Free-Standing N-Doped Carbon Nanotube Films with Tunable Defects as a High Capacity Anode for Potassium-Ion Batteries.

Potassium-ion batteries (KIBs) have aroused enormous interest for future energy storage technology. However, the current anodes for KIBs greatly suffer from the rapid capacity fading and inferior rate capability. Herein, a free-standing flexible anode, that is, nitrogen-doped carbon nanotube paper (NCTP), which is derived from the pyrolysis of organic polypyrrole materials, is demonstrated for high-performance potassium storage. The correlations between the material structure and electrochemical properties have been investigated by a series of material analysis and characterizations, as well as electrochemical tests. The research results show that the annealing temperature dramatically affects the N-doping content, the carbon defects, and the graphitization degree. Electrochemical tests indicate that the NCTP annealed at 700 °C displays the best performances with a high reversible capacity of 250.1 mA h g-1 at 100 mA g-1 and superior rate capability retaining 133 mA h g-1 at 5 A g-1. The excellent electrochemical properties are derived from a synergic contribution from the moderate N-doping, carbon defect, and high electronic conductivity of the materials. The facile pyrolysis strategy and the appealing performances involved in this work could provide some hints to manipulate high-performance anode materials of KIBs.