00/03426 SOFC technology development at Rolls-Royce

Abstract

In recent years, the valve-regulated lead-acid (VRLA) battery has been developed into a versatile and extremely reliable energy-storage device. When given a correctly specified battery design technology for the required product application, the VRLA battery will offer the end-user, some, if not all, of the following characteristics: high current capability; good reliability under cyclic, deep-discharge conditions (cycle life); good power density; high recharge efficiency; rapid rechargeability; resistant to overcharge; good charge stability (resistant to thermal runaway); no addition of water (topping-up) during service life (maintenance-free); long service life; wide operating temperature; robust design; low cost per Wh; high volumetric energy density (Wh/l); low self-discharge; high gravimetric energy density (Wh kg−1); may be stored and used in any position (orientation); resistant to shock and vibration; no need to be recharged immediately after discharge and environmentally ‘safe’. The most commonly used gelling agent, fumed silica, has many disadvantages such as, contamination of the local working environment, particularly during paste-mixing, and occupational hygiene and handling problems. It is also bulky to transport and has long gel times unless used at very high concentrations. There is, therefore, an increasing demand for an alternative gelling agent for sulfuric acid in the production of gelled-electrolyte (GEL) VRLA batteries. Silica sols can provide a solution to all of these problems, and moreover at a lower cost to the battery producer.