Chek Hai Lim

Graphene-supported Na3V2(PO4)(3) as a high rate cathode material for sodium-ion batteries

Substantial interest in sodium resources that are inexpensive and abundant in the earth has guided intense research on Na-based electrode materials. We report a facile synthetic strategy to improve the rate performance of Na-based electrode materials in sodium-ion batteries. Na3V2(PO4)3 (NVP) is one of the most promising cathode materials with a NASICON structure, and it has been synthesized on a graphene sheet surface using a simple method that combines sol–gel and solid-state reaction. The NVP/graphene composite displays an excellent high-rate performance; it delivers approximately 67% of the initial 0.2 C capacity at a 30 C rate, whereas bare NVP produces only 46% of the 0.2 C capacity at a 5 C rate. It also demonstrates high capacity retention both at 1 C and 10 C cycles as a promising cathode for rechargeable sodium-ion batteries. This outstanding result can be ascribed to the key role of graphene in enhancing the electronic conductivity of electrode materials compared with bare NVP.

Na2FeP2O7 as a positive electrode material for rechargeable aqueous sodium-ion batteries

An iron-based pyrophosphate compound, Na2FeP2O7, is investigated as a positive electrode material for aqueous sodium-ion batteries for the first time. The high rate capability and good cyclability of this material in aqueous electrolytes are advantageous for low-cost and safe battery systems.

Na3V2O2x(PO4)2F3−2x: a stable and high-voltage cathode material for aqueous sodium-ion batteries with high energy density

The reversible electrochemical activity of the Na3V2O2x(PO4)2F3−2x compound in an aqueous solution is reported for the first time. Na3V2O2x(PO4)2F3−2x with multi-walled carbon nanotubes (MWCNTs) exhibits a long-term stability for up to 1100 cycles in aqueous electrolytes. Two different types of Na-ion full-cells demonstrate the feasibility of the Na3V2O2x(PO4)2F3−2x/MWCNT composite as a cathode for aqueous sodium-ion batteries. A high full-cell voltage of 1.7 V and a high energy density of 84 W h kg−1 were achieved using Zn metal as an anode.

A high power density electrode with ultralow carbon via direct growth of particles on graphene sheets

The application of lithium ion batteries in high power applications such as hybrid electric vehicles and electric grid systems critically requires drastic improvement in the electronic conductivity using effective materials design and strategies. Here, we demonstrate that the growth of a multi-component structure of composition LiTi2(PO4)3 [LTP] on a reduced graphene oxide (rGO) surface via a facile synthetic strategy could achieve an ultrahigh rate capability with the total carbon content as low as 1.79 wt%. The rGO–LTP hybrid material has been prepared using a two-step approach, where the growth of TiO2 nanoparticles on the graphene oxide surface is followed by the high temperature growth of LTP on graphene sheets and simultaneous thermal reduction of graphene oxide. The LTP particles are densely packed within the ripples of rGO and form a compact, well-connected graphene network requiring no additional conductive carbon to facilitate fast electron transport from active materials to the current collector. Here, graphene not only acts as a stable conductive substrate but also helps to control the size of the formed particles. The rGO–LTP hybrid as a cathode in lithium ion batteries achieves an ultrahigh specific power of 10000 W kg−1 at a specific energy of 210 W h kg−1, which corresponds to a charge and discharge time of 36 s and also retains 92% of the initial capacity after 100 cycles at a 10 C charge–discharge rate. Such an excellent performance is attributed to the multifunctional roles performed by rGO such as controlling the particle size, enhancing the electronic conductivity through a highly conductive network and rendering stability during cycling. This provides an effective design strategy for growing complex hybrid materials on graphene and engineering graphene nanosheets for advanced energy storage applications.