Supplementary Information for:

Effect of Graphite and Copper Oxide on the Performance of High

Potential Li[Fe1/3Ni1/3Co1/3]PO4 Olivine Cathodes for Lithium Batteries

Gioele Pagot1,2, Federico Bertasi1,3, Graeme Nawn1, Enrico Negro2,3,4, Antoine Bach Delpeuch1, Keti

Vezzù1, Davide Cristofori5, and Vito Di Noto1,2,3*

1 Section of “Chemistry for the Technology” (ChemTec), Department of Industrial Engineering, University of Padova, Via Marzolo 1, I-35131 Padova (PD), Italy2 Centro Studi di Economia e Tecnica dell’Energia Giorgio Levi Cases, Via Marzolo 9, I-35131 Padova (PD), Italy3 INSTM, Via Marzolo 1, I-35131 Padova (PD), Italy4 Department of Chemical Sciences, University of Padova, Via Marzolo 1, I-35131 Padova (PD), Italy5 Department of Molecular Sciences and Nanosystems and Centre for Electron Microscopy “G. Stevenato”, University Ca’ Foscari Venice, Via Torino 155/B, I-30172 Venezia-Mestre (VE), Italy

* Author to whom correspondence should be addressed. E-mail address: vito.dinoto@unipd.it1

Broadband Electrical Spectroscopy of LFNCP materials.

The electric response of LFNCP materials in terms of structural relaxations and polarization

phenomena is investigated by Broadband Electrical Spectroscopy (BES) in the frequency and

temperature range of 10-2 Hz ≤ f ≤ 10 MHz and -80 ≤ T ≤ 150 °C, respectively. The spectra of

imaginary component of permittivity (ε’’() vs. f, where f is the frequency in Hz and =2f) are

shown in Fig. S6 and reveal that the electric response of LFNCP materials is modulated by: a) two

different dielectric relaxations detected in the medium (α) and high frequency wing (β) of the

spectra; b) a polarization event, corresponding to the ion dc conductivity of materials, measured in

the low frequency wing of ε’’() profiles. α and β modes are attributed to the dynamics of host

olivine matrices. In particular, α-mode is associated to the diffusion of conformational states along

phosphate repeat units of 3D-networks of LFNCP materials. Thus, α-mode, which describes the

concerted coupled motion of dipole moments of phosphate repeat units of materials, corresponds

to the typical segmental motion of LFNCP materials. β relaxation is attributed to the local

fluctuation of the dipole moments associated to distorted octahedral repeat units coordinating the

transition metals. The presence of these relaxation modes demonstrates that the backbone

structure of the proposed LFNCP materials is flexible. The dependence on temperature of

relaxation times of the α and β modes of LFNCP, LFNCP/Cu, and LFNCP/Cu+C samples is shown in

Fig. S7. This assignment is confirmed analysing the dependence on T of the α and β relaxation

frequencies, which, as expected, exhibits: a) Arrhenius-like (A) behaviours for β relaxations; and b)

the typical Vogel–Tammann–Fulcher-Hesse (VTFH) profiles for α modes. The activation energies of

α and β relaxations, summarized in Table S1, are determined by fitting the data of Fig. S7 by means

of the following VTFH and A equations, respectively [S1]:

f=A f ∙exp ( −EaR ∙ (T−T 0 ) )(VTFH ); A f ∙exp (−EaR ∙T )(A )

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where Af is the pre-exponential term, which is related to the density of charge carriers. R is the

universal gas constant. Ea is the activation energy value, and T0 is the thermodynamic ideal glass

transition temperature, this is the temperature at which the configurational entropy of material

becomes zero.

Results demonstrate that moving from pristine LFNCP toward LFNCP/Cu and LFNCP/Cu+C samples,

the split between α and β relaxations rises shifting the β-mode toward higher frequencies. This

indicates that the precursor treatment with Cu and Cu+C acts to yield LFNCP/Cu and LFNCP/Cu+C

materials, which, with respect to the pristine LFNCP, show: a) an increasing decoupling of the

dynamics of the α and β modes; b) a very fast β relaxation, which probably is responsible of the

improved rate of exchange of lithium cations between coordination sites along the 1D channels of

olivine materials.

The values of activation energy, shown in Table S1, clearly demonstrate that, with respect to

pristine LFNCP, the dynamics of both α and β modes of proposed materials are facilitated

increasing in the order LFNCP < LFNCP/Cu < LFNCP/Cu+C. Thus, the proposed precursor

treatments are very effective to facilitate the structural flexibility of proposed cathodic systems.

Indeed, for β relaxation the Ea values of LFNCP, LFNCP/Cu and LFNCP/Cu+C decrease in the order

54.79±0.53, 51.59±0.51 and 50.09±0.16 kJ·mol-1, respectively.

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Figure S1. TGA analyses. Thermogravimetric profiles of LFNCP/Cu (red dotted line) and

LFNCP/Cu+C (black solid line).

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Figure S2. EDX mapping of LFNCP/Cu.

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40 µm 40 µm

40 µm40 µm

40 µm 40 µm

Fe Ni

Co P

O Cu

Figure S3. EDX mapping of LFNCP/Cu+C.

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40 µm 40 µm

40 µm40 µm

40 µm 40 µm

Fe Ni

Co P

O Cu

Figure S4. Rietveld refinement pattern of LFNCP/Cu.

Figure S5. Rietveld refinement pattern of LFNCP/Cu+C.

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Figure S6. Broadband Electrical Spectroscopy. ε’’ vs. frequency for LFNCP (blue), LFNCP/Cu (red), and LFNCP/Cu+C (black) from -80 to 150 °C. α and β dielectric relaxations are highlighted with an arrow.

Figure S7. LFNCP (blue), LFNCP/Cu (red), and LFNCP/Cu+C (black) log f vs. 1/T plot.

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Figure S8. Cyclic voltammetry tests of cathodic mixture composed by 85.0 % of active material, 7.5 % of carbon, and 7.5 % of PVDF (by weight): (a) LFNCP/Cu (red line); and (b) LFNCP/Cu+C (black line) at different scan rates. c) CV test of LFNCP/Cu in a low range of potential (3.0-4.0 V), at a scan rate of 2.0 mV·s-1. d) CV test of LFNCP/Cu+C in a low range of potential (3.0-4.0 V), at a scan rate of 2.0 mV·s-1.

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Figure S9. Battery tests (electrode composition by weight: 85.0 % of active material, 7.5 % of carbon, and 7.5 % of PVDF). (a) Galvanostatic charge/discharge profiles of LFNCP/Cu (red line) and LFNCP/Cu+C (black line) during cycle number 1 (solid line) and cycle number 125 (dashed line). (b) Discharge cycling performance of LFNCP/Cu (●), and LFNCP/Cu+C (▲), and cycling stability of LFNCP/Cu (♦) and LFNCP/Cu+C (■). The difference in maximum discharge capacity of LFNCP/Cu and LFNCP/Cu+C is highlighted with a dashed-dot circle.

Figure S10. Rate capability tests of LFNCP/Cu (●) and LFNCP/Cu+C (▲) at different scan rates (electrode composition by weight: 85.0 % of active material, 7.5 % of carbon, and 7.5 % of PVDF).

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Table S1

Activation energies (kJ·mol-1) of ε’’ dielectric relaxations of LFNCP, LFNCP/Cu, and LFNCP/Cu+C.

Ea / kJ·mol-1 LFNCP LFNCP/Cu LFNCP/Cu+CαVTFH 16.75±0.23 16.64±0.13 15.32±0.06βA 54.79±0.53 51.59±0.51 50.09±0.16

A :Arrhenius fit. VTFH: Vogel–Tammann–Fulcher-Hesse fit.

References

[S1] C. A. C. Sequeira, D. Santos, Polymer Electrolytes: Fundamentals and Applications; Wood-head Publishing Limited: Oxford, UK, 2010.

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