Figure 1. Electrochemical performance of P3-Na0.6O2 layered oxides: (A) Typical charge and discharge curves at 0.1 C and 2.0 C rates; (B) Cycle performance at 0.1 C and 2.0 C rates.
Figure 2. Comparison of nPDF and xPDF for the initial and charged states of P3-Na0.6'Li0.2Mn0.8'O2
Figure 3. Analysis of charge state structure based on neutron diffraction refinement
Intrinsic Transition Metal Layered Oxide (AMO2, A = Li + or Na +, M = Transition Metal) is an important lithium ion / sodium ion battery cathode material.Traditionally, the redox reaction of transition metals provides ion deintercalation Therefore, the capacity of the cathode material is limited by the redox ability of the transition metal in the layered oxide material. However, this conventional concept is not satisfied with the lithium-ion battery lithium-rich layered oxide cathode material (O3 structure Li 'LixM1-x'O2) .The lithium-rich material has ultra-high reversible capacity (300mAh / g), but the source of this capacity can not be explained by only transition metal redox.A large number of studies have shown that lithium-rich Lattice Oxygen in Layered Materials Involves Gains and Losses in Energetic Processes to Provide Additional Capacity In fact, not only lithium-rich materials, many layered oxide materials can implement an electrochemical process that oxygen participates in providing additional capacity for charge compensation. However, how lattice oxygen participates in charge compensation, how to achieve reversible oxygen price change has always been a hot topic in the debate, and clarify the relationship between the crystal structure and the process of oxygen ion price change The key to the reaction mechanism.
Under the guidance of associate researcher Yu Xiqian and researcher Hu Yongsheng, the Institute of Physics, Chinese Academy of Sciences / Beijing Condensed Matter Physics Laboratory (Key Laboratory of Clean Energy Key Laboratory E01 group doctoral student Rong Xiaohui, etc.), with the United States Oak Ridge National Laboratory Dr. Liu Jue, Dr. Hu Enyuan and researcher Yang Xiaoqing from Brookhaven National Laboratory, USA, Yang Wanli, a researcher from Lawrence Berkeley National Laboratory of the United States, and Liu Yijin, researcher from Linear Accelerator Research Center of Stanford University in the United States. Through advanced techniques of neutron scattering and synchrotron radiation, , A detailed study of the sodium storage mechanism of the P3-Na0.6'Li0.2Mn0.8'O2 sodium-ion battery positive electrode material that is only highly reactive with oxygen ions in the redox reaction (Figure 1) illustrates that the material achieves reversible oxygen Structure-induced Reversible Anionic Redox Activity in Na Layered Oxide Cathode, published on Joule.
Using neutron pair distribution function (nPDF) combined with X-ray and neutron diffraction techniques, the research team investigated the effect of oxygen on the crystal structure of oxygen in the P3 anodic oxide before and after electrochemical reaction as well as oxygen-related Of the short-range structure changes, confirmed by the reversible variable oxygen-induced material reversible phase structure changes in the research method used to study oxygen charge compensation related crystal structure changes for the first time, the results shown in Figure 2. Neutron powder diffraction The refined results (Fig. 3) show that the material structure after charging is still a P-phase layered structure with a large number of stacking faults occurring. The oxygen occupancy obtained after finishing is still 1, demonstrating that after charging almost There is no lattice oxygen loss.Through the analysis of the above results, it is found that the crystal structure of the material has a key regulatory role for its reversible oxygen price change behavior: the P structure has a larger interlayer spacing (relative O3 phase) Bring the lattice distortion; at the same time a larger layer spacing can effectively inhibit the migration of cations to the alkali metal layer during charging (lithium-rich material occurs in the layered spinel structure Change), stability of the layered structure, so that the oxidation-reduction reaction of oxygen ions reversibly.
This study elucidates the mechanism of reversible redox reaction of oxygen ions from the viewpoint of material structure and provides a new idea for designing high voltage and high capacity lithium / sodium ion cathode materials with stable and reversible oxygen price change. The research introduced a neutron pair distribution function (nPDF) as a powerful tool to broaden the research dimension.
The research has been supported by the National Basic Research Program of China (973 Program), National Outstanding Youth Science Foundation, Innovative Research Group of National Natural Science Foundation of China, and the Chinese Academy of Sciences's Hundred Talents Program.
