The Application Of MOF-derived Metal Oxides And Carbon Composite As Lithium Ion Battery Anodes

Rechargeable lithium ion batteries?LIBs? as a new category of renewable energy source attract more and moe interest of researchers and the increasing attention of the public. With the continuous development of technology, the performance requirement of lithium ion is increasingly high. The electrochemical performance and capacity of LIBs currently hit the plateau. One of reasons is the current commercial anode graphite merely possesses a relatively low theory capacity of 372 mAh/g, which greatly limited the further development of LIBs. Improving the performance of anode materials is an effective way to enhance the electrochemical performance of LIBs. Therefore researchers devote themself to study the new high-performance anode materials to substitute graphite, such as metal oxide/carbon composites. This kind of composite material,which make full use of the advantages of metal oxide and carbon based materials, not only can greatly increase the material's conductivity, also help to promote the theoretical capacity of the material. As a result, the metal oxide and carbon composite material is a kind of ideal lithium battery cathode materialThis paper includes works primarily around the preparation of metal oxides/carbon composites derived from MOFs and application in LIBs anode. Detailed researches include the following four works.1. The preparation of ZnFe₂O₄/C@NCNT composites derived from Zn-Fe-MOFs as both sacrifice template and precursors have uniform size and novel morphology. Various characterizations were employed to detailedly study the composites and the electrochemical performance of the material is tested to be much better than the traditional graphite. The composites delivered an initial discharge of 2192 mAh/g and still reach a high reversible capacity of 844 mAh/g after 100 cycles at a current density of 100 mA/g. The sample also exhibits an exceptional rate capability of 747 mAh/g at a large current density of 1 A/g. The unusual construction in which ZnFe₂O₄ nanoparticles are homogeneously distributed in the entire carbon framework coated by NCNTs may mainly contribute to the good electrochemical performance. Therefore, the resulting porous ZnFe₂O₄/C@NCNT nanocomposites are potentially useful for rechargeable LIBs.2. In order to relieve the volume change during the insertion/extraction, we ulitized hydrothermal method to synthesize the hollow spherical MOFs with uniform size, which effectively alleviate the volume variation so that the composites provides a satisfied specific capacity. The electrochemical performance of spherical ZnO/C composites obtained by pyrolysis was better than that of hollow Zn O without carbon coating and commercial ZnO. Under the same current density of 100 mA/g, the discharge capacity of ZnO/C could approach 750 mAh/g after 100 cycles, while spherical ZnO without carbon coating and commercial ZnO only delivered 289 mAh/g and 248 mAh/g, respectively. It could be concluded that the carbon coating and hollow structure played a very good effect.3. Through the pyloysis of the prepared Fe-MOFs, Fe₃O₄@C composites were synthesized. Scanning electron microscope and transmission electron microscope are used to observe the morphology and electrochemical performance is tested. The unique octahedral Fe₃O₄/C played a very good promotion and enhancement during lithium ion intercalation and deintercalation process. Under the current density of 100 mAh/g, the specific capacity reached 861 mAh/g after 100 laps. When the current density as high as 1 A/g, the specific capacity released 450 mAh/g, which is much higher than the theoretical capacity of commercial graphite.4. The as-prepared spherical ZnO as template was in situ coated by ZIFs to generate the core/shell ZnO@ZIF-8 composites, which effectively enhanced the surface area and alleviate the volume change of ZnO crystals. The results of the test showed that the core/shell ZnO/C displayed good capacity and rate performance. We found that the core/shell ZnO@C composite material has a capacity of 932 mAh/g at current density of 100 mA/g after 100 charge/discharge tests, and its rate capability could approach 670 mAh/g at a current density of 1 A/g. This synthetic method is simple and convenient for mass production.