Pyrite FeS2 has been successfully applied in primary Li/FeS2 batteries, but its poor cyclability in traditional carbonate-based electrolytes seriously hinders its application in rechargeable batteries. To overcome this issue, efforts have been made to focus on the modification of FeS2. However, it is still difficult to improve the electrode performance especially for bare FeS2. Herein, we report that changing carbonate-based electrolytes to selected ether-based lithium bis(trifluoromethanesulfonyl)imide and diglyme electrolytes greatly enhances the reversibility of the electrochemical reaction. FeS2 microspheres with a high tap density of 2.2 g cm-3 show the stable discharge capacities of 680 mA h g-1 at 100 mA g-1 and 412 mA h g-1 even at 6000 mA g-1. Moreover, the capacity retention is 90% after 100 cycles at 1000 mA g-1. The main reason for the long cycling is to inhibit the side reaction of the intermediate polysulfides with electrolytes.