Patent Publication Number: US-2022238890-A1

Title: Secondary battery and manufacturing method thereof, battery module, and apparatus

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2020/089440, filed on May 9, 2020, the contents of which are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a technical field of batteries, and particularly relates to a secondary battery and manufacturing method thereof, a battery module and an apparatus. 
     BACKGROUND 
     Secondary batteries have advantages of high energy density, long service life, energy saving and environmental protection, etc., and are widely used in different fields such as alternative fuel vehicles and energy storage power stations. 
     In the prior art, a secondary battery includes an electrode assembly and a current collecting member. The electrode assembly includes a main body portion and tabs extending from the main body portion. In order to extract the electric energy of the electrode assembly to the outside of the secondary battery, the tabs and the current collecting member are usually connected, forming a connection region between them. 
     SUMMARY 
     However, during use of the secondary battery, the secondary battery is charged and discharged many times, and it is found that the connection region between the tab and the current collecting member has a poor current flowing capability, which affects the performance of the secondary battery. 
     The embodiment of the present application provides a secondary battery and manufacturing method thereof, a battery module and an apparatus, which can reduce the possibility of decrease of the current flowing capability of the tab. 
     On one aspect, the embodiment of the present application provides a secondary battery, including: 
     an electrode assembly including a main body portion and a tab extending out from the main body portion; 
     a current collecting member including a guiding section, the guiding section extending in a direction perpendicular to a length direction of the electrode assembly; 
     a transition connecting piece, the transition connecting piece and the current collecting member being separately provided, the transition connecting piece including a current collecting portion and a fixing portion, the current collecting portion being adapted to connect with the tab to form a first connection region, the fixing portion being adapted to connect with the guiding section to form a second connection region, and respective projections of the first connection region and the second connection region on a plane perpendicular to the length direction do not overlap. 
     On a further aspect, the embodiment of the present application provides a manufacturing method for a secondary battery, the method includes steps of: 
     providing an electrode assembly, the electrode assembly including a main body portion and a tab extending out from the main body portion; 
     providing a current collecting member, the current collecting member including a guiding section extending in a direction perpendicular to a length direction of the electrode assembly; 
     providing a transition connecting piece, the transition connecting piece including a current collecting portion and a fixing portion; and 
     connecting the current collecting portion with the tab to form a first connection region and connecting the fixing portion with the guiding section to form a second connection region, wherein respective projections of the first connection region and the second connection region on a plane perpendicular to the length direction do not overlap. 
     On another further aspect, the embodiment of the present application provides a battery module, including the secondary battery according to the above-mentioned embodiments. 
     On another further aspect, the embodiment of the present application provides an apparatus using a secondary battery as a power source, wherein the apparatus includes the secondary battery according to the above-mentioned embodiments. 
     In the secondary battery according to the embodiment of the present application, the tab of the electrode assembly and the current collecting portion of the transition connecting piece are connected to form a first connection region, and the fixing portion of the transition connecting piece and the guiding section of the current collecting member are connected to form a second connection region; when achieving the connection of the tab with the guiding section, the first connection region and the second connection region will not overlap, thereby improving the current flowing capability of the tab. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features, advantages, and technical effects of the exemplary embodiments of the present application will be described below with reference to the accompanying drawings. 
         FIG. 1  is a schematic structural diagram of a vehicle disclosed in an embodiment of the present application; 
         FIG. 2  is an explosive schematic diagram of a structure of a battery pack disclosed in an embodiment of the present application; 
         FIG. 3  is a partial structural schematic diagram of a battery module disclosed in an embodiment of the present application; 
         FIG. 4  is an explosive schematic diagram of a structure of a secondary battery disclosed in an embodiment of the present application; 
         FIG. 5  is a schematic structural diagram of a current collecting member according to an embodiment of the present application; 
         FIG. 6  is an enlarged view of portion A in  FIG. 4 ; 
         FIG. 7  is a schematic structural diagram of a transition connecting piece disclosed in an embodiment of the present application; 
         FIG. 8  is a schematic structural diagram of a transition connecting piece disclosed in another embodiment of the present application; 
         FIG. 9  is a schematic structural diagram of a transition connecting piece disclosed in a further embodiment of the present application; 
         FIG. 10  is a schematic structural diagram of a transition connecting piece disclosed in another further embodiment of the present application; 
         FIG. 11  is a partial schematic diagram of a structure of a secondary battery disclosed in another embodiment of the present application; 
         FIG. 12  is an explosive schematic diagram of a structure of a secondary battery disclosed in a further embodiment of the present application; 
         FIG. 13  is a partial schematic diagram of a structure of a secondary battery disclosed in another further embodiment of the present application. 
     
    
    
     In the drawings, the drawings are not drawn to actual scale. 
     REFERENCE NUMERALS 
     
         
         
           
               1 , vehicle; 
               10 , battery pack; 
               20 , battery module; 
               30 , secondary battery;  31 , casing;  32 , electrode assembly;  321 , main body portion;  321   a , end surface;  322 , tab; 
               40 , cap assembly;  41 , cap plate;  42 , electrode terminal;  43 , current collecting member;  431 , terminal connecting section;  432 , guiding section;  432   a , leg; 
               50 , transition connecting piece;  51 , current collecting portion;  51   a , accommodating recess;  52 , fixing portion; 
               60 , first sheet;  70 , second sheet;  80 , third sheet;  90 , busbar;  100 , first connection region;  200 , second connection region; 
             X, length direction; Y, thickness direction; Z, width direction. 
           
         
       
    
     DETAILED DESCRIPTION 
     The implementations of the present application are described below in further detail with reference to the accompanying drawings and embodiments. The following detailed description of the embodiments and the accompanying drawings are used to exemplarily illustrate the principle of the present application, but cannot be used to limit the scope of the present application, that is, the present application is not limited to the described embodiments. 
     In the description of the present application, it should be noted that, unless otherwise stated, “multiple” means two or more; the orientation or positional relationship indicated by the terms “upper”, “lower”, “left”, “right”, “inside”, “outside” or the like is merely used for convenience of describing the application and simplifying the description, rather than indicating or implying that the device or element referred to must have a particular orientation, or be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation to the present application. In addition, the terms “first”, “second”, “third”, or the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance. “Perpendicularity” does not mean a strict perpendicularity, but allows an error within an allowed range. “Parallel” does not mean a strict parallel but allows an error within an allowed range. 
     The orientation words appearing in the following description all refer to the directions shown in the drawings, and are not intended to define the specific structure of the present application. In the description of the present application, it should also be noted that, unless otherwise clearly defined and specified, the terms “install”, “connect”, and “couple” should be understood in a broad sense, for example, may refer to a fixed connection, a detachable connection, or an integral connection, may refer to a direct connection or an indirect connection through an intermediate medium. For the person skilled in the art, the specific meaning of the above-mentioned terms in the present application can be understood according to specific circumstances. 
     In order to better understand the present application, the embodiments of the present application are described below in combination with  FIGS. 1-13 . 
     The embodiment of the present application provides an apparatus that uses a secondary battery  30  as a power source. The apparatus may be but is not limited to, a vehicle, a ship, or an aircraft. Referring to  FIG. 1 , an embodiment of the present application provides a vehicle  1  including a vehicle body and a battery block. The battery block is provided on the vehicle body. The vehicle  1  may be a pure electric vehicle, a hybrid electric vehicle or an extended-range vehicle. The vehicle body is provided with a drive motor electrically connected to the battery block. The battery block provides power to the drive motor. The drive motor is connected to wheels on the vehicle body through a transmission mechanism to drive the vehicle to travel. Optionally, the battery block may be horizontally arranged at the bottom of the vehicle body. 
     As shown in  FIG. 2 , the battery block may be formed as a battery pack  10 . The battery pack  10  may be provided in various manners. In some optional embodiments, the battery pack  10  includes a housing and a battery module  20  disposed in the housing. There may be one or more battery modules  20 . The one or more battery modules  20  are arranged in a row in the housing. The type of the housing is not limited. The housing may be a frame-shaped housing, a disc-shaped housing, or a box-shaped housing. Optionally, the housing includes a lower housing for receiving the battery module  20  and an upper housing for closing the lower housing. After closing the lower housing, the upper housing together with the lower housing forms an accommodating portion for accommodating the battery module  20 . In other optional embodiments, the battery pack  10  includes a housing and a plurality of secondary batteries  30  directly arranged in the housing. 
     As shown in  FIG. 3 , the battery block may also be formed as a battery module  20 , and a plurality of battery modules  20  are arranged in a housing and installed on the vehicle body. 
     As shown in  FIG. 3 , the battery module  20  includes a plurality of secondary batteries  30 . The battery module  20  may be provided in various manners. In one embodiment, the battery module  20  includes an accommodating portion and a plurality of secondary batteries  30  located in the accommodating portion. The plurality of secondary batteries  30  are arranged side by side in the accommodating portion. The accommodating portion may be provided in various manners, and for example, the accommodating portion includes a shell and a cover plate covering the shell; or, the accommodating portion includes side plates and end plates that are connected one after another and define an enclosure; or, the accommodating portion includes two ends plates arranged oppositely and a strap band surrounding the end plates and the secondary batteries  30 . 
     As shown in  FIG. 4 , the secondary battery  30  according to the embodiment of the present application includes a casing  31 , an electrode assembly  32  disposed in the casing  31 , and a cap assembly  40  hermetically connected with the casing  31 . 
     The casing  31  according to the embodiment of the present application is formed in a cubic shape or other shapes. The casing  31  includes an internal space for accommodating the electrode assembly  32  and electrolyte, and an opening communicating with the internal space. The casing  31  may be made of materials such as aluminum, aluminum alloy, plastic or other else. 
     The electrode assembly  32  according to the embodiment of the present application can be formed by stacking or winding a first electrode plate, a second electrode plate, and a separator located between the first electrode plate and the second electrode plate, wherein the separator is an insulating member between the first electrode plate and the second electrode plate. 
     In the present embodiment, the 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. Both the positive electrode plate and the negative electrode plate include coated regions and uncoated regions, a positive electrode plate active material is coated on the coated region of the positive electrode plate, and a negative electrode plate active material is coated on the coated region of the negative electrode plate. On the coated region, the active material is coated on a region corresponding to a current collector formed by a thin metal foil. On the uncoated region, the current collector is directly exposed and no active material is coated. After being wound or stacked, the electrode assembly  32  includes two tabs  322 , namely, a positive tab and a negative tab. The coated regions of the positive electrode plate and the coated regions of the negative electrode plate constitute the main body portion  321 . The uncoated regions of the positive electrode plate are stacked to form the positive tab, and the uncoated regions of the negative electrode plate are stacked to form the negative tab. The tab  322  includes a plurality of layer structures. In the embodiment of the present application, the main body portion  321  includes two end surfaces  321   a  disposed opposite to each other in a length direction X, and the positive and negative tabs respectively extend out from the two end surfaces  321   a  of the main body portion  321  opposite to each other in the length direction X. 
     In the embodiment in which the electrode assembly  32  is in a wound configuration, the electrode assembly  32  as a whole are formed as a flat member. The electrode assembly  32  includes a wide surface and a narrow surface alternately arranged in a circumferential direction, wherein the wide surface is approximately parallel to a winding axis and is an outer surface which has the largest area. The wide surface may be a relatively flat surface, while not required to be a perfect flat plane. During use of the secondary battery  30 , the electrode assembly  32  may expand, which may cause the wide surface to be slightly deformed. In the present embodiment, the length direction X of the electrode assembly  32  is parallel to the winding axis and approximately parallel to the wide surface, and a thickness direction Y refers to a direction perpendicular to the wide surface. The length direction X and the thickness direction Y are perpendicular to a width direction Z, respectively. 
     In the embodiment where the electrode assembly  32  is in a stacked configuration, the length direction X of the electrode assembly  32  refers to a direction perpendicular to the end surface  321   a  of the main body portion  321  from which the tab  322  extends out, and the thickness direction Y refers to a stacking direction of the first electrode plate, the separator, and the second electrode plate. The length direction X and the thickness direction Y are perpendicular to the width direction Z, respectively. 
     Referring to  FIG. 4  and  FIG. 5 , the cap assembly  40  according to the embodiment of the present application includes a cap plate  41 , an electrode terminal  42  and a current collecting member  43 . The cap plate  41  according to the embodiment of the present application includes an outer surface and an inner surface opposite each other in the width direction Z of the electrode assembly  32  and an electrode lead-out hole (not shown in the drawings) penetrating through the cap plate  41  in the width direction Z. The cap plate  41  can close the opening of the casing  31  and is hermetically connected to the casing  31 . The electrode terminal  42  is provided on the cap plate  41  and disposed corresponding to the electrode lead-out hole. The electrode terminal  42  is at least partially exposed from the outer surface of the cap plate  41  for welding with a busbar  90 . The current collecting member  43  is adapted to connect the tab  322  with the electrode terminal  42 . The current collecting member  43  includes a terminal connecting section  431  and a guiding section  432 . The terminal connecting section  431  is adapted to connect with the electrode terminal  42 , and the guiding section  432  is adapted to connect with the tab  322 . The plane where the terminal connecting section  431  is located, is perpendicular to the width direction Z of the electrode assembly  32  and is approximately parallel to the plane wherein the cap plate  41  is located. The plane where the guiding section  432  is located, is perpendicular to the length direction X of the electrode assembly  32  and is approximately parallel to the end surface  321   a  of the main body portion  321 . In one example, the terminal connecting section  431  and the guiding section  432  are intersected, forming an L-shaped member. 
     After realizing the problem of a poor current flowing capability of the connection region between the tab  322  and the current collecting member  43 , Applicant conducted research and analysis on various components of the secondary battery  30 . Applicant found that in the process of connecting the tab  322  with the current collecting member  43 , in order to ensure the connection strength between the tab  322  and the current collecting member  43 , the multiple layer structures of the tab  322  are usually pre-connected, and then the tab  322  after the pre-connection is operated again to connect with the current collecting member  43 , which causes the tab  322  to undergo two connecting operations at a same region, and the connection regions of the two connecting operations overlap or at partially overlap in their projections on a plane perpendicular to the length direction X, thereby causing damage to the tab  322  in these regions, and thus affecting the current flowing capability of the tab  322 . 
     In view of the above-mentioned problem found by Applicant, Applicant has improved the configuration of the secondary battery  30 , and the embodiments of the present application will be further described below. 
     Referring to  FIGS. 4 and 6 , the secondary battery  30  provided by the embodiment of the present application further includes a transition connecting piece  50 . The transition connecting piece  50  and the current collecting member  43  are separately provided and connected to each other. The so-called “separately provided” means that the transition connecting piece  50  and the current collecting member  43  are two separately processed parts before being connected. The specific ways of connecting the transition connecting piece  50  with the current collecting member  43  include riveting, welding, and bonding. The transition connecting piece  50  is adapted to connecting the tab  322  with the guiding section  432  of the current collecting member  43 . As shown in  FIG. 7 , the transition connecting piece  50  includes a current collecting portion  51  and a fixing portion  52 . The current collecting portion  51  is adapted to connect with the tab  322  and form a first connection region  100 , and the fixing portion  52  is adapted to connect with the guiding section  432  and form a second connection region  200 . Projections of the first connection region  100  and the second connection region  200  on a plane perpendicular to the length direction X do not overlap. 
     As shown in  FIG. 6 , the first connection region  100  and the second connection region  200  are spaced apart in the width direction Z, so that their respective projections on a plane perpendicular to the length direction X do not overlap. In some other examples, the first connection region  100  and the second connection region  200  may be spaced apart in the thickness direction Y, so that their respective projections on a plane perpendicular to the length direction X do not overlap. 
     Referring to  FIG. 5  and  FIG. 6 , in the secondary battery  30  according to the embodiment of the present application, the tab  322  of the electrode assembly and the current collecting portion  51  of the transition connecting piece  50  are connected to form the first connection region  100 , so that the multiple layer structures of the tab  322  and the current collecting portion  51  are pre-connected together to prevent looseness among the layer structures. In other words, by pre-connecting the various layer structures of the tab  322  together, the gap between the various layer structures can be reduced. Meanwhile, in the process of connecting the various layer structures of the tab  322 , the transition connecting piece  50  can also protect the tab  322 , thereby preventing the tab  322  from being damaged. The fixing portion  52  of the transition connecting piece  50  and the guiding section  432  of the current collecting member  43  are connected to form the second connection region  200 , so that the tab  322  is electrically connected to the guiding section  432  through the transition connecting piece  50 , without directly connecting the tab  322  to the guiding section  432 . The electrical signal can be transmitted from the tab  322  to the current collecting portion  51 , from the current collecting portion  51  to the fixing portion  52 , and then from the fixing portion  52  to the guiding section  432  in order. Since after providing the transition connecting piece  50 , the first connection region  100  and the second connection region  200  can be independent of each other without interfering with each other, when achieving the connection of the tab  322  with the guiding section  432 , the first connection region  100  and the second connection region  200  do not overlap, and the tab  322  undergoes only one connecting operation when connected to the current collecting portion  51 . As such, during the process of connecting the tab  322  with the current collecting member  43 , the tab  322  will not undergo two connecting operations at a same region, which effectively reduces the possibility that micro cracks appear in at least some of the layer structures of the tab  322  and affect the current flowing capability of the tab  322  due to that the tab  322  undergoes two connecting operations at a same region. Further, in the prior art, the current collecting member  43  includes a bending section integrally formed with the guiding section  432 . The bending section needs to be bent after connected to the tab  322 . In the process of bending the bending section, the guiding section  432  will be stressed and deformed toward the main body portion  321  of the electrode assembly  32 , and thus there is a risk that the guiding section  432  interferes with the main body portion  321  and causes the main body portion  321  to be damaged or short-circuited. In the embodiment of the present application, since the tab  322  is pre-connected with the transition connecting piece  50 , and then the transition connecting piece  50  is connected with the guiding section  432 , and the transition connecting piece  50  is formed separately from the current collecting member  43  and does not need to be bent, the guiding section  432  will not be deformed toward the main body portion  321  of the electrode assembly  32 , thereby reducing the possibility of interference between the guiding section  432  and the main body portion  321 . 
     In one embodiment, the tab  322  is welded to the current collecting portion  51  to form the first connection region  100 . Optionally, the tab  322  and the current collecting portion  51  are welded by ultrasonic welding, which is beneficial to improve the reliability of the connection between the tab  322  and the current collecting portion  51 , and meanwhile can reduce the possibility of structural damage to the tab  322  when the tab  322  is welded. The fixing portion  52  is welded to the guiding section  432  to form the second connection region  200 . Optionally, the fixing portion  52  and the guiding section  432  are welded by laser welding, which is beneficial for improving the reliability of the connection between the fixing portion  52  and the guiding section  432 . During the connection process of the tab  322 , the transition connecting piece  50  and the guiding section  432 , the tab  322  and the current collecting portion  51  are both placed between an upper clamp and a lower clamp on an ultrasonic welding device to complete the welding operation, and then the transition connecting piece  50  and the guiding section  432  are placed in a laser welding device to complete the welding operation. If the tab  322  is directly welded to the guiding section  432 , the tab  322  will undergo a ultrasonic welding at first, then a laser welding at a same region, and in this case, the tab  322  that has experienced the ultrasonic welding operation will then be subjected to the laser welding operation, and thus structural damage such as micro cracks tends to appear in the tab  322 . In the present embodiment, since the regions of ultrasonic welding and laser welding do not overlap, the tab  322  is prevented from undergoing two connecting operations of ultrasonic welding and laser welding at a same region, the possibility that the structural damage such as micro cracks appears in the tab  322  is reduced, and thus it is ensured that the tab  322  has a good current flowing capacity. 
     In one embodiment, referring to  FIG. 6  and  FIG. 7 , the region of the transition connecting piece  50  covered by the tab  322  forms the current collecting portion  51 . Here, the region of the transition connecting piece  50  covered by the tab  322  refers to the portion of the transition connecting piece  50  blocked by the tab  322  while observed along the length direction X. The region of the transition connecting piece  50  which is not covered by the tab  322  forms the fixing portion  52 . Here, the region of the transition connecting piece  50  which is not covered by the tab  322  refers to the portion of the transition connecting piece  50  which is not blocked by the tab  322  while observed along the length direction X. 
     In one embodiment, the fixing portion  52  is located on one side of the tab  322  in the width direction Z, so that the size of the transition connecting piece  50  in the thickness direction Y can be reduced, that is, the width of the transition connecting piece  50  can be reduced. At least part of the current collecting portion  51  is connected to the tab  322  to form the first connection region  100 . In one example, the first connection region  100  is a continuous region, which is beneficial for improving the connection strength between the current collecting portion  51  and the tab  322 . At least part of the fixing portion  52  is connected to the guiding section  432  to form the second connection region  200 . Referring to  FIG. 6 , the transition connecting piece  50  includes two fixing portions  52 . The two fixing portions  52  are respectively located on two sides of the current collecting portion  51  in the width direction Z, that is, in the width direction Z, one fixing portion  52  is located on one side of the tab  322 , and the other fixing portion  52  is located on another side of the tab  322 . The two fixing portions  52  are respectively welded to the guiding section  432  to form two second connection regions  200 , which is beneficial for improving the connection strength between the transition connecting piece  50  and the guiding section  432 , and reduce the possibility of detachment of the transition connecting piece  50  from the guiding section  432 , and meanwhile is also beneficial for improving the current flowing capacity between the transition connecting piece  50  and the guiding section  432 . 
     In one embodiment, referring to  FIG. 6 , the transition connecting piece  50  is provided on a side of the guiding section  432  away from the main body portion  321  in the length direction X, so that the welding operation between the fixing portion  52  and the guiding section  432  can be performed from a side of the guiding section  432  away from the main body portion  321 , which is beneficial for improving the convenience of welding operation for connecting the fixing portion  52  with the guiding section  432 , and meanwhile, the transition connecting piece  50  will not occupy the space between the guiding section  432  and the main body portion  321 , a relatively large distance is maintained between the guiding section  432  and the main body portion  321 , which further reduces the possibility of structural damage to the main body portion  321  due to an external force. In the present embodiment, at least part of the fixing portion  52  is attached to a surface of the guiding section  432 . In one example, as shown in  FIG. 6 , an entire surface of the fixing portion  52  facing the guiding section  432  is attached to the guiding section  432 . In the present embodiment, the tab  322  is bent relative to the length direction X and connected to a surface of the current collecting portion  51  away from the guiding section  432  in the length direction X. 
     In another embodiment, the tab  322  is bent relative to the length direction X and is connected to a surface of the current collecting portion  51  close to the guiding section  432 . The transition connecting piece  50  and the guiding section  432  clamp the tab  322  and thus can protect the tab  322  and the first connection region  100 . In one example, as shown in  FIG. 8 , the current collecting portion  51  includes an accommodating recess  51   a . The accommodating recess  51   a  is formed by recessing a surface of the current collecting portion  51  close to the guiding section  432  toward a direction away from the guiding section  432 . The tab  322  extends into the accommodating recess  51   a  and is connected and fixed to the current collecting portion  51 . In the length direction X, at least part of the tab  322  is accommodated in the accommodating recess  51   a . Optionally, in the length direction X, a depth of the accommodating recess  51   a  is greater than a thickness of the entire tab  322 , so that the entire tab  322  is accommodated in the accommodating recess  51   a . As such, on one hand, it is beneficial for saving space in the length direction X, thereby increasing the energy density of the secondary battery  30 ; on the other hand, due to the accommodating recess  51   a , the current collecting portion  51  itself receives a smaller supporting stress from the tab  322  or even does not receive any supporting stress from the tab  322  after the transition collecting piece  50  is connected to the guiding section  432 , and thus, the second connection region  200  formed by the connection between the fixing portion  52  and the guiding section  432  receives a smaller supporting stress or even does not receive any supporting stress from the tab  322 , thereby reducing the possibility of fracture and separation of the second connection region  200  formed by the connection between the fixing portion  52  and the guiding section  432  due to a relatively large tensile stress. 
     In one embodiment, referring to  FIG. 7  and  FIG. 8 , the transition connecting piece  50  is an integrally formed single-layer sheet. The transition connecting piece  50  can be manufactured by stamping or machining. The thickness direction of the transition connecting piece  50  and the thickness direction of the guiding section  432  are both parallel to the length direction X. In the present embodiment, the transition connecting piece  50  is formed in a rectangular shape, but the shape of the transition connecting piece  50  is not limited here, as long as the transition connecting piece  50  can realize the function of connecting the tab  322  with the guiding section  432 . 
     In one embodiment, referring to  FIG. 9 , the transition connecting piece  50  includes a first sheet  60 , a second sheet  70  and a third sheet  80 . The first sheet  60  and the second sheet  70  are stacked in the length direction X. The third sheet  80  is bent into an arc shape and connected between the first sheet  60  and the second sheet  70 . The tab  322  is connected with the first sheet  60  to form the first connection region  100 . Before the transition connecting piece  50  and the tab  322  are connected, the first sheet  60  and the second sheet  70  are provided in an open state, and it is available to connect and fix the tab  322  with the first sheet  60  at first, then bend the second sheet  70  and stack it with the first sheet  60 . It facilitates welding the first sheet  60  of the transition connecting piece  50  to the tab  322 , thus reducing the difficulty of connecting the transition connecting piece  50  with the tab  322 . When connecting the transition connecting piece  50  to the guiding section  432 , the transition connecting piece  50  is connected to the guiding section  432  through both of the first sheet  60  and the second sheet  70  to form the second connection region  200 , thereby being beneficial for improving the connection strength between the fixing portion  52  of the transition connecting piece  50  and the guiding section  432 . In another embodiment, referring to  FIG. 10 , the second sheet  70  extends beyond the first sheet  60  in the width direction Z of the electrode assembly  32 . The second sheet  70  is provided with the fixing portion  52 . In the present embodiment, the portion of the second sheet  70  that extends beyond the first sheet  60  forms the fixing portion  52 . 
     In one embodiment, along the thickness direction Y, the guiding section  432  has two opposite edges. The tab  322  bypasses the edge of the guiding section  432  and is connected to a surface of the current collecting portion  51  away from the main body portion  321 . An outer surface of the third sheet  80  is formed as an arc-shaped surface. The third sheet  80  is located near a root portion of the tab  322 , and thus can effectively reduce the scratching between the tab  322  and the edges of the first sheet  60  and/or the second sheet  70  of the transition connecting piece  50  when the tab  322  is folded, which may cause the tab  322  pierced by the edges of the first sheet  60  and/or the second sheet  70 , or cause a stress concentration on the tab  322  due to the squeeze of the first sheet  60  and/or the second sheet  70 , which thus cause structural damage such as cracks in the tab  322 . 
     In one embodiment, as shown in  FIG. 11 , two transition connecting pieces  50  are provided. In the length direction X, the two transition connecting pieces  50  are stacked. The current collecting portions  51  of the two transition connecting pieces  50  clamp and connect to the tab  322 . At least one of the two transition connecting pieces  50  is connected with the tab  322  to form the first connection region  100 . Optionally, the two transition connecting pieces  50  are both connected with the tab  322  to form the first connection region  100 . The fixing portion  52  of at least one of the two transition connecting pieces  50  is connected to the guiding section  432 . Optionally, the fixing portions  52  of the two transition connecting pieces  50  are both connected to the guiding section  432 . 
     In one embodiment, two electrode assemblies  32  are provided. The two electrode assemblies  32  are arranged side by side in the thickness direction Y of the electrode assembly  32 , and the respective tabs  322  are respectively connected to at least one transition connecting piece  50 . As shown in  FIG. 12 , two transition connecting pieces  50  are provided on one guiding section  432 . The two transition connecting pieces  50  are arranged side by side in the thickness direction Y. The tab  322  of one of the two electrode assemblies  32  is connected to the current collecting portion  51  of one transition connecting piece  50 , and the tab  322  of the other electrode assembly  32  is connected to the current collecting portion  51  of the other transition connecting piece  50 . 
     In one embodiment, the guiding section  432  includes two legs  432   a . The two legs  432   a  are spaced apart in the thickness direction Y of the electrode assembly  32 , which is beneficial for reducing the weight of the guiding section  432  and improving the energy density of the secondary battery  30 . At least one transition connecting piece  50  is provided on each of the two legs  432   a . The electrode assemblies  32  and the legs  432   a  are set in one-to-one correspondence and have the same quantity. Referring to the embodiment shown in  FIG. 13 , the guiding section  432  includes two legs  432   a . Each of the two legs  432   a  is provided with one transition connecting piece  50 . The tab  322  of one of the two electrode assemblies  32  is connected to the current collecting portion  51  of one transition connecting piece  50 , and the tab  322  of the other electrode assembly  32  is connected to the current collecting portion  51  of the other transition connecting piece  50 . 
     In the secondary battery  30  according to the embodiment of the present application, the tab  322  of the electrode assembly  32  is connected to the guiding section  432  of the current collecting member  43  through a transition connecting piece  50 . The tab  322  of the electrode assembly  32  and the current collecting portion  51  of the transition connecting piece  50  are connected and form the first connection region  100 . The fixing portion  52  of the transition connecting piece  50  and the guiding section  432  of the current collecting member  43  are connected and form the second connection region  200 . By providing the transition connecting piece  50 , the first connection region  100  and the second connection region  200  can be made respectively independent without interfering with each other; therefore, when achieving the connection of the tab  322  with the guiding section  432 , the first connection region  100  and the second connection region  200  do not overlap, and thus the tab  322  undergoes only one connecting operation when connected to the current collecting portion  51 . As such, during the connection process between the tab  322  and the current collecting member  43 , the tab  322  will not undergo two connecting operations at a same region, which effectively reduces the possibility that at least some of the layer structures of the tab  322  may experience micro cracks on them due to that the tab  322  undergoes two connecting operations at a same region, which may further decrease the current flowing capability of the tab  322 . 
     The embodiment of the present application further provides a manufacturing method for the secondary battery  30 , the method includes steps of: 
     providing an electrode assembly  32 , the electrode assembly  32  including a main body portion  321  and a tab  322  extending out from the main body portion  321 ; 
     providing a current collecting member  43 , the current collecting member  43  including a guiding section  432 , and the guiding section  432  extending in a direction perpendicular to a length direction X of the electrode assembly  32 ; 
     providing a transition connecting piece  50 , the transition connecting piece  50  including a current collecting portion  51  and a fixing portion  52 ; and 
     connecting the current collecting portion  51  with the tab  322  to form a first connection region  100 , and connecting the fixing portion  52  with the guiding section  432  to form a second connection region  200 , wherein respective projections of the first connection region  100  and the second connection region  200  on a plane perpendicular to the length direction X do not overlap. 
     In one embodiment, the current collecting portion  51  is welded to the tab  322  to form the first connection region  100 . Optionally, the tab  322  and the current collecting portion  51  are welded by ultrasonic welding. The fixing portion  52  is welded to the guiding section  432  to form the second connection region  200 . Optionally, the fixing portion  52  and the guiding section  432  are welded by laser welding. 
     In one embodiment, first the current collecting portion  51  and the tab  322  are welded to form the first connection region  100 , and then the fixing portion  52  and the guiding section  432  are welded to form the second connection region  200 . During the connecting process of the tab  322 , the transition connecting piece  50  and the guiding section  432 , the tab  322  and the current collecting portion  51  are placed between an upper clamp and a lower clamp on an ultrasonic welding equipment at the same time, completing the welding operation between the tab  322  and the current collecting portion  51 , and then the transition connecting piece  50  and the guiding section  432  are placed at a laser welding equipment, completing the welding operation of the fixed portion  52  and the guiding section  432 . If the tab  322  is directly welded to the guiding section  432 , a same region of the tab  322  will undergo a ultrasonic welding first and then a laser welding in sequence, in which case structural damage such as micro cracks tends to appear on the tab  322  after the tab  322  undergoes the laser welding. In the present embodiment, since the regions of ultrasonic welding and laser welding do not overlap, the tab  322  is prevented from undergoing two connecting operations of ultrasonic welding and laser welding at a same region, thus reducing the possibility of structural damage such as micro cracks of the tab  322  and ensuring a good current flowing capacity of the tab  322 . 
     In the manufacturing method for the secondary battery  30  according to the embodiment of the present application, through connecting the current collecting portion  51  of the transition connecting piece  50  to the tab  322  of the electrode assembly  32  in advance, and then connecting the fixing portion  52  of the transition connecting piece  50  to the guiding section  432  of the current collecting member  43 , the connections of the tab  322 , the transition connecting piece  50  and the guiding section  432  are realized. Since the two connection positions are respectively located at the current collecting portion  51  and the fixing portion  52 , the tab  322  undergoes only one connecting operation during connection to the current collecting portion  51 , thus preventing a same region of the tab  322  from experiencing two connecting operations during direct connection of the tab  322  with the guiding section  432 , reducing a possibility of structural damage such as micro-crack of a same region of the tab  322  due to experiencing two times of connecting process, and ensuring a good current flowing capability of the tab  322 . 
     Although the present application has been described with reference to the preferred embodiments, various improvements can be made to the present application and the components therein can be replaced with equivalents, without departing from the scope of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any manner. The present application is not limited to the specific embodiments disclosed in the context, but includes all technical solutions falling within the scope of the claims.