Battery cell, method for producing the same, battery device, electric device, and energy storage device

Abstract

The application relates to the technical field of energy storage, and provides a battery monomer, a preparation method of the battery monomer, a battery device, a power utilization 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; the electrolyte contains modified cellulose nanocrystals, the surface of the modified cellulose nanocrystals is provided with a hydrophobic group, and the specific surface area of the modified cellulose nanocrystals is not less than 150 m 2 / g. Through the synergistic effect of the high specific surface area of the cellulose nanocrystals and the specific surface modification group, a modified SEI layer which has flexibility and ionic conductivity is formed at the electrode interface, so that the cycle stability and the first cycle coulombic efficiency of the battery are significantly improved.

Description

Technical Field

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

[0002] Silicon has a theoretical specific capacity of up to 4200 mAh / g, far exceeding graphite's 372 mAh / g, and is considered the most promising next-generation anode material. However, silicon-based anodes undergo dramatic volume expansion and contraction during lithiation / delithiation, with a volume change rate exceeding 300%, posing a severe challenge to electrode structural integrity and interface stability. Summary of the Invention

[0003] This application provides a battery cell and its preparation method, battery device, power supply device and energy storage device, which at least helps to solve the problems that existing cellulose nanocrystals are difficult to disperse stably in carbonate electrolytes, difficult to use as functional additives in liquid electrolytes, and that existing film-forming additives are difficult to simultaneously take into account interfacial flexibility, chemical stability and ion conductivity.

[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, wherein the electrolyte is located within the housing; The electrolyte contains modified cellulose nanocrystals, the surface of which has hydrophobic groups, and the specific surface area of ​​which is not less than 150 m². 2 / g.

[0005] Optionally, the hydrophobic group includes at least one of silyl, alkyl, fluoroalkyl, aryl, and siloxane segments.

[0006] Optionally, the amount of the modified cellulose nanocrystals added to the electrolyte is 0.1wt% to 2.0wt%.

[0007] Optionally, the dispersed particle size D90 of the modified cellulose nanocrystals does not exceed 500 nm.

[0008] Further optionally, the dispersed particle size D90 of the modified cellulose nanocrystals is 100nm~500nm.

[0009] Optionally, the modified cellulose nanocrystals have a length of 100nm~300nm, a diameter of 5nm~15nm, and an aspect ratio of not less than 10; and / or, the crystallinity of the modified cellulose nanocrystals is not less than 70%.

[0010] Further optionally, the modified cellulose nanocrystals have an aspect ratio of 10 to 60, and / or the crystallinity of the modified cellulose nanocrystals is 70% to 95%.

[0011] Optionally, the electrolyte further comprises a film-forming additive, which includes at least one of vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, and vinyl sulfate.

[0012] 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; The electrolyte contains modified cellulose nanocrystals, the surface of which has hydrophobic groups.

[0013] Optionally, the preparation method of the modified cellulose nanocrystals includes: Preparation of cellulose nanocrystal matrix; The cellulose nanocrystal matrix is ​​surface modified to obtain the modified cellulose nanocrystals; wherein the surface modification includes silanization modification, esterification modification or etherification modification.

[0014] Optionally, the silanization modification method includes: The cellulose nanocrystal matrix was dispersed in an organic solvent, a silane coupling agent was added, and the mixture was refluxed at 100°C to 120°C to obtain the modified cellulose nanocrystals.

[0015] Optionally, the esterification modification method includes: The cellulose nanocrystal matrix is ​​reacted with an acyl-containing compound to introduce ester groups onto the surface of the cellulose nanocrystal matrix.

[0016] Optionally, the acyl-containing compound includes at least one of fatty acids, fatty acyl chlorides, acid anhydrides, or fluorinated carboxylic acids.

[0017] Optionally, the etherification modification method includes: The cellulose nanocrystal matrix is ​​reacted with an ether compound to introduce ether groups onto the surface of the cellulose nanocrystal matrix.

[0018] Optionally, the ether compound includes at least one of haloalkanes, epoxides, or aryl compounds.

[0019] Optionally, the method for preparing the cellulose nanocrystal matrix includes a sulfuric acid hydrolysis method, which comprises the following steps: Cellulose was dispersed in sulfuric acid solution and hydrolyzed at 40℃~50℃ to obtain the hydrolysis product; After centrifuging the hydrolysis product, the supernatant was taken and subjected to dialysis and freeze-drying in sequence to obtain the cellulose nanocrystal matrix.

[0020] Optionally, the amount of the silane coupling agent is 10% to 20% of the dry weight of the cellulose nanocrystal matrix.

[0021] Optionally, the silane coupling agent includes at least one of γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, alkyltrialkoxysilane, fluoroalkyltrialkoxysilane, and phenyltrialkoxysilane.

[0022] Optionally, the preparation of the modified cellulose nanocrystals is carried out in an anhydrous environment.

[0023] Thirdly, this application provides a battery device, including a battery cell as described above, or a battery cell obtained by the preparation method described above, wherein the battery device includes one or more of a battery module, a battery pack, and an energy storage battery.

[0024] Fourthly, this application provides an electrical device, which includes a battery device as described above, the battery device being used to provide electrical energy.

[0025] Fifthly, this application provides an energy storage device, which includes a battery device as described above, the battery device being used to store electrical energy.

[0026] The technical solution provided in this application has at least the following advantages: This application provides an electrolyte composition containing surface-modified cellulose nanocrystals and a battery cell comprising the electrolyte composition. The high specific surface area (≥150m²) of the cellulose nanocrystals contributes to this composition. 2 Through the synergistic effect of modified cellulose nanocrystals ( / g) and specific surface-modifying groups, modified cellulose nanocrystals can participate in the construction of a modified SEI (solid electrolyte interphase) layer with both flexibility and ion conductivity at the electrode interface, thereby significantly improving the cycle stability and first-cycle coulombic efficiency of the battery.

[0027] The battery cells provided in this application can be widely used in battery fields requiring high energy density and long cycle life, including high-end electric vehicle battery systems, portable electronic devices, and large-scale energy storage power stations. The battery cells provided in this application can achieve large-capacity energy storage, comprehensively improving energy density, cycle life, and safety performance. They can meet the needs of long-term energy storage, achieving 4 hours or more of long-term energy storage, for example, in energy storage scenarios of 5 hours, 6 hours, and 8 hours. Long-term energy storage refers to the ability to continuously discharge at rated power for 4 hours or even longer, or to achieve large-scale, low-cost energy storage for several days or months. Attached Figure Description

[0028] One or more embodiments are illustrated by way of example with corresponding pictures in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the pictures 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 technology, 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.

[0029] Figure 1 A flowchart corresponding to the method for preparing a single battery cell provided in the embodiments of this application; Figure 2 This 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 the decomposition process; In the diagram: 100, battery assembly; 10, housing; 20, individual battery cell; 11, first part; 12, second part. Detailed Implementation

[0030] As the background technology indicates, in lithium-ion battery systems, the solid electrolyte interphase (SEI) film on the negative electrode surface has a decisive influence on battery performance. An ideal SEI should possess good ionic conductivity, electronic insulation, chemical stability, and mechanical integrity. For silicon-carbon negative electrodes, the SEI also needs sufficient flexibility to accommodate volume changes in the electrode material. However, SEIs naturally formed by the reduction and decomposition of electrolyte solvents and lithium salts often fail to simultaneously meet these requirements, especially exhibiting significant deficiencies in mechanical properties. Brittle SEIs repeatedly fracture during negative electrode volume changes, and the exposed fresh electrode surface continuously consumes electrolyte, leading to increased impedance, capacity decay, and decreased coulombic efficiency.

[0031] Electrolyte additives are a crucial means of improving SEI quality. By introducing functional molecules with specific electrochemical activities into the electrolyte, the composition and structure of the SEI can be controlled. Current mainstream film-forming additives, such as vinylene carbonate and fluoroethylene carbonate, can preferentially decompose at higher potentials than the solvent, forming an interface layer rich in polymers or fluorinated inorganic substances. However, the SEI formed by these additives is still dominated by rigid components, with limited adaptability to volume changes in silicon-carbon anodes. Therefore, developing novel additives capable of forming flexible, self-healing interface layers has become a key technological direction for solving the cycling stability problem of high-capacity anodes.

[0032] Cellulose nanocrystals, as nanomaterials derived from natural renewable resources, possess characteristics such as high specific surface area, excellent mechanical strength, good biocompatibility, and sustainability. In the field of lithium-ion batteries, cellulose nanomaterials have been widely studied for applications such as separator coatings and solid electrolyte frameworks. However, research on using cellulose nanocrystals as additives in liquid electrolytes is still lacking. The main technical challenge in this application direction lies in the fact that the surface of cellulose is rich in hydrophilic hydroxyl groups, resulting in poor compatibility with carbonate-based electrolyte solvents and making stable dispersion difficult. If this key obstacle can be overcome, cellulose nanocrystals are expected to bring new technological breakthroughs to the field of electrolyte additives.

[0033] Existing lithium-ion battery electrolyte additives primarily function through a preferential decomposition mechanism to form an interfacial film. These additives have a reduction potential higher than the main electrolyte solvent, and during the first charge, they preferentially undergo electrochemical reduction at the negative electrode surface. Their decomposition products participate in the formation of the SEI (interfacial interphase), thereby improving the composition and performance of the interfacial film.

[0034] Unsaturated carbonate additives, such as vinylene carbonate (VC), undergo ring-opening polymerization of their carbon-carbon double bonds at low potentials to generate organic polymer components like polyvinylene carbonate, which then coat the electrode surface to form a flexible organic layer. Fluoroethylene carbonate (FEC) enhances the reducing activity of its molecules through the inductive effect of fluorine atoms; its decomposition products contain inorganic components such as LiF, enabling the formation of a dense inorganic-organic composite SEI. Furthermore, sulfur-containing additives such as vinyl sulfate and phosphorus-containing additives such as triethyl phosphate have also been extensively studied, introducing sulfur- and phosphorus-containing interfacial components to improve specific SEI properties, respectively.

[0035] These additives share the common characteristic of dissolving in the electrolyte in small molecule form and transforming into interfacial film components through electrochemical reactions. Their working mechanism essentially relies on the electrochemical activity of the molecules themselves, and the resulting SEI structure and performance are limited by the inherent characteristics of the molecular decomposition products.

[0036] The current applications of cellulose nanomaterials in lithium-ion batteries mainly focus on the following areas: In membrane modification, cellulose nanocrystals or cellulose nanofibers are used as membrane coating materials. A hydrophilic coating is formed by dispersing cellulose nanomaterials in an aqueous or alcohol-based solvent and coating it onto the surface of a polyolefin membrane. This coating improves the electrolyte wettability of the membrane, enhances thermal stability, and inhibits lithium dendrite growth to some extent. In this application, the cellulose nanomaterials exist as a solid coating on the membrane surface and do not form a homogeneous system with the electrolyte.

[0037] In solid-state / gel electrolytes, cellulose nanomaterials are used as the framework or reinforcing phase of polymer electrolytes. Cellulose nanonetworks provide mechanical support, while lithium salts and plasticizers fill the network pores, forming quasi-solid or gel-like electrolyte systems. In these applications, cellulose materials perform structural functions rather than interfacial regulation, and the electrolyte morphology is significantly different from that of traditional liquid electrolytes.

[0038] In electrode binders, cellulose derivatives such as sodium carboxymethyl cellulose have been widely used as negative electrode binders, especially in silicon-based negative electrode systems. The hydroxyl and carboxyl groups of cellulose can form hydrogen bonds with the surface of silicon particles, providing good adhesion and a certain degree of flexibility. In this application, the cellulose material is an integral part of the electrode formulation, rather than an electrolyte component.

[0039] In the aforementioned prior art, cellulose nanomaterials exist in solid form and their application as additives in liquid electrolytes is not involved.

[0040] Existing SEIs formed by film-forming additives have fundamental limitations in terms of mechanical properties. Organic polymer additives, such as VC, while producing decomposition products with some flexibility, have limited mechanical strength in the polymer layer, making it difficult to withstand the stress caused by hundreds of times the volume change of a silicon-carbon anode. Fluorine-containing additives, such as FEC, form inorganic LiF layers with high ionic conductivity and chemical stability, but they are inherently brittle and prone to cracking during electrode volume changes. Neither purely organic nor purely inorganic SEIs can simultaneously meet the dual requirements of high-capacity anodes for both interfacial layer flexibility and stability.

[0041] Furthermore, existing additives have a single mechanism of action, primarily relying on the electrochemical decomposition of the molecules themselves. The SEI components formed are limited by the types of small-molecule decomposition products and lack multi-scale structural regulation capabilities. For silicon-carbon anode systems that need to cope with drastic volume changes, this microscopic level interface modification effect is limited.

[0042] The densely packed hydroxyl groups (-OH) on the surface of cellulose nanocrystals endow them with strong hydrophilicity, which is the basis for their good dispersion in aqueous systems, but also constitutes a major obstacle to their migration into carbonate electrolyte systems. The main solvents for electrolytes such as ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are moderately polar ester compounds, and their solubility parameters differ significantly from those of cellulose. Unmodified cellulose nanocrystals will rapidly aggregate and settle in these solvents, failing to form a stable dispersion.

[0043] Surface hydroxyl groups may also trigger side reactions with electrolyte components. Lithium hexafluorophosphate (LiPF6), the most commonly used lithium salt in electrolytes, decomposes to produce hydrofluoric acid (HF) in the presence of trace amounts of moisture. The hydroxyl groups on the surface of cellulose may promote this decomposition process or react with HF, leading to electrolyte performance degradation. Therefore, directly using unmodified cellulose nanocrystals as electrolyte additives is technically infeasible.

[0044] While existing methods of using cellulose nanomaterials for separator coating can improve battery performance to some extent, their mechanism of action differs fundamentally from that of electrolyte additives. The separator coating is located between the positive and negative electrodes and does not directly contact the electrode surfaces. Its function primarily lies in improving electrolyte wettability and blocking lithium dendrites, rather than directly participating in the formation and regulation of the electrolyte interphase (SEI). This "indirect action" mode fails to fully leverage the structural advantages of cellulose nanomaterials' high specific surface area and flexible framework, thus limiting its effectiveness in addressing the interfacial stability issues of silicon-carbon anodes.

[0045] 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. Similarly, "multiple sets" refers to two or more sets (including two sets), and "multiple pieces" refers to two or more pieces (including two pieces).

[0046] 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.

[0047] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0048] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application. For example, if the device or element in the illustration is inverted, then the element described as "below," "under," "below," or "bottom" of other elements or features will be oriented "above" or "top" of said other elements or features. Therefore, the term "below" may cover both above and below orientation depending on the context in which the term is used, which will be obvious to those skilled in the art. Materials may be oriented in other ways (e.g., rotated 90°, inverted, flipped), and the spatial relative descriptive terms used herein may be interpreted accordingly.

[0049] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0050] In the description of embodiments of this application, the terms "about," "approximately," "roughly," or "about" for a numerical value referring to a specific parameter include the numerical value, and those skilled in the art will understand that the deviation from the numerical value is within the acceptable tolerance of the specific parameter. For example, "about" or "about" for a numerical value may include additional numerical values ​​that are in the range of 90.0% to 110.0% of the numerical value, such as in the range of 95.0% to 105.0%, 97.5% to 102.5%, 99.0% to 101.0%, 99.5% to 100.5%, or 99.9% to 100.1%.

[0051] In the accompanying drawings corresponding to the embodiments of this application, the thickness and / or area of ​​layers, films, panels, regions, etc., are enlarged for better understanding and ease of description. Throughout the specification, the same reference numerals denote the same elements. Furthermore, when describing a component as being "generally" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a portion of the edge of the entire surface.

[0052] In the description of embodiments of this application, when a component "includes" another component, other components are not excluded unless otherwise stated, and may be further included. When describing a component (such as a layer, film, region, or substrate) on or on the surface of another component, the component may be "directly" located on the surface of the other component, or there may be an intermediate component between the two components. Conversely, when describing a component on the surface of another component, or a component "directly" on another component, or a component surface on which another component is formed or disposed, it indicates that there is no intermediate component between the two components. For simplicity and clarity, various components may be drawn at any scale. In the drawings, some components may be omitted for simplicity.

[0053] 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 "the component" is also intended to include the plural form unless the context clearly indicates otherwise.

[0054] The “components” mentioned above can refer to layers, membranes, regions, parts, plates, or structures, etc.

[0055] 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.

[0056] 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, wherein the electrolyte is located within the housing; The electrolyte contains modified cellulose nanocrystals, the surface of which has hydrophobic groups, and the specific surface area of ​​which is not less than 150 m². 2 / g.

[0057] The electrolyte contains surface-modified cellulose nanocrystals. Through the synergistic effect of the high specific surface area of ​​the cellulose nanocrystals and specific surface-modifying groups, a modified SEI layer with both flexibility and ionic conductivity is formed at the electrode interface, thereby significantly improving the cycle stability and first-cycle coulombic efficiency of the battery.

[0058] More specifically, this application, for the first time, uses surface-modified cellulose nanocrystals (CNCs) as a functional additive for liquid electrolytes, distinguishing them from existing applications of cellulose nanomaterials as membrane coatings or solid / gel electrolyte frameworks, thus opening up a new application direction for cellulose nanomaterials in the field of electrolytes. The surface of the cellulose nanocrystals is modified using a silane coupling agent, and the surface polarity of the CNCs is effectively reduced through the condensation reaction between silane groups and hydroxyl groups on the cellulose surface, overcoming the key technical obstacle of poor dispersion stability of cellulose nanomaterials in carbonate electrolyte solvents. Furthermore, the technical mechanism by which silanized CNCs participate in film formation at the negative electrode interface is established: the modified CNCs undergo electrochemical reduction at low potentials at the negative electrode, and the silane groups decompose into SiO₂. xThe inorganic components and cellulose skeleton provide a flexible organic matrix, synergistically forming an organic-inorganic hybrid SEI layer that combines ion conductivity and mechanical flexibility. A functional coupling threshold of "dispersed particle size D90 of 100nm~500nm and addition amount of 0.1wt%~2.0wt%" was designed to ensure the effective dispersion of modified CNC in the electrolyte and the full utilization of its interfacial function, providing a clear process control boundary for the implementation of the technical solution. A synergistic formulation design strategy of modified CNC and conventional film-forming additives (such as vinylene carbonate VC, fluoroethylene carbonate FEC, etc.) was proposed to achieve multi-component functional complementarity and further optimize the comprehensive performance of the SEI.

[0059] Optionally, the hydrophobic group includes at least one of silyl, alkyl, fluoroalkyl, aryl, and siloxane segments.

[0060] Optionally, the modified cellulose nanocrystals are added to the electrolyte at an amount of 0.1 wt% to 2.0 wt%, specifically at 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, or 2.0 wt%.

[0061] When the amount added is too low, the interface control effect is not significant; when the amount added is too high, it may affect the viscosity and ionic conductivity of the electrolyte.

[0062] Optionally, the dispersed particle size D90 of the modified cellulose nanocrystals does not exceed 500 nm.

[0063] Further optionally, the dispersed particle size D90 of the modified cellulose nanocrystals is 100nm~500nm, specifically 100nm, 200nm, 300nm, 400nm, or 500nm.

[0064] Optionally, the length of the modified cellulose nanocrystals is 100nm~300nm, specifically 100nm, 150nm, 200nm, 250nm, or 300nm, and the diameter is 5nm~15nm, specifically 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, or 15nm, with an aspect ratio of not less than 10, and / or the crystallinity of the modified cellulose nanocrystals is not less than 70%.

[0065] Further optionally, the aspect ratio of the modified cellulose nanocrystals is 10 to 60, specifically 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, and / or the crystallinity of the modified cellulose nanocrystals is 70% to 95%, specifically 70%, 75%, 80%, 85%, 90%, 95%.

[0066] A higher aspect ratio is beneficial for modified CNC to form a fiber-reinforced network structure at the electrode interface, but an excessively high aspect ratio will increase the difficulty of dispersion and increase the viscosity of the system; a higher crystallinity is beneficial for ensuring the mechanical strength and chemical stability of the cellulose skeleton, but excessive crystallinity may reduce the surface reactive sites, which is not conducive to surface modification and interfacial interaction.

[0067] Optionally, the electrolyte further comprises film-forming additives, including at least one selected from vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, and vinyl sulfate. These additives complement the modified CNC, further optimizing the overall performance of the SEI.

[0068] Optionally, the electrolyte further includes a lithium salt and an organic solvent. The lithium salt provides migratable lithium ions to the electrolyte and is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium tetrafluoroborate (LiBF4). The lithium salt concentration is conventionally designed to meet the ionic conductivity requirements of the electrolyte. The organic solvent is the main component of the electrolyte and is selected from a mixture of cyclic and chain carbonates. Cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), etc., and chain carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. The solvent composition and ratio are adjusted according to the specific requirements of the battery system.

[0069] Secondly, this application provides a method for preparing a battery cell as described above, such as... Figure 1 As shown, it includes: S1. Provide a battery cell assembly, the battery cell assembly including a negative electrode sheet, a separator and a positive electrode sheet stacked together; S2. Provide a housing and place the battery cell assembly inside the housing; S3. Provide electrolyte and inject the electrolyte into the casing; S4. Perform the formation step to obtain battery cells; The electrolyte contains modified cellulose nanocrystals, the surface of which has hydrophobic groups.

[0070] Optionally, the preparation method of the modified cellulose nanocrystals includes: Preparation of cellulose nanocrystal matrix; The cellulose nanocrystal matrix is ​​surface modified to obtain the modified cellulose nanocrystals; wherein the surface modification includes silanization modification, esterification modification or etherification modification.

[0071] Optionally, the silanization modification method includes: The cellulose nanocrystal matrix was dispersed in an organic solvent, a silane coupling agent was added, and the mixture was refluxed at 100°C to 120°C to obtain the modified cellulose nanocrystals.

[0072] The alkoxy group (-OR) of the silane coupling agent undergoes a condensation reaction with the hydroxyl group (-OH) on the cellulose surface to form a stable Si-OC covalent bond, transforming the hydrophilic hydroxyl group into a hydrophobic surface containing silane groups.

[0073] The modified cellulose nanocrystals have silane groups grafted onto their surface, and the degree of modification can be characterized by the Si-O-Si characteristic peaks in infrared spectroscopy or the silicon content in elemental analysis. A moderate degree of modification ensures the dispersion stability of CNCs in carbonate solvents while retaining some surface active sites for interfacial interactions.

[0074] Optionally, the amount of the silane coupling agent is 10% to 20% of the dry weight of the cellulose nanocrystal matrix, specifically 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%.

[0075] Optionally, the silane coupling agent includes at least one of γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, alkyltrialkoxysilane, fluoroalkyltrialkoxysilane, and phenyltrialkoxysilane.

[0076] Optionally, the preparation of the modified cellulose nanocrystals is carried out in an anhydrous environment to avoid the self-polymerization of the silane coupling agent.

[0077] Optionally, the esterification modification method includes: The cellulose nanocrystal matrix is ​​reacted with an acyl-containing compound to introduce ester groups onto the surface of the cellulose nanocrystal matrix.

[0078] Optionally, the acyl-containing compound includes at least one of fatty acids, fatty acyl chlorides, acid anhydrides, or fluorinated carboxylic acids.

[0079] Optionally, the etherification modification method includes: The cellulose nanocrystal matrix is ​​reacted with an ether compound to introduce ether groups onto the surface of the cellulose nanocrystal matrix.

[0080] Optionally, the ether compound includes at least one of haloalkanes, epoxides, or aryl compounds.

[0081] Modified cellulose nanocrystals should be stored in a dry, inert atmosphere to avoid moisture absorption and oxidation.

[0082] This application establishes a functional threshold system for modified CNC to ensure its effective dispersion in the electrolyte and full utilization of its interfacial function. The dispersion particle size (D90) of the modified CNC in the electrolyte should be controlled within the range of 100 nm to 500 nm. This threshold is set based on the following: if the dispersion particle size is too large, the modified cellulose nanocrystals are prone to agglomeration and sedimentation, affecting the dispersion stability of the electrolyte and potentially clogging the membrane pores; if the dispersion particle size is too small, the specific surface area is too large, which may lead to increased electrolyte viscosity and enhanced interfacial side reactions, making it difficult to balance dispersion stability and bulk transport performance. The dispersion particle size and the addition amount (0.1 wt% to 2.0 wt%) form a coupled constraint, jointly defining the effective implementation boundary of the technical solution.

[0083] This application establishes a functional threshold system for modified CNC to ensure its effective dispersion in electrolytes and full utilization of its interfacial functions. The particle size D90 of the modified CNC in the electrolyte should be controlled within the range of 100 nm to 500 nm. This threshold is set based on the following: The silanized modified CNC exists in a dispersed state in the electrolyte, wetting the electrode surface along with the electrolyte. During the first charge of the battery, the negative electrode potential gradually decreases. When the potential falls below the reduction potential of the silane group, the modified CNC undergoes an electrochemical reduction reaction on the negative electrode surface.

[0084] The decomposition pathway of silane groups at low potentials is as follows: Si-OC bond breaks, and the organosilane undergoes partial reduction decomposition to generate SiO. x (x≤2) Inorganic species. These silicon-containing inorganic species are deposited on the electrode surface and become part of the SEI. The cellulose skeleton also undergoes partial reduction decomposition at low potentials, and CO bonds break to generate carbon- and oxygen-containing organic fragments. These fragments, together with solvent decomposition products, constitute the organic components of the SEI.

[0085] Based on the above electrochemical process, the SEI formed by silanized CNC exhibits organic-inorganic hybrid structural characteristics. The SiO₂ generated from the decomposition of silane groups... x The inorganic framework provides high mechanical modulus and good lithium-ion conductivity; the cellulose decomposition products and solvent decomposition products provide the organic matrix, which has good flexibility and interfacial adhesion. The organic and inorganic phases interpenetrate and cooperate with each other at the nanoscale to form an interfacial layer that has both mechanical strength and deformation adaptability.

[0086] This organic-inorganic hybrid structure is particularly significant for high-capacity anodes. When the silicon-carbon anode undergoes volume changes during charge and discharge, the organic component in the hybrid SEI can adaptively deform, absorbing and dispersing mechanical stress; while the inorganic component maintains the chemical stability and ion conduction function of the interface. The synergy of the two components enables the SEI to adapt to electrode volume changes to a certain extent, reducing the cracking-regeneration cycle, thereby improving the cycle stability and coulombic efficiency of the battery.

[0087] When modified CNC is used in combination with conventional additives such as VC and FEC, the components participate in the formation of the SEI sequentially according to their differences in reduction potential. Additives with higher reduction potentials (such as FEC) decompose preferentially, forming the inner layer of the SEI; modified CNC and VC decompose at slightly lower potentials, forming the outer or middle layer of the SEI. This layered structure allows the SEI to possess the characteristics of each component simultaneously: the inner layer of fluorinated inorganic materials provides chemical stability, while the outer layer of organic-inorganic hybrid components provides mechanical flexibility.

[0088] Optionally, the method for preparing the cellulose nanocrystal matrix includes a sulfuric acid hydrolysis method, which comprises the following steps: Cellulose was dispersed in sulfuric acid solution and hydrolyzed at 40℃~50℃ to obtain the hydrolysis product; After centrifuging the hydrolysis product, the supernatant is collected and subjected to dialysis and freeze-drying or spray drying to obtain the cellulose nanocrystal matrix. Through centrifugation and dialysis, residual sulfuric acid and oligosaccharides can be removed to obtain a purified aqueous dispersion of cellulose nanocrystals.

[0089] Sulfuric acid preferentially hydrolyzes the amorphous regions of cellulose, retaining highly crystalline crystalline regions to form rod-shaped nanocrystals.

[0090] Optionally, the cellulose includes plant cellulose such as wood pulp, cotton pulp, and bamboo pulp, or bacterial cellulose.

[0091] Optionally, the method for preparing the electrolyte includes: Modified CNC powder needs to be pre-dispersed before being added to the electrolyte to ensure its uniform distribution. The modified CNC powder is added to a portion of an organic solvent (such as DMC or EMC) and then dispersed by ultrasonication or high-pressure homogenization to prepare a high-concentration pre-dispersion. The parameters for the pre-dispersion are determined based on equipment conditions, with the threshold requirement of the CNC particle size distribution D90 in the dispersion being within the range of 100nm to 500nm as the standard.

[0092] The electrolyte was prepared in an inert atmosphere glove box. First, the organic solvents were mixed thoroughly in the designed proportions. Then, lithium salt was added and stirred until dissolved. Next, modified CNC pre-dispersion was added, and finally, other functional additives were added. Each component was thoroughly stirred after addition to ensure uniform mixing. The prepared electrolyte should be tested for moisture content to ensure it meets battery-grade requirements.

[0093] Optionally, the assembly of the battery cells in this application is carried out according to conventional processes, including electrode preparation, stacking / winding, encapsulation, electrolyte injection, and formation. The electrolyte injection process is the same as that of conventional liquid electrolytes, and the presence of modified CNC does not affect the fluidity of the electrolyte or the electrolyte injection operation. The battery system can be a lithium-ion battery system with silicon-carbon anode and ternary cathode, or other battery systems such as graphite anode and lithium iron phosphate cathode.

[0094] In this application, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer comprising a positive electrode active material. As an example, the positive current collector has two opposing surfaces, and the positive electrode film layer is disposed on either or both of the opposing surfaces of the positive current collector.

[0095] The positive electrode current collector can be a metal foil or a composite current collector. For example, the metal foil may include, but is not limited to, aluminum foil. The composite current collector may include a base layer and a metal layer located on at least one surface of the base layer. For example, the base layer may be a polymer material base layer, including but not limited to polypropylene (PP) base layer, polyethylene terephthalate (PET) base layer, polybutylene terephthalate (PBT) base layer, polystyrene (PS) base layer, or polyethylene (PE) base layer. The material of the metal layer may include, but is not limited to, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy.

[0096] The positive electrode active material includes lithium salts, such as lithium-containing phosphates. Lithium-containing phosphates refer to phosphate materials containing lithium elements and can be detected by any method known in the art. For example, they can be detected by combining X-ray diffraction with energy dispersive spectroscopy (EDS) or inductively coupled plasma mass spectrometry (ICP-MS). As examples, lithium-containing phosphates include, but are not limited to, lithium iron phosphate, lithium iron phosphate doped and modified materials, or lithium iron phosphate coated and modified materials.

[0097] For example, the positive electrode active material can also be a high-voltage system with a working voltage greater than or equal to 4.3V, such as high-nickel ternary materials, high-voltage spinel materials, lithium manganese phosphate, or lithium-rich manganese-based materials.

[0098] For example, high-nickel ternary materials such as LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.15 Al 0.05 O2 (NCA) and other compounds possess operating voltages of 4.3V~4.6V and high specific capacity, making them ideal cathode choices for high-voltage lithium metal batteries. High-voltage spinel LiNi... 0.5 Mn 1.5 O4 operates at a voltage up to 4.7V, perfectly matching its high voltage stability. Lithium manganese iron phosphate, a type of lithium manganese phosphate, is an emerging high-voltage phosphate material that combines safety and high-voltage characteristics.

[0099] However, this application is not limited to the materials listed above, and other materials that can be used as positive electrode active materials in battery cells may also be used. These positive electrode active materials may be used alone, or two or more may be used in combination.

[0100] The positive electrode film may also include a binder and / or a conductive agent.

[0101] The binder may be selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), or polyacrylic acid (PAA). The conductive agent may be selected from one or more of conductive carbon black, superconducting carbon, Ketjen black, carbon dots, acetylene black, graphene, carbon nanotubes, carbon nanofibers, or graphite.

[0102] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material. As an example, the negative electrode current collector has two opposing surfaces, and the negative electrode film layer is disposed on either or both of the opposing surfaces of the negative electrode current collector.

[0103] The negative electrode current collector can be a metal foil or a composite current collector. For example, the metal foil may include, but is not limited to, copper foil. The composite current collector may include a base layer and a metal layer located on at least one surface of the base layer. For example, the base layer can be a polymer material, including but not limited to polypropylene (PP) base layer, polyethylene terephthalate (PET) base layer, polybutylene terephthalate (PBT) base layer, polystyrene (PS) base layer, or polyethylene (PE) base layer. The material of the metal layer may include, but is not limited to, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, or silver alloys.

[0104] The negative electrode active material can be any negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material can be at least one of the following materials, including but not limited to: graphite, carbon materials, silicon-based materials, tin-based materials, or lithium titanate. Graphite can be artificial graphite or natural graphite. Carbon materials can be soft carbon or hard carbon. Silicon-based materials can be selected from at least one of elemental silicon, silicon oxide, silicon-carbon compounds, silicon-nitrogen compounds, and silicon alloys. Tin-based materials can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other materials that can be used as negative electrode active materials for battery cells can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0105] Optionally, the negative electrode film may also include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0106] Optionally, the negative electrode film layer may also include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0107] Optionally, the negative electrode film may also include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0108] The membrane material can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. This application does not impose any particular limitation on the type of membrane; for example, a porous membrane with chemical and mechanical stability can be selected.

[0109] The separator can be a single-layer thin film or a multi-layer composite thin film; there are no particular restrictions. When the separator is a multi-layer composite thin film, the materials of each layer can be the same or different; there are no particular restrictions.

[0110] In some specific examples, the separator may include polypropylene (PP) separators, polyethylene (PE) separators, PP / PE / PP three-layer composite separators, ceramic-coated separators, high-strength polymer separators, or functionalized composite separators. PP and PE separators typically have a thickness of 12μm to 25μm and a porosity of 30% to 50%, exhibiting good mechanical strength and chemical stability. Ceramic-coated separators, with a coating of ceramic materials such as Al2O3, SiO2, and TiO2 (coating thickness 2μm to 5μm) on a polyolefin-based membrane, improve high-temperature resistance (thermal shut-off temperature >160℃) and puncture resistance. High-strength polymer separators (such as polyimide (PI), polyethylene terephthalate (PET), and aramid nanofiber separators) possess excellent mechanical properties and high-temperature resistance. Functionalized composite separators (such as separators containing solid electrolyte coatings or lithiophilic coatings) can further enhance lithium deposition stability.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] Fourthly, this application provides an electrical device, which includes a battery device as described above, the battery device being used to provide electrical energy.

[0117] Electrical devices include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0118] Fifthly, this application provides an energy storage device, which includes a battery device as described above, the battery device being used to store electrical energy.

[0119] Energy storage devices include, but are not limited to, residential energy storage cabinets, commercial energy storage cabinets, energy storage containers, energy storage racks, energy storage power stations, energy storage battery packs, or portable energy storage systems. Energy storage devices may also include energy management systems (EMS), battery management systems (BMS), and power conversion systems (PCS).

[0120] The innovation of this application is also reflected in the following aspects: 1. Innovation in application formats This application transfers cellulose nanocrystals from existing applications such as membrane coatings and solid electrolyte frameworks to the new field of liquid electrolyte additives. The fundamental significance of this shift lies in enabling cellulose nanomaterials to directly participate in the electrochemical processes at the electrode interface, rather than merely serving as a passive physical barrier or support structure. Modified CNC nanomaterials in a liquid dispersion state can be wetted and coated onto the electrode surface by the electrolyte, transforming in situ into interfacial film components under electrochemical driving, thus achieving a functional upgrade from "indirect action" to "direct participation."

[0121] 2. Solving the problem of dispersion stability This application addresses the dispersion stability issue of cellulose nanomaterials (CNCs) in carbonate solvents by transforming the hydrophilic hydroxyl groups on the cellulose surface into hydrophobic groups through hydrophobic surface modification. This represents a key technological breakthrough in enabling cellulose nanomaterials as electrolyte additives. The unique advantage of hydrophobic modification lies in its ability to not only solve the dispersion problem but also provide functional precursors for subsequent interfacial film formation—for example, silane groups can be converted into SiO2 under electrochemical reduction. x Inorganic components.

[0122] 3. Innovation in interfacial film formation mechanism This application establishes a technical mechanism for the formation of organic-inorganic hybrid SEIs through silanized CNC. Unlike existing additive-based SEIs formed purely organic or purely inorganically, this application's technical solution achieves in-situ composite formation of organic and inorganic phases in one step through the multi-component decomposition of a single additive. The silane group provides SiO₂. x The inorganic component and the cellulose framework provide a flexible organic matrix, and the two work synergistically to form a film at the interface. This "integrated hybrid film formation" mechanism simplifies formulation design while achieving structural synergistic effects.

[0123] 4. Multi-scale interface control capability The nanoscale rod-like morphology of cellulose nanocrystals endows them with unique interfacial modulation capabilities. Modified CNC can form a cross-linked network structure on the electrode surface, a multi-scale structural feature that is difficult to achieve with small molecule additives. The high aspect ratio of the nanorods gives the SEI layer a fiber-reinforced effect, improving the mechanical integrity and crack propagation resistance of the interfacial layer. This is of great significance for addressing volume changes in silicon-carbon anodes.

[0124] 5. Establishment of a functional threshold system This application establishes a functional coupling threshold system with a "dispersed particle size D90 of 100nm~500nm and an addition amount of 0.1wt%~2.0wt%". The technical basis for this threshold design is that the particle size threshold ensures sufficient dispersion of the modified CNC without clogging the membrane pores, while the addition amount threshold balances the interface regulation effect and the bulk performance of the electrolyte. This dual-parameter coupling constraint provides a clear boundary for the implementation of the technical solution and also provides more precise technical features for this application.

[0125] 6. Green and sustainable attributes Cellulose, as the most abundant natural polymer material on Earth, possesses environmentally friendly characteristics such as being renewable and biodegradable. This application introduces cellulose nanomaterials into the field of electrolyte additives. Compared with synthetic additives, cellulose-based additives have more sustainable raw material sources and lower environmental impact during production, providing a new approach for the green development of battery materials.

[0126] 7. Formulation compatibility and co-design The modified CNC described in this application is compatible with existing mainstream film-forming additives (VC, FEC, etc.) to form a functionally complementary composite additive system. The advantage of this design strategy is that it does not require complete replacement of existing additive formulations, allowing for incremental improvements based on existing technologies, thus reducing the barriers and risks associated with technology adoption. Different additives form films sequentially according to their reduction potential, creating a multi-layered SEI structure and comprehensively leveraging the performance advantages of each component.

[0127] To verify the technical solution proposed in this application, which uses surface-modified cellulose nanocrystals (CNC) as the core functional additive to construct an organic-inorganic hybrid solid electrolyte interface (SEI) to improve the interfacial stability of silicon-carbon anode lithium-ion batteries, a series of embodiments and comparative examples were designed, as shown in Tables 1-1 and 1-2. These examples systematically explored the necessity of silanization surface modification, the coupling functional boundary between the dispersion particle size threshold (D90 of 100nm~500nm) and the addition amount window (0.1wt%~2.0wt%), the synergistic film-forming mechanism of modified CNC and conventional film-forming additives (FEC, VC), and the influence of different silane coupling agent routes and different anode systems on the technical performance. The following details the specific parameters of the raw materials used, the preparation method of modified CNC, the electrolyte formulation process, the battery assembly scheme, and various performance testing methods.

[0128] (a) Raw material description The cellulose nanocrystals (CNC) matrix used in this application was prepared from cotton pulp cellulose raw material by sulfuric acid hydrolysis. Refined cotton pulp was hydrolyzed in a 64% sulfuric acid solution at 45°C for 2 hours. The hydrolysis product was centrifuged (8000 rpm, 15 min), dialyzed (molecular weight cutoff 12000 Da~14000 Da, dialyzed to pH ≥ 6), and freeze-dried to obtain CNC powder with a length of 100 nm~300 nm, a diameter of 5 nm~15 nm, an aspect ratio of not less than 10, and a crystallinity of not less than 75%. Its type II cellulose crystal form was confirmed by X-ray diffraction (XRD) for later use.

[0129] Silane coupling agents used were γ-methacryloyloxypropyltrimethoxysilane (KH-570, purity ≥98%, molecular weight 248.35 g / mol) and γ-aminopropyltriethoxysilane (APTES, purity ≥99%, molecular weight 221.37 g / mol), which were used for CNC surface modification in different embodiments. Ethyl methyl carbonate (EMC, battery grade), ethylene carbonate (EC, battery grade), dimethyl carbonate (DMC, battery grade), fluoroethylene carbonate (FEC, purity ≥99%), and vinylene carbonate (VC, purity ≥99%) were all purchased commercially and their water content was confirmed to be below 20 ppm by Karl Fischer titration before use. Lithium hexafluorophosphate (LiPF6, battery grade) had a water content below 10 ppm. The positive electrode active material was LiNi. 0.6 Co 0.2 Mn 0.2 O2 (NCM622, D50 = (10±1) μm, tap density 2.2 g / cm³) 3 The main test system used silicon-carbon composite material (Si-C, silicon content 15wt%, initial lithium insertion capacity approximately 1200mAh / g) as the negative electrode material. The application extension verification system (Example 7) used artificial graphite (D50=15μm, initial lithium removal capacity approximately 360mAh / g) as the negative electrode material, with lithium iron phosphate (LFP, D50=1.5μm) as the corresponding positive electrode. The lithium metal sheet used for half-cell assembly had a diameter of 15.6mm and a thickness of 0.5mm. All the above water- and oxygen-sensitive raw materials were tested at a dew point ≤ Store and use in a drying room at 40°C or in an argon glove box with both water and oxygen content below 0.1 ppm.

[0130] (II) Preparation of surface-modified cellulose nanocrystals Preparation of KH-570 silanized modified CNC (s-CNC, used in Examples 1, 3, 4, 5, and Examples 2-5): CNC powder was vacuum dried at 105°C for 24 h to fully remove adsorbed water, then dispersed in anhydrous toluene (water content <50 ppm) to prepare a 5 wt% CNC / toluene suspension. After ultrasonic dispersion (40 kHz, 100 W, 20 min), 15 wt% KH-570 (based on the dry weight of CNC) was added, and the mixture was stirred under reflux at 110°C for 6 h to allow the trimethoxysilyl groups on the KH-570 molecule to fully condense with the hydroxyl groups on the CNC surface. After the reaction was complete, the product was separated by centrifugation (8000 rpm, 15 min), washed three times with anhydrous ethanol to remove unreacted silane monomers and byproducts, and dried in a vacuum oven at 60°C for 24 h to obtain KH-570 modified CNC powder (denoted as s-CNC). 1083 cm⁻¹ from Fourier transform infrared (FT-IR) -1 The Si-O-Si stretching vibration peak appears at 3400 cm⁻¹. -1 The decrease in the intensity of the hydroxyl characteristic peak confirmed the successful modification, and elemental analysis verified that the Si content was within the target range (1.8wt%~2.2wt%).

[0131] Preparation of APTES-modified CNC (for Example 6): KH-570 was replaced with APTES, and the remaining process steps and parameters were exactly the same as those for KH-570-modified CNC, resulting in APTES-modified CNC powder. The powder was then analyzed by FT-IR at 3300 cm⁻¹. -1 The appearance of the NH stretching vibration peak in the vicinity and the elemental analysis of Si confirmed the successful modification.

[0132] Unmodified raw CNC (used for Comparative Example 2): Raw CNC powder prepared directly by acid hydrolysis without any surface modification treatment was used directly for subsequent electrolyte preparation.

[0133] CNC with particle size exceeding the threshold (used for comparative example 3): It was prepared using the same KH-570 modification process as s-CNC, but the ultrasonic power was deliberately reduced in the pre-dispersion step (40W, 10min) so that the dispersed particle size D90 in the final pre-dispersion liquid was kept at 800nm~1000nm, so as to form a single variable control group of "silylation completed but dispersed particle size exceeding the threshold".

[0134] Free KH-570 silane small molecule control solution (used for Comparative Example 6): Based on the amount of s-CNC added (0.5wt%) in Example 1 and its measured Si content, the corresponding mass of KH-570 was calculated according to the equivalent Si atomic weight. When preparing the electrolyte, the calculated amount of KH-570 was directly dissolved in the basic electrolyte without adding any CNC carrier. This was used to examine the independent effect of "free silane small molecules with equivalent Si content" as a common additive, and to distinguish the source of the technical effect of this application.

[0135] (III) Preparation of electrolyte The basic electrolyte system used in all embodiments and comparative examples consisted of 1.0 mol / L LiPF6 dissolved in a mixed solvent of EC / DMC / EMC (mass ratio 3:5:2), and the standard functional additive combination was 2.0 wt% FEC and 1.0 wt% VC (except for Comparative Example 4). The electrolyte was kept at a dew point ≤ Prepare the electrolyte in a 40℃ drying room according to the following steps: First, weigh EC, DMC and EMC according to the mass ratio and stir in a 50℃ water bath until EC is completely dissolved. After cooling to room temperature, add LiPF6 and stir thoroughly until completely dissolved. Then add FEC and VC (skip this step for comparative group 4), stir evenly, and the basic electrolyte is prepared.

[0136] The modified CNC was added using a pre-dispersion doping method. s-CNC powder was added to an appropriate amount of EMC and ultrasonically treated (40kHz, 100W, 20min) to prepare an s-CNC / EMC pre-dispersion. After confirming that the dispersed particle size D90 was within the range of 100nm~500nm, the required amount of pre-dispersion was added to the prepared base electrolyte and magnetically stirred (500rpm, 30min) until homogeneous. Comparative Example 2 (unmodified CNC) and Comparative Example 3 (s-CNC with particle size exceeding the threshold) were prepared using the same procedure, with the ultrasonic step in Comparative Example 3 changed to 40W×10min to intentionally retain a larger particle size (target D90 approximately 850nm). Comparative Example 6 directly added the calculated amount of KH-570 free silane to the base electrolyte and magnetically stirred for 30min without a pre-dispersion step. Comparative Example 1 was prepared without adding any CNC-related components, containing only the standard FEC / VC system. All prepared electrolytes were subjected to Karl Fischer water content determination, and only those with a water content of <20 ppm could proceed to the next process.

[0137] (iv) Battery assembly The negative electrode half-cell (button type, CR2032) was used for first-week coulombic efficiency (ICE) testing and electrochemical impedance spectroscopy (EIS) testing. The Si-C negative electrode half-cell used a Si-C electrode as the working electrode and a lithium metal sheet as the counter and reference electrode; the graphite negative electrode half-cell (only in Example 7) used a graphite electrode as the working electrode and a lithium metal sheet as the counter electrode. The Si-C negative electrode slurry formulation (mass ratio) was Si-C:Super P:CNT:PAA = 90:4:1:5, using deionized water as the slurry solvent. It was coated onto copper foil, vacuum dried at 110℃ for 12 hours, and the density after rolling was controlled at (4.5±0.2) mg / cm³. 2 Compacted density 1.5 g / cm³ 3 The areal density of the graphite anode sheet is (6.0±0.2) mg / cm³. 2 Compacted density 1.55 g / cm³ 3 All button cells have a dew point ≤ Assembled in a drying chamber at 40℃, with an electrolyte injection volume of 80μL / piece, and the diaphragm is a 16μm PP / PE / PP three-layer composite membrane.

[0138] The full cell (stacked soft pack, designed capacity 2.0Ah) was used for cycle capacity retention, high-temperature cycling, and rate performance testing. The positive electrode slurry formulation (mass ratio) for the Si-C / NCM622 full cell was NCM622:Super P:CNT:PVDF = 94:3:1:2, using N-methylpyrrolidone (NMP) as solvent, coated onto aluminum foil, and rolled to a density of (8.0±0.3) mg / cm³. 2 Compacted density 3.2 g / cm³ 3 Graphite / LFP full cell (Example 7): The positive electrode is an LFP electrode (area density (18.0±0.5) mg / cm³). 2 Compacted density 2.35 g / cm³ 3 The negative electrode is a graphite electrode. The separator of the full cell adopts a 12μm PP / PE / PP three-layer composite membrane, with an electrolyte injection volume of 4.5g / Ah. All assembly processes, including stacking, hot pressing, vacuum drying (85℃×6h), electrolyte injection, and sealing, are completed in a drying chamber. Formation method: The first cycle is charged at a constant current of 0.05C to 4.3V (Si-C / NCM622) or 3.65V (graphite / LFP), and after standing for 10min, discharged at 0.05C to the cutoff voltage; the second cycle completes the charge and discharge at 0.1C; the third cycle completes the charge and discharge at 0.2C. After formation, the cells are left to stand at room temperature for 48h for initial capacity calibration. Unless otherwise specified, at least 3 parallel cells are prepared for each group of battery performance tests, and the results are reported as the arithmetic mean.

[0139] (v) Performance testing methods 1. Dispersed particle size D90 test The particle size distribution of each group of pre-dispersed electrolyte containing CNC was determined using a laser diffractometer (wet dispersion mode). The dispersion medium was EMC, and the refractive index parameter was set with cellulose as a reference (n=1.47). Direct testing with the final electrolyte containing LiPF6 would affect the accuracy due to LiPF6 volatilization and water absorption; therefore, the pre-dispersed solution (s-CNC / EMC system) was used as the test object. D90 (nm) was recorded at two time points: 0h and 24h after preparation. Each sample was measured in triplicate, and the average value was taken. Comparative Example 1 (without CNC) and Comparative Example 6 (free silane small molecules, no CNC particles) were not suitable for this test and were recorded as N / A.

[0140] 2. Static Settlement Stability Test Each group of CNC-containing final electrolyte solutions (5 mL each) was injected into transparent sealed containers and allowed to stand at room temperature (25°C). Photographs were taken at 0, 1, 3, and 7 days to record changes in appearance (liquid transparency, sedimentation layer color, and morphology). On day 7, the sedimentation layer height (mm) was measured using a 0.1 mm vernier caliper, and the percentage (%) of the sedimentation layer to the total liquid column height was calculated to quantitatively evaluate dispersion stability. Comparative Examples 1 and 6, which did not contain CNC particles, were denoted as N / A.

[0141] 3. Ionic conductivity test (25℃) The ionic conductivity of each electrolyte group at 25℃ was determined using the blocked electrode method. The electrolyte was injected into a standard test fixture consisting of two stainless steel blocked electrodes (effective electrode area S = 1.13 cm²). 2 In an electrode spacing d = 1.0 mm, after equilibration in a constant temperature water bath at 25℃ for 30 min, electrochemical impedance spectroscopy (EIS) was performed using an electrochemical workstation under conditions of frequency range 0.01 Hz ~ 1 MHz and AC amplitude 10 mV. The solution resistance R (Ω) was obtained from the high-frequency intercept of the Nyquist plot, and the ionic conductivity (mS / cm) was calculated using the formula σ = d / (R × S), where d is in cm and S is in cm. 2 Each electrolyte group was measured in triplicate, and the average value was taken.

[0142] 4. Dynamic viscosity test (25℃) The dynamic viscosity of each electrolyte group was measured using a coaxial cylindrical rotational viscometer under constant temperature conditions of 25℃. The shear rate was set to 100 s. -1 After the readings stabilize, record the dynamic viscosity η (mPa·s). Each group was measured in triplicate, and the average value was taken.

[0143] 5. First Week Coulomb Efficiency (ICE) Test The first-week coulombic efficiency was measured using a coin cell with the negative electrode to directly characterize irreversible lithium consumption during the initial SEI formation process. The charge / discharge voltage window for the Si-C negative electrode half-cell (Si-C||Li) was set to 0.005V~1.5V (vs. Li / Li). + The charge / discharge voltage window for the graphite anode half-cell (Graphite||Li, only Example 7) was set to 0.005V~2.0V (vs. Li / Li). + The first cycle involved constant current discharge (lithium insertion) at 0.1C to the lower cutoff voltage, followed by resting for 10 minutes and constant current charging (lithium removal) at 0.1C to the upper cutoff voltage. The lithium insertion specific capacity Q was recorded for the first cycle. 嵌 (mAh / g) and the specific capacity Q of delithiation in the first week 脱 (mAh / g), according to the formula ICE (%) = (Q 脱 / Q 嵌 Calculate the first-week coulombic efficiency by multiplying the result by 100%. At least three parallel half-cells should be measured in each group, and the average value should be taken.

[0144] 6. 25℃ Cyclic Capacity Retention Rate Test Cyclic performance testing was conducted using full-cell (pouch) batteries in a constant-temperature environment of 25°C. The charge / discharge voltage window for Si-C / NCM622 full-cell batteries was set to 2.8V~4.3V, and for graphite / LFP full-cell batteries (Example 7), it was set to 2.5V~3.65V. Both were charged and discharged using a 1C constant-current charge / discharge regime (charging cutoff condition: constant current charging to the upper voltage limit followed by constant voltage charging to the cutoff current of 0.05C). All 13 examples and comparative examples were tested to 100 cycles, and the capacity retention rate was recorded on the 100th cycle. The core verification group (Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 4) and the parameter boundary verification group (Comparative Example 3, Comparative Example 5, Examples 2~5, Comparative Example 6, Example 6) were tested to 200 cycles, and the capacity retention rate was recorded on the 200th cycle. The application extension group, Example 7, was only tested to 100 cycles. The capacity retention rate was calculated as follows: Capacity retention rate (%) = Discharge capacity on the nth cycle / Calibrated discharge capacity on the 1st cycle × 100%. At least three parallel batteries were measured in each group, and the average value was taken.

[0145] 7. 45℃ High Temperature Cyclic Capacity Retention Rate Test High-temperature cycling tests were conducted in a 45°C constant-temperature chamber, with the charge / discharge regime and voltage window settings identical to those used in the 25°C cycling tests. This test was only performed on the key mechanism verification group (Example 1, Comparative Example 1, Comparative Example 4, and Comparative Example 6), and was conducted up to 100 cycles, with the capacity retention rate (%) recorded on the 100th cycle. At least three parallel cells were measured for each group, and the average value was taken. This test aims to amplify the differences in stability of different SEI chemical compositions at high temperatures through thermodynamic acceleration conditions.

[0146] 8. Rate performance test (3C / 0.2C capacity ratio) Rate performance testing used full cells (from the same batch as the cycle performance test) and was conducted only on four groups: Example 1, Comparative Example 1, Comparative Example 3, and Comparative Example 5. Charging conditions were fixed at 0.5C constant current to the cutoff voltage, followed by constant voltage charging to the cutoff current of 0.05C. Discharge rates were set at 0.2C and 3C, with three discharge cycles at each rate, and the average value of the last two cycles was taken. The rate performance index was calculated using the formula: 3C / 0.2C capacity ratio (%) = 3C average discharge capacity / 0.2C average discharge capacity × 100%. At least three parallel cells were tested for each group, and the average value was taken.

[0147] 9. Interfacial Impedance (RSEI) Test Interfacial impedance testing was conducted using Si-C negative electrode coin cells, and was carried out only for the core mechanism verification group (Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 4, and Comparative Example 6). Testing was performed after formation (referred to as the initial stage) and after 50 full-cell cycles (the cells from the same batch were disassembled, the Si-C electrodes were removed and reassembled into half-cells, and the cells were allowed to relax fully in a 50°C vacuum drying oven for 2 hours before testing). EIS testing conditions: frequency range 100kHz~0.01Hz, AC amplitude 10mV (vs. OCV), constant temperature 25°C. All groups underwent impedance fitting using a unified equivalent circuit model Rs-(RSEI||CPE1)-(Rct||CPE2), where Rs is the solution resistance, RSEI is the SEI film resistance, Rct is the charge transfer resistance, and CPE1 and CPE2 are constant-phase angle elements (to describe the frequency dispersion characteristics of the actual interface). All groups used the same initial model parameters and fitting boundary conditions to ensure the horizontal comparability of RSEI values ​​across groups. The converted RSEI values ​​were recorded. 初始 (Ω·cm) 2 ), after 50 laps RSEI 50圈 (Ω·cm) 2 ) and growth rate (%) = (RSEI 50圈 RSEI 初始 ) / RSEI 初始 ×100%. At least 3 parallel half-cells were measured in each group, and the average value was taken.

[0148] (vi) Data Description Unless otherwise specified, all performance data cited in the results analysis and discussion sections below are the arithmetic mean of the test results of at least three parallel samples (half-cell or full-cell) for each group. Electrolyte physicochemical tests (particle size, sedimentation, conductivity, viscosity) were repeated three times for each group, and the average value was taken. Typical test error ranges: physicochemical parameters of the electrolyte within ±2%; ICE within ±1 percentage point; cycle capacity retention within ±3 percentage points; RSEI within ±8%.

[0149] The following analysis and discussion of the test results of each embodiment and comparative example are conducted in groups according to the verification logic of the five core technical claims of this application (as shown in Tables 2-1 and 2-2), mainly including the following parts.

[0150] (i) Silanization surface modification is a technical prerequisite for the introduction of modified CNC into the liquid electrolyte system. The results of particle size and static sedimentation tests directly revealed the decisive significance of silanization surface modification for the dispersion stability of cellulose nanocrystals in carbonate electrolytes. KH-570-modified CNC (Example 1, D90 = 285 nm) maintained a relatively stable particle size after 24 hours in EMC pre-dispersion solution, and the sedimentation layer ratio after 7 days was less than 5%, exhibiting good colloidal stability and meeting the basic engineering requirements for liquid electrolyte additives. In stark contrast, the original CNC without any surface modification (Comparative Example 2, D90 > 2000 nm) rapidly and severely agglomerated after the addition of solvent; the particle size measurement after 24 hours exceeded the normal range of the instrument, and the sedimentation layer ratio after 7 days exceeded 60%, indicating complete failure of the dispersion system. This result confirms the presence of abundant hydrophilic hydroxyl groups on the CNC surface (… The presence of OH (hydroxyl) causes a significant mismatch between its solubility parameters and moderately polar carbonate solvents such as EC / DMC / EMC. The original CNC cannot maintain its dispersion in this system, making it technically infeasible to use it directly as an additive in liquid electrolytes.

[0151] Further noteworthy is that the first-week coulombic efficiency (ICE = 73.8%) of Comparative Example 2 was not only significantly lower than that of Example 1 (ICE = 83.5%) with modified CNC, but also significantly lower than that of the blank comparative example without any CNC, i.e., Comparative Example 1 (ICE = 77.2%). This negative result, "below baseline," has significant mechanistic evidentiary value: the severely agglomerated original CNC is randomly deposited as irregular large-sized agglomerates on the negative electrode surface, resulting in a more uneven SEI film formation process. This leads to a significant difference in electrochemical activity between the agglomerate-covered area and the exposed area, and irreversible lithium consumption is actually higher than that of the conventional electrolyte system without any CNC. The above results negatively demonstrate that silanization modification is not only a dispersion technique that "allows CNC to be added to the electrolyte," but also a necessary functional prerequisite for "exerting a positive interface regulation effect after addition," strongly supporting the technical rationality of one of the core innovations of this application. The 25℃ cycle capacity retention test (77.8% for Comparative Example 2 at the 100th cycle and 66.8% at the 200th cycle, both significantly lower than 82.2% and 71.5% for Comparative Example 1) further confirms the continued negative impact of unmodified CNC on battery performance from a long-term cycle perspective.

[0152] (ii) The dispersion particle size threshold D90 is 100nm~500nm, which has an independent and quantifiable functional boundary value. The experimental results of Comparative Example 3 demonstrate that the completion of silanization modification and the achievement of the functional threshold particle size are two independent technical conditions. Simply completing silanization modification without controlling D90 within 500 nm will not fully utilize the interface control function of the modified CNC. Comparative Example 3 used the exact same KH-570 modification process as Example 1, with the same degree of silanization in a chemical sense. However, by reducing the pre-dispersion ultrasonic energy, the final dispersion D90 was maintained at 852 nm (approximately 70% above the 500 nm threshold), and its 7-day sedimentation layer ratio also increased to approximately 22%, resulting in significantly worse dispersion stability than Example 1 (<5%).

[0153] In terms of electrochemical performance, the capacity retention rate of Comparative Example 3 at 25°C (85.5% at 100 cycles and 78.5% at 200 cycles) was better than that of the unmodified Comparative Example 2, but still significantly lower than that of Example 1 with well-controlled particle size (90.5% at 100 cycles and 85.2% at 200 cycles), with differences of 5.0 and 6.7 percentage points, respectively. In the rate performance test, the 3C / 0.2C capacity ratio of Comparative Example 3 (60.2%) was significantly lower than that of Example 1 (72.5%), with a decrease of about 17%. This result is presumably related to the random deposition of large-sized particles on the negative electrode surface, which hinders the local lithium-ion transport channels—when the particle D90 is significantly larger than the characteristic scale of the electrode surface, the spatial uniformity of the film formation decreases, and the particle accumulation area may form a local high-resistivity region, which is further amplified during high-rate charge and discharge. The above results indicate that a particle size threshold of D90 of 100 nm to 500 nm is a quantitative boundary to ensure that the modified CNC forms a uniform film on the negative electrode surface and exerts optimal interface control function. It has a technical contribution independent of silanization modification itself and provides direct experimental basis for the protection of the dispersion particle size threshold in this application.

[0154] (iii) The overall performance is excellent when the amount added is within the range of 0.1wt% to 2.0wt%, while exceeding the upper limit will result in a significant deterioration in the transmission performance of the main body. The gradient test data of dynamic viscosity and ionic conductivity (Examples 2, 3, 4, and 5) jointly verified the engineering rationality of the addition amount window established in this application. As the amount of modified CNC added increased from 0.1 wt% (Example 2) to 2.0 wt% (Example 5), the electrolyte viscosity monotonically increased from 2.90 mPa·s to 5.12 mPa·s, while the ionic conductivity gradually decreased from 10.6 mS / cm to 9.15 mS / cm, with an overall decrease of approximately 14%. Within this addition amount range, the change in the bulk transport performance of the electrolyte remained at an engineering acceptable level. At the same time, the ICE (78.8%~83.2%) and 200-cycle capacity retention rate (79.2%~85.8%) of each group were significantly better than those of the blank control example, Comparative Example 1 (ICE=77.2%, 200-cycle capacity retention rate=71.5%), proving that the modified CNC can provide effective interface improvement function throughout the entire addition amount range in this application.

[0155] The test results of Comparative Example 5 (3.0 wt%) with excessive addition provide quantitative evidence for the reverse setting of the upper limit of 2.0 wt%. The viscosity of Comparative Example 5 increased sharply to 7.52 mPa·s (an increase of about 167% compared to Comparative Example 1), the ionic conductivity decreased to 7.85 mS / cm (a decrease of about 27% compared to Comparative Example 1), and the rate performance 3C / 0.2C capacity ratio decreased to 55.8% (72.5% in Example 1, a decrease of about 23%), indicating that the rheological properties and ion transport capacity of the electrolyte were significantly impaired after excessive addition. It is worth noting that the capacity retention rate of Comparative Example 5 at 25°C (83.5% at 100 cycles, 76.2% at 200 cycles) was still slightly higher than that of the blank Comparative Example 1 (82.2% at 100 cycles, 71.5% at 200 cycles), indicating that the excessive addition still retains a certain interface protection effect under the scenario of room temperature cycling. However, given its significant deterioration on bulk ion transport and rate performance, the addition amount of 3.0 wt% does not constitute a condition for better performance. From the perspective of comprehensive performance trade-offs, the test results of Comparative Example 5 conversely support the scientific rationality of the upper limit of 2.0 wt% addition amount, while the gradient data of Examples 2 to 5 together provide sufficient quantitative basis for the entire addition amount range.

[0156] Within the optional addition range (0.3wt%~1.0wt%), the comprehensive performance of Examples 3 (0.3wt%) and 4 (1.0wt%) is closest to that of Example 1 (0.5wt%). The ICE (81.0%~83.5%), 200-cycle capacity retention rate (82.5%~85.8%), and electrolyte parameters of the three groups are all in the optimal range, supporting the technical basis of 0.3wt%~1.0wt% as an optional range.

[0157] (iv) The synergistic formulation design of modified CNC and VC / FEC is indispensable for the long-term stability of SEI. The experimental results of Comparative Example 4 (with VC and FEC removed from the formulation, otherwise identical to Example 1) profoundly reveal the functional complementarity between modified CNC and conventional fluorinated film-forming additives in SEI construction. In the early stages of cycling (within 100 cycles), the capacity retention rate of Comparative Example 4 (87.5% at 100 cycles) was relatively close to that of Example 1 (90.5%), indicating that the modified CNC itself can participate in SEI formation during the initial formation and impart a certain degree of mechanical flexibility to adapt to the volume changes of the Si-C anode. However, as cycling progressed, the capacity retention rate of Comparative Example 4 decreased to 74.8% at 200 cycles, widening the gap with Example 1 (85.2%) to 10.4 percentage points, exhibiting a significant accelerated decay characteristic. During high-temperature cycling at 45°C (100 cycles), the capacity retention rate of Comparative Example 4 further decreased to 67.2%, far lower than that of Example 1 (83.5%), with a difference of 16.3 percentage points, indicating that high-temperature thermal stress significantly accelerates the aging process of SEI lacking fluorinated chemically stable components.

[0158] Interface impedance testing provides quantitative mechanistic support for the aforementioned macroscopic performance differences. The initial RSEI of Comparative Example 4 (35.8 Ω·cm after conversion) 2 ) and Example 1 (30.5Ω·cm 2 The values ​​are relatively close, indicating that the participation of modified CNC in the formation stage resulted in little difference in the initial SEI thickness between the two groups; however, after 50 cycles, the RSEI of Comparative Example 4 increased to 82.5 Ω·cm. 2 (an increase of approximately 130%), while the RSEI of Example 1 only increased to 42.8 Ω·cm. 2 (Increase of approximately 40%). The RSEI growth rate of Comparative Example 4 was the highest among all test groups, far exceeding that of Example 1. This characteristic of "close to the initial RSEI, but with a significantly higher growth rate" is highly consistent with the following mechanistic explanation: In the absence of chemical stability support provided by FEC reduction decomposition products (fluorine-containing inorganic phases such as LiF), the hybrid SEI formed by modified CNC, which is mainly composed of organic components, undergoes continuous evolution of SEI composition due to the repeated Si-C volume expansion and contraction during cycling, as well as continuous chemical erosion from the electrolyte solvent. This leads to continuous accumulation of impedance and ultimately accelerated capacity decay. Therefore, the chemical stability support provided by VC / FEC and the mechanically flexible framework provided by modified CNC act on the SEI from the two dimensions of chemical stability and mechanical adaptability, respectively. Their synergistic cooperation is the key technology for achieving long-term SEI stability and together constitutes the complete scientific basis for the synergistic formulation design strategy of this application.

[0159] (v) The technical effect mainly comes from the in-situ film-forming function of the silanized nanocrystalline framework, rather than the additive effect of the free silane small molecules themselves. The experimental results of Comparative Example 6 (free KH-570 small molecules, converted to equivalent Si atomic weight, without CNC carrier framework) provide crucial indirect evidence from a mechanistic perspective for the source of the core technical effect of this application. While the first-week coulombic efficiency of Comparative Example 6 (78.5%) was slightly higher than that of blank Comparative Example 1 (77.2%), indicating that the decomposition products of free silane after electrochemical reduction at low potential can participate in SEI modification to some extent, this improvement (1.3 percentage points) is significantly lower than the improvement of Example 1 relative to Comparative Example 1 (6.3 percentage points). Furthermore, key indicators of Comparative Example 6, such as the 25°C cycling capacity retention (75.5% at the 200th cycle), the 50-cycle increase in interfacial impedance (approximately 83%), and the 45°C high-temperature cycling capacity retention (71.8%), all exhibit performance characteristics between Comparative Example 1 and Example 1, showing that free silane small molecules have a certain but limited interfacial improvement effect, with a clear gap compared to the systematic and significant advantage of Example 1 in all indicators.

[0160] Under conditions without morphological characterization methods (XPS / SEM / TEM, etc.), a systematic data comparison between Comparative Example 6 and Example 1 provides strong indirect support for the following technical judgment: The key source of the technical effect of this application does not lie in the ordinary additive effect of an equal amount of free silane small molecules, but in the special interface function of the silanized nanocrystal framework itself—the one-dimensional nanomorphology of cellulose nanocrystals with a high aspect ratio enables it to cover the negative electrode surface in a uniformly dispersed manner, forming an organic-inorganic hybrid SEI with spatial continuity and mechanical flexibility in situ under electrochemical drive; free small molecules lack the multi-scale spatial distribution advantages brought by the above-mentioned nanomorphology, and the spatial continuity of the film formed by their decomposition products and the uniformity of coverage of the entire surface of Si-C particles are significantly limited.

[0161] (vi) Different silane coupling agent routes have comparable technical feasibility. The key performance indicators of Example 6 (APTES aminosilane modified CNC, 0.5wt%, D90=268nm) are highly comparable to those of E1 (KH-570 modified CNC): ICE=83.0% (Example 1: 83.5%), and the capacity retention rates at 25℃ for the 100th / 200th cycles are 90.2% / 84.8% (Example 1: 90.5% / 85.2%), with all differences within the experimental error range (±3 percentage points). The dispersed particle size of Example 6 (D90=268nm) is slightly better than that of Example 1 (D90=285nm), which is presumably related to the steric stabilization effect of the amino (-NH2) functional groups introduced on the surface of the APTES-modified CNC in carbonate solvents. The above results demonstrate that silane coupling agents with different organic functional groups (KH-570 of methacryloyloxy and APTES of amino) exhibit technical feasibility in improving CNC dispersion stability and participating in film formation at the negative electrode interface, with comparable performance. This provides diverse examples to support the types of silane coupling agents (covering silane coupling agents containing various organic functional groups such as vinyl, amino, and epoxy groups).

[0162] (vii) The technical solution has good epitaxial applicability in the graphite / LFP system. Example 7 uses an artificial graphite / LFP system for testing (the other electrolyte formulations are the same as in Example 1). Its absolute values ​​for ICE (90.2%) and 100-cycle capacity retention (95.2%) are both higher than those of the main testing platform (Si-C / NCM622 system, Example 1: ICE = 83.5%, 100-cycle = 90.5%). This difference in absolute values ​​is due to the difference in the intrinsic properties of the anode materials in the two systems—the charge-discharge volume change of artificial graphite is approximately 10%~15%, far lower than the approximately 200% volume expansion of silicon-carbon anodes, and its SEI film formation pressure is inherently lower, thus resulting in higher absolute performance. This difference does not indicate that the technical solution is more effective in the graphite system, and the results of Example 7 are not included in the cross-platform horizontal absolute value comparison. The technical significance of Example 7 is that, compared with the control group without CNC in the same system, the addition of modified CNC still demonstrates a statistically significant improvement in ICE and cycle capacity retention, proving that the technical solution of this application is also compatible and effective for the graphite anode system.

[0163] (viii) Comprehensive performance evaluation and summary of technical advantages Based on the test data from all examples and comparative examples, the following systematic conclusions can be drawn. This application's complete technical solution (Example 1, s-CNC 0.5wt%, D90=285nm), using KH-570 silanized modified cellulose nanocrystals as the core additive and combined with an FEC / VC synergistic film-forming formulation, achieves comprehensive improvements in interfacial performance in the Si-C / NCM622 silicon-carbon system: the first-cycle coulombic efficiency increased from 77.2% (Comparative Example 1, conventional electrolyte) to 83.5% (an increase of approximately 6.3 percentage points); the capacity retention rate after 200 cycles at 25°C increased from 71.5% to 85.2% (an increase of approximately 13.7 percentage points); the capacity retention rate after 100 cycles at 45°C increased from 68.5% to 83.5% (an increase of approximately 15.0 percentage points); and the SEI interfacial impedance growth rate after 50 cycles decreased from approximately 81% to approximately 40%, demonstrating superior SEI chemical and mechanical stability.

[0164] The aforementioned performance improvements are the comprehensive result of the synergistic effect of the four core technical elements of this application. The independent contribution of each element has been quantitatively verified through comparative examples: silanization modification (Comparative Example 2) solves the problem of the feasibility of CNC dispersion in carbonate electrolytes, which is a physical prerequisite for the implementation of the technical solution; particle size control (Comparative Example 3) ensures the uniform film formation of modified CNC on the negative electrode surface, which is a necessary spatial condition for the interface regulation effect; optimized addition amount (Comparative Example 5) balances the interface regulation effect and the bulk transport performance of the electrolyte, which is a guarantee for engineering practicality; and the synergistic formulation with VC / FEC (Comparative Example 4) contributes to different functional layers of SEI from the dimensions of chemical stability and mechanical flexibility, which is the mechanistic basis for achieving long-term stability of SEI. The experimental results of Comparative Example 6 further prove that the above technical effects mainly come from the special structural function of silanized nanocrystal framework participating in interfacial film formation, rather than the ordinary additive effect of an equal amount of free silane small molecules, which clarifies the substantial difference between this application and related prior art from the mechanism level. The technical solution's good adaptability to various silane coupling agents such as APTES (Example 6) and the graphite / LFP system (Example 7) further expands the application scenarios of this application.

[0165] Table 1-1

[0166] Table 1-2

[0167] Table 2-1

[0168] Table 2-2

[0169] In Tables 2-1 and 2-2, Note 1: "—" indicates that the item is not a mandatory test item or has not been tested.

[0170] Note 2: "N / A" indicates that this project is not applicable to this group. Among them, Comparative Example 1 has no CNC particles, and Comparative Example 6 is free silane small molecules with no particle size.

[0171] Note 3: The lower ICE (73.8%) of Comparative Example 2 compared to Comparative Example 1 (77.2%) is the expected key negative control result: the random deposition of unmodified CNC agglomerates disrupts the uniformity of SEI film formation, resulting in performance inferior to "no CNC baseline", directly proving the technical necessity of silanization modification; Note 4: Although the conductivity and rate performance of Comparative Example 5 are significantly worse than those of Comparative Example 1, its ICE and room temperature cycling performance are still slightly better than those of Comparative Example 1. This is due to the residual interface protection effect of the excessive addition. The following analysis should state that "the excessive addition does not constitute a better implementation condition in terms of overall performance" rather than "completely worse than the baseline without CNC". Note 5: The focus of the analysis of Comparative Example 4 should be on the increase in RSEI (130% increase after 50 cycles, the highest among all groups) and the accelerated capacity decay after 200 cycles, rather than the absolute value of the initial RSEI (the relatively low initial value is due to the initial film formation provided by CNC). Note 6: Example 7★ is a graphite / LFP system. The absolute values ​​of ICE (90.2%) and cycle retention (95.2%) are higher than those of the main platform (silicon-carbon / NCM622) system due to system differences (smaller graphite volume change and lower SEI film formation pressure). It is not included in the cross-platform horizontal absolute value comparison. Its technical significance lies in proving that the modified CNC is "compatible and effective" for the graphite system.

[0172] 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, which is located inside the housing; The electrolyte contains modified cellulose nanocrystals, the surface of which has hydrophobic groups, and the specific surface area of ​​which is not less than 150 m². 2 / g.

2. The battery cell according to claim 1, characterized in that, The hydrophobic group includes at least one of silyl, alkyl, fluoroalkyl, aryl, and siloxane segments.

3. The battery cell according to claim 1 or 2, characterized in that, The modified cellulose nanocrystals are added to the electrolyte at a rate of 0.1 wt% to 2.0 wt%.

4. The battery cell according to claim 3, characterized in that, The dispersed particle size D90 of the modified cellulose nanocrystals does not exceed 500 nm.

5. The battery cell according to claim 4, characterized in that, The modified cellulose nanocrystals have a length of 100nm~300nm, a diameter of 5nm~15nm, and an aspect ratio of not less than 10; and / or, the crystallinity of the modified cellulose nanocrystals is not less than 70%.

6. The battery cell according to claim 1 or 5, characterized in that, The electrolyte also contains film-forming additives, which include at least one of vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, and vinyl sulfate.

7. A method for preparing a battery cell as described in any one of claims 1 to 6, 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; The electrolyte contains modified cellulose nanocrystals, the surface of which has hydrophobic groups.

8. The method for preparing a battery cell according to claim 7, characterized in that, The preparation method of the modified cellulose nanocrystals includes: Preparation of cellulose nanocrystal matrix; The cellulose nanocrystal matrix is ​​surface modified to obtain the modified cellulose nanocrystals; wherein the surface modification includes silanization modification, esterification modification or etherification modification.

9. The method for preparing a battery cell according to claim 8, characterized in that, The silanization modification method includes: The cellulose nanocrystal matrix was dispersed in an organic solvent, a silane coupling agent was added, and the mixture was refluxed at 100°C to 120°C to obtain the modified cellulose nanocrystals.

10. The method for preparing a battery cell according to claim 9, characterized in that, The amount of the silane coupling agent is 10% to 20% of the dry weight of the cellulose nanocrystal matrix.

11. The method for preparing a battery cell according to claim 9 or 10, characterized in that, The silane coupling agent includes at least one of γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, alkyltrialkoxysilane, fluoroalkyltrialkoxysilane, and phenyltrialkoxysilane.

12. The method for preparing a battery cell according to claim 8 or 9, characterized in that, The modified cellulose nanocrystals were prepared in an anhydrous environment.

13. The method for preparing a battery cell according to claim 8, characterized in that, The method for preparing the cellulose nanocrystal matrix includes a sulfuric acid hydrolysis method, which comprises the following steps: Cellulose was dispersed in sulfuric acid solution and hydrolyzed at 40℃~50℃ to obtain the hydrolysis product; After centrifuging the hydrolysis product, the supernatant was taken and subjected to dialysis and freeze-drying in sequence to obtain the cellulose nanocrystal matrix.

14. A battery device, characterized in that, The battery device includes a battery cell as described in any one of claims 1 to 6, or a battery cell obtained by the preparation method as described in any one of claims 7 to 13, and the battery device includes one or more of a battery module, a battery pack, and an energy storage battery.

15. An electrical appliance, characterized in that, The electrical device includes the battery device as described in claim 14, the battery device being used to provide electrical energy.

16. An energy storage device, characterized in that, The energy storage device includes the battery device as described in claim 14, the battery device being used to store electrical energy.

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