Meaning
Inorganic solid growth occurs when lithium hexafluorophosphate salt becomes insoluble due to dropping temperatures or increased local concentrations within the battery solvent. Preventing LiPF6 crystallization is vital for ensuring that ions can move freely through the electrolyte during operation in sub-zero climates. The presence of these solid crystals sharply increases internal resistance and can permanently damage the physical structure of the separator.
Cold Stress
Cooling reduces the energy of the solvent molecules, making them unable to keep the dissolved ions in a separated ionic state. Once LiPF6 crystallization starts it proceeds rapidly across the interface, forming a resistive layer that stops the flow of power. This change usually requires thermal warming of the entire pack to dissolve the solids back into the carrier fluid.
Channel Block
Microscopic pathways used by charge carriers are prone to obstruction by these descending solids. Because LiPF6 crystallization takes place inside the pores of the cathode and anode, it limits the total active area available for the chemical reaction. This leads to a drop in voltage output and a rise in the heat generated during usage.
System Recovery
Testing protocols must verify that a cell can return to normal impedance levels after a deep freeze event. Managing LiPF6 crystallization ensures that nomadic storage devices remain reliable even after long periods of unheated storage in extreme winters.
