DIFFUSION-LIMITED ADAPTIVE BATTERY CHARGING

• US 20090256528A1
• Filed: 09/30/2008
• Published: 10/15/2009
• Est. Priority Date: 04/11/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Ungar, P. Jeffrey, Athas, William C., Greening, Thomas C.
• Granted Patent: US 8,754,611 B2
• Time in Patent Office: Days
• US Class Current: 320/162
• CPC Class Codes: G01P 15/00 Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
• CPC Class Codes: G01P 3/56 for comparing two speeds
• CPC Class Codes: H01M 10/0525 Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: H01M 10/443 in response to temperature
• CPC Class Codes: H01M 10/48 Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569
• CPC Class Codes: H01M 2300/00 Electrolytes
• CPC Class Codes: H01M 50/00 Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02J 7/0042 characterised by the mechanical construction
• CPC Class Codes: H02J 7/007 Regulation of charging or discharging current or voltage
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

Some embodiments of the present invention provide a system that adaptively charges a battery, wherein the battery is a lithium-ion battery which includes a transport-limiting electrode governed by diffusion, an electrolyte separator and a non-transport-limiting electrode. During operation, the system determines a lithium surface concentration at an interface between the transport-limiting electrode and the electrolyte separator based on a diffusion time for lithium in the transport-limiting electrode. Next, the system calculates a charging current or a charging voltage for the battery based on the determined lithium surface concentration. Finally, the system applies the charging current or the charging voltage to the battery.

Claims

1. A method for adaptively charging a battery, wherein the battery is a lithium-ion battery which includes a transport-limiting electrode governed by diffusion, an electrolyte separator and a non-transport-limiting electrode, comprising:

determining a lithium surface concentration at an interface between the transport-limiting electrode and the electrolyte separator based on a diffusion time for lithium in the transport-limiting electrode;

calculating a charging current or a charging voltage for the battery based on the determined lithium surface concentration; and

applying the charging current or the charging voltage to the battery.

2. The method of claim 1, wherein the charging current or charging voltage is calculated to maintain the lithium surface concentration within set limits.

3. The method of claim 2, wherein calculating the charging current or charging voltage involves maximizing the charging current or charging voltage while maintaining the lithium surface concentration within the set limits.

4. The method of claim 1, wherein determining the lithium surface concentration involves:

measuring a diffusion time τ

for lithium in the transport-limiting electrode; and

estimating the lithium surface concentration between τ

measurements based on the diffusion time τ

, a cell capacity Q_max for the battery and a measured charging current I for the battery.

5. The method of claim 4, wherein measuring the diffusion time τ

involves periodically;

charging the battery with a fixed current for a fixed time period;

entering a zero current state in which the charging current is set to zero;

during the zero current state, measuring an open circuit voltage for the battery at two times while the open circuit voltage relaxes toward a steady state; and

calculating the diffusion time τ

based on the measured open circuit voltages.

6. The method of claim 1,

wherein the transport-limiting electrode is a negative electrode;

and

wherein the non-transport-limiting electrode is a positive electrode.

7. The method of claim 6,

wherein the negative electrode is comprised of graphite and/or TiS₂;

wherein the electrolyte separator is a liquid electrolyte comprised of LiPF₆, LiBF₄ and/or LiClO₄ and an organic solvent; and

wherein the positive electrode is comprised of LiCoO₂, LiMnO₂, LiFePO₄ and/or Li₂FePO₄F.

8. An adaptive charging mechanism for a battery, wherein the battery is a lithium-ion battery which includes a transport-limiting electrode governed by diffusion, an electrolyte separator and a non-transport-limiting electrode, comprising:

a current sensor configured to measure a charging current for the battery;

a voltage sensor configured to measure a voltage across terminals of the battery;

a charging source configured to apply a charging current or a charging voltage to the battery;

a controller configured to receive inputs from the current sensor and the voltage sensor and configured to send a control signal to the charging source;

wherein the controller is configured to;

determine a lithium surface concentration at an interface between the transport-limiting electrode and the electrolyte separator in the battery based on measurements obtained from the current sensor and the voltage sensor to determine a diffusion time for lithium in the transport-limiting electrode;

calculate a charging current or a charging voltage for the battery based on the lithium surface concentration; and

send a control signal to the charging source to apply the calculated charging current or charging voltage to the battery.

9. The adaptive charging mechanism of claim 8, wherein while calculating the charging current or charging voltage, the controller is configured to maintain the lithium surface concentration within set limits.

10. The adaptive charging mechanism of claim 8, wherein while calculating the charging current or charging voltage, the controller is configured to maximize the charging current or charging voltage while maintaining the lithium surface concentration within the set limits.

11. The adaptive charging mechanism of claim 8, wherein while determining the lithium surface concentration, the controller is configured to:

measure a diffusion time τ

for lithium in the transport-limiting electrode; and

estimate the lithium surface concentration between τ

measurements based on the diffusion time τ

, a cell capacity Q_max for the battery and a measured charging current I for the battery.

12. The adaptive charging mechanism of claim 11, wherein while measuring the diffusion time τ

, the controller is configured to periodically;

charge the battery with a fixed current for a fixed time period;

enter a zero current state in which the charging current is set to zero;

measure an open circuit voltage for the battery at two times during the zero current state while the open circuit voltage relaxes toward a steady state; and

calculate the diffusion time τ

based on the measured open circuit voltages.

13. A battery with an adaptive charging mechanism, comprising:

a transport-limiting electrode governed by diffusion;

an electrolyte separator;

a non-transport-limiting electrode;

a current sensor configured to measure a charging current for the battery;

a voltage sensor configured to measure a voltage across terminals of the battery;

a charging source configured to apply a charging current or a charging voltage to the battery;

a controller configured to receive inputs from the current sensor and the voltage sensor, and configured to send a control signal to the charging source;

wherein the controller is configured to;

determine a surface concentration at an interface between the transport-limiting electrode and the electrolyte separator in the battery based on measurements obtained from the current sensor and the voltage sensor to determine a diffusion time for lithium in the transport-limiting electrode;

calculate a charging current or a charging voltage for the battery based on the lithium surface concentration; and

send a control signal to the charging source to apply the calculated charging current or charging voltage to the battery.

14. The battery of claim 13, wherein while calculating the charging current or charging voltage, the controller is configured to maintain the lithium surface concentration within set limits.

15. The battery of claim 13, wherein while calculating the charging current or charging voltage, the controller is configured to maximize the charging current or charging voltage while maintaining the lithium surface concentration within the set limits.

16. The battery of claim 13,

wherein the battery is a lithium-ion battery;

and

wherein while determining the surface concentration, the controller is configured to;

measure a diffusion time τ

for lithium in the transport-limiting electrode; and

estimate the surface concentration between τ

measurements based on the diffusion time τ

, a cell capacity Q_max for the battery and a measured charging current I for the battery.

17. The battery of claim 16, wherein while measuring the diffusion time τ

, the controller is configured to periodically;

charge the battery with a fixed current for a fixed time period;

enter a zero current state in which the charging current is set to zero;

measure an open circuit voltage for the battery at two times during the zero current state while the open circuit voltage relaxes toward a steady state; and

calculate the diffusion time τ

based on the measured open circuit voltages.

18. The battery of claim 13,

wherein the transport-limiting electrode is a negative electrode;

and

wherein the non-transport-limiting electrode is a positive electrode.

19. The battery of claim 18,

wherein the battery is a lithium-ion battery;

wherein the negative is comprised of graphite and/or TiS₂;

wherein the electrolyte separator is a liquid electrolyte comprised of LiPF₆, LiBF₄ and/or LiClO₄ and an organic solvent; and

wherein the positive electrode is comprised of LiCoO₂, LiMnO₂, LiFePO₄ and/or Li₂FePO₄F.

20. A computer-readable storage medium storing instructions that when executed by a controller for a battery cause the controller to perform a method for adaptively charging a battery, wherein the battery is a lithium-ion battery which includes a transport-limiting electrode governed by diffusion, an electrolyte separator and a non-transport-limiting electrode, the method comprising:

determining a lithium surface concentration at an interface between the transport-limiting electrode and the electrolyte separator based on a diffusion time for lithium in the transport-limiting electrode;

calculating a charging current or a charging voltage for the battery based on the lithium surface concentration; and

applying the charging current or charging voltage to the battery.

21. The computer-readable storage medium of claim 20, wherein calculating the charging current or charging voltage involves calculating the charging current or charging voltage to maintain the lithium surface concentration within set limits.

22. The computer-readable storage medium of claim 20, wherein calculating the charging current or charging voltage involves maximizing the charging current or charging voltage while maintaining the lithium surface concentration within the set limits.

23. The computer-readable storage medium of claim 20, wherein determining the lithium surface concentration involves:

measuring a diffusion time τ

for lithium in the transport-limiting electrode; and

estimating the lithium surface concentration between τ

measurements based on the diffusion time τ

, a cell capacity Q_max for the battery and a measured charging current I for the battery.

24. The computer-readable storage medium of claim 23, wherein measuring the diffusion time τ

involves periodically;

charging the battery with a fixed current for a fixed time period;

entering a zero current state in which the charging current is set to zero;

during the zero current state, measuring an open circuit voltage for the battery at two times while the open circuit voltage relaxes toward a steady state; and

calculating the diffusion time τ

based on the measured open circuit voltages.

25. A method for adaptively charging a battery, comprising:

applying a charging current to the battery;

entering a zero current state in which the charging current is set to zero;

during the zero current state, measuring an open circuit voltage for the battery at two times while the open circuit voltage relaxes toward a steady state;

calculating an updated charging current or charging voltage for the battery based on the measured open circuit voltages; and

applying the updated charging current or charging voltage to the battery.

26. The method of claim 25, wherein calculating the updated charging current or charging voltage involves using additional parameters, including:

a cell capacity Q_max for the battery;

a state of charge q for the battery; and

a measured temperature T for the battery.

27. The method of claim 25, wherein applying the charging current or charging voltage to the battery involves charging the battery with a fixed current or a fixed voltage for a fixed time period.

28. The method of claim 25, wherein the battery is a lithium-ion battery.