Efficient flexible energy storage systems have received tremendous attention due to their enormous potential applications in self-powering portable electronic devices, including roll-up displays, electronic paper, and "smart" garments outfitted with piezoelectric patches to harvest energy from body movement. Unfortunately, the further development of these technologies faces great challenges due to a lack of ideal electrode materials with the right electrochemical behavior and mechanical properties. MXenes, which exhibit outstanding mechanical properties, hydrophilic surfaces, and high conductivities, have been identified as promising electrode material candidates. In this work, taking 2D transition metal carbides (TMCs) as representatives, we systematically explored several influencing factors, including transition metal species, layer thickness, functional group, and strain on their mechanical properties (e.g., stiffness, flexibility, and strength) and their electrochemical properties (e.g., ionic mobility, equilibrium voltage, and theoretical capacity). Considering potential charge-transfer polarization, we employed a charged electrode model to simulate ionic mobility and found that ionic mobility has a unique dependence on the surface atomic configuration influenced by bond length, valence electron number, functional groups, and strain. Under multiaxial loadings, electrical conductivity, high ionic mobility, low equilibrium voltage with good stability, excellent flexibility, and high theoretical capacity indicate that the bare 2D TMCs have potential to be ideal flexible anode materials, whereas the surface functionalization degrades the transport mobility and increases the equilibrium voltage due to bonding between the nonmetals and Li. These results provide valuable insights for experimental explorations of flexible anode candidates based on 2D TMCs.

Center for Integrated Computational Materials Engineering International Research Institute for Multidisciplinary Science Beihang University Beijing 100191 People's Republic of China

College of Arts and Sciences University of Nebraska Lincoln Lincoln NE 68588

Department of Chemistry Purdue University West Lafayette IN 47906;

Engineering Laboratory of Specialty Fibers and Nuclear Energy Materials Ningbo Institute of Materials Technology and Engineering Chinese Academy of Sciences Ningbo Zhejiang 315201 China

IT4Innovations Center VŠB Technical University of Ostrava CZ 70833 Ostrava Czech Republic

School of Materials Science and Engineering Beihang University Beijing 100191 People's Republic of China

School of Materials Science and Engineering Beihang University Beijing 100191 People's Republic of China;

Theoretical Division Los Alamos National Laboratory Los Alamos NM 87545

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