Research Article www.acsami.org
Cite This: ACS Appl. Mater. Interfaces 2018, 10, 44452−44462
Investigation of Fluorine and Nitrogen as Anionic Dopants in NickelRich Cathode Materials for Lithium-Ion Batteries Jan O. Binder,† Sean P. Culver,† Ricardo Pinedo,† Dominik A. Weber,†,§ Markus S. Friedrich,† Katharina I. Gries,‡ Kerstin Volz,‡ Wolfgang G. Zeier,*,† and Jürgen Janek*,† †
Downloaded via UNIV OF SOUTH DAKOTA on December 27, 2018 at 03:54:06 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
Institute of Physical Chemistry & Center for Materials Research, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 17, D-35392 Giessen, Germany ‡ Faculty of Physics & Materials Science Center, Philipps-University Marburg, Hans-Meerwein-Strasse, D-35032 Marburg, Germany S Supporting Information *
ABSTRACT: Advanced lithium-ion batteries are of great interest for consumer electronics and electric vehicle applications; however, they still suffer from drawbacks stemming from cathode active material limitations (e.g., insufficient capacities and capacity fading). One approach for alleviating such limitations and stabilizing the active material structure may be anion doping. In this work, fluorine and nitrogen are investigated as potential dopants in Li1.02(Ni0.8Co0.1Mn0.1)0.98O2 (NCM) as a prototypical nickelrich cathode active material. Nitrogen doping is achieved by ammonia treatment of NCM in the presence of oxygen, which serves as an unconventional and new approach. The crystal structure was investigated by means of Rietveld and pair distribution function analysis of X-ray diffraction data, which provide very precise information regarding both the average and local structure, respectively. Meanwhile, time-of-flight secondary-ion mass spectroscopy was used to assess the efficacy of dopant incorporation within the NCM structure. Moreover, scanning electron microscopy and scanning transmission electron microscopy were conducted to thoroughly investigate the dopant influences on the NCM morphology. Finally, the electrochemical performance was tested via galvanostatic cycling of half- and full-cells between 0.1 and 2 C. Ultimately, a dopant-dependent modulation of the NCM structure was found to enable the enhancement of the electrochemical performance, thereby opening a route to cathode active material optimization. KEYWORDS: lithium-ion-battery, anion doping, nickel-rich layered oxide, fluorine doping, nitrogen doping because of the intrinsic site disorder.7−9 During both the material synthesis and cycling of the battery, some reduced Ni ions occupy the 3b Wyckoff positions of Li, whereas Li ions occupy the 3a Wyckoff positions of Ni because of the similar size of the Li+ and Ni2+ cations.10,11 This behavior leads to capacity loss, as the disordered Ni can no longer be electronically accessed and also because of structural deterioration.12−15 Recently, several approaches have emerged toward overcoming the aforementioned issues (e.g., modifying the composition, surface coatings, and morphology tailoring of the active material particles).16−18 Among these approaches, one of the most promising and most used strategies is cation doping. However, cation doping strategies are still empirical, and the exact stabilization effects have yet to be elucidated.14,19−29 Up to now, the effects of cation doping can be summarized as follows:
1. INTRODUCTION The high demand for new electric devices in both the telecommunication and automotive sector has led to a steadily growing interest in lithium-ion battery (LIB) research. Batteries of this kind mostly use layered transition-metal (TM) oxides as the positive electrode and graphite as the negative electrode. For example, lithium cobalt oxide is commonly employed in cells for consumer electronics, being a layered intercalation material with a specific capacity of 150 mA h g−1. Unfortunately, lithium utilization in this material is relatively low (i.e.,
