| Lithium ions batteries(LIBs)have become one of the most promising energy storage devices because of their high energy density,long cycle life,fast response,and environmental protection.The development of modern science and technology has put forward higher requirements for LIBs.As an important part of the battery,the anode material has a great influence on improving the comprehensive performance of LIBs.Commercial graphite anodes are difficult to meet the rapidly developing energy storage needs due to low energy density and safety issues.Titanium-based materials usually have high safety and cycle performance,but there are problems with low energy density and low electronic conductivity.In this thesis,various titanium-based compounds including layered TiO2,LiTi2(PO4)3(LTP),reduced graphene oxide/NaTi2(PO4)3(rGO/NTP)were prepared by using MXene as a precursor to improve the electron and ion transport efficiency.The energy storage properties and related structure-activity relationships based on these compounds were further studied.The specific research contents are as follows:(1)2D TiO2 nanosheets were prepared as anode materials for LIBs with Ti3C2Tx as sacrificial template.Studies have shown that highly crystalline anatase TiO2 nanoparticles are tightly connected to form 2D nanosheets.Nitrogen adsorption/desorption isotherms indicated that the specific surface area(SSA)of the prepared TiO2 nanosheets reached 17.96 m2·g-1,and the large SSA provided more active sites for the diffusion of Li+.When it was used as the anode for LIBs,the initial discharge specific capacity is as high as 610.3 mAh·g-1 at the current density of 0.1 A·g-1,and the initial coulombic efficiency(ICE)can reach 53.7%.After 100 cycles,the capacity remains at 246.6 mAh·g-1.The morphological characterization after cycling showed that the structure of TiO2 nanosheets remains intact,indicating that it has high cyclic structural stability.(2)Based on the 2D TiO2 prepared in the third chapter,LTP was prepared by the rheological phase method as the anode material for LIBs.The result of the pore size distribution curve showed that the pore size of LTP was mainly distributed at 3.26 nm,indicating that LTP had abundant mesopores,which was beneficial to increase the contact between electrolyte and electrode,promoting the diffusion of Li+.At a current density of 0.1 A·g-1,the LTP anode exhibits a high initial discharge capacity of 677.7 mAh·g-1,and remains a high capacity of 184 mAh·g-1 after 100 cycles.Furthermore,the discharge specific capacity can still reach 100.1 mAh·g-1 after 700 cycles at a high current density of 1 A·g-1.(3)2D rGO/NTP nanocomposites with enhanced properties were prepared by using Ti3C2Tx as sacrificial template.The novel structure is beneficial to shorten the diffusion path of Li+ and improve the electronic conductivity.The first-principles calculation results showed that the number of electrons near the Fermi level of the rGO/NTP/NTP structure is higher than that of the NTP/NTP structure,so its electronic conductivity is higher.At the same time,the Li+diffusion coefficient of rGO/NTP anode is about 3.68 × 10-9 cm2·s-1,which is much higher than that of NTP(7.18×10-10 cm2·s-1),indicating that the composite structure effectively increases the diffusion rate of Li+.The results of electrochemical performance analysis showed that the discharge specific capacity of the rGO/NTP anode is 392.1 mAh·g1 after 100 cycles at a current density of 0.1 A·9-1,which was nearly double that of the NTP anode.Even if the current density changes from 0.1 A·g-1 to 2 A·g-1,the specific capacity of the rGO/NTP anode can reach 149.2 mAh·g-1.Therefore,the rGO/NTP anode has the excellent rate performance.Besides,after 100 cycles,the rGO/NTP anode still maintains a good layered structure,indicating that it has excellent cycle stability. |
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