Battery cell and method for producing a battery cell, battery device and energy storage device

Abstract

The application relates to the field of batteries, and provides a battery monomer, a preparation method of the battery monomer, a battery device and an energy storage device. The battery monomer comprises: an electrode core assembly, the electrode core assembly comprises a negative electrode sheet, a diaphragm and a positive electrode sheet which are arranged in a stack; a shell, the electrode core assembly is located in the shell; and an electrolyte, the electrolyte is located in the shell. An interface layer is attached to a side surface of the diaphragm facing the negative electrode sheet, and the interface layer comprises a polymer matrix and two-dimensional organic nanosheets. In the application, a two-dimensional organic nanosheet and a polymer composite functional interface layer are constructed on one side of the porous diaphragm close to the negative electrode sheet. Through the synergistic effect of space screening and chemical coordination, pre-desolvation and selective conduction of lithium ions are realized, the negative electrode interface kinetics under the condition of rapid charging is improved, and solvent co-intercalation and lithium precipitation are inhibited.

Description

Technical Field

[0001] This application relates to the field of batteries, and in particular to a battery cell and its preparation method, battery device and energy storage device. Background Technology

[0002] The fast-charging capability of lithium-ion batteries is a key performance indicator determining their application in electric vehicles and energy storage systems. However, high-rate fast charging poses severe challenges to battery materials and interfacial processes, with the interfacial dynamics of graphite anodes becoming a major bottleneck. Although graphite anodes have advantages such as moderate theoretical capacity, low and stable lithium intercalation potential, and good cycle stability, they exhibit significant limitations under fast-charging conditions. Summary of the Invention

[0003] This application provides a battery cell and its preparation method, battery device and energy storage device, which are at least beneficial to improving the negative electrode interface dynamics under fast charging conditions.

[0004] In a first aspect, this application provides a battery cell, comprising: A battery cell assembly, the battery cell assembly comprising a negative electrode, a separator and a positive electrode stacked together; The housing, in which the battery cell assembly is located; Electrolyte, which is located inside the housing; An interface layer is attached to the side of the separator facing the negative electrode, the interface layer comprising a polymer matrix and two-dimensional organic nanosheets.

[0005] Optionally, the dry film thickness of the interface layer is 0.1 μm to 1 μm.

[0006] Optionally, the polymer matrix has a mass fraction of 20% to 80%, the two-dimensional organic nanosheets have a mass fraction of 20% to 80%, and the sum of the mass percentages of the polymer matrix and the two-dimensional organic nanosheets is 100%.

[0007] Optionally, the two-dimensional organic nanosheets are arranged in a direction parallel to the surface of the membrane, with a sheet spacing of 0.6 nm to 2 nm.

[0008] Optionally, the thickness of the two-dimensional organic nanosheets does not exceed 10 nm, and the lateral dimensions are 50 nm to 5 μm.

[0009] Optionally, the two-dimensional organic nanosheets include at least one of functionalized graphene nanosheets, functionalized graphene oxide nanosheets, functionalized covalent organic framework nanosheets, functionalized aromatic polyimide nanosheets, and functionalized layered polymer nanosheets, wherein the functionalized graphene nanosheets, functionalized graphene oxide nanosheets, functionalized covalent organic framework nanosheets, functionalized aromatic polyimide nanosheets, and functionalized layered polymer nanosheets all contain polar functional groups.

[0010] Optionally, the polar functional group includes at least one selected from sulfonylimide, cyano, and etheroxy groups.

[0011] Optionally, the polymer matrix includes a crosslinked polymer containing ethylene glycol segments or ether oxygen segments.

[0012] Optionally, the crosslinked polymer includes at least one of crosslinked polyarylethers containing polyethylene glycol segments, polyurethanes containing ether oxygen units, and crosslinked polyesters containing ethylene glycol segments.

[0013] Optionally, the membrane has a porosity of 30% to 50% and / or a pore size of 50 nm to 200 nm.

[0014] Optionally, the membrane includes at least one of a single-layer polyolefin membrane and a multilayer composite polyolefin membrane.

[0015] Secondly, this application provides a method for preparing a battery cell as described above, comprising: A battery cell assembly is provided, the battery cell assembly comprising a negative electrode, a separator and a positive electrode stacked together; A housing is provided to house the battery cell assembly within the housing; Provide electrolyte and inject the electrolyte into the housing; A formation process is performed to obtain battery cells; An interface layer is attached to the side of the separator facing the negative electrode, the interface layer comprising a polymer matrix and two-dimensional organic nanosheets.

[0016] Optionally, the method for preparing the interface layer includes: Two-dimensional organic nanosheet dispersions and polymer solutions are available. The two-dimensional organic nanosheet dispersion and the polymer solution are mixed to obtain a composite slurry; The composite slurry is coated onto one side of the diaphragm and then dried.

[0017] Optionally, the solid content of the two-dimensional organic nanosheet dispersion is 0.5% to 5%.

[0018] Optionally, the preparation method of the two-dimensional organic nanosheets includes solution exfoliation, shear exfoliation, or ultrasonic-assisted exfoliation.

[0019] Optionally, the polymer solution has a mass fraction of 2% to 10%.

[0020] Optionally, after the drying step, a hot pressing step is also included, wherein the conditions for the hot pressing are: temperature of 60℃~100℃ and pressure of 0.1MPa~1MPa.

[0021] Thirdly, this application provides a battery device comprising a battery cell as described above, or a battery cell obtained by the method for preparing the battery cell as described above, wherein the battery device comprises one or more of a battery module, a battery pack, and an energy storage battery.

[0022] Fourthly, this application provides an energy storage device, which includes a battery device as described above, the battery device being used to store electrical energy.

[0023] The energy storage device includes a battery pack, which includes multiple batteries, an energy management system (EMS), a battery management system (BMS), and an energy storage converter (PCS).

[0024] The technical solution provided in this application has at least the following advantages: This application constructs a two-dimensional organic nanosheet and polymer composite functional interface layer on the side of a porous separator near the negative electrode. Through the synergistic effect of spatial sieving and chemical coordination, it achieves pre-desolvation and selective conduction of lithium ions, improving the negative electrode interface kinetics under fast charging conditions and suppressing solvent co-intercalation and lithium deposition. This application is particularly suitable for high-rate rechargeable battery systems employing graphite or graphite-silicon-carbon composite negative electrodes.

[0025] This application also facilitates the realization of high capacity in battery cells, making it suitable for long-term energy storage applications, such as energy storage systems that can operate continuously for 4 to 8 hours at rated power. Attached Figure Description

[0026] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the drawings in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A flowchart corresponding to the method for preparing a single battery cell provided in the embodiments of this application; Figure 2This is a schematic diagram of the structure of the battery device provided in the embodiments of this application; Figure 3 for Figure 2 A schematic diagram of its breakdown.

[0028] In the diagram: 100, battery assembly; 10, housing; 20, individual battery cell; 11, first part; 12, second part. Detailed Implementation

[0029] As the background technology indicates, the current fast-charging problem of graphite anodes stems from their lithium intercalation kinetics. Lithium ions entering graphite from the electrolyte undergo multiple consecutive steps, including bulk migration, passage through the solid electrolyte interface film, desolvation, interfacial charge transfer, interlayer and intralayer diffusion. At conventional rates, these steps are relatively synchronized, but under fast-charging conditions above 4C, desolvation and interfacial charge transfer become the rate-controlling factors. In carbonate-based electrolytes, lithium ions and solvent molecules form a solvation shell through coordination bonds, typically a coordination cluster containing about 3-4 carbonate molecules. These solvent molecules must be removed before lithium ions can intercalate into graphite, because the interlayer spacing of graphite is only about 0.335 nm, which cannot accommodate lithium ions with a complete solvation shell.

[0030] At high current densities, the desolvation rate may not keep up with the lithium intercalation demand, leading to two problems: first, the accumulation of lithium ion concentration at the interface increases concentration polarization, lowers the negative electrode potential, and causes lithium plating when it falls below the lithium deposition potential; second, some incompletely desolvated lithium ions may forcibly intercalate, resulting in solvent co-intercalation. Solvent co-intercalation causes the graphite interlayer spacing to expand from approximately 0.335 nm to 0.5 nm to 0.7 nm or even larger, causing carbon layer stripping, structural collapse, and irreversible capacity loss. Furthermore, the rapid and uneven growth of the solid electrolyte interfacial film under fast-charging conditions further increases interfacial impedance, exacerbating polarization and the risk of lithium plating, creating a vicious cycle.

[0031] The root cause of these problems lies in the mismatch between the solvation structure of lithium ions and the requirements for lithium intercalation in graphite, as well as the imbalance of interfacial dynamics under fast charging conditions. Therefore, regulating the solvation state and transport process of lithium ions from the perspective of interface engineering has become an important technical approach to improve the fast charging performance of graphite anodes.

[0032] To optimize the fast-charging performance of graphite anodes, the industry mainly focuses on two aspects: electrolyte modification and membrane functionalization.

[0033] Electrolyte additive technology involves adding functional small molecules, such as fluoroethylene carbonate and vinylene carbonate, to the base electrolyte. These molecules preferentially reduce and decompose at the negative electrode surface to form a solid electrolyte interfacial film. These additives can improve the composition and density of the interfacial film, enhancing lithium-ion conductivity and mechanical stability. However, the additives primarily function in the film-forming chemical process, having limited impact on the desolvation stage during lithium-ion transport from the bulk electrolyte to the negative electrode. Furthermore, the additives are uniformly distributed throughout the electrolyte, lacking targeted functionalization of the negative electrode interface, and are consumed rapidly, with their effectiveness diminishing after long cycles.

[0034] Membrane coating technology involves coating the surface of commercial polyolefin membranes with functional materials to improve performance. Ceramic coatings, using inorganic particles such as alumina and silica, primarily enhance thermal stability and mechanical strength, preventing membrane shrinkage or breakage at high temperatures. However, ceramic particles themselves do not conduct lithium ions; the coating mainly relies on interparticle gaps to maintain ion channels, lacking the ability to actively regulate solvation structures and desolvation processes. Graphene oxide coatings utilize the two-dimensional layered structure and oxygen-containing functional groups on the surface of graphene, providing certain mechanical strength and flame retardancy. However, graphene oxide has relatively low ionic conductivity, and its selective lithium-ion conduction and desolvation functions have not yet been systematically developed. Metal-organic framework (MOF) coatings utilize the regular pore structure of MOFs to achieve ion sieving. However, the chemical stability of MOFs in carbonate electrolytes presents challenges, and MOF coatings are typically composed of powdered particles, lacking a oriented two-dimensional layered structure.

[0035] Solid-state or quasi-solid-state electrolyte technology replaces liquid electrolytes with solid or gel electrolytes, fundamentally eliminating the solvent co-intercalation problem. However, solid-state electrolytes face challenges such as high interfacial impedance, poor low-temperature performance, and high manufacturing costs. Currently, they are mainly explored in small batteries and high-end applications, and have not yet been commercialized in large-scale fast-charging power batteries.

[0036] While the industry has made some progress in improving the fast-charging performance of graphite anodes, there are limitations in terms of targeting, effectiveness, and engineering, especially the lack of a systematic technical solution to achieve pre-solubilization and selective conduction through a structured interface layer before lithium ions reach the anode surface.

[0037] Despite various attempts by industry researchers to optimize fast charging of graphite anodes, the following inherent problems and unresolved technical challenges remain in practical applications: First, electrolyte additives have limited ability to regulate the desolvation process. Additives such as fluoroethylene carbonate mainly affect interfacial kinetics indirectly by improving the composition and properties of the solid electrolyte interfacial film, but they lack direct control over the solvation state of lithium ions before reaching the negative electrode surface. Under fast charging conditions, lithium ions with intact solvation shells still reach the negative electrode interface in large quantities, making desolvation the rate-controlling step, a bottleneck that additives cannot fundamentally solve. Furthermore, additives are uniformly distributed in the electrolyte, lacking spatial selectivity, and are gradually consumed with cycling, resulting in unstable long-term effects.

[0038] Secondly, ceramic membrane coatings lack ion-selective conductivity. Alumina, silica, and other ceramic materials themselves do not conduct ions; the ion transport in the coating primarily relies on the pore channels between particles. These channels are not selective for lithium ions, anions, and solvent molecules, making it impossible to control the solvation structure. While ceramic coatings improve the thermal stability and mechanical strength of the membrane, their effect on improving fast-charging kinetics is limited, particularly lacking an effective mechanism for reducing concentration polarization and suppressing solvent co-intercalation.

[0039] Third, the ionic conductivity and functional design of graphene oxide coatings are insufficient. Although graphene oxide has a two-dimensional layered structure and oxygen-containing functional groups on its surface, its ionic conductivity is relatively low, typically around 10. -5 S / cm~10 -4 The S / cm range can become a bottleneck for lithium transfer during high-rate charging. Furthermore, the carboxyl and hydroxyl groups on the surface of graphene oxide are primarily used to improve dispersibility and mechanical strength; their selective coordination of lithium ions and desolvation induction functions have not yet been systematically optimized. The interlayer spacing and orientation of graphene oxide also lack precise control, making it difficult to achieve fine sieving of the solvated shell.

[0040] Fourth, there are issues with the stability and structural continuity of metal-organic framework (MOF) coatings. While MOFs possess regular channels that allow for size sieving, most MOF materials exhibit limited chemical stability in carbonate electrolytes, potentially leading to hydrolysis or ligand exchange. MOF coatings typically exist in particulate form, with the particle packing lacking a directional two-dimensional layered structure, resulting in tortuous ion transport paths and high impedance. Furthermore, although the pore structure of MOFs is regular, its flexibility is limited, making it difficult to adapt to volume changes and stresses during battery charging and discharging.

[0041] Fifth, the interfacial impedance and engineering challenges of solid-state electrolytes. While solid or quasi-solid-state electrolytes can fundamentally avoid solvent co-intercalation, the contact impedance at the solid-solid interface is typically much higher than that at the liquid-solid interface, severely limiting fast-charging capabilities. The manufacturing process of solid-state electrolytes is complex and costly, and achieving uniformity and consistency in large-size batteries presents significant technical challenges.

[0042] Finally, the industry lacks a systematic design for pre-desolution at the interface level. Neither electrolyte additives nor separator coatings have been able to achieve a synergistic pre-desolution function of "spatial sieving + chemical coordination" through a structured interface layer before lithium ions reach the graphite surface. Such a functional interface layer should simultaneously possess selective lithium-ion conduction, regulation of the solvation shell, and sufficient ionic conductivity, areas where the industry has significant gaps.

[0043] In summary, although researchers in the industry have explored different directions, there are significant limitations in terms of relevance, effectiveness, and engineering feasibility. There is an urgent need to develop new interface engineering technologies to systematically solve the fast-charging bottleneck of graphite anodes from the perspective of solvation structure regulation.

[0044] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0045] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0046] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0047] In the description of the embodiments of this application, when a component "includes" another component, other components are not excluded unless otherwise stated, and other components may be further included. Furthermore, when a component such as a layer, film, region, or plate is referred to as being "on / located" on another component, it can be "directly on" the other component (i.e., located on the surface of the other component with no other components between them), or another component may be present therein. Moreover, when a component such as a layer, film, region, or plate is "directly located" on another component, or when a component such as a layer, film, region, or plate is located on the surface of another component, it indicates that no other components are located therein.

[0048] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the term "part" is also intended to include the plural form unless the context clearly indicates otherwise. Components include layers, films, regions, or plates, etc.

[0049] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0050] In a first aspect, this application provides a battery cell, comprising: A battery cell assembly, the battery cell assembly comprising a negative electrode, a separator and a positive electrode stacked together; The housing, in which the battery cell assembly is located; Electrolyte, which is located inside the housing; An interface layer is attached to the side of the separator facing the negative electrode, the interface layer comprising a polymer matrix and two-dimensional organic nanosheets.

[0051] This application constructs a two-dimensional organic nanosheet and polymer composite functional interface layer on the side of a porous membrane near the negative electrode. Through the synergistic effect of spatial sieving and chemical coordination, it achieves pre-desolvation and selective conduction of lithium ions, improving the negative electrode interface kinetics under fast charging conditions and suppressing solvent co-intercalation and lithium deposition. This application is particularly applicable to high-rate rechargeable battery systems using graphite or graphite-silicon-carbon composite negative electrodes, as well as fast-charging lithium-ion batteries incorporating this functional interface layer.

[0052] The interface layer is coated only on the side of the separator facing the negative electrode, while the other side remains in its original state or is coated with a conventional coating. This asymmetrical design allows the interface regulation function to be precisely applied to the negative electrode side, while simplifying the process and reducing costs.

[0053] When lithium ions cross this interface layer during transport from the bulk electrolyte to the negative electrode, the following synergistic effects occur: polar functional groups form moderate coordination interactions with lithium ions, inducing partial dissociation of solvent molecules in the solvation shell; the interlayer spacing creates steric hindrance for lithium ions with complete solvation shells (effective size approximately 1.0 nm to 1.5 nm) and free solvent molecules, while having little effect on the transport of smaller, partially desolvated lithium ions; the interface layer suppresses anion transport more strongly than lithium ion transport, significantly increasing the lithium ion transport number from approximately 0.3 to 0.4 in the bulk electrolyte to approximately 0.6 to 0.8. Through this mechanism, lithium ions undergo partial desolvation before reaching the graphite surface, reducing the number of solvent molecules in the solvation shell from approximately 3 to 4 to approximately 1 to 2, thereby reducing the risk of solvent co-intercalation. Simultaneously, the high lithium ion transport number can also reduce concentration polarization and mitigate the tendency for lithium plating.

[0054] Although the introduction of the interface layer will increase interfacial contact impedance to some extent, mechanisms such as increasing lithium-ion transferability to reduce concentration polarization impedance, pre-desolution to reduce interfacial charge transfer impedance, controlling the coating thickness to make the increase in ohmic impedance controllable, and the polymer matrix providing an effective conduction pathway can reduce or maintain the overall polarization level within an acceptable range under fast charging conditions, thereby achieving stable charging at higher rates. This application is compatible with existing electrolyte additives and battery structures, has moderate process implementation difficulty, and has good prospects for engineering applications.

[0055] Optionally, the dry film thickness of the interface layer is 0.1μm to 1μm, specifically 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, or any two of these thicknesses, such as 0.2μm to 0.6μm.

[0056] When the thickness is less than approximately 0.1 μm, the coating is not continuous and complete enough, limiting its functionality. When the thickness exceeds approximately 1.0 μm, although the functionality is enhanced, the interfacial impedance increases significantly, and the material cost rises. Within the thickness range of 0.2 μm to 0.6 μm, the interfacial layer remains continuous, dense, and flexible after being wetted by the electrolyte, and will not crack or detach due to volume changes during battery charging and discharging. The porosity of the interfacial layer mainly originates from the interlayer channels between nanosheets and the ion conduction pathways of the polymer matrix, maintaining good wettability to the electrolyte overall.

[0057] The coating area of ​​the interface layer is typically equal to or slightly larger than the electrode area, ensuring complete coverage within the electrode region. The adhesion between the coating process and the separator substrate is achieved through the adhesion of the polymer matrix and mild thermo-pressing, ensuring that the interface layer does not delaminate or peel during battery assembly and use. This asymmetric separator design with single-sided coating requires attention to orientation during assembly, ensuring that the functional interface layer faces the negative electrode.

[0058] Optionally, the polymer matrix has a mass fraction of 20% to 80%, the two-dimensional organic nanosheets have a mass fraction of 20% to 80%, and the sum of the mass percentages of the polymer matrix and the two-dimensional organic nanosheets is 100%.

[0059] Further optionally, the polymer matrix has a mass fraction of 30% to 70%, and the two-dimensional organic nanosheets have a mass fraction of 30% to 70%.

[0060] The mass ratio of two-dimensional organic nanosheets to the polymer matrix has a significant impact on the performance of the interfacial layer. When the nanosheet content is too low, the layer stacking is not dense enough, weakening spatial sieving and coordination functions; when the nanosheet content is too high, the coating becomes brittle, reducing mechanical integrity and adhesion to the membrane, and the reduced ion conduction pathways provided by the polymer may increase impedance. At the ratios provided in this application, the nanosheets provide the main functionality, while the polymer provides the necessary structural support and conduction pathways, working synergistically to achieve optimal overall performance.

[0061] Optionally, the two-dimensional organic nanosheets are arranged in a direction parallel to the surface of the membrane, with a sheet spacing of 0.6 nm to 2 nm.

[0062] By arranging nanosheets in a parallel orientation to form a microchannel structure with controllable interlayer spacing, and combining this with the appropriate coordination of lithium ions by polar functional groups, partial desolvation of lithium ions occurs as they pass through the interface layer. This reduces the number of solvent molecules in the solvated shell, thereby suppressing solvent co-intercalation at its source. Simultaneously, by increasing the lithium ion transference number and suppressing anion transport, concentration polarization is reduced, mitigating the tendency for lithium plating. The aim is to achieve the technical goals of significantly improving the stability of the negative electrode interface, extending cycle life, and enhancing safety under high-rate charging conditions.

[0063] One of the core functions of the interface layer is to spatially sieve the solvation shell through the interlayer spacing of two-dimensional organic nanosheets. After the two-dimensional organic nanosheets are stacked in the interface layer, the effective distance between the layers is controlled within the range of approximately 0.6 nm to 2 nm. This size window is chosen based on the size characteristics of the lithium-ion solvation shell. Lithium ions with complete solvation shells (such as [Li(EC)]) 3-4 ] +The effective size of lithium ions is approximately 1.0 nm to 1.5 nm, while partially desolvated lithium ions (such as [Li(EC)]) have a smaller effective size. 1-2 ] + The size of the ions is approximately 0.7 nm to 1.0 nm, and the ionic radius of bare lithium ions is approximately 0.076 nm. When the interlayer spacing is approximately 0.6 nm to 2 nm, it creates certain spatial and energy steric hindrance for lithium ions and free solvent molecules in the complete solvated shell, while having little impact on the transport of partially desolvated lithium ions, thereby achieving selective sieving.

[0064] Optionally, the thickness of the two-dimensional organic nanosheets does not exceed 10 nm, and the lateral dimensions are 50 nm to 5 μm. Specifically, the lateral dimensions can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 200 nm, 500 nm, 600 nm, 800 nm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm.

[0065] Optionally, the two-dimensional organic nanosheets include at least one of functionalized graphene nanosheets, functionalized graphene oxide nanosheets, functionalized covalent organic framework nanosheets, functionalized aromatic polyimide nanosheets, and functionalized layered polymer nanosheets, wherein the functionalized graphene nanosheets, functionalized graphene oxide nanosheets, functionalized covalent organic framework nanosheets, functionalized aromatic polyimide nanosheets, and functionalized layered polymer nanosheets all contain polar functional groups.

[0066] Graphene and its derivatives have a natural layered structure, making them easy to prepare nanosheets through oxidation-exfoliation or liquid-phase exfoliation.

[0067] The core function of two-dimensional organic nanosheets is to selectively coordinate lithium ions with polar functional groups, inducing partial desolvation, while simultaneously utilizing the layered structure to form controllable spatial channels for sieving the solvation shell. Therefore, nanosheet materials should meet the following requirements: they should be peelable into sheets with a thickness of less than about 10 nm, contain or be able to introduce polar functional groups on their surface, be chemically stable in carbonate electrolytes, and possess certain mechanical strength and flexibility.

[0068] Optionally, the polar functional group includes at least one selected from sulfonylimide, cyano, and etheroxy groups.

[0069] These polar groups endow nanosheets with selective coordination ability for lithium ions, while retaining the high mechanical strength and good electrochemical stability of graphene. For example, the sulfonylimide group (-SO2-NH-SO2-) is a preferred modifying group due to its strong polarity and affinity for lithium ions; the ether oxygen segment (-O-(CH2)) n -O-) can provide flexible coordination sites and enhance compatibility with the polymer matrix.

[0070] The structural characteristics of the modified two-dimensional organic nanosheets meet the following requirements. Taking graphene or graphene oxide nanosheets after surface functionalization modification as an example, their structural characteristics are as follows: (1) Basic structure: The two-dimensional carbon skeleton structure of graphene / graphene oxide remains intact, preserving its excellent mechanical strength and chemical stability.

[0071] (2) Functional group connection method: Polar functional groups are connected to the edge sites or surface defect sites of the carbon skeleton by covalent bonds (such as CS bonds, CN bonds or CO bonds) in a grafting manner. Unlike the "planar doping" modification in the industry that replaces carbon atoms with heteroatoms (such as N, B, S) and embeds them into the lattice plane, the polar functional groups in this application extend out of the nanosheet plane in the form of large-volume side groups to form a three-dimensional configuration.

[0072] (3) Typical functional group structure: - Sulfonylimide modification: Linked via -C-SO2-NH-SO2-R, where the sulfonylimide group has strong polarity and large steric hindrance; -Cyano modification: Provides a strongly polar site via a -C-CN bond; -Ether oxide chain modification: via -CO-(CH2) n -O- form connection provides flexible coordination chain segments.

[0073] (4) Stereoscopic effect of functional groups: These large-volume functional groups act as "molecular pillars" when nanosheets are stacked, maintaining the effective spacing between nanosheets through steric hindrance, preventing interlayer collapse or excessive swelling after electrolyte wetting, thereby stably maintaining sieve channels of 0.6 nm to 2 nm. This steric support effect cannot be achieved by planar atomic doping.

[0074] (5) Functional group density: The density of surface polar functional groups is moderate, ensuring sufficient coordination sites without excessively damaging the overall structure and conductivity of the nanosheets. In some embodiments, the functional group distribution makes the nanosheet surface partially hydrophilic, which is beneficial for electrolyte wetting and lithium ion transport.

[0075] Optionally, the polymer matrix includes a crosslinked polymer containing ethylene glycol segments or ether oxygen segments.

[0076] Optionally, the crosslinked polymer includes at least one of crosslinked polyarylethers containing polyethylene glycol segments, polyurethanes containing ether oxygen units, and crosslinked polyesters containing ethylene glycol segments.

[0077] Functions of the polymer matrix: The polymer matrix plays multiple roles in the interfacial layer, including bonding nanosheets to form a continuous coating, providing flexibility and mechanical integrity, enhancing adhesion to the membrane substrate, and providing lithium-ion conduction pathways. Therefore, the polymer matrix should possess a certain degree of lithium-ion conductivity, good flexibility, chemical stability with the carbonate electrolyte, and appropriate adhesion.

[0078] This application uses crosslinked polymers containing ethylene glycol segments or ether oxygen segments as the matrix. Typical materials include crosslinked polyarylethers containing polyethylene glycol segments, polyurethanes containing ether oxygen units, and those containing -O-(CH2CH2O). n - Crosslinked polyesters and other polymers. The ether oxygen segments of these polymers can undergo weak coordination interactions with lithium ions, providing a certain degree of ion conductivity. Simultaneously, the flexible segments impart good mechanical flexibility to the coating, enabling it to adapt to volume changes during battery charging and discharging. The degree of crosslinking of the polymer needs to be appropriately controlled; excessive crosslinking reduces ion conductivity and flexibility, while insufficient crosslinking results in insufficient mechanical strength and solvent stability. An optimal crosslinking density ensures that the polymer maintains its three-dimensional network structure without excessive swelling or dissolution after being immersed in the electrolyte.

[0079] Optionally, the membrane porosity is 30%~50%, specifically 30%, 35%, 40%, 45%, 50%, and / or the pore size is 50nm~200nm, specifically 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm.

[0080] Optionally, the membrane includes at least one of a single-layer polyolefin membrane and a multilayer composite polyolefin membrane.

[0081] Optionally, the membrane substrate may be a commercially available product such as a single-layer polypropylene, a single-layer polyethylene, or a polypropylene / polyethylene / polypropylene three-layer composite membrane.

[0082] The composite of two-dimensional organic nanosheets with an ion-conducting polymer matrix and its synergistic effect in lithium-ion transport are as follows: (1) Composite method: -Recombination mainly occurs through intermolecular forces, including hydrogen bonds, van der Waals forces, and electrostatic interactions. - The polar functional groups on the surface of nanosheets (such as -SO2-NH-SO2-, -CN, -O- segments, etc.) can interact with the ether oxygen segments (-O-(CH2CH2O) in the polymer matrix. n -) Formation of hydrogen bond networks, - An optional physical composite method can be used to maintain the flexibility of the interface layer and its adaptability to volume changes. - In some embodiments, mechanical stability can be further enhanced by forming a small number of covalent crosslinking points between the nanosheets and the polymer using a bifunctional crosslinking agent (such as an epoxy-containing compound), but this is not necessary.

[0083] (2) Synergistic conduction mechanism: The polymer matrix not only plays a binding role, but more importantly, it participates in the "coordination relay conduction" of lithium ions: -Ether oxygen segment (-O-(CH2CH2O)) n The oxygen atom in the -) can form a coordinate bond with the lithium ion. - When solvated lithium ions enter the interface layer, the ether oxygen groups on the polymer segments competitively replace some of the carbonate molecules in the solvated shell through coordination. This ligand exchange process between solvent molecules and polymer segments promotes the partial desolvation of lithium ions. Lithium ions are transported along polymer chain segments in a "jumping" manner, with the ether oxygen group acting as a relay baton. This solid-liquid hybrid conduction mechanism differs from the traditional membrane coating where the polymer acts only as an inert binder.

[0084] (3) Spatial distribution: The nanosheets are uniformly dispersed in the polymer matrix. By controlling the nanosheet content and orientation, the interlayer spacing is determined by the stacking density of the nanosheets and the filling of the polymer and maintained within the target range (0.6nm~2nm).

[0085] In bulk carbonate electrolytes, lithium ions typically form a first solvation shell with about 3-4 solvent molecules such as ethylene carbonate or methyl ethyl carbonate, forming a layer like [Li(EC)]. 3-4 ] + Or [Li(EC)2(EMC)2] + Isocoordinate clusters. When solvated lithium ions enter the interface layer and pass through the interlayer channels between nanosheets, the following processes occur: Polar functional groups in the interface layer (such as sulfonylimide, cyano, etheroxy groups, etc.) form moderate coordination interactions with lithium ions. Although this coordination is not as stable as carbonates, it is sufficient to have an impact on lithium ion transport. Under the combined effect of polar group coordination and steric confinement, some solvent molecules in the solvation shell are induced to dissociate, and the solvation state of lithium ions changes from about 3-4 coordination to about 1-2 coordination in a partially solvated state. At the same time, polar functional groups in the interface layer may temporarily participate in the coordination of lithium ions, forming a transitional coordination environment, i.e., [Li(ligand)(solvent)]. 1-2 Mixed coordination clusters, etc.

[0086] The reconstruction of this solvation shell is a dynamic and reversible process, not a complete trapping of lithium ions in the interface layer. After lithium ions pass through the interface layer, their solvation state changes significantly, and the number of solvent molecules they carry upon reaching the graphite surface is greatly reduced, thus lowering the risk of solvent co-intercalation. It is important to emphasize that this application does not aim for complete desolvation, as fully exposed lithium ions would undergo strong coordination with the interface layer, hindering transport. Instead, it achieves a balance between reducing the risk of co-intercalation and maintaining sufficient conductivity through "partial desolvation" or "thinning of the solvation shell."

[0087] The spatial dimensions of approximately 0.6 nm to 2 nm between the interlayer layers create differentiated transport resistance for species of different sizes. Lithium ions with complete solvation shells (effective diameter approximately 1.0 nm to 1.5 nm) and free solvent molecules (diameter approximately 0.5 nm) encounter significant steric hindrance and energy barriers when entering and passing through interlayer channels, thus inhibiting transport to some extent. In contrast, partially desolvated lithium ions, due to their smaller size, can pass through interlayer channels more easily. This size-selective spatial sieving, combined with the synergistic effect of chemical coordination of polar functional groups, jointly drives the solvation shell reconstruction of lithium ions in the interfacial layer.

[0088] The selection of the interlayer spacing from 0.6 nm to 2 nm is based on the critical matching relationship between the lithium-ion solvated shell size and the spatial sieving effect: (1) Solvation shell size: -In carbonate electrolytes, fully solvated lithium ions [Li(EC)] 3-4 ] + Or [Li(EC)2(DMC)2] + The effective hydraulic diameter is approximately 1.2 nm to 1.5 nm. - Partially desolvated lithium ions [Li(EC)] 1-2 ] + The effective diameter is approximately 0.7 nm to 1.0 nm. - The radius of a completely desolventized bare lithium ion is only about 0.076 nm, but it is difficult to remain stable for a long time in an electrolyte environment.

[0089] (2) Setting the lower limit of interlayer spacing (0.6nm): - Ensure that partially desolvated lithium ions (effective diameter 0.7nm~1.0nm) can pass through relatively smoothly. - Below 0.6 nm, even partially desolvated lithium-ion transport will be excessively hindered, leading to a significant increase in interfacial impedance. -0.6nm is close to the minimum critical size when lithium ions carry 1 to 2 solvent molecules.

[0090] (3) Setting the upper limit of interlayer spacing (2.0nm): - To form sufficient steric hindrance and energy barrier for a complete solvation shell (diameter 1.2nm~1.5nm), - If the particle size exceeds 2.0 nm, fully solvated lithium ions may pass through without desolvation, thus losing their screening function. Studies have shown that when the interlayer spacing exceeds 2.0 nm, the transport resistance of solvent molecules decreases sharply, while the risk of solvent co-intercalation increases significantly.

[0091] (4) Selectable range (0.7nm~1.5nm): Within this range, fully solvated lithium ions are subject to significant steric hindrance and must undergo partial desolvation to pass through. -At the same time, partially desolvated lithium ions can be transported relatively freely. This range achieves the best balance between "screening selectivity" and "transfer efficiency".

[0092] This application achieves selective sieving of lithium-ion solvation shells in carbonate solvent systems by precisely controlling the interlayer spacing within the window of 0.6 nm to 2.0 nm. This is the key to achieving pre-desolvation and suppressing solvent co-intercalation.

[0093] The lithium-ion transference number refers to the proportion of lithium ions contributing to the total ionic current. In ordinary carbonate electrolytes, the lithium-ion transference number is approximately 0.3 to 0.4, meaning that anions account for about 60% to 70% of the current transport. The interface layer of this application significantly improves the lithium-ion transference number through the following mechanism: the polar functional groups on the nanosheet surface, especially negatively charged or strongly polar groups (such as sulfonate groups and sulfonylimide groups), enhance the transference of anions (such as PF6). - FSI - Electrostatic repulsion or steric hindrance effects (such as those generated by the interlayer) inhibit the passage of anions through the interlayer; the narrow channels between the layers create stronger steric hindrance for larger anions; in contrast, lithium ions, due to their small size and coordination affinity with polar groups, experience less hindrance in transport. Through these mechanisms, the lithium ion transport number in the interlayer can reach approximately 0.6–0.8, significantly higher than that in the bulk electrolyte. A high lithium ion transport number means that anion migration is suppressed during fast charging, and concentration polarization is primarily determined by the lithium ion concentration gradient rather than anions, thereby reducing overall concentration polarization and associated impedance.

[0094] The introduction of an interface layer inevitably increases interfacial contact impedance to some extent due to the addition of an extra transport medium. However, this can be compensated for through the following mechanisms: the lithium-ion transference number increases from approximately 0.3–0.4 to approximately 0.6–0.8, significantly reducing concentration polarization impedance, especially at high-rate charging where concentration polarization is the primary source of impedance; pre-desolution ensures that lithium ions arrive at the graphite surface carrying fewer solvent molecules, accelerating the interfacial charge transfer process and reducing charge transfer impedance; the interface layer thickness is controlled at approximately 0.1–1 μm, only one-thousandth to one-ten-thousandth the thickness of the electrolyte layer, and even though its conductivity is slightly lower than that of the bulk electrolyte, its contribution to the total ohmic impedance is limited; the ether oxygen segments in the polymer matrix provide an effective lithium-ion conduction pathway, partially offsetting the transport resistance of the interlayer channels in the nanosheets. Under fast-charging conditions, the reduction in concentration polarization and charge transfer impedance often outweighs the increase in interfacial contact impedance, making it possible to reduce or maintain the overall polarization level within an acceptable range, thereby achieving stable charging at higher rates.

[0095] Secondly, this application provides a method for preparing a battery cell as described above, comprising: A battery cell assembly is provided, the battery cell assembly comprising a negative electrode, a separator and a positive electrode stacked together; A housing is provided to house the battery cell assembly within the housing; Provide electrolyte and inject the electrolyte into the housing; A formation process is performed to obtain battery cells; An interface layer is attached to the side of the separator facing the negative electrode, the interface layer comprising a polymer matrix and two-dimensional organic nanosheets.

[0096] Membranes containing functional interface layers can be directly used in the assembly of lithium-ion batteries. During assembly, care must be taken to place the functional interface layer facing the graphite anode to ensure that the interface layer provides pre-desolution and selective conduction for lithium-ion transport on the anode side. Other steps in battery assembly, including positive and negative electrode preparation, stacking or winding, electrolyte injection, and formation, are the same as conventional processes. During formation, the interface layer establishes a lithium-ion conduction network after being wetted by the electrolyte, and begins to perform its pre-desolution function.

[0097] The interface layer technology proposed in this application is highly compatible with existing battery manufacturing processes. It does not require changes to the electrode formulation or the basic composition of the electrolyte; it only requires adding a functional interface layer coating step in the separator coating process. The coating technology is mature, the equipment is similar to existing separator coating lines, the engineering implementation difficulty is moderate, and it has good prospects for large-scale application.

[0098] Optionally, the method for preparing the interface layer includes: Two-dimensional organic nanosheet dispersions and polymer solutions are available. The two-dimensional organic nanosheet dispersion and the polymer solution are mixed to obtain a composite slurry; The composite slurry is coated onto one side of the diaphragm and then dried.

[0099] Optionally, the solid content of the two-dimensional organic nanosheet dispersion is 0.5% to 5%, specifically 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%.

[0100] Optionally, the preparation method of the two-dimensional organic nanosheets includes solution exfoliation, shear exfoliation, or ultrasonic-assisted exfoliation.

[0101] Taking functionalized graphene nanosheets as an example, a typical preparation process includes: (1) Preparation of graphene oxide: Using the Hummers method or a modified method, natural graphite powder is reacted with concentrated sulfuric acid, sodium nitrate and potassium permanganate, and then oxidized, washed and dried to obtain graphene oxide.

[0102] (2) Surface functionalization: Graphite oxide is dispersed in a suitable solvent and the target polar functional groups are introduced through chemical reactions. For example, sulfonation can introduce sulfonic acid groups or sulfonyl imide groups, cyanation can introduce cyano groups, and ether oxidation can introduce ether oxygen segments. The reaction conditions are selected according to the target functional groups and are usually carried out at a temperature of 80℃~120℃ for several hours to tens of hours.

[0103] (3) Exfoliation and dispersion: Functionalized graphene oxide is ultrasonically treated in water or organic solvent to exfoliate into nanosheets. The ultrasonic power and time are adjusted according to the target size, and the ultrasonic treatment is usually about 1h to 6h. After exfoliation, the large layers and impurities that are not completely exfoliated are removed by centrifugation to obtain a nanosheet dispersion with a thickness of less than about 10nm and a lateral size of about 50nm to 5μm.

[0104] (4) Concentration adjustment: The concentration of the nanosheet dispersion is adjusted by concentration or dilution to make it suitable for subsequent coating processes. The typical solid content is about 0.5wt%~5wt%.

[0105] The selection of the size of two-dimensional organic nanosheets needs to balance functionality and dispersion stability. Nanosheets that are too small have good dispersion but are difficult to control in terms of sheet orientation and stacking, while nanosheets that are too large have strong functionality but are difficult to disperse and coat.

[0106] Optionally, the polymer solution has a mass fraction of 2% to 10%, specifically 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0107] Optionally, after the drying step, a hot-pressing step is also included. The conditions for the hot-pressing step are: a temperature of 60℃~100℃, specifically 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, or 100℃; and a pressure of 0.1MPa~1MPa, specifically 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa, 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa, 0.9MPa, or 1MPa.

[0108] In some embodiments, the method for preparing the interface layer includes the following specific steps: Polymer solution preparation: Dissolve the polymer precursor or crosslinkable polymer containing ethylene glycol or ether oxygen segments in a solvent compatible with the nanosheet dispersion, such as N-methylpyrrolidone, dimethylformamide, or a mixture thereof. If crosslinking is required, an appropriate amount of crosslinking agent can be added to the polymer solution.

[0109] Composite slurry mixing: Mix the nanosheet dispersion and polymer solution according to the designed mass ratio, which can be approximately 30:70 to 70:30. Use mechanical stirring or ultrasonic assistance during mixing to ensure thorough and uniform mixing of the two phases. The viscosity of the mixed composite slurry should be suitable for the coating process; if necessary, it can be adjusted by adding or evaporating solvents.

[0110] Coating process: The composite slurry is coated onto one side of a commercial polyolefin separator. Coating methods can include blade coating, slot extrusion coating, spraying, or dip-coating. In blade coating, the wet film thickness is controlled by adjusting the blade gap and slurry viscosity, thereby controlling the dried coating thickness to approximately 0.1 μm to 1 μm. The shearing action during coating helps induce the nanosheets to align parallel to the separator surface.

[0111] Drying and Curing: The coated diaphragm is dried at approximately 60°C to 120°C to evaporate the solvent. The drying time is adjusted according to the coating thickness and solvent type, typically ranging from approximately 10 minutes to 2 hours. If the polymer requires crosslinking, thermal crosslinking or UV crosslinking can be performed after or during drying.

[0112] Mild hot pressing: After drying and curing, mild hot pressing can be selectively performed at a temperature of approximately 60℃~100℃, a pressure of approximately 0.1MPa~1MPa, and a time of approximately several seconds to several minutes. Hot pressing helps to further improve the orientation of the nanosheets, enhance the density of the interface layer, and improve the adhesion to the membrane substrate.

[0113] Quality inspection: The uniformity and thickness of the coating are observed by scanning electron microscopy, the orientation and interlayer spacing of the nanosheets are characterized by X-ray diffraction or small-angle scattering, and the bonding strength between the coating and the membrane is verified by adhesion test.

[0114] Orientation optimization: Optionally, the two-dimensional organic nanosheets can be oriented to a certain degree in a direction parallel to the membrane surface through shear coating and mild hot pressing. Parallel orientation is beneficial for forming a continuous layered channel structure, reducing the tortuosity of ion transport, and improving the ionic conductivity of the interface layer. The degree of orientation can be characterized by X-ray diffraction, small-angle X-ray scattering, etc. However, it should be noted that perfect parallel orientation is not necessary. In some embodiments, even if the two-dimensional organic nanosheets exhibit a certain degree of random arrangement, as long as an appropriate interlayer spacing distribution and sufficient nanosheet content are maintained, pre-desolvation and selective conduction functions can still be achieved, although the effect may be slightly weakened. This flexibility in orientation requirements improves the process tolerance and practicality.

[0115] Pore ​​Structure: The microscopic pore structure of the interface layer originates from two aspects: interlayer channels between nanosheets and ion conduction pathways in the polymer matrix. Interlayer channels provide the primary ion transport and sieving functions, and their size is determined by the interlayer spacing. The conduction pathways formed by the ether oxygen segments in the polymer matrix under the action of lithium ions provide supplementary transport channels. The combination of these two aspects gives the interface layer a continuous three-dimensional ion conduction network after electrolyte wetting, ensuring sufficient ionic conductivity.

[0116] The functional interface layer containing two-dimensional organic nanosheets should meet the following design performance indicators after electrolyte wetting: Lithium-ion conductivity not less than approximately 1 × 10⁻⁶ at 25°C. -4 S / cm, ideally reaching approximately 5 × 10 -4 The S / cm or higher is required to ensure that it does not create significant additional ohmic impedance during fast charging. The lithium-ion transference number is significantly higher than that of the bulk carbonate electrolyte (approximately 0.3~0.4 in bulk), preferably reaching approximately 0.6~0.8, to effectively reduce concentration polarization. The interface layer should maintain mechanical integrity during battery charge-discharge cycles, without significant cracking, detachment, or delamination from the separator substrate, ensuring long-term functional stability.

[0117] This application applies to lithium-ion battery systems employing graphite or graphite-silicon-carbon composite anodes. The anode material can be artificial graphite, natural graphite, or graphite materials with surface coatings or modifications, or a composite anode of graphite and silicon-carbon, wherein the silicon-carbon content is typically below approximately 15 wt%. The cathode material can be selected from lithium iron phosphate, ternary materials (such as NCM532, NCM622, NCM811), nickel-cobalt-aluminum ternary materials, etc. The electrolyte system is a conventional carbonate-based electrolyte, such as a combination of ethylene carbonate and methyl ethyl carbonate, dimethyl carbonate, or diethyl carbonate. The lithium salt can be lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, etc., and conventional additives such as fluoroethylene carbonate and vinylene carbonate can be used in conjunction. The interface layer of this application is fully compatible with these existing systems and does not require changes to the electrode formulation or the basic composition of the electrolyte.

[0118] The technical solution of this application mainly targets high-rate fast charging scenarios, including the fast charging requirements of electric vehicles (such as 3C~6C charging, charging to 80% state of charge in 10min~20min) and the rapid response requirements of energy storage systems. In these applications, solvent co-intercalation and lithium plating of graphite anodes are the main technical bottlenecks. This application, through the synergistic effect of pre-desolution and high lithium-ion transference number, can significantly improve fast charging performance, suppress lithium plating, extend cycle life, and enhance safety.

[0119] Thirdly, this application provides a battery device, such as Figure 2 and Figure 3 As shown, the battery device includes the battery cell as described above, or the battery cell obtained by the preparation method described above, and the battery device includes one or more of the following: battery module, battery pack, and energy storage battery.

[0120] Specifically, the battery device 100 includes a housing 10 and individual battery cells 20, with the individual battery cells 20 housed within the housing 10. The housing 10 provides space for the individual battery cells 20, and the housing 10 can have various structures.

[0121] In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, and together define a receiving space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, with the first portion 11 covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 together define the receiving space; alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can be of various shapes, such as a cylinder, a cuboid, etc.

[0122] In the battery device 100, the battery cell 20 can be a single cell or multiple cells. Multiple battery cells 20 can be connected in series, parallel, or a combination thereof. A combination thereof means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or a combination thereof to form a whole, which is then housed within the housing 10. Alternatively, the battery device 100 can also consist of multiple battery cells 20 first connected in series, parallel, or a combination thereof to form battery modules, which are then connected in series, parallel, or a combination thereof to form a whole, which is also housed within the housing 10.

[0123] The battery device 100 may also include other structures, for example, the battery device 100 may also include a busbar for realizing electrical connection between multiple battery cells 20.

[0124] Fourthly, this application provides an energy storage device, which includes a battery device as described above, the battery device being used to store electrical energy.

[0125] The energy storage device includes a battery pack, which includes multiple batteries, an energy management system (EMS), a battery management system (BMS), and an energy storage converter (PCS). The electrical devices include vehicles, household appliances, electric motors, medical equipment, scientific instruments, and power grids.

[0126] Compared with existing graphite anode fast charging optimization technologies, this application has the following main differences and advantages: 1. Shifting and directing the functional position forward. In this field, electrolyte additives primarily function in the formation of the solid electrolyte interface film on the graphite surface, lacking regulation of the solvation state of lithium ions before reaching the negative electrode. The additives are uniformly distributed throughout the electrolyte, lacking spatial selectivity. While ceramic membrane coatings are located on the membrane, they are typically uniformly coated on both sides, primarily providing thermal stability and mechanical strength, without directional function for the solvation process on the negative electrode side.

[0127] This application innovatively constructs a functional interface layer precisely on the membrane near the graphite anode side, employing an asymmetric coating design that forces lithium ions to pass through this interface layer before reaching the graphite surface. This forward positioning transforms the regulation of solvation state from "post-treatment" (film formation on the graphite surface) to "pre-treatment" (pre-desolvation in the interface layer). By incorporating a functionalized pretreatment step along the transport path, the number of solvent molecules carried by lithium ions reaching the graphite surface is reduced at the source, suppressing solvent co-intercalation. This forward positioning and orientation result in more precise and efficient functionality without affecting the normal operation of the cathode side.

[0128] 2. Two-dimensional nanosheet structures achieve synergistic spatial sieving and chemical coordination. Ceramic membrane coatings utilize inorganic particles such as alumina and silica. These particles themselves do not conduct ions; the ion transport in the coating relies on the random porosity between particles, lacking selectivity for lithium ions, anions, and solvent molecules. While graphene oxide coatings possess a two-dimensional layered structure, their surface functional groups are primarily carboxyl and hydroxyl groups, used to improve dispersibility and mechanical properties. Their selective coordination of lithium ions and desolvation induction functions have not been systematically optimized, and graphene oxide exhibits relatively low ionic conductivity. Although metal-organic frameworks possess regular channels, they are mostly three-dimensional network structures existing in particle form, lacking oriented two-dimensional layered arrangement.

[0129] This application utilizes the parallel orientation of two-dimensional organic nanosheets to form an ordered stacked structure with a sheet spacing of approximately 0.6 nm to 2 nm. This structure achieves a synergistic effect of spatial sieving and chemical coordination: the size selectivity of the sheet spacing creates steric hindrance for lithium ions and free solvent molecules in the intact solvation shell, while having little impact on the transport of partially desolvated lithium ions; simultaneously, the polar functional groups on the nanosheet surface (such as sulfonylimide, cyano, and etheroxy groups) moderately coordinate lithium ions, inducing solvent molecules to dissociate from the solvation shell. This synergy of spatial and chemical effects ensures that lithium ions are not only physically sieved but also undergo chemical environmental regulation when passing through the interface layer, achieving the reconstruction of the solvation shell. In contrast, existing technologies either only employ physical barriers (ceramic coatings) or only rely on chemical effects (additives), lacking this systematic synergistic design.

[0130] 3. High lithium-ion transference number leads to a significant reduction in concentration polarization. In ordinary carbonate electrolytes, the lithium-ion transference number is approximately 0.3–0.4, meaning that anions carry the majority of the current transport. During fast charging, the migration of anions to the positive electrode and lithium ions to the negative electrode creates a concentration gradient, leading to significant concentration polarization. The inventors know that coatings such as ceramic coatings and graphene oxide coatings have similar levels of inhibition on the transport of anions and lithium ions, and cannot effectively improve the lithium-ion transference number. Although some solid-state electrolytes can achieve higher lithium-ion transference numbers, they have high interfacial impedance and are difficult to engineer.

[0131] This application achieves a lithium-ion transport number of approximately 0.6–0.8 in the interface layer by utilizing the repulsion of anions by polar functional groups on the nanosheet surface, the steric hindrance of large anions by narrow channels between the nanosheets, and the selective coordination and transport promotion of lithium ions. This is significantly higher than that of bulk electrolytes. A high lithium-ion transport number means that at the same current density, the lithium-ion concentration gradient is reduced, leading to lower concentration polarization. Under fast-charging conditions, concentration polarization is often the main source of impedance, and its reduction significantly improves the overall polarization level. This strategy of achieving a high lithium-ion transport number through interface layer structure design represents an innovative breakthrough that has not been effectively implemented in the industry.

[0132] 4. Pre-desolvation mechanism inhibits solvent co-intercalation at its source. Electrolyte additives such as fluoroethylene carbonate preferentially reduce lithium fluoride to form a lithium fluoride-rich solid electrolyte interfacial film on the graphite surface. While this interfacial film can block solvent molecules to some extent, its role is passive defense at the interface, occurring after lithium ions and solvent molecules have already reached the graphite surface. If a large number of lithium ions carrying solvent molecules reach the surface, the interfacial film's defensive capability is limited, especially under conditions of fast charging with high current density and non-uniform interfacial film, where solvent co-intercalation can still occur.

[0133] This application utilizes the pre-desolution function of the interface layer to reduce the number of solvent molecules in the solvation shell of lithium ions from approximately 3-4 to approximately 1-2 before they reach the graphite surface. This proactive upstream treatment reduces the risk of solvent co-intercalation at its source. Even if there are localized inhomogeneities in the interface film or it is not fully formed in the early stages of fast charging, the tendency for solvent co-intercalation is significantly reduced because lithium ions reaching the graphite surface have already undergone partial desolvation. This preventative mechanism is more proactive and fundamental than the passive defense of the interface film, especially during the fast-charging start-up phase and when the interface film is not yet stable, where the role of pre-desolution is even more crucial.

[0134] 5. Multiple mechanisms of compensation and net benefits in impedance trade-offs Any interface layer added to the lithium-ion transport path inevitably introduces additional interfacial contact impedance; this is an objective physical reality. The inventors know that while ceramic coatings and graphene oxide coatings provide certain functions (such as thermal stability and mechanical strength), they also increase impedance. However, these technologies often lack effective impedance compensation mechanisms, which can lead to an increase in total impedance even under fast charging conditions.

[0135] This application addresses the increased interfacial contact impedance introduced by the interface layer by achieving a net benefit through a systematic compensation mechanism. This compensation mechanism includes: increasing the lithium-ion transference number from approximately 0.3-0.4 to approximately 0.6-0.8, significantly reducing concentration polarization impedance. Under fast charging conditions, concentration polarization is the primary source of impedance, and its reduction often exceeds the increase in interfacial contact impedance; pre-desolution ensures that lithium ions are in a more easily embedded state upon reaching the graphite surface, accelerating the interfacial charge transfer process and reducing charge transfer impedance; the interface layer thickness is controlled at approximately 0.1 μm-1 μm, a very small proportion of the electrolyte layer thickness, and even though its conductivity is slightly lower than the bulk phase, its contribution to the total ohmic impedance is limited; the ether oxygen segments in the polymer matrix provide an effective lithium-ion conduction pathway, partially offsetting the transport resistance between nanosheet layers. This multi-mechanism compensation allows the overall polarization level to be reduced or maintained within an acceptable range under fast charging conditions. In contrast, the industry often focuses only on single functions while neglecting impedance trade-offs; the systematic design of this application demonstrates a higher level of technological maturity.

[0136] 6. Ease of engineering implementation and compatibility While solid-state or quasi-solid-state electrolytes can fundamentally solve the solvent co-intercalation problem, their manufacturing processes are complex, requiring redesign of battery structures and assembly processes. Interfacial impedance issues are difficult to resolve, costs increase significantly, and engineering implementation is challenging. Metal-organic framework coatings face challenges related to material stability and process complexity. The engineering implementation of solid-state or quasi-solid-state electrolytes in the industry often requires substantial modifications to battery manufacturing processes.

[0137] The interface layer in this application can be achieved by adding a functional coating step during the separator coating process. The coating technology is mature, and the equipment is similar to existing separator coating lines. It does not require changes to the formulation of the positive and negative electrode sheets, the basic composition of the electrolyte, or the battery assembly process. Only the orientation of the separator needs to be considered during assembly to ensure the functional interface layer faces the graphite negative electrode. This high compatibility allows this application to be easily integrated with existing battery manufacturing processes, reducing the difficulty and cost of engineering implementation and facilitating rapid industrial application. Furthermore, the materials for the interface layer, such as functionalized graphene and cross-linked polymers, are relatively mature chemical products or can be prepared using mature processes, resulting in a well-established material supply chain and further reducing engineering risks.

[0138] In summary, this application achieves several innovative advantages by constructing a two-dimensional organic nanosheet composite functional interface layer on the negative electrode side of the separator. These advantages include forward shift of the action site, synergy of spatial sieving and chemical coordination, high lithium-ion transference number, source suppression of pre-desolvation, multi-mechanism compensation in impedance trade-off, and ease of engineering implementation. This provides a systematic, efficient, and engineering-feasible new technical path for improving the fast-charging performance of graphite negative electrodes.

[0139] To verify the impact of the proposed fast-charging graphite anode protection technology based on a two-dimensional organic nanosheet desolvation interface layer on lithium-ion battery performance, this application designed a series of embodiments and comparative examples, as shown in Tables 1-1 to 1-3. The effects of interface layer coating location and method, nanosheet polar functional group type, nanosheet to polymer matrix ratio, interface layer thickness, interlayer spacing, and anode and electrolyte systems on the apparent lithium-ion transference number, interface impedance characteristics, and fast-charging cycle performance of the battery are systematically investigated. The following details the selection of raw materials, interface layer preparation, battery assembly, and results analysis.

[0140] I. The materials used in the following embodiments and comparative examples are as follows.

[0141] Functionalized graphene nanosheets were prepared using natural graphite powder (purity not less than 99%, D50 approximately 20 μm) as raw material and graphene oxide (GO) was prepared using a modified Hummers method. Subsequently, different types of polar functional groups were introduced in each embodiment. Sulfonylimide modification involved grafting graphene oxide with a sulfonylimide-containing precursor; cyano modification involved surface grafting with a cyano-containing functionalizing agent; ether-oxygen segment modification involved introducing flexible coordination segments through surface modification with a functionalizing agent containing ether-oxygen segments; and sulfonic acid modification involved introducing strongly polar sulfonic acid groups via sulfonation modification. The prepared functionalized nanosheets were subjected to ultrasonic exfoliation (400 W power, 40 kHz frequency, 2 h) and centrifugation (5000 rpm, 20 min). The resulting nanosheets had a thickness of less than 5 nm and a lateral dimension of approximately 200 nm to 1 μm.

[0142] The polymer matrix is ​​a cross-linked polymer containing ethylene glycol segments, with polyethylene glycol diacrylate (PEGDA, Mn about 700 g / mol, purity not less than 99%) as the main component, 2,2-dimethoxy-2-phenylacetophenone (DMPA, purity not less than 99%) as the photoinitiator (accounting for 1.5 wt% of the polymer mass), and an appropriate amount of curing accelerator is added. It is dissolved in N-methylpyrrolidone (NMP, moisture content less than 30 ppm) to prepare a polymer solution with a concentration of about 8 wt%.

[0143] The membrane substrate used was a commercially available three-layer PP / PE / PP composite membrane (20 μm thick, 38% porosity, and an average pore size of approximately 120 nm). Comparative Example 3 used a commercially available Al2O3 ceramic-coated membrane (double-sided coating, with a total ceramic layer thickness of approximately 2.0 μm).

[0144] Regarding electrode materials, the positive electrode uses carbon-coated lithium iron phosphate (LiFePO4 / C) active material (purity not less than 99%, D50 approximately 0.8μm). The positive electrode slurry formulation consists of 93wt% active material, 4wt% conductive agent Super P, and 3wt% binder polyvinylidene fluoride (PVDF), dissolved in NMP and coated onto a 15μm thick aluminum foil current collector. The surface density of the positive electrode is controlled at (16.5±0.3) mg / cm³. 2 The compacted density is 2.45 g / cm³. 3 The negative electrode body is made of artificial graphite (D50 approximately 15μm, specific capacity not less than 355mAh / g). The negative electrode slurry formulation consists of 95wt% active material, 1.5wt% sodium carboxymethyl cellulose (CMC) thickener, and 3.5wt% styrene-butadiene rubber (SBR) binder, prepared with deionized water as solvent, and coated onto an 8μm thick copper foil current collector. The anode surface density is controlled at (8.8±0.2) mg / cm³. 2Compacted density 1.55 g / cm³ 3 In Example 11, the negative electrode active material was changed to a graphite / silicon-carbon composite material (90wt% artificial graphite, 10wt% silicon-carbon component, D50 of about 14μm, and specific capacity of the composite material of not less than 420mAh / g), while the other negative electrode formulation parameters remained the same as those of the artificial graphite system.

[0145] The basic electrolyte was prepared by dissolving 1 mol / L lithium hexafluorophosphate (LiPF6, battery grade, purity not less than 99.9%) in a mixed solvent of ethylene carbonate / ethyl methyl carbonate / dimethyl carbonate (EC / EMC / DMC, volume ratio 1:1:1, water content of each solvent less than 20 ppm). For the additive-containing system (Comparative Example 2, Example 12), 5 wt% fluoroethylene carbonate (FEC, battery grade, purity not less than 99.5%) was added to the above basic electrolyte, and the mixture was stirred thoroughly before use.

[0146] All of the above operations that are sensitive to water and oxygen were performed in an argon atmosphere glove box, where the water and oxygen content was controlled to be below 0.5 ppm.

[0147] II. Preparation of the interface layer Functionalized graphene nanosheet dispersion (solid content approximately 2 wt%, using NMP as solvent) was mixed with polymer solution at the mass ratios specified in each embodiment. The mixture was stirred mechanically at 500 rpm for 30 min, followed by ultrasonic-assisted dispersion (200 W power) for 15 min to obtain a uniform composite slurry. The solid content of the composite slurry was adjusted to approximately 5 wt%, and the viscosity was controlled within the range of 800 mPa·s to 2000 mPa·s at 25°C to ensure coating quality.

[0148] The composite slurry was applied to a designated side (negative or positive electrode side, depending on the embodiment and comparative example) of the diaphragm substrate using an automatic doctor blade coating machine. The doctor blade speed was 5 mm / s, and the wet film thickness was adjusted by controlling the doctor blade gap, thereby controlling the final dry film thickness. Immediately after coating, the film was dried in a 60°C forced-air oven for 30 minutes to evaporate the solvent, followed by UV light (wavelength 365 nm, light intensity 25 mW / cm²). 2 The nanosheets were cured under irradiation for 120 seconds, and polymer crosslinking was completed under a nitrogen protective atmosphere. After curing, the examples requiring orientation treatment were subjected to mild hot-pressing at 80°C and 0.3 MPa for 60 seconds to further improve the orientation of the nanosheets parallel to the membrane surface and enhance the interlayer stacking density. Comparative Example 7 (random stacking group) was not subjected to hot-pressing after drying and curing to retain the random orientation state of the nanosheets. The dry film thickness of the interface layer in each example and comparative example was confirmed by cross-sectional observation using scanning electron microscopy, and the interlayer spacing was verified by small-angle X-ray scattering (SAXS) to ensure that the core structural parameters of each group of samples were consistent with the design values.

[0149] III. Battery Assembly This embodiment uses a 3Ah~5Ah lithium iron phosphate / graphite stacked soft-pack battery as a unified verification platform. Example 11 uses a lithium iron phosphate / silicon-carbon composite negative electrode stacked soft-pack battery. The battery assembly adopts a single-layer stacked structure, with the positive electrode, functional interface layer (or control separator), and negative electrode stacked sequentially. The functional interface layer is placed facing the graphite negative electrode to ensure that the interface layer has a pre-desolution and selective conduction effect on lithium-ion transport on the negative electrode side. In Comparative Example 4, the interface layer is flipped to face the positive electrode side. After stacking, the battery is placed in an aluminum-plastic composite film shell, vacuum sealed, and dried in an 80°C vacuum drying oven for 24 hours (dew point not higher than -40°C) to ensure that the internal moisture content of the battery is less than 50ppm.

[0150] Electrolyte injection was performed in a dry chamber with a dew point not exceeding -40°C. The injection volume was determined based on the electrode area and the separator's electrolyte absorption. After injection, the cells were allowed to stand for 24 hours to allow the electrolyte to fully wet the electrodes and interface layer. Formation employed a stepped charging strategy: constant current charging at 0.05C to 3.2V, followed by standing for 1 hour, then constant current charging at 0.1C to 3.65V with a constant voltage cutoff (cutoff current 0.02C), and finally constant current discharging at 0.2C to 2.5V, completing the first formation. This process was then repeated twice at 0.2C to activate the battery. After formation, all batteries underwent capacity testing and internal resistance screening. Batteries with capacity deviations within ±1% and DC internal resistance deviations within ±5% were retained for subsequent testing. Three parallel samples were set for each experimental condition, and the average of the three samples was used as the final reported data, along with the standard deviation.

[0151] IV. Testing Methods Test 1 (T1): Apparent lithium-ion transport number test. A Li / functional separator / Li symmetric coin cell (CR2032) was assembled using the Bruce-Vincent method in a glove box and allowed to stand for 24 hours to stabilize the interface. Under constant temperature of 25℃, a 10mV DC voltage was applied for polarization, and the current value was recorded every 5 minutes until the current reached a steady state (the rate of change was less than 1% / hour, typically about 2-4 hours). Electrochemical impedance spectroscopy was measured before and after polarization at a frequency range of 100kHz to 0.01Hz and an AC amplitude of 10mV to obtain the initial interfacial impedance R0 and the steady-state interfacial impedance Rss. Apparent lithium-ion transport number t + Calculate using the following formula: t + =Iss(ΔV-I0R0) / [I0(ΔV-I ss R ss ]], where ΔV is the applied voltage (10mV), I0 and I ssThe values ​​represent the initial current and steady-state current, respectively. Since the test object is an integral assembly system of the functional separator and polymer matrix under electrolyte wetting conditions, the results are reported as the apparent lithium-ion transference number, reflecting the overall ion-selective conduction characteristics of the assembly system. This test is not applicable to Comparative Example 4 (the coating directionality effect must be verified in a full-cell system) and Example 11 (the functional separator is the same as in Example 1, so the test is not repeated). Three parallel coin cells were tested in each group, and the average value was taken.

[0152] Test 2 (T2): Electrochemical Impedance Spectroscopy (EIS). After all pouch cells completed formation, the state of charge (SOC) was adjusted to 50%, and EIS was performed at 25°C with a frequency range of 100kHz to 0.01Hz and an AC amplitude of 10mV. A unified equivalent circuit (Rs+Rct / / CPE) was used to fit all samples, extracting the ohmic internal resistance (Rohm) and the interfacial charge transfer impedance (Rct). The changing trends of each group relative to Comparative Example 1 were analyzed to verify the impedance trade-off after the introduction of the interfacial layer. For representative samples that entered the T4, T5, and T6 deep cycling tests, EIS was repeated every 50 cycles under the same SOC conditions to track the evolution of the interfacial impedance.

[0153] Test 3 (T3), fast charging rate test. Under 25℃ conditions, the discharge regime was fixed at 1C constant current discharge to 2.5V. The charging rates were sequentially set to 0.2C, 0.5C, 1C, 2C, and 4C. Each rate was cycled 5 times. For each rate, constant current charging was used to the upper limit of 3.65V, followed by constant voltage charging to the cutoff current of 0.05C. Using the discharge capacity of the third cycle at 0.2C as the baseline (denoted as 100%), the percentage of the discharge capacity of the third cycle at each charging rate (0.5C, 1C, 2C, and 4C) relative to the baseline value was calculated; this represents the capacity retention rate at each charging rate.

[0154] Test 4 (T4), 4C fast charging cycle capacity retention test. Under 25℃ conditions, the battery was charged at 4C constant current to the upper limit voltage of 3.65V, then charged at constant voltage to the cutoff current of 0.05C, and finally discharged at 1C constant current to 2.5V, completing one charge-discharge cycle. This was repeated 200 times. The discharge capacity, charge capacity, and coulombic efficiency of each cycle were recorded. Using the discharge capacity of the first cycle as a baseline, the capacity retention rate of the 50th, 100th, 150th, and 200th cycles was calculated. The first-cycle coulombic efficiency was calculated using the following formula: first-cycle coulombic efficiency equals first-cycle discharge capacity divided by first-cycle charge capacity multiplied by 100%. Simultaneously, the charge-discharge curves of each cycle were differentially processed using dV / dQ. The presence of abnormal peaks within the pre-calibrated lithium plating characteristic voltage range was used as an indirect criterion for lithium plating risk. This analysis did not introduce additional experimental steps and was an auxiliary processing of existing charge-discharge data. The resulting lithium plating judgment results were qualitatively described using four levels: no lithium plating characteristic peak, slight characteristic peak, visible characteristic peak, and obvious characteristic peak. This test was performed only on the second layer of key representative samples (Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 6, Comparative Example 7, Comparative Example 8, Example 11, Example 12).

[0155] Test 5 (T5), standard cycle capacity retention test at room temperature. At 25°C, the sample was charged at a constant current of 1C to 3.65V, then constant voltage to a cutoff current of 0.05C, followed by discharge at a constant current of 1C to 2.5V. This cycle was repeated 500 times, and the discharge capacity was recorded for each cycle. The capacity retention rate and the first-cycle coulombic efficiency were calculated for the 100th, 200th, 300th, and 500th cycles. This test was performed only on the third-layer core samples (Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 11, and Example 12).

[0156] Test 6 (T6), high-temperature cycling capacity retention test. The test regime is the same as Test 5, but the test temperature is changed to 45°C, and the number of cycles is 200. The capacity retention rate is recorded at the 50th, 100th, 150th, and 200th cycles. This test is only performed on the third-layer core samples (Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 11, Example 12).

[0157] Tables 2-1 to 2-3 present the main test results obtained by the core innovation verification group (Example 1, Comparative Examples 1 to 8), functional group type verification group (Example 1 to 4), content and thickness optimization group (Example 5 to 8), interlaminar spacing control group (Example 9 and 10), and application expansion verification group (Example 11 and 12) according to the predetermined test levels. The following is a systematic analysis based on the data of each group.

[0158] 1. Core Innovation Verification Group From the perspective of apparent lithium-ion transference number, the apparent t in Example 1 of the complete technical solutionLi+ The apparent t of Comparative Example 2 was significantly higher than that of the blank separator in Comparative Example 1, with an improvement of approximately 0.27 to 0.40 units, confirming the core technology claim of the functional interface layer for selective lithium-ion conduction. Li+ The result is at the same level as Comparative Example 1, indicating that the introduction of FEC additives into the electrolyte has a limited contribution to improving the overall lithium-ion transference number of the system. This is consistent with the previous mechanistic analysis, namely that the additives mainly improve the film-forming chemistry of the solid electrolyte interphase (SEI) and lack direct regulation of the solvation state of lithium ions before reaching the negative electrode surface. The apparent t of Comparative Example 3 is at the same level as Comparative Example 1, indicating that the introduction of FEC additives into the electrolyte has a limited contribution to improving the overall lithium-ion transference number of the system. Li+ Similar to Comparative Example 1, this indicates that ordinary Al2O3 ceramic coatings lack selectivity for anions and solvent molecules, and cannot achieve effective ion-selective conduction. These two sets of data together confirm the uniqueness of the proposed technical approach compared to existing approaches in the industry regarding lithium-ion selective conduction.

[0159] In the item-by-item breakdown verification group, the apparent t of Comparative Example 6 (unfunctionalized GO) Li+ Although higher than Comparative Example 1, it is significantly lower than Example 1. This is because the coordination affinity of carboxyl and hydroxyl groups on the surface of ordinary graphene oxide for lithium ions is much weaker than that of strongly polar groups such as sulfonylimide groups, which cannot effectively induce the dissociation of solvent molecules in the solvation shell, resulting in insufficient pre-desolvation efficiency. Comparative Example 7 (non-oriented) shows an apparent t... Li+ The apparent t of Example 8 (polymer only) was lower than that of Example 1 but higher than that of Comparative Example 6, indicating that the presence of the nanosheets itself provides a certain degree of chemical coordination. However, the lack of parallel orientation leads to poor interlayer channel continuity and high tortuosity, significantly limiting the effectiveness of spatial sieving. Li+ The results, higher than Comparative Example 1 but lower than Comparative Example 7, indicate that the ether-oxygen segments of the polymer matrix can provide some selectivity for lithium-ion transport through a coordination relay mechanism. However, the polymer layer alone lacks spatial sieving function, and its effect is not as good as the system containing nanosheets. The above data clearly show that the high apparent t achieved in Example 1 is not as effective as the system containing nanosheets. Li+ It is the result of the synergistic effect of three characteristics: chemical coordination of polar functional groups, spatial sieving of parallel orientation of nanosheets, and ion conduction of polymer matrix. The absence of any one of these characteristics will lead to a decrease in performance to varying degrees.

[0160] Based on the EIS and fast charge rate data, Comparative Example 4 (positive electrode side coating) showed a lower improvement in both full-cell EIS and fast charge rate tests compared to Example 1. This indicates that the orientation of the interface layer is crucial. This is because the interface layer can only complete the pre-solubilization process before lithium ions reach the graphite surface if it is located on the negative electrode side. Positive electrode side coating cannot achieve this upstream pre-treatment function. Comparative Example 5 (double-sided coating) showed a lower apparent t Li+Similar to Example 1, but with a significantly higher Rohm, indicating that the additional coating on the positive electrode side brings additional transmission resistance without bringing an equivalent amount of fast charging kinetic benefits, which confirms the engineering optimality of the single-sided asymmetric design.

[0161] The EIS results of all samples showed a consistent pattern: Rohm in Example 1 increased slightly compared to Comparative Example 1, while Rct decreased significantly. The slight increase in Rohm is consistent with the expectation of introducing an additional transport medium through the interface layer; the significant decrease in Rct is due to the pre-desolvation, which greatly reduces the number of solvent molecules carried by lithium ions when they reach the graphite surface, thus lowering the energy barrier contribution of the desolvation step to the charge transfer process. The decrease in Rct exceeds the increase in Rohm, thereby achieving a net reduction in the overall polarization level under fast charging conditions, verifying the previous discussion on multi-mechanism compensation. Rct in Comparative Example 2 decreased, but the magnitude was much weaker than in Example 1, and Rct in Comparative Example 3 showed almost no improvement. The comparison between the two further highlights the effectiveness of the pre-desolvation mechanism in improving interfacial charge transfer kinetics. Rct in Comparative Examples 8 and 7 both decreased, but the magnitude was significantly smaller than in Example 1, further confirming that the spatial sieving function and ordered orientation of the nanosheets are indispensable for achieving complete pre-desolvation effectiveness.

[0162] The fast charging rate test results show that Example 1 has a significantly better capacity retention rate than Comparative Example 1 at a 4C charging rate, with a difference of approximately 20 to 25 percentage points. Comparative Examples 2 and 3 show some improvement compared to Comparative Example 1, but the improvement is limited, which is highly consistent with the trend of the EIS results. Among the comparative examples disassembled item by item, Comparative Examples 6 and 4 have the lowest 4C capacity retention rates, indicating that polar functional groups and coating position orientation are the two most critical factors for improving fast charging performance; Comparative Examples 7 and 8 are in the middle, indicating that both nanosheet orientation and the presence of the nanosheets themselves contribute to improving fast charging capacity, but the contribution is weaker than the effect of the complete realization of the chemical coordination mechanism.

[0163] The capacity retention rate after 200 cycles of 4C fast charging showed a high degree of consistency with the rate test results. The retention rate of Example 1 after 200 cycles was significantly better than that of Comparative Example 1, indicating that this application not only has higher instantaneous capacity under fast charging conditions, but also that the interface layer can continuously perform pre-solventization protection during repeated fast charging cycles, effectively suppressing the cumulative structural damage caused by solvent co-intercalation. The retention rate of Comparative Example 2 after 200 cycles was better than that of Comparative Example 1 but worse than that of Example 1, indicating that the continuous effectiveness of the FEC / SEI protection strategy has certain limitations; with increasing cycle count, the cumulative effects of lithium plating and solvent co-intercalation gradually become more prominent. dV / dQ differential curve analysis showed that the discharge curves of Comparative Examples 1, 2, 3, and 6 exhibited visible or obvious lithium plating characteristic peaks after cycling, while the dV / dQ curve of Example 1 did not show obvious lithium plating characteristics after 200 cycles, indicating that the pre-solventization mechanism effectively maintained the suppression of lithium plating risk during long-term fast charging cycles.

[0164] The results of 500 standard cycles at 25°C and 200 high-temperature cycles at 45°C show that Example 1 exhibits better capacity retention than Comparative Examples 1, 2, and 3 under both conditions. Under standard cycling conditions, the performance gap between the samples narrows compared to fast-charging cycles, consistent with the previous analysis: at a 1C charging rate, the lithium-ion desolvation rate does not constitute a significant rate control bottleneck, and the protective advantage of the interface layer is relatively reduced. However, Example 1 still maintains a certain advantage over Comparative Example 1, indicating that the functional interface layer has no side effects under normal conditions. Under high-temperature cycling conditions, the absolute gap between Example 1 and Comparative Example 1 further widens, indicating that the functional interface layer of this application has good structural stability under thermal stress conditions, while the SEI film of Comparative Example 1 shows a more significant trend of accelerated decomposition and thickening at high temperatures.

[0165] 2. Functional group type verification group The apparent t of the three sets of examples: cyano modification (Example 2), ether oxygen segment modification (Example 3), and sulfonic acid modification (Example 4) Li+ The 4C charging capacity retention rate is within the same range as that of Example 1 (sulfonylimide group modification), and the differences between them are within the statistical error range. The above data indicate that as long as functional groups with sufficient polarity and lithium-ion coordination ability are introduced onto the surface of two-dimensional organic nanosheets, pre-solvation and selective conduction functions can be effectively achieved. The core mechanism of this application does not depend on a specific type of functional group, but rather on the structural feature of the presence of polar functional groups. From subtle differences, the sulfonylimide and sulfonic acid groups show differences in apparent t Li+The lithium-ion transference number (Rct) is slightly higher than that of the cyano and etheroxy segment systems because the strong polarity of the sulfonyl group and its relatively stronger electrostatic repulsion effect on anions result in a relatively higher Rct. The etheroxy segment modified system shows the best synergy with the polymer matrix because the etheroxy functional group forms a continuous coordination network with the etheroxy segments in the polymer matrix, further reducing the activation energy of lithium-ion interfacial charge transfer. These subtle differences are all within a reasonable physicochemical logic, indicating that different polar functional groups each have their own emphasis but all can achieve the core functional objectives of this application.

[0166] 3. Content and Thickness Optimization Group Regarding the nanosheet to polymer ratio, the apparent t of Example 5 (30:70) Li+ Both the 4C capacity retention rates were lower than those of Example 1 (50:50), indicating that when the nanosheet content is low, the sheet stacking density is insufficient, the continuity of the spatial sieving channels and the density of chemical coordination sites decrease, and the pre-desolvation efficiency is reduced. The apparent t of Example 6 (70:30) was lower than that of Example 1 (50:50). Li+ The 4C capacity retention rate was slightly better than in Example 1, indicating that appropriately increasing the nanosheet content can further enhance sieving and coordination functions. However, the high nanosheet content led to increased coating brittleness, and the increase in Rohm was more significant, suggesting that excessively high nanosheet content would sacrifice the coating's mechanical flexibility and adhesion to the membrane substrate, posing a potential risk to the integrity of the interfacial layer during long-term cycling. Overall, a ratio around 50:50 achieved a good balance between functionality and mechanical properties, consistent with the recommended ratio range mentioned above.

[0167] Regarding the interface layer thickness, the apparent t of Example 7 (0.15 μm ~ 0.20 μm) Li+ The fast charging capacity retention rate is slightly lower than that of Example 1 because the thin coating has certain limitations in uniformity. Local discontinuous areas of coverage can form short-circuit transport channels, allowing lithium ions that have not undergone pre-desolution treatment to pass directly through, thus weakening the overall functional performance. The apparent t of Example 8 (0.70μm~0.90μm) Li+ Similar to Example 1, this indicates that the pre-solvation function of the thick coating is more complete; however, its Rohm increases significantly, leading to an increase in total polarization under fast charging conditions, and the 4C capacity retention is not better than that of Example 1. This result verifies the earlier prediction that the interfacial impedance increases significantly when the thickness exceeds about 1.0 μm, indicating that the area around 0.30 μm to 0.40 μm is the preferred thickness range that balances functionality and impedance control.

[0168] 4. Layer spacing control group Apparent t of Example 9 (layer spacing 0.70nm~0.80nm) Li+Slightly higher than Example 1, indicating that the spatial sieving effect of the solvated shell is further enhanced within this spacing range, and the suppression of the transport of anions and free solvent molecules is more effective. However, the 4C charging capacity retention rate of Example 9 is slightly lower than that of Example 1. This is because the narrower interlayer spacing, while increasing the sieving strength, also creates additional resistance to the transport of partially desolvated lithium ions, resulting in a slight decrease in interfacial transport kinetics. This trend is consistent with the previous analysis regarding 0.6 nm being close to the minimum size critical value of partially desolvated lithium ions, indicating that the spacing of Example 9 is close to the lower boundary of the balance between sieving and conduction. The apparent t of Example 10 (interlayer spacing of 1.40 nm to 1.60 nm) Li+ The 4C capacity retention was lower than in Example 1, indicating that the wider spacing reduced the resistance of fully solvated lithium ions through the interlayer channels, resulting in a decrease in pre-desolution efficiency and a weakening of spatial sieving function. The comparison results between Examples 9 and 10 and Example 1 jointly confirm the rationality of 0.70 nm to 1.50 nm as the preferred interlayer spacing range, and the scientific basis for using a wide range of 0.6 nm to 2.0 nm as the effective functional range.

[0169] 5. Application Expansion Verification Group Example 11 (graphite / silicon-carbon composite anode) exhibited performance indicators highly similar to those of Example 1 in the complete set of tests. Its capacity retention rates after 200 cycles at 4C, 500 cycles at 25°C, and 200 cycles at 45°C were superior to Comparative Example 1 and Comparative Example 3, and the differences from Example 1 were within the test error range. This result demonstrates that the functional interface layer of this application can effectively perform pre-solvation and selective conduction functions in the graphite / silicon-carbon composite anode system. The interface layer maintains good structural integrity under the volume expansion conditions of silicon-containing anodes, supporting the statement in the main document that the scope of this application covers graphite or graphite-silicon-carbon composite anodes.

[0170] Example 12 (formula of Example 1 synergistic with 5wt% FEC) outperformed Example 1 in almost all test metrics. Its fast charge cycle retention, standard cycle retention, and high temperature cycle retention were all higher than those of Example 1 using only the functional interface layer, and also higher than those of Comparative Example 2 using only FEC. Apparent t Li+The improvement in Rct was also more significant than in Example 1. The performance of Example 12 was superior to both Example 1 and Comparative Example 2, indicating a positive synergistic effect between the functional interface layer and the FEC additive. This synergy stems from the complementary mechanisms of the two technologies: the functional interface layer of this application pre-desolvates lithium ions from the upstream, reducing the number of solvent molecules reaching the graphite surface; while the FEC additive optimizes the composition and density of the SEI film on the graphite surface from the downstream. Both act on different stages of the solvent co-intercalation pathway, resulting in a combined effect that surpasses their individual effects. This result directly verifies the earlier assertion that this application is fully compatible with existing electrolyte additives.

[0171] In summary, this application, by constructing a composite functional interface layer of two-dimensional organic nanosheets modified with polar functional groups and an ion-conducting polymer matrix on the negative electrode side of the separator, systematically achieves a significant increase in apparent lithium-ion transference number, an effective reduction in interfacial charge transfer impedance, and a comprehensive improvement in cycle stability under fast charging conditions. Systematic comparative data from various embodiments and comparative examples confirm the crucial roles of the asymmetric coating position on the negative electrode side, the chemical coordination of polar functional groups, the ordered parallel orientation of the nanosheets, and the appropriate interlayer spacing window in achieving the aforementioned technical effects. Furthermore, it clarifies the effective range of key process parameters, providing comprehensive experimental support for the industrial application of this application.

[0172] Table 1-1

[0173] Table 1-2

[0174] Table 1-3

[0175] Table 2-1

[0176] Table 2-2

[0177] Table 2-3

[0178] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A battery cell, characterized in that, include: A battery cell assembly, the battery cell assembly comprising a negative electrode, a separator and a positive electrode stacked together; The housing, in which the battery cell assembly is located; Electrolyte, wherein the electrolyte is located within the housing; An interface layer is attached to the side of the separator facing the negative electrode, the interface layer comprising a polymer matrix and two-dimensional organic nanosheets.

2. The battery cell according to claim 1, characterized in that, The dry film thickness of the interface layer is 0.1 μm to 1 μm.

3. The battery cell according to claim 1, characterized in that, The polymer matrix has a mass fraction of 20% to 80%, the two-dimensional organic nanosheets have a mass fraction of 20% to 80%, and the sum of the mass percentages of the polymer matrix and the two-dimensional organic nanosheets is 100%.

4. The battery cell according to any one of claims 1 to 3, characterized in that, The two-dimensional organic nanosheets are arranged in a direction parallel to the plane of the diaphragm, with a spacing of 0.6 nm to 2 nm between the sheets.

5. The battery cell according to claim 4, characterized in that, The thickness of the two-dimensional organic nanosheets does not exceed 10 nm, and the lateral dimensions are 50 nm to 5 μm.

6. The battery cell according to claim 5, characterized in that, The two-dimensional organic nanosheets include at least one of functionalized graphene nanosheets, functionalized graphene oxide nanosheets, functionalized covalent organic framework nanosheets, functionalized aromatic polyimide nanosheets, and functionalized layered polymer nanosheets, wherein the functionalized graphene nanosheets, functionalized graphene oxide nanosheets, functionalized covalent organic framework nanosheets, functionalized aromatic polyimide nanosheets, and functionalized layered polymer nanosheets all contain polar functional groups.

7. The battery cell according to claim 6, characterized in that, The polar functional group includes at least one of sulfonylimide, cyano, and etheroxy groups.

8. The battery cell according to any one of claims 1 to 3, characterized in that, The polymer matrix includes cross-linked polymers containing ethylene glycol segments or ether oxygen segments.

9. The battery cell according to claim 8, characterized in that, The crosslinked polymer includes at least one of crosslinked polyarylethers containing polyethylene glycol segments, polyurethanes containing ether oxygen units, and crosslinked polyesters containing ethylene glycol segments.

10. The battery cell according to any one of claims 1 to 3, characterized in that, The membrane has a porosity of 30% to 50% and / or a pore size of 50 nm to 200 nm.

11. The battery cell according to claim 10, characterized in that, The diaphragm includes at least one of a single-layer polyolefin diaphragm and a multilayer composite polyolefin diaphragm.

12. A method for preparing a battery cell as described in any one of claims 1 to 11, characterized in that, include: A battery cell assembly is provided, the battery cell assembly comprising a negative electrode, a separator and a positive electrode stacked together; A housing is provided to house the battery cell assembly within the housing; Provide electrolyte and inject the electrolyte into the housing; A formation process is performed to obtain battery cells; An interface layer is attached to the side of the separator facing the negative electrode, the interface layer comprising a polymer matrix and two-dimensional organic nanosheets.

13. The method for preparing a battery cell according to claim 12, characterized in that, The method for preparing the interface layer includes: Two-dimensional organic nanosheet dispersions and polymer solutions are available. The two-dimensional organic nanosheet dispersion and the polymer solution are mixed to obtain a composite slurry; The composite slurry is coated onto one side of the diaphragm and then dried.

14. The method for preparing a battery cell according to claim 13, characterized in that, The solid content of the two-dimensional organic nanosheet dispersion is 0.5% to 5%.

15. The method for preparing a battery cell according to claim 14, characterized in that, The methods for preparing the two-dimensional organic nanosheets include solution exfoliation, shear exfoliation, or ultrasound-assisted exfoliation.

16. The method for preparing a battery cell according to claim 13, characterized in that, The polymer solution has a mass fraction of 2% to 10%.

17. The method for preparing a battery cell according to any one of claims 13 to 16, characterized in that, Following the drying step, a hot pressing step is also included, wherein the conditions for the hot pressing are: temperature of 60℃~100℃ and pressure of 0.1MPa~1MPa.

18. A battery device, characterized in that, The battery device includes a battery cell as described in any one of claims 1 to 11, or a battery cell obtained by the method for preparing a battery cell as described in any one of claims 12 to 17, and the battery device includes one or more of a battery module, a battery pack, and an energy storage battery.

19. An energy storage device, characterized in that, The energy storage device includes the battery device as described in claim 18, the battery device being used to store electrical energy.

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