Abstract
The inhomogeneous Li electrodeposition of lithium metal electrode has been a major impediment to the realization of rechargeable lithium metal batteries. Although single ion conducting ionomers can induce more homogeneous Li electrodeposition by preventing Li+ depletion at Li surface, currently available materials do not allow room-temperature operation due to their low room temperature conductivities. In the paper, we report that a highly conductive ionomer/liquid electrolyte hybrid layer tightly laminated on Li metal electrode can realize stable Li electrodeposition at high current densities up to 10 mA cm−2 and permit room-temperature operation of corresponding Li metal batteries with low polarizations. The hybrid layer is fabricated by laminating few micron-thick Nafion layer on Li metal electrode followed by soaking 1 M LiPF6 EC/DEC (1/1) electrolyte. The Li/Li symmetric cell with the hybrid layer stably operates at a high current density of 10 mA cm−2 for more than 2000 h, which corresponds to more than five-fold enhancement compared with bare Li metal electrode. Also, the prototype Li/LiCoO2 battery with the hybrid layer offers cycling stability more than 350 cycles. These results demonstrate that the hybrid strategy successfully combines the advantages of bi-ionic liquid electrolyte (fast Li+ transport) and single ionic ionomer (prevention of Li+ depletion).
Highlights
High energy density levels and long lifetimes of secondary batteries have been ceaselessly pursued with the rapid evolution of electric vehicles and state-of-the-art mobile devices
As a proof of principle and to demonstrate the efficacy of the proposed approach, we comparatively investigated the Li electrodeposition/dissolution behaviours of Li/Li symmetric cells based on bare Li metal electrodes coupled with a LE (1 M LiPF6 in ethylene carbonate (EC)/diethyl carbonate (DEC) (1/1)), thin NLs coated onto Li metal electrodes coupled with the LE (NL/LE hybrid), and bare Li metal electrodes coupled with an EC/DEC-swollen Nafion polymer electrolyte membrane (NPEM) (Fig. 1)
A solvent-free, dried NL on fluorinated ethylene propylene (FEP) film was transferred to a Li metal electrode by applying pressure at room temperature
Summary
High energy density levels and long lifetimes of secondary batteries have been ceaselessly pursued with the rapid evolution of electric vehicles and state-of-the-art mobile devices. Researchers have devised and tested numerous strategies to realize uniform and reversible Li deposition, including mechanical dendrite blocking by solid ceramic or polymer electrolytes[3,4,5,6,7], the in-situ modulation of a solid-electrolyte interface (SEI) by electrolyte additives[8,9,10,11,12,13,14,15], ex-situ Li metal surface coatings[16,17,18,19,20,21,22], and electrostatic shielding with a self-healing agent[23,24] These approaches have shown promising enhancements, attaining high cycling efficiency at www.nature.com/scientificreports/. Ta is correlated the with transference number of Li+ (tLi+) and the mobility of the anion (μa) and Li+ (μLi+), as given in equation (2) below
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