| The portable electronics with light weight and high flexibility attract significant attentions recently. One of the most important issues for such electronics is to develop the high performance lithium-ion batteries with good flexibility because the traditional lithium-ion batteries are heavy and not bendable. Obviously, to prepare the flexible lithium-ion batteries, all parts of the batteries should be bendable and the flexible electrode is critically important. Currently, the fabrication of flexible electrode materials suffers mainly two problems. On the one hand, material preparation efficiency is still too low. On the other hand, the electrochemical performance of the battery has not yet reached the level of conventional lithium-ion batteries. In this work, we have combined the electrospinning technology and the calcinations process to fabricate the electrode materials with high flexibility. The prepared electrode materials exhibit not only high fabrication efficiency and superior electrochemical performance, but also very good flexible bending performance. The main contents are as follows: I. Preparation of MoO2/C composite nanofibers for anode materials and its electrochemical performanceCombining electrospinning technology with high-pressure high-temperature calcination process, we have succeeded in the preparation of a flexible MoO2/C composite nanofibers anode material. In the material:1) The carbon matrix provides perfect conductive network, which improves the transmission efficiency of electrons; 2) MoO2 nano-particles disperse homogeneously in the carbon matrix, which promotes the transmission efficiency of the electron/ion, leads to a change of the lithium storage mechanism of MoO2 shifting to conversion reaction mechanism, and effectively improves the specific capacity of the battery; 3) Nanofiber network can help the battery to maintain a stable electrode material structure and improve the cycle stability when the MoO2 appears the large volume change in charging and discharging process. Moreover, we have also studied the formation mechanism of such nanostructures the first time. In addition, the integration of the design ideas of the anode material, without any binder and conductive agent, effectively improves the content of active substances. II. Preparation of MWCNTs@MoO2/C composite nanofibers anode materials and its electrochemical performanceTo further enhance the flexibility and electrochemical properties of the anode material, we introduced MWCNTs into the composite system and prepared a flexible MWCNTs@MoO2/C composite nanofibers anode material through the electrospinning technology and high-temperature calcination process. The prepared materials show novel ―nanocable‖ structure in which multi-walled carbon nanotubes serve as the core and MoO2/C composite shell acts as a cable jacket. Multi-walled carbon nanotubes with its high electrical conductivity and excellent mechanical properties of flexibility, not only improves the conductivity of the electrode material, but also enhances the flexible properties of the material and improves the rate of diffusion of lithium ions in the electrode material. In the premise of ensuring the flexibility, by controlling the calcination process conditions, we get more loading of active substances MoO2 in the anode material, and further improve the battery specific capacity. Particularly, when the mass percent of MWCNTs is 4%, the specific capacity of the battery still has 832.2mAh/g after 30 charge-discharge cycles at a current density of 50mA/g. III. Preparation of Graphene/MoO2/C compositesAs a new nano-carbon material, graphene possesses high electron mobility and excellent mechanical properties. Through eletrospinning technology, we introduced graphene oxide into spun fibers, and obtained a material containing graphene, MoO2, and carbon by controlling the conditions of the calcination process in a reducing atmosphere. In the process, graphene oxide was transmitted into graphene partly. In addition, we preliminarily studied the structure and the electrochemical performance of the material. However, due to the poor thermal stability of graphene oxide at high temperature, substantial degradation of graphene oxide occurs inevitably. This results in the decreasing of the grapheme content low in the composite material. Thus, no good performance has been achieved for the preparaed materials so far. The further investigation is necessary to optimize the structure and properties of the prepared composites for the anode materials. |
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