The combined effect of CaF2 and graphite two-layer coatings on improving the electrochemical performance of Li-rich layer oxide material

• Published in: Journal of solid state chemistry Vol. 272; pp. 38 - 46
• Main Authors: Li, Min, Wang, Huiya, Zhao, Limin, Zhang, Fang, He, Dannong
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.04.2019
• Subjects: CaF2 and Graphite two-coating; Capacity decay; Cathode material; Lithium-rich; Cathode material; Lithium-rich; Capacity decay; CaF2 and Graphite two-coating
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2019.01.022

Although Lithium-rich layered oxide material has a higher discharge specific capacity than conventional commercial cathode materials, the voltage/capacity decay, which are observed during cycle, limit its wider applicability. In this work, CaF2 and Graphite two-layer coatings is first employed to settle these problems. CaF2, acting as the inner coating layer, has excellent Lithium-ion migration velocity and good stability in acidic electrolytes. Graphite, acting as the outer coating layer, can decrease the interfacial resistance of lithium insertion/extraction and enhance the stability of inner material. Attributing to the combined effect of CaF2 and Graphite two-layer coatings, the electrochemical performance of CaF2 and Graphite two-layer coatings lithium-rich layered oxide material (named as LLMO-Ⅰ) has been improved notably. In details, compared with referential sample, the discharge specific capacity of LLMO-Ⅰ reaches 215.2 mA h g−1 at the 0.5 C and 90% of discharge specific capacity retention after 150 cycles. When the charge/discharge rate reaches 5 C, its specific discharge capacity also has 133.6 mA h g−1. Furthermore, the results of electrochemical impedance spectroscopy(EIS) also imply that LLMO-Ⅰ has the least electrode resistance in all samples because of the combined effect of CaF2 and Graphite two-layer coatings. To sum up, The CaF2 and Graphite two-layers coatings would be a promising method, which could further prompt the commercialization of Lithium-rich layered oxide materials. Figure shows the schematic illustration of the formation process of CaF2 and Graphite two-layer coatings lithium-rich layered oxide material and the electrochemical performance of all samples. Because of the CaF2&Graphite two-layer coating, CaF2 and Graphite two-layer coatings lithium-rich layered oxide material exhibits the best cycle performance and rate performance, which can be observed in figure. This indicates that CaF2&Graphite two-layer coatings can greatly improve the electrochemical performance of lithium-rich layer oxide material. [Display omitted] •CaF2 has good stability in acidic electrolyte.•Graphite can decrease the interfacial resistance for lithium insertion/extraction.•CaF2&Graphite two-layer coatings can take advantage of CaF2 demo-coating and Graphite demo-coating.