Design of Interfacial Layers for Energy Generation and Energy Storage Applications

Abstract

Surface modification is important and useful technique for changing the original properties of materials, including shape, thermal, electrical and plasmonic characteristics. In general, material characteristics, like hygroscopic, thermal stability, hydrophilic, hydrophobic, durability and chemical stability, can be significantly enhanced by surface modification using polymers, metallic and ceramic compounds. Also, the suitable design of material surface can be used as various application tools according to the purpose of application target. Solid oxide fuel cells (SOFCs) are promising energy generation devices which are efficient and environment friendly with no combustion. Furthermore, SOFCs can be designed with appropriate size to adapt various applications for generation of electricity from personal to industrial usage. Currently, hydrogen gas has been used as a fuel to anode side for normal SOFC operation. However, pure hydrogen is not competitive with price, because refinement of H2 gas from the air is very difficult and very expensive process. Meanwhile, hydrogen-containing gases, such as hydro-sulfide (H2S) and hydro-carbon (CH4, C2H6, C3H8), produce millions-of-tons as by-products in industries, so that many by-product gases can be used as a fuel with reasonable price rather than pure hydrogen. However, one of the big challenges still remains for practical usage on SOFCs with these by-product gases. The conventional anode materials of SOFC (i.e., Ni, Pt, and Ag) have high reactivity with carbon and sulfur species, resulting in instant degeneration of anode material during the operation. Therefore, alternative materials to conventional anode materials and/or catalysts which can protect from damaging source have been explored to improve tolerance of carbon coking and sulfur poisoning for stable operation of SOFCs. In addition to SOFCs, lithium ion batteries (LIBs) is useful energy storage devices for storing unused electrical power or for operating mobile electrical devices, such as cell phones, laptops and electric vehicles, due to their high power and high energy density. However, to meet the requirement of energy level and the longer operation of recent developed electrical equipment (i.e., electric-vehicles and robots), LIB technology should be boosted up with high specific energy, high energy density and longer life time. Recently, anode and cathode materials have been explored by many scientists to replace conventional graphite (anode) and lithium cobalt oxide (LCO, cathode). Currently, graphite has been used as an anode material in commercialized LIBs. Graphite shows stable electrochemical behaviors when lithium ions are intercalated and deintercalated between graphitic layers. However, limited specific capacity (ideally 375 mAh/g with a form of LiC6) is critical problem to use in high energy density LIBs. Among lithium hosting materials, silicon (Si) is one of the best candidates due to its abundant, cheap, low reaction potential window (<0.4V versus Li/Li+) and high theoretical capacity (4200 mAh/g with a form of Li4.4Si at high temperature). However, Si has a severe volume expansion of >300% when lithium ions inserted to metal alloying materials. Numerous works have been reported that the severe volume expansion leads to cracking of own Si structure, serious growth of solid-electrolyte-interface (SEI) layer, detachment of active materials from current collector, and a serious capacity drop. To overcome these critical problems, effective strategies including reduction of Si size, surface modification of Si, and nanostructuring of Si have been reported. Herein, we demonstrate novel designs which various surface modifications are applied to Ni- and Si-based materials. First, barium oxide nanorings combined with block copolymer patterning are generated on Ni substrate to enhance carbon coking resistance for SOFCs. Second, metal and metal silicide coated micro sized porous Si structure via metal assisted wet chemical etching process used as an anode material in LIBs. Third, aluminum trifluoride (AlF3) coated Si nanoparticles with facile synthetic routes are designed and used as an anode material in LIBs for high temperature operation. Fourth, barium titanium oxide (BaTiO3) coated Si nanoparticles are tested as an anode material in LIBs for long-term stability at high temperature operation. These surface modification tools can be applied to another electrodes material as an artificial protection layers and catalyst from severe undesirable side reactions.