Modified silicon material and use thereof

Abstract

The application provides a modified silicon material and application thereof, the modified silicon material comprising a core layer and a shell layer, the shell layer covering the core layer; the core layer comprising a silicon material; the shell layer comprising a copolymer, raw materials for preparing the copolymer comprising a first monomer and a second monomer; wherein the first monomer comprises one of monomer A and monomer B; the chemical structural formula of monomer A is R1, R2 and R3 are independently selected from at least one of H, -NO2 and ; R4 is independently selected from at least one of H and a phenyl group; the chemical structural formula of monomer B is R5-R 11 The second monomer comprises one of an oxysilane compound, a diene acid methyl ester compound, an unsaturated hydrocarbon and lithium organic acid. The application can inhibit the huge volume change of silicon in the charging and discharging process by coating the copolymer on the surface of the silicon material, and can improve the electrochemical performance of silicon by preparing the copolymer by matching the first monomer and the second monomer.

Description

Technical Field

[0001] This invention belongs to the field of batteries, and particularly relates to a modified silicon material and its applications. Background Technology

[0002] With the rapid development of mobile electronic devices, electric vehicles, and grid energy storage, the development of batteries with high energy density, high power density, long cycle life, and high safety has become a research hotspot and focus in the field of energy storage. Developing electrode materials with high capacity, high rate capability, and high cycle stability is an important way to achieve this goal. Silicon has attracted widespread attention due to its abundant reserves and extremely high theoretical charge specific capacity. However, due to its huge volume change (greater than 300%) during charge and discharge and its inherent low conductivity, silicon's lithium storage capacity decays rapidly during cycling, failing to meet the needs of practical applications.

[0003] In existing technologies, researchers have employed methods to modify silicon to mitigate its significant volume changes during charging and discharging. Current methods include silicon oxidation modification, porous modification, alloying modification, and composite modification.

[0004] One method, silicon oxidation modification, involves forming a stable oxide layer on the silicon surface through oxidation. This oxide layer can act as a buffer, reducing the volume expansion of silicon during charging and discharging. However, the oxide layer formed by this method affects the conductivity of silicon, thus impacting battery performance.

[0005] Alloying modification involves forming alloys with other metals to enhance the electrochemical performance of silicon. However, silicon alloy materials may undergo volume expansion and contraction during charging and discharging, affecting the cycle stability of the battery.

[0006] Composite modification involves combining silicon with carbon materials. Carbon materials, with their excellent electrical conductivity and mechanical stability, can effectively mitigate the volume expansion of silicon and provide support, preventing it from cracking during charging and discharging. However, combining silicon with carbon materials may compromise intrinsic properties such as high specific capacity. Summary of the Invention

[0007] In order to suppress the huge volume change of silicon during charging and discharging and improve the electrochemical performance of silicon, this invention provides a modified silicon material and its application.

[0008] According to one aspect of this application, a modified silicon material is provided, comprising a core layer and a shell layer, the shell layer covering the core layer; the core layer comprises silicon material; the shell layer comprises a copolymer, the raw materials for preparing the copolymer comprising a first monomer and a second monomer; wherein the first monomer comprises one of monomer A and monomer B; the chemical structural formula of monomer A is as follows: R1, R2, and R3 are independently selected from H, -NO2, At least one of them, R4 is independently selected from at least one of H and phenyl; the chemical structural formula of monomer B is R5~R 11 The monomer is independently selected from at least one of H and F; the second monomer includes one of oxysilane compounds, methyl dienoate compounds, unsaturated hydrocarbons, and lithium organic acids.

[0009] This invention suppresses the significant volume changes of silicon during charging and discharging by coating the surface of silicon with a copolymer, and improves the electrochemical performance of silicon by combining a first monomer and a second monomer to prepare the copolymer. Specifically, the invention enhances the toughness of the shell by introducing monomer A with a rigid benzene ring structure or monomer B with a long-chain structure, making the shell less prone to cracking due to silicon expansion. Furthermore, by limiting the types of branched functional groups in the first monomer, the electrochemical performance of the first monomer can be improved. In addition, the introduction of the second monomer can further improve the toughness and electrochemical performance of the copolymer.

[0010] Preferably, the first monomer includes monomer A, and the chemical structural formula of monomer A is: The second monomer is an oxysilane compound, including methacryloxypropyltriethoxysilane. The sulfonate structure in monomer A can serve as a lithium-ion storage medium, and methacryloxypropyltriethoxysilane, due to its strong electron-withdrawing ability, can act as a pathway for lithium-ion movement, thus endowing the polymer with high ionic conductivity and improving fast-charging performance. Furthermore, the silicon-oxygen bond in methacryloxypropyltriethoxysilane can react with hydrofluoric acid, improving the stability of silicon materials. Therefore, by combining monomer A with methacryloxypropyltriethoxysilane, silicon materials can be protected from corrosion.

[0011] Preferably, the molar ratio of monomer A to oxysilane compound is 1 to 5 to 1.

[0012] Preferably, the molar ratio of monomer A to oxysilane compound is 1 to 3 to 1.

[0013] Preferably, the copolymer obtained by copolymerizing monomer A and oxysilane compound has a molecular weight of 5,000 to 30,000.

[0014] Preferably, the first monomer includes monomer A, and the chemical structural formula of monomer A is as follows: The second monomer is a methyl dienoate compound, including (9Z,12E)-octadecanoic acid methyl ester. The imide moiety in monomer A has a strong electron-withdrawing portion, capable of forming weak covalent bonds with lithium ions, thereby improving the ionic conductivity of the modified silicon material. However, due to its rigidity, the shell structure formed alone is prone to breakage. This invention introduces a second monomer to increase the flexibility of the shell. This is because the second monomer contains alkyl segments and double bonds, exhibiting high flexibility, giving the polymer both flexibility and rigidity, thus better suppressing silicon expansion.

[0015] Preferably, the molar ratio of monomer A to methyl dienoate compound is 1 to 6 to 1.

[0016] Preferably, the molar ratio of monomer A to methyl dienoate compound is 1 to 3 to 1.

[0017] Preferably, the copolymer obtained by copolymerizing monomer A and methyl diene compound has a molecular weight of 5,000 to 30,000.

[0018] Preferably, the first monomer includes monomer A, and the chemical structural formula of monomer A is as follows: The second monomer is an unsaturated hydrocarbon, including allylamine and 1,3-butadiene. Introducing the flexible 1,3-butadiene can alleviate stress concentration and structural cracking caused by volume changes in silicon materials during charging and discharging, thereby enhancing the battery's cycle performance and lifespan. On the other hand, the polar nitro groups in the copolymer, through physical interaction with Li+, can improve the conductivity of the silicon material, thus significantly improving the battery's rate performance; while the nitro and amine groups have good flame-retardant effects, which can improve battery safety.

[0019] Preferably, the molar ratio is calculated as follows: monomer A: allylamine: 1,3-butadiene = 1-6: 1-3: 1-3.

[0020] Preferably, the molar ratio is calculated as follows: monomer A: allylamine: 1,3-butadiene = 4:1:2.

[0021] Preferably, the copolymer obtained by copolymerizing monomer A and unsaturated hydrocarbon has a molecular weight of 10,000 to 80,000.

[0022] Preferably, the first monomer includes monomer A, and the chemical structural formula of monomer A is as follows: The second monomer is an organic lithium acid, which includes at least one of lithium vinyl terephthalate and lithium acrylate. Organic lithium acids contain charged groups (Li... +This process can endow modified silicon materials with high ionic conductivity, a wide electrochemical window, and excellent chemical / electrochemical stability. On the other hand, the lithium carboxylate and lithium sulfonate groups of the copolymer can form hydrogen bonds with the hydroxyl groups on the surface of the silicon material, which can improve the adhesion between the core and shell layers of the modified silicon material, help maintain the structural integrity of the silicon-carbon core, reduce the shedding of silicon particles, and thus improve the performance of the battery.

[0023] Preferably, the molar ratio of monomer A to lithium organic acid is 1-4 to 1-9.

[0024] Preferably, the molar ratio of monomer A to lithium organic acid is 1:5 to 7.

[0025] Preferably, the first monomer includes monomer B, and the number of fluorine atoms N in monomer B is ≥1; the second monomer is an oxysilane compound, wherein the oxysilane compound includes acrylamidopropyltrimethoxysilane. Introducing monomer B into the polymer in combination with acrylamidopropyltrimethoxysilane can, on the one hand, form hydrogen bonds with the hydroxyl groups on the surface of the silicon material, increasing the interaction force between the core and shell layers; on the other hand, the oxysilane compound can absorb HF in the electrolyte, preventing HF from corroding the modified silicon material and improving rate cycling performance.

[0026] Preferably, the number N of fluorine atoms in monomer B satisfies: 1 ≤ N ≤ 15. The fluorine element in the polymer can reduce the surface energy of the electrode, thereby improving wettability with the electrolyte and enhancing rate performance.

[0027] Preferably, the molar ratio of monomer B to oxysilane compound is 1:1 to 5.

[0028] Preferably, the molar ratio of monomer B to oxysilane compound is 1:3 to 4.

[0029] Preferably, the preparation method of the copolymer includes the following steps: mixing the first monomer, the second monomer, and the organic solvent, adding an initiator, heating at 40-90°C under argon protection, and reacting for 5-9 hours to obtain solution I; then adding solution I to the precipitation solvent to obtain the copolymer.

[0030] Preferably, the organic solvent includes at least one of benzene, toluene, N-methyl-2-pyrrolidone (NMP), and N,N-dimethylformamide (DMF).

[0031] Preferably, the initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, or benzoyl peroxide (BPO).

[0032] Preferably, the mass content of the initiator added is 0.1% to 0.9% of the total amount of the first monomer and the second monomer.

[0033] Preferably, the precipitation solvent is one of propanol, isopropanol, and acetone.

[0034] Preferably, the preparation method of the modified silicon material includes the following steps: dissolving the copolymer in an organic solvent to prepare a solution II with a mass fraction of 5-30%; then adding the silicon material to solution II, stirring at 30-100°C for 4-10 hours to obtain solution III, and spray drying solution III to obtain the modified silicon material.

[0035] Preferably, the inlet temperature of the spray drying process is 100-200℃ and the outlet temperature is 60-90℃.

[0036] Preferably, the modified silicon material includes mesopores and micropores, wherein the pore diameter of the mesopores is 3nm to 40nm; the pore diameter of the micropores is 1nm to 2nm; and the content of mesopores is 45% to 90%; the content of micropores is less than 60%.

[0037] Preferably, the D of silicon material 50 The thickness is 4–10 μm, and the shell thickness is 10–150 nm.

[0038] Preferably, the silicon material includes silicon-carbon.

[0039] Preferably, in the silicon material, the mass ratio of silicon to carbon is 0.4 to 1.3.

[0040] Preferably, the specific surface area of ​​the silicon material is 1m². 2 / g~8m 2 / g.

[0041] Preferably, the modified silicon material is coated with an amorphous carbon layer, wherein the thickness of the amorphous carbon layer is 3-55 nm and the amorphous carbon content is 1-3%.

[0042] A second aspect of this application provides a negative electrode comprising the modified silicon material as described above.

[0043] A third aspect of this application provides a battery comprising a negative electrode as described above. Detailed Implementation

[0044] To enable those skilled in the art to better understand the technical solutions of this application, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0045] Example 1

[0046] 1. Preparation of modified silicon materials

[0047] The copolymer preparation method includes the following steps: mixing a first monomer, a second monomer, and an organic solvent, adding an initiator, heating at 70°C under argon protection, and reacting for 8 hours to obtain solution I; subsequently, solution I is added to a precipitation solvent to obtain the copolymer. In this embodiment, the first monomer is... The second monomer is methacryloyloxypropyltriethoxysilane, and the molar ratio of the first monomer to the second monomer is 3:1. The amount of initiator is 0.5% of the total amount of the first monomer and the second monomer.

[0048] The preparation method of modified silicon material includes the following steps: dissolving the copolymer in an organic solvent to prepare a 20% (w / w) solution II; then adding silicon material (silicon-carbon) to solution II, stirring at 60°C for 8 hours to obtain solution III, and spray drying solution III to obtain the modified silicon material. The spray drying parameters are: inlet temperature = 150°C, outlet temperature = 70°C; the core layer thickness of the obtained modified silicon material is 1–10 μm, and the shell layer thickness is 50 nm.

[0049] 2. Preparation of lithium-ion batteries

[0050] (1) Preparation of positive electrode sheet

[0051] The ternary material NCM811(LiNi) 0.8 Co 0.1 Mn 0.1 O2) positive electrode active material, binder PVDF (polyvinylidene fluoride), and conductive agent SP (conductive carbon black Super-P) are mixed and stirred evenly at a mass ratio of 96:2:2 to obtain a positive electrode slurry. The positive electrode slurry is then coated onto aluminum foil through a coating process, and after drying and cold pressing, a positive electrode sheet is obtained.

[0052] (2) Preparation of negative electrode sheet

[0053] Modified silicon material, conductive agent SP (Super-P conductive carbon black), SWCNT (single-walled carbon nanotubes), and binder PAA (polyacrylic acid) are mixed and stirred evenly in a mass ratio of 80:9:1:10 to obtain a negative electrode slurry. The solid content is controlled at 30%. The negative electrode slurry is then coated onto copper foil through a coating process. After vacuum drying and cold pressing, a negative electrode sheet is obtained.

[0054] (3) Selection of electrolyte

[0055] Lithium-ion batteries were prepared using EC:DMC:DEC:FEC = 20:40:30:10 and LiPF6 1mol / L.

[0056] (4) Selection of the separator

[0057] Polyethylene (PE) + ceramic was chosen as the separator for lithium-ion batteries.

[0058] (5) Preparation of lithium-ion batteries

[0059] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0060] Example 2

[0061] This embodiment refers to the formulation and method provided in Example 1 to prepare modified silicon materials and their application in negative electrodes and lithium-ion batteries. The difference from Example 1 is that the first monomer used in the preparation of the modified silicon material in this embodiment is... The second monomer is (9Z,12E)-octadecadienoate methyl ester. Apart from the differences mentioned above, the operation steps for preparing the modified silicon material and applying it to the negative electrode and lithium-ion battery in this embodiment are strictly consistent with those in Example 1.

[0062] Example 3

[0063] This embodiment refers to the formulation and method provided in Example 1 to prepare modified silicon materials and their application in negative electrodes and lithium-ion batteries. The difference from Example 1 is that the first monomer used in the preparation of the modified silicon material in this embodiment is... The second monomer is allylamine and 1,3-butadiene, and the mass ratio of monomer A: allylamine: 1,3-butadiene is 4:1:2. Apart from the above differences, the operation steps for preparing modified silicon materials and applying them to negative electrodes and lithium-ion batteries in this embodiment are strictly consistent with those in Example 1.

[0064] Example 4

[0065] This embodiment refers to the formulation and method provided in Example 3 to prepare modified silicon materials and their application in negative electrodes and lithium-ion batteries. The difference from Example 3 is that the first monomer used in the preparation of the modified silicon material in this embodiment is... Apart from the differences mentioned above, the operational steps for preparing modified silicon materials and applying them to negative electrodes and lithium-ion batteries in this embodiment are strictly consistent with those in Example 3.

[0066] Example 5

[0067] This embodiment refers to the formulation and method provided in Example 3 to prepare modified silicon materials and their application in negative electrodes and lithium-ion batteries. The difference from Example 3 is that the first monomer used in the preparation of the modified silicon material in this embodiment is... (CAS: 586-39-0) Apart from the differences mentioned above, the operation steps for preparing modified silicon materials and applying them to negative electrodes and lithium-ion batteries in this embodiment are strictly consistent with those in Example 3.

[0068] Example 6

[0069] This embodiment refers to the formulation and method provided in Example 1 to prepare modified silicon materials and their application in negative electrodes and lithium-ion batteries. The difference from Example 1 is that the first monomer used in the preparation of the modified silicon material in this embodiment is... The second monomer is lithium vinyl terephthalate, and the mass ratio of the first monomer to the second monomer is 1:6. Apart from the above differences, the operation steps for preparing the modified silicon material and its application in the negative electrode and lithium-ion battery in this embodiment are strictly consistent with those in Example 1.

[0070] Example 7

[0071] This embodiment refers to the formulation and method provided in Example 1 to prepare modified silicon materials and their application in negative electrodes and lithium-ion batteries. The difference from Example 1 is that the first monomer used in the preparation of the modified silicon material in this embodiment is... The second monomer is lithium acrylate, and the mass ratio of the first monomer to the second monomer is 1:6. Apart from the above differences, the operation steps for preparing the modified silicon material and applying it to the negative electrode and lithium-ion battery in this embodiment are strictly consistent with those in Example 1.

[0072] Example 8

[0073] This embodiment refers to the formulation and method provided in Example 1 to prepare modified silicon materials and their application in negative electrodes and lithium-ion batteries. The difference from Example 1 is that the first monomer used in the preparation of the modified silicon material in this embodiment is... (CAS: 16083-81-1), the second monomer is acrylamide propyltrimethoxysilane (CAS: 57577-96-5), and the mass ratio of the first monomer to the second monomer is 1:3.5. Apart from the above differences, the operation steps for preparing the modified silicon material and applying it to the negative electrode and lithium-ion battery in this embodiment are strictly consistent with those in Example 1.

[0074] Example 9

[0075] This embodiment refers to the formulation and method provided in Example 1 to prepare modified silicon materials and their application in negative electrodes and lithium-ion batteries. The difference from Example 1 is that the first monomer used in the preparation of the modified silicon material in this embodiment is... The second monomer is allylamine and 1,3-butadiene, and the mass ratio of the first monomer: allylamine: 1,3-butadiene is 4:1:2. Apart from the above differences, the operation steps for preparing the modified silicon material and applying it to the negative electrode and lithium-ion battery in this embodiment are strictly consistent with those in Example 1.

[0076] Example 10

[0077] This embodiment refers to the formulation and method provided in Example 1 to prepare modified silicon materials and their application in negative electrodes and lithium-ion batteries. The difference from Example 1 is that the first monomer used in the preparation of the modified silicon material in this embodiment is... The second monomer is methacryloxypropyltriethoxysilane. Apart from the differences mentioned above, the operation steps for preparing the modified silicon material and applying it to the negative electrode and lithium-ion battery in this embodiment are strictly consistent with those in Example 1.

[0078] Example 11

[0079] This embodiment refers to the formulation and method provided in Example 1 to prepare modified silicon materials and their application in negative electrodes and lithium-ion batteries. The difference from Example 1 is that the first monomer used in the preparation of the modified silicon material in this embodiment is... (CAS: 16083-81-1), the second monomer is allylamine and 1,3-butadiene, and the mass ratio of the first monomer: allylamine: 1,3-butadiene is 4:1:2. Apart from the above differences, the operation steps for preparing modified silicon materials and applying them to negative electrodes and lithium-ion batteries in this embodiment are strictly consistent with those in Example 1.

[0080] Comparative Example 1

[0081] This comparative example prepares a negative electrode and a lithium-ion battery using the formula and method provided in Example 1. The difference between this comparative example and Example 1 is that the negative electrode active material used in the preparation of the negative electrode is silicon-carbon. Apart from the above differences, the operation steps for preparing the modified silicon material and the negative electrode and lithium-ion battery using it in this comparative example are strictly consistent with those in Example 1.

[0082] Comparative Example 2

[0083] This comparative example uses the formulation and method provided in Example 1 to prepare modified silicon materials and their negative electrodes and lithium-ion batteries. The difference between this comparative example and Example 1 is that in preparing the modified silicon materials, an equal mass fraction of methacryloxypropyltriethoxysilane is used instead of the first monomer. Apart from the above differences, the operation steps for preparing the modified silicon materials and their negative electrodes and lithium-ion batteries in this comparative example are strictly consistent with those in Example 1.

[0084] Comparative Example 3

[0085] This comparative example uses the formulation and method provided in Example 2 to prepare modified silicon materials and their negative electrodes and lithium-ion batteries. The difference between this comparative example and Example 2 is that in preparing the modified silicon materials, an equal mass fraction of (9Z,12E)-octadecadienoic acid methyl ester is used instead of the first monomer. Apart from the above differences, the operation steps for preparing the modified silicon materials and their negative electrodes and lithium-ion batteries in this comparative example are strictly consistent with those in Example 2.

[0086] Comparative Example 4

[0087] This comparative example uses the formulation and method provided in Example 3 to prepare modified silicon materials and their negative electrodes and lithium-ion batteries. The difference between this comparative example and Example 3 is that in preparing the modified silicon materials, allylamine and 1,3-butadiene of equal mass fractions are used instead of the first monomer (wherein the mass ratio of allylamine and 1,3-butadiene remains unchanged). Apart from the above differences, the operation steps for preparing the modified silicon materials and their negative electrodes and lithium-ion batteries in this comparative example are strictly consistent with those in Example 3.

[0088] Comparative Example 5

[0089] This comparative example refers to the formulation and method provided in Example 6 to prepare modified silicon materials and the negative electrode and lithium-ion battery using them. The difference from Example 6 is that in this comparative example, the first monomer used is replaced with an equal mass fraction of vinyl terephthalate when preparing the modified silicon material. Apart from the above differences, the operation steps for preparing modified silicon materials and the negative electrode and lithium-ion battery using them in this comparative example are strictly consistent with those in Example 6.

[0090] Comparative Example 6

[0091] This comparative example refers to the formulation and method provided in Example 8 to prepare modified silicon materials and the negative electrode and lithium-ion battery using them. The difference from Example 8 is that in this comparative example, an equal mass fraction of acrylamide propyltrimethoxysilane is used instead of the first monomer when preparing the modified silicon material. Apart from the above differences, the operation steps for preparing the modified silicon material and the negative electrode and lithium-ion battery using it in this comparative example are strictly consistent with those in Example 8.

[0092] Comparative Example 7

[0093] This comparative example uses the formulation and method provided in Example 1 to prepare modified silicon materials and their negative electrodes and lithium-ion batteries. The difference between this comparative example and Example 1 is that in preparing the modified silicon materials, an equal mass fraction of the first monomer is used instead of the methacryloxypropyltriethoxysilane. Apart from the above differences, the operation steps for preparing the modified silicon materials and their negative electrodes and lithium-ion batteries in this comparative example are strictly consistent with those in Example 1.

[0094] Comparative Example 8

[0095] This comparative example uses the formulation and method provided in Example 2 to prepare modified silicon materials and their negative electrodes and lithium-ion batteries. The difference between this comparative example and Example 2 is that in preparing the modified silicon materials, an equal mass fraction of the first monomer is used instead of the (9Z,12E)-octadecadienoate methyl ester. Apart from the above differences, the operation steps for preparing the modified silicon materials and their negative electrodes and lithium-ion batteries in this comparative example are strictly consistent with those in Example 2.

[0096] Comparative Example 9

[0097] This comparative example uses the formulation and method provided in Example 3 to prepare modified silicon materials and their negative electrodes and lithium-ion batteries. The difference between this comparative example and Example 3 is that, in preparing the modified silicon materials, an equal mass fraction of the first monomer is used to replace the allylamine and 1,3-butadiene. Apart from the above differences, the operation steps for preparing the modified silicon materials and their negative electrodes and lithium-ion batteries in this comparative example are strictly consistent with those in Example 3.

[0098] Comparative Example 10

[0099] This comparative example refers to the formulation and method provided in Example 8 to prepare modified silicon materials and the negative electrode and lithium-ion battery using them. The difference from Example 8 is that in this comparative example, an equal mass fraction of the first monomer is used instead of acrylamide propyltrimethoxysilane when preparing the modified silicon material. Apart from the above differences, the operation steps for preparing the modified silicon material and the negative electrode and lithium-ion battery using it in this comparative example are strictly consistent with those in Example 8.

[0100] Test case

[0101] 1. Test Object

[0102] Modified silicon materials prepared in Examples 1 to 1 and Comparative Examples 1, and negative electrodes and lithium-ion batteries using them.

[0103] 2. Testing Methods

[0104] (1) Initial Coulombic Efficiency: Under conditions of 25℃, the lithium-ion battery is charged at a constant current and constant voltage rate of 0.33C to 4.2V, allowed to stand for 10 minutes, and then discharged at a constant current rate of 0.33C to 2.5V, allowed to stand for 10 minutes. The initial coulombic efficiency of the lithium-ion battery is calculated using the following formula:

[0105] Initial coulombic efficiency (%) = (Total capacity of lithium-ion battery during initial discharge at 0.33C / Total capacity of lithium-ion battery during initial charge at 0.33C) × 100%

[0106] (2) Capacity retention rate after 1200 cycles at 1C / 1C at room temperature: Under 25℃ conditions, the lithium-ion battery is charged at a 1C rate with constant current and constant voltage to 4.2V, with a cutoff current of 0.05C. After resting for 10 minutes, the lithium-ion battery is discharged at a 1C rate with constant current to 2.5V, and then rested for 10 minutes. This constitutes one charge-discharge cycle. The lithium-ion battery is charged and discharged for 1200 cycles using the above method. The capacity retention rate after 1200 cycles at 1C / 1C is calculated. The capacity retention rate is calculated using the following formula:

[0107] Capacity retention rate (%) of a lithium-ion battery after N cycles = (Discharge capacity of the Nth cycle / Initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0108] (3) 1C / 10C discharge capacity retention rate: The lithium-ion battery after capacity gradation was charged at 25℃ at a 1C rate to 4.2V under constant current and constant voltage, with a cutoff current of 0.05C; it was left to stand for 10 minutes; then the lithium-ion battery was discharged at a 1C rate to 2.5V under constant current, and its discharge capacity Q1C was recorded as the initial discharge capacity; then the lithium-ion battery was charged at 25℃ at a 1C rate to 4.2V under constant current and constant voltage, with a cutoff current of 0.05C; it was left to stand for 10 minutes; then the fully charged battery was discharged at a 10C rate to 2.5V under constant current, and its discharge capacity Q10C was recorded; the discharge capacity retention rate of the lithium-ion battery at 1C / 10C rate was calculated according to the following formula:

[0109] Discharge capacity retention rate (%) = Discharge capacity at 10C rate Q10C / Discharge capacity at 1C rate Q1C × 100%.

[0110] (4) Room temperature 6C rate performance - constant current charge ratio: At 25℃, the lithium-ion battery was discharged at a 1C rate to 2.5V under constant current, left to stand for 10 minutes, and then charged at a 6C rate to 4.2V under constant current and constant voltage, with a cutoff current of 0.05C. After standing for 10 minutes, the constant current charging capacity Q1 and the total constant current and constant voltage charging capacity Q2 of the lithium-ion battery were recorded. The constant current charge ratio of the 6C rate charging was calculated according to the following formula:

[0111] 6C rate charging constant current charging ratio = constant current charging capacity Q1 / total constant current and constant voltage charging capacity Q2 × 100%

[0112] (5) Cell thermal runaway (ARC) test: Start the ARC adiabatic thermal runaway test (the test sample is heated from room temperature to 45±2℃ in the chamber, and after being left for 90 minutes, the change in battery temperature rise rate is detected. If the temperature rise exceeds 0.2℃ within 10 minutes (i.e., SHR>0.02℃ / min), it is considered that a self-heating reaction has occurred inside the battery. Maintain the adiabatic environment until the battery thermal runaway occurs; if the temperature rise does not exceed 0.2℃ within 10 minutes (i.e., SHR≤0.02℃ / min) (Self-heating Rate, SHR, self-generated heat temperature rise rate), continue to the next step temperature rise test; each temperature step is 5℃, and the steps are repeated on each step. The ARC test temperature range is 45℃~300℃. The self-heating start temperature is T1 (temperature rise rate SHR>0.02℃ / min), and the thermal runaway start temperature is T2 (temperature rise rate SHR>1℃ / min).

[0113] 3. Test Results and Analysis

[0114] The test results for this test example are shown in Tables 1 and 2. The test data from Examples 1-11 and Comparative Examples 1-10 show that different combinations of the first and second monomers have different effects, thus affecting the initial coulombic efficiency, cycle capacity retention, and rate performance of the batteries using the corresponding modified silicon materials. Furthermore, the test data in Table 2 shows that the modified silicon materials provided in Examples 1-8 all exhibit good flame retardant effects, improving battery safety performance. Among them, the modified silicon material provided in Example 1 has the best flame retardant properties.

[0115] As demonstrated in Examples 1-11 and Comparative Examples 1-10, the sulfonate structure in monomer A, when combined with an oxysilane compound (methacryloyloxypropyltriethoxysilane), exhibits a high initial coulombic efficiency. This means that during the first charge-discharge cycle of the lithium battery, the conversion of electrical energy into chemical energy is more efficient, which helps to improve the battery's energy density and thus extend its runtime. Furthermore, when monomer A contains an imide and is combined with a dienoate methyl ester compound ((9Z,12E)-octadecanoate methyl ester), or when monomer B is combined with an oxysilane compound, the rate performance of the battery is enhanced, contributing to improved rapid charge-discharge capability. When monomer A containing a nitro group is combined with an unsaturated hydrocarbon (allylamine, 1,3-butadiene), or when monomer A containing a sulfonic acid structure is combined with an organic lithium acid, the initial coulombic efficiency, cycle capacity retention, and rate performance all maintain superior levels, contributing to extended battery life and improved battery safety.

[0116] Therefore, the data from this test example confirms that by coating silicon material with copolymers, the large volume change of silicon during charging and discharging can be suppressed, and by preparing copolymers by combining the first monomer and the second monomer, the electrochemical performance of silicon can be improved.

[0117] Table 1. Test results of this test case

[0118]

[0119] Table 2. Test results of thermal runaway (ARC) test of the battery cell in this test case.

[0120] Group <![CDATA[The self-heating start temperature is T1]]> <![CDATA[Thermal runaway starting temperature T2]]> Example 1 105.5℃ 159.8℃ Example 2 103.2℃ 158.1℃ Example 3 100.9℃ 155.2℃ Example 4 100.1℃ 153.8℃ Example 5 100.2℃ 150.8℃ Example 6 102.2℃ 154.1℃ Example 7 101.3℃ 155.9℃ Example 8 103.3℃ 157.9℃ Comparative Example 1 90.7℃ 141.8℃

[0121] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A modified silicon anode material, characterized in that, The modified silicon anode material includes a core layer and a shell layer, wherein the shell layer covers the core layer; the core layer includes silicon material; and the shell layer includes a copolymer, wherein the raw materials for preparing the copolymer include a first monomer and a second monomer. The first monomer includes one of monomer A and monomer B; The first monomer includes monomer A, and the chemical structural formula of monomer A is as follows: The second monomer is an oxysilane compound, including methacryloxypropyltriethoxysilane; or The first monomer includes monomer A, and the chemical structural formula of monomer A is as follows: The second monomer is a methyl dienoate compound, wherein the methyl dienoate compound includes (9Z,12E)-octadecanodienoate methyl ester; or The first monomer includes monomer A, and the chemical structural formula of monomer A is as follows: , , , At least one of the following, wherein the second monomer is an unsaturated hydrocarbon, said unsaturated hydrocarbon including allylamine and 1,3-butadiene; or The first monomer includes monomer B, and the chemical structural formula of monomer B is as follows: The second monomer is an oxysilane compound, including acrylamidopropyltrimethoxysilane.

2. The modified silicon anode material as described in claim 1, characterized in that, When the first monomer includes monomer A, the chemical structural formula of monomer A is: When the second monomer is the oxysilane compound, the molar ratio of monomer A to oxysilane compound is 1 to 5 to 1.

3. The modified silicon anode material as described in claim 1, characterized in that, When the first monomer includes monomer A, the chemical structural formula of monomer A is: When the second monomer is the methyl dienoate compound, the molar ratio of monomer A to methyl dienoate compound is 1 to 6 to 1.

4. The modified silicon anode material as described in claim 1, characterized in that, When the first monomer includes monomer A, the chemical structural formula of monomer A is: , , , In the case of at least one of the following, where the second monomer is the unsaturated hydrocarbon, and the unsaturated hydrocarbon includes the allylamine and the 1,3-butadiene, the molar ratio of monomer A: allylamine: 1,3-butadiene is 1-6: 1-3: 1-3.

5. The modified silicon anode material as described in claim 1, characterized in that, When the first monomer includes the monomer B and the second monomer is the oxysilane compound, the molar ratio of monomer B to oxysilane compound is 1:1 to 5.

6. The modified silicon anode material as described in claim 1, characterized in that, The modified silicon anode material includes mesopores and micropores, wherein the pore diameter of the mesopores is 3nm~40nm; the pore diameter of the micropores is 1nm~2nm; and the content of the mesopores is 45~90%; the content of the micropores is less than 60%.

7. The modified silicon anode material according to any one of claims 1 to 6, characterized in that, The silicon material D 50 The thickness of the shell is 4~10μm and the thickness of the shell layer is 10~150nm.

8. A negative electrode, characterized in that, The negative electrode comprises the modified silicon negative electrode material as described in any one of claims 1 to 7.

9. A battery, characterized in that, The battery includes the negative electrode as described in claim 8.

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