Electrochemical and microstructural analysis of the processes occurring in Si microwire-array anodes (and full-cells) for high capacity Lithium ion batteries
Final Report Abstract
This project revealed the fundamental properties and limitations of a free-standing highly-oriented silicon microwire array anode for li ion batteries in order to replace already existing graphite anodes. The top-down approach does not need any kind of precursor materials, but uses purely macropore etching to fabricate a large array of pores and wires. In many subsequent fabrication steps, the necessary mechanical stabilizations are already implemented and designed during the macropore etching (one of the earlier steps during the anode fabrication). The integrated copper current collector has a significant role in the excellent performance of these electrodes. By systematic microscopic analysis of the silicon wires during different steps of the lithiation as well as delithiation process, the crystal orientation and the crystallization process could be understood. Especially cycled samples were very air sensitive and required careful preparation prior to investigations by TEM. In parallel supporting experiments were conducted for a fundamental understanding of the central Li-Si system. Furthermore, the necessary criteria and parameter to maintain a high degree of crystallinity are evaluated by careful analysis of the interaction between the electrolyte and the silicon wires. In-situ as well as ex-situ Synchrotron Radiation Characterization as well as ex-situ TEM results showed that the charging conditions and the choice of an electrolyte highly depend on the crystallinity. For the here discussed silicon microwires, an electrolyte with propylene carbonate (PC) in addition to standard carbonaceous electrolytes (provided by BASF, Selectilyte LP 30) change not only the composition of the SEI layer, but also their mechanical properties. TEM mapping demonstrated totally intact microwires encapsulated in a PC enriched SEI, whereas former wires without PC showed due to stress inner cracks covered by electrolyte remains by responsible for higher inner resistances. The homogeneous SEI layer around each wire helps to suppress the stress during volume expansion and allows high C-rates of 5 C, which corresponds to charging times of only 12 minutes. For a full cell technology, a compatible sulfur cathode but also electrolyte has to be investigated. Due to the high areal capacity of the silicon wires, standard cathodes are not suitable. Therefore, the here developed cathode is a 3D grid-structure based on self-entangled carbon nanotubes. Those structures provide the necessary porosity in order to infiltrate enough sulfur, but also reduce the amount of electrolyte. The interaction between the electrolyte and the cathode as well as the anode structure is still ongoing, in order to fulfill the tight balancing act. During various cycling experiments the grid-structures showed high capacities of 1170 mAh/g with a C-rate of C/20 up to C/2. The areal capacity of this structure is comparable to the silicon anodes and thus providing an excellent choice for the full cell technology, if the interaction between the electrolytes is completely understood.
Publications
- “Alkali Metals Extraction Reactions with the Silicides Li15Si4 and Li3NaSi6: Amorphous Si versus allo-Si”, Chem. Mater., 26(22), 6603-6612, (2014)
M. Zeilinger, L. A. Jantke, L. M. Scherf, F. J. Kiefer, G. Neubüser, L. Kienle, A. J. Karttunen, S. Konar, U. Häussermann, T. F. Fässler
(See online at https://doi.org/10.1021/cm503371e) - “Synthesis, Crystal Structure, and TEM Analysis of Sr19Li44 and Sr3Li2: A Reinvestigation of the Sr–Li Phase Diagram”, Inorg.Chem., 54, (3), 733-739, (2014)
V. Smetana, L. Kienle, V. Duppel, A. Simon
(See online at https://doi.org/10.1021/ic5010165) - "Fabrication and Characterization of Silicon Microwire Anodes by Electrochemical Etchin g Techniques", ECS Trans, 60(6), (2015)
S. Nöhren, E. Quiroga-Gonzalez, J. Carstensen, H. Föll
(See online at https://doi.org/10.1149/06606.0027ecst) - Is there a universal reaction mechanism of Li insertion into oxidic spinels: a case study using MgFe2O4, J. Mater. Chem. A 3(4), 1549-1561 (2015)
S. Permien, S. Indris, M. Scheuermann, U. Schürmann, V. Mereacre, A. K. Powell, L. Kienle, W. Bensch
(See online at https://doi.org/10.1039/c4ta05054a) - "Electrochemical Fabrication and Characterization of Silicon Microwire Anodes for Li Ion Batteries", J.Electrochem.Soc. 163 A1 (2016)
S. Nöhren, E. Quiroga-González, J. Carstensen, and H. Föll
(See online at https://doi.org/10.1149/2.0111603jes) - "Size-dependent cyclic voltammetry study of silicon microwire anodes for lithium ion batteries", Electrochimica Acta 217, 283 (2016)
S. Hansen, E. Quiroga-Gonzalez, J. Carstensen, and H. Föll
(See online at https://doi.org/10.1016/j.electacta.2016.09.088) - Verfahren zur Herstellung von Flächenableitelektroden und Halbzeug zur Durchführung des Verfahrens: EP14184103.1 (17.03.2016)
S. Nöhren, J. Bahr, J. Carstensen
- “(Re-) crystallization mechanism of highly-oriented Si-microwires by TEM analysis”, J. Solid State Electrochem. 21, 1-7
G. Neubüser, S. Hansen, V. Duppel, R. Adelung, L. Kienle
(See online at https://doi.org/10.1007/s10008-017-3672-6) - „Size-dependent physicochemical and mechanical interactions in battery paste anodes of Si-microwires revealed by Fast-Fourier-Transform Impedance Spectroscopy”, J. Power Sourc. 349, 10 (2017)
S. Hansen, E. Quiroga-Gonzalez, J. Carstensen, R. Adelung and H. Föll
(See online at https://doi.org/10.1016/j.jpowsour.2017.03.025) - „Hochleistungsakkus: Weiter kommen mit Silicium“, Nachrichten aus der Chemie, 66 (2018)
S. Hansen, J. Carstensen, L. Kienle, R. Adelung
(See online at https://doi.org/10.1002/nadc.20184068906)
