Patent Publication Number: US-2022231320-A1

Title: Cell battery

Description:
FIELD OF THE INVENTION 
     The present invention relates to power supplier systems and, more particularly to batteries which can be used as power supplier, inter alia, for wear electronic devices. The present invention specifically relates to a cell comprising a case designed to form a housing, an assembly of stacked electrodes placed inside the housing and comprising one or more units each comprising a positive electrode, a negative electrode, a separator between the positive and negative electrodes, an electrolyte and holding means for holding the assembly together. 
     BACKGROUND OF THE INVENTION 
     Recent developments on portable and wearable electronic devices are requiring minimized power supplier systems, namely cells which can provide high volumetric energy and power density. The electrode stack is a suitable design that can effectively fulfill the requirements for such type of application. A stacked cell including a stack of positive and negative electrodes is known in the art. A separator is provided between the positive and negative electrodes to prevent short circuit, while allowing sufficient ionic conductivity from one half cell to the other. Such a battery including an assembly of stacked electrodes is disclosed for example in U.S. Pat. No. 3,907,599 B1, in patent publication EP 2610945 A1 or in patent publication EP 3139434 A1. The assembly of stacked electrodes is connected to an external circuitry via contact tabs protruding from the positive and negative electrodes respectively. 
     When designing the cell with these stacked electrodes, the person skilled in the art faces the problem of how to maximize the use of the available volume to optimize the overall power density of the cell and he or she needs to consider, among other aspects, the size and shape of the electrodes, the design of the terminal tabs, the design of the means of contact between the electrodes and the terminal tabs, as well as the design of the electrode packing. All the above considerations must also take into account that the overall manufacturing process of the designed cell has to be kept as simple and as cost-effective as possible. 
     Traditionally, packing tapes are applied around the electrodes stack to hold the single electrodes and separators together. The design of the prior art cells, however, provides for a small contact surface area between the flaps of the packing tape and the edges of the electrodes, thus leading to poor packing tightness and stacking alignment among the electrodes. These factors reduce the quality of the cell performance and require higher precision during the assembly process. The lack of packing tightness and stacking alignment causes a waste of volume within the cell itself, thus limiting its overall energy density. 
     Furthermore, the large empty space left by irregularly folded flaps enables the electrode stack to move against the metal case when external forces are applied. Therefore, the movement of the electrode stack increases the risk of defects and functional failure during transportation and/or use of the cell. 
     There is therefore a need for an alternative cell design enabling to overcome the drawbacks mentioned above. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the present invention relates to a cell comprising a case designed to form a housing, an assembly of stacked electrodes placed inside the housing and comprising one or more units each comprising a positive electrode, a negative electrode, a separator between the positive and negative electrodes, an electrolyte and holding means for holding the assembly together. According to the invention, at least each negative electrode of the one or more units comprises one or more notches, vertically aligned along the height of the assembly so to design a substantially flat contact surface for the holding means. 
     In one embodiment of the present invention, the case is made of metal and comprises a positive side, a negative side and a gasket. 
     In another embodiment of the present invention, the holding means are in form of adhesive tape, adhesive glues, clamps or combinations thereof. 
     In still another embodiment of the present invention, the holding means comprises rubber-based material, acrylic-based material, silicone-based material or combinations thereof. 
     In still another embodiment of the present invention, the cell comprises a packing tape comprising a basis placed between the assembly and the case. 
     In yet another embodiment of the present invention, the holding means comprises at least one packing flap which is integral with the basis. In an embodiment, the basis and the packing flap independently comprise a substrate made of polyesters, polyolefins, polyimides, fluoropolymers, vinyl polymers, styrol polymers, glass fiber based substrates, cellulose based material, derivatives thereof or combinations thereof. 
     In another embodiment of the present invention, the at least one packing flap comprises an adhesive layer facing the assembly. 
     In another embodiment of the present invention, the packing tape is an insulating packing tape to avoid electrical contact between the assembly and the case. 
     In still another embodiment of the present invention, each negative electrode has a larger surface than each positive electrode of the one or more units and only each negative electrode of the one or more units comprises the at least one notch. 
     In another embodiment of the present invention, each positive electrode comprises a cathode tab and each negative electrode comprises an anode tab, the cathode tabs being welded together to form a positive welding joint and the anode tabs being welded together to form a negative welding joint, the positive welding joint being folded substantially vertically towards the positive side of the case and the negative welding joint being folded substantially vertically towards the negative side of the case. 
     In still another embodiment of the present invention, the basis and the packing flap are a single piece. 
     In yet still another embodiment of the present invention, the packing tape comprises at least two packing flaps extending, preferably symmetrically, from either side of the insulator basis. 
     In yet still another embodiment of the present invention, the cell further comprises a contact tab placed between the packing tape and the positive metal case which is adjacent to said insulating packing tape, said contact tab being arranged to lead contact between the positive electrode of the one or more units and the positive side. 
     In a further embodiment of the present invention, the cell is a coin cell. 
     In a further aspect, the present invention relates to an assembly of stacked electrodes comprising one or more units each comprising a positive electrode, a negative electrode and a separator between the positive and the negative electrodes; holding means for holding the assembly together, characterized in that at least each negative electrode of the one or more units comprises one or more notches, vertically aligned along the height of the assembly so to design a substantially flat contact surface for the holding means. 
     In a further aspect, the present invention relates to a method for producing a cell as defined above, comprising the steps of:
         a) stacking together alternatively a positive electrode and a negative electrode by placing a separator in-between them to form an assembly of stacked electrodes;   b) applying holding means to the assembly of stacked electrodes to maintain the stacked electrodes permanently tight and aligned to each other;   c) filling the assembly of stacked electrodes obtained under b) with an electrolyte;   d) placing the assembly of stacked electrodes obtained under c) into the case;   e) assembling the cases.       

     Alternatively, steps c) and d) may be inverted in the method described above, that is the assembly of stacked electrodes is first placed into the case and then filled with an electrolyte. 
     The cell according to the present invention shows increased tightness and alignment of the electrode stack and provides better and more sustainable performance. Due to the presence of at least one notch, the contact surface between the electrodes and the holding means substantially increases and becomes a large flat area. This enables a perfect fit of the holding means and the electrode stack. 
     Furthermore, the cell according to the present invention enables an increased overall tightness of the electrode stack against the case of the cell and, accordingly, it ensures a more reliable performance when external forces are applied. 
     The cell according to the present invention enables to improve the volume utilization of the active electrode material, thus substantially increasing the cell energy density. 
     The assembly process of the cell is also less complex since the tightly aligned electrodes of the assembly do not have freedom to move once placed into the cell case. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The aims, advantages and features of the present invention will appear more clearly in the following detailed description of at least one embodiment of the invention, given solely by way of example, in a non-limiting manner and illustrated by the annexed drawings in which: 
         FIG. 1  illustrates a perspective view of a lithium coin cell of the present invention; 
         FIG. 2  illustrates schematically an exploded view of the lithium coin cell of  FIG. 1 ; 
         FIG. 3  is a perspective view from the negative welding joint of an assembly of stacked electrodes of the coin cell of  FIG. 1 ; 
         FIG. 4  is a perspective view from the positive welding joint of an assembly of stacked electrodes of the coin cell of  FIG. 1 ; 
         FIG. 5  is a detail of a perspective view of an assembly of stacked electrodes of the coin cell of  FIG. 1  with different holding means which can be used alone or in combination. 
         FIG. 6  is a cross section of a plan view of the coin cell of  FIG. 1  viewed from the top. 
         FIG. 7  is a cross section of the coin cell of  FIG. 1  showing the folded positive welding joint. 
         FIG. 8  is a perspective view of a pouch cell of the invention. 
         FIG. 9  is a longitudinal cross section of the pouch cell of  FIG. 8  showing the assembly of stacked electrodes. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1 to 7 , a lithium coin cell  100  comprises a case  119  consisting of two metallic sides, more specifically a lid  101  corresponding to the negative electrode case, and a cup  108 , corresponding to the positive electrode case. When the lid  101  and the cup  108  have been assembled, they form between each other a housing  117 , inside which an assembly of stacked electrodes  113  is placed ( FIG. 6 ). A gasket  107  is sandwiched between the lid  101  and the cup  108 , the lid  101  having been pressed into said gasket  107 . 
     The assembly  113  is made of several units  120  each comprising a negative electrode  104  (anode), electrolyte (not shown), a positive electrode  103  (cathode) and a separator  102  between the negative and positive electrodes  104 , 103 . Each negative electrode  104  comprises an anode tab  115  which is designed to lead contact to the lid  101 . Each positive electrode  103  has a cathode tab  114  which is designed to lead contact to the cup  108 . In an embodiment, all the anode tabs  115  are welded together to form a negative welding joint  112  which electrically connects the negative electrodes  104  to the lid  101  via a first negative electrode  104 ′ and all the cathode tabs  114  are welded together to form a positive welding joint  111  which electrically connects the positive electrodes  103  to the cup  108  via an additional positive contact tab  106 , as explained below. In an embodiment of the present invention, as shown in  FIG. 7 , the positive welding joint  111  is folded substantially vertically towards the positive side  108  of the case  119  and the negative welding joint  112  is folded substantially vertically towards the negative side  101  of the case  119  (not shown). In this way, it is possible to avoid accidental contact of the welding joints  111  and  112  to the wrong poles of the cell  100  during assembly and use, thus preventing the risk of short circuit. Furthermore, the cross section in  FIG. 7  clearly shows that the folding of the welding joints  111  and  112  enables to expand the assembly  113  closely to the gasket  107  thus increasing the energy density of the cell  100 . 
     In one embodiment, as shown for example in  FIG. 6 , the positive and negative welding joints  111 , 112  are positioned on opposite sides of the assembly  113 . Alternatively, the positive and negative welding joints  111 , 112  can be positioned in any other configuration around the edge of the assembly  113 . 
     Lithium metal or lithium contained alloy, graphite-like materials, metal oxide, sulphide, nitride etc. that have low reduction potential can be used as active anode materials. Generally, lithium salt dissolving in no aqueous system is used as electrolyte, gel-like electrolyte is applied in lithium polymer battery and solid electrolyte can be used in solid-state lithium battery. Cathodes are the compounds that can take the lithium ions into the structure along with electrochemical reaction and meanwhile produce energy. Compounds such as sulphur, metal oxide, sulphide, phosphate, silicate etc. can be used as cathode active materials. 
     The staked electrode construction is applied in lithium battery with high power performance. To achieve this goal, cathode and anode materials are coated on metallic foil or mesh, and then stacked together alternatively with the separator  102  placed in-between them. The materials of the separator  102  can be chosen among the polymers with porous structure, such as polyethylene (PE), polypropylene (PP), polyvinylidene fluorides (PVDF), polyethylene terephthalates (PET) or mixtures thereof. Electrolyte is filled into the stacked electrodes. 
     The electrodes  103  and  104  of the assembly  113  are substantially disc-shaped. The positive electrodes  103  are enclosed in bag-like separators  102  and the electrodes  103  and  104  are alternately stacked one upon the other in order to form the substantially cylindrical stack  113  having a certain height or thickness. The assembly  113  comprises a negative electrode  104  at both of end surfaces, a first negative electrode, also numbered  104 ′, being adjacent to the lid  101  and a last negative electrode, also numbered  104 ″, being placed at the other end of the stack. The negative electrodes  104 ,  104 ′ and  104 ″ are both side coated electrodes. In another embodiment, the negative electrodes  104 ′ and  104 ″ are single side coated, wherein the blank metallic sides face the lid  101  and optionally a tape  105 , respectively. In another embodiment, the blank metallic side of the negative electrodes  104 ′ and  104 ″ may comprise a conductive coating with carbon, structured as amorphous, crystalline, or graphene. 
     In one embodiment, the negative electrodes  104  have a total disc surface which is larger than the positive electrodes  103  and each negative electrode  104  comprises four notches  110  symmetrically positioned around its edge. The notches  110  of each negative electrode  104  are vertically aligned along the height of the assembly  113  so to design a substantially flat contact surface  116 , as shown in  FIGS. 2 to 6 . The notches  110  may have different shapes depending on which means are used for holding together the assembly  113 , as will be shown below. In one embodiment, the notches  110  have a substantially squared shape so to design a squared contact surface  116 . 
     As shown in the Figures, the coin cell  100  may further comprise an insulating packing tape  105  comprising an insulator basis  105   a  and, in this shown embodiment, four holding means, in form of packing flaps  105   b , extending symmetrically from either side of the insulator basis  105   a . The packing flaps  105   b  are designed in such a way to fit to the flat contact surface  116  formed by the notches  110  on the edge of the negative electrodes  104 . In other embodiments, the packing flaps  105   b  may comprise any other appropriate number of packing flaps wherein the corresponding flat contact surfaces  116  will be arranged accordingly. In another embodiment, as shown in  FIG. 5 , the holding means may be in form of an adhesive tape  118   b , adhesive glue (not shown), clamps  118   a ,  118   c ,  118   d . The shape of such alternative holding means is designed to fit the flat contact surface  116  of the assembly  113 . The holding means ( 105   b , 118   a , 118   b , 118   c , 118   d ) comprises rubber-based material, acrylic-based material, silicone-based material or combinations thereof. 
     The insulating packing tape  105  should be placed in such a way that the insulator basis  105   a  is between the assembly of stacked electrodes and one of the cases to avoid electrical contact between the assembly of stacked electrodes and said case and the packing flaps  105   b  hold the assembly  113  of stacked electrodes to form a compact electrode pack. More particularly, the insulating packing tape  105  is placed in such a way that the insulator basis  105   a  is between the last negative electrode  104 ″ and the cup  108  in order to avoid the electrical contact between said last negative electrode  104 ″ and the cup  108 . 
     The packing flaps  105   b  are folded along the height or the thickness of the assembly of stacked electrodes and folded back against the first negative electrode  104 ′ to hold and pack said assembly  113  of stacked electrodes tightly, as shown in  FIGS. 3, 4 and 6 . 
     In this embodiment, the insulator basis  105   a  and the packing flaps  105   b  form one piece. In another embodiment, the packing flaps  105   b  may be manufactured separately and then being made integral with or attached to the insulator basis  105   a  by any suitable means known to one skilled in the art. 
     The insulator basis  105   a  and the packing flaps  105   b  comprise a substrate made of a material selected from the group comprising polyesters, polyolefins, polyimides, fluoropolymers, vinyl polymers, and an adhesive layer facing the assembly of stacked electrodes. Said adhesive layer is made of a material selected from the group comprising rubber-based material, acrylic-based material and silicone-based material. In other embodiments, the adhesive layer may be provided only on the packing flaps  205   b  on its side facing the assembly of stacked electrodes. 
     In a preferred embodiment, the insulating packing tape  105  is made of Kapton® which comprises a polyimide substrate and an acrylate adhesive layer. 
     The shape of the insulating packing tape  105  can be designed according to the form of the positive and negative electrodes. Preferably, the insulator basis  105   a  has a larger area than the facing last negative electrode  104 ″ of the assembly of stacked electrodes, in order to minimize a short circuit risk from contacting the last negative electrode  104 ″ and cup  108 . 
     The coin cell  100  further comprises an additional metallic positive contact tab  106  placed between the insulating packing tape  105  and the cup  108 , said additional positive contact tab  106  being arranged to lead contact between the positive electrodes  103  to said cup  108 . Said additional positive contact tab  106  is arranged to be welded with the positive contact tabs  114 . 
     The coin cell  100  of the invention is assembled by a method comprising the steps of:
         a) stacking together alternatively the positive electrodes  103  and the negative electrodes  104 , by placing a separator  102  in-between them to form an assembly of stacked electrodes;   b) holding the assembly of stacked electrodes obtained under   a) with holding means  105   b , 118   a , 118   b , 118   c  and/or  118   d;      c) packing the assembly of stacked electrodes obtained under   b) with said insulating packing tape  105 ;   d) welding the anode tabs  114  together to form the negative welding point  112 , and the cathode tabs  115  with the additional positive contact tab  106  together to form a positive welding point  111 ;   e) optionally folding the welding joint  111  substantially vertically toward the positive side  108  of the case  119  and the negative welding joint  112  substantially vertically towards the negative side  101  of the case  119 .   f) filling assembly of stacked electrodes obtained under c) or d) with electrolyte;   g) placing the assembly of stacked electrodes obtained under e) into the lid  101  and the cup  108 .   h) assembling the lid  101  and the cup  108  by pressing the lid  101  into the gasket  107  to close the coin cell  100 .       

     The sequence of the steps f) and g) of filling the obtained assembly can be operated in either order. 
     Referring to  FIGS. 8 and 9 , a further embodiment of the present invention is described. A cell  200  comprises a case consisting of two parts of non-conductive pouch foil  201 , defining a housing  117 , which parts are sealed together by means of the sealing portion  205 . The housing  117  hosts an electrode assembly  113  as described above. The cathode and anode tabs of the electron assembly  113  are welded together to form a welding of anode tabs  206  and a welding of cathode tabs  207 , respectively. The welding of anode tabs  206  and the welding of cathode tabs  207  are connected to a negative terminal tab  202  and a positive terminal tab  203 , respectively, by means of a melt seal  204  allowing conductivity through the pouch foil  201 . 
     The pouch foil can be a sandwiched structure, wherein both outer layers are polymers and the middle layer is an aluminum foil. The pouch foil can also be a polymeric single or multi-layer structure made, for example, of polyesters, polyolefins, polyimides, fluoropolymers, vinyl polymers, styrol polymers, polyamide (nylon), polyacrylonitrile, poly lactic acid, polystyrene, polyurethane, poly vinyl chloride or mixtures thereof.