Journal of Power Sources 140 (2005) 139–144 Short communication Effect of electrode structure on performance of Si anode in Li-ion batteries: Si particle size and conductive additive Wei-Ren Liu a , Zheng-Zao Guo b , Wen-Shiue Young a , Deng-Tswen Shieh b , Hung-Chun Wu b , Mo-Hua Yang b , Nae-Lih Wu a,∗ a Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan 106, ROC b Materials Research Laboratories, ITRI, Chutung, Hsin-Chu, Taiwan 310, ROC Received 12 May 2004; accepted 21 July 2004 Available online 27 October 2004 Abstract The effects of Si particle size and the amount of carbon-based conductive additive (CA) on the performance of a Si anode in a Li-ion battery are investigated by adopting combinations of two different Si particle sizes (20 and 3 m on average) and CA contents (15 and 30 wt.%), respectively. The CA contains graphitic flakes and nano-sized carbon black. Cyclic voltammetry, charge–discharge tests, scanning electron microscopy and X-ray diffraction establish that the CA content has a profound effect on the cycle-life and irreversible capacity of the Si anode. The former increases, while the latter decreases significantly with increasing CA content. Reducing the particle size of Si, on the other hand, facilitates the alloying/de-alloying kinetics. For instance a cycle-life of over 50 cycles with >96% capacity retention at a charge capacity of 600 mAh per g-Si has been demonstrated by adopting of 30 wt.% CA and 3 m Si particles. © 2004 Elsevier B.V. All rights reserved. Keywords: Lithium ion battery; Silicon; Anode; Cycle-life 1. Introduction As an anode for the Li-ion battery, Si possesses a max- imum Li uptake of Li/Si = 4.4/1.0, which corresponds to a theoretical capacity of 4200 mAh g -1 . This is a sig- nificant improvement over the 372 mAh g -1 provided by graphite. These are, however, shortcomings when using silicon, namely, a dramatic volumetric variation during charge–discharge (i.e., alloy–de-alloy) cycling and the intrin- sic poor conductivity of Si. The former is claimed to cause poor cycle-life, and the latter results in high resistance and low Li uptake. Many attempts have been made recently to solve these problems by coating the surfaces of the Si par- ticles with different conducting materials via different tech- niques [1–12]. For instance, Yoshio et al. [1–3] demonstrated that graphitic coating of Si by thermal vapour deposition en- ∗ Corresponding author. Tel.: +886 2 2362 7158. E-mail address: nlw001@ntu.edu.tw (N.-L. Wu). abled tens cycles to be sustained at charging depths up to 1000 mAh per g-Si. This performance was far superior to un-coated silicon that gave a cycle-life of typically less than a few cycles. Less improvement was achieved by introduc- ing other secondary and/or coating materials, such as metals, oxides and nitrides [9–12]. Ironically, there have been few reports of systematic investigations of the effects due to the ‘original’ constituents, such as the Si particles and conductive additives, that are conventionally employed in constructing a Si anode. As these constitutents are expected to continue to be the major elements of the structure of the Si anode, even when a new secondary/coating material is introduced, optimizing their properties is crucial to the resulting performance. This work examines the effects of the particle size of Si and the amount of conductive additive (CA) on the perfor- mance, particularly cycle-life and irreversible capacity, of the Si anode. In brief, it is found that the CA content has a much more profound effect than the Si particle-size on cycle-life, which increases with increasing CA content. Electrodes with 0378-7753/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2004.07.032