Single-ion polymer solid electrolyte, preparation method thereof, diaphragm-free lithium secondary battery and lithium secondary battery

Abstract

The invention provides a single-ion polymer solid electrolyte, a preparation method thereof, a diaphragm-free lithium secondary battery and a lithium secondary battery. The polymer solid electrolyte comprises a sulfonate polymer as a component (A), a polymer base material as a component (B) and a lithium salt as a component (C), wherein the component (A) sulfonate polymer is derived from an unsaturated sulfonate monomer; the unsaturated sulfonate monomer comprises at least one of compounds as shown in a formula (I) and / or a formula (II): # imgabs0 #, wherein in the formula (I), R1 and R2 independently represent monovalent organic groups; (In formula (II), R3 represents a substituent-substituted or unsubstituted hydrocarbon group or hydrogen atom, the arc-shaped structure represents a lactone structure, and the arc-shaped structure has 3-6 carbon atoms on a lactone ring; component (A) is polymerized in situ in the solid electrolyte. The polymer solid electrolyte has high ionic conductivity, high lithium ion transference number and excellent mechanical properties.

Description

Technical Field

[0001] The invention relates to a single-ion polymer solid electrolyte, a preparation method thereof, a diaphragm-free lithium secondary battery and a lithium secondary battery, belonging to the technical field of lithium ion batteries. Background Art

[0002] In order to further improve the energy density and safety of lithium-ion batteries, all-solid-state batteries are an important direction for the development of lithium-ion batteries. Polymer solid electrolyte materials have the advantages of low cost, high processability, and environmental friendliness, and they occupy an important position in the industrialization of high-energy-density all-solid-state batteries. However, common polymer solid electrolytes, such as PEO (polyethylene oxide) and PMMA (polymethyl methacrylate), have problems such as high room temperature crystallinity and high glass transition temperature, which inhibit the movement of polymer chain segments, making the polymer lithium ion conductivity generally low, hindering its practical application. At the same time, polymer solid electrolytes also have the problem that the lithium ion migration number is generally less than 0.5 due to the high coupling between cations and Lewis base sites in the polymer matrix, and the polymer solid electrolyte has poor lithium conductivity.

[0003] Some documents disclose a single-ion polymer electrolyte, which grafts two functional monomers onto a polymer substrate to form a single-ion conductive polymer electrolyte system. The system has a high lithium ion migration number and good cycle performance under high temperature conditions. However, it does not solve the problem of low conductivity at room temperature, which limits its practical application.

[0004] In addition, for lithium-ion batteries, a diaphragm may or may not be used in its structure. The diaphragm material is non-conductive, and its physical and chemical properties have a great influence on the performance of the battery. In the case of using a diaphragm, the main function of the diaphragm is to separate the positive and negative electrodes of the battery to prevent the two electrodes from contacting and short-circuiting. In addition, it also has the function of allowing electrolyte ions to pass through. In the case of not using a diaphragm, the positive and negative electrodes are usually separated by the electrolyte itself to prevent short-circuiting, and ions are conducted by the electrolyte itself. From the perspective of the energy density of lithium secondary batteries, secondary batteries without diaphragms are advantageous. In particular, the use of solid electrolytes (such as quasi-solid or all-solid electrolytes) makes diaphragm-free batteries possible.

[0005] It can be seen that although a series of studies have been conducted in this field on the improvement of polymer electrolytes, there is still room for further improvement in the development of polymer solid electrolytes that have high ionic conductivity, excellent mechanical properties and high lithium ion migration numbers. Summary of the invention

[0006] Problem that the invention aims to solve

[0007] To address the problems of low ionic conductivity and low lithium ion migration number of traditional polymer solid electrolytes, the modification methods mainly include blending, copolymerization or adding inorganic fillers with organic polymers.

[0008] In the method of blending with organic polymers and copolymerization modification of polymer base materials, it is usually difficult to solve the problems of low ion conductivity and lithium ion migration number at the same time by polymerization modification of a single small molecule monomer. However, the addition of multiple small molecule monomers will make the structure and degree of polymerization after polymerization, the repeatability of the experiment, etc. more difficult to control and the cost is high. In addition, the method of adding organic fillers often has problems such as uneven mixing, easy agglomeration, and blocking of lithium ion migration channels.

[0009] Furthermore, as a previous research result of the applicant, in the Chinese patent application with application number 202410670877.5, in-situ polymerization was used to improve the performance of the final electrolyte. Although this achievement has aroused some interest in the subsequent in-situ polymerization modification route of the applicant, however, in the subsequent specific practice, it was also found that even if the in-situ polymerization method is adopted, the result is strongly dependent on the type of monomer. This is mainly due to the differences in compatibility, flexibility / crystallization, ion coordination, electrochemical window performance, voltage resistance / heat resistance, etc. between different monomers and their polymers. For example, many polar monomers are not suitable for this polymerization route, resulting in phase separation after in-situ polymerization, or the product of in-situ polymerization cannot achieve the required ion conductivity, stability and other requirements in electrical testing. Therefore, for the desired performance improvement, the type of monomer still needs to be selected very carefully.

[0010] In order to solve the above problems, based on further research, the present invention provides a single-ion polymer solid electrolyte, wherein the polymer solid electrolyte is prepared by introducing an unsaturated sulfonate monomer of a specific structure into a high polymer base material (such as PVDF, PEO, PMMA, PAN, etc.), and polymerizing the monomer in situ in the high polymer material. The sulfonate polymer of the specific structure not only improves the ion conductivity of the polymer solid electrolyte, but also improves the lithium ion migration number, and does not cause problems in processability.

[0011] Furthermore, the present invention also provides a method for preparing a polymer solid electrolyte. The preparation method can improve the interfacial compatibility of each component in the polymer solid electrolyte, make each polymer component fully compatible, and further improve the lithium ion transmission capacity and lithium ion migration number.

[0012] Furthermore, the present invention also provides a lithium secondary battery, which comprises the polymer solid electrolyte described above or the polymer solid electrolyte prepared by the preparation method described above.

[0013] Solutions for solving problems

[0014] The present invention first provides a single-ion polymer solid electrolyte, wherein the polymer solid electrolyte comprises a sulfonate polymer as component (A), a polymer base material as component (B) and a lithium salt as component (C);

[0015] Wherein, the component (A) sulfonate polymer is derived from unsaturated sulfonate monomers;

[0016] The unsaturated sulfonic acid ester monomer includes at least one of the compounds shown in formula (I) and / or formula (II):

[0017]

[0018] in:

[0019] In formula (I), R1 and R2 independently represent a monovalent organic group;

[0020] In formula (II), R3 represents a hydrocarbon group or a hydrogen atom which may be substituted or unsubstituted by a substituent, and the arc shape of formula (II) represents a lactone structure, and the arc shape has 3 to 6 carbon atoms on the lactone ring;

[0021] The component (A) is polymerized in situ in the solid electrolyte.

[0022] According to the polymer solid electrolyte of the present invention, wherein R1 and R2 are selected from aliphatic hydrocarbon groups, alicyclic hydrocarbon groups or aromatic hydrocarbon groups substituted or unsubstituted by substituents having 1 to 10 carbon atoms; and R3 represents an alkyl group having 2 to 4 carbon atoms or a hydrogen atom.

[0023] According to the polymer solid electrolyte of the present invention, the formula (I) and the formula (II) contain 1 to 3 unsaturated groups.

[0024] According to the polymer solid electrolyte of the present invention, the unsaturated group is an alkenyl group.

[0025] According to the polymer solid electrolyte of the present invention, the unsaturated sulfonate monomer comprises at least one of the compounds represented by formula (Ia) and / or formula (IIa):

[0026]

[0027] Said n=1 or 2.

[0028] According to the polymer solid electrolyte of the present invention, wherein R4 in the formula (Ia) represents a phenyl group or an alkyl group having 1 to 5 carbon atoms.

[0029] According to the polymer solid electrolyte of the present invention, the mass ratio of the component (A) to the component (B) is 1:(0.1-10).

[0030] According to the polymer solid electrolyte of the present invention, the unsaturated sulfonate monomer includes at least one of the compounds represented by formula (Ia-1), (Ia-2), (Ia-3) or (IIa-1):

[0031]

[0032] According to the polymer solid electrolyte of the present invention, the component (B) polymer base material includes one or more combinations of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trifluorochloroethylene copolymer, polyethylene oxide, polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene copolymer, polymethyl methacrylate, polyurethane, polyurea, polyvinyl chloride, polypropylene carbonate, etc.

[0033] In addition, the present invention also provides a method for preparing the single-ion polymer solid electrolyte according to the present invention, which comprises the following steps:

[0034] The polymer base material, lithium salt, unsaturated sulfonic acid ester monomer and initiator are mixed in an organic solvent to obtain a mixed solution;

[0035] The unsaturated sulfonate monomer is polymerized.

[0036] According to the preparation method of the present invention, the initiator is selected from free radical initiators; and the polymerization reaction is carried out under heating or irradiation conditions.

[0037] According to the preparation method of the present invention, the mass ratio of the unsaturated sulfonate monomer to the polymer base material is 1:(0.1-10);

[0038] The amount of the initiator is 0.01% to 1% by mass of the monomer;

[0039] The amount of the lithium salt used is 10% to 80% by mass of the sum of the mass of the polymer base material, the lithium salt and the unsaturated sulfonate monomer.

[0040] In addition, the present invention also provides a diaphragm-free lithium secondary battery, wherein the diaphragm-free lithium secondary battery comprises a positive electrode, a negative electrode, and comprises or uses the polymer solid electrolyte according to the present invention or the polymer solid electrolyte obtained by the preparation method according to the present invention.

[0041] Furthermore, the present invention also provides a lithium secondary battery, wherein the lithium secondary battery comprises a positive electrode, a negative electrode, a separator, and comprises or uses the polymer solid electrolyte according to the present invention or the polymer solid electrolyte obtained by the preparation method according to the present invention.

[0042] Effects of the Invention

[0043] 1) The polymer solid electrolyte provided by the present invention introduces sulfonate polymers, wherein the "sulfonate" functional groups have a synergistic effect with the existing functional groups in the polymer base material, which can effectively improve the ionic conductivity of the polymer solid electrolyte; in addition, the "sulfonate" functional groups can form a coupling with the anion part in the lithium salt, thereby inhibiting the migration of anions, providing more channels for the transmission of lithium ions, and achieving the purpose of improving the lithium ion migration ability.

[0044] 2) The preparation method of the polymer solid electrolyte provided by the present invention allows unsaturated sulfonate monomers to be in situ polymerized in the presence of a polymer base material, so that the two polymer molecular chains can be fully compatible, entangled, and form an interpenetrating network structure, thereby inhibiting the crystallinity of the polymer base material at room temperature, enhancing the movement of chain segments, and further improving the lithium ion transmission capacity.

[0045] 3) The sulfonate polymer provided by the present invention can be formed by polymerizing only one unsaturated sulfonate monomer, which can bring convenience in operation and cost.

[0046] 4) In some specific embodiments, when the unsaturated sulfonate monomer contains more than two carbon-carbon double bonds, it is more conducive to forming a cross-linked structure, promoting the formation of an interpenetrating network between the polymer base material and the sulfonate polymer molecular chain formed by in situ polymerization, thereby further inhibiting the crystallization ability of the polymer base material and improving the lithium ion transmission capacity. DETAILED DESCRIPTION

[0047] The following is a detailed description of the present invention. The following description of the technical features is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0048] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical values ​​A and B.

[0049] In the present specification, a numerical range expressed using "above" or "below" means a numerical range including the number.

[0050] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0051] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0052] In this specification, the term "normal temperature" or "room temperature" refers to an indoor ambient temperature of "23±2°C".

[0053] In this specification, the unit names used are all international standard unit names, and unless otherwise stated, the "%" used indicates weight or mass percentage.

[0054] In the present specification, the use of “substantially” or “essentially” means that the standard deviation from a theoretical model, theoretical data or target data is within a numerical range of 1%, preferably 0.8%, and more preferably 0.5%.

[0055] In this specification, when the terms “include” and / or “comprise” are used, they indicate the existence of features, steps, operations, devices, components and / or their combinations.

[0056] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0057] The present invention mainly provides a single-ion polymer solid electrolyte and a preparation method thereof. By introducing unsaturated sulfonate monomers into a traditional polymer base material and performing in-situ polymerization to modify the polymer base material, the ionic conductivity of the polymer solid electrolyte is improved while also improving the mechanical strength and lithium ion migration number.

[0058] The present invention is mainly obtained through the following insights:

[0059] In addition to the problem of low ion conductivity, traditional polymer solid electrolytes are all dual-ion electrolytes that conduct electricity simultaneously in the form of anions and cations. While conducting lithium ions, the anion portion of the lithium salt will conduct in the opposite direction. Therefore, the anions will compete with the lithium ions for the ion transmission channel to a certain extent. In addition, anions are usually large in size, which will hinder the transmission of lithium ions, resulting in a low lithium ion migration number.

[0060] As mentioned above, the previous methods of forming polymer electrolytes by blending and copolymerization modification have many shortcomings. Through the research of the present invention, it has been found that by introducing unsaturated sulfonate monomers with specific structures into the traditional polymer base and performing in-situ polymerization to modify the polymer base, the introduced "sulfonate" functional groups can form coupling effects with the anions in the lithium salt, thereby inhibiting the transmission of anions, forming single ion channels, providing more channels for the transmission of lithium ions, and achieving the effect of improving the migration ability of lithium ions. At the same time, the "sulfonate" functional groups have a synergistic effect with the existing functional groups in the polymer base, which can effectively improve the ionic conductivity of the polymer solid electrolyte.

[0061] Furthermore, the present invention also discovered that in the preparation of polymer solid electrolytes, the adverse effects caused by interface compatibility have a great impact on the electrochemical stability of polymer solid electrolytes. Therefore, the present invention enables unsaturated sulfonate monomers to be in situ polymerized in the presence of a polymer base material, so that the two polymer molecular chains can be fully compatible, entangled, and form an interpenetrating network structure, thereby effectively improving the interface compatibility of the components in the polymer solid electrolyte. In addition, the interpenetrating network can also inhibit the crystallinity of the polymer base material at room temperature, enhance the movement of chain segments, and further improve the lithium ion transmission capacity and mechanical properties.

[0062] Therefore, the prepared polymer solid electrolyte can not only improve the ionic conductivity and lithium ion migration number, but also effectively inhibit the problems caused by lithium dendrites and improve the cycle stability of the battery.

[0063] <First aspect>

[0064] A first aspect of the present invention provides a single-ion polymer solid electrolyte, which includes a sulfonate polymer as component (A), a polymer base material as component (B), and a lithium salt as component (C).

[0065] In addition, various functional additive components may be used in the polymer solid electrolyte composition without hindering the realization of the technical effects of the present invention.

[0066] Component (A)

[0067] The sulfonate polymer as component (A) described in the present invention is derived from unsaturated sulfonate monomers, wherein the unsaturated sulfonate monomers include at least one of the compounds represented by formula (I) and / or formula (II):

[0068]

[0069] in:

[0070] In formula (I), R1 and R2 independently represent a monovalent organic group.

[0071] Such a monovalent group may generally be a straight or branched chain aliphatic group, an alicyclic group having a cyclic structure, or an aromatic group having an aromatic ring structure, and such a group may optionally have a substituent such as a halogen, especially a F atom.

[0072] The above-mentioned aliphatic group is a chain group. In some specific embodiments, it can be a straight-chain or branched saturated or unsaturated alkyl group with 1 to 10 carbon atoms, preferably with 2 to 10 carbon atoms.

[0073] In some specific embodiments, the alicyclic group may be a saturated or unsaturated alkyl group containing a cycloalkyl group having 1 to 10 carbon atoms, preferably 2 to 10 carbon atoms.

[0074] For the above-mentioned aromatic group, in some specific embodiments, it is an aromatic group having at least one of carbon aromatics and heteroaromatics. Preferably, it can be an aromatic group having a benzene ring. Similarly, these aromatic groups can optionally have unsaturated groups other than the aromatic ring structure.

[0075] Furthermore, the formula (I) may have 1 to 3 unsaturated groups, that is, 1 to 3 polymerizable groups, and such unsaturated groups may be derived from R1 or R2, or both R1 and R2 may have such unsaturated groups. Moreover, such unsaturated groups are preferably double bonds.

[0076] In formula (II), R3 represents a hydrogen atom or a hydrocarbon group substituted or unsubstituted with a substituent, and the substituent may be a halogen, such as an F atom. In addition, the arc shape of formula (II) represents a lactone structure, and the arc shape may have 3 to 6 carbon atoms on the lactone ring.

[0077] In some specific embodiments, the hydrocarbon group may be an alkyl group having 2 to 4 carbon atoms.

[0078] Furthermore, the formula (II) may have 1 to 3 unsaturated groups, that is, 1 to 3 polymerizable groups, and such unsaturated groups may be derived from the R3 portion or the arc-shaped portion. Moreover, such unsaturated groups are preferably double bonds.

[0079] In some preferred embodiments of the present invention, the unsaturated sulfonate monomer comprises at least one of the compounds represented by formula (Ia) and / or formula (IIa):

[0080]

[0081] Said n=1 or 2.

[0082] Examples of R4 include alkyl groups having 1 to 5 carbon atoms which may be substituted with fluorine or phenyl groups, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl and phenyl groups.

[0083] The unsaturated sulfonate monomer is polymerized in situ through the unsaturated carbon-carbon double bond to form a sulfonate polymer, which forms a molecular chain entanglement with the polymer base material, disrupts the orderly arrangement of the polymer base material molecules, inhibits its crystallinity at room temperature, enhances the movement of the chain segments, and improves the transmission capacity of lithium ions. In some preferred embodiments, the unsaturated sulfonate monomer contains two or three carbon-carbon double bonds that can be polymerized by free radicals. When the unsaturated sulfonate monomer contains more than two carbon-carbon double bonds, it is more conducive to forming a cross-linked structure, promoting the formation of an interpenetrating network between the polymer base material and the sulfonate polymer molecular chain formed by in situ polymerization, thereby further inhibiting the crystallization ability of the polymer base material and improving the transmission capacity of lithium ions.

[0084] In a further preferred embodiment, the unsaturated sulfonate monomer of the present invention as shown in formula (Ia) can be selected from one or more of phenyl sulfonate (Ia-1), methyl sulfonate (Ia-2), ethyl sulfonate (Ia-3), etc.:

[0085]

[0086] In some preferred embodiments, the unsaturated sulfonate monomers of the present invention as represented by formula (IIa) may include propenyl-1,3-sultone (IIa-1) and the like.

[0087]

[0088] As for the unsaturated sulfonic acid ester monomers of the present invention, only one kind may be used, or a plurality of kinds may be used simultaneously when necessary.

[0089] In addition, in addition to the above-mentioned unsaturated sulfonate monomers, other unsaturated monomers can also be used in component (A) of the present invention. When other unsaturated monomers are used, these monomers account for less than 10% by mass of the total mass of all monomers, preferably less than 8% by mass, and more preferably less than 5% by mass.

[0090] Component (B)

[0091] The polymer binder as component (B) in the present invention is provided as a basic material.

[0092] The type of polymer base material may be a high molecular polymer material, which generally has a higher dielectric constant and can make the lithium salt described below ionized better.

[0093] In some specific embodiments of the present invention, such a polymer base material can be selected from one or more combinations of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-chlorotrifluoroethylene copolymer (PVDF-CTFE), polyethylene oxide (PEO), polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene copolymer (PVDF-TrFE-CTFE), polymethyl methacrylate (PMMA), polyurethane (PU), polyurea (PUA), polyvinyl chloride (PVC), polypropylene carbonate (PPC), etc.

[0094] In some preferred embodiments, the polymer base of the present invention may be one or more fluorine-containing polymers.

[0095] Component (C)

[0096] The lithium salt as component (C) described in the present invention is the source of active ions in the polymer solid electrolyte and is included in the polymer solid electrolyte system. Without the lithium salt, the polymer solid electrolyte will lose the function of conducting active ions and the entire battery will not work.

[0097] In some specific embodiments, the lithium salt can be selected from one or more salts formed by lithium ions and the following anions: PF6 - 、BF4 - , Cl - Br - ,I - 、ClO4 - 、AsF6 - 、CH3CO2 - CF3SO3 - 、N(CF3SO2)2 - 、N(FSO2)2 - 、C(CF2SO2)3 - 、C2BF2O4 - wait.

[0098] In some preferred embodiments, the lithium salt may be selected from a combination of one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0099] Composition of polymer solid electrolyte

[0100] Regarding the composition of the polymer solid electrolyte of the present invention, from the aspect of improving the electrical properties of the electrolyte, the content of each component of the present invention can be arranged as follows:

[0101] The mass ratio of the component (A) to the component (B) is 1:(0.1-10), preferably 1:(0.5-2), such as 1:8, 1:5, 1:3, 1:2, 1:1.3, 1:1, 1:0.7, 1:0.8, 1:0.6, 1:0.2, etc. Controlling the mass ratio of the component (A) to the component (B) within the above range can better inhibit crystallization, increase the number of lithium ion migration, fully crosslink, and strengthen the interaction between functional groups.

[0102] The amount of the component (C) is not particularly limited in principle, and can be carried out in accordance with the general specifications for the amount of lithium salts in the art. In some specific embodiments, the content of the component (C) is 10% to 80% by weight of the sum of the weights of the components (A), (B) and (C), preferably 20% to 40% by weight, such as 20%, 30%, 40%, 50%, 60%, 70%, etc. If the content of component (C) is too low, the lithium ion transmission capacity will be reduced; if the content of component (C) is too high, it will lead to an unnecessary increase in cost and may also affect the mechanical properties of the polymer solid electrolyte.

[0103] The (usage) form of polymer solid electrolyte

[0104] Regarding the form of the polymer solid electrolyte of the present invention, in some specific embodiments, the above-mentioned polymer solid electrolyte composition can be provided separately as an independently supported membrane, and in other specific embodiments, it can be provided integrally with the positive and negative electrode sheets.

[0105] In some specific embodiments, the polymer solid electrolyte obtained by the present invention substantially does not contain organic solvent or (at room temperature) liquid electrolyte.

[0106] <Second Aspect>

[0107] The second aspect of the present invention provides a method for preparing the single-ion polymer solid electrolyte of the first aspect.

[0108] The preparation method of the present invention comprises:

[0109] The polymer base material, lithium salt, unsaturated sulfonic acid ester monomer and initiator are mixed in an organic solvent to obtain a mixed solution;

[0110] The unsaturated sulfonate monomer is polymerized.

[0111] The types and amounts of the polymer base material, lithium salt, and unsaturated sulfonate monomer are the same as those in the first aspect and will not be described in detail herein.

[0112] The initiator described in the present invention is a free radical initiator, which is used to make the unsaturated sulfonate monomer undergo free radical polymerization in the polymer base material to form a cross-linked network.

[0113] The free radical initiator can be a thermal initiator or a photoinitiator.

[0114] The type of thermal initiator may be selected from one or more of azo initiators, organic peroxide initiators and the like.

[0115] In some specific embodiments, the thermal initiator may include one or more of azobisisobutyronitrile (AIBN), azobisisoheptanenitrile, dibenzoyl peroxide, diethylhexyl peroxydicarbonate, isopropylbenzene hydroperoxide, tert-butyl hydroperoxide, dodecyl peroxide, tert-butyl perbenzoate, tert-butyl pervalerate, diisopropyl peroxycarbonate, potassium persulfate, or ammonium persulfate.

[0116] The type of photoinitiator can be selected from a cleavage type or a hydrogen abstraction type. In some specific embodiments, the cleavage type can be selected from one or more of benzoin and its derivatives, acetophenones, aromatic ketones, and acylphosphine oxides; the hydrogen abstraction type can be selected from one or more of benzophenone, thioxanthone, camphor porquinone, and bisimidazole.

[0117] The amount of the initiator added is 0.01% to 1% by mass of the unsaturated sulfonate monomer, preferably 0.2% to 0.5% by mass, for example, 0.05%, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, etc. The amount of the initiator used can be used to control the sulfonate polymer to have a suitable degree of polymerization.

[0118] In principle, there is no particular restriction on the type of organic solvent, and for example, it can be selected from at least one of diethyl ether, ethanol, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebacononitrile.

[0119] In some specific embodiments, in the mixing step, in order to achieve the migration of lithium ions, the polymer base material and the lithium salt can be first mixed with the organic solvent and stirred thoroughly until dissolved to dissociate the lithium salt, and then the unsaturated sulfonic acid ester monomer and the initiator can be added.

[0120] In addition, the polymerization reaction may be controlled by, for example, irradiating or heating the polymerization reaction.

[0121] In some specific embodiments, the polymerization reaction may be caused by heating when a thermal initiator is used. There is no particular limitation on the reaction temperature, and the required reaction temperature may be used according to the type of initiator. In some preferred embodiments, the reaction temperature may be 40 to 80°C, such as 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, etc.; the reaction time may be 4 to 18 hours, such as 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, etc.

[0122] In some more specific embodiments, the reaction can be carried out under inert gas conditions, such as argon, etc. Specifically, after the mixing step, an inert gas can be introduced into the mixed solution to expel the air dissolved in the solvent and in the reaction container, and the mixture is sealed.

[0123] In other specific embodiments, free radicals can be formed and polymerization of monomers can be initiated by ultraviolet light irradiation when a photoinitiator is used. The polymerization reaction time can be several minutes. The advantages of photoinitiated polymerization are fast polymerization speed, less solvent volatilization, environmental friendliness, low cost, low energy consumption, etc.

[0124] In some specific embodiments, the preparation method further comprises a film-forming step, and the film-forming method may be a solution coating method, an extrusion casting method or the like.

[0125] In some more specific embodiments, the solution coating method includes applying the solution to a substrate and drying it, removing the substrate, thereby obtaining a film-like polymer solid electrolyte. There is no particular limitation on the substrate, for example, it can be a glass substrate, a ceramic substrate, a stainless steel substrate, a plastic substrate, etc. For the drying temperature and time, for example, it can be dried in a vacuum drying oven at 50 to 100°C, preferably 60 to 80°C for 4 to 10 hours, preferably 4 to 8 hours. After drying, a thin film on the substrate can be obtained. Peeling the film off the substrate (i.e., removing the substrate) can obtain a film-like polymer solid electrolyte. In addition, the obtained film-like polymer solid electrolyte can also be cut into a suitable shape and size as needed, for example, it can be cut into a circular electrolyte sheet of Φ16mm.

[0126] The preparation method of the present invention has many advantages such as low cost, simple method, environmental friendliness, and high safety of the prepared polymer solid electrolyte, and has extremely broad prospects in practical application.

[0127] <Third Aspect>

[0128] The third aspect of the present invention provides a lithium secondary battery, in particular a lithium secondary battery comprising or using the polymer solid electrolyte of the first aspect of the present invention or a polymer solid electrolyte prepared according to the preparation method described in the second aspect.

[0129] Such a lithium secondary battery at least includes a positive electrode, a negative electrode and a solid electrolyte. In addition, a diaphragm can be used when necessary. In some specific embodiments, a diaphragm is further used in the lithium secondary battery. There is no particular restriction on such a diaphragm, and an organic porous membrane can be used. In some other specific embodiments, the lithium secondary battery is a diaphragm-free lithium secondary battery. Preferably, the lithium secondary battery can be an all-solid-state battery, which is allowed to not contain a liquid electrolyte and a diaphragm, and relies on a solid electrolyte to isolate the positive and negative electrodes and transmit lithium ions.

[0130] For the positive electrode in the lithium secondary battery, a high-voltage oxide positive electrode material for lithium-ion batteries can be used, such as lithium cobalt oxide (LCO), lithium nickel manganese oxide (LNMO), and high-nickel content ternary positive electrode (6 series, 8 series) materials (such as NCM811, NCA622, etc.).

[0131] There is no particular limitation on the negative electrode, which may be a common negative electrode for solid polymer batteries. Preferably, the negative electrode is a lithium negative electrode.

[0132] Example

[0133] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0134] Example 1

[0135] Preparation of polymer solid electrolyte solution:

[0136] 4 g PVDF, 4 g lithium bis(trifluoromethanesulfonyl)imide (equivalent to 50% of the total mass of all polymers after polymerization) and 0.02 g AIBN were dissolved in 30 ml DMF and stirred magnetically until dissolved. 4 g phenyl vinyl sulfonate was added and the mixture was mixed for 30 min and heated and stirred at 75° C. for 4 h.

[0137] Preparation of composite solid polymer electrolyte membrane:

[0138] The mixed solution prepared above was poured onto a clean glass plate and dried in a vacuum drying oven at 80°C for 8 hours using a solution coating method. The film was then peeled off the glass plate and cut into a Φ16 mm circular electrolyte sheet.

[0139] The polymer solid electrolyte sheet prepared as above was used for testing, and the test results are shown in Table 1.

[0140] Example 2

[0141] The difference from Example 1 is that phenyl ethylene sulfonate is replaced by ethyl ethylene sulfonate, and the remaining steps are the same as those in Example 1, and a polymer solid electrolyte membrane is prepared for subsequent tests, as shown in Table 1.

[0142] Example 3

[0143] The difference from Example 1 is that PVDF is replaced by PU, and the remaining steps are the same as those of Example 1, and a polymer solid electrolyte membrane is prepared for subsequent tests, as shown in Table 1.

[0144] Example 4

[0145] The difference from Example 1 is that PVDF is replaced by PEO, and the solvent is replaced by DMAC instead of DMF. The remaining steps are the same as those in Example 1, and a polymer solid electrolyte membrane is prepared and subsequent performance tests are performed, as shown in Table 1.

[0146] Example 5

[0147] The difference from Example 1 is that the amount of phenyl ethylene sulfonate added is 2 g, and the remaining steps are the same as Example 1, and a polymer solid electrolyte membrane is prepared for subsequent performance tests. The details are shown in Table 1.

[0148] Example 6

[0149] The difference from Example 1 is that the amount of phenyl ethylene sulfonate added is 3 g, and the remaining steps are the same as Example 1, and a polymer solid electrolyte membrane is prepared and then subjected to subsequent performance tests. The details are shown in Table 1.

[0150] Example 7

[0151] The difference from Example 1 is that the amount of phenyl ethylene sulfonate added is 5 g, and the remaining steps are the same as Example 1, and a polymer solid electrolyte membrane is prepared for subsequent performance tests. The details are shown in Table 1.

[0152] Example 8

[0153] The difference from Example 1 is that the amount of phenyl ethylene sulfonate added is 6 g, and the remaining steps are the same as Example 1, and a polymer solid electrolyte membrane is prepared and then subjected to subsequent performance tests. The details are shown in Table 1.

[0154] Example 9

[0155] The difference from Example 1 is that ethylene sulfonate phenyl ester is replaced by ethylene sulfonate methyl ester, and the remaining steps are the same as those in Example 1, and a polymer solid electrolyte membrane is prepared and subsequent performance tests are performed, as shown in Table 1.

[0156] Example 10

[0157] The difference from Example 1 is that phenyl ethylene sulfonate is replaced by propenyl-1,3-sultone, and the remaining steps are the same as those in Example 1. A polymer solid electrolyte membrane is prepared and subsequent performance tests are performed, as shown in Table 1.

[0158] Comparative Example 1

[0159] The difference from Example 1 is that the mixed solution is not heated, and the remaining steps are the same as Example 1, and a polymer solid electrolyte membrane is prepared for subsequent ion conductivity testing. The details are shown in Table 1.

[0160] Comparative Example 2

[0161] The difference from Example 1 is that no unsaturated sulfonate monomer is added, and the remaining steps are the same as Example 1, and a polymer solid electrolyte membrane is prepared for subsequent ion conductivity testing. The details are shown in Table 1.

[0162] Comparative Example 3

[0163] The difference from Example 1 is that the unsaturated monomer added is methyl methacrylate, and the remaining steps are the same as Example 1, and a polymer solid electrolyte membrane is prepared for subsequent ion conductivity testing. The details are shown in Table 1.

[0164] Performance Testing

[0165] 1. Ionic conductivity: The polymer solid electrolyte membrane (CSEs) prepared above was combined with two stainless steel electrodes (SS) to form a SS / CSEs / SS simulated battery for testing. The battery assembly process was carried out in a glove box with a water and oxygen content of less than 0.1ppm. The electrochemical impedance spectroscopy (EIS) test used a frequency range of 0.01Hz to 106Hz to measure the electrochemical impedance of the polymer solid electrolyte at room temperature. The impedance data obtained from the EIS test was used to calculate the ionic conductivity of the prepared polymer solid electrolyte.

[0166] 2. Cyclic stability: The polymer solid electrolyte sheets (CSEs) prepared above are combined with ternary positive electrodes and lithium metal negative electrodes to form button cells. The preparation of the cells is carried out in a glove box. The cells are tested for charge and discharge cycles at a rate of 0.1C, and the attenuation of their discharge capacity is detected.

[0167] 3. Ion migration number: The lithium ion migration number is tested using the steady-state current method.

[0168] Table 1 Performance test results of embodiments and comparative examples

[0169]

[0170] The results of Examples 1-2, 5-10 and Comparative Example 2 show that the introduction of different types of sulfonate polymers can effectively improve the ionic conductivity and lithium ion migration number of the polymer solid electrolyte, and after being assembled into a button cell, its cycle stability is effectively improved.

[0171] The results of Examples 1 and 3-4 indicate that sulfonate polymers are also compatible with different polymer substrates, exhibiting high ionic conductivity, lithium ion transference number and cycle stability.

[0172] The results of Example 1 and Comparative Example 1 show that if only unsaturated sulfonate monomers are added without initiating polymerization, the liquid monomers will significantly reduce the mechanical properties of the polymer solid electrolyte, making it difficult to form a film.

[0173] It should be noted that, although the technical solution of the present invention is introduced with specific examples, those skilled in the art will appreciate that the present invention should not be limited thereto.

[0174] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A single-ion polymer solid electrolyte, characterized in that: The polymer solid electrolyte comprises a sulfonate polymer as component (A), a polymer base material as component (B) and a lithium salt as component (C); Wherein, the component (A) sulfonate polymer is derived from unsaturated sulfonate monomers; The unsaturated sulfonic acid ester monomer includes at least one of the compounds shown in formula (I) and / or formula (II): in: In formula (I), R1 and R2 independently represent a monovalent organic group; In formula (II), R3 represents a hydrocarbon group or a hydrogen atom which may be substituted or unsubstituted by a substituent, and the arc shape of formula (II) represents a lactone structure, and the arc shape has 3 to 6 carbon atoms on the lactone ring; The component (A) is polymerized in situ in the solid electrolyte.

2. The polymer solid electrolyte according to claim 1, characterized in that The R1 and R2 are selected from aliphatic hydrocarbon groups, alicyclic hydrocarbon groups or aromatic hydrocarbon groups substituted or unsubstituted with substituents having 1 to 10 carbon atoms; and the R3 represents an alkyl group having 2 to 4 carbon atoms or a hydrogen atom.

3. The polymer solid electrolyte according to claim 1 or 2, characterized in that: The formula (I) and formula (II) have 1 to 3 unsaturated groups.

4. The polymer solid electrolyte according to claim 3, characterized in that: The unsaturated group is an alkenyl group.

5. The polymer solid electrolyte according to any one of claims 1 to 4, characterized in that: The unsaturated sulfonic acid ester monomer includes at least one of the compounds shown in formula (Ia) and / or formula (IIa): Said n=1 or 2.

6. The polymer solid electrolyte according to claim 5, characterized in that: In the formula (Ia), R4 represents a phenyl group or an alkyl group having 1 to 5 carbon atoms.

7. The polymer solid electrolyte according to any one of claims 1 to 6, characterized in that: The mass ratio of the component (A) to the component (B) is 1:(0.1-10).

8. The polymer solid electrolyte according to any one of claims 1 to 7, characterized in that: The unsaturated sulfonic acid ester monomer includes at least one of the compounds represented by formula (Ia-1), (Ia-2), (Ia-3) or (IIa-1):

9. The polymer solid electrolyte according to any one of claims 1 to 8, characterized in that: The component (B) polymer base material includes one or more combinations of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-chlorotrifluoroethylene copolymer, polyethylene oxide, polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene copolymer, polymethyl methacrylate, polyurethane, polyurea, polyvinyl chloride, polypropylene carbonate, etc.

10. A method for preparing a single-ion polymer solid electrolyte according to any one of claims 1 to 9, characterized in that: The following steps are involved: The polymer base material, lithium salt, unsaturated sulfonic acid ester monomer and initiator are mixed in an organic solvent to obtain a mixed solution; The unsaturated sulfonate monomer is polymerized.

11. The preparation method according to claim 10, characterized in that: The initiator is selected from free radical initiators; the polymerization reaction is carried out under heating or irradiation conditions.

12. The preparation method according to claim 10 or 11, characterized in that: The mass ratio of the unsaturated sulfonate monomer to the polymer base material is 1:(0.1-10); The amount of the initiator is 0.01% to 1% by mass of the monomer; The amount of the lithium salt used is 10% to 80% by mass of the sum of the mass of the polymer base material, the lithium salt and the unsaturated sulfonate monomer.

13. A diaphragm-free lithium secondary battery, characterized in that: The separator-free lithium secondary battery comprises a positive electrode, a negative electrode and comprises or uses the polymer solid electrolyte according to any one of claims 1 to 9 or the polymer solid electrolyte obtained by the preparation method according to any one of claims 10 to 12.

14. A lithium secondary battery, characterized in that: The lithium secondary battery comprises a positive electrode, a negative electrode, a separator and comprises or uses the polymer solid electrolyte according to any one of claims 1 to 9 or the polymer solid electrolyte obtained by the preparation method according to any one of claims 10 to 12.

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