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.
Carbonate Solvent Evaporation
Meaning
Physical phase transitions occur when the liquid electrolyte components of a battery escape into a gaseous state. Excessive carbonate solvent evaporation reduces the ionic conductivity of the cell and increases internal resistance by depleting the medium required for lithium transport. This process is accelerated by high temperatures and compromised seals which allow volatile molecules to leave the system.
Volatility Profile
Different chemical species within the electrolyte blend possess distinct boiling points and vapor pressures. Because cyclic and linear molecules are used together, carbonate solvent evaporation often targets the more volatile components like dimethyl carbonate first. This selective loss alters the chemical balance of the remaining liquid.
The shifting concentration changes the freezing point and viscosity of the electrolyte over time.
Capacity Loss
Dry out occurs when the volume of liquid falls below the level needed to saturate the porous separator and electrode structures. As carbonate solvent evaporation continues, the active surface area of the electrodes is no longer fully accessible to the lithium ions. This reduction in effective area leads to a permanent drop in the energy the cell can deliver.
High power discharge becomes difficult as the internal resistance climbs.
Safety Risk
Pressure buildup within a sealed pouch or canister stems from the rapid expansion of gas during a heat event. If carbonate solvent evaporation happens too quickly, the internal stress may exceed the mechanical strength of the housing. This leads to a controlled venting or a more violent rupture of the cell.
Maintaining a low temperature prevents the liquid from reaching the critical vapor pressure.