Electrolyte, application thereof and lithium metal battery

Abstract

The invention discloses an electrolyte which comprises an electrolyte composed of composite lithium salt and a composite solvent. The dissociation capacities of the three solvents in the composite solvent are different, so that a gradient solvent system is formed, the energy barrier in the desolvation process of solvated Li < + > is reduced, the ionic conductivity is also greatly improved, and meanwhile, the rate capability and the cycle performance are improved. The electrolyte adopts a composite lithium salt system, and under a specific proportion, anion functional groups of three lithium salts jointly form a stable state in a first solvation structure layer, so that lithium nucleation overpotential is reduced, migration of Li < + > on the surface of an electrode is accelerated, and uniform nucleation of lithium on the surface of a negative electrode is facilitated. According to the electrolyte provided by the invention, various lithium salts and the composite solvent are introduced, and under the combined action of a lithium salt synergistic action mechanism and solvent structure optimization, and by combining the refractive orientation of a crystal face (110) on the surface of lithium metal, the SEI uniformity can be remarkably improved, dendritic crystal growth is inhibited, and the cycling stability of a lithium metal negative electrode is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium metal batteries, and in particular to an electrolyte and applications thereof, and a lithium metal battery. Background Art

[0002] Lithium metal anodes are considered an ideal choice for next-generation high-energy-density batteries due to their high theoretical capacity (3860 mAh / g) and low electrochemical potential (-3.04 V vs. standard hydrogen electrode). However, lithium metal anodes still face numerous challenges, including lithium dendrite growth, unstable solid electrolyte interface (SEI), and electrolyte corrosion of high-voltage cathode materials, which severely restrict their application.

[0003] In the related art, in order to solve the above-mentioned problems of lithium metal negative electrodes, improvements can be attempted from many aspects such as artificial SEI film, solid electrolyte and liquid electrolyte modification. Among them, due to the low preparation cost and simple preparation method, modification of the electrolyte has become a popular strategy. At present, a single main salt (such as LiFSI) can be used in combination with a local high concentration strategy. Although it can partially improve the stability of lithium metal, the dissociation ability of lithium salts in lithium metal batteries is limited, resulting in low efficiency of lithium metal insertion and extraction, affecting the cycle performance of the battery, and the electrolyte viscosity is too high and the ionic conductivity is insufficient. Moreover, current lithium metal electrolytes mostly use ether-based solvents. Although they have good compatibility with lithium metal, high-concentration electrolytes (such as LiFSI-based systems) have defects such as high cost, high viscosity, and poor low-temperature performance. Not only that, a single solvation structure can also easily lead to SEI inhomogeneity and lithium dendrite growth, making it easy for the lithium metal negative electrode to form dendrites during the cycle, resulting in battery short circuit and capacity decay.

[0004] Therefore, it is of great significance to solve the problems of insufficient ion mobility of lithium salts, unreasonable solvent structure, poor SEI uniformity and lithium dendrite growth in current lithium metal electrolytes, which in turn lead to insufficient battery cycle stability, and provide a new electrolyte system that can achieve long-cycle stability, low corrosion and high ion mobility. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides an electrolyte, its application, and a lithium metal battery, aiming to address the problems of current lithium metal electrolytes, such as insufficient ion mobility of lithium salts, irrational solvent structure, poor SEI uniformity, and lithium dendrite growth, which in turn lead to insufficient battery cycle stability.

[0006] In a first aspect of the present invention, an electrolyte is provided, comprising an electrolyte and a composite solvent; the electrolyte comprises a first lithium salt, a second lithium salt, and a third lithium salt; the composite solvent comprises a highly dissociated solvent, a moderately dissociated solvent, and a lowly dissociated solvent; in the electrolyte, the molar ratio of the first lithium salt, the second lithium salt, and the third lithium salt is in the range of 1:(0.1-1):(0.1-1).

[0007] The electrolyte according to the embodiment of the present invention has at least the following beneficial effects: The present invention proposes an electrolyte comprising an electrolyte composed of a composite lithium salt and a composite solvent. On the one hand, due to the presence of three solvents with different dissociation abilities in the composite solvent, their dissociation abilities are different, forming a gradient solvent system: the solvent with high dissociation ability can approach lithium ions, and within a certain radius close to the lithium ions, a first solvation structure layer is formed, in which the density of anions and solvents is the highest, and the high dissociation solvent is mainly embedded in the first solvation structure layer, which can promote the lithium + Rapid migration; the low dissociation ability of the low dissociation solvent makes it the second layer support structure of the gradient distribution, reducing the viscosity of the electrolyte (electrolyte viscosity ≤ 15mPa·s); the medium dissociation solvent has a medium dissociation ability, and because fluorine-containing solvents are more difficult to approach lithium ions, they are mainly used to connect the first layer and the second layer to stabilize the solvation network. Under the joint action of the high, medium and low dissociation solvents, a gradient solvent system is constructed to form a complete solvation structure. In the above optimized solvent structure, the solvated Li + The energy barrier of the desolvation process is reduced, the ionic conductivity is greatly increased (≥8mS / cm), and the rate performance and cycle performance are improved. On the other hand, the electrolyte of the present invention adopts a composite lithium salt system composed of three lithium salts. The combination of composite lithium salts has a synergistic effect: in the first solvation structure layer, the anion functional groups of the three lithium salts exist at the same time, and the specific ratio of the three lithium salts causes the difference in the spatial distribution density of the lithium salt anion functional groups, as well as the lithium salt anion and the solvation structure center Li + At the above specific ratio, the three anionic functional groups form a stable state in the first solvation structure layer, reducing the lithium nucleation overpotential and accelerating Li + The migration of lithium on the electrode surface is conducive to the uniform nucleation of lithium on the negative electrode surface. Ultimately, the electrolyte provided by the present invention, by introducing multiple lithium salts and complex solvents, can significantly improve the SEI uniformity, inhibit dendrite growth, and enhance the cycling stability of the lithium metal negative electrode through the combined action of the lithium salt synergy mechanism and solvent structure optimization.

[0008] In some embodiments of the present invention, the first lithium salt comprises lithium difluorooxalatoborate (LiDFOB).

[0009] In some embodiments of the present invention, the second lithium salt includes at least one of lithium tetrafluoroborate (LiBF4) and lithium bis(oxalato)borate (LiBOB).

[0010] In some embodiments of the present invention, the third lithium salt includes lithium nitrate (LiNO3).

[0011] In some embodiments of the present invention, in the electrolyte, the molar ratio range of the first lithium salt, the second lithium salt, and the third lithium salt is 1:(0.1 - 1):(0.1 - 1), preferably 1:(0.2 - 0.6):(0.4 - 0.8), more preferably 1:(0.3 - 0.5):(0.5 - 0.7), and most preferably about 1:0.4:0.6.

[0012] Specifically, in the electrolyte, the molar ratio range of lithium difluoro(oxalato)borate, lithium tetrafluoroborate, and lithium nitrate is 1:(0.1 - 1):(0.1 - 1), preferably 1:(0.2 - 0.6):(0.4 - 0.8), more preferably 1:(0.3 - 0.5):(0.5 - 0.7), and most preferably about 1:0.4:0.6.

[0013] Specifically, in the electrolyte, the molar ratio range of lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, and lithium nitrate is 1:(0.1 - 1):(0.1 - 1), preferably 1:(0.2 - 0.6):(0.4 - 0.8), more preferably 1:(0.3 - ......

[0014] The electrolyte of the present invention adopts a composite lithium salt system, and there is a synergistic effect in the combination of composite lithium salts (LiDFOB, LiBF4 or LiBOB, LiNO3): three kinds of anion functional groups coexist in the first solvation structure layer, and the specific ratio of the above three lithium salts causes the difference in the spatial distribution density of lithium salt anion functional groups in the first solvation structure layer (LiBF4 or LiBOB < LiNO3 < LiDFOB), as well as the difference in the distance between the lithium salt anion and the solvation structure center Li + (LiDFOB < LiBF4 or LiBOB < LiNO3); under the above specific ratio, the three anion functional groups jointly form a stable state in the first solvation structure layer, reduce the lithium nucleation overpotential, accelerate the migration of Li + on the electrode surface, and is beneficial to the uniform nucleation of lithium on the negative electrode surface.

[0015] In some embodiments of the present invention, in the composite solvent, the molar ratio of the high dissociation solvent, the medium dissociation solvent, and the low dissociation solvent is in the range of (5-15): (1-10): (5-25), preferably (7-9): (6-8): (10-12), and more preferably about 8:7:11. Due to the presence of three solvents with different dissociation abilities in the composite solvent of the present invention, their dissociation abilities are different, forming a gradient solvent system: the solvent with high dissociation ability can approach lithium ions, and within a certain radius close to lithium ions, a first solvation structure layer is formed, in which the density of anions and solvents is the highest, and the high dissociation solvent is mainly embedded in the first solvation structure layer, which can promote the dissociation of Li + Rapid migration; the low dissociation ability of the low dissociation solvent makes it the second layer support structure of the gradient distribution, reducing the viscosity of the electrolyte (electrolyte viscosity ≤ 15mPa·s); the medium dissociation solvent has a medium dissociation ability, and because fluorine-containing solvents are more difficult to approach lithium ions, they are mainly used to connect the first layer and the second layer to stabilize the solvation network. Under the joint action of the high, medium and low dissociation solvents, a gradient solvent system is constructed to form a complete solvation structure. In the above optimized solvent structure, the solvated Li + The energy barrier of the desolvation process is reduced, and the ionic conductivity is greatly increased (≥8mS / cm), while the rate performance and low-temperature cycle performance are also improved.

[0016] In some embodiments of the present invention, the high dissociation solvent includes at least one of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), and triethylene glycol dimethyl ether (TEGDME or G3).

[0017] In some embodiments of the present invention, the intermediate dissociation solvent includes at least one of fluoroethylene carbonate (FEC) and trifluoroethyl methyl carbonate (FEMC).

[0018] In some embodiments of the present invention, the low dissociation solvent includes at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OFE).

[0019] In some specific embodiments of the present invention, the composite solvent includes ethylene glycol dimethyl ether, fluoroethylene carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0020] More specifically, in the composite solvent, the molar ratio of ethylene glycol dimethyl ether, fluoroethylene carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is in the range of (5-15):(1-10):(5-25), preferably (7-9):(6-8):(10-12), and more preferably about 8:7:11. In the above composite solvent, due to the different dissociation abilities of the three solvents DME, FEC, and TTE, a gradient solvent system is formed: DME has a high dissociation ability, and the oxygen of DME can approach lithium ions. Within a certain radius close to lithium ions, a first solvation structure layer is formed. The density of anions and solvents in this space is the highest. DME is mainly embedded in the first solvation structure layer, which can promote Li + Rapid migration; and the low dissociation ability of TTE makes it the second layer support structure of gradient distribution, reducing the viscosity of the electrolyte (electrolyte viscosity ≤ 15mPa·s); FEC has a medium dissociation ability, and because fluorine-containing solvents are more difficult to approach lithium ions, FEC is mainly used to connect the first layer and the second layer to stabilize the solvation network. Under the joint action of DME, FEC, and TTE, a gradient solvent system is constructed to form a complete solvation structure. In the above optimized solvent structure, the solvated Li + The energy barrier of the desolvation process is reduced, and the ionic conductivity is greatly increased (≥8mS / cm), while the rate performance and low-temperature cycle performance are also improved.

[0021] In some embodiments of the present invention, in the electrolyte solution, the molar concentration of the electrolyte is 0.8 to 5 mol / L, preferably 1.32 mol / L.

[0022] In some embodiments of the present invention, the viscosity of the electrolyte is ≤15 mPa·s. The reduction in viscosity is mainly due to the presence of TTE in the solvent. The low dissociation ability of TTE allows it to serve as a second layer support structure with a gradient distribution, thereby reducing the viscosity of the electrolyte.

[0023] In some embodiments of the present invention, the viscosity of the electrolyte is 2-15 mPa·s, preferably 5-10 mPa·s. Viscosity may affect electrolyte concentration polarization and thus affect the number of cycles, so the viscosity selected in the present invention is moderate.

[0024] In some embodiments of the present invention, the ionic conductivity of the electrolyte is ≥8 mS / cm.

[0025] In some embodiments of the present invention, the ionic conductivity of the electrolyte is 8 to 30 mS / cm.

[0026] The second aspect of the present invention provides a use of the above-mentioned electrolyte in the preparation of a lithium metal battery.

[0027] In a third aspect of the present invention, a lithium metal battery is provided, comprising a negative electrode, a positive electrode and the above-mentioned electrolyte.

[0028] Since the lithium metal battery adopts all the technical solutions of the electrolyte of the above embodiment, it has at least all the beneficial effects brought by the technical solutions of the above embodiment, namely, significantly improving SEI uniformity, inhibiting dendrite growth, and improving the cycle stability of the lithium metal negative electrode.

[0029] In some embodiments of the present invention, the negative electrode includes one or more of metallic lithium, lithium alloy, lithium metal oxide, and lithium metal nitride.

[0030] In some embodiments of the present invention, the lithium metal battery further includes a separator, which is disposed between the positive electrode and the negative electrode, and the electrolyte infiltrates the positive electrode, the negative electrode, and the separator.

[0031] In some embodiments of the present invention, the material of the diaphragm includes at least one of polyethylene, polypropylene, and polyvinylidene fluoride. In actual production, the material and structure of the diaphragm are not strictly limited. For example, it can be a multi-layer structure formed by stacking the above materials, a single-layer structure formed by mixing the above materials, or a single-layer structure formed by a single material; as long as it can perform the basic function of a diaphragm.

[0032] In some embodiments of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode coating covering at least one side of the positive electrode current collector.

[0033] In some embodiments of the present invention, the positive electrode coating comprises a positive electrode active material.

[0034] In some embodiments of the present invention, the positive electrode active material includes LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiMnPO4, LiFePO4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2 and LiNi 0.85 Co 0.15 Al 0.05 At least one of O2.

[0035] In some embodiments of the present invention, the positive electrode current collector is a common positive electrode current collector in the art, such as aluminum foil, but not limited thereto. The conductive agent, binder, etc. used in preparing the positive electrode sheet are all conventional materials in the art and will not be described in detail here.

[0036] In some embodiments of the present invention, the crystal plane of lithium deposition on the surface of the negative electrode is a (110) crystal plane.

[0037] In some embodiments of the present invention, the crystal plane of lithium deposited on the surface of the negative electrode is (110) crystal plane, accounting for 50% to 80%, preferably 60 to 80%, and more preferably 75 to 80%.

[0038] In some embodiments of the present invention, the method for adjusting the proportion of the crystal plane of lithium deposition on the surface of the negative electrode to (110) crystal plane comprises the steps of: fixing the long ends of the two ends of the negative electrode material in an environment where the dew point is lower than -40 ° C, applying 15N / cm 2 The negative electrode material is stretched by a tensile force, and after being stretched to an elongation of 60%, the fixing clamp is released, and the negative electrode material is folded in half; after repeating the fixing-stretching-folding steps for a predetermined number of times, the negative electrode material is coated with a polymer film, and then the negative electrode material is rolled to obtain a negative electrode material with a predetermined (110) crystal plane ratio.

[0039] Specifically, the negative electrode material includes one or more of metallic lithium, lithium alloy, lithium metal oxide, and lithium metal nitride.

[0040] Specifically, the aspect ratio of the negative electrode material is 1:1.

[0041] Specifically, the thickness of the negative electrode material is reduced by 55% after rolling.

[0042] Specifically, the fixing-stretching-folding steps are repeated 2 to 7 times, preferably 4 to 7 times, and more preferably 5 to 6 times. The present invention utilizes different cycles of the fixing-stretching-folding steps to adjust the (110) crystal plane ratio and obtain a lithium negative electrode with uniform thickness and smooth surface.

[0043] In the present invention, FEC and anion DFOB - The adsorption on the lithium (110) crystal surface promotes the preferential exposure of the (110) crystal surface, and the (110) crystal surface is formed as the main crystal surface during the dense deposition of lithium. + Under transport conditions, the rapidly growing Li(200) crystal plane induces the growth of vertical Li(200) oriented dendrites. The (110) crystal plane has a low energy barrier, and the specific solvation structure of the present invention can provide fast and sufficient Li +Under ideal conditions, the growth of Li follows the Bravais rule and the Curie-Wulff principle, ultimately achieving planar Li(110) oriented Li deposition.

[0044] The high surface energy of the (110) crystal plane can inhibit the vertical growth of lithium dendrites, improve the uniformity of lithium deposition, and enhance the cycle performance. In addition, the (110) crystal plane of the lithium metal anode is the main crystal plane, and the lithium (110) crystal plane can preferentially adsorb DFOB. - , the charge transfer barrier on this crystal plane is low, which is conducive to rapid charge migration, DFOB - 、BF4 - Formation of an inorganic-organic composite SEI rich in LiF and BO; NO3 - Decomposes to form Li3N and LiN x O γ , thus enhancing the mechanical strength of the inorganic SEI. Ultimately, the electrolyte provided by the present invention, by introducing a variety of lithium salts and composite solvents, under the combined action of the lithium salt synergistic mechanism and solvent structure optimization, combined with the preferred orientation of the (110) crystal plane on the lithium metal surface, can significantly improve the SEI uniformity, inhibit dendrite growth, and enhance the cycle stability of the lithium metal negative electrode.

[0045] A fourth aspect of the present invention provides an application of the above-mentioned lithium metal battery in an energy storage device, an electrical device or an electronic device. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0047] In the description of the present invention, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0048] In the description of the present invention, unless otherwise indicated, the numerical range "a-b" is an abbreviation for any combination of real numbers between a and b, where a and b are real numbers. Unless otherwise indicated, the individual reactions or steps may or may not be performed sequentially. Preferably, the reaction methods of the present invention are performed sequentially.

[0049] If no specific techniques or conditions are specified in the following examples, the methods were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments without manufacturer specified are commercially available conventional products.

[0050] Example 1

[0051] Preparation of electrolyte:

[0052] At room temperature, in an argon-protected glove box, the electrolyte was prepared: lithium difluorooxalatoborate (LiDFOB), lithium tetrafluoroborate (LiBF4), and lithium nitrate (LiNO3) were added to a mixed solvent of ethylene glycol dimethyl ether (DME), fluoroethylene carbonate (FEC), and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) to obtain a mixed solution (total salt concentration of 1.32 mol / L). After thorough stirring, a uniform electrolyte was obtained with an electrolyte viscosity of 6.2±0.2 mPa.s.

[0053] The molar ratio of LiDFOB:LiBF4:LiNO3 is 1:0.4:0.6, and the molar ratio of DME:FEC:TTE is 8:7:11.

[0054] Preparation of lithium metal batteries:

[0055] Using lithium cobalt oxide (surface capacity 2.5mAh / cm 2 ) as the positive electrode, 20 μm lithium foil as the negative electrode, PP membrane as the separator, and the above-prepared electrolyte were assembled into a battery.

[0056] The method for exposing the lithium (110) crystal surface of the lithium foil negative electrode comprises the following steps: fixing the long ends of the lithium foil with an aspect ratio of 1:1 under an environment with a dew point below -40°C, applying 15N / cm 2 The lithium foil is stretched with a tensile force, and the fixing clamp is released after stretching to 60% elongation. The lithium foil is folded in half, and the fixing-stretching-folding steps are repeated 6 times. The lithium foil is coated with a polymer film, and then the lithium foil is rolled. After rolling, the thickness is reduced by 55% to form a lithium foil negative electrode with uniform thickness and smooth surface, and its lithium (110) crystal surface accounts for 75%.

[0057] Example 2

[0058] The difference from Example 1 is that the molar ratio of LiDFOB:LiBF4:LiNO3 is 1:0.6:0.4. The rest is the same as Example 1 and will not be repeated here.

[0059] Example 3

[0060] The difference from Example 1 is that the molar ratio of LiDFOB:LiBF4:LiNO3 is 1:0.8:0.2. The rest is the same as Example 1 and will not be repeated here.

[0061] Example 4

[0062] The difference from Example 1 is that the molar ratio of LiDFOB:LiBF4:LiNO3 is 1:0.2:0.8. The rest is the same as Example 1 and will not be repeated here.

[0063] Example 5

[0064] The difference from Example 3 is that the molar ratio of DME:FEC:TTE is 8:7:6, and the total salt concentration of the electrolyte is 2.04 mol / L. Furthermore, when preparing the lithium foil negative electrode, the fixation-stretching-folding steps are repeated four times, resulting in a lithium foil negative electrode with a lithium (110) crystal plane ratio of 60%. The remaining details are the same as in Example 3 and are not further described.

[0065] Example 6

[0066] The difference from Example 3 is that the molar ratio of DME:FEC:TTE is 8:7:22, and the total salt concentration of the electrolyte is 0.85 mol / L. The rest is the same as Example 3 and will not be repeated here.

[0067] Example 7

[0068] The difference from Example 3 is that the molar ratio of DME:FEC:TTE is 15:7:11, and the total salt concentration of the electrolyte is 1.05 mol / L. The rest is the same as Example 3 and will not be repeated here.

[0069] Example 8

[0070] The difference from Example 3 is that the molar ratio of DME:FEC:TTE is 5:7:11, and the total salt concentration of the electrolyte is 1.52 mol / L. Furthermore, when preparing the lithium foil negative electrode, the fixation-stretching-folding steps are repeated seven times, resulting in a lithium foil negative electrode with a lithium (110) crystal plane ratio of 80%. The remaining details are the same as in Example 3 and are not further described.

[0071] Example 9

[0072] The difference from Example 3 is that lithium tetrafluoroborate (LiBF4) is replaced by lithium bis(oxalatoborate) (LiBOB), and the molar ratio of LiDFOB:LiBOB:LiNO3 is 1:0.8:0.2. The rest is the same as Example 3 and will not be repeated here.

[0073] Example 10

[0074] The difference from Example 3 is that triethylene glycol dimethyl ether (G3) replaces ethylene glycol dimethyl ether (DME), the molar ratio of G3:FEC:TTE is 8:7:11, and the total salt concentration of the electrolyte is 1.32 mol / L. The rest is the same as Example 3 and will not be repeated here.

[0075] Example 11

[0076] The difference from Example 3 is that 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OFE, CAS No. 16627-71-7) is used instead of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), the molar ratio of DME:FEC:OFE is 8:7:11, and the total salt concentration of the electrolyte is 1.32 mol / L. The rest is the same as Example 3 and is not repeated here.

[0077] Example 12

[0078] The difference from Example 3 is that when preparing the lithium foil negative electrode, the fixing-stretching-folding steps are repeated twice, and the lithium (110) crystal plane of the obtained lithium foil negative electrode accounts for 48%. The rest is the same as Example 3 and will not be repeated.

[0079] Comparative Example 1

[0080] The difference from Example 1 is that LiNO 3 is not contained, and the molar ratio of LiDFOB:LiBF 4 is 1:1. The rest is the same as Example 1 and will not be repeated here.

[0081] Comparative Example 2

[0082] The difference from Example 1 is that LiDFOB and LiNO3 are not contained, the amount of LiBF4 is doubled, and the total salt concentration of the electrolyte is still 1.32 mol / L. The rest is the same as Example 1 and will not be repeated here.

[0083] Comparative Example 3

[0084] The difference from Example 1 is that FEC and TTE are not contained, the number of parts of DME is still 8 parts, and the total salt concentration of the electrolyte is 4.99 mol / L. The rest is the same as Example 1 and will not be repeated.

[0085] Comparative Example 4

[0086] The difference from Example 1 is that TTE is not contained, the molar ratio of DME:FEC is 8:7, and the total salt concentration of the electrolyte is 2.97 mol / L. The rest is the same as Example 1 and will not be repeated here.

[0087] Performance Testing

[0088] (1) Interface impedance test

[0089] Electrochemical impedance spectroscopy (EIS) can be used to study the kinetics of the electrode. -2 ~10 5 The test is performed with an amplitude of 5mV in the hz frequency range.

[0090] The electrochemical impedance spectroscopy (EIS) test of lithium-ion batteries was performed using a Zahner electrochemical workstation. First, select the EIS mode, enter the parameter setting interface, select different modes of impedance testing, and set the test frequency range (10 -2 ~10 5 hz), starting frequency point, frequency test sequence, sampling interval, etc. to get the test results.

[0091] The impedance spectrum is then fitted to the equivalent circuit (EIS) using Zsimpwin fitting software. First, open the impedance spectrum to be fitted, select the Nyquist graphical representation, and click the "Model Circuit" icon to create an equivalent circuit model. Click "Add" to add the required circuit components and connect them using connection points. Then, provide a frequency range to generate a simulation plot. After simulation, open the simulation plot in the graphics window. To fit the simulated spectrum to the measured EIS spectrum, select "Original," then "Simulate," and click "Fit." Finally, save and export the fitted data.

[0092] (2) Ionic conductivity test

[0093] Ionic conductivity was measured using a Shanghai Leici DDS-308F conductivity tester at 25°C. The electrodes were cleaned with pure water, gently blotted dry with filter paper, rinsed with the solution to be tested, and then placed in the solution to be tested. Wait for the data to stabilize, and then read the measurement results.

[0094] (3) Cyclic performance test

[0095] Take 5 lithium metal batteries prepared in the comparative example and the embodiment, and repeatedly charge and discharge the lithium metal batteries through the following steps, and record the number of cycles when the cycle capacity retention rate of the lithium metal battery is 80% (test conditions: 25°C, 0.5C charge and discharge, cycle voltage 3.0~4.6V).

[0096] First, in an environment of 25°C, the first charge and discharge were carried out, and constant current and constant voltage charging was performed at a charging current of 0.5C (i.e., the current value at which the theoretical capacity is completely discharged within 2 hours) until the upper limit voltage reached 4.6V. Then, constant current discharge was performed at a discharge current of 0.5C until the final voltage reached 3V, and the charge / discharge capacity of the first cycle was recorded; then, charge and discharge cycles were performed until the cycle capacity retention rate dropped to 80%, and the number of cycles was recorded.

[0097] (4) XRD test

[0098] The lithium metal negative electrodes in the comparative examples and examples were subjected to X-ray diffraction (XRD) testing. X-ray diffraction (XRD) is primarily used to study the crystal structure within a material. Because X-rays have a wavelength close to the spacing between crystal planes and have a certain degree of penetrating power, a beam of X-rays diffracts through a crystal. Analyzing the diffraction pattern allows for phase identification and structural analysis.

[0099] Test conditions: Cu Kα radiation, operating current 250 mA, continuous scanning, operating voltage 40 kV, scanning range 2θ 10-80°, scanning speed 2°·min -1 .

[0100] The specific steps are as follows: in a glove box filled with high-purity argon (O2 <0.1ppm, H2O <0.1ppm), fresh batteries are disassembled, and lithium metal anode samples are separated and prepared. The sample surface is ensured to be flat to avoid surface contamination or oxidation. Then, XRD is performed with a step width of 0.02°, a scan speed of 2° / min, and a scan range of 2θ set to 10° to 80°. After the XRD test is completed, the obtained diffraction pattern is analyzed. The (110) crystal plane fraction is obtained by calculating the ratio of the (110) peak intensity to the total intensity of all major lithium diffraction peaks (or using the texture coefficient).

[0101] The test data of the lithium metal batteries of the embodiment and the comparative example are shown in Table 1:

[0102] Table 1

[0103]

[0104] As shown in Table 1, compared with the comparative example, the interface impedance of the embodiment is greatly reduced (Example 1 is as low as 20.118Ω·cm 2), indicating that lithium salts can form a relatively stable solvation structure with a set formula composition, thereby improving the electrolyte interface dynamics. At the same time, a reasonable solvent ratio can also improve the ionic conductivity (the ionic conductivity of Example 1 reaches 9.152mS / cm), and high ionic conductivity can improve the cycle performance. In addition, the present invention also adjusts the proportion of (110) crystal planes on the surface of the lithium negative electrode so that it maintains more (110) crystal planes. The surface diffusion energy barrier of lithium ions on the lithium (110) crystal plane is low, and it tends to generate high-dimensional structures rather than one-dimensional dendrites, thereby improving the stability of the lithium metal negative electrode and improving the cycle performance.

[0105] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that: including electrolytes and complex solvents; The electrolyte includes a first lithium salt, a second lithium salt, and a third lithium salt; The composite solvent includes a high dissociation solvent, a medium dissociation solvent, and a low dissociation solvent; In the electrolyte, the molar ratio of the first lithium salt, the second lithium salt, and the third lithium salt is in the range of 1:(0.1-1):(0.1-1).

2. The electrolyte according to claim 1, characterized in that The first lithium salt includes lithium difluorooxalatoborate; and / or, the second lithium salt comprises at least one of lithium tetrafluoroborate and lithium bis(oxalatoborate); And / or, the third lithium salt includes lithium nitrate.

3. The electrolyte according to claim 1, characterized in that In the composite solvent, the molar ratio of the high dissociation solvent, the medium dissociation solvent, and the low dissociation solvent is in the range of (5-15):(1-10):(5-25); and / or, the high dissociation solvent comprises at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether; and / or, the medium dissociation solvent comprises at least one of fluoroethylene carbonate and trifluoroethyl methyl carbonate; And / or, the low dissociation solvent includes at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

4. The electrolyte according to claim 1, characterized in that In the electrolyte solution, the molar concentration of the electrolyte is 0.8 to 5 mol / L.

5. The electrolyte according to claim 1, characterized in that The viscosity of the electrolyte is 2 to 15 mPa·s; And / or, the ionic conductivity of the electrolyte is 8-30 mS / cm.

6. Use of the electrolyte according to any one of claims 1 to 5 in the preparation of a lithium metal battery.

7. A lithium metal battery, characterized in that: The lithium metal battery comprises a negative electrode, a positive electrode and the electrolyte according to any one of claims 1 to 5.

8. The lithium metal battery according to claim 7, characterized in that The negative electrode includes one or more of metallic lithium, lithium alloy, lithium metal oxide, and lithium metal nitride.

9. The lithium metal battery according to claim 7, characterized in that The crystal plane of lithium deposited on the surface of the negative electrode is (110) crystal plane, accounting for 50-80%.

10. Use of the lithium metal battery according to any one of claims 7 to 9 in an energy storage device, an electrical device or an electronic device.

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