Asymmetric ether electrolyte, preparation method thereof and lithium metal battery

Abstract

The invention discloses an asymmetric ether electrolyte, a preparation method thereof and a lithium metal battery, and relates to the technical field of batteries, the asymmetric ether electrolyte comprises a first solvent, a second solvent, a lithium salt, an additive and a diluent; the first solvent is an asymmetric ether solvent and has any one of the following structural formula: # imgabs0 #, R1 is alkyl CnH2n + 1, R2 and R3 are halogenated alkyl CmHyX2m + 1-y, X is a halogen element, n is 1-10, m is 1-10, and y is 0-20; the second solvent is a solvent with a co-dissolution effect. The lithium salt has the beneficial effects that the asymmetric ether is adopted as the first solvent, one side of the asymmetric ether is alkyl, the other side of the asymmetric ether is halogenated alkane, a-CH2-group separated between R2 and O in the first solvent is beneficial to ensuring that the lithium salt has certain solubility, and meanwhile, the second solvent playing a co-dissolution role is also added to enhance the solubility of the lithium salt.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to an asymmetric ether electrolyte and a preparation method thereof, and a lithium metal battery. Background Art

[0002] High-voltage lithium metal-based batteries can reach 500Wh kg -1 The high specific energy limit of lithium ions makes it one of the strong competitors for the next generation of battery technology. However, in lithium metal batteries, lithium ions tend to preferentially deposit at the tips, protrusions or defects of the microstructure on the electrode surface to form crystal nuclei and grow into dendrites. Rapid charging and discharging or high current density will aggravate this phenomenon. This problem seriously affects battery performance. The growing dendrites can pierce the diaphragm and trigger thermal runaway, leading to safety accidents such as fire and explosion, and causing the battery temperature to rise sharply. In addition, dendrite growth will reduce the coulombic efficiency because part of the active lithium is consumed in dendrite formation rather than charge and discharge reactions, resulting in battery capacity attenuation and shortened cycle life, and destroying the solid electrolyte interface phase (SEI), resulting in SEI reconstruction and consumption, further consuming electrolyte and active lithium, and worsening battery performance.

[0003] To inhibit lithium dendrite growth, the electrolyte, as a core component of the battery, is also a necessary and sufficient condition for optimizing the performance of lithium metal batteries. The carbonate electrolytes used in traditional commercial lithium-ion batteries often cannot form a high-quality SEI, resulting in very uneven lithium deposition morphology and easy reaction with the lithium metal anode, causing loss of available capacity. For example, Chinese patents CN117936908A and CN118572194A disclose high-voltage electrolytes for lithium metal batteries, which are mainly carbonate electrolytes or electrolytes with added ionic liquids. Ether electrolytes have strong stability with lithium metal and can form a tough polyether-rich SEI, thereby improving the reversibility of lithium metal deposition. However, the poor thermal stability, oxidation resistance, and limited solubility of ether electrolytes in lithium salts seriously hinder their application in practical batteries, such as Chinese patents CN118572194A, CN115483437A, and CN116031490A. Even though the invention of highly concentrated electrolytes can alleviate these problems, the excessive use of salt greatly increases the cost of the electrolyte, and such electrolytes usually cause severe corrosion to the current collector. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art and to provide an asymmetric ether electrolyte, a preparation method thereof, and a lithium metal battery, specifically a preparation method of an asymmetric ether electrolyte suitable for high-voltage lithium metal batteries and a lithium metal battery.

[0005] The present invention aims to study and improve the performance of ether electrolytes with medium and low salt concentrations. By providing a class of ether electrolytes suitable for high-energy lithium metal batteries, it can achieve high lithium metal negative electrode deposition efficiency (up to 99.4%) under limited salt concentration conditions. At the same time, compared with traditional ether electrolytes, its high voltage tolerance performance is greatly improved, and it can achieve stable operation of the medium-nickel ternary NCM622 positive electrode at a cutoff voltage of 4.6V. Using 50μm lithium metal and 3mAh cm -2 The high-voltage NCM622 positive electrode assembled battery test showed that its capacity retention rate was higher than 90.0% after 200 cycles (0.33C / 0.5C charge and discharge), and the average coulombic efficiency was higher than 99.9%. Even in the battery using Ni92 positive electrode, it showed excellent capacity retention rate, and the capacity retention rate was above 90% after 100 cycles.

[0006] The technical solutions of the present invention are as follows:

[0007] A first aspect of the present invention provides an asymmetric ether electrolyte comprising the following components: a first solvent, a second solvent, a lithium salt, an additive, and a diluent;

[0008] The first solvent is an asymmetric ether solvent, and the first solvent has any of the following structural formulas:

[0009]

[0010] Wherein R1 is an alkyl C n H 2n+1 , R2 and R3 are both halogenated alkyl C m H y X 2m+1-y , X is a halogen element, n is 1 to 10, m is 1 to 10, and y is 0 to 20;

[0011] The second solvent is a solvent having a co-solvent effect.

[0012] Preferably, X is at least one of Cl, F and Br, n is 1-5, m is 1-5, and y is 0-10.

[0013] Preferably, the first solvent is at least one of methyl 2,2,3,3,3-pentafluoropropyl ether, 2-chloroethyl methyl ether, methyl 2,2,3,3-tetrafluoropropyl ether, ethyl 2,2,3,3-tetrafluoropropyl ether, ethyl 1,1,2,2-tetrafluoroethyl ether and hexafluoroisopropyl methyl ether.

[0014] Preferably, the second solvent is at least one of 1,2-bismethoxyethane, 1,2-bisethoxyethane, 1,2-bis(2-chloroethoxy)ethane, bis[2-(2-chloroethoxy)ethyl]ether, diethylene glycol methyl ethyl ether, 2-methyltetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, 2-methyl-1,4-dioxane and 1,3-dioxane.

[0015] Preferably, the components in the electrolyte are calculated in proportion by mass as follows: 30% to 60% of the first solvent, 5% to 30% of the second solvent, 5% to 20% of the lithium salt, 0.1% to 10% of the additive, and 0.1% to 30% of the diluent.

[0016] Preferably, the lithium salt is at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethanesulfonyl)imide and lithium tetrafluoroborate.

[0017] Preferably, the additive is at least one of lithium nitrate, lithium trifluoroacetate, lithium difluorophosphate, lithium difluorooxalatoborate, fluoroethylene carbonate, vinylene carbonate, bisfluoroethylene carbonate, vinyl sulfate, 1,3-propane sultone and 1,3-propylene sultone.

[0018] Preferably, the diluent is ethoxy (pentafluoro) cyclotriphosphazene, pentafluoro (phenoxy) cyclotriphosphazene, hexachlorotriphosphazene, hexafluorocyclotriphosphazene, hexa(1H, 1H, 3H-perfluoropropoxy)phosphazene, hexa(2,2-difluoroethoxy)phosphazene, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether, 2,2,3,3-tetrafluoropropyl difluoro At least one of methyl ether, 2,2,2-trifluoroethyl ether, 1,1,2,2,3,4,4-octafluoro-5-methoxypentane, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, toluene, trifluoromethoxybenzene, fluorobenzene, 1,2-fluorobenzene, 1,3-fluorobenzene and 2,3-difluorophenyl ether, trifluoromethylbenzene and hexafluorobenzene.

[0019] A second aspect of the present invention provides a method for preparing an asymmetric ether electrolyte, comprising the following steps:

[0020] mixing the first solvent and the second solvent to obtain a mixed solvent;

[0021] uniformly mixing the mixed solvent and the lithium salt to obtain a solution;

[0022] adding additives to the solution and mixing uniformly;

[0023] The diluent is continuously added to the solution to obtain an asymmetric ether electrolyte.

[0024] A third aspect of the present invention provides a lithium metal battery comprising the asymmetric ether electrolyte.

[0025] The present invention has at least one of the following beneficial effects:

[0026] The present invention uses an asymmetric ether as the first solvent, one side of which is an alkyl group and the other side is a halogenated alkane. The -CH2- group separating R2 and O in the first solvent helps to ensure that the lithium salt has a certain solubility. The solubility of lithium salts and the coordination ability of lithium ions of this asymmetric ether electrolyte are between those of conventional ethers and diluents. When coordinating with lithium ions, the non-halogenated short chain end is biased towards the lithium ion, while the long chain end is away from the lithium ion. Therefore, when it is solvated, oxygen coordinates with the lithium ion, and the long-chain halogenated alkyl can form the outer layer of the oxidation-resistant solvation shell, protecting the inner layer's α-H from oxidation. At the same time, the introduction of a diluent can form a second shell to protect the ether molecules, so that even under relatively dilute salt-solution ratio conditions, very good oxidation resistance can still be achieved. At the same time, the present invention also adds a second solvent that acts as a co-solvent to enhance the solubility of the lithium salt.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. Compared with Chinese patents CN117936908A and CN118572194A which mainly use carbonate electrolytes or electrolytes with added ionic liquids, the present invention only uses ether solvents as electrolyte solvents to achieve high reversibility of lithium metal and stable operation of the positive electrode.

[0029] 2. Compared with the ether electrolyte of Chinese patent CN118572194A which is mainly composed of one or more common symmetrical ether molecules with strong polarity and solvation ability, the present invention is mainly composed of asymmetric, weakly solvating ether molecules with fluorinated functional groups.

[0030] 3. Compared with Chinese patent CN115483437A which focuses on using fluorination strategy to replace α-H in ether main solvents, the present invention regulates the orientation of ether molecules in the solvation structure through asymmetric design, thereby reducing the instability of α-H in ether main solvents under high voltage.

[0031] 4. Compared with the electrolyte disclosed in Chinese patent CN116031490A, which mainly uses a single solvent as the main solvent and has a limited ability to dissolve lithium salts, the present invention uses two ether solvents. By adjusting the optimal ratio between the first solvent and the second solvent, the diffusion of lithium ions is accelerated, which has great advantages in improving the lithium ion transference number and ionic conductivity.

[0032] 5. The ether electrolytes in Chinese patent CN118213613A often use medium-low nickel ternary positive electrodes, lithium cobalt oxide or lithium manganese oxide positive electrodes, or even lithium iron phosphate low-voltage positive electrodes, and cannot achieve ultra-high nickel ternary electrodes, such as LiNi 0.92 Co 0.06 Mn 0.02 O2, and often use a smaller positive electrode load and thicker lithium metal for testing. Compared with the patent, the present invention uses a high-load positive electrode (3mAh cm -2 or higher areal capacity conditions) and thin lithium metal electrodes (50μm) were fully verified. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the charge-discharge curve of the first cycle of the Li||Ni92 button battery assembled with the electrolyte prepared in Example 1.

[0034] Figure 2 Electrochemical impedance spectroscopy (EIS) electrochemical test graph of a stainless steel||stainless steel symmetrical cell assembled into a battery using the electrolytes prepared in Example 1, Example 4 and Comparative Example 1.

[0035] Figure 3 Electrochemical test diagram of lithium ion transference number of a Li||Li symmetric battery assembled with the electrolyte prepared in Example 1. DETAILED DESCRIPTION

[0036] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] The solid electrolyte interphase (SEI) formed by carbonate electrolytes in traditional liquid batteries on the surface of the lithium metal anode exhibits poor stability and uniformity, making it ineffective in suppressing lithium dendrite growth. During charge-discharge cycling, the volume change of the lithium metal causes the SEI to continuously break down and rebuild, consuming significant amounts of active lithium and electrolyte, leading to reduced battery Coulombic efficiency and rapid capacity decay. Even with the addition of additives such as FEC that can generate a fluorine-rich interphase, their intrinsic compatibility with lithium metal is poor and they are depleted by reactions. Furthermore, they are unable to prevent corrosion of the lithium metal by other highly active carbonate molecules. Meanwhile, most ether electrolytes are relatively stable toward lithium metal and readily form an SEI rich in polyether fragments. However, ether electrolytes generally have poor oxidative stability and are prone to oxidative decomposition at high voltages, limiting their application in high-voltage lithium metal batteries. The oxidizing environment at high voltages causes them to decompose, producing gases and other byproducts that negatively impact battery performance and life.

[0038] To address the above technical issues, most patents in the prior art adopt the following cumulative strategies to solve the problem of positive and negative electrode stability: (1) Improving the stability of the positive and negative electrodes by increasing the salt concentration. This type of electrolyte uses excessive lithium salts, and the resulting solvation configuration is relatively limited in wide temperature scenarios, and is also costly and has low ionic conductivity. (2) Forming a more stable interface through specific additives. However, excessive addition of additives will have a counterproductive effect, so their usage is often low, and they are consumed quickly, making them unable to continuously maintain battery life.

[0039] To this end, the present invention introduces an asymmetric ether electrolyte, one side of which is an alkyl group and the other side is a halogenated alkane. In order to ensure that the ether electrolyte can dissolve lithium salts, it is necessary to ensure that there are no halogen atoms on the carbon atoms adjacent to the ether oxygen atom. The solubility of this asymmetric ether electrolyte for lithium salts and its coordination ability for lithium ions are between conventional ethers and diluents. When coordinated with lithium ions, the non-halogenated short chain end is biased toward the lithium ion, while the long chain end is away from the lithium ion. Therefore, when it is solvated, oxygen coordinates with the lithium ion, and the long-chain halogenated alkyl can form the outer layer of the oxidation-resistant solvation shell to protect the inner layer α-H from being oxidized. At the same time, the introduction of a diluent can form a second shell to protect the ether molecules, so that even under relatively dilute salt ratio conditions, very good oxidation resistance can still be achieved. In addition, the solvation ability of this type of asymmetric ethers with lithium salts is significantly weaker than that of traditional ethers, especially the double-zigzag chelate type solvation coordination ethers (such as Li + -DME), so the energy barrier of its desolvation process is lower, and it is easy to achieve better rate performance.

[0040] The technical solutions of the present invention are as follows:

[0041] One embodiment of the present invention provides an asymmetric ether electrolyte comprising the following components: a first solvent, a second solvent, a lithium salt, an additive, and a diluent;

[0042] The first solvent is an asymmetric ether solvent having any of the following structural formulas:

[0043]

[0044] Wherein R1 is an alkyl C n H 2n+1 , R2 and R3 are both halogenated alkyl C m H y X 2m+1-y , X is a halogen element, n is 1 to 10, m is 1 to 10, and y is 0 to 20;

[0045] The second solvent is a solvent having a co-solvent effect.

[0046] The present invention uses an asymmetric ether as the first solvent, one side of which is an alkyl group and the other side is a halogenated alkane. The -CH2- group separating R2 and O in the first solvent helps to ensure that the lithium salt has a certain solubility. The solubility of lithium salts and the coordination ability of lithium ions of this asymmetric ether electrolyte are between those of conventional ethers and diluents. When coordinating with lithium ions, the non-halogenated short chain end is biased towards the lithium ion, while the long chain end is away from the lithium ion. Therefore, when it is solvated, oxygen coordinates with the lithium ion, and the long-chain halogenated alkyl can form the outer layer of the oxidation-resistant solvation shell, protecting the inner layer's α-H from oxidation. At the same time, the introduction of a diluent can form a second shell to protect the ether molecules, so that even under relatively dilute salt-solution ratio conditions, very good oxidation resistance can still be achieved. At the same time, the present invention also adds a second solvent that acts as a co-solvent to enhance the solubility of the lithium salt.

[0047] In some embodiments, X is at least one of Cl, F, and Br, n is 1 to 5, m is 1 to 5, and y is 0 to 10. Preferably, X is at least one of Cl and F, n is 1 to 4, m is 1 to 4, and y is 0 to 8; more preferably, X is F, n is 1 to 3, m is 1 to 3, and y is 0 to 6.

[0048] In some embodiments, the components of the electrolyte are calculated by mass as follows: 30% to 60% first solvent, 5% to 30% second solvent, 5% to 20% lithium salt, 0.1% to 10% additive, and 0.1% to 30% diluent. Preferably, the first solvent is 35% to 55%, the second solvent is 8% to 25%, the lithium salt is 8% to 17%, the additive is 1% to 9%, and the diluent is 3% to 25%. More preferably, the first solvent is 40% to 50%, the second solvent is 10% to 20%, the lithium salt is 11% to 14%, the additive is 3% to 8%, and the diluent is 5% to 20%. Specifically, the first solvent is 50%, the second solvent is 20%, the lithium salt is 15%, the additive is 5%, and the diluent is 10%; or the first solvent is 45%, the second solvent is 25%, the lithium salt is 14%, the additive is 5%, and the diluent is 11%; or the first solvent is 40%, the second solvent is 25%, the lithium salt is 14%, the additive is 8%, and the diluent is 13%, etc.

[0049] In some embodiments, the first solvent is one or more of methyl 2,2,3,3,3-pentafluoropropyl ether (M-5FE), 2-chloroethyl methyl ether, methyl 2,2,3,3-tetrafluoropropyl ether (M-4FE), ethyl 2,2,3,3-tetrafluoropropyl ether, ethyl 1,1,2,2-tetrafluoroethyl ether, and hexafluoroisopropyl methyl ether.

[0050] In some embodiments, the second solvent is one or more of 1,2-bismethoxyethane, 1,2-bisethoxyethane, 1,2-bis(2-chloroethoxy)ethane, bis[2-(2-chloroethoxy)ethyl]ether, diethylene glycol methyl ethyl ether (DGEME), 2-methyltetrahydrofuran (2-Me-THF), 1,4-dioxane (1,4-DX), 1,3-dioxolane (DOL), tetrahydrofuran (THF), 2-methyl-1,4-dioxane (2-Me-1,4-DX), and 1,3-dioxane (1,3-DX).

[0051] In some embodiments, the lithium salt is one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide, and lithium tetrafluoroborate (LiBF4).

[0052] In some embodiments, the additive is one or more of lithium nitrate (LiNO3), lithium trifluoroacetate (LiTFA), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), fluoroethylene carbonate (FEC), vinylene carbonate (VC), bisfluoroethylene carbonate (DFEC), vinyl sulfate (DTD), 1,3-propane sultone (PS), and 1,3-propylene sultone (PST).

[0053] In some embodiments, the diluent is ethoxy (pentafluoro) cyclotriphosphazene (PFPN), pentafluoro (phenoxy) cyclotriphosphazene, hexachlorotriphosphazene, hexafluorocyclotriphosphazene, hexa(1H,1H,3H-perfluoropropoxy)phosphazene, hexa(2,2-difluoroethoxy)phosphazene, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (TFTFE), 2,2,3,3-tetrafluoropropyl difluoro One or more of methyl ether, 2,2,2-trifluoroethyl ether (BTFE), 1,1,2,2,3,4,4-octafluoro-5-methoxypentane (OFE-1), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OFE-2), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, toluene, trifluoromethoxybenzene, fluorobenzene, 1,2-fluorobenzene, 1,3-fluorobenzene and 2,3-difluorophenyl ether, trifluoromethylbenzene, hexafluorobenzene.

[0054] A second aspect of the present invention provides a method for preparing an asymmetric ether electrolyte, comprising the following steps:

[0055] mixing the first solvent and the second solvent to obtain a mixed solvent;

[0056] uniformly mixing the mixed solvent and the lithium salt to obtain a solution;

[0057] adding additives to the solution and mixing uniformly;

[0058] The diluent is continuously added to the solution to obtain an asymmetric ether electrolyte.

[0059] The present invention can prepare an asymmetric ether electrolyte by mixing various raw materials, and the preparation method is simple and highly practical.

[0060] In some embodiments, the preparation method specifically comprises:

[0061] (1) Weigh a certain amount of the first solvent and mix it with the second solvent to obtain a mixed solvent.

[0062] (2) Weigh a certain amount of mixed solvent and lithium salt, mix them, and stir at room temperature until the lithium salt is completely dissolved.

[0063] (3) Add a certain volume of additive to the solution obtained in step (2) above, and heat and stir at 60°C for 2 h to completely dissolve it.

[0064] (4) Adding a certain volume of diluent to the solution obtained in the above step (3) to obtain an ether electrolyte.

[0065] (5) The positive electrode, negative electrode and separator of the button battery are fully moistened with the ether electrolyte obtained in step (4), the button battery is assembled, and the battery is allowed to stand for 12 hours; or a certain amount of ether electrolyte is directly injected into the soft-pack battery, and the battery is allowed to stand for 12-24 hours to allow the battery to be fully soaked, and then an electrochemical characterization test is performed.

[0066] A third aspect of the present invention provides a lithium metal battery comprising the asymmetric ether electrolyte.

[0067] The asymmetric ether electrolyte of the present invention can be used in high-voltage batteries. It can achieve high lithium metal negative electrode deposition efficiency (up to 99.4%) under limited salt concentration conditions. At the same time, compared with traditional ethers, its high voltage tolerance performance is greatly improved, and it can achieve stable operation of the nickel ternary NCM622 positive electrode at a cutoff voltage of 4.6V. -2 The high-voltage NCM622 positive electrode assembled battery test showed that its capacity retention rate was higher than 90.0% after 200 cycles (0.33C / 0.5C charge and discharge), and the average coulombic efficiency was higher than 99.9%. Even in the battery using Ni92 positive electrode, it showed excellent capacity retention rate, and the capacity retention rate was above 90% after 100 cycles.

[0068] The present invention is further described in detail below with reference to specific examples, but the present invention is not limited to the following specific examples.

[0069] Example 1:

[0070] This embodiment provides a method for preparing an asymmetric ether electrolyte, comprising the following steps:

[0071] 10 mmol, or 1.87 g, of LiFSI was dissolved in 5 mL of methyl 2,2,3,3,3-pentafluoropropyl ether (M-5FE) and 2 mL of 1,2-bismethoxyethane (DME) to prepare a mixed solvent. 0.4 mL of fluoroethylene carbonate (FEC) was then added. The resulting mixture was stirred at 60°C until completely dissolved, and then 3 mL of TTE diluent was added and mixed to obtain an asymmetric ether electrolyte.

[0072] Example 2:

[0073] The difference from Example 1 is that “1.87 g LiFSI” in Example 1 is changed to “2.87 g LiTFSI”, and other conditions remain unchanged.

[0074] Example 3:

[0075] The difference from Example 1 is that the "0.4 mL FEC" in Example 1 is changed to "0.069 g LiNO3", and other conditions remain unchanged.

[0076] Example 4:

[0077] The difference from Example 1 is that in the electrolyte preparation process described in Example 1, 1 mL of DME was added instead of 2 mL of DME, and other conditions remained unchanged.

[0078] Example 5:

[0079] The difference from Example 1 is that the solvent in Example 1 is changed to 2-chloroethyl methyl ether, and other conditions remain unchanged.

[0080] Example 6:

[0081] The difference from Example 1 is that the type of the first solvent is changed, M-5FE is replaced by 2-chloroethyl methyl ether, and other conditions remain unchanged.

[0082] Example 7:

[0083] The difference from Example 1 is that the type of the first solvent is changed, M-5FE is replaced by methyl 2,2,3,3-tetrafluoropropyl ether, and other conditions remain unchanged.

[0084] Example 8:

[0085] The difference from Example 1 is that the type of the first solvent is changed, M-5FE is replaced by ethyl 2,2,3,3-tetrafluoropropyl ether, and other conditions remain unchanged.

[0086] Example 9:

[0087] The difference from Example 1 is that the type of the first solvent is changed, M-5FE is replaced by ethyl 1,1,2,2-tetrafluoroethyl ether, and other conditions remain unchanged.

[0088] Example 10:

[0089] The difference from Example 1 is that the type of the first solvent is changed, M-5FE is replaced by hexafluoroisopropyl methyl ether, and other conditions remain unchanged.

[0090] Comparative Example 1:

[0091] The difference from Example 1 is that the "5 mL of methyl 2,2,3,3,3-pentafluoropropyl ether (M-5FE) and 2 mL of 1,2-bismethoxyethane (DME)" mentioned in Example 1 is changed to "7 mL of DME", that is, the first solvent is not added, and other conditions remain unchanged.

[0092] Comparative Example 2:

[0093] The difference from Example 1 is that: in the electrolyte preparation process in Example 1, the 2 mL of DME is not added, that is, the second solvent is not added, and other conditions remain unchanged.

[0094] The electrolytes prepared in Examples 1 to 10 and Comparative Examples 1 to 2 were assembled into batteries, and the performance of the batteries was tested using the following method:

[0095] 1. Li||Ni92 button battery assembly and testing

[0096] (1) 9 g of nickel 9 series ternary material (Ni92) or 6 series ternary material (NCM622), 0.5 g of conductive carbon black, and 0.5 g of polyvinylidene fluoride were added to 10 ml of NMP solution and stirred (rotation speed 1000 rpm) for 10 min to prepare a slurry; the slurry was coated on aluminum foil and vacuum-baked at 80°C for 12 h to obtain a Ni92 positive electrode sheet.

[0097] (2) The positive electrode sheet was cut into discs with a diameter of 14 mm, and a CR2032 button battery was assembled with a lithium metal disc or a silicon carbon-graphite composite negative electrode disc. The electrolyte described in different embodiments and comparative examples of the present invention was then injected into the battery. The constant current charge and discharge test was performed at 0.33C / 0.5C for 100 or 200 cycles, and the capacity retention rate was compared.

[0098] 2. Stainless steel || stainless steel symmetrical battery assembly and testing

[0099] CR2032 button cells were assembled using stainless steel||stainless steel, and the electrolytes described in different embodiments and comparative examples were injected into the cells. After standing for a period of time at room temperature, the cells were subjected to electrochemical impedance spectroscopy (EIS) testing.

[0100] 3. Li||Li symmetric battery assembly and testing

[0101] CR2032 button cells were assembled with Li||Li, and the electrolytes described in different embodiments and comparative examples were injected therein. After standing for a period of time at room temperature, the lithium ion migration number of the cells was tested.

[0102] The test results are as follows Figures 1 to 3 , as shown in Table 1 and Table 2:

[0103] Figure 1 This is the charge and discharge curve of the first cycle of the Li||Ni92 button battery assembled with the electrolyte prepared in Example 1. Figure 1 It can be seen that the Li||Ni92 button battery assembled with the electrolyte prepared in Example 1 has good charge and discharge performance.

[0104] Figure 2 Electrochemical impedance spectroscopy (EIS) electrochemical test diagram of stainless steel || stainless steel symmetrical battery assembled into a battery using electrolytes prepared in Example 1, Example 4 and Comparative Example 1. Figure 2 It can be seen that the ionic conductivity is affected by regulating the ratio between the first solvent and the second solvent. Specifically, the ionic conductivity corresponding to Example 1 is higher than that of Example 4, indicating that a reasonable ratio can achieve rapid diffusion of lithium ions, even if its ionic conductivity is slightly lower than that of Comparative Example 1.

[0105] Figure 3 The electrolyte prepared in Example 1 is assembled into a Li||Li symmetric battery and the migration number electrochemical test diagram is shown. Figure 3 It can be seen that the Li||Li symmetric battery assembled with the electrolyte prepared in Example 1 has good electrochemical performance.

[0106] Table 1 Cycling and rate performance of lithium metal full batteries

[0107]

[0108] Table 2 Basic electrochemical properties of electrolytes

[0109]

[0110]

[0111] Table 1 summarizes the cycle performance of various electrolytes involved in the embodiments and comparative examples in the ternary battery with few lithium conditions, among which the electrolyte using asymmetric ether electrolytes has obvious advantages in cycle performance and rate performance. For example, Example 1 is compared with Comparative Example 1. It can be seen that Example 1 replaces DME with M-5FE. Compared with the pure DME solvent (Comparative Example 1), it shows a fundamental improvement in cycle stability under the same concentration conditions and with the assistance of additives. In terms of conductivity, as shown in Table 2, due to the assistance of a small amount of DME in Example 1, even with the use of the symmetrical molecule, the electrolyte in Example 1 also achieves extremely high ionic conductivity, and the conductivity is slightly lower than that of Comparative Example 1. However, Example 1 and Comparative Example 1 use the same lithium salt LiFSI, and the electrolyte of Example 1 using asymmetric ethers shows a more significantly improved oxidation potential performance than Comparative Example 1, indicating that the special structure of the asymmetric ether can fundamentally protect the oxidation-intolerant α-H and achieve high-voltage stability of the electrolyte.

[0112] As shown in Table 1, by comparing Example 1 with Comparative Example 2, it can be seen that Example 1 contains both M-5FE and DME. Compared with Comparative Example 2 containing only M-5FE, Example 1 has certain advantages in both cycle performance and rate performance. In terms of conductivity, as shown in Table 2, the conductivity of Example 1 is much greater than that of Comparative Example 2, indicating that DME plays a co-solvent role, can enhance the solubility of lithium salts, can accelerate the diffusion of lithium ions, and has great advantages in improving the lithium ion migration number and ionic conductivity.

[0113] By comparing Example 1 and Example 4, it can be seen that the volume ratio of M-5FE to DME in Example 1 is 5:2, and the volume ratio of M-5FE to DME in Example 4 is 5:1. The conductivity of Example 1 is better than that of Example 4. Therefore, the ratio between the first solvent and the second solvent will affect the conductivity. The present invention accelerates the diffusion of lithium ions by regulating the optimal ratio between the first solvent and the second solvent, and has great advantages in improving the lithium ion migration number and ionic conductivity.

[0114] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. An asymmetric ether electrolyte, characterized in that The method comprises the following components: a first solvent, a second solvent, a lithium salt, an additive and a diluent; The first solvent is an asymmetric ether solvent, and the first solvent has any of the following structural formulas: Wherein R1 is an alkyl C n H 2n+1 , R2 and R3 are both halogenated alkyl C m H y X 2m+1-y , X is a halogen element, n is 1 to 10, m is 1 to 10, and y is 0 to 20; The second solvent is a solvent having a co-solvent effect.

2. The asymmetric ether electrolyte according to claim 1, characterized in that X is at least one of Cl, F and Br, n is 1-5, m is 1-5, and y is 0-10.

3. The asymmetric ether electrolyte according to claim 1, characterized in that The first solvent is at least one of methyl 2,2,3,3,3-pentafluoropropyl ether, 2-chloroethyl methyl ether, methyl 2,2,3,3-tetrafluoropropyl ether, ethyl 2,2,3,3-tetrafluoropropyl ether, ethyl 1,1,2,2-tetrafluoroethyl ether and hexafluoroisopropyl methyl ether.

4. The asymmetric ether electrolyte according to claim 1, characterized in that The second solvent is at least one of 1,2-bismethoxyethane, 1,2-bisethoxyethane, 1,2-bis(2-chloroethoxy)ethane, bis[2-(2-chloroethoxy)ethyl]ether, diethylene glycol methyl ethyl ether, 2-methyltetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, 2-methyl-1,4-dioxane and 1,3-dioxane.

5. The asymmetric ether electrolyte according to claim 1, characterized in that The components in the electrolyte are calculated by mass fraction as follows: 30% to 60% of the first solvent, 5% to 30% of the second solvent, 5% to 20% of the lithium salt, 0.1% to 10% of the additive and 0.1% to 30% of the diluent.

6. The asymmetric ether electrolyte according to claim 1, characterized in that The lithium salt is at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethanesulfonyl)imide and lithium tetrafluoroborate.

7. The asymmetric ether electrolyte according to claim 1, characterized in that The additive is at least one of lithium nitrate, lithium trifluoroacetate, lithium difluorophosphate, lithium difluorooxalatoborate, fluoroethylene carbonate, vinylene carbonate, bisfluoroethylene carbonate, vinyl sulfate, 1,3-propane sultone and 1,3-propylene sultone.

8. The asymmetric ether electrolyte according to claim 1, characterized in that The diluent is ethoxy (pentafluoro) cyclotriphosphazene, pentafluoro (phenoxy) cyclotriphosphazene, hexachlorotriphosphazene, hexafluorocyclotriphosphazene, hexa(1H, 1H, 3H-perfluoropropoxy)phosphazene, hexa(2,2-difluoroethoxy)phosphazene, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether , 2,2,2-trifluoroethyl ether, 1,1,2,2,3,4,4-octafluoro-5-methoxypentane, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, toluene, trifluoromethoxybenzene, fluorobenzene, 1,2-fluorobenzene, 1,3-fluorobenzene and 2,3-difluorophenyl ether, trifluoromethylbenzene and hexafluorobenzene.

9. The method for preparing an asymmetric ether electrolyte according to any one of claims 1 to 8, characterized in that: The following steps are involved: mixing the first solvent and the second solvent to obtain a mixed solvent; uniformly mixing the mixed solvent and the lithium salt to obtain a solution; adding additives to the solution and mixing uniformly; The diluent is continuously added to the solution to obtain an asymmetric ether electrolyte.

10. A lithium metal battery, characterized in that: The invention comprises the asymmetric ether electrolyte according to any one of claims 1 to 8.

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