An intrinsically safe and efficient electrolyte for rechargeable zinc ion batteries and its preparation and application

Abstract

The present invention relates to an intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery and its preparation and application. The electrolyte comprises a zinc salt and an organic solvent. The organic solvent is a mixed solvent composed of a high-boiling-point non-combustible nitrogen-containing solvent and a highly safe non-combustible ionic liquid. Compared with the prior art, the present invention is non-flammable and significantly improves the safety performance of the battery. In addition, the introduced ionic liquid can be adsorbed on the zinc surface to adjust the local current distribution near the tip of the zinc metal negative electrode, thereby achieving uniform zinc deposition at a higher current density. The prepared intrinsically safe electrolyte can achieve long-term stable circulation without dendrites under high current conditions, as well as ultra-high zinc deposition dissolution efficiency, which is more advantageous than other organic electrolyte systems and aqueous electrolyte systems.

Description

Technical Field

[0001] The invention belongs to the technical field of electrolytes, and relates to an intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery and a preparation method thereof. Background Art

[0002] Rechargeable zinc-ion batteries use metallic zinc as the negative electrode and have a high specific capacity (820mAh g -1 ), low electrochemical potential (-0.762V compared to the standard hydrogen electrode), low cost, abundant resources, and environmental friendliness are the development direction of the next generation of batteries.

[0003] The aqueous electrolyte commonly used in rechargeable zinc-ion batteries exhibits thermal instability and will inevitably undergo hydrogen evolution reaction, thereby forming a passivation layer on the surface of the negative electrode and deteriorating the electrochemical performance of the zinc-ion battery. Recently, a large number of organic solvents have been reported and applied to rechargeable zinc-ion battery electrolytes, which can effectively eliminate the unfavorable hydrogen evolution reaction. However, problems such as zinc dendrite growth still exist, and the reported organic solvents are usually volatile and flammable solvents, which pose great safety hazards. Our research group recently reported an organic electrolyte based on phosphate combustion aid (Adv. Mater. 2019, 31, 1900668; Angew. Chem. Int. Ed. 2019, 58, 2760), which can achieve highly safe and stable circulation of zinc metal, but under high current conditions, there are still problems such as interfacial side reactions. Summary of the invention

[0004] The purpose of the present invention is to provide an intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery and its preparation and application, so as to improve the zinc negative electrode interface and achieve high-efficiency and stable circulation under high current conditions.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] One of the technical solutions of the present invention provides an intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery, comprising a zinc salt and an organic solvent, wherein the organic solvent is a mixed solvent composed of a high-boiling-point non-combustible nitrogen-containing solvent and a highly safe non-combustible ionic liquid.

[0007] Furthermore, the high-boiling-point non-combustible nitrogen-containing solvent is selected from one or more combinations of N,N-dimethylpropylene urea, 1,3-dimethyl-2-imidazolidinone, 1-methyl-2-imidazolidinone, and 2-imidazolidinone.

[0008] Furthermore, the highly safe and non-combustible ionic liquid is selected from 3-n-dodecyl-1-vinyl imidazole hexafluorophosphate (C 12VIm-PF6), or at least one of other conventional imidazole ionic liquids (1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium perchlorate, 1-ethyl-3-methylimidazolium bistrifluoromethanesulfonyl imide, 1-ethyl-3-methylimidazolium bisfluorosulfonyl imide, etc.).

[0009] Furthermore, the highly safe and non-combustible ionic liquid is a functionalized ionic liquid C 12 VIm-PF6.

[0010] Furthermore, the volume ratio of the high boiling point non-combustible nitrogen-containing solvent to the highly safe non-combustible ionic liquid is 1:0.05-20.

[0011] Furthermore, the volume ratio of the high boiling point non-combustible nitrogen-containing solvent to the high safety non-combustible ionic liquid is 1:0.1-1, and more preferably, the volume ratio of the nitrogen-containing solvent to the ionic liquid is 9:1. Too low an ionic liquid content cannot effectively optimize the zinc negative electrode interface; too high an ionic liquid content will increase the viscosity of the electrolyte.

[0012] Furthermore, the zinc salt is selected from one or more of zinc chloride (ZnCl2), zinc nitrate (Zn(NO3)2), zinc sulfate (ZnSO4), zinc hexafluorophosphate (Zn(PF6)2), zinc tetrafluoroborate (Zn(BF4)2), zinc perchlorate (Zn(ClO4)2), zinc trifluoromethanesulfonate (Zn(CF3SO3)2), bistrifluoromethanesulfonic acid amide zinc (Zn(TFSI)2), and bis(fluorosulfonyl)imide zinc salt (Zn(FSI)2).

[0013] Furthermore, the amount of zinc salt added satisfies: its concentration in the electrolyte is 0.05-2 mol·L -1 .

[0014] The second technical solution of the present invention provides a method for preparing an intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery. Zinc salt is added to an organic solvent and completely dissolved to obtain the target product, an intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery.

[0015] A third technical solution of the present invention provides an application of an intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery, wherein the electrolyte is used in a rechargeable zinc ion battery.

[0016] The high-boiling-point nitrogen-containing solvent and ionic liquid used in the present invention are both non-flammable, which greatly improves the safety performance of the battery. At the same time, solvents such as N,N-dimethylpropylene urea serve as good solvents for zinc salts to achieve rapid zinc ion transfer. The functionalized ionic liquid is adsorbed on the zinc surface to adjust the local current distribution near the tip of the zinc metal negative electrode, thereby achieving uniform zinc deposition at a higher current density. In addition, the vinyl part and zinc-philic sites (Zn-N, Zn-F) introduced into the ionic liquid can effectively improve the zinc negative electrode interface and inhibit interfacial side reactions. The prepared intrinsically safe electrolyte can be used at high currents (5mA cm -2 ) conditions, achieving dendrite-free stable long cycle and ultra-high zinc deposition and dissolution efficiency (99.44%).

[0017] Compared with the prior art, the electrolyte of the present invention significantly improves the safety performance of rechargeable zinc ion batteries and the stability of zinc negative electrodes, especially achieving long-term stable cycling without dendrites under high current, as well as ultra-high zinc deposition and dissolution efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the functionalized ionic liquid (C 12 VIm-PF6) structural formula.

[0019] Figure 2 is the functionalized ionic liquid (C 12 H-NMR characterization of VIm-PF6).

[0020] Figure 3 The N,N-dimethylpropylene urea (DMPU) and the functionalized ionic liquid (C 12 VIm-PF6), a mixed solvent of the two (volume ratio of 9:1) and C 12 Combustion conditions of the electrolyte when VIm-PF6+DMPU (volume ratio is 1:9) (non-flammable).

[0021] Figure 4 The solvents used in Example 3 are 1,3-dimethyl-2-imidazolidinone (DMI), 1,3-dimethyl-2-imidazolidinone and a mixed solvent of a functionalized ionic liquid (volume ratio of 1:9) and C 12 Combustion conditions of the electrolyte when VIm-PF6+DMI (volume ratio of 9:1) (non-flammable).

[0022] Figure 5 The DMPU-based electrolyte and C in Example 4 12 Contact angle test of VIm-PF6+DMPU (volume ratio of 1:9) based electrolyte on Celgard porous polyethylene membrane.

[0023] Figure 6 The symmetric zinc battery deposition dissolution curve of the DMPU-based electrolyte obtained in Example 5 was tested at a temperature of 25°C and a current density of 1 mA cm -2 , with a surface capacity of 1 mAh cm -2 .

[0024] Figure 7 is C obtained in Example 6 12 The zinc symmetric battery deposition dissolution curve of VIm-PF6+DMPU (volume ratio of 1:9) based electrolyte, the test temperature is 25℃, the current density is 1mA cm -2 , with a surface capacity of 1 mAh cm -2 .

[0025] Figure 8 is C obtained in Example 7 12 The zinc symmetric battery deposition dissolution curve of VIm-PF6+DMPU (volume ratio 1:3) based electrolyte, the test temperature is 25℃, the current density is 0.5mA cm -2 , with a surface capacity of 0.5 mAh cm -2 .

[0026] Fig. 9 The electrolyte obtained in Example 8 is DMPU-based electrolyte and C 12 The zinc deposition morphology after failure of the zinc symmetric battery in the VIm-PF6+DMPU (volume ratio of 1:9) based electrolyte, the test temperature was 25 °C, the current density was 1 mA cm -2 , with a surface capacity of 1 mAh cm -2 .

[0027] Fig.10 The method of Example 9 using C 12 Deposition dissolution curve of zinc symmetric battery under high current conditions in VIm-PF6+DMPU (volume ratio of 1:9) based electrolyte, test temperature is 25℃, current density is 5mA cm -2 , with a surface capacity of 5 mAh cm -2 .

[0028] Fig.11 The method of Example 9 using C 12 Deposition dissolution curve of zinc symmetric battery under large deposition capacity conditions in VIm-PF6+DMPU (volume ratio of 1:9) based electrolyte, test temperature 25℃, current density 1mA cm -2 , with a surface capacity of 10 mAh cm -2 .

[0029] Fig.12 The DMPU-based electrolyte obtained in Example 10 and C 12Comparison of the coulombic efficiency of VIm-PF6+DMPU (volume ratio 1:9) based electrolytes, test temperature 25°C, current density 0.5 mA cm -2 , with a surface capacity of 0.5 mAh cm -2 .

[0030] Fig.13 The method of Example 11 using C 12 Analysis of fluorine components at the negative electrode interface of zinc symmetric battery after 100 cycles in VIm-PF6+DMPU (volume ratio 1:9) based electrolyte, test temperature 25°C, current density 1mA cm -2 , with a surface capacity of 1 mAh cm -2 .

[0031] Fig.14 The method of Example 11 using C 12 Analysis of nitrogen components at the negative electrode interface of a zinc symmetric battery after 100 cycles in a VIm-PF6+DMPU (volume ratio 1:9) based electrolyte at a test temperature of 25°C and a current density of 1 mA cm -2 , with a surface capacity of 1 mAh cm -2 . DETAILED DESCRIPTION

[0032] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0033] In the following examples, unless otherwise specified, the rest of the raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0034] Example 1

[0035] Functionalized ionic liquid C 12 Preparation of VIm-PF6: First, 1-vinylimidazole and dodecane bromide were weighed in a molar ratio of 15:7 for quaternization reaction to prepare 3-n-dodecyl-1-vinylimidazole bromide; then 3-n-dodecyl-1-vinylimidazole bromide and hexafluorophosphate amine were weighed in a molar ratio of 1:1, dissolved in a methanol / water mixed solvent (volume ratio of 15:85), and the bromide ions were replaced by hexafluorophosphate ions. In the process of the fluorine-containing hydrophobic hexafluorophosphate ions gradually replacing the hydrophilic bromide ions, the relative hydrophobicity of the product gradually increased, and finally the functionalized ionic liquid C was obtained. 12 VIm-PF6, structural formula is as follows Figure 1 shown.

[0036] The obtained product was analyzed by nuclear magnetic resonance spectroscopy. Figure 2 As shown in the figure, the hydrogen chemical shifts at different positions in the theoretical product structure and the actual product NMR results can correspond, indicating that the high-purity functionalized ionic liquid C was successfully synthesized. 12 VIm-PF6.

[0037] Example 2

[0038] N,N-dimethylpropylene urea (DMPU) and functionalized ionic liquid (C 12 VIm-PF6), stirred evenly to obtain a mixed solvent, the volume ratio of the two solvents was 9:1, and Zn(CF3SO3)2 was added to the mixed solvent to obtain 0.2M Zn(CF3SO3)2 / C 12 VIm-PF6+DMPU electrolyte (i.e. the concentration of Zn(CF3SO3)2 in the electrolyte is 0.2mol / L, the same below). Through the combustion test, it can be known that Figure 3 The two solvents used, their mixed solvents and the configured electrolyte are non-combustible.

[0039] Example 3

[0040] 1,3-Dimethyl-2-imidazolidinone (DMI) and functionalized ionic liquid (C 12 VIm-PF6), stirred evenly to obtain a mixed solvent, the volume ratio of the two solvents was 9:1, and Zn(CF3SO3)2 was added to the mixed solvent to obtain 0.2M Zn(CF3SO3)2 / C 12 VIm-P F6+DMI electrolyte. Through the combustion test, it can be seen that Figure 4 The two solvents used, their mixed solvents and the configured electrolyte are non-combustible.

[0041] Example 4

[0042] Add Zn(CF3SO3)2 to N,N-dimethylpropylene urea (DMPU) to obtain 0.2M Zn(CF3SO3)2 / DMPU electrolyte, referred to as DMPU-based electrolyte. 12 VIm-PF6+DMPU (volume ratio 1:9) electrolyte, referred to as C 12 VIm-PF6+DMPU (volume ratio of 1:9) based electrolyte was dropped on Celgard porous polyethylene diaphragm for contact angle test. Figure 5 Compared with DMPU-based electrolyte (~60°), C 12The VIm-PF6+DMPU (volume ratio of 1:9) based electrolyte exhibits a smaller contact angle, indicating that the introduction of ionic liquids can effectively increase the membrane wettability of the electrolyte.

[0043] Example 5

[0044] A zinc symmetric button cell was constructed using 0.2M Zn(CF3SO3)2 / DMPU as the electrolyte and a 25-micron thick Celgard porous polyethylene membrane as the separator.

[0045] Deposition / stripping cycles were performed at 25 °C with a current density of 1 mA cm -2 , with a surface capacity of 1 mAh cm -2 ,like Figure 6 As shown, the symmetric cell short-circuited after 40 h, indicating the poor compatibility of the DMPU-based electrolyte with the Zn metal anode.

[0046] Example 6

[0047] 0.2M Zn(CF3SO3)2 / C 12 VIm-PF6+DMPU (volume ratio 1:9) is the electrolyte, and 25-micron-thick Celgard porous polyethylene membrane is the separator, forming a zinc symmetrical button cell.

[0048] Deposition / stripping cycles were performed at 25 °C with a current density of 1 mA cm -2 , with a surface capacity of 1 mAh cm -2 ,like Figure 7 As shown, the symmetrical battery maintains a stable voltage curve within 1600 hours, indicating that the introduction of an appropriate amount of functionalized ionic liquid can effectively improve the zinc negative electrode interface and achieve stable long-term cycling of the zinc negative electrode.

[0049] Example 7

[0050] 0.2M Zn(CF3SO3)2 / C 12 VIm-PF6+DMPU (volume ratio 1:3) is the electrolyte, and 25-micron-thick Celgard porous polyethylene membrane is the separator, forming a zinc symmetrical button cell.

[0051] Deposition / stripping cycles were performed at 25 °C with a current density of 0.5 mA cm -2 , with a surface capacity of 0.5 mAh cm -2 ,like Figure 8 As shown in the figure, the voltage curve of the symmetrical battery fluctuates after 100 hours. Even at a lower current density, the stability of the zinc anode is still lower than that of the C 12 VIm-PF6+DMPU (volume ratio of 1:9) based electrolyte is the zinc negative electrode.

[0052] Example 8

[0053] When using DMPU-based electrolyte and C 12 After the zinc symmetric battery failed when the electrolyte was VIm-PF6+DMPU (volume ratio was 1:9), the zinc negative electrode was analyzed by scanning electron microscope to observe the zinc deposition morphology, such as Fig. 9 shown.

[0054] The Zn metal anode using DMPU-based electrolyte exhibits loose Zn dendrite morphology. 12 The zinc metal anode of VIm-PF6+DMPU (volume ratio of 1:9) based electrolyte presents a three-dimensional interconnected zinc deposition morphology, and the voids within the three-dimensional framework are evenly distributed.

[0055] Example 9

[0056] 0.2M Zn(CF3SO3)2 / C 12 VIm-PF6+DMPU (volume ratio 1:9) is the electrolyte, and 25-micron-thick Celgard porous polyethylene membrane is the separator, forming a zinc symmetrical button cell.

[0057] High current deposition / stripping cycles were performed at 25 °C with a current density of 5 mA cm -2 , with a surface capacity of 5 mAh cm -2 ,like Fig.10 As shown, the symmetric battery exhibits stable cycling for more than 200 h, indicating an extremely strong ability to withstand high currents.

[0058] Simultaneously, large-area capacity deposition / stripping cycles were performed at 25 °C with a current density of 1 mA cm -2 , surface capacity is 10 mAh cm -2 ,like Fig.11 As shown, the symmetric cell exhibits stable cycling for more than 1000 h.

[0059] Example 10

[0060] DMPU-based electrolyte and C 12 VIm-PF6+DMPU (volume ratio of 1:9) based electrolyte, 25 micron thick Celgard porous polyethylene membrane as separator, constitute zinc to stainless steel half-cell.

[0061] Deposition / stripping cycles were performed at 25 °C with a current density of 0.5 mA cm -2 , with a surface capacity of 0.5 mAh cm -2 ,like Fig.12 As shown, compared with DMPU-based electrolyte (98.64%), C 12VIm-PF6+DMPU (volume ratio of 1:9) based electrolyte exhibits higher coulombic efficiency, with an average coulombic efficiency of up to 99.44% after long cycles.

[0062] Embodiment 11

[0063] For using C 12 The interface components of the zinc metal anode after 100 cycles of VIm-PF6+DMPU (volume ratio 1:9) based electrolyte were analyzed. Fig.13 and Fig.14 As shown, an interfacial layer rich in Zn-F and Zn-N is formed at the zinc metal interface, which is conducive to the uniform deposition of zinc.

[0064] Example 12

[0065] This embodiment is substantially the same as Embodiment 6, except that, in this embodiment, the high boiling point nitrogen-containing solvent in the mixed solvent is 1,3-dimethyl-2-imidazolidinone (DMI).

[0066] Embodiment 13

[0067] This embodiment is substantially the same as Embodiment 6, except that, in this embodiment, the high boiling point nitrogen-containing solvent in the mixed solvent is 1-methyl-2-imidazolidinone MMI.

[0068] Embodiment 14

[0069] This embodiment is basically the same as embodiment 6, except that in this embodiment, the high boiling point nitrogen-containing solvent in the mixed solvent is 2-imidazolidinone (MI)

[0070] Embodiment 15

[0071] This embodiment is substantially the same as Embodiment 6, except that, in this embodiment, the ionic liquid in the mixed solvent is 1-ethyl-3-methylimidazolium hexafluorophosphate.

[0072] Example 16

[0073] This embodiment is substantially the same as Embodiment 6, except that, in this embodiment, the ionic liquid in the mixed solvent is 1-butyl-3-methylimidazolium hexafluorophosphate.

[0074] Embodiment 17

[0075] This embodiment is substantially the same as Embodiment 6, except that, in this embodiment, the ionic liquid in the mixed solvent is 1-ethyl-3-methylimidazolium tetrafluoroborate.

[0076] Embodiment 18

[0077] This embodiment is basically the same as Embodiment 6, except that, in this embodiment, the ionic liquid in the mixed solvent is 1-ethyl-3-methylimidazole perchlorate, 1-ethyl-3-methylimidazole bistrifluoromethanesulfonyl imide, and 1-ethyl-3-methylimidazole bisfluorosulfonyl imide.

[0078] Embodiment 19

[0079] This embodiment is substantially the same as Embodiment 6, except that, in this embodiment, the ionic liquid in the mixed solvent is 1-ethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt.

[0080] Embodiment 20

[0081] This embodiment is substantially the same as Embodiment 6, except that, in this embodiment, the ionic liquid in the mixed solvent is 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide salt.

[0082] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. An intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery, characterized in that: It comprises a zinc salt and an organic solvent, wherein the organic solvent is a mixed solvent consisting of a high-boiling-point non-combustible nitrogen-containing solvent and a highly safe non-combustible ionic liquid; The high-boiling-point non-combustible nitrogen-containing solvent is selected from a combination of one or more of N,N-dimethylpropylene urea, 1,3-dimethyl-2-imidazolidinone, 1-methyl-2-imidazolidinone, and 2-imidazolidinone; The highly safe and non-combustible ionic liquid is selected from at least one of 3-n-dodecyl-1-vinyl imidazolium hexafluorophosphate, 1-ethyl-3-methyl imidazolium hexafluorophosphate, 1-butyl-3-methyl imidazolium hexafluorophosphate, 1-ethyl-3-methyl imidazolium tetrafluoroborate, 1-ethyl-3-methyl imidazolium perchlorate, 1-ethyl-3-methyl imidazolium bis trifluoromethanesulfonyl imide salt, and 1-ethyl-3-methyl imidazolium bis fluorosulfonyl imide salt.

2. The intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery according to claim 1, characterized in that: The highly safe and non-combustible ionic liquid is 3-n-dodecyl-1-vinyl imidazole hexafluorophosphate C 12 VIm-PF6.

3. The intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery according to claim 1, characterized in that: The volume ratio of the high boiling point non-combustible nitrogen-containing solvent to the highly safe non-combustible ionic liquid is 1:0.05~20.

4. The intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery according to claim 3, characterized in that: The volume ratio of the high boiling point non-combustible nitrogen-containing solvent to the highly safe non-combustible ionic liquid is 1:0.1~1.

5. The intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery according to claim 1, characterized in that: The zinc salt is selected from one or more of zinc chloride, zinc nitrate, zinc sulfate, zinc hexafluorophosphate, zinc tetrafluoroborate, zinc perchlorate, zinc trifluoromethanesulfonate, bistrifluoromethanesulfonic acid amide zinc, and bisfluorosulfonyl imide zinc salt.

6. The intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery according to claim 1, characterized in that: The amount of zinc salt added is such that its concentration in the electrolyte is 0.05-2 mol·L -1 .

7. The method for preparing an intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery according to any one of claims 1 to 6, characterized in that: Zinc salt is added into an organic solvent and after complete dissolution, the target product, an intrinsically safe and efficient electrolyte for rechargeable zinc ion batteries, is obtained.

8. The use of the intrinsically safe and efficient electrolyte for a rechargeable zinc ion battery as claimed in any one of claims 1 to 6, characterized in that: The electrolyte is used in rechargeable zinc ion batteries.

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