Patent Publication Number: US-9837651-B2

Title: Electric core for thin film battery

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application No. 61/839,873, filed Jun. 27, 2013, which is included in its entirety herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the field of batteries. More particularly, the present invention relates to a bendable, robust electric core for thin film batteries and manufacturing method thereof. 
     2. Description of the Prior Art 
     Lithium-ion secondary batteries or lithium-ion batteries are getting more and more attentions and have been widely used in various kinds of electronic products such as laptops and mobile phones. In secondary batteries, the electron producing and consuming reactions are for the most part reversible, and therefore such a battery can be cycled between a charged and discharged state electrochemically. 
     When the rechargeable battery is charged, ions formed of the cathode material pass from the cathode through the electrolyte to the anode, and when the battery is discharged these ions travel back from the anode through the electrolyte to the cathode. For example, in batteries having a cathode comprising lithium, such as a LiCoO 2  or LiMnO 2  cathode, lithium species originating from the lithium-containing cathode travel from the cathode to the anode and vice versa during the charging and discharging cycles, respectively. 
       FIG. 1  illustrates a conventional structure of a lithium-ion battery. As shown in  FIG. 1 , the lithium-ion battery  1  includes an electrochemical cell comprising an anode active material layer  11  disposed on one side surface of a separator  10 , a cathode active material layer  21  disposed on the other side surface of the separator  10 , an anode current collector  12 , and a cathode current collector  22 . The separator  10  may be made of polymers such as polyimide (PI), polyprolene (PP), polyethylene (PE), polyvinyl chloride (PVC) or polycarbonate (PC) having porous structure to only allow the passage of the lithium ions, while preventing internal shorting between the anode active material layer  11  and the cathode active material layer  21 . To electrically connect the anode current collector  12  and the cathode current collector  22  to an external circuit or device, the lithium-ion battery  1  may further include two outwardly extended tabs  12   a  and  22   a.    
     Typically, the separator  10 , the anode active material layer  11  and the cathode active material layer  21  are wetted with a liquid electrolyte solution or gel electrolyte. The electrochemical cell is typically enclosed in a parallelepipedic metal case  20  such as an aluminum case in a gas-tight manner with a sealant layer  24  securely sealing a gap between the tabs  12   a  and  22   a.    
       FIG. 2  illustrates another form of a lithium-ion battery known in the art. As shown in  FIG. 2 , the lithium-ion battery  3  is integrated with a circuit substrate  30  such as a copper clad laminate (CCL) substrate. The base dielectric of the CCL substrate may include polyimide (PI), polyethylene terephthalate (PET) or glass fiber. The circuit substrate  30  includes a separator portion  30   a  having therein a plurality of through holes or porous structures for the passage of lithium ions. The separator portion  30   a  is sandwiched by a pair of electrodes  41  and  51 . A current collector  42  is disposed directly on a top surface of the electrode  41 . The electrode  41  is sealed by a packaging unit  43 . Likewise, a current collector  52  is disposed directly on a top surface of the electrode  51 . The electrode  51  is sealed by a packaging unit  53 . Both of the current collectors  42  and  52  are typically made of expensive CCL substrates. The use of CCL substrates increases manufacturing cost/complexity and battery weight. 
     Portable electronic devices have been progressively reduced in size and weight and improved in performance. It is therefore required to develop a rechargeable lithium-ion battery or lithium-ion secondary cell having a high energy density and a high output, which is also cost-effective. Further, after being stored or circled for certain numbers, gas may be generated in lithium-ion batteries, especially at high temperature, which will reduce life span of the lithium-ion battery. What is needed, therefore, is to provide a robust electric core for lithium-ion thin film batteries which has desirable life span. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a bendable, robust electric core for lithium-ion thin film batteries, which is cost-effective, and has simple structure, high capacity, desirable life span, and cycle performance. 
     Another object of the present invention is to provide a bendable, robust electric core for lithium-ion thin film batteries, which has improved ability of gas resistance and moisture resistance. 
     According to one embodiment, a laminated electric core for a lithium-ion battery includes a first current collecting substrate, a first electrode active material layer coated on an inner surface of the first current collecting substrate, a second current collecting substrate, a second electrode active material layer coated on an inner surface of the second current collecting substrate, a separator sandwiched between the first electrode active material layer and the second electrode active material layer, an electrolyte retained at least in the separator. 
     An adhesive layer may be provided to tightly bond the first electrode active material layer to the separator. In another embodiment, an adhesive layer may be provided to tightly bond the first/second electrode active material layer to the first/second current collecting substrate. Optionally, the adhesive layer may have a large number of through holes that communicate the first electrode active material layer with the separator. The adhesive layer may create an intimate interfacial contact between adjacent layers and effectively prevent delamination between layers when the battery cell is bent. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the embodiments, and are incorporated in and constitute apart of this specification. The drawings illustrate some of the embodiments and, together with the description, serve to explain their principles. In the drawings: 
         FIG. 1  illustrates a conventional structure of a lithium-ion battery; 
         FIG. 2  illustrates another form of a lithium-ion battery known in the art; 
         FIGS. 3 and 4  schematically illustrate a method for fabricating a bendable, robust electric core for thin film lithium-ion batteries according to one embodiment of the invention; 
         FIGS. 5 and 6  show exemplary structures of the adhesive layer in  FIGS. 3 and 4  in accordance with the invention; 
         FIG. 7  to  FIG. 9  show some other embodiments of the invention; and 
         FIGS. 10 and 11  schematically illustrate a method for fabricating a bendable, robust electric core for thin film lithium-ion batteries according to another embodiment of the invention. 
     
    
    
     It should be noted that all the figures are diagrammatic. Relative dimensions and proportions of parts of the drawings are exaggerated or reduced in size, for the sake of clarity and convenience. The same reference signs are generally used to refer to corresponding or similar features in modified and different embodiments. 
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are given to provide a thorough understanding of the invention. It will, however, be apparent to one skilled in the art that the invention may be practiced without these specific details. Furthermore, some well-known system configurations and process steps are not disclosed in detail, as these should be well-known to those skilled in the art. 
     Likewise, the drawings showing embodiments of the apparatus are semi-diagrammatic and not to scale and some dimensions are exaggerated in the figures for clarity of presentation. Also, where multiple embodiments are disclosed and described as having some features in common, like or similar features will usually be described with like reference numerals for ease of illustration and description thereof. 
     The following sets forth a detailed description of a mode for carrying out the invention. The description is intended to be illustrative of the invention and should not be taken to be limiting. It is understood that present invention may be applicable to both primary batteries and secondary batteries, although some embodiments take the secondary battery as an example. 
       FIG. 3  and  FIG. 4  schematically illustrate a method for fabricating an electric core for thin film lithium-ion batteries according to one embodiment of the invention. 
     As shown in  FIG. 3  and  FIG. 4 , a first substrate  100   a  and a second substrate  100   b  are prepared. According to the embodiment, the first substrate  100   a  comprises a first current collecting substrate  102 , a first electrode active material layer  111  on an inner surface of the first current collecting substrate  102 , and a thin adhesive layer  114  directly coated or sprayed onto the first electrode active material layer  111 . The first electrode active material layer  111  may be formed by using coating, stencil printing, gravure printing, letterpress or screen printing techniques. According to the embodiment, the thin adhesive layer  114  may be coated on the bottom surface  111   a  of the first electrode active material layer  111  and the sidewall of the first electrode active material layer  111 . However, in another embodiment, the thin adhesive layer  114  may be coated only on the bottom surface  111   a  of the first electrode active material layer  111 . The outer surface of the first current collecting substrate  102  may be covered with a covering insulation layer  132  such as polyimide (PI), polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), polycarbonate (PC), polyurethane (PU), or polyethylene terephthalate (PET), but not limited thereto. According to the embodiment, the thin adhesive layer  114  may include, but not limited to, polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyimide (PI), polypropylene (PP), polyethylene (PE), silica gel, acrylic, polymethyl-methacrylate (PMMA), or epoxy materials. 
     According to another embodiment, the thin adhesive layer  114  may be sprayed on the bottom surface  111   a  of the first electrode active material layer  111  and the sidewall of the first electrode active material layer  111 . The thin adhesive layer  114  may be formed in various patterns and may be discontinuous across the bottom surface  111   a  of the first electrode active material layer  111 . For example, the thin adhesive layer  114  may be sprayed into dotted pattern or lattice pattern such that after lamination the adhesive layer becomes thinner and the total resistance of the battery is reduced. 
     According to the embodiment, the first electrode active material layer  111  is then subjected to a curing process at relatively higher temperatures to remove the solvent from the first electrode active material layer  111 . Along the peripheral edges of the first electrode active material layer  111 , a sealant layer  122   a  is provided after curing the first electrode active material layer  111 . The sealant layer  122   a  may be formed on the inner surface of the first current collecting substrate  102  by using any suitable techniques known in the art, for example, screen printing, stencil printed, gravure printed, letterpress or coating. The ingredients of the sealant layer  122   a  permeate through the thin adhesive layer  114  into the porous structure of the first electrode active material layer  111  to thereby form an elastic and robust overlapping interface  123  along the peripheral edges of the first electrode active material layer  111 . According to the embodiment, no space or gap is remained between the sealant layer  122   a  and the peripheral edges of the first electrode active material layer  111  because of the formation of the elastic and robust overlapping interface  123 . According to the embodiment, the elastic and robust overlapping interface  123  prevents cracking of the first electrode active material layer  111  along the peripheral edges even after frequent bending of the electric core. 
     According to the embodiment, the second substrate  100   b  comprises a second current collecting substrate  104 , a second electrode active material layer  113  coated, stencil printed, gravure printed, letterpress or screen printed on an inner surface of the second current collecting substrate  104 , and a separator  112  directly covering a top surface and sidewall of the second electrode active material layer  113 . On the bottom surface of the second current collecting substrate  104 , a covering insulation layer  142  may be provided. The covering insulation layer  142  may comprise polyimide (PI), polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), polycarbonate (PC), polyurethane (PU), or polyethylene terephthalate (PET), but not limited thereto. According to the embodiment, the first electrode active material layer  111 , the thin adhesive layer  114 , the separator  112 , and the second electrode active material layer  113  they all have porous structures to allow passage of the lithium ions or electrolyte. 
     Likewise, along the peripheral edges of the second electrode active material layer  113 , a sealant layer  122   b  is provided after curing the second electrode active material layer  113 . The sealant layer  122   b  may be formed on the inner surface of the second current collecting substrate  104  by using any suitable techniques known in the art, for example, screen printing, stencil printed, gravure printed, letterpress or coating. The ingredients of the sealant layer  122   b  permeate through the separator  112  into the porous structure of the second electrode active material layer  113  to thereby form an elastic and robust overlapping interface  125  along the peripheral edges of the second electrode active material layer  113 . According to the embodiment, no space or gap is remained between the sealant layer  122   a / 122   b  and the peripheral edges of the first/second electrode active material layer  111 / 113  because of the formation of the elastic and robust overlapping interface  123 / 125 . 
     According to the embodiment, the first current collecting substrate  102  may be a positive current collecting substrate, the first electrode active material layer  111  may be a positive electrode active material layer, the second current collecting substrate  104  may be a negative current collecting substrate, and the second electrode active material layer  113  may be a negative electrode active material layer. However, it is understood that the aforesaid polarities may be interchangeable. For example, in another embodiment, the first current collecting substrate  102  may be a negative current collecting substrate, the first electrode active material layer  111  may be a negative electrode active material layer, the second current collecting substrate  104  may be a positive current collecting substrate, and the second electrode active material layer  113  may be a positive electrode active material layer. 
     According to the embodiment, the first electrode active material layer  111  and the second electrode active material layer  113  may be both wetted with a liquid or gel electrolyte solution. According to another embodiment, the first electrode active material layer  111  and the second electrode active material layer  113  may be surrounded by an electrolyte gel or a solid-state electrolyte such as a solid polymer electrolyte. 
     According to the embodiment, the thin adhesive layer  114  is provided to tightly bond the first electrode active material layer  111  to the separator  112 . Optionally, the thin adhesive layer  114  may have a large number of through holes that communicate the first electrode active material layer  111  with the separator  112 . The thin adhesive layer  114  may create an intimate interfacial contact between adjacent layers and effectively prevent delamination between layers when the battery cell is bent. The thin adhesive layer  114  may be coated or sprayed onto the first current collecting substrate  102 . Alternatively, the thin adhesive layer  114  may be formed by using transfer printing or indirect printing techniques. In another embodiment, the adhesive layer  114  may be in a form of a dry film. 
     As shown in  FIG. 4 , the first substrate  100   a  and the second substrate  100   b  may be bonded together by using vacuum laminating under heating and pressing conditions, thereby forming a laminate structure of an electric core  100 . For example, the first substrate  100   a  and the second substrate  100   b  may be bonded together in a heating-type vacuum press apparatus. However, it is understood that, in some cases, a vacuum laminating (without heating) and pressing process may be adequate. In other embodiments, the first substrate  100   a  and the second substrate  100   b  may be bonded together by chemical reactions. The sealant layers  122   a  and  122   b  immerge with one another and bonded together to form a sealant layer  122 . 
     In other embodiments, the sealant layers  122   a  and  122   b  may be bonded together by adhesive to form a sealant layer  122 . Additionally, a packaging layer  124  may be provided to further seal the battery cell  100 . During the heating and pressing process, the insulating coating  206  in the thin adhesive layer  114  melts and thus provides intimate interfacial contact between adjacent layers and effectively prevent delamination or cracking between layers when the battery cell is bent. 
       FIGS. 5 and 6  show two exemplary structures of the thin adhesive layer  114  in accordance with the invention. Generally, the thin adhesive layer  114  may comprise insulating particles and polymeric binder matrix including but not limited to styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), carboxyl methyl cellulose (CMC) or the like. As shown in  FIG. 5 , the thin adhesive layer  114  comprises a plurality of particles  202  dispersed in the binder  210  including but not limited to SBR, PVDF or CMC. At least some of the particles  202  are provided with an insulating coating  206 . The insulating coating  206  may include, but not limited to, polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyimide (PI), polypropylene (PP), polyethylene (PE), silica gel, acrylic, or epoxy materials. According to the embodiment, the particles  202  are non-conductive particles such as metal oxide, glass fiber particles or ceramic particles. For example, the metal oxide may include titanium oxide, silicon oxide, aluminum oxide, or combination thereof. The particles  202  may have irregular shapes and various dimensions. According to the embodiment, the thin adhesive layer  114  may be coated or sprayed onto the irregular surface of the separator  112  and some of the particles may extend and be embedded into the separator  112  to thereby form a strong bonding. 
     As shown in  FIG. 6 , the thin adhesive layer  114  may comprise two different kinds of particles  302  and  304  dispersed in the binder  310 . The binder  310  may include but not limited to SBR, PVDF or CMC. The carrier particles  302  may include non-conductive particles such as metal oxide, glass fiber particles or ceramic particles. For example, the metal oxide may include titanium oxide, silicon oxide, aluminum oxide, or combination thereof. The particles  304  may comprise polymeric particles such as PVC, PET, PI, PP, or PE. Alternatively, the two kinds of particles  302  and  304  may be polymeric particles having different physical properties such as melting points or chemical properties such as ability to participate in an addition reaction or condensation reaction. Likewise, the particles  302  and  304  may have irregular shapes and various dimensions. The thin adhesive layer  114  may be coated or sprayed onto the irregular surface of the separator  112  and some of the particles  302 / 304  may be inlaid into the separator  112  to thereby form a strong bonding. 
     Still referring to  FIG. 3 , the first current collecting substrate  102  may be any conductor well known in the art such as an aluminum, nickel, steel foil, carbon foil, graphene, or copper foil. According to the embodiment, the first electrode active material layer  111  may comprise a positive electrode active substance and an adhesive, in which the positive electrode active substance may be any one known in the art for the lithium ion battery. According to the embodiment of the present disclosure, the positive electrode active substance may comprise LiCoO 2 , LiFePO 4 , LiMn 2 O 4 , or any suitable three-component substances known in the art. The adhesive may be any one well known in the art such as PVDF. According to some embodiments of the present disclosure, the positive electrode active material layer may also comprise positive electrode additives. The positive electrode additive may be any one well known in the art and may be selected from conductive agents, for example, at least one of acetylene black, conductive carbon black and conductive graphite. 
     The second current collecting substrate  104  may be any one well known in the art such as aluminum, nickel, steel foil, carbon foil, grapheme, or copper foil. According to the embodiment, the second electrode active material layer  113  may comprise a negative electrode active substance and an adhesive. The negative electrode active substance may be anyone commonly used in lithium ion batteries, such as natural graphite and artificial graphite. The adhesive may be any one well known in the art such as PVDF and polyvinyl alcohol. 
     The first electrode active material layer  111  and the second electrode active material layer  113  may be wetted or surrounded by an electrolyte. For example, the electrolyte may comprise a lithium salt electrolyte and solvent. However, it is understood that, in some cases, solvent-free electrolyte or solid-state electrolyte or gel electrolyte may be used. The lithium salt electrolyte may be at least one selected from lithium hexafluorophosphate (LiPF 6 ), lithium perchlorate (LiClO 4 ), lithium tetrafluoroborate (LiBF 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium halide, lithium aluminum tetrachloride and lithium fluoro-alkyl sulfonate. The solvent may comprise an organic solvent, such as a mixture of chain-like acid esters or cyclic acid esters. The chain-like acid ester may comprise at least one selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC) and other fluorine-containing, sulfur-containing or unsaturated bond-containing chain-like organic esters. 
     The separator  112  is electrically insulated and also has good electrolyte retaining performance. According to some embodiments of the present disclosure, the separator  112  may be any kind of separators used in lithium-ion batteries known in the art, such as polyolefin micro-porous membrane, polyethylene felt, glass fiber felt or ultrafine glass fiber paper. 
       FIG. 7  to  FIG. 9  show some other embodiments of the invention, wherein like numeral numbers designate like layers, regions, and elements. As shown in  FIG. 7 , the thin adhesive layer  114  is directly coated or sprayed onto the sop surface of the separator  112  instead of forming on the first electrode active material layer  111 . As shown in  FIG. 8 , the separator  112  may be in a form of a film or a foil, and is laminated with the first substrate  100   a  and second substrate  100   b . A first adhesive layer  114   a  is coated on the first electrode active material layer  111 . A second adhesive layer  114   b  is coated on the second electrode active material layer  113 . As shown in  FIG. 9 , the second electrode active material layer  113 ′ is made of a metal material. The sealant layer  122  only diffuses into the first electrode active material layer  111 , the separator  112 , and the thin adhesive layer  114 . 
       FIGS. 10 and 11  schematically illustrate an exemplary method for fabricating a bendable, robust electric core for thin film lithium-ion batteries according to another embodiment of the invention, wherein like numeral numbers designate like layers, regions, and elements. As shown in  FIG. 10  and  FIG. 11 , likewise, a first substrate  100   a  and a second substrate  100   b  are prepared. According to the embodiment, the first substrate  100   a  comprises a first current collecting substrate  102  and a thin adhesive layer  114  directly coated or sprayed onto an inner surface of the first current collecting substrate  102 . The outer surface of the first current collecting substrate  102  may be covered with a covering insulation layer  132  such as polyimide (PI), polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), polycarbonate (PC), polyurethane (PU), or polyethylene terephthalate (PET), but not limited thereto. According to the embodiment, the adhesive layer  114 ′ comprises conductive materials including, but not limited to, polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyimide (PI), polypropylene (PP), polyethylene (PE), silica gel, acrylic, polymethylmethacrylate (PMMA), or epoxy materials mixed copper powder, aluminum powder, nickel powder, carbon powder. 
     The second substrate  100   b  comprises a second current collecting substrate  104 , a second electrode active material layer  113  coated or screen printed on an inner surface of the second current collecting substrate  104 , a separator  112  directly covering a top surface and sidewall of the second electrode active material layer  113 , and a first electrode active material layer  111 . On the bottom surface of the second current collecting substrate  104 , a covering insulation layer  142  may be provided. The covering insulation layer  142  may comprise polyimide (PI), polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), polycarbonate (PC), polyurethane (PU), or polyethylene terephthalate (PET), but not limited thereto. 
     Along the peripheral edges of the second electrode active material layer  113 , a sealant layer  122  is provided. The sealant layer  122  may be formed on the inner surface of the second current collecting substrate  104  by using any suitable techniques known in the art, for example, screen printing or coating. The ingredients of the sealant layer  122  permeate into the first electrode active material layer  111 , the separator  112 , and the second electrode active material layer  113  to thereby form an elastic and robust overlapping interface along the peripheral edges of the second electrode active material layer  113 . According to the embodiment, no space or gap is remained between the sealant layer  122  and the peripheral edges of the second electrode active material layer  113  because of the formation of the elastic and robust overlapping interface. 
     According to the embodiment, the first current collecting substrate  102  may be a positive current collecting substrate, the first electrode active material layer  111  may be a positive electrode active material layer, the second current collecting substrate  104  may be a negative current collecting substrate, and the second electrode active material layer  113  may be a negative electrode active material layer. However, it is understood that the aforesaid polarities may be interchangeable. For example, in another embodiment, the first current collecting substrate  102  may be a negative current collecting substrate, the first electrode active material layer  111  may be a negative electrode active material layer, the second current collecting substrate  104  may be a positive current collecting substrate, and the second electrode active material layer  113  may be a positive electrode active material layer. 
     According to the embodiment, the first electrode active material layer  111  and the second electrode active material layer  113  may be both wetted with a liquid electrolyte solution. According to another embodiment, the first electrode active material layer  111  and the second electrode active material layer  113  may be surrounded by an electrolyte gel or a solid-state electrolyte such as a solid polymer electrolyte. 
     As shown in  FIG. 11 , the first substrate  100   a  and the second substrate  100   b  may be bonded together by using vacuum laminating under heating and pressing conditions, thereby forming a laminate structure of an electric core  100 ′. For example, the first substrate  100   a  and the second substrate  100   b  may be bonded together in a heating-type vacuum press apparatus. However, it is understood that, in some cases, a vacuum laminating (without heating) and pressing process may be adequate. In other embodiments, the first substrate  100   a  and the second substrate  100   b  may be bonded together by chemical reactions. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.