Abstract:
A lithium metal electrode is disclosed in this invention. The lithium metal electrode includes a lithium metal layer, several gate layers and a current collector layer having several openings. The gate layers are located in the openings. The lithium metal layer is located corresponding to the gate layers and is substantially contacted with the current collector layer. The lithium metal layer is insulated via the gate layers and/or the current collector layer before formation. While the gate layers are alloyed with the lithium ions from the media such as the electrolyte, the alloyed gate layers may provide the ionic access for the lithium metal layer so that the lithium metal layer may feedback the lithium ions back to the chemical system of the electricity supply system. Also, at the same time, the potentials of all the gate layers may be kept equally to the potential of the lithium metal layer.

Description:
[0001]    This application claims the benefit of priority based on Taiwan Patent Applications No. 103124344, filed on Jul. 16, 2014 and No. 104120087, filed on Jun. 23, 2015, the contents of which are incorporated herein by reference in their entirety. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention is related to an anode electrode, in particular to an anode electrode having a conduction loading layer. 
         [0004]    2. Description of Related Art 
         [0005]    Recently, various portable smart devices are presented to the public. In order to improve the performances of the device, a battery having higher energy density, longer cycle life and safety is required so that the secondary lithium battery becomes one of the most popular solutions for it. However, the safety issue of the secondary lithium battery is unsolved for the serious polarization of the electrodes during charging and discharging. The great amount of the lithium dendrites are formed on the anode electrode rapidly because the ionic conductivity and the electrical conductivity of the battery become non-uniform. By the increasing times of charging and discharging, more and more lithium dendrites are formed and finally penetrate through the separator. Once the lithium dendrites penetrate the separator, the internal shortage of the battery occurs because the cathode and anode electrodes are electrically connected. The internal shortage would result in the great amount of heat generated in a short time and an explosion might come after. This issue becomes much more serious for the large-current battery. 
         [0006]    The most common way to solve the problem is to modify the current electrolyte of the battery. For instance, the pure organic electrolyte is exerted for improving the ionic conductivity to overcome the non-uniform ionic conductivity of the electrode. Or, some proper additives can be applied to the liquid-phase electrolyte for forming an oxidation layer, which has good ionic conductivity for the lithium ion, on the surface of the electrode in advance. Via the formation of the oxidation layer, the interface between the electrode and the electrolyte can be more stable and the formation of the lithium dendrite can be constrained. However, the formation of the lithium dendrite might be able to be constrained, but the leakage issue cannot be avoided due to the usage of the liquid-phase electrolyte. 
         [0007]    Accordingly, an anode electrode is disclosed in the present invention to overcome the above problems. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an objective of this invention to provide an anode electrode. A larger surface area for the lithium deposition can be implemented via the pores of the anode electrode. Also, a stable SEI (solid-electrolyte interphase) layer is formed as well as the amount of the formation of the lithium dendrite is reduced on the anode electrode so that the efficiency of the reversible reaction is increased. 
         [0009]    It is an objective of this invention to provide an anode electrode. The electrical conductivity of the anode electrode can be uniformed via applying a metal film covering the conduction loading layer of the anode electrode so that the amount of the formation of the lithium dendrite is reduced. 
         [0010]    It is an objective of this invention to provide an anode electrode. The lithium dendrite is formed close to the lithium metal layer and/or is formed on the lithium metal layer so that the lithium dendrites have no contact with the separator. Hence, it is impossible for the lithium dendrites to penetrate through the separator. Besides, via the lithium dendrite serving as the electrical connection, the electrical connecting surfaces between the porous conductive layer and the lithium metal layer are increased, that is, the electrical resistance between the porous conductive layer and the lithium metal layer is reduced so that the internal resistance of the battery can be reduced. 
         [0011]    The present invention discloses an anode electrode comprising a porous conductive layer and a lithium metal layer. The porous conductive layer includes a current collection layer and a conduction loading layer. The conduction loading layer has several first pores. At least some parts of the first pores are through the conduction loading layer. The current collector layer has several second pores. At least some parts of the second pores are through the current collector layer. The lithium metal layer is disposed adjacent to the either current collection layer or the conduction loading layer. The pores of the porous conductive layer provide more surface area of the anode electrode for lithium deposition so that a stable SEI layer can be formed, the amount of the lithium dendrites can be reduced and the efficiency of the reversible reaction can be increased. 
         [0012]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention will become more fully understood from the detailed description given hereinbelow illustration only, and thus are not limitative of the present invention, and wherein: 
           [0014]      FIG. 1A  illustrates the anode electrode of this present invention. 
           [0015]      FIG. 1B  illustrates the anode electrode further comprising an isolation region of this present invention. 
           [0016]      FIG. 1C  illustrates the anode electrode further comprising another isolation region of this present invention. 
           [0017]      FIG. 1D  illustrates the anode electrode further comprising an ionic conducting layer of this present invention. 
           [0018]      FIG. 1E  illustrates the anode electrode of this present invention. 
           [0019]      FIG. 2A  illustrates the anode electrode of this present invention. 
           [0020]      FIG. 2B  illustrates the anode electrode further comprising an isolation region of this present invention. 
           [0021]      FIG. 2C  illustrates the anode electrode further comprising another isolation region of this present invention. 
           [0022]      FIG. 2D  illustrates the anode electrode further comprising an ionic conducting layer of this present invention. 
           [0023]      FIG. 2E  illustrates the anode electrode of this present invention. 
           [0024]      FIG. 3A  illustrates the anode electrode of this present invention. 
           [0025]      FIG. 3B  illustrates the anode electrode further comprising an isolation region of this present invention. 
           [0026]      FIG. 3C  illustrates the anode electrode further comprising another isolation region of this present invention. 
           [0027]      FIG. 3D  illustrates the anode electrode further comprising an ionic conducting layer of this present invention. 
           [0028]      FIG. 3E  illustrates the anode electrode of this present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    The present invention discloses an anode electrode comprising a porous conductive layer and a lithium metal layer. The porous conductive layer includes a current collection layer and a conduction loading layer. The conduction loading layer has several first pores. At least some parts of the first pores are through the conduction loading layer. The current collector layer has several second pores. At least some parts of the second pores are through the current collector layer. The lithium metal layer is disposed adjacent to the either current collection layer or the conduction loading layer. 
         [0030]    In the present invention, a larger surface area for lithium depositing can be provided due to the pores of the anode electrode. The structure of the SEI layer formed on the surface of the anode electrode is more stable. Even after several times of the electrical-chemical reactions, there are still some un-reacted surfaces for the lithium to deposit so that the structure of the SEI layer can remain stable. Thus, the amount of the formation of the lithium dendrite is reduced and the reversible-reaction efficiency of the anode electrode is increased. Besides, the lithium dendrites are formed within the area between the porous conductive layer and the lithium metal layer. The internal shortage can be avoided because the lithium dendrites are formed close to the lithium metal layer. Meanwhile, the more electrical connecting surfaces between the porous conductive layer and the lithium metal layer are provided via the lithium dendrites, the less internal resistance between the porous conductive layer and the lithium metal layer is. 
         [0031]    Please refer to the  FIGS. 1A to 1E , an anode electrode of the present invention is illustrated. 
         [0032]    As  FIG. 1A  illustrated, the anode electrode  10  comprises a porous conductive layer  12  and a lithium metal layer  14 . The porous conductive layer  12  comprises a current collector layer  122  and a conduction loading layer  121 . In this embodiment, the lithium metal layer  14  is deposited adjacent to the current collector layer  122  of the porous conductive layer  12 , that is, the anode electrode  10  comprises the conduction loading layer  121 , the current collector layer  122  and the lithium metal layer  14  in order. The current collector layer  122  has several second pores H 2  and the conduction loading layer  121  has several first pores H 1 . At least parts of the second pores H 2  and the first pores H 1  are in the form of the through holes and, in this embodiment, all the first pores H 1  and second pores H 2  are through holes. Practically, it is common that only parts of the second pores H 2  penetrate through the current collector layer  122  and only parts of the first pores H 1  penetrate through the conduction loading layer  121 . Although  FIG. 1A  illustrates the corresponding positions of the pores H 2  and H 1 , the openings of the pores H 2  and H 1  are not necessary to substantially corresponding to each other, no matter if the pores H 2  and H 1  are the through holes or not. 
         [0033]    The anode electrode  10  further comprises at least an isolation region  20 , which is deposited on the surface of the porous conductive layer  12  that is away from the lithium metal layer  14 , as illustrated in  FIGS. 1B and 1C . The isolation region  20  illustrated in  FIG. 1B  is in the shape of the layer structure. The isolation region  20  illustrated in  FIG. 1C  is the surface with electrical-isolated treatment for making the isolation region  20  electrically inert. Under the condition of no isolation region  20 , before the lithium ions migrate into the pores H 1  and H 2  of the porous conductive layer  12 , the lithium ions are easy to deposit due to the electroplating on the surface of the porous conductive layer  12  that is away from the lithium metal layer  14  as closing to the over-charging state or over-discharging state. Under the condition of existence of the isolation region  20 , the lithium ions are not able to be deposited on the surface because the surface has been covered via the isolation region  20 . The lithium ions are able to migrate into the porous conductive layer  12  and no more lithium dendrites are formed on the surface of the of the porous conductive layer  12  that is away from the lithium metal layer  14  even as closing to the over-charging state or over-discharging state 
         [0034]    As  FIG. 1D  illustrated, the anode electrode of the present invention further comprises an ionic conducting layer  30 , which is disposed between the porous conductive layer  12  and the lithium metal layer  14 . The ionic conducting layer  30  is in the shape of porous structure, grid structure, rod structure or a combination thereof. Because the ionic conducting layer  30  directly contact with the lithium metal layer  14 , the ionic conducting layer  30  must be chemically inert to the lithium. For instance, the ionic conducting layer  30  has no alloy reaction with the lithium metal layer  14 . The ionic conducting layer  30  not only has the ionic conductivity, but also has the electrical conductivity via exerting specific materials and/or via the specific reactions such as the lithium deposition reaction to form the lithium dendrites. 
         [0035]    In  FIG. 1E , the conduction loading layer  121  and the current collector layer  122  of the porous conductive layer  12  are integrated as a unity. For instance, when the conduction loading layer  121  and the current collector layer  122  are made of the same material, via different process procedures, the second pores H 2  and the first pores H 1  can be produced for the current collector layer  122  and the conduction loading layer  121  individually, wherein the pores H 2  and H 1  are not necessary to be in the corresponding position. 
         [0036]    An anode electrode is illustrated in  FIG. 2A . 
         [0037]    Similar to the abovementioned, the anode electrode  10  comprises the porous conductive layer  12  and the lithium metal layer  14 , wherein the porous conductive layer  12  comprises a current collector layer  122  and a conduction loading layer  121 . However, the lithium metal layer  14  is deposited adjacent to the conduction loading layer  121  of the porous conductive layer  12 , that is, the anode electrode  10  comprises the current collector layer  122 , conduction loading layer  121  and the lithium metal layer  14  in order. 
         [0038]    The isolation region  20  and the ionic conducting layer  30  are respectively illustrated in  FIGS. 2B ,  2 C and  2 D, wherein the isolation region  20  can effectively prevent the lithium dendrite to form on the surface, which is away from the lithium metal layer  14 , of the conduction loading layer  121  as the conduction loading layer  121  is electrical conductive or is made of conductive materials. 
         [0039]    The current collector layer  122  and the conduction loading layer  121  illustrated in  FIG. 2E  are integrated as a unity. Except for having the same materials, the current collector layer  122  and the conduction loading layer  121  may have exactly the same structure or not. However, what is different from the embodiment in  FIG. 1E  is the lithium metal layer  14  of this embodiment is deposited adjacent to the conduction loading layer  121  of the porous conductive layer  12 . 
         [0040]    According to the embodiments above, the surface area of the anode electrode  10  is greatly increased due to the porous conductive layer  12 , especially the conduction loading layer  121  of the porous conductive layer  12 , so that the structure of the SEI layer formed on the anode electrode  10  can be more stable, the amount of the lithium dendrite can be reduced and the reversible-reaction efficiency can be increased. As the conduction loading layer  121  is made of the metal material, the electrical conductivity of the surface of the conduction loading layer  121  is quite uniform so that there is almost no any deviation of the electrical conductivities around the anode electrode  10 . Thus, the amount of the formation of the lithium dendrite can be reduced. Due to the direct contact of current collector layer  122  and the lithium metal layer  14 , the material of current collector layer  122  must be selected from the lithium-unalloyable material such as copper, nickel, iron, gold, zinc, silver, titanium or the combination thereof. As the conduction loading layer  121  and the current collector layer  122  are made of the same material, the material of the conduction loading layer  121  is also inert to the lithium. As illustrated, the second pores H 2  and the first pores H 1  substantially penetrate along the vertical direction through the current collector layer  122  and the conduction loading layer  121  correspondingly. The pores H 2  and H 1  can be produced via the post processing such as mechanical punching, etching and so on. Or, the pores H 2  and H 1  can also be produced via exerting the porous material for the current collector layer  122  and the conduction loading layer  121  to form the pores H 2  and H 1 . The pores H 2  and H 1  are in the shape of through hole, ant hole, blind hole and so on. The lithium metal layer  14  serves as the active material layer of the anode electrode  10 . Practically, the conduction loading layer  121  is a porous metal layer such as meshed metal, grid metal, foamed metal and so on. The ionic conducting layer  30  is made of a material selected from the group consisting of a ceramic material, a polymer material, a liquid-phase electrolyte, a solid-phase electrolyte, a gel-type electrolyte, a liquid ion, a conductive material or a combination thereof, and/or the combinations of the materials mentioned above with the pores of the ionic conducting layer  30 . The combinations of the materials with the pores of the ionic conducting layer  30  further comprise the implements of forming a thin metal film on the metal/metalloid/alloyed conductive material via patterned deposition, sputtering and/or electroplating. The conductive material includes the metal material, alloy material, conductive carbon material, such as the graphite, the graphene, the carbon particles, the carbon tube, the metal particles, and so on. The ceramic material includes the metal oxides, the metal sulfides, and the metal nitrides or acidized metal (ex. metal phosphates) and so on. 
         [0041]      FIGS. 3A and 3B  illustrates the anode electrode further comprising an isolation region of this present invention. 
         [0042]    The anode electrode  10  illustrated in  FIG. 3A  comprises a conduction loading layer  121 , a current collector layer  122  and a lithium metal layer  14 . The current collector layer  122  is deposited between the conduction loading layer  121  and the lithium metal layer  14  and has several second pores H 2 . The conduction loading layer  121  has several first pores H 1 . In the present embodiment, the conduction loading layer  121  is made of a conductive film, which has weaker structure. Thus, the current collector layer  122  can also serves as a carrier base to strengthen the structure of the anode electrode  10  besides collecting current. The conduction loading layer  121  comprises at least a conductive material CM and a non-conductive material nCM, wherein the conductive material CM includes the metal material such as metal particles and/or the non-metal material such as graphite, graphene, carbon particles, carbon tube and so on. 
         [0043]    Another anode electrode is illustrated in  FIG. 3B . 
         [0044]    The anode electrode  10  comprises a current collector layer  122  deposited between a conduction loading layer  121  and a lithium metal layer  14 . The surfaces of the conduction loading layer  121  and the first pores H 1  inside the conduction loading layer  121  are all covered via a metal film  16 . The metal film  16  are formed on the surfaces of the conduction loading layer  121  and the first pores H 1  via the method such as vapor deposition. 
         [0045]    The isolation region  20  and the ionic conducting layer  30  are respectively illustrated in  FIGS. 3C ,  3 D and  3 E. The material of current collector layer  122 , the conduction loading layer  121  and the metal film  16  are selected from the lithium-unalloyable material such as copper, nickel, iron, gold, zinc, silver, titanium or the combination thereof. 
         [0046]    Hence, according the embodiments of the anode electrode above, the porous structure provide larger surface area of the conduction loading layer  121  of the anode electrode  10  so that the more stable SEI layer can be formed, the amount of the lithium dendrites can be reduced and the efficiency of the reversible reaction can be increased. For instance, the surface area of the current collector layer can be increased via the high porosity design. The surface area of the conduction loading layer  121  can be increased via exerting conductive particles having various diameters such as micro-particles and nano-particles. The surfaces of the current collector layer and the conduction loading layer  121  are provided for forming the SEI layer. More precisely, after several times of Faradaic reaction, that is, the electrical-chemical reaction, there are still some un-reacted surfaces for the lithium ions to deposit, in other words, the SEI layers are barely overlapped. The structure of the SEI layer can remain stable due to no structural interference, no ionic conducting interference and no electrical conducting interference so that the SEI layers formed have less structural defects and more uniform electron transfer rate. Thus, the amount of the formation of the lithium dendrite is reduced and the reversible-reaction efficiency of the anode electrode  10  is increased. Comparing to the rough SEI layer, the compact and stable SEI layer has better ionic conductivity and firmed structure. Although few amount of lithium ions are consumed for the Faradaic reaction each time to form the SEI layer on the surface of the conduction loading layer  121 , the efficiency of the reversible reaction can still be increased for the compact and stable SEI layer. 
         [0047]    Besides the imperfect SEI layer, the existence of the deviations of the electrical conductivities of the surface of the conduction loading layer  121  is another reason for the formation of the lithium dendrite. The area of the surface for forming the lithium dendrites of the anode electrode  10  can be increased via applying the porous conduction loading layer  121 . The electrical conductivities of the surface of the conduction loading layer  121  are quite uniform so that the lithium ions are not deposited selectively. As the conduction loading layer  121  is made of material, there exists almost no deviation of the electrical conductivities around the surface of the conduction loading layer  121 . As the conduction loading layer  121  is made of the combination of conductive material and non-conductive material (ex. polymer material), the electrical conductivities of the surface corresponding to the conductive material are much higher than the electrical conductivities of the surface corresponding to the conductive material. Thus, the metal film  16  covered on the surface of the conduction loading layer  121  can modify the electrical conductivities around the surface to effectively avoid that the lithium ions selectively deposits on the certain area. However, even if greater amount of the lithium ions are formed and lead to the formation of lithium dendrites, because the lithium metal layer  14  is deposited adjacent to the porous conductive layer  12  (or further includes the ionic conducting layer  30 ), the lithium ions can only deposit inside the porous conductive layer  12  (and/or the ionic conducting layer  30 ) so that the lithium dendrites only exist adjacent to the lithium metal layer  14 . That is, the lithium dendrites are formed inside the porous conductive layer  12  and/or the ionic conducting layer  30 . The two ends of one lithium dendrite contact with the porous conducive layer and the lithium metal layer  14  respectively. The electrical conductivity of the battery system can be improved and the inner resistance can be reduced due to the conductive lithium dendrite. Comparing to the conventional battery system, the lithium dendrites do not cause any damage to the electrode and/or the separator. 
         [0048]    The amount of the lithium ion provided via the lithium metal layer  14  must not less than the amount of the lithium ion consumed to form the lithium dendrites. Hence, the thickness of the lithium metal layer  14  has a minimum limitation for providing enough amounts of the lithium ions. Besides, before reaching to the lithium metal layer  14 , the lithium ions from the electrolyte for instance could migrate through the first and second pores H 1  and H 2  which are connected to each other. Under this condition, the potentials of the current collector layer  122 , the conduction loading layer  121  are close to the potential of the lithium metal layer  14 . However, the distance in vertical between the first and second pores is further; the overvoltage between the current collector layer  122  and the conduction loading layer  121  is getting more obvious. It is because that, based on the potential of the lithium metal layer  14 , the potentials of the current collector layer  122  and the conduction loading layer  121  shift more seriously. As the longer ionic migration distance, the deposition rate of the lithium ion varies and the efficiency of deposition/dissolving reaction is reduced. Thus, the vertical distance between the first and second pores has its limitation. 
         [0049]    According to the anode electrode disclosed in the present invention, the lithium ions provided via the electrolyte (ex. liquid-phase, solid-phase, gel-type and so on) can form a stable and compact SEI layer on the surface of the anode electrode because the conduction loading layer provides a large surface area for SEI layer formation reaction, a good ionic conductivity and an uniform electrical conductivity. Meanwhile, the surface of the conduction loading layer is modified via the metal material having high electrical conductivity so that the selective deposition of the lithium ions can be reduced. Hence, the safety of the battery system can be greatly improved. 
         [0050]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.