Introducing Electrolyte Additive For Stable Lithium Metal Battery

It is true that there is increasing concerning of researchers for lithium metal battery due to its ultra-high capacity.However,the random growth of lithium dendrites may lead to a series of problem,such as short circuit and even explosion,thereby largely limiting the practical application of lithium metal batteries.To tackle this issue,many strategies have been proposed to suppress the growth of lithium dendrite.It is worth noting that introducing electrolyte additives exhibits many advantages because of its convenience and cost-effectiveness.Herein,we propose several electrolyte additives with different mechanism to suppress the growth of lithium dendrite.The main contents of this paper are as follows:（1）The di-fluoro ethylene carbonate（DFEC）was proposed as a SEI-forming additive for stable lithium metal batteries.DFEC additives with low LUMO energy can self-decompose into Li F and then form a stable and robust SEI layer on the lithium metal anode during lithium plating process.As a result,the growth of lithium dendrite was suppressed significantly.Based on this,the Coulombic efficiency of Li|Cu half-cell was improved from 89.8%to 97.4%at the present of DFEC additives.In term of cathode,due to its lower HOMO orbital,a higher oxidation potential of electrolyte than blank electrolyte can be achieved.Furthermore,a Li F-rich CEI film also can be formed on the NCM811cathode through self-decomposition of DFEC,so that the shuttle effect of transition metal ions can be inhibited significantly.Based on this,the Li||NCM811 full cell show a good performance by adding DFEC and a high capacity retention rate（～75%）was achieved after 200 cycle.（2）Nitrogen and sulfur co-doped carbon dots（N,S-CDs）were prepared through acetaldehyde and thiourea as precursor.Furthermore,the effect of N,S-CDs as a deposition-regulating additive to suppress the growth of lithium dendrite was also analyzed by means of confocal fluorescence microscope.Because there are various lithiophilic functional groups on the surface of N,S-CDs,lithium ions will prefer to be adsorbed on the surface of N,S-CDs during lithium plating process,and further co-deposit on the current collector,resulting in a homogeneous lithium deposition layer.Based on this,Li||Li symmetrical battery can cycle stably for 1200 and 300 h at the current density of 1.0 and 3.0 m A cm^-2at the present of N,S-CDs,respectively.Moreover,the capacity of Li-S full cell also can be significantly improved by adding N,S-CDs.