An article titled ”A Study on the Capacity Degradation in Na3.2V1.8Zn0.2(PO4)3 Cathode and Hard Carbon Anode Based Sodium-Ion Cells” authored by Lihil Uthpala Subasinghe, GAJJELA SATYANARAYANA REDDY, Chen Wang, Markas Law and Palani Balaya has been accepted for publication in Journal of The Electrochemical Society. [DOI:10.1149/1945-7111/ac7e6f]

Abstract

The impact of operating conditions such as voltage window and operating temperature on electrochemical performance and cycle life of Zn-substituted Na3.2V1.8Zn0.2(PO4)3 (NVZP) vs. hard carbon (HC) coin cells filled with 1 mol dm-3 NaBF4 in tetraglyme is presented. Initially, the cells are cycled for 500 times at C/2 charge and 1 C discharge in three different voltage windows (4.20–1.00, 4.05–1.00, and 4.05–1.50 V) and at two temperatures (28 and 40°C) and are subjected to periodic internal resistance and impedance measurements. The elemental composition of the electrodes harvested after cycling reveals that vanadium dissolution with accompanying deposition on the HC electrode and irreversible loss of sodium causes increased cell impedance. The identified degradation mechanisms, which causes severe capacity fade, are found to be accelerated in the cells cycled over wider voltage windows, particularly at elevated temperature. The best cycling performance and lowest impedance are recorded for the cells cycled within 4.05–1.50 V at 28°C owing to negligible vanadium dissolution. Under these optimized testing conditions, a prototype 18650 cell, shows impressive capacity retention of 77% after 1000 cycles.

A Fire-retarding Electrolyte using Triethyl Phosphate as Solvent for Sodium-ion Batteries” Kang Du, Chen Wang, Palani Balaya, Satyanarayana Reddy Gajjela and Markas Law, Chem.Comm., 2022, , 58, 533-536 [DOI:10.1039/d1cc04958e]

Abstract
We introduce a fire-retarding phosphate-based electrolyte, 1 M NaBF4 in triethyl phosphate with 3% vinylene carbonate as an SEI-forming additive, for sodium-ion batteries. With this electrolyte formulation, we achieved stable cycling performance with a capacity of 80.5 mA h g−1 and a retention of 77.8% after 200 cycles in the Na-ion full cell of Na3.2V1.8Zn0.2(PO4)3vs. hard carbon.

Impact of synthesis conditions in Na-rich Prussian Blue Analogs” Paula Sanz Camacho, Romain Wernert, Mathieu Duttine, Alain Wattiaux, Ashish Rudola, Palani Balaya, François Fauth, Romain Berthelot, Laure Monconduit, Dany Carlier and Laurence Croguennec, ACS Applied Materials & Interfaces, 2021, 13, 36, 42682–42692 [DOI:10.1111/ijac.13920]

Abstract

Sodium-rich iron hexacyanoferrates were prepared by coprecipitation, hydrothermal route, and under reflux, with or without dehydration. They were obtained with different structures described in cubic, orthorhombic, or rhombohedral symmetry, with variable compositions in sodium, water, and cationic vacancies and with a variety of morphologies. This series of sodium-rich Prussian blue analogues allowed addressing the relationship between synthesis conditions, composition, structure, morphology, and electrochemical properties in Na-ion batteries. A new orthorhombic phase with the Na1.8Fe2(CN)6·0.7H2O composition synthesized by an hydrothermal route at 140 °C is reported for the first time, whereas a phase of Na2Fe2(CN)6·2H2O composition obtained under reflux, previously described with a monoclinic structure, shows in fact a rhombohedral structure

“A mini review on cathode materials for sodium-ion batteries” Aniruddh Ramesh, Abhinav Tripathi and Palani Balaya, International Journal of Applied Ceramic Technology, 2021, 1-11 [DOI:10.1111/ijac.13920]

Abstract

Sodium-ion batteries are becoming potential solutions for replacement of batteries due to the abundance of sodium reserves and high recycling costs of lithium-based batteries. Sodium-based layered oxides are being widely explored as positive electrode material for sodium-ion battery due to their high capacities and high energy densities. However, oxide-based systems do suffer from thermal stability issues and exhibit low power density. On the other hand, polyanionic-based compounds and Prussian blue analogues demonstrate appreciable thermal stabilities and are useful in high power density applications. This article reviews recent trends of these cathode materials.

“Fundamentals, status and promise of sodium-based batteries” Robert Usiskin, Yaxiang Lu, Jelena Popovic, Markas Law, Palani Balaya, Yong-Sheng Hu, and Joachim Maier, Nature Reviews Materials, 2021, 210324 [DOI:10.1038/s41578-021-00324-w]

Abstract

Na-based batteries have shown substantial progress in recent years and are promising candidates for mitigating the supply risks associated with Li-based batteries. In this Review, Na and Li batteries are compared in terms of fundamental principles and specific materials. Principles for the rational design of a Na battery architecture are discussed. Recent prototypes are surveyed to demonstrate that Na cells offer realistic alternatives that are competitive with some Li cells in terms of performance.

“Investigations of Thermal Stability and SEI on Na2Ti3O7/C as a Non-Carbonaceous Anode Material for Sodium Storage Using Non-flammable Ether-based Electrolyte” K. Du, A. Rudola and P. Balaya, ACS Applied Materials & Interfaces, 2021, 10-1016-18670 [DOI:10.1021/18670]

Abstract

In order to become commercially viable, sodium-ion batteries need to deliver long cycle life with good capacity and energy density while still ensuring safety. Electrolyte plays a key role forming solid electrolyte interphase (SEI) layers at low potential, which affects the thermal stability and cycle life of the anode materials under consideration. In this study, an ether-based non-flammable electrolyte, 1 M NaBF4 in tetraglyme, is tested for sodium storage using a non-carbonaceous anode material Na2Ti3O7/C, and the results are compared with those obtained with the popularly used carbonate-based electrolyte, 1 M NaClO4 in ethylene carbonate (EC) and propylene carbonate (PC) (v/v = 1:1). The Na2Ti3O7/C versus Na cells using 1 M NaBF4 in tetraglyme show a much higher first cycle Coulombic efficiency (73%) than those using 1 M NaClO4 in EC/PC (33%). Thermal stability studies using differential scanning calorimetry (DSC) conclusively show that Na2Ti3O7/C electrodes cycled with 1 M NaBF4 in tetraglyme are more thermally stable than the one cycled with 1 M NaClO4 in EC/PC. Further investigations on the formation of SEI layers were performed using attenuated total reflection–Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, and DSC studies. These studies unambiguously demonstrate that the SEI formed on Na2Ti3O7/C using 1 M NaBF4 in tetraglyme is not only less resistive but also more stable than the SEI formed using 1 M NaClO4 in EC/PC.

“Key Design Considerations for Synthesis of Mesoporous α-Li3V2(PO4)3/C for High Power Lithium Batteries”, H.S. Lee, R. Vishwanathan, K. Saravanan, N. Mangayarkarasi, M. Law, C. Wang, A. Tripathi and P. Balaya, Electrochimica Acta, 2021,10-1016-137831 [DOI:10.1039/137831]

Abstract

In this article, we propose key design criteria to synthesis carbon coated α-Li3V2(PO4)3 positive electrode material for high power lithium batteries. A facile and scalable one-pot soft template method is adopted to synthesize α-Li3V2(PO4)3/C (LVP/C), which exhibits unique morphology of micron-size mesoporous secondary particles comprising interconnected primary nanoparticles showing good storage and rate performances with long cycle life. This cathode material displays high discharge capacities of 178, 90 and 59 mAh.g−1 at 0.1C, 30C and 80C, respectively. The mesoporous LVP/C with a 3D lithium diffusion network exhibits better rate performance (90 mAh.g−1 at 30C) as compared to the known phosphate, silicate or oxide cathode materials for lithium-ion batteries (LIBs). In addition, LVP/C electrode material retains 80% (at 1C) and 100% (at 20C) of its initial capacity after 1,000 cycles. The phase transitions during delitiation/litiation are discussed at different cutoff voltages, corresponding to the number of moles of lithium involved in the redox reactions. The reversibility of electrochemical extraction/insertion processes are confirmed using operando XRD measurements. Observed storage performances can be attributed not only to high crystallinity of LVP/C calcined at 800°C for 6 h; also to the unique mesoporous architecture of this carbon coated cathode material forming high packing density during the soft template synthesis. Obtained dense packed mesoporous architecture of LVP/C allows favourable (i) electrolyte wettability for lithium-incorporation from the electrolyte and (ii) long electronic wiring by the well-connected carbon coating towards the current collector.