A Nonflammable High-Voltage 4.7 V Anode-Free Lithium Battery

Abstract

Anode-free lithium-metal batteries employ in situ lithium-plated current collectors as negative electrodes to afford optimal mass and volumetric energy densities. The main challenges to such batteries include their poor cycling stability and the safety issues of the flammable organic electrolytes. Here, a high-voltage 4.7 V anode-free lithium-metal battery is reported, which uses a Cu foil coated with a layer (≈950 nm) of silicon-polyacrylonitrile (Si-PAN, 25.5 µg cm^-2 ) as the negative electrode, a high-voltage cobalt-free LiNi_0.5 Mn_1.5 O₄ (LNMO) as the positive electrode and a safe, nonflammable ionic liquid electrolyte composed of 4.5 m lithium bis(fluorosulfonyl)imide (LiFSI) salt in N-methyl-N-propyl pyrrolidiniumbis(fluorosulfonyl)imide (Py₁₃ FSI) with 1 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as additive. The Si-PAN coating is found to seed the growth of lithium during charging, and reversibly expand/shrink during lithium plating/stripping over battery cycling. The wide-voltage-window electrolyte containing a high concentration of FSI^- and TFSI^- facilitates the formation of stable solid-electrolyte interphase, affording a 4.7 V anode-free Cu@Si-PAN/LiNi_0.5 Mn_1.5 O₄ battery with a reversible specific capacity of ≈120 mAh g^-1 and high cycling stability (80% capacity retention after 120 cycles). These results represent the first anode-free Li battery with a high 4.7 V discharge voltage and high safety.

Keywords: anode-free lithium batteries; high-voltage; ionic liquid electrolytes; nonflammable materials.