High-Ni cathode material improved with Zr for stable cycling of Li-ion rechargeable batteries.

The Zr solvent solution method, which allows primary and secondary particles of LiNi0.90Co0.05Mn0.05O2 (NCM) to be uniformly doped with Zr and simultaneously to be coated with an Li2ZrO3 layer, is introduced in this paper. For Zr doped NCM, which is formed using the Zr solvent solution method (L-NCM), most of the pinholes inside the precursor disappear owing to the diffusion of the Zr dopant solution compared with Zr-doped NCM, which is formed using the dry solid mixing method from the (Ni0.90Co0.05Mn0.05)(OH)2 precursor and the Zr source (S-NCM), and Li2ZrO3 is formed at the pinhole sites. The mechanical strength of the powder is enhanced by the removal of the pinholes by the formation of Li2ZrO3 resulting from diffusion of the solvent during the mixing process, which provides protection from cracking. The coating layer functions as a protective layer during the washing process for removing the residual Li. The electrochemical performance is improved by the synergetic effects of suitable coatings and the enhanced structural stability. The capacity-retentions for 2032 coin cells are 86.08%, 92.12%, and 96.85% at the 50th cycle for pristine NCM, S-NCM, and L-NCM, respectively. The superiority of the liquid mixing method is demonstrated for 18 650 full cells. In the 300th cycle in the voltage range of 2.8-4.35 V, the capacity-retentions for S-NCM and L-NCM are 77.72% and 81.95%, respectively.

Linear stability analysis for step meandering instabilities with elastic interactions and Ehrlich-Schwoebel barriers.

Vicinal surfaces are known to exhibit morphological instabilities during step-flow growth. Through a linear stability analysis of step meandering instabilities, we investigate two effects that are important in many heteroepitaxial systems: elastic monopole-monopole interactions arising from bulk stress and the Ehrlich-Schwoebel (ES) barriers due to the asymmetric adatom incorporation rates. The analysis shows that the effects of the ES barriers increase as the average terrace width increases, whereas the effects of elastic monopole-monopole interactions decrease. The ES barriers favor an in-phase step pattern with a zero phase shift between consecutive steps, while elastic stress favors an out-of-phase pattern with a phase shift of pi. However, our analysis shows that the instability growth rate becomes nearly independent of the phase shift when either the ES-barrier effect or the stress effect is large. In particular, for ES-barrier-driven instability, the in-phase step pattern develops only within an intermediate range of terrace widths when bulk stress exists. Similarly, for the elastic-interaction-driven instability, an out-of-phase pattern only forms within a certain range of monopole strength; if the strength is too small, the ES barrier effect dominates, and if it is too large, the peak in the instability growth rate becomes delocalized in the phase shift and no patterns form. This transition between patterned and random step morphologies depends on the monopole strength, but is independent of the terrace width. A phase diagram that describes the regions of the ES-barrier-dominant instability and the elastic-interaction-dominant instability is established, along with the morphological phase diagrams that predict the step configurations as a function of the controlling parameters for the two types of instabilities.