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Operando studies reveal structural evolution with electrochemical cycling in Li-CoS2

: Butala, M.M.; Doan-Nguyen, V.V.T.; Lehner, A.J.; Göbel, C.; Lumley, M.A.; Arnon, S.; Wiaderek,K.M.; Borkiewicz, O.J.; Chapman, K.W.; Chupas, P.J.; Balasubramanian, M.; Seshadri, R.


Journal of physical chemistry. C, Nanomaterials and interfaces 122 (2018), Nr.43, S.24559-24569
ISSN: 1932-7447
ISSN: 1932-7455
Fraunhofer IWM ()
cathode material; lithium battery; solid state electolyte; functional battery material; sulfides

The drive toward high energy density alternatives to Li-ion batteries has led to great interest in energy storage materials not inherently constrained by the capacity limits of the currently employed intercalation electrode materials. Among the alternatives under consideration are electrode materials with theoretical capacities many times greater than intercalation electrodes that store charge through so-called conversion reactions. However, the significant structural changes that enable the high theoretical capacity of conversion systems contribute to issues of poor efficiency and short cycle life. To better understand cycling issues in conversion systems, we study the local structure evolution of CoS2 during Li storage. Being metallic and potentially capable of redox on both anion and cation sites, CoS2 would be expected to display promise as a cathode material. Through combined ex situ X-ray absorption near-edge spectroscopy and pair distribution function analysis from operando X-ray total scattering, we describe the reactions that take place over the first 1.5 cycles. In doing so, we identify the irreversible formation of a Co9S8-like local structure with significantly limited electrochemical activity as the primary source of capacity fade. The methods employed here and the insights that emerge could inform the rational design of conversion systems for electrochemical energy storage.