A borate cross-linked self-healing polymer electrolyte, a preparation method and application thereof

Abstract

The application provides a preparation method of a borate crosslinking self-repairing polymer electrolyte, selects polyethylene glycol methyl ether methacrylate as a monomer, effectively inhibits crystallization, improves electrochemical performance, utilizes condensation reaction of boric acid on the structure of a crosslinking agent containing boric acid to form borate, introduces boron of a vacant p orbital, can accelerate lithium ion conduction, and ester exchange reaction of a dynamic borate bond can reestablish B-O covalent bond; the polymer electrolyte has self-repairing capability, the crosslinking density of polymer segments can be effectively controlled by using the crosslinking agent containing boric acid, so that the structure is controlled, and a flexible, efficient, safe and stable borate crosslinking self-repairing polymer electrolyte is obtained. The polymer electrolyte prepared by the application is amorphous, has a relatively high decomposition temperature, a glass transition temperature close to-45 DEG C, a potential stable window above 5.5V, can be self-repaired after being cut, fused into a whole, and has good self-repairing property.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrolyte materials, in particular to a borate cross-linked self-healing polymer electrolyte and a preparation method and application thereof. BACKGROUND

[0002] Commercialized lithium ion batteries mainly use organic carbonate liquid as electrolyte, since the organic carbonate liquid is highly flammable and can form dendrites, resulting in the risk of explosion of mobile phones, notebook computers, electric vehicles and the like assembled by lithium ion batteries prepared by using organic carbonate liquid as electrolyte, thereby constituting a safety hazard. Therefore, the development of high safety batteries becomes particularly important and urgent.

[0003] Recent studies have shown that the use of solid electrolytes instead of liquid electrolytes provides an opportunity to build safer LMBs. The low electrochemical performance and poor stability of solid-state electrolytes have affected its commercial application. Therefore, how to prepare a solid-state electrolyte with excellent electrochemical performance and good interface stability is a problem to be solved in the prior art. SUMMARY

[0004] The present application aims to provide a borate cross-linked self-healing polymer electrolyte and a preparation method and application thereof. The borate cross-linked self-healing polymer electrolyte prepared by the method provided by the present application has excellent electrochemical performance and good stability.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a preparation method of a borate cross-linked self-healing polymer electrolyte, comprising the following steps:

[0007] (1) mixing polyethylene glycol methyl ether methacrylate, 2,3-dihydroxypropyl methacrylate, a borate-containing cross-linking agent, a lithium salt, a photoinitiator and an organic solvent to obtain a mixed solution;

[0008] (2) pouring the mixed solution obtained in step (1) into a mold, and then performing light curing to obtain a borate cross-linked self-healing polymer electrolyte.

[0009] Preferably, the borate-containing cross-linking agent in step (1) is one or more of p-phenylenediboronic acid, 1,3,5-benzene trisboronic acid and diphenylboronic acid.

[0010] Preferably, the mass ratio of the borate-containing cross-linking agent to 2,3-dihydroxypropyl methacrylate in step (1) is (0.2-0.6):1.

[0011] Preferably, the molar ratio of oxygen atoms in the polyethylene glycol segment in the polyethylene glycol methyl ether methacrylate to lithium atoms in the lithium salt in step (1) is (6-26):1.

[0012] Preferably, the photoinitiator in step (1) is one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, azobisisobutyronitrile and benzoyl peroxide.

[0013] Preferably, the amount of substance of the photoinitiator in step (1) is 0.01% to 5% of the total amount of substance of the polyethylene glycol methyl ether methacrylate and the 2,3-dihydroxypropyl methacrylate.

[0014] Preferably, after the casting is completed in step (1), the thickness of the mixed solution in the mold is 80-220 μm.

[0015] Preferably, the wavelength of the light source used for photocuring in step (1) is 240-810 nm, and the photocuring time is 4-6 min.

[0016] The application also provides a borate cross-linked self-repairing polymer electrolyte prepared by the preparation method described in the above technical solution.

[0017] The application also provides the use of the borate cross-linked self-repairing polymer electrolyte described in the above technical solution in lithium ion batteries.

[0018] The application provides a preparation method of borate crosslinked self-repairing polymer electrolyte, first, polyethylene glycol methyl ether methacrylate (OE) is subjected to photopolymerization with 2,3-dihydroxypropyl methacrylate (HGMA) under the action of a photoinitiator to form a random block copolymer, then 2,3-dihydroxypropyl on the side chain of the random block copolymer is subjected to condensation reaction with a crosslinking agent containing boric acid to form a polymer with crosslinked network structure, meanwhile, lithium salt is uniformly dispersed in the network of the polymer, and finally the borate crosslinked self-repairing polymer electrolyte is obtained. The short comb-shaped side chain of the polyethylene glycol methyl ether methacrylate selected as a polymer host monomer for transporting lithium ions can effectively inhibit crystallization, improve the movement ability of the polymer electrolyte segment, and improve the electrochemical performance of the polymer electrolymer, the condensation reaction between boric acid on the structure of the crosslinking agent containing boric acid and 2,3-dihydroxypropyl on the side chain of the random block copolymer forms borate, first, boron is introduced into the polymer matrix, boron has a vacant p orbital as a Lewis acid center to interact with the anion of the electrolyte salt to effectively capture the anion in the electrolyte matrix, which plays a role similar to that of a single-ion conductor in fixing anions and accelerating lithium ion conduction, and second, the borate belongs to a dynamic covalent bond and has higher bond energy, so that the polymer electrolyte has good mechanical properties and repairability, and the safety of the electrolyte is improved, and when the polymer electrolyte is broken during use, the rearrangement of the topological structure caused by the ester exchange reaction of the dynamic borate bond and the reestablishment of the B-O covalent bond enable the polymer electrolyte to be repaired in time, so that the polymer electrolyte has self-repairing ability, the crosslinking agent containing boric acid can effectively regulate the crosslinking density of the polymer segment, so that a flexible, diverse and covalently adaptable comb-shaped polymer electrolyte structure is obtained, and the borate crosslinked self-repairing polymer electrolyte has good thermal stability and dendrite-free morphology, and is flexible, efficient, safe and stable; and the uneven deposition of lithium at the lithium negative electrode during the general battery charging and discharging cycle can cause lithium dendrites to be generated, which affects the cycle performance of the battery, and as the lithium dendrites grow, the battery may even be short-circuited to cause safety problems, but the crosslinking between the segments of the polymer electrolyte film prepared by the application gives it good mechanical strength, which can inhibit the growth of dendrites, and the solid polymer electrolyte containing borate can resist the brittle fracture of the polymer caused by dendrite growth due to the network rearrangement induced by the exchange of borate bonds; in addition, the anion in the lithium salt is fixed on the polymer skeleton by the borate which is an electron capture group, the interface side reaction is reduced, a stable and uniform solid electrolyte interface film (SEI film) is easily formed on the lithium negative electrode, and the polymer electrolyte is expected to be applied in lithium metal batteries to ensure the safety of the batteries and improve the service life of the batteries.The results of the embodiments show that the borate cross-linked self-healing polymer electrolyte prepared by the application is substantially amorphous, which is conducive to the conduction of lithium ions, thereby improving the ionic conductivity of the polymer electrolyte; the polymer electrolyte has a relatively high decomposition temperature (~370℃), and under high temperature conditions, the polymer electrolyte still has good thermal stability, which can meet the safety requirements of the actual application of the lithium metal battery; the glass transition temperature (Tg) of the polymer electrolyte is close to -45℃, in a non-crystalline state, at the same time, the low Tg value leads to the reduction of crystallization and the enhancement of molecular chain segment movement, which is conducive to improving the electrochemical performance of the polymer electrolyte; the potential stability window is above 5.5V, the polymer electrolyte has good electrochemical stability, and can be matched with most cathode materials, which is used in the lithium metal battery and is expected to be applied to the lithium metal battery to ensure the safety of the battery and further improve the service life of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The infrared spectrum of the borate cross-linked self-healing polymer electrolyte prepared in Example 3 of the application;

[0020] Figure 2 The XRD graph of the borate cross-linked self-healing polymer electrolyte prepared in Example 3 of the application;

[0021] Figure 3 The element mapping graph of the borate cross-linked self-healing polymer electrolyte prepared in Example 3 of the application;

[0022] Figure 4 The TGA graph of the borate cross-linked self-healing polymer electrolyte prepared in Example 3 of the application;

[0023] Figure 5 The DSC graph of the borate cross-linked self-healing polymer electrolyte prepared in Example 3 of the application;

[0024] Figure 6 The graph of the change of the conductivity of the borate cross-linked self-healing polymer electrolyte prepared in Examples 1-3 of the application with temperature;

[0025] Figure 7 The graph of the change of the conductivity of the borate cross-linked self-healing polymer electrolyte prepared in Examples 3-5 of the application with temperature;

[0026] Figure 8 The LSV graph of the borate cross-linked self-healing polymer electrolyte prepared in Example 3 of the application;

[0027] Figure 9 The repair performance graph of the borate cross-linked self-healing polymer electrolyte prepared in Example 3 of the application;

[0028] Figure 10The constant current polarization test diagram of the borate crosslinking self-repairing polymer electrolyte thin film prepared for the embodiment case 3 of the present application is assembled into a lithium-lithium symmetric battery. DETAILED DESCRIPTION

[0029] The present application provides a preparation method of a borate crosslinking self-repairing polymer electrolyte, comprising the following steps:

[0030] (1) mixing polyethylene glycol methyl ether methacrylate, 2,3-dihydroxypropyl methacrylate, a borate-containing crosslinking agent, a lithium salt, a photoinitiator and an organic solvent to obtain a mixed solution;

[0031] (2) casting the mixed solution obtained in the step (1) into a mold, and then performing light curing to obtain a borate crosslinking self-repairing polymer electrolyte.

[0032] In the present application, the raw materials used are all conventional commercially available products in the art unless otherwise specified.

[0033] The present application mixes polyethylene glycol methyl ether methacrylate, 2,3-dihydroxypropyl methacrylate, a borate-containing crosslinking agent, a lithium salt, a photoinitiator and an organic solvent to obtain a mixed solution.

[0034] The present application does not have special limitations on the source of 2,3-dihydroxypropyl methacrylate, and commercially available products known to those skilled in the art can be used, or the product can be prepared according to the preparation method known to those skilled in the art.

[0035] In the present application, the preparation method of the 2,3-dihydroxypropyl methacrylate preferably comprises the following steps:

[0036] The glycidyl methacrylate and ultrapure water are mixed and then subjected to a hydrolysis reaction to obtain 2,3-dihydroxypropyl methacrylate.

[0037] In the present application, the volume ratio of the glycidyl methacrylate and ultrapure water is preferably (0.06-0.1):1, and more preferably (0.07-0.09):1. The present application controls the volume ratio of the glycidyl methacrylate and ultrapure water within the above range, which is beneficial to better hydrolysis of the glycidyl methacrylate to obtain the target product with a higher yield.

[0038] In the present application, the mixing of the glycidyl methacrylate and ultrapure water is preferably carried out under stirring. The present application does not have special limitations on the stirring rate, and the components can be mixed uniformly. In the present application, the stirring time is preferably 4-8h, and more preferably 5-7h.

[0039] In the present application, the temperature of the hydrolysis reaction is preferably 70-85°C, more preferably 75-83°C; the time of the hydrolysis reaction is preferably 22-26h, more preferably 23-25h. Controlling the temperature and time of the hydrolysis reaction within the above ranges is advantageous for improving the conversion rate of the reaction.

[0040] After the hydrolysis reaction is completed, the product of the hydrolysis reaction is preferably subjected to rotary evaporation in the present application to obtain 2,3-dihydroxypropyl methacrylate.

[0041] In the present application, the temperature of the rotary evaporation is preferably 70-85°C, more preferably 75-83°C; the time of the rotary evaporation is preferably 20-40min, more preferably 25-35min. Controlling the temperature and time of the rotary evaporation within the above ranges is advantageous for fully removing the aqueous solvent.

[0042] In the present application, the boronic acid-containing crosslinking agent is preferably one or more of p-benzeneboronic acid, 1,3,5-benzeneboronic acid and diphenylboronic acid. In the present application, the molar ratio of the boronic acid-containing crosslinking agent to 2,3-dihydroxypropyl methacrylate is preferably (0.2-0.6):1, more preferably (0.25-0.5):1. Controlling the molar ratio of the boronic acid-containing crosslinking agent to 2,3-dihydroxypropyl methacrylate within the above ranges is effective for regulating the crosslinking degree of the polymer structure, ensuring a more relaxed polymer network and enhanced movement ability of the chain segments on the basis of guaranteeing the mechanical strength of the polymer electrolyte, endowing the polymer electrolyte with excellent electrochemical performance, avoiding too low an amount of the boronic acid-containing crosslinking agent, which would also reduce the mechanical strength and repairability of the polymer electrolyte, and avoiding too high an amount of the boronic acid-containing crosslinking agent, which would cause too high a crosslinking degree and thus reduce the free movement ability of the polymer chain segments and the transport capacity of lithium ions.

[0043] In the present application, the lithium salt is preferably one or more of lithium perchlorate, lithium tetrafluoroborate and lithium bistrifluoromethylsulfonimide. In the present application, the molar ratio of the oxygen atoms in the polyethylene glycol chain segments of the polyethylene glycol methyl ether methacrylate to the lithium atoms in the lithium salt is (6-26):1, more preferably (7-25):1, and further preferably 8:1, 16:1 or 24:1. Controlling the molar ratio of the oxygen atoms in the polyethylene glycol chain segments of the polyethylene glycol methyl ether methacrylate to the lithium atoms in the lithium salt within the above ranges is advantageous for regulating the oxygen-lithium ratio, thus improving the ionic conductivity value and avoiding too high an amount of lithium ions in the polymer electrolyte, which would form ion aggregates and thus reduce the ionic conductivity.

[0044] In the present application, the photoinitiator is preferably one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, azobisisobutyronitrile and benzoyl peroxide. In the present application, the amount of substance of the photoinitiator is preferably 0.01% to 5%, more preferably 0.02% to 4%, of the total amount of substance of polyethylene glycol methyl ether methacrylate and 2,3-dihydroxypropyl methacrylate. In the present application, when the photoinitiator is azobisisobutyronitrile, the amount of substance of azobisisobutyronitrile is preferably 0.02% to 0.2% of the total amount of substance of polyethylene glycol methyl ether methacrylate and 2,3-dihydroxypropyl methacrylate; when the photoinitiator is benzoyl peroxide, the amount of substance of benzoyl peroxide is preferably 1% to 4% of the total amount of substance of polyethylene glycol methyl ether methacrylate and 2,3-dihydroxypropyl methacrylate; when the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone, the amount of substance of 2-hydroxy-2-methyl-1-phenyl-1-propanone is preferably 1% to 4% of the total amount of substance of polyethylene glycol methyl ether methacrylate and 2,3-dihydroxypropyl methacrylate. The present application controls the amount of substance of the photoinitiator within the above range, avoiding excessive use of the photoinitiator, which can affect the polymerization degree and make the molecular weight too large, and can also cause chain transfer and make the molecular weight distribution wider, while avoiding insufficient use of the photoinitiator, which can interrupt the polymerization reaction due to lack of free radicals, make the molecular weight small and difficult to crosslink and cure, and thus fail to obtain the polymer electrolyte.

[0045] In the present application, the organic solvent is preferably one or more of acetonitrile, tetrahydrofuran, methanol and N,N-dimethylformamide. In the present application, the ratio of the volume of the organic solvent to the amount of substance of 2,3-dihydroxypropyl methacrylate is preferably 1 mL:1 mmol.

[0046] In the present application, the mixing is preferably carried out under stirring. The present application does not have a special limitation on the rate of stirring, as long as the components can be mixed uniformly. In the present application, the stirring time is preferably 4 to 7 hours, more preferably 5 to 6 hours.

[0047] After obtaining the mixed solution, the present application casts the mixed solution into a mold, then performs photocuring to obtain a borate crosslinked self-healing polymer electrolyte.

[0048] In the present application, after casting, the thickness of the mixed solution in the mold is preferably 80 to 220 μm, more preferably 90 to 210 μm. The present application controls the thickness of the mixed solution in the mold within the above range to control the film thickness of the polymer electrolyte prepared, thereby facilitating the improvement of the electrochemical performance of the polymer electrolyte.

[0049] In the present application, the material of the mold is preferably polytetrafluoroethylene. The present application selects polytetrafluoroethylene as the material of the mold to avoid the prepared polymer electrolyte and the mold from sticking together, facilitating the separation of the polymer electrolyte from the mold.

[0050] In the present application, the wavelength of the light source used for photocuring is preferably 240-810 nm, and more preferably 250-800 nm. The present application controls the wavelength of the light source used for photocuring within the above range, which is conducive to the absorption of the energy of the wavelength by the photoinitiator to generate free radicals, thereby initiating the crosslinking and curing of the monomers and the polymerization reaction. In the present application, the time for photocuring is preferably 4-6 min, and more preferably 4.5-5.5 min. The present application controls the time for photocuring within the above range, which is conducive to the control of the rate of the polymerization reaction, the rapid stabilization of the polymerization reaction after the light source is turned off, and the accurate control of the molecular weight of the polymer, thereby optimizing the most relaxed polymer chain segment and preparing the borate crosslinked self-healing polymer electrolyte with excellent electrical properties.

[0051] After the photocuring is completed, the present application preferably dries the photocured product to obtain the borate crosslinked self-healing polymer electrolyte.

[0052] In the present application, the temperature for drying is preferably 50-70℃, and the time for drying is preferably 46-50 h.

[0053] The preparation method of the borate crosslinked self-healing polymer electrolyte provided by the present application has a simple operation process, mild reaction conditions, and is suitable for large-scale production.

[0054] The present application also provides the borate crosslinked self-healing polymer electrolyte prepared by the preparation method described in the above technical solution.

[0055] The present application also provides the application of the borate crosslinked self-healing polymer electrolyte described in the above technical solution in lithium ion batteries.

[0056] The technical solutions in the present application will be described clearly and completely in combination with the embodiments in the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0057] Example 1

[0058] I. Preparation method of 2,3-methyl acrylate dihydroxypropyl ester

[0059] 50 mmol of glycidyl methacrylate GMA and 80 mL of ultrapure water were added into a 250 mL flask, mixed and stirred for 1 hour, the solution became turbid, then the temperature was raised to 80℃ for hydrolysis reaction for 24 hours, the two-phase system was changed into a colorless transparent solution (homogeneous phase), the product of the hydrolysis reaction was rotary evaporated at 80℃ for 30 min to obtain 2,3-dihydroxypropyl methacrylate (HGMA);

[0060] The volume ratio of the glycidyl methacrylate and the ultrapure water is 0.08:1.

[0061] II. Preparation method of borate cross-linked self-repairing polymer electrolyte

[0062] (1) Polyethylene glycol methyl ether methacrylate (1.00 g, 2 mmol), 2,3-dihydroxypropyl methacrylate (0.32 g, 2 mmol) prepared by the above method, borate-containing cross-linking agent p-phenylenediamine (0.083 g, 0.5 mmol), lithium salt lithium perchlorate (0.24 g, 2.26 mmol), photoinitiator 2-hydroxy-2-methylpropiophenone (0.0066 g, 0.04 mmol) and 2 mL of organic solvent acetonitrile were mixed under stirring to obtain a colorless transparent mixture;

[0063] The mass ratio of the borate-containing cross-linking agent and 2,3-dihydroxypropyl methacrylate is 0.25:1;

[0064] The mass ratio of oxygen atoms in the polyethylene glycol segment in the polyethylene glycol methyl ether methacrylate to lithium atoms in the lithium salt (i.e., the [O] / [Li + ] ratio) is 8:1;

[0065] The mass of the photoinitiator is 1% of the total mass of the polyethylene glycol methyl ether methacrylate and 2,3-dihydroxypropyl methacrylate.

[0066] (2) The mixture obtained in step (1) was cast into a mold, after casting was completed, the thickness of the mixture in the mold was 100 μm, then light curing was performed under a UV curing lamp with a wavelength of 365 nm for 5 min, and the light-cured product was dried in a vacuum drying oven at 60℃ for 48 h to obtain a borate cross-linked self-repairing polymer electrolyte.

[0067] Example 2

[0068] A borate cross-linked self-repairing polymer electrolyte was prepared according to the method of Example 1;

[0069] Different from example 1, lithium perchlorate (0.08 g, 0.76 mmol) was used as lithium salt in step (1), and the molar ratio of oxygen atoms in polyethylene glycol segments to lithium atoms in lithium salt (i.e. [O] / [Li + ] ratio) in the polyethylene glycol methyl ether methacrylate was 24:1.

[0070] Example 3

[0071] The borate cross-linked self-healing polymer electrolyte was prepared according to the method of example 1;

[0072] Different from example 1, lithium perchlorate (0.12 g, 1.13 mmol) was used as lithium salt in step (1), and the molar ratio of oxygen atoms in polyethylene glycol segments to lithium atoms in lithium salt (i.e. [O] / [Li + ] ratio) in the polyethylene glycol methyl ether methacrylate was 16:1.

[0073] Figure 1 The infrared spectrum of the borate cross-linked self-healing polymer electrolyte prepared in example 3 can be seen from Figure 1 that the borate cross-linked self-healing polymer electrolyte prepared in example 3 has absorption peaks of boron-oxygen bond (B-O-B) at 689 and 750 cm -1 , indicating the formation of borate and the effective cross-linking of the polymer, which shows that the borate cross-linked self-healing polymer electrolyte prepared in example 3 is successfully prepared.

[0074] Figure 2 The XRD pattern of the borate cross-linked self-healing polymer electrolyte prepared in example 3 can be seen from Figure 2 that the polymer after adding lithium salt has a flat peak at 20°, indicating that the borate cross-linked self-healing polymer electrolyte prepared in example 3 is basically amorphous, which is helpful for the conduction of lithium ions, thereby improving the ionic conductivity of the polymer electrolyte.

[0075] Figure 3 The element mapping of the borate cross-linked self-healing polymer electrolyte prepared in example 3 prepared in example 3 can be seen from Figure 3 that the borate cross-linked self-healing polymer electrolyte prepared in example 3 has a boron atom mapping, which is consistent with the boron atom mapping of the borate cross-linked self-healing polymer electrolyte prepared in example 3, indicating that the borate cross-linked self-healing polymer electrolyte prepared in example 3 is successfully prepared.

[0076] Figure 4 The TGA pattern of the borate cross-linked self-healing polymer electrolyte prepared in example 3 can be seen from Figure 3It can be seen that: it can be clearly seen that the borate cross-linked self-repairing polymer electrolyte prepared in Example 3 has a relatively high decomposition temperature (~ 370℃), which indicates that the polymer electrolyte still has good thermal stability even under high temperature conditions, indicating that the polymer electrolyte can meet the safety requirements of lithium metal battery practical application.

[0077] Figure 5 The DSC graph of the borate cross-linked self-repairing polymer electrolyte prepared in Example 3, from Figure 5 It can be seen that the glass transition temperature (Tg) of the borate cross-linked self-repairing polymer electrolyte prepared in Example 3 is close to -45℃, and the melting peak disappears, indicating that the polymer electrolyte is in an amorphous state, and at the same time, the low Tg value leads to the reduction of crystallization and the enhancement of molecular chain segment movement, which is beneficial to improve the electrochemical performance of the polymer electrolyte.

[0078] Figure 7 The graph of the conductivity of the borate cross-linked self-repairing polymer electrolyte prepared in Examples 1-3 with the change of temperature, with the increase of the ratio of [O] / [Li + ]value, the initial increase of ionic conductivity is mainly due to the increase of charge carriers, when the amount of lithium salt is further increased, the movement performance of the polymer chain segment is limited due to the coordination between lithium ions and oxygen atoms in the polyethylene glycol chain, thereby limiting the increase of conductivity.

[0079] Figure 8 The LSV graph of the borate cross-linked self-repairing polymer electrolyte prepared in Example 3, from Figure 8 It can be seen that the potential stability window of the borate cross-linked self-repairing polymer electrolyte prepared in Example 3 is above 5.5V, which indicates that the polymer electrolyte has good electrochemical stability and can be matched with most cathode materials for lithium metal batteries.

[0080] Figure 9 The repair performance graph of the borate cross-linked self-repairing polymer electrolyte prepared in Example 3, from Figure 9 It can be seen that: an intact borate cross-linked self-repairing polymer electrolyte prepared in Example 3 (cut into two pieces of uniform size with a knife, connect the crack and treat the crack with a drop of water, at room temperature, the two halves fuse into a whole, and can hang a 20g weight, indicating that the borate cross-linked self-repairing polymer electrolyte prepared in Example 3 has good self-repairing property, and is expected to be applied in lithium metal batteries to ensure the safety of the battery and thus improve the service life of the battery.

[0081] Figure 10 The constant current polarization test graph of the lithium-lithium symmetric battery assembled by the borate cross-linked self-repairing polymer electrolyte film prepared in Example 3, from Figure 10As can be seen from the data, the lithium-lithium symmetric battery assembled from the borate ester crosslinked self-healing polymer electrolyte film prepared in Example 3 achieves a current density of 0.1 mA cm⁻¹. -2 and 0.2mA cm -2 At that time, with low overpotentials of 5mV and 12mV, the lithium-lithium symmetric battery exhibited stable peeling / electroplating reversibility and no short circuit phenomenon, indicating that the lithium electrode has good compatibility with the polymer electrolyte prepared in Example 3, which enables uniform deposition of lithium ions and makes it difficult to generate lithium dendrites.

[0082] Example 4

[0083] Borate ester crosslinked self-healing polymer electrolyte was prepared according to the method in Example 1;

[0084] Unlike Example 1, step (1) uses a boric acid-containing crosslinking agent, terephthalic acid (0.17 g, 1 mmol), and a lithium salt, lithium perchlorate (0.12 g, 1.13 mmol). The molar ratio of the boric acid-containing crosslinking agent to dihydroxypropyl 2,3-methacrylate is 0.5:1. The molar ratio of oxygen atoms in the polyethylene glycol segments of the polyethylene glycol methyl ether methacrylate to lithium atoms in the lithium salt (i.e., [O] / [Li)) is... + The ratio is 16:1.

[0085] Example 5

[0086] Borate ester crosslinked self-healing polymer electrolyte was prepared according to the method in Example 1;

[0087] Unlike Example 1, step (1) uses a boric acid-containing crosslinking agent, terephthalic acid (0.11 g, 0.67 mmol), and a lithium salt, lithium perchlorate (0.12 g, 1.13 mmol). The molar ratio of the boric acid-containing crosslinking agent to dihydroxypropyl 2,3-methacrylate is 0.335:1. The molar ratio of oxygen atoms in the polyethylene glycol segments of the polyethylene glycol methyl ether methacrylate to lithium atoms in the lithium salt (i.e., [O] / [Li)) is... + The ratio is 16:1.

[0088] Figure 6 The graph shows the change in conductivity of the borate ester crosslinked self-healing polymer electrolytes prepared in Examples 3-5 as a function of temperature. Figure 6 It can be seen that the amount of crosslinking agent in the polymer matrix also affects the ionic conductivity. When the molar ratio of terephthalic acid and dihydroxypropyl 2,3-methacrylate is 0.25:1, and the oxygen-to-lithium ratio of the polymer electrolyte (i.e., [O] / [Li]) is... +When the ratio (B / A) is 16:1, the conductivity of the borate cross-linked self-healing polymer electrolyte prepared in Example (3) reaches the maximum value of 0.74 mS / cm.

[0089] In conclusion, the borate cross-linked self-healing polymer electrolyte prepared in the application is basically amorphous, which is helpful for the conduction of lithium ions, thereby improving the ionic conductivity of the polymer electrolyte; has a relatively high decomposition temperature (about 370℃), under high temperature conditions, the polymer electrolyte still has good thermal stability, which can meet the safety requirements of the practical application of lithium metal batteries; the glass transition temperature (Tg) of the polymer electrolyte is close to-45℃, in a non-crystalline state, at the same time, the low Tg value leads to the reduction of crystallization and the enhancement of molecular chain segment movement, which is conducive to improving the electrochemical performance of the polymer electrolyte; the potential stability window is above 5.5V, the polymer electrolyte has good electrochemical stability, can be matched with most cathode materials, and is used in lithium metal batteries; the polymer electrolyte can be self-healed after being cut, fused into a whole, has good self-healing property, and is expected to be applied in lithium metal batteries to ensure the safety of the batteries and thereby improve the service life of the batteries.

[0090] The above only describes the preferred embodiments of the application, and it should be pointed out that, for ordinary skilled in the art, without departing from the principles of the application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. A method for preparing a borate cross-linked self-healing polymer electrolyte, comprising the following steps: (1) mixing polyethylene glycol methyl ether methacrylate, 2,3-dihydroxypropyl methacrylate, a borate-containing cross-linking agent, a lithium salt, a photoinitiator and an organic solvent to obtain a mixed solution; (2) casting the mixed solution obtained in step (1) into a mold, and then performing photo-curing to obtain a borate cross-linked self-healing polymer electrolyte. The borate-containing cross-linking agent in step (1) is one or more of p-phenylenediboronic acid, 1,3,5-benzene triboronic acid and diphenyldiboronic acid; and the mass ratio of the borate-containing cross-linking agent to 2,3-dihydroxypropyl methacrylate in step (1) is (0.2-0.6) :

1.

2. The production method according to claim 1, characterized by, The mass ratio of oxygen atoms in the polyethylene glycol segment of polyethylene glycol methyl ether methacrylate to lithium atoms in the lithium salt in step (1) is (6-26) :

1.

3. The production method according to claim 1, characterized by, The photoinitiator in step (1) is one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, azobisisobutyronitrile and benzoyl peroxide.

4. The production method according to claim 1 or 3, characterized by, The mass of the photoinitiator in step (1) is 0.01%-5% of the total mass of polyethylene glycol methyl ether methacrylate and 2,3-dihydroxypropyl methacrylate.

5. The preparation method according to claim 1, characterized in that, After casting is completed in step (1), the thickness of the mixed solution in the mold is 80-220 μm.

6. The method of claim 1, wherein, The wavelength of the light source used for photo-curing in step (1) is 240-810 nm, and the photo-curing time is 4-6 min. 7.The borate cross-linked self-healing polymer electrolyte prepared by the method of any one of claims 1-6. 8.The borate cross-linked self-healing polymer electrolyte of claim 7 for use in a lithium ion battery.

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