Goodenough perspective on Li-ion batteries; in transportation, PHEVs for the near-term, longer term requires new electrochemical strategies
Dr. John Goodenough at the University of Texas at Austin and colleague Kyu-Sung Park have written a perspective paper on Li-ion batteries (LIBs), published in the Journal of the American Chemical Society. Dr. Goodenough invented lithium cobalt oxide cathode materials while at Oxford University; his technology was used in the first commercial Li-ion battery, launched by Sony in 1991. More recently, at the University of Texas, Austin, Dr. Goodenough patented a new class of iron phosphate materials. (Earlier post.)
The paper covers the basics of the electrochemistry of LIBs and the development of new materials and electrolytes in the search for higher capacities; it also addresses the challenge of energy storage in transportation applications with the target of displacing the internal combustion engine.
Achieving—or approaching—that outcome will require new strategies such as using electrode hosts with two-electron redox centers; replacing the cathode hosts by materials that undergo displacement reactions (e.g. sulfur) by liquid cathodes that may contain flow-through redox molecules, or by catalysts for air cathodes; and developing a Li+ solid electrolyte separator membrane that allows an organic and aqueous liquid electrolyte on the anode and cathode sides, respectively, the authors said. “Opportunities exist for the chemist to bring together oxide and polymer or graphene chemistry in imaginative morphologies.”
...a LIB using solid rechargeable electrodes is capable of a long cycle life at acceptable rates of charge/discharge, but the energy density of individual cells, even with a 4 V cell, makes difficult the manufacture of a cost-competitive battery of sufficient energy density to displace the internal combustion engine of an automobile with long driving range between rapid and convenient liquid-fuel refills.
A first step will be plug-in hybrids [PHEVs] used for daily commuting. This interim solution would offer a distributed store of electrical energy that can spread the cost of storing off-peak power in a rechargeable battery. Stationary storage of electrical energy from alternative energy sources (wind, solar, nuclear) calls for larger capacities than can be realized with an oxide-host cathode, but the energy density requirement of a mobile battery is relaxed. However, cost is a constraint that has made difficult even replacement of lead-acid batteries with the 2 V Li[Li1/3Ti5/3]O4/LiFePO4 cell. These challenges are calling for consideration of alternative strategies for storage of electrical energy in an electrochemical cell.
...Realization of this situation has led to consideration of either multiple-electron redox couples and/or multivalent working ions such as Mg2+ in place of Li+. This shift of emphasis leads inevitably to the electrolyte, catalysts, and organic multiple-electron redox centers. We have emphasized here the potential of a Li+ electrolyte membrane separating two different liquid electrolytes, a material that will require a composite of a polymer and an inorganic Li+ electrolyte. We have not commented on efforts to introduce 3D current collectors that enable thicker electrodes and flow-through liquid cathodes, an effort that has particular relevance for electrochemical capacitors of higher energy density. We have also not commented on efforts to develop a Na-ion battery to eliminate vulnerability to sources of lithium and to lower material costs. This effort is more challenging because the larger Na+ ion is adequately mobile only in framework oxides with a larger interstitial volume than is available in a close-packed oxide-ion array.—Goodenough and Park
John B. Goodenough and Kyu-Sung Park (2013) The Li-Ion Rechargeable Battery: A Perspective. Journal of the American Chemical Society doi: 10.1021/ja3091438