MXene, a new kind of two-dimensional (2D) material, has a unique combination of excellent physical and chemical properties. Via computations on density functional theory and deformation potential theory, we investigated the electronic structure and predicted the carrier mobility of Ti2CO2 (a typical MXene) monolayers and nanoribbons. The Ti2CO2 monolayer is a semiconductor with a band gap of 0.91 eV, and the hole mobility in the monolayer reaches 10(4) orders of magnitude along both x and y directions, which is much higher than that of MoS2, while the electron mobility is about two orders of magnitude lower. The dramatic difference between the hole and electron mobilities also exists in nanoribbons. Moreover, our results suggest that width controlling and edge engineering would be effective in adjusting the carrier mobility of Ti2CO2 nanoribbons, and endow experimentally available Ti2CO2 with wide applications to field-effect transistors and photocatalysts.

Aqueous zinc-ion batteries have drawn increasing attention due to the intrinsic safety, costeffectiveness and high energy density. However, parasitic reactions and non-uniform dendrite growth on the Zn anode side impede their application. Herein, a multifunctional additive, ammonium dihydrogen phosphate (NHP), is introduced to regulate uniform zinc deposition and to suppress side reactions. The results show that the NH 4 + tends to be preferably absorbed on the Zn surface to form a "shielding effect" and blocks the direct contact of water with Zn. Moreover, NH 4 + and (H 2 PO 4 ) À jointly maintain pH values of the electrode-electrolyte interface. Consequently, the NHP additive enables highly reversible Zn plating/stripping behaviors in Zn//Zn and Zn//Cu cells. Furthermore, the electrochemical performances of Zn//MnO 2 full cells and Zn//active carbon (AC) capacitors are improved. This work provides an efficient and general strategy for modifying Zn plating/stripping behaviors and suppressing side reactions in mild aqueous electrolyte.

Based on density functional theory calculations of iodide-type compounds Li3MI6 (M = Sc, Y, and La), Li3LaI6 with stable octahedral Li occupation is theoretically found to meet the requirements of high lithium ionic conductivity, deformability, and chemical and electrochemical stability simultaneously, which sulfide-type solid-state electrolytes alone have not achieved so far. The underlying mechanism of superior lithium ion conduction in such a halide superionic conductor with stable octahedral Li occupations compared to the spinel ones with tetrahedral Li occupations has been uncovered. The Li migration enthalpies of those materials with face-centered-cubic anion frameworks are found to be not only strongly related to the ratio of anion charge over bond length (|q anion|/d) but also dependent on the lithium ion coordination number, which could be a universal design principle for searching new superionic conductors.

First-principles calculations indicate that a novel atomic hollow structure of graphyne and graphdiyne made up of sp- and sp2-hybridized carbon atoms reinforces not only the Na storage capacity but also the Na diffusion.