A porous lithium salt-coated silicon-based composite material, a preparation method and application thereof

Abstract

The present application relates to the field of lithium ion battery materials, in particular to a porous lithium salt coated silicon-based composite material and a preparation method and application thereof.The present application provides a preparation method of a porous lithium salt coated silicon-based composite material, which comprises the following steps: 1) adding a silane coupling agent and nano silicon powder into an organic solution containing an organic nickel salt and a lithium salt, stirring, filtering, and drying to obtain a precursor material; 2) calcining the precursor material to obtain a nickel oxide and lithium salt coated silicon-based material; 3) placing the nickel oxide and lithium salt coated silicon-based material in an acid gas atmosphere for etching to obtain the porous lithium salt coated silicon-based composite material. In summary, the porous lithium salt coated silicon-based composite material prepared by the preparation method of the porous lithium salt coated silicon-based composite material has low expansion and good conductivity, and has excellent rate performance and cycle performance when applied to a battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials, specifically to a porous lithium salt-coated silicon-based composite material, its preparation method, and its application. Background Technology

[0002] The negative electrode material in a lithium-ion battery serves as the primary storage medium for lithium. During the charging and discharging process, lithium ions repeatedly insert and extract into the negative electrode material, undergoing electrochemical oxidation / reduction reactions. Currently, commercially available lithium-ion batteries primarily use carbon-based materials for their negative electrodes. However, the theoretical capacity of carbon-based negative electrodes is only 372 mAh / g, which is insufficient to meet the future market demands for higher battery energy densities.

[0003] Silicon anode materials possess advantages such as a high theoretical specific capacity of 4200 mAh / g, a low voltage plateau, abundant resources, and low cost, making them a very promising anode material for lithium batteries. However, silicon anode materials have two drawbacks that need to be overcome. The first drawback is that anisotropic expansion occurs during the insertion and extraction of lithium ions, causing structural instability in silicon anode materials. This structural instability leads to reduced coulombic efficiency and poor cycle performance in batteries made from silicon anode materials. The second drawback is the low intrinsic conductivity of silicon, resulting in a low electrochemical kinetic rate, which in turn leads to poor rate performance in batteries made from silicon anode materials. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of silicon-based materials in the prior art, such as large volume expansion and low electrical conductivity, which affect the rate performance and cycle performance of batteries, thereby providing a porous lithium salt coated silicon-based composite material, its preparation method and application.

[0005] This invention provides a method for preparing porous lithium salt-coated silicon-based composite materials, comprising the following steps:

[0006] 1) Add silane coupling agent and nano-silicon powder to an organic solution containing organonitrile and lithium salts, stir, filter, and dry to obtain the precursor material;

[0007] 2) The precursor material is calcined to obtain a silicon-based material coated with nickel oxide and lithium salt;

[0008] 3) The nickel oxide and lithium salt coated silicon-based material is etched in an acidic gas atmosphere to obtain the porous lithium salt coated silicon-based composite material.

[0009] Preferably, the organonitrile salt includes at least one of nickel acetylacetonate, nickel dicerocene, nickel stearate, and nickel acetate;

[0010] The lithium salt includes at least one of lithium titanate, lithium zirconate, lithium aluminate, and lithium niobate.

[0011] The organic solvent of the organic solution includes at least one of xylene, toluene, cyclohexane, butanediol, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and carbon tetrachloride.

[0012] Preferably, the silane coupling agent comprises at least one of vinyltriethoxysilane, vinyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and γ-ureopropyltriethoxysilane.

[0013] Preferably, the average particle size of the nano-silicon powder in step 1) is 100-500 nm.

[0014] Preferably, the mass ratio of the organonitrile salt, lithium salt, organic solvent, silane coupling agent and nano-silicon powder in step 1) is (1-5):(1-5):(350~1100):(1~10):100.

[0015] Preferably, in step 2), calcination is carried out under inert gas protection, with a calcination temperature of 400-900℃ and a calcination time of 1-6h.

[0016] Preferably, the etching temperature in step 3) is 100-200℃ and the etching time is 0.5-2h.

[0017] Preferably, the acidic gas is selected from sulfuric acid vapor, nitric acid vapor, and hydrochloric acid vapor;

[0018] The sulfuric acid concentration in the sulfuric acid vapor is 20-80 wt%.

[0019] The nitric acid concentration in the nitric acid vapor is 20-80 wt%.

[0020] The concentration of hydrochloric acid in the hydrochloric acid vapor is 20-37 wt%.

[0021] Step 3) after etching is completed also includes cooling, washing and drying steps.

[0022] The present invention also provides a porous lithium salt-coated silicon-based composite material, which is prepared by the above-described method for preparing porous lithium salt-coated silicon-based composite materials.

[0023] The present invention also provides a lithium-ion battery comprising the porous lithium salt-coated silicon-based composite material described above.

[0024] The technical solution of this invention has the following advantages:

[0025] The present invention provides a method for preparing a porous lithium salt-coated silicon-based composite material, comprising the following steps: 1) adding a silane coupling agent and nano-silicon powder to an organic solution containing organic nickel salt and lithium salt, dispersing, filtering, drying and calcining to obtain a nickel oxide / lithium salt-coated silicon-based material; 2) acid etching the nickel oxide / lithium salt-coated silicon-based material obtained in step 1) to obtain the porous lithium salt-coated silicon-based composite material.

[0026] This invention obtains a nickel oxide and lithium salt-coated silicon-based material by adding organonickel salts and lithium salts to a precursor material and then calcining it. The lithium salt coating improves the ionic conductivity of the material and isolates the core silicon from the electrolyte, enhancing the initial efficiency and storage performance. During calcination, the decomposition of the organonickel salts as they form nickel oxide leaves pores in the coating layer. Acid etching further dissolves the nickel oxide, creating nano- and micro-pores in the coating layer, increasing the overall specific surface area of ​​the composite material. The synergistic effect of these two types of pores reduces the expansion of the composite material during charge and discharge, improving its structural stability. Furthermore, the addition of a silane coupling agent forms a network structure of nano-silicon, preventing its aggregation and reducing expansion and contraction during charge and discharge, further enhancing structural stability. This improved structural stability reduces the irreversible capacity of the composite material and improves the initial efficiency of batteries prepared using porous lithium salt-coated silicon-based composite materials. Meanwhile, the lithium salt provides ample lithium ions, enhancing the conductivity of the composite material. Furthermore, the porous lithium salt coating increases the specific surface area of ​​the composite material, thereby improving its liquid absorption and retention properties, as well as the lithium-ion conductivity. This results in improved rate performance of batteries prepared using the porous lithium salt-coated silicon-based composite material. In summary, the porous lithium salt-coated silicon-based composite material prepared using the method described in this application exhibits low expansion and good conductivity, demonstrating excellent rate and cycle performance when applied to batteries.

[0027] Furthermore, the etching process is carried out in an acidic gas environment, which has the advantages of process controllability and simple operation. Attached Figure Description

[0028] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is a scanning electron microscope image of the porous lithium salt-coated silicon-based composite material prepared by the preparation method of Example 1 of the present invention. Detailed Implementation

[0030] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0031] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0032] Example 1

[0033] This embodiment provides a method for preparing porous lithium salt-coated silicon-based composite materials, including the following steps:

[0034] 1) Add 3g of nickel acetylacetonate and 3g of lithium titanate to 800ml of xylene organic solvent to prepare an organic solution. Add 5g of vinyltriethoxysilane and 100g of nano-silicon powder (average particle size of 200nm) to the organic solution. Stir at 500 rpm for 1h. After uniform dispersion, filter and then vacuum dry at 80℃ for 24h to obtain the precursor material.

[0035] 2) The precursor material was transferred to a tube furnace and calcined for 3 hours in an argon atmosphere at a temperature of 700°C to obtain a nickel oxide and lithium salt coated silicon-based material.

[0036] 3) The nickel oxide and lithium salt coated silicon-based material obtained in step 2) is transferred to a rotating three-necked flask. During the rotation, concentrated sulfuric acid vapor (sulfuric acid concentration of 60 wt%) is introduced. The nickel oxide and lithium salt coated silicon-based material is acid etched at 150°C for 1 hour. After cooling to room temperature, it is washed with deionized water and then vacuum dried at 80°C for 24 hours to obtain the porous lithium salt coated silicon-based composite material.

[0037] Example 2

[0038] This embodiment provides a method for preparing porous lithium salt-coated silicon-based composite materials, including the following steps:

[0039] 1) Add 1g of nickel dicene and 1g of lithium zirconate to 500ml of cyclohexane organic solvent to prepare an organic solution. Add 1g of vinyltrimethoxysilane and 100g of nano-silicon powder (average particle size of 100) to the organic solution. Stir at 500 rpm for 1h. After uniform dispersion, filter and then vacuum dry at 80℃ for 24h to obtain the precursor material.

[0040] 2) The precursor material was transferred to a tube furnace and calcined for 4 hours in an argon atmosphere at a temperature of 400°C to obtain a nickel oxide and lithium salt coated silicon-based material.

[0041] 3) The nickel oxide and lithium salt coated silicon-based material obtained in step 2) is transferred to a rotating three-necked flask. During the rotation, concentrated nitric acid vapor (20 wt%) is introduced. The nickel oxide and lithium salt coated silicon-based material is acid-etched at 150°C for 2 hours. After cooling to room temperature, it is washed with deionized water and then vacuum-dried at 80°C for 24 hours to obtain the porous lithium salt coated silicon-based composite material.

[0042] Example 3

[0043] This embodiment provides a method for preparing porous lithium salt-coated silicon-based composite materials, including the following steps:

[0044] 1) Add 5g of nickel alkylate and 5g of lithium aluminate to 1000ml of N-methylpyrrolidone organic solvent to prepare an organic solution. Add 10g of γ-aminopropyltriethoxysilane and 100g of nano-silicon powder (average particle size of 500nm) to the organic solution. Stir at 500 rpm for 1h. After uniform dispersion, filter and then vacuum dry at 80℃ for 24h to obtain the precursor material.

[0045] 2) The precursor material was transferred to a tube furnace and calcined for 1 hour in an argon atmosphere at a temperature of 900°C to obtain a nickel oxide and lithium salt coated silicon-based material.

[0046] 3) The nickel oxide and lithium salt coated silicon-based material obtained in step 2) is transferred to a rotating three-necked flask. Concentrated hydrochloric acid vapor (hydrochloric acid concentration of 37wt%) is introduced during the rotation. The nickel oxide and lithium salt coated silicon-based material is acid etched at 200℃ for 0.5h. After cooling to room temperature, it is washed with deionized water and then vacuum dried at 80℃ for 24h to obtain the porous lithium salt coated silicon-based composite material.

[0047] Comparative Example 1

[0048] This comparative example provides a method for preparing a silicon-based composite material, which differs from Example 1 in that lithium titanate is not added in step 1).

[0049] Comparative Example 2

[0050] This comparative example provides a method for preparing a silicon-based composite material, which differs from Example 1 in that nickel acetylacetone is not added in step 1).

[0051] Comparative Example 3

[0052] This comparative example provides a method for preparing a silicon-based composite material. The difference between this method and Example 1 is that in step 3), the silicon-based material coated with nickel oxide and lithium salt obtained in step 2) is washed with deionized water and then vacuum dried at 80°C for 24 hours to obtain the silicon-based composite material.

[0053] Test case

[0054] 1. Morphology Testing: The porous lithium salt-coated silicon-based composite material obtained in Example 1 was subjected to scanning electron microscopy (SEM). The test results are as follows: Figure 1 As shown. By Figure 1 It can be seen that the porous lithium salt-coated silicon-based composite material exhibits a granular structure with a uniform and reasonable particle size distribution, and the particle size is between 2-8 μm.

[0055] 2. The specific surface area, tap density, carbon content, and trace element content (nickel) of the materials obtained in the examples and comparative examples were tested according to GB / T 38823-2020 "Silicon Carbon" standard, and the electrical conductivity of the silicon-based composite material was tested using a four-probe tester.

[0056] The silicon-based composite materials prepared in Examples 1-3 and Comparative Examples 1-3 were used as negative electrode materials for lithium-ion batteries to prepare coin cells. The preparation process is as follows:

[0057] A binder, conductive agent, and solvent were added to the composite material, stirred to form a slurry, coated onto copper foil, and then dried and rolled to obtain the negative electrode sheet. The binder used was polyvinylidene fluoride (PVDF), the conductive agent was conductive carbon black (SP), and the solvent was N-methylpyrrolidone (NMP). The ratio of composite material, SP, PVDF, and NMP was 95g:1g:4g:220mL. The electrolyte was a 1mol / L solution with LiPF6 as the electrolyte, and the solvent was a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) by volume. A lithium metal sheet served as the counter electrode, and a polypropylene (PP) membrane was used as the separator. The button cell assembly was performed in an argon-filled glove box.

[0058] Full-charge expansion: The thickness D1 of the negative electrode sheet of the rolled coin cell is measured. Then, the coin cell is fully charged to 100% SOC (where SOC is the state of charge of the battery), and the full-charge thickness D2 of the negative electrode sheet is dissected. The expansion rate is then calculated.

[0059] Expansion rate = (D2D-1D1)×100%;

[0060] Electrochemical performance was tested using a Wuhan Landian CT2001A battery tester. The charge / discharge voltage range was 0.005V to 2.0V, and the charge / discharge rate was 0.1C. The initial discharge specific capacity (mAh / g) and initial efficiency (%) of the battery were tested. The test results are shown in Table 1.

[0061] Table 1

[0062]

[0063]

[0064] As can be seen from the data in Table 1, the batteries prepared using the porous lithium salt-coated silicon-based composite materials obtained by the methods in Examples 1-3 exhibit significantly better initial discharge specific capacity and initial efficiency than the batteries prepared using the comparative composite materials. This is because coating the silicon-based surface with inorganic lithium salts reduces irreversible silicon loss, thereby improving the initial efficiency of the battery; simultaneously, etching away nickel oxide increases the specific surface area of ​​the coating material, further reducing the overall expansion of the composite material and improving its structural stability.

[0065] 4. Pouch Battery Testing

[0066] The silicon-based composite materials of Examples 1-3 and Comparative Examples 1-3, doped with artificial graphite, were used as negative electrode materials (the mass ratio of silicon-based composite material to artificial graphite was 1:9), and were used with ternary positive electrode materials (LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 The battery is assembled with O2, electrolyte, and separator to form a 5Ah soft-pack battery. The separator is Celegard 2400, and the electrolyte is a LiPF6 solution (the solvent is a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 volume ratio, and the concentration of LiPF6 is 1.3mol / L).

[0067] 4.1 The following performance tests were performed on the negative electrode:

[0068] a. Liquid absorption capacity test

[0069] Using a 1 mL burette, 1 mL of electrolyte was added dropwise to the electrode surface and timed until the electrolyte was completely absorbed. The time t was recorded, and the absorption rate V / t of the electrode was calculated. The test results are shown in Table 2.

[0070] b. Liquid retention rate test

[0071] The theoretical liquid absorption capacity m1 of the electrode was calculated based on the electrode parameters, and the weight m2 of the electrode was measured. The electrode was then immersed in the electrolyte for 24 hours, and its weight m3 was measured. The liquid absorption capacity m3-m2 was calculated, and the liquid retention rate was calculated using the following formula: Liquid retention rate = (m3-m2)*100% / m1. The test results are shown in Table 2.

[0072] Table 2

[0073] Example 1 5.9 92.1％ Example 2 4.8 91.2％ Example 3 4.5 90.4％ Comparative Example 1 3.4 87.7％ Comparative Example 2 3.0 85.8％ Comparative Example 3 1.8 82.9％

[0074] As shown in Table 2, the electrode materials prepared using the porous lithium salt-coated silicon-based composite materials obtained in Examples 1-3 exhibit significantly higher liquid absorption and retention capabilities than those in the comparative examples. This may be because the porous lithium salt-coated silicon-based composite materials in the examples have a larger specific surface area, thus enhancing their liquid absorption and retention capabilities.

[0075] 4.2 Rate and cycle performance tests were conducted on the pouch cells:

[0076] Cyclic performance test: The charge / discharge voltage range was 2.5–4.2V, the temperature was 25±3.0℃, the charge / discharge rate was 0.5C / 1.0C, and the number of cycles was 500. Rate test: The constant current ratio of the material under 2C conditions was tested. The test results are shown in Table 3.

[0077] Table 3

[0078]

[0079]

[0080] As shown in Table 3, the lithium-ion batteries prepared using the porous lithium salt-coated silicon-based composite materials obtained by the preparation methods of Examples 1-3 all exhibit better cycle performance than the comparative examples. This is because the porous lithium salt-coated silicon-based composite materials of the present invention have lower expansion, and the porous structure and high specific surface area enhance the liquid retention of the material, thereby improving cycle performance. At the same time, the porous lithium salt-coated silicon-based composite materials of the examples have higher powder conductivity, which improves the kinetic performance of the lithium-ion battery, thereby improving the constant current ratio during the charge and discharge process, i.e., improving the power performance of the lithium-ion battery.

[0081] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a porous lithium salt-coated silicon-based composite material, characterized by, The method comprises the following steps: 1) adding a silane coupling agent and nano-silicon powder into an organic solution containing an organic nickel salt and a lithium salt, stirring, filtering, and drying to obtain a precursor material; 2) calcining the precursor material to obtain a nickel oxide and lithium salt-coated silicon-based material; 3) etching the nickel oxide and lithium salt-coated silicon-based material in an acid gas atmosphere to obtain the porous lithium salt-coated silicon-based composite material; The acid gas is selected from one of sulfuric acid vapor, nitric acid vapor, and hydrochloric acid vapor; The organic nickel salt comprises at least one of nickel acetylacetone, nickelocene, nickel stearate, and nickel acetate; The lithium salt comprises at least one of lithium titanate, lithium zirconate, lithium meta-aluminate, and lithium niobate; In step 1), the mass ratio of the organic nickel salt, lithium salt, organic solvent, silane coupling agent, and nano-silicon powder is (1-5):(1-5):(350-1100):(1-10):

100.

2. The preparation method according to claim 1, wherein The organic solvent of the organic solution comprises at least one of dimethylbenzene, toluene, cyclohexane, butanediol, N-methylpyrrolidone, N,N dimethylformamide, N,N dimethylacetamide, and carbon tetrachloride.

3. The method of claim 1, wherein, The silane coupling agent comprises at least one of vinyltriethoxysilane, vinyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and γ-ureidopropyltriethoxysilane.

4. The method of claim 1, wherein, In step 1), the average particle size of the nano-silicon powder is 100-500 nm.

5. The preparation method according to claim 1, characterized in that, In step 2), the calcination is performed under the protection of an inert gas, the calcination temperature is 400-900 ℃, and the calcination time is 1-6 h.

6. The method of claim 1, wherein, In step 3), the etching temperature is 100-200 ℃, and the etching time is 0.5-2 h.

7. The preparation method according to claim 1, characterized in that, The sulfuric acid concentration in the sulfuric acid vapor is 20-80 wt%; The nitric acid concentration in the nitric acid vapor is 20-80 wt%; The hydrochloric acid concentration in the hydrochloric acid vapor is 20-37 wt%; After the etching in step 3) is completed, the method further comprises the steps of cooling, washing, and drying.

8. A porous lithium salt-coated silicon-based composite material, characterized by, The porous lithium salt-coated silicon-based composite material is prepared by the method according to any one of claims 1-7.

9. A lithium-ion battery, characterized by The porous lithium salt-coated silicon-based composite material according to claim 8.

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