UCLA

Due to the inherently intermittent nature of renewable energy sources, there is an urgent demand to develop cheap, reliable, high-performance energy storage systems for electrical transportation and grid-storage.Li-ion batteries have been widely used in electrical transportation due to their decent energy density, power density, and energy efficiency commercial Li-ion batteries adopt graphite as the anode currently. The low theoretical capacity of the graphite has hindered the further improvement of Li-ion batteries to match the increasing energy density requirement. However, high-capacity anodes (e.g., Si, metal oxides, et.al,) suffer from large volume change and low electrical conductivity, leading to deteriorated capacity and lifespan. Two types of novel anode materials (i.e., Si-C anode and MnO-C anode) were synthesized for advanced Li-ion batteries. Si-C composites were synthesized by in situ growth of spheres of graphene and carbon nanotubes (CNTs) around silicon particles. These composites possess high electrical conductivity and mechanical resiliency, which can sustain the high-pressure calendering process in industrial electrode fabrication and the stress-induced during the charging and discharging of the electrodes. The resulting electrodes exhibit outstanding cyclic durability (~ 90% capacity retention at 2 A g-1 after 700 cycles or a capacity fading rate of 0.014% per cycle), calendering compatibility (sustain pressure over 100 MPa), and adequate volumetric capacity (1006 mAh cm-3), providing a novel design strategy towards better silicon anode materials. A graphene coated MnO anode was synthesized by directly growing high-quality graphene on MnO particles. To avoid the sintering process of MnO fine particles, amorphous carbon was introduced to block the physical contact between MnO fine particles. The resulting MnO anode was coated by high-quality graphene (ID:IG = 0.14), delivering high specific capacity and excellent cycling performance (934 mAh g-1 after 500 cycles; 355 mAh g-1 after 1000 cycles, ~71% capacity retention). Mild aqueous Zn-Mn batteries are competitive candidates in the rapidly expanding large-scale grid-storge due to their unpatrolled advantages of low cost, facile to manufacture, high safety, and environmental friendliness. The performance of current MnO2 cathodes is not satisfying due to their tunnel-like crystal structure. A novel layered δ-MnO2 cathode was synthesized by reversible layer-to-layer electrochemical transition from β-MnOOH, affording outstanding electrochemical activity (320 mAh g-1 at 0.1 A g-1,127 mAh g-1 at 5 A g-1)) and cycling stability (84% capacity retention at 0.5 A g-1 after 500 cycles).