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High specific capacity materials that can store potassium (K) are essential for next-generation K-ion batteries. One such candidate material is phosphorene (the 2D allotrope of phosphorus (P)), but the potassiation capability of phosphorene has not yet been established. Here we systematically investigate the alloying of few-layer phosphorene (FLP) with K. Unlike lithium (Li) and sodium (Na), which form Li3P and Na3P, FLP alloys with K to form K4P3, which was confirmed by ex situX-ray characterization as well as density functional theory calculations. The formation of K4P3results in high specific capacity (∼1200 mAh g–1) but poor cyclic stability (only ∼9% capacity retention in subsequent cycles). We show that this capacity fade can be successfully mitigated by the use of reduced graphene oxide (rGO) as buffer layers to suppress the pulverization of FLP. We studied the performance of rGO and single-walled carbon nanotubes (sCNTs) as buffer materials and found that rGO being a 2D material can better encapsulate and protect FLP relative to 1D sCNTs. The half-cell performance of FLP/rGO could also be successfully reproduced in a full-cell configuration, indicating the possibility of high-performance K-ion batteries that could offer a sustainable and low-cost alternative to Li-ion technology.

In the present work, lithium vanadium oxide (Li1.1V3O8) particles synthesized at two different temperatures were coated with an amorphous lithium phosphorous oxynitride (LiPON) film for the first time, and the effects of the LiPON coating on the electrochemistry of the Li1.1V3O8 materials with different morphologies were systematically investigated by comparing uncoated Li1.1V3O8 and Li1.1V3O8 coated with LiPON of various thicknesses. Galvanostatic discharge-charge cycling revealed increased functional capacity for the LiPON-coated materials. Post-cycling electrochemical impedance spectroscopy showed that LiPON-coated Li1.1V3O8 materials developed less interfacial resistance with extended cycling, rationalized by vanadium migration into the LiPON coating seen by electron energy loss spectra. Post-mortem quantitative analysis of the anodes revealed more severe vanadium dissolution for the more irregularly shaped Li1.1V3O8 materials with less LiPON coverage. Thus, this study highlights the specific benefits and limitations of LiPON coatings for stabilizing a moderate voltage Li1.1V3O8 cathode material under extended cycling in liquid electrolyte, and describes a generally applicable approach for comprehensive characterization of a composite electroactive material which can be used to understand interfacial transport properties in other functional systems.

In the present work, lithium vanadium oxide (Li1.1V3O8) particles synthesized at two different temperatures were coated with an amorphous lithium phosphorous oxynitride (LiPON) film for the first time, and the effects of the LiPON coating on the electrochemistry of the Li1.1V3O8materials with different morphologies were systematically investigated by comparing uncoated Li1.1V3O8and Li1.1V3O8coated with LiPON of various thicknesses. Galvanostatic discharge-charge cycling revealed increased functional capacity for the LiPON-coated materials. Post-cycling electrochemical impedance spectroscopy showed that LiPON-coated Li1.1V3O8materials developed less interfacial resistance with extended cycling, rationalized by vanadium migration into the LiPON coating seen by electron energy loss spectra. Post-mortem quantitative analysis of the anodes revealed more severe vanadium dissolution for the more irregularly shaped Li1.1V3O8materials with less LiPON coverage. Thus, this study highlights the specific benefits and limitations of LiPON coatings for stabilizing a moderate voltage Li1.1V3O8cathode material under extended cycling in liquid electrolyte, and describes a generally applicable approach for comprehensive characterization of a composite electroactive material which can be used to understand interfacial transport properties in other functional systems.