Nearly all high energy density cathodes for rechargeable lithium batteries are well-ordered materials where lithium and other cations occupy distinct sites. Cation-disordered materials are generally disregarded as cathodes because lithium diffusion tends to be limited by their structures. The performance of Li1.211Mo0.467Cr0.3O2 shows that lithium diffusion can be facile in disordered materials. Using ab initio computations, we demonstrate that this unexpected behavior is due to percolation of certain diffusion channels that are active in disordered structures, but is unique to Li excess materials. This leads to a unified understanding of high performance in both layered and Li excess materials, and opens up an exciting new direction for designing disordered electrode materials with high capacity and high energy density.

http://science.sciencemag.org/content/sci/early/2014/01/08/science.1246432.full.pdf

Unlocking the potential of cation-disordered oxides for rechargeable lithium batteries

Hydrogen storage alloys are of particular interest as a novel group in functional materials owing to their potential and practical applications in Ni/MH rechargeable batteries. This review is devoted to the specific alloy families developed for high-energy and high-power Ni/MH batteries in the last decades, especially for EV, HEV and PHEV applications. The scope of the work encompasses principles of Ni/MH batteries, electrochemical hydrogen storage thermodynamics and kinetics, prerequisites for hydrogen storage electrode alloys and recent advances in hydrogen storage electrode alloys. Rare earth AB5-type alloys, Ti- and Zr-based AB2-type alloys, Mg-based amorphous/nanocrystalline alloys, rare earth-Mg–Ni-based alloys and Ti–V-based alloys are highlighted. Additionally, the challenges met in developing advanced hydrogen storage alloys for Ni/MH rechargeable batteries are pointed out and some research directions are suggested.

Advanced hydrogen storage alloys for Ni/MH rechargeable batteries

A unifying theory is presented to explain the lithium exchange capacity of rocksalt-like structures with any degree of cation ordering, and how lithium percolation properties can be used as a guideline for the development of novel high-capacity electrode materials is demonstrated. The lithium percolation properties of the three most common lithium metal oxide phases, the layered α-NaFeO2 structure, the spinel-like LT-LiCoO2 structure, and the γ-LiFeO2 structure, are demonstrated and a strong dependence of the percolation thresholds on the cation ordering and the lithium content is observed. The poor performance of γ-LiFeO2-type structures is explained by their lack of percolation of good Li migration channels. The spinel-like structure exhibits excellent percolation properties that are robust with respect to off-stoichiometry and some amount of cation disorder. The layered structure is unique, as it possesses two different types of lithium diffusion channels, one of which is, however, strongly dependent on the lattice parameters, and therefore very sensitive to disorder. In general it is found that a critical Li-excess concentration exists at which Li percolation occurs, although the amount of Li excess needed depends on the partial cation ordering. In fully cation-disordered materials, macroscopic lithium diffusion is enabled by ≈10% excess lithium.

The Configurational Space of Rocksalt‐Type Oxides for High‐Capacity Lithium Battery Electrodes

For lithium-ion rechargeable batteries to meet society's ever-growing demands in electrical energy storage, e.g. for the electrification of transportation, for portable electronics and for grid storage applications, novel electrode materials with a large charge storage capacity and a high energy density are needed. Over the last five years, several experimental and theoretical studies have demonstrated the feasibility of disordered rocksalt (DRX) cathodes, that is, lithium transition metal oxide cathodes with a crystalline rocksalt structure but with a disordered arrangement of lithium and transition metal on the cation lattice. We provide here an overview of the current understanding of DRX materials, in terms of their structural and compositional characteristics, as well as their electrochemical properties. We also present important considerations for the design of high performance DRX cathodes and suggest future research directions. Because no specific order is needed, DRX compounds can be composed of a wide variety of transition metal species, which can create long-term benefits for the lithium battery industry by making it less reliant on scarce and expensive raw materials. While some DRX compositions can simply be synthesized at high temperature to induce thermal cation disorder, other compositions require mechanochemical methods to induce a disordered arrangement of cation species. Cation disorder leads to unique lithium transport properties, small volume changes during charge–discharge cycling and sloping electrochemical profiles. Fluorine substitution for oxygen and the incorporation of high-valent d0 transition metals in the bulk DRX structure are two strategies used to increase the lithium content in the material, improve lithium percolation and to keep the valence of redox-active metal species low so that high transition metal redox capacity can be obtained. Short-range cation order, which is affected by thermal treatment, metal composition and fluorine substitution, has a significant impact on electrochemical performance. Moreover, fluorine substitution for oxygen improves long-term capacity retention by significantly reducing anion-based charge compensation mechanisms during charge. Fluorinated DRXs have recently demonstrated reversible capacities >300 mA h g−1 and extremely high energy densities approaching 1000 W h kg−1, holding promise for a nearly two-fold increase in the energy density of commercial lithium-ion batteries.

/pdf/cation-disordered-rocksalt-transition-metal-oxides-and-1uomfsy81z.pdf

Cation-disordered rocksalt transition metal oxides and oxyfluorides for high energy lithium-ion cathodes

Electrochemical hydrogen storage: Opportunities for fuel storage, batteries, fuel cells, and supercapacitors

Electrochemical properties of MmNi3.8Co0.75Mn0.4Al0.2 hydrogen storage alloy modified with nanocrystalline nickel

Effect of surface treatment on electrochemical properties of MmNi3.8Co0.75Mn0.4Al0.2MmNi3.8Co0.75Mn0.4Al0.2 hydrogen storage alloy

An amorphous Ti2Ni alloy, prepared by mechanical milling of a crystalline Ti2Ni alloy, was heat-treated at several temperatures. The crystalline behavior of the amorphous alloy was studied , relative to a multi-stage crystallization mode, using X-ray diffraction, differential scanning calorimetry, and electron diffraction. X-Ray photoelectron spectroscopy was performed to analyze the surface structure of the alloys. The alloy that was heat-treated at 693 K, with a non-equilibrium bulk structure and a protective surface layer, has a high discharge capacity and good cycling stability. The issue of severe capacity loss of Ti2Ni-based alloys, which has caused problems for many years, has been significantly improved.

Ti2Ni alloy: a potential candidate for hydrogen storage in nickel/metal hydride secondary batteries

Li2CoTiO4 as a new titanate cathode material for Li-ion batteries was successfully synthesized by a sol–gel process. It had a cation disordered rock salt structure and showed an excellent cycle stability at room temperature. After coating with carbon, the Li2CoTiO4 possessed a high discharge capacity of 144.3 mAh g−1. The poor conductivity and lithium ion diffusion coefficient of pure Li2CoTiO4 are the main reasons for the limited electrochemical performance of the lithium batteries. The irreversible capacity loss during the first cycle was assigned to the irreversibility of the structural changes.

Cation disordered rock salt phase Li2CoTiO4 as a potential cathode material for Li-ion batteries

Effect of Ti addition on mechanical properties and corrosion resistance of Ni-free Zr-based bulk metallic glasses for potential biomedical applications

Yi Ding

Papers

Electrochemical properties of MmNi3.8Co0.75Mn0.4Al0.2 hydrogen storage alloy modified with nanocrystalline nickel

Effect of surface treatment on electrochemical properties of MmNi3.8Co0.75Mn0.4Al0.2MmNi3.8Co0.75Mn0.4Al0.2 hydrogen storage alloy

Ti2Ni alloy: a potential candidate for hydrogen storage in nickel/metal hydride secondary batteries

Cation disordered rock salt phase Li2CoTiO4 as a potential cathode material for Li-ion batteries

Effect of Ti addition on mechanical properties and corrosion resistance of Ni-free Zr-based bulk metallic glasses for potential biomedical applications