Modified hard carbon-silicon carbon composite material, preparation method and application thereof, and lithium ion battery

Abstract

The application relates to a modified hard carbon silicon-carbon composite material and a preparation method and application thereof and a lithium ion battery, which comprises the following steps: mixing a hard carbon precursor with silicon monoxide to perform first calcination to prepare a hard carbon silicon-carbon composite material; mixing the hard carbon silicon-carbon composite material with carbon nanotubes filled with an organic lithium compound to perform second calcination to prepare a pre-lithiated hard carbon silicon-carbon composite material; and mixing the pre-lithiated hard carbon silicon-carbon composite material with a nitrogen source, a phosphorus source and an organic polymer to perform third calcination. The steps jointly act on each other, so that the modified hard carbon silicon-carbon composite material prepared has high first cycle efficiency and gram capacity when used as a negative electrode material, and has good cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and particularly to a modified hard carbon silicon-carbon composite material, its preparation method and application, and lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries (LIBs) and sodium-ion batteries (NIBs) are increasingly used in digital, power, and energy storage applications. Traditional negative electrode materials for LIBs and NIBs include natural graphite, artificial graphite, hard carbon, soft carbon, silicon-carbon, and lithium titanate. Among these, hard carbon exhibits good cycle performance as a negative electrode material, but its initial cycle efficiency and specific capacity are relatively low.

[0003] Therefore, it is of great significance to provide a hard carbon silicon-carbon composite material with high initial cycle efficiency and specific capacity, as well as good cycle performance. Summary of the Invention

[0004] Based on this, the present invention provides a modified hard carbon silicon-carbon composite material with high initial cycle efficiency and specific capacity, and good cycle performance, as well as its preparation method and application in lithium-ion batteries.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows.

[0006] A method for preparing a modified hard carbon-silicon-carbon composite material includes the following steps:

[0007] Hard carbon silicon-carbon composite material is prepared by mixing hard carbon precursor with silicon suboxide and then calcining it.

[0008] The hard carbon silicon carbon composite material was mixed with carbon nanotubes filled with organic lithium compounds and subjected to a second calcination to prepare a pre-lithiated hard carbon silicon carbon composite material.

[0009] The pre-lithiated hard carbon silicon-carbon composite material is mixed with a nitrogen source, a phosphorus source, and an organic polymer and then subjected to a third calcination.

[0010] In some embodiments, the preparation method of the modified hard carbon silicon-carbon composite material includes the following steps:

[0011] The hard carbon precursor is prepared by sequentially carbonizing and pulverizing biomass materials.

[0012] In some embodiments, in the preparation method of the modified hard carbon silicon carbon composite material, the biomass material is selected from at least one of walnut peel, tangerine peel, peanut shell, coconut shell, starch, sugarcane, corn, sweet potato, seaweed, wheat straw, wood and fruit shell.

[0013] In some embodiments, in the preparation method of the modified hard carbon silicon-carbon composite material, the mass ratio of the hard carbon precursor to the silicon suboxide is (3-100):(0.01-30).

[0014] In some embodiments, the preparation method of the modified hard carbon silicon-carbon composite material includes the following steps:

[0015] Carbon nanotubes, organolithium compounds, and organic solvents are mixed and refluxed.

[0016] In some embodiments, the carbon nanotubes in the preparation method of the modified hard carbon silicon carbon composite material have a diameter of 3 nm to 100 nm.

[0017] In some embodiments, in the preparation method of the modified hard carbon silicon carbon composite material, the mass ratio of the hard carbon silicon carbon composite material to the carbon nanotubes filled with organolithium compounds is (2-100):(0.01-20).

[0018] In some embodiments, in the preparation method of the modified hard carbon silicon carbon composite material, the mass ratio of the pre-lithiated hard carbon silicon carbon composite material, the nitrogen source, the phosphorus source and the organic polymer is (2-100):(0.1-20):(0.1-20):(0.2-50).

[0019] In some embodiments, in the preparation method of the modified hard carbon silicon-carbon composite material, the nitrogen source is selected from at least one of ammonia, ethylenediamine, propylenediamine, butanediamine, hexamethylenediamine, urea, pyridine, pyrrole, nitrogen-containing ionic liquid, ammonium hydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, ammonium carbonate, and ammonium bicarbonate.

[0020] In some embodiments, in the preparation method of the modified hard carbon silicon-carbon composite material, the phosphorus source is selected from at least one of elemental phosphorus, phosphorus pentoxide, lithium phosphate, ammonium hydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, and calcium phosphate.

[0021] In some embodiments, in the method for preparing the modified hard carbon silicon carbon composite material, the organic polymer is selected from at least one of epoxy resin, phenolic resin, polystyrene, polymethyl methacrylate, polyaniline, polyvinyl alcohol, and asphalt.

[0022] In some embodiments, in the preparation method of the modified hard carbon silicon carbon composite material, the first calcination temperature is 500℃~1500℃ and the time is 5h~40h.

[0023] In some embodiments, in the preparation method of the modified hard carbon silicon carbon composite material, the second calcination temperature is 200℃~1000℃ and the time is 1h~20h.

[0024] In some embodiments, in the preparation method of the modified hard carbon silicon-carbon composite material, the third calcination temperature is 300℃~1500℃ and the time is 1h~15h.

[0025] In some embodiments, the method for preparing modified hard carbon silicon-carbon composite material further includes, after the third calcination step, a step of coating the obtained doped pre-lithiated hard carbon silicon-carbon composite material.

[0026] In some embodiments, the coating treatment in the preparation method of the modified hard carbon silicon-carbon composite material includes the following steps:

[0027] The doped pre-lithiated hard carbon silicon-carbon composite material and a coating agent are mixed and subjected to a fourth calcination. The coating agent is selected from at least one of oxides, fluorides and phosphates.

[0028] In some embodiments, in the method for preparing the modified hard carbon silicon-carbon composite material, the oxide is selected from at least one of titanium oxide, aluminum oxide, zirconium oxide, magnesium oxide, iron oxide, niobium oxide, tungsten oxide, strontium oxide, copper oxide, cerium oxide, and yttrium oxide.

[0029] In some embodiments, in the method for preparing the modified hard carbon silicon-carbon composite material, the fluoride is selected from at least one of aluminum fluoride, zirconium fluoride, magnesium fluoride, calcium fluoride, lithium fluoride, sodium fluoride, and potassium fluoride.

[0030] In some embodiments, in the method for preparing the modified hard carbon silicon-carbon composite material, the phosphate is selected from at least one of lithium phosphate, sodium phosphate, aluminum phosphate, zirconium phosphate, calcium phosphate, and potassium phosphate.

[0031] The present invention also provides a modified hard carbon silicon carbon composite material, comprising a pre-lithiated hard carbon silicon carbon composite material A and a first coating layer B disposed on the surface of A;

[0032] A comprises a uniformly dispersed lithium composite a1 and a hard carbon-silicon-carbon composite a2;

[0033] a1 includes: carbon nanotubes and lithium compounds and carbon materials filled within the carbon nanotubes;

[0034] a2 includes: hard carbon, nano-silicon, and silicon dioxide, wherein nano-silicon and some silicon dioxide are dispersed in hard carbon, and some silicon dioxide is coated on the surface of hard carbon and nano-silicon particles.

[0035] B includes nitrogen and phosphorus-doped pyrolytic carbon.

[0036] In some embodiments, the modified hard carbon silicon-carbon composite material is doped with nitrogen and phosphorus elements.

[0037] In some embodiments, in the modified hard carbon silicon-carbon composite material, a second coating layer is provided on the surface of the first coating layer, the second coating layer comprising at least one of oxides, fluorides and phosphates.

[0038] This invention provides a modified hard carbon silicon carbon composite material prepared by the above-described method, or the application of the above-described modified hard carbon silicon carbon composite material in the preparation of lithium-ion batteries.

[0039] The present invention provides a lithium-ion battery, comprising a positive electrode, a separator, and a negative electrode, wherein the positive electrode and the negative electrode are disposed on opposite sides of the separator, and the material of the negative electrode comprises the modified hard carbon silicon carbon composite material described above.

[0040] Compared with the prior art, the preparation method of the modified hard carbon silicon carbon composite material of the present invention has the following beneficial effects:

[0041] The above-mentioned method for preparing modified hard carbon silicon-carbon composite materials effectively improves the crystal structure stability of hard carbon by mixing hard carbon precursors with silicon suboxide and then performing a first calcination. Specifically, silicon suboxide disproportionates to generate nano-silicon and silicon dioxide. Some of the silicon dioxide and nano-silicon are uniformly distributed within the hard carbon structure, effectively mitigating the volume change of the modified hard carbon silicon-carbon composite material during charge and discharge. Another portion of the silicon dioxide coats the surface of the nano-silicon and hard carbon particles, effectively mitigating the erosion of the nano-silicon and hard carbon by the electrolyte, thereby effectively improving the first cycle efficiency of the modified hard carbon silicon-carbon composite material. Furthermore, the prepared... Hard carbon-silicon-carbon composite materials are mixed with carbon nanotubes filled with organolithium compounds and then subjected to a second calcination. The organolithium compounds, filling the interior of the carbon nanotubes, effectively prevent side reactions caused by contact with oxygen, nitrogen, carbon dioxide, and moisture in the air, thus avoiding the loss of reactivity and effectively improving the stability of the organolithium compounds. After the second calcination, hydrocarbons are converted into carbon materials, which then combine with lithium elements within the carbon nanotubes, such as LiCx, further enhancing the stability of the organolithium compounds. The carbon nanotubes are uniformly dispersed in the hard carbon-silicon-carbon composite material, and the lithium elements within the carbon nanotubes... Abundant lithium sources, including elemental lithium and oxidized lithium, are provided to compensate for irreversible lithium loss during charge and discharge, effectively improving the initial cycle efficiency and specific capacity of the modified hard carbon silicon-carbon composite material. The prepared pre-lithiated hard carbon silicon-carbon composite material is then mixed with nitrogen, phosphorus, and organic polymers for a third calcination. Nitrogen and phosphorus doping in the pre-lithiated hard carbon silicon-carbon composite material forms ionic or covalent bonds with lithium and carbon, respectively. This facilitates the formation of a solid electrolyte film through electrochemical reactions between the surface of the modified hard carbon silicon-carbon composite material and the electrolyte during cycling, effectively reducing the intercalation of metal ions in the cathode material, thereby effectively improving the efficiency and specific capacity. The modified hard carbon silicon-carbon composite material exhibits excellent cycling performance. Furthermore, the carbon nitride, lithium nitride, silicon nitride, lithium phosphide, carbon phosphide, and silicon phosphide formed by nitrogen and phosphorus with lithium and carbon, respectively, possess electrical conductivity, thus effectively improving the conductivity of the modified hard carbon silicon-carbon composite material. Additionally, the organic polymer undergoes carbonization and decomposition, uniformly distributing on the surface of the pre-lithiated hard carbon silicon-carbon composite material, forming a nitrogen and phosphorus-doped pyrolytic carbon layer on the surface. This effectively reduces side reactions and irreversible capacity loss during cycling, while simultaneously improving the conductivity of the modified hard carbon silicon-carbon composite material. The combined effect of these steps results in a modified hard carbon silicon-carbon composite material exhibiting high initial cycle efficiency and specific capacity, as well as good cycling performance, when used as a negative electrode material. Attached Figure Description

[0042] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0043] Figure 1 SEM image of carbon nanotubes filled with n-butyllithium prepared in step (1) of Example 1;

[0044] Figure 2 The image shows a SEM image of the black hard carbon / silicon carbon composite material prepared in step (3) of Example 1.

[0045] Figure 3 SEM image of the modified hard carbon silicon carbon composite material prepared in step (6) of Example 1;

[0046] Figure 4 The image shows a SEM image of the modified hard carbon silicon-carbon composite material prepared in step (6) of Example 2.

[0047] Figure 5 The graph shows the cycle capacity retention of coin cells made from the modified hard carbon silicon-carbon composite material prepared in Example 1.

[0048] Figure 6 The graph shows the cycle capacity retention of coin cells made from the modified hard carbon silicon-carbon composite material prepared in Example 2.

[0049] Figure 7 The graph shows a comparison of the cycle capacity retention rates of thin-film batteries made from the modified hard carbon silicon-carbon composite materials of Examples 1-5 and Comparative Examples 1-5. Detailed Implementation

[0050] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. It should be understood that these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0052] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0053] The weights of the relevant components mentioned in the embodiments of this invention can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this invention is within the scope disclosed in the embodiments of this invention. Specifically, the weights mentioned in the embodiments of this invention can be well-known units of mass in the chemical industry, such as μg, mg, g, and kg.

[0054] An embodiment of the present invention provides a method for preparing a modified hard carbon silicon carbon composite material, comprising steps S10 to S30.

[0055] Step S10: Mix hard carbon precursor with silicon suboxide and perform a first calcination to prepare hard carbon silicon carbon composite material.

[0056] By mixing hard carbon precursors with silicon suboxide and performing a first calcination, silicon suboxide disproportionates to generate nano-silicon and silicon dioxide. Some of the silicon dioxide and nano-silicon are uniformly distributed in the hard carbon structure, effectively mitigating the volume change of the modified hard carbon silicon-carbon composite material during charge and discharge. Another part of the silicon dioxide coats the surface of the nano-silicon and hard carbon particles, effectively mitigating the erosion of the nano-silicon and hard carbon by the electrolyte, thereby effectively improving the first cycle efficiency of the modified hard carbon silicon-carbon composite material.

[0057] In some of these examples, in step S10, the mass ratio of hard carbon precursor to silicon suboxide is (3-100):(0.01-30).

[0058] In some of these examples, in step S10, the mass ratio of hard carbon precursor to silicon suboxide is (3-100):1.

[0059] It is understood that the mass ratio of hard carbon precursor to silicon suboxide includes, but is not limited to, 3:1, 4:1, 5:1, 5.7:1, 6:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, and 100:1.

[0060] Optionally, in step S10, the mass ratio of hard carbon precursor to silicon suboxide is (3-10):1.

[0061] Further, in step S10, the mass ratio of hard carbon precursor to silicon suboxide is (3-6):1.

[0062] In some of these examples, in step S10, the temperature of the first calcination is 500℃~1500℃ and the time is 5h~40h.

[0063] It is understood that the temperature of the first calcination includes, but is not limited to, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1100℃, 1200℃, 1300℃, and 1500℃; and the time includes, but is not limited to, 5h, 8h, 10h, 12h, 15h, 18h, 20h, 25h, 30h, 35h, and 40h.

[0064] Optionally, the temperature of the first calcination is 800℃~1200℃, and the time is 8h~20h.

[0065] In some of these examples, in step S10, a first calcination is performed under a protective atmosphere.

[0066] Furthermore, the protective atmosphere is selected from at least one of nitrogen, helium, and argon.

[0067] In some of these examples, step S10, the preparation of the hard carbon precursor includes step S11.

[0068] Step S11: Carbonize and pulverize the biomass material sequentially to prepare a hard carbon precursor.

[0069] In some of these examples, in step S11, the carbonization temperature is 100℃~500℃ and the time is 3h~20h.

[0070] It is understood that the carbonization temperature includes, but is not limited to, 100℃, 150℃, 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, and 500℃; and the carbonization time includes, but is not limited to, 3h, 5h, 10h, 12h, 15h, 18h, and 20h.

[0071] Optionally, the carbonization temperature is 300℃~400℃.

[0072] In some of these examples, in step S11, the carbonization process is carried out under a vacuum or protective atmosphere.

[0073] Furthermore, the protective atmosphere is selected from at least one of nitrogen, helium, and argon.

[0074] It is understandable that the carbonization product is crushed to obtain granular hard carbon precursor.

[0075] In some of these examples, in step S11, the biomass material is a biomass material rich in phenyl functional groups.

[0076] In some of these examples, in step S11, the biomass material is selected from at least one of walnut husks, tangerines, peanut shells, starch, coconut shells, sugarcane, corn, sweet potatoes, seaweed, wheat straw, wood, and fruit shells.

[0077] It is understandable that walnut husks, tangerine peels, peanut shells, starch, sugarcane, coconut shells, corn, sweet potatoes, seaweed, wheat straw, wood, and fruit shells each contain varying amounts of benzene ring compounds.

[0078] Walnut husks, a waste product of the walnut industry, are rich in benzene ring compounds, such as total polyphenols, flavonoids, and polysaccharides. Walnut husk juice and husk residue contain more than 100 mg / g of total polyphenols and more than 60 mg / g of flavonoids, making them a good source of hard carbon materials.

[0079] Biomass materials are rich in phenyl functional groups. When mixed with silicon suboxide and calcined, they can effectively improve the crystal structure stability of hard carbon and further enhance the recycling performance of modified hard carbon-silicon-carbon composites.

[0080] Step S20: The hard carbon silicon carbon composite material prepared in step S10 is mixed with carbon nanotubes filled with organolithium compounds and subjected to a second calcination to prepare a pre-lithiated hard carbon silicon carbon composite material.

[0081] Hard carbon-silicon-carbon composite materials are mixed with carbon nanotubes filled with organolithium compounds and then subjected to a second calcination. The carbon nanotubes filled with organolithium compounds are uniformly dispersed in the hard carbon-silicon-carbon composite material, and the organolithium compounds are filled inside the carbon nanotubes. This effectively avoids side reactions between the organolithium compounds and oxygen, nitrogen, carbon dioxide, and moisture in the air, which would cause the organolithium compounds to lose their reactivity, thus effectively improving the stability of the organolithium compounds. After the second calcination, hydrocarbon elements are converted into carbon materials and combined with lithium elements inside the carbon nanotubes, such as LiCx, further improving the stability of the organolithium compounds. The carbon nanotubes are uniformly dispersed in the hard carbon-silicon-carbon composite material, and the lithium elements in the carbon nanotubes provide abundant lithium sources in the form of elemental lithium and oxidized lithium, replenishing irreversible lithium resources during charge and discharge, effectively improving the first cycle efficiency and specific capacity of the modified hard carbon-silicon-carbon composite material.

[0082] In some of these examples, in step S20, the mass ratio of the hard carbon silicon carbon composite material to the carbon nanotubes filled with organolithium compounds is (2-100):(0.01-20).

[0083] Optionally, in step S20, the mass ratio of the hard carbon silicon carbon composite material to the carbon nanotubes filled with organolithium compounds is (2-100):1.

[0084] It is understood that the mass ratio of hard carbon silicon carbon composite material to carbon nanotubes filled with organolithium compounds includes, but is not limited to, 2:1, 3:1, 4:1, 5:1, 5.7:1, 6:1, 10:1, 15:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, and 100:1.

[0085] Further, in step S20, the mass ratio of the hard carbon silicon carbon composite material to the carbon nanotubes filled with organolithium compounds is (5-20):1.

[0086] In some of these examples, in step S20, the temperature of the second calcination is 200℃~1000℃ and the time is 1h~20h.

[0087] It is understood that the temperature of the second calcination includes, but is not limited to, 200℃, 300℃, 400℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, and 1000℃; and the time includes, but is not limited to, 1h, 3h, 5h, 8h, 10h, 12h, 15h, 18h, and 20h.

[0088] Optionally, in step S20, the temperature of the second calcination is 400℃~800℃.

[0089] In some of these examples, in step S20, a second calcination is performed under a protective atmosphere.

[0090] Furthermore, the protective atmosphere is selected from at least one of nitrogen, helium, and argon.

[0091] In some of these examples, in step S20, the product obtained from the second calcination is pulverized.

[0092] In some of these examples, step S20, the preparation of carbon nanotubes filled with organolithium compounds, includes step S21.

[0093] Step S21: Mix and reflux the carbon nanotubes, organolithium compounds and organic solvents.

[0094] In some of these examples, in step S21, the diameter of the carbon nanotubes is 3 nm to 100 nm.

[0095] In some of these examples, in step S21, at least one end of the carbon nanotube is open.

[0096] In some of these examples, in step S21, the organolithium compound is selected from at least one of substituted or unsubstituted methyllithium, ethyllithium, butyllithium, hexyllithium, phenyllithium, tolyllithium, xylyllithium, triphenyllithium, and naphthyllithium.

[0097] In some of these examples, in step S21, the organic solvent is selected from at least one of ether solvents, tetrahydrofuran, tetrahydrofuran derivatives, benzene, toluene, xylene, and trimethylbenzene.

[0098] It is understood that ether solvents include, but are not limited to, diethyl ether and propylene oxide.

[0099] Furthermore, in step S21, the organic solvent is tetrahydrofuran.

[0100] In some of these examples, step S21 further includes the addition of at least one of an alkane derivative and an aromatic hydrocarbon derivative during the mixing reflux process.

[0101] Furthermore, the alkane derivatives are haloalkanes, and the aromatic hydrocarbon derivatives are haloaromatics.

[0102] In some of these examples, in step S21, reflux is performed in a vacuum or protective gas.

[0103] In some of these examples, in step S21, the reflux temperature is 100℃~200℃ and the time is 3h~100h.

[0104] In some examples, in step S21, after reflux, the reaction solution is sequentially filtered, washed, and dried. Further, petroleum ether is used for washing.

[0105] It is understandable that the product obtained in step S21 is an organolithium compound filled inside carbon nanotubes.

[0106] Step S30: The pre-lithiated hard carbon silicon-carbon composite material prepared in step S20 is mixed with a nitrogen source, a phosphorus source and an organic polymer and subjected to a third calcination to obtain a doped pre-lithiated hard carbon silicon-carbon composite material.

[0107] The pre-lithiated hard carbon silicon-carbon composite material is mixed with a nitrogen source, a phosphorus source, and an organic polymer and then subjected to a third calcination. Nitrogen and phosphorus doping in the pre-lithiated hard carbon silicon-carbon composite material forms ionic or covalent bonds with lithium and carbon, respectively. This facilitates the formation of a solid electrolyte film through electrochemical reactions between the surface of the modified hard carbon silicon-carbon composite material and the electrolyte during cycling, effectively reducing the intercalation of metal ions in the cathode material and thus improving the cycling performance of the modified hard carbon silicon-carbon composite material. Furthermore, the carbon nitride, lithium nitride, silicon nitride, lithium phosphide, carbon phosphide, and silicon phosphide formed by nitrogen and phosphorus with lithium and carbon, respectively, are conductive, thereby effectively improving the conductivity of the modified hard carbon silicon-carbon composite material. Additionally, the organic polymer undergoes carbonization and decomposition, uniformly distributing on the surface of the pre-lithiated hard carbon silicon-carbon composite material, forming a nitrogen and phosphorus-doped pyrolytic carbon layer on the surface of the pre-lithiated hard carbon silicon-carbon composite material. This effectively reduces side reactions and irreversible capacity loss during cycling, while simultaneously improving the conductivity of the modified hard carbon silicon-carbon composite material.

[0108] In some examples, in step S30, the mass ratio of the pre-lithiated hard carbon silicon-carbon composite material, nitrogen source, phosphorus source and organic polymer is (2-100):(0.1-20):(0.1-20):(0.2-50).

[0109] It is understandable that a substance can contain nitrogen and phosphorus elements, meaning that the nitrogen source and phosphorus source can be the same substance. In this case, the mass ratio of the pre-lithiated hard carbon silicon carbon composite material to the total mass of the nitrogen and phosphorus sources, and the mass ratio of the organic polymer are (2-100):(0.2-40):(0.2-50).

[0110] Furthermore, it can be understood that the mass of the nitrogen source is set to 1, and the mass of the pre-lithiated hard carbon silicon carbon composite material includes, but is not limited to, 2, 5, 10, 20, 30, 40, 50, 60, 80, and 100; the mass of the phosphorus source includes, but is not limited to, 0.1, 0.5, 1, 2, 5, 10, and 20; and the mass of the organic polymer includes, but is not limited to, 0.2, 0.5, 1, 2, 5, 10, 15, 20, 30, 40, and 50.

[0111] In some of these examples, in step S30, the nitrogen source is selected from at least one of ammonia, ethylenediamine, propylenediamine, butanediamine, hexamethylenediamine, urea, pyridine, pyrrole, nitrogen-containing ionic liquid, ammonium hydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, ammonium carbonate, and ammonium bicarbonate.

[0112] In some of these examples, in step S30, the phosphorus source is selected from at least one of elemental phosphorus, phosphorus pentoxide, lithium phosphate, ammonium hydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, and calcium phosphate.

[0113] In some of these examples, in step S30, the organic polymer is selected from at least one of epoxy resin, phenolic resin, polystyrene, polymethyl methacrylate, polyaniline, polyvinyl alcohol, and bitumen.

[0114] The benzene ring structure contained in organic polymers decomposes into a hard carbon structure during pyrolysis, which has a higher interlayer spacing than ordinary graphite, thus improving the ion insertion and migration rates.

[0115] In some of these examples, in step S30, the temperature of the third calcination is 300℃~1500℃ and the time is 1h~15h.

[0116] It is understood that the temperature of the first calcination includes, but is not limited to, 300℃, 350℃, 400℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1100℃, 1200℃, 1300℃, and 1500℃; and the time includes, but is not limited to, 1h, 3h, 5h, 8h, 10h, 12h, and 15h.

[0117] Optionally, in step S30, the temperature of the third calcination is 400℃~1000℃.

[0118] In some of these examples, in step S30, a third calcination is performed under a protective atmosphere.

[0119] Furthermore, the protective atmosphere is selected from at least one of nitrogen, helium, and argon.

[0120] In some of these examples, in step S30, the product obtained from the third calcination is pulverized.

[0121] In some of these examples, the preparation method of the modified hard carbon silicon carbon composite material also includes step S40.

[0122] Step S40: Coating the doped pre-lithiated hard carbon silicon-carbon composite material obtained in step S30.

[0123] Coating the doped pre-lithiated hard carbon silicon-carbon composite material with a coating process can further improve the protective ability of the modified hard carbon silicon-carbon composite material.

[0124] In some of these examples, step S40, the coating process includes the following steps:

[0125] The doped pre-lithiated hard carbon silicon-carbon composite material and the coating agent are mixed and subjected to a fourth calcination. The coating agent is selected from at least one of oxides, fluorides and phosphates.

[0126] In some of these examples, in step S40, the oxide is selected from at least one of titanium oxide, aluminum oxide, zirconium oxide, magnesium oxide, iron oxide, niobium oxide, tungsten oxide, strontium oxide, copper oxide, cerium oxide, and yttrium oxide.

[0127] In some of these examples, in step S40, the fluoride is selected from at least one of aluminum fluoride, zirconium fluoride, magnesium fluoride, calcium fluoride, lithium fluoride, sodium fluoride, and potassium fluoride.

[0128] In some of these examples, in step S40, the phosphate is selected from at least one of lithium phosphate, sodium phosphate, aluminum phosphate, zirconium phosphate, calcium phosphate, and potassium phosphate.

[0129] By controlling the type of coating agent, side reactions of the electrolyte on the negative electrode material can be further prevented or reduced, thereby improving the coulombic efficiency and cycle performance of the modified hard carbon silicon-carbon composite material.

[0130] In some of these examples, in step S40, the mass ratio of the doped pre-lithiated hard carbon silicon-carbon composite material to the coating agent is (1-100):(0.001-20).

[0131] In some of these examples, in step S40, the mass ratio of the doped pre-lithiated hard carbon silicon-carbon composite material to the coating agent is 1:(0.001 to 20).

[0132] It is understood that the mass ratio of the doped pre-lithiated hard carbon silicon carbon composite material to the coating agent includes, but is not limited to, 0.001:1, 0.01:1, 0.011:1, 0.02:1, 0.05:1, 0.08:1, 0.10:1, 0.12:1, 0.13:1, and 0.15:1.

[0133] Optionally, in step S40, the mass ratio of the doped pre-lithiated hard carbon silicon carbon composite material to the coating agent is 1:(0.01~0.15).

[0134] In some of these examples, in step S40, the fourth calcination temperature is 200℃~1000℃ and the time is 1h~15h.

[0135] It is understood that the fourth calcination temperature includes, but is not limited to, 200℃, 300℃, 400℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, and 1000℃; and the time includes, but is not limited to, 1h, 3h, 5h, 8h, 10h, 12h, and 15h.

[0136] Optionally, the fourth calcination temperature is 400℃~800℃, and the time is 5h~12h.

[0137] In some of these examples, in step S40, a first calcination is performed under a protective atmosphere.

[0138] Furthermore, the protective atmosphere is selected from at least one of nitrogen, helium, and argon.

[0139] In some of these examples, in step S40, the product obtained from the fourth calcination is pulverized.

[0140] The above-mentioned method for preparing modified hard carbon silicon-carbon composite materials works together to produce a modified hard carbon silicon-carbon composite material with high initial cycle efficiency and specific capacity when used as a negative electrode material, as well as good cycle and high and low temperature performance.

[0141] One embodiment of the present invention provides a modified hard carbon silicon carbon composite material, which is prepared by the above-described method for preparing modified hard carbon silicon carbon composite materials.

[0142] One embodiment of the present invention provides a modified hard carbon silicon carbon composite material, comprising a pre-lithiated hard carbon silicon carbon composite material A and a first coating layer B disposed on the surface of A;

[0143] A comprises a uniformly dispersed lithium composite a1 and a hard carbon-silicon-carbon composite a2;

[0144] a1 includes: carbon nanotubes and lithium compounds and carbon materials filled within the carbon nanotubes;

[0145] a2 includes: hard carbon, nano-silicon and silicon dioxide, wherein nano-silicon and some silicon dioxide are dispersed in hard carbon, and some silicon dioxide is coated on the surface of hard carbon and nano-silicon particles;

[0146] B includes nitrogen and phosphorus-doped pyrolytic carbon.

[0147] In some of these examples, the modified hard carbon silicon-carbon composite material is pre-lithiated hard carbon silicon-carbon composite material doped with nitrogen and phosphorus elements.

[0148] It is understandable that the lithium composite a1 and the hard carbon silicon carbon composite a2 are doped with nitrogen and phosphorus elements.

[0149] In some of these examples, in the modified hard carbon silicon-carbon composite material, a second coating layer is disposed on the surface of the first coating layer, the second coating layer comprising at least one of oxides, fluorides, and phosphates.

[0150] One embodiment of the present invention provides a modified hard carbon silicon-carbon composite material prepared by the above-described method for preparing the modified hard carbon silicon-carbon composite material, or the application of the above-described modified hard carbon silicon-carbon composite material in the preparation of lithium-ion batteries. Another embodiment of the present invention provides a lithium-ion battery negative electrode material comprising the modified hard carbon silicon-carbon composite material prepared by the above-described method for preparing the modified hard carbon silicon-carbon composite material, or the above-described modified hard carbon silicon-carbon composite material.

[0151] The modified hard carbon silicon carbon composite material prepared by the above-mentioned method, or the modified hard carbon silicon carbon composite material used in the preparation of lithium-ion battery anode materials, can impart higher first-cycle efficiency and specific capacity to lithium-ion battery anode materials.

[0152] In some embodiments, the lithium-ion battery anode material may be a modified hard carbon silicon-carbon composite material prepared by the above-described method for preparing modified hard carbon silicon-carbon composite material, or the above-described modified hard carbon silicon-carbon composite material itself; that is, the lithium-ion battery anode material may be directly prepared using the modified hard carbon silicon-carbon composite material prepared by the above-described method for preparing modified hard carbon silicon-carbon composite material, or the above-described modified hard carbon silicon-carbon composite material. In other embodiments, the lithium-ion battery cathode material may include, in addition to the modified hard carbon silicon-carbon composite material prepared by the above-described method for preparing modified hard carbon silicon-carbon composite material, or the above-described modified hard carbon silicon-carbon composite material, other materials.

[0153] One embodiment of the present invention provides a lithium-ion battery, including a positive electrode, a separator, and a negative electrode. The positive electrode and the negative electrode are disposed on both sides of the separator. The material of the negative electrode includes the modified hard carbon silicon carbon composite material prepared by the above-mentioned method for preparing modified hard carbon silicon carbon composite material or the above-mentioned modified hard carbon silicon carbon composite material.

[0154] One embodiment of the present invention provides the application of the above-described lithium-ion battery in electronic devices, power tools, electric vehicles, or energy storage systems. Another embodiment of the present invention provides electronic devices, power tools, electric vehicles, or energy storage systems incorporating the above-described lithium-ion battery. Specific Implementation

[0156] The following examples of the modified hard carbon silicon-carbon composite material, its preparation method, its application, and lithium-ion batteries according to the present invention are not limited to the following embodiments.

[0157] In the following examples, surface morphology was measured using a JEOL JSM-6510 scanning electron microscope (SEM) and a Zeiss EV018 scanning electron microscope (SEM) (Germany), and D50 was measured using a Malvern Mastersizer 2000 laser particle size analyzer (UK).

[0158] The dehydration steps of anhydrous tetrahydrofuran used in the following examples are as follows: Tetrahydrofuran is placed in a distillation flask, metallic sodium is added to the bottom, vacuum is drawn, and the mixture is heated to 150°C and refluxed for 48 hours to obtain anhydrous tetrahydrofuran.

[0159] Example 1

[0160] (1) Place 1000 mL of anhydrous tetrahydrofuran in a round-bottom flask, add 100 g of multi-walled carbon nanotubes (inner diameter 10 nm, tube length > 50 μm), 5 g of lithium metal and 30 g of n-butyl chloride, add a magnetic stir bar, evacuate, stir and reflux at 180 °C for 20 h, cool to room temperature, filter under an argon protective atmosphere, wash three times with petroleum ether, filter dry, and obtain carbon nanotubes filled with n-butyl lithium, which are then sealed and stored; the SEM image of the prepared carbon nanotubes filled with n-butyl lithium is shown below. Figure 1 As shown;

[0161] (2) 2000g of green walnut skin was washed and dried, carbonized at 400℃ under nitrogen atmosphere, mechanically crushed and passed through a 100-mesh sieve to prepare 1140g of hard carbon precursor.

[0162] (3) The 1140g hard carbon precursor and 200g silicon suboxide (99.0%) obtained in step (2) were mixed evenly with anhydrous ethanol, dried, mechanically pulverized and passed through a 50-mesh sieve, placed in a muffle furnace, heated to 1100℃ under a nitrogen atmosphere at a heating rate of 5℃ / min, held for 8h, naturally cooled to room temperature, mechanically pulverized and passed through a 100-mesh sieve to prepare a black hard carbon / silicon carbon composite material. Its SEM image is shown below. Figure 2 As shown;

[0163] (4) Mix 1000g of the hard carbon / silicon carbon composite material obtained in step (3) and 50g of the carbon nanotubes filled with n-butyllithium obtained in step (1) in a nitrogen atmosphere, place them in a muffle furnace, heat them in a nitrogen atmosphere at a rate of 3℃ / min, heat them to 400℃, keep them at that temperature for 5h, cool them naturally to room temperature, mechanically crush them, and pass them through a 100-mesh sieve to prepare a black pre-lithiated hard carbon / silicon carbon composite material.

[0164] (5) Mix 1000g of pre-lithiated hard carbon / silicon carbon composite material obtained in step (4) with 20g of ethylenediamine, 10g of phosphorus pentoxide and 200g of phenolic resin particles with anhydrous ethanol, dry, mechanically crush and pass through a 50-mesh sieve, place in a muffle furnace, heat under a nitrogen atmosphere at a muffle furnace heating rate of 5℃ / min, heat to 1200℃, keep at the temperature for 10 hours, cool naturally to room temperature, mechanically crush and pass through a 400-mesh sieve to prepare black nitrogen and phosphorus doped pre-lithiated hard carbon / silicon carbon composite material;

[0165] (6) Mix 1000g of the black nitrogen-phosphorus doped pre-lithiated hard carbon / silicon-carbon composite material obtained in step (5) with 5g of alumina, 3g of magnesium fluoride and 5g of lithium phosphate in a high-speed mixer. Heat the mixture to 500℃ in a muffle furnace at a heating rate of 3℃ / min under a nitrogen atmosphere, hold for 8 hours, cool naturally to room temperature, mechanically pulverize, and pass through a 400-mesh sieve to obtain the black alumina, magnesium fluoride and lithium phosphate coated nitrogen-phosphorus doped pre-lithiated hard carbon / silicon-carbon composite material, i.e., modified hard carbon silicon-carbon composite material. Its SEM image is shown below. Figure 3 As shown.

[0166] Example 2

[0167] It is basically the same as Example 1, except that:

[0168] (1) Replace the n-butyl chloride in Example 1 with an equal amount of benzyl chloride;

[0169] (2) The biomass materials are 1000g of green walnut husks and 1000g of orange stalks;

[0170] (3) Mix 1000g of hard carbon precursor and 300g of silicon suboxide (99.0%) with anhydrous ethanol until homogeneous;

[0171] (4) Mix 1000g of the hard carbon / silicon carbon composite material obtained in step (3) and 100g of the carbon nanotubes filled with n-butyllithium obtained in step (1) evenly under a nitrogen atmosphere.

[0172] (5) Mix 1000g of pre-lithiated hard carbon / silicon carbon composite material obtained in step (4) with 10g of ammonium phosphate, 100g of epoxy resin, 100g of polymethyl methacrylate and 100g of petroleum asphalt particles with anhydrous ethanol.

[0173] (6) Mix 1000g of the black nitrogen-phosphorus doped pre-lithiated hard carbon / silicon carbon composite material obtained in step (5) with 5g of titanium oxide and 5g of sodium phosphate in a high-speed mixer until uniform;

[0174] The final SEM image of the modified hard carbon silicon-carbon composite material is shown below. Figure 4 As shown.

[0175] Example 3

[0176] It is basically the same as Example 1, except that:

[0177] (1) Multi-walled carbon nanotubes (inner diameter 7nm, tube length >70μm), replacing n-butyl chloride in Example 1 with an equal amount of naphthol;

[0178] (2) Biomass materials consist of 400g each of sugarcane stalks, sweet potato stalks, and corn stalks;

[0179] (4) Mix 1000g of the hard carbon / silicon carbon composite material obtained in step (3) and 200g of the carbon nanotubes filled with n-butyllithium obtained in step (1) evenly under a nitrogen atmosphere, place them in a muffle furnace, heat them under a nitrogen atmosphere at a heating rate of 3℃ / min, heat them to 450℃, and keep them at that temperature for 5h.

[0180] (5) Mix 1000g of pre-lithiated hard carbon / silicon carbon composite material obtained in step (4) with 10g of ionic liquid 1-butyl-3-methylimidazolium dinitrile amine salt, 10g of calcium phosphate, 50g of polystyrene, 50g of polymethyl methacrylate, and 50g of polyaniline particles with anhydrous ethanol.

[0181] (6) Mix 1000g of the black nitrogen-phosphorus doped pre-lithiated hard carbon / silicon carbon composite material obtained in step (5) with 5g of tungsten oxide, 5g of copper oxide and 5g of potassium phosphate in a high-speed mixer.

[0182] Example 4

[0183] It is basically the same as Example 1, except that:

[0184] (1) Multi-walled carbon nanotubes (inner diameter 5nm, tube length >80μm), replacing n-butyl chloride in Example 1 with an equal amount of chlorotoluene;

[0185] (2) The biomass materials are 500 grams of green walnut skin and 500 grams of starch;

[0186] (3) Mix 1000g of hard carbon precursor and 300g of silicon suboxide (99.0%) obtained in step (2) with anhydrous ethanol, dry, mechanically pulverize and pass through a 50-mesh sieve, place in a muffle furnace, heat under a nitrogen atmosphere, the muffle furnace heating rate is 5℃ / min, heat to 1050℃, and hold for 5h.

[0187] (4) Mix 1000g of the hard carbon / silicon carbon composite material obtained in step (3) and 200g of the carbon nanotubes filled with n-butyllithium obtained in step (1) evenly under a nitrogen atmosphere.

[0188] (5) Mix 1000g of pre-lithiated hard carbon / silicon carbon composite material obtained in step (4) with 15g of pyridine, 10g of ammonium monohydrogen phosphate, 100g of polymethyl methacrylate and 100g of polyaniline particles with anhydrous ethanol.

[0189] (6) Mix 1000g of the black nitrogen-phosphorus doped pre-lithiated hard carbon / silicon carbon composite material obtained in step (5) with 5g of iron oxide, 3g of niobium oxide and 4g of potassium phosphate in a high-speed mixer.

[0190] Example 5

[0191] It is basically the same as Example 1, except that:

[0192] (1) Replace the n-butyl chloride in Example 1 with an equal amount of chloroethane;

[0193] (2) The biomass materials consist of 5000g of wood and 5000g of wheat straw;

[0194] (3) Mix 1000g of hard carbon precursor and 250g of silicon suboxide (99.0%) with anhydrous ethanol, dry, mechanically pulverize and pass through a 50-mesh sieve, place in a muffle furnace, heat under a nitrogen atmosphere at a rate of 5℃ / min, heat to 1250℃, and hold for 5h.

[0195] (5) Mix 1000g of pre-lithiated hard carbon / silicon carbon composite material obtained in step (4) with 10g of pyrrole, 10g of ammonium phosphate, 100g of polyvinyl alcohol and 100g of asphalt particles with anhydrous ethanol until homogeneous.

[0196] (6) Mix 1000g of the black nitrogen-phosphorus doped pre-lithiated hard carbon / silicon carbon composite material obtained in step (5) with 2g of titanium oxide, 2g of niobium oxide, 2g of yttrium oxide and 5g of zirconium phosphate in a high-speed mixer.

[0197] Example 6

[0198] It is basically the same as Example 1, except that step (6) is omitted.

[0199] Comparative Example 1

[0200] (1) 2000g of green walnut skin was washed and dried, carbonized at 400℃ under nitrogen atmosphere, mechanically crushed and passed through a 100-mesh sieve to prepare 1140g of hard carbon precursor.

[0201] (2) The hard carbon precursor and n-butyllithium were mixed evenly under a nitrogen atmosphere, placed in a muffle furnace, heated under a nitrogen atmosphere at a heating rate of 3℃ / min, heated to 400℃, held for 5h, cooled naturally to room temperature, mechanically crushed, and passed through a 100-mesh sieve to prepare the pre-lithiated hard carbon material.

[0202] (3) Mix 1000g of pre-lithiated hard carbon material, 5g of alumina, and 5g of lithium phosphate in a high-speed mixer. Heat the mixture in a nitrogen atmosphere at a muffle furnace heating rate of 3℃ / min to 500℃, hold for 8 hours, cool naturally to room temperature, mechanically crush, and pass through a 400-mesh sieve to prepare the hard carbon composite material.

[0203] Comparative Example 2

[0204] It is basically the same as Example 1, except that it does not include steps (1) and (4). In step (5), the black hard carbon / silicon carbon composite material, ethylenediamine, phosphorus pentoxide, and phenolic resin particles are stirred evenly with anhydrous ethanol.

[0205] Comparative Example 3

[0206] It is basically the same as Example 1, except that step (1) is not included, and the carbon nanotubes filled with n-butyllithium in step (4) of Example 1 are replaced with n-butyllithium.

[0207] Comparative Example 4

[0208] The process is basically the same as in Example 1, except that step (3) is omitted and step (4) involves mixing 1000g of the hard carbon composite material obtained in step (2) and 50g of the carbon nanotubes filled with n-butyllithium obtained in step (1) under a nitrogen atmosphere.

[0209] Comparative Example 5

[0210] It is basically the same as Example 1, except that step (5) is omitted.

[0211] Comparative Example 6

[0212] It is basically the same as Example 1, except that in step (5), ethylenediamine and phenolic resin particles are not added.

[0213] Button cell battery test

[0214] The modified hard carbon silicon-carbon composite materials, conductive agent Super P, and binder PVDF (HSV900) prepared in each embodiment and comparative example were dissolved in N-methylpyrrolidone at a mass ratio of 90:2:8. The mixture was stirred with a magnetic stirrer for 15 hours under argon protection in a glove box to prepare the slurry required for button batteries. The coating machine was an MSK-AFA-Ⅲ automatic coating and drying machine from Shenzhen Kejing Zhida Technology Co., Ltd., with a coating gap of 25 μm and a speed of 5 cm / min. The slurry was uniformly coated onto a 9 μm thick, 99.8% pure smooth copper foil produced by Meixian Jinxiang Copper Foil Co., Ltd. The foil was vacuum dried at 120℃ for 12 hours and then stamped into electrode sheets with a diameter of approximately 16 mm using a Shenzhen Kejing MSK-T06 button battery stamping machine. These sheets served as the positive electrode. The negative electrode was a 15.8 mm diameter, 99.99% pure high-purity lithium sheet. The separator was a 16 μm thick ENTEK membrane from the USA. The LP16 type PE membrane, with an electrolyte of DMC:EMC in a mass ratio of 60:40, 2% VC (based on the total mass of DMC and EMC) and 1.3 mol / L LiPF6 were added. The electrical performance of the membrane was tested on a CT2001A tester from Wuhan Landian Electronics Co., Ltd. The specific capacity and initial coulombic efficiency are shown in Table 1.

[0215] Table 1

[0216]

[0217]

[0218] As shown in Table 1, compared with the comparative example, the modified hard carbon silicon-carbon composite material prepared in the examples has higher initial coulombic efficiency and specific capacity when used as a negative electrode material.

[0219] The coin cell made using the modified hard carbon-silicon-carbon composite material prepared in Example 1 exhibits the following capacity retention rate during cycling at 45°C: Figure 5 As shown, the capacity retention rate reached 95.57% after 50 laps;

[0220] The coin cell made using the modified hard carbon-silicon-carbon composite material prepared in Example 2 exhibits the following capacity retention rate during cycling at 45°C: Figure 6 As shown, the capacity retention rate reached 96.27% after 50 laps.

[0221] Thin-film battery testing

[0222] The positive electrode material was prepared according to the ratio of active material NCM523: conductive agent: binder (mass ratio of 96:2:2); the negative electrode material was prepared according to the modified hard carbon silicon carbon composite material prepared in each example and comparative example: conductive agent: binder (mass ratio of 92:3:3), and the test voltage was 3.0V to 4.25V.

[0223] The capacity retention curve of the fabricated thin-film battery at 45℃, with a charge / discharge cycle of 0.7C / 1C and a discharge cycle of 0.7C / 0.2C every 25 cycles, is shown below. Figure 7 As shown, the horizontal axis represents the number of cycles, and the vertical axis represents the capacity retention rate; from Figure 7 It can be seen that, compared with the comparative examples, the embodiments have a higher capacity retention rate and better cycling performance when cycling at high temperature; while the cycling performance of comparative examples 2 and 5 is worse than that of other comparative examples; and the cycling performance of comparative example 6 is also worse than that of other comparative examples.

[0224] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0225] The embodiments described above are merely illustrative of several implementations of the present invention, designed to facilitate a detailed understanding of the technical solutions of the present invention, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided by the present invention through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this invention patent should be determined by the content of the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A method for producing a modified hard carbon silicon-carbon composite material, characterized by, The method comprises the following steps: carbonizing and crushing a biomass material to prepare a hard carbon precursor; the biomass material is a biomass material rich in phenyl functional groups, and the biomass material rich in phenyl functional groups is at least one of walnut green husk, orange pole, peanut shell, coconut shell, corn stalk, wheat straw, wood and fruit shell; mixing the hard carbon precursor and silicon monoxide to perform first calcination to prepare a hard carbon silicon-carbon composite material; the mass ratio of the hard carbon precursor to the silicon monoxide is (3-100):1; mixing the hard carbon silicon-carbon composite material and carbon nanotubes filled with an organic lithium compound to perform second calcination to prepare a pre-lithiated hard carbon silicon-carbon composite material; mixing the pre-lithiated hard carbon silicon-carbon composite material, a nitrogen source, a phosphorus source and an organic polymer to perform third calcination to obtain a doped pre-lithiated hard carbon silicon-carbon composite material; the nitrogen source is at least one of ammonia, ethylenediamine, propylenediamine, butylenediamine, hexylenediamine, urea, pyridine, pyrrole, a nitrogen-containing ionic liquid, ammonium hydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, ammonium carbonate and ammonium bicarbonate; the phosphorus source is at least one of elemental phosphorus, diaphosphorus pentoxide, lithium phosphate, ammonium hydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate and calcium phosphate; and the organic polymer is at least one of epoxy resin, phenolic resin, polystyrene, polymethyl methacrylate, polyaniline, polyvinyl alcohol and pitch; mixing the doped pre-lithiated hard carbon silicon-carbon composite material and a coating agent to perform fourth calcination; the coating agent comprises at least an oxide and a phosphate; the oxide is at least one of titanium oxide, aluminum oxide, zirconium oxide, magnesium oxide, iron oxide, niobium oxide, tungsten oxide, strontium oxide, copper oxide, cerium oxide and yttrium oxide; and the phosphate is at least one of lithium phosphate, sodium phosphate, aluminum phosphate, zirconium phosphate, calcium phosphate and potassium phosphate.

2. The production method according to claim 1, wherein The carbonization temperature is 100-500°C, and the carbonization time is 3-20 hours.

3. The production method according to claim 1, wherein The mass ratio of the hard carbon precursor to the silicon monoxide is (3-10):

1.

4. The production method according to any one of claims 1 to 3, wherein The preparation of the carbon nanotubes filled with the organic lithium compound comprises the following steps: mixing the carbon nanotubes, the organic lithium compound and an organic solvent to reflux.

5. The production method according to claim 4, wherein The diameter of the carbon nanotubes is 3-100 nm.

6. The production method according to any one of claims 1 to 3, 5, wherein The mass ratio of the hard carbon silicon-carbon composite material to the carbon nanotubes filled with the organic lithium compound is (2-100):(0.01-20).

7. The production method according to any one of claims 1 to 3, 5, wherein The mass ratio of the pre-lithiated hard carbon silicon-carbon composite material, the nitrogen source, the phosphorus source and the organic polymer is (2-100):(0.1-20):(0.1-20):(0.2-50).

8. The production method according to any one of claims 1 to 3, 5, wherein The preparation method satisfies at least one of the following conditions (1), (2) and (3): (1) the first calcination temperature is 500-1500°C, and the first calcination time is 5-40 hours; (2) the second calcination temperature is 200-1000°C, and the second calcination time is 1-20 hours; (3) the third calcination temperature is 300-1500°C, and the third calcination time is 1-15 hours.

9. The production method according to any one of claims 1 to 3, 5, wherein The coating agent further comprises a fluoride.

10. The production method according to claim 9, wherein The fluoride is selected from at least one of aluminum fluoride, zirconium fluoride, magnesium fluoride, calcium fluoride, lithium fluoride, sodium fluoride and potassium fluoride.

11. A modified hard carbon silicon-carbon composite material, characterized by, The pre-lithiated hard carbon silicon-carbon composite material A and a first coating layer B arranged on the surface of A are included. A includes a uniformly dispersed lithium compound a1 and a hard carbon silicon-carbon composite material a2. a1 includes carbon nanotubes and lithium compounds and carbon materials filled in the carbon nanotubes; a2 includes hard carbon, nano-silicon and silicon dioxide, wherein the nano-silicon and part of the silicon dioxide are dispersed in the hard carbon, and part of the silicon dioxide is coated on the surface of the hard carbon and nano-silicon particles; The pre-lithiated hard carbon silicon-carbon composite material A is doped with nitrogen and phosphorus elements; B includes nitrogen and phosphorus doped pyrolytic carbon; The preparation raw material of the hard carbon is a biomass material rich in phenyl functional groups, and the biomass material rich in phenyl functional groups is selected from at least one of walnut green skin, orange pole, peanut shell, coconut shell, corn stalk, wheat straw, wood and fruit shell; the surface of the first coating layer is provided with a second coating layer, and the second coating layer at least includes an oxide and a phosphate, the oxide is selected from at least one of titanium oxide, aluminum oxide, zirconium oxide, magnesium oxide, iron oxide, niobium oxide, tungsten oxide, strontium oxide, copper oxide, cerium oxide and yttrium oxide, and the phosphate is selected from at least one of lithium phosphate, sodium phosphate, aluminum phosphate, zirconium phosphate, calcium phosphate and potassium phosphate.

12. A lithium-ion battery, characterized by, The modified hard carbon silicon-carbon composite material prepared by the preparation method of the modified hard carbon silicon-carbon composite material according to any one of claims 1-10 or the modified hard carbon silicon-carbon composite material according to claim 11 is included in the positive electrode, the separator and the negative electrode, and the positive electrode and the negative electrode are arranged on both sides of the separator.

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