ABSTRACT
All-solid-state Li-ion batteries are of considerable interest as safer alternatives to Li-ion batteries containing flammable organic electrolytes. To date, however, achieving sufficient charging and discharging rates, in addition to capacity, at room temperature using these all-solid-state batteries has been challenging. To overcome these issues, material simulations and informatics investigations of a relatively new Na superionic conductor (NASICON)-type LiZr2(PO4)3 (LZP) electrolyte were conducted to elucidate its characteristics and material functions. The following thermodynamic and/or kinetic properties of NASICON-type Li-ion conductive oxides were investigated with respect to the crystal structure mainly using material simulation and informatics approaches: (1) the electrochemical stabilities of LZP materials with respect to Li metal and (2) Li-ion conductivities in the bulk and at the grain boundaries. An efficient materials informatics search method was employed to optimise the material functions of the LZP electrolyte via Bayesian optimisation. This study should promote the application of LZP in all-solid-state batteries for use in technologies such as mobile devices and electric vehicles and enable more complex composition and process control.
ABSTRACT
Dependence on lithium-ion batteries for automobile applications is rapidly increasing. The emerging use of anionic redox can boost the energy density of batteries, but the fundamental origin of anionic redox is still under debate. Moreover, to realize anionic redox, many reported electrode materials rely on manganese ions through π-type interactions with oxygen. Here, through a systematic experimental and theoretical study on a binary system of Li3NbO4-NiO, we demonstrate for the first time the unexpectedly large contribution of oxygen to charge compensation for electrochemical oxidation in Ni-based materials. In general, for Ni-based materials, e.g., LiNiO2, charge compensation is achieved mainly by Ni oxidation, with a lower contribution from oxygen. In contrast, for Li3NbO4-NiO, oxygen-based charge compensation is triggered by structural disordering and σ-type interactions with nickel ions, which are associated with a unique environment for oxygen, i.e., a linear Ni-O-Ni configuration in the disordered system. Reversible anionic redox with a small hysteretic behavior was achieved for LiNi2/3Nb1/3O2 with a cation-disordered Li/Ni arrangement. Further Li enrichment in the structure destabilizes anionic redox and leads to irreversible oxygen loss due to the disappearance of the linear Ni-O-Ni configuration and the formation of unstable Ni ions with high oxidation states. On the basis of these results, we discuss the possibility of using σ-type interactions for anionic redox to design advanced electrode materials for high-energy lithium-ion batteries.
