PHOSPHORIC-ACID AS AN ELECTROLYTE ADDITIVE FOR LEAD ACID BATTERIES INELECTRIC-VEHICLE APPLICATIONS/

The influence of the addition of phosphoric acid to the electrolyte on the performance of lied lead/acid electric-vehicle batteries is inves tigated. This additive reduces the reversible capacity decay of the po sitive electrode significantly which is observed upon extended cycling when recharge of the battery is performed at low initial rate. This i s important when low-rate on-board chargers are used. Pulsed discharge , typical for electric-vehicle application, induces reversible capacit y decay more than constant-current discharge at a same depth-of-discha rge, as well with as without the addition of phosphoric acid. By contr ast, hindrance in presence of H3PO4 for both the recharge and the disc harge reaction helps to homogenize the state of many individual cells during cycling in long battery strings. Reversible capacity loss, whic h occurs after extended cycling and when pulsed discharge is applied, can be recovered by a single discharge at very low rare with batteries with and without the addition of phosphoric acid. The discharge-rate dependency of the capacity is significantly reduced when phosphoric ac id is added. The pulse discharge behaviour may be better, even if the nominal capacity is reduced. The experimental findings of the influenc e of phosphoric acid addition is discussed in terms of the aggregate-o f-spheres model of reversible capacity decay. (C) 1997 Published by El sevier Science S.A.