cycle capacity retention at 25℃ or 45℃: Battery 300 was subjected to charge-discharge cycle testing on a charge-discharge tester (Nebula Charge-Discharge Test System-BAT-NEEFLCT-05-V010) at a test temperature of 25℃ or 45℃. Battery 300 was charged at a constant power of 0.25P to the charging cut-off voltage of 3.65V, and the initial charging capacity was recorded. After the battery 300 was left to stand for 10 minutes, it was discharged at a constant power of 0.25P to the discharge cut-off voltage of 2V, and the discharge capacity was recorded. Wherein, P refers to the rated charging or discharging power of battery 300, which is the nominal voltage U of battery 300 multiplied by the current density of 1C. The nominal voltage of lithium iron phosphate battery 300 is 3.2V, and 0.25P refers to 0.25 times the rated power.

[0195] The formula for calculating the capacity retention rate after cycling is: Capacity retention rate after the nth cycle = (Discharge capacity after the nth cycle / Discharge capacity in the first cycle) × 100%.

[0196] Table 1 Performance parameters of carbon sources in each embodiment and comparative example

[0197] Example 1 5.7 78.9 6.3 14.8 Example 2 3.6 74.5 4.8 21.7 Example 3 3.1 67.2 8.4 24.4 Example 4 2.1 55.7 12.1 32.2 Example 5 1.4 42.8 15.5 41.7 Comparative Example 1 0.8 14.6 30.6 54.8 Comparative Example 2 0.6 8.7 28.9 62.4

[0198] Table 2 Performance parameters of graphite particles and battery 300 prepared in each embodiment and comparative example

[0199]

[0200] As shown in Tables 1 and 2, with the increase of the ratio (x+y) / z of the sum of the volume fractions x of the embedded structure and y of the block structure to the volume fraction z of the linear structure in the polarization structure of the carbon source, the La / Lc (the ratio of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles) of the prepared graphite particles gradually decreases, the orientation degree OI of the graphite particles gradually decreases, the first efficiency of the battery 300 using the graphite particles gradually increases, and the cycle capacity retention rate of the battery 300 using the graphite particles at room temperature (25℃) and at high temperature (45℃) gradually increases. When the ratio (x+y) / z of the sum of the volume fractions x of the embedded structure and y of the block structure in the polarization structure of the carbon source to the volume fraction y of the linear structure is too low (as in Comparative Example 1 and Comparative Example 2), the La / Lc and OI of the obtained graphite particles are too high, and the first efficiency, room temperature (25℃) cycle capacity retention rate and high temperature (45℃) cycle capacity retention rate of the battery 300 using the graphite particles are all low.

[0201] Furthermore, as the volume fraction y of the bulk structure in the polarization structure of the carbon source gradually decreases, the first-efficiency, room-temperature (25℃) cycle capacity retention rate, and high-temperature (45℃) cycle capacity retention rate of the battery 300 made from the graphite particles gradually increase; as the volume fraction z of the linear structure in the polarization structure of the carbon source gradually decreases, the first-efficiency, room-temperature (25℃) cycle capacity retention rate, and high-temperature (45℃) cycle capacity retention rate of the battery 300 made from the graphite particles gradually increase.

[0202] Furthermore, as shown in Tables 1 and 2, both excessively large and small ID / IG ratios of the graphite particles reduce the initial efficiency, room temperature (25°C) cycle capacity retention, and high temperature (45°C) cycle capacity retention of the battery 300 using these graphite particles. When the ID / IG ratio is between 0.05 and 0.1, the battery 300 using these graphite particles exhibits higher initial efficiency, higher room temperature (25°C) cycle capacity retention, and higher high temperature (45°C) cycle capacity retention.

[0203] Figure 8 This is a graph showing the change in capacity of a pouch cell 300 made from graphite particles according to Embodiment 2 and Comparative Example 1 during the formation stage, as a function of voltage (dQ / dV-V). Figure 8 It can be seen that, compared with the battery 300 of Comparative Example 1, the peak value of the battery 300 of Example 2 of this application is reduced at around 2.5V. This indicates that the negative electrode 330 of the battery 300 of Example 2 of this application consumes less electrolyte during the formation stage and has a higher first efficiency and cycle capacity retention rate.

[0204] Figure 9 These are the Raman spectra of the graphite particles in Example 2 and Comparative Example 1 of this application, obtained by... Figure 9 It can be seen that, compared with the graphite particles of Comparative Example 1, the graphite particles of Example 2 of this application have a smaller ID / IG and fewer defects.

[0205] Figure 10 This is a graph showing the cycle capacity retention rate versus the number of cycles of the battery 300 made from graphite particles in Example 2 and Comparative Example 1 of this application, after constant power charge-discharge cycles at 25°C and 0.5P. Figure 11 This is a graph showing the cycle capacity retention rate versus the number of cycles for the battery 300 made of graphite particles from Embodiment 2 and Comparative Example 1 of this application, after constant power charge-discharge cycling at 45°C with a power of 1P. Figure 10 and Figure 11 The test results show that, compared with Comparative Example 1, the battery 300 made of graphite particles in Example 2 of this application has a higher room temperature cycle capacity retention rate and a higher high temperature cycle capacity retention rate. After 800 constant power charge-discharge cycles at 0.5P at 25°C, the cycle capacity retention rate of the battery 300 made of graphite particles in Example 2 of this application is still higher than 99%; after 1500 constant power charge-discharge cycles at 5P at 45°C, the cycle capacity retention rate of the battery 300 made of graphite particles in Example 2 of this application is still higher than 87%.

[0206] Figure 12 This is a scanning electron microscope image of the graphite particles in Embodiment 2 of this application, wherein the magnification is 1000x. Figure 13 This is a scanning electron microscope image of the graphite particles in Embodiment 2 of this application, wherein the magnification is 5000x. Figure 14 This is a scanning electron microscope image of the graphite particles in Comparative Example 1 of this application, with a magnification of 1000x. Figure 15 This is a scanning electron microscope (SEM) image of the graphite particles in Comparative Example 1 of this application, at a magnification of 3000x. Figures 12 to 15 The scanning electron microscope (SEM) images show that the graphite particles in Example 2 and Comparative Example 1 are both single particles with similar particle sizes. However, the graphite particles in Example 2 have more directional orientations, which allows for better release of lithium intercalation stress during lithium insertion, reducing the expansion of the negative electrode along the z-axis. This, in turn, lowers the battery's expansion rate during charge-discharge cycles and improves the battery's initial efficiency and cycle capacity retention. In contrast, the graphite particles in Comparative Example 1 have a more uniform orientation, with larger La / Lc and OI ratios, resulting in lower initial efficiency and cycle capacity retention.

[0207] Please see Figure 16 This application embodiment also provides an energy storage device 400, which includes a housing 410 and a battery 300 as described in this application embodiment, wherein the battery 300 is housed within the housing 410.

[0208] The energy storage device 400 of this application can be applied to, but is not limited to, energy storage on the generation side, energy storage on the grid side, and energy storage on the consumption side.

[0209] Optionally, the number of batteries 300 can be one or more. When there are multiple batteries 300, the multiple batteries 300 can be connected in parallel; or the multiple batteries 300 can be connected in series; or the multiple batteries 300 can be partially connected in parallel and partially connected in series (in other words, mixed connection). This application does not specifically limit the connection method of multiple batteries 300 of the same energy storage device 400.

[0210] Understandably, the housing 410 has accommodating cavities (not shown) in which multiple batteries 300 are housed. In some embodiments, each accommodating cavity houses one battery 300. In other embodiments, each accommodating cavity houses multiple batteries 300.

[0211] Optionally, the energy storage device 400 may include, but is not limited to, battery modules, battery packs, battery systems, energy storage cabinets, energy storage boxes, energy storage containers, etc. The actual application form of the energy storage device 400 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 400.

[0212] In this application, the terms "embodiment" and "implementation" mean that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of this application. The appearance of these phrases in various places in the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this application can be combined with other embodiments. Furthermore, 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 depart from the spirit and scope of the technical solution of this application, provided there is no contradiction between them.

[0213] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A type of graphite particle, characterized in that, The graphite particles satisfy the following relationship: 0.8≤La / Lc≤1.6, where La is the average crystallite length of the graphite particles and Lc is the average crystallite height of the graphite particles; the graphite particles are obtained by pre-carbonization and graphitization of a carbon source, and the polarization structure of the carbon source includes an inlaid structure, a block structure and a linear structure, and the volume fraction x of the inlaid structure in the polarization structure of the carbon source is in the range of 40%≤x≤80%.

2. The graphite particles according to claim 1, characterized in that, The average crystallite length La of the graphite particles is in the range of 35nm≤La≤55nm.

3. The graphite particles according to claim 1, characterized in that, The average crystallite height Lc of the graphite particles is in the range of 30nm≤Lc≤45nm.

4. The graphite particles according to claim 1, characterized in that, The orientation degree (OI) of the graphite particles is in the range of 2.1 ≤ OI ≤ 4.

0.

5. The graphite particles according to claim 1, characterized in that, The graphite particles satisfy the following relationship: 0.05≤ID / IG≤0.1, where ID is the intensity of the D peak in the Raman spectrum of the graphite particles, and IG is the intensity of the G peak in the Raman spectrum of the graphite particles.

6. The graphite particles according to any one of claims 1-5, characterized in that, The carbon source includes at least one of petroleum coke and pitch coke.

7. The graphite particles according to claim 6, characterized in that, The polarization structure of the carbon source satisfies the following relationship: 1≤(x+y) / z≤4, where x+y+z=1, x is the volume fraction of the mosaic structure in the polarization structure of the carbon source, y is the volume fraction of the block structure in the polarization structure of the carbon source, and z is the volume fraction of the linear structure in the polarization structure of the carbon source.

8. The graphite particles according to claim 7, characterized in that, The volume fraction y of the bulk structure in the polarization structure of the carbon source is in the range of 4% ≤ y ≤ 16%.

9. The graphite particles according to claim 7 or 8, characterized in that, The volume fraction z of the linear structure in the polarization structure of the carbon source is in the range of 15% ≤ z ≤ 50%.

10. A method for preparing graphite particles, characterized in that, The preparation method includes: Provide carbon source; and The carbon source is pretreated and graphitized to obtain graphite particles, wherein the graphite particles satisfy the relationship: 0.8≤La / Lc≤1.6, where La is the average crystallite length of the graphite particles and Lc is the average crystallite height of the graphite particles; the polarization structure of the carbon source includes an embedded structure, a block structure and a linear structure, and the volume fraction x of the embedded structure in the polarization structure of the carbon source is in the range of 40%≤x≤80%.

11. The method for preparing graphite particles according to claim 10, characterized in that, The polarization structure of the carbon source satisfies the following relationship: 1≤(x+y) / z≤4, where x+y+z=1, x is the volume fraction of the mosaic structure in the polarization structure of the carbon source, y is the volume fraction of the block structure in the polarization structure of the carbon source, and z is the volume fraction of the linear structure in the polarization structure of the carbon source.

12. The method for preparing graphite particles according to claim 10, characterized in that, The volume fraction y of the bulk structure in the carbon source is in the range of 4% ≤ y ≤ 16%.

13. The method for preparing graphite particles according to claim 10, characterized in that, The volume fraction z of the linear structure in the polarization structure of the carbon source is in the range of 15% ≤ z ≤ 50%.

14. The method for preparing graphite particles according to any one of claims 10-13, characterized in that, The carbon source satisfies at least one of the following conditions: The mass fraction of sulfur in the carbon source ranges from 0.2% to 2%. The mass fraction of volatile matter in the carbon source ranges from 5% to 15%. The mass fraction of ash in the carbon source ranges from 0.1% to 1%; and The mass fraction of water in the carbon source ranges from 3% to 9%.

15. A battery, characterized in that, include: An electrolyte, a positive electrode, a separator, and a negative electrode, wherein the negative electrode includes a negative active layer, and the negative active layer includes graphite particles as described in any one of claims 1-9 or graphite particles prepared by the method described in any one of claims 10-14.

16. An energy storage device, characterized in that, include: Box; as well as The battery of claim 15, wherein the battery is housed within the casing.

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