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Dissertation-Xiaodi Ren.pdf (7.48 MB)

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Rechargeable Potassium-Oxygen Battery for Low-Cost High-Efficiency Energy Storage

Ren, Xiaodi, Ren
http://orcid.org/0000-0002-2025-7554
http://rave.ohiolink.edu/etdc/view?acc_num=osu1468857236

Abstract Details

2016, Doctor of Philosophy, Ohio State University, Chemistry.
Due to the lack of efficient energy storage methods, the entire electricity infrastructure has to be designed for the peak load and therefore is being underused most of the time. Meanwhile, the implementation of renewable energies (e.g. solar, wind) is largely being hurdled by their intermittency. Therefore, batteries are widely regarded as the solution to the problem by storing excess or inconstant electricity and using it during peak times. Among various battery chemistry, lithium-oxygen battery was identified as one of the most promising solutions due to its simple design and high energy density (potentially 10 times higher than Li-ion). However, the difficulty of charging the battery causes a low energy efficiency of 60% and poor cycle life. This dissertation is focusing on solving the issues of Li-O2 batteries and developing new low-cost, high efficiency energy storage solutions. In order to avoid the formation of lithium peroxide (Li2O2) as the discharge product, a potassium anode was used to replace the Li anode. With a larger ionic radius, K+ could stabilize the generated superoxide ions (O2-) during discharge to form KO2. The superior reversibility of the single electron redox couple O2/KO2 greatly decreases the charging overpotential, improving the round-trip efficiency up to 98% without using electrocatalysts. Based on analysis, the cost of K-O2 batteries was estimated to be only $89/kWh, which is about ¼ of Li-ion batteries. However, the cyclability of K-O2 batteries was found to be limited by the decay of the K anode. The overgrowth of the anode surface layer not only causes the huge increase of battery internal resistance, but also results in the depletion of both the anode and the electrolyte. In order to understand the reason for the anode decay, the anode surface layer composition was both qualitatively and quantitatively studied. Based on this result and theoretical calculations, the anode side reaction mechanism was proposed, which shows that the O2 crossover to the anode is the main reason. It was also found out that the electrolyte decomposition on the anode is greatly accelerated by the coupling between the electron transfer process to O2 and the subsequent O2- attack. Different electrolytes (solvents, salts and additives) were studied to improve the K-O2 battery performance. The compatibility of the electrolyte with both the K anode and KO2 in the cathode was found to be critical for K-O2 batteries. It is confirmed that a stable anode interface is necessary for stabilizing the reactive K anode. A solvent- and O2-impermeable protection layer was in-situ formed on K anode surface when using potassium bis(trifluoromethanesulfonyl)imide (KTFSI) salt in ether electrolyte. The excellent protection ability of this interfacial layer greatly enhanced the K anode stability, enablingvery stable cycling over 700 hours even under pressurized O2 environment (2 atm). In order to suppress the influence of O2 crossover on the K anode, O2-blocking membrane separators were employed in K-O2 batteries. A K+ exhanged Nafion membrane separator was able to increase the battery cycle life apparently. A polymer composite membrane with a defined lamellar structure was fabricated using the layer-by-layer (LBL) method. Single layer graphene oxide (GO) sheets were arranged within the membrane planner surface, acting as O2-blocking layers. Although with a thickness of 1/10 of the Nafion membrane, the LBL membrane has one half the O2 permeation rate of that of Nafion and has a resistance 70 times lower than Nafion. Apart from K metal anode, an alternative K ion anode was studied for future safety concerns. The layered hexagonal MoS2 was found to be an excellent K+ storage material. The intercalation of K+ results in the formation of hexagonal K0.4MoS2 with a capacity around 70 mAh/g. The layer structure of MoS2 is proved to have superior cycling stability for K+ storage, with very high capacity retention over 200 cycles.
Yiying Wu (Advisor)
Patrick Woodward (Committee Member)
Anne Co (Committee Member)
187 p.
Chemistry
Battery; energy storage; metal-air battery; metal-O2 battery; superoxide; electrolyte; membrane; anode protection

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Citations

  • Ren, Ren, X. (2016). Rechargeable Potassium-Oxygen Battery for Low-Cost High-Efficiency Energy Storage [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1468857236

    APA Style (7th edition)

  • Ren, Ren, Xiaodi. Rechargeable Potassium-Oxygen Battery for Low-Cost High-Efficiency Energy Storage. 2016. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1468857236.

    MLA Style (8th edition)

  • Ren, Ren, Xiaodi. "Rechargeable Potassium-Oxygen Battery for Low-Cost High-Efficiency Energy Storage." Doctoral dissertation, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1468857236

    Chicago Manual of Style (17th edition)

osu1468857236
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This open access ETD is published by The Ohio State University and OhioLINK.