A key issue with Na-ion batteries is the development of active materials with stable electrochemical reversibility through the understanding of their sodium storage mechanisms. We report a sodium storage mechanism and properties of a new anode material, digenite Cu_1.8S, based on its crystallographic study. It is revealed that copper sulfides (Cu_xS) can have metal-rich formulas (x ≥ 1.6), due to the unique oxidation state of +1 found in group 11 elements. These phases enable the unit cell to consist of all strong Cu–S bonds and no direct S–S bonds, which are vulnerable to external stress/strain that could result in bond cleavage as well as decomposition. Because of its structural rigidness, the Cu_1.8S shows an intercalation/deintercalation reaction mechanism even in a low potential window of 0.1–2.2 V versus Na/Na⁺ without irreversible phase transformation, which most of the metal sulfides experience through a conversion reaction mechanism. It uptakes, on average, 1.4 Na⁺ ions per unit cell (∼250 mAh g^–1) and exhibits ∼100% retention over 1000 cycles at 2C in a tuned voltage range of 0.5–2.2 V through an overall solid solution reaction with negligible phase separation.

中文翻译：

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Na-离子电池中富含金属的Cu _1.8 S中异常的Na ⁺离子嵌入/去嵌入

Na离子电池的关键问题是通过了解钠存储机理，开发具有稳定电化学可逆性的活性材料。我们基于其晶体学研究报告了一种新型负极材料，重铬铁矿Cu _1.8 S的钠存储机理和性能。据透露，硫化铜（铜_X S）可以具有富金属式（X ≥1.6），由于11个族元素发现1独特的氧化态。这些阶段使晶胞能够由所有强固的Cu-S键组成，而没有直接的S-S键，它们容易受到外部应力/应变的影响，可能导致键断裂和分解。由于其结构刚性，Cu _1.8S相对于Na / Na ^+而言，即使在0.1-2.2 V的低电势窗口中也显示出插层/脱嵌反应机理，而没有不可逆的相变，大多数金属硫化物通过转化反应机理而经历。通过整个固溶反应几乎可以忽略不计，它每单位电池平均吸收1.4 Na ⁺离子（约250 mAh g ^–1），在2C的1000个循环中，在0.5–2.2 V的可调电压范围内，表现出约100％的保留。相分离。