Effect of ion distribution on conductivity of block copolymer electrolytes.
Energy-filtered transmission electron microscopy (EFTEM) was used to determine the distribution of lithium ions in solid polymer electrolytes for lithium batteries. The electrolytes of interest are mixtures of bis(trifluoromethane)sulfonimide lithium salt and symmetric poly(styrene-block-ethylene oxide) copolymers (SEO). In contrast to current solid and liquid electrolytes, the conductivity of SEO/salt mixtures increases with increasing molecular weight of the copolymers. EFTEM results show that the salt is increasingly localized in the middle of the poly(ethylene oxide) (PEO) lamellae as the molecular weight of the copolymers is increased. Calculations of the inhomogeneous local stress field in block copolymer microdomains, modeled using self-consistent field theory, provide a quantitative explanation for this observation. These stresses, which increase with increasing molecular weight, interfere with the ability of PEO chains to coordinate with lithium cations near the walls of the PEO channels where ion mobility is expected to be low.
Gomez
Enrique D
ED
Department of Chemical Engineering, University of California, Berkeley, California 94720, USA.
Panday
Ashoutosh
A
Feng
Edward H
EH
Chen
Vincent
V
Stone
Gregory M
GM
Minor
Andrew M
AM
Kisielowski
Christian
C
Downing
Kenneth H
KH
Borodin
Oleg
O
Smith
Grant D
GD
Balsara
Nitash P
NP
D000465:Algorithms; D002412:Cations; D004553:Electric Conductivity; D004573:Electrolytes; D007477:Ions; D008094:Lithium / Q000737:chemistry; D046529:Microscopy, Electron, Transmission; D008956:Models, Chemical; D008970:Molecular Weight; D036103:Nanotechnology / Q000379:methods*; D011092:Polyethylene Glycols / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*
D002412:Cations; D004573:Electrolytes; D007477:Ions; D011108:Polymers; D011092:Polyethylene Glycols; D008094:Lithium