Investigation Of Preparation Methods And Electrochemical Properties Of Ruthenium-based Lithium-rich Cathode Materials

The widespread use of lithium-ion batteries has created an urgent need for the development of high energy density layered cathode materials.Lithium-rich materials,as one of the cathode materials with the highest energy density at present,suffer from severe structural transformation of layered-to-spinel phase,which results in severe voltage attenuation and capacity loss in cycling.Therefore,it is of great practical significance to design and synthesize new cathode materials with excellent electrochemical properties.In this paper,a series of excellent cathode materials have been obtained by modificating ruthenium based lithium-rich materials.The specific research contents and results are summarized as follows:?1?Li₂RuO₃ cathode material was synthesized by step-by-step calcination method.The structure and morphology of Li₂RuO₃ cathode material were characterized by X-ray powder diffraction and scanning electron microscopy,and its electrochemical performance was tested.The results showed that higher crystallinity of microstructure can be reached when the materials were obtained by step-by-step calcination instead of one-step calcination.And the obtained materials possessed appreciable electrochemical properties,such as the first discharge capacity can reach 280 mAh/g under the current density of 32mA/g and the discharge capacity can maintain about200 mAh/g after 100 cycles,and surprisingly,when the current density increased to160mA/g,the first discharge capacity can still reach to 276 mAh/g.These results showed that Li₂RuO₃ is a promising cathode material.?2?Molybdenum was doped to modify one-step synthesis Li₂RuO₃ material by high temperature solid-state method.The results showed that the sample0.98Li₂RuO₃-0.02Li₂MoO₃,whose doping content of molybdenum is 2%,possess really high discharge capacity of 307 mAh/g in the first cycle under the current density of 32mA/g.And after 100 cycles of galvonastatic charge and discharge,the capacity can be still maintained at about 210 m Ah/g.Also when the current density increased to 160 mA/g,the initial discharge capacity can achieve 298 mAh/g and still hold 180 mAh/g after 100 cycles.During the rate performance test,the 2%sample can deliver a capacity of 200 mAh/g at the current density of 800 mA/g,which fully demonstrate its excellent rate capability.However,when the doping amount of molybdenum increased to 5%,the doped product started to fade in capacity.The XPS results showed that the doping ions exist in the form of Mo⁶⁺and Mo⁴⁺.Mo⁶⁺plays a role of stabilizing the structure.The presence of Mo⁴⁺can benefit to the capacity of the system,but when the doping amount get higher,it will lead to distinct migration of transition metal migrate to Li layer,which consequently will reduce the electrochemical performance of Li₂RuO₃.?3?Li₂RuO₃-Li₂MnO₃-Li₂SnO₃ ternary materials were synthesized by high temperature solid phase method.With the increase of Ru content,the ternary system evolved from the composite phase to a single solid solution.Ru⁴⁺acts as a buffer ion in the system,reducing the lattice distortion caused by the large difference in ionic radius of Mn⁴⁺and Sn⁴⁺ions.The results of electrochemical tests show that once the ternary system is changed from a composite phase to a solid solution phase,the performance of the battery will increase rapidly.In addition to the Ru content,the molar ratio of Mn/Sn in the ternary system has a significant effect on the cycle performance.The sample with high Mn content undergoes severe migration of Mn⁴⁺and Ru⁴⁺from the octahedral site in the transition metal layer to the tetrahedral sites in the lithium layer during the cycle,resulting in the phase transition and capacity decay of the ternary compound.The Sn⁴⁺ion can effectively block the migration of Mn⁴⁺and Ru⁴⁺ions from the transition metal layer to the Li layer.The sample with high Sn content will be beneficial to improve the structural stability and cycle performance of the system.The electrochemical performance of Li₂RuO₃-Li₂MnO₃-Li₂SnO₃ system can be further improved by optimizing the composition.The derivative system will become a promising candidate of cathode materials with high energy density lithium-ion battery?In this paper,the electrochemical behavior of ruthenium based lithium-rich cathode materials under different systems is studied,which provides some new ideas and thoughts for the development of next generation high performance lithium-ion battery cathode materials.