Multifunctional Polymeric Materials for High-Energy Lithium Ion Batteries

Abstract:
Lithium-ion (Li-ion) batteries adopted in electric vehicles (EVs) require significant increase in energy density (>750 Wh/L) and reduction of costs to enable widespread commercialization. To address these challenges, R&D efforts have been directed towards (a) finding materials with high energy density (b) improving electrode design and (c) enhancing conductivity of the electrode materials. The former strategy involves implementing Nickel and Manganese based chemistries such as NMC, LNMO. In particular, the LNMO spinel cathode material is a promising material which provides high energy densities of 650 Wh/kg due to increased operating voltage of 4.75 Vvs Li/Li+. However, the increased voltage also accelerates oxidative decomposition reactions in the electrolyte and causes capacity fade in LNMO full cells paired with graphite anode. Using a composite binder can help passivate the carbon and cathode material surfaces against decomposition products from the electrolyte. Further, the composite binder also has the advantage of using water as the solvent making the process environmentally benign and cheaper compared with currently adopted N-Methyl 2-Pyrrolidone (NMP) solvent. The second strategy includes minimizing the use of inactive materials (e.g., current collectors and separators) and increasing the thickness of electrodes (>250 µm), which in turn offers improved energy density with reduced cost. To achieve this an aqueous composite binder system is utilized which can sustain high thickness of electrodes while creating unique electrode architectures conducive to ionic and electronic conductivity. The third strategy utilizes a conductive polymer additive to create ion and electron conducting interfaces across the cathode material surface thereby providing better cycle and rate performance. The performance improvement in each of these strategies is demonstrated through electrochemical tests and their mechanisms are understood by utilizing several characterization techniques. A combination of one or more strategies can help achieve fully functional high energy density lithium-ion battery performance.

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Committee Members
Dr. Jung-Hyun Kim
Dr. Jay Sayre
Dr. Hanna Cho
Dr. Christopher Brooks