Performance degradation upon Li-ion battery lifetime is rooted in chemical processes mostly determined by battery material components and operation conditions.
Batteries start to degrade as soon as they are assembled, just as human beings start to age from the moment they are born. The process depends on biological/genetic factors (which can be assimilated to battery materials and design), environmental/behavioral aspects (battery operation conditions) and access to medical care (optimized Battery Management System).
Performance degradation upon Li-ion battery lifetime is ultimately rooted in chemical processes the extent of which is mostly determined by battery material components and operation conditions (charge/discharge rates, voltage operation limits and temperature) and can also be influenced by battery design. The two major factors contributing to loss of negative electrode performance are the instability of the passivation layers formed at the electrode/electrolyte interface (enhanced at higher temperatures) and lithium metal plating (intensified at low temperatures). In contrast, capacity fading at the positive electrode mostly result from partial dissolution of the active material during cycling/storage or electrolyte solvent oxidation, which is promoted by temperature and high potential. While it would be most useful to be able to monitor degradation at all levels while the cell is being cycled, the feasibility of this approach remains limited, and most approaches involve accelerated testing with ante/post mortem characterization. Yet, the use of suitable protocols for battery opening and disassembling is crucial to avoid biased interpretation.
Understanding such issues is crucial to extend cycle life of Li-ion batteries to successfully embrace larger scale applications such as transportation or grid. Overall, battery ageing is a very complex and challenging research topic with a too broader scope to be addressed by conventional research approaches and one which will clearly benefit from synergies between academia (model systems, fundamental research with cross cutting characterization techniques available) and industry (real commercial systems, large empiric know how and cumulated knowledge about battery response in real operation).
Understanding ageing in Li-ion batteries: a chemical issue.
Chem. Soc. Rev. 47, 4924-4933 (2018)
Schematics of a Li-ion battery and different possible evolutions of capacity vs. cycle number for Li-ion cells as a result of differences in operation conditions.