Method for synergistically optimizing electrochemical stability window and ionic conductivity of aqueous sodium-ion battery electrolyte

Abstract

The invention relates to a method for synergistically optimizing an electrochemical stability window and ionic conductivity of an aqueous sodium-ion battery electrolyte, and belongs to the technical field of aqueous sodium-ion batteries. According to the invention, a trifluoromethanesulfonate system electrolyte is used as an aqueous sodium ion battery electrolyte, the trifluoromethanesulfonate system electrolyte is composed of sodium trifluoromethanesulfonate, an additive and deionized water, and the additive is a C2H5NO-(NH4) 2SO4 mixed additive or a C2H5NO-NH4OTf mixed additive; and the concentration of sodium trifluoromethanesulfonate in the electrolyte of the trifluoromethanesulfonate system is 0.8-1 mol / L. The additive C2H5NO is added into the trifluoromethanesulfonate system electrolyte, abundant hydrogen bond ligands are provided, and a cross-linked structure among water molecules is destroyed, so that an electrochemical stability window of the electrolyte is effectively widened; and meanwhile, (NH4) 2SO4 or NH4OTf is introduced as a regulator, so that the problem that the ionic conductivity is reduced due to addition of acetamide is solved, and the overall performance of the electrolyte is optimized.

Description

Technical Field

[0001] The present invention relates to a method for collaboratively optimizing the electrochemical stability window and ionic conductivity of an aqueous sodium ion battery electrolyte, and belongs to the technical field of aqueous sodium ion batteries. Background Art

[0002] A key challenge for aqueous sodium-ion batteries (NAIBs) is the narrow electrochemical stability window (ESW) of water (only 1.23 V), resulting in low energy density. In recent years, researchers have developed "water-in-salt" electrolytes (WISEs) and their derivatives. Recent studies have shown that the development of WISE electrolyte systems and their improved formulations has brought significant breakthroughs in aqueous battery technology. These systems can in situ form a protective SEI film on the anode surface, significantly extending the electrolyte stability window. For example, Suo's team demonstrated that using a high-concentration electrolyte system of 21 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) resulted in a voltage window of approximately 3.0 V. However, these systems still have several shortcomings that require urgent improvement. The current electrochemical window is still insufficient to meet commercialization requirements, and ion transport kinetics are suboptimal. Against this backdrop, polyethylene glycol (PEG) polymers, with their excellent properties, have attracted widespread attention. PEG chains contain abundant -OH groups, which readily form HBs with water molecules, disrupting the hydrogen bonding network between water molecules. In 2020, Lu's team designed a "molecularly crowded electrolyte" for the first time by introducing PEG as an electrolyte additive for high-voltage aqueous lithium-ion batteries. This extended the electrochemical window of the electrolyte to ~3.2V. However, although the electrochemical stability window was widened, its ionic conductivity was significantly reduced to only 0.8mScm. −1 Therefore, we need to find a new electrolyte system with both high electrochemical stability window and high ionic conductivity to provide theoretical support and technical guarantee for the practical application of aqueous sodium ion batteries. Summary of the Invention

[0003] In response to the problems of low electrochemical stability window and improved ionic conductivity of existing aqueous electrolytes, the present invention proposes a method for synergistically optimizing the electrochemical stability window and ionic conductivity of aqueous sodium ion battery electrolytes. By adding the additive C2H5NO to the trifluoromethanesulfonate system electrolyte, rich hydrogen bonding ligands are provided to destroy the cross-linking structure between water molecules, thereby effectively widening the electrochemical stability window of the electrolyte; at the same time, (NH4)2SO4 or NH4OTf is introduced as a regulator to compensate for the decrease in ionic conductivity caused by the addition of acetamide, thereby optimizing the overall performance of the electrolyte.

[0004] A method for synergistically optimizing the electrochemical stability window and ionic conductivity of an aqueous sodium ion battery electrolyte, wherein a trifluoromethanesulfonate system electrolyte is used as the aqueous sodium ion battery electrolyte, the trifluoromethanesulfonate system electrolyte being composed of sodium trifluoromethanesulfonate, an additive, and deionized water, wherein the additive is a C2H5NO-(NH4)2SO4 mixed additive or a C2H5NO-NH4OTf mixed additive; The concentration of sodium trifluoromethanesulfonate in the trifluoromethanesulfonate system electrolyte is 0.8-1 mol / L.

[0005] Preferably, when the additive is a C2H5NO-(NH4)2SO4 mixed additive, the concentration of C2H5NO is 9~9.6mol / L, and the concentration of (NH4)2SO4 is 0.8~1.1mol / L.

[0006] Preferably, when the additive is a C2H5NO-NH4OTf mixed additive, the concentration of C2H5NO is 9-9.6 mol / L, and the concentration of NH4OTf is 0.98-1.2 mol / L.

[0007] Preferably, the electrochemical stability window of the trifluoromethanesulfonate system electrolyte is 3.2-3.61 V, and the conductivity value is 21.3-42.6 mS / cm.

[0008] Preferably, the negative electrode material of the aqueous sodium ion battery is a titanium-based polyanion compound NaTi2(PO4)3 / C, and the positive electrode material is a vanadium-based polyanion compound Na3V2(PO4)3 / C.

[0009] The present invention coordinates the mechanism of improving the electrochemical stability window and ionic conductivity of aqueous sodium ion battery electrolyte: using C2H5NO with rich hydrogen bonding ligands, water molecules and acetamide generate more hydrogen bonds, forming acetamide-water complexes, destroying the cross-linking structure between water molecules, resulting in a reduction in the number of free water molecules, thereby effectively widening the electrochemical stability window of the electrolyte. At the same time, (NH4)2SO4 or NH4OTf is introduced as a regulator. Due to the NH4 + The coordination number with water and acetamide is extremely low, which increases the number of free ions and leads to increased conductivity; it compensates for the decrease in ionic conductivity caused by the addition of acetamide, thereby optimizing the overall performance of the electrolyte.

[0010] The beneficial effects of the present invention are: (1) The present invention adds a C2H5NO-(NH4)2SO4 mixed additive or a C2H5NO-NH4OTf mixed additive to the trifluoromethanesulfonate system electrolyte. The C2H5NO additive can destroy the hydrogen bond network of water, thereby expanding the electrochemical stability window. However, due to the addition of the C2H5NO4 additive, the ionic conductivity decreases from 42.6mS / cm to 21.3mS / cm; the addition of the additive (NH4)2SO4 or NH4OTf can compensate for the decrease in ionic conductivity caused by the addition of acetamide, thereby increasing the ionic conductivity to 33.1-35.2mS / cm. At the same time, it also has a wider electrochemical stability window of 3.54-3.61V; (2) The aqueous sodium ion full battery electrolyte of the present invention forms a solid electrolyte interface layer during the cycle process, which improves the structural stability and electrochemical performance of the positive and negative electrode materials in the trifluoromethanesulfonate aqueous electrolyte, thereby enhancing the cycle stability of the aqueous sodium ion battery. It is low in cost and simple to operate. The addition of C2H5NO can keep it in liquid form in low temperature domains. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 1 is a linear sweep voltammetry curve of the trifluoromethanesulfonate electrolyte in Example 1; Figure 2 1 is a linear sweep voltammetry curve of the trifluoromethanesulfonate electrolyte in Example 2; Figure 3 The electrochemical performance test of the triflate electrolyte in Example 1 is as follows: Figure 4 The electrochemical performance test of the trifluoromethanesulfonate electrolyte in Example 2 is as follows; Figure 5 The electrochemical performance test of the trifluoromethanesulfonate electrolyte in Example 1 is as follows; Figure 6 This is the electrochemical performance test of the trifluoromethanesulfonate system electrolyte in Example 2. DETAILED DESCRIPTION

[0012] The present invention will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0013] Example 1: A method for synergistically optimizing the electrochemical stability window and ionic conductivity of an aqueous sodium ion battery electrolyte, wherein a trifluoromethanesulfonate system electrolyte is used as the aqueous sodium ion battery electrolyte, the trifluoromethanesulfonate system electrolyte consisting of sodium trifluoromethanesulfonate, an additive (C2H5NO-(NH4)2SO4) and deionized water, wherein the concentration of sodium trifluoromethanesulfonate in the trifluoromethanesulfonate system electrolyte is 0.8 mol / L, the concentration of the additive (C2H5NO) is 9 mol / L, and the concentration of the additive ((NH4)2SO4) is 0.8 mol / L; Electrochemical tests were performed by linear sweep voltammetry using a triflate electrolyte without C2H5NO-(NH4)2SO4 as a reference and Ag / AgCl as a reference electrode; Figure 1 As shown, the electrochemical stability window of the trifluoromethanesulfonate system electrolyte without adding C2H5NO-(NH4)2SO4 is about 3.2V, and its ionic conductivity is 42.6mS / cm at room temperature; the electrochemical stability window of the trifluoromethanesulfonate system electrolyte with adding C2H5NO-(NH4)2SO4 in this embodiment is about 3.58V, and its ionic conductivity is 33.1mS / cm at room temperature; In this embodiment, the GCD curves of Na3V2(PO4)3 / C and NaTi2(PO4)3 / C electrode materials in an electrolyte are tested by a three-electrode system, including a working electrode (active material is Na3V2(PO4)3 / C or NaTi2(PO4)3 / C), a reference electrode (Ag / AgCl), a counter electrode (graphite carbon rod) and a trifluoromethanesulfonate system electrolyte, wherein the working electrode comprises a stainless steel current collector and a Na3V2(PO4)3 / C or NaTi2(PO4)3 / C material layer coated on the surface of the stainless steel current collector, wherein the Na3V2(PO4)3 / C material layer comprises a Na3V2(PO4)3 / C active material, a conductive agent (carbon black C65) and a binder (PTFE), and the NaTi The 2(PO4)3 / C material layer includes NaTi2(PO4)3 / C active material, conductive agent (carbon black C65) and binder (PTFE); in terms of mass percentage, Na3V2(PO4)3 / C accounts for 70%, conductive agent (carbon black C65) accounts for 20%, and binder (PTFE) accounts for 10% of the Na3V2(PO4)3 / C material layer; in terms of mass percentage, NaTi2(PO4)3 / C accounts for 80%, conductive agent (carbon black C65) accounts for 20%, and binder (PTFE) accounts for 10% of the NaTi2(PO4)3 / C material layer; the weight of the Na3V2(PO4)3 material layer on the stainless steel mesh is 3.5 mg, and the weight of the NaTi2(PO4)3 / C material layer on the positive electrode stainless steel mesh is 4 mg; like Figure 3As shown, the trifluoromethanesulfonate electrolyte without adding C2H5NO-(NH4)2SO4 is -1 At this current density, the first discharge specific capacity of Na3V2(PO4)3 / C is 63.56mAhg -1 , the coulombic efficiency is 42.23%, and the discharge capacity gradually decreases with the increase of cycle number. The discharge capacity of the sixth cycle is 53.89 mAh / g, and the coulombic efficiency is 97.89%. Figure 5 As shown, at 0.1Ag -1 Under the current density, NaTi2(PO4)3 / C in 0.8MNaOTF electrolyte has a serious HER, which makes the negative electrode unable to discharge normally; the trifluoromethanesulfonate electrolyte with C2H5NO-(NH4)2SO4 additive has a high HER under the current density of 0.1Ag. -1 At the current density of 0.1A, the first discharge capacity of Na3V2(PO4)3 / C reached 57.52mAh / g, and its coulombic efficiency was 79%. The discharge capacity gradually increased with the increase of cycle number. The discharge capacity of the sixth cycle was 58.31mAh / g, and the coulombic efficiency was 88.63%. -1 Under the current density, the first discharge capacity of NaTi2(PO4)3 / C reaches a specific capacity of 50.12mAh / g, and the discharge specific capacity gradually increases with the number of cycles to reach a discharge capacity of 63.1mAh / g in the sixth cycle.

[0014] Example 2: A method for synergistically optimizing the electrochemical stability window and ionic conductivity of an aqueous sodium ion battery electrolyte, wherein a trifluoromethanesulfonate system electrolyte is used as the aqueous sodium ion battery electrolyte, the trifluoromethanesulfonate system electrolyte consisting of sodium trifluoromethanesulfonate, an additive (C2H5NO-(NH4)2SO4) and deionized water, wherein the concentration of sodium trifluoromethanesulfonate in the trifluoromethanesulfonate system electrolyte is 0.8 mol / L, the concentration of the additive (C2H5NO) is 9.3 mol / L, and the concentration of the additive ((NH4)2SO4) is 1 mol / L; Taking the trifluoromethanesulfonate electrolyte without adding C2H5NO-(NH4)2SO4 as a reference and Ag / AgCl as a reference electrode, the electrochemical test was carried out by linear sweep voltammetry. The electrochemical stability window of the trifluoromethanesulfonate electrolyte without adding C2H5NO-(NH4)2SO4 was about 3.2V, and its ionic conductivity was 42.6mS / cm at room temperature. Figure 2 As shown, the electrochemical stability window of the triflate system electrolyte solution with C2H5NO-(NH4)2SO4 added in this embodiment is about 3.56V, and its ionic conductivity is 33.8mS / cm at room temperature; In this embodiment, the GCD curves of Na3V2(PO4)3 / C and NaTi2(PO4)3 / C electrode materials in an electrolyte are tested by a three-electrode system, including a working electrode (active material is Na3V2(PO4)3 / C or NaTi2(PO4)3 / C), a reference electrode (Ag / AgCl), a counter electrode (graphite carbon rod) and a trifluoromethanesulfonate system electrolyte, wherein the working electrode comprises a stainless steel current collector and a Na3V2(PO4)3 / C or NaTi2(PO4)3 / C material layer coated on the surface of the stainless steel current collector, wherein the Na3V2(PO4)3 / C material layer comprises a Na3V2(PO4)3 / C active material, a conductive agent (carbon black C65) and a binder (PTFE), and the NaTi The 2(PO4)3 / C material layer includes NaTi2(PO4)3 / C active material, conductive agent (carbon black C65) and binder (PTFE); in terms of mass percentage, Na3V2(PO4)3 / C accounts for 70%, conductive agent (carbon black C65) accounts for 20%, and binder (PTFE) accounts for 10% of the Na3V2(PO4)3 / C material layer; in terms of mass percentage, NaTi2(PO4)3 / C accounts for 80%, conductive agent (carbon black C65) accounts for 20%, and binder (PTFE) accounts for 10% of the NaTi2(PO4)3 / C material layer; the weight of the Na3V2(PO4)3 material layer on the stainless steel mesh is 3.5 mg, and the weight of the NaTi2(PO4)3 / C material layer on the positive electrode stainless steel mesh is 4 mg; The trifluoromethanesulfonate electrolyte without adding C2H5NO-(NH4)2SO4 was -1 At this current density, the first discharge specific capacity of Na3V2(PO4)3 / C is 63.56mAhg -1 , the coulombic efficiency is 42.23%, and the discharge capacity gradually decreases with the increase of cycle number. The discharge capacity of the sixth cycle is 53.89mAh / g, and the coulombic efficiency is 97.89%; at 0.1Ag -1 Under the current density, NaTi2(PO4)3 / C in 0.8MNaOTF electrolyte has a serious HER, which makes the negative electrode unable to discharge normally; Figure 4 As shown, the trifluoromethanesulfonate electrolyte with C2H5NO-(NH4)2SO4 additive is added at 0.1Ag -1 Under the current density, the first discharge capacity of Na3V2(PO4)3 / C reaches 56.42mAh / g, and its coulombic efficiency is 78.48%. The discharge capacity gradually increases with the increase of cycle number. The discharge capacity of the sixth cycle is 58.61mAh / g, and the coulombic efficiency is 86.83%. Figure 6 As shown, at 0.1Ag -1Under the current density, the first discharge capacity of NaTi2(PO4)3 / C reached a specific capacity of 49.92mAh / g, and the discharge specific capacity gradually increased with the number of cycles to a discharge capacity of 62.22mAh / g in the sixth cycle; this is in sharp contrast to the serious HER that occurred in the electrolyte without adding C2H5NO-(NH4)2SO4, which resulted in the negative electrode being unable to discharge normally.

[0015] Example 3: A method for synergistically optimizing the electrochemical stability window and ionic conductivity of an aqueous sodium ion battery electrolyte, wherein a trifluoromethanesulfonate system electrolyte is used as the aqueous sodium ion battery electrolyte, the trifluoromethanesulfonate system electrolyte consisting of sodium trifluoromethanesulfonate, an additive (C2H5NO-(NH4)2SO4) and deionized water, wherein the concentration of sodium trifluoromethanesulfonate in the trifluoromethanesulfonate system electrolyte is 0.8 mol / L, the concentration of the additive (C2H5NO) is 9.6 mol / L, and the concentration of the additive ((NH4)2SO4) is 1.1 mol / L; Taking the trifluoromethanesulfonate system electrolyte without adding C2H5NO-(NH4)2SO4 as a reference and Ag / AgCl as a reference electrode, an electrochemical test was performed by linear sweep voltammetry. The electrochemical stability window of the trifluoromethanesulfonate system electrolyte without adding C2H5NO-(NH4)2SO4 was about 3.2V, and its ionic conductivity was 42.6mS / cm at room temperature; the electrochemical stability window of the trifluoromethanesulfonate system electrolyte with added C2H5NO-(NH4)2SO4 in this embodiment was about 3.54V, and its ionic conductivity was 34mS / cm at room temperature; In this embodiment, the GCD curves of Na3V2(PO4)3 / C and NaTi2(PO4)3 / C electrode materials in an electrolyte are tested by a three-electrode system, including a working electrode (active material is Na3V2(PO4)3 / C or NaTi2(PO4)3 / C), a reference electrode (Ag / AgCl), a counter electrode (graphite carbon rod) and a trifluoromethanesulfonate system electrolyte, wherein the working electrode comprises a stainless steel current collector and a Na3V2(PO4)3 / C or NaTi2(PO4)3 / C material layer coated on the surface of the stainless steel current collector, wherein the Na3V2(PO4)3 / C material layer comprises a Na3V2(PO4)3 / C active material, a conductive agent (carbon black C65) and a binder (PTFE), and the NaTi The 2(PO4)3 / C material layer includes NaTi2(PO4)3 / C active material, conductive agent (carbon black C65) and binder (PTFE); in terms of mass percentage, Na3V2(PO4)3 / C accounts for 70%, conductive agent (carbon black C65) accounts for 20%, and binder (PTFE) accounts for 10% of the Na3V2(PO4)3 / C material layer; in terms of mass percentage, NaTi2(PO4)3 / C accounts for 80%, conductive agent (carbon black C65) accounts for 20%, and binder (PTFE) accounts for 10% of the NaTi2(PO4)3 / C material layer; the weight of the Na3V2(PO4)3 material layer on the stainless steel mesh is 3.5 mg, and the weight of the NaTi2(PO4)3 / C material layer on the positive electrode stainless steel mesh is 4 mg; The trifluoromethanesulfonate electrolyte without adding C2H5NO-(NH4)2SO4 was -1 At this current density, the first discharge specific capacity of Na3V2(PO4)3 / C is 63.56mAhg -1 , the coulombic efficiency is 42.23%, and the discharge capacity gradually decreases with the increase of cycle number. The discharge capacity of the sixth cycle is 53.89mAh / g, and the coulombic efficiency is 97.89%; at 0.1Ag -1 Under the current density, NaTi2(PO4)3 / C in 0.8MNaOTF electrolyte has a serious HER, which makes the negative electrode unable to discharge normally; the trifluoromethanesulfonate electrolyte with C2H5NO-(NH4)2SO4 additive has a high HER under the current density of 0.1Ag. -1 At the current density of 0.1A, the first discharge capacity of Na3V2(PO4)3 / C reached 55.2mAh / g, and its coulombic efficiency was 77.8%. The discharge capacity gradually increased with the increase of cycle number. The discharge capacity of the sixth cycle was 57.61mAh / g, and the coulombic efficiency was 85.83%. -1Under the current density, the first discharge capacity of NaTi2(PO4)3 / C reaches a specific capacity of 48.82mAh / g, and the discharge specific capacity gradually increases with the number of cycles to reach a discharge capacity of 61.12mAh / g in the sixth cycle.

[0016] Example 4: A method for synergistically optimizing the electrochemical stability window and ionic conductivity of an aqueous sodium ion battery electrolyte, wherein a trifluoromethanesulfonate system electrolyte is used as the aqueous sodium ion battery electrolyte, the trifluoromethanesulfonate system electrolyte consisting of sodium trifluoromethanesulfonate, an additive (C2H5NO-NH4OTf) and deionized water, wherein the concentration of sodium trifluoromethanesulfonate in the trifluoromethanesulfonate system electrolyte is 0.9 mol / L, the concentration of the additive (C2H5NO) is 9 mol / L, and the concentration of the additive (NH4OTf) is 0.98 mol / L; Taking the triflate system electrolyte without adding C2H5NO-NH4OTf as a reference and Ag / AgCl as a reference electrode, electrochemical testing was performed by linear sweep voltammetry. The electrochemical stability window of the triflate system electrolyte without adding C2H5NO-NH4OTf was about 3.2V, and its ionic conductivity was 42.6mS / cm at room temperature; the electrochemical stability window of the triflate system electrolyte with added C2H5NO-NH4OTf in this embodiment was about 3.59V, and its ionic conductivity was 33.4mS / cm at room temperature; In this embodiment, the GCD curves of Na3V2(PO4)3 / C and NaTi2(PO4)3 / C electrode materials in an electrolyte are tested by a three-electrode system, including a working electrode (active material is Na3V2(PO4)3 / C or NaTi2(PO4)3 / C), a reference electrode (Ag / AgCl), a counter electrode (graphite carbon rod) and a trifluoromethanesulfonate system electrolyte, wherein the working electrode comprises a stainless steel current collector and a Na3V2(PO4)3 / C or NaTi2(PO4)3 / C material layer coated on the surface of the stainless steel current collector, wherein the Na3V2(PO4)3 / C material layer comprises a Na3V2(PO4)3 / C active material, a conductive agent (carbon black C65) and a binder (PTFE), and the NaTi The 2(PO4)3 / C material layer includes NaTi2(PO4)3 / C active material, conductive agent (carbon black C65) and binder (PTFE); in terms of mass percentage, Na3V2(PO4)3 / C accounts for 70%, conductive agent (carbon black C65) accounts for 20%, and binder (PTFE) accounts for 10% of the Na3V2(PO4)3 / C material layer; in terms of mass percentage, NaTi2(PO4)3 / C accounts for 80%, conductive agent (carbon black C65) accounts for 20%, and binder (PTFE) accounts for 10% of the NaTi2(PO4)3 / C material layer; the weight of the Na3V2(PO4)3 material layer on the stainless steel mesh is 3.5 mg, and the weight of the NaTi2(PO4)3 / C material layer on the positive electrode stainless steel mesh is 4 mg; The trifluoromethanesulfonate electrolyte without adding C2H5NO-NH4OTf was -1 At this current density, the first discharge specific capacity of Na3V2(PO4)3 / C is 64mAhg -1 The coulombic efficiency is 43%, and the discharge capacity gradually decreases with the increase of cycle number. The discharge capacity of the sixth cycle is 54.68mAh / g, and the coulombic efficiency is 98%. -1 Under the current density, NaTi2(PO4)3 / C in 0.8MNaOTF electrolyte has a serious HER, which makes the negative electrode unable to discharge normally; the trifluoromethanesulfonate electrolyte with C2H5NO-NH4OTf additive has a high HER under the current density of 0.1Ag. -1 At the current density of 0.1A, the first discharge capacity of Na3V2(PO4)3 / C reached 57.1mAh / g, and its coulombic efficiency was 79.3%. The discharge capacity gradually increased with the increase of cycle number. The discharge capacity of the sixth cycle was 58.8mAh / g, and the coulombic efficiency was 87%. -1 Under the current density, the first discharge capacity of NaTi2(PO4)3 / C reaches a specific capacity of 50.1mAh / g, and the discharge specific capacity gradually increases with the number of cycles to reach a discharge capacity of 61.21mAh / g in the sixth cycle.

[0017] Example 5: A method for synergistically optimizing the electrochemical stability window and ionic conductivity of an aqueous sodium ion battery electrolyte, wherein a trifluoromethanesulfonate system electrolyte is used as the aqueous sodium ion battery electrolyte, the trifluoromethanesulfonate system electrolyte consisting of sodium trifluoromethanesulfonate, an additive (C2H5NO-NH4OTf) and deionized water, wherein the concentration of sodium trifluoromethanesulfonate in the trifluoromethanesulfonate system electrolyte is 1 mol / L, the concentration of the additive (C2H5NO) is 9.4 mol / L, and the concentration of the additive (NH4OTf) is 1.1 mol / L; Taking the trifluoromethanesulfonate system electrolyte without adding C2H5NO-NH4OTf as a reference and Ag / AgCl as a reference electrode, electrochemical testing was performed by linear sweep voltammetry. The electrochemical stability window of the trifluoromethanesulfonate system electrolyte without adding C2H5NO-NH4OTf was about 3.2V, and its ionic conductivity was 42.6mS / cm at room temperature; the electrochemical stability window of the trifluoromethanesulfonate system electrolyte with added C2H5NO-NH4OTf in this embodiment was about 3.6V, and its ionic conductivity was 34.58mS / cm at room temperature; In this embodiment, the GCD curves of Na3V2(PO4)3 / C and NaTi2(PO4)3 / C electrode materials in an electrolyte are tested by a three-electrode system, including a working electrode (active material is Na3V2(PO4)3 / C or NaTi2(PO4)3 / C), a reference electrode (Ag / AgCl), a counter electrode (graphite carbon rod) and a trifluoromethanesulfonate system electrolyte, wherein the working electrode comprises a stainless steel current collector and a Na3V2(PO4)3 / C or NaTi2(PO4)3 / C material layer coated on the surface of the stainless steel current collector, wherein the Na3V2(PO4)3 / C material layer comprises a Na3V2(PO4)3 / C active material, a conductive agent (carbon black C65) and a binder (PTFE), and the NaTi The 2(PO4)3 / C material layer includes NaTi2(PO4)3 / C active material, conductive agent (carbon black C65) and binder (PTFE); in terms of mass percentage, Na3V2(PO4)3 / C accounts for 70%, conductive agent (carbon black C65) accounts for 20%, and binder (PTFE) accounts for 10% of the Na3V2(PO4)3 / C material layer; in terms of mass percentage, NaTi2(PO4)3 / C accounts for 80%, conductive agent (carbon black C65) accounts for 20%, and binder (PTFE) accounts for 10% of the NaTi2(PO4)3 / C material layer; the weight of the Na3V2(PO4)3 material layer on the stainless steel mesh is 3.5 mg, and the weight of the NaTi2(PO4)3 / C material layer on the positive electrode stainless steel mesh is 4 mg; The trifluoromethanesulfonate electrolyte without adding C2H5NO-NH4OTf was -1At this current density, the first discharge specific capacity of Na3V2(PO4)3 / C is 64.1mAhg -1 , the coulombic efficiency is 43%, and the discharge capacity gradually decreases with the increase of cycle number. The discharge capacity of the sixth cycle is 54.58mAh / g, and the coulombic efficiency is 98.1%. -1 Under the current density, NaTi2(PO4)3 / C in 0.8MNaOTF electrolyte has a serious HER, which makes the negative electrode unable to discharge normally; the trifluoromethanesulfonate electrolyte with C2H5NO-NH4OTf additive has a high HER under the current density of 0.1Ag. -1 At the current density of 0.1A, the first discharge capacity of Na3V2(PO4)3 / C reached 57.2mAh / g, and its coulombic efficiency was 79.5%. The discharge capacity gradually increased with the increase of cycle number. The discharge capacity of the sixth cycle was 60.8mAh / g, and the coulombic efficiency was 87%. -1 Under the current density, the first discharge capacity of NaTi2(PO4)3 / C reached a specific capacity of 52.1mAh / g, and the discharge specific capacity gradually increased with the number of cycles to reach a discharge capacity of 62.21mAh / g in the sixth cycle.

[0018] Example 6: A method for synergistically optimizing the electrochemical stability window and ionic conductivity of an aqueous sodium ion battery electrolyte, wherein a trifluoromethanesulfonate system electrolyte is used as the aqueous sodium ion battery electrolyte, the trifluoromethanesulfonate system electrolyte consisting of sodium trifluoromethanesulfonate, an additive (C2H5NO-NH4OTf) and deionized water, wherein the concentration of sodium trifluoromethanesulfonate in the trifluoromethanesulfonate system electrolyte is 1 mol / L, the concentration of the additive (C2H5NO) is 9.6 mol / L, and the concentration of the additive (NH4OTf) is 1.2 mol / L; Taking the trifluoromethanesulfonate system electrolyte without adding C2H5NO-NH4OTf as a reference and Ag / AgCl as a reference electrode, electrochemical testing was performed by linear sweep voltammetry. The electrochemical stability window of the trifluoromethanesulfonate system electrolyte without adding C2H5NO-NH4OTf was about 3.2V, and its ionic conductivity was 42.6mS / cm at room temperature; the electrochemical stability window of the trifluoromethanesulfonate system electrolyte with added C2H5NO-NH4OTf in this embodiment was about 3.61V, and its ionic conductivity was 35.2mS / cm at room temperature; In this embodiment, the GCD curves of Na3V2(PO4)3 / C and NaTi2(PO4)3 / C electrode materials in an electrolyte are tested by a three-electrode system, including a working electrode (active material is Na3V2(PO4)3 / C or NaTi2(PO4)3 / C), a reference electrode (Ag / AgCl), a counter electrode (graphite carbon rod) and a trifluoromethanesulfonate system electrolyte, wherein the working electrode comprises a stainless steel current collector and a Na3V2(PO4)3 / C or NaTi2(PO4)3 / C material layer coated on the surface of the stainless steel current collector, wherein the Na3V2(PO4)3 / C material layer comprises a Na3V2(PO4)3 / C active material, a conductive agent (carbon black C65) and a binder (PTFE), and the NaTi The 2(PO4)3 / C material layer includes NaTi2(PO4)3 / C active material, conductive agent (carbon black C65) and binder (PTFE); in terms of mass percentage, Na3V2(PO4)3 / C accounts for 70%, conductive agent (carbon black C65) accounts for 20%, and binder (PTFE) accounts for 10% of the Na3V2(PO4)3 / C material layer; in terms of mass percentage, NaTi2(PO4)3 / C accounts for 80%, conductive agent (carbon black C65) accounts for 20%, and binder (PTFE) accounts for 10% of the NaTi2(PO4)3 / C material layer; the weight of the Na3V2(PO4)3 material layer on the stainless steel mesh is 3.5 mg, and the weight of the NaTi2(PO4)3 / C material layer on the positive electrode stainless steel mesh is 4 mg; The trifluoromethanesulfonate electrolyte without adding C2H5NO-NH4OTf was -1 At this current density, the first discharge specific capacity of Na3V2(PO4)3 / C is 64.4mAhg -1 The coulombic efficiency is 43.1%, and the discharge capacity gradually decreases with the increase of cycle number. The discharge capacity of the sixth cycle is 54.69 mAh / g, and the coulombic efficiency is 98%. -1 Under the current density, NaTi2(PO4)3 / C in 0.8MNaOTF electrolyte has a serious HER, which makes the negative electrode unable to discharge normally; the trifluoromethanesulfonate electrolyte with C2H5NO-NH4OTf additive has a high HER under the current density of 0.1Ag. -1 At the current density of 0.1A, the first discharge capacity of Na3V2(PO4)3 / C reached 57.28mAh / g, and its coulombic efficiency was 79.2%. The discharge capacity gradually increased with the increase of cycle number. The discharge capacity of the sixth cycle was 61.5mAh / g, and the coulombic efficiency was 87.2%. -1 Under the current density, the first discharge capacity of NaTi2(PO4)3 / C reaches a specific capacity of 52.6mAh / g, and the discharge specific capacity gradually increases with the number of cycles to reach a discharge capacity of 62.28mAh / g in the sixth cycle.

[0019] The above describes the specific embodiments of the present invention in detail, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope of the present invention.

Claims

1. A method for synergistically optimizing the electrochemical stability window and ionic conductivity of an aqueous sodium-ion battery electrolyte, characterized in that: A trifluoromethanesulfonate system electrolyte is used as an aqueous sodium ion battery electrolyte, wherein the trifluoromethanesulfonate system electrolyte is composed of sodium trifluoromethanesulfonate, an additive and deionized water, and the additive is a C2H5NO-(NH4)2SO4 mixed additive or a C2H5NO-NH4OTf mixed additive; The concentration of sodium trifluoromethanesulfonate in the trifluoromethanesulfonate system electrolyte is 0.8-1 mol / L.

2. The method for collaboratively optimizing the electrochemical stability window and ionic conductivity of an aqueous sodium ion battery electrolyte according to claim 1, characterized in that: When the additive is a C2H5NO-(NH4)2SO4 mixed additive, the concentration of C2H5NO is 9-9.6 mol / L, and the concentration of (NH4)2SO4 is 0.8-1.1 mol / L.

3. The method for collaboratively optimizing the electrochemical stability window and ionic conductivity of an aqueous sodium ion battery electrolyte according to claim 1, characterized in that: When the additive is a C2H5NO-NH4OTf mixed additive, the concentration of C2H5NO is 9-9.6 mol / L, and the concentration of NH4OTf is 0.98-1.2 mol / L.

4. The method for collaboratively optimizing the electrochemical stability window and ionic conductivity of an aqueous sodium ion battery electrolyte according to claim 1, characterized in that: The electrochemical stability window of the trifluoromethanesulfonate system electrolyte is 3.2-3.61V, and the conductivity value is 21.3-42.6mS / cm.

5. The method for collaboratively optimizing the electrochemical stability window and ionic conductivity of an aqueous sodium ion battery electrolyte according to claim 1, characterized in that: The negative electrode material of the aqueous sodium ion battery is a titanium-based polyanion compound NaTi2(PO4)3 / C, and the positive electrode material is a vanadium-based polyanion compound Na3V2(PO4)3 / C.

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