Preparation And Properties Of A Self-healing Asymmetrical Capacitor Based On Polyvinyl Alcohol

Asymmetric capacitor is a kind of electrochemical energy storage device,which possesses the characteristics of both electrochemical double layer capacitors and Faraday pseudocapacitors.It has higher energy density than conventional supercapacitors,higher power density and cycle stability than batteries,but it will lose their energy-storage functions and even cause safety issues in the case of violent physical damage or deformation.Here we report a self-healable asymmetric capacitor that can withstand severe mechanical damage,and provide a strategy to design smart asymmetric capacitors with excellent reliability,outstanding safety and easy maintenance,which has potential application in wearable/flexible electronics,intelligent clothes or soft robot,and so on.In this paper,a KNi Fe?CN?₆//AC asymmetric capacitor using KNiFe?CN?₆ as the cathode and activated carbon?AC?as the anode was assembled in 1 mol L^-1KNO₃solution,firstly.Compared with AC symmetric capacitors,the operating voltage range of this capacitor is widened to 0-1.5V.The specific capacitance of KNiFe?CN?₆ and AC electrodes are 337.4 F g^-1and 105.3 F g^-1,respectively.In consequence,the mass ratio of anode to cathode is 3.2:1 in KNiFe?CN?₆//AC.The capacity retention of KNiFe?CN?₆//AC at 5 A g^-1(137.7 F g^-1)is as high as 91.4%compared with the specific capacitance at 0.5 A g^-1(160.2 F g^-1),which showing excellent rate performance.The capacitor has a specific capacitance of 145.5 F g^-1at a current density of 2 A g^-1,and about 95.9%of the capacity is maintained after 2000 cycles,showing excellent cycle performance.Based on the research of KNiFe?CN?₆//AC in 1 mol L^-1KNO₃ solution,we further fabricate a KNiFe?CN?₆//AC self-healing asymmetric capacitor based on dynamic boron ester bonds.The mechanical properties of the capacitor have been basically restored to the initial state at 30 min and can withstand at least 5 times of cut/repair.After self-healing,the microcosmic morphology,mechanical properties and electrical conductivity of the electrolyte and electrode can all recover to the initial state,and the mechanical and electrochemical properties of the capacitor can also be basically repaired.The original capacitor delivers a specific capacitance of 158.8 F g^-1,150.7 F g^-1,142.7 F g^-1,136 F g^-1,130.7 F g^-1and 126 F g^-1at the current density of 0.5,1,2,3,4,and 5 A g^-1,respectively.Furthermore,only a slight decrease arose in capacity after 5 times' healing,which was 4.21%at 5 A g^-1maximally.It still delivered a specific capacitance of 142.7F g^-1at 2.0 A g^-1after 1500 cycles of charge/discharge,showing a capacitance retention rate of 90.3%,and the capacitor after 5th restoration reached 87.9%.In summary,this study demonstrated the fabrication of a self-healable asymmetric capacitor by integrating its electroactive components into a PVA-based network cross-linked by borate ester bonding.Owing to the dynamic nature of the network,the capacitor was able to restore all its broken components autonomously,resulting in the recovery of configuration integrity,mechanical and capacitive properties.The self-healing process was repeatable for at least 5 times at ambient environments without any external stimulus.More interestingly,the healed capacitor also exhibited high specific capacitance,excellent rate capability and good cycling stability.