One-Step Synthesis of Stoichiometric LiNi_0.80Co_0.15Al_0.05O₂ Precursor in Acidic Environment and Its Facile Growth into Single Crystals at Low Temperatures for Li-Ion Batteries

Ni-rich layered oxides Li[Ni_xCo_yAl_1-x-y]O₂ (NCA) have become the state-of-the-art cathode materials for high-energy-density Li-ion batteries (LIBs). However, the solubility product of Al(OH)₃ is much lower than that of Ni(OH)₂ and Co(OH)₂, which makes it difficult to produce the NCA precursor with a stoichiometric amount and uniform distribution of Al element in one step by using the coprecipitation method. In addition, high temperatures or complex procedures are required to obtain the single-crystalline Ni-rich cathode materials from the coprecipitation-derived precursor. Here, we develop a modified cation chelation and reassembly process to produce the stoichiometric NCA precursor in a single step. During this process, the addition of acetic acid causes Ni, Co, and Al species to exist in solution as free metal ions instead of hydroxide precipitates, which can be efficiently chelated by ethylenediaminetetraacetic acid and then reassembled into the crystalline precursor. After the lithiation treatment at 500 °C for 6 h and 750 °C for 12 h, the obtained single-crystalline NCA cathode exhibits a high discharge capacity (203.1 mA h g^-1 at 0.1C between 3.0 and 4.3 V), good cycling stability (87.2% capacity retention after 100 cycles), and excellent rate capability (126.5 mA h g^-1 at 10C). The outstanding electrochemical performance can be attributed to the cooperation of the single crystal together with the stoichiometric amount and uniform distribution of Al element, which can suppress the Li⁺/Ni²⁺ mixing level and stabilize the layer structure, enabling fast Li⁺ diffusivity and electronic conductivity.