Design Strategies for Multivalent Energy Dense Cathode Materials
Authors: Ceder Gerbrand , Rong Ziqin , Liu Miao , Hannah Daniel C. , Gautam Gopalakrishnan Sai , Canepa Pieremanuele , Persson Kristin A 
Published: February 2020

Multi-valent (MV) ion intercalation batteries that replace Li+ ions with MV cations such as Mg2+, Zn2+ and Ca2+ constitute a promising strategy to meet the energy density requirements of the next generation of electrical devices. One of the most pressing obstacles to the development of high-energy density MV-ion systems is the discovery of cathode materials offering sufficiently high voltage and, most importantly, high MV cation mobility. To date, there have only been a limited number of examples demonstrating the feasibility of rechargeable multivalent batteries, with most of the focus placed on Mg-cycling. Thus, it is important to assess the feasibility of several chemical spaces as multivalent intercalation cathodes. We will present a detailed analysis, based on first-principles DFT calculations, of multivalent ion intercalation in various promising candidates such as the spinel AnB2X4
(A = MV as Mg, Zn or Ca, B = transition metal and X = O2- or S2-), olivine AnFePO4

and various vanadium pentoxide AnV2O5
polymorphs [1-5]. Emphasis will be given to host structures exhibiting enhanced Mg or Zn mobility, and in particular to the chemical and structural descriptors which govern this property. Our findings show that matching the MV site preference to the diffusion topology of the host controls the ionic mobility, more significantly than any other factor, providing design guidelines to find fast-diffusing MV conductors. For example, Zn ions are expected to diffuse well in hosts where Zn ions are in non-preferred but stable octahedral sites and migrate through favored unstable tetrahedral site. We will also show some experimental data that validates these design rules. The results demonstrate that computational materials science is a powerful tool to enable the successful development and optimization of new materials for energy dense multivalent batteries. The work is entirely supported by the Department of Energy as part of the Joint Center for Energy Storage Research (JCESR).

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