Patent Publication Number: US-2011059365-A1

Title: Process for manufacture and assembly of battery modules and sections

Description:
FIELD OF THE INVENTION 
     The present invention is directed to an advanced method of manufacturing and assembling battery modules and sections, namely batteries based on Lithium-Ion electrochemical cells and related chemical analogues. In particular, the present invention is directed to a method of assembling components of lithium-ion polymer battery modules and sections. 
     BACKGROUND OF THE INVENTION 
     Lithium ion batteries represent the state-of-the-art in rechargeable battery technology. A rechargeable lithium ion battery contains an electrolyte through which lithium atoms from a source electrode move between electrodes during charge/discharge cycles. Each individual lithium-ion cell is comprised of a conductive polymer membrane in a lithium salt matrix sandwiched between an anode and a cathode. Lithium-ion batteries are often packaged such that multiple cells are connected either in series or parallel depending on the application, which are further arranged into modules. 
     A battery module is comprised of stacking multiple lithium-ion polymer cells together. Each cell is encompassed by a frame. Cooling fins generally made of aluminum or other efficient heat dissipating materials are sandwiched between the stacked cells. Foam spacers are generally used to fill additional spacing to support a uniform module structure. Several assembled modules comprise what is known as a section. Several sections are electrically connected to form a rechargeable energy storage system, such as used by the automotive industry in hybrid vehicles. 
     Despite advances in the field of electrochemical storage, the conventional process for manufacturing such batteries remains complex and expensive, comprising a multiplicity of independently executed steps. In general, an electrochemical cell is constructed by individually cutting a plurality of anodes, cathodes and separators to the required shape and size. Individual anodes are then sandwiched between two separators. The anode-separator assembly is subsequently sandwiched between a pair of cathodes. Finally, a number of cells are stacked upon one another to make a complete battery. In batteries of the type that have a thin film polymer electrolyte and sheet-like anode and cathode layers, it is common that a relatively large number of individual cells form a battery. 
     Each cell is generally sandwiched between separators. The separator is necessarily comprised of a non-conductive polymer, such as polyvinyl chloride or polyvinyl fluoride. The separator provides structural rigidity while also preventing cell contact. Some thin film lithium ion polymeric cells encase the anode and cathode in a polymer providing a homogenous structure. Once the anode, cathode, and separator are combined into a unit, the current collectors are affixed. 
     In fabricating batteries, it is generally necessary to connect an anode to an anode current collector and a cathode to a cathode current collector so that electric energy can be drawn from the battery by an external load. In multi-cell batteries, current collectors are generally connected to each anode and each cathode, and the current connectors connected to each anode are electrically connected together and the current collectors connected to each cathode are electrically connected together. 
     Once the current collectors are in place, the cells are assembled into a frame or casing. The frame or casing is generally comprised of a non-conductive plastic. The frame or casing provides protection for the cells and encases the cells into a cohesive package that can be organized efficiently in larger groups of batteries which are further assembled into modules. 
     As it is evident from the above steps, lithium ion battery manufacturing involves many labor intensive handling operations, each of which incurs substantial investments of time and capital. The conventional manufacturing process described above represents a labor-intensive “pick and place” operation that retards the manufacturing process and thereby accelerates the costs associated therewith. Individual handling of cells is not only tedious; it also fosters improper alignment of the components of the cell assembly, leading to improper cell performance and limited yield of the number of batteries produced per production run. 
     It is therefore desirable to provide an improved method of assembling lithium ion batteries which not only amplifies the number of units produced but also optimizes the arrangement of components in each unit while maintaining unit integrity. 
     SUMMARY OF THE INVENTION 
     The present invention reduces the difficulties and disadvantages of the prior art by providing an improved rechargeable battery and assembly thereof the method including the steps of providing at least one pair of electrically biased sheets to form a plurality of positive and negative electrodes; forming a cell element from three positive electrodes spaced from three negative electrodes in an overlying orientation with a positive and negative lead terminal extending respectively therefrom; separating each of said positive and negative electrodes with a polymer layer; electrically aligning said positive lead terminals and negative lead terminals; applying a heat protectant to the positive lead terminals and the negative lead terminals; shaping said positive and negative lead terminals for connecting to a pair of electrode current collectors, one of said current collectors being associated with said positive lead terminal and the other being associated with said negative lead terminal; and providing a frame for sequentially receiving plural cell elements, whereby said rechargeable battery provides the desired electrical characteristics. The present invention also includes a rechargeable battery addressing the difficulties and disadvantages of the prior art including plural pairs of positive and negative electrodes arranged in an overlying orientation presenting a positive and negative lead terminal, a polymer layer associated with an active biasing material associated with each of said positive and negative electrodes, a heat protectant associated with said positive electrodes and said negative electrodes, a pair of electrode current collectors connected to said lead terminals forming a cell assembly, and a frame having an outer frame member adapted for receiving plural said cell assemblies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an environmental view illustrating a process of assembly of lithium ion batteries. 
         FIG. 2  is a perspective view of a cell according to  FIG. 1 . 
         FIG. 3  is a perspective view of a cell assembly according to  FIG. 1 . 
         FIG. 4  is a sectional view of stacked cell assemblies according to  FIG. 1 . 
         FIG. 5  is a top plan view of the battery module according to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to a lithium-ion cell assembly and method of manufacture thereof. Generally, the present invention relates to a battery pack, a lithium ion battery, for example, and a method of manufacturing such battery pack. 
     Hereinbelow, a preferred embodiment of the present invention will be described with reference to the drawings according to the assembling order. In  FIGS. 1-5 , reference numeral  20  generally references to a cell for a battery made of lithium ion, for example. The cell  20  includes a cell element  24  and is generally covered with a hard laminate material  22  designed to protect the cell  20 . 
     The cell element  24  includes a positive electrode  24   a , a negative electrode  24   b , and is adapted for receiving a polymer and/or a separator  30  disposed between the positive and negative electrodes  24   a , 24   b . The electrodes  24   a , 24   b  are generally positioned in an overlying orientation in relation to each other, wherein the positive electrode  24   a  and the negative electrode  24   a  are electrically connected to lead terminals  34  and  36 , respectively. 
     The positive and negative electrodes  24   a , 24   b  are generally sheets of material with one side having a chemically active material. In the case of the negative electrode  24   b , the active material is negatively biased. In the case of the positive electrode  24   a , the active material is positively biased. 
     The polymer layer  30  is adapted for positioning between the active material on the positive electrode  24   a  sheet and the active material on the negative-electrode  24   b  sheet. The positive electrode and the negative electrode are provided with a positive-electrode terminal  34  and a negative-electrode terminal  36 , respectively, from which a current generated by a potential between the negative  24   b  and positive electrode  24   a  is extracted. 
     The polymer  30  may be used to insulate the overlying positive and negative electrodes  24   a , 24   b  from each other preventing any undesired current leakage. The polymer  30  is generally flexible and suitable for use in the described lithium ion batteries. Alternatively, the polymer  30  may include electrolytes dissolved throughout the polymer for placement between the positive and negative electrodes  24   a , 24   b.    
     The lead terminals  34 , 36  are electrically aligned and prepared for receiving a heat protecting element  40  such as a negative temperature coefficient (NTC) thermistor or metal insulator transition (MIT) thermistor between the lead terminals  34 , 36 . Generally the heat protecting element  40  has high stability, productivity, resistivity, and temperature coefficient which allow it to be used as a temperature sensor. In operation, the heat protecting element  40  decreases resistance as the internal temperature increases, which is dependant, in part, upon the resistance coefficient of the heat protecting element  40 . As the lithium-ion battery generates heat or is exposed to a high-temperature environment due to a change in the external environment, an internal short, other external impacts, the resistance associated with the heat protecting element  40  is lowered. As a result, the lead terminals  34 , 36  are shorted, forcibly discharged the lithium ion battery, and avoiding adverse effects. 
     In a typical configuration, the cell elements  24  may be assembled as a plurality of bi-cells which are produced from a number of sandwiched polymer layers  30  positioned between the positive  24   a  and negative electrodes  24   b . In accordance with one aspect of the present invention, an improved process includes forming three of these bi-cells by selecting three positive electrodes  24   a  and three negative electrodes  24   b , overlying each positive electrode  24   a  with the corresponding negative electrode  24   b  and separating them with the polymer  30 , forming three bi-cells which are referred to collectively as a cell assembly  28 . In this way, an improved method of manufacture is provided by the present invention. 
     The resulting battery may include any number of these cell assemblies  20  to create the desired electrical characteristics based upon the characteristics and dimensions of the utilized electrical material which may depend in-part on the desired use. As used herein, the depicted embodiment is within the automotive industry, although other applications may be utilized as understood by others. 
     As further illustrated in  FIG. 1 , the battery is configured with a number of cell  20  elements which are electrically connected to an anode collector  42  or cathode collector  44  respectively. In addition, the assembly of the bi-cell comprises a number of independent steps including providing a cell assembly, selecting three assemblies, applying foam between the cell assemblies, turning the cell assemblies bending of tabs, turning the cell assemblies for polarizing and applying a thermistor. In addition, at the time of selecting the cell assemblies an OCV test may be used to disregard failed cells. In operation, the steps described may facilitate a high speed assembly process which allows for the assembly of various battery components such as cells, frames and foam spacers into battery modules which may then be assembled into larger sections in comparison to the Honda Fuel Cell stacker system used to created fuel cell stacks. 
     The positive electrode  24   a  includes an active material layer formed on a sheet-like material having an extension associated with lead terminals  34 , 36  and adapted for receipt by the anode and cathode current collector  42 , 44  respectively. 
     In the positive electrode  24   a , the active material may include, a metal oxide, a metal sulfide, or a specific polymer can be used according to the type of the desired battery. The negative active material may include a lithium-containing composite oxide comprised mainly of Li x MO 2 , wherein M represents at least one transition metal, and x generally represents 0.05 to 1.10, which varies depending on the charged state or discharged state of the battery. As the transition metal M constituting the lithium-containing composite oxide, Co, Ni, or Mn is preferred. 
     Specific examples of the lithium ion-containing composite oxides include LiCoO 2 , LiNiO 2 , LiNi y Co 1-y O 2  wherein 0&lt;y&lt;1, and LiMn 2 O 4 . These lithium-containing composite oxides can exhibit high voltage and excellent energy density. Alternatively, as the cathode active material, a metal sulfide or oxide having no lithium, such as TiS 2 , MoS 2 , NbSe 2 , or V 2 O 5 , may be used. In the positive electrode, a plurality of these negative active materials may be used in combination. Further, when the positive electrode is formed using the above-mentioned negative active material, an electrical conductor, a binder, or the like may be added. 
     Generally, the negative electrode  24   b  may include a material capable of being doped with lithium and dedoped. For example, a carbonaceous material, such as a non-graphitizable carbon material or a graphite material, can be used. More specifically, a carbonaceous material, such as pyrolytic carbon, coke (e.g., pitch coke, needle coke, petroleum coke), graphite, glassy carbon, a calcined product of an organic polymer compound (e.g., obtained by carbonization of a phenolic resin, a furan resin, or the like by calcining it at an appropriate temperature), carbon fiber, or activated carbon, can be used. Further, as the material capable of being doped with lithium and dedoped, a polymer, such as polyacetylene or polypyrrole, or an oxide, such as SnO 2 , can be used. When the negative electrode  24   b  is formed from the above material, a binder (not shown) or the like may be added. 
     The polymer  30  material has such a property that it is compatible with the positive and negative electrode  24   a , 24   b  such as a silicone gel, an acrylic gel, an acrylonitrile gel, a polyphosphazene modified polymer, polyethylene oxide, polypropylene oxide, or a composite polymer, crosslinked polymer, or modified polymer thereof, or a fluorine polymer, a polymer material, such as poly(vinylidene fluoride), poly(vinylidene fluoride-co-tetrafluorosafluoropropylene), or poly(vinylidene fluoride-co-trifluoroethylene), or a mixture thereof. 
     The cell assembly  28  may include a casing  46  having an outer protective material such as a laminate to help protect the cell assembly  20 . In addition, plural cell assemblies  20  may be arranged into a battery module  50  having a frame  52  with a pair of outer module members  54  for receiving cell assemblies  20  and an inner module member  56  disposed between the outer module members  54 . The cell assemblies  20  are mounted between the outer  54  and inner module members  56 . The inner module member  56  having a plurality of elongated slots  58  allowing for receipt of the cell assemblies  20 . The inner module  56  members include an electrical network  60  having a negative element  62  and a positive element  64  in which the collectors  42 , 44  of the cell assembly  28  are electrically aligned. The frame  52  and the battery module  50  may provide space for cooling fins generally made of aluminum or other efficient heat dissipating materials to reduce any excess heat from the cell assemblies. In addition, the frame  52  may include a number of aluminum end caps. 
     A plurality of battery modules  50  may be successively joined into a battery section (not shown) while the cell assemblies  20  are mounted in each battery module  50 . When successive battery modules  50  are connected, the outer casing of the neighboring modules provides inner module members  56  to the battery module  50  providing additional structural and operational support. Generally, the frame  52  therefore provides a plurality of grooves (not shown) to the outer module members  54 , which are connected with outer module members  54  of the neighboring battery modules  50  in a stacked fashion (not shown). Also, a plurality of battery modules  50  may be electrically connected with each other to manufacture a high-output, large-capacity battery system (or battery pack). Preferably, the battery system (not shown) may include additional coupling members for coupling plural battery modules  50 . 
     A method for manufacturing, according to the present invention, includes the steps of electrically biasing a sheet  110  with an active material to form plural positive  24   a  and negative electrodes  24   b , forming a cell  20  element by positioning the positive electrode  24   a  and negative electrode  24   b  in an overlying orientation with the positive and negative lead terminals  34 , 36  extending respectively therefrom, providing a polymer layer  30  corresponding to said positive and negative electrodes  24   a , 24   b . Three polarized cells are then selected  112  to form a cell assembly  28 , separating the positive and negative electrodes  24   a , 24   b  being generally separated with the polymer layer  30 . One side of the polymer layer  30  is generally associated with the active material on the positive electrode  24   a  and another side is generally associated with the negative electrode  24   b . The cell assembly  28  is generally electrically aligned with the positive lead terminals  34  and negative lead terminals  36  being rotated. The positive electrode terminal  24   a  associated with said positive lead terminal  34  and negative terminal  24   b  associated with the negative lead terminal  36  are then bent and a heat protectant  40  (thermistor) is applied  116 . The anode and cathode current collectors  42 , 44  are electrically connected to a plurality of positive and negative electrode lead terminals  34 , 36 . The cell assembly  28  is inserted into a frame  52 , forming the rechargeable battery. The frame  52  may be assembled  132  connecting  130  outer members  54  and inner members  56  in a parallel process where the formed frame  52  is configured during the development of the cell assembly  28  for receipt  134  of the cell assembly  28  upon completion of the formed frame. 
     The present invention has been described in an illustrative manner. It is understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described methods, compositions and techniques that fall within the spirit and scope of the invention as set forth in the appended claims.