Lead acid Battery improvement using graphene derivatives

The Lead acid battery is the oldest rechargeable battery with over 150 years of history. However, the conventional battery technology is facing several challenges and there is a great need to modify this technology to meet the current energy need. Lead acid batteries continue to be one of the most widely used rechargeable batteries with around 70% of battery market share worldwide. They have a relatively short life cycle (~500 cycles) and must be replaced frequently resulting in increased replacement costs.

Whether in hybrid electric vehicles (HEV) or in SLI systems, the battery should be operated continuously in partial-state-of-charge (PSoC). It experiences high charge and discharge process under High-Rate-Partial-State-of-Charge (HRPSoC) cycling duty, when the vehicle braking is heavy.

Lead-acid batteries designed for starting automotive engines are not able to sustain deep discharge. Repeated deep discharge will result in capacity loss and ultimately in premature failure of the battery. This occur due to disintegration of electrodes under continuous mechanical stress, arising from cycling process. Low acid concentration limits the plate activation, promotes corrosion and reduces performance. High acid concentration, on the other hand, raises the open circuit voltage and the battery appears fully charged but provides a low CCA.

Research in lead-acid batteries is of great interest in developing countries like India and China due to their low manufacturing cost, high material abundance, low temperature performance, low self-discharge rate, easy recycling and higher safety. One of the major limitation of lead-acid battery is its limited cycle life due to sulfation that is caused by the crystallization of non-conductive lead sulfate (PbSO4) crystals, which gradually decreases the amount of usable active material.

The research at Log 9 Materials have shown a major improvement in Lead-Acid battery. The research is being done with a lead acid battery having 6 cells with nominal cell voltage of 2.1 V per cell, making the overall voltage of 12 V. Such 12 V batteries are commonly used in automobiles. Initial formulations prepared and tested at Log 9 have shown that with an addition of graphene derivatives, the energy density of battery show an increment up to 30% and the power density show an increment up to 30 – 35 %. Also, the partial state of charge (PSoC) cycle life improved by 1.3 times as compared to commercially available lead acid batteries. Further optimization of graphene and its derivatives can be done and it is expected that the battery can be further modified to show an increment up to 50% in power density (Confidential Report. All Rights Reserved. ©Log 9 Materials, 2017) and an increase up to 1.5 times or more, in cycle life. Another advantage of incorporating graphene is that there is no need of changing the basic structure of battery and only modification in composition is required. Application of graphene and its derivatives can help in reduction of weight of battery cells, thus resulting in lighter lead-acid batteries. This can reduce the amount of active material used in battery and thus producing smaller batteries with similar or higher efficiency than currently available batteries. Graphene sheets can be modified by creating gaps in them and inserting other atoms between them. The resulting structure can show higher power density as well as higher energy density and enhancement in charge/discharge cycles also. Since only 0.1 to 0.5 wt% of Graphene is needed in the batteries, performance in terms of charge and cycle life can be significantly improved for a 150 Ah battery with under 20% increase in cost.