Low-porosity solid-state battery negative electrode and preparation method thereof

Abstract

The invention relates to the technical field of batteries, and particularly discloses a low-porosity solid-state battery negative electrode and a preparation method thereof.The negative electrode slurry of the negative electrode comprises a polymer electrolyte A and a small molecule mixture B. The polymer electrolyte A is obtained by polymerizing an acrylic acid monomer, an acrylonitrile monomer and a sulfydryl-containing monomer; the small molecule mixture B at least comprises a flexible chain segment, fluorinated acrylate, a lithium salt, a plasticizer and a free radical initiator. In-situ polymerization is carried out in the coating process of the small molecule mixture B to generate a self-adaptive pore polymer electrolyte so as to reduce pores, and the polymer electrolyte A not only can improve the conversion rate of in-situ polymerization of the small molecule mixture B, but also can interact with the small molecule mixture B to form a dynamic cross-linked network for improving the stripping force of the pole piece; under the synergistic effect, the negative electrode / solid electrolyte interface contact is optimized, and the problems of poor interface contact and large interface impedance between the negative electrode active material and the solid electrolyte of the existing solid-state battery are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a low-porosity solid-state battery negative electrode and a preparation method thereof. Background Art

[0002] With the rapid development of electric vehicles and portable electronic devices, the market demand for energy storage devices with high energy density, high safety, and long cycle life is becoming increasingly urgent. Traditional liquid lithium-ion batteries, due to their use of flammable organic electrolytes, have safety risks such as thermal runaway and leakage. Their energy density is already close to its theoretical limit, making it difficult to meet future high-energy storage needs. Solid-state batteries, due to their use of non-flammable solid electrolytes instead of liquid electrolytes, offer greater safety and energy density potential and are considered an important development direction for next-generation battery technology.

[0003] However, the commercialization of solid-state batteries still faces many technical challenges, among which the anode / solid electrolyte interface problem is particularly prominent. Due to the solid-solid contact between the solid electrolyte and the anode, the anode produced by traditional methods produces many pores due to solvent volatilization, resulting in large interfacial contact impedance, low lithium ion transfer efficiency, increased battery internal resistance, and reduced rate performance. In addition, during the charge and discharge process, the anode material (such as silicon, metallic lithium, etc.) will undergo significant volume expansion and contraction, which can easily lead to interfacial contact failure, thereby affecting the battery's cycle stability and safety.

[0004] In response to the above problems, existing technologies have proposed a variety of solutions, mainly including: interface modification: introducing a buffer layer (such as LiF, Li3N, etc.) between the negative electrode and the solid electrolyte to improve the interface contact and reduce the interface impedance; composite negative electrode: compounding the negative electrode material (such as silicon, metallic lithium) with the solid electrolyte to construct a continuous lithium ion transmission channel; three-dimensional structure design: through porous or gradient structure design, the contact area between the electrode and the electrolyte is increased to optimize the lithium ion transmission path.

[0005] However, these methods still have the following shortcomings: complex process: interface modification or the preparation of composite negative electrodes usually involves complex processes such as high-temperature sintering and vapor deposition, which are difficult to mass produce; high cost: some modified materials (such as Li3N) or special structural designs significantly increase manufacturing costs; insufficient performance stability: after long-term cycling, the interface may still degrade, resulting in battery performance degradation.

[0006] Therefore, developing a negative electrode preparation method with simple process, controllable cost and scalable production to optimize the negative electrode / solid electrolyte interface contact, reduce the interface impedance, and improve the battery's rate performance and cycle stability is of great significance to promoting the commercial application of solid-state batteries. Summary of the Invention

[0007] In response to the shortcomings of the existing technology, the present invention provides a low-porosity solid-state battery negative electrode and a preparation method thereof, aiming to solve the problems of poor interface contact between the existing solid-state battery negative electrode and the solid electrolyte, low lithium ion transmission efficiency, and cyclic expansion.

[0008] In order to achieve the above objectives, the main technical solutions adopted by the present invention include:

[0009] In one aspect, the present invention provides a low-porosity solid-state battery negative electrode, comprising a negative electrode slurry, wherein the negative electrode slurry includes, in addition to a negative electrode active material and a conductive agent, a polymer electrolyte A and a small molecule mixture B;

[0010] The polymer electrolyte A is obtained by polymerizing acrylic acid monomer, acrylonitrile monomer and mercapto group-containing monomer, wherein the ratio of the three monomers during polymerization is: acrylic acid monomer 4wt%-10wt%, acrylonitrile monomer 75wt%-96wt% and mercapto group-containing monomer 0.05wt%-21wt%;

[0011] The small molecule mixture B includes the following components: 0.1wt%-20wt% of a flexible segment, 0.1wt%-30wt% of a fluoroacrylate, 0-35wt% of a carbonate containing a carbon-carbon unsaturated bond, 0-10wt% of an amine substance, 10wt%-30wt% of a lithium salt, 0.1wt%-35wt% of a plasticizer, and 0.01wt%-1wt% of a free radical initiator.

[0012] In the prior art, acrylonitrile is a relatively common monomer for the polymerization of acrylic binders and is generally used in combination with acrylic acid monomers. Given that acrylonitrile polymers have relatively strong rigidity but are inferior to acrylic acid in terms of degree of polymerization, flexibility, and toughness, when used to prepare binders, especially negative electrode binders, their addition should not be excessive. Otherwise, the resulting binder's elastic buffering properties will deteriorate, making it unable to adapt to the volume expansion of the negative electrode sheet. Furthermore, the viscosity and fluidity will deteriorate, leading to increased glass transition temperature, brittle and prone to cracking of the electrode sheet, reduced elongation, and decreased flexibility and toughness. Furthermore, the highly polar cyano group increases the electrode sheet's surface energy, impairs electrolyte wettability, hinders lithium ion transmission, and affects rate performance. Furthermore, after being used in the electrode sheet, chain segment shrinkage may occur during drying, leading to electrode sheet warping, among other issues. The present invention has discovered that when a small amount of a mercapto-containing monomer is used, the amount of acrylonitrile added can be significantly increased. By rationally matching the content of acrylic acid monomer, acrylonitrile monomer, and mercapto-containing monomer, not only can the adverse effects of high acrylonitrile content on the binder preparation process and binder properties be avoided, but also a lithium battery negative electrode binder with good adhesion, strong cohesion, excellent elastic cushioning, high mechanical strength, and good thermal and electrochemical stability can be obtained. The present invention speculates that the reason for this is that during the polymerization reaction of the mercapto-containing monomer, the mercapto group (SH) may undergo a nucleophilic addition reaction with the cyano group (CN) of acrylonitrile to form a thioamide structure, which in turn reduces the order and crystallinity of the polyacrylonitrile and changes the thermodynamic properties of the polymer, such as the glass transition temperature. Ultimately, the adhesion of the copolymer is improved, resulting in good mechanical strength and strong cohesion, as well as good softness, elasticity, and toughness. The small molecule mixture B is initially added to the negative electrode slurry in liquid form. The liquid substance has good adaptability to pores, and its components trigger an in-situ polymerization reaction during the coating process to generate a polymer electrolyte C with an appropriate glass transition temperature. The polymer electrolyte C has further adaptive pore capabilities, which can significantly eliminate the pores inside the negative electrode caused by solvent volatilization.

[0013] The present invention combines polymer electrolyte A and small molecule mixture B and adds them to the negative electrode slurry. On the one hand, polymer electrolyte A acts as a binder, and the negative electrode slurry can achieve an appropriate viscosity without the need for additional binder. It not only helps the slurry to be evenly dispersed and smoothly coated to form a continuous ion path, but also inhibits the interface peeling between the electrolyte and the active material. On the other hand, its rich strong polar components can better dissolve the various components in the small molecule mixture B, promote their uniform distribution in the electrode, and better reduce the porosity; on the one hand, the small molecule mixture B is evenly distributed in the electrode under the action of polymer electrolyte A, and on the other hand, after being heated, it is in situ polymerized to generate a polymer electrolyte C with good adaptive porosity. The rigid support of polymer electrolyte A and the flexible adaptive porosity of polymer electrolyte C form a "rigid and flexible" structure. The synergistic effect enables the negative electrode with low porosity and strong peeling force to be obtained after the negative electrode slurry is coated on the negative electrode current collector.

[0014] In addition, the present invention unexpectedly discovered that: the higher the thiol content in the polymer electrolyte A, the higher the conversion rate of the in situ polymerization of the small molecule mixture B. The presumed reason is that the thiol-containing monomer in the polymer electrolyte A can react with the residual monomer that is not completely polymerized in the small molecule mixture B, such as the double bond-containing monomer, thereby improving the conversion rate of the in situ polymerization of the small molecule mixture B and enhancing the porosity reduction effect; the cyano and acrylic groups in the polymer electrolyte A will form hydrogen bond interactions with the amino groups and fluorine atoms in the small molecule mixture B (as shown in Formula 1, this is the hydrogen bond interaction when there is no thiol group, and as shown in Formula 2, this is the hydrogen bond interaction when there is a thiol group), generating a dynamic cross-linked network, and further improving the peeling force of the electrode.

[0015]

[0016] Furthermore, the mercapto-containing monomer is selected from at least one of allyl mercaptan, para-mercaptostyrene, 1-mercapto-1-propylene, mercaptopropyl methacrylate, 2-mercaptoethyl acrylate, 4-mercaptobutyl acrylate, 3-mercaptopropionic acid acrylate, 2-mercaptoacetic acid acrylate, mercaptosuccinic acid monoacrylate, mercaptopolyethylene glycol acrylate, and mercapto methacrylate; among the above-mentioned mercapto-containing monomers, mercapto-containing acrylates are particularly preferred.

[0017] Preferably, at least a portion of the acrylic acid monomer is pre-neutralized with a base such as NaOH, KOH, LiOH, etc. to form a carboxylate. Pre-neutralization can significantly improve the solubility of the acrylic acid monomer, regulate the polymerization reaction, and optimize the properties of the final polymer.

[0018] In this embodiment, the aforementioned mercapto-containing monomer is copolymerized with acrylic acid and acrylonitrile monomers. The intermolecular forces of various functional groups in the raw materials, such as carboxyl groups, cyano groups, double bonds, ester groups, and ether oxygen bonds, collectively determine the glass transition temperature of the resulting polymer electrolyte A. When the three monomers are combined in the required ratio, the resulting product exhibits high elastic modulus, tensile strength, and elongation at break, and exhibits timely rebound during cell cycling, facilitating the construction of a cyclic conductive network and reducing cell expansion.

[0019] Furthermore, the polymer electrolyte A has a molecular weight of 15W-20W and a glass transition temperature of -20-110°C.

[0020] Tests have found that when the above-mentioned raw materials react according to a specified ratio, the molecular weight of the obtained product is 15W-25W. Polymer electrolyte A within this molecular weight range has good solubility in oily solvents, which helps to obtain a glue with moderate viscosity and good fluidity. When it is used in the preparation of negative electrode sheets, it has both good adhesion and coating properties.

[0021] Furthermore, differential scanning calorimetry (DSC) testing revealed that binders within this molecular weight range have a glass transition temperature (Tg) of -20-110°C, which can provide sufficient bonding strength to prevent cracking of the electrode while maintaining a certain toughness to avoid embrittlement. During charge and discharge, binders with this Tg value can buffer stress through elastic deformation, reducing damage to the electrode structure, and also have an appropriate degree of swelling in the electrolyte, ensuring that the electrolyte fully infiltrates the electrode pores without causing bonding failure. This also forms a stable SEI, reducing side reactions. In summary, the addition of polymer electrolyte A to the negative electrode slurry helps to build a circulating conductive network and effectively inhibits cell expansion, thereby improving the battery's rate performance, cycle life, and safety.

[0022] Specifically, the preparation method of the polymer electrolyte A comprises: adding a mercapto-containing monomer, an acrylonitrile monomer, and an acrylic acid monomer to a hydroalcohol solvent in order according to a certain proportion, then adding an emulsifier and a dispersant and stirring to obtain a suspension; heating the suspension and adding an initiator dropwise while stirring to polymerize under an inert atmosphere; filtering, washing, drying, crushing, and sieving;

[0023] The hydroalcoholic solvent is a mixed solvent of water and ethanol, and the volume of water is greater than the volume of ethanol; the emulsifier is at least one of sodium lauryl sulfate, sodium dodecylbenzenesulfonate, Span 80, and Tween 20; the dispersant is at least one of polyvinyl pyrrolidone, polyvinyl alcohol, hydroxypropyl cellulose, gelatin, and polyacrylate; the initiator is one of potassium persulfate, sodium persulfate, azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate; the added mass of the initiator is 0.2%-1% of the total mass of the monomers; the polymerization temperature is 60-80°C, and the polymerization time is 12-18 hours;

[0024] It should be noted that the above preparation method is only one way to obtain the binder of the present invention. Other preparation methods in the technical field are also possible. The present invention only lists them and does not limit them.

[0025] Furthermore, the small molecule mixture B includes the following components: 1 wt%-5 wt% of a flexible segment, 15 wt%-25 wt% of a fluoroacrylate, 15 wt%-25 wt% of a carbonate containing a carbon-carbon unsaturated bond, 1 wt%-5 wt% of an amine substance, 20 wt%-30 wt% of a lithium salt, 10 wt%-20 wt% of a plasticizer, and 0.03 wt%-0.5 wt% of a free radical initiator;

[0026] Wherein, the flexible segment is selected from at least one of butadiene, isoprene, caprolactone and adipate glycol ester; the fluoroacrylate is selected from trifluoroethyl methacrylate, trifluoroethyl acrylate, tetrafluoropropyl acrylate, tetrafluoropropyl methacrylate, hexafluorobutyl acrylate, hexafluorobutyl methacrylate, octafluoropentyl acrylate, octafluoropentyl methacrylate, isobutyl octafluoroacrylate, n-heptyl dodecafluoroacrylate, heptyl dodecafluoromethacrylate, perfluorooctyl ethyl acrylate, perfluorooctyl ethyl methacrylate, perfluorohexyl ethyl acrylate, perfluorohexyl ethyl methacrylate, p-trifluoromethylphenyl acrylate, p-trifluoromethylphenyl methacrylate, perfluoropolyether acrylate, fluorocyclohexyl acrylate esters; the carbonate containing a carbon-carbon unsaturated bond is selected from at least one of vinylene carbonate and ethylene carbonate; the amine substance is selected from at least one of acrylamide and aminostyrene; the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, and lithium difluorophosphate; the plasticizer is selected from at least one of succinonitrile, 3-methoxypropionitrile, glutaronitrile, adiponitrile, and γ-butyrolactone; the free radical initiator is selected from at least one of benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, and azobisisoheptonitrile;

[0027] The components in the small molecule mixture B are in situ polymerized by heating to form a polymer electrolyte C. The polymer electrolyte C has a glass transition temperature Tg of -30 to 30°C, a Young's modulus of 1MPa-1GPa, a tensile strength of 1-50MPa, and an elongation at break of ≥200%.

[0028] On the other hand, the present invention also proposes a method for preparing a low-porosity solid-state battery negative electrode, firstly, the negative electrode active material, conductive agent, polymer electrolyte A and small molecule mixture B are added to an oily solvent for homogenization to obtain a negative electrode slurry, and the temperature is controlled at 25-40°C during the homogenization process, and then the obtained negative electrode slurry is coated on the negative electrode collector, and then photothermal composite curing is adopted.

[0029] Furthermore, after drying, the obtained negative electrode is rolled at 45-80°C. The polymer electrolyte A and polymer electrolyte C are softened by heat, and the pores inside the electrode can be further eliminated under mechanical action. After rolling, slitting, slotting and die-cutting are performed.

[0030] The negative electrode binder proposed in the present invention has a high cohesive force after the negative electrode slurry is formed. The high cohesive force can not only prevent the edge of the electrode from losing powder or delamination during slitting or grooving, but also reduce the burr rate, improve the electrode processing accuracy, and maintain structural integrity during the winding or lamination process. More importantly, it can maintain a high cohesive force after the battery is cycled for 50cls, 100cls, and 150cls, effectively inhibiting the electrode from losing powder and material during the cycle, which is beneficial to ensuring the integrity of the conductive network between the binder and the negative electrode main material (especially for high-silicon negative electrodes with silicon doping of more than 30wt%) during the cycle, improving long-term cycle stability and inhibiting cycle expansion; in addition, the raw materials for preparing the binder contain reducing thiol groups. When added to the negative electrode slurry, the thiol groups can scavenge free radicals in the negative electrode slurry, delaying the oxidation and degradation of the negative electrode slurry, while exerting good bonding properties, and also improving the chemical stability of the negative electrode slurry.

[0031] Furthermore, the negative electrode active material, the conductive agent, the polymer electrolyte A and the small molecule mixture B are added to the oily solvent in the following proportions: 80 wt%-97 wt% of the negative electrode active material, 0.05 wt%-5 wt% of the conductive agent, 0.1-5 wt% of the polymer electrolyte A, and 0.1 wt%-15 wt% of the small molecule mixture B;

[0032] Preferably, the oily solvent is selected from at least one of dimethylacetamide, N-methylpyrrolidone, acetone, and dimethyl sulfoxide;

[0033] Preferably, the solid content of the negative electrode slurry is 38%-50%;

[0034] Preferably, the viscosity of the negative electrode slurry is 2000-7000 mPa·S;

[0035] Preferably, the specific operation of the photothermal composite curing is: first irradiate with ultraviolet light with a surface power of 4500-15000mW / cm2 and a wavelength of 365nm, then heat at 40-60℃ for 5-20min, heat at 50-80℃ for 30-150min, and heat at 70-100℃ for 20-60min.

[0036] In addition, the present invention also proposes another method for preparing a low-porosity solid-state battery negative electrode, first dispersing polymer electrolyte A in an oily solvent to prepare a polymer electrolyte A solution, then mixing a portion of the polymer electrolyte A solution with the negative electrode active material, the conductive agent, and the small molecule mixture B to obtain a muddy mixture with a solid content of 70wt%-99.9wt%, heating the muddy mixture to solidify it, and then adding the remaining part of the polymer electrolyte A solution, mixing again to obtain a negative electrode slurry, and finally coating the negative electrode slurry on the negative electrode collector, heating to solidify, and drying.

[0037] Furthermore, after drying, the obtained negative electrode is rolled at 45-80°C. The polymer electrolyte A and polymer electrolyte C are softened by heat, and the pores inside the electrode can be further eliminated under mechanical action. After rolling, slitting, slotting, and die-cutting are performed.

[0038] Preferably, the specific operation of the heating curing is: first heating at 40-60°C for 5-40 minutes, then heating at 50-80°C for 40-150 minutes, and finally heating at 70-100°C for 40-100 minutes;

[0039] Preferably, the specific operation of the drying is: baking in five temperature zones, with the temperature of zone one being 80-90°C, the temperatures of zones two to four being 80-100°C, the temperature of zone five being 80-95°C, and the temperatures of zones two to four being not lower than the temperatures of zone one and zone five; considering that the polyacrylonitrile material lacks flexible segments in its molecular chain, its impact strength at room temperature is low, it is prone to brittle fracture, and it is sensitive to moisture, and its strong polar cyanide group easily forms hydrogen bonds with moisture, resulting in a strong hygroscopicity of the material. After moisture absorption, it may not only cause a decrease in adhesion and an increase in the risk of electrolyte compatibility, but may also further reduce the toughness of the polyacrylonitrile material, resulting in an increase in microcracks in the electrode after drying. Therefore, the use of five temperature zones for zoned baking can sequentially achieve solvent volatilization, preliminary curing and complete curing, while further improving the peel strength and cohesion of the electrode, and at the same time ensuring that the oily solvent is completely volatilized, significantly improving the interface phase. Capacitance makes the negative electrode slurry film more uniform, reducing cracks and falling off; if one temperature zone is used for baking, if the temperature in the temperature zone is too high, the surface of the negative electrode plate will dry too quickly, the surface of the plate will be densified, and the internal solvent residue will form bubbles, resulting in blockage of the lithium ion transmission channel; if the temperature in the temperature zone is too low, the oily solvent will not evaporate sufficiently, which will cause the roller to stick during rolling, and the resulting plate will have poor flexibility, many edge burrs, and poor mechanical properties, and will also cause battery bloating and increased internal resistance, and poor rate performance; even if the temperature is suitable, there will be a temperature gradient between the surface and internal temperature of the electrode during the drying process, the surface temperature will be higher than the internal temperature, the surface will dry first, and the substance concentration will be higher than the internal concentration. Under such driving force, the binder will gradually enrich and migrate to the surface as the solvent evaporates, and float up, and precipitate on the surface of the active material and the conductive agent, resulting in a decrease in the bonding force between the active material and the current collector, and the plate will easily fall off during rolling, and the peel strength will deteriorate.

[0040] Preferably, when preparing the slurry mixture, the amount of the polymer electrolyte A solution added is 10 wt% to 35 wt% of the total polymer electrolyte A solution, and the slurry mixture is solidified and then mixed with the remaining polymer electrolyte A solution;

[0041] Preferably, the temperature of zone 1 is 80-85°C, the temperatures of zones 2 to 4 are all 95-100°C, and the temperature of zone 5 is 80-90°C. The gradient temperature control method takes into account the structure and performance of the electrode after film formation, and achieves a balance between baking effect and baking efficiency.

[0042] It should be noted that the dispersion of polymer electrolyte A in an oily solvent to prepare a polymer electrolyte A solution needs to be carried out at a controlled dew point of -35°C or below to avoid certain organic solvents such as NMP absorbing water and gelling or causing side reactions.

[0043] Compared with the existing technology, the present invention obtains a solid-state battery negative electrode with a low porosity of no more than 10% through the synergistic effect of polymer electrolyte A and small molecule mixture B initially added in liquid form. The solid-state battery negative electrode not only has low porosity, but also has strong peeling force and a certain ionic conductivity. It can achieve lithium ion transmission even in the absence of electrolyte, significantly optimizes the negative electrode / solid electrolyte interface contact, helps to reduce the battery cell cycle expansion rate, and is of great significance for improving the rate and cycle performance of solid-state batteries and promoting the commercial application of solid-state batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0045] Figure 1 Schematic diagram of the structure of a soft-pack battery. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, and are not all embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0047] The chemical raw materials involved in the following examples and comparative examples were all commercially available. The preparation operations or testing operations not described in detail in the following examples and comparative examples are all conventional preparation operations or testing operations in the art and are well known to those skilled in the art.

[0048] Example 1

[0049] A low-porosity solid-state battery anode was prepared according to the following operation: a silicon-carbon composite material (the composite material was doped with 30 wt% silicon), a conductive agent (conductive carbon and carbon nanotubes in a mass ratio of 1:1), a polymer electrolyte A, and a small molecule mixture B were added to NMP in the order of 92%, 2%, 3%, and 3% by mass, and homogenized to obtain a negative electrode slurry with a solid content of 43 wt%. The homogenization process was controlled to be stable at 35° C. The obtained negative electrode slurry was then coated on a copper foil, cured by photothermal composite, and finally roller pressed at 60° C.

[0050] The polymer electrolyte A is obtained by polymerizing acrylic acid, acrylonitrile, and mercapto methacrylate in proportions of 4%, 88%, and 8%, respectively. The specific operation is as follows: mercapto methacrylate, acrylonitrile, and acrylic acid are added in order in a water-ethanol solvent with a volume ratio of 6:4, followed by adding sodium dodecylbenzenesulfonate (0.7% of the total weight of the monomers) and polyvinylpyrrolidone (1% of the total weight of the monomers) and stirring to obtain a suspension; heating the suspension to 60° C. and adding azobisisoheptanenitrile dropwise while stirring under an inert atmosphere for 16 hours, wherein the amount of azobisisoheptanenitrile added is 0.5% of the total weight of the monomers; filtering, washing, drying, crushing, and sieving to obtain a powdery product;

[0051] The small molecule mixture B includes the following components in mass percentages: 10% butadiene, 20% tetrafluoropropyl methacrylate, 20% ethylene carbonate, 5% acrylamide, 15% lithium difluorooxalatoborate, 29.9% gamma-butyrolactone, and 0.1% azobisisobutyronitrile;

[0052] Among them, the specific operation of photothermal composite curing is: first irradiate with ultraviolet light with a surface power of 12000mW / cm2 and a wavelength of 365nm, then heat at 50℃ for 12min, 60℃ for 90min, and 85℃ for 40min.

[0053] Example 2

[0054] Compared with Example 1, the composition of the small molecule mixture B was adjusted, specifically including the following components in mass percentage: 10% butadiene, 25% tetrafluoropropyl methacrylate, 25% vinyl ethylene carbonate, 5% acrylamide, 15% lithium difluorooxalatoborate, 19.9% ​​γ-butyrolactone, and 0.1% azobisisobutyronitrile; the raw materials and proportions for the preparation of polymer electrolyte A were adjusted, specifically, acrylic acid, acrylonitrile, and allyl mercaptan were polymerized in mass percentages of 10%, 85.37%, and 4.63%, respectively, and the rest were consistent with Example 1.

[0055] Example 3

[0056] Compared with Example 1, the ratio of raw materials for preparing polymer electrolyte A was adjusted. Acrylic acid, acrylonitrile and mercapto methacrylate were polymerized at 4%, 86% and 10% by mass. The rest remained the same as in Example 1.

[0057] Example 4

[0058] Compared with Example 1, the ratio of raw materials for preparing polymer electrolyte A was adjusted. Acrylic acid, acrylonitrile and mercapto methacrylate were polymerized at 5%, 93% and 2% by mass. The rest remained the same as in Example 1.

[0059] Example 5

[0060] Compared with Example 1, the composition and ratio of small molecule mixture B are adjusted, specifically including the following components in mass percentage: 10% butadiene, 25% tetrafluoropropyl methacrylate, 25% vinyl ethylene carbonate, 20% lithium bis(trifluoromethanesulfonyl)imide, 19.9% ​​succinonitrile, and 0.1% azobisisobutyronitrile, and the rest are consistent with Example 1.

[0061] Example 6

[0062] Compared with Example 1, the composition and ratio of the small molecule mixture B were adjusted, specifically including the following components in mass percentage: 5% butadiene, 25% tetrafluoropropyl methacrylate, 25% ethylene carbonate, 5% acrylamide, 20% lithium bis(trifluoromethanesulfonyl)imide, 19.9% ​​succinonitrile, and 0.1% azobisisobutyronitrile. The rest were consistent with Example 1.

[0063] Example 7

[0064] Compared with Example 6, except that roller pressing is not performed, the rest are consistent with Example 6.

[0065] Example 8

[0066] Compared with Example 6, the composition and ratio of small molecule mixture B were adjusted, specifically including the following components in mass percentage: 19.9% ​​butadiene, 25% tetrafluoropropyl methacrylate, 10% acrylamide, 20% lithium bis(trifluoromethanesulfonyl)imide, 25% succinonitrile, and 0.1% azobisisobutyronitrile. The rest were consistent with Example 6.

[0067] Example 9

[0068] Compared with Example 6, the composition and ratio of small molecule mixture B were adjusted, specifically including the following components in mass percentage: 19.9% ​​butadiene, 25% tetrafluoropropyl methacrylate, 20% lithium bis(trifluoromethanesulfonyl)imide, 35% succinonitrile, and 0.1% azobisisobutyronitrile, and the rest were consistent with Example 6.

[0069] Example 10

[0070] Compared with Example 9, the ratio of each component in preparing the negative electrode slurry was adjusted, specifically: silicon-carbon composite material (the composite material is doped with 30 wt% silicon), conductive agent (conductive carbon and carbon nanotubes in a mass ratio of 1:1), polymer electrolyte A and small molecule mixture B were added to NMP in sequence according to the mass percentages of 93%, 1%, 3% and 3%, respectively. The rest remained the same as Example 9.

[0071] Example 11

[0072] Compared with Example 6, the solid content of the negative electrode slurry was adjusted from 43 wt % to 50 wt %, and the rest remained the same as Example 6.

[0073] Example 12

[0074] Compared with Example 6, the ratio of each component and the solid content of the negative electrode slurry were adjusted during the preparation of the negative electrode slurry. Specifically, the silicon-carbon composite material (the composite material is doped with 30 wt% silicon), the conductive agent (conductive carbon and carbon nanotubes in a mass ratio of 1:1), the polymer electrolyte A and the small molecule mixture B were added with NMP in the order of 94%, 2.9%, 0.1% and 3% by mass; the solid content was adjusted from 43 wt% to 38 wt%, and the rest remained the same as in Example 6.

[0075] Example 13

[0076] Compared with Example 1, the ratio of raw materials for preparing polymer electrolyte A is adjusted. Acrylic acid, acrylonitrile and mercapto methacrylate are polymerized according to mass percentages of 4%, 75% and 21%, respectively. The rest are the same as in Example 1.

[0077] Example 14

[0078] Compared with Example 1, the ratio of raw materials for preparing polymer electrolyte A was adjusted. Acrylic acid, acrylonitrile and mercapto methacrylate were polymerized at 4%, 94% and 2% by mass. The rest remained the same as in Example 1.

[0079] Example 15

[0080] Compared with Example 6, the composition and ratio of the small molecule mixture B were adjusted, specifically including the following components in mass percentage: 1% butadiene, 30% tetrafluoropropyl methacrylate, 15% ethylene carbonate, 1% acrylamide, 30% lithium bis(trifluoromethanesulfonyl)imide, 22.9% succinonitrile, and 0.1% azobisisobutyronitrile. The rest were consistent with Example 6.

[0081] Example 16

[0082] Compared with Example 6, the composition and ratio of small molecule mixture B were adjusted, specifically including the following components in mass percentage: 3% butadiene, 15% tetrafluoropropyl methacrylate, 35% ethylene carbonate, 1% acrylamide, 10% lithium bis(trifluoromethanesulfonyl)imide, 35% succinonitrile, and 1% azobisisobutyronitrile. The rest were consistent with Example 6.

[0083] Example 17

[0084] Compared with Example 1, the composition of small molecule mixture B was adjusted to include the following components in mass percentage: 10% glycol adipate, 20% trifluoroethyl acrylate, 20% vinylene carbonate, 5% aminostyrene, 15% lithium hexafluorophosphate, 29.9% 3-methoxypropionitrile, and 0.1% azobisisoheptanenitrile; the raw material ratio during the synthesis of polymer electrolyte A was adjusted to include: acrylic acid, acrylonitrile, and mercapto methacrylate polymerized in mass percentages of 4%, 95.95%, and 0.05%, respectively. The rest remained the same as in Example 1. Comparative Example 1

[0085] Compared with Example 6, the components and ratios were adjusted during the preparation of the negative electrode slurry. Specifically, the silicon-carbon composite material (the composite material is doped with 30 wt% silicon), the conductive agent (conductive carbon and carbon nanotubes in a mass ratio of 1:1), the polymer electrolyte A and the small molecule mixture B were added to NMP in the order of 95%, 2%, 3% and 0% by mass, that is, the small molecule mixture B was not added. The rest remained the same as in Example 6.

[0086] Comparative Example 2

[0087] Compared with Example 6, when preparing the negative electrode slurry, the polymer electrolyte A was replaced with an equal amount of PVDF, and the rest remained the same as Example 6.

[0088] Comparative Example 3

[0089] Compared with Example 6, when preparing the negative electrode slurry, the polymer electrolyte A was replaced with an equal amount of PMMA, and the rest remained the same as Example 6.

[0090] Comparative Example 4

[0091] Compared with Example 6, when preparing the negative electrode slurry, the polymer electrolyte A was replaced with an equal amount of polyacrylonitrile, and the rest remained the same as Example 6.

[0092] Comparative Example 5

[0093] Compared with Example 6, the components and ratios were adjusted during the preparation of the negative electrode slurry. Specifically, the silicon-carbon composite material (the composite material was doped with 30 wt% silicon), the conductive agent (conductive carbon and carbon nanotubes in a mass ratio of 1:1), the polymer electrolyte A and the small molecule mixture B were added to NMP in the order of 95%, 2%, 0% and 3% by mass, that is, the polymer electrolyte A was not added. The rest remained the same as in Example 6.

[0094] Comparative Example 6

[0095] Compared with Example 1, the raw materials for preparing the polymer electrolyte do not contain mercapto methacrylate, the masses of acrylic acid and acrylonitrile are consistent with those in Example 1, and the rest are also consistent with those in Example 1.

[0096] The important technical parameters of each embodiment and comparative example are shown in Table 1. For the convenience of description, Example 1, Example 2, ... are sequentially represented as S1, S2, ..., and Comparative Example 1, Comparative Example 2, ... are sequentially represented as D1, D2, ....

[0097] Table 1

[0098]

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105] The thiol content in the raw materials for preparing the polymer electrolyte A involved in each embodiment and comparative example (the mass percentage of the mass of the thiol group to the total mass of the raw materials for preparing the polymer A), the polymerization conversion rate of the small molecule mixture B to form the polymer electrolyte C, the elongation at break / ionic conductivity / Tg value of the polymer electrolyte C, the viscosity of the negative electrode slurry, the porosity / peel strength / heat treatment weight loss rate of the negative electrode sheet (heat treatment at 120°C for 6h) (all the test methods involved are conventional test methods in the field) were tested and statistically analyzed, as shown in Table 2 for details.

[0106] Table 2

[0107]

[0108]

[0109] In addition, the negative electrodes obtained in Comparative Example 1, Example 2, Example 4, and Example 6 were Figure 1 The structure shown was assembled into a soft pack battery and the battery capacity and negative electrode half-electric expansion rate of the obtained soft pack battery were tested. The test results are shown in Table 3. However, in Comparative Example 5, due to insufficient slurry viscosity, the negative electrode sheet could not be prepared, and thus the soft pack battery could not be assembled. Figure 1In the figure, 1 is the positive electrode (the positive electrode current collector is aluminum foil and the active material is lithium cobalt oxide), 2 is the separator, and 3 is the corresponding negative electrode; after the soft-pack battery is charged and discharged at a rate of 0.2C in the voltage range of 3.0V-4.53V for one week, it is charged to a half-charged state of 50% SOC, the battery is disassembled, and the negative electrode sheet is inspected. The half-charge expansion rate of the negative electrode is calculated using the thickness of the negative electrode sheet in the half-charged state and the thickness of the negative electrode sheet in the initial state without expansion.

[0110] Table 3

[0111] negative electrode Battery capacity (mAh) Negative electrode half-electric expansion rate % D1 7530 63 D5 - - S2 7592 55 S4 7613 49 S6 7650 42

[0112] As shown in Tables 1 to 3:

[0113] It can be seen from the test results of each embodiment that by adding the polymer electrolyte A and the small molecule mixture B proposed in the present invention in proportion to the negative electrode slurry and following the preparation method defined in the present invention, the production of a solid-state battery negative electrode with a porosity of no more than 10% is achieved. The solid-state electrode also has a certain ionic conductivity, strong peel strength and a heat treatment weight loss rate of no more than 0.5%.

[0114] Furthermore, a comparison of the test results of Examples 5, 6, 8, and 9 shows that when vinyl ethylene carbonate (i.e., a carbonate containing carbon-carbon unsaturated bonds) and / or acrylamide (i.e., an amine) is not added to the small molecule mixture B, the heat treatment weight loss rate of the resulting negative electrode sheet is relatively small, but the porosity and peel strength are slightly worse than those when vinyl ethylene carbonate and acrylamide are added. Clearly, the addition of carbonates containing carbon-carbon unsaturated bonds and amines to the small molecule mixture B helps further reduce the porosity and improve the peel strength of the electrode sheet.

[0115] Furthermore, from the comparison of the test results of Example 6 and Example 7, it can be seen that: after the negative electrode sheet is prepared, the polymer electrolyte A and the polymer electrolyte C are softened by heat and squeezed through hot rolling. The synergy of heat and pressure helps to further eliminate the pores inside the electrode sheet and reduce the heat treatment weight loss rate of the electrode sheet.

[0116] The test results of Example 6, Comparative Example 1, and Comparative Example 5 show that when polymer electrolyte A is added to the negative electrode slurry without small molecule mixture B, the resulting negative electrode sheet has higher peel strength and lower heat treatment weight loss, but the porosity is as high as 25%. When small molecule mixture B is added to the negative electrode slurry without polymer electrolyte A, the resulting negative electrode slurry viscosity is too low and does not meet coating requirements. Both polymer electrolyte A and small molecule mixture B are indispensable. Furthermore, when Example 6 and Comparative Example 1 are assembled into a soft-pack battery, the capacity of the soft-pack battery of Example 6 is significantly improved compared to Comparative Example 1, and the negative electrode half-charge expansion rate is significantly reduced.

[0117] Further testing found that the molecular weight of the polymer electrolyte A in each embodiment is 15W-20W, and the glass transition temperature is -20-110°C. On the one hand, it plays the role of a binder. If it is missing, the negative electrode slurry will not be able to be coated due to its low viscosity. On the other hand, the thiol content therein also has a positive promoting effect on the conversion rate of the in-situ polymerization of the small molecule mixture B; further testing found that the glass transition temperature of the polymer electrolyte C generated by the in-situ polymerization of the small molecule mixture B in each embodiment is -30 to 30°C, the Young's modulus is 1MPa-1GPa, and the tensile strength is 1-50MPa. The liquid small molecule mixture B and the polymer electrolyte C have good adaptive pore capabilities. If they are missing, too many pores will remain after the negative electrode slurry dries, and it relies on more electrolyte filling.

[0118] Furthermore, the test results of Comparative Examples 2, 3, and 4 demonstrate that when polymer electrolyte A is replaced with an equal amount of a conventional negative electrode binder such as PVDF, PMMA, or polyacrylonitrile, the resulting negative electrode slurry exhibits a viscosity that meets coating requirements and exhibits high peel strength after coating, but still exhibits high porosity. This indicates that polymer electrolyte A assists the small molecule mixture B in reducing porosity. The porosity of the negative electrode obtained in the present invention, which is no greater than 10%, is the result of the combined action of polymer electrolyte A and small molecule mixture B.

[0119] In summary, the present invention, through the synergistic effect of polymer electrolyte A and small molecule mixture B initially added in liquid form, helps to obtain a solid-state battery anode with a low porosity of no more than 10%. This solid-state battery anode has a certain ionic conductivity, so it can achieve lithium ion transmission even in the absence of electrolyte. It also has strong stripping force, which helps to reduce the battery cell's cyclic expansion rate. The low-porosity solid-state battery anode proposed by the present invention is of great significance for improving the rate and cycle performance of solid-state batteries and promoting their commercial application.

[0120] Although embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are illustrative and are not to be construed as limiting the present invention. Those skilled in the art may alter, modify, replace, and modify the above embodiments within the scope of the present invention. Furthermore, those skilled in the art may combine and incorporate the various embodiments or examples described in this specification, as well as features thereof, without conflicting requirements.

Claims

1. A low-porosity solid-state battery negative electrode, comprising a negative electrode slurry, characterized in that: The negative electrode slurry includes, in addition to the negative electrode active material and the conductive agent, a polymer electrolyte A and a small molecule mixture B; The polymer electrolyte A is obtained by polymerizing acrylic acid monomer, acrylonitrile monomer and mercapto group-containing monomer, wherein the ratio of the three monomers during polymerization is: acrylic acid monomer 4wt%-10wt%, acrylonitrile monomer 75wt%-96wt% and mercapto group-containing monomer 0.05wt%-21wt%; The small molecule mixture B includes the following components: 0.1wt%-20wt% of a flexible segment, 0.1wt%-30wt% of a fluoroacrylate, 0-35wt% of a carbonate containing a carbon-carbon unsaturated bond, 0-10wt% of an amine substance, 10wt%-30wt% of a lithium salt, 0.1wt%-35wt% of a plasticizer, and 0.01wt%-1wt% of a free radical initiator.

2. The low-porosity solid-state battery negative electrode according to claim 1, characterized in that: The mercapto-containing monomer is at least one selected from the group consisting of allyl mercaptan, p-mercaptostyrene, 1-mercapto-1-propylene, mercaptopropyl methacrylate, 2-mercaptoethyl acrylate, 4-mercaptobutyl acrylate, 3-mercaptopropionic acid acrylate, 2-mercaptoacetic acid acrylate, mercaptosuccinic acid monoacrylate, mercaptopolyethylene glycol acrylate, and mercaptomethacrylate; Preferably, the acrylic acid monomer is at least partially pre-neutralized.

3. The low-porosity solid-state battery negative electrode according to claim 1, characterized in that: The polymer electrolyte A has a molecular weight of 15W-20W and a glass transition temperature of -20-110°C.

4. The low-porosity solid-state battery negative electrode according to claim 1, characterized in that: The preparation method of the polymer electrolyte A comprises: adding a mercapto-containing monomer, an acrylonitrile monomer, and an acrylic acid monomer in a water-alcohol solvent in order according to a certain proportion, then adding an emulsifier and a dispersant and stirring to obtain a suspension; heating the suspension and adding an initiator dropwise while stirring to polymerize under an inert atmosphere; filtering, washing, drying, crushing, and sieving; The method comprises the following steps: the hydroalcoholic solvent is a mixed solvent of water and ethanol, and the volume of water is greater than that of ethanol; the emulsifier is at least one of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, Span 80, and Tween 20; the dispersant is at least one of polyvinyl pyrrolidone, polyvinyl alcohol, hydroxypropyl cellulose, gelatin, and polyacrylate; the initiator is one of potassium persulfate, sodium persulfate, azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate; the added mass of the initiator is 0.2%-1% of the total mass of the monomers; the polymerization temperature is 60-80° C., and the polymerization time is 12-18 hours.

5. The low-porosity solid-state battery negative electrode according to claim 1, characterized in that: The small molecule mixture B comprises the following components: 1 wt%-5 wt% of a flexible segment, 15 wt%-25 wt% of a fluoroacrylate, 15 wt%-25 wt% of a carbonate containing a carbon-carbon unsaturated bond, 1 wt%-5 wt% of an amine substance, 20 wt%-30 wt% of a lithium salt, 10 wt%-20 wt% of a plasticizer, and 0.03 wt%-0.5 wt% of a free radical initiator; Preferably, the soft segment is selected from at least one of butadiene, isoprene, caprolactone and adipate glycol ester; the fluoroacrylate is selected from trifluoroethyl methacrylate, trifluoroethyl acrylate, tetrafluoropropyl acrylate, tetrafluoropropyl methacrylate, butyl hexafluoroacrylate, butyl hexafluoromethacrylate, octafluoropentyl acrylate, octafluoropentyl methacrylate, isobutyl octafluoroacrylate, n-heptyl dodecafluoroacrylate, heptyl dodecafluoromethacrylate, perfluorooctyl ethyl acrylate, perfluorooctyl ethyl methacrylate, perfluorohexyl ethyl acrylate, perfluorohexyl ethyl methacrylate, p-trifluoromethylphenyl acrylate, p-trifluoromethylphenyl methacrylate, perfluoropolyether acrylate, fluorocyclohexylpropylene At least one of esters; the carbonate containing a carbon-carbon unsaturated bond is selected from at least one of vinylene carbonate and ethylene carbonate; the amine substance is selected from at least one of acrylamide and aminostyrene; the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, and lithium difluorophosphate; the plasticizer is selected from at least one of succinonitrile, 3-methoxypropionitrile, glutaronitrile, adiponitrile, and γ-butyrolactone; the free radical initiator is selected from at least one of benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, and azobisisoheptonitrile; Preferably, the components in the small molecule mixture B are in situ polymerized by heating to form a polymer electrolyte C, and the polymer electrolyte C has a glass transition temperature of -30 to 30°C, a Young's modulus of 1MPa-1GPa, a tensile strength of 1-50MPa, and an elongation at break ≥200%.

6. A method for preparing a low-porosity solid-state battery negative electrode according to any one of claims 1 to 5, characterized in that: First, the negative electrode active material, conductive agent, polymer electrolyte A and small molecule mixture B are added to an oily solvent for homogenization to obtain a negative electrode slurry. The temperature is controlled at 25-40°C during the homogenization process. The obtained negative electrode slurry is then coated on the negative electrode collector and then photothermal composite curing is adopted.

7. The preparation method according to claim 6, characterized in that: After drying, the obtained negative electrode was roll-pressed at 45-80°C.

8. The preparation method according to claim 6, characterized in that: The negative electrode active material, conductive agent, polymer electrolyte A and small molecule mixture B are added to the oily solvent in the following proportions: 80wt%-97wt% of the negative electrode active material, 0.05wt%-5wt% of the conductive agent, 0.1wt%-5wt% of the polymer electrolyte A, and 0.1wt%-15wt% of the small molecule mixture B; Preferably, the oily solvent is selected from at least one of dimethylacetamide, N-methylpyrrolidone, acetone, and dimethyl sulfoxide; Preferably, the solid content of the negative electrode slurry is 38%-50%; Preferably, the viscosity of the negative electrode slurry is 2000-7000 mPa·S; Preferably, the specific operation of the photothermal composite curing is: first use a surface power of 4500-15000mW / cm 2 , irradiated with ultraviolet light with a wavelength of 365nm, and then heated at 40-60℃ for 5-20min, 50-80℃ for 30-150min, and 70-100℃ for 20-60min.

9. A method for preparing a low-porosity solid-state battery negative electrode according to any one of claims 1 to 5, characterized in that: First, polymer electrolyte A is dispersed in an oily solvent to prepare a polymer electrolyte A solution, and then a portion of the polymer electrolyte A solution is evenly mixed with the negative electrode active material, the conductive agent, and the small molecule mixture B to obtain a muddy mixture with a solid content of 70wt%-99.9wt%. The muddy mixture is heated to solidify it, and then the remaining portion of the polymer electrolyte A solution is added and mixed again to obtain a negative electrode slurry. Finally, the negative electrode slurry is coated on the negative electrode current collector, heated to solidify, and dried.

10. The preparation method according to claim 9, characterized in that: After drying, the obtained negative electrode is roller pressed at 45-80°C; Preferably, the specific operation of the heating curing is: first heating at 40-60°C for 5-40 minutes, then heating at 50-80°C for 40-150 minutes, and finally heating at 70-100°C for 40-100 minutes; Preferably, the specific operation of the drying is: baking in five temperature zones, with the temperature of zone 1 being 80-90°C, the temperatures of zones 2 to 4 being 80-100°C, and the temperature of zone 5 being 80-95°C, and the temperatures of zones 2 to 4 being not lower than the temperatures of zones 1 and 5; Preferably, when preparing the slurry mixture, the amount of the polymer electrolyte A solution added is 10 wt% to 35 wt% of the total polymer electrolyte A solution; Preferably, the temperature of zone 1 is 80-85°C, the temperatures of zones 2 to 4 are all 95-100°C, and the temperature of zone 5 is 80-90°C.

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