Electroless plating constructs lithium fluoride/sodium composite interface for metal lithium anode

This article is from the WeChat public account: X-MOLNews

Lithium metal has high theoretical specific capacity (3860 mAh g-1) and low potential (-3.04 V, relative to standard hydrogen electrode), which is an ideal negative electrode for constructing high specific energy batteries Materials, but there are problems such as dendrite pulverization, volume change, solid electrolyte interphase (SEI) instability, etc., which restrict the practical application of lithium metal batteries. Therefore, the development of lithium metal anode stabilization strategies has important research significance. The current common lithium metal improvement strategies include electrolyte optimization, electrode/electrolyte interface engineering, and load-type electrode structure design. The root of the growth of lithium dendrites lies in the non-uniform peeling and deposition of lithium ions, and the construction of a stable and high-strength SEI film is the key to stabilizing the lithium metal anode. In recent years, fluorinated interface film (LiF-SEI) has attracted attention. As an excellent electronic insulator, LiF can effectively prevent electron tunneling, thereby inhibiting side reactions between the electrolyte and the lithium metal negative electrode. Compared with other conventional SEI components, LiF has excellent interface properties, which can induce the lateral dispersion of lithium ions, promote vertical transmission, and facilitate uniform lithium deposition. Similar to LiF, NaF also plays an important role in sodium metal negative electrode SEI, and NaF has a higher Young's modulus and excellent mechanical strength, which can effectively inhibit dendritic growth. The effective combination of LiF and NaF to build a composite interface film is expected to improve the performance of lithium metal anodes.

Recently, the Nankai University Cheng Fangyi research group proposed a lithium fluoride/sodium composite interface for stabilizing a new strategy of lithium metal anode . Through a simple and controllable pre-soaking method, the lithium metal and the NaPF6 electrolyte are replaced by a substitution reaction, and then placed in the LiPF6 electrolyte, and a lithium fluoride/sodium composite interface is constructed through fluorination etching. Combining electron microscopy, spectroscopy, energy spectroscopy, atomic force and other means to characterize different metal lithium,The results show that the composite SEI film formed by the two-step treatment is denser, composed of a variety of inorganic and organic components, and has a high fluoride content and higher mechanical strength. DFT calculations and electrode kinetics studies show that the interface energy between NaF and Li is high, and the coexistence of NaF and LiF is beneficial to promote the rapid lateral transport of lithium ions at the interface, induce uniform nucleation of lithium, and inhibit vertical lithium dendrite growth. The untreated metal lithium electrode has a large charge and discharge polarization, and obvious dendritic behavior appears during the cycle. The fluorinated metal lithium electrode can be cycled stably in a symmetrical battery, and the surface remains flat. The high surface capacity of 10 mAh cm-2 can be cycled stably for more than 1300 hours.

Figure 1. Different SEI film construction methods and schematic diagrams of their inhibitory effects on lithium dendrites

img3 span3 metal Analysis of the surface morphology and cross-sectional element distribution of the anode

Figure 3. The SEI composition analysis of several metal lithium anodes _span112

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This work uses the two-step chemical immersion method of electroless plating.Successfully constructed a uniform and dense lithium fluoride/sodium composite interface film, which effectively inhibited the growth of lithium dendrites, realized the long-period stable cycle of the metal lithium anode, and provided a simple and easy way for the interface design of the active metal electrode .

related results were published in J. Am. Chem. Soc is the first graduate student of Nankai University. Professor Cheng Fangyi.