Method for preparing silicon-based composite material in one step and application of silicon-based composite material in all-solid-state battery

Abstract

The invention belongs to the technical field of all-solid-state battery electrode materials based on silicon-containing compounds, and discloses a method for preparing a silicon-based composite material in one step and application of the silicon-based composite material in all-solid-state batteries, and the method comprises the following steps: uniformly mixing a Li source, a silicon source and a sulfur source in a vacuum or inert protective atmosphere, and then carrying out high-energy vibration ball milling treatment to obtain the silicon-based composite material. The in-situ composite construction of the silicon material and the amorphous sulfide fast ion conductor material is realized through a mechanical alloying one-step process, and the 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, so that the solid electrolyte is more stable in performance. Therefore, the first-circle coulombic efficiency and cycling stability of the silicon-based all-solid-state battery are improved, and the prepared all-solid-state battery also has excellent performance at high temperature.

Description

Technical Field

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

[0002] With the growing demand for higher energy density and higher safety of 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 are composed only of solid components (positive electrode, solid-state electrolyte, negative electrode), which can solve problems such as poor safety and low capacity related to traditional flammable liquid electrolytes. Among various solid-state electrolytes, sulfide electrolytes have become the focus of current research due to their ultra-high ionic conductivity and excellent mechanical properties. At the same time, the selection of negative electrode materials for sulfide-based all-solid-state batteries also plays a key role in improving the energy density and safety of the entire battery. Silicon negative electrode materials have become one of the most promising negative electrode materials for the commercialization of all-solid-state batteries due to their high theoretical specific capacity, low lithium intercalation potential, and low cost.

[0003] As a typical semiconductor material, the silicon negative electrode has the core problems of insufficient intrinsic electronic conductivity and ion mobility, which directly restricts its practical application in all-solid-state battery systems. Traditional strategies usually use an ex-situ mechanical mixing process to compound silicon negative electrode materials with sulfide solid-state electrolytes, conductive additives, and binders to construct an ion / electron transport pathway. However, this ex-situ composite method has multiple limitations: First, a high proportion of solid-state electrolyte (>30 wt%) must be introduced to achieve effective charge transport, resulting in a significant reduction in the proportion of active substances in the composite electrode, seriously affecting the energy density and economy of the battery system; Second, there are a large number of contact defects at the heterogeneous interfaces formed by physical mixing, leading to an increase in interface impedance and continuous deterioration of charge transport kinetics during battery cycling; More critically, the severe volume expansion (>300%) of silicon materials during electrochemical cycling will cause mechanical failure of the composite structure. Conventional methods rely on increasing the amount of binder to alleviate the volume effect, but this scheme is not only difficult to effectively inhibit the fragmentation and pulverization of silicon particles but also reduces the energy density due to the decrease in the effective proportion of electrode active materials. 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 method for one-step preparation of 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 the one-step mechanical alloying process, improve the ionic conductivity of silicon-based materials, and improve the interfacial contact between the negative electrode and the solid electrolyte when used in all-solid-state batteries, limit the volume expansion of the silicon negative electrode, and thus improve the energy density and cycle stability of all-solid-state batteries.

[0005] To achieve the purpose, the present invention adopts the following technical solutions: In the first aspect, the present invention first discloses a method for one-step preparation of silicon-based composite materials, specifically: in a vacuum or inert protective atmosphere, according to the molar ratio of Li, Si, and S elements of 2:1~100:3, after mixing the Li source, silicon source, and sulfur source evenly, high-energy vibration ball milling treatment is carried out to obtain a silicon-based composite material. The obtained silicon-based composite material is composed of silicon materials and amorphous Li2SiS3 fast ion conductor materials, and the proportion of silicon materials in the silicon-based composite material can be adjusted by controlling the addition amount of the silicon source.

[0006] Preferably, the inert protective atmosphere is a mixture of one or more of nitrogen, argon, and helium.

[0007] 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 sublimed 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 in the micron or nanometer range, silicon-carbon powder, SiS2 powder, and lithium-silicon alloy powder.

[0008] Preferably: the time of the high-energy vibration ball milling treatment is 20~100h, and the ball milling speed is 400~1200rpm.

[0009] Taking Li2S powder, sublimed sulfur powder, and silicon powder as examples, this one-step in-situ preparation method of the present invention utilizes the alloying reaction of lithium sulfide with silicon powder and sulfur powder under the ultra-high energy provided by high-energy ball milling. The reaction equation can be expressed as follows:

[0010] In the second aspect, the present invention further provides a negative electrode for an all-solid-state lithium-ion battery, which uses the above-mentioned silicon-based composite material as the active material. To further improve the performance of the negative electrode, the mass percentage of silicon materials in the silicon-based composite material used is 80%~98%.

[0011] In a third aspect, the present invention also provides an all-solid-state lithium-ion battery, which includes a sulfide solid electrolyte and a composite cathode, and further includes the anode using the silicon-based composite material as the active material described above. This all-solid-state battery has a high initial coulombic efficiency, cycle stability, and excellent high-temperature electrochemical performance.

[0012] Further, the sulfide 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 or one or more of them.

[0013] Further, the composition of the composite cathode in the all-solid-state lithium-ion battery can be: a cathode active material, a solid electrolyte, and a conductive agent. The cathode active material includes, but is not limited to, one or more of lithium cobaltate, lithium iron phosphate, high-nickel ternary materials, and lithium-rich manganese-based materials. 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 or one or more of them. The conductive agent includes, but is not limited to, one or more of carbon black, carbon nanotubes, carbon fibers, Ketjen black, and acetylene black materials.

[0014] Compared with the prior art, the beneficial effects of the present invention are reflected in: 1. Through the one-step mechanical alloying process, the present invention realizes the in-situ composite construction of silicon materials and amorphous sulfide fast ion conductor materials. This one-step in-situ composite construction strategy realizes the uniform composite of silicon and amorphous sulfide fast ion conductors, which can significantly improve the ionic conductivity of the silicon-based anode material. At the same time, the amorphous sulfide fast ion conductor has strong mechanical properties, and the surface stress buffer layer formed by in-situ composite significantly inhibits the volume expansion effect of silicon particles during cycling, effectively alleviating the stress concentration phenomenon at the anode / solid electrolyte interface. In addition, the amorphous sulfide fast ion conductor constructed in-situ in the present invention has similarities with the sulfide solid electrolyte in the all-solid-state battery in terms of chemical composition and physical and chemical properties. This structural feature significantly improves the interfacial chemical compatibility between the anode and the solid electrolyte, thereby effectively improving the contact state and interfacial stability of the anode-solid electrolyte interface, providing a unique advantage for constructing a stable solid-solid interface.

[0015] 2. When the silicon-based composite material of the present invention is assembled into an all-solid-state battery, there is no need to add any solid electrolyte powder and binder for ion conduction. It is only necessary to directly mix the silicon-based composite material with a conductive agent.

[0016] 3. The silicon-based composite material of the present invention can improve the initial Coulomb efficiency and cycle stability of the silicon-based all-solid-state battery, and can also achieve good cycle performance at high temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. By reading the detailed descriptions of the embodiments with reference to the following drawings, other features, objects, and advantages of the present invention will become more obvious.

[0018] Figure 1 It is the powder X-ray diffraction (XRD) pattern of the silicon-based composite material prepared in the embodiment of the present invention; Figure 2 It is the 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; Figure 3 It is the cycle performance diagram of the all-solid-state half-cell assembled with each silicon-based negative electrode material in the embodiment of the present invention; Figure 4 It is the AC impedance diagram of the all-solid-state half-cell assembled with each silicon-based negative electrode material in the embodiment of the present invention; Figure 5 It 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 OF THE EMBODIMENTS

[0019] The following further describes and illustrates the silicon-based composite negative electrode material of the all-solid-state battery prepared by the one-step method of the present invention through specific embodiments and drawings. It should be understood that the specific embodiments described herein are only used to help understand the present invention and are not used for the specific limitation of the present invention.

[0020] Example 1 This example provides a preparation method for an amorphous Li2SiS3 fast ion conductor, and the specific steps are as follows: In a glove box filled with argon, the raw materials are weighed according to the molar ratio of Li2S: Si powder: S powder = 1: 1: 2, ground and mixed for 15 minutes, then put into a stainless steel ball milling tank, and zirconia balls are added according to the ball-to-material mass ratio of 40: 1 for ball milling. The rotation speed of the ball mill is 1200 rpm, and the ball milling time is 40 hours to obtain an amorphous Li2SiS3 fast ion conductor (a-Li2SiS3).

[0021] Example 2 This example provides a method for preparing a silicon-based composite material, and the specific steps are as follows: In a glove box filled with argon, weigh each raw material according to the molar ratio of Li2S: Si powder: S powder = 1:45:2, grind and mix for 15 minutes, then put it into a stainless steel ball milling tank, add zirconia balls according to the ball-to-material mass ratio of 40:1 for ball milling, the rotation speed of the ball mill is 1200 rpm, and the ball milling time is 40 hours, so as to obtain a silicon-based composite material (Si@a-Li2SiS3-10%) with the mass ratio of amorphous Li2SiS3 fast ionic conductor being 10%.

[0022] Example 3 This example provides a method for preparing a silicon-based composite material, and the specific steps are as follows: In a glove box filled with argon, weigh each raw material according to the molar ratio of Li2S: Si powder: S powder = 1:21:2, grind and mix for 15 minutes, then put it into a stainless steel ball milling tank, add zirconia balls according to the ball-to-material mass ratio of 40:1 for ball milling, the rotation speed of the ball mill is 1200 rpm, and the ball milling time is 40 hours, so as to obtain a silicon-based composite material (Si@a-Li2SiS3-20%) with the mass ratio of amorphous Li2SiS3 fast ionic conductor being 20%.

[0023] The samples obtained in the above examples were tested as follows: 1. XRD test Use an X-ray powder diffractometer to test the materials obtained in each example, and the results are as Figure 1 shown. It can be seen that: there are no obvious diffraction peak intensities of the a-Li2SiS3 fast ionic conductor in the X-ray diffraction pattern, indicating that this sulfide fast ionic conductor exists in an amorphous state. Diffraction peaks appear at the positions of 28°, 47° and 56° in the silicon-based composite materials (Si@a-Li2SiS3-10% and Si@a-Li2SiS3-20%), which correspond one by one to the peak positions of the Si PDF#27-1402 card, indicating that the main phase of the synthesized silicon-based composite material is silicon, and it also shows the reliability and high efficiency of the synthesis process.

[0024] 2. Ionic conductivity test Press the amorphous a-Li2SiS3 fast ionic conductor powder obtained in Example 1 into a tablet and test its ionic conductivity. The results are as Figure 2 shown. After calculation, its ionic conductivity at room temperature is 1.08×10 -4 S / cm.

[0025] For comparison, crystalline c-Li2SiS3 powder was prepared. Its preparation method is the same as that of a-Li2SiS3 in Example 1, except that the ball milling time is 8h. FromFigure 1 Its crystallinity can be determined by XRD. After testing, its ionic conductivity is 1.05×10 -5 S / cm.

[0026] 3. Half-cell performance test Assemble all-solid-state half-cells using amorphous a-Li2SiS3 fast ion conductor powder or silicon-based composites (Si@a-Li2SiS3-10% or Si@a-Li2SiS3-20%): Take 100 mg of commercial Li 5.5 PS 4.5 Cl 1.5 electrolyte powder and press it into a tablet. Take 9 mg of a-Li2SiS3 or silicon-based composites (Si@a-Li2SiS3-10% or Si@a-Li2SiS3-20%) and mix it evenly with 1 mg of conductive carbon black, then spread it on one side of the electrolyte tablet and press for 3 min. On the other side of the electrolyte tablet, lay a lithium-indium alloy, and then keep the pressure for 5 min to assemble a half-cell, and then it can be tested.

[0027] For comparison, use silicon powder to make a working electrode and assemble a half-cell: First, take 100 mg of commercial Li 5.5 PS 4.5 Cl 1.5 electrolyte powder and press it into a tablet. Take 7 mg of silicon powder, 1 mg of conductive carbon black and 2 mg of Li 5.5 PS 4.5 Cl 1.5 electrolyte powder (the corresponding battery is denoted 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) and mix them evenly, spread them on one side of the electrolyte tablet and press for 3 min. On the other side of the electrolyte tablet, lay a lithium-indium alloy, and then keep the pressure for 5 min to assemble a half-cell, and then it can be tested.

[0028] The test voltage is -0.61~1.38 V. In the first 3 cycles, test at a current density of 0.3 A g -1 , and then cycle at a current density of 0.6 A g -1 . The test results are as Figure 3 shown. It can be seen from the battery cycle test that the in-situ prepared silicon-based composites in the examples have higher initial Coulomb efficiency and discharge specific capacity than pure silicon materials or composites prepared by non-in-situ methods (Table 1). In addition, when directly using amorphous a-Li2SiS3 powder as the anode material, the discharge specific capacity is only 38 mA h / g, which indicates that amorphous a-Li2SiS3 powder is not suitable for directly serving as the anode material.

[0029] Table 1 Initial Coulombic Efficiency and Discharge Specific Capacity of All-Solid-State Half-Cells Assembled with Various Silicon-Based Anode Materials

[0030] 4. Electrochemical AC Impedance Test According to the above method, Si@a-Li2SiS3-10%, Si@a-Li2SiS3-20% and silicon powder were assembled into all-solid-state half-cells for electrochemical AC impedance test to compare the impedance values. The results are as Figure 4 shown. It can be seen from the figure that the impedance of the silicon powder electrode is 70 Ω, while the impedances of the Si@a-Li2SiS3-10% electrode and the Si@a-Li2SiS3-20% electrode are 18 Ω and 35 Ω respectively, which are 1 / 4 and 1 / 2 of the impedance of the silicon powder electrode.

[0031] 5. All-Cell Performance Test The anode active material was the silicon-based composite material (Si@a-Li2SiS3-10%) prepared in Example 2, the electrolyte was commercial Li 5.5 PS 4.5 Cl 1.5 electrolyte powder, and the cathode active material was 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 evenly in a planetary mixer according to a mass ratio of 8:1:1 to obtain the composite cathode powder. 100 mg of commercial Li 5.5 PS 4.5 Cl 1.5 electrolyte powder was pressed into a sheet. After 4 mg of the silicon-based composite material (Si@a-Li2SiS3-10%) and 1 mg of conductive carbon black were mixed evenly in a planetary mixer, they were spread on one side of the electrolyte sheet and pressed for 3 min. Then, 25 mg of the composite cathode powder was evenly spread on the other side of the electrolyte sheet and pressed into a sheet, and then held under pressure for 5 min to assemble into an all-solid-state battery. The test voltage was 2.8~4.3 V. In the first 3 cycles, it was tested at a current density of 0.1 C (1 C = 180 mAh g -1 ) and then cycled at a current density of 0.5 C for 3 cycles, and finally continued to cycle at a current density of 1 C. The test temperature was 55 °C. The test results are as Figure 5 shown, indicating that the silicon-based composite material also has good initial Coulombic efficiency (76%) and rate performance at 55 °C.

[0032] These results all indicate that the amorphous sulfide fast ion conductor prepared by 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, promote the rapid transmission of lithium ions, thereby obtaining excellent capacity performance and cycle stability, and also helpful for the first Coulomb efficiency of the silicon-based all-solid-state battery.

[0033] As described above, there is no any formal limitation to the present invention. Although the present invention has been disclosed with the preferred embodiments as above, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the technical solution of the present invention still fall 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 a vacuum or an inert protective atmosphere, according to the molar ratio of Li, Si, and S elements being 2:1 to 100:3, after uniformly mixing the Li source, the silicon source, and the sulfur source, high-energy vibration ball milling treatment is carried out to obtain a silicon-based composite material.

2. The method for preparing the silicon-based composite material in one step according to claim 1, wherein: The silicon-based composite material is composed of a silicon material and an amorphous Li2SiS3 fast ion conductor material.

3. The method for preparing the 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.

4. The method for preparing the silicon-based composite material in one step according to claim 1, characterized in that: 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 sublimed sulfur powder, Li2S powder, and SiS2 powder; the silicon source is selected from one or more of silicon powder with a particle size in the micron or nanometer range, silicon-carbon powder, SiS2 powder, and lithium-silicon alloy powder.

5. The method for preparing the silicon-based composite material in one step according to claim 1, wherein: The time of the high-energy vibration ball milling treatment is 20 to 100 h, and the ball milling rotation speed is 400 to 1200 rpm.

6. A silicon-based composite material prepared by the method according to any one of claims 1 to 5.

7. An application of the silicon-based composite material according to claim 6 as a negative electrode material in a all-solid-state lithium-ion battery.

8. A negative electrode for an all-solid-state lithium-ion battery, characterized in that: Using the silicon-based composite material according to claim 6 as the active material.

9. The negative electrode for all-solid-state lithium-ion battery according to claim 8, wherein: In the silicon-based composite material, the mass percentage of the silicon material is 80% to 98%.

10. A all-solid-state lithium-ion battery, characterized in that: Using the negative electrode according to claim 8 or 9.

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