Presentation on theme: "0.65 V Identifying Redox Active Molecules to Understand Electrochemistry of Functionalized Silicon Anodes for Lithium-ion Batteries Kate Scholz with Laura."— Presentation transcript:
0.65 V Identifying Redox Active Molecules to Understand Electrochemistry of Functionalized Silicon Anodes for Lithium-ion Batteries Kate Scholz with Laura Slaymaker and Dr. Robert Hamers Background Silicon anodes have great promise in Lithium-ion batteries because they have a much greater capacity for lithium intercalation than the more commonly used graphite anodes. However, when cycled silicon anodes expand up to 300% this creates the ability for the greater amount of intercalation, but also causes some problems. With this expansion the SEI (solid electrolyte interface) layer, created when the electrolyte reacts with the anode, can lose adhesion and crumble away leaving new surface area for reaction and eventually depleting the electrolyte. Goals Primary: The goal is to prevent electrolyte from reacting with the surface of the anode by creating a layer of surface attached molecules in an interconnected net, through the silanation of the silicon's surface, that will expand and contract more easily with the anode and thus protecting it from reacting with the electrolyte. Methods To pursue my goals I used a three electrode system (see picture) to do cyclic voltammetry in an inert atmosphere. Reducing Silanes Identifying An Indicator Molecule Criteria: be reversible on Si at a very low potential.5V vs Li to.75V vs Li because Li reduces at -3.04V vs SHE Lanthanides are a good candidate because of their low reduction potentials around -2.3 V vs SHE Conclusions Octadecyltrimethoxysilane does not apparently reduce on silicon Neither holmium nor samarium are apparently reversible on silicon Both holmium and samarium are easily reversible on platinum Intermediate : To test that net, an indicator molecule had to be identified to test the how the “net” effects the electrochemical properties. Also, some of the silanes’ electrochemical properties had to be characterized. Phenathrenyltriethoxysilane (PATES) Naphthyltriethoxysilane (NTES) Styrylethyltrimethoxysilane (STMES) Octadecyltrimethoxysilane (OTMES) SEI Layer Anode Three Electrode System Electrodes Working Electrode (Si wafer or Pt): takes the measurement Counter Electrode (Pt): Balances current during experiment Reference Electrode (Li): Provides the baseline for measurements Solution 0.01M tetrabutylammonium perchlorate in dimethyl formamide Working Electrode Counter Electrode Reference Electrode Functionalization: To functionalize the silicon wafers in silanes, the wafers where cleaned in hydrogen peroxide under UV light and then left over night in a toluene and silane solution. Understanding the electrochemical properties of these silanes is fundamental to later understanding how the layers of these molecules with effect the anode. Platinum Working Electrode Holmium as an Indicator: (holmium(III) trifluoromethansulfonate neat in solution) P-type Silicon Working Electrode Samarium as an Indicator: (samarium(III) trifluoromethansulfonate neat in solution) Platinum Working electrode Silicon Working Electrode 0.55 V 0.58 V 50 Sample CV Reduction Peaks Oxidation Peaks References Su, X.; Wu, Q.; Li, J.; Xiao, X.; Lott, A.; Lu, W.; Sheldon, B. W.; Wu, J. Adv. Energy Mater. 2014, 4, 1300882. Liu, X. H.; et al. ACS Nano 2012, 6, 1522–1531. P. Silberzan et al., Langmuir, 1991, 7, 1647-1651.