![]() ![]() In our previous study, we overcame this problem using LE 34– 38. In general, SiGe requires high temperatures for impurity activation therefore, high σ would not be obtained in low-temperature processes 34, 35. ![]() Although fabricating bulk SiGe requires a complicated process owing to its melting point difference, it is easy to prepare thin films because SiGe alloys are all-proportional solid solutions 31– 33. For example, it has been reported that the Si and Ge alloy alleviates the volumetric change during Li intercalation 21, 27. SiGe alloys are promising materials for anodes because they possess the advantageous properties of Si and Ge, while compensating for the disadvantages of the individual materials 20– 30. Ge anodes, although inferior to Si in theoretical capacity (e.g., 1625 mAh g –1 for Li 4.4Ge), exhibit good rate performance and cycle characteristics owing to their 100 times higher electrical conductivity ( σ), 400 times higher Li + diffusivity than Si, and lower volume expansion than Si 16– 19. ![]() While Si anodes have a considerably high theoretical capacity (e.g., 3580 mAh g –1 for Li 15Si 4), the high-rate capacity and cycle characteristics are limited by their low electrical and ionic conductivities 12– 15. Herein, we demonstrated the anode operation of MLG thin films synthesized by LE 4 however, the capacity was limited to its low theoretical capacity of 372 mAh g –1 3.Īs new anode materials, IV group materials such as Si and Ge, which are well known in the field of semiconductors, are attracting increasing attention because of their high theoretical capacity 9– 11. LE will be suitable for microfabrication of devices because it can synthesize crystalline thin films with controlled thicknesses on arbitrary substrates at low temperatures 7, 8. In LE, an amorphous layer crystallizes through LE between the amorphous layer and metal catalyst layer 5, 6. Although graphite is generally synthesized at high temperatures (> 2000 ☌), we achieved low-temperature synthesis of graphite thin films (i.e., multilayer graphene (MLG)) on plastic films (polyimide: heat resistance of up to 400 ☌) via metal-induced layer exchange (LE) 4. Graphite has been used as an anode material in conventional LIBs with liquid electrolyte 3. All-solid-state batteries have the advantages of high energy and power densities, good capacity retention for thousands of charge/discharge cycles, and high safety 2, in addition to increasing the feasibility of flexible batteries. In recent years, research on all-solid-state batteries has become increasingly important for battery innovation. Conventional Li-ion batteries (LIBs) use a liquid electrolyte, which inhibits flexibility and ease of handling. ![]() To sustain the further development of flexible electronics in the future, thin, lightweight, and flexible batteries are highly desirable 1. These results will pave the way for the next generation of flexible batteries based on SiGe anodes. Thus, we revealed the relationship between SiGe composition and anode characteristics for the SiGe layers formed by LE at low temperatures. In particular, the Si 1− xGe x layers with x ≥ 0.8 showed excellent current rate performance owing to their high electrical conductivity and low volume expansion, maintaining a high capacity (> 500 mAh g –1) even at a high current rate (10 C). Si-rich samples exhibited high initial capacity and low capacity retention, while Ge-rich samples showed contrasting characteristics. While the discharge capacities almost reflected the theoretical values at each x at 0.1 C, the capacity degradation with increasing current rate strongly depended on x. All Si 1− xGe x anodes showed clear charge/discharge operation and high coulombic efficiency (≥ 97%) after 100 cycles. Moreover, the Si 1− xGe x layer synthesized by the same process was adopted as the anode for the lithium-ion battery. The resulting SiGe layers exhibited high electrical conductivity (up to 1200 S cm −1), reflecting the self-organized doping effect of LE. Here, we demonstrate the synthesis of Si 1− xGe x ( x = 0–1) layers on plastic films using Al-induced LE. Metal-induced layer exchange (LE) is a unique technique used for the low-temperature synthesis of SiGe layers on arbitrary substrates. SiGe is a promising anode material for replacing graphite in next generation thin-film batteries owing to its high theoretical charge/discharge capacity. ![]()
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