Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2000-04-05
2001-05-08
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320S139000, C324S427000
Reexamination Certificate
active
06229285
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to batteries and, in particular, to battery charging devices and methods that include determining the battery charge acceptance and/or state of charge of a battery, and then efficiently charging the battery based on the battery charge acceptance and/or state of charge determination.
2. Description of Related Art
Devices and methods for charging and recharging various types and sizes of batteries, such as Ni/Cd batteries, lead-acid batteries, etc., are well known in the prior art. The conventional charging methods include, for example: constant current charging, constant voltage charging, and combinations of constant current and voltage charging, among others. These methods, however, have inherent shortcomings, such as causing excessive gas production (i.e. in lead acid and Ni based batteries), excessive heat production, electrolyte decomposition (i.e. in lithium ion batteries), and overcharging (particularly when utilizing a high charging current or voltage). These prior art charging methods also yield low coulombic efficiency and low energy efficiency which results in decreased service life of a battery and potentially higher charging costs.
Another prior art method for charging a battery is trickle charging. This charging method includes charging a battery with a low power charge over a long charging period and typically does not require the use of protective devices, such as over-charging or over-temperature protection circuitry, in order to protect the battery being charged from damage that can result from improper charging. Trickle charging, however, has met with some disfavor as the need for faster charging methods have become more prevalent. For example, many devices, such as electric vehicles, portable tools, etc, have become common place and consumer demand has dictated that these items be readily available for use at a moment's notice, thereby necessitating the use of fast-charge methodologies for charging and recharging the batteries which power these devices.
Prior art fast-charge methods typically utilize relatively large charge current levels in order to charge batteries within a relatively short period of time. Large current levels, however, can cause rapid heating of a battery, and can otherwise result in low charging efficiency as well as a reduction of battery service life.
U.S. Pat. Nos. 5,680,031 and 5,179,335 disclose methods of charging a battery by controlling charging power based upon the battery's resistance-free voltage (see also, K. Kordesch et al., “Sine Wave Pulse Current Tester for Batteries,” J. Electrochem Soc. Vol. 107, 480-83 (1960). As is well known, the resistance-free voltage of a battery is an effective measure of the electrochemical potential of the battery without regard to the internal resistance of the battery. The principle of the charging mechanisms disclosed in the aforementioned patents is to provide a battery with a constant charging current until the resistance-free voltage of the battery increases to a first predetermined level. Once the resistance-free voltage reaches the predetermined level, the charging current is reduced to a lower constant charging current and the resistance-free voltage in the battery is then allowed to rise to a second predetermined level. This process is repeated until the battery is charged to a desired resistance-free voltage. Although these methods provide a means for determining a battery's internal condition and for charging the battery in accordance with the measured internal conditions of the battery, these methods have not addressed the need to improve charging efficiency by increasing battery charge acceptance.
For various batteries, charge acceptance typically is high when battery state of charge (SOC) is low. As the SOC increases during battery charging, charge acceptance gradually decreases with charge acceptance typically decreasing sharply when SOC reaches approximately 50% of maximum SOC, and decreasing sharply once again when SOC reaches over approximately 85%. Therefore, when utilizing a conventional charging method, battery charging efficiency typically is low when the battery's SOC is low, with the charging efficiency increasing sharply to a relatively high value until SOC reaches over approximately 85%. As charging continues beyond approximately 85%, charging efficiency typically decreases sharply. This low charging efficiency is caused by excessive gas and heat production which can also result in decreased service life of a battery.
Additionally, U.S. Pat. No. 5,307,000 and 4,829,225 disclose methods of battery charging which utilize one or more high, positive current pulses and which include applying one or more negative current or depolarization pulses to the battery for short durations between successive positive current pulses. However, these methods do not address the problems associated with a changing battery SOC.
Due to charge current step-down protocol, which is well known in the prior art, excessive battery heating and overvoltage conditions may occur when charging a battery.
Therefore, there is a need to provide improved devices and methods for charging batteries which include determining a battery's SOC and/or BCA during the charging process and which adjust their charging algorithms accordingly.
SUMMARY OF THE INVENTION
The present invention relates to devices and methods for charging a battery and includes determining the state of charge (SOC) and/or battery charge acceptance (BCA) of the battery, and then charging the battery in a manner which is responsive to the determined SOC/BCA in an iterative process. This is accomplished in a preferred embodiment by applying an alternating current (a-c) pulse to a battery before initiating a charging sequence and recording the battery's response to the a-c pulse. The recorded impedance response, which can include series and parallel equivalent circuit parameters, i.e. resistance, capacitance and phase angle, among others, are then processed with battery condition information, such as temperature and internal pressure, in order to calculate the SOC of the battery. The battery's SOC can then be displayed in a conventional manner, i.e. on a monitor, gauge, etc, thereby providing an updated SOC reference or fuel gauge for the battery user.
Electro-chemical overvoltage also can be derived from application of a single current or voltage test pulse to a battery before initiating the charge pulse. Recording the battery response to the test pulse will enable SOC to be determined by correlation, voltage, current, and resistance free voltage, among others. The recorded response, which can include voltage, current, and electrochemical overvoltage, among others, are then processed with battery condition information, such as temperature and internal pressure, in order to calculate the SOC of the battery. The battery's SOC can then be displayed in a conventional manner, i.e. on a monitor, gauge, etc, thereby providing an updated SOC reference or fuel gauge for the battery user.
Following SOC determination, a charging sequence is initiated which includes applying a series of charging pulses to the battery. In a fast charging mode, a delay or rest period is provided between each charging pulse in order to stimulate battery charge acceptance. Charging pulses also can be applied to the battery in groups of multiple charging pulses with an additional rest period provided between each group of pulses. The charging pulses can be positive pulses, negative pulses, or a combination of both, with the pulse width of each pulse and the rest period between consecutive pulses varying, in some embodiments, according to predetermined criteria for maintaining temperature and gas production of the respective battery within specified limits during charging.
In embodiments of the invention utilizing current charging pulses during the charging sequence, the amplitude of each current pulse can be from approximately 0.003 C (charge rate) to app
Georgia Tech Research Corporation
Thomas Kayden Horstemeyer & Risley LLP
Toatley Jr. Gregory J
Wong Peter S.
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