Graphite material with widened interlayer spacing as well as preparation method and application of graphite material

Abstract

The invention provides a graphite material with widened interlayer spacing. The interlayer spacing at the boundary in a graphite material crystal is 0.36-0.41 nm. The invention also provides a preparation method of the graphite material, which comprises the following steps: firstly, in an inert gas atmosphere, performing high-temperature heat treatment on the graphene oxide stacked in multiple layers, so that the graphene oxide is converted into a graphite phase, and the interlayer spacing at the crystal boundary of the graphite phase is widened; then crushing and granulating the graphite phase to obtain a graphite material with broadened interlayer spacing; and the interlayer spacing at the boundary of the graphite material is 0.36-0.41 nm. The invention further provides a lithium ion battery, and the surface of a negative electrode of the lithium ion battery is coated with the graphite material or the graphite material obtained by the preparation method.

Description

Technical Field

[0001] The present invention belongs to the technical field of material application, and in particular relates to a graphite material with widened interlayer spacing and a preparation method and application thereof. Background Art

[0002] The excessive use of non-renewable fossil fuels has led to an energy crisis, threatening the sustainable development of society and economy. In order to meet this challenge, research and development of renewable energy has become the focus of public attention. Since its advent in the 1970s, lithium-ion batteries have become an indispensable part of modern life. With its advantages such as high energy density, long cycle life and no memory effect, lithium-ion batteries have become the main power source of modern electronic devices and electric vehicles. However, with the development of science and technology and the progress of society, the performance of existing lithium-ion batteries has gradually failed to meet market demand. Problems such as safety, fast charging rate and temperature sensitivity of lithium-ion batteries also require continuous technological innovation and improvement to solve.

[0003] As a key component of lithium-ion batteries, the performance of negative electrode materials is the key to determining the rate and low-temperature performance of lithium-ion batteries. At present, graphite negative electrode materials can reversibly embed and extract lithium ions to form LiC6 compounds, which makes it an ideal negative electrode material for lithium-ion batteries. However, the low lithium ion diffusion rate of graphite under high current density and low temperature conditions is the main factor affecting its application, and it is also the main problem for commercialization of fast charging and low-temperature technology.

[0004] Therefore, it is necessary to develop a graphite negative electrode material with a fast lithium ion diffusion channel that can enable lithium ions to be quickly transferred from the edge of the graphite to the inside, thereby achieving high mass specific capacity and cycle stability of lithium-ion batteries under fast charging and low temperature conditions. Summary of the invention

[0005] In view of this, in order to at least partially solve at least one of the above-mentioned technical problems, the present disclosure provides a graphite material with a widened interlayer spacing, and the interlayer spacing at the boundary within the graphite material crystal is 0.36~0.41 nanometers.

[0006] According to an embodiment of the present disclosure, the particle size of the graphite material is 5-10 microns.

[0007] According to an embodiment of the present disclosure, the bulk interlayer spacing within the crystal of the graphite material is 0.335-0.34 nanometers, and the oxygen content of the graphite material is 1%-3%.

[0008] In another aspect of the present disclosure, a method for preparing the aforementioned graphite material is provided, comprising:

[0009] In an inert gas atmosphere, the multi-layer stacked graphene oxide is heat treated to transform the graphene oxide into a graphite phase and widen the interlayer spacing at the crystal boundary of the graphite phase to 0.36-0.41 nanometers;

[0010] Then the graphite phase is crushed and granulated to obtain a graphite material with a widened interlayer spacing.

[0011] According to an embodiment of the present disclosure, heat treating graphene oxide includes:

[0012] Performing a first heat treatment on the graphene oxide to decompose and remove the oxygen-containing groups in the graphene oxide;

[0013] The multilayer graphene oxide is subjected to a second heat treatment to promote the hybridization of carbon atoms and form an ordered graphite phase layered structure;

[0014] The temperature of the second heat treatment is higher than that of the first heat treatment.

[0015] According to an embodiment of the present disclosure, in the first heat treatment, the heating temperature is 600-1000°C; in the second heat treatment, the heating temperature is 2000-3000°C.

[0016] According to an embodiment of the present disclosure, the oxygen content of graphene oxide is 1%-5%, and the number of graphene oxide layers is 0.5-20,000.

[0017] In another aspect of the present disclosure, a lithium ion battery is provided, wherein the surface of the negative electrode of the lithium ion battery is coated with the aforementioned graphite material, or the graphite material obtained by the aforementioned preparation method.

[0018] According to the embodiment of the present disclosure, the lithium ion diffusion rate of the negative electrode is 10 -8 ~10 -12 cm 2 s -1 The lithium ion diffusion energy barrier of the negative electrode is 0.14 eV~0.01 eV.

[0019] According to an embodiment of the present disclosure, the negative electrode to positive electrode capacity ratio of the lithium ion battery is 1 to 1.2; the operating temperature of the lithium ion battery is -40°C to 30°C.

[0020] According to the embodiments of the present disclosure, the present disclosure proposes a graphite material with a widened interlayer spacing of the grains in the internal crystal structure, and the graphite with a widened interlayer spacing can eliminate the anisotropy of the graphite surface. Among them, when the graphite material with a widened interlayer spacing of the grains is used as the negative electrode material of a lithium-ion battery, the larger interlayer spacing of the graphite material makes the channel for the diffusion of lithium ions between the layers more spacious, thereby reducing the resistance encountered by lithium ions during the embedding and extraction process. This means that lithium ions can move faster between graphite layers, which increases the diffusion rate of lithium ions, allowing lithium ions to reach or leave the electrode surface faster, reducing the polarization phenomenon caused by concentration differences. At the same time, the wider interlayer channels also help to reduce the damage to the graphite structure during the embedding and extraction of lithium ions, improve the cycle stability of the battery, and extend the battery life. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a transmission electron microscope image (High Resolution Transmission Electron Microscope, HRTEM) of the interlayer spacing widened graphite prepared in Example 1 of the present disclosure;

[0022] Figure 2 A curve diagram showing the diffusion rate of the interlayer-widened graphite prepared in Example 1 of the present disclosure at 30° C. as a function of the lithium insertion potential;

[0023] Figure 3 A curve diagram showing the diffusion rate of the interlayer-widened graphite prepared in Example 1 of the present disclosure at -20°C as a function of the lithium insertion potential;

[0024] Figure 4 This is a transmission electron microscope image of the interlayer-widened graphite prepared in Example 2 of the present disclosure;

[0025] Figure 5 This is a transmission electron microscope image of the interlayer-widened graphite prepared in Example 3 of the present disclosure;

[0026] Figure 6 The diffusion energy barrier diagram of graphite with different lattice spacing prepared in the embodiment of the present disclosure;

[0027] Figure 7 This is a transmission electron microscope image of the interlayer-widened graphite prepared in Comparative Example 1 of the present disclosure;

[0028] Figure 8 This is a capacity comparison chart of a full battery composed of graphite with widened interlayer spacing and ternary NCM obtained in Examples 1 and 2 of the present disclosure;

[0029] Fig. 9 This is a high rate performance diagram of a full battery composed of interlayer-widening graphite and ternary NCM obtained in Example 1 of the present disclosure;

[0030] Fig.10 The cycle performance diagram of the full battery composed of interlayer-widened graphite and ternary NCM obtained in Example 1 of the present disclosure;

[0031] Fig.11 The charge and discharge curves of the full battery composed of interlayer-widened graphite and ternary NCM obtained in Example 1 of the present disclosure at different test temperatures. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0033] The endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this disclosure.

[0034] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0035] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0036] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present disclosure shall have the usual meanings understood by persons with ordinary skills in the field to which the present disclosure belongs. If the full text involves descriptions such as "first", "second", etc., the descriptions such as "first", "second", etc. are only used to distinguish similar objects, and cannot be understood as indicating or implying their relative importance, order of precedence, or implicitly indicating the number of technical features indicated. It should be understood that the data described by "first", "second", etc. can be interchangeable under appropriate circumstances.

[0037] In order to make the purpose, technical solution and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of them.

[0038] Similarly, in order to simplify the present disclosure and help understand one or more of the various disclosed aspects, in the above description of the exemplary embodiments of the present disclosure, the various features of the present disclosure are sometimes grouped together into a single embodiment, figure, or description thereof. The description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0039] In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this disclosure.

[0040] In the present disclosure, the term "bulk phase interlayer spacing" means the distance between adjacent graphite layers in a graphite crystal, i.e., in a relatively complete region away from boundaries or defects. This distance is a relatively constant value in a graphite crystal, and the bulk phase interlayer spacing of graphite is approximately 0.335 nanometers (or 3.35 Å). This distance is an important parameter of the graphite crystal structure, which determines the physical and chemical properties of graphite, such as electrical conductivity, thermal conductivity, and the diffusion rate of lithium ions.

[0041] In the present disclosure, the term "interlayer spacing at the boundary" is used to mean the distance between adjacent graphite layers near the boundary or defect of graphite crystal. Due to the existence of the boundary or defect, the graphite interlayer spacing in this area may be different from the bulk interlayer spacing. The graphite layers at the boundary may be affected by factors such as lattice distortion, stress concentration or chemical bond changes, resulting in changes in interlayer spacing. Such changes may affect the performance of graphite, especially in nanoscale or high energy density applications.

[0042] Graphite has a layered structure, each layer is composed of carbon atoms arranged into a hexagonal lattice through strong covalent bonds, and the layers interact with each other through weak van der Waals forces. In the process of realizing the technical concept of the present disclosure, it is found that if the graphite interlayer spacing is increased by chemical treatment or physical methods, the diffusion rate of lithium ions in graphite can be increased, the electrode polarization phenomenon can be reduced, the charge and discharge performance can be improved, and the performance improvement of lithium-ion batteries and other energy storage technologies can be provided with strong support. Therefore, the present disclosure performs high-temperature heat treatment on multi-layer stacked graphene oxide materials to widen the interlayer spacing at the boundary of the graphite material, thereby improving its application effect as a negative electrode material for lithium-ion batteries.

[0043] The present disclosure provides a graphite material with a widened interlayer spacing, and the interlayer spacing at the boundary within the graphite material crystal is 0.36~0.41 nanometers, for example, it can be 0.36 nanometers, 0.365 nanometers, 0.37 nanometers, 0.375 nanometers, 0.38 nanometers, 0.385 nanometers, 0.39 nanometers, 0.395 nanometers, 0.40 nanometers, 0.405 nanometers, 0.41 nanometers, etc.

[0044] According to the embodiments of the present disclosure, the present disclosure proposes a graphite material with a widened interlayer spacing of the grains in the internal crystal structure, and the graphite with a widened interlayer spacing can eliminate the anisotropy of the graphite surface. Among them, when the graphite material with a widened interlayer spacing of the grains is used as the negative electrode material of a lithium-ion battery, the larger interlayer spacing of the graphite material makes the channel for the diffusion of lithium ions between the layers more spacious, thereby reducing the resistance encountered by lithium ions during the embedding and extraction process. This means that lithium ions can move faster between graphite layers, which increases the diffusion rate of lithium ions, allowing lithium ions to reach or leave the electrode surface faster, reducing the polarization phenomenon caused by concentration differences. At the same time, the wider interlayer channels also help to reduce the damage to the graphite structure during the embedding and extraction of lithium ions, improve the cycle stability of the battery, and extend the battery life.

[0045] According to an embodiment of the present disclosure, the particle size of the graphite material is 5-10 microns, for example, it can be 5 microns, 5.5 microns, 6 microns, 6.5 microns, 7 microns, 7.5 microns, 8 microns, 8.5 microns, 9 microns, 9.5 microns, 10 microns, etc.

[0046] According to an embodiment of the present disclosure, the bulk interlayer spacing within the crystal of the graphite material is 0.335-0.34 nanometers, for example, it may be 0.335 nanometers, 0.336 nanometers, 0.337 nanometers, 0.338 nanometers, 0.339 nanometers, 0.34 nanometers, etc. Calculated by mass fraction, the oxygen content of the graphite material is 1%-3%.

[0047] In another aspect of the present disclosure, a method for preparing the aforementioned graphite material is proposed, comprising the following steps S101-S102:

[0048] Step S101: heat-treating the multi-layer stacked graphene oxide in an inert gas atmosphere, so that the graphene oxide is transformed into a graphite phase, and the interlayer spacing at the crystal boundary of the graphite phase is widened to 0.36-0.41 nanometers;

[0049] Step S102: The graphite phase is then crushed and granulated to obtain a graphite material with a widened interlayer spacing.

[0050] According to the embodiments of the present disclosure, during the high-temperature heat treatment process, oxygen-containing functional groups such as epoxy and hydroxyl groups on the surface of graphene oxide will decompose to generate gases such as carbon dioxide and water vapor. When the generation rate of these gases is greater than the rate at which they are released from the graphene oxide interlayer, interlayer pressure will be generated. This pressure may exceed the van der Waals force between the graphene oxide layers, resulting in a significant increase in the interlayer spacing. At the same time, during the rapid thermal expansion process, the increase in interlayer pressure and the thermal expansion effect of the lattice work together to significantly widen the interlayer spacing.

[0051] According to an embodiment of the present disclosure, heat treating graphene oxide includes:

[0052] Performing a first heat treatment on the graphene oxide to decompose and remove the oxygen-containing groups in the graphene oxide;

[0053] The multilayer graphene oxide is subjected to a second heat treatment to promote the hybridization of carbon atoms and form an ordered graphite phase layered structure;

[0054] The temperature of the second heat treatment is higher than that of the first heat treatment.

[0055] According to an embodiment of the present disclosure, in the first heat treatment, the heating temperature is 600-1000°C; in the second heat treatment, the heating temperature is 2000-3000°C.

[0056] According to the embodiments of the present disclosure, during the first heat treatment, volatile impurities and unstable chemical groups, such as oxygen-containing groups, in the graphene oxide material are removed, and a relatively disordered amorphous carbon structure is generated, wherein the heating temperature is 600°C to 1000°C, for example, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, etc., preferably 700°C to 900°C, for example, 700°C, 750°C, 800°C, 850°C, 900°C, etc.; in the second heat treatment, the high The temperature promotes the formation of the sp² hybrid structure of carbon atoms, arranges the carbon atoms into a hexagonal lattice on a two-dimensional plane, and gradually forms an ordered graphite phase layered structure, wherein the heating temperature is 2000℃~3000℃, for example, it can be 2000℃, 2100℃, 2200℃, 2300℃, 2400℃, 2500℃, 2600℃, 2700℃, 2800℃, 2900℃, 3000℃, 3000℃, etc., preferably 2500℃~2800℃, for example, it can be 2500℃, 2600℃, 2700℃, 2800℃, etc.

[0057] In some specific embodiments, the material obtained by only performing the first heat treatment is not graphitized and cannot be used as a negative electrode material for lithium insertion. The lack of the first low-temperature heat treatment may affect the overall structure and performance of the material. The first heat treatment helps to remove impurities and stabilize the graphite phase structure, preparing for the subsequent second heat treatment. In order to ensure the best material performance and structural stability, the preparation method of the graphite material proposed in the present disclosure is indispensable to follow the two heat treatment processes.

[0058] According to an embodiment of the present disclosure, the oxygen content of graphene oxide is 1%-5%, and the number of graphene oxide layers is 0.5-20,000.

[0059] According to the embodiments of the present disclosure, graphene oxide is rich in a large number of oxygen-containing functional groups such as hydroxyl, carboxyl, epoxy, etc., and its oxygen content is 1% to 5%, for example, it can be 1%, 2%, 3%, 4%, 5%, etc., preferably 2% to 4%, for example, it can be 2%, 2.5%, 3%, 3.5%, 4%, etc.

[0060] According to an embodiment of the present disclosure, high-temperature heat treatment of graphene oxide is performed in an inert gas atmosphere to ensure the stability of the generated graphite material. The inert gas may be nitrogen or argon.

[0061] In another aspect of the present disclosure, a lithium ion battery is provided, wherein the surface of the negative electrode of the lithium ion battery is coated with the aforementioned graphite material, or the graphite material obtained by the aforementioned preparation method.

[0062] According to the embodiments of the present disclosure, the graphite with widened boundary layer spacing can eliminate the anisotropy of the graphite surface, so that lithium ions are quickly transferred from the edge of the graphite to the inside, thereby increasing the diffusion rate of lithium ions. When the graphite material proposed in the present disclosure is used as the negative electrode of a lithium-ion battery, it has a high lithium ion diffusion rate and a low diffusion energy barrier. The graphite with widened interlayers is used as a negative electrode material, so that the secondary battery has a fast lithium ion transmission channel under low temperature and fast charging conditions. It matches the commercial positive electrode material and can effectively improve the rate and cycle stability of the full battery under fast charging and low temperature conditions.

[0063] In some specific embodiments, the experimental results show that as a negative electrode material for lithium-ion batteries, after full battery testing, the full battery assembled with the graphite negative electrode and the positive electrode containing lithium cobalt oxide, lithium iron phosphate or ternary materials has excellent fast charging and low temperature performance: the mass specific capacity retention rate at 2C, 5C and 10C is 94%, 87.2% and 78.3%. At 0℃, -20℃, -30℃ and -40℃, the battery capacity remains at 96.9%, 87.5%, 77.0% and 51.8% of that at room temperature.

[0064] According to the embodiment of the present disclosure, the lithium ion diffusion rate of the negative electrode is 10 -8~10 -12 cm 2 s -1 The lithium ion diffusion energy barrier of the negative electrode is 0.14 eV~0.01eV.

[0065] According to an embodiment of the present disclosure, graphite is composed of multiple layers of carbon atoms stacked in a hexagonal mesh structure, and the layers interact with each other through weak van der Waals forces. This layered structure provides a possible space for the insertion and extraction of lithium ions. When the interlayer spacing of graphite increases, the channels for lithium ions to diffuse between the layers become more spacious, thereby reducing the resistance encountered by lithium ions during the insertion and extraction process. This means that lithium ions can move faster between graphite layers, increasing the diffusion rate of lithium ions. At the same time, since the widened interlayer spacing provides more diffusion channels for lithium ions, the resistance to the diffusion of lithium ions between the layers is reduced. In addition, the increased interlayer spacing can also effectively reduce the expansion and contraction of the graphite structure during the insertion / extraction of lithium ions, thereby improving the stability and cycle performance of the battery.

[0066] In some specific embodiments, the lithium ion diffusion rate is obtained by constant current intermittent titration technology, and the test temperature can be controlled to decrease from 30°C to -20°C; the lithium ion diffusion energy barrier is obtained by calculating the combined transformation into an AC impedance spectrum.

[0067] In some specific embodiments, the positive electrode material of the lithium-ion battery can be a ternary positive electrode material such as lithium iron phosphate, lithium cobalt oxide or nickel cobalt manganese oxide; the electrolyte in the electrolyte is lithium hexafluorophosphate, and the solvent is a carbonate such as ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0068] In some specific embodiments, the negative electrode of the lithium-ion battery further includes a conductive agent and a binder, wherein the conductive agent includes acetylene black, Super P, Ketjen Black, etc., and the binder includes polyvinylidene fluoride, carboxymethyl cellulose, polyacrylic acid, etc.

[0069] According to an embodiment of the present disclosure, the negative electrode to positive electrode capacity ratio of the lithium ion battery is 1~1.2, for example, it can be 1, 1.1, 1.2, etc., and more preferably 1.05~1.10; the operating temperature of the lithium ion battery is -40℃~30℃, the current density of the lithium ion battery is 0.05C~10C, and the high rate performance test condition of the lithium ion battery is 1C~10C.

[0070] According to the embodiments of the present disclosure, using graphite material with widened interlayer spacing as the negative electrode of the battery is conducive to the rapid transfer of lithium ions from the edge of the graphite to the inside, which can effectively improve the diffusion kinetics of lithium-ion batteries and improve the performance of lithium-ion batteries under low temperature and fast charging conditions. The low temperature range tested is -40℃~0℃. The negative electrode to positive electrode capacity ratio (N / P) of 1~1.2 can make full use of the active materials of the positive and negative electrodes, thereby improving the actual capacity and energy density of the battery.

[0071] It should be noted that the described embodiments are only part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure, other embodiments obtained by ordinary technicians in the field without creative work are all within the scope of protection of the present disclosure.

[0072] Example 1

[0073] Under the protection of argon atmosphere, the multi-layer stacked graphene oxide was first pre-oxidized at 300°C for 2 hours, then subjected to the first heat treatment at 1000°C for 2 hours, and then graphitized at 2900°C. Finally, after crushing and screening, the graphite material with widened interlayer spacing was obtained, and its C / O ratio was 99 / 1~97 / 3. Among them, the number of stacked layers of graphene oxide was 5,000-20,000, and the C / O ratio was 70 / 30~90 / 10.

[0074] The structure and morphology of the graphite material obtained in Example 1 were characterized by transmission electron microscopy.

[0075] Figure 1 This is a transmission electron microscope image (High Resolution Transmission Electron Microscope, HRTEM) of the interlayer spacing widened graphite prepared in Example 1 of the present disclosure.

[0076] like Figure 1 As shown, it can be seen that the bulk lattice spacing of the graphite material is 0.335 nm, while the lattice spacing at the boundary is 0.38 nm.

[0077] The graphite material with widened boundaries obtained in Example 1 was coated with a conductive agent and a binder in a ratio of 8:1:1 to form a film, and assembled into a button-type battery. The lithium ion diffusion rate thereof was tested using a constant current intermittent titration technique.

[0078] Figure 2 , Figure 3 They are curves showing the diffusion rate of the interlayer spacing widened graphite prepared in Example 1 of the present disclosure at 30° C. and −20° C. as a function of the lithium insertion potential.

[0079] like Figure 2 ,3 As shown in the figure, under the test condition of 30℃, the diffusion rate of lithium ions in the lithium insertion process is 10 -8 ~10 -11 cm 2 s -1 Under the test condition of low temperature -20℃, the diffusion rate of lithium ions in the lithium insertion process is 10 -8 ~10 -12 cm 2 s -1 Due to the larger interlayer spacing, the negative electrode material obtained in Example 1 has a higher lithium ion diffusion rate.

[0080] Example 2

[0081] This embodiment provides a graphite negative electrode material with a widened interlayer spacing, which is different from Embodiment 1 only in that the multi-layer stacked graphene oxide (pre-oxidized at 300°C for 2 hours) is first subjected to a low-temperature heat treatment at 900°C for 2 hours and then graphitized at 2800°C to obtain graphite material 2, and the remaining parameters and steps are consistent with Embodiment 1.

[0082] The structure and morphology of the graphite material obtained in Example 2 were characterized by transmission electron microscopy.

[0083] Figure 4 This is a transmission electron microscope image of the interlayer spacing widened graphite prepared in Example 2 of the present disclosure.

[0084] like Figure 4 As shown, it can be seen that the bulk lattice spacing of the graphite material is 0.335 nm, while the lattice spacing at the boundary is 0.41 nm.

[0085] Example 3

[0086] This embodiment provides a graphite negative electrode material with a widened interlayer spacing. The only difference from Embodiment 1 is that the multi-layer stacked graphene oxide (pre-oxidized at 300°C for 2 hours) is first subjected to a low-temperature heat treatment at 800°C for 2 hours and then graphitized at 2700°C. The remaining parameters and steps are consistent with Embodiment 1.

[0087] The structure and morphology of the graphite material obtained in Example 3 were characterized by transmission electron microscopy.

[0088] Figure 5 This is a transmission electron microscope image of the interlayer spacing widened graphite prepared in Example 3 of the present disclosure.

[0089] like Figure 5 As shown, it can be seen that the bulk lattice spacing of the graphite material is 0.335, while the lattice spacing at the boundary is 0.41 nm.

[0090] Example 4

[0091] This embodiment provides a graphite negative electrode material with a widened interlayer spacing. The only difference from Embodiment 1 is that the multi-layer stacked graphene oxide (pre-oxidized at 300°C for 2 hours) is first subjected to a low-temperature heat treatment at 700°C for 2 hours and then graphitized at 2600°C. The remaining parameters and steps are consistent with Embodiment 1.

[0092] Theoretical calculation simulation and variable temperature AC impedance test were carried out on graphite materials with different lattice spacing.

[0093] Figure 6 Diffusion energy barrier diagram of graphite with different lattice spacing prepared in the embodiments of the present disclosure.

[0094] like Figure 6 As shown, when the lattice spacing is between 3.5-4.0, the larger the boundary layer spacing, the lower the diffusion energy barrier of lithium ions.

[0095] Comparative Example 1

[0096] This comparative example provides a graphite negative electrode material with a widened interlayer spacing, which differs from Example 1 in that the multi-layer stacked graphene oxide (the number of stacked layers is 5,000-20,000) is replaced by a few-layer stacked graphene oxide, the number of stacked layers is 1,000-5,000, and the other parameters and steps are consistent with Example 1.

[0097] Figure 7 This is a transmission electron microscope image of graphite with widened interlayers prepared in the comparative example of the present disclosure.

[0098] As shown in the figure, it can be seen that the bulk lattice spacing of the graphite material is 0.335 nm, while the lattice spacing at the boundary is 0.348 nm. It can be seen that when the number of stacking layers of the raw material graphene oxide is too small, it is not conducive to lattice widening.

[0099] Performance Testing

[0100] The graphite material with widened border obtained in Example 1 was mixed with a conductive agent (SP) and a binder (PVDF) in a mass ratio of 8:1:1 to form a slurry, and then coated into a pole piece with a thickness of about 250±10 μm. The prepared pole piece had a loading of about 2.0±0.1 mg / cm 2 .

[0101] It was used as the negative electrode and assembled into a button-type full battery with ternary nickel cobalt manganese oxide or lithium cobalt oxide to evaluate its electrochemical performance. The electrolyte was 1M LiPF6 / EC:EMC:DMC (1:1:1) provided by Tianci Materials, and the diaphragm was Celgard polypropylene diaphragm. The assembly process was carried out in a Braun glove box to ensure that the ratio of oxygen and water was less than 0.1ppm. The battery test was carried out using the Xinwei battery test system or the Blue Power battery test system.

[0102] Figure 8 This is a capacity comparison chart of a full battery composed of interlayer-widened graphite and ternary NCM obtained in Example 1 of the present disclosure and Comparative Example 1.

[0103] like Figure 8 As shown, the full battery performance capacity composed of a graphite negative electrode with a boundary layer spacing of 0.38nm and ternary nickel cobalt manganese oxide lithium is the best. It is verified that the graphene oxide material needs to have a certain number of stacked layers to ensure that its interlayer spacing is stably widened after heat treatment.

[0104] Fig. 9 The high rate performance diagram of the full battery composed of graphite and ternary NCM with widened interlayer spacing obtained in Example 1 of the present disclosure, Fig.10 The cycle performance diagram of the full battery composed of graphite and ternary NCM with widened interlayer spacing obtained in Example 1 of the present disclosure, Fig.11 The charge and discharge curves of the full battery composed of interlayer-widened graphite and ternary NCM obtained in Example 1 of the present disclosure at different test temperatures.

[0105] like Fig. 9 As shown in Figure 2, the specific capacity retention rates at 2C, 5C and 10C rates are 94%, 87.2% and 78.3%. Fig.10 As shown in Figure 2, the cycle stability of the full battery is about 90% to 99%. Fig.11 As shown, the results of the low-temperature performance test of the full battery showed excellent performance: at 0°C, -20°C, -30°C and -40°C, the capacity remained at 96.9%, 87.5%, 77.0% and 51.8% of that at room temperature.

[0106] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A graphite material with widened interlayer spacing, characterized in that: The interlayer spacing at the boundary within the graphite material crystal is 0.36-0.41 nanometers.

2. The graphite material according to claim 1, wherein The particle size of the graphite material is 5-10 microns.

3. The graphite material according to claim 1, wherein The bulk interlayer spacing in the crystal of the graphite material is 0.335-0.34 nanometers, and the oxygen content of the graphite material is 1%-3%.

4. A method for preparing a graphite material as claimed in any one of claims 1 to 3, comprising: In an inert gas atmosphere, heat-treating the multi-layer stacked graphene oxide so that the graphene oxide is transformed into a graphite phase and the interlayer spacing at the crystal boundary of the graphite phase is widened to 0.36-0.41 nanometers; Then the graphite phase is crushed and granulated to obtain a graphite material with widened interlayer spacing.

5. The preparation method according to claim 4, wherein The step of heat treating graphene oxide comprises: Performing a first heat treatment on the graphene oxide to decompose and remove oxygen-containing groups in the graphene oxide; Performing a second heat treatment on the multilayer graphene oxide to promote carbon atom hybridization and form an ordered graphite phase layered structure; The temperature of the second heat treatment is higher than the temperature of the first heat treatment.

6. The preparation method according to claim 5, wherein: In the first heat treatment, the heating temperature is 600-1000° C.; In the second heat treatment, the heating temperature is 2000-3000°C.

7. The preparation method according to claim 4, wherein The oxygen content of the graphene oxide is 1%-5%, and the number of layers of the graphene oxide is 0.5-20,000.

8. A lithium ion battery, characterized in that: The negative electrode surface of the lithium ion battery is coated with the graphite material according to claim 1 or 2, or the graphite material obtained by the preparation method according to any one of claims 4 to 7.

9. The lithium ion battery according to claim 8, wherein: The lithium ion diffusion rate of the negative electrode is 10 -8 ~10 -12 cm 2 s -1 , the lithium ion diffusion energy barrier of the negative electrode is 0.14 eV~0.01 eV.

10. The lithium ion battery according to claim 8, wherein: The negative electrode and positive electrode capacity ratio of the lithium ion battery is 1 to 1.2; The operating temperature of the lithium ion battery is -40°C to 30°C.

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