Carbon coating and Al-doping to improve the electrochemistry of Li 2 CoSiO 4 polymorphs as cathode materials for lithium-ion batteries.

Li 2 CoSiO 4 has the potential for use as a high safety, high energy-density cathode material for lithium-ion batteries but suffers from bad electrochemical performance. Herein, we demonstrate a profound study on the effects of carbon coating and Al-doping on the electrochemistry of Li 2 CoSiO 4 synthesized by a two-step method. The synthesized 4 at% Al-doped Li 2 CoSiO 4 /C allows two lithium removals between 2.5 and 4.6 V, showing a first charge and discharge capacity of 331 and 140 mA h g -1 , respectively, and a high capacity retention in cycling with no voltage degradation. The relationship between the improved performance and the supporting structural characteristics was studied by galvanostatic charge/discharge measurements and electrochemical impedance spectroscopy, coupled with material characterizations. This work demonstrates that electrical conductivity plays a central role in controlling the electrochemical performance of the modified Li 2 CoSiO 4 . Both the reversibility of delithiation and the irreversible capacity loss are strongly dependent on the electrical condition of the particles, which can be modified by Al-doping and carbon coating. The characteristics of carbon layers are analyzed because of their importance in improving the electrical properties and achieving a solution to the challenges with Li 2 CoSiO 4 . We that show Li 2 CoSiO 4 could have unique electrochemical characteristics that satisfy all the requirements of high safety, high energy density, and high compatibility with the current organic electrolytes if appropriately modified.