Patent Publication Number: US-2021184319-A1

Title: Battery pack having structure capable of preventing overcharge, and vehicle comprising same

Description:
TECHNICAL FIELD 
     The present disclosure relates to a battery pack having a structure capable of preventing overcharging and a vehicle including the battery pack, and more particularly to, a battery pack including a current blocking member capable of blocking a current between battery modules electrically connected to each other by changing a shape of the current blocking member according to a potential difference applied between both surfaces and a vehicle including the battery pack. 
     The present application claims priority to Korean Patent Application No. 10-2018-0138451 filed on Nov. 12, 2018 in the Republic of Korea, the disclosures of which are incorporated herein by reference. 
     BACKGROUND ART 
     Fuse devices which are currently used in secondary batteries include a positive temperature coefficient (PTC) thermistor, a thermal cut-out (TCO), a thermal fuse, etc. However, in the case of the thermal fuse, there is a disadvantage of one-time use, and although the PTC thermistor or the TCO is repeatedly usable, there is a disadvantage that the resistance thereof increases as the operation is repeated, which increases the overall resistance on the circuit. 
     In addition, all of the above-mentioned devices operate by heat generated by an overcurrent. That is, the above-mentioned devices correspond to devices that operate to block the flow of a current when the overcurrent is generated on a circuit current path due to overcharging, etc., and thus the temperature increases. 
     Therefore, in the case of the above-mentioned devices, it is possible to block the overcurrent by operating after a situation where safety may be threatened due to the heat, and it is impossible to block the overcurrent immediately when a cause for increasing the temperature occurs. 
     In addition, in the case of the above-mentioned devices, since the devices operate simply according to the temperature, it is difficult to use the devices in a secondary battery exhibiting a high output such as a battery pack used in a vehicle. In other words, in the case of a vehicle battery pack, a high c-rate is required, which also accordingly requires a large amount of heat. There is a problem in that the devices such as the PTC thermistor, the TCO, and the thermal fuse operate too early when placed in such a high temperature environment. 
     Therefore, there is a need for a secondary battery to which a device that is reusable and is usable even in an environment where a high current flows, and is capable of previously blocking the current when an event that may cause such a temperature rise occurs before the temperature rises is applied. 
     DISCLOSURE 
     Technical Problem 
     The present disclosure is designed to solve the problems of the related art, and therefore the present disclosure is directed to providing a battery pack having a structure in which a current blocking member capable of previously blocking a current before the temperature of the battery pack rises by heat generated due to overcharging of the battery pack, etc. is installed. 
     These and other objects and advantages of the present disclosure may be understood from the following detailed description and will become more fully apparent from the exemplary embodiments of the present disclosure. Also, it will be easily understood that the objects and advantages of the present disclosure may be realized by the means shown in the appended claims and combinations thereof. 
     Technical Solution 
     In one aspect of the present disclosure, there is provided a battery pack including a battery module assembly including a first battery module and a second battery module; a first connector connected to a first electrode of the first battery module; a second connector connected to a second electrode of the second battery module and spaced apart from the first connector; a switch configured to connect the first connector and the second connector; a current blocking member connected to one side of the switch in a longitudinal direction and configured to turn off the switch by causing a bending deformation when a potential difference formed between both electrodes of the battery module is equal to or greater than a reference value. 
     The battery module may include a plurality of battery cells electrically connected to each other. 
     One side of the switch in the longitudinal direction may be formed as a free end to be in contact with the first connector and to release a contact state between the switch and the first connector by the bending deformation of the current blocking member, and the other side of the switch in the longitudinal direction may be formed as a fixed end fixed to the second connector. 
     One side of the current blocking member in the longitudinal direction may be a free end of which position is changeable by the bending deformation, and the other side of the current blocking member may be a fixed end directly or indirectly connected to the battery module or a ground. 
     The current blocking member may include an electro active polymer (EAP) layer; a first metal layer formed on one side of the EAP layer; and a second metal layer formed on the other side of the EAP layer. 
     The EAP layer may include at least one polymer electrolyte selected from Nafion, polypyrrole, polyaniline and polythiophene. 
     The first metal layer and the second metal layer may include at least one metal selected from the group comprising platinum, silver and copper. 
     The first metal layer may be electrically connected to a negative electrode of the battery module, and the second metal layer may be electrically connected to a positive electrode of the battery module. 
     The current blocking member may be located above the switch, and the first metal layer may face the switch. 
     The battery pack may further include a connecting rod configured to connect between the switch and the first metal layer and having non-conductivity. 
     The connecting rod may be hinged to each of the switch and the first metal layer. 
     In another aspect of the present disclosure, there is provided a vehicle including the battery pack as described above. 
     Advantageous Effects 
     According to an aspect of the present disclosure, in the use of a battery pack, before an event such as overheating and/or explosion of the battery pack due to overcharging of the battery pack, etc. occurs, a current may be blocked by previously detecting a potential difference equal to or greater than a reference value that causes occurrence of the event, thereby securing safety in the use of the battery pack. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing a battery pack according to an embodiment of the present disclosure; 
         FIG. 2  is a diagram showing an individual battery module included in the battery pack shown in  FIG. 1 ; 
         FIG. 3  is a diagram showing an individual battery cell included in the battery module shown in  FIG. 2 ; 
         FIG. 4  is a diagram showing a current blocking member applied to the battery pack shown in  FIG. 1 ; 
         FIG. 5  is a diagram showing a shape deformation of the current blocking member when a potential difference equal to or greater than a reference value is formed between a first metal layer and a second metal layer of the current blocking member shown in  FIG. 4 ; 
         FIG. 6  is a diagram showing a modification of the connection structure of the current blocking member shown in  FIG. 1  and a connecting plate; and 
         FIG. 7  is a diagram showing a vehicle according to an embodiment of the present disclosure. 
     
    
    
     MODE FOR DISCLOSURE 
     Hereinafter, 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 used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but 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 description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the disclosure, so it should be understood that other equivalents and modifications could be made thereto without departing from the scope of the disclosure. 
     First, referring to  FIGS. 1 to 5 , the overall configuration of a battery pack according to an embodiment of the present disclosure will be described. 
       FIG. 1  is a diagram showing a battery pack according to an embodiment of the present disclosure.  FIG. 2  is a diagram showing an individual battery module included in the battery pack shown in  FIG. 1 .  FIG. 3  is a diagram showing an individual battery cell included in the battery module shown in  FIG. 2 . Also,  FIG. 4  is a diagram showing a current blocking member applied to the battery pack shown in  FIG. 1 .  FIG. 5  is a diagram showing a shape deformation of the current blocking member when a potential difference equal to or greater than a reference value is formed between a first metal layer and a second metal layer of the current blocking member shown in  FIG. 4 . 
     First, referring to  FIG. 1 , the battery pack according to an embodiment of the present disclosure includes a plurality of battery modules  100 , a first connector  200 , a second connector  300 , a switch  400 , a current blocking member  500 , and a connecting rod  600 . 
     Referring to  FIGS. 1 and 2  together, the plurality of battery modules  100  forms one battery module assembly electrically connected to each other. The battery module  100  may include a plurality of battery cells  10  connected in series, in parallel, or a mixture of series and parallel with each other. In addition, a cell stack formed by electrically connecting the battery cells  10  may be electrically connected to a first electrode terminal  110  and a second electrode terminal  120  that are formed in outside of the battery module  100 . 
     In the drawings of the present disclosure, a case where the first electrode terminal  110  is a negative electrode terminal and the second electrode terminal  120  is a positive electrode terminal is shown as an example, but the present disclosure is not limited thereto, and a case where the first electrode terminal  110  is a positive electrode terminal and the second electrode terminal  120  is a negative electrode terminal may be possible. 
     Referring to  FIG. 3 , as each of the battery cells  10  included in the battery pack, for example, a pouch type battery cell may be applied. Referring to  FIG. 3 , the pouch type battery cell  10  may include an electrode assembly (not shown), an electrode lead  11 , a cell case  12 , and a sealing tape  13 . 
     Although not shown in the drawings, the electrode assembly has a structure in which separators are interposed between positive electrode plates and negative electrode plates that are alternately and repeatedly stacked, and the separators may be positioned on both outermost sides for insulation. 
     The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer coated on one surface or both surfaces thereof, and at one end thereof, a negative electrode non-coating portion which is not coated with a negative electrode active material is formed and a negative electrode non-coating region functions as a negative electrode tab. 
     The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer coated on one surface or both surfaces thereof, and at one end thereof, a positive electrode non-coating portion which is not coated with a positive electrode active material is formed and a positive electrode non-coating region functions as a positive electrode tab. 
     In addition, the separator is interposed between the negative electrode plate and the positive electrode plate to prevent direct contact between the electrode plates having different polarities and may be formed of a porous material to enable the movement of ions by using an electrolyte as a medium between the negative electrode plate and the positive electrode plate. 
     The electrode lead  11  is connected to the electrode tab and is withdrawn to the outside of the cell case  12 . The battery cells  10  adjacent to each other may be electrically connected in series, parallel, or a mixture of series and parallel through the electrode lead  11  to form a single cell stack. 
     The cell case  12  includes two regions of an accommodation portion  12   a  that accommodates the electrode assembly and a sealing portion  12   b  that extends in the circumferential direction of the accommodation portion  12   a  and is thermally fused in a state where the electrode lead  11  is withdrawn to seal the cell case  12 . 
     Although not shown in the drawings, the cell case  12  is sealed by contacting and thermally fusing edges of an upper case and a lower case configured as a multilayer pouch film in which a resin layer/metal layer/resin layer are sequentially stacked. 
     The sealing tape  13  is attached to the circumference of the electrode lead  11  and is interposed between the sealing portion  12   b  of the cell case  12  and the electrode lead  11 . The sealing tape  13  is a component for preventing the degradation of sealing property of the cell case  12  due to a low adhesion force between the inner surface of the cell case  12  and the electrode lead  11  in a region in which the electrode lead  11  is withdrawn in the sealing portion  12   b  of the cell case  12 . 
     Referring back to  FIG. 1 , the first connector  200  and the second connector  300  may have the shape of a metal plate of a conductive material. The first connector  200  is fastened to the second electrode terminal  120  of the first battery module  100  located on one side of a pair of battery modules  100  adjacent to each other. In addition, the second connector  300  is fastened to the first electrode terminal  110  of the second battery module  100  located on the other side of the pair of battery modules  100  adjacent to each other. The first connector  200  and the second connector  300  are spaced apart from each other by a predetermined distance. 
     The switch  400  connects a pair of connectors  200  and  300  spaced apart from each other. Specifically, the switch  400  may be installed to connect between upper surfaces of each of the first connector  200  and the second connector  300 . 
     One side of the switch  400  in the longitudinal direction is formed as a free end which is in contact with the first connector  200  and moves together upon bending deformation of the current blocking member  500  such that a contact state between the switch  400  and the first connector  200  may be released. Unlike this, the other side of the switch  400  in the longitudinal direction is formed as a fixed end which is fixed to the second connector  300  by welding or the like. 
     The current blocking member  500  causes the bending deformation when voltage applied to both surfaces is equal to or greater than a reference value and is connected to the switch  400  by the connecting rod  600  to move the switch  400  to perform an off operation upon bending deformation. 
     In order to perform this function, the current blocking member  500  may be disposed above the switch  400 . In addition, one side of the current blocking member  500  in the longitudinal direction may be formed as a free end of which position may change by the bending deformation, and the other side of the current blocking member  500  in the longitudinal direction may be formed as a fixed end fixed directly or indirectly to the battery module  100  or the ground. 
     In order to allow the switch  400  to perform the off operation by the bending deformation of the current blocking member  500 , the connecting rod  600  connects the free end of the current blocking member  500  and the free end of the switch  400 . 
     The connecting rod  600  may be formed of, for example, a plastic material, and both ends thereof may be attached to the lower surface of the current blocking member  500  and the upper surface of the switch  400 , respectively. 
     Meanwhile, referring to  FIGS. 4 and 5 , in order to be able to block an overcurrent due to a shape deformation according to a potential difference formed between both surfaces, the current blocking member  500  may include an electro active polymer (EAP) layer  510 , a first metal layer  520  formed on one side surface of the EAP layer  510 , and a second metal layer  530  formed on the other side surface of the EAP layer  510 . 
     The EAP layer  510 , i.e., the electroactive polymer layer, corresponds to a layer formed of a polymer electrolyte having an excellent ion transfer property, and may include at least one polymer electrolyte selected from, for example, Nafion, polypyrole, polyaniline, and polythiophene. 
     The first metal layer  520  and the second metal layer  530  are formed on both surfaces of the EAP layer  510  and may be formed of a metal having excellent electrical conductivity. The metal layers  520  and  530  may include at least one metal selected from, for example, platinum (Pt), gold (Au), silver (Ag), and copper (Cu). 
     The current blocking member  500  causes the shape deformation when voltage equal to or greater than a reference value is applied through the metal layers  510  and  520  formed on both surfaces of the EAP layer  510 . 
     That is, the first metal layer  520  is electrically connected to the negative electrode of the battery module  100 , and the second metal layer  530  is electrically connected to the positive electrode of the battery module  100  such that a potential difference corresponding to the voltage of the battery module  100  is formed between the pair of metal layers  520  and  530 . 
     When the potential difference formed between the pair of metal layers  520  and  530  as described above reaches a large numerical value exceeding a safety range considering the specification of the battery module  100  due to an issue such as overcharging, etc., mobility cations present inside the polymer electrolyte forming the EAP layer  510  move in the direction of the negatively charged first metal layer  520  while hydrated in water. In this case, an osmotic pressure is caused by an imbalance in the ion concentration between the first metal layer  520  and the second metal layer  530 , which increases an amount of water molecules toward the negatively charged first metal layer  520 , and thus the bending deformation occurs in the current blocking member  500  in the direction toward the second metal layer  530 . 
     For such a shape deformation of the current blocking member  500  and a resulting operation of the switch  400 , the first metal layer  520  faces the switch  400  and is connected to the negative electrode of the battery module  100 , and the second metal layer  530  is connected to the positive electrode of the battery module  100  on the contrary thereto. 
     In addition, both ends of the connecting rod  600  are fixed to the first metal layer  520  and the switch  400 , respectively, and are formed of a non-conductive material. This is because if the connecting rod  600  has conductivity, the first metal layer  520  is connected to both the positive electrode and the negative electrode of the battery module  100  such that the current blocking member  500  may cause the bending deformation. 
     Meanwhile, the magnitude of the voltage that may cause the shape deformation of the current blocking member  500  varies depending on the type of the polymer electrolyte constituting the EAP layer  510  applied to the current blocking member  500 . 
     That is, the reference value of the voltage mentioned in the present specification may vary according to the type of the polymer electrolyte applied, and accordingly, a suitable polymer electrolyte may be selected according to the safety voltage range of each of the battery modules  100  constituting the battery pack to which the current blocking member  500  is applied, thereby quickly blocking the current when an event such as overcharging of the battery pack occurs. 
     Next, a modification of the connection structure of the current blocking member  500  and the switch  400  shown in  FIG. 1  will be described with reference to  FIG. 6 . 
       FIG. 6  is a diagram showing a modification of the connection structure of the current blocking member  500  shown in  FIG. 1  and a connecting plate. 
     Referring to  FIG. 6 , both ends of the connecting rod  600  may be hinged to the upper surface of the switch  400  and the first metal layer  520 , respectively. As such, when the connecting rod  600  is hinged to the switch  400  and the current blocking member  500 , a relative rotation between the switch  400 , the current blocking member  500 , and the connecting rod  600  is possible. Therefore, when a free end of the current blocking member  500  moves upward due to a bending deformation of the current blocking member  500 , a free end of the switch  400  may also move upward smoothly without a shape deformation, such as bending, of the connecting rod  600 . 
     As described above, the battery pack according to the present disclosure is configured to perform an on/off operation of the switch  400  that electrically connects between the battery modules  100  adjacent to each other by using the current blocking member  500  that causes the bending deformation according to the voltage of the battery module  100 , thereby securing safety in the use of the battery pack. 
     Meanwhile, a vehicle according to an embodiment of the present disclosure shown in  FIG. 7  includes the battery pack according to the present disclosure as described above. 
     The present disclosure has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the disclosure, are given by way of illustration only, since various changes and modifications within the scope of the disclosure will become apparent to those skilled in the art from this detailed description.