Silicon/Carbon Nano-Composite Based Anodes for Advanced Lithium-Ion Batteries

Abstract

In the recent years, rechargeable lithium-ion batteries have gained in importance for electronic devices and electric vehicles. Thus, research and development focuses on improving energy and power densities as well as durability of lithium-ion batteries. Especially for high energy and power densities, the electrode materials must possess high specific storage capacities and coulometric efficiencies. However, state-of-the-art anode and cathode electrode materials, e.g. graphite and LiFePO4 exhibit high coulometric efficiencies but rather low theoretical storage capacities (372 and 170 mAh/g, respectively). In the last decade silicon has become a promising anode material due to its high theoretical specific capacity of 3579 mAh/g at ambient temperature. However, this high specific storage capacity owing to host up to 3.75 lithium atoms per silicon atom leads to extreme volume expansion up to 280 % during lithiation, which results in pulverization and delamination of the electrode material after few cycles. Various approaches have been conducted to overcome these issues e.g. by using nano-sized active material or carbon coated silicon composite material. In addition to the materials science the electrode structure is of particular importance for the electrochemical performance. Electrode composition, binding mechanism due to the use of suitable binder polymers or particle size distribution of the active material are some exemplary parameters to stabilize the electrode structure and to handle such high mechanical stress during lithiation/delithiation. Here we present electrochemical investigations of high capacity and high efficiency graphene coated silicon nanocomposite based electrodes prepared by using a wet chemical doctor blade manufacturing process. This active material provides a capacity of >2000 mAh/g with efficiencies >99% over more than 500 cycles. Investigations focus on influence of the stability of the electrode structure by using impedance spectroscopy, scanning electron microscopy, confocal microscopy and estimation of the coating adhesion strength. Cyclic voltammetry and galvanostatic cycling will show the applicability of improved Si/C composite based electrodes compared to conventional graphite based electrodes for lithium-ion batteries both in half cells as well as full cells in combination with commercially available cathode material.