Intelligent responsive microcapsule additive, and preparation method and application thereof

Abstract

This invention discloses a smart responsive microcapsule additive, its preparation method, and its application, belonging to the field of lithium-ion battery technology. It includes a core functional material and a shell encapsulating the core functional material; the core functional material includes a flame retardant and an interface repair film-forming agent. The microcapsules provided by this invention remain stable during normal battery operation and are only triggered when local overheating or dendrite puncture causes stress concentration, instantly releasing a substance with both flame-retardant and interface repair functions, achieving precise and efficient active safety protection.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a smart responsive microcapsule additive, its preparation method and application. Background Technology

[0002] Lithium metal anodes are considered the ultimate anode material for next-generation high-energy-density batteries due to their extremely high theoretical specific capacity and lowest electrochemical potential. However, the commercialization of lithium metal batteries faces two major challenges: first, the growth of lithium dendrites may puncture the separator, causing internal short circuits, leading to thermal runaway or even fire and explosion; second, the continuous and violent side reactions between lithium metal and electrolyte result in the continuous consumption of active lithium and electrolyte, leading to low coulombic efficiency and short cycle life.

[0003] To improve safety, a common approach is to add flame retardants, such as organophosphorus compounds, to the electrolyte. However, these flame retardants typically degrade the ionic conductivity of the electrolyte and the stability of the negative electrode interface, leading to a significant decrease in the battery's rate performance and cycle performance—a passive strategy of "sacrificing performance for safety." On the other hand, film-forming additives such as FEC are often added to stabilize the interface, but these are consumed uniformly during cycling and cannot provide rapid and concentrated repair for localized, sudden dendrite growth or short circuits.

[0004] Therefore, how to provide a new type of safety strategy that can "respond on demand," only function when a danger occurs, and simultaneously achieve both "firefighting" and "repair" functions is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a smart responsive microcapsule additive, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A smart responsive microcapsule additive includes a core functional substance and a shell encapsulating the core functional substance; The shell ruptures when subjected to a local pressure greater than 50 MPa or a temperature higher than 80°C. The core functional materials include flame retardants and interface repair film-forming agents.

[0007] Beneficial Effects: The microcapsule additive provided by this invention has a hybrid shell with dual "pressure-heat" response characteristics, encapsulating a core containing a "flame retardant-repair" synergistic functional system, thus constructing a smart microcapsule. This microcapsule remains stable during normal battery operation and is only triggered when local overheating or dendrite puncture causes stress concentration, instantly releasing substances with both flame retardant and interface repair functions, achieving precise and efficient active safety protection.

[0008] Preferably, the thickness of the shell layer is 50-500 nm, and the diameter of the microcapsule additive is 0.5-10 μm.

[0009] Preferably, the shell is a hybrid shell of polymer and inorganic materials.

[0010] Preferably, the polymer comprises one or more of polyvinylidene fluoride-hexafluoropropylene, polyacrylonitrile, or polymethyl methacrylate; and / or, The inorganic material includes one or more of nano-silica, boron nitride, or aluminum oxide.

[0011] Beneficial Effects: The shell layer provided by this invention adopts a polymer-inorganic hybrid design. The selected polymer (such as PVDF-HFP) provides good flexibility and thermal responsiveness (softening at ~80-120℃), ensuring that the shell strength does not decrease under localized overheating. Inorganic nanoparticles (such as nano-SiO2) provide mechanical strength, and their interface with the polymer matrix is ​​a weak point in terms of stress. When sharp dendrites penetrate or localized pressure increases sharply, stress concentrates around the inorganic particles, inducing microcracks in the shell layer that rapidly propagate and rupture. This design makes the microcapsule extremely sensitive to mechanical penetration.

[0012] Preferably, the flame retardant includes one or more of fluorophosphate, hexamethylphosphoric acid triamine, and ammonium polyphosphate.

[0013] Preferably, the interface repair film-forming agent includes one or more of fluoroethylene carbonate, lithium difluorooxalate borate, lithium nitrate, and lithium iodide.

[0014] More preferably, the mass ratio of the interface repair film-forming agent to the flame retardant is 1:5-5:1.

[0015] Beneficial Effects: The core of this invention employs a synergistic functional design, where flame retardants (such as fluorophosphates) rapidly diffuse to the surrounding area after capsule rupture, extinguishing early sparks or flames through a gas-phase free radical quenching mechanism. The interface repair film-forming agent (such as FEC+LiDFOB) reacts violently with exposed highly reactive lithium metal, preferentially decomposing over conventional electrolytes, to generate a dense and robust SEI film rich in LiF and lithium borate in situ. This film effectively passivates dendrite tips, preventing further growth, and repairs interfaces pierced by dendrites.

[0016] A method for preparing a smart responsive microcapsule additive includes the following steps: (1) The core functional material is dispersed in water to obtain an inner aqueous phase; the raw material of the shell is dispersed in an organic solution to obtain an oil phase; the inner aqueous phase and the oil phase are mixed and emulsified to form a primary emulsion; (2) The primary emulsion is mixed with the external aqueous phase for secondary emulsification, and after removing the solvent, it is post-processed to obtain the microcapsule additive.

[0017] More preferably, the organic solvent in step (1) is dichloromethane.

[0018] Preferably, the external aqueous phase in step (2) includes polyvinyl alcohol.

[0019] Beneficial effects: During solvent evaporation, polyvinyl alcohol in the aqueous phase self-assembles to form a dense "brick-mortar" structure. This shell exhibits good chemical inertness to the electrolyte solvent and lithium metal, while also possessing pressure-thermal dual response characteristics.

[0020] Preferably, the solvent removal in step (2) is achieved by slowly removing the solvent by vacuum distillation at 40°C.

[0021] Beneficial effect: Under these conditions, the shell polymer is deposited and solidified at the droplet interface to form a hybrid shell.

[0022] More preferably, the post-processing includes centrifugation, washing, and drying.

[0023] Application of a smart responsive microcapsule additive in lithium batteries.

[0024] An electrolyte for a lithium battery includes a lithium salt, an organic solvent, and the aforementioned microcapsule additive.

[0025] The mass fraction of the microcapsule additive in the electrolyte is 0.5-10%.

[0026] A separator for lithium batteries, wherein the microcapsule additive is loaded in the matrix material of the separator or on at least one surface of the matrix material.

[0027] An electrode sheet in which the above-mentioned microcapsule additive is loaded in an active material layer.

[0028] A lithium-ion battery comprising one or more of the above-mentioned electrolyte, separator, or electrode sheet.

[0029] Beneficial effects: During battery operation, lithium dendrites may grow on the lithium metal electrode. When the lithium dendrites grow to a certain extent, they can come into contact with the microcapsules in the electrolyte / separator, etc. The microcapsule shell punctures and releases the film-forming agent / flame retardant, which coats the surface of the lithium dendrites or deposits on the surface of the lithium metal, preventing the further growth of lithium dendrites.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects: This invention provides a smart responsive microcapsule safety additive. The core concept involves designing a pressure-heat dual-response hybrid shell encapsulating a flame-retardant-repairing synergistic core. The shell employs a polymer-inorganic hybrid design, making the microcapsule sensitive to mechanical penetration. The synergistic core design allows the flame retardant to extinguish early sparks or flames, while the interface repair film-forming agent generates a dense and robust SEI film in situ, effectively passivating dendrite tips, preventing their growth, and repairing the interface, achieving precise and efficient active safety protection. Furthermore, the microcapsule additive provided by this invention has a simple preparation method, readily available raw materials, and is easy to promote and apply. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, 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: Figure 1 This is a schematic diagram of the triggering repair mechanism of the microcapsules obtained in Example 1 under dendrite puncture. Figure 2 The graph shows the cycle performance results of the batteries obtained from Application Examples 1-3 and Comparative Application Example 1. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] This invention provides a smart responsive microcapsule additive, comprising a core functional substance and a shell encapsulating the core functional substance; The shell ruptures when subjected to a local pressure greater than 50 MPa or a temperature higher than 80°C. The core functional materials include flame retardants and interface repair film-forming agents.

[0035] In a preferred embodiment, the flame retardant includes one or more of fluorophosphate, hexamethylphosphoric acid triamine, and ammonium polyphosphate.

[0036] In a preferred embodiment, the interface repair film-forming agent includes one or more of fluoroethylene carbonate, lithium difluorooxalate borate, lithium nitrate, and lithium iodide.

[0037] In a more preferred embodiment, the mass ratio of the interface repair film-forming agent to the flame retardant is 1:5-5:1, more preferably 2:1.

[0038] In a preferred embodiment, the shell layer has a thickness of 50-500 nm, and the microcapsule additive has a diameter of 0.5-10 μm.

[0039] In a preferred embodiment, the shell is a hybrid shell of polymer and inorganic materials.

[0040] In a preferred embodiment, the polymer comprises one or more of polyvinylidene fluoride-hexafluoropropylene, polyacrylonitrile, or polymethyl methacrylate; and / or, The inorganic material includes one or more of nano-silica, boron nitride, or aluminum oxide.

[0041] This invention also provides a method for preparing a smart responsive microcapsule additive, comprising the following steps: (1) The core functional material is dispersed in water to obtain an inner aqueous phase; the raw material of the shell is dispersed in an organic solution to obtain an oil phase; the inner aqueous phase and the oil phase are mixed and emulsified to form a primary emulsion; (2) The primary emulsion is mixed with the external aqueous phase for secondary emulsification, and after removing the solvent, it is post-processed to obtain the microcapsule additive.

[0042] In a more preferred embodiment, the organic solvent is dichloromethane.

[0043] In a preferred embodiment, the external aqueous phase in step (2) includes an inorganic nanoparticle stabilizer; the inorganic nanoparticle stabilizer includes polyvinyl alcohol.

[0044] In a preferred embodiment, the solvent removal is achieved by slowly evaporating the solvent using vacuum distillation at 40°C.

[0045] In a more preferred embodiment, the post-processing includes centrifugation, washing, and drying.

[0046] This invention also provides an application of a smart responsive microcapsule additive in lithium batteries.

[0047] This invention also provides an electrolyte for a lithium battery, comprising a lithium salt, an organic solvent, and the aforementioned microcapsule additive.

[0048] The mass fraction of the microcapsule additive in the electrolyte is 0.5-10%.

[0049] The present invention also provides a separator for lithium batteries, wherein the microcapsule additives are loaded in the matrix material of the separator or on at least one surface of the matrix material.

[0050] The present invention also provides an electrode sheet in which the above-mentioned microcapsule additives are loaded in the active material layer of the electrode sheet.

[0051] This invention also provides a lithium-ion battery, comprising one or more of the electrolyte, separator, or electrode sheet described above.

[0052] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels; The molecular weight of the PVDF-HFP copolymer is 455,000.

[0053] Unless otherwise specified, room temperature or normal temperature in the embodiments of the present invention refers to 25±3℃.

[0054] Example 1 A method for preparing a smart responsive microcapsule additive includes the following steps: (1) 2g of interfacial repair film-forming agent (fluoroethylene carbonate FEC) and 1g of flame retardant (hexamethylphosphoric triamine HMPA) were mixed evenly in 10g of water to obtain an inner aqueous phase; 0.5g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) copolymer was dissolved in 20g of dichloromethane, and 0.1g of oleophilic nano-SiO2 particles were added and ultrasonically dispersed evenly to obtain an oil phase. The inner aqueous phase was added to the oil phase and emulsified at 10000 rpm for 2 minutes to form a water / oil primary emulsion.

[0055] (2) The primary emulsion was quickly poured into 200g of an external aqueous phase containing 1 wt% polyvinyl alcohol (the external aqueous phase is obtained by directly dissolving polyvinyl alcohol in water). A water / oil / water complex emulsion was formed by stirring at 500 rpm. The emulsion was then transferred to a rotary evaporator, where dichloromethane was slowly evaporated at 40°C under reduced pressure. The shell material gradually deposited and solidified at the droplet interface, forming microcapsules. After centrifugation, washing with water, and vacuum drying, white powdery microcapsules were obtained. SEM analysis showed that the microcapsule diameter was 2-5 μm and the shell thickness was 200 nm.

[0056] The triggered repair mechanism of the obtained microcapsules under dendrite puncture is as follows Figure 1 As shown, lithium dendrites may grow on the lithium metal electrode during battery operation. When the lithium dendrites grow to a certain extent, they can come into contact with the microcapsules in the electrolyte / separator, etc. The microcapsule shell punctures and releases a film-forming agent / flame retardant, which wraps around the surface of the lithium dendrites or deposits on the surface of the lithium metal, preventing the lithium dendrites from growing further.

[0057] Example 2 A method for preparing a smart responsive microcapsule additive includes the following steps: (1) 2 g of interfacial repair film-forming agent (LiDFOB) and 1 g of flame retardant (hexamethylphosphoric acid triamine HMPA) were mixed evenly in 10 g of water to obtain an inner aqueous phase; 0.5 g of PVDF-HFP copolymer was dissolved in 20 g of dichloromethane, and 0.1 g of oleophilic nano-SiO2 particles were added and ultrasonically dispersed evenly to obtain an oil phase. The inner aqueous phase was added to the oil phase and emulsified under high-speed shear at 10000 rpm for 2 minutes to form a water / oil primary emulsion.

[0058] (2) Re-emulsification: The primary emulsion was rapidly poured into 200g of an external aqueous phase containing 1 wt% polyvinyl alcohol, and a water / oil / water re-emulsion was formed under stirring at 500 rpm. The emulsion was then transferred to a rotary evaporator, where dichloromethane was slowly evaporated at 40 ℃ under reduced pressure. The shell material gradually deposited and solidified at the droplet interface, forming microcapsules. After centrifugation, washing with water, and vacuum drying, white powdery microcapsules were obtained. SEM analysis showed that the microcapsule diameter was 5-6 μm and the shell thickness was approximately 200 nm.

[0059] Example 3 A method for preparing a smart responsive microcapsule additive includes the following steps: (1) 2 g of interfacial repair film-forming agent (1 g fluoroethylene carbonate FEC + 1 g LiDFOB) and 1 g of flame retardant (hexamethylphosphoric acid triamine HMPA) were mixed evenly in 10 g of water to obtain an inner aqueous phase; 0.5 g of PVDF-HFP copolymer was dissolved in 20 g of dichloromethane, and 0.1 g of oleophilic nano-SiO2 particles were added and ultrasonically dispersed evenly to obtain an oil phase. The inner aqueous phase was added to the oil phase and emulsified at 10000 rpm for 2 minutes to form a water / oil primary emulsion.

[0060] (2) Re-emulsification: The primary emulsion was rapidly poured into 200g of an external aqueous phase containing 1 wt% polyvinyl alcohol, and a water / oil / water re-emulsion was formed under stirring at 500 rpm. The emulsion was then transferred to a rotary evaporator, where dichloromethane was slowly evaporated at 20 ℃ under reduced pressure. The shell material gradually deposited and solidified at the droplet interface, forming microcapsules. After centrifugation, washing with water, and vacuum drying, white powdery microcapsules were obtained. SEM analysis showed that the microcapsule diameter was 1-2 μm and the shell thickness was approximately 200 nm.

[0061] Comparative Example 1 The only difference from Example 1 is that step (2) does not include the recombination of the external aqueous phase, and specifically includes the following steps: Step (1) is the same as in Example 1; (2) The primary emulsion was transferred to a rotary evaporator, and dichloromethane was slowly evaporated at 40°C under reduced pressure. The shell material gradually deposited and solidified at the droplet interface, forming microcapsules. After centrifugation, washing with water, and vacuum drying, white powdery microcapsules were obtained. SEM analysis showed that the microcapsule diameter was 4-6 μm and the shell thickness was 200 nm.

[0062] Comparative Example 2 The only difference from Example 1 is that the oil phase in step (1) does not include oleophilic nano-SiO2 particles, and specifically includes the following steps: (1) Mix 2g of fluoroethylene carbonate (FEC) and 1g of hexamethylphosphoric triamine (HMPA) in 10g of water to obtain an inner aqueous phase; dissolve 0.5g of PVDF-HFP copolymer in 20g of dichloromethane and disperse it evenly by ultrasonication to obtain an oil phase. Add the inner aqueous phase to the oil phase and emulsify it under high-speed shear at 10000 rpm for 2 minutes to form a water / oil primary emulsion.

[0063] Step (2) is the same as in Example 1.

[0064] Application Example 1 A method for preparing a lithium-ion battery includes the following steps: (1) Electrolyte preparation: In an argon glove box, 1.0 M LiPF6 was dissolved in a mixed solvent of EC / EMC / DEC (volume ratio 1:1:1) as the base electrolyte. Then, 3 wt% of the microcapsules obtained in Example 1 were added to the mixture and stirred until homogeneous to obtain the electrolyte.

[0065] (2) Battery assembly: Using lithium metal as the negative electrode, NCM811 as the positive electrode, Celgard 2500 as the separator, and the electrolyte obtained in step (1), a 2032 type button battery is assembled.

[0066] Application Example 2 The only difference from Application Example 1 is that in step (1), the microcapsules obtained in Example 1 are replaced with microcapsules obtained in Example 2 of equal mass.

[0067] Application Example 3 The only difference from Application Example 1 is that in step (1), the microcapsules obtained in Example 1 are replaced with microcapsules obtained in Example 3 of equal mass.

[0068] Application Example 4 A method for preparing a lithium-ion battery, comprising loading the microcapsules obtained in Example 1 onto a substrate material of a separator, specifically including the following steps: (1) Separator preparation: The microcapsules obtained in Example 1 were mixed with PVDF and N-methylpyrrolidone (NMP) at a mass ratio of 1:1:5. The mixture was then uniformly coated onto a Celgard 2500 separator using a scraper. The coated separator was dried in a vacuum oven (60°C) to remove the solvent for battery preparation.

[0069] (2) Battery assembly: Using lithium metal as the negative electrode and NCM811 as the positive electrode, the membrane coated with microcapsules is dried and assembled with the electrolyte obtained in step (1) of Application Example 1 to form a 2032 button battery.

[0070] Application Example 5 A method for preparing a lithium-ion battery, comprising loading the microcapsules obtained in Example 1 into the active material layer of an electrode sheet, specifically including the following steps: (1) Separator preparation: The microcapsules obtained in Example 2 were mixed with PVDF and N-methylpyrrolidone (NMP) at a mass ratio of 1:1:5. The mixture was then uniformly coated onto a Celgard 2500 separator using a scraper. The coated separator was dried in a vacuum oven (60°C) to remove the solvent for battery preparation.

[0071] (2) Battery assembly: Using lithium metal as the negative electrode and NCM811 as the positive electrode, the membrane coated with microcapsules is dried and assembled with the electrolyte obtained in step (1) of Application Example 1 to form a 2032 button battery.

[0072] Comparative Application Example 1 The only difference from Application Example 1 is that the microcapsules obtained in Example 1 are not added in step (1), and the specific steps include: (1) Electrolyte preparation: In an argon glove box, 1.0 M LiPF6 was dissolved in a mixed solvent of EC / EMC / DEC (volume ratio 1:1:1) as the basic electrolyte.

[0073] (2) Battery assembly: Using lithium metal as the negative electrode, NCM811 as the positive electrode, Celgard 2500 as the separator, and the basic electrolyte obtained in step (1), a 2032 button battery is assembled together.

[0074] Compare and contrast with example 2-3 The only difference from Application Example 1 is that the microcapsules obtained in Example 1 in step (1) are replaced with the microcapsules obtained in Comparative Examples 1-2, specifically including the following steps: (1) Electrolyte preparation: In an argon glove box, 1.0 M LiPF6 was dissolved in a mixed solvent of EC (ethylene carbonate) / EMC (ethyl methyl carbonate) / DEC (diethyl carbonate) (volume ratio 1:1:1) to prepare the base electrolyte. Then, 3 wt% of the microcapsules obtained from Comparative Example 1 (Comparative Application Example 2) and Comparative Example 2 (Comparative Application Example 3) were added to the mixture and stirred until homogeneous to obtain the electrolyte.

[0075] (2) Battery assembly: Using lithium metal as the negative electrode, NCM811 as the positive electrode, Celgard 2500 as the separator, and the electrolyte obtained in step (1), a 2032 button battery is assembled together.

[0076] Technical effects: After assembling the battery, it was left to stand for 10 hours, and then the electrochemical performance was tested under a constant temperature of 25 ℃. The test voltage range was set to 2.8~4.3V. All batteries were activated at 01C for 3 cycles and then directly subjected to long-term 1C cycle testing.

[0077] Test results are as follows Figure 2 As shown, it can be seen that the battery obtained in Application Example 1 short-circuited directly after 48 cycles of 1C, indicating that lithium dendrite growth is relatively rapid; while the batteries obtained in Application Examples 1-3 release FEC or LiDFOB or a mixture of FEC+LiDFOB when the dendrites come into contact with the microcapsules in the early stage of deposition. Hexamethylphosphoric triamine reacts with lithium to generate related substances to form a stable SEI film. Among them, the battery in Application Example 3 runs stably for 200 cycles.

[0078] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A smart responsive microcapsule additive, characterized in that, It includes a core functional material and a shell that encloses the core functional material; The shell ruptures when subjected to a local pressure greater than 50 MPa or a temperature higher than 80°C. The core functional materials include flame retardants and interface repair film-forming agents.

2. The intelligent responsive microcapsule additive according to claim 1, characterized in that, The shell layer has a thickness of 50-500 nm, and the microcapsule additive has a diameter of 0.5-10 μm.

3. The intelligent responsive microcapsule additive according to claim 2, characterized in that, The shell is a hybrid shell of polymer and inorganic materials.

4. The intelligent responsive microcapsule additive according to claim 3, characterized in that, The polymer includes one or more of polyvinylidene fluoride-hexafluoropropylene, polyacrylonitrile, or polymethyl methacrylate; and / or, The inorganic material includes one or more of nano-silica, boron nitride, or aluminum oxide.

5. The intelligent responsive microcapsule additive according to claim 1, characterized in that, The flame retardant includes one or more of fluorophosphates, hexamethylphosphoric acid triamine, and ammonium polyphosphate.

6. The intelligent responsive microcapsule additive according to claim 1, characterized in that, The interface repair film-forming agent includes one or more of fluoroethylene carbonate, lithium difluorooxalate borate, lithium nitrate, and lithium iodide.

7. A method for preparing a smart responsive microcapsule additive as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) The core functional material is dispersed in water to obtain an inner aqueous phase; the raw material of the shell is dispersed in an organic solution to obtain an oil phase; the inner aqueous phase and the oil phase are mixed and emulsified to form a primary emulsion; (2) The primary emulsion is mixed with the external aqueous phase for secondary emulsification, and after removing the solvent, it is post-processed to obtain the microcapsule additive.

8. The method for preparing a smart responsive microcapsule additive according to claim 7, characterized in that, The external aqueous phase mentioned in step (2) includes polyvinyl alcohol.

9. The method for preparing a smart responsive microcapsule additive according to claim 7, characterized in that, The solvent removal in step (2) is achieved by slowly removing the solvent by vacuum distillation at 40℃-60℃.

10. The application of a smart responsive microcapsule additive as described in any one of claims 1-6 in lithium batteries.

Images