Sodium‐deficient nickel–manganese oxides exhibit a layered structure, which is flexible enough to acquire different layer stacking. The effect of layer stacking on the intercalation properties of P3‐NaxNi0.5Mn0.5O2 (x=0.50, 0.67) and P2‐Na2/3Ni1/3Mn2/3O2, for use as cathodes in sodium‐ and lithium‐ion batteries, is examined. For P3‐Na0.67Ni0.5Mn0.5O2, a large trigonal superstructure with 2√3 a×2√3 a×2 c is observed, whereas for P2‐Na2/3Ni1/3Mn2/3O2 there is a superstructure with reduced lattice parameters. In sodium cells, P3 and P2 phases intercalate sodium reversibly at a well‐expressed voltage plateau. Preservation of the P3‐type structure during sodium intercalation determines improving cycling stability of the P3 phase within an extended potential range, in comparison with that for the P2 phase, for which a P2–O2 phase transformation has been found. Between 2.0 and 4.0 V, P3 and P2 phases display an excellent rate capability. In lithium cells, the P3 phase intercalates lithium, accompanied by a P3–O3 structural transformation. The in situ generated O3 phase, containing lithium and sodium simultaneously, determines the specific voltage profile of P3‐NaxNi0.5Mn0.5O2. The P2 phase does not display any reversible lithium intercalation. The P3 phase demonstrates a higher capacity at lower rates in lithium cells, whereas in sodium cells P3‐NaxNi0.5Mn0.5O2 operates better at higher rates. These findings reveal the unique ability of sodium‐deficient nickel–manganese oxides with a P3‐type structure for application as low‐cost electrode materials in both sodium‐ and lithium‐ion batteries.

The study demonstrates unusual capabilities of phospho-olivine NaMnPO4 to intercalate lithium and sodium reversibly, which makes it attractive electrode material instead of the conventional lithium analogue LiMnPO4.

The development of lithium and sodium ion batteries without using lithium and sodium metal as anodes gives the impetus for elaboration of low-cost and environmentally friendly energy storage devices. In this contribution we demonstrate the design and construction of a new type of hybrid sodium-lithium ion cell by using unique electrode combination (Li4Ti5O12 spinel as a negative electrode and layered Na3/4Co1/3Ni1/3Mn1/3O2 as a positive electrode) and conventional lithium electrolyte (LiPF6 salt dissolved in EC/DMC). The cell operates at an average potential of 2.35 V by delivering a reversible capacity of about 100 mAh/g. The mechanism of the electrochemical reaction in the full sodium-lithium ion cell is studied by means of postmortem analysis, as well as ex situ X-ray diffraction analysis, HR-TEM, and electron paramagnetic resonance spectroscopy (EPR). The changes in the surface composition of electrodes are examined by ex situ X-ray photoelectron spectroscopy (XPS).

Sodium-deficient nickel–manganese oxides with a layered type of structure are, nowadays, of great interest as electrode materials for both lithium- and sodium-ion batteries since they are able to intercalate lithium and sodium ions reversibly within a broad concentration range. Herein, we report new data on the effects of the particle sizes and of the electrolyte salt on the intercalation properties of Na2/3Ni0.5Mn0.5O2 with a P3-type of structure. The morphology of layered Na2/3Ni0.5Mn0.5O2 oxides has been varied by changing the type of the precursor used: from Na–Ni–Mn acetates to Na–Ni–Mn mixed nitrate acetates. The structure, particle dimensions, and particle size distribution of oxides have been determined by means of powder X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light-scattering measurements, and X-ray photoelectron spectroscopy (XPS). The intercalation properties of Na2/3Ni0.5Mn0.5O2 have been studied in model electrochemical cells versus Li metal as the anode. We used two kinds of lithium salts dissolved in organic solutions as the electrolytes: 1 M LiPF6 in EC:DMC and 1 M LiBF4 in EC:DMC. The mechanism of the lithium intercalation into Na2/3Ni0.5Mn0.5O2 is discussed on the basis of e x situ XRD, HRTEM, and X-ray photoelectron spectroscopy analyses. It has been discovered that the lithium salt in the electrolyte salt contributes to the mechanism of the electrochemical reaction, while particle dimensions determine the capacity stability during continuous cycling, as well as the surface reactivity of oxide electrodes.

De-alloying, i.e. selective dissolution of alloys, is currently studied to produce nanoporous gold items suited for use in catalysis, electrochemical applications, sensors and actuators. Both crystalline and amorphous alloys can be selectively etched. In the former, less noble atoms are removed from surface terraces of grains layer by layer, while noble ones form mounds. These evolve by undercutting and electrolytepercolation to form a ligament network. The mechanism of ligament development by de-alloying amorphous alloys is unknown. Here we show that for de-alloying a Au-based glass, in this case Au 40 Cu 28 Ag 7 Pd 5 Si 20 , percolation of the electrolyte through cracks of the native surface oxide initiates the formation of protuberances which are soon undercut. An interlayer develops, where Au crystals germinate, grow to nanometer size by diffusion and impinge. This is how ligaments start to coarsen. The interlayer is found at all stages between coarsened ligaments and amorphous phase. The ligaments are defective polycrystals, as opposed to single crystals obtained from crystalline alloys.