Preparation method of lithium metal negative electrode of lithium metal battery as well as product and application thereof

Abstract

The invention belongs to the field of energy materials, and discloses a preparation method of a lithium metal negative electrode of a lithium metal battery and a product and application of the lithium metal negative electrode of the lithium metal battery, and the preparation method comprises the following steps: using a conductive substrate as a working electrode, using an electrode composed of a lithium-containing substance as a counter electrode, and performing electro-deposition on the working electrode in a pure solvent or a low-salt solution to obtain the lithium metal negative electrode of the lithium metal battery. The correspondingly obtained working electrode is the lithium metal negative electrode. By using a pure solvent or a low-salt solution, high-efficiency electrochemical deposition of lithium can be carried out without participation of a traditional electrolyte of high-content lithium salt, correspondingly, the metallic lithium elementary substance (or lithium alloy) deposited on the working electrode is high in density, and the performance of the lithium ion battery is improved. The obtained electrode deposited with the lithium metal can be particularly used as a negative electrode to be applied to a lithium ion battery, and has the advantages of being simple in method, low in cost, controllable, expandable, high in industrial adaptability and convenient for large-scale operation.

Description

Technical Field

[0001] The present invention belongs to the field of energy materials, and more specifically, relates to a method for preparing a lithium metal negative electrode of a lithium metal battery and its products and applications. Background Art

[0002] Lithium-ion batteries are widely used in mobile electronic products, electric vehicles and energy storage power stations due to their many advantages such as high energy density, high power density and long cycle life. Ultrathin lithium negative electrodes can improve the utilization rate of lithium negative electrodes and further improve the energy density of lithium batteries. At present, common industrial technologies for preparing ultrathin lithium include mechanical rolling, evaporation and electrochemical deposition: due to the poor viscosity and mechanical shearing properties of metallic lithium, the physical mechanical rolling method is difficult to operate, and requires precise instruments and complex operations, and has high production costs; the evaporation method can only evaporate ultra-thin thickness (generally less than 1μm), and it is difficult to prepare thin lithium of suitable thickness (such as <30μm); the thickness and uniformity of thin lithium prepared by electrochemical deposition on a conductive substrate are affected by the electrolyte and operating parameters, especially when using traditional high lithium salt content electrolytes (lithium salt concentration is usually The cost of using a thin film of lithium metal is usually not less than 1 mol / L, and it is easy to have residual lithium salts, which has a negative impact on the subsequent stability and reaction kinetics of the electrode material. Therefore, complex post-treatment is required (such as multiple cleaning of residual lithium salts with a large amount of pure solvent, drying to remove the solvent, collection and treatment of the treatment solution, etc.; at the same time, attention should be paid to safety management when using a large amount of solvent) to remove the residual electrolyte. In addition, the electrochemical deposition of lithium metal electrodes using traditional electrolytes has problems such as non-dense deposition of lithium metal (high porosity) and poor mechanical stability (easy to peel off), making it difficult to achieve practical application. Therefore, there is a lack of cost-effective, simple, controllable and large-scale industrially feasible methods for preparing thin lithium. Summary of the invention

[0003] In view of the above defects or improvement needs of the prior art, the purpose of the present invention is to provide a method for preparing a lithium metal negative electrode of a lithium metal battery, and its products and applications, wherein the overall process flow design of the electrodeposition process, the setting of process parameter conditions, etc. are improved, and pure solvents or low-salt solutions are used. In the absence of the participation of traditional electrolytes with high lithium salt content, efficient electrochemical deposition of lithium can be carried out. Accordingly, the metallic lithium element (or lithium alloy) deposited on the working electrode (i.e., the conductive substrate) has a high density (lithium metal is deposited on a modified current collector to form a lithium alloy). The electrode deposited with lithium metal thus obtained can be especially used as a negative electrode in lithium-ion batteries, and has the advantages of simple method, low cost, controllable and scalable, strong industrial adaptability and convenience for large-scale operation.

[0004] To achieve the above object, according to one aspect of the present invention, a method for preparing a lithium metal negative electrode of a lithium metal battery is provided, characterized in that the method uses a conductive substrate as a working electrode, uses an electrode composed of a lithium-containing substance as a counter electrode, and performs electrodeposition on the working electrode in a pure solvent or a low-salt solution, and the corresponding working electrode obtained is a lithium metal negative electrode;

[0005] Wherein, the pure solvent is an organic solvent, does not contain water, and does not contain electrolyte;

[0006] The low-salt solution is obtained by adding non-lithium salt and / or lithium salt to the pure solvent; and the lithium ion concentration contained in the low-salt solution does not exceed 200 mmol / L.

[0007] As a further preferred embodiment of the present invention, the current density used in the electrodeposition is 0.01 μA-10 mA / cm 2 , the temperature is -100℃~100℃.

[0008] As a further preferred embodiment of the present invention, the thickness of the lithium metal formed by electrodeposition in the lithium metal negative electrode is 50 nm-50 μm.

[0009] As a further preferred embodiment of the present invention, the pure solvent includes at least one of an ester solvent, an ether solvent, a sulfone solvent, and other organic solvents;

[0010] Wherein, the ester solvent is selected from: ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP), butylene carbonate (BC), ethyl butyl carbonate (BEC), 1,2-dimethylethylene carbonate (1,2-BC), methyl butyl carbonate (BMC), dibutyl carbonate (DBC), chloroethylene carbonate (ClEC), trifluoromethylethylene carbonate (CF3-EC), di-n-propyl carbonate (DPC), diisopropyl carbonate (DIPC), ethyl propyl carbonate (EPC), ethyl isopropyl carbonate (EIPC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC);

[0011] The ether solvent is selected from: ethylene glycol dimethyl ether (DME), tetrahydrofuran (THF), 1,3-dioxolane (DOL), diethoxyethane (DEE), 2-methyltetrahydrofuran (MeTHF), diethylene glycol dimethyl ether (DGM), triethylene glycol dimethyl ether (TGM), tetraethylene glycol dimethyl ether (TEGM);

[0012] The sulfone solvent is selected from: sulfolane (SL), dimethyl sulfoxide (DMSO);

[0013] The other organic solvent is selected from: acetonitrile (CAN), N-methylpyrrolidone (NMP), methyl ethyl ketone (MEK), pyridine (Py), N,N-dimethylformamide (DMF), and acetone (DMK).

[0014] As a further preferred embodiment of the present invention, the lithium salt is selected from alkyl lithium, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(difluorosulfonyl imide), lithium bis(trifluoromethylsulfonyl imide), lithium difluorobis(oxalatophosphate), lithium nitrate, lithium fluoride, lithium nitride, lithium oxide, lithium carbonate, lithium hydroxide, lithium hydride, aryl lithium, and lithium amide;

[0015] The non-lithium salt is a non-lithium ionic compound.

[0016] As a further preferred embodiment of the present invention, the lithium-containing substance is at least one of elemental metallic lithium and a lithium-containing compound;

[0017] Preferably, the lithium-containing compound is one or more of lithium alloy, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium-rich manganese, lithium vanadate, lithium oxide, lithium peroxide, lithium hydroxide, lithium carbonate, lithium fluoride, lithium nitride, lithium chloride, lithium hydride, aryl lithium, and lithium amide; wherein, in addition to lithium, the alloy components in the lithium alloy also include one or more of sodium, magnesium, tin, silver, aluminum, zinc, boron, silicon, and carbon.

[0018] As a further preferred embodiment of the present invention, the conductive substrate is at least one of copper, carbon, titanium, and stainless steel electrodes;

[0019] Preferably, the conductive substrate has also been pre-modified inorganically and / or organically; wherein the inorganic modification is specifically modification of gold, silver, tin, titanium dioxide, silicon dioxide, aluminum oxide, zinc oxide or carbon nanotubes, and the organic modification is specifically modification of polyacrylic acid, polyvinylidene fluoride, polyethylene glycol or polyethylene oxide.

[0020] According to another aspect of the present invention, the present invention provides a lithium metal negative electrode prepared by the above preparation method.

[0021] According to another aspect of the present invention, the present invention provides the use of the above-mentioned lithium metal negative electrode in a lithium battery.

[0022] Compared with the prior art, the above technical solutions conceived by the present invention can achieve the following

[0023] Beneficial effects:

[0024] (1) The present invention uses pure solvent or low-salt solution for electrochemical deposition of lithium, which has the advantages of simple process and easy operation. The traditional electroplating process uses an electrolyte with a high lithium salt content (lithium salt + solvent, the concentration of lithium salt is often not less than 1 mol / L). In this field, technicians often believe that pure solvents cannot be used for electroplating lithium because they do not contain free ions. The present invention uses lithium-containing substances to spontaneously react with organic solvents to form trace amounts of lithium-conducting substances, thereby realizing the metal lithium deposition reaction. For example, due to the low potential characteristics and high reactivity of lithium metal and lithium alloys, lithium metal will spontaneously react with organic solvents to generate trace amounts of organic group-rich substances with lithium ion conductivity characteristics, the components of which include alkyl lithium carbonate (ROCO2Li, R is an alkyl group containing or not containing F, Cl, P, N, B elements), alkyl lithium (ROLi), lithium-containing inorganic substances (lithium oxide, lithium hydroxide, lithium carbonate, lithium fluoride) and one or more non-conductive polymers. As for lithium-containing compounds, lithium-containing compounds can be slightly soluble in solvents to form lithium-conducting substances. For example, lithium-containing compounds (lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium-rich manganese oxide, lithium vanadate) will partially dissolve in the solvent, and the residual alkali (such as lithium carbonate, lithium hydroxide, lithium sulfate) present on the surface will also partially dissolve in the solvent to form lithium-conducting substances; lithium-containing compounds (lithium oxide, lithium peroxide, lithium hydroxide, lithium carbonate, lithium fluoride, lithium nitride, lithium chloride, lithium hydride, aryl lithium, lithium amide) can also be partially dissolved in the solvent to form lithium-conducting substances. Compared with the prior art using electrolyte (conventional concentration is 1 mol / L), the use of pure solvents can form a lithium solvation structure (mainly solvent) with high desolvation energy, thereby slowing down the electrochemical reaction kinetics, promoting two-dimensional uniform deposition of lithium, avoiding the problem of uneven electrodeposition reaction, and obtaining uniform and dense ultra-thin lithium (thickness is also controllable). In addition, in addition to using organic solvents as pure solvents for electrodeposition, the present invention can also introduce low-concentration salts as functional additives during the operation to promote lithium deposition by regulating the solvation structure and the electric field and interface structure at the electrode interface, and to help form a functional interface on the surface of metallic lithium (for example, forming an interface layer that is resistant to electrolyte corrosion or isolated from air).

[0025] The inventor of the present invention has previously studied a method for pre-lithiation of lithium-ion battery electrode materials and its products and applications (see Chinese patent document CN114335414A). Although it also uses pure organic solvents for pre-lithiation, the previous results only studied that the solvent can dissolve lithium metal to form lithium-conducting substances, and did not reveal that the spontaneously formed lithium salt can further realize the electrochemical deposition reaction of lithium metal. The present application further utilizes the spontaneously formed lithium salt for electrodeposition reaction, and utilizes the characteristics of this new lithium salt to promote the uniform deposition of lithium metal.

[0026] (2) The method of the present invention uses pure solvent or low-salt solution, which can greatly reduce the cost of preparing thin lithium. In addition, the organic solvent is easy to volatilize without residue, avoiding side reactions caused by lithium salt residues and reducing subsequent cleaning steps. It has the advantages of simple operation, low production cost and easy industrialization.

[0027] (3) The method of the present invention uses a pure solvent or a low-salt solution, which can reduce the corrosion problem caused by using a traditional electrolyte for lithium electrodeposition, because lithium metal and a conductive substrate will cause galvanic corrosion in the presence of an electrolyte. Using a pure solvent or a low-salt solution for lithium electrodeposition can form a stable SEI and obtain a stable thin lithium.

[0028] (4) In addition, based on the present invention, the lithium metal negative electrode with different electrochemical deposition effects can be further obtained by adjusting the parameters such as the lithium conductive solution (such as different solvents or salts), lithium-containing electrode, conductive substrate, reaction temperature and time. Taking the regulation of pure solvent or lithium conductive solution and lithium-containing electrode as an example, it can react with lithium metal to form a solvated lithium structure with different desolvation energies (for example, the lithium salt spontaneously formed after the pure fluorinated solvent reacts with lithium metal has a high desolvation energy, and the lithium deposition overpotential can be regulated by increasing the desolvation energy to promote dense deposition; the introduction of linear solvents can promote the formation of spontaneous lithium conductive substances, thereby increasing the lithium ion conductivity and improving the electrodeposition rate; the introduction of low-concentration salts can increase the ion conduction rate based on the spontaneous lithium salt solution; the introduction of other non-ionic salts can improve the interfacial chemical properties of the electrodeposited lithium metal in the spontaneous lithium salt solution system and improve the interface stability); taking the regulation of the conductive substrate as an example, different substrate materials and different interface modification layers can be used in the reaction. The formation of thin lithium with different deposition morphologies and compositions is promoted in pure solvents or low-salt solutions (for example, highly conductive carbon conductive substrates can increase the deposition rate of lithium metal in salt-free / low-salt solution systems and improve density; lithium-philic silver can reduce nucleation overpotential and promote uniform deposition; polyacrylic acid organic layer can isolate electrolyte to reduce corrosion and improve the chemical / electrochemical activity of lithium metal); taking the regulation of reaction temperature and reaction time as an example, the temperature parameter will regulate the electrochemical deposition kinetics of lithium, and the time parameter will regulate the thickness of the electrochemical deposition of lithium metal negative electrode, which can be flexibly adjusted according to the actual demand for the degree of lithium metal, and pure solvents or low-salt solutions have better ion conductivity at low temperatures (e.g., below 10°C) due to the large amount of free solvents. When the temperature is below 10°C, the viscosity of conventional electrolytes increases, and the commonly used solvent EC will solidify, lithium salts will precipitate, and ion conductivity will decrease; and further lowering the temperature will limit ion conduction due to thermodynamic effects. Due to the low viscosity characteristics of low-concentration solutions, and the rich organic groups of self-formed lithium salts can achieve weak solvation structures, promoting the release of solvation structures at low temperatures. At low temperatures, the particles of lithium metal deposition are smaller, and a special structure of lithium morphology can be obtained. However, due to the limited ion conduction of conventional electrolytes, dendrites will be formed. The present invention can improve ion conduction at low temperatures, reduce dendrite formation at low temperatures, promote the formation of refined grains and dense deposition, and can be used to guide the design of low-temperature electrolytes.

[0029] The commonly used electrolyte has a lithium ion concentration of 1 mol / L. Pure solvents do not contain lithium ions and do not have the ability to conduct lithium. Technicians often believe that solvents cannot conduct lithium ions and therefore cannot achieve lithium deposition reactions. The present invention discovers for the first time that pure solvents or low-salt solutions can be used for lithium metal electrochemical deposition reactions, and by optimizing the solvent composition and the composition of lithium-containing substances, modifying the current collector, and regulating the electrodeposition temperature and time, lithium metal with controllable thickness and good uniformity is obtained; the process is simple, easy to operate, reduces costs, and is easy to industrialize. The deposition is dense and uniform, and a stable SEI can be formed, reducing the corrosion problem of electrodeposited lithium, and obtaining stable lithium metal.

[0030] In summary, the present invention can realize electrochemical deposition of lithium through a simple pure solvent or a low-salt solution, and the prepared lithium metal negative electrode has controllable thickness, is uniform and dense, and has high stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The scanning electron microscope (SEM) images of lithium metal electrochemically deposited with pure solvent and conventional electrolyte, respectively; wherein, Figure 1 (a) corresponds to the electrode of lithium metal electrodeposited by pure solvent (the scale in the figure represents 10 μm). Figure 1 (b) corresponds to the electrode of lithium metal electrodeposited using traditional electrolyte (the size scale in the figure represents 10μm), and the inset is an optical photograph of the corresponding electrode.

[0032] Figure 2 Electrochemical curves of the first deposition / dissolution reaction of Li||Cu batteries assembled using pure solvent (solvent) and electrolyte (electrolyte) respectively.

[0033] Figure 3 The time-voltage diagram of electrochemical lithium deposition in Li||Cu soft-pack batteries assembled using pure solvent and electrolyte respectively.

[0034] Figure 4 Optical photographs of lithium metal electrodes prepared by electrochemical deposition of lithium using pure solvent and electrolyte respectively.

[0035] Figure 5 The time-voltage curves of symmetrical batteries assembled from lithium metal electrodes prepared by electrochemical deposition of lithium using pure solvents and electrolytes and commercial 50-micron thin lithium electrodes. In the figure, the blue curve is basically overlapped with the red curve.

[0036] Figure 6 The charge-discharge curves and cycle curves of the full battery assembled with lithium metal electrodes prepared by electrochemically depositing lithium using pure solvent and electrolyte respectively; Figure 6 (a) corresponds to the first charge and discharge curve. Figure 6(b) in the figure corresponds to the cycle curve.

[0037] Figure 7 The charging curve of NCM||Cu battery assembled using pure solvent.

[0038] Figure 8 Optical photograph of the lithium metal electrode prepared after charging of the NCM||Cu battery assembled using pure solvent.

[0039] Fig. 9 This is a SEM image of an electrode electrochemically deposited with lithium using a low-salt solution solvent (the scale bar in the figure represents 2 μm).

[0040] Fig.10 This is a SEM image of an electrode electrochemically deposited with lithium using a pure solvent (the scale bar in the figure represents 1 μm). DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0042] In general, the method for preparing a lithium metal negative electrode of a lithium metal battery in the present invention uses a conductive substrate as a working electrode and an electrode composed of a lithium-containing substance as a counter electrode, and performs electrodeposition on the working electrode in a pure solvent or a low-salt solution to obtain a lithium metal negative electrode with controllable thickness. The concentration of lithium ions in the low-salt solution does not exceed 200mmol / L.

[0043] The following are specific embodiments:

[0044] Embodiment 1

[0045] A button cell was assembled using a copper conductive substrate and lithium metal as an electrode. The electrochemical deposition test was performed using an equal amount (i.e., equal volume; the same below) of pure EC / DEC / EMC mixed solvent and a commercial carbonate electrolyte (1 M LiPF6 in EC / DEC / EMC). The test conditions were 0.25 mA cm at 25 °C. -2 The discharge was carried out for 16 hours. The morphology of the copper conductive substrate after electrochemical lithium deposition was characterized.

[0046] Figure 1This is the morphology of the electrode prepared by electrochemically depositing lithium in Example 1, and the inset is an optical photograph of the electrode after electrochemical deposition. As shown in the figure, the lithium metal electrochemically deposited by solvent is large particles with uniform and dense morphology; the lithium metal electrochemically deposited by electrolyte is uneven and non-dense, with large particles and dendritic particles. It can be seen that when electrochemical deposition is performed using electrolyte, due to sufficient lithium ion concentration, the tip effect can easily lead to uneven deposition behavior (such as dendrites), and this uneven active lithium can easily cause galvanic corrosion of active lithium on the electrolyte and copper substrate, so the electrochemical deposition morphology is uneven. Using solvent for electrochemical deposition can regulate the deposition reaction kinetics and achieve uniform and dense electrochemical deposition behavior, and since there are only trace amounts of spontaneously formed lithium-conducting substances, galvanic corrosion of active lithium will not occur.

[0047] Embodiment 2

[0048] A button cell was assembled using a copper conductive substrate and lithium metal as electrodes. The electrochemical coulombic efficiency was tested using an equal ratio of pure FEC / DME binary mixed solvent and a commercial carbonate electrolyte (1M LiPF6 in EC / DEC). The test conditions were 0.25 mA cm at 0 °C. -2 The battery was discharged for 20 h to electrochemically deposit lithium, and then charged to 1 V for de-lithiation. The capacity ratio of de-lithiation and deposition was calculated as the coulombic efficiency.

[0049] Figure 2 It is the curve of the electrochemical deposition of lithium in Example 2. As shown in the figure, when a solvent is used for electrochemical deposition of lithium, the nucleation overpotential is larger, so the nucleation rate is higher and it is helpful for grain refinement. Therefore, the coulomb efficiency of the electrochemical deposition / dissolution reaction using a solvent is 92.7%, which is higher than the coulomb efficiency of the electrolyte, indicating that the electrochemical deposition of lithium using a solvent has good reversibility. It can be seen that the electrochemical deposition of lithium using a solvent has the advantages of uniform deposition and high capacity retention rate.

[0050] Embodiment 3

[0051] A copper conductive substrate and lithium metal were used as electrodes to assemble a soft-pack battery. Equal amounts of pure DME / DOL binary mixed solvent and commercial ether electrolyte (1 M LiTFSI in DME / DOL) were used for electrochemical deposition of lithium. The test conditions were 0.05 mA cm at 50 °C. -2 The discharge treatment was performed for 80 hours to electrochemically deposit lithium.

[0052] Figure 3This is an electrochemical curve of electrochemically deposited lithium in Example 3. As shown in the figure, the equilibrium overpotential when discharging with a solvent is 100mV, and the equilibrium overpotential when discharging with an electrolyte is 2mV. It can be seen that using a solvent as a lithium-conducting medium has a large polarization, which is due to the low electrochemical reaction kinetics caused by the low lithium ion concentration. Figure 4 This is the lithium electrode after electrochemical deposition of lithium. It can be seen that when the solvent is used for electrochemical deposition of lithium in the soft pack scale, the deposition morphology is uniform and dense. However, when the electrolyte is used for deposition, the lithium metal morphology is uneven, and there is copper leakage, which may be the result of uneven deposition and corrosion.

[0053] Embodiment 4

[0054] A soft-pack battery was assembled using a copper conductive substrate and lithium metal as electrodes. Lithium was electrochemically deposited using pure DMSO / SL solvent and commercial ester electrolyte (1 M LiPF6 in EC / DEC) in equal proportions. The test conditions were 0.25 mA cm at 25 °C. -2 The electrodes after electrochemical lithium deposition were assembled into lithium metal symmetric cells. The test conditions of the charge and discharge steps were 1 mA cm -2 、1mAh cm -2 The electrodeposited lithium electrode was assembled into a full battery with a commercial lithium cobalt oxide positive electrode, and the test conditions were 100mAg -1 The constant current charge and discharge test was carried out under the current, and the charge and discharge voltage was 4.5-3.0V.

[0055] Figure 5 The electrochemical curve of the lithium metal symmetric battery assembled by the electrode after the electrochemical deposition of lithium in Example 4 is shown in FIG. Figure 5 The electrochemical curves of lithium metal symmetric cells assembled using commercial 50-micron thin lithium electrodes were also compared. As shown in the figure, the overpotential of the cycle curve of the lithium metal symmetric cell electrodeposited using solvent and electrolyte is significantly lower than the overpotential of commercial lithium foil, indicating that the electrodeposited lithium foil has good electrochemical reaction activity due to its large active specific surface area. Figure 6 The charge-discharge curve and cycle curve of the full battery of electrochemically deposited lithium and lithium cobalt oxide. As can be seen from the figure, the first-cycle electrochemical performance of the full battery assembled with the two electrodes is similar. The specific capacity of the full battery using solvent electrochemical deposition of lithium after a long cycle is higher than that of the full battery using electrolyte deposition of lithium, indicating that solvent electrochemical deposition of thin lithium helps to improve the electrochemical performance of the battery.

[0056] Embodiment 5

[0057] The battery was assembled using a copper conductive substrate and nickel cobalt manganese oxide (NCM) as electrodes, and lithium was electrochemically deposited using an equal ratio of EC / DEC solvent. The test conditions were constant current charging at 0.01C (1C=200mAh / g) at 25°C, with a cut-off voltage of 4.5V.

[0058] Figure 7 This is the electrochemical curve of the NCM||Cu battery in Example 5. As shown in the figure, the lithium ions of NCM can be successfully extracted by using a solvent, and no electrolyte side reaction occurs. Figure 8 This is the copper electrode after the electrodeposition reaction. As shown in the figure, the lithium metal deposited on the surface of the copper electrode is uniform and dense.

[0059] Embodiment 6

[0060] A low-salt solution (1 mmol / L sodium chloride + 199 mmol / L lithium fluoride in MA / FEC, MA / FEC is an equal ratio) was used to assemble a Li||Cu battery for electrochemical lithium deposition. The test conditions were -100 °C at 0.01 μA cm -2 The discharge was carried out for 100 hours. The morphology of the electrode after electrochemical lithium deposition was characterized.

[0061] Fig. 9 This is a morphology diagram of the electrode after the electrochemical deposition of lithium in Example 6. As shown in the figure, the electrochemical deposition at low temperature using a low-salt solution can successfully obtain uniform and dense lithium metal.

[0062] Embodiment 7

[0063] Take 0.8g of nano silver powder and 0.2g of polyacrylic acid (PAA), where the mass fraction of PAA in water solvent is 5%, mix the weighed materials evenly, slurry, coat on the titanium current collector, and bake at 80℃ and vacuum conditions for 12h to obtain a titanium conductive substrate modified with a nano silver / polyacrylic acid composite layer. Use pure solvent (equally proportioned PC / DMF mixed solvent) and titanium conductive substrate modified with nano silver / polyacrylic acid composite layer to assemble Li||Ti battery for electrochemical deposition of lithium. The test conditions are 100℃ and 10mA cm -2 The discharge was performed for 0.1 h. The morphology of the electrode after electrochemical lithium deposition was characterized.

[0064] Fig.10 This is a morphology diagram of the electrode after the electrochemical deposition of lithium in Example 6. As shown in the figure, uniform and dense lithium metal can be successfully obtained by electrochemical deposition at high temperature using a titanium substrate.

[0065] The above embodiments are only examples. For example, for low-salt solutions, lithium salts + pure solvents can be used for preparation, non-lithium salts + pure solvents can be used for preparation, or lithium salts + non-lithium salts + pure solvents can be used for preparation. In addition to sodium chloride, non-lithium salts can also be ionic compounds whose cations are non-lithium cations, which can be easily soluble, soluble, slightly soluble or poorly soluble in pure solvents, as long as the lithium ion concentration contained in the low-salt solution does not exceed 200mmol / L. In addition, whether the conductive substrate has been pre-modified inorganically and / or organically can also be carried out according to actual needs.

[0066] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a lithium metal negative electrode for a lithium metal battery, characterized in that: The method uses a conductive substrate as a working electrode, uses an electrode composed of a lithium-containing substance as a counter electrode, and performs electrode deposition on the working electrode in a pure solvent or a low-salt solution, and the corresponding working electrode obtained is a lithium metal negative electrode; Wherein, the pure solvent is an organic solvent, does not contain water, and does not contain electrolyte; The low-salt solution is obtained by adding non-lithium salt and / or lithium salt to the pure solvent; and the lithium ion concentration contained in the low-salt solution does not exceed 200 mmol / L.

2. The preparation method according to claim 1, characterized in that: The current density used in the electrodeposition is 0.01 μA-10 mA / cm 2 , the temperature is -100℃~100℃.

3. The preparation method according to claim 1, characterized in that: The thickness of the lithium metal formed by electrodeposition in the lithium metal negative electrode is 50nm-50μm.

4. The preparation method according to claim 1, characterized in that: The pure solvent includes at least one of an ester solvent, an ether solvent, a sulfone solvent, and other organic solvents; Wherein, the ester solvent is selected from: ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP), butylene carbonate (BC), ethyl butyl carbonate (BEC), 1,2-dimethylethylene carbonate (1,2-BC), methyl butyl carbonate (BMC), dibutyl carbonate (DBC), chloroethylene carbonate (ClEC), trifluoromethylethylene carbonate (CF3-EC), di-n-propyl carbonate (DPC), diisopropyl carbonate (DIPC), ethyl propyl carbonate (EPC), ethyl isopropyl carbonate (EIPC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC); The ether solvent is selected from: ethylene glycol dimethyl ether (DME), tetrahydrofuran (THF), 1,3-dioxolane (DOL), diethoxyethane (DEE), 2-methyltetrahydrofuran (MeTHF), diethylene glycol dimethyl ether (DGM), triethylene glycol dimethyl ether (TGM), tetraethylene glycol dimethyl ether (TEGM); The sulfone solvent is selected from: sulfolane (SL), dimethyl sulfoxide (DMSO); The other organic solvent is selected from: acetonitrile (CAN), N-methylpyrrolidone (NMP), methyl ethyl ketone (MEK), pyridine (Py), N,N-dimethylformamide (DMF), and acetone (DMK).

5. The preparation method according to claim 1, characterized in that: The lithium salt is selected from alkyl lithium, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(difluorosulfonyl imide), lithium bis(trifluoromethylsulfonyl imide), lithium difluorobis(oxalatophosphate), lithium nitrate, lithium fluoride, lithium nitride, lithium oxide, lithium carbonate, lithium hydroxide, lithium hydride, aryl lithium, and lithium amide; The non-lithium salt is a non-lithium ionic compound.

6. The preparation method according to claim 1, characterized in that: The lithium-containing substance is at least one of elemental metallic lithium and a lithium-containing compound; Preferably, the lithium-containing compound is one or more of lithium alloy, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium-rich manganese, lithium vanadate, lithium oxide, lithium peroxide, lithium hydroxide, lithium carbonate, lithium fluoride, lithium nitride, lithium chloride, lithium hydride, aryl lithium, and lithium amide; wherein, in addition to lithium, the alloy components in the lithium alloy also include one or more of sodium, magnesium, tin, silver, aluminum, zinc, boron, silicon, and carbon.

7. The preparation method according to claim 1, characterized in that: The conductive substrate is at least one of copper, carbon, titanium, and stainless steel electrodes; Preferably, the conductive substrate has also been pre-modified inorganically and / or organically; wherein the inorganic modification is specifically modification of gold, silver, tin, titanium dioxide, silicon dioxide, aluminum oxide, zinc oxide or carbon nanotubes, and the organic modification is specifically modification of polyacrylic acid, polyvinylidene fluoride, polyethylene glycol or polyethylene oxide.

8. A lithium metal negative electrode prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the lithium metal negative electrode as claimed in claim 8 in a lithium battery.

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