Lithium phosphate modified silicon-based anode material, preparation method thereof, and lithium ion battery and anode electrode thereof

Abstract

The application provides a lithium phosphate modified silicon-based anode material, a preparation method thereof, a lithium ion battery and an anode electrode thereof. The lithium phosphate modified silicon-based anode material comprises silicon nanoparticles, carbon and lithium phosphate, and has a core-shell structure, wherein the core is the silicon nanoparticles, the shell is a carbon layer, the carbon layer is coated on the surface of the silicon nanoparticles, and the lithium phosphate is distributed on the surface of the carbon layer. The preparation method of the anode material comprises dispersing glucose and silicon nanoparticles in phosphoric acid to form a first solution, performing a hydrothermal reaction to obtain carbon-coated silicon nanoparticles, mixing the carbon-coated silicon nanoparticles with phosphoric acid and lithium hydroxide to form a second solution, evaporating the solvent of the second solution to obtain an intermediate product, and performing heat treatment to obtain the lithium phosphate modified silicon-based anode material. The application also provides the anode electrode and the lithium ion battery made of the anode material. The anode material can promote the formation of a stable SEI film rich in lithium phosphate during the battery cycle process, and improve the rate performance and stability of the battery.

Description

Technical Field

[0001] This invention relates to the field of electrode materials technology, and in particular to a lithium phosphate modified silicon-based anode material, its preparation method, and a lithium-ion battery and its anode electrode. Background Technology

[0002] Currently, lithium-ion batteries using commercial graphite as an anode face challenges due to their suboptimal energy density and slow charging rate. Silicon-based anodes, with their high energy density of 4200 mAh / g and voltage plateau below 0.4V, are considered the most promising alternative to commercial graphite. However, silicon particles are highly susceptible to volume expansion, leading to breakage and pulverization, resulting in an unstable SEI film and significantly reduced battery capacity and lifespan. While nano- and structural designs of silicon particles can suppress breakage and pulverization, volume expansion remains unavoidable, and the damage to the SEI film remains unresolved. The SEI film plays a crucial role in determining battery lifespan, cycle stability, ion transport rate, and rate capability. Therefore, designing high-performance silicon-based anode materials and constructing stable SEI films remains challenging, and finding a simple way to synthesize high-performance silicon-based composite anode materials for commercial production is of great significance.

[0003] Therefore, it is necessary to solve the problem that silicon-based anode materials in the existing technology produce unstable SEI films due to volume expansion and crushing, which leads to low capacity and short service life. Summary of the Invention

[0004] To overcome the above problems, the present invention aims to provide a lithium phosphate-modified silicon-based anode material, its preparation method, and a lithium-ion battery and its anode electrode. This lithium phosphate-modified silicon-based anode material can promote the formation of a stable, lithium phosphate-rich SEI film during battery cycling, improving the lithium-ion battery's ability to withstand lithium oxidation. + The adsorption energy of Li accelerates + Improve the rate performance and stability of the battery by reducing the desolvation rate in the solvent.

[0005] To achieve the above objectives, the present invention provides a lithium phosphate modified silicon-based anode material, which includes silicon nanoparticles, carbon, and lithium phosphate. The anode material has a core-shell structure, wherein the core of the anode material is silicon nanoparticles, the shell of the anode material is a carbon layer, the carbon layer covers the surface of the silicon nanoparticles, and the lithium phosphate (Li3PO4, abbreviated as LPO) is distributed on the surface of the carbon layer.

[0006] In the aforementioned lithium phosphate-modified silicon-based anode material, the lithium phosphate typically exists in discrete particle form, with Li3PO4 particles uniformly distributed on the carbon layer surface. Lithium phosphate exhibits good ionic conductivity, which promotes ion transport. Furthermore, lithium phosphate is effective against Li...+ The high adsorption energy of Li can make Li + The lithium ion detaches more quickly from the solvent sheath of the electrolyte, accelerating lithium-ion transport kinetics. Furthermore, lithium phosphate is a semiconductor; a continuous lithium phosphate layer reduces electron transport rate and causes polarization in the battery. In contrast, the discrete distribution of lithium phosphate particles in the aforementioned anode material provides better conductivity, which is beneficial for improving lithium-ion battery performance.

[0007] In the aforementioned lithium phosphate modified silicon-based anode material, the silicon nanoparticles have a particle size of 50-500 nm, specifically 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc., or a range with any two of the above specific values ​​as endpoints. Further, it can be 100-200 nm.

[0008] In the above-mentioned lithium phosphate modified silicon-based anode material, the thickness of the carbon layer is 4-5 nm, specifically 4 nm, 4.1 nm, 4.2 nm, 4.3 nm, 4.4 nm, 4.5 nm, 4.6 nm, 4.7 nm, 4.8 nm, 4.9 nm, 5 nm, etc., and a range with any two of the above specific values ​​as endpoints.

[0009] According to the specific implementation scheme, in the above-mentioned anode material, the mass ratio of lithium phosphate to the sum of the masses of carbon and silicon nanoparticles is 1:5-1:15; that is, the mass ratio of lithium phosphate to (carbon + silicon nanoparticles) can be 1:5-1:15; specifically, it can be 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, etc., and a range with any two of the above specific values ​​as endpoints.

[0010] This invention also provides a method for preparing a lithium phosphate modified silicon-based anode material, the method comprising:

[0011] S1. A carbon source and silicon nanoparticles (SiNPs) are dispersed in phosphoric acid to form a first solution, and a hydrothermal reaction is carried out to obtain carbon-coated silicon nanoparticles (Si@C);

[0012] S2. The carbon-coated silicon nanoparticles are mixed with a phosphorus source and a lithium source to form a second solution. The solvent in the second solution is evaporated to obtain an intermediate product. The intermediate product is then heat-treated in a protective atmosphere to obtain the lithium phosphate modified silicon-based anode material (Si@C@LPO).

[0013] The above preparation method can obtain the lithium phosphate modified silicon-based anode material provided by the present invention.

[0014] In the above preparation method, the carbon-coated silicon nanoparticles obtained in S1 can be silicon nanoparticles coated with hydroxyl-rich carbon layers, providing a large number of anchor sites for the subsequently generated Li3PO4. At the same time, the carbon layer plays the role of coating (inhibiting silicon volume expansion) and enhancing conductivity.

[0015] In the above preparation method, in step S1, mixing a carbon source, silicon nanoparticles, and phosphoric acid yields silicon nanoparticles with a hydroxyl-modified carbon layer. The carbon source provides hydroxyl groups, and the phosphoric acid further provides hydroxyl groups. After a hydrothermal reaction, silicon nanoparticles coated with a hydroxyl-rich carbon layer are obtained.

[0016] In the above preparation method, in S1, the mass ratio of the carbon source to the silicon nanoparticles can be (0.1-5):(0.5-5). That is, by mass parts, the carbon source can be 0.1-5 parts, such as 0.1 parts, 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, etc., and any two of the above specific values ​​as endpoints; the silicon nanoparticles can be 0.5-5 parts, such as 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, etc., and any two of the above specific values ​​as endpoints.

[0017] In the above preparation method, in S1, the particle size of the silicon nanoparticles can be 50-500nm, specifically 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, etc., and a range with any two of the above specific values ​​as endpoints; further, it can be 100-200nm.

[0018] In the above preparation method, in S1, the addition of phosphoric acid helps to form oxygen-containing functional groups on the surface of the carbon layer; these oxygen-containing functional groups can be used to anchor the lithium phosphate formed in S2. The molar ratio of phosphoric acid to the carbon source is (20-50):1, specifically 20:1, 25:1, 30:1, 35:1, 37:1, 38:1, 40:1, 45:1, 50:1, etc., and a range with any two of the above specific values ​​as endpoints.

[0019] In the above preparation method, in step S1, the carbon source generally has hydroxyl groups. The carbon source may include one or more of glucose, sucrose, starch, phenolic resin, and dopamine.

[0020] In the above preparation method, in step S1, the phosphoric acid can be added in the form of a phosphoric acid solution with a concentration of 2-5 mol / L, for example, 3.5 mol / L. Specifically, the formation process of the phosphoric acid solution can be as follows: diluting the raw phosphoric acid (e.g., concentrated phosphoric acid with a concentration of 85%) in a first solvent (ethanol and / or water), and then subjecting it to ultrasonic treatment (to promote uniform dispersion) to obtain the phosphoric acid solution. Further, the ultrasonic treatment time can be 10 min-120 min. In some specific embodiments, the amount of concentrated phosphoric acid used can be 20-70 ml, the amount of the first solvent used to dilute the concentrated phosphoric acid can be 80-120 ml, and finally the volume is adjusted to 250 ml to obtain the phosphoric acid solution.

[0021] In some specific embodiments, in S1, the amount of carbon source can be 0.1g-5g, and the amount of silicon nanoparticles can be 0.5g-5g. The volume of the phosphoric acid solution (concentration 2-5mol / L) mixed with glucose and silicon nanoparticles can be 50-80ml.

[0022] In the above preparation method, S1 may further include ultrasonic treatment of the first solution before the hydrothermal reaction to promote uniform dispersion. The ultrasonic treatment time is 20-40 min, for example, 20 min, 25 min, 30 min, 35 min, 40 min, etc., and a range with any two of the above specific values ​​as endpoints; in some specific embodiments, 30 min may be used.

[0023] In the above preparation method, in S1, the temperature of the hydrothermal reaction is 100-200℃, specifically 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, etc., and a range with any two of the above specific values ​​as endpoints; the time of the hydrothermal reaction is 5-20 hours, specifically 5 hours, 6 hours, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours, etc., and a range with any two of the above specific values ​​as endpoints.

[0024] In some specific implementations, the hydrothermal reaction can be carried out in a high-pressure reaction vessel, such as a stainless steel high-pressure reaction vessel.

[0025] In the above preparation method, in S2, the molar ratio of the phosphorus source and the lithium source can be 1:3-1:4, specifically 1:3, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9, 1:4, etc., as well as a range with any two of the above specific values ​​as endpoints.

[0026] This invention reveals that excessive lithium phosphate generated during anode material preparation leads to poor conductivity and low capacity, while insufficient lithium phosphate fails to promote lithium-ion desolvation. By controlling the mass ratio of generated lithium phosphate to carbon-coated silicon nanoparticles (Si@C), a uniform and stable Li3PO4-enriched SEI film can be formed on the anode surface. This effectively reduces electrolyte decomposition on the electrode surface, improves battery cycle stability and coulombic efficiency, enhances lithium-ion transport efficiency, optimizes Li3PO4 content in the SEI film, maximizes lithium-ion transport efficiency, facilitates fast charging, strengthens electrode mechanical stability, reduces electrode material pulverization and detachment, and extends battery life. If the above ratio is too small, the Li3PO4 content in the SEI film will be insufficient, leading to a decrease in the stability and ionic conductivity of the SEI film. This will also weaken the SEI film's ability to adsorb and transport lithium ions, slowing down the transport speed of lithium ions within the SEI film and hindering the improvement of fast charging performance. Furthermore, the mechanical stability of the SEI film will deteriorate, failing to effectively mitigate the volume expansion of silicon during charging and discharging, thus exacerbating the pulverization and shedding of electrode materials and affecting battery lifespan. If the above ratio is too large, it will result in an excessively thick SEI film, increasing the resistance to lithium ion transport, reducing the battery's rate performance and fast charging capability; decreasing the utilization rate of electrode active materials, affecting the overall energy density of the battery; and increasing the battery's internal resistance, reducing the battery's charging and discharging efficiency and output power. The mass ratio of lithium phosphate (i.e., lithium phosphate generated by the S2 reaction) in the intermediate product to the carbon-coated silicon nanoparticles is 1:5-1:15, specifically 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, etc., and any two of the above specific values ​​as endpoints; in some embodiments, 1:10 can be used.

[0027] In the above preparation method, in S2, the lithium source includes lithium hydroxide and / or lithium dihydrogen phosphate.

[0028] In the above preparation method, in step S2, the lithium source can be nanoparticles. Specifically, the particle size of the lithium source can be below 20 nm to match the particle size of the silicon nanoparticles.

[0029] In the above preparation method, in step S2, the phosphorus source may include one or a combination of two or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphorus pentoxide. The phosphoric acid and phosphorus pentoxide can react with a lithium source to generate lithium phosphate, and the ammonium dihydrogen phosphate and diammonium hydrogen phosphate can decompose to form phosphoric acid.

[0030] In the above preparation method, the phosphorus source and lithium source used in S2 can be added in the form of a mixed solution. Specifically, the phosphorus source and lithium source can be first dispersed in a second solvent to form a mixed solution, the mixed solution is ultrasonically treated to promote uniform dispersion, and then the ultrasonically treated mixed solution is thoroughly mixed to obtain a second solution. In some specific embodiments, the second solvent may include ethanol; the ultrasonic treatment time can be 20-40 min, for example 20 min, 25 min, 30 min, 35 min, 40 min, etc., or a range with any two of the above specific values ​​as endpoints; in some specific embodiments, 30 min may be used.

[0031] In the above preparation method, in step S2, the evaporation solvent can be evaporated by heating. The evaporation temperature is 40-80℃, specifically 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, etc., or a range with any two of these specific values ​​as endpoints. In some specific embodiments, grinding can accompany the evaporation process. Grinding allows the solid particles to fully contact the second solvent, accelerates the evaporation of the second solvent, and prevents the solid particles from agglomerating during evaporation. Grinding can increase the surface area of ​​the solid particles, improve evaporation efficiency, and make the components in the intermediate product (precursor mixture) uniformly distributed.

[0032] Specifically, the process of evaporating the solvent can be as follows: heating the second solution to 40-80°C for evaporation and grinding until the solvent is completely evaporated.

[0033] In the above preparation method, in step S2, the heat treatment is used for carbonization to improve the conductivity of the carbon layer. The temperature of the heat treatment (i.e., annealing) is 500-1000℃, specifically 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, etc., or any two of the above specific values ​​as endpoints; the time of the heat treatment is 2-5 hours, specifically 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, etc., or any two of the above specific values ​​as endpoints. In some specific embodiments, the heat treatment can be carried out in a horizontal tube furnace.

[0034] In the above preparation method, in step S2, the heat treatment can be carried out in a protective atmosphere, which may include argon.

[0035] In the above preparation method, the lithium phosphate in the product of S2 is a discretely distributed particle; specifically, lithium phosphate is anchored to the carbon layer surface in a discrete form through interaction with oxygen-containing functional groups. This invention, by controlling the amount of phosphorus and lithium sources added relative to the carbon-coated silicon nanoparticles, and by controlling the amount of hydroxyl groups in the carbon-coated silicon nanoparticles, facilitates the obtaining of discrete lithium phosphate particles. This invention uses hydrothermal products directly (without high-temperature treatment) as precursors mixed with phosphorus and lithium sources to prepare lithium phosphate, which is beneficial for controlling the anchoring points (number of hydroxyl groups) on the amorphous carbon layer surface of the carbon-coated silicon nanoparticles.

[0036] According to a specific embodiment of the present invention, the preparation method of the above-mentioned lithium phosphate modified silicon-based anode material may specifically include:

[0037] S1. Dilute concentrated phosphoric acid in the first solvent and sonicate for 10-120 min to obtain a phosphoric acid solution;

[0038] A carbon source and silicon nanoparticles with a particle size of 50-500 nm are dispersed in the above phosphoric acid solution at a mass ratio of (0.1-5):(0.5-5) and stirred thoroughly. The solution is then sonicated for 20-40 min to form a first solution. The molar ratio of phosphoric acid to carbon source in the first solution is (20-50):1. The first solution is subjected to a hydrothermal reaction at 100-200℃ for 5-20 h to obtain carbon-coated silicon nanoparticles.

[0039] S2. Disperse phosphorus source and lithium source (particle size less than 20 nm) in a molar ratio of 1:3-1:4 in the second solvent, and sonicate for 20-40 min to obtain a mixed solution;

[0040] The carbon-coated silicon nanoparticles are mixed with the above mixed solution to form a second solution. The second solution is heated to 40-80°C for evaporation and grinding until the solvent is completely evaporated to obtain an intermediate product. The intermediate product contains lithium phosphate and carbon-coated silicon nanoparticles in a mass ratio of 1:5 to 1:15. The intermediate product is then heat-treated in a protective atmosphere at a temperature of 500-1000°C for 2-5 hours to obtain the lithium phosphate modified silicon-based anode material.

[0041] The present invention also provides a lithium-ion battery anode electrode, which is made of the above-mentioned lithium phosphate modified silicon-based anode material.

[0042] According to a specific embodiment of the present invention, the method for preparing the lithium-ion battery anode electrode may include: mixing anode material, conductive carbon black and binder to form a slurry, coating it on a conductive substrate, drying it, and stamping it to obtain the lithium-ion battery anode.

[0043] In the above method for preparing the anode electrode of a lithium-ion battery, the drying temperature can be 80-100℃ and the drying time can be 8-12 hours. The drying can be carried out in a vacuum oven.

[0044] In the above-mentioned method for preparing the anode electrode of a lithium-ion battery, the binder includes one or a combination of two or more of PAA-Li, sodium alginate, SBR, and chitosan.

[0045] In the above-mentioned method for preparing the anode electrode of a lithium-ion battery, the mass ratio of the anode material, conductive carbon black and binder can be 6-8:1-2:1-2.

[0046] In the above-described method for preparing the anode electrode of a lithium-ion battery, the slurry may further include water, which ensures that the slurry has good viscosity, dispersibility, and coating performance. Specifically, the mass of the water may be 1-5 times the mass of the anode material.

[0047] In the above-mentioned method for preparing the anode electrode of a lithium-ion battery, the conductive substrate can be copper foil.

[0048] Furthermore, the aforementioned anode electrode can be used to fabricate a lithium-ion battery. In some specific embodiments, a 1.4 cm diameter anode electrode can be used to assemble a button cell-type lithium-ion battery.

[0049] The present invention also provides a lithium-ion battery comprising the above-described lithium-ion battery anode electrode. That is, the anode electrode of the lithium-ion battery can be made from the above-described lithium phosphate modified silicon-based anode material provided by the present invention.

[0050] This invention utilizes lithium phosphate-modified silicon-based anode material to prepare the anode electrode, which significantly improves the desolvation capability and current density of the anode electrode, effectively enhancing the fast-charging performance and cycle stability of lithium-ion batteries. In some specific embodiments, lithium-ion batteries made from this anode material exhibit a 73.3% capacity retention rate after 100 cycles at 1 A / g.

[0051] The lithium phosphate-modified silicon-based anode material provided by this invention is used to manufacture lithium-ion batteries. The Li3PO4 on the surface of the lithium phosphate-modified silicon-based anode material provides a favorable interfacial environment for the formation of the SEI film, promoting its formation and stability. During cycling, this lithium-ion battery can generate a lithium phosphate-rich SEI film. This is because, in the anode electrode made of the anode material, lithium phosphate is located on the anode electrode surface, and the SEI film forms on the outer surface of the anode electrode. The lithium phosphate present on the anode electrode surface forms part of the SEI film. The lithium phosphate in the SEI film has the following advantages:

[0052] (1) Li3PO4 has a high lithium-ion adsorption energy (Ea = -1.465 eV), which can reduce the solvation effect of lithium ions on the electrode surface, thereby reducing the decomposition reaction of solvent molecules on the electrode surface. Reducing solvent decomposition can not only reduce interfacial side reactions, but also improve the stability of the SEI film.

[0053] (2) Li3PO4 has high ionic conductivity, which can promote the transport of lithium ions in the SEI film, reduce the accumulation of lithium ions on the electrode surface, and reduce the possibility of interfacial side reactions.

[0054] (3) The mechanical stability of the SEI film rich in Li3PO4 is also improved, effectively reducing the volume expansion and structural damage of the electrode material during charging and discharging.

[0055] (4) Li3PO4 exhibits good electrochemical stability and can remain stable over a wide potential range. This makes the SEI film less prone to decomposition or structural changes during charging and discharging.

[0056] The beneficial effects of this invention include:

[0057] The lithium-ion battery made from the lithium phosphate-modified silicon-based anode material provided by this invention generates a lithium phosphate-rich SEI film after cycling. The inherently high adsorption energy of lithium phosphate enhances its adsorption of Li. + The affinity of Li and the acceleration of Li at the anode interface + The desolvation process improves the rate performance and fast charging performance of lithium-ion batteries. Furthermore, the SEI film, rich in lithium phosphate, effectively reduces interfacial side effects and eliminates particle breakage caused by volume expansion, thereby enhancing the stability of the SEI film and ultimately improving the cycle stability of the electrode during use. Attached Figure Description

[0058] Figure 1 The images are scanning electron microscope (SEM) images of the anode materials of Example 1, Comparative Example 1, and Comparative Example 2.

[0059] Figure 2 This is a TEM image of Si@C@LPO from Example 1.

[0060] Figure 3 The image shows the SEM image and elemental mapping of Si@C@LPO in Example 1.

[0061] Figure 4 The images show the XRD patterns of the anode materials of Example 1, Comparative Example 1, and Comparative Example 2.

[0062] Figure 5 The graph shows the cycle performance of lithium-ion batteries prepared using the anode materials of Example 1, Comparative Example 1, and Comparative Example 2.

[0063] Figure 6 The rate performance diagram shows the lithium-ion battery prepared using the anode material of Example 1.

[0064] Figure 7 XPS images of the SEI films generated in lithium-ion batteries prepared from the anode materials of Examples 1, 1, and 2.

[0065] Figure 8 High-resolution TEM images of the SEI films generated in lithium-ion batteries prepared from the anode materials of Examples 1, 1, and 2.

[0066] Figure 9 TOF-SIMs images of SEI films generated from lithium-ion batteries prepared using the anode materials of Examples 1, 1, and 2.

[0067] Figure 10 AFM images of the SEI films generated from lithium-ion batteries prepared using the anode materials of Examples 1, 1, and 2. Detailed Implementation

[0068] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0069] Example 1

[0070] This embodiment provides a lithium phosphate modified silicon-based anode material, the preparation method of which includes:

[0071] (1) Dissolve 58.5 ml of 85% concentrated phosphoric acid in 100 ml of deionized water, bring the solution to a final volume of 250 ml, and then sonicate for 30 minutes to obtain a 3.5 mol / L phosphoric acid solution.

[0072] (2) Disperse 1g of glucose and 1g of silicon nanoparticles (SiNPs) with a particle size of 100-200nm in 60ml of the phosphoric acid solution obtained in step (1) and stir thoroughly, then sonicate for 30min to obtain the first solution.

[0073] The first solution was added to a stainless steel high-pressure reaction vessel and subjected to a hydrothermal reaction at 190°C for 12 hours to obtain carbon-coated silicon nanoparticles (Si@C).

[0074] (3) Phosphoric acid and lithium hydroxide nanoparticles (particle size less than 20 nm) were dissolved in 10 ml of anhydrous ethanol at a molar ratio of 1:3 to form a mixed solution, and ultrasonically treated for 30 min. The ultrasonically treated mixed solution was thoroughly mixed with Si@C powder to form a second solution. The second solution was heated and maintained at 60 °C, and continuously ground in a mortar until the solvent in the solution was completely evaporated to obtain a powdered intermediate product. The mass ratio of lithium phosphate to Si@C in the intermediate product was 1:10. The obtained intermediate product was placed in a horizontal tube furnace and heat-treated in an argon atmosphere (800 °C, heating rate 5 °C / min, holding for 3 h) to obtain the final product of lithium phosphate modified silicon-based anode material (Si@C@LPO).

[0075] This embodiment also provides an anode electrode, the preparation method of which includes:

[0076] Based on the total mass of the components in the slurry excluding the dispersant being 100%, the slurry is composed of 80wt% Si@C@LPO, 10wt% carbon black, and 10wt% PAA-Li binder, with the dispersant being deionized water, the mass of which is 1-5 times the mass of Si@C@LPO.

[0077] The slurry was uniformly coated onto the copper current collector, and the coated substrate was dried in a vacuum oven at 100°C for 10 hours until the solvent was completely evaporated, yielding the electrode. The electrode was then stamped into a disc with a diameter of 1.4 cm to obtain an anode electrode made of lithium phosphate modified silicon-based anode material.

[0078] This embodiment also provides a lithium-ion battery, the preparation method of which includes:

[0079] The battery was assembled in the inert environment of an argon-filled glove box, with water and oxygen content strictly controlled below 0.1 ppm. An 80 μL electrolyte, a polypropylene (PP) separator, a lithium sheet, and an anode electrode were assembled into a 2032-type button cell, which is a lithium-ion battery.

[0080] The electrolyte is composed of a 1.0 mol L⁻¹ lithium hexafluorophosphate (LiPF6) electrolyte prepared by using ethylene carbonate (EC): diethyl carbonate (DEC): methyl ethyl carbonate (DMC) in a volume ratio of 1:1:1. This electrolyte contains 5% by volume of fluoroethylene carbonate (FEC) additive.

[0081] Comparative Example 1

[0082] This comparative example provides an anode electrode. The difference between the preparation method of this anode electrode and the anode cell preparation method in Example 1 is that the anode material in this comparative example is replaced by lithium phosphate modified silicon-based anode material with SiNPs with a particle size of 100-200 nm.

[0083] A lithium-ion battery was fabricated using the anode electrode of this comparative example, following the method of Example 1.

[0084] Comparative Example 2

[0085] This comparative example provides an anode electrode. The difference between the preparation method of this anode electrode and the anode battery preparation method in Example 1 is that the anode material in this comparative example is replaced by the lithium phosphate modified silicon-based anode material in Example 1 with Si@C obtained in step (2) of Example 1.

[0086] A lithium-ion battery was fabricated using the anode electrode of this comparative example, following the method of Example 1.

[0087] Figure 1 The images show scanning electron microscope (SEM) images of SiNPs (the raw material of Example 1), Si@C (the product of step 2 in Example 1), and Si@C@LPO (the final product of Example 1). Figure 1 In the image, a and d are SEM images of SiNPs, b and e are SEM images of Si@C, and c and f are SEM images of Si@C@LPO. According to... Figure 1 The morphology of the samples shown indicates that the processed samples still retain the shape of nanospheres.

[0088] Figure 2 This is a TEM image of Si@C@LPO from Example 1. Figure 2 The detection of lattice fringes of lithium phosphate confirms its successful synthesis. Figure 2 It can be seen that the material has a core-shell structure, with silicon nanoparticles wrapped in an amorphous carbon layer. The silicon nanoparticles have a particle size of about 100-200 nm, the carbon layer has a thickness of about 4.5 nm, and LPO (Li3PO4) exists on the surface in the form of dispersed small particles. Figure 2 The part circled in the middle is an amorphous oxide layer, which is formed when the product is exposed to air.

[0089] Figure 3 The images show the SEM image and elemental mapping of Si@C@LPO from Example 1. Figure 3 The elemental mapping results shown indicate that Si, C, O, and P elements are evenly distributed in this material. The overlap of O and P element signals further confirms the successful synthesis of lithium phosphate.

[0090] Figure 4 The images show the XRD patterns of the anode materials for Example 1 (Si@C@LPO), Comparative Example 1 (SiNPs), and Comparative Example 2 (Si@C). From... Figure 4It can be seen that the anode material of Example 1 has diffraction peaks of lithium phosphate, while the samples of Comparative Examples 1 and 2 do not have diffraction peaks of lithium phosphate, proving that the preparation method of Example 1 successfully synthesized lithium phosphate, and that lithium phosphate is in a crystalline state. Furthermore, the anode material of Example 1 did not show obvious carbon characteristic peaks, indicating that carbon exists in an amorphous form.

[0091] Figure 5 The graph shows the cycle performance of lithium-ion batteries prepared using the anode materials of Example 1, Comparative Example 1, and Comparative Example 2. The test method was as follows: the test samples were activated using a current density of 0.1 A / g during the first three cycles, and the test was conducted at a current density of 1 A / g starting from the fourth cycle. The measured capacity is the capacity after activation starting from the fourth cycle.

[0092] from Figure 5 It can be seen that the anode of the battery in Example 1 is at 1Ag -1 After 100 cycles at a given current density, the battery exhibits a capacity of 1695.4 mAh / g. Calculations show a capacity retention rate of 73.3% after 100 cycles, indicating a significant improvement in both rate performance and cycle life. In this invention, the capacity retention rate is calculated as: Capacity retention rate = (Discharge capacity after cycles / Initial discharge capacity) × 100%.

[0093] Figure 6 The rate performance diagram shows the lithium-ion battery prepared using the anode material of Example 1. Figure 6 The test method is as follows: using lithium-ion batteries from Comparative Example 1, Comparative Example 2, and Example 1 as samples, respectively, within a voltage range of 0.005V to 3.0V, at a concentration of 0.2Ag... -1 0.5Ag -1 1Ag -1 2Ag -1 4Ag -1 and 8Ag -1 Charge-discharge tests were conducted at different current densities, with 6 cycles performed at each current density. The discharge capacity of each cycle was recorded, and the capacity retention rate at different current densities was calculated.

[0094] like Figure 6 As shown, in Example 1, the anode of the battery is at 8Ag -1 It exhibits a specific capacity of 605.67 mAh / g at current density.

[0095] The lithium-ion batteries prepared in Comparative Example 1, Comparative Example 2, and Example 1 were subjected to 8Ag. -1 Under constant current charge-discharge conditions at a current density of 1Ag, the lithium-ion battery in Comparative Example 1 exhibited a specific capacity of 34.23 mAh / g, while the lithium-ion battery in Comparative Example 2 exhibited a specific capacity of 289.87 mAh / g. -1After 100 cycles at the specified current density, the battery in Comparative Example 1 showed a failure state, while the battery in Comparative Example 2 showed a capacity of 1102.9 mAh / g and a capacity retention rate of 48.5%.

[0096] Figures 7 to 10 The characterization results are for the SEI films generated after cycling of lithium-ion batteries prepared with anode materials of Example 1, Comparative Example 1, and Comparative Example 2. Figures 7 to 10 The SEI film to be tested is according to Figure 5 SEI film generated by a lithium-ion battery after 100 cycles of testing.

[0097] Figure 7 XPS images of the SEI films generated by the lithium-ion batteries of Example 1, Comparative Example 1, and Comparative Example 2 are shown. In each column, the etching amount gradually increases from top to bottom, and the etching times from top to bottom are 100s, 200s, 500s, and 1000s, respectively. Figure 7 Figures a to c represent the characterization results of C1s after 100 cycles. It can be seen that, compared with the Si@C@LPO electrode, the amount of organic components (RO-CO2 Li) and Li2CO3 in the SEI film of the SiNP and Si@C electrodes increases with continued etching, while the Si@C@LPO electrode shows the opposite trend. Figure 7 Figures d to f represent the P 2p characterization results after 100 cycles. It can be seen that as etching continues, the amount of Li3PO4 in the SEI film of the Si@C@LPO electrode increases, while the amount of Li3PO4 in the SiNP and Si@C electrodes remains basically unchanged.

[0098] The adsorption energy and stability of Li3PO4 for lithium ions are much higher than those of Li2CO3. As can be seen from the above results, the Si@C@LPO and the SEI film generated in Example 1 are rich in more Li3PO4, and therefore the adsorption energy and stability of lithium ions are higher than those of Comparative Example 1 and Comparative Example 2.

[0099] Figure 8 High-resolution TEM images of the SEI films generated from the lithium-ion batteries of Example 1, Comparative Example 1, and Comparative Example 2. From... Figure 8It can be seen that the Si lattice fringes disappear, which further confirms that the Si particles transform into an amorphous state after cycling. Simultaneously, observing the lattice fringes present in each SEI film sample, a comparison reveals that Li3PO4 lattice fringes can be observed in the SEI film generated by Si@C@LPO, further confirming the above findings. Furthermore, electron microscopy results show that significant Li2O was detected in the SEI film of Example 1, while no significant Li2O was detected in Comparative Examples 1 and 2. Li2O has good chemical stability and mechanical strength, which can enhance the stability of the SEI film, reduce electrolyte decomposition and anode material volume expansion; moreover, Li2O can improve the interfacial characteristics between the anode material and the electrolyte, increase lithium-ion transport efficiency, and improve interfacial stability, thereby improving battery performance. The above results also show that the SEI film of Example 1 has better stability than the SEI films of Comparative Examples 1 and 2.

[0100] Figure 9 The time-of-flight secondary ion mass spectrometry (TOF-SIMs) analysis results of the SEI films generated from the lithium-ion batteries of Example 1, Comparative Example 1, and Comparative Example 2 are presented. The test conditions are as follows: depth profiling conditions: sputtering source type Cs source (1 keV) and Bi source (30 keV); imaging conditions: image size of 100 × 100 μm and sputtering area of ​​100 × 100 μm; profiling time: the relative elemental content of the test samples remained basically constant (test time was approximately within 1000 s).

[0101] from Figure 9 Li2PO4 can be found in the Si@C@LPO sample. - The fragment content was the highest (indicating that it contained the most Li3PO4), which corroborates the XPS and TEM results mentioned above.

[0102] Figure 10 AFM images of the SEI films produced from lithium-ion batteries of Examples 1, 1, and 2 are shown, where a to c represent the roughness of the SEI film, and d to f represent the Young's modulus of the SEI film. Figure 10 As can be seen from a to c, the SEI film of the Si@C@LPO sample is the smoothest and most even, exhibiting the best integrity. Compared to the Si@C@LPO electrode, the SiNP and Si@C electrodes display rougher and more irregular surfaces. Figure 10 As can be seen from d to f, the Young's modulus of the SEI film formed in the Si@C@LPO electrode (average 18 GPa) exceeds that of the SiNPs (14 GPa) and Si@C (16 GPa) electrodes. This indicates that the Si@C@LPO SEI film has the highest Young's modulus, demonstrating its ability to withstand the highest stress and its superior ability to adapt to volumetric deformation without cracking. This, in turn, contributes to improved cycle stability.

[0103] The desolvation of lithium in the anode materials of Example 1, Comparative Example 1, and Comparative Example 2 will be explained:

[0104] Carbon exhibits a slightly higher desolvation effect on lithium than silicon; however, lithium phosphate demonstrates a significantly higher desolvation effect on lithium than both carbon and silicon. The lithium-ion battery of Example 1 can generate an SEI film rich in lithium phosphate, promoting lithium-ion desolvation.

[0105] The above results indicate that the lithium phosphate-modified silicon-based anode material provided by this invention helps the battery generate a more stable SEI film rich in lithium phosphate during cycling. During cycling, lithium phosphate increases its affinity for lithium, reduces interfacial side reactions at the electrode, eliminates particle breakage caused by volume expansion, and improves Li-energy efficiency. + The desolvation process improves the fast charging performance and electrode stability of lithium-ion batteries.

[0106] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium phosphate modified silicon-based anode material, the method comprising: S1. Disperse carbon source and silicon nanoparticles in phosphoric acid to form a first solution, and carry out a hydrothermal reaction to obtain carbon-coated silicon nanoparticles. The molar ratio of phosphoric acid to the carbon source is (20-50):1; the mass ratio of the carbon source to the silicon nanoparticles is (0.1-5):(0.5-5); the temperature of the hydrothermal reaction is 100-200℃, and the time of the hydrothermal reaction is 5-20 hours. S2. The carbon-coated silicon nanoparticles are mixed with a phosphorus source and a lithium source to form a second solution. The solvent in the second solution is evaporated to obtain an intermediate product. The intermediate product is heat-treated in a protective atmosphere to obtain the lithium phosphate modified silicon-based anode material. The intermediate product contains lithium phosphate in a mass ratio of 1:5 to 1:15 to carbon-coated silicon nanoparticles. The anode material comprises silicon nanoparticles, carbon, and lithium phosphate. The anode material has a core-shell structure, with the core being silicon nanoparticles and the shell being a carbon layer. The carbon layer covers the surface of the silicon nanoparticles, and the lithium phosphate is distributed on the surface of the carbon layer, existing in discrete particle form.

2. The preparation method according to claim 1, wherein, The silicon nanoparticles have a particle size of 50-500 nm.

3. The preparation method according to claim 2, wherein, The silicon nanoparticles have a particle size of 100-200 nm.

4. The preparation method according to claim 1, wherein, The carbon source includes one or more of glucose, sucrose, starch, phenolic resin, and dopamine.

5. The preparation method according to claim 1, wherein, In S2, the molar ratio of the phosphorus source to the lithium source is 1:3-1:

4.

6. The preparation method according to claim 1, wherein, In S2, the lithium source includes lithium hydroxide and / or lithium dihydrogen phosphate.

7. The preparation method according to claim 1, wherein, In S2, the particle size of the lithium source is less than 20 nm.

8. The preparation method according to claim 1, wherein, In S2, the phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphorus pentoxide.

9. The preparation method according to claim 1, wherein, In S2, the temperature of the evaporating solvent is 40-80℃; And / or, the heat treatment temperature is 500-1000℃, and the heat treatment time is 2-5 hours.

10. A lithium phosphate modified silicon-based anode material, which is obtained by the preparation method of the lithium phosphate modified silicon-based anode material according to any one of claims 1-9.

11. The lithium phosphate modified silicon-based anode material according to claim 10, wherein, The silicon nanoparticles have a particle size of 50-500 nm; The thickness of the carbon layer is 4-5 nm.

12. The lithium phosphate modified silicon-based anode material according to claim 10, wherein, The silicon nanoparticles have a particle size of 100-200 nm.

13. The lithium phosphate modified silicon-based anode material according to claim 10, wherein, The mass ratio of the lithium phosphate to the sum of the masses of the carbon and silicon nanoparticles is 1:5 to 1:

15.

14. A lithium-ion battery anode electrode, which is made of the lithium phosphate modified silicon-based anode material as described in any one of claims 10-13.

15. A lithium-ion battery comprising the lithium-ion battery anode electrode of claim 14.

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