Synthesis And Electrochemical Performance Of LiFePO₄ Modified With Metal Phthalocyanine Bonded Carbon Nanotube As Cathode Material

With the increase in energy demand,there have been some environmental issues.And the requirements of new energy technologies have become more and more urgent.Among them,lithium-ion battery technology is the most representative and the most promising technology in new energy.Lithium iron phosphate?LiFePO₄?material has many advantages in a large number of cathode materials of lithium ion battery.However,there are different ways to improve the shortcomings of LiFePO₄ materials.LiFePO₄ modified materials can improve the electrochemical properties of the material itself,which is conductive to promoting lithium-ion batteries in electric vehicles,hybrid vehicles and other applications.In this paper,two different methods of solvothermal and mechanical milling are used to synthesize LiFePO₄ materials.Modification of Li FePO₄ materials is achieved by adding four different additives,mononuclear amino metal phthalocyanine bonded carbon nanotubes?MPcTa-CNTs?,binuclear amino metal phthalocyanine bonded carbon nanotubes?M₂?PcTa?₂O-CNTs?,mononuclear amino metal phthalocyanine/carbon nanotubes?MPcTa/CNTs?andbinuclearaminometalphthalocyanine/carbonnanotubes?M₂?PcTa?₂O/CNTs?(M=Mn²⁺,Co²⁺,Ni²⁺,Cu²⁺,Zn²⁺).The composite materials are all characterized.And the electrochemical performance of the materials are evaluated by testing the charge/discharge,cyclic voltammetry,impedance,rate performance and cycle performance of the assembled coin cell containing the corresponding material.A series of test results are summarized as follows:?1?The electrochemical performance of Li FePO₄composites synthesized by solvothermal is better than that of mechanical milling.?2?The electrochemical performance of LiFePO₄ composites synthesized by metal phthalocyanine bonded carbon nanotubes as modifier is better than that of metal phthalocyanine/carbon nanotubes whether solvothermal or mechanical milling methods are used.?3?Compared with the LiFePO₄ composites synthesized by two different methods,in general,binuclear metal phthalocyanines as additives have better electrochemical performance than mononuclear metal phthalocyanine.?4?The electrochemical performance of Li FePO₄ materials modified by the metal phthalocyanines with cental metal as manganese is the best in each series.?5?Overall,the Li FePO₄ composites prepared by solvothermal method have better electrochemical performance than those prepared by mechanical milling.Among them,the composites modified with Mn₂?PcTa?₂O-CNTs have the best electrochemical performance,the initial discharge specific capacity is 165.4 mAh g^-1at 0.1 C rate,the coulomb efficiency up to99.2%.Moreover,the capacity retention of the most excellent sample after 50 cycles is 97.2%,which has remarkable electrochemical performance.