Meaning
Empty spaces created within an electrode or at an interface during manufacturing or cycling disrupt ion transport and reduce the active surface area available for reactions. these microscopic gaps can occur due to the consumption of material during chemical reactions or the mechanical separation of layers under stress. Void formation is a significant degradation mechanism in solid state batteries where the solid electrolyte cannot flow to fill the gaps created by the shrinking of the anode during discharge. Once these voids are present, the contact resistance between the layers increases, leading to a loss of power and the potential for uneven current distribution.
This phenomenon is a primary target for research into the cycle life and stability of advanced energy storage technologies.
Morphological Change
Evolution of the internal structure of the battery during use leads to the development of pores and gaps that were not present in the original design. Void formation is often driven by the large volume changes associated with the lithiation of materials like silicon or lithium metal. As the lithium is removed from the anode, the remaining structure may collapse or leave behind empty spaces if the external pressure is insufficient.
These changes in morphology are monitored using advanced imaging techniques like x ray tomography and electron microscopy.
Transport Barrier
Presence of empty spaces within the electrolyte or the electrodes blocks the direct path for ions to move between the positive and negative terminals.
Quality Control
Careful management of the manufacturing environment and the processing parameters can reduce the initial occurrence of these defects in the battery cell. Using high pressure during the assembly of solid state cells helps ensure that the materials are in intimate contact and reduces the likelihood of void formation during the first few cycles. Manufacturers also explore the use of compliant interlayers and specialized binders that can accommodate some level of volume change without losing contact.
The data from cycle testing is used to determine the rate at which voids grow and how they affect the long term health of the battery. If the density of the voids becomes too high, the battery will no longer be able to deliver the required power and must be replaced. Reducing the impact of these internal gaps is a requirement for the commercialization of high energy solid state battery systems.
