A method for dry-process fabrication of silicon anode electrode for sulfide solid-state batteries

Abstract

This invention relates to the field of dry electrode fabrication technology, specifically a method for preparing a silicon anode dry electrode for sulfide solid-state batteries. In a glove box, any two of the following raw materials—pre-lithiated silicon, silicon powder, and a binder—are placed in a ball mill jar, sealed, transferred, and fixed on a rotating support within the ball mill. The ball mill then performs its first cycle. After the mill stops, the jar is removed and transferred back to the glove box. Inside the glove box, the jar is opened and removed to obtain a primary mixture. A binder is added to the primary mixture, and the ball mill cycle is repeated to obtain a secondary mixture. This invention achieves carbon coating on the surface of pre-lithiated silicon and silicon, mitigating the volume expansion of the silicon anode during charging and discharging, maintaining the high ionic conductivity of the sulfide electrolyte, and achieving the preparation of a high-silicon-to-content, high-energy-density silicon anode through dry electrolysis.

Description

Technical Field

[0001] This invention relates to the field of dry electrode fabrication technology, specifically to a method for fabricating a silicon anode dry electrode for sulfide solid-state batteries. Background Technology

[0002] As one of the four mainstream routes for all-solid-state batteries, the silicon anode is based on the sulfide route. Its core material, the sulfide electrolyte, is widely used in electrolyte layers, anode layers, or anode buffer layers due to its advantages such as high ionic conductivity and good reduction stability. However, silicon undergoes a volume expansion of approximately 300% during the lithiation-delithiation process of charging and discharging, which greatly limits the practical application of this material. Selecting a suitable binder for sulfide solid-state batteries, improving the coulombic efficiency of the silicon anode during the first charge and discharge cycle, and overcoming the volume expansion problem during silicon charging and discharging are key to the application of silicon anode dry electrodes in sulfide solid-state batteries. Fluorinated binders have become the main component of dry electrolyte membranes for sulfide solid-state batteries. Silicon pre-lithiation and surface coating technologies have also become the main means in the industry to solve the problems of low initial efficiency and large volume expansion of silicon anodes. However, due to the high reactivity of pre-lithiated silicon, it is easy for it to react violently with fluorinated binders. The complex silicon coating process and methods severely restrict its application and development.

[0003] Existing silicon anodes exhibit low initial charge-discharge coulombic efficiency, requiring pre-lithiation treatment. However, pre-lithiated silicon is highly reactive, causing fluorinated binders compatible with sulfide solid electrolytes to react violently and lose activity. Furthermore, the volume expansion of the silicon anode requires complex coating methods to mitigate it. To keep the volume expansion within a controllable range, the silicon content in the anode is relatively low, leading to a decrease in the overall energy density of the silicon anode. Therefore, this method does not meet the current requirements. To address this, we propose a dry electrode preparation method for silicon anodes in sulfide solid-state batteries. Summary of the Invention

[0004] The purpose of this invention is to provide a dry electrode preparation method for silicon anodes in sulfide solid-state batteries, in order to solve the problems mentioned in the background art, such as the low coulombic efficiency of existing silicon anodes during the first charge and discharge, the need for pre-lithiation treatment, the high reactivity of pre-lithiated silicon which causes fluorine-containing binders adapted to sulfide solid electrolytes to react violently and lose their activity, and the volume expansion of silicon anodes which requires complex coating methods to mitigate. In order to keep the volume expansion within a controllable range, the silicon content in the anode is relatively low, resulting in a decrease in the overall energy density of the silicon anode.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a silicon negative electrode for sulfide solid-state batteries using a dry method, comprising the following steps: S1: In the glove box, any two of the following materials are used as raw materials: pre-lithiated silicon, silicon powder and binder. They are placed in a ball mill jar, sealed, transferred and fixed on the turntable support inside the ball mill. Then, the first running process of the ball mill is executed. After the running stops, the ball mill jar is taken out and transferred to the glove box. The ball mill jar is opened and taken out in the glove box to obtain the primary mixture. S2: Add a binder to the primary mixture and repeat the ball milling process to obtain a secondary mixture; S3: Weigh the secondary mixture, put it back into the ball mill jar and seal it, and repeat the ball mill operation process to obtain the tertiary mixture; S4: Weigh the tertiary mixture and the sulfide electrolyte, put them back into the ball mill jar and seal it, and repeat the first run of the ball mill to obtain the quaternary mixture; S5: The fourth-stage mixture, binder, and conductive agent are loaded into a ball mill jar in proportion and sealed. After performing the second run of the ball mill and ensuring that the materials are fully mixed, the final mixture is obtained. S6: Roll the final mixture into a film to obtain a silicon anode dry electrode, and simultaneously set up a comparison sample.

[0006] Preferably, the primary mixture has two types, namely primary mixture A and primary mixture B. Primary mixture A is obtained by mixing pre-lithiated silicon with a binder, and primary mixture B is obtained by mixing silicon powder with a binder. The mass ratio of pre-lithiated silicon to binder in primary mixture A is 95:5, and the mass ratio of silicon powder to binder in primary mixture B is 95:5.

[0007] Preferably, the secondary mixture comprises two types, namely secondary mixture A and secondary mixture B. Secondary mixture A is obtained by mixing primary mixture A with a binder, and secondary mixture B is obtained by mixing primary mixture B with a binder. The mass ratio of primary mixture A to binder in secondary mixture A and the mass ratio of primary mixture B to binder in secondary mixture B are both 97:3. The tertiary mixture is obtained by mixing secondary mixture A and secondary mixture B, and the mass ratio of secondary mixture A to secondary mixture B in the tertiary mixture is 1:1.

[0008] Preferably, the primary mixture is obtained by mixing pre-lithiated silicon and silicon powder, the mass ratio of the primary mixture to the binder in the secondary mixture is 95:5, and the tertiary mixture is obtained by mixing the secondary mixture and the binder, the mass ratio of the secondary mixture to the binder in the tertiary mixture is 97:3.

[0009] Preferably, the tertiary mixture is obtained by mixing the primary mixture and the binder, wherein the mass ratio of the primary mixture to the binder in the tertiary mixture is 92:8.

[0010] Preferably, the water content and oxygen content in the glove box are both below 0.01 ppm. The grinding jar has an agate inner liner and three different sizes of grinding beads. The grinding beads are made of agate and are located inside the agate inner liner. The mass ratio of the grinding beads in the three grinding jars in S1, S2 and S3 is 1:10, and the particle sizes of the three types of grinding beads are 3 mm, 5 mm and 10 mm, respectively, with a mass ratio of 1:3:6. The pre-lithiated silicon is Li3.75Si, the binder is PTFE, the sulfide electrolyte is Li5.5PS4.5Cl1.5, and the conductive agent is VGCF.

[0011] Preferably, the mass ratio of the tertiary mixture and the sulfide electrolyte in S4 is 70:25, and the mass ratio of the quaternary mixture, the binder, and the conductive agent in S5 is 95:3:2.

[0012] Preferably, the first operating process of the ball mill is as follows: after preliminary mixing at 100 rpm for 3 minutes, the speed is adjusted to 300 rpm and ball milling is performed for 15 minutes. The second operating process of the ball mill is as follows: ball milling is performed at 200 rpm for 60 minutes.

[0013] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention utilizes the reactivity of pre-lithiated silicon to induce a vigorous combustion reaction with a binder during high-speed ball milling, achieving rapid carbon coating of pre-lithiated silicon and silicon. This is followed by coating with a sulfide solid electrolyte, and finally, mixing with a binder and conductive strip before dry-processing of the silicon negative electrode. The carbon-coated pre-lithiated silicon and silicon are formed through binder combustion, and ball milling with the sulfide electrolyte achieves uniform mixing and coating of the electrolyte layer. After this double coating of carbon and electrolyte layers, the highly reactive pre-lithiated silicon is fully isolated from the binder, protecting the binder. Silicon and pre-lithiated silicon coexist in the negative electrode system. During charging, the volume expansion of the un-lithiated silicon compresses the better carbon-coated pre-lithiated silicon, while active lithium is released during discharge, simultaneously mitigating volume change and replenishing the lithium source, thus improving the internal structural stability of the negative electrode and increasing coulombic efficiency. 2. This invention is the first to propose a strategy of reducing the activity of pre-lithiated silicon by reacting it with a binder under external force to form a carbon layer. It is also the first to propose a strategy of using an electrolyte layer to perform secondary coating on carbon-coated pre-lithiated silicon or silicon to achieve full contact between the electrolyte and silicon, while blocking the reaction between pre-lithiated silicon and binder. Furthermore, it is the first to propose a strategy of using carbon-coated silicon and carbon-coated pre-lithiated silicon to limit the volume deformation of silicon anodes during charging and discharging. A stepwise mixing strategy is also used to prepare a dry electrode for silicon anodes in sulfide solid-state batteries. Attached Figure Description

[0014] Figure 1 This is a schematic diagram illustrating the fabrication of the dry silicon negative electrode of the present invention. Figure 2 This is a flowchart of the entire invention. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0016] Please see Figure 1 and Figure 2 The present invention provides an embodiment of a method for preparing a dry silicon negative electrode for a sulfide solid-state battery, comprising the following steps: S1: In the glove box, any two of the following materials are used as raw materials: pre-lithiated silicon, silicon powder and binder. They are placed in a ball mill jar, sealed, transferred and fixed on the turntable support inside the ball mill. Then, the first running process of the ball mill is executed. After the running stops, the ball mill jar is taken out and transferred to the glove box. The ball mill jar is opened and taken out in the glove box to obtain the primary mixture. S2: Add a binder to the primary mixture and repeat the ball milling process to obtain a secondary mixture; S3: Weigh the secondary mixture, put it back into the ball mill jar and seal it, and repeat the ball mill operation process to obtain the tertiary mixture; S4: Weigh the tertiary mixture and the sulfide electrolyte, put them back into the ball mill jar and seal it, and repeat the first run of the ball mill to obtain the quaternary mixture; S5: The fourth-stage mixture, binder, and conductive agent are loaded into a ball mill jar in proportion and sealed. After performing the second run of the ball mill and ensuring that the materials are fully mixed, the final mixture is obtained. S6: Roll the final mixture into a film to obtain a silicon anode dry electrode.

[0017] The pre-lithiated silicon is Li3.75Si, the binder is PTFE, the sulfide electrolyte is Li5.5PS4.5Cl1.5, and the conductive agent is VGCF.

[0018] The water and oxygen content in the glove box are both below 0.01 ppm. The grinding jar contains an agate inner liner and three different sizes of grinding beads. The grinding beads are made of agate and are located inside the agate inner liner. The mass ratio of the grinding beads in the three grinding jars S1, S2 and S3 is 1:10, and the particle sizes of the three grinding beads are 3 mm, 5 mm and 10 mm respectively. The mass ratio of the three grinding beads is 1:3:6. The first running process of the ball mill is as follows: after initial mixing at 100 rpm for 3 minutes, the speed is adjusted to 300 rpm and ball milling is performed for 15 minutes. The second running process of the ball mill is as follows: ball milling is performed at 200 rpm for 60 minutes.

[0019] The mass ratio of the tertiary mixture to the sulfide electrolyte is 70:25, and the mass ratio of the quaternary mixture to the binder and conductive agent in S5 is 95:3:2.

[0020] Example 1: A method for preparing a dry silicon anode electrode for sulfide solid-state batteries includes the following steps: S1: Inside the glove box, pre-lithiated silicon and silicon powder binder are used as raw materials. They are placed into two ball mill jars, sealed, transferred, and fixed on the turntable support inside the ball mill. Then, the first running process of the ball mill is executed. After the running stops, the two ball mill jars are taken out and transferred to the glove box. The ball mill jars are opened and taken out inside the glove box to obtain two primary mixtures, namely primary mixture A and primary mixture B. The two primary mixtures are obtained by mixing pre-lithiated silicon and binder and silicon powder and binder, respectively. The mass ratio of pre-lithiated silicon to binder in primary mixture A and silicon powder to binder in primary mixture B are both 95:5. S2: Add binder to both primary mixtures and repeat the ball mill operation to obtain two secondary mixtures, namely secondary mixture A and secondary mixture B. The mass ratio of the two primary mixtures to the binder is 97:3. S3: Weigh the two secondary mixtures and put them back into the two ball mill jars and seal them. Repeat the ball mill operation to obtain a tertiary mixture, wherein the mass ratio of the two secondary mixtures is 1:1. S4: Weigh the tertiary mixture and the sulfide electrolyte, put them back into the ball mill jar and seal it, and repeat the first run of the ball mill to obtain the quaternary mixture; S5: The fourth-stage mixture, binder, and conductive agent are loaded into a ball mill jar in proportion and sealed. After performing the second run of the ball mill and ensuring that the materials are fully mixed, the final mixture is obtained. S6: Roll the final mixture into a film to obtain a silicon anode dry electrode.

[0021] Example 2: A method for preparing a dry silicon anode electrode for sulfide solid-state batteries includes the following steps: S1: In the glove box, pre-lithiated silicon and silicon powder are used as raw materials. They are placed into a ball mill jar, sealed, transferred and fixed on the turntable support inside the ball mill. Then, the first running process of the ball mill is executed. After the running stops, the ball mill jar is taken out and transferred to the glove box. The ball mill jar is opened and taken out in the glove box to obtain the primary mixture. S2: Add binder to primary mixture and repeat ball mill operation to obtain secondary mixture. The mass ratio of primary mixture to binder is 95:5. S3: Weigh the secondary mixture and binder, then put them back into the ball mill jar and seal it. The mass ratio of the secondary mixture to the binder is 97:3. Repeat the ball mill operation to obtain the tertiary mixture. S4: Weigh the tertiary mixture and the sulfide electrolyte, put them back into the ball mill jar and seal it, and repeat the first run of the ball mill to obtain the quaternary mixture; S5: The fourth-stage mixture, binder, and conductive agent are loaded into a ball mill jar in proportion and sealed. After performing the second run of the ball mill and ensuring that the materials are fully mixed, the final mixture is obtained. S6: Roll the final mixture into a film to obtain a silicon anode dry electrode.

[0022] Example 3: The difference from Example 2 is that the tertiary mixture is obtained by mixing the primary mixture and the binder, and the mass ratio of the primary mixture to the binder in the tertiary mixture is 92:8.

[0023] Comparative Example 1: Silicon powder, pre-physicochemical silicon, sulfide electrolyte, binder, and conductive agent were directly loaded into a ball mill jar at a mass ratio of 32.25:32.25:25:8.5:2, sealed, and then installed on a ball mill. The ball mill was then operated at 100 rpm for 3 minutes, and then adjusted to 300 rpm for 15 minutes. The operation of the ball mill was repeated three times after a 20-minute interval. Finally, the mixture was thoroughly mixed at 200 rpm for 60 minutes and then rolled into a film to obtain the ball-milled comparison sample.

[0024] In summary, Examples 1 to 3 all utilize the reactivity of pre-lithiated silicon to undergo a violent combustion reaction with the binder under high-speed ball milling, thereby achieving rapid carbon coating of pre-lithiated silicon and silicon, followed by sulfide solid electrolyte coating, and finally mixing with binder and conductive tape before dry-processing of silicon negative electrode rolling. The difference is that in Example 1, carbon coating is first achieved on the surface of pre-lithiated silicon, and then it is ball-milled with silicon and binder. This allows the pre-lithiated silicon that was not coated during the ball milling process to be coated again. Along with the full ball milling process, some of the carbon generated by combustion is simultaneously attached to the silicon surface, forming a coating on the silicon. In Example 2, the pre-lithiated silicon and silicon are first ball-milled to achieve thorough mixing before being mixed with a binder and ball-milled. The binder reacts with the active pre-lithiated silicon, simultaneously achieving the coating of the pre-lithiated silicon and silicon.

[0025] The carbon-coated pre-lithiated silicon and silicon, formed by the combustion of the binder, are ball-milled with the sulfide electrolyte to achieve uniform mixing and coating of the electrolyte layer. After the double coating of the carbon layer and the electrolyte layer, the highly reactive pre-lithiated silicon is fully isolated from the binder, and the binder is protected. Silicon and pre-lithiated silicon coexist in the negative electrode system. During the charging process, the pre-lithiated silicon, which is not compressed by the volume expansion of the pre-lithiated silicon, has better carbon coating. During the discharge process, active lithium is released, which plays a role in simultaneously slowing down the volume change and replenishing the lithium source, improving the internal structural stability of the negative electrode and improving the coulombic efficiency.

[0026] This application can solve the problem that when a large amount of binder is added at once, the active pre-lithiated silicon reacts violently with the binder, the high temperature causes the sulfide electrolyte to decompose, and the violent combustion causes carbon agglomeration. Even after ball milling, the carbon particles are not evenly dispersed in the mixed material, and the effect of uniform carbon coating is not formed. A large amount of binder is consumed, and some carbon particles are not evenly mixed with the electrolyte to form a conductive network, which seriously affects the subsequent battery performance.

[0027] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a dry silicon anode electrode for sulfide solid-state batteries, characterized in that, Includes the following steps: S1: In the glove box, any two of the following materials are used as raw materials: pre-lithiated silicon, silicon powder and binder. They are placed in a ball mill jar, sealed, transferred and fixed on the turntable support inside the ball mill. Then, the first running process of the ball mill is executed. After the running stops, the ball mill jar is taken out and transferred to the glove box. The ball mill jar is opened and taken out in the glove box to obtain the primary mixture. S2: Add a binder to the primary mixture and repeat the ball milling process to obtain a secondary mixture; S3: Weigh the secondary mixture, put it back into the ball mill jar and seal it, and repeat the ball mill operation process to obtain the tertiary mixture; S4: Weigh the tertiary mixture and the sulfide electrolyte, put them back into the ball mill jar and seal it, and repeat the first run of the ball mill to obtain the quaternary mixture; S5: The fourth-stage mixture, binder, and conductive agent are loaded into a ball mill jar in proportion and sealed. After performing the second run of the ball mill and ensuring that the materials are fully mixed, the final mixture is obtained. S6: Roll the final mixture into a film to obtain a silicon anode dry electrode, and simultaneously set up a comparison sample.

2. The method for preparing a dry silicon anode electrode for a sulfide solid-state battery according to claim 1, characterized in that: The primary mixture has two types, namely primary mixture A and primary mixture B. Primary mixture A is obtained by mixing pre-lithiated silicon with a binder, and primary mixture B is obtained by mixing silicon powder with a binder.

3. The method for preparing a dry silicon anode electrode for a sulfide solid-state battery according to claim 2, characterized in that: The mass ratio of pre-physicochemical silicon to binder in the primary mixture A is 95:5, and the mass ratio of silicon powder to binder in the primary mixture B is 95:

5.

4. The method for preparing a dry silicon anode electrode for a sulfide solid-state battery according to claim 3, characterized in that: The secondary mixture has two types, namely secondary mixture A and secondary mixture B. Secondary mixture A is obtained by mixing primary mixture A with a binder, and secondary mixture B is obtained by mixing primary mixture B with a binder.

5. The method for preparing a dry silicon anode electrode for a sulfide solid-state battery according to claim 4, characterized in that: The mass ratio of primary mixture A to binder in secondary mixture A and the mass ratio of primary mixture B to binder in secondary mixture B are both 97:

3. The tertiary mixture is obtained by mixing secondary mixture A and secondary mixture B, and the mass ratio of secondary mixture A to secondary mixture B in the tertiary mixture is 1:

1.

6. The method for preparing a dry silicon anode electrode for a sulfide solid-state battery according to claim 1, characterized in that: The primary mixture is obtained by mixing pre-lithiated silicon and silicon powder. The mass ratio of the primary mixture to the binder in the secondary mixture is 95:

5. The tertiary mixture is obtained by mixing the secondary mixture and the binder. The mass ratio of the secondary mixture to the binder in the tertiary mixture is 97:

3.

7. The method for preparing a dry silicon anode electrode for a sulfide solid-state battery according to claim 1, characterized in that: The tertiary mixture is obtained by mixing the primary mixture and the binder, wherein the mass ratio of the primary mixture to the binder in the tertiary mixture is 92:

8.

8. A method for preparing a dry silicon negative electrode for a sulfide solid-state battery according to any one of claims 5-7, characterized in that: The glove box contains less than 0.01 ppm of water and oxygen. The grinding jar contains an agate liner and three different sizes of grinding beads. The grinding beads are made of agate and are located inside the agate liner. The mass ratio of grinding beads in the three grinding jars S1, S2 and S3 is 1:10, and the particle sizes of the three grinding beads are 3 mm, 5 mm and 10 mm, respectively. The mass ratio of the three grinding beads is 1:3:

6. The pre-lithiated silicon is Li3.75Si, the binder is PTFE, the sulfide electrolyte is Li5.5PS4.5Cl1.5, and the conductive agent is VGCF.

9. A method for preparing a dry silicon anode electrode for a sulfide solid-state battery according to claim 8, characterized in that: The mass ratio of the tertiary mixture and the sulfide electrolyte in S4 is 70:25, and the mass ratio of the quaternary mixture, the binder, and the conductive agent in S5 is 95:3:

2.

10. A method for preparing a dry silicon anode electrode for a sulfide solid-state battery according to claim 9, characterized in that: The first operating process of the ball mill is as follows: after initial mixing at 100 rpm for 3 minutes, the speed is adjusted to 300 rpm and ball milling is performed for 15 minutes. The second operating process of the ball mill is as follows: ball milling is performed at 200 rpm for 60 minutes.

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