The Modification Of Silicon As Anodic Active Materials For Lithium-ion Batteries

Due to the strong demand for the high specific capacity energy, silicon-based materials have become the darling as anode materials for lithium-ion batteries. But the silicon anode has so many defects, such as poor electrical conductivity, volume effect, the unstable SEI film and so on. Hence, many silicon/carbon composites which have a high specific capacity, a good cycling performance and a high coulomb efficiency as li-ion battery anode materials were prepared successfully by combining doping, nanocrystallization and the composite in this paper. On the one hand, the phosphorus-doped n-type silicon was used for the anode material and the n-Si/C composite material was prepared by carbon-coated. Meanwhile, the preparation process was optimized and the electrochemical properties were analyzed; On the other hand, the three different kinds of silicon/grapheme composites also were prepared and characterized by electrochemical workstation and charge-discharge test. In addition, the intrinsic reaction kinetics of the composite was also discussed preliminarily.1, Reducing the size of silicon particle can improve its cycling stability. P(or B) doping does not change silicon’s structure, but can significantly improve its conductivity and cycling performance. N-type silicon and submicron silicon both are ideal silicon electrode.2, The n-Si/C composite materials were prepared by high temperature solid phase, its reversible discharge capacity was 1101.4 mAhg – 1 after 30 cycles, the efficiency was up to 85.6% in the first cycle. The preparation process was discussed and optimized: the sintering process was 600 ℃ for 1 h, the carbon source is glucose, the ratio of n-Si:C is 1:1; After introducing graphite, both the discharge capacity and cycling performance were greatly improved, and the efficiency was up to 81.1% for the first time; By twice coating, the cycling reversibility and efficiency of the n-Si/C composite were improved, the discharge capacity was 1054.3 mAhg– 1 after 30 cycles; In the production process of electrode, the copper foil is better as the current collector, the very dry temperature was 80 ℃, the heat treatment is also useful.3, The MS @ Si/GNS, nano @ Si/GNS and p- Si/GNS composites which have good cycling performance, high specific capacity, good electrical conductivity were prepared via in-situ recombination and mechanical mixture. The process parameters for MS @ Si/GNS was studied, the various Characterizations indicted that, the SG1 has a higher discharge capacity and coulomb efficiency for the first time,so do with the electrical conductivity; Along with the increase of the graphene, the first discharge capacity became lower, cycling performance became better and the resistance was smaller; The addition of CNT and heat treatment can contribute to the improvement of cycling performance and electrical conductivity for MS @ Si/GNS.4, The SSCV test and EIS test was done, the lithium ion diffusion coefficient was calculated, results indicated that MS @ Si/GNS has a excellent cycling reversibility and high speed lithium ion diffusion; the DLi can reach to 2.9 x 10-12 cm2 s – 1; the resistance just has a small change and the electrode structure kept stability in the cycles.