Controllable Synthesis Of Graphene-based Composite And Application In Aqueous Batteries

With the rapid depletion of fossil fuels and the growing demand for wearable electronic products and electric vehicles,the development of high-performance energy storage devices is of great importance.Nowadays,lithium ion batteries with high energy density have been widely used,but rising cost and safety issues limit their large-scale applications.Recently,much attention has been paid to aqueous energy storage devices.Among these,aqueous zinc/sodium ion batteries not only have high energy density,high power density,long cycle life,but also low cost,abundant resources,and high safety.However,as one of the indicators to measure the performance of the battery,the volumetric energy density is often overlooked.At present,most of the electrode materials reported in the literature have low tap density,leading to low volumetric energy density.Therefore,the development of high-performance electrode materials has become a huge challenge for researchers.This paper mainly focuses on the controllable preparation of graphene-based composite materials in terms of its three-dimensional assembly and structural design.We start from the aspects of electrode density,conductivity,regulating the pore structure and pore size distribution of the material,balancing electrode density and porosity,and electrode wettability.We can obtain the electrode material with a large specific surface area,high porosity,and short ion transmission path.It can greatly improve the space utilization rate and electrochemical reaction rate of the electrode material,leading to improve its energy storage performance in the aqueous system.The specific methods are as follows:?1?In order to improve the density of electrode materials and shorten the diffusion distance of electrolyte ions.We develop a simple and effective method to prepare ultra-dense Ni S₂/r GO composite cathode materials with adjustable density and excellent electrochemical performance.The unique structure of nanoporous Ni S₂ within compact r GO networks could not only facilitate electron transport and ion diffusion,but also strengthen the electrode structure,resulting in reliable electrochemical performance of the constructed Ni-Zn battery.The as-fabricated HD-Ni S₂/r GO//Zn battery is able to yield a remarkable volumetric energy density(18.7 m Wh cm^-3)and gravimetric energy density(357.7 Wh kg^-1)as well as excellent cycling performance?more than 80.5%capacity retention after 2000 cycles?.Furthermore,this Ni-Zn battery also exhibits outstanding impact-proof properties,showing its great potential as stable energy storage device under impact environment.This proposed strategy can also be extended to boost the electrochemical properties of other metal sulfides electrodes for compact energy storage.?2?In order to further improve the conductivity of the electrode material,we coat Mn O₂and r GO by polyaniline?PANI?to prepare a three-dimensional dense assembly to achieve a high-performance zinc ion battery.On the one hand,the dense skeleton composed of interconnecting graphene nanosheets can effectively improve the conductivity and diffusion rate.On the other hand,Mn O₂ tightly coated by r GO and PANI can inhibit the dissolution of Mn to improve rate performance and cycling stability of the Mn O₂/r GO/PANI electrode materials for ZIBs.Benefiting from the compositional and structural features,the performance of the aqueous Mn O₂/r GO/PANI//Zn battery was obviously enhanced to 241.1 m Ah g^-1 at 0.1 A g^-1,which is much higher than those of the control samples(178.8 m Ah g^-1for Mn O₂/r GO,and 177.4 m Ah g^-1 for Mn O₂).More importantly,the aqueous Mn O₂/r GO/PANI//Zn battery demonstrated a highly reversible performance even after 600 cycles with 82.7%capacity retention.Furthermore,galvanostatic intermittent titration technique?GITT?measurements were conducted to illustrate reaction kinetics for the fabricated electrodes.?3?To balance the electrode density and effective porosity,we use sulfur as an expanding agent to control the microstructure of the dense electrode.This electrode has excellent electrochemical performance and can be used in aqueous sodium ion batteries.The HD Fe S₂/r GO-S₃ electrode with more micro-mesoporous structure is beneficial to the shuttle of ions and electrons,and wettability of the electrode treated with sulfur expander is better.In addition,nanoporous Fe S₂ promotes the rapid diffusion of electrolyte ions and provides abundant active sites for redox reactions.HD Fe S₂/r GO-S₃ electrode has excellent volumetric specific capacity(182.9 m Ah cm^-3),gravimetric specific capacity(86.7 m Ah g^-1)and excellent cycle performance?capacity retention is still 96.5%after 100 cycles?.In addition,we use electrochemical active surface area,electrochemical impedance spectroscopy,constant current intermittent technology?GITT?methods to prove that the HD Fe S₂/r GO-S₃ electrode has a higher active area,faster ion channels,and faster diffusion kinetics.This proposed strategy can also be extended to boost the electrochemical properties of other metal sulfides electrodes for compact energy storage.