Silicon-based active materials, their preparation and use

Abstract

This invention belongs to the field of battery materials, specifically disclosing a method for preparing silicon-based active materials, which involves silicon oxide, MX... n A mixture of LiX and metallic N is subjected to pressure gradient heat treatment to obtain a heat-treated material, which is then acid-treated to obtain a precursor. Subsequently, the precursor is combined with a carbon source and subjected to carbonization treatment to obtain the final product. M is at least one of Al and Zn, n is the valence of M, X is a halogen, and N is Mg and / or Al. The pressure gradient heat treatment process is performed at 0.2–2 MPa and includes a first holding process at 200–350°C and a second holding process at 450–600°C. This invention also includes silicon-based active materials prepared by the above method and their applications. The materials described in this invention possess excellent electrochemical properties, particularly excellent high-temperature stability.

Description

Technical Field

[0001] This invention relates to the field of battery materials, specifically to the field of lithium-ion battery anode materials. Background Technology

[0002] Graphite's specific capacity (372 mAh / g) is insufficient for high energy density requirements, making silicon anodes a new choice. Pure silicon expands significantly during cycling (≈300%), resulting in poor battery cycle performance. SiO x The material has relatively low expansion (≈150%) and better cycle performance, but SiO x The first-efficacy rate is relatively low (≈75%).

[0003] To address the challenges faced by silicon-based materials, existing technologies offer several solutions, primarily involving the composite of silicon and porous carbon. For instance, Chinese patent publication CN 116504986A discloses a method for alternating silicon-carbon layers on a porous carbon substrate, which improves conductivity and buffers silicon expansion. Similarly, Chinese patent publication CN 117038855A discloses a similar method for vapor-phase deposition of silicon on porous carbon.

[0004] Although existing technologies have reported some ways to improve silicon-based materials and can better solve the problem of silicon volume expansion, the problems affecting the first-efficiency performance and high-temperature stability of silicon-based materials have not been well solved. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a method for preparing silicon-based active materials, which aims to suppress silicon grains during the preparation process and improve its initial efficiency and stability at high temperatures.

[0006] The second objective of this invention is to provide a silicon-based active material prepared by the aforementioned method and its application in lithium-ion batteries.

[0007] A third objective of this invention is to provide a lithium-ion battery comprising the silicon-based active material and its negative electrode.

[0008] A method for preparing silicon-based active materials, comprising silicon oxide, MX n A mixture of LiX and metallic N is subjected to pressure gradient heat treatment to obtain a heat-treated material, which is then acid-treated to obtain a precursor. Subsequently, the precursor and a carbon source are combined and carbonized to obtain the final product.

[0009] M is at least one of Al and Zn, n is the valence of M, X is a halogen, and N is Mg and / or Al;

[0010] The pressure gradient heat treatment process is 0.2 to 2 MPa, and includes a first heat preservation process at a temperature of 200 to 350°C and a second heat preservation process at a temperature of 450 to 600°C.

[0011] This invention innovatively combines silicon oxide and MX n A mixture of LiX and metallic N is subjected to pressure gradient heat treatment, based on the aforementioned MX n The combination of LiX and pressurized, two-stage gradient reactions can unexpectedly and effectively control the nucleation of silicon grains and induce the formation of inert active sites in situ. This can synergistically improve the performance of the prepared materials, especially their first-efficiency and stability at high temperatures.

[0012] In this invention, the Lewis acid type MX n The combination with LiX, along with the aforementioned two-stage pressurized heat treatment method and conditions, can unexpectedly achieve synergy, regulate the nucleation behavior of silicon during the reaction process, and construct in situ Li silicate-type inert active sites, thereby improving its performance.

[0013] In this invention, the chemical formula of the silicon oxide is SiO. X The 0 mentioned <x≤2。

[0014] In this invention, there are no special requirements for the particle size of the silicon oxide, as long as it meets the requirements for battery use. For example, its D50 can be 3um to 10um.

[0015] In this invention, silicon oxide and MX are used. n The synergistic reaction of LiX and metallic N, based on the physicochemical characteristics of the reaction stages, can catalyze SiO2. X It can reduce nucleation and control grain agglomeration. In addition, it can form abundant inert active sites in situ, thereby synergistically improving its performance.

[0016] In this invention, M is preferably Al;

[0017] In this invention, X is a halogen such as Cl or Br, preferably Cl;

[0018] In this invention, the metal N is Mg.

[0019] In this invention, the molar ratio of metallic N to silicon oxide is (0.05–0.5):1, and can further be 0.2–0.4:1;

[0020] The silicon oxide, MX n The weight ratio of LiX is 1:2 to 20:1 to 10, and can be further expressed as 1:5 to 10:2 to 4.

[0021] In this invention, in the silicon oxide, MX n With the synergistic combination of LiX and metallic N, and further combined with subsequent pressure gradient heat treatment, the grain size during the reaction process can be controlled, and the reaction sites can be constructed in situ, thereby improving the rate capability and high-temperature performance of the prepared material.

[0022] In this invention, the pressure gradient heat treatment process employs a protective atmosphere for pressure control. The protective atmosphere is at least one of nitrogen and an inert gas.

[0023] The present invention demonstrates that by further controlling the pressure during the reaction process under the aforementioned pressure gradient heat treatment process, the process synergy can be further improved, which helps to further improve the initial efficiency and high-temperature performance of the prepared material.

[0024] Preferably, the pressure during the pressure gradient heat treatment stage is 0.4–0.6 MPa;

[0025] Preferably, the temperature of the first heat preservation process is 280–320°C;

[0026] Preferably, the duration of the first heat preservation process is 2–4 hours;

[0027] Preferably, the temperature of the second heat preservation process is 480–520°C;

[0028] Preferably, the duration of the second heat preservation process is 1 to 4 hours.

[0029] In this invention, the product of pressure gradient heat treatment is placed in an acid solution for acid treatment. The acid solution used in the acid treatment process is an inorganic acid solution with a concentration of 0.1–5 M, more preferably 0.2–1 M; preferably at least one of HCl, HNO3, and H2SO4.

[0030] In this invention, the amount of acid used in the acid treatment is not less than the amount of excess MX. n Amount removed.

[0031] In this invention, the precursor is obtained by acid treatment followed by water washing and drying.

[0032] In this invention, the precursor can be carbon-coated using conventional methods.

[0033] In this invention, the carbon source is at least one of gaseous carbon source, liquid carbon source, and solid carbon source;

[0034] For example, the carbonization process is carried out in a protective atmosphere;

[0035] For example, the temperature of the carbonization process is 500–1000°C, and more specifically 700–850°C;

[0036] For example, the carbonization process can take 1 to 5 hours, or even 1 to 3 hours.

[0037] For example, one exemplified carbonization process of the present invention involves treating a precursor in a gas-phase carbon source system within a rotary kiln. The gas-phase carbon source is one or a mixture of several selected from methane, ethane, propane, ethylene, propylene, acetylene, and butene. A dilution gas may also be added during the gas-phase carbonization process; this dilution gas can be at least one of nitrogen or an inert atmosphere. The content of the gas-phase carbon source during the gas-phase carbonization process can be between 10% and 100%, preferably between 10% and 40%. The gas-phase treatment temperature is 500–1000°C, and the treatment time is 1–5 hours.

[0038] The present invention also provides a silicon-based active material prepared by the preparation method described above.

[0039] In this invention, based on the innovative preparation method, the prepared material can be endowed with special physicochemical properties, such as adjustable grain size and dispersed in-situ distribution of inert active sites. The material prepared by this method can unexpectedly improve its initial efficiency and high-temperature performance.

[0040] The present invention also provides an application of the silicon-based active material prepared by the above preparation method, which is used as a negative electrode active material for the preparation of lithium-ion batteries.

[0041] In this invention, the silicon-based active material prepared by the method described herein can be used as the negative electrode active material to prepare a lithium-ion battery based on known processes. For example, the silicon-based active material can be combined with a conductive agent and a binder to obtain a negative electrode material. Further, the negative electrode material is slurried with a solvent to form a negative electrode slurry, which is then coated onto a current collector, cured, and dried to obtain a negative electrode sheet. Finally, the negative electrode sheet is assembled to obtain a lithium-ion battery.

[0042] The present invention also provides a negative electrode for a lithium-ion battery, comprising a current collector and a negative electrode material composite thereon, wherein the negative electrode material comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based active material obtained by the preparation method described above.

[0043] Preferably, the negative electrode material may also contain a conductive agent and a binder.

[0044] The present invention also provides a lithium-ion battery, including a cell and an electrolyte soaking the cell, wherein the cell includes a positive electrode, a separator and a negative electrode sequentially combined, and the negative electrode is the negative electrode described in the present invention.

[0045] The lithium-ion battery and its negative electrode described in this invention, except for the silicon-based active material prepared by the preparation method described in this invention, can have conventional structures, components, preparation operations and parameters.

[0046] Beneficial effects

[0047] This invention innovatively combines silicon oxide and MX n A mixture of LiX and metallic N is subjected to pressure gradient heat treatment, based on the aforementioned MX n The combination of LiX and pressurized, two-stage gradient reactions can unexpectedly and effectively control silicon nucleation grains and induce the formation of inert active sites, thus synergistically improving the properties of the prepared material, particularly its initial efficiency and stability at high temperatures. Furthermore, the preparation method of this invention is simple, uses low-cost raw materials, and is easy to implement. Attached Figure Description

[0048] Figure 1 The XRD pattern of the material finally obtained in Example 1;

[0049] Figure 2 The image shows the XRD pattern of the final material prepared in Comparative Example 4. Detailed Implementation

[0050] In the following cases, the pressure during the pressure gradient heat treatment stage can be increased using Ar.

[0051] Example 1

[0052] Step 1: - First stage of pressurized heat treatment:

[0053] 100g aluminum chloride, 32g lithium chloride, 1.8g Mg, and 10g SiO were placed in a pressure-resistant reaction vessel, and the air was replaced with Ar. The vessel was pressurized to 0.5MPa and heated to 300℃, and the reaction was maintained at the same temperature and pressure for 3 hours.

[0054] Step 2: - Second stage of pressurized heat treatment:

[0055] Continue heating at a rate of 5℃ / min to 500℃, and hold at that temperature and pressure for 2 hours (pressure as in step 1). Then depressurize and cool with the furnace to obtain the heat-treated material.

[0056] Step 3: Wash the heat-treated material in a 0.5M dilute hydrochloric acid solution to remove aluminum chloride, wash with water until neutral, and then dry to obtain the precursor;

[0057] Step 4: Place the precursor in a rotary furnace, first introduce argon gas to purge the air, then introduce acetylene (acetylene-Ar mixture, in which the acetylene content is 40% v%) and keep it at 750℃ for 2 hours to coat it with a layer of carbon, thus obtaining the silicon-based active material.

[0058] Using the finished products from each case (the final negative electrode active material, acetylene black, and PVDF were prepared in a weight ratio of 90:5:5) as the working electrode, lithium metal as the negative electrode, 1 mol / L LiPF6 EC / EMC (volume ratio 1:1) as the electrolyte, and PE-PP composite membrane as the separator, CR2025 coin cells were assembled in an argon-filled dry glove box. The voltage range was 0.001-2V, and the cycling stability at room temperature (25℃) and high temperature (60℃) was tested at 0.1C.

[0059] The results showed that a high-efficiency silicon-oxygen material with a silicon grain size of 3.1 nm, an initial efficiency of 93%, and a capacity of 1355 mAh / g was obtained. The capacity retention rate after 100 cycles at 0.1C and 60℃ was 85%.

[0060] Example 2

[0061] Compared with Example 1, in step 1, the amount of aluminum chloride used is 50g and the amount of lithium chloride used is 22g, while other operations and parameters remain the same as in Example 1.

[0062] The test results showed a silicon grain size of 3.8 nm, an initial efficiency of 92.1%, and a capacity of 1370 mAh / g. The capacity retention rate after 100 cycles at 0.1C and 60℃ was 83%.

[0063] Example 3

[0064] Compared to Example 1, the only difference is that the pressure in step 1 is changed, specifically:

[0065] Group A: Pressure is 0.4 MPa;

[0066] Group B: Pressure is 0.6 MPa;

[0067] The results are as follows:

[0068] Group A: A silicon-oxygen material with a silicon grain size of 3.2 nm, an initial efficiency of 92.7%, and a capacity of 1361 mAh / g was obtained. The capacity retention rate after 100 cycles at 0.1C and 60℃ was 81%.

[0069] Group B: A silicon-oxygen material with a silicon grain size of 3.9 nm, an initial efficiency of 93.2%, and a capacity of 1356 mAh / g was obtained. The capacity retention rate after 100 cycles at 0.1C and 60℃ was 82%.

[0070] Example 4

[0071] Compared to Example 1, the only difference is that the temperatures in steps 1 and 2 were changed, and the experimental groups were as follows:

[0072] Group A: Step 1 temperature is 320℃, time is 2h; Step 2 temperature is 520℃, time is 1H.

[0073] Group B: Step 1 temperature is 280℃, time is 4h; Step 2 temperature is 480℃, time is 3h.

[0074] The results are as follows:

[0075] Group A: A high-efficiency silicon-oxygen material with a silicon grain size of 3.5 nm, an initial efficiency of 92.8%, and a capacity of 1349 mAh / g was obtained. The capacity retention rate after 100 cycles at 0.1C and 60℃ was 83%.

[0076] Group B: A high-efficiency silicon-oxygen material with a silicon grain size of 3.0 nm, an initial efficiency of 91.9%, and a capacity of 1325 mAh / g was obtained. The capacity retention rate after 100 cycles at 0.1C and 60℃ was 86%.

[0077] Example 5

[0078] Compared with Example 1, the only difference is that in step 4, acetylene is replaced with methane, and during the deposition process, the methane atmosphere content is 10 v%, the deposition temperature is 800°C, and the time is 3 hours.

[0079] The results showed a silicon grain size of 3.2 nm, an initial efficiency of 93%, and a capacity of 1361 mAh / g. The capacity retention rate after 100 cycles at 0.1C and 60℃ was 84%.

[0080] Comparative Example 1

[0081] Compared to Example 1, the only difference is that in step 1, aluminum chloride is omitted, and the missing amount is made up by weight with LiCl. Other operations, parameters, and testing methods are the same as in Example 1.

[0082] The results showed a silicon grain size of 4.1 nm, an initial efficiency of 79%, and a capacity of 1290 mAh / g. The capacity retention rate after 100 cycles at 0.1°C and 60°C was 71%.

[0083] Comparative Example 2

[0084] Compared to Example 1, the only difference is that in step 1, an equal weight of lithium hydroxide is used instead of aluminum chloride. All other operations, parameters, and testing methods are the same as in Example 1.

[0085] The result was a high-efficiency silicon-oxygen material with a silicon grain size of 6.2 nm, an initial efficiency of 91.3%, and a capacity of 1285 mAh / g. The capacity retention after 100 cycles at 0.1C and 60℃ was 66%.

[0086] Comparative Example 3

[0087] Compared to Example 1, the only difference is that in step 1, lithium chloride is omitted, and the missing amount is made up by weight with an equivalent amount of AlCl3. Other operations, parameters, and testing methods are the same as in Example 1.

[0088] The results showed that a high-efficiency silicon-oxygen material with a silicon grain size of 3.6 nm, an initial efficiency of 85.1%, and a capacity of 1275 mAh / g was obtained. The capacity retention rate after 100 cycles at 0.1C and 60℃ was 72%.

[0089] Comparative Example 4

[0090] Compared to Example 1, the only difference is that the pressure in steps 1 and 2 is atmospheric pressure. Other operations, parameters, and testing methods are the same as in Example 1.

[0091] The result is:

[0092] The silicon grain size is 5.7nm, with an initial efficiency of 90.7% and a capacity of 1252mAh / g. The capacity retention rate after 100 cycles at 0.1C and 60℃ is 73%.

[0093] Comparative Example 5

[0094] Compared to Example 1, the only difference is that the first heat treatment process in step 1 is omitted, and instead, a heat treatment is performed directly in step 2, with a heat treatment time of 5 hours. Other operations, parameters, and testing methods are the same as in Example 1.

[0095] The result is:

[0096] The silicon grain size is 7.2 mm, the initial efficiency is 91.1%, and the capacity is 1310 mAh / g. The capacity retention rate is 67% after 100 cycles at 0.1C and 60℃.

Claims

1. A method for preparing a silicon-based active material, characterized in that, silicon oxide, MX n A mixture of LiX and metallic N is subjected to pressure gradient heat treatment to obtain a heat-treated material, which is then acid-treated to obtain a precursor. Subsequently, the precursor and a carbon source are combined and carbonized to obtain the final product. M is at least one of Al and Zn, n is the valence of M, X is a halogen, and N is Mg and / or Al; the molar ratio of metallic N to silicon oxide is (0.05-0.5):1; The silicon oxide, MX n The weight ratio of Li to X is 1:2~20:1~10; The pressure gradient heat treatment process is 0.4~0.6MPa, and includes a first heat preservation process at a temperature of 200~350℃ and a second heat preservation process at a temperature of 450~600℃. The pressure gradient heat treatment process uses a protective atmosphere for pressure control.

2. The method for preparing the silicon-based active material as described in claim 1, characterized in that, The chemical formula of the silicon oxide is SiO. X The 0 mentioned <x≤2。 3. The method for preparing the silicon-based active material as described in claim 1, characterized in that, The D50 of the silicon oxide is 3µm to 10µm.

4. The method for preparing the silicon-based active material as described in claim 1, characterized in that, The M mentioned above is Al; X is Cl; The metal N mentioned is Mg.

5. The method for preparing the silicon-based active material as described in claim 1, characterized in that, The protective atmosphere is at least one of nitrogen and an inert gas.

6. The method for preparing the silicon-based active material as described in claim 1, characterized in that, The temperature for the first heat preservation process is 280~320℃.

7. The method for preparing the silicon-based active material as described in claim 1, characterized in that, The first heat preservation process takes 2-4 hours.

8. The method for preparing the silicon-based active material as described in claim 1, characterized in that, The temperature for the second insulation process is 480~520℃.

9. The method for preparing the silicon-based active material as described in claim 1, characterized in that, The second heat preservation process takes 1 to 4 hours.

10. The method for preparing the silicon-based active material as described in claim 1, characterized in that, The acid solution used in the acid treatment process is an inorganic acid solution with a concentration of 0.1~5M.

11. The method for preparing the silicon-based active material as described in claim 10, characterized in that, The acid solution used in the acid treatment process is at least one of HCl, HNO3, and H2SO4.

12. The method for preparing the silicon-based active material as described in claim 1, characterized in that, The precursor was obtained by acid treatment followed by washing with water and drying.

13. The method for preparing the silicon-based active material as described in claim 1, characterized in that, The carbon source is at least one of gaseous carbon source, liquid carbon source, and solid carbon source.

14. The method for preparing the silicon-based active material as described in claim 1, characterized in that, The carbonization process is carried out in a protective atmosphere.

15. The method for preparing the silicon-based active material as described in claim 1, characterized in that, The carbonization process is carried out at a temperature of 500~1000℃.

16. The method for preparing the silicon-based active material as described in claim 1, characterized in that, The carbonization process takes 1 to 5 hours.

17. A silicon-based active material prepared by the preparation method according to any one of claims 1 to 16.

18. The application of a silicon-based active material prepared by the preparation method according to any one of claims 1 to 16, characterized in that, Used as a negative electrode active material.

19. The application of a silicon-based active material prepared by the preparation method according to any one of claims 1 to 16, characterized in that, Used in the manufacture of lithium-ion batteries.

20. A negative electrode for a lithium-ion battery, comprising a current collector and a negative electrode material composited thereon, said negative electrode material comprising a negative electrode active material, characterized in that, The negative electrode active material includes the silicon-based active material prepared by the preparation method according to any one of claims 1 to 16.

21. The negative electrode of the lithium-ion battery as described in claim 20, characterized in that, The negative electrode material may also contain conductive agents and binders.

22. A lithium-ion battery, comprising a cell and an electrolyte soaking the cell, wherein the cell comprises a positive electrode, a separator, and a negative electrode sequentially laminated together, characterized in that, The negative electrode is the negative electrode as described in claim 20 or 21.

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