Additive composition for lithium metal battery electrolyte, electrolyte, preparation method of electrolyte and lithium metal battery

Abstract

The invention provides an additive composition for an electrolyte of a lithium metal battery, the electrolyte, a preparation method of the electrolyte and the lithium metal battery, and the additive composition comprises vinylene carbonate, lithium nitrate and fluoroborate. The electrolyte for the lithium metal battery comprises a basic electrolyte and an additive, and the additive is the additive composition for the electrolyte for the lithium metal battery; based on the total volume of the basic electrolyte, the volume fraction of the vinylene carbonate is 1-3 vol%, the concentration of the lithium nitrate is 0.2-0.6 mol / L, and the concentration of the fluoborate is 0.01-0.03 mol / L. The LiNCM811 total battery using the electrolyte containing the additive composition provided by the invention shows excellent cycling stability, and the rate capability is good.

Description

Technical Field

[0001] The present invention relates to an additive composition for lithium metal battery electrolyte, electrolyte and preparation method thereof, and lithium metal battery, belonging to the technical field of lithium metal batteries. Background Art

[0002] With the increasing demand for high energy density batteries, lithium metal anode (LMA) and nickel-rich layered oxide cathode (such as LiNi 0.8 Co 0.1 Mn 0.1 The combination of Li||NCM811 (LiO2) has become a research hotspot. However, practical applications of Li||NCM811 batteries face numerous challenges, such as poor electrode-electrolyte interface stability, severe microstructural degradation, and uncontrollable electrolyte side reactions. These challenges significantly limit battery applications and pose significant safety risks. Electrolyte design is an effective approach to addressing these issues, and utilizing electrolyte additives to efficiently and cost-effectively design modified electrolytes is a key approach to addressing existing challenges in high-energy-density batteries.

[0003] Recently, the use of film-forming additives to modify electrolytes has become a focus of attention. Among them, lithium nitrate (LiNO3) is a commonly used film-forming additive in ether-based electrolytes. It can adjust the composition of the solid electrolyte interface (SEI), improve the lithium deposition morphology, inhibit side reactions, and improve the lithium coulombic efficiency. However, ether-based electrolytes decompose when the voltage exceeds 4V and are not compatible with NCM811 cathodes. In addition, LiNO3 has low solubility in oxidatively stable carbonate-based electrolytes, which greatly limits its application.

[0004] Therefore, developing strategies to improve the solubility of LiNO3 in carbonate-based electrolytes is crucial. Summary of the Invention

[0005] In order to solve the above-mentioned shortcomings and deficiencies, the object of the present invention is to provide an additive composition for lithium metal battery electrolyte, electrolyte and preparation method thereof, and lithium metal battery.

[0006] To achieve the above objectives, in one aspect, the present invention provides an additive composition for lithium metal battery electrolyte, wherein the additive composition comprises vinylene carbonate, lithium nitrate and fluoroborate.

[0007] As a specific embodiment of the additive composition of the present invention, wherein the fluoroborate comprises an inorganic fluoroborate M n (BF4) m and one or more combinations of organic fluoroborate R-BF3M;

[0008] Wherein, M includes one or more elements selected from aluminum, copper, lead, tin, nickel, zinc, cadmium, beryllium, magnesium, calcium, strontium, barium, cesium, rubidium, manganese, iron, cobalt, silver, indium and thallium; R includes one or more organic groups selected from hydrocarbons, alcohols, ethers, esters, ketones, carboxylic acids, phenols and the like; 0.2≤n≤5, 0.2≤m≤8.

[0009] As a specific embodiment of the additive composition described above, the fluoroborate is one or a combination of zinc tetrafluoroborate, magnesium tetrafluoroborate, silver tetrafluoroborate, and stannous tetrafluoroborate.

[0010] On the other hand, the present invention also provides an electrolyte for a lithium metal battery, comprising a base electrolyte and an additive, wherein the additive is the additive composition for a lithium metal battery electrolyte described above;

[0011] Based on the total volume of the basic electrolyte, the volume fraction of vinylene carbonate is 1-3 vol%, the concentration of lithium nitrate is 0.2-0.6 mol / L, and the concentration of fluoroborate is 0.01-0.03 mol / L;

[0012] Preferably, based on the total volume of the basic electrolyte, the volume fraction of vinylene carbonate is 2 vol%, the concentration of lithium nitrate is 0.4 mol / L, and the concentration of fluoroborate is 0.02 mol / L.

[0013] As a specific embodiment of the electrolyte described above in the present invention, the basic electrolyte comprises a carbonate solvent and a lithium salt, wherein the concentration of the lithium salt is 0.7-1.5M, preferably 1M, based on the total volume of the carbonate solvent.

[0014] As a specific embodiment of the electrolyte of the present invention, the carbonate solvent includes ethylene carbonate (EC) and diethyl carbonate (DEC);

[0015] And / or the lithium salt includes at least one of LiPF6, LiBF4, LiClO4, LiAsF6, etc.

[0016] As a specific embodiment of the above-mentioned electrolyte of the present invention, the volume ratio of ethylene carbonate to diethyl carbonate is 3:7-6:4, preferably 1:1.

[0017] In another aspect, the present invention further provides a method for preparing the electrolyte for a lithium metal battery as described above, wherein the preparation method comprises:

[0018] Vinylene carbonate, lithium nitrate and fluoroborate are sequentially added to the basic electrolyte, and stirred evenly in a glove box to obtain the electrolyte for lithium metal batteries.

[0019] As a specific embodiment of the preparation method described above of the present invention, the electrolyte for lithium metal batteries is obtained by stirring in a glove box at a temperature of 40-80° C., preferably 50° C., for 2-6 hours, preferably 4 hours.

[0020] On the other hand, the present invention also provides a lithium metal battery, comprising a positive electrode, an electrolyte and a negative electrode, wherein the electrolyte is the electrolyte for lithium metal batteries described above.

[0021] Compared with the prior art, the beneficial technical effects achieved by the present invention include:

[0022] The additive composition of the present invention utilizes a "small-size carrier solubilizer" strategy, with vinylene carbonate (VC) as the key additive. It also contains lithium nitrate (LiNO3) and fluoroborate. VC, with its moderate molecular polarity and small size, serves as a solvent carrier for the lithium nitrate. When added to an electrolyte for lithium metal batteries containing a carbonate solvent, VC improves the solubility of LiNO3 in the carbonate solvent, optimizes the electrolyte solvation structure, and enhances the stability of the electrode-electrolyte interface. At lithium metal anodes, it can inhibit side reactions and dendrite growth; at cathodes, such as NCM811 cathodes, it can mitigate irreversible phase transitions and transition metal dissolution, improving ion transport kinetics.

[0023] In summary, the additive composition of the present invention can achieve the following technical effects:

[0024] First, VC additives are used to regulate the interaction of solvent molecules in the electrolyte, thereby improving the solubility of LiNO3 in carbonate solvents;

[0025] Second, the additive composition is low in cost and is added to the electrolyte in a relatively small amount, which can achieve low-cost and high-efficiency improvement of the electrochemical performance of the basic electrolyte;

[0026] Third, through the film-forming effect and solvation structure improvement of the additives, the performance of the positive electrode side, the negative electrode side and the bulk electrolyte side can be simultaneously improved;

[0027] Fourth, the Li||NCM811 full battery using the electrolyte containing the additive composition provided by the present invention exhibits excellent cycle stability and good rate performance; specifically, in some embodiments of the present invention, the capacity retention rate of the Li||NCM811 full battery after 600 cycles is approximately 83.8%;

[0028] Fifth, the preparation method of the electrolyte containing the additive composition is simple, the amount of additive used is small, and it has the potential for large-scale application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1a Raman spectra of BASE electrolyte and OPT electrolyte.

[0031] Figure 1b The NMR spectra of BASE electrolyte and OPT electrolyte ( 13 C).

[0032] Figure 1c The NMR spectra of BASE electrolyte and OPT electrolyte ( 7 Li).

[0033] Figure 2a The Coulombic efficiency of the Li||Cu half-cell assembled with BASE electrolyte and OPT electrolyte respectively changes with the number of cycles.

[0034] Figure 2b The Coulombic efficiency of the Li||Cu half-cell assembled with ED11VN2 electrolyte changes with the number of cycles.

[0035] Figure 2c The Coulombic efficiency of the Li||Cu half-cell assembled with V3 electrolyte changes with the number of cycles.

[0036] Figure 2d The Coulombic efficiency of the Li||Cu half-cell assembled with V4 electrolyte changes with the number of cycles.

[0037] Figure 2e The graphs show the cycling stability and rate performance of Li||Li symmetric batteries assembled with BASE electrolyte and OPT electrolyte at different current densities.

[0038] Figure 2f The Li||Li symmetric battery assembled with BASE electrolyte and OPT electrolyte at a current density of 1 mA cm -2 , areal capacity of 1 mAh cm -2 Cycling stability and rate performance diagram under different conditions.

[0039] Figure 3a-Figure 3lSEM images of the lithium deposition morphology on the copper electrode surface after 5 cycles of Li||Cu half-cells assembled with BASE electrolyte and OPT electrolyte respectively under different current densities and different surface capacities.

[0040] Figure 4a This is the SEM image of the NCM811 positive electrode material after 100 cycles of the Li||NCM811 full battery assembled with BASE electrolyte.

[0041] Figure 4b This is the SEM image of the NCM811 positive electrode material assembled with OPT electrolyte after 100 cycles of the Li||NCM811 full battery.

[0042] Figure 4c These are the XRD spectra of the original NCM811 positive electrode material and the NCM811 positive electrode material obtained after Li||NCM811 full battery cycling assembled with BASE electrolyte and OPT electrolyte respectively.

[0043] Figure 5a This is the XPS graph of the lithium metal anode obtained after 100 cycles of the Li||NCM811 full battery assembled with BASE electrolyte.

[0044] Figure 5b This is the XPS graph of the lithium metal negative electrode obtained after 100 cycles of the Li||NCM811 full battery assembled with OPT electrolyte.

[0045] Figure 5c-5e This is the XPS graph of the NCM811 positive electrode material obtained after 100 cycles of the Li||NCM811 full battery assembled with BASE electrolyte.

[0046] Figure 5f-5j This is the XPS graph of the NCM811 positive electrode material obtained after 100 cycles of the Li||NCM811 full battery assembled with BASE electrolyte.

[0047] Figure 6a Figure 2 is the rate performance diagram of Li||NCM811 full battery assembled with BASE electrolyte and OPT electrolyte respectively.

[0048] Figure 6b Figure 2 shows the cycling stability performance of Li||NCM811 full batteries assembled with BASE electrolyte and OPT electrolyte respectively.

[0049] Figure 6c The cycling stability performance diagram of Li||NCM811 full battery assembled with BASE electrolyte and ED11VN2 electrolyte respectively.

[0050] Figure 6d This is the impedance performance diagram of the Li||NCM811 full battery assembled with OPT electrolyte.

[0051] Figure 6e Impedance performance diagram of Li||NCM811 full battery assembled with BASE electrolyte.

[0052] Figure 6f The impedance performance comparison chart of Li||NCM811 full batteries assembled with BASE electrolyte and ED11VN2 electrolyte respectively.

[0053] Figure 6g This is the charge and discharge curve of the Li||NCM811 full battery assembled with OPT electrolyte.

[0054] Figure 6h This is the discharge curve of the Li||NCM811 full battery assembled with BASE electrolyte.

[0055] Figure 7 Schematic diagram of the mechanism of action of the additive composition used in the examples of the present invention in the electrolyte. DETAILED DESCRIPTION

[0056] It should be noted that the term "comprise" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or apparatus.

[0057] The "range" disclosed in the present invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges defined in this way are combinable, i.e., any lower limit can be combined with any upper limit to form a range. For example, a range of 60-120 and 80-110 is listed for a particular parameter, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​listed are 3, 4, and 5, then the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0058] In the present invention, unless otherwise specified, the numerical range "ab" is an abbreviation for any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed in this invention, and "0-5" is merely an abbreviation for these numerical combinations.

[0059] In the present invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in the present invention can be combined with each other to form a new technical solution.

[0060] In the present invention, unless otherwise specified, all technical features and preferred features mentioned in the present invention can be combined with each other to form a new technical solution.

[0061] In the present invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, the method comprising steps (a) and (b) indicates that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, the method further comprising step (c) indicates that step (c) may be added to the method in any order, for example, the method may comprise steps (a), (b) and (c), or may comprise steps (a), (c) and (b), or may comprise steps (c), (a) and (b), etc.

[0062] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and Examples. The following embodiments are part of the present invention, rather than all of the embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0063] Electrolyte Examples and Comparative Examples

[0064] Comparative Example 1

[0065] This comparative example provides a basic electrolyte (denoted as BASE electrolyte), which comprises a carbonate solvent and LiPF6, and the concentration of the lithium salt is 1M based on the total volume of the carbonate solvent;

[0066] Wherein, the carbonate solvent comprises EC and DEC in a volume ratio of 1:1.

[0067] Example 1

[0068] This embodiment provides an electrolyte for a high energy density lithium metal battery (denoted as OPT electrolyte), which comprises the basic electrolyte and the additive composition provided in Comparative Example 1, wherein the additive composition consists of VC, LiNO3 and Zn(BF4)2. Based on the total volume of the basic electrolyte, the volume fraction of VC is 2 vol%, the concentration of LiNO3 is 0.4 mol / L, and the concentration of Zn(BF4)2 is 0.02 mol / L.

[0069] The preparation method of the OPT electrolyte provided in this embodiment includes:

[0070] Accurately weigh 2 mL of BASE electrolyte, and add VC, LiNO3 and Zn(BF4)2 to the BASE electrolyte in sequence according to the volume fraction of VC being 2 vol%, the concentration of LiNO3 being 0.4 mol / L and the concentration of Zn(BF4)2 being 0.02 mol / L. Stir at 50°C for 4 h in a glove box to prepare the OPT electrolyte.

[0071] Battery Examples and Comparative Examples

[0072] In a glove box, commercial polycrystalline NCM811 was used as the cathode active material. It was mixed with a conductive agent (SuperP) and a binder (PVDF) in a mass ratio of 8:1:1 to obtain a slurry. The slurry was evenly coated on aluminum foil and dried to form a cathode electrode.

[0073] Using 45μm ultra-thin lithium foil as the anode and the prepared electrolyte (i.e., BASE electrolyte or OPT electrolyte), CR2032 model button batteries such as Li||NCM811 full cell, Li||Cu half cell, and Li||Li symmetric cell were assembled in a glove box for subsequent performance testing.

[0074] Comparative Example 2

[0075] This comparative example provides an electrolyte for a high energy density lithium metal battery (denoted as V1 electrolyte), which comprises the basic electrolyte and the additive composition provided in Comparative Example 1, wherein the additive composition consists of LiNO3 and Zn(BF4)2, and the concentration of LiNO3 is 0.4 mol / L and the concentration of Zn(BF4)2 is 0.02 mol / L, based on the total volume of the basic electrolyte.

[0076] The preparation method of the V1 electrolyte provided in this comparative example includes:

[0077] 2 mL of BASE electrolyte was accurately weighed. LiNO₃ and Zn(BF₄)₂ were added sequentially to the BASE electrolyte at a LiNO₃ concentration of 0.4 mol / L and a Zn(BF₄)₂ concentration of 0.02 mol / L. The mixture was stirred at 50°C in a glove box for over 4 hours. It was observed that the lithium salts did not completely dissolve. Comparing the experimental results of Example 1 and Comparative Example 2 demonstrates that the present invention utilizes a VC additive to regulate the interactions between solvent molecules in the electrolyte, effectively improving the solubility of LiNO₃ in carbonate solvents.

[0078] Comparative Example 3

[0079] This comparative example provides an electrolyte for a high energy density lithium metal battery (denoted as ED11VN2 electrolyte), which comprises the basic electrolyte and the additive composition provided in Comparative Example 1, wherein the additive composition consists of LiNO3 and VC, and based on the total volume of the basic electrolyte, the volume fraction of VC is 2 vol%, and the concentration of LiNO3 is 0.4 mol / L.

[0080] The preparation method of the ED11VN2 electrolyte provided in this comparative example includes:

[0081] Accurately weigh 2 mL of BASE electrolyte, and add VC and LiNO3 to the BASE electrolyte in sequence according to the volume fraction of VC being 2 vol% and the concentration of LiNO3 being 0.4 mol / L. Stir at 50°C in a glove box for 4 h to prepare ED11VN2 electrolyte.

[0082] Comparative Example 4

[0083] This comparative example provides an electrolyte for a high energy density lithium metal battery (denoted as V3 electrolyte), which comprises the basic electrolyte and the additive composition provided in Comparative Example 1, wherein the additive composition consists of LiNO3, VC and Zn(BF4)2. Based on the total volume of the basic electrolyte, the volume fraction of VC is 2 vol%, the concentration of LiNO3 is 0.8 mol / L, and the concentration of Zn(BF4)2 is 0.02 mol / L.

[0084] The preparation method of the V3 electrolyte provided in this comparative example includes:

[0085] Accurately weigh 2 mL of BASE electrolyte, and add VC, LiNO3 and Zn(BF4)2 to the BASE electrolyte in sequence according to the volume fraction of VC being 2 vol%, the concentration of LiNO3 being 0.8 mol / L and the concentration of Zn(BF4)2 being 0.02 mol / L. Stir at 50°C for 4 h in a glove box to prepare V3 electrolyte.

[0086] Comparative Example 5

[0087] This comparative example provides an electrolyte for a high energy density lithium metal battery (denoted as V4 electrolyte), which comprises the basic electrolyte and the additive composition provided in Comparative Example 1, wherein the additive composition consists of LiNO3, VC and Zn(BF4)2. Based on the total volume of the basic electrolyte, the volume fraction of VC is 5 vol%, the concentration of LiNO3 is 0.4 mol / L, and the concentration of Zn(BF4)2 is 0.02 mol / L.

[0088] The preparation method of the V4 electrolyte provided in this comparative example includes:

[0089] Accurately weigh 2 mL of BASE electrolyte, and add VC, LiNO3 and Zn(BF4)2 to the BASE electrolyte in sequence according to the volume fraction of VC being 5 vol%, the concentration of LiNO3 being 0.4 mol / L and the concentration of Zn(BF4)2 being 0.02 mol / L. Stir at 50°C for 4 h in a glove box to prepare V4 electrolyte.

[0090] Comparative Example 6

[0091] This comparative example provides an electrolyte for a high energy density lithium metal battery (denoted as V5 electrolyte), which comprises the basic electrolyte and the additive composition provided in Comparative Example 1, wherein the additive composition consists of fluoroethylene carbonate (FEC), LiNO3 and Zn(BF4)2. Based on the total volume of the basic electrolyte, the volume fraction of FEC is 2 vol%, the concentration of LiNO3 is 0.4 mol / L, and the concentration of Zn(BF4)2 is 0.02 mol / L.

[0092] The preparation method of the V5 electrolyte provided in this comparative example includes:

[0093] 2 mL of BASE electrolyte was accurately weighed. FEC, LiNO3, and Zn(BF4)2 were sequentially added to the BASE electrolyte, with a FEC volume fraction of 2 vol%, a LiNO3 concentration of 0.4 mol / L, and a Zn(BF4)2 concentration of 0.02 mol / L. The mixture was stirred in a glove box at 50°C for over 4 hours. It was observed that the lithium salts did not completely dissolve. Comparing the experimental results of Example 1 and Comparative Example 6, the present invention utilizes a VC additive to regulate the interactions between solvent molecules in the electrolyte. Compared to conventional additives such as FEC, the use of the VC additive can indeed improve the solubility of LiNO3 in carbonate solvents.

[0094] Performance Test Example 1

[0095] In this performance test example, nuclear magnetic resonance spectroscopy (NMR) analysis and Raman spectroscopy (Raman) analysis were performed on the BASE electrolyte and the OPT electrolyte respectively. The obtained Raman spectra are shown in the figure below. Figure 1a The obtained NMR spectrum is shown in Figure 1b and Figure 1c shown.

[0096] In such Figure 1a In the Raman spectrum shown, the -1 The peak near 891cm is the symmetrical ring deformation peak of coordinated ethylene carbonate (Coordinate EC), and -1 Nearby is the symmetric stretching vibration peak of Coordinate EC. Comparing the Raman spectra of BASE electrolyte and OPT electrolyte, it is found that the positions of these two peaks in OPT electrolyte show a significant red shift, which means that the number of Coordinate EC has decreased, that is, the degree of EC coordination has decreased.

[0097] use 13 C NMR technology can further observe the coordination of solvent molecules in the electrolyte. Figure 1b shown 13 In the C NMR spectrum, the carbonyl carbon signals of diethyl carbonate (DEC) and ethylene carbonate (EC) are located at 156.88 ppm and 155.28 ppm, respectively. By monitoring the shift changes of these two solvent peaks, the coordination state of the solvent in the electrolyte can be effectively characterized. The study found that compared with the BASE electrolyte, both of these solvent peaks in the OPT electrolyte have undergone a significant upward shift, indicating that the coordination number of the solvent in the OPT electrolyte has decreased.

[0098] exist 7 In Li NMR analysis, due to Li + With NO3 - There is a strong interaction between them, which causes the peak position of Li in the OPT electrolyte to shift significantly upward, as shown in Figure 1c shown 7 Li NMR spectrum.

[0099] These results of Raman spectroscopy and nuclear magnetic resonance (NMR) are mutually confirmed with the results of molecular dynamics (MD) simulation. It proves that after the present invention successfully introduces LiNO3 through the strategy of "small-size carrier solubilizer", due to NO3 - Has high electron donor ability and competes with solvent molecules for Li + The coordination of LiNO3 decreases the coordination number of the solvent in the OPT electrolyte, while the coordination number of the anion increases accordingly, thereby optimizing the solvent structure of the electrolyte and improving the solubility of LiNO3 in carbonate solvents.

[0100] Performance Test Example 2

[0101] In this performance test example, charge and discharge tests were performed on the Li||Cu half-cell and Li||Li symmetrical battery assembled using OPT electrolyte, ED11VN2 electrolyte, V3 electrolyte, V4 electrolyte and BASE electrolyte in the battery examples and comparative examples in the Xinwei battery test system to test the rate performance and cycle performance of the battery.

[0102] in, Figure 2a The Coulombic efficiency of the Li||Cu half-cell assembled with BASE electrolyte and OPT electrolyte varies with the number of cycles. Figure 2a It can be seen that compared with the BASE electrolyte, the OPT electrolyte exhibits higher lithium deposition coulombic efficiency and better cycle stability. Specifically, for the Li||Cu half-cell equipped with the OPT electrolyte, it can stably cycle for more than 250 cycles at a lithium deposition coulombic efficiency (CE) of up to 98%. However, for the Li||Cu half-cell equipped with the BASE electrolyte, although the initial coulombic efficiency is relatively high, the lithium deposition coulombic efficiency gradually decreases with the increase in the number of cycles, and the fluctuation is relatively large, indicating that the charge loss of the Li||Cu half-cell equipped with the BASE electrolyte gradually increases after multiple cycles, and its performance has declined.

[0103] The coulombic efficiency of the Li||Cu half-cell assembled with ED11VN2 electrolyte changes with the number of cycles as shown in the figure Figure 2b As shown. Figure 2b It can be seen that the coulombic efficiency of the Li||Cu half-cell assembled using the ED11VN2 electrolyte containing only LiNO3 additives and VC additives has been greatly improved, with an average coulombic efficiency of about 97%, which is better than the BASE electrolyte, but the cycle stability is poor, lower than that of the OPT electrolyte.

[0104] In addition, the coulombic efficiency of the Li||Cu half-cell assembled with V3 electrolyte and V4 electrolyte respectively changes with the number of cycles as shown in the figure Figure 2c and Figure 2d As shown. Figure 2c and Figure 2d As can be seen, the cycling stability of the Li||Cu half-cells assembled using the V3 electrolyte containing an excess of LiNO3 and the V4 electrolyte containing an excess of VC respectively is poor, with performance lower than that of the BASE electrolyte and the OPT electrolyte. This indicates that the combination of VC, LiNO3, and Zn(BF4)2 as additives for lithium metal battery electrolytes in the embodiments of the present invention must be controlled within a certain range. Excessive use of additives will reduce battery performance, thereby producing negative effects.

[0105] Figure 2e Figure 2 shows the cycling stability and rate performance of Li||Li symmetric batteries assembled with BASE electrolyte and OPT electrolyte at different current densities. Figure 2f The Li||Li symmetric battery assembled with BASE electrolyte and OPT electrolyte at 1 mA cm -2 、1mAh cm -2 Cyclic stability and rate performance diagram under the following conditions. Figure 2e and Figure 2f It can be seen that the Li||Li symmetric cell equipped with the OPT electrolyte exhibits excellent performance, capable of stable cycling for more than 400 hours while maintaining a low polarization overpotential of approximately 69mV. However, the Li||Li symmetric cell equipped with the BASE electrolyte performs poorly. After 200 hours of charge and discharge testing, the voltage rises rapidly and a short circuit occurs, with a polarization overpotential as high as 117mV. The above experimental results show that the embodiments of the present invention effectively improve the compatibility of the electrolyte with the lithium metal negative electrode by modifying the base electrolyte by adding an additive composition to the base electrolyte, reducing the consumption of active lithium, and thus improving the coulombic efficiency of the battery.

[0106] Performance Test Example 3

[0107] In this performance test example, scanning electron microscopy (SEM) characterization and analysis were performed on the copper electrodes of Li||Cu half-cells assembled with BASE electrolyte and OPT electrolyte respectively after 5 cycles under different current densities and different areal capacities to observe the lithium deposition morphology on the copper electrode surface under different test conditions. The SEM images of the lithium deposition morphology on the copper electrode surface are shown in Figure 2. Figure 3a-Figure 3l As shown. Figure 3a-Figure 3l It can be seen that at a current density of 0.5 mA / cm 2 , surface capacity is 1mAh / cm 2 Under the test conditions of 100 μm, when the OPT electrolyte was used in the Li||Cu half-cell, the copper electrode surface exhibited a uniform bulk lithium deposition morphology, with a lithium deposition thickness of only 5.47 μm, which is very close to the theoretical thickness (approximately 4.87 μm). Even under test conditions of higher current or larger surface capacity, the copper electrode surface in the Li||Cu half-cell using the OPT electrolyte still exhibited a uniform bulk lithium deposition morphology, in stark contrast to the situation when the BASE electrolyte was used.

[0108] Performance Test Example 4

[0109] This performance test example is based on the BASE electrolyte and OPT electrolyte with a 45 μm ultra-thin lithium anode and a surface loading of 12 mg cm -2The Li||NCM811 full battery was assembled with the NCM811 positive electrode of the BASE electrolyte. After the Li||NCM811 full battery was cycled for 100 cycles at a charge rate of 0.3C and a discharge rate of 0.5C, it was disassembled to obtain the cycled NCM811 positive electrode material. The structural integrity of the positive electrode NCM811 secondary particles was then observed using a scanning electron microscope (SEM). The SEM image of the NCM811 positive electrode material of the Li||NCM811 full battery assembled with the BASE electrolyte after 100 cycles is shown in FIG. Figure 4a As shown in the figure, the SEM image of the NCM811 cathode material after 100 cycles of the Li||NCM811 full battery assembled with OPT electrolyte is shown in the figure. Figure 4b As shown. Figure 4a and Figure 4b It can be seen that after 100 cycles, the structure of the positive electrode NCM811 secondary particles of the Li||NCM811 full battery based on OPT electrolyte is intact and no obvious changes have occurred. However, after 100 cycles, the positive electrode NCM811 secondary particles of the Li||NCM811 full battery based on BASE electrolyte have produced a large number of cracks and even particle breakage.

[0110] This performance test example also performed X-ray diffraction (XRD) analysis on the original NCM811 positive electrode material and the NCM811 positive electrode material obtained after the Li||NCM811 full battery cycle assembled with BASE electrolyte and OPT electrolyte respectively, to observe the degradation of the positive electrode microstructure, and to explore the changes in the positive electrode microstructure before and after the cycle by calculating the intensity ratio of the (003) peak to the (104) peak. The obtained XRD spectrum is shown in the figure below. Figure 4c As shown. The study found that compared with the original NCM811 cathode material, the intensity ratio of the (003) / (104) peak of the NCM811 cathode material sample obtained after the Li||NCM811 full battery cycle based on BASE electrolyte dropped sharply from 1.53 to 0.68; while the NCM811 cathode material sample obtained after the Li||NCM811 full battery cycle based on OPT electrolyte can still maintain a high degree of structural order. This shows that the NCM811 cathode material in the Li||NCM811 full battery based on OPT electrolyte has good cycle stability, which brings excellent cycle performance to the full battery.

[0111] Performance Test Example 5

[0112] This performance test example is for the BASE electrolyte and OPT electrolyte with a 45 μm ultra-thin lithium anode and a surface loading of 12 mg cm -2The Li||NCM811 full battery was assembled with an NCM811 positive electrode. After 100 cycles at a charge rate of 0.3C and a discharge rate of 0.5C, the battery was disassembled. The cycled lithium metal negative electrode was then analyzed using XPS depth profiling technology to observe the distribution of O, Li, N, and Zn elements in the solid electrolyte interface (SEI) layer of different electrolytes at etching times of 0s, 300s, and 600s. The experimental results are shown in Figure 2. Figure 5a and Figure 5b As shown. Figure 5a and Figure 5b As can be seen from the O 1s spectrum, the OPT electrolyte sample has a higher Li2O content, and this content increases with etching time. The Li 1s spectrum shows that the OPT electrolyte sample has a higher LiF and Li2O content than the BASE electrolyte sample, and the deeper the etching, the stronger the metallic lithium peak intensity. The Li3N peak in the N 1s spectrum confirms that lithium nitrate in the OPT electrolyte participates in SEI formation, and the Zn 2p spectrum shows that Zn 2+ Also involved.

[0113] This performance test also uses XPS depth profiling technology to analyze the NCM811 cathode material after cycling to examine the composition and distribution of the cathode electrolyte interface (CEI). The experimental results are as follows: Figure 5c-5e As shown, Figure 5c-5e The XPS graph of the NCM811 cathode material obtained after 100 cycles of the Li||NCM811 full battery assembled with BASE electrolyte and Figure 5f-5j This is the XPS graph of the NCM811 cathode material obtained after 100 cycles of the Li||NCM811 full battery assembled with BASE electrolyte. Figure 5c-5e and Figure 5f-5j It can be seen that because BF 4- and NO 3- With the addition of , the cathode CEI of the OPT electrolyte sample after circulation contains inorganic components such as Li3N and related components such as BON. Its CC peak intensity decreases, the LiF peak intensity increases, and no dissolved transition metal peak is detected.

[0114] From the above XPS results, it can be seen that the embodiment of the present invention has successfully achieved effective control of the interface composition of the positive and negative electrodes by introducing specific additives into the electrolyte. In terms of the negative electrode SEI layer, it not only changes the distribution of elements such as O, Li, N, and Zn, but also increases the content of inorganic components such as Li2O and Li3N, and also promotes the formation of Zn 2+ Participating in the formation of SEI, it improves the stability and performance of SEI. In the positive electrode CEI layer, the addition of additives significantly changes the composition of CEI, increasing the inorganic component and reducing the organic component, effectively inhibiting the dissolution of transition metals.

[0115] Performance Test Example 6

[0116] This performance test example is for BASE electrolyte, ED11VN2 electrolyte, V3 electrolyte and OPT electrolyte, respectively, with 45μm ultra-thin lithium anode and surface loading of 12mg cm -2 The rate performance, cycle stability and impedance performance of the Li||NCM811 full battery assembled with the NCM811 positive electrode were investigated using conventional methods in the field. The rate performance of the Li||NCM811 full battery assembled with BASE electrolyte and OPT electrolyte is shown in the figure below. Figure 6a As shown, from Figure 6a As can be seen from the results, the Li||NCM811 full cell based on the OPT electrolyte exhibits superior rate performance. Due to the ultra-high interfacial stability of the Li||NCM811 full cell assembled with the OPT electrolyte, the cell's specific capacity reaches 174.1 mAh / g at a 1C rate. At a 4C rate, the specific capacity is 104.6 mAh / g, with a capacity retention rate of approximately 60%. Both the specific capacity and capacity retention are significantly better than those of the Li||NCM811 full cell assembled with the BASE electrolyte.

[0117] Among them, the cycle stability of Li||NCM811 full batteries assembled with BASE electrolyte and OPT electrolyte were tested under 0.3C / 0.5C conditions. The cycle stability performance diagram is shown in the figure below. Figure 6b As shown, from Figure 6b It can be seen that the initial specific capacity of the Li||NCM811 full battery assembled with OPT electrolyte reaches 190.9mAh / g. After 600 long cycles, the specific capacity is still 160.1mAh / g, and the capacity retention rate is about 83.8%, which is significantly better than the Li||NCM811 full battery assembled with BASE electrolyte.

[0118] The cycling performance of Li||NCM811 full batteries assembled with BASE electrolyte and ED11VN2 electrolyte are shown in the figure. Figure 6c As shown, from Figure 6cIt can be seen that compared with the BASE electrolyte, the cycle stability of the Li||NCM811 full battery assembled based on the ED11VN2 electrolyte is improved, but compared with the OPT electrolyte provided in Example 1 of the present invention, the cycle stability of the Li||NCM811 full battery assembled based on the ED11VN2 electrolyte is poor. This shows that adding VC and LiNO3 to the basic electrolyte can improve the performance of the battery to a certain extent, but the performance of the ED11VN2 electrolyte obtained by adding only VC and LiNO3 to the basic electrolyte is significantly worse than the performance of the OPT electrolyte obtained by adding VC, LiNO3 and Zn(BF4)2 to the basic electrolyte at the same time. That is, the present invention uses a combination of VC, LiNO3 and Zn(BF4)2 as an additive for lithium metal battery electrolyte to improve the performance of the corresponding full battery.

[0119] For Li||NCM811 full batteries with different cycle times, the impedance performance is obtained by electrochemical impedance spectroscopy (EIS) analysis. The experimental results are as follows: Figure 6d and Figure 6e The results show that the impedance performance of the Li||NCM811 full cell based on the OPT electrolyte remains relatively stable over 100 cycles, with almost no significant changes in the interfacial impedance and charge transfer impedance. In sharp contrast, the interfacial impedance and charge transfer impedance of the Li||NCM811 full cell based on the BASE electrolyte increase significantly with increasing cycle number. The increasing impedance accelerates the degradation of the full cell performance.

[0120] The impedance performance comparison of Li||NCM811 full batteries assembled with BASE electrolyte and ED11VN2 electrolyte after 10 cycles is shown in the figure below. Figure 6f As shown. Figure 6f Combined with Figure 6d and Figure 6e It can be seen that under the same number of cycles, the interfacial impedance and charge transfer impedance of the Li||NCM811 full cell based on OPT electrolyte, the Li||NCM811 full cell based on ED11VN2 electrolyte, and the Li||NCM811 full cell based on BASE electrolyte increase in turn, and a larger impedance will accelerate the degradation of the full cell performance. This further illustrates that the present invention uses a combination of VC, LiNO3, and Zn(BF4)2 as an additive for the lithium metal battery electrolyte to improve the performance of the corresponding full cell.

[0121] In addition, the charge and discharge curves of the Li||NCM811 full battery assembled with OPT electrolyte are shown in the figure below. Figure 6g The discharge curve of the Li||NCM811 full battery assembled with BASE electrolyte is shown in Figure 6h As shown. Figure 6g and Figure 6h It can be seen that the Li||NCM811 full cell assembled using the OPT electrolyte can still maintain a high capacity after 600 charge-discharge cycles, while the Li||NCM811 full cell assembled using the BASE electrolyte has a low capacity decay after 100 charge-discharge cycles. This comparison shows that compared with the BASE electrolyte, the OPT electrolyte provided by the embodiment of the present invention significantly improves the cycling stability of the Li||NCM811 full cell and increases the battery's capacity retention rate.

[0122] In summary, the mechanism of action of the additive composition used in the embodiment of the present invention in the electrolyte is shown in the figure below: Figure 7 As shown. Figure 7 It can be seen that the additive composition uses VC with moderate molecular polarity and small size as a solvent carrier for lithium nitrate. It has the dual advantages of improving the solubility of lithium nitrate in carbonate solvents while not compromising its compatibility with lithium metal anodes. This characteristic makes it a "small-size carrier solubilizer". Due to its small molecular volume, VC can easily enter the first solvation layer and participate in the dissociation process of lithium salts. Moreover, the small molecular volume enables it to avoid the steric hindrance effect caused by the close distance when interacting with DEC molecules, thereby ensuring that the dissociation process of LiNO3 is not inhibited by linear DEC.

[0123] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, substitutions of equivalent components, or equivalent changes and modifications made within the scope of patent protection, should still fall within the scope of this patent. Furthermore, the technical features of this invention may be freely combined with one another, with other technical inventions, and with other technical inventions.

Claims

1. An additive composition for lithium metal battery electrolyte, wherein: The additive composition includes vinylene carbonate, lithium nitrate, and fluoroborate.

2. The additive composition according to claim 1, wherein The fluoroborate includes inorganic fluoroborate M n (BF4) m and one or more combinations of organic fluoroborates R-BF3M; Wherein, M includes one or more elements selected from aluminum, copper, lead, tin, nickel, zinc, cadmium, beryllium, magnesium, calcium, strontium, barium, cesium, rubidium, manganese, iron, cobalt, silver, indium and thallium; R includes one or more organic groups selected from hydrocarbons, alcohols, ethers, esters, ketones, carboxylic acids and phenols; 0.2≤n≤5, 0.2≤m≤8.

3. The additive composition according to claim 1, wherein The fluoroborate is one or a combination of zinc tetrafluoroborate, magnesium tetrafluoroborate, silver tetrafluoroborate and stannous tetrafluoroborate.

4. An electrolyte for a lithium metal battery, comprising a basic electrolyte and an additive, wherein: The additive is the additive composition for lithium metal battery electrolyte according to any one of claims 1 to 3; Based on the total volume of the basic electrolyte, the volume fraction of vinylene carbonate is 1-3 vol%, the concentration of lithium nitrate is 0.2-0.6 mol / L, and the concentration of fluoroborate is 0.01-0.03 mol / L.

5. The electrolyte according to claim 4, wherein The basic electrolyte comprises a carbonate solvent and a lithium salt, wherein the concentration of the lithium salt is 0.7-1.5M based on the total volume of the carbonate solvent.

6. The electrolyte according to claim 5, wherein The carbonate solvent comprises ethylene carbonate and diethyl carbonate; And / or the lithium salt includes at least one of LiPF6, LiBF4, LiClO4, and LiAsF6.

7. The electrolyte according to claim 6, wherein The volume ratio of ethylene carbonate to diethyl carbonate is 3:7-6:

4.

8. The method for preparing an electrolyte for a lithium metal battery according to any one of claims 4 to 7, wherein: The preparation method comprises: Vinylene carbonate, lithium nitrate and fluoroborate are sequentially added to the basic electrolyte, and stirred evenly in a glove box to obtain the electrolyte for lithium metal batteries.

9. The preparation method according to claim 8, wherein In a glove box, the mixture is stirred at a temperature of 40-80° C. for 2-6 hours to obtain the electrolyte for lithium metal batteries.

10. A lithium metal battery comprising a positive electrode, an electrolyte and a negative electrode, wherein: The electrolyte is the electrolyte for a lithium metal battery according to any one of claims 4 to 7.

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