Low temperature charging of Li-ion cells
View Patent ↗A battery cell charging system, including a charger and a controller, for low-temperature (below about zero degrees Celsius) charging a lithium ion battery cell, the battery cell charging system includes: a circuit for charging the battery cell using an adjustable voltage charging-profile to apply a charging voltage and a charging current to the battery cell wherein the adjustable voltage charging-profile having: a non-low-temperature charging stage for charging the battery cell using a charging profile adapted for battery cell temperatures above about zero degrees Celsius; and a low-temperature charging stage with a variable low-temperature stage charging current that decreases responsive to a battery cell temperature falling below zero degrees Celsius.
1. A charging system, comprising:
a lithium ion energy storage element;
a charger; and
a battery management system that (i) determines when the lithium ion energy storage element has a temperature below 32 degrees Fahrenheit, and (ii) in response to the determination, applies a charging profile that sets a temperature-dependent current limit and a temperature-dependent voltage limit for the charger, wherein when the lithium ion energy storage element does not have the temperature below 32 degrees Fahrenheit, the battery management system applies a temperature-independent current limit, at least up to a maximum temperature, and a temperature-independent voltage limit.
2. The charging system of claim 1 , wherein the maximum temperature is 104 degrees Fahrenheit.
3. The charging system of claim 1 , wherein a DC model for the lithium ion energy storage element includes an imaginary R Bad resistance in series with an R Nominal resistance, wherein said R Bad includes a function component responsive to one or more of said R Nominal , a state-of-charge (SOC) of the lithium ion energy storage element, and a temperature of the lithium ion energy storage element such that V cell is about equal to a maximum battery cell voltage minus charging current times R Bad , wherein the circuit adjusts R Bad over time using the function component so that a change in resistance of the battery cell is compensated for.
4. The charging system of claim 3 , wherein said R Bad includes a component that is about equal to a first constant k1 times R Nominal minus a second constant k2 times SOC wherein said first constant k1 is about between 0 and 1 and wherein said second constant k2 is about 0.001/SOC %.
5. The charging system of claim 4 , wherein said first constant k1 is about equal to 0.1.
6. The charging system of claim 3 , wherein said R Nominal is determined from a lookup table responsive to cell temperature, age, and SOC.
7. The charging system of claim 3 , wherein said R Bad is determined from a lookup table responsive to cell temperature, age, and SOC.
8. The charging system of claim 3 , wherein said R Bad is estimated in real-time or over time.
9. A charging method, comprising:
determining when a lithium ion energy storage element in a charging system has a temperature below 32 degrees Fahrenheit;
in response to the determination, applying a charging profile that sets a temperature-dependent current limit and a temperature-dependent voltage limit for a charger of the charging system; and
when the lithium ion energy storage element does not have the temperature below 32 degrees Fahrenheit, applying a temperature-independent current limit, at least up to a maximum temperature, and a temperature-independent voltage limit.
10. The charging method of claim 9 , wherein the maximum temperature is 104 degrees Fahrenheit.
11. The charging method of claim 9 , wherein a DC model for the lithium ion energy storage element includes an imaginary R Bad resistance in series with an R Nominal resistance, wherein said R Bad includes a function component responsive to one or more of said R Nominal , a state-of-charge (SOC) of the lithium ion energy storage element, and a temperature of the lithium ion energy storage element such that V cell is about equal to a maximum battery cell voltage minus charging current times R Bad , wherein the circuit adjusts R Bad over time using the function component so that a change in resistance of the battery cell is compensated for.
12. The charging method of claim 11 , wherein said R Bad includes a component that is about equal to a first constant k1 times R Nominal minus a second constant k2 times SOC wherein said first constant k1 is about between 0 and 1 and wherein said second constant k2 is about 0.001/SOC %.
13. The charging method of claim 12 , wherein said first constant k1 is about equal to 0.1.
14. The charging method of claim 11 , wherein said R Nominal is determined from a lookup table responsive to cell temperature, age, and SOC.
15. The charging method of claim 11 , wherein said R Bad is determined from a lookup table responsive to cell temperature, age, and SOC.
16. The charging method of claim 11 , wherein said R Bad is estimated in real-time or over time.