Abstract
P2-type Na2/3Ni1/3Mn2/3O2 is an air-stable cathode material for sodium-ion batteries. However, it suffers irreversible P2-O2 phase transition in 4.2-V plateau and shows poor cycling stability and rate capability within this plateau. To evaluate the practicability of this material in 2.3–4.1 V voltage range, single-crystal micro-sized P2-type Na2/3Ni1/3Mn2/3O2 with high rate capability and cycling stability is synthesized via polyvinylpyrrolidone (PVP)-combustion method. The electrochemical performance is evaluated by galvanostatic charge-discharge tests. The kinetics of Na+ intercalation/deintercalation is studied detailly with potential intermittent titration technique (PITT), galvanostatic intermittent titration technique (GITT) and cyclic voltammetry (CV). The discharge capacity at 0.1 C in 2.3–4.1 V is 87.6 mAh g−1. It can deliver 91.5% capacity at 40 C rate and keep 89% after 650 cycles at 5C. The calculated theoretical energy density of full cell with hard carbon anode is 210 Wh kg−1. The moderate energy density associated with high power density and long cycle life is acceptable for load adjustment of new-energy power, showing the prospect of practical application.
Highlights
In recent years, sodium-ion batteries have been paid more and more attentions by researchers due to the high demand of resources for large-scale applications such as electric vehicles and energy storage[1,2,3,4,5,6,7,8]
The analysis of the phase purity and the structural characterization were made by X-ray powder diffraction (XRD) using a Bruker D2 PHASER diffractometer equipped with Cu Kα radiation
All the diffraction peaks can be labeled as hexagonal P2-type structure and P63/mmc space group[20, 22, 31]
Summary
Sodium-ion batteries have been paid more and more attentions by researchers due to the high demand of resources for large-scale applications such as electric vehicles and energy storage[1,2,3,4,5,6,7,8]. Chen et al point out that TMO materials have high energy density and large space to improve cycling and rate performance, so they are the most promising cathode materials for sodium-ion batteries[6]. Because of the large volume of sodium ions, this migration barrier is relatively high, resulting relatively poor rate capability for O-type structure. The initial discharge capacity of this material in 1.6-4.5 V voltage range is over 200 mAh g-1 but the cycling stability and rate capability are very poor due to the irreversible. With this method, we prepared some TMO materials for Li-ion and Na-ion batteries with high rate capability and cycling stability[26,27,28,29,30].
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