ABSTRACT
Defect engineering is one of the effective ways to improve the electrochemical property of electrode materials for lithium-ion batteries (LIB). Herein, an organic functional molecule of p-phenylenediamine is embedded into two-dimensional (2D) layered TiO2 as the electrode for LIB. Then, the 2D carbon/TiO2 composites with the tuning defects are prepared by precise control of the polymerization and carbothermal atmospheres. Low valence titanium in metal oxide and nitrogen-doped carbon nanosheets can be obtained in the carbon/TiO2 composite under a carbonization treatment atmosphere of N2/H2 gas, which can not only increase the electronic conductivity of the material but also provide sufficient electrochemical active sites, thus producing an excellent rate capability and long-term cycle stability. The prepared composite can provide a high capacity of 396.0 mAh g-1 at a current density of 0.1 A g-1 with a high capacitive capacity ratio. Moreover, a high specific capacity of 80.0 mAh g-1 with retention rate of 85% remains after 10,000 cycles at 3.0 A g-1 as well as the Coulomb efficiency close to 100%. The good rate-capability and cycle-sustainability of the layered materials are ascribed to the increase of conductivity, the lithium-ion transport channel, and interfacial capacitance due to the multi-defect sites in the layered composite.
ABSTRACT
Interfacial energy storage contributes a new mechanism to the emergence of energy storage devices with not only a high-energy density of batteries but also a high-power density of capacitors. In this study, success was achieved in preparing a highly ordered two-dimensional (2D) carbon/TiO2 (C/TiO2) nanosheet composite using commercially available organic molecules with multifunctional groups and taking advantage of the wedge effects, oxidative polymerization, and carbonization. An experiment was conducted to validate the excellent performance of this 2D composite with respect to interfacial energy storage. The coin cell with 2D C/TiO2 nanosheet composite demonstrates a specific capacity of as high as 510 mAh g-1 and a high specific energy of 390.9 Wh kg-1 at a specific power of 75.9 W kg-1 with a current density of 0.1 A g-1, and it also remains 39.0 Wh kg-1 at a specific power of 8.2 kW kg-1 with a high current density of 12.8 A g-1. The excellent electrochemical performance can be attributed to the superior artificial interface capacitive Li+ storage capability, which would bridge the energy and power density gap between batteries and capacitors. Meanwhile, there are two varieties of carbon derivatives, 2D carbon nanosheet stacks and exfoliated carbon nanosheets, which can be obtained by wet-chemical etching and mechanical peeling. The experimental route is simple from commercially available raw materials, and it could be scalable at a low cost and large scale, which makes it suitable for application in various fields such as energy storage, nanocatalysis, sensors, and so on.
ABSTRACT
Intercalation of carbon nanosheets into two-dimensional (2D) inorganic materials could enhance their properties in terms of mechanics and electrochemistry, but sandwiching these two kinds of materials in an alternating sequence is a great challenge in synthesis. Herein, we report a novel strategy to construct TiO2 nanosheets into 2D pillar-layer architectures by employing benzidine molecular assembly as pillars. Then, 2D carbon/TiO2 nanosheet composite with a periodic interlayer distance of 1.1 nm was obtained following a polymerization and carbonization process. This method not only alleviates the strain arising from the torsion of binding during carbonization but also hinders the structural collapse of TiO2 due to the intercalation of the carbon layer by rational control of annealing conditions. The composite material possesses a large carbon/TiO2 interface, providing abundant active sites for ultrafast pseudocapacitive charge storage, thus displaying a superior high-rate performance with a specific capacity of 67.8 mAh g-1 at a current density of 12.8 A g-1 based on the total electrode and excellent cyclability with 87.4% capacity retention after 3000 cycles.
