Engineering the structure-directed functional properties of brominated organic additives for high-performance Li-CO₂ batteries

In recent years, functional brominated organic additives in electrolytes have been widely studied during the CO₂ER (CO₂ evolution reaction) and CO₂RR (CO₂ reduction reaction) processes for Li-CO₂ batteries. Due to their different structures, the functions of these additives are always unpredictable, multiple and limited. There seems to be a lot of materials to choose from for an additive, but there is no well-established and effective methodology to guide the selection. Herein, we introduced B3BPE, E4BCT and BPB into electrolytes for Li-CO₂ batteries and focused on the structure-directed engineering of additives, including the position of halide substituent groups, the chain length of organic materials, their chain-break product as well as their corresponding difference in electrochemical properties, as additives for comparison. As a result, B3BPE has the longest chain length and strongest polarity. Experiments coupled with density functional theory simulations indicate that this structure exhibits the stronger interaction with Li₂CO₃, which benefits the CO₂ER process, the charging voltage can be maintained at 3.90 V for 120 cycles even with a Super P cathode. In this work, we provided an electrolyte-selection engineering for brominated organic compounds, further inspiring in-depth understanding for bromide additives in future high-performance Li-CO₂ batteries.