Patent Publication Number: US-2022238945-A1

Title: End cover assembly, battery cell, battery pack, apparatus and liquid-injection method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of International Application No. PCT/CN2021/089810, filed on Apr. 26, 2021, which claims priority to Chinese Patent Application No. 202010426530.8, filed on May 19, 2020, titled “END COVER ASSEMBLY, BATTERY CELL, BATTERY PACK, APPARATUS AND LIQUID-INJECTION METHOD”, both of which are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present application relates to a technical filed of energy storage equipment, and specifically relates to an end cover assembly, a battery cell, a battery pack, apparatus and a liquid-injection method. 
     BACKGROUND 
     With the improvement of electric vehicle technology, electric vehicles are getting more and more closely associated with people&#39;s lives, and at the same time, electric vehicles have higher and higher requirements for the performance of their energy-providing batteries. 
     Because a lithium-ion battery cell has extremely high requirements on the sealing of the structure, the electrolyte is not allowed to leak during use, otherwise it will pollute the surrounding air and environment. At the same time, impurities such as vapor and the like are not allowed to enter a battery pack, which reduces the operation life of the battery. 
     SUMMARY 
     The embodiments of the present application provides an end cover assembly, a battery cell, a battery pack, apparatus and a liquid injection method, aiming to improve the sealing performance of the end cover assembly. 
     In an aspect, an end cover assembly for a battery cell is provided by embodiments of the present application. The end cover assembly includes an end cover plate including a through hole for injecting electrolyte and a fixing portion arranged around the through hole, and a nail body including an accommodating portion for receiving the fixing portion. The accommodating portion is in a shape of annular and includes two inner walls arranged to be spaced apart from each other in a radial direction of the accommodating portion, and an inner wall and an outer wall of the fixing portion are respectively pressed against and engaged with the two inner walls of the accommodating portion to seal the through hole. 
     In some embodiments, the nail body includes a column body for sealing the through hole and a cover cap connected to an end of the column body, the cover cap includes a convex portion arranged around the column body, the convex portion and the column body enclose to form the accommodating portion, the column body is pressed against and engaged with the inner wall of the fixing portion, and the convex portion is pressed against and engaged with the outer wall of the fixing portion. 
     In some embodiments, the end cover assembly further includes a sealing member, arranged between the nail body and the fixing portion, to realize the nail body pressed against and engaged with the fixing portion. The column body and the convex portion respectively form two side walls of the accommodating portion, and the column body and the convex portion provide the position limitations in two directions to the fixing portion, so that the force exerted to the fixing portion is more balanced, and the sealing performance of the end cover assembly can be improved. 
     In some embodiments, the end cover assembly further includes the sealing member, arranged between the nail body and the fixing portion, to realize the nail body pressed against and engaged with the fixing portion. By arranging the sealing member, the nail body can be in an interference fit with the fixing portion, and the sealing performance of the end cover assembly can be improved. 
     In some embodiments, the sealing member includes a first sealing member, arranged to be sleeved between the column body and the inner wall of the fixing portion. By arranging the first sealing member, the column body can be in the interference fit with the fixing portion, and the sealing performance of the end cover assembly can be improved. 
     In some embodiments, a first accommodating groove is arranged in the inner wall of the fixing portion and/or the column body to locate the first sealing member in the first accommodating groove. The first sealing member may be located in the first accommodating groove, and the position limitation can be provided to the first sealing member through the first accommodating groove, so as to prevent the first sealing member from being misaligned, and ensure the stability of a relative position between the first sealing member and the fixing portion and/or the nail body. 
     In some embodiments, the sealing member includes a second sealing member, arranged to be sleeved between the outer wall of the fixing portion and the convex portion. By arranging the second sealing member, the convex portion can be in the interference fit with the fixing portion, and the sealing performance of the end cover assembly can be improved. 
     In some embodiments, a second accommodating groove is arranged in the outer wall of the fixing portion and/or the convex portion to locate the second sealing member in the second accommodating groove. The second sealing member may be located in the second accommodating groove, and the position limitation can be provided to the second sealing member through the second accommodating groove, so as to prevent the second sealing member from being misaligned, and ensure the stability of a relative position between the second sealing member and the fixing portion and/or the nail body. 
     In some embodiments, the sealing member includes an annular wall portion. 
     The cross section of the annular wall portion is in a shape of circle; in the case of the annular wall portion with the circular cross-section, the nail body can receive less resistance force when pressed into the through hole, so that it is convenient for assembling. 
     Or a cross section of the annular wall portion is in a shape of rectangle, so that the sealing member is in face-to-face contact with the fixing portion and/or the nail body. By the face-to-face contact between the sealing member and the fixing portion and/or the nail body, a contact area between the sealing member and the fixing portion and/or the nail body can be increased, and the sealing performance of the end cover assembly can be improved. 
     In some embodiments, the end cover assembly further includes a locking member. The locking member has an annular structure and is configured to sleeve and lock outside the cover cap, so that the nail body is pressed against and engaged with the fixing portion. By arranging the locking member, a force can be exerted from the outside of the nail body to the nail body and the fixing portion to ensure the tight engagement of the nail body and the fixing portion. 
     In some embodiments, the fixing portion is arranged to protrude from a surface of the end cover. The nail body is engaged with the fixing portion, and the fixing portion protrudes from the surface of the end cover plate, so that at least part of the nail body is arranged to protrude from the surface of the end cover plate, and it is convenient for disassembling or mounting the nail body. 
     In some embodiments, a surface of the end cover plate is recessed to form a sinking platform, and the fixing portion is connected to a bottom face of the sinking platform, so that it can ensure the flatness of an outer surface of the end cover plate and reduce the space occupied by the end cover assembly. 
     In another aspect, a battery cell is provided by embodiments of the present application, including a case, including an opening, and the end cover assembly as described above to sealing the opening. 
     In another aspect, a battery pack is provided by embodiments of the present application, including the battery cell as described above, and a housing configured to receive the battery cell. 
     In another aspect, apparatus is provided by the embodiments of the present application, including the battery cell as described above for supplying electrical power. 
     In another aspect, a liquid injection method to a battery cell is provided by embodiments of the present application, the method including 
     injecting electrolyte through a through hole on an end cover plate in an end cover assembly of the battery cell; 
     sealing a nail body into a injecting-liquid hole, so that a fixing portion is accommodated in an annular accommodating portion of the nail body, and an inner wall and an outer side wall of the fixing portion are pressed against and engaged with inner wall of the accommodating portion. 
     In the end cover assembly in the embodiments of the present application, the end cover assembly includes the end cover plate and the nail body, a through hole is formed in the end cover plate, and the nail body is configured to seal the through hole. The fixing portion is arranged at an outer periphery of the through hole, and the nail body is engaged with the fixing portion and an inner wall of the through hole to increase the contact area between the nail body and the end cover plate, thereby improving the sealing effect. In addition, the nail body includes the annular accommodating portion, and two inner walls of the annular accommodating portion can be pressed against and engaged with the inner wall and the outer wall of the fixing portion. The annular accommodating portion can provide the position limitations in two directions to the fixing portion, so that the force exerted to the fixing portion is balanced, not only can prevent the fixing portion from obliquely deforming, but also can increase the contact area between the nail body and the fixing portion to improve the sealing effect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings to be used in the description of the embodiments of the present application will be described briefly below. Obviously, the drawings in the following description are merely some embodiments of the present application. For those skilled in the art, other drawings can also be obtained according to these drawings without the inventive labor. 
         FIG. 1  shows a structural schematic view of a vehicle according to the embodiments of the present application; 
         FIG. 2  shows a structural schematic view of a battery pack according to an embodiment of the present application; 
         FIG. 3  shows a structural schematic view of a battery module according to an embodiment of the present application; 
         FIG. 4  shows a structural schematic view of a battery cell according to an embodiment of the present application; 
         FIG. 5  shows a perspective view of an end cover assembly according to an embodiment of the present application; 
         FIG. 6  shows a top view of an end cover assembly according to an embodiment of the present application; 
         FIG. 7  shows a cross-sectional view at a line A-A in  FIG. 6 ; 
         FIG. 8  shows an enlarged schematic view of a portion I in  FIG. 7  according to an embodiment of the present application; 
         FIG. 9  shows an enlarged schematic view of a portion I in  FIG. 7  according to another embodiment of the present application; 
         FIG. 10  shows an enlarged schematic view of a portion I in  FIG. 7  according to another embodiment of the present application; 
         FIG. 11  is a structural schematic view of a first sealing member of an end cover assembly according to an embodiment of the present application; 
         FIG. 12  is a structural schematic view of a second sealing member of an end cover assembly according to an embodiment of the present application; 
         FIG. 13  shows a top view of an end cover assembly according to another embodiment of the present application; 
         FIG. 14  shows a cross-sectional view at a line B-B in  FIG. 13 ; 
         FIG. 15  shows an enlarged schematic view of a portion II in  FIG. 14 ; 
         FIG. 16  shows a structural schematic view of a nail body of an end cover assembly according to the embodiments of the present application; 
         FIG. 17  shows a cross-sectional view at a line C-C in  FIG. 16 ; 
         FIG. 18  shows a structural schematic view of a locking portion of an end cover assembly according to the embodiments of the present application; 
         FIG. 19  shows a cross-sectional view at a line D-D in  FIG. 18 ; 
         FIG. 20  shows a flowchart of a liquid injection method to a battery cell according to an embodiment of the present application. 
     
    
    
     REFERENCE SIGNS 
     
         
         
           
               1  battery pack;  11  battery module;  12  housing;  2  vehicle main body; 
               10  battery cell;  20  receiving portion; 
               100  end cover assembly; 
               110  end cover plate;  111  through hole;  112  fixing portion;  113  sinking platform;  113   a -bottom face; 
               120  nail body;  121  column body;  122  cover cap;  123  convex portion; 
               130  sealing member;  130   a  first sealing member;  130   b  second sealing member;  131 -annular wall portion; 
               140  locking portion;  141  wall portion;  142  notch;  143  connecting portion; 
               200  case; 
               300  electrode assembly. 
           
         
       
    
     DETAILED DESCRIPTION 
     The features and exemplary embodiments of various aspects of the present application will be described in detail below. In the following detailed description, many specific details are proposed in order to provide a comprehensive understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present application by showing examples of the present application. In the drawings and the following description, at least part of the well-known structures and technologies are not shown in order to avoid unnecessary ambiguity to the present application; and, for clarity, the size of some structures may be exaggerated. In addition, the features, structures or characteristics described below may be combined in one or more embodiments in any suitable manner. 
     In the description of the present application, it should be noted that, unless otherwise specified, “plurality” means more than two; the terms “upper”, “lower”, “left”, “right”, “inner”, “outer”, etc. indicate the orientation or positional relationship only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or the element referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms “first”, “second”, etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance. 
     The orientation words appearing in the following description are all directions shown in the drawings, and do not limit the specific structure of the present application. In the description of the present application, it should also be noted that, unless otherwise clearly specified and limited, the terms “mount” and “connect” should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection, it can be a direct connection, or it can be connected indirectly through an intermediary. For those of ordinary skill in the art, the specific meaning of the above-mentioned terms in the present application can be understood according to specific situations. 
     At present, in order to realize a secondary liquid injection of some lithium-ion batteries, a sealing member usually seals a liquid injection port by means of plugging and unplugging. Lithium ions may generate gas during the operation process, so that it may deform a case of a lithium-ion battery. The liquid injection port is flush with other portions of the case, a portion of the case corresponding to the liquid injection port has a large deformation, and the sealing member may be displaced with the deformation of the case, which may eventually lead to the failure of the sealing of the liquid injection port. 
     In order to solve the above problems, the present application is provided. 
     In order to better understand the present application, an electrically connecting assembly and a battery module set of the embodiments of the present application will be described in detail below with reference to  FIGS. 1 to 20 . 
     Referring to  FIG. 1 ,  FIG. 1  shows a structural schematic view of a vehicle according to the embodiments of the present application. As shown in  FIG. 1 , the vehicle includes a battery pack  1  and a vehicle main body  2 , and the battery pack  1  is provided in the vehicle main body  2 . 
     The vehicle is a new energy vehicle, which can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle. The vehicle main body  2  is provided with a driving motor, electrically connected to the battery pack  1 , and the battery pack  1  can supply electric power. The driving motor is connected to wheels on the vehicle main body  2  through a transmission mechanism to drive the vehicle move forward. In some embodiments, the battery pack  1  may be horizontally arranged in the bottom of the vehicle main body  2 . 
     Referring to  FIG. 2 ,  FIG. 2  shows a structural schematic view of the battery pack  1  according to the embodiments of the present application. In some embodiments, the battery pack  1  includes a housing  12  and a battery module  11  arranged in the housing  12 . 
     The number of the battery module  11  may be one or more. When there are a plurality of battery modules  11 , the plurality of battery modules  11  are arranged in array in the housing  12 . There are many types of the housing  12 , and the housing  12  may be a frame-shaped housing, a disk-shaped housing or a box-shaped housing. Specifically, the housing  12  may include a lower housing for accommodating the battery module and an upper housing covered and closed with the lower housing. 
     Referring to  FIG. 3 ,  FIG. 3  shows a structural schematic view of the battery module  11  according to the embodiments of the present application. There are many ways to arrange the battery module  11 . In some embodiments, the battery module  11  includes a receiving portion  20  and a plurality of battery cells  10  located in the receiving portion  20 , and the plurality of battery cells  10  are arranged side by side in the receiving portion  20 . 
     There are many ways to arrange the receiving portion  20 , for example, the receiving portion  20  includes a case and a cover plate arranged at the case; or the receiving portion  20  includes side plates and end plates that are successively connected with one another to enclose; or the receiving portion  20  includes end plates arranged opposite each other and a band surrounding the end plates and the battery cells; or, as shown in  FIG. 3 , the receiving portion  20  includes side plates, end plates and a band. 
     The battery cell  10  can be used not only in the vehicle but also in other apparatus. The embodiment of the present application also provides apparatus that uses the battery cell  10  as a power source. The apparatus can be, but is not limited to, a vehicle, a ship, an aircraft or the like. 
     Referring to  FIG. 4 ,  FIG. 4  shows a structural schematic view of the battery cell  10  according to an embodiment of the present application. 
     As shown in  FIG. 4 , in some embodiments, the battery cell  10  includes a case  200  including an opening, and an end cover assembly  100  arranged to cover the case  200 . An electrode assembly  300  is also arranged in the case  200  of the battery cell  10 . 
     In some embodiments, the case  200  is provided with electrolyte inside, and the end cover assembly  100  is provided with a through hole  111  used as a liquid injection port and a nail body  120  for sealing the through hole  111 . The electrolyte can be injected into the case  200  through the through hole  111 , and the through hole  111  can be sealed through the nail body  120 . 
     Referring to  FIG. 5  to  FIG. 7  together,  FIG. 5  shows a perspective view of the end cover assembly  100  according to an embodiment of the present application,  FIG. 6  shows a top view of the end cover assembly  100  according to an embodiment of the present application, and  FIG. 7  shows a cross-sectional view at a line A-A in  FIG. 6 . 
     The end cover assembly  100  according to the embodiments of the present application includes an end cover plate  110  including the through hole  111  for injecting electrolyte and a fixing portion  112  arranged around the through hole  111 , and the nail body  120  including an accommodating portion for receiving the fixing portion  112 . The accommodating portion is in a shape of an annular and includes two inner walls arranged to be spaced apart from each other in a radial direction of the accommodating portion, and an inner wall and an outer wall of the fixing portion  112  are respectively pressed against and engaged with the two inner walls of the nail body  120  to seal the through hole  111 . 
     The above-mentioned end cover assembly  100  can not only be used in the battery cell  10  to arrange to cover the opening of the case  200  of the battery cell  10 , but also can be arranged to cover openings of other apparatus. 
     The inner wall of the fixing portion  112  refers to an inner wall face of the fixing portion  112  facing toward the through hole  111 , and the outer wall of the fixing portion  112  refers to an outer wall face of the fixing portion  112  away from the through hole  111 . The accommodating portion includes an accommodating space for receiving the fixing portion  112 , and the inner walls of the accommodating portion refers to inner wall faces of the accommodating portion facing toward the accommodating space. 
     In the end cover assembly  100  of the embodiments of the present application, the end cover assembly  100  includes the end cover plate  110  and the nail body  120 , the through hole  111  is formed in the end cover plate  110 , and the nail body  120  is configured to seal the through hole  111 . The fixing portion  112  is arranged at an outer periphery of the through hole  111 , and the nail body  120  is engaged with the fixing portion  112  and the inner wall of the through hole  111  to increase a contact area between the nail body  120  and the end cover plate  110 , thereby improving the sealing effect. At the same time, the fixing portion  112  is arranged around the through hole  111  and protrudes relative to other portions of the end cover plate  110 . The deformation of the fixing portion  112  transmitted from the deformation of the end cover plate  110  is less, so that it can reduce the impact of the deformation of the end cover plate  110  of the battery cell  10  on a sealing interface, thereby further improving the sealing effect. In addition, the nail body  120  includes the annular accommodating portion, and two inner walls of the annular accommodating portion can be pressed against and engaged with the inner wall and the outer wall of the fixing portion  112 . The annular accommodating portion can provide the position limitations in two directions to the fixing portion  112 , so that the force exerted to the fixing portion is balanced. In this way, not only can the fixing portion  112  be prevented from obliquely deforming, but also the contact area between the nail body  120  and the fixing portion  112  can be increased, so that the displacement of the nail body  120  along with the deformation of the end cover plate  110  can be avoided, and the sealing effect can be improved. 
     In the end cover assembly  100  in the embodiments of the present application, the battery cell  10  may generate gas during an operation process, so that the end cover assembly  100  may be convexly deformed. Since the fixing portion  112  is arranged around the through hole  111 , a mating distance between the nail body  120  and the end cover plate  110  in a thickness direction thereof can be increased. When the end cover assembly  100  is convexly deformed, a transmitting distance of the deformation can be increased, so that it may be difficult for the deformation to be transmitted to the fixing portion  112 , thereby ensuring the tight engagement of the nail body  120  and the fixing portion  112 . 
     In the embodiment of the present application, since the nail body  120  and the through hole  111  of the end cover assembly  100  are closely engaged with each other, the nail body  120  can be engaged with the through hole  111  and the fixing portion  112  by interference fit, so that the nail body  120  is detachably arranged on the end cover plate  110 . During the operation of the battery cell  10 , in the case that the electrolyte decreases as the number of charging and discharging of the battery cell  10  increases, the nail body  120  can be removed to facilitate the secondary liquid injection of the battery cell  10 . 
     Referring to  FIG. 8  and  FIG. 9  together,  FIG. 8  shows an enlarged schematic view of a portion I in  FIG. 7  according to an embodiment of the present application, and  FIG. 9  shows an enlarged schematic view of a portion I in  FIG. 7  according to another embodiment of the present application. 
     As shown in  FIG. 8 , there are many ways to arrange the fixing portion  112 , and the fixing portion  112  can be arranged to be directly protruded from a surface of the end cover plate  110 . In these embodiments, the fixing portion  112  protrudes from the surface of the end cover plate  110 , and the nail body  120  is engaged with the fixing portion  112 , so that at least part of the nail body  120  is arranged to protrude from the surface of the end cover plate  110 , thereby facilitating the action of the removal or the installation of the nail body  120 . 
     As shown in  FIG. 9 , in other embodiments, the surface of the end cover plate  110  is recessed to form a sinking platform  113 , and the fixing portion  112  is connected to a bottom face  113  a of the sinking platform  113 . In these embodiments, the fixing portion  112  is located in the sinking platform  113 , so that it can ensure the flatness of an outer surface of the end cover plate  110  and reduce the space occupied by the end cover assembly  100 . 
     In some embodiments, when the nail body  120  seals in the through hole  111 , the nail body  120  is located in the sinking platform  113 , so that it can reduce the space occupied by the end cover assembly  100 . 
     There are many materials for the nail body  120 . In some embodiments, the material of the nail body  120  includes one of steel, aluminum or other hard metal materials, or the material of the nail body  120  includes the engineering plastics or the like. 
     There are many ways to arrange the nail body  120 . In some embodiments, the nail body  120  includes a column body  121  and a cover cap  122  connected to an end of the column body. The column body  121  is used to seal the through hole  111 . The cover cap  122  includes a convex portion  123  arranged around the column body  121 , so that the annular accommodating portion is formed between the convex portion  123  and the column body  121 . The column body  121  is pressed against and engaged with the inner wall of the fixing portion  112 , and the convex portion  123  is pressed against and engaged with the outer wall of the fixing portion  112 . 
     In these embodiments, the column body  121  and the convex portion  123  respectively form two inner walls of the accommodating portion, and the column body  121  and the convex portion  123  provide the position limitations in two directions to the fixing portion  112 , so that the force exerted to the fixing portion  112  can be more balanced, and the sealing performance of the end cover assembly  100  can be improved. 
     In some embodiments, in order to further improve the sealing performance of the end cover assembly  100 , the end cover assembly  100  further includes a sealing member  130 , arranged between the nail body  120  and the fixing portion  112 , to realize the nail body  120  pressed against and engaged with the fixing portion  112 . 
     In these embodiments, by arranging the sealing member  130 , the nail body  120  can be in an interference fit with the fixing portion  112 , and the sealing performance of the end cover assembly  100  can be improved. 
     There are many ways to arrange the sealing member  130 . In some embodiments, the sealing member  130  includes a first sealing member  130   a  arranged to be sleeved between the column body  121  and the inner wall of the fixing portion  112 , so that the column body  121  can be closely engaged with the fixing portion  112 . By arranging the first sealing member  130   a , the column body  121  can be in the interference fit with the fixing portion  112 , and the sealing performance of the end cover assembly  100  can be improved. 
     In some embodiments, a first accommodating groove (not shown) is arranged in the fixing portion  112  and/or the column body  121  to locate the first sealing member  130   a  in the first accommodating groove. In these embodiments, the first sealing member  130   a  may be located in the first accommodating groove, and the position limitation can be provided to the first sealing member  130   a  through the first accommodating groove, so as to prevent the first sealing member  130   a  from being misaligned, and ensure the stability of a relative position between the first sealing member  130   a  and the fixing portion  112  and/or the nail body  120 . 
     In other embodiments, the sealing member  130  further includes a second sealing member  130   b  arranged to be sleeved between the outer wall of the fixing portion  112  and the convex portion  123 , so that the convex portion  123  can be closely engaged with the fixing portion  112 . By arranging the two sealing members  130 , the convex portion  123  can be in the interference fit with the fixing portion  112 , and the sealing performance of the end cover assembly  100  can be improved. 
     In some embodiments, a second accommodating groove (not shown) is arranged in the fixing portion  112  and/or the convex portion  123  to locate the second sealing member  130   b  in the second accommodating groove. In these embodiments, the second sealing member  130   b  may be located in the second accommodating groove, and the position limitation can be provided to the second sealing member  130   b  through the second accommodating groove, so as to prevent the second sealing member  130   b  from being misaligned, and ensure the stability of a relative position between the second sealing member  130   b  and the fixing portion  112  and/or the nail body  120 . 
     In another embodiments, the sealing member  130  includes the first sealing member  130   a  and the second sealing member  130   b , so that the column body  121  can be closely engaged with the fixing portion  112 , the convex portion  123  also can be closely engaged with the fixing portion  112 , the balance of the force exerted to the fixing portion  112  can be ensured, and the sealing performance of the end cover assembly  100  can be improved. 
     The shape of the sealing member  130  is not limited. Referring to  FIG. 9  continuously, in some embodiments, the sealing member  130  includes an annular wall portion  131 , a cross section of the annular wall portion is in a shape of circle. The cross section of the annular wall portion  131  is a face perpendicular to a radial direction of the sealing member  130 . In these embodiments, because of the annular wall portion  131  with the circular cross-section, the nail body  120  receives less resistance force when pressed into the through hole  111 , so that the assembly is convenient. 
     In another embodiment, referring to  FIG. 10  to  FIG. 12  together, the cross section of the annular wall portion  131  is in a shape of rectangle, so that the sealing member  130  is connected to the fixing portion  112  and/or the nail body  120  by means of face-to-face contact. By the face-to-face contact between the sealing member  130  and the fixing portion  112  and/or the nail body  120 , a contact area between the sealing member  130  and the fixing portion  112  and/or the nail body  120  can be increased, and the sealing performance of the end cover assembly  100  can be improved. 
     When the sealing member  130  includes the first sealing member  130   a  and the second sealing member  130   b , the shape of the cross-section of the first sealing member  130   a  and the shape of the cross-sectional of the second sealing member  130   b  may be the same, that is, each of the cross-sections of the first sealing member  130   a  and the second sealing member  130   b  can be in the shape of circle or rectangle. Or the shape of the cross-section of the first sealing member  130   a  and the shape of the cross-sectional of the second sealing member  130   b  may be different, that is, one of the cross sections of the first sealing member  130   a  and the second sealing member  130   b  is in the shape of circle, and the other is in the shape of rectangle. 
     There are many ways to arrange the material of the sealing member  130 . In some embodiments, the material of the sealing member  130  may include at least one of rubber and foam, as long as the sealing member  130  has some elasticity such that the nail body  120  can be in interference fit with the fixing portion  112  through the sealing member  130 . 
     Referring to  FIG. 13  to  FIG. 19  together, in some embodiments, the end cover assembly  100  further includes a locking member  140 . The locking member  140  has an annular structure and is configured to lock outside the end cover plate  110 , so that the nail body  120  can be pressed against and engaged with the fixing portion  112 . 
     In these embodiments, by arranging the locking member  140 , a force can be exerted from the outside of the nail body  120  to the nail body  120  and the fixing portion  112  to ensure the tight engagement of the nail body  120  and the fixing portion  112 . 
     There are many ways to arrange the locking member  140 . In some embodiments, the locking member  140  has a wall portion  141  and a hollow space enclosed by the wall portion  141 . The size of the hollow space is adjustable, so that the locking member  140  can lock the nail body  120  and the fixing portion  112 . 
     For example, the wall portion  141  is elastic. The nail body  120  and the fixing portion  112  can be locked by the elastic deformation of the wall portion  141 . 
     Or a notch  142  communicating with the hollow space is formed in the wall portion  141 , so that the locking member  140  is not in the shape of a closed annular, and the nail body  120  and the fixing portion  112  can be locked by means of adjusting a size of the notch  142 . 
     In some embodiments, the wall portion  141  includes connecting portions  143  at two ends of the notch  142 , each of the connecting portions  143  includes a penetrating hole therethrough, and two penetrating holes at the two ends of the notch  142  can be connected to each other through an intermediate connecting member. 
     In some embodiments, the end cover assembly  100  further includes a soluble glue, which is arranged at the end cover plate  110  and used to connect the nail body  120  and the end cover plate  110 . The soluble glue covering the nail body  120  can further ensure the stability of the relative position between the nail body  120  and the end cover plate  110 . The soluble glue can be made of, for example, a fusible material. When a secondary liquid injection is required, a dissolution operation can be performed to the soluble glue, so that the soluble glue can be deformed and melted, thereby facilitating the removal of the nail body  120  from the through hole  111 . 
     Referring to  FIG. 20 ,  FIG. 20  shows a flowchart of a liquid injection method for the battery cell according to another embodiment of the present application. The battery cell  10  may be the battery cell  10  according to any one of the above-mentioned embodiments. The liquid injection method to the battery cell includes 
     step S 1 : injecting electrolyte through the through hole on the end cover plate in the end cover assembly of the battery cell; 
     step S 2 : sealing the nail body into the through hole, so that the fixing portion can be accommodated in the annular accommodating portion of the nail body, and the inner wall and the outer side wall of the fixing portion are pressed against and engaged with the inner wall of the accommodating portion. 
     In these embodiments, the electrolyte is injected into the battery cell  10  through the through hole  111 , and then the nail body  120  is sealed in the through hole  111 , so that the inner wall and the outer side wall of the fixing portion are pressed against and engaged with the inner walls of the accommodating portion. The annular accommodating portion can provide the position limitations in two directions to the fixing portion  112 , so that the force exerted to the fixing portion  112  is balanced. In this way, not only can the fixing portion  112  be prevented from obliquely deforming, but also the contact area between the nail body  120  and the fixing portion  112  can be increased, and the sealing effect can be improved. 
     In other embodiments, when the battery cell  10  has been used for a long time and the capacity of the electrolyte is reduced, the liquid injection method further includes: when the battery cell  10  is used for a long time and the capacity of the electrolyte is reduced, the liquid injection method further includes: unplugging the nail body  120  out of the through hole  111 , injecting the electrolyte through the through hole  111 , and re-sealing the nail body  120  into the through hole  111 , so as to realize the secondary liquid injection of the battery cell  10 . 
     The present application can be implemented in other specific forms without departing from its gist and essential characteristics. For example, the algorithm described in the specific embodiment can be modified, and the system architecture does not deviate from the basic gist of the application. Therefore, the current embodiment is considered to be exemplary rather than limiting in all respects. The scope of the present application is defined by the appended claims rather than the above description. In addition, all changes that fall within the meaning of the claims and the scope of equivalents are thus included in the scope of the present application.