High‐Entropy Atomic Layers of Transition‐Metal Carbides (MXenes)

High-entropy materials (HEMs) have great potential for energy storage and conversion due to their diverse compositions, and unexpected physical and chemical features. However, high-entropy atomic layers with fully exposed active sites are difficult to synthesize since their phases are easily segregated. Here, it is demonstrated that high-entropy atomic layers of transition-metal carbide (HE-MXene) can be produced via the selective etching of novel high-entropy MAX (also termed Mn+1AXn (n = 1, 2, 3), where M represents an early transition-metal element, A is an element mainly from groups 13–16, and X stands for C and/or N) phase (HE-MAX) (Ti1/5V1/5Zr1/5Nb1/5Ta1/5)2AlC, in which the five transition-metal species are homogeneously dispersed into one MX slab due to their solid-solution feature, giving rise to a stable transition-metal carbide in the atomic layers owing to the high molar configurational entropy and correspondingly low Gibbs free energy. Additionally, the resultant high-entropy MXene with distinct lattice distortions leads to high mechanical strain into the atomic layers. Moreover, the mechanical strain can efficiently guide the nucleation and uniform growth of dendrite-free lithium on HE-MXene, achieving a long cycling stability of up to 1200 h and good deep stripping–plating levels of up to 20 mAh cm−2.