Qingdao Institute of Energy, Chinese Academy of Sciences / Qingdao University of Science and Technology unveils a new mechanism for cathode reaction of magnesium batteries

On April 14, 2022, Cui Guanglei, a researcher at the Qingdao Institute of Bioenergy of the Chinese Academy of Sciences, a researcher of Dong Shanmu, and Professor Zhou Xinhong of Qingdao University of Science and Technology collaborated to publish an article entitled “Charge-Compensation in Displacement Mg2+ Storage Cathodethrough” at the Angewandte Chemie International Edition Polyselenide Mediated Anion Redox” latest research results.

The research team used the transformed magnesium storage cathode Cu2-xSe as the model material to elucidate its special anion compensation charge storage mechanism, and modified it on this basis to significantly improve its electrochemical properties. The corresponding authors of the paper are Researcher Cui Guanglei, Researcher Dong Shanmu and Professor Zhou Xinhong, and the co-first author is Master Student Qu Xuelian and Postdoctoral Fellow Du Aobing, and Qingdao Institute of Bioenergy of the Chinese Academy of Sciences is the first unit to complete.

Based on the advantages of high natural abundance, low cost, high safety and high capacity of magnesium metal, magnesium metal battery has become one of the candidate battery systems with good development prospects after lithium-ion batteries. Looking back at the research and development of magnesium batteries, the research of magnesium electrolytes has made great progress, but there are still major challenges in the development of magnesium-ion cathode materials. Transition metal chalcogenoids are considered to be important conversion magnesium storage cathode materials to achieve high energy density in magnesium batteries, but problems such as low initial coulomb efficiency and rapid capacity attenuation are common. In addition, the magnesium storage mechanism in these materials has not yet been clarified, which also brings difficulties to the screening of more high-energy magnesium storage cathodes.

Recently, the team of cui guanglei researchers and Professor Zhou Xinhong of the Qingdao Institute of Bioenergy and Process Technology of the Chinese Academy of Sciences and Qingdao University of Science and Technology found that the magnesium storage mechanism of Cu2-xSe is the soluble polyselenide-mediated Sen2-/Se2-anion compensation mechanism. Different from the previously reported Cu2+ step-by-step displacement reaction, the study also demonstrated that the corresponding reactions of the two discharge platforms were the conversion reaction of Cu2-xSe and Cu2Se and the displacement reaction of Cu2Se and Mg2+, respectively. The unique anionic redox process facilitates charge storage, however the irreversible dissolution of polyselenide can lead to a decrease in battery performance. To solve the above problems, by introducing Mo6S8 in the Cu2-xSe cathode, the resulting embed-transformative composite (ICH) positive electrode can effectively fix the polyselenide. This modification significantly improves the electrochemical properties. This work provides a deeper understanding of the research of the cathode of sulfur conversion magnesium storage, and is of great significance for the development of a new high-energy magnesium storage cathode.

Figure 1: Characterization and electrochemical properties of Cu2-xSe

Figure 2: Characterization of the Cu2-xSe magnesium storage mechanism

The nanoCu2-xSe was synthesized by solution to prepare a positive electrode, and the electrochemical charge-discharge curve showed two discharge platforms. A series of characterization methods such as in-situ XRD, XPS and XANES were used to prove that the two platforms corresponded to the conversion reaction of Cu2-xSe and the displacement reaction of Cu2Se and Mg2+, respectively. Subsequently, the anion compensation mechanism mediated by polyselenide in Cu2-xSe was further demonstrated by tests such as in-situ Raman, ICP-MS and UV-vis.

Figure 3: Cu2-xSe vs. ICH cathode performance comparison

To further improve the electrochemical properties, a small amount (10%) of the Shefre phase Mo6S8 was introduced into the Cu2-xSe positive electrode to prepare the ICH cathode, and the capacity decay was inhibited by adsorption of polyselenides. Finally, at a current density of 100 mA g-1, the reversible capacity is increased from 140 mAh g-1 to 220 mAh g-1. In addition, the magnification performance and long cycle stability have also been improved to varying degrees.

Figure 4: Schematic diagram of cu2-xSe magnesium storage mechanism

The study revealed the magnesium storage mechanism of the transformative cathode Cu2-xSe, demonstrating Sen2-/Se2-anion redox. By introducing Mo6S8 to inhibit the irreversible dissolution of polyselenides and improve the electrochemical properties, it provides a new idea for the development and modification of the positive electrode of magnesium storage. (Source: Science Network)

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