Patent Publication Number: US-2021194008-A1

Title: Electrode Configuration with a Protrusion Inhibiting Separator

Description:
CLAIM OF PRIORITY 
     This application claims priority to U.S. Provisional Application Ser. No. 62/678,734 entitled “Battery Having a Protrusion Inhibiting Separator” filed May 31, 2018, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to batteries, and more particularly to layer configurations for batteries. 
     BACKGROUND 
     In batteries, ions transfer between the negative electrode (“anode”) and positive electrode (“cathode”) during charge and discharge cycles. For instance, when discharging, electrons flow from the negative electrode, through an external circuit, to the positive electrode to generate an electrical current in the external circuit. During this process, positive ions, for example lithium ions in a lithium-ion battery, travel within the battery from the negative electrode, through an electrolyte, to the positive electrode. Conversely, when charging, the external circuit supplies current that reverses the flow of electrons from the positive electrode, through the external charging circuit, and back to the negative electrode, while the positive ions move within the battery from the positive electrode through the electrolyte to the negative electrode. 
     A typical lithium-ion (“Li-ion”) battery has a battery separator interposed between the negative electrode and positive electrode. The separator layer includes an electrolyte that conducts lithium ions so as to provide a continuous ionic pathway for lithium ions to be transported between the two electrodes. 
     One of the current limitations in implementation of lithium negative electrode is the inability to cycle lithium at high current densities. As the current density is increased, lithium protrusions, or dendrites, form on the surface of lithium. During the life of the battery, these protrusions can grow through the battery separator and create a contact between the two electrodes, causing a short circuit inside the battery. 
     Separators in conventional batteries are designed to be electronic insulators so that the electrons cannot flow between the electrodes of the battery. The requirement that the separators are electronic insulators, however, limits the materials that can be used in the separators to inhibit formation or growth of lithium protrusions. 
     What is needed therefore is an improved separator that can limit the growth of lithium protrusions and thus increase the current density at which the lithium negative electrode can be operated. 
     SUMMARY 
     In one embodiment, an electrode configuration for a battery comprises a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. The separator includes an electrically conductive protrusion inhibiting layer and a first insulating layer interposed between and electrically insulating the protrusion inhibiting layer from one of the positive and negative electrode. 
     In another embodiment, the protrusion inhibiting layer of the electrode configuration is configured to mechanically inhibit growth of lithium protrusions on the other of the positive and negative electrode. 
     In a further embodiment, the protrusion inhibiting layer comprises one or more of carbon nanotubes, silver nanowires, particles of silver, particles of steel, particles of copper, and particles of lithium. 
     Some embodiments of the electrode configuration include a protrusion inhibiting layer that further comprises a primary lithium ion conducting material that includes at least one material selected from the group consisting of polyethylene oxide, lithium-lanthanum-zirconium-oxide (LLZO), lithium phosphorus oxynitride (LiPON), lithium-aluminum-titanium-phosphate (LATP), Li 2 S—P 2 S 5 , and Li 3 PS 4 . 
     In yet another embodiment, the protrusion inhibiting layer is configured to chemically inhibit growth of lithium protrusions on the other of the positive and negative electrode. 
     In some embodiments, the protrusion inhibiting layer comprises an alloying material that alloys with lithium in the battery so as to inhibit growth of lithium protrusions. The alloying material may, in one particular embodiment, include one or more material selected from the group consisting of aluminum, tin, magnesium, silicon, silver, and gold. 
     The first electronically insulating layer, in one embodiment, includes one or more materials selected from the group consisting of: PEO with conducting salt; gels with the addition of carbonate solvent and conducting salt; ceramic single ion conductors; lithium-lanthanum-zirconium-oxide (LLZO); lithium phosphorus oxynitride (LiPON); lithium-aluminum-titanium-phosphate (LATP); glassy single ion conductors; atomic layer deposition layers of lithium conducting, electronically insulating materials; Al 2 O 3 ; Li 3 P; Si 3 N 4 ; cation exchange polymers; and Nafion. 
     In another embodiment, the first electronically insulating layer has low permeability to counter-ions. 
     In yet another embodiment, the first electronically insulating layer includes a single ion conducting layer. 
     In one embodiment of the electrode configuration, the separator further comprises a second insulating layer that electrically insulates the protrusion inhibiting layer from the other of the positive and negative electrode. 
     In another embodiment, a battery cell includes an electrode configuration comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. The separator comprises an electrically conductive protrusion inhibiting layer and a first insulating layer interposed between one of the positive and negative electrode and electrically separating the protrusion inhibiting layer from the one of the positive and negative electrode. 
     In some embodiments of the battery cell, the protrusion inhibiting layer is configured to mechanically inhibit growth of lithium protrusions on the other of the positive and negative electrode. 
     In a further embodiment of the battery cell, the protrusion inhibiting layer comprises one or more of carbon nanotubes, silver nanowires, particles of silver, particles of steel, particles of copper, and particles of lithium. 
     The protrusion inhibiting layer may further comprise a primary lithium ion conducting material that includes at least one material selected from the group consisting of polyethylene oxide, lithium-lanthanum-zirconium-oxide (LLZO), lithium phosphorus oxynitride (LiPON), lithium-aluminum-titanium-phosphate (LATP), Li 2 S—P 2 S 5 , and Li 3 PS 4 . 
     In yet another embodiment, the protrusion inhibiting layer is configured to chemically inhibit growth of lithium protrusions on the other of the positive and negative electrode. 
     In one embodiment of the battery cell, the protrusion inhibiting layer comprises an alloying material that alloys with lithium in the battery so as to inhibit growth of lithium protrusions. The alloying material, in some embodiments, includes one or more material selected from the group consisting of aluminum, tin, magnesium, silicon, silver, and gold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a battery pack according to the disclosure. 
         FIG. 2  is a schematic view of a battery electrode configuration of the battery pack of  FIG. 1  having a separator layer that includes a lithium protrusion inhibiting layer separated from each of the electrodes by a respective electronically insulating layer. 
         FIG. 3  is a schematic view of a battery cell of the battery pack of  FIG. 1  having a separator layer that includes a lithium protrusion inhibiting layer separated from the positive electrode by an electronically insulating layer. 
         FIG. 4  is a schematic view of a battery cell of the battery pack of  FIG. 1  having a separator layer that includes a lithium protrusion inhibiting layer separated from the negative electrode by an electronically insulating layer. 
         FIG. 5  is a schematic view of a battery cell of the battery pack of  FIG. 1  having a separator layer in which a lithium protrusion inhibiting layer includes a lithium ion conducting layer and a protrusion growth inhibiting constituent that improves the mechanical properties of the lithium protrusion inhibiting layer. 
         FIG. 6  is a schematic view of a battery cell of the battery pack of  FIG. 1  having a separator layer in which a lithium protrusion inhibiting layer includes a lithium ion conducting layer and a protrusion growth inhibiting constituent that chemically reacts with the lithium protrusions. 
     
    
    
     DETAILED DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the embodiments described herein, reference is now made to the drawings and descriptions in the following written specification. No limitation to the scope of the subject matter is intended by the references. This disclosure also includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the described embodiments as would normally occur to one skilled in the art to which this document pertains. 
     The terms “comprising,” “including,” “having,” and the like, as used with respect to embodiments of the disclosure, are synonymous. As used herein, the term “approximately” refers to values that are within ±10% of the reference value. 
     The embodiments of the disclosure discussed below are applicable to any desired battery chemistry. Some examples refer to lithium-ion batteries for illustrative purposes. As used herein, the term “lithium-ion battery” refers to any battery which includes lithium as an active material. In particular, lithium-ion batteries include, without limitation, lithium batteries having liquid electrolytes, solid electrolytes, gel electrolytes, and batteries commonly referred to as lithium-polymer batteries or lithium-ion-polymer batteries. As used herein, the term “gel electrolyte” refers to a polymer infused with a liquid electrolyte. 
     Referring now to  FIG. 1 , a battery pack  100  includes a plurality of battery cells  102  arranged in a pack housing  104 . Each of the battery cells  102  includes a cell housing  106 , from which a positive terminal  108  and a negative terminal  112  are exposed. In a parallel arrangement, the positive terminals  108  may be connected to one another by a current collector  116 , and the negative terminals  112  may be connected to one another by a different current collector  120 . In a series arrangement, the positive terminals  108  may be connected to adjacent negative terminals  112  by a current collector. The current collectors  116 ,  120  are connected to respective positive and negative battery pack terminals  124 ,  128 , which connect to an external circuit  132  that may be powered by the battery pack  100 , or may be configured to charge the battery pack  100 . 
     Each battery cell  102  includes an electrode configuration  200 , illustrated schematically in  FIG. 1 . The electrode configuration  200  includes a positive electrode (“cathode”)  204 , a separator layer  208 , and a negative electrode (“anode”)  212 . In some embodiments, multiple layers of the electrode configuration  200  are stacked on top of one another so as to form an electrode stack. In other embodiments, the electrode configuration  200  is wound around itself in a spiral shape so as to form what is known as a “jelly-roll” or “Swiss-roll” configuration. In the illustrated embodiment, the battery electrode configuration  200  is a solid-state battery configuration. 
     In one embodiment, the positive electrode  204  includes or consists of a composite including: a polymer, liquid, ceramic, or glass, optionally with a conductive Li salt, for example LiPF 6  or LiTFSI (lithium bis(trifluoromethanesulfonyl)imide); an electronically conductive additive such as carbon black; and an active material that reacts reversibly with Li ions, such as for example lithium metal oxide (Li x MO 2 , wherein M is one or more of Ni, Co, Mn, Al, and/or other transition metals). 
     In some embodiments, the negative electrode  212  of the battery includes or consists of a bare current collector, for example copper or lithium metal. In other embodiments, the negative electrode  212  includes or consists of: a composite including a polymer, liquid, ceramic, or glass, optionally with a conductive Li salt, such LiPF 6  or LiTFSI; an electronically conductive additive such as carbon black; and an active material that reacts reversibly with lithium ions, for example graphite, silicon, silicon oxide, a mixture of graphite, silicon, and/or silicon oxide, or other desired materials. 
     The separator layer  208  is interposed between the positive electrode  204  and the negative electrode  212  so as to electronically separate the positive electrode  204  and negative electrode  212  from one another. The separator layer  208  includes at least one electrically insulating and ionically conducting separator component layer  220   a ,  220   b  next to either one or both electrodes  204 ,  212  in a Li-ion battery to allow the use of another separator layer, for instance a protrusion inhibiting layer  224 , that has a non-negligible electronic conductivity, but can limit the growth of lithium protrusions through excellent mechanical, chemical, or ionic transport properties. As used herein, the term “protrusion inhibiting layer” refers to a layer that is configured, adapted, and designed to reduce or eliminate the growth of lithium protrusions through the separator layer. 
     Each of  FIGS. 2-6  illustrates a different configuration of a separator layer  208 ,  208   a ,  208   b ,  208   c ,  208   d . The separator layers  208 ,  208   a ,  208   b ,  208   c ,  208   d  each include at least one electronically insulating layer  220   a ,  220   b  and an electrically conductive protrusion inhibiting layer  224 . 
     In  FIG. 2 , the electronically insulating layers  220   a ,  220   b  are continuous electronically insulating and ionically conducting layers. One of the electronically insulating layers  220   a ,  220   b  is positioned adjacent to each of the positive electrode  204  and negative electrode  212 , respectively. In some embodiments, the two electronically insulating layers  220   a ,  220   b  are formed of the same material, while in other embodiments the two electronically insulating layers  220   a ,  220   b  are formed of different materials. Each of the electronically insulating layers is formed of materials that are chemically compatible with the respective adjacent electrode  204 ,  212 . 
     In the electrode configuration  200   a  of  FIG. 3 , the separator layer  208   a  includes an electronically insulating layer  220   a  on only the positive electrode  204  side of the separator layer  208 . In the embodiment of  FIG. 3 , the protrusion inhibiting layer  224  is chemically compatible with the negative electrode  212  and in contact with the negative electrode  212 . While the electrons can be conducted through the protrusion inhibiting layer  224 , the electronically insulating layer  220   a  prevents conduction to the positive electrode  204  and thus prevents a short-circuit in a Li-ion battery with the electrode configuration  200   a.    
     In the electrode configuration  200   b  of  FIG. 4 , the separator layer  208   b  includes an electronically insulating layer  220   b  only on the negative electrode  212  side of the separator layer  208 . The protrusion inhibiting layer  224  is chemically compatible with the positive electrode  204  and in contact with the positive electrode  204 . While the electrons are able to flow through the protrusion inhibiting layer  224  of the separator layer  208   b , the electronically insulating layer  220   b  prevents conduction to the negative electrode  212  and thus prevents a short-circuit of the electrode configuration  200   b.    
     The electronically insulating layers  220   a ,  220   b  may have various compositions, and may include, for example, ceramic, glass, and/or polymer materials. In some embodiments, the electronically insulating layers  220   a ,  220   b  are continuous homogenous layers, while in other embodiments the electronically insulating layers  220   a ,  220   b  include particles or flakes or a layer containing defects such as pinholes or cracks, provided that the introduced gaps between particles/flakes or defects in the layer are electronically insulating. 
     In some embodiments, the electronically insulating layers  220   a ,  220   b  have a thickness of less than 2 μm, while in other embodiments the electronically insulating layers  220   a ,  220   b  have a thickness of less than 1 μm, and, in still further embodiments, have a thickness of less than 0.5 μm. In the embodiments of the electronically insulating layers  220   a ,  220   b  that include particles, the dimensions of the particles are less than the overall thickness of the electronically insulating layers  220   a ,  220   b.    
     In various embodiments, the electronically insulating layers  220   a ,  220   b  include one or more of the following materials: PEO with conducting salt; gels with the addition of carbonate solvent and conducting salt; ceramic single ion conductors such as LLZO (lithium-lanthanum-zirconium-oxide or lithium-lanthanum-zirconate), LiPON (lithium phosphorus oxynitride), LATP (lithium-aluminum-titanium-phosphate), etc.; glassy single ion conductors; ALD (atomic layer deposition) layers of Li conducting, electronically insulating materials such as Al 2 O 3 , Li 3 P, Si 3 N 4 ; and cation exchange polymers such as Nafion. In some embodiments, the electronically insulating layers may have electrical conductivity of less than 10 −4  S/m. In further embodiments, the electronically insulating layer has electrical conductivity of less than 10 −6  S/m. 
     In some embodiments, the electronically insulating layer(s)  220   a ,  220   b  have low permeability to counter-ions, which are the ions that do not participate in the electrode reactions. As used herein, “low permeability to counter-ions” is defined to mean that the layer has a lower permeability to the counter-ions as compared to the permeability of the ions involved in the electrode reactions. For example, one salt that may be used in a lithium-ion battery is LiPF 6  (lithium hexafluorophosphate). The lithium ions, Li + , react at the electrodes during operation of the battery. The PF 6   −  ions do not react at the electrodes and are therefore considered as the counter-ions. Examples of layers with low permeability to counter-ions are described in U.S. Patent Publication No. 2018/0358598, the entire contents of which are incorporated herein by reference. 
     The use of a low counter-ion permeability layer as the electronically insulating layer(s)  220   a ,  220   b  enables battery  100  to have different counter-ions adjacent to the positive electrode  204  than adjacent to the negative electrode  212 . For example, in one embodiment, LiBF 4  (lithium tetrafluoroborate) is used to provide the counter-ions adjacent to the positive electrode  204 , while LiTFSI (lithium(bis(trifluoromethanesulfonyl) imide) is used to provide the counter-ions near the negative electrode  212 . Using different counter-ions at the positive electrode  204  and negative electrode  212  provides greater voltage stability, reduces production cost, and/or enables greater current densities as compared to batteries that use of a single salt throughout a battery. 
     In embodiments in which a low counter-ion permeability layer that is one or more of the electronically insulating layers  220   a ,  220   b  and which also has low permeability to solvents further enables the battery  100  to have different solvents near the positive electrode  204  than near the negative electrode  212 . For instance, in one embodiment, the solvent polyethylene oxide (or a block copolymer containing polyethylene oxide) is used as an electrolyte in the separator  208 , while acetonitrile is used as the electrolyte in the positive electrode  204 . This combination advantageously enables a higher voltage positive electrode active material, for example NCA, to be used due to the high voltage stability of acetonitrile, increasing energy density, while also allowing a low voltage stable mechanically robust separator  208 . 
     In one particular embodiment, the concentration of salt near the negative electrode  212  is greater than the concentration of salt near the positive electrode  204 . The use of different salt concentrations enables the battery  100  to have greater charging rate capability, and also decreases aging of the battery  100 . The range of concentrations near the negative electrode may be between 10% and 99% by mass, while the range of concentrations near the positive electrode may be between 10% and 99% by mass. 
     Furthermore, in some embodiments, the addition of a low counter-ion permeability layer as the electronically insulating layer(s)  220   a ,  220   b  enables the use of different additives near the negative electrode  212  and near the positive electrode  204 , provided that it is also a low permeability layer for the additives. Such additives may improve interfacial stability between materials in the electrode configuration  200 . For example, vinylene carbonate may be used against the negative electrode  212  in some embodiments. 
     In other embodiments, one or both of the electronically insulating layers  220   a ,  220   b  may include a single ion conducting (SIC) layer. Examples of SIC layers that are used in various embodiments as the electronically insulating layer are described in U.S. Patent Publication No. 2019/0036158, the entire contents of which are incorporated herein by reference. 
     The SIC electronically insulating layer(s)  220   a ,  220   b  may be relatively thin, continuous, single-ion conducting layer deposited on one or both of the electrodes  204 ,  212 . In some embodiments, the SIC electronically insulating layer(s)  220   a ,  220   b  may be formed of Lithium phosphorous oxy-nitride (“LiPON”), which has a low ionic conductivity at room temperature (approximately 10 −6  S/cm), but can be deposited as a thin film to reduce the ionic resistance of the SIC electronically insulating layer(s)  220   a ,  220   b.    
     The SIC electronically insulating layer(s)  220   a ,  220   b  serve to compartmentalize the salt in each electrode  204 ,  212 , thereby reducing counter-ion transport and decreasing salt polarization or concentration differences at high currents. As a result, the charge and discharge rate capability of the battery cell is improved over a conventional battery. 
     Since the electronically insulating layer(s)  220   a ,  220   b  serve to prevent short-circuit of the battery through the separator  208 , a wider variety of materials may be used for the protrusion inhibiting layer  224 . In particular, because the electronically insulating layer(s)  220   a ,  220   b  prevent the battery from short-circuiting, the protrusion inhibiting layer may have non-negligible electronic conductivity due to incorporation of a constituent material that effectively limits the growth of lithium protrusions through the separator  208 . When the material for the protrusion inhibiting layer  224  is not limited by the requirement that it must be electronically insulating, there are numerous options for limiting the growth of lithium protrusions through the separator  208 . For instance, the growth of lithium protrusions may be limited as a result of mechanical robustness of the protrusion inhibiting layer  224 , ability of the protrusion inhibiting layer  224  to chemically terminate lithium protrusions, or the layer  224  may have superior ionic transport compared to the current state-of-the-art. In some embodiments, for example, the protrusion inhibiting layer has an electrical conductivity that is greater than 10 −4  S/m, while in other embodiments the protrusion inhibiting layer  224  has an electrical conductivity that is greater than 0.01 S/m. 
     In some embodiments, the protrusion inhibiting layer  224  consists of a pure material, while in other embodiments, the protrusion inhibiting layer  224  includes or consists of a composite that includes several constituent materials. The protrusion inhibiting layer  224  may include at least one constituent material that inhibits growth of lithium protrusions, but renders the protrusion inhibiting layer  224  electronically conductive and therefore unsuitable for use as a separator in a conventional battery cell structure. 
       FIG. 5  illustrates an embodiment in which the protrusion inhibiting layer  224   a  of the separator  208   c  is formed from a primary lithium ion conducting material  236   a  and at least one lithium protrusion growth inhibiting constituent  240   a . In some embodiments, the lithium ion conducting material  236   a  includes or consists of a solid lithium ion electrolyte such as polyethylene oxide, LLZO, LiPON, LATP, Li 2 S—P 2 S 5 , Li 3 PS 4  and/or any other desired solid lithium ion conductor. 
     The protrusion inhibiting layer  224   a  further includes at least one constituent  240  that inhibits growth of lithium protrusions through improvement in the mechanical properties of layer  224   a , for example, by increasing the ductility, tensile strength, or fracture toughness of the protrusion inhibiting layer  224   a . The lithium protrusion growth inhibiting constituent  240  that improves mechanical properties of the electrolyte, but leads to non-negligible electronic conductivity of the protrusion inhibiting layer  224   a  may include or consist of, for example, carbon nanotubes, silver nanowires, particles of silver, steel, copper, or lithium, or other desired materials that are electronically conducting and have either high tensile strength, high ductility, or high fracture toughness. For example, the protrusion inhibiting layer  224   a  may be mechanically robust layer with a shear modulus of greater than 1/10 of the shear modulus of lithium metal and, in one particular embodiment, greater than double the shear modulus of lithium metal at the operating temperature of the battery. Additionally or alternatively, the mechanically robust protrusion inhibiting layer  224   a  may, in some embodiments, have a fracture toughness of greater than 10 4  Pa*m 1/2 , while in other embodiments the mechanically robust protrusion inhibiting layer  224   a  has a fracture toughness of greater than 105 Pa*m 1/2    
       FIG. 6  illustrates an embodiment in which the protrusion inhibiting layer  224   b  of the separator  208   d  includes a lithium ion conducting material  236   b  and a lithium protrusion growth inhibiting constituent  240   b  that chemically reacts with lithium protrusions so as to limit the growth of lithium protrusions. The lithium conducting material  236   b  may be, for example, a solid lithium ion electrolyte such as polyethylene oxide, LLZO, LiPON, LATP, Li 2 S—P 2 S 5 , Li 3 PS 4  or any other solid lithium ion conductor. The lithium protrusion growth inhibiting constituent chemically reduces or terminates the growth of lithium protrusions by, for example, alloying with the lithium in the protrusions. The growth inhibiting constituent  240   b  may include, for example, one or more of aluminum, tin, magnesium, silicon, silver, and gold, or any other suitable materials that chemically reacts with lithium. The growth inhibiting constituent  240   b  is configured such that once the growth inhibiting constituent  240   b  begins reacting with the lithium to alloy with the lithium, the protrusion growth of the lithium is reduced or terminated. 
     In conventional batteries, the material from which a separator is formed is limited to materials that are electronically insulating so as to avoid short-circuiting the battery. In the present disclosure, however, the electronically insulating layer(s)  220   a ,  220   b  provide the electronic insulation, thereby enabling use of a material that is electronically conductive as a lithium protrusion inhibiting layer  224 ,  224   a ,  224   b . As a result, since lithium protrusion formation or growth is inhibited, the battery can be operated at higher current densities than conventional batteries without risking protrusions causing a short circuit in the battery. 
     It will be appreciated that variants of the above-described and other features and functions, or alternatives thereof, may be desirably combined into many other different systems, applications or methods. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements may be subsequently made by those skilled in the art that are also intended to be encompassed by the foregoing disclosure.