Abstract: The Ca-doping properties of P2-NaxCoO2 cathode materials for sodium ion batteries had been studied by first-principles calculations based on density functional theory. The doping Ca prefers to locate at the site in the center of the triangular prisms sharing edges with adjacent CoO6 octahedrons. Ca forms a relatively strong chemical interaction with surrounding oxygen by electron transfer, and weaken the adjacent Co-O bonds. The Ca-CoO2 interactions are stronger than Na-CoO2 interactions. The intercalation energy of Ca is calculated to be 7.90 eV, which is almost twice that of Na (~4.25 eV). The stable configurations for two Na or one Na and one Ca are studied to reveal Ca-Na and Na-Na interactions. The effect of Ca-Na makes it difficult for Na to approach Ca, reducing the probability of Na distribution around Ca. Molecular dynamics studies have shown that stronger Ca-Na interaction can suppress the drastic changes of Na distribution as a function of Na content. Finally, it can be concluded that performance improvement of battery by Ca-doping in P2-NaxCoO2 can be ascribed to the strong interactions of Ca-CoO2 and Ca-Na, which slow down the structural change in the charge-discharge process and improve the cycle stability.
1 Armand M, Tarascon J M. Nature, 2008, 451(7179), 652. 2 Hoffert M I, Caldeira K, Benford G, et al. Science, 2002, 298(5595), 981. 3 Kang B, Ceder G. Nature, 2009, 458(7235), 190. 4 Zhao L N, Zhang T, Zhao H L, et al. Materials Today Nano, 2020, 10, 100072. 5 Zhu W, Wang Y S, Liu D Q, et al. Energies,2018, 11(11),2963. 6 Gao R M, Zheng Z J, Wang P F, et al. Energy Storage Materials, 2020, 30, 9. 7 Deng J Q, Luo W B, Chou S L, et al. Advanced Energy Materials, 2018, 8(4), 1701428. 8 Lao M M, Zhang Y, Luo W B, et al. Advanced Materials, 2017, 29(48), 1700622. 9 Kim H, Kim H, Ding Z, et al. Advanced Energy Materials, 2016, 6(19), 1600943. 10 Ong S P, Chevrier V L, Hautier G, et al. Energy & Environmental Science, 2011, 4(9), 3680. 11 Chen J. Acta Physico-Chimica Sinica, 2019, 35(4), 347 (in Chinese). 陈军. 物理化学学报,2019, 35(4), 347. 12 Molenda J, Delmas C, Hagenmuller P. Solid State Ionics, 1983, 9-10(Part 1), 431. 13 Molenda J, Delmas C, Dordor P, et al. Solid State Ionics, 1984, 12, 473. 14 Delmas C, Braconnier J J, Fouassier C, et al. Solid State Ionics, 1981, 3-4, 165. 15 Fang Y J, Chen Z X, Ai X P, et al. Acta Physico-Chimica Sinica, 2017, 33(1), 211(in Chinese). 方永进, 陈重学, 艾新平, 等.物理化学学报,2017, 33(1), 211. 16 Takahashi Y, Gotoh Y, Akimoto J. Journal of Solid State Chemistry, 2003, 172(1), 22. 17 Meng Y S, Hinuma Y, Ceder G. The Journal of Chemical Physics, 2008, 128(10),104708. 18 Shibata T, Kobayashi W, Moritomo Y. Applied Physics Express, 2013, 6(9), 097101. 19 Stokosa A, Molenda J, Than D. Solid State Ionics, 1985, 15(3), 211. 20 Zhao C, Wang Q, Yao Z, et al. Science, 2020, 370(6517), 708. 21 Ding J J, Zhou Y N, Sun Q, et al. Electrochimica Acta, 2013, 87, 388. 22 Rai A K, Anh L T, Gim J, et al. Ceramics International, 2014, 40(1), 2411. 23 Baster D, Dybko K, Szot M, et al. Solid State Ionics, 2014, 262, 206. 24 Shibata T, Kobayashi W, Moritomo Y. AIP Advances, 2013, 3(3).032104. 25 Sun Y, Guo S, Zhou H. Advanced Energy Materials, 2018, 9(23).1800212. 26 Yang P, Zhang C, Li M, et al. ChemPhysChem, 2015, 16(16), 3408. 27 Chen T, Liu W, Zhuo Y, et al. Chemical Engineering Journal, 2020, 383, 123087. 28 Matsui M, Mizukoshi F, Imanishi N. Journal of Power Sources, 2015, 280, 205. 29 Han S C, Lim H, Jeong J, et al. Journal of Power Sources, 2015, 277, 9. 30 Roger M, Morris D J P, Tennant D A, et al. Nature, 2007, 445(7128), 631. 31 Shu G J, Prodi A, Chu S Y, et al. Physical Review B, 2007, 76(18), 184115. 32 Zandbergen H W, Foo M, Xu Q, et al. Physical Review B, 2004, 70(2), 024101. 33 Kresse G, Furthmüller J. Computational Materials Science, 1996, 6(1), 15. 34 Blöchl P E. Physical Review B, 1994, 50(24), 17953. 35 Perdew J P, Burke K, Wang Y. Physical Review B, 1996, 54(23), 16533. 36 Sun Y, Guo S, Zhou H. Energy & Environ Science, 2019, 12(3), 825. 37 Kang S M, Park J H, Jin A, et al. ACS Applied Materials & Interfaces 2018, 10(4), 3562. 38 Tang W, Sanville E, Henkelman G. Journal of Physics Condensed Matter, 2009, 21(8), 084204. 39 Sanville E, Kenny S D, Smith R, et al. Journal of Computational Che-mistry, 2007, 28(5), 899. 40 Henkelman G, Andri A, Jónsson H. Computational Materials Science, 2006, 36, 354. 41 Nos'E S. The Journal of Chemical Physics, 1984, 81(1), 511. 42 Hoover W G. Physical Review A, 1985, 31(3), 1695.