Development of environmentally friendly lithium-ion battery components

Nowadays, it is fully ascertained that the massive use of fossil fuel has a detrimental impact on the environment and the population health. These adverse aspects of using fossil fuels, mostly in mobility, have been intensively discussed worldwide resulting in new regulations to reduce the emissions of harmful exhaust gases. Concerning to this point, the search for more efficient and low emission energy source has gained considerable attention. The use of electricity as an energy source instead of combustion of gasoline and diesel has gained a great interest in the automotive industry. For this propose, lithium-ion batteries (LIB) have becoming the choice to store electricity and power vehicles. LIB offer remarkable advantages such as high energy and power capability with respect to lead acid and Nickel-Metal hydride (Ni-MH) batteries, and long cycle life. However, LIB components, as electrodes, electrolytes and separator, are mostly manufactured using expensive and toxic materials. In this context, this thesis focuses on study new materials and processes for the realization of more environmentally friendly LIB. In particular, this dissertation deals with the manufacture of electrodes and separator with reduced environmental impact and improved performance. The LIB components studied in this thesis are made using water soluble polymers from renewable sources. In Chapter 3, a novel porous membrane based on silicon dioxide (SiO2) filler and hydroxypropyl guar gum (HPG) binder is presented and tested as a separator for LIB. The HPG binder shows to be thermally stable at 200 °C and 250 °C in O2 and N2 atmosphere respectively. Therefore, the membrane exhibits high thermal stability and no dimensional-shrinkage at high temperatures thanks to the integration of the ceramic filler and the thermally stable bio-derived polymer. Moreover, the separator offers superior wettability and high electrolyte uptake due to the optimised porosity of ca. 52% and the favourable affinity of SiO2 and guar gum microstructure towards commercial organic liquid electrolytes. The electrochemical tests demonstrate the satisfactory electrochemical stability of the separator in a wide range of potential, as well as its outstanding cycle performance when coupled with lithium nickel manganese cobalt oxide (NMC) and lithium titanate (LTO) electrodes. Moreover, Chapter 4 described the study of aqueous processed LTO electrodes. The use of phosphoric acid (PA) to control the pH of LTO slurries is investigated. The additional of PA avoided the corrosion of the Al current collector and enhanced the adhesion and the electrochemical performance of LTO electrodes. Additionally, LTO electrodes were manufactured via the aqueous process using sodium carboxymethylcellulose (CMC), guar gum (GG) or pectin as binders and these electrodes were investigated regarding of morphology, adhesion strength and electrochemical performance. Finally, the full lithium-ion cell made utilising only aqueous processing electrodes, namely NMC cathodes and LTO anodes offers a stable discharge capacity of ~120 mAh·g−1 (based on cathode active material) with high coulombic efficiencies. GG binder is also used in graphite and NMC electrodes as the main binder. Full cell using these electrodes delivered a stable discharge capacity of ~ 110 mAh g-1 (based on cathode active material) with high coulombic efficiencies. The surface of pristine and cycled electrodes prepared using GG or CMC were investigated using X-ray Photoelectron Spectroscopy (XPS). Post-mortem investigation of cycled graphite electrodes from full lithium-ion cells revealed the formation of a thinner solid electrolyte interface (SEI) when GG is employed instead of CMC. This thesis shows that polymers from bio-sources can be used as binders in the preparation of LIB components. The use of these bio-polymers instead of the state-ofart fluorinated binder accounts to lower environmental impact in LIB production. The study here developed gives an important contribution to the improvement of LIB towards environmentally friendly methods and materials, which are crucial to the continuous expansion of renewable energy sources is our society.