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

Abstract

The invention provides graphite particles, a preparation method thereof, a battery and an energy storage device. The graphite particles meet the relational expression that La / Lc is larger than or equal to 0.8 and smaller than or equal to 1.6, La is the average microcrystal length of the graphite particles, and Lc is the average microcrystal height of the graphite particles. The graphite particles provided by the embodiment of the invention have relatively high cycle performance.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and specifically to graphite particles, 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. However, the cycle life of graphite materials in related technologies is relatively low and remains to be improved. Summary of the Invention

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

[0004] In a first aspect, an embodiment of the present application provides a graphite particle, wherein the graphite particle satisfies the relationship: 0.8≤La / Lc≤1.6, wherein 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 35 nm ≤ La ≤ 55 nm.

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

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

[0008] Furthermore, the graphite particles satisfy the relationship: 0.05≤ID / IG≤0.1, wherein 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, and the carbon source includes at least one of petroleum coke and pitch coke.

[0010] Furthermore, the polarized structure of the carbon source includes a mosaic structure, a block structure and a linear structure, and the volume fraction x of the mosaic structure in the polarized structure of the carbon source is in the range of 40%≤x≤80%.

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

[0012] Furthermore, the volume fraction y of the block structure in the polarized structure of the carbon source is in the range of 4%≤y≤16%.

[0013] Furthermore, the volume fraction z of the linear structure in the polarized structure of the carbon source is in the range of 15%≤z≤50%.

[0014] In a second aspect, an embodiment of the present application further provides a method for preparing graphite particles, the preparation method comprising:

[0015] providing a 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, wherein La is the average crystallite length of the graphite particles, and Lc is the average crystallite height of the graphite particles.

[0017] Furthermore, the polarized structure of the carbon source includes a mosaic structure, a block structure and a linear structure, and the volume fraction x of the mosaic structure in the polarized structure of the carbon source is in the range of 40%≤x≤80%.

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

[0019] Furthermore, the volume fraction y of the block 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 polarized structure of the carbon source is in the range of 15%≤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 volatile matter in the carbon source ranges from 5% to 15%;

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

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

[0026] In a third aspect, an embodiment of the present application further provides a battery comprising: an electrolyte, a positive electrode plate, a separator and a negative electrode plate, wherein the negative electrode plate comprises a negative electrode active layer, and the negative electrode active layer comprises the graphite 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] The battery described in the embodiment of the present application is housed in the box.

[0030] The ratio La / Lc of the average crystallite length La of the graphite particles in the embodiment of the present application to the average crystallite height Lc of the graphite particles is 0.8 to 1.6, so that the orientation degree OI value of the graphite particles is small, the interior of the graphite particles has more orientation (i.e., it has more orientation directions), and the graphite particles are applied to the battery. During the lithium insertion process, the lithium insertion stress can be better released, and the expansion of the negative electrode plate in the z-axis direction can be reduced, thereby reducing the expansion rate of the battery during the charge and discharge cycle, and improving the initial efficiency and cycle capacity retention rate of the battery. In addition, when the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles is 0.8 to 1.6, the battery using the graphite particles can consume less during the initial film formation in the formation stage, reduce the rupture and recombination of the solid electrolyte interface film (SEI film) and the consumption of active lithium during the cycle, and improve the cycle capacity retention rate of the battery, so that the battery has a higher number of cycles and a longer cycle life. 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 A schematic flow chart of a method for preparing graphite particles according to an embodiment of the present application.

[0033] Figure 2 Schematic diagram of the process of pretreatment and graphitization of a carbon source according to one embodiment of the present application.

[0034] Figure 3 Schematic diagram of the structure of a battery according to an embodiment of the present application.

[0035] Figure 4 The battery of one embodiment of the present application is Figure 3 Schematic diagram of the cross-sectional structure in the AA direction.

[0036] Figure 5 Schematic diagram of the cross-sectional structure of the negative electrode sheet according to one embodiment of the present application.

[0037] Figure 6 It is a schematic cross-sectional structural diagram of a positive electrode plate according to an embodiment of the present application.

[0038] Figure 7 2 is the XRD diagram of the graphite particles of Example 2 and Comparative Example 1 of the present application.

[0039] Figure 8 2 is a graph showing the change in battery capacity versus voltage (dQ / dV-V) during the formation stage of soft-pack batteries made from graphite particles in Example 2 and Comparative Example 1 of the present application.

[0040] Figure 9 It is the Raman spectrum of the graphite particles of Example 2 and Comparative Example 1 of the present application.

[0041] Figure 10 It is a graph showing the cycle capacity retention rate and the number of cycles of batteries made of graphite particles in Example 2 and Comparative Example 1 of the present application, which are subjected to constant power charge and discharge cycles at 0.5P at 25°C.

[0042] Figure 11 1 is a graph showing the cycle capacity retention rate and the number of cycles of batteries made of graphite particles in Example 2 and Comparative Example 1 of the present application, which are subjected to constant power charge and discharge cycles at 1P at 45°C.

[0043] Figure 12 This is a scanning electron microscope image of the graphite particles of Example 2 of the present application, where the magnification is 1000 times.

[0044] Figure 13 This is a scanning electron microscope image of the graphite particles of Example 2 of the present application, wherein the magnification is 5000 times.

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

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

[0047] Figure 16 It is a structural diagram of an energy storage device according to an embodiment of the present application.

[0048] Description of reference numerals:

[0049] 300-battery, 310-positive electrode plate, 311-positive electrode current collector, 312-positive electrode active layer, 320-diaphragm, 330-negative electrode plate, 331-negative electrode current collector, 332-negative electrode active layer, 340-shell, 350-end cover assembly, 400-energy storage device, 410-case. DETAILED DESCRIPTION

[0050] 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.

[0051] 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.

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

[0053] 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.

[0054] 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. However, the cycle life of graphite materials in related technologies is relatively low and remains to be improved.

[0055] In view of this, an embodiment of the present application provides a graphite particle.

[0056] An embodiment of the present application provides graphite particles, wherein the graphite particles satisfy the relationship: 0.8≤La / Lc≤1.6, wherein La is the average crystallite length of the graphite particles, and Lc is the average crystallite height of the graphite particles.

[0057] The graphite particles of the embodiments of the present application can be used as, but not limited to, negative electrode active materials for negative electrode sheets of lithium-ion batteries.

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

[0059] The calculation formula for 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 stacking of the graphite particles, θ1 is the half diffraction angle of the diffraction peak of the 110 crystal plane stacking in the XRD pattern of the graphite particles, k1 is a constant, and λ is the wavelength of the X-ray.

[0060] The calculation formula for 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 stacking of the graphite particles, θ2 is the half diffraction angle of the diffraction peak of the 002 crystal plane stacking in the XRD pattern of the graphite particles, k2 is a constant, and λ is the wavelength of the X-ray.

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

[0062] Specifically, the ratio La / Lc of the average crystallite length La of the graphite particles 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 of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles increases, the orientation degree of the graphite particles gradually increases (i.e., the OI value gradually increases), the first efficiency (referred to as first efficiency) of the battery using the graphite particles gradually decreases, and the cycle capacity retention rate of the battery using the graphite particles also gradually decreases; therefore, when the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles is too large, the first efficiency and cycle capacity retention rate of the battery using the graphite particles are reduced.

[0063] The ratio La / Lc of the average crystallite length La of the graphite particles in the embodiment of the present application to the average crystallite height Lc of the graphite particles is 0.8 to 1.6, so that the orientation degree OI value of the graphite particles is small, the interior of the graphite particles has more orientation (i.e., it has more orientation directions), and the graphite particles are applied to the battery. During the lithium insertion process, the lithium insertion stress can be better released, and the expansion of the negative electrode plate in the z-axis direction can be reduced, thereby reducing the expansion rate of the battery during the charge and discharge cycle, and improving the initial efficiency and cycle capacity retention rate of the battery. In addition, when the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles is 0.8 to 1.6, the battery using the graphite particles can consume less during the initial film formation in the formation stage, reduce the rupture and recombination of the solid electrolyte interface film (SEI film) and the consumption of active lithium during the cycle, and improve the cycle capacity retention rate of the battery, so that the battery has a higher number of cycles and a longer cycle life.

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

[0065] In some embodiments, the average crystallite length La of the graphite particles is in the range of 35 nm ≤ La ≤ 55 nm.

[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 first efficiency, room temperature (25°C) cycle capacity retention rate, and high temperature (45°C) cycle capacity retention rate of the battery using the graphite particles show a downward trend. When the average crystallite length La of the graphite particles is too large, the first efficiency and cycle capacity retention rate of the battery using the 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 can be made smaller, and the interior of the graphite particles has more orientation. When the graphite particles are applied to batteries, they can better release the lithium insertion stress during the lithium insertion process and reduce the expansion of the negative electrode in the z-axis direction, thereby reducing the expansion rate of the battery during the charge and discharge cycle and improving the cycle capacity retention rate of the battery. In addition, 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 in the formation stage, reducing the rupture and recombination of the solid electrolyte interface film (SEI film for short) and the consumption of active lithium during the cycle, thereby improving the battery's cycle capacity retention rate.

[0068] In some embodiments, the average crystallite height Lc of the graphite particles is in the range of 30 nm ≤ Lc ≤ 45 nm.

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

[0070] In this embodiment, when the range of the average crystallite height Lc of the graphite particles is 30nm≤Lc≤45nm, the orientation degree OI value of the graphite particles can be made smaller, and the interior of the graphite particles has more orientation. When the graphite particles are applied to the battery, during the lithium insertion process, the lithium insertion stress can be better released, and the expansion of the negative electrode plate in the z-axis direction can be reduced, thereby reducing the expansion rate of the battery during the charge and discharge cycle, and improving the initial efficiency and cycle capacity retention rate of the battery. In addition, when the range of the average crystallite height Lc of the graphite particles is 30nm≤Lc≤45nm, the battery using the graphite particles can consume less during the initial film formation in the formation stage, reducing the rupture and recombination of the solid electrolyte interface film (SEI film) and the consumption of active lithium during the cycle, and improving the cycle capacity retention rate of the battery.

[0071] In some embodiments, the graphite particles have an orientation index OI in the range of 2.1≤OI≤4.0.

[0072] Specifically, the orientation degree OI of the graphite particles may 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 index (OI) of the graphite particles, the smaller the expansion rate of the negative electrode sheet in the Z-axis direction during the battery's lithium insertion process when the graphite particles are used in the battery's negative electrode plate, which is also beneficial for improving the battery's initial efficiency and cycle capacity retention rate. However, if the orientation index (OI) of the graphite particles is too small, the difficulty of preparing the graphite particles increases. As the orientation index (OI) of the graphite particles increases, the initial efficiency and cycle capacity retention rate of the battery using the graphite particles gradually decrease. Therefore, when the orientation index (OI) of the graphite particles is within the range of 2.1 ≤ OI ≤ 4.0, the battery using the graphite particles can achieve higher initial efficiency and cycle capacity retention rate.

[0074] In some embodiments, the graphite particles satisfy the relationship: 0.05≤ID / IG≤0.1, wherein 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] It can be understood that 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, the first efficiency and cycle capacity retention rate of the battery using the graphite particles will be reduced.

[0078] In some embodiments, the graphite particles are obtained by pre-carbonizing and graphitizing a carbon source, and 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 allows the ratio of the average crystallite length La of the prepared graphite particles to the average crystallite height Lc of the graphite particles, La / Lc, to fall within the range of 0.8 to 1.6. This results in a smaller orientation index (OI) value for the graphite particles and a greater degree of orientation within the graphite particles. When applied to batteries, the graphite particles can better release lithium insertion stress during lithium insertion, reducing the z-axis expansion of the negative electrode sheet, thereby reducing the battery's expansion rate during charge and discharge cycles and improving the battery's initial efficiency and cycle capacity retention. Furthermore, when the ratio of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles, La / Lc, is between 0.8 and 1.6, the battery using the graphite particles consumes less during the initial film formation phase, reducing the rupture and recombination of the solid electrolyte interface film (SEI film) and the consumption of active lithium during the cycle, thereby improving the battery's cycle capacity retention.

[0080] In some embodiments, the polarized structure of the carbon source includes a mosaic structure (also known as a mosaic-type structure), a block structure (also known as a block domain structure or a regional structure) and a linear structure (also known as a linear domain structure or a fiber-type structure), and the volume fraction (i.e., volume proportion) x of the mosaic structure in the polarized structure of the carbon source is in the range of: 40%≤x≤80%.

[0081] It can be understood that 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 mosaic structure in the polarized 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 mosaic structure in the polarized structure of the carbon source is too small, the orientation of the prepared graphite particles will be too large, and the expansion rate of the battery using the graphite particles during the lithium insertion process will be too large, thereby reducing the battery's first efficiency and cycle capacity retention rate; as the volume fraction of the mosaic structure in the polarized structure of the carbon source increases, the first efficiency and cycle capacity retention rate of the battery using the graphite particles gradually increase. When the volume fraction of the mosaic structure in the polarized structure of the carbon source is too large, the requirements for the carbon source are increased, and the preparation cost of the graphite particles is increased. When the volume fraction x of the mosaic structure in the polarized structure of the carbon source is in the range of 40% ≤ x ≤ 80%, the battery using the graphite particles can have a higher first efficiency and cycle capacity retention rate, and a lower preparation cost.

[0084] In some embodiments, the polarized structure of the carbon source satisfies the relationship: 1≤(x+y) / z≤4, wherein x+y+z=1, x is the volume fraction of the mosaic structure in the polarized structure of the carbon source, y is the volume fraction of the block structure in the polarized structure of the carbon source, and z is the volume fraction of the linear structure in the polarized 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 graphite particles will be too oriented, resulting in excessive expansion during lithium insertion in batteries using these graphite particles, thereby reducing the battery's initial efficiency and cycle capacity retention. If (x+y) / z is too large, the carbon source requirements increase, increasing the cost of preparing the graphite particles. When the polarization structure of the carbon source satisfies the relationship 1≤(x+y) / z≤4, the battery using these graphite particles can achieve higher initial efficiency and cycle capacity retention, while also having lower production costs.

[0087] In some embodiments, the volume fraction y of the block structure in the polarization structure of the carbon source is in the range of 4%≤y≤16%.

[0088] Specifically, the volume fraction y of the block structure in the polarized 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 polarized 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 insertion process, and is beneficial to improve the first efficiency and cycle capacity retention rate of the battery using the graphite particles. If the volume fraction y of the block structure in the polarized structure of the carbon source is too high, it will reduce the first 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 polarized structure of the carbon source is in the range of 15%≤z≤50%.

[0091] Specifically, the linear volume fraction z in the polarized 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 polarized 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 insertion process, and is beneficial to improve the first efficiency and cycle capacity retention rate of the battery using the graphite particles. If the volume fraction z of the linear structure in the polarized structure of the carbon source is too high, it will reduce the first 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 volatile matter in the carbon source ranges from 5% to 15%;

[0096] The mass fraction of ash in the carbon source is in the range of 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. If the mass fraction of sulfur in the carbon source is too low or too high, the quality of the produced graphite particles will be reduced, and the cycle performance of the battery using the graphite particles will be reduced.

[0099] Specifically, the mass fraction of volatile matter 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 volatile matter in the carbon source is too low, the porosity of the graphite particles produced will be too low, which will increase the impedance of the graphite particles, reduce the dynamic performance of the graphite particles, increase the expansion force of the graphite particles during the lithium insertion process, and reduce the cycling performance of the graphite particles. If the mass fraction of volatile matter in the carbon source is too high, the compacted density of the graphite particles produced will be reduced, and the specific capacity and energy density of the graphite particles will be reduced.

[0100] Specifically, the mass fraction of ash in the carbon source may be, but is not limited to, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, etc. If the mass fraction of ash in the carbon source is too low or too high, the quality of the produced graphite particles will be reduced, and the cycle performance of the battery using the graphite particles will be reduced.

[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. If the mass fraction of water in the carbon source is too low or too high, the quality of the produced graphite particles will be reduced, and the cycle performance of the battery using the graphite particles will be reduced.

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

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

[0104] Specifically, the value of Dv90-Dv10 can be, but is 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 value of Dv90-Dv10, the narrower the particle size distribution of the graphite particles. After the graphite particles 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 particles. However, when the graphite particles 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; the particle size distribution of the graphite particles is wider, and the gram capacity of the graphite particles is slightly increased. However, when the graphite particles are made into the negative electrode active layer of the negative electrode sheet, the pores between the graphite particles are too small, which easily causes insufficient infiltration of the electrolyte and reduces the cycle capacity retention rate of the battery.

[0106] Optionally, the BET specific surface area of ​​the graphite particles is in the range of 1.0 m2 / g ≤ BET ≤ 1.8 m2 / g. Specifically, the BET specific surface area of ​​the graphite particles may 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, and the like. In this embodiment, if the BET specific surface area of ​​the graphite particles is too small, the kinetic performance of the battery using the graphite particles is reduced; if the BET specific surface area of ​​the graphite particles is too large, the side reaction between the graphite particles and the electrolyte is increased, thereby reducing the cycle capacity retention rate of the battery using the graphite particles.

[0107] Optionally, the gram capacity of the graphite particles ranges from 340 mAh / g to 350 mAh / g. Specifically, the gram 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 the present application have a relatively high gram capacity.

[0108] Optionally, the tap density of the graphite particles is in the range of 1.1 g / cm 3 Up to 1.4g / cm 3 Specifically, the tap density of graphite particles can be, but is not limited to, 1.1 g / cm 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 is in the range of 25 cm 3 / g≤OAV≤40cm 3 Specifically, the oil absorption value OAV of the graphite particles can be, but is not limited to, 25 cm 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 If the oil absorption value (OAV) of the 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 the graphite particles is too high, the cost of the graphite particles will increase or even become unattainable.

[0110] The graphite particles 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 particles of the present application and should not be understood as limiting the graphite particles provided in the embodiments of the present application.

[0111] See Figure 1The present invention also provides a method for preparing graphite particles, the method comprising:

[0112] S201, providing a carbon source; and

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

[0114] The ratio La / Lc of the average crystallite length La of the graphite particles prepared by the preparation method of the graphite particles of the embodiment of the present application to the average crystallite height Lc of the graphite particles is 0.8 to 1.6, so that the orientation degree OI value of the graphite particles is small, and the interior of the graphite particles has more orientation. The graphite particles are applied to batteries. During the lithium insertion process, the lithium insertion stress can be better released, and the expansion of the negative electrode plate in the z-axis direction can be reduced, thereby reducing the expansion rate of the battery during the charge and discharge cycle, and improving the battery's initial efficiency and cycle capacity retention rate. In addition, when the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles is 0.8 to 1.6, the battery using the graphite particles can consume less during the initial film formation in the formation stage, reduce the rupture and recombination of the solid electrolyte interface film and the consumption of active lithium during the cycle, and improve the battery's cycle capacity retention rate.

[0115] In some embodiments, the polarization structure of the carbon source includes a mosaic structure, a block structure, and a linear structure, and the volume fraction x of the mosaic structure in the polarization structure of the carbon source is in the range of 40%≤x≤80%.

[0116] Specifically, the volume fraction x of the mosaic structure in the polarized 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 mosaic structure in the polarized structure of the carbon source is too small, the orientation of the prepared graphite particles will be too large, and the expansion rate of the battery using the graphite particles during the lithium insertion process will be too large, thereby reducing the battery's first efficiency and cycle capacity retention rate; as the volume fraction of the mosaic structure in the polarized structure of the carbon source increases, the first efficiency and cycle capacity retention rate of the battery using the graphite particles gradually increase. When the volume fraction of the mosaic structure in the polarized structure of the carbon source is too large, the requirements for the carbon source are increased, and the preparation cost of the graphite particles is increased. When the volume fraction x of the mosaic structure in the polarized structure of the carbon source is in the range of 40% ≤ x ≤ 80%, the battery using the graphite particles can have a higher first efficiency and cycle capacity retention rate, and a lower preparation cost.

[0118] In some embodiments, the polarized structure of the carbon source satisfies the relationship: 1≤(x+y) / z≤4, wherein x+y+z=1, x is the volume fraction of the mosaic structure in the polarized structure of the carbon source, y is the volume fraction of the block structure in the polarized structure of the carbon source, and z is the volume fraction of the linear structure in the polarized 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 graphite particles will be too oriented, resulting in excessive expansion during lithium insertion in batteries using these graphite particles, thereby reducing the battery's initial efficiency and cycle capacity retention. If (x+y) / z is too large, the carbon source requirements increase, increasing the cost of preparing the graphite particles. When the polarization structure of the carbon source satisfies the relationship 1≤(x+y) / z≤4, the battery using these graphite particles can achieve higher initial efficiency and cycle capacity retention, while also having lower production costs.

[0121] In some embodiments, the volume fraction y of the block structure in the polarization structure of the carbon source is in the range of 4%≤y≤16%.

[0122] Specifically, the volume fraction y of the block structure in the polarized 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 polarized 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 insertion process, and is beneficial to improve the first efficiency and cycle capacity retention rate of the battery using the graphite particles. If the volume fraction y of the block structure in the polarized structure of the carbon source is too high, it will reduce the first 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 polarized structure of the carbon source is in the range of 15%≤z≤50%.

[0125] Specifically, the linear volume fraction z in the polarized 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 polarized 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 insertion process, and is beneficial to improve the first efficiency and cycle capacity retention rate of the battery using the graphite particles. If the volume fraction z of the linear structure in the polarized structure of the carbon source is too high, it will reduce the first 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 volatile matter in the carbon source ranges from 5% to 15%;

[0130] The mass fraction of ash in the carbon source is in the range of 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. If the mass fraction of sulfur in the carbon source is too low or too high, the quality of the produced graphite particles will be reduced, and the cycle performance of the battery using the graphite particles will be reduced.

[0133] Specifically, the mass fraction of volatile matter 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 volatile matter in the carbon source is too low, the porosity of the graphite particles produced will be too low, which will increase the impedance of the graphite particles, reduce the dynamic performance of the graphite particles, increase the expansion force of the graphite particles during the lithium insertion process, and reduce the cycling performance of the graphite particles. If the mass fraction of volatile matter in the carbon source is too high, the compacted density of the graphite particles produced will be reduced, and the specific capacity and energy density of the graphite particles will be reduced.

[0134] Specifically, the mass fraction of ash in the carbon source may be, but is not limited to, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, etc. If the mass fraction of ash in the carbon source is too low or too high, the quality of the produced graphite particles will be reduced, and the cycle performance of the battery using the graphite particles will be reduced.

[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. If the mass fraction of water in the carbon source is too low or too high, the quality of the produced graphite particles will be reduced, and the cycle performance of the battery using the graphite particles will be reduced.

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

[0137] S2021, crushing the carbon source to obtain precursor particles;

[0138] Optionally, the carbon source is crushed by a jaw crusher and then ground into fine powder by a jet mill to obtain precursor particles, which are then sieved to ensure that the particle size of the precursor particles satisfies the following conditions: Dv90-Dv10≤18.5 μm.

[0139] S2022, pre-treating the precursor particles at a first temperature T1 in the range of 900°C ≤ T1 ≤ 1300°C to obtain intermediate particles; and

[0140] Specifically, the first temperature T1 may be, but is not limited to, 900° C., 950° C., 1000° C., 1050° C., 1100° C., 1150° C., 1200° C., 1250° C., 1300° C., etc. In this embodiment, if the pretreatment temperature is too low, it will not significantly affect the volatilization of volatiles, and will not play a role in internal pore formation, thereby reducing the porosity of the prepared graphite particles and increasing the expansion force of the graphite particles during the lithium insertion process; if the pretreatment temperature is too high, it will increase the preparation cost of the graphite particles, and will also increase the size of the pores in the prepared graphite particles, thereby reducing the compaction density of the graphite particles.

[0141] Optionally, the pretreatment time ranges from 2 hours to 4 hours. Specifically, the pretreatment time may 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 the graphite particles will increase.

[0142] S2023 , placing the intermediate particles at a second temperature T2 in the range of 2800° C. ≤ T2 ≤ 3100° C. for graphitization treatment to obtain graphite particles.

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

[0144] Optionally, the holding time of the graphitization treatment ranges from 12 hours to 96 hours. Specifically, the holding time of 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, 96 hours, etc. If the graphitization treatment time is too short, the graphitization degree of the graphite particles is reduced, the conductivity and specific capacity of the graphite particles are reduced, thereby further reducing the kinetic properties of the graphite particles; if the graphitization treatment time is too long, the preparation cost of the graphite particles is increased.

[0145] See Figure 3 、 Figure 4 and Figure 5The 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, the negative electrode plate 330 includes a negative electrode active layer 332, and the negative electrode active layer 332 includes the graphite particles described in the embodiment of the present application (not shown in the figure).

[0146] The battery 300 in the embodiment of the present application may be, but is not limited to, at least one of a lithium battery, a sodium battery, a lithium-sodium hybrid battery, and the like.

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

[0148] 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.

[0149] It can be understood that the positive electrode sheet 310 and the negative electrode sheet 330 are respectively located on opposite sides of the separator 320 , and the separator 320 is used to separate the positive electrode sheet 310 from the negative electrode sheet 330 .

[0150] It should be noted that the graphite particles serve as the negative electrode active material of the negative electrode active layer 332 .

[0151] 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 (not shown). 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.

[0152] See Figure 5 Optionally, the negative electrode sheet 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 can be understood that the negative electrode active layer 332 can cover one surface or two opposite surfaces of the negative electrode current collector 331.

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

[0154] Optionally, the negative electrode active layer 332 further includes a negative electrode conductor, 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 for short), acetylene black, carbon nanotubes, carbon fibers, graphene, and the like.

[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, polyvinylether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, and 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 polymethacrylate (PMA).

[0158] See Figure 6 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.

[0159] Optionally, the positive electrode current collector 311 may 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 conductor, a positive electrode binder, and a positive electrode thickener.

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

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

[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, polyvinylether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, and 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 polymethacrylate (PMA).

[0165] 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.

[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, and the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalatoborate) (LiBOB), lithium difluorodioxalatophosphate (LOIDFP), lithium difluorooxalatoborate (LOIDFB), lithium difluorophosphate (LiPO2F2), lithium trifluoromethanesulfonate (CF3SO3Li), etc.

[0168] Optionally, the organic solvent includes at least one of a cyclic carbonate and a chain carbonate. Cyclic carbonate has a high dielectric constant and high ionic conductivity, and can form a stable SEI film on the surface of the negative electrode plate 330, but its viscosity is relatively high. Chain carbonate has a lower viscosity than cyclic carbonate, better electrochemical stability, and can improve the low-temperature performance of the electrolyte. Therefore, when a mixed solvent of cyclic carbonate and chain carbonate is used, the electrolyte can have a more suitable viscosity and low-temperature stability, and the battery 300 using the electrolyte can also perform better film formation.

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

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

[0171] Optionally, the organic solvent further comprises 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 plate 310 and the negative electrode plate 330 and maintain the stability of the interface film.

[0173] Optionally, the film-forming additive includes at least one of fluoroethylene carbonate (FEC), vinyl sulfate (DTD), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, adiponitrile, succinonitrile, and 1,3,6-hexanetrinitrile.

[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 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.

[0175] The graphite particles and the battery 300 according to the embodiment of the present application are further described below through specific examples.

[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 water 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 polarized structure of the carbon source are shown in Table 1 below.

[0179] (2) crushing the petroleum coke by a jaw crusher and grinding it into fine powder by a jet mill; screening the finely ground carbon source particles to obtain precursor particles;

[0180] (3) pre-treating the precursor particles at 1000° C. to obtain intermediate particles; and

[0181] (4) The intermediate particles are placed in a graphite furnace at 3100°C for graphitization to obtain graphite particles.

[0182] The graphite particles of each embodiment and comparative example were assembled into a soft pack battery 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% polyvinyl pyrrolidone (PVP, additive) are dispersed in methyl pyrrolidone (NMP) in a mass ratio to prepare a positive electrode slurry; the positive electrode slurry is coated on aluminum foil (positive electrode current collector 311), and the positive electrode sheet 310 is obtained by drying, rolling, and cutting in sequence;

[0184] (2) 96.7% of graphite particles (negative electrode active material), 2.5% of aqueous carboxymethyl cellulose binder (negative electrode binder), and 0.8% of conductive carbon black (negative electrode conductive agent) are dispersed in deionized water according to a mass ratio to prepare a negative electrode slurry; the negative electrode slurry is evenly coated on the surface of a copper foil (negative electrode current collector 331), and the negative electrode sheet 330 is obtained by drying, rolling, and cutting in sequence;

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

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

[0187] (5) Assembling the soft-pack battery 300: stack the positive electrode sheet 310, the separator 320, and the negative electrode sheet 330 in order, so that the separator 320 is located between the positive electrode sheet 310 and the negative electrode sheet 330 to play an isolating role, and then wind the battery to obtain a battery cell. After the battery cell is hot-pressed, welded, shelled, injected with electrolyte and divided into volumes, the soft-pack battery 300 is obtained.

[0188] Various performance tests were performed 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: X-ray diffractometer was used to measure XRD patterns, using a wide-angle test mode for phase analysis, with a test range of 5° to 85° and a scanning rate of 10° / min. The calculation formula for 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 stacking of graphite particles, and θ1 is the half-diffraction angle of the diffraction peak of the 110 crystal plane stacking in the XRD pattern of graphite particles. The calculation formula for 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 stacking of graphite particles, and θ2 is the half-diffraction angle of the diffraction peak of the 002 crystal plane stacking in the XRD pattern of graphite particles. The XRD patterns of the graphite particles in Example 2 and Comparative Example 1 of the present application are as follows: Figure 7 shown.

[0190] (2) Measurement of the volume fraction of mosaic structure, block structure, and linear structure in the carbon source: Polarized light photographs were taken using a polarizing microscope with a magnification of 100 times. The volume fractions of mosaic structure, block structure, and linear structure in the carbon source were calculated based on the area ratios of the mosaic structure, block structure, and linear structure in the polarized light photographs.

[0191] (3) ID / IG measurement: Raman spectrometer is used for measurement, with a laser wavelength of 535nm and a test range of 1000cm -1 Up to 3500cm -1 .

[0192] (4) Measurement of the orientation degree (OI) of graphite particles: X-ray diffractometer was used to measure the XRD pattern, in which a wide-angle test mode was used for phase analysis, the test range was 5° to 85°, and the scanning rate was 10° / min; the OI of the 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 efficiency test of battery 300: The battery 300 is subjected to the first charge and discharge test on a charge and discharge instrument (Nebula Charge and Discharge Test System - BAT-NEEFLCT-05-V010). The test temperature is 25°C. The battery 300 is charged at a constant power of 0.33C to a charge cut-off voltage of 3.65V. The initial charge capacity is recorded. The battery 300 is left to stand for 10 minutes. The battery 300 is discharged at a constant power of 0.33C to a discharge cut-off voltage of 2V. The first discharge capacity of the battery 300 is recorded. Wherein, C refers to the charge or discharge current rate of the battery 300. The first charge and discharge capacity retention rate (i.e., the first efficiency) = (first discharge capacity / first discharge capacity) × 100%.

[0194] (6) 25°C or 45°C cycle capacity retention rate: 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-05-V010) at a test temperature of 25°C or 45°C. The battery 300 was charged at a constant power of 0.25P to a charge cut-off voltage of 3.65V, and the initial charge capacity was recorded. The battery 300 was then left to stand for 10 minutes. The battery 300 was discharged at a constant power of 0.25P to a discharge cut-off voltage of 2V, and the discharge capacity of the battery 300 was recorded. Wherein, P refers to the rated charge or discharge power of the battery 300, and its value is the nominal voltage U of the battery 300 multiplied by the current density of 1C. The nominal voltage of the lithium iron phosphate battery 300 is 3.2V, and 0.25P refers to 0.25 times the rated power.

[0195] The capacity retention rate after the cycle is calculated as follows: capacity retention rate after the nth cycle = (discharge capacity after the nth cycle / discharge capacity after the first cycle) × 100%.

[0196] Table 1 Performance parameters of carbon sources in various embodiments and comparative examples

[0197] Example (x+y) / z x(％) y(％) z(％) 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 obtained in various embodiments and comparative examples

[0199]

[0200] It can be seen from the test structures in Tables 1 and 2 that with the increase of the ratio (x+y) / z of the sum of the volume fraction x of the mosaic structure and the volume fraction y of the block structure in the polarized structure of the carbon source to the volume fraction z of the linear structure, 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 normal temperature (25°C) cycle capacity retention rate and the high temperature (45°C) cycle capacity retention rate of the battery 300 using the graphite particles gradually increase. When the ratio (x+y) / z of the sum of the volume fraction x of the mosaic structure and the volume fraction y of the block structure in the polarized structure of the carbon source to the volume fraction y of the linear structure is too low (such as Comparative Examples 1 and 2), the La / Lc and OI of the prepared graphite particles are too high, and the first efficiency, room temperature (25°C) cycle capacity retention rate and high temperature (45°C) cycle capacity retention rate of the battery 300 using the graphite particles are all low.

[0201] In addition, as the volume fraction y of the block structure in the polarized structure of the carbon source gradually decreases, the first effect, room temperature (25°C) cycle capacity retention rate and high temperature (45°C) cycle capacity retention rate of the battery 300 made of the prepared graphite particles gradually increase; as the volume fraction z of the linear structure in the polarized structure of the carbon source gradually decreases, the first effect, room temperature (25°C) cycle capacity retention rate and high temperature (45°C) cycle capacity retention rate of the battery 300 made of the prepared graphite particles gradually increase.

[0202] Furthermore, the test results in Tables 1 and 2 show that when the ID / IG ratio of the graphite particles is too large or too small, the first efficiency, room temperature (25°C) cycle capacity retention rate, and high temperature (45°C) cycle capacity retention rate of the battery 300 using the graphite particles will be reduced. When the ID / IG ratio is between 0.05 and 0.1, the battery 300 using the graphite particles has a higher first efficiency, a higher room temperature (25°C) cycle capacity retention rate, and a higher high temperature (45°C) cycle capacity retention rate.

[0203] Figure 8 : is a graph showing the capacity of the soft-pack battery 300 as a function of voltage (dQ / dV-V) during the formation stage of the graphite particles of Example 2 and Comparative Example 1 of the present application. Figure 8 It can be seen that compared with the battery 300 of comparative example 1, the peak of the battery 300 of embodiment 2 of the present application at around 2.5V is lower, which indicates that the negative electrode plate 330 of the battery 300 of embodiment 2 of the present application consumes less electrolyte during the formation stage and has a higher first efficiency and cycle capacity retention rate.

[0204] Figure 9 is the Raman spectrum of the graphite particles of Example 2 and Comparative Example 1 of the present application, Figure 9 It can be seen that compared with the graphite particles of Comparative Example 1, the graphite particles of Example 2 of the present application have a smaller ID / IG and fewer defects.

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

[0206] Figure 12 This is a scanning electron microscope image of the graphite particles of Example 2 of the present application, where the magnification is 1000 times. Figure 13 This is a scanning electron microscope image of the graphite particles of Example 2 of the present application, wherein the magnification is 5000 times. Figure 14 This is a scanning electron microscope image of the graphite particles in Comparative Example 1 of the present application, wherein the magnification is 1000 times. Figure 15 This is a scanning electron microscope image of the graphite particles of Comparative Example 1 of the present application, wherein the magnification is 3000 times. Figures 12 to 15 The scanning electron microscope 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 a more directional orientation, which can better release the lithium insertion stress during the lithium insertion process and reduce the expansion of the negative electrode in the z-axis direction, thereby reducing the battery's expansion rate during the charge and discharge cycle and improving the battery's initial efficiency and cycle capacity retention rate. In contrast, the graphite particles in Comparative Example 1 have a more singular orientation, with larger La / Lc and OI, resulting in lower initial efficiency and cycle capacity retention rate.

[0207] See Figure 16 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, and the battery 300 is accommodated in the box 410 .

[0208] 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.

[0209] Optionally, the number of the batteries 300 may be one or more. When the number of batteries 300 is multiple, the multiple batteries 300 may be connected in parallel with each other; or the multiple batteries 300 may be connected in series with each other; or the multiple batteries 300 may 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 the multiple batteries 300 of the same energy storage device 400.

[0210] It is understood that the housing 410 has a receiving cavity (not shown) in which multiple batteries 300 are received. In some embodiments, each receiving cavity receives one battery 300. In other embodiments, each receiving cavity receives multiple batteries 300.

[0211] Optionally, the energy storage device 400 may include, but is not limited to, a battery module, a battery pack, a battery system, an energy storage cabinet, an energy storage box, an energy storage container, etc. 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 above, 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.

[0212] 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.

[0213] 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 limiting. Although the present application has been described in detail with reference to the above preferred implementation modes, ordinary technicians in this field should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A graphite particle, characterized in that The graphite particles satisfy the relationship: 0.8≤La / Lc≤1.6, wherein La is the average crystallite length of the graphite particles, and Lc is the average crystallite height of the graphite particles.

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

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

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

0.

5. The graphite particles according to claim 1, characterized in that The graphite particles satisfy the relationship: 0.05≤ID / IG≤0.1, wherein 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 to 5, characterized in that 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.

7. The graphite particles according to claim 6, characterized in that The polarized structure of the carbon source includes a mosaic structure, a block structure and a linear structure. The volume fraction x of the mosaic structure in the polarized structure of the carbon source is in the range of 40%≤x≤80%.

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

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

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

11. A method for preparing graphite particles, characterized in that: The preparation method comprises: providing a carbon source; and 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, wherein La is the average crystallite length of the graphite particles, and Lc is the average crystallite height of the graphite particles.

12. The method for preparing graphite particles according to claim 11, wherein The polarized structure of the carbon source includes a mosaic structure, a block structure and a linear structure. The volume fraction x of the mosaic structure in the polarized structure of the carbon source is in the range of 40%≤x≤80%.

13. The method for preparing graphite particles according to claim 12, characterized in that: The polarized structure of the carbon source satisfies the relationship: 1≤(x+y) / z≤4, wherein x+y+z=1, x is the volume fraction of the mosaic structure in the polarized structure of the carbon source, y is the volume fraction of the block structure in the polarized structure of the carbon source, and z is the volume fraction of the linear structure in the polarized structure of the carbon source.

14. The method for preparing graphite particles according to claim 12, wherein: The volume fraction y of the block structure in the carbon source is in the range of 4%≤y≤16%.

15. The method for preparing graphite particles according to claim 12, wherein: The volume fraction z of the linear structure in the polarized structure of the carbon source is in the range of 15%≤z≤50%.

16. The method for preparing graphite particles according to claim 11, wherein: 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 is in the range of 0.1% to 1%; and The mass fraction of water in the carbon source ranges from 3% to 9%.

17. A battery, characterized in that: include: An electrolyte, a positive electrode sheet, a separator and a negative electrode sheet, wherein the negative electrode sheet includes a negative electrode active layer, and the negative electrode active layer includes the graphite particles according to any one of claims 1 to 10 or the graphite particles prepared by the method for preparing the graphite particles according to any one of claims 11 to 16.

18. An energy storage device, characterized in that: include: Box; as well as The battery according to claim 17, wherein the battery is housed in the casing.

Images