JPH1083806A - Lithium secondary battery and lithium secondary battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent ignition and explosion and provide a safe and reliable secondary battery by intercalating and evacuating lithium ion working for a secondary battery into a previously produced third electrode in the battery based on a received signal of abnormality occurrence or the judgment of the battery itself. SOLUTION: Besides both electrodes, three or four mesh sheets made of aluminum coated with polyethylene are used as third electrode plates into which Li ion is intercalated and evacuated at the time when abnormal state is caused. The third electrodes are layered and the layered body is inserted into a battery case, conductive lead wires 6 are connected with a charging and discharging testing apparatus 8, an electrolytic solution is poured into the space of the case, and the resultant battery is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery having a small size and a large charge / discharge capacity, and more particularly to a battery case having a positive electrode, a separator, a negative electrode, and an electrolytic solution and accommodating them. Regarding the safety of lithium secondary batteries.

[0002]

2. Description of the Related Art A lithium secondary battery is a battery having a charge / discharge mechanism in which Li ions are introduced into and taken out of positive and negative electrode active materials through a nonaqueous electrolyte, which is a combustible material. A minute lithium metal precipitates and grows, causing a micro-short due to the tip contacting the counter electrode, causing a rapid rise in battery temperature. Even if the charging operation is stopped by the formation, the temperature rise does not stop and the battery temperature rises at once, that is, a so-called thermal runaway occurs, which leads to the explosion and ignition of the battery.

For this reason, various methods have been studied to prevent this, and various methods have been proposed.

[0004] For example, a proposal for making an electrolyte non-combustible (Japanese Unexamined Patent Publication No.
83205 and JP-A-6-150968) and proposals for monitoring the temperature inside a battery (JP-A-5-266878 and JP-A-3-291866). In these proposals, making the electrolyte non-flammable is a drastic measure, and it is considered to be an effective proposal, but at present, there are still problems in terms of capacity density and cycle life as a secondary battery. Battery temperature monitoring is also effective as a method for preventing explosion and fire accidents due to thermal runaway, but is insufficient in reliability due to fluctuations in outside air temperature.

Further, in these prior arts, even if the thermal runaway is started and the operation of the battery is stopped, the fact that the temperature of the battery continues to rise is not considered, which is a safety problem.

[0006]

In order to solve the above-mentioned problem, it is necessary to reduce and stop the supply of lithium to the lithium metal that is deposited and grown on the dendritec which causes the thermal runaway phenomenon. Become.

[0007]

SUMMARY OF THE INVENTION The above-described problem is caused by one of the lithium ions that are constantly operating as a secondary battery at the initial stage of occurrence of an abnormality such as the start of local heat generation due to a minute short circuit caused by the growth of dendritic lithium metal. The problem is solved by inserting or retreating a part or the whole to another third pole which is not regularly used.

More specifically, the problem can be solved by preparing a third electrode into which lithium can be inserted in the battery case itself or in the battery case, and letting the lithium which is constantly operating due to the occurrence of an abnormality flow into the third electrode.

[0009] Here, the problem arises in the method of obtaining an abnormality occurrence signal, and there are roughly two methods: a method of detecting an abnormality other than the third pole and a method of detecting an abnormality by the third pole itself. As the former method, a method of grasping by measuring the temperature of the battery or quantitatively grasping the distortion amount of the battery case and making a judgment by setting a threshold value is presented. Note that, in this case, the third pole and the electrode terminal are in an insulated state in a steady state, and the present invention is achieved by being brought into a conductive state by receiving an abnormality occurrence signal.

On the other hand, in the latter method, the third electrode is provided by using an insulating film which is destroyed by heat so as not to come into direct contact with the electrolytic solution, and one of the electrode terminals is connected to the third electrode.
May be electrically connected to the other pole. As a result, the sudden rise in temperature after the start of thermal runaway during overcharging / discharging breaks the insulating film and causes direct contact with the electrolyte, whereby lithium is inserted into and retracted from the third electrode, and lithium metal precipitates and grows. , Heat generation due to a minute short circuit is reduced.

As a material into which lithium used as the third pole can be inserted and retracted in the event of an abnormality, aluminum or a carbon material which alloys with Li at a high potential is suitable for measures against thermal runaway during overcharge. As a countermeasure against thermal runaway, copper, nickel, or the like that alloys with Li at a low potential is preferable.

It is desirable that the third electrode does not hinder the movement of lithium ions that are constantly used as a secondary battery and does not lower the energy density of the battery. Inserting and evacuating lithium into the case itself is effective with less reduction in energy density. On the other hand, in terms of the reliability of suppressing thermal runaway, a mesh-like or foamed metal through which lithium ions can pass through from the front and back using a material into which lithium can be inserted, such as a metal that can be alloyed with lithium, an alloy, or a material into which lithium can be inserted. It is also effective to use a plate-like structure in which the plate is sandwiched between electrode plates. Further, the insulating synthetic resin which is surely destroyed by local heat generation on the electrode surface before the thermal runaway and is not electrically connected to the electrolytic solution before that is preferably polyethylene, polypropylene or polycarbonate.

On the other hand, if the battery to which the present invention can be applied is a lithium secondary battery, its structure is not limited to a coin, a wound, a square plate-shaped laminated type, and the like.

The present invention relates to versatile electric equipment products, for example, personal computers, electric vehicles, portable information terminal equipment, video cameras, air conditioners, computer games, portable telephones, electric bicycles, electric wheelchairs, and power supplies for charging stations. It is suitable for use as a lithium secondary battery incorporated in a home power leveling power source and a system equipped with a lithium secondary battery.

The positive electrode of the lithium secondary battery is made of LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , L capable of inserting and removing lithium.
Using iMn ₂ O _4, LiFeO ₂ lithium transition metal composite chalcogen compound or a transition metal chalcogen compound, the negative electrode was used lithium metal, lithium alloy or a carbon material or metal carrying carbon material lithium can intercalate, the ceramic anode cell Can be applied to

The electrolyte is propylene carbonate, 2-methyltetrahydrofuran, dioxolen, tetrahydrofuran, 1,2-dimethoxyethane, ethylene carbonate, γ-butyrolactone, dimethyl sulfoxide, acetonitrile, formamide, dimethylformamide,
One or more aprotic organic solvents such as nitromethane are used as LiClO ₄ , LiAlCl ₄ , LiBF ₄ , LiCl,
A lithium salt such as LiPF ₆ or LiAsF ₆ can be used in combination.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to examples, but the present invention is not limited to the following examples. Note that all of the battery production and measurement in the examples were performed in an argon atmosphere.

Embodiment 1 FIG. 1 shows a schematic configuration of a lithium secondary battery manufactured in this embodiment.

From FIG. 1, the electrode plate comprises a conductive end portion 5 of 1.0 × 2.0 cm and electrode mixture application portions 1 and 2 of 5.0 × 7.0 cm. Is a nonwoven fabric made of polypropylene, and the mixture applied portion of the negative electrode plate 2 was wrapped with a separator made of a microporous film. The number of electrodes used per battery is two positive plates and three negative plates. In the present invention, four aluminum mesh plates 3 coated with polyethylene were used as the third electrodes other than the two electrode plates into which Li ions were inserted and retracted when an abnormality occurred. The third pole is laminated as shown in FIG. 1, this laminate is inserted into a battery case, connected to a charge / discharge test device 8 using a conductive wire 6, and an electrolyte is injected into a space 7 in the case. Used.

The battery case 4 is made of a steel plate having a thickness of 0.3 mm and has dimensions of 6 × 10 cm and a thickness of 0.6 cm.

Next, the positive electrode plate is a mixed metal powder composed of 9.0 wt% of carbon powder as a conductive agent, 4.0 wt% of PVDF as a binder, and LiNiO _{2 as} a balance on an expanded metal plate made of a rectangular mesh made of aluminum. Is coated with an electrode mixture kneaded with N-methyl-pyrrolidone (NMP), and vacuum-dried at 140 ° C. The coated substrate of the negative electrode plate is made of a copper expanded metal in the form of a square mesh plate, and the negative electrode active material is a graphite-based carbon powder. The compounding ratio of the negative electrode was 90.0% by weight of carbon powder as an active material, and PVDF as a binder was 10.0% by weight.
0 wt%.

A detailed description of the third pole 3 of the present invention is as follows.

In this embodiment, the size is 5.0 × 7.0 cm and the thickness is 0.2 m.
m, aluminum expanded metal with a mesh spacing of 2.0 mm was pressed with a hydraulic press to a thickness of 0.1 mm.
The polyethylene which melted at 20 ° C. was coated. In addition,
Confirmation of the coatability with polyethylene was performed by measuring the resistance value between the electrolytic solution and the polyethylene net coated with polyethylene.

The electrolyte is a mixed solvent solution of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) of LiPF _{6 having} a concentration of 1.0 M.

As an evaluation method, a CA-type thermocouple having a wire diameter of 67.0 μm is arranged at the center point 10 of the outer case outer surface of the battery shown in FIG.
After the charge / discharge cycle test between 7 V and 4.3 V was performed five times, the charge in the sixth cycle was charged to the overcharge state by the 2C operation, and the temperature rise of the battery and the third pole 3 of the present invention. Was evaluated by comparing with the temperature rise of the battery in the conventional method in which no battery was provided. FIG. 2 shows the evaluation results. From this figure, it can be seen from the figure that the battery temperature in the conventional method rises rapidly from around 40 ° C. in the overcharge test, and the temperature at which thermal runaway starts is nearly 120 ° C., indicating that the battery is used as a secondary battery. Some action such as suspension is required. On the other hand, according to the results of the present invention, although the battery temperature starts to rise after 30 minutes or more, the rise in temperature is suppressed and the temperature is kept at 30 ° C. where thermal runaway is unlikely to occur. Thus, it can be seen that the present invention is effective for improving reliability with respect to safety.

Embodiment 2 FIG. 3 shows the structure of a lithium secondary battery manufactured in this embodiment.

FIG. 3 shows that the structure of the battery is almost the same as that of the first embodiment, but a pressed aluminum expanded metal plate is used as a third electrode into which lithium is inserted in the event of an abnormality without coating with polyethylene. At the start of the evaluation, the lithium insertion plate and the negative electrode terminal are kept electrically insulated as shown in FIG. 3, and when the temperature of the battery case reaches 40 ° C., the switch is connected to the negative terminal using the switch 9 and thereafter. The two points are that the increase in the battery temperature was compared and evaluated. Since the method of manufacturing the battery component is exactly the same as that in Example 1, the description in this example is omitted.

FIG. 4 shows the evaluation results. According to this figure, the battery connected to the negative electrode terminal after the battery temperature reached 40 ° C. has a maximum value of about 50 ° C., and although the maximum value is somewhat higher, the battery temperature tends to decrease thereafter. It is clear that the possibility of starting thermal runaway is low even if it is continued, which is effective for improving reliability regarding safety.

(Embodiment 3) FIG. 5 shows the structure of a lithium secondary battery manufactured in this embodiment.

From FIG. 5, the third pole in this embodiment is the battery case itself in which the inner surface of the case is covered with a polyethylene film,
The polyethylene film was damaged by the heat generated by the micro-short, the electrolyte came into contact with the case, and the active lithium was inserted into and retracted from the battery case. The temperature rise situation at that time was compared and evaluated.

Other than that, since it is completely the same as the first embodiment, the description in this section is omitted.

FIG. 6 shows the evaluation results. From this figure, it can be seen that the rise in battery temperature is suppressed from around 45 ° C., and no temperature decrease was observed, but the temperature did not reach such a high level as to cause thermal runaway.

From these facts, it can be seen that even if the charging is continued, the possibility of starting thermal runaway is low, which is effective for improving the reliability with respect to safety.

[0034]

According to the battery of the present invention, a lithium ion operating as a secondary battery is inserted and evacuated into the third electrode prepared in advance in the battery upon reception of a signal indicating occurrence of an abnormality or judgment of the battery itself. This prevents ignition and explosion of the lithium secondary battery due to thermal runaway, and makes it possible to supply a safe and highly reliable secondary battery.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a lithium secondary battery manufactured in Example 1. FIG. 4 is an explanatory view of a battery in which an aluminum mesh plate covered with a synthetic resin is sandwiched between positive and negative electrode plates.

FIG. 2 is an explanatory diagram of evaluation results of the lithium secondary battery manufactured in Example 1. Explanatory drawing of the external surface temperature rise situation of a battery at the time of overcharge in 2C.

FIG. 3 is an explanatory diagram of a lithium secondary battery manufactured in Example 2.

FIG. 4 is an explanatory diagram of evaluation results of the lithium secondary battery manufactured in Example 2.

FIG. 5 is an explanatory diagram of a lithium secondary battery manufactured in Example 3. Explanatory drawing of the battery which produced the battery case from aluminum and covered the inner surface with the insulating synthetic resin.

FIG. 6 is an explanatory diagram of evaluation results of the lithium secondary battery manufactured in Example 3.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Positive electrode plate, 2 ... Negative electrode plate, 3 ... Place where working lithium is inserted and retracted, 4 ... Battery case, 5 ... Conductive terminal, 6 ... Conductive wire, 7 ... Electrolyte, 8 ... Charge / discharge test equipment, 9 ... Switch ,
10 thermocouple.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Eritoshi Honbo 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Inside the Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Ren Muranaka Omikamachi, Hitachi City, Ibaraki Prefecture No. 1-1, Hitachi Research Laboratory, Hitachi Ltd.

Claims (13)

[Claims] 1. A lithium secondary battery having a positive electrode, a separator, a negative electrode, and an electrolytic solution and comprising a battery case accommodating the positive electrode, a separator, a negative electrode, and an electrolyte. A lithium secondary battery and a lithium secondary battery system, wherein a third pole through which part or all of lithium constantly inserted and desorbed upon sensing is inserted and retracted is provided other than the positive and negative electrode plates. . 2. The battery according to claim 1, wherein a part or all of the battery can is made of a material into which lithium can be inserted.
2. The lithium electrode according to claim 1, wherein the negative electrode is electrically connected to the electrolyte, but is not connected to any of the positive and negative terminals, and is connected to any one of the positive and negative electrode terminals upon reception of an abnormal signal. Secondary battery and lithium secondary battery system. 3. The third electrode is disposed between the battery case and the electrode plate laminate, and is electrically connected to the electrolyte but not to any of the positive and negative terminals during normal operation. 2. The lithium secondary battery and the lithium secondary battery system according to claim 1, wherein the lithium secondary battery is electrically connected to one of the positive and negative electrode terminals upon reception of a signal indicating occurrence of an abnormality. 4. A network which is electrically connected to said electrolyte during normal operation, but does not conduct to any of the positive and negative terminals, but can conduct to either one of the positive and negative electrode terminals upon reception of a signal indicating occurrence of an abnormality. The lithium secondary battery and the lithium secondary battery system according to claim 1, wherein a plate-like member is disposed between the stacked electrode plates as a third pole. 5. A third electrode made of a material into which lithium can be inserted at normal time is connected to one of the positive and negative electrodes and is insulated by an electrically insulating synthetic resin film which is destroyed by heat. The lithium secondary battery and the lithium secondary battery system according to claim 1, wherein the lithium secondary battery is covered and insulated from the electrolyte. 6. The battery according to claim 1, wherein the third electrode is a battery can and the inner surface of the can is covered with an electrically insulating synthetic resin film which is connected to one of the positive and negative terminals and is destroyed by heat. Lithium secondary battery and lithium secondary battery system. 7. The third electrode is disposed between the battery case and the electrode plate laminate, and is connected to either one of the positive and negative electrodes and is covered with an electrically insulating synthetic resin film which is destroyed by heat. The lithium secondary battery and the lithium secondary battery system according to claim 1. 8. A third pole in the form of a mesh plate is disposed between electrode plates and connected to one of the positive and negative terminals, and this is covered with an electrically insulating synthetic resin film which is destroyed by heat. The lithium secondary battery and the lithium secondary battery system according to claim 1, wherein the lithium secondary battery is insulated from the electrolyte. 9. The lithium secondary battery and the lithium secondary battery system according to claim 1, wherein the third electrode is made of a carbon material or aluminum. 10. The lithium secondary battery and the lithium secondary battery system according to claim 1, wherein the third electrode is made of a nickel material or copper. 11. The method according to claim 1, wherein when an abnormality occurs, the third electrode conducts between the negative electrode terminals when the third electrode is made of carbon material or aluminum, and conducts with the positive electrode terminal when the third electrode is made of nickel or copper. Lithium secondary battery and lithium secondary battery system. 12. The lithium secondary battery and the lithium secondary battery system according to claim 1, wherein the electrically insulating synthetic resin film which is broken by heat is made of polyethylene, polypropylene or polycarbonate. 13. A system equipped with the lithium secondary battery according to claim 1 is a personal computer, an electric vehicle, a portable information terminal, a video camera, an air conditioner, a computer game, a portable telephone, an electric A system equipped with a lithium-ion battery, which is a bicycle, electric wheelchair, charging stand power supply, and home power leveling power supply.