Abstract Divalent ion batteries are potential substitutes to existing rechargeable batteries because of the high-energy density, safety, and low cost. However, the applications of divalent batteries are strongly dependent on the availability of efficient electrode materials. We herein report the adsorption and migration mechanism of divalent ions like Mg+2 and Ca+2, on two-dimensional carbon nitride monolayer (C4N). The adsorption of both Mg and Ca ions are much stronegr on C4N saturated with functional groups like hydrogen (-H), hydroxyl (-OH), and carboxylic (-COOH) as compared to the pristine monolayers, which implies the improvement in metal storage caused by the functional groups. On functionalized C4N, the first Mg binds within the binding energy range of 1.5-2.2 eV having migration barrier, at the saturated sites, of around 0.5 eV, which indicates desirable binding and robust diffuse. However, the functional groups tend to act as the trapping sites for Ca ions and the diffusion might get hindered as compared to Mg ions. In addition to binding and diffusion mechanism, charge transfer, electronic structures and open circuit volatges have also been calculated for both Mg and Ca on pristine and functionalized C4N monolayers. We find that -H, -OH, and -COOH play important role for the cyclic performance of C4N as the prospective anode material for divalent ion batteries.

中文翻译：

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C4N 纳米片上二价离子的吸附和迁移改善：二价电池的潜在阳极

摘要 二价离子电池具有能量密度高、安全性好、成本低等优点，是现有可充电电池的潜在替代品。然而，二价电池的应用在很大程度上取决于有效电极材料的可用性。我们在此报告了二价离子如 Mg+2 和 Ca+2 在二维氮化碳单层 (C4N) 上的吸附和迁移机制。与原始单层相比，Mg 和 Ca 离子在具有氢 (-H)、羟基 (-OH) 和羧基 (-COOH) 等官能团饱和的 C4N 上的吸附更强，这意味着金属存储的改善由官能团引起。在功能化的 C4N 上，第一个 Mg 在 1.5-2.2 eV 的结合能范围内结合，在饱和位点具有大约 0.5 eV 的迁移势垒，这表明理想的结合和强大的扩散。然而，官能团往往充当 Ca 离子的捕获位点，与 Mg 离子相比，扩散可能会受到阻碍。除了结合和扩散机制，还计算了原始和功能化 C4N 单层上 Mg 和 Ca 的电荷转移、电子结构和开路电压。我们发现-H、-OH和-COOH对C4N作为二价离子电池的预期负极材料的循环性能起着重要作用。还计算了原始和功能化 C4N 单层上的 Mg 和 Ca 的电子结构和开路电压。我们发现-H、-OH和-COOH对C4N作为二价离子电池的预期负极材料的循环性能起着重要作用。还计算了原始和功能化 C4N 单层上的 Mg 和 Ca 的电子结构和开路电压。我们发现-H、-OH和-COOH对C4N作为二价离子电池的预期负极材料的循环性能起着重要作用。