Lithium sulfur rechargeable battery fuel gauge systems and methods

Abstract

Systems and methods for accurately determining the state of charge and the relative age of lithium sulfur batteries are provided. The cell resistance and taper input charge of a particular type of lithium sulfur battery are respectively measured to determine the state of charge and age of the battery.

1 . A method for determining the age of a lithium sulfur battery of a particular type using a look-up table of taper input charge versus age for said particular type of lithium sulfur battery, said method comprising the steps of:
 a) inputting a battery type into a computer;   b) measuring a taper input charge for said battery, said taper input charge being input into said computer;   c) executing a taper input charge correlation algorithm based on inputs comprising:
 i) the type of said battery inputted into said computer; and 
 ii) the measured taper input charge for said battery; and 
   d) determining the age of said lithium sulfur battery based on said taper input charge correlation algorithm.   
     
     
         2 . The method of  claim 1 , wherein said inputs to said taper input charge correlation algorithm further comprise measured battery temperature. 
     
     
         3 . A system for creating a look-up table of cell resistance versus state of charge for a lithium sulfur battery of a particular type and determining the capacity thereof, said system comprising:
 a) means for charging said battery until a voltage across said battery increases to a predetermined maximum voltage;   b) means for continuing to charge said battery at said predetermined maximum voltage until an input current to said battery decreases to a predetermined minimum current;   c) means for measuring a cell resistance for said battery, said cell resistance being defined as the cell resistance at 100% state of charge for said particular type of lithium sulfur battery;   d) means for recording said cell resistance at 100% state of charge;   e) means for discharging said battery at a discharge rate to a predetermined lower cutoff voltage and means for recording a discharge time period;   f) means for integrating said discharge time period with said discharge rate and means for storing the result, said integration result being defined as the battery capacity for said particular type of lithium sulfur battery;   g) means for measuring a cell resistance for said battery, said cell resistance being defined as the cell resistance at 0% state of charge for said particular type of lithium sulfur battery;   h) means for recording said cell resistance at 0% state of charge;   i) means for charging said battery with a predetermined percentage of said battery capacity so that a present battery state of charge exceeds a previous battery state of charge;   j) means for measuring a cell resistance for said battery, said cell resistance being defined as the cell resistance at the present state of charge for said particular type of lithium sulfur battery;   k) means for recording said cell resistance at the present state of charge; and   l) means for creating said look-up table of cell resistance versus state of charge for state of charge values from 0% to 100%.   
     
     
         4 . A system for determining the age of a lithium sulfur battery of a particular type using a look-up table of taper input charge versus age for said particular type of lithium sulfur battery, said method comprising the steps of:
 a) means for inputting a battery type into a computer;   b) means for measuring a taper input charge for said battery;   c) means for inputting said taper input charge into said computer;   d) means for executing a taper input charge correlation algorithm based on inputs comprising:
 i) the type of said battery inputted into said computer; and 
 ii) the measured taper input charge for said battery; and 
   e) means for determining the age of said lithium sulfur battery based on said taper input charge correlation algorithm.