Complementary lithium aluminum borate coating of Ni-rich cathode by synergetic boric acid and aluminum hydroxide for lithium-ion batteries

Abstract

Substituting Ni for Co in high-Ni layered oxide cathodes is highly effective in enhancing the range of delithiation and reducing production costs, but the reactive Ni3+ and unavoidable residual surface impurities critically limit the cycleability of lithium-ion batteries (LIBs). Although the wet-coating method is one solution suitable for widespread industrial production, wet-coating of high-Ni layered oxides is complicated due to chemical delithiation, corrosion, and the inhomogeneous coating caused by their instability. Herein, we applied wet-coating chemistry to coat LiNi0.88Co0.06Mn0.06O2 (NCM88) with a thin boron–aluminum oxide layer using eco-friendly aqueous solutions. Under acidic H3BO3 conditions, Al(OH)3 is critical in preserving the fragile surface of Ni-rich layered oxides and forming a homogeneous coating. Furthermore, structural characterization reveals the formation of an amorphous Li2O–LiAlO2–LiBO2 (LABO) coating layer. A highly homogeneous LABO-coated NCM88 exhibits significantly improved cyclability, retaining 75.5% of its capacity after 250 cycles of charging/discharging. This is a much higher capacity retention rate than those of bare NCM88 (7%) and NCM88 coated with Al(OH)3 (64.4%) or H3BO3 (65.2%). The LABO-coated layer also demonstrates improved rate capability with charge voltages of 4.25 and 4.5 V.