Semi-solid electrolyte precursor solution, semi-solid electrolyte, preparation method of semi-solid electrolyte precursor solution and semi-solid electrolyte, and lithium ion battery

Abstract

The invention discloses a semi-solid electrolyte precursor solution, a semi-solid electrolyte, a preparation method of the semi-solid electrolyte and a lithium ion battery, and relates to the technical field of batteries, and the semi-solid electrolyte precursor solution comprises a phosphate flame retardant, melamine, a polymer monomer and a liquid electrolyte. According to the semi-solid electrolyte precursor solution provided by the invention, the flame retardant property of the semi-solid electrolyte can be improved, so that the safety performance and the cycle performance of the lithium ion battery can be improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a semi-solid electrolyte precursor solution, a semi-solid electrolyte, a method for preparing the same, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, as highly efficient energy storage carriers, have become dominant in consumer electronics, electric vehicles, and large-scale energy storage systems due to their high energy density, long cycle life, and lightweight characteristics. However, their core component—the electrolyte—poses a serious safety hazard due to its inherent flammability. Traditional electrolyte systems are typically based on low-flash-point, volatile organic carbonate solvents (such as EC, DEC, and DMC) combined with thermally unstable lithium salts (such as LiPF6). Under conditions of abuse such as overcharging, internal short circuits, high-temperature environments, or mechanical damage, they are highly susceptible to thermal runaway chain reactions, leading to catastrophic consequences such as fires and explosions. This has become a key bottleneck restricting the further development of lithium-ion batteries, especially high-energy-density battery technology.

[0003] Given the aforementioned problems with lithium-ion batteries, solidifying the electrolyte is considered the ultimate solution. Existing technologies, such as CN118983513A, provide a high-temperature resistant, flame-retardant PVDF-based semi-solid electrolyte. This electrolyte system is constructed by pre-preparing a porous PVDF membrane containing flame-retardant particles such as melamine, and then adsorbing liquid electrolyte. While this method improves safety to some extent, the use of physical blending fillers and post-wetting processes means the flame retardant is only dispersed as solid particles in the matrix, failing to achieve uniform and stable bonding with the liquid components at the molecular level. This results in insufficient overall electrolyte structural uniformity and limited utilization and synergistic effect of the flame-retardant components. CN117044003A discloses a quasi-solid electrolyte containing encapsulated flame-retardant additives. The flame retardant is encapsulated in an inert shell and released only at extreme temperatures. This passive triggering mechanism has a slow response and cannot exert its flame-retardant effect promptly and efficiently in the early stages of thermal runaway, leading to a lag and uncertainty in safety assurance.

[0004] Therefore, there is an urgent need to develop a semi-solid electrolyte with good flame retardant properties to improve the safety and cycle performance of lithium-ion batteries. Summary of the Invention

[0005] This application provides a semi-solid electrolyte precursor solution, a semi-solid electrolyte, a method for preparing the same, and a lithium-ion battery to improve the safety and cycle performance of lithium-ion batteries.

[0006] In one aspect, this application provides a semi-solid electrolyte precursor liquid, comprising: a phosphate ester flame retardant, melamine, a polymer monomer, and a liquid electrolyte.

[0007] In some embodiments, the mass percentage of the phosphate ester flame retardant is 3%-15% based on the total mass of the semi-solid electrolyte precursor solution.

[0008] In some embodiments, the phosphate ester flame retardant includes at least one of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, polyphosphate, bisphenol A bis(diphenyl phosphate), and resorcinol bis(diphenyl phosphate).

[0009] In some embodiments, the mass percentage of melamine is 1%-5% based on the total mass of the semi-solid electrolyte precursor solution.

[0010] In some embodiments, the polymer monomers account for 2%-10% of the total mass of the semi-solid electrolyte precursor solution.

[0011] In some embodiments, the polymer monomer includes at least one of the monomers containing unsaturated bonds and / or cyclic monomers such as acrylic acid, methacrylic acid, methyl methacrylate, polyethylene glycol diacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, acrylonitrile, ethylene carbonate, and vinylene carbonate.

[0012] In some embodiments, the liquid electrolyte includes lithium salts, carbonate solvents, and additives.

[0013] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, and lithium difluorooxalateborate.

[0014] In some embodiments, the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0015] In some embodiments, the additive includes at least one selected from fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, 1,3-propane sulcolone, vinyl sulfate, and tris(trimethylsilane)borate.

[0016] Secondly, this application provides a solid electrolyte, wherein the raw material components of the semi-solid electrolyte include the semi-solid electrolyte precursor liquid and initiator described in the first aspect.

[0017] In some embodiments, the initiator is 0.01%-3% by mass, based on the total mass of the raw material components of the semi-solid electrolyte.

[0018] In some embodiments, the initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate.

[0019] Thirdly, this application provides a method for preparing a semi-solid electrolyte, comprising: mixing a liquid electrolyte, a phosphate ester flame retardant, melamine, a polymer monomer and an initiator and then solidifying the mixture in situ to obtain a semi-solid electrolyte.

[0020] In some embodiments, the in-situ curing step includes a first in-situ curing and a second in-situ curing performed sequentially.

[0021] In some embodiments, the temperature of the first in-situ curing is 40°C-65°C.

[0022] In some embodiments, the first in-situ curing time is 3-4 hours.

[0023] In some embodiments, the temperature of the second in-situ curing is 65°C-80°C.

[0024] In some embodiments, the second in-situ curing time is 0.5h-1h.

[0025] Fourthly, this application provides a lithium-ion battery, including a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the electrolyte includes the semi-solid electrolyte described in the second aspect or a semi-solid electrolyte obtained by the preparation method of the semi-solid electrolyte in the third aspect.

[0026] The technical solutions provided in this application have the following advantages compared with the prior art: 1) Phosphate ester flame retardants decompose at high temperatures to produce phosphoric acid and polyphosphoric acid. These acidic substances react with the electrode surface to form a stable phosphate protective layer. This protective layer can isolate heat and oxygen, preventing further propagation of the combustion reaction. Phosphate ester flame retardants have good physical compatibility with polymer monomers. While the phosphate ester flame retardant is acting, it releases phosphorus-oxygen intermediates during combustion, capturing active free radicals (such as H· and OH·) in the combustion chain reaction and inhibiting the combustion chain reaction. Melamine can decompose at high temperatures to produce inert gases such as ammonia (NH3) and nitrogen (N2). The produced NH3 and N2 can dilute the concentration of oxygen and combustible gases, thereby inhibiting combustion. Melamine can be used alone as a flame retardant or as an auxiliary flame retardant additive. It can react with other phosphorus-based flame retardants to form an intumescent char layer, thereby improving flame retardant efficiency.

[0027] 2) The combined effect of phosphate ester flame retardants and melamine can also achieve dual flame retardant effects in both the gas phase and condensed phase: phosphate ester flame retardants inhibit combustion by forming a protective layer and capturing free radicals, while melamine further isolates heat and oxygen by releasing inert gases and forming a char layer. The acidic environment of phosphate esters can also catalyze the release of NH3 and N2 from melamine. The two work together to form an intumescent flame retardant system, which can significantly improve the flame retardant performance of the electrolyte and reduce the negative impact on the electrochemical performance of lithium-ion batteries.

[0028] 3) In-situ solidification ensures a uniform and dense electrolyte structure within the battery, improving its ionic conductivity and electrochemical stability. This invention utilizes in-situ polymerization to form a three-dimensional cross-linked network that encapsulates the liquid electrolyte, creating a gel electrolyte framework that provides mechanical strength and ion transport channels. Phosphate ester flame retardants, acting as co-solvents in the polymerization system, can directly and simply regulate electrolyte performance through coordination without affecting the polymer matrix structure, promoting monomer dissolution and enhancing monomer polymerization kinetics. Melamine, as another "filler," is dispersed within the polymer network, enhancing its mechanical strength. Furthermore, the nitrogen-containing groups in melamine participate in the formation of the SEI film at the electrode interface, strengthening interfacial stability. By encapsulating and fixing the phosphate ester flame retardant—melamine—with the polymer network, the high ionic conductivity of the in-situ electrolyte is maintained while achieving flame retardancy and dendrite suppression in the semi-solid electrolyte, thus improving the safety performance of lithium-ion batteries.

[0029] 4) In summary, when lithium-ion batteries adopt in-situ curing technology and simultaneously use phosphate ester flame retardants and melamine, the risk of thermal runaway in lithium-ion batteries can be effectively reduced, further improving the safety and cycle life of lithium-ion batteries, and providing ideas and technical support for the development of safer lithium-ion battery electrolytes. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application are clearly and completely described. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0031] Lithium-ion batteries, due to their high energy density and long cycle life, have become core energy components in consumer electronics, electric vehicles, and energy storage systems. However, their traditional electrolytes typically use flammable organic carbonate solvents and thermally unstable lithium salts (such as LiPF6), which are highly susceptible to combustion or even explosion under conditions of thermal abuse, overcharging, or mechanical damage, posing serious safety hazards. With the increasing adoption of high-energy-density systems (such as high-nickel cathodes and silicon-carbon anodes) and the ever-increasing safety requirements of electric vehicles and large-scale energy storage, developing highly safe electrolyte systems has become a key technological challenge that urgently needs to be overcome in this field.

[0032] To address these challenges, semi-solid electrolytes have attracted widespread attention as a solution that balances high ionic conductivity with good safety. These electrolytes combine a liquid electrolyte with a solid matrix, effectively suppressing leakage and combustion while maintaining ion migration capabilities, thus significantly improving battery safety.

[0033] Currently, numerous studies have focused on the development of semi-solid electrolytes. For example, CN118983513A discloses a high-temperature resistant, flame-retardant PVDF-based semi-solid electrolyte, which is formed by blending polyvinylidene fluoride (PVDF) with a swelling polymer, inorganic filler, and flame-retardant particles (such as melamine or its polyphosphate) to form a porous membrane, which is then adsorbed into an electrolyte to form a semi-solid electrolyte. Although this technology introduces flame-retardant components, the flame retardant is physically blended into the polymer matrix in the form of solid particles, failing to achieve in-situ uniform dispersion and fixation in the liquid electrolyte. This may result in an inhomogeneous electrolyte structure, insufficient interfacial stability, and limited flame-retardant efficiency.

[0034] CN117044003A discloses a quasi-solid-state or solid-state battery, whose electrolyte is formed by polymerization of polymerizable monomers, lithium salts, crosslinking agents / initiators, and inorganic solid electrolyte particles, and includes encapsulated flame-retardant additives. This flame retardant is released only above a specific temperature and cannot function under normal temperatures, making it difficult to provide timely and continuous flame-retardant protection. The high-temperature safety response is delayed, and it cannot fundamentally solve the risk of thermal runaway.

[0035] Therefore, existing semi-solid electrolyte technology still has significant shortcomings in terms of the uniformity of flame retardant dispersion, mechanism of action, and timeliness. There is an urgent need to develop a new electrolyte system that can achieve efficient synergistic and uniform and stable dispersion of flame retardants, and can be constructed in situ with both high ionic conductivity and immediate flame retardant function.

[0036] In view of this, this application provides a semi-solid electrolyte precursor solution, a semi-solid electrolyte, a method for preparing the same, and a lithium-ion battery, in order to improve the safety and cycle performance of lithium-ion batteries.

[0037] In a first aspect, this application provides a semi-solid electrolyte precursor liquid. According to an embodiment of this application, the semi-solid electrolyte precursor liquid includes: a phosphate ester flame retardant, melamine, a polymer monomer, and a liquid electrolyte.

[0038] This application utilizes the synergistic effect of phosphate ester flame retardants and melamine to construct a highly efficient dual flame retardant mechanism in both the gas phase and condensed phase, significantly improving the safety performance of the semi-solid electrolyte system. Under high-temperature conditions, the phosphate ester flame retardants rapidly decompose, producing acidic substances such as phosphoric acid and polyphosphoric acid. These acidic components react with the electrode surface to form a dense and thermally stable phosphate protective layer, effectively isolating heat and oxygen transfer and inhibiting the spread of the combustion reaction. Furthermore, the phosphorus-oxygen free radical intermediates released during combustion can efficiently capture active free radicals (such as H· and OH·) in the combustion chain reaction, interrupting the combustion reaction at the gas phase level, thereby improving the safety of lithium-ion batteries.

[0039] Meanwhile, melamine decomposes at high temperatures, producing large amounts of inert gases such as ammonia (NH3) and nitrogen (N2), which rapidly dilute the concentration of combustible gases and oxygen, further inhibiting combustion. Moreover, the acidic environment created by the decomposition of phosphate ester flame retardants catalyzes the decomposition process of melamine, accelerating the release of inert gases and enhancing the gas-phase flame retardant effect. Furthermore, the reaction products of phosphate ester flame retardants and melamine can form an expanded, dense carbon layer on the material surface. This carbon layer acts as an excellent heat and oxygen barrier, preventing internal combustibles from contacting the heat source, thus achieving condensed-phase flame retardancy and further improving the safety and cycle performance of lithium-ion batteries.

[0040] Optionally, the liquid electrolyte described above provides excellent electrochemical performance for the electrolyte and includes lithium salts, carbonate solvents, and additives; wherein the lithium salts include, but are not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO2F2), and lithium difluorooxalate borate (LiDFOB); the carbonate solvents include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC); the additives include, but are not limited to, at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), 1,3-propane sulpholactone (PS), ethylene sulfate (DTD), and tris(trimethylsilane)borate (TMSB). The additives mentioned above are mainly used to improve the SEI film, reduce battery swelling, improve battery charge-discharge performance, enhance battery cycle performance, and improve the battery's electrochemical performance.

[0041] In conjunction with the first aspect, in some embodiments provided in this application, the mass percentage of the phosphate ester flame retardant is 3%-15% based on the total mass of the semi-solid electrolyte precursor solution. The inventors have found that if too little phosphate ester flame retardant is added, a flame-retardant effect cannot be achieved; if too much phosphate ester flame retardant is added, the physical properties of the electrolyte (such as viscosity) will be affected, thereby reducing the electrolyte's lifespan and electrochemical performance. Therefore, by limiting the mass percentage of the phosphate ester flame retardant within the aforementioned range, the lifespan and electrochemical performance of the semi-solid electrolyte can be improved, thereby improving the cycle performance and safety of the lithium-ion battery.

[0042] As an example, the mass percentage of the phosphate ester flame retardant can be 3%, 6%, 9%, 15%, etc.

[0043] In conjunction with the first aspect, in some embodiments provided in this application, the phosphate ester flame retardant includes at least one of trimethyl phosphate (TMP), triethyl phosphate (TEP), triphenyl phosphate (TPP), polyphosphate (PPE), bisphenol A bis(diphenyl phosphate) (BDP), and resorcinol bis(diphenyl phosphate) (RDP). The above-mentioned phosphate ester flame retardants significantly inhibit the electrolyte combustion chain reaction through rapid decomposition at high temperatures and free radical capture mechanisms, which is beneficial to improving the safety performance of lithium-ion batteries.

[0044] In conjunction with the first aspect, in some embodiments provided in this application, the mass percentage of melamine is 1%-5% based on the total mass of the semi-solid electrolyte precursor solution. The inventors have found that if the amount of melamine added is too small, it cannot produce a sufficient synergistic flame-retardant effect with phosphate ester flame retardants, resulting in the overall flame-retardant efficiency of the electrolyte system failing to reach its optimal level. Conversely, if excessive amounts of melamine are added, its inherent rigid molecular structure and physicochemical properties will hinder the free migration of lithium ions, significantly reducing the ionic conductivity of the electrolyte. The decrease in ion transport rate directly leads to increased battery polarization. During charging, lithium ions cannot be inserted into the negative electrode in a timely manner, which not only affects the rate performance of the battery but may also cause local charge accumulation, increasing the risk of local overcharging and thermal runaway. Therefore, limiting the mass percentage of melamine within the aforementioned range can effectively improve the safety and cycle performance of the electrolyte, thereby contributing to improved safety and cycle performance of lithium-ion batteries.

[0045] As an example, the mass percentage of melamine can be 1%, 2%, 3%, 5%, etc.

[0046] In conjunction with the first aspect, in some embodiments provided in this application, the mass percentage of the polymer monomer is 2%-10% based on the total mass of the semi-solid electrolyte precursor liquid. The inventors have found that when the content of the polymer monomer is too low, the polymerization reaction cannot reach the gel point required to form a continuous and complete three-dimensional network, resulting in a loose and unstable polymer skeleton structure. This defective structure, under high temperature or long-term cycling conditions, is difficult to effectively bind the liquid solvent components, easily leading to solvent evaporation or seepage, which in turn causes problems such as electrolyte drying, electrode / electrolyte interface contact failure, significantly increased interface impedance, and accelerated battery capacity decay. Conversely, if the polymer monomer content is too high, a highly dense and excessively cross-linked rigid network structure will be formed after polymerization. On the one hand, this structure has poor flexibility and is difficult to adapt to the volume expansion and contraction of the electrode material during battery cycling, easily generating microcracks and damaging the structural integrity of the electrolyte; on the other hand, overly dense polymer segments will severely hinder the migration of lithium ions, causing a sharp increase in ion migration resistance, resulting in a significant decrease in the bulk ionic conductivity of the electrolyte, thereby deteriorating the battery's rate performance and cycle life. Therefore, limiting the mass percentage of polymer monomers within the above range can effectively improve the safety and cycle performance of lithium-ion batteries.

[0047] As an example, the mass percentage of the polymer monomer can be 2%, 4%, 6%, 10%, etc.

[0048] Furthermore, the mass ratio of the phosphate ester flame retardant, the melamine, and the polymer monomer is 3:1:2. At this ratio, the phosphate ester flame retardant can fully exert its flame-retardant performance, avoiding increased electrolyte viscosity and decreased electrochemical performance due to excessive amounts. The amount of melamine can synergistically with the phosphate ester to construct a highly efficient intumescent flame-retardant system, while avoiding the decrease in ionic conductivity and the risk of local overcharging caused by excessive introduction of rigid molecules. The proportion of the polymer monomer ensures that in-situ polymerization forms a continuous, stable, and well-connected three-dimensional cross-linked network with ample ion migration channels. This effectively encapsulates the liquid components, inhibiting solvent evaporation and dendrite growth, while avoiding mechanical brittleness and ion transport obstruction caused by excessive cross-linking. Therefore, by limiting the mass ratio of the phosphate ester flame retardant, melamine, and polymer monomer within the above range, the flame-retardant performance of the electrolyte can be improved, thereby contributing to improved battery safety and cycle performance.

[0049] In conjunction with the first aspect, in some embodiments provided in this application, the polymer monomer includes at least one of the following monomers containing unsaturated bonds and / or cyclic monomers: acrylic acid, methacrylic acid, methyl methacrylate, polyethylene glycol diacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, acrylonitrile, ethylene carbonate, and vinylene carbonate. Introducing the above-mentioned polymer monomers into a lithium battery system allows for the construction of a stable, uniform polymer matrix with excellent interfacial compatibility through controlled in-situ polymerization. This enables the solidification of the electrolyte and the stabilization of the interface. Simultaneously, the cross-linked polymer network possesses good mechanical strength, effectively suppressing the growth and penetration of lithium dendrites in the lithium battery, thus improving safety.

[0050] Secondly, this application provides a solid electrolyte. According to an embodiment of this application, the raw material components of the solid electrolyte include the solid electrolyte precursor liquid and the initiator of the first aspect.

[0051] In the embodiments of this application, a chemical cross-linking reaction of polymer monomers in the solid electrolyte precursor solution is initiated by an initiator, and a uniform, three-dimensional cross-linked polymer network is formed under subsequent heating conditions, thereby efficiently encapsulating and fixing the liquid components, and finally obtaining a solid electrolyte with a dense structure, uniform composition and stable performance.

[0052] In conjunction with the second aspect, in some embodiments provided in this application, based on the total mass of the raw material components of the semi-solid electrolyte, the mass percentage of the initiator is 0.01%-3%. Its content directly determines the reaction rate and degree of polymerization of the polymerization reaction. Limiting the mass percentage of the initiator within the above range ensures that the polymerization reaction can proceed efficiently and completely, while minimizing the impact of harmful byproducts generated by excessive addition. Ultimately, a solid electrolyte network with excellent electrochemical performance can be obtained, meeting the requirements of high-performance lithium batteries.

[0053] As an example, the mass percentage of the initiator can be 0.01%, 0.1%, 1%, 3%, etc.

[0054] In conjunction with the second aspect, in some embodiments provided in this application, the initiator includes at least one selected from azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), and dimethyl azobisisobutyrate (AIBME). Using the aforementioned initiator can generate free radicals, initiating the polymerization reaction of the monomers, thereby converting the liquid electrolyte into a semi-solid polymer electrolyte.

[0055] Thirdly, this application provides a method for preparing the semi-solid electrolyte described in the second aspect, comprising mixing a liquid electrolyte, a phosphate ester flame retardant, melamine, a polymer monomer and an initiator and then performing in-situ curing to obtain a semi-solid electrolyte.

[0056] This preparation method involves uniformly mixing liquid electrolyte, phosphate ester flame retardant, melamine, polymer monomers, and initiator in a single system and then performing in-situ solidification. The in-situ solidification process ensures a uniform and dense electrolyte structure within the battery, improving its ionic conductivity and electrochemical stability. Furthermore, in-situ polymerization forms a three-dimensional cross-linked network that encapsulates the liquid electrolyte, forming a gel electrolyte framework that provides mechanical strength and ion transport channels. The phosphate ester flame retardant, acting as a co-solvent, participates in the polymerization system, allowing for simple regulation of electrolyte performance through coordination without affecting the polymer matrix structure, promoting monomer dissolution and enhancing monomer polymerization kinetics. Melamine, as another "filler," is dispersed within the polymer network, improving its mechanical strength. The nitrogen-containing groups in melamine participate in the formation of the SEI film at the electrode interface, enhancing interfacial stability. By encapsulating and fixing the phosphate ester flame retardant—melamine—with the polymer network, the high ionic conductivity of the in-situ electrolyte is maintained, achieving flame retardancy and dendrite suppression capabilities in a semi-solid electrolyte, providing a solution for high-safety lithium-ion batteries.

[0057] Furthermore, the specific preparation method of the semi-solid electrolyte includes first mixing lithium salt with a carbonate solvent to obtain a mixed solvent containing lithium salt; then adding additives to the mixed solvent containing lithium salt to form a simple liquid electrolyte; next, adding a phosphate ester flame retardant, melamine, and polymer monomers to the simple liquid electrolyte and mixing them evenly to obtain an electrolyte precursor solution; then adding an initiator to the prepared electrolyte precursor solution and mixing evenly to form a transparent and colorless in-situ cured precursor, which is then cured in-situ by changing the temperature. When the temperature is changed, the polymer monomers undergo a chemical reaction with the added initiator to form a polymer with a cross-linked network structure. At higher temperatures, the polymer monomers are more uniformly dispersed in the mixed system, thus curing in-situ into a uniform in-situ cured electrolyte.

[0058] In conjunction with the third aspect, in some embodiments provided in this application, the in-situ curing step includes a first in-situ curing and a second in-situ curing performed sequentially. Through the sequential first and second curing processes, the controllable construction and functional regulation of the polymer network structure are achieved. Specifically, the first-stage in-situ curing ensures that the liquid electrode material can fully contact and be fully wetted with the liquid electrolyte, thereby ensuring efficient lithium-ion transport and guaranteeing the curing effect during the in-situ curing process, thus improving battery safety performance. The second-stage in-situ curing accelerates the curing effect and shortens the curing time, and allows the curing agent to be more uniformly dispersed. Therefore, at higher in-situ curing temperatures, the polymer monomers are more uniformly dispersed in the mixed system, resulting in a uniform in-situ cured electrolyte in different states.

[0059] In conjunction with the third aspect, in some embodiments provided in this application, the temperature of the first in-situ curing is 40℃-65℃, and the time of the first in-situ curing is 3h-4h. By performing the first in-situ curing at 40℃-65℃ for 3h-4h, the electrode material of the lithium battery can be fully wetted after contacting the liquid electrolyte, thereby ensuring the efficient transport of lithium ions in the lithium battery and ensuring the curing effect of the in-situ curing process, thus improving the safety performance of the battery. If the temperature is too high or the time is too long, it will lead to the in-situ curing speed being too fast to a certain extent, resulting in insufficient wetting of the electrode material by the electrolyte and uneven curing, which will hinder the transport of lithium ions and thus affect the electrochemical performance of the battery. If the temperature is too low or the time is too long, the in-situ curing effect will not be achieved, and the cured electrolyte will not be obtained, thus affecting the safety performance of the battery.

[0060] As an example, the temperature of the first in-situ curing can be 40℃, 45℃, 50℃, 65℃, etc.; the time of the first in-situ curing can be 3h, 3.5h, 4h, etc.

[0061] In conjunction with the third aspect, in some embodiments provided in this application, the temperature for the second in-situ curing is 65℃-80℃, and the curing time is 0.5h-1h. After the first in-situ curing is completed, a second in-situ curing operation is required. The second in-situ curing is performed at 65℃-80℃ for 0.5h-1h. This accelerates the curing process, shortens the curing time, and allows for a more uniform distribution of polymer monomers and initiators. If the temperature is too high or the time is too long, excessive side reactions may occur in the electrolyte, leading to a decrease in electrolyte performance. If the temperature is too low or the time is too short, it may hinder further improvement in the in-situ curing effect and the uniformity of the curing agent.

[0062] As an example, the temperature of the second in-situ curing can be 65℃, 70℃, 75℃, 80℃, etc.; the time of the second in-situ curing can be 0.5h, 0.8h, 1h, etc.

[0063] Fourthly, this application provides a lithium-ion battery. According to an embodiment of this application, the lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The electrolyte includes the semi-solid electrolyte described in the second aspect or a semi-solid electrolyte prepared by the method of the third aspect.

[0064] In this embodiment, the lithium-ion battery exhibits high safety and comprises a positive electrode, a negative electrode, an electrolyte, and a separator. Under a protective atmosphere, the positive and negative electrode materials (after coating), the separator, and the electrolyte are assembled into a lithium-ion battery. The electrolyte is the aforementioned in-situ cured precursor. By varying the heating process, the polymer monomers are uniformly dispersed within the lithium battery cavity as the temperature increases, and undergo a chemical reaction with an added initiator to form a polymer with a cross-linked network structure, thereby assembling a semi-solid-state lithium-ion battery with high safety, good cycle performance, and long lifespan.

[0065] Furthermore, before in-situ curing, the lithium-ion battery is allowed to stand for 24-48 hours. By allowing the lithium-ion battery to stand before in-situ curing, the liquid electrolyte injected into the lithium battery can fully and uniformly wet all components of the battery and complete some preliminary chemical stabilization processes, providing a foundation for subsequent uniform in-situ polymerization and curing.

[0066] In conjunction with the fourth aspect, in some embodiments provided in this application, the cathode material includes at least one of nickel-cobalt-manganese ternary cathode material, lithium cobalt oxide cathode material, lithium iron phosphate cathode, and lithium manganese iron phosphate cathode.

[0067] In conjunction with the fourth aspect, in some embodiments provided in this application, the negative electrode includes at least one of a graphite negative electrode, a silicon-oxygen negative electrode, and a novel silicon-carbon negative electrode.

[0068] In conjunction with the fourth aspect, in some embodiments provided in this application, the diaphragm includes one of a polyolefin membrane, a glass fiber diaphragm, and a coated diaphragm.

[0069] The lithium-ion battery is based on the above-mentioned semi-solid electrolyte. The specific raw material composition of the semi-solid electrolyte can be referred to the above embodiments. Since the semi-solid lithium-ion battery adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0070] The technical solutions provided in this application will be described in detail below with reference to the embodiments.

[0071] Examples 1-3 Examples 1-3 of this application provide a semi-solid electrolyte precursor solution, comprising a phosphate ester flame retardant, melamine, polymer monomers, and a liquid electrolyte, the parameters of which are shown in Table 1: Table 1 Semi-solid electrolyte precursor solutions of Examples 1-3

[0072] The semi-solid electrolyte precursor solutions provided in Examples 1 to 3 can be prepared by the following methods: Step 1: Add lithium salts: 0.6 M lithium hexafluorophosphate (LiPF6) and 0.4 M lithium difluorosulfonamide (LiFSI) to a solution composed of ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) to form a solvent-lithium salt mixture, wherein the solvent ratio (volume ratio) is EC:EMC:DEC = 20:70:10, to obtain the lithium salt mixture; Step 2: Based on the lithium salt mixture from Step 1, fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sulpholactone (PS), and vinyl sulfate (DTD) are added to form a simple liquid electrolyte, which is designated as the liquid electrolyte precursor; the mass percentage of each additive to the lithium salt mixture is FEC:VC:PS:DTD:lithium salt mixture = 6:1:1:1:91; Step 3: Add 3%~15% of phosphate ester flame retardant, 1%~5% of melamine and 2%~10% of polymer monomer to the liquid electrolyte precursor formed in step 2 and mix evenly. The mass ratio of phosphate ester flame retardant, melamine and polymer monomer is 3:1:2 to obtain a semi-solid electrolyte precursor liquid.

[0073] Examples 4-6 Examples 4-6 of this application provide a semi-solid electrolyte, wherein the raw material components of the semi-solid electrolyte include a semi-solid electrolyte precursor solution and an initiator, and the semi-solid electrolyte can be prepared by the following method: Step 1: Weigh 0.01%-3% of the initiator and add it to the prepared semi-solid electrolyte precursor solution. Mix well to form a transparent and colorless in-situ solidified precursor. Step 2: The in-situ cured precursor obtained in Step 1 is subjected to a first in-situ curing and a second in-situ curing. The temperature of the first in-situ curing is 40℃-65℃ and the heating time is 3-4 h. The temperature of the second in-situ curing is 65-80℃ and the heating time is 0.5-1.0 h. A semi-solid electrolyte is obtained.

[0074] The specific parameters of the semi-solid electrolytes in Examples 4-6 are shown in Table 2: Table 2. Parameters of semi-solid electrolytes in Examples 4-6

[0075] Comparative Example 1 Comparative Example 1 of this application provides a conventional liquid electrolyte, similar to Example 1, except that it does not contain phosphate ester flame retardants, melamine, and polymer monomers.

[0076] Comparative Example 2 Comparative Example 2 of this application provides a semi-solid electrolyte, similar to Example 5, except that it does not contain melamine.

[0077] Comparative Example 3 Comparative Example 3 of this application provides a semi-solid electrolyte, similar to Example 5, except that it does not contain phosphate ester flame retardants and melamine.

[0078] Comparative Example 4 Comparative Example 4 of this application provides a semi-solid electrolyte, similar to Example 5, except that it does not contain phosphate ester flame retardants.

[0079] Performance testing (1) The ignition time (TTI) and self-extinguishing time (SET) of the electrolytes prepared in Examples 1-6 and Comparative Examples 1-4 were monitored using a cone calorimeter. The electrolytes were first exposed to a radiant heat source for 240 s. The specific test results are shown in Table 3. Table 3. Ignition time (TTI) and self-extinguishing time (SET) of Examples 1-6 and Comparative Examples 1-4 after 240 s from the radiant heat source.

[0080] As shown in Table 3, when conducting electrolyte safety behavior tests, the electrolytes with phosphate ester flame retardants, melamine, and polymer monomers, and after adding initiators and undergoing in-situ curing (Examples 4-6), have significantly better safety performance than the uncured electrolytes of Examples 1-2 and the electrolytes of Comparative Examples 1-4.

[0081] (2) After assembling lithium-ion batteries with the electrolytes prepared in Examples 1-6 and Comparative Examples 1-4, and completing the in-situ solidification process for Examples 4-6 and Comparative Examples 2-4, taking the semi-solid electrolyte of Example 5 as an example, the lithium-ion battery can be prepared by the following method: The lithium-ion battery includes: a positive electrode, a negative electrode, an electrolyte, and a separator; wherein, the electrolyte is the in-situ solidified precursor obtained in Example 4; the preparation method of the negative electrode is as follows: weigh the appropriate mass of commercial artificial graphite and porous silicon-carbon material (graphite:silicon-carbon = 80:20) and grind them evenly in a mortar, then transfer them to a 2mL test tube, add conductive carbon black (super P) and binder (PAA), and mix them evenly at a mass ratio of 85:9:6 to obtain a slurry. Then, coat the slurry onto the current collector copper foil and dry it in a vacuum drying oven at 110°C for 12 hours to obtain the negative electrode; a lithium metal sheet is used as the counter electrode, and a polypropylene membrane is used as the separator; assemble the positive electrode, negative electrode, electrolyte, and separator into a CR2032 type coin cell in an argon-filled glove box; place the assembled and settled coin cell in an oven, let the battery stand for 24 hours, and use the same two-stage in-situ solidification process as in Example 5 to obtain a semi-solid lithium-ion battery.

[0082] All prepared lithium-ion batteries were subjected to charge-discharge tests at room temperature under charge-discharge conditions of 0.5 C / 0.2 C, and the capacity retention rate was recorded after 50 cycles. Specific test results are shown in Table 4. Table 4. Capacity retention of lithium-ion batteries in Examples 1-6 and Comparative Examples 1-4 after 50 room temperature cycles.

[0083] The results in Table 4 show that, when the cycling performance of the in-situ solidified electrolyte synthesized in this invention is comparable to that of the liquid electrolyte, when the cycling performance is tested at room temperature, the cycling performance is comparable.

[0084] (3) The electrolytes prepared in Examples 1-6 and Comparative Examples 1-4 were used to prepare lithium-ion pouch cells, and the lithium-ion pouch cells obtained in Examples 4-6 and Comparative Examples 2-4 were subjected to in-situ curing process. Taking the electrolyte of Example 5 as an example, the lithium-ion pouch cells can be prepared by the following method: Commercially available NCM811 is used as the positive electrode material, the same negative electrode material used in lithium-ion coin cells is used as the negative electrode material, and a commercially available coated separator is used as the separator. The prepared positive electrode, negative electrode, liquid electrolyte precursor, and commercially available coated separator are stacked, heat-sealed, and injected with liquid in an environmentally controlled pilot production line to assemble small soft-pack batteries. All prepared and cured soft-pack batteries were subjected to hot box testing, with three parallel experiments set up for each group. The specific test results are shown in Table 5. Table 5. Thermal chamber test results of semi-solid lithium-ion batteries in Examples 4-6 and Comparative Examples 2-4

[0085] The results in Table 5 show that the semi-solid lithium batteries (Examples 4-6) containing phosphate flame retardants, melamine, and polymer monomers, and cured in situ after adding an initiator, all passed the 150°C and 180°C heat chamber tests; the semi-solid lithium batteries (Comparative Example 2) containing only phosphate flame retardants and polymer monomers, and cured in situ after adding an initiator, all passed the 150°C heat chamber test, but only some passed the 180°C heat chamber test; the semi-solid lithium batteries (Comparative Example 3) containing only polymer monomers, without phosphate flame retardants and melamine, and cured in situ, failed all safety performance tests; and the semi-solid lithium batteries (Comparative Example 4) containing only melamine and polymer monomers, without phosphate flame retardants, and cured in situ, partially passed the 150°C heat chamber test, but none passed the 180°C heat chamber test.

[0086] (4) The electrolytes prepared in Examples 1-6 and Comparative Examples 1-4 were used to prepare lithium-ion pouch cells according to the above method. The lithium-ion pouch cells obtained in Examples 4-6 and Comparative Examples 2-4 were subjected to in-situ curing. The lithium-ion pouch cells prepared in Examples 1-6 and Comparative Examples 1-4 were then subjected to charge-discharge tests at 45°C and 1.0 C / 1.0 C. The capacity retention rate after 250 cycles was recorded. The specific test results are shown in Table 6. Table 6. Capacity retention of lithium-ion batteries from Examples 1-6 and Comparative Examples 1-4 after 250 high-temperature cycles.

[0087] The results in Table 6 show that, during high-temperature cycling performance testing, the liquid electrolytes (Examples 1-3) and in-situ cured electrolytes (Examples 4-6) containing phosphate ester flame retardants, melamine, and polymer monomers exhibit significantly better cycling stability than the comparative examples 1-4.

[0088] In summary, this application achieves a dual flame-retardant mechanism in both the gas and condensed phases through the synergistic effect of phosphate ester flame retardants and melamine. At high temperatures, the phosphate ester flame retardant decomposes to generate phosphoric acid substances, forming a stable phosphate protective layer on the electrode surface. This effectively isolates heat and oxygen, and releases phosphorus-oxygen free radicals to capture reactive free radicals, interrupting the chain combustion reaction. Simultaneously, melamine decomposes upon heating, releasing inert gases such as ammonia and nitrogen, diluting the concentration of oxygen and combustible gases. Its decomposition products can also synergistically form a dense, expanded char layer with the phosphate ester flame retardant, further blocking heat transfer and diffusion. The synergistic effect of both significantly improves the flame-retardant efficiency, and the acidic environment created by the decomposition of the phosphate ester flame retardant catalyzes the decomposition process of melamine, accelerating the release of inert gases and enhancing the gas-phase flame-retardant effect. The lithium-ion battery of this application, when using phosphate ester flame retardants and melamine in synergy, also employs an in-situ curing process involving thermal polymerization. This allows the flame-retardant system to be uniformly encapsulated and fixed through a polymer network, significantly improving the flame retardancy and safety of the electrolyte without affecting ion transport performance, thus maintaining the electrolyte's high ionic conductivity (10). -5 ~10 -3 It features a wide electrochemical stability window (0~5 V) and the ability to suppress lithium dendrite growth, which helps improve the safety and cycle performance of lithium-ion batteries.

[0089] In the description of this specification, the references to terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example is included in at least one embodiment / mode or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0090] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this application, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly specified.

[0091] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A semi-solid electrolyte precursor fluid, characterized by, Comprising: a phosphate ester flame retardant, melamine, a polymer monomer, and a liquid electrolyte.

2. The semi-solid electrolyte precursor fluid of claim 1, wherein, The mass percentage of the phosphate ester flame retardant is 3%-15% based on the total mass of the semi-solid electrolyte precursor liquid; and / or, The phosphate ester flame retardant comprises at least one of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, polyphosphate, bisphenol A bis(diphenyl phosphate), and resorcinol bis(diphenyl phosphate).

3. The semi-solid electrolyte precursor of claim 1, wherein The mass percentage of the melamine is 1%-5% based on the total mass of the semi-solid electrolyte precursor liquid; and / or, The mass percentage of the polymer monomer is 2%-10% based on the total mass of the semi-solid electrolyte precursor liquid; and / or, The polymer monomer comprises at least one of a monomer containing an unsaturated bond and / or a cyclic monomer, acrylic acid, methacrylic acid, methyl methacrylate, polyethylene glycol diacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, acrylonitrile, ethylene carbonate, and vinylene carbonate.

4. The semi-solid electrolyte precursor of claim 1, wherein, The liquid electrolyte comprises a lithium salt, a carbonate solvent, and an additive; and / or, The lithium salt comprises at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, and lithium difluoro oxalate borate; and / or, The carbonate solvent comprises at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; and / or, The additive comprises at least one of fluoroethylene carbonate, vinylene carbonate, ethylene vinyl ether, 1,3-propane sultone, ethylene sulfate, and tris(trimethylsilyl)borate.

5. A semi-solid electrolyte characterized by, The raw material components of the semi-solid electrolyte comprise the semi-solid electrolyte precursor liquid and an initiator.

6. The semi-solid electrolyte of claim 5, wherein The mass percentage of the initiator is 0.01%-3% based on the total mass of the raw material components of the semi-solid electrolyte; and / or, The initiator comprises at least one of azobisisobutyronitrile, azobisisoheptyl nitrile, and dimethyl azobisisobutyrate.

7. A method of producing the semi-solid electrolyte as claimed in claim 5 or 6, characterized by, Comprising: Mixing the liquid electrolyte, the phosphate ester flame retardant, the melamine, the polymer monomer, and the initiator for in-situ solidification to obtain the semi-solid electrolyte.

8. The production method according to claim 7, wherein The step of in-situ solidification comprises a first in-situ solidification and a second in-situ solidification arranged in sequence.

9. The production method according to claim 8, wherein The temperature of the first in-situ solidification is 40℃-65℃; and / or, The time of the first in-situ solidification is 3h-4h; and / or, The temperature of the second in-situ solidification is 65℃-80℃; and / or, The time of the second in-situ solidification is 0.5h-1h.

10. A lithium-ion battery, characterized by, Comprising a positive electrode, a negative electrode, an electrolyte, and a separator, the electrolyte comprising the semi-solid electrolyte of claim 5 or 6 or the semi-solid electrolyte obtained by the preparation method of any one of claims 7-9.

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