Elastic properties of olivine LixFePO4 from first principles
Elastic properties of olivine LixFePO4 from first principles
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DOI：
10.1103/physrevb.73.174112
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发表时间：
2006-05
影响因子：
3.7
通讯作者：
T. Maxisch;Gerband Ceder
中科院分区：
文献类型：
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作者：
T. Maxisch;Gerband Ceder
橄榄石系列是一种重要的矿物，最常见于地幔中。橄榄石以过渡金属硅酸盐或磷酸盐的形式存在，矿物学家和矿物学家对其进行了深入研究。最近，橄榄石磷酸盐受到了很多关注后，它表明，锂可以可逆地提取从磷酸铁锂。1.作为可充电锂电池的电极，该材料的理论容量为170 mAh/g，锂嵌入电位为3.5 V，2，并具有优异的热稳定性。此外，它价格低廉，对环境友好，使其成为大规模电池应用的兴趣。LixFePO 4 0 x 1在室温下是分相的，在充放电过程中发生了由磷杂FePO 4到锂铁磷酸盐LiFePO 4的相变。3-5为了更好地控制决定其电化学性能的材料性质，需要更好地理解其弹性性质。目前，关于机械性能如弹性常数或体积模量的实验数据不可用，因为LixFePO 4通常作为烧结粉末合成，并且已知较大晶体的生长非常困难。在这项研究中，我们专注于从第一性原理的弹性常数的计算，并从德拜温度和其他弹性性质的估计推断。LiFePO 4具有正交晶系橄榄石结构，空间群Pnma，实验晶格参数为a=10.3375，B=6.0112，c=4.6950。6它由扭曲的六方密堆积骨架组成，含有Fe 2+离子，这些离子通过氧原子六次配位，形成边缘共享八面体层。各层由PO 4四面体分隔，见图1。虽然FePO 4的平衡结构是钠长石，7，8空间群P3121，但锂可以从LiFePO 4中电化学去除而不改变橄榄石拓扑结构。这种脱锂FePO 4的实验晶格参数为a=9.7599，B=5.7519，c=4.7560。6根据第一原理计算弹性常数是一种公认的方法，该方法基于应变张量幂的内能展开。在这项研究中，我们重新获得了最基本的概念，并请读者参考Ravindran及其同事的工作，他们非常详细地报告了正交晶体的形式主义。对于九个独立的弹性
The olivine series forms an important class of minerals most commonly found in Earth’s mantle. Olivines occur as transition-metal silicates or phosphates and have been intensively studied by mineralogists and geophysicists. Recently, olivine phosphates have received much attention after it was shown that lithium can be reversibly extracted from triphylite LiFePO4. 1. As an electrode in rechargeable Li batteries, the material has a theoretical capacity of 170 mAh/g, combined with a lithium intercalation potential of 3.5 V,2 and exhibits an excellent thermal stability. In addition, it is inexpensive and environmentally benign, making it of interest for large-scale battery applications. LixFePO4 0 x 1 is phase separating at room temperature and undergoes a phase transformation between heterosite FePO4 and triphylite LiFePO4 during the charge and discharge process. 3–5 In order to better control the thermodynamical properties determining its electrochemical performance, a better understanding of its elastic properties is needed. At present, experimental data on mechanical properties such as elastic constants or bulk moduli are not available since LixFePO4 is usually synthesized as sintered powder and the growth of larger crystals is known to be very difficult. In this study, we focus on the calculation of the elastic constants from first principles and deduce from those estimates of the Debye temperature and other elastic properties. LiFePO4 has an orthorhombic olivine structure, space group Pnma, with experimental lattice parameters of a=10.3375 Å, b=6.0112 Å, and c=4.6950 Å.6 It consists of a distorted hexagonal close-packed framework containing Fe2+ ions which are sixfold coordinated by oxygen atoms forming layers of edge-sharing octahedra. Individual layers are separated by PO4 tetrahedra see Fig. 1 . Although the equilibrium structure of FePO4 is rodolicoite, 7,8 space group P3121, lithium can be electrochemically removed from LiFePO4 without changing the olivine topology. The experimental lattice parameters of such a delithiated FePO4 are a=9.7599 Å, b=5.7519 Å, and c=4.7560 Å.6 The computation of elastic constants from first principles is a well-established method which is based on the expansion of the internal energy in powers of the strain tensor. Within this study, we recapture the most essential concepts and refer the reader to the work of Ravindran and co-workers9 who have reported the formalism for orthorhombic crystals in great detail. For each of the nine independent elastic