All calculations were executed using the plane wave DFT code VASP using projector augmented wave pseudopotentials . We treat the Li 1s 2 and 2s 1 , Ni 3d, and O 2s 2 and 2p 4 electrons as valence. The HSE06 hybrid-DFT functional was used for all calculations for NiO 2 , except the initial calculations on the twin-boundary structure which was carried out using the PBEsol functional with a Hubbard U [67] correction of 6 eV applied to the nickel 3d orbital . Dispersion forces were included using Grimme's semiclassical D3 correction with Becke-Johnson damping . Convergence tests determined a plane-wave energy cut-off of 600 eV, to satisfy the energy tolerance threshold of 1 meV/atom in all systems studied. With any calculations that allowed the cell volume to change, the energy cut-off was increased to 780 eV (+30%) to minimize Pulay stress.