Low-concentration ether electrolyte adaptive to high-voltage high-nickel ternary lithium ion battery, preparation method of low-concentration ether electrolyte and lithium ion battery

Abstract

The invention discloses a low-concentration ether electrolyte adaptive to a high-voltage high-nickel ternary lithium ion battery, a preparation method of the low-concentration ether electrolyte and the lithium ion battery, and relates to the technical field of batteries. The ether electrolyte comprises a solvent and a solute; the solvent comprises an ether solvent, and is specifically at least one of 4-cyano tetrahydropyran, 2-(tetrahydro-2H-pyran-4-yl) acetonitrile, 2-methoxyacetonitrile, 2-ethyoxyl acetonitrile, 3-methoxypropionitrile, 3-ethyoxyl propionitrile, 3-butoxyl propionitrile, ethylene glycol bis (propionitrile) ether and 3-{2-[2-(2-cyano ethyoxyl) ethyoxyl] ethyoxyl} propionitrile. The ether solvent contains cyano groups, the strong electronegativity of the cyano groups enables the cyano groups to be coordinated with transition metal ions in the ternary material, and the cyano groups are preferentially adsorbed at the interface of the positive electrode material, so that the arrangement of solvent molecules at the interface has directivity, the proportion of ether oxygen bonds and carbon hydrogen atoms in double electric layers is reduced, and the performance of the positive electrode material is improved. And the sites which are easy to generate dehydrogenation reaction in the molecules are far away from the high-voltage positive electrode interface which is easy to generate oxidation reaction.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a low-concentration ether electrolyte suitable for a high-voltage, high-nickel ternary lithium-ion battery, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] With the rapid development of pure electric vehicles (EVs) and hybrid electric vehicles (HEVs), the demand for lithium-based batteries with higher energy density is very urgent. After years of development, commercial lithium-ion batteries have been able to achieve higher energy density. x Mn y Co 1-x-y O2 (NMC, x ≥ 0.8) ternary layered oxides have a high theoretical specific capacity and are expected to increase the battery specific energy to 500 Wh kg at high operating voltages (> 4.3 V) when combined with high specific energy negative electrode materials. -1 However, the harsh chemical environment on the high-voltage NCM cathode side during charging can cause the electrolyte to decompose violently, seriously affecting battery performance.

[0003] Electrolyte engineering, as a simple and effective strategy to achieve high-performance ternary lithium-ion batteries, has made considerable progress in recent years. The electrolytes currently used in lithium-ion batteries mainly include esters and ethers. Ether electrolytes are widely used due to their strong molecular polarity, good solubility, and ability to dissolve a variety of lithium salts such as lithium nitrate. In order to further develop ternary lithium-ion batteries with high cut-off voltage, nitrile solvents have been introduced into the electrolyte system. Their excellent oxidation resistance gives them a wide electrochemical stability window, making them suitable for most high-voltage cathode materials. At the same time, the unique adsorption behavior of cyanide groups on the positive electrode side with transition metals can protect the electrolyte from further oxidative decomposition.

[0004] However, at high charge cut-off voltages, the highly valent transition metals on the cathode side of high-nickel ternary materials have strong catalytic properties, resulting in a harsh chemical environment within the double layer at the cathode interface. During the charging state, ester or ether solvent molecules enter the double layer due to adsorption and are easily catalyzed to undergo dehydrogenation reactions at high cut-off voltages, leading to large-scale decomposition, forming an unstable solid electrolyte interface. This is accompanied by the generation of undesirable products such as hydrofluoric acid and the precipitation of lattice oxygen in the cathode material, ultimately leading to electrolyte depletion, structural damage to the cathode material, and battery performance degradation. Conventional ether electrolytes (~1 M) have very limited oxidative stability (<4.0 V). Furthermore, despite their high oxidation windows, ester electrolytes are still susceptible to decomposition by dehydrogenation reactions after entering the double layer due to the catalytic properties of the highly valent transition metal elements on the surface of the high-nickel material. This severely limits their application in high-voltage, high-activity high-nickel ternary lithium-ion batteries. Summary of the Invention

[0005] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art, and to provide a low-concentration ether electrolyte, a preparation method and a lithium-ion battery suitable for high-voltage, high-nickel ternary lithium-ion batteries. Specifically, in order to solve the decomposition reaction problem of traditional ether electrolytes on the high-nickel ternary positive electrode side, the present invention provides a new ether electrolyte, a preparation method and application thereof.

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

[0007] A first aspect of the present invention provides a low-concentration ether electrolyte adapted for a high-voltage, high-nickel ternary lithium-ion battery, the ether electrolyte comprising a solvent and a solute; the solvent comprising an ether solvent, the ether solvent being at least one of 4-cyanotetrahydropyran, 2-(tetrahydro-2H-pyran-4-yl)acetonitrile, 2-methoxyacetonitrile, 2-ethoxyacetonitrile, 3-methoxypropionitrile, 3-ethoxypropionitrile, 3-butoxypropionitrile, ethylene glycol bis(propionitrile) ether and 3-{2-[2-(2-cyanoethoxy)ethoxy]ethoxy}propionitrile.

[0008] In a preferred embodiment of the present invention, the solute is at least one of LiPF6, LiBF4, LiTFSI, LiFSI, LiNO3 and LiDFOB.

[0009] In a preferred embodiment of the present invention, the concentration of the solute in the ether electrolyte is 0.5 mol / L to 3 mol / L.

[0010] In a preferred embodiment of the present invention, the ether electrolyte further comprises lithium nitrate.

[0011] In a preferred embodiment of the present invention, the concentration of lithium nitrate in the ether electrolyte is 0.01 mol / L to 1 mol / L.

[0012] A second aspect of the present invention provides a method for preparing an ether electrolyte, comprising the following steps:

[0013] In a glove box filled with argon, the solute is added to the solvent or the solute and lithium nitrate are added to the solvent, stirred until completely dissolved, and mixed evenly to obtain an ether electrolyte.

[0014] A third aspect of the present invention provides a lithium-ion battery comprising the above-mentioned ether electrolyte.

[0015] In a preferred embodiment of the present invention, the positive electrode of the lithium-ion battery is at least one of lithium iron phosphate, lithium cobalt oxide, lithium nickel cobalt manganese oxide and lithium nickel manganese oxide.

[0016] In a preferred embodiment of the present invention, the negative electrode of the lithium-ion battery is at least one of mesocarbon microbeads, graphite, silicon carbon and lithium metal.

[0017] In a preferred embodiment of the present invention, the lithium ion separator is at least one of a glass fiber separator, a polytetrafluoroethylene separator, a polypropylene separator, a polyethylene separator and a cellulose separator.

[0018] The present invention has at least one of the following beneficial effects:

[0019] 1. Since there are more free solvents in the ether low-concentration electrolytes of the prior art, the free solvent enters the double layer on the positive electrode side due to electrostatic action, and the dehydrogenation side reaction is more serious at high cut-off voltages. The solid electrolyte interface formed is continuously stripped and regenerated, which leads to lower coulombic efficiency and capacity retention. In order to solve this technical problem, the solvent in the present invention uses an ether solvent containing a cyano group. On the one hand, the strong electronegativity of the cyano group enables it to coordinate with the transition metal ions in the ternary material, preferentially adsorbed at the interface of the positive electrode material, so that the arrangement of the solvent molecules at the interface has directionality, reducing the ratio of the ether oxygen bond and its connected carbon-hydrogen atoms in the double layer, thereby making the site in the molecule prone to dehydrogenation reaction away from the high voltage (>4.3V) positive electrode interface prone to oxidation reaction, achieving the effect of protecting the free solvent molecules, and finally realizing a low-concentration ether electrolyte compatible with high-voltage high-nickel ternary lithium-ion battery. On the other hand, the ether oxygen bonds of the ether solvents of the present invention retain the ability to dissolve a variety of solutes. In the electrolyte system of the present invention, lithium nitrate is dissolved. Nitrate ions can decompose at the electrode / electrolyte interface during the battery cycle to produce stable superionic conductors such as lithium nitride, which helps to form a stable solid electrolyte interface layer with high ionic conductivity. This can protect the electrolyte from highly catalytic transition metals at the interface of the positive electrode material and inhibit corrosion of the positive electrode material by other substances. At the same time, lithium nitrate has the characteristics of low cost and is therefore widely used as an electrolyte additive for lithium-ion batteries. In contrast, in the single nitrile or ester electrolytes used in the prior art, since there is no ether oxygen bond, the cyanide group makes it difficult to dissolve lithium nitrate, so a large amount of electrolyte additives cannot be added.

[0020] 2. The electrolyte system of the present invention further introduces a large amount of lithium nitrate components. Since the binding ability of the solvent and lithium ions is low, the nitrate ions can enter the inner solvation sheath. At the same time, the free nitrate ions will be preferentially adsorbed into the double electric layer on the positive electrode side due to electrostatic effects under high voltage. The decomposition of the anions constructs a CEI layer rich in inorganic substances, which blocks the adverse side reactions at the electrode / electrolyte interface and achieves a higher coulombic efficiency and capacity retention rate of the high-nickel ternary positive electrode.

[0021] 3. The electrolyte of the present invention has a low lithium salt concentration (0.5 mol / L to 3 mol / L), and the resulting electrolyte also has a lower density, with a smaller mass per volume. Furthermore, the electrolyte is compatible with high charge cut-off voltages (>4.3V) and high nickel (≥80%) lithium nickel cobalt manganese oxide cathode materials. Therefore, the use of this electrolyte can further improve the energy density of lithium-ion batteries. Furthermore, the low salt concentration also offers the advantage of low cost, and ether compounds are conventional industrial raw materials with a wide range of sources and low prices, greatly reducing the cost of the electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a digital photograph of the electrolyte prepared in Example 1 of the present invention after being uniformly dissolved and allowed to stand;

[0023] Figure 2 This is a digital photograph of the electrolyte prepared in Example 2 of the present invention after being uniformly dissolved and allowed to stand;

[0024] Figure 3 This is a digital photograph of the electrolyte prepared in Example 3 of the present invention after being uniformly dissolved and allowed to stand;

[0025] Figure 4 This is a digital photograph of the electrolyte prepared in Example 4 of the present invention after being uniformly dissolved and allowed to stand;

[0026] Figure 5 This is a digital photograph of the electrolyte prepared in Example 5 of the present invention after being uniformly dissolved and allowed to stand;

[0027] Figure 6 This is a digital photograph of the electrolyte prepared in Example 6 of the present invention after being uniformly dissolved and allowed to stand;

[0028] Figure 7 This is a digital photograph of the electrolyte prepared in Example 7 of the present invention after being uniformly dissolved and allowed to stand;

[0029] Figure 8 The voltage-current curves obtained by linear sweep voltammetry testing of the electrolytes of the experimental group and the control group in Example 4 of the present invention are shown;

[0030] Figure 9 1 is the cycle capacity curve of the lithium-NCM811 battery in the experimental group and the control group electrolyte in Example 4 of the present invention;

[0031] Figure 10 1 is the cycle capacity curve of the lithium-NCM811 battery in the experimental group electrolyte in Example 5 of the present invention;

[0032] Figure 11 1 is the cycle capacity curve of the lithium-MCMB battery in Example 4 of the present invention in the experimental group electrolyte;

[0033] Figure 12 This is a SEM image of NCM811 in Example 4 of the present invention after 100 cycles in the electrolyte of the experimental group;

[0034] Figure 13 This is an SEM image of NCM811 in Example 4 of the present invention after 100 cycles in the control group electrolyte;

[0035] Figure 14 1 is a leakage current test curve of the lithium-NCM811 battery in the electrolyte of the experimental group in Example 4 of the present invention;

[0036] Figure 15 1 is the cycle capacity curve of the MCMB-NCM811 full battery in the experimental group electrolyte in Example 4 of the present invention;

[0037] Figure 16 1 is the cycle capacity curve of the NCM811 half-cell in the experimental group electrolyte in Example 3 of the present invention;

[0038] Figure 17 This is the cycle capacity curve of the NCM811 half-cell in Example 6 of the present invention in the experimental group electrolyte. DETAILED DESCRIPTION

[0039] 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.

[0040] One embodiment of the present invention provides a low-concentration ether electrolyte suitable for a high-voltage, high-nickel ternary lithium-ion battery, the ether electrolyte comprising a solvent and a solute; the solvent comprising an ether solvent, the ether solvent being at least one of 4-cyanotetrahydropyran, 2-(tetrahydro-2H-pyran-4-yl)acetonitrile, 2-methoxyacetonitrile, 2-ethoxyacetonitrile, 3-methoxypropionitrile, 3-ethoxypropionitrile, 3-butoxypropionitrile, ethylene glycol bis(propionitrile) ether, and 3-{2-[2-(2-cyanoethoxy)ethoxy]ethoxy}propionitrile.

[0041] The electrolyte of the present invention uses an ether solvent containing a cyano group as a solvent for dissolving the solute. The solvent of the present invention is mainly used to dissociate lithium salts, regulate the solvation structure and conduct lithium ions between the positive and negative electrodes of the high-nickel ternary lithium-ion battery, inhibit the decomposition of the electrolyte solvent caused by the high voltage and highly catalytic transition metal elements in the high-nickel ternary positive electrode of the battery during the cycle, and protect the structural integrity of the high-nickel ternary positive electrode material at a high cut-off charging voltage. Specifically, on the one hand, the strong electronegativity of the cyano group enables it to coordinate with the transition metal ions in the ternary material, preferentially adsorbed at the interface of the positive electrode material, so that the arrangement of the solvent molecules at the interface has directionality, reducing the ratio of the ether oxygen bond and its connected carbon-hydrogen atoms in the double layer, thereby making the site in the molecule prone to dehydrogenation reaction away from the high voltage (>4.3V) positive electrode interface prone to oxidation reaction, thereby protecting the free solvent molecules. On the other hand, the ether oxygen bond of the ether solvent retains the ability to dissolve multiple solutes, thereby being able to dissolve multiple electrolyte additives such as lithium nitrate; whereas in a single nitrile or ester electrolyte, it is difficult for the cyano group to dissolve electrolyte additives such as lithium nitrate. Therefore, through the combined effect of the above two aspects, the electrolyte of the present invention can be adapted to high-voltage high-nickel ternary lithium-ion batteries, achieving a higher coulombic efficiency and capacity retention rate of the high-nickel ternary positive electrode.

[0042] Specifically, high nickel means that the content of nickel in the positive electrode material is ≥80wt%.

[0043] In some embodiments, the solute is at least one of LiPF6, LiBF4, LiTFSI, LiFSI, LiNO3, and LiDFOB.

[0044] In some embodiments, the concentration of lithium salt in the ether electrolyte is 0.5mol / L to 3mol / L. The electrolyte lithium salt concentration in the present invention is low (0.5mol / L to 3mol / L), and the constructed electrolyte also has a lower density, a smaller mass under the same volume, and is compatible with high charging cut-off voltage (>4.3V) and high nickel (≥80%) nickel cobalt manganese oxide positive electrode materials. Therefore, the use of this electrolyte can further improve the energy density of lithium-ion batteries. In addition, the low salt concentration also brings the advantage of low cost, and ether compounds are conventional industrial raw materials with a wide range of sources and low prices, which greatly reduces the cost of the electrolyte.

[0045] Preferably, the concentration of the lithium salt in the ether electrolyte is 0.5 mol / L to 2.5 mol / L, more preferably 0.5 mol / L to 2 mol / L, specifically 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L and 2.5 mol / L.

[0046] In some embodiments, the ether electrolyte further comprises lithium nitrate. The ether oxygen bond of the ether solvent in the present invention retains the ability to dissolve a variety of solutes. In this electrolyte system, lithium nitrate is dissolved, and nitrate ions can decompose at the electrode / electrolyte interface during the battery cycle to produce stable superionic conductors such as lithium nitride, which helps to form a stable solid electrolyte interface layer with high ionic conductivity, which can protect the electrolyte from the highly catalytic transition metal at the interface of the positive electrode material and inhibit the corrosion of the positive electrode material by other substances. At the same time, lithium nitrate has the characteristics of low cost, and is therefore widely used as an electrolyte additive for lithium-ion batteries.

[0047] In some embodiments, the concentration of lithium nitrate in the electrolyte is 0.01 mol / L to 1 mol / L. Preferably, the concentration of lithium nitrate in the electrolyte is 0.1 mol / L to 0.8 mol / L. More preferably, the concentration of lithium nitrate in the electrolyte is 0.2 mol / L to 0.6 mol / L. Specifically, it can be 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, etc. The electrolyte system in the present invention introduces a large amount of lithium nitrate components. Since the solvent of the present invention has a low binding ability with lithium ions, the nitrate ions can enter the inner solvation sheath. At the same time, the free nitrate ions will preferentially be adsorbed into the double electric layer on the positive electrode side due to electrostatic effects under high voltage. The decomposition of the anions constructs a CEI layer rich in inorganic substances, which blocks the adverse side reactions at the electrode / electrolyte interface and achieves a higher coulombic efficiency and capacity retention rate of the high nickel ternary positive electrode.

[0048] Another embodiment of the present invention provides a method for preparing an ether electrolyte, comprising the following steps:

[0049] In a glove box filled with argon, the solute is added to the solvent, stirred until completely dissolved, and mixed evenly to obtain an ether electrolyte.

[0050] The preparation method of the present invention only requires dissolving the solute in a solvent to prepare the ether electrolyte. The preparation method is simple, practical and low-cost.

[0051] In some embodiments, when the ether electrolyte further comprises lithium nitrate, the preparation method comprises the following steps:

[0052] In a glove box filled with argon, the solute and lithium nitrate are added to the solvent, stirred until completely dissolved, and mixed evenly to obtain an ether electrolyte.

[0053] Yet another embodiment of the present invention provides a lithium-ion battery comprising the ether electrolyte.

[0054] The lithium-ion battery of the present invention contains an ether electrolyte, which is preferentially adsorbed at the interface of the positive electrode material. This makes the arrangement of the solvent molecules at the interface directional, reduces the proportion of ether oxygen bonds and the carbon-hydrogen atoms connected thereto in the double electrical layer, and thus keeps the sites in the molecules susceptible to dehydrogenation reactions away from the high-voltage (>4.3V) positive electrode interface susceptible to oxidation reactions. Severe dehydrogenation side reactions do not occur at high cut-off voltages, thereby achieving higher coulombic efficiency and capacity retention.

[0055] In some embodiments, the positive electrode of the lithium-ion battery is at least one of lithium iron phosphate, lithium cobalt oxide, lithium nickel cobalt manganese oxide (NCM811, NCM622, Ni83, Ni90, Ni92) and lithium nickel manganese oxide.

[0056] In some embodiments, the negative electrode of the lithium-ion battery is at least one of mesocarbon microbeads (MCMB), graphite, silicon carbon, and lithium metal.

[0057] In some embodiments, the lithium ion separator is at least one of a glass fiber separator, a polytetrafluoroethylene separator, a polypropylene separator, a polyethylene separator, and a cellulose separator.

[0058] 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.

[0059] Example 1

[0060] In an argon-filled glove box, 0.001 mol of lithium bis(fluorosulfonyl)imide was added to 1 mL of 2-methoxyacetonitrile liquid and stirred evenly for 6 hours using a magnetic stirrer to obtain a clear and uniform solution. The lithium salt was completely dissolved in the solution, and a low-concentration ether electrolyte suitable for high-voltage, high-nickel ternary lithium-ion batteries was prepared. The actual solution is shown in the figure below. Figure 1 As shown in the actual picture, it can be seen that the electrolyte prepared in this example is a clear and uniform solution.

[0061] The prepared electrolyte was assembled into an NCM811 half-cell together with a lithium sheet, NCM811, and a separator. The cell was then tested at a rate of 0.5C. It cycled stably for 100 cycles at a charge cutoff voltage of 4.3V, with a capacity retention rate exceeding 75%.

[0062] Example 2

[0063] In an argon-filled glove box, 0.001 mol of lithium bis(fluorosulfonyl)imide was added to 1 mL of 2-ethoxyacetonitrile liquid and stirred evenly for 6 hours using a magnetic stirrer to obtain a clear and uniform solution. The lithium salt was completely dissolved in the solvent, and a low-concentration ether electrolyte suitable for high-voltage, high-nickel ternary lithium-ion batteries was prepared. The actual solution is shown in the figure below. Figure 2 As shown in the actual picture, it can be seen that the electrolyte prepared in this example is a clear and uniform solution.

[0064] The prepared electrolyte was assembled into an NCM811 half-cell together with a lithium sheet, NCM811, and a separator. The cell was then tested at a rate of 0.5C. It cycled stably for 100 cycles at a charge cutoff voltage of 4.3V, with a capacity retention rate exceeding 80%.

[0065] Example 3

[0066] In an argon-filled glove box, 0.001 mol of lithium bis(fluorosulfonyl)imide was added to 1 mL of 3-methoxypropionitrile liquid and mixed. The mixture was stirred evenly for 6 hours using a magnetic stirrer to obtain a clear and uniform solution. The lithium salt was completely dissolved in the solvent, and a low-concentration ether electrolyte suitable for high-voltage, high-nickel ternary lithium-ion batteries was prepared. The actual solution is shown in the figure below. Figure 3 As shown in the actual picture, it can be seen that the electrolyte prepared in this embodiment is a clear and uniform solution.

[0067] The prepared electrolyte was assembled into an NCM811 half-cell together with a lithium sheet, NCM811, and a separator. The half-cell was tested at a rate of 0.5C. The half-cell cycle was stable at a charge cut-off voltage of 4.3V for 100 cycles, and the capacity retention rate exceeded 80%. Figure 16 shown.

[0068] Example 4

[0069] In an argon-filled glove box, 0.001 mol of lithium bis(fluorosulfonyl)imide and 0.0004 mol of lithium nitrate were added to 1 mL of 4-cyanotetrahydropyran liquid and mixed. The mixture was stirred evenly for 6 hours using a magnetic stirrer to obtain a clear and uniform solution. The lithium salt was completely dissolved in the solvent, and a low-concentration ether electrolyte (experimental group) suitable for high-voltage, high-nickel ternary lithium-ion batteries was prepared. The actual solution is shown in the figure below. Figure 4 As shown in the actual picture, it can be seen that the electrolyte prepared in this embodiment is a clear and uniform solution.

[0070] Under the same preparation conditions, 0.001 mol of lithium hexafluorophosphate was added to 1 mL of ethylene carbonate and ethyl methyl carbonate (volume ratio of ethylene carbonate / ethyl methyl carbonate = 3:7) liquid and mixed, that is, lithium hexafluorophosphate with a molar concentration of 1 mol / L was mixed with ethylene carbonate and ethyl methyl carbonate to form a uniform solution, thereby obtaining a commercial electrolyte (control group).

[0071] The above two groups of electrolytes were assembled into batteries and the battery performance was tested as follows:

[0072] 1. The above two sets of electrolytes were used to assemble a battery stack with aluminum sheets, separators, and lithium sheets. Linear sweep voltammetry was performed at room temperature (25°C) with a sweep voltage range of 3V-5.5V and a sweep rate of 0.5mV / s. The experimental data of the electrolyte oxidation potential were as follows:

[0073] like Figure 8 As shown, the oxidation potential of the experimental group was 5V, while that of the control group was 4.6V.

[0074] 2. The two sets of electrolytes mentioned above were used to assemble NCM811 half-cells with lithium sheets, NCM811, and separators. The cells were tested at a rate of 0.5C. The results are as follows:

[0075] (1) After 100 stable cycles of the lithium-NCM811 battery using the experimental electrolyte, the battery was disassembled to remove the NCM811 positive electrode, and the NCM811 positive electrode material particles were photographed using a scanning electron microscope. Figure 12 As shown in the figure, the NCM811 particles in the experimental group after cycling have a complete structure and a uniform and dense surface. Figure 13 As shown, the NCM811 particles in the control group were more dispersed after circulation, with a rough and loose surface.

[0076] (2) Figure 9 As shown, the lithium-NCM811 battery using the experimental electrolyte was stably cycled for 500 cycles at a charge cut-off voltage of 4.5V, with a capacity retention rate exceeding 80%. The lithium-NCM811 battery using the control electrolyte was stably cycled for 300 cycles at a charge cut-off voltage of 4.5V, with a capacity retention rate of 33%.

[0077] 3. The above two sets of electrolytes were used together with lithium sheets, MCMB, and separators to assemble MCMB half-cells. The cells were tested at a rate of 0.2C. The results are as follows:

[0078] like Figure 11 As shown, the lithium-MCMB battery using the experimental group electrolyte was stably cycled for 350 cycles with a capacity retention rate of over 93%. The lithium-MCMB battery using the control group electrolyte was stably cycled for 350 cycles with a capacity retention rate of 90%.

[0079] 4. The two sets of electrolytes mentioned above were used to assemble NCM811 half-cells with lithium sheets, NCM811, and diaphragms for leakage current testing. The results are as follows:

[0080] like Figure 14As shown in the figure, under constant voltage charging at high cut-off voltages of 4.6V and 4.7V, the lithium-NCM811 battery using the experimental electrolyte did not show a large current change. However, the lithium-NCM811 battery using the control electrolyte showed a large leakage current.

[0081] 5. The above two sets of electrolytes were used together with MCMB, NCM811, and a separator to assemble a MCMB-NCM811 full battery. The battery was tested at a charge rate of 0.2C and a discharge rate of 0.5C. The results are as follows:

[0082] like Figure 15 As shown in the figure, the MCMB-NCM811 battery using the experimental electrolyte was stably cycled for 200 cycles at a charge cut-off voltage of 4.45V, with a capacity retention rate of over 75%. The MCMB-NCM811 battery using the control electrolyte was stably cycled for 200 cycles at a charge cut-off voltage of 4.45V, with a capacity retention rate of 73%.

[0083] Therefore, it can be seen from the above test data that compared with the battery using tetrahydropyran as the solvent, the battery using 4-cyanotetrahydropyran as the solvent to prepare the electrolyte composition has a higher oxidation potential, a higher capacity retention rate, and a higher stability.

[0084] Example 5

[0085] In an argon-filled glove box, 0.001 mol of lithium hexafluorophosphate was added to 1 mL of ethylene glycol bis(propionitrile) ether liquid and mixed. The mixture was stirred evenly for 6 hours using a magnetic stirrer to obtain a clear and uniform solution. The lithium salt was completely dissolved in the solution, and a low-concentration ether electrolyte suitable for high-voltage, high-nickel ternary lithium-ion batteries was prepared. The actual solution is shown in the figure below. Figure 5 As shown in the actual picture, it can be seen that the electrolyte prepared in this embodiment is a clear and uniform solution.

[0086] The prepared electrolyte was assembled into an NCM811 half-cell together with a lithium sheet, NCM811, and a separator. The half-cell was tested at a rate of 0.5C. The half-cell cycle was stable at a charge cut-off voltage of 4.3V for 100 cycles, and the capacity retention rate exceeded 80%. Figure 10 shown.

[0087] Example 6

[0088] In an argon-filled glove box, 0.001 mol of lithium bis(trifluoromethanesulfonyl)imide was added to 1 mL of 3-ethoxypropionitrile liquid and mixed. The mixture was stirred evenly for 6 hours using a magnetic stirrer to obtain a clear and uniform solution. The lithium salt was completely dissolved in the solution, and a low-concentration ether electrolyte suitable for high-voltage, high-nickel ternary lithium-ion batteries was prepared. The actual solution is shown in the figure below. Figure 6As shown in the actual picture, it can be seen that the electrolyte prepared in this embodiment is a clear and uniform solution.

[0089] The prepared electrolyte was assembled into an NCM811 half-cell with lithium sheet, NCM811 and separator, and tested at a rate of 0.5C. It cycled stably for 100 cycles at a charge cut-off voltage of 4.3V, with a capacity retention rate of more than 80%. Figure 17 shown.

[0090] Example 7

[0091] In an argon-filled glove box, 0.001 mol of lithium bis(trifluoromethanesulfonyl)imide was added to 1 mL of 3-butoxypropionitrile liquid and mixed. The mixture was stirred evenly for 6 hours using a magnetic stirrer to obtain a clear and uniform solution. The lithium salt was completely dissolved in the solution, and a low-concentration ether electrolyte suitable for high-voltage, high-nickel ternary lithium-ion batteries was prepared. The actual solution is shown in the figure below. Figure 7 As shown in the actual picture, it can be seen that the electrolyte prepared in this embodiment is a clear and uniform solution.

[0092] The prepared electrolyte was assembled into an NCM811 half-cell together with a lithium sheet, NCM811, and a separator. The cell was then tested at a rate of 0.5C. It cycled stably for 100 cycles at a charge cutoff voltage of 4.3V, with a capacity retention rate exceeding 80%.

[0093] The capacity retention rates of NCM811 half-cells assembled from the electrolytes prepared in Examples 1 to 7 are shown in Table 1.

[0094] Table 1

[0095]

[0096] Therefore, it can be seen from Table 1 that the electrolyte prepared by the present invention has a higher capacity retention rate, and, compared with the control group (commercial electrolyte) described in Example 4, the capacity retention rate of the electrolyte prepared by the present invention is greatly improved.

[0097] 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. A low-concentration ether electrolyte suitable for high-voltage, high-nickel ternary lithium-ion batteries, characterized in that: The ether electrolyte includes a solvent and a solute; The solvent includes an ether solvent, and the ether solvent is at least one of 4-cyanotetrahydropyran, 2-(tetrahydro-2H-pyran-4-yl)acetonitrile, 2-methoxyacetonitrile, 2-ethoxyacetonitrile, 3-methoxypropionitrile, 3-ethoxypropionitrile, 3-butoxypropionitrile, ethylene glycol bis(propionitrile) ether and 3-{2-[2-(2-cyanoethoxy)ethoxy]ethoxy}propionitrile.

2. The ether electrolyte according to claim 1, characterized in that The solute is at least one of LiPF6, LiBF4, LiTFSI, LiFSI, LiNO3 and LiDFOB.

3. The ether electrolyte according to claim 1, characterized in that The concentration of the solute in the ether electrolyte is 0.5 mol / L to 3 mol / L.

4. The ether electrolyte according to claim 1, characterized in that The ether electrolyte also includes lithium nitrate.

5. The ether electrolyte according to claim 4, characterized in that The concentration of lithium nitrate in the ether electrolyte is 0.01 mol / L to 1 mol / L.

6. The method for preparing an ether electrolyte according to any one of claims 1 to 5, characterized in that: The following steps are involved: In a glove box filled with argon, the solute is added to the solvent or the solute and lithium nitrate are added to the solvent, stirred until completely dissolved, and mixed evenly to obtain an ether electrolyte.

7. A lithium-ion battery, characterized in that: The invention comprises the ether electrolyte according to any one of claims 1 to 5.

8. The lithium-ion battery according to claim 7, characterized in that The positive electrode of the lithium-ion battery is at least one of lithium iron phosphate, lithium cobalt oxide, lithium nickel cobalt manganese oxide and lithium nickel manganese oxide.

9. The lithium-ion battery according to claim 7, wherein: The negative electrode of the lithium-ion battery is at least one of mesophase carbon microbeads, graphite, silicon carbon and lithium metal.

10. The lithium-ion battery according to claim 7, characterized in that The lithium ion separator is at least one of a glass fiber separator, a polytetrafluoroethylene separator, a polypropylene separator, a polyethylene separator and a cellulose separator.

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