JPH05115129A - Overdischarge preventive device for secondary battery - Google Patents

Abstract

PURPOSE:To materialize exact overdischarge prevention of a nonaqueous secondary battery using carbon material capable of doping it with lithium ions as negative electrode active materials or dedoping the lithium ions therefrom. CONSTITUTION:The overdischarge of a nonaqueous secondary battery B using carbon material, capable of doping it with lithium ions as negative electrode active materials or dedoping the lithium ions therefrom, is prevented at the time of discharging. This is equipped with a voltage detecting circuit 2, which detects the terminal voltage E of the nonaqueous secondary battery B having dropped to a set voltage Ee of approximately 35 to 65% of full charge terminal voltage, and a power supply stop circuit 3, which stops the power supply from the nonaqueous secondary battery B to a part M supplied with power upon function of the voltage detecting circuit 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention particularly relates to preventing over-discharge of a non-aqueous secondary battery using a carbonaceous material capable of doping or de-doping lithium ions as a negative electrode active material. Regarding the device.

[0002]

2. Description of the Related Art Lead storage batteries, nickel-cadmium batteries and the like are generally known as secondary batteries.
FIG. 4 shows the discharge characteristics of the nickel-cadmium battery. As is clear from the figure, in a nickel-cadmium battery, when a constant current is passed from a fully charged state for discharging, the terminal voltage Eo of the battery gradually decreases with the passage of time, and especially at the end of discharge, It shows the characteristic of falling to. Normally, the value of the terminal voltage Eo that causes such a sharp drop is about 70% of the terminal voltage Eop at the time of full charge when a discharge current of 0.5 C is applied, for example. Lead-acid batteries also show similar discharge characteristics.

By the way, in recent years, mobile communication devices, notebook personal computers, portable video cameras,
In response to the demand for higher capacity secondary batteries due to miniaturization and weight reduction of electronic devices such as headphone stereo players, new non-aqueous secondary batteries using a carbonaceous material that can be doped or dedoped with lithium ions as a negative electrode active material have been developed. A secondary battery has also been put into practical use (see Japanese Patent Laid-Open No. 62-90863). Such a non-aqueous secondary battery has high energy density (high capacity), is excellent in lightness and safety, and has characteristics such as little characteristic variation due to temperature.

When this type of non-aqueous secondary battery is compared with a lead storage battery, a nickel-cadmium battery or the like, there are significant differences in their discharge characteristics. Therefore, when an over-discharge prevention device is attached to this type of non-aqueous secondary battery, the existing over-discharge prevention device cannot realize accurate over-discharge prevention, and a new and There has been a demand for the practical application of an optimal overdischarge prevention device.

The present invention has responded to such a request,
In particular, an object of the present invention is to provide a secondary battery over-discharge prevention device that can realize accurate over-discharge prevention for a non-aqueous secondary battery using a carbonaceous material that can be doped or dedoped with lithium ions as a negative electrode active material. To do.

[0006]

The present invention provides a secondary battery for preventing over-discharge during discharge of a non-aqueous secondary battery B using a carbonaceous material capable of doping or dedoping lithium ions as a negative electrode active material. In constructing the battery over-discharge prevention device 1, in particular, it is confirmed that the terminal voltage E of the non-aqueous secondary battery B has dropped to the set voltage Ee set to approximately 35 to 65% of the terminal voltage Ep at the time of full charge. It is characterized by comprising a voltage detection circuit 2 for detecting and a power supply stop circuit 3 for stopping the power supply from the non-aqueous secondary battery B to the power-supplied part M by the detection of the voltage detection circuit 2. It is desirable that the over-discharge prevention device 1 be provided with a current limiting circuit 4 that limits the current flowing into the voltage detection circuit 2.

[0007]

According to the secondary battery over-discharge prevention device 1 of the present invention, the set voltage Ee in the voltage detection circuit 2 is set in advance.
It is set to approximately 35 to 65% of the terminal voltage Ep when fully charged. The charge / discharge characteristics of the non-aqueous secondary battery B using a carbonaceous material capable of being doped or dedoped with lithium ions as the negative electrode active material are as shown in FIG. 2, and a constant current was applied after the battery was fully charged after charging. When the secondary battery B is discharged, the terminal voltage E of the secondary battery B is gently decreased with the passage of time, and a rapid voltage drop at the end of discharge unlike a lead storage battery or a nickel-cadmium battery does not occur. Therefore, the voltage detection point for preventing over-discharge, that is, the set voltage Ee is the terminal voltage E when fully charged.
It can be set within a range of approximately 35 to 65% of p (Z range in FIG. 2).

As a result, during discharge, the voltage detection circuit 2
Causes the terminal voltage E of the non-aqueous secondary battery B to be the set voltage E
The power supply stop circuit 3 stops the power supply of the non-aqueous secondary battery B to the power-supplied part M based on the detection of the decrease to e, and prevents the secondary battery B from being over-discharged.

In this case, if the current flowing into the voltage detecting circuit 2 is limited by the current limiting circuit 4, further discharge of the non-aqueous secondary battery B is prevented, so that the voltage detecting circuit 2 and the power supply stopping circuit 3 operate. (Function) can be continued for a long time, and malfunction of the overdischarge prevention device 1 can be avoided. In a lead-acid battery, a nickel-cadmium battery, or the like, when the discharge continues after the overdischarge prevention device 1 is activated, the terminal voltage drops rapidly to a certain value. It may become inoperable.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments according to the present invention will be described in detail with reference to the drawings.

First, a suitable secondary battery B using the overdischarge prevention device 1 according to the present invention will be described with reference to FIG.

The secondary battery B is a non-aqueous system, and in principle has a positive electrode active material Y and a negative electrode active material X with a separator S interposed therebetween, and the current collector Yp in the positive electrode active material Y is a positive (+) electrode. The current collector Xp in the negative electrode active material X becomes a negative (−) electrode.

The positive electrode active material Y is a lithium ion (L
Any substance capable of dedoping or doping i ⁺ ),
Lithium cobalt oxide, such as Li _X Co _Y M _Z O
₂ (where M is at least one metal selected from Al, In and Sn, and X, Y and Z are each 0 <X ≦
1.1, 0.5 <Y ≦ 1, and Z ≦ 0.1, respectively. ), Li _X CoO ₂ (0 <X ≦ 1), Li _X Co _Y Ni
_Z O ₂ (0 <X ≦ 1, Y + Z = 1), lithium nickel oxide such as Li _X NiO ₂ (0 <X ≦ 1), lithium manganese oxide such as Li _X MnO ₂ , Li _X Mn ₂ O
₄ (0 <X ≦ 1), LiCo _X Mn _2-X O ₄ (0 <X ≦ 0.
5), lithium chrome oxides such as Li _X Cr ₃ O ₈
(0 <X ≦ 1), LiCrO ₂ , lithium vanadium oxide, for example, Li _X V ₂ O ₅ (0 <X ≦ 1), Li _X V ₆
O ₁₃ , Li _{1 + X} V ₃ O ₈ , lithium molybdenum oxide, for example Li _X MoO ₃ , lithium molybdenum disulfide, for example Li _X MoS ₂ , lithium titanium oxide, for example,
Li _X Ti ₂ O ₄ , lithium titanium sulfide, for example, Li _X
Ti ₂ S ₂ or the like is used. Particularly preferred are lithium cobalt oxide and lithium manganese oxide.

On the other hand, the negative electrode active material X is a carbonaceous material capable of being doped or dedoped with lithium ions (Li ⁺ ), for example, graphite, pyrolytic carbon, pitch coke, needle coke, petroleum coke, organic polymer firing. The body (phenol resin, furan resin, polyacrylonitrile, etc.) is used.

The positive electrode active material Y and the negative electrode active material X are each in the form of particles and are applied to the current collectors Yp and Xp using a metal foil, respectively. Then, it is spirally wound through the separator S, further housed in the battery can K and attached with lead wires, and impregnated with the electrolyte solution L (non-aqueous) and sealed.

The electrolyte in the non-aqueous electrolyte solution L is, for example, LiClO ₄ , LiAsF ₆ , LiPF ₆ ,
LiBF ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃
Any one kind or a mixture of two or more kinds of lithium salts such as SO ₂ ) ₂ NLi is used. The solvent of the electrolyte solution L is, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-
Any one kind or a mixture of two or more kinds of methyltetrahydrofuran, 1,3-dioxolane, sulfolane, methylsulfolane, acetonitrile, propionitrile, methyl formate, ethyl formate, methyl acetate, ethyl acetate and the like is used.

Further, the separator S is polyethylene,
One or more kinds of laminating films of polyolefin such as polypropylene and the like, a single film of non-woven fabric such as polyolefin, polyester, polyamide and cellulose, or a laminating film with the above microporous film is used. A polyethylene microporous film is particularly preferable.

Next, the structure of the over-discharge preventing device 1 according to the present invention attached to such a non-aqueous secondary battery B will be described with reference to FIG.

In the figure, reference numeral 10 is a secondary battery loading section,
Positive side terminal 10p and negative side terminal 10n in the loading section 10
The non-aqueous secondary battery B is loaded in between. The secondary battery B is usually connected in series with a plurality of cells. The embodiment shows three cells Ba, Bb and Bc connected in series. Then, the positive side terminal 10p and the negative side terminal 10n are connected to the power-supplied part M via the overdischarge prevention device 1.

The over-discharge prevention device 1 is roughly divided into a voltage detection circuit 2, a power supply stopping circuit 3 and a current limiting circuit 4. First, the positive terminal 10p in the secondary battery loading unit 10
The input side of the current limiting circuit 4 is connected to the positive side line 11p connected to the
Connect to the input side of. The current limiting circuit 4 has a function of limiting the magnitude of the current flowing from the positive side line 11p to the voltage detection circuit 2 side to 0.1 to 5 μA or less. The voltage detection circuit 2 is configured to include a comparator 13 and a reference voltage source 14 and the like, and the output side of the current limiting circuit 4 is connected to the inverting input section of the comparator 13. On the other hand, comparator 1
The non-inverting input part of 3 is connected to the positive side of the reference voltage source 14, and the negative side of the reference voltage source 14 is connected to the ground line 11n connected to the negative side terminal 10n of the secondary battery loading section 10. In this case, the reference voltage source 14 is a constant voltage source using the voltage applied from the non-aqueous secondary battery B, and the set voltage Ee is set. The magnitude of the set voltage Ee is set to approximately 35 to 65% of the terminal voltage Ep at the time of full charge.

On the other hand, the output part of the comparator 13 is connected to the power supply stopping circuit 3. The power supply stop circuit 3 is a transistor Q
1 and Q2, the transistor Q2 has a positive line 11
The positive side line 11p is opened / closed by connecting to the middle of p and turning on / off the transistor Q2. The transistor Q1 is connected between the transistor Q2 and the ground line 11n, and the transistor Q1 is turned on or off to control the transistor Q2 on / off. The transistor Q
The output of the comparator 13 is connected to the gate of 1.

Next, the operation of the overdischarge prevention device 1 according to the present invention will be described with reference to FIGS. 1 and 2.

First, the terminal voltage E of the non-aqueous secondary battery B is applied to the inverting input section of the comparator 13 via the current limiting circuit 4. Since the terminal voltage E is relatively high for a while after the start of discharging after charging, it is higher than the set voltage Ee. Therefore, the "1" level is output to the output part of the comparator 13, the transistor Q1 is turned on, and therefore the transistor Q2 is also turned on, and a current flows from the non-aqueous secondary battery B to the power-supplied part M to perform power supply. .. In this case, since the current flowing through the current limiting circuit 4 is limited to 0.1 to 5 μA or less, the voltage drop is small and almost the terminal voltage Ee is applied to the inverting input section of the comparator 13.

On the other hand, the terminal voltage E decreases as the discharge progresses. When the set voltage Ee set by the reference voltage source 14 is reached, the state of the output part of the comparator 13 is inverted, that is, the "0" level is output, the transistor Q1 is turned off, and therefore the transistor Q2 is also turned off. Become. Therefore, the positive side line 11p is opened and power supply is stopped.

The embodiment has been described in detail above.
The present invention is not limited to such an embodiment,
The detailed configuration, method, numerical values, quantity, etc. can be arbitrarily changed without departing from the scope of the present invention.

[0026]

As described above, in the overdischarge prevention device for a secondary battery according to the present invention, the terminal voltage of a non-aqueous secondary battery using a carbonaceous material capable of being doped or dedoped with lithium ions as a negative electrode active material is , The terminal voltage at full charge is about 35
Since the voltage detection circuit that detects that the voltage has dropped to the set voltage set to 65% and the power supply stop circuit 3 that stops the power supply from the non-aqueous secondary battery to the power-supplied part by the detection of the voltage detection circuit, The non-aqueous secondary battery is accurately prevented from being over-discharged, and the remarkable effect of being able to realize an optimal usage state is achieved.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an overdischarge prevention device according to the present invention,

FIG. 2 is a charging / discharging characteristic diagram of a non-aqueous secondary battery provided with the overdischarge prevention device,

FIG. 3 is a principle configuration diagram of a non-aqueous secondary battery,

FIG. 4 is a discharge characteristic diagram of a conventional secondary battery for explaining background art;

[Explanation of symbols]

 1 Over-discharge prevention device 2 Voltage detection circuit 3 Power supply stop circuit 4 Current limiting circuit B Non-aqueous secondary battery E Terminal voltage Ee Set voltage M Powered part

Claims (2)

[Claims] 1. A secondary battery overdischarge prevention device for preventing overdischarge during discharge of a non-aqueous secondary battery using a carbonaceous material capable of being doped or dedoped with lithium ions as a negative electrode active material, A voltage detection circuit that detects that the terminal voltage of the non-aqueous secondary battery has dropped to a set voltage set to approximately 35 to 65% of the terminal voltage when fully charged, and a non-aqueous secondary battery that is detected by the voltage detection circuit. An over-discharge prevention device for a secondary battery, comprising a power supply stop circuit for stopping power supply from a power supply unit to a power-supplied part. 2. The over-discharge prevention device for a secondary battery according to claim 1, further comprising a current limiting circuit that limits a current flowing into the voltage detection circuit.