Li-ion batteries have contributed to the commercial success of portable electronics and may soon dominate the electric transportation market provided that major scientific advances including new ...materials and concepts are developed. Classical positive electrodes for Li-ion technology operate mainly through an insertion-deinsertion redox process involving cationic species. However, this mechanism is insufficient to account for the high capacities exhibited by the new generation of Li-rich (Li(1+x)Ni(y)Co(z)Mn(1-x-y-z)O₂) layered oxides that present unusual Li reactivity. In an attempt to overcome both the inherent composition and the structural complexity of this class of oxides, we have designed structurally related Li₂Ru(1-y)Sn(y)O₃ materials that have a single redox cation and exhibit sustainable reversible capacities as high as 230 mA h g(-1). Moreover, they present good cycling behaviour with no signs of voltage decay and a small irreversible capacity. We also unambiguously show, on the basis of an arsenal of characterization techniques, that the reactivity of these high-capacity materials towards Li entails cumulative cationic (M(n+)→M((n+1)+)) and anionic (O(2-)→O₂(2-)) reversible redox processes, owing to the d-sp hybridization associated with a reductive coupling mechanism. Because Li₂MO₃ is a large family of compounds, this study opens the door to the exploration of a vast number of high-capacity materials.
Li-ion batteries have empowered consumer electronics and are now seen as the best choice to propel forward the development of eco-friendly (hybrid) electric vehicles. To enhance the energy density, ...an intensive search has been made for new polyanionic compounds that have a higher potential for the Fe²⁺/Fe³⁺ redox couple. Herein we push this potential to 3.90 V in a new polyanionic material that crystallizes in the triplite structure by substituting as little as 5 atomic per cent of Mn for Fe in Li(Fe(1-δ)Mn(δ))SO₄F. Not only is this the highest voltage reported so far for the Fe²⁺/Fe³⁺ redox couple, exceeding that of LiFePO₄ by 450 mV, but this new triplite phase is capable of reversibly releasing and reinserting 0.7-0.8 Li ions with a volume change of 0.6% (compared with 7 and 10% for LiFePO₄ and LiFeSO₄F respectively), to give a capacity of ~125 mA h g⁻¹.
Self-organized Sn-doped TiO2 nanotubes were fabricated by anodization of co-sputtered Ti–Sn thin films in a glycerol electrolyte containing NH4F. The Sn-doped TiO2nts were studied in terms of ...composition, morphology and structure by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and 119Sn Mössbauer spectroscopy. The electrochemical behaviour of the Sn-doped TiO2nts was evaluated in Li test cells as a possible negative electrode for 3D Li-ion micro batteries. The Sn-doped TiO2nts delivered much higher capacity values compared to simple TiO2nts. The outstanding electrochemical behaviour is proposed to be related to the enhanced lithium diffusivity evidenced with Cottrell plots, and the rutile-type structure imparted with the Sn doping.
► Sn-doped TiO2 nanotubes were fabricated by anodization of sputtered Ti–Sn thin films. ► The Sn-doped TiO2nts can be used as anodes for 3D Li-ion micro batteries. ► The electrochemical performance of Sn-doped TiO2nts was better than simple TiO2nts. ► The improved performance is related to enhanced lithium diffusivity with Sn doping. ► This synthesis approach is extendable for Fe/Sb/Nb-doping of TiO2 nanotubes.
The electrochemical properties of carbon and reduced graphene-coated Na
4
Ni
3
(PO
4
)
2
P
2
O
7
materials have been evaluated as high-voltage positive electrodes for sodium-ion batteries. Na
4
Ni
3
...(PO
4
)
2
P
2
O
7
exhibits the highest Ni
3+
/Ni
2+
redox potential of 4.8 V
vs
. Na
+
/Na with a theoretical capacity of 127 mAh g
−1
. Here, we report on the synthesis and characterizations of Na
4
Ni
3
(PO
4
)
2
P
2
O
7
-reduced graphene oxide and Na
4
Ni
3
(PO
4
)
2
P
2
O
7
-carbon composites. The high-voltage dimethyl carbonate–based electrolyte has been chosen to explore the electrochemical properties of Na
4
Ni
3
(PO
4
)
2
P
2
O
7
as a cathode. Carbon-coated Na
4
Ni
3
(PO
4
)
2
P
2
O
7
composite electrode delivers a stable discharge capacity of 51 mAh g
−1
at 0.1 C rate for 40 cycles which corresponds to a reversible intercalation/de-intercalation of 1.3 sodium ions. The structural deformation has been observed during the charge–discharge process beyond the removal of 1.3 Na
+
ions and has been confirmed by
in situ
PXRD measurements. The present results provide a guideline to improve the performances of the high-voltage Na
4
Ni
3
(PO
4
)
2
P
2
O
7
material for the next generation sodium-ion batteries.
Display omitted
► Si/Sn–Ni/C nanostructured composite is synthesized by ball milling. ► The composite is formed by Si nanoparticles embedded on a multi-element matrix. ► It exhibits a capacity of ...920mAhg−1 with good stability for 280 cycles. ► Si/Sn–Ni/C is a competitive anode material for lithium ion batteries.
A nanostructured composite with overall atomic composition Ni0.14Sn0.17Si0.32Al0.037C0.346 has been prepared combining powder metallurgy and mechanical milling techniques for being used as anode material in Li-ion battery. Chemical and structural properties of the nanocomposite have been determined by X-ray diffraction (XRD), 119Sn Transmission Mössbauer Spectroscopy (TMS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composite consists of Si particles with typical size ∼150nm embedded in a poorly crystallized and complex multielemental matrix. The matrix is composed mostly by Ni3.4Sn4, and disordered carbon. Electrochemical evaluation shows a high reversible capacity of 920mAhg−1, with reasonable reversible capacity retention (∼0.1% loss/cycle) over 280 cycles.
With the aim of developing 3V all-solid-state lithium microbatteries, Fe2(MoO4)3 thin films were prepared by radiofrequency magnetron sputtering from a home-made Fe2(MoO4)3 target using optimized ...sputtering conditions. In addition to elemental analyses, Mössbauer spectroscopy and XPS analyses, showing that Mo6+ and Fe3+ are the main detected species, confirmed the stoichiometric character of the films. Post-deposition annealing was necessary to form well-crystallized thin films. The best electrochemical performance was obtained with those annealed at 500 °C which were able to deliver a stable reversible capacity close to the theoretical one, i.e. 2 Li+ per Fe2(MoO4)3 formula unit. The corresponding voltage curve displays a plateau with a low hysteresis located at 3.0 V/Li+/Li and related to the Fe2(MoO4)3 – Li2Fe2(MoO4)3 two-phase system. Therefore, it was demonstrated for the first time the possible use of Fe2(MoO4)3 thin films as positive electrodes for 3 V lithium microbatteries.
•Optimization of the sputtering conditions to get thin films with a stoichiometric composition Fe2(MoO4)3.•Ability of these thin films to reversibly insert and deinsert 2 Li ions demonstrated for the first time.•Dense thin film well-adapted for an integration in all-solid-state microbatteries.
The electrochemical reaction of lithium ion with Mg2FeH6, Mg2CoH5 and Mg2NiH4 complex hydrides prepared by reactive grinding is studied here. Plateaus at an average potential of 0.25 V, 0.24 V and ...0.27 V corresponding to discharge capacities of 6.6, 5.5 and 3.6 Li can be achieved respectively for Mg2FeH6, Mg2CoH5 and Mg2NiH4. From in situ X-ray diffraction (XRD) characterizations of complex hydride based electrodes, dehydrogenation leads to a decrease of the intensities of the diffraction peaks suggesting a strong loss of crystallinity since formation of Mg and M (M = Fe, Co, Ni) peaks is not observed. 57Fe Mössbauer spectroscopy confirms the formation of nanoscale Fe or an amorphous Mg–Fe alloy during the decomposition of Mg2FeH6. Interestingly, lattice parameter variations suggest phase transitions in the Mg2NiH4 system involving the formation of low hydrogen content hydride Mg2NiH, while an increase of lattice parameters of Mg2CoH5 hydride could be attributed to the formation of a Mg2CoH5Lix solid solution compound up to x = 1.
► Electrochemical reactivity of Mg2FeH6, Mg2CoH5 and Mg2NiH4 hydrides with lithium ion. ► Plateaus at 0.25, 0.24, 0.27 V corresponding to discharge capacities of 6.6, 5.5, 3.6 lithium. ► Mg2FeH6: Formation of nano Fe or amorphous Mg–Fe alloy during the decomposition. ► Mg2CoH5: Formation of a Mg2CoH5Lix solid solution suggested. ► Mg2NiH4: Formation of Mg2NiH hydride proposed.
•Iron doped brownmillerite structures are investigated by X-ray diffraction and Mössbauer spectroscopy.•A crystallographic anomaly in cell parameters and crystallite size have been found for ...intermediate iron content.•Mössbauer spectroscopy shows that the majority of Fe is Fe3+, but that a small amount of Fe4+ is not excluded.
Iron doped brownmillerite oxides LaSrMn2−xFexO5 (0⩽x⩽0.5) have been prepared as pure powders by a conventional solid state reaction and studied by X-ray powder diffraction, scanning electronic microscope and Mössbauer spectroscopy. Rietveld analysis of X-ray diffraction patterns confirms that all samples crystallize in the orthorhombic system with Pnma space group and are isotypic with the Ca2Fe1.039Mn0.962O5 phase. Cell parameters and crystallite size show an anomaly around x=0.2 which is explained by the partial substitutions of Mn2+ and Mn3+ by Fe3+ and small amounts of Fe4+. A detailed analysis of the Mössbauer spectra for all compounds measured at room temperature shows that Fe3+ ions are located in distorted octahedral and tetrahedral sites. The environment and oxidation states of Mn and Fe are determined by bond valence sum calculations and the results for Fe are compared to the results from the Mössbauer study.
Understanding the reactivity of lithium toward new materials proposed for electrodes in lithium ion batteries is an important step to improve material performances. In this work, the reactivity with ...Li of a new negative electrode material with atomic composition Ni0.14Sn0.17Si0.32Al0.037C0.346 is carried out. Powerful characterization methods (Operando XRD, Transmission Mössbauer Spectroscopy TMS and Cyclic Voltammetry CV) have been used to investigate electrochemical and structural transformations along cycling. The excellent behavior of this new composite is achieved thanks to the reversible reactions of all components with lithium, namely Si, Ni3,4Sn4 and C phases. Formation of Li–Sn and Li–Si alloys is identified and discussed.
Display omitted
•Understanding Li reactivity toward Ni0.14Sn0.17Si0.32Al0.037C0.346 nano-composite.•Use powerful operando methods to study transformations along Li composite cycling.•Si forms amorphous Li–Si alloys while Ni3.4Sn4 decomposes reversibly in Li–Sn ones.
PDF
