A composite lithium metal negative electrode and its preparation method and lithium metal battery

Abstract

The present invention discloses a composite lithium metal anode, a preparation method thereof, and a lithium metal battery. The preparation method of the composite lithium metal anode comprises the following steps: providing a three-dimensional porous carbon-based substrate and a zinc salt solution; adding a nitrogen source and the three-dimensional porous carbon-based substrate to the zinc salt solution at a first preset temperature; soaking the three-dimensional porous carbon-based substrate for a first preset time, removing the substrate, drying it, and then annealing it to obtain a nitrogen-doped zinc oxide-loaded three-dimensional porous carbon-based substrate; and immersing the nitrogen-doped zinc oxide-loaded three-dimensional porous carbon-based substrate in molten metallic lithium to obtain the composite lithium metal anode. The composite lithium metal anode prepared by the present invention can reduce the significant volume change during lithium deposition and dissolution, inhibit the growth of lithium dendrites, and improve the cycle life of the battery.

Description

Technical Field

[0001] The present invention relates to the field of lithium metal batteries, and in particular to a composite lithium metal negative electrode and a preparation method thereof, and a lithium metal battery. Background Art

[0002] Lithium metal has a high theoretical specific capacity (3860 mAh g -1 ) and the lowest negative electrode electrochemical deposition potential (-3.04V vs. standard hydrogen electrode), it is considered to be one of the most promising negative electrode materials and is regarded as the "holy grail" of battery negative electrodes, and has received extensive research attention. In addition, in order to match the high-capacity lithium-free positive electrode and solid-state electrolyte, the pursuit of negative electrodes containing metallic lithium will become an inevitable development of the next generation of high-energy batteries. However, existing research results show that: in liquid electrolytes, metallic lithium negative electrodes will inevitably form lithium dendrites, resulting in volume expansion and some side reactions, which will lead to a decrease in battery cycle coulombic efficiency and a shortened battery life. In addition, the formation of lithium dendrites will pierce the diaphragm, causing a short circuit and leading to the risk of thermal runaway and explosion.

[0003] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a composite lithium metal negative electrode and its preparation method and a lithium metal battery, aiming to solve the problem that the existing lithium metal negative electrode is prone to form lithium dendrites and volume expansion.

[0005] The technical solutions of the present invention are as follows:

[0006] A first aspect of the present invention provides a method for preparing a composite lithium metal negative electrode, comprising the steps of:

[0007] Providing a three-dimensional porous carbon-based substrate and a zinc salt solution;

[0008] adding a nitrogen source and the three-dimensional porous carbon-based substrate to the zinc salt solution at a first preset temperature;

[0009] soaking the three-dimensional porous carbon-based substrate for a first preset time, taking it out, drying it, and then annealing it to obtain a nitrogen-doped zinc oxide-loaded three-dimensional porous carbon-based substrate;

[0010] The nitrogen-doped zinc oxide-supported three-dimensional porous carbon-based substrate is immersed in molten metallic lithium to obtain the composite lithium metal negative electrode.

[0011] Optionally, the three-dimensional porous carbon-based substrate is selected from at least one of carbon fiber cloth, carbon paper, carbon nanotube fiber cloth, and foam carbon.

[0012] Optionally, the step of adding the nitrogen source and the three-dimensional porous carbon-based substrate to the zinc salt solution specifically includes:

[0013] A nitrogen source, an alkaline regulator and the three-dimensional porous carbon-based substrate are added to the zinc salt solution.

[0014] Optionally,

[0015] The zinc salt is selected from at least one of zinc acetate, zinc nitrate, zinc sulfate, and zinc carbonate;

[0016] And / or, the nitrogen source is selected from at least one of thiourea, urea, and ammonium acetate;

[0017] And / or, the alkaline regulator is selected from at least one of ammonia water, ammonium dihydrogen carbonate, and ammonium bicarbonate.

[0018] Optionally, the first preset temperature is 55-80° C., and the first preset time is 2-12 hours.

[0019] Optionally, the drying is vacuum drying, the temperature of the vacuum drying is 50-110° C., and the time of the vacuum drying is 2-15 hours.

[0020] Optionally, the temperature of the annealing treatment is 500-800° C., the time of the annealing treatment is 0.5-3 hours, and the atmosphere of the annealing treatment is one of air, nitrogen, and argon.

[0021] Optionally, the method for preparing molten metallic lithium comprises the steps of:

[0022] Under the conditions that the O2 concentration is less than 0.1 ppm and the H2O concentration is less than 0.1 ppm, the metallic lithium is heated at a temperature of 180-400° C. until molten metallic lithium is obtained.

[0023] In a second aspect of the present invention, a composite lithium metal negative electrode is provided, wherein the composite lithium metal negative electrode is prepared using the preparation method of the present invention as described above.

[0024] A third aspect of the present invention provides a lithium metal battery, which includes the composite lithium metal negative electrode of the present invention as described above.

[0025] Beneficial effects: The present invention uses a three-dimensional porous carbon-based substrate loaded with nitrogen-doped zinc oxide as the host of the lithium metal negative electrode. Since the three-dimensional porous carbon-based substrate loaded with nitrogen-doped zinc oxide has the characteristics of high porosity, good conductivity, large specific surface area, light weight and good flexibility, it can effectively control the growth of lithium dendrites and the volume and expansion of lithium metal during the cycle, and has a lower density than the three-dimensional metal host, so it can effectively improve the mass energy density of the battery. At the same time, its good flexibility enables it to be applied to fields such as flexible energy storage devices. The present invention enhances the lithium affinity of the three-dimensional porous carbon-based substrate (which does not have lithium affinity itself) by introducing nitrogen-doped zinc oxide into the three-dimensional porous carbon-based substrate to modify the three-dimensional porous carbon-based substrate, and successfully prepares a composite lithium metal electrode with the three-dimensional porous carbon-based substrate loaded with nitrogen-doped zinc oxide as the lithium metal host. On the one hand, nitrogen-doped zinc oxide can form a Li-Zn alloy with molten lithium metal, which can reduce the nucleation energy barrier of lithium metal and thus improve the lithium affinity of the three-dimensional porous carbon-based substrate; on the other hand, nitrogen-doped zinc oxide can enhance the electrical conductivity and lithium ion conductivity of the three-dimensional porous carbon-based substrate, thereby significantly reducing the nucleation overpotential and polarization potential of lithium deposition, and uniformly distributing the electric field so that lithium metal is uniformly deposited, avoiding the growth of lithium dendrites during charging and discharging. The composite lithium metal negative electrode prepared by the present invention can reduce the huge volume change during lithium deposition and dissolution, inhibit the growth of lithium dendrites, and improve the cycle life of the battery, ultimately achieving a battery capacity of 1mA / cm 2 , 1mAh / cm 2 It can operate for more than 1600 hours under the charge and discharge conditions (polarization voltage is 9mV), and its nucleation overpotential is only 8mV. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 (a) is a schematic diagram of the preparation process of the composite lithium metal negative electrode in Example 1 of the present invention, (b) is a schematic diagram of the adsorption of molten lithium metal by carbon fiber cloth loaded with nitrogen-doped zinc oxide in Example 1 of the present invention, (c) is a schematic diagram of the adsorption of molten lithium metal by pure carbon fiber cloth in Example 1 of the present invention, (d) is an optical picture of pure carbon fiber cloth and carbon fiber cloth loaded with nitrogen-doped zinc oxide in Example 1 of the present invention, (e) is a front photo of N-ZnO / CC@Li in Example 1 of the present invention, (f) is a back photo of N-ZnO / CC@Li in Example 1 of the present invention, and (g) is an SEM picture of N-ZnO / CC@Li in Example 1 of the present invention.

[0027] Figure 2 2 are the XRD patterns of N-ZnO / CC prepared in Examples 1, 2 and 3 of the present invention.

[0028] Figure 3(a) is a SEM image of the N-ZnO / CC prepared in Example 1 of the present invention, (b) is a SEM image of the N-ZnO / CC prepared in Example 2 of the present invention, and (c) is a SEM image of the N-ZnO / CC prepared in Example 3 of the present invention.

[0029] Figure 4a This is a graph showing the results of a cycle test of a symmetrical battery assembled with the N-ZnO / CC@Li prepared in Example 1 of the present invention. Figure 4b This is a graph showing the results of a cycle test of a symmetrical battery assembled with the N-ZnO / CC@Li prepared in Example 2 of the present invention. Figure 4c This is a graph showing the results of cycle testing of a symmetrical battery assembled with the N-ZnO / CC@Li prepared in Example 3 of the present invention.

[0030] Figure 5 This is the impedance spectrum of the symmetrical battery assembled with N-ZnO / CC@Li prepared in Examples 4 and 5 of the present invention.

[0031] Figure 6 (a) is an SEM image of the N-ZnO / CC prepared in Example 5 of the present invention, (b) is an EDS image of the N-ZnO / CC prepared in Example 5 of the present invention, (c) is a statistical diagram of the distribution and content of C, O, N, and Zn in the N-ZnO / CC prepared in Example 5 of the present invention, (d) is a planar SEM image of the original carbon fiber cloth used in Example 5 of the present invention, (e) is a cross-sectional SEM image of the original carbon fiber cloth used in Example 5 of the present invention, and (f) is a cross-sectional SEM image of the N-ZnO / CC prepared in Example 5 of the present invention.

[0032] Figure 7a Symmetrical cells assembled from the N-ZnO / CC@Li prepared in Example 5 of the present invention, the ZnO / CC@Li prepared in Comparative Example 1, and pure lithium sheets were tested at 1 mA / cm 2 Cycling performance results at charge and discharge current density, Figure 7b Symmetrical cells assembled from the N-ZnO / CC@Li prepared in Example 5 of the present invention, the ZnO / CC@Li prepared in Comparative Example 1, and pure lithium sheets were tested at 2 mA / cm 2 Cycling performance results at charge and discharge current density, Figure 7c Symmetrical cells assembled from the N-ZnO / CC@Li prepared in Example 5 of the present invention, the ZnO / CC@Li prepared in Comparative Example 1, and pure lithium sheets were tested at 3 mA / cm 2 Cycling performance results at charge and discharge current density, Figure 7dSymmetrical cells assembled from N-ZnO / CC@Li and pure lithium sheets prepared in Example 5 of the present invention were tested at 0.5, 1, 2, 4, and 0.5 mA / cm 2 The rate performance results at the charge and discharge current density are shown.

[0033] Figure 8 The symmetrical battery composed of N-ZnO / CC@Li and pure lithium sheets prepared in Example 5 of the present invention was heated at 1 mA / cm 2 The interfacial impedance and morphology changes at different time stages are shown after cycling at a charge and discharge current density of , where (a) is the impedance spectrum of the initial state without cycling; (b) is the impedance spectrum after 50 cycles; (c) is the impedance spectrum after 100 cycles; (d) is the SEM image of the pure lithium sheet in the initial state without cycling; (e) is the SEM image of the pure lithium sheet after 50 cycles; (f) is the SEM image of the pure lithium sheet after 100 cycles; (g) is the SEM image of the N-ZnO / CC@Li sheet in the initial state without cycling; (h) is the SEM image of the N-ZnO / CC@Li sheet after 50 cycles; (i) is the SEM image of the N-ZnO / CC@Li sheet after 100 cycles. DETAILED DESCRIPTION

[0034] The present invention provides a composite lithium metal anode, a method for preparing the same, and a lithium metal battery. To clarify the objectives, technical solutions, and effects of the present invention, the present invention is described in further detail below. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0035] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0036] The unsupported structure of metallic lithium makes it different from embedded-host type electrode materials. It is a conversion-type host-free negative electrode with no three-dimensional matrix (such as copper foam, nickel foam, carbon fiber, etc.) to accommodate lithium deposition / dissolution. From the perspective of regulating the electric field strength and effective current density of the metallic lithium negative electrode, the development of a three-dimensional electronic conductive carrier is an effective method to control the nucleation and growth of lithium by alleviating charge concentration. Three-dimensional structural materials can confine lithium dendrites within the skeleton, thereby solving many of the inherent problems of metallic lithium, such as volume expansion, side reactions, and SEI film rupture. Compared with the framework of a two-dimensional structure, the three-dimensional structure can provide a larger surface area and volume to accommodate the deposited lithium metal, which can reduce the local current density of the negative electrode, regulate the electric field, and reduce the dendrite nucleation and growth rate, thereby minimizing the formation of dendrites.

[0037] Based on this, in the initial attempt of the present invention, the three-dimensional porous carbon-based substrate was directly used as the host of the lithium metal negative electrode. However, after extensive research, the inventors found that although the three-dimensional porous carbon-based substrate has the characteristics of high porosity, good conductivity, large specific surface area, light weight and good flexibility, it does not have lithium affinity, that is, lithium metal cannot be directly and effectively loaded on the three-dimensional porous carbon-based substrate. Figure 1 As shown in (c). In a further attempt of the present invention, an attempt was made to improve the lithium affinity of the three-dimensional porous carbon-based substrate by zinc oxide. However, after a lot of research, the inventors further found that: although zinc oxide is a naturally abundant, low-cost, and easy-to-prepare lithium-philic substance, zinc oxide is a semiconductor. Its electrical conductivity is low during the charge and discharge process, the diffusion of lithium ions is slow, and the volume changes greatly during the battery cycle, which will cause lithium dendrites to grow more easily and the battery capacity to decay seriously. Furthermore, the inventors proposed the following method for lithium-philic modification of the three-dimensional porous carbon-based substrate, and prepared a composite lithium metal negative electrode that can inhibit the volume expansion of lithium metal and the formation of lithium dendrites during the cycle process, so that the battery has a high cycle life. Specifically, an embodiment of the present invention provides a method for preparing a composite lithium metal negative electrode, which includes the steps of:

[0038] S1. providing a three-dimensional porous carbon-based substrate and a zinc salt solution;

[0039] S2. adding a nitrogen source and the three-dimensional porous carbon-based substrate to the zinc salt solution at a first preset temperature;

[0040] S3, taking out the three-dimensional porous carbon-based substrate after soaking for a first preset time, drying it, and then annealing it to obtain a nitrogen-doped zinc oxide-loaded three-dimensional porous carbon-based substrate;

[0041] S4. Immersing the nitrogen-doped zinc oxide-loaded three-dimensional porous carbon-based substrate in molten metallic lithium to obtain the composite lithium metal negative electrode.

[0042] In the present invention, nitrogen is introduced to replace part of the oxygen elements in the zinc oxide structure to form defects, thereby improving its electronic conductivity and lithium ion diffusion rate, and nitrogen-doped zinc oxide with high ionic conductivity and lithium ion diffusion rate is used as a lithiophilic site to modify the three-dimensional porous carbon-based substrate to improve its lithiophilicity, and the three-dimensional porous carbon-based substrate loaded with nitrogen-doped zinc oxide with lithiophilicity is used as the host of the lithium metal negative electrode. On the one hand, nitrogen-doped zinc oxide can form a Li-Zn alloy with molten metallic lithium, which can reduce the nucleation energy barrier of lithium metal and improve the lithiophilicity of the three-dimensional porous carbon-based substrate; on the other hand, nitrogen-doped zinc oxide can enhance the electrical conductivity and lithium ion conductivity of the three-dimensional porous carbon-based substrate, thereby significantly reducing the nucleation overpotential and polarization potential of lithium deposition, and uniform electric field distribution makes lithium metal uniformly deposited, avoiding the growth of lithium dendrites during charging and discharging. The three-dimensional porous carbon-based substrate loaded with nitrogen-doped zinc oxide in the present invention has the characteristics of high porosity, good conductivity, large specific surface area, light weight and good flexibility, etc., which provides a large internal storage space for metallic lithium. It is used as the host of the lithium metal negative electrode, which can reduce the local current density of the electrode, reduce the nucleation overpotential and polarization potential of lithium deposition, effectively control the growth of lithium dendrites and the volume expansion of lithium metal during the cycle, and has a lower density than the three-dimensional metal host, so it can effectively improve the mass energy density of the battery. At the same time, its good flexibility enables it to be used in fields such as flexible energy storage devices. The composite lithium metal negative electrode prepared by the present invention can reduce the huge volume changes in the process of lithium deposition and dissolution during the cycle, thereby improving the cycle life of the battery. Ultimately, the battery is achieved at 1mA / cm 2 , 1mAh / cm 2 It can operate for more than 1600 hours under the charge and discharge conditions (polarization voltage is 9mV), and its nucleation overpotential is only 8mV.

[0043] In step S1, in one embodiment, the three-dimensional porous carbon-based substrate is selected from at least one of carbon fiber cloth, carbon paper, carbon nanotube fiber cloth, and foam carbon.

[0044] In one embodiment, the step of providing a three-dimensional porous carbon-based substrate further comprises:

[0045] The three-dimensional porous carbon-based substrate is added to a cleaning agent, ultrasonically cleaned, and then rinsed with deionized water to remove impurities on the surface of the three-dimensional porous carbon-based substrate to prevent the impurities from affecting subsequent steps. In a specific implementation, the cleaning agent is selected from at least one of methanol, ethanol, acetone, nitric acid, and hydrochloric acid, but is not limited thereto. The amount of the cleaning agent used is 20-100 mL, and the ultrasonic cleaning time is 10-60 minutes.

[0046] In one embodiment, the method for preparing the zinc salt solution comprises the steps of:

[0047] The zinc salt is added to the solvent and mixed to obtain a zinc salt solution.

[0048] In one embodiment, the solvent is selected from at least one of methanol, ethanol, ethylene glycol, and water, but is not limited thereto.

[0049] These solvents do not react with substances in the system, thereby reducing interference, and can activate the three-dimensional porous multi-carbon-based substrate to make it easier to grow nitrogen-doped zinc oxide (lithiophilic substances) on its surface. Preferably, the solvent is selected from methanol. Methanol, as the simplest saturated monohydric alcohol, does not react with substances in the system when used as a solvent, reducing interference. Methanol can better activate the three-dimensional porous multi-carbon-based substrate to make it easier to grow nitrogen-doped zinc oxide (lithiophilic substances) on its surface.

[0050] In one embodiment, the zinc salt is selected from at least one of zinc acetate, zinc nitrate, zinc sulfate, and zinc carbonate, but is not limited thereto.

[0051] In step S2, in one embodiment, the step of adding the nitrogen source and the three-dimensional porous carbon-based substrate to the zinc salt solution specifically includes:

[0052] A nitrogen source, an alkaline regulator and the three-dimensional porous carbon-based substrate are added to the zinc salt solution.

[0053] In one embodiment, the nitrogen source is selected from at least one of thiourea, urea, and ammonium acetate, but is not limited thereto.

[0054] In one embodiment, the alkaline regulator is selected from at least one of aqueous ammonia, ammonium dihydrogen carbonate, and ammonium bicarbonate, but is not limited thereto.

[0055] In one embodiment, the mass content of ammonia in the ammonia water is 25-28%.

[0056] In one embodiment, when the alkaline regulator is selected from aqueous ammonia, the ratio of zinc salt to nitrogen source and alkaline regulator in the zinc salt solution is (0.06-0.1) mmol: (0.24-0.9) mmol: (0-7) mL.

[0057] When the alkaline regulator is selected from at least one of ammonium dihydrogen carbonate and ammonium bicarbonate, the ratio of the zinc salt to the nitrogen source and the alkaline regulator in the zinc salt solution is (0.06-0.1) mmol: (0.24-0.9) mmol: (0-1.2) mmol. In a further embodiment, the ratio of the zinc salt to the nitrogen source and the alkaline regulator in the zinc salt solution is (0.06-0.1) mmol: (0.24-0.9) mmol: (0.1-1.2) mmol.

[0058] In one embodiment, the first preset temperature is 55-80° C., and the first preset time is 2-12 hours.

[0059] In step S3, in one embodiment, the drying is vacuum drying at a temperature of 50-110° C. for 2-15 hours. In this embodiment, the drying can volatilize the residual solvent on the three-dimensional porous carbon-based substrate after soaking.

[0060] In one embodiment, the annealing treatment is performed at a temperature of 500-800° C., for a time of 0.5-3 hours, and in an atmosphere of air, nitrogen, or argon.

[0061] In a specific implementation, the dried product is placed in a crucible, and then the crucible is transferred to a tube furnace, heated to 500-800° C. at a heating rate of 1-10° C. / min, and then kept warm for 0.5-3 h.

[0062] In one embodiment, the crucible includes but is not limited to one of an alumina crucible, a magnesia crucible, a graphite crucible, and a Pt crucible.

[0063] In step S4, the nitrogen-doped zinc oxide-loaded three-dimensional porous carbon-based substrate is immersed in molten metallic lithium, and the liquid molten metallic lithium is adsorbed into the porous structure of the nitrogen-doped zinc oxide-loaded three-dimensional porous carbon-based substrate (to achieve hot injection of liquid molten metallic lithium). After natural cooling, the composite lithium metal negative electrode is obtained.

[0064] In one embodiment, the nitrogen-doped zinc oxide-supported three-dimensional porous carbon-based substrate is immersed in molten metallic lithium under conditions of an O2 concentration of <0.1 ppm and a H2O concentration of <0.1 ppm, and then naturally cooled to obtain the composite lithium metal anode. Because lithium metal is unstable in air and can spontaneously combust, this step must be performed under strict control of the O2 and H2O concentrations.

[0065] In one embodiment, the method for preparing molten metallic lithium comprises the steps of:

[0066] Under the conditions of O2 concentration <0.1ppm and H2O concentration <0.1ppm, metallic lithium (such as lithium sheets, lithium blocks, etc.) is heated at a temperature of 180-400°C until molten metallic lithium is obtained.

[0067] An embodiment of the present invention further provides a composite lithium metal negative electrode, which is prepared using the preparation method of the present invention as described above.

[0068] An embodiment of the present invention further provides a lithium metal battery comprising the composite lithium metal anode described above. In this embodiment, the lithium metal battery can effectively reduce the occurrence of lithium dendrites and volume expansion at the anode during cycling, and exhibits advantages such as high capacity retention and long cycle life.

[0069] The following describes it in detail through specific examples.

[0070] Example 1

[0071] Preparation of composite lithium metal anode, such as Figure 1 As shown in (a), the following steps are included:

[0072] (1) Place a 2.5cm×3.5cm carbon fiber cloth (such as Figure 1 The sample (shown in (d)) was added to 50 mL of methanol and ultrasonicated for 10 min to clean the surface impurities, and then rinsed with deionized water 5 times and set aside.

[0073] (2) A certain amount of zinc acetate was dissolved in 130 mL of methanol to obtain a zinc acetate solution with a concentration of 0.06 mM. Then, a certain amount of urea (so that the concentration of urea in the mixed solution was 0.24 mM) and 2 mL of ammonia water with an ammonia content of 25% by mass and the above-mentioned carbon fiber cloth were added under 55°C oil bath conditions. The carbon fiber cloth was soaked and reacted for 2 hours and then taken out. It was vacuum dried at 50°C for 2 hours and then placed in an alumina crucible under argon protection. The temperature was raised to 500°C in a tube furnace at a heating rate of 5°C / min for annealing for 2 hours and then naturally cooled to room temperature to obtain nitrogen-doped zinc oxide-loaded carbon fiber cloth (such as Figure 1 (shown in (d)), denoted as N-ZnO / CC.

[0074] (3) Figure 1 As shown in (b), N-ZnO / CC is transferred to a glove box filled with argon gas with an O2 concentration of <0.1ppm and a H2O concentration of <0.1ppm. The lithium sheet is then heated to 180°C on a heating table to melt it. The N-ZnO / CC is directly contacted with the molten metallic lithium to achieve the infusion of lithium metal. After natural cooling, a composite lithium metal anode is prepared (its actual state is shown in FIG). Figure 1 As shown in (e) and (f), the SEM images are as follows Figure 1 (g) in Figure 5), denoted as N-ZnO / CC@Li.

[0075] Example 2

[0076] The preparation method of the composite lithium metal negative electrode is basically the same as that of Example 1, except that 9 mL of ammonia water with an ammonia content of 25% by mass is added in step (2).

[0077] Example 3

[0078] The preparation method of the composite lithium metal negative electrode is basically the same as that of Example 1, except that 0 mL of ammonia water with an ammonia content of 25% by mass is added in step (2).

[0079] Example 4

[0080] The preparation method of the composite lithium metal negative electrode is basically the same as that of Example 1, except that 3 mL of ammonia water with an ammonia content of 25% by mass is added in step (2).

[0081] Example 5

[0082] The preparation method of the composite lithium metal negative electrode is basically the same as that of Example 1, except that 3 mL of ammonia water with an ammonia content of 25% by mass is added in step (2) and annealing is performed at a temperature of 650°C.

[0083] Comparative Example 1

[0084] The preparation method of the composite lithium metal negative electrode is basically the same as that of Example 1, except that in step (2), "adding a certain amount of urea (so that the concentration of urea in the mixed solution is 0.25 mM) and 2 mL of ammonia water with an ammonia mass content of 25% and the above-mentioned carbon fiber cloth under 55 ° C oil bath conditions" is replaced by "adding a certain amount of potassium hydroxide under 55 ° C oil bath conditions so that the concentration of potassium hydroxide in the mixed solution is 0.12 mM", and the obtained product is recorded as ZnO / CC@Li (i.e., without nitrogen doping).

[0085] test:

[0086] (1) The XRD results of N-ZnO / CC prepared in Examples 1, 2, and 3 are shown in FIG. Figure 2 As shown, compared with the standard spectrum of ZnO, the diffraction peaks of N-ZnO / CC in Examples 1, 2, and 3 shift to higher angles, indicating that N is successfully doped into ZnO. When ammonia water is added, the angular shift of the diffraction peak is more obvious, proving that the addition of ammonia water contributes to the doping of N.

[0087] (2) The SEM images of N-ZnO / CC prepared in Examples 1, 2, and 3 are shown in Figure 2. Figure 3 As shown in (a), (b) and (c), the results show that when no ammonia water is added, a small amount of nitrogen-doped zinc oxide is loaded, and when ammonia water is added, the loading amount of nitrogen-doped zinc oxide increases significantly.

[0088] (3) The N-ZnO / CC@Li prepared in Examples 1, 2, and 3 were assembled into symmetrical batteries for cycle testing, and a symmetrical battery prepared from pure lithium sheets was used as a comparison.

[0089] The N-ZnO / CC@Li prepared in Examples 1, 2, and 3 were respectively assembled into symmetrical batteries. The assembly method of the symmetrical battery was as follows: positive electrode shell-N-ZnO / CC@Li-electrolyte-diaphragm-electrolyte-N-ZnO / CC@Li-gasket-spring sheet-negative electrode shell was assembled in the order of positive electrode shell-N-ZnO / CC@Li-electrolyte-diaphragm-electrolyte-N-ZnO / CC@Li-gasket-spring sheet-negative electrode shell, wherein the battery shell was 2032 type, the electrolyte was 1M LiTFSI DOL / DME+1.0wt% LiNO3, the diaphragm was 16mm microporous PP film (Celgard 2400), and the N-ZnO / CC@Li electrode was a disc with a diameter of 10mm.

[0090] Pure lithium sheets are assembled into symmetrical batteries. The preparation method of the symmetrical battery is as follows: assemble in the order of positive electrode shell - lithium sheet - electrolyte - diaphragm - electrolyte - lithium sheet - gasket - spring sheet - negative electrode shell, wherein the battery shell adopts 2032 type, the electrolyte uses 1M LiTFSI DOL / DME + 1.0wt% LiNO3, the diaphragm uses 16mm microporous PP film (Celgard 2400), and the lithium sheet is a disc with a diameter of 10mm.

[0091] Cycling test: The N-ZnO / CC@Li prepared in Examples 1, 2, and 3 were assembled into symmetrical batteries and the results of the cycling test were as follows: Figures 4a-4c Compared with pure lithium sheets, the N-ZnO / CC@Li prepared in Examples 1, 2, and 3 have a longer cycle life than the symmetrical batteries assembled with pure lithium sheets.

[0092] (4) The N-ZnO / CC@Li prepared in Examples 4 and 5 were assembled into a symmetrical battery (the method is the same as above), and the impedance spectrum thereof is shown as follows: Figure 5 As shown, the results show that compared with pure lithium sheets, the N-ZnO / CC@Li prepared in Examples 4 and 5 has a lower impedance value and a higher lithium ion diffusion rate.

[0093] (5) The SEM image of N-ZnO / CC prepared in Example 5 is as follows Figure 6 As shown in (a), the EDS diagram is as follows Figure 6 As shown in (b), the distribution and content statistics of C, O, N, and Zn are as follows Figure 6 As shown in (c), the plane SEM image of the original carbon fiber cloth used in Example 5 is as follows Figure 6 As shown in (d), the cross-sectional SEM image of the original carbon fiber cloth used in Example 5 is as follows: Figure 6 As shown in (e), the cross-sectional SEM image of N-ZnO / CC prepared in Example 5 is as follows Figure 5 As shown in (f), the above results show that nitrogen is successfully doped into zinc oxide, and the nitrogen-doped zinc oxide is evenly loaded on the fibers in the carbon fiber cloth.

[0094] (6) The N-ZnO / CC@Li prepared in Example 5, the ZnO / CC@Li prepared in Comparative Example 1, and the pure lithium sheet were assembled into symmetrical batteries (using the same method as above), respectively recorded as: N-ZnO / CC@Li-N-ZnO / CC@Li, ZnO / CC@Li-ZnO / CC@Li, and Li-Li. The surface capacity of N-ZnO / CC@Li and ZnO / CC@Li used was 1 mAh / cm 2 These symmetrical cells are at 1 mA / cm 2 The cycling performance at the charge and discharge current density is as follows Figure 7a As shown, at 2mA / cm 2 The cycling performance at the charge and discharge current density is as follows Figure 7b As shown, at 3mA / cm 2 The cycling performance at the charge and discharge current density is as follows Figure 7c The symmetrical battery with fixed surface capacity of 1 mAh / cm2 was assembled by assembling N-ZnO / CC@Li and pure lithium sheets prepared in Example 5. 2 After that, the temperature was set at 0.5, 1, 2, 4, and 0.5 mA / cm 2 The rate performance at the charge and discharge current density is as follows Figure 6 As shown in d.

[0095] (7) The N-ZnO / CC@Li and pure lithium sheets prepared in Example 5 were assembled into symmetrical batteries. The unit area capacity of the N-ZnO / CC@Li used was 1 mAh / cm 2 During the cycling process, impedance tests were first performed at different time stages (initial state, after 50 cycles, and after 100 cycles). After the tests, the symmetrical battery was disassembled and SEM tests were performed on the pole pieces (N-ZnO / CC@Li, pure lithium pieces) at the corresponding time stages.

[0096] At 1 mA / cm 2 The charge and discharge current density is cycled, and the interface impedance and morphology changes at different time stages are as follows: Figure 8 As shown, (a) is the impedance spectrum of the initial state without cycling; (b) is the impedance spectrum after 50 cycles; (c) is the impedance spectrum after 100 cycles; (d) is the SEM image of the pure lithium sheet in the initial state without cycling; (e) is the SEM image of the pure lithium sheet after 50 cycles; (f) is the SEM image of the pure lithium sheet after 100 cycles; (g) is the SEM image of the N-ZnO / CC@Li sheet in the initial state without cycling; (h) is the SEM image of the N-ZnO / CC@Li sheet after 50 cycles; (i) is the SEM image of the N-ZnO / CC@Li sheet after 100 cycles.

[0097] From the above results, it can be seen that at different stages of the cycle, the impedance of the symmetrical battery assembled with N-ZnO / CC@Li prepared in Example 5 is smaller than that of the symmetrical battery assembled with pure lithium sheets. After 100 cycles, the surface of the pure lithium sheet cracks, while the surface of the N-ZnO / CC@Li sheet does not change significantly compared to the initial state without cycling.

[0098] In summary, the present invention provides a composite lithium metal negative electrode, a preparation method thereof, and a lithium metal battery. The present invention uses a three-dimensional porous carbon-based substrate loaded with nitrogen-doped zinc oxide as the host of the lithium metal negative electrode. Since the three-dimensional porous carbon-based substrate loaded with nitrogen-doped zinc oxide has the characteristics of high porosity, good conductivity, large specific surface area, light weight and good flexibility, it can effectively control the growth of lithium dendrites and the volume and expansion of lithium metal during the cycle, and has a lower density than the three-dimensional metal host, so it can effectively improve the mass energy density of the battery. At the same time, its good flexibility enables it to be applied to fields such as flexible energy storage devices. The present invention enhances the lithium affinity of the three-dimensional porous carbon-based substrate (which does not have lithium affinity itself) by introducing nitrogen-doped zinc oxide into the three-dimensional porous carbon-based substrate to modify the three-dimensional porous carbon-based substrate, and successfully prepares a composite lithium metal electrode with a three-dimensional porous carbon-based substrate loaded with nitrogen-doped zinc oxide as the lithium metal host. On the one hand, nitrogen-doped zinc oxide can form a Li-Zn alloy with molten lithium metal, which can reduce the nucleation energy barrier of lithium metal and thus improve the lithium affinity of the three-dimensional porous carbon-based substrate. On the other hand, nitrogen-doped zinc oxide can enhance the electrical conductivity and lithium ion conductivity of the three-dimensional porous carbon-based substrate, thereby significantly reducing the nucleation overpotential and polarization potential of lithium deposition. The uniform electric field distribution allows the lithium metal to be uniformly deposited, avoiding the growth of lithium dendrites during the charge and discharge process. The composite lithium metal negative electrode prepared by the present invention can reduce the huge volume change during lithium deposition and dissolution, inhibit the growth of lithium dendrites, and improve the cycle life of the battery, ultimately achieving a battery charge and discharge rate of 1mA / cm 2 , 1mAh / cm 2 It can operate for more than 1600 hours under the charge and discharge conditions (polarization voltage is 9mV), and its nucleation overpotential is only 8mV.

[0099] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for preparing a composite lithium metal negative electrode, characterized in that: Including steps: Providing a three-dimensional porous carbon-based substrate and a zinc salt solution; adding a nitrogen source and the three-dimensional porous carbon-based substrate to the zinc salt solution at a first preset temperature; soaking the three-dimensional porous carbon-based substrate for a first preset time, taking it out, drying it, and then annealing it to obtain a nitrogen-doped zinc oxide-loaded three-dimensional porous carbon-based substrate; Immersing the nitrogen-doped zinc oxide-loaded three-dimensional porous carbon-based substrate in molten metallic lithium to obtain the composite lithium metal negative electrode; the nitrogen-doped zinc oxide and the molten metallic lithium form a Li-Zn alloy; The three-dimensional porous carbon-based substrate is selected from at least one of carbon fiber cloth, carbon paper, carbon nanotube fiber cloth, and foam carbon; The nitrogen source is selected from at least one of thiourea, urea, and ammonium acetate; The temperature of the annealing treatment is 500-800° C., the time of the annealing treatment is 0.5-3 hours, and the atmosphere of the annealing treatment is one of air, nitrogen, and argon.

2. The method for preparing a composite lithium metal negative electrode according to claim 1, wherein The step of adding the nitrogen source and the three-dimensional porous carbon-based substrate to the zinc salt solution specifically includes: A nitrogen source, an alkaline regulator and the three-dimensional porous carbon-based substrate are added to the zinc salt solution.

3. The method for preparing a composite lithium metal negative electrode according to claim 2, wherein: The zinc salt is selected from at least one of zinc acetate, zinc nitrate, zinc sulfate, and zinc carbonate; And / or, the alkaline regulator is selected from at least one of ammonia water, ammonium dihydrogen carbonate, and ammonium bicarbonate.

4. The method for preparing a composite lithium metal negative electrode according to claim 1, wherein The first preset temperature is 55-80° C., and the first preset time is 2-12 h.

5. The method for preparing a composite lithium metal negative electrode according to claim 1, wherein The drying is vacuum drying, the temperature of the vacuum drying is 50-110° C., and the time of the vacuum drying is 2-15 h.

6. The method for preparing a composite lithium metal negative electrode according to claim 1, wherein: The method for preparing the molten metallic lithium comprises the steps of: Under the conditions of O2 concentration <0.1 ppm and H2O concentration <0.1 ppm, metallic lithium is heated at a temperature of 180-400°C until molten metallic lithium is obtained.

7. A composite lithium metal negative electrode, characterized in that The preparation method is described in any one of claims 1 to 6.

8. A lithium metal battery, characterized in that: Including the composite lithium metal negative electrode according to claim 7.

Images