Modeling of Effect of Double-Layer Capacitance and Failure of Lead-Acid Batteries in HRPSoC Application

Abstract

Lead-acid batteries fail faster in partial state-of-charge start-stop technology than in SLI application. Accumulation of lead sulfate on negative electrode's surface has been identified as the cause. It is also known that life can be enhanced by increasing capacitance of negative electrode. A bench-marking test cycle is used to explain these observations through a one-dimensional model. It is shown that, at the large discharge current densities used, faradaic reactions in the electrodes are spatially inhomogeneous, and charging is unable to reverse its effects. Consequently, lead sulfate deposit is larger on electrode's surface than at its center. Model uses a rate expression for charging modified to include diffusion of Pb 2+ , and predicts that sulfate continues to accumulate with cycling. A portion of electrode becomes inactive when volume fraction of sulfate reaches a critical value there. Battery fails when inactive area becomes large. It is shown that double-layer capacitance suppresses the non-uniformity in the faradaic reaction and alters the pattern of accumulation of sulfate. Negative electrode does not benefit from this since its capacitance is low. Sulfate accumulates in positive electrode also, but does not reach critical levels since positive electrode's capacitance is large. A large fraction of the demand for lead-acid batteries from automotive industries is for SLI application. But the demand is expected to decline as the auto industry moves toward Li batteries. However, as specifications become more stringent both on fuel economy and on emissions of green house gases, lead-acid battery has found a new application in stop-start technology of electric vehicles. Here, battery should be capable of rapid enough discharge to permit starting of the vehicle along with maintenance of other on-board electrical loads. Further, to facilitate charging by regenerative braking, the battery has to be in partial state of charge, which can be as low as 50%. This has come to be known as high rate partial-state-of-charge or for short, HRPSoC, duty. In the start-stop operation, the frequency of charging-discharging cycles is large. Equally importantly, while the discharge rate during cranking is about the same as in conventional SLI application, charging rate can be as large as thirty times more. The challenges faced in meeting this application have been well summarized by Moseley and Rand 1 and Moseley et al. 2 The main problem faced is the faster degradation of battery than encountered in the conventional SLI application. The diminished life has been attributed to accumulation of lead sulfate on the surface of the negative electrode. Conclusive evidence for this has been reported by Lam et al.3 based on tear-down analysis of failed batteries. Interestingly, it has been found that increasing the capacitance of the negative electrode enhances its life, and development of ultrabattery 4 is a well known demonstration of this. While a complete description of this device is not available in the open literature, it is s...

Modeling of Sulfation in a Flooded Lead-Acid Battery and Prediction of its Cycle Life

“…These are Ostwald ripening leading to reduction in area of sulfate particles, and spatially inhomogeneous deposition of sulfate caused when rate of discharge is significantly greater than that of charging. 6 These two will not be considered in this work. We also ignore grid corrosion and fatigue failure, whose effects have to be considered in a complete theory of failure.…”

“…Battery is discharged galvanostatically at a current density of about C/5 till a specified DoD is reached. To avoid complications referred 6 to earlier, battery is then charged galvanostatically at the same rate till either a cutoff voltage of 2.4 V is reached or all the coulombs discharged are charged back. This recharging protocol is repeated.…”

“…Expressions that include effect of mass transfer of lead ions on the rate of charge transfer reactions during charging phase have been derived. [6][7][8][9] Mass transfer from sulfate particles is not relevant during discharge. The rate expressions are then given by…”

Lead Oxide Enveloped in N-Doped Graphene Oxide Composites for Enhanced High-Rate Partial-State-of-Charge Performance of Lead-Acid Battery

“…Lead-acid batteries still dominate the rechargeable batteries market, especially as the starting power sources in the automotive industry . However, the operation status of high-rate partial-state-of-charge (HRPSoC) will lead to the irreversible sulfation of active materials in the negative plates and, consequently, will result in the quick failure of lead-acid battery in electric vehicles. , Recently, conductive carbon materials with high surface area were introduced to impede the sulfation degree of negative plates and to improve the HRPSoC cycle performance of lead-acid batteries. , However, carbon composites involved still suffer from serious hydrogen evolution, as they quickly dry out the electrolyte and cause a dangerous battery system . To this end, various carbon materials are modified by the surface functional groups to alter their surface chemistry for the repressive hydrogen evolution process. , For example, activated carbon (AC) modified by alkaline surface functional groups can inhibit the hydrogen evolution reaction (HER), while this process can be promoted by acidic surface functional groups .…”

“…1 However, the operation status of highrate partial-state-of-charge (HRPSoC) will lead to the irreversible sulfation of active materials in the negative plates and, consequently, will result in the quick failure of lead-acid battery in electric vehicles. 2,3 Recently, conductive carbon materials with high surface area were introduced to impede the sulfation degree of negative plates and to improve the HRPSoC cycle performance of lead-acid batteries. 4,5 However, carbon composites involved still suffer from serious hydrogen evolution, as they quickly dry out the electrolyte and cause a dangerous battery system.…”