SYNTHESIS AND CHARACTERIZATION OF CLAY/POLYMER NANOCOMPOSITE MATERIALS AND THEIR APPLICATION FOR LITHIUM BATTERIES

Batteries are essential components of most electrical devices. They are used as the power source in cars, laptops, smartphones, and other electronic appliances storing and generating electricity. Continuous effort and research take place in order to improve commercial batteries making them more efficient and affordable. The main priority of research projects and battery technology development has been, in the past recent years, to increase the energy density of lithium batteries. The goal is to meet the growing demand for mobile devices, which increasingly need more energy, and to increase the autonomy of second-generation electric vehicles, which demand higher capacity and more efficient batteries. On the one hand, although using metallic lithium anodes for next generation batteries would increase up to ten times the capacity obtained from actual batteries, lithium reactivity and dendrite formation and growth represent one of the main obstacles. One of the main focuses of research in post-lithium batteries are strategies to protect the metallic lithium anode. On the other hand, LiNi0.5Mn1.5O4 is a high voltage cathode material for lithium ion batteries and represents a promising alternative to the most common ones used in the market because of some properties like eco-friendliness and low cost. However, one of its main drawbacks is fast capacity fade due to manganese dissolution, migration and deposition on the anode material. In addition, commercial polyolefin separators used in lithium batteries have poor affinity towards carbonate-based electrolytes and low thermal stability. These mentioned problems concerning lithium batteries where faced in this thesis work. Firstly, a clay/polymer nanocomposite material was synthesized from polyaniline and an Argentinian montmorillonite with the aim of obtaining a synergistic combination of properties. Some chemical characterization techniques including: XRD, FTIR, TGA, XPS, and zeta potential measurements, where performed in order to study, analyse and verify that the composite obtained was in line with the synthesis purpose. Secondly, the obtained nanocomposite was applied as a coated membrane on to a commercial separator (Celgard®2500) commonly used in batteries in order to improve its properties, and it was electrochemically tested to study its stability and compatibility towards lithium plating and stripping as well as the performance as a metallic lithium protection strategy. The coated separator was then used in half and complete cells using a high voltage cathode (LiNi0.5Mn1.5O4) with the aim of working as a barrier in order to impede migration of manganese ions towards the graphite anode and therefore, increase the battery performance.