In-situ TEM study of electrochemically-driven phase transformations in battery storage compounds
EMSL Project ID
47778
Abstract
Many battery electrode materials, such as lithium transition metal olivines ( LiMPO4, M=Fe, Mn, etc) and oxide spinels (LiMn2O4, LiNi0.5Mn1.5O4, Li4Ti5O12, etc), exhibit phase transformation behaviors during lithiation/delithiation induced by large and variable electrochemical driving forces. In-situ characterization methods are needed to resolve real time information of these materials both macroscopically and microscopically in order to obtain predictive understanding of their dynamic phase transformation mechanisms, which further improvement of battery performance is probably contingent on. This proposal is mostly focused on LiFePO4 (LFP) and its derivatives, a cathode material with high capacity, excellent thermal stability, exceptional power performance and cycle life. Despite tens of MWh capacity already deployed in various fields, the phase transformation behavior of LFP has not been fully clarified. Previous studies reveal that phase transformation pathway between LFP and FePO4 (FP) is highly dependent on cation substitution, particle size and over-potential applied on the cathode material. Evidence of electrochemically-induced amorphization has also been observed.
There are a lot of controversies and disputes in this field. For example, Chen et al observed phase boundary between LFP and FP in bc plane in 2006, while Suo et al found that the phase boundary between two end members is roughly in ab plane instead in Nb-doped LFP, and these two works both employed ex-situ techniques. Obviously, real-time atomic-scale observation of lithiation/delithiation of LFP is critical to resolve these controversies and clarify the phase transformation mechanisms. However, such dynamic observations have not been achieved due to technique difficulties associated with the experiments. We propose to study the phase transformation mechanisms of LFP by in-situ transmission electron microscopy (TEM).
Under this proposal, in-situ TEM technique will be combined with other in-situ characterization techniques, such as in-situ powder X-ray diffraction (in-situ PXD), especially in-situ synchrotron powder X-ray diffraction (in-situ SR PXD) and in-situ powder neutron diffraction (in-situ PND) to systematically investigate on the phase transformation map of LFP with different varying parameters such as particle size, over-potential/under-potential. Rietveld Refinement, Pair Distribution Functions (PDF) analysis and phase-field modeling will also be used in this research.
Methods and understanding developed in this research can be conveniently employed to investigate other ion intercalation compounds with phase transformation behaviors and even systems with no phase transitions, such as battery materials involving conversion reactions. Besides, knowledge to control phase transformation pathways, which can be possibly derived from this research, is expected to give rise to new materials design criteria that improve battery performance with aspect to improving rate capability, reducing voltage hysteresis (or improving round-trip efficiency) and elongating cycle life.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2013-10-01
End Date
2014-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members