THESIS
2017
xxvi, 129 pages : illustrations ; 30 cm
Abstract
Lithium-sulfur (Li-S) batteries that undergo a multi-electron chemical reaction has
shown great potential to boost the endurance mileage of next-generation electric vehicles
(EV). The reduction of sulfur, in the form of lithium polysulfides and lithium sulfide via a
multistep process of complex equilibrium states between long- and short-chain
polysulfides, can theoretically boost the energy density to 2600 W h kg
-1. However, the
intermediate product, liquid polysulfides, is highly soluble in ether-based liquid
electrolyte (LE), which corrodes the lithium metal anode. Suppression of lithium
polysulfides dissolution in LE and addressing lithium metal safety concerns are critical to
the commercialization of Li-S batteries.
To address these issues, we replace LE with a gel polyme...[
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Lithium-sulfur (Li-S) batteries that undergo a multi-electron chemical reaction has
shown great potential to boost the endurance mileage of next-generation electric vehicles
(EV). The reduction of sulfur, in the form of lithium polysulfides and lithium sulfide via a
multistep process of complex equilibrium states between long- and short-chain
polysulfides, can theoretically boost the energy density to 2600 W h kg
-1. However, the
intermediate product, liquid polysulfides, is highly soluble in ether-based liquid
electrolyte (LE), which corrodes the lithium metal anode. Suppression of lithium
polysulfides dissolution in LE and addressing lithium metal safety concerns are critical to
the commercialization of Li-S batteries.
To address these issues, we replace LE with a gel polymer electrolyte (GPE). While
traditional GPE typically exhibits low ionic conductivity and poor electrode/GPE
interface, we report a facile in-situ synthesis of pentaerythritol tetraacrylate
(PETEA)-based GPE with an extremely high ionic conductivity (1.13×10
−2 S cm
−1).
Installation of a bare sulfur cathode with low electrode/GPE interfacial resistance did not
sacrifice rate capacity or retention, resulting in rates of 601.2 mA h g
−1 at 1 C and 81.9%
after 400 cycles at 0.5 C, respectively. In order to eliminate the commercial separator, we
synthesize a freestanding acrylate-based hierarchical electrolyte (AHE). The structural
similarity and synergetic compatibility between the matrix and the inner framework allow
for the AHE to exhibit a desirable ester-rich robust structure.
To enhance the safety index of the battery, we further replace the lithium metal with
a stable SnO
2 anode to be assembled as a lithium-ion sulfur polymer battery (LISPB). We
demonstrate that graphene and carboxymethyl cellulose (CMC) are able to form a robust
anode structure and simultaneously maintain a stable SEI in ether-based electrolyte, while
the acrylate-based GPE immobilizes the polysulfides and protects the anodic SEI from side deposition reactions. Moreover, the proposed LISPB exhibits strong recovery against
over-charge, over-discharge and short-circuiting, showing great potential for practical
operation and suitable for energy conversion.
Keywords: Li-S battery; Li-ion sulfur battery; Li-polysulfide battery; gel polymer
electrolyte; hierarchical electrolyte; electrolyte additive; ester functional group;
non-lithium anode; anode protection; energy density; power density.
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