Hydrometallurgical Refining and Precursor Hydroxide Crystallization Dynamics
Hydrometallurgical refining and coprecipitation dynamics dictate precursor particle morphology, phase purity, and electrochemical life in lithium-ion cells.
Nickel Oxyhydroxide
Meaning
Transition metal compounds act as the active materials in many secondary alkaline and nickel-based battery chemistries. As a primary electrode component, nickel oxyhydroxide participates in the reversible redox reactions that occur during the charge and discharge processes of nickel-metal hydride and nickel-iron batteries. This inorganic compound provides a stable platform for proton insertion and extraction.
Electrochemical Function
During the charging cycle, nickel hydroxide is oxidized to form nickel oxyhydroxide while releasing a proton and an electron. This chemical transformation is highly reversible, allowing the battery to undergo thousands of cycles. In the discharged state, the compound is reduced back, returning the active material to its initial oxidation state.
Phase Stability
The compound exists in different crystalline phases, known as beta and gamma, which affect the electrochemical capacity and electrode expansion. Structural transition to the gamma phase can cause significant volume changes, leading to mechanical degradation of the electrode. Controlling the operating voltage limits is necessary to suppress the formation of this unstable phase.
Production Route
Chemical synthesis of the precursor material requires precise control of the oxidation state of the nickel ions. This process is typically conducted by reacting nickel sulfate with sodium hydroxide and sodium hypochlorite under alkaline conditions.