We propose trapping of Mn cations by polymeric crown ethers as a mitigation measure for the consequences of Mn dissolution in Li-ion batteries (LIBs). Mn cations trapping by poly(vinylbenzo-18-crown-6) and poly(undecylenyloxymethyl-18-crown-6) was investigated for 1M LiPF6 solutions in binary carbonates containing Mn(11) salts and in lithium manganese oxide (LMO) spinel - graphite (GR) cells. Trapping site occupancies by Mn+2 exceeding 90% were measured in bench top experiments. Polyethylene separators coated with poly(vinylbenzo-18-crown-6) trapped Mn cations in LMO - OR cells and decreased capacity fade during 100 cycles at high temperature (60 degrees C) and C/4 rate, retaining 26% more capacity than the baseline cells. We also address the important distinction between using free (molecular) vs. tethered (polymeric) macrocycles, and its consequences for LIB performance. (C) 2014 The Electrochemical Society. All rights reserved.