Electrochemical Performance and Delithiation/Lithiation Characteristics of Mixed LiFe1-yMyPO4 (M = Co, Ni) Electrode Materials. Issue 14 (1st January 2015)

• Record Type: Journal Article
• Authors: Jalkanen, K.; Karppinen, M.
• Is Part Of: Journal of the Electrochemical Society. Volume 162:Issue 14(2015)
• Page Start: A2780
• Page End: A2788
• Publication Date: 2015-01-01
• Subjects: Chemical substitution -- Electrochemical performance -- Li-ion battery -- Lithium iron phosphate -- Positive electrode; Electrochemistry -- Periodicals; 541.3705
• DOI: 10.1149/2.0791514jes
• Languages: English
• ISSNs: 0013-4651

Abstract

Abstract : Solid solutions of LiFe1- y My PO4 /C ( M = Co, Ni) within the whole substitution range (0 ≤ y ≤ 1) are systematically investigated as safe high-voltage positive electrode materials for Li-ion battery. Especially the similarities and differences between the Co- and Ni-substitution schemes are highlighted. With increasing substitution level y, the orthorhombic unit cell shrinks and the Li + -ion diffusion channel area decreases, more rapidly for the smaller-sized Ni substituent. While the Co 2+ /Co 3+ redox couple shows reversible electrochemical activity, only an initial, partial delithiation is achieved for the Ni 2+ /Ni 3+ couple at all y . However, both substitution schemes similarly affect the Fe 2+ /Fe 3+ redox couple by increasing its potential and enhancing the kinetics. Particularly, a mutual influence of Fe and Co/Ni on the delithation/lithiation characteristics is proposed: ex situ XRD analysis shows signs of a phase-composition change in the Fe 2+ /Fe 3+ region for higher y, and correspondingly, a changed Co 2+ /Co 3+ redox mechanism for lower y is indicated by cyclic voltammetry. We suggest that this behavior is related to a substitution-induced decrease in the volume change between the lithiated and delithiated phases. For the Co-substitution scheme, a composition around y ≈ 0.5 seems optimal for combining a high energy density and a kinetically beneficial, diffusional single-phase delithiation/lithiation mechanism.