Amplification of the discharge current density of lithium-ion batteries with spinel phase Li(PtAu)0.02Mn1.98O4 nano-materials

Abstract

In this study the synergistic and catalytic properties of a novel nano-composite cathode material of nominal composition Li(M)(subx)Mn(sub2-x)O(sub4) (M = Pt-Au; x # 0.2) has been explored. Li(PtAu)xMn(sub2-x)O4 nanomaterial for use in lithium-ion batteries (LIB) was synthesized by incorporation of the Pt-Au (1:1) nanoparticles onto the spinel phase LiMn(sub2)O(sub4). Ultra-low scan rate (0.01 mV (sups-1)) cyclic voltammetry of the cathode material in 1 M LiPF(sub6) (in 1:1 EC:DMC), showed four sets of redox peaks, which reflect the typical redox process of the active material in the spinel structure due to lithium intercalation and deintercalation. The Li/Li(PtAu)(sub0.02)Mn(sub1.98)O(sub4) cell had less polarization as it effectively accommodates the structural transformation during Li(sup+) ion charge and discharge. The Li(PtAu)(sub0.02)Mn(sub1.98)O(sub4) cathode showed an increase in discharge currents densities with an exchange current density, i(sub0), value of 2.8 × 10(sup-4_ A cm(sup-2), which suggests increase in the rate of electron transfer compared to LiMn(sub2)O(sub4) (1.8 × 10(sup-4) A cm(sup-2)). Li(PtAu)(sub0.02)Mn(sub1.98)O(sub4) exhibited excellent capacity retention upon extended cycling and can release 90 mAh (supg-1) at 10C with a capacity retention of 99% after 50 cycles. Faster charge transportation at high current rates proved to prevent the pronounced pile-up of Li(sup+) ions and undesired Mn(sup3+) ions on the surfaces. The electrochemical impedance spectroscopy (EIS) results showed a decrease in charge transfer resistance for LiMn(sub2)O(sub4) after surface coverage with conductive PtAu NP's. For the lithium diffusion coefficient in Li(PtAu)(sub0.02)Mn(sub1.98)O(sub4) thin film, its magnitude order is 10(sup-11) cm2·s(sup-1).