Electrolyte functional additive, electrolyte and lithium metal battery

Abstract

The invention provides an electrolyte functional additive, an electrolyte and a lithium metal battery. The functional additive comprises rubidium nitrate and / or lithium nitrate. The lithium metal battery non-aqueous electrolyte comprises a lithium salt, a non-aqueous organic solvent and a functional additive. Rubidium nitrate (RbNO3) and lithium nitrate (LiNO3) are used as electrolyte dual additives, NO3 <-> is used as a film-forming additive to participate in formation and decomposition of an SEI film to form an SEI film component with high ionic conductivity, and the ionic conductivity of the SEI film is improved; and Rb + provides an electrostatic shielding effect, is not consumed in the circulation process, can continuously play a role in long-term circulation, and promotes uniform lithium deposition. Rubidium nitrate (RbNO3) and lithium nitrate (LiNO3) cooperate with each other, so that the coulombic efficiency is improved while lithium dendrites are inhibited, and dual targets of dendrite-free morphology and high coulombic efficiency of the lithium metal battery are achieved.

Description

Technical Field

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

[0002] With the rapid development of new energy vehicles such as electric vehicles and hybrid vehicles, people's requirements for battery performance are getting higher and higher, and the development of high-performance battery technology is crucial. The energy density provided by lithium-ion batteries has gradually been unable to meet the development needs of new energy vehicles, and lithium metal batteries, with their unique advantages, have shown a wide range of application prospects in the field of new secondary batteries. However, the commercialization of lithium metal batteries faces huge challenges, which is mainly attributed to the continuous generation of lithium dendrites during the cycle of lithium metal batteries. Severe lithium dendrites may pierce the diaphragm, causing internal short circuits in the battery, posing a safety hazard. In response to the above problems, scientific researchers have proposed a series of solutions such as diaphragm modification, design of three-dimensional current collectors, and electrolyte modification, which have greatly promoted the development of lithium metal batteries.

[0003] The electrolyte reacts with the lithium metal anode at the interface to form a SEI passivation film. The decomposition products of the electrolyte can directly affect the chemical composition and structure of the SEI film. In recent years, the strategies for optimizing the design of electrolytes to improve battery performance mainly include: solid electrolytes, ionic liquids, local high-concentration electrolytes, functional additives, etc. Among them, functional electrolyte additives are the simplest, most efficient and lowest-cost strategy to inhibit lithium dendrites. Electrolyte additives are divided into two types according to their mechanism of action: film-forming additives and deposition regulation additives. In the initial cycle stage of lithium metal batteries, the film-forming additives in the electrolyte will decompose first to form a stable SEI film on the surface of lithium metal. The film-forming additive is sacrificial and will be consumed as part of the SEI film during the battery cycle. Unlike film-forming additives, deposition regulation additives do not participate in the formation of the SEI film. They are adsorbed on the surface of the lithium metal anode through electrostatic action to form an electrostatic shielding layer to achieve uniform lithium deposition on the electrode surface. Therefore, the concentration of additives in the electrolyte will not decrease during the cycle, and the effectiveness of its electrostatic shielding effect will not decrease, and it can continue to play a role in long-term cycles.

[0004] The charge distribution is uneven on the uneven surface of the electrode sheet, and a stronger electric field is formed on the protrusions, resulting in a higher local current density. Lithium ions tend to deposit preferentially at the tips or protrusions with higher current density, thus forming lithium dendrites. + The concentration is much lower than that of Li +In the case of LiNO3, it has a lower reduction potential than lithium ions. Therefore, the added cations will preferentially gather around the initial growth tip and adsorb on the electrode surface with the help of the electric field force to form a positively charged electrostatic shielding layer. Then, through the "charge repulsion effect", the flat area of ​​lithium ions is evenly deposited, thereby effectively inhibiting the growth of lithium dendrites. Although the electrostatic shielding mechanism improves the problem of irregular dendrite growth during lithium deposition, the problem of low Coulomb efficiency of lithium metal batteries remains to be solved. The LUMO energy level of LiNO3 is lower than that of other components of the electrolyte, so it will be preferentially reduced and decomposed on the surface of the metallic lithium negative electrode to generate Li3N / LiN-rich with higher ionic conductivity. x O y The SEI passivation layer stabilizes the SEI film while accelerating the Li + Ester electrolytes are widely used in high-voltage lithium metal batteries due to their excellent oxidation stability. However, the solubility of LiNO3 in ester electrolytes is very low, which limits its application in high-voltage lithium metal batteries.

[0005] Therefore, there is an urgent need to provide an electrolyte additive and an electrolyte, aiming to effectively inhibit the growth of lithium dendrites and improve the coulombic efficiency of the battery. Summary of the invention

[0006] Based on the defects of the prior art, the first purpose of the present invention is to provide a functional additive for non-aqueous electrolyte of lithium metal batteries; the second purpose of the present invention is to provide a non-aqueous electrolyte of lithium metal batteries; the third purpose of the present invention is to provide a method for preparing non-aqueous electrolyte of lithium metal batteries; the fourth purpose of the present invention is to provide a lithium metal battery.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] On the one hand, the present invention provides a functional additive for a non-aqueous electrolyte of a lithium metal battery, wherein the functional additive comprises rubidium nitrate and lithium nitrate; the concentration of the rubidium nitrate in the non-aqueous electrolyte is 0.03 to 0.07 mol / L; the concentration of the lithium nitrate in the non-aqueous electrolyte is 0.05 to 0.2 mol / L.

[0009] Rubidium nitrate (RbNO3) and lithium nitrate (LiNO3) are dual additives for electrolytes and have an electrostatic shielding effect (Rb + ) and SEI membrane regulation (NO3 - )’s synergistic effect.

[0010] In lithium metal batteries, rubidium nitrate (RbNO3) is reacted with its cation Rb + The unique mechanism of action can achieve lithium dendrite inhibition. According to the Nernst equation, Rb +The reduction potential (about -2.98V vs.Li + / Li) is lower than lithium ions (-3.04V), so that it is preferentially adsorbed in the tip area of ​​lithium deposition (where the local electric field strength is higher), forming a positively charged electrostatic shielding layer. This shielding layer forces lithium ions to stay away from the high electric field tip area through Coulomb repulsion, guiding them to deposit evenly on the flat surface, thereby inhibiting dendrite nucleation. In addition, Rb + As a non-sacrificial additive, it is not consumed during the cycle and can maintain the stability of the shielding layer for a long time, avoiding the repeated formation of dendrites. This mechanism effectively eliminates the local current density difference, reduces the tip-preferential deposition of lithium, and reduces the accumulation of dead lithium and side reactions through macroscopic morphology control, significantly improving the cycle stability of the battery.

[0011] Nitrate ions (NO3) in lithium nitrate (LiNO3) - ) optimizes the SEI film of lithium metal anode through preferential reduction mechanism. - The LUMO energy level of the electrolyte is lower than that of other components, and it is preferentially reduced on the lithium metal surface to generate Li3N and LiN x O γ Among them, Li3N has extremely high ionic conductivity (>10 -3 S / cm), which is significantly higher than that of traditional SEI membrane components, thereby accelerating the transmembrane transport of lithium ions and reducing the interface impedance. - As a sacrificial additive, its solubility needs to be improved through solvent optimization (such as ethylene glycol dimethyl ether DME) to maintain its dynamic repair ability for the SEI film during the cycle. This mechanism not only enhances the mechanical strength and chemical stability of the SEI film, but also reduces the lithium ion transmission barrier through micro-interface optimization, effectively inhibits the continuous decomposition of the electrolyte, and ultimately achieves a significant improvement in coulombic efficiency.

[0012] The synergistic effect of rubidium nitrate and lithium nitrate is reflected in the complementarity of space and time dimensions. + The electrostatic shielding effect of NO3 inhibits dendrite nucleation and guides the uniform deposition of lithium through macroscopic morphology regulation. - The microstructure of the interface is optimized by generating a highly conductive SEI film, which reduces local polarization and improves lithium deposition kinetics. + The non-consumable nature of NO3 makes it continue to inhibit dendrite growth in long-term cycles. -The integrity of the SEI film is maintained by the dynamic replenishment of solvent carriers (such as DME) to compensate for its consumption as a sacrificial additive. The synergistic effect of the two achieves the dual goals of dendrite suppression and coulombic efficiency improvement: the electrostatic shielding effect blocks dendrite nucleation, and the high-conductivity SEI film inhibits dendrite penetration; at the same time, the dense lithium deposition morphology and the stable SEI film synergistically reduce lithium ion transmission loss and side reaction activity, thereby significantly extending the cycle life of lithium metal batteries.

[0013] Preferably, the cations having electrostatic shielding effect include Na + , K + , Cs + and Rb + .

[0014] On the other hand, the present invention also provides a non-aqueous electrolyte for a lithium metal battery, wherein the non-aqueous electrolyte for a lithium metal battery comprises a lithium salt, a non-aqueous organic solvent and the above-mentioned functional additive.

[0015] In the above-mentioned lithium metal battery non-aqueous electrolyte, preferably, the lithium salt is selected from one or more combinations of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), lithium bis(trifluorosulfonyl imide), lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(oxalatoborate) and lithium trifluoromethanesulfonate, but is not limited thereto.

[0016] In the above-mentioned non-aqueous electrolyte for lithium metal batteries, preferably, the concentration of the lithium salt in the non-aqueous electrolyte is 0.6 to 3 mol / L, excluding the concentration of the functional additive lithium nitrate.

[0017] In the above-mentioned non-aqueous electrolyte for lithium metal batteries, preferably, the non-aqueous organic solvent is selected from one or more combinations of organic esters, ethers, sulfones and nitrile solvents, but is not limited thereto.

[0018] In the above-mentioned non-aqueous electrolyte for lithium metal batteries, preferably, the non-aqueous organic solvent is an organic ester.

[0019] In the above-mentioned lithium metal battery non-aqueous electrolyte, preferably, the organic ester is selected from one or more combinations of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, ethyl butyrate, methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroethyl carbonate and di(2,2,2-trifluoroethyl) carbonate, but is not limited thereto.

[0020] In the above-mentioned lithium metal battery non-aqueous electrolyte, preferably, the functional additive is selected from rubidium nitrate and lithium nitrate.

[0021] In the above-mentioned non-aqueous electrolyte for lithium metal batteries, preferably, the concentration of rubidium nitrate in the non-aqueous electrolyte is 0.03-0.07 mol / L.

[0022] In the above-mentioned non-aqueous electrolyte for lithium metal batteries, preferably, the concentration of lithium nitrate in the non-aqueous electrolyte is 0.05-0.2 mol / L.

[0023] In the above-mentioned non-aqueous electrolyte for lithium metal batteries, preferably, the mass of the functional additive accounts for 0.1-2.0wt% of the total mass of the non-aqueous electrolyte for lithium metal batteries.

[0024] In the above-mentioned non-aqueous electrolyte for lithium metal batteries, preferably, the lithium nitrate is a lithium nitrate solution prepared using ethylene glycol dimethyl ether as a solvent.

[0025] In the above-mentioned lithium metal battery non-aqueous electrolyte, preferably, the concentration of the lithium nitrate solution is 1 mol / L.

[0026] In the present invention, DME is used as the carrier solvent of LiNO3 to increase NO3 - The concentration of LiNO3 in the electrolyte system can significantly increase the solubility of NO3 in the ester electrolyte. - Decomposition can form LiN x O y and Li3N SEI film with high ionic conductivity. + and NO3 - The combined effect of can promote the uniform deposition of lithium, thereby effectively inhibiting the growth of lithium dendrites and improving the coulombic efficiency of the battery.

[0027] In another aspect, the present invention also provides a method for preparing the above-mentioned lithium metal battery non-aqueous electrolyte, which comprises the following steps:

[0028] Before preparing the electrolyte, the non-aqueous organic solvent is dried by molecular sieves, and the functional additives and lithium salts are dried by vacuum drying; the electrolyte is prepared in a glove box filled with argon gas, and the lithium salt is first added to the non-aqueous organic solvent to prepare a lithium salt solution; then the functional additive is added and stirred until completely dissolved to obtain a lithium metal battery non-aqueous electrolyte.

[0029] On the other hand, the present invention also provides a lithium metal battery, and the raw materials for preparing the lithium metal battery include a positive electrode, a negative electrode, a separator and a lithium metal battery non-aqueous electrolyte.

[0030] In the above-mentioned lithium metal battery, preferably, the positive electrode material used for the positive electrode is selected from one or more combinations of lithium cobalt oxide, lithium manganese oxide, ternary nickel cobalt manganese lithium, lithium nickel manganese oxide, lithium iron phosphate and lithium manganese iron phosphate; more preferably, lithium iron phosphate.

[0031] In the above-mentioned lithium metal battery, preferably, the negative electrode material used for the negative electrode is selected from metallic lithium and / or lithium alloy; more preferably, it is lithium metal.

[0032] In the above-mentioned lithium metal battery, preferably, the separator is selected from polypropylene separator and / or polyethylene separator; more preferably, it is a polypropylene separator.

[0033] In the above-mentioned lithium metal battery, preferably, the lithium metal battery is a button battery.

[0034] Beneficial effects of the present invention:

[0035] (1) The present invention can form a self-healing electrostatic shielding effect by adding RbNO3 additive to the basic electrolyte. + It will not be consumed during the circulation process and can continue to play a role in long-term circulation. + The electrostatic shielding effect promotes uniform lithium deposition. Rubidium nitrate (RbNO3) and lithium nitrate (LiNO3) are used as dual additives in the electrolyte to achieve the dual goals of dendrite-free morphology and high coulombic efficiency of lithium metal batteries.

[0036] (2) The present invention uses DME as a carrier solvent for LiNO3 to increase NO3 - The concentration of LiNO3 in the electrolyte system can significantly increase the solubility of NO3 in the ester electrolyte. - Decomposition can form LiN x O y and Li3N SEI film with high ionic conductivity. + and NO3 - The combined effect of can promote the uniform deposition of lithium, thereby effectively inhibiting the growth of lithium dendrites and improving the coulombic efficiency of the battery.

[0037] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1SEM images comparing the lithium deposition morphology on the copper foil surface in Example 1 ((b) and (e) in the figure), Example 4 ((a) and (d) in the figure) and Comparative Example 1 ((c) and (f) in the figure) of the present invention. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention. The process, conditions, reagents, experimental methods, etc. for implementing the present invention, except for the contents specifically mentioned below, are all common knowledge and common common sense in the art, and the present invention does not particularly limit the contents.

[0041] Embodiment 1:

[0042] This embodiment provides a non-aqueous electrolyte. Before preparing the electrolyte, the non-aqueous organic solvent is dried by molecular sieve, rubidium nitrate and lithium salt are dried by vacuum, and then the electrolyte is prepared. The preparation method is as follows:

[0043] (1) In a glove box filled with argon (the contents of H2O and O2 are both less than 0.1 ppm), ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1 as an organic solvent. Lithium hexafluorophosphate (LiPF6) is added to the solvent, and then 10 wt% fluoroethylene carbonate (FEC) is added to prepare a 1 M LiPF6 solution.

[0044] (2) Using an electronic balance, weigh 14.7 mg of RbNO3 and add it to 2 ml of the LiPF6 solution prepared in step (1). Stir magnetically until the RbNO3 is completely dissolved to obtain a non-aqueous electrolyte solution having a RbNO3 concentration of 0.05 M.

[0045] Embodiment 2:

[0046] This embodiment provides a non-aqueous electrolyte. Before preparing the electrolyte, the non-aqueous organic solvent is dried by molecular sieve, rubidium nitrate and lithium salt are dried by vacuum, and then the electrolyte is prepared. The preparation method is as follows:

[0047] (1) In a glove box filled with argon (the contents of H2O and O2 are both less than 0.1 ppm), ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1 as an organic solvent. Lithium hexafluorophosphate (LiPF6) is added to the solvent, and then 10 wt% fluoroethylene carbonate (FEC) is added to prepare a 1 M LiPF6 solution.

[0048] (2) Using an electronic balance, weigh 8.82 mg of RbNO3 and add it to 2 ml of the LiPF6 solution prepared in step (1). Stir the mixture with a magnetic stirrer until the RbNO3 is completely dissolved to obtain a non-aqueous electrolyte having a RbNO3 concentration of 0.03 M.

[0049] Embodiment 3:

[0050] This embodiment provides a non-aqueous electrolyte. Before preparing the electrolyte, the non-aqueous organic solvent is dried by molecular sieve, rubidium nitrate and lithium salt are dried by vacuum, and then the electrolyte is prepared. The preparation method is as follows:

[0051] (1) In a glove box filled with argon (the contents of H2O and O2 are both less than 0.1 ppm), ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1 as an organic solvent. Lithium hexafluorophosphate (LiPF6) is added to the solvent, and then 10 wt% fluoroethylene carbonate (FEC) is added to prepare a 1 M LiPF6 solution.

[0052] (2) Weigh 20.58 mg of RbNO3 using an electronic balance and add it to 2 ml of the LiPF6 solution in step (1). Stir magnetically until the RbNO3 is completely dissolved to obtain a non-aqueous electrolyte. The concentration of RbNO3 in the electrolyte is 0.07 M.

[0053] Embodiment 4:

[0054] This embodiment provides a non-aqueous electrolyte. Before preparing the electrolyte, the non-aqueous organic solvent is dried by molecular sieve, rubidium nitrate and lithium salt are dried by vacuum, and then the electrolyte is prepared. The preparation method is as follows:

[0055] (1) In a glove box filled with argon (the contents of H2O and O2 are both less than 0.1 ppm), ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1 as an organic solvent. Lithium hexafluorophosphate (LiPF6) is added to the solvent, and then 10 wt% fluoroethylene carbonate (FEC) is added to prepare a 1 M LiPF6 solution.

[0056] (2) Using an electronic balance, weigh 14.7 mg of RbNO3 and add it to 2 ml of the LiPF6 solution prepared in step (1). Stir magnetically until the RbNO3 is completely dissolved to obtain a non-aqueous electrolyte solution having a RbNO3 concentration of 0.05 M.

[0057] (3) Weigh 69 mg of LiNO3 using an electronic balance and add it to 1 ml of ethylene glycol dimethyl ether (DME) solvent to prepare a solution with a LiNO3 concentration of 1 M. Use a pipette to draw 0.2 ml of DME lithium nitrate solution and add it to 1.8 ml of the non-aqueous electrolyte in step (2), and shake it thoroughly to obtain 2 ml of a uniform and transparent electrolyte.

[0058] Embodiment 5:

[0059] This embodiment provides a non-aqueous electrolyte. Before preparing the electrolyte, the non-aqueous organic solvent is dried by molecular sieve, rubidium nitrate and lithium salt are dried by vacuum, and then the electrolyte is prepared. The preparation method is as follows:

[0060] (1) In a glove box filled with argon (the contents of H2O and O2 are both less than 0.1 ppm), ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1 as an organic solvent. Lithium hexafluorophosphate (LiPF6) is added to the solvent, and then 10 wt% fluoroethylene carbonate (FEC) is added to prepare a 1 M LiPF6 solution.

[0061] (2) Using an electronic balance, weigh 14.7 mg of RbNO3 and add it to 2 ml of the LiPF6 solution prepared in step (1). Stir magnetically until the RbNO3 is completely dissolved to obtain a non-aqueous electrolyte solution having a RbNO3 concentration of 0.05 M.

[0062] (3) Weigh 69 mg of LiNO3 using an electronic balance and add it to 1 ml of ethylene glycol dimethyl ether (DME) solvent to prepare a solution with a LiNO3 concentration of 1 M. Use a pipette to draw 0.3 ml of DME lithium nitrate solution and add it to 1.7 ml of the non-aqueous electrolyte in step (2), and shake it thoroughly to obtain 2 ml of a uniform and transparent electrolyte.

[0063] Embodiment 6:

[0064] This embodiment provides a non-aqueous electrolyte. Before preparing the electrolyte, the non-aqueous organic solvent is dried by molecular sieve, rubidium nitrate and lithium salt are dried by vacuum, and then the electrolyte is prepared. The preparation method is as follows:

[0065] (1) In a glove box filled with argon (the contents of H2O and O2 are both less than 0.1 ppm), ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1 as an organic solvent. Lithium hexafluorophosphate (LiPF6) is added to the solvent, and then 10 wt% fluoroethylene carbonate (FEC) is added to prepare a 1 M LiPF6 solution.

[0066] (2) Using an electronic balance, weigh 14.7 mg of RbNO3 and add it to 2 ml of the LiPF6 solution prepared in step (1). Stir magnetically until the RbNO3 is completely dissolved to obtain a non-aqueous electrolyte solution having a RbNO3 concentration of 0.05 M.

[0067] (3) Weigh 69 mg of LiNO3 using an electronic balance and add it to 1 ml of ethylene glycol dimethyl ether (DME) solvent to prepare a solution with a LiNO3 concentration of 1 M. Use a pipette to draw 0.4 ml of DME lithium nitrate solution and add it to 1.6 ml of the non-aqueous electrolyte in step (2), and shake it thoroughly to obtain 2 ml of a uniform and transparent electrolyte.

[0068] Embodiment 7:

[0069] This embodiment provides a non-aqueous electrolyte. Before preparing the electrolyte, the non-aqueous organic solvent is dried by molecular sieve, rubidium nitrate and lithium salt are dried by vacuum, and then the electrolyte is prepared. The preparation method is as follows:

[0070] (1) In a glove box filled with argon (the contents of H2O and O2 are both less than 0.1 ppm), ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1 as an organic solvent. Lithium hexafluorophosphate (LiPF6) is added to the solvent, and then 10 wt% fluoroethylene carbonate (FEC) is added to prepare a 1 M LiPF6 solution.

[0071] (2) Using an electronic balance, weigh 14.7 mg of RbNO3 and add it to 2 ml of the LiPF6 solution prepared in step (1). Stir magnetically until the RbNO3 is completely dissolved to obtain a non-aqueous electrolyte solution having a RbNO3 concentration of 0.05 M.

[0072] (3) Weigh 69 mg of LiNO3 using an electronic balance and add it to 1 ml of ethylene glycol dimethyl ether (DME) solvent to prepare a solution with a LiNO3 concentration of 1 M. Use a pipette to draw 0.1 ml of DME lithium nitrate solution and add it to 1.9 ml of the non-aqueous electrolyte in step (2), and shake it thoroughly to obtain 2 ml of a uniform and transparent electrolyte.

[0073] Comparative Example 1:

[0074] This comparative example provides an electrolyte, and the preparation method is as follows:

[0075] In a glove box filled with argon (the contents of H2O and O2 are both less than 0.1ppm), ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed uniformly in a volume ratio of 1:1 as an organic solvent. Lithium hexafluorophosphate (LiPF6) is added to the solvent, and then 10wt% fluoroethylene carbonate (FEC) is added to prepare a 1M LiPF6 solution, which is the electrolyte of Comparative Example 1.

[0076] Preparation of lithium metal batteries:

[0077] The electrolytes of Examples 1 to 7 and Comparative Example 1 were used to prepare lithium metal batteries, respectively, as follows:

[0078] (1) Preparation of positive electrode sheet: The full battery of the present invention uses lithium iron phosphate (LiFePO4) as the positive electrode. The specific steps of preparing the positive electrode sheet are as follows:

[0079] First, the active material LiFePO4, the conductive agent SuperP, and the binder PVDF are put into a mortar in a mass ratio of 8:1:1 and ground until the three raw materials are evenly mixed.

[0080] Next, a proper amount of NMP solvent was added to the mixture to prepare slurry, and the slurry was sealed and placed on a magnetic stirrer to be stirred evenly.

[0081] Then, use a spatula to evenly coat the mixed slurry on the carbon-coated aluminum foil current collector, and put the coated aluminum foil into a 70° C. forced air drying oven to completely volatilize the NMP on the surface of the electrode.

[0082] Finally, the electrode was transferred to a 110°C vacuum drying oven for drying, and a manual sheet machine was used to punch the electrode into a 9 mm diameter disc for later use. According to calculations, the active material loading on the LFP electrode was about 15 mg cm -2 .

[0083] (2) Battery assembly: The button cells involved in the present invention include Li||Cu half-cells, Li||Li symmetric cells and Li||LFP full cells. In a glove box filled with argon (the contents of H2O and O2 are both less than 0.1ppm), the batteries are assembled in the order of negative electrode shell, shrapnel, gasket, negative electrode, diaphragm, positive electrode and positive electrode shell. Then use insulating tweezers to move the assembled battery to the MSK-110 sealing machine for compaction, and the pressure does not exceed 50kPa. All batteries use Celgard 2400 PP diaphragms, and the amount of electrolyte used is 50μL. Constant current charge and discharge tests are all carried out on the LAND battery testing system. Before testing, the battery needs to stand for several hours to ensure that the electrode sheet is completely infiltrated by the electrolyte.

[0084] According to the method, lithium metal batteries of Examples 1 to 7 and Comparative Example 1 were prepared, and electrochemical performance tests were performed respectively. The experimental results are shown in Tables 1 and Figure 1 As shown; Table 1 shows the cycle performance results of the lithium metal batteries in Examples 1 to 7 and Comparative Example 1; Figure 1 SEM images comparing the lithium deposition morphology on the copper foil surface in Example 1 ((b) and (e) in the figure), Example 4 ((a) and (d) in the figure) and Comparative Example 1 ((c) and (f) in the figure).

[0085] Table 1 Cyclic performance of lithium metal batteries in Examples 1 to 7 and Comparative Example 1

[0086] Group Cycle times Capacity retention rate (%) Average Coulombic efficiency (%) Comparative Example 1 200 71 95.96 Example 1 400 80 98.82 Example 2 400 80 98.05 Example 3 400 81 96.13 Example 4 500 87 99.26 Example 5 500 84 98.65 Example 6 500 83 98.47 Example 7 500 82 98.38

[0087] It can be seen from Table 1 that the electrolyte formula of Example 4 has the best improvement effect on the performance of lithium metal batteries, indicating that Rb + and NO3 - The synergistic effect is achieved, and the cycle performance and life of the battery are improved. Comparing Comparative Example 1 with Examples 1 to 3, the concentration of 0.05M Rb + The electrostatic shielding effect is the best, which can effectively regulate the uniform deposition of lithium and improve the cycle performance of the battery. - When the concentration is too low, it is not enough to form a stable SEI film on the surface of the lithium metal negative electrode, which increases the NO3 - The concentration of ions helps to form a SEI film with high ionic conductivity and improve the performance of lithium metal batteries.

[0088] Among the Li||LFP full cells under different electrolytes, the full cell in Example 4 has the slowest discharge capacity decay during the cycle and the longest cycle life at 2C. Its capacity retention rate after 500 stable cycles is 87%. In addition, under Example 1, the cycle performance of the Li||LFP full cell is also very stable. Its performance before 300 cycles is almost the same as that of the full cell in Example 4. However, compared with Example 4, the discharge capacity of the Li||LFP full cell in Example 1 is reduced from nearly 140 mAh g to 200 mAh g after 400 cycles. -1 Down to 112.8 mAh g -1 The cycle performance of the full battery in Comparative Example 1 is the worst. The capacity begins to decrease significantly after 120 cycles, and can only provide 100.6 mAh g after 200 cycles. -1The discharge capacity of the battery. The continuous growth of lithium dendrites and the continuous accumulation of dead lithium are the root causes of capacity decay. In order to compare the reversibility of lithium deposition / stripping behavior in different electrolytes, the Aurbach method was used to measure the average coulombic efficiency of Li||Cu batteries under different electrolytes. As shown in Table 1, in 20 deposition / stripping cycles, the average coulombic efficiency of the Li||Cu half-cells in Example 4 and Example 1 was as high as 99.26% and 98.82%, respectively, while the average coulombic efficiency of the battery in Comparative Example 1 was only 95.96%. This shows that the addition of additives can significantly improve the deposition and stripping kinetics of lithium. + and NO3 - Under the combined action of , the lithium deposition and stripping behaviors on copper foil are highly reversible.

[0089] Depend on Figure 1 It can be seen that in the electrolyte systems of Example 1 and Example 4, the deposition of metallic lithium presents a large strawberry-like densely packed morphology ( Figure 1 d, e in the figure). The strawberry-shaped lithium deposition morphology is a typical feature of the electrostatic shielding effect. In addition, the lithium deposited on the copper foil has a dense and uniform morphology, and there is no obvious lithium dendrite formation ( Figure 1 However, in Comparative Example 1, the lithium deposition on the surface of the copper foil exhibits a loose, porous, rough and uneven morphology ( Figure 1 c, f), this uneven porous structure will consume limited electrolyte and reduce the cycle stability of the battery.

[0090] In summary, the present invention uses rubidium nitrate (RbNO3) and lithium nitrate (LiNO3) as dual additives for the electrolyte, NO3 - As a film-forming additive, it participates in the formation of SEI film, decomposes to form SEI film components with high ionic conductivity, and improves the ionic conductivity of SEI film; Rb + It provides an electrostatic shielding effect and will not be consumed during the cycle. It can continue to play a role in long-term cycles and promote uniform lithium deposition. Rubidium nitrate (RbNO3) and lithium nitrate (LiNO3) work together to suppress lithium dendrites while improving coulombic efficiency, achieving the dual goals of dendrite-free morphology and high coulombic efficiency for lithium metal batteries.

[0091] The present invention uses specific embodiments to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A functional additive for non-aqueous electrolyte of lithium metal battery, characterized in that: The functional additive comprises rubidium nitrate and lithium nitrate; the concentration of the rubidium nitrate in the non-aqueous electrolyte is 0.03-0.07 mol / L; the concentration of the lithium nitrate in the non-aqueous electrolyte is 0.05-0.2 mol / L.

2. A non-aqueous electrolyte for lithium metal batteries, characterized in that: The non-aqueous electrolyte for lithium metal batteries comprises a lithium salt, a non-aqueous organic solvent and the functional additive according to claim 1.

3. The non-aqueous electrolyte for lithium metal batteries according to claim 2, characterized in that: The lithium salt is selected from one or more combinations of lithium hexafluorophosphate, lithium bistrifluoromethanesulfonyl imide, lithium bisfluorosulfonyl imide, lithium bistrifluorosulfonyl imide, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bisoxalatoborate and lithium trifluoromethanesulfonate.

4. The non-aqueous electrolyte for lithium metal batteries according to claim 2 or 3, characterized in that: The concentration of the lithium salt in the non-aqueous electrolyte is 0.6-3 mol / L.

5. The non-aqueous electrolyte for lithium metal batteries according to claim 2, characterized in that: The non-aqueous organic solvent is selected from one or more combinations of organic esters, ethers, sulfones and nitrile solvents; Preferably, the non-aqueous organic solvent is an organic ester; More preferably, the organic ester is selected from one or more combinations of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, ethyl butyrate, methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroethyl carbonate and di(2,2,2-trifluoroethyl) carbonate.

6. The non-aqueous electrolyte for lithium metal batteries according to claim 2, characterized in that: The weight of the functional additive accounts for 0.1-2.0 wt % of the total weight of the lithium metal battery non-aqueous electrolyte.

7. The non-aqueous electrolyte for lithium metal batteries according to claim 6, characterized in that: The lithium nitrate is a lithium nitrate solution prepared using ethylene glycol dimethyl ether as a solvent; Preferably, the concentration of the lithium nitrate solution is 1 mol / L.

8. A method for preparing a non-aqueous electrolyte for a lithium metal battery as claimed in claim 2, comprising the following steps: Before preparing the electrolyte, the non-aqueous organic solvent is dried by molecular sieves, and the functional additives and lithium salts are dried by vacuum drying; the electrolyte is prepared in a glove box filled with argon gas, and the lithium salt is first added to the non-aqueous organic solvent to prepare a lithium salt solution; then the functional additive is added and stirred until completely dissolved to obtain a lithium metal battery non-aqueous electrolyte.

9. A lithium metal battery, wherein raw materials for preparing the lithium metal battery include a positive electrode, a negative electrode, a separator and the lithium metal battery non-aqueous electrolyte according to claim 2.

10. The lithium metal battery according to claim 9, characterized in that: The positive electrode material used for the positive electrode is selected from one or more combinations of lithium cobalt oxide, lithium manganese oxide, ternary nickel cobalt manganese lithium, nickel manganese oxide, lithium iron phosphate and lithium manganese iron phosphate; preferably lithium iron phosphate; Preferably, the negative electrode material used in the negative electrode is selected from metallic lithium and / or lithium alloy; preferably lithium metal; Preferably, the diaphragm is selected from a polypropylene diaphragm and / or a polyethylene diaphragm; preferably a polypropylene diaphragm; Preferably, the lithium metal battery is a button cell.

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