Kinetically tunable O vacancies in LiFePO <sub>4</sub> for improved Li <sup>+</sup>/e <sup>-</sup> conduction and high-rate cycling
Yaduo Song, Hao Zhang, Sanqi Guo, Chengye Lin, Zixu Wang, Xin Hu, Minglei Cao, Long Qie, Dinggen Li, Ji Xiao, Jinming Guo, Yonggang Yao, Yunhui Huang
Abstract
Lithium iron phosphate (LFP) offers excellent structural and performance stability derived from the (PO<sub>4</sub>)<sup>3-</sup> polyanionic structure, which is beneficial for long-term usage. However, this inherent stability also come along with intrinsically poor ionic and electronic conductivities, which have been notoriously plaguing its high-rate performance and broader applications. Here, we present a gas-assisted transient synthesis (GATS, ~30 seconds) of LFP with controllable O<sub>v</sub> for enhanced rate performance yet without sacrificing structural integrity or cycling stability. Benefited by the ultrafast heating and a higher synthesis temperature, we revealed that the LFP synthesis in GATS followed an interface reaction mechanism (rapid core shrinking) with a low activation energy (E<sub>a</sub>), thus reducing the synthesis time from ~16.5 hours in tube furnace heating (TFH, often nuclei-growth mechanism) to merely seconds. The optimized LFP sample demonstrates an 8-fold enhancement in ionic conductivity and a 12-fold increase in electronic conductivity compared to LFP obtained by TFH, and attains exceptional cycling stability even at high rates of 10 C, as evidenced by a higher capacity retention of 93.8% (vs. 63.6% of commercial LFP) after 1000 cycles. Our strategy offers a kinetic pathway for rapid synthesis and structural engineering of LFP, thus unlocking its potential for broader energy storage applications.