| Spinel Li4Ti5O12(LTO)is considered as one of the most promising anode materials for lithium-ion batteries because it is featured with negligible volume change,superior cycling stability and stable voltage plateau.However,its moderate electronic and ionic conductivities lead to its poor rate performance,which significantly limits its wide use.To solve these detrimental drawbacks,several strategies have been proposed to enhance the electrochemical performance,such as doping with ions,surface coating,and size reduction.Among these strategies,decreasing the Li4Ti5O12 particle size is an efficient way to improve the rate capability because the transportation lengths of both lithium ions and electrons can be significantly shortened.Among the various synthetic methods reported so far,solid-state reaction is particularly attractive because it is practically relevant and scalable.However,it often suffers from a series of problems,such as inhomogeneity,irregular morphology,poorly controlled particle growth,and agglomeration.It is difficult to synthesize small LTO particles using the solid-state reaction method.Based on these methods,this thesis has adopted scalable solid-state reaction in situ synthesis of Li4Ti5O12/carbon nanohybrid to improve the electrochemical performance of Li4Ti5O12.Firstly,a facile scalable synthesis of hierarchical Li4Ti5O12/C nanohybrids with supersmall LTO nanoparticles(ca.17 nm in diameter)homogeneously embedded in the continuous submicrometer-sized carbon matrix is developed.Difunctional methacrylate monomers are used as solvent and carbon source to generate TiO2/C nanohybrid with different carbon content and controllable particle size range of TiO2.The TiO2/C nanohybrid is in situ converted to LTO/C via a solid-state reaction procedure.The carbon matrix effectively inhibits the particle growth of LTO particles during the solid reaction.Comparing to the control sample of the commercial LTO composited with carbon,the cycling stability and rate performance of the LTO/C nanohybrid have been significantly improved.After 1000 cycles at 175 mA/g,the reversible capacities of the LTO/C sample is still maintained at 185 mAh/g with capacity retention of 91%,where the control sample only exhibits a reversible capacity of 135 mAh/g and capacity retention of 78%.The rate performance of the LTO/C nanohybrid also has advantages over control sample,especially at high current densities.Secondly,CO2 activation under high temperature is used to modify the particle size,crystallinity,and carbon matrix content of the LTO/C nanohybrids.4,8,12 h durations of CO2 activation under 800? are used to treat the LTO/C nanohybrids.The same sample was treated under air atmosphere at 800? for 8 hours as the control samples.It is demonstrated that the LTO-A-CO2-12h and LTO-B-CO2-8h samples are featured with good crystallization,no TiO2 impurity phase,small LTO particles(20 nm,28 nm),and suitable carbon matrix content.That results in an improved electrochemical performance.Specifically,the initial charge specific capacities are 139 mAh/g and 148 mAh/g,respectively.After 1000 cycles,the discharge specific capacities are 122 mAh/g and 123 mAh/g with the capacity retention ratios of 90%and 83%respectively.The specific capacities can reach 65 mAh/g and 76 mAh/g respectively even at the highste current density of 8750 mA/g.The electrochemical performance was significantly improved compared with the same sample under air thermal treatment.Therfore,CO2 activation under proper temperature and with suitable duration can optimize the carbon matrix content,the crystallinity and the particle size of LTO,thus improving the rate performance and cyclic performance of LTO/C nanohybrids effectively. |
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