The active materials in lead-acid batteries consist of lead dioxide (PbO₂) for the positive plates and sponge lead (Pb) for the negative plates. These materials undergo precise manufacturing processes to ensure optimal performance, longevity, and efficiency. The composition and production of these active materials involve specific additives and treatments to enhance conductivity, prevent degradation, and maintain structural integrity.

The positive active material (PAM) is primarily composed of lead dioxide, which forms the electrochemical basis for the redox reactions during discharge and charge cycles. The lead dioxide exists in two crystalline forms: alpha-PbO₂ (orthorhombic) and beta-PbO₂ (tetragonal). Beta-PbO₂ is more prevalent in battery applications due to its higher electrochemical activity and better conductivity. The PAM is produced by oxidizing lead or lead oxide compounds in an acidic environment. The resulting material is a porous structure that facilitates electrolyte penetration and efficient ion transport.

The negative active material (NAM) consists of sponge lead, a highly porous form of metallic lead that provides a large surface area for electrochemical reactions. The porous structure is critical for maintaining performance over repeated charge-discharge cycles. The NAM is typically formed by reducing lead oxide compounds to metallic lead in the presence of sulfuric acid. The resulting sponge lead must remain porous to prevent sulfation, a common failure mode where lead sulfate crystals grow and reduce active material availability.

Additives play a crucial role in enhancing the performance of both positive and negative active materials. In the positive plate, conductive additives such as carbon or graphite are often incorporated to improve electron transfer and reduce resistance. These additives counteract the inherently low conductivity of lead dioxide, ensuring efficient charge transfer during high-rate discharge. Carbon materials may be added in small quantities, typically between 0.1% and 2% by weight, to optimize performance without compromising mechanical stability.

The negative plate benefits from additives that prevent irreversible sulfation and maintain porosity. Barium sulfate (BaSO₄) is a common additive that acts as a nucleating agent for lead sulfate formation, ensuring that sulfate crystals remain small and reversible during charging. Lignosulfonates, organic compounds derived from wood pulp, are also added to the negative paste to inhibit the formation of large lead sulfate crystals and prevent hardening of the active material. These expanders help maintain the spongy structure of the negative plate, extending cycle life.

The paste mixing process is a critical step in manufacturing lead-acid battery plates. The paste consists of lead oxide (PbO or Pb₃O₄), sulfuric acid, water, and additives. The lead oxide is typically produced via the Barton pot or ball mill process, resulting in a fine powder with controlled particle size distribution. During mixing, sulfuric acid is added to the lead oxide, initiating a reaction that forms lead sulfate and releases heat. The paste must be carefully mixed to ensure homogeneity and the correct consistency for subsequent processing. Overmixing or excessive heat generation can negatively impact paste properties, leading to poor plate performance.

The paste is then applied to the grid structure using pasting machines that ensure uniform distribution. After pasting, the plates undergo a curing process, which involves controlled drying and chemical conversion. Curing protocols vary depending on battery type but generally involve exposure to high humidity (80-95% relative humidity) and elevated temperatures (30-70°C) for several hours to days. This step allows the paste to harden and undergo further chemical reactions, forming a network of lead sulfate and basic lead sulfate compounds that later convert to active material during formation.

The formation process is the final step in activating the plates. Formation involves electrochemically converting the cured paste into the active materials—lead dioxide for the positive plate and sponge lead for the negative plate. This is achieved by immersing the plates in sulfuric acid and applying a controlled charging current. The formation parameters, including current density, temperature, and acid concentration, are carefully optimized to ensure complete conversion and uniform active material structure.

Quality control during active material manufacturing is essential to ensure consistent battery performance. Parameters such as paste density, moisture content, and additive distribution are monitored to maintain uniformity. Variations in these factors can lead to differences in plate performance, affecting capacity, cycle life, and efficiency.

Lead-acid batteries remain widely used due to their reliability, recyclability, and cost-effectiveness. The careful formulation and processing of active materials contribute significantly to their performance characteristics. Advances in additive technology and manufacturing precision continue to improve energy density, cycle life, and charge acceptance, ensuring the ongoing relevance of lead-acid batteries in automotive, industrial, and stationary applications.

The composition and manufacturing of lead-acid battery active materials involve a balance of chemical reactions, material science, and process engineering. By optimizing paste formulations, curing protocols, and formation processes, manufacturers can produce high-performance batteries capable of meeting diverse application demands. The use of specialized additives further enhances conductivity, prevents degradation, and extends service life, making lead-acid batteries a resilient and adaptable energy storage solution.