Multiple Chelation-Assisted Lithiation Improves the Performance of Phosphate-Modified LiNi0.8Co0.1Mn0.1O2

Abstract

Phytic acid, the main phosphorus repository for plant seeds, is enriched with phosphate acidic sites that can easily chelate with transition metal ions. In this article, a phosphate-modified LiNi0.8Co0.1Mn0.1O2 (P-NCM) cathode material was synthesized using a Phytic acid-assisted lithiation process involving multiple chelation between phytic acid and metal hydroxides. Characterized by X-ray diffraction, Ar+ sputtering assisted X-ray photoelectron spectroscopy, high-resolution transmission electron microscope, etc, it indicates that P-NCM indeed possesses the phosphorus dopant besides Li3PO4 coating. Through galvanostatic intermittent titration results, reflected electron energy loss spectra, and ultraviolet absorption spectra, it indicates that the optimal 0.2PA modified sample has a higher Li+ diffusion rate and electron conductivity, with an initial discharge capacity of 203.4 mAh g−1 and the retention of 92.4% after 100 cycles at 1 C and room temperature. In-situ XRD measurements indicate that the 0.2PA has fewer volume changes in the H2-H3 phase transition. Density Functional Theory calculations reveal that the phosphorus dopant probably occupies the tetrahedral interstice in the LiO6 layer, existing obvious charge transfers from the phosphorus dopant toward the neighboring atoms. This work illustrates the important role of phosphorus dopants in the improvement of the electrochemical properties of Ni-rich NCM cathode materials.