Electrode material with core-shell gradient structure and preparation method and application thereof

Abstract

The application provides an electrode material with a core-shell gradient structure and a preparation method and application thereof, and relates to the technical field of electrode materials. The preparation method of the electrode material with the core-shell gradient structure comprises the following steps: step 1, mixing a silicon-based material inner core with a molten metal under the protection of an inert gas at a temperature at which the metal reaches a molten state, and stirring to coat the silicon-based material inner core with a metal element, so that an intermediate product is obtained; and step 2, continuing to introduce an oxidizing gas into the intermediate product obtained in step 1 under the protection of the inert gas to perform oxidation treatment, so that the electrode material is obtained. The preparation method of the electrode material with the core-shell gradient structure provided by the application can realize the continuous gradient transition of metal elements from inside to outside, can effectively reduce interface stress and avoid the peeling of the coated shell layer, can realize the function cooperation of electronic transmission and interface stability, and can greatly improve the long cycle stability and high-rate charge-discharge performance of a battery.

Description

Technical Field

[0001] This invention relates to the field of electrode materials technology, specifically to an electrode material with a core-shell gradient structure, its preparation method, and its application. Background Technology

[0002] All-solid-state batteries are a core technology in the next generation of energy storage, with silicon anodes boasting a theoretical specific capacity of up to 4200 mAh•g. -1 Sulfide electrolytes have become a key material for improving the energy density of all-solid-state sulfide batteries, but their application has two major pain points: the volume expansion during charging and discharging can reach 300%, which can easily lead to electrode pulverization and conductive network breakage; and the poor interfacial compatibility with sulfide electrolytes can easily form a high-resistivity interfacial layer and cause side reactions, which can seriously reduce the cycle stability and rate performance of the battery. Summary of the Invention

[0003] Based on the above analysis, the present invention aims to provide an electrode material with a core-shell gradient structure, its preparation method and application, in order to solve at least one of the following problems: suppressing interfacial side reactions, reducing interfacial impedance, and achieving efficient compatibility with sulfide solid electrolytes.

[0004] The objective of this invention is mainly achieved through the following technical solutions: In a first aspect, the present invention provides a method for preparing an electrode material with a core-shell gradient structure, comprising: Step 1: under inert gas protection, at a temperature that allows the metal to reach a molten state, mixing a silicon-based material core with a molten metal, stirring, and coating the surface of the silicon-based material core with a metal element to obtain an intermediate product; Step 2: continuing under inert gas protection, introducing an oxidizing gas to oxidize the intermediate product obtained in Step 1 to obtain the electrode material; wherein, in Step 1, the metal is selected from at least one of gallium, indium, and tin; wherein, in Step 1, the mass ratio of the silicon-based material core to the metal is 100:(1~10); wherein, in Step 2, the oxidizing gas is ozone, and the volume percentage of ozone is 0.5%~2% based on the total volume of the inert gas and the oxidizing gas, the oxidation treatment duration is 4~6 min, and the oxidation treatment temperature is maintained at the temperature that allows the metal to reach a molten state in Step 1.

[0005] Preferably, in step 1, the silicon-based material core includes at least one of silicon powder, porous silicon, silicon-carbon composite material, and silicon oxide.

[0006] Preferably, the average particle size of the silicon-based material core is 50 nm to 5 μm.

[0007] Preferably, in step 1, the difference between the temperature at which the metal reaches a molten state and the melting point of the metal is 10~40℃.

[0008] Preferably, in step 1, the stirring speed is 400~600 r / min and the stirring time is 0.5~2h.

[0009] Preferably, the inert gas is argon.

[0010] In a second aspect, the present invention provides an electrode material having a core-shell gradient structure prepared by the preparation method provided in the first aspect of the present invention.

[0011] Preferably, the electrode material comprises a silicon-based material core, a metal element intermediate layer covering the surface of the silicon-based material core, and a metal oxide outer layer covering the surface of the metal element intermediate layer.

[0012] Thirdly, the present invention provides an application of the electrode material described in the second aspect of the present invention in an all-solid-state sulfide battery.

[0013] Fourthly, the present invention provides an all-solid-state sulfide battery, comprising a negative electrode material formed from the electrode material provided in the second aspect of the present invention.

[0014] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: A) The method for preparing electrode materials with a core-shell gradient structure provided by this invention achieves a dual improvement in electrode structure and conductivity: the inner metal layer, such as a gallium layer, constructs a stable electron transport pathway, and its plasticity effectively buffers the volume expansion of silicon-based materials and enables self-repair of cracks, adapting to the high-pressure compaction process requirements of all-solid-state sulfide battery systems and ensuring continuous good contact between the electrode and the electrolyte. Interface compatibility and impedance characteristics are significantly optimized: the outer metal oxide layer, such as a gallium oxide layer, effectively isolates metals such as gallium from the sulfide electrolyte, fundamentally suppressing the occurrence of interfacial side reactions, significantly reducing interfacial impedance, and highly matching the high ionic conductivity characteristics of the sulfide electrolyte. B) The electrode material with a core-shell gradient structure provided by the present invention achieves functional synergy and performance enhancement through the gradient structure: the continuous gradient transition structure of metal elements such as gallium from the inside to the outside can effectively reduce interface stress, prevent the shell from falling off, achieve functional synergy of electron transport and interface stability, and greatly improve the long cycle stability and high rate charge and discharge performance of the battery. Attached Figure Description

[0015] Figure 1 The charge-discharge cycle test diagrams of the all-solid-state batteries of Examples 1-2 and Comparative Examples 1-3 provided by the present invention at a rate of 0.5 C. Detailed Implementation

[0016] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0017] Existing gallium-based silicon-coated anode technologies are unsuitable for LPSCl sulfide electrolyte systems: while pure gallium coating can mitigate silicon volume expansion and optimize electrode conductivity due to gallium's plasticity and conductivity, gallium's high surface activity leads to the formation of high-resistivity impurities such as Ga-S and Ga-Cl upon reaction with LPSCl, resulting in a significant increase in interfacial impedance; pure gallium oxide coating can improve interfacial stability and suppress interfacial side reactions, but its poor conductivity fails to address electron transport obstruction, making it difficult to meet the performance requirements of LPSCl systems. Currently, these technologies are mostly designed for liquid lithium batteries or other solid-state electrolyte systems, and there is no gallium-based coating structure suitable for LPSCl systems that can simultaneously achieve both interfacial stability and high conductivity.

[0018] To address the shortcomings of existing gallium-based coated silicon anodes in compatibility with LPSCl-based all-solid-state batteries, as well as issues such as insufficient silicon volume expansion buffering, high interfacial impedance with LPSCl electrolyte, and frequent interfacial side reactions, and to resolve the drawbacks of single coatings of pure gallium and pure gallium oxide, including interface performance degradation and electron transport obstruction, this invention innovatively designs a gradient structure metal element / metal oxide (e.g., gallium / gallium oxide) composite coated silicon anode material. This constructs a three-layer core-shell structure of "silicon core - metal intermediate layer - metal oxide outer layer," achieving a continuous gradient transition of the metal element from the metallic state to the oxide state from the inside out. The inner metal layer provides both high conductivity and volume expansion buffering, while the outer metal oxide layer effectively isolates the metal from the sulfide electrolyte and suppresses interfacial side reactions. The gradient structure further reduces interfacial impedance, achieving highly efficient compatibility with sulfide solid-state electrolytes.

[0019] The present invention will now be described in detail.

[0020] In a first aspect, the present invention provides a method for preparing an electrode material having a core-shell gradient structure, comprising: Step 1: Under the protection of an inert gas and at a temperature that allows the metal to reach a molten state, the silicon-based material core is mixed with the molten metal and stirred. The metal element is then coated on the surface of the silicon-based material core to form an intermediate product. Step 2: Continue to oxidize the intermediate product obtained in Step 1 by introducing an oxidizing gas under inert gas protection to obtain the electrode material.

[0021] The preparation method provided by this invention includes step 1, forming a core-shell structure in which a silicon-based material core is coated with a metal element, and step 2, preparing a gradient structure composite anode material of "metal → metal / metal oxide mixture → metal oxide (e.g., metal Ga → Ga / Ga2O3 mixture → Ga2O3)" through in-situ controlled oxidation. This allows the electrode material to form a good interfacial contact with the sulfide solid electrolyte (e.g., LPSCl solid electrolyte) without significant phase separation.

[0022] In a specific embodiment of the present invention, in step 1, the silicon-based material core includes silicon powder, porous silicon, silicon-carbon composite material, and silicon oxide (e.g., SiO2). x One or more of the following, the particle size of the silicon-based material core is 50 nm to 5 μm.

[0023] In a specific embodiment of the present invention, in step 1, the metal is selected from at least one of gallium, indium, and tin.

[0024] In a specific embodiment of the present invention, step 1 further includes a step of pretreatment of silicon-based materials, including drying and protection under an inert atmosphere for later use.

[0025] In a specific embodiment of the present invention, in step 1, the mass ratio of the silicon-based material core to the metal is 100:(1~10), for example, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, or a range thereof, preferably 100:(4~6).

[0026] In a specific embodiment of the present invention, in step 1, the temperature at which the metal reaches a molten state is 10 to 40°C higher than the metal's melting point. For example, gallium (melting point approximately 29.8°C) needs to be heated to 60°C.

[0027] In a specific embodiment of the present invention, in step 1, the stirring speed is 400-600 r / min and the stirring time is 0.5-2h.

[0028] In a specific embodiment of the present invention, in step 1, the inert gas is argon.

[0029] In a specific embodiment of the present invention, in step 2, the oxidizing gas is ozone, and the volume percentage of ozone is 0.5% to 2% based on the total volume of the oxidizing gas and the inert gas.

[0030] In a specific embodiment of the present invention, in step 2, the oxidation treatment duration is 4-6 min, for example, 4, 4.2, 4.5, 4.8, 5, 5.3, 5.5, 5.8, 6 min or a range thereof, and the oxidation treatment temperature is maintained at the temperature in step 1 that brought the metal to a molten state.

[0031] Secondly, the present invention provides an electrode material with a core-shell gradient structure, comprising a silicon-based core, a metal elemental intermediate layer covering the surface of the core, and a metal oxide outer layer covering the surface of the intermediate layer.

[0032] The electrode material with a core-shell gradient structure provided by this invention has a three-layer structure without obvious interface breaks. The metal elements continuously transition from a pure metal state to an oxidized state from the inside to the outside, forming a gradient composite shell of "metal → metal / metal oxide mixture → metal oxide (e.g., metal Ga → Ga / Ga2O3 mixture → Ga2O3)". The gradient shell tightly covers the silicon-based core and can form good interfacial contact with the sulfide solid electrolyte without obvious phase separation.

[0033] It should be noted that the electrode material provided by this invention preferably uses the same type of metal in both elemental metals and metal oxides; if the type of metal is changed, the interface is prone to significant cracking and the material performance will deteriorate.

[0034] Thirdly, the present invention provides an application of the above-mentioned electrode material in an all-solid-state sulfide battery.

[0035] Fourthly, the present invention provides a negative electrode material in an all-solid-state sulfide battery, comprising the electrode material described above.

[0036] The following detailed description of preferred embodiments of the present invention illustrates the principles of the invention and is not intended to limit the scope of the invention.

[0037] Unless otherwise specified, all reagents used in the following examples are commercially available.

[0038] Example 1 This embodiment describes the performance testing of a gradient structure gallium / gallium oxide composite coated micron-sized silicon anode material adapted to LPSCl electrolyte and its battery.

[0039] (1) Preparation of negative electrode material Step 1: Pretreatment of silicon-based materials: Take micron-sized silicon powder with a particle size of 5μm, place it in a vacuum drying oven at 100℃ and vacuum dry for 3 h to completely remove surface adsorbed water and hydroxyl groups; after drying, quickly transfer it to an argon-protected glove box with a water and oxygen content of ≤1 ppm and seal it for later use. Preparation of Si@Ga core-shell structure by melt coating: The pretreated micron-sized silicon powder was added to a reactor under argon protection throughout the process, and 99.99% pure gallium powder was added at a mass ratio of Si:Ga=100:5; the reactor was heated to 60℃ and stirred at a constant temperature for 1 h at a stirring speed of 500 r / min to make the molten gallium uniformly and densely coat the surface of the micron-sized silicon powder; the argon protection atmosphere was maintained and the reactor temperature was maintained at 60℃ to obtain the Si@Ga core-shell structure material, which was then directly introduced into the subsequent oxidation step.

[0040] Step 2: In-situ controlled oxidation preparation of gradient structure Si@Ga@Ga2O3 composite anode material: Maintain the temperature inside the reactor at 60 ℃ and an argon protective atmosphere, slowly introduce 1% ozone by volume into the reactor as an oxidizing gas, and perform in-situ oxidation treatment for 5 min; form an outer layer of Ga2O3. After the oxidation is completed, continue to introduce argon gas to cool the reactor to room temperature, and obtain the gradient structure gallium / gallium oxide composite coated silicon anode material (Si@Ga@Ga2O3), which is then transferred to a glove box for sealed storage.

[0041] (2) Preparation of all-solid-state sulfide batteries: Electrode preparation: The above-mentioned Si@Ga@Ga2O3 composite anode material, pure LPSCl solid electrolyte, and conductive agent VGCF were mixed at a mass ratio of 85:12:3. 1.5 wt% (based on 100% of the total mass of the composite anode material, electrolyte, and conductive agent) of polyvinylidene fluoride binder was added, and the mixture was thoroughly ground until homogeneous in an argon glove box. The mixed powder was placed in a mold and pressed into electrode sheets, with the compaction density controlled at 1.2-1.8 g•cm³. -3 ,spare.

[0042] All-solid-state battery assembly: Using the prepared Si@Ga@Ga2O3 electrode sheet as the working electrode, Li-In alloy as the counter electrode, and pure LPSCl solid electrolyte as the electrolyte layer, the all-solid-state sulfide electrolyte mold battery was assembled in an argon glove box with a water oxygen content ≤1 ppm.

[0043] Electrochemical performance testing: Electrochemical performance testing was performed on the assembled battery. The charge / discharge voltage range was set (adjusted according to the all-solid-state battery system, e.g., -0.59 to 0.9 V), and charge / discharge cycle testing was conducted at a 0.5C rate. The results are shown in Table 1. Interfacial impedance was measured using an electrochemical workstation with electrochemical impedance spectroscopy (EIS) at a frequency range of 10 Hz. 5 Hz~10 -2 The test frequency was Hz, the AC disturbance voltage was 5mV; the test environment temperature was 25℃, the Nyquist plot was recorded, and the interface impedance (Ω) was calculated by fitting the equivalent circuit. The formula for calculating the coulombic efficiency is: Coulombic efficiency = (charge capacity / discharge capacity) × 100%.

[0044] The "Coulomb efficiency = (charge capacity / discharge capacity) × 100%" in this invention refers to the testing system for half-cells with negative electrode materials.

[0045] In the negative electrode half-cell testing system, the first cycle involves a discharge process (i.e., lithium ions intercalating into the negative electrode material, corresponding to the instrument's "discharge"), followed by a charging process (i.e., lithium ions being extracted from the negative electrode material, corresponding to the instrument's "charging"). Because some lithium ions are consumed during the first discharge (lithium intercalation) process due to SEI film formation or irreversible side reactions, the first discharge capacity is greater than the first charge capacity. Therefore, if (discharge capacity / charge capacity) × 100%, the efficiency value will be greater than 100%.

[0046] In order to be consistent with the conventional characterization practice in the field of “coulombic efficiency ≤ 100%”, the coulombic efficiency calculation formula in this invention is: Coulombic efficiency = (charge capacity / discharge capacity) × 100%; where “charge capacity” corresponds to the delithiation capacity of the negative electrode material and “discharge capacity” corresponds to the lithium insertion capacity of the negative electrode material, i.e. (delithiation capacity / lithium insertion capacity) × 100%.

[0047] Example 2 This embodiment describes the performance testing of a gradient structure gallium / gallium oxide composite coated micron-sized silicon anode material adapted to an LPSCl-I doped modified sulfide electrolyte and the battery.

[0048] (1) Preparation of negative electrode material: Same as in Example 1.

[0049] (2) Preparation of all-solid-state sulfide batteries: Electrode preparation: The above-mentioned Si@Ga@Ga2O3 composite anode material, LPSCl-I doped modified sulfide electrolyte, and conductive agent VGCF were mixed at a mass ratio of 85:12:3. 1.5 wt% (based on 100% of the total mass of the composite anode material, electrolyte, and conductive agent) of polyvinylidene fluoride binder was added, and the mixture was thoroughly ground until homogeneous in an argon glove box. The mixed powder was placed in a mold and pressed into electrode sheets, with the compaction density controlled at 1.2-1.8 g•cm³. - ³, for future use.

[0050] All-solid-state battery assembly: Using the prepared Si@Ga@Ga2O3 electrode sheet as the working electrode, Li-In alloy as the counter electrode, and LPSCl-I doped modified sulfide electrolyte as the electrolyte layer, the all-solid-state sulfide electrolyte mold battery was assembled in an argon glove box with a water and oxygen content ≤1 ppm.

[0051] Electrochemical performance testing: Same as in Example 1, the results are shown in Table 1.

[0052] Example 3 This embodiment describes the performance testing of a gradient structure indium / indium oxide composite coated micron-sized silicon anode material adapted to LPSCl electrolyte and its battery.

[0053] (1) Preparation of negative electrode material Step 1: Pretreatment of silicon-based materials: Same as in Example 1; The pretreated micron-sized silicon powder was added to a reactor under argon protection throughout the process. Indium powder with a purity of 99.99% was added at a mass ratio of Si:In = 100:5. The reactor was heated to 170°C (the melting point of indium is about 156.6°C, which is about 13.4°C higher than the melting point, and is comparable to the superheat of gallium in Example 1). The mixture was stirred at a constant temperature for 1 hour at a stirring speed of 500 r / min to make the molten indium uniformly and densely coat the surface of the micron-sized silicon powder. The reactor temperature was maintained at 170°C under the argon protection atmosphere to obtain the Si@In core-shell structure material.

[0054] Step 2: In-situ controlled oxidation preparation of gradient structure Si@In@In2O3 composite anode material: Maintain the temperature inside the reactor at 170℃ and an argon protective atmosphere, slowly introduce 1% ozone (by volume) into the reactor as an oxidizing gas, and perform in-situ oxidation treatment for 5 minutes; form an In2O3 outer layer. After oxidation, continue to introduce argon gas to cool the reactor to room temperature, and obtain gradient structure indium / indium oxide composite coated silicon anode material (Si@In@In2O3), which is then transferred to a glove box for sealed storage.

[0055] (2) Preparation of all-solid-state sulfide batteries: Electrode preparation: The above-mentioned Si@In@In2O3 composite anode material, pure LPSCl solid electrolyte, and conductive agent VGCF were mixed at a mass ratio of 85:12:3. 1.5 wt% (based on 100% of the total mass of the composite anode material, electrolyte, and conductive agent) of polyvinylidene fluoride binder was added, and the mixture was thoroughly ground until homogeneous in an argon glove box. The mixed powder was placed in a mold and pressed into electrode sheets, with the compaction density controlled at 1.2-1.8 g•cm³. -3 ,spare.

[0056] All-solid-state battery assembly: Using the prepared Si@In@In2O3 electrode sheet as the working electrode, Li-In alloy as the counter electrode, and pure LPSCl solid electrolyte as the electrolyte layer, the all-solid-state sulfide electrolyte mold battery was assembled in an argon glove box with a water oxygen content ≤1 ppm.

[0057] Electrochemical performance testing: Same as in Example 1, the results are shown in Table 1.

[0058] Example 4 This embodiment is basically the same as Embodiment 1, except that in the preparation of the negative electrode material, the oxidation time in the in-situ oxidation step corresponding to step 2 is shortened from 5 min to 2 min, while the other process parameters remain unchanged.

[0059] Electrochemical performance testing: Same as in Example 1, the results are shown in Table 1.

[0060] Example 5 This embodiment is basically the same as Embodiment 1, except that in the preparation of the negative electrode material, the oxidation time in the in-situ oxidation step corresponding to step 2 is increased from 5 min to 12 min, while the other process parameters remain unchanged.

[0061] Electrochemical performance testing: Same as in Example 1, the results are shown in Table 1.

[0062] Example 6 This embodiment is basically the same as Embodiment 1, except that in the preparation of the negative electrode material, in step 1, the mass ratio of Si:Ga is 100:10, and in step 2, the oxidation treatment conditions are the same as in Embodiment 1.

[0063] Comparative Example 1 This comparative example is a performance test of a sulfide-based all-solid-state battery with a pure micron-sized silicon anode.

[0064] (1) Pretreatment of silicon-based materials: Take micron silicon powder with a particle size of 5μm, dry it in a vacuum drying oven at 100℃ for 3h, and then transfer it to an argon glove box with a water and oxygen content of ≤1ppm for later use.

[0065] (2) Electrode sheet preparation: Pure micron-sized silicon powder, pure LPSCl solid electrolyte, and conductive agent VGCF are mixed at a mass ratio of 85:12:3. 1.5 wt% (based on 100% of the total mass of the composite negative electrode material, electrolyte, and conductive agent) of polyvinylidene fluoride binder is added, and the mixture is ground uniformly in an argon glove box. The mixture is then pressed into electrode sheets, with the compaction density controlled at 1.2-1.8 g•cm³. -3 .

[0066] (3) Assembly of all-solid-state battery: In an argon glove box, a pure silicon electrode sheet is used as the working electrode, a Li-In alloy is used as the counter electrode, and a pure LPSCl solid electrolyte is used as the electrolyte layer to assemble an all-solid-state sulfide electrolyte mold battery.

[0067] (4) Electrochemical performance test: Same as in Example 1, the results are shown in Table 1.

[0068] Comparative Example 2 This comparative example is the performance test of a sulfide-based all-solid-state battery with a pure gallium-coated micron-sized silicon anode (Si@Ga).

[0069] (1) Pretreatment of silicon-based materials: Same as in Example 1.

[0070] (2) Preparation of Si@Ga material by pure metal gallium coating: Si@Ga core-shell structure was prepared according to the process in Example 1. The in-situ controllable oxidation step was omitted. The Si@Ga core-shell structure was directly cooled to room temperature to form a pure metal Ga coating layer and stored in an argon glove box.

[0071] (3) Electrode preparation: The raw material ratio and binder selection for the electrode were the same as in Example 1, and the compaction density was controlled to be 1.2-1.8 g•cm. -3 Si@Ga electrode sheets were prepared in an argon glove box.

[0072] (4) Assembly of all-solid-state battery: The assembly process and selection of electrodes / electrolytes / counter electrodes are the same as in Example 1. Assemble an all-solid-state sulfide electrolyte mold battery.

[0073] (5) Electrochemical performance test: Same as in Example 1, the results are shown in Table 1.

[0074] Comparative Example 3 This comparative example is a performance test of a sulfide-based all-solid-state battery with a pure gallium oxide-coated micron-sized silicon anode (Si@Ga2O3).

[0075] (1) Pretreatment of silicon-based materials: Same as in Example 1.

[0076] (2) Preparation of Si@Ga2O3 material by pure gallium oxide coating: The step of metallic gallium molten coating is omitted. Atomic layer deposition (ALD) is used to deposit a Ga2O3 layer on the surface of pretreated micron-sized silicon powder. The mass ratio of Si:Ga2O3 is controlled to be 100:1 to obtain pure Ga2O3 coated Si@Ga2O3 material, which is then sealed and stored in an argon glove box.

[0077] (3) Electrode preparation: The raw material ratio and binder selection for the electrode were the same as in Example 1, and the compaction density was controlled to be 1.2-1.8 g•cm. -3 Si@Ga2O3 electrode sheets were prepared in an argon glove box.

[0078] (4) Assembly of all-solid-state battery: The assembly process and selection of electrodes / electrolytes / counter electrodes are the same as in Example 1. Assemble an all-solid-state sulfide electrolyte mold battery.

[0079] (5) Electrochemical performance test: Same as in Example 1, the results are shown in Table 1.

[0080] Table 1 Electrochemical performance tests of examples and comparative examples

[0081] In Table 1, Examples 1 to 6 employ a gradient structure metal / metal oxide composite coating. The inner metal layer ensures efficient electron transport, while the outer metal oxide layer suppresses interfacial side reactions between silicon and metal and sulfide electrolyte, reducing irreversible loss of active lithium. Therefore, the initial discharge capacity and coulombic efficiency are generally better than those of the comparative examples.

[0082] Example 1 is adapted to pure LPSCl electrolyte, with the best interface matching and optimal capacity and efficiency; in Example 1, in step 1 of the preparation of the negative electrode material, it is speculated that a metal Ga inner layer with a thickness of 15~20nm can be formed on the surface of silicon powder, and after the in-situ oxidation treatment in step 2, it is speculated that a Ga2O3 outer layer with a thickness of 2~3nm will be formed.

[0083] In Example 3, the metal was replaced with indium, which has slightly inferior plasticity and conductivity compared to gallium, and its ability to suppress side reactions at the interface is slightly weaker. Therefore, the initial capacity was slightly lower than that of Example 1.

[0084] Example 6 increases the amount of gallium metal and adjusts the Si:Ga mass ratio to 100:10. It is estimated that the thickness of the inner layer of gallium metal increases to 25~30 nm, which improves the volume buffering capacity and optimizes the conductive network. However, the excess gallium metal increases the number of side reaction sites. The overall performance is slightly lower than that of Example 3 but better than that of Example 4.

[0085] In Example 4, due to the shortened oxidation treatment time, it is speculated that the outer layer thickness of Ga2O3 was reduced to 1 nm, resulting in insufficient interfacial isolation and inability to effectively suppress side reactions. Consequently, the coulombic efficiency and cycle stability were lower than those in Examples 1, 3, and 6.

[0086] Example 2 uses an LPSCl-I doped electrolyte (iodine-doped lithium phosphorus sulfur chloride electrolyte), which has slightly higher interfacial ion diffusion loss and slightly lower capacity and efficiency than the pure LPSCl electrolyte system.

[0087] In Example 5, due to the increased oxidation treatment time, it is speculated that the outer layer of Ga2O3 thickened to 5-6 nm. The excessively thick insulating oxide layer significantly hindered the conduction of electrons and lithium ions, resulting in a significant decline in capacity and coulombic efficiency, and performance was weaker than all gradient coating examples.

[0088] Comparative Example 2, due to the lack of an insulating layer in the pure Ga coating, underwent side reactions with the electrolyte, resulting in the second-highest capacity and efficiency. Comparative Example 1, being pure micron-sized silicon, experienced severe side reactions and volume expansion, leading to a significant consumption of active lithium and further degrading performance. Comparative Example 3 is presumably formed with a gallium oxide layer of approximately 3 nm. However, due to the insulating properties of pure Ga2O3 hindering electron transport, the active sites could not be fully activated, resulting in the lowest initial capacity and coulombic efficiency.

[0089] Figure 1The retention rate after 100 cycles showed a significant negative correlation with the interfacial impedance. The retention rate ranking was: Example 1 (98.6%) > Example 2 (95%) > Comparative Example 3 (60.92%) > Comparative Example 2 (32%) > Comparative Example 1 (10%). The impedance ranking was exactly the opposite, with Example 1 having the lowest interfacial impedance after 100 cycles. The gradient coating structure of Examples 1 and 2 achieved optimal cycle stability by using the inner Ga layer to buffer silicon volume expansion and prevent electrode pulverization, and the outer Ga2O3 layer to isolate side reactions and stabilize the interfacial impedance (82~85 Ω). Example 2 had slightly higher impedance due to slightly more ion diffusion at the electrolyte interface, resulting in a slightly lower retention rate than Example 1. Although Comparative Example 3 suppressed side reactions, the insulating properties of Ga2O3 hindered electron transport, resulting in a moderate retention rate and relatively high impedance. Comparative Example 2 experienced a rapid increase in impedance and accelerated capacity decay due to continuous side reactions between Ga and the electrolyte. Comparative Example 1 suffered from dual failure due to volume expansion and side reactions, causing the interfacial impedance to soar to 228 Ω, and almost complete capacity loss after cycling. In summary, the gradient composite coating structure can simultaneously improve initial capacity, coulombic efficiency, and cycle stability, significantly outperforming single-coated and uncoated pure silicon systems.

[0090] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing an electrode material with a core-shell gradient structure, characterized in that, include: Step 1: Under inert gas protection and at a temperature that allows the metal to reach a molten state, the silicon-based material core is mixed with the molten metal and stirred. The metal element is then coated onto the surface of the silicon-based material core to obtain an intermediate product. Step 2: Continue to oxidize the intermediate product obtained in Step 1 by introducing an oxidizing gas under inert gas protection to obtain the electrode material; In step 1, the metal is selected from at least one of gallium, indium, and tin; In step 1, the mass ratio of the silicon-based material core to the metal is 100:(1~10). In step 2, the oxidizing gas is ozone, and the ozone volume percentage is 0.5% to 2% based on the total volume of inert gas and oxidizing gas. The oxidation treatment duration is 4 to 6 minutes, and the oxidation treatment temperature is maintained at the temperature in step 1 that brought the metal to a molten state.

2. The preparation method according to claim 1, characterized in that, In step 1, the silicon-based material core includes at least one of silicon powder, porous silicon, silicon-carbon composite material, and silicon oxide.

3. The preparation method according to claim 1, characterized in that, The average particle size of the silicon-based material core is 50 nm to 5 μm.

4. The preparation method according to claim 1, characterized in that, In step 1, the difference between the temperature at which the metal reaches a molten state and the melting point of the metal is 10~40℃.

5. The preparation method according to claim 1, characterized in that, In step 1, the stirring speed is 400~600 r / min and the stirring time is 0.5~2h.

6. The preparation method according to claim 1, characterized in that, The inert gas is argon.

7. An electrode material with a core-shell gradient structure prepared by the preparation method according to any one of claims 1-6.

8. The electrode material according to claim 7, characterized in that, The electrode material includes a silicon-based core, a metal element intermediate layer covering the surface of the silicon-based core, and a metal oxide outer layer covering the surface of the metal element intermediate layer.

9. The application of an electrode material according to claim 7 or 8 in an all-solid-state sulfide battery.

10. An all-solid-state sulfide battery, characterized in that, This includes a negative electrode material formed from the electrode material according to claim 7 or 8.

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