Leveling electrolyte for high-power lithium metal battery as well as preparation method and application of leveling electrolyte
By introducing electroplating leveling agents HEC and PBF into lithium metal batteries, a locally high-concentration electrolyte is formed, which solves the problem of lithium dendrite growth and achieves precise control of lithium deposition and improved battery performance.
Patent Information
- Application Number
- CN202512055711.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-31
- Publication Date
- 2026-02-27
AI Technical Summary
Lithium metal batteries suffer from uncontrollable lithium dendrite growth during cycling, leading to battery safety hazards and low coulombic efficiency. Existing electrolyte additives are insufficient to achieve precise control over lithium deposition morphology.
Hydroxyethyl cellulose (HEC), a high-molecular-weight polymer, and small-molecule polypeptide protein (PBF), a common ingredient in the electroplating industry, are introduced as leveling additives to form a locally high-concentration electrolyte. This electrolyte selectively adsorbs onto the microscopic protrusions on the surface of the lithium metal electrode, inhibiting lithium dendrite growth and constructing an organic-inorganic composite SEI film to achieve dense lithium deposition.
It significantly improves the cycle life and coulombic efficiency of lithium metal batteries, prevents SEI film rupture, ensures battery safety performance, and adapts to stable deposition under high areal capacity and high current conditions.
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Figure CN121584022A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of electrochemical energy storage, and relates to a leveling agent, in particular to a lithium metal battery electrolyte with a leveling function, a preparation method thereof and application of the lithium metal battery electrolyte in a lithium metal battery. BACKGROUND
[0002] Lithium metal is considered as the ultimate anode material for the next generation high-energy-density batteries (e.g. lithium-sulfur batteries, lithium-air batteries and solid-state batteries) due to its extremely high theoretical specific capacity (3860 mAh / g) and the most negative electrochemical potential (-3.04 V vs. standard hydrogen electrode). However, lithium metal anode suffers from uncontrollable growth of lithium dendrites during cycling. Lithium dendrites not only can pierce the separator to cause internal short circuit and induce thermal runaway, but also can continuously consume electrolyte and active lithium due to the formation of "dead lithium", leading to low coulombic efficiency and rapid capacity decay. These problems seriously hinder the commercialization of lithium metal batteries.
[0003] Currently, the strategies to improve the stability of lithium metal anode mainly focus on: 1) constructing artificial solid electrolyte interface (SEI) film; 2) designing three-dimensional structured current collector; 3) optimizing electrolyte composition. Among them, the electrolyte optimization strategy is concerned due to its easy implementation and relatively low cost. The conventional strategies include using high-concentration electrolyte, introducing film-forming additives (lithium nitrate: LiNO3, such as fluorinated ethylene carbonate: FEC, vinylene carbonate: VC) and the like. However, most of these additives form SEI by undergoing reduction decomposition on the surface of the negative electrode, and the process is random, which is difficult to achieve precise and active regulation of the lithium deposition nucleation and growth process. The formed SEI film has limited mechanical properties and is easy to break under the huge volume change of lithium deposition / stripping, leading to the re-growth of lithium dendrites at the defects, and the protection effect is difficult to last.
[0004] Notably, in the field of electroplating industry, in order to obtain bright and smooth metal plating layer, a kind of additive called "leveling agent" is widely used. Its core mechanism is to selectively adsorb on the micro convex part (high current density area) of the cathode (workpiece to be plated), inhibit the reduction deposition of metal ions at this part, so as to force the metal ions to deposit at the concave part, and finally realize the macroscopic smoothness of the plating layer. This "geometric leveling" or "positive leveling" and "negative leveling" idea provides a mature theoretical basis for regulating metal deposition morphology. However, the mature leveling agent concept and molecular design idea in the electroplating industry are creatively transferred to the electrolyte system of lithium metal battery to solve the problem of "deposition morphology out of control" of lithium dendrites, and there is no systematic research and related patent report at present. SUMMARY
[0005] The purpose of the present application is to provide a leveling electrolyte for high-power lithium metal batteries and its preparation method and application. The electrolyte can achieve active and accurate control of lithium metal deposition morphology by drawing on the principle of electroplating leveling, obtain a dense and flat lithium deposition layer, and thus fundamentally inhibit the growth of dendrites, greatly improve the cycle life, coulombic efficiency and safety performance of the battery. The process is simple and easy to industrialize. The present application first introduces a specific polymer derived from the electroplating industry, hydroxyethyl cellulose, and low molecular weight animal proteins / polypeptides into the electrolyte of lithium metal batteries, which produces unexpected synergistic "leveling" effect, and its performance is significantly better than that of conventional small molecule additives, providing a new and efficient solution for the field.
[0006] The purpose of the present application is achieved by the following technical solutions:
[0007] A leveling electrolyte for high-power lithium metal batteries is a local high-concentration electrolyte system, which comprises a lithium salt, a non-aqueous organic solvent and a leveling additive, wherein:
[0008] The leveling additive is selected from at least one of hydroxyethyl cellulose (HEC) and small molecule polypeptide protein (PBF), and the mass concentration of the leveling additive in the electrolyte is 0.001-5%, preferably 0.01-1%;
[0009] The number average molecular weight of the hydroxyethyl cellulose is 1000-150000000 Da;
[0010] The number average molecular weight of the small molecule polypeptide protein is 1000-50000000 Da;
[0011] The lithium salt is selected from at least one of lithium bisfluorosulfonylimide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate and lithium perchlorate, preferably lithium bisfluorosulfonylimide, and the concentration is 1-7 M;
[0012] The non-aqueous organic solvent is a mixture of a solvent and a low-viscosity diluent, and the molar ratio of the solvent to the low-viscosity diluent is 1:1-1:10, preferably 1.2:3;
[0013] The solvent is selected from at least one of lithium battery carbonate, carboxylic acid ester, phosphoric acid ester and ether solvent, preferably ethylene glycol dimethyl ether;
[0014] The low-viscosity diluent is selected from at least one of fluoroether, fluorobenzene, fluorocarbonate and linear ether, preferably 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.
[0015] A preparation method of the above-mentioned leveling electrolyte, comprising the following steps:
[0016] Step S1: Dissolve the lithium salt in a solvent under the protection of inert atmosphere, and stir to form a uniform transparent base solution;
[0017] Step S2: Add the leveling additive to the base solution obtained in step S1, continue to stir and heat moderately until the additive is completely dissolved or uniformly dispersed, forming a premix, and the heating temperature is 30-50℃;
[0018] Step S3: Add a low-viscosity diluent to the premix obtained in step S2, and stir uniformly to obtain a local high-concentration leveling electrolyte.
[0019] The application of the above leveling electrolyte in a lithium metal battery, wherein the lithium metal battery is a soft pack battery, a cylindrical battery or a square battery, including a secondary battery with a lithium metal negative electrode, such as a lithium-sulfur battery, a lithium-transition metal oxide battery (such as Li|NCM811), a lithium-air battery, and a solid-state or semi-solid battery using a lithium metal negative electrode.
[0020] Compared with the prior art, the present application has the following advantages:
[0021] 1. Innovative technical idea: The present application first introduces the mature "leveling agent" concept in the electroplating industry and high molecular materials (HEC / PBF) into the field of lithium metal batteries, providing a new perspective based on "deposition morphology active regulation" to solve the problem of lithium dendrites, and breaking through the design paradigm of traditional "passive film formation" additives.
[0022] 2. Excellent leveling effect and interface stability: The HEC and PBF used in the present application have rich polar functional groups such as hydroxyl, hydroxyethyl, peptide bond, ether bond and amide bond on their molecular chains. These high molecules can be preferentially adsorbed on the surface of lithium metal electrode, especially on the micro protrusions or dendrite tips (high curvature, high electric field intensity area). This selective adsorption is equivalent to setting a dynamic barrier at the "growth point", which increases the energy barrier of lithium ion reduction at this point, and some groups such as hydroxyl can react with lithium dendrites to achieve the ablation of lithium dendrites, on the other hand, it guides the lithium ion to flow to the more flat area to desolvate and deposit, thus perfectly realizing the "positive leveling" mechanism in electroplating, and promoting lithium to deposit in the form of dense and massive, thus fundamentally eliminating dendrites.
[0023] 3. Forming a stable SEI film with rigidity and flexibility: HEC and PBF can undergo controllable and slight reduction decomposition at the negative electrode interface in the initial stage of battery cycling. The oxygen-containing and nitrogen-containing decomposition products combine with the LiF-rich inorganic SEI generated by the electrolyte itself to jointly build an organic-inorganic composite SEI film. The composite SEI has the density and high ion conductivity of inorganic components and the flexibility of organic polymer components, can effectively adapt to the large volume change during lithium deposition / stripping, prevent repeated rupture and continuous consumption of the SEI, and greatly improve the mechanical and chemical stability of the interface.
[0024] 4. Excellent synergy with local high-concentration electrolyte: The leveling additive of the present application is combined with a local high-concentration electrolyte system, producing a "1+1>2" synergistic effect. LHCE itself has a unique solvation structure (rich in contact ion pairs and aggregates) and high intrinsic stability. The addition of HEC / PBF not only plays a leveling role, but also can further optimize the rheological properties and lithium ion transport path of the electrolyte, homogenize the ion concentration field and current density distribution on the electrode surface, thereby maintaining excellent deposition morphology under more severe conditions (high surface capacity, large current).
[0025] 5. Significantly improved full battery performance: Experiments show that the half-cell using the leveling electrolyte of the present application can achieve high coulombic efficiency, and the negative electrode after cycling does not produce a large number of dendrites; the soft pack full battery matching the high load positive electrode (such as NCM811) has a significantly improved cycle life under practical conditions (limited lithium source, high surface capacity), and has no safety hazards. This proves that the present application has very high practical value and commercial prospect. BRIEF DESCRIPTION OF DRAWINGS
[0026] Figure 1 Schematic diagram of the action mechanism of the leveling electrolyte (taking HEC as an example);
[0027] Figure 2 Scanning electron microscope of lithium negative electrode after cycling of ordinary electrolyte and leveling electrolyte;
[0028] Figure 3 Cycle life comparison curve of button cells of the examples and the comparative examples;
[0029] Figure 4 Long cycle performance comparison chart of soft pack batteries of the electrolyte of the examples and the electrolyte of the comparative examples. DETAILED DESCRIPTION
[0030] The technical solutions of the present application are further described below in conjunction with the examples, but are not limited thereto. Any modification or equivalent replacement of the technical solutions of the present application without departing from the spirit and scope of the present application shall be covered in the protection scope of the present application.
[0031] Example 1: HEC-containing leveling electrolyte and preparation thereof
[0032] In a glove box under argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm), the following operations were performed:
[0033] (1) 4.0 mol of lithium bisfluorosulfonylimide was weighed and dissolved in ethylene glycol dimethyl ether, and magnetically stirred for 12 hours to obtain a clear high-concentration base solution.
[0034] (2) 0.05% of the total mass of hydroxyethyl cellulose was added to the above base solution, and continuously stirred at 40°C for 24 hours until the HEC was completely dispersed, to obtain a uniform viscous premix.
[0035] (3) 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether was added to the premix and continuously stirred for 6 hours, and the molar ratio of ethylene glycol dimethyl ether and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether was 1.2:3, and the mixture was uniformly mixed to obtain HEC-containing leveling electrolyte A, the mechanism of which is shown in Figure 1 Figure 1 (a) shows that when there is no leveling agent, lithium ions are randomly deposited to form dendrites; and Figure 1 (b) shows that after adding HEC, the molecular chain thereof is preferentially adsorbed on the protruding tip to inhibit deposition thereat, and guide lithium ions to uniformly nucleate and grow on the plane to achieve a “leveling” effect.
[0036] Example 2: PBF-containing leveling electrolyte and preparation thereof
[0037] The difference between this embodiment and Example 1 is that the added leveling agent is replaced by 0.1% of the total mass of PBF (purchased from Changshu Heye Chemical Co., Ltd., model C009 2409) to obtain leveling electrolyte B.
[0038] Example 3: HEC-containing leveling electrolyte and preparation thereof
[0039] The difference between this embodiment and Example 1 is that the added solvent ethylene glycol dimethyl ether is replaced by diethylene glycol dimethyl ether to obtain leveling electrolyte C.
[0040] Example 4: HEC- and PBF-containing leveling electrolyte and preparation thereof
[0041] The difference between this embodiment and Example 1 is that the added leveling agent is replaced by 0.05% of the total mass of PBF and 0.05% of the total mass of HEC to obtain leveling electrolyte D.
[0042] Comparative Example 1: Blank electrolyte without additives
[0043] Without adding any leveling additive, the remaining steps are the same as Example 1 to prepare a blank electrolyte E.
[0044] Performance test and characterization
[0045] 1. Lithium deposition morphology characterization
[0046] CR2032 button cells were assembled with NCM as the positive electrode and lithium metal as the negative electrode, respectively containing electrolyte A and E, and subjected to charge-discharge cycling. After the end of the cycle, the battery was disassembled in the glove box, and the negative electrode was taken out, washed with dimethyl carbonate and vacuum dried. The morphology of the deposited lithium was observed by scanning electron microscopy, and the results are shown in Figure 2 It can be seen from Figure 2 that a large number of loose and porous mossy lithium and sharp needle-like dendrites grow on the surface of the lithium negative electrode using blank electrolyte E; while the lithium deposition layer on the surface of the negative electrode using electrolyte A containing HEC is dense, flat and presents a uniform block structure without any dendrite evidence, which directly proves the excellent "leveling" ability of HEC. The results of the cycle test in the voltage range of 3-4.35 V are shown in Figure 3 It can be seen from Figure 3 that the capacity of the button cell using blank electrolyte E decays to less than 80% of the initial capacity after 100 cycles, and the coulombic efficiency fluctuates greatly. While the capacity retention rate of the button cell using electrolyte E of the application is still as high as 92% after 300 cycles under the same conditions, and the coulombic efficiency is always stable at more than 99.8%.
[0047] 3. Performance test of soft-pack full cell
[0048] NCM811 positive electrode sheets with a surface capacity of 3 mAh / cm² were prepared, and assembled into soft-pack batteries with a capacity of 1 Ah together with ultra-thin lithium foil (50 μm) negative electrode and ceramic-coated separator. Electrolytes A, B and E were injected respectively, and subjected to cycle test in the voltage range of 3-4.35 V at 0.2 CC-1 CD charge-discharge rate, and the results are shown in Figure 4 It can be seen from Figure 4 that the capacity of the soft-pack battery using blank electrolyte C decays to less than 50% of the initial capacity after 200 cycles, and the coulombic efficiency fluctuates greatly, while the capacity retention rate of the soft-pack battery using electrolytes A and B of the application is still greater than 80% after 200 cycles under the same conditions, and the coulombic efficiency is always stable at more than 99.8%. After the cycle, it was found that the separator of the battery using electrolytes A and B was intact, and the negative electrode surface was smooth; while the separator of the battery using electrolyte E had multiple black spots caused by dendrite puncture. This test fully proves the great advantage of the leveling electrolyte of the application in practical application.
Claims
1. A leveling electrolyte for high-power lithium metal batteries, characterized in that... The leveling electrolyte comprises lithium salt, non-aqueous organic solvent and leveling additive, wherein: the leveling additive is selected from at least one of hydroxyethyl cellulose and small molecule polypeptide protein, and its mass concentration in the electrolyte is 0.001~5%; the concentration of the lithium salt is 1~7 M.
2. The leveling electrolyte for high-power lithium metal batteries according to claim 1, characterized in that... The mass concentration of the leveling additive in the electrolyte is 0.01~1%.
3. The leveling electrolyte for high-power lithium metal batteries according to claim 1, characterized in that... The hydroxyethyl cellulose has a number-average molecular weight of 1,000 to 150,000,000 Da, and the small molecule polypeptide protein has a number-average molecular weight of 1,000 to 50,000,000 Da.
4. The leveling electrolyte for high-power lithium metal batteries according to claim 1, characterized in that... The lithium salt is selected from at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, and lithium perchlorate.
5. The leveling electrolyte for high-power lithium metal batteries according to claim 4, characterized in that... The lithium salt is lithium difluorosulfonylimide.
6. The leveling electrolyte for high-power lithium metal batteries according to claim 1, characterized in that... The non-aqueous organic solvent is a mixture of solvent and low-viscosity diluent, with a molar ratio of solvent to low-viscosity diluent of 1:1 to 1:10; the solvent is selected from at least one of lithium battery carbonate, carboxylic acid ester, phosphate ester and ether solvent, and the low-viscosity diluent is selected from at least one of fluoroether, fluorobenzene, fluorocarbonate and straight-chain ether.
7. The leveling electrolyte for high-power lithium metal batteries according to claim 6, characterized in that... The solvent and the low-viscosity diluent have a molar ratio of 1.2:3, the solvent is ethylene glycol dimethyl ether, and the low-viscosity diluent is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.
8. A method for preparing a leveling electrolyte for a high-power lithium metal battery according to any one of claims 1-7, characterized in that... The method includes the following steps: Step S1: Under an inert atmosphere, dissolve the lithium salt in a solvent and stir to form a homogeneous and transparent base solution; Step S2: Add the leveling additive to the base solution obtained in step S1, stir continuously and heat moderately until the additive is completely dissolved or evenly dispersed to form a premixed solution. The heating temperature is 30~50℃. Step S3: Add a low-viscosity diluent to the premixed solution obtained in step S2 and stir until homogeneous to obtain a locally high-concentration leveling electrolyte.
9. The application of the leveling electrolyte for high-power lithium metal batteries as described in any one of claims 1-7 in lithium metal batteries.
10. The application of the leveling electrolyte for high-power lithium metal batteries according to claim 9 in lithium metal batteries, characterized in that... The lithium metal battery type is a pouch battery, cylindrical battery, or prismatic battery.