Synthesis of Nitrogen-Doped Mesoporous Structures from Metal-Organic Frameworks and Their Utilization Enabling High Performances in Hybrid Sodium-Ion Energy Storages.

Gyu Heon Lee,Jeung Ku Kang

doi:10.1002/advs.201902986

Abstract

Sodium‐ion energy storage is of the most attractive candidate for commercialization adoption due to the safety and cost demands of large‐scale energy storage systems, but its low energy density, slow charging capability, and poor cycle stability are yet to be overcome. Here, a strategy is reported to realize high‐performance sodium‐ion energy storage using battery‐type anode and capacitor‐type cathode materials. First, nitrogen‐doped mesoporous titanium dioxide (NMTiO2) structures are synthesized via the controlled pyrolysis of metal–organic frameworks. They exhibit interconnected open mesopores allowing fast ion transport and robust cycle stability with nearly 100% coulombic efficiency, along with rich redox‐reactive sites allowing high capacity even at a high rate of ≈90 C. Moreover, assembling the NMTiO2 anode with the nitrogen‐doped graphene (NG) cathode in an asymmetric full cell shows a high energy density exceeding its counterpart symmetric cell by more than threefold as well as robust cycle stability over 10 000 cycles. Additionally, it gives a high‐power density close to 26 000 W kg−1 outperforming that of a conventional sodium‐ion battery by several hundred fold, so that full cells can be charged within a few tens of seconds by the flexible photovoltaic charging and universal serial bus charging modules.

Highlights

Cost hybrid energy storages can be developed using an earth-abundant electrolyte including sodium (Na) ions.[8,9,10,11] Beyond the increasing demand for electric vehicles (EVs) and many electrode materials suffer from several obstacles such as portable devices,[1] a rechargeable electrochemical energy safety and poor capacity in a sodium-ion electrolyte
The dominating electrolyte. Titanium storage system (ESS) remains on a hybrid energy storage as it is capable of being operated at a low lithium-ion battery (LIB),[2] but the more challenging require- potential that is advantageous for safety
We realize hybrid sodium-based electrochemical energy storages on a new paradigm strategy, where both a nitrogen-doped mesoporous TiO2 (NMTiO2) structure synthesized through the controlled pyrolysis of a metal–organic framework (MOF) and a nitrogen-doped graphene (NG)

Summary

Gyu Heon Lee and Jeung Ku Kang*

electrode materials with high energy density allowing prolonged operation upon cialization adoption due to the safety and cost demands of large-scale energy a single charge, fast charging capability storage systems, but its low energy density, slow charging capability, and poor cycle stability are yet to be overcome. The hybrid NMTiO2// NG full-cell device was demonstrated to give the high energy density superior to that of a symmetric device by more than threefold, the high power density of 25 920 W kg−1 exceeding that of a typical sodium-ion battery by several hundred fold, and robust cycle stability over 10 000 charge–discharge cycles with excellent capacity retention. The NMTiO2//NG full-cell devices were demonstrated to be chargeable within a few tens of seconds by the USB LED charger and flexible photovoltaic charging module These results support that the hybrid sodium-ion energy storage full cells assembled with nitrogendoped mesoporous anode and nitrogen-doped graphene cathode electrodes provide rich active sites and rapid transport pathways for electrons and ions during repeated charging– discharging cycles, so that they show remarkably high energy density, ultrafast charging capability on excellent power density, and robust cycle stability over a long cycle life. We expect that our findings provide a new solution to realize high-performance electrode materials from metal–organic frameworks, adaptable to develop a diverse range of metal oxides usable for high-performance energy storage devices

Experimental Section

Conflict of Interest