Silicon-based Materials Used For Lithium Rechargeable Batteries

Since the first battery----Voltaic pile was invented by Volta about200years ago, many types of batteries were developed to meet various requirements. Li-ion batteries first commercialized in the early1990s, and soon become the dominant power source for portable electronics, because of the superior energy density compared with other kinds of batteries. The energy crisis and environmental issue require society to move towards sustainable and clean energy resources, which promotes a wider application of LIB from portable electronics to electric vehicles. However, LIBs still have many issues, because the ever-enlarging market of portable electronic products and the new demands of the transportation market and stationary energy storage impose more and more requirements on the cells, such as higher safety, higher energy/power density.According to these points, and with the consideration of the unique property and mature application of Si material in many fields, we studied the application of Si-based material in electrodes and electrolyte of LIBs and explore the possible strategy for enhancing energy/power density and safety. The thesis focuses on the investigation of new Si-based material, new approach for material property modification and improvement. We hope our work will supply more clues for LIBs' development. The main results are as following:1. Organometallic polymer material for energy storageRecently, organic electrode materials have attracted wide attention for energy storage because of the sustainability concern incurred by the large-scale application of the inorganic intercalation compound in lithium battery. Despite with more flexible backbone, faster reaction kinetics and more adjustable electrochemical property than the conventional transient metal oxide, most organic electrode materials are originally in an oxidative state, which make their application in a "real" Li or Na ion battery is rare. Aiming to this point, we proposed the cathode application of poly(ferrocenyl-methylsilane)(PFS) material. Although there have been numerous research about polyferrocene, a successful application of polyferrocene in energy storage has seldom been mentioned. Ring opening polymerization was used to obtain polyferrocene with high molecular weight. The cathode application of PFS was demonstrated in Li, Na and all-organic battery. Four conclusions can be obtained:?The PFS material well inherited the good reversibility and fast electrochemical response from Ferrocene and possesses very good energy/power density;?The material shows a good application perspective in membrane battery because of its film forming ability;?The working mechanism of PFS material involves the anion participation, which greatly wider the candidates of the applicable electrolyte, and thus a low-cost electrolyte can be expected;?The PFS material presents a self-voltage-regulation function through a "shuttle" reaction at relatively higher voltage, and shows a self-protecting feature when overcharging happens, the "shuttle" reaction voltage is about4.3V.2. Synthesis and characterization of Li2MnSiO/C nanocomposite cathode material for lithium ion batteriesThe multi-electrons reaction endows Li2MnSiO4material with much higher theoretical capacity of333mAh·g-1than many other commercial cathode material, and makes it a hot-spot in the recent years. Li2MnSiO4/C nanocomposite cathode material for lithium ion batteries was obtained through high-temperature sol-gel assisted solid-state method and a further optimization on Si sources, material ratio, calcination temperature and time. The material is able to deliver a reversible capacity of198mAh·g-1in the first cycle, indicating more than one electron exchange in the materials. The highly-dispersed nanocrystalline Li2MnSiO4and the thin carbon film at the surface was the cause of excellent performance of the materials.3. Synthesis of nanosized mesoporous silicon by Magnesium-thermal method used as anode material for lithium ion batterySi anode attracted much attention in the recent years, however, the pulverization during the repeated charge/discharge greatly deteriorated the cycling stability. We proposed a two-step preparation involving magnesium thermal reduction of silica and a following HF etching was proposed to prepare mesoporous nano-silicon. The results show that8%-HF etching post-treatment can produce mesoporous nano-silicon with best performance. The product shows a good cycling stability and rate capability. The mesoporous morphology, SiOx surface layer and ultrafine particle were considered to be the main reason of the improved property of the product. A further property enhancement can be expected with the introduction of conductive component or architecture design of the Si sample.4. Catalyst effect of MnOOH in Si/MnOOH anode materialMnOOH has been widely used as the catalyst in Li-air battery, we tried to its catalyzing effect in the alloying reaction between Si and Li. Nano MnOOH was prepared through a hydrothermal method, and then ball milled with silicon to from Si/MnOOH composite. The as-prepared Si/MnOOH composite demonstrated a high charge capacity of2735mAh·g-1with a Coulombic efficiency of76%at a rate of0.025C (0.1A·g-1) between1.5and0V in the first cycle, much higher than the pristine Si electrode. Additionally, the rate capability of Si/MnOOH composite is much better than Si electrode, which released the483mAh-g-1capacity at20A·g-1.5. Silica-RTIL composite soft solid electrolyte for lithium sulfur batteriesLi/S battery has been widely studied due to its low cost and high energy density, but its application is greatly hindered by the dissolution loss of the active material and thus-resulted capacity loss. Using solid-state electrolyte is an effective strategy to avoid dissolution loss, however, the degraded contact between the solid-state electrolyte and Li brings about poor cycling stability and the relatively lower conductivity reduces the capacity performance of the Li/S battery. Aiming to this, a three-layer battery construction design was proposed. The results show that12nm SiO2filled LiTFSI/BMPTFSI electrolyte has a good ambient conductivity and its quasi-solid state greatly helps to maintain a good contact between Li and electrolyte. In addition, the PEO/LiTFSI layer on the surface of S electrode can avoid the dissolution loss of active material, and the LiTFSI/DOL surface layer on Li anode can supply a protective function by suppressing the decomposition reaction of LiTFSI/BMPTFSI on Li. Compared with many other solid-state Li/S battery, the three-layerd solid-state Li/S battery has a higher ambient capacity and much better cycling stability.