Halogen anion batteries (HABs) are considered emerging and promising alternative technologies for metal-ion batteries due to their high abundance, energy density, environmental friendliness, and safety. But developing suitable electrode materials for HABs is still challenging. Here, by using first-principles calculations, we systemically investigated the adsorption, stability, diffusion, and electrochemical properties of 4 halogen anion (F⁻, Cl⁻, Br⁻ and I⁻) batteries with 9 M₂CT₂ (M = Ti, Zr, Hf; T = O, H, OH) MXenes. First of all, the electronegativity of the anions and the surface electronic properties of the MXenes significantly affected the adsorption ability. Next, 13 highly stable HAB models were screened from the above 36 models by using ab initio molecular dynamics simulations, and the intrinsic correlations of bond length, bond strength, and stability were established. Based on stable models, we found that the diffusivity of halogen anions on MXenes was better than that of other ions, especially the F ions in Zr₂C(OH)₂ and Hf₂C(OH)₂ exhibiting optimal diffusivity with low diffusion energy barriers of 0.095 eV and 0.120 eV, respectively. The electrochemical performance results indicated that the HABs with M₂CT₂ electrodes showed an excellent theoretical capacity of 488 mA h g⁻¹ (Ti₂CH₂), an attractive open-circuit voltage of 6.27 V (Hf₂C(OH)₂), and small voltage changes of 0.02 V (Hf₂CH₂). Interestingly, the different HABs with H-functionalized MXenes exhibited peculiar open-circuit voltage curves, that is, the voltage increases during discharge, which was determined by the offset of the H functional group, the binding strength between halogen ions and MXenes, and the electronic interaction between halogen anions. In conclusion, this study screens promising electrode materials and provides a theoretical basis for the development of novel HABs.

中文翻译：

---

具有 MXene 电极的高性能卤素阴离子电池的理论设计：官能团、金属和阴离子的影响

卤素阴离子电池 (HAB) 因其高丰度、能量密度、环境友好性和安全性而被认为是新兴且有前景的金属离子电池替代技术。但是为 HAB 开发合适的电极材料仍然具有挑战性。_{在这里，我们通过使用第一性原理计算，系统地研究了 9 M 2}​​ CT _{2的 4 卤素阴离子（F} ^-、Cl ^-、Br ^-和 I ^-）电池的吸附、稳定性、扩散和电化学性能。（M = Ti、Zr、Hf；T = O、H、OH）MXenes。首先，阴离子的电负性和 MXenes 的表面电子性质显着影响吸附能力。接下来，通过从头算分子动力学模拟，从上述 36 个模型中筛选出 13 个高度稳定的 HAB 模型，并建立了键长、键强度和稳定性的内在相关性。基于稳定的模型，我们发现卤素阴离子在 MXenes 上的扩散率优于其他离子，尤其是 Zr ₂ C(OH) ₂和 Hf ₂ C(OH) _{2中的 F 离子}表现出最佳扩散率，低扩散能垒分别为 0.095 eV 和 0.120 eV。电化学性能结果表明，具有M ₂ CT _{2电极的HAB具有488 mA hg} ^-1 (Ti ₂ CH ₂ )的优异理论容量，6.27 V (Hf ₂ C(OH) ₂ )的有吸引力的开路电压, 和 0.02 V 的小电压变化 (Hf ₂ CH ₂）。有趣的是，具有 H 功能化 MXenes 的不同 HAB 表现出奇特的开路电压曲线，即放电过程中电压升高，这取决于 H 官能团的偏移量、卤素离子和 MXenes 之间的结合强度以及卤素阴离子之间的电子相互作用。总之，本研究筛选了有前景的电极材料，并为新型HABs的开发提供了理论基础。