Abstract
The electrochemical lithiation and delithiation of the layered oxysulfide Sr2MnO2Cu4-δS3 has been investigated by using a combination of in situ powder X-ray diffraction and ex situ neutron powder diffraction, X-ray absorption and 7Li NMR spectroscopy, together with a range of electrochemical experiments. Sr2MnO2Cu4-δS3 consists of [Sr2MnO2] perovskite-type cationic layers alternating with highly defective antifluorite-type [Cu4-δS3] (δ ≈ 0.5) anionic layers. It undergoes a combined displacement/intercalation (CDI) mechanism on reaction with Li, where the inserted Li replaces Cu, forming Li4S3 slabs and Cu+ is reduced and extruded as metallic particles. For the initial 2-3% of the first discharge process, the vacant sites in the sulfide layer are filled by Li; Cu extrusion then accompanies further insertion of Li. Mn2.5+ is reduced to Mn2+ during the first half of the discharge. The overall charging process involves the removal of Li and re-insertion of Cu into the sulfide layers with re-oxidation of Mn2+ to Mn2.5+. However, due to the different diffusivities of Li and Cu, the processes operating on charge are quite different from those operating during the first discharge: charging to 2.75 V results in the removal of most of the Li, little reinsertion of Cu, and good capacity retention. A charge to 3.75 V is required to fully reinsert Cu, which results in significant changes to the sulfide sublattice during the following discharge and poor capacity retention. This detailed structure-property investigation will promote the design of new functional electrodes with improved device performance.
| Original language | English |
|---|---|
| Pages (from-to) | 3989-4005 |
| Number of pages | 17 |
| Journal | Chemistry of Materials |
| Volume | 33 |
| Issue number | 11 |
| Early online date | 24 May 2021 |
| DOIs | |
| Publication status | Published - 8 Jun 2021 |
| Externally published | Yes |
Bibliographical note
Funding Information:This work was supported as part of the Northeastern Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science. We thank the UK EPSRC for a studentship for PA and for funding through grants EP/E025447/1 and EP/P018874/1 and the UK STFC for access to the ISIS facility and Dr. R.I. Smith for assistance with NPD investigations. S.D. acknowledges DST Overseas Visiting Fellowship in Nano Science and Technology, Government of India (July 2018 to June 2019). J.L. acknowledges the funding from EPSRC grants EP/M009521/1 DJR00640 and EP/P003532/1. We also thank Dr. Anton Van der Ven from the University of Michigan for helpful discussions and making his work available before publication. The contribution to the work by JC was supported by Generalitat de Catalunya through a Beatriu de Pinós fellowship.