Negative active layer, preparation method and application

Abstract

The invention discloses a negative electrode active layer, a preparation method and application. The negative electrode active layer comprises an active component, carboxylic acid type anionic waterborne polyurethane and a conductive agent, the active component comprises a silicon-carbon material and graphite, a silanization organic layer is arranged on the surface of the silicon-carbon material, and the mass fraction of the silanization organic layer in the silicon-carbon material is 0.3-2.0 wt%; the content of carboxylate groups (-COO <->) in the carboxylic acid type anionic waterborne polyurethane is 0.2-1.0 mmol / g, and the acid-base neutralization degree is 50%-100%. The negative electrode active layer and the carboxylic acid type anionic waterborne polyurethane are matched for use, so that the binding force between the negative electrode active layer and the current collector is favorably improved, the volume expansion of the negative electrode active layer is inhibited, and the cycle performance is further favorably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a negative active layer, a preparation method and application. BACKGROUND

[0002] Silicon-based negative electrode materials have attracted much attention due to their significantly higher theoretical specific capacity (up to 4200 mAh / g) than graphite. However, the severe volume change (about 300%) during repeated lithium ion insertion / extraction process will lead to material structure degradation, which is manifested as active particle rupture, electrode sheet expansion and interface adhesion failure, ultimately triggering the increase of internal resistance and the rapid decay of capacity, etc. The current mainstream water-based binder system mainly uses physical blending of styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC), or polyacrylic acid (PAA) binder. Although it has the advantage of simple process, it has exposed several technical bottlenecks in practical application: the floating phenomenon during drying, insufficient interfacial shear strength, too high material brittleness, and poor size stability during long-term cycling, etc.

[0003] Therefore, how to realize high-strength interfacial bonding, low volume expansion and long cycle stability of silicon-based negative electrode materials has become a key technical problem to be solved in the field of lithium ion battery materials. SUMMARY

[0004] The purpose of the present application is to provide a negative active layer, a preparation method and application, which is beneficial to improve the cycle performance of the battery using the negative active layer.

[0005] The present application is implemented as follows: In a first aspect, the present application provides a negative active layer, comprising an active component, a carboxylic acid type anionic water-based polyurethane and a conductive agent. The active component includes silicon-carbon material and graphite, and the silicon-carbon material is provided with a silanized organic layer on the surface, and the mass fraction of the silanized organic layer in the silicon-carbon material is 0.3–2.0 wt%. The content of carboxylate groups (–COO - ) in the carboxylic acid type anionic water-based polyurethane is 0.2–1.0 mmol / g, and the acid-base neutralization degree is 50%–100%.

[0006] In an optional embodiment, the mass fraction of the silicon-carbon material in the active component is 5~35 wt%; And / or, the mass fraction of silicon in the silicon-carbon material is 10–30 wt%; And / or, in the negative active layer, the mass fraction of the carboxylic acid type anionic water-based polyurethane is 2.0–8.0%; And / or, in the negative electrode active layer, the mass fraction of the conductive agent is 0.5–6.0%, preferably 1–4%; And / or, the conductive agent comprises vapor-grown carbon fibers and graphene, wherein the mass ratio of the vapor-grown carbon fibers to graphite is 1:(0.2–1.0). And / or, the conductive agent does not include carbon nanotubes.

[0007] In an optional embodiment, the nitrogen content in the negative electrode active layer is 0.10–0.60 wt%. And / or, the sum of the area ratios of the characteristic peaks of Si–O–C and Si–O–Si in the X-ray photoelectron spectroscopy (O1s) spectrum of the negative electrode active layer is ≥8%; And / or, the Fourier transform infrared spectrum of the negative electrode active layer is at 1725±5 cm⁻¹. -1 The characteristic absorption peak of the urethane carbonyl group appears at position A, and A 1725 / A 2920 ≥0.08, where A 1725 1725±5 cm -1 The peak height of the characteristic peak, A 2920 2920±5 cm -1 The peak height of the characteristic peak.

[0008] In an optional embodiment, the glass transition temperature of the carboxylic acid-type anionic aqueous polyurethane is from –30 °C to 10 °C.

[0009] Secondly, the present invention provides a method for preparing the negative electrode active layer described in the foregoing embodiments, comprising: forming and shaping a slurry containing an active component, a carboxylic acid anionic aqueous polyurethane and a conductive agent to obtain the negative electrode active layer.

[0010] In an optional embodiment, the preparation of a carboxylic acid-type anionic aqueous polyurethane is also included: a mixture containing polycarbonate diol and dimethylpropionate diol and a solvent is mixed with diisocyanate isophorone and subjected to a prepolymerization reaction to obtain a prepolymer solution. The prepolymer solution is mixed with lithium hydroxide for neutralization reaction, and then the neutralized solution is poured into deionized water under high-speed shearing to form a PU emulsion; Ethylenediamine was added dropwise to the PU emulsion for chain extension, followed by solvent removal and aging to obtain an emulsion containing the carboxylic acid anionic waterborne polyurethane. And / or, the film forming and shaping includes: drying at 90-110℃ for 20-60 min under normal pressure in an inert atmosphere, followed by a roll forming process to obtain the negative electrode active layer; And / or, also includes the preparation of silicon-carbon materials: silanizing a silicon-carbon material matrix in an aqueous / alcoholic mixed solution containing a silane coupling agent, followed by drying to obtain the silicon-carbon material.

[0011] In an optional embodiment, the pH of the mixed solution is 4.5–5.5, the silanization treatment time is 0.5–3 h, and the mass ratio of the silane coupling agent to the silicon-carbon material matrix is ​​0.5–1.2%.

[0012] Thirdly, the present invention provides an electrode sheet comprising a current collector and a negative electrode active layer disposed on the current collector as described in the foregoing embodiments.

[0013] Fourthly, the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte.

[0014] In an optional embodiment, the positive electrode sheet includes a positive electrode active material with the molecular formula LiaNixCoyMnzMbO2; wherein 0.9 < a ​​< 1.2, 0.8 ≤ x ≤ 0.93, 0.1 ≤ y < 0.4, 0.05 ≤ z < 0.4, 0 ≤ b ≤ 0.1, and M represents at least one element selected from Zr, W, Ti, Al, Sr, La, B, and Nd. And / or, the electrolyte includes a lithium salt, which includes one or more combinations of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate borate, and lithium bis(trifluoromethanesulfonyl)imide. And / or, the electrolyte includes a solvent, the solvent including one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate and ethyl methyl carbonate; And / or, the electrolyte includes additives, the additives including one or more of fluoroethylene carbonate, difluoroethylene carbonate, ethylene sulfate, ethylene sulfite, vinylene carbonate, and vinyl carbonate; And / or, the ratio N / P of the capacity N of the negative electrode to the capacity P of the positive electrode is 1.02 to 1.20.

[0015] The present invention has the following beneficial effects: The negative electrode active layer of this application contains a silanized organic layer on the surface of the silicon-carbon material. This silanized organic layer can form sufficient Si–O–Si and Si–O–C anchoring bonds on the particle surface, significantly improving interfacial shear strength and load transfer efficiency, and effectively suppressing particle displacement and pore wall peeling during cycling. Furthermore, by using carboxylic acid-based anionic aqueous polyurethane as a binder and limiting the ion content and neutralization degree of the carboxylic acid-based anionic aqueous polyurethane, problems such as drying and floating, insufficient interfacial shear strength, excessive brittleness, and poor long-term dimensional stability in existing aqueous bonding systems are solved. This also avoids increased liquid absorption and bulk softening, which can lead to fluctuations in the binder phase modulus and deterioration of the pore structure during cycling. The use of the negative electrode active layer in conjunction with the carboxylic acid-based anionic aqueous polyurethane in this application is beneficial for improving the bonding force between the negative electrode active layer and the current collector, suppressing the volume expansion of the negative electrode active layer, and thus improving cycling performance. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0017] This invention provides a negative electrode active layer comprising an active component, a carboxylic acid-type anionic aqueous polyurethane, and a conductive agent; The active components include silicon-carbon material and graphite, and the surface of the silicon-carbon material is provided with a silanized organic layer, wherein the mass fraction of the silanized organic layer in the silicon-carbon material is 0.3–2.0 wt%. The carboxylic acid anionic waterborne polyurethane contains carboxylate groups (–COO). - The content is 0.2–1.0 mmol / g, and the acid-base neutralization degree is 50%–100%.

[0018] The negative electrode active layer of this application contains a silanized organic layer on the surface of the silicon-carbon material. This silanized organic layer can form sufficient Si–O–Si and Si–O–C anchoring bonds on the particle surface, significantly improving interfacial shear strength and load transfer efficiency, and effectively suppressing particle displacement and pore wall peeling during cycling. Furthermore, by using carboxylic acid-based anionic aqueous polyurethane as a binder and limiting the ion content and neutralization degree of the carboxylic acid-based anionic aqueous polyurethane, problems such as drying and floating, insufficient interfacial shear strength, excessive brittleness, and poor long-term dimensional stability in existing aqueous bonding systems are solved. This also avoids increased liquid absorption and bulk softening, which can lead to fluctuations in the binder phase modulus and deterioration of the pore structure during cycling. The use of the negative electrode active layer in conjunction with the carboxylic acid-based anionic aqueous polyurethane in this application is beneficial for improving the bonding force between the negative electrode active layer and the current collector, suppressing the volume expansion of the negative electrode active layer, and thus improving cycling performance.

[0019] In an optional embodiment, the mass fraction of silicon-carbon material in the active component is 5~35 wt%. The combination of silicon-carbon material and graphite can improve the anode capacity and cycle stability. However, if the proportion of silicon-carbon material is too high, it will cause excessive expansion of the anode active layer volume and increase the interfacial impedance, leading to rapid capacity decay and shortened cycle life.

[0020] In an optional embodiment, the silicon-carbon material has a silicon mass fraction of 10–30 wt%.

[0021] In an optional embodiment, the mass fraction of the carboxylic acid anionic aqueous polyurethane in the negative electrode active layer is 2.0–8.0%. As a binder, if the content of carboxylic acid anionic aqueous polyurethane is too low, the electrode will easily fall off; if the content is too high, the impedance will increase, both of which will significantly deteriorate the cycle stability of the negative electrode.

[0022] In an optional embodiment, the mass fraction of the conductive agent in the negative electrode active layer is 0.5–6.0%, preferably 1–4%. If the amount of conductive agent is too low, the on-chip resistance increases, polarization intensifies, side reactions increase, and the SEI thickens, leading to a decrease in capacity retention. If the amount of conductive agent is too high, it crowds out the pore volume, hinders ion diffusion, and results in limited or even diminished long-cycle benefits. When the amount of conductive agent is within the above range, carbon fiber and graphene can construct a through-structure, reducing impedance while maintaining both rate capability and cycle life.

[0023] In an optional embodiment, the conductive agent comprises vapor-grown carbon fiber and graphene, wherein the mass ratio of vapor-grown carbon fiber to graphene is 1:(0.2–1.0). The combination of vapor-grown carbon fiber (VGCF) and graphene can construct a three-dimensional conductive network: VGCF establishes long-range electron channels, while graphene fills the microscopic gaps, synergistically reducing resistance. Both combine pore structure and compaction, improving ion diffusion efficiency and helping the battery achieve both rate performance and cycle stability, thus meeting the requirements for high-capacity anodes.

[0024] In an optional embodiment, the conductive agent does not include carbon nanotubes. Using carbon nanotubes as a conductive agent would increase costs, and the poor dispersibility of carbon nanotubes would affect the conductivity, or require complex processes to assist in dispersion.

[0025] In an optional embodiment, the nitrogen content in the negative electrode active layer is 0.10–0.60 wt%, and the nitrogen content can characterize the binder content.

[0026] In an optional embodiment, the sum of the area ratios of the characteristic peaks of Si–O–C and Si–O–Si in the X-ray photoelectron spectroscopy O1s spectrum of the negative electrode active layer is ≥8%; sufficient Si–O–Si and Si–O–C anchoring bonds are formed on the surface of silicon-carbon material, the interfacial shear strength and load transfer efficiency are significantly improved, and particle displacement and pore wall peeling are effectively suppressed during cycling.

[0027] In an optional embodiment, the Fourier transform infrared spectrum of the negative electrode active layer is at 1725±5 cm⁻¹. -1 The characteristic absorption peak of the urethane carbonyl group appears at position A, and A 1725 / A 2920 ≥0.08, where A 1725 1725±5 cm -1 The peak height of the characteristic peak, A 2920 2920±5 cm -1 The peak height of the characteristic peak is 2920±5 cm. -1 The characteristic peak is the stretching peak of CH2.

[0028] In an optional embodiment, the glass transition temperature of the carboxylic acid-type anionic aqueous polyurethane is from –30 °C to 10 °C.

[0029] The present invention also provides a method for preparing the negative electrode active layer described in the foregoing embodiments, comprising: forming and shaping a slurry containing an active component, a carboxylic acid anionic aqueous polyurethane and a conductive agent to obtain the negative electrode active layer.

[0030] In an optional embodiment, the preparation of a carboxylic acid-type anionic aqueous polyurethane is also included: a mixture containing polycarbonate diol and dimethylpropionate diol and a solvent is mixed with diisocyanate isophorone and subjected to a prepolymerization reaction to obtain a prepolymer solution. The prepolymer solution is mixed with lithium hydroxide for neutralization reaction, and then the neutralized solution is poured into deionized water under high-speed shearing to form a PU emulsion; Ethylenediamine was added dropwise to the PU emulsion for chain extension, followed by solvent removal and aging to obtain an emulsion containing the carboxylic acid anionic waterborne polyurethane.

[0031] In an optional embodiment, the film formation and shaping includes: drying at 90-110℃ for 20-60 min under normal pressure under an inert atmosphere, followed by a roll forming process to obtain the negative electrode active layer.

[0032] In an optional embodiment, the preparation of the silicon-carbon material is further included: the matrix of the silicon-carbon material is silanized in a water / alcohol mixture containing a silane coupling agent, and then dried to obtain the silicon-carbon material.

[0033] In an optional embodiment, the pH of the mixed solution is 4.5–5.5, the silanization treatment time is 0.5–3 h, and the mass ratio of the silane coupling agent to the silicon-carbon material matrix is ​​0.5–1.2%. The content of the silanized organic layer in the silicon-carbon material can be adjusted to a suitable range by adjusting the parameters of the silanization treatment.

[0034] This invention also provides an electrode sheet, including a current collector and a negative electrode active layer disposed on the current collector as described in the foregoing embodiments.

[0035] The present invention also provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte.

[0036] In an optional embodiment, the positive electrode sheet includes a positive electrode active material with the molecular formula LiaNixCoyMnzMbO2; wherein 0.9 < a ​​< 1.2, 0.8 ≤ x ≤ 0.93, 0.1 ≤ y < 0.4, 0.05 ≤ z < 0.4, 0 ≤ b ≤ 0.1, and M represents at least one element selected from Zr, W, Ti, Al, Sr, La, B, and Nd.

[0037] In an optional embodiment, the electrolyte includes a lithium salt, which includes one or more combinations of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate borate, and lithium bis(trifluoromethylsulfonyl)imide.

[0038] In an optional embodiment, the electrolyte includes a solvent, which includes one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and methyl ethyl carbonate.

[0039] In an optional embodiment, the electrolyte includes an additive, which includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, ethylene sulfate, ethylene sulfite, ethylene carbonate, and vinyl carbonate.

[0040] In an optional embodiment, the ratio N / P of the capacity N of the negative electrode to the capacity P of the positive electrode is 1.02 to 1.20.

[0041] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0042] Example 1 This embodiment provides a method for preparing a lithium-ion battery, specifically including the following steps: 1. Preparation of the negative electrode active layer Weigh out the active component (945 g): the mass ratio of silicon carbide material (189 g) to graphite (756 g, spherical) is 20:80; PU-ionomer emulsion (on solids basis): 40 g (4.0 wt% of the negative electrode active layer), ion content 0.50 mmol·g - ¹, neutralization degree 80%; Conductive agent: 15 g (1.5 wt% of the negative electrode active layer), of which VGCF 11.538 g, graphene (rGO) 3.462 g, mass ratio (VGCF:rGO) = 1:0.3.

[0043] Among them, (1) the preparation method of PU-ionomer emulsion is as follows: 1.1 Raw materials and quantities (solids and equivalents) are shown in Table 1.

[0044] Table 1

[0045] 1.2 Synthetic Steps and Key Reactions a) Preparation of prepolymer (80 °C, N2) PCDL, DMPA, and a portion of acetone (solvent, analytical grade, to achieve a prepolymer solid content of approximately 70 wt%) were added to a stirred reactor and heated to 80 °C with stirring to dissolve. IPDI was added dropwise, controlling the NCO / OH equivalent ratio to 1.2. The mixture was kept at this temperature for 2 h until the -NCO% concentration stabilized, yielding the prepolymer solution. The reaction formula for the introduction of acidic ionic groups by DMPA to form urethane esters is as follows:

[0046] b) Neutralization (room temperature, pH≈8) The prepolymer solution was cooled to 30 °C, and 4.19 g of a 10 wt% LiOH·H2O solution was slowly added, while stirring for 20 min to convert -COOH to -COO. - Li +The degree of neutralization (the proportion of carboxyl groups converted to carboxylate ions) is 80%, and the reaction formula is: .

[0047] c) Dispersion (deionized water, shearing) The neutralized prepolymer was slowly poured into deionized water under high-speed shearing, and stirred at 3000 rpm for 10 min to form a PU emulsion.

[0048] d) Amine chain extension (25–30 °C) Add EDA solution (2.38 g of EDA dissolved in water to a mass fraction of 10 wt%) dropwise to the PU emulsion, and react at room temperature for 30 min to complete chain extension. The reaction formula (urea bond formation) is as follows: .

[0049] e) Desolventizing and aging The chain-extended emulsion was subjected to reduced pressure at 40 °C to remove acetone until the acetone mass fraction was <0.5 wt%; after aging at room temperature for 12 h, a PU-ionomer emulsion was obtained (solid content ≈40 wt%, ion content 0.50 mmol·g). - ¹, neutralization degree 80%).

[0050] According to the law of conservation of mass, the yield of emulsion is approximately 100 g, of which 40 g is PU-ionomer binder.

[0051] Ion content I = 0.50 mmol·g -1 That is, the number of acidic ionic groups (-COOH or its lithium salt -COO) contained in each 1 g of dry polymer. - Li + The number of millimoles of DMPA. DMPA introduces ionic groups; since each DMPA molecule contains one -COOH group, sodium = nDMPA.

[0052] (2) Preparation method of silicon-carbon materials 2.1 Raw materials and dosage Si@C powder: 189.0 g (dried at 80 ℃ for 2 h for later use) VTES (vinyltriethoxysilane, M≈190.29 g·mol) -1 ): 1.512 g (equivalent to 0.8 wt% relative to Si@C) The amount of substance n = 1.512 / 190.29 = 7.94 × 10 -3 mol Solvent: Ethanol / water volume ratio 60 / 40, total volume ≈ 500 mL Glacial acetic acid: a small amount, to adjust the pH to 5.0 ± 0.2. 2.2 Operation and Reaction a) Add ethanol / water to a stirred flask and adjust the pH to approximately 5.0 using glacial acetic acid; add VTES dropwise and pre-hydrolyze at room temperature for 10 min.

[0053] b) Heat to 50 °C, slowly add Si@C, and hold at 50 °C and 300-500 rpm for 60 min.

[0054] c) Filter to separate the solid phase, wash the separated solid phase with 100 mL of ethanol and 100 mL of water in sequence, and dry it with nitrogen blowing at 60 °C for 8 h to obtain about 189 g of silanized Si@C, i.e., silicon-carbon material.

[0055] The relevant reaction formulas are as follows: Hydrolysis (EtO)3Si-CH=CH2+3H2O→(HO)3Si-CH=CH2+3EtOH.

[0056] Condensation / anchoring with surface silanol ≡Si-OH+(HO)3Si-R→≡Si-O-Si(OH)2-R+H2O.

[0057] 2. Slurry preparation (solid content ≈ 50 wt%, powder added first, then binder) 2.1 Feeding and Sequence Add 600 g of deionized water to a planetary mixer; add 756 g of graphite and stir at 2000–3000 rpm for 20 min.

[0058] Next, add 11.538 g of VGCF and 3.462 g of rGO, increase the speed to 3500 rpm and stir for 10 minutes until uniform and free of agglomerates.

[0059] Next, reduce the rotation speed to 800–1000 rpm, add 189 g of silicon carbide material, and stir for 15–20 min to mix thoroughly.

[0060] Next, slowly add 100 g of PU-ionomer emulsion (40% solids content) and stir at 800 rpm for 10 min.

[0061] Next, add 340 g of deionized water to adjust the viscosity to 3000–5000 mPa·s (25 °C).

[0062] Next, in Vacuum degassing at 0.08 MPa for 10 min yielded a slurry with a solid content of approximately 50 wt%.

[0063] 2.2 Feeding Information Active ingredient = 945 g; conductive agent = 15 g; binder = 40 g; total 1000 g Internal ratio: Silicon carbide: Graphite = 189:756 = 20:80; VGCF: rGO = 11.538:3.462 = 1:0.3.

[0064] Key chemical reaction formula (PU-ionomer network formation and interfacial anchoring) Carbamate bond formation

[0065] Lithium carboxylate salt formation (neutralization)

[0066] Amine chain extension to form urea bonds

[0067] 3. Take the above slurry, coat it, cure it, and roll it to obtain the negative electrode sheet.

[0068] 4. Method for manufacturing positive electrode plates: The positive electrode active material NCM811, conductive carbon black, carbon nanotubes and polyvinylidene fluoride (PVDF) were taken and thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96:1:1:2 to obtain a positive electrode coating material. The positive electrode coating material was then coated on a 12.0 μm thick aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained. 5. Preparation of electrolyte: An electrolyte was prepared by mixing lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), and vinylene carbonate (VC) in a mass percentage ratio of 10.0: 22.0: 53.0: 3.0: 7.0: 5.0.

[0069] 6. Diaphragm: A high-porosity membrane was selected, in which the thickness of the PE base membrane was 9 μm, the thickness of the ceramic coating on both sides of the base membrane was 1.0 μm, and the thickness of the PVDF coating was 1.0 μm. 7. Assembly of lithium-ion batteries: After the positive and negative electrode sheets are rolled and slit, they are wound together with the separator according to a set process to form a 21700 cylindrical battery core. Subsequently, the battery core is fixed to a pre-made connecting piece by welding and then installed into a metal battery casing. After completing key processes such as electrolyte injection, sealing, and formation, the lithium-ion battery described in this embodiment is obtained. This lithium-ion battery uses a cylindrical casing with an external dimension of 21.0 mm in diameter and 70.0 mm in length, conforming to the 21700 standard specification.

[0070] Example 2 The difference between this embodiment and Example 1 is that, in the preparation process of silicon-carbon material, the amount of VTES is reduced from 0.8 wt% to 0.5 wt%, the hydrolysis pH is maintained at 5.0, and the treatment time is reduced from 45 min to 30 min, so that the mass fraction of the silanized organic layer in the silicon-carbon material is reduced to 0.5%. All other aspects are the same as in Example 1.

[0071] Example 3 The difference between this embodiment and Example 1 is that, in the preparation process of the silicon-carbon material, the amount of VTES is increased from 0.8 wt% to 1.2 wt%, the pH is maintained at 5.0, and the treatment time is extended to 90 min, so that the mass fraction of the silanized organic layer in the silicon-carbon material increases to 1.2%. All other aspects are the same as in Example 1.

[0072] Example 4 The difference between this embodiment and Example 1 is that the amount of DMPA added during the synthesis of PU-ionomer was changed, resulting in a reduction of the ion content I to 0.30 mmol·g. -1 The dosage of each raw material is adjusted adaptively, specifically I / 1000 = 0.0003; n D =0.01066 mol, which is equivalent to 1.43 g of DMPA; n IPDI =R(n P +n D =1.2(0.0130+0.01066)=0.02839mol, i.e., IPDI 6.31 g; n EDA =0.02839 mol, which is equivalent to 1.71 g of EDA; n LiOH =0.8×0.01066=0.00853mol, which is 3.58 g of 10 wt% LiOH·H2O solution; Everything else is the same as in Example 1.

[0073] Example 5 The difference between this embodiment and Example 1 is that the amount of DMPA added during the synthesis of PU-ionomer was changed to increase the ion content I to 0.80 mmol·g. -1 Specifically, I / 1000 = 0.0008; n D =0.03942 mol, which is equivalent to 5.29 g of DMPA; n IPDI =1.2(0.0130+0.03942)=0.06290mol, that is, IPDI 13.99 g; n EDA =0.06290mol, which is equivalent to 3.78 g of EDA; n LiOH =0.8×0.03942=0.02554mol, which is 10.72 g of 10 wt% LiOH·H2O solution; Everything else is the same as in Example 1.

[0074] Example 6 The difference between this embodiment and Example 1 is that the amount of LiOH used is adjusted to 0.60 times the acid equivalent, the degree of neutralization is adjusted from 80% to 60%, and the pH is controlled at 7.8–8.2. Everything else is the same as in Example 1.

[0075] Example 7 The difference between this embodiment and Example 1 is that the amount of LiOH used is adjusted to 1.00 times the acid equivalent, and the degree of neutralization is increased to 100%. Everything else is the same as in Example 1.

[0076] Example 8 The difference between this embodiment and Embodiment 1 is that the total amount of conductive agent is reduced from 1.5 wt% of the negative electrode active layer to 1.0 wt%, and the ratio of VGCF to graphene is reduced to 1:0.3. Everything else is the same as in Embodiment 1.

[0077] Example 9 The difference between this embodiment and Embodiment 1 is that the total amount of conductive agent is increased from 1.5 wt% of the negative electrode active layer to 3.0 wt%, and VGCF and graphene are increased in the same ratio of 1:0.3. All other aspects are the same as in Embodiment 1.

[0078] Example 10 The difference between this embodiment and Embodiment 1 is that the internal ratio of the active components is adjusted to Si:graphite = 15:85, while all other aspects are the same as in Embodiment 1.

[0079] Example 11 The difference between this embodiment and Embodiment 1 is that the internal ratio of the active components is adjusted to Si:graphite = 25:75, while all other aspects are the same as in Embodiment 1.

[0080] Comparative Example 1 The difference between this comparative example and Example 1 is that, in the preparation process of the silicon-carbon material, the amount of VTES was reduced to 0.05 wt%, and the treatment time was only 20 min, so that the mass fraction of the silanized organic layer in the silicon-carbon material was reduced to 0.05%. Everything else was the same as in Example 1.

[0081] Comparative Example 2 The difference between this comparative example and Example 1 is that the amount of DMPA added during the synthesis of PU-ionomer was changed to reduce the ion content I to 0.10 mmol·g. - ¹, The dosage of each raw material is adjusted adaptively, specifically I / 1000=0.0001; n D =(0.0001×30.405) / (1-0.0001×478.562)=0.003194mol, that is, m DMPA =0.003194 × 134.13 = 0.429 g; n IPDI =1.2(0.01300+0.003194)=0.01943mol, that is, m IPDI =4.32g n EDA =0.01943 mol, i.e., m EDA =1.17g; n LiOH =0.8 × 0.003194 = 0.002555 mol, which is the amount of 10 wt% LiOH·H2O solution in m 溶液 =0.002555×41.96 / 0.10=1.07 g; Everything else is the same as in Example 1.

[0082] Comparative Example 3 The difference between this comparative example and Example 1 is that the amount of LiOH used is reduced to 0.30 times the acid equivalent, while all other aspects are the same as in Example 1.

[0083] Comparative Example 4 The difference between this comparative example and Example 1 is that the total amount of conductive agent is reduced to 0.1 wt% of the negative electrode active layer, and the ratio of VGCF to graphene is maintained at 1:0.3. All other aspects are the same as in Example 1.

[0084] Comparative Example 5 The difference between this comparative example and Example 1 is that the internal ratio of the active components is adjusted to Si:graphite = 35:65, while all other aspects are the same as in Example 1.

[0085] Comparative Example 6 The difference between this comparative example and Example 1 is that the carboxylic acid type anionic waterborne polyurethane is replaced with sulfonic acid type anionic waterborne polyurethane, wherein the sulfonic acid type anionic waterborne polyurethane has a sulfonate group content of 0.25 mmol / g and an acid-base neutralization degree of 80%.

[0086] Comparative Example 7 The difference between this comparative example and Example 1 is that the silicon-carbon material is replaced with an equal mass of Si@C powder, and the carboxylic acid-type anionic waterborne polyurethane is replaced with an equal mass of nonionic waterborne polyurethane (without -COO). - / —SO3 - ).

[0087] The key parameters in the above embodiments and comparative examples are shown in Table 2.

[0088] Table 2

[0089] The lithium-ion batteries prepared in the above embodiments and comparative examples were tested as follows.

[0090] 1. First, discharge the lithium-ion battery to a constant current of 2.5V to ensure it is in a safe state, reducing the risk of short circuits or thermal runaway during disassembly. Carefully disassemble the battery inside a glove box (protected by argon or other inert atmosphere) and remove the electrodes from the cylindrical cell. Use plastic tweezers to peel off the electrodes, avoiding damage to the active material layer. Next, cut the removed electrodes to an appropriate size and soak them in anhydrous dimethyl carbonate (DMC) solution for 30 minutes to dissolve and remove residual electrolyte and possible byproducts. After removing the electrodes, gently wipe the surface with lint-free paper, then replace with fresh DMC solution, repeating the soaking-wiping process three times to ensure no residual contaminants remain on the electrode surface. Subsequently, rinse the electrodes with anhydrous ethanol and wipe again to further remove solvent and impurities. After cleaning, place the electrodes in a glove box and let them stand for 48 hours to ensure they are completely dry, preventing interference from residual solvents in subsequent tests. After drying, gently scrape off the active material layer from the electrodes using a plastic scraper, ensuring the collected powder is not contaminated. The scraped powder was transferred to centrifuge tubes containing anhydrous ethanol and ultrasonically dispersed for 30 minutes in an ultrasonic cleaner to further remove any possible residual electrolyte and impurities. After ultrasonic treatment, the sample was centrifuged (at 5000 rpm for 2 minutes), the supernatant was discarded, and the powder was redispersed with anhydrous ethanol, ultrasonicated again for 10 minutes, and then centrifuged again. This process was repeated three times to ensure the purity of the powder sample. Finally, the precipitate was collected and transferred to a vacuum drying oven and dried at 80°C for 12 hours to ensure complete removal of residual solvent. The dried powder was placed in a sealed bag or sealed sample box, immediately removed from the glove box, and the sample was quickly subjected to XRD, XPS, Raman, and HRTEM tests.

[0091] The specific XRD measurement method was as follows: A copper target X-ray diffractometer (Cu-Kα radiation, 1.54 Å, tube voltage 40 kV, tube current 40 mA) was used to uniformly disperse the sample on a silicon substrate, and XRD patterns were acquired at a scanning rate of 2° / min in the range of 2θ = 15°~70°.

[0092] The specific method for determining the intensity (height) of elemental characteristic peaks in XPS spectra: XPS testing was performed using a PHI-5000 Versa Probe instrument, with Al Kα (1486.6 eV) as the X-ray source and a power of 150 W (15 kV × 10 mA). The test included full-spectrum scanning (0–1100 eV, step size 1 eV), background subtraction was performed using Shirley background correction, and C 1s (284.8 eV) was used as an internal standard for data normalization and elemental quantitative analysis.

[0093] Raman spectral analysis: A 532 nm laser was used as the excitation source, with the laser power set to 1–5 mW to avoid sample ablation. The sample was uniformly dispersed on a silicon substrate. The sample was measured at 500–1700 cm⁻¹. -1 Raman spectra were collected within the range, with a spectral resolution set to 1 cm⁻¹. -1 The instrument performs 3-5 scans to improve the signal-to-noise ratio. It uses an XYZ automatic displacement platform for precise focusing and performs pre-scanning on a silicon wafer (520.7 cm²). -1 Calibration is performed to ensure data accuracy. The determination methods for HRTEM and HRTEM-EDS are as follows: The powder sample is ultrasonically dispersed in ethanol, and the suspension is dropped onto a copper microgrid (3 mm in diameter) and dried. In a 200 kV transmission electron microscope, the high-resolution mode is selected, and the coating layer is determined and its thickness is measured by selected area electron diffraction (SAED) and fast Fourier transform (FFT). At the same time, the EDS spectrometer is turned on, and the acquisition time is set to ≥30 seconds / point and the beam current is ≤1 nA. Elemental surface scan or line scan is performed to determine the distribution of Fe, N, B and C.

[0094] 2. Performance testing methods: Place the battery in a 45℃ constant temperature chamber for 6 hours and test it according to the following steps: (1) First round of constant current and constant voltage charging: charge at a constant current of 0.1C to 4.25V, then switch to constant voltage charging until the current drops to 0.01C.

[0095] (2) Let it stand for 30 minutes after charging is complete.

[0096] (3) Perform constant current discharge, and discharge to 2.5V at a rate of 0.1C.

[0097] (4) Cyclic charging and discharging process: constant current charging at a rate of 1C to 4.25V, then constant voltage charging until the current drops to 0.1C.

[0098] (5) Let it stand for another 30 minutes.

[0099] (6) Discharge at a constant current rate of 1C to 2.5V.

[0100] (7) Let it stand for another 30 minutes.

[0101] (8) Repeat the above (4)-(7) charging and discharging process for a total of 200 cycles.

[0102] 200-cycle capacity retention: Statistical analysis of battery discharge capacities Q1 and Q2 after 1 and 200 cycles. 200 Calculate the battery capacity retention rate: Q 200 / Q1×100%.

[0103] 3. Test method for peel force of negative electrode sheet: (1) First, the negative electrode sheet that has been washed with dimethyl carbonate and vacuum dried is cut into strips of standard size (2.0cm×10.0cm); (2) Next, use double-sided tape to fix the strip sample on a flat thin steel plate, ensuring that the tape is pasted in the center of the steel plate. Then peel off the protective layer of the double-sided tape, paste the strip sample of the electrode to be tested on the double-sided tape, and use a pressure roller to evenly roll the strip sample to ensure good adhesion. (3) Next, tear off the unattached end, bend the natural end of the torn electrode upward, and clamp it in the upper fixture of the tensile testing machine to perform a 180° peel test. Record the tensile force curve. Select the stable peeling section when the tensile force changes by no more than 10%. Finally, divide the average tensile force of the section by the width of the long sample electrode to calculate the peel strength of the negative electrode.

[0104] 4. Electrode Thickness Expansion Rate Test Method The thickness of the fresh negative electrode sheet after rolling was measured using a laser thickness gauge and recorded as H1. After the capacity retention rate test at 1C for 200 cycles, the battery electrode sheet was disassembled, washed with dimethyl carbonate to remove the electrolyte, and vacuum dried. The measured thickness was recorded as H2. Electrode expansion rate = (H2-H1) / H1*100%.

[0105] The results of the above tests performed on each embodiment and comparative example are shown in Table 3.

[0106] Table 3

[0107] Analyzing the above results, the following conclusions can be drawn: Regarding silane loading, comparing Examples 1 to 3 with Comparative Example 1, it is evident that a suitable level of silanization can form sufficient Si–O–Si and Si–O–C anchoring bonds on the particle surface, significantly improving interfacial shear strength and load transfer efficiency, and effectively suppressing particle displacement and pore wall peeling during cycling. When the loading is insufficient, the interface mainly relies on physical adsorption and mechanical interlocking, making microcracks and debonding more likely to accumulate and induce repeated SEI growth, resulting in decreased capacity retention and intensified electrode expansion. Conversely, excessive loading introduces a thicker organic layer, increasing the resistance to cross-interfacial electron and ion migration, increasing polarization, and tending to reduce long-cycle performance.

[0108] Regarding the ion content, comparing Examples 1, 4, 5, and Comparative Example 2, it can be seen that the ion content of PU-ionomer determines the ion cluster density, interchain electrostatic association strength, and water dispersibility. When the content is too low, the self-dispersibility and emulsion stability are insufficient, and the dry film is prone to phase separation and pore wall defects. The electrolyte preferentially penetrates into the defect area and triggers side reactions, leading to rapid accumulation of cyclic impedance. When the content is moderate, the ion clusters provide reversible physical crosslinking, ensuring both film continuity and toughness without excessive hydrophilicity, thereby maintaining low liquid absorption and stable size. Although the initial dispersion and spreadability are better when the content is too high, the enhanced electrophilicity leads to local softening of the binder phase and modulus fluctuations, and the expansion and retention rate are correspondingly limited.

[0109] Regarding the degree of neutralization, comparing Examples 1, 6, 7, and Comparative Example 3, it can be seen that the degree of neutralization adjusts the proportion of carboxyl groups converted to ionic states, thereby affecting the emulsion charge, particle size distribution, and ion cluster formation. When the neutralization is too low, insufficient charge leads to easy particle aggregation, a wider particle size distribution, abnormal coating pore connectivity, local softening after electrolyte wetting, and frequent side reactions. While excessively high neutralization can improve dispersion stability and coating rheology, it also increases the hydrophilicity of ion clusters, leading to increased liquid absorption and bulk softening, and slightly affecting dimensional stability and long-term cycling. A moderately high neutralization range maintains stable dispersion and continuous film formation while controlling liquid absorption, resulting in superior overall performance.

[0110] Regarding the total amount of conductive agent, comparing Examples 1, 8, 9, and Comparative Example 4, it can be seen that the total amount of conductive agent determines whether the electron channel crosses the percolation threshold and affects the balance between pores and compaction. When the total amount is too low, the on-cell resistance increases significantly, the battery polarization intensifies, the uneven current distribution leads to an increase in side reactions, the SEI thickens rapidly, and the capacity remains significantly reduced. When the total amount is moderate, the aspect ratio carbon fibers and sheet graphene work together to construct a through-framework, reducing resistance without significantly occupying pores, thus balancing rate capability and cycle life. When the total amount is too high, it crowds out the pore volume and active surface, lengthens the ion diffusion path, and disrupts compaction and pore structure. Although the DC resistance continues to decrease, the long-cycle benefits are limited or even decay.

[0111] Regarding the proportion of silicon in the active component, a comparison of Examples 1, 10, 11, and Comparative Example 5 shows that the silicon content directly determines the trade-off between capacity potential and volume effect intensity. Increasing the silicon proportion improves specific capacity but also enhances volume changes caused by lithium insertion / extraction, placing higher demands on interface anchoring and the three-dimensional network. Insufficient buffering leads to continuous exposure of fresh surfaces and repeated SEI formation, resulting in decreased capacity retention and increased electrode expansion. Decreasing the silicon proportion significantly reduces stress concentration and structural fatigue, making dimensional stability and adhesion easier to achieve, but correspondingly reduces the energy density per unit area. Maintaining silicon within a moderate range and coordinating it with the silane interface and PU-ionomer network can achieve a more reasonable overall performance in terms of energy density, expansion resistance, and long cycling duration.

[0112] Regarding the composition of the binder, comparing Example 1 with Comparative Examples 6-7, it can be seen that compared with sulfonic acid-type anionic waterborne polyurethane and nonionic waterborne polyurethane, carboxylic acid-type anionic waterborne polyurethane is more conducive to improving the dimensional stability of the negative electrode sheet and the adhesion between the negative electrode active layer and the current collector, which further contributes to the improvement of cycle performance.

[0113] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A negative electrode active layer, characterized in that, Includes active components, carboxylic acid anionic waterborne polyurethane, and conductive agents; The active components include silicon-carbon material and graphite, and the surface of the silicon-carbon material is provided with a silanized organic layer, wherein the mass fraction of the silanized organic layer in the silicon-carbon material is 0.3–2.0 wt%. The carboxylic acid anionic waterborne polyurethane contains carboxylate groups (–COO). - The content is 0.2–1.0 mmol / g, and the acid-base neutralization degree is 50%–100%.

2. The negative electrode active layer according to claim 1, characterized in that, The active component contains 5-35 wt% silicon-carbon material. And / or, the silicon-carbon material contains 10–30 wt% silicon by mass. And / or, in the negative electrode active layer, the mass fraction of the carboxylic acid-type anionic aqueous polyurethane is 2.0–8.0%; And / or, in the negative electrode active layer, the mass fraction of the conductive agent is 0.5–6.0%, preferably 1–4%; And / or, the conductive agent comprises vapor-grown carbon fibers and graphene, wherein the mass ratio of the vapor-grown carbon fibers to graphite is 1:(0.2–1.0). And / or, the conductive agent does not include carbon nanotubes.

3. The negative electrode active layer according to claim 1, characterized in that, The nitrogen content in the negative electrode active layer is 0.10–0.60 wt%. And / or, the sum of the area ratios of the characteristic peaks of Si–O–C and Si–O–Si in the X-ray photoelectron spectroscopy (O1s) spectrum of the negative electrode active layer is ≥8%; And / or, the Fourier transform infrared spectrum of the negative electrode active layer is at 1725±5 cm⁻¹. -1 The characteristic absorption peak of the urethane carbonyl group appears at position A, and A 1725 / A 2920 ≥0.08, where A 1725 1725±5 cm -1 The peak height of the characteristic peak, A 2920 2920±5cm -1 The peak height of the characteristic peak.

4. The negative electrode active layer according to claim 1, characterized in that, The glass transition temperature of the carboxylic acid-type anionic waterborne polyurethane is –30 °C to 10 °C.

5. A method for preparing the negative electrode active layer according to claim 1, characterized in that, include: The slurry containing active components, carboxylic acid anionic waterborne polyurethane, and conductive agents is film-formed and shaped to obtain the negative electrode active layer.

6. The method for preparing the negative electrode active layer according to claim 5, characterized in that, It also includes the preparation of carboxylic acid type anionic waterborne polyurethane: a mixture containing polycarbonate diol and dimethylpropionic acid diol and solvent is mixed with diisocyanate isophorone and subjected to a prepolymerization reaction to obtain a prepolymer solution; The prepolymer solution is mixed with lithium hydroxide for neutralization reaction, and then the neutralized solution is poured into deionized water under high-speed shearing to form a PU emulsion; Ethylenediamine was added dropwise to the PU emulsion for chain extension, followed by solvent removal and aging to obtain an emulsion containing the carboxylic acid anionic waterborne polyurethane. And / or, the film forming and shaping includes: drying at 90-110℃ for 20-60 min under normal pressure under an inert atmosphere, and then preparing the negative electrode active layer by a roll pressing process; And / or, also includes the preparation of silicon-carbon materials: silanizing a silicon-carbon material matrix in an aqueous / alcoholic mixed solution containing a silane coupling agent, followed by drying to obtain the silicon-carbon material.

7. The method for preparing the negative electrode active layer according to claim 5, characterized in that, The pH of the mixed solution is 4.5–5.5, the silanization treatment time is 0.5–3 h, and the mass ratio of silane coupling agent to silicon-carbon material matrix is ​​0.5–1.2%.

8. A negative electrode sheet, characterized in that, It includes a current collector and a negative electrode active layer disposed on the current collector as described in any one of claims 1-4.

9. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode as described in claim 8, a separator, and an electrolyte.

10. The lithium-ion battery according to claim 9, characterized in that, The positive electrode includes a positive electrode active material with the molecular formula LiaNixCoyMnzMbO2; wherein 0.9 < a ​​< 1.2, 0.8 ≤ x ≤ 0.93, 0.1 ≤ y < 0.4, 0.05 ≤ z < 0.4, 0 ≤ b ≤ 0.1, and M represents at least one element selected from Zr, W, Ti, Al, Sr, La, B, and Nd. And / or, the electrolyte includes a lithium salt, which includes one or more combinations of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate borate, and lithium bis(trifluoromethanesulfonyl)imide. And / or, the electrolyte includes a solvent, the solvent including one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and methyl ethyl carbonate; And / or, the electrolyte includes additives, the additives including one or more of fluoroethylene carbonate, difluoroethylene carbonate, ethylene sulfate, ethylene sulfite, vinylene carbonate, and vinyl carbonate; And / or, the ratio N / P of the capacity N of the negative electrode to the capacity P of the positive electrode is 1.02 to 1.20.

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