近年來，儲能技術已是最受關注的議題，並同時出現一系列新興技術，自1991年鋰離子電池商業化以來，便在攜帶式裝置中佔有舉足輕重的地位，為了滿足其方便性，高容量、高能量密度、高循環壽命……等必須不斷進步，例如具有高理論容量(3860 mAh/g)的鋰金屬負極以及高安全性的固態電解質等，但是目前鋰離子電池仍然存在沉積不均匀、庫倫效率偏低、锂枝晶等問題阻礙了其商業化應用，因此進一步了解了解鋰金屬的沉積過程及枝晶成長對於解決這些問題非常重要。
利用分子動力學(molecular dynamics, MD)探討鋰金屬枝晶在電解質中的生長狀態，其特點在於給予系統經驗勢能函數預估材料性質，無須從頭擬合(ab initio)材料性質，省去龐大的計算量和時間。本研究探討之鋰離子受電場影響在負極形成枝晶 ，鋰離子堆積過程中，一些表面鋰原子可能會通過庫侖相互作用被彈出，因此枝晶並非是呈線性持續增長；但直到短路之前的時刻，整體枝晶生長率在幾個 ps 之後幾乎保持不變，本模擬側重於陽極上枝晶的生長，因此，陰極只是一個離子供應器，它保持足夠低的發射率以避免相鄰離子之間的強烈相互作用，但又足夠快以將模擬時間減少到最低限度。基於這次模擬，電解質必須能承受高於 3.5 GPa 的壓力，以避免在不遭受結構損壞的情況下形成枝晶。未來鋰離子電池將會逐漸普及，此分子動力學模擬可用以提前預測電池的安全性，並開發更高充放電、高穩定性之鋰離子電池，促使全面商業化。

In recent years, energy storage technology has been the most concerned topic, and a series of emerging technologies have emerged at the same time. Since the commercialization of lithium-ion batteries in 1991, they have played a pivotal role in portable devices. To meet convenience, high capacity, high energy density, high cycle life, etc. must continue to improve, such as lithium metal negative electrodes with high theoretical capacity (3860 mAh/g) and high-safety solid electrolytes, etc. However, there are still uneven deposition of lithium-ion batteries. Problems such as low Coulomb efficiency and lithium dendrites hinder its commercial application. Therefore, a better understanding of the deposition process and dendrite growth of lithium metal is the key to solve these problems.
This research uses molecular dynamics (MD) to explore the growth state of lithium metal dendrites in the electrolyte. The characteristic of MD is to give the system an empirical potential energy function to estimate the material properties, without the need to ab initio the material properties, and save huge calculate the amount and time. The lithium ions discussed in this study are affected by the electric field to form dendrites on the negative electrode. During the accumulation of lithium ions, some surface lithium atoms may be ejected through the Coulomb interaction, so the dendrites do not continue to grow linearly, but until the moment before the short circuit. The overall dendrite growth rate remains almost unchanged after a few ps. This simulation focuses on the growth of dendrites on the anode, therefore, the cathode is just an ion-emitter, which maintains a sufficiently low emissivity to avoid interference between neighbor ions but fast enough to reduce simulation times to a minimum. Based on this simulation, the electrolyte must be able to withstand pressures higher than 3.5 GPa to avoid the formation of dendrites without suffering structural damage. In the future, lithium-ion batteries will gradually become popular. This molecular dynamics simulation can be used to predict the safety of batteries in advance, and to develop higher charge-discharge, high-stability lithium-ion batteries, and promote full commercialization.

[1] M. Kebede, Battery energy storage technologies for off-grid and transport applications. ee publishers, 2018.
[2] W. Lin, Y. Liu and T. cui. Reviving the lithium metal anode for high-energy batteries. Nature Nanotechnology, 3:194-206, 2017
[3] X. S. Yoon, K-J Park, U-H Kim, et al., High-Energy Ni-Rich Li [NixCoyMn1-x-y] O2 Cathodes via Compositional Partitioning for Next-Generation Electric Vehicle[J]. Chem. Mater, 29:10436-10445, 2017.
[4] L. Ji, Z. Lin, M. Alcoutlabi and X. Zhang. Recent developments in nanostructured anode materials for rechargeable lithium-ion batteries. Energy Environ. Sci., 4:2682-2699, 2011.
[5] D. Lin, Y. Liu and Y. Cui, Reviving the lithium transition-metal oxide for high-energy lithium-ion batteries. Angew. Chem., Int. Edit. 2015, 54: 4440-4457.
[6] H. Shimotake, Progress in Batteries and Solar Cells, JEC Press, 1990.
[7] G. Kucinskis, G. Bajars and J. Kleperis, Graphene in lithium ion battery cathode materials: A review, Journal of Power Sources, vol. 240, pp. 66-79, 2013.
[8] W. C. Choi, D. Byun, J. K. Lee. Electrochemical characteristics of silver- and nickel-coated synthetic graphite prepared by a gas suspension spray coating method for the anode of lithium secondary betteries. Electrochim. Acta, 2004, 50 (2): 523-529
[9] H. Y. Lee, J. K. Baek, S. M. Lee, et al. Effect of carbon coating on elevated temperature performance of graphite as lithium-ion battery anode material[J]. J. Power Sources, 2004, 128(1): 61-66.
[10] W. Guoping, Z. Bolan, Y. Min, et al. A modified graphite anode with high initial efficiency and excellent cycle life expectation. Solid State Ionics, 2005, 176(9): 905-909.
[11] C. Chae, H. Noh, J. K. Lee, et al. A High-Energy Li-Ion Battery Using a Silicon-Based Anode and a Nano-Structured Layered Composite Cathode, Advanced Functional Materials, vol. 24, no. 20, pp. 3036-3042, 2014.
[12] D. Lin, Y. Liu, Y. Cui, Reviving the lithium metal anode for high-energy batteries[J]. nature nanotech. 2017, 12: 194-206.
[13] L. O. Valøen and J. N. Reimers, Transport Properties of LiPF6-Based Li-Ion Battery Electrolytes, J. Electrochem, Soc. 152 A882, 2013
[14] R. Marom, O. Haik, Doron Aurbach, et al. Revisiting LiClO4 as an Electrolyte for Rechargeable Lithium-Ion Batteries, J. Electrochem. Soc. 157 A972, 2010.
[15] S. S. Zhang, K. Xu and T. R. Jow, Study of LiBF4 as an Electrolyte Salt for a Li-Ion Battery, J. Electrochem. Soc. 149 A586, 2002.
[16] G. S. MacGlashan, Y. G. Andreev and P. G. Bruce, Structure of the polymer electrolyte poly(ethylene oxide)6:LiAsF6, Nature, vol. 398, pp. 792–794, 1999.
[17] Y. Guo, H. Li and T. Zhai, Reviving Lithium-Metal Anodes for Next-Generation High-Energy Batteries, Advances Materials, vol. 29, no.29, 1700007, 2019.
[18] Q. Wang, L. Jiang, Y. Yu, et al., Progress of enhancing the safety of lithium-ion battery from the electrolyte aspect, Nano Energy, vol. 55, pp.93-114. 2019.
[19] J. W. Fergus, "Ceramic and Polymeric Solid Electrolytes for Lithium-ion Batteries," J Power Sources, vol. 195, no. 15, pp. 4554-4569, 2010.
[20] J. C. Bachman, S. Muy, A. Grimaud, H. H. Chang, N. Pour, S. F. Lux, O. Paschos, F. Maglia, S. Lupart, P. Lamp, L. Giordano, and Y. Shao-Horn, "Inorganic Solid-State Electrolytes for Lithium Batteries: Mechanisms and Properties Governing Ion Conduction," Chem Rev, vol. 116, no. 1, pp. 140-162, 2016.
[21] Liu N, Lu Z, Zhao J, et al. Apomegranate-inspired nanoscale design for large-volume-change lithium battery anodes[J]. Nature Nanotechnology, 2014, 9(3): 187-192.
[22] X. B. Cheng, R. Zhang, C. Z. Zhao, and Q. Zhang, "Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review," Chem. Rev. 2017, 117, 15, 10403–10473
[23] G. N. Lewis, F. G. Keyes. The Potential of The Lithium Electrode. J.am.chem.soc, 1913, 35(4):340-344
[24] M. S. Whittinggham, Lithium Batteries and Cathode Material, Chemical Reviews, 2004, 104(10): 4271-4301
[25] D. W. Murphy, F. J. D. Salvo, et al. Topochemical reactions of rutile related structures with lithium, Materials Research Bulletin, 1978. 13(12): 1395-1402.
[26] O. Borodin and G. D. Smith, Quantum Chemistry and Molecular Dynamics Simulation Study of Dimethyl Carbonate: Ethylene Carbonate Electrolytes Doped with LiPF6. J. Phys. Chem. B 2009, 113, 6, 1763–1776.
[27] P. G. Bruce, S. A. Freunberger, L. J. Hardwick, et al. Li-O2 and Li-S batteries with high energy storage. Nature materials, 2011, 11(1):19-29.
[28] M. D. Tikekar, L. A. Koch, Stabilizing electrodeposition in elastic solid electrolytes containing immobilized anions. Science Advances, 2016, 2(7):e1600320-e1600320.
[29] J. E. Lennard-Jones, Cohesion, Proceedings of the Physical Society, 43(5), 461, 1913.
[30] M. I. Baskes, “Modified embedded-atom potentials for cubic materials and impurities”. Phys Rev B Condens Matter, 1992, 46(5):2727-2742.
[31] B. Lee, J. W. Lee, “A modified embedded atom method interatomic potential for carbon”. Calphad, 2005,29(1):7-16.
[32] M. S. Daw and M. I. Baskes, Phys. Rev. Lett. 50, 1285 (1983).
[33] M. S. Daw and M. I. Baskes, Phys. Rev. B29, 6443 (1984).
[34] J. Tersoff , “ Modeling solid-state chemistry: Interatomic potentials for multicomponent systems,” Physical Review B, 1989,39(8):5566-5568.
[35] S. Plimpton, “Fast parallel algorithms for short-range molecular dynamics, ”Journal of computational physics,117(1),1-19.1995
[36] W. Humphrey, A. Dalke and K. Schulten, VMD: visual molecular dynamics[J]. J Mol Graph, 1996,14(1):33-38, 27-28.
[37] S. Alexander, Visualization and analysis of atomistic simulation data with OVITO–the Open Visualization Tool. Modelling and Simulation in Materials Science and Engineering, 2010,18(1):15012.
[38] J. M. Martinez and L. Martinez, Packing optimization for automated generation of complex system's initial configurations for molecular dynamics and docking, J. Comput. Chem., 2003, 24(7), 819–825.
[39] L. Mart´ınez, R. Andrade, E. G. Birgin and J. M. Mart´ınez, PACKMOL: a package for building initial configurations for molecular dynamics simulations, J. Comput. Chem., 2009, 30(13), 2157–2164.
[40] N. Kumar and J. M. Seminario, Lithium-Ion Model Behavior in an Ethylene Carbonate Electrolyte Using Molecular Dynamics, J. Phys. Chem. C, 2016, 120(30), 16322–16332.
[41] A. K. Rappe, C. J. Casewit, K. S. Colwell, W. A. Goddard and W. M. Skiff, UFF, a full periodic table forcefield for molecular mechanics and molecular dynamics simulations, J. Am. Chem. Soc., 1992, 114(25), 10024–10035.
[42] M. Masia, M. Probst and R. Rey, Ethylene Carbonate Li+: A Theoretical Study of Structural and Vibrational Properties in Gas and Liquid Phases, J. Phys. Chem. B, 2004, 108(6), 2016– 2027.
[43] R. Jorn, R. Kumar, D. P. Abraham and G. A. Voth, Atomistic Modeling of the Electrode–Electrolyte Interface in Li-Ion Energy Storage Systems: Electrolyte Structuring, J. Phys. Chem. C, 2013, 117(8), 3747–3761.
[44] D. E. Galvez-Aranda, V. Ponce and J. M. Seminario, Molecular dynamics simulations of the first charge of a Li-ion—Si-anode nanobattery, J. Mol. Model., 2017, 23(4), 120.
[45] M. J. Frisch, G. W. Trucks, H. B. Schlegel, et al., Gaussian 09, Revision D.01, Gaussian, Inc., Wallingford, CT, 2013.
[46] H. Sun, S. J. Mumby, J. R. Maple and A. T. Hagler, An Ab Initio CFF93 All-Atom Force Field for Polycarbonates, J. Am. Chem. Soc., 1994, 116(7), 2978–2987.
[47] G. Simmons, and H. Wang 1971 Single Crystal Elastic Constants and Calculated Aggregate Properties: a Handbook (Cambridge, MA: MIT Press)
[48] P. M. Derlet, R. Høier, R. Holmestad, K. Marthinsen, and N. Ryum, “The embedded-atom model applied to vacancy formation in bulk aluminium and lithium, ”J. Phys.: Condens. Matter 11 3663–77.
[49] W. Xu, J. Wang, F. Ding, X. Chen, E. Nasybulin, Y. Zhang and J.-G. Zhang, Lithium metal anodes for rechargeable batteries, Energy Environ. Sci., 2014, 7(2), 513–537.
[50] F. Ding, W. Xu, G. L. Graff, et al., Dendrite-Free Lithium Deposition via Self-Healing Electrostatic Shield Mechanism, J. Am. Chem. Soc., 2013, 135(11), 4450–4456.
[51] M. R. Nadler and C. P. Kempier, Crystallographic Data 186. Lithium, Anal. Chem., 1959, 31(12), 2109.