| Lithium ion capacitors（LICs）based on porous carbon as cathode and insertion-type battery materials as anode are regarded as a novel electrochemical energy storage device,which possesses the characteristics of both supercapacitors and lithium ion batteries（LIBs）.LICs exhibit higher power density and longer cyclic stability than LIBs,and high energy density compared to supercapacitors.The unbalance of reaction dynamics between battery-type anode and capacitive-type cathode is the main challenge for the development of high-performance LICs.Therefore,seeking high power battery-type anode materials is critical important.Compared with traditional anode materials(Li4Ti5O12,Ti O2),Nb2O5 with pseudo-capacitive property,which has high theoretical capacity(200m Ah g-1),low working potential（1.01.5 V vs Li+/Li）and two-dimensional transfer path for Li+.Nevertheless,the intrinsic low electrical conductivity(3×10-6 S cm-1)of Nb2O5 leads to unsatisfied rate capability.In order to improve the electrochemical properties of Nb2O5,in this context,we have designed Nb2O5 micro-nanospheres structure and composited with conductive mesoporous carbon material,aiming to shorten the transfer path and improve the electrical conductivity.The details are as follows:（1）Nb2O5 micro-nanospheres have been fabricated by utilizing anti-solvent method combined with high temperature calcination.As shown from the SEM and TEM,Nb2O5 nanospheres with the size arranging from 400 to 600 nm are composed of smaller secondary nanoparticles（50 nm）.When tested as anode for LIBs,the material delivers high rate performance and cyclic stability.At a rate of0.2 C,the discharge capacity of Nb2O5 micro-nanospheres is 165 m Ah g-1,it still can maintain 82m Ah g-1 at a rate of 5 C.Furthermore,the LICs constructed by the Nb2O5 micro-nanospheres as anode and activated carbon derived from peanut shell as cathode demonstrate a high energy and power density.（2）Nb2O5/CMK-3 nanocomposites have been prepared using CMK-3 as template via the nanocasting technology.CMK-3 not only affords a three dimensional conductive network structure to improve electronic conductivity,but also hinders the agglomeration of Nb2O5 nanoparticles during the heat treatment process.The discharge capacity of mesoporous Nb2O5/CMK-3 nanocomposite remains167 m Ah g-1 at the rate of 1 C after 50 cycles with nearly no capacity loss,indicative of superior cyclic stability.At a rate of 10 C,the discharge capacity of it is still achieves 96.6 m Ah g-1.Furthermore,a high performance LICs composed of the Nb2O5/CMK-3 nanocomposite as the anode and activated carbon derived from peanut shell as the cathode was constructed,which exhibits a high power density of 8750 W kg-1 at an energy density of 24.4 Wh kg-1.（3）One-step self-assembly strategy was developed to synthesis of the Nb2O5/mesoporous C composite materials by using phenolic resin as carbon source,F127 as soft templates and Nb Cl5 as niobium source.Compared with hard template method described as above,this method is simple and environment-friendly.Research results indicate that the Nb2O5/mesoporous C composite material has excellent performance.At a high rate of 10 C,the discharge capacity is up to 112.5 m Ah g-1.When assembled with peanut-derived carbon,the LICs possess a high energy density of 42.4 Wh kg-1 and an excellent cyclic performance with 80%capacity retention after 2000 cycles at the current density of 1A g-1. |
