Hybrid liquid-retaining agent, electrolyte, separator and lithium ion battery for cylindrical lithium ion battery

Abstract

This application relates to a hybrid liquid retainer, electrolyte, separator, and lithium-ion battery for cylindrical lithium-ion batteries. The hybrid liquid retainer includes: an adsorption-release unit as a core layer, having an internal porous structure to accommodate functional additives; and an interface self-healing unit as a shell layer. The interface self-healing unit comprises polymer segments capable of self-assembling to form a protective layer at the electrode and / or electrolyte interface; the polymer segments include fluoropolymer brushes; the liquid retainer has a liquid retention efficiency factor Φ satisfying: 0.004 ≤ Φ ≤ 0.08, and Φ = (σ... g ×t shell ×V pore ) / D core , where σ g chains / nm 2 t shell nm represents the grafting density and thickness of the interface self-healing unit; V pore cm 3 / g、D core nm represents the pore volume and particle size of the adsorption-release unit. This technology enables the sustained-release replenishment of functional additives and long-term interface stabilization, effectively inhibiting electrolyte decomposition and electrode degradation, and improving the performance of high-voltage lithium-ion batteries.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and in particular to a hybrid liquid retainer, electrolyte, separator, and lithium-ion battery for cylindrical lithium-ion batteries. Background Technology

[0002] With the increasing demands for energy density in lithium-ion batteries from electric vehicles and energy storage systems, raising the charging cut-off voltage of cathode materials to 4.4 V and above has become an important technological approach. Cylindrical all-tab batteries, represented by the 21650 type, effectively reduce internal resistance and improve rate performance through their all-tab structure. However, their wound structure presents unique challenges: the long liquid phase conduction path in the central region of the winding and the tight contact between electrode layers make electrolyte wetting difficult. Under high-voltage conditions, this problem is further amplified, easily leading to localized electrolyte drying and continuous interface degradation, thus placing higher demands on the long-term retention of electrolyte within the cell and interface stabilization.

[0003] To improve interfacial stability under high voltage, related technologies typically employ the introduction of film-forming additives or functional nanofillers into the electrolyte. A common strategy relies on functional additives such as vinylene carbonate and 1,3-propanesulfonic acid lactone to generate a protective layer on the positive and negative electrode surfaces through oxidation / reduction reactions. However, under high voltage conditions, these functional additives are rapidly and irreversibly consumed, and their effective concentration in the electrolyte continuously decreases with cycling, leading to a significant weakening of their protective ability at the electrode / electrolyte interface in the later stages of long cycle life, thus failing to achieve long-term stability. Another strategy involves directly dispersing inorganic nanoparticles such as alumina or silica into the electrolyte to improve its liquid retention capacity and thermal stability. However, these nanoparticles readily aggregate in organic electrolyte systems, making it difficult to form a uniform and dense protective film at the electrode interface. Furthermore, they lack the function of storing and replenishing consumable additives, thus contributing limitedly to extending cycle life. In addition, given the special requirements of the cylindrical all-tab battery winding structure, most existing separator coating technologies adopt a uniform coating scheme, which cannot compensate for the more stringent liquid retention and interface stability requirements in the winding center area, resulting in significant performance inhomogeneity within the cell.

[0004] In summary, in applications involving high-voltage lithium-ion batteries, especially 21650 cylindrical all-tab batteries, related technologies generally suffer from the problem of continuous degradation of electrode / electrolyte interface protection performance due to the irreversible consumption of functional additives during cycling and the inability to replenish them in a timely manner. Simultaneously, the lack of differentiated electrolyte retention solutions tailored to the characteristics of the cell's winding structure makes it difficult to achieve long lifespan and high stability across the entire cell range. Therefore, providing a solution that can sustainably replenish interfacial film-forming components and maintain interfacial stability has become a pressing technical problem to be solved in this field. Summary of the Invention

[0005] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a hybrid electrolyte retainer for cylindrical lithium-ion batteries. This hybrid electrolyte retainer preloads and stores functional additives by using an adsorption-release unit with an internal porous structure as a core layer, and covalently grafting an interface self-healing unit containing self-assembled film polymer segments onto the surface of the core layer, thus forming a hybrid electrolyte retainer. During battery operation, this electrolyte retainer can continuously release the stored functional additives from the core to replenish interface consumption, and can also form a stable protective layer on the electrode surface through in-situ self-assembly of the outer shell polymer. This achieves sustained-release replenishment of functional additives and long-term interface stabilization, effectively inhibiting electrolyte decomposition and electrode degradation, and improving the cycle life and safety of high-voltage lithium-ion batteries.

[0006] To solve the above-mentioned technical problems, the present invention is implemented as follows: A first aspect of the present invention provides a hybrid liquid retainer for cylindrical lithium-ion batteries, comprising: The adsorption-release unit, as the core layer, has an internal porous structure to accommodate functional additives. An interface self-healing unit serves as a shell and is attached to the outer surface of the adsorption and release unit; the interface self-healing unit contains polymer segments capable of self-assembling to form a protective layer at the electrode and / or electrolyte interface; The polymer segment includes a fluoropolymer brush; The liquid retention efficiency factor Φ of the liquid retention agent satisfies: 0.004≤Φ≤0.08, and Φ = (σ g × t shell ×V pore ) / D core , where σ g chains / nm 2 t is the grafting density of the interface self-healing unit; shell nm is the thickness of the interface self-healing unit; V pore cm 3 / g represents the pore volume of the adsorption and sustained-release unit; D core nm is the particle size of the adsorption-release unit.

[0007] In one embodiment, the polymer segments are obtained by surface-initiated atom transfer radical polymerization on the surface of the adsorption-release unit; In one embodiment, the grafting density σ of the interface self-healing unit g chains / nm 2 0.2~0.8 chains / nm 2 .

[0008] In one embodiment, the thickness t of the interface self-healing unit shell nm is 10~50 nm.

[0009] In one embodiment, the pore volume V of the adsorption-release unit pore cm 3 / g is 0.4~0.6 cm 3 / g.

[0010] In one embodiment, the particle size D of the adsorption-release unit core nm is 50~200 nm.

[0011] In one embodiment, the porous structure of the adsorption and sustained-release unit is preloaded with functional additives accounting for 15% to 40% of the total mass of the liquid-retaining agent.

[0012] In one embodiment, the liquid-retaining agent exists in the electrolyte in the form of a nano-dispersion, and its mass fraction in the electrolyte is 1% to 5%.

[0013] In one embodiment, the liquid-retaining agent is applied to the surface of the battery separator in a gradient coating manner, resulting in a gradient distribution of decreasing load from the inside to the outside along the separator winding direction. The inner layer load (Winner) near the winding center and the outer layer load (Wouter) near the periphery satisfy: 1.2 ≤ Winner / Wouter ≤ 2.0; where Winner is 4~10 g / m³. 2 The Wouter has a concentration of 2~6 g / m³. 2 .

[0014] In one embodiment, the interface self-healing unit is a fluoropolymer brush covalently grafted onto the surface of the adsorption and slow-release unit.

[0015] In one embodiment, the antioxidant potential of the interface self-healing unit is ≥4.8 V.

[0016] In one embodiment, the adsorption-release unit comprises mesoporous inorganic oxide nanospheres, wherein the specific surface area of ​​the mesoporous inorganic oxide nanospheres is ≥200 m². 2 / g, pore size 3~8 nm, pore volume ≥0.4 cm³ 3 / g.

[0017] In one embodiment, the mesoporous inorganic oxide nanospheres are selected from at least one of mesoporous alumina nanospheres, mesoporous silica nanospheres, and mesoporous titanium dioxide nanospheres.

[0018] In one embodiment, the average particle size D50 of the liquid-retaining agent is ≤ 500 nm.

[0019] In one embodiment, the functional additive is selected from at least one of vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfite, lithium difluorooxalate borate, and lithium oxalate borate.

[0020] A second aspect of the present invention provides a method for preparing a hybrid liquid-retaining agent, comprising the following steps: providing a mesoporous inorganic oxide core having an internal porous structure to accommodate functional additives; The initiator is immobilized on the core surface via covalent bonds; Using a core immobilized with an initiator as a macromolecular initiator, surface-initiated polymerization is carried out on the core surface to grow a shell containing polymer segments, which serves as an interface self-healing unit. Polymer segments can self-assemble at the electrode and / or electrolyte interface to form a protective layer.

[0021] In one embodiment, the specific process of the preparation method includes: (a) Prepare mesoporous inorganic oxide cores using a hydrothermal method or a sol-gel method; (b) Immobilization of ATRP initiator: The core obtained in step (a) is added to ATRP initiator and refluxed at 80~100℃ for 12~48 h. After centrifugation and washing, it is dried under vacuum. (c) SI-ATRP polymerization: Using fluorinated acrylate or vinyl ether monomers as monomers, Cu(I) / azaligand as catalytic system, and the core of the initiator immobilized in step (b) as the large initiator, SI-ATRP polymerization was carried out at 40~70℃ for 8~48 h under an inert atmosphere. After centrifugation and washing, the product was dried. (d) Functional additive preloading: The product obtained in step (c) is impregnated with a functional additive solution, and the solvent is evaporated after stirring at room temperature to obtain the hybrid liquid retainer.

[0022] A third aspect of the present invention provides an electrolyte comprising a lithium salt, a high-voltage solvent system, and the aforementioned hybrid liquid retainer; The high-voltage solvent system is selected from at least one of fluorocarbonates, chain carbonates, sulfones, and ionic liquids; The oxidation stability potential of the high-voltage solvent system is ≥4.8 V.

[0023] A fourth aspect of the present invention provides a diaphragm comprising a base membrane and a coating loaded on the surface of the base membrane, the coating comprising the aforementioned hybrid liquid-retaining agent.

[0024] In one embodiment, the base membrane is selected from at least one of polypropylene, polyethylene, PP / PE / PP three-layer composite membrane, and polyimide.

[0025] In one embodiment, the thickness of the base film is 12-40 μm and the porosity is 40%-65%.

[0026] In one embodiment, the functionalized diaphragm exhibits longitudinal and transverse thermal shrinkage rates of ≤10% and a liquid absorption rate of ≥200% under conditions of 150°C / 30 min.

[0027] A fifth aspect of the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte comprises the electrolyte described above. The diaphragm includes the diaphragm mentioned above.

[0028] In one embodiment, the hybrid liquid retainer is loaded in the diaphragm coating and dispersed in the electrolyte.

[0029] Implementing the technical solution of the present invention has at least the following beneficial effects: 1. This invention provides an adsorption-release unit with an internal porous structure as a core layer to preload and store functional additives. An interface self-healing unit containing self-assembled polymer segments is covalently attached to the core layer surface, forming a core-shell structure. During battery operation, functional additives are continuously released from the core to replenish interface consumption. Simultaneously, the shell polymer segments self-assemble in situ on the electrode surface to form a protective layer, thereby achieving sustained-release replenishment of functional additives and long-term interface stabilization. By limiting the preparation method of the polymer segments to surface-initiated atom transfer radical polymerization, a strong connection between the shell and core layers and the controllability of the chain structure are ensured. By introducing a liquid retention efficiency factor Φ composed of grafting density, shell thickness, pore volume, and core particle size and constraining its numerical range, the relationship between interface protection capability, additive sustained-release capacity, and particle size is quantitatively balanced. This avoids insufficient protection due to an excessively thin shell or hindering ion transport due to an excessively thick shell, effectively suppressing electrolyte decomposition and electrode degradation, and improving the cycle life of high-voltage lithium-ion batteries.

[0030] 2. The present invention further limits the grafting density to 0.2~0.8 chains / nm 2 To ensure the shell provides sufficient film-forming material to create a dense, self-assembled protective layer, while preventing excessive density from clogging the core pores or hindering lithium-ion transport; the shell thickness is limited to 10–50 nm to balance short ion transport paths and stable interface self-assembly capabilities; and the pore volume is limited to 0.4–0.6 cm³. 3 / g and provides a suitable particle size, which allows the core to accommodate sufficient functional additives and maintain a controlled slow release rate. At the same time, the particle size in the range of 50~200 nm ensures good dispersion stability in the electrolyte, avoiding agglomeration due to excessively small particles or sedimentation due to excessively large particles, thereby further optimizing the long-term liquid retention and interface stability effect of the liquid retainer in the battery.

[0031] 3. By selecting mesoporous alumina with high specific surface area, suitable pore size and sufficient pore volume as the core, this invention not only provides abundant physical adsorption and storage space for functional additives, but also its interconnected mesoporous channels facilitate the stable release of additives at a controlled rate during the cycle. The preload is set between 15% and 40%, so that the additive inventory can be continuously replenished throughout the cycle life without clogging the channels or causing an initial burst release due to overload, thereby achieving long-term and stable replenishment of interfacial film-forming components.

[0032] 4. This invention limits the pre-loading amount of functional additives to 15%~40%, ensuring that the total amount of functional additives stored in the core can continuously replenish the interface consumption during long cycles without clogging the channels or causing an initial explosive release due to overloading, thus achieving stable replenishment throughout the entire lifespan. The content of the liquid retainer in the electrolyte is limited to 1%~5%, providing sufficient interface self-healing nanoparticles while avoiding a sharp increase in electrolyte viscosity and a decrease in ionic conductivity due to excessive concentration, ensuring stable electrochemical transport. By setting a gradient distribution of the liquid retainer loading from the inside to the outside along the diaphragm winding direction and limiting the Winner / Wouter ratio to 1.2~2.0, a higher amount of liquid retainer and electrolyte is obtained in the winding center region, compensating for its longer liquid phase transport path, achieving liquid retention balance and consistent interface stability throughout the entire cell, effectively improving the wettability of the electrode in the center region and reducing local attenuation.

[0033] 5. By employing a fluoropolymer brush and limiting its antioxidant potential to ≥4.8 V, the inherent low HOMO energy level and high oxidation stability of the fluorinated segments ensure that the shell maintains structural integrity under high voltage conditions. This allows for self-assembly on the electrode surface to form a dense and uniform fluorinated protective layer, effectively preventing direct contact between the electrolyte and the highly active electrode and inhibiting oxidative decomposition. Furthermore, by selecting a brush with a specific surface area ≥200 m²... 2 / g, pore size 3~8 nm, pore volume ≥0.4 cm³ 3 / g of mesoporous inorganic oxide nanospheres serve as adsorption and slow-release units, providing ample physical adsorption and storage space for functional additives. Simultaneously, their interconnected mesopores facilitate the stable release of additives at a controlled rate. Limiting the average particle size D50 to ≤ 500 nm ensures uniform nano-dispersion of the liquid retainer in the electrolyte, preventing sedimentation or agglomeration due to excessively large particles. Selecting specific functional additives and utilizing their mature film-forming capabilities, combined with the slow-release mechanism, continuously repairs the interface, further enhancing the battery's cycle stability and safety.

[0034] 6. The overall performance of the battery prepared by this invention is improved, specifically: (1) Functional additive slow release: The mesoporous core can load 15%~40% of the total mass of functional additives, and continuously replenish the consumed additives during the cycle. After 500 cycles, the additive consumption rate in the electrolyte is ≤40% (compared to the blank group >80%); (2) High voltage interface stability: The fluoropolymer shell has an anti-oxidation potential >4.8 V, which can effectively inhibit the oxidation and decomposition of the electrolyte on the positive electrode surface under high voltage and reduce the interface impedance; (3) Balanced liquid retention in the winding center: The gradient coating of the separator increases the electrolyte retention in the winding center area by more than 30% compared with the uniform coating scheme, which significantly improves the wettability of the electrode in the center area; (4) Improved thermal safety: The alumina core can absorb the mechanical stress generated by the thermal shrinkage of the separator, and the fluoropolymer shell increases the self-closing temperature of the separator at 150℃ / 30 No fire or explosion occurred during the hot box test; (5) Compatible preparation process: The synthesis route is mature, and the polymer brush parameters can be precisely controlled by SI-ATRP, which is easy to scale up; the liquid retainer can be directly added to the electrolyte or gradient coated on the separator, which is fully compatible with the existing 21650 cylindrical all-tab battery manufacturing process; (6) Long cycle life: After 500 cycles at 4.4 V high voltage and 45℃, the capacity retention rate is ≥80%, which is better than the existing commercial high voltage electrolyte scheme. Attached Figure Description

[0035] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0036] Figure 1 This is a schematic cross-sectional view of the core-shell structure of the hybrid liquid-retaining agent prepared according to the present invention; wherein 1-adsorption and slow-release unit; 2-interface self-healing unit; 3-porous channel.

[0037] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0038] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0039] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0040] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0041] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0042] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0043] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0044] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0045] In this application, "hybrid liquid retainer" refers to any organic-inorganic composite nanomaterial with a core-shell structure that can retain functional additives in the core layer and achieve slow release during battery operation, while the shell layer can self-assemble to form a protective layer at the electrode and / or electrolyte interface. For example, it may include a hybrid liquid retainer with a mesoporous inorganic oxide, porous carbon, or metal-organic framework as the core layer and polymer segments with interfacial self-assembly capability grafted by covalent or ionic bonding as the shell layer.

[0046] In this application, "adsorption-release unit" refers to a component in a liquid-retaining agent that serves as a core layer, has an internal porous structure, and is capable of accommodating functional additives through physical adsorption and / or capillary action, releasing the additives into the electrolyte at a controlled rate during cycling. For example, the adsorption-release unit may be inorganic porous particles such as mesoporous alumina, mesoporous silica, mesoporous titanium dioxide, or porous carbon nanospheres, and preferably has radially interconnected mesoporous channels. In some embodiments, the specific surface area of ​​the adsorption-release unit is ≥200 m². 2 / g, pore size distribution of 3~8 nm, pore volume ≥0.4 cm³ 3 / g, its particle size D core nm is 50~200 nm.

[0047] In this application, "interface self-healing unit" refers to a polymer component in the liquid retainer that acts as a shell layer attached to the outer surface of the adsorption-release unit and can self-assemble at the electrode and / or electrolyte interface during battery charging and discharging to form a stable protective layer to suppress interfacial side reactions. For example, the interface self-healing unit can be a fluoropolymer brush, a polysiloxane brush, or other polymer segments with interfacial film-forming capabilities grafted onto the core surface via covalent bonds. In a preferred embodiment, the grafting density σ of the interface self-healing unit... g chains / nm 2 0.2~0.8 chains / nm 2 Shell thickness t shell The nm value is 10~50 nm, and its antioxidant potential is ≥4.8 V (vs. Li / Li + ).

[0048] In this application, the "liquid retention efficiency factor Φ" is determined by Φ = (σ g × t shell × V pore ) / D core The defined dimensionless parameter is used to comprehensively characterize the balance between the interfacial protection capability of core-shell liquid-retaining agents and the sustained-release potential of functional additives and particle-scale effects. Among them, σ... g chains / nm 2 t represents the grafting density of the interface self-healing unit; shell nm is the thickness of the interface self-healing unit; V pore cm 3 / g represents the pore volume of the adsorption-release unit; D core nm represents the particle size of the adsorption-release unit. When Φ < 0.004, it usually indicates that the shell is too thin or the pore volume is too small, resulting in insufficient release and interface protection; when Φ > 0.08, it usually indicates that the shell is too thick or the pore volume is too large, which can easily cause ion transport obstruction and particle agglomeration.

[0049] In this application, "grafting density σ" g chains / nm 2 "σ" refers to the number of covalently linked interfacial self-healing polymer chains on the core surface per unit area. For example, it can be determined by thermogravimetric analysis coupled with gel permeation chromatography, representing the anchoring density of fluoropolymer brushes on the mesoporous alumina surface. In a preferred embodiment, σ g chains / nm 2 It is controlled at 0.2~0.8 chains / nm 2 This ensures that the shell provides sufficient film-forming material to the interface without being too dense and clogging the pores of the core or hindering ion conduction.

[0050] In this application, "shell thickness t" shell "nm" refers to the average thickness of the shell formed by the interface self-healing units in a dry or swollen state. For example, it can be obtained through particle size difference analysis of core-shell particles using transmission electron microscopy or dynamic light scattering. When t shell When the nm value is 10~50 nm, the shell can balance excellent ion transport performance and stable interface self-assembly capability.

[0051] In this application, "Kong Rong V" pore cm 3 " / g" refers to the total pore volume of the porous structure within the adsorption-release unit, which can be determined using a nitrogen adsorption-desorption isotherm. A higher pore volume allows for the inclusion of more functional additives, and typically requires a Vg. pore cm 3 / g≥0.4 cm 3 / g.

[0052] In this application, "particle size D" core "nm" refers to the average particle size of the adsorption-release unit, which can be measured using scanning electron microscopy or dynamic light scattering. To achieve good dispersion stability and uniform membrane coating in the electrolyte, D... core nm is typically controlled within the range of 50~200 nm.

[0053] In this application, "mesoporous alumina nanospheres" specifically refers to nanospherical particles composed of alumina and possessing a mesoporous (pore size 2-50 nm) structure. For example, they can be γ-Al₂O₃ nanospheres prepared by hydrothermal or sol-gel methods using an aluminum source and a structure-directing agent, followed by calcination. In a preferred embodiment, the specific surface area of ​​the mesoporous alumina nanospheres is ≥200 m². 2 / g, pore size 3~8 nm, pore volume ≥0.4 cm³ 3 / g, and has radially interconnected mesoporous channels to facilitate the adsorption and sustained release of functional additives.

[0054] In this application, "preloading with functional additives" refers to the step of introducing functional additives into the porous structure of the adsorption-release unit before adding the liquid retainer to the electrolyte, and the resulting state of the liquid retainer preloading with functional additives. The functional additives are, for example, selected from at least one of vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfite, lithium difluorooxalate borate, and lithium oxalate borate. The preloading amount is determined by thermogravimetric analysis and typically accounts for 15% to 40% of the total mass of the liquid retainer to ensure continuous replenishment of consumed film-forming components throughout the cycle life, while avoiding pore blockage or initial burst release.

[0055] In this application, a "fluoropolymer brush" refers to an aggregate of fluoropolymer chains, one end of which is covalently bonded to the surface of an adsorption-release unit, while the other end extends freely. For example, it can be formed by immobilizing an ATRP initiator on the core surface, followed by surface-initiated atom transfer radical polymerization (SI-ATRP) to grow poly(perfluoroalkyl ethyl acrylate), poly(perfluoroalkyl vinyl ether), poly(vinylidene fluoride-co-perfluoroalkyl vinyl ether), and their copolymers. The number-average molecular weight of this fluoropolymer brush can be 5,000–80,000 g / mol, the molecular weight dispersion (PDI) ≤ 1.35, and the fluorine mass fraction 40%–75%. The fluoropolymer brush, due to its high antioxidant properties (antioxidant potential ≥ 4.8 V) and low surface energy, can self-assemble to form a uniform fluorinated protective layer at the electrode and / or electrolyte interface.

[0056] In this application, "surface-initiated atom transfer radical polymerization (SI-ATRP)" refers to a polymerization method in which monomers grow controllably from the surface outward through a living radical polymerization mechanism on the surface of a substrate immobilized with an ATRP initiator. For example, mesoporous alumina nanospheres modified with a bromoacyl triethoxysilane coupling agent can be used as macromolecular initiators, and Cu(I) / azaligands can be used as catalytic systems to polymerize fluorinated acrylate or vinyl ether monomers under an inert atmosphere, thereby obtaining a fluorinated polymer brush shell layer with precisely controllable graft density and chain length.

[0057] In this application, "nanodispersion" refers to a colloidal or suspension system formed by uniformly dispersing a liquid-retaining agent in the form of nanoparticles in an electrolyte. The average particle size D50 of the liquid-retaining agent particles is ≤ 500 nm, and its mass fraction in the electrolyte is 1%~5%. This provides sufficient interfacial self-healing active sites while avoiding a decrease in ionic conductivity due to particle agglomeration or excessive viscosity.

[0058] In this application, "gradient coating" refers to a structural design in which the liquid retaining agent is coated onto the surface of the battery separator in a manner that gradually decreases in loading from the inside to the outside along the separator winding direction. The region near the winding center (inner layer) has a higher loading, while the region near the periphery (outer layer) has a lower loading, ensuring that the ratio of the inner layer loading (Winner) to the outer layer loading (Wouter) satisfies 1.2 ≤ Winner / Wouter ≤ 2.0. Typically, the Winner is 4~10 g / m³. 2 Wouter typically has a concentration of 2~6 g / m³ 2 This gradient distribution compensates for the disadvantage of a long liquid phase conduction path in the central region of the cylindrical winding structure, promoting uniform liquid retention and interface stability across the entire cell.

[0059] With the continuous improvement of the energy density of lithium-ion batteries, increasing the charging cut-off voltage of the cathode material to 4.4V and above has become a common technical approach. Cylindrical all-tab batteries, represented by the 21650 type, effectively reduce internal resistance and improve rate performance through their all-tab structure. However, their wound structure results in a long liquid phase conduction path in the central region and tight contact between electrode layers, making electrolyte wetting difficult. Under high-voltage conditions, this problem is further amplified, easily leading to localized electrolyte drying and continuous interface degradation, placing higher demands on the long-term retention of electrolyte within the cell and interface stabilization.

[0060] To improve interfacial stability under high voltage, related technologies typically employ the introduction of film-forming additives or functional nanofillers into the electrolyte. A common strategy relies on functional additives such as vinylene carbonate and 1,3-propanesulfonic acid lactone to generate a protective layer on the positive and negative electrode surfaces through oxidation / reduction reactions. However, under high voltage conditions, these functional additives are rapidly and irreversibly consumed, and their effective concentration in the electrolyte continuously decreases with cycling, leading to a significant weakening of their protective ability at the electrode / electrolyte interface in the later stages of long cycle life, thus failing to achieve long-term stability. Another strategy involves directly dispersing inorganic nanoparticles such as alumina or silica into the electrolyte to improve its liquid retention capacity and thermal stability. However, these nanoparticles readily aggregate in organic electrolyte systems, making it difficult to form a uniform and dense protective film at the electrode interface. Furthermore, they lack the function of storing and replenishing consumable additives, thus contributing limitedly to extending cycle life. In addition, given the special requirements of the cylindrical all-tab battery winding structure, most existing separator coating technologies adopt a uniform coating scheme, which cannot compensate for the more stringent liquid retention and interface stability requirements in the winding center area, resulting in significant performance inhomogeneity within the cell.

[0061] Through research and analysis, the inventors recognized that the underlying reasons for the continued deterioration of the above problems include at least the following aspects: First, functional additives are sacrificial components, which are consumed when forming a protective layer on the electrode surface. As the number of cycles increases, the concentration of additives in the electrolyte gradually decreases, making it impossible to maintain the initial interface repair capability. Second, the degradation process of the electrode / electrolyte interface has a self-accelerating characteristic. Once the local protective layer is damaged, the exposed fresh and highly active electrode surface will further catalyze the oxidation and decomposition of the electrolyte, producing more acidic products and gases, exacerbating the damage to the protective layer and the unexpected consumption of additives. Third, there is a dynamic mismatch between the diffusion supply of additives and the interface consumption rate. Conventional physical dissolution methods cannot achieve precise control over the release behavior of additives, making it difficult to establish a long-term and balanced repair mechanism.

[0062] Based on the above analysis, this application provides a synergistic solution, the core of which lies in constructing a novel material—a hybrid liquid-retaining agent—that combines adsorption-release and interfacial self-healing functions. This liquid-retaining agent structurally defines functional regions: its core layer is an adsorption-release unit with an internal porous structure, specifically designed to contain and preload functional additives, continuously releasing them at a controlled rate during cycling to compensate for interfacial consumption; its shell layer is an interfacial self-healing unit firmly attached to the surface of the core layer via covalent bonds. This unit contains polymer segments capable of self-assembling to form a protective layer at the electrode and / or electrolyte interface. Through this core-shell structure, the three major processes of additive storage, sustained-release replenishment, and in-situ modification of the high-voltage interface are organically integrated into a single nanostructure unit, rather than a simple functional superposition.

[0063] With this synergistic mechanism, the battery interface maintenance mode changes from the conventional one-time addition and passive consumption of electrolyte to a closed-loop dynamic maintenance involving active adsorption and storage of electrolyte retainers, controlled slow release, and surface self-assembly into a film. The internal porous structure of the adsorption and slow release unit provides stable storage space and physical adsorption sites for functional additives. The capillary effect of the pores and the chemical affinity of the material surface slow down the release rate of the additives, avoiding the problems of initial instantaneous release and insufficient replenishment later. At the same time, the interface self-healing unit grafted onto the core layer surface, with its specific chemical structure, not only possesses stability against high-voltage oxidation but can also self-assemble on the electrode surface under the action of an electric field to form a continuous and dense protective barrier. The formation of this protective barrier is independent of the consumption process of free additives in the electrolyte, thus providing the interface with a durable and self-healing function.

[0064] To precisely balance the storage capacity, release kinetics, and ion transport requirements of the liquid-retaining agent, this embodiment further introduces the concept of a liquid-retaining efficiency factor Φ, which is used to correlate the core structural parameters of the liquid-retaining agent. This factor comprehensively considers the particle size and internal pore volume of the adsorption-release unit, as well as the grafting density and thickness of the interface self-healing unit, and incorporates the overall particle size into a unified quantification. By transforming the matching relationship between the core-shell structural parameters into a quantifiable numerical range, quantitative design and optimization of the long-term protective capability and ion conduction impedance of the liquid-retaining agent are achieved. When the structural parameters are not properly coordinated, problems such as insufficient interface protection due to an excessively thin shell, or lithium-ion transport lag and particle agglomeration caused by an excessively thick shell and excessively large pores may occur.

[0065] Furthermore, considering the varying requirements for electrolyte uniformity in specific battery structures—for example, in a cylindrical wound structure, the liquid phase transport path of the electrolyte differs significantly from the center of the core to the outer layer, with the central region more prone to local polarization and degradation due to electrolyte deficiency—the electrolyte retainer in this embodiment also supports a gradient distribution. By intentionally constructing a non-uniform spatial distribution of the electrolyte retainer, concentrating more electrolyte retainer and functional additives in regions with longer liquid phase transport paths, the interface stability and electrolyte retention across the entire battery can be made more balanced. This effectively suppresses non-uniform degradation problems such as local over-discharge and local heat accumulation, extending the overall service life of the battery.

[0066] Specifically, the present invention adopts the following technical solution: A method for preparing a hybrid liquid retainer for cylindrical lithium-ion batteries includes the following steps.

[0067] Step 1: Provide a mesoporous inorganic oxide core with an internal porous structure to accommodate functional additives.

[0068] In one example, the core of the mesoporous inorganic oxide is mesoporous alumina nanospheres. Its synthesis can be carried out using a hydrothermal method. The aluminum source, structure-directing agent, and precipitant are dissolved in a mixed solvent of water and ethanol, stirred until clear, and then transferred to a hydrothermal reactor and held at 150–200 °C for 12–36 h. For example, in one specific embodiment, 4 mmol of aluminum nitrate nonahydrate, 0.5 mmol of hexadecyltrimethylammonium bromide, and 20 mmol of urea are dissolved in 50 mL of a 3:1 (v / v) mixed solvent of water and ethanol, magnetically stirred for 30 min, and then transferred to a hydrothermal reactor and held at 180 °C for 24 h. After the reaction is complete, the solid product is obtained by centrifugation and washed three times each with water and anhydrous ethanol, and then dried at 120 °C. The dried product is placed in a muffle furnace and calcined at 400–650 °C for 2–6 h, for example, at 500 °C for 4 h, with a heating rate controlled at 2 °C per minute. This calcination process aims to remove the structure-directing agent and stabilize the mesoporous structure and crystalline phase of alumina. The resulting mesoporous alumina nanospheres are predominantly gamma-phase. The average particle size of the nanospheres can be controlled by adjusting the molar ratio of the aluminum source to the structure-directing agent.

[0069] In another example, the mesoporous alumina nanospheres can also be synthesized using the sol-gel method. Specifically, aluminum isopropoxide is used as the aluminum source, and hydrolysis and condensation are carried out in an acidic aqueous solution with the pH adjusted to 3 to 4 by hydrochloric acid. Triblock copolymer F127 is used as a structure directing agent, and the molar ratio of F127 to the aluminum source is controlled between 0.005 and 0.02. An ordered mesoscopic structure is formed through an evaporation-induced self-assembly process, followed by calcination at 600°C, which also yields mesoporous alumina nanospheres with uniform particle size and higher pore order.

[0070] The mesoporous inorganic oxide core synthesized by the above method has a rich porous structure, specifically, its specific surface area is greater than or equal to 200 m². 2 / g, and further, it can be 200 to 350m 2 / g. The pore size distribution of its internal channels is mainly concentrated between 3 and 8 nm, and these channels exhibit radial interconnection. Simultaneously, the pore volume of this core is greater than or equal to 0.4 cm³. 3 / g. These characteristics of high specific surface area, suitable pore size, and sufficient pore volume provide ample space for subsequent physical adsorption and storage of functional additives, and facilitate the controlled and stable release of functional additives in subsequent applications. It should be noted that the specific surface area, pore size distribution, and pore volume mentioned here and below can all be determined by conventional nitrogen adsorption-desorption methods in the art.

[0071] The average particle size of the core is one of the key structural parameters affecting its dispersion stability and electrolyte retention capacity. The inventors of this invention discovered that when the average particle size of the core is less than 50 nm, the surface energy of the particles is too high, making irreversible aggregation highly likely in subsequent electrolyte applications, and making it difficult to maintain a stable nano-dispersion. When the average particle size is greater than 200 nm, the gravitational sedimentation effect of the particles in the electrolyte becomes significant, again failing to maintain uniform dispersion, resulting in uneven concentration of the electrolyte retainer within the system and an inability to form a uniform protection at the electrode interface. In this invention, the average particle size of the core is controlled within the range of 50 to 200 nm. For example, its average particle size can specifically be 50 nm, 70 nm, 90 nm, 100 nm, 120 nm, 150 nm, 180 nm, or 200 nm.

[0072] Step 2: The polymerization initiator is covalently immobilized on the surface of the core obtained in Step 1.

[0073] In one specific embodiment, this is achieved through the reaction of a silane coupling agent with the hydroxyl groups on the core surface. 1.0 g of the mesoporous alumina nanospheres synthesized in step one were ultrasonically dispersed in 100 mL of anhydrous toluene, followed by the addition of 5 mmol of 2-bromoisobutyryloxypropyltriethoxysilane. The mixture was heated under reflux at 90 °C for 24 h. During this process, the ethoxysilane group at one end of the silane coupling agent molecule hydrolyzes and undergoes a condensation reaction with the hydroxyl groups on the surface of the alumina nanospheres, forming a stable silicon-oxygen-aluminum covalent bond, thereby anchoring the 2-bromoisobutyryloxy group at the other end to the nanosphere surface. After the reaction, the nanospheres were separated by centrifugation and washed three times each with toluene and ethanol to remove unreacted coupling agent. They were then vacuum dried at 60 °C for 12 h to obtain nanospheres with the initiator immobilized on their surface.

[0074] The silane coupling agent used is not limited to 2-bromoisobutyryloxypropyltriethoxysilane, but can also be other silane coupling agents containing 2-bromoisobutyryl derivatives or alpha-bromoacyl derivatives. These initiator groups can efficiently initiate subsequent surface-initiated atom transfer radical polymerization reactions. The immobilization density of the initiator on the nanosphere surface can be precisely controlled by adjusting the amount of silane coupling agent added. This immobilization density, i.e., the surface initiator density, can be quantified by elemental analysis or thermogravimetric analysis. Precise control of the initiator density is a prerequisite for achieving controllable brush grafting density of subsequent fluoropolymers.

[0075] Step three involves using the core with the initiator immobilized in step two as a macromolecular initiator to perform surface-initiated polymerization on the core surface, growing a shell containing polymer segments as an interface self-healing unit. These polymer segments can self-assemble at the electrode-electrolyte interface to form a protective layer.

[0076] In a specific example, the surface-initiated polymerization is a surface-initiated atom transfer radical polymerization. The specific procedure is as follows: In a dry Schlenk flask, 500 mg of alumina nanospheres modified with the initiator obtained in step two, 10 mmol of perfluoroalkyl ethyl acrylate monomer, 0.1 mmol of cuprous bromide, 0.2 mmol of 2,2'-bipyridine ligand, and 5 mL of a 1:1 volume ratio of ethanol and water were added. The system was rigorously degassed through three cycles of freeze-thaw cycles, vacuuming, and argon purging to remove oxygen and ensure controllable polymerization activity. Subsequently, under argon atmosphere protection, the reaction flask was placed in an oil bath at 50°C and stirred for 8 to 24 hours. The reaction time directly determines the growth thickness of the polymer brush. After the reaction was completed, the product was centrifuged and washed three times with a mixed solvent of ethanol and water to remove free polymer chains and residual monomers that were not grafted onto the surface of the nanospheres. Finally, it was vacuum dried to obtain a hybrid liquid retainer, denoted as mesoporous alumina-polyperfluoroalkyl ethyl acrylate.

[0077] By carefully selecting the monomer type, solvent system, and reaction conditions, fluoropolymer brushes with different compositions and structures can be grown. For example, when using perfluoroalkyl vinyl ether as a monomer and a mixed solvent of N,N-dimethylformamide and water at a volume ratio of 3:1 as the reaction medium, a reaction at 60°C for 12 to 36 hours yields a polyperfluoroalkyl vinyl ether polymer brush. When using a mixed monomer of vinylidene fluoride and perfluoroalkyl vinyl ether, with dimethyl sulfoxide as the solvent, a reaction at 65°C for 16 to 48 hours yields a poly(vinylidene fluoride-co-perfluoroalkyl vinyl ether) copolymer brush. Generally speaking, the polymer segments of the interface self-healing unit are selected from one or more of poly(perfluoroalkyl ethyl acrylate), poly(perfluoroalkyl vinyl ether), poly(vinylidene fluoride-co-perfluoroalkyl vinyl ether), and their copolymers.

[0078] To ensure the full functionality of the shell, particularly its antioxidant self-assembly capability under high voltage conditions and its influence on ion transport, precise control of the polymer brush's structural parameters is required. Specifically, the grafting density of the shell is controlled between 0.2 and 0.8 chains / nm. 2 Within a certain range. For example, its grafting density can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or 0.8 chains / nm. 2 The grafting density was calculated using thermogravimetric analysis combined with gel permeation chromatography analysis of the cleaved free polymer. The shell thickness, i.e., the thickness of the polymer brush, was controlled within the range of 10 to 50 nm. For example, its thickness could be 10, 15, 20, 25, 30, 35, 40, 45, or 50 nm. This shell thickness could be characterized using transmission electron microscopy and dynamic light scattering.

[0079] By employing surface-initiated atom transfer radical polymerization, a living polymerization technique, and selecting the specific initiator and catalytic system described above, precise control over the chain length and composition of the polymer brushes can be achieved. The number-average molecular weight of the prepared fluoropolymer brushes can be between 5,000 and 80,000 g / mol, for example, 5,000, 10,000, 20,000, 30,000, 40,000, 50,000, 60,000, 70,000, or 80,000 g / mol. Furthermore, its molecular weight distribution is very narrow, with a molecular weight dispersity index not exceeding 1.35, for example, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, or 1.35. The narrow molecular weight distribution means that the polymer brush length and structural height on the surface of different liquid retainer particles are uniform. This ensures that all liquid retainer particles can self-assemble at the electrode interface at a very similar rate and morphology, thereby forming a fluorinated protective layer with uniform thickness and few defects.

[0080] Furthermore, the fluorine content (by mass fraction) of this fluoropolymer brush is controlled between 40% and 75%, for example, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75%. The fluorine content can be verified using energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Sufficient fluorine content significantly reduces the highest occupied molecular orbital energy level of the shell, conferring high oxidation stability, with an antioxidant potential greater than or equal to 4.8 V. Utilizing the inherent low surface energy of the fluorinated segments, this polymer brush tends to accumulate on the positive electrode surface under an electric field and self-assembles to form a dense, uniform fluorinated interface film. This fluorinated protective layer effectively physically isolates the electrolyte from direct contact with the highly active electrode, continuously suppressing the oxidative decomposition of the electrolyte on the positive electrode surface under high voltage and the dissolution of transition metal ions.

[0081] At this point, step three is complete, and the core and shell are structurally integrated into a single particle, forming a dual-functional liquid-retaining agent. This liquid-retaining agent exhibits core-shell synergy, simultaneously possessing both long-lasting sustained release and interface self-healing functions. To achieve the optimal synergistic effect of these two functions and avoid negative effects, it is necessary to quantitatively correlate the core-shell structural parameters. The inventors of this invention have introduced a dimensionless liquid-retaining efficiency factor Φ, defined as: Φ = (σ g × t shell ×V pore ) / D core .

[0082] The Φ factor comprehensively reflects the effective liquid retention and interface protection capabilities provided by the core material per unit particle size. When the Φ value is less than 0.004, it means that the shell layer is too thin or the pore volume is too small at a specific core particle size. This leads to two problems: first, the total amount and rate of functional additives slowly released from the core are insufficient to replenish interface consumption in a long-term manner; second, the shell layer is too thin to form a complete and dense protective layer on the electrode surface, resulting in insufficient interface protection. Conversely, when the Φ value is greater than 0.08, it means that the shell layer is too thick or the pore volume is too large. An excessively thick polymer brush shell layer will significantly increase the transport path and impedance of lithium ions on the particle surface, hindering the rate performance of the battery; while an excessively large pore volume is often accompanied by an unstable pore structure, and the steric hindrance effect between particles is weakened, making it easy for agglomeration to occur, which in turn reduces the dispersibility of the effective liquid retention components. Therefore, in this invention, the liquid retention efficiency factor Φ is limited to the range of 0.004 to 0.08. For example, the value of Φ can be 0.004, 0.006, 0.008, 0.01, 0.02, 0.04, 0.06 or 0.08.

[0083] After obtaining the above-mentioned core-shell structure liquid-retaining agent, the method may further include a step of preloading functional additives.

[0084] Step four involves preloading a functional additive into the porous structure of the liquid-retaining agent. The functional additive is selected from at least one of vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfite, lithium difluorooxalate borate, and lithium oxalate borate. In one specific embodiment, the functional additive is pre-dissolved in a small amount of volatile solvent, and the liquid-retaining agent powder obtained in step three is impregnated with this solution. The mixture is stirred at room temperature for 12 hours to allow the functional additive molecules to fully enter and be stored in the mesoporous channels of the core under capillary forces and physical adsorption. Subsequently, the solvent is evaporated by vacuum distillation or heating to obtain the additive-preloaded hybrid liquid-retaining agent.

[0085] The preloading amount of functional additives can be precisely determined by thermogravimetric analysis under a nitrogen atmosphere, heated from 30°C to 600°C. This preloading amount is controlled between 15% and 40% of the total mass of the liquid retainer, for example, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 32%, 35%, 38%, or 40%. The inventors found that when the preloading amount is below 15%, the total amount of additives stored in the mesoporous channels is insufficient, making it impossible to continuously replenish the consumed interfacial film-forming components during the hundreds or even thousands of battery cycles. When the preloading amount is above 40%, excessive additive molecules will clog the channels, altering the kinetics of the slow-release mechanism, changing from controllable Fick diffusion to uncontrollable non-Fick behavior, easily leading to explosive release in the early stages of cycling, triggering severe side reactions, which are also detrimental to battery performance. Controlling the preloading amount within the range of 15% to 40% achieves a balance between the total reserve and the release rate, enabling long-term, stable replenishment throughout the entire cycle life.

[0086] The above preparation method yields a hybrid electrolyte retainer for cylindrical lithium-ion batteries. This electrolyte retainer can be added as a functional component to non-aqueous electrolytes to form a high-voltage non-aqueous electrolyte for lithium-ion batteries.

[0087] This non-aqueous electrolyte comprises a lithium salt, a non-aqueous solvent, and the aforementioned hybrid electrolyte retainer. The lithium salt can be selected from one or more combinations of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalate borate, with its total concentration in the electrolyte maintained within a conventional range of 0.8 to 1.5 mol / L. The non-aqueous solvent can be a high-voltage system, for example, composed of one or more mixtures of fluorocarbonates, chain carbonates, sulfones, or ionic liquids, with an oxidation stability potential greater than or equal to 4.8 volts to match high-voltage operating conditions.

[0088] The liquid retainer exists in the non-aqueous electrolyte in the form of a nano-dispersion. To ensure sufficient interfacial self-healing and dispersion stability, the mass fraction of the liquid retainer in the electrolyte is set to 1% to 5%. For example, its addition amount can be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, or 5.0%. The average particle size D50 is controlled below 500 nm. D50 can be measured by dynamic light scattering. The inventors found that when the addition amount of the liquid retainer is less than 1%, the concentration of nanoparticles for interfacial self-assembly in the electrolyte is too low, making it impossible to form a continuous and dense fluorinated protective layer on the surface of all electrode active sites, resulting in insufficient uniformity and long-term effectiveness of interfacial protection. When the addition amount is higher than 5%, the nanoparticle concentration is too high, which significantly increases the viscosity of the electrolyte and reduces its ionic conductivity, deteriorating the rate performance of the battery.

[0089] In this electrolyte system, there is a synergistic effect between the electrolyte retainer and the electrolyte components. The fluoropolymer segments of the outer shell and the high-voltage solvent, especially the fluorinated solvent, exhibit good compatibility due to the similarity of their chemical structures. This intermolecular interaction allows the electrolyte retainer to migrate more smoothly under the influence of an electric field and preferentially accumulate at the interface between the electrode and the electrolyte, subsequently self-assembling into a uniform fluorinated protective layer. Simultaneously, the mesoporous structure of its core locks free functional additives in the electrolyte within the pores through physical adsorption and capillary forces, releasing them at a controlled rate to replenish the concentration at the electrode interface as it is consumed, thus maintaining the dynamic stability of the interfacial film.

[0090] The aforementioned non-aqueous electrolyte can be directly used as an electrolyte in high-voltage lithium-ion batteries. A lithium-ion battery, in its core components, includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the aforementioned non-aqueous electrolyte containing a liquid-retaining agent.

[0091] In one specific application, the battery is a 21650 cylindrical all-tab battery, with a diameter of 21 mm, a height of 65 mm, and a nominal capacity of 5.0 Ah. Its positive electrode active material can be selected from layered high-nickel materials such as NCM622, NCM811, NCM9.5.5, NCA, or lithium-rich manganese-based materials. The charging cut-off voltage of these positive electrode materials is greater than or equal to 4.4 volts (relative to lithium / lithium-ion). The negative electrode active material can be selected from natural graphite, artificial graphite, or silicon-carbon composite materials. Thanks to the core-shell liquid retainer dispersed in its electrolyte, the battery retains more than or equal to 80% of its capacity after 500 charge-discharge cycles at 4.4 volts, 45°C, and a 0.5C rate. Furthermore, the battery did not catch fire or explode during a hot-box test at 150°C for 30 minutes.

[0092] In addition to adding the liquid retainer to the electrolyte, it can also be loaded onto a separator to prepare a functionalized separator for lithium-ion batteries. This functionalized separator includes a base film and a coating loaded on the surface of the base film, the coating containing the hybrid liquid retainer described above.

[0093] The base membrane material can be polypropylene, polyethylene, a polypropylene / polyethylene / polypropylene three-layer composite membrane, or polyimide nonwoven fabric with higher thermal stability. The thickness of the base membrane is typically 12 to 40 micrometers, and the porosity is between 40% and 65%.

[0094] Addressing the unique winding structure of the 21650 cylindrical all-tab battery, the inventors of this invention discovered that the electrode layers at the center of the winding have a small interlayer distance and a long liquid phase conduction path, making electrolyte wetting and retention far more difficult than in the outer regions near the outer casing. A uniformly coated separator cannot compensate for this central region's disadvantage in electrolyte retention. To solve this problem, this invention proposes a gradient coating structure. The electrolyte-retaining agent coating on this functionalized separator is not uniformly distributed but forms a gradient along the winding direction; that is, the electrolyte-retaining agent loading (Winner) in the inner region near the winding center and the electrolyte-retaining agent loading (Wouter) in the outer region near the periphery satisfy a specific ratio. Specifically, the ratio of Winner to Wouter ranges from 1.2 to 2.0, for example, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0. Through this loading method, the central region receives more electrolyte-retaining agent, thereby holding more electrolyte and compensating for the disadvantage of its long liquid phase transport path. In a series of tests, when Winner was 1.5 times that of Wouter, the electrolyte retention in the central area of ​​the winding was increased by more than 30% compared to the uniform coating scheme, achieving balanced electrolyte retention across the entire cell.

[0095] To achieve this gradient structure, the inner layer loading (Winner) is typically set between 4 and 10 grams per square meter (g / m²), for example, 4, 5, 6, 7, 8, 9, or 10 g / m². The outer layer loading (Wouter) is correspondingly set between 2 and 6 g / m², for example, 2, 3, 4, 5, or 6 g / m². When the Winner to Wouter ratio is less than 1.2, i.e., close to uniform coating, the compensation effect for the liquid retention disadvantage in the central region is limited, and the interfacial impedance in this region increases significantly after long cycling. When this ratio is greater than 2.0, the inner coating is too thick, leading to uneven thickness of the separator in some areas. During winding, this can excessively compress the electrode spacing in the central region, worsening wetting conditions and hindering lithium-ion transport. Here, the loading is defined as the mass of liquid retainer loaded on each square meter of the base film.

[0096] This functionalized separator combines the advantages of inorganic materials and organic polymers. The fluoropolymer in the electrolyte retention agent shell forms a highly compatible interface with the organic base film, resulting in a peel strength between the coating and the base film greater than or equal to 0.5 N / cm. The mesoporous alumina in the electrolyte retention agent core provides strong electrolyte storage and sustained-release capabilities for functional additives. At high temperatures, the alumina core absorbs some of the mechanical stress generated by the separator's thermal shrinkage, while the fluoropolymer in the shell increases the separator's self-closing temperature to above 145°C. This synergistic effect inhibits heat penetration, ensuring that after being placed at 150°C for 30 minutes, the longitudinal and transverse thermal shrinkage rates of this functionalized separator do not exceed 10%, and the liquid absorption rate is greater than or equal to 200%.

[0097] In some embodiments, the peel strength between the coating and the base film is not less than 0.5 N / cm. Peel strength can be determined by a 180° peel test: the functionalized diaphragm is cut into strips of a predetermined width, the coated surface is adhered to a standard tape or test substrate, and the test is performed at a peel speed of 100 mm / min to 300 mm / min. The average peel force during the stable peeling phase is recorded and converted into peel strength per unit width. By controlling the mass ratio of the hybrid liquid retainer to the binder to be 95:5 to 80:20, a high liquid absorption rate and ion channel patency can be maintained while ensuring coating adhesion.

[0098] In summary, the hybrid liquid retainer provided by this invention, its preparation method, and the electrolyte, battery, and functionalized separator containing it integrate adsorption and slow-release functions with interface self-healing functions into a single nanoparticle. Furthermore, it introduces a liquid retention efficiency factor Φ to quantitatively correlate core-shell structure parameters. Simultaneously, it designs a gradient liquid retention scheme tailored to the characteristics of the wound structure of cylindrical all-tab batteries. This systematically solves the core contradiction of rapid irreversible consumption of functional additives and continuous weakening of interface protection under high voltage, ultimately achieving long cycle life and high safety for the battery.

[0099] The present application will be described in detail below with reference to the accompanying drawings and embodiments. However, the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0100] Example 1 Step a: Synthesis of mesoporous alumina nanospheres.

[0101] Aluminum nitrate (Al(NO3)3·9H2O, 4 mmol), hexadecyltrimethylammonium bromide (CTAB, 0.5 mmol), and urea (20 mmol) were dissolved in a water / ethanol mixture (3:1, 50 mL, v / v) and stirred until clear. The solution was transferred to a hydrothermal reactor and kept at 180 °C for 24 h. After cooling, the solution was centrifuged, washed three times each with water and anhydrous ethanol, dried at 120 °C, and then calcined in a muffle furnace at 500 °C for 4 h (heating rate 2 °C / min) to obtain white mesoporous γ-Al2O3 nanosphere powder. The average particle size D of the nanospheres was... core With a nm value of 100 nm, the BET specific surface area is approximately 280 m². 2 / g, mesopore size distribution concentrated in 3~8nm, pore volume V pore cm 3 / g is approximately 0.52 cm 3 / g.

[0102] Step b: ATRP initiator surface fixation.

[0103] The mesoporous alumina nanospheres (1.0 g) obtained in step a were dispersed in anhydrous toluene (100 mL) and sonicated for 30 min. 2-bromoisobutyryloxypropyltriethoxysilane (BibTES, 5 mmol) was added, and the mixture was refluxed at 90 °C for 24 h. After the reaction, the nanospheres were centrifuged, washed three times each with toluene and ethanol, and dried under vacuum at 60 °C for 12 h to obtain nanospheres with ATRP initiator immobilized on their surface. Thermogravimetric analysis (TGA) showed that the surface initiator density was approximately 0.6 mmol / g.

[0104] Step c: SI-ATRP growth of fluoropolymer brushes.

[0105] In a dry Schlenk flask, initiator-modified nanospheres (500 mg) obtained in step b, perfluoroalkyl ethyl acrylate monomer (PFEA, 10 mmol), CuBr (0.1 mmol), 2,2'-bipyridine (bpy, 0.2 mmol), and an ethanol / water mixed solvent (v / v = 1:1, 5 mL) were added. After degassing by three freeze-thaw cycles, argon gas was introduced, and the reaction was stirred at 50 °C for 16 h. After the reaction, the nanospheres were washed three times with ethanol / water (1:1) and dried under vacuum to obtain a core-shell hybrid liquid-retaining agent, denoted as mAl2O3@PFEA. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) characterization showed that the shell thickness t of the fluoropolymer brush was... shell The grafting density σ is approximately 28 nm, calculated using TGA combined with GPC. g chains / nm 2 Approximately 0.42 chains / nm 2 The number-average molecular weight (Mn) of the fluoropolymer brush is approximately 32,000 g / mol, and the molecular weight dispersion (PDI) is approximately 1.18. EDS and XPS analyses showed a fluorine content (mass fraction) of approximately 58%. The antioxidant potential of this fluoropolymer brush, determined by linear sweep voltammetry, is 5.1 V (relative to Li / Li). + The liquid retention efficiency factor Φ of this liquid retention agent is calculated using the formula Φ = (σ g × t shell × V pore ) / D core The calculated value of Φ is approximately 0.0612.

[0106] Step d: Preload functional additives.

[0107] A functional additive prepared by mixing vinylene carbonate (VC) and 1,3-propanesulfonic acid lactone (PS) in a mass ratio of 1:1 was dissolved in a small amount of dimethyl carbonate and impregnated with the mAl2O3@PFEA powder obtained in step c (total additive mass: liquid retainer mass = 3:10, i.e., preloading amount is about 23 wt%). After stirring at room temperature for 12 h, the solvent was evaporated under reduced pressure to obtain the additive preloading hybrid liquid retainer.

[0108] Preparation of high-voltage electrolyte: In an argon-atmospheric glove box (H2O < 0.5 ppm, O2 < 0.5 ppm), lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent of fluoroethylene carbonate (FEC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC) (volume ratio 1:1:1), with a lithium salt concentration of 1.0 mol / L. Then, the above-mentioned hybrid electrolyte retainer was added under stirring to a mass fraction of 3%, and ethylene carbonate (2% by mass of the total electrolyte) was added as a basic additive. Stirring was continued for 2 h to obtain the high-voltage electrolyte. Dynamic light scattering analysis showed that the average particle size (D50) of the electrolyte retainer was approximately 280 nm.

[0109] Preparation of the functionalized separator: A 16 μm thick polypropylene (PP) monolayer separator with a porosity of 50% was used as the base membrane. The above-mentioned liquid retaining agent and polyvinylidene fluoride (PVDF) binder were mixed at a mass ratio of 9:1, and an appropriate amount of N-methylpyrrolidone (NMP) was added to prepare a slurry. Gradient coating was performed on one side of the separator using a gravure coating process. The relative movement speed between the coating roller and the base membrane and the slurry supply were controlled to ensure a gradient distribution of the coating along the length of the base membrane, and the coating surface was brought close to the positive electrode side during winding. Specifically, corresponding to the position near the center region after the cylindrical battery was wound, the liquid retaining agent loading was designed to be 6.0 g / m³. 2 The load on the outermost layer of the Wouter is 4.0 g / m². 2 The ratio of Winner to Wouter was 1.5. After coating, the membrane was dried at 60°C to obtain a functionalized diaphragm. Testing showed that the functionalized diaphragm exhibited a longitudinal heat shrinkage rate of 6.5%, a transverse heat shrinkage rate of 7.2%, and a liquid absorption rate of 235% under conditions of 150°C for 30 min.

[0110] Battery assembly and testing: Positive electrode preparation: NCM811 positive electrode active material, conductive carbon black (Super-P), and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96:2:2, and NMP is used as a solvent to make a slurry. The slurry is coated on an aluminum foil current collector, and then dried, rolled, and cut to form a positive electrode sheet.

[0111] Negative electrode preparation: Artificial graphite, conductive carbon black, styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) are mixed in a mass ratio of 95:1:2:2, and water is used as a solvent to make a slurry. The slurry is coated on a copper foil current collector, and then dried, rolled, and cut to form a negative electrode sheet.

[0112] The above-mentioned positive electrode, negative electrode and functionalized separator are wound into a cylindrical cell, installed in a 21650 stainless steel shell, connected by full tab welding, injected with the above-mentioned high-voltage electrolyte, and after aging and formation, a 21650 cylindrical full tab lithium-ion battery is obtained.

[0113] See structural diagram Figure 1 The structure of the hybrid liquid retainer prepared in this invention can be seen from the results. Furthermore, TEM characterization shows a core diameter of approximately 100 nm, a shell thickness of approximately 28 nm, and a clear core-shell interface. XPS analysis shows an F / Al atomic ratio of 3.8. Dynamic contact angle testing revealed that the contact angle of deionized water increased from 11° for Al₂O₃ to 102° for Al₂O₃@PFEA, while the contact angle of FEC was only 14°, confirming the excellent affinity of the fluorinated shell for fluorinated solvents.

[0114] Electrochemical performance: After 500 cycles at 4.4 V, 45 °C, and 0.5 °C, the capacity retention was 83.2%, and the DCIR growth rate was 25.3%. LC-MS quantitative analysis of the VC concentration in the electrolyte supernatant showed a VC consumption rate of 31.2% after 500 cycles. No fire or explosion was observed during hot-box testing at 150 °C for 30 min. The electrolyte retention in the wound center region was improved by 35% compared to the uniform coating method.

[0115] Example 2 group This set of examples is used to verify the impact of changing the liquid retention efficiency factor Φ, mainly by changing the shell thickness t. shell nm and grafting density σ g chains / nm 2 To adjust the Φ value.

[0116] This set of embodiments is based on Embodiment 1, except that the shell grafting density σ is adjusted individually or in combination. g chains / nm 2 Shell thickness t shell nm, kernel pore volume V pore cm 3 / g and kernel particle size D core The liquid retention efficiency factor Φ is changed by nm, as shown in Table 1. The adjustment methods for each embodiment are as follows: Example 2a: The polymerization time was shortened to 6 h, so that t shell nm is approximately 10 nm, σ g chains / nm2 Approximately 0.20 chains / nm 2 At the same time, select pore volume V pore cm 3 / g is 0.40 cm 3 / g, Particle size D core nm has a 200nm core and a Φ value of approximately 0.004.

[0117] Example 2b: Referring to Example 1, t shell nm is controlled at 50 nm, while σ is adjusted. g chains / nm 2 Up to 0.53 chains / nm 2 At the same time, the pore volume V is selected. pore cm 3 / g is 0.60 cm 3 / g, Particle size D core nm is a 200nm core with a Φ value of approximately 0.08.

[0118] Comparative Example 2c: The polymerization time was set to 2 h to obtain an extremely thin shell. shell nm is approximately 3 nm, σ g chains / nm 2 Approximately 0.12 chains / nm 2 At the same time, the pore volume V is selected. pore cm 3 / g is 0.60 cm 3 / g, Particle size D core nm has a 60nm core and a Φ value of approximately 0.0036.

[0119] Comparative Example 2d: Extending the polymerization time to 32 h and increasing the amount of perfluoroalkyl ethyl acrylate monomer to 15 mmol resulted in a thicker shell. shell nm is approximately 50 nm, σ g chains / nm 2 Approximately 0.68 chains / nm 2 At the same time, the pore volume V is selected. pore cm 3 / g is 0.45 cm 3 / g, Particle size D core The nm core is 180nm, and the Φ value is approximately 0.085.

[0120] Example 3 Group This set of examples is used to verify the impact of changes in the preloading amount of functional additives in the adsorption-release unit.

[0121] This set of embodiments is based on Embodiment 1, except that the preloading amount of the functional additive is changed by adjusting the mass ratio of the functional additive to the liquid retaining agent in the impregnation solution, as detailed below: Example 3a: The preload was adjusted to 15% of the total mass of the liquid retainer.

[0122] Example 3b: The preload was adjusted to be 40% of the total mass of the liquid retainer.

[0123] Comparative Example 3c: The preload was adjusted to 10% of the total mass of the liquid retainer.

[0124] Comparative Example 3d: The preload was adjusted to 48% of the total mass of the liquid retainer.

[0125] Example 4 group This set of examples is used to verify the effect of changing the amount of electrolyte retainer added.

[0126] This set of embodiments is based on Embodiment 1, except that the mass fraction of the liquid retaining agent in the electrolyte is changed, as follows: Example 4a: The mass fraction of the liquid retainer in the electrolyte was adjusted to 1.0%.

[0127] Example 4b: The mass fraction of the liquid retainer in the electrolyte was adjusted to 5.0%.

[0128] Comparative Example 4c: The mass fraction of the liquid retainer in the electrolyte was adjusted to 0.5%.

[0129] Comparative Example 4d: The mass fraction of the liquid retainer in the electrolyte was adjusted to 7.0%.

[0130] Example 5 group This set of examples is used to verify the impact of changing the Winner / Wouter gradient coating ratio of the diaphragm.

[0131] This set of embodiments follows the same procedure as Embodiment 1, except that the loading amounts and their ratios between the inner and outer layers are changed by adjusting the coating process parameters, as detailed below: Example 5a: Adjust the coating parameters to make Winner 6 g / m 2 Wouter is 5 g / m 2 Winner / Wouter is approximately version 1.2.

[0132] Example 5b: Adjust the coating parameters to make Winner 10 g / m 2 Wouter is 5 g / m 2 Winner / Wouter is version 2.0.

[0133] Comparative Example 5c: A uniform coating method was used to control the liquid retention agent loading at all points on the diaphragm to be 5 g / m². 2 Winner / Wouter is close to version 1.0.

[0134] Comparative Example 5d: Adjust the coating parameters to achieve a Winner of 12 g / m². 2 Wouter is 4 g / m 2 Winner / Wouter is version 3.0.

[0135] Example 6 group This set of examples is used to verify the particle size D of the adsorption-release unit. core and pore volume V pore The impact of the changes.

[0136] This set of examples follows Example 1, except that the average particle size D of the mesoporous alumina nanospheres is changed by altering the molar ratio of the aluminum source to the structure-directing agent or the reaction conditions during hydrothermal synthesis. core nm and corresponding pore volume V pore cm 3 / g, as detailed below: Example 6a: D was prepared core Mesoporous alumina nanospheres with a diameter of approximately 70 nm have a corresponding pore volume V. pore cm 3 / g is approximately 0.45 cm 3 / g, specific surface area is approximately 310 m² 2 / g.

[0137] Example 6b: Preparation of D core Mesoporous alumina nanospheres with a diameter of approximately 170 nm have a corresponding pore volume V. pore cm 3 / g is approximately 0.60 cm 3 / g, specific surface area is approximately 225 m² 2 / g.

[0138] Comparative Example 6c: D was prepared core Mesoporous alumina nanospheres with a diameter of approximately 30 nm have a corresponding pore volume V. pore cm 3 / g is approximately 0.25 cm 3 / g, specific surface area is approximately 380 m² 2 / g.

[0139] Comparative Example 6d: D was prepared core Mesoporous alumina nanospheres with a diameter of approximately 250 nm have a corresponding pore volume V. pore cm 3 / g is approximately 0.65 cm3 / g, specific surface area is approximately 170 m² 2 / g.

[0140] Example 7 group This set of examples is used to verify the effect of the composition and fluorine content of the fluoropolymer brush on its performance.

[0141] This set of embodiments is based on Embodiment 1, except that the fluorinated monomer is replaced, as detailed below: Example 7a: The perfluoroalkyl ethyl acrylate monomer was replaced with an equimolar amount of perfluoroalkyl vinyl ether monomer, and a mixed solvent of N,N-dimethylformamide and water at a volume ratio of 3:1 was used as the reaction medium. The reaction was carried out at 60°C for 20 h. The resulting fluoropolymer brush had a fluorine content of approximately 65%, a number-average molecular weight (Mn) of approximately 41,000 g / mol, a PDI of 1.22, and a shell thickness (t). shell nm is approximately 25 nm, σ g The chains / nm² is approximately 0.45 chains / nm², and the Φ value is approximately 0.0585.

[0142] Example 7b: The monomer was replaced with a comonomer of vinylidene fluoride and perfluoroalkyl vinyl ether (molar ratio 3:1), and the reaction was carried out at 65°C for 24 h using dimethyl sulfoxide as solvent. The resulting copolymer brush had a fluorine content of approximately 42%, a number-average molecular weight (Mn) of approximately 38,000 g / mol, a PDI of 1.25, and a shell thickness (t). shell nm is approximately 30 nm, σ g The chains / nm² is approximately 0.40 chains / nm², and the Φ value is approximately 0.0624.

[0143] Comparative Example 7c: The fluorinated monomer was replaced with the non-fluorinated monomer methyl methacrylate for polymerization, yielding a polymethyl methacrylate polymer brush. Shell thickness t shell nm is approximately 32 nm, σ g The chains / nm² is approximately 0.45 chains / nm², the Φ value is approximately 0.0750, the fluorine content is 0%, and the antioxidant potential is 3.9 V.

[0144] Comparative Example 1 Following the preparation process of Example 1, steps (b) and (c) were omitted. The mesoporous γ-Al₂O₃ nanospheres obtained in step (a) were directly used for preloading functional additives in step (d), with the preloading amount controlled at 23%. They were then dispersed at a mass fraction of 3.0% in the same electrolyte as in Example 1. The separator was uniformly coated using the same base film as in Example 1, with a loading of 5 g / m³. 2This comparative example lacks a covalently grafted fluoropolymer brush shell layer, consisting only of an inorganic oxide core.

[0145] Comparative Example 8 Following the preparation process of Example 1, the porous core was omitted, and non-porous solid silica nanospheres (average particle size 100 nm) were directly used as the substrate. Fluoropolymer brushes of equal thickness were grown on their surface according to steps (b) and (c), but the pre-loading of additives in step (d) was omitted. The nanospheres were dispersed at a mass fraction of 3.0% in the same electrolyte as in Example 1. The separator was uniformly coated using the same base film as in Example 1, with a loading of 5 g / m³. 2 This comparative example lacks an adsorption-release unit with an internal porous structure and has no ability to preload and store functional additives.

[0146] Comparative Example 9 The same electrolyte solvent and lithium salt system as in Example 1 were used, but no hybrid electrolyte retainer was added. Only 2.0% by mass of vinylene carbonate was added to the electrolyte as a functional additive. The separator was an uncoated polypropylene separator with the same base membrane as in Example 1.

[0147] Table 1 Key parameters and test results of the examples and comparative examples The testing method is as follows: Capacity retention and DC internal resistance growth rate test: Using the LAND CT2001A battery testing system, the battery was charged to 4.4 V at a constant current and voltage of 0.5C in a constant temperature environment of 45℃, with a cutoff current of 0.05C. After resting for 10 minutes, it was discharged to 2.8 V at 0.5C, and the discharge capacity was recorded. After 500 cycles, the capacity retention rate was calculated as: (500th discharge capacity / First discharge capacity) × 100%. After each cycle, the DC internal resistance (DCIR) was measured, and the growth rate was calculated as: (500th DCIR - First DCIR) / First DCIR × 100%.

[0148] Functional additive consumption rate test: The electrolyte after 500 cycles was used to quantitatively analyze the residual amount of vinylene carbonate by gas chromatography-mass spectrometry (GC-MS). The consumption rate was calculated as (initial VC content - residual amount) / initial VC content × 100% based on the initial VC content. The average value of 5 batteries was taken for each set of data, and the error was controlled within ±3%.

[0149] As shown in Table 1, in Examples 1 to 2b, when the Φ value was in the range of 0.004 to 0.08, the capacity retention rate after 500 cycles was above 78%, the DC internal resistance growth rate did not exceed 32.1%, and the vinylene carbonate consumption rate did not exceed 38.5%. When the Φ value was below this range, such as in Comparative Example 2c where the Φ value was 0.0036, the shell was too thin, the interface self-repair was insufficient, the vinylene carbonate consumption rate increased to 60.5%, and the capacity retention rate decreased to 68.4%. When the Φ value was above this range, such as in Comparative Example 2d where the Φ value was 0.085, the shell was too thick, hindering lithium-ion transport, and the particles were prone to agglomeration, the DC internal resistance growth rate increased to 53.4%, and the capacity retention rate decreased to 62.3%. This indicates that limiting Φ to 0.004 to 0.08 is a reasonable window for balancing interface protection, sustained-release capacity, and ion transport.

[0150] When the preloading of functional additives is in the range of 15% to 40%, as in Examples 1, 3a, and 3b, the capacity retention is above 77%, and the vinylene carbonate consumption rate does not exceed 42.1%. When the preloading is as low as 10%, as in Comparative Example 3c, the additive reserve is insufficient, making it difficult to continuously replenish the interfacial film-forming components in the later stages of cycling. The vinylene carbonate consumption rate reaches 61.2%, and the capacity retention rate drops to 66.8%. When the preloading is as high as 48%, as in Comparative Example 3d, excess additive molecules clog the mesoporous channels, leading to uncontrolled slow-release kinetics. The initial explosive release exacerbates side reactions, and the vinylene carbonate consumption rate rises to 65.8%, while the capacity retention rate drops to 63.5%. This supports setting the preloading to 15% to 40%.

[0151] When the mass fraction of the electrolyte retention agent is between 1% and 5%, as in Examples 1, 4a, and 4b, the batteries all exhibit good cycle stability. When the mass fraction decreases to 0.5%, as in Comparative Example 4c, the nanoparticle concentration is insufficient to form a continuous fluorinated protective layer on the electrode surface, resulting in a DC internal resistance increase of 49.8% and a capacity retention rate decrease to 64.2%. When the mass fraction increases to 7%, as in Comparative Example 4d, the electrolyte viscosity increases significantly, the ionic conductivity decreases, leading to an increase in the vinylene oxide consumption rate to 67.2% and a decrease in the capacity retention rate to 61.8%. Therefore, a mass fraction of 1% to 5% for the electrolyte retention agent is preferable.

[0152] When the gradient coating ratio of the separator (Winner / Wouter) is in the range of 1.2 to 2.0, as in Examples 1, 5a, and 5b, the capacity retention is above 79%. With uniform coating, as in Comparative Example 5c where the Winner / Wouter ratio is close to 1.0, insufficient liquid retention in the central region results in a capacity retention rate of 74.8%. When the Winner / Wouter ratio increases to 3.0, as in Comparative Example 5d, the excessively thick inner coating leads to uneven separator thickness, excessive compression of the electrode in the central region after winding, deteriorating wetting conditions, and a capacity retention rate of 67.3%. This demonstrates that a gradient ratio of 1.2 to 2.0 can effectively compensate for the disadvantage of a long liquid phase conduction path in the central region of the winding.

[0153] Particle size D of the adsorption-release unit core For particles in the nm range of 50 to 200 nm, such as in Examples 1, 6a, and 6b, the particles exhibit good dispersion stability and sufficient pore volume, with capacity retention rates all exceeding 79%. When D core When the nm is too small, such as in the comparative example 6c, the surface energy is too high, leading to irreversible aggregation, low pore volume, poor sustained-release effect, and a capacity retention rate reduced to 68.5%. When D... core When the nm size is too large, up to 250 nm, as in Comparative Example 6d, gravity sedimentation causes uneven particle distribution, inconsistent interface protection effect, and capacity retention rate drops to 65.1%.

[0154] The composition of the fluoropolymer brush in the interface self-healing unit directly affects its antioxidant capacity and self-assembly film-forming performance. Poly(perfluoroalkyl ethyl acrylate) with a fluorine content of 58% and poly(perfluoroalkyl vinyl ether) with a fluorine content of 65% both exhibit high oxidation stability, as seen in Examples 1 and 7a, and can self-assemble to form a dense fluorinated protective layer on the electrode surface, resulting in excellent battery performance. When a copolymer is used to reduce the fluorine content to 42%, as in Example 7b, the antioxidant capacity still meets cycle requirements, but the density of the protective layer decreases slightly. When a non-fluorinated polymer is used, as in Comparative Example 7c, the shell undergoes oxidative decomposition under high voltage, failing to form a stable protective layer; the vinylene carbonate consumption rate rises to 72.4%, and the capacity retention drops to 60.3%. Therefore, a fluorine content of 40% to 75% in the fluoropolymer brush is necessary, and the antioxidant potential must be ≥4.8V.

[0155] Comparative Example 1 only has an exposed mesoporous alumina core, lacking a self-healing outer shell, and cannot form a fluorinated protective layer. Under high voltage, the electrolyte continues to oxidize and decompose, resulting in a vinylene carbonate consumption rate as high as 85.6%. Comparative Example 8 only has a fluoropolymer shell without a core adsorption and slow-release unit. Although it can form a film in the early stages, it lacks continuous replenishment of consumable additives, and the interfacial protection deteriorates significantly in the later stages of cycling. Comparative Example 9 is a conventional system without liquid retainer or gradient liquid retainer design, and its performance is the worst. This indicates that a core-shell structure that integrates adsorption and slow-release with interfacial self-healing functions is a necessary condition for achieving a long cycle life.

[0156] Based on the above embodiments and mechanism analysis, those skilled in the art can reasonably foresee that within the range of a liquid retention efficiency factor Φ of 0.004 to 0.08, an effective balance between shell protection and ion conduction can be achieved by adjusting the grafting density, shell thickness, pore volume, and particle size accordingly. For the range of pre-loading amounts of 15% to 40%, the mass fraction of the liquid retention agent in the electrolyte of 1% to 5%, and the gradient loading ratio of 1.2 to 2.0, the mechanism of action is consistent with the embodiments, and effective replenishment of the functional additives and interface stabilization can be expected. For intermediate value points not directly tested, given the continuous trend of the experimental data, it can be reasonably inferred that they can also achieve the purpose of this invention. Regarding the core material, in addition to mesoporous alumina, mesoporous silica, mesoporous titanium dioxide, and other mesoporous inorganic oxide nanospheres also possess high specific surface area, suitable pore size, and pore volume, providing sufficient storage and sustained-release space for functional additives. For fluoropolymer brushes, in addition to the fluoropolymers already exemplified, other fluoropolymers or copolymers with similar fluorine content and antioxidant potential can also be controllably grown using SI-ATRP technology and self-assembled on the electrode surface to form a fluorinated protective layer. For functional additives, besides the already used vinylene carbonate and 1,3-propanesulfonate lactone, vinyl sulfite, lithium difluorooxalate borate, and lithium oxalate borate also possess mature film-forming capabilities and, combined with a sustained-release mechanism, can continuously repair the interface. For the diaphragm base membrane, besides polypropylene, polyethylene, three-layer composite diaphragms, or polyimide nonwoven fabrics can all be used as carriers. For high-voltage solvent systems, in addition to the already used combinations of fluorinated carbonates and chain carbonates, sulfones or ionic liquids can also be used to construct systems with an antioxidant potential ≥4.8V. Therefore, the technical solution of this invention has reasonable predictability within the parameter range.

[0157] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0158] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0159] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A hybrid liquid retainer for cylindrical lithium-ion batteries, characterized in that, The hybrid liquid retainer includes: An adsorption-release unit, serving as a core layer, has an internal porous structure to accommodate functional additives. An interface self-healing unit serves as a shell layer and is attached to the surface of the adsorption and release unit; the interface self-healing unit comprises polymer segments capable of self-assembling to form a protective layer at the electrode and / or electrolyte interface; The polymer segment includes a fluoropolymer brush; The liquid retention efficiency factor Φ of the liquid retention agent satisfies: 0.004≤Φ≤0.08, and Φ = (σ g ×t shell ×V pore ) / D core , Where, σ g chains / nm 2 t is the grafting density of the interface self-healing unit; shell nm is the thickness of the interface self-healing unit; V pore cm 3 / g represents the pore volume of the adsorption and sustained-release unit; D core nm is the particle size of the adsorption-release unit.

2. The hybrid liquid-retaining agent according to claim 1, characterized in that, The grafting density σ of the interface self-healing unit g chains / nm 2 0.2~0.8 chains / nm 2 ; And / or, the thickness t of the interface self-healing unit shell nm is 10~50 nm; And / or, the pore volume V of the adsorption-release unit pore cm 3 / g is 0.4~0.6 cm 3 / g; And / or, the particle size D of the adsorption-release unit core nm is 50~200 nm.

3. The hybrid liquid-retaining agent according to claim 1, characterized in that, The porous structure of the adsorption and slow-release unit is preloaded with functional additives accounting for 15% to 40% of the total mass of the liquid-retaining agent. And / or, the hybrid liquid-retaining agent exists in the electrolyte in the form of a nano-dispersion, and its mass fraction in the electrolyte is 1% to 5%; And / or, the liquid retaining agent is loaded onto the surface of the battery separator in a gradient coating manner, so that the load decreases from the inside to the outside along the separator winding direction. The inner layer load (Winner) near the winding center and the outer layer load (Wouter) near the periphery satisfy: 1.2 ≤ Winner / Wouter ≤ 2.0; wherein the Winner is 4~10 g / m 2 The Wouter has a concentration of 2~6 g / m³. 2 .

4. The hybrid liquid-retaining agent according to any one of claims 1 to 3, characterized in that, The interface self-healing unit is a fluoropolymer brush covalently grafted onto the surface of the adsorption and slow-release unit; And / or, the antioxidant potential of the interface self-healing unit is ≥4.8 V; And / or, the adsorption-release unit comprises mesoporous inorganic oxide nanospheres, wherein the specific surface area of ​​the mesoporous inorganic oxide nanospheres is ≥200 m². 2 / g, pore size 3~8 nm, pore volume ≥0.4 cm³ 3 / g; And / or, the mesoporous inorganic oxide nanospheres are selected from at least one of mesoporous alumina nanospheres, mesoporous silica nanospheres, and mesoporous titanium dioxide nanospheres; And / or, the average particle size D50 of the liquid-retaining agent is ≤ 500 nm; And / or, the functional additive is selected from at least one of vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfite, lithium difluorooxalate borate, and lithium oxalate borate.

5. The hybrid liquid-retaining agent according to claim 4, characterized in that, The fluoropolymer brush is grown by surface-initiated atom transfer radical polymerization after the ATRP initiator is immobilized on the surface of the adsorption and slow-release unit, and has controllable grafting density and chain length. The ATRP initiator includes a bromoacyl triethoxysilane coupling agent; And / or, the number-average molecular weight of the fluoropolymer brush is 5,000~80,000 g / mol, and the molecular weight dispersion PDI is ≤1.35; And / or, the fluoropolymer brush is selected from at least one of poly(perfluoroalkyl ethyl acrylate) or its copolymer, poly(perfluoroalkyl vinyl ether) or its copolymer, poly(vinylidene fluoride-co-perfluoroalkyl vinyl ether) or its copolymer; And / or, the fluorine mass fraction in the fluoropolymer brush is 40%~75%.

6. A method for preparing a hybrid liquid-retaining agent according to any one of claims 1 to 5, characterized in that, Includes the following steps: A mesoporous inorganic oxide core is provided, the core having an internal porous structure to accommodate functional additives; The initiator is covalently immobilized on the surface of the core. Using the core immobilized with the initiator as a macromolecular initiator, surface-initiated polymerization is carried out on the surface of the core to grow a shell containing polymer chain segments, which serves as an interface self-healing unit. The polymer segments can self-assemble at the electrode and / or electrolyte interface to form a protective layer.

7. The preparation method according to claim 6, characterized in that, The specific process includes: (a) Prepare mesoporous inorganic oxide cores using a hydrothermal method or a sol-gel method; (b) Immobilization of ATRP initiator: The core nanospheres obtained in step (a) were added to ATRP initiator and refluxed at 80~100℃ for 12~48 h. After centrifugation and washing, they were vacuum dried. (c) SI-ATRP polymerization: Using fluorinated acrylate or vinyl ether monomers as monomers, Cu(I) / azaligand as catalytic system, and the core of the initiator immobilized in step (b) as the large initiator, SI-ATRP polymerization was carried out at 40~70℃ for 8~48 h under an inert atmosphere. After centrifugation and washing, the product was dried. (d) Functional additive preloading: The product obtained in step (c) is impregnated with a functional additive solution, and the solvent is evaporated after stirring at room temperature to obtain the hybrid liquid retainer.

8. An electrolyte, characterized in that, The electrolyte is used in lithium-ion batteries; it comprises lithium salt, a high-voltage solvent system, and a hybrid electrolyte retainer as described in any one of claims 1 to 5. The high-voltage solvent system is selected from at least one of fluorocarbonates, chain carbonates, sulfones, and ionic liquids; The high-voltage solvent system has an oxidation stability potential ≥4.8 V.

9. A diaphragm, comprising a base membrane and a coating loaded on the surface of the base membrane, characterized in that, The separator is used in a lithium-ion battery; the coating comprises a hybrid liquid-retaining agent as described in any one of claims 1 to 5; And / or, the base film is selected from at least one of polypropylene, polyethylene, PP / PE / PP three-layer composite membrane, and polyimide; And / or, the thickness of the base film is 12~40 μm, and the porosity is 40%~65%; And / or, the functionalized diaphragm has a longitudinal and transverse thermal shrinkage rate of ≤10% and a liquid absorption rate of ≥200% under the condition of 150℃ / 30 min.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte includes the electrolyte according to claim 8; And / or, the diaphragm comprises the diaphragm of claim 9.

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