Surficial residual LiOH and/or Li2CO3 on Ni-rich cathodes arouse troubles for their practical applications, such as slurry gelling and durability degrading. To assure acceptable performance, the strategy of "washing and heat treatment" is generally utilized to remove them in industry, which is unavoidable to generate plenty of wastewater. In this work, we investigated the mechanism of slurry gelling caused by residual lithium on Ni-rich materials and then proposed a simple and efficient method to convert the detrimental residual lithium to the useful surface layer of LiF or LiBOB at 220 °C without water washing. As a result, the basicity of modified samples is lowered to 11.48 and 11.60 from 12.05 of the pristine, respectively. Owing to the beneficial effect of the surface layer, the treated samples deliver a discharge capacity of 189.5 and 187.9 mA h g-1 and retain 84.1 and 82.8% of the initial capacity under 1 C after 300 cycles, which is much better than that of the untreated material (57.8%). The comprehensive performances of the modified samples in this work are very close to those of the material treated with the industrial method, demonstrating the advantage of this strategy to further reduce the cost of material production.
Keywords: Ni-rich cathode; convert reaction; lithium ion batteries; low-temperature treatment; residual lithium.