Patent Publication Number: US-2023163347-A1

Title: Composite negative electrode structure

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Taiwan Application Serial Number 110143854, filed on Nov. 24, 2021, which is incorporated by reference herein. 
     BACKGROUND 
     Field of Invention 
     The present disclosure relates to a composite negative electrode structure. 
     Description of Related Art 
     With the rapid development of technology, various portable batteries have gradually come out, and people have higher demands for high performance and light weight of portable batteries. As these demands become stronger, lithium-ion batteries have received high attention and widespread use due to their high energy density and rapid charging capabilities. 
     However, during charging, due to reduction of lithium ions and random deposition of lithium ions on the surface of the electrode, when using the lithium metal negative electrode, the interlayer structure of the battery is prone to be propped up, resulting in the expansion of the battery and even the lithium dendrite penetration problem. Therefore, how to change the behavioral pattern of lithium deposition to improve the above-mentioned shortcomings is indeed the focus of research and development in the field. 
     SUMMARY 
     According to some embodiments of the present disclosure, the composite negative electrode structure includes a current collecting layer, a porous layer, a plurality of lithiophilic structures, and a solid-state electrolyte layer. The porous layer is located on a surface of the current collecting layer and includes a plurality of pores. The lithiophilic structures are located on the surface of the current collecting layer and is accommodated in some of the pores. The solid-state electrolyte layer is located on the porous layer. 
     In some embodiments of the present disclosure, the solid-state electrolyte layer is partially embedded in the porous layer. 
     In some embodiments of the present disclosure, the porous layer has a first portion near the current collecting layer and a second part away from the current collecting layer, and the abundance of the lithiophilic structures in the first portion is greater than the abundance of the lithiophilic structures in the second portion. 
     In some embodiments of the present disclosure, the porous layer further has a third portion, the second portion is located between the first portion and the third portion, and the abundance of the lithiophilic structures in the third portion is zero. 
     In some embodiments of the present disclosure, the average particle size of the lithiophilic structures ranges from 0.1 μm to 1 μm. 
     In some embodiments of the present disclosure, the average pore size of the pores ranges from 0.1 μm to 10 μm. 
     In some embodiments of the present disclosure, the porous layer includes a plurality of carbon nanomaterials, the carbon nanomaterials are staggeredly stacked on each other, and the pores are located between the adjacent carbon nanomaterials, in which the carbon nanomaterials comprise carbon nanowires, carbon nanotubes, carbon nanofilament, carbon nanofibers, or combinations thereof. 
     In some embodiments of the present disclosure, the total thickness of the porous layer ranges from 1 μm to 100 μm, and the total thickness of the lithiophilic structures ranges from 0.1 μm to 10 μm. 
     In some embodiments of the present disclosure, the material of the lithiophilic structures may include silver, gold, platinum, aluminum, zinc, magnesium, silicon, tin, nickel, an oxide of any of the foregoing metals, a combination of any of the foregoing metals and metal oxides, or an organic framework material (MOF) of any of the foregoing metals. 
     In some embodiments of the present disclosure, the solid-state electrolyte layer may include a lithium salt, a polymer, and a solid-state electrolyte. The polymer includes polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, or combinations thereof. The solid-state electrolyte includes lithium aluminium titanium phosphate, lithium lanthanum tantalum oxide, lithium lanthanum zirconium oxide, or combinations thereof. 
     In some embodiments of the present disclosure, the lithium aluminium titanium phosphate is Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , the lithium lanthanum tantalum oxide is La 0.57 Li 0.29 TiO 3 , and the lithium lanthanum zirconium oxide is Li 7 La 3 Zr 2 O 12 . 
     According to the aforementioned embodiments of the present disclosure, the composite negative electrode structure of the present disclosure is achieved by complementary relationship between the porous layer and the lithiophilic structures, in which the porous layer can alleviate the volume expansion of the negative electrode during charging, and the lithiophilic structures can enable the lithium ions in the solid-state battery to be reduced at the lithiophilic structures to form lithium metal. The lithium metal formed can then expand and grow outward with the lithiophilic structure as a nucleation point, and its growth can be restricted to the pores of the porous layer, and then deposited in an orderly manner. In this way, the deposition pattern of the lithium metal in the solid-state battery can be changed to promote the orderly deposition of the lithium metal, thus avoiding the massive generation of solid electrolyte interface (SEI) due to the high specific surface area of the porous layer and reducing the irreversible capacity after the first charge and discharge. The composite negative electrode structure of the present disclosure can therefore improve the volume expansion of the solid-state battery and the capacity loss at the first charge and discharge. In addition, the composite negative electrode structure of the present disclosure can also reduce the possibility of the lithium deposition on the electrode surface, and reduce the safety problems caused by lithium dendrite penetration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the disclosure can be more fully understandable by reading the following detailed description of the embodiments, with reference made to the accompanying drawings as follows: 
         FIG.  1    illustrates a schematic cross-sectional view of a composite negative electrode structure according to some embodiments of the present disclosure; 
         FIG.  2    illustrates a schematic cross-sectional view of a solid-state battery according to some embodiments of the present disclosure; and 
         FIG.  3    illustrates the voltage-time relationship for different stacked structures. 
     
    
    
     DETAILED DESCRIPTION 
     Several embodiments of the present disclosure will be disclosed in the following figures. For the sake of clarity, many practical details will be described in the following description. However, it should be understood that these practical details should not be used to limit the present disclosure. That is, in some embodiments of the present disclosure, these practical details are unnecessary, and therefore should not be used to limit the present disclosure. In addition, for the purpose of simplifying the drawings, some well-known structures and elements will be shown in a simple and schematic manner in the drawings. Furthermore, for the convenience of the reader, the size of each element in the drawings is not drawn according to the actual scale. 
     It should be understood that relative terms such as “lower” or “bottom” and “upper” or “top” may be used herein to describe the relationship of one element to another element, as shown in the figures. It should be understood that the relative terms are intended to include different orientations of the device other than those shown in the figures. For example, if a device an accompanying figure is turned over, elements described as being on the “lower” side of other elements will be oriented on the “upper” side of the other elements. Therefore, the exemplary term “lower” may include both “lower” and “upper” orientations, depending on the specific orientation of the drawing. Similarly, if the device in the accompanying figure is turned over, elements described as “below” other elements will be oriented “above” the other elements. Therefore, the exemplary term “below” may include both “above” and “below” orientations. 
     The present disclosure provides a composite negative electrode structure and a solid-state battery including the composite negative electrode structure. With the arrangement of the lithiophilic structures and the porous layer in the composite negative electrode structure, the deposition pattern of lithium metal in the solid-state battery can be effectively changed to promote the orderly deposition of lithium metal, which can not only improve the volume expansion of the solid-state battery, but also suppress the massive generation of solid electrolyte interface and reduces the capacity loss caused by the first charge and discharge. The composite negative electrode structure of the present disclosure can also reduce the possibility of the deposition of the lithium metal on the electrode surface and reduce the formation of lithium dendrites. 
     Referring to  FIG.  1   , a schematic cross-sectional view of a composite negative electrode structure  100  according to some embodiments of the present disclosure is shown. The composite negative electrode structure  100  includes a current collecting layer  110 , a porous layer  120 , lithiophilic structures  124 , and a solid-state electrolyte layer  130 . The porous layer  120  is located on a surface  111  of the current collecting layer  110 , and the surface  111  of the current collecting layer  110  has a plurality of lithiophilic structures  124 , that is, the lithiophilic structures  124  are located on the surface  111  of the current collecting layer  110 . The porous layer  120  has a plurality of pores H, and the lithiophilic structures  124  are located in some of the pores H. 
     In some embodiments, the current collecting layer  110  may be copper foil, stainless steel foil, nickel foil, or other suitable metal alloy foil. 
     In some embodiments, the porous layer  120  includes a plurality of carbon nanomaterials (CNM), and the carbon nanomaterials CNM are staggeredly stacked on top of each other on the surface  111  of the current collecting layer  110  to form a plurality of pores H, that is, the pores H are located between the adjacent carbon nanomaterials CNM. In some embodiments, the carbon nanomaterials CNM include carbon nanowires, carbon nanotubes, carbon nanofilaments, carbon nanofibers, or combinations thereof. In some embodiments, the carbon nanotube materials can be, for example, a single-walled carbon nanotube (SWCNT), a multi-walled carbon nanotube (MWCNT), or combinations thereof. It is worth noting that since the weight of the carbon-containing material is relatively small per unit volume (i.e., less dense), the overall weight of the solid-state battery can be substantially reduced when the porous layer  120  includes the carbon nanomaterials CNM. In some embodiments, the aspect ratio (i.e., length:diameter) of the carbon nanomaterial CNM may be greater than 20 to provide good mechanical strength and to facilitate the stacking of the carbon nanomaterials CNM to form an effective pore space, which further facilitates the accommodation of the lithiophilic structures  124  in the pores H. It should be understood that, in addition to the aforementioned carbon nanomaterials CNM, other carbon nanomaterials CNM with the above-mentioned aspect ratio are also covered by the present disclosure. 
     In some embodiments, the average pore size of the pores H may range from 0.1 μm to 10 μm to facilitate the accommodattion of the lithiophilic structures  124  and to provide sufficient space for the lithium metal to be deposited in the pores H in an orderly manner, thereby improving the problem of volume expansion of the solid-state battery during charging. On the other hand, the design of the above-mentioned pore size range also allows the solid-state electrolyte layer  130  to be more easily embedded in the porous layer  120 , which further increases the overall structural stability of the composite negative electrode structure  100 . In some embodiments, a thickness T 1  of the porous layer  120  may range from 1 μm to 100 μm, or range from 20 μm to 100 μm, to provide sufficient space for the orderly deposition of the lithium metal. 
     In some embodiments, the lithiophilic structures  124  may include silver, gold, platinum, aluminum, zinc, magnesium, silicon, tin, nickel, an oxide of any of the foregoing metals, a combination of any of the foregoing metals and metal oxides, or an organic framework material (MOF) of any of the foregoing metals. By disposing the lithiophilic structures  124  on the surface  111  of the current collector layer  110 , and through the selection of the above materials, the lithium ions generated by the solid-state battery tend to attach to the surface of the lithiophilic structures  124  and to be reduced to lithium metal, and thus the lithium metal is deposited around the lithiophilic structures  124  in an orderly manner. In other words, a lithiophilic structure  124  is equivalent to a nucleation point, allowing the lithium metal to grow and expand outwardly in an orderly manner with the nucleation point as a growth center. In this way, the massive formation of solid electrolyte interface (SEI) can be avoided, and the irreversible capacity of the first charge and discharge can be reduced. In addition, it also reduces the deposition of lithium metal on the electrode surface and the occurrence of lithium dendrite penetration, thus enhancing the safety of solid-state batteries. 
     In some embodiments, the average particle size of the lithiophilic structures  124  may range from 0.1 μm to 1 μm, so that the lithiophilic structures  124  have sufficient specific surface area for the reduction and deposition of lithium metal, thereby improving the efficiency of the cycle, and facilitating the accommodation of the lithiophilic structures  124  in the pores H. On the other hand, the average particle size range of the lithiophilic structures  124  is designed to enhance the dispersibility of the lithiophilic structures  124  in the solution during the process to facilitate the uniform formation of the lithiophilic structures  124  on the surface  111  of the current collecting layer  110 . In some embodiments, the total thickness T 2  of the lithiophilic structures  124  may range from 0.1 μm and 10 μm, so that the lithiophilic structures  124  are uniformly and appropriately distributed over the current collecting layer  110 . In detail, if the total thickness T 2  of the lithiophilic structures  124  is too small, it is not sufficient to induce the lithium metal to be preferentially reduced at the lithiophilic structure  124 ; if the total thickness T 2  of the lithiophilic structures  124  is too large, the porous layer  120  might accommodate less lithium metal, causing the volume of the solid-state battery to expand and the lithiophilic structures  124  located at a lower layer (e.g., closer to the current collecting layer  110 ) thus cannnot be effectively utilized, resulting in a waste of material and an increase in the overall weight of the solid-state battery. 
     The porous layer  120  and the lithiophilic structures  124  are complementary to each other, in which the porous layer  120  can alleviate the volume expansion of the battery during charging, and the lithiophilic structures  124  can allow the lithium ions in the solid-state battery to be reduced at the lithiophilic structure to form lithium metal, and the lithium metal formed can then expand and grow outward with the lithiophilic structure  124  as a nucleation point, and its growth can be restricted to the pores H of the porous layer  120  for orderly manner. In other words, both the porous layer  120  and the lithiophilic structure  124  are indispensable. For example, when the lithiophilic structures  124  are not provided, the lithium metal tends to randomly deposit on the surface  111  of the current collecting layer  110 , and cannot exactly be accommodated in the pores H of the porous layer  120 , and after the solid-state battery has been cycled several times, the lithium metal deposited on the surface  111  of the current collecting layer  110  may even directly prop up the entire porous layer  120 , causing the volume expansion of the solid-state battery. 
     In some embodiments, the lithiophilic structures  124  have a greater abundance closer to the current collecting layer  110  and the lithiophilic structures  124  have a lesser abundance further away from the current collecting layer  110 . In more detail, the porous layer  120  has a first portion  122   a  closer to the current collecting layer  110  and a second portion  122   b  further away from the current collecting layer  110 , and the abundance of the lithiophilic structures  124  in the first portion  122   a  is greater than the abundance of the lithiophilic structures  124  in the second portion  122   b.  In a further embodiment, the lithiophilic structures  124  may be distributed in the porous layer  120  in a “gradual” manner, that is, the abundance of the lithiophilic structures  124  may gradually decrease from the first portion  122   a  to the second portion  122   b  of the porous layer  120 . With the above-mentioned special design of the abundance of the lithiophilic structures  124 , the lithium ions can have the opportunity to contact with the lower layer of the lithiophilic structures  124  to enhance the reduction efficiency of the lithium ions, and the space of the pores H can be better utilized so that the lithium metal formed by reduction can be accommodated in the pores H in an orderly manner. 
     In some embodiments, the porous layer  120  further has a third portion  122   c  that is further away from the current collecting layer  110  than the second portion  122   b,  in which the second portion  122   b  is located between the first portion  122   a  and the third portion  122   c,  and the abundance of the lithiophilic structures  124  in the third portion  122   c  is zero. In other words, the porous layer  120  does not have any lithiophilic structure  124  in the upper layer (e.g., closer to the solid-state electrolyte layer  130 ). Based on the above configuration, the porous layer  120  may provide sufficient pore space for the lithium metal to be accommodated in the pores H in an orderly manner, thereby improving the problem of volume expansion of the solid-state battery during charging. It should be appreciated that, in some embodiments, the distribution profile (e.g., distribution of abundance) of the lithiophilic structures  124  in the porous layer  120  may be determined by performing Dnergy-Dispersive X-ray spectroscopy (EDX) analysis on the porous layer  120 . 
     In some embodiments, the solid-state electrolyte layer  130  may include a lithium salt, a polymer, and a solid-state electrolyte  132  (in which the lithium salt and polymer are not shown in the figure), and the lithium salt, polymer, and solid-state electrolyte  132  are uniformly mixed with each other. Specifically, the lithium salt may include, for example, lithium bis(fluorosulfonyl)imide (LiO 4 NS 2 F 2 , LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF 3 SO 2 ) 2 , LiTFSI), lithium perchlorate (LiClO 4 ), or combinations thereof; the polymer may include, for example, poly(methyl methacrylate), PMMA), polyethylene oxide (poly(ethylene oxide), PEO), polyvinylidene difluoride (polyvinylidene difluoride, PVDF), polyacrylonitrile (PAN), or combinations thereof; and the solid-state electrolyte  132  may include, for example, lithium lanthanum zirconium oxide (Li 7 La 3 Zr 2 O 12 , LLZO), lithium aluminum titanium phosphate (Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , LATP), lithium lanthanum tantalum oxide (La 0.57 Li 0.29 TiO 3 , LLTO), or combinations thereof. 
     In some embodiments, the solid-state electrolyte layer  130  overlaid on the porous layer  120 . In some embodiments, the solid-state electrolyte layer  130  may be partially embedded in the porous layer  120 . In some embodiments, the solid-state electrolyte layer  130  may be partially embedded into the porous layer  120  and extend toward the current collecting layer  110  and contact the surface  111  of the current collecting layer  110 . In some embodiments, the solid-state electrolyte layer  130  substantially encapsulates each of the lithiophilic structures  124  and each of carbon nanomaterials CNM of the porous layer  120 . In this way, the solid-state electrolyte layer  130  may provide complete encapsulation so that the composite negative electrode structure  100  as a whole may have a stronger structural strength as well as stability. In some embodiments, an average particle size of the solid-state electrolyte  132  may range from 0.1 μm to 10 μm to avoid the solid-state electrolyte  132  from entering the porous layer  120 , so that the solid-state electrolyte  132  can cover the porous layer  120 , and the pores H of the porous layer  120  can be used to accommodate more lithium metal, thereby enhancing the utilization of the pores H. In some embodiments, the average particle size of the solid-state electrolyte  132  is larger than the average pore size of the pores H. By selecting the average particle size of the solid-state electrolyte  132 , the solid-state electrolyte  132  is overlaid on the porous layer  120 , thereby the problem of lithium dendrite penetration can be reduced and the risk of short circuit can be reduced. On the other hand, since the solid-state electrolyte layer  130  has high ionic conductivity, it helps improve the overall performance of solid-state batteries and significantly enhance process convenience by integrating the lithium salt, polymer, and solid-state electrolyte  132  into a single layer. 
     Referring to  FIG.  2   , a schematic cross-sectional view of a solid-state battery  300  according to some embodiments of the present disclosure is illustrated. Specifically, when the composite negative electrode structure  100  is integrated into the solid-state battery  300 , an implementation thereof may be as shown in  FIG.  2   . In the embodiment shown in  FIG.  2   , the solid-state battery  300  includes a composite negative electrode structure  100  and a positive electrode  200 , and the positive electrode  200  is disposed on the side of the solid-state electrolyte layer  130  of the composite negative electrode structure  100  facing away from the current collecting layer  110 . In some embodiments, the positive electrode  200  may include a positive electrode material layer  210  and a positive electrode current collector  220 . In some embodiments, the solid-state electrolyte layer  130  and the positive electrode current collector  220  are respectively located on opposite surfaces of the positive electrode material layer  210 , such that the positive electrode material layer  210  is sandwiched between the positive electrode current collector  220  and the composite negative electrode structure  100 . In some embodiments, the positive electrode material layer  210  may include, for example, nickel cobalt manganese (NCM), nickel cobalt manganese aluminum (NCMA), lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), nickel cobalt aluminum (NCA), lithium iron phosphate (LiFePO 4 , LFP), lithium manganese iron phosphate (LMFP) or any combination thereof, and the positive electrode current collector  220  may include, for example, aluminum foil. 
     It should be understood that the connection relationships and effects of the components already described will not be repeated. In the following description, the effect of the present disclosure will be further verified through different stacked structures. 
     Referring to both  FIG.  1    and  FIG.  3   ,  FIG.  3    illustrates a voltage-time relationship of different stacked structures. In  FIG.  3   , the stacked structure  1  is a current collecting layer  110 , the material of which is copper foil; the stacked structure  2  includes a porous layer  120  on top of a current collecting layer  110 , where the material of the current collecting layer  110  is copper foil, the carbon nanomaterials CNM included in the porous layer  120  are carbon nanotubes, and the thickness T 1  of the porous layer  120  is 20 μm to 100 μm; the stacked structure  3  includes lithiophilic structures  124  on a current collecting layer  110 , in which the material of the current collecting layer  110  is copper foil, the material of the lithiophilic structures  124  is an organic framework material containing copper, and the total thickness T 2  of the lithiophilic structures  124  is 0.1 μm to 10 μm. As shown in  FIG.  3   , compared to the stacked structure  1 , the stacked structure  2  and the stacked structure  3  have smoother voltage transitions. It can be seen that either by providing a porous layer  120  on the current collecting layer  110  or by providing lithiophilic structures  124  on the current collecting layer  110 , both contribute to a slower and orderly growth of the lithium metal, allowing for a better controllability of the solid-state batteries. 
     According to the aforementioned embodiments of the present disclosure, the porous layer can accommodate lithium metal and alleviate the problem of volume expansion during charging of solid-state batteries. At the same time, the lithiophilic structures change the deposition pattern of lithium metal in the solid-state battery, which leads to the orderly deposition of lithium metal and prevents the massive generation of solid electrolyte interface due to the high specific surface area of the porous layer. As such, the irreversible capacity of the first charge and discharge is reduced, and the cycle stability and availability are improved. The negative composite structure of the present disclosure also inhibits lithium dentrite penetration and effectively improves battery safety. 
     Although the present disclosure has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure covers modifications and variations of this disclosure provided they fall within the scope of the following claims.