Polymer solid electrolyte and lithium secondary battery

Abstract

The present application provides a kind of polymer solid electrolyte and lithium secondary battery.The polymer solid electrolyte includes as component (A) modified polymer base, and as component (B) lithium salt;Wherein, the polymer base (A1) in the modified polymer base as component (A) includes the repeating unit with following structure (1):-R-O- (1) Wherein, R represents the straight-chain or branched-chain structure of alkylene group of carbon atom number 2~5, the modification includes by the polyisocyanate component as component (A2) the polyol as component (A3) is formed three-dimensional network structure with the polymer base (A1), and, the formation three-dimensional network structure at least partially in the presence of latent curing agent as component (A4).The polymer solid electrolyte of the present application can improve ionic conductivity and lithium ion migration number, the mechanical strength of base and the cycle performance and service life of secondary battery.

Description

Technical Field

[0001] This invention relates to a polymer solid electrolyte and a lithium secondary battery, belonging to the field of lithium-ion battery technology. Background Technology

[0002] Lithium-ion batteries, as highly efficient energy storage and conversion devices, possess high energy density and have attracted widespread attention due to their excellent cycle performance and high reliability. However, currently commercial lithium batteries typically use organic solutions containing various lithium salts as liquid electrolytes. In practical applications, liquid electrolytes suffer from numerous drawbacks and safety hazards, including poor chemical stability, flammability, and explosiveness. The use of solid electrolytes ensures the safety of lithium-ion batteries and offers advantages such as high energy density, good cycle performance, long lifespan, and a wide electrochemical window, making batteries safer, more durable, with higher energy density, and simpler battery structure design.

[0003] Solid electrolytes mainly include inorganic solid electrolytes and organic polymer solid electrolytes. In many polymer systems, PEO-based substrates are considered the most ideal polymer substrates. However, PEO solid electrolytes suffer from high crystallinity, which interferes with polymer chain movement and lithium-ion movement, resulting in low ionic conductivity and low lithium-ion transfer numbers, thus limiting their practical applications.

[0004] In addition, during the charging and discharging process, the positive electrode material of lithium batteries will be accompanied by the dissolution of metal ions (such as Ni, Co, Mn, Fe, Al, etc.) and their deposition on the surface of the negative electrode material, which will reduce the battery cycle life.

[0005] Some literature discloses a PEO solid electrolyte modified with aqueous polyurethane. This modification is achieved by combining aqueous polyurethane with PEO under aqueous conditions, thus improving ionic conductivity and mechanical properties. However, in an aqueous environment, the isocyanate in the polyurethane may react with water to generate carbon dioxide, thereby damaging the solid electrolyte structure and raising concerns about reduced battery cycle stability. Therefore, the issue of battery cycle life remains unresolved.

[0006] It is evident that although some research has been conducted on polymer solid electrolytes in this field, there is still room for further improvement in the development of polymer solid electrolytes that combine high ionic conductivity, high lithium-ion transport number, excellent mechanical properties, and good battery cycle life. Summary of the Invention

[0007] The problem the invention aims to solve

[0008] As mentioned above, PEO-based polymers have good ion conductivity due to the presence of strong electron-donating groups in their main chain. However, they are prone to crystallization, and the presence of crystalline regions limits their ion conductivity. In addition, PEO itself does not have outstanding mechanical properties and is not very resistant to dendrites.

[0009] In addition, although solid electrolytes based on materials such as PEO have advantages such as good safety, during the charging and discharging process of lithium battery positive electrode materials, metal ions (such as Ni, Co, Mn, Fe, Al, etc.) will dissolve and deposit on the surface of negative electrode materials, which will significantly reduce the battery cycle life.

[0010] To address the aforementioned problems, this invention provides a polymer solid-state electrolyte, primarily obtained through (chemical) modification of a PEO-based polymer matrix. Specifically, by introducing polyols into the polymer matrix and forming a three-dimensional network structure via polyisocyanates and a latent curing agent, not only is the crystallinity of the polymer matrix reduced, thereby increasing ionic conductivity and lithium-ion transference number, but the mechanical strength of the matrix is ​​also improved. Furthermore, the large number of nitrogen atoms introduced by the use of polyisocyanates, possessing lone pairs of electrons, can effectively complex metal ions dissolved from the battery's positive electrode. The overall result is an improved ionic conductivity and dendrite tolerance in the solid-state electrolyte, while also enhancing the cycle performance and lifespan of the secondary battery.

[0011] Furthermore, the present invention also provides a lithium secondary battery, wherein the lithium secondary battery comprises the polymer solid electrolyte described above.

[0012] Solution for solving the problem

[0013] The present invention first provides a polymer solid electrolyte, wherein the polymer solid electrolyte comprises a modified polymer matrix as component (A) and a lithium salt as component (B);

[0014] The modified polymer matrix (A1) of component (A) includes repeating units having the following structure (1):

[0015] -RO-(1)

[0016] Wherein, R represents a straight-chain or branched alkylene group having 2 to 5 carbon atoms.

[0017] The modification includes forming a three-dimensional network structure between a polyol (A3) and the polymer matrix (A1) by means of a polyisocyanate component (A2), and the formation of the three-dimensional network structure is at least partially carried out in the presence of a latent curing agent (A4).

[0018] According to the polymer solid electrolyte of the present invention, the polymer matrix as component (A1) includes polyoxyethylene.

[0019] According to the polymer solid electrolyte of the present invention, the polyisocyanate component (A2) includes one or more of aliphatic polyisocyanates, alicyclic polyisocyanates and aromatic polyisocyanates.

[0020] According to the polymer solid electrolyte of the present invention, the polyol of component (A3) includes polymer polyols having hydroxyl groups on their side chains.

[0021] According to the polymer solid electrolyte of the present invention, the polyol of component (A3) includes at least one of polyvinyl alcohol (PVA) and ethylene-vinyl alcohol copolymer (EVOH).

[0022] According to the polymer solid electrolyte of the present invention, the component (A4) latent curing agent is capable of decomposing to produce hydroxyl and / or amino groups under ambient humidity.

[0023] According to the polymer solid electrolyte of the present invention, wherein in the modified polymer matrix component (A), the molar ratio of the amount derived from component (A3) to the amount derived from the polymer matrix (A1) is 1:4 to 1:12; and / or,

[0024] In the modified polymer matrix component (A), the molar ratio of the amount derived from component (A3) to the amount derived from the polyisocyanate of component (A2) is 1:0.02 to 1:0.44; and / or,

[0025] In the modified polymer matrix component (A), the molar ratio of the amount derived from component (A3) to the amount derived from the latent curing agent in component (A4) is 1:0.2 to 1:0.4.

[0026] According to the polymer solid electrolyte of the present invention, the modification is carried out by one of the following methods:

[0027] a. The component (A3) polyol is grafted with the polymer matrix (A1) to obtain a grafted product, and then the grafted product completes the formation of the three-dimensional network structure in the presence of component (A2) polyisocyanate component and component (A4) latent curing agent;

[0028] b. The polyol of component (A3) is pre-reacted with the polyisocyanate component of component (A2) to obtain a pre-reactant, and then the pre-reactant is reacted with the polymer matrix in the presence of the latent curing agent of component (A4) to form the three-dimensional network structure.

[0029] According to the solid electrolyte of the present invention, in method a, the grafting reaction yields a comb-shaped graft with the molecular weight of the polymer base as the side chain; in method b, the method includes coating the pre-reactant onto the polymer base or blending the pre-reactant with the polymer base.

[0030] Furthermore, the present invention also provides a lithium secondary battery, wherein the lithium secondary battery includes or uses a polymer solid electrolyte according to the present invention, preferably, the lithium secondary battery is an all-solid-state electrolyte lithium secondary battery.

[0031] The effects of the invention

[0032] 1) The polymer solid electrolyte provided by this invention introduces polyols and uses polyisocyanates to form a three-dimensional network structure between the polyols and the polymer matrix, thereby inhibiting the formation of crystalline regions in the polymer matrix, reducing the crystallinity of the polymer matrix, enhancing the movement of chain segments and lithium ions, and improving the ionic conductivity and lithium ion transfer number of the polymer solid electrolyte; at the same time, the formed three-dimensional network structure improves the mechanical strength of the polymer solid electrolyte, enhances the polymer solid electrolyte's tolerance to lithium dendrites, and improves the safety performance of the battery.

[0033] 2) The N-atom lone pair electrons and polyols in the polyisocyanate in the modified polymer matrix can complex the multivalent metal ions dissolved from the positive electrode, preventing the dissolved ions from depositing on the negative electrode, thereby improving the cycle performance and cycle life of the battery.

[0034] 3) The three-dimensional network structure is ultimately formed in the presence of a latent curing agent, which can prevent the reaction of polyisocyanate with water to produce carbon dioxide, prevent the structure of the polymer solid electrolyte from being destroyed, eliminate the influence of water in the battery on the solid electrolyte, improve the structural stability of the polymer solid electrolyte, and further improve the ionic conductivity of the polymer solid electrolyte and the cycle performance of the battery.

[0035] 4) In some specific embodiments, the modified polymer matrix further contains aryl groups (e.g., aromatic isocyanates), which further improves the mechanical strength of the polymer solid electrolyte. Detailed Implementation

[0036] The present invention will now be described in detail. The descriptions of the technical features described below are 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:

[0037] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0038] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0039] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0040] In this specification, the terms "optional" or "optional" are used to indicate the use or omission of certain substances, components, procedures, application conditions, etc.

[0041] In this instruction manual, "normal temperature" or "room temperature" refers to an indoor ambient temperature of "23±2℃".

[0042] All unit names used in this manual are international standard unit names, and unless otherwise stated, the "%" used refers to weight or mass percentage.

[0043] In this specification, the terms "substantially" and "essentially" are used to indicate that the standard deviation from the theoretical model, theoretical data, or target data is within a range of 1%, preferably 0.8%, and more preferably 0.5%.

[0044] In this specification, the terms “comprising” and / or “including” are used to indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0045] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0046] This invention mainly provides a polymer solid electrolyte. By introducing polyol components into a traditional polymer matrix and forming a three-dimensional network structure through polyisocyanates, the mechanical strength, cycle stability, and cycle life of the polymer solid electrolyte can be improved while increasing the ionic conductivity and lithium-ion transference number.

[0047] This invention is mainly derived from the following insights:

[0048] To address the problem of low ion conductivity caused by the high crystallinity of traditional PEO-type polymer solid electrolytes at room temperature, this invention attempts to modify them using polyols and polyisocyanates, so that the polymer matrix and polyol form a three-dimensional network structure through the polyisocyanate.

[0049] The formation of this structure reduces the original crystallinity of PEO-based polymers, thus improving their ion transport capabilities. Furthermore, this three-dimensional network structure significantly enhances the mechanical properties of the polymer matrix, particularly its resistance to dendrite penetration, thereby improving battery life and safety.

[0050] In addition, by introducing a certain amount of polyisocyanate, N atoms with lone pairs of electrons can be introduced. These N atoms and polyols can complex high-valence metal ions, especially transition metal ions, thereby preventing transition metal ions (such as Ni, Co, Mn, Fe, Al, etc.) dissolved from the positive electrode from depositing on the surface of the negative electrode material.

[0051] <First Aspect>

[0052] A first aspect of the present invention provides a polymer solid electrolyte comprising a modified polymer matrix as component (A) and a lithium salt as component (B).

[0053] The modified polymer matrix (A1) of component (A) includes repeating units having the following structure (1):

[0054] -RO-(1)

[0055] Wherein, R represents a straight-chain or branched alkylene group having 2 to 5 carbon atoms.

[0056] The modification includes forming a three-dimensional network structure between a polyol (A3) and the polymer matrix (A1) by means of a polyisocyanate component (A2), and the formation of the three-dimensional network structure is at least partially carried out in the presence of a latent curing agent (A4).

[0057] (Component (A))

[0058] The modified polymer matrix (A) described in this invention is obtained by (chemical) modification of the polymer matrix (A1) with polyisocyanate (A2) and polyol (A3). The three components form a three-dimensional network structure, which improves the electrical and mechanical properties of the polymer matrix and endows it with good transition metal trapping ability.

[0059] Component (A1)

[0060] The polymer-based material (A1) that is the target of modification according to the present invention mainly includes polymers having repeating units having the above-described structure (1).

[0061] In some specific embodiments of the present invention, R can be an ethylene, propylene, or isopropylene structure, more preferably an ethylene, i.e., preferably, the polymer matrix (A1) of the present invention mainly comprises or is substantially formed therefrom polyoxyethylene.

[0062] There are no particular restrictions on the molecular weight or glass transition temperature of the above component (A1), and it can be configured in accordance with the existing principles of solid electrolytes.

[0063] Component (A2)

[0064] The polyisocyanate of component (A2) of the present invention is mainly used to enable component (A1) and component (A3) polyol described below to form a three-dimensional network structure.

[0065] There are no particular limitations on the polyisocyanates that can be used in this invention, and they can be selected from one or more of aliphatic polyisocyanates, alicyclic polyisocyanates, or aromatic polyisocyanates.

[0066] The number of isocyanate groups in the polyisocyanate is typically 2 or more, preferably 2 to 6, and in some preferred embodiments, the isocyanate groups are at least partially or entirely located at the end of the polyisocyanate structure.

[0067] As an aliphatic polyisocyanate, there is no particular limitation, including aliphatic polyisocyanates with straight or branched chains, such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate.

[0068] As an alicyclic polyisocyanate, there are no particular limitations; examples include isophorone diisocyanate, etc.

[0069] As aromatic polyisocyanates, there are no particular limitations, and examples include toluene diisocyanate, 4,4'-diphenylmethane diisocyanate (hereinafter sometimes abbreviated as "MDI"), phenyl dimethylene diisocyanate and naphthalene diisocyanate, triphenylmethane-4,4',4"-triisocyanate, 1,3,5-triisocyanophenyl, 2,4,6-triisocyanotoluene and 4,4'-dimethyldiphenylmethane-2,2',5,5'-tetraisocyanate, etc.

[0070] In addition to the polyisocyanates mentioned above as monomeric compounds, the polyisocyanates of the present invention can also be prepolymers with isocyanate groups at the ends. For example, these prepolymers can be obtained by prepolymerization of isocyanate monomers and polyol compounds. There are no particular limitations on such polyol compounds in principle, and they can include aliphatic linear or branched polyols, alicyclic polyols, aromatic polyols, polyester polyols, polyurethane polyols, polyether polyols, etc.

[0071] In a further preferred embodiment of the invention, from the perspective of improving the mechanical strength of the final polymer solid electrolyte, aromatic polyisocyanates can be used in component (A2) of the invention. There are no particular limitations on the content of aromatic polyisocyanates in component (A2), for example, it can be less than 50% by mass, preferably 10-30% by mass.

[0072] Component (A3)

[0073] For the polyol of component (A3) of the present invention, the number of hydroxyl groups per molecule is generally 3 or more, preferably 5 or more, and more preferably 10 or more.

[0074] In some preferred embodiments of the invention, such a polyol can be a polymeric polyol with hydroxyl groups on its side chain.

[0075] From the perspective of improving the crystallinity of component (A1), such a polyol can be one or more of polyvinyl alcohol (PVA) and ethylene-vinyl alcohol (EVOH). More preferably, component (A3) of the present invention can be polyvinyl alcohol. In addition, there is no particular limitation on the degree of saponification of polyvinyl alcohol in principle, which is generally 80% or more, preferably 90% or more, and more preferably 98% or more.

[0076] Furthermore, the molecular weight of polyols can typically range from 500 Da to 200 million Da, for example, 1500 Da, 2000 Da, 5000 Da, 10000 Da, 100,000 Da, 200,000 Da, 500,000 Da, 800,000 Da, 1 million Da, 2 million Da, 3 million Da, 5 million Da, 10 million Da, 20 million Da, 50 million Da, 100 million Da, 150 million Da, etc.

[0077] Component (A4)

[0078] The component (A4) of this invention is a latent curing agent, which can release active hydrogen groups in the presence of water.

[0079] In some specific embodiments of the present invention, the latent curing agent can react with moisture in the air at room temperature and normal humidity to release active hydrogen groups.

[0080] Furthermore, in some specific embodiments of the present invention, the active hydrogen can be one or both of amino and hydroxyl groups.

[0081] In some more specific embodiments, the latent curing agent may include one or more combinations of imine latent curing agents, oxazolidine latent curing agents, etc., wherein the imine latent curing agent may include one or more of triethylenediamine, polyethyleneimine, polycarbodiimide, etc.

[0082] The latent curing agent of this invention can prevent isocyanate groups from reacting with residual water in the system or water in the atmosphere to produce carbon dioxide and cause bubbles. Therefore, the quality of the crosslinked product can be improved.

[0083] Other ingredients

[0084] There are no particular restrictions in principle on other components that can be used as forming component (A). For example, various polyurethane forming catalysts can also be used when necessary to promote the reaction of the above components (A2) and (A3).

[0085] Dosage of each component

[0086] The amount of each component used when forming component (A) can be adjusted in principle according to the characteristics of component (A1).

[0087] In some preferred embodiments of the present invention, from the perspective of improving resistance to crystallization, mechanical properties, and the ability to capture transition metal ions:

[0088] The molar ratio of component (A3) to component (A1) can be 1:4 to 1:12, such as 1:6, 1:7, 1:8, 1:9, etc. When the molar ratio of component (A3) polyol to component (A1) polymer matrix is ​​1:4 to 1:12, on the one hand, the polyol of component (A3) can better reduce the crystallinity of component (A1) polymer matrix and improve ionic conductivity; on the other hand, the polyol of component (A3) can effectively complex the multivalent metal ions dissolved from the positive electrode, prevent the dissolved metal ions from depositing on the negative electrode, and improve the cycle life of the battery.

[0089] The molar ratio of component (A3) to component (A2) can be 1:0.02 to 1:0.44, for example, 1:0.05, 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, etc. When the molar ratio of component (A3) polyol to component (A2) polyisocyanate is 1:0.02 to 1:0.44, it can better form a three-dimensional network with component (A1) polymer matrix, reduce the crystallinity of polymer matrix, and improve mechanical strength while increasing ionic conductivity and lithium ion transfer number.

[0090] The molar ratio of component (A3) to component (A4) can be 1:0.2 to 1:0.4, for example, 1:0.22, 1:0.25, 1:0.28, 1:0.3, 1:0.32, 1:0.35, 1:0.38, etc. When the molar ratio of component (A3) polyol to component (A4) latent curing agent is 1:0.2 to 1:0.4, it can prevent carbon dioxide generated by the reaction of polyisocyanate and water during the polymerization of polyurethane compounds from destroying the structure of the solid electrolyte, improve the structural stability of the polymer solid electrolyte, and further improve the ionic conductivity and the cycle stability of the battery.

[0091] (Component (B))

[0092] The lithium salt described in this invention as component (B) is the source of active ions in the polymer solid electrolyte and is itself included in the polymer solid electrolyte system. Without the lithium salt, the polymer solid electrolyte will lose its function of conducting active ions, and the entire battery will not work.

[0093] Regarding the type of lithium salt, in some specific embodiments of the present invention, the lithium salt may 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 - Etc. Preferably, the lithium salt can be lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0094] (Other components)

[0095] In addition to components (A) and (B) described above, the polymer solid electrolyte of the present invention may optionally include other components.

[0096] For example, in some specific embodiments, the solid electrolyte may contain other polymer bases in addition to component (A).

[0097] There are no particular restrictions on the types of these other polymer bases in principle. They can be selected from one or more combinations of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-trifluorochloroethylene copolymer (PVDF-CTFE), polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene copolymer (PVDF-TrFE-CTFE), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyurethane (PU), and polyurea (PUA).

[0098] Furthermore, based on the total mass of the polymer matrix, the content of these other polymer matrix components can be less than 10% by mass, such as less than 8% by mass, less than 5% by mass, etc.

[0099] Forms of use of polymer solid electrolytes

[0100] Regarding the morphology of the polymer solid electrolyte of the present invention, in some specific embodiments, the above-described polymer solid electrolyte composition can be provided alone, and such composition can be used to prepare film materials.

[0101] Furthermore, the solid electrolyte of the present invention is essentially an all-solid electrolyte, that is, it does not contain any solvent or liquid electrolyte.

[0102] <Second aspect>

[0103] A second aspect of the present invention provides a method for preparing the polymer solid electrolyte described in the first aspect above.

[0104] In general, the polymer solid electrolyte of the present invention can be obtained by mixing component (A) and component (B) in any form.

[0105] For the preparation of component (A), it is preferred to carry out the preparation by one of the following methods:

[0106] a. The component (A3) polyol is grafted with the polymer matrix (A1) to obtain a grafted product, and then the grafted product completes the formation of the three-dimensional network structure in the presence of component (A2) polyisocyanate component and component (A4) latent curing agent;

[0107] b. The polyol of component (A3) is pre-reacted with the polyisocyanate component of component (A2) to obtain a pre-reactant, and then the pre-reactant is reacted with the polymer matrix (A1) in the presence of the latent curing agent of component (A4) to form the three-dimensional network structure.

[0108] Specifically:

[0109] Method a

[0110] In this route, the first step is to prepare a graft compound. This graft compound can be grafted onto component (A1) via anionic or cationic initiators.

[0111] In some preferred embodiments of the present invention, the above-mentioned graft can be a comb-shaped graft in which the component (A1) is grafted onto the hydroxyl groups on the side chain of the component (A3) to form a comb-shaped graft with the molecular chain of component (A1) as the side chain.

[0112] The grafted material retains hydroxyl groups at its ends; therefore, it is further reacted with component (A2) polyisocyanate in the presence of latent curing agent (A4). This reaction is typically carried out under anhydrous and oxygen-free conditions. Optionally, various organic solvents can be used; the type of organic solvent is not particularly limited and can be selected as needed, for example, one or more of acetonitrile, anisole, chloroform, dichloroethane, and dimethylformamide. Furthermore, in this reaction, the polyisocyanate can at least partially form a three-dimensional network structure between the grafted materials (on the side chains). When the resulting component (A1) is exposed to the atmosphere, the latent curing agent further decomposes due to the presence of atmospheric moisture, generating active hydrogen and thus completing the final three-dimensional network structure.

[0113] Furthermore, the grafts described above can be obtained through the grafting reaction or commercially available, for example, PVA-g-PEO can be obtained commercially.

[0114] Method b

[0115] In this route, the (A3) polyol can be pre-reacted with the (A2) polyisocyanate component to obtain a pre-reactant, which may have at least a partial three-dimensional network structure. Optionally, the pre-reaction can be carried out in the presence of an organic solvent. The amount of organic solvent used is not particularly limited in this invention, as long as it is sufficient to fully dissolve the reactants. In some specific embodiments, the concentration of the (A3) polyol in the pre-reaction solution is below 40 g / L, for example, 5 g / L, 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, etc.

[0116] Furthermore, the above reaction can also be carried out in the presence of a latent curing agent in component (A4), since the reaction is controlled under anaerobic and anhydrous conditions, and component (A4) does not substantially participate in the reaction. Further, the pre-reactant is brought into contact with component (A1), and finally, upon exposure to air, under the action of the latent curing agent, the pre-reactant and component (A1) complete the final three-dimensional network structure.

[0117] There are no particular limitations on the contact described herein; the pre-reactant can be coated onto the polymer matrix or blended with the polymer matrix. Coating here also includes allowing the pre-reactant to penetrate deep into the polymer matrix.

[0118] Furthermore, after obtaining component (A) as described above, it can be mixed with the lithium salt of component (B) to obtain the final solid electrolyte. In some preferred embodiments, the latent curing agent of component (A4) in component (A) can be added after mixing components (A1), (A2), (A3) and (B) to obtain the final solid electrolyte.

[0119] The final solid electrolyte can be pre-encapsulated using any optional method.

[0120] In some specific implementations, the preparation method further includes the step of forming a film from the solid electrolyte. The film forming method can be a solution coating method, an extrusion casting method, or other film forming methods.

[0121] In some more specific embodiments, the solution coating method includes applying a solution onto a substrate and drying it, then removing the substrate to obtain a film-like polymer solid electrolyte. The substrate is not particularly limited; for example, it can be a glass substrate, ceramic substrate, stainless steel substrate, plastic substrate, etc. For drying temperature and time, drying can be performed, for example, in a vacuum drying oven at 50–100°C, preferably 60–80°C, for 4–10 hours, preferably 4–8 hours. After drying, a thin film is obtained on the substrate. Peeling the film off the substrate (i.e., removing the substrate) yields the film-like polymer solid electrolyte. Alternatively, the obtained film-like polymer solid electrolyte can be cut into suitable shapes and sizes as needed, for example, into circular electrolyte sheets with a diameter of Φ16 mm.

[0122] 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.

[0123] <Third aspect>

[0124] A fourth aspect of the present invention provides a lithium secondary battery, particularly a lithium secondary battery comprising or using the polymer solid electrolyte of the first aspect of the present invention or the polymer solid electrolyte prepared according to the preparation method of the second aspect of the present invention.

[0125] Such a secondary battery includes at least a positive electrode, a negative electrode, and a solid electrolyte.

[0126] In addition, the positive electrode in the battery can be a lithium oxide doped with common transition metals, specifically, it can be a lithium oxide doped with transition metals such as Mn, Co, Al, Fe and Ni; preferably, the positive electrode can be an NCM or NCA positive electrode.

[0127] There are no particular restrictions on the negative electrode; it can be a negative electrode commonly used in solid polymer batteries. Preferably, the negative electrode is a lithium negative electrode.

[0128] Example

[0129] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0130] Example 1

[0131] Purchased PVA-g-PEO (PVA to PEO molar ratio 1:10), toluene diisocyanate, and lithium bis(fluorosulfonyl)imide (LiFSI) were dissolved in dimethylformamide, and then triethylenediamine was added to obtain a mixture. The molar ratio of PVA-g-PEO (based on PVA as the structural unit), toluene diisocyanate, and triethylenediamine in the mixture was 1:0.02:0.2, with a PVA concentration of 20 g / L and a LiFSI concentration of 10%. The mixture was heated under anhydrous and oxygen-free conditions to obtain a polymer solid electrolyte membrane.

[0132] Example 2

[0133] Purchased PVA-g-PEO (PVA to PEO molar ratio 1:10), toluene diisocyanate, and lithium bis(fluorosulfonyl)imide (LiFSI) were dissolved in dimethylformamide, and then triethylenediamine was added to obtain a mixture. The molar ratio of PVA-g-PEO (based on PVA as the structural unit), toluene diisocyanate, and triethylenediamine in the mixture was 1:0.044:0.2, with a PVA concentration of 20 g / L and a LiFSI concentration of 10%. The mixture was heated under anhydrous and oxygen-free conditions to obtain a polymer solid electrolyte membrane.

[0134] Example 3

[0135] Purchased PVA-g-PEO (PVA to PEO molar ratio 1:10), toluene diisocyanate, and lithium bis(fluorosulfonyl)imide (LiFSI) were dissolved in dimethylformamide, and then triethylenediamine was added to obtain a mixture. The molar ratio of PVA-g-PEO (based on PVA as the structural unit), toluene diisocyanate, and triethylenediamine in the mixture was 1:0.02:0.4, with a PVA concentration of 20 g / L and a LiFSI concentration of 10%. The mixture was heated under anhydrous and oxygen-free conditions to obtain a polymer solid electrolyte membrane.

[0136] Example 4

[0137] Purchased PVA (PVA to PEO molar ratio 1:10), toluene diisocyanate, and lithium bis(fluorosulfonyl)imide (LiFSI) were dissolved in dimethylformamide, and then triethylenediamine was added to obtain a mixture. The molar ratio of PVA (based on PVA as the structural unit), toluene diisocyanate, and triethylenediamine in the mixture was 1:0.44:0.4, with a PVA concentration of 20 g / L and a LiFSI concentration of 10%. The mixture was heated and reacted under anhydrous and oxygen-free conditions, and then coated onto the negative electrode side of the PEO solid electrolyte to obtain a polymer solid electrolyte membrane.

[0138] Example 5

[0139] Purchased PVA (PVA to PEO molar ratio 1:10), toluene diisocyanate, and lithium bis(fluorosulfonyl)imide (LiFSI) were dissolved in dimethylformamide, and then triethylenediamine was added to obtain a mixture. The molar ratio of PVA (based on PVA as the structural unit), toluene diisocyanate, and triethylenediamine in the mixture was 1:0.1:0.2, with a PVA concentration of 20 g / L and a LiFSI concentration of 10%. The mixture was heated and reacted under anhydrous and oxygen-free conditions, and then directly blended with PEO solid electrolyte to obtain a polymer solid electrolyte membrane.

[0140] Example 6

[0141] Purchased PVA-g-PEO (PVA to PEO molar ratio 1:5), toluene diisocyanate, and lithium bis(fluorosulfonyl)imide (LiFSI) were dissolved in dimethylformamide, and then triethylenediamine was added to obtain a mixture. The molar ratio of PVA-g-PEO (based on PVA as the structural unit), toluene diisocyanate, and triethylenediamine in the mixture was 1:0.02:0.2, with a PVA concentration of 20 g / L and a LiFSI concentration of 10%. The mixture was heated under anhydrous and oxygen-free conditions to obtain a polymer solid electrolyte membrane.

[0142] Example 7

[0143] The difference from Example 1 is that toluene diisocyanate is replaced with diphenylmethane diisocyanate (MDI).

[0144] Comparative Example 1

[0145] Purchased PVA-g-PEO (PVA to PEO molar ratio 1:10) was dissolved in dimethylformamide with toluene diisocyanate and lithium bis(fluorosulfonyl)imide (LiFSI) to obtain a mixture. The molar ratio of PVA-g-PEO (based on PVA as the structural unit) to toluene diisocyanate in the mixture was 1:0.044, with a PVA concentration of 20 g / L and a LiFSI concentration of 10%. The mixture was heated and reacted under anhydrous and oxygen-free conditions to obtain a polymer solid electrolyte membrane.

[0146] Comparative Example 2

[0147] The purchased PVA-g-PEO (PVA to PEO molar ratio 1:10) was used directly as the solid electrolyte.

[0148] Comparative Example 3

[0149] The difference from Example 1 is that triethylenediamine is not used.

[0150] Performance testing

[0151] 1. Ionic conductivity

[0152] The ionic conductivity of the polymer solid electrolyte membranes in the embodiments and comparative examples was measured using the four-electrode method, and the test results are shown in Table 1.

[0153] 2. Ion transfer number

[0154] The polymer solid electrolyte membranes from the embodiments and comparative examples were assembled into CR2032 button-type Li|electrolyte|Li symmetric cells. Then, the electrochemical impedance spectroscopy (EIS) and DC polarization were measured using the potentiostatic chronoamperometry method to obtain the ion transfer number. The test results are shown in Table 1.

[0155] 3. Battery cycle performance

[0156] The polymer solid electrolyte membranes from the embodiments and comparative examples were assembled into CR2032 type button-type NCM811 cathode|electrolyte|Li batteries, and their cycle stability was tested at a current density of 0.33C / 0.33C. The test was terminated at 80% SOH, and the test results are shown in Table 1.

[0157] Table 1 Performance test results of the examples and comparative examples

[0158]

[0159] As shown in Table 1, and comparing Examples 1-7 with Comparative Example 2, it can be seen that by adjusting the ratio between the polymer matrix and the polyol and introducing appropriate amounts of diisocyanate and latent curing agent, the ion transport performance and cycle performance of solid electrolytes can be effectively improved, thereby enhancing the electrochemical performance and lifespan of solid batteries.

[0160] The comparison between Comparative Examples 1 and 3 and Comparative Example 2 shows that although introducing diisocyanate into PVA-g-PEO can improve the ion transport performance and cycle performance of solid electrolytes to some extent, the improvement is limited. By further introducing a latent curing agent (Example 1), the ionic conductivity of polymer solid electrolytes and the cycle performance of batteries can be significantly improved.

[0161] It should be noted that although the technical solution of the present invention has been described with specific examples, those skilled in the art will understand that the present invention should not be limited thereto.

[0162] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A polymer solid electrolyte, characterized in that, The polymer solid electrolyte comprises a modified polymer matrix as component A and a lithium salt as component B. Wherein, the polymer matrix A1 in the modified polymer matrix as component A includes repeating units having the following structure (1): -RO- (1) Wherein, R represents a straight-chain or branched alkylene group having 2 to 5 carbon atoms. The modification includes forming a three-dimensional network structure between the polyol (component A3) and the polymer matrix A1 by means of a polyisocyanate component (component A2), and the formation of the three-dimensional network structure is at least partially carried out in the presence of a latent curing agent (component A4). Wherein, the polymer matrix A1 includes polyoxyethylene, The component A4 latent curing agent can decompose to produce hydroxyl and / or amino groups under ambient humidity.

2. The polymer solid electrolyte according to claim 1, characterized in that, The polyisocyanate component of component A2 includes one or more of aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates.

3. The polymer solid electrolyte according to claim 1 or 2, characterized in that, The polyol of component A3 includes polymeric polyols with hydroxyl groups on their side chains.

4. The polymer solid electrolyte according to claim 3, characterized in that, The polyol of component A3 includes at least one of polyvinyl alcohol and ethylene-vinyl alcohol copolymer.

5. The polymer solid electrolyte according to claim 1 or 2, characterized in that, In the modified polymer matrix component A, the molar ratio of the amount derived from component A3 to the amount derived from polymer matrix A1 is 1:4 to 1:12; and / or, In the modified polymer matrix component A, the molar ratio of the amount of component A3 to the amount of polyisocyanate from component A2 is 1:0.02 to 1:0.

44. And / or, In the modified polymer matrix component A, the molar ratio of the amount of component A3 to the amount of latent curing agent from component A4 is 1:0.2 to 1:0.

4.

6. The polymer solid electrolyte according to claim 1 or 2, characterized in that, The modification is performed by one of the following methods: a. Grafting component A3 polyol with polymer matrix A1 to obtain grafted product, and then forming the three-dimensional network structure in the presence of component A2 polyisocyanate component and component A4 latent curing agent; b. The polyol component A3 is reacted with the polyisocyanate component A2 to obtain a pre-reactant, and then the pre-reactant is reacted with the polymer matrix A1 in the presence of the latent curing agent component A4 to form the three-dimensional network structure.

7. The solid electrolyte according to claim 6, characterized in that, In method a, the grafting reaction yields a comb-shaped graft with polymer-based molecular chains as side chains; in method b, the pre-reactant is coated onto the polymer-based material or the pre-reactant is blended with the polymer-based material.

8. A lithium secondary battery, characterized in that, The lithium secondary battery includes the polymer solid electrolyte according to any one of claims 1 to 7.

9. The lithium secondary battery according to claim 8, characterized in that, The lithium secondary battery is an all-solid-state electrolyte lithium secondary battery.

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