Decoding ionic conductivity and reordering in cation-disordered pyrochlores

The ordered structure A 2 B 2 O 6 O’ in pyrochlores engenders twin rows of inequivalent anion sublattices each centred on alternating cations. While it is known that cation antisite disorder augments the ionic conductivity by several orders of magnitude, the local cation environment around the anions and the dynamic anion reordering during the cation disordering are not well-elucidated. Using atomistic simulations on Gd 2 Zr 2 O 7 , we first show that the anions engage in concerted hops to the neighbouring tetrahedral sites mostly along with the 〈1 0 0〉 direction while completely avoiding the octahedral sites. While the initially vacant 8 a sites start accommodating oxygen ions with increasing cation disorder, they show noticeable reluctance even at significant levels of disorder. We have also tracked both the distribution of available oxygen sites following random cation disorder, which is dependent only on cation disordering, and the probability of occupation of these sites. Interestingly, the available oxygen sites show a non-monotonic dependence on the number of B ions in the nearest neighbouring shell while the occupation probability of all the available oxygen sites increases monotonically. A tetrahedral oxygen site thus has a better probability of being occupied when it has a greater number of second neighbour B ions. This article is part of the Theo Murphy meeting issue 'Understanding fast-ion conduction in solid electrolytes'.

Superior Performances of B-doped LiNi0.84Co0.10Mn0.06O2 cathode for advanced LIBs

Boron-doped Ni-rich LiNi0.84Co0.10Mn0.06O2 (B-NCM) cathode material is prepared and its electrochemical performances are investigated. The structural properties indicate that the incorporation of boron leads to highly-ordered layered structure and low cation disordering. All samples have high areal loadings of active materials (approximately 14.6 mg/cm2) that meets the requirement for commercialization. Among them, the 1.0 wt% boron-doped NCM (1.0B-NCM) shows the best electrochemical performances. The 1.0B-NCM delivers a discharge capacity of 205. 3 mAh g−1, cyclability of 93.1% after 50 cycles at 0.5 C and rate capability of 87.5% at 2 C. As a result, we can conclude that the 1.0B-NCM cathode can be regarded as a promising candidate for the next-generation lithium ion batteries.

Facilitating Lithium-Ion Diffusion in Layered Cathode Materials by Introducing Li+/Ni2+ Antisite Defects for High-Rate Li-Ion Batteries

Li+/Ni2+ antisite defects mainly resulting from their similar ionic radii in the layered nickel-rich cathode materials belong to one of cation disordering scenarios. They are commonly considered harmful to the electrochemical properties, so a minimum degree of cation disordering is usually desired. However, this study indicates that LiNi0.8Co0.15Al0.05O2 as the key material for Tesla batteries possesses the highest rate capability when there is a minor degree (2.3%) of Li+/Ni2+ antisite defects existing in its layered structure. By combining a theoretical calculation, the improvement mechanism is attributed to two effects to decrease the activation barrier for lithium migration: (1) the anchoring of a low fraction of high-valence Ni2+ ions in the Li slab pushes uphill the nearest Li+ ions and (2) the same fraction of low-valence Li+ ions in the Ni slab weakens the repulsive interaction to the Li+ ions at the saddle point.

Rietveld structure refinement to optimize the correlation between cation disordering and magnetic features of CoFe2O4 nanoparticles

The effects of synthesis parameters on the structural and magnetic features of CoFe2O4 nanoparticles have been investigated and their mutual correlations optimized by using response surface methodology.