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在锂二次电池中, 硅酸锰锂作为正极材料得到广泛研究, 但其固有的电子和离子电导率较低, 直接影响着电池的功率密度和充放电速率. 本文建立了不同浓度的Na+离子替位掺杂Li+离子形成的Li1-xNaxMnSiO4(x=0, 0.125, 0.25, 0.5)结构, 采用第一性原理的方法, 研究了掺杂前后硅酸锰锂的电子结构以及Li+离子的跃迁势垒. 发现在Li+位替代掺杂Na+, 导带底的能级向低能方向发生移动, 降低了Li2MnSiO4 材料的禁带宽度, 有利于提升材料的电子导电性能. 随着掺杂浓度的升高, 禁带宽度逐渐变窄. CI-NEB结果表明, 在Li2MnSiO4体系中具有两条有效的Li+离子迁移通道, 掺杂Na+以后扩大了Li+ 离子在[100]晶向上的迁移通道, Li+离子的跃迁势垒由0.64 eV降低为0.48, 0.52和0.55 eV. 掺杂浓度为 x=0.125时, 离子迁移效果最佳. 研究表明Na+掺杂有利于提高Li2MnSiO4材料的离子和电子电导率.With the developments of electric vehicles, the portable electronics and the large-scale storage systems, the research of the Li-ion rechargeable battery has focused on its high gravimetric and volumetric capacity. As a potential cathode, the Li2MnSiO4 structure has been intensively studied, in which two lithium ions of per formula unit (f.u.) can be extracted, and it exhibits a high theoretical capacity of about 330 mAh/g. However the low intrinsic electron conductivity and the slow lithium diffusion prevent its further development. In this paper, we build three structures with different Na+ doping concentrations in Pmn21 symmetric Li2MnSiO4, the electronic properties and Li+ ion diffusion behavior are studied by using the first principle and considering the transition barrier of the Mn-3d. Within the GGA+U scheme, the pure Li2MnSiO4 structure is semiconducting with a large band gap (3.28 eV), which is primarily derived from Mn-3d and O-2p states. Because lithium and sodium ions in the same main group have similar chemical properties, all the doped Li2-xNaxMnSiO4 (x= 0.125, 0.25, 0.5) are still semiconducting with the analogous densities of state (DOSs) to the pure Li2MnSiO4, however the band gaps reduce to 3.23 eV, 3.19 eV and 3.08 eV, respectively. Thus Na+ substitution can improve the electron conductivity. In Li2MnSiO4, the Li+ ions have two major diffusion channels predicted by the climbing image-nudged elastic band (CI-NEB) method. Channel A is along the a-direction [100], and channel B is in the bc plane with a zigzag trajectory. In the migration process, each of all the structures has only one migration pathway of Li ions. In the doped structures, the volumes of the crystal structures are increased by 1.40%, 2.65% and 5.25% for Li2-xNaxMnSiO4 (x= 0.125, 0.25, 0.5), and thus enlarge the hopping distances. Along channel A, the longer Li-O bond makes the ionic diffusion channel wider, therefore Li2-xNaxMnSiO4 (x= 0.125, 0.25, 0.5) have lower activation barriers of 0.48, 0.52 and 0.55 eV than the pure Li2MnSiO4 (0.64 eV). However, in channel B, the strong Li-O bonds increase the activation barriers of Li ion migration. When the doping concentration is x=0.125, the Li+ ion migration effect is strongest. For the Li+ ion migration pathways, it is easier for Li ion to hop into the site near Na ion. It means that the crystal structures are stabler at the short Li-O bond site. Therefore, doping Na+ ions would be a feasible method to improve the electron conductivity and Li+ ion migration rate in Li2MnSiO4 of Pmn21 phase.
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Keywords:
- Li-ion battery /
- Na+ doped /
- electronic structure /
- Li+ ion diffuse /
- migration barrier
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[2] Xin X G, Shen J Q, Shi S Q 2012 Chin. Phys. B 21 128202
[3] Gummow R J, He Y 2014 J. Power Sources 253 315
[4] Guo Z F, Pan K, Wang X J 2016 Chin. Phys. B 25 017801
[5] Zhong G H, Li Y L, Yan P, Liu Z, Xie M H, Lin H Q 2010 J. Phys. Chem. C 114 3693
[6] Rangappa D, Murukanahally K D, Tomai T, Unemoto A, Honma I 2012 Nano Lett. 12 1146
[7] Dominko R, Bele M, Kokalj A, Gaberscek M, Jamnik J 2007 J. Power Sources 174 457
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[9] Huang X B, Li X, Wang H Y, Pan Z L, Qu M Z, Yu Z L 2010 Electrochim. Acta 55 7362
[10] Zhang S, Lin Z, Ji L W, Li Y, Xu G J, Xue L G, Li S, Lu Y, Toprakci O, Zhang X W 2012 J. Mater. Chem. 22 14661
[11] Chen R Y, Heinzmann R, Mangold S, Chakravadhanula K, Hahn H, Indris S 2013 J. Phys. Chem. C 117 884
[12] Jia M Z, Wang H Y, Chen Y Z, Ma C L, Wang H 2015 Acta Phys. Sin. 64 087101 (in Chinese) [嘉明珍, 王红艳, 陈元正, 马存良, 王辉 2015 64 087101]
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[14] Ong S P, Chevrier V L, Hautier G, Jain A, Moore C, Kim S, Ma X H, Ceder G 2011 Energy Environ. Sci. 4 3680
[15] Wu S Q, Zhu Z Z, Yang Y, Hou Z F 2009 T. Nonferr. Metal. Soc. 19 182
[16] Zhang P, Li X D, Yu S, Wu S Q, Zhu Z Z, Yang Y 2013 J. Electrochem. Soc. 160 A658
[17] Wang M, Yang M, Ma L Q Shen X D 2015 Chem. Phys. Lett. 619 39
[18] Duncan H, Kondamreddy A, Mercier P H J, Page Y L, Abu-Lebdeh Y, Couillard M, Whitfield P S, Davidson I J 2011 Chem. Mater. 23 5446
[19] Zhang P, Xu Y X, Zheng F, Wu S Q, Yang Y, Zhu Z Z 2015 Cryst. Eng. Comm. 17 2123
[20] Fisher C A J, Kuganathan N, Islam M S 2013 J. Mater. Chem. A 1 4207
[21] Kresse G, Joubert D 1999 Phys. Rev. B 59 1758
[22] Kresse G, Furthmller J 1996 Comp. Mater. Sci. 6 15
[23] Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865
[24] Anisimov V I, Zaanen J, Andersen O K 1991 Phys. Rev. B 44 943
[25] Henkelman G, Uberuaga B P, J nsson H 2000 J. Chem. Phys. 113 9901
[26] Nytén A, Abouimrane A, Armand M, Gustafsson T, Thomas J O 2005 Electrochem. Commun. 7 156
[27] Lee H, Park S D, Moon J, Lee H, Cho K, Cho M, Kim S Y 2014 Chem. Mater. 26 3896
[28] Wu S Q, Zhu Z Z, Yang Y, Hou Z F 2009 Comp. Mater. Sci. 44 1243
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[1] Nagaura T, Tozawa K 1990 Prog. Batteries Sol. Cells 9 209
[2] Xin X G, Shen J Q, Shi S Q 2012 Chin. Phys. B 21 128202
[3] Gummow R J, He Y 2014 J. Power Sources 253 315
[4] Guo Z F, Pan K, Wang X J 2016 Chin. Phys. B 25 017801
[5] Zhong G H, Li Y L, Yan P, Liu Z, Xie M H, Lin H Q 2010 J. Phys. Chem. C 114 3693
[6] Rangappa D, Murukanahally K D, Tomai T, Unemoto A, Honma I 2012 Nano Lett. 12 1146
[7] Dominko R, Bele M, Kokalj A, Gaberscek M, Jamnik J 2007 J. Power Sources 174 457
[8] Ellis B, Kan W H, Makahnouk W R M, Nazar L F 2007 J. Mater. Chem. 17 3248
[9] Huang X B, Li X, Wang H Y, Pan Z L, Qu M Z, Yu Z L 2010 Electrochim. Acta 55 7362
[10] Zhang S, Lin Z, Ji L W, Li Y, Xu G J, Xue L G, Li S, Lu Y, Toprakci O, Zhang X W 2012 J. Mater. Chem. 22 14661
[11] Chen R Y, Heinzmann R, Mangold S, Chakravadhanula K, Hahn H, Indris S 2013 J. Phys. Chem. C 117 884
[12] Jia M Z, Wang H Y, Chen Y Z, Ma C L, Wang H 2015 Acta Phys. Sin. 64 087101 (in Chinese) [嘉明珍, 王红艳, 陈元正, 马存良, 王辉 2015 64 087101]
[13] Kuganathan N, Islam M S 2009 Chem. Mater. 21 5196
[14] Ong S P, Chevrier V L, Hautier G, Jain A, Moore C, Kim S, Ma X H, Ceder G 2011 Energy Environ. Sci. 4 3680
[15] Wu S Q, Zhu Z Z, Yang Y, Hou Z F 2009 T. Nonferr. Metal. Soc. 19 182
[16] Zhang P, Li X D, Yu S, Wu S Q, Zhu Z Z, Yang Y 2013 J. Electrochem. Soc. 160 A658
[17] Wang M, Yang M, Ma L Q Shen X D 2015 Chem. Phys. Lett. 619 39
[18] Duncan H, Kondamreddy A, Mercier P H J, Page Y L, Abu-Lebdeh Y, Couillard M, Whitfield P S, Davidson I J 2011 Chem. Mater. 23 5446
[19] Zhang P, Xu Y X, Zheng F, Wu S Q, Yang Y, Zhu Z Z 2015 Cryst. Eng. Comm. 17 2123
[20] Fisher C A J, Kuganathan N, Islam M S 2013 J. Mater. Chem. A 1 4207
[21] Kresse G, Joubert D 1999 Phys. Rev. B 59 1758
[22] Kresse G, Furthmller J 1996 Comp. Mater. Sci. 6 15
[23] Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865
[24] Anisimov V I, Zaanen J, Andersen O K 1991 Phys. Rev. B 44 943
[25] Henkelman G, Uberuaga B P, J nsson H 2000 J. Chem. Phys. 113 9901
[26] Nytén A, Abouimrane A, Armand M, Gustafsson T, Thomas J O 2005 Electrochem. Commun. 7 156
[27] Lee H, Park S D, Moon J, Lee H, Cho K, Cho M, Kim S Y 2014 Chem. Mater. 26 3896
[28] Wu S Q, Zhu Z Z, Yang Y, Hou Z F 2009 Comp. Mater. Sci. 44 1243
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