A novel Li-ion supercapattery by K-ion vacant ternary perovskite fluoride anode with pseudocapacitive conversion/insertion dual mechanisms

An innovative K⁺ vacant ternary perovskite fluoride (K_0.89Ni_0.02Co_0.03Mn_0.95F_3.0, KNCMF-3#) anode was designed for advanced Li-ion supercapattery (i.e., Li-ion capacitors/batteries, LIC/Bs). Owing to the conversion/insertion dual mechanisms and fast pseudocapacitive control dynamics, the KNCMF-3# electrode exhibits superior electrochemical performance, especially the excellent cycle performance (467% (229 mAh·g⁻¹)/1000 cycles/2 A·g⁻¹). Moreover, the hybrid KNCMF-3#/reduced graphene oxide (rGO) electrode can further increase the electrochemical performance (217–97 mAh·g⁻¹/0.1–3.2 A·g⁻¹, 150% (197 mAh·g⁻¹)/1000 cycles/2 A·g⁻¹). Also, a novel capacitor/battery cathode, activated carbon (AC) + LiFePO₄ + graphene (AC + LFP + G), exhibits impressive performance (128–82 mAh·g⁻¹/0.1–3.2 A·g⁻¹, 84%/1000 cycles/2 A·g⁻¹). By the synergistic optimization of anode and cathode, the Li-ion supercapattery KNCMF-3#@rGO//AC + LFP + G demonstrates remarkable performance, for example, 111.9–23.8 Wh·kg⁻¹/0.4–8.0 kW·kg⁻¹/82%/2000 cycles/5 A·g⁻¹/0–4 V, which is superior to KNCMF-3#//AC LICs, KNCMF-3#@rGO//AC LICs, KNCMF-3#//AC + LFP + G LIC/Bs. In all, the novel Li-ion supercapattery idea adds a promising perspective to develop advanced energy storage devices.