The electrochemical properties of layered rock salt cathode materials are strongly influenced by defects. The three most common defects in LiNiO₂-based compounds, namely extra Ni, Li–Ni anti-site and oxygen vacancy defects have been investigated. The calculated defect formation energies are very low in LiNiO₂, consistent with the difficulty in synthesizing stoichiometric defect-free LiNiO₂. A systematic study is conducted to examine the effect of Co, Mn and Al substitution on defect formation. It is shown that the presence of Ni²⁺ in the Li layer can be rationalized using ideas of superexchange interactions. In addition, a correlation between oxygen vacancy formation energy and oxygen charge is noted. This explains the better thermal stability obtained by early transition metal or Al substitutions.

Organic–inorganic halide perovskites are attracting extraordinary attention in the field of energy materials. The reaction of hybrid lead halide perovskites with Li metal has recently been proposed for a number of potential applications. However, the mechanisms for Li uptake in such materials, such as intercalation and conversion, are still unknown. Using a combination of density functional theory and electrochemical and diffraction techniques, we consider Li intercalation and conversion reactions in CH₃NH₃PbI₃, CH₃NH₃PbBr₃, and CH₃NH₃PbCl₃. Our simulations suggest that conversion reactions with Li are far more energetically preferable in these materials than Li intercalation. Calculations confirm the formation of Pb metal as a result of Li conversion in all three materials, and this is supported by X-ray diffraction analysis of CH₃NH₃PbBr₃. The results of this study provide fresh insights into lithium and halide perovskite reactions that will hopefully drive further exploration of these materials for a wider variety of energy applications.

All-solid-state Li-ion batteries are currently attracting considerable research attention as they present a viable opportunity for increased energy density and safety when compared to conventional liquid electrolyte-based devices. The Li-rich anti-perovskite Li_3−xOH_xCl has generated recent interest as a potential solid electrolyte material, but its lithium and proton transport capabilities as a function of composition are not fully characterised. In this work, we apply a combination of ab initio molecular dynamics and ¹H, ²H and ⁷Li solid-state NMR spectroscopy to study the mobility of lithium ions and protons in Li_3−xOH_xCl. Our calculations predict a strongly exothermic hydration enthalpy for Li₃OCl, which explains the ease with which this material absorbs moisture and the difficulty in synthesising moisture-free samples. We show that the activation energy for Li-ion conduction increases with increasing proton content. The atomistic simulations indicate fast Li-ion diffusion but rule out the contribution of long-range proton diffusion. These findings are supported by variable-temperature solid-state NMR experiments, which indicate localised proton motion and long-range Li-ion mobility that are intimately connected. Our findings confirm that Li_3−xOH_xCl is a promising solid electrolyte material for all-solid-state Li-ion batteries.

Lattice compression through hydrostatic pressure has emerged as an effective means of tuning the structural and optoelectronic properties of hybrid halide perovskites. In addition to external pressure, the local strain present in solution-processed thin films also causes significant heterogeneity in their photophysical properties. However, an atomistic understanding of structural changes of hybrid perovskites under pressure and their effects on the electronic landscape is required. Here, we use high level ab initio simulation techniques to explore the effect of lattice compression on the formamidinium (FA) lead iodide compound, FA _{1 − x} Cs _x PbI ₃ ( x = 0, 0.25). We show that in response to applied pressure, the Pb-I bonds shorten, the PbI₆ octahedra tilt anisotropically, and the rotational dynamics of the FA⁺ molecular cation are partially suppressed. Due to these structural distortions, the compressed perovskites exhibit band gaps that are narrower (red-shifted) and indirect with spin-split band edges. Furthermore, the shallow defect levels of intrinsic iodide defects transform to deep-level states with lattice compression. This work highlights the use of hydrostatic pressure as a powerful tool for systematically modifying the photovoltaic performance of halide perovskites.