Aiming at the problem that conventional electrode modification methods (such as nano-crystallization and carbon coating) have limited improvement in the performance of FeS2 cathodes, the research team of Li Chilin of the Shanghai Institute of Ceramics, Chinese Academy of Sciences has proposed compact particles to achieve high rate and long-cycle FeS2 cathodes. New modification strategy for stack bonding and particle surface fluorination. Related results were published in the well-known journal of the American Chemical Society ACS Nano.
Related research background
The secondary lithium / sodium metal battery with metal lithium / sodium as the negative electrode has an energy density and power density far exceeding that of commercial lithium-ion batteries by virtue of its extremely high theoretical specific capacity and extremely low reaction potential. The green grid's large-scale energy storage system has broad application prospects. Fluoride and sulfide conversion reaction cathodes with energy density far exceeding that of conventional embedded cathodes have higher tap density and better electrochemical stability than S8 and O2 molecular anodes. In this case, a high load of active material and a compact electrode network can be achieved. Therefore, the development of high-rate, long-cycle fluorine-based / sulfur-based cathodes is a potential way to achieve commercialization of higher specific energy secondary alkali metal batteries. Among these suitable cathode materials, the economical and environmentally friendly Pyrite mineral phase ferrous disulfide (FeS2) has a high theoretical specific capacity (894 mAh / g) through a four-electron conversion reaction. FeS2, as a sulfur-based positive electrode, has much better stability in elementary electrolytes than elemental sulfur. The SS bond in the crystal lattice is "diluted" by Fe-S bonds, potentially reducing the formation and dissolution of polysulfides during cycling. Therefore, the Li / Na-FeS2 battery has better cycle stability and does not require additional electrolyte additives (such as LiNO3) to strengthen the SEI layer. In addition, FeS2 itself is a good electronic conductor, and the Fe nanodomains of its discharge products can also be used as electronic wiring inside the particles to achieve a built-in mixed conductive network, so there is no need to compound a large number of inactive conductive substrates to reduce the overall electrode storage. Energy efficiency. However, Li / Na-FeS2 batteries still have the problem of polysulfide dissolution during cycling, and the problems of poor reaction kinetics and rate performance still need to be solved.
Related research work
The research team successfully achieved the preparation of a high-capacity FeS2 cathode material with a thin carbon fluoride layer coating (less than 2nm) and tightly adhered particles through an open-frame ferrofluoride precursor bonded by a hot sulfurized ionic liquid. Particle bonding and coating thinning promote the penetration of the mixed conductive network inside and outside the particle, surface fluorination also improves the charge and mass transfer kinetics at the electrode-electrolyte interface, and accelerates the Li / Na-driven heterogeneous heterogeneous interface The conversion reaction between adjacent grains spreads, dissolves the polysulfide, significantly improves the overall electrode reaction kinetics, and achieves a high-rate, long-cycle FeS2-based lithium / sodium metal battery (at a 1C rate, cycle The reversible lithium storage capacity after 1000 laps is still 425 mAh / g, and the reversible sodium storage capacity after 1200 laps at 2C rate is still up to 450 mAh / g). Even at a high power density of 10,000 W / kg, the lithium / sodium energy density of the FeS2 substance can still reach 800 and 350 Wh / kg, respectively. Cross-linking of ionic liquids and fluorine-based materials can be an effective means for surface fluorination enhancement.
Researcher Li Chilin's team has been devoted to the research of high specific energy cathode materials for lithium / sodium metal batteries. Open frame iron fluoride cathode materials, such as pyrochlore phase FeF3 · 0.5H2O (J. Am. Chem. Soc. 2013, 135, 11425-11428), hexagonal tungsten bronze phase FeF3 · 0.33H2O (Chem. Mater. 2013, 25, 962-969), tetragonal tungsten bronze phase K0.6FeF3 (J. Mater. Chem. A, 2016, 4, 7382-7389), cubic perovskite phase KFeF3 (Adv. Funct. Mater. 2017, 27 , 1701130), and the use of a microphase-separated ionic liquid ionic thermal fluorination method to develop a reversible conversion reaction of large particle dehydrated tungsten bronze phase iron fluoride (J. Mater. Chem. A, 2016, 4, 16166–16174) .