High-rate negative-electrode-free sodium metal battery electrolyte as well as preparation method and application thereof

Abstract

The invention discloses a high-rate negative-electrode-free sodium metal battery electrolyte as well as a preparation method and application thereof, and belongs to the technical field of energy storage batteries. The high-rate negative-electrode-free sodium metal battery electrolyte provided by the invention comprises an organic solvent and sodium salt dissolved in the organic solvent, the organic solvent is prepared by mixing diethylene glycol dimethyl ether (Diglyme) and methyl perfluorobutyl ether (MPE). According to the electrolyte prepared by the invention, molecular arrangement of a solvation cluster is reconstructed through dipole-dipole interaction formed by Dillime and MPE, a preferential reduction sequence of the solvation cluster is changed, spontaneous chemical reaction can be carried out, and NaF-dominated primary SEI construction is directly participated, so that compact NaF SEI can be effectively generated before battery circulation, and the service life of the battery is prolonged. Uniform distribution of Na < + > flux and migration path optimization are realized, compact and uniform metal sodium deposition is promoted, and dendritic crystal growth is effectively inhibited. Therefore, the material has excellent cycling stability and has a wide application prospect in negative-electrode-free sodium metal batteries.

Description

Technical Field

[0001] The present application belongs to the technical field of energy storage batteries, and in particular relates to a high-rate negative-electrode-free sodium metal battery electrolyte, and a preparation method and application thereof. Background Art

[0002] Based on the sodium metal battery system, the negative electrode-free sodium metal battery eliminates the traditional pre-installed sodium negative electrode structure and instead completes the in-situ deposition of sodium metal on the surface of a metal current collector such as copper foil or aluminum foil during the charging process. This design not only significantly improves the volume and weight energy density of the battery, but also simplifies the manufacturing process, reduces safety hazards and production costs. However, it should be noted that during the first charge and discharge of the negative electrode-free sodium metal battery, the negative electrode interface needs to consume a large amount of active sodium provided by the positive electrode to form the SEI film. The accompanying irreversible side reactions will directly lead to battery capacity decay and shortened cycle life. Therefore, how to construct an electrolyte with high chemical stability and efficient sodium replenishment capacity is the key to breaking through the performance bottleneck of the negative electrode-free sodium metal battery.

[0003] Commonly used electrolytes for anode-free sodium metal batteries include ether electrolytes, carbonate electrolytes, and high-concentration electrolytes. However, ether electrolytes easily form organic SEI films, which are loose and unstable. Especially at high-rate charge and discharge, the accelerated sodium deposition rate prevents SEI film repair, exacerbating dendrite growth and capacity decay. Carbonate electrolytes react strongly with sodium metal, easily forming dendrites and a large amount of byproducts. High-concentration electrolytes have high viscosity, high cost, and low ion mobility, making them unsuitable for fast charging. Therefore, there is an urgent need to develop electrolytes with excellent overall performance to improve the electrochemical performance of anode-free sodium metal batteries and enhance their application effectiveness. Summary of the Invention

[0004] The present application discloses a high-rate negative electrode-free sodium metal battery electrolyte and its preparation method and application, aiming to solve the technical problems of poor electrochemical performance and poor cycle stability of existing electrolytes.

[0005] In order to achieve the above objectives, the technical solution of this application is:

[0006] A first aspect of the present application provides a high-rate negative electrode-free sodium metal battery electrolyte, comprising: an organic solvent and a sodium salt dissolved in the organic solvent;

[0007] The organic solvent is prepared by mixing diethylene glycol dimethyl ether and methyl perfluorobutyl ether.

[0008] In combination with the first aspect, preferably, the sodium salt is sodium hexafluorophosphate.

[0009] In combination with the first aspect, preferably, the concentration of the sodium salt is 0.9-1 mol / L.

[0010] Preferably in combination with the first aspect, the concentration of the sodium salt is 1 mol / L.

[0011] Preferably in combination with the first aspect, the volume ratio of the diglyme and the methyl perfluorobutyl ether is (7:3)-(8:2).

[0012] Preferably in combination with the first aspect, the volume ratio of the diglyme and the methyl perfluorobutyl ether is (7:3).

[0013] The second aspect of the present application provides a preparation method of the high-rate anode-free sodium metal battery electrolyte of the first aspect, and the preparation method comprises:

[0014] The sodium salt is dissolved in the mixed solvent prepared from the diglyme and the methyl perfluorobutyl ether, and the anode-free sodium metal battery electrolyte is obtained.

[0015] The third aspect of the present application provides an application of the high-rate anode-free sodium metal battery electrolyte prepared by the preparation method of the second aspect in an anode-free sodium metal battery.

[0016] The fourth aspect of the present application provides an anode-free sodium metal battery comprising the high-rate anode-free sodium metal battery electrolyte of the first aspect or the high-rate anode-free sodium metal battery electrolyte prepared by the preparation method of the second aspect.

[0017] Compared with the prior art, the advantages or beneficial effects of the embodiments of the present application at least include:

[0018] The anode-free sodium metal battery electrolyte provided by the present application is prepared by dissolving a sodium salt in diglyme (Diglyme) and methyl perfluorobutyl ether (MPE). On the one hand, based on the molecular arrangement of the dipole-dipole interaction of Diglyme and MPE to reconfigure the solvation cluster, the preferential reduction sequence is changed, the spontaneous chemical reaction is carried out, the original SEI construction dominated by NaF is directly involved, and the dense NaF SEI can be effectively generated before the battery cycle; on the other hand, the SEI layer rich in NaF realizes the uniform distribution of Na + flux and the optimization of migration path, thereby promoting the dense and uniform metal sodium deposition and effectively inhibiting the dendrite growth; at the same time, the SEI layer formed has an ultra-dense microstructure, has dual stability of anti-solvent decomposition and anti-humidity erosion, provides additional protection for the high-activity sodium metal anode, and has excellent cycle stability, and has a wide application prospect in the anode-free sodium metal battery. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0020] Figure 1 Coulomb efficiency plot of A1 -Negative Electrode Free Sodium Metal Battery Electrolyte (NGMPE), A2 -Negative Electrode Free Sodium Metal Battery Electrolyte (NGMPE (8:2)) and B1 -Negative Electrode Free Sodium Metal Battery Electrolyte (NGMPE (9:1)) in sodium copper half-cell;

[0021] Figure 2 First cycle charge-discharge plot of A1 -Negative Electrode Free Sodium Metal Battery Electrolyte (NGMPE), A2 -Negative Electrode Free Sodium Metal Battery Electrolyte (NGMPE (8:2)) and B1 -Negative Electrode Free Sodium Metal Battery Electrolyte (NGMPE (9:1)) in sodium copper half-cell;

[0022] Figure 3 Coulomb efficiency plot of A1 -Negative Electrode Free Sodium Metal Battery Electrolyte (NGMPE), A3 -Negative Electrode Free Sodium Metal Battery Electrolyte (0.9M NGMPE), B2 -Negative Electrode Free Sodium Metal Battery Electrolyte (0.8M NGMPE), B3 -Negative Electrode Free Sodium Metal Battery Electrolyte (0.7M NGMPE), B4 -Negative Electrode Free Sodium Metal Battery Electrolyte (0.6M NGMPE) and B5 -Negative Electrode Free Sodium Metal Battery Electrolyte (0.5M NGMPE) in sodium copper half-cell;

[0023] Figure 4 First cycle charge-discharge plot of A1 -Negative Electrode Free Sodium Metal Battery Electrolyte (NGMPE), A3 -Negative Electrode Free Sodium Metal Battery Electrolyte (0.9M NGMPE), B2 -Negative Electrode Free Sodium Metal Battery Electrolyte (0.8M NGMPE), B3 -Negative Electrode Free Sodium Metal Battery Electrolyte (0.7M NGMPE), B4 -Negative Electrode Free Sodium Metal Battery Electrolyte (0.6M NGMPE) and B5 -Negative Electrode Free Sodium Metal Battery Electrolyte (0.5M NGMPE) in sodium copper half-cell;

[0024] Figure 5 A1 -Negative Electrode Free Sodium Metal Battery Electrolyte (NGMPE) and B6 -Negative Electrode Free Sodium Metal Battery Electrolyte (NG2) provided by the embodiments of the present application in 5.0 mA / cm 2 and 5.0 mAh / cm 2 SEM image after cycling;

[0025] Figure 6 A1-NGMPE and B6-NG2 made C@Al||NVP full cells, at 8.0 mA / cm 2 and 4.0 mAh / cm 2 SEM images after cycling;

[0026] Figure 7 A1-NGMPE and B6-NG2 made C@Al||NVP full cells, at 8.0 mA / cm 2 and 4.0 mAh / cm 2 Micro-CT 3D reconstruction images of A1-NGMPE and B6-NG2 made C@Al||NVP full cells, at 8.0 mA / cm

[0027] Figure 8 Cryo-TEM images of A1-NGMPE made C@Al||NVP full cells, at 8.0 mA / cm

[0028] Figure 9 HRTEM images of A1-NGMPE made C@Al||NVP full cells, at 8.0 mA / cm

[0029] Figure 10 Estimated energy density plots of different batteries provided in the embodiments of the present application;

[0030] Figure 11 Coulombic efficiency plots of A1-NGMPE and B6-NG2 made C@Al||NVP full cells, at 10 mg cm -2 , 3C conditions;

[0031] Figure 12 Coulombic efficiency plots of A1-NGMPE and B6-NG2 made C@Al||NVP full cells, at 15 mg cm -2 , 1C conditions;

[0032] Figure 13 Voltage capacity distribution plots of A1-NGMPE and B6-NG2;

[0033] Figure 14Coulomb efficiency plots of C@Al||NVP full cells made by adding water to A1-NGMPE and B6-NG2 respectively;

[0034] Figure 15 Coulomb efficiency plots of C@Al||NVP full cells made by adding water to A1-NGMPE and B6-NG2 respectively, at 3mg cm -2 , 10C, 60℃;

[0035] Figure 16 SEM images of C@Al||NVP full cells after cycling of A1-NGMPE and B6-NG2 respectively;

[0036] Figure 17 Coulomb efficiency plots of NVP||Na full cells made by A1-NGMPE and B6-NG2 respectively, at 5mg cm -2 , 10C;

[0037] Figure 18 SEM images of NVP||Na full cells after cycling of A1-NGMPE and B6-NG2 respectively. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0039] In the following description of the present embodiment, the term "and / or" is used to describe the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B, which can represent the cases of A alone, B alone and A and B existing at the same time. Wherein A and B can be singular or plural. The character " / " generally represents that the associated objects before and after it are in an "or" relationship.

[0040] In the following description of the embodiments, the term "at least one" means one or more, and the term "multiple" means two or more. "At least one of the following (one)" or the like refers to any combination of the items, including any combination of single or multiple items. For example, "at least one of a, b or c", or "at least one of a, b and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0041] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of the serial numbers does not mean the order of execution, and some or all steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0042] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0043] It should be noted that all raw reagents in the embodiments of the present application are purchased on the market or prepared according to conventional methods well known to those skilled in the art.

[0044] In a first aspect, the embodiments of the present application provide a high-rate negative-free sodium metal battery electrolyte, comprising: an organic solvent and a sodium salt dissolved in the organic solvent.

[0045] The organic solvent is a mixture of diglyme and methyl perfluorobutyl ether.

[0046] On the one hand, the molecular arrangement of the solvent cluster is restructured by the dipole-dipole interaction between Diglyme and MPE, which changes the preferential reduction sequence, can spontaneously react, and directly participates in the construction of the original SEI dominated by NaF, ensuring that the dense NaF SEI can be effectively generated before the battery cycle; on the other hand, through the SEI layer rich in NaF, the uniform interface properties are realized, and the Na + The uniform distribution of flux and the optimization of migration path further promote the dense and uniform metal sodium deposition and effectively inhibit the growth of dendrites; at the same time, the formed SEI layer has an ultra-dense microstructure, has dual stability of anti-solvent decomposition and anti-humidity erosion, provides additional protection for the high-activity sodium metal negative electrode, and has excellent cycle stability, and has a wide application prospect in the negative-free sodium metal battery.

[0047] In the embodiments of the present application, the sodium salt is preferably sodium hexafluorophosphate. Among them, the sodium salt can be used to quickly in-situ construct an ultra-dense inorganic phase dominated primary solid-state electrolyte interface with diethylene glycol dimethyl ether and methyl perfluorobutyl ether, which promotes the rapid formation of an inorganic dominant SEI layer rich in NaF, accelerates the uniform distribution of Na + flux and the optimization of migration paths, thereby promoting the deposition of dense and uniform sodium metal, and further improving the electrochemical performance.

[0048] In the embodiments of the present application, the concentration of the sodium salt is preferably 0.9-1 mol / L, and more preferably 1 mol / L. Among them, by controlling the concentration of the sodium salt in the electrolyte, too high concentration causes the sodium salt to be unable to dissolve, and too low concentration cannot provide sufficient number of carrier ions and cannot provide high enough ionic conductivity of the electrolyte.

[0049] In the embodiments of the present application, the volume ratio of diethylene glycol dimethyl ether and methyl perfluorobutyl ether is preferably (7:3)-(8:2), and more preferably 7:3. Among them, by taking diethylene glycol dimethyl ether as the main solvent and methyl perfluorobutyl ether as the diluent, by controlling the volume ratio of diethylene glycol dimethyl ether and methyl perfluorobutyl ether, the main solvent is ensured to be dominant, the solubility and salt dissociation degree of the electrolyte are ensured to be sufficient, the ionic conductivity of the electrolyte is ensured, a part of the proportion of fluorinated solvent is ensured, the appropriate solvent-solvent interaction is ensured and sufficient fluorine source is provided, and the appropriate surface fluorination of sodium metal is induced.

[0050] It should be noted that the inorganic dominant SEI layer rich in NaF realizes the uniform distribution of Na + flux and the optimization of migration paths, thereby promoting the deposition of dense and uniform sodium metal. Experiments show that the system can effectively inhibit dendrite growth under high current density and large area capacity conditions. And it can effectively stabilize the electrode / electrolyte interface layer, realize the ultra-high rate charge and discharge and ultra-long cycle of the negative electrode-free sodium metal battery. At the same time, the formed SEI layer has an ultra-dense microstructure, and has dual stability of anti-solvent decomposition and anti-humidity erosion, which provides additional protection for high-activity sodium metal anode.

[0051] In a second aspect, the embodiments of the present application also provide a preparation method of the high-rate negative electrode-free sodium metal battery electrolyte of the first aspect, and the preparation method comprises:

[0052] dissolving the sodium salt in the mixed solvent prepared by diethylene glycol dimethyl ether and methyl perfluorobutyl ether to obtain the high-rate negative electrode-free sodium metal battery electrolyte.

[0053] The third aspect of the present application provides the application of the high-rate anode-free sodium metal battery electrolyte prepared by the preparation method of the first aspect in an anode-free sodium metal battery. Based on the excellent battery rate and cycle stability of the above-mentioned electrolyte, the anode-free sodium metal battery is endowed with excellent electrochemical performance, and has a wide market application prospect.

[0054] The fourth aspect of the present application provides an anode-free sodium metal battery comprising the high-rate anode-free sodium metal battery electrolyte of the first aspect or the high-rate anode-free sodium metal battery electrolyte prepared by the preparation method of the second aspect.

[0055] The technical solutions of the present application will be further described below in combination with specific embodiments.

[0056] Embodiment 1

[0057] The present embodiment provides a preparation method of A1-anode-free sodium metal battery electrolyte (NGMPE), which specifically comprises:

[0058] The configuration process of the electrolyte is carried out in an argon-filled glove box (O2<0.1 PPM, H2O<0.1 PPM), 1M NaPF6 is dissolved in a mixed solvent of diethylene glycol dimethyl ether and methyl perfluorobutyl ether in a volume ratio of 7:3, and slowly stirred at room temperature for 10h to obtain A1-anode-free sodium metal battery electrolyte (NGMPE).

[0059] Embodiment 2

[0060] The components, preparation operation and process parameters of the A2-anode-free sodium metal battery electrolyte (NGMPE(9:1)) prepared by the present application embodiment are basically the same as those of embodiment 1, and the difference lies in that the mixed solvent of diethylene glycol dimethyl ether and methyl perfluorobutyl ether in a volume ratio of 8:2 is used as the preparation material in the present embodiment, and A2-anode-free sodium metal battery electrolyte (NGMPE(8:2)) is prepared.

[0061] Embodiment 3

[0062] The components, preparation operation and process parameters of the A3-anode-free sodium metal battery electrolyte (0.9M NGMPE) prepared by the present application embodiment are basically the same as those of embodiment 1, and the difference lies in that the concentration of NaPF6 used as the preparation material in the present embodiment is 0.9M, and A3-anode-free sodium metal battery electrolyte (0.9M NGMPE) is prepared.

[0063] At the same time, in order to verify the comprehensive performance of the electrolyte prepared in the above embodiments, the present application provides the following comparative examples for detailed description.

[0064] Comparative Example 1

[0065] The component ratio and preparation operation, process parameters of the B1- negative electrode-free sodium metal battery electrolyte (NGMPE (9:1)) prepared in the present application are basically the same as those of Example 1, and the difference lies in that the mixed solvent of diethylene glycol dimethyl ether and methyl perfluorobutyl ether in a volume ratio of 9:1 is used as the raw material for preparation in the present application, and the B1- negative electrode-free sodium metal battery electrolyte (NGMPE (9:1)) is prepared.

[0066] Comparative Example 2

[0067] The component ratio and preparation operation, process parameters of the B2- negative electrode-free sodium metal battery electrolyte (0.8M NGMPE) prepared in the present application are basically the same as those of Example 1, and the difference lies in that the concentration of NaPF6 is 0.8M in the preparation material in the present application, and the B2- negative electrode-free sodium metal battery electrolyte (0.8M NGMPE) is prepared.

[0068] Comparative Example 3

[0069] The component ratio and preparation operation, process parameters of the B3- negative electrode-free sodium metal battery electrolyte (0.7M NGMPE) prepared in the present application are basically the same as those of Example 1, and the difference lies in that the concentration of NaPF6 is 0.7M in the preparation material in the present application, and the B3- negative electrode-free sodium metal battery electrolyte (0.7M NGMPE) is prepared.

[0070] Comparative Example 4

[0071] The component ratio and preparation operation, process parameters of the B4- negative electrode-free sodium metal battery electrolyte (0.6M NGMPE) prepared in the present application are basically the same as those of Example 1, and the difference lies in that the concentration of NaPF6 is 0.6M in the preparation material in the present application, and the B4- negative electrode-free sodium metal battery electrolyte (0.6M NGMPE) is prepared.

[0072] Comparative Example 5

[0073] The component ratio and preparation operation, process parameters of the B5- negative electrode-free sodium metal battery electrolyte (0.5M NGMPE) prepared in the present application are basically the same as those of Example 1, and the difference lies in that the concentration of NaPF6 is 0.5M in the preparation material in the present application, and the B5- negative electrode-free sodium metal battery electrolyte (0.5M NGMPE) is prepared.

[0074] Comparative Example 6

[0075] The B6- negative electrode-free sodium metal battery electrolyte (0.5M NGMPE) prepared by the comparative example of the present application has the same component ratio, preparation operation, and process parameters as those of Example 1, except that only diglyme is used as the preparation material in the comparative example to prepare the B6- negative electrode-free sodium metal battery electrolyte (NG2).

[0076] To verify the optimal ratio of the electrolyte prepared in the embodiments of the present application, the electrolyte prepared in the embodiments is made into a sodium-copper half battery for characterization comparison, and the results are shown in Figures 1-4 .

[0077] Sodium-copper half battery: carbon-coated aluminum foil is taken as the current collector, cut into a 10 mm diameter disc as the electrode sheet, and vacuum dried at 80°C for 6h as the working electrode, a 12 mm sodium sheet is taken as the negative electrode, the electrolyte prepared above is taken as the electrolyte, the separator is a Celgard 2325 separator, and a CR2032 type battery shell is used to assemble the Na||Cu half battery for electrochemical performance test.

[0078] According to Figure 1 , A1- negative electrode-free sodium metal battery electrolyte (NGMPE), A2- negative electrode-free sodium metal battery electrolyte (NGMPE (8:2)), and B1- negative electrode-free sodium metal battery electrolyte (NGMPE (9:1)) prepared by different solvent ratios are used, and the sodium-copper half battery has a current density of 5mA / cm 2 and a deposition capacity of 5mAh / cm 2 . The coulombic efficiency of the sodium-copper half battery is shown in the figure. The coulombic efficiency of NGMPE is 99.98% after 200 cycles of the Na||Cu half battery, the coulombic efficiency of NGMPE (9:1) is 90.5% after 200 cycles of the Na||Cu half battery, and the coulombic efficiency of NGMPE (8:2) is 99.16% after 200 cycles of the Na||Cu half battery.

[0079] According to Figure 2 , A1- negative electrode-free sodium metal battery electrolyte (NGMPE), A2- negative electrode-free sodium metal battery electrolyte (NGMPE (8:2)), and B1- negative electrode-free sodium metal battery electrolyte (NGMPE (9:1)) prepared by different solvent ratios are used, and the sodium-copper half battery has a current density of 8.0mA / cm 2 and a deposition capacity of 4.0mAh / cm 2 . The first cycle charge-discharge curve of the sodium-copper half battery is shown in the figure. The curve of NGMPE (9:1) shows an abnormal sharp peak or fluctuation, which may be a precursor of local short circuit before the sodium dendrite growth pierces the separator, but the curve of NGMPE (8:2) is slightly smoother, and the curve of NGMPE is obviously smoother, indicating that the electrochemical performance is more stable.

[0080] According toFigure 3 As known from the above, the A1- no negative electrode sodium metal battery electrolyte (NGMPE), A3- no negative electrode sodium metal battery electrolyte (0.9M NGMPE), B2- no negative electrode sodium metal battery electrolyte (0.8M NGMPE), B3- no negative electrode sodium metal battery electrolyte (0.7M NGMPE), B4- no negative electrode sodium metal battery electrolyte (0.6M NGMPE) and B5- no negative electrode sodium metal battery electrolyte (0.5M NGMPE) prepared by different solvent ratio, when the current density is 8.0mA / cm 2 and the deposition capacity is 4.0mAh / cm 2 , the coulombic efficiency diagram of sodium copper half battery. The coulombic efficiency of A1- no negative electrode sodium metal battery electrolyte (NGMPE) and A3- no negative electrode sodium metal battery electrolyte (0.9M NGMPE) is obviously better than the comparative example.

[0081] According to Figure 4 As known from the above, the A1- no negative electrode sodium metal battery electrolyte (NGMPE), A3- no negative electrode sodium metal battery electrolyte (0.9M NGMPE), B2- no negative electrode sodium metal battery electrolyte (0.8M NGMPE), B3- no negative electrode sodium metal battery electrolyte (0.7M NGMPE), B4- no negative electrode sodium metal battery electrolyte (0.6M NGMPE) and B5- no negative electrode sodium metal battery electrolyte (0.5M NGMPE) prepared by different solvent ratio, when the current density is 8.0mA / cm 2 and the deposition capacity is 4.0mAh / cm 2 , the first cycle charge-discharge curve diagram of sodium copper half battery. With the decrease of the concentration of NaPF6, the curve appears abnormal peak or fluctuation, while the NGMPE and 0.9M NGMPE curve is obviously smooth, which shows that the electrochemical performance is more stable.

[0082] In order to further verify the micro characteristics of the electrolyte in the operation of the battery, the SEI film formed after the operation of the battery is micro characterized.

[0083] According to Figure 5 In the above, when the current density is 5.0mA / cm 2 and the deposition capacity is 5.0mAh / cm 2 , the deposition morphology of Na||Cu half battery after 50 cycles. The blocky deposition of sodium is observed on the surface of copper foil in B6- no negative electrode sodium metal battery electrolyte (NG2), and cracks appear on the deposition surface. The uneven electric field of the protruding part and the holes on the contact surface of the copper foil and the electrolyte further induce the growth of dendrites. While the copper foil surface of NGMPE has no obvious dendrite protrusion, forming a uniform and orderly layer, which significantly inhibits the growth of dendrites.

[0084] According toFigure 6 At a current density of 8.0 mA / cm 2 and a deposition capacity of 4.0 mAh / cm 2 , the deposition morphology of Na||Cu half-cell after 50 cycles. The surface of copper foil in B6- negative electrode-free sodium metal battery electrolyte (NG2) became rough and had massive deposition, while the copper foil surface of NGMPE had no obvious dendritic protrusions, forming a uniform and ordered layer. At the same time, in order to further verify the morphology of the prepared electrolyte, according to the Micro-CT three-dimensional reconstruction of sodium metal anode shown in Figure 7 , the distribution and density of pores were displayed, and the density of NG2 was 0.35%, while the density of NGMPE was 0.002%.

[0085] According to Figure 8 , it was found that there was a dense SEI layer (about 200 nm) on the surface of the in-situ formed SEI deposit by cryo-TEM dynamic capture. At the same time, HRTEM was used for testing, according to Figure 9 , it was found that the dense SEI layer was mainly composed of various inorganic components, and the NaF component occupied a dominant position.

[0086] According to Figure 10 , it can be predicted that the negative electrode-free sodium metal battery has the potential of super-high energy density compared with the traditional sodium ion battery and the sodium metal battery with excess sodium metal.

[0087] In order to further test the comprehensive performance of the electrolyte, the electrolyte prepared above was used as the electrolyte to assemble a coin-type C@Al||NVP assembled full battery, and different electrochemical performance tests were carried out.

[0088] According to Figure 11 , the Coulombic efficiency graph (abscissa: cycle number, ordinate: Coulombic efficiency, discharge capacity) of the C@Al||NVP full battery prepared by A1- negative electrode-free sodium metal battery electrolyte (NGMPE) and B6- negative electrode-free sodium metal battery electrolyte (NG2) respectively, under the condition of 10 mg cm -2 , 3C, the negative electrode-free sodium metal battery showed super-long stable cycle, and still had more than 80% capacity retention rate after more than 400 cycles.

[0089] According to Figure 12It can be seen that the coulombic efficiency graph (abscissa: Cycle number, ordinate: Coulombic efficiency, Discharge capacity) of the C@Al||NVP full battery made of A1-NGMPE and B6-NG2 respectively, under the condition of 15 mg cm -2 , 1C, the sodium metal battery without negative electrode still provides an ultra-high initial specific discharge capacity of more than 100 mAh / g, and still maintains an ultra-long cycle of more than 480 cycles at 80% capacity under the condition of poor electrolyte (1 microliter / mg positive electrode).

[0090] According to Figure 13 It can be seen that the voltage capacity distribution graph (abscissa: Specific capacity, ordinate: Voltage) of A1-NGMPE and B6-NG2, compared with traditional NG2 electrolyte, NGMPE provides a stable voltage capacity curve of the battery, proving that short circuit and orderly sodium metal deposition / stripping rarely occur.

[0091] According to Figure 14 It can be seen that the coulombic efficiency graph (abscissa: Cycle number, ordinate: Coulombic efficiency, Discharge capacity) of the C@Al||NVP full battery made of A1-NGMPE and B6-NG2 respectively, under the condition of 10 mg cm -2 , 1C, the compact SEI formed by NGMPE electrolyte effectively resists the corrosion and reaction of trace water on the sodium metal negative electrode, ensuring the reversible cycle of sodium metal during the cycle process, and ensuring that the sodium metal battery without negative electrode can still maintain 83% of the initial capacity after 200 cycles.

[0092] According to Figure 15 It can be seen that the coulombic efficiency graph (abscissa: Cycle number, ordinate: Coulombic efficiency, Discharge capacity) of the C@Al||NVP full battery made of A1-NGMPE and B6-NG2 respectively, under the condition of 3 mg cm -2, 10C, 60℃, N / P ratio = 5, even under high temperature conditions, the reactivity of sodium metal with electrolyte increases, the compact SEI formed by NGMPE still effectively resists excessive solvent-sodium metal side reactions, and in the case of a small amount of excess sodium metal and ultra-high rate, the sodium metal battery still ensures more than 1000 cycles.

[0093] In order to prove the stability of the prepared electrolyte, the sodium metal anode in the cycled NVP||Na full battery was characterized by SEM.

[0094] According to Figure 16 It can be known that in the C@Al||NVP full battery, the cathode loading is 15mg cm -2 , 1C, after 50 cycles, the scanning electron microscope images of the surface morphology of the post-cycled sodium metal anode in the NG2 and NGMPE electrolyte, and the surface of the NGMPE electrolyte still shows obvious uniformity and smoothness. It can be fully explained that it has ultra-high cycle stability.

[0095] The NVP||Na full battery is composed of NVP positive electrode (5mg cm-2) and sodium metal negative electrode electrochemically deposited with corresponding NP ratio = 1. According to Figure 17 It can be known that in the Na||NVP full battery, different electrolytes are used under the condition of N / P ratio of 1, and the high rate of 10C is run, and three charge-discharge cycles are carried out under the condition of 0.2C. It can be known that the NVP||Na full battery can be cycled more than 1200 times.

[0096] According to Figure 18 It can be known that in the Na||NVP full battery, the cathode loading is 5mg cm-2, 10C, after 1200 cycles, the scanning electron microscope images of the surface morphology of the post-cycled sodium metal anode in the NG2 and NGMPE electrolyte, and the surface of the NGMPE electrolyte is obviously uniform and smooth.

[0097] Therefore, the negative electrode-free sodium metal battery electrolyte provided by the present application is prepared by dissolving sodium salt in diglyme and methyl perfluorobutyl ether (MPE). Through the intermolecular interaction regulation mechanism: by introducing the "non-coordination" diluent methyl perfluorobutyl ether (MPE) in the diglyme solvent, the molecular arrangement of the solvation cluster is restructured based on the special dipole-dipole interaction, and the preferential reduction sequence is changed. The highly fluorinated MPE diluent directly participates in the construction of the original SEI dominated by NaF through the spontaneous chemical reaction triggered by the dipole-dipole complex. Therefore, the film formation of SEI is spontaneous, rather than slowly formed in the process of electrochemical cycling in other electrolytes. This process is different from the film formation mechanism of electrochemical decomposition of traditional electrolytes, and realizes the rapid generation of ultra-compact inorganic SEI.

[0098] The various embodiments in the specification are described in a progressive manner, and the same or similar parts between the various embodiments can be mutually referred to, and each embodiment focuses on the difference from other embodiments.

[0099] The above examples are only used to illustrate the technical solutions of the present application, and are not limited to the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the present application.

Claims

1. A high-rate negative electrode-free sodium metal battery electrolyte, characterized in that: include: an organic solvent and a sodium salt dissolved in the organic solvent; The organic solvent is prepared by mixing diethylene glycol dimethyl ether and methyl perfluorobutyl ether.

2. The high-rate negative electrode-free sodium metal battery electrolyte according to claim 1, characterized in that The sodium salt is sodium hexafluorophosphate.

3. The high-rate negative electrode-free sodium metal battery electrolyte according to claim 2, characterized in that The concentration of the sodium salt is 0.9-1 mol / L.

4. The high-rate negative electrode-free sodium metal battery electrolyte according to claim 3, characterized in that The concentration of the sodium salt is 1 mol / L.

5. The high-rate negative electrode-free sodium metal battery electrolyte according to claim 1, characterized in that The volume ratio of diethylene glycol dimethyl ether to methyl perfluorobutyl ether is (7:3)-(8:2).

6. The high-rate negative electrode-free sodium metal battery electrolyte according to claim 5, characterized in that The volume ratio of diethylene glycol dimethyl ether to methyl perfluorobutyl ether is (7:3).

7. A method for preparing a high-rate negative electrode-free sodium metal battery electrolyte according to any one of claims 1 to 6, characterized in that: The preparation method comprises: The sodium salt is dissolved in a mixed solvent made of diethylene glycol dimethyl ether and methyl perfluorobutyl ether to obtain the negative electrode-free sodium metal battery electrolyte.

8. Use of the high-rate negative electrode-free sodium metal battery electrolyte prepared by the preparation method according to claim 7 in the preparation of a negative electrode-free sodium metal battery.

9. A negative electrode-free sodium metal battery, characterized in that: The invention comprises the high-rate negative electrode-free sodium metal battery electrolyte according to any one of claims 1 to 6 or the high-rate negative electrode-free sodium metal battery electrolyte prepared by the preparation method according to claim 7.

Images