KR20070094147A - Electrochemical device having advanced safety by using thermal expasion materials and preparation method thereof - Google Patents

Abstract

An electrochemical device, and a method for preparing the electrochemical device are provided to improve safety by increasing the volume and pressure inside a device. An electrochemical device is provided with a material whose volume is expanded by heat in the empty space of the inside of the device at a temperature above a certain point. Preferably the certain point(temperature) is 60 deg.C. Preferably the material is at least one selected from polyethylene, polypropylene, polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polytetrafluoroethylene, poly(vinyl fluoride), polyacrylonitrile, poly(vinyl chloride), poly(vinyl vinylidene), polymethyl methacrylate, polymethyl acrylate, poly(vinyl alcohol), polymethacrylonitrile, poly(vinyl acetate), poly(vinyl pyrrolidone), polycarbonate, polyethylene terephthalate, polycaprolactam, polyurethane, polyethyleneimine, polybutadiene, polystyrene, and polyisoprene.

Description

ELECTROCHEMICAL DEVICE HAVING ADVANCED SAFETY BY USING THERMAL EXPASION MATERIALS AND PREPARATION METHOD THEREOF}

Figure 1 is a schematic diagram showing the volume change according to the temperature change of the thermal expansion material inserted into the mandrel in accordance with the present invention.

The present invention introduces a thermally expandable material that increases in volume as the temperature increases, thereby increasing the volume of the thermally expandable material when the internal temperature of the device rises above an abnormal temperature range, such as high temperature storage and overcharging, such as an empty space in a sealed device. The present invention relates to an electrochemical device having improved safety by maximizing space reduction and pressure increase, and a method of manufacturing the same.

Recently, the demand for the diversification of functions and long-term use of portable electronic devices has increased. Accordingly, the demand for securing safety of lithium secondary batteries used as power sources of portable electronic devices has increased.

As a means for improving the safety of a lithium secondary battery, a large amount of gas is generated by side reaction between the positive electrode active material of the battery and the electrolyte during high temperature storage or overcharging, and when the pressure inside the battery increases over a certain range, There is a method of preventing further battery reaction by operating the pressure-sensitive device (eg, CID) provided therein.

In order to trigger the operation of the pressure sensitive element as described above, a method of adding a gas generating substance to the electrolyte under high temperature and high voltage has been reported, but a large amount of gas is generated to obtain sufficient pressure to operate the pressure sensitive element described above. There is a problem that needs to be done. In addition, there is a problem that the pressure sensitive element does not operate effectively during overcharging due to the limitation of the gas generation rate.

On the other hand, a method of improving the safety by increasing the resistance of the electrode when the temperature inside the battery increases by adding a portion of the thermal expansion material to the electrode active material, in this case, the loss of the overall battery capacity by the amount of the electrode active material replaced by the thermal expansion material There is a reduced problem.

The inventors have found that the above abnormal conditions (eg, 100 ° C. or more), instead of using an electrolyte additive that must generate a large amount of gas, to trigger the operation of the pressure sensitive element to promote battery safety during high temperature storage and / or overcharge. It is intended to increase the safety of the battery by introducing a thermal expansion material on an empty space inside the battery, which induces an increase in pressure due to an increase in the volume inside the sealed battery under temperature.

Accordingly, an object of the present invention is to provide an electrochemical device into which the above-described thermal expansion material is introduced and a method of manufacturing the same.

The present invention provides an electrochemical device, preferably a lithium secondary battery, characterized in that a material that is bulk-expanded by heat at a predetermined temperature or more on an empty space inside the device.

In addition, the present invention provides a method for manufacturing an electrochemical device using a core (mandrel), the method of manufacturing an electrochemical device comprising the step of coating or inserting a material that is expanded in volume by heat at a predetermined temperature or more inside the core. To provide.

In addition, the present invention comprises the steps of: (a) coating or inserting a material that is volume-expanded by heat at a temperature higher than a predetermined temperature on the inner top and bottom of the device case; (b) injecting a battery assembly manufactured using a cathode, an anode, and a separator interposed therebetween into the device case; And (c) it provides a method for producing an electrochemical device comprising the step of closing the electrolyte after the electrolyte in the device case.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is intended to operate the pressure-sensitive device provided inside the device in order to improve the safety of the electrochemical device under abnormal conditions such as high temperature storage, overcharge, etc., electrochemically the thermal expansion material that significantly increases in volume with increasing temperature It is characterized in that it is introduced into the top and / or bottom of the interior of the device, such as inside the mandrel or inside the electrochemical device case.

The effects that may occur due to the features of the present invention as described above are as follows.

1) In the prior art, the thermal expansion material was used as a component of the electrode slurry to improve the safety of the battery by increasing the electrode resistance when the temperature rises, but in this case, the capacity of the battery is reduced by the amount of the electrode active material replaced with the thermal expansion material. The problem was caused. In contrast, in the present invention, the thermal expansion material is introduced into the empty space inside the electrochemical device so that a problem such as a decrease in capacity of the battery does not occur at all.

2) In addition, the thermal expansion material used in the present invention is present in its original form in the empty space inside the device under normal conditions, as shown in FIG. 1, thus, does not affect the operation of the battery at all. When a certain temperature is reached by high temperature storage, overcharging, etc., a significant volume increase causes an empty space in the sealed device and an increase in pressure, thereby easily triggering the operation of the pressure sensitive device included in the same device. In this case, the pressure sensitive device may prevent further charging, thereby improving the safety of the electrochemical device.

According to the present invention, any thermally expandable material inserted into and / or coated on an internal void of an electrochemical device, preferably by filling, may be used without limitation as long as the material expands in volume by heat above a predetermined temperature. Is a material that thermally expands at a temperature of at least 60 ° C, more preferably at least 80 ° C. Non-limiting examples thereof include polyethylene, polypropylene, polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyacrylonitrile, polyvinyl chloride, polyvinyl chloride Leadene, polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinyl pyrrolidone, polycarbonate, polyethylene terephthalate, polycaprolactam, polyurethane, polyethyleneimine , Polybutadiene, polystyrene, polyisoprene or mixtures thereof.

The thermal expansion properties of the material are related to the melting temperature of the material itself, and volume expansion occurs when a certain temperature is reached, which leads to a reduction in the empty space in the device and thereby an increase in pressure.

When the above-mentioned thermally expandable material is inserted, there is no particular limitation on the usable content and / or thickness range during coating, and can be appropriately adjusted within a range that can easily trigger the operation of the pressure sensitive element. Do.

The position of the device into which the thermal expansion material is introduced according to the present invention can be introduced without particular limitation as long as it is an empty space inside the device. Particularly, the inside of the mandrel, the inside top and / or bottom of the device case are preferable. .

The case of the electrochemical device can be used in any can, pouch or case form known in the art, wherein the material, thickness or shape constituting the device case is not particularly limited.

The electrochemical device in which the thermal expansion material is introduced into the empty space inside the device according to the present invention includes a pressure sensitive device in the same device, preferably an integrated pressure sensitive device, or (i) a pressure sensitive device; (ii) conducting wires carrying current delivered from the pressure sensitive element; And (iii) safety means for stopping charging of the device or switching the charging state to a discharge state in response to the current transmitted through the conductive wire.

In this case, the pressure sensitive element refers to an element that senses a change in pressure in the sealed element, that is, a pressure rise, so that charging of the electrochemical element does not proceed any further, and includes both a safety element function and a function of the pressure sensitive element. It may be integral, and there may also be a pressure sensitive element and a safety element separately as described above. However, the type or manner thereof is not particularly limited as long as the above operation is performed in a specific pressure range.

Examples of the pressure sensitive device include a current interupt device (CID), a crystal having piezoelectricity that generates a current by detecting a change in pressure.

In the electrochemical device according to the present invention, when the internal temperature of the device rises to a temperature range where the volume of the thermally expandable material is increased, the pressure response is increased through the increase of the volume of the thermally expandable material inserted and coated on the empty space of the device and the internal pressure of the device. The operation of the device is promoted, which leads to an improvement in the safety of the device.

In this case, the pressure range in which the pressure sensitive element operates is not limited in particular as long as it is outside the normal device internal pressure and no explosion occurs, but is preferably in the range of 2 to 20 atmospheres.

The electrochemical device configured as described above may be applied to conventional electrochemical devices known in the art, that is, all devices that perform electrochemical reactions, but are preferably lithium secondary batteries, and specific examples thereof include lithium metal secondary batteries and lithium. Ion secondary batteries, lithium polymer secondary batteries or lithium ion polymer secondary batteries.

According to the present invention, a method of inserting and / or coating a thermally expandable material that causes a volume change with temperature change on an internal empty space of an electrochemical device may use conventional insertion and / or coating methods known in the art.

Hereinafter, an embodiment of the manufacturing method according to the present invention, in the manufacturing method of the electrochemical device using the core (mandrel), the coating or inserting a material that is bulk-expanded by heat at a predetermined temperature or more in the core core It may include a step.

1) Coat or insert a material that expands in volume by heat above a certain temperature inside the mandrel.

At this time, the content of the thermal expansion material may be filled up to 100% by volume of the inner core space in consideration of the increase in volume as the temperature changes, preferably about 10 to 80% of the inner core space. However, it is not limited thereto.

2) Wind the positive electrode, separator, negative electrode, and separator using the core in which the thermal expansion material is inserted as described above, and then insert it into the device case.

In this case, the thermal expansion material may be additionally coated or inserted into the upper and / or lower ends of the device case into which the wound is added.

In the above, the positive electrode is a foil and a cathode current collector, i.e., copper, gold, nickel, each of which is made of a cathode active material and a cathode active material by an anode current collector, that is, aluminum, nickel, or a combination thereof. Or it is comprised in the form bound to the foil manufactured by copper alloy or these combination.

As the cathode active material, a conventional cathode active material that can be used for the anode of a conventional electrochemical device can be used, and in particular, lithium manganese oxide (lithiated magnesium oxide), lithium cobalt oxide (lithiated cobalt oxide), lithium nickel oxide (lithiated nickel oxide) Or a lithium intercalation material such as a composite oxide formed by a combination thereof. In addition, the negative electrode active material may be a conventional negative electrode active material that can be used for the negative electrode of the conventional electrochemical device, in particular lithium metal, or lithium alloy and carbon (carbon), petroleum coke, activated carbon (activated carbon) Lithium adsorption materials such as graphite or other carbons are preferable.

The separator may be a porous separator, for example, a polypropylene-based, polyethylene-based, or polyolefin-based porous separator may be used, but is not limited thereto.

1) The electrolyte may be added to the device case and then sealed to complete manufacture of the electrochemical device.

The electrolyte used in the present invention is A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+, and comprising an alkali metal cation or an ion composed of a combination thereof, such as K ^+, B ^- is PF ₆ ^{- _{, BF 4 -, Cl -,}} Br -, I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO 2 ₃ ) Salts containing ions consisting of anions such as ₃ ^- or combinations thereof include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate. (dimethyl carbonate, DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran ), N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate preferably dissolved and dissociated in an organic solvent consisting of carbonate, EMC), gamma butyrolactone (GBL) or mixtures thereof.

In addition, for another embodiment of the manufacturing method according to the present invention, (a) coating or inserting a material that is volume-expanded by heat at a temperature higher than a predetermined temperature on the inner top and / or bottom of the device case; (b) injecting a battery assembly manufactured using a cathode, an anode, and a separator interposed therebetween into the device case; And (c) sealing the electrolyte after injecting the electrolyte into the device case.

At this time, the method of coating or inserting the thermal expansion material on the inner top and / or bottom of the device case according to the present invention can be carried out according to conventional methods known in the art, in particular, for example, the solvent evaporation method ( solvent evaporation), co-precipitation method, precipitation method, sol-gel method, post adsorption filter method, electrolytic plating or electroless plating.

The manufacturing method is applicable to all electrochemical device manufacturing methods except the method using a mandrel.

The external shape of the electrochemical device, preferably a lithium secondary battery, manufactured by the method presented in the present invention is not particularly limited, but may be a cylindrical, coin-shaped, square or pouch type of can.

The invention is explained in more detail based on the following examples and experimental examples. However, Examples and Experimental Examples are for illustrating the present invention and are not limited to these.

Example 1. Lithium Secondary Battery Preparation

(Anode manufacturing)

LiCoO ₂ is used as a positive electrode active material, and a conductive agent and a binder are added to NMP (N-methyl-2-pyrrolidone) to prepare a positive electrode slurry, and then coated on an aluminum (Al) current collector to prepare a positive electrode.

(Cathode production)

As the negative electrode active material, artificial graphite is used, and a binder is added to NMP to prepare a negative electrode slurry, and then coated on a copper (Cu) current collector to prepare a negative electrode.

(Electrolyte amount)

As electrolyte solution, an ethylene carbonate (EC) solution is used in 1M LiPF ₆ .

(Manufacture of core with inserted thermal expansion material)

A core is prepared by adding about 70% by volume of polyethylene with an empty space inside the core.

(Battery manufacturing)

A jelly roll prepared by winding a polyolefin-based separator between the positive electrode and the negative electrode based on the prepared core is introduced into a circular battery case, and then the electrolyte is prepared by injecting the electrolyte.

Comparative example  One

A lithium secondary battery was manufactured in the same manner as in Example 1, except that a conventional mandrel without polyethylene was used.

In the electrochemical device according to the present invention, a material that thermally expands at a temperature of 60 ° C. or more on an empty space in a device may implement safety improvement of a battery through increase in volume and pressure in the device according to temperature change.

Claims (13)

An electrochemical device, characterized in that a material that is bulk-expanded by heat above a predetermined temperature on an empty space inside the device. The electrochemical device of claim 1, wherein the constant temperature is 60 ° C. The electrochemical device of claim 1, wherein a content of the material that is expanded in volume by heat at a predetermined temperature or more is in a range of 10 to 100% of an empty space inside the device. The material of claim 1, wherein the material expands by heat above the predetermined temperature is polyethylene, polypropylene, polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, poly Acrylonitrile, polyvinyl chloride, polyvinylidene chloride, polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinyl pyrrolidone, polycarbonate, polyethylene terephthalate And at least one electrochemical device selected from the group consisting of polycaprolactam, polyurethane, polyethyleneimine, polybutadiene, polystyrene and polyisoprene. The electrochemical device of claim 1, wherein the void space of the device is selected from the group consisting of a mandrel inside, an inner top and a bottom of the device case. The electrochemical device of claim 1, wherein the device comprises a pressure sensitive device. The device of claim 6, wherein the device comprises: (i) a pressure sensitive device; (ii) conducting wires carrying current delivered from the pressure sensitive element; And (iii) safety means for stopping charging of the device or switching the charging state to a discharge state in response to a current delivered through the lead. The device of claim 1, wherein the device increases the volume of thermally expandable material inserted or coated onto the void in the device, decreases the void space in the device, and increases the internal temperature of the device to a temperature range that results in an increase in volume of the thermally expandable material. Electrochemical device characterized in that the operation of the pressure-sensitive device is promoted by increasing the pressure. The electrochemical device of claim 1, wherein the electrochemical device is a lithium secondary battery. A method of manufacturing an electrochemical device using a core (mandrel), the method of manufacturing an electrochemical device comprising the step of coating or inserting a material that is expanded in volume by heat above a predetermined temperature inside the core. The method of claim 10, wherein the manufacturing method (a) coating or inserting a material that expands in volume by heat above a predetermined temperature within a mandrel; (b) winding the positive electrode, the separator, the negative electrode, and the separator in the core and inserting the same into a device case; And (c) injecting an electrolyte into the device case and then sealing it Method of manufacturing an electrochemical device comprising a. 12. The method of claim 11, further comprising coating or inserting, between steps (b) and (c), a material that expands in volume by heat at a temperature higher than a predetermined temperature to an inner top, bottom, or top and bottom of the device case. Manufacturing method. (a) coating or inserting a volume-expanded material by heat at a temperature higher than a predetermined temperature on the inner upper and lower ends of the device case; (b) injecting a battery assembly manufactured using a cathode, an anode, and a separator interposed therebetween into the device case; And (c) injecting an electrolyte into the device case and then sealing it Method of manufacturing an electrochemical device comprising a.

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