Transition Metal Dissolution and Anode Cross Talk in High Voltage Formats
High-voltage cathode metal leaching drives anode cross-talk, destroying SEI layers and causing cell swelling that invalidates warranty and shipping files.
Crown Ether Separator
Meaning
Porous battery membranes containing macrocyclic polyethers can actively capture detrimental transition metal ions while permitting the passage of lithium ions. A crown ether separator employs specific cavity sizes within its embedded ring molecules to bind ions such as manganese or cobalt by size-exclusion and coordination. This functionalization prevents transition metals from crossing the membrane to degrade the anode.
Ion Transport
Selectivity is achieved because the cavity of the macrocycle matches the ionic radius of the target metal but remains poorly suited to accommodate the smaller lithium ion. Incorporating these functional separators into lithium-ion cells ensures that the metal crossover does not damage the solid electrolyte interphase. Lithium ions are thus free to migrate during charging and discharging, while the transition metals are trapped within the separator matrix.
Membrane Synthesis
Polymer membranes can be coated with crown ether molecules or have them copolymerized directly into the polyolefin backbone. This chemical modification is designed to remain stable under the high electrochemical potentials of the cell and does not compromise the overall porosity of the sheet. The modification process must ensure that the crown ethers do not leach out into the liquid electrolyte during operation.
Cell Performance
Preserving the graphite anode from metal poisoning results in improved capacity retention.