One-step preparation method of silicon-based composite materials and their application in all-solid-state batteries

Abstract

The present invention belongs to the technical field of all-solid-state battery electrode materials based on silicon-containing compounds, and discloses a one-step method for preparing a silicon-based composite material and its application in an all-solid-state battery. The method comprises uniformly mixing a lithium source, a silicon source, and a sulfur source under a vacuum or inert protective atmosphere, and then subjecting the mixture to high-energy vibration ball milling to obtain the silicon-based composite material. The present invention realizes the in-situ composite construction of silicon material and amorphous sulfide fast ion conductor material through a one-step mechanical alloying process. This one-step in-situ preparation method can improve the ionic conductivity of the silicon-based composite material and improve the interface contact between the silicon-based negative electrode and the solid electrolyte, thereby improving the first-cycle coulombic efficiency and cycle stability of the silicon-based all-solid-state battery. The prepared all-solid-state battery also has excellent performance at high temperatures.

Description

Technical Field

[0001] The present invention belongs to the technical field of all-solid-state battery electrode materials based on silicon-containing compounds, and in particular relates to a one-step method for preparing silicon-based composite materials and their application in all-solid-state batteries. Background Art

[0002] With the growing demand for higher energy density and improved safety in lithium-ion batteries, the development of all-solid-state batteries has become an important direction for the development of next-generation batteries. All-solid-state batteries, composed solely of solid components (positive electrode, solid electrolyte, negative electrode), can address the poor safety and low capacity issues associated with traditional flammable liquid electrolytes. Among the numerous solid-state electrolytes, sulfide electrolytes have become a focus of current research due to their ultra-high ionic conductivity and excellent mechanical properties. At the same time, the choice of anode material for sulfide-based all-solid-state batteries also plays a key role in improving the energy density and safety of the entire battery. Silicon anode materials have become one of the most promising anode materials for the commercialization of all-solid-state batteries due to their high theoretical specific capacity, low lithium insertion potential, and low cost.

[0003] As a typical semiconductor material, silicon anodes suffer from insufficient intrinsic electronic conductivity and ion mobility, which directly restricts their practical application in all-solid-state battery systems. Conventional strategies typically utilize ex situ mechanical mixing to composite silicon anode materials with sulfide solid electrolytes, conductive additives, and binders to establish ion / electron transport pathways. However, this ex situ composite approach has multiple limitations. First, a high proportion of solid electrolyte (>30 wt%) must be incorporated to achieve effective charge transfer, significantly reducing the active material content in the composite electrode, severely impacting the energy density and economics of the battery system. Second, the heterogeneous interface formed by physical mixing exhibits numerous contact defects, increasing interfacial impedance and causing persistent deterioration in charge transfer kinetics during battery cycling. More critically, the dramatic volume expansion (>300%) of silicon during electrochemical cycling can trigger mechanical failure of the composite structure. Conventional approaches rely on increasing the amount of binder to mitigate this volume effect, but this approach not only fails to effectively prevent silicon particle fragmentation and pulverization, but also reduces energy density due to the reduced effective proportion of electrode active material. Therefore, there is an urgent need to develop a simple and effective method for preparing silicon-based composite negative electrodes for all-solid-state batteries. Summary of the Invention

[0004] Based on the problems existing in the above-mentioned prior art, the present invention provides a one-step method for preparing silicon-based composite materials and their application in all-solid-state batteries, aiming to realize the in-situ composite construction of silicon materials and amorphous sulfide fast ion conductor materials through a one-step mechanical alloying process, thereby improving the ionic conductivity of silicon-based materials, so that when used in all-solid-state batteries, they can improve the interface contact between the negative electrode and the solid electrolyte, limit the volume expansion of the silicon negative electrode, and thus improve the energy density and cycle stability of the all-solid-state battery.

[0005] To achieve the purpose, the present invention adopts the following technical solutions:

[0006] In its first aspect, the present invention discloses a one-step method for preparing a silicon-based composite material. Specifically, under vacuum or an inert atmosphere, a lithium source, a silicon source, and a sulfur source are uniformly mixed in a molar ratio of Li, Si, and S of 2:1 to 100:3, followed by high-energy vibration ball milling to obtain the silicon-based composite material. The resulting silicon-based composite material is composed of silicon and an amorphous Li2SiS3 fast ion conductor. The proportion of silicon in the silicon-based composite material can be adjusted by adjusting the amount of silicon source added.

[0007] Preferably, the inert protective atmosphere is a mixture of one or more of nitrogen, argon and helium.

[0008] Preferably, the Li source includes but is not limited to one or more of Li2S powder, Li powder and lithium silicon alloy powder; the sulfur source includes but is not limited to one or more of sublimated sulfur powder, Li2S powder and SiS2 powder; the silicon source includes but is not limited to one or more of silicon powder with a particle size of micron or nanometer, silicon carbon powder, SiS2 powder and lithium silicon alloy powder.

[0009] Preferably, the high-energy vibration ball milling treatment time is 20-100 hours, and the ball milling speed is 400-1200 rpm.

[0010] Taking Li2S powder, sublimated sulfur powder and silicon powder as an example, the one-step in-situ preparation method of the present invention utilizes the alloying reaction between lithium sulfide and silicon powder and sulfur powder under the ultra-high energy provided by high-energy ball milling. The reaction equation can be expressed as follows:

[0011]

[0012] In a second aspect, the present invention further provides an anode for an all-solid-state lithium-ion battery, which utilizes the aforementioned silicon-based composite material as the active material. To further enhance the performance of the anode, the silicon-based composite material comprises 80% to 98% silicon by weight.

[0013] In a third aspect, the present invention also provides an all-solid-state lithium-ion battery comprising a sulfide solid electrolyte and a composite positive electrode, and also comprising the aforementioned negative electrode using the silicon-based composite material as the active material. This all-solid-state battery exhibits high first-cycle coulombic efficiency, cycling stability, and excellent high-temperature electrochemical performance.

[0014] Furthermore, sulfide solid electrolytes include but are not limited to Li2S-P2S5, Li7P3S 11 、Li6PS5Cl、Li 5.5 PS 4.5 Cl 1.5 、Li6PS5Br、Li6PS5I、Li 11 Si2PS 12 One or more of .

[0015] Furthermore, the composition of the composite positive electrode in the all-solid-state lithium-ion battery can be: positive electrode active material, solid electrolyte and conductive agent. The positive electrode active material includes but is not limited to one or more of lithium cobalt oxide, lithium iron phosphate, high nickel ternary material, lithium-rich manganese-based material. The solid electrolyte includes but is not limited to Li2S-P2S5, Li7P3S 11 、Li6PS5Cl、Li 5.5 PS 4.5 Cl 1.5 、Li6PS5Br、Li6PS5I、Li 11 Si2PS 12 The conductive agent includes, but is not limited to, one or more of carbon black, carbon nanotubes, carbon fibers, Ketjen black, and acetylene black.

[0016] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0017] 1. The present invention realizes the in-situ composite construction of silicon material and amorphous sulfide fast ion conductor material through a one-step mechanical alloying process. This one-step in-situ composite construction strategy realizes the uniform composite of silicon and amorphous sulfide fast ion conductor, which can significantly improve the ionic conductivity of silicon-based negative electrode materials. At the same time, the amorphous sulfide fast ion conductor has strong mechanical properties. The surface stress buffer layer formed by in-situ composite significantly suppresses the volume expansion effect of silicon particles during the cycle, and effectively alleviates the stress concentration phenomenon at the negative electrode / solid electrolyte interface. In addition, the amorphous sulfide fast ion conductor constructed by in-situ composite construction of the present invention is similar to the sulfide solid electrolyte in the all-solid-state battery in terms of chemical composition and physicochemical properties. This structural feature significantly improves the interfacial chemical compatibility between the negative electrode and the solid electrolyte, thereby effectively improving the contact state and interface stability of the negative electrode-solid electrolyte interface, and provides a unique advantage for constructing a stable solid-solid interface.

[0018] 2. When the silicon-based composite material of the present invention is assembled into an all-solid-state battery, it is not necessary to add any solid electrolyte powder and binder for conducting ions. The silicon-based composite material can be directly mixed with the conductive agent.

[0019] 3. The silicon-based composite material of the present invention can improve the first-cycle Coulomb efficiency and cycle stability of silicon-based all-solid-state batteries, and can also achieve good cycle performance at high temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. By reading the detailed description of the embodiments with reference to the following drawings, other features, purposes and advantages of the present invention will become more apparent.

[0021] Figure 1 is a powder X-ray diffraction (XRD) pattern of the silicon-based composite material prepared in an embodiment of the present invention;

[0022] Figure 2 2 is an AC impedance diagram of the amorphous sulfide fast ion conductor (a-Li2SiS3) and crystalline c-Li2SiS3 powder prepared in the embodiment of the present invention;

[0023] Figure 3 1 is a cycle performance diagram of all-solid-state half-cells assembled with various silicon-based negative electrode materials in the embodiments of the present invention;

[0024] Figure 4 : is an AC impedance diagram of an all-solid-state half-cell assembled with various silicon-based negative electrode materials in an embodiment of the present invention;

[0025] Figure 5 This is the cycle performance of the all-solid-state battery assembled with the silicon-based composite material (Si@a-Li2SiS3-10%) prepared in the embodiment of the present invention at 55°C. DETAILED DESCRIPTION

[0026] The following is a further description of the all-solid-state battery silicon-based composite negative electrode material prepared by the one-step method of the present invention through specific examples and drawings. It should be understood that the specific examples described here are only used to help understand the present invention and are not used to specifically limit the present invention.

[0027] Example 1

[0028] This embodiment provides a method for preparing an amorphous Li2SiS3 fast ion conductor, and the specific steps are as follows:

[0029] In an argon-filled glove box, the raw materials were weighed at a molar ratio of Li2S:Si powder:S powder = 1:1:2, ground and mixed for 15 minutes, and then placed in a stainless steel ball mill. Zirconia balls were added at a ball-to-material mass ratio of 40:1 and ball milled at a ball mill speed of 1200 rpm for 40 hours to obtain an amorphous Li2SiS3 fast ion conductor (a-Li2SiS3).

[0030] Example 2

[0031] This embodiment provides a method for preparing a silicon-based composite material, and the specific steps are as follows:

[0032] In an argon-filled glove box, the raw materials were weighed according to the molar ratio of Li2S:Si powder:S powder = 1:45:2, ground and mixed for 15 minutes, and then placed in a stainless steel ball mill. Zirconia balls were added at a ball-to-material mass ratio of 40:1 for ball milling. The ball mill speed was 1200 rpm and the ball milling time was 40 hours to obtain a silicon-based composite material (Si@a-Li2SiS3-10%) with an amorphous Li2SiS3 fast ion conductor mass proportion of 10%.

[0033] Example 3

[0034] This embodiment provides a method for preparing a silicon-based composite material, and the specific steps are as follows:

[0035] In an argon-filled glove box, the raw materials were weighed according to the molar ratio of Li2S:Si powder:S powder = 1:21:2, ground and mixed for 15 minutes, and then placed in a stainless steel ball mill. Zirconia balls were added at a ball-to-material mass ratio of 40:1 for ball milling. The ball mill speed was 1200 rpm and the ball milling time was 40 hours to obtain a silicon-based composite material (Si@a-Li2SiS3-20%) in which the mass of the amorphous Li2SiS3 fast ion conductor accounted for 20%.

[0036] The samples obtained from the above embodiments were tested as follows:

[0037] 1. XRD test

[0038] The materials obtained in each example were tested using an X-ray powder diffractometer. The results are as follows: Figure 1 As shown in the figure, it can be seen that the a-Li2SiS3 fast ion conductor does not show obvious diffraction peak intensity in the X-ray diffraction pattern, indicating that the sulfide fast ion conductor exists in an amorphous state. The silicon-based composite materials (Si@a-Li2SiS3-10% and Si@a-Li2SiS3-20%) show diffraction peaks at 28°, 47°, and 56°, which correspond to the peak positions of Si PDF#27-1402 card, indicating that the main phase of the synthesized silicon-based composite materials is silicon, which also proves the reliability and efficiency of the synthesis process.

[0039] 2. Ionic conductivity test

[0040] The amorphous a-Li2SiS3 fast ion conductor powder obtained in Example 1 was pressed into tablets and its ionic conductivity was tested. The results are as follows: Figure 2 As shown, after calculation, its ionic conductivity at room temperature is 1.08×10 -4 S / cm.

[0041] For comparison, crystalline c-Li2SiS3 powder was prepared by the same method as that of a-Li2SiS3 in Example 1, except that the ball milling time was 8 h. Figure 1 The XRD results show that it is crystalline. The ionic conductivity is 1.05×10 -5 S / cm.

[0042] 3. Half-cell performance test

[0043] Assemble all-solid-state half-cells using amorphous a-Li2SiS3 fast ion conductor powder or silicon-based composite materials (Si@a-Li2SiS3-10% or Si@a-Li2SiS3-20%): Take 100 mg of commercial Li 5.5 PS 4.5 Cl 1.5 The electrolyte powder is pressed into a tablet. 9 mg of a-Li2SiS3 or a silicon-based composite material (Si@a-Li2SiS3-10% or Si@a-Li2SiS3-20%) is mixed evenly with 1 mg of conductive carbon black. The mixture is then spread on one side of the electrolyte tablet and pressed for 3 minutes. A lithium-indium alloy is then applied to the other side of the tablet. The pressure is then maintained for 5 minutes. This completes the assembly into a half-cell, which is then ready for testing.

[0044] For comparison, silicon powder was used to make the working electrode and the half-cell was assembled: 100 mg of commercial Li 5.5 PS 4.5 Cl 1.5 The electrolyte powder is pressed into tablets. Take 7mg of silicon powder, 1mg of conductive carbon black and 2mg of Li 5.5 PS 4.5 Cl 1.5 Electrolyte powder (corresponding battery is marked as Si-Li 5.5 PS 4.5 Cl 1.5 ) or 2 mg of amorphous a-Li2SiS3 powder (the corresponding battery is denoted as Si-a-Li2SiS3) are mixed evenly, spread on one side of the electrolyte sheet and pressed for 3 minutes, and lithium-indium alloy is spread on the other side of the electrolyte sheet. Then the pressure is maintained for 5 minutes and assembled into a half-cell for testing.

[0045] The test voltage is -0.61~1.38V, and the first three cycles are at 0.3A g -1 The current density was tested at 0.6A g -1 The test results are as follows: Figure 3 As shown in Figure 2 , battery cycling tests show that the in situ-prepared silicon-based composite materials in the examples exhibit higher first-cycle Coulombic efficiency and discharge capacity than pure silicon or ex situ-prepared composite materials (Table 1). Furthermore, using amorphous a-Li2SiS3 powder directly as the negative electrode material yielded a discharge capacity of only 38 mA h / g, demonstrating that amorphous a-Li2SiS3 powder is unsuitable for direct negative electrode use.

[0046] Table 1 First-cycle Coulombic efficiency and discharge specific capacity of all-solid-state half-cells assembled with various silicon-based anode materials

[0047]

[0048] 4. Electrochemical AC impedance test

[0049] According to the above method, Si@a-Li2SiS3-10%, Si@a-Li2SiS3-20% and silicon powder were assembled into all-solid-state half-cells, and electrochemical AC impedance tests were performed to compare the impedances. The results are as follows: Figure 4 As shown in the figure, it can be seen that the impedance of the silicon powder electrode is 70Ω, while the impedance of the Si@a-Li2SiS3-10% electrode and the Si@a-Li2SiS3-20% electrode are 18Ω and 35Ω respectively, which are 1 / 4 and 1 / 2 of the silicon powder electrode impedance respectively.

[0050] 5. Full battery performance test

[0051] The negative electrode active material is the silicon-based composite material (Si@a-Li2SiS3-10%) prepared in Example 2, and the electrolyte is commercial Li 5.5 PS 4.5 Cl 1.5 Electrolyte powder, positive electrode active material uses LiNi 0.9 Co 0.05 Mn 0.05 O2 (NCM9055). NCM9055, commercial Li 5.5 PS 4.5 Cl 1.5 Electrolyte powder and conductive carbon fiber were mixed in a planetary mixer at a mass ratio of 8:1:1 to obtain composite cathode powder. 5.5 PS 4.5 Cl 1.5The electrolyte powder was pressed into a tablet. 4 mg of silicon-based composite material (Si@a-Li2SiS3-10%) was mixed with 1 mg of conductive carbon black in a planetary mixer. The mixture was then spread on one side of the electrolyte tablet and pressed for 3 minutes. 25 mg of composite cathode powder was evenly spread on the other side of the electrolyte tablet and pressed into a tablet. The tablet was then held at this pressure for 5 minutes to assemble the all-solid-state battery. The test voltage was 2.8-4.3 V, and the first three cycles were conducted at 0.1 C (1 C = 180 mAh g). -1 ) current density test, then cycled 3 times with a current density of 0.5C, and finally continued to cycle with a current density of 1C. The test temperature was 55°C. The test results are as follows Figure 5 As shown, the silicon-based composite material also has good first coulombic efficiency (76%) and rate performance at 55°C.

[0052] These results all indicate that the amorphous sulfide fast ion conductor prepared using the method of the present invention can significantly improve the ionic conductivity of the silicon-based composite material, reduce the contact impedance between the negative electrode interface and the sulfide electrolyte interface, optimize the interface contact between the negative electrode and the electrolyte, and promote the rapid transmission of lithium ions, thereby obtaining excellent capacity performance and cycle stability, and also contributing to the first coulombic efficiency of silicon-based all-solid-state batteries.

[0053] As mentioned above, the present invention is not limited in any form. Although the present invention has been disclosed as above with preferred implementation cases, any simple modifications, equivalent changes and modifications made to the above implementation cases based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a silicon-based composite material in one step, characterized in that: Under vacuum or inert protective atmosphere, according to the molar ratio of Li, Si and S elements of 2:1~100:3, a Li source, a silicon source and a sulfur source are uniformly mixed, and then subjected to high-energy vibration ball milling treatment at a ball milling speed of 400~1200rpm for 20~100h to obtain a silicon-based composite material, wherein the silicon-based composite material is composed of a silicon material and an amorphous Li2SiS3 fast ion conductor material; the Li source is selected from one or more of Li2S powder, Li powder and lithium-silicon alloy powder; the sulfur source is selected from one or more of sublimated sulfur powder, Li2S powder and SiS2 powder; the silicon source is selected from one or more of silicon powder with a particle size at the micron or nanometer level, silicon-carbon powder, SiS2 powder and lithium-silicon alloy powder.

2. The method for preparing a silicon-based composite material in one step according to claim 1, wherein: The inert protective atmosphere is a mixture of one or more of nitrogen, argon and helium.

3. A silicon-based composite material obtained by the method according to any one of claims 1 to 2.

4. Use of the silicon-based composite material according to claim 3 as a negative electrode material in an all-solid-state lithium-ion battery.

5. A negative electrode for an all-solid-state lithium-ion battery, characterized in that: The silicon-based composite material according to claim 3 is used as the active material.

6. The negative electrode for an all-solid-state lithium-ion battery according to claim 5, characterized in that: In the silicon-based composite material, the mass percentage of silicon material is 80% to 98%.

7. An all-solid-state lithium-ion battery, characterized in that: The negative electrode according to claim 5 or 6 is used.

Images