A low-residual-alkali long-circulation silicon monoxide carbon material and a preparation method thereof

Abstract

The application discloses a low-residual-alkali long-circulation silicon monoxide carbon material and a preparation method thereof, which comprises a low-crystal-grain-size silicon monoxide with a single lithium silicate phase as an inner core, a non-water-soluble silicate phase on the surface, and double carbon layers coated on the surface, wherein an inner layer of the double carbon layers is a hydrophobic carbon layer formed by CVD coating, and an outer carbon layer is a conductive carbon layer with a hydrophilic group. The application adopts a non-active lithium source to pre-lithiate at a constant high temperature for a long time, the non-active lithium source increases the oxygen content on the surface of the silicon monoxide, and surface passivation is completed, thereby inhibiting disproportionation reaction in the pre-lithiation process and surface reduction reaction when a subsequent active lithium source is pre-lithiated, further inhibiting the generation of crystal silicon, and lithium is diffused in the inner core to form a lithium silicate phase at a high temperature.

Description

Technical Field

[0001] This invention relates to the field of silicon suboxide composite material preparation technology, and in particular to a silicon suboxide carbon composite material with low residual alkali and long cycle life and its preparation method. Background Technology

[0002] Currently, with the increasing popularity of electric vehicles, the demand for high-energy-density lithium-ion batteries is growing. Silicon suboxide, with its high specific capacity, is increasingly being used as a negative electrode material in high-energy-density batteries. During the initial lithium insertion process in charge-discharge cycles, silicon suboxide forms an SEI film and a large amount of lithium silicate phase. These substances are irreversible during cycling, resulting in a large amount of irreversible capacity during the initial lithium insertion process, leading to a low initial coulombic efficiency. Pre-lithiation involves charging the silicon suboxide negative electrode material with lithium before electrochemical cycling, forming irreversible lithium silicate before the electrochemical cycle, thereby improving the initial efficiency of silicon suboxide. However, due to the large diffusion barrier and slow diffusion rate of lithium within silicon suboxide, pre-lithiation typically requires a high-temperature environment. The accompanying reduction and disproportionation reactions result in larger lithium grains in silicon suboxide, and the uneven pre-lithiation causes a non-uniform lithium silicate phase, leading to decreased material structural stability and affecting battery cycle performance. In addition, the lithium remaining on the surface during the pre-lithiation process can form lithium hydroxide or lithium carbonate in the air or slurry. This can damage the binder structure during the slurry preparation process, affect the slurry performance, increase the difficulty of coating, and also affect the cycle performance of the battery. Summary of the Invention

[0003] Based on the issues raised in the background technology regarding the large silicon grains and multiphase lithium silicate phase affecting the uniformity of the internal structure of silicon suboxide pre-lithiation materials after the first efficiency stage, as well as the high residual alkali after silicon suboxide pre-lithiation impacting the slurry preparation process and battery cycling, this invention addresses these problems. It employs a step-by-step synergistic pre-lithiation process using two lithium sources—an inactive lithium source and an active lithium source—with different characteristics to improve pre-lithiation uniformity and reduce silicon suboxide grain size. Then, surface modification with a water-insoluble silicate inhibits lithium silicate dissolution. Furthermore, aqueous and oil-based washing effectively removes residual alkali while minimizing lithium silicate dissolution. Finally, a secondary coating with an organic carbon source further reduces the contact between the material core and water during aqueous slurry preparation, inhibiting lithium silicate dissolution in the aqueous solution, improving slurry stability, reducing specific surface area, and increasing conductivity. Moreover, the organic carbon sources used all contain hydrophilic groups, effectively improving the material's dispersibility during slurry preparation.

[0004] The present invention proposes a low residual alkali long-cycle silicon suboxide carbon material and its preparation method, characterized in that it comprises a core of low silicon grain size silicon suboxide containing a single lithium silicate phase, a surface having a non-water-soluble silicate phase, and a double carbon layer coated on the surface, wherein the inner layer of the double carbon layer is a hydrophobic carbon layer formed by vapor deposition, and the outer carbon layer is a conductive carbon layer with hydrophilic groups.

[0005] The single lithium silicate phase includes one of Li2Si2O5, Li4SiO4 and Li2SiO3.

[0006] In the aforementioned anode material, the average particle size of the silicon suboxide core is 1–10 μm, the thickness of the double carbon layer is 2–40 nm, and the carbon content accounts for 1–8% of the material's mass fraction.

[0007] Its characteristic is that it includes the following preparation steps:

[0008] S1. Powder A is obtained by coating a highly conductive carbon layer with a thickness of 1nm to 20nm onto the surface of silicon suboxide particles using a CVD vapor phase coating process.

[0009] S2. Mix powder A with an inactive lithium source until homogeneous, and calcine at 700℃~850℃ for 3h~6h under an inert atmosphere to obtain powder B.

[0010] S3. Mix powder B with the active lithium source evenly, and calcine at a high temperature of 700℃~850℃ for 0.1h~1h under an inert atmosphere, and then calcine at a low temperature of 600℃~750℃ for 2h~10h to obtain powder C.

[0011] S4. Place powder C in a 0.01M to 0.1M stannous chloride solution and stir for 0.1 to 2 hours. Continue to add metal compounds to the solution to form a 0.1M to 2M homogeneous solution. Continue stirring for 1 to 3 hours. After filtration, dry the solution and calcine it at 500℃ to 800℃ for 3 to 6 hours under an inert atmosphere to obtain powder D.

[0012] S5. Powder D is first washed and dried with an aqueous detergent, and then washed and dried with an oil-based detergent to obtain powder F.

[0013] S6. Mix powder F with organic carbon source evenly, and calcine at 600℃~800℃ for 1h~3h in an inert atmosphere to obtain a low residual alkali long-cycle silicon suboxide carbon material with an external conductive carbon layer of 1nm~20nm hydrophilic groups.

[0014] Preferably, the CVD vapor phase coating process involves placing silicon suboxide into a CVD rotary furnace, replacing it with an inert gas, and then continuously calcining it at 650°C to 950°C for 0.5 to 3 hours. The inert gas is either argon or nitrogen, and the carbon source gas is either methane, acetylene, or propyne. The ratio of the inert gas to the carbon source gas is 2:1 to 1:2.

[0015] Preferably, in S2, the inactive lithium source is one of lithium oxide, lithium carbonate, lithium sulfate, and lithium nitrate, and the mass ratio of the inactive lithium source to powder A is 1:20 to 3:7.

[0016] Preferably, in step S4, the stirring speed is 100-300 r / min, the heating rate is 1℃ / min-10℃ / min, and the metal compound is one of magnesium nitrate, magnesium sulfate, calcium sulfate, calcium nitrate, magnesium hydroxide, and calcium hydroxide.

[0017] Preferably, in S5, the aqueous washing solution is 80wt%–99wt% deionized water and 20wt%–1wt% dispersion solution, wherein the dispersion solution is one of methanol, ethanol, and ethylene glycol; the oil-based washing solution is 40wt%–97wt% solute and 60wt%–3wt% residual alkali remover, wherein the solute is N-methylpyrrolidone, methanol, ethanol, and ethylene glycol; and the residual alkali remover is one or more of glycine, resorcinol, hydrogen cyanide, formic acid, acetic acid, trifluoroacetic acid, oxalic acid, and citric acid.

[0018] Preferably, in S6, the organic carbon source is one of sodium alginate, carob gum, polyacrylamide, and poly(N-polyacrylamide), and the mass ratio of powder F to organic carbon source is 10:1 to 50:1.

[0019] Preferably, the negative electrode material of the lithium-ion battery comprises the low residual alkali and long cycle silicon suboxide carbon material as described in claim 1 or 2.

[0020] In a specific preparation process of the present invention, a highly conductive carbon layer is first uniformly deposited on the surface of silicon suboxide powder using a CVD process to improve the conductivity of silicon suboxide. At the same time, it reduces the direct contact between the core and the active lithium source during the pre-lithiation process, reduces the reduction reaction between the lithium source and the core, inhibits the formation of crystalline silicon, and reduces the damage to the surface morphology of the core.

[0021] Subsequently, a non-active lithium source was used for long-term high-temperature isothermal pre-lithiation. The non-active lithium source increased the oxygen content on the silicon suboxide surface, completing surface passivation. This suppressed the disproportionation reaction during the pre-lithiation process and the surface reduction reaction during subsequent active lithium source pre-lithiation, further inhibiting the formation of crystalline silicon. At high temperature, lithium diffused into the core to form a lithium silicate phase. Then, an active lithium source was used for variable-temperature calcination pre-lithiation, employing a process of short-term high-temperature calcination followed by long-term low-temperature calcination. The high temperature triggered the pre-lithiation reaction, and lithium diffused rapidly at high temperatures, reducing the lithium source concentration on the material surface and minimizing surface reduction reactions and morphological damage. This process also reduced some of the oxygen content increased by the non-active lithium source, improving the material's specific capacity. The long-term low-temperature calcination then constituted the lithium diffusion stage. Lithium diffusion in solids is difficult, often exhibiting a gradient distribution within the material, leading to the formation of different lithium silicates depending on the lithium concentration. This results in uneven internal stress during lithium insertion / extraction, affecting the material's cycle performance. In this invention, a stepwise synergistic pre-lithiation process using an inactive lithium source and an active lithium source is employed to ensure uniform lithium distribution within the material, forming a structurally simple lithium silicate, as shown in the XRD pattern of Example 3. Subsequently, stannous chloride is used to sensitize the material surface, allowing the metal compound to be uniformly adsorbed onto the surface. Heating then forms a water-insoluble silicate, inhibiting the dissolution of lithium silicate in aqueous solution. A water-based washing process is then used to remove readily soluble lithium hydroxide and some lithium carbonate from the material surface, activating the remaining insoluble lithium carbonate. This process is short, resulting in minimal lithium silicate dissolution. Following this, an oil-based washing process removes residual alkali from the surface, and lithium silicate does not dissolve during this process, effectively reducing residual alkali on the material surface.

[0022] Finally, a secondary coating with an organic carbon source is used to further reduce the contact between the material core and water during aqueous pulping, inhibiting lithium silicate dissolution, improving pulp stability, reducing specific surface area, and increasing conductivity. Furthermore, the organic carbon sources used all contain hydrophilic groups, effectively improving the material's dispersibility during pulping.

[0023] The beneficial effects of this invention are as follows:

[0024] This invention proposes a low-residue, long-cycle silicon suboxide carbon material and its preparation method. The method includes first uniformly depositing a carbon layer on the surface of silicon suboxide powder using a CVD process. This reduces direct contact between the core and the lithium source during pre-lithiation, minimizing surface morphology damage and inhibiting surface reduction reactions, thus reducing the formation of crystalline silicon. Subsequently, a stepwise pre-lithiation process is employed, using a non-active lithium source for high-temperature isothermal calcination and an active source for variable-temperature sintering. This stepwise synergistic pre-lithiation utilizes the characteristics of different lithium sources to improve the uniformity of pre-lithiation, forming a structurally simple lithium silicate. Furthermore, the core is first passivated using a non-active lithium source for pre-lithiation, inhibiting silicon crystal growth during the active lithium source pre-lithiation process. This ultimately yields a pre-lithiated silicon suboxide material with low silicon grain size. Finally, aqueous and oil-based washing effectively removes surface residual alkali while minimizing lithium silicate dissolution. Finally, a secondary coating with an organic carbon source is used to further reduce the contact between the material core and water during aqueous pulping, inhibit the dissolution of lithium silicate, improve pulp stability, reduce specific surface area, and improve conductivity. In addition, the organic carbon sources used all contain hydrophilic groups, which effectively improve the dispersibility of the material during pulping. Attached Figure Description

[0025] Figure 1 This is a SEM image of the low residual alkali long-cycle silicon suboxide carbon material prepared in Example 2 of the present invention.

[0026] Figure 2 This is an XRD image of the low-residue, long-cycle silicon suboxide carbon material prepared in Example 3 of the present invention. This material contains Li₂Si₂O₅ and sparingly soluble Mg₂SiO₄ and MgSiO₃. Detailed Implementation

[0027] The technical solution of the present invention will now be described in detail through specific embodiments.

[0028] Example 1

[0029] Silica with an average particle size of 1 μm was placed in a CVD rotary furnace. After purging with argon, argon and methane were continuously introduced at a flow rate ratio of 2:1 and calcined at 650℃ for 0.5 h to coat the silica surface with a highly conductive carbon layer with a thickness of 1 nm. The resulting powder was mixed with lithium oxide at a mass ratio of 20:1 and calcined at 750℃ for 3 h under argon. The resulting powder was then mixed with lithium nitride at a mass ratio of 9:1 and calcined at 700℃ for 0.1 h under argon, followed by a temperature increase of 1℃ / min to 600℃ and calcination for 2 h to form a single Li2Si2O5 phase. The material was then placed in a 0.01M stannous chloride solution and stirred at 100 r / min for 0.1 h. Magnesium nitrate was added to the solution to form a 0.1M homogeneous solution, and stirring was continued for 1 h. After filtration and drying, the solution was placed in an argon atmosphere and calcined at 500℃ for 3 h at a heating rate of 3℃ / min. The obtained powder was first washed with a mixed solution of 80 wt% deionized water and 20 wt% methanol and then dried. Then it was washed and dried again with a mixed solution of 40 wt% N-methylpyrrolidone and 60 wt% glycine. The obtained powder was mixed with sodium alginate at a mass ratio of 50:1 and calcined at 600℃ for 1 h in an argon atmosphere to obtain a low-residue, long-cycle silicon suboxide carbon material with an outer carbon layer of 1 nm. The carbon content accounted for 1% of the material mass fraction.

[0030] Using the aforementioned negative electrode material, an electrode sheet was prepared as a reference positive electrode, and lithium metal was used as a reference negative electrode. A half-cell was then formed with a separator and electrolyte for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltage ranged from 0.005 to 0.8V. The negative electrode sheet achieved a discharge specific capacity of 1280 mAh / g, an initial efficiency of 89.2%, and retained 97.1% of its capacity after 100 cycles.

[0031] Example 2

[0032] Silica with an average particle size of 3 μm was placed in a CVD rotary furnace. After nitrogen purging, nitrogen and acetylene were continuously introduced at a flow rate ratio of 1:1 and calcined at 680℃ for 1 h to coat the silica surface with a highly conductive carbon layer with a thickness of 5 nm. The resulting powder was mixed with lithium carbonate at a mass ratio of 15:1 and calcined at 780℃ for 4 h under argon. The resulting powder was then mixed with lithium hydride at a mass ratio of 8:1 and calcined at 750℃ for 0.2 h under argon, followed by a temperature increase of 3℃ / min to 620℃ and calcination for 3 h to form a single Li₂Si₂O₅ phase. The material was then placed in a 0.02M stannous chloride solution and stirred at 150 r / min for 0.3 h. Magnesium sulfate was added to the solution to form a 0.5M homogeneous solution, and stirring was continued for 1.5 h. After filtration and drying, the solution was placed in an argon atmosphere and calcined at 600℃ for 3 h at a temperature increase rate of 5℃ / min. The obtained powder was first washed with a mixed solution of 85 wt% deionized water and 15 wt% ethanol and then dried. Then it was washed and dried again with a mixed solution of 50 wt% methanol and 50 wt% resorcinol. The obtained powder was mixed with carob gum at a mass ratio of 40:1 and calcined at 650℃ for 1.2 h in an argon atmosphere to obtain a low-residue, long-cycle silicon suboxide carbon material with an outer carbon layer of 5 nm. The carbon content accounted for 3% of the material mass fraction.

[0033] Using the aforementioned negative electrode material, an electrode sheet was prepared as a reference positive electrode, and lithium metal was used as a reference negative electrode. A half-cell was then formed with a separator and electrolyte for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltage ranged from 0.005 to 0.8V. The negative electrode sheet achieved a discharge specific capacity of 1250 mAh / g, an initial efficiency of 90.3%, and retained 98.5% of its capacity after 20 cycles.

[0034] Example 3

[0035] Silica with an average particle size of 5 μm was placed in a CVD rotary furnace. After nitrogen purging, nitrogen and acetylene were continuously introduced at a flow rate ratio of 1:1.5, and calcined at 700℃ for 1.5 h to coat the silica surface with a highly conductive carbon layer with a thickness of 12 nm. The resulting powder was mixed with lithium sulfate at a mass ratio of 10:3 and calcined at 800℃ for 4 h under nitrogen. The resulting powder was then mixed with lithium azide at a mass ratio of 7:1 and calcined at 780℃ for 0.5 h under nitrogen, followed by a temperature increase of 3℃ / min to 650℃ and calcination for 5 h to form a single Li2SiO3 phase. The material was then placed in a 0.05M stannous chloride solution and stirred at 200 r / min for 1 h. Calcium nitrate was added to the solution to form a homogeneous 0.8M solution, and stirring was continued for 2 h. After filtration and drying, the solution was placed in a nitrogen atmosphere and calcined at 700℃ for 4 h at a heating rate of 6℃ / min. The obtained powder was first washed with a mixed solution of 90wt% deionized water and 10wt% ethylene glycol and then dried. Then it was washed and dried again with a mixed solution of 80wt% ethanol and 20wt% hydrogen cyanide. The obtained powder was mixed with polyacrylamide at a mass ratio of 25:1 and calcined at 700℃ for 1.5h in a nitrogen atmosphere to obtain a low-residue, long-cycle silicon suboxide carbon material with an outer carbon layer of 10nm. The carbon content accounted for 5% of the material mass fraction.

[0036] Using the aforementioned negative electrode material, an electrode sheet was prepared as a reference positive electrode, and lithium metal was used as a reference negative electrode. A half-cell was then formed with a separator and electrolyte for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltage ranged from 0.005 to 0.8V. The negative electrode sheet achieved a discharge specific capacity of 1240 mAh / g, an initial efficiency of 91.5%, and retained 98.9% of its capacity after 20 cycles.

[0037] Example 4

[0038] Silica with an average particle size of 6 μm was placed in a CVD rotary furnace. After nitrogen purging, argon and propyne were continuously introduced at a flow rate ratio of 1:1.8 and calcined at 800℃ for 2 h to coat the silica surface with a highly conductive carbon layer with a thickness of 16 nm. The resulting powder was mixed with lithium nitrate at a mass ratio of 20:3 and calcined at 800℃ for 4 h under argon. The resulting powder was then mixed with lithium powder at a mass ratio of 7:1 and calcined at 800℃ for 0.6 h under argon, followed by a temperature increase of 8℃ / min to 700℃ and calcination for 6 h to form a single Li2SiO3 phase. The material was then placed in a 0.06M stannous chloride solution and stirred at 250 r / min for 1.5 h. Magnesium hydroxide was added to the solution to form a 1.5M homogeneous solution, and stirring was continued for 2.5 h. After filtration and drying, the solution was placed in an argon atmosphere and calcined at 750℃ for 5 h at a heating rate of 6℃ / min. The obtained powder was first washed and dried with a mixed solution of 95 wt% deionized water and 5 wt% ethylene glycol. Then it was washed and dried again with a mixed solution of 90 wt% ethylene glycol and 10 wt% acetic acid and trifluoroacetic acid, wherein the volume ratio of acetic acid and trifluoroacetic acid was 1:1. The obtained powder was mixed with poly(N-polyacrylamide) at a mass ratio of 40:1 and calcined at 750°C for 2 hours in an argon atmosphere to obtain a low-residue, long-cycle silicon suboxide carbon material with an outer carbon layer of 15 nm and a carbon content of 6% of the material mass fraction.

[0039] Using the aforementioned negative electrode material, an electrode sheet was prepared as a reference positive electrode, and lithium metal was used as a reference negative electrode. A half-cell was then formed with a separator and electrolyte for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltage ranged from 0.005 to 0.8V. The negative electrode sheet achieved a discharge specific capacity of 1250 mAh / g, an initial efficiency of 92.3%, and retained 89.5% of its capacity after 20 cycles.

[0040] Example 5

[0041] Silica with an average particle size of 10 μm was placed in a CVD rotary furnace. After nitrogen purging, argon and propyne were continuously introduced at a flow rate ratio of 1:2 and calcined at 950 °C for 3 h to coat the silica surface with a highly conductive carbon layer with a thickness of 20 nm. The resulting powder was mixed with lithium nitrate at a mass ratio of 7:3 and calcined at 850 °C for 6 h under argon. The resulting powder was then mixed with passivated lithium powder at a mass ratio of 6:1 and calcined at 850 °C for 1 h under argon, followed by a temperature increase of 8 °C / min to 750 °C and calcined for 10 h to form a single Li4SiO4 phase. The material was then placed in a 0.1 M stannous chloride solution and stirred at 300 r / min for 2 h. Calcium hydroxide was added to the solution to form a 2 M homogeneous solution, and stirring was continued for 3 h. After filtration and drying, the solution was placed in an argon atmosphere and calcined at 800 °C for 6 h at a heating rate of 10 °C / min. The obtained powder was first washed and dried with a mixed solution of 99 wt% deionized water and 1 wt% ethylene glycol. Then it was washed and dried again with a mixed solution of 97 wt% ethylene glycol and 3 wt% oxalic acid and citric acid, wherein the volume ratio of oxalic acid and citric acid was 1:1. The obtained powder was mixed with poly(N-polyacrylamide) at a mass ratio of 50:1 and calcined at 800℃ for 3 hours in an argon atmosphere to obtain a low-residue, long-cycle silicon suboxide carbon material with an outer carbon layer of 20 nm and a carbon content of 8% of the material mass fraction.

[0042] Using the aforementioned negative electrode material, an electrode sheet was prepared as a reference positive electrode, and lithium metal was used as a reference negative electrode. A half-cell was then formed with a separator and electrolyte for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltage ranged from 0.005 to 0.8V. The negative electrode sheet achieved a discharge specific capacity of 1050 mAh / g, with an initial efficiency of 98.3%, and retained 87.5% of its capacity after 20 cycles.

[0043] Comparative Example 1

[0044] Silicon suboxide with an average particle size of 4 μm was placed in a vapor deposition furnace and carbon-coated with argon and acetylene at 850 °C for 2 h to obtain silicon suboxide-based anode material. The gas flow rate of argon was 150 ml / min and the gas flow rate of acetylene was 100 ml / min. Then, the obtained powder was mixed with passivated lithium powder at a mass ratio of 9:1 and calcined at 800 °C under an argon atmosphere for 3 h to obtain pre-lithiated silicon suboxide.

[0045] Using the aforementioned negative electrode material, an electrode sheet was prepared as a reference positive electrode, and lithium metal was used as a reference negative electrode. A half-cell was then formed with a separator and electrolyte for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), with charge / discharge voltages ranging from 0.005 to 0.8V. The negative electrode sheet achieved a discharge specific capacity of 1100 mAh / g, with an initial efficiency of 86.3%. After 20 cycles, the capacity retention was only 56.2%.

[0046] Comparative analysis of the performance results of the materials prepared in the comparative examples and examples shows that the present invention uses an inactive lithium source for long-term high-temperature isothermal pre-lithiation. The inactive lithium source increases the oxygen content on the surface of silicon suboxide, completing surface passivation, which not only inhibits the disproportionation reaction during the pre-lithiation process but also the surface reduction reaction during subsequent pre-lithiation with an active lithium source, further suppressing the formation of crystalline silicon. At high temperature, lithium diffuses into the core to form a lithium silicate phase. Then, an active lithium source is used for variable-temperature calcination pre-lithiation, employing a process of short-term high-temperature calcination followed by long-term low-temperature calcination. The high temperature triggers the pre-lithiation reaction, and lithium diffuses rapidly at high temperatures, reducing the lithium source concentration on the material surface, minimizing surface reduction reactions and surface morphology damage. This process also reduces some of the oxygen content increased by the inactive lithium source, improving the material's specific capacity. The long-term low-temperature calcination then constitutes the lithium diffusion stage. Lithium diffusion in solids is difficult, often exhibiting a gradient distribution within the material, resulting in different lithium silicates formed depending on the lithium concentration. This causes uneven internal stress during lithium insertion / extraction, affecting the material's cycle performance. This invention employs a stepwise synergistic pre-lithiation process using both inactive and active lithium sources to ensure uniform lithium distribution within the material, forming a structurally simple lithium silicate. Subsequently, stannous chloride is used to sensitize the material surface, allowing the metal compound to be uniformly adsorbed onto the surface. Heating then forms a water-insoluble silicate, inhibiting the dissolution of lithium silicate in aqueous solution. Aqueous washing removes readily soluble lithium hydroxide and some lithium carbonate from the material surface, activating the remaining insoluble lithium carbonate. This process is short, resulting in minimal lithium silicate dissolution. Following this, an oil-based washing process removes residual alkali from the surface, and lithium silicate does not dissolve during this process, effectively reducing surface alkali residue. Finally, a secondary coating with an organic carbon source further reduces the contact between the material core and water during aqueous pulping, inhibiting lithium silicate dissolution, improving pulp stability, reducing specific surface area, and increasing conductivity. Furthermore, the organic carbon sources used all contain hydrophilic groups, effectively improving the dispersibility of the material during pulping.

[0047] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a low-residue, long-cycle silicon suboxide carbon material, characterized in that, Includes the following steps: S1. Powder A is obtained by coating a highly conductive carbon layer with a thickness of 1 nm to 20 nm onto the surface of silicon suboxide particles using a CVD vapor phase coating process. S2. Mix powder A with an inactive lithium source evenly, and calcine at 700℃~850℃ for 3h~6h under an inert atmosphere to obtain powder B; the inactive lithium source is one of lithium oxide, lithium carbonate, lithium sulfate, and lithium nitrate. S3. Mix powder B with the active lithium source evenly, and calcine at a high temperature of 700℃~850℃ for 0.1h~1h under an inert atmosphere, and then calcine at a low temperature of 600℃~750℃ for 2h~10h to obtain powder C; the active lithium source is one or more of lithium nitride, lithium hydride, lithium azide, and lithium powder. S4. Place powder C in a 0.01M to 0.1M stannous chloride solution and stir for 0.1h to 2h. Continue to add metal compounds to the solution to form a 0.1M to 2M homogeneous solution, continue stirring for 1h to 3h, filter, dry, and calcine at 500℃ to 800℃ under an inert atmosphere for 3h to 6h to obtain powder D. S5. Powder D is first washed and dried with an aqueous washing solution, and then washed and dried with an oil-based washing solution to obtain powder F. The aqueous washing solution consists of 80wt%–99wt% deionized water and 20wt%–1wt% dispersion solution, wherein the dispersion solution is one of methanol, ethanol, and ethylene glycol. The oil-based washing solution consists of 40wt%–97wt% solute and 60wt%–3wt% residual alkali remover, wherein the solute is N-methylpyrrolidone, methanol, ethanol, and ethylene glycol. The residual alkali remover is one or more of glycine, resorcinol, hydrogen cyanide, formic acid, acetic acid, trifluoroacetic acid, oxalic acid, and citric acid. S6. Mix powder F with organic carbon source evenly, and calcine at 600℃~800℃ for 1h~3h in an inert atmosphere to obtain a low residual alkali long-cycle silicon suboxide carbon material with an external conductive carbon layer of 1nm~20nm and hydrophilic groups. The aforementioned low-residue, long-cycle silicon suboxide carbon material comprises a core of low-grain-size silicon suboxide containing a single lithium silicate phase, a surface with a non-water-soluble silicate phase, and a double carbon layer coated on the surface; the inner layer of the double carbon layer is a hydrophobic carbon layer, and the outer carbon layer is a conductive carbon layer with hydrophilic groups; the single lithium silicate phase is one of Li2Si2O5, Li4SiO4, and Li2SiO3.

2. The method for preparing low-residue, long-cycle silicon suboxide carbon material according to claim 1, characterized in that, The average particle size of the silicon suboxide core is 1–10 μm, the thickness of the double carbon layer is 2–40 nm, and the carbon content accounts for 1–8% of the material mass fraction.

3. The method for preparing low-residue, long-cycle silicon suboxide carbon material according to claim 1, characterized in that, In S1, the CVD vapor phase coating process involves placing silicon suboxide into a CVD rotary furnace, replacing it with an inert gas, and then continuously introducing an inert gas and a carbon source gas for calcination at 650℃~950℃ for 0.5h~3h. The inert gas is either argon or nitrogen, and the carbon source gas is either methane, acetylene, or propyne. The ratio of the inert gas to the carbon source gas is 2:1~1:

2.

4. The method for preparing low-residue, long-cycle silicon suboxide carbon material according to claim 1, characterized in that, In S2, the mass ratio of the inactive lithium source to powder A is 1:20 to 3:

7.

5. The method for preparing low-residue, long-cycle silicon suboxide carbon material according to claim 1, characterized in that, In S3, the mass ratio of the active lithium source to powder B is 1:9 to 1:

6.

6. The method for preparing low-residue, long-cycle silicon suboxide carbon material according to claim 1, characterized in that, In S4, the stirring speed is 100-300 r / min, the heating rate is 1℃ / min-10℃ / min, and the metal compound is one of magnesium nitrate, magnesium sulfate, calcium sulfate, calcium nitrate, magnesium hydroxide, and calcium hydroxide.

7. The method for preparing low-residue, long-cycle silicon suboxide carbon material according to claim 1, characterized in that, In S6, the organic carbon source is one of sodium alginate, carob gum, polyacrylamide, and poly-N-polyacrylamide, and the mass ratio of powder F to organic carbon source is 10:1 to 50:

1.

8. A lithium-ion battery, characterized in that, The negative electrode material of the lithium-ion battery comprises a low-residue, long-cycle silicon suboxide carbon material prepared by the preparation method described in claim 1 or 2.

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