ABSTRACT
It is still challenging to construct stable 3D energy storage materials at the nanoscale by precise pore structure control and reasonable surface modification. Herein, a novel interwoven porous Co(CO3)0.35Cl0.20(OH)1.10 (CoCCHH)-CoSe heterogeneous-tube @PEDOT:PSS 3D foam with abundant active sites is presented as supercapacitor electrodes. The electrochemical results indicated that the pore structure provides ample space for redox reaction, and increases the number of ion transport channels. Besides, rational surface modification brings about sufficient active sites for redox reaction. The stable, porous PEDOT:PSS foam with a 3D elastic frame exhibited excellent electrical conductivity. Thus, the CoCCHH-CoSe@PEDOT:PSS foam possessed excellent specific capacitance and energy density, due to the synergistic effect of the unique 3D structure and surface defects. The home-made supercapacitor with CoCCHH-CoSe@PEDOT:PSS foam as cathode materials showed high specific capacitance (440.6F g-1 at 1 A g-1) and excellent energy density (137.7 Wh kg-1). This work provides a valuable strategy to develop potential materials for electrochemical energy storage.
ABSTRACT
Spinel LiMn2O4 (LMO) with a three-dimensional structure has become one of the cathode materials that has gained the most interest due to its safety, low price and abundant resources. However, the lithium ion transmission is limited by large particle size and particle agglomeration of LMO. Thus, reducing the particle size and agglomeration of LMO can effectively improve its lithium ion transmission. Here, we synthesized a LMO cathode material with a nanoscale crystal size using the flexible expanded graphite (EG) soft template and Pichini method. EG-controlled particle size and particle agglomeration of LMO is conducive to charge transfer and diffusion of lithium ions between LMO and the electrolyte, meanwhile, there are more redox sites on the nanosized LMO particles, which makes the redox reaction of LMO more thorough during the charge and discharge process, resulting in high capacitance performance. In order to obtain the considerably required lithium-ion capacitors (LICs) with high energy density and power density, we assembled aqueous LMO//activated carbon (AC) LICs with 5 M LiNO3 as the aqueous electrolytes, which are environmentally friendly, safe, low cost and have higher electrical conductivity than organic electrolytes. The optimal LIC has an energy density of 32.63 W h kg-1 at a power density of 500 W kg-1 and an energy density of 8.06 W h kg-1 at a power density of 10 000 W kg-1, which is higher than most of the LMO-based LICs in previous reports. After 2000 cycles, the specific capacitance retention rate was 75.9% at a current density of 3 A g-1. Therefore, our aqueous LMO//AC LICs synthesized by the soft template/Pichini method have wide prospects and are suitable for low-cost, high-safety and high-power applications.
