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

Abstract

The application belongs to the technical field of negative electrode materials, and particularly relates to a negative electrode active material, a preparation method thereof, a secondary battery and an electric device. The negative electrode active material provided by the application comprises a silicon-based material with a carbon layer arranged on at least part of the surface and a titanium-containing compound layer containing nitrogen arranged on the surface of the carbon layer. The titanium-containing compound layer containing nitrogen makes the negative electrode active material have more advantages in electrical conductivity and lithium ion transmission speed than a pure titanium-containing compound, and thus a lithium ion battery using the negative electrode active material has better electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of negative electrode material technology, specifically relating to negative electrode active materials and their preparation methods, secondary batteries and electrical equipment. Background Technology

[0002] The theoretical capacity of traditional graphite anodes is only 372 mAh g. -1 This severely limits the application and development of lithium batteries. Silicon has a theoretical capacity as high as 3579 mAh g. -1 Silicon has a conductivity approximately ten times that of industrial graphite, making it one of the most promising anode materials with broad application prospects. However, silicon exhibits poor conductivity and large volume changes (~300%) during lithium insertion and extraction, easily leading to electrode pulverization and gradual loss of electrical contact between the active material and the current collector. Furthermore, the pulverization of active particles easily exposes the surface, repeatedly forming a solid electrolyte interphase (SEI), resulting in rapid electrolyte consumption. These problems directly lead to poor cycle performance and rate capability of silicon-based anode materials.

[0003] Micro- and nanostructure design provides an effective method for addressing the volume expansion problem of silicon-based materials. Current research in micro- and nanostructure design mainly focuses on the creation of specialized silicon nanostructures and silicon-doped composite structures, such as nanoporous silicon and core-shell structures. In addition, the volume expansion of silicon can be modulated by secondary protective materials, such as carbon, NiO, and TiO2. Among these, titanium oxide exhibits the smallest volume change (~4%) and good mechanical stability during lithium insertion and extraction, making it an ideal material for constructing stable silicon anodes. However, the poor conductivity of titanium oxide limits its application in silicon anode protective materials. Summary of the Invention

[0004] Therefore, the technical problem to be solved by this application is to overcome the shortcomings of existing titanium oxide-coated silicon-based materials, such as limited improvement in electrical performance, the need for modification at high temperature which affects the electrochemical performance of silicon-based materials and high energy consumption, thereby providing a negative electrode active material and its preparation method, a secondary battery and an electrical device.

[0005] Therefore, this application provides the following technical solution:

[0006] A first aspect of this application provides a negative electrode active material, the negative electrode active material comprising a silicon-based material and a carbon layer disposed on at least a portion of the surface of the silicon-based material; a titanium-containing compound layer is disposed on the surface of the carbon layer, the titanium-containing compound layer containing nitrogen element.

[0007] Optionally, the nitrogen content is 0.13% to 3.5% based on the total mass of the negative electrode active material.

[0008] Optionally, the Raman spectrum of the negative electrode active material... D / I G The value ranges from 0.96 to 1.2, where I... D This indicates that the Raman displacement is within 1300±50cm. -1 The intensity of the nearby peak, I G This indicates that the Raman displacement is within 1480±50cm. -1 Peak intensity.

[0009] Optionally, the electron paramagnetic resonance spectrum of the negative electrode active material has a characteristic peak at g = 2.002 to 2.004.

[0010] Optionally, the titanium-containing compound includes titanium oxide.

[0011] A second aspect of this application provides a method for preparing a negative electrode active material, comprising the following steps:

[0012] S1, disperse at least a portion of the silicon-based material with a carbon layer on its surface in a solvent, add a surfactant, add ammonia water under stirring conditions, and keep stirring;

[0013] S2, add titanium source, keep stirring, separate solid and liquid, wash, dry, calcine to obtain solid product with titanium compound layer on surface;

[0014] S3, at room temperature, the solid product with a titanium compound layer on its surface is subjected to a first plasma-enhanced chemical vapor deposition treatment under the condition of argon gas introduction, and then a second plasma-enhanced chemical vapor deposition treatment is performed under a mixed gas of nitrogen and hydrogen to obtain the negative electrode active material.

[0015] Optionally, the power of the first plasma-enhanced chemical vapor deposition treatment is 250–400 W, and the time is 10–50 min.

[0016] Optionally, the power of the second plasma-enhanced chemical vapor deposition process is 200–400 W, and the time is 10–50 min.

[0017] Optionally, the flow rate ratio of nitrogen to hydrogen introduced during the second plasma-enhanced chemical vapor deposition process is (15-23):(5-13).

[0018] Optionally, the preparation method of the negative electrode active material satisfies at least one of the following (1)-(3):

[0019] (1) The surfactant includes hexadecylamine;

[0020] (2) The titanium source includes at least one of isopropyl titanate, tetrabutyl titanate, and tetraethyl titanate.

[0021] (3) The solvent includes at least one of ethanol, ethylene glycol, deionized water and propanol.

[0022] Optionally, in the preparation method of the negative electrode active material, the calcination temperature in step S2 is 400-500℃, and the calcination time is 2-5h.

[0023] Optionally, the silicon-based material includes at least one of silicon suboxide, silicon, and silicon alloys.

[0024] Optionally, the preparation method of the negative electrode active material specifically includes the following steps:

[0025] Step 1: Place the silicon-based material containing the carbon coating in ethanol and ultrasonically stir to disperse it evenly;

[0026] Step 2: Transfer the solution to a fume hood, add hexadecylamine to the fully dissolved solution, and keep the solution stirred.

[0027] Step 3: Add ammonia water in portions using a syringe, seal the container opening, and maintain stirring time;

[0028] Step 4: Open the container seal, add isopropyl titanate in portions, close the container opening, and keep stirring.

[0029] Step 5: After stirring for a certain period of time, immediately follow the steps below to centrifuge the obtained solution, and centrifuge the obtained solution in the order of solvent ethanol, deionized water, and ethanol under certain time and speed conditions.

[0030] Step 6: Place the centrifuged product into a vacuum oven and dry it under certain temperature and time conditions;

[0031] Step 7: After drying, the sample is placed in a tube furnace and heated to a certain temperature in an argon atmosphere. After holding the temperature for a period of time, it is finally cooled to room temperature under inert gas protection and taken out to obtain a silicon-based material coated with titanium compound.

[0032] Step 8: At room temperature, place the obtained titanium compound-coated silicon-based material in a plasma-enhanced chemical vapor deposition (PECVD) apparatus. A schematic diagram of the apparatus structure is shown below. Figure 1As shown, the left side of the device is the inlet end 1, and the right side is the outlet end 2. The outlet end 2 is connected to the vacuum pump system, and the inlet end 1 is connected to the gas and the corresponding flow meter. Near the inlet end 1, there is a copper wire wound on the glass tube, and connected to the copper wire are the RF power supply 3 and the RF power supply matching device 4. The RF power supply matching device 4 is used to adjust the circuit reflection power of the RF power supply 3. The specific operation is as follows: turn on the vacuum pump system, and after the intrinsic vacuum degree reaches a certain standard, first introduce a certain flow rate of argon gas, turn on the plasma power supply, set the plasma power, run for a certain time, then turn off the plasma and stop the introduction of argon gas, then introduce a certain flow rate of nitrogen gas or nitrogen-containing gas, and then introduce a certain flow rate of hydrogen gas, turn on the plasma power supply, set the plasma working power, keep the system running for a certain time, then turn off the entire PECVD system, and finally take it out to obtain the negative electrode active material.

[0033] A third aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active material layer disposed on the surface of the current collector, the negative electrode active material layer comprising the aforementioned negative electrode active material.

[0034] A fourth aspect of the present invention provides an electrical device comprising the aforementioned lithium-ion battery. The lithium-ion 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.

[0035] The technical solution of this application has the following advantages:

[0036] The negative electrode active material provided in this application includes a silicon-based material with a carbon layer on at least part of its surface and a titanium-containing compound layer containing nitrogen on the surface of the carbon layer. The titanium-containing compound layer containing nitrogen gives the negative electrode active material an advantage in conductivity and lithium-ion transport speed compared to pure titanium-containing compounds, thereby enabling lithium-ion batteries using this negative electrode active material to have better electrochemical performance. Attached Figure Description

[0037] 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.

[0038] Figure 1 This is a schematic diagram of the plasma-enhanced chemical vapor deposition apparatus used in this application;

[0039] Figure 2 This is the electron paramagnetic resonance spectrum of the negative electrode active material provided in Embodiment 1 of this application.

[0040] Figure label:

[0041] 1. Inlet; 2. Outlet; 3. RF power supply; 4. RF power matching unit. Detailed Implementation

[0042] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments. 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.

[0043] 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.

[0044] This application provides a negative electrode active material, the negative electrode active material comprising a silicon-based material and a carbon layer disposed on at least a portion of the surface of the silicon-based material; a titanium-containing compound layer is disposed on the surface of the carbon layer, the titanium-containing compound layer containing nitrogen element.

[0045] The negative electrode active material described in this application includes a titanium-containing compound layer containing nitrogen. The intrinsic conductivity and lithium-ion transport rate of the titanium-containing compound are not high, but the introduction of nitrogen doping adjusts the structure of the material, which can improve the ability of lithium ions to transport on the surface and inside the titanium-containing compound material, thereby improving the electrochemical performance of the entire material.

[0046] In some embodiments of this application, the titanium-containing compound includes titanium oxide.

[0047] To further improve the electrochemical performance of the negative electrode active material, in some embodiments of this application, the nitrogen content is 0.13% to 3.5% based on the total mass of the negative electrode active material. For example, the nitrogen content can be 0.13%, 0.4%, 0.7%, 1.0%, 1.3%, 1.6%, 1.9%, 2.2%, 2.5%, 2.8%, 3.0%, 3.2%, 3.5%, or a range consisting of any two of the above values.

[0048] In some embodiments of this application, the Raman spectrum of the negative electrode active material is I D / I G The value ranges from 0.96 to 1.2, where I... D This indicates that the Raman displacement is within 1300±50cm. -1 The intensity of the nearby peak, I GThis indicates that the Raman displacement is within 1480±50cm. -1 Peak intensity. For example, negative electrode active material I. D / I G The value can be 0.96, 0.98, 1.0, 1.02, 1.05, 1.08, 1.1, 1.15, 1.2, or a range consisting of any two of the above values. The I value in the Raman spectrum of the material... 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 0.96 and 1.2, the electrochemical performance of the negative electrode active material can be improved.

[0049] In some embodiments of this application, the electron paramagnetic resonance spectrum of the negative electrode active material exhibits a characteristic peak at g = 2.002–2.004. The spectral splitting factor, or g-factor or g-value for short, is a physical quantity. The g-value essentially reflects the characteristics of a local magnetic field within a molecule, primarily derived from the orbital magnetic moment. The stronger the coupling between spin and orbital motion, the greater the increase in the g-value for free electrons; therefore, the g-value provides information about the molecular structure. In this application, the presence of a characteristic peak at a specific g-value indicates the presence of oxygen vacancies on the surface of the titanium-containing compound layer. The presence of oxygen vacancies on the surface of the titanium-containing compound layer can adjust the material's structure, enhancing the transport capacity of lithium ions on and within the titanium-containing compound material, thereby improving the material's electrochemical performance. In another embodiment of this application, a method for preparing a negative electrode active material is also provided, comprising the following steps:

[0050] S1, disperse at least a portion of the silicon-based material with a carbon layer on its surface in a solvent, add a surfactant, add ammonia water under stirring conditions, and keep stirring;

[0051] S2, add titanium source, keep stirring, separate solid and liquid, wash, dry, calcine to obtain solid product with titanium compound layer on surface;

[0052] S3, at room temperature, the solid product with a titanium compound layer on its surface is subjected to a first plasma-enhanced chemical vapor deposition treatment under the condition of argon gas introduction, and then a second plasma-enhanced chemical vapor deposition treatment is performed under a mixed gas of nitrogen and hydrogen to obtain the negative electrode active material.

[0053] In some embodiments of this application, the power of the first plasma-enhanced chemical vapor deposition (PECVD) treatment is 250–400 W. For example, the power can be 250 W, 300 W, 350 W, 400 W, or a range consisting of any two of these values. The primary purpose of the first PECVD treatment is to introduce oxygen vacancies. When the power is controlled at 250–400 W, the concentration of oxygen vacancies in the material can be controlled within a suitable range, enhancing the transport capacity of lithium ions on and within the titanium-containing compound material, thereby improving the electrochemical performance of the material.

[0054] In some embodiments of this application, the duration of the first plasma-enhanced chemical vapor deposition (PECVD) treatment is 10–50 min. For example, the time can be 10 min, 20 min, 30 min, 40 min, 50 min, or a range consisting of any two of the above values. This allows for control of the oxygen defect concentration in the material within a suitable range, enhancing the transport capacity of lithium ions on and within the titanium-containing compound material, thereby improving the electrochemical performance of the material.

[0055] In some embodiments of this application, the power of the second plasma-enhanced chemical vapor deposition process is 200–400 W. For example, the power can be 200 W, 250 W, 300 W, 350 W, 400 W, or a range consisting of any two of the above values. When the power is controlled at 200–400 W, appropriate nitrogen doping levels and oxygen defect concentrations can be introduced to enhance the transport capability of lithium ions on and within the titanium-containing compound material, thereby improving the electrochemical performance of the material.

[0056] In some embodiments of this application, the duration of the second plasma-enhanced chemical vapor deposition (PECVD) treatment is 10–50 min. For example, the time can be 10 min, 20 min, 30 min, 40 min, 50 min, or a range consisting of any two of the above values. This allows for control of the amount of nitrogen doping and the concentration of oxygen vacancies in the material within appropriate ranges, enhancing the transport capacity of lithium ions on and within the titanium-containing compound material, thereby improving the electrochemical performance of the material.

[0057] In some embodiments of this application, the flow rate ratio of nitrogen to hydrogen introduced during the second plasma-enhanced chemical vapor deposition process is (15-23):(5-13). For example, it can be 15:13, 20:8, or 23:5. Adjusting the flow rate ratio of nitrogen to hydrogen can control the concentration of oxygen vacancies and the amount of nitrogen doping within a suitable range, thereby improving the electrochemical performance of the material.

[0058] In some embodiments of this application, the surfactant includes hexadecylamine; the titanium source includes at least one of isopropyl titanate, tetrabutyl titanate, and tetraethyl titanate; and the solvent includes at least one of ethanol, ethylene glycol, deionized water, and propanol.

[0059] In some embodiments of this application, the preparation method of the negative electrode active material, the calcination temperature in step S2 is 400-500°C and the calcination time is 2-5 hours.

[0060] In some embodiments of this application, the silicon-based material includes at least one of silicon suboxide, silicon, and silicon alloys.

[0061] This application also provides a lithium-ion battery, the lithium-ion battery including a negative electrode sheet, the negative electrode sheet including a current collector and a negative electrode active material layer disposed on the surface of the current collector, the negative electrode active material layer including the above-mentioned negative electrode active material.

[0062] This application also provides an electrical device comprising the aforementioned lithium-ion battery. The lithium-ion battery serves as the power source for the electrical device. The electrical device includes, but is not limited to, electric vehicles and energy storage devices.

[0063] Example 1

[0064] This embodiment provides a negative electrode active material, the preparation method of which includes the following steps:

[0065] Step 1: Place 60g of SiO (Shanghai Shanshan Technology) with carbon coating into 6L of ethanol and ultrasonically stir until it is evenly dispersed.

[0066] Step 2: Transfer the solution to a fume hood, add 0.95g of hexadecylamine to the fully dissolved solution, and keep the solution stirred.

[0067] Step 3: Add 0.8 mL of ammonia water in 5 portions using a syringe, seal the container opening, and keep stirring for 3 minutes.

[0068] Step 4: Open the container seal and add 150mL of isopropyl titanate (Aladdin, 99%) in 10 portions. Seal the container and keep stirring.

[0069] Step 5: After stirring for 10 minutes, centrifuge the obtained solution according to the following steps, centrifuge at 8000 r / min for 3 minutes, and then centrifuge the obtained solution in the order of ethanol, deionized water, and ethanol as solvents.

[0070] Step 6: Place the centrifuged product into a vacuum oven and dry it at 60°C for 12 hours.

[0071] Step 7: After drying, the sample is placed in a tube furnace and heated to 450°C in an Ar gas protective environment. After holding at this temperature for 2 hours, the sample is cooled to room temperature under Ar gas protection and then removed.

[0072] Step 8: At room temperature, place the material obtained in the above steps into a plasma-enhanced chemical vapor deposition (PECVD) apparatus (e.g., Figure 1 (As shown), turn on the vacuum pump system to evacuate the device until the intrinsic vacuum reaches 1.0 × 10⁻⁶. -2 ~1.0×10 -4 After Pa, 16 sccm of argon gas was introduced for the first plasma-enhanced chemical vapor deposition (PECVD) treatment. The plasma system power output was set to 300W. After running for 30 minutes, the plasma power was turned off. Then, 20 sccm of nitrogen gas and 8 sccm of hydrogen gas were introduced, and the PECVD system power was turned on for the second plasma-enhanced chemical vapor deposition (PECVD) treatment. The plasma working power was set to 300W. After running the system for 30 minutes, the entire PECVD system was turned off. Finally, the sample was taken out, and the result is the negative electrode active material.

[0073] Example 2

[0074] The difference between this embodiment and Embodiment 1 is that the PECVD system remains running for 20 minutes after nitrogen and hydrogen are introduced.

[0075] Example 3

[0076] The difference between this embodiment and Embodiment 1 is that the PECVD system remains running for 10 minutes after nitrogen and hydrogen are introduced.

[0077] Example 4

[0078] The difference between this embodiment and Embodiment 1 is that the PECVD system remains running for 40 minutes after nitrogen and hydrogen are introduced.

[0079] Example 5

[0080] The difference between this embodiment and Embodiment 1 is that the PECVD system remains running for 50 minutes after nitrogen and hydrogen are introduced.

[0081] Example 6

[0082] The difference between this embodiment and Embodiment 1 is that the PECVD system is kept running for 20 minutes after argon gas is introduced.

[0083] Example 7

[0084] The difference between this embodiment and Embodiment 1 is that the PECVD system is kept running for 10 minutes after argon gas is introduced.

[0085] Example 8

[0086] The difference between this embodiment and Embodiment 1 is that the PECVD system is kept running for 40 minutes after argon gas is introduced.

[0087] Example 9

[0088] The difference between this embodiment and Embodiment 1 is that the PECVD system is kept running for 50 minutes after argon gas is introduced.

[0089] Example 10

[0090] The difference between this embodiment and Embodiment 1 is that the PECVD system is kept running for 20 minutes after argon is introduced, and the PECVD system is kept running for 20 minutes after nitrogen and hydrogen are introduced.

[0091] Example 11

[0092] The difference between this embodiment and Embodiment 1 is that the PECVD system is kept running for 10 minutes after argon gas is introduced, and the PECVD system is kept running for 10 minutes after nitrogen and hydrogen gas are introduced.

[0093] Example 12

[0094] The difference between this embodiment and Embodiment 1 is that the PECVD system was kept running for 40 minutes after argon was introduced, and the PECVD system was kept running for 40 minutes after nitrogen and hydrogen were introduced.

[0095] Example 13

[0096] The difference between this embodiment and Embodiment 1 is that, during the first plasma-enhanced chemical vapor deposition process, the output power of the plasma system power supply is set to 250W.

[0097] Example 14

[0098] The difference between this embodiment and Embodiment 1 is that, during the first plasma-enhanced chemical vapor deposition process, the output power of the plasma system power supply is set to 400W.

[0099] Example 15

[0100] The difference between this embodiment and Embodiment 1 is that, during the second plasma-enhanced chemical vapor deposition process, the output power of the plasma system power supply is set to 200W.

[0101] Example 16

[0102] The difference between this embodiment and Embodiment 1 is that, during the second plasma-enhanced chemical vapor deposition process, the output power of the plasma system power supply is set to 400W.

[0103] Example 17

[0104] The difference between this embodiment and Embodiment 1 is that, during the second plasma-enhanced chemical vapor deposition process, the nitrogen flow rate is 15 sccm and the hydrogen flow rate is 13 sccm.

[0105] Example 18

[0106] The difference between this embodiment and Embodiment 1 is that, during the second plasma-enhanced chemical vapor deposition process, the nitrogen flow rate is 23 sccm and the hydrogen flow rate is 5 sccm.

[0107] Comparative Example 1

[0108] The negative electrode active material described in Comparative Example 1 is SiO containing a carbon coating layer, as described in Example 1.

[0109] Comparative Example 2

[0110] Compared to Example 1, the material is not modified in step eight.

[0111] test

[0112] 1. Physicochemical property testing

[0113] The surface of the negative electrode active materials provided in Examples 1-18 was scanned using EDS technology to obtain the nitrogen content in the materials, which is recorded in Table 1.

[0114] The electron paramagnetic resonance spectra of the negative electrode active materials provided in Examples 1-18 were obtained by measuring the EPR technique. Figure 2 This is the electron paramagnetic resonance spectrum of the negative electrode active material provided in Embodiment 1 of this application. Figure 2 As can be seen from the data, the negative electrode active material of Example 1 exhibits a characteristic peak at g = 2.002–2.004. The electron paramagnetic resonance spectra of the negative electrode active materials provided in Examples 2–18 are consistent with… Figure 2 Similarly, I will not elaborate further.

[0115] The surface of the negative electrode active materials provided in Examples 1-18 was measured using Raman spectroscopy, with I... D and I G I is calculated from the peak intensity. D / I G The size of I D / I G Recorded in Table 1.

[0116] 2. Electrochemical performance testing

[0117] (I) The negative electrode active materials obtained from the examples and comparative examples were used to fabricate coin cells CR2032 for electrochemical performance testing. The negative electrode ratio of the coin cells was active material: conductive agent SP: modified polyacrylic acid = 93:3:4, where the active material was the sample from the examples or comparative examples. Celgard 2500 was used as the separator. The main tests for the coin cells were the specific capacity and initial efficiency of the negative electrode, where initial efficiency = charge capacity / discharge capacity.

[0118] (II) The negative electrode active materials obtained in the examples and comparative examples were used to fabricate 3Ah soft-pack full cells for electrochemical performance testing. The negative electrode formulation of the soft-pack battery was an active material: conductive agent SP: modified polyacrylic acid mass ratio of 93:3:4. The positive electrode used was a conventional high-nickel cobalt manganese oxide lithium NCM811 positive electrode material, with an active material: conductive agent SP: binder (CMC) mass ratio of 97:2:1. The soft-pack battery was mainly characterized by cycle life and negative electrode thickness expansion. The negative electrode active material consisted of 12% of the negative electrode active material described in the examples or comparative examples and 88% artificial graphite. The electrolyte was 1.2 mol / L LiPF6, and the solvent was EC / DMC with 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). The separator was Celgard 2500.

[0119] 1) First-cycle negative electrode specific capacity performance test: first-cycle discharge capacity mAh / negative electrode active material mass g.

[0120] 2) First-cycle coulombic efficiency: First charge capacity / First discharge capacity × 100%.

[0121] 3) Initial charge specific capacity: Initial charge capacity / active material mass (mAh / g).

[0122] 4) 4C discharge capacity retention test: Battery 4C discharge capacity / Battery 1C discharge capacity.

[0123] 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. The 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 at 5C.

[0124] 6) Capacity retention test: ① Charging: Charge at a constant current density of 1C to 4.2V, let stand for 10 minutes; ② Discharging: Discharge at a constant current density of 1C to 2.5V, let stand for 10 minutes, and record the discharge capacity as Qn (n=1,2,3……400); ③ Repeat "①, ②" for 400 cycles. The capacity retention rate after 400 cycles is: Q400 / Q1.

[0125] 7) Volume expansion test: After 400 cycles of battery cycling, the battery is disassembled at full charge. The thickness is d2 on the micrometer caliper and d1 on the fresh electrode roll. The expansion after 400 full charge cycles is calculated as (d2-d1) / (d1-8).

[0126] 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 for full charge and disassemble to observe the negative electrode interface.

[0127] Table 1

[0128]

[0129]

[0130] Table 2

[0131] <![CDATA[Initial negative electrode specific capacity (mAh g -1 )]]> First lap Coulomb efficiency Example 1 1808.6 80.5％ Example 2 1745.1 79.7％ Example 3 1628.4 78.2％ Example 4 1723.8 79.1％ Example 5 1622.1 77.8％ Example 6 1634.8 78.2％ Example 7 1688.5 79.1％ Example 8 1719.4 78.9％ Example 9 1631.2 78.4％ Example 10 1737.4 79.2％ Example 11 1627.8 78.4％ Example 12 1645.8 78.9％ Example 13 1725.1 79.3％ Example 14 1739.3 79.5％ Example 15 1740.9 79.6％ Example 16 1720.8 78.8％ Example 17 1756.2 79.9％ Example 18 1726.0 79.4％ Comparative Example 1 1588.2 67.1％ Comparative Example 2 1624.1 71.6％

[0132] Table 3

[0133]

[0134] As shown in Tables 2 and 3 above, the experimental data indicate that Example 1 exhibits the best results in terms of oxygen defect and nitrogen doping treatment effects. The key parameters represented by Example 1 are argon treatment time (30 min) and nitrogen and hydrogen treatment time (30 min). With a simultaneous decrease in both treatment times (as in Examples 10 and 11), the electrochemical performance gradually declines; specifically, the specific capacity and coulombic first effect gradually decrease. This indicates that as the degree of oxygen defect and nitrogen doping increases, the overall electrochemical performance of the material is significantly improved, but not indiscriminately. When the reaction power and time increase to a certain extent, the electrochemical performance directly declines (as in Example 12). Therefore, within certain limits, controlling the effects of oxygen defect and nitrogen doping is beneficial for improving the properties of titanium-containing compound coatings. When the argon treatment time is kept high while the nitrogen and hydrogen treatment times are gradually reduced, the electrochemical performance of the material gradually decreases (as in Examples 2 and 3). Similarly, when the nitrogen and hydrogen treatment times are kept high while the argon treatment time is gradually reduced, the electrochemical performance of the resulting composite material gradually increases. This indicates that when oxygen defects and nitrogen doping have the same effect, they do not necessarily have a strong linear synergy in promoting the experimental results. Rather, the desired effect needs to be achieved within certain limits. This may be because the presence of hydrogen can promote the activity of N while also promoting the generation of oxygen defects, thus affecting the synergistic effect of the two.

[0135] As can be seen from the experimental data in Tables 2 and 3 above, the improvement in rate capability and cycling performance of the composite material after oxygen vacancies and nitrogen doping is obvious, with the nitrogen-doped and oxygen-vacancies-introduced material in Example 1 exhibiting the best performance. Compared to the comparative material, the full-charge expansion rate of the material in the examples was effectively suppressed, and the capacity retention rate was also significantly improved during long-term cycling at room temperature.

[0136] The material represented by Example 1 showed the best performance after the lithium plating test, with no lithium plating occurring, indicating a significant improvement in its kinetic performance. Similarly, the DCR test result of the material in Example 1 was indeed the lowest, indicating that the overall kinetics of the electrode was also significantly improved. The kinetic performance of the modified material and the lithium plating test result without lithium plating can be mutually verified.

[0137] 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, The invention includes a silicon-based material and a carbon layer disposed on at least a portion of the surface of the silicon-based material; a titanium-containing compound layer is disposed on the surface of the carbon layer, and the titanium-containing compound layer contains nitrogen. The electron paramagnetic resonance spectrum of the negative electrode active material has a characteristic peak at g=2.002~2.

004.

2. The negative electrode active material according to claim 1, characterized in that, Based on the total mass of the negative electrode active material, the nitrogen content is 0.13% to 3.5%.

3. The negative electrode active material according to any one of claims 1 to 2, characterized in that, The Raman spectrum of the negative electrode active material is I D / I G The value ranges from 0.96 to 1.2, where I... D This indicates that the Raman displacement is within 1300±50cm. -1 The intensity of the nearby peak, I G This indicates that the Raman displacement is within 1480±50cm. -1 Peak intensity.

4. A method for preparing a negative electrode active material, characterized in that, Includes the following steps: S1, disperse at least a portion of the silicon-based material with a carbon layer on its surface in a solvent, add a surfactant, add ammonia water under stirring conditions, and keep stirring; S2, add titanium source, keep stirring, separate solid and liquid, wash, dry, calcine to obtain solid product with titanium compound layer on surface; S3, at room temperature, the solid product with a titanium compound layer on its surface is subjected to a first plasma-enhanced chemical vapor deposition treatment for 20-30 min under the condition of argon gas introduction, and then subjected to a second plasma-enhanced chemical vapor deposition treatment for 20-30 min under a mixed gas of nitrogen and hydrogen to obtain the negative electrode active material.

5. The method for preparing the negative electrode active material according to claim 4, characterized in that, The power of the first plasma-enhanced chemical vapor deposition process is 250~400W.

6. The method for preparing the negative electrode active material according to claim 4, characterized in that, The power of the second plasma-enhanced chemical vapor deposition process is 200~400W.

7. The method for preparing the negative electrode active material according to claim 4, characterized in that, The flow rate ratio of nitrogen to hydrogen introduced during the second plasma-enhanced chemical vapor deposition process is (15~23):(5~13).

8. A lithium-ion battery, characterized in that, The invention includes a negative electrode sheet, wherein the negative electrode sheet comprises a current collector and a negative electrode active material layer disposed on the surface of the current collector, and the negative electrode active material layer comprises the negative electrode active material according to any one of claims 1 to 4 or the negative electrode active material prepared by the preparation method according to any one of claims 5 to 7.

9. An electrical appliance, characterized in that, Includes the lithium-ion battery as described in claim 8.

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