Graphite material, preparation method for graphite material, negative electrode, secondary battery and electric device

Abstract

A graphite material, a preparation method for a graphite material, a negative electrode, a secondary battery and an electric device. The graphite material comprises graphite particles, wherein for at least some of which, the degree of graphitization on at least one end face is lower than the degree of graphitization on the basal face.

Description

Graphite material, method for preparing graphite material, negative electrode, secondary battery, and electric device

[0001] Cross Reference to Related Applications

[0002] The present disclosure claims priority to the Chinese patent application No. 202411049892.4, filed on July 31, 2024, and entitled “Graphite material, method for preparing graphite material, negative electrode, secondary battery, and electric device”, the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure belongs to the field of batteries, and in particular, relates to a graphite material, a method for preparing graphite material, a negative electrode, a secondary battery, and an electric device. BACKGROUND

[0004] The key steps for improving the fast-charging capability of a battery mainly include two points: first, making the electrolyte quickly reach the negative active material particles, which requires building a smooth lithium ion diffusion path at the negative electrode sheet level; second, making the lithium ions quickly insert into the negative active material particles and quickly diffuse inside the negative active material particles, which requires that the negative active material particles have enough sites for lithium ions to insert, and the diffusion path of lithium ions inside the negative active material particles is short or / and smooth.

[0005] Graphite is a widely used negative active material for secondary batteries. The current methods for improving the fast-charging capability of graphite negative active material mainly focus on secondary granulation, amorphous carbon coating or mixing, non-carbon-based material coating and mixing, etc. Among them, secondary granulation can shorten the internal diffusion path, but the specific surface area of the secondary particle graphite increases, which affects the high-temperature performance (high-temperature cycle and / or high-temperature storage performance); amorphous carbon coating or mixing can increase the sites for lithium ions to insert, but the increase of the proportion of amorphous carbon in graphite poses a risk in high-temperature cycle and high-temperature storage of the battery.

[0006] Therefore, the existing graphite negative material still has the problem of poor high-temperature performance. SUMMARY

[0007] The present disclosure aims to provide a graphite material, a negative electrode, and a secondary battery that can balance high-temperature performance and fast-charging capability.

[0008] To achieve the above-mentioned purpose, the first aspect of the present disclosure provides a graphite material, the graphite material comprising graphite particles, and a graphitization degree of at least one end surface of at least part of the graphite particles is less than a graphitization degree of a basal surface.

[0009] The end face with low graphitization degree can increase the active sites at the position and increase the electrolyte retention, thereby promoting the fast deintercalation of lithium ions; and the base face with high graphitization degree can reduce the consumption of active lithium and the interface side reaction at high temperature, thereby prolonging the service life.

[0010] Optionally, at least one end face of at least part of the graphite particles comprises amorphous carbon, and the base face comprises carbon material with a graphitization degree higher than that of the amorphous carbon.

[0011] Optionally, the particle size D50 of the graphite particles is 1 μm to 20 μm.

[0012] The second aspect of the present disclosure provides a preparation method of a graphite material, which comprises:

[0013] The graphite particle precursor is treated to obtain the graphite material provided in the first aspect of the present disclosure.

[0014] Optionally, the treatment of the graphite particle precursor comprises differentiating the carbonization treatment of the end face and the base face of at least part of the graphite particle precursor.

[0015] Optionally, the treatment of the graphite particle precursor comprises differentiating the carbonization treatment of the end face and the base face of at least part of the graphite particle precursor by arranging at least part of the graphite particle precursor in a direction under the condition of an applied magnetic field.

[0016] Optionally, the direction of the applied magnetic field is parallel to the direction of the conjugated large plane structure of carbon atoms in the graphite particle precursor or perpendicular to the c-axis direction of the graphite particle precursor; and optionally, the strength of the applied magnetic field is 0.1 to 10 T.

[0017] Optionally, the differentiating carbonization treatment of the end face and the base face of at least part of the graphite particle precursor comprises at least one of the following (a), (b) and (c):

[0018] (a) the oxygen content at the position of at least one end face of at least part of the graphite particle precursor is higher than that at the position of the base face;

[0019] (b) the temperature at the position of at least one end face of at least part of the graphite particle precursor is lower than that at the position of the base face;

[0020] (c) at least part of the graphite particle precursor is placed in a carbon dioxide atmosphere.

[0021] Optionally, the differentiating carbonization treatment of the end face and the base face of at least part of the graphite particle precursor comprises:

[0022] The end face of at least part of the graphite particle precursor is coated with amorphous carbon.

[0023] Optionally, the graphite particle precursor comprises needle coke, and the temperature for treating the graphite particle precursor is 2000-3500°C.

[0024] Optionally, the coating amorphous carbon on at least one end surface of at least part of the graphite particle precursor comprises: coating an amorphous carbon source on at least one end surface of at least part of the graphite particle precursor, and carbonizing the amorphous carbon source to form amorphous carbon;

[0025] Optionally, the graphite particle precursor comprises graphite core particles, and the graphite core particles are carbon material particles with a graphitization degree greater than 0.8.

[0026] Optionally, the amorphous carbon source comprises pitch.

[0027] Optionally, the temperature for treating the graphite particle precursor is 800-1500°C.

[0028] Optionally, the volume ratio of carbon dioxide in the carbon dioxide atmosphere is greater than or equal to 5%.

[0029] A third aspect of the present disclosure provides a negative electrode, comprising a negative electrode material layer, wherein the graphitization degree G of the negative electrode material layer is G i when the compaction density is i, and the graphitization degree G of the negative electrode material layer is G i+Δi when the compaction density is i+Δi.

[0030] Δi is greater than 0, and G i+Δi is greater than G i .

[0031] When the negative electrode is used in a battery, both high-temperature performance and fast-charging capability can be considered.

[0032] Optionally, the OI value of the negative electrode material layer is OI i when the compaction density is i, and the OI value of the negative electrode material layer is OI i+Δi when the compaction density is i+Δi; and OI i+Δi is greater than OI i .

[0033] Optionally, i satisfies 0.5 g / cm 3 ≤i≤2.1 g / cm 3 , and Δi satisfies 0 g / cm 3 ≤Δi≤1.6 g / cm 3 ; preferably, i satisfies 0.5 g / cm 3 ≤i≤1.3 g / cm 3 , and Δi satisfies 0.4 g / cm 3 ≤Δi≤1.3 g / cm3 .

[0034] Optionally, G i+Δi -G i satisfies 0 < G i+Δi -G i ≤ 14%; preferably, G i+Δi -G i satisfies 1% < G i+Δi -G i ≤ 5%.

[0035] Optionally, OI i+Δi -OI i satisfies 0 < OI i+Δi -OI i ≤ 21; preferably, OI i+Δi -OI i satisfies 2 < OI i+Δi -OI i ≤ 7.

[0036] Optionally, the OI value of the negative electrode material layer ranges from 1 to 40; preferably, the OI value of the negative electrode material layer ranges from 3 to 12.

[0037] Optionally, the graphitization degree G of the negative electrode material layer ranges from 0.8 to 0.99.

[0038] Optionally, the negative electrode material layer comprises graphite.

[0039] Optionally, the negative electrode material layer comprises the graphite material of the first aspect of the present disclosure or the graphite material prepared by the preparation method of the second aspect of the present disclosure.

[0040] The fourth aspect of the present disclosure provides a secondary battery comprising the negative electrode provided by the third aspect of the present disclosure.

[0041] The secondary battery of the present disclosure can balance the high-temperature performance and the fast-charging capability.

[0042] The fifth aspect of the present disclosure provides a power-using device comprising the secondary battery provided by the fourth aspect of the present disclosure.

[0043] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0044] The accompanying drawings are included to provide a further understanding of the present disclosure and constitute a part of the specification, which together with the following detailed description, serve to explain the present disclosure. In the drawings:

[0045] FIG. 1 is an electron microscope photo of the graphite material provided by some embodiments of the present disclosure.

[0046] FIG. 2 is a schematic diagram of a graphite particle according to some embodiments of the present disclosure.

[0047] FIG. 3 is an XRD pattern of a graphite material according to Embodiment 1 of the present disclosure. DETAILED DESCRIPTION

[0048] The following detailed description of the present disclosure is provided. It should be understood that the detailed description is merely illustrative and explanatory, and is not intended to limit the present disclosure.

[0049] To solve the problem of high-temperature cycling and high-temperature storage of the battery, the following technologies can be used: (1) easy-graphitizable high-crystallinity graphite and hard carbon are subjected to secondary granulation treatment, then mixed with pitch for composite reaction, and then subjected to crushing, graphitization, modification and carbonization treatment to improve the capacity and fast-charging performance of the graphite; (2) graphite is used as the inner core, and the outer shell is sequentially formed from the inside to the outside by a solid electrolyte and an organic polymer containing lithium powder; (3) a fast-charging graphite material with a core-shell structure is used, the inner core of the graphite material includes porous graphite and a solid electrolyte, part of the solid electrolyte is embedded between the layers of the porous graphite, and the other part is attached to the surface of the porous graphite, and the outer shell of the composite material includes inorganic lithium salt, carbon nanotubes and the balance of amorphous carbon; (4) a high-energy-density fast-charging graphite negative electrode material is used, and the surface of the graphite in the material is coated with a titanium niobate compound, which can make the graphitization degree of the graphite negative electrode material reach 95%. However, there is still a problem of poor high-temperature resistance.

[0050] The first aspect of the present disclosure provides a graphite material, which includes graphite particles, and the graphitization degree of at least one end surface of at least part of the graphite particles is less than the graphitization degree of the basal surface.

[0051] In the present disclosure, the graphitization degree of at least one end surface of at least part of the graphite particles is less than the graphitization degree of the basal surface, which can be that the graphitization degree of at least one end surface of part of the graphite particles is less than the graphitization degree of the basal surface, or the graphitization degree of at least one end surface of all the graphite particles is less than the graphitization degree of the basal surface. For at least part of the single graphite particles, the graphite particles include two end surfaces, and the graphitization degree of only one end surface can be less than the graphitization degree of the basal surface, while the graphitization degree of the other end surface is the same as the graphitization degree of the basal surface, or the graphitization degree of both end surfaces is less than the graphitization degree of the basal surface.

[0052] In the present disclosure, the graphite particles with different graphitization degrees of the end surface and the basal surface can be regarded as including a graphite particle body, a first carbon layer and a second carbon layer, the first carbon layer is located at the end surface, and the second carbon layer is located at the basal surface. The graphitization degree of the second carbon layer can be the same as or different from that of the graphite particle body.

[0053] The graphitization degree of carbon is related to the order degree thereof. The order degree indicates the degree of three-dimensional ordered arrangement of the structure of the graphite material, and the higher the graphitization degree of the graphite material is, the higher the order degree thereof is. The order degree of the end face and the basal plane of the graphite particle can be detected by a transmission electron microscope (TEM).

[0054] In the present disclosure, the low graphitization degree of the end face increases the active sites at the position on the one hand and increases the electrolyte retention on the other hand, promotes the fast deintercalation of lithium ions, and the high graphitization degree of the basal plane can reduce the consumption of active lithium and the interface side reaction at high temperature, prolonging the service life.

[0055] FIG. 2 schematically shows a graphite particle 100 in some embodiments of the present disclosure, which includes a plurality of graphite layers 130, a first carbon layer 110, and a second carbon layer 120. The end face of the graphite particle 100 has the first carbon layer 110, and the basal plane of the graphite particle 100 has the second carbon layer 120. The basal plane of the graphite particle 100 is substantially parallel to the direction of the conjugated large plane structure of carbon atoms inside the graphite particle and is perpendicular to the c-axis direction; the end face of the graphite particle 100 is substantially parallel to the direction of the c-axis. The diffusion of lithium ions in the graphite particle has strong directionality and can only be inserted into the end face perpendicular to the c-axis direction of the graphite crystal.

[0056] In some embodiments of the present disclosure, the mass ratio m1 of the first carbon layer 110 in the graphite material satisfies 0 < m1 < 10%; and the mass ratio m2 of the second carbon layer 120 in the graphite material satisfies 0 < m2 < 10%.

[0057] Preferably, at least one end face of at least part of the graphite particles comprises amorphous carbon, and the basal plane comprises carbon material with a higher graphitization degree than the amorphous carbon. That is, for at least part of the single graphite particles, at least one end face comprises amorphous carbon, and the basal plane has a higher graphitization degree than the amorphous carbon. The low graphitization of the end face can increase the active sites at the position on the one hand and increase the electrolyte retention on the other hand, promoting the fast deintercalation of lithium ions; and through the high graphitization of the basal plane, the consumption of active lithium can be reduced and the interface side reaction at high temperature can be reduced, prolonging the service life.

[0058] The present disclosure also provides a preparation method of the graphite material, which comprises:

[0059] The graphite particle precursor is treated to obtain the graphite material provided by the present disclosure.

[0060] In some embodiments of the present disclosure, the above graphite particle precursor can only contain carbon sources such as petroleum coke, needle coke, pitch, etc., or can contain graphite and carbon sources such as petroleum coke, needle coke, pitch, etc.

[0061] In some embodiments of the present disclosure, graphite particles with different graphitization degrees of end faces and base faces can be obtained by differentiating the carbonization treatment of the end faces and base faces of at least part of the graphite particle precursors. For example, the carbonization treatment of the end faces and base faces of at least part of the graphite particle precursors can be differentiated in one or more of the following ways:

[0062] (1) the end faces and base faces are subjected to different temperatures;

[0063] (2) the end faces and base faces are subjected to different oxygen concentrations;

[0064] (3) the graphite particle precursors are subjected to a carbon dioxide atmosphere.

[0065] For methods (1) and (2), the temperature and oxygen concentration during the preparation process affect the graphitization degree. For example, when the end faces and base faces are subjected to different temperatures / oxygen concentrations, the end faces and base faces will have a certain difference in graphitization degree.

[0066] In some embodiments of the present disclosure, the oxygen content of at least one end face of at least part of the graphite particle precursors is higher than that of the base face, so as to make the degree of disorder of the end face of the graphite particle higher than that of the base face, and the graphitization degree of the end face lower than that of the base face.

[0067] In some embodiments of the present disclosure, the temperature of at least one end face of at least part of the graphite particle precursors is lower than that of the base face, so as to make the degree of disorder of the end face of the graphite particle higher than that of the base face, and the graphitization degree of the end face lower than that of the base face.

[0068] For method (3), the end faces of graphite particle precursors with a certain orientation, such as needle coke, are sensitive to carbon dioxide, and are affected by carbon dioxide, so that the end faces of the formed graphite particles have a higher degree of disorder and a lower graphitization degree.

[0069] In some embodiments of the present disclosure, the volume fraction of carbon dioxide in the carbon dioxide atmosphere is greater than or equal to 5%.

[0070] In some embodiments of the present disclosure, the temperature for treating the graphite particle precursors is 2000-3500°C.

[0071] In some embodiments of the present disclosure, the carbonization treatment can be performed under an applied magnetic field. Since the graphite particle precursors have a certain orientation, the graphite particle precursors will be arranged in a certain direction under the action of the applied magnetic field, thereby facilitating the differentiated carbonization treatment of the end faces and base faces of the graphite particle precursors. For example, the end faces of the graphite particle precursors are made to face the upward and downward directions under the applied magnetic field, and the upper and / or lower end faces are made to face the direction with a higher oxygen concentration than the base face. The carbonization under such conditions will make the end faces have a higher degree of disorder than the base face.

[0072] In some embodiments of the present disclosure, the direction of the applied magnetic field is parallel to the direction of the conjugated planar structure of carbon atoms in the graphite particle precursor or perpendicular to the c-axis direction of the graphite particle precursor. Optionally, the strength of the applied magnetic field is 0.1-10T. In this way, the directional arrangement of the graphite particle precursor can be further ensured, so as to facilitate the differential carbonization treatment of the end face and the basal plane of the graphite particle precursor.

[0073] In some embodiments of the present disclosure, the differential carbonization treatment of the end face and the basal plane of at least part of the graphite particle precursor includes: coating the at least one end face of at least part of the graphite particle precursor with amorphous carbon. The end face of the graphite particle precursor is coated with amorphous carbon with low graphitization degree, which on the one hand increases the active sites at this position, and on the other hand increases the electrolyte retention amount, so as to promote the rapid deintercalation of lithium ions.

[0074] In some embodiments of the present disclosure, the coating of the at least one end face of at least part of the graphite particle precursor with amorphous carbon includes: coating the at least one end face of at least part of the graphite particle precursor with an amorphous carbon source, and carbonizing the amorphous carbon source to form amorphous carbon. For example, a graphitized graphite core particle can be used as the graphite particle precursor, the graphite core particle is arranged with the end face upward under the condition of an applied magnetic field, and pitch is sprayed onto the upper end (i.e., the end face) of the graphite core particle from top to bottom, and then the pitch is carbonized at low temperature to form a graphite particle with amorphous carbon on the end face. The temperature of the low-temperature carbonization can be 800-1500℃, such as 800℃, 900℃, 1000℃, 1100℃, 1200℃, etc. In this way, the differential carbonization treatment of the end face and the basal plane of at least part of the graphite particle precursor can also be achieved, and the preparation process can be simplified.

[0075] It can be understood that the graphite core particle is the body of the graphite particle, which can be, for example, a carbon material particle with a graphitization degree greater than 0.8. The graphite core particle can be artificial graphite or natural graphite, and the raw material for manufacturing the artificial graphite can be easy-graphitizable coke or difficult-graphitizable coke; the graphite core particle can be a primary particle or a secondary particle.

[0076] The present disclosure also provides a negative electrode, which comprises a negative electrode material layer, wherein the graphitization degree of the negative electrode material layer is G i when the compaction density is i; the graphitization degree of the negative electrode material layer is G i+Δi when the compaction density is i+Δi; wherein Δi is greater than 0, and G i+Δi is greater than G i .

[0077] In the present application, the negative electrode can include a negative electrode current collector in addition to the negative electrode material layer, and the negative electrode material layer can be loaded on the negative electrode current collector. The negative electrode material layer can include a graphite negative electrode active material, and in addition, the negative electrode material layer can also include a small amount of a binder, a conductive agent, etc.

[0078] In the present application, the compaction density = the areal density / the thickness of the negative electrode material layer.

[0079] The graphitization degree is used to measure the degree to which the crystal structure of amorphous carbon after rearrangement approaches perfect graphite. The interlayer spacing of completely non-graphitized carbon is 0.3440 nm, and the interlayer spacing of ideal graphite crystal is 0.3354 nm. The graphitization degree G of the negative electrode material layer can reflect the degree to which the crystal structure of carbon material in the negative electrode material layer after rearrangement approaches perfect graphite.

[0080] In the present disclosure, the graphitization degree G of the negative electrode material layer is calculated using the following formula: G = (0.3440 - d002) / (0.3440 - 0.3354) x 100%, where d002 is the interlayer spacing of the crystal plane corresponding to the 002 characteristic peak in the X-ray diffraction spectrum of the negative electrode material layer. The diffraction angle of the 002 crystal plane can be measured by XRD, and then d002 can be calculated by the Bragg formula.

[0081] As the compaction density of the negative electrode material layer increases, the graphite particles tend to be arranged more transversely, that is, as the compaction density of the negative electrode material layer increases, the two end faces of the graphite particles tend to be arranged in a direction with a larger included angle with the thickness direction of the graphite material layer. In the present application, as the compaction density of the negative electrode material layer increases, the overall graphitization degree of the negative electrode material layer becomes larger, which means that the overall graphitization degree of the negative electrode material layer is larger when the graphite particles are arranged more transversely, that is, the basal plane graphitization degree is larger overall. For the graphite particles, in the "lithium extraction region", that is, the end face where lithium ions can be extracted, the graphitization degree is low, which can improve the lithium ion diffusion rate and improve the fast charging and rate performance; in the "non-lithium extraction region", that is, the basal plane without lithium ion extraction sites, the graphitization degree is high, which stabilizes the structure and improves the battery life and high-temperature performance. Therefore, the negative electrode that meets the above "the graphitization degree of the negative electrode material layer is G i when the compaction density is i; the graphitization degree of the negative electrode material layer is G i+Δi when the compaction density is i + Δi; where Δi is greater than 0, and G i+Δi is greater than G i " can comprehensively improve the fast charging, rate, life, and high-temperature performance of the battery.

[0082] In some embodiments of the present disclosure, the OI value of the negative electrode material layer is OI i when the compaction density is i; the OI value of the negative electrode material layer is OI i+Δi when the compaction density is i + Δi; OIi+Δi Greater than OI i .

[0083] The Orientation Index (OI) of the negative electrode material layer can be calculated by testing the intensity ratio of the (004) diffraction peak to the (110) diffraction peak in the X-ray diffraction pattern of the negative electrode material layer. The orientation OI value of the negative electrode material layer is calculated using the formula OI = I(004) / I(110), where I(004) is the peak intensity of the 004 characteristic peak in the X-ray diffraction pattern of the negative electrode material layer, and I(110) is the peak intensity of the 110 characteristic peak in the X-ray diffraction pattern of the negative electrode material layer. A decrease in the OI value is beneficial to lithium-ion insertion and diffusion. As the compaction density of the negative electrode material layer increases, if both the measurable OI value and the degree of graphitization of the negative electrode material layer increase, it indicates that the degree of graphitization of at least one end face of at least some graphite particles in the negative electrode material layer is less than the degree of graphitization of the basal surface. In this way, both the energy density and fast charging performance of the battery can be considered.

[0084] In some embodiments of this disclosure, i satisfies 0.5 g / cm³. 3 ≤i≤2.1g / cm 3 Δi satisfies 0 g / cm 3 <Δi≤1.6g / cm 3 Preferably, i satisfies 0.5 g / cm³ 3 ≤i≤1.3g / cm 3 Δi satisfies 0.4 g / cm 3 ≤Δi≤1.3g / cm 3 Increasing i is beneficial for improving energy density, but when i is too high, it may make it more difficult for the electrolyte to wet the surface of the graphite particles. At the same time, it is accompanied by an increase in the OI value of the negative electrode material layer, which is also not conducive to lithium ion insertion and diffusion. Therefore, i should be taken within the above range to balance the energy density and fast charging performance of the negative electrode.

[0085] In some embodiments of this disclosure, G i+Δi -G i Satisfying 0 < G i+Δi -G i ≤14%; preferably, G i+Δi -G i Satisfying 1% < G i+Δi -G i ≤5%. G i+Δi -G i Meeting the above ranges can balance the battery's energy density, fast charging performance, and high-temperature performance.

[0086] In some embodiments of this disclosure, OI i+Δi -OI i Satisfying 0 < OIi+Δi -OI i ≤21; preferably, OI i+Δi -OI i satisfies 2 < OI i+Δi -OI i ≤7. In this way, the energy density and the fast-charging performance of the battery can be balanced.

[0087] In some embodiments of the present disclosure, the OI value of the negative electrode material layer ranges from 1 to 40; preferably, the OI value of the negative electrode material layer ranges from 3 to 12. In this way, the energy density and the fast-charging performance of the battery can be further balanced.

[0088] In some embodiments of the present disclosure, the graphitization degree G of the negative electrode material layer ranges from 0.8 to 0.99. In this way, better stability and higher energy density can be obtained.

[0089] In some embodiments of the present disclosure, the particle size D50 of the graphite particles ranges from 1 μm to 20 μm, preferably from 5 μm to 15 μm. In this way, the energy density and the fast-charging performance of the negative electrode can be further balanced. D50 refers to the particle size corresponding to the cumulative volume percentage of 50% of the graphite particles. In the present application, the particle size D50 of the graphite particles in the negative electrode material layer can be obtained by scanning electron microscopy (SEM), specifically including the following steps: a) disassembling the battery after complete discharge to obtain the negative electrode, and then cutting the negative electrode material layer at any position by argon ion to obtain a cross-section sample; b) placing the above cross-section sample of the electrode piece in the SEM for observation, and adjusting the electron microscope voltage and magnification according to the actual needs to ensure that enough graphite particles in the sample can be clearly seen and photographed to obtain SEM photos; c) the obtained SEM photos can be imported into a gray scale debugging software (such as Geodict) to statistically analyze the particle size of the graphite particles; d) 20-100 experiments are cumulatively performed, and the number of particles in each experiment is not less than 500 pcs, and after the above results are statistically analyzed, the particle size distribution range and the D50 particle size of the graphite particles in the negative electrode are obtained.

[0090] In some embodiments of the present disclosure, the negative electrode material layer comprises graphite.

[0091] In some embodiments of the present disclosure, the negative electrode material layer comprises the graphite material provided by the present disclosure or the graphite material prepared by the preparation method of the graphite material provided by the present disclosure. In this way, the negative electrode has better charge-discharge rate, fast-charging performance and high-temperature performance.

[0092] The present disclosure further provides a secondary battery comprising the above negative electrode. The secondary battery with the above negative electrode has very good charge-discharge rate, fast-charging performance and high-temperature performance.

[0093] The present disclosure also provides a power consuming device, which can be a vehicle, a mobile electronic device, or an energy storage device, for example, comprising the secondary battery described above.

[0094] The present disclosure is further illustrated in detail by the following examples, but is not limited by the same. The raw materials used in the examples can be obtained by commercial channels.

[0095] Example 1

[0096] The preparation method of the graphite material of Example 1 comprises the following steps:

[0097] (1) The needle coke is crushed and shaped to obtain a graphite material precursor;

[0098] (2) The graphite material precursor is placed in a graphitization furnace equipped with a magnetic control system for graphitization treatment; the upper end of the graphitization furnace is open, the graphitization furnace has a magnetic field inside, the direction of the magnetic field is parallel to the up-down direction of the graphitization furnace, so that at least part of the graphite material precursor particles in the graphite material precursor are oriented arranged (end faces on the upper end and lower end of the particles); the temperature at the upper end and lower end of the graphitization furnace is controlled to be 2500℃, the temperature in the middle of the graphitization furnace is 3000℃, and part of the graphite material precursor is placed at the upper end of the graphitization furnace (the reaction temperature of the graphite material precursor at the upper end is 2500℃); the graphitization treatment time is 72 hours, and the graphite material is obtained.

[0099] Example 2

[0100] The preparation method of the graphite material of Example 2 is basically the same as that of Example 1, except that in step (2), CO2-containing air (CO2 gas concentration is 5% by volume) is introduced into the graphitization furnace. The graphite material obtained has an amorphous carbon layer formed in the direction of the two end faces, and the basal plane is a high graphitization degree carbon surface.

[0101] Example 3

[0102] The preparation method of the graphite material of Example 3 comprises the following steps:

[0103] (1) The needle coke is crushed and shaped to obtain a graphite material precursor;

[0104] (2) The graphite material precursor is subjected to graphitization treatment to obtain graphite core particles; the graphitization treatment temperature is 3000℃, and the time is 72 hours;

[0105] (3) The graphite core particles obtained in step (2) are placed in a graphitization furnace equipped with a magnetic control system, and the graphitization furnace has a magnetic field, the direction of which is parallel to the up-down direction of the graphitization furnace. At this time, the end faces of the graphite core particles are located at the upper and lower ends of the basal plane under the action of the magnetic field, and pitch is sprayed onto the graphite core particles from the upper end, so that the upper end face of the graphite core particle on the upper surface has pitch. Then, heat treatment is performed at a temperature of 1000°C for 48 hours, so that the pitch is decomposed to form amorphous carbon in the direction of the end face of the graphite particle, and the basal plane is a high graphitization degree surface.

[0106] Example 4

[0107] The preparation method of the graphite material of Example 4 is basically the same as that of Example 1, except that the graphite material precursor subjected to secondary granulation is prepared in step (1). Specifically, it comprises:

[0108] (1) The needle coke is crushed and shaped, and then mixed with the binder pitch at a mass ratio of 1:0.05 to obtain a graphite material precursor subjected to secondary granulation.

[0109] (2) The graphite material precursor subjected to secondary granulation is placed in a graphitization furnace equipped with a magnetic control system for graphitization treatment; wherein the upper end of the graphitization furnace is open, and the graphitization furnace has a magnetic field, the direction of which is parallel to the up-down direction of the graphitization furnace; the temperature at the upper end and the lower end of the graphitization furnace is controlled to be 2500°C, and the temperature in the middle of the graphitization furnace is 3000°C, and part of the graphite material precursor is placed at the upper end of the graphitization furnace (the reaction temperature of the graphite material precursor at the upper end is 2500°C); the graphitization treatment time is 72 hours, and the graphite material is obtained.

[0110] Example 5

[0111] The synthesis method of the graphite material of Example 5 is similar to that of Example 1, except that the needle coke has higher orientation, and the obtained material has higher orientation.

[0112] Example 6

[0113] The synthesis method of the graphite material of Example 6 is similar to that of Example 5, except that the needle coke has a larger D50, and the obtained material has a larger D50.

[0114] Example 7

[0115] The synthesis method of the graphite material of Example 7 is similar to that of Example 1, except that the needle coke has lower orientation, and the obtained material has lower orientation.

[0116] Example 8

[0117] The graphite material of Example 8 was synthesized in a similar manner to Example 1, except that the temperature at the upper end and the lower end of the graphitization furnace was 2200°C, the temperature at the middle of the graphitization furnace was 2700°C, and the precursor of the graphite material was placed at the upper end of the graphitization furnace (the reaction temperature of the precursor of the graphite material at the upper end was 2200°C). The resulting material had a lower overall graphitization degree.

[0118] Example 9

[0119] The graphite material of Example 9 was synthesized in a similar manner to Example 1, except that the compaction i after the formation of the electrode sheet was lower.

[0120] Example 10

[0121] The graphite material of Example 10 was synthesized in a similar manner to Example 9, except that the compaction i after the formation of the electrode sheet was the same, and the compaction i+Δi was higher.

[0122] Example 11

[0123] The graphite material of Example 11 was synthesized in a similar manner to Example 10, except that the D50 of the needle coke was smaller, and the D50 of the resulting graphite material was smaller.

[0124] Comparative Example 1

[0125] The graphite material of the present comparative example was synthesized in a similar manner to Example 3, except that:

[0126] In Step (3), the pitch and the graphite core particles obtained in Step (2) were uniformly mixed and subjected to carbon coating treatment. The resulting graphite particles had a surface uniformly coated with amorphous carbon.

[0127] Comparative Example 2

[0128] The graphite material of the present comparative example was synthesized in a similar manner to Example 3, except that:

[0129] In Step (3), the pitch and the graphite core particles obtained in Step (2) were uniformly mixed and subjected to carbon coating treatment, and the sintering temperature at the time of carbon coating was 3000°C. The resulting graphite particles had a surface uniformly coated with high graphitization degree carbon.

[0130] Comparative Example 3

[0131] The graphite material of the present comparative example was synthesized in a similar manner to Example 3, except that Step (3) was not performed, and the resulting graphite particles had no coating material on the surface.

[0132] Negative electrode: The graphite material obtained from Example 1-11 and Comparative Example 1-3, SP conductive carbon black, sodium carboxymethyl cellulose (CMC-Na), and butadiene-styrene rubber (SBR) were mixed and dispersed in a solvent (a mixed solvent of N-methyl pyrrolidone and water) at a mass ratio of 100:1:1.5:1.5, and were coated on both sides of a negative electrode current collector copper foil, and after drying and rolling, a negative electrode was obtained, which included the negative electrode current collector copper foil and a negative electrode material layer loaded on the copper foil, and the compaction density of the negative electrode material layer was i g / cm 3 . The negative electrode was then rolled with a certain force to increase the compaction density of the negative electrode material layer to i+Δi g / cm 3 .

[0133] The negative electrodes corresponding to Example 1-11 and Comparative Example 1-3 were subjected to XRD testing, and the testing method referred to GB / T 24533-2019 “Graphite-based negative electrode material for lithium ion batteries”.

[0134] The graphitization degree G and the orientation degree OI of the negative electrode material layer when the compaction density of the negative electrode material layer was i g / cm 3 , i+Δi g / cm 3 were calculated according to the XRD patterns of the negative electrodes corresponding to Example 1-11 and Comparative Example 1-3, respectively, and the results are shown in Table 1.

[0135] Table 1

[0136] As can be seen from Table 1, in the negative electrode corresponding to the graphite material provided by the present disclosure, the graphitization degree of the negative electrode material layer increases with the increase of the compaction density.

[0137] Battery performance test

[0138] Positive electrode: After the positive electrode active material NCM811, the conductive agent Ketjen black, and the binder polyvinylidene fluoride (PVDF) were fully stirred and mixed uniformly in N-methyl pyrrolidone (NMP) solvent at a mass ratio of 96:2:2, they were coated on both sides of a positive electrode current collector aluminum foil, and after drying and rolling, a positive electrode was obtained.

[0139] Separator: A polyethylene (PE) ceramic film was used.

[0140] Electrolyte: The lithium salt was lithium hexafluorophosphate LiPF6, and the organic solvents included ethylene carbonate (EC), methyl ethyl carbonate (EMC), and dimethyl carbonate (DMC).

[0141] The negative electrodes corresponding to Example 1-11 and Comparative Example 1-3 were assembled into 2 Ah batteries together with the above-prepared positive electrode, separator, and electrolyte, respectively, for battery performance test, as follows.

[0142] (1) Battery rate performance and fast charging performance test

[0143] The batteries corresponding to Examples 1-11 and Comparative Examples 1-3 were subjected to a normal temperature (25°C) rate test, respectively charged at 0.2C and then discharged at 2C, with a lower limit voltage of 2.5V and an upper limit voltage of 4.25V, and the 2C discharge capacity was recorded; respectively charged at 0.2C and then discharged at 0.2C, with a lower limit voltage of 2.5V and an upper limit voltage of 4.25V, and the 0.2 discharge capacity was recorded; the 2C / 0.2C discharge ratio = (2C discharge capacity / 0.2 discharge capacity)*100%. The results obtained from the charge-discharge test are shown in Table 2.

[0144] The batteries corresponding to Examples 1-11 and Comparative Examples 1-3 were subjected to a fast charging performance test at 25°C using a three-electrode system: specifically, the potential between the negative electrode and the three-electrode was monitored and converted into the lithium potential during the rate charging (7C, 6.5C, 6C, 5.5C, 5C, 4.5C, 4C, 3.5C, 3C, 2.5C, 2C, 1.5C, 1C, 0.5C, 0.33C) process of each battery corresponding to Examples 1-11 and Comparative Examples 1-3 in turn; the fast charging process was as follows: starting from a high rate (e.g. 7C) to charge, when the lithium potential of the negative electrode reached 0V, jumping to the next rate (e.g. 6.5C) to continue charging until the lithium potential of the negative electrode reached 0V, then jumping to the next rate (e.g. 6C) to continue charging until the lithium potential of the negative electrode reached 0V, until the charging was stopped at 80% SOC of the battery, and the sum of the charging time at each rate was calculated as the 10-80% SOC fast charging time of the battery. The time required for each battery corresponding to Examples 1-11 and Comparative Examples 1-3 to charge from 10% SOC to 80% SOC was compared as a parameter for measuring fast charging capacity. The measured 10-80% SOC fast charging time is shown in Table 2.

[0145] Table 2

[0146] According to Table 2, it can be found that the batteries prepared using the graphite material of the present disclosure have higher discharge ratios and better fast charging performance, and the performance is better than that of the graphite material with uniform amorphous carbon coating and the material with uniform high graphitization degree carbon coating and the material without coating.

[0147] (B) High temperature performance test of the battery

[0148] High temperature storage performance: the batteries corresponding to the graphite materials of examples 1-11 and comparative examples 1-3 were charged at 0.33C to 4.25V, constant voltage to 0.05C, then discharged at 0.33C to 2.5V, and the initial discharge capacity was recorded; each battery was fully charged at 0.33C to 4.25V, stored at 60℃ for 28 days, and then placed at room temperature for 6h to restore to room temperature. The batteries were charged at 0.33C to 4.25V, constant voltage to 0.05C, then discharged at 0.33C to 2.5V, and the cycle was repeated 3 times at room temperature. The maximum value of the discharge capacity was taken as the recovery capacity, and the ratio of the recovery capacity to the initial discharge capacity was the capacity recovery rate. The results of the capacity recovery rate are shown in Table 3.

[0149] High temperature cycle performance: at 45℃, the batteries prepared from examples 1-11 and comparative examples 1-3 were charged at 1C to 4.25V, constant voltage to 0.05C, then discharged at 1C to 2.5V, and the cycle was repeated 500 times. The discharge capacity of the first cycle was recorded as P0, and the discharge capacity of the 500th cycle was recorded as P500. The ratio of P500 to P0 was the capacity retention rate of the battery at 500 cycles, and the results are shown in Table 3. 500 500

[0150] Table 3

[0151] From the data in Table 3, it can be found that the batteries prepared from the graphite materials of the present disclosure have high high-temperature storage capacity recovery rate and high-temperature 500-cycle capacity retention rate.

[0152] The data in Tables 2 and 3 show that the batteries prepared from the graphite material with a uniform amorphous carbon-coated surface in comparative example 1 have good charge-discharge rate and fast-charging performance, but poor high-temperature performance; the batteries prepared from the graphite material with a uniform high-graphitization degree carbon-coated surface in comparative example 2 have good high-temperature performance, but poor charge-discharge rate and fast-charging performance, while the batteries prepared from the graphite material of the present disclosure have very good charge-discharge rate, fast-charging performance and high-temperature performance.

[0153] The above describes preferred embodiments of the present disclosure, but the present disclosure is not limited to the specific details in the above-described embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

[0154] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0155] ​​Furthermore, the various embodiments of the present disclosure can be arbitrarily combined with each other unless they contradict each other, and it should be understood that the same should be construed as being included in the disclosure of the present disclosure.

Claims

1. A graphite material, characterized by, The graphite material comprises graphite particles, and a graphitization degree of at least one end surface of at least part of the graphite particles is less than a graphitization degree of a basal surface.

2. The graphite material of claim 1, wherein At least one end surface of at least part of the graphite particles comprises amorphous carbon, and the basal surface comprises carbon material with a graphitization degree higher than the amorphous carbon.

3. The graphite material according to claim 1 or 2, characterized in that, The graphite particles have a particle size D50 of 1 μm to 20 μm.

4. A method of producing a graphite material, characterized by, The method comprises: treating graphite particle precursors to obtain the graphite material according to any one of claims 1 to 3.

5. The method of claim 4, wherein, The treatment of the graphite particle precursors comprises differentially carbonizing end surfaces and basal surfaces of at least part of the graphite particle precursors.

6. The method according to claim 4 or 5, characterized in that, The treatment of the graphite particle precursors comprises orienting at least part of the graphite particle precursors under an applied magnetic field, and differentially carbonizing end surfaces and basal surfaces of at least part of the graphite particle precursors.

7. The method of claim 6, wherein, The applied magnetic field is parallel to a direction of a conjugated planar structure of carbon atoms in the graphite particle precursors or perpendicular to a c-axis direction of the graphite particle precursors; optionally, the applied magnetic field has a strength of 0.1 to 10 T.

8. The method according to any one of claims 5 to 7, characterized in that, The differentially carbonizing of the end surfaces and the basal surfaces of at least part of the graphite particle precursors comprises at least one of the following (a), (b) and (c): (a) the oxygen content at a position of at least one end surface of at least part of the graphite particle precursors is higher than the oxygen content at a position of a basal surface; (b) the temperature at a position of at least one end surface of at least part of the graphite particle precursors is lower than the temperature at a position of a basal surface; (c) at least part of the graphite particle precursors are placed in a carbon dioxide atmosphere.

9. The method according to any one of claims 5 to 8, characterized in that, The differentially carbonizing of the end surfaces and the basal surfaces of at least part of the graphite particle precursors comprises: coating amorphous carbon on at least one end surface of at least part of the graphite particle precursors.

10. The method according to any one of claims 4 to 9, characterized in that, The graphite particle precursors comprise needle coke, and the treatment of the graphite particle precursors is performed at a temperature of 2000°C to 3500°C.

11. The method of claim 9, wherein, The coating of amorphous carbon on at least one end surface of at least part of the graphite particle precursors comprises coating an amorphous carbon source on at least one end surface of at least part of the graphite particle precursors, and carbonizing the amorphous carbon source to form amorphous carbon. Optionally, the graphite particle precursors comprise graphite core particles, and the graphite core particles are carbon material particles with a graphitization degree greater than 0.

8. Optionally, the amorphous carbon source comprises pitch. Optionally, the treatment of the graphite particle precursors is performed at a temperature of 800°C to 1500°C.

12. The method according to any one of claims 8 to 11, characterized in that, The volume ratio of carbon dioxide in the carbon dioxide atmosphere is greater than or equal to 5%.

13. A negative electrode characterized by comprising: The negative electrode material layer has a graphitization degree G of G i at a compacted density of i; and a graphitization degree G of G i+Δi at a compacted density of i+Δi. Δi is greater than 0, G i+Δi greater than G i .

14. The negative electrode according to claim 13, wherein The negative electrode material layer has an OI value of OI i at a compacted density of i; the negative electrode material layer has an OI value of OI i+Δi at a compacted density of i+Δi; OI i+Δi is greater than OI i .

15. The negative electrode according to claim 14, wherein said i satisfies 0.5 g / cm 3 ≤ i ≤ 2.1 g / cm 3 , Δi satisfies 0 g / cm 3 ≤ Δi ≤ 1.6 g / cm 3 ; preferably, said i satisfies 0.5 g / cm 3 ≤ i ≤ 1.3 g / cm 3 , Δi satisfies 0.4 g / cm 3 ≤ Δi ≤ 1.3 g / cm 3 .

16. The negative electrode according to claim 15, wherein G i+Δi -G i satisfies 0 < G i+Δi -G i ≤ 14%; preferably, G i+Δi -G i satisfies 1% < G i+Δi -G i ≤ 5%.

17. The negative electrode according to claim 15 or 16, characterized by OI i+Δi -OI i satisfies 0 < OI i+Δi -OI i ≤ 21; preferably, OI i+Δi -OI i satisfies 2 < OI i+Δi -OI i ≤ 7.

18. The negative electrode according to any one of claims 13 to 17, characterized by The OI value of the negative electrode material layer ranges from 1 to 40; preferably, the OI value of the negative electrode material layer ranges from 3 to 12.

19. The negative electrode according to any one of claims 13 to 18, characterized by The graphitization degree G of the negative electrode material layer ranges from 0.8 to 0.

99.

20. The negative electrode according to any one of claims 13 to 19, wherein The negative electrode material layer comprises graphite.

21. The negative electrode according to any one of claims 13 to 20, characterized by The negative electrode material layer comprises the graphite material according to any one of claims 1 to 3 or the graphite material prepared by the preparation method according to any one of claims 4 to 12.

22. A secondary battery characterized by comprising: The secondary battery comprises the negative electrode according to any one of claims 13 to 21.

23. An electric device comprising the secondary battery according to claim 22.

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