AbstractA new family of sulfur‐rich phosphorus sulfide molecules (P4S10+n) and their electrochemical reaction mechanism with metallic Li has been explored. These P4S10+n molecules are synthesized by the reaction between P4S10 and S. For Li batteries, the P4S40 molecule in the series of P4S10+n molecules provides the highest capacity, which has a first discharge capacity of 1223 mAh g−1 at 100 mA g−1 and stabilizes at approximately 720 mAh g−1 at 500 mA g−1 after 100 cycles. This new class of sulfur‐rich P4S10+n molecules and its electrochemical behavior for room‐temperature Li+ storage could provide novel insights for phosphorus sulfide molecules and high‐energy batteries.