In order to have a deeper understanding of the reaction mechanism of Li-air batteries, understand the reaction process, and improve the capacity and service life of batteries, it is necessary to comprehensively use a variety of modern characterization techniques to comprehensively characterize Li-air batteries. At present, the main methods to comprehensively characterize the positive and negative electrodes of lithium-air batteries include electrochemical voltammetry, impedance technology, Fourier transform infrared spectroscopy, X-ray electron spectroscopy, X-ray diffraction spectroscopy, Raman and surface-enhanced Raman spectroscopy, differential electrochemical mass spectrometry, scanning electron microscopy, high-resolution transmission electron microscopy, microfocus synchrotron X-ray diffraction techniques, atomic force microscopy, scanning probe microscopy, etc. The structural, compositional and morphological changes of electrode materials and SEI films can be systematically studied by applying the above techniques. Using various advanced in situ techniques, more precise and reliable scientific information can be obtained from the perspectives of spatial resolution, temporal resolution and energy resolution. Here is the website that recommends lithium-ion battery knowledges for you – tycorun.com
The classical electrochemical voltammetry technique can give the chemical information, kinetic information and thermodynamic information of the electrode reaction. For example, study the thermodynamic potential of the electrode reaction, determine whether there is a chemical reaction, whether there is an electron transfer step, initially identify the reaction mechanism, and give the reaction rate of each step of the electrode reaction within the range of voltammetry measurement capabilities, etc. However, traditional electrochemical voltammetry also has certain limitations, and other characterization methods must be combined to further confirm the specific process of the reaction.
On-site electrochemical Surface-Enhanced Raman Spectroscopy (SERS) technology is a research method produced by the combination of Raman spectroscopy and electrochemical methods. Since the surface-enhanced Raman scattering effect can significantly enhance the Raman signal of the surface species, the Raman scattering signal of the species adsorbed on the metal surface is enhanced by several orders of magnitude, it can avoid the interference of similar substances in the liquid or gas phase, and provide more comprehensive microscopic information of molecular species and electrode surface molecules in the electrochemical process.
Differential Electrochemical Mass Spectrometry (DEMS) technology has very high detection sensitivity and very fast response speed for the reaction gas involved in the electrode reaction, and the detection signal is not directly related to the active surface area of the positive electrode. Differential electrochemical mass spectrometry technology can give the number of electron transfer at any moment in the electrochemical reaction process, and identify whether there are elementary steps and reaction intermediate states in the reaction process. Due to its limitations, the classical electrochemical method can only speculate the electrode reaction mechanism through experimental results.
To this end, the development and use of advanced comprehensive on-site, online, and in-situ testing and characterization techniques can provide strong technical support for in-depth understanding and solving of the basic scientific problems of the lithium-air battery system.
As an environmentally friendly new battery system, the lithium-air battery has brought hope to people with its ultra-high theoretical energy density and has become the development direction of the battery in the future. Successfully solving the problems of battery safety, cycle stability and related material design and preparation, lithium-air batteries will become a major revolution in the history of energy. However, its development is still full of opportunities and challenges. There are many factors that affect the performance of Li-air batteries, mainly because of their special composition, such as air/oxygen relative humidity, oxygen partial pressure, catalyst selection, electrolyte composition and electrode structure. The key reaction of the lithium-air battery system is the oxygen electrode reaction in the positive electrode. The analysis of the oxygen reaction mechanism of the positive electrode has theoretical value and guiding significance for in-depth understanding and solving of the practical application of lithium-air batteries. For this reason, the unreasonable structure of the air cathode material, the low catalytic efficiency of the catalyst, the chemical and electrochemical instability of the electrolyte, and the unclear discharge and charge reaction mechanisms are all scientific problems that plague the development of lithium-air batteries and need to be solved urgently.
At present, many studies in this field are still in their infancy, and future development will mainly focus on the following aspects:
(1) The development of new electrode materials and new processes, the development of micro- and nano-structured air electrodes, and the optimization of reaction transmission paths.
(2) To seek a new electrolyte system with high chemical stability, high dissolved oxygen content, high electrical conductivity, low viscosity and wide electrochemical stability window.
(3) Develop bifunctional nanocatalysts with obvious catalytic effects on both oxygen reduction reaction and oxygen evolution reaction, to reduce the overpotential in the process of charging and discharging, improve the power density, charge-discharge cycle efficiency and battery life of the battery, and at the same time inhibit the occurrence of side reactions of the battery.
(4) Develop a metal lithium anode with chemical and electrochemical stability, oxygen inertness, and high safety, and improve its Coulombic efficiency.
(5) Design and develop advanced testing and characterization techniques to explore electrode reaction mechanisms, etc.
(6) Innovation of battery structure, dual flow, dual compartment, etc., limited control and reduced interference of electrode side reactions.
Therefore, there is still a long way to go on the road to practical application of lithium-air batteries.