Research On Structural Design And Doping Modification Of Li₄Ti₅O₁₂ Anode Materials

Spinel lithium titanate (Li4Ti5O12) has attracted considerable attentions as anode materials for lithium ion batteries owing to its intrinsic characteristics, such as structural stability and long cyclic life. Furthermore, Li4Ti5O12possesses higher charge/discharge plateaus, which circumvents the formation of SEI layers and suppresses lithium dendrite deposition on the surface of electrodes. Moreover, the Li4Ti5O12shows excellent cycle life due to the negligible volume change, therefore it has been considered as a zero-strain material. However, Li4Ti5O12suffers from poor electronic conductivity (<10-13S cm-1), which seriously retard its high power applications. This research through the introduction of different structure carbon materials with high conductivity, forming three-dimensional conductive network Li4Ti5O12/carbon nanocomposite and doping Br" in oxygen to improve their electrochemical performance.The Li4Ti5O12/carbon nanocomposites were designed via a facile liquid deposition method in the presence of four different carbons (Super-P, CNTs, ordered porous carbon, graphene). The effects of different carbons structure on the structures and electrochemical properties of Li4Ti5O12were studied. It is found that carbons materials can be used as a nano-reactor, which is beneficial to Li4Ti5O12formed nanostructures, and as a block, restrains the agglomeration of nanoparticles effectively. The Li4Ti5O12nanoparticles disperse uniformity in the carbon matrix, forming three-dimensional conductive network Li4Ti5O12/carbon nanocomposite, and these structures effectively improve rate performance. The Li4Ti5O12/graphene composite possess excellent electrochemical properties with high specific capacities of154mAh g-1(IOC) and149mAh g-1(20C), much higher than the results found in other literatures. The Li4Ti5O12/CNTs nanocomposite exhibits high-rate capacity of112mAh g-1at20C. Furthermore, the nanocomposite exhibit good cycle stability, retaining over98%of its initial capacity after100cycles at5C.In order to further improve rate performance of Li4Ti5O12/CNTs composite, C@Li4Ti5O12/CNTs composite was prepared via a simple liquid phase deposition with stearic acid as the surfactant and carbon source. The effects of carbons coated content on the structures and electrochemical properties of composites were studied. When the amount of carbon coated was0.3%, the obtained Li4Ti5O12nanoparticles homogeneously dispersed in CNTs matrix, and further coated with the carbon layers pyrolyzed from stearic acid. The C@Li4Ti5O12/CNTs composites display a high discharge capacity of145mAh g-1at20C, which is better than that of the Li4Ti5O12/CNTs composites.Br-doped Li4Ti5O12nanomaterials in the form of Li4Ti5BrxO12-x (0<x≤0.4) were synthesized via a simple liquid deposition reaction. The effects of Br doping on the structures and electrochemical properties of Li4Ti5O12nanomaterials were studied. It is found that Br atoms can enter the lattice structure and enlarge the lattice parameters. Although Br doping has not changed the phase composition, obvious effects on the particles morphology have been observed. The as-synthesized Li4Ti5O11.8Br0.2electrode presents much higher discharge capacity and better cycle stability than that of the other electrodes. The greatly enhanced electrochemical performance of Li4Ti5O11.8Br0.2may be attributed to the improved dispersion of nanoparticles and increased electrical conductivity.