Toward the Realization of High Energy Density Li-Ion Batteries with Si-Based Anodes and LiNi0.5Mn0.3Co0.2O2 Cathodes
Authors: Marinaro Mario , Yoon Dong-hwan , Figgemeier Egbert , Stegmeier Petra , Schmidt Gregory , Chauveau Jerome , Spurk Paul , Nelis Daniël , Axmann Peter , Wohlfahrt-Mehrens Margret 
Published: February 2020

Lithium ion batteries (LIBs) are nowadays very popular and used probably in all portable electronic devices such as laptops, cameras and mobile phones. However, future mass production of electrical vehicles (EV) and hybrid electrical vehicles (PHEV) requires improvements of the battery technology in terms of performance, costs and safety. To that aim further development of alternative electrode materials is of primary importance. Current Li-ion technology reaches energy densities of about 120 Wh/kg for prismatic and >200 Wh/kg for smaller 18650 cells. A projected energy density approaching 250 Wh/kg for prismatic cells is expected for advanced Li-ion cells in the next five years.
In order to reach those targets high capacity anode and cathode materials will have to be used. Si and Si-alloy compounds are among the most promising anode materials [1,2]. For this study we have used anodes comprising a Si-alloy (3M, Germany) having a reversible capacity of 1033 mAh/g and an irreversible capacity of only 180 mAh/g. We have recently introduced a new term called Efficient Capacity (Ceff), which takes into account both the reversible and the irreversible capacity of a given anode material (Ceff = CE
* CP
/(CP
+ Ci
) with CE
= reversible capacity of anode; Ci
= irreversible capacity of anode; CP
= discharge capacity of cathode), and found that few Si-based materials among those reported in literature have indeed the capabilities of outperforming state-of-the-art carbonaceous ones [3]. The calculated efficient capacity for the 3M Si-alloy (Ceff
= 494 mAh/g ) is one of the highest can be found in literature and almost double than that of state-of-the-art graphite. During anodes manufacturing process, the Si-alloy was eventually blended with synthetic graphite (Hitachi, Japan) in the composite electrode. The Si-alloy content was therefore varied between 55 wt.% and 91 wt.%. Nevertheless, the electrodes areal capacities were always above 3.5 mAh/cm2. Pouch cells have been constructed using LiNi0.5Mn0.3Co0.2O2 (Umicore AG & Co KG, Germany) as the cathode material. The cathode material could be easily processed and high mass loading electrodes have been achieved (>19 mg/cm2).
Several cathode-to-anode mass balancing have been evaluated in order to maximize the energy density output while still maintaining comparatively good cyclability. The electrochemical characterization has been carried out by means of galvanostatic cycling and electrochemical impedance spectroscopy (EIS). Furthermore we evaluated the swelling behavior of the pouch cells using an in-operando technique. We have been therefore able to quantify not only the variation of the cell height but also the variation of the pressure during the charge and discharge steps. Considerations about the volume variation at the electrodes/cell level during charge/discharge are of a primary importance especially in view of assembling hard-case prismatic cells where internal volume is fixed.

ACKNOWLEDGMENT

Financial support from the European Union's H2020 Framework Programme for research, technological development and demonstration (H2020-GV-2014) under grant agreement n° 653531 (FIVEVB) is gratefully acknowledged. Thanks are due to Paul Drews for help with the electrochemical measurements.

References

[1] M. N. Obrovac, V. L. Chevrier Chem. Rev. 114 11444−11502 (2014)
[2] V. L. Chevrier, L. Liu, D. Ba Le, J. Lund, B. Molla, K. Reimer, L. J. Krause, L. D. Jensen, E. Figgemeier, K. W. Eberman J. Electrochem. Soc. 161 (5) A783-A791 (2014)
[3] M. Marinaro, M. Weinberger, M. Wohlfahrt-Mehrens, Electrochimica Acta, accepted for publication

Figure 1