Pseudocapacitive Lithium Storage of Cauliflower-Like CoFe2O4 for Low-Temperature Battery Operation

Graphical Anode materials with a wide operating temperature are highly desirable for lithium-ion batteries. A CoFe 2 O 4 anode with a hierarchical cauliflower-like structure (see figure) is presented that shows high specific capacities of 907.5 and 664.5 mAh g −1 at 0.1 A g −1 at 0 and −25 °C. The full-cell battery assembled using cl-CoFe 2 O 4 as the anode and commercial LiFePO 4 as the cathode displays a high capacity of 612.7 mAh g −1 at 0.3 A g −1 after 140 cycles and can be used to successfully turn on an LED light. Binary transition-metal oxides (BTMOs) with hierarchical micro–nano-structures have attracted great interest as potential anode materials for lithium-ion batteries (LIBs). Herein, we report the fabrication of hierarchical cauliflower-like CoFe 2 O 4 (cl-CoFe 2 O 4 ) via a facile room-temperature co-precipitation method followed by post-synthetic annealing. The obtained cauliflower structure is constructed by the assembly of microrods, which themselves are composed of small nanoparticles. Such hierarchical micro–nano-structure can promote fast ion transport and stable electrode–electrolyte interfaces. As a result, the cl-CoFe 2 O 4 can deliver a high specific capacity (1019.9 mAh g −1 at 0.1 A g −1 ), excellent rate capability (626.0 mAh g −1 at 5 A g −1 ), and good cyclability (675.4 mAh g −1 at 4 A g −1 for over 400 cycles) as an anode material for LIBs. Even at low temperatures of 0 °C and −25 °C, the cl-CoFe 2 O 4 anode can deliver high capacities of 907.5 and 664.5 mAh g −1 at 100 mA g −1 , respectively, indicating its wide operating temperature. More importantly, the full-cell assembled with a commercial LiFePO 4 cathode exhibits a high rate performance (214.2 mAh g −1 at 5000 mA g −1 ) and an impressive cycling performance (612.7 mAh g −1 over 140 cycles at 300 mA g −1 ) in the voltage range of 0.5–3.6 V. Kinetic analysis reveals that the electrochemical performance of cl-CoFe 2 O 4 is dominated by pseudocapacitive behavior, leading to fast Li + insertion/extraction and good cycling life.