Electrochemistry and structure of the cobalt-free Li1+xMO2 (M = Li, Ni, Mn, Fe) composite cathode

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Royal Society of Chemistry
The development of cathode materials with high capacity and cycle stability is essential to emerging electric-vehicle technologies, however, of serious environmental concern is that materials with these properties developed so far contain the toxic and expensive Co. We report here the Li-rich, Co-free Li1+xMO2 (M = Li, Ni, Mn, Fe) composite cathode material, prepared via a template-free, one-step wet-chemical method followed by conventional annealing in an oxygen atmosphere. The cathode has an unprecedented level of cation mixing, where the electrochemically-active component contains four elements at the transition-metal (3a) site and 20% Ni at the active Li site (3b). We find Ni2+/Ni3+/Ni4+ to be the active redox-center of the cathode with lithiation/delithiation occurring via a solid-solution reaction where the lattice responds approximately linearly with cycling, differing to that observed for iso-structural commercial cathodes with a lower level of cation mixing. The composite cathode has ∼75% active material and delivers an initial discharge-capacity of ∼103 mA h g−1 with a reasonable capacity retention of ∼84.4% after 100 cycles. Notably, the electrochemically-active component possesses a capacity of ∼139 mA h g−1, approaching that of the commercialized LiCoO2 and Li(Ni1/3Mn1/3Co1/3)O2 materials. Importantly, our operando neutron powder-diffraction results suggest excellent structural stability of this active component, which exhibits ∼80% less change in its stacking-axis than for LiCoO2 with approximately the same capacity, a characteristic that may be exploited to enhance significantly the capacity retention of this and similar materials.
Cathodes, Oxygen, Elements, Metals, Neutron diffraction, Environment
Pang, W. K., Kalluri, S., Peterson, V. K., Dou, S. X., & Guo, Z. (2014). Electrochemistry and structure of the cobalt-free Li1+xMO2 (M = Li, Ni, Mn, Fe) composite cathode. [10.1039/C4CP02864C]. Physical Chemistry Chemical Physics, 16(46), 25377-25385. doi:10.1039/c4cp02864c