Optimization of electrochemical performance of NMC cathode via adjacent synthesis and test protocols

Kurzfassung

LiNixMnyCo1-x-yO2 (so-called NMC) has demonstrated the most effective combination of nickel, manganese, and cobalt for the cathode materials, yielding good performance in terms of specific power, life span, costs and safety [1]. Within NMC compositions, Nickel provides high energy density and good storage capacity, but suffers from low thermal stability and insufficient cycle life [2]. Considering that Manganese in NMC composition acts not only as a stabilizer, but also prevents Nickel oxidation and thus, reduces the risk of capacity fading, the development of core/shell structured NMC morphologies deserved a special attention. This morphology provides surface stabilization of Ni-rich NMC by keeping the energy storage capabilities at higher level and prevents degradation of cathode. The strong dependence of the NMC cathode functional properties on transition metal relative ratios, and insufficient understanding of the synergistic effect of core and shell during the electrochemical tests, force researches to explore new synthesis approaches to enhance the overall performance of cathodes. In this work Ni-rich Core/Mn-rich Shell cathode powders have been synthesized via cost efficient and easy process-controlled two-step co-precipitation method following variable process parameters. Different synthesis steps, co-precipitation agents, Li infiltration approaches, heat treatment conditions were probed and analysed in search of the proper synthesis protocols to fabricate NMC cathodes with a good electrochemical performance for Li-ion batteries. To identify morphological, dimensional, structural and compositional relations within the core/shell particles SEM, EDX and XRD techniques have been employed. It has been shown that thermal treatment (temperature, duration, heating rate) slightly effect the morphology of the obtained particles, but according to the XRD analysis play a significant role in the achievement of the best NMC crystalline phase composition and avoiding of non-desirable compounds. In turn, the non-efficient Li infiltration results in a poor electrochemical performance. Electrochemical characterization by means of EIS spectroscopy and CV tests indicated that crystalline phase composition, the presence of the residual Li-based compounds, as well as Li incorporation approach have a high impact on the electrochemical properties of the obtained NMC cathode powder. 1] J. Phys. Chem. 2017, 121, 21865–21876. 2] Energy Storage Materials, 2021, 36, 485-495.