Abstract: Transition metal phosphides are promising anode materials for lithium ion batteries (LIBS) because of their low potential and high specific capacity. Among them, ZnP₂ is a dual active anode material, and both Zn and P can react with Li, which is more competitive in capacity. However, the lithiation mechanism and the reaction products of ZnP₂ are still unclear. In this work, the electronic and electrochemical properties of ZnP₂ were studied by first-principle calculations and electrochemical measurement. The combination of theoretical calculations and experimental tests demonstrated the lithiation mechanism of ZnP₂. Firstly, density functional theory (DFT) calculations revealed the lithiation reaction products, lithium diffusion path, diffusion barrier and theoretical lithium storage capacity (1477 mAh/g) of ZnP₂. The calculation of the binding energy proved that the formation energies of LiZn and Li₃P were thermodynamically lower than that of LinZnP₂. The charge density difference analysis showed that the Zn—P bonds and P—P bonds were gradually broken during the Li^＋ insertion process, which was accompanied by the formation of Li—P bonds and Li—Zn bonds, and these all confirmed the conversion reaction occurred after Li^＋ was inserted into ZnP₂. The calculation result of the density of states proved that ZnP₂ changed from a semiconductor to a conductor with the insertion of Li^＋. The diffusion energy barrier was higher than that of general layered materials, which will reduce the rate performance of LIBs. Secondly, ZnP₂ nanosheets were synthesized by the direct current (DC) arc plasma and solid phase sintering method. The electrochemical test showed that the rate performance and cycle performance were slightly worse, which proved the correctness of the diffusion barrier results. The discharge curve showed that the discharge capacity of the first cycle is similar to the theoretical calculation result, which is 1439 mAh/g. Finally, the components of the discharge products detected by the thin film X-ray diffraction (XRD) were LiZn and Li3P, which were consistent with the DFT calculation results.

DOI: 10.6023/A21120552