Negative active material, method for preparing the same, secondary battery, and electric device

Abstract

The application discloses a negative active material, a preparation method of the negative active material, a secondary battery and an electric device, and the negative active material comprises a silicon-based material, a carbon coating layer arranged on the surface of the silicon-based material, and a titanium oxide layer arranged on the surface of the carbon coating layer, and the electron paramagnetic resonance spectrum of the negative active material has a characteristic peak at g=2.002-2.004. The application sets the titanium oxide layer containing oxygen defects on the surface of the carbon-coated silicon-based material, improves the rate performance on the basis of improving the initial coulomb efficiency and the cycle performance, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of silicon-based anode materials, specifically to anode active materials and their preparation methods, secondary batteries, and electrical devices. Background Technology

[0002] Silicon-based materials are a very promising anode material, with a theoretical capacity as high as 3579 mAh g⁻¹. -1 The potential is much higher than that of graphite anode materials. Meanwhile, silicon-based materials have a more suitable operating potential (~0.4V vs. Li / Li). + With its advantages of abundant resources, silicon anode material is expected to become the next generation of lithium-ion battery anode material. However, silicon anodes suffer from problems such as particle breakage due to high volume expansion, poor conductivity, continuous growth of the SEI film on the silicon surface, poor reversibility, and rapid capacity decay, which greatly hinder the commercial application of silicon anode materials.

[0003] Current methods mainly focus on the nanostructuring of silicon materials (nanospheres, nanowires, nanotubes, nanofibers) or their combination with other materials. A common composite material is carbon, but due to the insufficient stiffness of carbon, silicon expands significantly during cycling, and the carbon shell is prone to cracking, thus compromising the structural integrity of the brittle carbon layer and leading to low initial coulombic efficiency and cycling instability. Further coating with other rigid materials can improve initial coulombic efficiency and cycling performance to some extent, but this often results in poor rate performance. Summary of the Invention

[0004] Therefore, the purpose of this invention is to overcome the problems of low initial coulombic efficiency, unstable cycling, and poor rate performance of existing silicon-based active materials, and to provide a negative electrode active material, its preparation method, a secondary battery, and an electrical device.

[0005] The negative electrode active material of the present invention includes a silicon-based material, a carbon coating layer disposed on the surface of the silicon-based material, and a titanium oxide layer disposed on the surface of the carbon coating layer;

[0006] The electron paramagnetic resonance spectrum of the negative electrode active material has a characteristic peak at g = 2.002 to 2.004.

[0007] The negative electrode active material of this invention is further coated with a titanium oxide layer on top of a carbon coating, and the electron paramagnetic resonance (EPR) spectrum of the negative electrode active material exhibits a characteristic peak at g = 2.002–2.004. The g value in the EPR spectrum essentially reflects the characteristics of a local magnetic field within a molecule, which mainly originates from the orbital magnetic moment. In this invention, the presence of a characteristic peak at a specific g value indicates the presence of oxygen vacancies on the surface of the titanium oxide layer. The presence of oxygen vacancies on the titanium oxide surface can adjust the material's structure, enhancing the transport ability of active ions on and within the titanium oxide material, thereby improving the material's rate performance. Furthermore, titanium oxide exhibits good mechanical stability during the insertion / extraction of active ions, thus improving initial coulombic efficiency and cycle performance.

[0008] Furthermore, the Raman spectrum of the negative electrode active material has an I... D / I G The value is 0.80 to 1.10, where I D This indicates that the Raman displacement is within 1300±50cm. -1 peak intensity, I G This indicates that the Raman displacement is within 1480±50cm. -1 The peak intensity. For example, I. D / I G The value can be 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, or a range consisting of any two of the above values.

[0009] In carbon-containing materials, the I-phase of Raman spectroscopy D / I G The value characterizes the degree of disorder of carbon in a material; the higher the ratio, the greater the degree of disorder of C atoms. When I D / I G When the value is between 0.80 and 1.10, the electrochemical performance of the negative electrode active material can be improved.

[0010] Furthermore, the Ti in the titanium oxide layer 4+ With Ti 3+ The molar ratio is 1:(0.2~1.2). For example, the Ti in the titanium oxide layer... 4+ With Ti 3+ The molar ratio can be 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, or a range consisting of any two of the above values. Introducing oxygen vacancies will result in the presence of Ti in the titanium oxide layer. 3+ Therefore, Ti 4+ With Ti 3+ The molar ratio can reflect the concentration of oxygen vacancies, when Ti 4+ With Ti3+ When the molar ratio is 1:(0.2~1.2), the electrochemical performance of the material can be further improved.

[0011] Furthermore, the average thickness of the carbon coating layer is 10 nm to 75 nm. For example, the thickness of the carbon coating layer can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, or a range consisting of any two of the above values.

[0012] Furthermore, the average thickness of the titanium oxide layer is 10 nm to 30 nm. For example, the thickness of the titanium oxide layer can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, or any two of these values. This further improves the cycle performance and rate performance of the battery.

[0013] Furthermore, the silicon-based material includes silicon suboxide.

[0014] This invention also provides a method for preparing the above-mentioned negative electrode active material, comprising the following steps:

[0015] S1. Obtain carbon-coated silicon-based material. Mix the carbon-coated silicon-based material with a titanium source to react and form titanium oxide on the surface of the carbon-coated silicon-based material. After centrifugation, drying and sintering, obtain titanium oxide-coated silicon-based material.

[0016] S2. The silicon-based material coated with titanium oxide is treated with low-temperature plasma to obtain the negative electrode active material.

[0017] Furthermore, the process of the low-temperature plasma treatment is as follows: evacuate the vacuum, then introduce argon gas, and finally start the plasma treatment; the working power of the plasma is 200-350W, and the working time is 10-30min.

[0018] For example, the operating power can be 200W, 250W, 300W, 350W, or a range consisting of any two of the above values; the operating time can be 10min, 15min, 20min, 25min, or 30min. This allows for control over the degree of oxygen defect introduction, further improving the electrochemical performance of batteries using the negative electrode active material described in this invention.

[0019] Furthermore, the volumetric flow rate of the argon gas is 8 to 50 sccm. For example, the volumetric flow rate of the argon gas can be 8 sccm, 12 sccm, 16 sccm, 20 sccm, 24 sccm, 28 sccm, 32 sccm, 36 sccm, 40 sccm, 45 sccm, 50 sccm, or a range consisting of any two of the above values.

[0020] Further, step S1 specifically involves: dispersing the carbon-coated silicon-based material in a solvent, adding a surfactant, adding ammonia and a titanium source while stirring, and obtaining a titanium oxide-coated silicon-based material after stirring, centrifugation, drying, and sintering.

[0021] Furthermore, the solvent includes ethanol, the surfactant includes hexadecylamine, and the titanium source includes isopropyl titanate.

[0022] Furthermore, the sintering temperature is 400–500°C, and the sintering time is 1.5–3 hours.

[0023] The present invention also provides a secondary battery, the secondary battery comprising a negative electrode sheet, the negative electrode sheet comprising the aforementioned negative electrode active material. The secondary battery includes, but is not limited to, lithium-ion batteries and sodium-ion batteries.

[0024] The present invention also provides an electrical device, which includes the aforementioned secondary battery, and the secondary battery serves as the power supply for the electrical device. The electrical device includes, but is not limited to, electric vehicles and energy storage devices.

[0025] The technical solution of this invention has the following advantages:

[0026] This invention provides a titanium oxide layer containing oxygen defects on the surface of a carbon-coated silicon-based material. Titanium oxide exhibits good mechanical stability during the insertion and extraction of active ions. At the same time, the presence of oxygen defects on the surface of the titanium oxide layer can adjust the structure of the material and enhance the ability of active ions to transport on and within the titanium oxide material. This can improve the rate performance of the material while improving the initial coulombic efficiency and cycle performance. Detailed Implementation

[0027] 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.

[0028] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field.

[0029] The carbon-coated silicon-based material used in the embodiments and comparative examples of this invention was purchased from Ningbo Shanshan New Material Technology Co., Ltd., and its model number is P2LA.

[0030] Example 1

[0031] The specific preparation process of a negative electrode active material is as follows:

[0032] Step 1: Place 60g of carbon-coated SiO material (with an average carbon layer thickness of 20nm) in 6L of ethanol and ultrasonically stir until fully dispersed to form a dispersion.

[0033] Step 2: Transfer the dispersion to a fume hood, add 0.95g of hexadecylamine to the fully dispersed dispersion, and keep the solution stirred.

[0034] Step 3: Add 0.8 mL of ammonia water in several portions using a syringe, seal the container opening, and stir for 5 minutes;

[0035] Step 4: Open the container seal, add 10 μl of isopropyl titanate in several portions, close the container opening, and keep stirring for 10 minutes to allow isopropyl titanate to fully hydrolyze in alcohol to generate titanium oxide.

[0036] Step 5: After stirring for 10 minutes, wash the resulting solution in the order of ethanol, deionized water, and ethanol, and centrifuge (3 minutes, 8000 r / min) to remove unreacted isopropyl titanate and incompletely coated titanium oxide.

[0037] Step 6: Place the centrifuged product into a vacuum oven and dry it at 60°C for 3 hours.

[0038] Step 7: Place the dried sample in a tube furnace, heat it to 450°C in an argon atmosphere and hold it for 2 hours. Finally, cool it to room temperature under argon protection and take it out. The result is a silicon-based material coated with titanium dioxide.

[0039] Step 8: At room temperature, place the obtained titanium dioxide-coated silicon-based material in a plasma-enhanced chemical vapor deposition (PECVD) apparatus, evacuate, and after the vacuum degree reaches 0.001 Pa, introduce argon gas at a flow rate of 16 sccm, turn on the plasma power supply, set the plasma working power to 300 W, keep the system running for 30 minutes, then turn off the entire PECVD system, and finally take out the sample. The obtained sample is the negative electrode active material.

[0040] In this embodiment, the negative electrode active material was prepared, and the average thickness of the titanium oxide material layer was found to be 13 nm. The titanium oxide material layer contained Ti... 4+ With Ti 3+The molar ratio was 1:0.58. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was observed at g = 2.002. The I of the Raman spectrum... D / I G The value is 1.03.

[0041] Example 2

[0042] The difference between this embodiment and Embodiment 1 is that the time for the PECVD system to run after argon gas is introduced is changed from 30 minutes to 20 minutes, while the rest is the same as Embodiment 1.

[0043] In this embodiment, the negative electrode active material was prepared, and the average thickness of the titanium oxide material layer was found to be 13 nm. The titanium oxide material layer contained Ti... 4+ With Ti 3+ The content ratio was 1:0.41. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was observed at g = 2.002. The I value of the Raman spectrum was... D / I G The value is 0.91.

[0044] Example 3

[0045] The difference between this embodiment and Embodiment 1 is that the time for the PECVD system to run after argon gas is introduced is changed from 30 minutes to 10 minutes, while the rest is the same as Embodiment 1.

[0046] In this embodiment, the negative electrode active material was prepared, and the average thickness of the titanium oxide material layer was found to be 13 nm. The titanium oxide material layer contained Ti... 4+ With Ti 3+ The content ratio was 1:0.21. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was observed at g = 2.002. The I value of the Raman spectrum was... D / I G The value is 0.82.

[0047] Example 4

[0048] The difference between this embodiment and Embodiment 1 is that the time for the PECVD system to run after argon gas is introduced is changed from 300W to 200W, while the rest is the same as Embodiment 1.

[0049] In this embodiment, the negative electrode active material was prepared, and the average thickness of the titanium oxide material layer was found to be 13 nm. The titanium oxide material layer contained Ti... 4+ With Ti 3+ The content ratio was 1:0.48. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was observed at g = 2.002. The I value of the Raman spectrum was... D / IG The value is 0.97.

[0050] Example 5

[0051] The difference between this embodiment and Embodiment 1 is that the time for the PECVD system to run after argon gas is introduced is changed from 300W to 200W, and the time for the PECVD system to run is changed from 30min to 20min. The rest is the same as in Embodiment 1.

[0052] In this embodiment, the negative electrode active material was prepared, and the average thickness of the titanium oxide material layer was found to be 13 nm. The titanium oxide material layer contained Ti... 4+ With Ti 3+ The content ratio was 1:0.37. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was found at g = 2.002. The I value of the Raman spectrum was... D / I G The value is 0.87.

[0053] Example 6

[0054] The difference between this embodiment and Embodiment 1 is that the time for the PECVD system to run after argon gas is introduced is changed from 300W to 200W, and the time for the PECVD system to run is changed from 30min to 10min. The rest is the same as in Embodiment 1.

[0055] In this embodiment, the negative electrode active material was prepared, and the average thickness of the titanium oxide material layer was found to be 13 nm. The titanium oxide material layer contained Ti... 4+ With Ti 3+ The content ratio was 1:0.31. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was observed at g = 2.002. The I value of the Raman spectrum was... D / I G The value is 0.86.

[0056] Example 7

[0057] The difference between this embodiment and Embodiment 1 is that the time for which the PECVD system is kept running after argon gas is introduced is changed from 300W to 350W, while the rest is the same as in Embodiment 1.

[0058] In this embodiment, the negative electrode active material was prepared, and the average thickness of the titanium oxide material layer was found to be 13 nm. The titanium oxide material layer contained Ti... 4+ With Ti 3+ The content ratio was 1:1.2. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was found at g = 2.002. The I of the Raman spectrum... D / I GThe value is 1.10.

[0059] Example 8

[0060] The difference between this embodiment and Embodiment 1 is that the argon flow rate in step eight is 25 sccm, while the rest is the same as in Embodiment 1.

[0061] In this embodiment, the negative electrode active material was prepared, and the average thickness of the titanium oxide material layer was found to be 13 nm. The titanium oxide material layer contained Ti... 4+ With Ti 3+ The content ratio was 1:0.63. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was found at g = 2.002. The I value of the Raman spectrum was... D / I G The value is 0.95.

[0062] Example 9

[0063] The difference between this embodiment and Embodiment 1 is that the argon flow rate in step eight is 40 sccm, while the rest is the same as in Embodiment 1.

[0064] In this embodiment, the negative electrode active material was prepared, and the average thickness of the titanium oxide material layer was found to be 13 nm. The titanium oxide material layer contained Ti... 4+ With Ti 3+ The content ratio was 1:0.76. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was found at g = 2.002. The I value of the Raman spectrum was... D / I G The value is 1.03.

[0065] Example 10

[0066] The difference between this embodiment and Embodiment 1 is that the argon flow rate in step eight is 50 sccm, while the rest is the same as in Embodiment 1.

[0067] In this embodiment, the negative electrode active material was prepared, and the average thickness of the titanium oxide material layer was found to be 13 nm. The titanium oxide material layer contained Ti... 4+ With Ti 3+ The content ratio was 1:0.81. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was observed at g = 2.002. The I value of the Raman spectrum was... D / I G The value is 1.06.

[0068] Example 11

[0069] The difference between this embodiment and Embodiment 1 is that the argon flow rate in step eight is 8 sccm, while the rest is the same as in Embodiment 1.

[0070] In this embodiment, the average thickness of the titanium dioxide material layer prepared was determined to be 13 nm, and the Ti content in the titanium dioxide material layer was [missing information]. 4+ With Ti 3+ The content ratio was 1:0.27. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was found at g = 2.002. The I value of the Raman spectrum was... D / I G The value is 0.83.

[0071] Example 12

[0072] The difference between this embodiment and Embodiment 1 is that the average thickness of the carbon coating layer is 35 nm, while the rest is the same as in Embodiment 1.

[0073] In this embodiment, the average thickness of the titanium dioxide material layer prepared was determined to be 13 nm, and the Ti content in the titanium dioxide material layer was [missing information]. 4+ With Ti 3+ The content ratio was 1:0.57. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was found at g = 2.002. The I of the Raman spectrum... D / I G The value is 1.04.

[0074] Example 13

[0075] The difference between this embodiment and Embodiment 1 is that the average thickness of the carbon coating layer is 50 nm, while the rest is the same as in Embodiment 1.

[0076] In this embodiment, the average thickness of the titanium dioxide material layer prepared was determined to be 13 nm, and the Ti content in the titanium dioxide material layer was [missing information]. 4+ With Ti 3+ The content ratio was 1:0.59. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was found at g = 2.002. The I of the Raman spectrum... D / I G The value is 1.06.

[0077] Example 14

[0078] The difference between this embodiment and Embodiment 1 is that the average thickness of the carbon coating layer is 75 nm, while the rest is the same as in Embodiment 1.

[0079] In this embodiment, the average thickness of the titanium dioxide material layer prepared was determined to be 13 nm, and the Ti content in the titanium dioxide material layer was [missing information]. 4+ With Ti 3+ The content ratio was 1:0.62. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was found at g = 2.002. The I value of the Raman spectrum was...D / I G The value is 1.05.

[0080] Example 15

[0081] The difference between this embodiment and Embodiment 1 is that the average thickness of the carbon coating layer is 10 nm, while the rest is the same as in Embodiment 1.

[0082] In this embodiment, the average thickness of the titanium dioxide material layer prepared was determined to be 13 nm, and the Ti content in the titanium dioxide material layer was [missing information]. 4+ With Ti 3+ The content ratio was 1:0.56. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was found at g = 2.002. The I of the Raman spectrum... D / I G The value is 1.02.

[0083] Example 16

[0084] The difference between this embodiment and Embodiment 1 is that the time for the PECVD system to run after argon gas is introduced is changed from 30 minutes to 40 minutes, while the rest is the same as Embodiment 1.

[0085] In this embodiment, the negative electrode active material was prepared, and the average thickness of the titanium oxide material layer was found to be 13 nm. The titanium oxide material layer contained Ti... 4+ With Ti 3+ The content ratio was 1:1.05. After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, a corresponding characteristic peak was observed at g = 2.002. The I of the Raman spectrum... D / I G The value is 1.07.

[0086] Comparative Example 1

[0087] The negative electrode active material described in this comparative example is the carbon-coated SiO material used in Example 1.

[0088] The average thickness of the carbon material layer in the negative electrode active material described in this comparative example was found to be 20 nm.

[0089] Comparative Example 2

[0090] The negative electrode active material described in this comparative example is the titanium dioxide-coated silicon-based material prepared in step seven of Example 1.

[0091] The negative electrode active material described in this comparative example, after testing, showed that the average thickness of the titanium oxide material layer was 13 nm, and the thickness of the carbon material layer was 20 nm. The titanium oxide layer did not contain Ti. 3+After electron paramagnetic resonance spectroscopy and Raman spectroscopy tests, no corresponding characteristic peak was found at g = 2.002. The Ig of the Raman spectrum... D / I G The value is 0.92.

[0092] Performance testing

[0093] Using the materials from the examples and comparative examples, CR2032 coin cells and 3Ah soft-pack all-electric batteries were prepared, and the performance of the batteries was tested.

[0094] The negative electrode ratio of the coin cell is 93:3:4, where the active material is the sample from the example or comparative example. The coin cell is mainly tested for its specific capacity and initial efficiency. Initial efficiency = charging capacity / discharging capacity. (A coin cell is equivalent to a half cell, using metallic Li as the counter electrode. Some electrochemical properties of the negative electrode material itself can be obtained using coin cells.)

[0095] The negative electrode formulation of the pouch battery is as follows: active material: conductive agent SP: modified polyacrylic acid in a mass ratio of 93:3:4. The positive electrode uses conventional high-nickel cobalt manganese oxide lithium NCM811 positive electrode material, with an active material: conductive agent SP: binder mass ratio of 97:2:1. The pouch battery is primarily characterized by cycle life and negative electrode thickness expansion. The active material consists of 12% of the example or comparative sample and 88% artificial graphite. The electrolyte is 1.2 mol / L LiPF6, and the solvent is EC / DMC in a molar ratio of 1:1 plus 10 wt% FEC (equivalent to FEC being 10% of the total mass of EC and DMC). (EC: ethylene carbonate, DMC: dimethyl carbonate, FEC: fluoroethylene carbonate).

[0096] The performance testing method is as follows:

[0097] (1) First-cycle negative electrode specific capacity performance test: first-cycle discharge capacity mAh / mass of negative electrode active material g;

[0098] (2) First-cycle coulombic efficiency: First charge capacity / First discharge capacity * 100%;

[0099] (3) Initial charge specific capacity: Initial charge capacity / active material mass (mAh / g);

[0100] (4) 4C rate discharge capacity retention test: 4C discharge capacity / 1C discharge capacity;

[0101] (5) DC internal resistance DCR test: Divide the battery capacity and adjust it to 50% SOC. Discharge at 5C for 10s and test the discharge resistance. Resistance DCR = (V0-V10) / I, where V0 is the potential before discharge, V10 is the potential at the 10th second of discharge, and I is the discharge current 5C.

[0102] (6) Capacity retention test: ① Charging: Charge at a constant current density of 1C to 4.2V and then let stand for 10min; ② Discharging: Discharge at a constant current density of 1C to 2.5V and let stand for 0min. The discharge capacity is recorded as Qn (n=1,2,3……400); ③ Repeat “①, ②” for 400 cycles; The capacity retention rate of the soft pack battery after 400 cycles is: Q400 / Q1;

[0103] (7) Volume expansion rate test: 400 cycles, fully charged disassembly, micrometer caliper thickness is d2, fresh electrode sheet roll forming thickness is d1, soft pack battery full charge expansion rate calculation after 400 cycles: (d2-d1) / (d1-8);

[0104] (8) Lithium plating test: ① Charging: Charge at a constant current density of 2.4C to 4.2V and let stand for 10 minutes; ② Discharging: Discharge at a constant current density of 1C to 2.5V and let stand for 10 minutes; After 10 cycles, charge at a constant current density of 1.6C to 4.2V and disassemble to observe the negative electrode interface.

[0105] The test results are shown in Tables 1 and 2 below.

[0106] Table 1

[0107]

[0108]

[0109] As shown in Table 1 above, the composite material coated with titanium dioxide exhibits a significant improvement in specific capacity and first coulombic efficiency compared to pure SiO. Furthermore, the introduction of oxygen defects in titanium dioxide (as in Examples 1-7) results in a marked improvement in specific capacity and first coulombic efficiency compared to the defect-free Comparative Example 2.

[0110] Considering different defect introduction conditions, the improvement in specific capacity and initial coulombic efficiency is not simply an increase in plasma treatment time and plasma set operating power: taking Example 1 with the best performance as a benchmark, its plasma treatment time is 30 min and the plasma set operating power is 300 W. When its plasma treatment time is gradually reduced, its specific capacity and initial coulombic efficiency gradually decrease. Thus, under the current operating power condition of 300 W, the effect of time on electrochemical performance within 10 min to 30 min is correlated, and the electrochemical performance increases with the increase of treatment time (Examples 1-3); when the plasma operating power is changed to 200 W (as in Examples 4-6), the electrochemical performance does not simply increase with the increase of plasma treatment time. Instead, the electrochemical performance decreases after increasing from the initial 10 min to 20 min, and then rises to the best performance in Examples 4-6 after increasing from 20 min to 30 min. The reason for the different correlation between electrochemical performance and time under these two different power levels may be that when the plasma system power is 200W, the plasmaization state of the introduced gas is unstable, and the provided energy may not be sufficient to completely plasmaize the introduced gas. Therefore, it may be impossible to simply increase the effect with increasing processing time. In contrast, under the 300W operating power condition, the plasma effect in the reaction chamber may be more stable. As seen in Example 7, simply increasing the operating power from 300W to 350W did not directly enhance the electrochemical performance; instead, it decreased. This suggests that the effect of oxygen vacancies may not be better the more they are introduced.

[0111] Table 2

[0112]

[0113]

[0114] As can be seen from the experimental data in Table 2 above, Example 1 shows significant improvements in rate capability, long-cycle performance, and multiplication performance. This oxygen defect strategy can provide some practical significance for improving the performance of SiO.

[0115] 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 negative electrode active material, characterized in that, It includes a silicon-based material, a carbon coating layer disposed on the surface of the silicon-based material, and a titanium oxide layer disposed on the surface of the carbon coating layer; The electron paramagnetic resonance spectrum of the negative electrode active material has a characteristic peak at g = 2.002~2.004; The Raman spectrum of the negative electrode active material is I D / I G The value is 0.80~1.03, where I D This indicates that the Raman displacement is within 1300±50cm. -1 peak intensity, I G This indicates that the Raman displacement is within 1480±50cm. -1 The peak intensity; the Ti in the titanium oxide layer 4+ With Ti 3+ The molar ratio is 1:(0.2 ~ 0.58); The preparation method of the negative electrode active material includes the following steps: S1. Obtain carbon-coated silicon-based material. Mix the carbon-coated silicon-based material with a titanium source and react to form titanium oxide on the surface of the carbon-coated silicon-based material. After centrifugation, drying and sintering, obtain titanium oxide-coated silicon-based material. S2. The titanium oxide-coated silicon-based material is treated with plasma to obtain the negative electrode active material; the plasma treatment process is as follows: vacuuming, then introducing argon gas, and finally starting the plasma treatment; the working power of the plasma is 200~350W, and the working time is 10~40min; The volumetric flow rate of the argon gas is 8~50 sccm.

2. The negative electrode active material according to claim 1, characterized in that, The average thickness of the carbon coating layer is 10 nm to 75 nm.

3. The negative electrode active material according to claim 1, characterized in that, The average thickness of the titanium oxide layer is 10 nm to 30 nm.

4. A secondary battery, characterized in that, It includes a negative electrode sheet, wherein the negative electrode sheet comprises the negative electrode active material according to any one of claims 1 to 3.

5. An electrical device, characterized in that, Includes the secondary battery as described in claim 4.

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