Chemical Composition of Lithiated Nitrodonickelates Li3-xyNixN: Evidence of the Intermediate Valence of Nickel Ions from Ion Beam Analysis and Ab Initio Calculations.

Lamellar lithiated nitridonickelates have been investigated from both experimental and theoretical points of view in a wide range of compositions. In this study, we show that the nickel ion in lamellar lithiated nitridonickelates adopts an intermediate valence close to +1.5. This solid solution can therefore be written Li3-1.5xNixN with 0 ≤ x ≤ 0.68. Attempts to introduce more nickel into these phases systematically lead to the presence of the endmember of the solid solution, Li1.97Ni0.68N, with metallic nickel as an impurity. The LiNiN phase has never been observed, and first-principles calculations suggested that all the structural configurations tested were mechanically unstable.

Mechanistic Investigation of a Hybrid Zn/V2 O5 Rechargeable Battery with a Binary Li+ /Zn2+ Aqueous Electrolyte.

Low-cost, easily processable, and environmentally friendly rechargeable aqueous zinc batteries have great potential for large-scale energy storage, which justifies their receiving extensive attention in recent years. An original concept based on the use of a binary Li+ /Zn2+ aqueous electrolyte is described herein for the case of the Zn/V2 O5 system. In this hybrid, the positive side involves mainly the Li+ insertion/deinsertion reaction of V2 O5 , whereas the negative electrode operates according to zinc dissolution-deposition cycles. The Zn//3 mol L-1 Li2 SO4 -4 mol L-1 ZnSO4/ //V2 O5 cell worked in the narrow voltage range of 1.6-0.8 V with capacities of approximately 136-125 mA h g-1 at rates of C/20-C/5, respectively. At 1 C, the capacity of 80 mA h g-1 was outstandingly stable for more than 300 cycles with a capacity retention of 100 %. A detailed structural study by XRD and Raman spectroscopy allowed the peculiar response of the V2 O5 layered host lattice on discharge-charge and cycling to be unraveled. Strong similarities with the well-known structural changes reported in nonaqueous lithiated electrolytes were highlighted, although the emergence of the usual distorted δ-LiV2 O5 phase was not detected on discharge to 0.8 V. The pristine host structure was restored and maintained during cycling with mitigated structural changes leading to high capacity retention. The present electrochemical and structural findings reveal a reaction mechanism mainly based on Li+ intercalation, but co-intercalation of a few Zn2+ ions between the oxide layers cannot be completely dismissed. The presence of zinc cations between the oxide layers is thought to relieve the structural stress induced in V2 O5 under operation, and this resulted in a limited volume expansion of 4 %. This fundamental investigation of a reaction mechanism operating in an environmentally friendly aqueous medium has not been reported before.

Li2.0Ni0.67N, a Promising Negative Electrode Material for Li-Ion Batteries with a Soft Structural Response.

The layered lithium nitridonickelate Li2.0(1)Ni0.67(2)N has been investigated as a negative electrode in the 0.02-1.25 V vs Li+/Li potential window. Its structural and electrochemical properties are reported. Operando XRD experiments upon three successive cycles clearly demonstrate a single-phase behavior in line with the discharge-charge profiles. The reversible breathing of the hexagonal structure, implying a supercell, is fully explained. The Ni2+/Ni+ redox couple is involved, and the electron transfer is combined with the reversible accommodation of Li+ ions in the cationic vacancies. The structural response is fully reversible and minimal, with a maximum volume variation of 2%. As a consequence, a high capacity of 200 mAh g-1 at C/10 is obtained with an excellent capacity retention, close to 100% even after 100 cycles, which makes Li2.0(1)Ni0.67(2)N a promising negative electrode material for Li-ion batteries.

A comparative insight of potassium vanadates as positive electrode materials for Li batteries: influence of the long-range and local structure.

Potassium vanadates with ratio K/V = 1:3, 1:4, and 1:8, prepared by a fast and facile synthesis route, were investigated as positive electrode materials in lithium batteries. KV3O8 and K0.5V2O5 have layered structures, while K0.25V2O5 exhibits a tunnel framework isomorphic to that of ß-Na0.33V2O5. The Raman spectra of KV3O8, K0.5V2O5, and K0.25V2O5 compounds are reported here for the first time, and a detailed comparative analysis distinguishes spectral patterns specific to each structural arrangement. The electrochemical performances of these potassium vanadates toward lithium insertion were investigated. The potassium-richer compound KV3O8 shows a good rechargeability in spite of a low discharge capacity of 70 mAh g(-1), while the potassium-poorer bronze K0.25V2O5 exhibits the highest specific capacity of 230 mAh g(-1) but a slow and continuous capacity fade with cycling. We demonstrate that the K0.5V2O5 compound, with its double-sheet V2O5 layered framework characterized by a large interlayer spacing of 7.7 Å, is the best candidate as positive electrode for lithium battery among the potassium-vanadium bronzes and oxides. A remarkable specific capacity of 210 mAh g(-1), combined with excellent capacity retention, is achieved.

Colossal magnetoresistance in Mn2+ oxypnictides NdMnAsO(1-x)F(x).

Colossal magnetoresistance is a rare phenomenon in which the electronic resistivity of a material can be decreased by orders of magnitude upon application of a magnetic field. Such an effect could be the basis of the next generation of memory devices. Here we report CMR in the antiferromagnetic oxypnictide NdMnAsO(1-x)F(x) as a result of competition between an antiferromagnetic insulating phase and a paramagnetic semiconductor upon application of a magnetic field. Mn(2+) oxypnictides are relatively unexplored, and tailored synthesis of novel compounds could result in an array of materials for further investigation and optimization.

Giant magnetoresistance in oxypnictides (La,Nd)OMnAs.

A sizeable negative magnetoresistance (MR) has been observed for oxypnictides LnOMnAs (Ln = La,Nd). MR up to -24% is observed at 200 K for LaOMnAs which is unprecedented for divalent Mn(2+). Both materials are weak ferromagnets with transition temperatures above room temperature.

Synthesis and superconducting properties of CaC6.

Among the superconducting graphite intercalation compounds, CaC6 exhibits the highest critical temperature Tc=11.5 K. Bulk samples of CaC6 are obtained by immersing highly oriented pyrographite pieces in a well-chosen liquid Li-Ca alloy for 10 days at 350 °C. The crystal structure of CaC6 belongs to the [Formula: see text] space group. In order to study the superconducting properties of CaC6, magnetisation was measured as a function of temperature and direction of magnetic field applied parallel or perpendicular to the c-axis. Meissner effect was evidenced, as well as a type II superconducting behaviour and a small anisotropy. In agreement with calculations, experimental results obtained from various techniques suggest that a classical electron-phonon mechanism is responsible for the superconductivity of CaC6. Application of high pressure increases the Tc up to 15.1 K at 8 GPa.