Loss of lithium inventory (LLI) caused by SEI formation and other degradation mechanisms in Lithium-ion cells is one of the major reasons behind their capacity fade and shorter cycle life. Recent research in academia and industry has explored additives that sacrifice their lithium inventory to compensate for LLI. One such additive for LFP-based battery chemistries is Lithium Iron oxide (Li₅FeO₄). Over the last ~15 years, research has proven that LFO can be used as a sacrificing agent [1-4]. When the cell is overcharged, LFO releases its lithium inventory permanently, and once all its lithium is depleted, it turns into an inactive ‘dead’ material. Lab scale results show that LFO can compensate for LLI and help maintain stable cell performance [2, 4]. More recently, CATL & Rimac have demonstrated commercial use of LFO in Lithium-ion cells and claimed to have achieved zero degradation for extended periods. However, the specifics behind the methods and controls adopted to use LFO material for achieving such performance are not fully disclosed. Also, understanding around the commercial-level usage of LFO, control over lithium release from LFO and the fraction of LFO to be used for longer cell life is missing from the literature.
This work investigates ways by which one can effectively employ LFO material in LFP cells (LFP/LFO composite cells) to achieve a so-called ‘zero-degradation’ battery. A full-cell physics-based model consisting of a composite LFP/LFO positive electrode (PE) and Graphite negative electrode (NE) is built in PyBaMM. The model considers SEI formation, lithium plating, and porosity clogging on NE. Model predictions show that the optimum weight fraction of LFO in LFP/LFO composite PE and an optimized method to control lithium release from LFO are crucial for minimizing cell degradation and achieving long-lasting, zero-degradation batteries. Controlled slow (delayed & infrequent) lithium release maintains the cell balancing and reduces the degradation rates, while rapid (early & frequent) lithium release and excessive LFO content can accelerate the formation of SEI, lithium plating, and pore-clogging in the NE. Our findings also reveal that adding a higher LFO fraction appears beneficial in the beginning but is counterproductive as it promotes faster cell degradation resulting in a shorter cycle life of the cell. Hence this work concludes that achieving zero degradation requires more than just adding lithium-rich additives to cell electrodes but a suitable method to control lithium release and an optimized weight fraction of additives is even more crucial.

Reference
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[3] Dose, W. M., Maroni, V. A., Piernas-Munoz, M. J., Trask, S. E., Bloom, I., & Johnson, C. S. Assessment of Li-Inventory in Cycled Si-Graphite Anodes Using LiFePO₄ as a Diagnostic Cathode. Journal of The Electrochemical Society 165, A2389-A2396 (2018).
[4] Liu, X., Liu, J., Peng, J., Cao, S., Hu, H., Chen, J., Lei, Y., Tang, Y., & Wang, X. Addressing the initial lithium loss of lithium-ion batteries by introducing pre-lithiation reagent Li₅FeO₄/C in the cathode side. Electrochimica Acta 481, 143918 (2024).