Lead/acid batteries all use the same basic chemistry. The positive plate is comprised of lead dioxide and the negative of finely divided lead. Both of these active materials react with the sulphuric acid electrolyte to form lead sulphate on discharge and the reactions are reversed on recharge. Batteries are constructed with lead grids to support the active material and individual cells are connected to produce a battery in a plastic case. There are, however, major differences in battery construction depending on the duty cycle and application.
Chemical reactions
Charging
Total material conversion: 2 PbSO4 + 2 H2O
2 H2SO4 + PbO2 + Pb
Discharging
Total material conversion: 2 H2SO4 + PbO2 + Pb
2 PbSO4 + 2 H2O
Energy density
Typically 33 Wh / kg
Components of lead acid batteries
Electrolyte: Sulfuric acid, ca. 35 - 40 %
Positive & negative active mass based on lead sulphate
Grids carrying the active mass
Recovery of materials
Active mass, grids, other lead parts 100 % recyclability,
acid, plastic parts partly recyclable
Valve-regulated lead acid batteries (VRLA)
Features
Definition: Secondary battery in which cells are closed but have a valve that allows the escape of gas if the internal pressure exceeds a predetermined value
Starved electrolyte either on Glass fibers (AGM, Absorptive Glass Mat) or as a Gel (Gel technology)
Starved electrolyte allows internal gas circulation
Water loss by overcharge reduced to less than 10 % by recombination
Installation mode: Free orientation and no leakages because of absence of liquids
Maintenance free: Especially advantageous in remote area installations
Typical applications
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Features
Definition: Secondary cell having a cover provided with an opening through which products of electrolysis and evaporation are allowed to escape freely from the cells.
Liquid electrolyte
Battery closed with vent plug, gassing rate more than 4 times higher than valve regulated
Water loss by electrolysis during overcharge: Hydrogen + Oxygen gassing
Well established technology: Economical production
Maintenance of water refill depends on design features and application (reduction of refill by recombination plugs or custom refilling systems)
State of charge and age can be checked very easily
Typical applications
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