Synthesis of layered-layered composite for lithium ion battery cathode materials by flame spray pyrolysis

Abstract

Conventional cathode materials such as LiCoO2, LiNiO2, LiMnO2 and LiNi1/3CO1/3Mn1/3O2 have poor performances due to structural instabilities. Especially, the capacity, one of the performances is unsatisfactory for HEV and EV applications. Recently, xLi2MnO3??(1-x)LiMO2 (M=Ni, Co and Mn), which is electrode with two layered component, have attracted interest as an alternative cathode material. This cathode material has high capacity at high voltage without rapid phase transition, because of extra capacity and stabilizing role of Li2MnO3. The electrochemical performance of cathode materials is contingent on factors such as surface area, morphology, crystallinity, grain size, phase purity and cation distribution in structure. These factors are contingent on synthesis methods. Flame spray pyrolysis is a promising process because of following advantages

clear crystallinity, facilitation of size and morphology control, fast reaction, pure product, phase homogeneity and facilitation of large-scale manufacture. In this work, Li1.167Mn0.548Ni0.18Co0.105O2, which is 0.4Li2MnO3??0.6Li(Mn0.43Ni0.36Co0.21)O2 as two-component notation, is synthesized by flame spray pyrolysis. The investigation into effect of flame temperature on Li1.167Mn0.548Ni0.18 Co0.105O2 powders is conducted. All XRD patterns of synthesized Li1.167Mn0.548Ni0.18Co0.105O2 powder have main peaks of α-NaFeO3 structure with weak peaks related a Li2MnO3-like unit cell. Except powder obtained at 1,356oC, all powders have secondary phase that appeared in split peak, Li4MnO12 at 38o and 43o 2θ. This secondary phase results from volatilization of Li-ion. The investigation into effect of post-treatment temperature on Li1.167Mn0.548Ni0.18 Co0.105O2 powder, obtained at 1,356oC flame temperature, is conducted. The cathode material post-treated at 700oC has a highest capacity at all of C rate range. This cathode material has capacities of 255 and 195 mAh/g at 0.1 and 1C rate, respectively. As sintering temperature is increased, the capacity is decreased at each current density. On the other hand, the cycle performance is deteriorated with decreasing post treatment temperature. The cathode materials undergoing at different post-treatment temperature have capacity retentions of 82.1, 88.3, 89.6 and 94.9% from 700 to 1,000oC. All electrochemical performances, such as capacity, rate capability and cycle performance, are considered, the optimum post treatment temperature is 900oC. Li1.167Mn0.548Ni0.18Co0.105-xAlxO2 is synthesized by flame spray pyrolysis to overcome drawback of Li1.167Mn0.548Ni0.18 Co0.105O2 powder, such as poor cycle performance. The investigation into effect of dopant content on electrochemical performances is conducted. All XRD patterns of synthesized Li1.167Mn0.548Ni0.18Co0.105-xAlxO2 powder have main peaks of α-NaFeO3 structure with weak peaks related a Li2MnO3-like unit cell without secondary phase. The discharge capacity of Al-doped cathode materials decreases with increasing aluminum content. At low current density, rate capability gradually decreases with increasing aluminum content like decreasing capacity. At high current density, however, rate capability rapidly decreases with increasing aluminum content. The Al-doped cathode materials have better capacity retention as comparing to undoped cathode material. Especially, as the small amount of aluminum is substituted, cycle performance significantly increases.