Ether electrolyte containing 4-cyano tetrahydropyran and high-voltage lithium metal battery

Abstract

The ether electrolyte comprises a lithium salt and an ether solvent, the ether solvent is 4-cyano tetrahydropyrane (CNTHP), the solvation ability of ether oxygen atoms and Li < + > is reduced through the electron-withdrawing induction effect of cyano groups in CNTHP molecules and the steric hindrance of a six-membered ring, and thus the lithium ion battery is obtained. N atoms in cyano groups can provide weak coordination sites to promote Li < + > transmission, and meanwhile, a stable solid electrolyte interface (SEI) can be formed, so that generation of lithium dendrites is effectively inhibited. The electrolyte is excellent in performance, the coulombic efficiency of a Li-Cu battery can reach 99.3%, the capacity retention rate after a high-voltage Li-NMC811 battery circulates for 300 circles is 91%, the retention rate after the Li-NMC811 battery circulates for 200 circles at the high temperature of 60 DEG C is 77.5%, the electrolyte is further adaptive to a Li-NMC811 soft package battery, the battery safety is improved due to the high boiling point and the high flash point of CNTHP, a fluorinated solvent is not needed, and the industrialization requirement of the high-energy-density lithium metal battery can be met.

Description

TECHNICAL FIELD

[0001] The present application relates to lithium-ion battery technology, in particular to an ether electrolyte containing 4-cyanotetrahydropyran and a high-voltage lithium metal battery. BACKGROUND

[0002] The energy density of lithium-ion batteries is about to reach the theoretical limit (350 Wh kg -1 ). Higher energy density energy storage devices are being explored to meet the growing demand of people. Lithium metal is an ideal anode material because of its high theoretical specific capacity (3860 mAh g -1 ), low density (0.534 g cm -3 ) and the lowest redox potential (-3.04 V vs. standard hydrogen electrode), which can achieve a specific energy of more than 400 Wh kg -1 , so lithium metal batteries are gaining momentum. However, lithium metal is thermodynamically unstable, and reacts with the electrolyte to form an unstable solid-state-electrolyte interface phase (SEI), which collapses and rebuilds during repeated lithium plating and stripping, leading to electrolyte and active lithium loss, lithium dendrite formation and rapid capacity decay of the battery, which severely limits the practical application of lithium metal batteries. Therefore, establishing a stable and robust SEI is the key to realizing a stable lithium metal anode. The composition and structure evolution of SEI is closely related to the interaction between each component in the electrolyte. Based on this, researchers have reported different electrolyte formulations to explore the influence of solvation structure on the properties of SEI. Mainly including introducing functional additives in the traditional electrolyte, adjusting the proportion of each component, changing the type of solvent / salt, and introducing high-concentration electrolyte, local high-concentration electrolyte, weakly solvated electrolyte and other new concepts. In some improved electrolyte systems, the SEI derived from the anion induces uniform lithium deposition, improving the interface stability of lithium metal, but recent studies have shown that although some improved electrolytes can effectively inhibit the growth of lithium dendrites, but in the long-term cycling process, the electrolyte will penetrate to the lithium surface through the gap between the irregular lithium blocks or the broken SEI, causing the depletion of the electrolyte and the corrosion of lithium, shortening the cycle life of the lithium metal battery. Moreover, the fluorinated solvent as a co-solvent exists in the electrolyte, and there are still unstable solvent molecules to dissolve lithium salt, and the continuous parasitic reaction leads to the reduction of coulombic efficiency and the shortening of the life of the battery. In addition to the high cost and potential environmental hazards of fluorinated solvent molecules, this seriously limits its application as a main solvent in lithium metal battery electrolyte. Therefore, it is necessary and urgent to explore non-fluorinated solvent-containing electrolytes to achieve high stability of lithium metal batteries.

[0003] Studies have shown that weakly solvating electrolytes composed of ether solvents can improve the interfacial stability of lithium metal, increase the coulombic efficiency of lithium deposition / stripping, and greatly reduce the cost. However, the chemical stability and thermal stability of some ether-based electrolytes are limited. Therefore, it is necessary to further optimize the electrolyte formulation, improve the stability of the electrolyte, enhance the long cycle stability of the lithium negative electrode interface, and improve the potential of practical application of lithium metal batteries. SUMMARY

[0004] The main purpose of the present application is to overcome the defects in the background art, and to provide an ether-based electrolyte containing 4-cyanotetrahydropyran and a high-voltage lithium metal battery. The former is a high-performance ether-based electrolyte that does not rely on fluorinated solvents, has high safety and stability (especially at high temperatures), can form a stable SEI to inhibit lithium dendrites, and is suitable for high-performance high-voltage lithium metal batteries.

[0005] To achieve the above purpose, the following technical solutions are adopted: An ether-based electrolyte containing 4-cyanotetrahydropyran, comprising a lithium salt and an ether solvent, wherein the ether solvent is 4-cyanotetrahydropyran, which reduces the solvation ability of ether oxygen atoms and Li + by the electron-withdrawing inductive effect of the cyano group and the steric hindrance of the six-membered ring, and introduces weak coordination sites to promote Li + transport and form a stable solid-state electrolyte interface (SEI).

[0006] Further, the 4-cyanotetrahydropyran is the only solvent in the electrolyte.

[0007] Further, the lithium salt includes lithium bisfluorosulfonylimide (LiFSI) and lithium nitrate (LiNO3), wherein the concentration of LiFSI is 0.5-2.0 mol / L, and the concentration of LiNO3 is 0.15-0.3 mol / L.

[0008] Further, in the solvation structure of Li + in the electrolyte, the total proportion of contact ion pairs (CIPs) and ionic aggregates (AGGs) is not less than 90%.

[0009] A high-voltage lithium metal battery, comprising a positive electrode, a lithium metal negative electrode, a separator, and the ether-based electrolyte containing 4-cyanotetrahydropyran.

[0010] Further, the positive electrode material includes a ternary positive electrode material LiNi 0.8 Mn 0.1 Co 0.1 O2 (NMC811), a binder polyvinylidene fluoride (PVDF), and conductive carbon black Super P, with a mass ratio of 8:1:1.

[0011] Further, the ternary positive electrode material LiNi 0.8 Mn 0.1 Co 0.1 The active material loading of the O2 (NMC811) is 1.5-2.0 mg / cm 2 .

[0012] Further, the negative electrode material is a lithium metal sheet.

[0013] Further, the separator is Celgard 2500.

[0014] Further, the high-voltage lithium metal battery is a button cell or a soft-pack battery.

[0015] The present application has the following beneficial effects: The ether electrolyte containing 4-cyanotetrahydropyran (CNTHP) solvent provided by the present application uses 4-cyanotetrahydropyran as the only solvent, and the performance advantages thereof are derived from the unique molecular structure design and action mechanism: on the one hand, the electron-withdrawing induction effect of the cyano group (-CN) and the steric hindrance of the six-membered ring in CNTHP can effectively reduce the solvation ability of the ether oxygen atom (O atom) and Li + ; on the other hand, the introduction of -CN enables the N atom therein to coordinate with Li + , thereby increasing the weak coordination site (steric effect) of Li + , and further promoting the fast transmission of Li + ; meanwhile, CNTHP itself forms a non-chelating multidentate ligand (especially the CN at the outer end) that has a weak solvation effect with Li + . This weak solvation characteristic not only can improve the redox stability of the solvent, further accelerate the transmission rate of Li + , but also can promote more anion-cation pairs to participate in the solvation structure of Li + , especially beneficial for the anion to enter the inner solvation sheath of Li + , so as to finally generate a stable and strong double-layer solid electrolyte interface (SEI) rich in inorganic components, which can induce lithium to be deposited in the form of uniform, dense and smooth spheres, effectively avoiding the formation of lithium dendrites, thereby building a stable lithium negative electrode interface and laying a foundation for the excellent electrochemical performance of the lithium metal battery.

[0016] Meanwhile, the 4-cyanotetrahydropyran molecule itself has a high boiling point (224°C) and flash point (92.2°C), which further guarantees the stability and safety of the lithium metal battery in a high-temperature environment; and due to the regulation effect of CNTHP on the solvation structure of Li +The transmission capacity of the electrolyte liquid phase and the electrode interface phase is also significantly enhanced. In terms of specific performance, the Li-Cu battery with the electrolyte containing 4-cyanotetrahydropyran has a high coulomb efficiency of 99.3%, and the capacity retention rate of the high-voltage Li-NMC811 battery after 300 cycles is still as high as 91%, which is much better than that of the traditional ester electrolyte; even under the harsh condition of high temperature 60°C, the capacity retention rate of the Li-NMC811 battery corresponding to the electrolyte after the 200th cycle is still as high as 77.5% (relative to the 4th cycle after activation); in the soft package battery scenario closer to actual application, the Li-NMC811 soft package battery with the electrolyte containing 4-cyanotetrahydropyran can realize a high capacity of 1.25 Ah and can be stably cycled for 50 cycles.

[0017] The present application successfully constructs a stable lithium negative electrode interface through electrolyte molecular engineering design, effectively reduces the loss of electrolyte and the corrosion of lithium, breaks through the high-temperature performance bottleneck of traditional ether electrolyte in Li-NMC811 battery application, and significantly enhances the practical application potential of Li-NMC811 battery. The ether electrolyte containing functional functional groups solves the industry pain points of traditional ether electrolyte such as poor stability and poor high-temperature performance through solvent molecular structure optimization, and its core advantage can directly adapt to the industrialization demand of high-energy-density lithium metal battery, providing key technical support for the commercialization of lithium metal battery. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The long cycle performance graph of the Li-NMC811 CR2032 button cell containing three kinds of 4-cyanotetrahydropyran electrolyte in the present application example 1 at 0.2 C charging / 0.5 C discharging rate.

[0019] Figure 2 The capacity-voltage curve of the Li-NMC811 CR2032 button cell containing three kinds of 4-cyanotetrahydropyran electrolyte in the present application example 1 at 0.2 C charging / 0.5 C discharging rate.

[0020] Figure 3 The long cycle performance comparison graph of the Li-NMC811 CR2032 button cell containing 4-cyanotetrahydropyran electrolyte in the present application example 2 and the Li-NMC811 CR2032 button cell containing traditional ester electrolyte at 0.5 C rate.

[0021] Figure 4 The capacity-voltage curve of the Li-NMC811 CR2032 button cell containing 4-cyanotetrahydropyran electrolyte in the present application example 2 and the Li-NMC811 CR2032 button cell containing traditional ester electrolyte at 0.5 C rate.

[0022] Figure 5 EIS plots of Li-NMC811 CR2032 button cells containing 4-cyanotetrahydropyran electrolyte in Example 2 of the present invention before cycling and after 50 cycles.

[0023] Figure 6 Cycle performance comparison plots of Li-NMC811 CR2032 button cells containing 4-cyanotetrahydropyran electrolyte in Example 2 of the present invention and Li-NMC811 CR2032 button cells containing conventional ester-based electrolyte at different C-rates.

[0024] Figure 7 Long cycle performance comparison plots of Li-NMC811 CR2032 button cells containing 4-cyanotetrahydropyran electrolyte in Example 2 of the present invention and Li-NMC811 CR2032 button cells containing conventional ester-based electrolyte at high temperature 60 °C with 0.2 C charge / 0.5 C discharge.

[0025] Figure 8 Capacity-voltage plots of Li-NMC811 CR2032 button cells containing 4-cyanotetrahydropyran electrolyte in Example 2 of the present invention and Li-NMC811 CR2032 button cells containing conventional ester-based electrolyte at high temperature 60 °C with 0.2 C charge / 0.5 C discharge.

[0026] Figure 9 Cycle plots of Li-NMC811 pouch cells containing 4-cyanotetrahydropyran electrolyte in Example 3 of the present invention at 0.2 C rate.

[0027] Figure 10 Capacity-voltage plots of Li-NMC811 pouch cells containing 4-cyanotetrahydropyran electrolyte in Example 3 of the present invention at 0.2 C rate.

[0028] Figure 11 LSV plots of Li-Al CR2032 button cells containing 4-cyanotetrahydropyran electrolyte in Example 4 of the present invention.

[0029] Figure 12 Time-voltage plots of Li-Cu CR2032 button cells containing 4-cyanotetrahydropyran electrolyte in Example 4 of the present invention and Li-Cu CR2032 button cells containing conventional ester-based electrolyte using Aurbach method.

[0030] Figure 13Long cycle plot for Li||Li CR2032 button cell containing 4-cyanotetrahydropyran electrolyte in Example 4 of the present invention vs. Li||Li CR2032 button cell containing conventional ester electrolyte.

[0031] Figure 14 SEM image of lithium deposition on Cu current collector in Li-Cu CR2032 button cell containing 4-cyanotetrahydropyran electrolyte in Example 4 of the present invention.

[0032] Figure 15 SEM image of lithium deposition on Cu current collector in Li-Cu CR2032 button cell containing 4-cyanotetrahydropyran electrolyte in Example 4 of the present invention at high temperature 60 °C.

[0033] Figure 16 Raman spectra corresponding to electrolyte containing 4-cyanotetrahydropyran vs. electrolyte containing tetrahydropyran in Example 5 of the present invention. 17 O NMR and 7 Li NMR spectra.

[0034] Figure 17 Raman spectra corresponding to electrolyte containing 4-cyanotetrahydropyran vs. electrolyte containing tetrahydropyran in Example 5 of the present invention.

[0035] Figure 18 SEM top view image of lithium metal anode after 50th cycle in Li-NMC811 CR2032 button cell containing 4-cyanotetrahydropyran electrolyte in Example 6 of the present invention.

[0036] Figure 19 SEM cross-sectional image of lithium metal anode after 50th cycle in Li-NMC811 CR2032 button cell containing 4-cyanotetrahydropyran electrolyte in Example 6 of the present invention.

[0037] Figure 20 AFM 3D image of lithium metal anode after 50th cycle in Li-NMC811 CR2032 button cell containing 4-cyanotetrahydropyran electrolyte in Example 6 of the present invention.

[0038] Figure 21 Force-displacement curve of lithium metal anode surface after 50th cycle in Li-NMC811 CR2032 button cell containing 4-cyanotetrahydropyran electrolyte in Example 6 of the present invention.

[0039] Figure 22 XPS depth profile curve of lithium metal anode after 5th cycle in Li-NMC811 CR2032 button cell containing 4-cyanotetrahydropyran electrolyte in Example 6 of the present invention.

[0040] Figure 23 Low magnification Cryo-TEM image of the deposited lithium on the copper mesh in Li-Cu CR2032 button cell with 4-cyanotetrahydropyran electrolyte in Example 6 of the present invention.

[0041] Figure 24 High resolution Cryo-TEM image of the deposited lithium in Li-Cu CR2032 button cell with 4-cyanotetrahydropyran electrolyte in Example 6 of the present invention. The inset is the corresponding FFT image.

[0042] Figure 25 High resolution Cryo-TEM image of the deposited lithium in Li-Cu CR2032 button cell with 4-cyanotetrahydropyran electrolyte at high temperature 60 °C in Example 6 of the present invention.

[0043] Figure 26 Conceptual illustration of the formation of the solid electrolyte interphase (SEI) structure with 4-cyanotetrahydropyran-containing ether electrolyte in the present invention.

[0044] Figure 27 is a Li + Comparison of coordination strength in solvation structure. DETAILED DESCRIPTION

[0045] The following detailed description of the embodiments of the present invention is provided. It should be emphasized that the following description is merely exemplary and is not intended to limit the scope of the invention or its applications.

[0046] The embodiments of the present invention provide a 4-cyanotetrahydropyran-containing ether electrolyte, which includes a lithium salt and an ether solvent, wherein the ether solvent is 4-cyanotetrahydropyran, which reduces the solvation ability of the ether oxygen atom to Li + by the electron-withdrawing inductive effect of the cyano group and introduces weak coordination sites to facilitate Li + transport and form a stable solid electrolyte interphase (SEI).

[0047] In some embodiments, the 4-cyanotetrahydropyran is the only solvent in the electrolyte.

[0048] In some embodiments, the lithium salt includes lithium bisfluorosulfonylimide (LiFSI) and lithium nitrate (LiNO3), wherein the concentration of LiFSI is 0.5-2.0 mol / L and the concentration of LiNO3 is 0.15-0.3 mol / L.

[0049] In some embodiments, the Li +The total proportion of contact ion pairs (CIPs) and ion aggregates (AGGs) in the solvation structure is not less than 90%.

[0050] The ether electrolyte containing 4-cyanotetrahydropyran (CNTHP) solvent uses 4-cyanotetrahydropyran as the only ether solvent, and the performance advantage is derived from the unique molecular structure design and mechanism: on the one hand, by means of the electron-withdrawing induction effect of the cyano group (-CN) in CNTHP and the steric hindrance of the six-membered ring, the solvation ability of the ether oxygen atom (O atom) and Li + can be significantly reduced; on the other hand, the introduction of -CN enables the N atom therein to coordinate with Li + , which increases the weak coordination site (steric effect) of Li + , thereby promoting the fast transmission of Li + , while CNTHP itself forms a non-chelating multidentate ligand with weak solvation effect on Li + .

[0051] This weak solvation characteristic not only improves the redox stability of the solvent, further accelerates the transmission rate of Li + , but also promotes more anion-cation pairs to participate in the solvation structure of Li + , especially beneficial to the anion entering the inner solvation sheath of Li + , and finally generating a stable and robust double-layer solid electrolyte interface (SEI) rich in inorganic components. The SEI can effectively induce lithium to deposit in a uniform, dense and smooth spherical morphology, thereby constructing a stable lithium negative electrode interface.

[0052] When the ether electrolyte containing 4-cyanotetrahydropyran solvent is applied to a high-voltage lithium metal battery, through the synergistic effect of the above-mentioned molecular structure regulation, solvation behavior optimization and negative electrode interface stability construction, the high-voltage lithium metal battery ultimately has excellent electrochemical performance.

[0053] The embodiment of the present application also provides a high-voltage lithium metal battery, which comprises a positive electrode, a lithium metal negative electrode, a separator and the ether electrolyte containing 4-cyanotetrahydropyran.

[0054] In some embodiments, the positive electrode material comprises a ternary positive electrode material LiNi 0.8 Mn 0.1 Co 0.1 O2 (NMC811), a binder polyvinylidene fluoride (PVDF) and conductive carbon black Super P, and the mass ratio is 8:1:1.

[0055] In some embodiments, the ternary positive electrode material LiNi 0.8 Mn 0.1 Co 0.1The active material loading of O2(NMC811) is 1.5-2.0 mg / cm 2 .

[0056] In some embodiments, the negative electrode material is a lithium metal sheet. In one example, the thickness of the lithium sheet in the button cell is 450 pm, and the diameter is 15.6 mm.

[0057] In some embodiments, the separator is Celgard 2500.

[0058] In some embodiments, the high-voltage lithium metal battery is a button cell or a soft-pack battery.

[0059] In some embodiments, the preparation method of the positive electrode material is as follows: first, mix the active material NMC811, the binder PVDF, and the conductive carbon black Super P in a mass ratio of 8:1:1 uniformly, and dissolve them in N-methyl pyrrolidone to prepare a slurry. The slurry is coated on an aluminum foil, and then dried in a vacuum oven at 60°C for 12 hours.

[0060] In some embodiments, when the button cell is made, the ether-based electrolyte containing 4-cyanotetrahydropyran is added dropwise on both sides of the separator to make it fully contact with the positive / negative electrode, and the Li-NMC811 button cell is assembled.

[0061] In some embodiments, when the soft-pack battery is made, the ether-based electrolyte containing 4-cyanotetrahydropyran is injected into the Li-NMC811 soft-pack battery matrix to make it fully contact with the positive / negative electrode, and the Li-NMC811 soft-pack battery is assembled.

[0062] The ether-based electrolyte containing 4-cyanotetrahydropyran and the high-voltage lithium metal battery provided by the application are designed with the ether-based electrolyte with 4-cyanotetrahydropyran (CNTHP) as the only solvent. With the electron-withdrawing inductive effect of the cyano group and the steric hindrance of the six-membered ring in the CNTHP molecule, the Li + solvation behavior is optimized, and a weak coordination site is provided to accelerate the Li + transport, and its high boiling point and high flash point characteristics improve the high-temperature stability and safety of the battery; the electrolyte can induce the formation of a stable inorganic solid-state electrolyte interface (SEI), effectively inhibits the formation of lithium dendrites, and builds a stable lithium negative electrode interface; the electrochemical performance is better than that of the traditional ester-based electrolyte, which meets the needs of high-voltage lithium metal batteries, and does not need to rely on high-cost, potentially environmentally hazardous fluorinated solvents, solving the pain points of the traditional ether-based electrolyte, such as insufficient stability and poor high-temperature performance, and having industrial application potential.

[0063] The specific embodiments and experimental verification of the application are further described below.

[0064] Example 1

[0065] Three kinds of ether-based electrolytes containing 4-cyanotetrahydropyran were provided, including lithium salts and solvents, wherein the solvents were 4-cyanotetrahydropyran, the lithium salts were LiFSI and LiNO3, the concentration of LiFSI was 0.5 mol / L, 1.0 mol / L and 1.5 mol / L respectively, and the concentration of LiNO3 was 0.3 mol / L.

[0066] The 4-cyanotetrahydropyran-containing electrolyte obtained in this example was assembled into a Li-NMC811 CR2032 button cell together with an NMC811 positive electrode, a separator and a lithium metal negative electrode.

[0067] Preparation of NMC811 positive electrode: First, the active material NMC811, the binder PVDF and the conductive carbon black Super P were mixed uniformly in a mass ratio of 8:1:1, and then dissolved in N-methyl pyrrolidone to prepare a slurry. After stirring uniformly, the slurry was coated on an aluminum foil, and then dried in a vacuum oven at 60°C for 12 hours.

[0068] The lithium metal sheet had a thickness of 450 μm and a diameter of 15.6 mm.

[0069] The separator was Celgard 2500, with a diameter of 19 mm.

[0070] Electrochemical tests were performed on the Li-NMC811 button cells containing the three kinds of 4-cyanotetrahydropyran-containing electrolytes described above.

[0071] Figure 1 The long cycle performance of the Li-NMC811 batteries containing the three kinds of 4-cyanotetrahydropyran-containing electrolytes at a rate of 0.2C charging / 0.5C discharging, wherein when the concentration of LiTFSI was 1.0 mol / L, the Li-NMC811 battery had the most stable cycle performance and achieved the highest average specific capacity (185.7 mAh g -1 ).

[0072] Figure 2 The capacity-voltage curves of the Li-NMC811 batteries containing the three kinds of 4-cyanotetrahydropyran-containing electrolytes at a rate of 0.2C charging / 0.5C discharging, wherein it can be seen that when the concentration of LiTFSI was 1.0 mol / L, the Li-NMC811 battery had the smallest voltage hysteresis (0.23 V).

[0073] Example 2

[0074] An electrolyte containing 4-cyanotetrahydropyran is provided, including a lithium salt and a solvent, wherein the solvent is 4-cyanotetrahydropyran, the lithium salt is LiFSI and LiNO3, the concentration of LiFSI is 1.0 mol / L, and the concentration of LiNO3 is 0.3 mol / L. In addition, a conventional commercial ester-based electrolyte is used as a control group, which is 1.0 mol / L LiPF6 dissolved in ethylene carbonate (EC) and diethyl carbonate (DEC) solvents, wherein the volume ratio of EC / DEC is 1:1.

[0075] The electrolyte containing 4-cyanotetrahydropyran obtained in this example is assembled into a Li-NMC811 CR2032 button cell together with an NMC811 positive electrode, a separator, and a lithium metal negative electrode.

[0076] Preparation of NMC811 positive electrode: First, the active material NMC811, the binder PVDF, and the conductive carbon black Super P are mixed uniformly in a mass ratio of 8:1:1 and dissolved in N-methyl pyrrolidone to prepare a slurry. After stirring uniformly, the slurry is coated on an aluminum foil, and then dried in a vacuum oven at 60°C for 12 hours.

[0077] The lithium metal sheet has a thickness of 450 μm and a diameter of 15.6 mm.

[0078] The separator is Celgard 2500, with a diameter of 19 mm.

[0079] The Li-NMC811 button cell with the above-mentioned electrolyte containing 4-cyanotetrahydropyran is subjected to electrochemical testing.

[0080] Figure 3 is the long cycle performance curve of the Li-NMC811 battery containing the electrolyte containing 4-cyanotetrahydropyran and the Li-NMC811 battery containing the conventional ester-based electrolyte at 0.5 C rate. In the conventional ester-based electrolyte, the capacity of the Li-NMC811 battery decays rapidly, and the capacity retention rate is only 57% after 300 cycles. However, the Li-NMC811 battery containing the electrolyte containing 4-cyanotetrahydropyran has excellent long cycle stability, and the first cycle capacity is 189.1 mAh g -1 with a high discharge capacity and a capacity retention rate of 91% after 300 cycles.

[0081] Figure 4 is the capacity-voltage curve of the Li-NMC811 battery containing the electrolyte containing 4-cyanotetrahydropyran and the Li-NMC811 battery containing the conventional ester-based electrolyte at 0.5 C rate. It can be seen that the Li-NMC811 battery containing the electrolyte containing 4-cyanotetrahydropyran has higher capacity and smaller voltage polarization.

[0082] Figure 5 are 10 5 -10 -2 Electrochemical impedance spectroscopy (EIS) of Li-NMC811 battery with 4-cyanotetrahydropyran electrolyte before and after 50 cycles under the condition of frequency range of 10

[0083] Figure 6 Rate performance comparison of Li-NMC811 battery with 4-cyanotetrahydropyran electrolyte and Li-NMC811 battery with traditional ester electrolyte at different rates. Compared with Li-NMC811 battery with traditional ester electrolyte, Li-NMC811 battery with 4-cyanotetrahydropyran electrolyte shows good rate performance. When the rate is 0.2C and 0.5C, the discharge capacity is 198.0 and 191.2 mAh g -1 , respectively. With the increase of rate, it still maintains a high capacity, and when the rate returns to 0.2C, it returns to a high capacity of 203.3 mAh g -1 . The above results can show that at high current density, 4-cyanotetrahydropyran electrolyte can make Li-NMC811 battery have higher reaction kinetics to achieve fast charge and discharge.

[0084] Figure 7 Cycle curve of Li-NMC811 battery with 4-cyanotetrahydropyran electrolyte and Li-NMC811 battery with traditional ester electrolyte at 0.2C charge / 0.5C discharge at high temperature 60℃. Li-NMC811 battery with 4-cyanotetrahydropyran electrolyte shows superior cycle stability at high temperature, and achieves a high capacity of 204.3 mAh g -1 after 200 cycles (relative to the fourth cycle, the first three cycles are 0.2C activation).

[0085] Figure 8 Capacity-voltage curve of Li-NMC811 battery with 4-cyanotetrahydropyran electrolyte and Li-NMC811 battery with traditional ester electrolyte at 0.2C charge / 0.5C discharge at high temperature 60℃. It can be seen from the comparison that 4-cyanotetrahydropyran electrolyte makes Li-NMC811 battery still maintain good reversibility at high temperature.

[0086] Example 3

[0087] Provided is an electrolyte containing 4-cyanotetrahydropyran, comprising a lithium salt and a solvent, wherein the solvent is 4-cyanotetrahydropyran, the lithium salt is LiFSI and LiNO3, the concentration of LiFSI is 1.0 mol / L, and the concentration of LiNO3 is 0.3 mol / L.

[0088] The electrolyte containing 4-cyanotetrahydropyran obtained in the example was injected into a Li-NMC811 soft pack battery to assemble a Li-NMC811 soft pack battery. The soft pack battery was purchased from Guangdong Canrd New Energy Technology Co., LTD, and the total load of NMC811 was 6.2 g, and the mass of lithium was 0.42 g. In the example, only for testing.

[0089] The Li-NMC811 soft pack battery containing the above-mentioned electrolyte containing 4-cyanotetrahydropyran was subjected to electrochemical test.

[0090] Figure 9 It is the cycle curve of the Li-NMC811 soft pack battery containing 4-cyanotetrahydropyran electrolyte at 0.2C rate. The first circle obtains a high discharge capacity of 1.25 Ah, and the capacity is maintained at 85% after 40 cycles, and then slightly decreases, and maintains a capacity of 0.92 Ah after 50 cycles, indicating that even under severe conditions, the electrolyte containing 4-cyanotetrahydropyran still maintains good cycle stability for Li-NMC811 battery.

[0091] Figure 10 It is the capacity-voltage curve of the Li-NMC811 soft pack battery containing 4-cyanotetrahydropyran electrolyte at 0.2C rate. It can be observed that the capacity of the Li-NMC811 soft pack battery is highly reversible during charging and discharging, and the voltage polarization is small.

[0092] Example 4

[0093] Provided is an electrolyte containing 4-cyanotetrahydropyran, comprising a lithium salt and a solvent; wherein the solvent is 4-cyanotetrahydropyran, the lithium salt is LiFSI and LiNO3, the concentration of LiFSI is 1.0 mol / L, and the concentration of LiNO3 is 0.3 mol / L.

[0094] The electrolyte containing 4-cyanotetrahydropyran obtained in the example was injected into a Li-NMC811 soft pack battery to assemble a Li-NMC811 soft pack battery. The soft pack battery was purchased from Guangdong Canrd New Energy Technology Co., LTD, and the total load of NMC811 was 6.2 g, and the mass of lithium was 0.42 g. In the example, only for testing.

[0089] The Li-NMC811 soft pack battery containing the above-mentioned electrolyte containing 4-cyanotetrahydropyran was subjected to electrochemical test.

[0090] Figure 9 It is the cycle curve of the Li-NMC811 soft pack battery containing 4-cyanotetrahydropyran electrolyte at 0.2C rate. The first circle obtains a high discharge capacity of 1.25 Ah, and the capacity is maintained at 85% after 40 cycles, and then slightly decreases, and maintains a capacity of 0.92 Ah after 50 cycles, indicating that even under severe conditions, the electrolyte containing 4-cyanotetrahydropyran still maintains good cycle stability for Li-NMC811 battery.

[0091] Figure 10 It is the capacity-voltage curve of the Li-NMC811 soft pack battery containing 4-cyanotetrahydropyran electrolyte at 0.2C rate. It can be observed that the capacity of the Li-NMC811 soft pack battery is highly reversible during charging and discharging, and the voltage polarization is small.

[0092] Example 4

[0093] Provided is an electrolyte containing 4-cyanotetrahydropyran, comprising a lithium salt and a solvent; wherein the solvent is 4-cyanotetrahydropyran, the lithium salt is LiFSI and LiNO3, the concentration of LiFSI is 1.0 mol / L, and the concentration of LiNO3 is 0.3 mol / L.

[0094] The electrolyte containing 4-cyanotetrahydropyran obtained in the example was injected into a Li-NMC811 soft pack battery to assemble a Li-NMC811 soft pack battery. The soft pack battery was purchased from Guangdong Canrd New Energy Technology Co., LTD, and the total load of NMC811 was 6.2 g, and the mass of lithium was 0.42 g. In the example, only for testing.

[0095] Aluminum foil thickness is 15 pm, diameter is 19 mm.

[0096] Copper foil thickness is 10 pm, diameter is 19 mm.

[0097] Lithium metal piece thickness is 450 pm, diameter is 15.6 mm.

[0098] Separator is Celgard 2500, diameter is 19 mm.

[0099] Electrochemical tests were performed on Li-Al, Li-Cu and Li||Li half-cells with the above-mentioned 4-cyanotetrahydropyran electrolyte, and scanning electron microscope (SEM) tests were performed on the deposited lithium on the copper current collector in the Li-Cu battery.

[0100] Figure 11 The linear sweep voltammetry (LSV) curve of Li-Al battery with 4-cyanotetrahydropyran electrolyte shows that the 4-cyanotetrahydropyran electrolyte has high oxidation stability and can be compatible with high-voltage (4.3 V) NMC811 cathode.

[0101] Figure 12 The time-voltage curve of Li-Cu battery with 4-cyanotetrahydropyran electrolyte and Li-Cu battery with traditional ester electrolyte under the condition of current density of 0.5 mA cm -2 and capacity density of 1 mAh cm -2 , the reversibility of lithium deposition / stripping in Li-Cu battery was evaluated by Aurbach coulombic efficiency test method. Li-Cu battery with traditional ester electrolyte only achieved 81.5% coulombic efficiency, while Li-Cu battery with 4-cyanotetrahydropyran electrolyte achieved high coulombic efficiency of 99.3%, indicating that 4-cyanotetrahydropyran electrolyte has good compatibility with lithium metal negative electrode.

[0102] Figure 13 The time-voltage curve of Li||Li battery with 4-cyanotetrahydropyran electrolyte and Li||Li battery with traditional ester electrolyte under the condition of current density of 0.5 mA cm -2 and capacity density of 1 mAh cm -2 , Li||Li battery with traditional ester electrolyte has larger overpotential, and the battery fails at 470 h. Li||Li battery with 4-cyanotetrahydropyran electrolyte can maintain smaller overpotential and stably cycle for 1000 h, indicating that lithium has very high reversibility in repeated deposition / stripping.

[0103] Figure 14At a current density of 0.5 mA cm -2 The capacity density is 1 mAh cm⁻¹ -2 SEM images of lithium deposition on the Cu current collector in a Li-Cu battery containing 4-cyanotetrahydropyran electrolyte under specific conditions. The images show that the spherical lithium deposits exhibit a uniform and dense distribution. Furthermore, their smooth surface and small specific surface area effectively reduce electrolyte loss and prevent lithium dendrite formation, which is beneficial for achieving excellent lithium anode performance.

[0104] Figure 15 At a high temperature of 60°C and a current density of 0.5 mA / cm², -2 The capacity density is 1 mAh cm⁻¹ -2 SEM images of lithium deposition in a Li-Cu battery containing a 4-cyanotetrahydropyran electrolyte are shown. Even at a high temperature of 60°C, spherical lithium deposits remain, forming smooth planes. This indicates that the electrolyte containing 4-cyanotetrahydropyran and the SEI derived from it are sufficiently stable at high temperatures, which is beneficial for improving the performance of lithium metal batteries at high temperatures.

[0105] Example 5

[0106] An electrolyte containing 4-cyanotetrahydropyran is provided, comprising a lithium salt and a solvent; wherein the solvent is 4-cyanotetrahydropyran, and the lithium salt is LiFSI and LiNO3, with a LiFSI concentration of 1.0 mol / L and a LiNO3 concentration of 0.3 mol / L. Additionally, an electrolyte containing tetrahydropyran (THP) is provided (as a control in this embodiment only), comprising a lithium salt and a solvent, wherein the solvent is tetrahydropyran, and the lithium salt is LiFSI and LiNO3, with a LiFSI concentration of 1.0 mol / L and a LiNO3 concentration of 0.3 mol / L.

[0107] Nuclear magnetic resonance (NMR) spectroscopy analysis was performed on the electrolyte containing 4-cyanotetrahydropyran and the electrolyte containing tetrahydropyran. Raman spectroscopy was performed on the electrolyte containing 4-cyanotetrahydropyran.

[0108] Figure 16 The electrolyte containing 4-cyanotetrahydropyran and the corresponding electrolyte containing tetrahydropyran are shown. 17 O NMR and 7 Li NMR spectrum. The figure shows that, compared to the electrolyte containing tetrahydropyran, the solvent in the electrolyte containing 4-cyanotetrahydropyran... 17 The shift of the O peak to a lower field indicates that the outer electrons have reduced their shielding effect on the atomic nucleus. This is due to the electron-withdrawing effect of -CN, which lowers the electron cloud density on the O atom, thereby reducing the interaction between the O atom and Li. +coordination ability, and further illustrated that N atom in CNTHP dominated the coordination with Li + The obvious shift of Li 7 NMR spectrum peak to high field indicated that the electron cloud density around Li + increased, which produced stronger shielding effect on the nucleus, proving that more anions participated in the first solvation sheath of Li + .

[0109] Figure 17 The Raman spectrum of the electrolyte containing 4-cyanotetrahydropyran was analyzed and processed, and the results showed that the contact ion pair (CIPs) accounted for 73.8% in the solvation configuration of Li + , ion aggregates (AGGs) accounted for 20.0%, and free anions only accounted for 6.2%. The results showed that more cation-anion pairs were produced in the solvation configuration of Li + . Combined with the NMR spectrum analysis of the electrolyte, it can be inferred that in the electrolyte containing 4-cyanotetrahydropyran, the steric hindrance and electron-withdrawing effect of -CN weakens the binding between the solvent molecules and Li + , enhances the coordination of FSI - with Li + , leading to the increase of CIPs and AGGs solvation configuration, which helps to form stable SEI.

[0110] Example 6

[0111] An electrolyte containing 4-cyanotetrahydropyran is provided, which comprises a lithium salt and a solvent; wherein the solvent is 4-cyanotetrahydropyran, the lithium salt is LiFSI and LiNO3, the concentration of LiFSI is 1.0 mol / L, and the concentration of LiNO3 is 0.3 mol / L.

[0112] The electrolyte containing 4-cyanotetrahydropyran obtained in this example is assembled into Li-NMC811 and Li-Cu CR2032 button cells together with NMC811 positive electrode / copper foil, separator, and lithium metal negative electrode.

[0113] Preparation of NMC811 positive electrode: First, mix the active material NMC811, the binder PVDF, and the conductive carbon black Super P in a mass ratio of 8:1:1 uniformly, and dissolve them in N-methylpyrrolidone to prepare a slurry. After stirring uniformly, the slurry is coated on an aluminum foil, and then dried in a vacuum oven at 60 ℃ for 12 hours.

[0114] The thickness of the copper foil is 10 μm, and the diameter is 19 mm.

[0115] The thickness of the lithium metal sheet is 450 μm, and the diameter is 15.6 mm.

[0116] The separator is Celgard 2500, and the diameter is 19 mm.

[0117] The Li-NMC811 coin cell with 4-cyanotetrahydropyran electrolyte was subjected to charge-discharge cycling, and the lithium negative electrode after cycling was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), indentation test and x-ray photoelectron spectroscopy (XPS). The Li-Cu coin cell with 4-cyanotetrahydropyran electrolyte was cycled, and the deposited lithium on the copper mesh after cycling was characterized by cryogenic transmission electron microscopy (Cryo-TEM).

[0118] Figure 18 Figure is the SEM top view image of the lithium metal negative electrode of the Li-NMC811 battery with 4-cyanotetrahydropyran electrolyte after the 50th cycle at a rate of 0.2C, it can be observed that the lithium metal surface is flat and smooth.

[0119] Figure 19 The SEM cross-sectional image of the lithium metal negative electrode of the Li-NMC811 battery with 4-cyanotetrahydropyran electrolyte after the 50th cycle at a rate of 0.2C, lithium presents a dense and uniform deposition. It shows that 4-cyanotetrahydropyran electrolyte effectively avoids the pulverization of lithium and the expansion of the battery, improves the stability and safety of the battery.

[0120] Figure 20 The AFM three-dimensional image of the lithium metal negative electrode of the Li-NMC811 battery with 4-cyanotetrahydropyran electrolyte after the 50th cycle at a rate of 0.2C, the lithium surface is flat and uniform, and the average roughness Ra is only 38.0 nm.

[0121] Figure 21 The force-displacement curve of the lithium negative electrode surface of the Li-NMC811 battery with 4-cyanotetrahydropyran electrolyte after the 50th cycle at a rate of 0.2C. The SEI of the lithium surface achieves a high Young's modulus of 3.65Gpa, indicating that it has sufficient mechanical stability to adapt to the volume change of lithium deposition / stripping, and inhibits the generation of lithium dendrites.

[0122] Figure 22 The XPS depth profile curve of the lithium negative electrode of the Li-NMC811 battery with 4-cyanotetrahydropyran electrolyte after the 5th cycle at a rate of 0.2C, as the sputtering time increases, the signal peaks of LiF and Li3N gradually increase, while the signal peaks in the C1s spectrum gradually decrease, indicating that the inner layer of the SEI is composed of inorganic components rich in LiF and Li3N, and the outer layer contains more organic components, and the SEI presents a double-layer distribution.

[0123] Figure 23At a current density of 0.1 mA cm -2 The capacity is 0.2mAh cm -2 Low-magnification image of lithium deposited in a Li-Cu battery containing 4-cyanotetrahydropyran electrolyte under Cryo-TEM. The lithium is distributed in a spherical shape with a diameter of about 2 μm.

[0124] Figure 24 At a current density of 0.1 mA cm -2 The capacity is 0.2mAh cm -2 High-resolution Cryo-TEM images of lithium deposition in a Li-Cu battery containing 4-cyanotetrahydropyran electrolyte are shown. The inset is the corresponding FFT image, displaying the signals of crystalline Li3N and LiF in the SEI. A regularly distributed bilayer SEI, 20-30 nm thick, is clearly visible on the spherical lithium surface. The inner layer is an inorganic layer composed of highly ordered Li3N and LiF crystals, while the thinner outer layer consists of amorphous organic matter. Li3N and LiF contribute to the deposition of lithium in the SEI. + Rapid and uniform conduction and diffusion on the SEI surface and in the bulk phase, along with the good flexibility of organic materials, help suppress the growth of lithium dendrites, thereby reducing electrolyte consumption and lithium corrosion.

[0125] Figure 25 At a high temperature of 60°C and a current density of 0.1 mA / cm², -2 And a capacity of 0.2mAh cm -2 High-resolution Cryo-TEM images of lithium deposition in a Li-Cu battery containing a 4-cyanotetrahydropyran electrolyte are shown. Even at high temperatures, the SEI (Sediment Injection Layer) maintains a bilayer structure: a thicker inner layer composed of inorganic materials rich in Li3N and LiF, and an outer thin layer rich in amorphous organic matter. This indicates that the electrolyte containing 4-cyanotetrahydropyran and the SEI derived from it are sufficiently stable at high temperatures, thus enabling the battery to exhibit excellent cycle performance at high temperatures.

[0126] Figure 26 This conceptually illustrates the solid electrolyte interface (SEI) structure formed by the ether electrolyte containing 4-cyanotetrahydropyran of the present invention. Figure 27 comparatively illustrates the Li of the present invention. + The strength of coordination in the solvated structure.

[0127] In summary, the electrolyte containing 4-cyanotetrahydropyran solvent provided by this invention uses 4-cyanotetrahydropyran as the sole solvent. The 4-cyanotetrahydropyran molecule has a high boiling point (224°C) and flash point (92.2°C), which is beneficial for achieving the stability and safety of lithium metal batteries at high temperatures. Furthermore, the unique molecular structure of 4-cyanotetrahydropyran regulates the Li... +solvated structure, which promotes the formation of SEI rich in inorganic components, not only avoids the formation of lithium dendrites, but also enhances the Li + The 4-cyanotetrahydropyran-containing electrolyte has a transmission capacity in the bulk phase and the interface phase, and makes the Li-Cu battery have a high coulomb efficiency of 99.3%, and the capacity retention rate of the high-voltage Li-NMC811 battery after 300 cycles is as high as 91%, far exceeding the electrochemical performance of traditional ester electrolytes. Moreover, at a high temperature of 60°C, the capacity retention rate of the Li-NMC811 battery with the 4-cyanotetrahydropyran-containing electrolyte after the 200th cycle is 77.5% (relative to the 4th cycle after activation). Under more severe conditions, the Li-NMC811 soft package battery with the 4-cyanotetrahydropyran-containing electrolyte has a high capacity of 1.25 Ah, and is stably cycled for 50 cycles. Through electrolyte molecular engineering design, the research constructs a stable lithium negative electrode interface, reduces the loss of electrolyte and the corrosion of lithium, realizes the high-temperature performance of the Li-NMC811 battery in the ether electrolyte, and enhances the potential of the practical application of the Li-NMC811 battery. The proposal of the ether electrolyte containing functional functional groups solves the industry pain points of the traditional ether electrolyte, such as insufficient stability and poor high-temperature performance, through solvent molecular structure optimization, and its core advantage can directly adapt to the industrialization demand of high-energy-density lithium metal batteries.

[0128] The above is a further detailed description of the present application in combination with specific / preferred embodiments, and cannot be considered as limiting the specific implementation of the present application to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, without departing from the concept of the present application, they can make several alternatives or modifications to the described embodiments, and these alternatives or modifications shall be considered as belonging to the protection scope of the present application.

Claims

1. An ether electrolyte containing 4-cyanotetrahydropyran, characterized in that, including lithium salts and ether solvents, 4-cyanotetrahydropyran, which reduces the solvation ability of the ether oxygen atom with the electron-withdrawing inductive effect of the cyano group and the steric hindrance of the six-membered ring, and introduces weak coordination sites to facilitate Li + transport, forming a stable solid electrolyte interface (SEI). + ​ 2. The ether electrolyte according to claim 1, wherein The 4-cyanotetrahydropyran is the only solvent in the electrolyte.

3. The ether electrolyte according to claim 1 or 2, wherein The lithium salt includes lithium bisfluorosulfonylimide (LiFSI) and lithium nitrate (LiNO3), wherein the concentration of LiFSI is 0.5-2.0 mol / L, and the concentration of LiNO3 is 0.15-0.3 mol / L.

4. The ether electrolyte according to claim 1 or 2, wherein The total proportion of contact ion pairs (CIPs) and ion aggregates (AGGs) in the solvation structure of Li + in the electrolyte is not less than 90%.

5. A high voltage lithium metal battery, characterized in that, The 4-cyanotetrahydropyran-containing ether electrolyte as claimed in any one of claims 1-4, a positive electrode, a lithium metal negative electrode, a separator, and a lithium battery.

6. The high voltage lithium metal battery of claim 5, wherein, The positive electrode material includes a ternary positive electrode material LiNi 0.8 Mn 0.1 Co 0.1 O2(NMC811), a binder polyvinylidene fluoride (PVDF), and conductive carbon black Super P, with a mass ratio of 8:1:

1.

7. The high-voltage lithium metal battery of claim 6, wherein, The ternary positive electrode material LiNi 0.8 Mn 0.1 Co 0.1 The active material loading of O2(NMC811) is 1.5-2.0 mg / cm 2 .

8. The high voltage lithium metal battery of claim 5, wherein, The negative electrode material is a lithium metal sheet.

9. The high voltage lithium metal battery of claim 5, wherein, The separator is Celgard 2500.

10. The high voltage lithium metal battery of claim 5, wherein, It is a coin cell or a soft pack cell.

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