The solid-state chelation synthesis of LiNi_1/3Co_1/3Mn_1/3O₂ as a cathode material for lithium-ion batteries

A facile solid-state chelation method using citric acid as the solid chelant was investigated for the synthesis of layered LiNi_1/3Co_1/3Mn_1/3O₂ as a cathode material for rechargeable lithium-ion batteries. The reaction was promoted by high-energy ball milling. During the synthesis, PVP was used as an additive. For comparison, LiNi_1/3Co_1/3Mn_1/3O₂ was also synthesized by a conventional sol-gel method using citric acid as the chelant. The as-prepared samples were characterized by TG-DSC, XRD, FESEM, BET specific surface area and galvanostatic charge-discharge tests. Based on the XPS, TEM and ED results, the sample synthesized by the solid-state chelation method with the PVP as an additive and subsequent calcination at 900 °C for 12 h in air was well indexed to a pure-phase hexagonal α-NaFeO₂ structure with the highest crystallinity. The resulting sample showed an initial discharge capacity of 173 mA h g^-1 in the potential range of 2.6-4.5 V and at a rate of 0.1 C, higher than that of the sample prepared by the same method without the use of a PVP additive during the synthesis (146 mA h g^-1). Moreover, the electrochemical results at different current rates and the cycle performance for 100 cycles at 0.5 C indicated that the sample prepared by the solid-state chelation method exhibited better rate capability and cyclic stability than that prepared by the conventional sol-gel method. This phenomenon promises solid-state chelation as a new universal method for the preparation of functional materials.