Boosting Fast and Stable Alkali Metal Ion Storage by Synergistic Engineering of Oxygen Vacancy and Amorphous Structure

Abstract Alloy‐type anode materials exhibit great promise in alkali metal ion batteries (AMIBs), due to their high theoretical capacities and appropriate operation voltages. Nevertheless, their applications are severely obstructed by large volume expansion upon cycling. Herein, the synergistic cooperation of oxygen vacancy, amorphous structure, and bulky poly‐ anions in alloy‐based phosphates (SnP 2 O 7 , BiPO 4 , and SbPO 4 )/N‐doped carbon are reported for high‐performance anode materials of AMIBs. In this composite, bulky polyanions mitigate the structure stress, amorphous structure facilitates the ion transport, and oxygen vacancy changes the electronic structure as confirmed by control experiments and density functional theory calculations. Thus, the electrochemical performances of this composite are greatly improved. Using K‐storage performances of SnP 2 O 7 as an example, amorphous and oxygen‐deficient SnP 2 O 7− x /N‐doped carbon delivers a high specific capacity (376 mAh g –1 at 0.1 A g –1 ), a stable cycling performance (320.8 mAh g –1 after 5000 cycles at 1 A g –1 ), and a good rate capability (161.1 mAh g –1 at 10 A g –1 ). The K storage mechanism of SnP 2 O 7 is identified as a typical two‐step process, i.e., a conversion reaction and an alloying reaction.