Title: Unraveling the Complex Delithiation Mechanisms of Olivine-Type Cathode Materials, LiFe _x Co _{1– x} PO ₄

Abstract

The delithiation mechanisms occurring within the olivine-type class of cathode materials for Li-ion batteries have received considerable attention because of the good capacity retention at high rates for LiFePO₄. A comprehensive mechanistic study of the (de)lithiation reactions that occur when the substituted olivine-type cathode materials LiFe$$_x$$Co_1–$$_x$$PO₄ ($$x$$ = 0, 0.05, 0.125, 0.25, 0.5, 0.75, 0.875, 0.95, 1) are electrochemically cycled is reported here using in situ X-ray diffraction (XRD) data and supporting ex situ ³¹P NMR spectra. On the first charge, two intermediate phases are observed and identified: Li_1–$$_x$$(Fe³⁺)$$_x$$(Co²⁺)_1–$$_x$$PO₄ for $0 < x < 1$ (i.e., after oxidation of Fe²⁺ to Fe³⁺) and Li_2/3Fe$$_x$$Co_1–$$_x$$PO₄ for $0 ≤ x ≤ 0.5$ ($i.e.$, the Co-majority materials). For the Fe-rich materials, we study how nonequilibrium, single-phase mechanisms that occur discretely in single particles, as observed for LiFePO₄ at high rates, are affected by Co substitution. In the Co-majority materials, a two-phase mechanism with a coherent interface is observed, as was seen in LiCoPO₄, and we discuss how it is manifested in the XRD patterns. We then compare the nonequilibrium, single-phase mechanism with the bulk single-phase and coherent interface two-phase mechanisms. Despite the apparent differences between these mechanisms, we discuss how they are related and interconverted as a function of Fe/Co substitution and the potential implications for the electrochemistry of this system.

Authors:

Strobridge, Fiona C. ^[1]; Liu, Hao ^[1]; Leskes, Michal ^[1]; Borkiewicz, Olaf J. ^[2]; Wiaderek, Kamila M. ^[2]; Chupas, Peter J. ^[2]; Chapman, Karena W. ^[2]; Grey, Clare P. ^[3]

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+ Show Author Affiliations

1. Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, Cambridgeshire CB2 1EW, U.K.
2. X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States
3. Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, Cambridgeshire CB2 1EW, U.K., Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400, United States

Publication Date:

Wed Jun 01 00:00:00 EDT 2016

Research Org.:

Energy Frontier Research Centers (EFRC) (United States). Northeastern Center for Chemical Energy Storage (NECCES)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1257503

Alternate Identifier(s):

OSTI ID: 1371400

Grant/Contract Number:  

SC0001294

Resource Type:

Published Article

Journal Name:

Chemistry of Materials

Additional Journal Information:

Journal Name: Chemistry of Materials Journal Volume: 28 Journal Issue: 11; Journal ID: ISSN 0897-4756

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; 25 ENERGY STORAGE; energy storage (including batteries and capacitors); defects; charge transport; materials and chemistry by design; synthesis (novel materials)