Synthesis and optimization of nanoparticle Ge confined in a carbon matrix for lithium battery anode material

Ge nanoparticles with different particle sizes confined in a carbon matrix were prepared by annealing Ge nanoparticles terminated with butyl groups at 400, 600, and 800 degrees C. X-ray diffraction and transmission electron microscopy results showed that the Ge nanoparticles' size increased from 8 to 100 nm as the annealing temperature of the as-prepared samples increased from 400 to 800 degrees C. Raman spectra confirmed that the parts of the Ge nanoparticles were not covered by the carbon starting at 600 degrees C after annealing for 9 h. Moreover, the graphitization degree of the carbon increases with increasing temperature, and the sample, annealed at 800 degrees C for 3 h, showed the graphitization degree. Electrochemical cycling results revealed that the 10 nm Ge nanoparticles, confined in a carbon matrix obtained after annealing the as-prepared sample at 600 degrees C for 3 h, showed the best charge capacity of 1067 mAh/g with 12% capacity loss after 30 cycles. On the other hand, Ge nanoparticles that had not been covered with the carbon matrix showed a rapid capacity decrease, along with pulverization of Ge nanoparticles to a size of about 5-10 nm after cycling.