Rechargeable Batteries Based On P-Type Polymer Cathodes And Novel Electrolytes

Energy and environmental issues are the two major challenges for human beings.The development of clean and efficient energy storage technology is very urgent for the sustainable development of society.Among various energy storage technologies,lithium-ion batteries（LIBs）have the best overall performance,and have been achieved large-scale applications in consumer electronics devices,electric vehicles,and energy storage power station.As the increasing demands for the batteries with high energy density,power density,long-liftime,high-safety and low-cost,and the traditional inorganic cathode materials have faced with the shortage of Li,Co,and Ni resourses and environmental pollution,many different battery technologies are drawing increasing attention.Organic electrode materials have extensive application prospects in various rechargeable batteries because of their sustainability,structural diversity and ajustability.Among various organic electrode materials,p-type polymer electrode is considered as the promising cathode because of their high redox reversibility,fast reaction kinetics,and relatively higher voltage compared to n-type materials,which can match with various anode materials and electrolytes to constcuct dual-ion batteries（DIBs）.However,these materials always suffer from the low capacity utilization due to the structural instability at high voltage,as well as the limited electrochemical stability window of the electrolyte.Moreover,a deep understanding of the redox mechanisms might be worth further investigation.This paper is focused on the p-type polymer cathodes,on the one hand,improving the theoretical capcaity through the structure design and synthesis optimization,on the other hand,enhanceing the electrochemial reactivity through matching with the novel electrolytes.The main works and results are details as follows:1.A high-energy Li–polyviologen dual-ion battery based on chloride-inserted polyviologen cathode and LiCl/DMSO Electrolyte.P-type polymer cathodes typically display relativily high redox potential.However,their theoretical specific capacity is usually low and cannot be fully utilized due to the limitation of charging cut-off voltage.In addition,the anion comsuption from the electrolyte during the charge–discharge process of p-type polymer cathode will reduce the practical energy density.Among all the possible anions,Cl^-is the one with the smallest size and lowest molecular weight（except F^-）.To improve the energy density of DIBs,we propose employing Cl^–instead of conventional anions such as ClO₄^–,PF₆^–,and TFSI^–.Firstly,we have successfully synthesized three types of oxidized polyviologens doped with different anions,namely PBV-Br₂,PBV-Cl₂,and PBV-（PF₆）₂,and we confirmed that PBV-Cl₂ has the highest electrochemical potential.Secondly,we developed a novel and low-cost LiCl/DMSO（dimethyl sulfoxide）solution as electrochemically favorable electrolyte with a high ion conductivity of 5.6m S cm^–1 and electrochemial window（3.1 V vs.Li⁺/Li）that can meet the requirements of PBV-Cl₂ cathode.In addition,the working voltage of Li–PBV-Cl₂ battery was significantly improved with the greatly lowered Li⁺/Lipotential（by 0.5 V）in DMSO compared to that in conventional ester solvents.We further explored the electrochemicl performance and redox mechanisms of Li//1 M LiCl/DMSO//PBV-Cl₂ battery.The results show that PBV-Cl₂cathode exhibits a reverisble capacity of 183 m Ah g^–1 and energy density of 470 Wh kg^–1（based on the weight of PBV-Cl₂）,which is the superior to other reported p-type polymer cathodes under the same calculation method.After adding 2 wt%fluoroethylene carbonate（FEC）additive in the electrolyte,the compatibility between 1 M LiCl/DMSO electrolyte and Lianode was greatly improved thus significantly enhanced the cycling stability（88%after 300 cycles）and rate performance(75%at 5000 m A g^–1).The concepts of polyviologen p-type polymer cathode and LiCl-based electrolyte provide significant insights for the development of high-energy,low-cost,and sustainable DIBs.2.A nonaqueous Zn–polyaniline battery toward low temperature application.As a typical p-type polymer cathode,polyaniline（PAni）was widely studied in aqueous Zn-ion batteries in recent years.However,it is difficult for PAni cathode to simultaneously maintain high reversible capacity and good cycling performance in aqueous electrolytes due to the deprotonation of the polymer in electrolytes with low acidity,besides that,the capacity release was limited by the voltage window of water.In this work,we employed PAni to nonaqueous electrolytes to enhance the electrochemical performance of Zn–PAni battery.Fistly,we synthesized half-oxidized and dedoping PAni（emeraldine base,EB）,which has a higher theoretical capacity than typically studied doping PAni（emeraldine salt,ES）.Secondly,we compared the effects of 1 M Zn（OTf）₂ electrolyte based on H₂O,DMF,and AN（acetonitrile）solvents on their electrochemical performance and behavior.The results show that PAni cathde exhibits the best electrochemical performance in 1 M Zn（OTf）₂/AN electrolyte with a high reverisible capacity of 236 m Ah g^-1at 50 m A g^-1（corresponds to 84%of theoretical capacity）,a capcity retention of 73%at a high current density of 5000 m A g^-1and a capacity retention of 83%after 5000 cycles at 1000 m A g^-1.The overall performance was significantly better than the other reported Zn–PAni batteries.The redox mechanism of PAni cathode in 1 M Zn（OTf）₂/AN electrolyte was based mainly on a n-type reaction with ZnOTf⁺as carrier and in part on a p-type reaction with OTf^-as carrier,which also renewed the p-type mechanism cognition to PAni.Further low temperature performance investigation showed this battery system achieved a reversible capacity of 121 m Ah g^-1at-40℃,correspongding to 60%of the capcity at25℃,which is another advantage compared with aqueous Zn–PAni battery.This research gives an important insights for the development of high-energy,long-cycle,and superior low temperature performance Zn–organic battery.3.Nonaqueous Zn–polyaniline battery with flat voltage plateau.The redox potential of the p-type conducting polymers always depends on the doping level,thus exhibiting a sloping voltage curve.,which require additional transfermers to obtain an stable output voltage.On the basis of previous works,we extend the research of nonaquous Zn–PAni battery to 1 M Zn（TFSI）₂ electrolytes based on AN,DMF,and DMSO solvents.The results showed that the Zn–PAni battery using Zn（TFSI）₂/AN electrolyte exhibited two sloping voltage plateau at 1.1 V and 0.7 V while a surprising flat voltage plateau at 1.0 V when using Zn（TFSI）₂/DMF and Zn（TFSI）₂/DMSO electrolytes.The redox mechanisms exploration confirmed that the difference of electrochemical behaviors was derived from the solvated cation structures and their interaction with PAni main chain.For n-type reaction of PAni cahode,the cations is ZnTFSI⁺in AN-based electrolyte and Zn²⁺in DMF and DMSO-based electrolytes.The strong interaction of Zn²⁺with PAni chain results in the phase transition mechanism between PAni and PAni-Zn.In addition,using cheaper ZnCl₂ instead of expensive Zn（TFSI）₂has no obvious effects on the electrochemical behavior but better performance was obtained.Especially,the Zn–PAni battery using 2.5 M ZnCl₂/DMSO electrolyte exhibited a high reversible capacity of 212 m Ah g^–1at 50 m A g^–1 and a capacity retention of 95%after 500 cycles at 200 m A g^–1,showing an exellent overall electrochemical performance.This research not only developed a novel and low-cost nonaueous electrolyte for Zn–PAni battery but also provided a new insight into the redox mechanism of PAni.