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Garnet-based solid electrolytes have been proposed as promising candidates for next generation all-solid-state batteries. Whilst multiple cation substitution studies of these garnets have been undertaken to try and improve their overall performance, anion doping of garnets has rarely been attempted, owing to the synthetic challenges associated with this particular doping strategy. In this work, we present the halogenation (F, Cl) of the solid state electrolyte Li7La3Zr2O12 (LLZO) via a low temperature solid state synthetic route using PTFE and PVC polymers. A reduction in tetragonal distortion (F incorporation) and a tetragonal to cubic phase transition (Cl incorporation) is observed in halogenated LLZO, suggesting the replacement of O2− with F− or Cl− is associated with the creation of lithium vacancies. Combined solid-state NMR and computational studies support the presence of F− or Cl− in halogenated LLZO. The effects of surface fluorination were also investigated for Al-doped LLZO (Li6.4Al0.2La3Zr2O12, LLAZO) with the results suggesting that this strategy has the ability to prevent full dendrite penetration at high current densities (up to 10 mA cm−2).
Bibliographical noteFunding Information:
PRS and BD acknowledge the support of the EPSRC grant EP/R024006/1: ICSF Wave 1: GENESIS: Garnet Electrolytes for New Energy Storage Integrated Solutions, and EPSRC grant EP/T02349X/1 Capitol Award for Core Equipment. We would like to thank the University of Birmingham for the studentship funding of MPS and MSJ. KEJ and ARH would like to thank Dr David Apperley for experimental assistance and the EPRSC for an EPSRC Doctoral Partnership award (EP/N509462/1). PG and SRY acknowledge the support of EPSRC SUPERGEN grant, EP/N001982/1. PG and SRY are grateful for the use of the ‘Hydra’ High Performance System at Loughborough University in addition to time on the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk) supplied via our membership of the UK's HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202, EP/R029431). PG and SRY strongly acknowledge the use of Athena as part of the HPC Midlands+ consortium, funded by the EPSRC on grant EP/P020232/1. Raw experimental data can be found at: https://doi.org/10.25500/edata.bham.00000799.