Synchrotron Radiation Spectroscopic Studies of Mg~(2+) Storage Mechanisms in High-Performance Rechargeable Magnesium Batteries with Co-Doped FeS_2 Cathodes

摘要

Rechargeable magnesium batteries (RMBs) are one of the more promisingfuture energy storage systems. This work proposes a non-nucleophilic phenolate-based magnesium complex (PMC) electrolyte enabling reversible Mg stripping/plating with a low over-potential of 84.3 mV at 1 mA cm~(-2). Subsequently, Codoping is introduced to prepare FeS_2, Fe_(0.9)Co_(0.1)S_2, Fe_(0.75)Co_(0.25)S_2 and Fe_(0.5)Co_(0.5)S_2.Multiple characterizations confirm that Co doping can expand the crystal latticeand reduce particle sizes, thus benefiting cathode reactions. With Co doping, Feorbitals can be expected to transform from high spin to low spin states withoutvalence changes while the spin state of Co atoms is little influenced. Then, CodopedFeS_2 cathodes coated on copper collectors coupling with a PMC electrolytefor RMBs show superior electrochemical performance among reportedchalcogenide cathodes, displaying a maximum discharge capacity (700 mAh g~(-1))at 0.1 A g~(-1). Specifically, Fe_(0.5)Co_(0.5)S_2 cathodes exhibit the best cycling stabilityand shortest activation time. Even at 1 A g~(-1), a discharge capacity (164 mAh g~(-1))is still achieved after 1000 cycles. Mechanistic studies indicate that copper collectorparticipates in the cathode reactions accompanied by Cu_(1.8)S generationwhile Fe and Co species play a synergistic catalytic role, providing effective tacticsfor rational design of electrolytes, conversion type cathodes, and collectors.