A near dimensionally invariable high-capacity positive electrode material.

Delivering inherently stable lithium-ion batteries is a key challenge. Electrochemical lithium insertion and extraction often severely alters the electrode crystal chemistry, and this contributes to degradation with electrochemical cycling. Moreover, electrodes do not act in isolation, and this can be difficult to manage, especially in all-solid-state batteries. Therefore, discovering materials that can reversibly insert and extract large quantities of the charge carrier (Li+), that is, high capacity, with inherent stability during electrochemical cycles is necessary. Here lithium-excess vanadium oxides with a disordered rocksalt structure are examined as high-capacity and long-life positive electrode materials. Nanosized Li8/7Ti2/7V4/7O2 in optimized liquid electrolytes deliver a large reversible capacity of over 300 mAh g-1 with two-electron V3+/V5+ cationic redox, reaching 750 Wh kg-1 versus metallic lithium. Critically, highly reversible Li storage and no capacity fading for 400 cycles were observed in all-solid-state batteries with a sulfide-based solid electrolyte. Operando synchrotron X-ray diffraction combined with high-precision dilatometry reveals excellent reversibility and a near dimensionally invariable character during electrochemical cycling, which is associated with reversible vanadium migration on lithiation and delithiation. This work demonstrates an example of an electrode/electrolyte couple that produces high-capacity and long-life batteries enabled by multi-electron transition metal redox with a structure that is near invariant during cycling.

Nanoscale domain imaging of Li-rich disordered rocksalt-type cathode materials with X-ray spectroscopic ptychography.

Lithium-rich disordered rocksalt-type cathode materials are promising for high-capacity and high-power lithium-ion batteries. Many of them are synthesized by mechanical milling and may have heterogeneous structures and chemical states at the nanoscale. In this study, we performed X-ray spectroscopic ptychography measurements of Li-rich disordered rocksalt-type oxide particles synthesized by mechanical milling before and after delithiation reaction at the vanadium K absorption edge, and visualized their structures and chemical state with a spatial resolution of ∼100 nm. We classified multiple domains with different chemical states via clustering analysis. A comparison of the domain distribution trends of the particles before and after the delithiation reaction revealed the presence of domains, suggesting that the delithiation reaction was suppressed.