Mixed anion/cation redox in K0.78Fe1.60S2 for a high-performance cathode in potassium ion batteries,Inorganic Chemistry Frontiers

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Mixed anion/cation redox in K0.78Fe1.60S2 for a high-performance cathode in potassium ion batteries
Inorganic Chemistry Frontiers ( IF 6.1 ) Pub Date : 2020-04-02 , DOI: 10.1039/d0qi00184h
Su Cheol Han _{1,

2,

3,

4} , Woon Bae Park _{1,

2,

3,

4} , Kee-Sun Sohn _{4,

5,

6,

7} , Myoungho Pyo _{1,

2,

3,

4}

Affiliation

Cathode materials in potassium ion batteries (KIBs) generally exhibit low charge storage capabilities when compared with cathode materials implemented in lithium or sodium ion batteries. In this work, K_0.78Fe_1.60S₂ is described as a high capacity KIB cathode that exhibits mixed anion/cation redox behaviors during charge/discharge (C/D). When charged to 3.2 V vs. K/K⁺, K⁺ extraction occurs along with simultaneous oxidations of S²⁻ to S₂²⁻ and Fe(II) to Fe(III). During subsequent discharge to 1.5 V, this process is reversed, in addition to a further reduction of Fe(II) to Fe(I). After a few C/D cycles, K_0.78Fe_1.60S₂ reversibly delivers 0.69 K⁺ with a capacity of 100.5 mA h g⁻¹ (i.e., K_0.20Fe_1.60S₂ ⇆ K_0.89Fe_1.60S₂). The evolution of S²⁻ and Fe(II) valence states along with a lack of discernable changes in crystallographic dimensions clearly confirms the concomitant redox of anions and cations with C/D. Density functional theory calculations also validate the possibility of mixed redox reactions in K_0.78Fe_1.60S₂. Unique structural features of K_0.78Fe_1.60S₂ (layers consisting of edge-shared FeS₄ tetrahedra with partial Fe vacancies) result in high K⁺ diffusion coefficients that are unprecedented (ca. 10⁻⁹ cm² s⁻¹), which contributes to an excellent rate capability (56.3 mA h g⁻¹ at 1000 mA g⁻¹vs. 100.5 mA h g⁻¹ at 20 mA g⁻¹). Nudged elastic band calculations also reveal that the diffusion preferentially occurs along [100] directions with a low activation energy barrier of 0.41 eV.

中文翻译：

K0.78Fe1.60S2中的混合阴离子/阳离子氧化还原，用于钾离子电池中的高性能阴极

与锂或钠离子电池中使用的阴极材料相比，钾离子电池（KIB）中的阴极材料通常显示出较低的电荷存储能力。在这项工作中，K _0.78 Fe _1.60 S ₂被描述为一种高容量的KIB阴极，在充电/放电（C / D）期间表现出混合的阴离子/阳离子氧化还原行为。当充电至3.2 V vs. K / K ^+时，会发生K ⁺萃取，同时将S ^2-氧化为S ₂^2-和将Fe（II）氧化为Fe（III）。在随后放电至1.5 V的过程中，除了进一步还原Fe（II）至Fe（I）。几个C / d循环之后，K _0.78铁_1.60 š ₂可逆地提供0.69ķ ⁺与100.5毫安Hg的容量^-1（即，K _0.20铁_1.60 š ₂ ⇆ķ _0.89铁_1.60 š ₂）。S ^2-和Fe（II）价态的演变以及缺乏可分辨的晶体学尺寸变化，清楚地证实了C / D伴随着阴离子和阳离子的氧化还原。密度泛函理论计算也验证了K中混合氧化还原反应的可能性_0.78铁_1.60 S₂。K_0.78 Fe_1.60 S₂（由边缘共享的FeS₄四面体和部分Fe空位组成的层）的独特结构特征导致了前所未有的高K⁺扩散系数（约10^-9 cm² s^-1），这有助于到优异的倍率性能（56.3毫安汞柱^-1以1000mA克^-1与100.5毫安汞柱^-1 20毫安克^-1）。微调的弹性带计算还显示，扩散优先沿着[100]方向发生，活化能垒低至0.41 eV。

更新日期：2020-04-02

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