Patent Publication Number: US-2023155187-A1

Title: Electrochemical element for a battery and corresponding battery

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Patent Application No. PCT/EP2021/059006 filed Apr. 7, 2021, which claims priority of French Patent Application No. 20 03461 filed Apr. 7, 2020. The entire contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an electrochemical element for a battery, comprising
         a first electrode of a first polarity,   a first terminal of the first polarity,   a second electrode of a second polarity,   a second terminal of the second polarity,   a casing comprising a first wall and a second wall.       

     BACKGROUND 
     Batteries containing electrochemical cells are known. Such a battery is known from U.S. 61/59,253B1. 
     The battery in this paper comprises a steel case, an insulation coating and an electrochemical cell. The electrochemical cell comprises an anode assembly and a cathode assembly. The anode and cathode assemblies are stacked and wound. 
     Another battery is known from EP1742279 which comprises an electrochemical cell having a wound structure. 
     EP1453119 describes an electrochemical cell comprising a casing having an aluminium support layer bonded to a plastic outer protective layer and a thermoplastic inner layer. The materials that make up the casing are adapted to the required flexibility of the battery. 
     SUMMARY 
     The invention aims to provide an electrochemical cell and a corresponding battery that have high reliability and low volume for a given energy storage capacity. 
     The invention differs from known multi-layer pouch-type elements in that the casing does not have a thermoplastic layer on the inside at the welding points, which allows the walls of the casing to be laser-welded. Thus, a good hermetic seal of the electrochemical cell is ensured by a high reliability of the connection. In addition, to ensure continuity of this hermetic seal and insulation at the current outputs (terminals), the cell has suitable output elements. 
     In addition, the battery and the electrochemical cell according to the invention must be economical to manufacture, reliable and have a relatively low weight. 
     For this purpose, the invention relates to an electrochemical cell as indicated above, characterised in that the first wall and the second wall each comprise a base body and an electrically insulating layer, in that
         the base bodies are made of metal, in that   the electrically insulating layer comprises
           either a plastic coating,   or a layer resulting from a surface treatment, in that   
           each of the base bodies comprises a base body edge, in that   the edges of the base bodies are connected by a weld bead to form the casing, and in that   at the location of the weld bead, the base bodies are free of the electrically insulating layer.       

     In particular embodiments of the electrochemical cell, it may comprise one or more of the following optional features:
         the metal base bodies are made of aluminium or an aluminium-based alloy, or steel, preferably stainless steel or nickel-plated,   the base bodies have a thickness of between 80 μm and 500 μm, in particular between 120 μm and 460 μm, and especially between 180 μm and 460 μm   the casing comprises at least one opening for the passage of the first and/or second terminal,   the first and/or second terminal extends through the passage opening,   the electrochemical cell comprises means for electrically insulating the first and/or second terminal from the casing,   the electrical insulation means comprise
           a plastic electrical insulating element extending between the terminal and the casing, and   electrically insulating spacer elements, adapted to separate the terminal from the casing when the plastic material is in a liquid state,   
           the spacer elements comprise microballs of a material having a melting temperature above the melting temperature of the plastic material and the microballs having a diameter between 50 μm and 500 μm, preferably between 100 μm and 200 μ,   the microballs are embedded in the solidified molten plastic of the electrical insulating element,   the first and/or second terminal is a tab and the casing passage opening is formed
           either by two edges of the first and second walls of the casing diverging from each other,   or through an opening in one of the first and second walls of the casing,   
           the second terminal is a button, namely a washer,   the button either passing through only one of the first and second walls of the casing or passing through both the first and second walls of the casing,   the button comprises a circumferential groove, wherein the casing extends into the circumferential groove, and wherein the electrical insulation means comprises an insulation ring,   the second electrode comprises two electrode sheets and wherein either the second terminal is attached between the two electrode sheets or the second terminal is attached to one of the two electrode sheets and the other of the two electrode sheets is attached to one of the two electrode sheets.       

     The invention also relates to a battery, comprising a casing and at least two electrochemical cells, characterised in that the electrochemical cells are each an electrochemical cell as defined above, and in that the electrochemical cells are arranged in the casing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood upon reading the following description, given only as an example, and with reference to the attached drawings, in which: 
         FIG.  1    shows a perspective view of a battery according to a first embodiment of the invention comprising a plurality of electrochemical cells; 
         FIG.  2    shows a larger-scale perspective view and partial cross-section of a portion of the battery of  FIG.  1   , comprising an electrochemical cell according to the invention; 
         FIG.  3    shows a variant of the electrochemical cell of the battery of  FIGS.  1  and  2    in a view similar to that of  FIG.  2   ; 
         FIG.  4    shows a perspective view of a battery according to a second embodiment of the invention comprising a plurality of electrochemical cells; 
         FIG.  5    shows a larger-scale perspective view and partial cross-section of a portion of the battery of  FIG.  4   , comprising an electrochemical cell according to the invention; 
         FIG.  6    shows a variant of the electrochemical cell of the battery of  FIGS.  4  and  5    in a view similar to that of  FIG.  5   ; and 
         FIG.  7    shows, at a larger scale, a detail marked V in  FIG.  2   . 
     
    
    
     DETAILED DESCRIPTION 
     In the following, unless otherwise stated, the terms “insulation”, “insulating” and its derivatives refer to electrical insulation. 
     In the description of the various embodiments, similar elements have the same references. Also, unless otherwise stated, each feature described with reference to one embodiment of the invention or to a variant of an embodiment is applicable in isolation or in any possible technical combination to the other embodiments or variants. 
     The following description contains technical features of the invention. These technical features, although presented in a technical context and possibly in combination with other technical features, may be used individually without the other technical features, provided this is technically possible. 
       FIG.  1    shows a battery according to the invention, designated by the general reference  2 . Battery  2  is an electrochemical battery as commonly used in electric vehicles. However, other areas of application for the battery  2  can be envisaged, such as energy storage, electric mobility, aviation and rail. 
     The battery  2  comprises a housing  4  and at least two electrochemical cells  6 , one of which is shown in solid lines and the other in dashed lines in  FIG.  1   . The battery  2  may of course comprise any number of electrochemical cells  6 . 
     The electrochemical cells  6  are arranged in the housing  4  and are electrically connected to each other, in either a parallel or series electrical connection. 
     The housing  4  is, for example, a rectangular parallelepipedal housing made of metal or thermoplastic material. Alternatively, the housing has a cylindrical shape with a circular cross-section. The housing  4  has walls that are less deformable than the walls of the electrochemical cells (see below). 
       FIG.  2    shows the electrochemical cell  6  in perspective and at a larger scale, with part of the electrochemical cell omitted. 
     The electrochemical cell  6  comprises a first electrode  8  of a first polarity, a second electrode  10  of a second polarity, each having a current collector in the form of a metal strip coated over a portion with an active material, the uncoated portion being connected to a first terminal  12  of the first polarity and a second terminal  14  of the second polarity. 
     The first electrode  8  comprises a current collector formed from a metal strip, in this case substantially rectangular, for example made of aluminium, coated on both sides and on one portion with an active material. For example, in the case of a lithium secondary battery, the active material of the first electrode is a paste containing a metal oxide comprising lithium atoms, such as lithium cobalt dioxide (LiCoO 2 , “LCO”), NMC (LiNi x Mn y  Col 1-x-y  O 2 ), NCA (LiNi x CoyAl 1-x-y O 2 ), SLFP (LiFePO 4 ), LMO (LiMn 2 O 4 ) or similar layered compounds. The first electrode  8  is for example the positive electrode. 
     The second electrode  10  comprises two current collectors  18  formed of metal strips, in this case substantially rectangular, for example copper, coated with an active material on one portion. For example, in the case of a lithium secondary battery, the active material of the second electrode is a paste containing a carbonaceous material capable of inserting lithium atoms, such as graphite or amorphous nanocrystalline silicon, LTO (Li 4 Ti 6 O 12 ) or TNO (TiNb 2 O 7 ). The second electrode  10  is for example the negative electrode. 
     The two metal strips coated with an active material forming the second electrode  10  are arranged on either side of the first electrode  8 . 
     The electrochemical cell  6  comprises a separator  20 , separating the first electrode  8  from the second electrode  10 . In this case, the separator  20  comprises two separator sheets  22  which are arranged on both sides of the first electrode  8  between the first electrode  8  and the second electrode  10 . 
     In the case of a Li-Ion electrochemical cell, the separator  20  is permeable to lithium ions, but electronically insulating. 
     The separator  20  is, for example, made of a polyolefin membrane. 
     The electrochemical cell  6  also comprises an electrolyte  24 , which may be liquid, such as a LiPF 6  lithium salt electrolyte, solid or gel, such as Polyvinylidene Fluoride (PVDF) polymers or a Polyvinylidene Fluoride-Hexafluoropropylene (PVDF-HFP) copolymer. 
     In this case, the second terminal  14  is a tab  26  attached to the two electrode strips  18  in a portion not coated with the active material of the second electrode  10 . For example, the electrode strips  18  of the second electrode  10  are arranged on both sides of the tab  26 . The second terminal  14  is thus, in this embodiment, fixed between the two electrode strips  18 , by laser or ultrasonic welding. 
     The second terminal  14  is for example made of copper or nickel. 
     The electrochemical cell  6  comprises a casing  30  with a first wall  32  and a second wall  34 . The first wall  32  and the second wall  34  are joined at their periphery or are integrally formed along one edge of the casing  30  and joined on the other three sides of their periphery. The first wall  32  and the second wall  34  are for example substantially rectangular in shape. 
     The casing  30  contains the first electrode  8 , the second electrode  10 , the separator  20  and the electrolyte  23 . 
     In the present embodiment, the first electrode  8  is electrically connected to the casing  30 , so that the casing  30  forms the first terminal  12 . To make this connection, an uncoated portion of the first electrode  8  is welded to a part of the casing  30 , to the wall  32  or to the wall  34  by a laser or ultrasonic welding process. 
     The casing  30  comprises or forms a passage opening  36  of the second terminal  14  and the second terminal  14  extends through this passage opening  36 . 
     The electrochemical cell  6  is provided with means  40  for electrically insulating the second terminal  14  from the casing  30  and with means for sealing. These electrical insulation means  40  comprise an electrical insulating element  42  made of plastic extending between the second terminal and the casing and electrically insulating spacer elements  44  adapted to separate the second terminal from the casing when the plastic of the electrical insulating element  42  is in a liquid state. Preferably, the plastic electrical insulating element  42  comprises a portion on the second terminal  14  and a portion on the wall of the casing  30 . During assembly, these two parts are heated to seal the casing. As a result, the sealing means are conflated with the electrical insulating element. 
     Referring to  FIG.  7   , the spacer elements  44  comprise or consist of microballs made of a material having a melting temperature above the melting temperature of the plastic. The microballs have, for example, a diameter between 50 μm and 500 μm, preferably between 100 μm and 200 μm. The microballs are embedded in the molten and solidified plastic of the electrical insulating element  42 . 
     The micro-balls are preferably made of thermoplastic material, for example PET or PPS. 
     The first wall  32  and the second wall  34  each comprise a base body  50  and an electrically insulating layer  52  on their inner side (see  FIG.  7   ). 
     The base bodies  50  are made of metal and can each be formed by a metal sheet. The base bodies  50  may have a thickness of between 80 nm and 500 μm. In particular, this thickness can be between 120 μm and 460 μm, and especially between 180 μm and 460 μm. The base bodies  50  are for example made of aluminium, an aluminium-based alloy, steel, preferably stainless or nickel-plated steel. 
     The electrically insulating layer  52  may comprise or consist of either a plastic coating or a layer resulting from a surface treatment of the base body  50 . The electrically insulating layer  52  may be formed by anodising the base body  50 , and is in particular an aluminium oxide layer formed by anodising the base body  50 . In the case where the electrically insulating layer comprises or consists of a plastic coating, the coating may be either a layer of a polymer deposited in liquid form and then solidified, or a layer of a polymer deposited in powder form by electrostatic deposition. 
     In case the electrically insulating layer  52  is a layer resulting from a surface treatment of the base body  50 , it can be obtained by a ceramic-based surface treatment by plasma spraying. 
     Alternatively, or in addition to the electrically insulating layer  52 , the electrochemical cell assembly consisting of the first electrode  8 , the second electrode  10 , the separator sheets and the electrolyte are embedded in an insulating matrix, for example formed from a thermoplastic casing with a thickness of between 20 μm and 100 μm. 
     The base body  50  of the first wall  32  comprises a base body edge  502  and the base body  50  of the second wall  34  comprises a base body edge  504 . 
     Advantageously, the edges  502 ,  504  of the base bodies  50  are welded together by laser welding to form the casing  30 . Thus, the edges of the base bodies  50  are joined by a weld bead  56  to form the casing  30 . At the location of the weld bead  56 , the base bodies  50  are free of the electrically insulating layer. The mechanical connection between the base bodies  50  is therefore achieved by the material solidarity of the walls, i.e. by a metal-to-metal connection. 
     The passage opening  36  here is an opening in either the first or second wall of the casing  30 , namely in the second wall  34 . The passage opening  36  is therefore formed entirely by the second wall  34 . 
       FIG.  3    shows a variant of the electrochemical cell  6  of the battery  2  of  FIGS.  1  and  2   . The view in  FIG.  3    is similar to that in  FIG.  2   . In the following, only the differences from the previous embodiment will be described. Similar elements have the same references. 
     The passage opening  36  of the casing  30  is formed by two edges  60  and  62  of the first  32  and second  34  walls of the casing diverging locally. 
     The first wall  32  and second wall  34  are symmetrical about a plane of symmetry extending parallel to the general plane of the first electrode  8 . 
     The edges  60 ,  62  of the first  32  and second  34  walls are connected to each other adjacent to the passage opening  36  on both sides, but are locally spaced apart to form the passage opening  36 . Generally speaking, the edges  60 ,  62  of the first  32  and second  34  walls are connected to each other along their entire length except at the passage opening  36 . 
     This variant is easy to manufacture as it does not require an opening in one of the walls. 
       FIG.  4    shows a perspective view of a battery  2  according to a second embodiment of the invention comprising a plurality of electrochemical cells  6 .  FIG.  5    shows a larger-scale perspective and partial cross-section of an electrochemical cell from the battery in  FIG.  4   . 
     The view in  FIG.  4    is similar to the one in  FIG.  1    and the view in  FIG.  5    is similar to the one in  FIG.  2   . In the following, only the differences from the previous embodiment will be described. Similar elements have the same references. 
     The second terminal  14  is attached to one of the two electrode sheets  18  and the other of the two electrode sheets  18  is attached to one of the two electrode sheets. In other words, the two electrode sheets  18  are attached to each other and the two electrode sheets  18  are on the same side of the second terminal  14 . 
     Also, the second terminal  14  is not a tab, but is a button  26 , in this case a washer. 
     The passage opening  36  is provided in the first wall  32  of the casing  30 . The passage opening  36  is for example circular in shape. 
     The button  26  passes through only one of either the first  32  or second  34  wall of the casing  30  and thus through the passage opening  36 . In this case the button extends through the first wall  32 . 
     In addition, the passage opening  36  extends along a side face of the casing  30 , which is a large face of the casing. 
     After assembly, the button  26  comprises a circumferential groove  64 , and the casing  30  extends into the circumferential groove  64 . More specifically, the first wall  32  extends into the circumferential groove  64 . The button  26  is made of metal, for example, and is obtained by plastic deformation, for example by crimping or by assembling several parts by laser or friction. 
     These electrical insulation means  40  comprise one or more electrical insulating elements circular in shape  66  equipped with an electrical insulating element  42  made of plastic extending between the second terminal  14  and the casing  30  and electrically insulating spacer elements  44  adapted to separate the second terminal from the casing when the plastic of the electrical insulating element  42  is in a liquid state. The electrical insulating element  42  may be of a material as previously described. The spacer elements  44  may be microballs as previously described. 
       FIG.  6    shows a variant of the electrochemical cell  6  of the battery  2  of  FIGS.  4  and  5   . The view in  FIG.  6    is similar to that in  FIG.  5   . In the following, only the differences from the previous embodiment will be described. Similar elements have the same references. 
     The second terminal  14 , in the form of a button  26 , is attached to the two electrode sheets  18 , which are also pressed together at the second terminal  14 . 
     The passage opening  36  is formed in the first wall  32  of the casing  30  and in the second wall  34  of the casing  30 . The second terminal  14  thus extends through both the first  32  and second  34  walls of the casing. 
     In addition, the passage opening  36  in the first wall  32  of the casing  30  and in the second wall  34  of the casing each extend over a side face of the casing  30 . The two passage openings  36  are aligned and face each other. 
     The electrochemical cells according to the invention are easy to manufacture and have a high reliability due to the described components. 
     In particular, the electrical insulation means  44  ensure an electrical insulation distance between the two polarities. In addition, the walls  32 ,  34  represent a good compromise between rigidity and resource expenditure by being relatively rigid, but not very thick. The terminals  14  lead to reliable electrical contact and easy assembly of the battery. 
     Furthermore, the location of the current output terminals in the footprint of the electrochemical cell allows the energy density of the cell to be optimised. 
     The way the walls  32  and  34  are connected by laser welding in particular makes it possible to achieve an electrical connection with low electrical resistance, a high degree of tightness and stability over time, and a good mechanical connection. In this respect, the metal casing according to the invention is an advantageous alternative to the pouch-type casings with a multi-layer structure currently used, which can only be joined by heat welding. 
     In a variant not shown, the portion of the first electrode  8  not coated with active material defines or is connected to the first terminal  12  of the first polarity. In this case, the casing  30 , in particular the first  32  and second  34  walls, do not form the first terminal  12 , but the first terminal is a separate element from the casing  30 . In this case, the first terminal  12  may be a tab or button or other element electrically connected to the first electrode  8  in a manner similar to the second terminal  14  described above. 
     In this case, the casing  30  comprises or forms an additional passage opening of the first terminal  12  and the first terminal  12  extends through this additional passage opening. The additional passage opening may be formed in the same or similar manner to the above passage opening  36 . 
     The interface between the casing  30 , respectively the additional passage opening, and the first terminal  12  is designed in a similar manner to the interface between the casing  30  and the second terminal  14  and may comprise electrical insulation means identical to the electrical insulation means  40 . 
     Generally, the second terminal  14  is attached to one of the two electrode sheets  18  and the other of the two electrode sheets  18  is attached to one of the two electrode sheets. In other words, the two electrode sheets  18  are attached to each other and the two electrode sheets  18  are on the same side of the second terminal  14 . This feature is therefore not limited to the embodiment of  FIGS.  4  and  5   .