Excellent Performance of Highly Conductive Porous Na-embedded Carbon Nanowalls for Electric Double-layer Capacitors with Wide Operation Temperature Range
Porous Na-embedded carbon (Na@C), which was recently invented, possesses both very high electrical conductivity and large accessible surface area. Those unique properties can meet strict requirements for ideal electrode materials. Herein, it was revealed that the symmetrical electric double-layer capacitors (EDLCs) with Na@C electrodes exhibited an ultrahigh areal capacitance up to 1.14 F/cm2 at a large current density up to 10 A/g. Furthermore, a critical issue that the enhancement of mass loading usually sacrifices the gravimetric capacitance was solved with Na@C electrodes, namely, when the mass loading of the Na@C electrode increased from 4 to 8 mg/cm2, a negligible gravimetric capacitance drop (only 0.2 F/g) occurred at 1 A/g. The excellent performance remained almost unchanged with increasing temperature from -10 to 55C. In addition, the novel electrode exhibited excellent stability with almost 100% capacitance retention at 5 A/g after 4000 galvanostatic charge/discharge cycles. Na@C would be a very promising electrode material for commercial electric double-layer capacitors.