JP3456710B2 - Power system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a power supply system including a non-aqueous electrolyte secondary battery and a charging device for the same.

[0002]

2. Description of the Related Art In recent years, portable and cordless electronic devices such as AV devices and personal computers have been rapidly developed, and there has been a demand for a secondary battery having a small size, a light weight and a high energy density as a power source for driving these devices. high.
In this respect, there are great expectations for lithium secondary batteries,
Recently, non-aqueous secondary batteries having a negative electrode made of lithium, a lithium alloy, or a carbonaceous material capable of intercalating and deintercalating lithium have been put into practical use.

Further, regarding the commercialization thereof, a conventional sealed nickel-cadmium storage battery (hereinafter referred to as "nicad battery")
It is required to secure the safety of the battery including the charging device as well as the short-time charging (rapid charging).

However, for example, a non-aqueous secondary battery having a negative electrode made of lithium, a lithium alloy, a carbonaceous material or the like has excellent charging efficiency when charged at a constant current. Since there is no internal gas absorption mechanism, the gas generated by the decomposition of the electrolytic solution accumulates in the battery when it becomes overcharged, the internal pressure rises and the liquid may leak, or it may cause an explosion if charging is continued. .

In order to avoid such troubles at the time of charging, the non-aqueous electrolyte secondary battery is charged by a voltage-controlled charging method in which the charging current is cut off when a predetermined charging voltage is reached. By using a sensor together, the charging current is cut off when the battery heats above a predetermined temperature to prevent the battery from being overcharged.

Further, in order to carry out quick charging within 1 to 2 hours, a voltage control type capable of flowing a charging current of 0.5 CmA to 2.0 CmA (C; an unnamed number indicating the rated capacity of the battery) or more. A charging device is required, and a power supply block (see later) having a higher current capacity is used in consideration of stability. Therefore, if an excessive current flows through the circuit or battery due to an external short circuit or the like, the charging device or battery may generate heat, or may ignite or explode. However, since a protective element such as a fuse or PTC is incorporated, such troubles may occur. Even if it occurs, the excessive current does not usually exceed 10 CmA.

FIG. 1 shows an example of a basic circuit of a voltage-controlled power supply system. The conventional power supply system includes a battery 1 and a charging device 2, and the charging device 2 includes a power supply block 3 and a voltage control circuit 4. The power supply block 3 is composed of a step-down transformer 3a, a diode bridge 3b such as a silicon diode, and a smoothing capacitor 3c, and is converted into a DC voltage Vdc (normally 12 to 50V). The voltage control circuit 4 includes a power transistor 4a, a reference voltage generation unit (zener diode) 4b that applies a reference voltage to the base B of the transistor, and a resistor 4c.
A charge control voltage Vc (for example, 4 V / cell) is applied to the battery 1. By controlling the voltage using such a circuit, the battery 1 is prevented from being overcharged.

[0008]

However, when the voltage control circuit fails for some reason, for example, in the power transistor 4a in FIG. 1, when the connector C and the emitter E are short-circuited, the battery is fully charged. However, there was a problem that the charging current did not stop and the battery became overcharged and exploded.

According to the results of studies conducted by the present inventors, it has been found that the cause of such an explosion reaction is that an explosion occurs due to the phenomenon described below.

When the battery is overcharged, the battery voltage rises, and the internal resistance of the battery rises due to decomposition of the electrolytic solution, electric leakage, and the like. If the internal resistance rises, the battery temperature rises due to Joule heat, and the battery temperature rises to the melting point of the separator, which melts the separator and blocks the micropores, which prevents the ions in the battery from moving, causing the internal temperature to rise rapidly. The resistance rises significantly and the charging current decreases significantly. At this point, if the charging device and the battery are disconnected, the battery temperature drops and no abnormality other than the liquid leakage occurs.

However, if the charging voltage is not suppressed to a predetermined value due to a failure of the voltage control circuit and the charging is further continued, the battery voltage rises rapidly following the heat generation of the battery, and the battery container bursts and ignites. There were many things that led to (explosion).

This is because when a high voltage is applied to a battery having a high internal resistance value, a short circuit occurs in a part between the positive and negative electrodes and a spark is generated, and the active material or the electrolytic solution (organic solvent) is generated. , It is thought that the steam etc. are ignited.

Therefore, it is necessary to take safety measures so that the battery will not explode even if such a voltage control circuit fails.

Therefore, according to the present invention, even if the battery is overcharged due to a failure of the voltage control circuit or the like, the charging device is configured so that a high voltage is not applied to the battery itself, thereby ensuring safety. It is an object of the present invention to provide an explosion-proof non-aqueous secondary battery power supply system with improved reliability.

[0015]

In order to solve the above problems, the present invention provides a non-aqueous electrolyte secondary battery for a driving power source ,
Rapidly charge the battery with an initial current of 1C or more and 10C or less
In a power supply system including a voltage-controlled dedicated charging device, the maximum output voltage of the power supply block of the charging device is 10 V or less per battery cell even when the voltage control circuit fails .

The non-aqueous electrolyte secondary battery is generally composed of a negative electrode made of lithium metal, a lithium alloy or a carbonaceous material, and a positive electrode made of an oxide or a composite oxide mainly containing lithium and a transition metal. It is composed of an electrode plate group consisting of a separator formed of a porous synthetic resin film and an organic electrolytic solution.

[0017]

Operation When charging the non-aqueous electrolyte secondary battery, the conventional charging device is designed without any particular limitation on the DC output voltage of the power supply block, and a relatively high voltage ( 3 to 5 times the control voltage during charging, eg 12
Many were set to ~ 15V / cell).
Therefore, when the voltage control circuit fails and goes into an uncontrolled state, a high voltage is applied to the battery having increased internal resistance as described above, which causes the battery to explode.

According to the present invention having the above structure, even if the battery is overcharged due to a failure of the voltage control circuit or the like and the internal resistance of the battery increases, the high voltage is not applied to the battery. By thus preventing the high voltage from being applied to the battery, it is possible to prevent the occurrence of sparks and the explosion due to overcharge.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-aqueous electrolyte secondary battery power supply system according to a preferred embodiment of the present invention will be described below with reference to the accompanying drawings. Example 1 First, a non-aqueous electrolyte secondary battery was produced as follows.

Li ₂ CO ₃ and CoCO ₃ were mixed so that the atomic ratio of Li and Co was 1: 1 and 9 were mixed in air.
LiCoO ₂ synthesized by firing at 00 ° C for 5 hours was used as a positive electrode active material.

The positive electrode active material 100 thus synthesized
Parts by weight, acetylene black 4 parts by weight, graphite 4
By weight, 7 parts by weight of a fluororesin-based binder were mixed to prepare a positive electrode mixture, which was suspended in a carboxymethylcellulose aqueous solution to form a paste. This paste was applied to both sides of an aluminum foil, dried and rolled to obtain an electrode plate.

The negative electrode is a carbon material 100 obtained by firing coke.
10 parts by weight of a fluororesin-based binder was mixed with parts by weight and suspended in an aqueous carboxymethyl cellulose solution to form a paste. And apply this paste on both sides of the copper foil,
After drying, it was rolled into an electrode plate.

FIG. 2 shows a vertical sectional view of the cylindrical battery used in this embodiment. In FIG. 2, 11 is a battery case formed by processing an organic electrolytic solution resistant stainless steel plate, 12 is a sealing plate provided with a safety valve, and 13 is an insulating packing. The outer shape of the battery is φ14 mm, the height is 43 mm (corresponding to 4/5 AA), and the rated capacity is 500 mAh. Reference numeral 14 denotes an electrode plate group, in which the positive electrode and the negative electrode are spirally wound a plurality of times through a microporous polyethylene separator and housed in the case 11. From the positive electrode, the positive electrode lead 1
5 is drawn out and connected to the sealing plate 12, and the negative electrode lead 16 is drawn out from the negative electrode and connected to the bottom of the battery case 11. Insulating rings 17 are provided on the upper and lower portions of the electrode plate group 14, respectively. Further, as the electrolytic solution, a solution obtained by dissolving lithium perchlorate in a mixed solvent of equal volume of propylene carbonate and ethylene carbonate at a ratio of 1 mol / liter was used as a test battery.

As an exclusive charging device, based on the one shown in FIG. 1, the output voltage Vdc of the power supply block 3 is (A) 7
V, (B) 10V, (C) 12V, (D) 15V,
(E) The step-down transformer 3a, the diode bridge 3b, and the smoothing capacitor 3c are selected and configured to be 20 V, the control voltage of the voltage control circuit is 4.2 V / cell, and the initial charging current is 500 mA to 5 A (1 CmA to 10 CmA). Done 1
The time charging device 2 was manufactured.

The charging device and the test battery are combined to perform charging, and after confirming that the charging can be normally performed, the resistor 4c is removed and the power transistor 4 is removed.
Short the connector C of a and the emitter E to 0 ° C,
An overcharge test was performed in an atmosphere of 20 ° C and 45 ° C.

These batteries have a temperature of 45 ° C., 5 A (10 Cm
The behavior of the voltage and the battery temperature when the overcharge test is performed in A) is shown in FIG.

As shown in FIG. 3, the battery temperature rises as the battery is overcharged, and the power supply voltage Vdc is applied to the battery as it is when the temperature reaches the melting point of the separator (point M in the figure). When the power supply voltage Vdc is higher than 10 V as in the conventional power supply, an excessive voltage is applied to the battery as indicated by a broken line, spark is generated inside the battery, and an explosion occurs.

On the other hand, when the power supply voltage Vdc is set to 10 V or lower, as shown by the solid line in the figure, the power supply voltage Vdc is applied to the battery, but the voltage is low, so no spark occurs, Further, since the internal resistance of the battery is remarkably increased due to the blockage of the porosity due to the melting of the separator, almost no current flows and the battery temperature decreases, resulting in a safe state.

FIG. 4 shows the relationship between the overcharge current and the limit voltage at which explosion occurs. The limit voltage tends to decrease as the current value increases, and at 10 CmA, about 12 V is the limit voltage. The limit voltage may be further reduced at 10 CmA or more, but by using a protection circuit such as a fuse, the power supply system of the present invention has a limit voltage of 10 CmA.
Since no current flows, safety is ensured.

Table 1 shows each power supply voltage Vdc of (A) to (D).
At 1CmA, 2CmA, 5Cm
A shows the number of batteries that led to an explosion when 500 cells were run at 8 CmA and 10 CmA.

[0031]

[Table 1]

If the power supply voltage Vdc is 12 V or more, the probability of spark generation increases, and the battery will explode, while the power supply voltage Vdc is 10 V as shown in Table 1.
Below V, sparks do not occur because the voltage is low even if the overcharge current is 10 CmA, and the battery does not explode, thus ensuring safety.

In the overcharge test at 0 ° C. and 20 ° C., no abnormality other than battery leakage was observed at a power supply voltage Vdc of 10 V or less. Example 2 When the lithium secondary battery as shown in the present invention is used in an actual electronic device such as a camcorder, the lithium secondary battery is used as a battery pack by connecting two batteries in series. When charging with two or more cells, the parallel charging is preferable because the accuracy of voltage control decreases due to the variation in the characteristics of the battery. FIG. 5 shows an example of a circuit diagram of a charging system in a battery pack for series discharge-parallel charging. In FIG. 5, 21 is a battery pack,
Reference numeral 22 denotes a charging device, and the battery pack 21 and the charging device 22 can be removed. At the time of discharging, the battery pack 21 is removed from the charging device 22, and the switch 23 is connected to the side indicated by the dotted line, so that the series discharging occurs. On the other hand, at the time of charging, the battery pack 21 is attached to the charging device 22 as shown, and the switch 23
Can be charged in parallel by connecting to the one indicated by the solid line. With such a parallel charging circuit,
As shown in the present invention, the maximum output voltage of the charging device is 10V.
The safety of the battery can be ensured even when the pack is used as follows.

The battery capacity and form are φ20 mm,
65mm high battery with 1400mAh and 600m
An Ah prismatic battery was manufactured as a prototype, and the same tests as in Examples 1 and 2 were carried out in combination with respective dedicated 1-hour charging devices, but no deformation or explosion of the battery was observed.

In this example, a battery using a carbon material for the negative electrode was shown, but the same effect was obtained even when lithium metal or lithium alloy was used for the negative electrode. Further, in this embodiment, the polyethylene separator is used, but polypropylene or other materials may be used as well.

Further, as the electrolytic solution, a solution obtained by dissolving lithium perchlorate in an equal volume mixed solvent of propylene carbonate and ethylene carbonate at a ratio of 1 mol / liter was used, but other nonaqueous solvents and electrolytes were used. However, the same effect was obtained.

Further, LiCoO is used as the positive electrode active material.
_{Although 2} was used, similar effects can be obtained with other oxides or lithium composite oxides.

[0038]

As is apparent from the above description, the present invention
According to the non-aqueous electrolyte secondary battery for driving power source, and the battery
Voltage control to rapidly charge the battery with an initial current of 1C to 10C
In a power supply system consisting of a dedicated charging device
Even if the voltage control circuit fails,
The maximum output voltage of the power source block is 10V or less per battery cell
By setting below , even if the battery is overcharged due to failure of the voltage control circuit, etc., the explosion-proof non-aqueous secondary battery power supply system with improved safety and reliability that will not explode the battery Can be provided.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a power supply system according to an embodiment of the present invention and a conventional example.

FIG. 2 is a vertical sectional view of a cylindrical battery according to an embodiment of the present invention.

FIG. 3 is a diagram showing the voltage and temperature behavior of the battery during overcharge in the example of the present invention.

FIG. 4 is a diagram showing a relationship between an overcharge current and a limit voltage leading to an explosion in an example of the present invention.

FIG. 5 is a circuit diagram of a battery pack charging power supply system according to an embodiment of the present invention.

[Explanation of symbols]

1 battery (lithium secondary battery) 2 charger 3 power supply block 3a Step-down transformer 3b diode bridge 3c smoothing condenser 4 Voltage control circuit 4a power transistor 4b Reference voltage generator (Zener diode) 4c resistor 11 battery case 12 Seal plate 13 Insulation packing 14 electrode group 15 Positive electrode lead 16 negative lead 17 Insulation ring 21 Battery pack 22 Charger 23 Switch

Continuation of the front page (56) Reference JP-A-4-29530 (JP, A) JP-A-3-291848 (JP, A) Actually open 3-86742 (JP, U) (58) Fields investigated (Int .Cl. ⁷ , DB name) H01M 10/44 H02J ⁷ /00-7/34

Claims (2)

(57) [Claims] 1. A nonaqueous electrolyte secondary battery for driving power supply, before
A power supply system comprising a dedicated voltage-controlled charging device for rapidly charging a battery with an initial current of 1C or more and 10C or less, and the maximum power supply block of the charging device even if the voltage control circuit fails. Output voltage is 1 per battery cell
A power supply system characterized by being set to 0 V or less. 2. The non-aqueous electrolyte secondary battery comprises a negative electrode made of lithium metal, a lithium alloy or a carbonaceous material,
A positive electrode made of a composite oxide mainly composed of oxide or lithium and a transition metal, and a battery composed of an electrode plate group made of a separator formed of a microporous synthetic resin film and an organic electrolyte solution. The power supply system according to claim 1.