The active role of alumina, pentalithium aluminate (Li5AlO4, Li‐aluminate), and pentasodium aluminate (Na5AlO4, Na‐aluminate) as the surface protection coatings produced via atomic layer deposition on Li and Mn‐rich NCM cathode materials 0.33Li2MnO3·0.67LiNi0.4Co0.2Mn0.4O2 is discussed. A notable improvement in the electrochemical behavior of the coated cathodes has been found while tested in Li‐coin cells at 30 °C. Though all the coated cathodes demonstrate enhanced electrochemical cycling and rate performances, Na‐aluminate coated cathodes exhibit exemplary behavior. Prolonged cycling and rate capability testing demonstrate that after more than 400 cycles at 1 C rate, the uncoated cathode delivers only 63 mAh g−1, while those with alumina, Li‐aluminate, and Na‐aluminate coatings exhibit approximately two times higher specific capacities. The coated cathodes display steady average discharge potential and lower evolution of the voltage hysteresis during prolonged cycling compared to the uncoated cathode. Importantly, Na‐aluminate coated cathode shows a lowering in gases (O2, CO2, H2, etc.) evolution. Post‐cycling analysis of the electrodes demonstrates higher morphological integrity of the coated cathode materials and lower transition metals dissolution from them. The coatings mitigate undesirable side reactions between the electrodes and the electrolyte solution in the cells.

Na‐ion batteries (SIB) are considered promising systems for energy storage devices, however diversity of available cathode materials is lower compared to lithium ion batteries. Recently, Na3V2(PO4)2F3 (NVPF) has been demonstrated as promising cathode material for SIB owing to high specific capacity and electrochemical reversibility. However, most of reports demonstrates capacities lower than theoretical value and optimization of electrochemical performances by controlled morphology and crystal structure was not demonstrated yet. Here, we demonstrate a scalable synthesis strategy to tailor the crystal structure and morphology of NVPF and showed that our approach enables to optimize the Na+ ion accommodation, diffusion and stability. A flower morphology (NVPF‐F) crystalizes in tetragonal structure, demonstrates discharge capacity of 109.5 mA.h.g−1 and 98.1 % columbic efficiency whereas a hollow spherical morphology (NVPF‐S) with orthorhombic structure exhibits discharge capacity of 124.8 mA.h.g−1 (very close to theoretical value) and 99.5 % columbic efficiency. The observed discharge capacity for NVPF‐S is highest reported value which is ascribed due to stable crystal structure and monodispersed morphology. Long term stability with negligible capacity loss is demonstrated over 550 cycles. Our findings shed light on importance of crystal structure and morphology of NVPF on electrochemical response, and realization as cathode material for SIB.

Na‐ion batteries have recently emerged as a promising alternative to Li‐based batteries, driven by an ever‐growing demand for electricity storage systems. In the present work, we propose a cobalt‐free high‐capacity cathode for Na‐ion batteries, synthesized using a high‐entropy approach. The high‐entropy approach entails mixing more than five elements in a single phase; hence, obtaining the desired properties is a challenge since this involves the interplay between different elements. Here, instead of oxide, oxyfluoride is chosen to suppress oxygen loss during long‐term cycling. Supplement to this, Li was introduced in the composition to obtain high configurational entropy and Na vacant sites, thus stabilizing the crystal structure, accelerating the kinetics of intercalation/deintercalation, and improving the air stability of the material. With the optimization of the cathode composition, a reversible capacity of 109 mAh g−1 (2‐4 V) and 144 mAh g−1 (2‐4.3 V) is observed in the first few cycles, along with a significant improvement in stability during prolonged cycling. Furthermore, in‐situ and ex‐situ diffraction studies during charging/discharging reveal that the high‐entropy strategy is successful in suppressing the complex phase transition. The impressive outcomes of the present work strongly motivate the pursuit of the high‐entropy approach to develop efficient cathodes for Na‐ion batteries.This article is protected by copyright. All rights reserved

Hard carbon (HC) has emerged as potential anode material for sodium-ion batteries (SIB). However, it is plagued with several issues like low capacity, poor cyclability, significant electrolyte degradation on interface. Realization of HC as anode requires fundamental understanding of the effect of its porous structure/composition on electrochemical performance. Herein, we report the use of lignocellulosic orange peel precursor for HC synthesis with tuneable surface area (SA), controlled porosity using phosphoric acid treatment. Physicochemical properties of HC were further tailored using N-doping. The electrochemical response of various HCs was tested with careful attention to the effect of HC SA and nitrogen content on the performances as anode. We show that optimized bio-waste based HC exhibits Na+ specific capacity of 125 mAhg−1 at 70 mAg−1 with significantly suppressed CO2 evolution during cycling, indicating mitigated electrolyte degradation and superior performance. We believe that this study sheds light on design rules for bio-waste low-cost precursors for synthesizing HC with tailored physical and electrochemical properties. Using such design guidelines, is crucial for developing HC based anode materials for SIB’s.

High-energy cathode materials that are Li- and Mn-rich lithiated oxides—for instance, 0.35Li2MnO3.0.65LiNi0.35Mn0.45Co0.20O2 (HE-NCM)—are promising for advanced lithium-ion batteries. However, HE-NCM cathodes suffer from severe degradation during cycling, causing gradual capacity loss, voltage fading, and low-rate capability performance. In this work, we applied an effective approach to creating a nano-sized surface layer of Li2SO4 on the above material, providing mitigation of the interfacial side reactions while retaining the structural integrity of the cathodes upon extended cycling. The Li2SO4 coating was formed on the surface of the material by mixing it with nanocrystalline Li2SO4 and annealing at 600 °C. We established enhanced electrochemical behavior with ~20% higher discharge capacity, improved charge-transfer kinetics, and higher rate capability of HE-NCM cathodes due to the presence of the Li2SO4 coating. Online electrochemical mass spectrometry studies revealed lower CO2 and H2 evolution in the treated samples, implying that the Li2SO4 layer partially suppresses the electrolyte degradation during the initial cycle. In addition, a ~28% improvement in the thermal stability of the Li2SO4-treated samples in reactions with battery solution was also shown by DSC studies. The post-cycling analysis allowed us to conclude that the Li2SO4 phase remained on the surface and retained its structure after 100 cycles.