Patent ID: 12199310

BEST MODE

Hereinafter, the preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms or words used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, and should be interpreted based on the meanings and concepts corresponding to technical aspects of the present disclosure on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation.

Therefore, the embodiments described herein and illustrations shown in the drawings are just a most preferred embodiment of the present disclosure, but not intended to fully describe the technical aspects of the present disclosure, so it should be understood that other equivalents and modifications could be made thereto at the time of filing the application. In the drawings, like reference numerals denote like elements.

In the embodiments described below, a secondary battery refers to a lithium secondary battery. Here, the lithium secondary battery refers collectively to secondary batteries in which lithium ions act as working ions during charging and discharging, causing electrochemical reactions at the positive electrode plate and the negative electrode plate.

Meanwhile, it should be interpreted as that even if the name of the secondary battery changes depending on the type of the electrolyte or separator used in the lithium secondary battery, the type of the battery case used to package the secondary battery and the internal or external structure of the lithium secondary battery, the lithium secondary battery covers any secondary battery using lithium ions as working ions.

The present disclosure may be also applied to secondary batteries other than lithium secondary batteries. Accordingly, it should be interpreted that the present disclosure covers any type of secondary battery to which the technical aspects of the present disclosure may be applied, though working ions are not lithium ions.

Hereinafter, a terminal busbar embodiment of the present disclosure will be described with reference toFIGS.2and3.

FIG.2shows a terminal busbar according to an embodiment of the present disclosure.FIG.3shows a terminal busbar according to another embodiment of the present disclosure.

First, referring toFIG.2, the terminal busbar150includes a coupling portion160and a terminal portion170. The terminal portion170is a portion that is bent in the vertical direction at one end of the coupling portion160.

The coupling portion160is an approximately plate-shaped element having a small thickness T relative to a length L and a width W. The coupling portion160includes a first metal layer162, a material layer164and a second metal layer166stacked in that order from bottom to top along the extension direction of the terminal portion170, and the material layer164is conductive in a normal condition, and when the temperature rises, may act as resistance. The first metal layer162, the material layer164and the second metal layer166are stacked along the thicknesswise T direction. The thickness of the terminal portion170may be equal to the thickness T of the coupling portion160. The first metal layer162is integrally formed with the terminal portion170, and the second metal layer166provides a connection surface with the electrode lead of the battery cell. The terminal portion170may be used for an external input or to connect between battery modules. In general, a component that is connected to the electrode lead to form an electrical wiring is referred to as a busbar, so the component including the coupling portion160and the terminal portion170may be just called a busbar, but as opposed to other busbars, in addition to the coupling portion160, the component further includes the terminal portion170, and due to this difference, it is referred to as a terminal busbar in the present disclosure.

The first metal layer162and the second metal layer166may include metal having high electrical conductivity. For example, the first metal layer162and the second metal layer166may include at least one of aluminum, copper, nickel and SUS. The first metal layer162and the second metal layer166may include various types of materials used as the existing busbar materials. The first metal layer162and the second metal layer166may be a same type or different types.

The material layer164sandwiched between the first metal layer162and the second metal layer166includes a gas generating material that decomposes at a predetermined temperature or above to produce gas and increase the resistance. Preferably, the material layer164includes the gas generating material, a conductive material and an adhesive. The conductive material is connected and immobilized by the adhesive, and when the gas generating material produces gas, the connection of the conductive material may be disconnected, and the resistance may increase. The gas generating material may be a volume expandable resin.

The gas generating material is preferably melamine cyanurate that is a type of volume expandable resin. Melamine cyanurate is a material used as a nitrogen-phosphorus flame retardant containing a combination of nitrogen and phosphorus, and is available as a raw material having the average particle size on the level of a few tens of um through different manufactures.

Melamine cyanurate primarily used for flame retardancy undergoes endothermic decomposition of above 300° C. Melamine cyanurate decomposes into melamine and cyanuric acid. Evaporated melamine releases inactive nitrogen gas. The decomposition temperature is adjusted by adjusting the molecular weight of melamine cyanurate. The structural formula of melamine cyanurate is as below:

The conductive material is not limited to any particular type of material having the conductive property, and may include, for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers or metal fibers; metal powder such as fluorocarbon, aluminum, silver and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxide such as titanium oxide; and conductive materials such as polyphenylene derivatives.

The adhesive is a substance that assists in binding the gas generating material and the conductive material and binding to the first metal layer162and the second metal layer166. Examples of the adhesive may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene ter polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber and a variety of copolymers.

When the temperature rises above a predetermined level, for example, above 300° C., in abnormal situations, melamine cyanurate in the material layer164interposed between the first metal layer162and the second metal layer166decomposes to produce N2gas. Accordingly, the material layer164increases in resistance and acts as a resistance layer.

A method for manufacturing the terminal busbar150may include the following steps. First, a metal element M is prepared such that the first metal layer162is integrally formed with the terminal portion170and its cross section has an L shape. To make the total thickness the thickness T, the metal element M may be prepared such that the first metal layer162is thinner than the terminal portion170. The metal element M may be made by processing a metal plate. Subsequently, the material layer164is formed on the first metal layer162. Additionally, the second metal layer166is stacked on the material layer164. The thickness of each of the material layer164and the second metal layer166may be set so that the total thickness when the material layer164and the second metal layer166are stacked on the first metal layer162satisfies the thickness T.

When the material layer164includes the gas generating material, the conductive material and the adhesive, the method may further include pressing to adhere together after stacking the second metal layer166on the material layer164.

The material layer164may be formed by applying a paste or a slurry prepared by mixing the gas generating material, the conductive material and the adhesive onto the first metal layer162. When the second metal layer166is placed thereon and pressed upward and downward, the terminal busbar150having the material layer164interposed between the two metal layers162,166may be obtained. Additional thermal treatment may be performed where necessary.

The thickness T of the coupling portion160may be equal to the thickness of the existing busbar. The first metal layer162and the second metal layer166may be made of the same material as the existing busbar. When the conductive material in the material layer164is equal to or higher than the existing busbar material, the electrical conductivity of the material layer164in the normal condition may become similar to the electrical conductivity of the existing busbar.

Accordingly, in normal situations, conductivity of the material layer164in the terminal busbar150is maintained, and the battery module performance is exhibited on a similar level to the battery module performance when the existing busbar is used. When the temperature rises above a predetermined level in abnormal situations, the resistance of the material layer164increases, and is enough to shut off the current flow. Accordingly, when the temperature rises, the material layer164acts as resistance to shut off the current, thereby improving the safety of a battery module including the same.

The terminal busbar150′ shown inFIG.3is basically the same as the terminal busbar150ofFIG.2. The terminal busbar150′ further includes an opening168in the coupling portion160, the opening168through which the electrode lead passes. The number of openings168may be different depending on the number of electrode leads or the connection method. The terminal portion170further includes a hole172. The hole172is used for an external input or to connect between battery modules. The number of holes172may be different depending on the connection method.

The terminal busbar150or150′ provided by the present disclosure has a triple structure of the metal−the volume expandable resin+the conductive material+the adhesive−the metal, where the electrode lead is connected by welding (corresponding to the long axis of the busbar). In normal situations, the current may flow between the terminal busbar and the electrode lead, but the volume expandable resin in the volume expandable resin+the conductive material+the adhesive expands the volume at high temperature, forming a gap in the conductive material, resulting in increased resistance. Accordingly, the resistance between the terminal busbar and the electrode lead increases, which prohibits the current flow. As described above, the current flow through the terminal busbar is prohibited at abnormal temperature, and thus a battery module including the terminal busbar has improved safety.

FIG.4schematically shows a battery module including the terminal busbar according to another embodiment of the present disclosure.FIG.5is a front view of the terminal busbar included in the battery module ofFIG.4, andFIG.6is a cross-sectional view ofFIG.5taken along the line VI-VI′.FIG.7is a front view of the terminal busbar included in the battery module ofFIG.4.

The battery module1000ofFIG.4has a 4P3S connection. That is, three cell banks211are connected in series S, and each cell bank211includes four battery cells210connected in parallel P. Each battery cell210may be a pouch-type battery cell as shown inFIG.1. 4P3S is provided by way of illustration, and the battery module of the present disclosure is not limited thereto.

The battery cell210is a secondary battery, and has two electrode leads240extending out of a pouch case230. The electrode leads240are classified into the positive (+) lead and the negative (−) lead according to the electrical polarity and electrically connected to an electrode assembly (not shown) received in the hermetically sealed pouch case230. That is, the positive lead is electrically connected to the positive electrode plate of the electrode assembly, and the negative lead is electrically connected to the negative electrode plate of the electrode assembly. As described above, the battery cell210is a pouch-type secondary battery in which one end of the electrode leads240of the opposite polarities of the battery cell210is connected to each of two ends of the electrode assembly, the electrode assembly is received in the pouch case230together with the electrolyte solution, the pouch case230is hermetically sealed, and the other end of the electrode leads240is exposed to the outside of the pouch case230.

The electrode leads240extend out of the two ends of the battery cell210. Within the cell banks211connected in parallel, the electrode leads240are stacked such that the electrode leads240of the same polarity are arranged next to each other. Additionally, the electrode leads240are stacked in opposite polarities between the cell banks211. There may be many methods for connecting the electrode leads240, andFIGS.4to7show that the other end of the electrode lead240is bent left or right to provide a flat contact surface, which is placed over a busbar290or the terminal busbar150′ and connected by welding.

Referring toFIGS.4to7, the terminal busbar150′ connects the electrode leads240of the same polarity in one cell bank211. The busbar290connects the electrode leads240of the opposite polarities between the two cell banks211. In this embodiment, two terminal busbars150′ and two busbars290are provided.

The terminal busbar150′ and the busbar290are disposed between the bent parts of each electrode lead240, parallel to the stack direction of the battery cells210, and they are connected to the electrode leads240. The connection method may include methods commonly used in the art, for example, ultrasonic welding and laser welding, but is not limited thereto.

The terminal busbar150′ and the busbar290have openings168,296through which the electrode leads240pass. The description made with reference toFIGS.2and3is equally applied to the terminal busbar150′.

Seeing the front view of the terminal busbar150′ as shown inFIG.5and the front view of the busbar290as shown inFIG.7, an approximately O shape is formed around the opening168,296. After the electrode lead240passes through the opening168,296formed at the center and is bent, welding of the electrode lead240and the busbar150′,290is linearly performed along the long axis of the busbar150′,290.

Particularly, as shown inFIGS.4and5, four electrode leads240may be coupled to the second metal layer166of the coupling portion160of one terminal busbar150′. As described above, when four electrode leads240are coupled to the coupling portion160of one terminal busbar150′, two of the four electrode leads240may be stacked each other, bent left through the opening168and connected to the left side of the coupling portion160, and the remaining two electrode leads240may be bent left and connected to the right side of the coupling portion160.

In this instance, the four electrode leads240are each provided in four different battery cells210, and they have the same polarity. For example, the electrode leads240connected to the top right terminal busbar150′ ofFIG.4are all positive electrode leads. Accordingly, the top right terminal busbar150′ ofFIG.4may be referred to as a positive electrode terminal busbar. The electrode leads240connected to the bottom left terminal busbar150′ ofFIG.4are all negative electrode leads. Accordingly, the bottom left terminal busbar150′ ofFIG.4may be all referred to as a negative electrode terminal busbar.

Referring toFIGS.4and7, eight electrode leads240may be coupled to one busbar290. As described above, when eight electrode leads240are coupled to one busbar290, two of the eight electrode leads240are stacked each other, bent right and connected to the left side of the busbar290, and the remaining two electrode leads240are stacked each other, bent right through the left opening296of the two openings296and connected to the left side of the central part of the busbar290. The remaining two electrode leads240are stacked each other, bent left through the right opening296of the two openings and connected to the right side of the central part of the busbar290. The remaining two electrode leads240are bent left and connected to the right side of the busbar290.

In this instance, the eight electrode leads240are each provided in eight different battery cells210, and four electrode leads240on the left side have the same polarity while four electrode leads240on the right side have opposite polarities. For example, the electrode leads240connected to the busbar290are four positive electrode leads and four negative electrode leads.

Particularly, a current flow path running through the terminal busbar150′ of the present disclosure will be described in detail with reference toFIG.6. Referring toFIG.6, the current flow path into the battery module1000from the outside of the battery module (1000ofFIG.4) goes through the terminal portion170, the first metal layer162, the material layer164, the second metal layer166of the terminal busbar150′ and then to the electrode leads240. As described above, the material layer164is a material that is conductive in the normal condition, and may act as resistance when the temperature rises. When the temperature rises above a predetermined level, for example, above 300° C., in abnormal situations, melamine cyanurate decomposes in the material layer164to produce N2gas. Accordingly, the material layer164increases in resistance and acts as a resistance layer. Additionally, electrical connection may be disconnected through volume expansion.

Accordingly, in normal situations, conductivity of the material layer164in the terminal busbar150′ is maintained, and the battery module performance is exhibited on a similar level to the existing busbar. When the temperature rises above a predetermined level in abnormal situations, the resistance of the material layer164increases, which prohibits the current flowing to the terminal portion170and the first metal layer162from flowing to the material layer164and the second metal layer166. Accordingly, it is possible to shut off the current flow to the electrode leads240. Accordingly, when the temperature rises, the material layer164acts as resistance to shut off the current. Accordingly, even when the secondary battery protection circuit does not operate, it is possible to shut off the current flow to prevent the current from flowing any longer, for example, to prevent the secondary battery from being charged, thereby increasing the safety of the battery module1000. As described above, the battery module1000of the present disclosure improves the terminal busbar to automatically shut off the current flow when the temperature rises, thereby achieving the overcharge prevention function of the secondary battery protection circuit and ensuring the safety of the battery module1000. When the terminal busbar150′, not the busbar290, is configured as described above, it is possible to prevent the current flow to the battery module1000from coming from an external device or other battery module.

The main cause of safety reduction caused by a rapid rise in the temperature of the lithium secondary battery is a short circuit current, and it is very important to ensure the safety of the battery module or the battery pack including battery cells connected to each other when a short circuit occurs. As the short circuit resistance is lower, a higher short circuit current flows, and high temperature heat is generated, and when the battery cell cannot withstand the high temperature heat, a fire occurs. When the short circuit resistance is very low, in some cases, a safe outcome is obtained, and when heat generated during the flow of large current exceeds 660° C., the electrode leads melt and the current flow is shut off, thereby ensuring safety. When the temperature is lower than 660° C., the electrode leads do not melt, the current flow continues, high temperature heat increases, and when the battery cell cannot withstand the high temperature heat, a fire occurs. In contrast, a large current may flow even in normal situations. In situations such as fast charging, sudden acceleration or startup of an electric vehicle, a large current flows in the battery module and high temperature heat is generated from the electrode leads, and in this normal situation, operating should never be done. To prevent this, it is necessary to shut off the current flow at the temperature of about 250° C. or above.

In this embodiment, when the battery module1000reaches about 300° C., gas is generated in the material layer164of the terminal busbar150′ to increase the resistance of the material layer164. Accordingly, the shut off mechanism by the material layer164does not operate in the normal large current range, and is allowed to operate only when overheated above the temperature due to an actually occurred short circuit, thereby preventing a fire and explosion and ensuring safety. Additionally, as opposed to a PTC device or a fuse used to improve safety, it does not occupy the space in the module and does not reduce the energy density.

The battery module1000according to the present disclosure has high safety, and thus is suitable for a power source of medium- and large-scale devices requiring high temperature stability, long cycle characteristics and high rate characteristics. Preferable examples of the medium- and large-scale device may include, but are not limited to, power tools; electric vehicles including Electric Vehicles (EVs), Hybrid Electric Vehicles (HEVs) and Plug-in Hybrid Electric Vehicles (PHEVs); electric two wheelers including E-bikes and E-scooters; electric golf carts; and ESSs, which are powered on and work by power from an electric motor.

The terminal busbar150′ and the busbar290may have varying shapes and sizes to form a variety of electrical connection relationships. Additionally, an interconnect board (ICB) assembly in which the terminal busbar150′ and the busbar290are assembled on a plastic frame considering the wiring relationship is applied to the battery module manufacturing process, rather than the terminal busbar150′ and the busbar290used alone. The type of the frame and the type of the busbar combined with the frame are different depending on the connection relationship of the battery module. Accordingly, those skilled in the art will understand that a variety of variations may be made to the present disclosure.

FIG.8is a photographic image of an experimentally manufactured interconnect board (ICB) assembly.

The ICB assembly300includes the frame310, the busbar290and the terminal busbar150′.

The terminal busbar150′ may be fixed to the frame310through piercing, and thus when the material layer164such as the volume expandable resin+the conductive material+the adhesive is horizontally sandwiched between the first metal layer162and the second metal layer166as proposed by the present disclosure, there is no sliding or layer separation problem between the volume expandable resin+the conductive material+the adhesive and the first metal layer162, the volume expandable resin+the conductive material+the adhesive and the second metal layer166.

As described above, according to the present disclosure, safety may be enhanced through improvements in the terminal busbar of the battery module. When the battery module1000is manufactured using the terminal busbar150′ according to the present disclosure in place of the existing busbar, stability is improved, and the existing battery cell manufacturing process is used, thereby eliminating the need to change the process or adjust the mass-production process.

As described above, according to the present disclosure, in normal situations, conductivity of the material layer164in the terminal busbar150′ is maintained, the battery module performance is exhibited on a similar level to the existing battery module, and when the temperature rises above a predetermined level in abnormal situations, the current flow is shut off, thereby improving the safety of the battery module1000. Accordingly, it is possible to improve the safety of the battery module1000, a battery pack including the same, and a vehicle including the battery pack.

FIG.9is a diagram illustrating a battery pack according to still another embodiment of the present disclosure.

The battery pack1200includes at least two battery modules1000as described above. An inter-busbar1250connects the terminal portions170of the terminal busbars150′ between adjacent battery modules1000. That is, the inter-busbar1250connects the terminal portion170of the terminal busbar150′ of any one of the at least two battery modules1000to the terminal portion170of the terminal busbar150′ of the other battery module1000so as to connect the battery modules1000.

The inter-busbar1250may be in the shape of a plate that contacts the terminal portion170of the terminal busbar150′. For a simple shape of the inter-busbar1250, i.e., for the shortest distance between adjacent terminal busbars150′, the position of the terminal busbar150′ in the battery module1000may be adjusted. For example, the battery module1000ofFIG.4is located at the bottom ofFIG.9, and the battery module formed in left-right mirror symmetry of the battery module1000ofFIG.4is located at the top ofFIG.9.

In the structure ofFIG.9, the top right terminal busbar150′ is a negative electrode terminal busbar. The terminal portion170of the terminal busbar150′ has a negative electrode terminal electrically connected to an external terminal for an external input. The two terminal busbars150′ on the left side at the central part are a positive electrode terminal busbar and a negative electrode terminal busbar downwards from the top ofFIG.9. Accordingly, the inter-busbar1250connects the two terminal busbars150′ of opposite polarities in series. The bottom right terminal busbar150′ is a positive electrode terminal busbar. The terminal portion170of the terminal busbar150′ has a positive electrode terminal electrically connected to an external terminal for an external input.

Connection between the terminal busbar150′ and the inter-busbar1250may be accomplished by bolt-nut fastening using a hole172formed in the terminal portion170of the terminal busbar150′. Accordingly, the inter-busbar1250may have another hole for bolt-nut fastening at the location that matches the hole172.

The battery pack1200may further include a pack case to package the battery modules1000. Additionally, in addition to the battery module1000and the pack case, the battery pack1200according to the present disclosure may further include various types of devices to control the charge/discharge of the battery module1000, for example, a Battery Management System (BMS), a current sensor and a fuse.

FIG.10is a diagram illustrating a vehicle according to yet another embodiment of the present disclosure.

The battery pack1200may be provided in the vehicle1300as a fuel source of the vehicle1300. For example, the battery pack1200may be provided in the vehicle1300such as an electric vehicle, a hybrid electric vehicle and other applications using the battery pack1200as a fuel source.

Preferably, the vehicle1300may be an electric vehicle. The battery pack1200may be used as an electrical energy source to supply power to a motor1310of the electric vehicle to drive the vehicle1300. In this case, the battery pack1200has high nominal voltage of 100V or above. For hybrid vehicles, the battery pack1200is set to 270V.

The battery pack1200may be charged or discharged by an inverter1320by the operation of the motor1310and/or the internal combustion engine. The battery pack1200may be charged by the regenerative charger coupled to the brake. The battery pack1200may be electrically connected to the motor1310of the vehicle1300through the inverter1320.

As previously described, the battery pack1200includes a BMS. The BMS estimates the state of the battery cells in the battery pack1200, and manages the battery pack1200using the estimated state information. For example, the BMS estimate and manages the state information of the battery pack1200including the State Of Charge (SOC), the State Of Health (SOH), the maximum allowable input/output power and the output voltage of the battery pack1200. Additionally, the BMS controls the charge or discharge of the battery pack1200using the state information, and besides, may estimate when to replace the battery pack1200.

An Electronic Control Unit (ECU)1330is an electronic control device to control the state of the vehicle1300. For example, the ECU1330determines torque information based on information of the accelerator, the brake and the speed, and controls the output of the motor1310according to the torque information. Additionally, the ECU1330sends a control signal to the inverter1320to charge or discharge the battery pack1200based on the state information of the battery pack1200such as SOC and SOH received by the BMS. The inverter1320allows the battery pack1200to be charged or discharged based on the control signal of the ECU1330. The motor1310drives the vehicle1300based on the control information (for example, torque information) transmitted from the ECU1330using electrical energy of the battery pack1200.

The vehicle1300includes the battery pack1200according to the present disclosure, and the battery pack1200includes the battery module1000with improved safety as described previously. Accordingly, as stability of the battery pack1200is improved, and the battery pack1200provides high stability and long-term use, the vehicle1300including the same is safe and easy to operate.

Additionally, it is obvious that the battery pack1200may be provided in any other device, apparatus and equipment such as Energy Storage System (ESS) and BMS using secondary batteries other than the vehicle1300.

As the battery pack1200according to this embodiment and the device, apparatus and equipment including the battery pack1200such as the vehicle1300include the above-described battery module100, it is possible to implement the battery pack1200having all the above-described advantages of the battery module100and the device, apparatus and equipment including the battery pack1200such as the vehicle1300.

The battery module ofFIG.4is manufactured at a laboratory scale and tested for the current shutoff effect of the terminal busbar according to the present disclosure.

The battery cells of the battery module follow a method for manufacturing a general pouch-type battery cell. Example uses a busbar including a first metal layer, a material layer that is conductive in normal condition, but acts as resistance when the temperature rises and a second metal layer stacked in that order, like the terminal busbar150′ according to the present disclosure. The material layer that is conductive in normal condition, but when the temperature rises, may act as resistance, includes a gas generating material, a conductive material and an adhesive. The gas generating material is melamine cyanurate, the conductive material is silver (Ag) powder, and the adhesive is epoxy resin. The silver content is about 75˜85 wt %.

Comparative example 1 uses a busbar having a single metal layer. Comparative example 2 uses a busbar having a first metal layer and a second metal layer adhered to each other with a silver epoxy resin. The materials of the first metal layers and the second metal layers of the example and the comparative example 2 and the material of the busbar of the comparative example 1 are the same. In example and comparative examples 1 and 2, the busbars have the same size.

FIG.11is a graph showing the resistance and temperature of the battery modules used in the experiment over time. Changes in resistance and temperature over time are measured while applying an overcurrent of 600 A to the battery module. A 1000 A charger/discharger is used to apply the overcurrent, and the data measurement is made using a datalogger. The temperature at the busbar of the battery module is measured.

Referring toFIG.11, it can be seen that comparative example 1 increases in temperature almost linearly over time, the temperature nearly reaches 60° C. at the lapse of 30 seconds, and the resistance gradually increases for the duration, while the current continuously flows through the busbar. In the case of comparative example 2, it can be seen that the temperature rises over time faster than comparative example 1, and reaches 110° C. at the lapse of 30 seconds. The resistance of comparative example 2 gradually increases a little bit more than comparative example 1, but the current continuously flows through the busbar and it is found that there is no overcurrent shutoff effect.

According to example, there is a rapid increase in resistance at the laps of 8 seconds, and afterwards, the measured resistance is 0, and thus it can be seen from this that resistance measurement is impossible due to overcurrent shutoff. With the increasing temperature, there is an increase/decrease in resistance, and the resistance rapidly increases at a specific temperature. Due to these temperature characteristics, the busbar according to the present disclosure may be called a PTC busbar. According to the present disclosure, it can be seen that the resistance of the busbar rapidly increases at a specific time and there is an overcurrent shutoff effect.FIGS.12a,12b,13aand13bshow the external short circuit test results of the battery modules used in the experiment.FIGS.12aand12bshow comparative example 1, andFIGS.13aand13bshow the present disclosure example. The external short circuit test is performed by connecting in parallel the battery module to a shunt resistor having a known resistance value, measuring the shunt voltage applied to the shunt resistor while flowing a large current to cause a short circuit, and calculating the current. During the test, the cell voltage is measured, and the temperature of the busbar, the positive electrode, the negative electrode and the cell at the central part is measured. Likewise, the data measurement is made using a datalogger.

FIGS.12aand13aare voltage, temperature and current graphs over time, andFIGS.12band13bare diagrams showing the shunt voltage and the current at the time of external short circuit.

FIGS.12aand13ashow a result of forcibly causing an external short circuit in 10 minutes after the current is applied. As time goes by, in the case of comparative example 1 ofFIG.12a, the cell voltage is restored up to 3.15 V, while in the case of example ofFIG.13a, the cell voltage is restored up to 4.25V. The unrestored 1.1V in comparative example 1 implies that the current is not completely shut off. SeeingFIG.12bshowing the shunt voltage and the current at the time of actual external short circuit, in the case of comparative example 1, the current of 300 A or higher flows after the external short circuit, whileFIG.13bshows that the current is nearly 0 after the external short circuit.

When comparing the temperature of the busbar, in the case of the example ofFIG.13acompared with comparative example 1 ofFIG.12a, it can be seen that the resistance increases due to the rapid rise in temperature at the early stage, and as a result, the current is shut off and hardly flows. Due to the current shutoff effect of example, the positive and negative electrode temperature of comparative example 1 rise to approximately 100° C., while in the case of example, the temperature after the current shutoff is maintained at room temperature.

It can be seen through the above experimental results that the present disclosure example has a better current shutoff effect than comparative examples, and achieves a current shutoff function when the temperature actually rises.

While the present disclosure has been hereinabove described with regard to a limited number of embodiments and drawings, the present disclosure is not limited thereto and it is obvious to those skilled in the art that various modifications and changes may be made thereto within the technical aspects of the present disclosure and the equivalent scope of the appended claims.