Alternative electrode fabrication for Lithium-Ion batteries using flame spray pyrolysis

Conventional lithium-ion batteries (LIBs) are famous for their high energy and power density, efficiency, and long cycle life. These properties make LIBs a highly relevant power source for the electronic consumer market, electric vehicles, and stationary energy storage applications. Major drawbacks of LIBs are high production costs and safety issues arising from the flammability of the liquid electrolyte. All-solid-state lithium-ion batteries (ASSBs) incorporate incombustible solid-state electrolytes, avoiding leakages and burning hazards. ASSBs also suffer from high production costs and large-scale fabrication routes are unavailable yet, hampering their commercial launch. Electrode fabrication for both LIBs and ASSBs is complex and expensive, bearing a significant potential to reduce overall battery fabrication costs. Flame spray pyrolysis (FSP) has emerged as a promising tool for synthesizing ultrafine, phase-pure and crystalline battery electrode active materials. In this dissertation, it will be shown that FSP offers a cost-effective and facile synthesis of spinel Li4Ti5O12 (LTO) based electrodes for both LIBs and ASSBs. Four process-oriented key hypotheses were formulated and tested in anticipation of technical improvements of LIBs and ASSBs electrode manufacturing: (1) high-purity FSP-produced LTO powders perform comparable in LIB cells, independent of the underlying precursor solvent combinations, (2) LIB performances of carbon-coated LTO (LTO/C) composite electrodes, prepared by double flame spray pyrolysis (DFSP) and transfer-lamination technique, are improved for higher transfer-lamination pressures, (3) FSP-based in-situ deposition of well-crystallized LTO thin-films to flexible substrates, makes commonly applied thermal treatments for particle crystallization obsolete. Assembled in ASSBs, the flexible LTO electrodes are cyclable in flat and statically bent condition without mechanical deterioration, (4) adjusting the compression procedure of such in-situ deposited LTO thin-films leads to modified microstructures. Less porous particle networks promote the intrinsic charge carrier transports, resulting in larger practicable capacities. Based on the new scientific results, following conclusions have been drawn: (1) irrespective of the applied precursor solvent combination, electrochemical performances of FSP-synthesized phase-pure LTO are indeed comparable. This finding allows battery manufacturers to choose the combination that serves best their economic and ecologic needs, (2) the LIB performance of LTO/C electrodes, fabricated by DFSP/transfer-lamination, was enhanced for higher transfer-lamination pressures based on an enlarged electrically conductive particle network. Due to the optimized microstructure with favorable electrical and ionic transport properties, the stronger compressed LTO/C electrodes were electrochemically outperforming analogous electrodes prepared by conventional doctor blading technique. Remarkably, the novel transfer-lamination method was independent of any solvents and binding additives, (3) crystalline LTO powders were successfully deposited to temperature-sensitive flexible polymer substrates, without requiring any additional sintering step. Assembled into ASSBs, the flexible LTO electrodes showed excellent cycling stability. Upon static battery-cell bending, the capacities were slightly reduced, but the electrochemical reversibility of the LTO electrode was still remarkable, (4) yielded capacities of flexible LTO thin-film electrodes were significantly enhanced after reducing the porosity. Microstructural simulations indicated that this was due to enlarged LTO particle coordination numbers, and increased contact densities at interfaces to adjacent functional layers.