鋰離子電池是現今被廣泛使用的二次電池之一，它可應用在可攜式的電子產品，甚至也被應用在需要大電力如電動車中，鋰離子電池主要是由一正極、一負極、隔離膜以及電解液所組成。
本研究係針對由PP(polypropylene)/PE(polyethylene)/PP三層結構所組成的高分子隔離膜，隔離膜通常會置放於正極與負極之間，避免兩極直接接觸造成如短路等等的現象發生，以維持電池正常運作，而它必須擁有良好的離子傳導性、電化學穩定性以及好的機械性質，在電池運作期間只能允許鋰離子等通過，不參與其他任何反應。
從X-ray diffraction (XRD)的實驗中可以觀察到PP/PE/PP三層隔離膜有五個主要的繞射峰值，由小至大分別代表PP(110)、PP(040)、PP(130)、PE(110) 及PE(200)，從此可以得知隔離膜結構中除了非晶狀(amorphous)以外也有結晶狀(crystalline)，其中PP(040) 和PE(200)兩峰值向小角度產生明顯的偏移，由布拉格定律(Bragg’s law)可以得知隔離膜晶格間距擴張，這個結果顯示原本認為不參與反應的隔離膜，可能與電解液中的離子或分子有交互作用。
透過density functional theory(DFT)方法計算，並且使用Vienna Ab initio Simulation Package(VASP) 等軟體去模擬隔離膜在鋰離子電池中的行為，將不同的離子以及分子組合嵌入至隔離模中，其中若嵌入的是離子則會對此帶電系統(charge system)做能量修正，記錄各個能量並觀察晶格擴張變化，透過計算反應能(reaction energy)以及模擬XRD圖分析，便可以瞭解PP/PE/PP隔離膜在鋰離子電池中的機制。

Separator composed of Polypropylene (PP)/Polyethylene (PE)/PP three-layer structure plays an important role in lithium-ion battery (LIB). It is placed in between anode and cathode to avoid physical contact of the two electrodes in order to keep the battery working well. It usually has high ionic conductivity, good electrochemical stability and good mechanical properties. In the past, separators are usually considered as an inert material in LIB, allowing only lithium ions transfer through its porous part. From our recent synchrotron X-ray diffraction (XRD) experiments, however, the peaks of PP and PE shift toward low angles. The results indicate that the crystalline part of PP and PE which originally been thought having no function in LIB is now may also participate in the reactions with lithium ions and electrolyte. In this research first-principles calculation with density function theory (DFT) as implement in Vienna Ab initio Simulation Package (VASP) were used to study the reactions of lithium ions and electrolyte with separator. Different combinations of lithium ion/ electrolyte molecule insertion were calculated to identify the possible mechanisms that are responsible for the peak shifting. From the reaction energies and the simulated XRD patterns we have revealed the mechanism for unexpected lattice expansion of PP/PE/PP micro-porous separator in lithium-ion battery.

1. Yang, M. and J. Hou, Membranes in lithium ion batteries. Membranes, 2012. 2(3): p. 367-383.
2. Xu, K., Nonaqueous liquid electrolytes for lithium-based rechargeable batteries. Chemical reviews, 2004. 104(10): p. 4303-4418.
3. https://physicsandsocietybc.wordpress.com/2013/04/03/the-rocking-chair-battery-lithium-ion-battery/.
4. Data from Prof. Chia-Chin Chang, Prof. Tsan-Yao Chen, Dr. Po-Wei Yang, Mr. Yu-Fan Chen and Mrs. Pin-Ching Wu
5. Nishi, Y., Lithium ion secondary batteries; past 10 years and the future. Journal of Power Sources, 2001. 100(1): p. 101-106.
6. Wakihara, M., Recent developments in lithium ion batteries. Materials Science and Engineering: R: Reports, 2001. 33(4): p. 109-134.
7. Scrosati, B., Recent advances in lithium ion battery materials. Electrochimica Acta, 2000. 45(15): p. 2461-2466.
8. Thackeray, M., Lithium-ion batteries: An unexpected conductor. Nature Materials, 2002. 1(2): p. 81-82.
9. Agostini, M., S. Brutti, and J. Hassoun, High voltage Li-ion battery using exfoliated graphite/graphene nanosheets anode. ACS applied materials & interfaces, 2016. 8(17): p. 10850-10857.
10. Guo, P., H. Song, and X. Chen, Electrochemical performance of graphene nanosheets as anode material for lithium-ion batteries. Electrochemistry Communications, 2009. 11(6): p. 1320-1324.
11. Fu, L., et al., Surface modifications of electrode materials for lithium ion batteries. Solid State Sciences, 2006. 8(2): p. 113-128.
12. Novikov, D., et al., Electrochemical performance and surface chemistry of nanoparticle Si@ SiO 2 Li-ion battery anode in LiPF 6-based electrolyte. Electrochimica Acta, 2016. 208: p. 109-119.
13. Farmakis, F., et al., High energy density amorphous silicon anodes for lithium ion batteries deposited by DC sputtering. Journal of Power Sources, 2015. 293: p. 301-305.
14. Chen, Y., et al., High capacity, stable silicon/carbon anodes for lithium-ion batteries prepared using emulsion-templated directed assembly. ACS applied materials & interfaces, 2014. 6(7): p. 4678-4683.
15. Wen, Z., et al., High capacity silicon/carbon composite anode materials for lithium ion batteries. Electrochemistry Communications, 2003. 5(2): p. 165-168.
16. Aurbach, D., et al., Design of electrolyte solutions for Li and Li-ion batteries: a review. Electrochimica Acta, 2004. 50(2): p. 247-254.
17. 工業材料雜誌302期.
18. Xu, K., et al., LiBOB as salt for lithium-ion batteries: a possible solution for high temperature operation. Electrochemical and Solid-State Letters, 2002. 5(1): p. A26-A29.
19. Bordes, A., K. Eom, and T.F. Fuller, The effect of fluoroethylene carbonate additive content on the formation of the solid-electrolyte interphase and capacity fade of Li-ion full-cell employing nano Si–graphene composite anodes. Journal of Power Sources, 2014. 257: p. 163-169.
20. Chen, L., et al., Effect of vinylene carbonate (VC) as electrolyte additive on electrochemical performance of Si film anode for lithium ion batteries. Journal of Power Sources, 2007. 174(2): p. 538-543.
21. Jung, H.M., et al., Fluoropropane sultone as an SEI-forming additive that outperforms vinylene carbonate. Journal of Materials Chemistry A, 2013. 1(38): p. 11975-11981.
22. Li, B., et al., Prop-1-ene-1, 3-sultone as SEI formation additive in propylene carbonate-based electrolyte for lithium ion batteries. Electrochemistry Communications, 2012. 17: p. 92-95.
23. Xia, J., et al., Study of methylene methanedisulfonate as an additive for Li-ion cells. Journal of The Electrochemical Society, 2014. 161(1): p. A84-A88.
24. Huang, X., Separator technologies for lithium-ion batteries. Journal of Solid State Electrochemistry, 2011. 15(4): p. 649-662.
25. Zhang, S.S., A review on the separators of liquid electrolyte Li-ion batteries. Journal of Power Sources, 2007. 164(1): p. 351-364.
26. Peabody, C. and C.B. Arnold, The role of mechanically induced separator creep in lithium-ion battery capacity fade. Journal of Power Sources, 2011. 196(19): p. 8147-8153.
27. 江進福, 波函數與密度泛函.
28. Cohen, A.J., P. Mori-Sánchez, and W. Yang, Insights into current limitations of density functional theory. Science, 2008. 321(5890): p. 792-794.
29. Gross, E. and W. Kohn, Time-dependent density-functional theory. Advances in quantum chemistry, 1990. 21: p. 255-291.
30. Kohn, W., Nobel Lecture: Electronic structure of matter—wave functions and density functionals. Reviews of Modern Physics, 1999. 71(5): p. 1253.
31. Parr, R.G., Density functional theory of atoms and molecules, in Horizons of Quantum Chemistry. 1980, Springer. p. 5-15.
32. Car, R. and M. Parrinello, Unified approach for molecular dynamics and density-functional theory. Physical review letters, 1985. 55(22): p. 2471.
33. Jones, R.O. and O. Gunnarsson, The density functional formalism, its applications and prospects. Reviews of Modern Physics, 1989. 61(3): p. 689.
34. Kresse, G. and D. Joubert, From ultrasoft pseudopotentials to the projector augmented-wave method. Physical Review B, 1999. 59(3): p. 1758.
35. Kittel, C., Introduction to Solid State Physics. 1996: Wiley.
36. Bylaska, E.J. Introduction to Plane-Wave Basis Sets and Pseudopotential Theory.
37. Neerav Kharche, C.D., Brookhaven National Laboratory, VASP Calculations With Model Solvation. 2014.
38. Le Roux, S. and V. Petkov, ISAACS–interactive structure analysis of amorphous and crystalline systems. Journal of Applied Crystallography, 2010. 43(1): p. 181-185.
39. Seebauer, E.G. and M.C. Kratzer, Charged point defects in semiconductors. Materials Science and Engineering: R: Reports, 2006. 55(3): p. 57-149.
40. Richter, N., Charged point defects in oxides–a case study of MgO bulk and surface F centers. 2013, Technische Universität Berlin.
41. Klimeš, J., D.R. Bowler, and A. Michaelides, Chemical accuracy for the van der Waals density functional. Journal of Physics: Condensed Matter, 2009. 22(2): p. 022201.
42. Klimeš, J., D.R. Bowler, and A. Michaelides, Van der Waals density functionals applied to solids. Physical Review B, 2011. 83(19): p. 195131.
43. Mathew, K. and R.G. Hennig, Implicit self-consistent description of electrolyte in plane-wave density-functional theory. arXiv preprint arXiv:1601.03346, 2016.
44. Mathew, K., et al., Implicit solvation model for density-functional study of nanocrystal surfaces and reaction pathways. The Journal of chemical physics, 2014. 140(8): p. 084106.
45. http://cms.mpi.univie.ac.at/vasp/guide/node112.html