Quantifying Sodium Oxalate Decomposition Kinetics on Automated Formation Lines
Sodium oxalate oxidation kinetics dictate pouch formation degassing timing, where 3.85 V step holds prevent cell swelling and minimize solvent evaporation.
Hard Carbon Irreversible Capacity Loss
Meaning
Initial loss of active lithium ions occurs when they are permanently trapped in the disordered structure of non-graphitizable anode materials. A high hard carbon irreversible capacity loss reduces the energy density of sodium-ion or lithium-ion cells by locking up valuable charge carriers during the first cycle. This phenomenon is driven by the high specific surface area and structural defects of the carbon material.
Structural Cause
Trapping of ions happens because the carbon lattice contains numerous defects and functional groups that form strong bonds with lithium or sodium. The hard carbon irreversible capacity loss is further increased by the formation of a large solid electrolyte interphase across the extensive internal surface area. This permanent loss occurs almost entirely during the first full charge of the cell.
Sourcing Strategy
Battery purchasing and design teams must evaluate the first-cycle efficiency when choosing carbon materials from different suppliers. A material with a high hard carbon irreversible capacity loss requires the inclusion of more expensive cathode materials to maintain the desired nominal capacity. Minimizing this metric is a primary goal when sourcing anode raw materials.
Compensation Method
Pre-lithiation or pre-sodiumization of the electrodes can offset this initial deficit but adds complexity and cost to the cell manufacturing line.