The phenomenon of sulfation in lead-acid batteries has been a subject of scientific inquiry since the technology's inception in the mid-19th century. The lead-acid battery, invented by Gaston Planté in 1859, quickly became a cornerstone of electrochemical energy storage, but early adopters observed a gradual decline in performance over time. This degradation was eventually linked to the formation of lead sulfate crystals on the electrodes, a process that would later be termed sulfation. The investigation into sulfation unfolded through a series of empirical observations and theoretical advancements, culminating in foundational work by John Hall Gladstone and Alfred Tribe in the late 19th century.

In the early years following Planté's invention, researchers noted that discharged lead-acid batteries exhibited a white, crystalline deposit on both the positive and negative plates. This deposit was identified as lead sulfate (PbSO₄), a product of the electrochemical reactions during discharge. Initial observations suggested that while some of this lead sulfate could be reconverted to lead and lead dioxide during charging, a portion remained stubbornly adherent to the plates, accumulating over cycles and reducing the battery's capacity. The inability to fully reverse this reaction was recognized as a critical limitation, prompting deeper investigation into the underlying mechanisms.

By the 1870s, the scientific community had begun systematic studies of sulfation. Researchers observed that the morphology of lead sulfate deposits played a significant role in the reversibility of the reaction. Fine, amorphous lead sulfate formed during normal discharge could be readily converted back to active material, whereas coarse, crystalline deposits resisted reconversion. This distinction was crucial in understanding why some batteries exhibited more severe sulfation than others. Factors such as discharge rate, temperature, and electrolyte concentration were found to influence the formation of these crystalline structures. High discharge rates and low temperatures, for instance, tended to promote the growth of larger, more stable PbSO₄ crystals.

The most significant contributions to the understanding of sulfation came from the collaborative work of Gladstone and Tribe in the 1880s. Their experiments systematically explored the electrochemical behavior of lead-acid batteries under varying conditions. They demonstrated that sulfation was not merely a surface phenomenon but involved bulk transformations within the electrode material. Gladstone and Tribe's key insight was recognizing that sulfation resulted from thermodynamic and kinetic factors governing the dissolution and precipitation of lead sulfate. Their work established that the equilibrium between lead, lead dioxide, and lead sulfate was influenced by the local concentration of sulfuric acid, with lower acid concentrations favoring the formation of stable PbSO₄.

One of their critical findings was the role of overdischarge in accelerating sulfation. When a lead-acid battery was discharged beyond a certain point, the sulfuric acid concentration in the electrolyte dropped significantly, creating conditions favorable for the growth of irreversible lead sulfate crystals. This explained why batteries deeply discharged or left in a discharged state for extended periods suffered more severe sulfation. Gladstone and Tribe also investigated the effect of intermittent charging, showing that partial state-of-charge operation could exacerbate sulfation due to incomplete conversion of PbSO₄.

The late 19th century saw further refinement of these concepts as researchers developed more sophisticated experimental techniques. Microscopic examination of sulfated plates revealed that the crystalline deposits often grew in a dendritic or interlocking manner, physically impeding access to the active material and reducing the effective surface area for electrochemical reactions. This mechanical aspect of sulfation was recognized as an additional barrier to reversibility, beyond the purely chemical factors.

Quantitative studies during this period attempted to correlate the degree of sulfation with measurable battery parameters. Researchers found that sulfated batteries exhibited higher internal resistance and lower open-circuit voltage, consistent with the loss of active material. The relationship between sulfation and capacity fade was also quantified, with heavily sulfated batteries showing reductions in available capacity by as much as fifty percent or more. These measurements provided concrete evidence of the detrimental impact of sulfation on battery performance.

By the close of the 19th century, the fundamental understanding of sulfation had been firmly established through these cumulative investigations. The work of Gladstone and Tribe, in particular, provided a theoretical framework that explained the chemical and physical processes involved. Their research highlighted the importance of proper charging practices and avoidance of deep discharge in mitigating sulfation, principles that would guide battery maintenance for decades to follow. While modern lead-acid battery technology has introduced numerous refinements, the core insights into sulfation generated during this formative period remain relevant to the basic electrochemistry of these systems. The historical investigation of sulfation stands as a testament to the iterative nature of scientific progress, where empirical observation and theoretical analysis converge to unravel complex electrochemical phenomena.