A silicon-carbon anode material, its preparation method and application

Abstract

The present invention relates to a silicon-carbon negative electrode material, a preparation method thereof and an application. The silicon-carbon negative electrode material is a composite negative electrode material of silicon coated with pyrolytic carbon and lithium-supplemented graphite; wherein the lithium-supplemented graphite includes a porous graphite material and lithium elements distributed on the surface or between the layers of the porous graphite material; the porous graphite material has a macroporous structure; wherein, the lithium elements exist in the form of lithium metal or lithium-containing compounds, and the molar proportion of the lithium elements is 2-10% of the total amount of all elemental atoms.

Description

Technical Field

[0001] The present invention relates to a silicon-carbon anode material, a preparation method thereof, and an application thereof, belonging to the technical field of lithium-ion batteries. Background Art

[0002] With the continuous development of electric vehicles and the increasing requirement for battery energy density, traditional lithium-ion batteries with graphite as the anode gradually fail to meet the development needs. Therefore, silicon-carbon anode materials with high theoretical specific capacity have gradually become the focus of research. However, due to the huge volume change of silicon during charge / discharge, a large amount of irreversible SEI is formed, seriously reducing the Coulombic efficiency of the battery; at the same time, the volume change of silicon will also cause damage to the anode structure, resulting in the shedding of active substances from the current collector, which limits the content of silicon in the anode, affects the discharge specific capacity of the battery, and deteriorates the cycle performance.

[0003] Regarding the problem of low Coulombic efficiency of silicon-carbon materials, there have been many studies. For example, in Patent 1 (WO2022116588A1), a preparation method of a lithium-supplemented anode electrode sheet is disclosed to supplement lithium to the silicon-carbon anode. In Patent 2 (Chinese Patent Publication No. CN102610861A), a method of mechanically pressing a lithium sheet and the anode for lithium supplementation is disclosed; although the above methods effectively improve the first-cycle Coulombic efficiency of silicon-carbon anode batteries, they are costly and require an additional pre-lithiation step for lithium supplementation. Regarding the problems of low silicon loading and poor cycle performance of silicon-carbon materials, Patent 3 (Chinese Patent Publication No. CN110224125A) discloses a composite material of alkali-activated etched graphite and nano-silicon powder, which improves the cycle performance of the battery, but does not solve the problem of low first-cycle Coulombic efficiency well. Summary of the Invention

[0004] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a silicon-carbon anode material with high first-cycle Coulombic efficiency, high discharge specific capacity, and high cycle performance, and a preparation method thereof.

[0005] In a first aspect, the present invention provides a silicon-carbon anode material, which is a composite anode material of silicon coated with pyrolytic carbon and lithium-supplemented graphite; wherein the lithium-supplemented graphite includes a porous graphite material and lithium elements distributed on the surface or between the layers of the porous graphite material; the porous graphite material has a macroporous structure; wherein, the lithium elements exist in the form of lithium metal or lithium-containing compounds, and the molar ratio of the lithium elements to the total amount of all elemental atoms is 2-10%.

[0006] In the present invention, the pore channels of porous graphite accommodate the volume change during the silicon alloying process, improving the discharge specific capacity and cycling performance of the battery; meanwhile, the lithium metal and lithium-containing compounds generated during etching are used as lithium supplement agents, eliminating the need for an additional prelithiation step and improving the first-cycle Coulombic efficiency of the battery.

[0007] Preferably, the lithium element is in-situ generated on the surface or between the layers of graphite after calcination treatment of a lithium-containing alkaline substance and graphite loaded with transition metal particles; the molar proportion of the lithium element in the silicon-carbon negative electrode material is 1-5%.

[0008] Preferably, the pore diameter of the macroporous structure of the lithium-supplemented graphite is 0.01-2 μm, and the pore depth is 0.05-5 μm;

[0009] The content of the lithium-supplemented graphite is 45-90 wt%, preferably 50-85 wt%;

[0010] The pyrolytic carbon in the pyrolytic carbon-coated silicon accounts for 40-65 wt% of the total mass of the pyrolytic carbon-coated silicon.

[0011] In a second aspect, the present invention provides a method for preparing a silicon-carbon negative electrode material, comprising:

[0012] (1) Using metal-assisted chemical etching to etch holes in graphite powder to obtain lithium-supplemented graphite;

[0013] (2) Dispersing nano-silicon powder in a tetrahydrofuran solution dissolving pitch, mechanically stirring, and evaporating the solvent to obtain a silicon / pitch material;

[0014] (3) Mechanically mixing the obtained lithium-supplemented graphite and silicon / pitch material to obtain a composite material;

[0015] (4) Sintering the obtained composite material to obtain a composite negative electrode material of pyrolytic carbon-coated silicon and lithium-supplemented graphite.

[0016] Preferably, in step (1), the metal-assisted chemical etching method is catalytic metal-assisted LiOH alkali method for etching lithium-supplemented graphite, including:

[0017] 1) Mixing, stirring, and drying graphite loaded with transition metal particles and an aqueous solution of a lithium-containing alkaline substance, then transferring to a crucible, placing in an inert atmosphere for calcination treatment, and after natural cooling, obtaining rough-etched graphite;

[0018] 2) After washing the obtained rough-etched graphite, using an oxidizing solution to dissolve the transition metal particles, and then performing secondary washing and drying to obtain the lithium-supplemented graphite.

[0019] Preferably, the composition of the transition metal particles in the graphite loaded with transition metal particles is selected from at least one of transition metals Ni, Cu, Fe, Co, Mn, Mo, Ru, Au, and Pt; the particle size of the transition metal particles is 5 nm to 2 μm; the loading amount of the transition metal particles is 5 to 25 wt%.

[0020] Preferably, the method for preparing the graphite loaded with transition metal particles includes: mixing graphite powder and a metal salt solution, stirring and drying at 60 to 90 °C for 1 to 20 hours, then transferring to a crucible, placing it under an inert atmosphere, and performing high-temperature treatment at 400 to 800 °C. After natural cooling, graphite loaded with transition metal particles is obtained.

[0021] Preferably, the graphite powder is artificial graphite or natural graphite, and its particle size is 3 to 50 μm; preferably, artificial spherical graphite with a particle size of 5 to 10 μm;

[0022] The metal salt in the metal salt solution is an organic salt or / and inorganic salt of a metal element, preferably at least one of formate of a metal element, acetate of a metal element, ethanolate of a metal element, citrate of a metal element, acetylacetonate of a metal element, hydrochloride of a metal element, sulfate of a metal element, nitrate of a metal element, phosphate of a metal element, hypophosphite of a metal element, chlorate of a metal element, perchlorate of a metal element, and sulfamate of a metal element; the metal element is selected from at least one of Ni, Cu, Fe, Co, Mn, Mo, Ru, Au, and Pt;

[0023] The solvent of the metal salt solution is at least one of water, ethanol, and acetone;

[0024] The molar ratio of the metal salt to the graphite powder is 1:10 to 1:100;

[0025] The inert atmosphere is at least one of argon, nitrogen, helium, and carbon monoxide;

[0026] The temperature of the high-temperature treatment is 400 °C to 1000 °C / min, and the holding time is 1 to 10 hours. Preferably, the heating rate is 1 °C / min to 20 °C / min;

[0027] Preferably, the temperature of the high-temperature treatment is 500 to 700 °C, the holding time is 1 to 4 hours, and the heating rate is 5 to 10 °C / min.

[0028] Preferably, the lithium-containing basic substance includes at least one of lithium hydroxide or a lithium compound; the molar ratio of the lithium-containing basic substance to the graphite in the graphite loaded with transition metal particles is 1:10 to 10:1;

[0029] Preferably, the lithium-containing alkaline substance is lithium hydroxide or a mixture of lithium hydroxide and sodium hydroxide;

[0030] Preferably, the molar ratio of the lithium-containing alkaline substance to graphite in the graphite loaded with transition metal particles is 2:1 to 1:2;

[0031] The concentration of the aqueous solution of the lithium-containing alkaline substance is 1 to 6 mol / L;

[0032] The linear velocity of the stirring and drying is 0.5 to 3 m / s, the drying temperature is 80 to 120 °C, and the drying time is 1 to 4 hours.

[0033] Preferably, the temperature of the calcination treatment is 600 to 1000 °C / min, the heat preservation time is 2 to 16 h, and the preferred heating rate is 1 to 20 °C / min;

[0034] Preferably, the temperature of the calcination treatment is 700 to 900 °C, the heat preservation time is 6 to 10 hours, and the more preferred heating rate is 5 to 10 °C / min.

[0035] Preferably, the oxidant in the oxidizing solution is at least one of ferric chloride, potassium dichromate, hydrogen peroxide, sulfuric acid, and nitric acid;

[0036] The solvent in the oxidizing solution is selected from ethanol or water;

[0037] The concentration of the oxidizing solution is 0.1 to 5 mol / L;

[0038] The temperature of the dissolution is 40 to 80 °C, and the time is 4 to 20 hours.

[0039] Preferably, in step (2), the mass ratio of the nano-silicon powder to the pitch is 1:1 to 1:3; the stirring duration is 0.5 to 1 hour; the temperature for evaporating the solvent is 80 to 100 °C.

[0040] Preferably, in step (3), the mass ratio of the silicon / pitch material to the lithium-supplemented graphite is 2:1 to 1:5, preferably 1.8:1 to 1:5, more preferably 1.5:1 to 1:5; the duration of the mechanical mixing is 1 to 2 hours.

[0041] Preferably, in step (4), the sintering parameters include: in a tubular furnace under an inert atmosphere, heating to 300 °C at a rate of 5 to 10 °C / min and holding for 1 to 2 hours, and then heating to 800 to 1000 °C at a rate of 5 to 10 °C / min and holding for 1 to 2 hours.

[0042] In a third aspect, the present invention provides a lithium-ion battery comprising a negative electrode prepared from the above silicon-carbon negative electrode material.

[0043] Beneficial effects:

[0044] The preparation method of the silicon-carbon anode material containing a lithium supplement agent proposed by the present invention: on the one hand, the pores of the lithium-supplemented graphite accommodate the volume change during the silicon alloying process, improving the discharge specific capacity and cycling performance of the battery; on the other hand, the lithium metal or lithium-containing compound generated in-situ during etching is used as a lithium supplementation means (playing a pre-lithiation role), eliminating the need to introduce an extra pre-lithiation step and improving the first-cycle Coulombic efficiency of the battery. Thirdly, the silicon-carbon anode material containing a lithium supplement agent has excellent cycling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is the first-cycle charge-discharge curve of the silicon-carbon anode material in Example 1 of the present invention;

[0046] Figure 2 is the first-cycle charge-discharge curve of the KOH-etched graphite / silicon composite anode material in Comparative Example 1;

[0047] Figure 3 is the scanning electron micrograph of the microstructure of the silicon-carbon anode material in Example 1 of the present invention;

[0048] Figure 4 is the X-ray photoelectron spectroscopy of the silicon-carbon anode material in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0049] The present invention will be further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and not to limit the present invention.

[0050] In the present disclosure, the silicon-carbon anode material is a composite anode material of carbon-coated silicon and lithium-supplemented graphite, wherein the lithium-supplemented graphite is a lithium-rich porous graphite material treated by metal-assisted LiOH chemical etching. The lithium-supplemented graphite (or lithium-rich porous graphite material) contains macropores generated by the etching of lithium-containing alkaline substances catalyzed by transition metal particles, and the pore diameter is between 10 nm and 2 μm. Among them, lithium-rich means that the lithium element remains on the surface or between the layers of graphite after the reaction of the lithium-containing alkaline substance with graphite, and its molar ratio accounts for 2-10% of the total amount of elemental atoms. The total elements of the lithium-supplemented graphite material include C element, O element, Li element, and transition metal elements (containing at least one of Ni, Cu, Fe, Co, Mn, Mo, Ru, Au, Pt). Due to incomplete washing, a very small amount of transition metal elements will remain, and their content is 0-1 at% of the total element content. In the present invention, the lithium-supplemented graphite contains abundant macropores, has a rich lithium-ion transmission channel, and a short lithium-ion diffusion path, so it has good rate performance; a large number of defects are formed during the etching process to accommodate the reversible insertion and extraction of lithium ions, and it has a high reversible discharge specific capacity (350-450 mAh g -1 , preferably 410-450 mAh g -1);Meanwhile, the porous graphite has additional lithium source supplementation and a relatively high initial Coulombic efficiency (85 - 99.7%, preferably 87% - 99.7%). The silicon-carbon negative electrode material prepared by the present invention, which is a composite negative electrode material of carbon-coated silicon and lithium-supplemented graphite, has a relatively high reversible discharge specific capacity (600 - 1000 mAh g -1 , preferably 750 - 1000 mAh g -1 ), and a relatively high initial Coulombic efficiency (83 - 125%, preferably 87% - 125%, more preferably 95% - 125%).

[0051] In the present invention, the preparation method of the silicon-carbon negative electrode material comprises the following steps: First, lithium-supplemented graphite is prepared by metal-assisted LiOH alkali etching; second, nano-silicon is added to a tetrahydrofuran solution containing asphalt, stirred, and evaporated to dryness; the lithium-supplemented graphite and the nano-silicon / asphalt material are mechanically mixed and sintered in a tube furnace under an inert atmosphere to obtain a silicon-carbon negative electrode material containing lithium elements; wherein, the lithium element is lithium metal or a lithium-containing compound generated in-situ during the preparation of the lithium-supplemented graphite.

[0052] The preparation method of the silicon-carbon composite material of the present invention has a simple process, low cost, and is easy to realize industrial production. The preparation method of the silicon-carbon negative electrode material is exemplarily described below.

[0053] The present invention provides a method for obtaining lithium-supplemented graphite with high rate and high capacity by using a lithium-containing alkaline substance as an etchant, with metal particles on the graphite surface providing a catalytic effect, and achieving directional etching during the calcination process to generate abundant macropores.

[0054] Metal-assisted chemical etching is used to etch holes in the graphite to obtain lithium-supplemented graphite. Specifically, graphite powder is mixed with a metal salt solution and stirred and dried at 60 - 90 °C for 1 - 20 h to uniformly mix the metal salt and the graphite powder. Among them, the graphite powder is artificial graphite or natural graphite, and its particle size is 3 - 50 μm. More preferably, the used graphite powder is artificial spherical graphite with a particle size of 5 - 10 μm. The metal salt in the metal salt solution is an organic salt (such as formate, acetate, ethanolate, citrate, and acetylacetonate) or an inorganic salt (such as hydrochloride, sulfate, nitrate, phosphate, hypophosphite, chlorate, perchlorate, and sulfamate) of transition metals Ni, Cu, Fe, Co, Mn, Mo, Ru, Au, Pt. The molar ratio of the metal salt to the graphite can be 1:10 to 1:100. More preferably, the selected metal salt is nickel acetate. The atomic ratio of the metal salt to the graphite is 1:40. The solvent in the metal salt solution is one or more of water, ethanol, and acetone. More preferably, the selected solvent is a mixed solution of water and alcohol with a volume ratio of 9:1.

[0055] Transfer the stirred and dried mixed materials into a crucible, and then place it in a heating furnace for high-temperature treatment at 400-800 °C under an inert atmosphere. After natural cooling, a graphite precursor loaded with transition metal particles is obtained. The heating furnace used is a tube furnace, roller hearth kiln, tunnel kiln, pusher kiln, shuttle kiln or rotary kiln, and the inert atmosphere used is one or more of argon, nitrogen, helium, and carbon monoxide. The parameters of the high-temperature treatment include: the heating rate is 1 °C / min to 20 °C / min, the target temperature is 400 °C to 1000 °C / min, and the holding time is 1-10 h. More preferably, the heating rate is 5-10 °C / min, the target temperature is 500-700 °C, and the holding time is 1-4 h.

[0056] Mix the graphite precursor loaded with transition metal particles with a lithium-containing alkaline substance solution, stir and dry it, then transfer it into a crucible, and then place it in a heating furnace for calcination treatment under an inert atmosphere. After natural cooling, rough-etched graphite is obtained. The alkaline substance includes one or more of lithium hydroxide or lithium compounds, and the molar ratio of the lithium-containing alkaline substance to graphite is 1:10 - 10:1; more preferably, the alkaline substance is lithium hydroxide or a mixture of lithium hydroxide and sodium hydroxide, and the molar ratio of the lithium-containing alkaline substance to graphite is 2:1 - 1:2. Among them, the mixing is to put the graphite precursor into an aqueous solution of a lithium-containing alkaline substance (with a concentration of 1-6 mol / L), stir and dry it, the stirring linear velocity is 3-6 m / s, the drying temperature is 80-120 °C, and the drying time is 1-4 h. The crucible used is a corundum crucible, magnesia crucible, nickel crucible or platinum crucible. More preferably, the crucible used is a nickel crucible. Among them, the parameters of the calcination treatment include: the heating rate is 1-20 °C / min, the target temperature is 600-1000 °C / min, and the holding time is 2-16 h. More preferably, the heating rate is 5-10 °C / min, the target temperature is 700-900 °C, and the holding time is 6-10 h.

[0057] After washing the rough-etched graphite with deionized water, use an oxidizing solution to dissolve the transition metal particles. Then wash and dry the material with deionized water twice to obtain lithium-complemented graphite. The washing is carried out using industrial water or deionized water through filtration or centrifugation operations. The oxidizing solution can be an ethanol or aqueous solution of ferric chloride, potassium dichromate, hydrogen peroxide, sulfuric acid, or nitric acid, and the solution concentration is 0.1-5 mol / L. The dissolution temperature can be 40-80 °C, and the time can be 4-20 h.

[0058] On the basis of conforming to the common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present invention.

[0059] In the present invention, the lithium-supplemented graphite is free of impurities, and the final product is lithium-rich porous graphite which is porous graphite particles containing abundant macropores and deep pores. The porous graphite has good rate performance and improved reversible charge-discharge capacity; meanwhile, it has an additional lithium source supplement, low first irreversible capacity, and high first Coulombic efficiency.

[0060] Disperse nano-silicon powder (particle size 60 - 100 nm) in a tetrahydrofuran solution dissolving asphalt, and stir mechanically. Evaporate the solvent to obtain a silicon / asphalt material. Among them, the mass ratio of the nano-silicon powder to asphalt is 1:1 - 1:3. The stirring duration is 0.5 - 1 h, and the temperature for evaporating the solvent is 80 - 100 °C.

[0061] Mechanically mix the lithium-supplemented graphite with the silicon / asphalt material obtained in step two to obtain a composite material; the mass ratio of the lithium-supplemented graphite to the silicon / asphalt material obtained in step two is 1:1 - 1:4, and the duration of the mechanical mixing is 1 - 2 h.

[0062] Sinter the composite material to obtain a composite anode material of silicon coated with pyrolytic carbon and lithium-supplemented graphite. The specific process of the sintering is as follows: in a tubular furnace under an inert atmosphere, heat up to 300 °C at a first heating rate of 5 - 10 °C / min, keep warm for 1 - 2 h, then heat up to 800 - 1000 °C at a second heating rate of 5 - 10 °C / min, and keep warm for 1 - 2 h.

[0063] In a preferred embodiment of the present invention, lithium metal or lithium-containing compound remains between the layers or on the surface of the lithium-supplemented graphite. The nano-silicon powder is uniformly dispersed and all coated with pyrolytic carbon, and at the same time fills the pores of the lithium-supplemented graphite to form a silicon-carbon anode material containing lithium element.

[0064] The following further gives examples to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, rather than being limited to the specific values in the following examples.

[0065] Example 1

[0066] Preparation of LiOH-etched graphite (lithium-supplemented graphite):

[0067] 1) Dissolve 0.622 g of nickel acetate tetrahydrate in a mixture of 9 mL of water and 1 mL of alcohol to obtain solution A. Subsequently, take 1.2 g of graphite powder and disperse it in solution A, stir and dry at 80 °C for 2 h, and obtain precursor A after drying;

[0068] 2) Place the precursor A in a covered corundum crucible, put it in a vacuum tube furnace, introduce the inert gas argon with a flow rate of 60 mL / min. Set the heating program with a heating rate of 5 °C / min, heat to 600 °C in 2 h, keep the temperature for 2 h and then cool naturally to obtain the precursor B;

[0069] 3) Mix the precursor B with 33 mL of 3 mol / L lithium hydroxide aqueous solution, add 2 mL of absolute ethanol, stir and dry. The linear velocity of stirring is 3 m / s, the heating temperature is 100 °C, the heating time is 2 h. After drying, transfer the obtained material to a nickel crucible, put it into a vacuum tube furnace, introduce the inert gas argon with a flow rate of 60 mL / min. Set the heating program with a heating rate of 5 °C / min, heat to 800 °C in 2.7 h, keep the temperature for 6 h and then cool naturally to obtain the precursor C;

[0070] 4) Take out the precursor C, wash away the residual alkaline substances with water, then place the washed material in 20 mL of 0.1 mol / L iron(III) chloride ethanol solution, heat to 60 °C and keep for 4 h. After the dissolution is completed, filter and separate the acid solution from the mixture, then wash the graphite 3 times with deionized water, and dry to obtain the lithium-complemented graphite; the X-ray photoelectron spectrum of the obtained lithium-rich porous graphite shows the detection of lithium element signal with an atomic ratio of about 3.67%, and at the same time, oxygen element is also detected, corresponding to the contained lithium oxide;

[0071] 5) At room temperature, dissolve 0.42 g of asphalt in a tetrahydrofuran solution, add 0.2 g of nano-silicon powder, stir for 30 min, heat to 80 °C, evaporate the tetrahydrofuran solution to dryness, and collect the obtained powder. Mix mechanically for 1 h according to the mass ratio of 1.24:1 (after pyrolysis of 0.42 g of asphalt, about 71.4% remains, that is, 0.3 g, so it is added according to the mass ratio of 50, and the content of LiOH-etched graphite is 0.5 g) (at this time, the ratio of pyrolytic carbon / silicon to LiOH-etched graphite is 1:1) with the LiOH-etched graphite (0.5 g) prepared in Example 1. Place the obtained composite material in a tubular furnace with argon flowing through, heat to 300 °C at the first heating rate of 5 °C / min, keep the temperature for 2 h, then heat to 900 °C at the second heating rate of 5 °C / min, and keep the temperature for 2 h to obtain a silicon-carbon negative electrode material containing a lithium-complementing agent. The molar ratio of lithium element in the silicon-carbon negative electrode material is 5%. The mass content of lithium-complemented graphite in the silicon-carbon negative electrode material is 50 wt%. The pyrolytic carbon in the pyrolytic carbon-coated silicon accounts for 60 wt% of the total mass of the pyrolytic carbon-coated silicon.

[0072] Comparative Example 1:

[0073] Preparation method of KOH-etched graphite (potassium-complemented graphite) / silicon composite negative electrode material:

[0074] (1) Dissolve 0.622 g of nickel acetate tetrahydrate in a mixture of 9 mL of water and 1 mL of alcohol to obtain solution A. Subsequently, take 1.2 g of graphite powder and disperse it in solution A, stir and dry at 80 °C for 2 h to obtain precursor A after drying.

[0075] (2) Place precursor A in a covered corundum crucible, put it in a vacuum tube furnace, and introduce inert gas argon with a flow rate of 60 mL / min. Set the heating program with a heating rate of 5 °C / min, heat to 600 °C in 2 h, keep the temperature for 2 h and then cool naturally to obtain precursor B.

[0076] (3) Mix precursor B with 17 mL of 6 mol / L potassium hydroxide aqueous solution, add 2 mL of absolute ethanol, stir and dry. The stirring linear velocity is 3 m / s, the heating temperature is 100 °C, and the heating time is 2 h. After drying, transfer the obtained material to a nickel crucible, put it into a vacuum tube furnace, and introduce inert gas argon with a flow rate of 60 mL / min. Set the heating program with a heating rate of 5 °C / min, heat to 800 °C in 2.7 h, keep the temperature for 6 h and then cool naturally to obtain precursor C.

[0077] (4) Take out precursor C, wash away the residual alkaline substances with water, and then place the washed material in 20 mL of 0.5 mol / L iron(III) chloride ethanol solution, heat to 60 °C and keep for 4 h. After the dissolution is completed, filter and separate the acid solution from the mixture, and then wash the graphite 3 times with deionized water and dry to obtain a potassium-rich porous graphite material (the K element content is about 3.6 at%).

[0078] (5) At room temperature, dissolve 0.42 g of asphalt in tetrahydrofuran solution, add 0.2 g of nano-silicon powder, stir for 30 min, heat to 80 °C, evaporate the tetrahydrofuran solution to dryness, and collect the obtained powder. Mechanically mix it with KOH-etched graphite (0.5 g) at a mass ratio of 1.24:1 for 1 h. Place the obtained composite material in a tube furnace with argon flowing through, heat to 300 °C at a first heating rate of 5 °C / min, keep the temperature for 2 h, and then heat to 900 °C at a second heating rate of 5 °C / min and keep the temperature for 2 h to obtain a silicon-carbon anode material containing a lithium supplement agent.

[0079] Figure 1 This is the first-cycle charge-discharge curve of a silicon-carbon anode material in the first preferred embodiment of the present invention. As shown in the figure, the reversible capacity is 798 mAh g -1 , and the first-cycle Coulombic efficiency is 113%.

[0080] Figure 2 This is the first-cycle charge-discharge curve of the KOH-etched graphite / silicon composite anode material in the comparative example. As shown in the figure, the reversible capacity is 694 mAh g -1, the initial Coulomb efficiency is 82%, both of which are lower than the material properties in the preferred Embodiment 1 of the present invention.

[0081] Figure 3 It is a scanning electron micrograph of a silicon-carbon negative electrode material in the preferred Embodiment 1 of the present invention. As shown in the figure, the nano-silicon powder is uniformly coated with pyrolytic carbon and evenly dispersed on the surface and in the pores of the lithium-supplemented graphite.

[0082] Figure 4 It is an X-ray photoelectron spectroscopy diagram of a silicon-carbon negative electrode material in the preferred Embodiment 1 of the present invention, which proves the existence of lithium element in the lithium-supplemented graphite.

[0083] Embodiment 2

[0084] At room temperature, 0.2 g of pitch is dissolved in a tetrahydrofuran solution, 0.2 g of nano-silicon powder is added, and the mixture is stirred for 30 min and then heated to 100 °C. The tetrahydrofuran solution is evaporated to dryness, and the obtained powder is collected. It is mechanically mixed with the LiOH-etched graphite prepared in Embodiment 1 for 2 h according to a mass ratio of 1:1. The obtained composite material is placed in a tubular furnace filled with argon and heated to 300 °C at a first heating rate of 5 °C / min and held for 2 h, and then heated to 900 °C at a second heating rate of 5 °C / min and held for 2 h to obtain a silicon-carbon negative electrode material containing a lithium supplementing agent.

[0085] Embodiment 3

[0086] At room temperature, 0.3 g of pitch is dissolved in a tetrahydrofuran solution, 0.2 g of nano-silicon powder is added, and the mixture is stirred for 1 h and then heated to 90 °C. The tetrahydrofuran solution is evaporated to dryness, and the obtained powder is collected. It is mechanically mixed with the LiOH-etched graphite prepared in Embodiment 1 for 1 h according to a mass ratio of 1:3. The obtained composite material is placed in a tubular furnace filled with argon and heated to 300 °C at a first heating rate of 5 °C / min and held for 2 h, and then heated to 900 °C at a second heating rate of 5 °C / min and held for 2 h to obtain a silicon-carbon negative electrode material containing a lithium supplementing agent.

[0087] Embodiment 4

[0088] At room temperature, 0.5 g of pitch is dissolved in a tetrahydrofuran solution, 0.2 g of nano-silicon powder is added, and the mixture is stirred for 1 h and then heated to 80 °C. The tetrahydrofuran solution is evaporated to dryness, and the obtained powder is collected. It is mechanically mixed with the LiOH-etched graphite prepared in Embodiment 1 for 2 h according to a mass ratio of 1:3. The obtained composite material is placed in a tubular furnace filled with argon and heated to 300 °C at a first heating rate of 5 °C / min and held for 2 h, and then heated to 900 °C at a second heating rate of 5 °C / min and held for 2 h to obtain a silicon-carbon negative electrode material containing a lithium supplementing agent.

[0089] Embodiment 5

[0090] At room temperature, 0.42 g of asphalt was dissolved in a tetrahydrofuran solution, 0.2 g of nano-silicon powder was added, and the mixture was stirred for 30 min. Then it was heated to 80 °C, and the tetrahydrofuran solution was evaporated to dryness, and the obtained powder was collected. It was mechanically mixed with the LiOH-porous graphite prepared in Example 1 at a mass ratio of 2:1 for 1 h. The obtained composite material was placed in a tubular furnace filled with argon, heated to 300 °C at a first heating rate of 5 °C / min, held for 2 h, and then heated to 900 °C at a second heating rate of 5 °C / min and held for 2 h to obtain a silicon-carbon negative electrode material containing a lithium supplement agent.

[0091] Example 6

[0092] At room temperature, 0.42 g of asphalt was dissolved in a tetrahydrofuran solution, 0.2 g of nano-silicon powder was added, and the mixture was stirred for 30 min. Then it was heated to 80 °C, and the tetrahydrofuran solution was evaporated to dryness, and the obtained powder was collected. It was mechanically mixed with the LiOH-porous graphite prepared in Example 1 at a mass ratio of 1:1 for 1 h. The obtained composite material was placed in a tubular furnace filled with argon, heated to 300 °C at a first heating rate of 5 °C / min, held for 2 h, and then heated to 900 °C at a second heating rate of 5 °C / min and held for 2 h to obtain a silicon-carbon negative electrode material containing a lithium supplement agent.

[0093] Example 7

[0094] At room temperature, 0.42 g of asphalt was dissolved in a tetrahydrofuran solution, 0.2 g of nano-silicon powder was added, and the mixture was stirred for 30 min. Then it was heated to 80 °C, and the tetrahydrofuran solution was evaporated to dryness, and the obtained powder was collected. It was mechanically mixed with the LiOH-porous graphite prepared in Example 1 at a mass ratio of 1:2 for 1 h. The obtained composite material was placed in a tubular furnace filled with argon, heated to 300 °C at a first heating rate of 5 °C / min, held for 2 h, and then heated to 900 °C at a second heating rate of 5 °C / min and held for 2 h to obtain a silicon-carbon negative electrode material containing a lithium supplement agent.

[0095] Example 8

[0096] At room temperature, 0.42 g of asphalt was dissolved in a tetrahydrofuran solution, 0.2 g of nano-silicon powder was added, and the mixture was stirred for 30 min. Then it was heated to 80 °C, and the tetrahydrofuran solution was evaporated to dryness, and the obtained powder was collected. It was mechanically mixed with the LiOH-porous graphite prepared in Example 1 at a mass ratio of 1:3 for 1 h. The obtained composite material was placed in a tubular furnace filled with argon, heated to 300 °C at a first heating rate of 5 °C / min, held for 2 h, and then heated to 900 °C at a second heating rate of 5 °C / min and held for 2 h to obtain a silicon-carbon negative electrode material containing a lithium supplement agent.

[0097] Example 9

[0098] At room temperature, 0.42 g of asphalt was dissolved in a tetrahydrofuran solution, 0.2 g of nano-silicon powder was added, and the mixture was stirred for 30 min. Then it was heated to 80 °C, and the tetrahydrofuran solution was evaporated to dryness, and the obtained powder was collected. It was mechanically mixed with the LiOH-etched graphite prepared in Example 1 at a mass ratio of 1:4 for 1 h. The obtained composite material was placed in a tubular furnace filled with argon, heated to 300 °C at a first heating rate of 5 °C / min, held for 2 h, and then heated to 900 °C at a second heating rate of 5 °C / min and held for 2 h to obtain a silicon-carbon negative electrode material containing a lithium supplement agent.

[0099] Example 10

[0100] At room temperature, 0.42 g of asphalt was dissolved in a tetrahydrofuran solution, 0.2 g of nano-silicon powder was added, and the mixture was stirred for 30 min. Then it was heated to 80 °C, and the tetrahydrofuran solution was evaporated to dryness, and the obtained powder was collected. It was mechanically mixed with the LiOH-etched graphite prepared in Example 1 at a mass ratio of 1:5 for 1 h. The obtained composite material was placed in a tubular furnace filled with argon, heated to 300 °C at a first heating rate of 5 °C / min, held for 2 h, and then heated to 900 °C at a second heating rate of 5 °C / min and held for 2 h to obtain a silicon-carbon negative electrode material containing a lithium supplement agent.

[0101] Example 11

[0102] In this Example 11, the preparation process of the lithium-rich porous graphite refers to Example 1, and the only difference is that in step (3), the precursor B containing 1.2 g of raw material graphite was mixed with 66 mL of 3 mol / L lithium hydroxide aqueous solution, 6 mL of absolute ethanol was added, and the mixture was stirred and dried. The stirring linear velocity was 3 m / s, the heating temperature was 100 °C, the heating time was 2 h. After drying, the obtained material was transferred to a nickel crucible, placed in a vacuum tubular heating furnace, and inert gas argon was introduced at a flow rate of 60 mL / min. The heating program was set as a heating rate of 5 °C / min, heated to 900 °C in 3 h, held for 10 h and then cooled naturally to obtain the precursor C. The molar content of lithium element in the finally obtained lithium-rich porous graphite was 8.7%.

[0103] Preparation and testing of the electrode: The silicon-carbon negative electrode material prepared in the present invention, conductive carbon (Ketjen black), and binder (the mass ratio of CMC to SBR is 3:2) were stirred and mixed at a weight ratio of 8:1:1 to prepare an electrode slurry. CMC is carboxymethyl cellulose, and SBR is styrene-butadiene latex. The electrode slurry was evenly spread on the copper foil using a 250 μm high scraper, and then through pressing and cutting, a negative electrode sheet was prepared.

[0104] Performance tests were carried out on coin-type lithium-ion batteries. The battery assembly method is as follows: a lithium sheet is used as the counter electrode, Celgard 2300 is used as the separator, and the electrolyte is an EC-EMC (1:1) solution containing 1 M LiClO4. LiClO4 is lithium perchlorate, EC is ethylene carbonate, and EMC is ethyl methyl carbonate. During the test, the temperature was room temperature, constant current charge and discharge were used, the current density was 100 mA / g, and the voltage control range was 0.05 - 2 V.

[0105] Table 1 shows the partial battery performance test results of the examples and comparative examples:

[0106]

[0107]

[0108] The preferred specific embodiments of the present invention are described. It should be understood that those of ordinary skill in the art can make many modifications and variations according to the concept of the present invention without creative labor. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art should fall within the protection scope determined by the claims.

Claims

1. A silicon-carbon anode material containing a lithium supplement agent, characterized in that, The silicon-carbon anode material containing a lithium supplement agent is a composite anode material of silicon coated with pyrolytic carbon and lithium-supplemented graphite; wherein the lithium-supplemented graphite is a lithium-rich porous graphite material obtained by chemically etching a transition metal-assisted lithium-containing alkaline substance, including a porous graphite material and lithium elements distributed on the surface or between the layers of the porous graphite material; the lithium-rich porous graphite material has a macroporous structure generated by the etching of the lithium-containing alkaline substance catalyzed by transition metal particles; wherein, the lithium element exists in the form of lithium metal or lithium-containing compound in-situ generated during the preparation of the lithium-supplemented graphite, and the molar ratio of the lithium element is 2-10% of the total amount of all elemental atoms; The preparation method of the silicon-carbon anode material containing a lithium supplement agent includes: (1) The graphite powder is etched with holes by metal-assisted chemical etching to obtain lithium-supplemented graphite; wherein, the metal-assisted chemical etching method is to catalyze the metal-assisted lithium-containing alkaline substance to carry out alkaline etching to obtain lithium-supplemented graphite. The specific steps include: mixing and stirring the graphite loaded with transition metal particles and the aqueous solution of the lithium-containing alkaline substance, drying, then transferring to a crucible, placing it in an inert atmosphere for calcination treatment, and after natural cooling, obtaining the roughly etched graphite; after washing the obtained roughly etched graphite, using an oxidizing solution to dissolve the transition metal particles, and then washing and drying twice to obtain the lithium-supplemented graphite; (2) Dispersing the nano-silicon powder in a tetrahydrofuran solution dissolving asphalt, mechanically stirring, and evaporating the solvent to obtain a silicon / asphalt material; (3) Mechanically mixing the obtained lithium-supplemented graphite and the silicon / asphalt material to obtain a composite material; (4) Sintering the obtained composite material to obtain a composite anode material of silicon coated with pyrolytic carbon and lithium-supplemented graphite.

2. The silicon-carbon anode material containing a lithium supplement agent according to claim 1, characterized in that, The lithium element is in-situ generated on the surface or between the layers of graphite after calcination treatment of the lithium-containing alkaline substance and the graphite loaded with transition metal particles; the molar ratio of the lithium element in the silicon-carbon anode material is 1-5%.

3. The silicon-carbon anode material containing a lithium supplement agent according to claim 1 or 2, characterized in that, The pore diameter of the macroporous structure of the lithium-supplemented graphite is 0.01-2 μm, and the pore depth is 0.05-5 μm; The mass content of the lithium-supplemented graphite is 45-90 wt%; In the silicon coated with pyrolytic carbon, the pyrolytic carbon accounts for 40-65 wt% of the total mass of the silicon coated with pyrolytic carbon.

4. The silicon-carbon anode material containing a lithium supplement agent according to claim 3, characterized in that, The mass content of the lithium-supplemented graphite is 50-85 wt%.

5. A method for preparing a silicon-carbon anode material containing a lithium supplement agent according to any one of claims 1-4, characterized in that, Including: (1) The graphite powder is etched with holes by metal-assisted chemical etching to obtain lithium-supplemented graphite; wherein, the metal-assisted chemical etching method is to catalyze the metal-assisted lithium-containing alkaline substance to carry out alkaline etching to obtain lithium-supplemented graphite. The specific steps include: mixing and stirring the graphite loaded with transition metal particles and the aqueous solution of the lithium-containing alkaline substance, drying, then transferring to a crucible, placing it in an inert atmosphere for calcination treatment, and after natural cooling, obtaining the roughly etched graphite; after washing the obtained roughly etched graphite, using an oxidizing solution to dissolve the transition metal particles, and then washing and drying twice to obtain the lithium-supplemented graphite; (2) Dispersing the nano-silicon powder in a tetrahydrofuran solution dissolving asphalt, mechanically stirring, and evaporating the solvent to obtain a silicon / asphalt material; (3) Mechanically mixing the obtained lithium-supplemented graphite and the silicon / asphalt material to obtain a composite material; (4) Sinter the obtained composite material to obtain a composite anode material of silicon coated with pyrolytic carbon and lithium-complemented graphite.

6. The preparation method according to claim 5, wherein In the graphite loaded with transition metal particles, the composition of the transition metal particles is selected from at least one of transition metals Ni, Cu, Fe, Co, Mn, Mo, Ru, Au, Pt; the particle size of the transition metal particles is 5 nm to 2 μm; the loading amount of the transition metal particles is 5 to 25 wt%.

7. The preparation method according to claim 6, characterized in that, The preparation method of the graphite loaded with transition metal particles includes: mixing graphite powder and a metal salt solution, stirring and drying at 60 - 90 °C for 1 - 20 hours, then transferring to a crucible, placing it under an inert atmosphere, and performing high-temperature treatment at 400 - 800 °C. After natural cooling, graphite loaded with transition metal particles is obtained.

8. The preparation method according to claim 7, characterized in that, The graphite powder is artificial graphite or natural graphite, and its particle size is 3 - 50 μm; In the metal salt solution, the metal salt is an organic salt or / and inorganic salt of a metal element; the metal element is selected from at least one of Ni, Cu, Fe, Co, Mn, Mo, Ru, Au, Pt; The solvent of the metal salt solution is at least one of water, ethanol, and acetone; The molar ratio of the metal salt to the graphite powder is 1:10 - 1:100; The inert atmosphere is at least one of argon, nitrogen, helium, and carbon monoxide; The temperature of the high-temperature treatment is 400 °C - 1000 °C / min, the holding time is 1 - 10 hours, and the heating rate is 1 °C / min - 20 °C / min.

9. The preparation method according to claim 8, wherein The graphite powder is artificial spherical graphite with a particle size of 5 - 10 μm; The metal salt is at least one of formate of a metal element, acetate of a metal element, ethanolate of a metal element, citrate of a metal element, acetylacetonate of a metal element, hydrochloride of a metal element, sulfate of a metal element, nitrate of a metal element, phosphate of a metal element, hypophosphate of a metal element, chlorate of a metal element, perchlorate of a metal element, and aminosulfonate of a metal element; The temperature of the high-temperature treatment is 500 - 700 °C, the holding time is 1 - 4 hours, and the heating rate is 5 - 10 °C / min.

10. The preparation method according to claim 5, characterized in that, The lithium-containing basic substance includes at least one of lithium hydroxide or a lithium compound; the molar ratio of the lithium-containing basic substance to the graphite in the graphite loaded with transition metal particles is 1:10 - 10:1; The concentration of the aqueous solution of the lithium-containing basic substance is 1 - 6 mol / L; The linear velocity of the stirring and drying is 0.5 - 3 m / s, the drying temperature is 80 - 120 °C, and the drying time is 1 - 4 hours.

11. The preparation method according to claim 10, wherein, The lithium-containing basic substance is lithium hydroxide or a mixture of lithium hydroxide and sodium hydroxide; the molar ratio of the lithium-containing basic substance to the graphite in the graphite loaded with transition metal particles is 2:1 - 1:

2.

12. The preparation method according to claim 5, wherein The temperature of the calcination treatment is 600 - 1000 °C / min, the holding time is 2 - 16 h, and the heating rate is 1 - 20 °C / min.

13. The preparation method according to claim 12, characterized in that, The temperature of the calcination treatment is 700 - 900 °C, the holding time is 6 - 10 hours, and the heating rate is 5 - 10 °C / min.

14. The preparation method according to claim 5, characterized in that, The oxidant in the oxidizing solution is at least one of ferric chloride, potassium dichromate, hydrogen peroxide, sulfuric acid, and nitric acid; The solvent in the oxidizing solution is selected from ethanol or water; The concentration of the oxidizing solution is 0.1 - 5 mol / L; The temperature for dissolution is 40 - 80 °C, and the time is 4 - 20 hours.

15. The preparation method according to claim 5, characterized in that, In step (2), the mass ratio of the nano-silicon powder to the asphalt is 1:1 - 1:3; the stirring duration is 0.5 - 1 hour; the temperature for evaporating the solvent is 80 - 100 °C.

16. The preparation method according to claim 5, characterized in that, In step (3), the mass ratio of the silicon / asphalt material to the lithium-supplemented graphite is 2:1 - 1:5; the duration of mechanical mixing is 1 - 2 hours.

17. The preparation method according to claim 5, characterized in that, In step (4), the sintering parameters include: in a tubular furnace under an inert atmosphere, heating to 300 °C at a rate of 5 - 10 °C / min and holding for 1 - 2 hours, and then heating to 800 - 1000 °C at a rate of 5 - 10 °C / min and holding for 1 - 2 hours.

18. A lithium-ion battery, characterized in that, A negative electrode prepared from the silicon-carbon negative electrode material containing a lithium supplementing agent according to any one of claims 1 - 4.

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