The continuous demand for improved performance in electrical devices, ranging from small-scale applications like mobile phones to larger ones such as electric vehicles, necessitates an ongoing pursuit of enhancing battery energy density. A critical component defining energy density in batteries is the cathode material. Among the candidates for improving battery performance, high-nickel layered materials stand out as one of the best, offering higher capacity and voltage than currently employed alternatives [1].

Traditionally, these materials are used in the form of polycrystals, facing challenges associated with surface reactivity leading to microcrack formation during lithiation and delithiation [2]. In recent years, materials with single-crystal morphology have garnered significant attention, particularly in the context of advancing all-solid-state battery technologies. Single crystals, in contrast to polycrystals, exhibit substantially lower specific surface area, which can be a tremendous advantage for materials with limited structural and electrochemical stability towards the electrolyte.

The most commonly used method for producing single crystals is based on the molten salts technique, which, however, is time-consuming and energy-intensive. This study introduces a synthesis method for high-Ni NMC955 materials using the Pechini process followed by annealing. Diverse morphologies were achieved by adjusting synthesis parameters at various stages. This developed synthesis method provides a tool for tailoring the morphology of single-crystal NMC for future applications in cells with both liquid and solid electrolytes.

Testing was conducted across different voltage ranges, examining the effect of the electrolyte on cell performance, life cycle, and the formation, stability, and morphology of the cathode/electrolyte interface (CEI). Results indicate that single crystals exhibit better cyclability than polycrystals in full cells. In-depth characterization of the cathode/electrolyte interface in cells with different electrolytes was performed. Charge transfer and interface stability were further assessed through Electrochemical Impedance Spectroscopy (EIS) during the lithiation/delithiation process for both all-solid-state and traditional cells.

Single crystals demonstrated superior performance within a wider voltage window compared to polycrystals. Interestingly, the increase in the voltage window did not lead to capacity fade, contrasting with the polycrystal case. These findings underscore the importance of investigating single-crystal materials for the development of high-energy-density lithium-ion battery technologies, particularly in cells with solid-state electrolytes. The results also contribute significantly to the understanding and characterization of interfaces in single-crystal NMC, with potential implications for future advancements in battery technology.