Rheological characterization and optimization of gelled electrolyte for sealed lead–acid batteries by small amplitude dynamic oscillation measurement

Rheological behavior of silica gel in sulfuric acid was investigated with a small amplitude dynamic oscillation measurement method in which storage modulus was monitored with time. For the purpose of quantitative discussion, gelation rate was defined as the time required for the storage modulus to be 1000 Pa, and denoted as t1000. The storage modulus was defined as ‘gel strength’. As silica content, sulfuric acid concentration, or the amount of added polyacrylamide increased, the gel strength and gelation rate were increased at the same time. While the increase of gel strength is desirable for long service life of a gel battery, the increase of gelation rate makes it difficult to fill the gel into the battery. However, this increase of gelation rate was found to be compensated by lowering the gelation temperature. A phase plane plot of gelation time (t1000) against gel strength (G′) was proposed to optimize the gel in terms of gel strength and gelation time. By using this phase plane plot, the gel strength was found to be increased by 40% without sacrificing the gelation rate. This was possible because the slopes on the phase plane plot are different depending on the independent variables.