Craig Gunnett

Article Summary:
[Full Marks JCB]
High-performance lithium battery anodes using silicon nanowires:

Silicon anodes provide a high energy capacity and long cycle life in rechargeable lithium batteries. However attractive this may be, volume expansion and pulverization regularly occurs and causes capacity limitations. By applying silicon nanowires, higher tensile strength can be achieved and pulverization is minimized while maintaining conduction.

Several other Si materials have been studied as applicable anodes for lithium batteries. Bulk films, nanocomposite anodes, and amorphous thin films all exhibited limitations. The geometry of 1D nanomaterials provides several advantages including the accommodation for large volume increases without pulverization, as well as collective contribution to the current because all wires are directly connected to the metallic collector. Nanowires also provide an efficient transfer pathway because of their 1 D geometry.

The voltage profile generated a 73% coulombic efficiency with an initial capacity of 4277 mAh g^-1 and a discharge capacity of 3124 mAh g^-1. The second charge capacity decreased to 3541 mAh g^-1 and the discharge capacesity increased slightly to a coulombic efficiency of 90%. After 10 subsequent cycles, little fading was observed.

Si nanowires also performed well at high current, at least five times the capacity of graphite anodes was observed. One downfall was the irreversible capacity loss in the first cycle.

The structures of Si nanowires were observed before and after usage. Before they were smooth and exhibited good contact with the metallic collector. After usage they showed lightly textured sides and more than doubled in diameter. Despite these changes, they did not break and remained in good contact with the collector.

After lithiation the nanowires exhibited not only a diameter change, but also an increased length. These changes resulted in a 400% volume change.

Single nanowires were analyzed to show the efficiency of electron transport before and after lithiation. A plot of current vs voltage on an unlithiated wire showed a linear relationship ithe a 25 kOhm resistance. Wires that had experienced one cycle became amorphous but still had linear relationships with an 8 MOhm resistance.

The volume change shown in the nanowires is a result of atomic structure change due to lithiation. The main contributor is the loss of crystalline Si and the formation of amorphous Li_x_Si.

TEM confirmed the presence of two phases of Si materials (crystalline and amorphous). At a voltage of 10 mV all of the Si had changed to amorphous lithiated silicon.

FINAL PROJECT: I would like to investigate the applications of silicon nano-wires in electronics.

Chemical Properties:
Chemical - Naphthalen-2-amine
[Added to cheminfoval sheet to reserve for you JCB]
Specific Gravity
Flash Point
LD 50 Rat Oral
232 (F)
583 (F)
315 (F)
111.5 (C)
111-113 (C)
306 (C)
1.061 (g/ml)

727 mg/kg
111-133 (C)
306 (C)
1.061 (g/ml)
113 (C)
306.1 (C)

727 mg/kg
wolfram alpha
112 (C)
306 (C)
1.061 g/ml
157 (C)
110.2-113 (C)
306 (C)
1.061 g/ml
157 (C)
111-113 (C)
300 (C)
1.05-1.10 g/ml

779 mg/kg
Images for Validation Sheet: