Titanium-oxygen cluster electrolyte additive as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electrochemical energy storage materials, and particularly relates to a titanium-oxygen cluster electrolyte additive as well as a preparation method and application thereof. The titanium-oxygen cluster and the polycaprolactone derivative are jointly placed in an organic solvent and subjected to an exchange reaction, a modified titanium-oxygen cluster solution is obtained, and after the solvent is volatilized, the titanium-oxygen cluster electrolyte additive is obtained. The preparation method provided by the invention is simple to operate and easy to popularize, and the titanium-oxygen cluster electrolyte additive can be oxidized and decomposed in situ on the surface of an electrode in the battery cycle process to form a TiO2-rich inert interface protection layer only by being mixed into the electrolyte. The titanium-oxygen cluster electrolyte additive can act on a positive electrode interface and a negative electrode interface at the same time, and a formed TiO2 interface protection layer can inhibit surface reactivity, prevent surface reconstruction and impedance accumulation, protect a positive electrode material structure from being damaged, inhibit non-uniform growth of negative electrode lithium dendrites and improve the service life of the lithium ion battery. And the cycling stability and safety of the lithium metal battery under high voltage are effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of electrochemical energy storage materials, and in particular to a titanium oxide cluster electrolyte additive and a preparation method and application thereof. Background Art

[0002] In recent years, with the rapid development of the new energy vehicle industry and the rise of the energy storage market, traditional lithium-ion batteries can no longer meet people's demand for higher energy density due to the theoretical energy density limitations of their positive and negative electrode materials. Metallic lithium has the lowest redox potential (-3.04V) and extremely high theoretical specific capacity (3860mAh / g). Therefore, using lithium metal directly as the negative electrode of lithium secondary batteries and matching it with high-voltage high-nickel ternary positive electrode materials can greatly improve the energy density of lithium batteries. However, such batteries currently have the disadvantages of low cycle efficiency and poor safety, and cannot be commercialized. The main reason is that the surface activity of the positive and negative electrodes is difficult to control, resulting in continuous side reactions with the electrolyte during the cycle, resulting in a poor electrode-electrolyte interface. On the positive electrode side, the high-nickel ternary positive electrode material has a decreased thermodynamic stability under high voltage conditions, and produces violent side reactions with the electrolyte, resulting in structural degradation, microcracks, dissolution with transition metal ions, and mixed discharge of metal cations, resulting in a decrease in the cycle life and performance of the battery. On the negative electrode side of lithium metal, uncontrollable lithium dendrite growth will not only penetrate the separator, causing internal short circuits in the battery and creating safety issues, but will also form "dead lithium", thereby increasing the interface resistance. It can be seen that the unstable interface causes the volume of lithium metal to change infinitely, ultimately causing battery performance to deteriorate.

[0003] Therefore, it is very important to reduce the surface reactivity of the positive and negative electrode materials to inhibit the side reactions of the electrode electrolyte. An effective strategy is to modify an inert protective layer on the surface of the positive and negative electrodes, such as TiO 2 、Al 2 O 3 Metal oxides are coated on the surface of the positive and negative electrodes to form a passivation layer, establishing a physical barrier between the electrode surface and the electrolyte to inhibit the occurrence of side reactions. However, it is challenging to directly coat the positive and negative electrode surfaces with a uniform, fully conformal inert coating. Currently, most studies are to fully mix the positive electrode particles and metal oxides and then sinter them at high temperatures to attach an inert protective layer to the surface of the positive electrode material. Although this method can successfully reduce the surface reactivity of the positive electrode material, it is easy to damage the structure of the positive electrode material and is difficult to apply to the surface of the lithium metal negative electrode. Summary of the invention

[0004] In order to solve the deficiencies of the above-mentioned prior art, the present invention provides a titanium oxide cluster electrolyte additive and a preparation method and application thereof. The present invention forms an inert protective layer in situ on the surfaces of the positive and negative electrodes simultaneously through the strategy of oxidative decomposition of the additive. The present invention uses titanium oxide clusters and polycaprolactone derivatives as raw materials, mixes the two in an organic solvent, and then performs a functional group exchange reaction. The titanium oxide clusters are modified with polycaprolactone derivatives to improve the solubility of the titanium oxide clusters in the electrolyte, and then vacuum dried to obtain a titanium oxide cluster electrolyte additive. In response to the problems of electrolyte corrosion and instability of solid electrolyte interface films existing in existing high-voltage lithium metal batteries, the present invention provides a titanium oxide cluster electrolyte additive for high-voltage lithium metal batteries. The obtained titanium oxide cluster electrolyte additive can be oxidatively decomposed in situ at the interface of the positive and negative electrodes during the battery cycle, forming a layer of inert TiO 2 The interface protective layer, the protective layer formed in situ not only does not damage the structure of the positive electrode material, but also can achieve close fit with the surface of the positive and negative electrodes, reduce the interface resistance, and to a certain extent overcome the technical defects of the existing technology of coating the inert protective layer.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for preparing a titanium oxide cluster electrolyte additive comprises the following steps:

[0007] Titanium oxide clusters and polycaprolactone derivatives are dissolved together in an organic solvent. In the solution phase, the unstable sites of monodentate coordinated ethylene glycol on the surface of the titanium oxide clusters are easily exchanged by functional groups in the solution. The polycaprolactone derivatives contain a large number of ester groups. At this time, the unstable sites of monodentate coordinated ethylene glycol on the surface of the titanium oxide clusters undergo exchange reactions with the ester groups of the polycaprolactone derivatives, thereby modifying the titanium oxide clusters with ester functional groups, thereby producing a modified titanium oxide cluster solution with multiple surface functions.

[0008] The solvent of the modified titanium oxide cluster solution is volatilized under vacuum conditions. The modified titanium oxide clusters are easily hydrolyzed when exposed to moisture in the air, so vacuum conditions are required to volatilize them to obtain titanium oxide cluster electrolyte additives. The titanium oxide cluster electrolyte additive contains ester groups, which makes it easy to dissolve in carbonate electrolytes, overcoming the technical defect of poor solubility of titanium oxide clusters in electrolytes, and then realizing the application of titanium oxide clusters as titanium oxide cluster electrolyte additives.

[0009] In a preferred embodiment of the present invention, the mass percentage of the titanium oxide clusters in the organic solvent is 5 wt % to 20 wt %. Too little solvent will not allow the titanium oxide clusters to be completely dissolved, while too much solvent will be detrimental to the volatilization of the solvent.

[0010] In a preferred embodiment of the present invention, the organic solvent is selected from dichloromethane, chloroform, dichloropropane or dimethyl sulfoxide.

[0011] In a preferred embodiment of the present invention, the titanium oxide cluster is selected from spherical titanium oxide clusters, polyhedral titanium oxide clusters, ring titanium oxide clusters or heterometallic wheel titanium oxide clusters.

[0012] In a preferred embodiment of the present invention, the conditions for the exchange reaction are: stirring the reaction at 25-35°C for 2-4h. If the reaction time is too short, the reaction is incomplete; if the reaction time is too long, the titanium oxide clusters are easily decomposed; the reaction temperature range is mainly carried out at room temperature. Too high or too low temperature will affect the stability of the titanium oxide clusters and the structure of the polycaprolactone derivatives, thereby affecting the experimental results.

[0013] In a preferred embodiment of the present invention, the polycaprolactone derivative is selected from one of polycaprolactone diol, polycaprolactone triol, polycaprolactone dimethacrylate, and polycaprolactone trimethacrylate, the mass ratio of the polycaprolactone derivative to the titanium oxide cluster is 1 to 10:1, and the amount of the polycaprolactone derivative ≥ the amount of the titanium oxide cluster promotes the modification of the ester functional group.

[0014] Another object of the present invention is to provide a titanium oxide cluster electrolyte additive prepared by the above preparation method.

[0015] The third object of the present invention is to provide the use of the above-mentioned titanium oxide cluster electrolyte additive in the preparation of a high-voltage lithium metal battery electrolyte additive. The application method is: the titanium oxide cluster electrolyte additive is fully stirred and dissolved in a commercial carbonate electrolyte. The titanium oxide cluster electrolyte additive will be in situ oxidized and decomposed on the surface of the positive and negative electrodes during the battery cycle to form a layer rich in TiO 2 The inert interface layer, the mass percentage of the titanium oxide cluster electrolyte additive in the carbonate electrolyte is 0.5wt% to 5wt%. If the titanium oxide cluster electrolyte additive is too little, there will be no obvious improvement effect. If it is too much, unnecessary components will be introduced, which will reduce the battery performance.

[0016] In a preferred embodiment of the present invention, the stirring speed is 400-800 r / min, and the stirring and dissolving time is 4 h to 24 h.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The present invention uses titanium oxide clusters and polycaprolactone derivatives as raw materials, mixes the two in an organic solvent, and then the unstable sites of monodentate coordinated ethylene glycol on the surface of the titanium oxide clusters undergo exchange reaction with the ester groups of the polycaprolactone derivatives, and then vacuum-drying is performed to obtain a titanium oxide cluster electrolyte additive.

[0019] The titanium oxide cluster of the present invention is a crystalline metal oxide cluster material with a size between atoms and nanoparticles, which has both excellent aggregation activity of nanoparticles and a structure that can be accurately measured. However, studies have shown that the solubility of titanium oxide clusters in electrolytes is very poor and is basically insoluble, so they need to be modified before they can be used.

[0020] The titanium oxide cluster has multiple functional group sites, among which the unstable sites of monodentate coordinated ethylene glycol are easily exchanged by functionalized functional groups, so that the titanium oxide cluster obtains specific functions. The polycaprolactone derivative of the present invention contains a large number of ester groups, and the ester groups of the polycaprolactone derivatives are exchanged with the unstable sites of monodentate coordinated ethylene glycol on the surface of the titanium oxide cluster, and then a large number of ester functional groups are modified on the titanium oxide cluster to obtain a titanium oxide cluster electrolyte additive, and the TiO 2 Nanomaterials play an important role in the interface layer of the positive and negative electrodes of lithium metal batteries. They can improve electrochemical stability, improve ion transport, inhibit lithium dendrite growth, alleviate volume expansion, increase interface stability and improve conductivity, significantly improving the performance and safety of lithium metal batteries.

[0021] 2. The present invention utilizes the principle of like dissolves like, dissolves the obtained titanium oxide cluster electrolyte additive in a carbonate electrolyte, and obtains a high-voltage lithium metal battery electrolyte. By adding the titanium oxide cluster electrolyte additive to the electrolyte, during the battery cycle, a layer rich in TiO is formed by in-situ oxidation and decomposition at the positive and negative electrodes. 2 This method is fundamentally different from the currently common method of directly coating the positive and negative electrode surfaces with a metal oxide inert protective layer. The inert protective layer formed by in-situ decomposition as an electrolyte additive will not only not destroy the surface structure of the positive and negative electrode materials, but also ensure good interface contact with the positive and negative electrode surfaces, thereby reducing interface resistance.

[0022] The present invention uses metal oxygen clusters as electrolyte additives to form an inert protective layer in situ on the surface of the positive and negative electrodes, which is similar to the solid electrolyte interphase (SEI) forming additives commonly used in graphite negative electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 In the figure, (a) is a dissolution diagram of the titanium oxide cluster electrolyte additive in Example 1 in the carbonate electrolyte, and (b) is a dissolution diagram of the titanium oxide cluster in the carbonate electrolyte.

[0024] Figure 2In the figure, Figure A is an SEM image and corresponding mapping diagram of the surface of the high-nickel ternary positive electrode material of the lithium metal battery assembled using the high-voltage lithium metal battery electrolyte of Example 1 after cycling, and Figure B is an SEM image and corresponding mapping diagram of the cross-section of the high-nickel ternary positive electrode material of the lithium metal battery assembled using the high-voltage lithium metal battery electrolyte of Example 1 after cycling.

[0025] Figure 3 In the figure, Figure A is an SEM image and corresponding mapping diagram of the surface of the lithium metal negative electrode material of the lithium metal battery assembled using the high-voltage lithium metal battery electrolyte of Example 1 after cycling, and Figure B is an SEM image and corresponding mapping diagram of the cross-section of the lithium metal negative electrode material of the lithium metal battery assembled using the high-voltage lithium metal battery electrolyte of Example 1 after cycling.

[0026] Figure 4 The hydrogen nuclear magnetic resonance spectra of the titanium oxide cluster electrolyte additive, titanium oxide cluster and polycaprolactone derivative of Example 1 and Example 3 are shown.

[0027] Figure 5 This is a Ti2p diagram of an X-ray photoelectron spectroscopy test on the surface of a high-nickel ternary positive electrode material after cycling a lithium metal battery assembled using the high-voltage lithium metal battery electrolyte of Example 1.

[0028] Figure 6 In the figure, Figure A is a cycle performance diagram of a lithium metal battery assembled with high-nickel ternary positive electrode materials having different nickel contents; Figure B is a charge and discharge curve diagram of a lithium metal battery assembled with high-nickel ternary positive electrode materials having different nickel contents.

[0029] Figure 7 This is a cycle performance diagram of a lithium metal battery assembled using the high-voltage lithium metal battery electrolyte of Example 1 and high-nickel ternary positive electrode materials of nickel, cobalt and manganese with different loadings.

[0030] Figure 8 This is a cycle performance diagram of a lithium metal battery assembled using the high-voltage lithium metal battery electrolyte of Example 1 at a high cut-off voltage of 4.5V.

[0031] Fig. 9 This is a comparison chart of the rate performance of batteries assembled using the high-voltage lithium metal battery electrolyte of Example 1 and the electrolyte of Comparative Example 1. DETAILED DESCRIPTION

[0032] The following is a detailed description of the technical solutions in the embodiments of the present invention in combination with the preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] It should be noted that all professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods.

[0034] The present invention provides a titanium oxide cluster electrolyte additive that can be applied to high-voltage lithium metal batteries, wherein the titanium oxide cluster is modified by an exchange reaction with a polycaprolactone derivative to obtain the function of an ester functional group, and then dissolved into a commercial carbonate electrolyte according to the principle of like dissolves like, and in situ oxidatively decomposes on the surface of the positive and negative electrodes during the battery cycle to form a TiO-rich 2 Inert interface protective layer. On the positive electrode side, this inert protective layer can effectively prevent cracks in the high-nickel ternary positive electrode sheet, ensuring the structural stability of the positive electrode during cycling; on the negative electrode side, this inert protective layer tightly adheres to the surface of lithium metal, effectively inhibiting the growth of lithium dendrites, promoting uniform deposition of lithium ions, isolating lithium metal from contacting the electrolyte to produce side reactions, and effectively improving the cycle stability and safety performance of lithium metal batteries.

[0035] Example 1

[0036] A method for preparing a titanium oxide cluster electrolyte additive comprises the following steps:

[0037] (1) Weigh 0.15 g of cyclic titanium oxide clusters, add them into 2 mL of dichloromethane, stir them thoroughly to dissolve, and obtain a light yellow transparent cyclic titanium oxide cluster solution.

[0038] (2) Weigh 0.5 g of polycaprolactone triol and add it to the cyclic titanium oxide cluster solution. After stirring and reacting at 25° C. for 4 h, a modified titanium oxide cluster solution is obtained.

[0039] (3) placing the modified titanium oxide cluster solution in a vacuum oven and volatilizing the organic solvent at 30° C. to obtain a titanium oxide cluster electrolyte additive.

[0040] Preparation of high voltage lithium metal battery electrolyte:

[0041] 0.06 g of the titanium oxide cluster electrolyte additive was weighed and added to 3 mL of a commercial carbonate electrolyte, and the mixture was stirred at 500 r / min for 4 h to dissolve, thereby obtaining a high-voltage lithium metal battery electrolyte containing 2 wt % of the titanium oxide cluster electrolyte additive.

[0042] Example 2

[0043] A method for preparing a titanium oxide cluster electrolyte additive comprises the following steps:

[0044] (1) Weigh 0.20 g of spherical titanium oxide clusters, add them into 3 mL of chloroform, stir them thoroughly to dissolve, and obtain a light yellow transparent spherical titanium oxide cluster solution.

[0045] (2) Weigh 0.6 g of polycaprolactone triol and add it to the spherical titanium oxide cluster solution. After stirring and reacting at 25° C. for 4 h, a modified titanium oxide cluster solution is obtained.

[0046] (3) placing the modified titanium oxide cluster solution in a vacuum oven and volatilizing the organic solvent at 30° C. to obtain a titanium oxide cluster electrolyte additive.

[0047] Preparation of high voltage lithium metal battery electrolyte:

[0048] 0.06 wt% of the titanium oxide cluster electrolyte additive was weighed and added to 2 mL of a commercial carbonate electrolyte, and the mixture was stirred at 600 r / min for 6 h to dissolve, thereby obtaining a high-voltage lithium metal battery electrolyte containing 3 wt% of the titanium oxide cluster electrolyte additive.

[0049] Example 3

[0050] A method for preparing a titanium oxide cluster electrolyte additive comprises the following steps:

[0051] (1) Weigh 0.3 g of cyclic titanium oxide clusters, add them into 2 mL of dichloromethane, stir them thoroughly to dissolve, and obtain a light yellow transparent cyclic titanium oxide cluster solution.

[0052] (2) Weigh 0.3 g of polycaprolactone diol and add it to the cyclic titanium oxide cluster solution. After stirring and reacting at 25° C. for 3 h, a modified titanium oxide cluster solution is obtained.

[0053] (3) placing the modified titanium oxide cluster solution in a vacuum oven and volatilizing the organic solvent at 30° C. to obtain a titanium oxide cluster electrolyte additive.

[0054] Preparation of high voltage lithium metal battery electrolyte:

[0055] 0.06 g of the titanium oxide cluster electrolyte additive was weighed and added to 6 mL of a commercial carbonate electrolyte, and the mixture was stirred at 700 r / min for 12 h to dissolve, thereby obtaining a high-voltage lithium metal battery electrolyte containing 1 wt % of the titanium oxide cluster electrolyte additive.

[0056] Example 4

[0057] A method for preparing a titanium oxide cluster electrolyte additive comprises the following steps:

[0058] (1) Weigh 0.20 g of polyhedral titanium oxide clusters, add them into 2 mL of dichloromethane, stir them thoroughly to dissolve, and obtain a light yellow transparent polyhedral titanium oxide cluster solution.

[0059] (2) Weigh 0.8 g of polycaprolactone dimethacrylate and add it to the polyhedral titanium oxide cluster solution. After stirring and reacting at 30° C. for 2 h, a modified titanium oxide cluster solution is obtained.

[0060] (3) placing the modified titanium oxide cluster solution in a vacuum oven and volatilizing the organic solvent at 35° C. to obtain a titanium oxide cluster electrolyte additive.

[0061] Preparation of high voltage lithium metal battery electrolyte:

[0062] 0.1 g of the titanium oxide cluster electrolyte additive was weighed and added to 2 mL of a commercial carbonate electrolyte, and the mixture was stirred at 800 r / min for 5 h to dissolve, thereby obtaining a high-voltage lithium metal battery electrolyte containing 5 wt % of the titanium oxide cluster electrolyte additive.

[0063] Example 5

[0064] A method for preparing a titanium oxide cluster electrolyte additive comprises the following steps:

[0065] (1) Weigh 0.40 g of heterometallic wheel-shaped titanium oxide clusters, add them into 3 mL of dimethyl sulfoxide, stir them thoroughly to dissolve, and obtain a light yellow transparent heterometallic wheel-shaped titanium oxide cluster solution.

[0066] (2) Weigh 1 g of polycaprolactone trimethacrylate and add it to the heterometallic wheel-shaped titanium oxide cluster solution. After stirring and reacting at 25° C. for 4 h, a modified titanium oxide cluster solution is obtained.

[0067] (3) placing the modified titanium oxide cluster solution in a vacuum oven and volatilizing the organic solvent at 40° C. to obtain a titanium oxide cluster electrolyte additive.

[0068] Preparation of high voltage lithium metal battery electrolyte:

[0069] 0.08 g of the titanium oxide cluster electrolyte additive was weighed and added to 2 mL of a commercial carbonate electrolyte, and stirred at 600 r / min for 10 h to dissolve, thereby obtaining a high-voltage lithium metal battery electrolyte containing 4 wt % of the titanium oxide cluster electrolyte additive.

[0070] Example 6

[0071] A method for preparing a titanium oxide cluster electrolyte additive comprises the following steps:

[0072] (1) Weigh 0.25 g of polyhedral titanium oxide clusters, add them into 2 mL of dichloropropane, stir them thoroughly to dissolve, and obtain a light yellow transparent polyhedral titanium oxide cluster solution.

[0073] (2) Weigh 2.5 g of polycaprolactone triol and add it to the polyhedral titanium oxide cluster solution. After stirring and reacting at 30° C. for 3 h, a modified titanium oxide cluster solution is obtained.

[0074] (3) placing the modified titanium oxide cluster solution in a vacuum oven and volatilizing the organic solvent at 30° C. to obtain a titanium oxide cluster electrolyte additive.

[0075] Preparation of high voltage lithium metal battery electrolyte:

[0076] 0.04 g of the titanium oxide cluster electrolyte additive was weighed and added to 2 mL of a commercial carbonate electrolyte, and the mixture was stirred at 600 r / min for 6 h to dissolve, thereby obtaining a high-voltage lithium metal battery electrolyte containing 2 wt % of the titanium oxide cluster electrolyte additive.

[0077] Comparative Example 1

[0078] Commercial carbonate electrolyte.

[0079] Examples 1-6 of the present invention all prepare titanium oxide cluster electrolyte additives that can be in situ oxidatively decomposed at the interface of the positive and negative electrodes to form an inert interface protective layer, and use the titanium oxide cluster electrolyte additives to prepare high-voltage lithium metal battery electrolytes. The titanium oxide cluster electrolyte additives and high-voltage lithium metal battery electrolytes of Examples 1 and 3 are used as examples for research, and are compared with Comparative Example 1. The specific research methods and results are as follows:

[0080] 1. Morphology test

[0081] (1) Macromorphology test

[0082] Taking the titanium oxide cluster electrolyte additive and the ring-shaped titanium oxide cluster of Example 1 as an example, the macroscopic morphology thereof was tested. The test results are as follows: Figure 1 shown.

[0083] (a) shows the dissolution of the titanium oxide cluster electrolyte additive in Example 1 in a commercial carbonate electrolyte, and (b) shows the dissolution of the cyclic titanium oxide cluster in a commercial carbonate electrolyte. Figure 1 It can be seen that titanium oxide clusters themselves are insoluble in commercial carbonate electrolytes and cannot be used as electrolyte additives. However, titanium oxide cluster electrolyte additives modified with polycaprolactone derivatives have a large number of ester functional groups and can be dissolved in commercial carbonate electrolytes and used as functional additives.

[0084] (2) Micromorphology test

[0085] Test method: After assembling the lithium metal battery, the lithium metal battery is cycled. The assembly method of the lithium metal battery is as follows: a commercial lithium sheet with a diameter of 16 mm is used as the negative electrode, an industrialized NCM811 high-nickel ternary positive electrode material is used as the positive electrode, the electrolyte is the high-voltage lithium metal battery electrolyte of Example 1, the diaphragm is a PP diaphragm (polypropylene diaphragm), and the battery shell model is CR2032.

[0086] The cycle conditions are as follows: the first two cycles are charged and discharged at a rate of 0.2C to activate the battery, and then a charge and discharge rate of 1C is used for the charge and discharge cycle test. The test temperature is 25°C, the charge and discharge voltage range is 3.0-4.3V, and the number of cycles is 50.

[0087] The titanium oxide cluster electrolyte additive of Example 1 is used to in-situ oxidatively decompose the titanium oxide cluster electrolyte additive at the positive and negative electrode interfaces during the lithium metal battery cycle to form a TiO-rich 2 Taking the inert interface protective layer of the lithium metal battery as an example, the surface and cross-sectional micromorphology and element distribution of the positive and negative electrodes of the lithium metal battery before and after cycling were characterized and tested, and the test results are as follows: Figure 2 and Figure 3 shown.

[0088] Depend on Figure 2 and Figure 3 It can be seen that after cycling, the particle surface of the NCM811 high-nickel ternary cathode material has obvious Ti, O, and C element signal mapping, indicating that the prepared titanium oxide cluster electrolyte additive successfully oxidized and decomposed in situ on the surface of the NCM811 high-nickel ternary cathode material to uniformly form a TiO-rich 2 inert protective layer.

[0089] 2. Nuclear Magnetic Resonance Test (NMR)

[0090] Taking the titanium oxide cluster electrolyte additives prepared in Example 1 and Example 3 as examples, nuclear magnetic resonance tests were performed on the titanium oxide cluster electrolyte additives, titanium oxide clusters and polycaprolactone derivatives, respectively. The test results are as follows: Figure 4 shown.

[0091] And by Figure 4It can be seen that the titanium oxide cluster electrolyte additive retains most of the characteristic peaks of titanium oxide clusters and polycaprolactone derivatives, but the hydrogen signal with a chemical shift of about 1.5 ppm has a significant decrease relative to the polycaprolactone derivative. It can be seen that the polycaprolactone derivative has a ligand exchange reaction with the titanium oxide cluster, and the ester group has been successfully modified on the titanium oxide cluster to obtain a functionalized titanium oxide cluster electrolyte additive.

[0092] 3. X-ray photoelectron spectroscopy (XPS)

[0093] Taking the titanium oxide cluster electrolyte additive prepared in Example 1 as an example, the NCM811 high nickel ternary cathode material after cycling was tested by X-ray photoelectron spectroscopy. The test results are as follows: Figure 5 shown.

[0094] Depend on Figure 5 It can be seen that Ti2p has two peaks at binding energies of 458.34 eV and 464.12 eV, corresponding to Ti2p 3 / 2 and Ti2p 1 / 2 , with TiO 2 This further illustrates that the functionalized titanium oxide cluster electrolyte additive oxidizes and decomposes on the surface of NCM811 high nickel ternary cathode material during the battery cycle to form TiO 2 , TiO 2 Participates in the formation of an inert interface protective layer.

[0095] 4. Cycle performance test

[0096] (1) Test on the effect of different nickel contents and different loadings of high nickel ternary cathode materials on the cycle performance of lithium metal batteries:

[0097] Taking the high-voltage lithium metal battery electrolyte of Example 1 as an example, the cycle performance of lithium metal batteries was tested for high nickel ternary cathode materials with different nickel contents and different nickel, cobalt and manganese loadings according to the following test methods. The test results are as follows: Figure 6 and Figure 7 shown.

[0098] Test method: A commercial lithium sheet with a diameter of 16 mm was used as the negative electrode, and different nickel contents (including Ni80, Ni86, Ni96) and different nickel, cobalt and manganese loadings (including 12 mg / cm 2 , 20mg / cm 2 、28mg / cm 2 ) is the positive electrode, the electrolyte is the high-voltage lithium metal battery electrolyte of Example 1, the diaphragm is a PP diaphragm (polypropylene diaphragm), and the battery shell model is CR2032.

[0099] Test conditions: The first two cycles are charged and discharged at a rate of 0.2C to activate the battery, and then the charge and discharge cycle test is performed at a rate of 1C. The test temperature is 25°C and the charge and discharge voltage range is 3.0~4.3V.

[0100] Depend on Figure 6 and Figure 7 The test results show that in the assembled lithium metal batteries, no matter whether they are matched with different nickel contents or different loadings of high-nickel ternary positive electrode materials, the high-nickel ternary positive electrode materials can undergo stable charge and discharge cycles, indicating that titanium oxide cluster electrolyte additives are universal in improving the cycle stability of lithium metal batteries.

[0101] (2) Cycling performance test of high nickel cathode lithium metal battery under high voltage:

[0102] Taking the high voltage lithium metal battery electrolyte of Example 1 as an example, the high voltage cycle performance of the lithium metal battery was tested according to the following test method. The test results are as follows: Figure 8 shown.

[0103] Test method: A commercial lithium sheet with a diameter of 16 mm was used as the negative electrode, and NCM811 high-nickel ternary positive electrode material was used as the positive electrode. The nickel, cobalt and manganese loading of NCM811 high-nickel ternary positive electrode material was 12 mg / cm 2 The electrolyte is the high-voltage lithium metal battery electrolyte of Example 1, the diaphragm is a PP diaphragm (polypropylene diaphragm), and the battery shell model is CR2032.

[0104] Test conditions: The first two cycles are charged and discharged at a rate of 0.2C to activate the battery, and then the charge and discharge cycle test is performed at a rate of 0.5C. The test temperature is 25°C and the charge and discharge voltage range is 3.0-4.5V.

[0105] Depend on Figure 8 It can be seen that after using the high-voltage lithium metal battery electrolyte of Example 1, the lithium metal battery not only exhibits a higher energy density at a high cut-off voltage, but also maintains a relatively stable cycle performance.

[0106] 5. Rate performance test

[0107] According to the following method, Example 1 and Comparative Example 1 were assembled into button batteries, and their rate performance was tested respectively. The test results are shown in FIG. Fig. 9 shown.

[0108] Test method of Example 1: A commercial lithium sheet with a diameter of 16 mm is used as the negative electrode, NCM811 high-nickel ternary positive electrode material is used as the positive electrode, and the nickel, cobalt and manganese loading is 12 mg / cm 2 The electrolyte is the high-voltage lithium metal battery electrolyte of Example 1, the diaphragm is a PP diaphragm (polypropylene diaphragm), and the battery shell model is CR2032.

[0109] The test method of comparative example 1 is as follows: a positive electrode with a polymer protective layer, a negative electrode with a polymer protective layer, a commercial carbonate electrolyte, a PP diaphragm (polypropylene diaphragm) and a battery shell are assembled, and the battery shell model is CR2032.

[0110] Test conditions: charge and discharge tests were carried out at 0.2C, 0.5C, 1C, 2C, 3C, 4C, and 5C conditions, with current density increasing first and then decreasing (1C = 200mAh / g), the test temperature was 25°C, and the charge and discharge voltage range was 3.0V to 4.3V.

[0111] Depend on Fig. 9 The test results show that the use of the titanium oxide cluster electrolyte additive in Example 1 can make the lithium metal battery have better rate performance, and to a large extent alleviate the specific capacity decay of the lithium metal battery under high rate charge and discharge. And under the high rate 5C charge and discharge conditions, the cycle performance of the battery in Comparative Example 1 is unstable. In contrast, the battery in Example 1 still maintains a stable cycle with a higher capacity.

[0112] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a titanium oxide cluster electrolyte additive, characterized in that: The following steps are involved: The titanium oxide cluster and the polycaprolactone derivative are dissolved in an organic solvent, the monodentate coordinated ethylene glycol on the surface of the titanium oxide cluster is an unstable site, the ethylene glycol and the ester group of the polycaprolactone derivative undergo an exchange reaction, and the ester functional group is modified on the titanium oxide cluster to obtain a modified titanium oxide cluster solution; The solvent of the modified titanium oxide cluster solution is volatilized under vacuum conditions to obtain a titanium oxide cluster electrolyte additive.

2. The method for preparing a titanium oxide cluster electrolyte additive according to claim 1, characterized in that: The exchange reaction conditions are: stirring the reaction at 25-35°C for 2-4 hours.

3. The method for preparing a titanium oxide cluster electrolyte additive according to claim 1, characterized in that: The mass ratio of the titanium oxide cluster to the polycaprolactone derivative is 1:1-10.

4. The method for preparing a titanium oxide cluster electrolyte additive according to claim 1, characterized in that: The mass percentage of the titanium oxide clusters in the organic solvent is 5wt% to 20wt%.

5. The method for preparing a titanium oxide cluster electrolyte additive according to claim 1, characterized in that: The titanium oxide cluster is selected from spherical titanium oxide clusters, polyhedral titanium oxide clusters, ring titanium oxide clusters or heterometallic wheel titanium oxide clusters.

6. The method for preparing a titanium oxide cluster electrolyte additive according to claim 1, characterized in that: The polycaprolactone derivative is selected from polycaprolactone diol, polycaprolactone triol, polycaprolactone dimethacrylate or polycaprolactone trimethacrylate.

7. The method for preparing a titanium oxide cluster electrolyte additive according to claim 1, characterized in that: The organic solvent is selected from dichloromethane, chloroform, dichloropropane or dimethyl sulfoxide.

8. A titanium oxide cluster electrolyte additive prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the titanium oxide cluster electrolyte additive according to claim 8 in preparing a high-voltage lithium metal battery electrolyte.

10. The use according to claim 9, characterized in that: The application method is: Adding a titanium oxide cluster electrolyte additive to the electrolyte and completely dissolving it to obtain a high voltage lithium metal battery electrolyte; The electrolyte is selected from carbonate electrolyte, and the mass percentage of the titanium oxide cluster electrolyte additive in the carbonate electrolyte is 0.5wt% to 5wt%.

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