Engineering the Transformation Strain in LiMnyFe1-yPO4 Olivines for Ultrahigh Rate Battery Cathodes

TitleEngineering the Transformation Strain in LiMnyFe1-yPO4 Olivines for Ultrahigh Rate Battery Cathodes
Publication TypeJournal Article
Year of Publication2016
AuthorsRavnsbaek, DB, Xiang, K, Xing, W, Borkiewicz, OJ, Wiaderek, KM, Gionet, P, Chapman, KW, Chupas, PJ, Tang, M, Chiang, YM
JournalNano Letters
Volume16
Issue4
Pagination2375 - 2380
Date Published2016/04//
ISBN Number1530-6984
Keywordscathode, deintercalation, electrodes, kinetics, Li-ion batteries, lifepo4 nanoparticles, lithium manganese iron phosphate, lithium iron phosphate, lixfepo4, misfit strain, operando, pathways, phase transformation, phase-transformation, rate capability, substitution, transition, X-ray diffraction
Abstract

Alkali ion intercalation compounds used as battery electrodes often exhibit first-order phase transitions during electro-chemical cycling, accompanied by significant transformation strains. Despite 30 years of research into the behavior of such compounds, the relationship between transformation strain and electrode performance, especially the rate at which working ions (e.g., Li) can be intercalated and deintercalated, is still absent. In this work, we use the LiMnyFe1-yPO4 system for a systematic study, and measure using operando synchrotron radiation powder X-ray diffraction (SR-PXD) the dynamic strain behavior as a function of the Mn content (y) in powders of similar to 50 nm average diameter. The dynamically produced strain deviates significantly from what is expected from the equilibrium phase diagrams and demonstrates metastability but nonetheless spans a wide range from 0 to 8 vol % with y. For the first time, we show that the discharge capacity at high C-rates (20-50C rate) varies in inverse proportion to the transformation strain, implying that engineering electrode materials for reduced strain can be used to maximize the power capability of batteries.

Short TitleNano Lett.