KR100858414B1 - Lithium Secondary Battery For High Rate Charge And Discharge - Google Patents

Abstract

The present invention provides a cap assembly in which the gasket is installed insulated from the bead portion of a cylindrical battery can, wherein a safety vent is electrically connected to an anode lead coupled to an anode of a power generator, and has an upper end projecting upward. A cap is connected to the safety vent along its outer circumferential surface, and provides a lithium secondary battery capable of high rate charge / discharge, which is composed of a structure in which the upper cap and the connection portion of the safety vent are welded.

Lithium secondary battery according to the present invention can exhibit a high energy density and instantaneous high output per unit volume of the battery to achieve high rate charge and discharge, and also the resistance of the contact surface during external physical shock such as vibration, dropping It can be used suitably as a power supply for a power tool since it can provide a uniform output without being changed.

Description

Lithium Secondary Battery For High Rate Charge And Discharge             

1 is a schematic cross-sectional view showing a representative upper structure of a conventional lithium secondary battery;

2 is a schematic cross-sectional view showing an upper structure of a lithium secondary battery according to one embodiment of the present invention;

3 is a schematic cross-sectional view showing an upper structure of a lithium secondary battery according to another embodiment of the present invention;

4A and 4B are perspective views of safety vents and current blocking members used in the battery of FIG. 3;

5A to 5C are cross-sectional schematic diagrams illustrating an operation process when a pressurized gas is generated in the battery of FIG. 3;

6A is a perspective view of a current blocking member according to still another embodiment, and FIG. 6B is a cross-sectional view taken along the cutting line AA of FIG. 6A.

The present invention relates to a high-rate charge-discharge lithium secondary battery, and more particularly, to a lithium secondary battery that provides a stable output even by an external impact such as instantaneous high output and vibration required for a power source for power tools.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is increasing rapidly. Among them, many researches have been conducted and commercialized on lithium secondary batteries with high energy density and high discharge voltage. It is widely used.

When a secondary battery is used as a power source for a mobile phone or a laptop, a lithium secondary battery that provides a stable output is required, whereas when used as a power source of a power tool such as an electric drill, a high output can be instantaneously provided. There is a need for a lithium secondary battery that can be and can be stable against external physical shocks such as vibration and dropping.

In this regard, the structure of a conventional cylindrical lithium secondary battery is disclosed in FIG. 1. In general, the secondary battery 10 includes a cylindrical can 20, a power generator 30 accommodated in the can 20, and a cap assembly 40 coupled to an upper portion of the can 20.

The generator 30 has a structure in which it is wound in a jelly-roll shape with a separator 33 interposed between the anode 31 and the cathode 32, and the anode lead 34 is attached to the anode 31. It is connected to the cap assembly 40, and a cathode lead (not shown) is attached to the cathode 32, and is connected to the lower end of the can 20.

The cap assembly 40 may include a top cap 41 forming a positive electrode terminal, a positive temperature coefficient element 42 blocking a current by greatly increasing battery resistance when the temperature inside the battery increases, and a pressure increase inside the battery. Safety vent 43 to cut off current or exhaust gas, insulating member 44 to electrically separate safety vent 43 from cap plate 45, except for a specific portion, anode lead connected to anode 31 The cap plate 45 to which the 34 is connected is laminated | stacked sequentially.

However, the lithium secondary battery having such a structure is not only difficult to provide a high output instantaneously, but also it is difficult to provide a uniform output because the resistance of the contact surface is changed during external shock such as vibration. Specifically, the PTC element 42 generally exhibits an electrical resistance of about 7 to 32 mΩ even at room temperature, and further causes a steep rise in resistance due to an increase in temperature. Therefore, it can act as a great deterrent to providing instantaneous high power. In addition, the contact surface of the upper cap 41, the PTC element 42, the safety vent 43 and the cap plate 45 during the external impact such as vibration does not provide a uniform output because the change of resistance is very large.

Therefore, the cap assembly structure of the conventional cylindrical secondary battery as shown in Figure 1 does not exhibit the desired effect in using as a lithium secondary battery for power tools.

 The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After repeated studies and various experiments, the present inventors removed a PCT element from a cap assembly structure of a conventional lithium secondary battery, electrically connected a safety vent to the anode lead, and welded a contact portion between the upper cap and the safety vent. When fabricated in the furnace, high energy density and instantaneous high output per unit volume of the battery can be exerted to achieve high rate charge and discharge, and the contact surface resistance does not change even during external physical shocks such as vibration and drop. It has now been found that the present invention can be completed and the present invention can be improved by further improving the stability of the battery when the safety vent is made to the specific structure described below.

The secondary battery according to the present invention for achieving this purpose is a lithium secondary battery capable of high rate charge and discharge, in the cap assembly is installed insulated from the bead of the cylindrical battery can via a gasket, the safety vent is a positive electrode of the power generator The safety cap is connected along the outer circumferential surface of the upper cap which is electrically connected to the anode lead coupled to the upper cap, and the connecting portion of the upper cap and the safety vent is welded. Consists of.

According to the experiments of the present inventors, the lithium secondary battery having such a cap assembly structure was found to be very useful as a power source for power tools. In general, power tools require high output instantaneously, and often require discontinuous operation rather than long continuous operation, and are subject to internal or external physical shocks such as vibration and dropping due to the nature of the working environment. many.

In order to meet these requirements, first, it must provide greater energy density in a limited cell volume, second, the internal resistance of the cell must be small, and third, the coupling or connection state of the cell components must be stable.

In the present invention, in order to satisfy the first requirement, the structure of the cap assembly is changed to make the thickness thereof thinner, thereby increasing the relative size of the volume occupied by the power generator composed of the anode / membrane / cathode in the battery. In detail, even when some components such as PTC elements are removed and a current blocking member is mounted, it is manufactured in a specific structure so that the insulating member interposed between the safety vent and the cap plate is not required in the prior art.

The removal of the PTC element also simultaneously satisfies the second requirement, since the PTC element, which is generally used as one of the battery safety elements, can rather hinder high rate charge and discharge. One of the representative causes of battery safety problems is a temperature increase inside the battery caused by a long continuous discharge. Therefore, when discontinuous operation is generally required, such as a power tool, it may be desirable to remove the PTC device. . For this reason, the present invention provides a cam assembly structure in which the PTC element is removed, but the removal of the PTC element alone cannot satisfy the third requirement.                     

As described above, the portion of the cap assembly from which the elements are removed is in physical contact for electrical coupling between the top cap and the safety vent. For example, in the case of power tools such as electric drills, which cause very high vibrations during use, such vibrations are transmitted as is to the power supply, and these physical shocks are caused by the top cap and safety vents, which make electrical coupling by physical contact. The contact surface between them is nonuniform and in some cases causes a large resistance. The inventors have found that unexpectedly significant effects are obtained when welding contact surfaces in such an electrically connected state. Such a result can be confirmed through the Example and comparative example which are demonstrated later.

Therefore, the lithium secondary battery of the present invention removes some elements essential in the conventional battery, electrically connects a positive electrode lead coupled to the positive pole of the power generator to the safety vent, and physical contact between the upper cap and the safety vent. By the construction of welding the site, all of the above requirements required for the power tool power source can be achieved.

A cap assembly structure according to one embodiment of the present invention is shown in FIG.

Referring to FIG. 2, the battery 100 according to the present invention inserts the generator 300 into the can 200 and injects the electrolyte therein, and the cap assembly 400 in the upper opening of the can 200. It is manufactured by mounting.

The cap assembly 400 is installed in close contact with the upper cap 410 and the safety vent 420 for lowering the internal pressure in the airtight gasket 500 installed in the upper beading part 210 of the can 200. . The upper cap 410 protrudes upward, and serves as a positive electrode terminal by connection with an external circuit. Regardless of the shape specified in FIG. 2, the safety vent 420 is capable of eliminating abnormal pressure rise in the battery and is not particularly limited as long as it is conductive, and has various structures known in the art. Can be applied. The lower end of the safety vent 420 is electrically connected to the anode of the power generator 300 through the anode lead 310.

The contact surface of the upper cap 410 and the safety vent 420 forms the weld 600 in at least one place. Preferably, the weld 600 is formed in a symmetrical structure in two places, four places, six places, and eight places, for example, so that the welding part 600 may be simultaneously formed at the radially symmetric position. The term "welding" used in the present invention is used in the concept including not only welding in the literal sense of laser welding, ultrasonic welding, resistance welding, but also a fastening method such as soldering. Welding may be performed in the process of assembling the cap assembly 400 itself, or may be performed even when the cap assembly 400 is mounted on the bead portion 210 of the can 200.

Compared to the cap assembly 40 of FIG. 1, the cap assembly 400 of FIG. 2 has become very thin overall, which can result in a larger volume of the generator 300 accommodated in the can 100.

In one preferred embodiment, the cap assembly of the present invention has a structure that further improves stability by discharging the gas to the outside when the internal pressure of the battery rises and at the same time block the flow of current.

For example, one or more gas outlets are formed in the upper cap, and the safety vent has a shape in which the central part is recessed, and a first notch and a second notch are formed at its upper and lower bent portions, respectively. Under the safety vent, one or more gas outlets and pressure-removable and upwardly projecting protrusions are included, the protrusions are coupled to the bottom of the safety vents and the anode lead is connected to a portion other than the protrusions. It further comprises a current blocking member that is present. Such a representative example is shown in FIG. 3.

Referring to FIG. 3, the upper cap 410 has a central portion projecting upward, and has a structure in which a plurality of holes 412 through which the compressed gas in the can 200 can be discharged are formed along the periphery of the protrusion. have.

The safety vent 420 is a thin film through which current flows, and a central portion of the safety vent 420 is recessed to form a groove 422, and two notches having different depths are respectively formed at upper and lower bending portions of the groove 422. 424 and 426 are formed. As shown in FIG. 4A, a first notch 424 formed at an upper portion of the notches 424 and 426 forms a closed curve, and a second notch 426 formed at a lower portion thereof has an open curved structure. It is. In addition, since the engagement force of the second notch 426 is made smaller than the engagement force of the first notch 424, the second notch 426 is dug deeper than the first notch 424.

The upper cap 410 and the safety vent 420 are installed in close contact with each other inside the gasket 500 to be sealed on the top of the can 200, and the welding part 600 is formed at at least one of the close contact portions. have. The material of the safety vent 420 is not particularly limited, and an aluminum-based material may be preferably used.

Due to the structure as described above, when the internal pressure of the can 200 rises above the critical pressure, the second notch 426 of the safety vent 420 does not withstand the pressure and breaks, so that the pressurized gas inside the can 200 is broken. It exits through the hole 412 of the top cap 410.

In this process, the current blocking member 700 for discharging the gas inside the battery and at the same time blocking the current is provided below the safety vent 420. The current blocking member 700 is provided in the auxiliary gasket 510 as a member of the conductive plate. Preferably, the material of the current blocking member 700 is made of the same material as the safety vent 420, and the auxiliary gasket 510 can prevent the current blocking member 700 and the safety vent 420 from being energized. It is made of polypropylene material.

4B shows an example of the current blocking member. Referring to this, the current blocking member 700 has a plurality of holes 710 (gas outlets) through which gas is discharged from the side, and the center portion protrudes upward. Protruding portion 720 is formed, and the protruding portion 720 is easily detachable from the current blocking member 700 and has a structure that is welded to the bottom surface of the groove 422 of the safety vent (420 of FIG. 3).

According to one embodiment of the invention, the current blocking member 700 is made of an aluminum material with a thickness of 0.4 ~ 0.5 mm with respect to the outer diameter 11 mm, the hole 710 is 6 mm around the center with a diameter of 2 mm The protrusion 720 formed in the center portion may be press-processed to have a diameter of 2.4 mm and a protrusion height of 0.38 mm so that the thickness of the interface between the protrusion 720 and the current blocking member 700 is about 0.12 mm. . Since the thickness of the boundary surface of the current blocking member 700 is thin, when the vent is deformed by the pressure, the protrusion 720 can be easily separated. Attaching the bottom of the groove 422 of the safety vent 420 and the protrusion 720 of the current blocking member 700 may be achieved by, for example, laser welding, ultrasonic welding, resistance welding.

Referring to the manufacturing process of the safety vent 420 and the current blocking member 700 of such a structure, the current blocking member 700 is inserted into the auxiliary gasket 510, and the protrusions 720 protruding upwardly; After welding the downward protruding groove 422 of the safety vent 420, the upper cap 410 is welded with the safety vent 420, and then inserted into the gasket 500 and the bead portion of the can 200. Crimped by mounting on 210 and pressing. However, as described above, other methods may naturally be applied as long as the battery structure of FIG. 3 can be manufactured.

5a to 5c illustrate the principle of operation of the structure.

Referring to FIG. 5A, when the pressure inside the battery rises due to the gas generated by abnormal operation of the battery, the pressurized gas is discharged through the gas outlet 710 formed in the current blocking member 700. Pressure is applied to 420. When the pressure of the gas is equal to or higher than the threshold (hereinafter, abbreviated as "first threshold pressure"), the groove 422 formed in the safety vent 420 by the pressure of the gas for pressurizing the safety vent 420. This is lifted upwards. At this time, the protrusion 720 of the current blocking member 700 which is welded to the bottom of the groove 422 is lifted together with the groove 422 while being separated from the current blocking member 700 as shown in FIG. 5B. The blocking member 700 is to be disconnected.

As such, the groove 422 of the safety vent 420 may be lifted up because of the first notch 424 and the second notch 426 formed in the safety vent 420. The notches 422 and 424 formed at the upper and lower bent portions of 422 are flexed flexibly to lift the grooves 422 which are bent downward. Thus, the first current blocking member 700 and the safety vent 420 and the upper cap 410 is connected to the current 720 is attached to the safety vent 420 current that is energized is separated from the current blocking member 700 As it falls, the current is cut off.

If there is additional gas generation even after the primary current is cut off, the safety vent 420 is continuously energized by the increased gas pressure, and the gas pressure is abbreviated as a threshold value (hereinafter, "second threshold pressure"). If more than one, as shown in Figure 5c, the second notch 426 of the safety vent 420 is broken to discharge the gas inside the battery to the outside. That is, when the second notch 426 of the lower bent portion formed in the safety vent 420 is broken without enduring gas pressure inside the battery, the groove 422 of the safety vent 420 is cut out from the safety vent 420. The gas leaked out through the breakage gap is discharged to the outside through the hole 412 formed in the upper cap 410 to lower the internal pressure of the battery. At this time, since the second notch 426 is a curved line and a part of which the notch is not formed, the part of which the notch is not formed is not broken, and only the part where the notch is formed is broken, and the groove 422 is a safety vent ( It is in a state of being stuck without falling completely from 420.

In one preferred example, the first critical pressure is 5 to 15 kgf / cm ² , preferably 10 to 12 kgf / cm ² , and the second critical pressure is 17 to 25 kgf / cm ² , preferably 19 to 21 kgf / cm ² .

In the present invention, the current blocking member may preferably have a structure in which a bridge in which notches are formed and connecting the through holes of 3 to 5 and the through holes are formed concentrically about the protrusion.

Therefore, when the pressure inside the battery rises above the first threshold pressure, the current is more easily separated from the current blocking member, thereby blocking the energization from the current blocking member to the safety vent.

6A schematically illustrates a structure according to an embodiment of the current blocking member as described above.

Referring to FIG. 6A, the current blocking member 701 has a plurality of through holes 710 through which gas is discharged along a side surface thereof, and an upwardly protruding protrusion 721 is formed in the center of the current blocking member 701. It is different from the current blocking member 700 of FIG. 4B in that three through holes 730 and three bridges 740 connecting the through holes 730 are symmetrically formed at the center. . As shown in FIG. 6B, the notch 750 is formed in the bridge 740 such that when the gas pressurized above the first threshold pressure is applied to the safety vent 420, the indentation part 422 enters. The protrusion 721 welded to the indent 422 while being raised is separated from the main body of the current blocking member 701 as the notch 750 is cut off.

As an example, the current blocking members 701 may be made of aluminum having a thickness of 0.4 to 0.5 mm with respect to an outer diameter of 8 to 11 mm, and six through holes 710 having a diameter of 1.0 to 1.5 mm around the center. The protrusion 721 has a diameter of 1.4 to 1.6 mm and a protrusion height of 0.15 to 0.3 mm, and the through hole 730 has a width of 0.4 to 0.7 mm and a circumferential length of 1.5 to 3.5 mm as its center radius. The distance (distant from the center of the protrusion) is 1.0 to 2 mm, and the notch 750 of the bridge 740 is composed of about 40 to 100 m in thickness.

Hereinafter, the present invention will be described in detail by way of examples, but the scope of the present invention is not limited thereto.

Example 1

The upper cap is made of SPC-3 (cold rolled steel sheet) plated with Ni, and the safety vent of the structure as shown in FIG. 4A and the current blocking member as shown in FIG. 4B are made using the aluminum plate (Al1050-H24). Each of them was manufactured, and the cap assembly was manufactured by laser welding the upper cap and the safety vent as shown in FIG. 3. The safety vent is a plate having an outer diameter of 16 mm and a thickness of 0.3 mm, wherein the first notch forming the upper bent portion thereof has a diameter of 10 mm and the thickness of 0.10 mm, the second notch forming the lower bent portion. Was made with a diameter of 4 mm and a thickness of 0.05 mm. The current blocking member is a plate having an outer diameter of 11 mm and a thickness of 0.45 mm, and six gas outlets having a diameter of 2 mm are radially drilled, and a protrusion having a diameter of 2.4 mm and a protrusion height of 0.38 mm in a half-blanking method in the center thereof. Was formed.

Using such a cap assembly, a cylindrical lithium battery of 18650 (diameter 18 mm, length 65 mm) was fabricated. The battery thus prepared was fully charged up to 100 mA at 4 A and 4.2 V, placed in an octagonal drum, rotated at a speed of 66 rpm for 30 minutes, and then the internal resistance of the battery was measured. The results are shown in Table 1 below.

Comparative Example 1

The battery was prepared in the same manner as in Example 1 except that the top cap and the safety vent were not welded in Example 1 and the drum test was performed. The results are shown in Table 1 below.

As shown in Table 1, the battery of Example 1 manufactured by the method according to the present invention had almost no change in resistance value before and after the drum test, whereas the battery of Comparative Example 1 had a significant increase in resistance after the test. Able to know.

As described above, the lithium secondary battery according to the present invention can exhibit a high energy density and instantaneous high output per unit volume of the battery to achieve high rate charge and discharge, and also during external physical shock such as vibration and dropping. Even if the resistance of the contact surface does not change, it can provide a uniform output, it can be preferably used as a power tool for power tools. In addition, it is possible to improve the stability of the battery when the safety vent to a specific structure.

Claims (6)

In a cap assembly mounted insulated from the bead of a cylindrical battery can via a gasket, a safety vent is electrically connected to the positive lead which is coupled to the positive pole of the power generator and has a top cap protruding upward from the center. The safety vent is connected along the outer circumferential surface of the, and the upper cap and the connection portion of the safety vent is composed of a structure welded; One or more gas outlets are formed in the top cap; The safety vent has a shape in which a central portion is recessed and a first notch and a second notch are formed at its upper and lower bent portions, respectively; Under the safety vent, one or more gas outlets and pressure-removable and upwardly projecting protrusions are included, the protrusions are coupled to the bottom of the safety vents and the anode lead is connected to a portion other than the protrusions. A lithium secondary battery capable of high rate charging and discharging, characterized in that the current blocking member is included. The lithium secondary battery according to claim 1, wherein the welding portion is formed in a mutually radial symmetric structure as two or more. The lithium secondary battery according to claim 1, wherein the welding is performed by laser welding, ultrasonic welding, resistance welding or soldering. delete The lithium secondary battery according to claim 1, wherein the current blocking member comprises a bridge having a notch formed between the through holes and the through holes of 3 to 5 concentrically about the protrusion. The lithium secondary battery according to any one of claims 1 to 3 and 5, wherein the battery is used as a power source for a power tool.

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