PATENT DOCUMENT

Publication Number: US-11309540-B1
Application Number: US-202016919151-A
Country: US
Kind Code: B1

Title: Anode structure for a lithium metal battery

Abstract:
An anode for a lithium metal battery includes a host structure configured to be between an anode current collector and a separator, the host structure having void spaces configured to host metallic lithium during charging, wherein the host structure has a void space of ≥60% and ≤80%. Another anode for a lithium metal battery includes a current collector, a separator, and a host structure between the current collector and the separator, the host structure having void spaces configured to host metallic lithium during charging, wherein the host structure is formed of fibers.

Claims:
What is claimed is: 
     
       1. An anode for a lithium metal battery, comprising:
 a host structure configured to be between an anode current collector and a separator, the host structure having void spaces configured to host metallic lithium during charging, wherein the host structure has a void space of ≥60% and ≤80%, wherein the host structure is a layer of material having columnar voids created through a thickness of the layer, each columnar void having a diameter of between 0.5 μm and 5 μm, inclusive. 
 
     
     
       2. The anode of  claim 1 , further comprising:
 a coating of seed material on internal surfaces of the void spaces to promote wetting of the metallic lithium. 
 
     
     
       3. The anode of  claim 1 , wherein the material of the host structure is formed of fibers selected from the group consisting of polyvinylidene fluoride, polyacrylonitrile, cellulose, polyvinyl alcohol, glass, aramid fibers, porous polyimide and combinations thereof. 
     
     
       4. The anode of  claim 3 , wherein the fibers have a coating of seed material to promote wetting of the metallic lithium. 
     
     
       5. The anode of  claim 1 , wherein the host structure is formed of a porous foam metal. 
     
     
       6. The anode of  claim 5 , wherein the porous foam metal is nickel or copper. 
     
     
       7. A lithium metal battery comprising the anode of  claim 1 . 
     
     
       8. An anode for a lithium metal battery, comprising:
 a current collector; 
 a separator; and 
 a host structure between the current collector and the separator, the host structure having void spaces configured to host metallic lithium during charging, wherein the host structure is formed of fibers and individual void spaces each have a diameter between 0.5 μm and 5.0 μm, inclusive. 
 
     
     
       9. The anode of  claim 8 , further comprising:
 a seed layer comprising a seed material selected to promote electrochemical plating of metallic lithium onto the seed layer, the seed layer deposited on the current collector on a surface facing the host structure. 
 
     
     
       10. The anode of  claim 9 , further comprising:
 a first adhesion layer bonding the host structure to the seed layer. 
 
     
     
       11. The anode of  claim 9 , further comprising:
 a first adhesion layer bonding the host structure to the seed layer; and 
 a second adhesion layer bonding the host structure to the separator. 
 
     
     
       12. The anode of  claim 11 , wherein the first adhesion layer and the second adhesion layer are a polymer electrolyte. 
     
     
       13. The anode of  claim 10 , further comprising:
 a second adhesion layer bonding the host structure to the separator. 
 
     
     
       14. The anode of  claim 8 , wherein the fibers of the host structure are of a material selected from the group consisting of polyvinylidene fluoride, polyacrylonitrile, cellulose, polyvinyl alcohol, glass, aramid fibers, porous polyimide and combinations thereof. 
     
     
       15. The anode of  claim 8 , wherein the host structure has a total void space of ≥60% and ≤80%. 
     
     
       16. The anode of  claim 8 , further comprising:
 a coating of seed material on internal surfaces of the void spaces to promote wetting of the metallic lithium. 
 
     
     
       17. A lithium metal battery comprising the anode of  claim 8 .

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. application Ser. No. 16/102,863, filed on Aug. 14, 2018, now U.S. Pat. No. 10,741,835, which claims the benefit of U.S. Provisional Application No. 62/547,152, filed on Aug. 18, 2017, the contents of which are hereby incorporated by reference in their entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     This application generally relates to anodes of lithium metal batteries. 
     BACKGROUND 
     Lithium metal batteries have a higher energy density than conventional lithium ion batteries. During battery operation, lithium is continuously deposited and removed. However, as lithium is deposited, the lithium may not deposit and grow uniformly. Rather, the lithium metal can form dendrites. The formation of dendrites results in a non-uniform lithium surface which further results in greater non-uniform lithium deposition. As the dendrites grow from this non-uniform deposition, battery deterioration occurs, for example, as the lithium dendrites reach the other electrode, short circuiting the battery. 
     SUMMARY 
     The disclosed embodiments provide an anode for a lithium metal battery that includes a current collector, a seed layer deposited onto the current collector, the seed layer comprising a seed material selected to promote electrochemical plating of metallic lithium onto the seed layer, a separator, a host structure between the seed layer and the separator, the host structure having void spaces configured to host metallic lithium during charging, a first adhesion layer bonding the host structure to the seed layer, and a second adhesion layer bonding the host structure to the separator. 
     In some embodiments, each of the first adhesion layer and the second adhesion layer is one of a porous PVDF or a polymer electrolyte. 
     In some embodiments, the host structure has a void space of ≥60% and ≤80%. 
     In some embodiments, the host structure is a layer of material having columnar voids created through a thickness of the layer, each columnar void having a diameter of between 0.5 μm and 5 μm, inclusive. 
     In some embodiments, the columnar voids are each the same diameter. 
     In some embodiments, a coating of additional seed material is formed on an internal surface of the columnar voids to promote wetting of the metallic lithium. 
     In some embodiments, the host structure is formed of fibers of a material selected from the group consisting of PVDF, PAN, cellulose, PVA, glass, aramid fibers, porous polyimide and combinations thereof. 
     In some embodiments, the host structure has voids each having a diameter of between 0.5 μm and 5 μm. 
     In some embodiments, a coating of additional seed material is formed on the fibers to promote wetting of the metallic lithium. 
     In some embodiments, the host structure has a thickness that is ≥20 μm and ≤40 μm. 
     In some embodiments, the seed layer is a first layer of one or more of copper, tin, zinc, silicon. 
     In some embodiments, the seed layer comprises a second layer of lithium metal deposited on the first layer. 
     In some embodiments, the seed layer is one or more of Sn, SnO and SnN. 
     In some embodiments, the seed layer is one or a combination of lithium and lithium alloys. 
     In some embodiments, the seed layer has a thickness that is ≥10 nm and ≤200 nm. 
     Also disclosed is an anode for a lithium metal battery having a current collector, a seed layer deposited onto the current collector, the seed layer comprising a material that promotes lithium plating, a separator, a host structure between and bonded to the seed layer and the separator, the host structure having a total void space of ≥60% and ≤80% and individual void spaces having a diameter between 0.5 μm and 5.0 μm, inclusive, and a coating of a lithiophilic material on a surface of the host structure defining the individual void spaces. 
     Also disclosed is an anode for a lithium metal battery including a host structure configured to be between an anode current collector and a separator, the host structure having void spaces configured to host metallic lithium during charging, wherein the host structure has a void space of ≥60% and ≤80%. 
     Also disclosed in an anode for a lithium metal battery including a current collector, a separator, and a host structure between the current collector and the separator, the host structure having void spaces configured to host metallic lithium during charging, wherein the host structure is formed of fibers. 
     Also disclosed is a lithium metal battery comprising a cathode having a cathode current collector, a cathode active material comprising a lithium transition metal oxide, an electrolyte and an anode as disclosed herein. 
     Another aspect of the disclosed embodiments is a battery pack having a plurality of lithium metal batteries. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-section of an exemplary lithium metal anode as described herein. 
         FIG. 2  is a schematic cross-section of another exemplary lithium metal anode as described herein. 
         FIG. 3  is a scanning electron microscope (SEM) image of an exemplary host structure of the lithium metal anodes disclosed herein. 
         FIG. 4  is a scanning electron microscope (SEM) image of another exemplary host structure of the lithium metal anodes disclosed herein. 
         FIG. 5  is a scanning electron microscope (SEM) image of another exemplary host structure of the lithium metal anodes disclosed herein. 
         FIG. 6  is a scanning electron microscope (SEM) image of another exemplary host structure of the lithium metal anodes disclosed herein. 
         FIG. 7  is a scanning electron microscope (SEM) image of another exemplary host structure of the lithium metal anodes disclosed herein. 
         FIGS. 8A and 8B  are scanning electron microscope (SEM) images of other exemplary host structures of the lithium metal anodes disclosed herein. 
         FIG. 9  is a cross-sectional view of an exemplary lithium metal battery. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments of the lithium metal anode and the lithium metal battery disclosed herein provide increased surface area onto which lithium will uniformly deposit during charging. The lithium is deposited along the surface area of the host structure, reducing or eliminating the dendrite formation that typically occurs. The bonding of the host structure to adjacent layers prevents lithium from growing between the host structure and adjacent layers, maintaining a constant anode thickness. The improved surface morphology provides improved lithium distribution, thereby improving battery performance and reducing the potential for short circuiting. 
       FIG. 1  is an embodiment of an anode for a lithium metal battery as disclosed herein. The anode  100  includes a current collector  102 , a seed layer  104  deposited onto the current collector  102 , a separator  106  and a host structure  108  between the seed layer  104  and the separator  106 . A first adhesion layer  110  bonds the host structure  108  to the seed layer  104 , and a second adhesion layer  112  bonds the host structure  108  to the separator  106 . 
     The current collector  102  is a metal such as copper or nickel and can be in sheet or foil form, as non-limiting examples. The current collector  102  has a thickness between approximately 8 μm and 14 μm. 
     The seed layer  104  is a seed material that is deposited onto the current collector  102  using thin film techniques such as electroplating or electrochemical deposition. The term “layer” as used herein includes both a uniform and a non-uniform thin coating or deposition. A non-uniform coating or deposition will have one or more of holes, craters, voids, bumps, thinner areas, thicker areas and other defects that occur naturally due to one or both the type of application and the morphology of the substrate on which the layer is formed. The seed layer  104  can have a thickness of between 10 nm and about 3 μm. More particularly, the seed layer  104  can have a thickness of between about 10 nm and about 200 nm or between about 10 nm and about 100 nm. 
     The seed material of the seed layer  104  is selected to improve electrochemical plating of metallic lithium during charging of the lithium metal battery. Lithium plates to the seed material of the seed layer  104  better than the lithium plates to the material of the current collector  102 . Seed materials include, but are not limited to, Sn, Zn, Si, Cu, SnO, SnN, ZnO and SiO 2 . The seed material can also be lithium or a lithium alloy such as LiMg or LiAl. The seed material can be pre-alloyed with lithium by heating the materials together at the requisite temperature (e.g. ˜160° C.) until the materials are reacted. Pre-alloying with lithium may prevent an initial loss of capacity when cycling is initiated as the lithium first deposited on a seed layer having no pre-alloyed lithium will be unavailable for further reaction. 
     As illustrated in  FIG. 2 , an anode  200  can have a seed layer  204  that includes a first layer  214  of seed material and a second layer  216  of lithium metal on the seed material of the first layer  214 . Like the pre-alloyed lithium, this lithium metal second layer  216  prevents an initial loss of capacity when cycling is initiated as the lithium first deposited on a seed layer having no pre-alloyed lithium will be unavailable for further reaction. 
     The host structure  108  of the anode  100 ,  200  is configured to host plated metallic lithium on the internal surfaces of the host structure  108  during charging. The host structure  108  is a scaffold-like structure that provides void space in which the deposited lithium can build. The host structure  108  has a void space between ≥60% and ≤80%, inclusive. The host structure  108  is made of a material that is wetted well by the electrolyte material and is a material onto which the lithium will plate. Polar polymers such as polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), cellulose, polyvinyl alcohol (PVA), polyimide, glass and aramid fibers may be used. Porous metals having a pore size between about 0.2 μm to 2.0 μm may also be the material from which the host structure  108  is made. 
       FIGS. 3-8  illustrate different host structures  108  that can be used as the anodes disclosed herein.  FIG. 3  illustrates a host structure  308  that is a layer of material having columnar voids  320  created through a thickness of the layer. Each columnar void  320  has a diameter D of between 0.5 μm and 5 μm, inclusive. The columnar voids  320  can be uniform in both distribution and diameter D as illustrated. The columnar voids  320  can also have a non-uniform distribution. The columnar voids  320  can also vary in diameter D, so long as the diameter D is between 0.5 μm and 5 μm, inclusive. As noted, the total void space in the host structure  308  is between ≥60% and ≤80%. 
     The diameter D of the columnar voids is selected to confine the lithium. Lithium plates with a somewhat characteristic scale. Without any confinement, lithium will typically show “nugget-like” features of ˜1-5 μm in size. The more lithium that plates, the more these small nuggets will branch and create lower density features, such as dendrites. The host structures herein are designed to contain the lithium on the length scale similar to these nuggets, with the lithium remaining dense and confined by the host structure. 
       FIG. 4  illustrates another aspect of the host structure  308  of  FIG. 3 . Host structure  408  is also a layer of material having columnar voids  420  created through a thickness of the layer. Each columnar void  420  has a diameter D of between 0.5 μm and 5 μm, inclusive.  FIGS. 3 and 4  are non-limiting examples of distribution, shape and uniformity of the columnar voids  320 ,  420 . Other distributions, shapes and uniformities are contemplated. 
       FIGS. 5-8  illustrate different host structures that are scaffold structures formed of varying materials that provide the requisite void space. The host structures can be non-uniform, and be of a foam-like material, each host structure having void spaces between 0.5 μm and 5 μm, inclusive, with a total void area of between ≥60% and ≤80%. The host structure  508  shown in the SEM image in  FIG. 5  is made of nickel. The host structure  608  shown in the SEM image in  FIG. 6  is made of copper. The host structure  708  shown in the SEM image in  FIG. 7  is made of porous polyamide. A host structure can be made, for example, by molding wax pellets to define the void spaces of the host structure, adding the host material around the molded wax pellets to form the host structure and melting the wax pellets to create the void space. 
     The host structure  108  can be formed of fibers. The fibers may be conductive, the fibers may be nonconductive, or a portion of the fibers may be conductive. Conductive fibers may be used only near the current collector  102  to encourage penetration of the lithium metal through the host structure  108 . The fibers can be free-standing or formed in a mat, mesh or other fibrous structure, as non-limiting examples, made of the requisite material with the requisite void space. The fibers may be electrospun fibers.  FIG. 8A  is an SEM image of a fiber-based host structure  808 . The fibers in  FIG. 8A  are a mix of PAN and cellulose, with the microfibers providing strength and the nano-fibers providing porosity.  FIG. 8B  is an SEM image of electrospun fibers of PAN as a host structure  808 ′. 
     To further promote lithium plating onto the host structure  108 , the internal surface area of the host structure  108 , the surfaces defining the void spaces, can be coated with a coating. The coating can be seed material that is the same seed material used in the seed layer  104 , a lithium metal layer, or both, as described with respect to the seed layer  204  in  FIG. 2 . Known thin-film techniques can be used to apply the coating. The coating can cover anywhere from a portion to all the internal surface area of the host structure  108 . For example, the portion of the host structure  108  closest to the current collector  102  can be coated, as an extension of the seed layer  104 , to promote the penetration of the lithium through the host structure  108  from the separator  106  to the current collector  102 . The internal surface area is, for example, the internal surfaces  322 ,  422  of the columnar voids  320  of  FIGS. 3 and 4  or the internal voids  522  of  FIG. 5 . The fibers  824  of  FIGS. 8A and 8B  may be coated with the seed material, ensuring that void spaces between fibers are defined by the coated surface. 
     The host structure  108  prevents “breathing” of the lithium metal anode as it charges and discharges. Breathing occurs with conventional lithium metal anodes because as the cell charges and discharges, the amount of lithium in the anode increases and decreases. Therefore, the thickness of the anode increases and decreases. The host structure  108  has a thickness that is ≥20 μm and ≤40 μm. The host structure  108  provides a fixed thickness and the void space  114  of the host structure  108  fills and empties as the battery cycles. The thickness of the anode does not change during charge and discharge. The choice of the thickness of the host structure  108  will depend on the amount of lithium required to meet cell design parameters, including the excess amount of lithium desired and targeted cycle life. 
     In order to prevent breathing, the host structure  108  is bonded to the adjacent layers, such as the separator  106  and the seed layer  104 . The bonding is achieved with the adhesion layers  110 ,  112 . The inventors have found that bonding of the particular materials is best achieved using a porous PVDF, with or without a ceramic particle filler, or a polymer electrolyte. The separator  106  can be polyethylene or polypropylene, as examples. Lithium does not like to plate on the separator material, the separator  106  acting as a lid on the host structure  108  so that the lithium metal plates only within the area of the host structure  108 , thereby preventing short circuiting. The host structure  108  is firmly attached to the separator  106  to avoid lithium plating at the interface. As a non-limiting example, the adhesive layers  110 ,  112  can be applied to the areas to be laminated and heated with pressure (e.g. ˜85° C.). Other methods and adhesives known to those skilled in the art are contemplated herein. The adhesive layers  110 ,  112  can be of the same material or can be different materials. 
     An aspect of the disclosed embodiments is a lithium metal battery  10 , the layers of which are shown in cross-section in  FIG. 9 . The lithium metal battery  10  has an anode  2  as described herein with the current collector  4  representing current collector  102 . The anode layer  6  represents the seed layers  104 ,  204  and host structures  108  as disclosed herein. The lithium metal battery  10  also has a cathode  8  with a cathode current collector  16  and a cathode active material  12  disposed over the cathode current collector  16 . The cathode  8  and the anode  2  are separated by a separator  14  representing separator  106 . 
     The cathode current collector  16  can be, for example, an aluminum sheet or foil. Cathode active materials  12  can include one or more lithium transition metal oxides which can be bonded together using binders and optionally conductive fillers such as carbon black. Lithium transition metal oxides can include, but are not limited to, LiCoO 2 , LiNiO 2 , LiNi 0.8 Co 0.15 Al 0.05 O 2 , LiMnO 2 , Li(Ni 0.5 Mn 0.5 )O 2 , LiNi x Co y Mn z O 2 , Spinel Li 2 Mn 2 O 4 , LiFePO 4  and other polyanion compounds, and other olivine structures including LiMnPO 4 , LiCoPO 4 , LiNi 0.5 Co 05 PO 4 , and LiMn 0.33 Fe 0.33 Co 0.33 PO 4 . 
     In some embodiments, the electrolyte may include a liquid electrolyte, a polymer ionic liquid, a gel electrolyte, or a combination thereof. The electrolyte can be an ionic liquid-based electrolyte mixed with a lithium salt. The ionic liquid may be, for example, at least one selected from N-Propyl-N-methylpyrrolidinium bis(flurosulfonyl)imide, N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. The salt can be or include, for example, a fluorosulfonyl (FSO) group, e.g., lithium bisfluorosulfonylimide (LiN(FSO 2 ) 2 , (LiFSI), LiN(FSO 2 ) 2 , LiN(FSO 2 )(CF 3 SO 2 ), LiN(FSO 2 )(C 2 F 5 SO 2 ). 
     In some embodiments, the electrolyte is or includes a cyclic carbonate (e.g., ethylene carbonate (EC) or propylene carbonate, a cyclic ether such as tetrahydrofuran (THF) or tetrahydropyran (TH), a glyme such as dimethoxyethane (DME) or diethoxyethane, an ether such as diethylether (DEE) or methylbutylether (MBE), their derivatives, and any combinations and mixtures thereof. 
     The foregoing descriptions of various embodiments have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art.

Metadata:
Filing Date: 20200702
Publication Date: 20220419
Grant Date: 20220419
Priority Date: 20170818
Inventors: BROWN, KARL M.
RITCHIE, ALAN A.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01M2004/021", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01M4/366", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01M4/62", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/0445", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M50/461", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/667", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y02E60/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01M4/667", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/382", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M10/052", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01M4/382", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/661", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/661", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/622", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M2004/027", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01M10/0525", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/664", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/134", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01M4/045", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/62", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/045", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M2004/021", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01M4/0445", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/366", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01M4/667", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M10/0525", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M2004/027", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01M4/661", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/382", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 71994190