UC Riverside

The increasing concern about global energy crisis and continuing deteriorating environmental issues has pushed the investigation and use of clean and renewable energies. However, in order to efficiently utilize these intermittent energies, an advanced energy storage system must be developed. Lithium ion batters (LIBs) are among the most promising energy storage devices with high energy and power density at relatively low cost. Although commercial LIBs have being announced for more than 30 years, the major electrode materials still remain the same. The rising number of electric vehicles and portable electronics requires advanced lithium ion batteries with higher capacity at lower weight and more affordable price. Herein, there anode materials systems were developed with three dimensional (3D) hybrid nanostructure for improving current commercial graphite anode, as well as enhancing the next-generation silicon based anode.

Three dimensional carbon nanotubes (CNTs) on graphite foam was fabricated as free-standing LIB anode. Morphologies of carbon nanotube were controlled via annealing process during growth. The resulting bundled vs. dispersed CNTs show different electrochemical performances. Dispersed CNTs yields superior capacity (over 800 mAh/g) over 120 cycles due to high surface area and efficient ion/electron transportation.

A novel 3D networks synergizing conductive polymers, polypyrrole and polyaniline, with nanostructured silicon particles for lithium ion battery anode was fabricated. The bindery hybrid structures show much enhanced battery performance compared with silicon/non-conductive polymer anode. Si nanoparticles (Si NPs) with polypyrrole hybrid structure shows ~1050 mAh/g capacity at fast charging rate of 1C. The three dimensional hydrogel butters the stress caused by silicon expansion during lithiation. The higher conductivity of polypyrrole over polyaniline contributes to its excellent battery performance.

High performance conductive binder, polypyrrole, was used to form hybrid 3D network with Si nanowires fabricated via directly metal-assisted chemical etching of silicon wafers. The hybrid nanocomposites exhibit outstanding battery performance of 1689 mAh/g over 600 cycles, which significantly out-performed Si NWs with traditional poly acrylic acid binder. Such enhancement is ascribed to the cylindrical nanostructure of single crystal silicon that could withstand stress during volume expansion and the highly conductive 3D network of polypyrrole provides space accommodating internal stress and enhanced electrode conductivity.