Gel electrolyte precursor solution, gel electrolyte, and solid-state battery

Abstract

This invention discloses a gel electrolyte precursor solution, a gel electrolyte, and a solid-state battery, relating to the field of secondary battery technology. The gel electrolyte precursor solution comprises a basic electrolyte and a phosphate ester polymer, the structural formula of which is shown in Formula I, and the number-average molecular weight of the phosphate ester polymer is 20 kDa to 60 kDa. By introducing a phosphate ester polymer with a specific structure, an in-situ polymerization process is achieved to form a three-dimensional network structure, while utilizing the flame-retardant properties of the phosphate ester groups to achieve highly efficient flame retardancy, a wide voltage window, and excellent lithium-ion transport performance of the electrolyte.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and more specifically, to a gel electrolyte precursor solution, a gel electrolyte, and a solid-state battery. Background Technology

[0002] With the rapid development of portable electronic devices, electric vehicles, and large-scale energy storage systems, lithium-ion batteries are widely used as energy storage devices due to their advantages such as high energy density, long cycle life, and low self-discharge rate. In traditional lithium-ion batteries, liquid organic electrolytes are the main medium for ion transport. Liquid electrolytes are usually composed of lithium salts dissolved in carbonate or ether organic solvents, possessing good ionic conductivity and wettability of electrode materials, thus ensuring high rate performance and cycle stability of the battery. However, the main components of liquid electrolytes are flammable alkyl carbonates or ether solvents, posing serious safety hazards such as volatility, leakage, low flash point, and poor thermal stability, which can easily induce battery thermal runaway or even fire and explosion. To solve the safety problems of liquid electrolytes, researchers have focused on developing inorganic solid electrolytes and polymer solid electrolytes. Although they possess certain flame retardancy and mechanical strength, they generally suffer from bottlenecks such as low room temperature ionic conductivity, high electrode-electrolyte interface impedance, and complex processing technology. Although gel polymer electrolytes have shown advantages in balancing ionic conductivity and mechanical stability, they still rely on a large amount of flammable plasticizers, resulting in insufficient flame retardancy and difficulty in meeting the stringent safety requirements of high-energy-density batteries. Especially in high-voltage cathode (such as NCM811) systems, existing gel electrolytes often cannot simultaneously achieve a synergistic effect of high conductivity, wide electrochemical window (>5.0V), and efficient flame retardancy. Summary of the Invention

[0003] The main objective of this invention is to provide a gel electrolyte precursor solution, a gel electrolyte, and a solid-state battery to solve the problem that gel electrolytes in the prior art cannot simultaneously achieve high conductivity, a wide electrochemical window, and high flame retardancy.

[0004] To achieve the above objectives, according to one aspect of the present invention, a gel electrolyte precursor solution is provided, comprising a base electrolyte and a phosphate ester polymer, the phosphate ester polymer having the structural formula shown in Formula I:

[0005] ;

[0006] Formula I;

[0007] Among them, R1, R2, and R3 are each independently selected. , , , , Any one of R1, R2, and R3, and at least one of them is selected from... , Any one of R1, R2, and R3, at least one of them is selected from , Any one of them, the number average molecular weight of phosphate ester polymers is 20kDa~60kDa.

[0008] Furthermore, R1, R2, and R3 are all different.

[0009] Furthermore, the structural formula of the phosphate ester polymer is selected from any one of P1 to P6:

[0010]

[0011] .

[0012] Furthermore, the basic electrolyte includes a lithium salt and a solvent; wherein the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalateborate, lithium hexafluorophosphate, and lithium tetrafluoroborate, and the solvent includes dimethyl carbonate, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate.

[0013] Furthermore, based on the total mass of the gel electrolyte precursor solution, the mass content of the phosphate ester polymer is 0.3%~2%, the mass content of the lithium salt is 5%~20%, and the remainder is solvent.

[0014] Furthermore, in the basic electrolyte, the mass ratio of dimethyl carbonate, ethylene carbonate, propylene carbonate and fluoroethylene carbonate is (20~30):(40~45):(15~25):(10~15).

[0015] According to a second aspect of the present invention, a gel electrolyte is provided, which is obtained by heating a gel electrolyte precursor solution of the first aspect.

[0016] According to a third aspect of the present invention, a solid-state battery is provided, comprising a gel electrolyte formed by heating a gel electrolyte precursor solution as described in the first aspect, or a gel electrolyte as described in the second aspect.

[0017] Furthermore, the solid-state battery also includes a positive electrode sheet, which includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. The positive active layer includes a positive electrode material, wherein the positive current collector is a carbon-coated aluminum foil, and the positive electrode material includes any one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, and lithium nickel cobalt manganese oxide.

[0018] Furthermore, solid-state batteries also include a separator, which may be any one of cellulose separator, polyethylene separator, polypropylene separator, or polyethylene-polypropylene composite separator.

[0019] By applying the technical solution of this invention, by introducing phosphate ester polymers with specific structures, a three-dimensional network structure is formed through in-situ polymerization, while utilizing the flame-retardant properties of phosphate ester groups to achieve highly efficient flame retardancy, a wide voltage window, and excellent lithium-ion transport performance of the electrolyte. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] As described in the background section of this invention, existing gel electrolytes suffer from the problem of simultaneously achieving high conductivity, a wide electrochemical window, and high flame retardancy. To address these issues, in a typical embodiment of this invention, a gel electrolyte precursor solution is provided, comprising a base electrolyte and a phosphate ester polymer, the structural formula of which is shown in Formula I:

[0022] ;

[0023] Formula I;

[0024] Among them, R1, R2, and R3 are each independently selected. , , , , Any one of R1, R2, and R3, and at least one of them is selected from... , Any one of R1, R2, and R3, at least one of them is selected from , Any one of them, the number average molecular weight of phosphate ester polymers is 20kDa~60kDa.

[0025] In the above structural formula of this application, Represents the connection site.

[0026] Electrolytes function to conduct ions between the positive and negative electrodes. The gel electrolyte precursor solution of this invention is used to form a gel electrolyte. The gel electrolyte precursor solution can be directly injected into the assembled battery. After static soaking, the battery is heated. Under heating conditions, the gel electrolyte precursor solution transforms into a solid or solid-liquid mixed gel electrolyte.

[0027] The gel electrolyte precursor solution provided by the present invention introduces a phosphate ester polymer with a specific structure, wherein at least one of R1, R2, and R3 contains an epoxy group, and at least one of R1, R2, and R3 contains an alkenyl segment, so that the molecular chain of the phosphate ester polymer contains phosphate ester groups and epoxy groups.

[0028] The molecular chains of phosphate ester polymers contain phosphate ester groups. When these groups decompose under heat, they catalyze the dehydration and cross-linking reactions of the polymer and solvent molecules, promoting the formation of a dense carbonized layer rich in carbon elements. This carbonized layer is mainly composed of a carbon skeleton, with phosphorus atoms embedded as cross-linking nodes, forming a phosphorus-carbon hybrid network with high thermal stability. It plays a dual protective role in battery thermal runaway: on the one hand, the carbonized layer acts as a physical barrier to isolate heat and oxygen, thereby inhibiting further pyrolysis of the polymer matrix; on the other hand, the carbonized layer fixes the flammable volatiles generated by thermal decomposition through chemical bonding, preventing them from escaping and participating in gas-phase combustion, thereby achieving highly efficient flame retardancy and helping to improve the safety performance of solid-state batteries assembled with gel electrolytes. Furthermore, the phosphorus-oxygen (P=O) double bond in the phosphate ester group has strong polarity and coordinates with lithium ions, which is beneficial to promoting the dissociation of lithium salts and reducing the activation energy of lithium ion migration, thereby promoting the rapid conduction of lithium ions and helping to improve the ionic conductivity of solid-state batteries. At the same time, the phosphate ester group has a low HOMO energy level, exhibiting excellent antioxidant stability and resisting oxidative decomposition under high pressure, which helps to broaden the electrochemical window. This allows the prepared gel electrolyte to be compatible with high-voltage cathode materials (such as nickel-cobalt-manganese 811, lithium cobalt oxide, etc.), meeting the application requirements of high-energy-density lithium-ion batteries.

[0029] Phosphate ester polymers contain epoxy groups in their molecular chains. During heat treatment, these epoxy groups undergo ring-opening polymerization in the base electrolyte, causing the main chains of the phosphate ester polymers to form a dense three-dimensional network structure. This three-dimensional network structure can effectively bind liquid solvent molecules, preventing their migration and leakage under high temperature or mechanical stress. This helps to solve the problem of easy leakage in traditional liquid electrolytes, effectively improves the component stability of gel electrolytes during long-cycle processes, and extends the service life of solid-state batteries.

[0030] This invention limits the number-average molecular weight of the phosphate ester polymer to 20kDa~60kDa, so that the phosphate ester polymer has sufficient length to form a dense three-dimensional cross-linked network, effectively binding the electrolyte, preventing leakage, and providing sufficient mechanical strength to inhibit lithium dendrite growth. At the same time, it reduces the surge in solution viscosity and the obstruction of chain segment movement caused by excessively long polymer chains, and promotes the rapid transport of lithium ions in the gel network.

[0031] This invention introduces phosphate ester polymers containing epoxy groups, utilizing the strong polarity of their P=O double bonds to optimize the lithium-ion solvation structure, significantly reducing the desolvation energy barrier and promoting lithium salt dissociation, thus improving the ionic conductivity of the gel electrolyte. Simultaneously, the lower HOMO energy level of the phosphate ester groups endows the gel electrolyte with excellent antioxidant stability. Combined with the three-dimensional cross-linked network formed by in-situ polymerization, it effectively suppresses side reactions at the high-voltage cathode interface and achieves a wide electrochemical window >5.0V. This allows the gel electrolyte to be compatible with high-voltage cathode materials such as NCM811, helping to achieve efficient flame retardancy while improving energy density, thus solving the problem of traditional gel electrolytes' difficulty in simultaneously achieving safety and electrochemical performance.

[0032] Specifically, the number-average molecular weight of phosphate ester polymers can be in the range of 20kDa, 25kDa, 30kDa, 35kDa, 40kDa, 45kDa, 50kDa, 55kDa, 60kDa, or any combination thereof.

[0033] In some embodiments, R1, R2, and R3 are all different. When R1, R2, and R3 are different, this asymmetric structure effectively reduces the crystallinity of the phosphate ester polymer, increases the proportion of amorphous regions, and helps improve the mobility of the phosphate ester polymer, thereby further enhancing the ionic conductivity of the gel electrolyte at room temperature. Furthermore, the asymmetric molecular structure helps optimize intermolecular interactions.

[0034] To further improve the lithium-ion transport performance, high flame retardancy, and voltage window of the gel electrolyte, in some embodiments, the structural formula of the phosphate ester polymer is selected from any one of P1 to P6:

[0035]

[0036] .

[0037] In some embodiments, the base electrolyte comprises a fluorinated lithium salt and a solvent; wherein the fluorinated lithium salt is selected from, but is not limited to, at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalateborate, lithium hexafluorophosphate, and lithium tetrafluoroborate. These fluorinated lithium salts serve as the primary source of active lithium ions in the gel electrolyte and can participate in the formation of a solid electrolyte interface film, contributing to the optimization of electrode-electrolyte interface performance. The solvent can be a carbonate compound, a carboxylic acid ester compound, an ether compound, a nitrile compound, other organic solvents, or combinations thereof. For example, solvents include dimethyl carbonate, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. Fluorinated carbonates, as film-forming additives and plasticizers, contribute to the formation of a lithium fluoride-rich solid electrolyte interface film, which can induce uniform lithium ion deposition and stripping and inhibit lithium dendrite formation. Simultaneously, small-molecule fluorinated carbonates can participate in lithium ion transport, further enhancing the lithium ion transport performance of the electrolyte.

[0038] In some embodiments, based on the total mass of the gel electrolyte precursor solution, the mass content of the phosphate ester polymer is 0.3% to 2%, the mass content of the lithium salt is 5% to 20%, and the mass content of the solvent is 70% to 95%. By controlling the mass content of each component, it is possible to enable the phosphate ester polymer to form an effective cross-linked network with extremely low addition amounts, providing strong flame retardancy while ensuring high mechanical strength and leak prevention, and reducing production costs.

[0039] Specifically, based on the total mass of the gel electrolyte precursor solution, the mass content of the phosphate ester polymer can be in the range of 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, or any two of these; the mass content of the lithium salt can be in the range of 5%, 6%, 8%, 10%, 12%, 15%, 18%, 20%, or any two of these; and the mass content of the solvent can be in the range of 70%, 75%, 80%, 85%, 90%, 95%, or any two of these.

[0040] The preparation method of phosphate ester polymers includes the following steps: placing the monomer alkenyl phosphate ester in a reaction vessel, adding an initiator, eliminating oxygen interference (e.g., by freeze-thaw degassing or nitrogen protection), and then placing it in a constant temperature water bath or oil bath to react at 60°C. After the reaction is complete, a solid or viscous liquid containing the phosphate ester polymer is obtained. The initiator can be azobisisobutyronitrile (AIBN) or BPO; the specific type of initiator can be selected according to actual needs.

[0041] In some embodiments, the mass ratio of dimethyl carbonate, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate in the base electrolyte is (20-30):(40-45):(15-25):(10-15). Ethylene carbonate (EC), as a high dielectric constant main solvent, helps promote the full dissociation of lithium salts and provides the initial basis for SEI film formation. Dimethyl carbonate (DMC) helps reduce viscosity, improve low-temperature performance, and increase ion migration rate. Propylene carbonate (PC) helps further reduce viscosity and improve ionic conductivity, while its high oxidation stability helps broaden the electrochemical window. Fluoroethylene carbonate (FEC), as a film-forming additive, preferentially decomposes to form a high-modulus SEI / CEI film rich in LiF, effectively suppressing side reactions at high-voltage cathodes (such as NCM811) and stabilizing the lithium anode interface, contributing to further improved ionic conductivity, high voltage compatibility, and flame retardancy.

[0042] In a second aspect, the present invention provides a gel electrolyte, which is obtained by heating the gel electrolyte precursor solution described in the first aspect.

[0043] In some embodiments, the preparation method of the gel electrolyte includes the following steps: dissolving a lithium salt in a solvent and stirring for 60 min to 120 min to obtain a basic electrolyte; adding a phosphate ester polymer to the basic electrolyte and stirring to obtain a gel electrolyte precursor solution; and heating the gel electrolyte precursor solution to obtain a gel polymer electrolyte, wherein the heating temperature is 30°C to 60°C and the curing time is 4 h to 48 h.

[0044] A third aspect of the present invention provides a solid-state battery comprising the gel electrolyte described in the second aspect. Due to the inclusion of the high-performance gel electrolyte, the solid-state battery exhibits high ionic conductivity, high voltage compatibility, and excellent safety performance.

[0045] Specifically, the solid-state battery includes a casing, an electrode assembly, and a gel electrolyte. Both the electrode assembly and the gel electrolyte are located within the casing. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode.

[0046] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as a carbon-coated aluminum foil. The positive active layer includes a positive electrode material, which includes a compound capable of reversibly inserting and deintercalating lithium ions. In some embodiments, the positive electrode material may include a lithium transition metal composite oxide. This lithium transition metal composite oxide may be, for example, at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, and nickel-cobalt-manganese cathode materials.

[0047] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one side of the negative electrode current collector. The negative electrode active layer includes a negative electrode material. The negative electrode current collector can be at least one of copper foil and nickel foil. The negative electrode active layer includes a negative electrode material, which includes, but is not limited to, at least one of graphite and silicon carbide.

[0048] In some embodiments, the positive electrode active layer and the negative electrode active layer further include a binder. In some embodiments, the binder includes, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, and epoxy resin. The positive electrode active layer and the negative electrode active layer may also include a conductive agent, which includes, but is not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof.

[0049] Solid-state batteries also include a separator, which includes a membrane layer with a porous structure, including but not limited to any one of cellulose separators, polyethylene separators, polypropylene separators, and polyethylene-polypropylene composite separators.

[0050] In some embodiments, the method for preparing a solid-state battery includes the following steps: dissolving a lithium salt in a solvent and stirring for 60 min to 120 min to obtain a basic electrolyte; adding a phosphate ester polymer to the basic electrolyte and stirring to obtain a gel electrolyte precursor solution; injecting the gel electrolyte precursor solution into the battery containing a separator, a positive electrode, and a negative electrode, allowing it to stand until the positive electrode material and the negative electrode material are fully wetted, and finally performing a heat treatment to obtain a solid-state battery.

[0051] The present application will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. Unless otherwise specified, the raw materials and equipment used in this invention are commonly used in the art; unless otherwise specified, the methods used in this invention are conventional methods in the art.

[0052] In the following examples, all alkenyl phosphate monomers used were purchased from Chongqing Futeng Pharmaceutical Co., Ltd.

[0053] Example 1

[0054] The preparation of the gel electrolyte precursor solution in this embodiment includes the following steps:

[0055] At room temperature, in an argon-filled glove box, dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC) were mixed uniformly in a mass ratio of 25:43:20:12 to obtain a mixed solvent. LiPF6 (lithium hexafluorophosphate), accounting for 12.5% ​​of the total mass of the gel electrolyte precursor, was added to the mixed solvent in three batches, with the interval between batches determined by the solution temperature. The next batch was added when the solution temperature returned to room temperature (25°C). After complete dissolution, a basic electrolyte, a colorless and transparent liquid, was obtained. A phosphate ester polymer (as shown in P1, with a number average molecular weight of 52 kDa), equivalent to 0.5% of the total mass of the gel electrolyte precursor solution, was added to the basic electrolyte and stirred until dissolved to obtain a colorless and transparent solution, which is the gel electrolyte precursor solution of this embodiment.

[0056] ;

[0057] P1;

[0058] The phosphate ester polymer with the structure shown in P1 is prepared as follows: An alkenyl phosphate monomer as shown in Formula P1-1 is placed in a clean reaction vessel, and an initiator, azobisisobutyronitrile (AIBN), is added. The amount of initiator is controlled to be 0.3 mol% of the monomer molar amount. Oxygen interference is eliminated (e.g., by freeze-thaw degassing or nitrogen protection). The vessel is then placed in a constant-temperature water bath or oil bath and reacted at 60°C. After the reaction, a polymer solid or viscous liquid is obtained. Its number-average molecular weight is determined to be 52 kDa by gel permeation chromatography (GPC).

[0059] ;

[0060] P1-1.

[0061] The solid-state battery preparation method of this embodiment includes the following steps:

[0062] I. Preparation of the negative electrode

[0063] Graphite, silicon carbide, conductive agent (CNT), and binder (SBR) were mixed evenly in a mass ratio of 76:20:1:3 and uniformly dispersed in deionized water to prepare a black slurry, which yielded the negative electrode slurry. The negative electrode slurry was coated on both sides of a copper foil, and after baking, rolling, and cutting, a compacted density of 1.65 g / cm³ was obtained. 3 The negative electrode.

[0064] II. Preparation of the positive electrode sheet

[0065] LiNi 0.8 Co 0.1 Mn 0.1O2, conductive agent (CNT), and binder (PVDF) are mixed evenly at a mass ratio of 97:2:1, and then uniformly dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. The positive electrode slurry is coated on both sides of an aluminum foil, and after baking, rolling, and cutting, a compacted density of 3.5 g / cm³ is obtained. 3 The positive electrode plate.

[0066] III. Preparation of the diaphragm

[0067] A coated polyimide film with a thickness of 7 μm was used as the separator.

[0068] IV. Solid-state battery fabrication

[0069] After stacking the prepared positive electrode, separator, and negative electrode in sequence, with the separator positioned between the positive and negative electrode to act as a separator, and welding tabs, an electrode assembly is obtained. The electrode assembly is then placed in an aluminum-plastic film packaging bag, dried under high temperature and vacuum until the moisture content meets the standard, and then injected with the aforementioned gel electrolyte precursor solution. After vacuum sealing and standing at 45°C, the assembly is further processed. o Solid-state batteries are obtained by heating and curing at C for 12 hours, followed by formation, degassing, secondary sealing and capacity testing.

[0070] Example 2

[0071] The difference from Example 1 is that, in the preparation of the gel electrolyte precursor solution, the phosphate ester polymer is replaced with a phosphate ester polymer with the structure shown in P2, and the number average molecular weight is 35 kDa.

[0072] ;

[0073] P2;

[0074] Phosphate ester polymers with the structure shown in P2 are prepared using alkenyl phosphate ester monomers as shown in formula P2-1.

[0075] ;

[0076] P2-1.

[0077] Example 3

[0078] The difference from Example 1 is that, in the preparation of the gel electrolyte precursor solution, the phosphate ester polymer is replaced with a phosphate ester polymer with the structure shown in P3, and the number average molecular weight is 48 kDa.

[0079] ;

[0080] P3;

[0081] Phosphate ester polymers with structures as shown in P3 are prepared using alkenyl phosphate ester monomers as shown in P3-1.

[0082] ;

[0083] P3-1.

[0084] Example 4

[0085] The difference from Example 1 is that, in the preparation of the gel electrolyte precursor solution, the phosphate ester polymer is replaced with a phosphate ester polymer with the structure shown in P4, and the number average molecular weight is 38 kDa.

[0086] ;

[0087] P4;

[0088] Phosphate ester polymers with structures as shown in P4 are prepared using alkenyl phosphate ester monomers as shown in P4-1.

[0089] ;

[0090] P4-1.

[0091] Example 5

[0092] The difference from Example 1 is that, in the preparation of the gel electrolyte precursor solution, the phosphate ester polymer is replaced with a phosphate ester polymer with the structure shown in P5, and the number average molecular weight is 40 kDa.

[0093] ;

[0094] P5;

[0095] Phosphate ester polymers with the structure shown in P5 are prepared using monomers as shown in P5-1.

[0096] ;

[0097] P5-1.

[0098] Example 6

[0099] The difference from Example 1 is that, in the preparation of the gel electrolyte precursor solution, the phosphate ester polymer is replaced with a phosphate ester polymer with the structure shown in P6, and the number average molecular weight is 23 kDa.

[0100] ;

[0101] P6;

[0102] Phosphate ester polymers with the structure shown in P6 are prepared using alkenyl phosphate ester monomers as shown in P6-1.

[0103] ;

[0104] P6-1.

[0105] Example 7

[0106] The difference from Example 1 is that, in the preparation of the gel electrolyte precursor solution, the mass content of the phosphate ester polymer (as shown in P1) is 0.3% based on the total mass of the gel electrolyte precursor solution.

[0107] Example 8

[0108] The difference from Example 1 is that, in the preparation of the gel electrolyte precursor solution, the mass content of the phosphate ester polymer (as shown in P1) is 1% based on the total mass of the gel electrolyte precursor solution.

[0109] Example 9

[0110] The difference from Example 1 is that, in the preparation of the gel electrolyte precursor solution, the mass content of the phosphate ester polymer (as shown in P1) is 1.5% based on the total mass of the gel electrolyte precursor solution.

[0111] Example 10

[0112] The difference from Example 1 is that, in the preparation of the gel electrolyte precursor solution, the mass content of the phosphate ester polymer (as shown in P1) is 3.0% based on the total mass of the gel electrolyte precursor solution.

[0113] Comparative Example 1

[0114] The difference from Example 1 is that no phosphate ester polymer (as shown in P1) is added in the preparation of the gel electrolyte precursor solution.

[0115] Comparative Example 2

[0116] The preparation of this comparative gel electrolyte precursor solution includes the following steps:

[0117] At room temperature, in an argon-filled glove box, dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC) were mixed uniformly in a mass ratio of 25:43:20:12 to obtain a mixed solvent. LiPF6 (lithium hexafluorophosphate), accounting for 12.5% ​​of the total mass of the gel electrolyte precursor, was added to the mixed solvent in three batches, with the interval between batches determined by the solution temperature. The next batch was added when the solution temperature returned to room temperature (25°C). After complete dissolution, a basic electrolyte, a colorless and transparent liquid, was obtained. Diethyl vinyl phosphate (0.5% of the total mass of the gel electrolyte precursor solution) and AIBN (0.015% of the total mass of the gel electrolyte precursor solution) were added to the basic electrolyte, and the mixture was stirred to dissolve, yielding a colorless and transparent solution, which is the gel electrolyte precursor solution of this embodiment.

[0118] Comparative Example 3

[0119] The difference from Comparative Example 2 is that diethyl vinyl phosphate is replaced with triethyl phosphate.

[0120] Test methods

[0121] 1. Ionic conductivity

[0122] Ionic conductivity was determined by alternating current impedance spectroscopy. The test frequency range was 1 Hz to 1 MHz, and the AC voltage amplitude was 10 mV. The bulk resistivity (Ro) of the electrolyte was obtained by fitting a Nyquist spectrum. b The ionic conductivity (σ) is calculated using the formula σ = L / (Rb × A), where L is the electrolyte membrane thickness (cm) and A is the effective contact area of ​​the electrode (cm²). 2 The test results are the average of three parallel samples.

[0123] 2. Lithium-ion transference number

[0124] Lithium-ion transport number was determined by combining constant-voltage polarization and AC impedance spectroscopy. First, a 10mV DC voltage was applied to the battery for polarization, and the initial current (I0) and steady-state current (I0) were recorded. ss AC impedance tests were performed before and after polarization to obtain the initial resistance (R0) and steady-state resistance (R). ss Lithium-ion transport number (t) + ) Calculated according to the Bruce-Vincent-Evans formula: t + =[Iss×(V-I0×R0)] / [I0×(VI ss ×R ss [); where V is the polarization voltage (10mV). Each group of samples was tested at least three times, and the average value was taken as the final result.

[0125] 3. Electrochemical window

[0126] Oxidation stability was determined by linear sweep voltammetry (LSV). The scan range was from open circuit potential to 6.0 V (vs. Li). + / Li), with a scan rate of 0.5 mV / s. The upper limit of the electrochemical window is defined as the current density increasing to 0.1 mA / cm². 2 The corresponding voltage value. Each group of samples was tested three times, and the average value was taken.

[0127] 4. Self-extinguishing time

[0128] Weigh 1.0g of gel electrolyte and place it in the positive electrode casing of the button cell. The self-extinguishing time is the time from the ignition of the electrolyte to its extinction. For example, if the time from ignition to extinction of a sample is 10s, then the self-extinguishing time of this sample is 10s / g.

[0129] The test results are shown in Table 1.

[0130] Table 1

[0131]

[0132] As shown in Table 1, compared to Comparative Examples 1-3, Examples 1-10 all added phosphate ester polymers containing epoxy functional groups. Comparative Example 1 did not contain phosphate ester polymers, and the electrolyte extinguished only after complete combustion. Comparative Example 2 contained diethyl vinyl phosphate, obtained through in-situ polymerization initiated by AIBN thermal initiation to obtain diethyl polyvinyl phosphate; however, at the same concentration (0.5%), this comparative example did not exhibit flame retardancy. Comparative Example 3 contained triethyl phosphate, a small molecule compound, and also did not exhibit flame retardancy at the same concentration. The gel electrolytes obtained in Examples 1-7 were almost non-flammable. For Examples 8-10, when the content of phosphate ester polymers increased, the gel electrolytes became completely non-flammable. The reason for the lower conductivity was that the increased content of phosphate ester polymers increased the degree of cross-linking, resulting in stronger binding ability of the electrolyte and hindering lithium-ion transport. The electrochemical window of the solid-state batteries assembled with the gel electrolytes obtained in Examples 1-9 was greater than 5.0V. Solid-state batteries assembled with gel electrolytes in Examples 1-10 exhibit good room-temperature lithium-ion transport capability, high-voltage resistance, and flame retardancy.

[0133] The above description is merely a preferred embodiment of the present invention and is not intended to limit the 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 gel electrolyte precursor solution, characterized in that, It includes a basic electrolyte and a phosphate ester polymer, the structural formula of which is shown in Formula I: ； Formula I; Among them, R1, R2, and R3 are each independently selected. , , , , Any one of R1, R2, and R3, and at least one of them is selected from... , Any one of R1, R2, and R3, at least one of which is selected from , The phosphate ester polymer has a number-average molecular weight of 20 kDa to 60 kDa, whichever is correct.

2. The gel electrolyte precursor solution according to claim 1, characterized in that, R1, R2, and R3 are all different.

3. The gel electrolyte precursor solution according to claim 2, characterized in that, The structural formula of the phosphate ester polymer is selected from any one of P1 to P6: ； ； 。 4. The gel electrolyte precursor solution according to any one of claims 1 to 3, characterized in that, The basic electrolyte comprises a lithium salt and a solvent; wherein the lithium salt comprises at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalateborate, lithium hexafluorophosphate, and lithium tetrafluoroborate, and the solvent comprises dimethyl carbonate, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate.

5. The gel electrolyte precursor solution according to claim 4, characterized in that, Based on the total mass of the gel electrolyte precursor solution, the mass content of the phosphate ester polymer is 0.3% to 2%, the mass content of the lithium salt is 5% to 20%, and the remainder is the solvent.

6. The gel electrolyte precursor solution according to claim 4, characterized in that, In the basic electrolyte, the mass ratio of dimethyl carbonate, ethylene carbonate, propylene carbonate and fluoroethylene carbonate is (20~30):(40~45):(15~25):(10~15).

7. A gel electrolyte, characterized in that, It is prepared by heating the gel electrolyte precursor solution according to any one of claims 1 to 6.

8. A solid-state battery, characterized in that, The solid-state battery includes a gel electrolyte obtained by heating the gel electrolyte precursor solution according to any one of claims 1 to 6, or the gel electrolyte according to claim 7.

9. The solid-state battery according to claim 8, characterized in that, The solid-state battery further includes a positive electrode sheet, which includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. The positive active layer includes a positive electrode material, wherein the positive current collector is a carbon-coated aluminum foil, and the positive electrode material includes any one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, and lithium nickel cobalt manganese oxide.

10. The solid-state battery according to claim 8, characterized in that, The solid-state battery also includes a separator, which includes any one of cellulose separator, polyethylene separator, polypropylene separator, and polyethylene-polypropylene composite separator.

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