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Aviation emissions contribute adversely to climate change and air pollution due to combustion emissions. While biofuels can reduce the lifecycle CO2 emissions and combustion soot emissions, and hybrid- or turbo-electric aircraft may result in reduced fuel burn and overall emissions, only all-electric aircraft offer a potential opportunity for zero in-flight emissions in the long term. Over the past decade, more than 70 all-electric conceptual, experimental, and commercial aircraft have been researched, with a particular focus on light aircraft. These designs are reviewed, along with progress in battery technology. An all-electric aircraft design and optimization program, TASOPTe, has been developed from an existing version for conventionally-powered aircraft, TASOPT. Both programs are largely based on first-principles, enabling the design of aircraft with unusually short design ranges. A series of optimized 180-passenger aircraft based on the Airbus A320neo configuration are designed and evaluated at 200-1600 nmi design ranges with 2-10 propulsors and 400-2000 Wh/kg batteries. The performance of these all-electric aircraft is compared to advanced conventionally-powered aircraft optimized for the same design ranges. Optimized all-electric aircraft are found to use two or four propulsors, depending on the design range and specific energy assumed. The design range limits for each specific energy are determined, which are restricted by aircraft weight and performance penalties. A factor of four increase in battery pack specific energy from current values of 200 Wh/kg to 800 Wh/kg enables 500 nmi flights. However, lower design ranges provide improved energy and environmental performance. The required grid power generation characteristics for commercial all-electric aircraft to become net environmentally beneficial are determined for each specific energy assumption. The entire energy conversion chain, including charging, transport, and discharging of electrical energy, is considered. Despite the higher total energy use, narrow-body all-electric aircraft have the potential for lower equivalent CO2 emissions than conventionally-power aircraft if the electrical grid transitions toward renewable energy. This is largely enabled by the complete elimination of all high-altitude emissions, which would remove associated non-CO2 warming.