A high-entropy suspension ether-based electrolyte and its lithium-ion battery

Abstract

The present invention provides a high-entropy suspension ether-based electrolyte and a lithium-ion battery thereof, belonging to the technical field of lithium-ion batteries. The raw materials of the high-entropy suspension ether-based electrolyte of the present invention are: a basic ether-based electrolyte, an organic additive, and an inorganic additive; wherein the inorganic additive is a mixture of lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate. In the present invention, an inorganic additive and an organic additive are added to the basic ether-based electrolyte. The synergistic effect of the organic additive and the inorganic additive can form a stable SEI film, reduce the activation energies in the diffusion process of the electrolyte and the charge transfer process, significantly reduce the diffusion impedance of lithium ions, accelerate the diffusion kinetics of lithium ions, and improve the electrochemical performance and low-temperature performance of the lithium-ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a high-entropy suspension ether-based electrolyte and a lithium-ion battery thereof. Background Art

[0002] Lithium-ion batteries are the most successful commercially available secondary batteries nowadays, and they have advantages such as high actual energy density and long cycle life. However, the booming electric vehicle (EV) industry has put forward more stringent requirements for battery performance, such as fast charging ability and safety within a wide temperature range. Specifically, the negative electrode is regarded as a limiting factor for battery safety and fast charging performance due to its slow electrochemical reaction kinetics. In practical applications, the graphite negative electrode has a high theoretical specific capacity (372 mAh·g -1 ), good electronic and ionic conductivity, and a long cycle life. Coupled with its low lithium intercalation potential (<0.2 V vs Li + / Li), the battery can achieve a relatively high energy density, so it has become a commonly used negative electrode material for commercial lithium-ion batteries (LIB). However, there is a problem of co-insertion of ether solvents in the graphite negative electrode in the basic ether-based electrolyte, resulting in exfoliation and poor performance during the cycling of graphite. In addition, when charging at low temperatures, lithium ions cannot be inserted into graphite and lithium metal is deposited on its surface, thus posing a safety hazard. It can be seen that the interfacial stability problem between the graphite negative electrode and the electrolyte is a difficult problem that hinders the improvement of electrolyte performance and even the development of lithium-ion battery technology.

[0003] Therefore, it is of great significance to study a high-entropy suspension ether-based electrolyte and use it in lithium-ion batteries to solve the co-insertion problem of the graphite negative electrode and ether solvents and improve the electrochemical performance of lithium-ion batteries. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-entropy suspension ether-based electrolyte and a lithium-ion battery thereof to solve the problems of co-insertion of ether solvents in the graphite negative electrode in the basic ether-based electrolyte and poor electrochemical performance of the lithium-ion battery.

[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a high-entropy suspension ether-based electrolyte, comprising the following raw materials: a basic ether-based electrolyte, an organic additive, and an inorganic additive; the inorganic additive is a mixture of lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate.

[0007] Preferably, the basic ether-based electrolyte is composed of an ether solvent, a halogen-containing lithium salt, and lithium nitrate.

[0008] Preferably, the ether solvent includes one or more of ethylene glycol dimethyl ether, 1,3-dioxolane, tetraethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether.

[0009] Preferably, the halogen-containing lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium difluoro(oxalato)borate, and lithium tetrafluoroborate.

[0010] Preferably, in the basic ether electrolyte, the concentration of lithium ions is 0.5 - 2 mol / L; in the basic ether electrolyte, the mass of lithium nitrate is 1 - 3% of the total mass of the basic ether electrolyte.

[0011] Preferably, the organic additive includes fluoroethylene carbonate and / or vinylene carbonate.

[0012] Preferably, the volume of the organic additive accounts for 3 - 7% of the total volume of the high-entropy suspension ether electrolyte.

[0013] Preferably, in the high-entropy suspension ether electrolyte, the concentrations of lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate are independently 0.05 - 0.5 mol / L.

[0014] The present invention also provides a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and the above-mentioned high-entropy suspension ether electrolyte.

[0015] Preferably, the positive electrode includes a positive current collector and a positive electrode film; the negative electrode includes a negative current collector and a negative electrode film; the positive electrode film includes a positive active material, a conductive agent, and a binder; the negative electrode film includes a negative active material, a conductive agent, and a binder.

[0016] Advantages of the present invention:

[0017] (1) In the present invention, inorganic additives and organic additives are added to the basic ether electrolyte. The synergistic effect of the organic additives and inorganic additives can form a stable SEI film, reduce the activation energy in the diffusion process of the electrolyte and the charge transfer process, significantly reduce the diffusion impedance of lithium ions, and accelerate the diffusion kinetics of lithium ions.

[0018] (2) The high-entropy suspension ether electrolyte of the present invention can significantly reduce the solvent co-insertion phenomenon of the graphite negative electrode in the electrolyte, and improve the rate performance and low-temperature performance of the lithium-ion battery. Description of the Drawings

[0019] Figure 1Appearance state of the high-entropy suspension ether-based electrolyte (1.4 M LDD-4S + 5% FEC) of Example 1;

[0020] Figure 2 Appearance states of 1.4 M LDD-LiF + 5% FEC of Comparative Example 2, 1.4 M LDD-Li2O + 5% FEC of Comparative Example 3, 1.4 M LDD-Li2CO3 + 5% FEC of Comparative Example 4, and 1.4 M LDD-LiNO3 + 5% FEC of Comparative Example 5;

[0021] Figure 3 Raman spectra, infrared spectra, and 7 Li nuclear magnetic resonance spectra of LDD of Comparative Example 1, 1.4 M LDD + 5% FEC of Comparative Example 6, and 1.4 M LDD-4S + 5% FEC of Example 1, where a is the Raman spectrum of LDD, 1.4 M LDD + 5% FEC, and 1.4 M LDD-4S + 5% FEC, b is the infrared spectrum of LDD, 1.4 M LDD + 5% FEC, and 1.4 M LDD-4S + 5% FEC, and c is the 7 Li nuclear magnetic resonance spectrum of LDD and 1.4 M LDD-4S + 5% FEC;

[0022] Figure 4 Ionic conductivity comparison chart of LDD of Comparative Example 1 and 1.4 M LDD-4S + 5% FEC of Example 1, R ct Activation energy and R sei Activation energy comparison chart, where a is the ionic conductivity comparison chart, b is the R ct Activation energy comparison chart, c is the R sei Activation energy comparison chart;

[0023] Figure 5 Charge-discharge curve of lithium-ion battery DII-1;

[0024] Figure 6 CV curves and dQ / dV differential capacity curves of lithium-ion batteries DII-1 and II-1, where a is the CV curve of lithium-ion battery DII-1, b is the CV curve of lithium-ion battery II-1, c is the dQ / dV differential capacity curve of lithium-ion battery DII-1, and d is the dQ / dV differential capacity curve of lithium-ion battery II-1;

[0025] Figure 7 EIS diagrams of lithium-ion batteries DII-1 and II-1;

[0026] Figure 8The charge-discharge curve diagram of lithium-ion battery II-1, and the rate performance diagram and cycle performance diagram of lithium-ion batteries DII-1 and II-1, where a is the charge-discharge curve diagram of lithium-ion battery II-1, b is the rate performance diagram of lithium-ion batteries DII-1 and II-1, and c is the cycle performance diagram of lithium-ion batteries DII-1 and II-1;

[0027] Figure 9 The charge-discharge curve diagrams of lithium-ion batteries DII-7, DII-8, DII-9, and DII-10 at a current density of 0.1C, where a is the charge-discharge curve diagram of DII-7, b is the charge-discharge curve diagram of DII-8, c is the charge-discharge curve diagram of DII-9, and d is the charge-discharge curve diagram of DII-10;

[0028] Figure 10 The cycle performance diagram and Coulomb efficiency diagram of lithium-ion batteries II-1, DII-1, DII-7, DII-8, DII-9, and DII-10, where a is the cycle performance diagram and b is the Coulomb efficiency diagram;

[0029] Figure 11 The charge-discharge curve diagram of lithium-ion battery DII-6 and the rate performance diagram of lithium-ion batteries DII-6 and II-1, where a is the charge-discharge curve diagram of lithium-ion battery DII-6 and b is the rate performance diagram of lithium-ion batteries DII-6 and II-1;

[0030] Figure 12 The rate performance diagrams of lithium-ion batteries DII-2, DII-3, DII-4, and DII-5;

[0031] Figure 13 The low-temperature performance diagram of lithium-ion batteries DII-1 and II-1, where a is the electrochemical performance of DII-1 and II-1 at different temperatures, b is the charge-discharge curve of DII-1 at different temperatures, and c is the charge-discharge curve of II-1 at different temperatures. Specific embodiments

[0032] The present invention provides a high-entropy suspension ether-based electrolyte, comprising the following raw materials: a basic ether-based electrolyte, an organic additive, and an inorganic additive; the inorganic additive is a mixture of lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate.

[0033] In the present invention, the basic ether-based electrolyte is composed of an ether solvent, a halogen-containing lithium salt, and lithium nitrate.

[0034] In the present invention, the ether solvent includes one or more of ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), tetraethylene glycol dimethyl ether (TEGDME), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), diethylene glycol dimethyl ether (DIGLYME), and triethylene glycol dimethyl ether (TEDM). Preferably, it is one or more of ethylene glycol dimethyl ether, 1,3-dioxolane, tetraethylene glycol dimethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. More preferably, it is ethylene glycol dimethyl ether and 1,3-dioxolane. When there are two or more of the above ether solvents, the present invention has no special limitation on the ratio of different types of ether solvents.

[0035] In the present invention, the halogen-containing lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium perchlorate (LiClO4), lithium difluoro(oxalato)borate (LiDFOB), and lithium tetrafluoroborate (LiBF4). Preferably, it is one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium perchlorate. More preferably, it is lithium hexafluorophosphate and / or lithium bis(trifluoromethanesulfonyl)imide.

[0036] In the present invention, in the basic ether-based electrolyte, the concentration of lithium ions is 0.5 - 2 mol / L, preferably 0.8 - 1.5 mol / L, and more preferably 1 - 1.2 mol / L; in the basic ether-based electrolyte, the mass of lithium nitrate is 1 - 3% of the total mass of the basic ether-based electrolyte, preferably 2%.

[0037] In the present invention, the organic additive includes fluoroethylene carbonate (FEC) and / or vinylene carbonate (VC), preferably fluoroethylene carbonate. The addition of fluoroethylene carbonate (FEC) and / or vinylene carbonate (VC) is beneficial to the formation of an inorganic film and can also increase the organic components in the SEI film, forming an organic-inorganic composite SEI film, and the SEI film has high toughness and better ionic conductivity.

[0038] In the present invention, the volume of the organic additive accounts for 3 - 7% of the total volume of the high-entropy suspension ether-based electrolyte, preferably 4 - 6%, and more preferably 5%.

[0039] In the present invention, in the high-entropy suspension ether-based electrolyte, the concentrations of lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate are independently 0.05 - 0.5 mol / L, preferably 0.1 - 0.4 mol / L.

[0040] In the present invention, the addition of inorganic additives such as lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate can form a high-entropy system Li+ The solvation structure, the weaker solvation effect caused by the higher disorder of the system, improves the kinetics of lithium ions. The solvation structure rich in anions promotes the rapid formation of a stable interface on the electrode surface at low temperatures, which is beneficial to improving the low-temperature performance of lithium-ion batteries.

[0041] The present invention also provides a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and the high-entropy suspension ether-based electrolyte described above.

[0042] In the present invention, the positive electrode includes a positive current collector and a positive electrode sheet, and the negative electrode includes a negative current collector and a negative electrode sheet; the positive electrode sheet contains a positive active material, a conductive agent, and a binder; the negative electrode sheet contains a negative active material, a conductive agent, and a binder.

[0043] In the present invention, the positive active material includes one or more of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium iron phosphate, and lithium manganate, preferably one or more of lithium cobaltate, lithium iron phosphate, and lithium manganate, and further preferably lithium cobaltate and / or lithium iron phosphate.

[0044] In the present invention, the negative active material includes one or more of metallic lithium, natural graphite, artificial graphite, mesocarbon microbeads (abbreviated as MCMB), hard carbon, soft carbon, silicon, and silicon-carbon composites, preferably one or more of natural graphite, artificial graphite, hard carbon, soft carbon, silicon, and silicon-carbon composites, and further preferably one or more of natural graphite, artificial graphite, and silicon-carbon composites.

[0045] The technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0046] The basic ether-based electrolyte used in Examples 1 to 3 and Comparative Examples 1 to 10 of the present invention is a commercial ether-based electrolyte purchased from Kelude, with the model number MA-EN-EL-0O0516.

[0047] Example 1

[0048] The composition of the basic ether-based electrolyte is as follows: the volume ratio of ethylene glycol dimethyl ether (DME) to 1,3-dioxolane (DOL) is 1:1, the halogen-containing lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), the concentration of lithium ions is 1 mol / L, and the mass concentration of lithium nitrate is 2%. It is denoted as 1MLiTFSI-DOL / DME + 2%LiNO3, abbreviated as LDD.

[0049] In the basic ether-based electrolyte, lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate are sequentially added so that the concentrations of lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate are all 0.1 mol / L. After mixing evenly, fluoroethylene carbonate (FEC) (the volume of fluoroethylene carbonate accounts for 5% of the total volume of the high-entropy suspended ether-based electrolyte) is added, and stirred for 24 h to obtain a high-entropy suspended ether-based electrolyte, denoted as 1M LiTFSI-DOL / DME + 2% LiNO3 + 0.1M LiF + 0.1M Li2O + 0.1M Li2CO3 + 0.1M LiNO3 + 5% FEC, simply referred to as 1.4M LDD-4S + 5% FEC.

[0050] Preparation of the positive electrode sheet: Lithium iron phosphate, binder polyvinylidene fluoride, and conductive agent acetylene black are mixed in a mass ratio of 8:1:1, and then N-methylpyrrolidone solvent (the mass-volume ratio of binder polyvinylidene fluoride and N-methylpyrrolidone is 40 mg:1 mL) is added and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on aluminum foil by a film coater, and the coating thickness is 100 μm. The heating plate of the film coater is heated to 80 °C to preliminarily dry the positive electrode. The preliminarily dried electrode is placed in a vacuum drying oven and dried at 120 °C for 10 h. Finally, the dried electrode is cut into a positive electrode sheet with a diameter of 12 mm by a wafer slicing machine.

[0051] Preparation of the negative electrode sheet: Natural graphite, binder polyvinylidene fluoride, and conductive agent acetylene black are mixed in a mass ratio of 90:5:5, and then N-methylpyrrolidone (NMP) (the mass-volume ratio of binder polyvinylidene fluoride and pyrrolidone is 40 mg:1 mL) is added and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry is coated on copper foil by a film coater, and the coating thickness is 100 μm. The heating plate of the film coater is heated to 80 °C to preliminarily dry the negative electrode. The preliminarily dried electrode is placed in a vacuum drying oven and dried at 120 °C for 10 h. Finally, it is cut into a negative electrode sheet with a diameter of 12 mm by a wafer slicing machine.

[0052] The positive electrode sheet, negative electrode sheet, glass fiber membrane (GF / A), and high-entropy suspended ether-based electrolyte are assembled into a lithium-ion battery (denoted as II-1) in a glove box. The addition amount of the high-entropy suspended ether-based electrolyte is 90 μL. After the lithium-ion battery is left standing for 10 h, electrochemical tests are carried out.

[0053] In this Example 1, a commercial 1M LiTFSI-DOL / DME + 2% LiNO3 (abbreviated as LDD) was selected as the basic ether-based electrolyte, and then LiF, Li2O, Li2CO3, LiNO3, and FEC were added to the basic ether-based electrolyte. The concentrations of LiF, Li2O, Li2CO3, and LiNO3 were all 0.1M, and the volume content of FEC was 5%. A high-entropy suspended ether-based electrolyte was prepared, which was a suspension with high disorder (as Figure 1 shown).

[0054] Example 2

[0055] The composition of the basic ether-based electrolyte was as follows: the volume ratio of ethylene glycol dimethyl ether (DME) to 1,3-dioxolane (DOL) was 1:1, the halogen-containing lithium salt was lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), the concentration of lithium ions was 1 mol / L, and the mass concentration of lithium nitrate was 2%. It was denoted as 1M LiTFSI-DOL / DME + 2% LiNO3, abbreviated as LDD.

[0056] Lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate were sequentially added to the basic ether-based electrolyte, such that the concentrations of lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate were all 0.2 mol / L. After mixing evenly, fluoroethylene carbonate (FEC) (the volume of fluoroethylene carbonate accounted for 3% of the total volume of the high-entropy suspended ether-based electrolyte) was added, and stirred for 24 h. After mixing evenly, a high-entropy suspended ether-based electrolyte was obtained, denoted as 1M LiTFSI-DOL / DME + 2% LiNO3 + 0.2M LiF + 0.2M Li2O + 0.2M Li2CO3 + 0.2M LiNO3 + 3% FEC, abbreviated as 1.8M LDD-4S + 3% FEC.

[0057] Preparation of the positive electrode sheet: Lithium iron phosphate, binder polyvinylidene fluoride, and conductive agent acetylene black were mixed in a mass ratio of 8:1:1, and then N-methylpyrrolidone solvent (the mass-volume ratio of binder polyvinylidene fluoride to pyrrolidone was 40 mg:1 mL) was added and mixed evenly to obtain the positive electrode slurry. The positive electrode slurry was coated on the aluminum foil using a film coater, and the coating thickness was 100 μm. The heating plate of the film coater was heated to 80 °C to preliminarily dry the positive electrode. The preliminarily dried electrode was placed in a vacuum drying oven and dried at 120 °C for 10 h. Finally, it was cut into a positive electrode sheet with a diameter of 12 mm using a circular slicer.

[0058] Preparation of the negative electrode sheet: Natural graphite, binder polyvinylidene fluoride, and conductive agent acetylene black were mixed in a mass ratio of 90:5:5, and then N-methylpyrrolidone (NMP) was added (the mass-volume ratio of binder polyvinylidene fluoride to pyrrolidone was 40 mg:1 mL) and mixed evenly to obtain the negative electrode slurry. The negative electrode slurry was coated on a copper foil using a film coater, with a coating thickness of 100 μm. The heating plate of the film coater was heated to 80 °C to preliminarily dry the negative electrode. The preliminarily dried electrode was placed in a vacuum drying oven and dried at 120 °C for 10 h. Finally, it was cut into negative electrode sheets with a diameter of 12 mm using a circular slicer.

[0059] The positive electrode sheet, negative electrode sheet, glass fiber membrane (GF / A), and high-entropy suspended ether electrolyte were assembled into a lithium-ion battery (denoted as II-2) in a glove box, and the addition amount of the high-entropy suspended ether electrolyte was 90 μL.

[0060] Example 3

[0061] The composition of the base ether electrolyte was as follows: The volume ratio of ethylene glycol dimethyl ether (DME) to 1,3-dioxolane (DOL) was 1:1, the halogen-containing lithium salt was lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), the concentration of lithium ions was 1 mol / L, and the mass concentration of lithium nitrate was 2%, denoted as 1M LiTFSI-DOL / DME + 2% LiNO3, abbreviated as LDD.

[0062] Lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate were sequentially added to the base ether electrolyte so that the concentrations of lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate were all 0.5 mol / L. After mixing evenly, fluoroethylene carbonate (FEC) was added (the volume of fluoroethylene carbonate accounted for 7% of the total volume of the high-entropy suspended ether electrolyte), and stirred for 24 h. After mixing evenly, the high-entropy suspended ether electrolyte was obtained, denoted as 1M LiTFSI-DOL / DME + 2% LiNO3 + 0.5M LiF + 0.5M Li2O + 0.5M Li2CO3 + 0.5M LiNO3 + 7% FEC, abbreviated as 3M LDD-4S + 7% FEC.

[0063] Preparation of the positive electrode sheet: Lithium iron phosphate, binder polyvinylidene fluoride, and conductive agent acetylene black were mixed in a mass ratio of 8:1:1, and then N-methylpyrrolidone solvent was added (the mass-volume ratio of binder polyvinylidene fluoride to pyrrolidone was 40 mg:1 mL) and mixed evenly to obtain the positive electrode slurry. The positive electrode slurry was coated on an aluminum foil using a film coater, with a coating thickness of 100 microns. The heating plate of the film coater was heated to 80 °C to preliminarily dry the positive electrode. The preliminarily dried electrode was placed in a vacuum drying oven and dried at 120 °C for 10 h. Finally, the dried electrode was cut into positive electrode sheets with a diameter of 12 mm using a circular slicer.

[0064] Preparation of the negative electrode sheet: Natural graphite, binder polyvinylidene fluoride, and conductive agent acetylene black were mixed in a mass ratio of 90:5:5, and then N-methylpyrrolidone (NMP) was added (the mass-volume ratio of binder polyvinylidene fluoride to pyrrolidone was 40 mg:1 mL) and mixed evenly to obtain the negative electrode slurry. The negative electrode slurry was coated on the copper foil using a film coater, with a coating thickness of 100 μm. The heating plate of the film coater was heated to 80 °C to preliminarily dry the negative electrode. The preliminarily dried electrode was placed in a vacuum drying oven and dried at 120 °C for 10 h. Finally, the dried electrode was cut into negative electrode sheets with a diameter of 12 mm using a circular wafer slicer.

[0065] The positive electrode sheet, negative electrode sheet, glass fiber membrane (GF / A), and high-entropy suspended ether electrolyte were assembled into a lithium-ion battery (denoted as II-3) in a glove box, and the addition amount of the high-entropy suspended ether electrolyte was 90 μL.

[0066] Comparative Example 1

[0067] The difference from Example 1 was that the electrolyte used in assembling the lithium-ion battery was a basic ether electrolyte (abbreviated as LDD), and other conditions were the same. The assembled lithium-ion battery was denoted as DII-1.

[0068] Comparative Example 2

[0069] The difference from Example 1 was that only lithium fluoride, an inorganic additive, was added, and the concentration of lithium fluoride was 0.4 mol / L. Other conditions were the same, and a mixed ether electrolyte was obtained, denoted as 1M LiTFSI + DOL / DME + 2% LiNO3 + 0.4M LiF + 5% FEC, abbreviated as 1.4MLDD-LiF + 5% FEC. The assembled lithium-ion battery was denoted as DII-2.

[0070] Comparative Example 3<{

[0071] The difference from Example 1 was that only lithium oxide nanoparticles, an inorganic additive, were added, and the concentration of lithium oxide nanoparticles was 0.4 mol / L. Other conditions were the same, and a high-entropy suspended ether electrolyte was obtained, denoted as 1M LiTFSI + DOL / DME + 2% LiNO3 + 0.4M Li2O + 5% FEC, abbreviated as 1.4MLDD-Li2O + 5% FEC. The assembled lithium-ion battery was denoted as DII-3.

[0072] Comparative Example 4

[0073] The difference from Example 1 is that only one inorganic additive, nano-lithium carbonate, is added, and the concentration of nano-lithium carbonate is 0.4 mol / L. Other conditions are the same, and a high-entropy suspension ether electrolyte is obtained, which is recorded as 1M LiTFSI+DOL / DME+2%LiNO3+0.4M Li2CO3+5%FEC, abbreviated as 1.4MLDD-Li2CO3+5%FEC, and the assembled lithium-ion battery is recorded as DII-4.

[0074] Comparative Example 5

[0075] The difference from Example 1 is that only one inorganic additive, lithium nitrate, was added, and the concentration of lithium nitrate was 0.4 mol / L. Other conditions were the same, and a mixed ether electrolyte was obtained, which was recorded as 1MLiTFSI+DOL / DME+2%LiNO3+0.4MLiNO3+5%FEC, abbreviated as 1.4MLDD-LiNO3+5%FEC, and the assembled lithium-ion battery was recorded as DII-5.

[0076] Comparative Example 6

[0077] The difference from Example 1 is that no inorganic additives were added, and LiTFSI was added to prepare a mixed ether electrolyte so that the concentration of LiTFSI in the mixed ether electrolyte was 1.4 mol / L. Other conditions were the same, and it was recorded as 1.4 M LiTFSI + DOL / DME + 2% LiNO3 + 5% FEC, abbreviated as 1.4MLDD + 5% FEC, and the assembled lithium ion battery was recorded as DII-6.

[0078] Comparative Example 7

[0079] The difference from Example 1 is that only one inorganic additive, lithium fluoride, is added, the concentration of lithium fluoride is 0.4 mol / L, and no fluoroethylene carbonate is added. Other conditions are the same, and a mixed ether electrolyte is obtained, which is recorded as 1MLiTFSI+DOL / DME+2%LiNO3+0.4M LiF, abbreviated as 1.4MLDD-LiF, and the assembled lithium ion battery is recorded as DII-7.

[0080] Comparative Example 8

[0081] The difference from Example 1 is that only one inorganic additive, nano-lithium oxide, was added, the concentration of nano-lithium oxide was 0.4 mol / L, and no fluoroethylene carbonate was added. Other conditions were the same, and a mixed ether electrolyte was obtained, which was recorded as 1MLiTFSI+DOL / DME+2%LiNO3+0.4M Li2O, abbreviated as 1.4M LDD-Li2O, and the assembled lithium-ion battery was recorded as DII-8.

[0082] Comparative Example 9

[0083] The difference from Example 1 is that only one inorganic additive, lithium carbonate nanoparticles, is added, and the concentration of lithium carbonate nanoparticles is 0.4 mol / L. Fluoroethylene carbonate is not added, and other conditions are the same. A mixed ether electrolyte is obtained, denoted as 1 M LiTFSI + DOL / DME + 2% LiNO3 + 0.4 M Li2CO3, abbreviated as 1.4 M LDD-Li2CO3. The assembled lithium-ion battery is denoted as DII-9.

[0084] Comparative Example 10

[0085] The difference from Example 1 is that only one inorganic additive, lithium nitrate, is added, and the concentration of lithium nitrate is 0.4 mol / L. Fluoroethylene carbonate is not added, and other conditions are the same. A mixed ether electrolyte is obtained, denoted as 1 M LiTFSI + DOL / DME + 2% LiNO3 + 0.4 M LiNO3, abbreviated as 1.4 M LDD-LiNO3. The assembled lithium-ion battery is denoted as DII-10.

[0086] Figure 2 Figures show the appearance states of the electrolytes of Comparative Examples 2 to 5. Among them, 1.4 M LDD-LiF + 5% FEC of Comparative Example 2 and 1.4 M LDD-LiNO3 + 5% FEC of Comparative Example 5 are transparent solutions, while 1.4 M LDD-Li2O + 5% FEC of Comparative Example 3 and 1.4 M LDD-Li2CO3 + 5% FEC of Comparative Example 4 are suspensions.

[0087] Raman, FTIR, 7 Li nuclear magnetic resonance (NMR) and other methods were used to study the influence of the addition of inorganic additives on the Li + solvation environment in the basic ether electrolyte, and the results are as Figure 3 shown. As can be seen from Figure 3 a, there is a stronger coordination peak between Li + and the DME solvent in 1.4 M LDD + 5% FEC, while this peak is relatively weak in 1.4 M LDD-4S + 5% FEC. As can be seen from Figure 3 b, the peaks at 1351 cm -1 and 1332 cm -1 in the basic ether electrolyte (LDD) correspond to the cleavage of the O=S=O bond of LiTFSI, the peak at 1456 cm -1 is caused by the bending vibration of the C-H bond in the DOL solvent, and the peak at 1080 cm -1 corresponds to the C-O bond of the DOL solvent. In 1.4 M LDD-4S + 5% FEC of Example 1, 1058 cm -1 and 1186 / 1104 cm -1The peaks at [specific position] respectively correspond to the cleavage of the S–N–S and C–F bonds of LiTFSI. The peak of free DME at 849 cm in the 1.4M LDD + 5% FEC and 1.4M LDD-4S + 5% FEC electrolytes weakens, which is attributed to the addition of lithium-containing inorganic additives, increasing the concentration of lithium ions in the electrolyte and resulting in more DME coordinating with Li -1 At [specific position], the coordination. Correspondingly, the coordination peak of Li + with DME at 867 cm -1 strengthens in 1.4M LDD + 5% FEC, while increases less in 1.4M LDD-4S + 5% FEC, indicating a weaker interaction between Li + and the DME solvent in 1.4M LDD-4S + 5% FEC. As can be seen from + c in [reference], compared with the NMR spectrum of LDD, the 1.4M LDD-4S + 5% FEC has a positive chemical shift of Li, further proving that the addition of multiple inorganic additives weakens the interaction between Li Figure 3 and the solvent and enhances the interaction with anions. + By adding inorganic additives to the basic ether-based electrolyte, the present invention changes the solvation structure of the basic ether-based electrolyte. After the dissociation of lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles and lithium nitrate, the coordination of Li

[0088] -solvent is weakened. Therefore, the high-entropy suspended ether-based electrolyte of the present invention forms a weak solvation environment. + The lithium-ion batteries of Example 1 and Comparative Examples 1 to 10 were subjected to performance tests:

[0089] (1) Cyclic voltammetry test of lithium-ion batteries

[0090] The test voltage range of the graphite half-cell is 0.005 - 2.0V vs Li / Li

[0091] , the scanning speed is 0.1 - 20 mV·s + , and the test temperature is room temperature. -1 (2) Constant current charge and discharge tests of lithium-ion batteries at room temperature and low temperature:

[0092] The test voltage range of the half-cell is 0.005 - 2.0V vs Li / Li

[0093] , the test current density is 0.1 - 3C (1C = 372 mA·g + ), and the test temperature is 25°C. The test voltage range of the full cell of graphite and lithium iron phosphate is 2.0 - 3.65V vs Li / Li -1 ), and the test temperature is 25°C. +, the scanning speed is 0.1 - 20 mV·s -1 , the test current density is 0.1 - 5 C (1 C = 170 mAh·g -1 ), the test temperatures are 25°C, -10°C, -20°C, -30°C. When testing at low temperatures, after standing for 1 h under each temperature condition, the test is started. Before the cycle performance test, it is cycled for 3 weeks at a current density of 0.1 C and then the test is started.

[0094] (3) Impedance EIS test of lithium-ion batteries

[0095] The test voltage range is 0.005 - 2.0 V vs Li / Li + , the test frequency range is 0.01 - 100000 Hz. After the lithium-ion battery is assembled, it is left standing for 10 h, and the impedance before the test cycle is measured. The impedance of the battery after charge and discharge at a rate of 0.1 C for 5 weeks is measured for the test cycle.

[0096] Figure 4 As shown in a, the ionic conductivity of LDD at room temperature is 8.73 mS / cm, and the ionic conductivity of 1.4 M LDD-4S+5% FEC is 7.99 mS / cm. The desolvation barriers of Li in LDD and 1.4 M LDD-4S+5% FEC are studied by fitting the electrochemical impedance spectra (EIS) of fresh Li||Li symmetric cells at different temperatures (the results are shown in + b and c). According to the classical Arrhenius law (Equation 1), the EIS spectra are fitted to obtain the activation energy and desolvation energy of lithium ions passing through the SEI film in different electrolytes. Figure 4 In Equation (1), k is the rate constant, T is the thermodynamic temperature, R

[0097]

[0098] is the ion transfer resistance, A is the pre-exponential constant, E ct / SEI is the activation energy, and R is the standard gas constant. By fitting the separated semicircles of the impedance of the Li||Li symmetric cell (R a , R SEI ), the activation energy E ct is obtained. R a represents the resistance of Li passing through the SEI at medium frequencies; R SEI represents the charge transfer resistance of Li at the SEI / electrolyte interface at lower frequencies. According to the fitted R + and R ct , the corresponding activation energy E + is obtained from the Arrhenius equation. As shown in SEI and ct . a As shown in Figure 4As shown in b and c, fitting calculations found that, compared with the relatively high SEI film impedance in LDD, the activation energy in 1.4M LDD-4S+5% FEC is lower, indicating that the SEI film formed by 1.4M LDD-4S+5% FEC can significantly reduce the diffusion impedance of lithium ions and accelerate the diffusion kinetics of lithium ions. In addition, several anions can participate in the solvation layer of lithium ions, replacing some solvent molecules and reducing the desolvation energy of lithium ions.

[0099] Therefore, the ionic conductivity of 1.4M LDD-4S+5% FEC prepared in Example 1 of the present invention is lower than that of the basic electrolyte LDD, but the activation energies in the diffusion process and charge transfer process of the 1.4M LDD-4S+5% FEC electrolyte are both lower, thus having better Li + kinetics.

[0100] Figure 5 is the charge-discharge curve of lithium-ion battery DII-1. Figure 6 are the CV curves and dQ / dV differential capacity curves of lithium-ion batteries DII-1 and II-1. From Figure 5 and Figure 6 it can be seen that in the basic ether-based electrolyte (LDD), the graphite negative electrode is prone to co-insertion of solvents, and subsequent decomposition is likely to cause exfoliation of the graphite structure, resulting in a decrease in capacity and cycle stability. Therefore, LDD is not compatible with the graphite negative electrode.

[0101] Figure 7 is the EIS diagram of lithium-ion batteries DII-1 and II-1. It can be seen that compared with LDD, 1.4M LDD-4S+5% FEC has a lower impedance. Figure 8 In a, is the charge-discharge curve of lithium-ion battery II-1. Figure 8 In b, is the rate performance diagram of lithium-ion batteries DII-1 and II-1. Figure 8 In c, is the cycle performance diagram of lithium-ion batteries DII-1 and II-1. From Figure 8 it can be seen that by adding 4 inorganic additives to 1MLiTFSI+DOL / DME+2% LiNO3 (LDD), the obtained 1.4MLDD-4S+5% FEC exhibits excellent electrochemical performance, and there is no typical solvent co-insertion phenomenon in the basic ether-based electrolyte. Compared with LDD, 1.4MLDD-4S+5% FEC has excellent electrochemical performance, and the capacities at current densities of 0.1C, 0.2C, 0.5C, 1C, 2C, and 3C are 360 mA h·g -1 、346 mAh·g -1 、324 mAh·g -1 、280 mAh·g -1 、221 mAh·g-1 and 165 mAh·g-1

[0102] Figure 9 are the charge-discharge curves of lithium-ion batteries DII-7, DII-8, DII-9, and DII-10 at a current density of 0.1C. Figure 10 are the cycling performance and Coulomb efficiency graphs of lithium-ion batteries II-1, DII-1, DII-7, DII-8, DII-9, and DII-10. It can be seen from Figure 9 and Figure 10 that when a single inorganic additive is added to the basic ether electrolyte (LDD), there is a similar solvent co-insertion phenomenon as in LDD and a relatively low capacity is exhibited. At 1C, there is only a capacity of about 50 mAh·g -1 or so.

[0103] Figure 11 In [figure number], a is the charge-discharge curve of lithium-ion battery DII-6, and b is the rate performance graph of lithium-ion batteries DII-6 and II-1. It can be seen from Figure 11 that adding the organic additive FEC to the basic ether electrolyte can form a stable SEI film.

[0104] Figure 12 are the rate performance graphs of lithium-ion batteries DII-2, DII-3, DII-4, and DII-5. Figure 12 shows the electrochemical performance of lithium-ion batteries in electrolytes of 1.4M LDD-Li2O + 5% FEC, 1.4M LDD-Li2CO3 + 5% FEC, 1.4M LDD-LiF + 5% FEC, and 1.4M LDD-LiNO3 + 5% FEC. It is found that combining FEC with a single inorganic additive can effectively inhibit the solvent co-insertion phenomenon, but the rate performance is still inferior to that of 1.4M LDD-4S + 5% FEC. Therefore, adding several inorganic additives and organic additives to LDD simultaneously in the present invention can effectively improve the electrochemical performance of the graphite negative electrode.

[0105] The present invention tested the low-temperature performance of lithium-ion batteries DII-1 and II-1. The test process was as follows: Lithium-ion batteries DII-1 and II-1 were cycled at -10°C to form SEI. The results are shown in Figure 13 . It can be seen from Figure 13 that lithium-ion battery DII-1 showed an extremely low capacity at -10°C, and almost no capacity at -20°C and -30°C. While lithium-ion battery II-1 showed a capacity close to 300 mAh·g -1 . This indicates that the addition of several inorganic additives enables the electrolyte to quickly form a stable SEI even at low temperatures, and the low desolvation energy enables it to exhibit excellent rate performance.

[0106] As can be seen from the above embodiments, the present invention provides a high-entropy suspended ether-based electrolyte and a lithium-ion battery thereof. The raw materials of the high-entropy suspended ether-based electrolyte of the present invention are: a basic ether-based electrolyte, an organic additive, and an inorganic additive; wherein the inorganic additive is a mixture of lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate. In the present invention, an inorganic additive and an organic additive are added to the basic ether-based electrolyte. The synergistic effect of the organic additive and the inorganic additive can form a stable SEI film, reduce the activation energy in the diffusion process of the electrolyte and the charge transfer process, significantly reduce the diffusion impedance of lithium ions, accelerate the diffusion kinetics of lithium ions, and improve the electrochemical performance and low-temperature performance of the lithium-ion battery.

[0107] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A high-entropy suspended ether-based electrolyte, characterized in that, It comprises the following raw materials: a basic ether-based electrolyte, an organic additive, and an inorganic additive; the inorganic additive is a mixture of lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate; The organic additive is fluoroethylene carbonate; In the high-entropy suspended ether-based electrolyte, the concentrations of lithium oxide nanoparticles, lithium fluoride, lithium carbonate nanoparticles, and lithium nitrate are independently 0.05 - 0.5 mol / L; The basic ether-based electrolyte is composed of an ether solvent, a halogen-containing lithium salt, and lithium nitrate; In the basic ether-based electrolyte, the mass of lithium nitrate is 1 - 3% of the total mass of the basic ether-based electrolyte.

2. The high-entropy suspension ether-based electrolyte according to claim 1, wherein The ether solvent includes one or more of ethylene glycol dimethyl ether, 1,3-dioxolane, tetraethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether.

3. The high-entropy suspended ether-based electrolyte according to claim 1 or 2, characterized in that, The halogen-containing lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium difluoro(oxalato)borate, and lithium tetrafluoroborate.

4. The high-entropy suspended ether-based electrolyte according to claim 3, characterized in that In the basic ether-based electrolyte, the concentration of lithium ions is 0.5 - 2 mol / L.

5. The high-entropy suspension ether-based electrolyte according to claim 4, wherein, The volume of the organic additive accounts for 3 - 7% of the total volume of the high-entropy suspended ether-based electrolyte.

6. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and the high-entropy suspended ether-based electrolyte according to any one of claims 1 - 5.

7. The lithium ion battery according to claim 6, characterized in that, The positive electrode includes a positive current collector and a positive electrode film; the negative electrode includes a negative current collector and a negative electrode film; the positive electrode film includes a positive active material, a conductive agent, and a binder; the negative electrode film includes a negative active material, a conductive agent, and a binder.

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