β-MnO2 nanorods with exposed tunnel structures as high-performance cathode materials for sodium-ion batteries

Abstract

Sodium-ion batteries are being considered as a promising system for stationary energy storage and conversion, owing to the natural abundance of sodium. It is important to develop new cathode and anode materials with high capacities for sodium-ion batteries. Herein, we report the synthesis of b-MnO 2 nanorods with exposed tunnel structures by a hydrothermal method. The as-prepared b-MnO 2 nanorods have exposed {111} crystal planes with a high density of (1 Â 1) tunnels, which leads to facile sodium ion (Na-ion) insertion and extraction. When applied as cathode materials in sodium-ion batteries, b-MnO 2 nanorods exhibited good electrochemical performance with a high initial Na-ion storage capacity of 350 mAh g À1 . b-MnO 2 nanorods also demonstrated a satisfactory high-rate capability as cathode materials for sodium-ion batteries. Keywords: b-MnO 2 ; nanorods; cathode material; tunnel structure; sodium-ion batteries INTRODUCTION Sodium-ion (Na-ion) batteries have recently been considered as an alternative battery system for large-scale energy storage and conversion due to the availability of low-cost and widespread terrestrial reserves of sodium mineral salts. 1 Na-ion batteries share many similarities with lithium-ion batteries (Li-ion batteries), such as an intercalating cathode and anode, a nonaqueous electrolyte and an ion shuttle mechanism. Computational studies on the voltage, stability and diffusion barrier of Na-ion and Li-ion materials indicate that Naion systems are competitive with Li-ion systems. 2 However, the large ionic size of sodium (1.02 Å versus lithium (0.76 Å )) limits the choice of electrode materials for Na-ion batteries. Many cathode materials have been investigated for Na-ion batteries, including phosphate polyanion materials (NaFePO 4 ), 3,4 Na 4 Mn 9 O 18 , 5-7 fluoride-based cathode materials-NaMF 3 (M ¼ Fe, Mn, V and Ni), 8,9 fluorophosphates, 10,11 fluorosulfates, 12 À14 and layered transition metal oxides, such as P2-Na x CoO 2 , 15,16 P2-Na 2/3 (Fe 1/2 Mn 1/2 )O 2,

Electrode Materials for Sodium-Ion Batteries: Considerations on Crystal Structures and Sodium Storage Mechanisms

“…Surprisingly, when the β-MnO 2 exposed (111) facets, which had exposed (1 × 1) ionic diameter tunnels that provide facile transport for Na-ion insertion, accommodation [48]. Copyright 2013, Wiley and extraction, it delivered a high initial specific capacity of 350 mAh g −1 and achieved good high-rate performance [50]. This confirms the importance of the electrochemical intercalation anisotropy for different crystalline facets of electrode materials.…”

“…The dominantly exposed (100) crystal planes provided facile ionic transport for Na + -ion insertion and extraction. They further investigated different β-MnO 2 nanorod electrode materials for the Na-ion batteries and clearly demonstrated that, with different exposed crystal planes, there are hugely different electrochemical performances [49,50]. As shown in Fig.…”

Understanding sodium-ion diffusion in layered P2 and P3 oxides via experiments and first-principles calculations: a bridge between crystal structure and electrochemical performance

“…[2][3][4][5][6] Rechargeable sodium-ion batteries have chemical storage mechanisms similar to their lithium-ion counterparts and are expected to be low cost and chemically sustainable as a result of an almost infinite supply of sodium. [7][8][9][10][11][12][13][14][15] Meanwhile, the feasible replacement of Cu with Al current collectors (an alloying reaction does not occur between Na and Al) will further reduce the substantial costs and weight for nextgeneration batteries.Layered sodium oxide Na x MeO 2 (Me = 3d transition metal) materials, owing to their large specific capacity and reversible insertion/ …”

MnOx/carbon nanotube/reduced graphene oxide nanohybrids as high-performance supercapacitor electrodes

“…Among various pseudocapacitive materials, manganese oxides (MnO x ) have attracted the strongest interest because of their natural abundance, low cost and environmental friendliness. 10 Numerous studies have reported the hybrid structures of carbon materials with electrochemically active manganese oxide (MnO x ), most commonly MnO 2 . 7 However, the maximum specific capacitance of MnO 2 in these reports remains low, at approximately 300-400 F g − 1 , and the capacitance of overall hybrids is even lower, typically o200 F g − 1 ; 11 MnO 2 still displays low electrical conductivity, limited stability and poor integration in hybrid electrode systems.…”