SiO@C Modified Active Materials and Their Preparation and Application

Abstract

This invention belongs to the field of battery materials, specifically relating to a SiO@C modification method. The method involves mixing SiO@C and a synergistic modifier, subjecting them to a two-stage calcination process under varying pressure, followed by acid treatment to obtain the SiO@C modified active material. The synergistic modifier includes component A and component B. Component A is at least one of magnesium hydride and Mg; component B is at least one of LiH, Li, Li₂O, lithium carbonate, lithium dihydrogen phosphate, lithium borate, and lithium salicylate. The two-stage calcination process includes a first-stage calcination under high negative pressure and a second-stage calcination under low negative pressure. The first-stage calcination temperature is 350-500℃, and the pressure is less than or equal to 0.1 Pa; the second-stage calcination temperature is 800-900℃, and the pressure is greater than 1 Pa and less than or equal to 100 kPa. This invention also includes the material obtained by the above preparation method and its application in lithium secondary batteries. The method described in this invention can significantly improve the initial efficiency and high-temperature cycling performance of the SiO@C modified material.

Description

Technical Field

[0001] This invention belongs to the field of battery material technology, specifically relating to a negative electrode material. Background Technology

[0002] Silicon suboxide is a novel high-energy-density anode material for lithium-ion batteries, with an initial capacity reaching 1600 mAh / g, approximately 4.5 times that of currently commercially available graphite anodes (350 mAh / g). Adding silicon suboxide to graphite anodes is a common method for improving battery energy density. Furthermore, adding high-energy-density silicon suboxide allows for thinner anode layers, thus improving battery charging capabilities. Therefore, the addition of silicon suboxide is an important approach to preparing high-energy-density lithium-ion batteries with fast-charging performance. Tesla vehicles, internationally renowned for their batteries, incorporate a certain amount of silicon suboxide to achieve their superior battery performance.

[0003] Although silicon suboxide possesses excellent electrochemical properties, its significantly low initial coulombic efficiency limits its larger-scale application. Silicon suboxide has the molecular formula SiO, and due to its unstable structure, it readily decomposes into Si and SiO2. Therefore, its interior can be considered as a mixture of silicon-rich and oxygen-rich microregions. During the initial lithium insertion, Li... + It will react with oxygen-rich regions to form silicates such as Li₂SiO₃, Li₄SiO₄, and Li₂Si₂O₅. Since most silicate reactions are irreversible, a large amount of Li will be consumed. + This results in a severely low initial coulombic efficiency. Currently, commercially available silicon suboxide with carbon coating only achieves an initial efficiency of 74-77%, far lower than that of graphite anodes (92-95%). This leads to the consumption of available Li in the cathode during full cell operation. + This results in a loss of capacity. Because of this issue, the amount of silicon suboxide added to power batteries is generally less than 10%, severely limiting further improvements in battery energy density.

[0004] To address these issues, direct lithium supplementation of the material or electrode lithium supplementation is generally employed. Currently, direct lithium supplementation of the material can improve the initial efficiency of silicon suboxide to 85-88%, but the resulting material is highly alkaline, leading to poor processing performance when used as a slurry and preventing direct commercial use. While electrode lithium supplementation can also improve initial efficiency, its manufacturing cost is extremely high, and safety is difficult to guarantee, making direct commercialization currently challenging. Summary of the Invention

[0005] To address the issues of low initial efficiency and unsatisfactory electrochemical performance of SiO@C, the primary objective of this invention is to provide a SiO@C modification method, which aims to modify the material to obtain a negative electrode active material with excellent initial efficiency and cycle performance.

[0006] The second objective of this invention is to provide a SiO@C modified active material prepared by the aforementioned method.

[0007] The third objective of this invention is to provide the application of the SiO@C modified active material prepared by the aforementioned method in lithium secondary batteries.

[0008] The fourth objective of this invention is to provide a lithium secondary battery comprising the SiO@C modified active material prepared by the aforementioned method, as well as its negative electrode and negative electrode material.

[0009] To address the issues of unsatisfactory initial performance and overall properties of SiO@C materials, this invention provides the following modification method, specifically:

[0010] A method for modifying SiO@C involves mixing SiO@C and a synergistic modifier, subjecting the mixture to a two-stage calcination process under variable pressure, followed by acid treatment, to obtain the SiO@C modified active material.

[0011] The synergistic modifier includes component A and component B; wherein component A is at least one of magnesium hydride and Mg; and component B is at least one of LiH, Li, Li2O, lithium carbonate, lithium dihydrogen phosphate, and lithium salicylate.

[0012] The aforementioned two-stage calcination process includes a first-stage calcination under high negative pressure and a second-stage calcination under low negative pressure; wherein, the temperature of the first-stage calcination is 350-500℃ and the pressure is less than or equal to 0.1 Pa; the temperature of the second-stage calcination is 800-900℃ and the pressure is greater than or equal to 1 Pa and less than or equal to 100 kPa.

[0013] In this invention, SiO@C is innovatively calcined in a combined modifier, and further combined with a gradient negative pressure two-stage calcination-acid treatment process and parameters. This achieves synergy, enabling the construction of a suitable physical structure and chemical properties for lithium-ion storage and intercalation-deintercalation, reducing oxygen content, and synergistically improving first-efficiency and electrochemical performance, especially significantly improving electrochemical performance under extreme conditions such as high temperature.

[0014] In this invention, the carbon-coated structure of SiO@C is utilized, combined with the calcination treatment of the co-modifier in the same system, and further combined with the special gradient negative pressure and temperature gradient control, so as to realize the gas-solid-liquid three-phase physicochemical transformation of component A and component B in a synergistic system under carbon isolation. This can unexpectedly synergistically improve the initial efficiency and comprehensive electrochemical performance of the prepared material.

[0015] In this invention, carbon-coated silicon suboxide, combined with subsequent innovative modification methods, can utilize the confinement effect of the carbon shell to further synergistically improve the physicochemical modification effect, reduce oxygen content and residual alkali, and further improve the first-efficiency and electrochemical performance of the modified material.

[0016] In this invention, the SiO@C can be a commercial product or can be prepared using existing methods. For example, in this invention, the D50 of the SiO@C particles is 3-7 micrometers, and the carbon content is 3.5-6.5%.

[0017] In this invention, the combination of the synergistic modifiers within the same system is key to synergistically improving the physicochemical modification effect of SiO@C, adapting it to lithium-ion requirements, and improving its initial efficiency and electrochemical performance.

[0018] Preferably, in the synergistic modifier, component A is magnesium hydride and component B is LiH. Research unexpectedly revealed that the preferred combination of components A and B can achieve a superior synergistic effect, and when combined with gradient negative pressure technology, can further enhance the performance of SiO@C modified materials.

[0019] Preferably, the molar ratio of SiO@C, component A, and component B is 1:0.8-1.05:0.1-0.5; more preferably, it is 1:0.9-1:0.3-0.4.

[0020] In this invention, under the combined effect of the carbon coating structure of SiO@C and the synergistic modifier, and further combined with the gradient negative pressure technology, the gas-solid-liquid three-phase modification is carried out in advance under negative pressure, and then the pressure is changed to low negative pressure. This helps to further promote the chemical transformation and microstructure construction of lithium ion adaptation, thereby synergistically improving the first efficiency and integrated electrochemical performance.

[0021] As a preferred option, in the two-stage variable pressure roasting process, the negative pressure of the first stage of roasting is 0.001 to 0.1 Pa. Considering the processing cost and effect, it is preferably 0.01 to 0.1 Pa; more preferably 0.05 to 0.1 Pa.

[0022] Preferably, the pressure during the second roasting process is 1 to 20 Pa, and more preferably 2 to 4 Pa.

[0023] In this invention, the combined use of gradient negative pressure and temperature control helps to synergistically regulate the physicochemical properties of lithium ions, thereby improving initial efficiency and overall electrochemical performance.

[0024] The temperature for the first stage of roasting is 400–450℃.

[0025] Preferably, the roasting time for the first stage is 1 to 3 hours;

[0026] The second stage of roasting is carried out at a temperature of 800–850℃.

[0027] Preferably, the second stage of roasting takes 1 to 3 hours;

[0028] Preferably, the acid solution in the acid treatment stage is an inorganic strong acid solution, preferably an aqueous solution of at least one of hydrochloric acid, phosphoric acid, or hydrofluoric acid.

[0029] Preferably, the concentration of the solute in the acid solution is 0.02-0.1 mol / L;

[0030] During acid treatment, the liquid-to-solid ratio of the acid to the calcined material is, for example, 5 to 50 ml / g.

[0031] Preferably, the acid treatment time is 1 to 5 hours.

[0032] The present invention also provides a SiO@C modified active material prepared by the preparation method described above.

[0033] This invention has revealed that the specific preparation method described above can create unique physicochemical properties. Furthermore, the materials prepared by this method exhibit excellent initial efficiency and comprehensive electrochemical performance.

[0034] This invention also provides the application of the SiO@C modified active material prepared by the aforementioned modification method as a negative electrode active material for the preparation of lithium secondary batteries and their negative electrodes and negative electrode materials.

[0035] In this invention, apart from using the SiO@C modified active material described in this invention as the active material, other materials and preparation methods can be known.

[0036] The present invention also provides a lithium secondary battery anode comprising the SiO@C modified active material obtained by the SiO@C modification method;

[0037] Preferably, the lithium secondary battery is a lithium-ion battery.

[0038] The present invention also provides a lithium secondary battery comprising the aforementioned negative electrode.

[0039] Beneficial effects:

[0040] In this invention, SiO@C is innovatively calcined in a combined modifier, and further combined with a gradient negative pressure two-stage calcination-acid treatment process and parameters. This enables synergy, constructing a suitable physical structure and chemical properties for lithium-ion storage and intercalation-deintercalation, and synergistically improving first-efficiency and electrochemical performance, especially significantly improving electrochemical performance under extreme conditions such as high temperature. Detailed Implementation

[0041] The present invention will be described in detail below with reference to embodiments, but the present invention is not limited thereto.

[0042] In this invention, the molar amount of SiO@C is calculated based on silicon. The molar amount of component A is calculated based on Mg, and the molar amount of component B is calculated based on Li. In the following examples, the heating rate is not particularly required, for example, 4-6 °C / min.

[0043] Example 1

[0044] ① Commercially available carbon-coated silicon suboxide (SiO@C) powder was selected as the raw material, with a D50 of 4 micrometers and a carbon content of 5%.

[0045] ② In a glove box, mix SiO@C with component A (Mg powder) and component B (Li powder) in a Si:Mg:Li molar ratio of 1:1:0.3 until homogeneous. Then place the mixture in a heat treatment furnace, first evacuate to a negative pressure (P1: recorded pressure 0.05 Pa), and heat to 450℃ (T1) under this negative pressure and hold for 3 hours. Then control the pressure to (P2; 1 Pa), heat to 800℃ (T2) and hold for 1 hour. After heating, allow the mixture to cool to room temperature under an argon atmosphere.

[0046] ③ Take out the powder after the above reaction, wash it with 0.02mol / L hydrochloric acid (the liquid-solid ratio of the acid and the calcined material in step 2 is 20ml / g), filter and separate the liquid, then wash it with water-based powder three times, and finally wash it with anhydrous ethanol once and dry it to obtain the desired high-efficiency silicon suboxide anode material (modified material, that is, electrode active material).

[0047] Performance testing

[0048] Battery performance testing: The prepared electrode active material was used as the electrode material (active material) to make electrode slurry and electrode sheets. The slurry ratio was electrode material: binder (PAA): conductive agent (SP) = 80:10:10. After the slurry was stirred evenly, it was coated on copper foil and then dried under vacuum. The dried electrode sheet was used as the working electrode of the coin cell, and the lithium sheet was used as the counter electrode. The electrolyte was 1 mol / L lithium hexafluorophosphate (LiPF6) electrolyte dissolved in ethylene carbonate (EC) and diethyl carbonate (DEC) electrolyte in a volume ratio of 1:1. A constant-temperature battery cycle test was conducted at 50°C, and the initial coulombic efficiency and capacity retention after 50 cycles were tested at a current density of 0.1C.

[0049] The results showed that the initial coulombic efficiency of untreated silicon suboxide (SiO@C) was 75.2%, and the capacity retention rate after 50 cycles at high temperature was 47%.

[0050] However, after the modification treatment in steps 1 to 3, its coulombic efficiency is 92.2%, and its capacity retention rate after 50 cycles at high temperature is 93%.

[0051] Example 2

[0052] Compared to Example 1, the only difference is that the types of components A and B are changed, specifically:

[0053] Group 1: Component A is (MgH2), and component B is (LiH); the weight ratio of the components is the same as in Example 1.

[0054] Group 2: Component A is (MgH2), and component B is (Li2O); the weight ratio of the components is the same as in Example 1.

[0055] Group 3: Component A is (Mg), and component B is (Li2CO3); the weight ratio of the components is the same as in Example 1.

[0056] Group 4: SiO@C is mixed with component A (Mg powder) and component B (Li powder) at a molar ratio of Si:Mg:Li of 1:0.85:0.25.

[0057] Group 5: SiO@C is mixed with component A (Mg powder) and component B (Li powder) at a molar ratio of Si:Mg:Li of 1:0.95:0.4.

[0058] Other operations and parameters are the same as in Example 1.

[0059] Electrochemical performance was measured according to the method in Example 1, and the results are shown in Table 1:

[0060] Table 1

[0061]

[0062]

[0063] Example 3

[0064] Compared with Example 1, the only difference is that the gradient negative pressure treatment process is changed, specifically:

[0065] Group 1: Compared with Example 1, the only difference is that the pressure of P1 is 0.1 Pa; the pressure of P2 is 20 Pa.

[0066] Group 2: Compared with Example 1, the only difference is that T1 is 350°C; T2 is 900°C.

[0067] Group 3: Compared with Example 1, the only difference is that T1 is 400°C; T2 is 850°C.

[0068] Group 4: Compared with Example 1, the only difference is that T1 is 500℃ for 1 hour; T2 is 900℃ for 2 hours.

[0069] Other operations and parameters are the same as in Example 1.

[0070] Electrochemical performance was measured according to the method in Example 1, and the results are shown in Table 2:

[0071] Table 2

[0072] Material First Coulomb efficiency Volume retention rate after 50 laps Group 1 93.4％ 94％ Group 2 91.3％ 89％ Group 3 93.1％ 92％ Group 4 91.1％ 88％

[0073] Example 4

[0074] ① Commercially available carbon-coated silicon suboxide (SiO@C) powder was used as the raw material, as in Example 1.

[0075] ② In a glove box, mix SiO@C with components A (MgH2) and B (LiH) at a molar ratio of Si:Mg:Li of 1:0.95:0.4 until homogeneous. Then place the mixture in a heat treatment furnace, first evacuate to a negative pressure (P1: recorded pressure 0.05 Pa), and heat to 400℃ (T1) under this negative pressure and hold for 2 hours. Then control the pressure to P2 (2 Pa), and heat to 800℃ (T2) and hold for 1.5 hours. After heating, allow the mixture to cool to room temperature under an argon atmosphere.

[0076] ③ Take out the powder after the above reaction, wash it with 0.02mol / L hydrochloric acid (the liquid-solid ratio of acid and calcined material in step 2 is 20ml / g), filter and separate the liquid, then wash it with water-based powder three times, and finally wash it with anhydrous ethanol once and dry it to obtain the desired high-efficiency silicon suboxide anode material (modified material, that is, electrode active material).

[0077] The performance was measured using the method of Example 1, and the results showed that its coulombic efficiency was 97.7% and its capacity retention rate was 97% after 50 cycles at high temperature.

[0078] Comparative Example 1

[0079] Compared to Example 1, the only difference is that component A is not added to the raw materials. All other operations are the same as in Example 1.

[0080] Comparative Example 2

[0081] Compared to Example 1, the only difference is that component B is not added to the raw materials. All other operations are the same as in Example 1.

[0082] Comparative Example 3

[0083] Compared to Example 1, the only difference is that components A and B are not treated together in the same system. The difference in step 2 is as follows: SiO@C is mixed evenly with component A (Mg powder) (the amount is the same as in Example 1) in a glove box. Then it is placed in a heat treatment furnace, first evacuated to a negative pressure (P1: recorded pressure 0.05 Pa), and heated to 450°C (T1) under this negative pressure and held for 3 hours. After cooling, it is cleaned with 0.02 mol / L hydrochloric acid, and then mixed with component B (the amount is the same as in Example 1) under a controlled pressure of P2 (1 Pa), and then heated to 800°C (T2) and held for 1 hour. Heating is then stopped, and the mixture is cooled to room temperature under an argon atmosphere. Then step 3 is performed. Other operations are the same as in Example 1.

[0084] Comparative Example 4

[0085] Compared with Example 1, the only difference is that the high negative pressure-low negative pressure gradient pressure change treatment was not carried out in the two-stage roasting stages. That is, the pressure of stage P1 is the same as that of stage P2, which is 1 Pa.

[0086] Comparative Example 5

[0087] Compared to Example 1, the only difference is that the process involves first applying a low negative pressure followed by a high negative pressure; that is, the pressure at P1 is 1 Pa, and the pressure at P2 is 0.05 Pa. All other operations are the same as in Example 1.

[0088] Comparative Example 6

[0089] Compared with Example 1, the only difference is that the temperature of T1 is 550°C and the temperature of T2 is 950°C. Other operations are the same as in Example 1.

[0090] Comparative Example 7

[0091] Compared with Example 1, the only difference is that the temperature of T1 is 250°C and the temperature of T2 is 750°C. Other operations are the same as in Example 1.

[0092] Comparative Example 8:

[0093] Compared to Example 1, the difference is that the acid washing process is not used. That is, the product after the two-step heat treatment reaction is directly used as the negative electrode material.

[0094] Electrochemical measurements were performed according to the protocol of Example 1, and the results are shown in Table 3:

[0095] Table 3

[0096] Material First Coulomb efficiency Volume retention rate after 50 laps Comparative Example 1 86.3％ 63％ Comparative Example 2 80.2％ 65％ Comparative Example 3 87.4％ 82％ Comparative Example 4 86.9 81％ Comparative Example 5 88.1％ 83％ Comparative Example 6 85.9％ 86％ Comparative Example 7 79.3％ 59％ Comparative Example 8 85.2％ 49％

[0097] Thus, it can be seen that by using the synergistic modifier described in this invention, and further combining it with the special gradient negative pressure-temperature control technology and the joint control of temperature, synergy can be achieved, which can significantly improve the initial performance of the modified material. In addition, it can also significantly improve its cycling stability at high temperatures.

Claims

1. A SiO@C modification method, characterized by, The SiO@C modified active material is prepared by mixing SiO@C and a synergistic modifier, carrying out pressure-variable two-stage calcination, and then acid treatment. The synergistic modifier comprises component A and component B; wherein the component A is at least one of MgH2 and Mg, and the component B is at least one of LiH, Li, Li2O, lithium carbonate, lithium dihydrogen phosphate and lithium salicylate. The pressure-variable two-stage calcination comprises a first-stage calcination at high negative pressure and a second-stage calcination at low negative pressure; wherein the temperature of the first-stage calcination is 350-500 DEG C, and the pressure is less than or equal to 0.1 pa. The temperature of the second-stage calcination is 800-900 DEG C, and the pressure is greater than or equal to 1 Pa and less than or equal to 100 kPa.

2. The SiO@C modification method according to claim 1, wherein In the raw material, the D50 of the SiO@C particles is 3-7 microns, and the carbon content is 3.5-6.5%.

3. The SiO@C modification method according to claim 1, wherein In the synergistic modifier, the component A is MgH2, and the component B is LiH.

4. The SiO@C modification method according to claim 1, wherein The molar ratio of SiO@C, component A and component B is 1:0.8-1.05:0.1-0.

5.

5. The SiO@C modification method according to claim 1, wherein In the pressure-variable two-stage calcination stage, the pressure of the negative pressure in the first-stage calcination stage is 0.001-0.1 pa.

6. The SiO@C modification method according to claim 1, wherein The pressure in the second-stage calcination process is 1-20 pa.

7. The SiO@C modification method according to claim 1, wherein The temperature of the first-stage calcination is 400-450 DEG C.

8. The SiO@C modification method according to claim 1, wherein The time of the first-stage calcination is 1-3 h.

9. The SiO@C modification method according to claim 1, wherein The temperature of the second-stage calcination is 800-850 DEG C.

10. The SiO@C modification method according to claim 1, wherein The time of the second-stage calcination is 1-3 h.

11. The SiO@C modification method according to claim 1, wherein The acid solution in the acid treatment stage is a strong inorganic acid solution.

12. The SiO@C modification method according to claim 11, wherein The strong inorganic acid solution is an aqueous solution of at least one of hydrochloric acid, phosphoric acid and hydrofluoric acid.

13. The SiO@C modification method according to claim 11, wherein In the acid solution, the concentration of the solute is 0.02-0.1 mol / L. The time of the acid treatment is 1-5 h.

14. A SiO@C modified active material prepared by the SiO@C modification method according to any one of claims 1-13.

15. A lithium secondary battery negative electrode, characterized by, A SiO@C modified active material prepared by the SiO@C modification method according to any one of claims 1-13.

16. The lithium secondary battery anode of claim 15, wherein the carbon material is selected from the group consisting of graphite, hard carbon, soft carbon, and a mixture thereof. The lithium secondary battery is a lithium ion battery.

17. A lithium secondary battery, characterized by comprising: A negative electrode of the lithium secondary battery according to claim 15 or 16.

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