Abstract
Despite the importance of studying the instability of delithiated cathode materials, it remains difficult to underpin the degradation mechanism of lithium-rich cathode materials due to the complication of combined chemical and structural evolutions. Herein, we use state-of-the-art electron microscopy tools, in conjunction with synchrotron X-ray techniques and first-principle calculations to study a 4d-element-containing compound, Li2Ru0.5Mn0.5O3. We find surprisingly, after cycling, ruthenium segregates out as metallic nanoclusters on the reconstructed surface. Our calculations show that the unexpected ruthenium metal segregation is due to its thermodynamic insolubility in the oxygen deprived surface. This insolubility can disrupt the reconstructed surface, which explains the formation of a porous structure in this material. This work reveals the importance of studying the thermodynamic stability of the reconstructed film on the cathode materials and offers a theoretical guidance for choosing manganese substituting elements in lithium-rich as well as stoichiometric layer-layer compounds for stabilizing the cathode surface.
Highlights
Despite the importance of studying the instability of delithiated cathode materials, it remains difficult to underpin the degradation mechanism of lithium-rich cathode materials due to the complication of combined chemical and structural evolutions
We find that after extended cycling, a three-dimensional porous structure is formed in lithium-rich ruthenium-manganese oxide (LRMO) and segregation of ruthenium and manganese at the submicron scale can be observed
We find that ruthenium is expelled from the reconstructed oxide surface and forms metallic clusters at the nanoscale
Summary
Despite the importance of studying the instability of delithiated cathode materials, it remains difficult to underpin the degradation mechanism of lithium-rich cathode materials due to the complication of combined chemical and structural evolutions. Cation doping with electrochemical inactive elements, such as Al, Ti, Mg, has been widely used to enhance the crystal structure stability of lithium-rich layered cathode materials[18,19,20,21], and a recent computational study shows that Os, Sb, Ru, Ir, or Ta are the top-ranking dopants that can retain oxygens on the surface of Li2MnO322. A series of new model compounds, Li2IrO3 for example[30], has been successfully applied to investigating the oxygen anion redox contribution to the charge capacity Unlike their 3d counterparts, most prior studies of 4d or 5d element containing layered oxides have focused on the pristine state of these compounds but overlooked the cycling-induced oxygen loss and surface reconstruction. Imaging results of this material show no hint of elemental segregation even after 50 charge/discharge cycles, which experimentally validates our theoretical prediction
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
