The development of new additives to improve charge recovery of automotive (auxiliary) and industrial (energy storage) batteries represent a good opportunity for Lead battery innovation.
Car manufacturers are particularly concerned about the reliability of auxiliary batteries under partial state of charge (50%) and very low temperatures (-18ºC), whereas Energy Storage Systems (ESS) require very long cycle life to reduce the Total Cost of Energy Storage.
The latest draft of the international norm IEC 60095-8 includes new test procedures to measure Charge Recovery (CR) and State of Function (SoF) of auxiliary batteries. The most recently published data about both CR & SOF of different lead technologies (Standard Flooded, EFB & AGM) provide interesting and not always expected test results.
The presentation discusses several strategies to improve charge recovery and tries to define the role of additives in the positive (PAM) and negative (NAM) active materials.
PAM additives have been historically the subject of many investigations with a limited success up to now. The main reason behind is the instability of conductive materials (Carbon, Metals…) to the highly oxidative conditions in the positive plate. However, there are new materials (like Synthetic Graphite or Silica doped compounds) that are more corrosion resistant and may improve charge recovery by modifying the PAM microstructure.
NAM additives play a key role in charge recovery as they control the negative overpotential, allowing to increase the positive plate state of charge. Carbon (and potentially BaSO4) increase NAM surface area, whereas lignin reduces it. By increasing Carbon and BaSO4, while reducing lignin content in the expander composition, it is possible to improve charge recovery and thus cycle life. New types of additive materials can also be used to improve the recharge ability of Auxiliary and ESS batteries.