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Bi@Graphite was synthesized as an ultra-fast and ultra-stable anode material for SIBs with 70% capacity retention at 300C with respect to 1C.

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Layered metal oxides have been widely used as the best cathode materials for commercial lithium-ion batteries and are being intensively explored for sodium-ion batteries. However, their application to potassium-ion batteries (PIBs) is hampered because of the poor cycling stability and low rate capability due to the larger ionic size of K than of Li or Na. Herein, a facile self-templated strategy was used to synthesize unique P2-type KCoO microspheres that consist of aggregated primary nanoplates as PIB cathodes. The unique KCoO microspheres with aggregated structure significantly enhanced the kinetics of the K intercalation/deintercation and also minimized the parasitic reactions between the electrolyte and KCoO. The P2-KCoO microspheres demonstrated a high reversible capacity of 82 mAh g at 10 mA g, high rate capability of 65 mAh g at 100 mA g, and long cycle life (87% capacity retention over 300 cycles). The high reversibility of the P2-KCoO full cell paired with a hard carbon anode further demonstrated the feasibility of PIBs. This work not only successfully demonstrates exceptional performance of P2-type KCoO cathodes and microspheres KCoO∥hard carbon full cells, but also provides new insights into the exploration of other layered metal oxides for PIBs.

Li-rich layered-oxide cathodes have the highest theoretical energy density among all the intercalated cathodes, which have attracted intense interests for high-energy Li-ion batteries. However, O3-structured layered-oxide cathodes suffer from a low initial Coulombic efficiency (CE), severe voltage fade, and poor cycling stability because of the continuous oxygen release, structural rearrangements due to irreversible transition-metal migration, and serious side reactions between the delithiated cathode and electrolyte. Herein, we report that these challenges are migrated by using a stable O2-structured Li1.2­Ni0.13­Co0.13­Mn0.54­O2 (O2-LR-NCM) and all-fluorinated electrolyte. The O2-LR-NCM can restrict the transition metals migrating into the Li layer, and the in situ formed fluorinated cathode–electrolyte interphase (CEI) on the surface of the O2-LR-NCM from the decomposition of all-fluorinated electrolyte during initial cycles effectively restrains the structure transition, suppresses the O2 release, and thereby safeguards the transition metal redox couples, enabling a highly reversible and stable oxygen redox reaction. O2-LR-NCM in all fluorinated electrolytes achieves a high initial CE of 99.82%, a cycling CE of >99.9%, a high reversible capacity of 278 mAh/g, and high capacity retention of 83.3% after 100 cycles. The synergic design of electrolyte and cathode structure represents a promising direction to stabilize high-energy cathodes.