Investigation of Electrochemically Li-ion Active Materials for Li-ion Batteries

Being the battery of the 2l8t century, Li-ion batteries have been making headway towards replacing traditional medium to large scale energy storage devices. Recent applications ranging from EVs to grid-level energy storage, have driven the design criteria of Li-ion batteries to evolve at a rapid pace. Three major goals are low cost, high electrochemical performance, and improved safety. New targets set by the DOE to make Li-ion batteries more competitive in their new market sectors have been to decrease cost to US$ 125 kWh-1 and increase gravimetric and volumetric energy density to 235 Wh kg-1 and 500 Wh L - 1 , respectively [1]. This thesis presents works on the three major components of a Li-ion battery: sustainable wheat derived-carbon anodes, high capacity V2O5 IGraphene-nanoplatelets (GNPs) composite cathodes, and rare earth nickelates (specifically SmNiO3 as a potential solid-state electrolyte for improved safety. Systematic solid-state processmg, structural, and electrochemical studies were conducted on wheat-derived carbons. Coupling carbonization temperatures and structural evolution of biomass-derived carbons (in this case wheat) , lithium insertion properties can be tuned, to create a high capacity and sustainable anode material. An optimal condition presents itself at a carbonization temperature of 600°C with a stable lithiation capacity of 390 mAh g-1 . In the Li-ion cell, the limit ing factor in the total output capacity (mAh g-1) 1s governed mainly by the cathode materials, as cathode materials tend to be lithiumbased transitional metal oxides (high density compared to anode materials). Having one of the highest lithium storage capacity, V2O5 is a cathode material that suffers from low electronic conductivity and particle fragmentation upon continuous lithium insertion and extraction. In this work, sonochemistry is utilized in the synthesis of V2O5|Graphene-nanoplatelets (GNPs) composites to improve electronic conductivity and kinetics of lithium-insertion and extraction. Surface modification of the graphene nanoplatelets during sonication of GNPs allows for in situ growth of V2O5 nanoparticles. With the size reduction of the V2O5 particles and the conductive GNPs backbone, the composite achieved 248 mAh g−1 specific cathode capacity; retaining 83% of initial capacity after 50 cycles. Part 1 and 2 of this study illustrate strategies to create a low-cost and high electrochemical performance Li-ion battery via sustainable material implementation, structural and morphology control, and composite formation. The third part studies the electrochemical properties of perovskite rare-earth nickelates (specifically SmNiO3) and its’ integration as a solid-state electrolyte in an all-solid-state lithium-ion battery. Upon insertion of Li+ ion, SmNiO3 undergoes Mott-transition, simultaneously allowing for a large amount of mobile Li+ to be stored at the interstitial sites (approaching a ratio of one dopant per unit-cell). The combination of a lattice expansion (∼10% increase) and the interstitial doping creates a perfect condition for fast Li+ conduction with reduced activation energy. Initial efforts to integrate LiSmNiO3 in a solid-state-cell with LiCoO2|LiSmNiO3|Si configuration results with initial charging capacity of 1338 mAh g−1

Investigation of Electrochemically Li-Ion Active Materials for Li-Ion Batteries

Being the battery of the 21st century, Li-ion batteries have been making headway towards replacing traditional medium to large scale energy storage devices. Recent applications ranging from EVs to grid-level energy storage, have driven the design criteria of Li-ion batteries to evolve at a rapid pace. Three major goals are low cost, high electrochemical performance, and improved safety. New targets set by the DOE to make Li-ion batteries more competitive in their new market sectors have been to decrease cost to US$ 125 kWh-1 and increase gravimetric and volumetric energy density to 235 Wh kg-1 and 500 Wh L-1, respectively [1]. This thesis presents works on the three major components of a Li-ion battery: sustainable wheat derived-carbon anodes, high capacity V2O5:Graphene-nanoplatelets (GNPs) composite cathodes, and rare earth nickelates (specically SmNiO3 as a potential solid-state electrolyte for improved safety. Systematic solid-state processing, structural, and electrochemical studies were conducted on wheat-derived carbons. Coupling carbonization temperatures and structural evolution of biomass-derived carbons (in this case wheat), lithium insertion properties can be tuned, to create a high capacity and sustainable anode material. An optimal condition presents itself at a carbonization temperature of 600˚C with a stable lithiation capacity of 390 mAh g-1. In the Li-ion cell, the limiting factor in the total output capacity (mAh g-1) is governed mainly by the cathode materials, as cathode materials tend to be lithium based transitional metal oxides (high density compared to anode materials). Having one of the highest lithium storage capacity, V2O5 is a cathode material that suffers from low electronic conductivity and particle fragmentation upon continuous lithium insertion and extraction. In this work, sonochemistry is utilized in the synthesis of V2O5:Graphene-nanoplatelets (GNPs) composites to improve electronic conductivity and kinetics of lithium-insertion and extraction. Surface modification of the graphene nanoplatelets during sonication of GNPs allows for in situ growth of V2O5 nanoparticles. With the size reduction of the V2O5 particles and the conductive GNPs backbone, the composite achieved 248 mAh g-1 specific cathode capacity; retaining 83% of initial capacity after 50 cycles. Part 1 and 2 of this study illustrate strategies to create a low-cost and high electrochemical performance Li-ion battery via sustainable material implementation, structural and morphology control, and composite formation. The third part studies the electrochemical properties of perovskite rare-earth nickelates (specifically SmNiO3) and its\u27 integration as a solid-state electrolyte in an all-solid-state lithium-ion battery. Upon insertion of Li+ ion, SmNiO3 undergoes Mott-transition, simultaneously allowing for a large amount of mobile Li+ to be stored at the interstitial sites (approaching a ratio of one dopant per unit-cell). The combination of a lattice expansion (~10% increase) and the interstitial doping creates a perfect condition for fast Li+ conduction with reduced activation energy. Initial efforts to integrate LiSmNiO3 in a solid-state-cell with LiCoO2:LiSmNiO3:Si configuration results with initial charging capacity of 1338 mAh g-1

Tailored Carbon Anodes Derived from Biomass for Sodium-Ion Storage

Sodium-ion batteries are emerging as an alternative energy storage system for lithium-ion batteries because of the abundance and low cost of sodium. Various carbon-based anode materials have been investigated in order to improve sodium battery performance and cycle life. In this study, because of its abundance and high porosity, pistachio shell was selected as the primary carbon source, and carbonization temperatures ranged from 700 to 1500 °C. Pistachio shell carbonized at 1000 °C resulted in a highly amorphous structure with specific surface area 760.9 m² g^–1 and stable cycle performance (225 mA h g^–1 at 10 mA g^–1). Our initial results obtained from carbonized pistachio shell suggest that sufficient electrochemical performance may be obtained from biowaste materials, offering new pathways for sustainable electro-mobility and other battery applications

Parallel Nanoshaping of Brittle Semiconductor Nanowires for Strained Electronics

Semiconductor nanowires (SCNWs) provide a unique tunability of electro-optical property than their bulk counterparts (e.g., polycrystalline thin films) due to size effects. Nanoscale straining of SCNWs is desirable to enable new ways to tune the properties of SCNWs, such as electronic transport, band structure, and quantum properties. However, there are two bottlenecks to prevent the real applications of straining engineering of SCNWs: strainability and scalability. Unlike metallic nanowires which are highly flexible and mechanically robust for parallel shaping, SCNWs are brittle in nature and could easily break at strains slightly higher than their elastic limits. In addition, the ability to generate nanoshaping in large scale is limited with the current technologies, such as the straining of nanowires with sophisticated manipulators, nanocombing NWs with U-shaped trenches, or buckling NWs with prestretched elastic substrates, which are incompatible with semiconductor technology. Here we present a top-down fabrication methodology to achieve large scale nanoshaping of SCNWs in parallel with tunable elastic strains. This method utilizes nanosecond pulsed laser to generate shock pressure and conformably deform the SCNWs onto 3D-nanostructured silicon substrates in a scalable and ultrafast manner. A polymer dielectric nanolayer is integrated in the process for cushioning the high strain-rate deformation, suppressing the generation of dislocations or cracks, and providing self-preserving mechanism for elastic strain storage in SCNWs. The elastic strain limits have been studied as functions of laser intensity, dimensions of nanowires, and the geometry of nanomolds. As a result of 3D straining, the inhomogeneous elastic strains in GeNWs result in notable Raman peak shifts and broadening, which bring more tunability of the electrical–optical property in SCNWs than traditional strain engineering. We have achieved the first 3D nanostraining enhanced germanium field-effect transistors from GeNWs. Due to laser shock induced straining effect, a more than 2-fold hole mobility enhancement and a 120% transconductance enhancement are obtained from the fabricated back-gated field effect transistors. The presented nanoshaping of SCNWs provide new ways to manipulate nanomaterials with tunable electrical–optical properties and open up many opportunities for nanoelectronics, the nanoelectrical–mechanical system, and quantum devices