Critical design factors for kinetically favorable P-based compounds toward alloying with Na ions for high-power sodium-ion batteries†,Energy & Environmental Science

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Critical design factors for kinetically favorable P-based compounds toward alloying with Na ions for high-power sodium-ion batteries†
Energy & Environmental Science ( IF 32.4 ) Pub Date : 2019-02-15 00:00:00 , DOI: 10.1039/c9ee00283a
Duho Kim _{1,

2,

3,

4} , Kai Zhang _{4,

5,

6,

7} , Maenghyo Cho _{4,

8,

9,

10} , Yong-Mook Kang _{4,

5,

6,

7}

Affiliation

First-principles calculations with experimental validation enable us to radically predict and compare the electron transport, elastic softness, and thermodynamic phase stabilities of black phosphorus (BP) and GeP₃ to figure out the crucial factors for designing the most kinetically favorable P-based compounds toward alloying with Na ions. From the viewpoint of electron transport, Ge is able to provide P with electrons due to the difference of electronegativity, causing GeP₃ to have a significantly reduced band gap and a lower electron-hopping barrier compared to BP. Because the structure of GeP₃ looks more elastically softened than that of BP, its Na⁺ migration barriers in the sodiated states must be lower than those of the sodiated BP structure as proven by the higher Na⁺ diffusion coefficients of GeP₃. The thermodynamic phase stabilities of BP and GeP₃ could be predicted by calculating their mixing enthalpy values and thereby homogeneous bulk free energies were obtained for Na_1−x(GeP₃) (0.0 ≤ x ≤ 0.5) indicating that no phase separation occurs in the sodiated GeP₃ because of an additional stable single-phase at x = 0.25. By contrast, the sodiated P easily gets separated into NaP and Na_0.5P with the same sodiation content. The suppressed phase separation in GeP₃ makes the Na⁺ distribution homogeneous as confirmed by TEM-EDS color mapping and thus contributes to increasing Na⁺ diffusion coefficients because Na⁺ migration can be primarily interrupted by the interfaces or grain boundaries between the separated phases. Taking into account three enhanced physicochemical properties, the GeP₃ electrodes may well present a superior rate capability to the BP electrode, underscoring that electron transport, elastic softness, and thermodynamic phase stabilities must be the most important design factors for realizing kinetically favorable P-based compounds toward alloying with Na⁺. In detail, even at an ultrahigh current density of 20 A g⁻¹, the capacity of the GeP₃ electrode still comes to 0.197 A h g⁻¹. At 1 A g⁻¹, GeP₃ could maintain a discharge capacity of 0.499 A h g⁻¹ even after 1000 cycles. This study may provide promising guidelines for the design of alloy-based electrode materials for high power and energy SIBs.

中文翻译：

大功率钠离子电池中具有动力学优势的P基化合物与Na离子合金化的关键设计因素†

通过第一性原理计算和实验验证，我们能够从根本上预测和比较黑磷（BP）和GeP ₃的电子传递，弹性软度和热力学相稳定性，从而找出设计最具有动力学优势的P基化合物的关键因素与Na离子合金化。从电子传输的角度来看，由于电负性的差异，Ge能够为P提供电子，与BP相比，GeP _3的带隙显着减小，电子跃迁势垒更低。由于GeP ₃的结构看起来比BP的弹性更软，因此它的Na ⁺如GeP ₃的较高的Na ⁺扩散系数所证明的，在固态状态下的迁移势垒必须低于在BP结构下的迁移势垒。BP和的GEP的热力学相稳定性₃可以通过计算它们的混合焓值，从而均匀散装自由能的Na获得预测_1-_X（GEP ₃）（0.0≤ X ≤0.5），这表明没有相分离的发生因为在x = 0.25时有一个额外的稳定单相，所以生成了GeP ₃。相比之下，纯净的P容易分离为NaP和Na _0.5P具有相同的添加量。GeP _3中抑制的相分离使TEM-EDS色彩映射所证实的Na ⁺分布均匀，因此有助于提高Na ⁺扩散系数，因为Na ⁺迁移主要被分离相之间的界面或晶界中断。考虑到三种增强的理化特性，GeP ₃电极可能具有比BP电极更高的倍率能力，强调电子传输，弹性柔软度和热力学相稳定性必须是实现动力学上有利的P基电极的最重要设计因素。化合物与Na ⁺合金化。详细地，即使在20A g ^-1的超高电流密度下，GeP ₃电极的容量仍然达到0.197 A hg ^-1。在1 A g ^-1下，即使经过1000次循环，GeP ₃仍可保持0.499 A hg ^-1的放电容量。这项研究可能为高功率和高能量SIB的合金基电极材料的设计提供有希望的指导。

更新日期：2019-02-15

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