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Summary: The LiNiO2 (LNO) positive electrode material is one of the most promising high‐voltage alternatives for the layered oxide materials such as LiCoO2 (LCO). However, the poor cyclability still limits widespread commercialization of LNO, whereas crack formation is one of the main issues leading to its premature aging. In this study, a series of Al‐doped LNO (LiNi1−xAlxO2, x = 0, 0.02, 0.04, 0.06) positive electrode materials are synthetized via a simple sol‐gel method. Overall, this study aims at providing new insights of the sol‐gel method and Al‐doped strategy for LNO positive electrode materials. The synthesis is found to readily yield in small nanosized crystals, which alleviate the cracking issue. Besides, the optimized Al‐doping amount (2 at%) in LNO decreases cation mixing and primary particle size resulting in improved layered structure stability attributed to more reversible H2‐H3 phase transitions. As a result, the assembled lithium ion batteries equipped with LiNi0.98Al0.02O2 can smoothly run for 400 cycles with a relatively high capacity retention of 81% at 100 mA g−1 charging‐discharging and a wide operating voltage window of 2.5‐4.5 V. [ABSTRACT FROM AUTHOR]

Carbon nanostructures are promising electrode materials for energy storage devices because of their unique physical and chemical properties. Modification of the surface improves the electrochemical properties of those materials because of the changes in morphology, diffusion properties, and inclusion of additional contributions to redox processes. Oxygen-containing functional groups and nitrogen doped into the carbon matrix significantly contribute to the electrochemical behavior of reduced graphite oxide (RGO). In this work, RGO was synthesized during hydrothermal treatment of graphite oxide with a hydrazine sulfate aqueous solution. Different amounts of hydrazine sulfate were used to synthesize RGO with different nitrogen contents in the structure, and the same synthesis conditions made it possible to obtain a material with a similar composition of oxygen-containing functional groups. The materials with different nitrogen concentrations and similar amounts of oxygen were compared as electrode materials for a supercapacitor and as a negative electrode material for a Li-ion battery. It was shown that the presence of oxygen-containing functional groups has the greatest influence on the behavior and efficiency of supercapacitor electrode materials, while nitrogen atoms embedded in the graphene lattice play the largest role in lithium intercalation. [ABSTRACT FROM AUTHOR]