Lithium metal batteries (LMBs) are a dazzling star in electrochemical energy storage thanks to their high energy density and low redox potential. However, LMBs have a deadly lithium dendrite problem. Among the various methods for inhibiting lithium dendrites, gel polymer electrolytes (GPEs) possess the advantages of good interfacial compatibility, similar ionic conductivity to liquid electrolytes, and better interfacial tension. In recent years, there have been many reviews of GPEs, but few papers discussed the relationship between GPEs and solid electrolyte interfaces (SEIs). In this review, the mechanisms and advantages of GPEs in inhibiting lithium dendrites are first reviewed. Then, the relationship between GPEs and SEIs is examined. In addition, the effects of GPE preparation methods, plasticizer selections, polymer substrates, and additives on the SEI layer are summarized. Finally, the challenges of using GPEs and SEIs in dendrite suppression are listed and a perspective on GPEs and SEIs is considered.

Lithium (Li) metal is strongly considered to be the ultimate anode for next-generation high-energy-density rechargeable batteries. Carbon materials and their composites with excellent structure tunability and properties have shown great potential applications in Li metal anodes.

Although expanded graphite prepared from flake graphite has been well developed, the expanded mechanism of graphite with a confined structure has not been well researched. Herein, we systematically reveal how confined graphite is transformed into bamboo shoot-like graphite by a modified Hummers’ method using microsized graphitic onion-like carbon (GOC). Unlike the parallel stacked open structure of natural flake graphite (NFG), GOC covered by carbon basal planes presents a restricted polyhedral structure, which makes GOC present a different expansion pattern from the longitudinal extension of NFG, but dissociates into bamboo shoot-like expanded graphite along different directions of the polyhedron. Notably, different from the planar structure of expanded natural flake graphite (ENFG), expanded graphitic onion-like carbon (EGOC) exhibits a helical structure with plenty of wavy wrinkles, and presents a higher structural stability than ENFG. EGOC exhibits superior potassium-ion storage performance with high reversible capacity (404 mA h g⁻¹ at 0.2C), outstanding rate capability (218 mA h g⁻¹ at 5C) and superior cyclability (275 mA h g⁻¹ after 1000 cycles at 2C). Furthermore, EGOC is used as the anode to assemble potassium-ion capacitors that deliver an ultrahigh energy/power density (113.8 W h kg⁻¹ and 12.92 kW kg⁻¹, respectively). Our work further perfects the thermal expansion mechanism of spherical graphite and provides new insights for the design and development of competitive expanded graphite from GOC.