In Situ Formation of a LiBO₂ Coating Layer and Spinel Phase for Ni-Rich Cathode Materials from a Boric Acid-Etched Precursor

Abstract

Ni-rich cathode materials exhibit superior energy densities and have attracted interest among both research and industrial fields; whereas, their practical application is hindered by the intrinsic drawbacks brought by the high nickel content such as structural instability and rapid capacity fading. Herein, in situ formation of a LiBO 2 coating layer and spinel phase layer is achieved on the surface of a Ni-rich cathode material via a boric acid etching method at the precursor state. The spinel phase is considered to have a 3D lithium diffusion tunnel and hence faster diffusion kinetics. Moreover, the LiBO 2 layer possesses excellent (electro)chemical inertness and can suppress electrolyte decomposition, resulting in a more inorganic and stable cathode−electrolyte interface. The surface reconstructed sample exhibits better cyclic stability (93.3% capacity retention vs 85.3% for the pristine sample at 1 C for 100 cycles) and rate performance. The superiority of this surface reconstruction is demonstrated by a series of electrochemical techniques and characterization methods including high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), post-mortem X-ray photoelectron spectroscopy (XPS) analysis, and density functional theory (DFT) calculations.

B/Al Codoped/Coated Ultra-High Nickel Cobalt-Free Material with Excellent High Voltage/Rate Cycle Stability

“…Among all coating materials, Li + conductors, such as LiNbO 3 , LiW 2 O 4 , LiBO 2 , LiAlO 2 , and so on, are more favored by researchers because they have better ionic conductivity than that of simple oxides, flurides, and phosphates. − These Li + conductors can form on the surface of the materials by using the harmful alkali residues as reactants, which not only facilitate the Li + insertion/extraction but also provide a physical protective layer to reduce the direct attack of the electrolyte on the electrode surface/interface . Considering that LiBO 2 and LiAlO 2 are excellent Li + conductors, and B and Al have different enhancement mechanisms to electrochemical properties, we adopt a B/Al codoping/coating strategy to synergistically enhance the surface/interface and crystal structure stability of the NM90 material.…”