Thesis advisor: Udayan Mohanty / Thesis advisor: Dunwei Wang / With the fast development of society, the demand for batteries has been increasing dramatically over the years. To satisfy the ever-increasing demand for high energy density, different chemistries were explored. From the first-generation lead–acid batteries to the state-of-the-art LIBs (lithium ion batteries), the energy density has been improved from 40 to over 200 Wh kg⁻¹. However, the development of LIBs has approached the upper limit. Electrode materials based on insertion chemistry generally deliver a low capacity of no more than 400 mAh/g. To break the bottleneck of current battery technologies, new chemistries are needed. Moving from the intercalation chemistry to conversion chemistry is a trend. The conversion electrode materials feature much higher capacity than the conventional intercalation-type materials, especially for the O₂ cathode and Li metal anode. The combination of these two can bring about a ten-folds of energy density increase to the current LIBs. Moreover, to satisfy the safety requirements, either using non-flammable electrolytes to reduce the safety risk of Li metal anode or switch to dendrite-free Mg anode is a good strategy toward high energy density batteries. First, to enable the conversion-type O₂ cathode, a wood-derived, free-standing porous carbon electrode was demonstrated and successfully be applied as a cathode in Li-O₂ batteries. The spontaneously formed hierarchical porous structure exhibits good performance in facilitating the mass transport and hosting the discharge products of Li₂O₂. Heteroatom (N) doping further improves the catalytic activity of the carbon cathode with lower overpotential and higher capacity. Next, to solve the irreversible Li plating/stripping and safety issues related with Li metal anode, we introduced O₂ as additives to enable Li metal anode operation in non-flammable triethyl phosphate (TEP) electrolyte. The electrochemically induced chemical reaction between O₂- derived species and TEP solvent molecules facilitated the beneficial SEI components formation and effectively suppressed the TEP decomposition. The promise of safe TEP electrolyte was also demonstrated in Li-O₂ battery and Li-LFP battery. If we think beyond Li chemistries, Mg anode with dendrite-free property can be a promising candidate to further reduce the safety concerns while remaining the high energy density advantage. Toward the end of this thesis, we developed a thin film metal–organic framework (MOF) for selective Mg²⁺ transport to solve the incompatibility issues between the anode and the cathode chemistry for Mg batteries. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.