Employment of ultra-thin carbon layer-coated porous tin oxide as anode in lithium-ion capacitor

A porous SnO2 electrode with an ultra-thin 2-nm-thick coating of carbon (SnO2@C) was prepared by a hydrothermal method. The thin carbon layer acted as a relaxant layer alleviating the stress of the volume expansion of the SnO2 active material during intercalation/de-intercalation of lithium ions. The pre-lithiated SnO2@C was employed as an anode material for a non-aqueous lithium-ion capacitor (LIC) using commercial activated carbon (YP-80F) as the cathode. Different states of discharge of the pre-lithiated SnO2@C anode were characterized. At different lithiation degrees, phase transformation and morphology changes of the SnO2 active material affected the electrochemical performance of the LIC system. Shallow lithiation provided insufficient lithium ions to the activated carbon cathode, yielding poor specific energy. Excessively deep lithiation risked severe crack formation on the surfaces of the SnO2 particles, affecting the electrochemical performance at high current densities. Other parameters, including the negative-to-positive electrode mass balance and cut-off voltage control, were also studied regarding their effects on performance. The fabricated LIC (SnO2@C/Activated carbon) delivered a maximum energy of 130 W h kg−1 and a maximum specific power of 6900 W kg−1.