Sustainable and efficient energy storage devices are crucial to meet the soaring global energy demand. In this context, Na‐ion batteries (NIBs) have emerged as one of the excellent alternatives to the Li‐ion batteries, due to the uniform geographical distribution, abundance, cost‐effectiveness, comparable operating voltage as well as similar intercalation chemistry. However, due to larger size of Na and other related issues, a subtle strategy of research is required for the development of electrode materials for NIBs to enhance overall electrochemical performance. Here, we provide a comprehensive review on recent advances of polyanionic cathode materials for NIBs for cost effective and large scale energy storage applications. Owing to their great thermal and chemical stability, high redox potential (inductive effect), and rich structural diversity, polyanionic cathodes have been considered potential candidates in recent years. We cover a large number of polyanionic materials and conclude with the strategies to improve the energy and power density of NIB. This article is categorized under: Energy Research & Innovation > Science and Materials Energy and Development > Science and Materials Energy and Transport > Science and Materials

We report the detailed analysis of electrochemical investigation of honeycomb structured Na$_{2}$Ni$_{2}$TeO$_{6}$ material as a cathode for sodium-ion batteries using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge (GCD)...

In recent years, the mixed phosphate-based polyanionic electrode materials have attracted great attention in sodium-ion batteries (SIBs) due to their structural stability during cycling and open framework for ion diffusion. Here, we report the electrochemical performance of a Na 4 Co 3 (PO 4 ) 2 P 2 O 7 /nitrogen-doped carbon (NCPP/NC) composite as a negative electrode (anode) for SIBs in the working potential range of 0.01−3.0 V. It delivers a reversible discharge capacity of 250 mA h g −1 at 0.5 C current rate, which corresponds to the insertion/extraction of four sodium ions. The rate capability study indicates the reversible mechanism and highly stable capacity (61 mA h g −1 ) even at a high rate of up to 5 C as compared to pristine NCPP. The incorporation of the N-doped carbon spheres in the composite is expected to enhance the electronic/ionic conductivity, which plays an important role in improving the performance and stability up to 400 cycles at 1 C rate. Intriguingly, the analysis of cyclic voltammetry data measured at different scan rates confirms the capacitive/diffusive-controlled mechanism, and the extracted diffusion coefficient is found to be around 10 −10 cm 2 s −1 . Our results demonstrate that the NCPP/NC composite is also a potential candidate as an anode in SIBs due to its three-dimensional framework, cost effectiveness, enhanced specific capacity, and further possibility of improving the stability.

In search of the potential cathode materials for sodium-ion batteries and to understand the diffusion kinetics, we report the detailed analysis of electrochemical investigation of honeycomb structured Na2Ni2TeO6 material using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge (GCD) and galvanostatic intermittent titration technique (GITT). We found the discharge capacities of 82 and 77 mAhg −1 at 0.05 C and 0.1 C current rates, respectively, and the mid-working potential of ≈3.9 V at 1 C and high capacity retention of 80% after 500 cycles at 0.5 C as well as excellent rate capability. The analysis of CV data at different scan rates reveals the pseudo-capacitive mechanism of sodium-ion storage. Interestingly, the in-situ EIS measurements show a systematic change in the charge-transfer resistance at different charge/discharge stages as well as after different number of cycles. The diffusion coefficient extracted using CV, EIS and GITT lies mainly in the range of 10 −10 to 10 −12 cm 2 s −1 and the de-insertion/insertion of Na + -ion concentration during electrochemical cycling is consistent with the ratio of Ni 3+ /Ni 2+ valence state determined by photoemission study. Moreover, the post-cyclic results of retrieved active material show very stable structure and morphology even after various charge-discharge cycles. Our detailed electrochemical investigation and diffusion kinetics studies establish the material as a high working potential and long life electrode for sodium-ion batteries.

In recent years, the mixed phosphates based polyanionic electrode materials have attracted great attention in sodium-ion batteries due to their structural stability during cycling and open framework for ion diffusion. Here, we report the electrochemical performance of Na4Co3(PO4)2P2O7/nitrogen doped carbon (NCPP/NC) composite as a negative electrode (anode) for sodium ion batteries in the working potential range of 0.01-3.0 V. It delivers a reversible discharge capacity of 250 mAhg −1 at 0.5 C current rate, which corresponds to the insertion/extraction of four sodium ions. The rate capability study indicates the reversible mechanism and highly stable capacity (61 mAhg −1 ) even at high rate up to 5 C as compared to pristine NCPP. The incorporation of the N doped carbon spheres in the composite is expected to enhance the electronic/ionic conductivity, which plays an important role in improving the performance and stability up to 400 cycles at 1 C rate. Intriguingly, the analysis of cyclic voltammetry data measured at different scan rates confirm the capacitive/diffusive controlled mechanism and the extracted diffusion coefficient is found to be around 10 −10 cm 2 s −1 . Our results demonstrate that the NCPP/NC composite is also a potential candidate as anode in sodium-ion batteries due to its three dimensional framework, cost effectiveness, enhanced specific capacity as well as further possibility of improving the stability.