Among underwater applications lithium/water systems are the most attractive from the point of view of energy density. Lithium is generally considered to be too reactive, and evolves hydrogen as a parasitic reaction, but exhibits a very negative OCP (-3 VSCE). We have extensively studied the lithium/water system and have found that lithium in alkaline electrolytes forms a bilayer passive film (LiH and LiOH) at the metal/electrolyte interface. LiH forms as a thin, compact inner layer that forms on the surface of the lithium metal. The outer layer is a porous precipitated LiOH layer that forms on the LiH layer. The outer layer is found to regulate lithium dissolution. However, the passive film does not completely inhibit hydrogen evolution, leading to poor coulombic efficiency during discharge. We propose to substitute the naturally created passive layer with a cationically conducting polymer membrane, which is placed on the lithium surface. The role of the membrane is to suppress the hydrogen evolution while permitting lithium discharge. Our initial experiments performed with polyphosphazene membranes have been encouraging, but they point to a need to more carefully design the polymer in terms of the balance between hydrophilic and hydrophobic properties. We believe that the extraordinary energy densities that are available with lithium, together with the fact that metal/water batteries can be mechanically (and hence rapidly) refuelled, renders them ideal for a wide range of stationary power applications in both domestic and military service.
Benefit: New generation of primary batteries for underwater applications. They will offer a simple design, high energy and power densities, zero-emission, and safety storage and operation.
Keywords: Energy, Energy, Applications, Underwater, Batteries, Primary, High, density, lithium
