High-voltage lithium metal battery and preparation method thereof

Abstract

The invention discloses a high-voltage lithium metal battery which comprises a positive plate, a lithium negative plate, a diaphragm and a modified electrolyte, the positive plate adopts a positive material Li (Nix1Cox2Mnx3) O2, X1 is more than 0.58 and less than 0.62, X2 is more than 0.18 and less than 0.22, X3 is more than 0.18 and less than 0.22, and X1 + X2 + X3 = 1; and the modified electrolyte contains a polyfluoroalkoxy additive. According to the invention, the polyfluoroalkoxy additive is taken as the electrolyte additive, and the optimized positive electrode material system and the electrolytic solvent system are combined, so that the obtained lithium metal battery can still effectively ensure and improve the capacity retention ratio of the battery under the conditions of high voltage and high rate; the problems of lithium dendrite growth, lithium-nickel mixed arrangement of positive electrode materials, instability of a negative electrode / electrolyte interface and instability of a positive electrode / electrolyte interface and the like of the negative electrode of the high-voltage lithium metal battery in the battery circulation process are effectively solved, and the service life of the high-voltage lithium metal is effectively prolonged.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical technology, and particularly relates to a high-voltage lithium metal battery and a preparation method thereof. Background Art

[0002] With the development of industries such as electric vehicles, the demand for energy density is increasing day by day. Metallic lithium is the ultimate choice for the negative electrode of lithium batteries, with the highest theoretical specific capacity (3,860 mAh g -1 , 2,061 mAh cm -3 ) and the lowest redox potential (-3.04 V vs. standard hydrogen electrode) (Guo Y, Li H, Zhai T. Reviving Lithium-Metal Anodes for Next-Generation High-Energy Batteries[J]. Advanced Materials, 2017, 29(29): 1700007.). Lithium metal batteries composed of high-voltage cathode combinations such as NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2) and LNP (LiNiPO4) can provide a relatively high energy density (>550 Wh kg -1 and >1400 Wh L -1 ). The lithium metal negative electrode has obvious advantages compared with the currently commercial graphite negative electrode, and its application in lithium batteries has attracted wide attention.

[0003] Currently, there are still many problems with the lithium metal negative electrode that limit its practical application: 1) Different from the graphite negative electrode, due to the alkali metal characteristics of lithium metal, Li + tends to deposit in the form of dendrites. The continuous growth of dendrites will cause internal short circuits in the battery and even pierce the diaphragm, triggering an explosion; 2) It is also prone to problems such as lithium-nickel mixing in the cathode material under high-voltage conditions; 3) The high activity of lithium metal causes it to continuously react with the electrolyte, generating a solid electrolyte interface layer (SEI) with low strength and high thickness, resulting in the consumption of lithium and electrolyte and the increase of interface resistance. The deposition / shedding of the lithium metal negative electrode during the reaction will bring about huge volume changes, leading to a lack of spatial control of lithium deposition and exacerbating the instability of the lithium negative electrode and the growth of lithium dendrites.

[0004] Although the existing positive electrodes have certain effects through electrolyte modification (such as additives, high-concentration salts) or artificial SEI layer design, they have defects such as complex processes, high costs, or poor compatibility. Although lithium nitrate additives have certain effects on protecting lithium metal anodes and inhibiting the growth of lithium dendrites, their strong oxidizing properties may pose safety hazards in actual production and large-scale applications. Therefore, there is an urgent need for a simple and efficient method to simultaneously stabilize the interfaces of both the positive and negative electrodes during the operation of the battery (especially under high-voltage conditions) without causing safety hazards. Summary of the Invention

[0005] The main object of the present invention is to address the problems and deficiencies such as the growth of lithium dendrites in the negative electrode of high-voltage lithium metal batteries during battery cycling, the mixing of lithium and nickel in the positive electrode material, and the low battery life caused by the instability of the negative electrode / electrolyte interface and the positive electrode / electrolyte interface. A high-voltage lithium metal battery is provided, which can still exhibit good high-current charge and discharge performance and cycle stability under the test conditions where the charging cut-off voltage reaches 4.5V, and has good safety.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A high-voltage lithium metal battery includes a positive electrode sheet, a lithium negative electrode sheet, a separator, and a modified electrolyte. Among them, the positive electrode material used for the positive electrode sheet is Li(Ni x1 Co x2 Mn x3 )O2, 0.58 < X1 < 0.62, 0.18 < X2 < 0.22, 0.18 < X3 < 0.22, and X1 + X2 + X3 = 1; the modified electrolyte contains a polyfluoroalkoxy additive.

[0008] Further, the current collector used for the positive electrode sheet is Al foil, Cu foil, Ti foil, etc.; the thickness is 5 - 10μm.

[0009] Further, the preparation method of the positive electrode sheet includes: mixing the positive electrode material, polyvinylidene fluoride, and carbon fiber (VGCF) in a certain mass ratio, and controlling the mass ratio to be 7 - 9:1.8 - 2.2:2; grinding and then dispersing in an organic solvent (such as N-methylpyrrolidone, etc.) to form a slurry; coating the obtained slurry on the current collector and drying to obtain the positive electrode sheet.

[0010] In the above solution, the relative molecular weight of the polyvinylidene fluoride is 500,000 - 600,000.

[0011] In the above solution, the carbon fiber is a vapor-grown carbon fiber, its diameter is 100 - 150nm, and its length is 20 - 30μm.

[0012] In the above solution, one or more of trifluoroethyl perfluorobutanesulfonate (TPFS), 1,1,2,2 - tetrafluoroethyl - 2,2,3,3 - tetrafluoropropyl ether (HFE), etc. can be selected as the polyfluoroalkoxy additive.

[0013] In the above solution, one or more of LiPF6, LiTFPS, and LiFSI can be selected as the lithium salt.

[0014] In the above solution, the concentration of the lithium salt is 0.8 - 1.2 mol / L.

[0015] In the above solution, the electrolytic solvent used in the modified electrolyte is a carbonate solvent or an ether solvent.

[0016] Further, the carbonate - based electrolyte contains one or more of ethylene carbonate (EC) and dimethyl carbonate (DMC).

[0017] Further, the mass ratio of ethylene carbonate to dimethyl carbonate is 0 - 1.2:1.

[0018] Further, the mass ratio of ethylene carbonate to dimethyl carbonate is 0.8 - 1.2:1.

[0019] Further, the ether - based electrolyte contains one or more of 1,3 - dioxolane (DOL) and dimethoxyethane (DME).

[0020] Further, the mass ratio of 1,3 - dioxolane (DOL) to dimethoxyethane is 0 - 1.2:1.

[0021] In the above solution, the polyfluoroalkoxy additive accounts for 0.1 - 20% of the total mass of the base electrolyte.

[0022] During the application process, the polyfluoroalkoxy additive introduced in the present invention is reduced and decomposed on the surface of the negative electrode to form a solid electrolyte interface layer (SEI) rich in LiF, which inhibits the growth of lithium dendrites and guides the uniform deposition of lithium ions; it is oxidized and decomposed on the surface of the positive electrode to form a positive electrode electrolyte interface layer (CEI), which inhibits the dissolution of transition metal ions (Ni, Co, Mn); both the SEI layer and the CEI layer can reduce the respective electrode - interface impedance, increasing the battery cycle life to more than 290 times and the capacity retention rate to higher than 80%.

[0023] In the above solution, the modified electrolyte is mixed by magnetic stirring until it becomes homogeneous and transparent. The stirring conditions are 500 - 1500 rpm, the time is 1 - 3 h, and the ambient temperature is 20 - 25°C.

[0024] In the above solution, the lithium negative electrode uses a lithium foil, and its surface is physically polished before use. The processing tools are not limited to ceramic blades, sandpaper or stainless steel scrapers to remove the surface oxides and particulate contaminants.

[0025] In the above solution, the separator can be selected from one of Celgard 2325, Celgard 2400, Celgard 2500, etc.

[0026] The present invention also provides a preparation method of the above high-voltage lithium metal battery, including the following steps: stack the positive electrode sheet, the separator, and the lithium negative electrode sheet in sequence to form a battery housing, and inject the modified electrolyte into the battery housing in an argon glove box, where the electrolyte is added to both the positive electrode side and the negative electrode side, and then encapsulate.

[0027] Furthermore, the lithium metal battery is a symmetric battery or a full battery, where: the charge-discharge test conditions for the symmetric battery are a current density of 1 mA cm -2 , and a capacity of 0.5 mAh cm -2 ; the charge-discharge test voltage range for the full battery is 3.0 - 4.5 V.

[0028] Compared with the prior art, the beneficial effects of the present invention include:

[0029] 1) Polishing the lithium foil can effectively remove surface oxides, contaminants and micro-defects, which is beneficial to improving the surface smoothness and chemical homogeneity of the lithium metal, reducing the electrode / electrolyte interface impedance, promoting uniform deposition of lithium ions, inhibiting the uncontrollable growth of lithium dendrites, reducing the risk of short circuit and side reactions, and promoting the improvement of the cycle stability, safety and Coulomb efficiency of the battery.

[0030] 2) The present invention uses a polyfluoroalkoxy additive as an electrolyte additive and applies it to a lithium metal battery. During the battery cycle, it is preferentially reduced and decomposed at the negative electrode of the battery to form a LiF-rich SEI layer, which inhibits the growth of lithium dendrites, forms a smoother SEI interface, guides the uniform deposition of lithium ions, and is safe and environmentally friendly; at the same time, it oxidizes and decomposes at the positive electrode of the battery to form a CEI passivation layer, which inhibits the dissolution of transition metal ions (Ni, Co, Mn), reduces the loss of the positive electrode material, and promotes a longer cycle life; in addition, the addition of the modified electrolyte reduces the interface impedance of the electrode and achieves better ionic conductivity.

[0031] 3) Under high voltage conditions of 4.5 V and high rate (1 - 5C), the battery system adopted (modified electrolyte (basic electrolyte + additive) combined with the cathode material system, etc.) can still effectively ensure and improve the capacity retention rate of the battery: a dense SEI film rich in LiF is formed on the surface of the lithium anode to inhibit dendrite growth and continuous decomposition of the electrolyte; at the same time, the stability of the cathode CEI film is optimized in situ and the interfacial impedance is reduced, alleviating the dissolution of transition metals and structural collapse under high voltage, while enhancing the thermodynamic stability and lithium ion migration efficiency of the electrolyte, so that the capacity retention rate of the battery is greater than 75% after 300 cycles, and it can still maintain more than 65% of the initial capacity under high rate charge and discharge (5C). Description of the Drawings

[0032] Figure 1 This is a comparison chart of the constant current charge and discharge cycle performance of the Li||Li symmetric battery obtained in Example 1 of the present invention;

[0033] Figure 2 This is an electrochemical impedance comparison chart of the Li||Li symmetric battery obtained in Example 1 of the present invention;

[0034] Figure 3 This is the SEM diagram after cycling of the symmetric battery composed of electrolyte A0 and A1 obtained in Example 1 of the present invention and lithium foil. Among them, (a) is the low magnification diagram after using electrolyte A0, (c) is the low magnification diagram after using electrolyte A1, (b) is the high magnification diagram after using electrolyte A0, and (d) is the high magnification diagram after using electrolyte A1;

[0035] Figure 4 This is the deposition diagram of the Li||Li symmetric battery composed of electrolyte A0 and A1 obtained in Example 1 of the present invention under in-situ optical microscope observation. Among them, (a) is using electrolyte A1, and (b) is using electrolyte A0;

[0036] Figure 5 This is the TEM diagram after cycling of the Li||Li symmetric battery assembled with electrolyte A0 and A1 obtained in Example 1 of the present invention; among them, (a) is using electrolyte A0, and (b) is using electrolyte A1;

[0037] Figure 6 This is the XPS component diagram after cycling of the Li||NCM622 full battery assembled with electrolyte A0 and A1 obtained in Example 1 of the present invention; among them, (a, b, c) are the C1s, Li1s, and F 1s energy spectrum images obtained using electrolyte A0, and (d, e, f) are obtained using electrolyte A1; the C1s, Li 1s, and F 1s energy spectrum images;

[0038] Figure 7 This is a comparison chart of the cycle performance of the constant current charge and discharge of the Li||NCM622 full battery obtained in Example 1 of the present invention;

[0039] Figure 8 Cycling performance comparison diagram of the rate at high voltage of the Li||NCM622 full cell assembled with electrolyte A0 and A1 obtained in Example 1 of the present invention; (a) uses electrolyte A1, and (b) uses electrolyte A0;

[0040] Figure 9 TEM diagram of the Li||NCM622 full cell assembled with electrolyte A0 and A1 obtained in Example 1 of the present invention after cycling; where (a) uses electrolyte A0 and (b) uses electrolyte A1;

[0041] Figure 10 XPS component diagram of the Li||NCM622 full cell assembled with electrolyte A0 and A1 obtained in Example 1 of the present invention after cycling; where (a) and (b) use electrolyte A0, and (c) and (d) use electrolyte A1;

[0042] Figure 11 ICP-MS component diagram of the Li||NCM622 full cell assembled with electrolyte A0 and A1 obtained in Example 1 of the present invention after cycling;

[0043] Figure 12 Cycling performance comparison diagram of constant current charge and discharge of the Li||Li symmetric cell assembled with electrolyte A1 obtained in Example 1 of the present invention, electrolyte A2 obtained in Example 2, and electrolyte A3 obtained in Example 3;

[0044] Figure 13 Electrochemical impedance comparison diagram of the Li||Li symmetric cell assembled with electrolyte A1 obtained in Example 1 of the present invention, electrolyte A2 obtained in Example 2, and electrolyte A3 obtained in Example 3;

[0045] Figure 14 Charge and discharge curve diagram of the Li||Li symmetric cell assembled with electrolyte A1 obtained in Example 1 of the present invention without surface treatment of the lithium metal;

[0046] Figure 15 Charge and discharge curve comparison diagram of the Li||Li symmetric cell assembled with electrolyte A1 obtained in Example 1, electrolyte A4 obtained in Comparative Example 2, and electrolyte A5 obtained in Comparative Example 3;

[0047] Figure 16 Charge and discharge curve of the Li-NMC622 full cell obtained in Comparative Example 4. Detailed implementation mode

[0048] The present invention will be further described in detail below through specific implementation cases. These implementation cases are carried out on the premise of the technology of the present invention, and the detailed implementation methods and specific operation processes are given. However, the scope of protection of the present invention is not limited to the following implementation cases.

[0049] In the following examples, the basic electrolyte contains LiPF6 and a solvent. Among them, the concentration of LiPF6 is 1M, and the solvent is a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a weight ratio of 1:1.

[0050] In the following examples, the Li||NCM622 full cell includes a positive electrode, a negative electrode, a separator, and a modified electrolyte. The positive electrode uses NCM622 single crystal material as the main raw material, and its chemical composition is LiNi 0.6 Co 0.2 Mn 0.2 O2, purchased from Cyber Electrochemical Network; the negative electrode is a lithium metal foil; the separator is Celgard 2325.

[0051] The preparation method of the positive electrode includes: mixing NCM622 single crystal (particle size 3 - 8μm), polyvinylidene fluoride (molecular weight 5 million), and vapor-grown carbon fiber (VGCF, diameter 100 - 150nm, length 20 - 30μm) in a mass ratio of 8:2:2, grinding and then dispersing in N-methylpyrrolidone to form a slurry; coating the slurry on an aluminum foil, drying in vacuum at 60°C for 12 hours, and stamping into a disk with a diameter of 10mm.

[0052] The preparation steps of the lithium metal battery include: injecting the modified electrolyte into the battery case in an argon glove box, adding 40μL of electrolyte to each of the positive electrode side and the negative electrode side; stacking the positive electrode, separator, and negative electrode in sequence and then encapsulating.

[0053] Example 1

[0054] A lithium metal battery system, and its preparation method includes the following steps:

[0055] (1) At room temperature, in a glove box filled with Ar gas, take 5g of the basic electrolyte as the reference electrolyte (Blank) denoted as A0, add 1% of its mass of trifluoroethyl perfluorobutyl sulfonate (TPFS) to A0, and stir magnetically (1000rpm, 2h) until transparent and homogeneous to obtain the modified electrolyte denoted as A1;

[0056] (2) Battery assembly;

[0057] 1) Symmetric battery;

[0058] Lithium foils polished physically are used on both sides of the separator, and 40 μL of electrolyte is added to each side respectively and then assembled into a symmetric cell. Among them, the electrolytes used are A0 and A1 respectively, and two symmetric cells (Li||Li symmetric cells) are obtained.

[0059] 2) Li||NCM622 full cell;

[0060] The prepared NCM622 cathode material is used on the positive electrode side of the separator, and the lithium foil polished physically is used on the negative electrode side. And 40 μL of electrolyte (using A0 and A1 respectively) is added to each side respectively and then assembled into a Li||NCM622 full cell.

[0061] The obtained Li||Li symmetric cells are subjected to constant current charge-discharge tests in a Blue-Energy test system, and the test conditions are 1 mA cm -2 , 0.5 mAh cm -2 ;

[0062] The comparison chart of the constant current charge-discharge cycling performance of the Li||Li symmetric cells obtained in this example is as Figure 1 shown. It can be seen that the addition of the electrolyte additive TPFS effectively improves the constant current charge-discharge life of the Li||Li symmetric cells.

[0063] The Li||Li symmetric cells obtained by using different electrolytes in this example are respectively subjected to electrochemical impedance tests, and the results are as Figure 2 shown. Due to the selection of the VGCF conductive agent and the uniform deposition of lithium ions guided by TPFS, the electrochemical impedance of the Li||Li symmetric cells using the TPFS additive is effectively reduced.

[0064] For the Li||Li symmetric cells obtained by using different electrolytes in Example 1 of this embodiment, after cycling, the negative electrode is observed by scanning electron microscope, and the results are as Figure 3 shown. The TPFS additive shows an effective inhibitory effect on the growth of lithium dendrites. Whether at high magnification or low magnification, the surface of the lithium negative electrode using the TPFS additive shows a smoother electrode surface.

[0065] For the electrolytes A0 and A1 obtained in this example, their lithium deposition conditions are observed under an in-situ optical microscope at a current density of 1 mA cm -2 , 0.5 mAh cm -2 . The results are as Figure 4 shown. The TPFS additive can guide the uniform lithium deposition process. On the contrary, irregular dendrite growth appears at the electrode interface without using the TPFS additive, and it deepens continuously with the progress of the deposition time.

[0066] In this example, the Li||Li symmetric cells obtained using different electrolytes were observed by transmission electron microscopy on their negative electrodes after cycling. The results are as Figure 5 shown. There is an obvious delamination phenomenon in the SEI layer of the negative electrode in the Blank electrolyte system, which is caused by the low ionic conductivity in this system. On the contrary, the SEI layer in the TPFS system is thinner and more evenly distributed, which also proves the important role of the TPFS additive in forming an excellent SEI film on the lithium negative electrode;

[0067] For the Li||Li symmetric cells obtained using different electrolytes in this example, XPS analysis was performed on their negative electrodes after cycling. The results are as Figure 6 shown. In the spectrum of C1S, the peak at 289.7 eV is related to the formation of Li2CO3, which helps to consolidate a strong SEI film. The peaks at 286.1 eV and 284.8 eV correspond to C-O / C═O and C-C / C-H respectively. In the TPFS electrolyte system, the area of this peak remains basically unchanged with the increase of the etching depth, proving that the additive effectively inhibits the further decomposition of the electrolyte. In the spectrum of Li 1S, the peaks at 53.7 eV, 55.2 eV and 55.4 eV correspond to ROCO2-Li, Li2CO3 and LiF respectively. With the increase of the etching time, the content of Li2CO3 in the SEI under the TPFS system decreases, but the content of LiF increases, which proves that the TPFS additive does form a LiF-rich SEI layer on the metallic lithium negative electrode prior to the electrolyte. In contrast, the content of LiF in the SEI of the metallic lithium negative electrode in the Blank system is always very low. The same problem can also be found in the F1s spectrum, where the peaks at 685.1 eV and 687.2 eV come from Li-F and C-F bonds. The peak intensities of C-F and Li-F in the SEI under the TPFS system are significantly higher than those in the SEI under the Blank system before and after etching, which further proves the outstanding role of TPFS in constructing a LiF-rich SEI structure;

[0068] The Li||NCM622 full cells obtained in this example were subjected to charge-discharge tests under the test condition of 0.5C.

[0069] The comparison chart of the constant current charge-discharge cycling performance of the Li||NCM622 full cells obtained in this example is as Figure 7 shown. It can be seen that the addition of the electrolyte additive TPFS effectively improves the rate charge-discharge performance of the full cell;

[0070] The Li||NCM622 full cells obtained in this example were subjected to rate charge-discharge tests at high voltages under the test conditions of 0.5C - 5C.

[0071] The comparison chart of high-voltage rate charge and discharge of the Li||NCM622 full cell obtained in this example is as follows Figure 8 shown. Under the condition of 4.5V high voltage, the use of TPFS additive effectively reduces the attenuation of the charge and discharge specific capacity of the full cell. Especially under the high rate condition of 5C, the discharge specific capacity in the Blank system drops to 108.1 mAh·g -1 , while the TPFS system still maintains a high discharge specific capacity of 123.3 mAh·g -1 . This proves that the addition of the electrolyte additive TPFS effectively improves the charge and discharge performance of the full cell under high-voltage conditions and the improvement of the battery capacity under high rates.

[0072] For the Li||NCM622 full cells obtained using different electrolytes in this example, after cycling, the surface of the positive electrode was observed by transmission electron microscopy, and the results are as follows Figure 9 shown; an extremely uneven CEI layer can be observed on the surface of the positive electrode material in the Blank system, with a thickness of 25 nm and being very loose, which may cause the transition metals in the positive electrode material to overflow into the electrolyte; on the contrary, a dense and uniform CEI layer is formed on the surface of the positive electrode material in the TPFS electrolyte system, and the thickness is only 5 nm, indicating that the addition of TPFS additive can also effectively protect the positive electrode side of the battery.

[0073] For the Li||NCM622 full cells obtained using different electrolytes in this example, after cycling, XPS analysis was performed on the surface of the positive electrode, and the results are as follows Figure 10 ; in the spectrum of C1S, the content of C-C / C-H bonds in the TPFS battery is low, which proves that the CEI film effectively prevents the excessive consumption of the electrolyte. In the spectrum of O1s, an obvious M-O peak appears on the surface of the positive electrode in the Blank system, which is the oxidation peak of transition metals, while it is not observed on the surface of the positive electrode in the TPFS system. This difference indicates that the CEI layer assisted by TPFS can protect the structure of NCM622 and prevent the transition metals from overflowing and dissolving from the positive electrode;

[0074] For the Li||NCM622 full cells obtained using different electrolytes in Example 1 of this example, after cycling, ICP-MS test was performed on the electrolyte, and the results are as follows Figure 11 shown. The contents of transition metals Ni, Co, and Mn in the Blank system are 0.428 mg·L -1 , 0.126 mg·L -1 and 0.512 mg·L -1 , respectively. However, due to the improvement of the positive electrode CEI by the TPFS additive, the contents of transition metals in the TPFS system are effectively suppressed, and the contents are reduced to 0.089 mg·L -1 , 0.077 mg·L-1 and 0.397 mg·L -1 。

[0075] Example 2

[0076] A lithium metal battery system, the preparation method of which is substantially the same as that of Example 1, except that 0.5% by mass of trifluoroethyl perfluorobutanesulfonate (TPFS) is added to the reference electrolyte, denoted as A2.

[0077] Example 3

[0078] A lithium metal battery system, the preparation method of which is substantially the same as that of Example 1, except that 2% by mass of trifluoroethyl perfluorobutanesulfonate (TPFS) is added to the reference electrolyte, denoted as A3.

[0079] Referring to the above method, three symmetric cells were assembled using electrolytes A1, A2, and A3 respectively. The obtained symmetric cells were subjected to constant current charge-discharge tests in a blue electrochemical workstation, and the test conditions were 1 mA cm -2 , 0.5 mAh cm -2 ; A cyclic performance comparison chart was obtained, as shown in Figure 12 shown.

[0080] The symmetric cells obtained using different electrolytes in Comparative Example 1 were repeatedly obtained and subjected to electrochemical impedance tests, and the results are as shown in Figure 13 shown.

[0081] Comparative Example 1

[0082] A lithium metal battery system, the preparation method of which is substantially the same as that of Example 1, except that the lithium foil is not polished before use.

[0083] The comparison chart of the overpotential of the first deposition of the two assembled symmetric cells is as shown in Figure 14 shown. It can be seen that without treating the lithium metal surface, the overpotential of the symmetric cell will increase.

[0084] Comparative Example 2

[0085] A lithium metal battery system, the preparation method of which is substantially the same as that of Example 1, except that the basic electrolyte used is replaced with LiPF6 dissolved in a mixed solvent of ethylene carbonate (DMC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), and trifluoroethyl perfluorobutanesulfonate (TPFS); wherein, the concentration of LiPF6 is 1 M, and the mass ratio of TPFS in the total electrolyte is 1%. This electrolyte is denoted as A4.

[0086] Comparative Example 3

[0087] A lithium metal battery system, the preparation method of which is substantially the same as that of Example 1, except that the basic electrolyte used is replaced with LiPF6 dissolved in a mixed solvent of ethylene carbonate (DMC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), and trifluoroethyl perfluorobutanesulfonate (TPFS); wherein, the concentration of LiPF6 is 1M, and the mass ratio of TPFS in the total electrolyte is 2%. This electrolyte is denoted as A5.

[0088] Referring to the above method, a symmetric battery was assembled and subjected to constant current charge and discharge tests in a Blue Energy test system, and the test conditions were 1 mA cm -2 , 0.5 mAh cm -2 .

[0089] The charge and discharge data of the symmetric batteries obtained in Example 1, Comparative Example 2, and Comparative Example 3 can be seen in Figure 15 , and it can be seen that under the same test conditions, the overpotential of the battery with electrolyte A1 is 62 mV, the overpotential of the battery with electrolyte A4 is 100 mV, and the overpotential of the battery with electrolyte A5 is 83 mV. The lithium salt concentrations in electrolyte A4 and electrolyte A1 are both 1M, and the TPFS contents are the same, both 1 wt%, and the difference between the two is that electrolyte A4 does not contain ethylene carbonate (EC) solvent and contains another additive 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE).

[0090] Comparative Example 4

[0091] A lithium metal battery system, the preparation method of which is substantially the same as that of Example 1, except that trifluoroethyl perfluorobutanesulfonate (TPFS) is not introduced to obtain a 1M LiPF6 in DMC / HFE electrolyte, denoted as A6.

[0092] The prepared A6 electrolyte was assembled into a Li-NMC622 full battery for charge and discharge tests, and the test conditions were 0.5C.

[0093] Its charge and discharge curve is as Figure 16 shown. Due to the absence of TPFS, the electrolyte will corrode the inside of the battery, making it impossible to charge to the set high voltage of 4.5V.

[0094] The present invention is not limited to the above embodiments. For those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also considered within the protection scope of the present invention. The content not described in detail in this specification belongs to the prior art well-known to those of ordinary skill in the art.

Claims

1. A high-voltage lithium metal battery, characterized in that, It includes a positive electrode sheet, a lithium negative electrode sheet, a separator and a modified electrolyte. Among them, the positive electrode material used for the positive electrode sheet is Li(Ni x1 Co x2 Mn x3 )O2, 0.58 < X1 < 0.62, 0.18 < X2 < 0.22, 0.18 < X3 < 0.22, and X1 + X2 + X3 = 1; the modified electrolyte contains a polyfluoroalkoxy additive.

2. The high-voltage lithium metal battery according to claim 1, wherein The polyfluoroalkoxy additive is one or more of trifluoroethyl perfluorobutanesulfonate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

3. The high-voltage lithium metal battery according to claim 1, wherein, The method for preparing the positive electrode sheet includes: mixing a positive electrode material, polyvinylidene fluoride, and carbon fiber in proportion; dispersing the mixture in an organic solvent after grinding to form a slurry, coating the obtained slurry on a current collector, and drying to obtain the positive electrode sheet.

4. The high-voltage lithium metal battery according to claim 3, characterized in that, The mass ratio of the positive electrode material, polyvinylidene fluoride, and carbon fiber is 7-9:1.8-2.2:

2.

5. The high-voltage lithium metal battery according to claim 3, characterized in that, The carbon fiber is a vapor-grown carbon fiber with a diameter of 100-150 nm and a length of 20-30 μm.

6. The high-voltage lithium metal battery according to claim 3, wherein The lithium salt is one or more of LiPF6, LiTFPS, and LiFSI; the concentration of the lithium salt is 0.8-1.2 mol / L.

7. The high-voltage lithium metal battery according to claim 1, characterized in that, The electrolytic solvent used in the modified electrolyte is a carbonate solvent or an ether solvent.

8. The high-voltage lithium metal battery according to claim 7, wherein, The polyfluoroalkoxy additive accounts for 0.1-20% of the total mass of the electrolytic solvent.

9. The high-voltage lithium metal battery according to claim 1, characterized in that, The lithium negative electrode uses a lithium foil, and its surface is physically polished before use.

10. The preparation method of the high-voltage lithium metal battery according to any one of claims 1 to 9, characterized in that, It includes the following steps: stacking a positive electrode sheet, a separator, and a lithium negative electrode sheet in sequence to form a battery casing, injecting the modified electrolyte into the battery casing in an argon glove box, adding the electrolyte to both the positive electrode side and the negative electrode side, and encapsulating.

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