Enabling Lithium Metal Anode in Nonflammable Phosphate Electrolyte with Electrochemically Induced Chemical Reactions

Abstract

Lithium metal anode holds great promises for next‐generation battery technologies but is notoriously difficult to work with. The key to solving this challenge is believed to lie in the ability of forming stable solid‐electrolyte interphase (SEI) layers. To further address potential safety issues, it is critical to achieve this goal in nonflammable electrolytes. Building upon previous successes in forming stable SEI in conventional carbonate‐based electrolytes, here we report that reversible Li stripping/plating could be realized in triethyl phosphate (TEP), a known flame retardant. The critical enabling factor of our approach was the introduction of oxygen, which upon electrochemical reduction induces the initial decomposition of TEP and produces Li3PO4 and poly‐phosphates. Importantly, the reaction was self‐limiting, and the resulting material regulated Li plating by limiting dendrite formation. In effect, we obtained a functional SEI on Li metal in a nonflammable electrolyte. When tested in a symmetric Li∥Li cell, more than 300 cycles of stripping/plating were measured at a current density of 0.5 mA cm−2. Prototypical Li‐O2 and Li‐ion batteries were also fabricated and tested to further support the effectiveness of this strategy. The mechanism by which the SEI forms was studied by density functional theory (DFT), and the predictions were corroborated by the successful detection of the intermediates and products.

Air exposure towards stable Li/Li10GeP2S12 interface for all-solid-state lithium batteries

“…The compound, Li 4 P 2 S 6 , have been reported to exhibit considerable ionic conductivity and good interface stability towards lithium metal [27][28][29][30], making it desirable for interface protection for Li 10 GeP 2 S 12 . Besides, both LiH 2 PO 4 and Li 3 PO 4 have been proven to be efficient protective layers for Li/solid electrolyte interface [16,[31][32][33][34], indicating phosphide, such as Li 2 HPO 3 , can stabilize the Li/Li 10 GeP 2 S 12 interface. Figures S3 and S4 presents the surface and cross-section morphology of Li 10 GeP 2 S 12 pellets before and after air exposure, showing the obvious decomposition layer coated on the surface of Li 10 GeP 2 S 12 pellet.…”

Strategies toward anode stabilization in nonaqueous alkali metal–oxygen batteries

“…12,93 The metallic anode can be protected by using a modified solvent. 8,94,95 For example, Lai et al formed a local strong solvation effect electrolyte (LSSE) by combining DMSO as a high donor number solvent, TEGDME as a low donor number solvent and LiTFSI as a Li salt, which showed stability against the reactive oxygen species and Li metal. 96 To alleviate the anodic corrosion caused by the RM shuttle effect, Yu et al reported a volatilization-dissolution strategy to supply RMs by introducing TEMPO into the O 2 atmosphere (TEMPO-O 2 ) outside an assembled cell.…”

Dendrite‐accelerated thermal runaway mechanisms of lithium metal pouch batteries

“…[46][47][48][49] Beside these, thermal decomposition and combustion of electrolytes themself can also aggravate the safety risks. 50 However, the detailed reactions sequence and heat contribution during thermal runaway of high-energy-density LMBs in working conditions are still tightly sealed to researchers. Therefore, it is of great importance to understand the safety characteristics and the roots of working LMBs based on the practically adopted cell patterns, such as pouch cells.…”

“…Meanwhile, Li dendrites can increase the specific surface area of Li anode and intensify the serious exothermic reactions between Li metal and other cell components, such as SEI, electrolytes (non‐aqueous and solid‐state electrolytes), and cathodes 46–49 . Beside these, thermal decomposition and combustion of electrolytes themself can also aggravate the safety risks 50 . However, the detailed reactions sequence and heat contribution during thermal runaway of high‐energy‐density LMBs in working conditions are still tightly sealed to researchers.…”