Preparation And Electrochemical Properties Of Hydroquinone-formaldehyde Polymer

Lithium-ion batteries have become the most promising electrochemical energy storage devices in today and in the future due to their environmental protection,high quality and high efficiency.The positive electrode material is the most important part of the lithium ion battery,which determines the voltage platform and specific capacity of the battery and affects many other electrochemical properties.Therefore,research and development of environmentally friendly high-performance positive electrode materials have important strategic significance for the development of chemical power sources.As a new engineering plastic,polymer conductive polymer materials have become a research hotspot of electrode materials in recent years.In this paper,hydroquinone and formaldehyde was used as raw material to synthesis hydroquinone-formaldehyde polymers by polycondensation under acidic conditions.The suitable reaction conditions for the polymer with good electrochemical performance were as follows:reaction temperature 90°C,reaction time 8h,the ratio of the amount of formaldehyde/hydroquinone material is 2.5.The structure of the polymer was characterized by IR.The results showed that the polymer molecular chain contained multi-polymer phenolic hydroxyl groups and methylene ether bonds,etc.,which were the target polymer structures.By SEM,when the ratio of formaldehyde/hydroquinone substance is n_f/n_h exceeds 2,the synthesized polymer exhibits a highly porous linear structure with high porosity.Thermal properties of the polymer by thermogravimetric analyzer,studies have shown that with the increase of formaldehyde content,the polymer has better thermal stability,and the polymer quality is reduced by 35%to 65%at 200-800°C.Secondly,the electrochemical properties of the polymer were studied by cyclic voltammetry.The results showed that in the 0.5 mol/L Li₂SO₄ solution,the single-electron reversible oxidation reaction of hydroquinone-formaldehyde polymer occurs at low scanning speed,and the reaction is controlled by diffusion.As the scanning speed increases,the electrochemical reversibility and specific capacitance of the polymer decrease.When the scanning speed is 5 mV/s and the voltage range is 1.7 V,the mass of the polymer The specific capacitance C_spp can reach 203.25 F/g,the equivalent specific capacitance is 95.98 mAh/g.And after 50 scans or 4°C after freeze-drying for 7 d,the peak shape of the cyclic voltammetry curve is identical,which showing good electrochemical reversibility and stability.The polymer was tested for constant current charge and discharge at a current density of0.5 A/g.The results show that at the same current density,the specific capacity of the polymer increases first and then decreases with the increase of formaldehyde content in the polymer.The specific capacity of PHQF4 is as high as 85.11 mAh/g,which is consistent with the results of CV analysis.When the molar ratio of n?formaldehyde?/n?hydroquinone?is greater than or equal to 2.5,the electrodes PHQF4 and PHQF5 have a higher capacity retention rate after 200 cycles,reaching 82%or more,and the cycle stability is better.