Low-temperature Li-S battery enabled by CoFe bimetallic catalysts

Lithium-sulfur (Li-S) batteries are considered promising energy storage devices. To ensure practical applications in a natural environment, Li-S batteries must be capable of performing normally at low temperature. However, the intrinsic characteristics of S, such as large volume variation, low conductivity, and shuttle effect, hinder its low-temperature applications. Moreover, Li+ transport is poor at low temperatures, resulting in fast capacity deterioration, low-capacity output, and large overpotential. In this study, a free-standing host embedded with CoFe bimetallic nanoparticles has been designed. CoFe functions as an efficient catalyst for the polysulfide conversion. The in situ growth of graphite shells around CoFe bimetallic nanoparticles function as a nanoreactor to confine and absorb polysulfides, and the host is an ideal porous conductivity network for rapid ion transportation, preventing the accumulation of Li2S and alleviating the volume changes during the lithiation/delithiation process. Density functional theory (DFT) calculations prove that the successive lithiation process from S-8 to Li2S on CoFe is thermodynamically spontaneous, and CoFe has a kinetic catalytic activity for this series of lithiation reactions. Experimentally, rationally designed CoFe@C@CNF cathodes are introduced into Li-S batteries for low-temperature applications. The cathode delivers superior rate capacity (828 mA h g(-1) at 10C) and a low fading rate (0.053% per cycle over 300 cycles). An enhanced capacity (836 mA h g(-1) at 0.2C) and cycling stability (capacity retention rate of 94.5% after 100 cycles) were achieved at -20 degrees C. This study provides a feasible method for developing high-rate and long-life Li-S batteries for low-temperature applications.

Automated summary

In this study, a free-standing host embedded with CoFe bimetallic nanoparticles is designed to enhance the performance of Li-S batteries at low temperature. The results show that the new designed cathode delivers superior rate capacity and cycling stability under low-temperature conditions, providing a feasible method for developing high-rate and long-life Li-S batteries for low-temperature applications.