On the energetic stability and electrochemistry of Li2MnSiO4 polymorphs
On the energetic stability and electrochemistry of Li2MnSiO4 polymorphs
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DOI：
10.1021/cm801036k
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发表时间：
2008-09-09
影响因子：
8.6
通讯作者：
Moran, E.
中科院分区：
文献类型：
--
作者：
Arroyo-deDompablo, M. E.;Dominko, R.;Moran, E.
采用实验和计算相结合的方法研究了Li 2 MnSiO 4多晶型物的热力学稳定性及其作为锂电池电极的电化学性能。三种可能的Li 2 MnSiO 4形式被认为在Pmnb，Pmn 2（1）（β-Li 3 PO 4衍生物）和P2（1）/n（γ-Li 3 PO 4衍生物）空间群（S.G.）中结晶。我们首先证明了β-和γ-Li 3 PO 4多晶型物的相对稳定性可以通过密度泛函理论（DFT）方法（LDA，GGA）很好地再现。对于Li_2MnSiO_4，Pmnb形式被预测为2.4 meV/f. u。和65 meV/f.u.分别比Pmn 2（1）和P2（1）/n形式更稳定（GGA + U结果）。计算结果表明，对其它多晶型或它们的混合物进行高压/高温处理，可以得到更致密的Pmn 2（1）多晶型。在900 ℃下制备的Li 2 MnSiO 4样品由多晶型物的混合物组成，如通过XRD检测并通过SAED和Li-6 MAS-NMR确认的。如从DFT结果所预期的，将如此制备的Li 2 MnSiO 4样品暴露于高压/高温（压力范围2-8 GPa，温度范围600-900 ℃）允许分离Pmn 21多晶型物。晶体结构对双电子过程的平均嵌锂电压具有较小影响（Pmnb、Pmn 2（1）和P2（1）/n的GGA+U计算电压分别为4.18、4.19和4.08 V）。在锂从P2（1）/n多晶型物中脱嵌的情况下，预期主要的结构重排，如先前在β-Li 3 PO 4衍生物中发现的，使得任何MnSiO 4脱锂主体迅速转变为更稳定的结构或它们的混合物。
The thermodynamic stability of Li2MnSiO4 Polymorphs and their electrochemical properties as electrode for Li batteries are investigated combining experimental and computational methods. Three possible Li2MnSiO4 forms have been considered crystallizing in Pmnb, Pmn2(1) (beta-Li3PO4 derivatives) and P2(1)/n (gamma-Li3PO4 derivative) space groups (S.G.). We have first demonstrated that the relative stability of beta-and gamma-Li3PO4 polymorphs is well-reproduced by density functional theory (DFT) methods (LDA, GGA). For Li2MnSiO4, the Pmnb form is predicted to be 2.4 meV/f.u. and 65 meV/f.u. more stable than the Pmn2(1) and P2(1)/n forms, respectively (GGA + U results). Computational results indicate that the denser Pmn2(1) polymorph can be obtained by high pressure/high temperature treatment of the other polymorphs or their mixtures. A sample of Li2MnSiO4 prepared at 900 degrees C consists of a mixture of polymorphs, as detected by XRD and confirmed by means of SAED and Li-6 MAS-NMR. As expected from DFT results, exposing the as-prepared Li2MnSiO4 sample to high pressure/high temperature (pressure range 2-8 GPa, temperature range 600-900 degrees C) allows to isolate the Pmn21 polymorph. The crystal structure has a minor impact in the average lithium intercalation voltage for the two electron process (GGA+U calculated voltages are 4.18, 4.19, and 4.08 V for Pmnb, Pmn2(1) and P2(1)/n, respectively). Major structural rearrangements are expected under lithium deinsertion from the P2(1)/n polymorph, as previously found for the beta-Li3PO4 derivatives, rendering any MnSiO4 delithiated hosts prompt to transform into a more stable structure or a mixture of them.