Overall conductivity and NCL-type relaxation behavior in nanocrystalline sodium peroxide Na 2 O 2 —Consequences for Na-oxygen batteries

Partial electronic conductivity of nanocrystalline Na2O2

“…This ratio is also obtained when we look at the initial current I(t = 0) ≈ 8 × 10 −13 A; it is indeed twice the final one and hence in good agreement with our earlier AC impedance data. With I(t = 0) = 0.8 pA (pellet A) we end up with σ total = 2.2 × 10 −13 S cm −1 at 293 K, see also [10]. For pellet B the same ratio I(t = 0)/I(t → ∞) ≈ 0.6/0.29 ≈ 2 can be estimated.…”

“…The efficiency and long-term behavior of the batteries is expected to significantly depend on the electric and dynamic properties of the discharge products formed [7]; the same holds for the Li-oxygen system. Such information is, however, rarely available so far [8][9][10]. To our knowledge, the electric conductivity of defect-rich nanocrystalline Na 2 O 2 at room temperature has not been reported as yet.…”

“…Here we used potentiostatic polarization measurements to record the partial electronic conductivity of nanocrystalline Na 2 O 2 at room temperature. A recent study [10] has shown that the overall conductivity of nanocrystalline Na 2 O 2 , which was prepared by high-energy ball-milling of coarse-grained Na 2 O 2 , is by one order of magnitude higher than that of Na 2 O 2 with µm-sized crystallites, see also [13]. It has been demonstrated that in nanostructured Na 2 O 2 , for which we expect a large number of defects introduced during mechanical treatment, the total conductivity approached an upper limit [10].…”

“…A recent study [10] has shown that the overall conductivity of nanocrystalline Na 2 O 2 , which was prepared by high-energy ball-milling of coarse-grained Na 2 O 2 , is by one order of magnitude higher than that of Na 2 O 2 with µm-sized crystallites, see also [13]. It has been demonstrated that in nanostructured Na 2 O 2 , for which we expect a large number of defects introduced during mechanical treatment, the total conductivity approached an upper limit [10]. This peak value, which is much lower than for mechanically treated oxides [14,15], was almost reached after the sample had been ball milled in Ar atmosphere for 60 min [10].…”

“…It has been demonstrated that in nanostructured Na 2 O 2 , for which we expect a large number of defects introduced during mechanical treatment, the total conductivity approached an upper limit [10]. This peak value, which is much lower than for mechanically treated oxides [14,15], was almost reached after the sample had been ball milled in Ar atmosphere for 60 min [10]. It is expected to be governed by (i) the defect chemistry, (ii) the increased volume fraction of (locally) disordered interfacial regions [14][15][16][17] as well as (iii) by the non-negligible effect of overlapping space charge zones known to play a pivotal role in nanostructured systems [18].…”