A sodium-ion battery negative electrode sheet based on the synergistic effect of physical anchoring and chemical bonding and its preparation method.

Abstract

This invention discloses a sodium-ion battery negative electrode sheet based on the synergistic effect of physical anchoring and chemical bonding, and its preparation method. The preparation method includes the following steps: mixing hard carbon, a conductive agent, a binder, and water; sequentially adding alkaline particles and a coupling agent to obtain an aqueous negative electrode slurry; coating the aqueous negative electrode slurry onto the surface of an aluminum foil current collector to obtain a wet electrode sheet; drying the wet electrode sheet; and rolling the dried electrode sheet to obtain the sodium-ion battery negative electrode sheet. This invention, without increasing the preparation process or cost, utilizes alkaline particles to achieve controllable in-situ corrosion of the aluminum foil to form a physical anchoring structure, and constructs chemical bonds at the interface through a suitable coupling agent. Simultaneously, it avoids side reactions between the alkaline particles and the coupling agent, significantly improving the interfacial adhesion between the aqueous negative electrode slurry and the aluminum foil current collector, and ensuring the consistency of electrode sheet processing and electrochemical stability.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery electrode technology, specifically to a sodium-ion battery negative electrode sheet based on the synergistic effect of physical anchoring and chemical bonding, and its preparation method. Background Technology

[0002] Sodium-ion batteries have broad application prospects in energy storage and low-speed power fields due to their abundant resources, low cost, and good safety. Hard carbon materials have advantages such as stable layered structure, moderate sodium intercalation potential, and long cycle life, making them suitable as anodes for sodium-ion batteries. Currently, hard carbon anodes are typically prepared by coating an aluminum foil current collector with an aqueous slurry based on carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR). The interfacial bonding strength between the electrode coating and the current collector directly determines the battery's processing yield, cycle stability, and safety performance. Existing technologies for improving electrode adhesion mainly fall into two categories: one is current collector pretreatment, including pre-coating a conductive carbon layer on the aluminum foil surface, preparing porous / microporous aluminum foil, electrochemical etching, or mechanical roughening. These methods require additional specialized equipment and processing steps, significantly increasing production costs and making them difficult to adapt to high-speed continuous production; the other is additive modification, which involves adding adhesion promoters to the slurry or using chemical substances to perform in-situ etching of the aluminum foil to increase the interfacial contact area and mechanical interlocking effect. In the existing technology, there have been attempts to use alkaline substances to etch aluminum foil to increase the specific surface area, but there are defects such as difficulty in accurately controlling the degree of corrosion, easy to cause excessive corrosion of aluminum foil or uneven local corrosion, resulting in poor electrode consistency.

[0003] Physical anchoring alone offers limited improvement in adhesion and cannot meet the stringent requirements of high-power, long-cycle batteries. However, combining physical etching with interfacial chemical bonding, and using coupling agents to construct stable covalent bonds between the coating and the current collector, can achieve a synergistic enhancement effect. However, conventional coupling agents often contain strong coordinating groups such as carboxyl and phosphonic acid groups, which are prone to chelation reactions with metal ions in alkaline etchants. This leads to premature decomposition of alkaline particles, loss of their corrosive function, and additive compatibility conflicts, severely affecting the stability and electrochemical performance of the electrode fabrication. Summary of the Invention

[0004] The purpose of this invention is to address the technical problems of existing technologies that struggle to simultaneously achieve simplified processes, controllable costs, and the absence of additive side reactions, as well as the inability to synergistically achieve physical anchoring and chemical bonding, and the difficulty in efficiently and stably improving the interfacial adhesion of aqueous anode sheets in sodium-ion batteries. This invention provides a sodium-ion battery anode sheet based on the synergistic effect of physical anchoring and chemical bonding, and its preparation method. Without increasing the number of preparation steps or costs, this invention utilizes alkaline particles to achieve controlled in-situ corrosion of aluminum foil to form a physical anchoring structure, and constructs chemical bonds at the interface using a suitable coupling agent. Simultaneously, it avoids side reactions between alkaline particles and the coupling agent, significantly improving the interfacial adhesion between the aqueous anode slurry and the aluminum foil current collector, and ensuring the consistency of electrode processing and electrochemical stability.

[0005] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0006] The first aspect of this invention provides a method for preparing a negative electrode sheet for a sodium-ion battery, comprising the following steps:

[0007] (1) Mix hard carbon, conductive agent, binder and water to obtain negative electrode aqueous slurry;

[0008] (2) Add alkaline particles to the aqueous negative electrode slurry obtained in step (1), disperse evenly, and then add a coupling agent to obtain an aqueous negative electrode mixed slurry; the alkaline particles are calcium carbonate and / or magnesium carbonate, and the amount of alkaline particles added is 0.1%-3% of the dry basis mass of the aqueous negative electrode slurry; the coupling agent is a silane coupling agent and / or titanate coupling agent that does not chelate with calcium and magnesium ions, and the amount of coupling agent added is 0.3%-2.0% of the dry basis mass of the aqueous negative electrode slurry;

[0009] (3) The negative electrode aqueous mixed slurry obtained in step (2) is coated on the surface of the aluminum foil current collector to obtain a wet electrode sheet; the wet electrode sheet is dried at 80-130 °C, and the dried electrode sheet is rolled to obtain the sodium-ion battery negative electrode sheet.

[0010] In the drying process of preparing the sodium-ion battery negative electrode sheet according to this invention, as the water in the wet electrode sheet continues to evaporate, the synergistic construction of interfacial physical anchoring and chemical bonding is completed simultaneously. The specific process is as follows: On the one hand, during the slurry drying process, water continues to evaporate, the water film on the surface of the alkaline particles gradually thins, and the dissolved carbonate ions (CO3) are released. 2- The inability of CO32- to diffuse in a timely manner leads to a sharp increase in its local concentration near the particles, thereby shifting the hydrolysis equilibrium to the right (CO32-). 2- + H2O HCO3 - +OH - ), hydroxide ions (OH-) -Local accumulation eventually forms highly alkaline micro-regions with pH > 10 around the alkaline particles, causing pitting corrosion on the aluminum foil current collector surface and forming micron-sized pit structures. After drying, these pit structures physically anchor the negative electrode coating. On the other hand, the coupling agent migrates to the interface between the aluminum foil and the negative electrode coating with the evaporation of moisture. Among them, the silane coupling agent hydrolyzes to generate silanol groups (Si-OH), which can undergo a condensation reaction with Al-OH on the aluminum foil surface to form Al-O-Si covalent bonds, and the titanate coupling agent can combine with the aluminum foil surface to form Ti-O-Al covalent bonds. At the same time, the organic functional groups (epoxy groups or pyrophosphate oxy groups) at the other end of the coupling agent can chemically combine with the polar groups on the surface of the hard carbon particles, as well as the hydroxyl and carboxyl groups in the binder, thereby constructing a continuous and stable covalent bond network at the interface between the aluminum foil and the negative electrode coating, achieving interfacial chemical bonding.

[0011] Further, in step (1), the dry basis mass ratio of the hard carbon, conductive agent and binder is (90-95):(0.5-2):(3-6).

[0012] Further, in step (1), the conductive agent is conductive carbon black Super P (abbreviated as conductive agent SP).

[0013] Further, in step (1), the adhesive is sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), and the dry basis mass ratio of sodium carboxymethyl cellulose to styrene-butadiene rubber is (1-3):(1-3).

[0014] Furthermore, in step (1), the solid content of the aqueous slurry is 50%-70%.

[0015] Specifically, in step (1), hard carbon, conductive agent, and binder are added to the slurry mixer at a dry basis mass ratio of (90-95):(0.5-2):(3-6), water is added as a solvent, the solid content of the slurry is controlled to be 50%-70%, and the mixture is dispersed at high speed for 180-240 min under a vacuum of -0.080 MPa to -0.095 MPa to obtain a negative electrode aqueous slurry.

[0016] Further, in step (2), the particle size of the alkaline particles is 0.5-20 μm, preferably 3-8 μm.

[0017] Furthermore, in step (2), the coupling agent does not contain strong coordinating groups (such as phosphonic acid groups, carboxyl groups, etc.) and will not react with calcium ions (Ca). 2+ ), magnesium ions (Mg 2+ The alkaline particles undergo chelation to form stable complexes, thus ensuring that they remain intact and exert a localized corrosive effect during the subsequent drying process.

[0018] Further, in step (2), the silane coupling agent is γ-glycidyl etheroxypropyltrimethoxysilane (KH-560), and the titanate coupling agent is isopropyltris(dioctyl pyrophosphate) titanate.

[0019] Specifically, in step (2), alkaline particles are added to the aqueous slurry of the negative electrode, and the particles are stirred for 5-10 min to disperse them evenly. Then, a coupling agent that does not chelate with calcium and magnesium ions is added, and the mixture is stirred at a low speed of 40-60 rpm for 10-20 min to allow the coupling agent to be evenly adsorbed on the alkaline particles and the surface of hard carbon, thus obtaining the aqueous mixed slurry of the negative electrode.

[0020] Specifically, in step (3), an extrusion coating machine is used to coat the negative electrode aqueous mixed slurry onto the surface of the aluminum foil current collector. The coating speed is 1.5-10 m / min, and the coating thickness matches the design surface density of the negative electrode sheet to obtain a wet electrode sheet. The wet electrode sheet is placed in an oven at 80-130 ℃, and the dried electrode sheet is compacted by a roller press to obtain a sodium-ion battery negative electrode sheet.

[0021] The second aspect of this invention provides a sodium-ion battery negative electrode sheet prepared by the preparation method described in the first aspect.

[0022] The above-described technical solution of the present invention has the following beneficial effects:

[0023] 1. This invention achieves a significant improvement in the interfacial adhesion between the negative electrode coating and the aluminum foil current collector through the dual synergistic effect of physical anchoring and chemical bonding. Specifically, the pit structure formed by the in-situ corrosion of the aluminum foil by alkaline particles (physical anchoring agent) can form a stable mechanical locking effect with the coating, providing reliable physical anchoring; the covalent bond network constructed at the interface by the coupling agent (chemical bonding agent) enables molecular-level bonding between the coating and the current collector. The two processes do not interfere with each other and work synergistically, resulting in a 100%-150% increase in electrode adhesion compared to unmodified electrodes.

[0024] 2. This invention effectively avoids compatibility conflicts and side reactions between functional additives (alkaline particles and coupling agents) by screening suitable coupling agent systems, ensuring the stability and controllability of the electrode preparation process. The selected coupling agent does not chelate with calcium and magnesium ions, preventing premature dissolution and failure of alkaline particles, ensuring that alkaline particles can stably exert a localized corrosion effect during the drying stage, achieving controllable pitting corrosion on the aluminum foil surface. The size of the corrosion sites is mainly determined by the particle size of the alkaline particles, preferably 3-8 μm, which corresponds to corrosion pits with a diameter of about 5-15 μm. The corrosion depth is constrained by the weak alkaline system of calcium carbonate and magnesium carbonate and the drying temperature of 80-130 ℃, and can be stably controlled in the nanometer range of 50-500 nm. The density of corrosion sites can be adjusted by controlling the amount of alkaline particles added to the slurry solid content and the uniformity of particle dispersion in the slurry, thereby constructing a uniformly distributed, isolated and high-density micron-scale pit structure on the aluminum foil surface, providing a stable and reliable physical anchoring effect between the negative electrode coating and the aluminum foil current collector.

[0025] 3. This invention has excellent process compatibility. All functional additives are added simultaneously during the aqueous slurry preparation stage. There is no need to add additional processes such as pre-coating carbon layer, surface etching, and roughening pretreatment to the aluminum foil current collector. It can be directly adapted to the existing continuous production line of sodium-ion battery electrodes, with only a very low cost increase, and has extremely high industrial application value.

[0026] 4. This invention improves interfacial adhesion without increasing electrode resistance, thus fully ensuring the electrochemical performance of the negative electrode. The coupling agent forms a monolayer or sub-monolayer structure at the interface, which does not increase the contact resistance between the coating and the current collector. At the same time, the physical anchoring effect increases the effective contact area between the coating and the aluminum foil. Actual tests show that the resistivity of the modified electrode remains basically unchanged compared with the unmodified electrode, and may even decrease slightly, which can fully meet the application requirements of high-power, long-cycle sodium-ion batteries. Attached Figure Description

[0027] Figure 1 This is an optical microscope image (scale bar: 20 μm) of the aluminum foil current collector surface after removing the negative electrode coating from the sodium-ion battery negative electrode sheet prepared in Example 1. Detailed Implementation

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0031] Example 1

[0032] A method for preparing a negative electrode sheet for a sodium-ion battery includes the following steps:

[0033] (1) Weigh 1000 g of hard carbon, conductive agent SP, CMC and SBR in a dry basis mass ratio of 93.5:1.2:2.8:2. Add hard carbon, conductive agent SP, CMC and SBR to the mixing machine in sequence, add deionized water as solvent, control the solid content of the slurry to 55%, and disperse at high speed for 200 min under vacuum of -0.080 MPa to obtain negative electrode aqueous slurry.

[0034] (2) Add 10 g of calcium carbonate powder (D50=5 μm) to the uniformly mixed aqueous negative electrode slurry. The amount added is 1.0% of the dry basis mass of the aqueous negative electrode slurry. Stir for 8 min to make the particles uniformly dispersed. Then add 6 g of KH-560 silane coupling agent. The amount added is 0.6% of the dry basis mass of the aqueous negative electrode slurry. Stir at 50 rpm for 15 min to make the coupling agent uniformly adsorbed on the calcium carbonate powder and hard carbon surface to obtain the aqueous negative electrode slurry.

[0035] (3) The negative electrode aqueous mixture slurry was coated onto the surface of a 12 μm thick aluminum foil current collector using an extrusion coating machine. The coating speed was 5 m / min and the coating thickness was 110 μm, resulting in a wet electrode sheet coated with a negative electrode coating. The wet electrode sheet was placed in an oven at 100 ℃ and the dried electrode sheet was compacted by a roller press to obtain a sodium-ion battery negative electrode sheet.

[0036] The sodium-ion battery negative electrode sheet prepared in Example 1 was immersed in water to remove the negative electrode coating adhering to its surface. The surface of the aluminum foil current collector was then observed using an optical microscope. The test results are as follows: Figure 1 As shown, a large number of corrosion pits are formed on the surface of the aluminum foil current collector. The pit structure is generated by the local high-alkalinity micro-regions formed by alkaline particles in the mixed slurry during the drying process. It can form a stable mechanical bond with the negative electrode coating and provide a reliable physical anchoring effect for the electrode.

[0037] Example 2

[0038] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that: in step (2), 20 g of magnesium carbonate powder (D50=8 μm) is added to the uniformly mixed aqueous negative electrode slurry, the amount added is 2.0% of the dry basis mass of the aqueous negative electrode slurry, and after stirring for 8 min to make the particles uniformly dispersed, 12 g of isopropyltris(dioctylpyrophosphoyloxy)titanate is added, the amount added is 1.2% of the dry basis mass of the aqueous negative electrode slurry, and after stirring at 50 rpm for 15 min to make the coupling agent uniformly adsorbed on the magnesium carbonate powder and the hard carbon surface, a mixed aqueous negative electrode slurry is obtained.

[0039] Example 3

[0040] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (2), calcium carbonate powder (D50=5 μm) is replaced with calcium carbonate powder (D50=1 μm).

[0041] Example 4

[0042] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (2), calcium carbonate powder (D50=5 μm) is replaced with calcium carbonate powder (D50=3 μm).

[0043] Example 5

[0044] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (2), 10 g of calcium carbonate powder (D50=5 μm) is replaced with 5 g of calcium carbonate powder (D50=5 μm), and the amount added is 0.5% of the dry basis mass of the negative electrode aqueous slurry.

[0045] Example 6

[0046] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (2), 10 g of calcium carbonate powder (D50=5 μm) is replaced with 20 g of calcium carbonate powder (D50=5 μm), and the amount added is 2% of the dry basis mass of the negative electrode aqueous slurry.

[0047] Example 7

[0048] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (2), 6 g of KH-560 silane coupling agent is replaced with 10 g of KH-560 silane coupling agent, and the amount added is 1% of the dry basis mass of the negative electrode aqueous slurry.

[0049] Example 8

[0050] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (3), the wet electrode sheet is placed in an oven at 120 °C.

[0051] Comparative Example 1

[0052] A method for preparing a negative electrode sheet for a sodium-ion battery includes the following steps:

[0053] (1) Weigh 1000 g of hard carbon, conductive agent SP, CMC and SBR in a dry basis mass ratio of 93.5:1.2:2.8:2. Add hard carbon, conductive agent SP, CMC and SBR to the mixing machine in sequence, add deionized water as solvent, control the solid content of the slurry to 55%, and disperse at high speed for 200 min under vacuum of -0.080 MPa to obtain negative electrode aqueous slurry.

[0054] (2) The negative electrode aqueous slurry is coated onto the surface of a 12 μm thick aluminum foil current collector using an extrusion coating machine. The coating speed is 5 m / min and the coating thickness is 110 μm to obtain a wet electrode sheet. The wet electrode sheet is placed in an oven at 100 ℃ and the dried electrode sheet is compacted by a roller press to obtain a sodium-ion battery negative electrode sheet.

[0055] Comparative Example 2

[0056] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (2), 10 g of calcium carbonate powder (D50=5 μm) is added to the uniformly mixed aqueous negative electrode slurry. The amount added is 1.0% of the dry basis mass of the aqueous negative electrode slurry. After stirring for 8 min to make the particles uniformly dispersed, the aqueous negative electrode slurry is obtained.

[0057] Comparative Example 3

[0058] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (2), 6 g of KH-560 silane coupling agent is added to the uniformly mixed aqueous negative electrode slurry. The amount added is 0.6% of the dry basis mass of the aqueous negative electrode slurry. The mixture is stirred at low speed of 50 rpm for 15 min to allow the coupling agent to be uniformly adsorbed on the hard carbon surface, thereby obtaining an aqueous mixed negative electrode slurry.

[0059] Comparative Example 4

[0060] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (2), 10 g of calcium carbonate powder (D50=5 μm) is replaced with 50 g of calcium carbonate powder (D50=5 μm), and the amount added is 5.0% of the dry basis mass of the negative electrode aqueous slurry.

[0061] Comparative Example 5

[0062] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (2), 10 g of calcium carbonate powder (D50=5 μm) is replaced with 10 g of sodium hydroxide powder (D50=5 μm).

[0063] Comparative Example 6

[0064] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (2), 6 g of KH-560 silane coupling agent is replaced with 6 g of 3-(trimethoxysilyl)propionic acid.

[0065] Comparative Example 7

[0066] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (2), calcium carbonate powder (D50=5 μm) is replaced with calcium carbonate powder (D50=30 μm).

[0067] Comparative Example 8

[0068] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (2), 6 g of KH-560 silane coupling agent is replaced with 30 g of KH-560 silane coupling agent, and the amount added is 3% of the dry basis mass of the negative electrode aqueous slurry.

[0069] Comparative Example 9

[0070] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (3), the wet electrode sheet is placed in an oven at 70 °C.

[0071] Comparative Example 10

[0072] A method for preparing a sodium-ion battery negative electrode sheet is basically the same as that in Example 1, except that in step (3), the wet electrode sheet is placed in an oven at 150 °C.

[0073] Test Example 1

[0074] The sodium-ion battery negative electrode sheets prepared in Examples 1-8 and Comparative Examples 1-10 were subjected to peel strength and resistivity tests, and the test methods are as follows:

[0075] (1) The adhesion of the electrode sheet was tested using the 180° peel method. The electrode sheet to be tested was cut into strips 25 mm wide and 250 mm long, ensuring that the edges of the sample were flat and burr-free to avoid interference with the test results. 3M 610 standard test tape was selected and flatly pasted onto the negative electrode coating surface of the sample. A 2 kg standard pressure roller was used to roll back and forth on the tape 3 times at a speed of 300 mm / min to ensure that the tape and coating were completely and tightly bonded without air bubbles. The aluminum foil current collector side of the sample was fixed to the lower clamp of the tensile testing machine. The free end of the tape pasted on the coating surface was folded 180° in the opposite direction and clamped onto the upper clamp of the testing machine, ensuring that the force axis of the sample coincided with the tensile direction of the testing machine after clamping. The tensile testing machine was started and subjected to vertical tension at a constant speed of 200 mm / min. The equipment automatically recorded the force curve during the peeling process in real time. Discard the unsteady-state data segments corresponding to the first and last 25 mm of the force value curve, take the force value of the middle 50 mm steady-state segment to calculate the average peel force, and calculate the peel strength according to the following formula: Peel strength (N / m) = average peel force (N) / sample width (m).

[0076] (2) Resistivity test: The electrode to be tested is cut into rectangular samples of 50 mm × 100 mm, ensuring that the coating surface is flat, smooth, wrinkle-free, and free of impurities. The test is performed using an RTS-9 dual-electric four-probe tester. At least three different locations are selected for repeated testing of each sample, and the arithmetic mean of the multiple measurements is taken as the final resistivity test result.

[0077] The test results are shown in Table 1:

[0078] Table 1

[0079]

[0080] Using the unmodified Comparative Example 1 as the performance benchmark, its electrode resistivity is 5.20 mΩ·cm, which is within the reasonable range of 3-8 mΩ·cm for hard carbon anodes. This comparative example did not add alkaline particles or coupling agents, and relied solely on the physical adsorption between the CMC / SBR binder and the aluminum foil, resulting in the weakest interfacial bonding force and the lowest peel strength.

[0081] Comparative Examples 2 and 3, which only adopted a single modification method, showed limited performance improvement: Comparative Example 2 only added alkaline particles and did not introduce coupling agents. It relied solely on physical anchoring and lacked interfacial chemical bonding reinforcement. Although the corrosion pits on the aluminum foil surface slightly increased the contact area, the edges of the pits were prone to inducing microcracks in the coating and the porosity increased slightly. The final resistivity remained at 5.20 mΩ·cm, the same as the benchmark, and the improvement in adhesion was limited. Comparative Example 3 only added a suitable coupling agent and did not introduce alkaline particles. It relied solely on interfacial covalent bonding without physical pit mechanical locking. Although the coupling agent could optimize the contact state between particles and reduce the resistivity to 5.18 mΩ·cm (a slight decrease of 0.4% compared to the benchmark), the improvement in interfacial adhesion was also limited.

[0082] Comparative Examples 4-10 all exhibited performance degradation due to improper process or material selection: In Comparative Example 4, the alkaline particle addition was as high as 5.0%, resulting in excessively dense particle arrangement. During the drying process, the localized high-alkalinity micro-regions around each particle overlapped, causing the aluminum foil surface to change from controllable pitting corrosion to large-area continuous excessive corrosion, even leading to localized perforation. The electrode peel strength plummeted to 6.5 N / m (lower than Comparative Example 1), and the resistivity increased significantly to 6.35 mΩ·cm. The structural integrity of the aluminum foil was destroyed, and the electrical performance deteriorated significantly. In Comparative Example 5, sodium hydroxide was used instead of carbonate alkaline particles. Sodium hydroxide is extremely water-soluble and causes severe uncontrollable corrosion of the aluminum foil during the slurry preparation stage, easily leading to localized perforation and coating damage, resulting in electrode performance failure and scrapping. In Comparative Example 6, KH-560 was replaced with 3-(trimethoxysilyl)propionic acid containing carboxyl groups. Its carboxyl groups can undergo a strong chelation reaction with calcium ions on the surface of calcium carbonate (reaction formula: CaCO3 + 2 R-COOH → Ca). The reaction (R-COO)2 + H2O + CO2↑ continues during the slurry stage, causing premature dissolution of calcium carbonate and preventing the formation of localized highly alkaline micro-regions. This results in no in-situ corrosion pits on the aluminum foil (due to a lack of physical anchoring). Furthermore, the CO2 released from the reaction leaves residual bubbles, pores, and microcracks within the coating, compromising its density and ultimately leading to a loose interface, coating cracking and peeling, and significantly reduced peel strength and resistivity. Comparative Example 7 uses calcium carbonate particles with a larger particle size, resulting in excessively large corrosion pits. This leads to localized stress concentration at the interface, causing a decrease in coating adhesion and affecting electrical properties. Comparative Example 8... Excessive addition of coupling agent can easily lead to the formation of an insulating enrichment layer at the interface, which not only increases the interfacial contact resistance but also causes a reverse decrease in coating adhesion and overall performance degradation. In Comparative Example 9, the drying temperature was too low, resulting in insufficient alkaline particle hydrolysis corrosion and coupling agent condensation reaction. The synergistic effect of physical anchoring and chemical bonding was not fully utilized, and the electrode adhesion and resistivity performance did not meet expectations. In Comparative Example 10, the drying temperature was too high, leading to thickening of the oxide layer on the aluminum foil surface and thermal decomposition of the coupling agent. At the same time, drying stress was generated inside the coating, causing cracking, and the interfacial adhesion and conductivity deteriorated simultaneously.

[0083] All embodiments of this invention achieve electrode performance optimization through the synergistic effect of physical anchoring and chemical bonding: Example 1 uses a compound of calcium carbonate and KH-560 silane coupling agent, forming uniform micron-sized corrosion pits on the aluminum foil surface, with complete interfacial covalent bonding and excellent overall performance. Example 2 uses a combination of magnesium carbonate and titanate coupling agent, further enhancing interfacial bonding, lowering charge transport resistance, and improving resistivity. Example 3 uses calcium carbonate particles with a smaller particle size, resulting in shallower corrosion pits, weakening the physical anchoring effect, and limiting the improvement of adhesion. Example 4 uses calcium carbonate particles within a preferred particle size range, resulting in uniform and fine corrosion pits and optimal physical anchoring effect. Example 5 has a low amount of alkaline particles, resulting in insufficient density of corrosion sites on the aluminum foil surface, limiting the contribution of physical anchoring. Example 6 has an optimal addition amount, with moderate density of corrosion sites, balancing anchoring effect and conductivity. Example 7 moderately increases the amount of KH-560, resulting in more complete interfacial covalent bonding and a steady increase in peel strength. Example 8 has a drying temperature within the optimal process window, resulting in good overall performance.

[0084] In summary, this invention achieves a significant improvement in electrode interfacial adhesion and ensures stable electrical performance by combining the physical anchoring effect of in-situ corrosion of alkaline particles with the construction of an interfacial covalent bond network using a suitable coupling agent, compared to the blank control and single modification methods. In contrast, excessive alkaline particles, unsuitable particle size, improper selection / dosage of coupling agent, deviation of drying temperature from the preferred range, or the use of highly corrosive alkaline substances can all lead to deterioration of electrode performance.

[0085] Test Example 2

[0086] CR2032 coin-type sodium-ion batteries were assembled using the sodium-ion battery negative electrode sheets prepared in Examples 1-8 and Comparative Examples 1-10: A metallic sodium sheet was used as the counter electrode, and a 9 μm thick polyethylene film was used as the separator. Sodium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) at a volume ratio of 1:1 to prepare an electrolyte with a sodium hexafluorophosphate concentration of 1 mol / L. The negative electrode sheet, separator, counter electrode, and separator were stacked sequentially and packaged to obtain the CR2032 coin-type sodium-ion battery. Specific capacity and cycle stability were tested using the following methods:

[0087] (1) Specific capacity test: The battery was charged / discharged at a rate of 1 C within a voltage range of 1.5 V-4.2 V. According to the formula C=Q D / M calculates the specific capacity of hard carbon, where Q D M represents the battery discharge capacity, and M represents the mass of hard carbon loaded on the negative electrode.

[0088] (2) Cyclic stability test: First, capacity calibration was performed at a 1 C rate, and the initial discharge capacity was recorded as C0; then, charge and discharge cycles were performed at a constant 1 C rate, with a charging cut-off voltage of 2.0 V and a discharging cut-off voltage of 0 V, and the discharge capacity C of the 200th cycle was recorded. 200 The capacity retention rate is calculated using the following formula: R = C 200 / C0 × 100% is used to evaluate the capacity decay and cycle stability of the battery after 200 cycles.

[0089] The test results are shown in Table 2:

[0090] Table 2

[0091]

[0092] As shown in Table 2, the 1C rate specific capacities of Examples 1-8, which adopted the synergistic modification of this invention, all reached 276-290 mAh / g, and the capacity retention rate remained between 89% and 94% after 200 cycles, significantly better than all comparative examples. Among them, Example 2 (magnesium carbonate + titanate coupling agent) achieved a specific capacity of 290 mAh / g and a capacity retention rate as high as 93.8% due to its lowest interfacial resistance (4.98 mΩ·cm) and highest peel strength (19.5 N / m). Examples 4 (particle size 3 μm) and 7 (coupling agent 1%) also exhibited excellent electrochemical stability (capacity retention rates of 93.0% and 93.2%, respectively), confirming that the uniform and dense corrosion pits and sufficient interfacial covalent bond network can effectively inhibit the peeling and cracking of the coating during cycling, ensuring close electrical contact between the active material and the current collector. In contrast, the specific capacity of single physical anchoring (Comparative Example 2) or single chemical bonding (Comparative Example 3) is only about 270-272 mAh / g, with a capacity retention of 85%-86.5%, which is much lower than that of the synergistic modification examples. This shows that the absence of either effect will lead to weakened interfacial bonding, and the coating is prone to local detachment and increased contact resistance during long-term cycling. Comparative Example 4 (5% excess alkaline particles) suffered from excessive corrosion and even perforation of the aluminum foil, resulting in a sharp drop in specific capacity to 240 mAh / g and a capacity retention rate of only 70.5%. Comparative Example 5 (NaOH strong alkali) experienced severe corrosion during the slurry stage, leading to electrode failure and a specific capacity of only 210 mAh / g with a capacity retention rate of 55%. Comparative Example 6 (non-compliant coupling agent containing carboxyl groups) suffered from numerous coating defects due to the destruction of alkaline particles and the generation of bubbles caused by the chelation reaction, resulting in a specific capacity of 235 mAh / g and a capacity retention rate of 68%. Comparative Example 7 (30 μm particle size) had excessively large pits and stress concentration, making the coating prone to peeling after cycling, with a retention rate of 81%. Comparative Example 8 (3% coupling agent) had a thickened interfacial insulating layer, resulting in a decrease in both specific capacity and capacity retention rate. Comparative Examples 9 and 10 also showed significant performance degradation due to incomplete reactions or coating cracking caused by excessively low or high drying temperatures.

[0093] The above data fully demonstrates that only within the range of alkaline particle types, particle size, addition amount, coupling agent type and addition amount, and drying temperature specified in this invention can the synergistic effect of physical anchoring and chemical bonding be achieved, thereby obtaining high specific capacity and excellent long-term cycling stability.

[0094] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art should understand that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a negative electrode sheet for a sodium-ion battery, characterized in that, Includes the following steps: (1) Mix hard carbon, conductive agent, binder and water to obtain negative electrode aqueous slurry; (2) Add alkaline particles to the aqueous negative electrode slurry obtained in step (1), disperse evenly, and then add a coupling agent to obtain an aqueous negative electrode mixed slurry; the alkaline particles are calcium carbonate and / or magnesium carbonate, and the amount of alkaline particles added is 0.1%-3% of the dry basis mass of the aqueous negative electrode slurry; the coupling agent is a silane coupling agent and / or titanate coupling agent that does not chelate with calcium and magnesium ions, and the amount of coupling agent added is 0.3%-2.0% of the dry basis mass of the aqueous negative electrode slurry; (3) The negative electrode aqueous mixed slurry obtained in step (2) is coated on the surface of the aluminum foil current collector to obtain a wet electrode sheet; the wet electrode sheet is dried at 80-130 °C, and the dried electrode sheet is rolled to obtain the sodium-ion battery negative electrode sheet.

2. The preparation method according to claim 1, characterized in that, In step (1), the dry basis mass ratio of the hard carbon, conductive agent and binder is (90-95):(0.5-2):(3-6).

3. The preparation method according to claim 1, characterized in that, In step (1), the adhesive is sodium carboxymethyl cellulose and styrene-butadiene rubber, and the dry basis mass ratio of sodium carboxymethyl cellulose to styrene-butadiene rubber is (1-3):(1-3).

4. The preparation method according to claim 1, characterized in that, In step (1), the solid content of the aqueous slurry is 50%-70%.

5. The preparation method according to claim 1, characterized in that, In step (1), hard carbon, conductive agent, and binder are added to the slurry mixer at a dry basis mass ratio of (90-95):(0.5-2):(3-6), water is added as a solvent, the solid content of the slurry is controlled to be 50%-70%, and the mixture is dispersed at high speed for 180-240 min under a vacuum of -0.080 MPa ~ -0.095 MPa to obtain the negative electrode aqueous slurry.

6. The preparation method according to claim 1, characterized in that, In step (2), the particle size of the alkaline particles is 0.5-20 μm.

7. The preparation method according to claim 1, characterized in that, In step (2), the silane coupling agent is γ-glycidoxypropyltrimethoxysilane.

8. The preparation method according to claim 1, characterized in that, In step (2), the titanate coupling agent is isopropyltris(dioctylpyrophosphate) titanate.

9. The preparation method according to claim 1, characterized in that, In step (3), the negative electrode aqueous mixture slurry is coated onto the surface of the aluminum foil current collector using an extrusion coating machine at a speed of 1.5-10 m / min to obtain a wet electrode sheet. The wet electrode sheet is placed in an oven at 80-130 ℃, and the dried electrode sheet is compacted by a roller press to obtain the negative electrode sheet of sodium-ion battery.

10. A sodium-ion battery negative electrode sheet prepared by the preparation method according to any one of claims 1-9.

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