Methods for heating and charging energy storage devices at very low temperatures

Abstract

A method for heating an energy storage device having a core with an electrolyte, the method including: providing the energy storage device having inputs and characteristics of a capacitance across the electrolyte and the core and internal surface capacitance between the inputs which can store electric field energy between internal electrodes of the energy storage device that are coupled to the inputs; switching between an input voltage and a grounding input provided to one of the inputs at a frequency sufficient to effectively short the internal surface capacitance of the energy storage device to generate heat and raise a temperature of the electrolyte; and discontinuing the switching when the temperature of the electrolyte is above a predetermined temperature that is considered sufficient to increase a charging efficiency of the energy storage device.

What is claimed is: 
     
         1 . A method for heating an energy storage device having a core with an electrolyte, the method comprising:
 providing the energy storage device having inputs and characteristics of a capacitance across the electrolyte and the core and internal surface capacitance between the inputs which can store electric field energy between internal electrodes of the energy storage device that are coupled to the inputs;   switching between an input voltage and a grounding input provided to one of the inputs at a frequency sufficient to effectively short the internal surface capacitance of the energy storage device to generate heat and raise a temperature of the electrolyte; and   discontinuing the switching when the temperature of the electrolyte is above a predetermined temperature that is considered sufficient to increase a charging efficiency of the energy storage device.   
     
     
         2 . The method of  claim 1 , comprising providing the input voltage through a first switch and providing the grounding input through a second switch, wherein the switching comprises simultaneously coupling the input voltage to the one input through operation of the first switch and decoupling the grounding input from the one input through operation of the second switch during a first time interval and thereafter, simultaneously decoupling the input voltage from the one input through operation of the first switch and coupling the grounding input to the one input during a second time interval through operation of the second switch, wherein the first interval and the second interval are subsequently repeated at the frequency sufficient to effectively short the internal surface capacitance of the energy storage device. 
     
     
         3 . The method of  claim 2 , wherein the first switch is a normally closed switch that couples the input voltage to the one input when a first switching voltage is below a first predetermined voltage. 
     
     
         4 . The method of  claim 3 , wherein the second switch is a normally open switch that decouples the grounding voltage from the one input when a second switching voltage is below a second predetermined voltage. 
     
     
         5 . The method of  claim 2 , wherein the providing the grounding input comprises coupling the one input to a circuit ground through the second switch and a sink resistor. 
     
     
         6 . The method of  claim 5 , comprising selecting the input voltage and a resistance of the sink resistor such that nearly the same charge of the energy storage device occurs during the first time interval as discharge from the energy storage device occurs during the second time interval. 
     
     
         7 . The method of  claim 1 , wherein the predetermined temperature is a first predetermined temperature, the method comprising initiating the switching when the temperature of the electrolyte is below a second predetermined temperature that is considered to at least reduce the charging efficiency of the energy storage device, wherein the second predetermined temperature is a lower temperature than the first predetermined temperature. 
     
     
         8 . The method of  claim 1 , comprising obtaining at least one of a measurement and an approximation of the temperature of the electrolyte. 
     
     
         9 . The method of  claim 8 , wherein the obtaining comprises directly measuring the temperature of the electrolyte with a temperature sensor positioned at one or more of the electrolyte and a surface of the energy storage device. 
     
     
         10 . The method of  claim 8 , wherein the obtaining comprises: applying an initial charging input to the energy storage device, measuring a rate of charging using the initial charging input, and determining a charging rate at the initial charging input, wherein if a rate of charging is determined to be less than a predetermined charging rate, the electrolyte temperature is approximated as being less than the predetermined temperature. 
     
     
         11 . The method of  claim 1 , comprising providing a controller for controlling the switching and the discontinuing. 
     
     
         12 . The method of  claim 11 , comprising obtaining by the controller at least one of a measurement and an approximation of the temperature of the electrolyte. 
     
     
         13 . The method of  claim 12 , wherein the obtaining comprises directly measuring the temperature of the electrolyte with a temperature sensor coupled to the controller and positioned at one or more of the electrolyte and a surface of the energy storage device. 
     
     
         14 . The method of  claim 12 , wherein the obtaining is performed periodically. 
     
     
         15 . The method of  claim 1 , comprising producing the input voltage from an AC source provided through an AC to DC converter. 
     
     
         16 . The method of  claim 1 , comprising:
 obtaining an energy storage type for the energy storage device; and   retrieving from a look-up table the predetermined temperature that corresponds to the obtained energy storage type, wherein the look-up table correlates different energy storage types with corresponding predetermined temperatures.   
     
     
         17 . The method of  claim 1 , comprising coupling the input voltage to the one input to charge the energy storage device while the temperature of the electrolyte is above the predetermined temperature. 
     
     
         18 . The method of  claim 1 , wherein the energy storage device is a lithium ion battery or a supercapacitor. 
     
     
         19 . A method for charging an energy storage device having a core with an electrolyte, the method comprising:
 providing the energy storage device having inputs and characteristics of a capacitance across the electrolyte and the core and internal surface capacitance between the inputs which can store electric field energy between internal electrodes of the energy storage device that are coupled to the inputs;   switching between an input voltage and a grounding input provided to one of the inputs at a frequency sufficient to effectively short the internal surface capacitance of the energy storage device to generate heat and raise a temperature of the electrolyte;   periodically obtaining a measurement that correlates to the temperature of the electrolyte,   wherein the switching is initiated when the measurement indicates that the temperature of the electrolyte is below a low temperature threshold that is considered to at least reduce the charging efficiency of the energy storage device, wherein the switching is discontinued when the measurement indicates that the temperature of the electrolyte is above a high temperature threshold that is considered sufficient to increase a charging efficiency of the energy storage device, and wherein the low temperature threshold is a lower temperature than the high temperature threshold; and   providing the input voltage to the one input to charge the energy storage device while the measurement indicates that the temperature of the electrolyte is above the high temperature threshold.