Precursor-oriented ultrathin Zr-based gradient coating on Ni-riched cathodes

We present a simple and low-cost interfacial precipitation-conversion reaction strategy, which employs the precursors as orientators to coat ultrathin and surface-gradient layers for reserving the structural integrality and stability of particularize materials. Using the typical high-nickel layered cathode (LiNi0.8Co0.15Al0.05O2, NCA) as a prototype, we successively processed NCA carbonate oxalate precursors with (NH4)2HPO4 and ZrOCl2 solutions to chemically induce Zr species on the NCA surfaces via strong M-PO4-Zr interactions (M = Ni, Co). An ultrathin Zr-contained gradient layer is in-situ self-assembled spontaneously and conformably (NCA@ZP) after calcination. The as-designed NCA@ZP cathode delivers a high capacity of 219.7 mA h·g−1, 23% higher than NCA (179.0 mA h·g−1) at 0.1 C, and exhibits superior rate capability (128.2 mA h·g−1 capacity at 16 C) and cycling stability. Experimental characterization together with calculation further reveal that the residential Zr element at Li+ sites strengthen the adjacent M-O bonds, inhibiting the oxygen evolution and dissolution of transition metal, buffering the internal strains, stabilizing the cathode-electrolyte interface, improving the electrical conductivity and consequently benefiting the cyclability and rate capability. Such a simple precursor-oriented strategy can be easily scaled-up and extended to various application scenarios who encounter unwanted side-reactions or structural degradation during chemical reactions.