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Title:Self-healing strategies for lithium-ion battery anodes
Author(s):Kang, Sen
Director of Research:Sottos, Nancy R.
Doctoral Committee Chair(s):Sottos, Nancy R.
Doctoral Committee Member(s):White, Scott R.; Braun, Paul V.; Kilian, Kristopher A.
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
conductivity restoration
Li-ion batteries
Si composite anodes
electrical interfaces
carbon black functionalization
polydopamine coating
capsule stability
dynamic bonding
ionic bonding
Abstract:Thermal-mechanical failure of microelectronic devices often involves in the loss of conductivity of the metal traces and vias, which shortens the lifetime and requires replacement of the entire unit. High-capacity Si composite electrodes in lithium-ion batteries also suffer from the damage of electrical interfaces (particle/binder interfaces) during battery operation, leading to rapid capacity loss. In this dissertation, autonomous restoration of electrical conductivity upon damage is demonstrated in composite battery anodes and a simple electrical circuit via two different approaches. The first approach for conductivity restoration relies on the release of microencapsulated conductive particles to the fracture plane to reconstruct the damaged conductive pathways. In the second approach, dynamic ionic bonds are incorporated at the interface of polymer binder and Si nanoparticles in a composite battery electrode. Robust microcapsules are prepared with carbon black suspensions high in solids loading (up to 0.2 g/mL) for electrical conductivity restoration. Octadecyl groups are covalently functionalized on oxidized carbon black surfaces by two different synthetic routes. Functionalization significantly increases particle hydrophobicity, and improves dispersability and suspension stability in hydrophobic solvents such as o-dichlorobenzene (o-DCB), enabling encapsulation by in situ emulsion polymerization. Upon rupture, microcapsules containing functionalized carbon black (FCB) suspensions exhibit significant particle release relative to microcapsules filled with unfunctionalized carbon black. Two types of core thickeners, epoxy resin or poly 3-hexylthiophene (P3HT), are used to enhance particle release from microcapsules. Microcapsules containing FCB suspensions enable ex-situ conductivity restoration of damaged Si electrodes and an electric circuit. Rupturing of the microcapsules on the line crack of Si electrodes lead to the release of conductive FCB particles to the crack region and eventually full recovery (100 % restoration efficiency) of electrode conductivity. Similarly, partial conductivity restoration is achieved for a damaged electric circuit upon FCB release from microcapsules. A protective polydopamine (PDA) coating is applied to the microcapsule surfaces to enhance the capsule stability in battery electrolytes and other harsh environments. The polymerization of dopamine monomers is initiated by the addition of an oxidant (i.e. ammonium persulfate) in an aqueous solution of neutral pH. The resulting PDA coating is a dense and uniform layer (ca. 50 nm thick). The PDA protective coating significantly increases the capsule stability at elevated temperature (180 oC) as well as in a variety of organic solvents and acidic/basic solutions that otherwise lead to deflation and loss of core content of uncoated microcapsules. Most importantly, the PDA coated microcapsules show significantly reduced core loss in battery electrolyte over 60 days as compared to uncoated microcapsules. Intrinsic conductivity restoration relies on the reversible dissociation and formation of dynamic chemical bonds. Dynamic ionic bonds are incorporated at the interface of Si nanoparticles and polymer binders inside Si composite anodes. The presence of ionic bonds is confirmed by X-ray photoelectron and Raman spectroscopy. The dynamic ionic bonds effectively mitigate the large volume change of Si anodes during lithium intercalation. Si composite anodes with dynamic ionic bonding exhibit excellent cycling stability with a cycle life of 400 cycles and 80 % capacity retention at a current density of 2.1 mA/g.
Issue Date:2015-04-21
Rights Information:Copyright 2015 Sen Kang
Date Available in IDEALS:2015-07-22
Date Deposited:May 2015

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