© Philadelphia Scientific 2006 Monobloc Batteries: High Temperatures, Life and Catalysts Harold A. Vanasse Daniel Jones Philadelphia Scientific

© Philadelphia Scientific 2006 Outline What does design life mean? How does temperature affect design life? How does actual life compare with design life? Does a catalyst impact actual life at high temperature?

© Philadelphia Scientific 2006 Introduction We have been approached by people concerned about life of their 12-volt Monobloc VRLA batteries. They are very popular in outside plant (OSP) applications. –Easy to install & support. –High power density. Shorter than expected life is becoming an issue. Can we apply our experience in larger 2-volt cells to the Monobloc design?

© Philadelphia Scientific 2006 Life Expectations Definitions: Design Life = The life of the battery as expected by the battery producer. Actual Life = The life of the battery as experienced by the battery owner.

© Philadelphia Scientific 2006 Problems happen when Design Life  Actual Life

© Philadelphia Scientific 2006 Designer’s Toolbox Factors used by battery designer: –Positive grid corrosion rate (purity). –Positive grid thickness. –Electrolyte reserve. –Others: Strap corrosion, post seals, jar to cover seals & vent design.

© Philadelphia Scientific 2006 Positive Plate Life For a long lived plate: –Minimize corrosion rate and … –Maximize plate thickness … –Within cost constraints. The above parameters determine how long the positive plate lasts. The plate life is based on 25°C (77°F).

© Philadelphia Scientific 2006 Battery Life Positive plate life has been determined. –Design is always a function of the particular application with inherent tradeoffs. –10 year design has thicker plates than 5 year design. No other factors should have a shorter life expectancy than positive plate. –Competent design should eliminate these. Design Life = Positive Plate Life at 25°C.

© Philadelphia Scientific 2006 But … The real world does not run at 25°C!

© Philadelphia Scientific 2006 Number of Days > 90° F 60 days or more 15 to 30 days

© Philadelphia Scientific 2006 Temperature OSPs are exposed to high environmental temperature in summer. –Cabinet temperatures are higher than ambient. Past Battcon papers identify ill effects of high temperature on Monobloc batteries: –Vacarro (2004) & McCluer (2003) –High temperatures drastically shorten life of Monobloc batteries. –Failure modes: Dry out & grid growth/corrosion.

© Philadelphia Scientific 2006 Impact of High Temperature on Batteries Effect of High TemperatureReason Why Increased current drawCell reactions increase with temperature. Arrhenius equation. Increased water lossElectrolysis of water is directly related to current. Faraday’s law (1830’s). Increased positive grid corrosion.Corrosion is directly related to current and temperature.

© Philadelphia Scientific 2006 Temperature vs. Float Current

© Philadelphia Scientific 2006 Arrhenius who? Dr. Svante Arrhenius –Swedish scientist in late 1800’s quantifies impact of temperature rise on rate of chemical reactions. –Nobel prize in His equation (generalized): For every increase of 10°C, reaction (corrosion) rate doubles. Life of positive plate is cut in half with each 10°C rise in temperature.

© Philadelphia Scientific 2006 What does this tell us? The theory and the data both indicate that high temperature is bad for batteries. But how bad? What can we expect for Design Life?

© Philadelphia Scientific 2006 Design Life at Temperature Temperature (°C (°F) ) 5-Year Design (Years) 10-Year Design (Years) 25 (77) (95) (113) (131) (149)

© Philadelphia Scientific 2006 Design Life Summary Design life at high temperatures is MUCH shorter than at 25°C.

© Philadelphia Scientific 2006 Actual Life Only you know what your actual life is. How does it compare to the table of Design Life at Temperature? Our sources and testing indicate that real batteries are coming up short.

© Philadelphia Scientific 2006 Closing the Gap What is the effect of a catalyst on Monobloc batteries at high temperature?

© Philadelphia Scientific 2006 Catalyst Refresher VRLA batteries can become unbalanced leading to a depolarized negative plate. The catalyst affects the polarization of both plates. –Negative polarization increases. –Positive polarization decreases. Lander curve describes affect on corrosion rate. –Optimum positive polarization minimizes corrosion rate.

© Philadelphia Scientific 2006 Lander Curve

© Philadelphia Scientific 2006 Catalyst Refresher Oxygen and Hydrogen recombine on the negative plate and reduce it’s polarization. The catalyst prevents a small amount of O 2 from reaching the negative plate. The negative stays polarized. The positive polarization is reduced. The float current of the cell is lowered. –We generally find current reduced by half.

© Philadelphia Scientific 2006 Proof of Concept Testing Four 12 V (100 Ah) Monobloc batteries. –10-Year Design. Two Monobloc batteries equipped with catalysts. –One catalyst per cell (6 per battery). Microcat™ catalysts used for test. –Too large for Monobloc batteries. Float charged at 2.27 VPC.

© Philadelphia Scientific 2006 Proof of Concept Testing Batteries run at 3 different temperatures: –14 30°C –14 40°C –328 50°C –Average test temperature = 48.8°C Parameters measured: current, capacity & conductance.

© Philadelphia Scientific 2006 Float Current vs. Temperature Float current reduced by half at all temperatures. Temperature (°C (°F) ) Current (mA/100 Ah) Ratio Catalyst Batteries Non-Catalyst Batteries 30 (86) (104) (122)

© Philadelphia Scientific 2006 Capacity at Day 356

© Philadelphia Scientific 2006 Estimated Time to Failure 40% Increase in life from Catalyst Batteries Estimated Time to Battery Failure (Results inferred from conductance readings) Catalyst Batteries350 Days Non-Catalyst Batteries250 Days

© Philadelphia Scientific 2006 Tear Down Results Observations from non-catalyst batteries: –Dry out –Positive grid corrosion & growth –Internal shorting –Battery jar cracks Observations from catalyst batteries: –Sufficiently wet –Minimal positive grid corrosion & growth

© Philadelphia Scientific 2006 Conclusions Design life = Positive plate life at 25°C. Significant reduction in design life at higher temperature. –10 year design at 45°C (113°F) = 2.5 years Only you know actual life. Preliminary proof-of-concept catalyst test showed promising result.