Engineering structure constructed CoP anode with enhanced bulk phase diffusion ability for superior potassium-ion storage

Due to its considerable theoretical capacity and high availability through conversion reaction, CoP is regarded as a promising candidate for potassium-ion batteries (PIBs). However, huge volume change and low intrinsic conductivity seriously impede the further development of CoP anode in PIBs. Generally, structural design and composition regulation can well improve potassium storage performance of CoP via increasing capacitive contribution rate, but are unfavorable for realizing a high energy density in a K-full cell. Therefore, how to optimize the bulk phase diffusion ability of CoP to enhance the diffusion-dominated potassium storage is of great importance. Herein, CoP nanoparticles (about 20-40 nm) with enormous voids embedded in carbon-cage structure encapsulated in N-doped amorphous carbon are reported (CoP/C@NCPDA), in which CoP particles with appropriate nano-size benefit the bulk phase diffusion process. Besides, the existence of amorphous carbon coating layer and voids can provide sufficient space to buffer volume expansion, while carbon-cage architecture and its high graphitization degree accelerate fast ions/electrons transfer, respectively. As a result, CoP/C@NC-PDA achieves an excellent diffusion-controlled capacity ratio (77.5% at 0.05 A g-1, 75.0% at 1.0 A g-1), and a good cycle lifespan over 1000 cycles with nearly 100% Coulombic efficiency.