2015 AIChE Annual Meeting Proceedings

(496j) Bulk Silicon/Graphite Alloy Anode Material for High Energy Density Li-Ion Batteries

Authors

Myongjai Lee - Presenter, XALT Energy, LLC
Vishal Mahajan - Presenter, XALT Energy, LLC
Kevin Dahlberg - Presenter, University of Michigan
Fabio Albano - Presenter, XALT Energy, LLC
Subhash Dhar - Presenter, XALT Energy, LLC

Silicon anodes are an optimum alternative to traditional graphite anodes because of their higher lithium ion storage capacity. However, the massive first cycle irreversible capacity loss and large fade during cycling have hindered its commercialization. In this paper, we present a solution for these issues in the form of commercial grade silicon/graphite alloy. A silicon-carbon alloy structure with carbon-coated silicon nanoparticles gives an ability to buffer volume changes and retain the silicon amorphous phase. The material in our approach achieved a first cycle reversible capacity of over 480 mAh/g when cycled between 0.01-1.5V at a c-rate of 0.05C, with first cycle efficiency of close to 95%. The capacity of the silicon alloy was ~30 mAh/g even at 10C rate after cycling, and recovered to a reversible capacity of 480 mAh/g at 0.05C. We performed further studies using galvanostatic intermittent titration (GITT) technique which showed the diffusion coefficient to be 10-9 to 10-12 cm2/sec. Nyquist plots were obtained using electrochemical impedance spectroscopy (EIS) at every 5%SOC. 95x64 mm pouch cells (2Ah) with the silicon alloy coupled with a high capacity NMC cathode had impressive long term cycling, over 500 cycles, at a high c-rate (1C/1C), and stable c-rate performance at 10C. The cells were disassembled after cycling to study the SEI formation, electrode expansion, and coating stability. Physical measurement of electrodes and SEM analysis of active materials showed that even after long term cycling, the coating was intact without minor cracks or paste delamination.