Mechanical failures, of battery materials,

The combination of the multiple pertinent physics in the battery cell, incorporating the interplay of manufacturing- and service-induced loads and failure mechanisms, will surely inform advanced modeling. Of the commonly recognized battery performance degradation mechanisms, namely electrolyte decomposition, active material dissolution, passive layer formation, lithium deposition, and mechanical failure of battery materials, mechanical failure is the least understood at present, although there is ample evidence of the importance of these effects, and they are the subject of this chapter. 

Mechanical failure of battery materials has been putatively linked to battery performance degradation over time [1, 2]. It has been postulated that mechanical failure of battery active materials (i) increases surface area of active materials subjected to side reactions and consumes active material (which causes capacity loss), (ii) results in loss of electric contact between the active material particles and between active materials and current collectors [3, 4], increasing the internal impedance for charge transfer, and (iii) potentially redistributes active material particles and decreases volume fraction of electrolyte, making the hthium ion (Li-ion) transport become electrolyte phase limited [5-9]. Mechanical failure of... 

Experimental efforts to understand the mechanics in single-particle electrodes are twofold. One group of studies has attempted to find evidence to connect failure mechanisms and mechanics. Mechanical failure of battery materials (i.e., particle fracture) has been considered to be one of the major failure mechanisms of Li-ion batteries, causing loss of electrical contact through separated electrodes. 

In order to eUminate the complexity of stochastic microstructures of battery materials, single-particle models have been used to understand the underlying physics of stress generation and mechanical failure. 

Furthermore, there are other well-known failure mechanisms in li-ion batteries, but it is not clear how and how much cell mechanics is interrelated with those failure mechanisms dissolution of electrode materials has been known to result in a loss of capacity, as in the case of Mn dissolution from IiMn204 cathodes. Instability of the electrolyte is another well-known failure mechanism in Li-ion batteries decomposition of the liquid electrolyte includes reaction of the solvent at electrode surfaces to form a passivation layer (i.e., soHd-electrolyte interface, SEI layer), resulting in an increase in internal resistance and excessive polari2ation. 

In a different battery test with a simulated EV load pattern, a SWP-7 cell with an assembly pressure of 60 kPa achieved 450 cycles versus 270 cycles for an AGM cell with 73 kPa. The failure mode was found not to be the expansion of positive plate but, rather, sulfation of the negative plate. This led to the conclusion that the favourable mechanical properties of SWP-type separators suppress degradation of the positive active-material. 

Mechanical Failure Analysis of Battery Cells and Materials Significance and Challenges... 

Materials and battery assemblies may be characterized and optimized for performance and safety by various means and techniques. The techniques evaluate the stability of materials, electrode formulations, cell construction, and battery assemblies for responses to a variety of off-normal conditions that simulate abusive events such as mechanical, electrical, and thermal abuse. Additionally, battery packs have other failure modes such as inter-ceU shorting and cell imbalance that can cause overcharge and overdischarge. 

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