A Valence Gradient Protective Layer for Dendrite‐Free and Highly Stable Lithium Metal Anodes

Abstract

The uncontrolled growth of Li dendrites on Li metal anodes may cause short circuit of a working cell, even electrolyte combustion and cell explosion. [4] Li dendrites may be converted to electrochemically inactive dead Li covered by SEI due to loss of electrical contact with the anode. The accumulation of dead Li may even lead to anode pulverization. [5] All these behaviors lead to a low Coulombic efficiency (CE), fast capacity fading and rapid cell failure. [6] To tackle the issues regarding Li metal anodes, various approaches have been proposed to optimize Li anodes in recent years, [7] including Li host design, [8] composite anode engineering, [9] electrolyte composition adjustment, [10] separator modification, [11] solid electrolyte employment, [12] SEI generation, [13] and artificial protective layer construction. [14] A three-dimensional hybrid host consisting of silver nanoparticles and carbon macroporous fibers enabled a dendrite-free Li plating/stripping behavior with a high CE. [8a] A molecular-level SEI was designed by using a reactive polymer composite, which effectively suppressed electrolyte consumption in the formation and maintenance of the SEI. [13a] An SEI with high inorganic components was stabilized in highly corrosive cyclic carbonates by tuning polymer-solvent interactions. [13c] Recently, artificial protective layers have attracted much interest due to the following advantages: a) the composition, structure, mechanical strength and ionic conductivity of the protective layer can be tuned and optimized; b) the ion flux through the protective layer can be homogenized at the anode surface, resulting in uniform Li deposition; c) the side reactions between the electrolyte and Li metal are reduced since solvent or anion molecules are expelled by the protective coating. [15] Yu and coworkers prepared a mixed Li 2 S/Li 2 Se protection layer based on the gas-solid reaction between SeS 2 and Li metal. The cycle performance of symmetric cells with an ether-based electrolyte was greatly improved due to the high Li + conductivity of the protection layer. [16] Huang and co-workers obtained a dual-layered protective layer with an inorganic inner layer and an organic outer one to protect Li anodes by immersing Li foils in fluoroethylene carbonate (FEC). Through this facile process, uniform Li deposition and a stable cycle performance were achieved. [17] Song and co-workers coated Li metal anodes with a LiF-polymer composite layer by a simple roll-press method. Such a composite coating Li metal is the next-generation anode material for high-energy-density Li-ion batteries. Unfortunately, its practical application is hampered by drawbacks such as an unstable solid electrolyte interphase and undesirable Li dendrites. Herein, an Fe-based protective layer with a valence gradient is constructed on Li anodes, which consists of an Fe 3+ /Fe 2+ -rich outer layer and an Fe 0containing inner layer. The protective layer not only isolates the underlying Li metal from the corrosive carbonate electrolyte, but al...

Effects of Molecular Weight on the Electrochemical Properties of Poly(vinylidene difluoride)-Based Polymer Electrolytes

“…According to the XPS spectra, the interface layers are mainly composed of LiF, Li 2 O, LiOH, Li 2 CO 3 , Li x N, Li 2 S, Li 2 S x , and Li 2 SO x , which is supported by the results of the TOF-SIMS depth profiling (Figure S9). A peak of metallic Li appears in the Li 1s spectrum for the case of PVDF 761, but it does not exist in the case of PVDF 5130, indicating that the interface layer between the PVDF 5130-based electrolyte and a Li electrode is uniform and dense enough to fully cover the underlying metallic Li (Figure e). , This accords with the SEM results in Figure c,d. The signal of LiF in the F 1s spectrum for the case of PVDF 5130 is much stronger than that for the case of PVDF 761; therefore, more LiF, which is beneficial for the interfacial stability and battery performance, was produced due to the reaction between the PVDF 5130-based electrolyte and a Li electrode. , LiF may be originated from the dehydrofluorination of PVDF chains or the decomposition of LiFSI.…”

“…A peak of metallic Li appears in the Li 1s spectrum for the case of PVDF 761, but it does not exist in the case of PVDF 5130, indicating that the interface layer between the PVDF 5130-based electrolyte and a Li electrode is uniform and dense enough to fully cover the underlying metallic Li (Figure 3e). 34,55 This accords with the SEM results in Figure 3c,d. The signal of LiF in the F 1s spectrum for the case of PVDF 5130 is much stronger than that for the case of PVDF 761; therefore, more LiF, which is beneficial for the interfacial stability and battery performance, was produced due to the reaction between the PVDF 5130-based electrolyte and a Li electrode.…”

An organic additive assisting with high ionic conduction and dendrite resistance of polymer electrolytes

“…A strong peak of metallic Li at 52.4 eV appears in the Li 1s spectrum of Li/P-PE, indicating the existence of a large amount of metallic Li on the surface. 4,29 In contrast, the peak of metallic Li is much weaker in the case of Li/AP-PE, while the peak of Li + centered at 54.4 eV is much stronger, implying that the surface of the Li foil is covered with a layer of lithium compounds. 4,29 Based on the deconvolution results of the S 2p, F 1s, and N 1s spectra, it can be concluded that the interface layer for Li/AP-PE is mainly composed of Li 2 S x (161.6 and 162.6 eV), Li 2 SO 3 (169.8 eV), LiF (685.3 eV), and Li 3 N (396.9 eV).…”

“…With the increasing demand for secondary batteries with high energy and power densities, a lithium (Li) metal anode has drawn much attention during the past few decades due to its ultrahigh theoretical specic capacity. [1][2][3][4] However, owing to the high electrochemical activity of Li metal, Li metal batteries always suffer from severe anode/electrolyte corrosion and uncontrolled Li-dendrite growth, resulting in serious safety issues. If a Li metal anode is used in liquid-based batteries, the battery packs burn easily or explode violently in the case of thermal runaway.…”

Revisiting the Role of Physical Confinement and Chemical Regulation of 3D Hosts for Dendrite-Free Li Metal Anode

“…The R ct (Fig. S26) of the Li-Ni/Li 3 N-NS@CC anode still maintains the lowest value due to the lowest Li + diffusion energy barrier of Li 3 N [ 83 ]. Exchange current density ( I 0 ) obtained from the Tafel plot can reflect charge transfer kinetics between the electrode and electrolyte components.…”