Capstone – Electric Vehicle Battery
Zainab Alghazal, Karly Joe, Phuong Quang, Xiaorong Zhang
Preliminary Report
Although fossil fuels continue to dominate the market, the inevitability of their decline has led to innovation of alternative technology to operate vehicles. The first electric vehicles were invented in the late 1800s; however, serious, successful development did not occur until the 21st century. Since then, many companies have made efforts in creating vehicles powered by batteries. Regardless of these efforts, improvements still must be made to increase the mile range per charge on the vehicle in order for the electric vehicle to be a serious competitor to the gas fueled vehicle. The purpose of this Capstone project is to design such a battery to operate an electric vehicle at increased distances, considering usable materials, packaging, safety, cost, and lifetime expectancy.
Several companies have produced electric vehicles as of 2016. Makers such as Mitsubishi, Ford, Chevrolet, and Nissan sell the more affordable cars, ranging on average from $25,000 to $35,000. These cars, while comparable in price to their gas-guzzling counterparts, cannot even drive 100 miles on a full charge before needing to be recharged. On the other end of the spectrum, the top-performing electric vehicle, the Tesla Model S, costs up to $106,000 but can drive around 250 miles on a single full charge.1 For this project, however, the driver commutes every day to Oklahoma City from Norman and back, a total of 50 miles a day and 300 miles a week, preferably on a single charge. The battery averaging 300 miles per charge (MPC) will be designed by incorporating elements of these current electric vehicles with new innovative technologies.
The process for designing this battery begins with deciding on what materials to use. Factors such as high energy density, capacity, safety, cost, and lifetime of the materials will help decide which cathode, anode, and electrolyte to use. After the materials are chosen, it must be decided how to package the battery and where to place in on the vehicle. The shape, cost, and weight are factors to consider when determining this. The safety issues will then be investigated, ensuring any problems that present themselves can be combated and resolved. Cost must then be evaluated for the entire project, including materials used for the battery as well as the packaging. The lifetime of the battery is then estimated, giving it an overall stamp of approval. While the safety, cost, and lifetime factors are originally considered with materials and packaging, they will further be developed and discussed later on in the project.
The first step of the project began with research of the battery and its function. The battery was then broken down into the three key components that would need further study: the cathode, anode, and electrolyte. Beginning with the cathode, it was known that the material chosen must have a high energy density, which would allow it to store a greater amount of energy per unit volume or mass. Research of current electric vehicles gave insight for a better idea of which cathodes to consider. Among the most popular ions used include: cobalt, iron phosphate, titanate oxide, manganese oxide, and titanate phosphate.2 Each lithium-ion combination presents several advantages and disadvantages as to how they would perform in a car battery. The book Lithium Batteries and Other Electrochemical Storage Systems by Glaize and Genies proves to be a valuable reference for these statistics and more. In terms of cost and safety, the lithium-ion batteries containing titanate oxide, manganese oxide, and titanate phosphate have shown to be the safest and cheapest options; however, they all operate with low energy densities and capacities, ruling them out as options for this project.2 Due to both the cobalt oxide and the iron phosphate ions’ high energy density, the deciding factors were then weighed to determine which would be the overall best fit to accomplish the task. The disadvantages of a Lithium Cobalt Oxide (LCO) come from the expensiveness and toxicity of the metal, as well as the fact that it is unstable at high temperatures when only low amounts of lithium are present. This puts the battery at significant risks for fire and explosions.2 These problems however can be fixed by incorporating other metals into the mix, such as aluminum, nickel, and manganese, reducing the amount of cobalt in the ion. For this reason, the high energy density and capacity of the LCO outweigh the problems that come with it. This decision to use a lithium-cobalt-oxide-mixture as the cathode for the battery coincides with many electric vehicles’ batteries in today’s market.
Typically, the anode of the battery would consist of carbon graphite sheets that store lithium ions between layers. A goal in designing an effective anode is to use less anode material if possible, leaving extra space to have more cathode material. This would effectively increase the overall energy and capacity within the same volume of the battery. If silicon were used as the anode, it would be able to absorb more lithium ions and have a higher theoretical specific capacity than graphite, but at a cost.3 Through charging and discharging, the silicon particles repeatedly expand and contract in large volumetric fluctuations, inevitably reducing the cycle life of the anode much quicker. For this reason, engineers at Tesla have decided to keep a primarily graphite anode but slowly begin incorporating silicon into it.4 That is the inspiration for the structure of the anode for the project’s battery: graphite sheets with small amounts of silicon in between the layers, taking advantage of both materials as assets. This will reduce the volume slightly while increasing the energy capacity, without causing damage to the battery and its integrity.
Once the cathode and anode were chosen, an electrolyte to go between the two needed to be determined. Two considerations were the nanostructured polymer electrolyte (NPE) and molten chloroaluminate sodium (NaAlCl4), often referred to as “hot salt.” This salt has a reasonable energy density and lifetime; however, it falters in the fact that it must be heated to use, which wastes energy and causes problems in terms of long-term charge storage.5 The NPE, on the other hand, has a high energy density, compatible with a battery for an electric vehicle. Researchers at the Lawrence Berkeley National Laboratory claim that when “used with high-performance electrode materials, it may achieve even high specific energy suitable for powering zero-emission electric vehicles.1 Its initial roughening on its borders provide for a greater lifetime, but may grow into dendrite upon further use. In comparison between these two electrolytes, there seems to be no debate that the electrolyte used in this project is the nanostructured polymer.
Outlining these materials to be used in this Capstone project provides a great start to the development of the electric vehicle battery to be designed. Through further research and progress, constructing a battery to last 300 miles on a single charge will be obtained.
References
[1] S. Edelstein. “Electric Car Price Guide: Every 2015-2016 Plug-In Car With Specs: UPDATED.” Green Car Reports: 27 January 2016. http://www.greencarreports.com/news/1080871_electric-car-price-guide-every-2015-2016-plug-in-car-with-specs-updated
[2] C. Glaize and S. Genies. Lithium Batteries and Other Electrochemical Storage Systems. Wiley-ISTE: 22 July 2013.
[3] C. Ruoff. “Paraclete Energy says its low-cost silicon nanoparticles can at least double your current anode capacity.” Charged, Electric Vehicles Magazine: 6 Jan. 2016. https://chargedevs.com/features/paraclete-energy-says-its-low-cost-silicon-nanoparticles-can-at-least-double-your-current-anode-capacity/
[4] C. Ruoff. “Telsa tweaks its battery chemistry: a closer look at silicon anode development.” Charged, Electric Vehicles Magazine: 23 Sept. 2015. https://chargedevs.com/features/tesla-tweaks-its-battery-chemistry-a-closer-look-at-silicon-anode-development/
[5] “Berkeley Lab’s Solid Electrolyte May Usher in a New Generation of Rechargeable Lithium Batteries for Vehicles.” http://ipo.lbl.gov/seeo/
[6] N. Balsara, H. Eltouni, and M. Singh. “Nanostructured Polymer Electrolyte.” U.S. Department of Energy: Lawrence Berkeley National Laboratory. https://gaia.lbl.gov/people/mwbeck/public/EERE_Posters/EERE%20Posters/Poster_1.pdf
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