Study On Polythiophene And Its Derivatives Modified Lithium Nickel Manganese Oxide Cathode Material For Lithium-ion Batteries

In recent years,with the rapid development of technologies such as new energy vehicles,higher requirements have been placed on the energy density,cycle and rate performance of lithium-ion secondary batteries.The high voltage spinel LiNi_0.5Mn_1.5O₄?LNMO?cathode material has the advantages of high working voltage,high energy density and good power performance,and is one of the most promising cathode material for lithium-ion batteries.However,there are still problems such as poor cycle stability,rate performance and high temperature performance in practical applications.In this paper,the functional modification layer is constructed on the surface of the LNMO cathode electrode material through adding electrolyte additives,surface coating and electrode sheet surface coating to improve the cycle stability,high current rate and high temperature stability of LNMO.The relationship between LNMO structure and electrochemical properties was further studied.By using thiophene as a functional electrolyte additive,the electrochemical polymerization process of thiophene in LNMO lithium-ion batteries and the effect of polythiophene on the structure and electrochemical performance of LNMO were studied.It is proved by means of SEM,TEM and XPS that thiophene forms poly-thiophene on the surface of LNMO by electrochemical polymerization.Thiophene-containing functional electrolytes can effectively improve the cyclic stability and rate performance of LNMO.0.5%thiophene added to the electrolyte formed a relatively complete coating layer on the surface of LNMO,which significantly increased the discharge specific capacities?120 mAh/g and 110 mAh/g?of the cathode materials at 5C and 10C.The composite electrode materials of conductive polymer PEDOT and PEDOT:PSS coated LNMO were synthesized by in-situ polymerization and solution impregnation.The effects of coating methods,types of conductive polymers and electrical conductivity on the structure and electrochemical properties of LNMO were investigated.The results showed that the conductive polymer layer formed on the LNMO surface by in-situ polymerization was more uniform and could more effectively improve the electrochemical performance of the cathode materials.The discharge capacity of 3 wt%PEDOT@LNMO?in-situ polymerization?composite electrode was106.5 mAh/g after 200 cycles,and the capacity retention rate was 86%.The discharge specific capacity of 3 wt%PEDOT:PSS@LNMO?in-situ polymerization?composite electrode was 118 mAh/g after 200 cycles,and the capacity retention rate was 94%.The structure and electrolyte composition of the recycled LNMO electrode material were characterized by ICP,XPS and XRD,and the modification mechanism of the conductive polymer was analyzed.The results show that the improvement of electrochemical performance is due to the surface-coated conductive polymer layer,which can not only improve the conductivity of LNMO,but also effectively inhibit the dissolution of Mn and improve the stability of crystal structure.A new modification technology of LNMO cathode material was proposed.The electrochemical performance of LNMO cathode material at room temperature and high temperature was improved by coating a high conductivity conductive polymer PEDOT:PSS on the surface of LNMO electrode sheet.This study has not been reported.The results show that PEDOT:PSS coated LNMO electrode has higher electronic conductivity.The specific discharge capacity of the modified battery is 98.8 mAh/g after 500 cycles at room temperature,the capacity retention rate is 79.6%,and the specific discharge capacity is above 110 mAh/g at 5 C.The discharge specific capacity is 120 mAh/g and 110.4 respectively after 120 cycles at 50°C and 55°C.When the temperature rises to 60°C,the discharge capacity reaches 78.1mAh/g after 70 cycles.The composition of the electrolyte and the structure of the electrode sheet after cycling were tested by ICP and XRD.The mechanism of improving LNMO properties by PEDOT:PSS coating was discussed.The results show that PEDOT:PSS coating can exist stably at high temperature,effectively inhibit the corrosion of LNMO by electrolyte,and improve the cyclic stability of LNMO crystal structure.