Structural and magnetic phase transition of mixed olivines LixFe1−yNiyPO4 by lithium deintercalation

Abstract

The structural and magnetic phase transitions of LixFe1–yNiyPO4 were investigated by x-ray diffraction (XRD), superconducting quantum interference device magnetometry, and Mössbauer spectroscopy. Rietveld refinement of XRD patterns of LiFe1–yNiyPO4 (0.0 ≤ y ≤ 0.6) revealed that the lattice parameters a0 = 10.328, b0 = 6.007, and c0 = 4.692 Å for LiFePO4 changed linearly to a0 = 10.154, b0 = 5.923, and c0 = 4.687 Å for LiFe0.4Ni0.6PO4 with the substitution of Ni ions. Also, the fully lithium-deintercalated Fe1–yNiyPO4 (0.0 ≤ y ≤ 0.6) series had enhanced lattice distortions along the c axis compared to LiFe1-yNiyPO4 because the Jahn–Teller distortion changed as the unit cell volume decreased due to lithium ion deintercalation. LiFe1–yNiyPO4 has an antiferromagnetic order; the magnetic Nèel temperature (TN) decreased from 51 K for LiFePO4 to 36 K for LiFe0.4Ni0.6PO4. Fully deintercalated Fe1–yNiyPO4 has strong antiferromagnetic order; TN decreased from 114 K for FePO4 to 62 K for Fe0.4Ni0.6PO4 due to the charge transition of Fe2+/Fe3+ and Ni2+/Ni3+, mediated by lithium ion vacancies in an olivine structure. The Mössbauer spectra below the TN of LixFe1–yNiyPO4 (x = 0, 1, 0.0 ≤ y ≤ 0.6) were fitted with eight asymmetrical Lorentzian functions. The electric quadrupole splitting value (ΔEQ) of LiFe1–yNiyPO4 is larger than that of Fe1–yNiyPO4 due to more asymmetric charge distributions around Fe2+ (3d6) than Fe3+ (3d5) in FeO6 sites.

Local structures in mixed Li Fe1−M PO4 (M=Co, Ni) electrode materials

“…δ, 2ε Q , Γ and the relative area ratio S for the Fe 2+ doublet are presented in Table 1. The isomer shift and quadrupole splitting values of Fe 2+ in LiFe 1-y Co y PO 4 do not show a coherent change with y, whereas in LiFe 1-y Ni y PO 4 samples, a very minor but still a consistent trend of slightly increasing quadrupole splitting value with increasing y is observed; a similar trend was seen by Lee et al [24] for their Ni-substituted Li(Fe,Ni)PO 4 samples. A higher quadrupole splitting value implies a more asymmetric charge distribution in the Fe 2+ local environment.…”

“…The Ni 2+ /Ni 3+ couple is inactive after the partial delithiation during the initial charge (inset in Fig. 7 Lee et al [24] investigated chemically delithiated Fe 1-y Ni y PO 4 materials and also measured decreasing quadrupole splitting values for Fe 3+ with increasing y (1.530 mm s -1 for y = 0 and 1.004 mm s -1 for y = 0.6). This implies that the M2 site occupancy also affects the Fe 3+ environment, assuming the delithiation in Ref.…”

“…This implies that the M2 site occupancy also affects the Fe 3+ environment, assuming the delithiation in Ref. [24] was complete. In our study, for both the substitution schemes M 2+ is smaller than Fe 2+ but larger than Fe 3+ , and M 3+ is smaller than Fe 2+ and Fe 3+ .…”

Electrochemical Performance and Delithiation/Lithiation Characteristics of Mixed LiFe1-yMyPO4(M= Co, Ni) Electrode Materials

“…For the delithiated Fe 1-y Ni y PO 4 phase, a and b lattice parameters were observed to increase with increasing y, whereas c decreased, and the lattice distortion along c axis was attributed to changed Jahn-Teller distortion when Fe and Ni changed their valence state. 65 As a result, the volumes of delithiated and lithiated phases approach each other with increasing y. Bramnik et al 60 observed ≤ 3% volume change between the different co-existing phases in LiFe 0.4 Co 0.6 PO 4 , which is smaller than observed for the co-existing x = 1 and x = 0 phases in the end members, y = 0 (LiFePO 4 ) or y = 1 (LiCoPO 4 ). In our study, indications of a decreased volume difference between the co-existing phases with increasing y were 64 ) is between x = 1 and x = 0.09 and for Li x Fe 0.5 Co 0.5 PO 4 (Kosova et al 33 ) between x = 1 and x = 0.04. suggested, too.…”

High-throughput ab initio screening of binary solid solutions in olivine phosphates for Li-ion battery cathodes

“…The M2 site is also accessible to doping or substitution by other TMs at a fixed stoichiometry and over a wide range of chemical compositions in order to optimize the Li-ion mobility, redox potential and cyclability. The investigated systems include Li-(Sc/Fe)PO 4 [13], Li-(Ti/Fe)PO 4 [13,18], Li-(Zr/Fe)PO 4 [18], Li-(V/Fe)PO 4 [13,19,20], Li-(Mn/Fe)PO 4 [21][22][23][24][25][26][27], Li-(Fe/Ni)PO 4 [28], Li-(Co/Ni)PO 4 [29], Li-(Mn/Co)PO 4 [30], Li-(Mn/Ni)PO 4 [26], Li-(Mn/Mg)PO 4 [26], Li-(Mn/Zn)PO 4 [26], Li-(Fe/Cu)PO 4 [31], Li-(Fe/Zn)PO 4 [32], Li-(Mo/Fe)PO 4 [33], Li-(Mg/Fe)PO 4 [18], Li-(Mn/Fe/Co)PO 4 [21,[34][35][36], Li-(Mn/Fe/Mg)PO 4 [37], Li-(Mn/Co/Ni)PO 4 [30] and Li-(Mn/Fe/Co/Ni)PO 4 [38,39]. The established approaches to increase the conductivity of FePO 4 such as carbon coating can also be applied to such multi-component solid-solution compounds [40] with even improved performance [41].…”