Abstract: A method of operating an energy storage device comprises applying external pressure onto an electrochemical cell during charging and/or discharging. The cell comprises a sulfur-based cathode within a compressible vessel. An energy storage system may include plates and at least one electrochemical cell that includes—within a compressible vessel—a cathode, an anode, and an electrolyte. The cathode comprises a sulfur-based active material. In a method of assembling a system for operating an energy storage device, at least one electrochemical cell is disposed between a pair of plates and adjacent pressure sensor(s). A distance between the plates is fixed at which a measured pressure is within a range from greater than about 0 kPa to about 689 kPa above ambient pressure. The plate-separation distance is maintained while charging or discharging the electrochemical cell(s).