Cu/Fe Coordination And Its Derivates Prepared By Electrodeposition And Electrochemical Performances

Lithium-ion batteries?LIBs?have become one of the most widely used products in today's society,having been an integral part of the new energy field.Transition metal oxides,as one of the most promising anode electrode materials,have the advantages of higher theoretical specific capacity?600¹200mAh/g?,richer resource,lower prices,and simple preparing processes.But transition metal oxide anode electrode materials have the disadvantages of short conductivity and severe volume expansion,lead to rapid capacity decay and poor cycle performance.using carbon-based material as the conductive network can improve the electrochemical performance of the transition metal oxide anode,but it is prone to the disadvantages of larger particles,poor dispersion,and complicated preparation process.In view of this,in this paper,the electrodeposition method was used to prepare Cu/Fe carboxylic complexes in situ,and nanostructured metal oxide/carbon materials were formed after heat treatment,and their electrochemical performance as anode electrode materials were studied respectively.The details are as follows:?1?Applying the anode deposition method,the copper succinate film?thickness¹0?m?,copper adipate?thickness⁶?m?,copper suberate film?thickness¹0?m?and copper sebacate film?thickness¹0?m?can be formed on the surface of the anode copper foil in situ after 3 hours.It can be observed by SEM that the copper succinate film is composed of nanofibers with the length of⁸0?m and the width of⁵00 nm;the copper adipic acid film is composed of book-like nanosheets with the length and width of about 5-8?m;the copper suberate film is composed of micro-flowered nanosheets with size of 20-30?m;the copper sebacate film is composed of micrometer flowers with a diameter of¹5?m.According to XRD and TG tests,the decomposition temperature of copper carboxylate decreases with the increase of carbon chain length;after heat treatment,to form nanoscale Cu₂O/C composite material at last.It can be seen from SEM and TEM that after heat treatment of copper carboxylate,the copper succinate nanofibers are bent,and irregular Cu₂O particles with the size of about 200nm are evenly embedded in the nanofibers.The lamellar structure of copper adipate,the nanosheets and nanorods serving as petals in copper suberic acid and copper sebacate become the loose network structure,and Cu₂O particles of 50-100 nm are evenly dispersed in the carbon network.Electrochemical performance test results show that:at0.2C current,the Cu₂O/C-4@550 electrode performed 509.9mAh/g at first cycle,reach779.2 mAh/g after 150 cycle,the Coulomb efficiency reach to 98%;the Cu₂O/C-6@550electrode reached 391mAh/g at first time,maintain the capacity of 328.5 mAh/g after150 times,capacity retention rate reached 84%;the Cu₂O/C-8@550 electrodes show the capacity 479.9mAh/g at first time and 392.8 mAh/g after 150,capacity retention rate reached 81.8%;Cu₂O/C-10@550 reached 524.3mAh/g at first cycle and maintain the capacity of 393.3 mAh/g after 150 cycles,capacity retention rate reached 75%.At a current of 0.2C,the first capacity of the Cu₂O/C-4@400 electrode is 358.6mAh/g,and the capacity after 250 cycles is 648.5mAh/g;the first capacity of the Cu₂O/C-6@400electrode can reach 452.5mAh/g,the capacity drops to 346.5mAh/g after 150 times,and the capacity retention rate is 76.6%;the first discharge capacity of Cu₂O/C-8@400electrode is 462.7mAh/g,and the capacity remains at 367.6mAh/g after 150 cycles.The retention rate reached 79.4%;the first discharge capacity of the Cu₂O/C-10@400electrode reached 465mAh/g,and after 150 cycles,the capacity reached 372.5mAh/g,and the capacity retention rate was 80.1%.The reasons for the difference in performance are as follows:the four carboxylic acids have different morphologies,and the specific surface area of the material has a large difference,which affects its electrochemical performance.For example,the nanorod structure is activated during the cycle,and the capacity rises;Although the loose network-like lamellar structure can improve the material's own conductivity,but its Cu₂O particles are simply dispersed on its surface,it is difficult to achieve capacity increase;when subjected to high temperature treatment,the crystallinity of the material improves and its surface roughness increases,increased transmission paths for electrons and ions.As can be seen from the Nyquist diagram,Cu₂O/C composites formed by in-situ preparation of copper carboxylate compounds by electrodeposition and after heat treatment,without binders and conductive agents,with the combination of Cu₂O,C,and copper foil,it can effectively reduce the charge transfer resistance and speed up the electron transport.As the carbon content of the material increases,there is a big difference in conductivity.?2?Adopt cathode deposition method,a three-dimensional lamellar iron terephthalate film with a thickness of 2?m was formed in situ on the surface of the cathode copper foil after 3h.It can be known from the SEM test that the three-dimensional lamellar film is formed by stacking nanosheets with a size of 2?m and a thickness of 10-20 nm.The electrochemical performance showed that the capacity was407.6mAh/g for the first time at 0.2C current,and after 150 cycles,its capacity increased to 936.4mAh/g.The capacity at the current of 0.5C was 390.3mAh/g for the first time,and after 250 cycles,its capacity increased to 914.3mAh/g.The reason for the improved performance is mainly due to the increased number of cycles,the material is fully activated,and the reaction of Li⁺intercalating with terephthalate is more thorough.?3?Adopt cathode deposition method,formed in situ on the surface of the cathode copper foil as a three-dimensional sheet-shaped iron terephthalate with a thickness of 2?m and a micro-flower-like iron 2,6-pyridinedicarboxylate film with a thickness of 10?m on the surface of the cathode copper foil after 3h.After heat treatment in N₂atmosphere,Fe₃O₄/C and Fe₃O₄/C-N composite materials can be obtained respectively.Electrochemical test results show that at 0.2C current,the first discharge of the Fe₃O₄/C-N electrode is 1128.8mAh/g,the capacity of 150 cycles is maintained at850.3mAh/g,and the capacity retention rate reaches 75.3%;the first discharge capacity of the Fe₃O₄/C electrode is 933.9mAh/g,maintained at 814.9mAh/g after 150 times.The reason for the good performance is mainly due to the preparation process of in-situ growth,which increases the binding force between the active material and the current collector,and Fe₃O₄,C,N form a unique conductive network,which can effectively avoid particle agglomeration and slow down the volume expansion.The destruction of the electrode and the rough surface can strengthen the material's wettability to the electrolyte,increase the transmission channels of ions and electrons,and accelerate the reaction rate.