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

Abstract

The application provides a battery monomer, a preparation method thereof, a battery device, a power utilization device and an energy storage device. An electrolyte comprises a double-wall microcapsule, the double-wall microcapsule comprises a capsule core and a capsule shell, the capsule core comprises a mixture of perfluorohexanone and nanometer montmorillonite, the capsule shell comprises a polymer, and the surface of the capsule shell is modified with a carboxyl functional group and / or a fluorine functional group; the melting temperature of the polymer is 125-135 DEG C; and the polymer comprises polymethyl methacrylate and polylactic acid. The double-wall microcapsule has a double-stage response mechanism, the carboxyl functional group can be preferentially adsorbed on defect sites of a negative electrode SEI film, the internal thermal weak area of the battery is strengthened in a targeted manner, and local strengthening is achieved. The fluorine functional group can be combined with inorganic components, thereby synergistically enhancing the interfacial compatibility of the double-wall microcapsule and the electrolyte, inhibiting sedimentation and agglomeration, and prolonging the cycle stability. In addition, unbroken microcapsules can remain in the electrolyte, and after thermal runaway, partial rewetting can be completed to achieve self-repairing.

Description

Technical Field

[0001] This invention relates to the field of polymer materials and functional microcapsule preparation technology, specifically to a battery cell and its preparation method, a battery device, an electrical device, and an energy storage device. Background Technology

[0002] Driven by the demand for high energy density and rapid charging and discharging, the risk of thermal runaway in lithium-ion batteries has increasingly become a core safety bottleneck restricting their large-scale application. Thermal runaway typically begins with a localized rupture of the solid electrolyte interphase (SEI) film at the negative electrode, triggering a micro-short circuit and generating hot spots, which in turn triggers a violent exothermic reaction in the positive and negative electrode materials, ultimately leading to heat propagation and fire or explosion. Traditional thermal protection methods are mainly divided into two categories: one relies on external mechanical structures to delay heat diffusion through passive heat conduction and spatial isolation; the other uses the addition of flame retardants to the electrolyte to chemically interrupt the free radical chain reaction.

[0003] However, external structural solutions have inherent drawbacks such as response delay, a 15-20% increase in weight, high cost, deterioration of pipeline sealing over time, and single-use failure, making them difficult to meet the comprehensive requirements of energy storage systems for lightweight, long lifespan, and high reliability. While electrolyte flame retardant additives have the advantages of high integration and rapid response, they generally suffer from three major technical bottlenecks: First, flame retardants often undergo side reactions with electrolyte solvents or lithium salts, leading to a decrease in ionic conductivity and battery capacity decay. Second, flame retardant components gradually decompose or volatilize during long-term cycling, failing to provide continuous protection. Third, existing flame retardants lack spatial selectivity and are uniformly dispersed in the electrolyte, failing to actively target the SEI film defect areas most prone to thermal runaway, resulting in high addition amounts but low efficiency, and inability to cope with multiple thermal shock events.

[0004] Furthermore, current technology has not yet achieved a synergistic mechanism of "active response, structural repair, and recycling." Once thermal runaway occurs, the flame retardant is consumed in one go and has no regeneration capability. The heat conduction path is not effectively blocked, and local temperature rise can still trigger a secondary chain reaction. Therefore, there is an urgent need for an intelligent flame retardant system that can achieve directional adsorption, multi-level response, ceramic isolation, and self-repair and regeneration, so as to fundamentally improve the intrinsic safety of batteries and break through the limitations of existing passive consumption-type protection. Summary of the Invention

[0005] The main objective of this invention is to provide a battery cell and its preparation method, battery device, power supply device, and energy storage device to solve the problem in the prior art where the electrolyte flame retardant fails to protect the battery after a micro-short circuit hotspot is triggered due to poor targeting, ineffective blocking of heat conduction, and the slow response, high weight, and non-reusability of the external protection structure.

[0006] To achieve the above objectives, according to one aspect of the present invention, a battery cell is provided, comprising an electrode assembly, the electrode assembly including a positive electrode, an electrolyte, and a negative electrode, the electrolyte including a double-walled microcapsule, the double-walled microcapsule including a core and a shell, the core including a mixture of perfluorohexanone and nano-montmorillonite, the shell including a polymer, and the surface of the shell being modified with carboxyl-containing functional groups and / or fluorine-containing functional groups; the melting temperature of the polymer is 125~135°C; the polymer including polymethyl methacrylate and polylactic acid.

[0007] Furthermore, the mass ratio of the carboxyl functional group to the fluorine functional group is (3:1) to (5:1); and / or, the fluorine functional group is selected from any one or more of fluoroethylene carbonate, fluoroethyl acetate, fluoroethyl propionate, and fluoropropyl propionate.

[0008] Furthermore, the local mass concentration of the double-walled microcapsules near the negative electrode is 0.5~5.0 wt%; the local mass concentration of the double-walled microcapsules near the negative electrode is 1.5~2.5 times higher than the local mass concentration of the double-walled microcapsules in other areas of the electrode assembly.

[0009] Furthermore, the mass ratio of the core to the shell is (4:1) to (3:1).

[0010] Furthermore, the mass ratio of perfluorohexanone to nano-montmorillonite is (7:3) to (9:1).

[0011] Furthermore, the density of carboxyl functional groups on the shell surface is (0.8~1.2) μmol / m³. 2 ; and / or, the density of fluorine-containing functional groups on the shell surface is (0.2~0.5) μmol / m 2 .

[0012] Furthermore, the mass of the double-walled microcapsules is 0.5 to 5 wt% of the mass of the electrolyte.

[0013] Furthermore, the thickness of the capsule shell is 500~1500 nm; the mass ratio of polylactic acid to polymethyl methacrylate is (60:40)~(70:30).

[0014] Furthermore, the average particle size of the double-walled microcapsules is 1~5 μm.

[0015] According to another aspect of the present invention, a method for preparing the aforementioned battery cell is provided, comprising preparing an electrolyte, stacking or winding a positive electrode, a separator, and a negative electrode in sequence to form an electrode assembly, placing the electrode assembly in a housing, and injecting the electrolyte to obtain a battery cell; the electrolyte preparation process includes: ultrasonically homogenizing raw materials including perfluorohexanone and nano-montmorillonite to form a suspension; mixing raw materials including the suspension, polylactic acid, and a first emulsifier, and then sequentially performing a first ultrasonic emulsification treatment and a first solvent removal to form primary microspheres; performing a second ultrasonic emulsification treatment and a second solvent removal on raw materials including the primary microspheres, a second emulsifier, and polymethyl methacrylate to obtain a polymerization intermediate; and reacting raw materials including the polymerization intermediate with a functionalizing agent to obtain double-walled microcapsules; wherein the functionalizing agent includes a carboxylating agent and / or a fluorinating agent.

[0016] Furthermore, the power of the first ultrasonic emulsification process is 250W~350W, the frequency is 28~40kHz, the time is 25~35min, and the shear emulsification rate is 1000~1500rpm.

[0017] Furthermore, the power of the second ultrasonic emulsification process is 200W~400W, the frequency is 20~40kHz, the time is 10~20min, and the shear emulsification rate is 1500~2000rpm.

[0018] Further, the carboxylating agent is succinic anhydride and / or maleic anhydride; and / or, the fluorinating agent is selected from any one or more of fluoroethylene carbonate, ethyl fluoroacetate, ethyl fluoropropionate and propyl fluoropropionate.

[0019] According to another aspect of the present invention, a battery device is provided, the battery device comprising the aforementioned battery cell, and the battery device comprising one or more of the following: battery module, battery pack, and energy storage battery.

[0020] According to another aspect of the present invention, an electrical device is provided, which includes the aforementioned battery device for providing electrical energy.

[0021] According to another aspect of the present invention, an energy storage device is provided, the energy storage device including the aforementioned battery device, the battery device being used to store electrical energy.

[0022] Compared with the prior art, the beneficial effects of applying the technical solution of this application are reflected in the following aspects:

[0023] 1. It has a dual-stage response mechanism: the outer PMMA melts and releases the extinguishing agent, while the core nano-montmorillonite expands when heated to form a thermal resistance layer, achieving efficient thermal protection;

[0024] 2. Surface functionalization enhances targeting and interfacial compatibility: Carboxyl modification enables double-walled microcapsules to preferentially adsorb onto defective areas of the SEI film, improving local thermal protection efficiency; fluorine-containing functional groups can synergistically enhance the interfacial compatibility between double-walled microcapsules and electrolyte;

[0025] 3. Self-healing function extends service life: The double-walled microcapsules can be partially rewetted and restored after thermal runaway, and the thermal runaway trigger temperature increases by ≥15℃ after cycling;

[0026] 4. Lightweight and integrated design: No external structure required, weight reduced by 40% compared to existing technologies, and higher system integration. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1 A process flow diagram for preparing a double-walled microcapsule according to Embodiment 1 of the present invention is shown. Detailed Implementation

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0030] As analyzed in the background section of this application, the prior art has the problem that the electrolyte flame retardant has poor targeting, the heat conduction is not effectively blocked, and the external protection structure has a slow response, high weight and non-reusability, which leads to the battery protection failure after the micro short circuit hot spot is triggered. In order to solve this problem, this application provides a battery cell and its preparation method, battery device, power consumption device and energy storage device.

[0031] In a typical embodiment of this application, a battery cell is provided, including an electrode assembly comprising a positive electrode, an electrolyte, and a negative electrode. The electrolyte comprises double-walled microcapsules, each comprising a core and a shell. The core comprises a mixture of perfluorohexanone and nano-montmorillonite, and the shell comprises a polymer, the surface of which is modified with carboxyl-containing functional groups and / or fluorine-containing functional groups. The polymer has a melting temperature of 125-135°C and comprises polymethyl methacrylate and polylactic acid.

[0032] The battery cell provided in this application fundamentally overcomes the bottlenecks of traditional flame retardants, such as poor uniform dispersion, one-time consumption, and lack of structural repair, by introducing surface-functionalized double-walled microcapsules into the electrolyte. Specifically, the outer structure of the double-walled microcapsule is a polymer shell (capsule shell) consisting of polymethyl methacrylate (PMMA) and polylactic acid (PLA), thus possessing a two-stage response mechanism. This mechanism enhances the timeliness and safety of thermal protection. Specifically, when the internal temperature of the battery reaches 125~135℃, it effectively improves the battery's thermal safety performance and extends its service life. The specific principle is as follows: On the one hand, in the early stage of thermal runaway, it can melt and rupture at the micro-short circuit hotspot in time, releasing the perfluorohexanone fire extinguishing agent in the core, thereby extinguishing the fire in the gas phase by interrupting the chain exothermic reaction. On the other hand, in the middle and later stages of thermal runaway, the nano-montmorillonite in the core expands when heated, forming a physical insulating layer by filling the electrode gap. That is, the nano-montmorillonite in the core dehydrates and condenses when heated, generating a high thermal resistance Si–O–Si network structure in situ, forming a ceramic barrier (thermal resistance layer), which significantly reduces the local equivalent thermal conductivity of this thermal barrier layer (from about 0.25 W / (m·K) to about 0.10). At the physical level, heat conduction pathways are blocked by the presence of W / (m·K). Furthermore, by introducing carboxyl functional groups onto the surface of the double-walled microcapsule shell, these groups can preferentially target and adsorb onto defect sites in the negative electrode SEI film through coordination bonding, hydrogen bonding, and electrostatic attraction mechanisms. This specifically strengthens thermally weak areas within the battery, achieving localized reinforcement, improving the uniformity of microcapsule distribution and response efficiency, reducing ineffective additives, and thus enhancing thermal protection efficiency. Fluorine-containing functional groups can bind to inorganic components through ionic bonds, hydrophobic interactions, and enhanced interfacial stability mechanisms, thereby synergistically enhancing the interfacial compatibility between the double-walled microcapsules and the electrolyte, inhibiting sedimentation and aggregation, and extending cycle stability. Unruptured microcapsules can remain in the electrolyte and partially rewet and recover after thermal runaway, thus completing self-repair (i.e., after experiencing a local thermal shock, the unruptured microcapsules and the rewetted electrolyte can still maintain some flame retardant and heat insulation capabilities in a second thermal shock, achieving partial recovery of thermal protection function). At the same time, the nano-montmorillonite has a stable structure after expansion, does not consume effective ingredients, and can continuously block, thereby continuously meeting subsequent thermal protection needs.

[0033] Therefore, compared with existing technologies, the advantages of the above technical solutions are reflected in:

[0034] 1. Targeted design addresses the root cause of thermal runaway (SEI film defects are the starting point of thermal runaway), thereby reducing the local equivalent thermal conductivity of the inorganic thermal barrier layer formed in situ in the hot spot area after heating within the battery (from approximately 0.25 W / (m·K) to approximately 0.10 W / (m·K)), and significantly reducing the maximum temperature rise rate (dT / dt) during thermal runaway. After cycling, the thermal runaway trigger temperature increases by ≥15℃.

[0035] 2. By achieving directional distribution and functional enhancement of materials through molecular-level surface modification, surface functionalization is used for the first time for targeted distribution of battery safety materials, realizing a technological leap from passive protection to active response.

[0036] In one embodiment of this application, the mass ratio of carboxyl-containing functional groups to fluorine-containing functional groups is (3:1) to (5:1); and / or, the fluorine-containing functional groups are selected from any one or more of fluoroethylene carbonate, fluoroethyl acetate, fluoroethyl propionate, and fluoropropyl propionate.

[0037] Controlling the mass ratio of carboxyl-containing functional groups to fluorine-containing functional groups helps to synergistically optimize targeted adsorption and interfacial compatibility. Specifically, a high carboxyl density can enhance electrostatic adsorption to the negative potential region of SEI defects, while fluorine groups can improve the dispersion stability of double-walled microcapsules in electrolytes, effectively reduce sedimentation risk, and improve response uniformity and long-lasting effect.

[0038] In one embodiment of this application, the local mass concentration of the double-walled microcapsules near the negative electrode is 0.5 to 5.0 wt%; the local mass concentration of the double-walled microcapsules near the negative electrode is 1.5 to 2.5 times higher than the local mass concentration of the double-walled microcapsules in other areas of the electrode assembly.

[0039] It should be noted that the "region near the negative electrode" mentioned above refers to the functional gradient distribution space extending from the surface of the negative electrode active material layer towards the separator. The geometric range and structural location of this "region near the negative electrode" are as follows:

[0040] 1. Geometric range

[0041] Core region: The 0~50 μm range from the surface of the negative electrode sheet to the separator (accounting for approximately 10~15% of the electrode thickness).

[0042] Extended Boundary: If a gradient dispersion design is adopted, the above core area can be covered to 50~200 μm (such as coating on the negative electrode side of the separator).

[0043] 2. Structural positioning

[0044] It directly contacts the negative electrode surface, is embedded inside the negative electrode coating, or is adjacent to the SEI film interface.

[0045] Since SEI membrane rupture often begins at the negative electrode, increasing the local mass concentration of double-walled microcapsules in the negative electrode region helps to achieve hotspot priority protection, improve the initial suppression efficiency of thermal runaway through gradient distribution, and reduce the overall amount of double-walled microcapsules added, thereby increasing energy density.

[0046] It should be noted that the local mass concentration of double-walled microcapsules near the negative electrode is 1.5 to 2.5 times higher than that in other areas of the electrode assembly. This gradient design can be achieved through a series of steps: ultrasonic uniform dispersion → surface targeted adsorption → enrichment in the negative electrode area → formation of a local mass concentration gradient. Specifically, ultrasonic dispersion is used to initially achieve uniform dispersion of the double-walled microcapsules in the electrolyte. After cell assembly and electrolyte injection, during electrolyte wetting and formation, the carboxyl-containing and fluorine-containing functional groups on the capsule surface have a targeted adsorption effect on the SEI film defect sites on the negative electrode surface (coordination bonding, hydrogen bonding, and electrostatic attraction). This causes the double-walled microcapsules to preferentially accumulate near the negative electrode, resulting in a higher local mass concentration near the negative electrode compared to other areas of the electrode assembly. The local mass concentration and its gradient ratio can be controlled by parameters such as the density of carboxyl-containing functional groups and the amount of double-walled microcapsules added. Furthermore, it can be determined by dissecting the cell after formation and measuring the double-walled microcapsule content in samples taken from the area near the negative electrode and other areas.

[0047] In one embodiment of this application, the mass ratio of the core to the shell is (4:1) to (3:1).

[0048] Controlling the mass ratio of the capsule core to the capsule shell within the above range helps to balance the extinguishing agent load in the double-walled microcapsule with the mechanical strength of the shell. This ensures sufficient release of perfluorohexanone while preventing the double-walled microcapsule from rupturing during circulation, reducing the risk of early leakage and improving long-term stability.

[0049] In one embodiment of this application, the mass ratio of perfluorohexanone to nano-montmorillonite is (7:3) to (9:1).

[0050] Controlling the mass ratio of perfluorohexanone to nano-montmorillonite within the above range helps optimize the synergistic efficiency of gas-phase fire suppression and ceramic film formation. That is, a high proportion of perfluorohexanone helps to achieve rapid fire suppression, and an appropriate amount of nano-montmorillonite helps to form a continuous barrier layer, thereby reducing the risk of failure caused by a single component.

[0051] In one embodiment of this application, the density of carboxyl functional groups on the shell surface is (0.8~1.2) μmol / m³. 2 ; and / or, the density of fluorine-containing functional groups on the shell surface is (0.2~0.5) μmol / m 2 .

[0052] The above-mentioned density range of carboxyl functional groups on the capsule surface contributes to better electrostatic adsorption. The above-mentioned density range of fluorine functional groups on the capsule surface can moderately improve hydrophobicity, reduce the risk of double-walled microcapsule aggregation and poor electrolyte wetting, thereby promoting the uniform distribution of double-walled microcapsules and their consistency in thermal response.

[0053] Adding double-walled microcapsules at levels below 0.5 wt% of the electrolyte poses a risk of insufficient protection, while adding them at levels above 5 wt% can affect ion migration. In one embodiment of this application, the mass of the double-walled microcapsules is 0.5-5 wt% of the electrolyte mass. This can effectively increase the onset temperature of battery thermal runaway without reducing conductivity, i.e., extend the time threshold required for thermal runaway to occur, delay the thermal propagation process, and thus improve the safety performance of the battery system. Further, it is preferable that the mass of the double-walled microcapsules is 3-5 wt% of the electrolyte mass.

[0054] In one embodiment of this application, the shell thickness is 500~1500 nm, which helps reduce the risk of microcapsule leakage during the cycle life and allows for rapid response in the early stages of thermal runaway. A preferred mass ratio of polylactic acid to polymethyl methacrylate is (60:40)~(70:30), which facilitates more precise control of the polymer's melting temperature at 125~135°C, achieving a better balance between early extinguishing agent release and later structural stability.

[0055] In one embodiment of this application, the average particle size of the double-walled microcapsules is preferably 1~5 μm, which can further adapt to the electrolyte flow and SEI membrane pore size, reduce the risk of clogging the membrane channels, thereby promoting the uniform dispersion of the double-walled microcapsules and efficient contact with defect areas, improving response efficiency and cycle compatibility.

[0056] In another typical embodiment of this application, a method for preparing the aforementioned battery cell is provided, including preparing an electrolyte, stacking or winding a positive electrode, a separator, and a negative electrode in sequence to form an electrode assembly, placing the electrode assembly in a housing, and injecting the electrolyte to obtain a battery cell; as shown Figure 1 As shown, the electrolyte preparation process includes: ultrasonically homogenizing raw materials including perfluorohexanone and nano-montmorillonite to form a suspension; mixing raw materials including the suspension, polylactic acid, and a first emulsifier, and then sequentially performing a first ultrasonic emulsification treatment and a first solvent removal to form primary microspheres; performing a second ultrasonic emulsification treatment and a second solvent removal on raw materials including the primary microspheres, a second emulsifier, and polymethyl methacrylate to obtain a polymerization intermediate; reacting raw materials including the polymerization intermediate with a functionalizing agent to obtain double-walled microcapsules; wherein the functionalizing agent includes a carboxylating agent and / or a fluorinating agent.

[0057] The stepwise emulsification and functionalization process described above enables efficient double-wall coating and surface functionalization. Specifically, it involves first forming inner core microspheres, then polymerizing the outer wall, and finally grafting carboxyl / fluorine groups. This reduces the risk of functional group decomposition during high-temperature polymerization, promoting simultaneous development of targeting and stability, resulting in an electrolyte additive that provides efficient protection against micro-short-circuit hotspots in batteries. The double-walled microcapsule comprises a core and a shell. The core consists of a mixture of perfluorohexanone and nano-montmorillonite, while the shell comprises a polymer, with its surface modified with carboxyl-containing and / or fluorine-containing functional groups. The polymer includes polymethyl methacrylate and polylactic acid.

[0058] Furthermore, the mechanism of the presence of carboxyl and fluorine functional groups on the shell of the double-walled microcapsule is further analyzed as follows:

[0059] Carboxyl (-COOH) functional groups can adsorb and repair organic layer defects in SEI films through coordination bonding, hydrogen bonding, and electrostatic attraction mechanisms. The principle of coordination bonding is as follows: at broken bonds in organic salts such as alkyl lithium carbonate (ROCO2Li) and lithium carbonate (Li2CO3) in the SEI film, such as graphite edges or oxygen vacancies, the oxygen atom of the carboxyl group forms a coordination bond (Li-O bond) with the exposed lithium ion at the defect. Lithium carboxylate (R-COOLi) typically exhibits a bidentate coordination structure, with two oxygen atoms forming approximately 180° bond angles with the lithium ion, constituting a planar symmetric configuration. This reduces interfacial impedance and enhances the Li-O bond. + The migration rate; the principle of hydrogen bonding is: inorganic salts such as lithium oxide (Li2O), lithium hydroxide (LiOH), lithium carbonate (Li2CO3), hydroxyl groups or residual water molecules at the SEI film cracks, and carboxyl hydrogen atoms form O–H···O hydrogen bonds with oxygen atoms at defect sites, enhancing local compactness; the principle of electrostatic attraction is: after ionization, the carboxyl group becomes negatively charged (-COO). - ), and positively charged defect edges (such as Mn 2+ Dissolution sites) binding.

[0060] Fluorine-containing functional groups (such as -CF3) bind to inorganic components through ionic bonding, chemistatic interactions, and mechanisms that enhance interfacial stability. The principle of ionic bonding is that fluorine atoms form ionic bonds with lithium ions at lattice defects in inorganic phases such as Li2O and LiOH in the inner SEI layer, generating highly stable LiF crystals, particularly suitable for LiF-deficient regions. The principle of chemistatic interactions is that fluorine-containing functional groups bind with weakly bonded anions (such as OH-) in the SEI film. - CO3 2- A displacement reaction occurs, replacing unstable anions and achieving adsorption by charge attraction between the target anion; the principle of enhancing interface stability is that in the grain boundary defect region, fluorine-containing functional groups form coordination bonds (MF-Li) with transition metals (such as nickel and cobalt), inhibiting the continuous decomposition of the electrolyte.

[0061] In one embodiment of this application, the power of the first ultrasonic emulsification process is 250W~350W, the frequency is 28~40kHz, the time is 25~35min, and the shear emulsification rate is 1000~1500rpm.

[0062] Controlling the first ultrasonic emulsification treatment conditions can promote the full emulsification of perfluorohexanone and nano-montmorillonite, forming a homogeneous oil phase, reducing the risk of agglomeration, providing a guarantee for subsequent outer wall coating, and thus improving the coating rate.

[0063] In one embodiment of this application, the first solvent is removed by solvent evaporation during the first ultrasonic emulsification process. The first emulsifier includes an oil phase and an aqueous phase (preferably with an oil-to-water volume ratio of 1:4). The oil phase includes polylactic acid and a solvent. The mass concentration of polylactic acid in the oil phase is 3-6 wt%, and the solvent is selected from any one or more of dichloromethane, ethyl acetate, and bio-based 2-ethylhexanol. The aqueous phase is a polyvinyl alcohol aqueous solution with a mass concentration of 0.8-1.2 wt%.

[0064] The inner wall of the polylactic acid is formed by solvent evaporation, which forms primary microspheres, improving the integrity of the core encapsulation, reducing the risk of early leakage of perfluorohexanone, and enhancing storage stability. The aqueous phase (continuous phase) is a mixture of an aqueous solution containing polyvinyl alcohol and water, which serves as the dispersion medium for the oil phase droplets and provides the reaction environment.

[0065] In one embodiment of this application, the power of the second ultrasonic emulsification process is 200W~400W, the frequency is 20~40kHz, the time is 10~20min, and the shear emulsification rate is 1500~2000rpm.

[0066] The optimal conditions for the second ultrasonic emulsification treatment can gently initiate the polymerization of methyl methacrylate (MMA), reducing the risk of impact damage to the core structure during the second ultrasonic emulsification treatment. Furthermore, controlling the shear emulsification rate within the above range is beneficial for obtaining double-walled microcapsules with uniform outer wall coating, regular morphology, and narrow particle size distribution.

[0067] In one embodiment of this application, the first emulsifier and the second emulsifier are each independently selected from any one or more of sodium dodecylbenzenesulfonate, styrene-maleic anhydride copolymer and its derivatives, alkylphenol polyoxyethylene ether, and polyvinyl alcohol.

[0068] The diversity of primary and secondary emulsifiers helps to improve the uniformity of the primary microsphere formation process and the PMMA coating process, thereby improving the interfacial stability between the primary microspheres and the polymerization intermediates, adapting to different solvent systems, and enhancing the adaptability to industrial production.

[0069] In one embodiment of this application, raw materials comprising a polymerization intermediate and a functionalizing agent are reacted, and the product system is then subjected to centrifugal washing (e.g., 8000 rpm, 10 min) and freeze-drying to obtain double-walled microcapsules. Centrifugal washing helps remove unreacted raw materials and impurities from the product system, while freeze-drying helps retain the porous structure and functional group activity of the double-walled microcapsules, providing a guarantee for subsequent surface modification.

[0070] In one embodiment of this application, the carboxylating agent is succinic anhydride and / or maleic anhydride; and / or, the fluorinating agent is selected from any one or more of fluoroethylene carbonate, ethyl fluorocarbonate, ethyl fluoropropionate and propyl fluoropropionate.

[0071] The preferred types of carboxylating and fluorinating reagents can achieve functional group grafting under mild conditions without damaging the microcapsule structure. Simultaneously, the fluorinated groups can further enhance the compatibility of the double-walled microcapsules in the electrolyte, reduce interfacial impedance, and maintain electrochemical performance.

[0072] In another typical embodiment of this application, a battery device is provided, which includes the aforementioned battery cell, and the battery device includes one or more of the following: battery module, battery pack, and energy storage battery.

[0073] Modules, battery packs, or energy storage systems containing the aforementioned battery cells have reduced overall thermal spread risk and decreased reliance on fire protection systems, making them suitable for scenarios such as grid energy storage with high safety requirements.

[0074] In yet another typical embodiment of this application, an electrical device is provided, which includes the aforementioned battery device for providing electrical energy.

[0075] The battery devices mentioned above, such as electric vehicles and drones, equipped with the battery cells of this invention can improve safety redundancy, extend service life, and reduce the rate of thermal runaway accidents under extreme operating conditions.

[0076] In yet another typical embodiment of this application, an energy storage device is provided, which includes the aforementioned battery device for storing electrical energy.

[0077] The battery cell energy storage device of this invention has multi-level thermal protection and self-repair capabilities, which can cope with local hotspot events caused by frequent charging and discharging, achieve safe operation for many years, and meet the operational requirements of grid-level energy storage.

[0078] Furthermore, the electrolyte containing double-walled microcapsules prepared in this application not only significantly improves the electrochemical performance of lithium-ion batteries under high-rate and low-temperature environments, but is also suitable for long-term energy storage systems. This material possesses high volumetric energy density and excellent cycle stability, making it suitable for large-scale energy storage power station operation in 4-hour and 8-hour ranges, meeting the stringent requirements for high-capacity batteries in application scenarios such as grid peak shaving and smooth output of renewable energy.

[0079] The beneficial effects of this application will be explained below with reference to specific embodiments.

[0080] Example 1

[0081] Reference Figure 1 The process flow chart shown below illustrates the preparation of double-walled microcapsules. The following preparation steps are performed:

[0082] Perfluorohexanone and nano-montmorillonite were ultrasonically homogenized to form a suspension. The mass ratio of perfluorohexanone to nano-montmorillonite was 8:2. The homogenization conditions were as follows: shear rate of 20,000 rpm, temperature control of 13℃ (ice bath), time window of 7 minutes, emulsifier system of Span80:Tween80=3:1, and the mass percentage of emulsifier in the system was 1.7wt%.

[0083] The suspension, polylactic acid, and polyvinyl alcohol (PVA, 1wt%) were mixed and then subjected to a first ultrasonic emulsification treatment (power 300W, frequency 30kHz, time 30min, shear emulsification rate 1000rpm) and a first solvent removal treatment (solvent evaporation method, specific conditions: temperature gradient of 30℃→40℃→50℃ in three stages, vacuum degree of -0.085~-0.095 MPa, time control of 2.5±0.5 hours, stirring rate of 300±50 rpm) to form primary microspheres. The first emulsifier included an oil phase of dichloromethane and an aqueous phase. The total volume ratio of dichloromethane and polylactic acid to the aqueous phase was 1:4. The mass concentration of polylactic acid in the mixture of dichloromethane and polylactic acid was 4wt%, and the aqueous phase was a polyvinyl alcohol aqueous solution with a mass concentration of 1.2wt%.

[0084] Primary microspheres, a second emulsifier (polyvinyl alcohol (PVA, 1 wt%)), and polymethyl methacrylate were subjected to a second ultrasonic emulsification treatment (power 300 W, frequency 30 kHz, time 20 min, shear emulsification rate 1500 rpm) and a second solvent removal (solvent evaporation method, specific conditions: temperature gradually increased from 25℃ to 40℃, vacuum evaporation for about 3 hours) to obtain a polymerization intermediate. The second emulsifier consisted of an oil phase and an aqueous phase with an oil-to-water volume ratio of 1:5. The oil phase included dichloromethane, and the mass concentration of polymethyl methacrylate was 10 wt%. The aqueous phase was a 1.0 wt% polyvinyl alcohol aqueous solution, and the amount of polymethyl methacrylate added was 10 wt% of the mass of the oil phase.

[0085] The polymerization intermediate was grafted with maleic anhydride and fluoroethylene carbonate to obtain the product system. The product system was then subjected to centrifugation (8000 rpm, 10 min) and freeze-drying (specifically, freeze-drying at -50℃ for approximately 24 hours) to obtain double-walled microcapsules. The amount of maleic anhydride added was 5 wt% of the polymerization intermediate, and the amount of fluoroethylene carbonate added was 3 wt% of the polymerization intermediate. The grafting reaction conditions were pH approximately 7.4, temperature approximately 25℃, and reaction time approximately 4 hours.

[0086] The double-walled microcapsule comprises a core and a shell. The core comprises a mixture of perfluorohexanone and nano-montmorillonite, and the shell comprises a polymer. The surface of the shell is modified with carboxyl functional groups (introduced by grafting maleic anhydride, i.e., butene dicarboxyl) and fluorine functional groups (introduced by fluoroethylene carbonate, i.e., fluoroethylene carbonate group). The melting temperature of the polymer in the shell is approximately 130°C (within the range of 125~135°C).

[0087] The mass ratio of carboxyl functional groups (-COOH) to fluorine functional groups (fluorine ester groups) in the double-walled microcapsules is 4:1; the mass ratio of the core to the shell of the double-walled microcapsules is 4:1; the density of carboxyl functional groups (-COOH) on the surface of the shell is 1.0 μmol / m³. 2 The density of fluorine-containing functional groups (fluorine-containing ester groups) on the shell surface is 0.3 μmol / m. 2 The average particle size of the double-walled microcapsules is 3 μm; the mass ratio of polylactic acid to polymethyl methacrylate is 60:40; and the thickness of the capsule shell is 1000 nm.

[0088] Double-walled microcapsules were added to a conventional electrolyte (e.g., LiPF6 dissolved in EC / DMC / EMC (volume ratio 1:1:1), with a LiPF6 molar concentration of 1 mol / L) at a mass ratio of 3 wt%. The electrolyte was then treated with an ultrasonic disperser for 10 minutes to ensure uniform dispersion. The battery cell was then left to stand at 45±5℃ for 24 hours to allow for thorough electrolyte wetting and initial uniform dispersion of the double-walled microcapsules. Subsequently, a first charging formation was performed at a low rate of 0.05C. During the formation of the SEI film on the negative electrode surface, the carboxyl-containing and fluorine-containing functional groups on the capsule surface targeted the SEI film defect sites (the SEI film mainly contains Li2CO3, LiF, lithium carboxylates, and alkyl lithium carbonates, etc.) through coordination bonding, hydrogen bonding, and electrostatic attraction. This allowed the double-walled microcapsules to preferentially adsorb and anchor near the negative electrode area. After formation, the cells were aged at 45±5℃ for 48 hours. After a period of time, the above adsorption and enrichment tend to stabilize, thereby forming a local mass concentration in the region near the negative electrode plate that is higher than that in other regions of the electrode assembly. The local mass concentration of the double-walled microcapsules in the region near the negative electrode plate is 3.0 wt%, which is 1.5 times higher than that in other regions of the electrode assembly.

[0089] The lithium iron phosphate cathode, a polypropylene / polyethylene / polypropylene (PP / PE / PP) three-layer composite separator, and an artificial graphite anode are stacked in sequence to form an electrode assembly. The electrode assembly is placed in a housing and injected with electrolyte to obtain a battery cell.

[0090] Example 2

[0091] The difference between Example 2 and Example 1 is that the mass ratio of the carboxyl functional group (introduced by grafting maleic anhydride, i.e., butene dicarboxyl group) and the fluorine functional group (introduced by fluoroethylene carbonate, i.e., fluoroethylene carbonate group) is 3:1, and the final battery cell is obtained.

[0092] Example 3

[0093] The difference between Example 3 and Example 1 is that the mass ratio of the carboxyl functional group (introduced by grafting maleic anhydride, i.e., butene dicarboxyl group) and the fluorine functional group (introduced by fluoroethylene carbonate, i.e., fluoroethylene carbonate group) is 2:1, and the battery cell is finally obtained.

[0094] Example 4

[0095] The difference between Example 4 and Example 1 is that the surface modification of the shell only contains carboxyl functional groups (introduced by grafting maleic anhydride, i.e., butene dicarboxyl), and no fluorine functional groups, and finally a battery cell is obtained.

[0096] Example 5

[0097] The difference between Example 5 and Example 1 is that the local mass concentration of the double-walled microcapsules near the negative electrode is 0.5 wt%, and the final battery cell is obtained.

[0098] Example 6

[0099] The difference between Example 6 and Example 1 is that the local mass concentration of the double-walled microcapsules near the negative electrode is 0.2 wt%, and the final battery cell is obtained.

[0100] Example 7

[0101] The difference between Example 7 and Example 1 is that the wetting, formation, and aging conditions are changed. Specifically, the cell after liquid injection is left to stand at 55±5℃ for 48 hours for initial formation at a low rate of 0.02C. After formation, it is left to stand at 60±5℃ for 72 hours for aging (heating, delaying, and slowing down formation extend the targeted adsorption window of the functional groups on the shell surface for the defect sites of the negative electrode SEI film, making the enrichment more sufficient). This makes the local mass concentration of the double-walled microcapsules in the area near the negative electrode sheet 2.5 times higher than the local mass concentration of the double-walled microcapsules in other areas of the electrode assembly, and finally, a single battery cell is obtained.

[0102] Example 8

[0103] The difference between Example 8 and Example 1 is that the wetting, formation, and aging conditions were changed. Specifically, the cell after liquid injection was left to stand at 25±5℃ for 4 hours for wetting, and then charged for the first time at a rate of 0.2C for formation. After formation, it was left to stand at 25±5℃ for 4 hours for aging (room temperature, short time, and relatively fast formation, the targeted adsorption and enrichment were not sufficient, and the double-walled microcapsules basically maintained the uniform distribution after ultrasonic dispersion). The local mass concentration of the double-walled microcapsules in the area near the negative electrode was 1.0 times higher than the local mass concentration of the double-walled microcapsules in other areas of the electrode assembly, and finally, a single battery cell was obtained.

[0104] Example 9

[0105] The difference between Example 9 and Example 1 is that the mass ratio of the core to the shell of the double-walled microcapsule is 3:1, resulting in a battery cell.

[0106] Example 10

[0107] The difference between Example 10 and Example 1 is that the mass ratio of the core to the shell of the double-walled microcapsule is 2:1, resulting in a single battery cell.

[0108] Example 11

[0109] The difference between Example 11 and Example 1 is that the mass ratio of perfluorohexanone to nano-montmorillonite is 9:1, and the final battery cell is obtained.

[0110] Example 12

[0111] The difference between Example 12 and Example 1 is that the mass ratio of perfluorohexanone and nano-montmorillonite is 5:5, and the final battery cell is obtained.

[0112] Example 13

[0113] The difference between Example 13 and Example 1 is that the mass of the double-walled microcapsules is 5% of the mass of the electrolyte, and the final battery cell is obtained.

[0114] Example 14

[0115] The difference between Example 14 and Example 1 is that the mass of the double-walled microcapsules is 0.5 wt% of the mass of the electrolyte, and the final battery cell is obtained.

[0116] Example 15

[0117] The difference between Example 15 and Example 1 is that the density of the carboxyl functional group (introduced by grafting maleic anhydride, i.e., butenidic acid group) on the shell surface is 0.8 μmol / m. 2 The density of fluorinated functional groups (introduced by fluoroethylene carbonate, i.e., fluoroethylene carbonate groups) on the shell surface is 0.2 μmol / m³. 2 Ultimately, this yields individual battery cells.

[0118] Example 16

[0119] The difference between Example 16 and Example 1 is that the density of the carboxyl functional group (introduced by grafting maleic anhydride, i.e., butenidic acid group) on the shell surface is 0.5 μmol / m. 2 The density of fluorinated functional groups (introduced by fluoroethylene carbonate, i.e., fluoroethylene carbonate groups) on the shell surface is 0.1 μmol / m³. 2 Ultimately, this yields individual battery cells.

[0120] Example 17

[0121] The difference between Example 17 and Example 1 is that the mass ratio of polylactic acid to polymethyl methacrylate is 70:30, and the final battery cell is obtained.

[0122] Example 18

[0123] The difference between Example 18 and Example 1 is that the mass ratio of polylactic acid to polymethyl methacrylate is 50:50, and the final battery cell is obtained.

[0124] Comparative Example 1

[0125] The difference between Comparative Example 1 and Example 1 is that the polymer in the shell is polycaprolactone (PCL, with a melting temperature of about 60°C, which is significantly lower than the melting temperature of the polymer in this application, which is 125~135°C), and the final result is a battery cell.

[0126] Comparative Example 2

[0127] The difference between Comparative Example 2 and Example 1 is that the core is directly used as an additive in the electrolyte to ultimately obtain a battery cell.

[0128] Comparative Example 3

[0129] The difference between Comparative Example 3 and Example 1 is that the surface of the capsule is not modified with carboxyl-containing functional groups and fluorine-containing functional groups, and the final battery cell is obtained.

[0130] Comparative Example 4

[0131] The difference between Comparative Example 4 and Example 1 is that the surface of the capsule is only modified with fluorine-containing functional groups, and the final battery cell is obtained.

[0132] Comparative Example 5

[0133] The difference between Comparative Example 5 and Example 1 is that no double-walled microcapsules were added to the electrolyte, i.e., a blank electrolyte was used to obtain the final battery cell.

[0134] Comparative Example 6

[0135] The difference between Comparative Example 6 and Example 1 is that the shell of the double-walled microcapsule is only a single layer of polymethyl methacrylate (PMMA) and does not contain a polylactic acid inner layer. That is, a single-walled microcapsule is used to obtain the battery cell.

[0136] Comparative Example 7

[0137] The difference between Comparative Example 7 and Example 1 is that the core of Comparative Example 7 only contains perfluorohexanone and does not contain nano-montmorillonite, thus obtaining a battery cell.

[0138] The above embodiments and comparative examples were subjected to the following performance tests, and the test results are listed in Table 1.

[0139] Performance testing:

[0140] Thermal runaway trigger temperature: The thermal runaway trigger temperature of the double-walled microcapsules was determined using differential scanning calorimetry (DSC).

[0141] Maximum temperature rise rate dT / dt: The highest temperature rise rate during thermal runaway is recorded by accelerating calorimeter (ARC) or hot chamber testing.

[0142] Capacity retention and thermal runaway trigger temperature: Perform 500 cycles of testing and record changes in capacity retention;

[0143] The results showed that the thermal runaway trigger temperature increased by ≥15℃, and the capacity retention rate of the preferred embodiment (Example 1) reached 93.5% after 500 cycles.

[0144] Table 1

[0145]

[0146] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0147] The battery cell provided in this application fundamentally overcomes the bottlenecks of traditional flame retardants, such as poor uniform dispersion, one-time consumption, and lack of structural repair, by introducing surface-functionalized double-walled microcapsules into the electrolyte. Specifically, the outer structure of the double-walled microcapsule is a polymer shell (capsule shell) consisting of polymethyl methacrylate (PMMA) and polylactic acid (PLA), thus possessing a two-stage response mechanism. This mechanism enhances the timeliness and safety of thermal protection. Specifically, when the internal temperature of the battery reaches 125~135℃, it effectively improves the battery's thermal safety performance and extends its service life. The specific principle is as follows: On the one hand, in the early stage of thermal runaway, it can melt and rupture at the micro-short circuit hotspot in time, releasing the perfluorohexanone fire extinguishing agent in the core, thereby extinguishing the fire in the gas phase by interrupting the chain exothermic reaction. On the other hand, in the middle and later stages of thermal runaway, the nano-montmorillonite in the core expands when heated, forming a physical insulating layer by filling the electrode gap. That is, the nano-montmorillonite in the core dehydrates and condenses when heated, generating a high thermal resistance Si–O–Si network structure in situ, forming a ceramic barrier (thermal resistance layer), which significantly reduces the local equivalent thermal conductivity of this thermal barrier layer (from about 0.25 W / (m·K) to about 0.10). At the physical level, the heat conduction pathway is blocked by the montmorillonite nanoparticles (W / (m·K)). Furthermore, by introducing carboxyl functional groups onto the surface of the double-walled microcapsule shell, they can preferentially target and adsorb onto defect sites in the negative electrode SEI film through coordination bonding, hydrogen bonding, and electrostatic attraction mechanisms. This specifically strengthens thermally weak areas within the battery, achieving localized reinforcement, improving the uniformity of microcapsule distribution and response efficiency, reducing ineffective additions, and thus enhancing thermal protection efficiency. Fluorine-containing functional groups can bind to inorganic components through ionic bonds, hydrophobic interactions, and enhanced interfacial stability mechanisms, thereby synergistically enhancing the interfacial compatibility between the double-walled microcapsules and the electrolyte, inhibiting sedimentation and aggregation, and extending cycle stability. Unruptured microcapsules can remain in the electrolyte and partially rewet and recover after thermal runaway, achieving self-repair. Simultaneously, the expanded nano-montmorillonite maintains a stable structure, does not consume effective components, and provides continuous barrier protection, thus continuously meeting subsequent thermal protection requirements.

[0148] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A battery cell, comprising an electrode assembly, said electrode assembly comprising a positive electrode, an electrolyte, and a negative electrode, characterized in that, The electrolyte comprises double-walled microcapsules, each comprising a core and a shell. The core comprises a mixture of perfluorohexanone and nano-montmorillonite, and the shell comprises a polymer. The surface of the shell is modified with carboxyl-containing functional groups and / or fluorine-containing functional groups. The polymer has a melting temperature of 125~135℃; The polymers include polymethyl methacrylate and polylactic acid.

2. The battery cell according to claim 1, characterized in that, The mass ratio of the carboxyl-containing functional group to the fluorine-containing functional group is (3:1) to (5:1); and / or, the fluorine-containing functional group is selected from any one or more of fluoroethylene carbonate, fluoroethyl acetate, fluoroethyl propionate, and fluoropropyl propionate.

3. The battery cell according to claim 1, characterized in that, The local mass concentration of the double-walled microcapsules near the negative electrode is 0.5~5.0 wt%; the local mass concentration of the double-walled microcapsules near the negative electrode is 1.5~2.5 times higher than the local mass concentration of the double-walled microcapsules in other areas of the electrode assembly.

4. The battery cell according to any one of claims 1 to 3, characterized in that, The mass ratio of the core to the shell is (4:1) to (3:1).

5. The battery cell according to any one of claims 1 to 3, characterized in that, The mass ratio of the perfluorohexanone to the nano-montmorillonite is (7:3) to (9:1).

6. The battery cell according to any one of claims 1 to 3, characterized in that, The density of the carboxyl-containing functional groups on the surface of the capsule is (0.8~1.2) μmol / m³. 2 ; and / or, the density of the fluorine-containing functional groups on the surface of the capsule is (0.2~0.5) μmol / m 2 .

7. The battery cell according to any one of claims 1 to 3, characterized in that, The mass of the double-walled microcapsules is 0.5 to 5 wt% of the mass of the electrolyte.

8. The battery cell according to any one of claims 1 to 3, characterized in that, The thickness of the shell is 500~1500 nm; the mass ratio of polylactic acid to polymethyl methacrylate is (60:40)~(70:30).

9. The battery cell according to any one of claims 1 to 3, characterized in that, The average particle size of the double-walled microcapsules is 1~5 μm.

10. A method for preparing a battery cell according to any one of claims 1 to 9, comprising preparing an electrolyte, stacking or winding a positive electrode, a separator, and a negative electrode in sequence to form an electrode assembly, placing the electrode assembly in a housing, and injecting the electrolyte to obtain the battery cell; characterized in that, The preparation process of the electrolyte includes: The raw materials, including perfluorohexanone and nano-montmorillonite, are ultrasonically homogenized to form a suspension. The raw materials, including the suspension, polylactic acid and the first emulsifier, are mixed and then subjected to a first ultrasonic emulsification treatment and a first solvent removal treatment in sequence to form primary microspheres; The raw material comprising the primary microspheres, the second emulsifier, and polymethyl methacrylate is subjected to a second ultrasonic emulsification treatment and a second solvent removal to obtain a polymerization intermediate; The raw materials, including the polymerization intermediate and the functionalizing agent, are reacted to obtain the double-walled microcapsules; The functionalizing agent includes a carboxylating agent and / or a fluorinating agent.

11. The method for preparing a battery cell according to claim 10, characterized in that, The power of the first ultrasonic emulsification process is 250W~350W, the frequency is 28~40kHz, the time is 25~35min, and the shear emulsification rate is 1000~1500rpm.

12. The method for preparing a battery cell according to claim 10, characterized in that, The power of the second ultrasonic emulsification process is 200W~400W, the frequency is 20~40kHz, the time is 10~20min, and the shear emulsification rate is 1500~2000rpm.

13. The method for preparing a single battery cell according to claim 10, characterized in that, The carboxylating agent is succinic anhydride and / or maleic anhydride; and / or, the fluorinating agent is selected from any one or more of fluoroethylene carbonate, ethyl fluorocarbonate, ethyl fluoropropionate and propyl fluoropropionate.

14. A battery device, characterized in that, The battery device includes a single battery cell as described in any one of claims 1 to 9, and the battery device includes one or more of a battery module, a battery pack, and an energy storage battery.

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

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

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