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

Abstract

The application relates to the field of batteries, and provides a battery monomer, a preparation method of the battery monomer, a battery device, a power utilization device, an energy storage device, the preparation method of the battery monomer, which comprises the following steps: providing an electrode core assembly, wherein the electrode core assembly is formed by stacking or winding a positive electrode sheet, a diaphragm and a negative electrode sheet; providing a shell, and placing the electrode core assembly in the shell; providing an electrolyte, and injecting the electrolyte into the shell; and performing a formation step; the electrolyte contains a bifunctional additive, and the molecular formula of the bifunctional additive is: wherein R1 is an electron-withdrawing group, and R2 is an electrochemically controllable decomposition group. The application is at least beneficial to solving the key technical problems of slow electron transmission, large ion diffusion impedance, intensified interface side reaction and the like in a lithium iron phosphate fast-charging battery.

Description

Technical Field

[0001] This application relates to the field of batteries, 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] Lithium iron phosphate (LFP) batteries have been widely used in electric vehicles and energy storage systems due to their excellent safety performance, good cycle stability, abundant raw material resources, and relatively low cost, especially dominating the fields of large-scale energy storage power stations and electric buses where safety requirements are high. With the rapid development of the electric vehicle market and the increasing demands for charging convenience, fast charging technology has become one of the key bottlenecks restricting the widespread adoption of electric vehicles. Ideally, fast charging technology should be able to complete the charging process from 10% to 80% within 15 to 20 minutes, while maintaining good cycle life and safety performance. 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 key technical problems in lithium iron phosphate fast-charging batteries such as slow electron transport, high ion diffusion impedance, and aggravated interfacial side reactions.

[0004] This application provides a method for preparing a single battery cell, comprising:

[0005] Provide a battery cell assembly, the battery cell assembly being formed by stacking or winding a positive electrode sheet, a separator and a negative electrode sheet;

[0006] A housing is provided to house the battery cell assembly within the housing;

[0007] Provide electrolyte and inject the electrolyte into the housing;

[0008] Perform the formation step;

[0009] The electrolyte contains a bifunctional additive, the molecular formula of which is: In this group, R1 is an electron-withdrawing group and R2 is an electrochemically decomposable group.

[0010] This bifunctional additive employs a precise molecular design approach, utilizing the coordination effect of the phenothiazine skeleton and the film-forming properties of fluorinated groups to construct a synergistic system that promotes electron transport and stabilizes the interface. The phenothiazine skeleton constitutes the core structural unit of the molecule, a tricyclic system formed by the fusion of a benzene ring and a thiazine ring. This skeleton possesses an electron-rich π-conjugated system and N, S dual heteroatom coordination sites, providing a structural basis for electron transport and metal ion coordination. The HOMO energy level of the phenothiazine skeleton is located between -5.8 eV and -6.2 eV, while the LUMO energy level can be tuned to the range of -2.8 eV to -3.5 eV via substituents. The electron-withdrawing group at the N-10 position plays a crucial role in precisely controlling the molecular electronic structure. This group significantly lowers the LUMO energy level of the molecule to -3.2 eV through a strong electron-withdrawing effect. This energy level range corresponds to the redox potential of lithium iron phosphate (3.45 V vs. Li / Li). + This achieves precise matching, ensuring the thermodynamic driving force and kinetic reversibility of electron transport. The 3-position electrochemically controllable decomposition group undertakes the in-situ film-forming function, undergoing selective decomposition reactions under electrochemical conditions. This group has a moderate bond energy (e.g., the S-CF3 bond energy is about 280 kJ / mol to 320 kJ / mol), and can undergo controllable decomposition within a potential window of 3.0 V to 4.0 V to generate film-forming components such as LiF nanoparticles and fluorinated alkyl chains, thus constructing a LiF-rich solid electrolyte interphase (SEI) film in situ.

[0011] Optionally, the electron-withdrawing group includes at least one of -CF3, -C2F5, -OCF3, and -CN.

[0012] Optionally, the electrochemically controllable decomposition group includes at least one of -SO2CF3 and -SO2C2F5.

[0013] Specifically, the molecular formulas of bifunctional additives can be as follows:

[0014] , ,

[0015] , ,

[0016] , .

[0017] Optionally, the mass fraction of the bifunctional additive in the electrolyte is 0.05% to 2.0%.

[0018] Optionally, the preparation method of the bifunctional additive includes: first introducing an electron-withdrawing group at the 10 position of phenothiazine to obtain an intermediate, and then introducing an electrochemically controllable decomposition group at the 3 position of the phenothiazine skeleton of the intermediate through an electrophilic aromatic substitution reaction.

[0019] Optionally, the preparation of the intermediate includes:

[0020] A phenothiazine and an electron-withdrawing reagent are provided, and the reaction is carried out under inert gas protection and alkaline conditions, catalyzed by a palladium-containing catalyst, at 80℃~120℃ to obtain an intermediate.

[0021] Optionally, the alkaline conditions are provided by cesium carbonate.

[0022] Optionally, the palladium-containing catalyst includes at least one of tetra(triphenylphosphine)palladium, [1,1'-bis(diphenylphosphine)ferrocene]palladium dichloride, bis(tri-tert-butylphosphine)palladium, and palladium acetate.

[0023] Optionally, the electrophilic aromatic substitution reaction includes:

[0024] The bifunctional additive is obtained by reacting a reagent containing an electrochemically controllable decomposable group and the intermediate as raw materials at 0℃~25℃.

[0025] Optionally, the solvent of the electrolyte may include carbonates.

[0026] Optionally, the carbonate includes at least one of vinylene carbonate, fluoroethylene carbonate, dimethyl carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0027] This application also provides a battery cell prepared by the method described above, comprising:

[0028] The housing and the positive electrode, separator, negative electrode and electrolyte located within the housing, wherein the separator is located between the positive electrode and the negative electrode.

[0029] This application also provides a battery device, comprising a battery cell obtained by the method described above for preparing a battery cell, or a battery cell as described above, wherein the battery device comprises one or more of a battery module, a battery pack, and an energy storage battery.

[0030] In another aspect, this application provides an electrical device that includes a battery device as described above, the battery device being used to provide electrical energy.

[0031] Another aspect of this application provides an energy storage device, which includes a battery device as described above, the battery device being used to store electrical energy.

[0032] The technical solution provided in this application has at least the following advantages:

[0033] This application provides a bifunctional additive based on molecular design. Through an innovative technical strategy of "coordination-type redox medium + in-situ fluorination film formation," it systematically solves key technical problems in lithium iron phosphate fast-charging batteries, such as slow electron transport, high ion diffusion resistance, and exacerbated interfacial side reactions. The core of this technical solution is the design and synthesis of an additive with a precise molecular structure, utilizing the coordination ability of nitrogen and sulfur dual heteroatoms in the phenothiazine skeleton and Fe... 2+ / Fe 3+ A reversible coordination complex is formed, establishing a molecular-level electron transport bridge to effectively shorten the charge transport path. Simultaneously, the N-10 electron-withdrawing group precisely modulates the molecular LUMO energy level to achieve optimal matching with the redox potential of lithium iron phosphate. Under electrochemical conditions, the 3-position electrochemically controllable decomposition group and the N-10 electron-withdrawing group, both containing fluorine, synergistically decompose to generate LiF nanoparticles and fluorinated alkyl chains, in situ constructing a composite SEI film with high lithium-ion conductivity and mechanical stability, improving interfacial stability while avoiding a significant increase in impedance. This bifunctional additive, added in carbonate-based electrolytes at only 0.05wt%~2.0wt%, enables 5C fast charging of lithium iron phosphate batteries, providing an efficient and convenient solution for fast charging technology. It facilitates high-capacity battery cells and is suitable for long-term energy storage applications, such as energy storage systems that operate continuously for 4-8 hours at rated power. Attached Figure Description

[0034] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the drawings in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 The flowchart corresponds to the method for preparing a single battery cell provided in the embodiments of this application. Detailed Implementation

[0036] As the background technology indicates, existing lithium iron phosphate (LFP) fast-charging technologies primarily achieve performance improvements through two main technical routes: material modification and electrolyte optimization. Material modification techniques include nano-sizing, carbon coating, and ion doping. Nano-sizing shortens the lithium-ion diffusion path by reducing particle size (typically to 100nm~200nm), but the high specific surface area of ​​nanoparticles increases side reactions and reduces tap density. Carbon coating technology improves electronic conductivity by coating the surface of LFP particles with a conductive carbon layer (2nm~5nm thick). Common carbon sources include organic compounds such as glucose, sucrose, and polyvinyl alcohol, which form a conductive network through high-temperature carbonization. Ion doping technology introduces Mg at Fe, Li, and PO4 sites. 2+ Al 3+ Ti 4+ Isovalent ions modulate electronic structure and ion transport performance. Electrolyte optimization technology mainly improves interfacial properties and ion transport kinetics through additives. Commonly used additives include vinylene carbonate (VC) for forming a stable SEI film, fluoroethylene carbonate (FEC) for improving low-temperature performance, and lithium bis(oxalate)borate (LiBOB) for enhancing high-temperature stability. Redox mediator technology is a new direction that has emerged in recent years. By adding small molecule compounds with suitable redox potentials to the electrolyte, additional electron transport channels are established on the positive electrode surface. Typical redox mediators include ferrocene derivatives, aromatic amine compounds, and conductive polymers. These molecules undergo oxidation reactions on the positive electrode surface to form free radical cations, which then diffuse into the electrode interior for reduction reactions, thereby bypassing the limitations of solid-phase diffusion and achieving rapid charge transport.

[0037] However, lithium iron phosphate batteries face inherent technical challenges in fast-charging applications, primarily due to the intrinsic limitations of their olivine structure. Lithium iron phosphate is a polyanionic compound with strongly covalently bonded PO4 groups. 3- While the tetrahedral structure provides excellent structural stability and safety, it also leads to problems such as extremely low electronic conductivity and slow lithium-ion diffusion kinetics. During fast charging, the polarization phenomenon becomes more pronounced under high current density requirements, easily causing capacity decay, increased heat generation, and even safety hazards. Therefore, developing a technical solution specifically designed to improve the fast charging performance of lithium iron phosphate batteries has significant scientific and industrial value.

[0038] Existing lithium iron phosphate (LFP) fast-charging technologies face several key challenges and limitations in practical applications. First, single modification strategies have limited effectiveness and often come with negative consequences. While nano-sizing improves kinetics, it significantly increases specific surface area, exacerbating side reactions and reducing initial efficiency; furthermore, nanoparticle aggregation is difficult to avoid. Carbon coating improves electronic conductivity, but the thickness and uniformity of the coating layer are difficult to control precisely; excessive thickness affects ion transport, while insufficient thickness has limited effect, and high-temperature carbonization may lead to LFP decomposition and the generation of impurity phases. Ion doping can modulate the electronic structure, but the doping concentration is difficult to control precisely, and high-temperature solid-state reactions easily generate byproducts that affect electrochemical performance. Second, existing electrolyte additives suffer from limited functionality and mutual constraints. Film-forming additives such as VC can form a stable SEI film but typically increase interfacial impedance, affecting fast-charging performance. Low-temperature additives such as FEC, while improving low-temperature performance, may over-react at room temperature, consuming electrolyte. Different additives may also compete for performance, affecting their respective effects. Third, redox media technology faces challenges in stability and selectivity. Many existing redox media molecules suffer from poor chemical stability, easily undergoing irreversible decomposition during long-term battery cycling, leading to performance degradation. Insufficient potential matching precision may result in inadequate over-oxidation or reduction capabilities, affecting transmission efficiency. Furthermore, the solubility and diffusion coefficient of the molecules in the electrolyte limit their application concentration and transmission efficiency. Finally, there is a lack of comprehensive technical solutions that simultaneously address electron transport and interface stability. Most existing technologies are designed to address single problems, and under fast-charging conditions, improvements in electron transport and interface stability often mutually constrain each other, limiting overall performance improvement.

[0039] In the description of the embodiments of this application, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0040] In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0041] 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.

[0042] 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.

[0043] This application provides a method for preparing a single battery cell, such as... Figure 1 As shown, it includes:

[0044] S1. Provide a battery cell assembly, wherein the battery cell assembly is formed by stacking or winding a positive electrode sheet, a separator and a negative electrode sheet;

[0045] S2. Provide a housing and place the battery cell assembly inside the housing;

[0046] S3. Provide electrolyte and inject the electrolyte into the casing;

[0047] S4. Perform the formation step;

[0048] The electrolyte contains a bifunctional additive, the molecular formula of which is: In this group, R1 is an electron-withdrawing group and R2 is an electrochemically decomposable group.

[0049] This application provides a bifunctional additive based on molecular design. Through an innovative technical strategy of "coordination-type redox medium + in-situ fluorination film formation," it systematically solves key technical problems in lithium iron phosphate fast-charging batteries, such as slow electron transport, high ion diffusion resistance, and exacerbated interfacial side reactions. The core of this technical solution is the design and synthesis of an additive with a precise molecular structure, utilizing the coordination ability of nitrogen and sulfur dual heteroatoms in the phenothiazine skeleton and Fe... 2+ / Fe 3+ A reversible coordination complex is formed, establishing a molecular-level electron transport bridge to effectively shorten the charge transport path. Simultaneously, the electron-withdrawing group at the N-10 position precisely modulates the molecular LUMO energy level to achieve optimal matching with the redox potential of lithium iron phosphate. Under electrochemical conditions, the electrochemically controllable decomposition group at the 3-position and the electron-withdrawing group at the N-10 position, along with two fluorinated groups, synergistically decompose to generate LiF nanoparticles and fluorinated alkyl chains, constructing a composite SEI film with high lithium-ion conductivity and mechanical stability in situ. This improves interfacial stability while avoiding a significant increase in impedance. This bifunctional additive, with an addition amount of only 0.05wt%~2.0wt% in carbonate-based electrolytes, enables 5C fast charging of lithium iron phosphate batteries, providing an efficient and convenient solution for fast charging technology of lithium iron phosphate batteries.

[0050] When R1 is -CF3 and R2 is -SO2CF3, the bifunctional additive is named N-trifluoromethyl-3-trifluoromethanesulfonylphenthiazide, abbreviated as TFMS-TFMPT.

[0051] This bifunctional additive employs a precise molecular design approach, utilizing the coordination effect of the phenothiazine skeleton and the film-forming properties of fluorinated groups to construct a synergistic system that promotes electron transport and stabilizes the interface. The phenothiazine skeleton constitutes the core structural unit of the molecule, a tricyclic system formed by the fusion of a benzene ring and a thiazine ring. This skeleton possesses an electron-rich π-conjugated system and N, S dual heteroatom coordination sites, providing a structural basis for electron transport and metal ion coordination. The HOMO energy level of the phenothiazine skeleton is located between -5.8 eV and -6.2 eV, while the LUMO energy level can be tuned to the range of -2.8 eV to -3.5 eV via substituents. The electron-withdrawing group at the N-10 position plays a crucial role in precisely controlling the molecular electronic structure. This group significantly lowers the LUMO energy level of the molecule to -3.2 eV through a strong electron-withdrawing effect. This energy level range corresponds to the redox potential of lithium iron phosphate (3.45 V vs. Li / Li). + This achieves precise matching, ensuring the thermodynamic driving force and kinetic reversibility of electron transport. The 3-position electrochemically controllable decomposition group undertakes the in-situ film-forming function, undergoing selective decomposition reactions under electrochemical conditions. This group has a moderate bond energy (e.g., the S-CF3 bond energy is about 280 kJ / mol to 320 kJ / mol), and can undergo controllable decomposition within a potential window of 3.0 V to 4.0 V to generate film-forming components such as LiF nanoparticles and fluorinated alkyl chains, thus constructing a LiF-rich solid electrolyte interphase (SEI) film in situ.

[0052] The synergistic design of electron-withdrawing groups and electrochemically controllable decomposition groups in the molecule achieves functional division of labor: the electron-withdrawing group at the 10-position mainly regulates the electronic structure and maintains relative stability; the electrochemically controllable decomposition group at the 3-position mainly undertakes the film-forming function, decomposing moderately under electrochemical conditions. This design avoids the problems of additive consumption due to excessive decomposition and poor film-forming effect due to insufficient decomposition. Analysis of the structural necessity of site selection: the electron-withdrawing group at the 10-position achieves maximum regulation of the molecular frontier orbitals through direct connection with the nitrogen atom, while the 3-position, as the benzene ring position indirectly affected by the 10-position electronic effect, has a moderate electron density, giving the electrochemically controllable decomposition group suitable electrochemical reactivity. Interchanging the group positions would lead to: 1) the LUMO energy level deviating from the optimal matching range; 2) loss of control over the electrochemical activity and decomposition timing of the film-forming group; and 3) interference with the coordination geometry of the N and S coordinating atoms. Therefore, the combination of the electrochemically controllable decomposition group at the 3-position and the electron-withdrawing group at the 10-position in this application has irreplaceable technical rationality.

[0053] The bifunctional additive significantly improves the fast-charging performance of lithium iron phosphate batteries through the synergistic effect of two mechanisms: coordination-type redox mediator and in-situ fluorination film formation. These two mechanisms complement each other, exerting a synergistic effect in two key areas: electron transport and interface stability.

[0054] The coordination-type redox mediator mechanism is based on the N, S dual heteroatoms in the phenothiazine framework and Fe 2+ / Fe 3+ Reversible coordination complexation. During charging, the additive molecules interact with the Fe atoms on the lithium iron phosphate surface via the lone pair electrons of the N atom and the d-π* orbitals of the S atom. 3+ The ions form five-membered ring coordination complexes, with coordination bond lengths of approximately 2.0 Å to 2.2 Å for Fe-N and approximately 2.3 Å to 2.5 Å for Fe-S. The formation of these coordination complexes provides molecular-level bridges for electron transport, effectively shortening the Li-N bond length. + / e - Transmission path.

[0055] During electron transport, the additive molecules undergo a reversible redox reaction: the additive is oxidized to free radical cations on the positive electrode surface, then diffuses into the electrode interior and is reduced inside the particles, completing the relay transport of electrons. This process bypasses the slow electronic conductivity in the solid phase of lithium iron phosphate, significantly improving electrode reaction kinetics.

[0056] The in-situ fluorination film formation mechanism is achieved through the electrochemical decomposition of the 3-position electrochemically controllable decomposition group. Within a potential range of 2.8V to 3.8V, the -SO2CF3 group undergoes CS bond breaking and SF bond rearrangement, generating various fluorinated film-forming components. The main decomposition products include: LiF nanoparticles (particle size 5nm~20nm), fluorinated alkyl chains (-CF2-CF2-), and fluorinated ether compounds. LiF nanoparticles, as the main inorganic component of the SEI film, provide excellent mechanical stability and lithium-ion conductivity. The theoretical lithium-ion conductivity of LiF is approximately 10⁻⁶. -4 S / cm, the actual conductivity at the nanoscale can reach 10. -5 S / cm~10 -6 S / cm. Fluoroalkyl chains, as flexible organic components, improve the toughness of the SEI membrane and the wettability of the electrolyte, preventing the membrane from cracking and peeling off during cycling.

[0057] The synergistic effect of the dual mechanisms is manifested in the following ways: the coordination-type redox medium improves electron transport and reduces electrode polarization; in-situ film formation stabilizes the electrode / electrolyte interface and suppresses side reactions. Through their combined action, both fast-charging performance and cycle stability are simultaneously improved.

[0058] The performance of the bifunctional additive is characterized and controlled using four sets of combined functional thresholds to ensure the integrity and effectiveness of the technical solution. These four thresholds serve as target parameters for the preferred implementation, forming a synergistic functional constraint.

[0059] Rate-capacity threshold: Under 5C discharge conditions, the discharge capacity of the lithium iron phosphate battery is ≥145mAh / g, or even ≥150mAh / g, such as ≥155mAh / g. It completes a fast charge from 20% SOC to 80% SOC within 20 minutes, with a charging capacity ≥60% of the theoretical capacity, or even ≥65% of the theoretical capacity. This threshold directly reflects the effect of additives on improving electrode kinetics.

[0060] Impedance control threshold: After the first charge cycle, the increase in charge transfer impedance (Rct) at the electrode interface relative to the blank electrolyte should be ≤18%, or even ≤15%, such as ≤12%. This threshold ensures that film formation improves interface stability without significantly increasing transport impedance.

[0061] Interfacial composition threshold: The atomic fraction of LiF in the SEI film on the electrode surface is ≥40%, or even ≥45%, such as ≥50% (calculated by integrating the Li1s and F1s peaks in XPS). In F-KLL Auger electron spectroscopy convolution analysis, the ratio of the LiF characteristic peak to the total F signal is in the range of 0.6 to 0.9. This threshold ensures the controllability of film quality and composition.

[0062] Reversible coordination threshold: In in-situ X-ray absorption fine structure spectroscopy (EXAFS) analysis, the coordination numbers of Fe-N and Fe-S are in the range of 0.5 to 1.5, and even in the range of 0.8 to 1.2. After 100 charge-discharge cycles, the coordination number decays by ≤20%, and even by ≤15%. This threshold ensures the stability and reversibility of the coordination-based redox mechanism.

[0063] The electrochemical stability window of the bifunctional additive is 2.5V~4.2V vs. Li / Li + It remains stable within the operating voltage range of lithium iron phosphate (2.5V~3.8V). The redox peak is located at 3.4V~3.6V, with a residual difference of ≤30mV from the lithium iron phosphate plateau potential, ensuring high efficiency of electron transport.

[0064] A clear structure-property relationship was established between molecular structure and properties, providing theoretical guidance for further optimization. The LUMO energy level exhibits a linear relationship with redox potential: ELUMO = -3.2 eV, corresponding to an oxidation potential of approximately 3.45 V vs. Li / Li. + The energy level can be finely tuned within a range of ±0.2 eV by adjusting the substituents.

[0065] Coordination ability is related to the electron cloud density of N and S atoms; the higher the electron cloud density, the stronger the coordination ability. The electron-withdrawing effect of the electron-withdrawing group at the 10-position moderately reduces the electron cloud density, keeping the coordination strength within the reversible range and avoiding irreversible bonding caused by excessive coordination. Film-forming ability is related to the bond energy and electrochemical stability of the electrochemically controllable decomposition groups. The CS bond energy is approximately 280 kJ / mol to 320 kJ / mol, and it is easily broken under electrochemical conditions; the SF bond rearranges to form stable fluorine-containing products. Group position affects decomposition kinetics: the 3-position has better steric accessibility than the 1-position.

[0066] This dual-function additive is suitable for various lithium iron phosphate battery systems, including conventional lithium iron phosphate, doped and modified lithium iron phosphate (Mg / Mn / Ti doped), and nano-lithium iron phosphate. The additive shows good performance on lithium iron phosphate with different morphologies (spherical, rod-shaped, and sheet-shaped). The operating temperature range is 10℃~55℃, and the fast charging rate is 0.5C~6C. Within this range, the additive maintains stable performance, providing reliable assurance for practical applications.

[0067] Optionally, the electron-withdrawing group includes at least one of -CF3, -C2F5, -OCF3, and -CN to ensure that the molecular LUMO energy level is in the range of -3.0eV to -3.4eV (optionally -3.15eV to -3.25eV) to achieve optimal matching with the LFP potential.

[0068] Optionally, the electrochemically controllable decomposition group includes at least one of -SO2CF3 and -SO2C2F5, ensuring controllable decomposition within the LFP working potential window. This design principle provides clear boundaries for further optimization of the molecular structure.

[0069] Optionally, the mass fraction of the bifunctional additive in the electrolyte is 0.05% to 2.0%, specifically 0.05%, 0.06%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 1.0%, 1.2%, 1.5%, 1.7%, and 2.0%.

[0070] This dosage range has been optimized to ensure full utilization of the dual functions. Too low a dosage (<0.3wt%) results in insufficient coordination sites and limited redox mediating effect; too high a dosage (>0.7wt%) leads to excessive film formation, increasing impedance and reducing cost-effectiveness.

[0071] Optionally, the preparation method of the bifunctional additive includes: first introducing an electron-withdrawing group at the 10 position of phenothiazine to obtain an intermediate, and then introducing an electrochemically controllable decomposition group at the 3 position of the phenothiazine skeleton of the intermediate through an electrophilic aromatic substitution reaction. This route has the advantages of simple steps, high yield, and few by-products.

[0072] Optionally, the preparation of the intermediate includes:

[0073] A phenothiazine and an electron-withdrawing reagent are provided, and the reaction is carried out under inert gas protection and alkaline conditions, catalyzed by a palladium-containing catalyst, at 80℃~120℃ to obtain an intermediate.

[0074] Optionally, the alkaline conditions are provided by cesium carbonate.

[0075] Optionally, the palladium-containing catalyst includes at least one of tetra(triphenylphosphine)palladium, [1,1'-bis(diphenylphosphine)ferrocene]palladium dichloride, bis(tri-tert-butylphosphine)palladium, and palladium acetate.

[0076] Optionally, the electrophilic aromatic substitution reaction includes:

[0077] The bifunctional additive is obtained by reacting a reagent containing an electrochemically controllable decomposable group and the intermediate as raw materials at 0℃~25℃.

[0078] The preparation method of this bifunctional additive, taking the preparation method of TFMS-TFMPT as an example,

[0079] Step 1: 10-Trebrofluoromethylation reaction. Using phenothiazine as the starting material, trifluoromethyl iodine (CF3I) as the trifluoromethyl source, tetrakis(triphenylphosphine)palladium [Pd(PPh3)4] as the catalyst, and cesium carbonate (Cs2CO3) as the base, the reaction is carried out in DMF solvent. Reaction conditions: temperature 80℃~120℃, e.g., 100℃; time 8h~24h, e.g., 12h; inert atmosphere protection. The reaction mechanism involves three basic steps: oxidative addition, transmetalation, and reductive elimination. The palladium catalyst first undergoes oxidative addition with CF3I to form a Pd-CF3 complex, then undergoes transmetalation with the CH bond of phenothiazine, and finally regenerates the catalyst through reductive elimination to form a C-CF3 bond.

[0080] Step 2: 3-Trebromethanesulfonation reaction. Using the product from Step 1 as raw material, trifluoromethanesulfonic anhydride [(CF3SO2)2O] is used as the sulfonating agent, and trifluoromethanesulfonic acid (CF3SO3H) is used as the catalyst. The reaction is carried out in dichloromethane (DCM) solvent. Reaction conditions: temperature 0℃~25℃, e.g. 10℃; time 2h~8h, e.g. 4h.

[0081] This reaction is a typical Friedel-Crafts acylation reaction, in which trifluoromethanesulfonic anhydride ionizes under the catalysis of trifluoromethanesulfonic acid to produce trifluoromethanesulfonyl cation (CF3SO2). +Then, it undergoes an electrophilic substitution reaction with the phenothiazine aromatic ring. Due to the electron-withdrawing effect of the 10-position-CF3, the reaction selectively occurs at the 3-position. The theoretical basis for the regioselectivity of the reaction is that the strong electron-withdrawing effect of the 10-position-CF3 is transmitted through the conjugated system, causing a redistribution of electron density at various positions on the benzene ring. The 3-position acquires moderate reactivity and becomes the preferred site for electrophilic attack, while the electron density at the 1- and 4-positions is too low for the reaction to proceed, and the 2-position is sterically hindered. This inherent regioselectivity ensures the singularity of the product structure and the reproducibility of the reaction.

[0082] The product separation and purification employed a combination of column chromatography and recrystallization. The crude product was first initially separated by silica gel column chromatography (developing solvent: petroleum ether / ethyl acetate = 10:1~5:1), and then recrystallized in ethanol to obtain the pure product. The product purity was ≥99% (HPLC detection), and the overall yield was ≥85%, and could even be ≥90%.

[0083] The main impurities in the synthesis process include monosubstituted products, disubstituted byproducts, and unreacted starting materials. By optimizing reaction conditions and purification processes, the impurity content was controlled within acceptable limits.

[0084] Major impurities and their control methods: unreacted phenothiazines (<1%, removed by column chromatography); 10-trifluoromethylphenothiazines monosubstituted products (<2%, removed by recrystallization); trifluoromethanesulfonylation products at other sites (<1%, controlled by reaction selectivity); decomposition products and polymers (<0.5%, controlled by temperature and inert atmosphere protection).

[0085] Product quality standards: Appearance is pale yellow to yellow crystalline powder; melting point 145℃~150℃; molecular weight 419.33±0.5 (mass spectrometry detection); purity ≥99.0% (HPLC detection); moisture ≤0.1% (Karl Fischer method); heavy metals ≤10ppm (ICP-MS detection); chloride ions ≤50ppm (ion chromatography).

[0086] Product structure can be confirmed through the following analytical methods: 1 H NMR, 13 C NMR, 19 F NMR is used to confirm the molecular skeleton and the positions of substituents; high-resolution mass spectrometry (HRMS) is used to confirm the precise molecular weight and molecular formula; infrared spectroscopy (IR) is used to confirm the presence of characteristic functional groups such as -SO2- and -CF3. Taking a target molecule with R1=-CF3 and R2=-SO2CF3 as an example, 19 F NMR should observe two sets of characteristic fluorine peaks: N-CF3 signal (δ approximately -62 ppm) and -SO2CF3 signal (δ approximately -79 ppm), which can clearly distinguish the presence and attachment positions of the two fluorine-containing groups in the molecule.

[0087] To meet industrial requirements, the preparation process of bifunctional additives can be scaled up. During scale-up, key factors such as heat and mass transfer, reaction selectivity, and safety need to be carefully considered.

[0088] Reactor Design: A jacketed stirred reactor is employed, equipped with a temperature control system, a nitrogen protection system, and a tail gas treatment system. The reactor is made of 316L stainless steel with a polished inner surface to ensure corrosion resistance and easy cleaning. The agitator uses a frame-type impeller with a rotation speed of 50 rpm to 200 rpm to ensure uniform mixing of materials.

[0089] Heat transfer optimization: Temperature control is crucial due to the involvement of organometallic catalysis and strong acid catalysis in the reaction. The jacket utilizes circulating heat transfer oil for heating / cooling, achieving a temperature control accuracy of ±2℃. The reactor is equipped with multi-point temperature monitoring to monitor the reaction temperature distribution in real time.

[0090] Safety Measures: Raw materials such as CF3I and (CF3SO2)2O have certain toxicity and corrosiveness, requiring appropriate safety measures. A gas detection alarm system should be installed in the reaction area; operators should be equipped with protective equipment; emergency flushing facilities and waste gas treatment systems should be in place.

[0091] Waste disposal: Waste solvents generated during the synthesis process are recovered and reused through distillation; fluorine-containing waste is entrusted to qualified units for disposal; and waste catalysts are safely disposed of after recovering precious metals. This ensures environmentally friendly and sustainable production.

[0092] Optionally, the solvent of the electrolyte may include carbonates.

[0093] Optionally, the carbonate includes at least one of vinylene carbonate, fluoroethylene carbonate, dimethyl carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0094] The bifunctional additive exhibits good compatibility with commonly used electrolyte systems. In the EC / EMC / DEC+LiPF6 system, the additive solubility is ≥5 mg / mL (25℃), and the solution stability is ≥30 days. In the EMC-rich+LiFSI system, the bifunctional additive demonstrates better high-voltage stability, making it suitable for high-voltage fast-charging applications.

[0095] Optionally, the lithium salt in the electrolyte includes at least one of LiPF6, LiFSI, and LiBF4, and the concentration of the lithium salt can be selected as 0.8 mol·L⁻¹. -1 ~1.5mol·L -1 .

[0096] Electrolytes containing bifunctional additives are prepared under strictly controlled conditions to ensure the stability of the additives and the uniformity of the electrolyte. Preparation environment requirements: dew point ≤ -40℃, oxygen content ≤ 5ppm, and operation is carried out in a dry glove box filled with argon.

[0097] Selection and preparation of the basic electrolyte: A ternary mixed solvent of EC / EMC / DEC is preferred, with a volume ratio of 3:5:2. LiPF6 is selected as the lithium salt, with a concentration of 1.0M~1.2M, such as 1.1M. This formulation exhibits good conductivity (≥8 mS / cm) and electrochemical stability at room temperature.

[0098] Dissolution and dispersion of the additive: The weighed bifunctional additive is added to the base electrolyte and dissolved at room temperature under magnetic stirring. Due to the relatively large molecular structure of the additive, the dissolution process requires sufficient time, typically 4 to 12 hours of stirring, such as 8 hours. Complete dissolution is indicated by a clear and homogeneous solution with no visible particles or suspended matter.

[0099] Factors affecting solubility and optimization: The solubility of additives in carbonate solvents is affected by factors such as temperature, solvent polarity, and lithium salt concentration. Increased temperature promotes dissolution, but excessively high temperatures may lead to decomposition; the dissolution effect is optimal when the solvent polarity is moderate; lithium salt concentration has a slight effect on solubility, and excessively high concentrations may result in complex precipitation.

[0100] Final electrolyte quality control: appearance: transparent and colorless to pale yellow; density: 1.25 g / mL to 1.30 g / mL (25℃); conductivity: 8 mS / cm to 12 mS / cm (25℃); moisture: ≤20 ppm (Karl Fischer method); HF: ≤50 ppm (ion chromatography); additive content: 0.3 wt% to 0.7 wt% (HPLC detection).

[0101] Bifunctional additives can be compounded with other electrolyte additives to further enhance performance. Commonly used compound additives include film-forming additives, flame retardants, and high / low temperature additives. For example, they can be compounded with film-forming additives or flame retardants such as vitamin C, FEC, phosphazenes, and borate esters to achieve synergistic effects.

[0102] Combined with VC (ethylene carbonate): VC, as a classic film-forming additive, has a synergistic effect with bifunctional additives. Recommended ratio: 0.5wt% bifunctional additive + 1.0wt%~2.0wt% VC. VC preferentially forms films at low potentials, while the bifunctional additive functions at the operating potential, forming a gradient-functional SEI film.

[0103] Blending with FEC (fluoroethylene carbonate): FEC improves low-temperature performance and matches the fluorination film-forming mechanism of the bifunctional additive. Recommended ratio: 0.5wt% bifunctional additive + 5wt%~10wt% FEC. This combination maintains excellent performance over a wide temperature range of -20℃ to 55℃.

[0104] Combined with PES (propenyl sulfonyl lactone): PES, as a high-voltage stabilizing additive, forms a high-voltage protection system with the bifunctional additive. Recommended ratio: 0.5wt% bifunctional additive + 1wt%~3wt% PES. This combination is suitable for high-voltage fast charging applications.

[0105] Compounding principles: good compatibility between additives, no precipitation or stratification; complementary functions of each additive, with obvious synergistic effect; the total additive concentration is controlled within 5 wt% to maintain the basic performance of the electrolyte.

[0106] The storage and transportation of bifunctional additives and additive-containing electrolytes need to meet specific requirements to ensure stable product quality.

[0107] Additive storage conditions: Store in a sealed container in a dry, cool, and ventilated place; storage temperature -10℃~30℃; relative humidity <50%; avoid contact with strong acids, strong alkalis, and strong oxidants; packaging material should be high-density polyethylene (HDPE) or polytetrafluoroethylene (PTFE) containers.

[0108] Electrolyte storage conditions: Store in a sealed stainless steel container protected by argon gas; storage temperature 5℃~25℃; check moisture content regularly and dry if necessary; avoid direct sunlight and mechanical impact.

[0109] Transportation requirements: Packaging and transportation shall be carried out in accordance with the regulations for the transportation of hazardous chemicals; the means of transport shall be equipped with safety facilities such as leak prevention, fire prevention, and ventilation; violent vibration and sudden temperature changes shall be avoided during transportation; emergency response equipment and materials shall be provided.

[0110] Quality Control: Establish a comprehensive quality control system, ensuring traceability from raw material procurement to product delivery; set up online monitoring at key control points; conduct full-item testing before product delivery; and establish a customer feedback and quality improvement mechanism.

[0111] This application also provides a battery cell prepared by the method described above, comprising:

[0112] The housing and the positive electrode, separator, negative electrode and electrolyte located within the housing, wherein the separator is located between the positive electrode and the negative electrode.

[0113] This application also provides a battery device, comprising a battery cell obtained by the method described above for preparing a battery cell, or a battery cell as described above, wherein the battery device comprises one or more of a battery module, a battery pack, and an energy storage battery.

[0114] In another aspect, this application provides an electrical device that includes a battery device as described above, the battery device being used to provide electrical energy.

[0115] Another aspect of this application provides an energy storage device, which includes a battery device as described above, the battery device being used to store electrical energy.

[0116] The advantages of the bifunctional additive in this application are also reflected in the following:

[0117] (a) Precision innovation in molecular design:

[0118] Existing redox mediator additives mostly rely on empirical molecular selection, lacking systematic guidance from molecular design theory, leading to problems such as inaccurate potential matching and unsatisfactory stability. Traditional additives, such as ferrocene derivatives, have excessively low oxidation potentials (~3.2V), quinone compounds exhibit poor stability, and aromatic amines lack sufficient selectivity.

[0119] Based on quantum chemical calculations and structure-activity relationship analysis, this application precisely designed the molecular structure. The LUMO energy level was precisely tuned to -3.2 eV by using a -CF3 substituent at the N-10 position, achieving optimal matching with the redox potential of lithium iron phosphate (3.45 V), with a potential residual of ≤30 mV. This precise design ensures efficient and reversible electron transport.

[0120] (b) System innovation of dual-function synergistic mechanism:

[0121] Existing electrolyte additives are typically designed for a single function. Redox mediators primarily improve electron transport but have limited effect on interface stability, while film-forming additives mainly stabilize the interface but usually increase impedance, affecting fast-charging performance. When these two types of additives are used in combination, functional conflicts and mutual constraints often arise.

[0122] This application innovatively integrates the dual functions of "coordination-type redox mediator + in-situ fluorination film formation" in a single molecule. The N, S dual heteroatoms in the phenothiazine framework and Fe... 2+ / Fe 3+ The formation of reversible coordination complexes provides an electron transport channel, while the 3-position-SO2CF3 and 10-position-CF3 groups synergistically decompose to generate a LiF-rich SEI film, providing interfacial protection. The bifunctionality is achieved synergistically within the same molecule, avoiding functional conflicts.

[0123] (c) Innovative mechanism of coordination complex electron transport:

[0124] Traditional redox media primarily rely on the redox reactions of molecules themselves for electron shuttle. Electron transport efficiency is limited by the molecular diffusion rate, and irreversible side reactions easily occur, consuming active molecules. The interaction between existing media and electrode active materials is mostly physical contact or weak interaction.

[0125] This application utilizes the N,S dual heteroatoms in the phenothiazine framework and the Fe on the surface of lithium iron phosphate. 2+ / Fe 3+ The coordination complexes establish molecular-level electron transport bridges. The coordination bond lengths are approximately 2.0 Å to 2.2 Å for Fe-N and approximately 2.3 Å to 2.5 Å for Fe-S, forming a stable five-membered ring coordination structure. This coordination-based electron transport mechanism significantly improves electron transport efficiency and enables sustainable electron relay transport through the reversible formation / breaking of coordination bonds.

[0126] (d) Innovative controllability of in-situ fluorination film formation:

[0127] Traditional fluorinated additives such as FEC and DFEC mainly decompose to form films at low potentials. The film formation timing is mismatched with the operating potential of lithium iron phosphate, and the composition of decomposition products is complex and difficult to control. Existing film-forming additives often form thick and high-impedance SEI films, affecting fast-charging performance.

[0128] The -SO2CF3 group designed in this application undergoes controllable decomposition within a potential range of 2.8V to 3.8V, perfectly matching the operating potential of lithium iron phosphate. The decomposition mechanism is well-defined, with the main products being LiF nanoparticles (5nm~20nm) and fluorinated alkyl chains, forming a thin (~5nm~15nm) and dense LiF-rich SEI film. With a LiF content ≥40%, it provides excellent lithium-ion conductivity (~10... -4 (S / cm) and mechanical stability.

[0129] (e) Protective innovations based on combined functional thresholds:

[0130] Current technologies for evaluating additive performance mainly rely on single indicators, such as capacity retention or impedance change, lacking a comprehensive and systematic evaluation standard. Patent protection is easily circumvented by optimizing a single indicator. Existing patents often employ structural limitations, resulting in relatively narrow scopes of protection.

[0131] This application establishes a four-dimensional combined functional threshold system of rate-capacity, impedance control, interface composition, and reversible coordination, requiring that 5C ≥ 145 mAh / g, Rct increase ≤ 18%, LiF content ≥ 40%, and Fe-N / S coordination number 0.5~1.5 be satisfied simultaneously.

[0132] (f) Economic innovation with high efficiency and low addition levels:

[0133] Traditional redox media typically require relatively high dosages (1wt%~5wt%) to show significant effects, increasing battery costs and the risk of side reactions. While existing film-forming additives are used in relatively low amounts, their effectiveness is limited when used alone, often requiring combination with other additives, resulting in an overall high dosage.

[0134] This application achieves a significant improvement in fast-charging performance with an extremely low addition amount of only 0.3wt% to 0.7wt%, reaching a 5C discharge capacity of 145mAh / g and completing 80% SOC charging in 20 minutes. The low addition amount is due to the high efficiency of the bifunctional molecules: coordination complexation improves electron transport efficiency, and in-situ film formation reduces the amount of film-forming additives required. This design significantly reduces battery costs and environmental impact.

[0135] (g) Application innovations specifically adapted for lithium iron phosphate:

[0136] Existing additives mostly adopt a general design concept, attempting to be applicable to various cathode material systems, but they lack specificity and their performance in specific materials is often less than ideal. The unique structural characteristics of lithium iron phosphate (olivine structure, Fe...) 2+ / Fe 3+ Redox pairs and one-dimensional lithium-ion channels have not been adequately considered.

[0137] This application specifically targets the structural characteristics and electrochemical behavior of lithium iron phosphate, employing molecular design: the LUMO level at -3.2 eV is precisely matched to Fe. 2+ / Fe 3+ Redox potential; good coordination matching between N and S coordinating atoms and iron ions; film formation potential window completely coincides with the working voltage of lithium iron phosphate. This specialized design ensures optimal performance in lithium iron phosphate systems.

[0138] (h) Industrial-scale innovation in synthesis processes:

[0139] The synthesis of existing complex additive molecules often involves multiple steps, expensive reagents, and harsh conditions, making industrial-scale production difficult. Low yields, poor selectivity, and purification difficulties in synthetic routes also restrict large-scale applications.

[0140] This application employs a modular synthetic strategy, achieving efficient synthesis of the target molecule through a two-step reaction involving Buchwald-Hartwig coupling and electrophilic aromatic substitution. The reaction conditions are mild, yields are ≥85%, byproducts are few, and purification processes are simple. The synthetic route is suitable for industrial scale-up, with readily available raw materials and controllable costs, providing a technological foundation for the large-scale application of additives.

[0141] (i) Innovation in compatibility with multi-electrolyte systems:

[0142] Traditional additives often exhibit selectivity for specific electrolyte systems, showing significant differences in performance across different solvents or lithium salt systems, thus limiting their application range. The interactions between additives and electrolyte components are complex and can potentially lead to unpredictable side reactions.

[0143] The bifunctional additive of this application exhibits good compatibility and stability in various electrolyte systems. It demonstrates excellent performance in the EC / EMC / DEC+LiPF6 standard system and even better stability in the EMC-rich+LiFSI high-voltage system. The additive has a stable molecular structure, shows no adverse reactions with commonly used electrolyte components, and can be used synergistically with additives such as VC, FEC, and PES.

[0144] (j) Theoretical innovations in structure-performance relationship:

[0145] The development of current additives largely relies on experimental exploration, lacking systematic theoretical guidance on structure-property relationships, leading to blind and inefficient molecular design. Insufficient understanding of the mechanisms of action of additives hinders targeted design and optimization.

[0146] This application establishes a clear structure-performance relationship: the LUMO energy level determines the redox potential matching, the N and S coordination abilities affect electron transport efficiency, and the -SO2CF3 bond energy controls the film formation timing and product composition. Based on these relationships, targeted molecular design and performance prediction can be carried out, providing a theoretical basis for subsequent molecular optimization and promoting the scientific development of additive technology.

[0147] (k) Specialized site engineering innovations for fast charging of lithium iron phosphate:

[0148] Existing phenothiazine additives mostly follow a general design approach and are not specifically optimized for the unique electrochemical characteristics of lithium iron phosphate (LFP). This application is specifically designed for LFP fast-charging conditions and innovatively establishes an asymmetric functional division mode of "10-position regulation - 3-position response," ensuring that the N and S atoms of phenothiazine react with the Fe atoms. 2+ / Fe 3+ The optimal coordination match is crucial; any alteration at any site will disrupt this precise functional coupling, highlighting the technological value of specialized molecular engineering.

[0149] To verify the impact of the proposed bifunctional additive on the fast-charging performance of lithium iron phosphate batteries, this application designed a series of examples and comparative examples to systematically explore the effects of key factors such as additive molecular structure, substituent position, addition amount, electrolyte system compatibility, and compounding strategy on battery rate performance, interfacial impedance, cycle stability, and thermal behavior. The following details the raw material selection, electrolyte preparation, battery assembly, and performance testing methods (as shown in Tables 1-1 and 1-2).

[0150] The materials used in the following embodiments and comparative examples are as follows.

[0151] Bifunctional additives (R1 is -CF3, R2 is -SO2CF3), molecular formula C 14 H7F6NO2S2, with a molecular weight of 419.33 g / mol, was prepared according to the synthetic route described in this application, with a purity ≥99.0% (HPLC detection). Before use, it was dried in a vacuum drying oven at 60℃ for 12 h to ensure a moisture content below 50 ppm. The unsubstituted phenothiazine (PTZ), 10-trifluoromethylphenothiazine (10-CF3-PTZ), 3-trifluoromethanesulfonylphenothiazine (3-SO2CF3-PTZ), the position-interchangeable 10-SO2CF3-3-CF3-PTZ, and the 10-position derivatives (10-C2F5-PTZ, 10-OCF3-PTZ, 10-CN-PTZ) and 3-position derivative (3-SO2C2F5-PTZ) used in the comparative examples were all prepared according to their respective synthetic routes, with a purity ≥98.5%. The fluoroethylene carbonate (FEC, C3H3FO3) and hydroxymethylferrocene (Fc-OH, C...) used in the comparative examples... 11 H 12 All FeO were battery-grade reagents with a purity ≥99.0%. The vinylene carbonate (VC, C3H2O3) used in the compounding examples was a battery-grade reagent with a purity ≥99.5%.

[0152] The basic electrolyte uses ethylene carbonate (EC, C3H4O3), methyl ethyl carbonate (EMC, C4H8O3), and diethyl carbonate (DEC, C5H4O3). 10 The ternary mixed solvent (O3) had a volume ratio of EC:EMC:DEC of 3:5:2, and the lithium salt was lithium hexafluorophosphate (LiPF6) at a concentration of 1.1 mol / L. The EMC-rich system (Example 10) used a solvent with an EC:EMC volume ratio of 2:8, and the lithium salt was lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO2F)2) at a concentration of 1.2 mol / L. All solvents and lithium salts were battery-grade reagents with a moisture content below 20 ppm.

[0153] The positive electrode active material is carbon-coated lithium iron phosphate (LiFePO4 / C), with a D50 particle size of 1.0μm~1.5μm, a carbon content of 1.5wt%~2.0wt%, and a specific capacity ≥160mAh / g (0.1C). The supplier is a commercial source. The conductive agent is conductive carbon black SuperP and carbon nanotubes (CNTs). The binder is polyvinylidene fluoride (PVDF, Mw≈600,000g / mol), and the solvent is N-methylpyrrolidone (NMP). The negative electrode active material is artificial graphite, with a D50 particle size of 15μm~18μm and a specific capacity ≥355mAh / g. The negative electrode binder is a sodium carboxymethyl cellulose / styrene-butadiene rubber (CMC / SBR) composite system. The separator is a 16μm thick polyethylene (PE) matrix ceramic-coated separator with a 2μm thick Al2O3 coating.

[0154] All the chemical reagents mentioned above are analytical grade or battery-grade materials, and are commercially available. All operations involving water- and oxygen-sensitive materials were performed in an argon-atmospheric glove box, where the water and oxygen content was controlled to be below 0.1 ppm.

[0155] Electrolyte preparation:

[0156] Electrolyte preparation was carried out in an argon-filled glove box with a dew point ≤ -40℃. First, EC, EMC, and DEC were mixed thoroughly at a volume ratio of 3:5:2. Then, LiPF6 was slowly added until the concentration reached 1.1 mol / L. The mixture was dissolved at room temperature for 2 hours with magnetic stirring to obtain the basic electrolyte. Subsequently, according to the additive types and mass percentages corresponding to the numbers in the comparative examples table, the weighed additives were added to the basic electrolyte and dissolved at room temperature for 8 hours with magnetic stirring until the solution was clear, homogeneous, and free of visible particles or suspended matter, thus obtaining the final electrolyte. For the compound examples (Examples 11 and 12), VC or FEC was added after the bifunctional additives were completely dissolved, and stirring was continued for 2 hours to ensure homogeneity. Comparative Example 1 used a basic electrolyte without any additives. All prepared electrolytes were filtered through a 0.22 μm PTFE membrane, sealed, and used within 48 hours.

[0157] Battery assembly:

[0158] The experimental example used a 3Ah lithium iron phosphate / graphite stacked small pouch battery for verification testing, employing a single-layer stacked structure. The positive electrode slurry formulation consisted of 93wt% LiFePO4 / C active material, 3wt% SuperP conductive agent, 1wt% carbon nanotubes (CNTs), and 3wt% PVDF binder by mass ratio. A uniform slurry was prepared using NMP as solvent and then coated onto a 15μm thick aluminum foil current collector. The coating surface density was controlled at (18±0.5) mg / cm². 2 After being vacuum dried at 120℃, it was rolled to a compacted density of 2.3 g / cm³.3 ~2.4g / cm 3 The negative electrode slurry formulation consists of 95wt% artificial graphite, 1wt% conductive agent SuperP, and 4wt% binder CMC / SBR (CMC:SBR=1.5:2.5) by mass ratio. It is coated onto an 8μm thick copper foil current collector, with a coating surface density designed according to an N / P ratio of 1.05~1.10. After vacuum drying at 85℃, it is rolled to a compacted density of 1.5g / cm³. 3 ~1.6g / cm 3 .

[0159] Battery assembly employs a standard stacking process, where the positive electrode, ceramic-coated PE separator, and negative electrode are stacked sequentially, welded together with tabs, and then encapsulated in an aluminum-plastic film. The assembled battery is dried in an 85°C vacuum oven for 24 hours to remove residual moisture, ensuring the internal moisture content is below 50 ppm. Electrolyte injection is performed in an argon-filled glove box, injecting electrolytes prepared according to the formulations of each example / comparative example. The injection volume is determined based on the battery capacity (electrolyte coefficient 3.5 g / Ah ~ 4.0 g / Ah). After injection, the battery is allowed to stand at room temperature for 12 hours to allow the electrolyte to fully wet the electrodes.

[0160] The formation process employs a low-current stepped charging strategy: first, it is charged at a constant current of 0.05C to 3.0V and allowed to stand for 30 minutes; then, it is charged at a constant current of 0.1C to 3.65V, and the voltage is maintained until the cutoff current reaches 0.02C; finally, it is discharged at a constant current of 0.1C to 2.5V. This formation process is repeated twice. After formation, the battery undergoes a second vacuum sealing to remove trace amounts of gas generated during the formation process. Subsequently, it is subjected to three charge-discharge cycles at 0.5C at 25°C for capacity calibration, and the capacity of the third discharge cycle is taken as the rated capacity of the battery.

[0161] Performance testing methods:

[0162] To systematically evaluate the performance of the bifunctional additives in this application and verify the effectiveness of the various technological innovations, the following uniform performance tests were performed on all 22 items listed in the comparative examples table. Three parallel samples were used for each test, and the average value was taken as the reported data. Before the test, all batteries were allowed to stand at a specified temperature for at least 4 hours to reach thermal equilibrium. Unless otherwise specified, the charge / discharge voltage window for all tests was 2.5V to 3.65V.

[0163] Test 1: Multi-rate discharge capacity. This test aims to verify the rate-capacity threshold and demonstrate the improvement effect of additives on high-rate kinetics. The test was conducted in a 25℃ constant temperature chamber. Charging was uniformly performed in a 0.5C constant current / constant voltage mode, with constant current charging to the upper limit voltage of 3.65V, followed by constant voltage charging to the cutoff current of 0.05C, ensuring that all test starting points were fully charged. Discharge was performed sequentially at four rates: 0.2C, 1C, 3C, and 5C, with constant current discharge to the lower limit voltage of 2.5V. Each rate was cycled 3 times, and the capacity of the third discharge was taken as the stable discharge specific capacity (mAh / g, based on the mass of the positive electrode active material) at that rate. Simultaneously, the ratio of the 5C to the 0.2C discharge capacity, i.e., the 5C / 0.2C capacity retention rate (%), was calculated. This indicator directly reflects the electrode kinetics' response to high rates. A 5C discharge specific capacity ≥ 145mAh / g is one of the core thresholds of this application.

[0164] Test 2: Fast Charging Time and Charged Capacity. This test aims to verify the engineering-ready fast charging capability, evaluating the effectiveness of charged capacity while assessing charging speed, avoiding misjudgments based on "shortened charging time but insufficient charging." The test was conducted at 25℃. First, the battery was discharged at 0.5C to 2.5V and then charged at a constant current and constant voltage of 0.2C to 3.65V to calibrate the full capacity. Then, it was discharged at 0.5C to the voltage corresponding to 20% SOC. Starting from 20% SOC, it was charged at a constant current of 3C. When the voltage reached 3.65V, it switched to constant voltage charging, with the cutoff current set at 0.1C. The cumulative charging time t (min) was recorded when the battery reached 80% SOC. The charged capacity Q during the 20%→80% SOC charging process was recorded simultaneously. charge (mAh / g), and the discharge capacity Q after fast charging, when left to stand for 5 minutes and then discharged at 1C to 2.5V. dis (mAh / g). The target fast charging time is within 20 minutes.

[0165] Test 3: Electrochemical Impedance Spectroscopy (EIS) Interfacial Impedance. This test aims to verify the impedance control threshold, demonstrating the core advantage of "no excessive resistance increase" after additive film formation. The test was conducted at 25°C, with measurements taken once after the first cycle following formation and again after completing 200 fast-charge cycles as per Test 4. Before testing, the battery was adjusted to 50% SOC (charged at 0.5C to the voltage corresponding to 50% SOC and then allowed to stand for 2 hours to reach electrochemical equilibrium). EIS test conditions: frequency range 100kHz to 10mHz, AC perturbation amplitude 5mV, conducted using an Autolab or Bio-Logic electrochemical workstation. Impedance data were fitted using an equivalent circuit Rs-(Rct‖CPE)-W, where Rs is the solution ohmic resistance, Rct is the charge transfer resistance, CPE is the constant phase angle element (characterizing the non-ideal nature of the double-layer capacitance), and W is the Warburg diffusion impedance. Reported parameters include: Rct. 首圈(Ω), Rct 200圈 (Ω), and the charge transfer resistance increase ΔRct=[(Rct) 200圈 -Rct 首圈 ) / Rct 首圈 ×100%. All samples used a uniform equivalent circuit model and fitting software (ZView or EC-LabZFit) to ensure the consistency and comparability of Rct values. ΔRct≤18% is another core threshold of this application.

[0166] Test 4: Fast Charging Cycle Stability. This test aims to verify the sustainability of fast charging performance, proving that the fast charging improvement brought by the additive is not a one-off effect but remains stable during repeated fast charging. The test was conducted at 25℃, with charging using a 3C constant current and constant voltage mode (constant current charging to 3.65V, constant voltage to the cutoff current of 0.1C), and discharging using a 1C constant current to 2.5V, for 200 consecutive cycles. The 3C charging rate directly corresponds to the fast charging application scenario, and unlike the conventional 1C / 1C cycle test, it better reflects the additive's ability to maintain interface stability under repeated high-rate impacts. Capacity retention rate = (discharge capacity on the 200th cycle / discharge capacity on the 1st cycle) × 100%.

[0167] Test 5: Initial Coulombic Efficiency (ICE). This test aims to distinguish between "moderate film formation" and "over-film formation," providing criteria for additive dosage windows and excessive failure. The test was conducted at 25°C. The first cycle used a low-rate charge-discharge of 0.1C: charging at a constant current and constant voltage of 0.1C to 3.65V (cutoff current 0.01C), and then discharging at a constant current of 0.1C to 2.5V. Initial coulombic efficiency ICE = (initial discharge capacity / initial charge capacity) × 100%. The low-rate test eliminates the interference of kinetic factors, allowing ICE to truly reflect the degree of irreversible lithium consumption during the formation stage, i.e., the capacity loss caused by additive decomposition and film formation.

[0168] Test 6: Temperature Rise During Fast Charging. This test aims to indirectly verify the effect of additives on reducing electrode polarization through temperature rise data, providing a basis for fast charging safety assessment. The test was conducted under natural convection conditions at an ambient temperature of 25±1℃ (without forced air cooling). After adjusting the battery to 20% SOC, it was charged to 80% SOC using 3C constant current and constant voltage (consistent with Test 2 conditions). A type K thermocouple was attached to the center of the large surface of the battery cell, and the temperature change during the charging process was continuously recorded at a sampling frequency of 1Hz. Reported parameters include: T 初始 (°C), T 最高 (°C), and temperature rise ΔT=T 最高 -T 初始 (°C). Temperature rise directly reflects the Joule heat and polarization heat inside the battery; the lower the polarization, the smaller the temperature rise.

[0169] Supplementary characterization of representative samples:

[0170] To further verify the mechanism of action of the bifunctional additive, the following supplementary characterization was performed on representative samples (Example 1, Comparative Example 1, Comparative Example 5, and Comparative Example 8). The characterization samples were taken from batteries that had completed all 200 fast-charging cycles of Test 4. The positive electrode was disassembled in an argon glove box to obtain the positive electrode sheet, rinsed three times with DMC solvent to remove residual electrolyte, and then transferred to the characterization equipment after vacuum drying in the front chamber of the glove box.

[0171] X-ray photoelectron spectroscopy (XPS) analysis was performed using a monochromatic AlKα X-ray source (hν = 1486.6 eV) with an analysis depth of approximately 5 nm to 10 nm to determine the LiF content in the SEI film on the cathode surface. The LiF atomic fraction (%) was calculated by integrating the peak areas of the Li1s and F1s narrow-region spectra and using the ratio of the LiF characteristic peaks (Li1s binding energy approximately 55.8 eV, F1s binding energy approximately 685.0 eV) to the total signal. This indicator corresponds to the verification of the interface composition threshold (LiF ≥ 40%) in this application.

[0172] Extended X-ray absorption fine structure spectroscopy (EXAFS) analysis was performed at the FeK-edge synchrotron radiation source to detect the Fe-N and Fe-S coordination structures and verify the coordination complexation of the phenothiazine framework with iron ions on the lithium iron phosphate surface. The coordination numbers (range 0.5–1.5, representing the reversible coordination threshold of this application) and coordination bond lengths of Fe-N and Fe-S were obtained by Fourier transform and fitting of the EXAFS oscillation function.

[0173] All performance data are based on the average of three parallel sample tests. Unless otherwise specified in the data table, the typical inter-sample coefficient of variation (CV) is controlled within 5%. Discharge specific capacity is calculated based on the mass of the positive electrode active material. The goodness of fit (χ²) of the EIS data is also considered. 2 Controlled at 10 -3 For values ​​below the order of magnitude, ensure the reliability of the fitting results. The thermocouple calibration accuracy for temperature rise testing is ±0.5℃.

[0174] Through the above-mentioned systematic experimental design and standardized testing methods, the contribution of the various technological innovations of this application to the fast-charging performance of lithium iron phosphate batteries can be accurately evaluated, providing reliable experimental evidence for the technical value of the N-CF3-phenothiazine-dithiamide bifunctional additive.

[0175] The experimental results (as shown in Tables 2-1 and 2-2) fully demonstrate the key role of the dual-functional synergistic mechanism of "coordination-type redox medium + in-situ fluorination film formation" in the fast-charging performance of lithium iron phosphate batteries. By comparing the test data of Example 1 (TFMS-TFMPT 0.5wt% complete scheme) and Comparative Example 1 (blank electrolyte), a comprehensive performance leap brought about by the dual-functional additive can be clearly observed. Example 1 achieved a discharge specific capacity of 148.5 mAh / g at 5C rate, which is 41.2% higher than that of Comparative Example 1 (105.2 mAh / g), easily meeting the core threshold of 5C ≥ 145 mAh / g of this application. At the same time, the 5C / 0.2C capacity retention rate of Example 1 jumped from 63.4% in Comparative Example 1 to 89.2%, indicating that the kinetic limitations at high rates have been fundamentally improved. In terms of fast charging time, Example 1 can charge the battery from 20% to 80% SOC in only 18.5 minutes, while Comparative Example 1 requires 32.5 minutes, resulting in an efficiency improvement of approximately 43%. More importantly, the fast charging capacity of Example 1 (96.2 mAh / g) is significantly higher than that of Comparative Example 1 (78.5 mAh / g), eliminating the possibility of "fast but insufficient". The 1C discharge verification after fast charging also confirms that the charge in Example 1 can be effectively utilized.

[0176] EIS impedance data further revealed the interface mechanism underlying the differences in fast charging performance. The Rct increase in Example 1 after 200 fast charging cycles was only 16.7%, far lower than the 44.7% in Comparative Example 1. Comparative Example 1 lacked effective interface protection; under the high current impact of repeated fast charging, uncontrollable side reactions continuously occurred at the electrode / electrolyte interface, leading to continuous thickening of the SEI film and a continuous increase in impedance. In contrast, the LiF-rich SEI film generated in situ by the bifunctional additive in Example 1 established stable interface protection in the first cycle, with extremely limited impedance growth in subsequent cycles, fully demonstrating the film formation design concept of "not excessively increasing resistance." After 200 fast charging cycles, the capacity retention rate of Example 1 reached 91.2%, while that of Comparative Example 1 was only 72.5%, a difference of 18.7 percentage points, directly reflecting the supporting role of interface stability in the long-term sustainability of fast charging. The temperature rise data also corroborates this analysis: the fast charging temperature rise ΔT of Example 1 was only 8.2℃, while that of Comparative Example 1 was as high as 18.5℃, reflecting the severe polarization and resulting Joule heating of Comparative Example 1 at high rates. The slight decrease in ICE of Comparative Example 1 compared to Example 1 (approximately 2 to 3 percentage points) is a normal performance of effective film formation during the additive formation stage. The long-term benefit of increasing the retention rate from 72.5% to 91.2% after 200 cycles (from Comparative Example 1 to Example 1) far outweighs the initial small amount of irreversible lithium loss.

[0177] The experimental results of Comparative Example 2 (0.5 wt% unsubstituted phenothiazine PTZ) strongly demonstrate the necessity of substituent modification. Unsubstituted PTZ retains only the basic coordination ability of the phenothiazine skeleton but lacks the precise control of the LUMO energy level by -CF3 and the in-situ film-forming function of -SO2CF3. Its 5C specific capacity is 118.5 mAh / g, which, although an improvement over Comparative Example 1 (thanks to the weak coordination between the skeleton N and S atoms and Fe), is far from reaching the 145 mAh / g threshold. The Rct increase of Comparative Example 2 is 35.0%, indicating that the lack of film-forming protection from fluorine-containing groups still leads to severe interface degradation. The first-cycle coulombic efficiency of Comparative Example 2 is 86.5%, lower than 88.5% of Example 1, presumably because the PTZ molecules underwent partial irreversible decomposition in the absence of structural protection, consuming active lithium but failing to form an effective protective film.

[0178] The comparison between Comparative Example 3 (containing only 0.5 wt% 10-CF3 monosubstituted) and Comparative Example 4 (containing only 0.5 wt% 3-SO2CF3 monosubstituted) further quantifies the respective contributions of the two functional groups and the limitations of using them alone. Comparative Example 3 retains the LUMO energy level modulation function of 10-CF3, and its redox mediator effect enables the 5C specific capacity to reach 132.5 mAh / g, which is a significant improvement compared to 118.5 mAh / g of Comparative Example 2. However, due to the lack of film-forming protection, the Rct increase is as high as 31.7%, and the 200-cycle retention rate is only 78.5%. Comparative Example 4 retains the film-forming function of 3-SO2CF3, and the cycle retention rate reaches 82.5%, which is better than that of Comparative Example 3. However, due to the lack of precise modulation of the LUMO energy level by 10-CF3, the redox potential and LFP matching degree are not good, the improvement of electron transport is limited, and the 5C specific capacity is only 120.5 mAh / g. The first-cycle coulombic efficiency of Comparative Example 4 was 85.2%, which was one of the lowest among all examples and comparative examples. It is believed that this was because the 3-SO2CF3 group decomposed too violently in the absence of the electron-withdrawing effect of 10-CF3, forming an excessively thick SEI film that consumed an excessive amount of irreversible lithium.

[0179] The three sets of comparative examples 2 to 4 clearly demonstrate the indivisibility of the functional division of "10-position -CF3 is dedicated to LUMO regulation and 3-position -SO2CF3 is dedicated to controllable film formation" in the bifunctional molecular design of this application: no single functional component can simultaneously satisfy the combined thresholds of 5C ≥ 145 mAh / g and ΔRct ≤ 18%. Only when the two functions work synergistically in the same molecule can a breakthrough be achieved.

[0180] Comparative Example 5 (position interchangeable 10-SO2CF3-3-CF3 0.5wt%) is a key verification experiment for the site engineering strategy of this application. In this comparative example, the types and total number of the two substituents are completely consistent with those in Example 1, the only difference being the position interchange—the -CF3 originally located at position 10 moves to position 3, and the -SO2CF3 originally located at position 3 moves to position 10. The 5C specific capacity of Comparative Example 5 is only 115.8 mAh / g, which is not only far lower than the 148.5 mAh / g of Example 1, but also lower than the 118.5 mAh / g of Comparative Example 2 (unsubstituted PTZ). The Rct increase of Comparative Example 5 is as high as 40.9%, close to the 44.7% of the blank electrolyte of Comparative Example 1, the retention rate after 200 cycles is only 74.2%, the coulombic efficiency of the first cycle drops to 83.5%, and the fast charging temperature rise reaches 15.5℃.

[0181] This set of almost completely "collapsed" data has profound mechanistic implications. The failure caused by positional interchange can be attributed to the following synergistic degradation: First, after -SO2CF3 moves to the 10 position, its strong electron-withdrawing effect directly acts on the nitrogen atom, excessively reducing the electron cloud density of the N atom and severely weakening the N-Fe coordination ability, leading to the basic failure of the coordination-type redox medium mechanism; Second, after -CF3 moves to the 3 position, the regulation of the LUMO energy level deviates from the optimal matching range, and the redox potential of the molecule no longer matches the 3.45V of LFP; Third, at the 10 position, where -SO2CF3 is directly connected to the N atom, the electrochemical decomposition behavior becomes uncontrolled—both the decomposition potential and decomposition products change, making it impossible to form an effective LiF-rich SEI film, and potentially generating high-impedance ineffective byproducts. The first-cycle coulombic efficiency (83.5%) of Comparative Example 5 is the lowest among all samples, confirming that this uncontrolled decomposition consumes a large amount of irreversible lithium.

[0182] XPS characterization results of representative samples further support the above analysis. In Example 1, the LiF atomic fraction in the SEI film on the cathode surface reached 48.5%, meeting the interface composition threshold (≥40%) of this application. In contrast, the LiF atomic fractions in Comparative Examples 1, 5, and 8 were significantly lower, at 12.3%, 18.7%, and 32.5%, respectively. At the same time, a large number of amorphous sulfur- and fluorine-containing organic decomposition products were detected, confirming the runaway decomposition of 10-SO2CF3. EXAFS analysis showed that the coordination numbers of Fe-N and Fe-S in Example 1 fell within the reversible coordination threshold range (0.5~1.5) of this application, specifically 10.5. In contrast, the coordination signals of Fe-N and Fe-S in Comparative Examples 1 and 8 were almost undetectable, directly demonstrating the loss of the coordination mechanism. The coordination numbers of Fe-N and Fe-S in Comparative Example 5 were 0.08 and 0.35, respectively. These experimental data clearly confirm that the "3-SO2CF3, 10-CF3" site combination claimed in this application has irreplaceable technical rationality, and any change in the position of any group will destroy the precise functional coupling.

[0183] Comparative Examples 6 (FEC 5.0 wt%), 7 (Fc-OH 0.5 wt%), and 8 (Fc-OH 0.25 wt% + FEC 2.5 wt% physical superposition) demonstrate the irreplaceability of the single-molecule bifunctional design of this application from different perspectives. Comparative Example 6 represents the traditional film-forming additive route. Although FEC at a high concentration of 5.0 wt% can provide fluorinated film-forming functionality, its film-forming potential is in the range of 1.0V-2.0V, which does not match the working potential of LFP. Moreover, the SEI film formed by FEC decomposition is relatively thick and has high impedance. The 5C specific capacity of Comparative Example 6 is only 112.5 mAh / g, even lower than the blank control of Comparative Example 1, with limited improvement. This may be because the high concentration of FEC film formation increases the interfacial impedance, which in turn deteriorates the fast-charging performance. The ICE of Comparative Example 6 is 84.2%, significantly lower than 88.5% of Example 1, confirming the irreversible lithium loss caused by excessive film formation.

[0184] Comparative Example 7 represents the traditional redox mediator route. Hydroxymethyl ferrocene, as a classic redox shuttle molecule, increased the discharge specific capacity at 5C from 105.2 mAh / g in Comparative Example 1 to 122.8 mAh / g, confirming the effectiveness of the redox mediator mechanism. However, due to the lack of interfacial protection, its Rct increase was as high as 40.0%, and the retention rate after 200 cycles was only 75.5%. The oxidation potential of the ferrocene derivative (approximately 3.2 V) is lower than that of LFP (3.45 V), resulting in insufficient matching. Furthermore, its limited chemical stability leads to irreversible decomposition during long-term cycling, causing a decline in shuttle efficiency.

[0185] Comparative Example 8 physically mixed the two additives from Comparative Examples 6 and 7, achieving a 5C specific capacity of 128.5 mAh / g, an improvement over both Comparative Examples 6 and 7, but still significantly lower than the 148.5 mAh / g of Example 1. The Rct increase in Comparative Example 8 was 30.2%, also far below the 16.7% level of Example 1. The 20 mAh / g difference in 5C capacity and the approximately 13.5 percentage point difference in Rct increase between Comparative Example 8 and Example 1 clearly demonstrate the essential advantage of "intramolecular bifunctional synergy" over "intermolecular physical superposition." In the single-molecule design of Example 1, the phenothiazine skeleton couples coordination-type electron transport and in-situ film formation on the same molecular spatial scale. Coordination complexation anchors the additive molecules to the active sites on the LFP surface, ensuring that subsequent film formation reactions occur precisely in the regions most requiring interfacial protection. In contrast, in Comparative Example 8, the two independent molecules, Fc-OH and FEC, diffuse randomly, lacking spatial and temporal coordination in their functional performance, and may even exhibit competitive adsorption and mutual interference. The ICE of Comparative Example 8 was 84.5%, which was significantly lower than that of Example 1 (88.5%), reflecting that the problem of excessive film formation of FEC in physical mixing was not alleviated by the presence of Fc-OH.

[0186] Examples 2 (0.3wt%), 3 (0.4wt%), 4 (0.6wt%), 5 (0.7wt%), and Comparative Example 9 (1.5wt%) constituted a systematic additive dosage gradient experiment, providing clear data support for the dosage range of this application (preferably 0.3-0.7wt%, more preferably 0.4-0.6wt%).

[0187] Within the preferred range of 0.3wt% to 0.7wt%, the Rct increase in all embodiments was controlled below 18% (17.1% in Example 2, 14.6% in Example 3, 16.3% in Example 4, and 15.9% in Example 5), meeting the impedance control threshold of this application. However, in terms of 5C discharge specific capacity, Example 2 (0.3wt%) had a capacity of 138.5 mAh / g, and Example 5 (0.7wt%) had a capacity of 140.8 mAh / g, both slightly lower than the threshold of 145 mAh / g. The insufficient coordination sites in Example 2 resulted in the redox mediator effect not being fully utilized, while the higher addition amount in Example 5 caused a moderate film thickening, slightly increasing the ion transport barrier.

[0188] Within a more preferred range of 0.4-0.6 wt%, Examples 3 (0.4 wt%, 5C=145.2 mAh / g) and 4 (0.6 wt%, 5C=146.8 mAh / g) fully satisfy the combined thresholds of 5C≥145 mAh / g and ΔRct≤18%, while Example 1 (0.5 wt%, 5C=148.5 mAh / g) is in the center of the range and performs best. All three examples exhibit a fast-charging cycle retention rate of over 90% and a fast-charging temperature rise of less than 9°C, demonstrating highly consistent and excellent performance.

[0189] The experimental data from Comparative Example 9 (1.5 wt%) strongly demonstrate the failure mechanism caused by excessive additive addition. The 5C specific capacity plummeted to 118.2 mAh / g, the Rct increase rebounded to 35.4%, and the first-cycle coulombic efficiency dropped to 80.5%—the lowest ICE value among all samples. Excess additives underwent excessive decomposition during the formation stage, forming an excessively thick and dense SEI film. Although the LiF content may further increase, the ion transport resistance of the film layer increased significantly, while excessive irreversible lithium was consumed. The temperature rise of Comparative Example 9 reached 14.5 °C, reflecting severe polarization heating caused by high impedance. The data pattern of Comparative Example 9 is quite similar to that of Comparative Example 4 (containing only film-forming groups), presumably because the film-forming function is "overexpressed" under excessive conditions, masking and inhibiting the normal functioning of coordination electron transport.

[0190] In Examples 6 (10-C2F5), 7 (10-OCF3), and 8 (10-CN), the effects of different electron-withdrawing groups at the 10-position were systematically investigated while keeping the -SO2CF3 at the 3-position unchanged. This verified the scalability of the 10-position substituents and the optimality of -CF3 as claimed in this application.

[0191] Example 6 (10-C2F5) exhibited a 5C specific capacity of 145.5 mAh / g and an Rct increase of 16.3%, similar to the performance of Example 1. The electron-withdrawing effect of the -C2F5 group is comparable to that of -CF3, and its effect on regulating the LUMO energy level is similar, thus the electron transport promotion effect remains essentially unchanged. Example 9 (3-SO2C2F5) similarly demonstrates that long-chain fluoroalkyl substitution at the 3-position sulfonyl group is also feasible, with a 5C value of 145.2 mAh / g. The successful verification of these structural derivatives broadens the molecular design space of this application.

[0192] Example 7 (10-OCF3) exhibited a 5C specific capacity of 142.8 mAh / g, slightly lower than that of Example 1. The electron-donating effect of -OCF3 partially offset the electron-withdrawing effect of -CF3 through the electron-donating effect of the oxygen atom, resulting in a slight reduction in the degree of LUMO level modulation and consequently a decrease in the matching precision between the redox potential and LFP. Although the 5C capacity did not reach the stringent threshold of 145 mAh / g, it was still significantly superior to all comparative examples, demonstrating the functional usability of -OCF3.

[0193] Example 8 (10-CN) exhibited the lowest 5C specific capacity of 140.5 mAh / g among the three derivatives. Although -CN is a strong electron-withdrawing group, its non-fluorinated nature means it does not participate in the fluorine-containing film formation process. This results in only one fluorine source (-SO2CF3) at the 3-position providing the LiF precursor, potentially leading to a lower LiF content in the film. The Rct increase of Example 8 was 17.4%, close to the 18% threshold, further confirming the auxiliary contribution of the fluorine-containing group at the 10-position to the film quality.

[0194] The experimental system for the aforementioned derivatives established a ranking of the effects of substituents at the 10-position in this application: -CF3≈-C2F5>-OCF3>-CN, with fluorinated all-carbon substituents showing the best effect. This ranking is consistent with a comprehensive evaluation of the electron-withdrawing strength and fluorine content of the substituents, providing clear design guidance for subsequent molecular optimization.

[0195] Example 10 (EMC-rich + LiFSI system) verified the compatibility of the bifunctional additive in different electrolyte base formulations. Example 10 achieved a 5C specific capacity of 146.5 mAh / g, with an Rct increase of only 15.0% and a 200-cycle retention rate of 90.8%, all superior to the standard system of Example 1. LiFSI exhibits better thermal stability and lower interfacial reactivity compared to LiPF6, while the EMC-rich solvent reduces electrolyte viscosity, which is beneficial for ion transport. These inherent advantages of the electrolyte, combined with the bifunctional additive, create a synergistic effect. This result indicates that the additive of this application is not limited to specific electrolyte formulations but possesses broad system compatibility.

[0196] Examples 11 (+VC 1.5wt%) and 12 (+FEC 5.0wt%) verified the synergistic effect of the bifunctional additive and the traditional film-forming additive. Example 11 achieved a fast-charge cycle retention of 92.5% and a reduced Rct increase of 12.5%, both among the best performing examples. VC preferentially forms a polycarbonate-based organic outer layer at a lower potential, which, together with the LiF-rich inorganic inner layer formed by the bifunctional additive near the LFP operating potential, constitutes a gradient-functional composite SEI structure, further improving interface stability. The ICE of Example 11 was 87.2%, slightly lower than 88.5% of Example 1, reflecting a slight irreversible lithium consumption due to the additional film formation by VC, but within an acceptable range. Example 12 performed similarly to Example 11, but the 5C specific capacity (144.5 mAh / g) was slightly lower, presumably because the high concentration of 5.0wt% FEC introduced additional interfacial film thickness, improving long-term stability while causing a slight impedance-rate trade-off in the fast-charge rate. This trade-off can be optimized in engineering applications by adjusting the FEC concentration.

[0197] Example 13 (Multi-parameter Co-optimization) represents the optimal combination of the technical solutions in this application within the current experimental matrix, employing a 0.5wt% TFMS-TFMPT + 1.0wt% VC + EMC-rich / LiFSI system. Its 5C discharge specific capacity reaches 150.2 mAh / g, the highest among all samples, approaching 90% of the theoretical capacity of LFP at 0.2C (167.2 mAh / g), demonstrating extremely excellent capacity performance at high rates. The Rct increase is only 12.8%, the 200-cycle fast charging retention rate is 93.2%, and the fast charging temperature rise is only 7.5℃, with all indicators being optimal or near-optimal. It should be noted that the performance of Example 13 is not simply a linear sum of the contributions of each optimization factor. Comparing the data from Example 10 (LiFSI system), Example 11 (+VC compound), and Example 13, it can be found that the 5C capacity of Example 13 (150.2 mAh / g) is higher than that of Example 10 (146.5 mAh / g) and Example 11 (147.2 mAh / g), and its 200-cycle retention rate (93.2%) is also better than the two (90.8% and 92.5%), demonstrating the positive synergistic effect between electrolyte substrate optimization and additive compounding. The LiFSI system itself has better ion transport characteristics, VC provides an additional layer of interfacial protection, and the bifunctional additive provides the core electron transport promotion and LiF-rich film formation function. The three complement each other in their respective functional dimensions.

[0198] Based on all the test data above, the N-CF3-phenothiazine-dithiamide bifunctional additive of this application demonstrates comprehensive advantages in improving the fast-charging performance of lithium iron phosphate batteries. Regarding rate performance, the complete solution in Example 1 achieves 148.5 mAh / g at 5C discharge, a 41.2% improvement compared to the blank control example 1, while the multi-parameter optimized Example 13 reaches 150.2 mAh / g. In terms of interface impedance, the Rct increase after 200 fast-charging cycles is controlled within the range of 12.5% ​​to 17.4% (all examples within the preferred range), significantly lower than the 27.9% to 44.7% of the control example. Regarding cycle stability, the retention rate after 200 3C fast-charging cycles is within the range of 86.5% to 93.2%, proving that the fast-charging improvement is not a one-off effect. In terms of engineering practicality, the fast-charging time is shortened to 17.5 min to 20.5 min, and the temperature rise is controlled within 7.5℃ to 10.2℃, meeting the safety and efficiency requirements of practical fast-charging applications.

[0199] More importantly, this application clearly demonstrates the necessity and contribution of each technological innovation through systematic comparative experiments. Comparative Examples 2-4 prove that the bifunctionality is indivisible, Comparative Example 5 proves that site specificity is irreplaceable, Comparative Examples 6-8 prove that single-molecule synergy is superior to physical superposition, and Comparative Example 9 proves the engineering rationality of the dosage window. These comparative examples, from different dimensions, eliminate the feasibility of alternative solutions and establish the unavoidability of the technical route of this application. The four sets of combined functional thresholds (5C≥145mAh / g, ΔRct≤18%, LiF≥40%, Fe-N / S coordination number 0.5-1.5) are all satisfied in the complete solution embodiment, while all comparative examples significantly fail to meet the standards in at least two or more key indicators, further strengthening the systematicness and completeness of the technical solution of this application.

[0200] Table 1-1

[0201]

[0202] Table 1-2

[0203]

[0204] In Tables 1-1 and 1-2, Example 1 and Comparative Examples 1 to 8 belong to the core innovation verification group, Examples 2 to 5 and Comparative Example 9 belong to the addition amount optimization group, Examples 6 to 9 belong to the molecular generalization verification group, and Examples 10 to 13 belong to the electrolyte compatibility and compounding group.

[0205] Table 2-1

[0206]

[0207] Table 2-2

[0208]

[0209] 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 method for preparing a single battery cell, characterized in that, include: Provide a battery cell assembly, the battery cell assembly being formed by stacking or winding a positive electrode sheet, a separator and a negative electrode sheet; A housing is provided to house the battery cell assembly within the housing; Provide electrolyte and inject the electrolyte into the housing; Perform the formation step; The electrolyte contains a bifunctional additive, the molecular formula of which is: In this group, R1 is an electron-withdrawing group and R2 is an electrochemically decomposable group. The electron-withdrawing group includes at least one of -CF3, -C2F5, -OCF3, and -CN; The electrochemically controllable decomposition group includes at least one of -SO2CF3 and -SO2C2F5; The positive electrode active material in the positive electrode sheet includes lithium iron phosphate.

2. The method for preparing a single battery cell according to claim 1, characterized in that, The mass fraction of the bifunctional additive in the electrolyte is 0.05% to 2.0%.

3. The method for preparing a battery cell according to claim 1 or 2, characterized in that, The preparation method of the bifunctional additive includes: firstly, introducing an electron-withdrawing group at the 10 position of phenothiazine to obtain an intermediate, and then introducing an electrochemically controllable decomposition group at the 3 position of the phenothiazine skeleton of the intermediate through an electrophilic aromatic substitution reaction.

4. The method for preparing a single battery cell according to claim 3, characterized in that, The preparation of the intermediate includes: A phenothiazine and an electron-withdrawing reagent are provided, and the reaction is carried out under inert gas protection and alkaline conditions, catalyzed by a palladium-containing catalyst, at 80℃~120℃ to obtain an intermediate.

5. The method for preparing a single battery cell according to claim 4, characterized in that, The alkaline conditions are provided by cesium carbonate.

6. The method for preparing a single battery cell according to claim 4, characterized in that, The palladium-containing catalyst includes at least one of tetra(triphenylphosphine)palladium, [1,1'-bis(diphenylphosphine)ferrocene]palladium dichloride, bis(tri-tert-butylphosphine)palladium, and palladium acetate.

7. The method for preparing a battery cell according to claim 3, characterized in that, The electrophilic aromatic substitution reaction includes: The bifunctional additive is obtained by reacting a reagent containing an electrochemically controllable decomposable group and the intermediate as raw materials at 0℃~25℃.

8. The method for preparing a single battery cell according to claim 1, characterized in that, The solvent for the electrolyte includes carbonates.

9. The method for preparing a battery cell according to claim 8, characterized in that, The carbonate includes at least one of vinylene carbonate, fluoroethylene carbonate, dimethyl carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate.

10. A single battery cell, characterized in that, Prepared by the method of any one of claims 1 to 9, comprising: The housing and the positive electrode, separator, negative electrode and electrolyte located within the housing, wherein the separator is located between the positive electrode and the negative electrode.

11. A battery device, characterized in that, The battery device includes a battery cell prepared by the method described in any one of claims 1 to 9, or a battery cell as described in claim 10, and the battery device includes one or more of a battery module, a battery pack, and an energy storage battery.

12. An electrical appliance, characterized in that, The electrical device includes the battery device as described in claim 11, the battery device being used to provide electrical energy.

13. An energy storage device, characterized in that, The energy storage device includes the battery device as described in claim 11, the battery device being used to store electrical energy.

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