Kunfeng Chen

Nanoclay assisted electrochemical exfoliation of pencil core to high conductive graphene thin-film electrode

Nanoclay assisted electrochemical exfoliation was developed to in-situ form functionalized graphene electrode materials from pencil core with different ratios of graphite and clay. This method made a positive transformation from solid graphite to graphene colloidal solution, which can be used to construct binder- and additive-free thin-film electrodes. Exfoliated graphene can be served as both conductive current collector (film resistance of 33Ω/square) and electrode materials. Graphene thin-film electrodes from pencil cores displayed higher capacity of 224 than 80mAh/g of that from pure graphite. The electrochemical performance can be controlled by the ratio of graphite and clay and the oxidation reaction of surface oxygen functional groups. The described nanoclay-assisted electrochemical oxidation route shows great potential for the synthesis of functionalized graphene electrode materials for high-conductive thin-film lithium ion batteries and supercapacitors.

LiMn2O4-based materials as anodes for lithium-ion battery

LiMn2O4-based materials such as LiMn2O4 and LiMn1.53Ni0.47O3.67 were synthesized by both conventional-hydrothermal (CH), microwave-hydrothermal (MH) methods and calcination route. Both reaction temperature and reaction time during MH routes were lower than those of CH routes. LiMn2O4 electrode materials were assembled into lithium-ion battery anodes and their electrochemical performances were studied. The results proved that these LiMn2O4 electrodes can be served as conversion anode materials, and show electrochemical activity during the potential range of 0.01–3.0 V versus Li+/Li. For LiMn1.53Ni0.47O3.67 materials when used as lithium-ion battery anodes, we found that the introduction of Ni can change their electrochemical reaction and thus improve their electrochemical performances.

In situ electrochemical activation of Ni-based colloids from an NiCl2 electrode and their advanced energy storage performance

The formation of electrochemical activated cations in electrode materials to induce multiple-electron transfer reactions is a challenge for high-energy storage systems. Herein, highly electroactive Ni-based colloidal electrode materials have been synthesized by in situ electrochemical activation of a NiCl2 electrode. The highest specific capacitance of the activated Ni-based electrodes was 10 286 F g-1 at a current density of 3 A g-1, indicating that a three-electron Faradaic redox reaction (Ni3+ ↔ Ni) occurred. Upon potential cycling and constant potential activation, a decrease in the charge transfer resistance can be found. Activation and utilization of multiple-electron reactions is an efficient route to increase the energy density of supercapacitors. This newly designed colloidal pseudocapacitor is compatible with inorganic pseudocapacitor chemistry, which enables us to use metal cations directly via their commercial salts rather than their oxide/hydroxide compounds.

Synthesis of spinel LiMn2O4 cathode material by a modified solid state reaction

Spinel LiMn2O4 was synthesized by a modified solid state reaction. We pretreated the reactants using tartaric acid as complexing agent through a grinding process to obtain uniform distribution of metal ions at atomic level. The structures, morphologies and electrochemical properties of the products were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and galvanostatic charge-discharge test. The results show that adding tartaric acid during the chemical pretreatment plays an important role in the formation of regular and uniform particles, which is beneficial to the electrochemical performance of LiMn2O4. At the current density of 100 mA g-1, the discharge capacity is 118 mAh g-1 after 50 cycles with the capacity retention of 97%.