Flame-retardant polymer electrolyte, secondary battery and electric device

Abstract

The invention discloses a flame-retardant polymer electrolyte, a secondary battery and an electric device, and belongs to the technical field of battery materials. The flame-retardant polymer in the flame-retardant polymer electrolyte contains a phosphate ester group and / or a phosphite ester group, the phosphate ester group and / or the phosphite ester group generate phosphorus-containing free radicals at a high temperature, and the phosphorus-containing free radicals can capture hydrogen free radicals and hydroxyl free radicals in a combustion reaction, so that the combustion reaction is terminated, the combustion risk of the electrolyte is reduced, and the service life of the electrolyte is prolonged. The flame-retardant and / or non-combustible effect is realized, so that the safety of the secondary battery is improved; oxygen-containing groups in the flame-retardant polymer can be coordinated with lithium ions, so that lithium salt dissociation is promoted, the ion conductivity is enhanced, and the electrochemical performance of the secondary battery can be further improved.

Description

Technical Field

[0001] The present application relates to the technical field of battery materials, and in particular to a flame-retardant polymer electrolyte, a secondary battery, and an electrical device. Background Art

[0002] Currently, ether solvents and carbonates are commonly used as solvents for liquid electrolytes. Ether solvents and carbonates have high boiling points, are volatile and flammable, and are prone to leakage under battery abuse, posing safety hazards such as fire and explosion. Summary of the Invention

[0003] The purpose of the present disclosure is to overcome the deficiencies of the prior art and to provide a flame retardant polymer electrolyte, a secondary battery and an electrical device.

[0004] To achieve the above objectives, the technical solutions adopted in the present disclosure are as follows: In a first aspect, a flame-retardant polymer electrolyte is provided, wherein the flame-retardant polymer electrolyte comprises a flame-retardant polymer, and the general structural formula of the flame-retardant polymer is:

[0005]

[0006] wherein R1, R2, R1' and R2' are each independently selected from -C x H 2x+1 or -C x H 2x+1-y F y ; R3 and R3' are each independently selected from -C x H 2x -or-C x H 2x O z -, m is 0 or a positive integer, n is 0 or a positive integer, m and n are not 0 at the same time, 1≤x≤10, 1≤y≤2x+1, 1≤z≤x.

[0007] In some embodiments, the -C x H 2x+1 At least one selected from the following structural formulas:

[0008]

[0009] In some embodiments, the -C x H 2x+1-y F y At least one selected from the following structural formulas:

[0010]

[0011] In some embodiments, the -C x H 2x -At least one selected from the following structural formulas:

[0012]

[0013] In some embodiments, the -C x H 2x O z -At least one selected from the following structural formulas:

[0014]

[0015] In some embodiments, based on the mass of the flame retardant polymer electrolyte, the mass percentage of the flame retardant polymer is 55.5%-82%.

[0016] In some embodiments, the flame retardant polymer electrolyte further comprises a lithium salt and a plasticizer. Based on the mass of the flame retardant polymer electrolyte, the mass percentage of the plasticizer is 5%-20%, and the mass percentage of the lithium salt is 10%-25%.

[0017] In some embodiments, the plasticizer includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonates, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluorodimethyl carbonate, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, trimethyl phosphate, triethyl phosphate, trimethyl phosphite, and triethyl phosphite.

[0018] In some embodiments, the lithium salt is at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium perchlorate, and lithium trifluoromethanesulfonate.

[0019] In a second aspect, a method for preparing a flame retardant polymer electrolyte is provided, comprising the following steps:

[0020] Mixing polymer monomers, lithium salt, plasticizer, and initiator to form a precursor solution;

[0021] heating the precursor solution at 40-80° C. to form the flame-retardant polymer electrolyte;

[0022] The polymer monomers include a phosphate monomer as shown in formula I and / or a phosphite monomer as shown in formula II;

[0023]

[0024] wherein R1, R2, R1' and R2' are each independently selected from -C x H 2x+1 or -C x H 2x+1-y F y; R3 and R3' are each independently selected from -C x H 2x -or-C x H 2x O z -, 1≤x≤10, 1≤y≤2x+1, 1≤z≤x.

[0025] In some embodiments, based on the mass of the precursor solution, the mass of the polymer monomer is 55%-80%, the mass of the plasticizer is 5%-20%, the mass of the lithium salt is 10%-25%, and the mass of the initiator is 0.5%-2%.

[0026] In some embodiments, the initiator is at least one of azobisisobutyronitrile and dibenzoyl peroxide.

[0027] In a third aspect, a secondary battery is provided, comprising a battery cell and an electrolyte disposed in a packaging shell, wherein at least part of the structure of the battery cell is located in the electrolyte, and the electrolyte is the flame-retardant polymer electrolyte or a flame-retardant polymer electrolyte prepared by the preparation method of the flame-retardant polymer electrolyte.

[0028] In a fourth aspect, a method for preparing a secondary battery is provided, comprising the following steps:

[0029] Obtaining a battery cell and placing the battery cell in a packaging shell;

[0030] mixing polymer monomers, lithium salt, plasticizer and initiator to obtain a precursor solution;

[0031] The precursor solution is injected into the packaging shell, and the precursor solution in the packaging shell is heated at 40° C.-80° C. to obtain the flame-retardant polymer electrolyte or secondary battery.

[0032] In a fifth aspect, an electrical device is provided, comprising the secondary battery or the secondary battery prepared by the secondary battery preparation method.

[0033] Compared with the prior art, the beneficial effects of the present disclosure are as follows: the flame-retardant polymer in the flame-retardant polymer electrolyte of the present application contains phosphate groups and / or phosphite groups, and the phosphate groups and / or phosphite groups generate phosphorus-containing free radicals at high temperatures. The phosphorus-containing free radicals can capture hydrogen free radicals and hydroxyl free radicals in the combustion reaction, thereby terminating the combustion reaction, reducing the combustion risk of the electrolyte, achieving flame retardant and / or non-flammable effects, and thereby improving the safety of the secondary battery; the oxygen-containing groups in the flame-retardant polymer can coordinate with lithium ions, promote the dissociation of lithium salts, enhance ion conductivity, and thereby improve the electrochemical performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is the hydrogen spectrum of polymer monomer A1;

[0035] Figure 2 is the hydrogen spectrum of polymer monomer A5;

[0036] Figure 3 This is a test diagram of the coulombic efficiency of the lithium-copper half-cell in Example 1;

[0037] Figure 4 This is a test chart of the capacity retention rate of the lithium-high nickel ternary soft-pack battery in Example 1. DETAILED DESCRIPTION

[0038] To facilitate understanding of the present disclosure, a more comprehensive description will be given below. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present disclosure.

[0039] As used herein:

[0040] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0041] The conjunction "consisting of" excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim, rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0042] When amount, concentration or other value or parameter are represented with range, preferred range or the range that a series of upper preferred value and lower preferred value limit are expressed, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, and no matter whether this scope is disclosed separately.For example, when disclosing scope " 1-5 ", described scope should be interpreted as including scope " 1-4 ", " 1-3 ", " 1-2 ", " 1-2 and 4-5 ", " 1-3 and 5 " etc.When numerical range is described in this article, unless otherwise stated, otherwise this scope is intended to include its end value and all integers and fractions within this range.

[0043] In these examples, parts and percentages are by mass unless otherwise indicated.

[0044] "Parts by mass" refers to the basic unit of measurement used to express the mass ratio of multiple components. One part can represent any unit of mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, this means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, we could say that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number representing a multiplication factor). It's important to note that, unlike parts by mass, the sum of the mass of all components is not limited to 100 parts.

[0045] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0046] In a first aspect of the present application, a flame-retardant polymer electrolyte is provided. The flame-retardant polymer electrolyte comprises a flame-retardant polymer, and the general structural formula of the flame-retardant polymer is:

[0047]

[0048] wherein R1, R2, R1' and R2' are each independently selected from -C x H 2x+1 or -C x H 2x+1-y F y ; R3 and R3' are each independently selected from -C x H 2x -or-C x H 2x O z -, m is 0 or a positive integer, n is 0 or a positive integer, m and n are not both 0, 1≤x≤10, 1≤y≤2x+1, 1≤z≤x.

[0049] The flame-retardant polymer in the flame-retardant polymer electrolyte of the present application contains phosphate groups and / or phosphite groups. The phosphate groups and / or phosphite groups generate phosphorus-containing free radicals at high temperatures. The phosphorus-containing free radicals can capture hydrogen free radicals and hydroxyl free radicals in the combustion reaction, thereby terminating the combustion reaction, reducing the combustion risk of the electrolyte, achieving flame retardant and / or non-flammable effects, and thereby improving the safety of the secondary battery; the oxygen-containing groups in the flame-retardant polymer can coordinate with lithium ions, promote the dissociation of lithium salts, enhance ion conductivity, and thereby improve the electrochemical performance of the secondary battery.

[0050] In the above general formula, the value range of m is 0≤m≤1000. For example, m can be 0, 3, 5, 10, 30, 50, 80, 100, 200, 400, 700, 800, 900, 1000 or a range consisting of any two of the above values.

[0051] In the above general formula, n is in the range of 0 ≤ m ≤ 1000. For example, n can be 0, 2, 4, 7, 10, 20, 40, 70, 100, 300, 500, 700, 800, 900, 1000, or a range consisting of any two of these values. When m and n are within these ranges, the ionic conductivity of the flame-retardant polymer electrolyte is improved.

[0052] In the above general formula, the value range of x is 1≤x≤10 (x is an integer), for example, x can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range consisting of any two of the above values.

[0053] In the present application, the values ​​of m and n can be obtained by testing by the following method: after disassembling the battery, the flame-retardant polymer electrolyte is dissolved in DMF, and the total molecular weight of the flame-retardant polymer can be measured by gel permeation chromatography; the flame-retardant polymer electrolyte is dissolved in a deuterated reagent and subjected to nuclear magnetic resonance testing to obtain a nuclear magnetic hydrogen spectrum, or dissolved in THF and subjected to matrix-assisted laser desorption ionization time-of-flight mass spectrometry to test the repeating structural units to obtain the ratio of m and n; the values ​​of m and n can be calculated in combination with the total mass.

[0054] In one embodiment, at least one of R1, R2, R1' and R2' is selected from -C x H 2x+1-y F y ; At least one of the R3 and R3' is selected from -C x H 2x O z -.

[0055] Lithium metal anode has a high theoretical specific capacity (3860mAh g -1 ) and the lowest redox potential (-3.04 V vs. standard hydrogen electrode) and low density (0.534 g cm -3 ), is considered the ideal negative electrode in lithium-ion batteries. Lithium-ion batteries are currently widely used in digital products, power, and energy storage. Currently, commercial lithium-ion batteries primarily use liquid electrolytes. The high chemical and electrochemical activity of lithium metal itself leads to harmful side reactions between the lithium metal negative electrode and the liquid electrolyte, which continuously consumes lithium metal and liquid electrolyte. Furthermore, uneven lithium deposition leads to dendrite growth, which can easily pierce the separator and cause battery short circuits, posing a significant safety hazard.

[0056] Flame retardant polymer containing -Cx H 2x+1-y F y and / or -C x H 2x O z -When, -C x H 2x+1-y F y and / or -C x H 2x O z -The fluorine functional group and / or ether functional group in it can provide more electron-donating sites, have a strong solvation effect with the lithium salt, promote the dissociation of lithium ions, and construct a fast ion conduction SEI layer rich in LiF and lithium phosphate on the lithium metal negative electrode; it can also effectively improve the compatibility of the lithium metal negative electrode, induce uniform deposition of lithium, and improve the coulombic efficiency, thereby improving the cycle stability of the secondary battery; in addition, the flame retardant polymer partially decomposes at high temperature to produce fluorine free radicals, which can eliminate hydrogen free radicals and hydroxyl free radicals in the combustion reaction, terminate the combustion reaction, and further improve the flame retardant properties of the electrolyte.

[0057] Specifically, LiF and lithium phosphate in SEI can be tested by the following method: the battery cell is disassembled after cycling, and the negative electrode is characterized by XPS. The characteristic peak of LiF can be observed at 685eV in the F1s spectrum, and the molar ratio of the F element is 5%-10%; the characteristic peak of lithium phosphate can be observed at 134eV in the P 2p spectrum, and the molar ratio of the P element is 2%-5%.

[0058] In some embodiments, the -C x H 2x+1 At least one selected from the following structural formulas:

[0059]

[0060] In some embodiments, the -C x H 2x+1-y F y At least one selected from the following structural formulas:

[0061]

[0062] In some embodiments, the -C x H 2x -At least one selected from the following structural formulas:

[0063]

[0064] In some embodiments, the -C x H 2x O z -At least one selected from the following structural formulas:

[0065]

[0066] In some embodiments, the flame-retardant polymer electrolyte also includes a lithium salt and a plasticizer. Based on the mass of the flame-retardant polymer electrolyte, the mass percentage of the flame-retardant polymer is 55.5%-82%, the mass percentage of the plasticizer is 5%-20%, and the mass percentage of the lithium salt is 10%-25%. Among them, too low a content of the flame-retardant polymer will limit the flame retardant effect, and too high a content will lead to low electrolyte ion conductivity; too low a plasticizer content will lead to insufficient ionic conductivity, and too high a content will limit electrolyte safety; too low a lithium salt content will affect the ionic conductivity and the electrolyte / electrode interface stability, and too high a content will reduce the mechanical strength of the electrolyte.

[0067] In some embodiments, based on the mass of the flame retardant polymer electrolyte, the mass percentage of the flame retardant polymer is 55.5%-82%, for example, it can be 55.5%, 56%, 60%, 62%, 65%, 67%, 70%, 73%, 75%, 78%, 80%, 82% or a range consisting of any two of the above values.

[0068] In some embodiments, based on the mass of the flame retardant polymer electrolyte, the mass percentage of the plasticizer is 5%-20%, for example, it can be 5%, 7%, 9%, 11%, 13%, 15%, 18%, 20% or a range consisting of any two of the above values.

[0069] In some embodiments, based on the mass of the flame retardant polymer electrolyte, the mass percentage of the lithium salt is 10%-25%, for example, it can be 10%, 12%, 14%, 16%, 18%, 20%, 23%, 25% or a range consisting of any two of the above values.

[0070] In some embodiments, the plasticizer includes at least one of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonates (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), fluorodimethyl carbonate (FDMC), ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEC), trimethyl phosphate (TMP), triethyl phosphate (TEP), trimethyl phosphite (TMPi), and triethyl phosphite (TEPi).

[0071] In the present application, the plasticizer can promote the dissociation of lithium salts, thereby further improving ionic conductivity, while improving the lithium metal negative electrode interface, inducing uniform lithium deposition, and improving coulombic efficiency; thereby improving the cycle stability of the secondary battery.

[0072] In some embodiments, the lithium salt is at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium difluorooxalatoborate (LiDFOB), lithium tetrafluoroborate, lithium perchlorate, and lithium trifluoromethanesulfonate.

[0073] In a second aspect, a method for preparing a flame retardant polymer electrolyte is provided, comprising the following steps:

[0074] Mixing polymer monomers, lithium salt, plasticizer, and initiator to form a precursor solution;

[0075] Heating the precursor solution at 40-80° C. to polymerize the precursor solution in situ to form the flame-retardant polymer electrolyte;

[0076] The polymer monomers include a phosphate monomer as shown in formula I and / or a phosphite monomer as shown in formula II;

[0077]

[0078]

[0079] wherein R1, R2, R1' and R2' are each independently selected from -C x H 2x+1 or -C x H 2x+1-y F y ; R3 and R3' are each independently selected from -C x H 2x -or-C x H 2x O z -, 1≤x≤10, 1≤y≤2x+1, 1≤z≤x.

[0080] In the present application, a phosphate monomer as shown in Formula I and / or a phosphite monomer as shown in Formula II is used as a monomer of a flame-retardant polymer. The polymer monomer can serve as a solvent to dissolve the lithium salt. The plasticizer can also dissolve part of the lithium salt, so that the lithium salt is evenly dispersed in the precursor solution. Under the action of an initiator, the polymer monomer undergoes an in-situ polymerization reaction to prepare a flame-retardant polymer electrolyte in which each component is evenly distributed. The flame-retardant polymer in the flame-retardant polymer electrolyte contains phosphate groups and / or phosphite groups. The phosphate groups and / or phosphite groups generate phosphorus-containing free radicals at high temperatures. The phosphorus-containing free radicals can capture hydrogen free radicals and hydroxyl free radicals in the combustion reaction, thereby terminating the combustion reaction, reducing the combustion risk of the electrolyte, achieving a flame-retardant and / or non-flammable effect, and thereby improving the safety of the secondary battery. The oxygen-containing groups in the flame-retardant polymer can coordinate with lithium ions, promote the dissociation of lithium salts, enhance ion conductivity, and thereby improve the electrochemical performance of the secondary battery.

[0081] The present application uses an initiator to interconnect polymer molecules to generate a three-dimensional network structure, which has higher chemical stability and thermal stability, is beneficial to improving the stability of the flame-retardant polymer electrolyte, and makes the performance of the secondary battery stable and long-lasting.

[0082] It should be understood that R1, R2, R3, R1', R2' and R3' in the phosphate monomer shown in Formula I and / or the phosphite monomer shown in Formula II are compatible with R1, R2, R3, R1', R2' and R3' in the general structural formula of the flame retardant polymer.

[0083] In some embodiments, the method for preparing the phosphate monomer shown in Formula I comprises the following steps:

[0084] In the presence of triethylamine, phosphorus oxychloride, a compound containing R1 and a compound containing R2 undergo a first reaction to obtain an intermediate product;

[0085] The intermediate product is added to a compound containing R3, and a second reaction is carried out between the intermediate product and the compound containing R3. The mixture is filtered and extracted to obtain a phosphate monomer as shown in Formula I.

[0086] Illustratively, the molar ratio of phosphorus oxychloride, the compound containing R1, the compound containing R2, and the compound containing R3 is (0.9-1.1):(0.9-1.1):(0.9-1.1).

[0087] Exemplarily, the molar ratio of phosphorus oxychloride to triethylamine is 1:(3-3.5).

[0088] For example, the solvents used in the first reaction and the second reaction include dichloromethane and THF, and the amount of the solvent added is not particularly limited.

[0089] Illustratively, the first reaction and the second reaction are carried out under an inert atmosphere and an ice bath.

[0090] Exemplarily, the first reaction time is 2-4 hours; the second reaction time is 6-18 hours.

[0091] The reaction equation for preparing the phosphate monomer shown in Formula I is as follows:

[0092]

[0093] In some embodiments, the method for preparing the phosphite-based monomer as shown in Formula II comprises the following steps:

[0094] In the presence of triethylamine, phosphorus trichloride, the compound containing R1' and the compound containing R2' undergo a third reaction to obtain an intermediate product;

[0095] The intermediate product is added to the compound containing R3', and the intermediate product and the compound containing R3' are subjected to a fourth reaction, followed by filtration and extraction to obtain a phosphate monomer as shown in Formula I.

[0096] Illustratively, the molar ratio of phosphorus trichloride, the compound containing R1', the compound containing R2' and the compound containing R3' is (0.9-1.1):(0.9-1.1):(0.9-1.1).

[0097] Exemplarily, the molar ratio of phosphorus trichloride to triethylamine is 1:(3-3.5).

[0098] Illustratively, the solvents used in the third reaction and the fourth reaction include dichloromethane and THF, and the amount of the solvent added is not particularly limited.

[0099] Illustratively, the third reaction and the fourth reaction are carried out under an inert atmosphere and an ice bath.

[0100] Exemplarily, the third reaction time is 2-4 hours; the fourth reaction time is 6-18 hours.

[0101] The reaction equation for preparing the phosphite-based monomer shown in Formula II is as follows:

[0102]

[0103] In some embodiments, based on the mass of the precursor solution, the mass of the polymer monomer is 55%-80%, the mass of the plasticizer is 5%-20%, the mass of the lithium salt is 10%-25%, and the mass of the initiator is 0.5%-2%.

[0104] In some embodiments, based on the mass of the precursor solution, the mass of the polymer monomer is 55%-80%, for example, it can be 55%, 57%, 60%, 62%, 65%, 67%, 70%, 73%, 75%, 78%, or 80%.

[0105] In some embodiments, based on the mass of the precursor solution, the mass of the plasticizer is 5%-20%, for example, it can be 5%, 7%, 9%, 11%, 13%, 15%, 18%, 20% or a range consisting of any two of the above values.

[0106] In some embodiments, based on the mass of the precursor solution, the mass of the lithium salt is 10%-25%, for example, 10%, 12%, 14%, 16%, 18%, 20%, 23%, 25% or a range consisting of any two of the above values.

[0107] In some embodiments, based on the mass of the precursor solution, the mass of the initiator is 0.5%-2%, for example, it can be 0.5%, 0.7%, 1%, 1.3%, 1.5%, 1.8%, 2% or a range consisting of any two of the above values.

[0108] By controlling the masses of the polymer monomer, plasticizer, lithium salt and initiator in the precursor solution within the above range, the polymer monomer can be fully polymerized, effectively improving the flame retardant properties of the flame retardant polymer electrolyte and the electrochemical properties of the secondary battery.

[0109] In this application, an initiator is any compound capable of initiating a polymerization reaction between the first and second polymer monomers. The initiator can be selected from any known compound and is not specifically required by this application. For example, the initiator includes, but is not limited to, at least one of azobisisobutyronitrile (AIBN) and dibenzoyl peroxide (BPO). These initiators can increase the reaction rate of the polymerization reaction between the polymer monomers.

[0110] In a third aspect, a secondary battery is provided, comprising a battery cell and an electrolyte disposed in a packaging shell, wherein at least part of the structure of the battery cell is located in the electrolyte, and the electrolyte is the flame-retardant polymer electrolyte or a flame-retardant polymer electrolyte prepared by the preparation method of the flame-retardant polymer electrolyte.

[0111] It is understandable that the structure of the battery cell may be entirely located in the electrolyte, or, in another embodiment, the structure of the battery cell may be partially located in the electrolyte and another portion exposed outside the electrolyte, for example, the tabs of the battery cell are exposed outside the electrolyte.

[0112] In some embodiments, the positive electrode sheet includes a positive electrode active material layer, which may include but is not limited to a chemical formula such as Li a Ni x Co y M z O 2-b N b (wherein 0.95≤a≤1.2, x>0, y≥0, z≥0, and x+y+z=1, 0≤b≤1, M is selected from a combination of one or more of Mn and Al, and N is selected from a combination of one or more of F, P, and S), the positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 The positive electrode active material may be a combination of one or more of O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, TiS2, etc. The positive electrode active material may also be subjected to a modification treatment. Methods for modifying the positive electrode active material should be known to those skilled in the art. For example, the positive electrode active material may be modified by coating, doping, etc. The materials used for the modification treatment may include, but are not limited to, a combination of one or more of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, etc. The positive electrode current collector used in the positive electrode sheet is generally a structure or part that collects current. The positive electrode current collector may be any material suitable for use as a positive electrode current collector for lithium-ion batteries in the art. For example, the positive electrode current collector may include, but is not limited to, metal foil, and more specifically, may include, but is not limited to, aluminum foil.

[0113] In some embodiments, the negative electrode plate includes a negative electrode active material layer. The negative electrode active material may include, but is not limited to, one or more of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based materials, tin-based materials, lithium titanate, or other metals capable of forming alloys with lithium. The graphite may be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material may be selected from one or more of elemental silicon, silicon oxides, silicon-carbon composites, and silicon alloys; and the tin-based material may be selected from one or more of elemental tin, tin oxides, and tin alloys. The negative electrode current collector used in the negative electrode plate is typically a structure or component that collects current. The negative electrode current collector may be any material suitable for use as a negative electrode current collector in lithium-ion batteries. For example, the negative electrode current collector may include, but is not limited to, metal foil, and more specifically, may include, but is not limited to, copper foil.

[0114] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0115] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape.

[0116] In a fourth aspect, a method for preparing a secondary battery is provided, comprising the following steps:

[0117] Obtaining a battery cell and placing the battery cell in a packaging shell;

[0118] mixing polymer monomers, lithium salt, plasticizer and initiator to obtain a precursor solution;

[0119] The precursor solution is injected into the packaging shell, and the precursor solution in the packaging shell is heated at 40° C.-80° C. to form the flame-retardant polymer electrolyte or the flame-retardant polymer electrolyte prepared by the preparation method of the flame-retardant polymer electrolyte through in-situ polymerization to obtain a secondary battery.

[0120] In the present application, during the process of preparing a secondary battery, a flame-retardant polymer electrolyte is prepared inside the battery through an in-situ thermal polymerization process, so that there is good interface contact between the flame-retardant polymer electrolyte and the electrode material, thereby reducing the internal resistance of the battery; and the flame-retardant polymer electrolyte of the present application is solid, which limits the fluidity of the flame-retardant polymer, reduces the side reactions between the flame-retardant polymer and the electrode material, and improves the electrochemical performance and cycle stability of the secondary battery.

[0121] In a fifth aspect, an electrical device is provided, comprising the secondary battery or the secondary battery prepared by the secondary battery preparation method.

[0122] Exemplarily, the above-mentioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

[0123] To make the technical solutions and advantages of the present invention more clear, the present invention and its beneficial effects will be further described in detail below in conjunction with specific implementation methods, but the implementation methods of the present invention are not limited thereto.

[0124] In a specific embodiment of the present invention, the preparation method of polymer monomer A1 is:

[0125] Under inert atmosphere and ice bath conditions, 1 mol of phosphorus oxychloride was dissolved in dichloromethane to obtain solution A; 1 mol of the compound containing R1, 1 mol of the compound containing R2, and 3 mol of triethylamine were dissolved in dichloromethane to obtain solution B; 1 mol of the compound containing R3 was dissolved in dichloromethane to obtain solution C;

[0126] Under an inert atmosphere and an ice bath, solution B was added dropwise to solution A and stirred for 3 h to obtain an intermediate product solution. The intermediate product solution was then added to solution C and stirred for 12 h. The resulting product was filtered and extracted to obtain an organic layer solution, which was then distilled under reduced pressure to obtain polymer monomer A1.

[0127] Wherein, the compound containing R1 and the compound containing R2 are compounds of the following structural formula:

[0128]

[0129] The compound containing R3 is a compound of the following structural formula:

[0130]

[0131] The structural formula of the obtained polymer monomer A1 is shown below:

[0132]

[0133] The hydrogen spectrum of polymer monomer A1 is as follows Figure 1 It is understood that A1 belongs to the type of polymer monomer formula I.

[0134] In a specific embodiment of the present invention, the preparation method of polymer monomer A2 differs from that of polymer monomer A1 only in that the compound containing R1 is a compound of the following structural formula:

[0135]

[0136] The compound containing R2 is a compound of the following structural formula:

[0137]

[0138] The structural formula of the obtained polymer monomer A2 is shown below:

[0139]

[0140] It is understood that the structural formula of A2 can be obtained by replacing R1, R2, and R3 with corresponding structural formulas based on the polymer monomer formula I.

[0141] In a specific embodiment of the present invention, the preparation method of polymer monomer A3 differs from that of polymer monomer A1 only in that the compound containing R1 and the compound containing R2 are both compounds of the following structural formula:

[0142]

[0143] The structural formula of the obtained polymer monomer A3 is shown below:

[0144]

[0145] It is understood that the structural formula of A3 can be obtained by replacing R1, R2, and R3 with corresponding structural formulas based on the polymer monomer formula I.

[0146] In a specific embodiment of the present invention, the preparation method of polymer monomer A4 differs from that of polymer monomer A1 only in that the compound containing R3 is a compound of the following structural formula:

[0147]

[0148] The structural formula of the obtained polymer monomer A4 is shown below:

[0149]

[0150] It is understood that the structural formula of A4 can be obtained by replacing R1, R2, and R3 with corresponding structural formulas based on the polymer monomer formula I.

[0151] In a specific embodiment of the present invention, the preparation method of polymer monomer A5 is:

[0152] Under inert atmosphere and ice bath conditions, 1 mol of phosphorus trichloride was dissolved in dichloromethane to obtain solution A; 1 mol of the compound containing R1', 1 mol of the compound containing R2', and 3 mol of triethylamine were dissolved in dichloromethane to obtain solution B; 1 mol of the compound containing R3' was dissolved in dichloromethane to obtain solution C;

[0153] Under an inert atmosphere and an ice bath, solution B was added dropwise to solution A and stirred for 3 h to obtain an intermediate product solution. The intermediate product solution was then added to solution C and stirred for 12 h. The resulting product was filtered and extracted to obtain an organic layer solution, which was then distilled under reduced pressure to obtain polymer monomer A5.

[0154] Wherein, the compound containing R1' and the compound containing R2' are both compounds of the following structural formula:

[0155]

[0156] The compound containing R3' is a compound of the following structural formula:

[0157]

[0158] The structural formula of the obtained polymer monomer A5 is shown below:

[0159]

[0160] The hydrogen spectrum of the obtained polymer monomer A5 is as follows Figure 2 It is understood that A5 belongs to the type of polymer monomer formula II.

[0161] In a specific embodiment of the present invention, the preparation method of polymer monomer A6 differs from that of polymer monomer A5 only in that the compound containing R3' is a compound having the following structural formula:

[0162]

[0163] The structural formula of the obtained polymer monomer A6 is shown below:

[0164]

[0165] It is understood that the structural formula of A6 can be obtained by replacing R1', R2', and R3' with corresponding structural formulas based on the polymer monomer formula II.

[0166] In a specific embodiment of the present invention, the preparation method of polymer monomer A7 differs from that of polymer monomer A1 only in that the compound containing R1, the compound containing R2, and the compound containing R3 are all compounds of the following structural formula:

[0167]

[0168] The structural formula of the obtained polymer monomer A7 is shown below:

[0169]

[0170] It is understood that the structural formula of A7 can be obtained by replacing R1, R2, and R3 with corresponding structural formulas based on the polymer monomer formula I.

[0171] Example 1

[0172] Preparation of electrolyte precursor solution: At room temperature, in an argon-filled glove box (H2O <1ppm, O2 <1ppm), polymer monomer A1, fluoroethylene carbonate (plasticizer), LiFSI, and AIBN were measured in a mass ratio of 74:10:15:1, respectively, and stirred until uniformly mixed to obtain an electrolyte precursor solution.

[0173] Preparation of flame-retardant polymer electrolyte: The electrolyte precursor solution was placed in a sealed container and allowed to stand at 60°C for 6 hours to achieve in-situ polymerization of the electrolyte precursor solution to form a flame-retardant polymer electrolyte; the general structural formula of the flame-retardant polymer is:

[0174]

[0175] Wherein, m is 50, n is 0, and R1, R2, and R3 in the general structural formula of the flame-retardant polymer are derived from the corresponding R1, R2, and R3 in the aforementioned polymer monomer A1. It should be understood that R1, R2, R3, R1', R2', and R3' in the phosphate-based monomer of Formula I and / or the phosphite-based monomer of Formula II correspond to R1, R2, R3, R1', R2', and R3' in the general structural formula of the flame-retardant polymer.

[0176] Preparation of lithium-copper half-cell:

[0177] A copper counter electrode was obtained by cutting 6μm copper foil; the prepared copper counter electrode, PP separator, and 200μm lithium metal negative electrode were stacked in order and placed in a battery case, 30μL of electrolyte precursor solution was added dropwise with a pipette, and a button battery sealing machine was used for pressure packaging at a pressure of 30KPa and allowed to stand at a temperature of 60°C for 6h to achieve in-situ polymerization of the electrolyte precursor solution to form a flame-retardant polymer electrolyte, thereby obtaining a lithium-copper half-cell.

[0178] Preparation of lithium-high nickel ternary soft pack battery:

[0179] The positive electrode active material LiNi 0.92 Co 0.07 Mn 0.01 O2 (NCM), conductive agent acetylene black (Super P) and binder polyvinylidene fluoride (PVDF) are LiNi 0.92 Co 0.07 Mn 0.01 O2:Super P:PVDF=90:6:4 was mixed evenly and dispersed evenly in 1-methyl-2-pyrrolidone (NMP) to form a uniform black slurry. The mixed black slurry was coated on both sides of the aluminum foil, baked, rolled, and cut into pieces to obtain the positive electrode sheet. The positive electrode surface capacity was 4.5mAh / cm 2 ;

[0180] The prepared positive electrode sheet, PP separator, and 20μm lithium metal negative electrode sheet are stacked in order so that each positive electrode membrane layer and negative electrode membrane layer are covered with a PP separator. Then they are stacked into battery cells, hot pressed, and the tabs are welded and placed in an outer packaging shell. After baking and drying, the electrolyte precursor solution is injected with an injection volume of 2g / Ah. The electrolyte precursor solution is left to stand at a high temperature of 60°C for 6h to achieve in-situ polymerization of the electrolyte precursor solution. After formation, aging, and capacity separation, a lithium-high nickel ternary full battery is made.

[0181] Example 1-1

[0182] Different from Example 1, no fluoroethylene carbonate (plasticizer) was added to the flame-retardant polymer electrolyte prepared in this example.

[0183] Example 2

[0184] Different from Example 1, the polymer monomer in this example is polymer monomer A2.

[0185] The rest is the same as in Example 1 and will not be described again here.

[0186] Example 3

[0187] Different from Example 1, the polymer monomer in this example is polymer monomer A3.

[0188] The rest is the same as in Example 1 and will not be described again here.

[0189] Example 4

[0190] Different from Example 1, the polymer monomer in this example is polymer monomer A4.

[0191] The rest is the same as in Example 1 and will not be described again here.

[0192] Example 5

[0193] Different from Example 1, the polymer monomer in this example is polymer monomer A5.

[0194] The rest is the same as in Example 1 and will not be described again here.

[0195] Example 6

[0196] Different from Example 1, the polymer monomer in this example is polymer monomer A6.

[0197] The rest is the same as in Example 1 and will not be described again here.

[0198] Example 7

[0199] Different from Example 1, the polymer monomers in this example are polymer monomer A1 and polymer monomer A5, and the mass ratio of polymer monomer A1 to polymer monomer A5 is 1:1.

[0200] The rest is the same as in Example 1 and will not be described again here.

[0201] Example 8

[0202] Different from Example 1, in this embodiment, the mass ratio of polymer monomer A1, fluoroethylene carbonate, LiFSI, and AIBN is 64:20:15:1.

[0203] The rest is the same as in Example 1 and will not be described again here.

[0204] Example 9

[0205] Different from Example 1, the mass ratio of polymer monomer A1, fluoroethylene carbonate, LiFSI, and AIBN in this example is 79:5:15:1.

[0206] The rest is the same as in Example 1 and will not be described again here.

[0207] Example 10

[0208] Different from Example 1, in this example, the mass ratio of polymer monomer A1, fluoroethylene carbonate, LiFSI, and AIBN is 64:10:25:1.

[0209] The rest is the same as in Example 1 and will not be described again here.

[0210] Example 11

[0211] Different from Example 1, the mass ratio of polymer monomer A1, fluoroethylene carbonate, LiFSI, and AIBN in this example is 80:9:10:1.

[0212] The rest is the same as in Example 1 and will not be described again here.

[0213] Example 12

[0214] Different from Example 1, in this example, the mass ratio of polymer monomer A1, fluoroethylene carbonate, LiFSI, and AIBN is 73:10:15:2.

[0215] The rest is the same as in Example 1 and will not be described again here.

[0216] Example 13

[0217] Different from Example 1, in this example, the mass ratio of polymer monomer A1, fluoroethylene carbonate, LiFSI, and AIBN is 74.5:10:15:0.5.

[0218] The rest is the same as in Example 1 and will not be described again here.

[0219] Example 14

[0220] Different from Example 1, the mass ratio of polymer monomer A1, fluoroethylene carbonate, LiFSI, and AIBN in this example is 55:19:25:1.

[0221] The rest is the same as in Example 1 and will not be described again here.

[0222] Example 15

[0223] Different from Example 1, ethylene glycol dimethyl ether is used in this example to replace fluoroethylene carbonate.

[0224] The rest is the same as in Example 1 and will not be described again here.

[0225] Example 16

[0226] Different from Example 1, triethyl phosphate was used in this example to replace fluoroethylene carbonate.

[0227] The rest is the same as in Example 1 and will not be described again here.

[0228] Example 17

[0229] Different from Example 1, LiDFOB is used in this example to replace LiFSI.

[0230] The rest is the same as in Example 1 and will not be described again here.

[0231] Example 18

[0232] Different from Example 1, the preparation method of the electrolyte precursor solution in this embodiment is different. The preparation method of the electrolyte precursor solution in this embodiment is: at room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), polymer monomer A1, LiFSI, and AIBN are respectively measured in a mass ratio of 84:15:1, and stirred until uniformly mixed to obtain an electrolyte precursor solution.

[0233] The rest is the same as in Example 1 and will not be described again here.

[0234] Comparative Example 1

[0235] Different from Example 1, an electrolyte is used in this comparative example to replace the flame-retardant polymer electrolyte. The preparation method of the electrolyte in this comparative example is as follows: at room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), fluoroethylene carbonate and LiFSI are respectively measured in a mass ratio of 84:15, and stirred until uniformly mixed to obtain an electrolyte.

[0236] The rest is the same as in Example 1 and will not be described again here.

[0237] Comparative Example 2

[0238] Different from Example 1, the polymer monomer in this comparative example is polymer trimer A7, monomer 7 and ethylene carbonate are mixed in a molar ratio of 1:100 to obtain a mixed monomer 8 mainly composed of cyclic carbonate, and the mass ratio of the mixed monomer, LiFSI, and AIBN is 84:15:1.

[0239] The rest is the same as in Example 1 and will not be described again here.

[0240] Performance Testing

[0241] (1) Coulombic efficiency: At 25°C, the lithium-copper half-cell is charged at 0.5 mA / cm 2 First deposit 1mAh / cm 2 Lithium to copper current collector, charged to 1V, record lithium stripping capacity C1mAh / cm 2 , Coulomb efficiency CE1% = C1 * 100%; repeat this cycle for 200 times, and calculate the average Coulomb efficiency CE from the 11th to the 200th cycle Ave. %.

[0242] (2) Capacity retention: Single-layer soft-pack lithium-high nickel ternary full-cell batteries were charged and discharged at 25°C with a charge rate of 0.5C, a discharge rate of 0.2C, and a voltage range of 2.5-4.25V. The capacity retention at cycle n was recorded as Cap.n% = discharge capacity at cycle n / discharge capacity at cycle 1*100%. The capacity retention at cycle 200 was recorded.

[0243] (3) Flame retardancy: Take 1g of flame-retardant polymer electrolyte and put it in direct contact with the outer flame of an ignition source for 5s. After that, remove the ignition source and observe the time t required for the flame to extinguish. The self-extinguishing time is recorded as ts / g. If t≤5s / g, it indicates that the flame-retardant polymer electrolyte has excellent flame retardant properties. If there is no combustion after removing the ignition source, that is, t=0s, it indicates that the flame-retardant polymer electrolyte is non-flammable.

[0244] The test results are shown in Table 1 and Figure 3-4 shown.

[0245] Table 1

[0246]

[0247]

[0248] From the experimental data in Table 1, it can be seen that the self-extinguishing time of the flame-retardant polymer electrolyte of the present application is ≤3s / g. When it is used to prepare a secondary battery, the average coulombic efficiency of the obtained secondary battery is ≥94.7%, and the capacity retention rate after 200 cycles is ≥89.48%. This shows that the flame-retardant polymer electrolyte of the present application has excellent flame retardancy, and the secondary battery containing the flame-retardant polymer electrolyte has excellent electrochemical performance.

[0249] From the experimental data of Examples 1-4, it can be seen that the flame retardant polymer contains -C x H 2x+1-y F y and / or -C x H 2x O z -, the average coulombic efficiency of the secondary battery containing the flame retardant polymer electrolyte is ≥99%, and the capacity retention rate after 200 cycles is ≥96%; indicating that the flame retardant polymer contains -C x H 2x+1-y F y and / or -C x H 2x O z -, can improve the electrochemical performance of the secondary battery.

[0250] It can be seen from the experimental data of Example 1 and Comparative Examples 1-2 that the structural formula of the flame-retardant polymer is not within the scope of the present application, the self-extinguishing time of the obtained flame-retardant polymer electrolyte is ≥5s / g, and the capacity retention rate of the secondary battery containing the flame-retardant polymer electrolyte after 200 cycles is ≤79%; this shows that the flame-retardant polymer electrolyte including the general structural formula of the present application has excellent flame retardancy, and the obtained secondary battery has higher electrochemical performance.

[0251] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present disclosure rather than to limit the scope of protection of the present disclosure. Although the present disclosure has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present disclosure may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present disclosure.

Claims

1. A flame retardant polymer electrolyte, characterized in that: The flame-retardant polymer electrolyte comprises a flame-retardant polymer, and the general structural formula of the flame-retardant polymer is: wherein R1, R2, R1' and R2' are each independently selected from -C x H 2x+1 or -C x H 2x+1-y F y ; R3 and R3' are each independently selected from -C x H 2x -or-C x H 2x O z -, m is 0 or a positive integer, n is 0 or a positive integer, m and n are not both 0, 1≤x≤10, 1≤y≤2x+1, 1≤z≤x.

2. The flame retardant polymer electrolyte according to claim 1, wherein Said-C x H 2x+1 At least one selected from the following structural formulas: and / or, the -C x H 2x+1-y F y At least one selected from the following structural formulas:

3. The flame retardant polymer electrolyte according to claim 1, wherein Said-C x H 2x -At least one selected from the following structural formulas: and / or, the -C x H 2x O z -At least one selected from the following structural formulas:

4. The flame retardant polymer electrolyte according to claim 1, wherein Based on the mass of the flame retardant polymer electrolyte, the mass percentage of the flame retardant polymer is 55.5%-82%.

5. The flame-retardant polymer electrolyte according to any one of claims 1 to 4, characterized in that: The flame retardant polymer electrolyte further comprises a lithium salt and a plasticizer, wherein the mass percentage of the plasticizer is 5%-20% and the mass percentage of the lithium salt is 10%-25% based on the mass of the flame retardant polymer electrolyte; The plasticizer includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluorodimethyl carbonate, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, trimethyl phosphate, triethyl phosphate, trimethyl phosphite, and triethyl phosphite; and / or the lithium salt is at least one of bisfluorosulfonyl imide lithium salt, bistrifluoromethanesulfonic acid imide lithium, lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium perchlorate, and lithium trifluoromethanesulfonate.

6. A method for preparing a flame retardant polymer electrolyte, characterized in that: The following steps are involved: Mixing polymer monomers, lithium salt, plasticizer, and initiator to form a precursor solution; Heating the precursor solution at 40-80° C. to form the flame-retardant polymer electrolyte according to any one of claims 1 to 5; The polymer monomers include a phosphate monomer as shown in formula I and / or a phosphite monomer as shown in formula II; wherein R1, R2, R1' and R2' are each independently selected from -C x H 2x+1 or -C x H 2x+1-y F y ; R3 and R3' are each independently selected from -C x H 2x -or-C x H 2x O z -, 1≤x≤10, 1≤y≤2x+1, 1≤z≤x.

7. The method for preparing a flame-retardant polymer electrolyte according to claim 6, wherein: Based on the mass of the precursor solution, the mass of the polymer monomer is 55%-80%, the mass of the plasticizer is 5%-20%, the mass of the lithium salt is 10%-25%, and the mass of the initiator is 0.5%-2%; And / or, the initiator is at least one of azobisisobutyronitrile and dibenzoyl peroxide.

8. A secondary battery, characterized in that: The secondary battery includes a battery cell and an electrolyte arranged in a packaging shell, at least part of the structure of the battery cell is located in the electrolyte, and the electrolyte is the flame-retardant polymer electrolyte described in any one of claims 1 to 5 or a flame-retardant polymer electrolyte prepared by the preparation method of the flame-retardant polymer electrolyte described in any one of claims 6 to 7.

9. A method for preparing a secondary battery, characterized in that: The following steps are involved: Obtaining a battery cell and placing the battery cell in a packaging shell; mixing polymer monomers, lithium salt, plasticizer and initiator to obtain a precursor solution; The precursor solution is injected into the packaging shell, and the precursor solution in the packaging shell is heated at 40° C.-80° C. to obtain the flame-retardant polymer electrolyte according to any one of claims 1 to 5 or the secondary battery according to claim 8.

10. An electrical device, characterized in that: The invention also provides a secondary battery as claimed in claim 8 or a secondary battery prepared by the method for preparing a secondary battery as claimed in claim 9.

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