Rechargeable potassium-ion batteries (PIBs) show promise beyond Li-ion technology in large-scale electrical-energy storage due to the abundance and low cost of potassium resources. However, the intercalation of large-size K ~(+) generally results in irreversible structural degradation and short lifespan to the hosts, representing a major obstacle. Here, we report a new electrochemical K ~(+) -intercalation host, tungsten disulfide (WS _(2) ), which can store 0.62 K ~(+) per formula unit with a reversible capacity of 67 mA h g ~(?1) and well-defined voltage plateaus at an intrinsically safe average operation potential of 0.72 V versus K/K ~(+) . In situ X-ray diffraction and ex situ electron microscopy revealed the underlying intercalation mechanism, a relatively small cell volume change (37.81%), and high reversibility of this new battery chemistry. Such characteristics impart WS _(2) with ultrahigh structural stability and a long lifespan, regardless of deep or fast charging. WS _(2) achieved record-high cyclability among chalcogenides up to 600 cycles with 89.2% capacity retention at 0.3C, and over 1000 cycles with 96.3% capacity retention and an extraordinary average Coulombic efficiency of 99.90% at 2.2C. This intercalation electrochemistry may open up new opportunities for the design of long-cycle-life and high-safety PIBs.
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