A modified graphite material and its preparation method and application

Abstract

The present invention provides a modified graphite material, a preparation method and an application thereof. The preparation method comprises the following steps: mixing a graphite material, an additive and a dispersant by ball milling to obtain a ball mill material; the additive comprises a metal salt; and sintering the ball mill material to obtain the modified graphite material. The preparation method of the present invention is not only simple in process, but also can increase the interlayer spacing of the graphite material and can also incorporate other elements, so that the specific surface area of ​​the obtained modified graphite material is increased without significantly changing the particle size, and the mass specific capacity and rate capability can be significantly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries and relates to a modified graphite material and a preparation method and application thereof. Background Art

[0002] As a stable energy storage device, lithium-ion batteries are currently widely used in all aspects of social life. Graphite, as the most commercially used material in lithium-ion battery negative electrode materials, has the advantages of high specific capacity, stable charge and discharge platform, and cheap and widely available raw materials. However, in order to meet the development requirements of negative electrode materials in the future, the theoretical specific capacity and rate performance of graphite negative electrodes need to be further improved. In the existing technology, modification research on graphite negative electrode materials is carried out to improve their electrochemical properties. The modification directions include surface modification (surface coating and surface oxidation, etc.), structural modification (etching, preparation of expanded graphite and graphene, etc.) and doping modification. The above modification methods have significantly improved the capacity, rate and first coulombic efficiency of graphite negative electrodes.

[0003] For example, CN 112374552A discloses a composite modified graphite negative electrode material and a preparation method thereof. The method first involves mixing and stirring a graphite oxidizing agent (permanganate) and an expanding agent (acid) to obtain an intercalation product. The intercalation product is then washed to a certain degree, dried, and then calcined under certain conditions to obtain a target product. The resulting product is a manganese oxide-loaded sulfur-free expanded graphite. Although this material can improve its specific capacity and rate performance, the use of strong oxidizing agents and acids increases the difficulty and complexity of actual production, making it unsuitable for large-scale industrial production.

[0004] For example, CN 114853004A discloses a negative electrode material, a preparation method, and an application thereof, wherein porous graphite is prepared by a template method, including the following steps: S1: mixing a template agent with graphite to prepare a template agent-graphite intercalation compound; S2: microwave-treating the template agent-graphite intercalation compound to obtain a metal oxide-graphite intercalation compound; and S3: mixing the metal oxide-graphite intercalation compound with an acid to obtain a target product. The resulting product has increased capacity and reduced initial irreversible capacity, but the initial coulombic efficiency is still low, and the complex preparation process increases the difficulty and cost of actual production.

[0005] Based on the above research, it is necessary to provide a method for preparing a modified graphite material, which has low cost, simple process, can be produced on a large scale industrially, and the obtained modified graphite material has high capacity and excellent rate performance. Summary of the Invention

[0006] The object of the present invention is to provide a modified graphite material and a preparation method and application thereof. The preparation method is not only simple in process and can increase the interlayer spacing of the graphite material, but also can incorporate other elements, so that the obtained modified graphite material has an increased specific surface area without significantly changing the particle size, and the mass specific capacity and rate performance can be significantly improved.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a modified graphite material, the preparation method comprising the following steps:

[0009] (1) ball-milling the graphite material, the additive, and the dispersant to obtain a ball-milled material;

[0010] The additives include metal salts;

[0011] (2) Sintering the ball mill material of step (1) to obtain the modified graphite material.

[0012] The preparation method of the present invention is low in cost and easy to operate. The modified graphite material can be obtained by wet-mixing graphite and additives by ball milling in a dispersant and then sintering. The use of the additives can introduce hetero elements and increase the graphite interlayer spacing. The ball milling can not only roughen the graphite surface, but also reduce the particle size of the additives, so that the contact between the graphite and additive particles is more complete, which is beneficial to the uniformity of the modified graphite and also promotes the embedding of hetero elements into the graphite interlayer. Therefore, the present invention can not only increase the lithium storage position through the synergistic effect of ball milling treatment and element doping, but also promote the embedding of hetero atoms into the graphite interlayer. The embedding of hetero atoms increases the graphite interlayer spacing and ion transfer rate, and improves the capacity and rate performance of the graphite. The particle size of the obtained modified graphite material does not change significantly, but the specific surface area increases. With the incorporation of hetero elements, the mass specific capacity and rate performance are significantly improved.

[0013] Preferably, the metal salt in step (1) comprises a potassium salt.

[0014] Preferably, the potassium salt comprises any one or a combination of at least two of KCl, K2CO3, KHCO3, KNO3 or K2SO4, typical but non-limiting combinations include a combination of KCl and K2CO3, or a combination of KHCO3 and KNO3, preferably KNO3 and / or K2SO4.

[0015] The present invention adopts potassium salt as an additive to achieve potassium doping. Compared with other metal elements, potassium doping can increase the distance between graphite layers, which is beneficial to the rapid deintercalation of lithium ions.

[0016] At the same time, the potassium salt of the present invention preferably uses KNO3 and / or K2SO4. When KNO3 and / or K2SO4 are used, N and / or S elements can be doped at the same time, thereby further improving the performance of the modified graphite material.

[0017] Preferably, the mass ratio of the graphite material and the additive in step (1) is 1:(0.01-0.1); for example, it can be 1:0.01, 1:0.03, 1:0.05, 1:0.07, 1:0.09 or 1:0.1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] The mass ratio of the graphite material and the additive in the present invention is within a reasonable range, and a reasonable content of potassium can be incorporated. If the mass of the additive is relatively excessive, it will affect the structural stability of the graphite and the capacity of the negative electrode. If the mass of the additive is relatively small, there will be no obvious modification effect.

[0019] Preferably, the mass ratio of the graphite material to the dispersant in step (1) is 1:(0.5-1), for example, it can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] Preferably, the dispersant in step (1) comprises ethanol and / or acetone.

[0021] The dispersant of the present invention uses a solvent that is insoluble in potassium salt, which can play a good dispersing role during the ball milling process, so that the potassium salt can be evenly dispersed on the graphite surface and embedded in the interlayer. If a solvent that can dissolve potassium salt, such as water, is used, it is difficult to evenly disperse the potassium salt during ball milling, and it is also difficult to embed the potassium salt in the graphite interlayer. In addition, during subsequent drying, the potassium salt will recrystallize and agglomerate on the graphite surface, resulting in the potassium salt being unable to be evenly dispersed on the graphite surface, which is not conducive to the embedding of potassium ions in the graphite interlayer.

[0022] Preferably, the ball milling beads used in the ball milling in step (1) include zirconium beads.

[0023] Preferably, the mass ratio of the zirconium beads to the graphite material in step (1) is (3-20):1, for example, 3:1, 5:1, 10:1, 15:1 or 20:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] Preferably, the zirconium beads include large zirconium beads, medium zirconium beads and small zirconium beads in a quantity ratio of 1:(2-7):(8-20), for example, it can be 1:2:8, 1:5:10, 1:7:15 or 1:7:20, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] During ball milling, the present invention uses large zirconium beads, medium zirconium beads and small zirconium beads within a reasonable amount range to roughen the surface of the graphite, which is beneficial for the additive to enter the graphite interlayer, thereby achieving an excellent dispersion effect. At the same time, it can also ensure that the particle size of the graphite material does not change significantly, thereby avoiding graphite crushing.

[0026] The zirconium beads described in the present invention are zirconium oxide beads.

[0027] Preferably, the diameter of the large zircon beads is 8-11 mm, for example, 8 mm, 9 mm, 10 mm or 11 mm; the diameter of the medium zircon beads is 5-7 mm, for example, 5 mm, 6 mm or 7 mm; the diameter of the small zircon beads is 2-4 mm, for example, 2 mm, 3 mm or 4 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, the ball milling speed in step (1) is 150-300 r / min, for example, it can be 150 r / min, 175 r / min, 200 r / min, 225 r / min, 250 r / min, 275 r / min or 300 r / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] Preferably, the ball milling time in step (1) is 3-25 h, for example, 3 h, 5 h, 10 h, 15 h, 20 h or 25 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] The rotation speed and time of the ball milling described in the present invention will affect the properties of the modified graphite material obtained. If the ball milling speed is too high or the ball milling time is too long, the graphite will be severely crushed, thereby seriously increasing the specific surface area and reducing the initial coulomb efficiency. If the ball milling speed is too low or the ball milling time is too short, the dispersion effect cannot be guaranteed.

[0031] Preferably, the particle size D50 of the graphite material in step (1) is 5-20 μm, for example, 5 μm, 10 μm, 15 μm or 20 μm, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 8-20 μm.

[0032] Preferably, drying is performed before sintering in step (2).

[0033] The drying temperature of the present invention is determined according to the boiling point of the dispersant.

[0034] Preferably, the sintering temperature in step (2) is 400-1000°C, for example, it can be 400°C, 500°C, 600°C, 700°C, 800°C, 900°C or 1000°C, and the time is 3-7h, for example, it can be 3h, 4h, 5h, 6h or 7h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] Preferably, the heating rate of the sintering in step (2) is 5-10°C / min, for example, it can be 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] The sintering conditions of the present invention will also affect the properties of the modified graphite material. If the sintering temperature and time are unreasonable, it will be unfavorable for embedding. If the sintering rate is unreasonable, it will cause the potassium salt to decompose rapidly, affecting the embedding effect.

[0037] Preferably, the sintering in step (2) is carried out in a protective atmosphere.

[0038] Preferably, the protective atmosphere comprises any one of nitrogen, argon, helium or krypton, or a combination of at least two of them.

[0039] The sintering of the present invention is carried out in a porcelain ark which does not react with potassium salt.

[0040] Preferably, after the sintering in step (2), washing, filtering and drying steps are also performed.

[0041] Preferably, the washing is performed with deionized water.

[0042] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises the following steps:

[0043] (1) ball milling the additive, dispersant, and graphite material with a particle size D50 of 8-20 μm using zirconium beads at a speed of 150-300 r / min for 3-25 hours to obtain a ball mill material;

[0044] The additive includes potassium salt, the mass ratio of the graphite material to the additive is 1:(0.01-0.1), the mass ratio of the graphite material to the dispersant is 1:(0.5-1), and the mass ratio of the zirconium beads to the graphite material is (3-20):1;

[0045] The zirconium beads include large zirconium beads, medium zirconium beads and small zirconium beads in a quantity ratio of 1:(2-7):(8-20);

[0046] (2) drying the ball mill material of step (1), and then sintering it at 400-1000° C. for 3-7 h at a heating rate of 5-10° C. / min under a protective atmosphere, and then washing, filtering and drying to obtain the modified graphite material.

[0047] In a second aspect, the present invention provides a modified graphite material, which is prepared by the preparation method described in the first aspect.

[0048] In a third aspect, the present invention provides a battery, comprising the modified graphite material as described in the second aspect.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The present invention enables potassium salt to be embedded in the layers of graphite material through ball milling, thereby achieving potassium doping, and making the ball milling treatment and element doping play a synergistic role, which not only increases the lithium storage position, but also promotes the embedding of heteroatoms between graphite layers. The embedding of heteroatoms increases the graphite layer spacing and ion transmission rate, improves the capacity and rate performance of graphite, and does not significantly change the particle size of the obtained modified graphite material, but increases the specific surface area. With the incorporation of heteroelements, the mass specific capacity and rate performance are significantly improved. At the same time, the present invention can make the surface of the graphite material rough by strictly controlling the ball milling conditions, so that the graphite material and the additive can be fully contacted and dispersed, and it can also ensure that the graphite material will not be seriously broken and the particle size of the graphite material will not change significantly, but can increase the specific surface area. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a flow chart of the preparation method described in Example 1 of the present invention;

[0052] Figure 2 This is a SEM image of the graphite raw material in Example 1 of the present invention;

[0053] Figure 3 This is an SEM image of the modified graphite material described in Example 1 of the present invention;

[0054] Figure 4 This is a mapping diagram of the C element in the modified graphite material described in Example 1 of the present invention;

[0055] Figure 5 This is a mapping diagram of the O element in the modified graphite material described in Example 1 of the present invention;

[0056] Figure 6 This is a mapping diagram of the K element in the modified graphite material described in Example 1 of the present invention;

[0057] Figure 7This is an SEM image of the modified graphite material described in Example 2 of the present invention;

[0058] Figure 8 This is a rate performance diagram of the modified graphite materials described in Examples 1 and 4 of the present invention and the graphite raw material in Example 1;

[0059] Figure 9 The XRD patterns of the modified graphite material (modified sample) and the graphite raw material described in Example 5 of the present invention are as follows;

[0060] Figure 10 This is an enlarged view of the XRD pattern of the modified graphite material (modified sample) and the graphite raw material described in Example 5 of the present invention;

[0061] Figure 11 This is an SEM image of the modified graphite material described in Example 6 of the present invention;

[0062] Figure 12 This is the SEM image of the modified graphite material described in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0063] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0064] Example 1

[0065] This embodiment provides a method for preparing a modified graphite material. The flow chart of the preparation method is as follows: Figure 1 As shown, the preparation method comprises the following steps:

[0066] (1) Additives, dispersants, and graphite material with a particle size D50 of 15 μm were ball-milled using zirconium beads at a speed of 150 r / min for 5 h to obtain a ball-milled material;

[0067] Wherein, the additive is KCl, the dispersant is ethanol, the mass ratio of the graphite material to the additive is 1:0.05, the mass ratio of the graphite material to the dispersant is 1:0.5, and the mass ratio of the zirconium beads to the graphite material is 4:1;

[0068] The zircon beads include large zircon beads, medium zircon beads and small zircon beads in a quantity ratio of 1:2:8, the diameter of the large zircon beads is 8 mm, the diameter of the medium zircon beads is 5 mm, and the diameter of the small zircon beads is 2 mm;

[0069] (2) drying the ball mill material of step (1) at 80° C., sintering the ball mill material at 1000° C. for 4 h at a heating rate of 10° C. / min under an argon atmosphere, washing the ball mill material with deionized water, filtering the ball mill material and drying the ball mill material to obtain the modified graphite material;

[0070] The graphite material in step (1) of this embodiment is a graphite raw material, and its SEM image is as follows Figure 2 As shown in the figure, the rate performance diagram is as follows Figure 8 As shown, the SEM image of the modified graphite material is as follows Figure 3 As shown, the mapping diagram of the C element is as follows Figure 4 As shown, the mapping diagram of O element is as follows Figure 5 As shown, the mapping diagram of K elements is as follows Figure 6 As shown, the rate performance diagram of the modified graphite material is shown in Figure 8 shown.

[0071] Example 2

[0072] This embodiment provides a method for preparing a modified graphite material, the preparation method comprising the following steps:

[0073] (1) Additives, dispersants, and graphite material with a particle size D50 of 8 μm were ball-milled using zirconium beads at a speed of 300 r / min for 5 h to obtain a ball-milled material;

[0074] Wherein, the additive is KNO3, the dispersant is ethanol, the mass ratio of the graphite material to the additive is 1:0.02, the mass ratio of the graphite material to the dispersant is 1:2 / 3, and the mass ratio of the zirconium beads to the graphite material is 4:1;

[0075] The zircon beads include large zircon beads, medium zircon beads and small zircon beads in a quantity ratio of 1:2.5:9, the diameter of the large zircon beads is 11 mm, the diameter of the medium zircon beads is 7 mm, and the diameter of the small zircon beads is 4 mm;

[0076] (2) drying the ball mill material of step (1) at 100° C., sintering the ball mill material at 700° C. for 3 h at a heating rate of 6° C. / min under an argon atmosphere, washing the ball mill material with deionized water, filtering the ball mill material and drying the ball mill material to obtain the modified graphite material;

[0077] The SEM image of the modified graphite material in this embodiment is as follows: Figure 7 shown.

[0078] Example 3

[0079] This embodiment provides a method for preparing a modified graphite material, the preparation method comprising the following steps:

[0080] (1) Additives, dispersants, and graphite material with a particle size D50 of 15 μm were ball-milled at a speed of 150 r / min for 25 h to obtain a ball-milled material;

[0081] Wherein, the additive is KCl, the dispersant is acetone, the mass ratio of the graphite material to the additive is 1:0.01, the mass ratio of the graphite material to the dispersant is 1:1, and the mass ratio of the zirconium beads to the graphite material is 20:1;

[0082] The zircon beads include large zircon beads, medium zircon beads and small zircon beads in a quantity ratio of 1:7:20, the diameter of the large zircon beads is 8 mm, the diameter of the medium zircon beads is 5 mm, and the diameter of the small zircon beads is 2 mm;

[0083] (2) The ball mill material of step (1) is dried at 60° C., and then sintered at 1000° C. for 3 h at a heating rate of 6° C. / min under an argon atmosphere, and then washed with deionized water, filtered and dried to obtain the modified graphite material.

[0084] Example 4

[0085] This embodiment provides a method for preparing a modified graphite material, the preparation method comprising the following steps:

[0086] (1) Additives, dispersants, and graphite material with a particle size D50 of 20 μm were ball-milled at a speed of 200 r / min for 3 h to obtain a ball-milled material;

[0087] Wherein, the additive is KNO3, the dispersant is ethanol, the mass ratio of the graphite material to the additive is 1:0.03, the mass ratio of the graphite material to the dispersant is 1:0.5, and the mass ratio of the zirconium beads to the graphite material is 4:1;

[0088] The zircon beads include large zircon beads, medium zircon beads and small zircon beads in a quantity ratio of 1:4:9, the diameter of the large zircon beads is 8 mm, the diameter of the medium zircon beads is 5 mm, and the diameter of the small zircon beads is 2 mm;

[0089] (2) drying the ball mill material of step (1) at 80° C., sintering the ball mill material at 700° C. for 3 h at a heating rate of 10° C. / min under an argon atmosphere, washing the ball mill material with deionized water, filtering the ball mill material and drying the ball mill material to obtain the modified graphite material;

[0090] The rate performance diagram of the modified graphite material in this embodiment is as follows: Figure 8 shown.

[0091] Example 5

[0092] This embodiment provides a method for preparing a modified graphite material, the preparation method comprising the following steps:

[0093] (1) Additives, dispersants, and graphite material with a particle size D50 of 15 μm were ball-milled at a speed of 150 r / min for 25 h to obtain a ball-milled material;

[0094] Wherein, the additive is K2CO3, the dispersant is ethanol, the mass ratio of the graphite material to the additive is 1:0.05, the mass ratio of the graphite material to the dispersant is 1:0.5, and the mass ratio of the zirconium beads to the graphite material is 4:1;

[0095] The zircon beads include large zircon beads, medium zircon beads and small zircon beads in a quantity ratio of 1:2.5:8, the diameter of the large zircon beads is 8 mm, the diameter of the medium zircon beads is 5 mm, and the diameter of the small zircon beads is 2 mm;

[0096] (2) drying the ball mill material of step (1) at 80° C., sintering the ball mill material at 400° C. for 4 h at a heating rate of 5° C. / min under an argon atmosphere, washing the ball mill material with deionized water, filtering the ball mill material and drying the ball mill material to obtain the modified graphite material;

[0097] The graphite material in step (1) of this embodiment is graphite raw material. The XRD patterns of the modified graphite material and the graphite raw material are as follows: Figure 9 The enlarged view of the XRD pattern is shown in Figure 10 shown.

[0098] Example 6

[0099] This embodiment provides a method for preparing a modified graphite material, the preparation method comprising the following steps:

[0100] (1) Additives, dispersants, and graphite material with a particle size D50 of 8 μm were ball-milled using zirconium beads at a speed of 300 r / min for 10 h to obtain a ball-milled material;

[0101] Wherein, the additive is K2CO3, the dispersant is acetone, the mass ratio of the graphite material to the additive is 1:0.1, the mass ratio of the graphite material to the dispersant is 1:1, and the mass ratio of the zirconium beads to the graphite material is 4:1;

[0102] The zircon beads include large zircon beads, medium zircon beads and small zircon beads in a quantity ratio of 1:2.5:8, the diameter of the large zircon beads is 8 mm, the diameter of the medium zircon beads is 5 mm, and the diameter of the small zircon beads is 2 mm;

[0103] (2) drying the ball mill material of step (1) at 80° C., sintering the ball mill material at 400° C. for 4 h at a heating rate of 5° C. / min under an argon atmosphere, washing the ball mill material with deionized water, filtering the ball mill material and drying the ball mill material to obtain the modified graphite material;

[0104] The SEM image of the modified graphite material in this embodiment is as follows: Figure 11 shown.

[0105] Example 7

[0106] This embodiment provides a method for preparing a modified graphite material. The preparation method is the same as that of Example 1 except that the mass of KCl in step (1) is replaced by MgCl2.

[0107] Example 8

[0108] This embodiment provides a method for preparing a modified graphite material. The preparation method is the same as that of Example 1 except that the mass of KCl in step (1) is replaced by AlCl3.

[0109] Example 9

[0110] This embodiment provides a method for preparing a modified graphite material. The preparation method is the same as that of Example 1 except that the mass of KCl in step (1) is replaced by KNO3.

[0111] Example 10

[0112] This embodiment provides a method for preparing a modified graphite material. The preparation method is the same as that of Example 1, except that the mass ratio of the graphite material to the additive in step (1) is 1:0.005.

[0113] Example 11

[0114] This embodiment provides a method for preparing a modified graphite material. The preparation method is the same as that of Example 1, except that the mass ratio of the graphite material to the additive in step (1) is 1:0.15.

[0115] Example 12

[0116] This embodiment provides a method for preparing a modified graphite material. The preparation method is the same as that of Example 1, except that in step (1), only large zirconium beads with a diameter of 8 mm are used.

[0117] Example 13

[0118] This embodiment provides a method for preparing a modified graphite material. The preparation method is the same as that of Example 1, except that the zirconium beads in step (1) only use medium zirconium beads with a diameter of 5 mm.

[0119] Example 14

[0120] This embodiment provides a method for preparing a modified graphite material. The preparation method is the same as that of Example 1, except that in step (1), only small zirconium beads with a diameter of 2 mm are used.

[0121] Example 15

[0122] This embodiment provides a method for preparing a modified graphite material. The preparation method is the same as that of Example 1 except that the rotation speed of the ball mill in step (1) is 100 r / min.

[0123] Example 16

[0124] This embodiment provides a method for preparing a modified graphite material. The preparation method is the same as that of Example 1 except that the rotation speed of the ball mill in step (1) is 400 r / min.

[0125] Example 17

[0126] This embodiment provides a method for preparing a modified graphite material. The preparation method is the same as that of Example 1 except that the dispersant in step (1) is water.

[0127] Comparative Example 1

[0128] This comparative example provides a method for preparing a modified graphite material. The preparation method is the same as Example 1 except that no additive is added in step (1).

[0129] Comparative Example 2

[0130] This comparative example provides a method for preparing a modified graphite material, which is the same as Example 1 except that the additive, dispersant and graphite material in step (1) are directly stirred and mixed for 5 hours;

[0131] The SEM image of the modified graphite material in this comparative example is as follows: Figure 12 shown.

[0132] Comparative Example 3

[0133] This comparative example provides a method for preparing a modified graphite material, which is the same as Example 1 except that no dispersant is added in step (1);

[0134] The modified graphite materials obtained in the above examples and comparative examples were subjected to ICP testing using PerkinElmer to obtain the potassium content, XRD testing using an X-ray diffractometer (Malvern Panalytical), specific surface area testing using Quantachrome, and surface morphology testing using SEM testing using Thermo Fisher Scientific. The modified graphite materials obtained in the above examples and comparative examples were made into 2032 button half-cells, and the electrochemical performance was tested using a blue electric test system.

[0135] The button half-cell production process is as follows: the modified graphite material and graphite raw material obtained in the above embodiments and comparative examples are mixed with conductive carbon and polyvinylidene fluoride (PVDF) in a mass ratio of 92:3:5, and then an appropriate amount of N-methylpyrrolidone (NMP) is added and stirred into a uniform slurry. After mixing evenly, the slurry is applied to a copper foil current collector, and then dried, rolled and sliced. The button half-cell is assembled in an argon-filled glove box, with a metal lithium sheet as the counter electrode, an electrolyte of 1 mol / L LiPF6+EC+DMC, and a diaphragm of a polypropylene composite microporous membrane. The capacity first effect and rate tests are performed on a battery tester, with a charge and discharge voltage range of 0.001-2V and a charge and discharge rate of 0.1C, 0.2C, 1C and 2C.

[0136] The test results are shown in Table 1:

[0137] Table 1

[0138]

[0139]

[0140] From Table 1, we can see the following points:

[0141] (1) The modified graphite material provided by the present invention has a larger interlayer spacing and Figure 6 It can be seen that the graphite material is successfully doped with potassium, the specific surface area is of appropriate size, and the capacity, first efficiency and rate performance are significantly improved; it can be seen from Example 1 and Examples 7-8 that the preferred doping element of the present invention is K, and the electrochemical properties of the modified graphite material obtained can be significantly improved compared with other metal elements; it can be seen from Example 1 and Example 9 that when potassium nitrate is used as an additive, N element can also be added, thereby further improving the electrochemical properties of the modified graphite material obtained; it can be seen from Example 1 and Examples 10-11 that the content of the additive can further improve the electrochemical performance within a reasonable range; it can be seen from Example 1 and Examples 12-14 that the use of an appropriate number of large, medium and small zirconium beads during ball milling can ensure that the graphite surface is rough, but the particle size does not change significantly and the structure is not destroyed, thereby promoting the entry of the additive into the graphite layer.

[0142] (2) As can be seen from Example 1 and Examples 15-16, the rotation speed of ball milling will also affect the morphology and dispersion effect of graphite, and needs to be within a reasonable range; As can be seen from Example 1 and Example 17, the dispersant adopts a solvent that is insoluble in potassium salt, which can play a good dispersing role in the ball milling process. If a solvent such as water that can dissolve potassium salt is adopted, it is difficult to disperse the potassium salt evenly during ball milling, and it is also difficult to embed the potassium salt into the graphite interlayer. Moreover, during subsequent drying, the potassium salt will recrystallize and agglomerate on the graphite surface, resulting in the potassium salt not being able to be evenly dispersed on the graphite surface, which is not conducive to the embedding of potassium ions into the graphite interlayer; As can be seen from Example 1 and Comparative Example 1, no additive is added to Comparative Example 1, the specific surface area increases, the interlayer spacing becomes smaller, and the electrochemical performance decreases; As can be seen from Example 1 and Comparative Example 2, no ball milling is used for mixing, the obtained sample has poor uniformity, a small potassium ion content, a decreased capacity and rate performance, and Figure 12 It can be seen that without ball milling treatment, the graphite surface is relatively smooth, which is not conducive to the contact between the additive and the graphite, and is not conducive to the doping of miscellaneous elements, and the content of the doping elements is reduced; from Example 1 and Comparative Example 3, it can be seen that during dry ball milling, the uniformity of the modified graphite material obtained decreases, which is not conducive to the incorporation of doping elements, and the performance of the obtained material decreases.

[0143] In summary, the present invention provides a modified graphite material, a preparation method and an application thereof. The preparation method is not only simple in process, but also can increase the interlayer spacing of the graphite material, and can also incorporate other elements, so that the obtained modified graphite material has an increased specific surface area without significantly changing the particle size, and the mass specific capacity and rate capability can be significantly improved.

[0144] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a modified graphite material, characterized in that: The preparation method comprises the following steps: (1) ball-milling the graphite material, additives and dispersant to obtain a ball-milled material; The additive comprises a metal salt, and the metal salt comprises KNO3 and / or K2SO4; The rotation speed of the ball mill is 150-300 r / min; The mass ratio of the graphite material to the additive is 1:(0.01-0.1); the ball milling beads used in the ball mill include zirconium beads, and the zirconium beads include large zirconium beads, medium zirconium beads and small zirconium beads with different diameters; The dispersant includes ethanol and / or acetone; (2) Sintering the ball mill material in step (1) to obtain the modified graphite material.

2. The preparation method according to claim 1, characterized in that The mass ratio of the graphite material to the dispersant in step (1) is 1:(0.5-1).

3. The preparation method according to claim 1 or 2, characterized in that The mass ratio of the zirconium beads to the graphite material in step (1) is (3-20):

1.

4. The preparation method according to claim 1 or 2, characterized in that The zirconium beads include large zirconium beads, medium zirconium beads and small zirconium beads in a quantity ratio of 1:(2-7):(8-20).

5. The preparation method according to claim 1 or 2, characterized in that The diameter of the large zircon beads is 8-11 mm, the diameter of the medium zircon beads is 5-7 mm, and the diameter of the small zircon beads is 2-4 mm.

6. The preparation method according to claim 1, characterized in that The ball milling time in step (1) is 3-25h.

7. The preparation method according to claim 1 or 2, characterized in that The particle size D50 of the graphite material in step (1) is 5-20 μm.

8. The preparation method according to claim 7, characterized in that The particle size D50 of the graphite material in step (1) is 8-20 μm.

9. The preparation method according to claim 1, characterized in that In step (2), drying is also performed before sintering.

10. The preparation method according to claim 1, characterized in that The sintering temperature in step (2) is 400-1000°C and the sintering time is 3-7h.

11. The preparation method according to claim 1, characterized in that The heating rate of the sintering in step (2) is 5-10°C / min.

12. The preparation method according to claim 1, characterized in that The sintering in step (2) is carried out in a protective atmosphere.

13. The preparation method according to claim 12, characterized in that The protective atmosphere includes any one of nitrogen, argon, helium or krypton, or a combination of at least two of them.

14. The preparation method according to claim 1, characterized in that After the sintering in step (2), washing, filtration and drying steps are also carried out.

15. The preparation method according to claim 1, characterized in that The preparation method comprises the following steps: (1) Additives, dispersants and graphite material with a particle size D50 of 8-20 μm are ball-milled using zirconium beads at a speed of 150-300 r / min for 3-25 hours to obtain ball-milled material; The additive includes potassium salt, and the potassium salt includes KNO3 and / or K2SO4. The mass ratio of the graphite material to the additive is 1:(0.01-0.1), the mass ratio of the graphite material to the dispersant is 1:(0.5-1), and the mass ratio of the zirconium beads to the graphite material is (3-20):

1. The zirconium beads include large zirconium beads, medium zirconium beads and small zirconium beads in a quantity ratio of 1:(2-7):(8-20); The dispersant includes ethanol and / or acetone; (2) The ball mill material of step (1) is dried, and then sintered at 400-1000°C for 3-7h at a heating rate of 5-10°C / min under a protective atmosphere, and then washed, filtered and dried to obtain the modified graphite material.

16. A modified graphite material, characterized in that: The modified graphite material is prepared by the preparation method according to any one of claims 1 to 15.

17. A battery, characterized in that: The battery comprises the modified graphite material according to claim 16.

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