Effect of polyols on the electrochemical behavior of gel valve-regulated lead-acid batteries

• Chain length of straight chain polyols has significant effects on silica dispersion.
• A relationship between the chain length and dispersion time was proposed.
• The dispersion time decreases as high as 88% when a branched chain polyols was used.
• While using branched chain polyols, the capacity is stable with agitation time.
• Present of pentaerythritol guarantees a porous gel structure, and ensure the gel resistance reduced 72.3%.

The effects of three types of straight chain polyols (propanetriol, butantetraol, and pentitol) and one branched chain polyols pentaerythritol as electrolyte additives on the electrochemical properties of gelled electrolyte valve-regulated lead-acid (GEL-VRLA) batteries were systematically studied. Our result shows that a moderate mechanical dispersion of fumed silica in H2SO4 solution is beneficial to improve the electrochemical properties of the gelled electrolyte. Adding of straight chain polyols (propanetriol, butantetraol, and pentitol) can decrease not only the optimum dispersion time, but also the electrolyte resistance of the gel. The optimum dispersion time needed is pure (90 minutes) > adding pentitol (80 minutes) > adding butantetraol (70 minutes) > adding propanetriol (60 minutes). Furthermore, the optimum agitation time can be reduced by 88% with adding of branch chain polyols pentaerythritol. Also, the charge-transfer resistance (Rct) of gel can be reduced by more than one order of magnitude. More important, the peak current (capacity) of the lead electrode is stable with agitation time, which is significant for practical application. The adding of pentaerythritol makes the gel more uniform and porous, demonstrating that it is a promising gel electrolyte for VRLA batteries.