A gel electrolyte precursor, its preparation, a gel electrolyte, and a lithium metal battery

Abstract

The present invention discloses a gel electrolyte precursor and its preparation, a gel electrolyte, and a lithium metal battery. The gel electrolyte precursor includes a lithium salt, an organic solvent, a crosslinking agent monomer, and a thermal initiator. The lithium salt includes lithium nitrate and lithium bis(trifluoromethanesulfonyl)imide. The crosslinking agent monomer includes polyethylene glycol diacrylate or 1-vinylimidazole bis(trifluoromethanesulfonyl)imide. The gel electrolyte is obtained by in-situ free radical polymerization of the gel electrolyte precursor through thermal initiation. The lithium metal battery provided by the present invention includes the gel electrolyte. The gel electrolyte of the present invention has a high ionic conductivity, good mechanical flexibility, and a wide electrochemical window. There is good compatibility, interface stability, and low interface impedance between the gel electrolyte and metallic lithium. Side reactions are effectively inhibited, and the prepared lithium metal battery has good cycle stability, capacity retention rate, and Coulomb efficiency.

Description

Technical Field

[0001] The present invention relates to a gel electrolyte precursor, a preparation method thereof, a gel electrolyte, and a lithium metal battery, belonging to the technical field of new energy batteries. Background Art

[0002] The rapid development of electronic devices and electric vehicles has brought greater challenges to the energy system. To meet the demand for long endurance, there is an urgent need for batteries with higher energy density. Metallic lithium has advantages such as high theoretical specific capacity and low reduction potential, and is one of the ideal anode materials for high-energy-density lithium batteries. However, there are also some problems in the practical application of lithium metal batteries. The battery assembly environment has strict requirements, side reactions occur between the electrolyte and metallic lithium, and during the use of the battery, there is a problem that lithium ions are unevenly deposited on the surface of metallic lithium to form a large number of lithium dendrites, resulting in safety problems. Solid electrolytes have certain mechanical strength and can inhibit the growth of lithium dendrites to a certain extent, but there are problems of low ionic conductivity and poor interfacial contact with the electrode.

[0003] The in-situ polymerization gel electrolyte battery is expected to be an ideal solution to solve the above problems. Liquid electrolytes have the advantages of high conductivity, perfect wettability, and maximized electrolyte / electrode contact area, and solid electrolytes have the advantage of high safety. The gel electrolyte prepared by the in-situ polymerization method is expected to combine the advantages of both and reduce their disadvantages at the same time. The gel electrolyte formed inside the battery by in-situ polymerization has characteristics such as low viscosity, easy handling, and strong wetting ability, can fully infiltrate the active material, generate ideal interfacial contact, thereby obtaining a good ion migration path and inhibiting the growth of lithium dendrites. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a gel electrolyte precursor, a preparation method thereof, a gel electrolyte, and a lithium metal battery.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] In a first aspect, the present invention provides a gel electrolyte precursor, which comprises a lithium salt, an organic solvent, a crosslinking agent monomer and a thermal initiator. The lithium salt comprises lithium nitrate and lithium bis(trifluoromethanesulfonyl)imide. The organic solvent is a mixed solvent composed of ethylene glycol dimethyl ether and 1,3-dioxolane. The crosslinking agent monomer comprises polyethylene glycol diacrylate or 1-vinylimidazole bis(trifluoromethanesulfonyl)imide, and the mass percentage of polyethylene glycol diacrylate or 1-vinylimidazole bis(trifluoromethanesulfonyl)imide in the crosslinking agent monomer is above 75%. In the liquid electrolyte composed of the lithium salt and the organic solvent, the concentrations of lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate are 230 - 340 mg / mL and 20 - 50 mg / mL respectively. The masses of the crosslinking agent monomer and the thermal initiator respectively account for 8 - 20% and 0.08 - 0.2% of the total mass of the gel electrolyte precursor.

[0007] Preferably, in the mixed solvent composed of ethylene glycol dimethyl ether and 1,3-dioxolane, the volume ratio of ethylene glycol dimethyl ether to 1,3-dioxolane is 1:0.5 - 2, and most preferably 1:1.

[0008] Preferably, the thermal initiator is an azo thermal initiator, such as azobisisobutyronitrile.

[0009] Preferably, the crosslinking agent monomer further comprises at least one of pentaerythritol tetraacrylate, ethoxylated trimethylolpropane triacrylate, and triethylene glycol diacrylate.

[0010] Preferably, in the liquid electrolyte composed of the lithium salt and the organic solvent, the concentrations of lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate are 273 - 301 mg / mL and 48 - 53 mg / mL respectively, and more preferably 287.1 mg / mL and 50 mg / mL.

[0011] Preferably, the lithium salt further comprises lithium difluoro(oxalato)borate. In the liquid electrolyte composed of the lithium salt and the organic solvent, the concentration of lithium difluoro(oxalato)borate is 14 - 43 mg / mL -1 , and more preferably 27 - 30 mg / mL.

[0012] Preferably, the crosslinking monomer is polyethylene glycol diacrylate or a combination of polyethylene glycol diacrylate and at least one of pentaerythritol tetraacrylate, ethoxylated trimethylolpropane triacrylate, and triethylene glycol diacrylate. The lithium salt consists of lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, and lithium nitrate. In the liquid electrolyte composed of the lithium salt and an organic solvent, the concentrations of lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, and lithium nitrate are 273 - 301 mg / mL, 27 - 30 mg / mL, and 48 - 53 mg / mL, respectively. Further preferably, the concentrations of lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, and lithium nitrate are 273 - 301 mg / mL, 27 - 30 mg / mL, and 50 mg / mL, respectively. Even more preferably, the concentrations of lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, and lithium nitrate are 287.1 mg / mL, 28.8 mg / mL, and 50 mg / mL, respectively.

[0013] Preferably, the crosslinking monomer is 1 - vinylimidazole bis(trifluoromethanesulfonyl)imide, and the lithium salt consists of lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate. In the liquid electrolyte composed of the lithium salt and an organic solvent, the concentrations of lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate are 273 - 301 mg / mL and 48 - 53 mg / mL, respectively. Further preferably, they are 273 - 301 mg / mL and 50 mg / mL, respectively. Even more preferably, they are 287.1 mg / mL and 50 mg / mL;

[0014] Alternatively, the lithium salt consists of lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, and lithium nitrate. In the liquid electrolyte composed of the lithium salt and an organic solvent, the concentrations of lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, and lithium nitrate are 273 - 301 mg / mL, 27 - 30 mg / mL, and 48 - 53 mg / mL, respectively. Further preferably, they are 273 - 301 mg / mL, 27 - 30 mg / mL, and 50 mg / mL, respectively. Even more preferably, they are 287.1 mg / mL, 28.8 mg / mL, and 50 mg / mL, respectively.

[0015] Preferably, the masses of the crosslinking monomer and the thermal initiator account for 14 - 16% and 0.14 - 0.16% of the total mass of the gel electrolyte precursor, respectively.

[0016] Preferably, the gel electrolyte precursor consists of a lithium salt, an organic solvent, a crosslinking monomer, and a thermal initiator.

[0017] In a second aspect, the present invention provides a method for preparing the gel electrolyte precursor described in the first aspect, and the preparation method is as follows: Dissolve a lithium salt in an organic solvent and stir well to obtain a liquid electrolyte; add a crosslinking monomer and a thermal initiator to the liquid electrolyte and stir well to obtain a gel electrolyte precursor.

[0018] In a third aspect, the present invention provides a gel electrolyte, which is obtained by in-situ free radical polymerization of the gel electrolyte precursor described in the first aspect.

[0019] Preferably, the polymerization conditions are: the polymerization temperature is 50 - 70 °C, more preferably 60 °C; the polymerization time is 2 - 12 h, further preferably 4 - 7 h, and even more preferably 6 h.

[0020] In a fourth aspect, the present invention provides a lithium metal battery, which includes a positive electrode, a negative electrode, and an electrolyte, and the electrolyte is the gel electrolyte described in the third aspect.

[0021] In the lithium metal battery described above, the positive electrode and the negative electrode can both adopt the positive electrode and the negative electrode commonly used in lithium metal batteries, and the assembly method can also be carried out in a conventional manner.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: Through the preferred combination of a lithium salt, an organic solvent, and a crosslinking monomer, the present invention prepares a gel electrolyte with certain mechanical strength by in-situ polymerization technology and applies it to a lithium metal battery. The beneficial effects are as follows:

[0023] 1. The gel electrolyte of the present invention has high ionic conductivity, good mechanical flexibility, and a wide electrochemical window. There is good compatibility, interfacial stability, and low interfacial impedance between the gel electrolyte and metallic lithium, and side reactions are effectively inhibited, so that it shows a high stable cycle time and low overpotential in a lithium symmetric battery.

[0024] 2. The lithium metal full battery prepared with the gel electrolyte of the present invention has good cycle stability, capacity retention rate, and Coulomb efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is an optical photograph of the in-situ polymerization gel electrolyte prepared in Example 1 of the present invention.

[0026] Figure 2 It is a test chart of the lithium ion transference number of the in-situ polymerization gel electrolyte prepared in Example 1 of the present invention.

[0027] Figure 3 It is a comparative chart of the cycle tests of the lithium symmetric batteries prepared in Example 1 (adding LiDFOB) and Example 6 (not adding LiDFOB) of the present invention.

[0028] Figure 4 It is a comparative graph of cycle tests of lithium iron phosphate || lithium batteries prepared in Example 1 (i.e., gel electrolyte) and Comparative Example 1 (i.e., liquid electrolyte) of the present invention.

[0029] Figure 5 It is a cycle test graph of the lithium iron phosphate || lithium battery prepared in Example 1 of the present invention.

[0030] Figure 6 It is the first-cycle capacity-voltage curve graph of the lithium iron phosphate || lithium battery prepared in Example 2 of the present invention.

[0031] Figure 7 It is the linear sweep voltammogram of the in-situ polymerized gel electrolyte prepared in Example 4 of the present invention.

[0032] Figure 8 It is a cycle test graph of the lithium symmetric battery prepared in Example 4 of the present invention.

[0033] Figure 9 It is an ionic conductivity test graph of the in-situ polymerized gel electrolyte prepared in Example 5 of the present invention.

[0034] Figure 10 It is a cycle test graph of the lithium iron phosphate || lithium battery prepared in Example 5 of the present invention. Specific Embodiments

[0035] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Assembly of the battery: Assemble a CR2032 coin cell in a glove box filled with argon. Place the positive electrode sheet into the positive electrode case, put on the glass fiber separator, drop 50 μL of the in-situ polymerized gel electrolyte precursor, then place the negative electrode sheet, stainless steel gasket, stainless steel spring piece, and negative electrode case in sequence, and finally press and seal on a sealing machine.

[0037] The following detections are carried out on an in-situ polymerized gel electrolyte prepared in the following examples: Among them, the test temperature is 30 °C.

[0038] 1. Test the ionic conductivity of the in-situ polymerized gel electrolyte by the alternating current impedance method.

[0039] Assemble the test system into a stainless steel symmetric battery, select electrochemical impedance spectroscopy (EIS) test on a CHI660E electrochemical workstation, and the frequency range is 10 -1 -10 6 Hz.

[0040] 2. Test the impedance of the lithium symmetric battery by the alternating current impedance method.

[0041] The test system was assembled into a lithium symmetric battery, and electrochemical impedance spectroscopy (EIS) test was selected on a CHI660E electrochemical workstation, with a frequency range of 10 -1 -10 6 Hz.

[0042] 3. The lithium ion transference number of the in-situ polymerization gel electrolyte was tested by chronoamperometry.

[0043] The test system was assembled into a lithium symmetric battery, and chronoamperometry (i-t) test was selected on a CHI660E electrochemical workstation, with a voltage of 10 mV and a time of 1200 s.

[0044] 4. The electrochemical window of the in-situ polymerization gel electrolyte was tested by linear sweep voltammetry.

[0045] The test system was assembled into a stainless steel||lithium battery, and linear sweep voltammetry test was selected on a CHI660E electrochemical workstation, with a voltage range from the open circuit voltage of the battery to -5.5 V.

[0046] The test system was assembled into a lithium iron phosphate||lithium battery. The lithium iron phosphate electrode was purchased from Kelude, with a coating areal density of 12.3 mg cm -2 . Cyclic voltammetry test was selected on a CHI660E electrochemical workstation, with a voltage range of 2.5 - 4.2 V.

[0047] 5. Charge-discharge cycle performance test.

[0048] The battery was subjected to charge-discharge cycling using a Neware battery test system. The main test contents included:

[0049] (1) The lithium symmetric battery was tested for lithium deposition / stripping cycling at a current density of 0.5 mA cm -2 and an areal capacity of 0.5 mAh cm -2 .

[0050] (2) The cycle stability, capacity retention rate, Coulombic efficiency, etc. of the lithium iron phosphate||lithium battery were tested under cycling at 0.2 C and 0.5 C rates, with a voltage range of 2.5 - 4.2 V.

[0051] Example 1

[0052] 1) Lithium nitrate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluoro(oxalato)borate were added to an equal-volume mixed solvent of ethylene glycol dimethyl ether and 1,3-dioxolane and stirred well to obtain a liquid electrolyte; among them, the concentration of lithium nitrate was 50 mgmL -1 , and the concentration of lithium bis(trifluoromethanesulfonyl)imide was 287.1 mg mL -1, the concentration of lithium difluorooxalate borate is 28.8 mg / mL -1 ; the stirring speed is 400 rpm and the stirring time is 4 h.

[0053] 2) Add polyethylene glycol diacrylate monomer and azobisisobutyronitrile to the liquid electrolyte prepared in step 1) and stir well to obtain an in-situ polymerization gel electrolyte precursor solution; wherein, polyethylene glycol diacrylate accounts for 15% of the total mass of the in-situ polymerization gel electrolyte, and azobisisobutyronitrile accounts for 0.15% of the total mass of the in-situ polymerization gel electrolyte; the stirring speed is 400 rpm and the stirring time is 4 h.

[0054] 3) Heat the in-situ polymerization gel electrolyte precursor solution prepared in step 2) to initiate cross-linking polymerization reaction to obtain an in-situ polymerization gel electrolyte; wherein, the heating temperature is 60 °C and the heating time is 6 h.

[0055] Figure 1 is the optical photograph of the in-situ polymerization gel electrolyte of Example 1 of the present invention; the in-situ polymerization gel electrolyte in this example is yellow.

[0056] Figure 2 is the test chart of the lithium ion transference number of the in-situ polymerization gel electrolyte of Example 1 of the present invention; according to the current and interfacial impedance values of the steady state and the initial state, the calculated lithium ion transference number can reach 0.68; a higher lithium ion transference number means that during charge and discharge, lithium ions can be transferred between the positive and negative electrodes more efficiently.

[0057] Figure 3 is the comparison chart of the deposition / stripping cycle test of the lithium symmetric battery of Example 1 of the present invention and Comparative Example 1; the lithium symmetric battery of Example 1 can be stably cycled for 3000 h, and the overpotential can be maintained at about 11 mV for a long time.

[0058] Figure 4 is the comparison chart of the cycle test of the lithium iron phosphate || lithium battery of Example 1 of the present invention and Comparative Example 2, and the charge and discharge rate is 0.2 C; the initial discharge specific capacity of the battery of Example 1 is 169.3 mAh / g -1 , the initial Coulomb efficiency is 96.8%, and the capacity retention rate is still 82.3% after 200 cycles.

[0059] Figure 5 is the cycle test chart of the lithium iron phosphate || lithium battery of Example 1 of the present invention; discharging at a rate of 0.5 C, the initial discharge specific capacity of the battery of Example 1 is 160.2 mAh / g -1 , the initial Coulomb efficiency is 96.1%, and the capacity retention rate is still 91.2% after 100 cycles.

[0060] The ionic conductivity of the in-situ polymerized gel electrolyte prepared in this example is 2.1×10 -3 S cm -1 , and the electrochemical window is 4.7 V.

[0061] Example 2

[0062] 1) Lithium nitrate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluoro(oxalato)borate were added to an equal-volume mixed solvent of ethylene glycol dimethyl ether and 1,3-dioxolane and stirred well to obtain a liquid electrolyte; among them, the concentration of lithium nitrate was 20 mgmL -1 , the concentration of lithium bis(trifluoromethanesulfonyl)imide was 287.1 mg mL -1 , and the concentration of lithium difluoro(oxalato)borate was 28.8 mgmL -1 ; the stirring speed was 400 rpm, and the stirring time was 4 h.

[0063] 2) Polyethylene glycol diacrylate monomer and azobisisobutyronitrile were added to the liquid electrolyte prepared in step 1) and stirred well to obtain an in-situ polymerized gel electrolyte precursor solution; among them, polyethylene glycol diacrylate accounted for 15% of the total mass of the in-situ polymerized gel electrolyte, and azobisisobutyronitrile accounted for 0.15% of the total mass of the in-situ polymerized gel electrolyte; the stirring speed was 400 rpm, and the stirring time was 4 h.

[0064] 3) The in-situ polymerized gel electrolyte precursor solution prepared in step 2) was heated to initiate a cross-linking polymerization reaction to obtain an in-situ polymerized gel electrolyte; among them, the heating temperature was 60 °C, and the heating time was 6 h.

[0065] Figure 6 is the first-cycle capacity-voltage curve of the lithium metal battery prepared in Example 2 of the present invention; the in-situ polymerized gel electrolyte prepared in this example is yellow; the lithium symmetric battery can be stably cycled for 1000 h; at a discharge rate of 0.2 C, the first-cycle discharge specific capacity of lithium iron phosphate || lithium battery is 160.3 mAh g -1 , and the first-cycle Coulombic efficiency is 94.3%.

[0066] Example 3

[0067] 1) Lithium nitrate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluoro(oxalato)borate were added to an equal-volume mixed solvent of ethylene glycol dimethyl ether and 1,3-dioxolane and stirred well to obtain a liquid electrolyte; among them, the concentration of lithium nitrate was 50 mgmL -1 , the concentration of lithium bis(trifluoromethanesulfonyl)imide was 287.1 mg mL -1 , and the concentration of lithium difluoro(oxalato)borate was 28.8 mgmL -1; The stirring speed is 400 rpm and the stirring time is 4 h.

[0068] 2) Add polyethylene glycol diacrylate monomer, pentaerythritol tetraacrylate monomer and azobisisobutyronitrile to the liquid electrolyte prepared in step 1) and stir well to obtain an in-situ polymerization gel electrolyte precursor solution; wherein, polyethylene glycol diacrylate accounts for 12% of the total mass of the in-situ polymerization gel electrolyte, pentaerythritol tetraacrylate accounts for 3% of the total mass of the in-situ polymerization gel electrolyte, and azobisisobutyronitrile accounts for 0.15% of the total mass of the in-situ polymerization gel electrolyte; the stirring speed is 400 rpm and the stirring time is 4 h.

[0069] 3) Heat the in-situ polymerization gel electrolyte precursor solution prepared in step 2) to initiate a cross-linking polymerization reaction to obtain an in-situ polymerization gel electrolyte; wherein, the heating temperature is 60 °C and the heating time is 6 h.

[0070] The in-situ polymerization gel electrolyte prepared in this example is yellow; the lithium symmetric battery can be stably cycled for 2500 h, and the overpotential can be maintained at about 7 mV for a long time; at a discharge rate of 0.2 C, the initial discharge specific capacity of the lithium iron phosphate || lithium battery is 157.1 mAh g -1 , the initial Coulombic efficiency is 96.5%, and the capacity retention rate is still 75.5% after 180 cycles.

[0071] Example 4

[0072] 1) Add lithium nitrate and lithium bis(trifluoromethanesulfonyl)imide to an equal-volume mixed solvent of ethylene glycol dimethyl ether and 1,3-dioxolane and stir well to obtain a liquid electrolyte; wherein, the concentration of lithium nitrate is 50 mg mL -1 , and the concentration of lithium bis(trifluoromethanesulfonyl)imide is 287.1 mg mL -1 ; the stirring speed is 400 rpm and the stirring time is 4 h.

[0073] 2) Add 1-vinylimidazole bis(trifluoromethanesulfonyl)imide monomer and azobisisobutyronitrile to the liquid electrolyte prepared in step 1) and stir well to obtain an in-situ polymerization gel electrolyte precursor solution; wherein, 1-vinylimidazole bis(trifluoromethanesulfonyl)imide accounts for 15% of the total mass of the in-situ polymerization gel electrolyte, and azobisisobutyronitrile accounts for 0.15% of the total mass of the in-situ polymerization gel electrolyte; the stirring speed is 400 rpm and the stirring time is 4 h.

[0074] 3) Heat the in-situ polymerization gel electrolyte precursor solution prepared in step 2) to initiate a cross-linking polymerization reaction to obtain an in-situ polymerization gel electrolyte; wherein, the heating temperature is 60 °C and the heating time is 6 h.

[0075] Figure 7 It is the linear sweep voltammogram of the in-situ polymerization gel electrolyte prepared in Example 4 of the present invention; the electrochemical window of this gel electrolyte can reach 5.0 V.

[0076] Figure 8 It is the cycle test chart of the lithium symmetric battery prepared in Example 4 of the present invention; the lithium symmetric battery of Example 4 can be stably cycled for 700 h.

[0077] The in-situ polymerization gel electrolyte prepared in this example is colorless; discharged at a rate of 0.5 C, the initial discharge specific capacity of the lithium iron phosphate || lithium battery is 158.0 mAh g -1 , the initial coulombic efficiency is 93.6%, and the capacity retention rate is still 75.8% after 100 cycles.

[0078] Example 5

[0079] 1) Lithium nitrate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorooxalate borate were added to an equal-volume mixed solvent of ethylene glycol dimethyl ether and 1,3-dioxolane and stirred well to obtain a liquid electrolyte; among them, the concentration of lithium nitrate was 50 mgmL -1 , the concentration of lithium bis(trifluoromethanesulfonyl)imide was 287.1 mg mL -1 , the concentration of lithium difluorooxalate borate was 28.8 mgmL -1 ; the stirring speed was 400 rpm, and the stirring time was 4 h.

[0080] 2) 1-Vinylimidazole bis(trifluoromethanesulfonyl)imide monomer and azobisisobutyronitrile were added to the liquid electrolyte prepared in step 1) and stirred well to obtain an in-situ polymerization gel electrolyte precursor solution; among them, 1-vinylimidazole bis(trifluoromethanesulfonyl)imide accounted for 15% of the total mass of the in-situ polymerization gel electrolyte, and azobisisobutyronitrile accounted for 0.15% of the total mass of the in-situ polymerization gel electrolyte; the stirring speed was 400 rpm, and the stirring time was 4 h.

[0081] 3) The in-situ polymerization gel electrolyte precursor solution prepared in step 2) was heated to initiate a cross-linking polymerization reaction to obtain an in-situ polymerization gel electrolyte; among them, the heating temperature was 60°C, and the heating time was 6 h.

[0082] Figure 9 It is the ion conductivity test chart of the in-situ polymerization gel electrolyte prepared in Example 5 of the present invention; the ion conductivity of this gel electrolyte can reach 4.0×10 -3 S cm -1 ; the relatively high ion conductivity plays a positive role in the lithium ion transport of the battery, promotes the cycle stability of the battery, and extends the battery life.

[0083] Figure 10 This is a cycle test diagram of the lithium iron phosphate||lithium battery prepared in Example 5 of the present invention; at a discharge rate of 0.5 C, the first cycle discharge specific capacity of the lithium iron phosphate||lithium battery is 155.0 mAh g -1 The first-cycle coulombic efficiency is 95.0%, and the capacity retention rate is still 77.7% after 100 cycles.

[0084] The in-situ polymerized gel electrolyte prepared in this example is colorless; the lithium symmetric battery can be stably cycled for 80 h.

[0085] Example 6

[0086] The in-situ polymerized gel electrolyte was prepared using the same method as in Example 1, except that lithium difluorooxalatoborate was not added in this example.

[0087] The in-situ polymerized gel electrolyte prepared in this embodiment is yellow; Figure 3 As shown in the figure, the lithium symmetric battery can be stably cycled for 1000 h, and the overpotential can be maintained at about 13 mV for a long time. When discharged at a rate of 0.2 C, the first cycle discharge capacity of the lithium iron phosphate||lithium battery is 163.0 mAh g -1 The first cycle coulombic efficiency is 95.3%, and the capacity retention rate after 40 cycles is 85.1%.

[0088] A comparison of the experimental data of Example 6 and Example 1 shows that, when preparing the gel electrolyte, if lithium difluorooxalatoborate is not added, the lithium symmetric battery still exhibits good cycling stability for metallic lithium and a low overpotential. However, if lithium difluorooxalatoborate is not added, the performance of the entire battery will deteriorate because the gel electrolyte without lithium difluorooxalatoborate cannot form a stable boron-containing interface film at the negative electrode, resulting in corrosion of the positive electrode current collector and thus attenuation of battery performance.

[0089] Comparative Example 1

[0090] The liquid electrolyte was prepared using the method of step 1) in Example 1.

[0091] The liquid electrolyte prepared by this comparative example is colorless; Figure 4 As shown, the first cycle discharge capacity of lithium iron phosphate||lithium battery is 165.8 mAh g -1 The first cycle coulombic efficiency is 98.9%, and the capacity retention rate is 63.6% after 200 cycles.

[0092] From the comparison of the experimental data between Comparative Example 1 and Example 1, it can be seen that when preparing the electrolyte, if polyethylene glycol diacrylate is not added, it will lead to a decline in battery performance. Because the liquid electrolyte without the participation of polyethylene glycol diacrylate does not have sufficient mechanical strength to inhibit the growth of lithium dendrites, resulting in the attenuation of battery performance.

[0093] Comparative Example 2

[0094] Prepare the liquid electrolyte using the method in step 1) of Example 3.

[0095] The liquid electrolyte prepared using this comparative example is colorless; the electrochemical window is 4.7 V; the lithium symmetric battery can be stably cycled for 150 h; when discharging at a rate of 0.5 C, the initial discharge specific capacity of the lithium iron phosphate || lithium battery is 161.3 mAh g -1 , the initial Coulombic efficiency is 97.6%, and the capacity retention rate after 100 cycles is 64.3%.

[0096] From the comparison of the experimental data between Comparative Example 2 and Example 4, it can be seen that when preparing the electrolyte, if 1-vinylimidazole bis(trifluoromethanesulfonyl)imide is not added, it will lead to a decline in battery performance. Because the liquid electrolyte without the participation of 1-vinylimidazole bis(trifluoromethanesulfonyl)imide does not have sufficient mechanical strength to inhibit the growth of lithium dendrites, resulting in the attenuation of battery performance.

[0097] The technical features of the above-described embodiments can be combined arbitrarily. The above content is only the preferred embodiments of the present invention. However, as long as the combination of these technical features does not conflict, it should be considered as within the scope described in this specification. Any equivalent changes and improvements made according to the scope of the present invention application should still fall within the scope covered by the patent of the present invention.

Claims

1. A gel electrolyte precursor, characterized in that: The gel electrolyte precursor includes a lithium salt, an organic solvent, a crosslinking monomer, and a thermal initiator. The lithium salt includes lithium nitrate and lithium bis(trifluoromethanesulfonyl)imide. The organic solvent is a mixed solvent composed of ethylene glycol dimethyl ether and 1,3-dioxolane. The crosslinking monomer is polyethylene glycol diacrylate or a combination of polyethylene glycol diacrylate and at least one of pentaerythritol tetraacrylate, ethoxylated trimethylolpropane triacrylate, and triethylene glycol diacrylate. The mass percentage of polyethylene glycol diacrylate in the crosslinking monomer is above 75%. Alternatively, the crosslinking agent is 1-vinylimidazole bis(trifluoromethanesulfonyl)imide. In the liquid electrolyte composed of the lithium salt and the organic solvent, the concentrations of lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate are 230 - 340 mg / mL and 20 - 50 mg / mL in sequence. The masses of the crosslinking monomer and the thermal initiator respectively account for 8 - 20% and 0.08 - 0.2% of the total mass of the gel electrolyte precursor.

2. The gel electrolyte precursor according to claim 1, wherein: The thermal initiator is an azo thermal initiator.

3. The gel electrolyte precursor according to claim 1, wherein: The lithium salt further includes lithium difluoro(oxalato)borate. In the liquid electrolyte composed of the lithium salt and the organic solvent, the concentration of lithium difluoro(oxalato)borate is 14 - 43 mg mL -1 .

4. The gel electrolyte precursor according to claim 1, wherein: The crosslinking monomer is polyethylene glycol diacrylate or a combination of polyethylene glycol diacrylate and at least one of pentaerythritol tetraacrylate, ethoxylated trimethylolpropane triacrylate, and triethylene glycol diacrylate. The lithium salt is composed of lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, and lithium nitrate. In the liquid electrolyte composed of the lithium salt and the organic solvent, the concentrations of lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, and lithium nitrate are 273 - 301 mg / mL, 27 - 30 mg / mL, and 48 - 53 mg / mL in sequence. Alternatively, the crosslinking monomer is 1-vinylimidazole bis(trifluoromethanesulfonyl)imide. The lithium salt is composed of lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate. In the liquid electrolyte composed of the lithium salt and the organic solvent, the concentrations of lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate are 273 - 301 mg / mL and 48 - 53 mg / mL in sequence. Or the lithium salt is composed of lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, and lithium nitrate. In the liquid electrolyte composed of the lithium salt and the organic solvent, the concentrations of lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, and lithium nitrate are 273 - 301 mg / mL, 27 - 30 mg / mL, and 48 - 53 mg / mL in sequence.

5. The gel electrolyte precursor according to claim 1, characterized in that: The gel electrolyte precursor is composed of a lithium salt, an organic solvent, a crosslinking monomer, and a thermal initiator.

6. A method for preparing a gel electrolyte precursor as described in any one of claims 1-5, characterized in that: The preparation method is as follows: Dissolve the lithium salt in the organic solvent and stir well to obtain a liquid electrolyte; add the crosslinking monomer and the thermal initiator to the liquid electrolyte and stir well to obtain the gel electrolyte precursor.

7. A gel electrolyte is obtained by in-situ free radical polymerization of the gel electrolyte precursor according to any one of claims 1 - 5 through thermal initiation.

8. The gel electrolyte according to claim 7, characterized in that: The polymerization conditions are: the polymerization temperature is 50 - 70 °C; the polymerization time is 2 - 12 h.

9. A lithium metal battery, comprising a positive electrode, a negative electrode and an electrolyte, characterized in that: The electrolyte is the gel electrolyte according to claim 7.

10. The lithium metal battery according to claim 9, characterized in that: The lithium metal battery further includes a glass fiber separator.

11. The lithium metal battery according to claim 9 or 10, characterized in that: The lithium metal battery is a lithium symmetric battery or a lithium iron phosphate || lithium battery.

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