Spanish-dagger shaped CoP blooms decorated N-doped carbon branch anode for high-performance lithium and sodium storage

Abstract

The transition metal phosphide has been widely used as an anode material for lithium and sodium-ion batteries (LIBs and SIBs) due to its high discharge capacity and stable voltage platform. However, some shortcomings such as poor electronic conductivity and low ionic mobility seriously affected its electrochemical performance. To solve these problems, we designed and synthesized the multi-hierarchy structure of Spanish-dagger shaped CoP nanosheets decorated carbon sponge (CoP/CS). The structure is composed of the primary hyperfine CoP nanorods, the secondary micro-size flowers, the tertiary flower/branch carbon skeleton, and the quaternary electrode with a vibrant spatial three-dimensional (3D) network. This unique structure can not only restrict the volume expansion and self-aggregation of CoP but also can reduce the transport length of Li+/Na+. Besides, it has been verified that CoP and CS are bonded by chemical bonds. The CoP/CS electrode has been confirmed to have higher conductivity and lower resistivity than pure CS. Besides, the natural N-doped CS can further provide more active sites for in-situ growth of Co(OH)F precursor (based on the Co-N bonds). As a result, the CoP/CS composite exhibits the impressing capacity (2.4 mAh cm–2 at 0.6 mA cm–2 after 70 cycles in LIBs and 0.834 mAh cm–2 at 0.2 mA cm–2 after 50 cycles in SIBs) and outstanding rate performance. Meanwhile, the excellent cycling stability (0.514 mAh cm–2 at 1 mA cm–2 after 900 cycles) has been verified in SIBs. This work offers a new strategy for the design of multi-hierarchy materials, which may enable the high energy density storage for devices.