Today, lithium-ion batteries represent the most widely used secondary battery. They play an important role in the further development of electric mobility or mobile applications (smartphones, laptops). They are characterized by their high energy and/or power density. In order to meet the needs of the future, higher energy and power densities, longer cycle life and higher safety standards are required. Due to their wide range of applications, the expectations of their lifetime and performance are increasing. The energy density is a critical factor for future energy storage systems in mobile applications. In order to achieve higher energy densities, an anode material must combine high specific capacities with high columbic efficiencies.

Due to its low average voltage, low voltage hysteresis, good rate capability, low irreversible capacity, low volume expansion during lithiation causing excellent cycle life, graphite has been the material of choice as anode material [1].

However, the low theoretical specific capacity limits the application potential of graphite anodes. With its high theoretical specific capacity, silicon is the most promising anode material. However, the use of pure silicon is severely restricted by its mechanical behavior during charge/discharge cycling. Crystallization effects and massive volume changes during cycling seriously limit the cycle life of battery cells with Silicon as main component [2]. Therefore, Silicon/graphite blends seem to be the preferred route towards high energy anode formulations with relevant life times.

In this context it is essential to understand the interplay between the various components of the blend electrodes for optimized performances, which is addressed in the current publication.

Different industrially available graphites (KS6, KS6L. MCMB, LFP2, ECC Graphit) and a Silicon alloy material were used for anode preparation in order to investigate their structural morphologies and electrochemical performance of the resulting electrodes. The electrodes were tested in coin cell assemblies and charged and discharged at various rates. The morphologies of fresh and aged electrodes were investigated by means of optical and electron microscopy. Furthermore the volume changes of cells were monitored in order to relate it with the morphological appearance, porosity and graphite type.

References

[1] M. N. Obrovac and V. L. Chevrier, “Alloy Negative Electrodes for Li-Ion Batteries,” Chemi. Rev., pp. 11444–11502, 2014.

[2] W. J. Zhang, “A review of the electrochemical performance of alloy anodes for lithium-ion batteries,” J. Power Sources, vol. 196, no. 1, pp. 13–24, 2011.