The relentless development and integration of microscale electronics, such as micro-electromechanical systems, microrobots, implantable medical sensors, radiofrequency identification tags, remote environmental sensors, portable and wearable electronics, and their wireless self-powered micro/nano-systems, have greatly accelerated the ever-increasing need for microscale electrochemical energy storage systems. Micro-batteries (MBs) and micro-supercapacitors (MSCs) are two representative microscale electrochemical energy storage devices, which can be manufactured on the micro/nanoscale to be directly coupled with microelectronics as standalone microscale power sources or integrated with miniaturized energy harvesters, such as solar cells and nanogenerators to form integrated systems, mitigating the discontinuity, periodicity, and indeterminacy of renewable solar and mechanical energy. Aside from high electrochemical performance, MBs and MSCs are highly required to possess diversified form factors including light-weight, flexibility, tailored sizes and shapes, aesthetic versatility and integration to match next-generation smart microelectronics.

We have synthesized a series of high-performance 2D materials such as graphene (doped graphene, porous graphene, graphene based heterostructure), MXene, phosphorene, conductive polymers, metal oxides and metal nitrides, and developed various micro-fabrication strategies, e.g., photolithography, mask-assisted vacuum filtration, photo-chemical reduction, spray coating, screen printing, inkjet printing, and 3D printing to construct advanced microscale energy storage systems including aqueous MSCs, asymmetric MSCs, ionogel MSCs, lithium-ion micro-capacitors and lithium-ion MBs, greatly enhancing energy density, power density and cycle stability. Moreover, diversified microscale energy storage devices have already been fabricated including arbitrary-shaped MSCs, integrated MSCs, stretchable MSCs, shapeless MSCs in order to satisfy severe requirements of new-generation microscale electronics with form factors for multi-functional integrated systems.

Moreover, planar device geometry composed of positive and genitive microelectrodes arranged on one substrate separated by an empty interspace allows simultaneous in-situ observation to two electrodes by multiple characterization techniques, extremely advantageous for deep understanding and establishment of quantitative model to electrochemical processes.

Selected Publications

1.High-Energy MnO₂ Nanowire/Graphene and Graphene Asymmetric Electrochemical Capacitors. ACS Nano, 2010, 4 (10): 5835-5842.
2.Anchoring Hydrous RuO₂ on Graphene Sheets for High-Performance Electrochemical Capacitors, Adv. Funct. Mater., 2010, 20 (20): 3595-3602. 
3.Three-Dimensional Nitrogen and Boron Co-Doped Graphene for High-Performance All-Solid-State Supercapacitors. Adv. Mater., 2012, 24 (37): 5130-5135. 
4.Three-Dimensional Graphene-Based Macro- and Mesoporous Frameworks for High-Performance Electrochemical Capacitive Energy Storage. J. Am. Chem. Soc., 2012, 134 (48): 19532-19535.
5.Graphene-Based in-Plane Micro-Supercapacitors with High Power and Energy Densities. Nat. Commun., 2013, 4 (4), 2487-2495.
6.Recent Advances in Graphene-Based Planar Micro-Supercapacitors for on-Chip Energy Storage. Natl. Sci. Rev., 2014, 1 (2): 277-292.
7.Alternating Stacked Graphene-Conducting Polymer Compact Films with Ultrahigh Areal and Volumetric Capacitances for High-Energy Micro-Supercapacitors Adv. Mater., 2015, 27 (27): 4054-4061. 
8.Ultrathin Printable Graphene Supercapacitors with Ac Line-Filtering Performance. Adv. Mater., 2015, 27 (24): 3669-3675.
9.Fabrication of Graphene/Polyaniline Composite Paper Via in Situ Anodic Electropolymerization for High-Performance Flexible Electrode. ACS Nano, 2009, 3 (7): 1745-1752.