Na 2 MnSiO 4 as an attractive high capacity cathode material for sodium-ion battery Markas Law, Vishwanathan Ramar, Palani Balaya * Department of Mechanical Engineering, National University of Singapore, 117575, Singapore highlights graphical abstract  Na 2 MnSiO 4 is prepared via a modi- fied two-step route.  It delivered the highest discharge capacity for a polyanion-based compound.  Na 2 MnSiO 4 registered impressive so- dium storage performance of 210 mAh g 1 at 0.1 C.  Electrolyte additive VC forms a meta- stable passivation film on electrode surface.  The amount of VC added greatly in- fluences electrochemical perfor- mance of Na 2 MnSiO 4 . article info Article history: Received 25 March 2017 Received in revised form 12 May 2017 Accepted 19 May 2017 Keywords: Sodium manganese silicate Sodium-ion battery Cathode material Energy storage Polyanion compound abstract Here we report a polyanion-based cathode material for sodium-ion batteries, Na 2 MnSiO 4 , registering impressive sodium storage performances with discharge capacity of 210 mAh g 1 at an average voltage of 3 V at 0.1 C, along with excellent long-term cycling stability (500 cycles at 1 C). Insertion/extraction of ~1.5 mol of sodium ion per formula unit of the silicate-based compound is reported and the utilisation of Mn 2þ ! Mn 4þ redox couple is also demonstrated by ex-situ XPS. Besides, this study involves a systematic investigation of influence of the electrolyte additive (with different content) on the sodium storage performance of Na 2 MnSiO 4 . The electrolyte additive forms an optimum protective passivation film on the electrode surface, successfully reducing manganese dissolution. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Rechargeable lithium battery technologies have been the fore- runner in stationary and mobile energy storage, and have now evolved to empower green electric vehicles. Ever since its com- mercialisation in 1990, demand for the lithium battery technology has soared to unprecedented heights. Large-scale energy storage systems utilised in the micro-grids and the hybrid vehicles require huge amounts of lithium [1], which resulted in the anxiety con- cerning the shortage of lithium reserves. This issue has become the driving force to recognise sodium battery as a promising replace- ment because of the abundance and wide distribution of sodium resources for power-grid applications where space/volume is not a big concern [2,3]. However, energy density of this technology is limited because of its low capacity and slow kinetics, owing to the * Corresponding author. E-mail address: mpepb@nus.edu.sg (P. Balaya). Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour http://dx.doi.org/10.1016/j.jpowsour.2017.05.069 0378-7753/© 2017 Elsevier B.V. All rights reserved. Journal of Power Sources 359 (2017) 277e284