Anode prelithiation for lithium-ion batteries [electronic resource]

Rapid progress has been made in realizing battery electrode materials with high capacity and long-term cyclability in the past decade. However, low first-cycle Coulombic efficiency as a result of the formation of a solid electrolyte interphase (SEI) and lithium trapping at the anodes, remains unresolved. Here, I develop nanoscale lithium alloys (LixSi, LixGe, LixSn, LixAl etc.) as excellent prelithiation reagents with high specific capacity to compensate the first-cycle capacity loss for both graphite and alloy-type anode materials. However, because of the high chemical reactivity and low anode potential, lithium alloys are not stable in humid air and react vigorously with the standard slurry solvent N-methyl-2-pyrrolidinone (NMP), indicating they are not compatible with the real battery fabrication process. In this thesis, I report different coatings (Li2O, artificial SEI, LiF, graphene etc.) and different structures (core-shell nanostructure and nanocomposite), and improve the stability of lithium alloys. With the protection of crystalline and dense LiF coating, LixSi nanoparticles can be processed in anhydrous NMP with a high capacity of 2504 mAh/g. With low solubility of LiF in water, this protection layer also allows LixSi to be stable in humid air (∼40% relative humidity (RH)). Traditional lithium-ion batteries based on lithium free anodes and lithium metal oxide cathodes are rapidly falling behind the high-energy storage demands of portable electronics and electric vehicles. Significant increase in energy density of batteries must be achieved by exploring new materials and cell configurations. Alloy anodes with much higher capacity have been recognized as promising alternatives to graphite. Without pre-stored lithium in anodes, the energy density is limited by the low capacity of lithium metal oxide cathodes. Recently, lithium metal has received renewed interest as a high-capacity anode, but faces many challenges resulting from its high reactivity and uncontrolled dendrite growth. Here I develop a series of lithium alloys based anodes as alternatives to lithium metal, inheriting the desirable properties of alloy anodes and pure metal anodes. The large-scale freestanding LixM/graphene foil (M = Si, Sn, Al etc.) consists of fine nanostructures of densely-packed LixM nanoparticles encapsulated by large graphene sheets. LixM/graphene foils are stable in air, owing to their unique structure as well as the hydrophobicity and gas impermeability of graphene sheets. With fully-expanded LixM confined in the highly-conductive and chemically-stable graphene matrix, this foil maintains a stable structure and cyclability in half cells. The LixSi/graphene foil is successfully paired with high-capacity lithium free cathodes, such as V2O5 and sulfur, to achieve stable full-cell cycling. Stabilized lithium alloys serve as prelithiation reagents or excellent anode materials by themselves, which bring huge benefit to both the existing lithium-ion batteries and next-generation lithium metal batteries.

Keywords: Materials Science and Engineering.
Advisor: Cui Yi
Bao Zhenan advisor. Thesis advisor
McGehee Michael