2, LeydenJar Technologies, Leiden, , Netherlands
3, Technical University of Delft, Delft, , Netherlands
4, ZSW, Ulm, , Germany
Silicon is an ideal anode material for Li-ion batteries, provided it can accommodate the large volume changes between charging and discharging. We present a method, based on Plasma Enhanced Chemical Vapor Deposition (PECVD), to create self-organized nano-structured silicon layers, which can accommodate the large volume changes. Large advantage of this method is that it does not require any pre- or posttreatment of the silicon to obtain the nano-structuring and high porosity. The nanometer scale porosity of these layers can be tuned between 30 and 70%, leading to specific areas of more than 200 m2/g (as measured by BET analysis).
The layers are deposited in a pilot roll-to-roll PECVD deposition system, in which we can handle foils with a width up to 30 cm. The linear plasma sources, however, can be easily extended to a width of more than 1 meter, offering perspectives to cost-effective high throughput mass production of the silicon layers.
We tested this material both in half cells with Li counter electrode and in full cells with an NMC cathode, with a silicon mass load of approximately 1 mg/cm2. Half cells, charged at 1000 mAh/g at C/5 show no capacity fading and a CE of 99.5% after more than 350 cycles, using a standard electrolyte LiPF6 containing FEC. Small pouch cells (3x3 cm2) could be charged/discharged more than 100 cycles at 1000 mAh/gSi without capacity fading but with a CE of about 98%. Further improvement of the lifetime is expected through modifications of the electrolyte to increase the Coulombic efficiency in full cells.