Safe chemistry LiMN means reduced risk of venting with flame or explosion. Due to the safety inherent in IMR-safe chemistry batteries, no protection circuitry is added or built-in. This provides a slightly shorter battery length to fit most mods well.

To ensure longevity, allowing the battery to discharge below 2.5V is not recommended.
Efest IMR 18500 LiMn 1100mAh Battery – Flat Top

Please note that due to their inherent safety, IMR cells don’t have a built-in protection circuit. They should never be discharged below 2.5 volts, or cycle life/performance will be reduced. The maximum charge voltage is 4.25 volts.