Increasing the Capacity of Graphite Cathode by Intercalating Anions
graphite cathode is an important component in lithium-ion batteries as it is able to withstand high operating currents and has the potential to achieve a very large energy density. However, its low capacity limits its utility in applications such as electric arc steel production. This article investigates a new way to increase the capacity of graphite cathode by intercalating anion anions with different structures and sizes into a multilayered graphite structure.
This is accomplished by using a free-standing natural graphite (NG) film bonded to a conducting carbon tape current collector. The electrodes were tested for rate capability, cyclability and kinetics of the intercalation process. The rate performance data showed that the NG cathode can survive at high current rates of 20-100 C with no significant polarization between the charge-discharge plateaus and without any degradation in capacitance and cycle life. The cyclic voltammograms of the NG cathode with PF 6 - ions exhibited clear intercalation and deintercalation regions, indicating ultrafast kinetics.
The GSI measurements confirmed that the PF 6 - anions intercalated into the graphite layers by a four-stage process, starting from the outside of the layer and moving to the inside. This explains the higher reversible capacity and discharge voltage of NG compared to two synthetic graphite materials used as commercial anodes, KS6 and MCMB.
The GSI data also showed that the reversible capacity of NG is dominated by the intercalated PF 6 - anions, rather than by redox reactions between Li + and n-type ions. The cyclic voltammograms also showed that the redox peaks in NG are clearly separated with high current efficiency. In addition, the redox characteristics of the NG cathode show that they meet the requirements for pseudocapacitance, including a linear dependence on the charge, an independence of capacity from rate and well-defined redox peaks.
