Lithium Iron Phosphate Enhances the Performance of High-Areal-Capacity Sulfur Composite Cathodes
Xiaosi Gao, Changyang Zheng, Yiqi Shao, Vaidik Shah, Shuo Jin, Jin Suntivich, Yong Lak Joo
Abstract
Lithium iron phosphate (LiFePO 4, “LFP”) was investigated as an additive in the cathode of lithium–sulfur (Li–S) batteries. LFP addition boosted the sulfur utilization during Li–S cycling, achieving an initial capacity of 1465 mAh/g S and a long cycle life (>300 cycles). Polysulfide adsorption experiments showed that LFP attracted polysulfides, and thus, the presence of LFP should alleviate the shuttle effect, a common failure mode. Postmortem characterization found iron phosphides, iron phosphates, and LiF in the electrode, indicating that LFP underwent dynamic reconstruction during Li–S cycling. We suspect that the formation of these species played a role in the observed performance. From the processing standpoint, adding LFP improved slurry rheology, making the preparation of a high-loading electrode more consistent. Benefiting from the high sulfur utilization and the ability to prepare electrodes with high mass loading, the S-LFP hybrid cell showed an excellent areal capacity of 2.65 mAh/cm 2 and could be stably cycled at 2 mAh/cm 2 for 250 cycles. Our results demonstrated the LFP addition as a promising strategy for realizing Li–S batteries with high sulfur loading and areal capacity.