Preparation And Electrochemical Performance Of Si / Cu / N-C Composite Negative Electrode Materials

Chemical reduction-mechanical alloying(MA) methods were used to synthesize Si/Cu composite anode materials in this paper. Si/Cu materials were modified by PANI which was served as the carbon source. Through experimental, we found that first efficiency and cycle performance on Si/Cu/N-C composite anode materials had been significantly improved. Anode materials, structure, morphology and electrochemical properties were testified by modern testing and analyzing techniques such as X-ray diffraction(XRD), field-emission scanning electron microscopy(FESEM),Transmission electron microscopy(TEM), The results were as follows:1. Si and Cu were applied to synthesize new immiscible Si/Cu composite anode materials through MA method.When the milling time was insufficient, the silicon and copper were not fully mixed. when the milling time taken too long, it will increased the amount of Cu2 O and decreased the initial efficiency and cycle stability. Finally, we obtained 7h was the suitable milling time because of excellent cycle performance.In the content of Si have great influence on capacity of the Si: Cu = a:b( a:b = 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1) anode materials, when the ratio of Si and Cu was 1.5:1. The first discharge capacity was 1018.6 m Ah/g, and after 100 cycles the capacity was 499.2 m Ah/g, showed best cycle performance. The cycling stability was improved by restricting either the upper or lower cutoff voltage, which prevented the anode materials from powdering and shredding after the lithium ions became trapped in the electrode materials.2. PANI was used as a carbon source to ameliorate Si1.5/Cu materials. TEM showed that Si1.5/Cu/(N-C)x composite anode materials were core-shell structure. When the value of x was 0.45,the first discharge capacity was 1147.7 m Ah/g and second discharge capacity was 972.6 m Ah/g, after 100 cycles the capacity was still up 857.9m Ah/g. For this Si1.5/Cu/(N-C)0.45 composite anode materials, the first efficiency was 84.7%, the capacity retention rate was 88.20% after 100 cycles. First efficiency and capacity retention rate was respectively increased by 21.4% and10.82% respectively, which compared to not coated. We suppose that the reason may be due to the formation of vacancies and dangling bonds around the nitrogen sites.