Modified graphite negative electrode material, preparation method thereof and lithium ion battery

Abstract

The invention provides a modified graphite negative electrode material, a preparation method thereof and a lithium ion battery, and relates to the technical field of lithium ion battery graphite negative electrodes. The invention discloses a preparation method of a modified graphite negative electrode material. The preparation method comprises the following steps: S1, heating and uniformly mixing a lithium-containing compound, a soft carbon precursor or a hard carbon precursor in the atmosphere of protective gas to obtain a lithium-containing coating agent; s2, adding the lithium-containing coating agent in the step S1 into the graphite main body material, uniformly mixing, and sintering in the atmosphere of shielding gas to obtain a first modified graphite negative electrode material; and S3, uniformly dispersing the first modified graphite negative electrode material in the step S2 into deionized water, adding a hydrophobic surface modifier, uniformly stirring, standing, and drying to obtain the modified graphite negative electrode material. The lithium ion battery containing the modified graphite negative electrode material provided by the invention has excellent first efficiency, cycling stability, liquid absorption performance of a negative electrode and rate capability of a battery cell.

Description

Technical Field

[0001] The invention relates to the technical field of graphite negative electrodes for lithium ion batteries, and in particular to a modified graphite negative electrode material and a preparation method thereof, and a lithium ion battery. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in various portable electronic devices, and have gradually been applied to emerging fields such as electric vehicles and large-scale energy storage. These emerging fields have put forward higher requirements on the capacity and cycle performance of lithium-ion batteries. The negative electrode materials of lithium-ion batteries currently used are mostly graphite negative electrode materials. Commercial graphite negative electrode materials have low initial efficiency, resulting in irreversible capacity loss, poor cycle performance, and long infiltration time of the negative electrode, which is not conducive to the performance of rate performance. Summary of the invention

[0003] Based on the technical problems existing in the background technology, the present invention proposes a modified graphite negative electrode material and a preparation method thereof and a lithium ion battery.

[0004] The invention provides a modified graphite negative electrode material, which comprises a graphite main material, a lithium-containing coating agent and a hydrophobic surface modifier.

[0005] Preferably, the lithium-containing coating agent includes a lithium-containing compound; the lithium-containing coating agent also includes a soft carbon precursor or a hard carbon precursor.

[0006] More preferably, the mass ratio of the lithium-containing compound to the soft carbon precursor or the hard carbon precursor is 1:(20-100).

[0007] The lithium-containing coating agent in the present invention includes a lithium-containing compound, a soft carbon precursor or a hard carbon precursor, which helps to improve the initial efficiency, cycle performance and rate performance of the material. The mass ratio of the lithium-containing compound, the soft carbon precursor or the hard carbon precursor within a certain range helps to achieve the best coating effect with the coating surface of the graphite material, so that the prepared modified graphite negative electrode material has a high capacity.

[0008] More preferably, the lithium-containing compound is selected from one or more of lithium powder, lithium hydride, lithium aluminum hydride, and butyl lithium.

[0009] The selection of the type of lithium-containing compound helps to form an artificial SEI film on the graphite surface in advance, thereby improving the initial efficiency and cycle performance of the material.

[0010] More preferably, the soft carbon precursor is selected from one or more of low-temperature asphalt, medium-temperature asphalt and high-temperature asphalt.

[0011] More preferably, the hard carbon precursor is selected from one or more of liquid phase resin and solid phase resin.

[0012] The selection of soft carbon precursor or hard carbon precursor helps to form a soft carbon layer on the graphite surface, which increases the active sites for lithium ion migration and diffusion, and is beneficial to improving the rate performance of the material.

[0013] Preferably, the hydrophobic surface modifier is selected from one or more of sodium stearate, sodium dodecylbenzene sulfonate, sodium tripolyphosphate, and polysiloxane.

[0014] The selection of hydrophobic surface modifiers helps to form oleophilic functional groups on the graphite surface, which is beneficial to the wettability of the material with the electrolyte.

[0015] Preferably, the graphite main material is selected from at least one or more of natural graphite, natural spherical graphite, natural flake graphite, artificial graphite, and mesophase carbon microspheres.

[0016] More preferably, the graphite main material is a black powder material with a particle size of 5 μm-60 μm.

[0017] The particle size of the graphite main material within a certain range is conducive to better bonding between the coating layer and the graphite.

[0018] The present invention also provides a method for preparing a modified graphite negative electrode material, comprising the following steps:

[0019] S1, heating and mixing the lithium-containing compound, the soft carbon precursor or the hard carbon precursor in an atmosphere of protective gas to obtain a lithium-containing coating agent;

[0020] S2, adding the lithium-containing coating agent S1 to the graphite main material and mixing them evenly, and sintering them under a protective gas atmosphere to obtain a first modified graphite negative electrode material;

[0021] S3, uniformly dispersing the first modified graphite negative electrode material S2 in deionized water, adding a hydrophobic surface modifier, stirring evenly, standing and drying to obtain a modified graphite negative electrode material.

[0022] The present invention improves the initial efficiency of the material by pre-reacting the lithium-containing coating agent with the defects on the graphite surface, and the coated soft and hard carbons have a developed pore structure, which is conducive to the rate performance; then the first modified graphite negative electrode material is subjected to hydrophobic surface modification to form some hydrophobic functional groups on the outermost surface of the graphite, which is conducive to the rapid and full infiltration of the graphite and the electrolyte, which improves the liquid absorption performance of the negative electrode on the one hand, and is conducive to the full contact between the negative electrode and the electrolyte on the other hand, thereby improving the rate performance of the material.

[0023] Preferably, in said S1, the heating temperature is 50-100°C.

[0024] Heating temperature within a certain range helps to protect the activity of the coating agent.

[0025] Preferably, in S1 and S2, the protective gas is nitrogen.

[0026] Preferably, in the step S2, the sintering temperature is 800-1200° C. and the sintering time is 3-5 h.

[0027] Controlling the sintering temperature and time within a certain range is conducive to the formation of the graphite surface coating layer and ensures the stability of the coating layer structure.

[0028] Preferably, in the S2, the mass ratio of the lithium-containing coating agent to the graphite main material is (1-10):100.

[0029] Controlling the mass ratio of the lithium-containing coating agent and the graphite main material within a certain range helps to ensure the uniformity of the graphite surface coating layer.

[0030] Preferably, in S3, the mass ratio of the hydrophobic surface modifier, the first modified graphite negative electrode material, and deionized water is (1-5):1000:2000.

[0031] Controlling the mass ratio of the hydrophobic surface modifier, the first modified graphite negative electrode material, and deionized water within a certain range is helpful to improve the wettability of the material with the electrolyte.

[0032] The present invention also provides a lithium-ion battery, comprising a negative electrode sheet, a positive electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises the modified graphite negative electrode material described above or the modified graphite negative electrode material prepared according to the preparation method described above.

[0033] Preferably, the positive electrode material in the positive electrode sheet is selected from LiMn2O4, LiCoO2, LiNiO2, LiFePO4, LiNi x Co y Mn z O2(x+y+z=1,x*y*z≠0) or more.

[0034] Preferably, the electrolyte is selected from one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, fluoroethylene carbonate, lithium hexafluorophosphate, lithium bis(oxalatoborate)fluoride, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, perfluoropolyether, and tetrabutylammonium fluoride.

[0035] Preferably, the diaphragm is PE or PP.

[0036] The beneficial effects of the present invention are:

[0037] The modified graphite negative electrode material obtained by the two-step modification method of modified sintering-surface hydrophobic modification of the present invention is beneficial to improving the initial efficiency and cycle stability of lithium-ion batteries, improving the liquid absorption performance of the negative electrode, and improving the rate performance of the battery core. The present invention improves the initial efficiency of the material by pre-reacting the lithium-containing coating agent with the defects on the graphite surface in advance, and the coated soft and hard carbon has a developed pore structure, which is beneficial to the rate performance; then the first modified graphite negative electrode material is subjected to hydrophobic surface modification, and some hydrophobic functional groups are formed on the outermost surface of the graphite, which is beneficial to the rapid and sufficient infiltration of the graphite and the electrolyte, on the one hand, improving the liquid absorption performance of the negative electrode, on the other hand, it is beneficial to the full contact between the negative electrode and the electrolyte, and improving the rate performance of the material. At the same time, the modification technology scheme provided by the present invention is easy to operate and can be integrated with the current mainstream graphite negative electrode production process. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is described in detail through specific embodiments.

[0039] In the following examples and comparative examples, the specific information of the raw materials used is as follows:

[0040] Medium temperature asphalt: Dalian Mingqiang MQ200.

[0041] Solid phase resin: Fangxin FX-9003 hydroxy acrylic resin.

[0042] Example 1

[0043] A method for preparing a modified graphite negative electrode material comprises the following steps:

[0044] S1. Mix 1 g of lithium powder and 100 g of medium-temperature asphalt at 80° C. under a nitrogen atmosphere to obtain a lithium-containing coating agent;

[0045] S2, adding 5 g of lithium-containing coating agent to 100 g of petroleum coke artificial graphite (D50 is 15 μm), mixing evenly, and sintering at 1100° C. under a nitrogen atmosphere to obtain a first modified graphite negative electrode material;

[0046] S3. Evenly disperse 50 g of the first modified graphite negative electrode material in 100 g of deionized water, add 0.1 g of sodium tripolyphosphate modifier, stir evenly, let stand for 24 hours, and dry at 100° C. to obtain the modified graphite negative electrode material.

[0047] Example 2

[0048] A method for preparing a modified graphite negative electrode material comprises the following steps:

[0049] S1. Mix 1 g of lithium hydride and 100 g of medium-temperature asphalt at 80° C. under a nitrogen atmosphere to obtain a lithium-containing coating agent;

[0050] S2, adding 5 g of lithium-containing coating agent to 100 g of petroleum coke artificial graphite (D50 is 15 μm), mixing evenly, and sintering at 1100° C. under a nitrogen atmosphere to obtain a first modified graphite negative electrode material;

[0051] S3. Evenly disperse 50 g of the first modified graphite negative electrode material in 100 g of deionized water, add 0.1 g of sodium tripolyphosphate modifier, stir evenly, let stand for 24 hours, and dry at 100° C. to obtain the modified graphite negative electrode material.

[0052] Example 3

[0053] A method for preparing a modified graphite negative electrode material comprises the following steps:

[0054] S1. Mix 3 g of lithium hydride and 100 g of medium-temperature asphalt at 80° C. under a nitrogen atmosphere to obtain a lithium-containing coating agent;

[0055] S2, adding 5 g of lithium-containing coating agent to 100 g of petroleum coke artificial graphite (D50 is 15 μm), mixing evenly, and sintering at 1100° C. under a nitrogen atmosphere to obtain a first modified graphite negative electrode material;

[0056] S3. Evenly disperse 50 g of the first modified graphite negative electrode material in 100 g of deionized water, add 0.1 g of sodium tripolyphosphate modifier, stir evenly, let stand for 24 hours, and dry at 100° C. to obtain the modified graphite negative electrode material.

[0057] Example 4

[0058] A method for preparing a modified graphite negative electrode material comprises the following steps:

[0059] S1. Mix 1 g of lithium hydride and 100 g of medium-temperature asphalt at 80° C. under a nitrogen atmosphere to obtain a lithium-containing coating agent;

[0060] S2, adding 5 g of lithium-containing coating agent to 100 g of petroleum coke artificial graphite (D50 is 15 μm), mixing evenly, and sintering at 1100° C. under a nitrogen atmosphere to obtain a first modified graphite negative electrode material;

[0061] S3. Evenly disperse 50 g of the first modified graphite negative electrode material in 100 g of deionized water, add 0.1 g of sodium dodecylbenzene sulfonate modifier, stir evenly, let stand for 24 hours, and dry at 100° C. to obtain the modified graphite negative electrode material.

[0062] Example 5

[0063] A method for preparing a modified graphite negative electrode material comprises the following steps:

[0064] S1. Mix 1 g of lithium hydride and 100 g of medium-temperature asphalt at 80° C. under a nitrogen atmosphere to obtain a lithium-containing coating agent;

[0065] S2, adding 5 g of lithium-containing coating agent to 100 g of petroleum coke artificial graphite (D50 is 15 μm), mixing evenly, and sintering at 1100° C. under a nitrogen atmosphere to obtain a first modified graphite negative electrode material;

[0066] S3. Evenly disperse 50 g of the first modified graphite negative electrode material in 100 g of deionized water, add 0.2 g of sodium tripolyphosphate modifier, stir evenly, let stand for 24 hours, and dry at 100° C. to obtain the modified graphite negative electrode material.

[0067] Example 6

[0068] A method for preparing a modified graphite negative electrode material comprises the following steps:

[0069] S1. Mix 1 g of lithium powder and 100 g of medium-temperature asphalt at 80° C. under a nitrogen atmosphere to obtain a lithium-containing coating agent;

[0070] S2, adding 5 g of lithium-containing coating agent to 100 g of natural graphite (D50 is 15 μm), mixing them evenly, and sintering them at 1100° C. under a nitrogen atmosphere to obtain a first modified graphite negative electrode material;

[0071] S3. Evenly disperse 50 g of the first modified graphite negative electrode material in 100 g of deionized water, add 0.1 g of sodium tripolyphosphate modifier, stir evenly, let stand for 24 hours, and dry at 100° C. to obtain the modified graphite negative electrode material.

[0072] Example 7

[0073] A method for preparing a modified graphite negative electrode material comprises the following steps:

[0074] S1. Mix 1 g of butyl lithium and 100 g of medium-temperature asphalt at 80° C. under a nitrogen atmosphere to obtain a lithium-containing coating agent;

[0075] S2, adding 5 g of lithium-containing coating agent to 100 g of natural graphite (D50 is 15 μm), mixing them evenly, and sintering them at 1100° C. under a nitrogen atmosphere to obtain a first modified graphite negative electrode material;

[0076] S3. Evenly disperse 50 g of the first modified graphite negative electrode material in 100 g of deionized water, add 0.1 g of sodium tripolyphosphate modifier, stir evenly, let stand for 24 hours, and dry at 100° C. to obtain the modified graphite negative electrode material.

[0077] Example 8

[0078] A method for preparing a modified graphite negative electrode material comprises the following steps:

[0079] S1, mixing 1 g of lithium powder and 100 g of solid phase resin at 80° C. under a nitrogen atmosphere to obtain a lithium-containing coating agent;

[0080] S2, adding 5 g of lithium-containing coating agent to 100 g of natural graphite (D50 is 15 μm), mixing them evenly, and sintering them at 1100° C. under a nitrogen atmosphere to obtain a first modified graphite negative electrode material;

[0081] S3. Evenly disperse 50 g of the first modified graphite negative electrode material in 100 g of deionized water, add 0.1 g of sodium tripolyphosphate modifier, stir evenly, let stand for 24 hours, and dry at 100° C. to obtain the modified graphite negative electrode material.

[0082] Example 9

[0083] A method for preparing a modified graphite negative electrode material comprises the following steps:

[0084] S1. Mix 1 g of lithium powder and 150 g of medium-temperature asphalt at 80° C. under a nitrogen atmosphere to obtain a lithium-containing coating agent;

[0085] S2, adding 5 g of lithium-containing coating agent to 100 g of natural graphite (D50 is 15 μm), mixing them evenly, and sintering them at 1100° C. under a nitrogen atmosphere to obtain a first modified graphite negative electrode material;

[0086] S3. Evenly disperse 50 g of the first modified graphite negative electrode material in 100 g of deionized water, add 0.1 g of sodium tripolyphosphate modifier, stir evenly, let stand for 24 hours, and dry at 100° C. to obtain the modified graphite negative electrode material.

[0087] Example 10

[0088] A method for preparing a modified graphite negative electrode material comprises the following steps:

[0089] S1. Mix 1 g of butyl lithium and 100 g of medium-temperature asphalt at 80° C. under a nitrogen atmosphere to obtain a lithium-containing coating agent;

[0090] S2, adding 5 g of lithium-containing coating agent to 100 g of natural graphite (D50 is 15 μm), mixing them evenly, and sintering them at 1100° C. under a nitrogen atmosphere to obtain a first modified graphite negative electrode material;

[0091] S3. Evenly disperse 50 g of the first modified graphite negative electrode material in 100 g of deionized water, add 0.1 g of a polysiloxane modifier, stir evenly, let stand for 24 h, and dry at 100° C. to obtain a modified graphite negative electrode material.

[0092] Comparative Example 1

[0093] Commercially available petroleum coke artificial graphite, D50: 15μm.

[0094] Comparative Example 2

[0095] Commercially available natural graphite, D50: 15μm.

[0096] Comparative Example 3

[0097] The difference from Example 1 is that no lithium-containing coating agent is added, and the rest is the same as Example 1.

[0098] Comparative Example 4

[0099] The difference from Example 1 is that no sodium tripolyphosphate modifier is added, and the rest is the same as Example 1.

[0100] Comparative Example 5

[0101] The difference from Example 6 is that no lithium-containing coating agent is added, and the rest is the same as Example 6.

[0102] Comparative Example 6

[0103] The difference from Example 6 is that no medium-temperature asphalt is added, and the rest is the same as Example 6.

[0104] Comparative Example 7

[0105] The difference from Example 6 is that no sodium tripolyphosphate modifier is added, and the other steps are the same as Example 6.

[0106] Test example

[0107] The negative electrode materials, conductive carbon black and SBR prepared in the above Examples 1-10 and Comparative Examples 1-7 were mixed evenly in a mass ratio of 95:2:3 to obtain a negative electrode slurry, and the negative electrode slurry was coated on a copper foil and vacuum dried at 100°C for 8 hours to obtain a negative electrode sheet; lithium iron phosphate, conductive carbon black and PVDF were mixed evenly in a mass ratio of 95:2:3 to obtain a positive electrode slurry, and the positive electrode slurry was coated on an aluminum foil and vacuum dried at 100°C for 5 hours to obtain a positive electrode sheet; the positive electrode sheet, the negative electrode sheet, the separator and the electrolyte were assembled into a lithium-ion battery. After the assembled lithium-ion battery was left to stand for 3 hours, its first efficiency, 100-week capacity retention rate and the liquid absorption performance and rate performance (3C / 1C) of the negative electrode sheet were tested. The test results are shown in Table 1.

[0108] Table 1 Lithium-ion battery performance test data

[0109]

[0110]

[0111] From the data in Table 1, it can be seen that the first efficiency, 100-week capacity retention rate, and liquid absorption performance and rate performance (3C / 1C) of the lithium-ion battery containing the modified graphite negative electrode material provided by the present invention. The present invention effectively improves the first efficiency of the material by using a lithium-containing coating agent, and at the same time greatly improves the cycle performance of the material; the liquid absorption time of the negative electrode can be effectively shortened by using a surfactant and surface carbon coating, greatly improving the rate performance of the material.

[0112] In summary, the lithium ion battery containing modified graphite negative electrode material provided by the present invention has excellent initial efficiency, cycle stability, liquid absorption performance of the negative electrode and rate performance of the battery cell. The lithium ion battery provided by the present invention can meet the requirements of the capacity and cycle performance of lithium ion batteries in emerging fields such as electric vehicles and large-scale energy storage.

[0113] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A modified graphite negative electrode material, characterized in that: It includes a graphite main material, a lithium-containing coating agent, and a hydrophobic surface modifier; the lithium-containing coating agent includes a lithium-containing compound; the lithium-containing coating agent also includes a soft carbon precursor or a hard carbon precursor; the mass ratio of the lithium-containing compound to the soft carbon precursor or the hard carbon precursor is 1: (20-100); the soft carbon precursor is selected from one or more of low-temperature asphalt, medium-temperature asphalt, and high-temperature asphalt; the hard carbon precursor is selected from one or more of liquid phase resins and solid phase resins.

2. A modified graphite negative electrode material according to claim 1, characterized in that: The lithium-containing compound is selected from one or more of lithium powder, lithium hydride, lithium aluminum hydride, and butyl lithium.

3. A modified graphite negative electrode material according to claim 1, characterized in that: The hydrophobic surface modifier is selected from one or more of sodium stearate, sodium dodecylbenzene sulfonate, sodium tripolyphosphate and polysiloxane.

4. The modified graphite negative electrode material according to claim 1, characterized in that: The main graphite material is selected from at least one or more of natural graphite, natural spherical graphite, natural flake graphite, artificial graphite, and mesophase carbon microspheres; the main graphite material is a black powder material with a particle size of 5μm-60μm.

5. A method for preparing the modified graphite negative electrode material according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, heating and mixing the lithium-containing compound, the soft carbon precursor or the hard carbon precursor in an atmosphere of protective gas to obtain a lithium-containing coating agent; S2, adding the lithium-containing coating agent S1 to the graphite main material and mixing them evenly, and sintering them under a protective gas atmosphere to obtain a first modified graphite negative electrode material; S3, uniformly dispersing the first modified graphite negative electrode material S2 in deionized water, adding a hydrophobic surface modifier, stirring evenly, standing and drying to obtain a modified graphite negative electrode material.

6. The preparation method according to claim 5, characterized in that: In the S1, the heating temperature is 50-100°C; in the S1 and S2, the protective gas is nitrogen; in the S2, the sintering temperature is 800-1200°C, and the mass ratio of the lithium-containing coating agent to the graphite main material is (1-10):

100.

7. The preparation method according to claim 5, characterized in that: In the S3, the mass ratio of the hydrophobic surface modifier, the first modified graphite negative electrode material, and deionized water is (1-5):1000:2000.

8. A lithium-ion battery comprising a negative electrode sheet, a positive electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises the modified graphite negative electrode material according to any one of claims 1 to 4 or the modified graphite negative electrode material prepared by the preparation method according to any one of claims 5 to 7.

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