Hard carbon-soft carbon composite material with high initial efficiency, its preparation method and application

Abstract

The present invention relates to the technical field of lithium-ion battery materials, and particularly to a hard carbon-soft carbon composite material with high initial efficiency, its preparation method and application. The preparation method includes the following steps: S1. Lithium carboxymethyl cellulose is added to an aqueous solution of a hydrocarbon, and the resulting viscous composition is coated on the surface of a foam metal. The viscous composition and the foam metal are pressed together to obtain a precursor electrode sheet; S2. The precursor electrode sheet is transferred to a carbonization furnace for oxidation and then carbonization to obtain a hard carbon-soft carbon coated foam metal composite material; S3. The hard carbon-soft carbon coated foam metal composite material is placed in an inorganic acid or an organic acid for reaction, and the solid after filtration is pressed into tablets to obtain a hard carbon-soft carbon composite material with high initial efficiency. By adding lithium carboxymethyl cellulose to the aqueous solution of the hydrocarbon through a liquid phase method in the present invention, the surface of the material is loose and porous after carbonization, and the initial efficiency is higher than 96.5%, which is significantly higher than the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery materials, and particularly to a hard carbon-soft carbon composite material with high initial efficiency, a preparation method thereof, and an application thereof. Background Art

[0002] Hard carbon materials refer to carbons that are difficult to graphitize, with a highly disordered structure, good low-temperature performance, low expansion, and good cycling performance. However, their tap density is relatively low (about 1.0 g / cm 3 ), and their initial efficiency is relatively low (about 80%). The above properties limit the improvement of their energy density. Soft carbon belongs to the carbon material formed after the carbonization of asphalt, with a disordered structure and a moderate tap density (1.2 - 1.4 g / cm 3 ). However, it has a high voltage plateau, general rate performance, and slightly worse power performance than hard carbon. Therefore, developing a hard carbon / soft carbon composite material that combines the excellent rate performance and low voltage plateau of hard carbon with the high tap density of soft carbon can exert the synergistic effect between the two, thereby improving expansion, improving power, enhancing the initial efficiency, and increasing the energy density.

[0003] Chinese Patent CN107240680B discloses a hard carbon-metal oxide-soft carbon composite material, a preparation method thereof, and an application thereof. The initial Coulombic efficiency of the composite material is 72%. Chinese Patent CN113594461B discloses a carbon-silicon composite material, a preparation method thereof, and an application thereof. The highest initial efficiency is 87.9%. It can be seen that it is difficult for the materials in the prior art to break through 90% in terms of initial efficiency. Summary of the Invention

[0004] In order to solve the technical problem of the low initial efficiency of hard carbon materials, the first aspect of the present invention provides a preparation method of a hard carbon-soft carbon composite material with high initial efficiency. The preparation method includes the following steps:

[0005] S1. Lithium carboxymethyl cellulose is added to an aqueous solution of a hydrocarbon, and the obtained viscous composition is coated on the surface of a foam metal. The viscous composition and the foam metal are pressed together to obtain a precursor electrode sheet.

[0006] S2. The precursor electrode sheet is transferred to a carbonization furnace for oxidation and then carbonization to obtain a hard carbon-soft carbon coated foam metal composite material.

[0007] S3. The hard carbon-soft carbon coated foam metal composite material is placed in an inorganic acid or an organic acid for reaction, and the solid after filtration is pressed into tablets to obtain a hard carbon-soft carbon composite material with high initial efficiency.

[0008] In some embodiments, the mass ratio of the hydrocarbon to lithium carboxymethyl cellulose is 10:(1 - 5), and examples include 10:1, 10:1.1, 10:1.2, 10:1.3, 10:1.4, 10:1.5, 10:1.6, 10:1.7, 10:1.8, 10:1.9, 10:2, 10:3, 10:4, 10:5, but are not limited thereto.

[0009] The applicant found in the exploration that when the mass ratio of the hydrocarbon to lithium carboxymethyl cellulose is 10:(1 - 5), the specific capacity and the initial efficiency of the prepared hard carbon-soft carbon composite material are the highest. This may be because the hard carbon obtained after the carbonization of the hydrocarbon stores more lithium ions or sodium ions to provide capacity, and lithium carboxymethyl cellulose provides lithium ions to improve the initial efficiency. When the addition amount of lithium carboxymethyl cellulose is too small, the improvement of the initial efficiency and the rate performance of the material is not obvious, while too much addition will result in a lower specific capacity of the material.

[0010] In some embodiments, the hydrocarbon may be selected from at least one of glucose, sucrose, lignin, cellulose, starch, phenolic resin, polyacrylonitrile, epoxy resin, or may also be selected from other water-soluble hydrocarbons, and is not limited thereto. The concentration of the hydrocarbon aqueous solution is 10 - 30 wt%.

[0011] In some embodiments, the porous metal includes at least one of copper foam, nickel foam, aluminum foam, iron foam, iron-nickel foam, silver foam.

[0012] In some embodiments, the porosity of the porous metal is 50 - 90%, and the pore diameter is 1 mm - 10 mm.

[0013] To improve the electronic conductivity, it is preferred that the porous metal is copper foam with a porosity of 50 - 90% and a pore diameter of 1 mm - 10 mm, purchased from Suzhou Jiashide Porous Metal Co., Ltd., model 25PPI. The applicant found that the porosity and pore diameter of the porous metal have a great influence on the performance of the hard carbon-soft carbon composite material. If the porosity is too high, the electronic conductivity is poor, which reduces the rate performance and the mechanical strength of the material. If the porosity is too low, the loading amount of the hard carbon is too low, which is not conducive to improving the rate of the material and will also reduce the rate performance. Appropriate porosity and pore diameter can not only increase the loading amount, reduce the impedance and improve the rate, but also enhance the strength of the material.

[0014] In some embodiments, the single-sided coating thickness of the coating is 80 - 300 μm.

[0015] The coating thickness is closely related to the content of the pressed foam metal. If the coating amount is too low, after pressing, the coated substance does not cover the metal surface, and the metal directly contacts the electrolyte or the separator, which is likely to pierce the separator and cause a short circuit or the metal directly contacts the electrolyte to catalyze the electrolyte, resulting in more side reactions. If the coating amount is relatively large, the material is prone to powder falling during the process of pressing the electrode sheet, and the short-circuit rate is relatively high.

[0016] In some embodiments, the temperature of pressing in S1 is 50 - 100 °C, and the pressure is 1T - 5T.

[0017] In some embodiments, the oxidation conditions in S2 are oxidation for 30 - 300 min in an oxygen-containing mixed gas at a temperature of 200 - 400 °C and a flow rate of 100 - 500 mL / min.

[0018] Preferably, the oxygen-containing mixed gas includes oxygen and an inert gas, and the volume ratio of oxygen to the inert gas is 1:(5 - 10). The inert gas specifically includes any one of helium and nitrogen.

[0019] In some embodiments, the carbonization conditions in S2 are a temperature of 700 - 1100 °C and carbonization for 1 - 6 h.

[0020] In some embodiments, S3 includes: placing the hard carbon - soft carbon coated foam metal composite material in an inorganic acid or an organic acid for reaction, filtering, pressing the solid into tablets, pressing a lithium sheet on the surface, and dropping the electrolyte to obtain a hard carbon - soft carbon composite material with a high first efficiency.

[0021] Further, the hard carbon - soft carbon coated foam metal composite material is placed in an inorganic acid and soaked at a temperature of 30 - 100 °C for 12 - 36 h.

[0022] Further, the hard carbon - soft carbon coated foam metal composite material is placed in an inorganic acid, soaked at a temperature of 30 - 100 °C for 12 - 36 h, filtered, vacuum dried at 60 - 80 °C for 12 - 48 h, the obtained solid is pressed into tablets, the thickness after pressing is 50 - 200 μm, and a lithium sheet (the thickness of the lithium sheet is 0.5 - 3 mm) is pressed on its surface, and the electrolyte is dropped and left standing for 12 - 36 h to obtain a hard carbon - soft carbon composite material with a high first efficiency.

[0023] Further, the inorganic acid can be selected from any one of hydrochloric acid, sulfuric acid, and nitric acid, but is not limited thereto.

[0024] The second aspect of the present invention provides a hard carbon - soft carbon composite material with a high first efficiency.

[0025] In some embodiments, the first charge - discharge efficiency of the hard carbon - soft carbon composite material is higher than 96.5%.

[0026] The third aspect of the present invention provides an application of the described preparation method or the described hard carbon-soft carbon composite material in the field of lithium batteries.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. Compared with the prior art which generally adopts the solid-phase method, the present invention obtains a viscous composition by adding lithium carboxymethylcellulose to an aqueous solution of hydrocarbons through a liquid-phase method. The dispersion uniformity is good, and the addition of lithium carboxymethylcellulose makes the surface of the material porous and loose after carbonization. The first efficiency is higher than 96.5%, significantly higher than the prior art.

[0029] 2. The present invention coats the viscous composition on copper foam, which can further improve the electronic conductivity of the hard carbon-soft carbon composite material. Moreover, using network-shaped copper foam has better dispersion uniformity and lower expansion rate than adding copper powder.

[0030] 3. The present invention presses a lithium sheet on the surface of the hard carbon-soft carbon composite material, which can further improve the first efficiency of the material and improve the cycling and rate performance. Description of the Drawings

[0031] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0032] Figure 1 SEM image of the hard carbon-soft carbon composite material prepared in Example 1. Detailed Embodiments

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0034] Example 1

[0035] The first aspect of this example provides a preparation method of a hard carbon-soft carbon composite material with high first efficiency. The preparation method includes the following steps:

[0036] Step S1:

[0037] 100 g of glucose and 500 g of deionized water were formulated into a 20 wt% solution, and 30 g of lithium carboxymethyl cellulose was added thereto and mixed evenly to obtain a viscous composition, which was coated on copper foam (porosity: 60%, pore diameter: 5 mm), with a coating thickness of 150 μm, and pressed at a temperature of 80 °C and a pressure of 3 T for 1 h to obtain a precursor electrode sheet;

[0038] Step S2:

[0039] The precursor electrode sheet was transferred to a carbonization furnace, and an oxygen-containing mixed gas (V / V oxygen: argon = 3:10) was introduced, and oxidized at a temperature of 300 °C and a flow rate of 300 mL / min for 120 min to obtain an oxidized precursor electrode sheet; the oxidized precursor electrode sheet was transferred to a tube furnace and carbonized at a temperature of 900 °C for 3 h to obtain a hard carbon-soft carbon coated copper foam composite material;

[0040] Step S3:

[0041] 100 g of the hard carbon-soft carbon coated copper foam composite material was added to 500 g of hydrochloric acid (concentration 10 wt%), soaked at a temperature of 80 °C for 24 h, filtered to remove copper oxide, and vacuum dried at 80 °C for 24 h; the obtained solid was pressed into a sheet structure (thickness: 100 μm), and a lithium sheet (thickness 1 mm) was pressed on its surface, and an electrolyte was dropped and allowed to stand for 24 h to obtain a hard carbon-soft carbon composite material with a high first efficiency.

[0042] The second aspect of this embodiment provides a hard carbon-soft carbon composite material with a high first efficiency.

[0043] The third aspect of this embodiment provides an application of the hard carbon-soft carbon composite material in the field of lithium batteries.

[0044] Example 2

[0045] The first aspect of this embodiment provides a preparation method of a hard carbon-soft carbon composite material with a high first efficiency, and the preparation method includes the following steps:

[0046] Step S1:

[0047] 100 g of sucrose and 1000 g of deionized water were formulated into a 10 wt% solution, and 10 g of lithium carboxymethyl cellulose was added thereto and mixed evenly to obtain a viscous composition, which was coated on copper foam (porosity: 50%, pore diameter: 1 mm), with a coating thickness of 80 μm, and pressed at a temperature of 50 °C and a pressure of 5 T for 1 h to obtain a precursor electrode sheet;

[0048] Step S2:

[0049] Transfer the precursor electrode to a carbonization furnace, and introduce an oxygen-containing mixed gas (V / V oxygen: argon = 1:10). Oxidize it at a temperature of 200 °C and a flow rate of 100 mL / min for 300 min to obtain an oxidized precursor electrode; transfer the oxidized precursor electrode to a tubular furnace and carbonize it at a temperature of 700 °C for 6 h to obtain a hard carbon-soft carbon coated copper foam composite material;

[0050] Step S3:

[0051] Add 100 g of the hard carbon-soft carbon coated copper foam composite material to 500 g of hydrochloric acid (10 wt%), soak it at a temperature of 30 °C for 36 h, filter to remove copper oxide, and dry it in vacuum at 80 °C for 24 h; press the obtained solid into a sheet structure (thickness of 50 μm), press a lithium sheet (thickness of 0.5 mm) on its surface, and drop the electrolyte and let it stand for 36 h to obtain a hard carbon-soft carbon composite material with a high first efficiency.

[0052] The second aspect of this embodiment provides a hard carbon-soft carbon composite material with a high first efficiency.

[0053] The third aspect of this embodiment provides an application of the hard carbon-soft carbon composite material in the field of lithium batteries.

[0054] Example 3

[0055] The first aspect of this embodiment provides a preparation method of a hard carbon-soft carbon composite material with a high first efficiency, and the preparation method includes the following steps:

[0056] Step S1:

[0057] Prepare a 30 wt% solution by mixing 100 g of lignin and 333 g of deionized water, add 50 g of lithium carboxymethylcellulose to it and mix evenly to obtain a viscous composition, then coat it on copper foam (porosity is 90%, pore diameter is 10 mm), the coating thickness is 300 μm, and press it at a temperature of 100 °C and a pressure of 5 T for 1 h to obtain a precursor electrode;

[0058] Step S2:

[0059] Transfer the precursor electrode to a carbonization furnace, and introduce an oxygen-containing mixed gas (V / V oxygen: argon = 5:10). Oxidize it at a temperature of 400 °C and a flow rate of 500 mL / min for 300 min to obtain an oxidized precursor electrode; transfer the oxidized precursor electrode to a tubular furnace and carbonize it at a temperature of 1100 °C for 1 h to obtain a hard carbon-soft carbon coated copper foam composite material;

[0060] Step S3:

[0061] 100 g of hard carbon-soft carbon coated copper foam composite was added to 500 g of hydrochloric acid (10 wt%), soaked at 100 °C for 12 h, copper oxide was filtered off, and vacuum dried at 80 °C for 24 h; the obtained solid was pressed into a sheet structure (thickness 200 μm), a lithium sheet (thickness 3 mm) was pressed on its surface, and electrolyte was dropped and left standing for 12 h to obtain a hard carbon-soft carbon composite with high initial efficiency.

[0062] The second aspect of this embodiment provides a hard carbon-soft carbon composite with high initial efficiency.

[0063] The third aspect of this embodiment provides an application of the hard carbon-soft carbon composite in the field of lithium batteries.

[0064] Comparative Example 1

[0065] The first aspect of this comparative example provides a preparation method of a hard carbon-soft carbon composite with high initial efficiency. The specific implementation manner is the same as that of Example 1, except that the addition amount of lithium carboxymethyl cellulose is 0.

[0066] The second aspect of this comparative example provides a hard carbon-soft carbon composite with high initial efficiency.

[0067] The third aspect of this comparative example provides an application of the hard carbon-soft carbon composite in the field of lithium batteries.

[0068] Comparative Example 2

[0069] The first aspect of this comparative example provides a preparation method of a hard carbon-soft carbon composite with high initial efficiency. The specific implementation manner is the same as that of Example 1, except that the addition amount of lithium carboxymethyl cellulose is 70 g.

[0070] The second aspect of this comparative example provides a hard carbon-soft carbon composite with high initial efficiency.

[0071] The third aspect of this comparative example provides an application of the hard carbon-soft carbon composite in the field of lithium batteries.

[0072] Comparative Example 3

[0073] The first aspect of this comparative example provides a preparation method of a hard carbon-soft carbon composite with high initial efficiency. The specific implementation manner is the same as that of Example 1, except that step S3 includes adding 100 g of hard carbon-soft carbon coated copper foam composite to 500 g of hydrochloric acid (concentration 10 wt%), soaking at 80 °C for 24 h, filtering off copper oxide, and vacuum drying at 80 °C for 24 h; the obtained solid was pressed into a sheet structure (thickness 100 μm) to obtain a hard carbon-soft carbon composite with high initial efficiency.

[0074] The second aspect of this comparative example provides a hard carbon-soft carbon composite material with high initial efficiency.

[0075] The third aspect of this comparative example provides an application of the hard carbon-soft carbon composite material in the field of lithium batteries.

[0076] Performance testing

[0077] The hard carbon-soft carbon composite materials prepared in the examples and comparative examples were subjected to the following tests, and the test methods are as follows:

[0078] (1) Morphology characterization: The obtained hard carbon-soft carbon composite material was characterized by scanning electron microscopy.

[0079] Figure 1 For Example 1 of the present invention, a hard carbon-soft carbon composite material with high initial efficiency was prepared, which consisted of Figure 1 It can be seen that the obtained material is in the form of particles with a particle size between 5 - 10 μm, and the bright substances on the surface are lithium compound materials.

[0080] (2) Physical and chemical properties and coin cell tests

[0081] 2.1 Conductivity test: The hard carbon-soft carbon composite powder material was pressed into a block structure, and the conductivity was measured using a four-probe tester.

[0082] 2.2 Tap density test: Weigh 1 g of the hard carbon-soft carbon composite powder material and place it in a mold (10 mm). Press it with a pressure of 2 T for 10 s, measure and calculate the height difference h (mm) before and after pressing, and further calculate the tap density. The formula is as follows:

[0083] Tap density = 1 * 1000 / (π * 5 * 5 * h);

[0084] 2.3 Coin cell test:

[0085] Add LA132 binder, SP conductive agent, and solvent (secondary distilled water) to the hard carbon-soft carbon composite material in a weight ratio of 95:1:4:220. Stir and mix evenly to make a negative electrode slurry. Coat the negative electrode slurry (thickness 150 μm) on copper foil, dry it, roll it, and cut it to obtain a negative electrode sheet. Using a metal lithium sheet as the counter electrode, a polyethylene (PE) film, a polypropylene (PP) film, or a polyethylene-propylene (PEP) composite film as the separator, and LiPF6 / EC + DEC (the concentration of LiPF6 is 1.3 mol / L, and the volume ratio of EC and DEC is 1:1) as the electrolyte, assemble the battery in a glove box filled with argon.

[0086] The electrochemical performance tests were carried out on a Wuhan Blue Electric CT2001A battery tester. The charge-discharge voltage range was from 0.005 V to 2.0 V, and the charge-discharge rate was 0.1 C. At the same time, the specific capacity of its materials at a rate of 2 C was tested, and the rate performance (2 C / 0.1 C) was calculated. The test results are shown in Table 1;

[0087] Table 1

[0088]

[0089]

[0090] As can be seen from Table 1, the conductivity and rate performance of the powder materials of the materials in the examples are better than those of the comparative examples. The reason is that the viscous composition is coated on the copper foam, and the copper with high electronic conductivity is relied on to improve the electronic conductivity of the materials and the rate performance; at the same time, doping lithium carboxymethyl cellulose in the materials can reduce the irreversible capacity of the materials and improve the first efficiency of the materials.

[0091] (3) Soft-pack battery test

[0092] The negative electrodes were prepared from the hard carbon-soft carbon composite materials prepared in the examples and comparative examples respectively, the positive electrodes were prepared from ternary materials (LiNi 1 / 3Co 1 / 3 Mn 1 / 3 O2), and 2 Ah soft-pack batteries were prepared with LiPF6 (the solvent was EC + DEC, volume ratio 1:1, concentration 1.3 mol / L) as the electrolyte and Celgard 2400 as the separator.

[0093] The preparation method of the negative electrode was the same as that in the button battery test in 2.3.

[0094] When preparing the positive electrode, PVDF binder, SP conductive agent, and solvent (N-methylpyrrolidone) were added to the positive electrode material in a weight ratio of 93:3:4:140, and the mixture was stirred evenly to form a positive electrode paste. The positive electrode paste was coated on the aluminum foil, dried, rolled, and cut to obtain a positive electrode sheet.

[0095] 3.1 Rate performance test

[0096] The charge-discharge voltage range was 2.8 - 4.2 V, the test temperature was 25 ± 3.0 °C, and the batteries were charged at 1.0 C, 2.0 C, 3.0 C, and 5.0 C respectively and discharged at 1.0 C. The constant current ratio and temperature of the batteries under different charging modes were tested. The results are shown in Table 2:

[0097] Table 2

[0098]

[0099]

[0100] As can be seen from Table 2, the rate charge performance of the pouch cells of the embodiments of the present invention is significantly better than that of the comparative examples, and the charging time is shorter, indicating that the high first efficiency hard carbon-soft carbon composite material of the present invention has good fast charging performance. The reason may be that lithium oxide formed after the doping of lithium carboxymethyl cellulose in the hard carbon-soft carbon composite material improves the lithium ion diffusion rate during the charge and discharge process, thereby improving the rate performance; at the same time, lithium supplementation of the electrode sheet increases the number of lithium ions in the material and further improves the rate performance of the material.

[0101] 3.2 Cycle performance test

[0102] The pouch cells prepared from the hard carbon-soft carbon composite materials prepared in the examples and comparative examples as the negative electrode materials were subjected to the following experiments: at a charge-discharge rate of 2C / 2C and a voltage range of 2.8 - 4.2V, 100 times, 300 times, and 500 times of charge-discharge cycles were carried out in sequence, and their capacity retention rates were tested. The results are shown in Table 3:

[0103] Table 3

[0104]

[0105] As can be seen from Table 3, doping the hard carbon with a lithium compound by using the preparation method of the present invention can reduce its irreversible capacity, and lithium supplementation of the electrode sheet increases the number of lithium ions during the charge and discharge process, thereby improving the cycle performance.

[0106] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle described in the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. Preparation method of high first-efficiency hard carbon-soft carbon composite material, characterized in that, The preparation method comprises the following steps: S1. Lithium carboxymethyl cellulose is added to an aqueous solution of a hydrocarbon, and the obtained viscous composition is coated on the surface of a foam metal. The viscous composition and the foam metal are pressed together to obtain a precursor electrode sheet. The hydrocarbon may be selected from at least one of glucose, sucrose, lignin, cellulose, starch, phenolic resin, polyacrylonitrile, and epoxy resin; S2. The precursor electrode sheet is transferred to a carbonization furnace for oxidation and then carbonization to obtain a hard carbon-soft carbon coated foam metal composite material. The oxidation conditions are oxidation for 30-300 min in an oxygen-containing mixed gas at a temperature of 200-400 °C and a flow rate of 100-500 mL / min; S3. The hard carbon-soft carbon coated foam metal composite material is placed in an inorganic acid or an organic acid for reaction. After filtration, the solid is pressed into tablets to obtain a hard carbon-soft carbon composite material with a high first efficiency.

2. The preparation method of the high first efficiency hard carbon-soft carbon composite material according to claim 1, characterized in that The mass ratio of the hydrocarbon to lithium carboxymethyl cellulose is 10:(1-5).

3. The preparation method of the high initial efficiency hard carbon-soft carbon composite material according to claim 1, characterized in that, The carbonization conditions in S2 are a temperature of 700-1100 °C and carbonization for 1-6 h.

4. The preparation method of the high first-efficiency hard carbon-soft carbon composite material according to claim 1, wherein The foam metal includes at least one of foam copper, foam nickel, foam aluminum, foam iron, foam iron-nickel, and foam silver.

5. The preparation method of the high initial efficiency hard carbon-soft carbon composite material according to claim 4, characterized in that, The porosity of the foam metal is 50-90%, and the pore diameter is 1 mm-10 mm.

6. The preparation method of the high initial efficiency hard carbon-soft carbon composite material according to claim 1, characterized in that, S3 includes: placing the hard carbon-soft carbon coated foam metal composite material in an inorganic acid or an organic acid for reaction. After filtration, the solid is pressed into tablets and a lithium sheet is surface-pressed. After dropping an electrolyte, a hard carbon-soft carbon composite material with a high first efficiency is obtained.

7. A hard carbon-soft carbon composite material with a high first efficiency obtained by the preparation method according to any one of claims 1-6.

8. The high first-efficiency hard carbon-soft carbon composite material according to claim 7, characterized in that, The first charge-discharge efficiency of the hard carbon-soft carbon composite material is higher than 96.5%.

9. Application of the preparation method according to any one of claims 1-6 or the hard carbon-soft carbon composite material according to claim 7 in the field of lithium batteries.

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