Application of Anisotropic Graphite to Sealed Lead‐Acid Batteries

Abstract

Anisotropic graphite was used as an additive to the positive paste to improve the discharge performance of sealed lead-acid batteries. The discharge capacity increased with the amount of graphite, particularly at high discharge rates and at low temperatures. This is attributed to the increased amount of electrolyte retained in the pores of the swollen positive plates that result from the addition of the graphite.

The Effect of Various Graphite Additives on Positive Active Mass Utilization of the Lead-Acid Battery

“…Firstly, there is an insufficient supply of ions into the interior of the plate, causing reaction currents to be limited by electrolyte diffusion. Other processes that lower discharge utilization include surface coverage of PbSO 4 that can starve the plate interior from sulfuric acid solution, and progressive PbSO 4 build-up that lowers the effective conductivity of the material, while isolating the reaction interface from remaining undischarged parts of the PbO 2 plate [3][4][5].…”

“…Natural anisotropic graphite, added to the positive plate of a flooded and sealed lead-acid battery, actively facilitates acid transport due to the insertion of bisulfate ions between the graphite layers and pore volume expansion of the PAM. 4,5 Other studies have recognized graphite for its electroosmotic pumping role and wetting properties, thus aiding the permeation of sulfuric acid solution through the PAM's layers. 6,7 Despite major performance benefits, graphitic carbon has not had commercial success as a PAM additive.…”

“…12 In another study, Tokunaga et al more closely examined the mechanism by which natural graphite benefits PAM utilization. 4,5 In addition to functioning as a porosity enhancer, graphite was shown to increase the compression of the cell due to an increase of positive plate thickness. 4,5 While the study observed some decrease in the amount of graphite with cycle life, the positive plate capacity remained higher with graphite throughout the battery life and increased the cycle life by nearly 30% due to improved compression effects.…”

“…4,5 In addition to functioning as a porosity enhancer, graphite was shown to increase the compression of the cell due to an increase of positive plate thickness. 4,5 While the study observed some decrease in the amount of graphite with cycle life, the positive plate capacity remained higher with graphite throughout the battery life and increased the cycle life by nearly 30% due to improved compression effects. 4,13 Graphite is a generally beneficial additive because it enhances PAM utilization and often increases the cycle life of the battery.…”