Solid polymer electrolyte and solid secondary battery

Abstract

The invention provides a solid polymer electrolyte capable of working in a wide temperature range. The solid polymer electrolyte is obtained by carrying out in-situ polymerization on a precursor solution on the surface of a base material, wherein the precursor solution is prepared from a first type of polymeric monomer, a second type of polymeric monomer, an initiator and electrolyte salt; the first polymeric monomer is an electron donor, and the electron donor is at least one of cyclic ether and olefin monomers; the second polymeric monomer is an electron acceptor, and the electron acceptor is one or more of cyclic ester, olefin monomers and anhydride monomers. The solid polymer electrolyte keeps good mechanical performance and high ionic conductivity in a wide temperature range, and an assembled solid secondary battery has good electrical performance and cycling stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and particularly relates to solid polymer electrolytes and solid secondary batteries. Background Art

[0002] Facing the temperature fluctuations caused by global climate change, along with the development of the electric vehicle and renewable energy industries, in order to meet the demands of modern technology for high-performance batteries and significantly enhance the applicability and reliability of batteries in various strict working environments, it is urgent to research wide-temperature batteries. A wide-temperature battery refers to a battery that can work efficiently within a relatively wide temperature range and maintain stable performance. Such a battery still has good charge and discharge characteristics under extreme temperature conditions (such as high temperature or low temperature) and is suitable for a variety of application scenarios, such as military and aerospace applications, outdoor and polar expeditions, electric vehicles, smart grids, outdoor electronic products, etc.

[0003] There are still several challenges in the development of wide-temperature batteries. For example, the ionic conductivity of the electrolyte usually drops significantly at low temperatures, the battery performance severely deteriorates, and the electrochemical reaction rates and stabilities of electrode materials are different in high and low temperature environments. To address the problem of low ionic conductivity of the electrolyte at low temperatures, optimizing the material composition, modifying or decorating the electrolyte material are common solutions. For example, selecting electrolyte salts with high ionic conductivity, doping different electrolyte components, cross-linking and blending composites, etc., to modify polymer electrolytes, improve crystal structures, and prepare functional electrolytes. The main problem faced by the electrolyte at high temperatures is the aggravation of side reactions, so the chemical stability and thermal stability of the electrolyte become particularly important.

[0004] Currently, most reports on low-temperature batteries are based on liquid electrolytes, but the use of liquid batteries still has safety hazards. Dendrites are easily formed at low temperatures, which not only greatly reduces the cycling performance of the lithium anode, increases concentration polarization, but also pierces the separator, leading to safety problems such as short circuits and fires. Replacing traditional liquid electrolytes with solid polymer electrolytes can overcome several problems brought by liquid electrolytes, avoid the growth of dendrites, and also avoid the leakage of liquid electrolytes, thereby improving the thermal stability, mechanical properties, safety, cycle life, and Coulomb efficiency of the battery; and it can also be fabricated into any shape and size, enabling lithium (sodium) ion batteries to develop in the direction of miniaturization and thinness.

[0005] However, solid polymer electrolytes usually have low ionic conductivity at low temperatures and are difficult to maintain a solid state at high temperatures, and cannot guarantee high mechanical properties, so their applications are limited. One of the earliest proposed classical polymer electrolytes is PEO [(CH 2 CH 2 O) n, due to its low room-temperature ionic conductivity, it is difficult to be used at room temperature and low temperature, and it is generally used under high-temperature conditions. However, the polymer PEO melts into a flowing state at high temperatures, unable to maintain its original size and mechanical properties, and it is difficult to inhibit the nucleation / growth of lithium dendrites at the negative electrode. Therefore, classical linear polymer electrolytes still face challenges at high temperatures. The reason why PEO still faces the problems of crystallization and low ionic conductivity at room temperature is that the structure of linear polymers is regular and the polymer molecular chains are prone to entanglement. Therefore, in order to solve the problems of low room-temperature conductivity, inapplicability at low temperatures, and high-temperature conditions of traditional linear polymer electrolytes, it is necessary to modify the polymer electrolyte, aiming to improve the movement ability of the chain segments, reduce the crystallinity and glass transition temperature of the polymer, so as to improve the ionic conductivity of the polymer electrolyte. Electron cloud modulation is one of the means to modify polymer electrolytes. By regulating the spatial distribution of electrons moving around the atomic nucleus, that is, the shape and distribution of the electron cloud, it can have an important impact on the chemical properties and physical characteristics of materials. The specific methods for electron cloud modulation of polymer electrolytes include structural designs such as branching, grafting, and crosslinking, making it less likely for polymer molecular chains to entangle, with lower viscosity, and the ionic conductivity of the polymer electrolyte is improved. However, there are still some problems with existing electron cloud modulation methods, and the main problem is that only the electron cloud distribution in local regions can be regulated. Summary of the Invention

[0006] This application provides a solid polymer electrolyte that can work over a wide temperature range, without the need to additionally add a plasticizer that does not participate in the polymerization reaction, and its polymer backbone presents a non-single-link structure.

[0007] To achieve the above object, this application proposes the following technical solutions: In the first aspect, an electron cloud modulation solid polymer electrolyte that can work over a wide temperature range is provided. The solid polymer electrolyte is obtained by in-situ polymerization of a precursor solution prepared from a first type of polymerization monomer, a second type of polymerization monomer, an initiator, and an electrolyte salt on the surface of a substrate. The first type of polymerization monomer is an electron donor, and the electron donor is at least one of a cyclic ether and an olefin monomer. The second type of polymerization monomer is an electron acceptor, and the electron acceptor is one or more of a cyclic ester, an olefin monomer, and an anhydride monomer. The first type of polymerization monomer and the second type of polymerization monomer are different substances.

[0008] Furthermore, the electron donor is at least one of a cyclic ether and an olefin monomer with electron-rich characteristics and C2~C7, and the olefin monomer contains one or more of an alkyl group, a cycloalkyl group, an amino group, a hydroxyl group, a mercapto group, and a derivative group. The molecular weight of the electron donor is 40~300.

[0009] Furthermore, the electron donor is ethylene oxide (C with group substitution or without substitution2 H 4 O), propylene oxide (C 3 H 6 O), isobutylene oxide (C 4 H 8 O), butylene oxide (C 4 H 8 O), epichlorohydrin (C 3 H 5 ClO), tetrahydrofuran (C 4 H 8 O), 1,3-dioxolane (C 3 H 6 O 2 ), 1,3-dioxane (C 4 H 8 O 2 ), trioxane (C 3 H 6 O 3 ), or one or more of the like; the substituent group is one or more of an alkyl group, a cycloalkyl group, an amino group, a hydroxyl group, a mercapto group, and a derivative group.

[0010] Furthermore, the electron acceptor is at least one of a cyclic ester, an olefin monomer, and an acid anhydride monomer having an electron-withdrawing property and C2 to C7, and the olefin monomer contains one or more of a carbonyl group, an aldehyde group, an ester group, and a derivative group; the molecular weight of the electron acceptor is 40 to 300.

[0011] Furthermore, the electron acceptor is ethylene carbonate (C 3 H 4 O 3 ), vinylene carbonate (C 3 H 2 O 3 ), propylene carbonate (C 4 H 6 O 3 ), glutaric anhydride (C 5 H 6 O 3 ), succinic anhydride (C 4 H 6 O 3 ), methyl methacrylate, or one or more of the like; the substituent group is one or more of a carbonyl group, an aldehyde group, an ester group, and a derivative group.

[0012] In a second aspect, there is provided a solid secondary battery including the aforementioned solid polymer electrolyte.

[0013] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: The solid polymer electrolyte provided by the present invention maintains good mechanical properties and high ionic conductivity within a wide temperature range, thus ensuring the normal use of solid-state lithium (sodium) secondary batteries under different temperature conditions. Compared with existing commercial liquid batteries, the solid-state polymer lithium (sodium) secondary battery prepared by the present invention has good safety, and the dendrite problem on the lithium negative electrode side at low temperature is suppressed, greatly improving the cycle life and Coulomb efficiency; compared with traditional solid polymer batteries, the solid polymer electrolyte of the present invention does not crystallize at low or normal temperature and still maintains high ionic conductivity, and does not melt or decompose at high temperature and still maintains high mechanical properties and safety.

[0014] The preparation method using electronic modulation in this invention can redistribute the electron cloud distribution of the polymer electrolyte from the molecular size, and improve the electrolyte properties by combining in-situ polymerization means. The method is simple, the reaction conditions are mild, and the prepared electrode solid polymer electrolyte has good interfacial compatibility, which is suitable for large-scale commercial applications. At the same time, the solid polymer electrolyte obtained by this invention is used in solid-state lithium (sodium) secondary batteries, which can broaden the applicable temperature range of the batteries, improve the safety and cycle stability of the batteries, and has good application prospects. Brief Description of the Drawings

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0016] Figure 1 It is a differential scanning calorimetry characterization diagram of the solid polymer electrolyte prepared in Example 1.

[0017] Figure 2 It is the electron cloud density distribution diagram of different chain segments of the solid polymer electrolyte prepared in Example 1.

[0018] Figure 3 It is the variation of the ionic conductivity of the solid polymer electrolyte prepared in Example 1 with temperature.

[0019] Figure 4 It is the SEM diagram after cycling at room temperature of the lithium metal negative electrode matched with the solid polymer electrolyte prepared in Example 1 and the lithium metal negative electrode matched with the liquid electrolyte prepared in Comparative Example 1.

[0020] Figure 5 It is the SEM diagram after cycling at low temperature of the lithium metal negative electrode matched with the solid polymer electrolyte prepared in Example 1 and the lithium metal negative electrode matched with the liquid electrolyte prepared in Comparative Example 1.

[0021] Figure 6 SEM images of the lithium metal anode paired with the solid polymer electrolyte prepared in Example 1 and the lithium metal anode paired with the liquid electrolyte prepared in Comparative Example 1 after cycling at high temperature.

[0022] Figure 7 Long cycle curves of the lithium-lithium symmetric cell paired with the solid polymer electrolyte prepared in Example 1 and the lithium-lithium symmetric cell paired with the liquid electrolyte prepared in Comparative Example 1 at a current density of 2 mA / cm 2 and an areal capacity of 2 mAh / cm 2 2.

[0023] Figure 8 Long cycle curves of the lithium-lithium symmetric cell paired with the solid polymer electrolyte prepared in Example 1 and the lithium-lithium symmetric cell paired with the liquid electrolyte prepared in Comparative Example 1 at -10 °C at a current density of 0.5 mA / cm 2 and an areal capacity of 0.5 mAh / cm 2 2.

[0024] Figure 9 Long cycle curves of the lithium-lithium symmetric cell paired with the solid polymer electrolyte prepared in Example 1 and the lithium-lithium symmetric cell paired with the liquid electrolyte prepared in Comparative Example 1 at 60 °C at a current density of 2 mA / cm 2 and an areal capacity of 2 mAh / cm 2 2.

[0025] Figure 10 Charge-discharge curves at low temperature of the lithium iron phosphate battery assembled with the solid polymer electrolyte prepared in Example 1 and the lithium iron phosphate battery assembled with the liquid electrolyte prepared in Comparative Example 1.

[0026] Figure 11 Charge-discharge curves at high temperature of the lithium iron phosphate battery assembled with the solid polymer electrolyte prepared in Example 1 and the lithium iron phosphate battery assembled with the liquid electrolyte prepared in Comparative Example 1.

[0027] Figure 12 Charge-discharge curves at low temperature of the lithium nickel cobalt manganese ternary metal oxide battery assembled with the solid polymer electrolyte prepared in Example 1 and the lithium nickel cobalt manganese ternary metal oxide battery assembled with the liquid electrolyte prepared in Comparative Example 1.

[0028] Figure 13 Charge-discharge curves at high temperature of the lithium nickel cobalt manganese ternary metal oxide battery assembled with the solid polymer electrolyte prepared in Example 1 and the lithium nickel cobalt manganese ternary metal oxide battery assembled with the liquid electrolyte prepared in Comparative Example 1. Detailed implementation manners

[0029] The applicant has found through research that by using electron donor polymerization monomers such as cyclic ethers and olefins and electron acceptor polymerization monomers such as cyclic esters, olefins, and anhydrides as raw materials for polymerization monomers, combining the means of electron cloud modulation with in-situ polymerization, the electron cloud of polymer molecules is rearranged at the molecular level, obtaining a solid polymer electrolyte that maintains good mechanical properties and high ionic conductivity within a wide temperature range, ensuring that the battery can be used at both high and low temperatures. This solid polymer electrolyte will not melt at high temperatures and can maintain a solid morphology for use, and can inhibit the generation of electrolyte side reactions, significantly broadening the scope of application and solving the problem that most current solid polymer electrolytes cannot be used at room temperature or low temperatures. Based on this, the present invention has been completed.

[0030] Specifically, the present invention provides an electron cloud modulation solid polymer electrolyte that can operate within a wide temperature range. The solid polymer electrolyte is obtained by in-situ polymerization of a precursor solution prepared from a first type of polymerization monomer, a second type of polymerization monomer, an initiator, and an electrolyte salt on the surface of a substrate. The first type of polymerization monomer is an electron donor, and the electron donor is a cyclic ether and / or an olefin monomer. The second type of polymerization monomer is an electron acceptor, and the electron acceptor is one or more of a cyclic ester, an olefin monomer, and an anhydride monomer.

[0031] Specifically, the provided electron cloud modulation solid polymer electrolyte that can operate within a wide temperature range has polymerization monomers with different types of electron cloud distributions, and the polymer backbone is composed of multiple chain segments with different electron cloud density distributions. Specifically, the chain segments of the polymer backbone are composed of more than one type of chain segment structure, and the electron cloud distribution (electrostatic potential) within each chain segment is different.

[0032] In-situ polymerization refers to an in-situ cationic polymerization, in-situ anionic polymerization, or in-situ radical polymerization reaction of different types of polymerization monomers initiated by an initiator.

[0033] The substrate can be selected from key materials and components used in lithium (sodium) secondary batteries, including but not limited to a metallic lithium (sodium) negative electrode, a graphite-based or other conductive carbon negative electrode, a silicon-based negative electrode, a germanium-based negative electrode, a tin-based negative electrode, a phosphorus-based negative electrode, an antimony-based negative electrode, a metal oxide negative electrode, a metal sulfide negative electrode, a metal nitride negative electrode, a lithium titanate negative electrode, a commercial separator (such as a polypropylene (PP) film, a polyethylene (PE) film, a PP / PE composite film, a PP / PE / PP composite film, etc.), a modified separator, a metal current collector (such as a copper foil, an aluminum foil, a nickel foam, etc.), a carbon current collector, a ternary material positive electrode, a lithium cobaltate positive electrode, a lithium iron phosphate positive electrode, a lithium manganese oxide positive electrode, a metal fluoride positive electrode, etc.).

[0034] In some preferred embodiments, the electron donor is an organic compound having electron-rich properties (i.e., having Lewis basicity) and C2-C7 (at least one of cyclic ethers and olefin monomers), the olefin monomer contains one or more of alkyl, cycloalkyl, amino, hydroxyl, mercapto and derivative groups, and the molecular weight of the electron donor is 40-300; the electron donor is further preferably ethylene oxide (C 2 H 4 O), propylene oxide (C 3 H 6 O), isobutylene oxide (C 4 H 8 O), butylene oxide (C 4 H 8 O), epichlorohydrin (C 3 H 5 ClO), tetrahydrofuran (C 4 H 8 O), 1,3-dioxolane (C 3 H 6 O 2 ), 1,3-dioxane (C 4 H 8 O 2 ), trioxane (C 3 H 6 O 3 ), tri(ethylene glycol) divinyl ether, or one or more thereof; the substituent group is one or more of alkyl, cycloalkyl, amino, hydroxyl, mercapto and derivative groups.

[0035] In some preferred embodiments, the electron acceptor is an organic compound having electron-deficient properties (Lewis acidity) and C2-C7 (at least one of cyclic esters, olefin monomers and acid anhydride monomers), wherein the olefin monomer contains one or more of carbonyl, aldehyde, ester and derivative groups, and the molecular weight of the electron acceptor is 40-300; the electron acceptor is further preferably ethylene carbonate (C 3 H 4 O 3 ), vinylene carbonate (C 3 H 2 O 3 ), propylene carbonate (C 4 H 6 O 3 ), glutaric anhydride (C 5 H 6 O 3 ), succinic anhydride (C 4 H 6 O 3), one or more of methyl methacrylate; the substituent groups are one or more of carbonyl, aldehyde, ester group and derivative groups.

[0036] In some preferred embodiments, the molecular weight of the solid polymer electrolyte is 1,000 to 50,000, preferably 3,000 to 20,000, such as 3,000, 4,000, 5,000, 6,000, 7,000, 8,000, 9,000, 10,000, 11,000, 12,000, 13,000, 14,000, 15,000, 16,000, 17,000, 18,000, 19,000, 20,000, etc.

[0037] In some preferred embodiments, the electrolyte salt is a lithium ion compound salt or a sodium ion compound salt.

[0038] In some preferred embodiments, the lithium ion compound salt is lithium trifluoromethanesulfonate (LiCF 3 SO 2 ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF 3 SO 2 ), lithium perchlorate (LiClO 2 ), lithium bis(oxalato)borate (LiBOB), lithium chloride (LiCl), lithium iodide (LiI) and their analogs, derivatives; further preferably one or two of lithium trifluoromethanesulfonate and lithium bis(trifluoromethanesulfonyl)imide. 4 )

[0039] In some preferred embodiments, the sodium ion compound salt is sodium perchlorate (NaClO 4 ), sodium trifluoromethanesulfonate (NaCF 3 SO 2 ), sodium bis(trifluoromethanesulfonyl)imide (NaN(CF 3 SO 2 ), sodium chloride (NaCl), sodium iodide (NaI), sodium fluoride (NaF) and their analogs, derivatives; further preferably sodium perchlorate. 2 )

[0040] In some preferred embodiments, in the precursor solution, the concentration of the electrolyte salt is 0.1 to 10 mol / L, preferably 1.0 to 3.0 mol / L, such as 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.5 mol / L, 2.8 mol / L, 3.0 mol / L, etc.

[0041] In some preferred embodiments, the initiator is a first - type initiator or a second - type initiator; the first - type initiator is a non - lithium - salt and non - sodium - salt initiator; the second - type initiator is a lithium - salt initiator or a sodium - salt initiator. When the assembled battery is a sodium - ion battery, the initiator used is a sodium - salt initiator, and when the assembled battery is a lithium - ion battery, the initiator used is a lithium - salt initiator.

[0042] The first - type initiator is boron trifluoride diethyl ether (BF 3 ·C 2 H 5 OC 2 H 5 ), phosphorus pentafluoride (PF 5 ), aluminum trifluoromethanesulfonate ((CF 3 SO 3 ), 3 sodium ethoxide (CH 3 CH 2 ONa), benzoyl peroxide (BPO), azobisisobutyronitrile (AIBN), or one or more of them.

[0043] The second - type initiator is lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium difluoro(oxalato)borate (LiDFOB), sodium hexafluorophosphate (NaPF 6 ), or one or more of them.

[0044] In some preferred embodiments, in the precursor solution, the mass fraction of the first - type initiator is 0.1% - 20%, preferably 0.1% - 5%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3.0%, 3.2%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5%, 4.8%, 5.0%, etc.

[0045] In some preferred embodiments, in the precursor solution, the concentration of the second - type initiator is 0.1 - 10 mol / L, preferably 1.0 - 3.0 mol / L, such as 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, 2.2 mol / L, 2.5 mol / L, 2.8 mol / L, 3.0 mol / L, etc.

[0046] In some preferred embodiments, the molar amount of the first type of polymerizable monomer accounts for no less than 50% of the total molar amount of the first type and the second type of polymerizable monomers, more preferably 50% to 95%, such as 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc.; the total molar amount of the second type of polymerizable monomers accounts for no more than 50% of the total molar amount of the first type and the second type of polymerizable monomers, more preferably 5% to 50%, such as 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc. In some embodiments, the polymerizable monomer A 1 :A 2 :A 3 :...A n (n = 2, 3...) has a molar ratio of 1:(0.05 to 1):(0.05 to 1):...(0.05 to 1), that is, the polymerizable monomer comprises two or more substances, and the molar ratio of one of the substances in the polymerizable monomer to each of the other substances is within the range of 1:(0.05 to 1).

[0047] In some preferred embodiments, the temperature of the in-situ polymerization is 0 to 60 °C, preferably 20 to 40 °C, such as 20 °C, 22 °C, 25 °C, 28 °C, 30 °C, 32 °C, 35 °C, 38 °C, 40 °C, etc. The time of the in-situ polymerization is 0.5 to 120 h, preferably 3 to 24 h, such as 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, 24 h, etc.

[0048] In some preferred embodiments, the operating temperature range of the solid polymer electrolyte is -65 to 100 °C, such as -65 °C, -60 °C, -55 °C, -50 °C, -45 °C, -40 °C, -35 °C, -30 °C, -25 °C, -20 °C, -15 °C, -10 °C, -5 °C, 0 °C, 5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, etc., more preferably -20 to 60 °C; the range of the room temperature ionic conductivity is 1.0×10 -6 ~1.0×10 -3 S / cm, more preferably 1.0×10 -4 ~1.0×10 -3 S / cm, such as 1.0×10 -4 S / cm, 2.0×10 -4 S / cm, 3.0×10 -4S / cm, 4.0×10 -4 S / cm, 5.0×10 -4 S / cm, 6.0×10 -4 S / cm, 7.0×10 -4 S / cm, 8.0×10 -4 S / cm, 9.0×10 -4 S / cm, 1.0×10 -3 S / cm, etc.

[0049] The present invention also provides a solid-state secondary battery, including the above-mentioned electronically cloud-modulated solid polymer electrolyte capable of operating over a wide temperature range.

[0050] The electronically cloud-modulated solid polymer electrolyte provided by the present invention can maintain high mechanical properties and high ionic conductivity within a wide temperature range (-65~100 o °C). Compared with traditional solid polymer electrolytes, this solid polymer electrolyte has low crystallinity and high ionic conductivity at low temperatures, can meet the kinetic requirements of electrochemical reactions at low temperatures, and will not melt or decompose at high temperatures, can maintain the morphology and mechanical properties at room temperature, and inhibit the occurrence of side reactions. Moreover, the present invention modulates the electronic cloud of the polymer by means of in-situ polymerization, that is, two types of polymer monomers and initiators are added to the electrolyte in a certain proportion and mixed evenly, and polymerization is initiated under certain external conditions, so as to complete the preparation and battery assembly in one step. The reaction conditions are mild, suitable for large-scale production, effectively reduce the production cost and improve the production efficiency, and can also ensure sufficient contact between the electrolyte and the electrode, with small interfacial polarization, and avoid a large amount of waste of solvents, preventing environmental pollution caused by solvent escape. Using the solid polymer electrolyte of the present invention to construct a solid-state lithium (sodium) secondary battery can effectively broaden the working temperature range of the battery and solve many problems of the lithium (sodium) secondary battery system based on liquid electrolyte within a wide temperature range, such as the dendrite problem of the lithium metal negative electrode and the side reaction problem between the electrolyte and the electrode, and improve the safety and cycle stability of the battery under extreme working conditions.

[0051] To facilitate the understanding of the present invention, the following will describe the present invention more comprehensively and meticulously in conjunction with the accompanying drawings of the specification and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0052] Example 1 I. Assemble a solid polymer lithium metal symmetric battery: Step 1) Prepare a bare battery cell: Stack lithium sheets, the separator Celgard and lithium sheets in sequence in the electrode case under high-purity argon to form a bare battery cell.

[0053] Step 2) Preparation of polymer precursor solution: The polymer precursor solution is prepared under high-purity argon. First, the polymerization monomers 1,3-dioxolane (C 3 H 6 O 2 ), propylene carbonate (C 4 H 6 O 3 ), and vinylene carbonate (C 3 H 2 O 3 ) (volume ratio 7:2:1) are added, and then the lithium salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with a concentration of 1 mol·L -1 is added. Finally, the initiator lithium difluoro(oxalato)borate (LiDFOB) with a concentration of 1 mol·L -1 is added. After stirring and mixing evenly, the polymer precursor solution is obtained. After injecting it into the battery cell, it reacts at room temperature (25 °C) for 24 hours to polymerize into polymer macromolecules. The differential scanning calorimetry characterization diagram is as shown in Figure 1 . It can be seen from Figure 1 that different from the traditional crystalline polymer electrolytes, the solid polymer electrolyte obtained in Example 1 shows an amorphous state, without a melting peak, but shows a glass transition temperature. The electron cloud density distribution diagrams of different segments of the prepared solid polymer electrolyte are as shown in Figure 2 . It can be seen from the color difference in Figure 2 that there is a large difference in the electron cloud distribution density between the electron donor and the electron acceptor, which is beneficial to the progress of the polymerization reaction and the rearrangement of the electron cloud density of the total polymer chain segments. The variation of the ionic conductivity of the prepared solid polymer electrolyte with temperature is as shown in Figure 3 . It can be seen from Figure 3 that the degree of variation of the ionic conductivity of the solid polymer electrolyte with temperature is small, and it shows a high ionic conductivity even at low temperatures, with the ionic conductivity ranging from 4 to 28 mS / cm.

[0054] Step 3) Liquid injection and in-situ polymerization: The polymer precursor solution obtained in Step 2) is injected into the bare battery cell. After the battery cell is fully infiltrated, the battery case is completely sealed. After standing at room temperature (25 °C) for 24 hours for in-situ polymerization to be completed, a solid polymer metal lithium symmetric battery is obtained.

[0055] Performance test of solid polymer metal lithium symmetric battery: 1. Performance test of solid polymer metal lithium symmetric battery The obtained solid polymer metal lithium symmetric battery is subjected to constant current charge and discharge tests at room temperature, low temperature (-10 °C), and high temperature (60 °C) on a charge and discharge tester. The current density of the constant current charge and discharge is 1 mA / cm 2 , and the cycle capacity is 1 mAh / cm2 The test results of the obtained battery are listed in Table 1.

[0056] 2. Morphology Characterization of Lithium Metal Anode after Cycling After the above-mentioned solid polymer lithium metal symmetric battery was cycled 100 times, the battery was disassembled in an argon glove box, and the dendritic growth on the surface of the lithium metal anode was observed with a cold field emission scanning electron microscope (SEM). The test statistical results are listed in Table 1.

[0057] II. Assembly of Solid Polymer Lithium Nickel Cobalt Manganese Ternary Metal Battery: Step 1) Preparation of bare battery cell: Weigh NCM523, Super P, and PVDF according to a mass ratio of 80:10:10, add N-methylpyrrolidone (NMP) and grind them for mixing, coat a positive electrode film on aluminum foil, and after drying, stack the positive electrode film, separator Celgard, and lithium sheet in sequence in the electrode shell under high-purity argon to form a bare battery cell.

[0058] Step 2) and Step 3) are exactly the same as Step 2) and Step 3) for assembling the solid polymer lithium metal symmetric battery.

[0059] Electrochemical Performance Test of Solid Polymer Lithium Nickel Cobalt Manganese Ternary Metal Battery: The above-assembled battery was subjected to charge and discharge tests at room temperature on a charge and discharge tester. The test voltage range was 2.5 - 4 V. The battery capacity and charge and discharge rate were calculated based on the mass of the active material lithium iron phosphate. The battery was subjected to charge and discharge cycles at a rate of 0.1 C at low temperature (-10 °C), room temperature (25 °C), and high temperature (60 °C), and the test results are listed in Table 2.

[0060] III. Assembly of Solid Polymer Lithium Iron Phosphate Metal Battery: Step 1) Preparation of bare battery cell: Weigh LiFePO 4 , Super P, and PVDF according to a mass ratio of 80:10:10, add N-methylpyrrolidone (NMP) and grind them for mixing, coat a positive electrode film on aluminum foil, and after drying, stack the positive electrode film, separator Celgard, and lithium sheet in sequence in the electrode shell under high-purity argon to form a bare battery cell.

[0061] Step 2) and Step 3) are exactly the same as Step 2) and Step 3) for assembling the solid polymer lithium metal symmetric battery.

[0062] Electrochemical Performance Test of Solid Polymer Lithium Iron Phosphate Metal Battery: The above-assembled battery was subjected to charge and discharge tests at room temperature on a charge and discharge tester. The test voltage range was 2.5 - 4 V. The battery capacity and charge and discharge rate were calculated based on the mass of the active material lithium nickel cobalt manganese ternary (LiNi 0.5 Co 0.2 Mn0.3 O 2 ) The quality calculation. The battery is charged and discharged cyclically at a rate of 0.1C at low temperature (-10°C), room temperature (25°C), and high temperature (60°C). The test results are listed in Table 3.

[0063] Example 2 The difference between this example and Example 1 is only that the volume ratio of the polymerization monomers 1,3-dioxolane (C 3 H 6 O 2 ), propylene carbonate (C 4 H 6 O 3 ), and vinylene carbonate (C 3 H 2 O 3 ) is different. In this example, the volume ratio of 1,3-dioxolane (C 3 H 6 O 2 ) to propylene carbonate (C 4 H 6 O 3 ) and vinylene carbonate (C 3 H 2 O 3 ) is 5:4:1.

[0064] The test performance of the assembled battery is listed in Tables 1, 2, and 3.

[0065] Example 3 The difference between this example and Example 1 is only that the type of initiator is different. Specifically, the initiator is lithium hexafluorophosphate.

[0066] The test performance of the assembled battery is listed in Tables 1, 2, and 3.

[0067] Example 4 The difference between this example and Example 1 is only that the polymerization monomer is different. In this example, the polymerization monomers are 1,3-dioxolane (C 3 H 6 O 2 ), ethylene carbonate (C 3 H 4 O 3 ), and vinylene carbonate (C 3 H 2 O 3 ), and the volume ratio of 1,3-dioxolane (C 3 H 6 O 2 ) to ethylene carbonate (C 3 H 4 O 3 ) and vinylene carbonate (C3 H 2 O 3 ) has a volume ratio of 7:2:1.

[0068] The test performances of the assembled batteries are listed in Tables 1, 2, and 3.

[0069] Example 5 The difference between this example and Example 1 is only that the polymerization monomers are different. In this example, the polymerization monomers are trioxane, propylene carbonate, and vinylene carbonate, and the volume ratio of trioxane, propylene carbonate, and vinylene carbonate is 7:2:1.

[0070] The test performances of the assembled batteries are listed in Tables 1, 2, and 3.

[0071] Example 6 The difference between this example and Example 4 is only that the initiator concentration is different. In this example, the initiator concentration is 2 mol / L.

[0072] The test performances of the assembled batteries are listed in Tables 1, 2, and 3.

[0073] Example 7 The difference between this example and Example 1 is that the polymerization monomers are different. In this example, the polymerization monomers are 1,3-dioxolane and glutaric anhydride, and the volume ratio of 1,3-dioxolane and glutaric anhydride is 7:3.

[0074] The test performances of the assembled batteries are listed in Tables 1, 2, and 3.

[0075] Example 8 The differences between this example and Example 1 are that the polymerization monomers and the initiator are different. In this example, the polymerization monomers are tri(ethylene glycol) divinyl ether and methyl methacrylate, and the volume ratio of tri(ethylene glycol) divinyl ether and methyl methacrylate (MMA) is 7:3. In this example, the initiator is azobisisobutyronitrile (AIBN), and the addition amount of azobisisobutyronitrile (AIBN) is 1% of the mass of the polymer precursor solution.

[0076] The test performances of the assembled batteries are listed in Tables 1, 2, and 3.

[0077] The relative molecular weights of the polymer macromolecules formed by polymerization in each example were detected by the following method, and the test results are shown in Table 4: The relative molecular weight (molecular weight distribution) of the high molecular compound was measured by a gel permeation chromatograph (Gel Permeation Chromatography, GPC). N,N-dimethylformamide was used as the solvent and mobile phase to measure the molecular weight of the sample. Its basic principle is to separate and analyze according to the difference in the migration rates of the polymer in chromatographic columns with different pore sizes.

[0078] Steps for measuring molecular weight by GPC: (1) Sample preparation: Dissolve the polymer sample in a suitable solvent and filter to remove insoluble substances.

[0079] (2) Column selection: Select a GPC column suitable for the test. The column type and size are selected according to the characteristics of the sample.

[0080] (3) Set the mobile phase: Use a suitable mobile phase (usually a solvent similar to the sample solvent) to ensure good separation effect.

[0081] (4) Sample injection: Inject the sample into the chromatographic system and start data collection.

[0082] (5) Detector: Commonly used detectors include refractive index detector (RI), ultraviolet detector (UV), etc., which are used to detect the signals of the samples passing through the column.

[0083] (6) Data analysis: Draw a control chart according to the response of the detector.

[0084] (7) Combine with standard samples (such as polystyrene standard) to calculate the relative molecular weight and degree of polymerization of the sample.

[0085] Comparative Example 1 Assemble a liquid lithium secondary battery using a traditional electrolyte: Prepare the electrolyte solution for the liquid battery: Under high-purity argon, mix 1,3-dioxolane (C 3 H 6 O 2 ), propylene carbonate (C 4 H 6 O 3 ), and vinylene carbonate (C 3 H 2 O 3 ) in a volume ratio of 7:2:1, and then add lithium salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) at a concentration of 1 mol·L -1 Stir and mix evenly to obtain the electrolyte solution for the liquid battery.

[0086] Assemble liquid metal lithium symmetric batteries, lithium iron phosphate metal lithium batteries, and nickel cobalt manganese ternary metal lithium batteries. Except that the preparation of the polymer precursor solution in Example 1 is changed to the preparation of the electrolyte solution for the liquid battery, other conditions are exactly the same. The test performances are listed in Tables 1, 2, and 3.

[0087] The SEM images of the symmetric cells assembled with the lithium metal anode matched with the solid polymer electrolyte prepared in Example 1 and the lithium metal anode matched with the liquid electrolyte prepared in Comparative Example 1 after 100 cycles at room temperature, low temperature, and high temperature are shown in Figure 4 , Figure 5 and Figure 6 respectively. It can be seen from Figures 4 - 6 that compared with the lithium battery assembled with the traditional liquid electrolyte, the surface of the lithium metal anode of the lithium battery assembled with the above solid polymer electrolyte is smoother and flatter after cycling at different temperatures. This indicates that the above solid polymer electrolyte can effectively improve the dendrite problem of the lithium metal anode.

[0088] The long-term cycling curves of the lithium-lithium symmetric cells assembled with the lithium matched with the solid polymer electrolyte prepared in Example 1 and the lithium-lithium symmetric cells assembled with the lithium matched with the liquid electrolyte prepared in Comparative Example 1 at room temperature with a current density of 2 mA / cm 2 and an areal capacity of 2 mAh / cm 2 are shown in Figure 7 ; the long-term cycling curves of the lithium-lithium symmetric cells assembled with the solid polymer electrolyte prepared in Example 1 and the lithium-lithium symmetric cells assembled with the liquid electrolyte prepared in Comparative Example 1 at -10 °C with a current density of 0.5 mA / cm 2 and an areal capacity of 0.5 mAh / cm 2 are shown in Figure 8 ; the long-term cycling curves of the lithium-lithium symmetric cells assembled with the solid polymer electrolyte prepared in Example 1 and the lithium-lithium symmetric cells assembled with the liquid electrolyte prepared in Comparative Example 1 at 60 °C with a current density of 2 mA / cm 2 and an areal capacity of 2 mAh / cm 2 are shown in Figure 9 . It can be seen from Figures 7 - 9 that compared with the lithium battery assembled with the traditional liquid electrolyte, the polarization voltage of the lithium battery assembled with the solid polymer electrolyte is more stable at different temperatures and is less likely to short-circuit.

[0089] The charge-discharge curves of the lithium iron phosphate battery assembled with the solid polymer electrolyte prepared in Example 1 and the lithium iron phosphate battery assembled with the liquid electrolyte prepared in Comparative Example 1 at low temperature and high temperature are shown in Figure 10 , Figure 11 respectively. The charge-discharge curves of the nickel-cobalt-manganese ternary metal lithium battery assembled with the solid polymer electrolyte prepared in Example 1 and the nickel-cobalt-manganese ternary metal lithium battery assembled with the liquid electrolyte prepared in Comparative Example 1 at low temperature and high temperature are shown in Figure 12 , Figure 13 respectively. It can be seen from Figures 10 - 13It can be seen that the discharge specific capacities of the lithium iron phosphate battery and the nickel cobalt manganese ternary metal lithium battery assembled with the solid polymer electrolyte prepared in Example 1 are significantly higher than those in Comparative Example 1 at both low and high temperatures. This indicates that compared with the lithium iron phosphate battery and the nickel cobalt manganese ternary metal lithium battery assembled with traditional liquid electrolytes, the lithium iron phosphate battery and the nickel cobalt manganese ternary metal lithium battery assembled with the solid polymer electrolyte have more excellent low-temperature and high-temperature performance.

[0090] Table 1 Performance of Lithium Metal Symmetric Batteries Table 2 High-Temperature and Low-Temperature Electrochemical Performance of Lithium Iron Phosphate Batteries Table 3 High-Temperature and Low-Temperature Electrochemical Performance of Nickel Cobalt Manganese Ternary Metal Lithium Batteries Table 4 Relative Molecular Weights of Polymer Macromolecules Prepared in Examples 1-8 As can be seen from Tables 1-3, compared with the batteries assembled in Example 1 and Comparative Example 1, the solid polymer electrolyte with electron cloud modulation obtained by in-situ polymerization from special monomers containing multiple functional groups shows a stronger lithium dendrite inhibition effect than the liquid electrolyte. Therefore, the lithium metal symmetric battery, the nickel cobalt manganese ternary metal lithium battery, and the lithium iron phosphate metal lithium battery assembled with this solid polymer electrolyte all exhibit higher electrochemical performance in a wide temperature range.

[0091] It can also be seen from Tables 1-3 that the batteries assembled with the solid polymer electrolytes prepared in each example have good electrochemical performance and cycling performance at room temperature, low temperature, and high temperature. In summary, the present invention uses the selection of polymerization monomer types, polymerization monomer ratios, lithium salts, and initiators, and prepares an electron cloud modulation solid polymer electrolyte with a wide operating temperature range and high ionic conductivity by in-situ polymerization. The assembled solid lithium (sodium) secondary battery shows high discharge capacity and Coulomb efficiency both at high and low temperatures, and has obvious advantages compared with liquid batteries or solid polymer batteries prepared by traditional methods. Thus, the present invention provides a simple and low-cost method to prepare an electron cloud modulation solid polymer electrolyte that can work in a wide temperature range, and makes the assembled battery show higher environmental temperature adaptability, safety, and cycling stability, with excellent application prospects.

[0092] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A solid polymer electrolyte, characterized in that The solid electrolyte is obtained by in-situ polymerization on the surface of a substrate using a precursor solution prepared with a first type of polymerizable monomer, a second type of polymerizable monomer, an initiator and an electrolyte salt; the first type of polymerizable monomer is an electron donor, which is at least one of a cyclic ether and an olefin monomer; the second type of polymerizable monomer is an electron acceptor, which is one or more of a cyclic ester, an olefin monomer and an anhydride monomer, and the first type of polymerizable monomer and the second type of polymerizable monomer are different substances.

2. The solid polymer electrolyte according to claim 1, characterized in that The electron donor is at least one of a cyclic ether and an olefin monomer having electron-rich properties and C2-C7, wherein the olefin monomer contains one or more of an alkyl group, a cycloalkyl group, an amino group, a hydroxyl group, a thiol group and a derivative group; the molecular weight of the electron donor is 40-300; Preferably, the electron donor is one or more of substituted or unsubstituted ethylene oxide (C2H4O), propylene oxide (C3H6O), isobutylene oxide (C4H8O), butylene oxide (C4H8O), epichlorohydrin (C3H5ClO), tetrahydrofuran (C4H8O), 1,3-dioxolane (C3H6O2), 1,3-dioxane (C4H8O2), trioxymethylene (C3H6O3), tri(ethylene glycol) divinyl ether; the substituted group is one or more of alkyl, cycloalkyl, amino, hydroxyl, thiol and derivative groups.

3. The solid polymer electrolyte according to claim 1, characterized in that The electron acceptor is at least one of a cyclic ester, an olefin monomer and an anhydride monomer having electron-deficient characteristics and C2-C7, wherein the olefin monomer contains one or more of a carbonyl group, an aldehyde group, an ester group and a derivative group; the molecular weight of the electron acceptor is 40-300; Preferably, the electron acceptor is one or more of substituted or unsubstituted ethylene carbonate (C3H4O3), vinylene carbonate (C3H2O3), propylene carbonate (C4H6O3), glutaric anhydride (C5H6O3), succinic anhydride (C4H6O3), and methyl methacrylate; the substituent group is one or more of a carbonyl group, an aldehyde group, an ester group, and a derivative group.

4. The solid polymer electrolyte according to claim 1, characterized in that The molecular weight of the solid polymer electrolyte is 1000-50000, preferably 3000-20000.

5. The solid polymer electrolyte according to claim 1, characterized in that The electrolyte salt is a lithium ion compound salt or a sodium ion compound salt; The lithium ion compound salt is one or more of lithium trifluoromethylsulfonate (LiCF3SO2), lithium bis(trifluoromethylsulfonyl)imide (LiN(CF3SO2)2), lithium perchlorate (LiClO4), lithium bis(oxalatoborate) (LiBOB), lithium chloride (LiCl), lithium iodide (LiI) and analogs and derivatives thereof; preferably, the lithium ion compound salt is one or two of lithium trifluoromethylsulfonate and lithium bis(trifluoromethylsulfonyl)imide; The sodium ion compound salt is one or more of sodium perchlorate (NaClO4), sodium trifluoromethanesulfonate (NaCF3SO2), sodium bis(trifluoromethylsulfonyl)imide (NaN(CF3SO2)2), sodium chloride (NaCl), sodium iodide (NaI), sodium fluoride (NaF) and their analogs and derivatives; preferably, the sodium ion compound salt is sodium perchlorate; In the precursor solution, the concentration of the electrolyte salt is 0.1-10 mol / L, preferably 1.0-3.0 mol / L.

6. The solid polymer electrolyte according to claim 1, characterized in that The initiator is a first type initiator or a second type initiator, the first type initiator is a non-lithium salt or non-sodium salt initiator, and the second type initiator is a lithium salt initiator or a sodium salt initiator; The first type of initiator includes at least one of boron trifluoride etherate (BF3·C2H5OC2H5), phosphorus pentafluoride (PF5), aluminum trifluoromethanesulfonate ((CF3SO3)3Al), sodium ethoxide (CH3CH2ONa), benzoyl peroxide (BPO), and azobisisobutyronitrile (AIBN); The second type of initiator includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiDFOB), and sodium hexafluorophosphate (NaPF6); In the precursor solution, the mass fraction of the first type of initiator is 0.1-20%, preferably 0.1-5%; In the precursor solution, the concentration of the second type of initiator is 0.1-10 mol / L, preferably 1.0-3.0 mol / L.

7. The solid polymer electrolyte according to claim 1, characterized in that The total molar amount of the first type of polymerizable monomers accounts for no less than 50% of the total molar amount of the first type of polymerizable monomers and the total molar amount of the second type of polymerizable monomers.

8. The solid polymer electrolyte according to claim 1, characterized in that The temperature of the in-situ polymerization is 0-60° C., preferably 20-40° C.; the time of the in-situ polymerization is 0.5-120 h, preferably 3-24 h.

9. The solid polymer electrolyte according to claim 1, characterized in that The operating temperature range of the solid polymer electrolyte is -65~100°C, preferably -20~60°C; the room temperature ionic conductivity range is 1.0×10 -6 ~1.0×10 -3 S / cm, preferably 1.0×10 -4 ~1.0×10 -3 S / cm.

10. A solid-state secondary battery, characterized in that: Comprising the solid polymer electrolyte as described in any one of claims 1 to 9.

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