Preparation method and application of composite lithium negative electrode for garnet solid-state electrolyte

Abstract

The application discloses a preparation method and application of a composite lithium negative electrode for a garnet solid-state electrolyte, and belongs to the technical field of solid-state lithium metal batteries; the preparation method is as follows: MXene nanosheets and iodide are added into a solvent, uniformly stirred in the dark, and then freeze-dried to obtain an MXene bifunctional additive containing iodide; the bifunctional additive is added into high-temperature molten Li and uniformly mixed to obtain a lithium metal composite negative electrode; the composite negative electrode is stable in structure, can form a close contact with an electrolyte, effectively reduces the interface impedance, and enables the solid-state lithium metal battery to maintain a low overpotential in a cycle process, thereby improving the cycle stability of the solid-state battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of all-solid-state lithium metal batteries, and particularly relates to a preparation method and application of a composite lithium anode for a garnet solid-state electrolyte. BACKGROUND

[0002] With the vigorous development of new energy vehicles, people have put forward higher requirements for the energy density and safety of batteries. In order to improve the energy density, the design of the battery must be improved. The all-solid-state lithium battery using a lithium metal anode and a solid electrolyte is the most promising to achieve a high energy density of 500 Wh / kg. In addition, it does not need to use flammable and explosive organic electrolyte, can reduce the cost of the battery, and can completely solve the safety problem of the liquid lithium ion battery. Therefore, the solid-state lithium metal battery has attracted widespread attention in the society.

[0003] The biggest problem of the lithium metal anode applied to the solid-state electrolyte is that the solid-solid contact causes a large interface gap, which in turn causes a large interface impedance, easily leading to uneven distribution of electric field and gradually forming lithium dendrites. The formation of dendrites not only consumes the active lithium in the battery and reduces the energy density of the battery, but also penetrates the electrolyte. At the same time, the lithium metal is easy to react with the solid-state electrolyte, causing the interface to be unstable, thereby increasing the overpotential of the lithium metal solid-state battery during the cycle process.

[0004] At present, people often use methods such as introducing an intermediate layer and constructing an alloy interface layer to improve the interface wettability and inhibit the growth of lithium dendrites. Although some works effectively reduce the interface impedance, they mainly solve the problem from the garnet electrolyte, for example, CN117096423A discloses a method of depositing a nanolayer on the surface of a garnet solid-state electrolyte sheet by using ion beam deposition technology. The nanolayer is heated to react with lithium. Although the interface impedance can be reduced to a certain extent, the technical requirements are high, the experimental operation process takes a long time, and it is not conducive to large-scale processing and application.

[0005] In recent years, MXene, a kind of two-dimensional transition metal carbide, nitride and carbonitride material, is widely used in solid-state batteries due to its rich surface functional groups. Wang et al. (Journal of Energy Chemistry, 2023, 78, 47-55) prepared a gel polymer interlayer containing MXene by compounding MXene material with PVDF and Li salt. It was proved that due to the excellent conductivity of MXene, the interlayer formed by adding MXene could improve the interface wettability and inhibit the formation of dendrites. However, the introduction of the polymer electrolyte layer increases the interface between the polymer electrolyte and the garnet electrolyte, and the transmission energy barrier between lithium ions is large. In addition, the assembled lithium metal battery needs to be operated at a high temperature of 60 ℃, and the overpotential of the battery increases significantly during the cycle process, which means that this modification method will still cause significant capacity decay after a large number of cycles, and cannot maintain good cycle effect.

[0006] Liao et al. (ACS Appl. Mater. Interfaces, 2023, 15, 44413-44421) first deposited a Pt thin layer on the surface of the garnet solid-state electrolyte using magnetron sputtering technology, and then introduced MXene to prepare a composite anode. Although it has a certain effect on stabilizing the interface layer, it still needs multiple steps, complicated preparation process and high cost, and cannot avoid the construction of the interface interlayer in the electrolyte layer. In addition, the thickness of the plated nanolayer is difficult to ensure uniformity. SUMMARY

[0007] In view of the above, the purpose of the present application is to provide a simple and efficient preparation method of lithium metal composite anode, aiming to solve the problems of poor interface compatibility of metal lithium and garnet solid-state electrolyte and obvious change of overpotential during cycle process. The lithium metal composite anode modified by the bifunctional additive containing MXene and iodide can make Li + The uniform transmission at the interface of the garnet solid-state electrolyte and the effective reduction of the impedance at the interface are due to the rich oxygen-containing and fluorine-containing functional groups on the surface of MXene, which can greatly improve the interface wettability between the garnet electrolyte and the electrolyte. As a redox medium, iodide can stabilize the interface and effectively improve the long cycle stability of the battery.

[0008] The preparation method of the composite anode modified by the bifunctional additive of MXene and iodide in the present application is simple and efficient, and the whole process is controllable, which is very beneficial to large-scale production for full solid-state lithium metal batteries.

[0009] In a first aspect, the present application provides a preparation method of lithium metal composite anode for solid-state battery, the steps of the method are:

[0010] Step one: MXene nanosheets, iodide are added to a solvent, stirring in the dark, followed by freeze-drying, to obtain a MXene bifunctional additive containing iodide, the mass of the iodide is 5-25% of the mass of the MXene;

[0011] Step two: heating and melting the lithium metal, and scraping off the impurity layer on the surface to expose the lithium, adding the bifunctional additive obtained in step one to the liquid molten lithium, mixing uniformly, to obtain a MXene-lithium metal composite negative electrode containing iodide, the mass of the bifunctional additive is 10-30% of the mass of the lithium metal.

[0012] Preferably, in step one, the MXene nanosheets are Ti3C2T x -MXene (T is O, OH, F), Ti2CT x -MXene, Ti4N3T x -MXene, Ta4C3T x -MXene, further selected as Ti3C2T x -MXene.

[0013] Preferably, in step one, the iodide is one or more of LiI, NaI, KI, CuI2.

[0014] Further, in step one, the mass of the iodide is 5-25% of the mass of the MXene.

[0015] Further, in step two, the mass of the MXene mixture containing iodine is 10-30% of the mass of the lithium metal.

[0016] Preferably, in step one, the stirring time is 0.5-3h, and the stirring speed is 200-500rpm.

[0017] Preferably, in step two, the heating temperature is in the range of 180℃-260℃.

[0018] Preferably, in step two, the heating and melting time is 0.5-2.5h.

[0019] In a second aspect, the present application also provides a solid-state lithium metal battery, which is prepared by the following method: Step one: MXene nanosheets, iodide are added to a solvent, stirring in the dark, followed by freeze-drying, to obtain a MXene bifunctional additive containing iodide.

[0020] Step two: heating and melting the lithium metal, and scraping off the impurity layer on the surface to expose the fresh and bright lithium, adding the bifunctional additive obtained in step one to the molten lithium metal, mixing uniformly, to obtain a MXene-Li composite negative electrode containing iodide.

[0021] Step three: combine the iodide-containing MXene-Li composite negative electrode with the garnet solid-state electrolyte sheet, assemble a lithium symmetric battery and a solid-state lithium metal battery.

[0022] In a third aspect, the present application also provides a use of the composite negative electrode provided in the first aspect for preparing a solid-state lithium metal battery.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] A simple method is provided for preparing an iodide-containing MXene-Li composite negative electrode. x The surface of MXene contains a large number of fluorine-containing and oxygen-containing functional groups, which have high activity. After being combined with molten lithium, the surface tension of Li can be adjusted, and the interfacial wettability between the garnet solid-state electrolyte can be effectively solved. However, it is difficult to avoid higher polarization in the subsequent cycle process. The addition of iodine salt can form a stable interfacial layer, improve the interfacial stability of the solid-state battery, and be beneficial to uniform lithium deposition. The problems of volume expansion and lithium dendrite of pure lithium as the negative electrode of the lithium metal battery are solved, and the long cycle stability, coulombic efficiency and rate performance of the solid-state lithium metal battery are improved.

[0025] The present application requires a small number of devices, a simple preparation method, easy operation, and has extremely wide application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Optical photo of the interfacial wettability of the composite negative electrode prepared in Example 1 and the garnet solid-state electrolyte.

[0027] Figure 2 Optical photo of the interfacial wettability of the pure lithium negative electrode prepared in Comparative Example 3 and the garnet solid-state electrolyte.

[0028] Figure 3 Charging and discharging performance of the lithium metal solid-state battery assembled by the composite negative electrode prepared in Example 1 at 0.2 C current density in the first cycle and the 50th cycle.

[0029] Figure 4 Charging and discharging performance of the lithium metal solid-state battery assembled by the pure lithium negative electrode prepared in Comparative Example 3 at 0.2 C current density in the first cycle and the 50th cycle.

[0030] Figure 5 Long cycle performance chart of the lithium metal solid-state battery assembled by the composite negative electrode prepared in Example 1 at 0.2 C current density. DETAILED DESCRIPTION

[0031] In order to better illustrate the purposes, technical solutions and advantages of the present application, the present application will be further described below in combination with specific examples. The raw materials, reagents and the like used without the manufacturer indicated are all conventional products that can be purchased on the market. Example 1

[0032] (1): 0.5 g MXene nanosheets, 0.05 g LiI were weighed and dissolved in ultrapure water, avoiding light, stirring at 400 rpm for 1.5 h to obtain a mixed solution containing LiI, and then freeze-drying to obtain a MXene@LiI mixture, the mass of LiI obtained is 10% of the mass of MXene.

[0033] (2): 1 g of metallic lithium sheet was heated and melted, the temperature was 240℃, and the impurity layer on the surface was scraped off with tweezers to expose fresh and shiny lithium, 0.15 g of MXene@LiI mixture obtained in step one was added to the molten metallic lithium to mix uniformly to obtain a Li-MXene@LiI composite negative electrode, wherein the mass of MXene@LiI is 15% of the mass of metallic Li.

[0034] (3): The above molten Li-MXene@LiI composite negative electrode was combined with a garnet-type solid-state electrolyte sheet to assemble a lithium symmetric battery and a solid-state lithium metal battery. Example 2

[0035] Different from example 1, the mass of LiI added in step one is 0.025 g, the mass of LiI obtained is 5% of the mass of MXene, and other operation steps and conditions are the same as those of example 1. Example 3

[0036] Different from example 1, the mass of LiI added in step one is 0.075 g, the mass of LiI obtained is 15% of the mass of MXene, the mass of MXene@LiI mixture weighed in step two is 0.3 g, the mass of MXene@LiI obtained is 30% of the mass of metallic Li, and other operation steps and conditions are the same as those of example 1. Example 4

[0037] Different from example 1, the mass of LiI added in step one is 0.125 g, the mass of LiI obtained is 25% of the mass of MXene, and other operation steps and conditions are the same as those of example 1. Example 5

[0038] (1): Take 0.5 g MXene nanosheets, 0.075 g NaI, dissolve in ultrapure water, avoid light, stir at 400 rpm for 1.5 h, obtain a mixed solution containing NaI, then freeze-dry to obtain a MXene@NaI mixture, the mass of NaI obtained is 15% of the mass of MXene.

[0039] (2): Take 1 g of lithium metal sheet, heat and melt, the temperature is 240℃, and use tweezers to remove the impurity layer on the surface to expose fresh and bright lithium, take 0.2 g of MXene@NaI mixture obtained in step one, add it to the molten metal lithium to mix evenly, obtain Li-MXene@NaI composite negative electrode, the mass of MXene@NaI obtained is 20% of the mass of metal Li.

[0040] (3): The above molten Li-MXene@NaI composite negative electrode is combined with a garnet-type solid-state electrolyte sheet to assemble a lithium symmetric battery and a solid-state lithium metal battery. Example 6

[0041] Different from example 5, 0.1 g of NaI is added in step one, the mass of NaI obtained is 20% of the mass of MXene, the mass of MXene@NaI mixture taken in step two is 0.25 g, the mass of MXene@LiI obtained is 25% of the mass of metal Li, and other operation steps and conditions are the same as example 5. Example 7

[0042] (1): Take 0.5 g MXene nanosheets, 0.05 g KI, dissolve in ultrapure water, avoid light, stir at 400 rpm for 1.5 h, obtain a mixed solution containing KI, then freeze-dry to obtain a MXene@KI mixture, the mass of KI obtained is 10% of the mass of MXene.

[0043] (2): Take 1 g of lithium metal sheet, heat and melt, the temperature is 240℃, and use tweezers to remove the impurity layer on the surface to expose fresh and bright lithium, take 0.27 g of MXene@KI mixture obtained in step one, add it to the molten metal lithium to mix evenly, obtain Li-MXene@KI composite negative electrode, the mass of MXene@KI obtained is 27% of the mass of metal Li.

[0044] (3) The above molten Li-MXene@KI composite negative electrode is combined with a garnet-type solid-state electrolyte sheet to assemble a lithium symmetric battery and a solid-state lithium metal battery. Comparative Example 1

[0045] Different from example 1, no iodide is added, the specific operation is as follows:

[0046] Take 1 g of lithium metal sheet, heat and melt, the temperature is 240 ℃, and use tweezers to remove the surface impurity layer, expose fresh bright lithium, take 0.1 g MXene nanosheet and add to the molten metal lithium, mix evenly, get Li-MXene composite negative electrode, the mass of MXene is 10% of the mass of metal Li, then combined with the garnet solid electrolyte sheet, assemble lithium symmetric battery and solid-state lithium metal battery. Comparative example 2

[0047] Take 1 g of lithium metal sheet, heat and melt, the temperature is 240 ℃, and use tweezers to remove the surface impurity layer, expose fresh bright lithium, take 0.2 g MXene nanosheet and add to the molten metal lithium, mix evenly, get Li-MXene composite negative electrode, the mass of MXene is 20% of the mass of metal Li, then combined with the garnet solid electrolyte sheet, assemble lithium symmetric battery and solid-state lithium metal battery. Comparative example 3

[0048] Take 1 g of lithium metal sheet, heat and melt, the temperature is 240 ℃, and use tweezers to remove the surface impurity layer, expose fresh bright lithium, then combined with the garnet solid electrolyte sheet, assemble lithium symmetric battery and solid-state lithium metal battery.

[0049] The lithium symmetric battery assembled by the MXene lithium metal composite negative electrode prepared in examples 1-7 has a low initial interfacial impedance, which benefits from the rich surface functional groups in MXene, which can well improve the surface tension of molten Li and improve the interfacial wettability. In addition, the addition of iodide has a low interfacial energy barrier, so that Li + can be uniformly deposited, greatly reducing the interfacial impedance. The critical current density is defined as the highest applicable voltage value at which the lithium symmetric battery does not short circuit, and especially the composite negative electrode of example 1 has an ultra-high critical current density value of 1.35 mA cm -2 .

[0050] The pure molten Li negative electrode has a large surface tension of liquid lithium, which causes a large gap between the interface and the garnet solid electrolyte, and point-to-point contact leads to increased interfacial impedance, which is prone to lithium dendrite and short circuit. Therefore, the critical current density value of comparative example 3 is low, only 0.3 mA cm -2 .

[0051] Comparative example 1 and comparative example 2 are Li-MXene negative electrodes only added with MXene modification, although they have a more obvious improvement effect compared with the pure molten Li negative electrode in comparative example 3, but the interfacial impedance is still large.

[0052] Embodiments 1-7 all have excellent first circle discharge specific capacity, and the polarization voltage remains basically unchanged after 50 cycles, especially in embodiment 1, the overpotential still remains at 121 mV after 50 cycles, fully indicating the superiority of the composite negative electrode prepared by the bifunctional additive modified metal lithium, and the added iodide can make the Li + uniformly deposited, and the interface is stable.

[0053] In summary, the superiority of the composite negative electrode prepared in the application is illustrated, the MXene can improve the interface wettability of Li and the garnet electrolyte, the addition of the iodide can further stabilize the interface layer in the solid-state lithium metal battery, and the solid-state battery can have good cycle performance.

[0054] The above-described embodiments are only to express the implementation methods of the present disclosure, and the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the disclosed patent, and it should be pointed out that any modification, equivalent replacement, improvement, etc. made by those skilled in the art without departing from the concept of the present disclosure shall be included in the protection scope of the present application.

Claims

1. A method for preparing a composite lithium negative electrode for a garnet-type solid electrolyte, characterized in that: The method steps are: Step 1: Add MXene nanosheets and iodide to a solvent, stir in the dark, and then freeze-dry to obtain a MXene bifunctional additive containing iodide, wherein the mass of the iodide is 5-25% of the mass of the MXene; Step 2: Heat the molten lithium metal and scrape off the impurity layer on the surface to expose the lithium. Add the bifunctional additive obtained in step 1 to the liquid molten lithium and mix them evenly to obtain a MXene lithium metal composite anode containing iodide. The mass of the bifunctional additive is 10-30% of the mass of the lithium metal. In step 1, the MXene nanosheet is Ti3C2T x -MXene, Ti2CT x -MXene, Ti4N3T x -MXene, Ta4C3T x -MXene, wherein T in the formula is O, OH or F; In step 1, the iodide is one or more of LiI, NaI, KI, and CuI2.

2. The method for preparing a composite lithium negative electrode for a garnet-type solid electrolyte according to claim 1, wherein: In step 1, the stirring time in the dark is 0.5-3 h, and the stirring speed is 200-500 rpm.

3. The method for preparing a composite lithium negative electrode for a garnet-type solid electrolyte according to claim 1, wherein: In step 1, the stirring time in the dark is 0.5-2 h, and the stirring speed is 200-400 rpm.

4. The method for preparing a composite lithium negative electrode for a garnet-type solid electrolyte according to claim 1, wherein: The heating temperature range in step 2 is 180°C-260°C.

5. The method for preparing a composite lithium negative electrode for a garnet-type solid electrolyte according to claim 1, wherein: The heating temperature in step 2 is in the range of 200°C to 250°C.

6. The method for preparing a composite lithium negative electrode for a garnet-type solid electrolyte according to claim 1, wherein: The heating and melting time in step 2 is 0.5-2.5 h.

7. The method for preparing a composite lithium negative electrode for a garnet-type solid electrolyte according to claim 1, wherein: The heating and melting time in step 2 is 0.5-1.5h.

8. Application of the composite lithium negative electrode prepared by the method according to any one of claims 1 to 7, characterized in that: Used in the preparation of lithium batteries, the composite lithium negative electrode is combined with the garnet-type solid electrolyte sheet to assemble a lithium symmetrical battery, namely a solid-state lithium metal battery.

9. A battery, characterized in that: The composite lithium negative electrode is prepared using the method according to any one of claims 1 to 7.

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