In situ magnesiothermic reduction synthesis of a Ge@C composite for high-performance lithium-ion batterie anodes

Abstract

Metallothermic, especially magnesiothermic, solid-state reactions have been widely applied to synthesize various materials. However, further investigations regarding the use of this method for composite syntheses are needed because of the high reactivity of magnesium. Herein, we report an in situ magnesiothermic reduction to synthesize a composite of Ge@C as an anode material for lithium-ion batteries. The obtained electrode delivered a specific capacity of 454.2 mAh·g^-1 after 200 cycles at a specific current of 1000 mA·g^-1. The stable electrochemical performance and good rate performance of the electrode (432.3 mAh·g^-1 at a specific current of 5000 mA·g^-1) are attributed to the enhancement in distribution and chemical contact between Ge nanoparticles and the biomass-based carbon matrix. A comparison with other synthesis routes has been conducted to demonstrate the effectiveness of contact formation during in situ synthesis.

Keywords: Ge anode; in situ synthesis; lithium-ion batteries; magnesiothermic reduction.

Figure 1

(a) XRD patterns, (b) FTIR spectra, and (c) Raman spectra of pure Ge, Ge/C-iM750, Ge/C-HT180, Ge/C-SS750, and BC-800 (see Experimental section for sample denominations).

Figure 2

SEM images of (a) Ge and (b) Ge/C-iM750; TEM images of (c) Ge, (d) Ge/C-iM750, (e) Ge/C-HT180, and (f) Ge/C-SS750.

Figure 3

CV measurements of (a) pure Ge, (b) Ge/C-iM750, (c) Ge/C-HT180, and (d) Ge/C-SS750 electrodes.

Figure 4

GCPL profiles for the three first cycles of (a) pure Ge, (b) Ge/C-iM750, (c) Ge/C-HT180, and (d) Ge/C-SS750 electrodes.

Figure 5

(a) Cycling, (b) rate performance, (c) Nyquist plots of pure Ge, Ge/C-iM750, Ge/C-HT180, and Ge/C-SS750 electrodes, and (d) fit results of the real part of the impedance (Z′, Ω) as a function of the angular frequency to the power of −0.5 (ω^−0.5, s^−0.5).