SUPPORTING INFORMATION Na2Ti3O7: the lowest voltage ever ...

Na2Ti3O7 and 30% carbon black (blue curve) once the contribution from carbon black has been substracted. The inset shows derivative curves for the first two ...
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SUPPORTING INFORMATION

Na2Ti3O7: the lowest voltage ever reported oxide insertion electrode material for sodium ion batteries Premkumar Senguttuvan,‡† Gwenaëlle Rousse,# Vincent Seznec,† Jean-Marie Tarascon, ¥† M.Rosa Palacín ‡*

‡ Institut de Ciència de Materials de Barcelona (ICMAB-CSIC) Campus UAB, E-08193 Bellaterra, Catalonia, (Spain) ALISTORE ERI European Research Institute † Laboratoire de Réactivité et Chimie des Solides, UPJV, CNRS UMR6007, 33 rue Saint Leu 80039 Amiens, (France). ALISTORE ERI European Research Institute # Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC) UMR 7590 CNRS-Université Pierre et Marie Curie, Case courrier 115, 4 Place Jussieu, 75252 Paris Cedex 05, (France) ¥ Collège de France, 11 Place Marcelin Berthelot, 745005 Paris (France)

Figure S1: Rietveld refinement of the XRD pattern (Cu K) of pristine Na2Ti3O7. Red dots are experimental points, black line is the calculated pattern. The blue line is the difference curve. Green tick bars indicate Bragg reflections of space group P21/m. Insets show the crystal structure and typical SEM image.

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Table 1 Crystallographic data of pristine Na2Ti3O7 resulting from refinements of the structure against the X-Ray powder diffraction data at room temperature. In addition to the atomic positions derived from the Rietveld refinement, is indicated the valence bonds sum for each atom (see text).

atom Wyckoff Na1 Na2 Ti1 Ti2 Ti3 O1 O2 O3 O4 O5 O6 O7

2e 2e 2e 2e 2e 2e 2e 2e 2e 2e 2e 2e

space group

P21/m

a (Å) b (Å) c (Å) β (°)

8.5642(3) 3.8012(1) 9.1265(3) 101.598(2)

V (Å3) RBragg (%) RF (%) 2

291.05(1) 10.8 10.1 1.58

x

y

z

Biso(Å2)

0.677(2) 0.494(2) 0.030(1) 0.252(1) 0.149(1) 0.228(2) 0.155(3) 0.445(3) 0.334(3) 0.020(3) 0.794(3) 0.907(3)

¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼

0.590(2) 0.160(2) 0.281(1) 0.676(1) 0.989(1) 0.196(3) 0.461(3) 0.645(3) 0.913(2) 0.752(2) 0.320(3) 0.041(3)

1.6(2) 1.6(2) 1.6(2) 1.6(2) 1.6(2) 0.2(2) 0.2(2) 0.2(2) 0.2(2) 0.2(2) 0.2(2) 0.2(2)

BVS 1.04(4) 1.01(3) 3.84(8) 4.07(11) 3.75(9) 1.83(6) 2.09(7) 2.00(10) 1.77(7) 2.01(3) 2.00(4) 2.00(4)

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250

150

40 20

dx/dV

Capacity (mAh/g) Capacity (mAh/g)

200

100

0 -20 -40 -60

50

0

0.2

0.4

0.6

+

0.8

1

Potential Vs Na /Na (V)

0 0

1

2

3 cycle number

4

5

6

Cycle number

Figure S2: Capacity versus cycle number for the reduction of a composite electrode containing Na2Ti3O7 and 30% carbon black (blue curve) once the contribution from carbon black has been substracted. The inset shows derivative curves for the first two cycles and the blank experiment containing only carbon black (in blue). The comparison clearly evidences that the redox process observed at ca. 0.7V is due to reaction of carbon black with sodium electrolyte and does not involve Na2Ti3O7.

S3