In battery materials, a phase transition refers to a change in the crystal structure (phase) of an electrode material that can occur during charging or discharging. Many battery electrodes undergo phase transitions as they react; for example, lithium intercalation might change a cathode’s structure from one phase to another once a certain amount of lithium is extracted. Some of these transitions are benign or even reversible, while others can be detrimental. For instance, during overcharging of an NMC cathode, a phase transition can occur that makes the structure less stable, contributing to potential for thermal runaway. Phase transitions can also cause mechanical stress; if one phase has a larger volume than another, the change can strain particles or even cause cracking and / or loss of electrical conductivity.
NOVONIX investigates phase transitions by combining electrochemical testing with analytical techniques. They use dQ/dV analysis (derivative of the charge curve) to spot voltage plateaus associated with phase changes. They can use X-ray diffraction (XRD) to directly observe structural changes in materials at different states of charge. When testing a new material, if NOVONIX sees an unexpected voltage plateau or a change in behavior after a certain cycle, they might suspect a phase transition and examine it further. By understanding phase transitions, NOVONIX helps in tailoring materials and operating conditions to avoid the “bad” transformations that lead to degradation, thereby extending battery life.
