Abstract
High-power Na-ion batteries have tremendous potential in various large-scale applications. However, conventional charge storage through ion intercalation or double-layer formation cannot satisfy the requirements of such applications owing to the slow kinetics of ion intercalation and the small capacitance of the double layer. The present work demonstrates that the pseudocapacitance of the nanosheet compound MXene Ti2C achieves a higher specific capacity relative to double-layer capacitor electrodes and a higher rate capability relative to ion intercalation electrodes. By utilizing the pseudocapacitance as a negative electrode, the prototype Na-ion full cell consisting of an alluaudite Na2Fe2(SO4)3 positive electrode and an MXene Ti2C negative electrode operates at a relatively high voltage of 2.4 V and delivers 90 and 40 mAh g−1 at 1.0 and 5.0 A g−1 (based on the weight of the negative electrode), respectively, which are not attainable by conventional electrochemical energy storage systems.
Highlights
High-power Na-ion batteries have tremendous potential in various large-scale applications
High-power electrochemical capacitors make up many markets ranging from electronics to transportation and stationary applications, but the low energy density is a serious disadvantage[3,4]
This tradeoff between the power and energy densities of electrochemical energy storage has been well recognized, which intrinsically originates from the charge storage mechanism of the electrodes: ionintercalation in batteries and double-layer formation in electrochemical capacitors
Summary
High-power Na-ion batteries have tremendous potential in various large-scale applications. The present set of negativeelectrode materials for Na-ion batteries mainly consists of Na-ion intercalation, alloying or conversion materials such as hard carbon, expanded graphite, TiO2, Na2Ti3O7, phosphorus, Sb2S3, Sn4 þ xP3, SnS2 and P2-Na0.66[Li0.22Ti0.78]O2 (refs 11–19). Their energy and power densities severely suffer from the trade-off, and the large volume change accompanied by the reaction with the large Na ion generally results in poor cycle stability, both of which have spurred us to develop new negative electrodes based on pseudocapacitive charge storage for advanced. MXenes have been developed as a novel family of nanosheet compounds by Gogotsi, Barsoum and colleagues[20,21,22,23,24,25]
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