Lithium Ion Capacitor with Massive Power Density Using Electrodes from Silicon Oxycarbide and Activated Carbon Derived from Zalacca Salacca Peels
Authors: Halim Martin , Lee Joong Kee 
Published: February 2020

Although batteries have been successfully employed in light-duty vehicles (hybrid and fully electric cars), batteries still find it is hard to satisfy power-hungry platforms such as trucks, trams, and buses. Conventional lithium ion batteries (LIB) could provide power density less than 3 kW/kg with relatively moderate energy density. On the other side, supercapacitors (SCs) that are known to provide power density of more than 10 kW/kg have a very low energy density of less than 1 Wh/kg and thus, SCs could not be used solely as energy storage. However, employing anode from LIB and electrode from SC together in a single system would benefit both high energy and power density, which system is-so called lithium ion capacitor (LIC). To date, so many attempts have been done to investigate the best anode material combination with activated carbon (AC) to obtain high performance LIC. The anode materials that are commonly utilized in LIB such as graphite, hard carbon, Li4Ti5O12 (LTO), Fe3O4, SnO2, and silicon based material have been extensively studied for LIC. Graphite that is known as an ubiquitous anode material in LIBs provided relatively high energy density of c.a. 100 Wh/kg and maximum power density of less than 2 kW/kg in LIC. Among all, LTO application was found to be the least desirable material for LIC since it provided relatively low maximum energy and power density, which was merely less than 40 Wh/kg and 2 kW/kg, respectively, due to its low conductivity and high voltage plateau at around 1.5 V. Grphene has been used to reinforce rate capability of Fe3O4 and it demonstrated promising energy density as high as 86 Wh/kg. However, the maximum power density of the enhaced electrode material was only 2.6 kW/kg. Higher power LIC can be achieved by harnessing hard carbon anode material, which displayed maximum power density of about 50 kW/kg. However, the high power density of hard caron in LIC was compensated by extremely low energy density of less than 2 Wh/kg. Herein, we investigate the electrochemical performance of LIC by using silicon oxycarbide (SiOC) as the anode and the AC from biomass (Zalacca salacca) peels as the cathode to provide massive power while maintaining the energy density relatively high. SiOC showed an outstanding rate capability performance indicated by relatively high discharge capacity of over than 200 mAh/g at current density of 80 A/g. The excelent rate capability was attributed to the fast lithium diffusion in SiOC, which was represented by high lithium diffusion coefficient (DLi+) of 5.1 × 10-6 cm2/s. Meanwhile, the AC derived from biomass is promising since its surface area (c.a. 2600 m2/g) and capacitance (163.7 F/g) was significantly higher than that of commercial AC. Combination of SiOC and AC derived from Zalacca salacca in a single unit of LIC could be used to provide a massive power density of 155kW/kg while maintained relatively high energy density of 25 Wh/kg. Moreover, the resulting LIC demonstrated highly stable cycle retention at high C-rate. After reaching equilbrium state, the cycle retention of LIC at 50C was 99.4% after more than 40,000 cycles. At higher C-rate of 100C, the cycle retention of the LIC was 99% even after more than 75,000 cycles. The present study indicates that LIC design based on SiOC and AC from Zalacca salacca peels is suitable for energy storage in high-duty platforms such as trucks, trams, and buses.