Organic radical polymers [1] and conjugated polymers provide exceptionally high rate capability when used as cathode materials for lithium-ion batteries.  Upon charge (oxidation), these materials absorb anions from the electrolyte.  In contrast, traditional inorganic cathode materials release lithium cations into the electrolyte during charge.  All known negative electrode materials for lithium-ion batteries absorb lithium cations during charge.  If a lithium-absorbing negative electrode is paired with a lithium-releasing positive electrode, then there is no net change in the salt content of the electrolyte (although there will be gradients in salt composition as lithium ions are transported from the anode to the cathode).  However, salt content will decrease during charge of a cell with lithium-absorbing negative electrode and anion-absorbing positive electrode. 

Most experimental results published to date [1] have used thin, highly porous cathodes in small flooded laboratory cells.  Such cells have a large excess of electrolyte, so the effects of salt consumption have not been strongly evident.  However, many important applications, such as electric vehicles and portable power, highly value both volumetric energy density and fast charge capability.  These applications also want to minimize cell resistance, so the electrolyte composition is selected to maximize conductivity.  Typical carbonate electrolytes show a maximum in conductivity between 1.0 and 1.1 M concentration of LiPF₆ salt.   In a conventional high-energy-density cell design, the salt needed for charging the organic-radical-polymer positive electrode would exceed the total salt content of such a typical electrolyte in the cell.  Some [2,3] have explored composites of anion-absorbing active materials (eg polypyrrole or PTMA) with lithium-iron phosphate.  However, even if the anion-absorbing material is limited to 10 volume% of the positive electrode, it will cause the overall cell salt content to decrease by > 0.6 M in practical high-energy cell designs. 

Full-cell-sandwich simulations [4] can evaluate the impact of electrode design on the salt concentration distribution in the battery.  Here we use a model that includes a composite positive electrode containing both inorganic lithium-releasing active material and organic anion-absorbing active material.  The model is used to evaluate design tradeoffs for maximizing volumetric energy density.

References

[1] K. Oyaizu and H. Nishide, Polyradicals in Batteries.  Encyclopedia of Radicals in Chemistry, Biology, and Materials, John Wiley & Sons Ltd: 2012, DOI 10.1002/9780470971253.rad083.

[2] A. Vlad, N. Singh, J. Rolland, S. Melinte, P. M. Ajayan, and J. F. Gohy, Scientific Reports 2014, DOI 10.1038/srep04315.

[3] Y.H. Huang and J. B. Goodenough, Chem. Mater. 2008, vol. 20#23 p. 7237.

[4] T. Fuller, C. M. Doyle, and J. Newman, J. Electrochem. Soc. 1994 vol. 141 p. 1; K. E. Thomas-Alyea, J. Newman, G. Chen, and T. J. Richardson, J. Electrochem. Soc. 2004 vol. 151 p. A509.