Negative electrode material and its preparation method and application, negative electrode sheet and application

Abstract

The present invention relates to the field of carbon materials, and discloses a negative electrode material and a preparation method and application thereof, and a negative electrode sheet and application thereof. The negative electrode material has the following characteristics: (1) the total pore volume of the negative electrode material is ≤0.02 cm 3 / g, and the mesopore volume with a pore size of 2-50 nm is 0.0001-0.02 cm 3 / g; (2) the height ratio of the D peak and the G peak obtained by Raman spectroscopy of the negative electrode material satisfies the following condition: 0.20≤ID / IG≤1. The negative electrode material has high structural density and small grain size, so that the battery containing the negative electrode material not only has high charge and discharge capacity, high first coulomb efficiency, and excellent rate performance, but also has excellent continuous high rate cycle performance, and the preparation method is simple and low in cost.

Description

Technical Field

[0001] The present invention relates to the field of carbon materials, and in particular to a negative electrode material and a preparation method and application thereof, and a negative electrode sheet and application thereof. Background Art

[0002] The negative electrode of lithium-ion batteries is mainly made of carbon materials, including amorphous carbon, natural graphite and artificial graphite. Graphite has a regular layered structure and excellent conductivity. Its theoretical specific capacity is 372mA·h / g and it has high efficiency. It is the current mainstream negative electrode material. At present, there are three main types of raw materials for developing artificial graphite: isotropic coke, asphalt glue and needle coke. Isotropic coke-based artificial graphite has low crystallinity, high isotropy, low capacity and high power. Needle coke-based artificial graphite has high capacity and relatively poor magnification. Asphalt glue is generally between the two.

[0003] CN104681786A discloses a coal-based negative electrode material. The coal-based negative electrode material is composed of a graphitized inner layer of the coal-based material, an intermediate layer, and an outer layer distributed on the surface. The preparation method thereof includes: pulverizing the coal-based material; adding a binder, or mixing a binder and a modifier; and then pressing and high-temperature graphitizing to make a finished product.

[0004] CN111232970A discloses a graphite negative electrode material, a lithium ion battery, a preparation method and an application. The preparation method comprises the following steps: subjecting a mixture of mesophase carbon microspheres, anthracite powder and a catalyst to graphitization at high temperature; wherein the mass ratio of the mesophase carbon microspheres to the anthracite powder is 1:9-8:1; the particle size D of the anthracite powder is 50 10-20μm.

[0005] CN111628146A discloses a process for preparing negative electrode materials for lithium-ion batteries by using asphalt-filled microcrystalline graphite. The process comprises the following steps: using microcrystalline graphite as raw material, adding medium-low temperature coal tar to mix and kneading to obtain modified microcrystalline graphite; transferring the modified microcrystalline graphite into a reaction kettle, adding liquid medium-temperature asphalt to mix, heating to 350-500°C, evacuating and letting stand for 1-3 hours, then filling with inert gas, pressurizing and letting stand for 2-5 hours, and releasing the pressure to obtain asphalt-filled microcrystalline graphite; and then subjecting the asphalt-filled microcrystalline graphite to sheet rolling, powdering, carbonization, screening and demagnetization to obtain the target product.

[0006] The structure and process of the negative electrode materials provided by the above-mentioned prior art are complex and costly, and although the prepared negative electrode materials can provide higher battery capacity and initial coulombic efficiency, the battery's continuous high-rate cycle performance is insufficient and cannot meet the actual needs of the market. Summary of the invention

[0007] The purpose of the present invention is to overcome the problems of complex structure, poor sustained high-rate cycle performance, complex preparation process and high cost of negative electrode materials in the prior art, and to provide a negative electrode material and its preparation method and application. The negative electrode material has high structural density and small grain size, so that a battery containing the negative electrode material not only has high charge and discharge capacity, high first coulomb efficiency, and excellent rate performance, but also has excellent sustained high-rate cycle performance, and the preparation method is simple and low in cost.

[0008] In order to achieve the above object, the first aspect of the present invention provides a negative electrode material, characterized in that the negative electrode material has the following characteristics:

[0009] (1) The total pore volume of the negative electrode material is ≤ 0.02 cm 3 / g, the mesopore volume with pore size of 2-50nm is 0.00001-0.02cm 3 / g;

[0010] (2) The height ratio of the D peak and the G peak of the negative electrode material obtained by Raman spectroscopy satisfies the following condition: 0.20≤ID / IG≤1.

[0011] A second aspect of the present invention provides a method for preparing a negative electrode material, wherein the method comprises the following steps:

[0012] (1) crushing coal to obtain coal particles;

[0013] (2) graphitizing the coal particles to obtain a graphitized material;

[0014] (3) mixing the graphitized material with a modifier to obtain a mixture;

[0015] (4) pre-oxidizing the mixture under air atmosphere to obtain a pre-oxidized sample;

[0016] (5) Carbonizing the pre-oxidized sample under an inert atmosphere to obtain the negative electrode material.

[0017] The third aspect of the present invention provides a negative electrode material prepared by the above method.

[0018] A fourth aspect of the present invention provides the use of the above-mentioned coal-based negative electrode material in a lithium-ion battery.

[0019] Through the above technical solution, the negative electrode material provided by the present invention and its preparation method and application obtain the following beneficial effects:

[0020] (1) The negative electrode material provided by the present invention has a compact structure and a small grain size, and a battery containing the negative electrode material has excellent continuous high-rate cycle performance.

[0021] (2) The battery containing the negative electrode material provided by the present invention not only has excellent charge and discharge capacity and first coulomb efficiency, but also has excellent continuous high-rate cycle performance. Specifically, the charge and discharge capacity of the negative electrode material of the present invention is ≥330mAh / g, the first coulomb efficiency is ≥92%, the rate performance is excellent, and the capacity retention rate after 1500 continuous high-rate cycles at 5C is ≥80%.

[0022] (3) In the negative electrode material preparation method provided in the present invention, the coal particles are sequentially graphitized, mixed with a modifier, pre-oxidized and carbonized, which can significantly improve the structural density of the obtained negative electrode material. The obtained negative electrode material has a small grain size, multiple channels for lithium ion insertion and extraction, and fast diffusion, thereby significantly improving the continuous high-rate cycle performance of the negative electrode material.

[0023] (4) The negative electrode sheet containing the negative electrode material provided by the present invention has a low OI value. Specifically, when the compaction density of the negative electrode sheet is 1.4-1.6 g / cm 3 When the OI of the negative electrode sheet is ≤15, it indicates that the negative electrode sheet has excellent orientation and high isotropy, so that the battery containing the negative electrode sheet has excellent rate performance and continuous high rate cycle performance. DETAILED DESCRIPTION

[0024] The endpoints and any values ​​of the ranges disclosed in this article 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, which should be considered as specifically disclosed in this article.

[0025] A first aspect of the present invention provides a negative electrode material, characterized in that the negative electrode material has the following characteristics:

[0026] (1) The total pore volume of the negative electrode material is ≤ 0.02 cm 3 / g, and the pore volume of mesopores with a pore size of 2-50nm is 0.00001-0.02cm 3 / g;

[0027] (2) The height ratio of the D peak and the G peak of the negative electrode material obtained by Raman spectroscopy satisfies the following condition: 0.20≤ID / IG≤1;

[0028] In the present invention, the negative electrode material that meets the above conditions has few pores, and the negative electrode material has a dense structure, few defects, and a small grain size, thereby significantly improving the continuous high-rate cycle performance while maintaining a high charge and discharge capacity, first coulomb efficiency, and rate performance.

[0029] In the present invention, the total pore volume of the negative electrode material and the pore volume of mesopores with a pore diameter of 2-50 nm are measured by a nitrogen adsorption specific surface area method.

[0030] Furthermore, when the total pore volume of the negative electrode material is 0.0001-0.01 cm 3 / g, and the pore volume of mesopores with a pore size of 2-50nm is 0.00001-0.01cm 3 / g, the lithium ion battery using the negative electrode material as the negative electrode has high charge and discharge capacity, first coulomb efficiency and rate performance, and has excellent continuous high-rate cycle performance.

[0031] Furthermore, when the total pore volume of the negative electrode material is 0.0002-0.007 cm 3 / g, and the pore volume of mesopores with a pore size of 2-50nm is 0.0001-0.007cm 3 / g, the lithium ion battery using the negative electrode material as the negative electrode has high charge and discharge capacity, first coulomb efficiency and rate performance, and has excellent continuous high-rate cycle performance.

[0032] Furthermore, when the height ratio of the D peak and the G peak of the negative electrode material obtained by Raman spectroscopy satisfies the following conditions: 0.25≤ID / IG≤0.9, preferably 0.30≤ID / IG≤0.8, the lithium ion battery using the negative electrode material as the negative electrode has a high charge and discharge capacity and first coulombic efficiency, and has excellent continuous high-rate cycle performance.

[0033] According to the present invention, the interlayer spacing d of the (002) crystal plane of the negative electrode material obtained by powder XRD is 002 Meet the following conditions: 0.3340nm≤d 002 ≤0.3400nm.

[0034] According to the present invention, the crystallite size L in the c-axis direction of the negative electrode material obtained by powder XRD is c Meet the following conditions: 25nm≤L c ≤70nm.

[0035] According to the present invention, the anode material is obtained by XRD to obtain the crystallite size L in the a-axis direction. a Meet the following conditions: 40nm≤L a ≤150nm.

[0036] In the present invention, the interlayer spacing d of the (002) crystal plane of the negative electrode material is 002 , crystallite size L in the c-axis direction c and the crystallite size L in the a-axis direction a Obtained by performing powder XRD testing on the negative electrode material.

[0037] In the present invention, when the interlayer spacing d of the (002) crystal plane of the negative electrode material is 002 , crystallite size L in the c-axis direction c and the crystallite size L in the a-axis direction a When the above conditions are met, the negative electrode material has the characteristics of small grain size, multiple channels for lithium ion insertion and extraction, and short distance, which can further improve the rate performance of the battery containing the negative electrode material.

[0038] Furthermore, the interlayer spacing d of the (002) crystal plane of the negative electrode material obtained by powder XRD is 002 Meet the following conditions: 0.3350nm≤d 002 ≤0.3390nm, preferably 0.3364nm≤d 002 ≤0.3370nm.

[0039] According to the present invention, the crystallite size L in the c-axis direction of the negative electrode material obtained by powder XRD is c Meet the following conditions: 28nm≤L c ≤60nm, preferably 30nm≤L c ≤50nm.

[0040] According to the present invention, the anode material is obtained by XRD to obtain the crystallite size L in the a-axis direction. a Meet the following conditions: 45nm≤L a ≤120nm, preferably 50nm≤L a ≤100nm.

[0041] According to the present invention, the graphitization degree (G) of the negative electrode material satisfies the following conditions:

[0042] 82≤graphitization degree≤95, preferably 84≤graphitization degree≤91, more preferably 85≤graphitization degree≤90.

[0043] In the present invention, the graphitization degree G of the negative electrode material is calculated according to the following formula:

[0044] G=(0.344-d 002 ) / (0.344-0.3354), where d 002 Calculated using the Bragg equation.

[0045] According to the present invention, the specific surface area (BET) of the negative electrode material is 0.1-10m 2 / g, preferably 0.5-5m 2 / g, more preferably 1-3m 2 / g.

[0046] In the present invention, the specific surface area of ​​the negative electrode material is measured by a nitrogen adsorption specific surface area method.

[0047] According to the present invention, the negative electrode material comprises a first phase carbon of coal-based graphite and a second phase carbon of amorphous carbon;

[0048] Part or all of the surface of the first phase carbon is coated with the second phase carbon;

[0049] Alternatively, the second phase carbon is dispersed in the first phase carbon.

[0050] According to the present invention, based on the total weight of the negative electrode material, the mass ratio of the first phase carbon to the second phase carbon is 2-99:1.

[0051] In the present invention, the contents of the first phase carbon and the second phase carbon in the negative electrode material are calculated based on the feed amount of the raw materials and the residual carbon rate.

[0052] Further preferably, based on the total weight of the negative electrode material, the mass ratio of the first phase carbon to the second phase carbon is 4-70:1.

[0053] A second aspect of the present invention provides a method for preparing a negative electrode material, wherein the method comprises the following steps:

[0054] (1) crushing coal to obtain coal particles;

[0055] (2) graphitizing the coal particles to obtain a graphitized material;

[0056] (3) mixing the graphitized material with a modifier to obtain a mixture;

[0057] (4) pre-oxidizing the mixture under air atmosphere to obtain a pre-oxidized sample;

[0058] (5) Carbonizing the pre-oxidized sample under an inert atmosphere to obtain the negative electrode material.

[0059] In the present invention, in the process of preparing the negative electrode material, the modifier is mixed with the graphitized material obtained by graphitizing coal, and then pre-oxidation and carbonization treatment are carried out in sequence, which can significantly reduce the pore volume of the negative electrode material and improve the density of the negative electrode material, thereby significantly improving the continuous high-rate cycle performance of the lithium-ion battery containing the negative electrode material.

[0060] Furthermore, the present invention uses coal as raw material, and when the negative electrode material is prepared by the above method, not only can the preparation cost of the negative electrode material be significantly reduced, but also high value-added utilization and clean and efficient conversion of coal can be achieved.

[0061] According to the present invention, the coal meets the following conditions: vitrinite reflectance ≥ 2; volatile matter ≤ 10wt%; ash content ≤ 15wt%.

[0062] In the present invention, coal that meets the above conditions is selected as raw material for preparing negative electrode materials, and negative electrode materials with moderate crystallinity, small grain size and dense structure can be obtained, thereby making the lithium ion battery containing the negative electrode material have high charge and discharge capacity, high first coulomb efficiency and excellent continuous high-rate cycle performance.

[0063] In the present invention, the vitrinite reflectance of the coal is measured by the national standard GB / T 6948 method, and the volatile matter content and ash content of the coal are measured by the national standard GB / T30732 method.

[0064] According to the present invention, the coal meets the following conditions: vitrinite reflectance ≥ 2.3; volatile matter ≤ 10wt%; ash content ≤ 6wt%.

[0065] In the present invention, conventional equipment in the art, such as a jet mill, a mechanical mill, a Raymond mill, etc., can be used to pulverize the coal.

[0066] In the present invention, in step (1), the particle size D of the coal particles is 50 It is 1-100 μm, preferably 2-50 μm.

[0067] In the present invention, the particle size D of the coal particles is 50 Measured by laser particle size analyzer.

[0068] According to the present invention, in step (2), the graphitization conditions include: the graphitization temperature is above 2900° C., and the graphitization time is 0.5-100 h.

[0069] According to the present invention, the graphitization conditions include: a graphitization temperature of 3000-3500° C. and a graphitization time of 1-80 h.

[0070] According to the present invention, the modifier is a precursor of amorphous carbon.

[0071] Furthermore, the modifier is selected from asphalt and / or resin.

[0072] In the present invention, the asphalt can be selected from at least one of coal asphalt, petroleum asphalt, mesophase asphalt and oxidized asphalt.

[0073] In the present invention, when the modifier is asphalt, the modifier satisfies the following conditions: the softening point of the modifier is ≥50°C, and the viscosity of the modifier at 400°C is ≤1000 Pa·s.

[0074] In the present invention, the graphitized material obtained in step (2) is modified by using the above-mentioned modifier having a specific softening point and viscosity. The modifier can enter the pores of the graphitized material obtained by graphitizing coal, thereby significantly reducing the pore volume in the obtained negative electrode material. At the same time, the graphitized material obtained by graphitizing coal is surface modified, significantly reducing the specific surface area and improving the structural density of the product, thereby making the lithium ion battery containing the negative electrode material have a higher first coulombic efficiency and a more excellent continuous high-rate cycle performance.

[0075] Furthermore, the softening point of the modifier is ≥150°C, preferably 200-360°C; the viscosity of the modifier at 400°C is ≤100 Pa·s; preferably ≤20 Pa·s.

[0076] According to the present invention, the usage ratio of the graphitized material to the modifier is 1-99.9:1.

[0077] In the present invention, when the amounts of graphitized material and modifier meet the above ranges, the obtained negative electrode material can have an optimal ratio, and the negative electrode material obtained thereby has excellent comprehensive performance. Specifically, if the amount of modifier is too high, the second phase carbon obtained will aggregate due to the presence of excessive modifier, thereby reducing the charge and discharge capacity and the first coulombic efficiency; and if the amount of modifier is too small, the effect of the modifier on the surface modification of the graphitized material will be insufficient, ultimately resulting in a decrease in the first coulombic efficiency of the negative electrode material and the continuous high-rate cycle performance.

[0078] Furthermore, the usage ratio of the graphitized material to the modifier is 4-99:1, preferably 6-99:1, and more preferably 8-99:1.

[0079] According to the present invention, in step (3), the pre-oxidation conditions include: a pre-oxidation temperature of 50-600° C. and a pre-oxidation time of 1-100 h.

[0080] In the present invention, the mixture is pre-oxidized under the above conditions, which can significantly improve the structural density of the second phase carbon, and enable the above-mentioned densely structured second phase carbon to better fill the pores of the first phase carbon and modify the surface of the first phase carbon, ultimately significantly improving the structural density of the prepared negative electrode material, thereby enabling the battery containing the negative electrode material to significantly improve the continuous high-rate cycle performance while maintaining a relatively high charge and discharge capacity, first coulomb efficiency and rate performance.

[0081] Further preferably, the pre-oxidation temperature is 100-550° C., more preferably 200-500° C.; and the pre-oxidation time is 3-80 h.

[0082] According to the present invention, the carbonization conditions include: a carbonization temperature of 800-1500° C. and a carbonization time of 0.1-100 h.

[0083] In the present invention, the pre-oxidized sample is carbonized under the above conditions, which can remove the volatile matter in the pre-oxidized sample while fully retaining the active components and rearrange the carbon, thereby improving the density of the product and making the comprehensive performance of the obtained negative electrode material more excellent.

[0084] More preferably, the carbonization temperature is 900-1400° C., more preferably 1000-1300° C.; the carbonization time is 0.5-80 h, more preferably 1-50 h.

[0085] The third aspect of the present invention provides a negative electrode material prepared by the above preparation method.

[0086] A fourth aspect of the present invention provides a negative electrode sheet, characterized in that the negative electrode sheet comprises the above-mentioned negative electrode material.

[0087] In the present invention, the negative electrode sheet further comprises a conductive agent and a binder. The amounts of the negative electrode material, the conductive agent and the binder can be conventional amounts in the art, specifically, the amount ratio of the negative electrode material, the conductive agent and the binder is 80-98:1-10:1-10.

[0088] As for the types of the conductive agent and the binder, conventional conductive agents and binders in the art may be used.

[0089] In the present invention, the preparation method of the negative electrode sheet can be prepared according to the conventional method in the art. Specifically, the negative electrode material, the conductive carbon black Super P, the binder polyvinylidene fluoride (PVDF) and the thickener CMC are mixed uniformly according to the ratio, deionized water is added, and a slurry mixer is used to adjust the negative electrode slurry to a uniform negative electrode slurry with a solid content of 40-50wt%. The negative electrode slurry is evenly coated on the copper foil with a coating machine, dried, and cut into pieces to obtain the negative electrode sheet.

[0090] According to the present invention, when the compaction density of the negative electrode sheet is 1.4-1.6 g / cm 3 When the OI of the negative electrode sheet is less than or equal to 15.

[0091] In the present invention, the OI value of the negative electrode sheet refers to the ratio of the peak intensity I004 of the (004) crystal plane of the negative electrode sheet obtained by XRD to the peak intensity I110 of the (110) crystal plane.

[0092] In the present invention, the negative electrode sheet has a low OI value, indicating that the negative electrode sheet has excellent orientation and high isotropy, thereby making the battery containing the negative electrode sheet have excellent electrochemical performance.

[0093] Furthermore, when the OI value of the negative electrode material is 0.1-15, preferably 1-10, the lithium ion battery containing the negative electrode sheet has high charge and discharge capacity and first coulomb efficiency, and has excellent continuous high-rate cycle performance.

[0094] A fourth aspect of the present invention provides use of the above-mentioned negative electrode material or negative electrode sheet in a lithium-ion battery.

[0095] In the present invention, the lithium-ion battery comprising the above negative electrode material or negative electrode sheet has excellent electrochemical performance. Specifically, the charge and discharge capacity of the lithium-ion battery comprising the above negative electrode material is ≥330 mAh / g, the first coulombic efficiency is ≥92%, and the capacity retention rate after 1500 cycles at 5C continuous high rate is ≥80%.

[0096] The present invention will be described in detail below through examples.

[0097] (1) XRD analysis

[0098] The interlayer spacing d of the negative electrode material 002 , L a , L c The OI values ​​of the negative electrode sheet and the negative electrode sheet were obtained by testing and analyzing the D8 Advance X-ray diffractometer of Bruker AXS GmbH, Germany; the calibration was performed by the silicon internal standard method, d 002 The value is calculated by the Bragg formula, L a , L c Calculated by Scherrer formula;

[0099] (2) Graphitization degree G

[0100] The graphitization degree G of the negative electrode material is calculated according to the following formula:

[0101] G=(0.344-d 002 ) / (0.344-0.3354), where d 002 Calculated using the Bragg equation.

[0102] (3) BET and pore volume

[0103] The BET and pore volume of the negative electrode material were measured using a Micromeritics 3flex N2 adsorption-desorption instrument. The test method was carried out in accordance with the national standard, and the sample pretreatment conditions were: temperature 350°C, time 6 hours.

[0104] (4) Particle size

[0105] Coal D 50The results were obtained by testing with Malvern Mastersizer 2000 laser particle size analyzer produced by Malvern Instruments Ltd., UK.

[0106] (5) The vitrinite reflectance of coal was measured using the national standard GB / T 6948 method, and the volatile matter content and ash content of coal were measured using the national standard GB / T 30732 method.

[0107] (6) Softening point of modifier: The softening point of asphalt was tested by Mettler titration method.

[0108] (7) Viscosity of the modifier: tested by MARS40 rotational rheometer from HAAKE, Germany, at a test temperature of 400°C and a shear rate of 10 / s.

[0109] (8) Battery performance

[0110] a. Battery charge and discharge capacity and first coulomb efficiency were tested by battery test system CT2001A battery tester of Wuhan Blue Electric Electronics Co., Ltd., with current of 0.1C (1C=350mAh / g) and voltage of 0-3V.

[0111] b. 5C continuous high rate cycle performance was tested by charging and discharging with a Xinwei battery tester. The test conditions were: at room temperature, 5C constant current to constant voltage charging to 4.2V, cut-off current 0.05C, and 5C constant current discharge to 2.5V.

[0112] Example 1

[0113] (1) Coal (vitrinite reflectance 2.445; volatile matter 7.7 wt%; ash 2.6 wt%) was crushed by a mechanical crusher to obtain D 50 =10μm coal particles;

[0114] (2) graphitizing the coal particles at 3000° C. for 25 h to obtain a graphitized material;

[0115] (3) 93 parts of the graphitized material and 7 parts of petroleum asphalt (softening point of 240°C, viscosity of 8.553 Pa·s at 400°C) were mixed to obtain a mixture, wherein the mass ratio of the graphitized material to the modifier petroleum asphalt was 13.3:1;

[0116] (4) pre-oxidizing the mixture at 300° C. for 20 h in an air atmosphere to obtain a pre-oxidized sample;

[0117] (5) The pre-oxidized sample was carbonized at 1200° C. for 5 hours under an inert gas atmosphere, and the negative electrode material A1 was obtained by sieving.

[0118] Example 2

[0119] (1) Coal (vitrinite reflectance 2.445; volatile matter 7.7 wt%; ash 2.6 wt%) was crushed by a mechanical crusher to obtain D 50 =10μm coal particles;

[0120] (2) graphitizing the coal particles at 3000° C. for 25 h to obtain a graphitized material;

[0121] (3) 85 parts of the graphitized material and 15 parts of petroleum asphalt (softening point of 240°C, viscosity of 8.553 Pa·s at 400°C) were mixed to obtain a mixture, wherein the mass ratio of the graphitized material to the modifier petroleum asphalt was 5.7:1;

[0122] (4) pre-oxidizing the mixture at 300° C. for 20 h in an air atmosphere to obtain a pre-oxidized sample;

[0123] (5) The pre-oxidized sample was carbonized at 1200° C. for 5 hours under an inert gas atmosphere, and the negative electrode material A2 was obtained by sieving.

[0124] Example 3

[0125] Negative electrode material A3 was prepared according to the method of Example 1, except that: the amount of graphitized material used was 97 parts, the amount of modifier used was 3 parts, and the mass ratio of the two was 32.3:1. Negative electrode material A3 was obtained.

[0126] Example 4

[0127] Negative electrode material A4 was prepared according to the method of Example 1, except that the amount of graphitized material was 70 parts, the amount of modifier was 30 parts, and the mass ratio of the two was 2.3:1. Negative electrode material A4 was obtained. Negative electrode material A4 was obtained.

[0128] Example 5

[0129] Negative electrode material A5 was prepared according to the method of Example 1, except that the petroleum asphalt with a softening point of 240°C and a viscosity of 8.553 Pa·s at 400°C was replaced by mesophase asphalt with a softening point of 260°C and a viscosity of 0.557 Pa·s at 400°C. Negative electrode material A5 was obtained.

[0130] Example 6

[0131] Negative electrode material A6 was prepared according to the method of Example 1, except that oxidized asphalt with a softening point of 280°C and a viscosity of 10.580 Pa·s at 400°C was used instead of petroleum asphalt with a softening point of 240°C and a viscosity of 8.553 Pa·s at 400°C. Negative electrode material A6 was obtained.

[0132] Example 7

[0133] Negative electrode material A7 was prepared according to the method of Example 1, except that a composite modifier was used instead of petroleum asphalt with a softening point of 240°C and a viscosity of 8.553 mPa·s at 400°C; wherein the composite modifier was a mixture of mesophase asphalt (softening point of 260°C and viscosity of 0.557 mPa·s at 400°C) and oxidized asphalt (softening point of 280°C and viscosity of 10.580 mPa·s at 400°C) in a mass ratio of 4:3. Negative electrode material A7 was obtained.

[0134] Example 8

[0135] The negative electrode material A8 was prepared according to the method of Example 1, except that the pre-oxidation temperature was 180° C. and the time was 4 h. Thus, the negative electrode material A8 was obtained.

[0136] Example 9

[0137] The negative electrode material A9 was prepared according to the method of Example 1, except that the pre-oxidation temperature was 400° C. and the time was 10 h. Thus, the negative electrode material A9 was obtained.

[0138] Example 10

[0139] The negative electrode material A10 was prepared according to the method of Example 1, except that sucrose was used instead of the petroleum asphalt in the example. The negative electrode material A10 was prepared.

[0140] Comparative Example 1

[0141] The negative electrode material was prepared according to the method of Example 1, except that step (3), step (4) and step (5) were not performed, to obtain negative electrode material D1. Negative electrode material D1 was homogeneous and did not contain a second phase of carbon.

[0142] Comparative Example 2

[0143] The negative electrode material was prepared according to the method of Example 1, except that the pre-oxidation step (4) was not performed to obtain the negative electrode material D2.

[0144] Comparative Example 3

[0145] The negative electrode material was prepared according to the method of Example 1, except that coal and petroleum asphalt were directly mixed to obtain a mixture, and the mixture was graphitized according to the graphitization step of Example 1 to obtain negative electrode material D3. In the negative electrode material D3, the petroleum asphalt was completely graphitized, and the negative electrode material D3 did not contain amorphous carbon of the second phase.

[0146] Comparative Example 4

[0147] The negative electrode material was prepared according to the method of Example 1, except that petroleum asphalt was not contained in step (3). The negative electrode material D4 was obtained. The negative electrode material D4 was homogeneous and did not contain a second phase of carbon.

[0148] The negative electrode materials obtained in the examples and comparative examples were characterized, and the results are shown in Table 1.

[0149] Table 1

[0150]

[0151]

[0152] V1 refers to the total pore volume of the negative electrode material; V2 refers to the mesoporous volume of the negative electrode material; M1 refers to the mass of the first phase carbon in the negative electrode material, and M2 refers to the mass of the second phase carbon in the negative electrode material. The OI value is the compaction density of 1.55 g / cm 3 The OI value at that time.

[0153] Test Case

[0154] (1) Half-cell performance test:

[0155] The negative electrode material prepared in the embodiment and the comparative example was mixed with the conductive carbon black Super P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 92:3:5, and a solvent N-methylpyrrolidone (NMP) was added and stirred into a uniform negative electrode slurry. The negative electrode slurry was evenly coated on a copper foil with a scraper and dried to obtain a negative electrode sheet. After cutting, the sheet was transferred to an MBraun2000 glove box (Ar atmosphere, H2O and O2 concentrations less than 0.1×10 -6 Volume %), with metal lithium sheet as reference electrode, assembled into button cell. The charge and discharge capacity and first coulomb efficiency of the button cell were tested, and the test results are shown in Table 2.

[0156] (2) Full battery performance test:

[0157] The negative electrode material prepared in the embodiment and the comparative example is used as an active material and mixed with conductive carbon black Super P, binder polyvinylidene fluoride (PVDF) and thickener CMC in a mass ratio of 94:2:3:1, deionized water is added, and a uniform negative electrode slurry is prepared with a slurry mixer, and the solid content is controlled at 40-50wt%. The negative electrode slurry is evenly coated on the copper foil with a coating machine, dried, and cut to obtain a negative electrode sheet; the ternary positive electrode material NCM523 is matched, and the electrolyte and the diaphragm are added to assemble into a soft pack battery. The soft pack battery is subjected to a 5C continuous high rate cycle life test. The cycle process is: 5C constant current to constant voltage charging to 4.2V, cut-off current 0.05C, 5C constant current discharge to 2.5V, and cycled back and forth in sequence. The capacity retention rate of the discharge capacity / first discharge capacity when the cycle is cycled to 1500 times is calculated, which is calculated as the capacity retention rate of 1500 cycles of 5C continuous high rate cycles, and the test results are shown in Table 2.

[0158] Table 2

[0159]

[0160] It can be seen from the results in Table 1 and Table 2 that the negative electrode material prepared by the embodiment of the present invention has the characteristics of dense structure and small grain size, and the battery containing the negative electrode material can significantly improve the continuous high-rate cycle performance while maintaining a high charge and discharge capacity, first coulomb efficiency and rate performance.

[0161] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A negative electrode material, characterized in that: The negative electrode material has the following characteristics: (1) The total pore volume of the negative electrode material is ≤0.02 cm³ / g, and the pore volume of the mesopores with a pore size of 2-50 nm is 0.00001-0.02 cm³ / g; (2) The height ratio of the D peak and the G peak of the negative electrode material obtained by Raman spectroscopy satisfies the following condition: 0.20≤ID / IG≤1; The crystallite size L of the negative electrode material in the c-axis direction obtained by powder XRD c Meet the following conditions: 25nm≤L c ≤38.1nm.

2. The negative electrode material according to claim 1, wherein The total pore volume of the negative electrode material is 0.0001-0.01 cm³ / g, and the pore volume of mesopores with a pore diameter of 2-50 nm is 0.00001-0.01 cm³ / g.

3. The negative electrode material according to claim 1 or 2, wherein The total pore volume of the negative electrode material is 0.0002-0.007 cm³ / g, and the pore volume of mesopores with a pore diameter of 2-50 nm is 0.0001-0.007 cm³ / g.

4. The negative electrode material according to claim 1 or 2, wherein The height ratio of the D peak and the G peak of the negative electrode material obtained by Raman spectroscopy satisfies the following condition: 0.25≤ID / IG≤0.

9.

5. The negative electrode material according to claim 1 or 2, wherein The height ratio of the D peak and the G peak of the negative electrode material obtained by Raman spectroscopy satisfies the following condition: 0.3≤ID / IG≤0.

8.

6. The negative electrode material according to claim 1 or 2, wherein The interlayer spacing d of the (002) crystal plane of the negative electrode material obtained by powder XRD 002 Meet the following conditions: 0.3340nm≤d 002 ≤0.3400nm.

7. The negative electrode material according to claim 1 or 2, wherein The interlayer spacing d of the (002) crystal plane of the negative electrode material obtained by powder XRD 002 Meet the following conditions: 0.3350nm≤d 002 ≤0.3390nm.

8. The negative electrode material according to claim 1 or 2, wherein The interlayer spacing d of the (002) crystal plane of the negative electrode material obtained by powder XRD 002 Meet the following conditions: 0.3364nm≤d 002 ≤0.3370nm.

9. The negative electrode material according to claim 1 or 2, wherein The crystallite size L of the negative electrode material in the c-axis direction obtained by powder XRD c Meet the following conditions: 28nm≤L c ≤38.1nm.

10. The negative electrode material according to claim 1 or 2, wherein The crystallite size L of the negative electrode material in the c-axis direction obtained by powder XRD c Meet the following conditions: 30nm≤L c ≤38.1nm.

11. The negative electrode material according to claim 1 or 2, wherein The crystallite size L of the negative electrode material in the a-axis direction is obtained by XRD. a Meet the following conditions: 40nm≤L a ≤150nm.

12. The negative electrode material according to claim 1 or 2, wherein The crystallite size L of the negative electrode material in the a-axis direction is obtained by XRD. a Meet the following conditions: 45nm≤L a ≤120nm.

13. The negative electrode material according to claim 1 or 2, wherein The crystallite size L of the negative electrode material in the a-axis direction is obtained by XRD. a Meet the following conditions: 50nm≤L a ≤100nm.

14. The negative electrode material according to claim 1 or 2, wherein The graphitization degree of the negative electrode material meets the following condition: 82≤graphitization degree≤95.

15. The negative electrode material according to claim 1 or 2, wherein: The graphitization degree of the negative electrode material meets the following condition: 84≤graphitization degree≤91.

16. The negative electrode material according to claim 1 or 2, wherein: The graphitization degree of the negative electrode material meets the following condition: 85≤graphitization degree≤90.

17. The negative electrode material according to claim 1 or 2, wherein: The specific surface area of ​​the negative electrode material is 0.1-10m 2 / g.

18. The negative electrode material according to claim 1 or 2, wherein The specific surface area of ​​the negative electrode material is 0.5-5m 2 / g.

19. The negative electrode material according to claim 1 or 2, wherein: The specific surface area of ​​the negative electrode material is 1-3m 2 / g.

20. The negative electrode material according to claim 1 or 2, wherein The negative electrode material comprises a first phase carbon of coal-based graphite and a second phase carbon of amorphous carbon; Part or all of the surface of the first phase carbon is coated with the second phase carbon; Alternatively, the second phase carbon is dispersed in the first phase carbon.

21. The negative electrode material according to claim 20, wherein Based on the total weight of the negative electrode material, the mass ratio of the first phase carbon to the second phase carbon is 2-99:

1.

22. The negative electrode material according to claim 20, wherein Based on the total weight of the negative electrode material, the mass ratio of the first phase carbon to the second phase carbon is 4-70:

1.

23. A method for preparing the negative electrode material according to any one of claims 1 to 22, characterized in that: The method comprises the following steps: (1) crushing coal to obtain coal particles; (2) graphitizing the coal particles to obtain a graphitized material; (3) mixing the graphitized material and the modifier to obtain a mixture; (4) pre-oxidizing the mixture under air atmosphere to obtain a pre-oxidized sample; (5) carbonizing the pre-oxidized sample under an inert atmosphere to obtain the negative electrode material; The coal meets the following conditions: vitrinite reflectance ≥ 2; volatile matter ≤ 10wt%; ash content ≤ 15wt%; Wherein, in step (3), the pre-oxidation conditions include: the pre-oxidation temperature is 50-600°C, and the pre-oxidation time is 1-100h.

24. The method according to claim 23, wherein: The coal meets the following conditions: vitrinite reflectance ≥ 2.3; volatile matter ≤ 10wt%; ash content ≤ 6wt%.

25. The method according to claim 23 or 24, wherein: In step (2), the graphitization conditions include: graphitization temperature is 2900° C. or above, and graphitization time is 0.5-100 h.

26. The method according to claim 23 or 24, wherein: In step (2), the graphitization conditions include: graphitization temperature of 3000-3500° C., and graphitization time of 1-80 h.

27. The method according to claim 23 or 24, wherein: The modifier is a precursor of amorphous carbon.

28. The method of claim 23, wherein: The modifier is selected from asphalt and / or resin.

29. The method of claim 23, wherein: When the modifier is asphalt, the modifier meets the following conditions: the softening point of the modifier is ≥50°C; the viscosity of the modifier at 400°C is ≤1000 Pa·s.

30. The method of claim 29, wherein: When the modifier is asphalt, the modifier satisfies the following conditions: the softening point of the modifier is ≥150°C; the viscosity of the modifier at 400°C is ≤100 Pa·s.

31. The method according to claim 30, wherein: When the modifier is asphalt, the modifier meets the following conditions: the softening point of the modifier is 200-360° C.; the viscosity of the modifier at 400° C. is ≤20 Pa·s.

32. The method according to claim 23 or 24, wherein: The usage ratio of the graphitized material to the modifier is 1-99.9:

1.

33. The method according to claim 23 or 24, wherein: The usage ratio of the graphitized material to the modifier is 4-99:

1.

34. The method according to claim 23 or 24, wherein: In step (3), the pre-oxidation conditions include: the pre-oxidation temperature is 100-550°C.

35. The method according to claim 23 or 24, wherein: In step (3), the pre-oxidation conditions include: the pre-oxidation temperature is 200-500°C.

36. The method according to claim 23 or 24, wherein: In step (3), the pre-oxidation conditions include: the pre-oxidation time is 3-80 hours.

37. The method according to claim 23 or 24, wherein: In step (5), the carbonization conditions include: a carbonization temperature of 800-1500° C. and a carbonization time of 0.1-100 h.

38. The method according to claim 23 or 24, wherein: In step (5), the carbonization conditions include: carbonization temperature of 900-1400° C., and carbonization time of 0.5-80 h.

39. The method according to claim 23 or 24, wherein: In step (5), the carbonization conditions include: a carbonization temperature of 1000-1300° C. and a carbonization time of 1-50 h.

40. A negative electrode material obtained by the preparation method according to any one of claims 23 to 39.

41. A negative electrode sheet, characterized in that: The negative electrode sheet comprises the negative electrode material according to any one of claims 1-22 and 40.

42. The negative electrode sheet according to claim 41, wherein: When the compaction density of the negative electrode is 1.4-1.6g / cm 3 When the OI of the negative electrode sheet is less than or equal to 15.

43. The negative electrode sheet according to claim 41 or 42, wherein: When the compaction density of the negative electrode is 1.4-1.6g / cm 3 When the OI of the negative electrode sheet is 0.1-15.

44. The negative electrode sheet according to claim 41 or 42, wherein: When the compaction density of the negative electrode is 1.4-1.6g / cm 3 When the OI of the negative electrode sheet is 1-10.

45. Use of the negative electrode material according to any one of claims 1 to 22 and 40 or the negative electrode sheet according to any one of claims 41 to 44 in a lithium ion battery.

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