Crystal-pinned reinforced silicon materials, their preparation and applications in lithium-ion batteries

Abstract

This invention belongs to the field of battery anode materials, specifically relating to a crystal-pinned reinforced silicon material, which is a material in which at least one reinforcing unit selected from stacking dislocations, dislocations, twins, and moiré crystals is pinned within the silicon crystal. This invention also provides the preparation and application of the aforementioned material. The material described in this invention exhibits excellent structural stability and demonstrates superior cycling stability in bare silicon.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrode material technology, and in particular relates to a method for silicon anode materials. Background Technology

[0002] Lithium-ion batteries are among the most sought-after new energy devices in today's society. Due to escalating energy and environmental problems, as well as the rapid development of consumer electronics, electric vehicles, and large-scale energy storage, existing commercial lithium-ion batteries can no longer meet people's needs. Lithium-ion batteries mainly consist of a positive electrode, a negative electrode, a separator, and an electrolyte, with the positive and negative electrodes being the most critical. The positive electrode is limited by currently known materials, such as ternary materials, lithium cobalt oxide, and lithium iron phosphate, and significant breakthroughs are unlikely in the short term. However, alloy materials in the negative electrode, with their unique lithium intercalation mechanism, can achieve several times the theoretical capacity of currently commercial graphite negative electrodes. Silicon, as the alloy negative electrode material with the highest theoretical capacity, is particularly valuable in lithium intercalation. 22 The Si5 form boasts a capacity of 4200mAh / g, attracting significant attention.

[0003] However, silicon has a fatal flaw during charging and discharging: a huge volume effect (up to 300%). This can cause silicon to break down at some point during cycling, leading to pulverization of the negative electrode or even detachment from the current collector, resulting in a sharp drop in capacity. Therefore, improving the mechanical properties of silicon is particularly important. Traditional approaches include nano-sizing, porousing, buffer structure design, doping, and compositing with other materials. But essentially, these are all improvements based on silicon particles and do not address the root cause of the problem. Therefore, after so many years of development, silicon anodes have remained stagnant and unable to achieve true application.

[0004] Silicon has long been considered superior due to its amorphous structure and ability to isotropically conduct stress. However, this view is one-sided and limited by past technological and scientific understanding. The isotropic nature of amorphous silicon stems from its inherent internal disorder, which cannot be utilized or modified, necessitating external improvements. Crystal strengthening has long been a mature and stable material optimization technique in traditional materials science. Its limited application to lithium-ion battery silicon anode materials stems from earlier research showing that crystalline silicon becomes completely amorphous after the first cycle, negating the purpose of crystal structure modification and strengthening. However, our latest research reveals that silicon with different crystallinities and structures exhibits inconsistent performance during electrochemical cycling. While some silicon becomes completely amorphous, others retain unique crystal structures that provide pinning reinforcement. This intrinsic self-crystallization significantly enhances the micromechanical properties of silicon, thereby greatly improving the cycle performance of lithium-ion batteries without external force. The key challenge lies in the preparation of crystal-strengthened silicon materials. Achieving long-term cycling of bare silicon remains an industry-wide problem. Summary of the Invention

[0005] To address the problem of unsatisfactory electrochemical performance of existing silicon materials, the primary objective of this invention is to provide a special crystal pinned reinforced silicon material, which aims to improve the mechanical strength and long-cycle stability of elemental silicon.

[0006] The second objective of this invention is to provide a method for preparing the aforementioned crystal pinned reinforced silicon material, which aims to prepare a material with the special crystal strengthening characteristics and excellent electrochemical performance.

[0007] A third objective of this invention is to provide the application of the aforementioned crystal pinned reinforced silicon material in lithium-ion batteries.

[0008] A fourth objective of this invention is to provide a lithium-ion battery comprising the crystal pinned reinforced silicon material, and its negative electrode and negative electrode material.

[0009] Silicon has a complex and diverse crystal structure. During heat treatment, the injection of external heat energy makes silicon atoms more active, and as the heat treatment progresses, silicon atoms undergo thermal motion. How to control the thermal motion of silicon atoms in different silicon raw materials through heat treatment to achieve a specific strengthened crystal structure is a technical challenge. To address the problems of complex silicon raw materials, difficulty in controlling silicon atoms, difficulty in regulating crystal structure, and unsatisfactory electrochemical performance, this invention provides the following solutions:

[0010] Crystal pinned reinforced silicon material is a material in which at least one reinforcing unit selected from stacked faults, dislocations, twins, and moiré crystals is pinned in silicon crystal.

[0011] To improve the performance of elemental silicon anodes, the industry consensus is to use amorphous silicon or porous silicon. This invention overcomes this conventional view by innovatively providing a specially pinned-strength crystalline silicon material. It has been found that, compared to amorphous silicon and other types of crystalline silicon, this material overcomes the problems of poor mechanical properties, large cycle expansion, and unsatisfactory long-cycle stability of single-crystal silicon active materials, exhibiting excellent long-cycle stability, particularly excellent high-silicon surface-load long-cycle stability. This enables the use of bare silicon in lithium-ion battery systems.

[0012] In this invention, the crystallinity of the silicon crystal in the crystal pinned reinforced silicon material is 70-85%; the grain size is below 100 nm (more preferably below 20 nm, and even more preferably 4-20 nm); and the micro-stress within the crystal is 0.05-0.2%.

[0013] The present invention also provides a method for preparing the crystal pinned reinforced silicon material, wherein the silicon raw material (silicon elemental raw material) is mechanically homogenized to obtain pretreated silicon raw material; then it is heated to temperature T1 and held at that temperature for a first stage of heat treatment, and then heated to temperature T2 for a second stage of treatment to obtain the crystal pinned reinforced silicon material.

[0014] The temperature T1 is 450–650℃; the temperature T2 is 800–1300℃.

[0015] This invention innovatively homogenizes silicon and further combines it with a two-stage gradient heat treatment process and temperature control, which unexpectedly achieves special pinning reinforcement of elemental silicon materials. This unexpectedly solves the problems of poor mechanical strength and large cycling expansion of elemental silicon anode materials, and can improve their performance, especially their long-cycle stability under high silicon surface load.

[0016] In this invention, the silicon raw material is at least one of bulk silicon, powdered silicon, monocrystalline silicon, polycrystalline silicon, amorphous silicon, and metallurgical silicon.

[0017] The size of the silicon raw material is less than 5*5*5cm 3 Further preferred is an equivalent diameter of less than 100 μm.

[0018] Mechanical homogenization processes include ball milling, sand milling, or vibratory milling.

[0019] The rotational speed for mechanical homogenization is, for example, 200 r / min or higher, and further 300 to 500 r / min.

[0020] There are no special requirements for the time of mechanical homogenization treatment. For example, it can be more than 5 hours, or even 5 to 24 hours, or even 10 to 15 hours.

[0021] Furthermore, the mechanical homogenization described in this invention includes two mechanical homogenization processes, wherein the rotational speed of the first homogenization stage is 300-350 r / min; and the rotational speed of the second homogenization stage is 450-500 r / min. The duration of the first homogenization stage can be, for example, 5-10 hours, and the duration of the second homogenization stage can be, for example, 4-5 hours.

[0022] The medium for mechanical homogenization is one of air, argon, nitrogen, polyethylene glycol, or ethanol.

[0023] The particle size after mechanical homogenization is controlled between 100 nm and 20 μm; more preferably between 200 and 600 nm.

[0024] Preferably, the temperature of the mechanical homogenization process is controlled between 30 and 60°C.

[0025] In this invention, there are no special requirements for the heating rate v1 at the temperature T1 stage. For example, considering the preparation efficiency, it can be 5 to 20 °C / min.

[0026] In this invention, the temperature T1 is 500–630°C; further, 580–620°C; and even further, 590–610°C. In this invention, at the preferred temperature T1, better process synergy can be achieved, and the long-range stability of bare silicon can be further improved.

[0027] In this invention, the heat preservation time t1 at temperature T1 is 2 to 10 hours, further can be 3 to 6 hours, and even further can be 4 to 5 hours.

[0028] In this invention, there are no special requirements for the heating rate v2 at the stage of heating to temperature T2. For example, considering the preparation efficiency, it can be 0.5 to 20 °C / min, or even 1 to 5 °C / min.

[0029] The preferred temperature T2 is 1000℃~1200℃, and more preferably 1050~1150℃. In this invention, at the preferred temperature T2, better process synergy can be obtained, and the long-range stability of bare silicon can be further improved.

[0030] In this invention, the heat preservation time t2 at temperature T2 is 5 to 48 hours. Considering the preparation efficiency, it is further 15 to 30 hours, even further 18 to 24 hours, and even further 19 to 21 hours.

[0031] In this invention, the temperature rise stages T1 and T2, as well as the heat preservation stage, are carried out in a protective atmosphere.

[0032] Preferably, the protective gas is at least one selected from nitrogen, argon, helium, carbon dioxide, and hydrogen.

[0033] Preferably, the flow rate of the protective gas is 0.01 to 1 L / min.

[0034] In this invention, the temperature rise and holding stages T1 and T2 are carried out under negative pressure. This invention also demonstrates that, under the combined control of mechanical homogenization strengthening, two-stage gradient heat treatment, and temperature, further control of negative pressure can unexpectedly enhance the induction of the pinned strengthening structure, thereby further improving the material's mechanical strength and long-cycle stability under high surface loads.

[0035] In this invention, the negative pressure is below 0.5 atm, and more specifically below 100 Pa.

[0036] After holding at temperature T2, the material is cooled and collected to obtain the crystal pinned reinforced silicon material.

[0037] In this invention, the rapid cooling method is furnace-in-furnace cooling, or, considering cooling efficiency and effect, the cooling method can be cooling medium-assisted cooling. Cooling medium-assisted cooling refers to the step of using a cooling medium in contact with the outer wall of the second-stage insulated reaction tube for auxiliary cooling. The contact between the cooling medium and the outer wall can be achieved through spraying or an insulating sleeve.

[0038] The cooling medium includes at least one of liquid nitrogen, dry ice, cold air, and cooling brine.

[0039] In this invention, the cooling rate is above 5°C / min, and considering the preparation efficiency and effect, it can be further increased to 5-500°C / min.

[0040] In this invention, considering the preparation efficiency and effect, the time to cool to room temperature (meaning the temperature is reduced to a level where the material can be discharged and operated, for example, 15 to 50°C) can be 0.5 to 5 hours.

[0041] The present invention also provides an application of the crystal pinned reinforced silicon material described above, using it as a negative electrode active material for the preparation of alkali metal ion batteries, preferably lithium ion batteries.

[0042] In this invention, the crystal pinned reinforced silicon material described herein can be used as a negative electrode active material by means of conventional methods and approaches to prepare the desired battery, such as a lithium-ion battery.

[0043] The present invention also provides a negative electrode material for a lithium-ion battery, including a negative electrode active material, wherein the negative electrode active material comprises the crystal pinned reinforced silicon material.

[0044] In this invention, the content of the crystal pinned reinforced silicon material in the negative electrode active material can be adjusted as needed. However, in order to further enhance the performance of the material, its content can be above 50 wt.%, and more specifically above 80 wt.%.

[0045] In this invention, the negative electrode material further includes at least one of a binder and a conductive agent.

[0046] In the aforementioned negative electrode material, the content of the active material is above 70 wt.%, further to 75-95 wt.%, and even further to 80-90 wt.%.

[0047] The present invention also provides a negative electrode for a lithium-ion battery, comprising a current collector and a negative electrode material composited on its surface, wherein the negative electrode material is the aforementioned negative electrode material.

[0048] In this invention, the isal load of silicon in the negative electrode is not particularly required and can be controlled as needed. However, considering the structural and stability advantages of the active material described in this invention, it is particularly suitable for preparing negative electrodes with high isal load. For example, the isal load of silicon in the negative electrode can be 0.5 mg / cm³. 2 The above can be further reduced to 1–1.5 mg / cm³. 2 .

[0049] The present invention also provides a lithium-ion battery comprising the aforementioned negative electrode.

[0050] The lithium-ion battery and its negative electrode and negative electrode material described in this invention, except for the crystal pinned reinforced silicon material described in this invention, can have other conventional components and parts.

[0051] Beneficial effects

[0052] This invention provides a novel crystalline silicon material with enhanced crystal characteristics, and further discovers that it overcomes the conventional understanding of elemental silicon anode materials in the industry, and can unexpectedly exhibit excellent mechanical strength and stability, as well as excellent long-cycle stability, especially exhibiting excellent long-cycle stability of bare silicon under high surface load.

[0053] Silicon materials suffer from problems such as large volume changes during charge and discharge, easy pulverization and detachment from the current collector, precipitous degradation during electrochemical cycling, and difficulty in fundamentally improving their performance. To address these obstacles hindering the practical application of silicon materials and further improve their performance, this invention innovatively employs the aforementioned pre-grinding process, combined with a step-by-step two-stage heat treatment that precisely controls the thermal motion of silicon atoms. This achieves uniform and reliable crystal structure strengthening, resulting in a silicon anode material with uniform particle size and morphology, excellent micromechanical properties, and outstanding electrochemical performance. This material can achieve stable electrochemical cycling without the intervention of any additional phases.

[0054] The silicon material prepared by this invention exhibits a regularly stable pinned strong defect structure in its crystal structure, which facilitates pinning reinforcement within the microstructure. This fundamentally improves the material's mechanical properties, enabling it to remain unaffected by large volume changes during electrochemical cycling. It achieves ultra-stable electrochemical lithium insertion and extraction without the intervention of any external materials, capabilities not found in existing technologies. Furthermore, this invention demonstrates that the pinning reinforcement structure can be further induced under the aforementioned two-stage negative pressure heat treatment, further enhancing the material's mechanical properties and high silicon surface load long-cycle stability. Attached Figure Description

[0055] Appendix Figure 1 This is a SEM image of the high-performance lithium-ion battery crystal-reinforced silicon anode material prepared in Example 1.

[0056] Appendix Figure 2 The image shows an HRTEM image of the high-performance lithium-ion battery crystal-reinforced silicon anode material prepared in Example 1.

[0057] Appendix Figure 3 The image shows the HRTEM image of the material prepared in Comparative Example 3.

[0058] Appendix Figure 4 The image shows the HRTEM image of the material prepared in Comparative Example 4. Detailed Implementation

[0059] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0060] Example 1

[0061] ① Take 20g of silicon powder (silicon raw material) with a size of 1-10μm and argon gas and seal them in a ball mill jar at a volume ratio of 1:2;

[0062] ② The ball mill jar from step ① is subjected to mechanical homogenization and strengthening in a planetary ball mill. The first stage of mechanical homogenization and strengthening has a rotation speed of 350 r / min and a time of 5 h, and the second stage has a rotation speed of 450 r / min and a time of 5 h. The temperature throughout the process is 35℃, and homogenized silicon powder is obtained.

[0063] ③ The homogenized silicon powder obtained in step ② is loaded into an alumina crucible with a filling capacity of 75%. Then, it is placed in the heating chamber of a tube furnace and an argon atmosphere with a flow rate of 0.1 L / min is introduced into the tube furnace to purge the air. After the air is purged, a two-stage heat treatment is performed. The first stage heat treatment is performed by heating to 500℃ (marked as T1) at a rate of 10℃ / min (marked as v1) and holding for 5 hours (marked as t1). After the holding is completed, the second stage heat treatment is started by heating to 1200℃ (marked as T2) at a rate of 2℃ / min (marked as v2) and holding for 24 hours (marked as t2).

[0064] ④ After the second stage of heat treatment and holding in step ③ is completed, the tubular high-temperature furnace is closed, and while argon gas continues to flow in, dry ice is sprayed to cool the outer wall of the heating tube. After cooling to room temperature (cooling time to room temperature is 1±0.1h), the tubular high-temperature furnace is opened and the corundum crucible is removed to obtain high-performance crystal-reinforced silicon anode material for lithium-ion batteries; SEM and HRTEM results are shown in [reference needed]. Figure 1 and 2 From the appendix Figure 1 It can be seen that the high-performance lithium-ion battery crystal-reinforced silicon anode material prepared in Example 1 of this invention has a uniform morphology and a size of 0.2–2 μm; (The last part, "from the attached...", appears to be a fragment and doesn't translate directly.) Figure 2 It can be seen that the crystal-strengthened silicon anode material obtained after processing in Example 1 of the present invention has abundant defects.

[0065] The obtained high-performance crystal-reinforced silicon anode material has a uniform morphology, with abundant stacked fault reinforcement structures pinned inside the crystal, and a grain size of 10–50 nm; a crystallinity of 76%; and a microstress of 0.08% within the crystal.

[0066] The electrochemical performance of this material was tested using a 2032-type lithium half-cell:

[0067] Using Super P as the conductive agent, sodium alginate as the binder, and deionized water as the solvent, a slurry was prepared according to a mass ratio of active material to conductive agent to binder of silicon anode material of 8:1:1. This slurry was then uniformly coated onto copper foil to achieve a surface cross-section of 1.0 mg / cm². 2 After drying, the electrodes are punched and cut into plates, and then assembled into 2032 coin cells with lithium plates as the counter electrode. The electrolyte is a silicon-based negative electrode electrolyte (1 mol / L LiPF6, EC:DEC = 1:1, 10% FEC), and the separator is made of PP / PE / PP material.

[0068] The half-cell was charged and discharged using a CT2001A battery testing system manufactured by Wuhan Landian Electronics Co., Ltd. The test range was 0.01V to 1.2V, and the test temperature was 25℃.

[0069] After being assembled into a half-cell, the initial coulombic efficiency at 0.2C charge-discharge was 85.2%, and the reversible capacity after 500 cycles was 2050.1 mAh / g. After disassembly, the electrode structure was intact, without pulverization or cracking, and the electrode material was in close contact with the current collector.

[0070] Example 2

[0071] Compared to Example 1, the only difference is the change in silicon raw materials and mechanical homogenization conditions. The experimental groups are as follows:

[0072] Group A: The silicon raw material used was bulk metallurgical silicon, and all other conditions were the same as in Example 1;

[0073] Group B: The first stage of mechanical homogenization strengthening was carried out at a rotation speed of 300 r / min for 8 h, and the second stage was carried out at a rotation speed of 500 r / min for 4 h. The temperature throughout the process was 30℃, and all other conditions were the same as in Example 1.

[0074] Group C: Mechanical homogenization method: high-energy vibration mill mechanical homogenization enhancement, all other conditions are the same as in Example 1;

[0075] Group D: Single-segment homogenization method is adopted, that is, the rotation speed of the first segment and the rotation speed of the second segment are the same, both 450 r / min; other operations and parameters are the same as in Example 1;

[0076] The test was conducted according to the method in Example 1, and the results are as follows:

[0077] Group A: The obtained materials have a particle size of 10-25 μm and uniform morphology. After being assembled into a half-cell, the initial coulombic efficiency at 0.2C charge-discharge is 88.5%, and the reversible capacity after 500 cycles is 1820.5 mAh / g. After disassembly, the electrode structure is intact, without pulverization or cracking, and the electrode material is in close contact with the current collector.

[0078] Group B: The obtained materials have a particle size of 1-10 μm and uniform morphology. After being assembled into a half-cell, the initial coulombic efficiency at 0.2C charge-discharge is 86.3%, and the reversible capacity after 500 cycles is 2006.5 mAh / g. After disassembly, the electrode structure is intact, without pulverization or cracking, and the electrode material is in close contact with the current collector.

[0079] Group C: The obtained materials have a particle size of 0.7-8μm and uniform morphology. After being assembled into a half-cell, the initial coulombic efficiency at 0.2C charge and discharge is 85.9%, and the reversible capacity after 500 cycles is 2088.3mAh / g. After disassembly, the electrode structure is intact, without pulverization or cracking, and the electrode material is in close contact with the current collector.

[0080] Group D: The obtained materials, when assembled into a half-cell, have an initial coulombic efficiency of 84.7% at 0.2C charge-discharge, and a reversible capacity of 2008.6 mAh / g after 500 cycles. After disassembly, the electrode structure is intact, without pulverization or cracking, and the electrode material is in close contact with the current collector.

[0081] As can be seen from Examples 1 and 2, the method of the present invention does not have special requirements for elemental silicon raw materials. Even if low-value-added elemental silicon is used, it can still obtain ideal long-cycle capability of bare silicon. In addition, the two-stage gradient homogenization method can be further combined with the process of the present invention to further enhance the twill structure of the material and further enhance its long-cycle stability of bare silicon.

[0082] Example 3

[0083] Compared to Example 1, the only difference is that the key condition ranges for the two heat treatment stages are changed, for example:

[0084] Group A: v1 / T1 was changed to 5℃ / min / 600℃ and t1 to 4h; v2 / T2 was changed to 2℃ / min / 1000℃ and t2 to 24h, and all other conditions were the same as in Example 1;

[0085] Group B: Change v1 / T1 to 20℃ / min / 600℃ and t1 to 5h; v2 / T2 to 5℃ / min / 1100℃ and t2 to 20h, and keep all other conditions the same as in Example 1;

[0086] The test was conducted according to the method in Example 1, and the results are as follows:

[0087] Group A: The obtained material has a particle size of 0.5-5 μm, uniform morphology, and abundant twins, moiré crystals, and stacking fault reinforcement structures pinned inside the crystal. The size is 10-15 nm. After being assembled into a half cell, the initial coulombic efficiency at 0.2C charge and discharge is 86.5%, and the reversible capacity after 500 cycles is 2424.2 mAh / g. After disassembly, the electrode structure is intact, without pulverization or cracking, and the electrode material has tight current-current contact with the current collector.

[0088] Group B: The obtained materials have a particle size of 0.5-5 μm, uniform morphology, and abundant twins, moiré crystals, and stacking fault reinforcement structures pinned inside the crystals. The size is 5-12 nm. After being assembled into a half cell, the initial coulombic efficiency at 0.2C charge and discharge is 88.2%, and the reversible capacity after 500 cycles is 2523.2 mAh / g. After disassembly, the electrode structure is intact, without pulverization or cracking, and the electrode material is in close contact with the current collector.

[0089] As can be seen from Examples 1 and 3, controlling the temperature of T1 at 590–610°C and the temperature of T2 at 1050–1150°C can further strengthen the crystal pinning structure and further improve the long-cycle stability of the prepared bare silicon.

[0090] Example 4

[0091] The heating and holding stages (T1 and T2) were conducted under a negative pressure below 50 Pa. The experimental groups were as follows:

[0092] Group A: Compared with Example 1, the only difference is that the heating and holding stages T1 and T2 are carried out under a negative pressure of less than 50 Pa. All other operations and parameters are the same as in Example 1.

[0093] Group B: Compared with Example 3B, the only difference is that the heating and holding stages T1 and T2 are carried out under a negative pressure of less than 50 Pa. All other operations and parameters are the same as in Example 1.

[0094] The test was conducted according to the method in Example 1, and the results are as follows:

[0095] Group A: The obtained materials have a particle size of 0.5-5 μm, uniform morphology, and a specific stacking fault reinforcement structure pinned inside the crystals, with a size of 15-30 nm. After being assembled into a half-cell, the initial coulombic efficiency at 0.2C charge and discharge is 84.6%, and the reversible capacity after 500 cycles is 2263.5 mAh / g. After disassembly, the electrode structure is intact, without pulverization or cracking, and the electrode material is in close contact with the current collector.

[0096] Group B: The obtained material has a particle size of 0.5-5 μm, uniform morphology, and abundant twins, moiré crystals, and stacking fault reinforcement structures pinned inside the crystal. The size is 5-10 nm. After being assembled into a half cell, the initial coulombic efficiency at 0.2C charge and discharge is 88.7%, and the reversible capacity after 500 cycles is 2563.1 mAh / g. After disassembly, the electrode structure is intact, without pulverization or cracking, and the electrode material has tight current-current contact with the current collector.

[0097] As can be seen from Examples 1, 3 and 4, performing the two-stage treatment under the negative pressure can further induce the crystal pinning reinforcement structure, which can further improve the long-cycle stability of bare silicon under high surface load.

[0098] Example 5

[0099] Compared with Example 1, the only difference is that the cooling method is furnace cooling (cooling time to room temperature is 5±0.3h), and all other operations and parameters are the same as in Example 1.

[0100] The test was conducted according to the method in Example 1, and the results were as follows: The obtained material has a particle size of 0.5-5 μm, uniform morphology, and internal crystals with stacked faults, dislocations, and twin reinforcement structures. The size is 5-10 nm. After being assembled into a half-cell, the initial coulombic efficiency at 0.2C charge and discharge is 83.2%, and the reversible capacity after 500 cycles is 1998.6 mAh / g. After disassembly, the electrode structure is intact, without pulverization or cracking, and the electrode material is in close contact with the current collector.

[0101] Example 6

[0102] Compared to Example 1, the only difference is that the mass ratio of silicon anode material in the battery is 90 wt.% (mass ratio of silicon anode material active material: conductive agent: binder = 9:0.5:0.5), and the areal load reaches 1.2 mg / cm². 2 Other operations and parameters are the same as in Example 1.

[0103] The test was conducted according to the method in Example 1. The results were as follows: after being assembled into a half-cell, the initial coulombic efficiency at 0.2C charge and discharge was 81.3%, and the reversible capacity after 500 cycles was 1785.6 mAh / g. After disassembly, the electrode structure was intact, without pulverization or cracking, and the electrode material was in close contact with the current collector.

[0104] As can be seen from Examples 1 and 6, the crystal-strengthened material of the present invention can still exhibit excellent bare silicon stability under high surface loading.

[0105] Comparative Example 1

[0106] Compared with Example 1, the only difference is that the silicon raw material was not subjected to the mechanical homogenization treatment in steps ① and ②, but was directly subjected to the treatment in steps ③ and ④.

[0107] The resulting material has an uneven morphology and inconsistent particle size. The crystal contains a few reinforcing structures such as dislocations pinned inside, with a size of 1-5 nm. When assembled into a half-cell according to the method in Example 1, the initial coulombic efficiency at 0.2C charge and discharge is 79.9%, and the reversible capacity after 500 cycles is 1206.4 mAh / g.

[0108] Comparative Example 2

[0109] Compared with Example 1, the only difference is that steps ③ and ④ were not performed. Instead, the ground material was used as an active material and its electrochemical performance was directly tested.

[0110] The obtained material, without a crystal-strengthened structure, exhibited a first coulombic efficiency of 75.2% after being assembled into a half-cell according to the method in Example 1, and a reversible capacity of 500.8 mAh / g after 500 cycles.

[0111] Comparative Example 3

[0112] Compared to Example 1, the only difference is that in step ③, the heat treatment is performed in a single stage (T1). After T1, no further heating is performed; the temperature is maintained at t2. That is, the temperature of T2 is the same as that of T1. Everything else is exactly the same as in Example 1. (Appendix) Figure 3 The image shows an HRTEM image of the material prepared in Comparative Example 3. (From Appendix) Figure 3 It can be seen that the material obtained in Comparative Example 3 of the present invention has no crystal structure.

[0113] The obtained material has no internal crystalline strengthening structure, as shown in the attached figure. Figure 3 As shown, after assembling the half-cell according to the method of Example 1, the first coulombic efficiency at 0.2C charge and discharge was 81.6%, and the reversible capacity after 100 cycles was 532.4 mAh / g.

[0114] Comparative Example 4

[0115] Compared with Example 1, the only difference is that in step ③, a single-stage T2 heat treatment is performed, that is, the homogenized silicon powder is directly heated to T1, and the temperature of T1 is the same as that of T2. Everything else is the same as in Example 1.

[0116] Appendix Figure 4 The image shows the HRTEM image of the material prepared in Comparative Example 4.

[0117] From the appendix Figure 4 It can be seen that the material obtained in Comparative Example 4 of this invention has some disordered defects.

[0118] The obtained material has some internal defects and irregularities, as shown in the attached document. Figure 4 As shown, after assembling a half-cell according to the method of Example 1, the initial coulombic efficiency at 0.2C charge and discharge was 76.3%, and the reversible capacity after 200 cycles was only 253.4 mAh / g.

[0119] Comparative Example 5

[0120] Compared with Example 1, the only difference is that the temperature in step ③ is not within the range required by the present invention, that is, T1 is controlled at 200℃ and T2 is 700℃; everything else is exactly the same as Example 1.

[0121] After being assembled into a half-cell according to the method in Example 1, the initial coulombic efficiency at 0.2C charge-discharge was 72.3%, and the reversible capacity after 100 cycles was 785.4 mAh / g.

[0122] Comparative Example 6

[0123] Compared with Example 1, the only difference is that the temperature in step ③ is not within the range required by the present invention, that is, T1 is controlled at 200℃ and T2 is 1000℃; everything else is exactly the same as Example 1.

[0124] After being assembled into a half-cell according to the method in Example 1, the initial coulombic efficiency at 0.2C charge-discharge was 76.5%, and the reversible capacity after 200 cycles was 1106.3 mAh / g.

[0125] Comparative Example 7

[0126] Compared with Example 1, the only difference is that the temperature in step ③ is not within the range required by the present invention, that is, T1 is controlled at 500℃ and T2 is 750℃; otherwise, it is exactly the same as Example 1.

[0127] After being assembled into a half-cell according to the method in Example 1, the initial coulombic efficiency at 0.2C charge-discharge was 68.6%, and the reversible capacity after 100 cycles was 865.3 mAh / g.

Claims

1. A crystal-pinned reinforced silicon material, characterized in that, A material used as a negative electrode active material having at least one reinforcing unit selected from stacked faults, dislocations, twins, and moiré crystals pinned in a silicon crystal; The crystallinity of silicon crystals is 70-85%; the grain size is less than 100 nm; and the micro-stress within the crystal is 0.05-0.2%.

2. A method for preparing the crystal pinned reinforced silicon material according to claim 1, characterized in that, The silicon raw material is mechanically homogenized to obtain pretreated silicon raw material; then it is heated to temperature T1 and held at that temperature for the first stage of heat treatment, and then heated to temperature T2 for the second stage of treatment to obtain the crystal pinned reinforced silicon material. The temperature T1 is 450~650℃; the temperature T2 is 800~1300℃.

3. The method for preparing crystal-pinned reinforced silicon material as described in claim 2, characterized in that, The silicon raw material is at least one of bulk silicon, powdered silicon, monocrystalline silicon, polycrystalline silicon, amorphous silicon, and metallurgical silicon.

4. The method for preparing crystal-pinned reinforced silicon material as described in claim 3, characterized in that, The size of the silicon raw material is less than 5×5×5cm 3 .

5. The method for preparing crystal-pinned reinforced silicon material as described in claim 4, characterized in that, The equivalent diameter of silicon raw materials is less than 100 μm.

6. The method for preparing crystal-pinned reinforced silicon material as described in claim 2, characterized in that, Mechanical homogenization processes include ball milling, sand milling, or vibratory milling.

7. The method for preparing crystal-pinned reinforced silicon material as described in claim 6, characterized in that, The rotation speed for mechanical homogenization is above 200 r / min.

8. The method for preparing crystal-pinned reinforced silicon material as described in claim 7, characterized in that, The rotation speed for mechanical homogenization is 300~500 r / min.

9. The method for preparing crystal-pinned reinforced silicon material as described in claim 2, characterized in that, The mechanical homogenization process takes 5 to 24 hours.

10. The method for preparing crystal-pinned reinforced silicon material as described in claim 2, characterized in that, Mechanical homogenization consists of two stages: the rotation speed in the first stage is 300-350 r / min, and the rotation speed in the second stage is 450-500 r / min.

11. The method for preparing crystal-pinned reinforced silicon material as described in claim 10, characterized in that, The first homogenization stage lasts 5-10 hours, and the second homogenization stage lasts 4-5 hours.

12. The method for preparing crystal-pinned reinforced silicon material as described in claim 2, characterized in that, The medium for mechanical homogenization is one of air, argon, nitrogen, polyethylene glycol, or ethanol.

13. The method for preparing crystal-pinned reinforced silicon material as described in claim 2, characterized in that, The particle size after mechanical homogenization is controlled between 100 nm and 20 μm.

14. The method for preparing crystal-pinned reinforced silicon material as described in claim 13, characterized in that, The particle size after mechanical homogenization is 200~600nm.

15. The method for preparing crystal-pinned reinforced silicon material as described in claim 2, characterized in that, The temperature for mechanical homogenization is controlled at 30~60℃.

16. The method for preparing crystal-pinned reinforced silicon material as described in claim 2, characterized in that, The heating rate v1 at the stage of heating to temperature T1 is 5~20℃ / min.

17. The method for preparing crystal-pinned reinforced silicon material as described in claim 2, characterized in that, The heat preservation time t1 at temperature T1 is 2~10h.

18. The method for preparing crystal-pinned reinforced silicon material as described in claim 2, characterized in that, The heating rate v2 during the stage of heating to temperature T2 is 0.5~20℃ / min.

19. The method for preparing crystal-pinned reinforced silicon material as described in claim 2, characterized in that, The heat preservation time t2 at temperature T2 is 5~48h.

20. The method for preparing crystal-pinned reinforced silicon material as described in claim 2, characterized in that, The temperature rise and hold phases (T1, T2) are carried out in a protective atmosphere.

21. The method for preparing crystal-pinned reinforced silicon material as described in claim 20, characterized in that, The protective gas in the protective atmosphere is at least one of nitrogen, argon, helium, carbon dioxide, and hydrogen.

22. The method for preparing crystal-pinned reinforced silicon material as described in claim 20, characterized in that, The flow rate of the protective gas is 0.01~1L / min.

23. The method for preparing crystal-pinned reinforced silicon material according to any one of claims 2 to 22, characterized in that, The temperature rise and hold phases (T1, T2) are carried out under negative pressure.

24. The method for preparing crystal-pinned reinforced silicon material as described in claim 23, characterized in that, The negative pressure is below 0.5 atm.

25. The method for preparing crystal-pinned reinforced silicon material as described in claim 24, characterized in that, The negative pressure is below 100 Pa.

26. The method for preparing crystal-pinned reinforced silicon material according to any one of claims 2 to 25, characterized in that, After holding at temperature T2, the material is cooled and collected to obtain the crystal pinned reinforced silicon material.

27. The method for preparing crystal-pinned reinforced silicon material as described in claim 26, characterized in that, The cooling process is either furnace-assisted cooling or cooling with a cooling medium; the cooling medium includes at least one of liquid nitrogen, dry ice, cold air, and cooling brine.

28. The method for preparing crystal-pinned reinforced silicon material as described in claim 27, characterized in that, The cooling rate is above 5°C / min.

29. The application of the crystal pinned reinforced silicon material according to claim 1 or the crystal pinned reinforced silicon material prepared by the preparation method according to any one of claims 2 to 28, characterized in that, It is used as a negative electrode active material in the preparation of alkali metal ion batteries.

30. The application as described in claim 29, characterized in that, Alkali metal ion batteries are lithium-ion batteries.

31. A negative electrode material for a lithium-ion battery, comprising a negative electrode active material, characterized in that, The negative electrode active material comprises the crystal pinned reinforced silicon material according to claim 1 or the crystal pinned reinforced silicon material prepared by the preparation method according to any one of claims 2 to 28.

32. The negative electrode material of the lithium-ion battery as described in claim 31, characterized in that, In the aforementioned negative electrode active material, the content of the crystal pinned reinforced silicon material is above 50 wt.%.

33. The negative electrode material of the lithium-ion battery as described in claim 31, characterized in that, The negative electrode material also includes at least one of a binder and a conductive agent.

34. A negative electrode for a lithium-ion battery, comprising a current collector and a negative electrode material composited on its surface, characterized in that, The negative electrode material is the negative electrode material according to any one of claims 31 to 33.

35. A lithium-ion battery, characterized in that, It includes the negative electrode as described in claim 34.

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