Abstract
Nickel and sulfur doped lithium manganese spinels with a nominal composition of LiMn2−xNixO4–ySy (0.1 ≤ x ≤ 0.5 and y = 0.01) were synthesized by a xerogel-type sol-gel method followed by subsequent calcinations at 300 and 650 °C in air. The samples were investigated in terms of physicochemical properties using X-ray powder diffraction (XRD), transmission electron microscopy (EDS-TEM), N2 adsorption-desorption measurements (N2-BET), differential scanning calorimetry (DSC), and electrical conductivity studies (EC). Electrochemical characteristics of Li/Li+/LiMn2−xNixO4–ySy cells were examined by galvanostatic charge/discharge tests (CELL TEST), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The XRD showed that for samples calcined at 650 °C containing 0.1 and 0.2 mole of Ni single phase materials of Fd-3m group symmetry and nanoparticles size of around 50 nm were obtained. The energy dispersive X-ray spectroscopy (EDS) mapping confirmed homogenous distribution of nickel and sulfur in the obtained spinel materials. Moreover, it was revealed that the adverse phase transition at around room temperature typical for the stoichiometric spinel was successfully suppressed by Ni and S substitution. Electrochemical results indicated that slight substitution of nickel (x = 0.1) and sulfur (y = 0.01) in the LiMn2O4 enhances the electrochemical performance along with the rate capability and capacity retention.
Highlights
The search for low weight, high energy and power density lithium-ion batteries (LIBs) has increased in recent years due to a growing demand for energy storage in the field of large scale applications (e.g., hybrid electric vehicles, electric vehicles, and stationary energy storage systems (ESS)) [1,2,3].One of the most attractive cathode materials for rechargeable LIBs is lithium manganese oxide spinel (LiMn2 O4, LMO)
The decrease of capacity is generally attributed to the phase transition occurring in the LMO spinel at room temperature owing to Jahn-Teller distortion of high spin Mn3+ ions [10,11,12], and even more importantly, the increased surface reactivity between electrolyte and highly delithiated cathode material, leading to dissolution of manganese in the electrolyte [13,14]
In this work we report the synthesis of nanostructured Ni and S doped lithium manganese oxides using a xerogel-type sol-gel method [27,34,38,39]
Summary
One of the most attractive cathode materials for rechargeable LIBs is lithium manganese oxide spinel (LiMn2 O4 , LMO). Materials 2016, 9, 366 fading during electrochemical charging/discharging processes [8,9]. This limits its cycle ability along with the rate performance and prevents its broad commercialization. The decrease of capacity is generally attributed to the phase transition occurring in the LMO spinel at room temperature owing to Jahn-Teller distortion of high spin Mn3+ ions [10,11,12], and even more importantly, the increased surface reactivity between electrolyte and highly delithiated cathode material, leading to dissolution of manganese in the electrolyte [13,14]. One method is to introduce a heterogeneous atom into the LMO structure [15,16,17,18,19,20]
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