Li-ion capacitors that combine the advantages of batteries and supercapacitors. In this presentation, we will discuss the impacts of crystallinity, defects, and nanocomposites on the electrochemical properties of Mn-based electrodes and the energy storage performance of Li-ion capacitors. The first example is MnO nanoparticles with cationic vacancies and discrepant crystallinity and encapsulated in porous carbon were prepared through one step hydrothermal synthesis followed with calcination at different temperatures. Such synergistic structure endowed MnO with an excellent electrochemical properties including a much enhanced capacity of 650 mAh/g at a current density of 1000 mA/g. Li-ion capacitors based on such MnO anode and activated carbon cathode achieved the maximum energy density of 220 Wh/Kg, and capacitance retention was 95.3% after 3600 cycles at a rate of 5 A/g. Mesocrystal MnO synthesized through polyvinyl alcohol (PVA) assisted hydrothermal growth and homoepitaxial aggregation. Such mesocrystal MnO demonstrated a high capacity of 637 mAh/g at 100 mA/g. The high voltage (4V) Li-ion capacitor, a full cell with mesocrystal MnO cubes as anode and activated carbon as cathode, demonstrated excellent cycling performance with the degradation rate of 0.002% per cycle, and the achieved maximum energy in full capacitor reached 227 Wh/kg that calculated on the total weight of the active materials in both electrodes. A new lithium ion anode, MnNCN, was synthesized through a facile solvothermal method in one step. The long length of Mn-N bond and weak Pauling electronegativity of N endow more covalent nature in the chemical bonds in MnNCN, the covalent bonding leads to a decreased energy for electrons to be added to or extracted from 3d orbital of Mn2+ and makes a lower discharge potential in Li-ion batteries. MnNCN delivered a high reversible discharge capacity of 725 mAh/g at 100 mA/g through conversion reaction with excellent rate capability and stable cycling performance. A high voltage capacitor built on MnNCN anode and activated carbon cathode demonstrated a high energy density of 103 Wh/kg and a high power density of 8,533 W/kg. The Li-ion capacitor showed no detectable degradation after 5,000 cycles at a rate of 5 A/g, demonstrating an excellent cycling stability.

MnO and MnNCN for Li-ion capacitors

253rd National Meeting (2017)

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