Partially diluted high-concentration electrolyte, its preparation method, and lithium metal battery

Abstract

The partially diluted high-concentration electrolyte, its preparation method, and the partially diluted high-concentration electrolyte for lithium metal batteries comprise a non-aqueous organic solvent, a lithium salt, and a diluent. The non-aqueous organic solvent comprises a phosphate ester solvent and an auxiliary organic solvent, with the volume fraction of the phosphate ester solvent relative to the non-aqueous organic solvent being 50% or more. The auxiliary organic solvent has a dielectric constant of 2.8 C / V·m or more. By using a main solvent containing highly safe components and a highly flame-retardant phosphazene compound as the main diluent, it is possible to effectively interrupt the chain reaction caused by hydroxyl radicals between the high-nickel ternary positive electrode and the metallic lithium negative electrode during thermal runaway of the battery, significantly improving battery safety and improving the cycle life of the lithium metal battery.

Description

[Technical Field]

[0001] The present invention relates to the technical field of lithium metal batteries, and in particular to a partially diluted high-concentration electrolyte, a method for preparing the same, and a lithium metal battery.

[0002] Cross-reference to related applications This application claims priority based on a Chinese application filed with the China Patent Office on December 29, 2022, bearing application number 202211715875.0 and entitled "Partially diluted high-concentration electrolyte, preparation method thereof, and lithium metal battery," the entire contents of which are incorporated herein by reference. [Background technology]

[0003] Lithium metal has the lowest chemical potential (-3.04V) and a high theoretical capacity of 3860mAh / g. When used in combination with a high-nickel ternary positive electrode, it can achieve high energy density in batteries, making it highly promising for applications requiring long range, such as electric vehicles and unmanned aerial vehicles.

[0004] However, due to the poor thermal stability of high-nickel ternary cathode materials and the high reactivity of lithium metal, safety issues remain regarding the combination of these materials in high-nickel lithium metal battery systems. In lithium-ion batteries using graphite anodes, lithium ions are reversibly inserted and extracted between the intercalation compound layers at the anode. In contrast, lithium metal anodes undergo electrochemical deposition and dissolution by lithium ions during charge and discharge. In practical applications of lithium metal batteries, non-uniform deposition of lithium ions on the surface of the lithium metal anode can easily lead to the formation of lithium dendrites, which can cause short circuits in the battery and reduce its lifespan and safety.

[0005] According to Sand's time theory (proposed by H. J. S. Sand in 1901), higher lithium salt concentrations and lithium ion transport numbers can significantly delay the formation of lithium dendrites, thereby improving the cycle life of lithium metal batteries. High-concentration electrolytes are a novel electrolyte that has attracted attention in recent years. Unlike conventional lithium-ion-concentration electrolytes, they have a unique solvation structure. This structure significantly improves the oxidation resistance potential of the electrolyte while providing a long life for lithium metal batteries without the need for large amounts of fluorine- or nitro-based additives. However, the preparation cost of high-concentration electrolytes is high, and the viscosity of the electrolyte is high, posing challenges to the low-temperature performance of battery systems using high-concentration electrolytes. Summary of the Invention

[0006] The present disclosure provides a partially diluted, high-concentration electrolyte to solve the problems of poor cycling performance and safety of conventional lithium metal negative electrode batteries.

[0007] The present disclosure also provides a method for preparing the partially diluted high-concentration electrolyte, as well as a lithium metal battery using the electrolyte.

[0008] The present disclosure employs the following technical solutions to solve the above technical problems.

[0009] That is, the partially diluted high-concentration electrolyte may include a non-aqueous organic solvent, a lithium salt, and a diluent.

[0010] The non-aqueous organic solvent includes a phosphate ester solvent and an auxiliary organic solvent, and the volume fraction of the phosphate ester solvent relative to the non-aqueous organic solvent is 50% or more.

[0011] Furthermore, the auxiliary organic solvent has a dielectric constant of 2.8 C / V·m or more.

[0012] The partially diluted high-concentration electrolyte according to the present disclosure uses a main solvent containing highly safe components, thereby effectively blocking a chain reaction caused by hydroxyl radicals that occurs between the high-nickel ternary positive electrode and the metallic lithium negative electrode during thermal runaway of the battery, thereby significantly improving the safety of the battery and improving the cycle life of the lithium metal battery.

[0013] In a specific embodiment of the present disclosure, the phosphate ester solvent may include one or more selected from the group consisting of trimethyl phosphate (TMP), triethyl phosphate (TEP), dimethyl methylphosphonate (DMMP), tris(trimethylsilyl) phosphate (TMSP), tricresyl phosphate, tris(isopropylphenyl) phosphate (IPPP), tributyl phosphate, trioctyl phosphate, and cresyldiphenyl phosphate (CDP).

[0014] In a specific embodiment of the present disclosure, the auxiliary organic solvent may include one or more selected from the group consisting of carboxylic acid esters, ethers, silane esters, carbonates, fluorinated carbonates, and sulfones.

[0015] In a specific embodiment of the present disclosure, the carboxylic acid ester may include one or more selected from the group consisting of ethyl acetate, methyl acetate, butyl formate, and n-butyl acetate.

[0016] In a specific embodiment of the present disclosure, the ether system may include one or more selected from the group consisting of ethylene glycol dimethyl ether, 1,2-dimethoxypropane, dimethoxymethane, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0017] In a specific embodiment of the present disclosure, the silane ester may include one or more selected from the group consisting of tris(trimethylsilyl) phosphate, tris(trimethylsilyl)borate, tris(trimethylsilyl) phosphite, vinyltrimethoxysilane, phenyltrimethoxysilane, isocyanatotrimethylsilane, and 3-trimethylsilyl-2-oxazolidinone.

[0018] In a specific embodiment of the present disclosure, the carbonate ester may include one or more selected from the group consisting of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0019] In a specific embodiment of the present disclosure, the fluorinated carbonate ester may include one or more selected from the group consisting of fluoroethylene carbonate, fluorinated ethyl methyl carbonate, and difluoroethylene carbonate.

[0020] In a specific embodiment of the present disclosure, the sulfone may include one or more selected from the group consisting of sulfolane, dimethyl sulfoxide, difluoromethyl phenyl sulfone, and methyl phenyl sulfoxide.

[0021] In a specific embodiment of the present disclosure, the volume ratio of the phosphate ester solvent to the auxiliary organic solvent may be 1:(0.3 to 1).

[0022] In a specific embodiment of the present disclosure, the diluent may include a phosphazene-based compound, which may optionally include one or more compounds selected from the group consisting of ethoxy(pentafluoro)cyclotriphosphazene (PFPN), pentafluoro(phenoxy)cyclotriphosphazene (FPPN), hexakis(1H,1H,7H-perfluoroheptoxy)phosphazene, hexamethoxycyclotriphosphazene (HMTP), and hexaethoxycyclotriphosphazene (HETP).

[0023] In a specific embodiment of the present disclosure, the diluent may further include a second diluent. The second diluent may include one or more selected from the group consisting of fluoroether and / or fluorobenzene. Optionally, the volume fraction of the second diluent relative to the diluent is 0% to 20%.

[0024] In a specific embodiment of the present disclosure, the fluoroether may include one or two selected from the group consisting of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and bis(2,2,2-trifluoroethyl) ether (BTFE).

[0025] In a specific embodiment of the present disclosure, the lithium salt may include an imide-based lithium salt. Optionally, the imide-based lithium salt may include one or more selected from the group consisting of lithium bis(fluoromethylsulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), lithium (nonafluorobutanesulfonyl)(trifluoromethanesulfonyl)imide, lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide, and lithium perfluoropropanedisulfonylimide.

[0026] In a specific embodiment of the present disclosure, the concentration of the lithium salt in the non-aqueous organic solvent is 3 to 6M.

[0027] In a specific embodiment of the present disclosure, the lithium salt may further include a lithium salt for blending, which may include one or more selected from the group consisting of lithium difluoro(oxalato)borate (LiODFB), lithium bis(oxalato)borate (LiBOB), lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), and lithium nitrate (LiNO).

[0028] In a specific embodiment of the present disclosure, the molar ratio of the imide lithium salt to the blending lithium salt may be (5 to 20):1.

[0029] In addition, in a specific embodiment of the present disclosure, the concentration of the lithium salt may be 0.6 to 1.8 M after being diluted with a diluent.

[0030] Furthermore, in a specific embodiment of the present disclosure, the volume ratio of the diluent to the high-concentration lithium salt solution may be 3:2 to 9:1, where the high-concentration lithium salt solution is a mixture of a non-aqueous organic solvent and a lithium salt.

[0031] The present disclosure further provides a method for preparing the partially diluted high-concentration electrolyte solution described above, which may include the steps of:

[0032] A process of uniformly mixing the lithium salt with the non-aqueous organic solvent to obtain a highly concentrated lithium salt solution.

[0033] a step of uniformly mixing the high-concentration lithium salt solution with a diluent to obtain a partially diluted high-concentration electrolyte solution;

[0034] The present disclosure also provides a lithium metal battery, which may include any of the partially diluted high-concentration electrolytes described above.

[0035] The present disclosure has at least the following beneficial effects compared to the related art:

[0036] (1) The partially diluted high-concentration electrolyte according to the present disclosure uses a main solvent containing highly safe components, thereby effectively blocking a chain reaction caused by hydroxyl radicals that occurs between the high-nickel ternary positive electrode and the metallic lithium negative electrode during thermal runaway of the battery, thereby significantly improving the safety of the battery and improving the cycle life of the lithium metal battery.

[0037] (2) The partially diluted high-concentration electrolyte according to the present disclosure is based on a high-concentration electrolyte, but by adding a non-polar diluent that does not dissolve lithium salts, the viscosity of the electrolyte is reduced while maintaining the properties of a high-concentration lithium ion solution, thereby further improving the rate performance of lithium metal batteries and expanding the operating temperature range.

[0038] (3) Lithium metal batteries using the partially diluted high-concentration electrolyte according to the present disclosure exhibit significant improvements in safety and cycle performance.

[0039] In order to more clearly describe the specific embodiments of the present disclosure or the technical solutions of the related art, the drawings necessary for describing the specific embodiments or the related art are briefly described below. These drawings illustrate some embodiments of the present disclosure and do not limit the technical scope of the present disclosure. Those skilled in the art can obtain other drawings based on these drawings. [Brief explanation of the drawings]

[0040] [Figure 1] FIG. 1 is a graph comparing the cycle performance of lithium metal negative electrode secondary batteries according to Examples 1 to 6 of the present disclosure and Comparative Examples 1 to 6. DETAILED DESCRIPTION OF THE INVENTION

[0041] The technical configuration of the present disclosure will be clearly and completely explained below with reference to the drawings and specific embodiments. The examples described below are merely some of the embodiments for illustrating the present disclosure and are not intended to limit the technical scope of the present disclosure. Those skilled in the art may make various modifications and alterations based on the examples of the present disclosure without requiring inventive ability, and such variations are also considered to be within the technical scope of the present disclosure. Furthermore, unless specific conditions are specified in the examples, the examples may be carried out under conditions conventionally known in the relevant technical field or under conditions recommended by the equipment or manufacturer. Furthermore, even if the manufacturer of the reagents or equipment used is not specified, commercially available, known products may be used as appropriate.

[0042] The partially diluted high concentration electrolyte may include a non-aqueous organic solvent, a lithium salt, and a diluent.

[0043] The non-aqueous organic solvent contains a phosphate ester solvent and an auxiliary organic solvent, and the volume fraction of the phosphate ester solvent relative to the non-aqueous organic solvent is 50% or more.

[0044] The auxiliary organic solvent has a dielectric constant of 2.8 C / V·m or more.

[0045] The partially diluted high-concentration electrolyte according to the present disclosure uses a main solvent containing highly safe components, thereby effectively blocking a chain reaction caused by hydroxyl radicals that occurs between the high-nickel ternary positive electrode and the metallic lithium negative electrode during thermal runaway of the battery, thereby significantly improving the safety of the battery and improving the cycle life of the lithium metal battery.

[0046] For example, in another embodiment, the volume fraction of the phosphate ester solvent relative to the non-aqueous organic solvent may be exemplarily 50% or more, 60% or more, or 70% or more.

[0047] In a specific embodiment of the present disclosure, the phosphate ester solvent may include one or more selected from the group consisting of trimethyl phosphate (TMP), triethyl phosphate (TEP), dimethyl methylphosphonate (DMMP), tris(trimethylsilyl) phosphate (TMSP), tricresyl phosphate, tris(isopropylphenyl) phosphate (IPPP), tributyl phosphate, trioctyl phosphate, and cresyldiphenyl phosphate (CDP).

[0048] In a specific embodiment of the present disclosure, the auxiliary organic solvent may include one or more selected from the group consisting of carboxylic acid esters, ethers, silane esters, carbonates, fluorinated carbonates, and sulfones.

[0049] The carboxylic acid ester may include one or more selected from the group consisting of ethyl acetate, methyl acetate, butyl formate, and n-butyl acetate.

[0050] The ether-based solvent may include one or more selected from the group consisting of ethylene glycol dimethyl ether, 1,2-dimethoxypropane, dimethoxymethane, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0051] The silane ester may include one or more selected from the group consisting of tris(trimethylsilyl) phosphate, tris(trimethylsilyl)borate, tris(trimethylsilyl) phosphite, vinyltrimethoxysilane, phenyltrimethoxysilane, isocyanatotrimethylsilane, and 3-trimethylsilyl-2-oxazolidinone.

[0052] The carbonate ester may include one or more selected from the group consisting of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0053] The fluorinated carbonate ester may include one or more selected from the group consisting of fluoroethylene carbonate, fluorinated ethyl methyl carbonate, and difluoroethylene carbonate.

[0054] The sulfone-based solvent may include one or more selected from the group consisting of sulfolane, dimethyl sulfoxide, difluoromethyl phenyl sulfone, and methyl phenyl sulfoxide.

[0055] In a specific embodiment of the present disclosure, the volume ratio of the phosphate ester solvent to the auxiliary organic solvent (phosphate ester solvent:auxiliary organic solvent) may be 1:(0.3 to 1).

[0056] For example, in another embodiment, the volume ratio of the phosphate ester solvent to the auxiliary organic solvent may be illustratively 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, or 1:1.

[0057] In a specific embodiment of the present disclosure, the diluent may include a phosphazene-based compound, which may optionally include one or more compounds selected from the group consisting of ethoxy(pentafluoro)cyclotriphosphazene (PFPN), pentafluoro(phenoxy)cyclotriphosphazene (FPPN), hexakis(1H,1H,7H-perfluoroheptoxy)phosphazene, hexamethoxycyclotriphosphazene (HMTP), and hexaethoxycyclotriphosphazene (HETP).

[0058] In a specific embodiment of the present disclosure, the diluent may further include a second diluent. The second diluent may include one or more selected from the group consisting of fluoroether and / or fluorobenzene. Optionally, the volume fraction of the second diluent relative to the diluent may be 0% to 20%.

[0059] For example, in another embodiment, the volume fraction of the second diluent relative to the diluent may illustratively be 0% (i.e., no second diluent is added), 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, or 20%.

[0060] In a specific embodiment of the present disclosure, the fluoroether may include one or two selected from the group consisting of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and bis(2,2,2-trifluoroethyl) ether (BTFE).

[0061] In a specific embodiment of the present disclosure, the lithium salt may include an imide-based lithium salt. Optionally, the imide-based lithium salt may be lithium bis(fluoromethylsulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), or lithium (nonafluorobutanesulfonyl)(trifluoromethanesulfonyl)imide (molecular formula: CF 12The filler may contain one or more selected from the group consisting of LiNO4S2, CAS number: 176719-70-3), lithium (fluorosulfonyl) (trifluoromethanesulfonyl) imide, and lithium perfluoropropanedisulfonylimide.

[0062] In a specific embodiment of the present disclosure, the concentration of the lithium salt in the non-aqueous organic solvent may be 3 to 6M.

[0063] For example, in another embodiment, the concentration of the lithium salt in the non-aqueous organic solvent can be 3M, 3.5M, 4M, 4.5M, 5M, 5.5M, or 6M.

[0064] In a specific embodiment of the present disclosure, the lithium salt may further include a blending lithium salt, which may include one or more selected from the group consisting of lithium difluoro(oxalato)borate (LiODFB), lithium bis(oxalato)borate (LiBOB), lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), and lithium nitrate (LiNO).

[0065] In a specific embodiment of the present disclosure, the molar ratio of the imide lithium salt to the blending lithium salt (imide lithium salt: blending lithium salt) may be (5 to 20:1).

[0066] For example, in other embodiments, the molar ratio of the imide lithium salt to the blending lithium salt may illustratively be 5:1, 8:1, 10:1, 12:1, 15:1, 18:1, or 20:1.

[0067] In addition, in a specific embodiment of the present disclosure, the concentration of the lithium salt may be 0.6 to 1.8 M after being diluted with a diluent.

[0068] For example, in another embodiment, the concentration of the lithium salt after dilution with a diluent (i.e., the concentration of the lithium salt in a partially diluted high-concentration electrolyte) may be, for example, 0.6 M, 0.8 M, 1 M, 1.2 M, 1.4 M, 1.5 M, 1.6 M, or 1.8 M.

[0069] In a specific embodiment of the present disclosure, the volume ratio of the diluent to the high-concentration lithium salt solution (diluent:high-concentration lithium salt solution) may be 3:2 to 9:1, provided that the high-concentration lithium salt solution is a mixture of a non-aqueous organic solvent and a lithium salt, and is expressed in terms of the volume of the mixture.

[0070] For example, in another embodiment, the volume ratio of the diluent to the highly concentrated lithium salt solution may illustratively be 3:2, 9:5, 9:4, 3:1, 9:2, or 9:1.

[0071] The present disclosure further provides a method for preparing any of the partially diluted high-concentration electrolyte solutions described above, which may include the following steps:

[0072] A process of uniformly mixing the lithium salt with the non-aqueous organic solvent to obtain a highly concentrated lithium salt solution.

[0073] a step of uniformly mixing the high-concentration lithium salt solution with a diluent to obtain a partially diluted high-concentration electrolyte solution;

[0074] The present disclosure also provides a lithium metal battery, which may include any of the partially diluted high-concentration electrolytes described above.

[0075] Furthermore, in the following specific examples of the present disclosure, the purity of the reagents used is 99.5% or higher.

[0076] Examples 1 to 6 The method for producing the lithium metal batteries according to Examples 1 to 6 includes the following steps.

[0077] (1) Preparation of lithium metal battery cathode The ternary positive electrode active material, nickel cobalt manganese oxide (NCM811, 80% molar ratio of nickel to the main positive electrode elements), the conductive agent, SuperP conductive carbon black, and the binder, polyvinylidene fluoride, were dissolved in N-methylpyrrolidone (NMP) in a weight ratio of 92:4:4 and uniformly stirred to obtain a positive electrode slurry with a solids concentration of 50% to 65%. The uniformly dispersed positive electrode slurry was applied to aluminum foil and dried to a thickness of 105 μm to 200 μm, and the positive electrode surface density was adjusted to 28 to 50 mg / cm. 2 , e.g., 30.5 mg / cm 2 After drying, the positive electrode sheet was rolled and cut to obtain a positive electrode sheet having a size of 56 mm x 96 mm.

[0078] (2) Preparation of lithium metal battery anode A pure lithium metal foil sheet was used for the negative electrode, cut to a size of 58 mm x 98 mm, and a tab was secured.

[0079] (3) Preparation of separator The separator was made of polyethylene, and had a size of 60 mm x 100 mm and a thickness of 20 μm.

[0080] (4) Preparation of electrolyte (1) Solvent: Phosphate ester-based main solvent and other auxiliary solvents were weighed. (2) The imide-based lithium salt and auxiliary lithium salt were added quantitatively to the above (1) and stirred at room temperature of 25°C to prepare a high-concentration lithium salt solution (the concentration of the imide-based lithium salt shown in the table means the concentration of the imide-based lithium salt in the prepared high-concentration lithium salt solution). (3) A phosphazene compound or a mixture of phosphazene and fluoroether was weighed as a diluent, and added to the high-concentration lithium salt solution obtained in (2) above, followed by stirring uniformly to prepare an electrolyte solution.

[0081] (5) The positive electrode, separator, and negative electrode prepared in steps (1) to (3) were stacked in this order to form a cell structure, and then the tab was pulled out and sealed with an aluminum-plastic film. Then, an electrolyte solution was added at a mass of 1‰ to 5‰ (e.g., 2‰) of the cell's design capacity, and the cell was placed in a vacuum drying oven for a 10 to 20 hour penetration treatment. This was followed by a second sealing and chemical formation treatment.

[0082] Specific composition information of the electrolyte solutions of Examples 1 to 6 is shown in Table 1. All electrolyte solutions were prepared under an inert gas atmosphere, and the purity of the reagents used was 99.5% or higher.

[0083] Table 1: Specific composition information of the electrolyte solutions in Examples 1 to 6 JPEG2026500729000002.jpg169163

[0084] where TEP = triethyl phosphate, TMP = trimethyl phosphate, EA = ethyl acetate, FEC = fluoroethylene carbonate, TMS = sulfolane, DME = ethylene glycol dimethyl ether, LiPF6 = lithium hexafluorophosphate, LiNO3 = lithium nitrate, LiODFB = lithium difluoro(oxalato)borate, LiFSI = lithium bis(fluorosulfonyl)imide, PFPN = ethoxy(pentafluoro)cyclotriphosphazene, TTE = 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether

[0085] Example 7 Example 7 was produced using the same configuration and preparation procedure as Example 1, except that the composition of the electrolyte was different.

[0086] In this example, the lithium salt contains only LiFSI, and the concentration of the high-concentration lithium salt solution is 3 mol / L.

[0087] Example 8 Example 8 was produced using the same configuration and preparation procedure as Example 1, except that the composition of the electrolyte was different.

[0088] In this example, the diluent contains only TTE.

[0089] Comparative Examples 1 to 6 Comparative Examples 1 to 6 were produced using the same configuration and preparation procedure as Example 1, except that the composition of the electrolyte solution was different.

[0090] Specific composition information of the electrolyte solutions of Comparative Examples 1 to 6 is shown in Table 2. All the electrolyte solutions were prepared under an inert gas atmosphere.

[0091] Table 2: Specific composition information of the electrolyte solutions of Comparative Examples 1 to 6 JPEG2026500729000003.jpg150149

[0092] where EA = ethyl acetate, FEC = fluoroethylene carbonate, TMS = sulfolane, DME = ethylene glycol dimethyl ether, EC = ethylene carbonate, EMC = ethyl methyl carbonate, DEC = diethyl carbonate, LiPF6 = lithium hexafluorophosphate, VC = vinylene carbonate, LiODFB = lithium difluoro(oxalato)borate, LiFSI = lithium bis(fluorosulfonyl)imide, TTE = 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether

[0093] Comparative Example 7 Comparative Example 7 was produced using the same configuration and preparation procedure as Example 1, except that the composition of the electrolyte solution was different.

[0094] In Comparative Example 7, the solvent contains TEP and FEC, and the volume ratio thereof (TEP:FEC) is 1:1.1.

[0095] Experimental example In order to confirm the performance of different electrolyte solutions, performance tests were carried out on lithium metal negative electrode secondary batteries using the electrolyte solutions of each Example and Comparative Example. The test items and specific methods are as follows.

[0096] (a) Electrolyte self-extinguishing time test (SET) A certain amount of glass fiber cotton was weighed in a dry environment with a dew point of -30°C or less, and this was designated as weight M1 (unit: g). The weighed glass fiber cotton was immersed in a certain amount of the electrolyte to be tested, and then its weight M2 (unit: g) was measured. The glass fiber cotton immersed in the electrolyte was ignited, and the time t (unit: seconds) required from the start of combustion to self-extinguishing was recorded. If ignition was not possible, t = 0 was recorded.

[0097] The self-extinguishing time SET was calculated using the following formula: SET = t / (M2-M1) [s / g] The test results are shown in Table 3.

[0098] (b) Effective cycle test Using the battery obtained in step (5), charge / discharge cycles were performed at room temperature of 25°C at a rate of 0.3 C of the designed capacity. The cutoff voltage was set to 4.3 V for charge and 3.0 V for discharge, and the cutoff current was set to 0.02 C for charge and 1 C for discharge, and the number of effective cycles was tested.

[0099] The effective cycle count was determined by determining the capacity of the lithium metal battery, then charging and discharging it at a room temperature of 25°C, a 0.3C rate, and a voltage of 3.0 to 4.3V. The effective cycle count was the number of cycles at which the capacity decreased to 80% of the design capacity. The test results are shown in Table 3.

[0100] (c) Calculation of the average Coulombic efficiency The average coulombic efficiency of the battery over the effective number of cycles was calculated from the charge-discharge efficiency of the battery after formation. The test results are shown in Table 3.

[0101] Table 3. Test results for different examples and comparative examples JPEG2026500729000004.jpg146128

[0102] The above table shows the performance evaluation results for the self-extinguishing time (SET) of the electrolytes of different examples and comparative examples, the number of effective cycles, and the average coulombic efficiency of the lithium metal negative electrode secondary batteries using the electrolytes. Overall, by using the electrolyte according to the present disclosure, the lithium metal negative electrode secondary battery was able to achieve effective cycles of 400 or more (3.0V to 4.3V, 0.3C charge, 1C discharge) and a self-extinguishing time (SET) of 0.2 s / g or less, which significantly improved the safety of the battery.

[0103] Specifically, in Examples 1 to 6 of the present disclosure, a phosphate ester-based solvent (TMP, TEP) was used as the main solvent, and a carbonate ester-based solvent (FEC, EMC), a carboxylic acid ester (EA), a sulfone-based solvent (TMS), or an ether-based solvent (DME) was used as the auxiliary solvent. The main salt used was bis(fluorosulfonyl)imide lithium salt (LiFSI), with a concentration of this lithium salt relative to the solvent of 3 to 6 M. In addition to the imide-based lithium salt, other auxiliary lithium salts (LiPF6, LiODFB, LiNO3) were also included in molar ratios relative to the main salt ranging from 1:5 to 1:20. Furthermore, in Examples 1 to 4, a phosphazene-based diluent (PFPN) was used, while in Examples 5 and 6, a combination of a phosphazene-based diluent (PFPN) and a fluoroether-based diluent (TTE) in a volume ratio of 4:1 was used.

[0104] Comparative Examples 1 and 2 used a current, common high-concentration salt electrolyte. This type of electrolyte (HCE) consists solely of a high-concentration lithium salt solution without the addition of a diluent. In lithium metal battery cycle tests, these electrolytes achieved 371 and 334 cycles, respectively, with average cycle coulombic efficiencies of 98.18% and 98.26%, both of which were inferior to the examples of the present disclosure. Furthermore, in self-extinguishing time (SET) tests, the self-extinguishing times of Comparative Examples 1 and 2 were 12.2 s / g and 11.3 s / g, respectively, significantly longer than the examples of the present disclosure, and no flame-retardant effect was confirmed.

[0105] The electrolytes in Comparative Examples 3 and 4 were combinations of conventional, partially diluted, high-concentration electrolytes. Unlike the examples of the present disclosure, Comparative Examples 3 and 4 used a mixed solvent of ethers (DME), sulfones (TMS), carboxylic acid esters (EA), or carbonate esters (FEC) as the solvent, an imide-based lithium salt (LiFSI) as the solute, and a fluoroether diluent (TTE) alone. As is clear from the results in Table 3, although the fluoroether system exhibited a certain degree of flame retardancy, the self-extinguishing time test was still longer than that of the examples of the present disclosure, indicating that the flame retardancy effect was limited. Furthermore, the effective cycle was less than 300 cycles, and the average coulombic efficiency was approximately 98%, which was inferior to that of the examples of the present disclosure.

[0106] Comparative Example 5 used a conventional high-fluorine electrolyte commonly used in current lithium metal batteries, while Comparative Example 6 used a typical electrolyte used in conventional lithium-ion batteries. It was found that the batteries using these electrolytes exhibited low effective cycle counts and low coulombic efficiencies. Furthermore, the electrolytes were found to be highly flammable, with self-extinguishing times of 17.3 s / g and 21.2 s / g, respectively.

[0107] 1 is a comparative diagram showing the cycle performance of lithium metal negative electrode secondary batteries using the electrolyte solutions according to Examples 1 to 6 of the present disclosure and Comparative Examples 1 to 6. As can be seen from the diagram, the batteries of Examples 1 to 6 show a clear advantage in effective cycle performance over the batteries of Comparative Examples 1 to 6.

[0108] From the above results, the partially diluted high-concentration electrolyte according to the present disclosure, by using a main solvent containing highly safe components, can effectively block the chain reaction caused by hydroxyl radicals that occurs between the high-nickel ternary positive electrode and the metallic lithium negative electrode during thermal runaway of the battery, significantly improving the safety of the battery and improving the cycle life of the lithium metal battery. Furthermore, by adding a non-polar diluent that does not dissolve lithium salts to the high-concentration electrolyte, the viscosity of the electrolyte can be reduced while maintaining the performance of the high-concentration lithium ion solvent, further improving the rate performance of the lithium metal battery and expanding the usable temperature range.

[0109] Finally, it should be noted that the above-described embodiments are merely examples for explaining the technical ideas of the present disclosure and do not limit the technical scope of the present disclosure. While the contents of the present disclosure have been described in detail using the above embodiments, those skilled in the art can appropriately modify the technical content described in the above embodiments or replace part or all of the technical configurations included in the above embodiments with substantially equivalent means. None of these modifications or substitutions depart from the essence of the technical ideas of the present disclosure and are included in the technical scope of the embodiments of the present disclosure.

[0110] Industrial Potential The present disclosure relates to the technical field of lithium metal batteries, and in particular to a partially diluted high-concentration electrolyte, a preparation method thereof, and a lithium metal battery. The partially diluted high-concentration electrolyte comprises a non-aqueous organic solvent, a lithium salt, and a diluent. The non-aqueous organic solvent contains a phosphate ester solvent and an auxiliary organic solvent, the volume fraction of the phosphate ester solvent relative to the non-aqueous organic solvent being 50% or more, and the dielectric constant of the auxiliary organic solvent being 2.8 C / V m or more.

[0111] The partially diluted high-concentration electrolyte according to the present disclosure uses a main solvent containing highly safe components and a highly flame-retardant phosphazene compound as the main diluent, thereby effectively blocking a chain reaction caused by hydroxyl radicals that occurs between the high-nickel ternary positive electrode and the metallic lithium negative electrode during thermal runaway of the battery, thereby significantly improving the safety of the battery and improving the cycle life of the lithium metal battery.

[0112] The partially diluted high-concentration electrolyte, its preparation method, and lithium metal battery according to the present invention are highly reproducible and can be applied to various industrial applications, for example, the technical field of lithium metal batteries.

Claims

1. a non-aqueous organic solvent, a lithium salt, and a diluent; the non-aqueous organic solvent includes a phosphate ester-based solvent and an auxiliary organic solvent, and the volume fraction of the phosphate ester-based solvent relative to the non-aqueous organic solvent is 50% or more; The dielectric constant of the auxiliary organic solvent is 2.8 C / V·m or more. A partially diluted high-concentration electrolyte solution.

2. the phosphate ester solvent includes at least one solvent selected from the group consisting of trimethyl phosphate, triethyl phosphate, dimethyl methylphosphonate, tris(trimethylsilyl) phosphate, tricresyl phosphate, tris(isopropylphenyl) phosphate, tributyl phosphate, trioctyl phosphate, and cresyl diphenyl phosphate; and / or 2. The partially diluted high-concentration electrolyte solution according to claim 1, wherein the auxiliary organic solvent comprises at least one selected from the group consisting of carboxylic acid esters, ethers, silane esters, carbonates, fluorinated carbonates, and sulfones.

3. 3. The partially diluted high-concentration electrolyte according to claim 2, wherein the carboxylic acid ester comprises at least one selected from the group consisting of ethyl acetate, methyl acetate, butyl formate, and n-butyl acetate.

4. 4. The partially diluted high-concentration electrolyte according to claim 2, wherein the ether-based electrolyte contains one or more selected from the group consisting of ethylene glycol dimethyl ether, 1,2-dimethoxypropane, dimethoxymethane, tetrahydrofuran, and 2-methyltetrahydrofuran.

5. 5. The partially diluted high-concentration electrolyte solution according to claim 2, wherein the silane ester comprises at least one selected from the group consisting of tris(trimethylsilyl) phosphate, tris(trimethylsilyl)borate, tris(trimethylsilyl) phosphite, vinyltrimethoxysilane, phenyltrimethoxysilane, isocyanatotrimethylsilane, and 3-trimethylsilyl-2-oxazolidinone.

6. 6. The partially diluted high-concentration electrolyte solution according to claim 2, wherein the carbonate ester comprises at least one selected from the group consisting of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

7. 7. The partially diluted high-concentration electrolyte solution according to claim 2, wherein the fluorinated carbonate ester comprises at least one selected from the group consisting of fluoroethylene carbonate, fluorinated ethyl methyl carbonate, and difluoroethylene carbonate.

8. The partially diluted high-concentration electrolyte solution according to any one of claims 2 to 7, characterized in that the sulfone-based electrolyte contains one or more selected from the group consisting of sulfolane, dimethyl sulfoxide, difluoromethyl phenyl sulfone, and methyl phenyl sulfoxide.

9. 9. The partially diluted high-concentration electrolyte solution according to claim 1, wherein the volume ratio of the phosphate ester solvent to the auxiliary organic solvent is 1:(0.3 to 1).

10. the diluent comprises a phosphazene compound; The partially diluted high-concentration electrolyte solution according to any one of claims 1 to 9, wherein the phosphazene-based compound preferably includes one or more compounds selected from the group consisting of ethoxy(pentafluoro)cyclotriphosphazene, pentafluoro(phenoxy)cyclotriphosphazene, hexakis(1H,1H,7H-perfluoroheptoxy)phosphazene, hexamethoxycyclotriphosphazene, and hexaethoxycyclotriphosphazene.

11. the diluent further comprises a second diluent; the second diluent comprises one or more selected from the group consisting of fluoroether and / or fluorobenzene; Preferably, the volume fraction of the second diluent relative to the diluent is 0% to 20%; Preferably, the fluoroether contains one or two selected from the group consisting of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and bis(2,2,2-trifluoroethyl) ether.

12. the lithium salt includes an imide-based lithium salt, Preferably, the imide-based lithium salt comprises one or more selected from the group consisting of lithium bis(fluoromethylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium (nonafluorobutanesulfonyl)(trifluoromethanesulfonyl)imide, lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide, and perfluoropropanedisulfonylimide lithium; Preferably, the concentration of the lithium salt in the non-aqueous organic solvent is 3 to 6 M. The partially diluted high-concentration electrolyte according to any one of claims 1 to 11.

13. the lithium salt further comprises a blending lithium salt; the lithium salt for incorporation includes at least one selected from the group consisting of lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium nitrate; The partially diluted high-concentration electrolyte solution according to claim 12, wherein the molar ratio of the imide lithium salt to the blending lithium salt is preferably (5-20):

1.

14. The concentration of the lithium salt is 0.6 to 1.8 M after dilution with a diluent; and / or the volume ratio of the diluent to the high-concentration lithium salt solution is 3:2 to 9:1, and the high-concentration lithium salt solution is a mixture of a non-aqueous organic solvent and a lithium salt.

15. a step of uniformly mixing a lithium salt with a non-aqueous organic solvent to obtain a highly concentrated lithium salt solution; The method for preparing a partially diluted high-concentration electrolyte according to any one of claims 1 to 14, further comprising the step of uniformly mixing the high-concentration lithium salt solution with a diluent to obtain a partially diluted high-concentration electrolyte.

16. A lithium metal battery comprising the partially diluted high-concentration electrolyte solution according to any one of claims 1 to 14.

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