A Hybrid Capacitor Based on a Li[Ni1/3Co1/3Mn1/3]O2 as Li-Ion Battery Cathode synthesized via carbonate coprecipitation and Active Carbon

Abstract

Introduction Batteries and capacitors are regarded as electrical energy storage device. Batteries deliver high energy density but limited power output. Capacitors have attracted considerable attention in recent years for their use in high power application. Recently, many researchers on the electrochemical capacitors aim to increase power and energy density. Compared with Electrochemical double layer capacitors (EDLCs), hybrid capacitors which have two different electrodes show high power density and a corresponding cycle life that was recently reported by many groups.[1-4] The most useful approach is to develop hybrid systems that typically consist of an EDLC electrode and a battery electrode, such as activated carbon (AC)/Ni(OH)2[1], AC/LiMn2O4[2] aqueous cell, AC/Li4TI5O12[3], AC/LiNi0.5Mn1.5O4[4] nonaqueous cell. Battery electrodes have very high energy density compared with EDLC electrode, but power density which depends on rate capability is lower than activated carbon one. Park et al.[5] successfully prepared Li[Ni1/3Co1/3Mn1/3]O2 powders based on the carbonate coprecipitation process. This is useful powders for cathode of hybrid capacitor which have good cycle life and rate capability. In this paper, we exploited the Li[Ni1/3Co1/3Mn1/3]O2 powders synthesized by carbonate co-precipitation method as the positive electrode in combination with an activated carbon negative electrode to fabricate a hybrid capacitor. The preliminary electrochemical properties of hybrid capacitor system are reported.

Experimental Spherical Li[Ni1/3Co1/3Mn1/3]O2 powder was prepared as carbonate co-precipitation method.[5] Powder X-rat diffraction (Rigaku, Rint-2000) employing Cu Kα radiation was used to identify the crystalline phase of the prepared powders at each stage. The prepared powders were also observed using scanning electron microscopy (SEM, JSM-6340F, JEOL). Cell tests were done using the 2032 coin-type cell with activated carbon as the negative electrode. The cells were charged and discharged between 0.2 and 2.2 V by applying a constant current of 1.6A g-1 based on cathode weight at 30oC. Results and discussion Figure 1 shows charge-discharge curve at the 10th cycle of EDLC and hybrid capacitor. While an EDLC stores energy of only 20 mAh/g between 0 and 2.7V, a hybrid capacitor has capacity of 33 mAh/g between 0.2 and 2.2V. Figure 2 shows cycling profile of the hybrid capacitor cell between 0.2 and 2.2V and the EDLC cell between 0 and 2.7V at 15C-rate. While the capacity retention was 90% of the initial capacity in the hybrid capacitor, the EDLC cell retained the capacity retention of 95% after 300cycles.