JP5178998B2 - Lithium secondary battery and lithium secondary battery pack - Google Patents

Description

  The present invention relates to a lithium secondary battery and a lithium secondary battery pack, and more particularly, to a lithium secondary battery and a lithium secondary battery pack excellent in overdischarge characteristics.

In recent years, electronic devices such as video cameras and headphone stereos have been remarkably improved in performance and size, and the demand for higher capacity secondary batteries serving as power sources for these electronic devices has also increased. A lithium secondary battery using a carbonaceous material as a negative electrode active material and lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material can be used for dendrite growth and lithium powder by utilizing lithium doping / dedoping. Therefore, it is possible to achieve excellent cycle life performance, and to achieve high energy density and high capacity.

  On the other hand, the above-described lithium secondary battery has a problem that charge / discharge characteristics deteriorate when overdischarged. In other words, even when the electronic device using the battery has an abnormality or when the cutoff voltage is not set for the electronic device, the open circuit voltage is not restored even when the discharge voltage is 0V. However, if the battery is charged and discharged after that, the battery capacity is remarkably reduced, and an internal short circuit is caused in some cases. Thus, the charge / discharge characteristics in the case of overdischarge to 0 V are extremely important for practical use of the secondary battery, and measures against the deterioration of the charge / discharge characteristics are indispensable.

The cause of deterioration and shortening of the service life at the time of overdischarge is that the potential of copper as the negative electrode current collector is pulled to a high positive electrode operating potential of 3.5 V (vs. Li) or more in the final stage of overdischarge. This exceeds the precipitation dissolution potential of 3.45 V (vs. Li), which causes a copper dissolution reaction.
Therefore, recently, by attaching an overdischarge protection circuit to the lithium secondary battery, if an abnormality occurs on the electronic device side, the discharge of the lithium secondary battery is stopped to minimize the decrease in battery capacity due to overdischarge. Means to suppress have been proposed. In addition, as such a protection circuit, a protection circuit having both overcharge protection and overdischarge protection functions is usually used.
Japanese Patent Laid-Open No. 9-63652

  However, in the conventional lithium secondary battery, it takes time and cost to install the overdischarge protection circuit, and it is necessary to design the overdischarge protection circuit individually depending on the electronic device to be used.

  The present invention has been made in view of the above circumstances, and includes a lithium secondary battery and a lithium secondary battery pack that prevent dissolution of the negative electrode current collector during overdischarge and eliminates the need for an overdischarge protection circuit. The purpose is to provide. Further, the present invention is applied to a battery having a design that does not require an overcharge protection circuit using an overcharge additive, a polymer electrolyte, or the like, so that a low-cost and safe lithium secondary battery and a lithium secondary battery without a protection circuit are provided. It aims at providing the next battery pack.

In order to achieve the above object, the present invention employs the following configuration.
The lithium secondary battery of the present invention conducts lithium ions, a positive electrode capable of inserting and extracting lithium, a negative electrode capable of inserting and extracting lithium bonded to a negative electrode current collector made of Cu or Cu alloy, and the like. And a Cu affinity compound having two or more functional groups and having a strong affinity for Cu or a Cu alloy is added to the electrolyte.
The Cu affinity compound includes a dinitrile compound having two nitrile groups, a trinitrile compound having three nitrile groups, a thiodialkylnitrile compound having two nitrile groups and a thioether group in the molecule. 1 type or 2 types or more can be illustrated.
In particular, the Cu affinity compound is preferably a mixture of the dinitrile compound and the trinitrile compound or a mixture of the trinitrile compound and the thiodialkylnitrile compound.

  According to the above configuration, the Cu affinity compound added to the electrolyte is accumulated at a high concentration on the surface of the negative electrode current collector. Thereby, the dissolution potential of Cu or Cu alloy constituting the negative electrode current collector is improved. For this reason, even when the lithium secondary battery reaches an overdischarged state, there is no possibility that the negative electrode current collector is dissolved, and a reduction in battery capacity can be prevented. In the present invention, a dinitrile compound having two nitrile groups in the molecule, a trinitrile compound having three nitrile groups in the molecule, and a thiodialkylnitrile having two nitrile groups and having a thioether group in the molecule Since the compound is excellent in adsorptivity to Cu or the like, the ability to prevent dissolution of Cu or the like is superior to a nitrile compound having only one nitrile group in the molecule.

Moreover, in the lithium secondary battery of this invention, it is preferable that the density | concentration of the said Cu affinity compound in the said electrolyte is the range of 0.1 to 50 mass%.
In the lithium secondary battery of the present invention, the dinitrile compound is preferably at least one of succinonitrile, glutaronitrile, and adiponitrile.
In the lithium secondary battery of the present invention, the trinitrile compound is preferably cyclohexanetricarbonitrile.
In the lithium secondary battery of the present invention, the thiodialkylnitrile compound is preferably thiodipropionitrile.

In the lithium secondary battery of the present invention, it is preferable that the electrolyte is at least one of a polymer electrolyte and a flame retardant electrolyte.
Moreover, the lithium secondary battery pack of the present invention comprises any of the lithium secondary batteries described above, and does not comprise an electronic protection circuit that controls battery charge / discharge abnormality by battery voltage detection. To do.

  According to the lithium secondary battery of the present invention, dissolution of the negative electrode current collector during overdischarge can be prevented, an overdischarge protection circuit can be dispensed with, and labor and cost for attaching the overdischarge protection circuit can be reduced. Can be reduced. In addition, according to the lithium secondary battery pack of the present invention, since an overdischarge protection circuit is not required, it is possible to realize a lightweight and high-performance battery pack that is optimal as a power source for a mobile phone.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The lithium secondary battery according to the present embodiment includes a positive electrode capable of inserting and extracting lithium, a negative electrode capable of inserting and extracting lithium by being bonded to a negative electrode current collector made of Cu or Cu alloy, and a positive electrode and a negative electrode. It comprises a separator disposed between and an electrolyte that conducts lithium ions, and a Cu affinity compound having two or more functional groups and a strong affinity for Cu or Cu alloy is added to the electrolyte. Has been configured. Specifically, a dinitrile compound, a trinitrile compound, a thiodialkylnitrile compound, or a mixture thereof is added to the electrolyte.

The positive electrode is formed by mixing a positive electrode active material powder with a binder such as polyvinylidene fluoride and a conductive additive such as carbon black, and forming the sheet into a sheet or the like. The positive electrode is bonded to the positive electrode current collector. Examples of the positive electrode current collector include metal foils or metal nets such as aluminum and stainless steel.
Further, as the positive electrode active material, at least one selected from the group consisting of a complex oxide of lithium and at least one selected from cobalt, manganese, and nickel is preferable. Specifically, LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , V ₂ O _{5 and the} like are preferable. Moreover, you may use what can occlude / release lithium, such as TiS, MoS, an organic disulfide compound, or an organic polysulfide compound.

The negative electrode is formed by mixing a negative electrode active material powder with a binder such as polyvinylidene fluoride and, if necessary, a conductive additive such as carbon black, and forming the sheet. This negative electrode is joined to the negative electrode current collector. Examples of the negative electrode current collector include a metal foil or a metal net made of Cu or a Cu alloy.
Examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, graphitized mesocarbon microbeads, and amorphous carbon. Moreover, the metal substance simple substance which can be alloyed with lithium, and the composite containing this metal substance and carbonaceous material can be illustrated as a negative electrode active material. Examples of metals that can be alloyed with lithium include Al, Si, Sn, Pb, Zn, Bi, In, Mg, Ga, and Cd. A metal lithium foil can also be used as the negative electrode active material.

  As the separator, a known separator such as a porous polypropylene film or a porous polyethylene film can be appropriately used.

  Next, the electrolyte conducts lithium ions and includes a nonaqueous solvent, a lithium salt, and a Cu affinity compound.

Of the Cu affinity compounds, the dinitrile compound has two nitrile groups in the molecule and is excellent in affinity with Cu or Cu alloy constituting the negative electrode current collector. For this reason, the dinitrile compound added to the electrolyte is accumulated at a high concentration on the surface of the negative electrode current collector. Thereby, the dissolution potential of Cu or Cu alloy constituting the negative electrode current collector is increased. For this reason, even when the lithium secondary battery reaches an overdischarged state, there is no possibility that the negative electrode current collector is dissolved, and a reduction in battery capacity can be prevented.
Similarly, among the Cu affinity compounds, the trinitrile compound has three nitrile groups in the molecule, and is superior in affinity with Cu or Cu alloy constituting the negative electrode current collector, and is added to the electrolyte. The obtained trinitrile compound is accumulated at a high concentration on the surface of the negative electrode current collector. As a result, the dissolution potential of Cu or Cu alloy constituting the negative electrode current collector increases, and even when the lithium secondary battery reaches an overdischarged state, the negative electrode current collector is not likely to be dissolved, and the battery capacity is reduced. Can be prevented.
Further, the thiodialkylnitrile compound has two nitrile groups in the molecule and a thioether group (-S-) in the molecule, and has a total of three functional groups.
This thiodialkylnitrile compound is excellent in affinity with Cu or Cu alloy constituting the negative electrode current collector, and the thiodialkylnitrile compound added to the electrolyte is accumulated at a high concentration on the surface of the negative electrode current collector, As a result, the dissolution potential of Cu or Cu alloy constituting the negative electrode current collector increases, and even when the lithium secondary battery reaches an overdischarged state, the negative electrode current collector is not likely to be dissolved, and the battery capacity is reduced. Can be prevented.

Specific examples of the dinitrile compound capable of increasing the dissolution potential include malononitrile, succinonitrile, glutaronitrile, adiponitrile, glutaronitrile, pimelonitrile, suberonitrile, azeronitrile, sebacononitrile, undecandinitrile, dodecandinitrile, 3- Examples include hexenedinitrile, phthalonitrile, isophthalonitrile, tetraphthalonitrile, methylglutarotolyl, dimethylmalononitrile, tert-butylmalononitrile, oxydipropionitrile, ethylene glycol bispropionitrile ether, and the like. Of these, succinonitrile (NC (CH ₂ ) ₂ CN), glutaronitrile (NC (CH ₂ ) ₃ CN), and adiponitrile (NC (CH ₂ ) ₄ CN) are particularly preferable.
Specific examples of the trinitrile compound include cyclohexanetricarbonitrile, triscyanoethylamine, triscyanoethoxypropane, and the like. Of these, cyclohexanetricarbonitrile is particularly preferred.
Moreover, thiodipropionitrile etc. can be illustrated as a specific example of a thiodialkyl nitrile compound.

In the present invention, a mixture of a dinitrile compound and a trinitrile compound or a mixture of a trinitrile compound and a thiodialkylnitrile compound may be added to the electrolyte.
In this case, examples of the mixture of the dinitrile compound and the trinitrile compound include a mixture of succinonitrile and cyclohexanetricarbonitrile. Moreover, as a mixture of a trinitrile compound and a thiodialkyl nitrile compound, a mixture of cyclohexanetricarbonitrile and thiodipropionitrile can be exemplified.

  In these Cu affinity compounds, the distance between the functional groups in the molecule is important, and if the distance between the functional groups in the molecule is too large, the affinity with Cu or Cu alloy is reduced, so the effect Becomes smaller. Further, if the distance between the functional groups in the molecule is too small, the affinity with lithium ions becomes larger than the affinity with Cu or Cu alloy, which causes a decrease in battery capacity. The functional group in the molecule is not limited to a nitrile group or a thioether group as long as it is an aprotic electron donating group, such as a nitro group, methoxy group, ethoxy group, dimethylamino group, phenyl group, pyridinyl group, etc. Can be illustrated.

  The concentration of the Cu affinity compound in the electrolyte is preferably in the range of 0.1% by mass to 50% by mass, and more preferably in the range of 0.5% by mass to 15% by mass. If the concentration is less than 0.1% by mass, the effect of improving the dissolution potential is not sufficient, and if the concentration exceeds 50% by mass, the lithium ion conductivity of the electrolyte is lowered.

Next, examples of the solvent contained in the electrolyte include a mixture of a cyclic carbonate and a chain carbonate.
As cyclic carbonate, what contains 1 or more types in ethylene carbonate, butylene carbonate, propylene carbonate, (gamma) -butyrolactone, etc. is preferable, for example. Since these cyclic carbonates easily solvate with lithium ions, the ionic conductivity of the electrolyte itself can be increased.
Moreover, as chain carbonate, what contains 1 or more types in dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate, for example is preferable. Since these chain carbonates have a low viscosity, the viscosity of the electrolyte itself can be lowered to increase the ionic conductivity. However, since these chain carbonates have a low flash point, if added excessively, the flash point of the electrolyte is lowered, so care must be taken not to add excessively.

Further, LiPF ₆ , LiBF ₄ , Li [N (SO ₂ C ₂ F ₆ ) ₂ ], Li [B (OCOCF ₃ ) ₄ ], Li [B (OCOC ₂ F ₅ ) ₄ ] should be used as the lithium salt. Can do. The concentration of these lithium salts in the electrolyte is preferably 0.5 mol / L or more and 2.0 mol / L or less. By including these lithium salts in the electrolyte, the ionic conductivity of the electrolyte itself can be increased.

The electrolyte may be a polymer electrolyte, a flame retardant electrolyte, or a polymer electrolyte impregnated with a flame retardant electrolyte.
Examples of polymer electrolytes include polymers such as PEO, PPO, PAN, PVDF, PMA, PMMA, etc. These polymers may be impregnated with Cu affinity compounds, and the above solvents containing Cu affinity compounds in these polymers These polymers may be impregnated, and these polymers may be impregnated with the following organic fluorinated ether compounds containing a Cu affinity compound.
As the flame retardant _{electrolyte, HCF 2 (CF 2) 3} CH 2 OCF 2 CF 2 H, CF 3 CF 2 CH 2 OCF 2 CFHCF 3, HCF 2 CF 2 CH 2 OCF 2 CF 2 H, HCF 2 CF ₂ CH ₂ OCF ₂ CFHCF ₃ , HCF ₂ (CF ₂ ) ₃ CH ₂ OCF ₂ CFHCF ₃ containing one or more organic fluorinated ether compounds as a solvent can be exemplified. By adding the Cu affinity compound, the electrolyte of this embodiment can be configured.

  As described above, according to the lithium secondary battery of this embodiment, the Cu affinity compound is added to the electrolyte, and this Cu affinity compound is accumulated at a high concentration on the surface of the negative electrode current collector. Since the dissolution potential of the negative electrode current collector is improved, even when the lithium secondary battery reaches an overdischarged state, the negative electrode current collector is not likely to be dissolved, and the battery capacity can be prevented from decreasing.

Hereinafter, the present invention will be described in more detail with reference to experimental examples.
(Experimental example 1)
In Experimental Example 1, a lithium secondary battery was manufactured by adding a dinitrile compound to the electrolyte, and an overdischarge test was performed to investigate the presence or absence of elution of the negative electrode current collector.
The battery was manufactured as follows. First, a positive electrode active material made of LiCoO _{2 having} an average particle size of 10 μm, a binder made of polyvinylidene fluoride, and a conductive additive made of carbon powder having an average particle size of 3 μm were mixed, and further N-methyl-2- Pyrrolidone was mixed to make a positive electrode slurry. This positive electrode slurry was applied onto a positive electrode current collector made of an aluminum foil having a thickness of 20 μm by a doctor blade method and dried in a vacuum atmosphere at 120 ° C. for 24 hours to volatilize N-methyl-2-pyrrolidone. Rolled. Thus, the positive electrode which consists of a positive electrode active material, a binder, and a conductive support material was formed on the positive electrode current collector.

  Next, 95 parts by weight of artificial graphite having an average particle size of 15 μm was mixed with a binder composed of 5 parts by weight of polyvinylidene fluoride, and further mixed with N-methyl-2-pyrrolidone to form a negative electrode slurry. . This negative electrode slurry was applied onto a negative electrode current collector made of Cu foil having a thickness of 14 μm by a doctor blade method, and dried in a vacuum atmosphere at 120 ° C. for 24 hours to volatilize N-methyl-2-pyrrolidone. Rolled. In this way, a negative electrode composed of a negative electrode active material and a binder was formed on the negative electrode current collector.

Next, LiPF ₆ having a concentration of 1.3 mol / L is mixed in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a ratio of EC: DEC = 30: 70, and the concentration is further increased. An electrolyte solution was prepared by adding 3% by mass of succinonitrile.

  Furthermore, after placing a polypropylene porous separator between the positive electrode and the negative electrode, they are wound in a spiral shape, and then stored in a laminate-type battery case, and further injected with the electrolyte. After that, the battery case was sealed to manufacture the lithium secondary battery of Example 1.

Further, a lithium secondary battery of Comparative Example 1 was produced in the same manner as in Example 1 except that succinonitrile was not added to the electrolytic solution.
In addition, the design value of the discharge capacity of Example 1 and Comparative Example 1 is 820 mAh.

About the lithium secondary battery of Example 1 and Comparative Example 1, the overdischarge test was done and the relationship between discharge time and battery voltage was investigated. In the overdischarge test, the battery is charged in advance until the battery voltage reaches 4.2V, discharged to 3V at a current of 300 mA, then discharged to 2.7 V at 3 mA, and finally discharged to 0 V at 1 mA. It was done in.
The relationship between the discharge time and the battery voltage is shown in FIG.

  As shown in FIG. 1, in Example 1, the discharge curve at the time of 1 mA discharge is almost linearly lowered. From this behavior, in Example 1, it is considered that the elution of the negative electrode current collector (Cu) during discharge hardly occurred. On the other hand, in Comparative Example 1, a plateau region was found in the discharge curve at the end of discharge during 1 mA discharge. This plateau corresponds to the dissolution of the negative electrode current collector (Cu). That is, in the lithium secondary battery of Comparative Example 1, it is considered that Cu was dissolved during overdischarge.

  From the above results, it can be seen that by adding succinonitrile (dinitrile compound) to the electrolyte, elution of the negative electrode current collector during overdischarge can be prevented.

(Experimental example 2)
Various dinitrile compounds were added to the electrolyte to produce lithium polymer secondary batteries, and overdischarge cycle characteristics and initial characteristics of the lithium secondary batteries were evaluated. This lithium polymer secondary battery was manufactured with a design that does not require an overcharge protection circuit.
The battery was manufactured as follows. First, in the same manner as in Example 1, a positive electrode made of a positive electrode active material, a binder, and a conductive additive was formed on a positive electrode current collector made of an Al foil. In the same manner as in Example 1, a negative electrode made of a negative electrode active material and a binder was formed on a negative electrode current collector made of Cu foil.

Next, in a mixed solvent obtained by mixing ethylene carbonate (EC), gamma butyrolactone (GBL) and diethyl carbonate (DEC) at a ratio of EC: GBL: DEC = 30: 50: 20, a concentration of 1.3 mol / L LiPF ₆ is mixed, fluoroethylene carbonate (FEC) with a concentration of 3% by mass, succinonitrile with a concentration of 1 to 10% by mass is added, and polymerization with a diacryl monomer is started as a polymer electrolyte forming material By adding the agent, an electrolytic solution for the polymer electrolyte was prepared.

  Furthermore, after placing a polypropylene porous separator between the positive electrode and the negative electrode, they are wound in a spiral shape, and then stored in a laminate-type battery case, and further injected with the electrolyte. Then, the battery case was sealed and heated at 80 ° C. for 4 hours to form a polymer electrolyte in the battery. In this way, lithium polymer secondary batteries of Test Examples 1 to 4 were manufactured. Further, a lithium polymer secondary battery of Comparative Example 1 was produced in the same manner as in Test Examples 1 to 4 except that succinonitrile was not added.

About each lithium secondary battery, the discharge capacity of the 2nd cycle at the time of 164 mA discharge was measured as an initial characteristic. Moreover, the overdischarge cycle test was done as an overdischarge characteristic. In the overdischarge cycle test, the battery is charged in advance until the battery voltage reaches 4.2 V, then discharged to 3 V at a current of 300 mA, then discharged to 2.7 V at 3 mA, and finally discharged to 0 V at 1 mA. Charging / discharging was made into 1 cycle, and this charging / discharging cycle was repeated 3 times.
Table 1 shows the evaluation results of the succinonitrile concentration, initial capacity, and capacity at the third overdischarge cycle for each test example.

  As shown in Table 1, in the lithium polymer secondary battery, it is understood that the overdischarge characteristics are improved when the amount of succinonitrile added is 3% by mass or more. In addition, since this lithium polymer secondary battery is designed without an overcharge protection circuit, it can be seen that a battery without a protection circuit could be realized.

(Experimental example 3)
The overdischarge cycle characteristics when the type and amount of the Cu affinity compound were changed were evaluated.
The battery was manufactured as follows. First, in the same manner as in Example 1, a positive electrode made of a positive electrode active material, a binder, and a conductive additive was formed on a positive electrode current collector made of an Al foil. In the same manner as in Example 1, a negative electrode made of a negative electrode active material and a binder was formed on a negative electrode current collector made of Cu foil.

Next, LiPF ₆ having a concentration of 1.3 mol / L is mixed with a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at a ratio of EC: DEC = 30: 70, and Cu An electrolyte solution was prepared by adding an affinity compound.

  Furthermore, after placing a polypropylene porous separator between the positive electrode and the negative electrode, they are wound in a spiral shape, and then stored in a laminate-type battery case, and further injected with the electrolyte. After that, the battery case was sealed. Thus, laminate type lithium secondary batteries of Test Example 5 to Test Example 11 were manufactured.

  About the lithium secondary battery of each test example, it carried out similarly to said Experimental example 2, and evaluated the overdischarge cycle characteristic. Table 2 shows the evaluation results of the type and concentration of the dinitrile compound and overdischarge characteristics for each test example. The battery of Comparative Example 1 was also evaluated in the same manner. In Table 2, TDPN is thiodipropionitrile, SN is succinonitrile, and CTN is cyclohexanetricarbonitrile. The mixing ratio of SN and CTN is SN / CTN = 1/1 by mass ratio, and the mixing ratio of TDPN and CTN is TDPN / CTN = 1/1 by mass ratio.

As shown in Table 2, in the lithium secondary battery in which the electrolyte is a non-aqueous electrolyte, it can be seen that good results are obtained even when the concentration of the dinitrile compound is about 0.5%. Moreover, it turns out that the effect of the improvement of an overdischarge cycle characteristic is seen also about any of a succinonitrile, glutaronitrile, and adiponitrile.
Furthermore, it can be seen that even with TDPN alone, a mixture of SN and CTN, or a mixture of TDPN and CTN, good characteristics are exhibited with an addition amount of about 0.5 to 1%.
Furthermore, the lower concentration than the lithium polymer secondary battery of Experimental Example 2 is more effective because the liquid system is more likely to accumulate dinitrile compounds at a higher concentration on the surface of the negative electrode current collector than the polymer electrolyte system. It is believed that there is.

FIG. 1 is a graph showing the relationship between the discharge voltage and the discharge time for Example 1 and Comparative Example 1.

Claims (6)

A positive electrode capable of inserting and extracting lithium, a negative electrode capable of inserting and extracting lithium bonded to a negative electrode current collector made of Cu or Cu alloy, and an electrolyte that conducts lithium ions. A Cu affinity compound having two or more groups and having a strong affinity with Cu or a Cu alloy is added to the electrolyte;
The Cu affinity compound is a dinitrile compound having two nitrile groups, a trinitrile compound having three nitrile groups, two or more kinds of thiodialkylnitrile compounds having two nitrile groups and having a thioether group in the molecule The lithium secondary battery is a mixture of the dinitrile compound and the trinitrile compound or a mixture of the trinitrile compound and the thiodialkylnitrile compound.   2. The lithium secondary battery according to claim 1, wherein a concentration of the Cu affinity compound in the electrolyte is in a range of 0.1 mass% to 50 mass%.   2. The lithium secondary battery according to claim 1, wherein the dinitrile compound is one or more of succinonitrile, glutaronitrile, and adiponitrile.   The lithium secondary battery according to claim 1, wherein the trinitrile compound is cyclohexanetricarbonitrile, and the thiodialkylnitrile compound is thiodipropionitrile.   The lithium secondary battery according to any one of claims 1 to 4, wherein the electrolyte is at least one of a polymer electrolyte and a flame retardant electrolyte. Comprises a lithium secondary battery according to any one of claims 1 to 5, the lithium rechargeable battery pack, characterized in that does not include an electronic protection circuit for controlling the battery voltage detecting abnormality when the battery charge and discharge .

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