In the path of achieving a sustainable and cost-effective energy storage technology, organic materials (OMs) for sodium-ion batteries (SIBs) are considered to be a promising solution. Eliminating the use of transition metals in the battery active materials is in line with “Affordable and Clean Energy,” noted as the Sustainable Development Goal (SDG-7) of the United Nations. OMs used in post lithium-ion batteries are cost-effective, environmentally friendly, and can deliver reasonably high energy density. A diverse class of OMs, such as n-type, p-type, bipolar, and conducting polymers, which contains carbonyl, pyrazine, nitroxy radical-based, and azo-based functional groups, has been investigated. With respect to the type of active material and operating voltage, OMs exhibit a variety of storage mechanisms. Despite this, achieving practical organic sodium-ion batteries (OSIBs) still faces hurdles arising from low operating voltage, poor electronic conductivity, low material loading of organic materials and low cycle life. Despite numerous review articles available for OSIBs, a review paper focused on storage mechanisms of different OSIBs, recent progress, and a solution-oriented perspective for attaining high-performance OMs is still lacking. Here, we have compiled different types of OMs and discussed their storage mechanisms. Highlighted recent research outcomes on OMs, including metal/covalent organic frameworks for high-energy OSIBs. Further, we have discussed different possible all-OSIBs based on the electrode configurations and included a detailed perspective describing how to improve energy density and cycle life to attain practical all-OSIBs.

The rational tuning of layered metal oxide cathodes is central to advancing sodium‐ion battery performance, particularly under high‐voltage operation. Herein, the role of light weight boron as a covalent dopant is investigated to modulate the charge dynamics and structural robustness of P2‐type Na 0.67 Ni 0.33 Mn 0.67 O 2 cathodes. Through strategic boron (B) doping at the oxygen framework, a reconfiguration of local bonding environments is observed, which mitigates transition‐metal migration and stabilizes the layered lattice during high‐voltage cycling. Electrochemical analyses reveal a trade‐off between enhanced voltage retention and marginal capacity suppression at elevated doping levels, attributed to altered Na + diffusion pathways and phase evolution dynamics. Complementary structural and spectroscopic studies indicate suppressed phase transitions due to anionic redox, underscoring the dual role of boron in reinforcing both electronic transport and structural resilience. This work delineates the nuanced impact of B‐doping on layered oxide chemistry, offering insight into defect‐driven performance engineering for next‐generation Na‐ion energy storage systems.

P2-type Na0.67Ni0.33Mn0.67O2 cathode, prominent for its high Na-ion diffusion kinetics and rate performance, suffers from limited first charge capacity due to its deficient sodium content (x = 0.67) and structural instability associated with P2-O2 phase transitions and Na+/vacancy ordering. In this study, the incorporation of Li+ and Mg2+ dual dopants into the lattice sites enhanced the sodium content through effective charge balancing thereby mitigating Na+/vacancy issues. Li doping contributed to stabilizing the Na+ distribution while Mg2+ promoted cationic ordering and suppressed undesirable phase transitions, collectively improving the structural integrity. The resulting layered cathode Na0.85Ni0.32Mn0.60Mg0.03Li0.05O2 exhibited a biphasic P2/O3 structure, leveraging the synergistic benefits of both phases for improved electrochemical performance. In-operando X-ray diffraction and electrochemical analysis revealed that the material maintained structural integrity during cycling, while phase transition was significantly suppressed. The dual-doped cathode delivered a capacity retention of 89% after 150 cycles at 1C, with a smoother voltage profile indicative of suppressed phase transitions. This work highlighted the effectiveness of Li-Mg dual-doping strategy in optimizing the performance and stability of layered oxides, offering a pathway for high-performance sodium-ion batteries.

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.

Manganese-based cathode materials have attracted significant interest in zinc-ion batteries (ZIBs) due to their high theoretical capacity, affordability, and environmentally friendly nature. Recently, Na2Mn3O7 (NMO) has emerged as a promising electrode material for ZIBs owing to its unique triclinic crystal structure, which consists of infinite parallel [Mn3O7]2⁻ layers. This layered framework includes a vacancy at one of the seven Mn sites, which plays a crucial role in facilitating the insertion and accommodation of incoming Zn2+ ions. This structural feature allows for efficient zinc intercalation, transforming NMO into a Zn-Mn-based system electrochemically. In this study, the focus is on investigating the mechanism of self-ion exchange occurring in NMO, utilizing an electrolyte composed of 2 M ZnSO4 and 0.1 M MnSO4, exhibiting a reversible capacity of ∼240 mAh g-1 at a C/10 rate with a Coulombic efficiency of ∼99%. The self-ion exchange mechanism and structural changes during the battery operation were investigated using ex-situ x-ray diffraction and x-ray photoelectron spectroscopy analysis. The reversible phase transformations between hydrated and partially dehydrated states suggest a robust mechanism for Zn2+ ion insertion and extraction, contributing to the stability and performance of the Zn-Mn electrode material in ZIB applications.

Rechargeable aqueous Zn-Mn batteries have emerged as a promising candidate for grid-scale energy storage application, offering high specific energy, cost-effectiveness, environmental sustainability, and superior safety characteristics. ZnMn3O7 (ZMO) has recently gained attention as a potential cathode for aqueous energy storage systems, attributed to its layered structure, abundant manganese redox centers, and intrinsic vacancy sites that enable efficient ion diffusion. However, direct synthesis of ZMO remains challenging, as it preferentially transforms into the Zn-deficient spinel structure (Zn0.75Mn0.25)Mn2O4. In this study, we approach a synthesis method for ZMO via chemical ion-exchange method, employing Na2Mn3O7 (NMO) as the starting precursor. The process involves a chemical ion-exchange reaction facilitated by 5 M ZnSO4 as the ionic solution, enabling efficient cation exchange at the vacancy sites of Na2Mn3O7. Hydrated ZnMn3O7.3H2O was prepared and subjected to controlled calcination within a temperature range of 100-600 degrees C to study its phase transitions and structural evolution. This investigation provided valuable insights into its thermal stability and the transformation mechanisms responsible for forming the anhydrous ZnMn3O7 phase. The ion-exchange mechanism was systematically studied through structural and morphological characterizations at different calcination stages. Electrochemical testing of ZMO with 1 M Zn(CF3SO3)2 + 0.1 M MnSO4 as the electrolyte demonstrated outstanding cycling stability, delivering a reversible discharge capacity of around 140 mAh g-1 and 99% Coulombic efficiency over 100 cycles at a 1 C rate. These findings highlight the material's promise as a high-performance cathode for advanced energy storage applications.

Among cathodes for sodium-ion batteries (SIBs), layered transition metal oxides Na x MO 2 (M = transition metal) are very promising due to their easy synthesis and high theoretical capacity. 1,2 In this class, Ni/Mn/Fe-based layered oxides are attractive due to the high redox potential of Ni 2+ / Ni 4+ and Jahn Teller inactive centers (Ni 2+ , Fe 3+ ,and Mn 4+ ). 3 However, complex phase transitions, Na + /vacancy ordering and transition-metal (TM) migration degrade their electrochemical performances. 4 To address the issues, a widely studied cathode- P2-type Na 0.67 [Ni 0.33 Mn 0.67 ]O 2 is chosen and Li + is substituted in the TM-layer to tailor a series of high Na-content cathodes. Among them, Na 0.85 [Li 0.14 Ni 0.29 Mn 0.57 ]O 2 cathode with optimal Li-substitution exhibits a reversible capacity of 168 mAh g -1 at 0.1 C rate and good cycling stability (82% retention after 100 cycles). 5 In-situ XRD measurement reveals a complete solid-solution formation and X-ray absorption spectroscopy studies confirm the participation of Ni 4+ /Ni 2+ and Mn 4+ /Mn 3+ redox couples during Na + -extraction/insertion. Lastly, a full Na-ion cell with hard carbon is demonstrated with an energy density of 420 Wh kg -1 . In subsequent work, a Li and Ti co-substitution strategy is applied to design a high-entropy O3-type NaLi x Ni y Fe z Mn 0.5 Ti 0.5-a O 2 cathode. 6 It retains 77% of its initial capacity after 400 cycles at a 2 C rate with a facile O3-P3-OP2-P3-O3 phase transition. The co-substitution strategy uplifts the average voltage of the system, improves the reversibility of the high-voltage OP2 phase, and enhances the Na-ion diffusion rate. A mere 1.32% unit cell volume change and diminishing electrochemical cell resistance over cycling ensure its superior long-term cycling performance. A full cell is fabricated, which holds 62% of its initial capacity even after 1000 cycles at a 0.5 C rate. Therefore, mono- and di-ion substitution strategies hold enormous potential for designing high-performing P2- and O3-type cathode materials for practical SIBs. References T. Hosaka, K. Kubota, A. S. Hameed, and S. Komaba, Chem. Rev. , 120 , 6358–6466 (2020). J. Y. Hwang, S. T. Myung, and Y. K. Sun, Chem. Soc. Rev. , 46 , 3529–3614 (2017). F. Zhang, J. Liao, L. Xu, W. Wu, and X. Wu, ACS Appl. Mater. Interfaces , 13 , 40695–40704 (2021). Z. Lu and J. R. Dahn, J. Electrochem. Soc. , 148 , A1225 (2001). A. Ghosh, B. Senthilkumar, S. Ghosh, P. Amonpattaratkit, and P. Senguttuvan, J. Electrochem. Soc. , 170 , 030538 (2023). A. Ghosh, R. Hegde, and P. Senguttuvan, J. Mater. Chem. A. , submitted(2023).

P2-NaxTMO2, (x <= 0.67, TM-transition metal) oxides are promising cathode materials for Na-ion batteries, however they suffer from Na+-vacancy ordering and huge structural transformations (P2 -> O2 -> OP4). In contrast, high Na content in P2-type cathodes enables high structural stability and promotes active elements to their lower oxidation state and thereby achieving high capacity and cycling stability. Herein, light-weight elements boron and lithium doped in P2-type Na0.67Ni0.33Mn0.67O2 using cationic potential approach, aiming to improve the Na content. Li-B doped Na0.8Ni0.3Mn0.6Li0.05B0.05O2 delivers a capacity of 85 mAh/g and excellent capacity retention (88 % after 500 cycles). The effects of Li-B doping in P2-type Na0.67Ni0.33Mn0.67O2 are systematically investigated.

The high-entropy concept is receiving attention as an advanced design strategy to functionalize material properties by tuning the disorderliness of the system. High-entropy materials have garnered significant recognition in the realm of energy storage due to their versatile and diverse material properties. In recent times, there has been active exploration of traditional materials as positive electrodes in sodium-ion batteries. Nevertheless, under profound sodiated conditions, these materials tend to exhibit sluggish kinetics and unfavourable phase transitions, leading to significant capacity degradation and subpar rate capability. High-entropy concepts successfully tune the configurational entropy by adjusting the stoichiometric balance of active/inactive cations to address the drawbacks. The recent developments and research progress on high-entropy materials for sodium-ion batteries are reviewed in this article, with a focus on the advantages of configurational entropy modulation for improving electrochemical performances. The positive aspects of high-entropy cathode materials as well as the key challenges are finally outlined to realize practical sodium-ion batteries.

P2-type Na0.67[Ni0.33Mn0.67]O2 layered oxide cathode is attractive for practical Na-ion battery application due to its high voltage Ni4+/Ni2+ redox and good air-stability. However, it suffers from rapid capacity decay originating from high voltage P2-O2 transformation. To alleviate this issue, herein we explore optimum Li-substitution into the transition metal layer of Na0.67[Ni0.33Mn0.67]O2 to tailor a series of high Na-content P2-type cathodes. Among them, Na0.85[Li0.14Ni0.29Mn0.57]O2 cathode with optimal Li-substitution exhibits reversible capacities of ∼168 mAh g−1 at 0.1C rate and good cycling stability (82% of retention after 100 cycles at 1C rate). In-situ XRD measurement reveals the formation of complete solid-solution and X-ray absorption spectroscopy studies confirm the participation of Ni4+/Ni2+ and Mn4+/Mn3+ redox couples during Na (de)intercalation of the Na0.85[Li0.14Ni0.29Mn0.57]O2. A full Na-ion cell (Na0.85[Li0.14Ni0.29Mn0.57]O2||hard carbon) is demonstrated with an energy density of 420 Wh kg−1.

P2 and O3-type sodium layered oxides (NaxTMO2) have been considered as most promising cathodes for sodium-ion batteries. The P2-type oxides are superior to O3 in terms of fast Na diffusion and high-rate kinetics. However, the deficient Na (x < 0.7) in the P2-structure has low initial charge capacity and it limits practical application. In addition to Na deficiency, P2-O2 phase transition and Na+/vacancy ordering degrades the performance during cycling. To address this issue, dual doping strategy can be employed, synergistic effect of the dopants can mitigate both the Na+/vacancy ordering and the P2-O2 phase transitions. Herein, effect of Li-Cu dual doping in P2-type Na0.67Ni0.33Mn0.67O2 is systematically investigated. Dual doped high-Na P2-type cathode achieved high capacity similar to 110 mAh g(-1) with a cycling stability of similar to 85 % even following 200 cycles. Remarkably, the voltage profile is completely changed from multiple plateaus to a slow gradient which indicates a solid-solution pathway. Li present in TM layer and the strong Cu-O binding can suppress the irreversible P2-O2 phase transition. Structural analysis has ensured that there is no O2/OP4 phase formation during the charge up to 4.2 V. The present result reflects that the sufficient sodium and structural stabilization can improve the performance of P2-type cathodes.

Pyrochlore type-Bi2Sn2O7/carbon composite (BSO/C), prepared via ball milling, is explored as a potential K-ion anode. It delivers reversible capacities of greater than 295 mAh g(-1) for 100 cycles at 50 mA g(-1) in 5 M KFSI in EC/DEC electrolyte, while a severe capacity fade is noticed in a KPF6-based electrolyte system. A full K-ion battery comprising K4Fe(CN) 6 and BSO/C as the cathode and the anode respectively, is also demonstrated.

Designing new cathode materials remains crucial in developing (post) Li-ion batteries. Mn-based oxide cathodes have received wide attention due to their sustainable nature, low cost, elemental abundance, structural diversity/polymorphism, and rich oxidation states (2+ to 7+), offering tunable redox potential [1]. Here, we have investigated different oxide-based cathode insertion compounds for secondary metal-ion batteries. i) We have demonstrated tunnel-type sodium insertion material Na44MnO2(NMO) as an intercalation host for Li-ion and K-ion batteries. The solution combustion synthesized Na0.44MnO2 assuming an orthorhombic structure (space group Pbam), exhibited rod-like morphology. After electrochemical ion exchange from NMO, we obtained Na0.11K0.27MnO2 (NKMO) and Na0.18Li0.51MnO2 (NLMO) cathodes for K-ion batteries and Li-ion batteries, respectively [2]. These new compositions, NKMO and NLMO, showed excellent cycling stability with capacities of ∼74 and 141 mAh g–1 (first cycle, C/20 current rate). The underlying mechanistic features concerning charge storage and structural modifications in these cathode compositions were probed by combining ex-situ structural, spectroscopy, and electrochemical tools [3]. ii) Using composite formation, we have tried to improve the P2-type layered material. Here, the stable Na7(Li1/18Mn1/18Ni3/18Fe2/18χ1/18)O2–xNa2MoO4 biphasic composite was synthesized using Mo doping. Overall, the redox chemistry was investigated using various spectroscopy techniques to prove the net capacity resulted from both cationic and anionic redox reactions [4]. Keywords: energy storage; batteries; cathode; manganese oxides; intercalation; doping References: [1] N. O. Vitoriano et al., T. Rojo, Energy Environ. Sci. 2017, 10 (5), 1051−1074. [2] K. Sada, B. Senthilkumar, P. Barpanda, Chem. Commun. 2017, 53 (61), 8588−8591. [3] S.P. Vanam et al., P. Barpanda, Inorg. Chem. 2022, 61 (9), 3959−3969. [4] S.P. Vanam, P. Barpanda, Electrochim. Acta. 2022, 431, 141122.

The rational design of novel cathode materials remains a key pursuit in the development of (post) Li-ion batteries. Considering the relative ionic and Stokes radii and open frameworks with large tunnels, Na-based compounds can act as versatile cathodes for monovalent Li-ion and post-Li-ion batteries. Here, tunnel-type sodium insertion material Na0.44MnO2 is demonstrated as an intercalation host for Li-ion and K-ion batteries. The rod-shaped Na0.44MnO2 was synthesized by a solution combustion method assuming an orthorhombic structure (space group Pbam), which led to Na0.11K0.27MnO2 (NKMO) and Na0.18Li0.51MnO2 (NLMO) cathodes for K-ion batteries and Li-ion batteries, respectively, via facile electrochemical ion exchange from Na0.44MnO2. These new compositions, NKMO and NLMO, exhibited capacities of ∼74 and 141 mAh g-1, respectively (at a rate of C/20), with excellent cycling stability. The underlying mechanistic aspects (structural changes and charge storage mechanism) in these cathode compositions were probed by combining ex situ structural, spectroscopy, and electrochemical tools. Tunnel-type Na0.44MnO2 forms a versatile cathode material for non-aqueous alkali-ion batteries.

Noble-metal-free bifunctional catalysts are vital to improve high-performance, cost-effective metal-air batteries. This work presents highly porous carbon (HPC), derived from waste tree leaves, as a low-cost carbon-based bifunctional electrocatalyst. To further improve the catalytic activity, nitrogen and sulfur doping in HPC is achieved by treating it with urea (CO(NH2)(2)) and thiourea (CS(NH2)(2)), respectively. The electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity of the HPC, N-doped HPC, and S-doped HPC have been investigated. Among them, the N-doped HPC was found to show excellent bifunctional electrocatalytic (ORR/OER) activity. The N-doped HPC exhibited a superior bifunctional catalytic activity with an onset potential of 0.95 V (vs RHE) at a current density of 6.31 mA cm(-2), whereas in the case of the OER, the observed onset potential was 1.4 V (vs RHE), which is comparable to that of the benchmark RuO2 (1.45 V vs RHE) catalyst. The assembled hybrid Na-air battery exhibited reversible electrochemical performance with a round-trip efficiency of similar to 83% over 30 cycles. These economical bifunctional HPC-based catalysts can be effectively employed as air cathodes in hybrid sodium-air battery applications.

The development of low-cost and sustainable rechargeable batteries is attractive for storing energy from renewable sources. At present, the expansion of Na-ion batteries (NIBs) serves as an appealing solution from the perspective of both raw material abundance as well as the cost in comparison with the existing Li-ion batteries.1 However, the energy densities of NIBs are lower compared to their Li-ion counterparts due to thermodynamic reasons. To address this issue, researchers have turned their attention towards the development of high energy density cathodes, such as Na3V2(PO4)2F3 and Na3V2(PO4)3-type materials,2 in which the operation of multi-redox couples render high storage capacities. Moving forward, the replacement of PO4 3- by SO4 2- provides higher intercalation voltages (due to inductive effect), thereby further improving the overall energy density of cathode. 3 The inclusion of fluoride into the sulphate based polyanionic frameworks will help to increase the operating voltage through inductive effects.4 This will enhance cationic mobility by reducing electrostatic interactions along conduction channels, thereby, lead to increase in cell capacity. Herein, we report synthesis, structural and electrochemical properties of two classes of sodium transition metal fluorosulfates, namely Na3MF2(SO4)2 and jarosites NaM3(SO4)2(OH/F)6 (M= V and Mn etc.,). The Na2VF3(SO4)2 framework consists of chains of trans-VO2F4 octahedra linked to each other via vertex sharing of F atoms and bridged by SO4 tetrahedron as adjacent pairs. 5 Jarosite is a natural mineral to be found in acidic and sulfate-rich environments with a general formula of AM3(SO4)2(OH)6, where A = K+, Na+, and NH4 + and M = Fe3+, Cr3+, V3+, Ga3+, Al3+, and In3+. Jarosite crystals stabilize in a trigonal system with space group R3m. The structure is composed of 2D uneven layers formed by linkage of transition metal octahedra [MO2(OH)4] and sulfate tetrahedra (SO4), that are stacked along the c direction. 6 We unveil the details of growth mechanism of these materials in hydro- and solvo-thermal conditions using X-ray diffraction and microscopy techniques. Further, the mechanism of electrochemical (de)sodiation reactions in these materials will be presented using galvanostatic cycling and in-operando XRD measurements. References: Hwang, J. Y.; Myung, S. T.; Sun, Y. K. Sodium-Ion Batteries: Present and Future. Soc. Rev. 2017, 46 (12), 3529–3614. Lalère, F.; Seznec, V.; Courty, M.; David, R.; Chotard, J. N.;Masquelier, C. Mater. Chem. A. 2015, 3, 16198-16205 Lander, L.; Tarascon, J. M.; Yamada, A. Chem. Rec. 2018, 18, 1394–1408 Senthilkumar, B.; Murugesan, C.; Sharma, L.; Lochab, S.; Barpanda, P. Small methods 2019, 3, 1800253 Wang, Q.; Madsen, A.; Owen, J. R.; Weller, M. T. Commun. 2013, 49 (21), 2121–2123. Gnanavel, M.;Pralong, V.; Lebedev, I.; Caignaert, V.; Bazin, P.; Raveau, B.Chem. Mater. 2014, 26, 15, 4521–4527

Lithium solid state batteries are one of the state of the art energy storage systems due to their high safety. However, ionic conductivity in solid electrolytes is a concern, because at present it does not match the ionic conductivity of non-aqueous Li-ion batteries, thus resulting in sluggish electrochemical kinetics. In this report, we enhance the ionic conductivity of Li-argyrodites (Li6PS5Cl0.5Br0.5) through Si substitution at the P-site using a dry ball milling process. Among the silicon substitutions, Li6.2Si0.2P0.8S5Cl0.5Br0.5 exhibited the high ionic conductivity of 5.12 mS cm(-1) compared to pristine Li6PS5Cl0.5Br0.5 at 4.02 mS cm(-1). The Rietveld refinement analysis revealed that after silicon substitution, volume of the unit cell gets increased that allows the lithium at T2-site, that promotes the fast Li-ion transport. Moreover, the optimized solid electrolyte was utilized in a solid state battery system, and demonstrated a high initial capacity of 148.1 mAh g(-1) at 0.1 C rate compared to pristine argyrodite (135.1 mAh g(-1)). Further, we demonstrated the interface phenomena between electrode and solid electrolyte using ex-situ XPS analysis. This confirmed the formation of interface products such as LiCl, Li2S, lithium polysulfides and P2Sx, which influence the cycling stability of the ASSLBs. (C) 2021 Elsevier Ltd. All rights reserved.