A polymer electrolyte and its preparation method and application

Abstract

The present invention provides a polymer electrolyte and a preparation method and application thereof, wherein the polymer electrolyte comprises a polymer and a lithium salt, wherein the polymer comprises a crosslinked product obtained by copolymerization of a compound represented by #imgabs0# and a compound represented by #imgabs1#, wherein in formula I, m is an integer selected from 2 to 20; and in formula II, R is selected from bistrifluoromethylsulfonyl imide, bisfluorosulfonyl imide, perchlorate, tetrafluoroborate, dioxalate borate, difluorooxalate borate or trifluoromethylsulfonate, and n is an integer selected from 1 to 10. The polymer electrolyte of the present invention has excellent ionic conductivity, lithium ion migration number and mechanical strength.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries and relates to a polymer electrolyte and a preparation method and application thereof. Background Art

[0002] Electrolyte is an important component of lithium secondary batteries, which plays the role of transporting ions and conducting current between the positive and negative electrodes. Compared with liquid electrolytes, solid electrolytes have higher mechanical strength and stability, can effectively inhibit the growth of lithium dendrites, and reduce the risk of battery short circuit. In addition, they can maintain good performance in a wide temperature range and have good temperature stability. Solid electrolytes have good chemical stability and are not easy to react with electrodes, which is conducive to extending the cycle life of the battery. Polymer solid electrolytes are a widely used solid electrolyte with good flexibility and processability, and have been widely studied. Polyethylene oxide (PEO) has a wide range of sources and good compatibility with lithium salts. It is usually used as the main raw material for polymer solid electrolytes. However, the existing polyethylene oxide solid electrolytes still have problems such as low ionic conductivity, low lithium ion migration number, and poor mechanical strength during use, resulting in poor rate performance, cycle performance and safety performance of the battery. Summary of the invention

[0003] The present invention provides a polymer electrolyte having excellent ion conductivity, lithium ion transference number and mechanical strength.

[0004] The present invention also provides a method for preparing a polymer electrolyte, wherein a lithium salt is added before the polymerization of the compound represented by Formula I and the compound represented by Formula II, so that the lithium salt is uniformly dispersed in the cross-linked body formed by the polymerization, thereby obtaining the above-mentioned polymer electrolyte with excellent ionic conductivity, lithium ion migration number and mechanical strength.

[0005] The present invention also provides a battery, which comprises the polymer electrolyte and thus has excellent rate performance, cycle performance and safety performance.

[0006] The present invention also provides an electronic device. Since the electronic device comprises the battery, the electronic device also has excellent rate performance, cycle performance and safety performance during use.

[0007] The present invention provides a polymer electrolyte, comprising a polymer and a lithium salt, wherein the polymer comprises a crosslinked body obtained by copolymerization of a compound represented by Formula I and a compound represented by Formula II:

[0008]

[0009] In formula I, m is an integer selected from 2 to 20;

[0010] In formula II, R is selected from bis(trifluoromethylsulfonyl)imide, bis(fluorosulfonyl)imide, perchlorate, tetrafluoroborate, dioxalatoborate, difluorooxalatoborate or trifluoromethylsulfonate, and n is selected from an integer between 1 and 10.

[0011] The polymer electrolyte as described above, wherein the copolymerization molar ratio of the compound represented by formula I to the compound represented by formula II is (70-95):(5-30).

[0012] The polymer electrolyte as described above, wherein the molar ratio of the sum of the polyethylene glycol structural units in the compound represented by Formula I and the compound represented by Formula II to the lithium salt is (10-25):1.

[0013] The polymer electrolyte as described above, wherein the lithium salt includes one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium dioxalatoborate, and lithium perchlorate.

[0014] The present invention also provides a method for preparing the polymer electrolyte as described above, comprising the following steps:

[0015] A free radical initiator is added to a mixed system of the compound represented by formula I, the compound represented by formula II and a lithium salt to initiate a polymerization reaction, thereby obtaining the polymer electrolyte.

[0016] The preparation method as described above, wherein the compound represented by formula II is prepared by a method comprising the following steps:

[0017] 1) reacting 1-vinylimidazole with the compound represented by formula III to obtain the compound represented by formula IV;

[0018]

[0019] In formula III, X is selected from Cl, Br or I;

[0020] 2) allowing the compound represented by formula IV to undergo an ion exchange reaction with LiR to obtain the compound represented by formula II;

[0021] .

[0022] The preparation method as described above, wherein the polymerization reaction temperature is 60-100° C. and the time is 4-12 hours.

[0023] The present invention also provides a battery, comprising a positive electrode, a negative electrode and an electrolyte layer located between the positive electrode and the negative electrode, wherein the electrolyte layer comprises the polymer electrolyte as described above.

[0024] In the battery as described above, the thickness of the electrolyte layer is 20-50 μm.

[0025] The present invention also provides an electronic device, comprising the battery as described above.

[0026] The implementation of the present invention has at least the following beneficial effects:

[0027] 1) The polymer of the polymer electrolyte of the present invention includes a crosslinked body obtained by copolymerization of the compound shown in formula I and the compound shown in formula II. After copolymerization, the polyethylene glycol segment of the compound shown in formula I is located on the side chain of the crosslinked body, has better mobility, can better conduct lithium ions, and copolymerization can also make the crosslinked body have a lower crystallinity, thereby improving the ion conductivity of the electrolyte. In addition, the compound shown in formula II can also introduce imidazolium ion liquid units into the crosslinked body. The imidazolium ion liquid unit can adsorb anions in lithium salts through electrostatic action, increase the number of lithium ion migration, reduce concentration polarization, and improve the rate performance of the battery. The crosslinked body after copolymerization still retains an appropriate amount of polyethylene glycol segments, and the three-dimensional network structure of the crosslinked body can also make the electrolyte have a higher mechanical strength, so that the electrolyte has both good flexibility and mechanical strength, and has good compatibility with the positive and negative electrode interfaces to reduce the interface impedance, while also avoiding the positive and negative electrodes from contacting short circuits, thereby improving the battery's cycle performance and safety performance. In summary, the polymer electrolyte of the present application has high ionic conductivity, lithium ion transference number and mechanical strength, and the battery including the polymer electrolyte has excellent cycle performance, safety performance and rate performance.

[0028] 2) The preparation method of the polymer electrolyte provided by the present invention comprises adding a lithium salt before the polymerization of the compound represented by Formula I and the compound represented by Formula II. On the one hand, the compound represented by Formula I and the compound represented by Formula II can dissolve the lithium salt. On the other hand, the addition before the polymerization can make the lithium salt uniformly dispersed in the cross-linked body formed by the polymerization, thereby obtaining a polymer electrolyte with excellent ionic conductivity, lithium ion migration number and mechanical strength. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] PEO molecular chains have a high dielectric constant and can dissolve many lithium salts. They are recognized as a matrix suitable for preparing all-solid-state electrolytes. However, pure PEO polymers are easy to crystallize, resulting in less amorphous phase structures that can conduct lithium ions, which in turn makes the ionic conductivity of solid electrolytes low. In order to improve its ionic conductivity, the operating temperature can be increased to reduce the crystallinity of PEO polymers, but after the crystallinity decreases, the mechanical strength of the electrolyte also decreases, resulting in easy contact and short circuit between the positive and negative electrodes. In addition, the principle of PEO conducting lithium ions is to coordinate with lithium ions through the lone pair of electrons in the oxygen atoms of the molecular chain, thereby realizing the transmission of lithium ions, but the anions in the lithium salts will not interact with the polymers, so the transmission ability of anions under the electric field is stronger than that of lithium ions, resulting in a lower migration number of lithium ions. Accordingly, the battery is prone to concentration polarization and uneven lithium ion deposition during the charge and discharge process, which ultimately makes the battery's safety performance, rate performance and cycle performance poor.

[0031] Based on this, the present invention provides a polymer electrolyte, comprising a polymer and a lithium salt, wherein the polymer comprises a crosslinked body obtained by copolymerization of a compound represented by Formula I and a compound represented by Formula II:

[0032]

[0033] In formula I, m is an integer selected from 2 to 20;

[0034] In formula II, R is selected from bis(trifluoromethylsulfonyl)imide, bis(fluorosulfonyl)imide, perchlorate, tetrafluoroborate, dioxalatoborate, difluorooxalatoborate or trifluoromethylsulfonate, and n is selected from an integer between 1 and 10.

[0035] The compound shown in formula I is an acrylate compound containing a polyethylene glycol chain segment, and the compound shown in formula II is a compound obtained by chemically modifying the polyethylene glycol chain segment using vinyl imidazole. It contains two double bonds at both ends and acts as a cross-linking agent. After copolymerization with the compound shown in formula I, the two can be cross-linked to form a cross-linked body with a three-dimensional network structure.

[0036] On the one hand, after copolymerization, the polyethylene glycol segment of the compound shown in Formula I is located on the side chain of the cross-linked body, has better mobility, and can better conduct lithium ions. On the other hand, copolymerization can also make the cross-linked body have a lower crystallinity, thereby improving the ion conductivity of the electrolyte through the above two effects.

[0037] By introducing an imidazole-type ionic liquid unit in the cross-linked body, anions in lithium salts can also be adsorbed by electrostatic action, the number of lithium ion migration can be increased, concentration polarization can be reduced, and the rate performance of the battery can be improved. In addition, the present invention embeds an imidazole ionic liquid unit in the compound shown in formula II, rather than directly using a cross-linking agent of an imidazole ionic liquid with a diene group to copolymerize with the compound shown in formula I. The reason is that when the imidazole ionic liquid monomer containing a diene group is copolymerized with the compound shown in formula I, the polarity difference between the two is too large, and phase separation phenomenon is prone to occur. The obtained polymer is similar to a salt compound, and the glass transition temperature and the crystalline melting temperature will be higher, which is not conducive to the conduction of lithium ions. The present application introduces an imidazole-type ionic liquid at both ends of the polyethylene glycol segment, so that the compound shown in formula II has a similar polarity to the compound shown in formula I, avoiding the phase separation when the two copolymerize, so that the obtained polymer can maintain a lower glass transition temperature and crystalline melting temperature, which is conducive to the conduction of lithium ions.

[0038] The cross-linked body obtained after copolymerization still contains polyethylene glycol segments with appropriate content distribution, which can make the electrolyte have good flexibility and good compatibility with the positive and negative electrode interfaces, which is beneficial to reducing the interface resistance and improving the cycle performance of the battery.

[0039] Compared with the linear polymer molecular structure, the three-dimensional network structure of the cross-linked body can make the polymer electrolyte have higher mechanical strength. Even when used in lithium metal solid-state batteries with a high surface density positive electrode, it is not easy to cause short circuit between the positive and negative electrodes, so that the battery has both excellent energy density and safety performance.

[0040] In summary, the present invention enables the polymer electrolyte to have higher ionic conductivity, lithium ion migration number and mechanical strength by making the polymer electrolyte include a cross-linked body obtained by copolymerization of the compound represented by formula I and the compound represented by formula II, thereby enabling the battery to have excellent energy density, rate performance, cycle performance and safety performance.

[0041] In a preferred embodiment, the copolymerization molar ratio of the compound represented by Formula I and the compound represented by Formula II is (70-95): (5-30). Exemplarily, the copolymerization molar ratio of the compound represented by Formula I and the compound represented by Formula II can be 70:30, 80:20, 90:10, 95:5, etc.

[0042] It should be noted that the copolymerization molar ratio in the present invention can be regulated by the feed ratio of the compound shown in Formula I and the compound shown in Formula II. For example, the copolymerization molar ratio of the compound shown in Formula I and the compound shown in Formula II can be 70:30 by controlling the feed molar ratio of the compound shown in Formula I and the compound shown in Formula II to be 70:30.

[0043] When the content of the compound shown in Formula II is low, the strength of the obtained cross-linked body is low, the battery has a short circuit defense line, and it is not conducive to the improvement of the ion migration number. When the content of the compound shown in Formula II is high, the rigidity of the obtained cross-linked body is too strong, the contact with the positive and negative electrodes is poor, and the ionic conductivity of the electrolyte is also low.

[0044] As mentioned above, the oxygen atoms in the polyethylene glycol segments can promote the conduction of lithium ions. Based on this, the present invention studies the usage ratio of the polyethylene glycol segments and lithium salts in the polymer, and finds that when the molar ratio of the polyethylene glycol segments to the lithium salts in the polymer is (10-25):1, the electrolyte can have a higher ion conductivity. Exemplarily, the molar ratio of the polyethylene glycol segments to the lithium salts can be 10:1, 13:1, 15:1, 18:1, 20:1, 23:1, 25:1 or a range consisting of any two of the above molar ratios.

[0045] The present invention does not specifically limit the type of lithium salt, which can be selected from one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium dioxalatoborate, and lithium perchlorate.

[0046] The present invention also provides a method for preparing the polymer electrolyte as described above, comprising the following steps:

[0047] A free radical initiator is added to a mixed system of the compound represented by formula I, the compound represented by formula II and a lithium salt to initiate a polymerization reaction, thereby obtaining the polymer electrolyte.

[0048] The preparation method of the present invention comprises adding a free radical initiator to a mixed system of a compound represented by formula I, a compound represented by formula II and a lithium salt, initiating in-situ polymerization of the compound represented by formula I and the compound represented by formula II during the preparation of the electrolyte, and while forming a cross-linked body, making the lithium salt uniformly distributed in the cross-linked body, thereby obtaining a polymer electrolyte having excellent ionic conductivity, lithium ion migration number and mechanical strength.

[0049] The compound represented by formula I can be obtained from commercial sources or prepared by using techniques known in the art.

[0050] The compound represented by formula II can be prepared by referring to conventional methods in the art. For example, the compound represented by formula II can be prepared by a method comprising the following steps:

[0051] 1) reacting 1-vinylimidazole with the compound represented by formula III to obtain the compound represented by formula IV;

[0052]

[0053] In formula III, X is selected from Cl, Br or I;

[0054] 2) allowing the compound represented by formula IV to undergo an ion exchange reaction with LiR to obtain the compound represented by formula II;

[0055] .

[0056] The 1-vinylimidazole and the compound represented by formula III in step 1) can be purchased commercially or synthesized by known means. The reaction between the two can be carried out without adding a solvent. The two can be mixed in a molar ratio of at least 2:1 and reacted. The reaction temperature of the two is 60-100°C and the reaction time is 4-12h.

[0057] The ion exchange reaction in step 2) can be carried out according to the following specific operations:

[0058] The compound represented by formula IV is dissolved in deionized water to obtain an aqueous solution of the compound represented by formula IV, which is then added dropwise to the aqueous solution of LiR and stirred to allow the ion exchange reaction to proceed fully. After the precipitate is completely precipitated, excess water is poured off, and the compound represented by formula II is obtained after washing and drying.

[0059] The definition of R in LiR is consistent with the definition of R in the compound of formula II.

[0060] The present invention does not specifically limit the free radical initiator used in the polymerization reaction, which can be selected from free radical initiators conventionally used in the art, including but not limited to peroxy free radical initiators, azo initiators or photoinitiators.

[0061] Furthermore, the amount of the free radical initiator used can be 0.5% to 5% of the total mass of the compound represented by Formula I and the compound represented by Formula II.

[0062] The cross-linking reaction can be cured by heating or by ultraviolet light irradiation. Preferably, the cross-linking reaction is cured by heating. The heating temperature can be 50-80° C. and the time can be 1-5 hours.

[0063] The present invention also provides a battery, comprising a positive electrode, a negative electrode and an electrolyte layer located between the positive electrode and the negative electrode, wherein the electrolyte layer comprises the polymer electrolyte as described above.

[0064] Since the polymer electrolyte of the present invention has high ion conductivity, lithium ion migration number and mechanical strength, the battery also has excellent rate performance, cycle performance and safety performance.

[0065] The electrolyte layer of the present invention can be a solid electrolyte including only the above polymer electrolyte, or a semi-solid electrolyte obtained by mixing the above polymer electrolyte and a liquid electrolyte. Correspondingly, the resulting battery can be either a semi-solid battery or a solid battery.

[0066] It can be understood that the greater the thickness of the electrolyte layer, the better the safety performance of the battery. However, a larger thickness will also increase the resistance to lithium-ion transmission, resulting in an increase in battery impedance, a deterioration in the rate performance of the battery, and a deterioration in the energy density of the battery. Based on the above considerations, the thickness of the electrolyte layer is preferably 20-50 μm. Exemplarily, the thickness of the electrolyte layer can be 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or a range composed of any two of the above values.

[0067] Both the positive electrode and the negative electrode of the present invention can refer to the conventional positive and negative electrode compositions in the art.

[0068] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector.

[0069] The present invention does not specifically limit the composition of the positive electrode current collector, which can be selected from the positive electrode current collectors commonly used in the art, such as aluminum foil.

[0070] In a specific embodiment, the positive electrode active material layer includes a positive electrode active material, a conductive agent, a binder, a lithium salt, and a plasticizer.

[0071] The present invention does not specifically limit the types of the positive electrode active material, the conductive agent, the binder, the lithium salt, and the plasticizer, and they can all be selected from the substances commonly used in the art.

[0072] Specifically, the positive electrode active material can be selected from one or more of lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), lithium iron phosphate (LiFePO4), lithium cobalt phosphate (LiCoPO4), lithium manganese phosphate (LiMnPO4), lithium nickel phosphate (LiNiPO4), lithium manganate (LiMnO2), binary material LiNi x A (1-x) O2 (A is selected from one of Co and Mn, 0 < x < 1), ternary material LiNi m B n C (1-m-n) O2 (B and C are independently selected from at least one of Co, Al, and Mn, and B and C are different, 0 < m < 1, 0 < n < 1).

[0073] The conductive agent can be selected from one or more of acetylene black, Super P, Super S, graphene, carbon fiber, carbon nanotube, and Ketjen black.

[0074] The binder can be selected from one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polyacrylonitrile, polypropylene carbonate, styrene-butadiene rubber, nitrile rubber, sodium carboxymethyl cellulose, polyethylene oxide, and ethylene oxide-propylene oxide copolymer.

[0075] The plasticizer can be selected from one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol dimethyl ether, tetrapropylene glycol dimethyl ether, dipropylene glycol diethyl ether, tripropylene glycol diethyl ether, tetrapropylene glycol diethyl ether, 1,3-dioxolane, 1,4-dioxane, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, succinonitrile and adiponitrile.

[0076] The selection of lithium salts can refer to the selection of lithium salts in polymer electrolytes, which will not be described in detail here.

[0077] In a preferred embodiment, the mass ratio of the positive electrode active material, the conductive agent, the binder, the lithium salt and the plasticizer in the positive electrode active material layer is (50-90): (1-10): (9-20): (0-10): (0-10).

[0078] The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0079] The present invention does not specifically limit the composition of the negative electrode current collector, which can be selected from negative electrode current collectors commonly used in the art, such as copper foil.

[0080] In a specific embodiment, the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, a lithium salt and a plasticizer.

[0081] The present invention does not specifically limit the types of the negative electrode active material, the conductive agent, the binder, the lithium salt and the plasticizer, and they can all be selected from materials commonly used in the art.

[0082] Specifically, the negative electrode active material can be selected from lithium metal, lithium metal alloy, graphite, silicon, silicon oxide, silicon carbon composite or silicon alloy. When the negative electrode active material is selected from lithium metal and lithium metal alloy, the negative electrode active material layer does not contain components such as conductive agent, binder, lithium salt and plasticizer.

[0083] The types of the conductive agent, binder, lithium salt and plasticizer in the negative electrode active material layer can refer to the selection of the conductive agent, binder, lithium salt and plasticizer in the positive electrode active material layer, and will not be repeated here.

[0084] In a preferred embodiment, the mass ratio of the negative electrode active material, the conductive agent, the binder, the lithium salt and the plasticizer in the negative electrode active material layer is (50-90): (1-10): (9-20): (0-10): (0-10).

[0085] The present invention does not impose any particular limitation on the method for preparing the battery, and the battery can be prepared by referring to conventional methods in the art.

[0086] For example, in a specific embodiment, a battery can be prepared by the following steps:

[0087] 1) dispersing a positive electrode active material, a conductive agent, a binder, a lithium salt and a plasticizer in a solvent according to a specific mass ratio to form a positive electrode active material layer slurry, then coating the positive electrode active material layer slurry on a positive electrode current collector, and drying to obtain a positive electrode;

[0088] 2) Compounding metallic lithium on the negative electrode current collector to obtain a negative electrode;

[0089] 3) The positive electrode, polymer electrolyte, and negative electrode are assembled in order to obtain a cell, and the battery is obtained after the cell is packaged.

[0090] The present invention also provides an electronic device, comprising the battery as described above. The present invention does not specifically limit the electronic device, which can be any electrical device comprising the battery, including but not limited to mobile phones, laptop computers, electric bicycles, electric cars, electric toys, energy storage devices, etc.

[0091] The polymer electrolyte provided by the present invention and its preparation method and application will be further described in detail below through specific examples.

[0092] Unless otherwise specified, the reagents, materials and instruments used in the following examples are conventional reagents, conventional materials and conventional instruments in the art and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0093] In the following examples, the compounds represented by formula III-1, formula III-2, formula III-3, formula III-5, formula I-1, formula I-2, formula I-3, formula I-4, formula I-5, and formula b were all purchased from Sigma-Aldrich.

[0094] Example 1

[0095] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is as follows:

[0096] 1. Preparation of polymer electrolyte

[0097] 1) 1-vinylimidazole and the compound represented by formula III-1 were mixed evenly in a round-bottom flask at a molar ratio of 2.1:1, and heated to 60° C. for 4 h to obtain a mixed solution.

[0098]

[0099] 2) The mixed solution was dissolved in deionized water, and the obtained solution was added dropwise to the aqueous solution of LiTFSI, stirred for 4 hours to allow the ion exchange reaction to proceed fully, and then the excess water was poured off, the precipitate was washed with water three times, and dried to obtain the compound represented by formula II-1.

[0100]

[0101] 3) The compound represented by formula I-1 and the compound represented by formula II-1 are mixed in a molar ratio of 80:20 to obtain a mixture, and LiTFSI is added to the mixture in a molar ratio of 18:1 between the sum of the polyethylene glycol structural units in the compound represented by formula I-1 and the compound represented by formula II-1 and LiTFSI, and then 0.5% of AIBN based on the total mass of the compound represented by formula I-1 and the compound represented by formula II-1 is added as an initiator, and the mixture is heated to 60° C. for polymerization for 4 hours to obtain a polymer electrolyte.

[0102]

[0103] 2. Preparation of all-solid-state batteries

[0104] 1) Lithium iron phosphate, Super P, polyethylene oxide with a molecular weight of 600,000, lithium bis(trifluoromethylsulfonyl)imide and succinonitrile were mixed in N,N-dimethylformamide at a mass ratio of 78:2:10:5:5 to obtain a positive electrode active material layer slurry, and then the positive electrode active material layer slurry was applied on an aluminum current collector with a thickness of 15 μm with a scraper, and then dried at 60 ° C for 1 h and at 80 ° C for 3 h to obtain a positive electrode with a thickness of 75 μm, in which the surface loading of lithium iron phosphate was 15 mg / cm 2 .

[0105] 2) Cut the positive electrode prepared above into 4.5×6cm 2 , a 25 μm thick lithium-copper composite strip (lithium layer thickness 15 μm, copper layer thickness 10 μm) was used as the negative electrode and cut into 4.7×6.2 cm 2 The polymer electrolyte prepared above was cut into 4.8×6.3cm 2 , with a thickness of 40μm. In a glove box filled with argon (O2 content ≤ 0.5ppm, H2O content ≤ 0.5ppm), the battery cell is assembled in the order of positive electrode, polymer electrolyte, and lithium copper composite tape, and an all-solid-state battery is obtained after packaging.

[0106] Example 2

[0107] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that of Embodiment 1, except that, in the preparation of the polymer electrolyte, in step 3), the molar ratio of the compound represented by Formula I-1 and the compound represented by Formula II-1 is replaced to 90:10.

[0108] Example 3

[0109] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that of Embodiment 1, except that, in the preparation of the polymer electrolyte, in step 3), the molar ratio of the compound represented by Formula I-1 and the compound represented by Formula II-1 is replaced to 70:30.

[0110] Example 4

[0111] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that of Embodiment 1, except that, in the preparation of the polymer electrolyte, in step 3), the molar ratio of the compound represented by Formula I-1 and the compound represented by Formula II-1 is replaced to 60:40.

[0112] Example 5

[0113] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that of Embodiment 1, except that, in the preparation of the polymer electrolyte, in step 3), the compound represented by Formula I-1 is replaced by the compound represented by Formula I-2.

[0114]

[0115] Example 6

[0116] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that in Embodiment 1, except that, in the preparation of the polymer electrolyte, in step 3), the compound represented by Formula I-1 is replaced by the compound represented by Formula I-3.

[0117]

[0118] Example 7

[0119] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that of Embodiment 1, except that, in the preparation of the polymer electrolyte, the compound represented by formula III-1 in step 1) is replaced by the compound represented by formula III-2, and correspondingly, the compound represented by formula II-2 is obtained in step 2), and the compound represented by formula II-1 is also replaced by the compound represented by formula II-2 in step 3).

[0120]

[0121] Example 8

[0122] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that of Embodiment 1, except that, in the preparation of the polymer electrolyte, the compound represented by formula III-1 in step 1) is replaced by the compound represented by formula III-3, and correspondingly, the compound represented by formula II-3 is obtained in step 2), and the compound represented by formula II-1 is also replaced by the compound represented by formula II-3 in step 3).

[0123]

[0124] Example 9

[0125] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that of Example 1, except that, in the preparation of the polymer electrolyte, in step 3), the molar ratio of the sum of the polyethylene glycol structural units in the compound represented by Formula I-1 and the compound represented by Formula II-1 to LiTFSI is replaced with 10:1.

[0126] Example 10

[0127] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that of Example 1, except that, in the preparation of the polymer electrolyte, in step 3), the molar ratio of the sum of the polyethylene glycol structural units in the compound represented by Formula I-1 and the compound represented by Formula II-1 to LiTFSI is replaced with 25:1.

[0128] Embodiment 11

[0129] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that of Example 1, except that, in the preparation of the polymer electrolyte, in step 3), the molar ratio of the sum of the polyethylene glycol structural units in the compound represented by Formula I-1 and the compound represented by Formula II-1 to LiTFSI is replaced with 8:1.

[0130] Example 12

[0131] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that of Example 1, except that, in the preparation of the polymer electrolyte, in step 3), the molar ratio of the sum of the polyethylene glycol structural units in the compound represented by Formula I-1 and the compound represented by Formula II-1 to LiTFSI is replaced with 30:1.

[0132] Example 13

[0133] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is substantially the same as that of Embodiment 1, except that, in the preparation of the all-solid-state battery, the thickness of the polymer electrolyte is replaced with 20 μm.

[0134] Embodiment 14

[0135] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that of Embodiment 1, except that in the preparation of the all-solid-state battery, the thickness of the polymer electrolyte is replaced with 50 μm.

[0136] Embodiment 15

[0137] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is substantially the same as that of Embodiment 1, except that, in the preparation of the all-solid-state battery, the thickness of the polymer electrolyte is replaced with 15 μm.

[0138] Example 16

[0139] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that of Embodiment 1, except that in the preparation of the all-solid-state battery, the thickness of the polymer electrolyte is replaced with 60 μm.

[0140] Embodiment 17

[0141] This embodiment provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that of Example 1, except that, in the preparation of the polymer electrolyte, LiTFSI in step 2) and step 3) is replaced with lithium perchlorate, and in step 2), a compound represented by formula II-4 is obtained, and in step 3), the compound represented by formula II-1 is replaced with a compound represented by formula II-4.

[0142]

[0143] Comparative Example 1

[0144] This comparative example provides a polymer electrolyte and an all-solid-state battery. The steps for preparing the polymer electrolyte are as follows:

[0145] The compound represented by formula I-1 and LiTFSI were mixed in a molar ratio of polyethylene glycol structural units to LiTFSI of 18:1, and then 0.5% AIBN based on the mass of the compound represented by formula I-1 was added to the mixture as an initiator, and the mixture was heated to 60° C. for polymerization for 4 hours to obtain a polymer electrolyte.

[0146] The preparation method of the all-solid-state battery refers to Example 1.

[0147] Comparative Example 2

[0148] This comparative example provides a polymer electrolyte and an all-solid-state battery. The steps for preparing the polymer electrolyte are as follows:

[0149] Step 1) and step 2) are consistent with Example 1, and step 3) is replaced by: mixing the compound represented by formula II-1 with LiTFSI in a molar ratio of polyethylene glycol structural unit to LiTFSI of 18:1, and then adding 0.5% AIBN as an initiator based on the mass of the compound represented by formula II-1 to the mixture, heating to 60°C for polymerization for 4 hours to obtain a polymer electrolyte.

[0150] The preparation method of the all-solid-state battery refers to Example 1.

[0151] Comparative Example 3

[0152] This comparative example provides a polymer electrolyte and an all-solid-state battery. The steps for preparing the polymer electrolyte are as follows:

[0153] 1) Referring to the preparation method of formula II-1 in Example 1, the raw material formula III-1 is replaced by , to prepare the compound represented by formula a;

[0154] 2) The compound represented by formula a and the compound represented by formula b are mixed in a molar ratio of 80:20 to obtain a mixture, LiTFSI is added to the mixture in a ratio of 18:1 between the polyethylene glycol structural unit and LiTFSI in the mixture, and 0.5% of AIBN based on the total mass of the compound represented by formula a and the compound represented by formula b is added as an initiator, and the mixture is heated to 60° C. for polymerization for 4 hours to obtain a polymer electrolyte.

[0155]

[0156] The preparation method of the all-solid-state battery refers to Example 1.

[0157] Comparative Example 4

[0158] This comparative example provides a polymer electrolyte and an all-solid-state battery. The steps for preparing the polymer electrolyte are as follows:

[0159] The compound represented by formula I-1 and the compound represented by formula b are mixed in a molar ratio of 80:20 to obtain a mixture, and LiTFSI is added to the mixture in a ratio of 18:1 between the polyethylene glycol structural unit and LiTFSI in the mixture, and then 0.5% of AIBN based on the total mass of the compound represented by formula I-1 and the compound represented by formula b is added as an initiator, and the mixture is heated to 60° C. for polymerization for 4 hours to obtain a polymer electrolyte.

[0160] Comparative Example 5

[0161] This comparative example provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that in Example 1, except that, in the preparation of the polymer electrolyte, in step 3), the compound represented by formula I-1 is replaced by the compound represented by formula I-4.

[0162]

[0163] Comparative Example 6

[0164] This comparative example provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that of Example 1, except that, in the preparation of the polymer electrolyte, in step 3), the compound represented by formula I-1 is replaced by the compound represented by formula I-5.

[0165]

[0166] Comparative Example 7

[0167] This comparative example provides a polymer electrolyte and an all-solid-state battery, and the preparation method thereof is basically the same as that in Example 1, except that, in the preparation of the polymer electrolyte, the compound represented by formula III-1 in step 1) is replaced by the compound represented by formula III-5, and correspondingly, the compound represented by formula II-5 is obtained in step 2), and the compound represented by formula II-1 is also replaced by the compound represented by formula II-5 in step 3).

[0168]

[0169] Test Case

[0170] 1. The following properties of the polymer electrolytes prepared in the above examples and comparative examples were tested:

[0171] 1. Lithium ion migration number

[0172] Test method: Use a lithium sheet with a diameter of 16 mm as an electrode, cut the polymer electrolyte into a disc with a diameter of 19 mm, assemble it into a Li||Li symmetric battery, and test the lithium ion migration number and ion conductivity of the Li||Li symmetric battery. Use an electrochemical workstation to apply a polarization voltage of 10 mV to the battery, and the polarization time is 2 hours. Test the current and impedance of the symmetric battery before and after polarization, and calculate the lithium ion migration number according to the following formula.

[0173]

[0174] Among them, t + is the lithium ion migration number, I0 and I ss are the current before polarization begins and the current after polarization stabilizes, R0 and R ss are the impedance before polarization begins and the impedance after polarization stabilizes, and ∆V is the polarization voltage.

[0175] 2. Ionic conductivity

[0176] Test method: Use a punching machine to cut stainless steel sheets with a diameter of 16 mm and a thickness of 200 μm, and a polymer electrolyte membrane with a diameter of 19 mm; stack the stainless steel sheets and polymer electrolyte membrane in order, so that the polymer electrolyte membrane is between the stainless steel sheets, and assemble a stainless steel symmetrical battery. Put the stainless steel symmetrical battery in a 60°C oven for 10 minutes and then test the impedance of the stainless steel symmetrical battery.

[0177] The ionic conductivity of the polymer electrolyte was calculated according to the following formula:

[0178]

[0179] Wherein, σ is the ionic conductivity of the electrolyte, L is the thickness of the polymer electrolyte membrane, S is the area of ​​the stainless steel sheet, and R is the impedance of the stainless steel symmetric cell.

[0180] The above test results are shown in Table 1.

[0181] 2. The following performance tests were performed on the all-solid-state batteries prepared in the above embodiments and comparative examples:

[0182] 1. Cycle performance

[0183] Test method: At 60℃, charge the battery to 3.8V at a constant current of 0.05C, let it stand for 5 minutes, and then discharge it to 2.5V at a constant current of 0.05C. Repeat the above process 3 times. Then charge it to 3.8V at a rate of 0.2C, and charge it to 0.01C at 3.8V, let it stand for 5 minutes, and finally discharge it to 2.5V at a rate of 0.2C, let it stand for 5 minutes. Repeat this cycle until the specific capacity of the battery is 80% of the initial capacity, and record the number of cycles at this time.

[0184] 2. Rate performance

[0185] Test method: At 60°C, charge the battery to 3.8V at a constant current of 0.05C, let it stand for 5 minutes, and then discharge it to 2.5V at a constant current of 0.05C. Repeat the above process 3 times. Then charge it to 3.8V at a rate of 0.1C, let it stand for 5 minutes, then discharge it to 2.5V at a rate of 0.1C, let it stand for 5 minutes, then charge it to 3.8V at a rate of 0.5C, record the charging capacity of 0.5C and 0.1C, and calculate the 0.5C / 0.1C rate charging capacity retention rate by 0.5C charging capacity / 0.1C charging capacity.

[0186] The test results of the above values ​​are listed in Table 1.

[0187] Table 1

[0188]

[0189] The following conclusions can be drawn from Table 1:

[0190] 1) From the comparison of Examples 1 to 8 and Comparative Examples 5 to 7, it can be seen that the proportion of imidazole ionic liquid units has a significant effect on the lithium ion migration number of the polymer electrolyte. The greater the proportion of imidazole ionic liquid units, the higher the lithium ion migration number; the content of polyethylene glycol segments has a significant effect on the ionic conductivity of the polymer electrolyte. The content of polyethylene glycol segments is related to the values ​​of n and m. The smaller the content of polyethylene glycol segments, the more it affects the transmission of lithium ions, resulting in low ionic conductivity. When the content of polyethylene glycol segments is higher, it is easy to increase the crystallinity of the polymer electrolyte, which also leads to a decrease in ionic conductivity. Among them, compared with the other embodiments, Example 4 has a larger proportion of the compound represented by Formula II and a relatively high imidazole content, so it has a higher lithium ion migration number, but in comparison, the content of polyethylene glycol segments is relatively low, resulting in lower ionic conductivity, and thus the cycle performance and rate performance are relatively poor.

[0191] 2) From the comparison of Examples 1 and 9 to 12, it can be seen that when the molar ratio of the polyethylene glycol segment to LiTFSI in the compound represented by Formula I-1 and the compound represented by Formula II is in the range of (10 to 25): 1, the polymer electrolyte has both excellent lithium ion migration number and ion conductivity, and the battery has both excellent cycle performance and rate performance. However, when the molar ratio of the two is outside the above range, namely 8: 1 and 30: 1, respectively, the content of the lithium salt is too much or too little. When the content of the lithium salt is too much, the lithium salt cannot be dissociated, resulting in a small number of lithium ions that can be dissociated and transmitted. When the content of the lithium salt is too little, it will also lead to a small number of lithium ions transmitted, which will lead to a low lithium ion migration number and ion conductivity of the polymer electrolyte, and the cycle performance and rate performance of the battery are also relatively poor.

[0192] 3) From the comparison of Examples 1 and 13 to 16, it can be seen that the thickness of the polymer electrolyte has a certain influence on the cycle performance and rate performance of the battery. When the thickness of the polymer electrolyte is within 20 to 50 μm, the battery can have both relatively excellent lithium ion cycle performance and rate performance. When the thickness of the polymer electrolyte is low (15 μm), the lithium ion transmission path is shorter and has more excellent rate performance, but the battery is more prone to short circuit, resulting in poor cycle performance. When the thickness of the polymer electrolyte is high (60 μm), the battery is not prone to short circuit and has better cycle performance, but the lithium ion transmission path is longer, resulting in poor rate performance of the battery.

[0193] 4) From the comparison between Examples 1 and 17, it can be seen that different types of lithium salts and R anions can make the polymer electrolyte have both excellent lithium ion transference number and ion conductivity, and the battery has both excellent cycle performance and rate performance.

[0194] 5) From the comparison between Example 1 and Comparative Examples 1 and 2, it can be seen that when only the polymer obtained by using the compound shown in Formula I-1 as a monomer is mixed with a lithium salt to obtain a polymer electrolyte, the obtained polymer has no cross-linking and has poor mechanical strength, which causes the battery to be easily short-circuited. The battery has poor performance in all aspects, especially the cycle performance. When only the polymer obtained by using the compound shown in Formula II-1 as a monomer is mixed with a lithium salt to obtain a polymer electrolyte, the obtained polymer has too much cross-linking, resulting in the polymer electrolyte being too rigid, having poor compatibility with the positive and negative electrode interfaces, and having poor contact, which in turn leads to poor ionic conductivity, cycle performance and rate performance.

[0195] 6) From the comparison between Example 1 and Comparative Example 3, it can be seen that when the compound represented by Formula a and the compound represented by Formula b are cross-linked and polymerized, microphase separation is likely to occur, thereby reducing the lithium ion migration number and ion conductivity of the polymer electrolyte, and the cycle performance and rate performance of the battery are also poor.

[0196] 7) From the comparison between Example 1, Comparative Example 3 and Comparative Example 4, it can be seen that when the two polymerized monomers of Comparative Example 4 do not contain imidazolium ionic liquid groups, although the presence of the polyethylene glycol segment can make the electrolyte have a higher ionic conductivity, the lithium ion migration number is poor, and accordingly, the cycle performance and rate performance of the battery are also poor.

[0197] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polymer electrolyte comprising a polymer and a lithium salt, characterized in that: The polymer includes a cross-linked product obtained by copolymerizing the compound represented by Formula I and the compound represented by Formula II: ； ； In formula I, m is 9; In formula II, R is selected from bis(trifluoromethylsulfonyl)imide, bis(fluorosulfonyl)imide, perchlorate, tetrafluoroborate, dioxalate borate, difluorooxalate borate or trifluoromethylsulfonate, and n is 3; The copolymerization molar ratio of the compound represented by formula I and the compound represented by formula II is (70-80): (20-30); The molar ratio of the sum of the polyethylene glycol structural units in the compound represented by formula I and the compound represented by formula II to the lithium salt is (10-25):

1.

2. The polymer electrolyte according to claim 1, characterized in that The lithium salt includes one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium dioxalatoborate, and lithium perchlorate.

3. A method for preparing a polymer electrolyte according to any one of claims 1 to 2, characterized in that: The following steps are involved: A free radical initiator is added to a mixed system of the compound represented by formula I, the compound represented by formula II and a lithium salt to initiate a polymerization reaction, thereby obtaining the polymer electrolyte.

4. The preparation method according to claim 3, characterized in that: The compound represented by formula II is prepared by a method comprising the following steps: 1) reacting 1-vinylimidazole with the compound represented by formula III to obtain the compound represented by formula IV; ， In formula III, X is selected from Cl, Br or I; 2) allowing the compound represented by formula IV to undergo an ion exchange reaction with LiR to obtain the compound represented by formula II; 。 5. The preparation method according to claim 4, characterized in that: The polymerization reaction temperature is 60-100° C. and the reaction time is 4-12 hours.

6. A battery comprising a positive electrode, a negative electrode and an electrolyte layer between the positive electrode and the negative electrode, characterized in that: The electrolyte layer comprises the polymer electrolyte according to any one of claims 1 to 2; The thickness of the electrolyte layer is 20-50 μm.

7. An electronic device, characterized in that: Comprising the battery as claimed in claim 6.

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