Method for predicting the equilibrated open-circuit voltage of an electrochemical energy store

• US 6,653,818 B2
• Filed: 06/06/2002
• Issued: 11/25/2003
• Est. Priority Date: 06/08/2001
• Status: Active Grant

• Current Assignee: Clarios Germany GmbH & Co. KG (Michael Tojner, PhD, LLD)
• Original Assignee: VB Autobatterie GmbH
• Inventors: Meissner, Eberhard, Laig-Horstebrock, Helmut
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US10/163,808
• Publication Number:
  US 20030001542A1
• Time in Patent Office: 537 Days
• Field of Search: 320/127, 320/128, 320/132, 320/134, 320/136, 320/150, 324/426, 324/427, 324/430, 324/433
• US Class Current: 320/132
• CPC Class Codes: G01R 31/388 involving voltage measurements

Abstract

In a method for predicting the equilibrated open-circuit voltage of an electrochemical energy store by measuring the voltage settling response Uo(t) in a load-free period, a formulaic relationship between the equilibrated open-circuit voltage Uoo and the decaying voltage Uo(t) of the form Uoo=Uo(t)−w*ln(t)−w*F(T) is used, the prefactor w being the experimentally determined slope of the dependency of Uo on ln(t) at the time t, w=−(uo(t2)−Uo(t1))/ln(t2/t1), and Uo(t1) being the unloaded voltage Uo at the time t1 and Uo(t2) being the unloaded voltage Uo at the later time t2>t1, and F(T) being a function which depends only on the absolute temperature T of the energy store. The function F(T) has the general form F(T)=(K|E/T)/(1+q*w)/f(T), K, E and q being experimentally determined constants, T being the absolute temperature in kelvin, and f(T) being a function which contains only the absolute temperature T as a free parameter.

Claims

1. A method for predicting an equilibrated open-circuit voltage of an electrochemical storage battery comprising measuring a voltage settling response Uo(t) in a load-free period using a relationship (1) between an equilibrated open-circuit voltage Uoo and a decaying voltage Uo(t)

2. The method as claimed in claim 1, wherein F(T)=(K+E/T)/(1+q*w)/f(T), and wherein K, E and q are experimentally determined constants, T is absolute temperature in kelvin, and f(T) is a function which contains only the absolute temperature T as a free parameter.

3. The method as claimed in claim 2, wherein the function f(T) of the absolute temperature T has the general form f(T)=a+b*EXP(−

(T−

c)/d).

4. The method of claim 3, wherein the battery is a lead-acid battery, and constants a, b, c, d are selected from:

a between about 0.01 and about 0.2,

b between about 0.001 and about 0.05,

c between about 250 and about 350, and

d between about 5 and about 50.

5. The method as claimed in claim 3, wherein a is about 0.04, b is about 0.009, c is about 270 and d is about 17.

6. The method as claimed in claim 2, wherein the battery is a lead-acid battery, and constants K, E and q for an individual cell, when an unloaded phase was preceded by charging, are selected from:

E between about 50 K and about 500 K,

K between about −

0.1 and about −

2, and

q between about 50 V<sup>−

1</sup> and about 1000 V<sup>−

1</sup>.

7. The method as claimed in claim 2, wherein E is about 116 K, K is about −

0.34, and q is about 190 V<sup>−

1</sup>.

8. The method as claimed in claim 2, wherein the battery is a lead-acid battery, and constants E, K and q for an individual cell, when an unloaded phase was preceded by discharging, are selected from:

E between about 10 K and about 500 K,

K between about −

0.05 and about −

1, and

q between about −

50 V<sup>−

1</sup> and about −

1000 V<sup>−

1</sup>.

9. The method as claimed in claim 2, wherein E is about 60 K, K is about −

0.19, and q is about −

150 V<sup>−

1</sup>.

10. The method as claimed in claim 1, wherein measurement is not carried out until at least one hour after the beginning of the load-free period.

11. The method as claimed in claim 1, further comprising calculating a time interval according to the formula $\mathrm{to}=-t-\frac{\hat{u}}{}$

Uo

(t)/

t,

at time t after the beginning of the load-free period, wherein dUo(t)/dt is the time derivative of the decaying voltage Uo and û

is a constant, and the time determination for the measurement of the voltage response during the load-free period is carried out and offset by time interval t according to formula (2);

12. The method as claimed in claim 11, wherein the battery is a lead-acid battery, and constant û

for an individual battery cell has a value of approximately 0.002 V to approximately 0.02 V, at 25°

C., and a value of approximately 0.003 V to approximately 0.03 V, at −

20°

C., and is linearly interpolated or extrapolated for other temperatures.

13. The method as claimed in claim 12, wherein constant û

is about 0.007 V at 25°

C. and about 0.01 V at −

20°

C.

14. A method of predicting state of charge comprising:

measuring the voltage settling response of the storage battery according to the method of claim 1; and

comparing the voltage settling response to true open-circuit voltage Uoo and the decay voltage Uo(t) to determine the state of charge.