The transition to next-generation energy storage, specifically rechargeable batteries like sodium-ion, polyanionic, and all-solid-state batteries, requires optimizing complex architectures where light mobile ions (Z ≤ 11) migrate through heavy transition-metal frameworks. Although X-ray diffraction and electron microscopy are widely used for structural characterization, they face intrinsic limitations when visualizing light elements (Li, Na, H, O) and buried interfaces in bulk battery devices. As neutrons interact directly with the atomic nuclei via the strong force, neutron-based techniques offer a non-destructive and highly penetrating probe that overcomes many of these barriers. This review focuses on how neutron-based techniques make it possible to directly observe structural features that are often inaccessible to X-ray or electron probes but can critically influence battery performance. We capture how Neutron Powder Diffraction (NPD) locates sodium/lithium vacancies to map diffusion pathways, how neutron reflectivity (NR) quantifies the density and evolution of the in situ solid-electrolyte interphase (SEI), and how small angle neutron scattering (SANS) and neutron imaging (NI) reveal mesoscale porosity and macroscopic electrolyte wetting. By correlating these atomic-to-macroscopic insights with electrochemical data, neutron methodologies are summarized as guiding tools to establish specific material design rules for enhancing the rate capability and thermal stability of sustainable battery chemistries.

The practical application of zinc-ion batteries (ZIBs) is constrained by persistent anode instabilities arising from nonuniform Zn nucleation, dendritic growth, corrosion, and parasitic hydrogen evolution. To mitigate these issues, polymer coatings have recently emerged as an effective interfacial engineering approach owing to their tuneable chemistry, mechanical adaptability, and ability to regulate ion transport at the metal-electrolyte boundary. This review summarizes recent advances in polymer-based stabilization strategies for Zn metal anodes, with emphasis on polymers containing coordinating functional groups, polymer-carbon hybrid interphases, and hydrophilic or adhesion-enhanced coatings. We discuss how tailored chemical functionalities- such as carbonyl, pyridyl, amine, and sulfonic groups- govern Zn2+ adsorption strength, surface charge distribution, desolvation behaviour, and preferred crystallographic growth, enabling controlled Zn deposition. Across these platforms, polymeric interphases demonstrate marked improvements in Coulombic efficiency, overpotential, corrosion resistance, and long-term cycling stability, even at high current densities. The review concludes with key design principles and emerging opportunities for next-generation polymer interfaces aimed at realizing highly reversible, dendrite-free Zn metal anodes for durable aqueous energy storage systems.

This review includes: structural design approaches, performance-enhancing modifications, and emerging application prospects of advanced Na-ion cathodes; optimization strategies and future applications of stable Na-ion cathodes.

Mechanochemically activated perovskite Ba 2 FeCoO 6 exhibits trifunctional electrocatalytic activity toward oxygen/hydrogen evolution and oxygen reduction reaction in alkaline media. It works as an air cathode in a rechargeable Zn–air battery.

The crystal and magnetic structure and properties of tavorite LiFePO 4 OH hydroxyphosphate cathode have been unravelled. Its underlying redox mechanism has been reported using operando X-ray diffraction.

The oxygen evolution reaction (OER) is key to the operation of various sustainable technologies like water-splitting devices and metal-air batteries. Realization of efficient OER depends on robust electrocatalyst materials as well as optimized electrolytes. The cations in electrolytes have a pronounced impact on the kinetics of OER. However, the mechanistic origin of this effect remains poorly addressed. In this study, using cobalt vanadium oxide Co3V2O8 (CVO) as a model electrocatalyst, the cation-dependent OER activity was investigated using fundamental electrochemical study in conjunction with ex situ (electron microscopy and Raman spectroscopy) analyses. The results demonstrate that OER performance is not only affected by surface/bulk reconstruction, but also governed by electrolyte cation adsorption. In situ Raman study in 1 M KOH electrolyte identified the generation of Co-oxyhydroxide species accompanied by vanadium dissolution, whereas ex situ Raman spectra revealed a more distinct VO bond in catalysts when subjected to 1 M CsOH. While partial amorphization was noticed in LiOH and NaOH systems, structural retention with irregular Co(O)OH domains was observed in CVO after catalysis in KOH and CsOH electrolytes. Electrochemical evaluation further establishes exchange current density as the sole parameter significantly affected due to the presence of different cations, directly correlating with reduced overpotential (320 mV) and extended durability (>12 hr continuous electrolysis). These findings highlight the critical role of electrolyte cations in modulating the intrinsic kinetics of Co3V2O8 toward OER electrocatalysts.

Sodium-ion batteries (SIBs) are progressively recognized as a viable alternative to lithium-ion batteries due to their operational and economic viability. However, their practical application is limited by lower energy density and intermediate cycling performance, predominantly limited by the cathodes. The exploration of anionic redox in layered oxides has introduced a new approach to enhance the energy density of rechargeable Na-ion batteries. By exploiting anionic redox activity, various positive electrodes are capable of providing additional capacity beyond their theoretical capacity. This additional capacity emerges from the combined contributions of anionic and cationic redox processes. However, the anionic capacity achieved during charge is often only partially reversible upon discharge, posing a significant challenge for practical use. This review offers a comprehensive analysis of anionic redox phenomena in sodium-based layered oxides, summarizing recent research strategies aimed at improving the anionic and cationic redox performance of these cathode insertion materials. It also elucidates the relationship between structure, function, and electrochemical performance. Eventually, it provides insights into the future research directions for Na-based layered oxide cathodes for energy storage applications.

Aqueous zinc‐ion batteries are emerging as potential candidates to cater low‐cost stationary energy storage due to the abundance, economic and ecological benignity of zinc. Among the various cathode materials, vanadium‐based compounds have garnered significant attention owing to their structural diversity, Zn 2+ storage capability, and high theoretical capacity. The electrochemical activities in these cathodes can be tuned by modulating their structure, particle morphology, surface coatings and local structural (dis)ordering. This study probes the role of disorder on the electrochemical performance of ZnV 2 O 4 spinel cathodes. Without any surface or structural optimization, ZnV 2 O 4 delivers a specific capacity of 150 mAh g −1 with stability over ≈1000 cycles at a current density of 1 A g −1 . Using operando and ex situ techniques – including electron microscopy, X‐ray diffraction, X‐ray absorption, and Raman spectroscopy – it is revealed that initial cycling induces a conversion reaction, forming a disordered Zn‐deficient vanadium oxide phase. This phase enables reversible Zn 2+ (co)insertion, enhancing long‐term performance. This findings highlight the critical role of disorder dynamics in tuning the electrochemical behavior of spinel ZnV 2 O 4 , offering valuable insights for designing advanced spinel cathodes for secondary zinc‐ion batteries.

Manganese-based oxides can function as economical cathode materials for Li-ion batteries. Various metastable manganese oxides can exhibit efficient Li+ (de)insertion activity. One such system is chemically derived Li0.44MnO2 offering reversible Li+ intercalation involving the Mn4+/Mn3+ redox reaction albeit with poor rate kinetics. In this work, the electrochemical activity of tunnel-structured Li0.44MnO2 has been enhanced by tailoring its crystal structure and particle morphology by Ti-doping into Mn sites. X-ray diffraction and spectroscopy analyses revealed successful Ti-doping while retaining the original structure. Varying degrees of Ti-doping were found to exhibit improved electrochemical performance, with Li0.44Mn0.89Ti0.11O2 delivering the highest capacity of 129 mAh g-1 at a rate of C/20. Ti-doping was further found to improve the Li+ diffusivity and rate kinetics. This enhancement in electrochemical activity can be ascribed to the combined effect of Ti-induced lattice expansion and decrease in particle size. Electrochemical titration and ex situ analyses revealed the occurrence of a single-phase (solid-solution) redox mechanism. Ti-doped Li0.44MnO2 can be harnessed as an economical cathode for Li-ion batteries.

Electrochemical water splitting using earth-abundant materials is crucial for enabling green hydrogen production and energy storage. In recent years, molybdenum trioxide (MoO3), a semiconducting material, has been proposed as a candidate catalyst for the oxygen evolution reaction (OER). Here, we advance nickel (Ni) doping of MoO3 as a strategy to increase the activity and stability of the material during alkaline electrochemical water splitting, thereby overcoming the typical activity-stability trade-off encountered with OER catalysts. The instability of MoO3 in alkaline media can be mitigated by doping with Ni, whose oxide is stable under such conditions. Using density functional theory (DFT) with Hubbard corrections, we show that Ni doping reduces the thermodynamic OER overpotential on the MoO3 basal plane to 0.64 V. Experiments demonstrate that Ni-doped MoO3 requires an overpotential of 0.34 V for an OER current density of 10 mA/cm2 (and 0.56 V at 100 mA/cm2), as opposed to a value of 0.40 V for pure MoO3. Further, Ni-doped MoO3 exhibits a lower Tafel slope of 74.8 mV/dec, compared to 98.3 mV/dec for the pristine material under alkaline conditions. While Mo leaches in alkaline conditions, X-ray photoelectron spectroscopy reveals enhanced stability with Ni doping. Overall, our work advances Ni-doped MoO3 as a promising water-splitting electrocatalyst and provides new insights into its OER mechanism and stability in alkaline media. More generally, the work sheds light on choosing a dopant to increase a material's activity and stability, which will also find applications in other catalytic materials.

The quest for innovative cathode materials is crucial for advancing secondary potassium-ion batteries (KIBs). Dedicated efforts have led to the exploration of broadly four distinct classes of materials, namely layered transition metal oxides, polyanion, Prussian blue analogues and organic materials [1]. However, synthesizing cathodes for KIBs, especially those based on layered 3d-series transition metals, pose significant challenges. These include the low concentration of K-ions due to electrostatic repulsion, hygroscopic instability, and decomposition susceptibility. In our current study, we addressed these complex synthetic challenges by employing the ambient ion-exchange synthesis method to create metastable cathode materials suitable for stationary energy storage applications. Integrating diffraction and spectroscopic techniques, we have elucidated that the ion exchange reaction proceeds via an overlay ordered structure formation (Figure 1) mechanism [2-6]. Additionally, we have conducted comprehensive investigations into the structural, morphological, electronic, and electrochemical characteristics of ion-exchanged materials [4]. To analyze the K+ insertion mechanism, we employed both ex-situ and in-situ X-ray diffraction analysis, along with potentio/galvanostatic titration techniques. Synergizing experimental tools with the theoretical calculations, we have unveiled the efficacy of ambient ion-exchange reactions to prepare promising novel cathode materials. Two case studies will be presented as noted below. Chemical ion-exchange route was employed to obtain a novel P2-type KxCo1/3Mn2/3O2 cathode for KIBs. With due material optimization and usage of suitable electrolytes, this oxide can be harnessed as a high-voltage cathode for KIBs operating at ~ 2.9 V at room and high (40-50 °C) temperatures (Figure 1c) [7-8]. Following, two novel compounds analogous to Na2Mn3O7 has been successfully synthesized via ambient chimie douce This discovery reveals the utilization of a cost-effective, scalable, and energy-efficient K-Mn-O ternary mixture as an extensively studied cathode material for KIBs (Figure 1d) [9]. Finally, this work provides a new dimension in obtaining targeted battery material beyond traditional synthetic route for the development of KIBs for next generation stationary energy storage system. References: Hosaka et al., Chem. Rev., 2020, 120, 6358-6466. K. Jha et al., Small, In press, 2024. K. Jha et al., Inorg. Chem, 2023, 62, 14971-14979 K. Jha et al., Curr. Opin. Electrochem., 2023, 38, 101216. K. Jha and P. Barpanda, Inorg. Chem. In press, 2024. K. Jha and P. Barpanda, Indian Provisional Patent Application 202341033225. K. Jha et al., Manuscript submitted. K. Jha et al., Indian Provisional Patent Application 202341088484. K. Jha et al., Manuscript submitted. Figure 1

Use of sustainable electrode components in Li-ion battery technology is essential for large-scale applications while addressing environmental concerns. Considering elemental abundance, Fe-based compounds can, in principle, work as the most economic cathodes. Fe-based hydroxysulfates LixFeSO4OH (x = 0 -1) can be harnessed as low-cost, sustainable, high-voltage, and moisture-resistant battery cathode materials. In this system, monoclinic (m) FeSO4OH and layered m-FeSO4OH were previously reported as Li-ion battery cathode materials. Here, we introduce orthorhombic (o) FeSO4OH as a potential low-cost cathode for Li-ion batteries synthesized by using a facile low-temperature hydrothermal route. The o-FeSO4OH cathode delivers a reversible capacity of 100 mA h/g at a current rate of C/20 (1e- = 159 mAh/g) at a working potential of ca. 3.2 V vs Li+/Li. A higher overpotential and faster rate kinetics compared with that of m-FeSO4OH stem from the subtle deviations in the structural framework affecting the Li coordination environment. Operando analytical tools, electrochemical titration techniques, and computational modeling are combined to characterize the complex phase transformation during the (de)lithiation process.

Alluaudites, a naturally occurring mineral, are best known as the intercalation-based cathode materials in the field of sodium-ion batteries.1 The 3D tunnel like structure of alluaudite facilitates easy alkali-ion migration making it (de)insertion host. The structural formula can be expressed as A(1)A(2)M(1)M(2)2(XO4)3, where A and M sites are alkali and transition metal ions respectively and XO4 denotes the polyanionic moieties (SO4, PO4, AsO4, MoO4, WO4 and so on). Depending on the inductive effect of the electronegative element, the potential of the materials can be tuned. In 2014, Yamada group reported alluaudite-structured Na2Fe2(SO4)3 as 3.8 V cathode material which benchmarked the highest potential ever observed by Fe2+/Fe3+ redox couple because of the presence of electronegative SO4 moiety.2 In 2017, the first molybdate-based alluaudite material, Na2.67Mn1.67(MoO4)3 was reported as a 3.45 V cathode by probing Mn2+/Mn3+ redox.3 Except Mn, Mo can also serve as another redox centre by using its range of oxidation states from +6 to 0. However, there is an open question remains whether we can access these redox states of Mo to impart extra capacity in these materials. To address the above issue, two case-studies will be discussed. Molybdate alluaudite: A series of molybdate-based alluaudites (TM= Co, Ni) were synthesized by using wet-chemical solution-combustion route. The Co-based alluaudite, Na36Co1.32(MoO4)3 was found to act as a high-voltage cathode (4 V vs Na/Na+ and 4.1 V vs Li/Li+) involving Co3+/Co2+ redox center while cycling between 3.0 V to 4.3 V.4 An intercalation-type of mechanism was proved by ex-situ studies combined with first principle calculations. All the above-mentioned alluaudite consists of Mo species, which can be redox-active at lower voltage. When cycled in a low-voltage window (0.01 V to 3.0 V), Na3.36Co1.32(MoO4)3 was found to act as an anode in Na-ion batteries. High capacity (ca. 400-500 mAh/g) was obtained with a central potential ~0.6 V involving conversion and (de)insertion reaction mechanism. The Ni-analogue, Na3.6Ni1.2(MoO4)3 alluaudite, was studied as an anode material in both Li-ion and Na-ion batteries involving conversion and (de)intercalation redox mechanisms like the Co analogue. The underlying redox mechanism will be described for both cases involving post-mortem diffraction, electron microscopy, and spectroscopic tools along with density functional theory (DFT) calculations. Tungstate alluaudite: The first-ever tungstate alluaudite, Na4Mn(WO4)3, prepared by a solid-state route, was found to work as a 0.4 V anode (vs. Na+/Na) material while cycled in the voltage window of 0.01 V to 3.0 V. Similar to molybdenum, W can also show multiple redox chemistries. A conversion- type mechanism was probed with the help of in-situ XRD, ex-situ TEM, XAS and XPS techniques. References: [1] D. Dwibedi, P. Barpanda, A. Yamada, Small Methods 4 (2020) 2000051. [2] P. Barpanda, G. Oyama, S. Nishimura, S.-C. Chung, A. Yamada, Nat. Commun. 5 (2014) 4358. [3] J. Gao, P. Zhao, K. Feng, Chem. Mater. 29 (2017) 940-944. [4] P. Barman, P.K. Jha, A. Chaupatnaik et al, P. Barpanda, Mater. Today Chem. 27 (2023) 101316.

To improve the cycle life of sodium-ion batteries, it is essential to understand the microscopic processes that lead to cell degradation. The mismatched response time of anode and cathode has profound but poorly understood impact on cycle life. In this work, we combine electrochemical and materials characterization along with electrochemical modeling to investigate the root cause of degradation in sodium-ion full cells made from Na4Fe3(PO4)(2)P2O7 (NFPP) cathodes and hard carbon (HC) anode. Our results pinpoint to the slow diffusion of Na in HC as the main cause of diffusional polarization that leads to cathode experiencing high local potentials and ultimately to active material loss over cycling. We demonstrate that by reducing the anode particle size, the diffusional timescales in anode can be matched with that of cathode to improve both extractable capacity as well as cycle life. These observations shed light on non-intuitive and intricate ways in which cathode and anode can interact with each other to cause degradation in Na-ion batteries and how microscopic understanding of these cause and effects can help design long lasting batteries.