The Effect of V2O5 + TiO2 Composite Cathodes on the Cyclability and Specfific Capacity of Iron-ion Batteries
General Overview
The foundation of human society is energy production, consumption, and management. Without electricity and all the ways we produce/store it, the world would not be able to run at the pace it does today; computers, lights, and transportation would grind to a halt without our impressive energy. However, we are dependent on fossil fuels to produce this energy, which generates carbon dioxide that contributes to global warming. The effects are evident right now, especially with the Australian wildfires, California droughts, and Hurricanes Irma and Maria having been intensified by global warming. Renewable energies are growing cheaper and more efficient, which holds promise in reducing CO2 emissions, but power output varies wildly with the weather, requiring massive battery banks to stabilize overproduction and underproduction. Additionally, electric vehicles, another way to reduce carbon dioxide emissions, still face the problem of high cost and low range. Iron-ion batteries, or FIBs, can solve both of these issues, and it holds many advantages over other batteries currently available. Developed by researches in India during the summer of 2019, it is more energy-dense than lithium-ion batteries, costs far less with significantly more available materials, and does not carry the risk of explosion. However, it cannot be commercialized at the moment due to the fact that charge retention decreases precipitously after repeated charge and discharge.
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With these problems in mind, the purpose of this research was to improve the performance of FIBs by applying varying ratios of vanadium to titanium in the cathode. In vanadium pentoxide cathodes alone, iron ions become lodged in the crystal lattice, and the addition of titanium dioxide into the lattice both increases the interlayer spacing of the crystal structure and promotes the formation of only one specific type of iron ion, Fe2+, by preferentially reducing from Ti4+ to Ti3+ only. Too much titanium can negatively impact recharge ability, so the aim of this research was to find the ratio of titanium to vanadium that led to the highest specific capacity (charge held per unit weight) and lowest rate of charge loss.
Left: Diagram of an iron-ion battery. Iron ions intercalate into V2O5 during discharge.
Center: Example crystal structure of a V2O5 + TiO2 cathode with intercalated Fe2+ ions.
Right: The desired intercalation equation on top and unwanted conversion below.
Intercalation:
Conversion:
Battery cases were 3D-printed to accommodate 2cm x 3cm iron strips and carbon cloth, which were the anode and cathode during discharge, respectively. Iron and carbon cloth strips were cut accordingly, with the carbon cloth specifically undergoing an electrodeposition procedure to deposit V2O5 and TiO2 in ratios of 1:0, 1:1, 2:1, and 0:1 V:Ti, respectively. These batteries were discharged for 10 minutes, with voltage and current measured. They were then recharged using 1.5 V AA batteries and discharged four more times, with specific capacity (amp-hours per gram anode mass) calculated for each round. What unfortunately occurred, however, was that currents and voltages for almost all experimental groups were essentially zero, leading to specific capacities that were also zero. The only exception was the 2:1 V:Ti group with an average specific capacity of -4.38E-5 Ah/g, which is not only incredibly small but also doesn't make sense, as batteries cannot store negative energy, and current should not be flowing in the opposite direction. The reason these results occurred was because of electrodeposition failing to deposit sufficient quantities of V2O5 and TiO2 from solution. Small amounts of red-orange material were observed on the carbon cloth, indicating V2O5 deposition, but at only a few hundredths of a gram additional mass, this was not enough material to support intercalation, leading to no effective discharge. Because of this, recharge of the batteries was not attempted, as no discharge occurred in the first place.
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Unfortunately, a conclusion cannot be made about which ratio of vanadium to titanium in the cathode best improves FIB performance. It can, however, be deduced that electrodeposition is not the method to use for cathode synthesis. A second round of investigation using sol-gel electrophoresis, which uses V2O5 and TiO2 nanoparticles in solution, was proposed as another synthesis method that does not require chemical reactions per se, but due to the COVID-19 pandemic, this process could not be executed. Despite the setback, FIBs hold significant potential as a competitor against lithium-ion batteries, being cheaper, safer, environmentally friendly, and more powerful, and as this novel technology is further developed, stable renewable energy grids and the electrification of transportation will become a reality, helping to create a greener, healthier, cooler world.
Presentation of the poster board at IJAS regionals, 2020.
The posterboard without any distractions.
An example of an unwanted reaction that occurred during electrodeposition, where the alligator clip corroded and contaminated the carbon cloth.
Presentation of the poster board at IJAS regionals, 2020.