Ledwoch, Daniela; (2021) New direction in electrode design for electrochemical energy storage. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

With the electrification of transport, the increase in cordless appliances, and the intention of many countries to switch to renewable energy production, the demand in energy storage, especially in batteries, is rapidly increasing. At present, lithium-ion batteries are used to power most electric cars and portable devices.[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11] However, lithium is a rare material with an appearance in the upper earth crust of less than 70 ppm and its primary resources in China and Bolivia.[12] Sodium-ion batteries are discussed as a potential alternative to replace lithium-ion batteries partly.[13, 14, 15, 16, 17, 18] Like lithium-ion batteries, sodium-ion batteries contain transition metal materials on the cathode side, e.g., layered oxide or phosphates, paired with a carbon comprising anode. Graphite cannot be reversibly cycled in sodium-ion batteries when carbonated electrolytes are used, so amorphous hard carbon is the anode of choice for sodium-ion batteries.[13, 19, 20] But improvements in the observed charge rate are required for many potential applications such as power tools, e-mobility and stationary energy storage. An improvement in electrode design is required to enable fast charging of sodium-ion batteries and eliminate metallic dendrite growth on the electrodes. In this work, fundamental research is undertaken to understand the limitations in cell testing design and the influence of testing parameters to build up a reliable and repeatable test regime. The then tested composite electrodes are determined in terms of electrochemical performance and physical properties with the aim to link manufacturing parameters to performance and implement those findings to improve the overall battery performance. The results emphasize the importance and limitations of ionic transport within hard carbon electrodes, and the required optimization between electronic and ionic conductivity for sodium-ion transport in these electrodes. By adding the ionic conductor zeolite to the composite electrode, better rate performance and improved ageing characteristics were observed, which may enable faster charging of sodium-ion batteries.

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