A silicon-based anode material for all-solid-state batteries, its preparation method and application

Abstract

The present invention discloses a silicon-based anode material for all-solid-state batteries, its preparation method and application. When used as the anode of a sulfide all-solid-state lithium-ion battery, the silicon-based anode material of the present invention can operate stably without external pressure. The preparation of the silicon-based anode material uses Si and LiBF4 as raw materials and is obtained by one-step annealing under inert gas protection. The final product mainly consists of Si, LiF, and LiBO2. Electrochemically stable and high Young's modulus LiF can inhibit the decomposition of the Li6PS5Cl electrolyte and limit the volume effect of Si, and LiBO2 can compensate for the lithium loss of silicon during charge and discharge. Thanks to the synergistic effect of LiF and LiBO2, the modified Si-based anode exhibits a high initial Coulomb efficiency and can achieve stable operation in all-solid-state batteries without external pressure.

Description

Technical Field

[0001] The present invention relates to the field of all-solid-state battery preparation, and particularly to a silicon-based anode material for all-solid-state batteries, a preparation method thereof, and applications thereof. Background Art

[0002] All-solid-state lithium-ion batteries are gradually becoming the core R & D direction of the next-generation energy storage system due to their high energy density, excellent safety performance, and long cycle life. Compared with traditional liquid lithium-ion batteries, all-solid-state batteries use solid electrolytes to replace liquid electrolytes, thus fundamentally eliminating the risks of electrolyte leakage and battery explosion, and greatly improving the safety of the batteries.

[0003] In the field of solid electrolytes, sulfide solid electrolytes have attracted much attention due to their excellent ionic conductivity and good mechanical properties. Sulfide solid electrolytes can not only exhibit a high ionic conductivity at room temperature, effectively promoting the migration of lithium ions, but also form good interfacial contact with the anode and cathode materials, reducing the interfacial resistance, thereby improving the overall performance of the battery. Therefore, sulfide solid electrolytes are regarded as one of the key materials for realizing high-performance all-solid-state lithium-ion batteries.

[0004] Silicon (Si) is regarded as the most promising anode material for all-solid-state lithium-ion batteries because of its theoretical capacity as high as 4200 mAh / g, which is much higher than that of graphite anodes, and the abundant silicon resources and low cost. Especially in sulfide all-solid-state lithium-ion batteries, the application of silicon-based anodes is expected to significantly improve the energy density of the batteries and promote technological innovation in fields such as electric vehicles and energy storage systems.

[0005] However, the practical application of silicon-based anodes in sulfide all-solid-state batteries faces many challenges. Among them, the volume effect of silicon is particularly prominent. During the charge and discharge process, the volume of silicon will change significantly, resulting in the destruction of the electrode structure and the rapid decay of battery performance. In order to limit the volume effect of silicon and maintain good interfacial contact, the traditional approach is to apply a high stacking pressure to the battery. However, such high-pressure conditions not only increase the manufacturing cost and usage difficulty of the battery, but also limit the energy density and cycle life of the battery system.

[0006] So far, although researchers have made significant progress in the modification of silicon-based anodes and the interface optimization between electrolytes and anodes, most studies on silicon-based anodes in sulfide all-solid-state batteries still require an external pressure of more than 50 MPa to achieve stable operation. Such high-pressure conditions seriously hinder the large-scale application of silicon-based anodes in all-solid-state batteries.

[0007] Therefore, how to prepare a silicon-based negative electrode material that can operate stably without external pressure has become a key issue that needs to be solved in the current field of all-solid-state lithium-ion batteries. This requires not only in-depth research on the failure mechanism of silicon-based negative electrodes in sulfide all-solid-state batteries, but also the exploration of new material preparation methods and structural design strategies to achieve the optimization and stabilization of silicon-based negative electrode performance. By comprehensively applying knowledge from multiple disciplines such as materials science, electrochemistry, and engineering technology, it is expected to open up new paths for the large-scale application of silicon-based negative electrodes in all-solid-state batteries. Summary of the invention

[0008] The purpose of the present invention is to solve the difficult problem that the silicon negative electrode is difficult to operate stably in a sulfide all-solid-state battery without external pressure. A silicon-based negative electrode material with high first coulombic efficiency and stable structure is prepared, which realizes long-term stable operation in the all-solid-state battery.

[0009] The present invention utilizes silicon (Si) and lithium tetrafluoroborate (LiBF 4 ) Through high temperature annealing, chemical reactions occurred to obtain Si, LiF, LiBO 2 Multiphase hybrid silicon-based composite materials. LiF is derived from LiBF 4 Thermal decomposition of LiBO 2 It is LiBF 4 and the oxide layer on the Si surface (SiO x ) is a product of thermal reaction. The electrochemical stability and high Young's modulus of LiF can inhibit the 6 PS 5 The decomposition of Cl electrolyte and the volume effect of limiting silicon, LiBO 2 It can make up for the lithium loss of silicon during the charging and discharging process. Therefore, the modified Si-based negative electrode can achieve stable operation in all-solid-state batteries without external pressure.

[0010] To achieve the above-mentioned purpose, the technical solution of the present invention is as follows:

[0011] The present invention provides a method for preparing a silicon-based negative electrode material for an all-solid-state battery, comprising the following steps:

[0012] (1) mixing silicon and lithium tetrafluoroborate in a certain proportion to obtain a mixture;

[0013] (2) The mixture in step (1) is subjected to high temperature annealing treatment under the protection of an inert gas to obtain a silicon-based negative electrode material.

[0014] Preferably, in step (1), the molar ratio of silicon to lithium tetrafluoroborate is 5-20:1.

[0015] More preferably, the molar ratio of silicon to lithium tetrafluoroborate is 12:1.

[0016] Preferably, in step (2), the temperature of the high-temperature annealing treatment is 400-1200 °C, and the time of the high-temperature annealing treatment is 1-10 hours.

[0017] More preferably, the temperature of the high-temperature annealing treatment is 800 °C, and the time of the high-temperature annealing treatment is 5 hours.

[0018] The present invention also provides a silicon-based anode material prepared by the preparation method described above.

[0019] The present invention also provides the use of the silicon-based anode material described above, or the silicon-based anode material prepared by the preparation method described above, in a all-solid-state lithium-ion battery.

[0020] The present invention also provides a negative electrode sheet for a all-solid-state battery, and the negative electrode sheet includes the silicon-based anode material described above.

[0021] The present invention also provides a preparation method for the negative electrode sheet for a all-solid-state battery, including the following steps:

[0022] Weigh the silicon-based anode material as an active material, electrolyte Li 6 PS 5 Cl, a conductive agent, and a binder in a certain proportion, disperse them in an organic solvent, and mix them to prepare a slurry; coat the slurry on a metal foil and dry it to obtain a negative electrode sheet;

[0023] The mass ratio of the active material, electrolyte, conductive agent, and binder is 30-80:10-50:5-30:1-5.

[0024] The conductive agent can be a vapor-grown carbon nanofiber, the binder can be ethyl cellulose, and the organic solvent is anhydrous ethanol.

[0025] The present invention also provides a all-solid-state battery, including a lithium positive electrode sheet, electrolyte Li 6 PS 5 Cl, and a negative electrode sheet, and the negative electrode sheet includes the negative electrode sheet for a all-solid-state battery described above.

[0026] The present invention also provides an assembly method for a all-solid-state battery, including:

[0027] Place the electrode sheet in a mold;

[0028] Add an appropriate amount of electrolyte Li 6 PS 5 Cl on the electrode sheet, and press it under a pressure of 20 MPa for 1 minute to compact it;

[0029] Place a lithium positive electrode sheet above the electrolyte and compact it with a pressure of 1 MPa to form a three-layer structure battery cell; assemble the battery cell in a 2032-type button battery case for constant current charge and discharge testing. During the constant current charge and discharge testing, the battery operates without external pressure and only relies on the internal pressure of the battery.

[0030] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0031] (1) The preparation method of the present invention is simple, and an integrated multi-phase composite Si-based composite material of Si, LiF, and LiBO is prepared by one-step annealing. 2

[0032] (2) In the Si-based composite material prepared by the present invention, LiF and LiBO exhibit a unique synergistic effect. LiF with electrochemical stability and high Young's modulus can inhibit the decomposition of the Li 2 PS 6 5 Cl electrolyte and limit the volume effect of silicon, and LiBO 2 can make up for the lithium loss of silicon during charge and discharge.

[0033] (3) The structurally stable Si-based composite material prepared by the present invention exhibits a high initial Coulomb efficiency of 89.7% in all-solid-state lithium-ion batteries and can operate stably without external pressure. Description of the Drawings

[0034] Figure 1 XRD pattern of the F-Si powder prepared in Example 1.

[0035] Figure 2 TEM image of the F-Si powder prepared in Example 1.

[0036] Figure 3 First charge and discharge curve of the F-Si electrode prepared in Example 1.

[0037] Figure 4 Cycling performance of the F-Si electrode prepared in Example 1 at different current densities; among them, (a) is the cycling performance at a current density of 0.05 Ag -1 and (b) is the cycling performance at a current density of 0.1 A g -1 . Detailed Embodiments

[0038] The technical solutions of the present invention will be further described below with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0039] Example 1

[0040] Mix Si powder and LiBF4 The powders were mixed evenly at a molar ratio of 12:1 and then placed in a tube furnace. After annealing at 800 °C for 5 hours in an inert gas atmosphere, a Si-based composite material, named F-Si, was obtained.

[0041] The X-ray diffraction pattern and transmission electron microscope image of the F-Si powder are as Figure 1 and Figure 2 shown. Figure 1 The X-ray diffraction pattern indicates that the F-Si powder mainly consists of Si and LiF. Figure 2 The transmission electron microscope image further confirms the presence of Si and LiF, and it is also found that LiBO exists in the F-Si powder. 2 This indicates that the F-Si powder is composed of a three-phase composite of Si, LiF, and LiBO. 2

[0042] Active material F-Si, electrolyte Li 6 PS 5 Cl, conductive agent vapor-grown carbon nanofibers, and binder ethyl cellulose were weighed at a mass ratio of 40:40:15:5. A slurry was prepared using absolute ethanol as a solvent. The evenly mixed slurry was coated on a copper foil and dried to obtain a 12-mm negative electrode sheet.

[0043] The above-mentioned negative electrode sheet was placed in a mold, and about 120 mg of Li 6 PS 5 Cl electrolyte was added. It was compacted under a pressure of 20 MPa for 1 minute and then finally compacted again with a lithium sheet under a pressure of 1 MPa. The above-mentioned cold-pressed three-layer structure battery cell was taken out and assembled in a 2032-type button battery.

[0044] Example 2

[0045] Si powder and LiBF 4 powder were mixed evenly at a molar ratio of 12:1 and then placed in a tube furnace. After annealing at 1200 °C for 10 hours in an inert gas atmosphere, a Si-based composite material, named F-Si, was obtained.

[0046] Active material F-Si, electrolyte Li 6 PS 5 Cl, conductive agent vapor-grown carbon nanofibers, and binder ethyl cellulose were weighed at a mass ratio of 50:30:10:10. A slurry was prepared using absolute ethanol as a solvent. The evenly mixed slurry was coated on a copper foil and dried to obtain a 12-mm negative electrode sheet.

[0047] The above-mentioned negative electrode sheet was placed in a mold, and about 120 mg of Li 6 PS 5The Cl electrolyte was compacted under a pressure of 20 MPa for 1 minute, and finally a lithium sheet was placed and compacted again under a pressure of 1 MPa. The three-layer structure battery cell formed by the above cold pressing was taken out and assembled into a 2032-type button cell.

[0048] Example 3

[0049] The Si powder and LiBF 4 powder were mixed evenly at a molar ratio of 5:1 and placed in a tubular furnace. After annealing at 400 °C for 1 hour in an inert gas atmosphere, a Si-based composite material was obtained and named F-Si.

[0050] The active material F-Si, the electrolyte Li 6 PS 5 Cl, the conductive agent vapor-grown carbon nanofibers, and the binder ethyl cellulose were weighed at a mass ratio of 60:25:15:5, and a slurry was prepared using absolute ethanol as a solvent. The uniformly mixed slurry was coated on a copper foil and dried to obtain a 12-mm negative electrode sheet.

[0051] The above negative electrode sheet was placed in a mold, and about 120 mg of Li 6 PS 5 Cl electrolyte was added, compacted under a pressure of 20 MPa for 1 minute, and finally a lithium sheet was placed and compacted again under a pressure of 1 MPa. The three-layer structure battery cell formed by the above cold pressing was taken out and assembled into a 2032-type button cell.

[0052] Example 4

[0053] The Si powder and LiBF 4 powder were mixed evenly at a molar ratio of 20:1 and placed in a tubular furnace. After annealing at 1200 °C for 1 hour in an inert gas atmosphere, a Si-based composite material was obtained and named F-Si.

[0054] The active material F-Si, the electrolyte Li 6 PS 5 Cl, the conductive agent vapor-grown carbon nanofibers, and the binder ethyl cellulose were weighed at a mass ratio of 70:20:5:5, and a slurry was prepared using absolute ethanol as a solvent. The uniformly mixed slurry was coated on a copper foil and dried to obtain a 12-mm negative electrode sheet.

[0055] The above negative electrode sheet was placed in a mold, and about 120 mg of Li 6 PS 5 Cl electrolyte was added, compacted under a pressure of 20 MPa for 1 minute, and finally a lithium sheet was placed and compacted again under a pressure of 1 MPa. The three-layer structure battery cell formed by the above cold pressing was taken out and assembled into a 2032-type button cell.

[0056] Test Example 1

[0057] The first charge-discharge curve of the F-Si electrode prepared in Example 1 is as Figure 3 shown, and the test voltage range is 0.01 - 2 V, and the current density is 0.05 A g -1 . During the battery test, there is no external pressure, and only the internal pressure of the battery is relied on. The F-Si electrode shows a high first Coulomb efficiency of 89.7%, meeting the industrial requirements.

[0058] The cycling performance of the F-Si electrode prepared in Example 1 at different current densities is as Figure 4 shown, and the test voltage range is 0.01 - 2 V, and the current densities are (a) 0.05 A g -1 and (b) 0.1 A g -1 . During the battery test, there is no external pressure, and only the internal pressure of the battery is relied on. After cycling 50 times at a current density of 0.05 A g -1 , the reversible capacity of the F-Si electrode is as high as 1752 mA h g -1 . After cycling 120 times at a current density of 0.1 A g -1 , the reversible capacity is as high as 1087 mA h g -1 . This research gets rid of the dependence on external stacking pressure during the operation of Si-based all-solid-state batteries and realizes stable operation without external pressure.

[0059] Only the preferred implementation schemes of the present invention are listed above. The protection scope of the present invention is not limited thereto. Any changes made by those skilled in the art within the scope of the claims of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a silicon-based negative electrode material for an all-solid-state battery, characterized in that: The following steps are involved: (1) mixing silicon and lithium tetrafluoroborate in a certain proportion to obtain a mixture; (2) The mixture in step (1) is subjected to high temperature annealing treatment under the protection of an inert gas to obtain a silicon-based negative electrode material.

2. The method for preparing a silicon-based negative electrode material for an all-solid-state battery according to claim 1, characterized in that: In step (1), the molar ratio of silicon to lithium tetrafluoroborate is 5-20:

1.

3. The method for preparing a silicon-based negative electrode material for an all-solid-state battery according to claim 2, characterized in that: The molar ratio of silicon to lithium tetrafluoroborate is 12:

1.

4. The method for preparing a silicon-based negative electrode material for an all-solid-state battery according to claim 1, characterized in that: In step (2), the temperature of the high temperature annealing treatment is 400-1200° C., and the time of the high temperature annealing treatment is 1-10 hours.

5. The method for preparing a silicon-based negative electrode material for an all-solid-state battery according to claim 4, characterized in that: The temperature of the high temperature annealing treatment is 800° C., and the time of the high temperature annealing treatment is 5 hours.

6. The silicon-based negative electrode material prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the silicon-based negative electrode material according to claim 6 in an all-solid-state lithium-ion battery.

8. A negative electrode sheet for an all-solid-state battery, characterized in that: The negative electrode sheet comprises the silicon-based negative electrode material according to claim 6.

9. The method for preparing the negative electrode sheet for the all-solid-state battery according to claim 8, characterized in that: The following steps are involved: The silicon-based negative electrode material as an active material, the electrolyte Li6PS5Cl, the conductive agent and the binder are weighed in a certain proportion, dispersed in an organic solvent, and mixed to prepare a slurry; the slurry is coated on a metal foil, and dried to obtain a negative electrode sheet; The mass ratio of the active material, electrolyte, conductive agent and binder is 30-80:10-50:5-30:1-5.

10. An all-solid-state battery, comprising a lithium positive electrode sheet, an electrolyte Li6PS5Cl and a negative electrode sheet, characterized in that: The negative electrode sheet comprises the negative electrode sheet for the all-solid-state battery according to claim 8.

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