KR19980044210A - Safety exhaust device of lithium polymer secondary battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery using a polymer electrolyte, and more particularly, a lithium secondary battery equipped with a gas exhaust device having excellent safety by discharging the gas generated in the lithium secondary battery to the outside of the secondary battery safely through a valve. to be.

According to a first embodiment of the present invention, in the lithium polymer secondary battery, when gas is generated inside the battery due to over discharge or over charge, a positive pressure is applied to the gas to discharge the gas to the outside. It is a lithium secondary battery equipped with a gas exhaust device, characterized in that the gas discharge port (2) having a weak fracture resistance material is provided.

Description

Safety exhaust device of lithium polymer secondary battery

The present invention relates to a lithium secondary battery using a polymer electrolyte, and more particularly, to a lithium polymer secondary battery equipped with a gas exhaust device having an excellent safety by safely discharging the gas generated in the lithium polymer secondary battery through a valve to the outside of the battery. It is a battery.

Recently, due to the rapid development of the information industry, miniaturization, light weight, and thinning of all electronic devices are possible, and the necessity of a secondary battery having high portable density and high energy density is emerging.

Lithium secondary batteries have high energy density, light weight, and have become a target of great interest as small portable power sources. Secondary batteries using liquid electrolytes have been developed in Japan, and have been successfully commercialized. It is used in notebook computers and camcorders.

In general, lithium secondary batteries are classified into two types, a lithium ion battery using a liquid electrolyte and a lithium polymer battery using an ion conductive polymer as an electrolyte.

Lithium oxide such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiNi _X Co _1-X O ₂ is used as a positive electrode active material used in a lithium ion battery, and natural graphite, artificial graphite, carbon, carbon fiber , Cokes and the like are used.

In addition, the positive electrode used in the lithium secondary battery is made of sludge by mixing an active material, a conductive material (acetylene black, ketcheon black, graphite, etc.) and a binder, and coated with a thickness of 80 to 120 μm on a 20 μm aluminum foil. Make it. In addition, the cathode electrode does not need a conductive material when graphite is used, but the carbon system must be added to the conductive material, the binder is added to make a slurry, and then coated on a copper foil of 10 ~ 12㎛ thickness to a thickness similar to the anode .

The lithium ion battery uses a polyolefin-based separator, and the lithium polymer battery simultaneously serves as a separator and an electrolyte by using an electrolyte prepared by adding a lithium salt and an organic solvent to an ion conductive polymer.

Assembly of lithium ion battery is made by stacking positive electrode, separator, and negative electrode in turn, and then rolling it into a rolled form, inserting into a battery can, and adding a liquid electrolyte to make a finished product.

In addition, a polymer battery may be manufactured by winding three layers of a positive electrode, a polymer electrolyte, and a negative electrode in the same manner as an ion battery, or by stacking a plurality of electrodes and not adding a liquid electrolyte.

The liquid electrolyte used in the lithium ion battery is a mixture of two or more kinds of organic solvents such as propylene carbonate, ethylene carbonate, diethyl carbonate and dimethyl carbonate, and the alkali salts LiClO ₄ , LiPF ₆ , LiBF ₄ , LiA _S F ₆ , LiCF ₃ SO ₃ and the like is dissolved and used as an electrolyte.

As the separator, a polyolefin-based porous membrane is used, and there are a single membrane, a double membrane, and a triple membrane.

However, when the lithium ion battery is overcharged and the voltage rises to about 4.5V, the electrolyte of the carbonate-based electrolyte is decomposed, gas such as carbon dioxide or carbon monoxide is released to increase the pressure in the battery, and there is a problem of the possibility of explosion.

In addition, when an overcurrent flows due to over-discharge or short-circuit, a lithium ion battery increases in temperature inside the battery, and an organic solvent having a low boiling point such as diethyl carbonate or dimethyl carbonate is changed into a gas, resulting in an increase in the internal pressure of the battery and lithium. The salt may decompose and generate HF gas. In fact, due to battery pressure increase and battery ignition, safety problems have been raised.

In addition, polyvinylidene fluoride (polyvinyllidene fluoride, PVDF) or a composite is used as a binder to form an electrode of a lithium ion battery. In the case of using a lot of liquid electrolyte, there is also a phenomenon that PVDF having polarity is easily dissolved and eluted in the polar organic electrolyte, which may cause the cycle life of the battery or decrease the capacity, and generate an extreme short circuit. There is a problem that can be done.

In contrast, a lithium polymer battery is a battery having greatly improved safety compared to an ion battery. The amount of organic solvent used is much smaller than that of lithium ion batteries, and the organic solvent itself is also impregnated inside the polymer electrolyte and does not exist in liquid form. Therefore, compared with lithium ion batteries, the probability of gas generation due to overcharge and overdischarge is greatly reduced and safety is greatly improved.

In addition, since the lithium polymer battery does not have a binder dissolution, the strong binding between the current collector and the active material maintains conductivity and cycle life is superior to that of the lithium ion battery. However, even in a lithium polymer battery, a small amount is generated due to decomposition of the electrolyte during internal short circuit, overcharge, and overdischarge, but gas may be generated due to gas generation.

Therefore, an object of the present invention is to further improve the safety of the battery by safely discharging the gas generated in the lithium polymer battery to the outside.

1 is a perspective view of a lithium polymer secondary battery having a gas discharge port showing a first embodiment of the present invention;

FIG. 2A is a schematic perspective view of a lithium secondary battery 1 equipped with a gas exhaust device in which a check valve 3 as a second embodiment of the present invention is provided at an upper end of a secondary battery,

FIG. 2B is a schematic sectional view of the check valve 3 in FIG. 2A,

3A is a schematic cross-sectional view of a lithium polymer secondary battery 1 equipped with a gas exhaust device and an overcharge short circuit device, in which a piston valve 10 as a third embodiment of the present invention is installed,

FIG. 3B is a schematic cross-sectional view of the piston valve 10 in FIG. 3A,

Fig. 3C is an enlarged partial sectional view showing a portion of the piston-type valve in which the piston-type valve 10 according to the present invention raises the external terminal of the battery to the pressure of the exhaust gas.

Hereinafter, the present invention will be described in detail.

According to a first embodiment of the present invention, in a lithium polymer battery, when gas is generated inside the battery due to overdischarge or overcharging, a positive pressure is applied to impinge the gas to the outside of the front surface of the battery 1 to discharge the gas to the outside. It is a lithium polymer secondary battery equipped with a gas exhaust device, characterized in that the gas discharge port (2) having a weak thermal material is provided.

According to a second embodiment of the present invention, in a lithium polymer battery, when gas is generated inside the battery due to overdischarge or overcharge, and a positive pressure is applied, the gas inside the battery 1 is discharged to the outside and the inflow of outside air is prevented. A check valve 3 capable of shutting off is a lithium polymer secondary battery equipped with a gas exhaust device, which is provided at the upper end of the battery 1.

According to a third embodiment of the present invention, in a lithium polymer battery, when a gas is generated inside the battery due to over discharge or over charge, positive pressure is applied to the gas, the gas is discharged to the outside, and the overcharge is automatically prevented. Is a lithium battery equipped with a gas exhaust device, characterized in that the piston valve 10 is provided at the upper end of the battery.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a perspective view of a lithium battery with a gas discharge port showing a first embodiment of the present invention. In FIG. 1, in the lithium polymer battery 1, a material having a weak fracture resistance is formed at the upper end of the front surface of the battery so that gas may be discharged to the outside when gas is generated inside the battery due to over discharge or over charge. The gas outlet 2 which has is provided. As the material of the gas outlet 2, the plastic pack made of PE, which is used as a container pack of a polymer battery, is made of a material having a lower rupture resistance than that of a plastic, for example, a thin vinyl film or an aluminum thin film is preferable.

Another embodiment of the invention is shown in FIG.

FIG. 2A is a schematic perspective view of a lithium polymer secondary battery 1 in which a check valve 3 of a second embodiment of the present invention is equipped with a gas exhaust device at an upper end of a battery, and FIG. 2B shows a check valve 3 in FIG. 2A. It is a schematic cross section of. In FIG. 2B, when a gas is generated inside the battery due to over-discharge or overcharging, and a positive pressure is applied, a check valve 3 capable of releasing the gas inside and blocking the inflow of outside air is provided at the upper end of the battery. Is installed. The smaller the size of the valve 3 in this apparatus, the better, and the thickness of the valve should be less than the thickness 4 of the lithium polymer battery. In addition, as the material of the outer body 5 of the check valve 3, plastic, stainless steel, aluminum, etc. may be used, and plastic material is most preferable when insulation is required. The material of the valve 6 inside the shock valve 3 is most suitable for thin steel having excellent elasticity. The shape of the valve 3 is a thin square and is provided between the positive and negative terminals. The gas generated inside the electrons in the direction of the arrow 7 in the valve 3 is discharged through the valve 6 to the cell outward direction 8, at which time no air flows into the reverse direction 9.

Another embodiment of the present invention is shown in FIG.

FIG. 3A is a schematic cross-sectional view of a lithium battery 1 equipped with a gas exhaust device and an overcharge short circuit device in which a piston valve 10 as a third embodiment of the present invention is installed, and FIG. 3B is a piston valve 10 in FIG. 3A. 3C is an enlarged portion of the piston-type valve which pushes up the charging external terminal of the battery to the pressure of the exhaust gas by the piston-type valve 10 according to the present invention, and disconnects the connection with the external terminal. It is a partial cross section shown.

In FIG. 3A, the upper end of the battery includes a piston valve 10 inserted into the battery body 1, an external terminal 11 serving as a terminal when charging the battery, and an outer pack 12 of the battery.

Figure 3b is an enlarged cross-sectional view of the piston valve 10 in Figure a, the piston valve 10 is an exhaust gas inlet 13 through which the exhaust gas is introduced, the piston body rising upward by the force from which the gas is exhausted (14), the discharge port 16 for discharging the exhaust gas to the outside of the battery through the body gas passage 15 by the piston body ascending upward, a spring that serves to return the piston after the exhaust gas is discharged ( 17), the piston head 18 is moved up and down by the piston force and serves to properly disconnect the external terminal.

In the above, the exhaust gas is exhausted in more detail, as shown in FIG. 3C. That is, when the pressure inside or outside the battery is the same or similar, the piston body 14 is positioned downward by the force of the spring 17 to close the valve. However, gas is generated inside the battery and the inside of the battery is generated. When the pressure rises, the piston valve body is pushed up to raise the piston body as shown in Fig. 3c, in which case the discharge port 16 and the inside of the piston body 14 are discharged to the outside of the valve. The formed gas passage 15 and the discharge port 16 are connected to discharge the gas, which is a factor that increases the pressure inside the battery, to the outside. In this case, when the piston body 14 rises to the pressure of the exhaust gas, the piston head 18 connected to the piston body also rises up at the same time, and by this lifting force, the charging external terminal 11 of the battery is pushed up to the battery ( It is disconnected from the electrode terminal 19 of 1). Therefore, this action prevents the battery from overcharging and safely discharges the gas generated inside the battery.

The elasticity of the spring 17 is suitable if the elasticity of the degree that the positive pressure is applied to the inside of the battery and the internal pressure is expanded so that the pressure of the elevated battery can be released to the outside. Although the charging external terminal 11 of the battery and the electrode terminal 19 of the battery are connected or spaced apart from each other, there is no problem, but the charging external terminal 11 and the electrode terminal 19 of the battery are disconnected in order to generate gas at the same time. ) Is preferably connected. It is preferable that the material of the valve is plastic for insulation and the shape of the valve is cylindrical having a small diameter.

Hereinafter, the present invention will be described in more detail with reference to the following examples.

EXAMPLE

Examples 1 to 3

A positive electrode was prepared by coating LiMn ₂ O ₄ as an active material, acetylene black, KS6 as a conductive material, and using PVDF as a binder to coat a 40 μm thick aluminum foil. The negative electrode was prepared by coating a 40 μm thick copper foil using a carbon material and PVDF. The electrolyte was prepared by dissolving polyacrylonitrile (PAN) and LiClO ₄ in ethylene carbonate and propylene carbonate.

The positive electrode, the negative electrode, and the electrolyte were prepared in a battery having the capacity as shown in Table 1 below, and each of the cells was equipped with a check valve to manufacture a lithium polymer battery. By overcharging the battery prepared in each example to measure the expansion rate of the battery pack due to gas generation is shown in Table 1 below.

Comparative Examples 1 to 3

A battery was manufactured in the same manner as in the above example, except that the exhaust gas check valve was not mounted. By overcharging the batteries prepared in each of the comparative examples, the expansion ratio of the battery pack due to gas generation was measured and shown in Table 1 below.

Table 1

In Table 1, the battery prepared in Examples 1 to 3 did not have expansion of the battery pack due to overcharging, but the battery without the exhaust device manufactured in Comparative Examples 1 to 3 caused expansion of about 150 to 200% by volume upon overcharging. .

In the battery provided with the valve according to the present invention, gas is smoothly discharged to the outside to prevent an increase in the pressure inside the battery, and there is no swelling phenomenon of the battery. Therefore, in the case of a conventional lithium polymer battery, gas pressure rises inside the battery due to gas decomposition in the battery due to decomposition of the electrolyte, reaction of the current collector and salt, and the like due to various minute reactions in the interior, resulting in battery explosion, ignition, etc. Although the lithium polymer battery equipped with the exhaust device according to the present invention has a risk of being unsafe, there is no volume expansion and pressure increase due to the exhaust gas, and it is possible to manufacture a battery which does not have a decrease in battery performance or a lifespan due to overcharging. have.

Claims (7)

In a lithium polymer battery, a gas chamber having a material having a weak tear resistance at the upper end of the front surface of the battery 1 in order to allow gas to be discharged to the outside when a gas is generated inside the battery due to over discharge or over charge and a positive pressure is applied thereto. Lithium battery equipped with a gas exhaust device, characterized in that the outlet (2) is provided. The lithium battery according to claim 1, wherein the gas discharge port (2) is made of a vinyl film or an aluminum thin film. In a lithium polymer battery, a check valve (3) capable of releasing gas inside the battery (1) and blocking the inflow of external air when gas is generated inside the battery due to overdischarge or overcharge and a positive pressure is applied thereto. Lithium battery equipped with a gas exhaust device, characterized in that installed in the upper end of the temporary battery (1). The lithium battery according to claim 3, wherein the material of the outer body (5) of the check valve (3) is plastic, stainless, or aluminum. 4. The lithium battery according to claim 3, wherein the valve (6) is formed of a thin steel material having excellent elasticity. In a lithium polymer battery, when a gas is generated inside the battery due to over-discharge or overcharging, the piston-type valve 10 is provided in the battery 1 so that the gas is discharged to the outside when the positive pressure is applied and the overcharge is automatically prevented. Lithium battery equipped with a gas exhaust device, characterized in that installed in the upper end of the battery. 7. The piston valve (10) according to claim 6, wherein the piston valve (10) has an exhaust gas inlet (13) through which exhaust gas flows, a piston body (14) which rises upward by a force through which the gas is exhausted, and the piston body is raised upward. A discharge port 16 which discharges the exhaust gas to the outside of the battery through the gas passage 15, a spring 17 which serves to return the piston after the exhaust gas is discharged, moves up and down by the piston force A lithium battery equipped with a gas exhaust device, characterized by comprising a piston head (18) which serves to short-circuit the terminal properly.