Nanorod and Nanoparticle Shells in Concentration Gradient Core-Shell Lithium Oxides for Rechargeable Lithium Batteries

• Published in: ChemSusChem Vol. 7; no. 12; pp. 3295 - 3303
• Main Authors: Yoon, Sung-June, Myung, Seung-Taek, Noh, Hyung-Joo, Lu, Jun, Amine, Khalil, Sun, Yang-Kook
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.12.2014; WILEY‐VCH Verlag; Wiley Subscription Services, Inc; ChemPubSoc Europe
• Subjects: batteries; concentration gradient; core-shell; Electric Power Supplies; Electrodes; lithium; Lithium - chemistry; Microscopy, Electron, Scanning; Microscopy, Electron, Transmission; Nanoparticles; nanorods; Nanotubes; Oxides - chemistry; positive electrode; shell; lithium; nanorods; batteries; positive electrode; shell; concentration gradient; core-shell
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201402389

The structure, electrochemistry, and thermal stability of concentration gradient core–shell (CGCS) particles with different shell morphologies were evaluated and compared. We modified the shell morphology from nanoparticles to nanorods, because nanorods can result in a reduced surface area of the shell such that the outer shell would have less contact with the corrosive electrolyte, resulting in improved electrochemical properties. Electron microscopy studies coupled with electron probe X‐ray micro‐analysis revealed the presence of a concentration gradient shell consisting of nanoparticles and nanorods before and after thermal lithiation at high temperature. Rietveld refinement of the X‐ray diffraction data and the chemical analysis results showed no variations of the lattice parameters and chemical compositions of both produced CGCS particles except for the degree of cation mixing (or exchange) in Li and transition metal layers. As anticipated, the dense nanorods present in the shell gave rise to a high tap density (2.5 g cm−3) with a reduced pore volume and surface area. Intimate contact among the nanorods is likely to improve the resulting electric conductivity. As a result, the CGCS Li[Ni0.60Co0.15Mn0.25]O2 with the nanorod shell retained approximately 85.5 % of its initial capacity over 150 cycles in the range of 2.7–4.5 V at 60 °C. The charged electrode consisting of Li0.16[Ni0.60Co0.15Mn0.25]O2 CGCS particles with the nanorod shell also displayed a main exothermic reaction at 279.4 °C releasing 751.7 J g−1 of heat. Due to the presence of the nanorod shell in the CGCS particles, the electrochemical and thermal properties are substantially superior to those of the CGCS particles with the nanoparticle shell. Shell values: The structure, electrochemistry, and thermal stability of concentration gradient core–shell (CGCS) particles for rechargeable lithium batteries are evaluated and compared. By varying the synthesis conditions, the morphology of the CGSC shell Li[Ni0.60Co0.15Mn0.25]O2 material can be varied from nanoparticles to nanorods. The particles with a nanorod shell exhibit substantially superior electrochemical and thermal properties compared to particles with a nanoparticle shell.