Associate Professor Dekehua of the School of Metallurgy, Northeastern University and Yang Wanli and Liu Gao of Lawrence Berkeley National Laboratory in the United States and other researchers from more than a dozen units collaborated on key issues affecting the cycle life of high-capacity lithium / sodium ion battery cathode materials Made important theoretical breakthroughs. On December 12, the result was published online in the sister journal Joule of the international top journal Cell, entitled High Reversibility of Lattice Oxygen Redox Quantified by Direct Bulk Probes of both Anionic and Cationic Redox Reactions (DOI: 10.1016 / j.joule.2018.11 .014), Northeastern University is the first unit of thesis. This research will provide directional theoretical basis for the further development of new secondary battery cathode materials with high capacity and long life.
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It is reported that at present, people are eager for rechargeable batteries with higher capacity, longer life and lower cost. Among the main components of lithium-ion batteries and emerging sodium-ion batteries, the positive electrode materials mainly composed of transition metal oxides are the main constraints to increase energy density. Therefore, how to increase the capacity of the positive electrode material is the focus of common concern of the scientific community, industry and the whole society.
In the process of battery charging and discharging, along with the occurrence of current, redox reactions of gain and loss of electrons also occur inside the battery. These reactions are the key to affecting the battery capacity. In traditional cathode materials, only metal ions undergo such reactions. Studies in recent years have found that designing new materials and activating the oxygen element in the chemical reaction can obtain more than double the capacity, which is expected to greatly increase the energy density of the battery.
But there is a deadly "black cloud" floating above this new chemical reaction, which is the reversibility of the reaction. The response must be highly reversible for the battery to have a long life while greatly increasing its capacity. Some research scholars previously believed that only expensive oxides of ruthenium, iridium and other elements can realize the reversible reaction of oxygen, which will inevitably increase the cost of the battery; some scholars believe that the oxygen reaction is fundamentally difficult to achieve reversible, so it should be suppressed To improve the cycle life of the cathode material. Therefore, the accurate, reliable, and quantitative analysis of the reversibility of the lattice oxygen redox reaction in transition metal oxides with low cost (without four or five periodic metal elements) has become a crucial issue at the moment.
In response to the above urgent problems, this study uses the world's first ultra-high-efficiency resonance inelastic X-ray scattering full spectrum (mRIXS) to achieve reliable quantification of lattice oxygen reaction reversibility and cycle retention rate, as well as bulk metal cation reactions Direct quantitative analysis. The study clarified the previous vague understanding of the reversibility of the lattice oxygen reaction in the third period transition metal oxide (3d TM-O) through reliable quantitative characterization, indicating that a highly reversible and stable cycle is achieved in the inexpensive 3d TM-O The lattice oxygen reaction is feasible. In this way, at the key "crossroads", this research points out the correct and feasible direction for the continued development and improvement of high-capacity battery cathode materials, which has extremely important theoretical and practical significance.
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