Mesoscopic Mass Transfer In All Vanadium Flow Battery Electrode And Its Experiments

All vanadium flow batteries(VRB)is a new type of electrochemical energy storage device with high efficiency.The storage and release of electric energy are realized through the mutual conversion of different valences of vanadium ions in VO2+/VO2+ electric pair of positive electrode and V2+/N3+ electric pair of negative electrode.The VRB has the advantages of long life,high efficiency and environmental protection,and it's an effective way to solve the energy and environmental problems.But the battery has some deficiencies,such as low energy density and high demand of environment.The key to promoting all vanadium flow battery is to improve charge-discharge characteristics and electrolyte stability of battery.In this paper,the performance of VRB was tested and analyzed by the test method.The mass transfer characteristics of VRB were simulated and analyzed by means of mesoscopic simulation.And the basis for improving the overall efficiency of the battery was provided by this thesis.This thesis introduced the development overview,working principle,the study of key materials of all vanadium flow battery,etc.The electrochemical theory of all vanadium flow battery was described to reveal the essence of heat transfer and mass transfer.The battery cell was assembled,and the VRB testing platform was built in this thesis.In this thesis,five kinds of batteries with different electrode compressive rates were obtained by using different thickness electrode frames.The volt-ampere characteristic curve,AC impedance characteristic curve and charge/discharge characteristic curve of different compression ratio were tested by flow cell test device.The coulombic efficiency,voltage efficiency and energy efficiency of the VRB were calculated to analyze the effect of electrode compressibility on mass transfer performance of all-vanadium flow battery.The study found that when the compression rate is 60 percent,the battery performance is the best.The mesoscale simulation method was used to analyze the mass transfer characteristics in all vanadium flow battery electrodes.The mesocite module of Materials Studio software was used to build mesoscopic model for the positive and negative electrodes of the battery.Based on the Martini force field,the coarse-grained molecular dynamics simulation method was used to simulate the mass transfer characteristics of each particle in the battery electrolyte.The influence of temperature,carbon nanotube length,and carbon nanotube concentration on the distribution and diffusion of particles were investigated.The results showed that the diffusion coefficient increases with the increase of temperature,but decreases with the increase of carbon nanotubes length.As the increasing of concentration of carbon nanotubes,the diffusion coefficient in the negative electrode decreases,but the diffusion coefficient in the positive electrode increases.By controlling the temperature,the carbon nanotubes length and the concentration of carbon nanotubes,diffusion rate can be optimized,so as to reduce the influences of concentration polarization caused by mass transfer and improve the whole performance of the all vanadium flow battery.