Patent Publication Number: US-2023163310-A1

Title: Secondary battery and method of manufacturing the secondary battery

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 16/666,754, which is filed on Oct. 29, 2019 and claims priority to Chinese Patent Application No. 201811320340.7, filed on Nov. 7, 2018, both of which are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a technical filed of batteries, and particularly relates to a secondary battery and a method of manufacturing the secondary battery. 
     BACKGROUND 
     New energy vehicles are widely promoted in China and the world, but there are still many improvements that need to be made to completely replace fuel vehicles with the new energy vehicles. For example, problems, such as small driving distance, high cost of a battery pack, and low reliability of the battery pack still need to be further solved. In view of the above problems, higher requirements have been placed on secondary batteries, core parts of electric vehicles, for example, the secondary batteries are required to have a higher energy density, a lower cost, and the like. 
     In the prior art, a secondary battery includes a case, an electrode assembly disposed in the case, a cap plate coupled to the case, and an electrode terminal disposed on the cap plate. The cap plate is provided with a mounting hole, and the electrode terminal is mounted in the mounting hole, with a part located on an outer side of the cap plate, and a part located on an inner side of the cap plate. Both of the part of the electrode terminal located on the outer side of the cap plate and the part of the electrode terminal located on the inner side of the cap plate extend beyond the mounting hole in a radial direction of the mounting hole, so as to fix the electrode terminal to the cap plate. In this case, since a part of the electrode terminal is located on the inner side of the cap plate, the electrode terminal occupies some space in the case. As a result, a gap between the electrode assembly and the cap plate is too large to fully utilize the space in the case, thereby causing a low energy density of the entire secondary battery. 
     SUMMARY 
     The embodiments of the present disclosure disclose a secondary battery and a method of manufacturing the secondary battery. The configuration of the secondary battery is conducive to increasing energy density. 
     On one aspect, embodiments of the present disclosure discloses a secondary battery, including: a case; an electrode assembly, accommodated in the case and including a main body and a tab connected to the main body; a cap plate, coupled to the case; an electrode terminal, located on an outer side of the cap plate and including a first metal layer and a second metal layer disposed one on top of another, wherein the second metal layer is located on a side of the first metal layer away from the cap plate, and the first metal layer and the second metal layer are made of different materials, and wherein the electrode terminal is provided with a stepped hole, which includes a first hole segment penetrating through the first metal layer and a second hole segment penetrating through the second metal layer and extending into the first metal layer; and a current collecting member, connected between the tab and the electrode terminal, wherein the current collecting member includes an extending portion extending toward the electrode terminal and protruding into the first hole segment, and directly connected to the first metal layer, and the first metal layer is made of the same material as the current collecting member. 
     According to one aspect of the embodiments of the present disclosure, both of the first metal layer and the current collecting member are made of copper, and the second metal layer is made of aluminum; or both of the first metal layer and the current collecting member are made of aluminum, and the second metal layer is made of copper. 
     According to one aspect of the embodiments of the present disclosure, the second hole segment has a diameter larger than that of the first hole segment, and the extending portion is welded to the first metal layer. 
     According to one aspect of the embodiments of the present disclosure, the second hole segment includes a sink portion disposed in the first metal layer, and a top surface of the extending portion is flush with a bottom surface of the sink portion. 
     According to one aspect of the embodiments of the present disclosure, a composite connection interface is formed between the first metal layer and the second metal layer, and the secondary battery further includes a connecting member abutting against the second metal layer and forming a contact interface together with the second metal layer, wherein the contact interface is located above the composite connection interface. 
     According to one aspect of the embodiments of the present disclosure, the extending portion and the first metal layer are welded to each other, by which an annular welding seam is formed so as to connect the extending portion and the first metal layer in a sealed manner. 
     According to one aspect of the embodiments of the present disclosure, the current collecting member further includes a connecting portion connected to the extending portion, and the connecting portion is located on an inner side of the cap plate and directly connected to the tab, wherein the connecting portion is formed in a sheet-like shape and is made of the same material as the tab. 
     According to one aspect of the embodiments of the present disclosure, the current collecting member further includes a projection connected between the extending portion and the connecting portion, and a recess is formed on a side of the projection away from the electrode terminal by forming the projection. 
     According to one aspect of the embodiments of the present disclosure, the extending portion, the projection and the connecting portion are formed into an integral member. 
     According to one aspect of the embodiments of the present disclosure, the projection is provided with a through hole, and the extending portion is adapted to pass through the through hole; and the current collecting member further includes a support portion connected with the extending portion, and the support portion is accommodated in the recess. 
     According to one aspect of the embodiments of the present disclosure, the support portion is adapted to extend beyond an inner wall of the through hole in a radial direction of the through hole. 
     According to one aspect of the embodiments of the present disclosure, the extending portion is formed as a hollow cylindrical member having a blind hole, and the blind hole is provided with an opening toward the electrode assembly. 
     According to one aspect of the embodiments of the present disclosure, the second hole segment has a diameter larger than that of the first hole segment, and the extending portion is welded to the first metal layer. 
     According to one aspect of the embodiments of the present disclosure, the second hole segment includes a sink portion disposed in the first metal layer, and a top surface of the extending portion is flush with a bottom surface of the sink portion. 
     On a further aspect, embodiments of the present disclosure proposes a battery module including a plurality of secondary batteries according to any of the above embodiments. 
     On a further aspect, embodiments of the present disclosure proposes a battery pack including at least one battery module according to any of the above embodiments. 
     On a further aspect, embodiments of the present disclosure proposes an apparatus using a secondary battery as a power source, wherein the secondary battery is a secondary battery according to any of the above embodiments. 
     On a further aspect, embodiments of the present disclosure discloses a method of manufacturing a secondary battery, including steps of:
         providing an electrode assembly including a main body and a tab connected to the main body;   providing a current collecting member, and connecting and fixing the tab to the current collecting member, wherein the current collecting member includes an extending portion;   providing an electrode terminal and a cap plate, wherein the electrode terminal is located on an outer side of the cap plate and includes a first metal layer and a second metal layer disposed one on top of another, and the second metal layer is located on a side of the first metal layer away from the cap plate and is made of different material from the first metal layer, and wherein the electrode terminal is provided with a stepped hole, which includes a first hole segment penetrating through the first metal layer and a second hole segment penetrating through the second metal layer and extending into the first metal layer;   inserting the extending portion into the first hole segment from an inner side of the cap plate, wherein the first metal layer is made of the same material as the current collecting member; and   providing a case, loading the electrode assembly into the case, and performing laser welding from the outer side of cap plate so as to weld the extending portion to the first metal layer by the laser welding.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical effects of the present disclosure will be described below with reference to accompanying drawings. 
         FIG.  1    schematically shows a cross-sectional view of a secondary battery according to an embodiment of the present disclosure. 
         FIG.  2    schematically shows a partial exploded view of a secondary battery according to an embodiment of the present disclosure. 
         FIG.  3    schematically shows a cross-sectional view of a combination of a cap assembly and a current collecting member according to an embodiment of the present disclosure. 
         FIG.  4    schematically shows a partial cross-sectional view of a cap assembly according to an embodiment of the present disclosure. 
         FIG.  5    schematically shows a cross-sectional view of a combination of a cap plate and a current collecting member according to a further embodiment of the present disclosure. 
         FIG.  6    schematically shows an enlarged view of a portion A in  FIG.  5   . 
         FIG.  7    schematically shows an enlarged view of a portion B in  FIG.  6   . 
         FIG.  8    schematically shows a partial exploded view of a secondary battery according to a further embodiment of the present disclosure. 
         FIG.  9    schematically shows a cross-sectional view of a combination of a cap assembly and a current collecting member according to a further embodiment of the present disclosure. 
         FIG.  10    schematically shows an enlarged view of a portion C in  FIG.  9   . 
         FIG.  11    schematically shows a cross-sectional view of a combination of a cap assembly and a current collecting member according to a still further embodiment of the present disclosure. 
         FIG.  12    schematically shows an enlarged view of a portion D in  FIG.  11   . 
         FIG.  13    is a flow chart showing a method of manufacturing a secondary battery according to an embodiment of the present disclosure. 
         FIG.  14    schematically shows a battery module according to an embodiment of the present disclosure. 
         FIG.  15    is an exploded view of the battery module as shown in  FIG.  14   . 
         FIG.  16    is an exploded view of a battery pack according to an embodiment of the present disclosure. 
         FIG.  17    schematically shows an apparatus using a secondary battery as a power source according to an embodiment of the present disclosure. 
     
    
    
     In the drawings, the drawings are not drawn to scale. 
     Reference Numerals: 
       10 , secondary battery; 
       20 , case; 
       30 , electrode assembly;  301 , main body;  302 , tab; 
       40 , cap assembly; 
       50 , cap plate;  501 , electrode lead-out hole; 
       60 , electrode terminal;  601 , first metal layer;  601   a,  first hole segment;  602 , second metal layer;  602   a,  second hole segment;  602   b,  sink portion;  603 , composite connection interface;  604 , flange;  604   a,  contact interface; 
       70 , current collecting member;  701 , extending portion;  701   a,  top surface;  702 , connecting portion;  702   a,  projection;  702   b,  recess;  703 , support portion; 
       80 , connecting member; 
       90 , insulating member; 
       100 , sealing member. 
     DETAILED DESCRIPTION 
     Below, embodiments of the present disclosure will be further described in detail with reference to the accompanying drawings and embodiments. The detailed description of the embodiments and the accompanying drawings are intended to exemplarily illustrate the principles of the present disclosure and are not intended to limit the scope of the present disclosure. That is, the present disclosure is not limited to the described embodiments. 
     In the description of the present disclosure, it should be noted that, unless otherwise stated, the meaning of “a plurality of” is two or more; the orientation or positional relationship indicated by the term “upper”, “lower”, “left”, “right”, “inner”, “outer” or the like is merely for the purpose of describing the present disclosure and simplifying the description, and is not intended to indicate or imply that the device or component referred to has a particular orientation, or is constructed and operated in a particular orientation, and therefore cannot be understood to be a limitation of the present disclosure. Moreover, the terms “first”, “second” and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. 
     In the description of the present disclosure, it should be noted that, unless otherwise stated and defined clearly, the terms “installation”, “couple”, and “connection” are to be understood broadly, and may be, for example, a fixed connection, a disassemble connection, or an integral connection, and may be a direct connection or an indirect connection through an intermediate medium. The specific meaning of the above terms in the present disclosure may be understood by the person skilled in the art according to actual circumstance. 
     In order to better understand the present disclosure, a secondary battery  10  according to an embodiment of the present disclosure will be described in detail below with reference to  FIGS.  1 - 12   . 
     Referring to  FIG.  1   , the secondary battery  10  according to an embodiment of the present disclosure includes a case  20 , an electrode assembly  30  disposed in the case  20 , and a cap assembly  40  coupled to the case  20  in a sealed manner. 
     The case  20  of the present embodiment may be formed in a hexahedral shape or in other shapes. The case  20  has an internal space for accommodating the electrode assembly  30  and electrolyte. The case  20  may be made of a material such as aluminum, aluminum alloy, or plastic. 
     The electrode assembly  30  of the present embodiment may include a main body  301 , which is formed by stacking or winding a first electrode plate, a second electrode plate and a separator together, wherein the separator is an insulator interposed between the first electrode plate and the second electrode plate. In the present embodiment, description is made by exemplarily taking the first electrode plate as a positive electrode plate, and taking the second electrode plate as a negative electrode plate. Similarly, in other embodiments, the first electrode plate may be a negative electrode plate, and the second electrode plate is a positive electrode plate. Further, a positive active material is coated on a coating region of the positive electrode plate, and a negative active material is coated on a coating region of the negative electrode plate. A plurality of uncoated regions extending out from the main body  301  serve as a tab  302 . The electrode assembly  30  includes two tabs  302 , that is, a positive tab and a negative tab. The positive tab extends out from the coated region of the positive electrode plate, and the negative tab extends out from the coated region of the negative electrode plate. 
     Below, a technical solution of the secondary battery  10  is further described by means of specific embodiments. However, the following specific embodiments are not intended to limit a protective scope of the claims of the present disclosure. 
       FIG.  2    schematically shows a partial exploded view of a secondary battery  10  according to an embodiment of the present disclosure. Referring to  FIG.  2   , the cap assembly  40  of the present embodiment includes a cap plate  50  coupled to the case  20  in a sealed manner, an electrode terminal  60  disposed on the cap plate  50 , and a current collecting member  70  connected to the electrode terminal  60 . The cap plate  50  of the present embodiment is provided with an electrode lead-out hole  501 . In the present embodiment, an insulating member  90  is disposed between the cap plate  50  and the electrode assembly  30 , to keep an insulation between the cap plate  50  and the electrode assembly  30 . Two opposite ends of the insulating member  90  may abut against the electrode assembly  30  to prevent a movement of the electrode assembly  30  in the case  20 . A sealing member  100  is disposed between the electrode terminal  60  and the cap plate  50 . The sealing member  100  surrounds the electrode lead-out hole  501 , and a sealing between the electrode terminal  60  and the cap plate  50  is kept by the sealing member  100 . 
       FIG.  3    schematically shows a partial cross-sectional view of a combination of a cap assembly and a current collecting member according to an embodiment of the present disclosure.  FIG.  4    schematically shows a partial cross-sectional view of a cap assembly according to an embodiment of the present disclosure. Referring to  FIG.  3    and  FIG.  4   , the electrode terminal  60  is located on an outer side of the cap plate  50  and is provided with a stepped hole. In the present embodiment, the stepped hole of the electrode terminal  60  is disposed corresponding to the electrode lead-out hole  501  of the cap plate  50 . In the present embodiment, the electrode terminal  60  is fixed with the cap plate  50 . In the present embodiment, the current collecting member  70  includes an extending portion  701  and a connecting portion  702  connected to the extending portion  701 . The connecting portion  702  is located on an inner side of the cap plate  50  and is directly connected to the tab  302  of the electrode assembly  30 . Preferably, the connecting portion  702  is formed in a sheet-like shape, and the connecting portion  702  is connected to the tab  302  by ultrasonic welding. The extending portion  701  extends toward the electrode terminal  60  and protrudes into the stepped hole. The extending portion  701  is connected to the electrode terminal  60 . Preferably, the extending portion  701  and the electrode terminal  60  are connected by laser welding. After protruding into the stepped hole, the extending portion  701  is exposed to a side of the electrode terminal  60  facing away from the cap plate  50 . Laser light may be irradiated from the outer side of the cap plate  50  to regions to be connected of the extending portion  701  and of the electrode terminal  60 , such that a portion of the extending portion  701  exposed to the side of the electrode terminal  60  facing away from the cap plate  50  may be connected to the electrode terminal  60  by laser welding. Since the laser light is incident from the outer side of the cap plate  50 , metal particles generated by the laser welding will not fall into the inner side of the cap plate  50  (i.e., inside the case  20 ), and thus will not cause a short circuit of the electrode assembly  30 . That is, a security risk brought by the laser welding may be eliminated. 
     In the present embodiment, the electrode terminal  60  includes a first metal layer  601  and a second metal layer  602  disposed one on top of another. The second metal layer  602  is located on a side of the first metal layer  601  away from the cap plate  50 . The first metal layer  601  and the second metal layer  602  are made of different materials. The stepped hole of the electrode terminal  60  penetrates through the first metal layer  601  and the second metal layer  602 . Referring to  FIG.  4   , the stepped hole of the electrode terminal  60  includes a first hole segment  601   a  and a second hole segment  602   a  The second hole segment  602  penetrates through the second metal layer  602  and extends into the first metal layer  601 . The first hole segment  601   a  penetrates through the first metal layer  601 . The current collecting member  70  is connected between the tab  302  and the electrode terminal  60 . The extending portion  701  included in the current collecting member  70  extends toward the electrode terminal  60  and protrudes into the first hole segment  601   a.  The extending portion  701  is directly connected to the first metal layer  601 . The first metal layer  601  and the current collecting member  70  are made of the same material. Since the extending portion  701  of the current collecting member  70  and the first metal layer  601  of the electrode terminal  60  are made of the same material, the extending portion  701  and the first metal layer  601  may be connected and fixed to each other by laser welding, and the welding connection between the both is reliable, stable and has a high strength. Further, in the embodiment in which the extending portion  701  and the first metal layer  601  are connected and fixed to each other, the extending portion  701  does not protrude into the second hole segment  602   a,  and thus, the extending portion  701  does not interfere with a connection and fixing of a bus bar to the second metal layer  602 . 
     In one embodiment, both of the first metal layer  601  and the current collecting member  70  are made of copper, and the second metal layer  602  is made of aluminum; or, both of the first metal layer  601  and the current collecting member  70  are made of aluminum, and the second metal layer  602  is made of copper. Since the second hole segment  602   a  penetrates through the second metal layer  602  and extends into the first metal layer  601  such that an upper surface of the first metal layer  601  is exposed, during the laser welding from the outer side of the cap plate  50 , the second metal layer  602  may be prevented from being melted and mixed into a welding pool generated when the first metal layer  601  and the current collecting member  70  are welded. Since the first metal layer  601  and the second metal layer  602  are made of different materials, if the second metal layer  602  is melted and mixed into the welding pool generated when the first metal layer  601  and the current collecting member  70  are welded, a brittle metal compound will be generated and a welding strength will be lowered. 
     In the present embodiment, the second hole segment  602   a  has a diameter larger than that of the first hole segment  601   a.  The extending portion  701  is welded to the first metal layer  601 . Since the diameter of the second hole segment  602   a  is larger than that of the first hole segment  601   a,  regions to be welded of the extending portion  701  and of the first metal layer  601  may be exposed by the second hole segment  602   a,  and thus laser light may be prevented from being irradiated on the second metal layer  602  during the laser welding, thereby facilitating a welding apparatus to weld the regions to be welded. In one embodiment, the extending portion  701  and the first metal layer  601  are welded by the laser welding, by which an annular welding seam is formed so as to connect the extending portion  701  and the first metal layer  601  in a sealed manner. 
     Referring to  FIG.  3   , the extending portion  701  of the present embodiment is a hollow member provided with a blind hole  704 . The blind hole  704  of the extending portion  701  has an opening toward the electrode assembly  30 . Such design of the extending portion  701  of the present embodiment is conducive to reducing an overall weight of the current collecting member  70  and increasing an energy density of the secondary battery  10 . Meanwhile, the blind hole  704  of the extending portion  701  may accommodate gas generated when the secondary battery  10  is charged or discharged, thereby lowering an internal pressure of the case  20 . In one example, the extending portion  701  and the connecting portion  702  may be formed by stamping for one time in a manner of stamping a sheet blank. 
     Referring to  FIG.  4   , in the present embodiment, a composite connection interface  603  is formed between the first metal layer  601  and the second metal layer  602 . The secondary battery  10  further includes a connecting member  80 . The connecting member  80  is connected to the cap plate  50 . The connecting member  80  abuts against the second metal layer  602  and a contact interface  604   a  (referring to  FIG.  7   ) is formed between the connecting member  80  and the second metal layer  602 , so as to fix the electrode terminal  60  to the cap plate  50 . The contact interface  604   a  is located above the composite connection interface  603 . As such, a portion of the connecting member  80  is located above the composite connection interface  603 , and thus may apply a pressure to the second metal layer  602 , thereby preventing the composite connection interface  603  from being broken due to tensile stress. A sealing member  100  is disposed between the electrode terminal  60  and the cap plate  50 . Since the electrode terminal  60  as a whole is restrained by the connecting member  80 , the electrode terminal  60  cannot move in an axial direction of the electrode lead-out hole. As a result, on the one hand, a possibility of the electrode terminal  60  being disconnected from the sealing member may be lowered, and stability of the sealing between the electrode terminal  60  and the cap plate  50  may be improved; on the other hand, the welding seam formed between the extending portion  701  and the first metal layer  601  will not be subjected to a shear stress in the axial direction of the electrode lead-out hole, or will be subjected to a small shear stress in the axial direction of the electrode lead-out hole. In one embodiment, the second metal layer  602  has a flange  604  near an edge of the first metal layer  601 , and the connecting member  80  abuts against the flange  604  and contacts with a surface of the flange  604  facing away from the first metal layer  601 . 
     In the present embodiment, the connecting portion  702  is located on the inner side of the cap plate  50  and directly connected to the tab  302 , and the connecting portion  702  is formed in a sheet-like shape, which is conducive to reducing an occupation ratio of the connecting portion  702  to the internal space of the case  20 , and increasing the energy density of the secondary battery  10 . Meanwhile, the connecting portion  702  and the tab  302  are made of the same material, and since the tab  302  is a sheet-like member, the tab  302  and the connecting portion  702  may be connected by ultrasonic welding, which may lower a possibility of metal particles being generated during the welding process of the tab  302  and the connecting portion  702 , generate a large connection area between the tab  302  and the connecting portion  702 , and make the welding connection reliable and stable. 
     The secondary battery  10  according to an embodiment of the present disclosure includes a cap plate  50 , an electrode terminal  60  located on an outer side of the cap plate  50 , and a current collecting member  70  connected to the electrode terminal  60 . The electrode terminal  60  according to the embodiment of the present disclosure is connected to the cap plate  50  and located on the outer side of the cap plate  50 , and the electrode assembly  30  is electrically connected to the electrode terminal  60  through the current collecting member  70 . Since the electrode terminal  60  does not pass through the cap plate  50 , the electrode terminal  60  does not occupy the internal space of the case  20 . Therefore, a size of the electrode assembly  30  may be increased, which is conducive to increasing the energy density of the secondary battery  10 . Further, the tab  302  of the electrode assembly  30  is electrically connected to the electrode terminal  60  through the current collecting member  70 . During assembly of the secondary battery  10 , the tab  302  of the electrode assembly  30  may be first connected and fixed to the current collecting member  70  (preferably by ultrasonic welding); then, the extending portion  70   a  included in the current collecting member  70  is mounted to the first hole segment  601   a  of the electrode terminal  60 , the electrode assembly  30  is further loaded into the case  20 , and the cap plate  50  is coupled to the case  20 ; finally, laser light is irradiated from the outer side of the cap plate  50  such that the extending portion  70   a  and the electrode terminal  60  is connected by laser welding. As such, a possibility that metal particles generated during the laser welding of the extending portion  701  and the electrode terminal  60  fall into the inside of the case  20  may be lowered, and an internal short circuit of the electrode assembly  30  may be avoided. 
       FIG.  5    schematically shows a cross-sectional view of a combination of a cap assembly and a current collecting member according to an embodiment of the present disclosure.  FIG.  6    schematically shows an enlarged view of a portion A in  FIG.  5   .  FIG.  7    schematically shows an enlarged view of a portion B in  FIG.  6   . In  FIGS.  5  to  7   , the same elements as those shown in  FIGS.  2  to  4    are denoted by the same reference numerals, and description of the same configurations will not be repeated, while different configurations will be mainly illustrated. Referring to  FIGS.  5  to  7   , the current collecting member  70  of the present embodiment further includes a projection  702   a.  The projection  702   a  is connected between the extending portion  701  and the connecting portion  702 . Meanwhile, a recess  702   b  is formed on a side of the projection  702   a  away from the electrode terminal  60  by forming the projection  702   a.  The projection  702   a  of the present embodiment is provided with a through hole  705 . The through hole  705  is disposed corresponding to the first hole segment  601   a.  Preferably, the through hole  705  is disposed coaxially with the first hole segment  601   a.  The extending portion  701  of the present embodiment passes through the through hole  705  and protrudes into the first hole segment  601   a  of the stepped hole, and meanwhile, is directly connected to the first metal layer  601  of the electrode terminal  60 . The current collecting member  70  of the present embodiment further includes a support portion  703  connected to the extending portion  701 . The support portion  703  is received in the recess  702   b.  The extending portion  701  of the present embodiment is formed as a solid member. The support portion  703  is received in the recess  702   b  and extends beyond an inner wall of the through hole  705  in a radial direction of the through hole  705 . Preferably, the extending portion  701  is connected to the first metal layer  601  of the electrode terminal  60  by laser welding. During the laser welding, laser light is incident from the outer side of the cap plate  50 , and thus it is possible to effectively prevent metal particles generated during the laser welding from falling into the case  20 . After the extending portion  701  is connected and fixed to the electrode terminal  60 , the support portion  703  may tightly pull the projection  702   a  upward, and the projection  702   a  may be clamped by the support portion  703  and the electrode terminal  60  together, to maintain a positional stability of the projection  702   a.  In one embodiment, the support portion  703  is formed as a disk-like member. 
     Referring to  FIG.  6   , the second hole segment  602   a  of the present embodiment includes a sink portion  602   b.  The sink portion  602   b  is disposed in the first metal layer  601 . A top surface  701   a  of the extending portion  701  is flush with a bottom surface of the sink portion  602   b.  When the extending portion  701  and the first metal layer  601  are connected and fixed by laser welding, laser light is incident from the outer side of the cap plate  50  and in a direction perpendicular to the bottom surface of the sink portion  602   b.  The laser light melts the extending portion  701  and the first metal layer  601 . Since the top surface  701   a  of the extending portion  701  is flush with the bottom surface of the sink portion  602   b,  a power requirement of a laser generating apparatus may be advantageously lowered. 
       FIG.  8    schematically shows a partial exploded view of a secondary battery  10  according to another embodiment of the present disclosure.  FIG.  9    schematically shows a cross-sectional view of a combination of a cap assembly and a current collecting member according to another embodiment of the present disclosure.  FIG.  10    schematically shows an enlarged view of a portion C in  FIG.  9   . In  FIGS.  8  to  10   , the same elements as those shown in  FIGS.  2  to  4    are denoted by the same reference numerals, and description of the same configurations will not be repeated, while different configurations will be mainly illustrated. Referring to  FIG.  8   , the current collecting member  70  of the present embodiment further includes a projection  702   a.  The projection  702   a  is connected between the extending portion  701  and the connecting portion  702 . Referring to  FIGS.  9  and  10   , a recess  702   b  is formed on a side of the projection  702   a  away from the electrode terminal  60  by forming the projection  702   a  In the present embodiment, the extending portion  701 , the projection  702   a,  and the connecting portion  702  is formed into an integral member. The projection  702   a  of the present embodiment has a top surface facing the cap plate  50 . The extending portion  701  of the present embodiment is connected to the top surface of the projection  702   a.    
       FIG.  11    schematically shows a cross-sectional view of a combination of a cap assembly and a current collecting member according to still another embodiment of the present disclosure.  FIG.  12    schematically shows an enlarged view of a portion D in  FIG.  11   . In  FIGS.  11  and  12   , the same elements as those shown in  FIGS.  8  to  10    are denoted by the same reference numerals, and description of the same configurations will not be repeated, while different configurations will be mainly illustrated. In one embodiment, referring to  FIGS.  11  and  12   , the extending portion  701  is formed as a solid columnar member and has a high rigidity, and thus the connection of the extending portion  701  with the electrode terminal  60  is stable and reliable. In another embodiment, referring to  FIG.  10   , the extending portion  701  is formed as a hollow cylindrical member having a blind hole  704 . The blind hole  704  has an opening toward the electrode assembly  30 . The blind hole  704  of the extending portion  701  is in communication with the recess  702   b.  Thus, on the one hand, it is conducive to reducing the overall weight of the current collecting member  70  and thus increasing the energy density of the secondary battery  10 ; on the other hand, both of the blind hole  704  and the recess  702   b  of the extending portion  701  may accommodate the gas generated when the secondary battery  10  is charged and discharged, thereby effectively lowering the internal pressure of the case  20 . 
     Referring to  FIG.  13   , an embodiment of the present disclosure further discloses a method of manufacturing a secondary battery  10 , wherein the method includes the following steps:
         providing an electrode assembly  30 , wherein the electrode assembly  30  includes a main body  301  and a tab  302  connected to the main body  301 ;   providing a current collecting member  70 , and connecting and fixing the tab  302  to the current collecting member  70 , wherein the current collecting member  70  includes an extending portion  701 ;   providing an electrode terminal  60  and a cap plate  50 , wherein the electrode terminal  60  is disposed on an outer side of the cap plate  50  and includes a first metal layer  601  and a second metal layer  602  disposed one on top of another, and the second metal layer  602  is located on a side of the first metal layer  601  away from the cap plate  50  and is made of different material from the first metal layer  601 , and wherein the electrode terminal  60  is provided with a stepped hole, which includes a first hole segment  601   a  penetrating through the first metal layer  601  and a second hole segment  601   b  penetrating through the second metal layer  602  and extending into the first metal layer  601 ;   inserting the extending portion  701  into the first hole segment  601   a  from an inner side of the cap plate  50 , and the first metal layer  601  and the current collecting member  70  are made of the same material; and   providing a case  20 , loading the electrode assembly  30  into the case  20 , and performing laser welding from the outer side of cap plate  50  so as to weld the extending portion  701  to the first metal layer  601  by the laser welding.       

     In one embodiment, the tab  302  and the connecting portion  702  are connected and fixed by ultrasonic welding, which may lower a possibility of generation of metal particles during the welding process, and is conducive to improving safety of the secondary battery  10 . 
     In the method of manufacturing the secondary battery  10  according to the embodiment of the present disclosure, the current collecting member  70  and the tab  302  are connected and fixed to each other at first, and then the current collecting member  70  and the electrode terminal  60  are assembled with each other and the electrode assembly  30  is loaded into the case  20 . Finally, laser welding is performed on the outer side of the cap plate  50  to connect and fix the extending portion  701  included in the current collecting member  70  to the electrode terminal  60 . Thus, metal particles generated during the laser welding process of the extending portion  701  of the current collecting member  70  and the first metal layer  601  of the electrode terminal  60  will not fall into the case  20 , thereby effectively ensuring a cleanliness of an internal space of the case  20 , and lowering a possibility of occurrence of a short circuit of the electrode assembly  30 . 
     In the present embodiment, the extending portion  701  and the electrode terminal  60  are welded in a sealed manner by laser welding, to ensure a stable connection between the extending portion  701  and the electrode terminal  60  with a high connection strength. 
     In one embodiment, the extending portion  701  is interference-fitted with the first hole segment  601   a.  Therefore, before the extending portion  701  and the electrode terminal  60  are connected and fixed to each other, it is not easy for the extending portion  701  to fall off from the first hole segment  601   a  or displace in the first hole segment  601   a,  thereby ensuring a connection stability of the current collecting member  70  and the electrode terminal  60  during assembly of the secondary battery  10 , which is conducive to improving an efficiency of the following connecting and fixing operation of the extending portion  70   a  included in the current collecting member  70  and the electrode terminal  60 . Further, since the extending portion  701  is interference-fitted with the first hole segment  601 , there is no gap between the extending portion  701  and the electrode terminal  60 . 
     The present disclosure further proposes a battery module including a plurality of secondary batteries according to any of the above embodiments. In one embodiment, referring to  FIG.  14    and  FIG.  15   , a battery module  200  includes a plurality of secondary batteries  10  and a housing  201  for accommodating the secondary batteries  10 . The housing  201  includes a cavity and the secondary batteries are disposed in the cavity side by side. The housing  201  includes a pair of side plates  2011  and a pair of end plates  2012 , which are connected to each other to form the housing  201 . The arrangement of the secondary batteries and the configuration of the housing are not limited to the above embodiments, and any other suitable arrangements and configurations are available. 
     The present disclosure further proposes a battery pack including at least one battery module according to any of the above embodiments. In one embodiment, referring to  FIG.  16   , a battery pack  300  includes a plurality of battery modules  200  and a casing for accommodating the battery modules  200 . The casing includes a cavity and the battery modules  200  are disposed in the cavity side by side. The casing is formed as a box, and includes a lower case  302  for receiving the battery modules  200  and a cover  301  for closing the lower case  302 . The arrangement of the battery modules and the configuration of the casing are not limited to the above embodiments, and any other suitable arrangements and configurations are available. For example, the casing may be formed into a frame shape, or a disk shape. 
     The present disclosure further proposes an apparatus using the secondary battery according to any of the above embodiments as a power source. The apparatus may be a movable device, such as a vehicle, a ship, a small aircraft, etc. The vehicle may be a new energy vehicle, for example, a pure electric vehicle or a hybrid vehicle. In one embodiment, referring to  FIG.  17   , a vehicle  400  includes a battery pack  300  according to any of the above embodiments, and uses the battery pack  300  as a power source. As shown in  FIG.  17   , the battery pack  300  is located a lower portion of the vehicle  400 . However, the present disclosure is not limited to the above embodiment, and the battery pack  300  may be located at any other suitable positions of the vehicle  400 . 
     Although the present disclosure has been described with reference to the preferred embodiments, various modifications may be made to the present disclosure and components may be replaced with equivalents without departing from the scope of the present disclosure. In particular, the technical features mentioned in the various embodiments may be combined in any manner as long as there is no structural conflict. The present disclosure is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.