Abstract:

Graphite has been extensively employed as commercial anode material in Li-ion batteries due to its high abundance, low cost, and negative electrode potential. Furthermore, it has demonstrated significant potential for use in K-ion batteries. However, distinct structural damage caused by the larger radius of K-ion (0.138 nm) compared to that of Li-ion (0.076 nm) leads to obvious capacity decay and unstable cycle life. It is crucial to improve the cycling stability of graphite in potassium ion batteries (PIBs). Herein, we design a stable interface of graphite anode by graphene coating with a simple and efficient microwave method. According to X-ray photoelectron spectroscopy (XPS), microwave reduction can effectively remove the oxygen group of graphene oxide (GO) within 10 s. The graphene coating can buffer the volume expansion of the graphite to suppress structural collapse; it can also accelerate electronic transmission to improve rate performance. As a result, the graphene-coating graphite anode, named GCG, exhibits super cycling stability with a capacity of 262 mAh∙g⁻¹ after 3000 cycles at a current density of 0.2 A∙g⁻¹, which means it can operate smoothly for one year. In contrast, at the same current density, graphite exhibits capacity fading to less than 150 mAh∙g⁻¹ after 150 cycles. Moreover, compared to graphite, GCG demonstrates better rate performance achieving a capacity of 161.2 mAh∙g⁻¹ at 500 mA∙g⁻¹. Further electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) tests show that GCG exhibits faster electrical conductivity and ion diffusion compared to graphite. Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) images after cycling verify that the graphene buffer interface benefits the integrity of the electrode structure and improves the stability of the solid electrolyte interphase (SEI). Compared to graphite, the GCG anode exhibits better performance, as follows: 1) The graphene coating inhibits exfoliation of graphite during cycling, solving the problem of graphite anode' short cycling life, and 2) the graphene protective layer improves the ion diffusion rate, resulting in better rate performance of the GCG. In addition, this approach offers the advantages of simple operation and low cost, hopefully enabling large-scale applications of potassium-ion batteries.

Key words: Potassium ion battery, Anode, Graphene, Microwave reduction, Interface