JP2011109840A - Charging system which guarantees lifespan of secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging system capable of guaranteeing the lifespan of a secondary battery, along with an electrical apparatus or computer equipped with such a charging system, a battery pack which achieves such a charging system, and a method which guarantees the lifespan of the secondary battery. <P>SOLUTION: A line 23-1 represents a full charge capacity ratio measured under a low battery voltage that does not cause storage degradation. A line 21 represents a full charge capacity ratio measured under a standard use condition that guarantees a lifespan. A line 23-2 represents a modified full charge capacity ratio given by translating the line 23-1 to match its lifespan termination to the lifespan termination tf of the line 21. When the full charge capacity of a secondary battery charged with a voltage under the standard use condition decreases by following the lines 25-1 and 25-2, the secondary battery is charged with a low charge voltage so that the secondary battery degrades by following the line 23-2 after the times t1 and t2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for guaranteeing the lifetime of a secondary battery.

  A battery pack incorporating a lithium ion battery is used in a notebook personal computer (hereinafter referred to as a notebook PC), which is an example of a portable electronic device. Secondary batteries, not limited to lithium-ion batteries, deteriorate as the usage time elapses, resulting in a reduction in capacity. Although the lifetime of the secondary battery varies depending on the use environment and the charging method, the deterioration mode of the lithium ion battery can be roughly divided into two. One is cycle degradation due to electrochemical and physical changes that occur during repeated charge / discharge cycles of the lithium ion battery, and the other is while the lithium ion battery maintains a constant charge state. Storage degradation or calendar degradation due to electrochemical changes that occur in

  Patent Document 1 discloses an invention for extending the cycle life of a lithium ion battery. The invention of this document makes the actual charging voltage lower than the upper limit and the discharge voltage higher than the lower limit while the chargeable / dischargeable capacity of the lithium battery used is large. Further, as the chargeable / dischargeable capacity becomes smaller, the charging voltage is made closer to the upper limit and the discharging voltage is made closer to the lower limit. At the end of the life, the charge voltage is set to the upper limit and the discharge voltage is set to the lower limit, thereby reducing the decrease in chargeable / dischargeable capacity and extending the life.

  Patent Document 2 discloses an invention that suppresses performance deterioration and shortening of battery pack performance. This document describes that a lithium ion battery has a property that its capacity deterioration greatly proceeds when left or stored in a fully charged state or close to it. In addition, lithium-ion batteries are more likely to have their capacity deteriorated as the charging time of the battery is fully charged or close to it, and as the temperature rises, the once the capacity has deteriorated, the capacity can be recovered. It is stated that it is not possible. In the invention of this document, when the temperature of the battery pack is relatively high, the target charge capacity of the battery pack is set to be relatively small, and when the temperature of the battery pack is relatively low, the target charge capacity is set to be relatively small. By setting it large, the battery pack is not charged until it is fully charged.

Japanese Patent Laid-Open No. 9-120843 JP 2005-287092 A

  In recent years, a system for guaranteeing the lifetime of a lithium ion battery mounted on an electric device for a predetermined period such as three years or five years by an electric device manufacturer is about to be started. In order to guarantee the lifetime, the usage conditions related to factors that strongly affect the capacity deterioration such as the number of charge / discharge cycles (hereinafter referred to as the cycle number), the battery temperature, and the battery voltage are set as standard usage conditions. However, the lifetime can be guaranteed if the user uses it in accordance with the standard usage conditions. However, since the user may actually use the standard usage conditions, the lifetime may not be guaranteed. Therefore, there is a demand for a charging system that can guarantee the lifetime of a lithium ion battery even if it is used outside the standard use conditions.

  Accordingly, an object of the present invention is to provide a charging system that can guarantee the lifetime of a secondary battery. It is a further object of the present invention to provide an electric device or computer equipped with such a charging system. Furthermore, the objective of this invention is providing the battery pack which implement | achieves such a charging system. It is a further object of the present invention to provide a method for guaranteeing the lifetime of a secondary battery.

  The present invention provides a charging system that can guarantee the lifetime of a secondary battery. The lifetime of the secondary battery targeted by the present invention is largely governed by storage degradation mainly due to battery temperature and battery voltage. Specifically, it is intended for a secondary battery in which the storage deterioration is severe when the battery temperature is higher than a predetermined value and the battery voltage is higher than a predetermined value. Since the battery temperature is determined by the environmental temperature at which the secondary battery is used, the charging system cannot be controlled. The charging system according to the present invention guarantees the lifetime by reducing the battery voltage when it is determined that the capacity deterioration is progressing. The charge control circuit sets, as a threshold, a deterioration characteristic value related to the magnitude of capacity deterioration of the secondary battery when a predetermined time has elapsed while setting a first charging voltage value in the charger and repeating a charge / discharge cycle. In comparison, it is determined whether it is necessary to switch the charging voltage. The charge / discharge cycle may include a period in which the secondary battery is spontaneously discharged after being disconnected from the charge / discharge circuit in addition to the charge period and the discharge period. The charging control circuit sets a second charging voltage value lower than the first charging voltage value in the charger when determining that the deterioration characteristic value has reached the threshold value.

  The first charging voltage value can be a charging voltage value under standard use conditions set as a premise for guaranteeing the lifetime. If the second charging voltage value is set to a value that will cause little storage degradation even when the battery temperature is higher than the standard usage conditions and the rated capacity can be secured, the storage degradation after changing the charging voltage will be In this case, the lifetime can be assured with less suppression. The secondary battery according to the present invention is preferably a lithium ion battery in which the positive electrode is formed of cobalt-based lithium. However, the secondary battery is of a type in which the lifetime is strongly controlled by storage deterioration and can be controlled by the charging voltage. It can be applied to batteries in general.

  As the deterioration characteristic value, it is possible to select a time in the first deterioration promoting state or a cumulative time in which the battery temperature is equal to or higher than the first temperature value and the battery voltage is equal to or higher than a predetermined value. As the deterioration characteristic value, a deterioration amount indicating the degree of deterioration of the secondary battery can be selected. The amount of deterioration can be selected from the full charge capacity, the internal impedance of the secondary battery, and the change value of the battery voltage per unit capacity when the secondary battery is discharged. Further, the charging voltage may be switched by adding a logical operation to the relationship between the plurality of selected deterioration characteristic values and the corresponding threshold value.

  When the second deterioration promotion state in which the battery temperature is equal to or higher than the second temperature value and the battery voltage is equal to or higher than the predetermined value continues for a predetermined time, the charge control circuit It can be discharged to a voltage. If the second deterioration promoting state is set to a state that is more severe than the first deterioration promoting state such that the second temperature value is higher than the first temperature value, the rapid deterioration progresses. Can be relaxed by forced discharge.

  According to the present invention, a charging system capable of guaranteeing the lifetime of the secondary battery can be provided. Furthermore, according to the present invention, an electric device or a computer equipped with such a charging system can be provided. Further, according to the present invention, a battery pack that realizes such a charging system can be provided. Furthermore, the present invention can provide a method for guaranteeing the lifetime of the secondary battery.

It is a figure explaining the outline | summary of the method of ensuring the lifetime of the lithium ion battery which uses cobalt series lithium for a positive electrode. It is a functional block diagram of the basic charging system concerning this Embodiment. It is a figure explaining the method of guaranteeing a lifetime when full charge capacity ratio is selected as a deterioration characteristic value. It is a figure explaining the method of determining the threshold value for guaranteeing a lifetime, when the continuation time of a deterioration promotion state is selected as a deterioration characteristic value. It is a flowchart which shows the procedure in which a charging system guarantees the lifetime of a lithium ion battery based on a deterioration characteristic value. It is a functional block diagram which shows the outline | summary of the charging system comprised by the notebook PC carrying a battery pack and a battery pack. It is a functional block diagram which shows the internal structure of the battery pack based on a smart battery system (SBS) specification.

[Lifetime of lithium-ion batteries]
The lifetime of the secondary battery can be defined as a period in which a full charge capacity of a predetermined ratio or more remains with respect to the full charge capacity at the start of use. In order to guarantee the lifetime of the lithium ion battery, it is necessary to determine the degree of capacity deterioration during use and to appropriately control the control factor. According to the inventor's experiment, it has been found that the lithium-ion battery has different factors that greatly affect the deterioration depending on the material of the positive electrode. Currently, cobalt-based lithium and nickel-based lithium are mainly used as positive electrode materials for lithium-ion batteries. As the cobalt-based lithium, lithium cobaltate or a material obtained by mixing lithium cobaltate and lithium manganate is mainly used. As nickel-based lithium, a material in which lithium nickelate and lithium cobaltate or lithium manganate are mixed is mainly used.

  When examining the relationship between positive electrode material and capacity deterioration, lithium ion batteries using cobalt-based lithium as the positive electrode have a high battery temperature, which is the surface temperature of the battery, and the terminal voltage when disconnected from the charge / discharge circuit. It was found that when a certain battery voltage continues to be high, the capacity deterioration becomes severe, and the storage deterioration is dominant. It was also found that cycle deterioration can be suppressed by lowering the battery voltage even when the battery temperature is high. On the other hand, in lithium ion batteries using lithium nickelate as the positive electrode, it was found that when the number of cycles exceeded the capacity deterioration, the capacity deterioration became severe and the cycle deterioration was dominant. It was also found that storage degradation was small even when the battery temperature was high, and that cycle degradation could not be suppressed even when the battery voltage was lowered.

  The battery deteriorates due to various factors after the start of use. Among the deterioration factors, there are factors that can be controlled by the charging system, such as the battery voltage governed by the charging voltage, and the battery temperature governed by the environmental temperature. There are factors that cannot be controlled. In order to reliably guarantee the lifetime without excessively restricting the use conditions, it is necessary to specify an appropriate control factor in advance. In the present embodiment, a lithium-ion battery using cobalt-based lithium as a positive electrode will be exemplified, and a charging system capable of appropriately controlling usage conditions and guaranteeing a lifetime will be described.

[Overview of how to guarantee the lifetime]
FIG. 1 is a diagram for explaining an outline of a method for guaranteeing the lifetime of a lithium ion battery using cobalt-based lithium as a positive electrode. Lines 11, 13, and 15 all represent the ratio of the full charge capacity measured for each elapsed time with respect to the initial full charge capacity. Hereinafter, the ratio of the value after a predetermined elapsed time to the initial value of the full charge capacity is referred to as the full charge capacity ratio. The full charge capacity is the maximum amount of electricity that can be stored in the battery at that time, and is a value that decreases with time due to physical and chemical changes in the lithium ion battery. The lithium ion battery is charged by a constant current constant voltage (CCCV) method. In the constant current constant voltage method, charging is started by constant current charging, and switching to constant voltage charging is performed when the battery voltage rises to a predetermined value. When constant voltage charging is continued, the charging current gradually decreases. The charging is terminated when the charging current reaches the discharge end current.

  Therefore, the battery voltage is governed by the charging voltage, which is the voltage immediately before stopping charging. The full charge capacity can be measured as the total amount of electricity accumulated in the battery while charging from the discharge end voltage or near it to the discharge end current. The battery voltage when a plurality of batteries are connected in series refers to the voltage of a single battery (battery cell). In the present embodiment, standard use conditions are set in order to guarantee the lifetime of the lithium ion battery as a predetermined period of 2 years or 3 years. The items constituting the standard use conditions are summarized in the charge voltage, the battery temperature, and the number of cycles, but the charge voltage and the battery temperature are particularly important in a lithium ion battery having a positive electrode of cobalt-based lithium. It is generally known that if the charging voltage is lowered, the lifetime will be longer. However, if the charging voltage is lowered, the battery will not be charged up to its full charge capacity, and the amount of electricity available for discharge will decrease, so the lifetime is not guaranteed. The charging voltage has been 4.2V so far. Here, the ratio of the amount of electricity actually stored in the battery with respect to the full charge capacity is referred to as RSOC (%) (Relative State Of Charge).

  The charging voltage corresponds to the voltage applied to each battery cell during charging in the constant voltage region in the constant current / constant voltage charging. When the charging voltage is set to 4.2 V, it is difficult to satisfy the life span of 3 years even if the battery temperature and the number of cycles are within the range of the standard use conditions. Therefore, in this embodiment, the initial charging voltage is 4 as an example. Set to 1V. The standard use conditions are 4.1 V as the charging voltage, 25 degrees as the battery temperature averaged over time, and 800 times as the total number of cycles during the lifetime. The rated capacity of the battery is defined by RSOC (%) when charged at 4.1V. In this embodiment, the full charge capacity ratio at the end tf of 3 years, which is the lifetime, is set to be 60% or more. However, other values may be employed for the full charge capacity ratio and the life period at the end tf of the life period.

  The battery temperature is a temperature obtained by averaging the values measured on the surface of the battery cell when the lithium ion battery is being charged, discharged, or opened from the charge / discharge circuit. is there. However, for safety reasons, when the battery temperature exceeds a predetermined value, charging is limited. In that case, measurement is performed in either a discharging state or an open state. Line 11 shows the secular change of the full charge capacity ratio under the standard use condition, and shows that the lifetime is guaranteed. Line 13 shows the secular change of the full charge capacity ratio when the battery temperature is 40 degrees and the battery voltage is 4.1 V, indicating that the lifetime cannot be guaranteed. Line 15 shows the secular change of the full charge capacity ratio when the battery temperature is 60 degrees and the battery voltage is 4.1 V. In this use state, the lithium ion battery reaches the end of its life at time tx. Yes.

  A line 17 indicated by a dotted line shows the secular change of the full charge capacity ratio when the charge voltage is lowered from the initial charge voltage to 4.05 V at time t1. When the full charge capacity ratio of the line 15 at the time t1 is smaller than the full charge capacity ratio of the line 11, the deterioration has progressed more than when used under the standard use conditions. Even if used under operating conditions, the lifetime cannot be guaranteed. In lithium-ion batteries that use cobalt-based lithium as the positive electrode, experiments show that if the battery voltage is lowered to about 4.05 V or less, even if the battery temperature is high, the subsequent storage degradation progresses less than in the standard operating conditions. I know.

  Therefore, in the present embodiment, when it is found that the capacity deterioration has progressed by a predetermined amount or more than in the standard use condition using the above characteristics, the storage voltage is deteriorated by lowering the subsequent charging voltage. Suppresses and guarantees the lifetime. A charging voltage (4.05 V) after time t1 in the line 17 is referred to as a deterioration suppression voltage, and a time t1 at which the charging voltage is changed is referred to as a charging voltage switching timing. It can be said that the deterioration suppression voltage is a charging voltage that can suppress the progress of storage deterioration even at the maximum environmental temperature allowed for the electric device on which the lithium ion battery is mounted, compared to the case of the standard use state.

[Charging system]
FIG. 2 is a functional block diagram of a basic charging system according to the present embodiment. The charging system 50 can be mounted on electric devices such as electric devices, information devices, electric tools, and automobiles. The DC power supply 51 supplies DC voltage power to the charger 55 and the load 65. The DC power source 51 does not have to be part of the constant charging system 50 and can be charged, and may be connected to the switch 53 only when the lithium ion battery 57 needs to be charged. The charger 55 performs switching control on the DC voltage supplied from the DC power supply 51 to convert it to a predetermined DC voltage, and charges the lithium ion battery 57 by constant current / constant voltage control. The charger 55 detects the voltage supplied by the DC power supply 51 and notifies the charging control circuit 61 that the DC power supply 51 is connected. The lithium ion battery 57 employs cobalt-based lithium for the positive electrode.

  The current measuring circuit 54 measures the charging current or discharging current flowing through the lithium ion battery 57 and sends the value to the charging control circuit 61. The voltage measurement circuit 56 measures the voltage of the battery cell constituting the lithium ion battery 57 and sends it to the charge control circuit 61. The temperature measurement circuit 59 measures the surface temperature of the lithium ion battery 57 and sends it to the charge control circuit 61.

  The charge control circuit 61 controls the operation of the charger 55 based on data received from the current measurement circuit 54, the voltage measurement circuit 56 and the temperature measurement circuit 59. The charging control circuit 61 sets the charging voltage when operating in the constant voltage region and the charging current when operating in the constant current region in the charger 55. The charge control circuit 61 counts the number of cycles executed since the start of use of the lithium ion battery 57 based on the data received from the current measurement circuit 54. The charge control circuit 61 measures the elapsed time after starting to use the lithium ion battery 57.

  The charge control circuit 61 confirms that a voltage is applied to the charger 55 every predetermined number of cycles or every predetermined elapsed time, and then forces the lithium ion battery 57 to the end-of-discharge voltage or the vicinity thereof. The full charge capacity is calculated from the total amount of electricity when the battery is discharged until the end of charge current. The charge control circuit 61 measures the deterioration characteristic value related to the deterioration amount of the lithium ion battery 57 to determine that the switching time has come, and changes the charging voltage set in the charger 55. The charge control circuit 61 measures the time during which the deterioration promoting state in which the battery voltage is equal to or higher than the predetermined value and the battery temperature is equal to or higher than the predetermined value, and the accumulated time as the deterioration characteristic value. The deterioration promotion state and its duration are used to determine the switching time or the forced discharge time.

  The charge control circuit 61 includes an EEPROM 62. In the EEPROM 62, data such as specific information relating to charging / discharging of the lithium ion battery 57, a threshold value of the deterioration characteristic value, the number of accumulated cycles, and elapsed time are written. The charging control circuit 61 recognizes that the DC power source 51 is connected to the switch 53 through the charger 55. The load 65 operates by receiving power from the lithium ion battery 57 or the DC power source 51.

[Deterioration characteristic value]
Next, the deterioration characteristic value of the lithium ion battery 57 will be described. If a lithium ion battery is used outside the standard usage conditions, the capacity will deteriorate more than expected when the lifetime is guaranteed, and the predetermined lifetime cannot be guaranteed. In the present embodiment, the deterioration characteristic value of the lithium ion battery 57 is measured every predetermined time or every predetermined number of cycles after the start of use, and the degree of deterioration is judged to change the charging voltage when necessary. To do. Alternatively, the charging voltage is changed when it is determined that the deterioration characteristic value has reached the threshold value after the start of use. The deterioration characteristic value can be a deterioration amount related to the magnitude of capacity deterioration of the lithium ion battery 57. The deterioration characteristic value can be expressed as a ratio of the deterioration value after the start of use to the deterioration value at the start of use. The full charge capacity ratio is a deterioration characteristic value indicating direct capacity deterioration when the amount of deterioration at the start of use is zero.

  There is a correlation between the full charge capacity and the internal impedance of the battery cell. Further, the change value of the battery voltage per unit capacity when discharged (hereinafter referred to as the capacity voltage change rate (ΔV / ΔC)) is also correlated with the full charge capacity. As the full charge capacity decreases, the internal impedance rises and the capacity voltage change rate also rises. Therefore, the ratio of the internal impedance ratio or the capacity voltage change rate is calculated as a ratio to each initial value, and the full charge capacity is calculated. Instead of the ratio, they can be adopted as deterioration characteristic values. The ratio between the internal impedance ratio and the capacity voltage change rate can also be used as a value that decreases with elapsed time in the same manner as the full charge capacity ratio by using the reciprocal.

  As the deterioration characteristic value of the lithium-ion battery 57, information related to a factor that causes deterioration can be adopted in addition to the deterioration amount directly indicating the degree of deterioration of the battery. Lithium-ion battery 57 undergoes severe capacity deterioration when the battery temperature is at or above a predetermined value and the battery voltage is at or above a predetermined value. Therefore, the continuation time or accumulated time in which the lithium ion battery 57 is in a deterioration promoting state defined by a predetermined battery temperature and a predetermined battery voltage in advance can be adopted as the deterioration characteristic value.

[Lifetime warranty]
Next, a method for guaranteeing the lifetime by selecting the full charge capacity ratio as the deterioration characteristic value will be described with reference to FIG. The line 21 in FIG. 3 shows the full charge capacity when used under standard operating conditions (battery temperature 25 degrees, battery voltage 4.1 V) to guarantee a full charge capacity ratio of 60% or more at the end tf of the lifetime. It shows the aging of the ratio. Line 23-1 shows the secular change of the full charge capacity ratio when the battery temperature is 60 degrees and the battery voltage is lowered to 4.05V. The line 23-2 is obtained by translating the line 23-1 downward so that the full charge capacity ratio at the end tf of the lifespan coincides with that of the line 21.

  Line 25-1 shows the change of the full charge capacity ratio when the battery voltage is 4.1V and the battery temperature is 60 degrees, and line 25-2 is the full charge when the battery voltage is 4.1V and the battery temperature is 55 degrees. It shows the secular change of capacity ratio. When the battery temperature exceeds 55 ° C., charging to the lithium ion battery is prohibited, so the lines 23-1, 25-1, and 25-2 are not in a state where the lithium ion battery 57 is in a state other than charging. It is a characteristic when it is. At the time t1, the full charge capacity ratio is C1% under the standard usage conditions indicated by the line 21, but when the battery temperature indicated by the line 25-1 is 60 degrees, it is reduced to C2%.

  However, if the charge voltage is changed to 4.05 V, which is the deterioration suppression voltage, at time t1, the capacity decreases according to the line 23-2, so that the full charge capacity ratio of 60% is maintained at the end tf of the lifetime. Can do. Although the lifetime can be satisfied by changing the charging voltage to the deterioration suppressing voltage before time t1, it is desirable to change the charging voltage at time t1 because the amount of electricity that can be stored decreases when charging with the deterioration suppressing voltage. In addition, when the capacity decreases according to the line 25-1, if the charging voltage is changed to the deterioration suppression voltage after the time t1 has elapsed, the line 23-2 further shifts downward and the lifetime is satisfied. become unable.

  At the time t2, the full charge capacity ratio is C3% under the standard usage conditions indicated by the line 21, but when the battery temperature indicated by the line 25-2 is 55 degrees, it is reduced to C4%. However, when the charge voltage is changed to 4.05 V, which is the deterioration suppression voltage, at time t2, the capacity decreases according to the line 23-2, so that the full charge capacity ratio of 60% may be satisfied at the end tf of the lifetime. it can. Although the lifetime can be satisfied by changing the charging voltage to the deterioration suppressing voltage before time t2, the amount of electricity that can be stored is reduced when charging with the deterioration suppressing voltage as in the case of the line 25-1. When it deteriorates at -2, it is desirable to switch at time t2. From these facts, it can be seen that the optimum switching time can be determined as the time when the full charge capacity ratio is reduced to the line 23-2 at each time.

  When the internal impedance ratio or the capacity voltage change rate ratio is adopted as the deterioration characteristic value, the relationship between these values and the full charge capacity is obtained in advance by experiments. As in the case of the full charge capacity ratio, it is possible to determine the switching time by experimentally determining the secular change when using each value under the standard use condition and the secular change when charging with the deterioration suppression voltage.

  When the duration of the deterioration promotion state defined by the battery temperature and the battery voltage is adopted as the deterioration characteristic value, the threshold value as the accumulation time of the deterioration promotion state is determined so that the full charge capacity ratio approaches the line 23-2. Thus, the optimum switching time can be determined. FIG. 4 is a diagram for explaining a method of determining a cumulative time threshold value for guaranteeing the lifetime when the deterioration promotion state duration is selected as the deterioration characteristic value. The line 23-2 in FIG. 4 is the same as that described in FIG. The deterioration promoting state can be set, for example, such that the battery temperature is 45 degrees or higher and the battery voltage is 4.1 V or higher.

  The deterioration promoting state may occur continuously or intermittently depending on the usage environment of the lithium ion battery 57. Therefore, the elapsed time when the deterioration promoting state reaches a predetermined cumulative time varies depending on the use environment. As indicated by the line 23-2, the amount of deterioration that can be permitted for the guarantee of the lifetime increases as the elapsed time increases. Therefore, if the full charge capacity ratio corresponding to the threshold for the accumulated time is the line 23-2, the threshold can be increased as the elapsed time is longer.

  For example, the deterioration amount Δ1 can be allowed at time t1, and the deterioration amount Δ2 (Δ2> Δ1) can be allowed at time t2. Therefore, the threshold for the accumulated time in the deterioration promotion state may be determined as a function of the elapsed time. As an example, in the case where the deterioration promotion state occurs continuously, the threshold of the accumulated time when the elapsed time t1 is 2400 hours is 2400 hours, and the threshold of the accumulated time when the elapsed time t2 is 12000 hours is 3000 hours. It is desirable to set the threshold value so that the full charge capacity ratio is as close as possible to the line 23-2 at each elapsed time.

  When the duration of the deterioration promoting state is adopted as the deterioration characteristic value, it is easy to realize because it is only necessary to calculate the battery temperature, the battery voltage, and the accumulated time, and it is not necessary to measure the amount of deterioration. Further, the switching time may be determined by setting a plurality of deterioration amounts and deterioration promoting states and performing an operation such as logical sum or logical product on the relationship between the deterioration amount and the threshold value. For example, the deterioration configured by each battery temperature set by switching the charging voltage when the full charge capacity ratio and the cumulative time of the deterioration promotion state both reach the threshold, or by setting multiple battery temperatures constituting the deterioration promotion state It is possible to perform a logical operation between the acceleration state and the deterioration amount to determine the switching time.

[Procedure for guaranteeing the lifetime]
Next, a procedure for assuring the lifetime of the lithium ion battery 57 based on the deterioration characteristic value in the charging system 50 will be described with reference to the flowchart of FIG. Blocks 101 to 105 show a procedure for obtaining a threshold value to be applied to the deterioration characteristic value in order to determine the switching timing and storing it in the EEPROM 62 of the charging control circuit 61. Blocks 107 to 121 show the actual charging system 50. The operation procedure is shown. In block 101, experimental data relating to the deterioration with time of the deterioration characteristic value when the battery voltage as indicated by the line 23-1 in FIG. The battery temperature during the experiment is assumed to be the maximum temperature that can be predicted within the range allowed for the electric device in which the lithium ion battery 57 is mounted.

  In block 103, the end of the life period tf, the initial charging voltage, and the battery temperature are set, and experimental data of deterioration characteristic values under standard use conditions as shown in the line 21 of FIG. 3 are acquired. In block 105, the experimental data is modified so that the deterioration characteristic value at the end of life of the experimental data acquired in block 101 matches the deterioration characteristic value at the end of life of the experimental data acquired in block 103, and line 23- in FIG. The correction data as shown in 2 is acquired. When the deterioration amount is selected as the deterioration characteristic value, the correction data becomes a threshold for determining the switching time. When the deterioration promoting state duration is selected as the deterioration characteristic value, a threshold for the accumulated time is set based on the procedure shown in FIG. The correction data and the accumulated time threshold value are stored in the EEPROM 62 of the charge control circuit 61.

  In block 107, use of the lithium ion battery 57 is started. The switch 53 is normally on. The charging control circuit 61 sets an initial charging voltage (4.1 V) and charging current in the charger 55. When the DC power supply 51 is connected to the switch 53, the charger 55 detects the voltage, and the charge control circuit 61 recognizes it and turns off the switch 63. When power is supplied from the DC power source 51 to the load 65 and the voltage measurement circuit 56 detects a battery voltage that has been reduced to the charge start voltage due to natural discharge, the charge control circuit 61 operates the charger 55 to start charging. The charging control circuit 61 stops the operation of the charger 55 when it is determined that the charging current measured by the current measuring circuit 54 has reached the charging end current.

  When the DC power supply 51 is stopped or disconnected from the switch 53, the charge control circuit 61 turns on the switch 63 to supply power from the lithium ion battery 57 to the load 65. Next, when recognizing that the DC power supply 51 is connected, the charge control circuit 61 operates the charger 55 to start charging, and supplies power from the DC power supply 51 to the load 65. The operation of the charging system 50 continues in such a series of cycles.

  In block 109, the charging control circuit 61 performs predetermined time intervals or predetermined cycles based on the battery temperature measured by the temperature measuring circuit 59, the battery voltage measured by the voltage measuring circuit 56, and the charging current measured by the current measuring circuit 54. Measure the degradation characteristics for each number. In block 111, the charge control circuit 61 determines whether or not the lithium ion battery 57 is in a deterioration promoting state that requires forced discharge.

  Forced discharge is an operation in which when the lithium-ion battery 57 has been in a state of accelerated deterioration with a high battery temperature and battery voltage for a predetermined period of time, the charge is once discharged through the load 65 to lower the battery voltage and release from the accelerated state of deterioration. is there. Forced discharge coincides with the operation of switching the charging voltage in order to suppress deterioration, but is different in that it is temporarily performed when it is determined that deterioration is extremely likely to proceed. As an example of the determination of the necessity of forced discharge, the duration of the deterioration promotion state defined by the battery temperature of 60 ° C. or more and the battery voltage of 4.1 V or more is adopted as the deterioration characteristic value, Set two consecutive hours.

  When the charge control circuit 61 confirms that the DC power supply 51 is connected and further confirms that the deterioration promoting state for forced discharge has reached the threshold value, the charge control circuit 61 turns off the switch 53 and turns off the switch 63 in block 113. The battery is turned on to forcibly discharge the lithium ion battery 57 through the load 65 to lower the battery voltage. Discharging is performed such that the battery voltage is larger than the voltage at which charging is started, for example, up to about 3.75V. After the forced discharge is completed, the charging control circuit 61 supplies power to the load 65 from the DC power supply 51 by turning on the switch 53 and turning off the switch 63. Thereafter, charging is resumed by the charger 55 when the battery voltage drops to the charging start voltage by natural discharge. By setting the voltage to stop the discharge so that the time until recharging is a relatively long time such as one week to two weeks, the lithium ion battery 57 is released from the deterioration promotion state during that time. Forced discharge is particularly suitable for suppressing deterioration in a charging system in which the DC power supply 51 is always connected and the lithium ion battery 57 is maintained in a fully charged state.

  In block 115, when the deterioration amount is adopted as the deterioration measurement value, the charging control circuit 61 determines whether or not the deterioration characteristic value has reached a threshold value for determining the switching timing for every predetermined number of cycles or for a predetermined elapsed time. Judge every. At this time, the charge control circuit 61 determines whether or not the deterioration amount has reached the correction data acquired in the block 105 and stored in the EEPROM 105. When the deterioration promotion state is adopted as the deterioration characteristic value, the charging control circuit 61 determines whether or not the accumulated time of the deterioration promotion state for determining the switching time has reached the threshold value stored in the EEPROM 62. In any case, when it is determined that the threshold has been reached, the process proceeds to block 117, and when it is determined that the threshold has not been reached, the process returns to block 109.

  In block 117, the charging control circuit 61 sets a deterioration suppression voltage (4.05 V) in the charger 55. In block 119, the charging control circuit 61 determines whether or not the elapsed time has reached the end tf of the lifetime, and if it has reached the end, the procedure for guaranteeing the lifetime is ended in block 121. If the end has not been reached, return to block 109. In this procedure, the charging voltage is switched only once in block 117, but the deterioration suppression voltage may be set in a step shape and changed twice or more based on the deterioration characteristic value. In addition, the procedure for guaranteeing the lifetime is explained by taking as an example a lithium ion battery in which the positive electrode is formed of a cobalt-based lithium material, but the present invention mainly uses the battery temperature and the battery voltage as the lifetime. The present invention can also be applied to other types of secondary batteries in which storage degradation is dominant.

[Application to notebook PC]
The charging system according to the present invention can be applied to a notebook PC. FIG. 6 is a functional block diagram showing an outline of a charging system including a battery pack and a notebook PC on which the battery pack is mounted. The charging system includes a notebook PC 200, an AC adapter 201, and a battery pack 300. The notebook PC 200 shows only the part related to the charging system.

  The battery pack 300 conforms to the standard of the smart battery system (SBS) and is detachably attached to the casing of the notebook PC 200. The AC adapter 201 converts an AC voltage into a DC voltage and is connected to a power supply terminal of the notebook PC 200. The charger 209 has constant current and constant voltage characteristics. The charger 209 includes a switching control circuit that performs on / off control of the input voltage by a PWM method, and a smoothing circuit. The charger 209 converts the DC voltage input from the AC adapter 201 into a DC voltage suitable for charging the battery pack 300 and outputs the DC voltage. The charger 209 includes a feedback circuit for making the output current or output voltage coincide with the set charging current or charging voltage. The charger 209 operates so that the output voltage matches the charging voltage during the constant voltage control period. Further, the charger 209 operates so that the output current matches the charging current during the constant current control period.

  A charging voltage and a charging current are set in the charger 209 by an embedded controller (EC) 211. The charger 209 operates so that the output voltage does not exceed the charging voltage and the output current does not exceed the charging current. Therefore, the charger 209 operates at constant current control so that the output current matches the charging current in the initial stage of charging, but the constant voltage is set so that the output voltage matches the charging voltage when charging proceeds and the charging voltage rises. Operates with control.

  The EC 211 is an integrated circuit that controls many hardware elements constituting the notebook PC 200 in addition to the power supply. The EC 211 communicates with the battery pack 300 to acquire information such as the surface temperature of the battery generated by the battery pack 300, the battery voltage, the charging current, the remaining capacity, the full charge capacity, and the charging voltage and charging current set in the charger. can do. Based on the instruction received from the battery pack 300, the EC 211 operates or stops the charger 209.

  The DC / DC converter 215 converts the DC voltage received from the AC adapter 201 or the battery pack 300 into a predetermined DC voltage and supplies power to the system load in the notebook PC 200. The system load includes various devices such as a CPU, a liquid crystal display, a wireless module, a hard disk device, and a controller. The FET 205 and the FET 207 are switches for controlling charging / discharging of the battery pack 300, and are connected to the charging / discharging circuit of the battery pack 300.

  The FET 208 is connected between the battery pack 300 and the DC / DC converter 215 and is a switch for forming a discharge circuit from the battery pack 300 to the DC / DC converter 215. The FET 203 is connected to a circuit that supplies power from the AC adapter 201 to the DC / DC converter 215. When power is being supplied from the AC / DC adapter 201 to the DC / DC converter 215, the FET 203 is temporarily turned off when the battery enters a deterioration promoting state, and power is supplied from the battery pack 300 to the DC / DC converter 215. It can be supplied and forcedly discharged. The FET drive circuit 213 controls the FETs 203, 205, 207 and 208 based on an instruction from the EC 211.

[Battery pack]
FIG. 7 is a functional block diagram showing an internal configuration of the battery pack 300 compliant with the smart battery system (SBS) standard. In the battery pack 300, a power line 301, a communication line 303, and a ground line 305 are connected to the notebook PC 200 through a P terminal, a D terminal, and a G terminal, respectively. A charge protection switch 307 and a discharge protection switch 309 each made of a p-type MOS-FET are connected to the power supply line 301 in series. A positive electrode of a battery set 317 composed of three lithium ion battery cells 311, 313, and 315 is connected to the discharge protection switch 309 in series. A discharging current from the battery set 317 and a charging current for the battery set 317 flow between the notebook PC 200 through a charging / discharging circuit including a power supply line 301 and a ground line 305.

  The voltage side terminals of the battery cells 311 to 315 constituting the battery set 317 are connected to the analog input V1 to V3 terminals of the analog / interface 319. One to a plurality of temperature elements 321 such as a thermistor are attached to the surface of the battery set 317. The temperature element 321 measures the surface temperature of the battery cells 311 to 315 and outputs it to the T terminal of the MPU 323. The surface temperature may be measured by either a contact type in which the sensor is brought into contact with the casing of the battery cells 311 to 315 or a non-contact type in which the sensor is separated from the casing. A current sense resistor 325 is connected to the ground line 305 between the negative terminal and the G terminal of the battery cell 315. Both ends of the current sense resistor 325 are connected to the I1 and I2 terminals of the analog / interface 319.

  The analog / interface 319 includes analog input terminals V1, V2, and V3 that acquire respective cell voltages of the battery cells 311 to 315, and analog input terminals I1 and I2 that detect a potential difference between both ends of the current sense resistor 325. The analog / interface 319 further includes analog output terminals C-CTL and D-CTL that output signals for controlling on / off of the charge protection switch 307 and the discharge protection switch 309. The analog / interface 319 measures the cell voltage of the battery set 317, converts it into a digital value, and sends it to the MPU 323.

  The analog / interface 319 measures the values of the charging current and discharging current flowing through the battery set 317 from the voltage detected by the current sense resistor 325, converts them into digital values, and sends them to the MPU 323. The MPU 323 is an integrated circuit provided with a RAM of about 8 to 16 bits, a RAM, a ROM, a flash memory, a timer, and the like in one package. The MPU 323 can communicate with the analog / interface 319, calculates the amount of charged electricity and the amount of discharged electricity based on the voltage and current relating to the battery set 106 sent from the analog / interface 319, and further compares the full charge capacity ratio. Is calculated and stored in the flash memory.

  The MPU 323 also has an overcurrent protection function, an overvoltage protection function (also referred to as an overcharge protection function), and a low voltage protection function (also referred to as an overdischarge protection function), from the voltage and current received from the analog / interface 319. When an abnormality is detected in the battery cells 311 to 315, the charge protection switch 307 and / or the discharge protection switch 309 are turned off through the analog / interface 319. The overcurrent protection function, the overvoltage protection function, and the low voltage protection function are configured by a program executed by the MPU 323.

  From the MPU 323, the communication line 303 is connected to the EC 211 of the notebook PC 200 through the D terminal to enable communication. The communication line 303 includes a clock line. The MPU 323 sends a charging current and a charging voltage set in the charger 209 to the EC 211. When the MPU 323 stores the charging voltage and charging current data in the register, the data is transferred by the EC 211 periodically reading it. The EC 211 sets this set value in the charger 209 via a reference voltage source (not shown), and starts or stops the operation of the charger 209.

  The MPU 323 stores a threshold for switching the charging voltage and a threshold for determining the necessity of forced discharge in the method described in the procedure of FIG. The MPU 323 calculates the number of cycles after the start of use and the elapsed time and stores the data in the ROM. The MPU 323 determines whether or not the deterioration promoting state for switching the charging voltage or forcibly discharging the charger 209 has reached the threshold based on the surface temperature of the battery set 317 and the cell voltage. The MPU 323 determines whether or not the deterioration amount has reached a threshold value.

  Although the present invention has been described with the specific embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and is known so far as long as the effects of the present invention are achieved. It goes without saying that any configuration can be adopted.

50 ... Charging system 200 ... Notebook PC charging system 300 ... Battery pack

Claims (15)

A rechargeable battery charging system,
A charger for charging the secondary battery;
A measurement circuit for measuring a deterioration characteristic value related to the magnitude of capacity deterioration of the secondary battery;
When it is determined that the deterioration characteristic value has reached a threshold value when a predetermined time has elapsed while repeating a charging / discharging cycle including a charging period and a discharging period by the charger in which the first charging voltage value is set A charging system comprising: a charging control circuit that sets a second charging voltage value lower than the first charging voltage value in the charger.   The charging system according to claim 1, wherein the secondary battery is a lithium ion battery having a positive electrode formed of cobalt-based lithium.   The charging system according to claim 1 or 2, wherein the first charging voltage value is a charging voltage value under a standard use condition set to guarantee the lifetime.   4. The method according to claim 1, wherein the deterioration characteristic value includes a cumulative time of a first deterioration promotion state in which a battery temperature of the secondary battery is equal to or higher than a first temperature value and a battery voltage is equal to or higher than a predetermined value. The charging system according to Crab.   The charging system according to any one of claims 1 to 4, wherein the deterioration characteristic value includes a deterioration amount indicating a degree of deterioration of the secondary battery.   The deterioration amount is any one selected from the group consisting of a full charge capacity of the secondary battery, an internal impedance of the secondary battery, and a change value of the battery voltage per unit capacity when the secondary battery is discharged. The charging system according to claim 5, wherein the charging system is set based on one or a plurality of combinations.   The charge control circuit charges the secondary battery when a second deterioration promotion state in which the battery temperature of the secondary battery is equal to or higher than a second temperature value and the battery voltage is equal to or higher than a predetermined value continues for a predetermined time. The charging system according to claim 1, wherein the charging system is discharged to a predetermined voltage higher than the start voltage.   The charging system according to claim 7, wherein the second temperature value is higher than the first temperature value.   An electric device equipped with the charging system according to any one of claims 1 to 8. A battery pack that can be attached to an electrical device equipped with a charger,
A secondary battery charged by the charger;
A measurement circuit for measuring a deterioration characteristic value related to the magnitude of capacity deterioration of the secondary battery;
A communication circuit for communicating with the electrical device;
The deterioration characteristic value when a predetermined time has elapsed while repeating a charging / discharging cycle including a charging period and a discharging period of the secondary voltage by the charger in which the first charging voltage value is set has reached a threshold value A battery pack comprising: a processor that sets a second charging voltage value lower than the first charging voltage value in the charger through the communication circuit when determined. A portable computer with a charger,
A system load receiving power from an AC adapter or a secondary battery; and
A measurement circuit for measuring a deterioration characteristic value related to the magnitude of capacity deterioration of the secondary battery;
It is determined that the deterioration characteristic value has reached a threshold value when a predetermined time has elapsed while repeating a charging / discharging cycle including a charging period by the charger set with a first charging voltage value and a discharging period by the system load. And a controller that sets a second charging voltage value lower than the first charging voltage value in the charger. A method for guaranteeing the lifetime of a secondary battery by controlling the operation of a charger in a charging system,
Providing a threshold for changing a charging voltage set in the charger based on a deterioration characteristic value associated with a decrease in the full charge capacity of the secondary battery;
Setting a first charging voltage value in the charger and repeating a charge / discharge cycle;
Determining whether or not the deterioration characteristic value at the time when a predetermined time has elapsed from the start of use has reached the threshold;
And a step of setting a second charging voltage value lower than the first charging voltage value in the charger and repeating a charging / discharging cycle when the deterioration characteristic value reaches the threshold value.   The method according to claim 12, wherein the first charging voltage value is selected so that the lifetime can be guaranteed when a battery temperature of the secondary battery is a standard temperature.   Even if the battery temperature is higher than the standard temperature, the second charge voltage value is higher than the full charge capacity than when the first charge voltage is set in the charger and the charge / discharge cycle is repeated. 14. The method of claim 13, wherein the method is selected to reduce degradation. Lowering the battery voltage when a deterioration promoting state in which the battery temperature of the secondary battery is equal to or higher than a predetermined value and the battery voltage is equal to or higher than a predetermined value continues for a predetermined time;
The method according to claim 12, further comprising a step of spontaneously discharging the secondary battery until charging starts after the battery voltage decreases.

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