Electrolyte and lithium metal battery

Abstract

The application discloses an electrolyte and a lithium metal battery. The electrolyte comprises a lithium salt, a solvent, a diluent and an additive; the solvent is a phosphoric acid ester-based solvent and / or a fluorine-containing phosphoric acid ester-based solvent; the diluent is a fluorinated phosphazene-based flame retardant; and the additive comprises a fluorinated solvent. Further, the fluorinated phosphazene-based flame retardant is selected from at least one of hexafluorocyclotriphosphazene, ethoxy pentafluorocyclotriphosphazene, trifluoroethoxy pentafluorocyclotriphosphazene and (phenoxy) pentafluorocyclotriphosphazene. Further, the additive further comprises an organic salt. The electrolyte can improve the oxidation resistance of a local high-concentration electrolyte, improve the flame retardation of the electrolyte, reduce the viscosity of the electrolyte and improve the wettability, so that the high-energy-density LMB can be safely and durably operated; meanwhile, the electrolyte can reduce the adverse effect of the phosphoric acid ester-based solvent on the lithium metal interface, effectively improve the lithium ion deposition / peeling stability, and realize high-stable cycle of the high-voltage lithium metal battery.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more particularly to an electrolyte and a lithium metal battery. Background Technology

[0002] Lithium metal anodes are characterized by their ultra-high theoretical specific capacity (3860 mAh g). -1 Its extremely low potential (-3.04V vs. SHE) is considered a promising candidate to replace carbon-based anodes as the core anode material for next-generation energy storage systems. Meanwhile, high-voltage lithium metal batteries (LMBs) using NCM ternary cathodes and lithium-rich manganese (LRMO) cathodes and lithium metal anodes will provide over 400Wh / kg capacity. -1 High energy density is a key advantage of lithium metal batteries. However, the development of electrolytes with wide electrochemical windows remains lagging, leading to difficulties in stabilizing the electrode-electrolyte interface in high-voltage lithium metal batteries. This hinders the development of lithium metal batteries due to problems such as lithium dendrite formation, low cycle coulombic efficiency, and poor oxidation stability of the high-voltage cathode. Electrolyte engineering is one of the best strategies to address these issues. Furthermore, the cycling behavior of the lithium metal anode is highly dependent on the electrolyte, which significantly affects interfacial chemistry and the resulting lithium metal growth morphology.

[0003] In traditional carbonate electrolytes, the lithium-ion solvation structure exhibits a solvent-separated ion-pair solvation sheath structure, leading to the formation of solvent-derived, organic-rich, and unstable electrode interfaces, resulting in poor performance of lithium metal batteries. Researchers have proposed increasing the lithium salt concentration in the electrolyte to form high-concentration electrolytes (HCEs). These HCEs possess a unique lithium solvation structure (contact ion pairs and aggregated ion clusters), and reduced free solvent decomposition, allowing for the formation of robust anion-derived passivation layers on both the positive and negative electrodes, ensuring stable cycling of high-voltage lithium metal batteries. However, HCEs suffer from low ionic conductivity, high viscosity, high cost, and poor wettability, hindering their practical application. To overcome these problems, researchers have proposed adding a non-soluble diluent to HCEs to form locally high-concentration electrolytes (LHCEs). In LHCEs, the diluent is miscible with the solvent but hardly dissolves the lithium salt, thus preserving the unique solvation structure of HCEs. Simultaneously, the overall lithium salt concentration and electrolyte viscosity are significantly reduced. Figures showing different solvation structures and SEI layers in conventional electrolytes, high-concentration electrolytes, and locally high-concentration electrolytes are shown below. Figure 1 Kaoru Dokko et al. (J. Electrochem. Soc. 2013, 160, A1304.) first introduced 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) as a diluent for LiTFSI-tetramelamine (G4) electrolyte. TTE does not react with Li... + Ion coordination, therefore [Li(G4)] is retained. +-[TFSI] - The original ion-pair structure. Later, some hydrofluoroethers, such as 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE) and bis(2,2,2-trifluoroethyl) ether (BTFE), were proposed and applied to lithium metal batteries. Currently, most diluents for LHCEs are hydrofluorocarbons, which have low boiling points (<100°C) and high volatility, limiting the temperature operating window. Furthermore, the low flash points and toxic decomposition products of hydrofluorocarbon diluents also raise safety and environmental concerns. Summary of the Invention

[0004] The purpose of this invention is to provide an electrolyte and a lithium metal battery that addresses the problems of poor oxidation resistance and low flash point and toxic decomposition products of traditional locally high-concentration electrolytes. This invention replaces linear ether solvents with phosphate esters or fluorinated phosphate ester-based solvents to improve the electrolyte's oxidation resistance. Simultaneously, a novel diluent, a fluorinated phosphazene flame retardant, is introduced. This commercially available flame retardant additive has a boiling point as high as 125°C, enabling the safe and long-lasting operation of high-energy-density lithium metal batteries, especially ensuring battery safety at high temperatures. Furthermore, synergistic lithium protection additives (fluorinated solvents such as FEC or DFEC and organometallic salts such as aluminum trifluoromethanesulfonate-Al(oTF)3) reduce the adverse effects of phosphate esters on the interface, thereby achieving stable cycling of high-voltage lithium metal batteries.

[0005] In a first aspect, the present invention provides an electrolyte comprising a lithium salt, a solvent, a diluent, and an additive;

[0006] The solvent is a phosphate ester-based solvent and / or a fluorinated phosphate ester-based solvent;

[0007] The diluent is a fluorinated phosphazene flame retardant;

[0008] The additives include fluorinated solvents.

[0009] In the electrolyte described above, the fluorinated phosphazene flame retardant is selected from at least one of hexafluorocyclotriphosphazene (HFPN), ethoxypentafluorocyclotriphosphazene (PFPN), trifluoroethoxypentafluorocyclotriphosphazene (TFPN), and (phenoxy)pentafluorocyclotriphosphazene (FPPN).

[0010] In the electrolyte described above, the solvent is selected from at least one of dimethyl methylphosphonate, trimethyl phosphate (TMP), triethyl phosphate (TEP), and bis(2,2,2-trifluoroethyl)methyl phosphate; the volume fraction of the solvent in the electrolyte is 20% to 40%, such as 30% or 35%; and the volume fraction of the diluent in the electrolyte is 60% to 80%, such as 70% or 65%.

[0011] In the above electrolyte, the solvent is selected from at least one of tributyl phosphate, triisobutyl phosphate, triphenyl phosphate (TPP), trioctyl phosphate, and tris(butoxyethyl) phosphate; the volume fraction of the solvent in the electrolyte is 10% to 30%, such as 25%, 20%; the volume fraction of the diluent in the electrolyte is 70% to 90%, such as 75%, 80%.

[0012] In the above electrolyte, the fluorinated solvent is selected from at least one of fluorinated ethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); the weight ratio of the fluorinated solvent in the electrolyte is 3% to 5%, such as 5%, 3%, 4%.

[0013] In the above electrolyte, the lithium salt is selected from at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalate borate, lithium hexafluorophosphate, and lithium tetrafluoroborate;

[0014] The molar concentration of the lithium salt in the electrolyte is 1 to 1.5 M, such as 1.2 M, 1.5 M, 1.15 M, 1.05 M.

[0015] In the above electrolyte, the additive further includes an organometallic salt;

[0016] The organometallic salt is selected from at least one of magnesium trifluoromethanesulfonate, aluminum trifluoromethanesulfonate, zinc trifluoromethanesulfonate, and silver trifluoromethanesulfonate;

[0017] The mass ratio of the organometallic salt in the electrolyte is 0.1% to 0.5%, such as 0.1%, 0.2%, 0.3%.

[0018] In a second aspect, the present invention provides a lithium metal battery, including a negative electrode sheet, a positive electrode sheet, a separator, and an electrolyte, and the electrolyte is the electrolyte described in any one of the above.

[0019] In the above lithium metal battery, the positive electrode sheet includes a high-nickel ternary positive electrode material or a lithium-rich manganese-based positive electrode material.

[0020] Further, the high-nickel ternary positive electrode material is LiNi x Co y Mn z O2, x + y + z = 1, 0.6 ≤ x < 1;

[0021] The lithium-rich manganese-based positive electrode material is xLi2MnO3·(1 - x)LiMeO2, 0 < x < 1, Me = Mn, Ni or Co.

[0022] As an example, the high-nickel ternary positive electrode material is LiNi 0.8 Co x Mny O2, x+y=0.2 (e.g., LiNi) 0.8 Co 0.1 Mn 0.1 O2) or LiNi 0.88 Co x Mn y O2, x+y=0.12 (e.g., LiNi) 0.88 Co 0.06 Mn 0.06 O2);

[0023] The lithium-rich manganese-based cathode material is Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2.

[0024] The present invention has the following beneficial effects:

[0025] (1) Using phosphate ester solvents or fluorinated phosphate ester-based solvents (such as dimethyl methylphosphonate, bis(2,2,2-trifluoroethyl)methyl phosphate, trioctyl phosphate, etc.) combined with novel fluorinated phosphazene flame retardant diluents (such as ethoxy(pentafluoro)cyclotriphosphine (PFPN)) can not only improve the antioxidant capacity of locally high-concentration electrolytes, but also improve the flame retardant capacity of electrolytes, enabling high-energy-density LMBs to operate safely and sustainably.

[0026] (2) Introducing fluorinated phosphazene flame retardant diluents into phosphate ester-based electrolytes can effectively reduce the overall viscosity of the electrolyte. At the same time, it improves the wettability of the electrolyte with the separator and electrodes, which helps to enhance the capacity under high active material loading, thereby achieving lithium metal batteries with higher energy density.

[0027] (3) Introducing fluorinated solvents such as FEC or DFEC and organometallic salts such as aluminum trifluoromethanesulfonate-Al(oTF)3 as synergistic additives for lithium protection to form a bifunctional lithium-loving and lithium-repellent SEI: The Li-Al alloy SEI can effectively reduce the interfacial resistance and avoid the corrosion of the lithium anode by phosphate esters such as TMP during the desolvation process. At the same time, the Li-Al alloy SEI layer can effectively reduce the interfacial resistance and is rich in LiF and LiN. x O y The inorganic layer has high interface energy and electron blocking effect for lithium, effectively preventing dendrite growth. Attached Figure Description

[0028] Figure 1 The illustrations show different solvation structures and SEI layers in conventional electrolytes, high-concentration electrolytes, and locally high-concentration electrolytes in the background art.

[0029] Figure 2 This is the linear volt-ampere test curve in Embodiment 10 of the present invention.

[0030] Figure 3 This is the linear volt-ampere test curve in Comparative Example 1 of the present invention. Detailed Implementation

[0031] Traditional locally concentrated electrolytes typically use linear ethers such as dimethyl glycol ether (DME) as solvents, which have poor high-voltage stability (≤4V) and cannot meet the requirements for ternary high-voltage cathode materials. Furthermore, the safety risks posed by highly volatile and flammable components (such as DME or TTE) in conventional locally concentrated electrolytes pose a significant challenge to lithium metal batteries. Therefore, this invention provides an electrolyte comprising at least one of the following: lithium salt (such as lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalate borate, lithium hexafluorophosphate, and lithium tetrafluoroborate), solvent, diluent, and additives; wherein the solvent is a phosphate ester-based solvent or a fluorinated phosphate ester-based solvent (such as dimethyl methylphosphonate, trimethyl phosphate, triethyl phosphate, bis(2,2,2-trifluoroethyl)methyl phosphate, tributyl phosphate, triisobutyl phosphate, and triphenyl phosphate). The electrolyte comprises phosphate esters (TPP), trioctyl phosphate, tri(butoxyethyl) phosphate, etc.; the diluent is a fluorinated phosphazene flame retardant diluent (such as hexafluorocyclotriphosphazene (HFPN), ethoxy(pentafluoro)cyclotriphosphazene, trifluoroethoxypentafluorocyclotriphosphazene, (phenoxy)pentafluorocyclotriphosphazene); the additives include fluorinated solvents (such as FEC or DFEC) and organometallic salts (such as magnesium trifluoromethanesulfonate, aluminum trifluoromethanesulfonate, zinc trifluoromethanesulfonate, silver trifluoromethanesulfonate, etc.). Firstly, the electrolyte of this invention uses phosphate ester solvents and / or fluorinated phosphate ester solvents (such as triethyl phosphate-TEP) to replace the DME linear ether solvent, improving the antioxidant capacity of locally high-concentration electrolytes. Simultaneously, phosphate esters have low volatility and flame retardant properties, which can improve the flame retardancy of the electrolyte and enhance battery safety. Secondly, fluorinated phosphazene flame retardants, such as ethoxy(pentafluoro)cyclotriphosphine (PFPN), are commercially available flame retardant additives with a high boiling point of 125°C. They exhibit a large band gap and poor lithium salt solubility, enabling high-energy-density lithium batteries (LMBs) to operate safely and sustainably, especially at high temperatures. Compared to hydrofluorocarbon diluents, PFPN is the optimal choice for high-voltage LMBs, offering both high inherent safety and a wide electrochemical window. Thirdly, to mitigate the adverse effects of phosphate ester-based solvents on the lithium metal anode interface, this invention introduces fluorinated solvents—FEC or DFEC—and organometallic salts, such as aluminum trifluoromethanesulfonate-Al(oTF)3, as synergistic additives for lithium protection, forming a bifunctional lithium-loving / lithium-repellent SEI. Simultaneously, the Li-Al alloy SEI layer effectively reduces interfacial resistance and is rich in LiF and LiN. x O yThe inorganic layer has a high interface energy and electron blocking effect for lithium, effectively preventing dendrite growth. In this invention, phosphate ester-based solvents and / or fluorinated phosphate ester solvents are used as the main solvents. At least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalate borate, lithium hexafluorophosphate, and lithium tetrafluoroborate is selected as the lithium salt. Fluorinated phosphazene flame retardants such as ethoxy(pentafluoro)cyclotriphosphine (PFPN) are used as diluents. Fluorinated solvents -FEC or DFEC and organometallic salts such as aluminum trifluoromethanesulfonate -Al(oTF)3 are used as synergistic additives for lithium protection. Experiments have shown that when a stainless steel sheet is used as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and an SS|Li half-cell is assembled, and linear voltammetry (LSV) is performed, the electrolyte of this invention can meet the requirements for use with NCM ternary and lithium-rich manganese cathodes (LRMO), and the Li|Li symmetric cell achieves a voltage drop of 1 mA / cm². 2 It can cycle stably for over 300 hours at current density.

[0032] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0033] Unless otherwise specified, the methods used in the following embodiments are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0034] Example 1

[0035] 5 wt% fluoroethylene carbonate (FEC) was first dissolved in trimethyl phosphate (TMP). Then, 1.5 M LiFSI was dissolved in the above solution. After complete dissolution, ethoxy(pentafluoro)cyclotriphosphine (PFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TMP was 30%, and the volume fraction of PFPN diluent was 70%.

[0036] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 4.82 V, which meets the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, and adding the aforementioned electrolyte between the electrodes, a Li|Li symmetric cell was assembled. At 1 mA / cm², [the cell's performance was assessed]. 2 It can cycle stably for over 200 hours at current density.

[0037] Example 2

[0038] 0.1 wt% aluminum trifluoromethanesulfonate and 5 wt% fluoroethylene carbonate (FEC) were first dissolved in trimethyl phosphate (TMP). Then, 1.5 M LiFSI was dissolved in the above solution. After complete dissolution, ethoxy(pentafluoro)cyclotriphosphorus benzene (PFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TMP was 30%, and the volume fraction of PFPN diluent was 70%.

[0039] Using stainless steel sheets as the positive electrode, lithium sheets as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 4.85V, meeting the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 300 hours at current density.

[0040] Example 3

[0041] 0.1 wt% aluminum trifluoromethanesulfonate and 5 wt% fluoroethylene carbonate (FEC) were first dissolved in triethyl phosphate (TEP). Then, 1.2 M LiFSI was dissolved in the above solution. After complete dissolution, ethoxy(pentafluoro)cyclotriphosphine (PFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TEP was 35%, and the volume fraction of PFPN diluent was 65%.

[0042] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 4.86V, meeting the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 320 hours at current density.

[0043] Example 4

[0044] 3 wt% difluoroethylene carbonate (DFEC) was first dissolved in triethyl phosphate (TEP). Then, 1.2 M LiFSI was dissolved in the above solution. After complete dissolution, ethoxy(pentafluoro)cyclotriphosphine (PFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TEP was 35%, and the volume fraction of PFPN diluent was 65%.

[0045] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 4.86V, meeting the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 260 hours at current density.

[0046] Example 5

[0047] 0.1 wt% aluminum trifluoromethanesulfonate and 3 wt% difluoroethylene carbonate (DFEC) were first dissolved in triethyl phosphate (TEP). Then, 1.2 M LiFSI was dissolved in the above solution. After complete dissolution, ethoxy(pentafluoro)cyclotriphosphine (PFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TEP was 35%, and the volume fraction of PFPN diluent was 65%.

[0048] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 4.86V, meeting the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 350 hours at current density.

[0049] Example 6

[0050] 0.2 wt% zinc trifluoromethanesulfonate and 4 wt% difluoroethylene carbonate (DFEC) were first dissolved in tributyl phosphate (TBP). Then, 1.15 M LiFSI was dissolved in the above solution. After complete dissolution, trifluoroethoxypentafluorocyclotriphosphazene (TFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TBP was 25%, and the volume fraction of TFPN diluent was 75%.

[0051] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 4.92 V, which meets the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 310 hours at current density.

[0052] Example 7

[0053] 4 wt% difluoroethylene carbonate (DFEC) was first dissolved in triphenyl phosphate (TPP). Then, 1.05 M LiTFSI was dissolved in the above solution. After complete dissolution, trifluoroethoxypentafluorocyclotriphosphazene (TFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TPP was 20%, and the volume fraction of TFPN diluent was 80%.

[0054] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 5.02 V, which meets the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 240 hours at current density.

[0055] Example 8

[0056] 0.3 wt% magnesium trifluoromethanesulfonate and 4 wt% difluoroethylene carbonate (DFEC) were first dissolved in triphenyl phosphate (TPP). Then, 1.05 M LiTFSI was dissolved in the above solution. After complete dissolution, trifluoroethoxypentafluorocyclotriphosphazene (TFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TPP was 20%, and the volume fraction of TFPN diluent was 80%.

[0057] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 5.02 V, which meets the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 320 hours at current density.

[0058] Example 9

[0059] 3 wt% of fluoroethylene carbonate (FEC) was first dissolved in bis(2,2,2-trifluoroethyl)methyl phosphate. Then, 1.3 M LiFSI was dissolved in the above solution. After complete dissolution, (phenoxy)pentafluorocyclotriphosphazene (FPPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of bis(2,2,2-trifluoroethyl)methyl phosphate was 40%, and the volume fraction of FPPN diluent was 60%.

[0060] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 5.2V, which meets the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 260 hours at current density.

[0061] Example 10

[0062] 0.4 wt% silver trifluoromethanesulfonate and 3 wt% fluoroethylene carbonate (FEC) were first dissolved in bis(2,2,2-trifluoroethyl)methyl phosphate. Then, 1.3 M LiFSI was dissolved in the above solution. After complete dissolution, (phenoxy)pentafluorocyclotriphosphazene (FPPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of bis(2,2,2-trifluoroethyl)methyl phosphate was 40%, and the volume fraction of FPPN diluent was 60%.

[0063] A half-cell of SS|Li was assembled using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte. Linear voltammetry (LSV) was performed, and the oxidation peak potential was approximately 5.2V. Figure 2 This technology can meet the requirements for both NCM ternary cathodes and lithium-rich manganese (LRMO) cathodes. Using lithium sheets as both positive and negative electrodes, and with electrolyte added between the electrodes, a Li|Li symmetric cell is assembled, achieving a current of 1 mA / cm². 2 It can cycle stably for over 350 hours at current density.

[0064] Comparative Example 1

[0065] 1.2 M LiFSI was dissolved in dimethyl ethylene glycol (DME). After complete dissolution, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of DME was 40%, and the volume fraction of TTE diluent was 60%.

[0066] A half-cell of SS|Li was assembled using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, and a Celgard separator. Linear current-voltage (LSV) testing was performed, and the oxidation peak potential was approximately 4.1V. Figure 3 This does not meet the requirements for using NCM ternary cathodes.

[0067] Comparative Example 2

[0068] 1.5M LiFSI was first dissolved in trimethyl phosphate (TMP). After complete dissolution, ethoxy(pentafluoro)cyclotriphosphine (PFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TMP was 30%, and the volume fraction of PFPN diluent was 70%.

[0069] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 4.8V, which meets the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 60 hours at current density.

[0070] Comparative Example 3

[0071] 0.1 wt% aluminum trifluoromethanesulfonate was first dissolved in trimethyl phosphate (TMP). Then, 1.5 M LiFSI was dissolved in the above solution. After complete dissolution, ethoxy(pentafluoro)cyclotriphosphine (PFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TMP was 30%, and the volume fraction of PFPN diluent was 70%.

[0072] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 4.8V, which meets the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 100 hours at current density.

[0073] Comparative Example 4

[0074] 1.2 M LiFSI was first dissolved in triethyl phosphate (TEP). After complete dissolution, ethoxy(pentafluoro)cyclotriphosphine (PFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TEP was 35%, and the volume fraction of PFPN diluent was 65%.

[0075] Using stainless steel sheets as the positive electrode, lithium sheets as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 4.85V, meeting the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 70 hours at current density.

[0076] Comparative Example 5

[0077] 0.1 wt% aluminum trifluoromethanesulfonate was first dissolved in triethyl phosphate (TEP). Then, 1.2 M LiFSI was dissolved in the above solution. After complete dissolution, ethoxy(pentafluoro)cyclotriphosphine (PFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TEP was 35%, and the volume fraction of PFPN diluent was 65%.

[0078] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 4.82V, which meets the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 120 hours at current density.

[0079] Comparative Example 6

[0080] 1.15 M LiFSI was dissolved in tributyl phosphate (TBP). After complete dissolution, trifluoroethoxypentafluorocyclotriphosphazene (TFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TBP was 25%, and the volume fraction of TFPN diluent was 75%.

[0081] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 4.92 V, which meets the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 75 hours at current density.

[0082] Comparative Example 7

[0083] 0.2 wt% zinc trifluoromethanesulfonate was first dissolved in tributyl phosphate (TBP). Then, 1.15 M LiFSI was dissolved in the above solution. After complete dissolution, trifluoroethoxypentafluorocyclotriphosphazene (TFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TBP was 25%, and the volume fraction of TFPN diluent was 75%.

[0084] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 4.96 V, which meets the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 120 hours at current density.

[0085] Comparative Example 8

[0086] 1.05 M LiTFSI was dissolved in triphenyl phosphate (TPP). After complete dissolution, trifluoroethoxypentafluorocyclotriphosphazene (TFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TPP was 20%, and the volume fraction of TFPN diluent was 80%.

[0087] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 5.02 V, which meets the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 80 hours at current density.

[0088] Comparative Example 9

[0089] 0.3 wt% magnesium trifluoromethanesulfonate was first dissolved in triphenyl phosphate (TPP). Then, 1.05 M LiTFSI was dissolved in the above solution. After complete dissolution, trifluoroethoxypentafluorocyclotriphosphazene (TFPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of TPP was 20%, and the volume fraction of TFPN diluent was 80%.

[0090] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 5.02 V, which meets the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 130 hours at current density.

[0091] Comparative Example 10

[0092] 1.3 M LiFSI was dissolved in bis(2,2,2-trifluoroethyl)methyl phosphate. After complete dissolution, (phenoxy)pentafluorocyclotriphosphazene (FPPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of bis(2,2,2-trifluoroethyl)methyl phosphate was 40%, and the volume fraction of FPPN diluent was 60%.

[0093] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 5.2V, which meets the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 100 hours at current density.

[0094] Comparative Example 11

[0095] 0.4 wt% silver trifluoromethanesulfonate was first dissolved in bis(2,2,2-trifluoroethyl)methyl phosphate. Then, 1.3 M LiFSI was dissolved in the above solution. After complete dissolution, (phenoxy)pentafluorocyclotriphosphazene (FPPN) was added as a diluent to form the final locally high-concentration electrolyte. The volume fraction of bis(2,2,2-trifluoroethyl)methyl phosphate was 40%, and the volume fraction of FPPN diluent was 60%.

[0096] Using a stainless steel sheet as the positive electrode, a lithium sheet as the negative electrode, a Celgard separator, and the aforementioned electrolyte, an SS|Li half-cell was assembled and linear voltammetry (LSV) was performed. The oxidation peak potential was approximately 5.2V, which meets the requirements for NCM ternary cathodes and lithium-rich manganese cathodes (LRMO). Using lithium sheets as both positive and negative electrodes, with electrolyte added dropwise between the electrodes, a Li|Li symmetric cell was assembled, achieving a voltage of 1 mA / cm². 2 It can cycle stably for over 150 hours at current density.

[0097] Example of effect

[0098] The electrolytes prepared in Examples 1-10 and Comparative Examples 1-10 were used to perform full-cell performance tests. The specific test method was as follows: Ni88 high-nickel ternary electrolytes (LiNi) were selected. 0.88 Co 0.06 Mn 0.06 O2) The surface capacity is 5mAh / cm² 2 The positive electrode was selected from copper-lithium composite strips with a single-sided thickness of 30µm, and the negative electrode was selected from copper-lithium composite strips. A commercially available separator coated with PE on both sides of alumina was used to assemble a 1.5Ah pouch cell with four positive and five negative electrodes. First-cycle coulombic efficiency and cycle performance were tested. The first-cycle coulombic efficiency was measured by dividing the discharge capacity at 0.1C by the charge capacity. The cycle test was conducted at a rate of 0.2C charge and 0.5C discharge, with a voltage cutoff condition of 2.8–4.3V. The results are shown in Table 1.

[0099] Table 1 shows the test results of different electrolytes in the examples and comparative examples.

[0100]

[0101] As can be seen from the results of the above embodiments and comparative examples, the present invention uses a phosphate ester-based solvent combined with a phosphazene diluent, which can not only improve the antioxidant capacity of locally high-concentration electrolytes, but also improve the flame retardancy of the electrolytes, reduce electrolyte viscosity, and improve wettability, enabling high-energy-density lithium metal batteries to operate safely and sustainably. Simultaneously, using fluorinated organic solvents and organometallic salts as synergistic additives for lithium protection can reduce the adverse effects of phosphate ester solvents on the lithium metal interface, effectively improving lithium-ion deposition / stripping stability, and achieving stable operation of lithium symmetric batteries exceeding 300 hours, thus realizing highly stable cycling of high-voltage lithium metal batteries.

[0102] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including modifications made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. An electrolyte, characterized by: The lithium salt, the solvent, the diluent and the additive; The solvent is a phosphate-based solvent and / or a fluorine-containing phosphate-based solvent; The diluent is a fluorinated phosphazene-based flame retardant; The additive includes a fluorinated solvent; The fluorinated phosphazene-based flame retardant is selected from at least one of hexafluorocyclotriphosphazene, ethoxy-pentafluorocyclotriphosphazene, trifluoroethoxy-pentafluorocyclotriphosphazene, and (phenoxy)-pentafluorocyclotriphosphazene; When the solvent is selected from at least one of dimethyl methylphosphonate, trimethyl phosphate, triethyl phosphate, and bis(2,2,2-trifluoroethyl)methyl phosphonate, the volume fraction of the solvent in the electrolyte is 20% to 40%; the volume fraction of the diluent in the electrolyte is 60% to 80%; When the solvent is selected from at least one of tributyl phosphate, triisobutyl phosphate, triphenyl phosphate, trioctyl phosphate, and tri(butoxyethyl) phosphate, the volume fraction of the solvent in the electrolyte is 10% to 30%; the volume fraction of the diluent in the electrolyte is 70% to 90%; The fluorinated solvent is selected from at least one of fluorinated ethylene carbonate and bis-fluorinated ethylene carbonate; The weight proportion of the fluorinated solvent in the electrolyte is 3% to 5%; The additive further includes an organic metal salt; The organic metal salt is selected from at least one of magnesium triflate, aluminum triflate, zinc triflate, and silver triflate; The mass proportion of the organic metal salt in the electrolyte is 0.1% to 0.5%.

2. The electrolyte according to claim 1, characterized in that: The lithium salt is selected from at least one of lithium bisfluorosulfonylimide, lithium bistrifluoromethanesulfonylimide, lithium difluoro(oxalato)borate, lithium hexafluorophosphate, and lithium tetrafluoroborate; The molar concentration of the lithium salt in the electrolyte is 1 to 1.5 M.

3. A lithium metal battery, characterized by: The battery includes a negative electrode tab, a positive electrode tab, a separator, and an electrolyte, and the electrolyte is the electrolyte according to claim 1 or 2.

4. The lithium metal battery of claim 3, wherein: The positive electrode tab includes a high-nickel ternary positive electrode material or a lithium-rich manganese-based positive electrode material.

5. The lithium metal battery of claim 4, wherein: The high-nickel ternary positive electrode material is LiNi x Co y Mn z O2, x+y+z=1, 0.6≤x<1; The lithium-rich manganese-based positive electrode material is xLi2MnO3•(1-x)LiMeO2, 0 < x < 1, and Me = Mn, Ni, or Co.

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