TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Cell: In the electrochemical cell, the second electrode is a positive electrode. The active material comprises a form of sulfur. It further comprises: a mixed conductor in the second electrode and connected to the separator and the active material within the second electrode for transfer of electrons and lithium ions for transfer of electrons and lithium ions. The first electrode is a negative electrode. The active material comprises a form of lithium. The variable volume reservoir is located external to the second electrode, the electrochemical cell further comprises: a fluid in contact with the active material and in fluid contact with the variable volume reservoir, so that changes in the volume of the active material cause the fluid to move into or out of the variable volume reservoir. The fluid is a gas. The variable volume reservoir comprises: a resilient membrane in contact with the fluid. The variable volume reservoir is located within the second electrode. The variable volume reservoir comprises a compressible gas in contact with the active material. The variable volume reservoir comprises a compressible elastomer in contact with the active material. The pressure within the variable volume reservoir is less than atmospheric pressure. Alternatively, the electrochemical cell comprises: a first electrode; a second electrode spaced apart from the first electrode, the second electrode including active material particles; a separator positioned between the first electrode and the second electrode; and at least one first variable volume reservoir in fluid connection with the active material particles, so that changes in the volume of the active material particles cause changes in volume of the at least one first variable volume reservoir. It further comprises: a mixed conductor in the second electrode and connected to the separator and to each of the active material particles for transfer of electrons and lithium ions. It further comprises: a second variable volume reservoir in fluid connection with the first electrode, so that changes in the volume of a component of the first electrode causes changes in volume of the second variable volume reservoir. The at least one first variable volume reservoir comprises: first variable volume reservoirs. Each of the first variable volume reservoirs is located within the second electrode. Each of the first variable volume reservoirs comprises an elastomer. Each of the first variable volume reservoirs comprises an inert gas.