Brett Ammundsen

Proton insertion and lithium-proton exchange in spinel lithium manganates

Abstract The protonic species formed in spinel λ-MnO 2 by proton exchange for lithium ions in Li 1+ x Mn 2− x O 4 precursors have been characterised by infrared and inelastic neutron scattering spectroscopies. Proton diffusion into the lattice appears to depend on the presence of octahedral manganese vacancies, with formation of lattice hydroxyl co-existing with water. Mechanisms of proton transfer are considered in relation to lithium-proton exchange during reinsertion of lithium into the materials, and for insertion of additional protons by chemical reduction.

Local structure and defect chemistry of substituted lithium manganate spinels : X-ray absorption and computer simulation studies

Abstract The charge distributions and effects on local structure resulting from substitution of Mn by Ti, Cr, Co and Ga in LiMn 2 O 4 are determined by X-ray absorption spectroscopy. Atomistic simulation methods are used to obtain additional insights into local structure and to calculate the energetics of lithium disorder and migration in lattices containing these substitutional ions or Li on octahedral Mn sites. The formation of protonic species in spinel lithium manganates is discussed in relation to a tetrahedral–octahedral vacancy pair model.

Intercalation Reactions of Layered Manganese(III, IV) Oxides

Layered hydrated birnessite-type manganese oxides have been intercalated with n-alkylammonium ions by ion-exchange for interlayer sodium or potassium, and by acid-base reactions. The expanded phases have modified interlayer environments and can be used as precursors for intercalation of aniline, which is oxidised and polymerised between the layers.

EXAFS: A Structural Probe for Cathode Materials in Lithium Ion Batteries

The use of lithium manganate spinels as cathode materials in advanced batteries is dependent upon their lithium extraction and insertion properties. These compounds are particularly versatile in terms of tailoring their electrochemical behaviour, as they are able to incorporate large amounts of substitutional ions and changes in lithium and oxygen stoichiometry while retaining the spinel crystal structure. In particular, the substitution of Mn3+ in the mixed-valence Mn3+/Mn4+ spinel LiMn2O4 by other trivalent ions of the transition element series has been explored to improve the cyclability as cathode materials [1–5]. However, while many of the studies so far published have examined the bulk structural characteristics and electrochemical properties of substituted lithium manganates, very little is known about the local structures of the compounds. Knowledge of the local modifications associated with lattice defects should lead to new insights into the chemistry and electrochemistry of lithium manganate spinels, and to the design and development of materials having desired chemical and electronic properties.

Computer Modelling of Lithium and Proton Intercalation in Spinel Lithium Manganates: Effect of Octahedral Vacancies

The effect of octahedral Mn vacancies on lithium and proton intercalation in the spinel structure of lithium manganate is investigated by means of atomistic simulation techniques. Prefered insertion sites and migration pathways for Li ions in the interstitial space of the lattice are calculated. The computations indicate an energetic preference for both Li ions and protons to cluster around the octahedral defects to compensate the local charge.