Influence of Conducting Carbons on the Capacity Retention of NiO//LiCoO2 and Graphite//LiCoO2 Full Cell Lithium Ion Batteries

Lithium ion batteries are the dominant energy storage system in the market today. Based on its high energy density, power density and ideal cycleability, research on lithium ion batteries has gone through several generations in a short timeframe. However, the constantly increasing demand for this portable energy source, which could be used for hybrid electric vehicles, tablets, computers, phones and even micro-electronics for medical apparatus and instruments, drives the design of next generation materials and designs with improved performance and safety. In this thesis, the influence of conductivity on Lithium-ion battery half cell capacity retention was investigated with graphite and NiO anodes, and a LiCoO2 cathode, which were fabricated with different amounts of conductive carbon addition. Half cells with more conductive carbon highly improved performance in terms of both energy density and cycleability. The high carbon addition active materials were then used to fabricate graphite/LiCoO2 and NiO/LiCoO2 full cells which showed good performance – especially the NiO/ LiCoO2 full cell which has more than 100 mAh g-1 capacity left after 25 cycles. This has not been reported in the literature previously. All active materials and fabricated cells were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry and charge/discharge measurements. Comparing with half cells, full cell fabrication and testing has more difficulties to achieve good performance. Some of the important variables are: cell conductivity, lithium ion source, increased side reactions and cut off voltage. For instance, in half cells, the lithium metal counter electrode is an unlimited lithium source with highest energy density, meaning that small parasitic chemical losses in Li are not observed; however, in full cells there is a finite amount of lithium contained in the cathode during assembly and full cell performance is therefore very sensitive to this unwanted reactions. Carbon is the most common commercial lithium battery anode material today because of its good conductivity and stability. However, the demands of new automotive and grid-scale applications are driving the need for new materials with higher energy density, but maintain the low cost and reliable safety of existing materials. Metal oxides are a promising alternative class of materials currently under development because of the possibility to achieve more than twice the storage capacity of graphite; however, very little work has been done in the literature regarding metal oxide full cells. Therefore, the overall objective of this thesis is to develop a methodology for creating stable full cell lithium ion batteries with a metal oxide, NiO, anode and commercial LiCoO2 cathode. Particularly, the effects of the electrode recipe, lower full cell cut off voltage, and capacity match between the anode and cathode on the capacity retention are illustrated