Lithium (Li)‐metal anodes are of great promise for next‐generation batteries due to their high theoretical capacity and low redox potential. However, Li‐dendrite growth during cycling imposes a tremendous safety concern on the practical application of Li‐metal anodes. Herein, an effective approach to suppress Li‐dendrite growth by coating a polypropylene (PP) separator with a thin layer of ultrastrong diamond‐like carbon (DLC) is reported. Theoretical calculations indicate that the DLC coating layer undergoes in situ chemical lithiation once assembled with the lithium‐metal anode, transforming the DLC/PP separator into an excellent 3D Li‐ion conductor. This in situ lithiated DLC/PP separator can not only mechanically suppress Li‐dendrite growth by its intrinsically high modulus (≈100 GPa), but also uniformly redistributes Li ions to render dendrite‐free lithium deposition. The twofold effects of the DLC/PP separator result in stable cycling of lithium plating/stripping (over 4500 h) at a high current density of 3 mA cm−2. Remarkably, this approach enables more than 1000 stable cycles at 5 C with a capacity retention of ≈71% in a Li || LiFePO4 coin cell and more than 200 stable cycles at 0.2 C in a Li || LiNi0.5Co0.3Mn0.2O2 pouch cell with cathode mass loading of ≈9 mg cm−2.

Potassium-ion batteries are promising candidates for large-scale energy storage applications owing to their merits of abundant resources, low cost, and high working voltage. However, the unsatisfying rate performance and cycling stability caused by sluggish K + diffusion kinetics and dramatic volume expansion hinder the development of potassium-ion batteries. In this study, we design a flexible potassium-ion hybrid capacitor (PIHC) by combining the K-Sn alloying mechanism on the Sn anode and the fast capacitive behavior on the AC cathode with high surface area and mesoporous structure. After optimization, the fabricated Sn||AC PIHC achieves both a high energy density of 120 W h kg −1 and high power density of 2850 W kg −1 , much better than other similar hybrid devices. Moreover, a gel polymer electrolyte with a 3D porous structure and high ionic conductivity was employed to improve the structural stability of the Sn anode, which not only realizes good flexibility but also achieves long cycling stability with a capacity retention of nearly 100% for 2000 cycles at a high current density of 3.0 A g −1 .

Alloy‐type anodes are one of the most promising classes of next‐generation anode materials due to their ultrahigh theoretical capacity (2–10 times that of graphite). However, current alloy‐type anodes have several limitations: huge volume expansion, high tendency to fracture and disintegrate, an unstable solid–electrolyte interphase (SEI) layer, and low Coulombic efficiency. Efforts to overcome these challenges are ongoing. This Review details recent progress in the research of batteries based on alloy‐type anodes and discusses the direction of their future development. We conclude that improvements in structural design, the introduction of a protective interface, and the selection of suitable electrolytes are the most effective ways to improve the performance of alloy‐type anodes. Furthermore, future studies should direct more attention toward analyzing their synergistic promoting effect.