Battery-powered electric vehicles (EV’S) are likely to become increasingly common in the next 50 years because of growing concern over pollution caused by vehicles using combustion engines. The reason for the current meagre commercial success of EV’s is that the battery specifications must have a performance and cost profile comparable to conventionally powered vehicles.Lead acid batteries are extensively used as portable power sources for vehicles and traction. A lead acid battery capable of efficient recharging has an energy density of 40 wh./kg.In the current evolution of EV batteries, the most promising long term solution is the rechargeable light weight lithium ion battery. Such batteries are under intensive investigation worldwide and hold also promise for the storage of electricity from solar cells. Their weight is 1/3rd of a lead-acid battery. It has a high specific capacity and electrode potential. A common positive electrode material is the environmentally benign spinel type LiMn2O4. The spinel structure comprises. A matrix of cube close packed oxide ions, stabilized by lithium ions in tetrahedral sites and manganese ions in octahedral sites. In LiMn2O4 half of the manganese ions has an oxidation state +3 and half the oxidation state +4. The lead acid battery represented by

Pb (s) | PbSO4(s) | H2SO4 (aq) | PbSO4 (s) | PbO2(s) | Pb(s)

A lithium battery is represented by

Li (s) | Li+ - conducting (solid) electrolyte (s) | LiMn2O4(s)

upon discharge the insertion product Li2Mn2O4 is formed. Charging the battery leads to the products Li (s) & LiMn2O4.

(i) What is the discharge reaction of the lead storage battery ?