Electrochemical Evaluation and Structural Characterization of Commercial LiCoO[sub 2] Surfaces Modified with MgO for Lithium-Ion Batteries

Abstract

Commercial cathode material LiCoO 2 was modified by coating its surface with a thin layer of amorphous magnesium oxide ͑MgO͒. The surface morphology, crystalline structure, and electrochemical performance of the modified cathode material were characterized and compared with that of pristine LiCoO 2 . It is found that surface modification can improve the structural stability of LiCoO 2 without decreasing its available specific capacity. Specific capacities of 145, 175, and 210 mAh/g were obtained in test cells composed of MgO-coated LiCoO 2 cathode material when charged to 4.3, 4.5, and 4.7 V (Li ϩ /Li), respectively. This improvement is attributed to the pillaring effect of the Mg 2ϩ ions in the interslab space of the lattice and the protective effect of the MgO film against the escape of Co 4ϩ ions from the bulk of LiCoO 2 particles.

Stabilization of the Electronic Structure at the Cathode/Electrolyte Interface via MgO Ultra-thin Layer during Lithium-ions Insertion/Extraction

“…20 However, different morphologies of MgO coating layer have been reported by other research group. 6,[21][22][23][24] In order to examine the morphology effect, we prepared two types of MgO coated-LiCoO 2 thin film electrodes at room temperature and high temperature. The stability at high potential cycling was investigated by electrochemical measurements.…”

Research on Advanced Materials for Li‐ion Batteries

“…[102,103] We developed a simple co-precipitation method to coat Al 2 O 3 or MgO on commercial LiCoO 2 (Nippon Chemical Industry) and nano-LiCoO 2 in 2002. [104][105][106] As shown in Figure 13a, Figure 13b shows the effect of an Al 2 O 3 coating on improving the cyclic performance. [105] The understanding of the coating mechanism was argued at that time.…”

A Review on Nanocomposite Materials for Rechargeable Li-ion Batteries

“…Significant number of studies was conducted to understand the capacity fading mechanism over 4.2 V as well as to improve the capacity of LiCoO 2 by pushing the upper cut-off voltage above 4.2 V while keeping the cycle life at a reasonable level (i.e.,~500 cycles) [34][35][36][37]. It was shown by many that the cycle life of LiCoO 2 at higher voltages (i.e., >4.2 V) can be improved by metal oxide coatings such as Al 2 O 3 , SnO 2 , ZrO 2 , TiO 2 , MgO, [34,[38][39][40][41][42], metal phosphate coatings such as AlPO 4 [43][44][45][46], metal fluoride coatings such as AlF 3 and LaF 3 [47,48] and multicomponent metal fluoride coatings such as aluminum-tungsten-fluoride (AlW x F y ) [49]. Although the underlying reasons for such an improvement in cycle life of LiCoO 2 at higher cut-off voltages due to coatings are still debatable [35,50,51], following mechanisms have been suggested: coating (i) inhibits the structural transformation [34,52], (ii) acts as a physical barrier, Figure 9, between the electrolyte and the active material, and prevents the trace amounts of hydrogen fluoride (HF) and water present in the electrolyte from reaching the active material thus effectively suppresses cobalt dissolution and the associated oxygen evolution [53,54], (iii) converts Lewis acids which in return corrode the insulating surface species and improves the electronic conductivity of the solid electrolyte interface (SEI) layer on LiCoO 2 [50].…”