Preparation Of Modified Spinel Li₄Ti₅O₁₂ And Its Application In Lithium Ion Batteries

Spinel Li4Ti5O12 is called as “zero-strain”material and owns excellent cycling performance. It possesses a higher lithium insertion/extraction voltage, which can avoid the lithium dendrite deposition on the surface of the electrode. Moreover, Li4Ti5O12 has been considered as the most promising anode material for high power lithium-ion batteries owning to its good thermal stability, wide range of the raw material and low cost. However, Li4Ti5O12 still lacks commercial application because of its low electrical conductivity and ionic conductivity. In this article, some modified approaches have been utilized to improve the rate capability of Li4Ti5O12, including coating with conductive polymer PEDOT, self-doping of Ti3+ and rational designing the construction of self-supported Li4Ti5O12/reduced graphene oxide electrode. These concrete research contents are as follows:(1) Li4Ti5O12 nanorods were synthesized through hydrothermal method and then PEDOT was deposited on the surface of Li4Ti5O12 nanorods through chemical polymerization. The one dimensional nanostructure can effectively shorten the diffusion pathways for Li+. And the uniform PEDOT coating layer which formed the internal conductive network dramatically increased the conductivity of the material and promoted the transport of lithium ions and electrons between the active material and the electrolyte. Electrochemical tests showed that Li4Ti5O12/PEDOT electrode exhibited excellent electrochemical performance. The reversible capacity can be up to 135.2 m A h g-1 at the high rate of 10 C and the capacity retention reached as high as 99.5% after 100 cycles at the rate of 1 C.(2) Ti3+ self-doped Li4Ti5O12 was prepared by a facile solid state method using Ti2O3 as the raw material and its electrochemical behavior has been discussesed in detail. Test measures such as ESR?XRD and XPS confirmed that part of Ti4+ was replaced by Ti3+ with larger radius, creating a mixed state of Ti3+/Ti4+ and oxygen vacancies which could lead to an increased electrical conductivity and ionic conductivity. In addition, Ti3+ self-dopng didn't destroy the structure of Li4Ti5O12. Consequently, the rate capability was effectively improved while the excellent cycling performance was still maintained. At the rate of 10 C, Ti3+ self-doped Li4Ti5O12 sample exhibited a discharge capacity of 117.6 m A h g-1. After 500 cycles at 10 C, the capacity retention of the sample was 97.0%.(3) Self-supported Li4Ti5O12/reduced graphene oxide electrode material with sandwich structure(S-LTO-RGO) was prepared through vacuum filtration and subsequent heat treatment. Li4Ti5O12 nanofibers dispersed between the graphene sheets forming the three-dimensional network structure, which promoted the transfer of lithium ions and electrons during the charge-discharge process. Moreover, binder, conductive agent and collector were dispansable during the process of battery assembling, which could cause lower resistance. Electrochemical tests showed that the reversible capacity of the sample was 131.7 m A h g-1 at 10 C, and the capacity loss was only 1% after 100 cycles.