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The bottleneck in the implementation of hybrid lithium-sodium-ion batteries is the lack of anode materials with a desired rate capability. Herein, we provide an in-depth examination of the Li-storage performance of sodium titanate nanowires as negative electrodes in hybrid Li,Na-ion batteries. Titanate nanowires were prepared by a simple and reproducible hydrothermal method. At a low reaction pressure, the well-isolated nanowires are formed, while by increasing the reaction pressure from 2 to 30 bar, the isolated nanowires tend to bundle. In nanowires, the local coordinations of Na and Ti atoms deviate from those in Na2Ti3O7 and Na2Ti6O13 and slightly depend on the reaction pressure. During the annealing at 350 °C, both Na and Ti coordinations undergo further changes. The nanowires are highly defective, and they easily crystallize into Na2Ti6O13 and Na2Ti3O7 phases. The lithium storage properties are evaluated in lithium-ion cells vs. lithium metal anode and titanate electrodes fabricated with PVDF and carboxymethyl cellulose (CMC) binders. The Li-storage by nanowires proceeds by a hybrid capacitive-diffusive mechanism between 0.1 and 2.5 V, which enables to achieve a high specific capacity. Sodium titanates accommodate Li+ by formation of mixed lithium-sodium-phase Na2−xLixTi6O13, which is decomposed to the distinct lithium phases Li0.54Ti2.86O6 and Li0.5TiO2. Contrary to lithium, the sodium storage is accomplished mainly by the capacitive reactions, and thus the phase composition is preserved during cycling in sodium ion cells. The isolated nanowires outperform bundled nanowires with respect to rate capability. [ABSTRACT FROM AUTHOR]

The energy storage by redox intercalation reactions is, nowadays, the most effective rechargeable ion battery. When lithium is used as intercalating agents, the high energy density is achieved at an expense of non‐sustainability. The replacement of Li+ with cheaper monovalent ions enables to make greener battery alternatives. The utilization of polyvalent ions instead of Li+ permits to multiplying the battery capacity. Contrary to Li+, the realization of quick and reversible intercalation of bigger monovalent and of polyvalent ions is a scientific challenge due to kinetic constraints, polarizing ion effects and Coulomb interactions. Herein we provide a vision how to make the intercalation of these ions feasible. The idea is to perform dual intercalation of ions having different charges, radii, preferred coordination and diffusion pathway topology. All these features are demonstrated by the recent knowledge on selective and non‐selective intercalation properties of oxides and polyanion compounds with layered and tunnel structures. Based on dual intercalation properties, the fabrication of hybrid metal ion batteries is presented and discussed. This personal account provides a vision for the energy storage by a radical change in the kind of the intercalating ions and intercalation matrices. The idea is to utilize the dual intercalation of monovalent and polyvalent ions in various compounds instead of conventional single Li+ intercalation. This approach will be of significance for elaboration a new type of hybrid metal ion batteries. [ABSTRACT FROM AUTHOR]

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-Na xNi0.5Mn0.5O2 ( 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-Na xNi0.5Mn0.5O2. 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-Na xNi0.5Mn0.5O2 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. [ABSTRACT FROM AUTHOR]

We report precursor-based methods for low-temperature synthesis of two structure modifications of NaMnPO4. The maricite phase is thermodynamically more stable, while the olivine phase is of great interest as a positive-electrode material for lithium and sodium ion batteries. The advantage of synthetic procedures is the formation of defectless NaMnPO4 in the temperature range of 200–400 °C. The structure and morphology characterizations of two modifications are performed by powder XRD, SEM and TEM analyses. The oxidation state of the Mn ions in NaMnPO4 is determined by X-ray photoelectron spectroscopy. The local environment of Na in both structure modifications is assessed by 23Na MAS NMR spectroscopy. The synthesis methods are based on the formation of appropriate precursors that are easily transformed to target NaMnPO4. Thermal decomposition of freeze-dried phosphate–formate precursor yields NaMnPO4 with a maricite structure at 400 °C. KMnPO4·H2O with a dittmarite-type structure acts as a structure-template precursor for the preparation of NaMnPO4 with an olivine structure by an ion exchange reaction. Both olivine and maricite NaMnPO4 do not accommodate any anti-site mixing and Na,Mn deficiency. The morphology of NaMnPO4 consists of nano-sized particles (less than 50 nm) that are closely bound together into aggregates, the shape of the aggregates being dependent on the synthesis procedure used. [ABSTRACT FROM AUTHOR]

To create both greener and high-power metal-ion batteries, it is of prime importance to invent an unprecedented electrode material that will be able to store a colossal amount of charge carriers by a redox mechanism. Employing periodic DFT calculations, we modeled a new metal-organic framework, which displays energy density exceeding that of conventional inorganic and organic electrodes, such as Li- and Na-rich oxides and anthraquinones. The designed MOF has a rhombohedral unit cell in which an Ni(II) node is coordinated by 2,5-dicyano-p-benzoquinone linkers in such a way that all components participate in the redox reaction upon lithiation, sodiation and magnesiation. The spatial and electronic changes occurring in the MOF after the interaction with Li, Na and Mg are discussed on the basis of calculated electrode potentials versus Li0/Li+, Na0/Na+ and Mg0/Mg2+, respectively. In addition, the specific capacities and energy densities are calculated and used as a measure for the electrode applicability of the designed material. Although the highest capacity and energy density are predicted for Li storage, the greater structural robustness toward Na and Mg uptake suggests a higher cycling stability in addition to lower cost. The theoretical results indicate that the MOF is a promising choice for a green electrode material (with <10% heavy metal content) and is well worth experimental testing. [ABSTRACT FROM AUTHOR]

Hydrothermal activation was used to modify the lithium-insertion properties of graphitized carbon nanotubes. The resulting solids showed a net improvement in their performance as anodes for advanced lithium-ion batteries. The mechanism of the electrochemical reaction with lithium of the modified carbon nanotubes was studied by X-ray diffraction and a combined use of two powerful resonance spectroscopies: solid-state nuclear magnetic resonance and electron paramagnetic resonance. Lithium was first intercalated in the activated multiwalled nanotubes between graphene layers, forming n-stages. Interlayer expansion and misfit between curved layers caused fracture and exfoliation of the nanotubes with an irreversible loss of staging phenomena. The resulting solids displayed an improved capacity retention on successive cycles. The line shape of electron paramagnetic resonance and Knight shifts in nuclear magnetic resonance reveal the electronic changes induced by lithium incorporation-removal in activated nanotubes. These results suppose a new strategy to improve the electrochemical performance of graphitized carbon nanotubes. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical extraction/insertion of Li from/into LiCoMnO4 in the potential range of 3.7–5.25V is studied by electron paramagnetic resonance (EPR) of Mn4+. Structural characterization of initial LiCoMnO4 has been performed by neutron diffraction. The EPR spectra are consistent with a single-phase mechanism of electrochemical extraction/insertion of Li from/into LiCoMnO4. During Li extraction, the intensity of the main EPR signal due to Mn4+ ions in Mn4+/Co3+ environment decreases drastically concomitantly with the appearance of resonance absorption from magnetically correlated Mn4+–Co4+ spins. From EPR, the complex [Co n+–Mn3+–Mn4+] clusters indicative of the oxygen non-stoichiometry of LiCoMnO4 also take part in the electrochemical reaction, especially up to 4.7V. During the Li reinsertion, the EPR signal from Mn4+ ions in Mn4+/Co3+ environment is recovered, but its intensity remains lower (30%) as compared to that of the initial composition, which is consistent with an unrecovered composition of LiCoMnO4 electrode after first charge/discharge. Contrary to the narrow main signal, there is a reverse reduction of the paramagnetic ions present in the clusters, but their oxidation state as compared to the initial composition is not recovered. [Copyright &y& Elsevier]