Monitoring and balancing capacity in lithium sulfur cells arranged in series

Abstract

Apparatus for monitoring relative capacity and state of charge between at least two cells, or cell modules, A and B of a plurality of Lithium Sulfur cells arranged in series, comprising: a timer; a voltage monitoring module configured to monitor a voltage drop across each of the Lithium Sulfur cells or cell modules arranged in series based on signals received from a voltage monitoring circuit; and a cell monitoring module coupled to the timer and the voltage monitoring module and configured to, during a charging cycle in which the cells are charged at a constant current: record a time stamp T(Cell A) at which the monitored voltage of the first cell, cell A, leading the charging reaches a first voltage V(cell A) set to be near top of charge as the rate of change of the monitored voltage measurably increases; record a time stamp T(Cell B) at which the monitored voltage of the cell B following the charging reaches the first voltage V(Cell A); record a time stamp T(Cell A) at which the monitored voltage of the leading cell A reaches a second voltage V(Cell A) set to be substantially at a deemed top of charge; record a monitored voltage V(Cell B) of the following cell B at T(Cell A); and determine, based on at least T(Cell A), T(Cell B), V(Cell A) and V(Cell B), a metric indicative of a relative capacity difference between cell A and cell B.