| Phenolic resin is a kind of abundant and cheap polymers and can be used in transportation, construction, military and other industry fields. Phenolic resin-based carbon belongs to hard carbon. Lithium ion batteries (LIBs) have high energy density, long life, environment friendly, no memory effect and so on, and have widely used in IT products, such as mobile phones, MP3and laptop. In order to meet the needs of emerging markets such as electric vehicles, the energy density, power density, energy storage system, service life, economy and security of LIBs, that all should be optimized, modified and improved. whatever, the performance of LIBs is determined by the structure and properties of electrode materials. Servicing the emerging markets and human health and sustainable development, the design and preparation of new electrode materials for LIBs are especially important.Phenolic resin microspheres with good morphology and average size of1.13μm have been prepared from the polymerization of phenol and formaldehyde by a stewing reverse emulsion method using sodium hydroxide and Span-80as the catalyst and surfactant, respectively. The factors that affect the morphology of microspheres were studied. Then, the microspheres were carbonized to get the carbon microspheres. The microspheres or carbon microspheres had been post-treated by different methods, and the obtained carbon microspheres were used as the negative electrode material for LIBs. The morphology, structure and performance of carbon microspheres were investigated by SEM, TG-DSC, TEM, BET, IR, XRD and several electrochemical test techniques.The results showed that (NH4)2S2O8could affect the rate of polymerization, the more used of it, the more microspheres had, but the worse morphology had. The emulsion stability increased with Span-80presence, the more used of Span-80, the less microspheres had. The molar ratio of phenol to formaldehyde had great influence on sphericity of microspheres, when it changes from1:1.5to1:3, the sphericity was transformation from0.823to0.346with58%reducement. The role of NaOH and (NH4)2S2O8had contrary effect in the synthesis of microspheres, When the use of (NH4)2S2O8was0.09g and the molar ratio of catalyst to phenol was0.05, the products have good disperssion and good morphology of microspheres. Lower concentration of raw solution could effectively reduce the diameter of microspheres. When the volume ratio of raw solution to oil was1to14, the morphology was well. If increased or reduced this volume ratio, the emulsion was unstable and could not have good morphology of microspheres.The higher temperature and the longer time of polymerization reaction, the curing extent of microspheres was enchanced. If reaction time was too short, microspheres was not completely cured, so it could not keep the spherical morphology, but if holding long time at lower temperature, it also could not have good morphology, such as the samples had bad morphology at70℃for18h. If reaction temperature was too higher, the polymerization rate was so fast, leading to the serious adherence between microspheres, such as the samples at115℃could cure only for1h but had bad morphology. According to the effects of temperature and time of reaction, the best condition was that100℃for more than10h. Stirring time and ultrasound had important influence on morphology and diameter of microspheres.When the amount of Span-80and (NH4)2S2O8was2g and0.09g, respectively, the molar ratio of phenol to formaldehyde was1to2, the molar ratio of catalyst to phenol was0.05, the volume ratio of raw solution to oil was1to14, with stirring for1h at room, ultraphonic3min and heating for more than10h at100℃, the resulting phenolic resin microspheres had good morphology, uniform grading and with an average size of1.13μm.Microspheres was carbonized at700℃for2h in N2atmosphere and then obtained carbon microspheres.Carbon microsphere electrodes had the capacity of200mAh/g. The carbon microspheres were first oxidized by different concentration of HNO3and then heated at400℃for3.5h in air, the obtained carbon microspheres showed improved electrochemical properties:the initial/reversible capacity was as high as1450.1/921.3mAh/g, and still had478.2mAh/g after50th cycle, compared with the untreated carbon microspheres, rising143.4%/268.8%and135.9%, respectively... |
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