Improving cyclic stability and rate capability of LiNi0.5Mn1.5O4 cathode via protective film and conductive polymer formed from thiophene

Abstract

In this work, we report a new finding that thiophene can be used as an electrolyte additive to form simultaneously protective cathode film and conductive polymer and thus to improve significantly the cyclic stability and rate capability of LiNi0.5Mn1.5O4 cathode for a high-voltage lithium-ion battery. The contribution of thiophene is evaluated in a Li/LiNi0.5Mn1.5O4 cell, with charge/discharge test, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier-transformed infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS). The charge/discharge tests demonstrate that the capacity retention of LiNi0.5Mn1.5O4 with 1-C (1 C = 147 mA g−1) rate is improved from 37.2 to 78.8 % at 55 °C after 100 cycles, and the discharge capacity with 10-C rate is enhanced from 83 to 111 mAh g−1 when adding 0.5 % thiophene into 1 M LiPF6 in ethylene carbonate (EC)/ dimethyl carbonate (DMC) (1/2, v/v) solution. CV shows that thiophene is oxidized at 4.5 V (vs. Li/Li+), forming a protective film on and conductive polymer among LiNi0.5Mn1.5O4 particles, which can be confirmed by EIS, XRD, SEM, TEM, FTIR, and XPS.