Structural Evolution of Layered Manganese Oxysulfides during Reversible Electrochemical Lithium Insertion and Copper Extrusion

Sunita Dey; Dongli Zeng; Paul Adamson; Jordi Cabana; Sylvio Indris; Jingyu Lu; Simon J Clarke; Clare P Grey

doi:10.1021/acs.chemmater.1c00375

Structural Evolution of Layered Manganese Oxysulfides during Reversible Electrochemical Lithium Insertion and Copper Extrusion

Chem Mater. 2021 Jun 8;33(11):3989-4005. doi: 10.1021/acs.chemmater.1c00375. Epub 2021 May 24.

Authors

Sunita Dey¹, Dongli Zeng², Paul Adamson³, Jordi Cabana², Sylvio Indris², Jingyu Lu¹, Simon J Clarke³, Clare P Grey^{1

2}

Affiliations

¹ Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.
² Department of Chemistry, State University of New York, Stony Brook, New York 11794-3400, United States.
³ Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, U.K.

Abstract

The electrochemical lithiation and delithiation of the layered oxysulfide Sr₂MnO₂Cu_4-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. Sr₂MnO₂Cu_4-δS₃ consists of [Sr₂MnO₂] perovskite-type cationic layers alternating with highly defective antifluorite-type [Cu_4-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. Mn^2.5+ 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 Mn^2.5+. 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.