Abstract:
In one embodiment, a solid state battery includes a first cell stack including a first solid-electrolyte separator positioned between a first cathode and a first anode, a first base layer including a first base portion positioned directly beneath the first anode, and including a first lateral extension extending laterally beyond the first anode, a second cell stack beneath the first base layer and including a second solid-electrolyte separator positioned between a second cathode and a second anode, a second base layer including a second base portion positioned directly beneath the second anode, and including a second lateral extension extending laterally beyond the second anode, wherein the second base portion extends laterally beyond the first lateral extension, and a multiplexor (i) in electrical communication with the first base portion through the first lateral extension, and (ii) in electrical communication with the second base portion through the second lateral extension.

Description:
CROSS REFERENCE 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/870,269 filed Aug. 27, 2013, the entire contents of which is herein incorporated by reference. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates to batteries and more particularly to solid state batteries. 
       BACKGROUND 
       [0003]    Rechargeable lithium-ion batteries are attractive energy storage systems for portable electronics and electric and hybrid-electric vehicles because of their high specific energy compared to other electrochemical energy storage devices. A typical Li-ion cell contains a negative electrode, a positive electrode, and a separator region between the negative and positive electrodes. Both electrodes contain active materials that insert or react with lithium reversibly. In some cases the negative electrode may include lithium metal, which can be electrochemically dissolved and deposited reversibly. The separator contains an electrolyte with a lithium cation, and serves as a physical barrier between the electrodes such that none of the electrodes are electronically connected within the cell. 
         [0004]    Typically, during charging, there is generation of electrons at the positive electrode and consumption of an equal amount of electrons at the negative electrode, and these electrons are transferred via an external circuit. In the ideal charging of the cell, these electrons are generated at the positive electrode because there is extraction via oxidation of lithium ions from the active material of the positive electrode, and the electrons are consumed at the negative electrode because there is reduction of lithium ions into the active material of the negative electrode. During discharging, the exact opposite reactions occur. 
         [0005]    Batteries with a lithium metal negative electrode afford exceptionally high specific energy (in Wh/kg) and energy density (in Wh/L) compared to batteries with conventional carbonaceous negative electrodes. However, the cycle life of such systems is rather limited due to (a) significant volume changes in the cell sandwich during every cycle as the Li metal is stripped and plated, (b) formation of dendrites during recharge that may penetrate the separator and short the cell and/or result in fragmentation and capacity loss of the negative electrode; (c) morphology changes in the metal upon extended cycling that result in a large overall volume change in the cell; and (d) changes in the structure and composition of the passivating layer that forms at the surface of the metal when exposed to certain electrolytes, which may isolate some metal and/or increase the resistance of the cell over time. 
         [0006]    When high-specific-capacity negative electrodes such as a metal are used in a battery, the maximum benefit of the capacity increase over conventional systems is realized when a high-capacity positive electrode active material is also used. For example, conventional lithium-intercalating oxides (e.g., LiCoO 2 , LiNi 0.8 Co 0.15 Al 0.05 O 2 , Li 1.1 Ni 0.3 Co 0.03 Mn 0.3 O 2 ) are typically limited to a theoretical capacity of ˜280 mAh/g (based on the mass of the lithiated oxide) and a practical capacity of 180 to 250 mAh/g, which is quite low compared to the specific capacity of lithium metal, 3863 mAh/g. The highest theoretical capacity for which some practical cycling has been achieved for a lithium-ion positive electrode is 1168 mAh/g (based on the mass of the lithiated material), which is shared by Li 2 S and Li 2 O 2 . Other high-capacity materials include BiF 3  (303 mAh/g, lithiated), FeF 3  (712 mAh/g, lithiated), LiOH.H 2 O (639 mAh/g), and others. Unfortunately, all of these materials react with lithium at a lower voltage compared to conventional oxide positive electrodes, hence limiting the theoretical specific energy; however, the theoretical specific energies are still very high (&gt;800 Wh/kg, compared to a maximum of ˜500 Wh/kg for a cell with lithium negative and conventional oxide positive electrodes). 
         [0007]      FIG. 1  depicts a chart  2  showing the range achievable for a vehicle using battery packs of different specific energies versus the weight of the battery pack. In the chart  10 , the specific energies are for an entire cell, including cell packaging weight, assuming a 50% weight increase for forming a battery pack from a particular set of cells. The U.S. Department of Energy has established a weight limit of 200 kg for a battery pack that is located within a vehicle. Accordingly, only a battery pack with about 600 Wh/kg or more can achieve a range of 300 miles. 
         [0008]    Lithium-based batteries have a sufficiently high specific energy (Wh/kg) and energy density (Wh/L) that they are now being used in electric-powered vehicles. However, in order to power a full-electric vehicle with a range of several hundred miles, a battery with a higher specific energy than the present state of the art (an intercalation system with a graphite anode and transition-metal oxide cathode) is necessary. 
         [0009]    Some options which provide higher specific energy as compared to the currently utilized batteries are possible. For example,  FIG. 2  depicts a chart  4  which identifies the specific energy and energy density of various lithium-based chemistries. In the chart  4 , only the weight of the active materials, current collectors, binders, separator, and other inert material of the battery cells are included. The packaging weight, such as tabs, the cell can, etc., are not included. As is evident from the chart  4 , the lithium-sulfur battery, which uses a lithium metal negative electrode and a positive electrode that reduces sulfur to form lithium sulfide, has a significantly higher specific energy than the present state of the art. 
         [0010]    There are significant challenges that must be addressed for the lithium-sulfur system to become commercially viable. Important challenges include increasing the cycle life (current state of the art is 100 to several hundred cycles; target is &gt;500, preferably &gt;2000), increasing the utilization of sulfur (typical utilization is below 75% due to passivation of the positive electrode by Li 2 S or Li 2 S 2 , which are electronically insulating), increasing the mass fraction of sulfur in the positive electrode (typically the mass fraction is below 50%), and increasing the rate capability of the cell (target discharge rate is 1C or higher). While some Li/S cells described in the literature fulfill some of the objectives for cycle life, specific energy, and specific power, none of these cells adequately address all of the issues as would be needed to realize a commercial cell. 
         [0011]    What is needed, therefore, is a solid state electrochemical cell which addresses one or more of the above identified issues. 
       SUMMARY 
       [0012]    In accordance with one embodiment a solid state battery includes a first cell stack including a first solid-electrolyte separator positioned between a first cathode and a first anode, a first base layer including a first base portion positioned directly beneath the first anode, and including a first lateral extension extending laterally beyond the first anode, a second cell stack beneath the first base layer and including a second solid-electrolyte separator positioned between a second cathode and a second anode, a second base layer including a second base portion positioned directly beneath the second anode, and including a second lateral extension extending laterally beyond the second anode, wherein the second base portion extends laterally beyond the first lateral extension, and a multiplexor (i) in electrical communication with the first base portion through the first lateral extension, and (ii) in electrical communication with the second base portion through the second lateral extension. 
         [0013]    In one or more embodiments, a battery includes a first insulator, the first insulator positioned above the first base portion and extending along a first side of the first anode, a second side of the first cathode, and a third side of the first separator, and a second insulator, the second insulator positioned above the second base portion and extending along a fourth side of the second anode, a fifth side of the second cathode, and a sixth side of the second separator. 
         [0014]    In one or more embodiments, a battery includes a first conductive member extending upwardly from the first lateral extension, and a second conductive member extending upwardly from the second lateral extension, wherein the multiplexor is in electrical communication with the first base portion through the first lateral extension and the first conductive member, the multiplexor is in electrical communication with the second base portion through the second lateral extension and the second conductive member, and the second insulator is positioned between the first conductive member and the second conductive member. 
         [0015]    In one or more embodiments the first conductive member is an upwardly extending portion of the first base layer, and the second conductive member is an upwardly extending portion of the second base layer. 
         [0016]    In one or more embodiments the first conductive member is a first multiplexor lead, and the second conductive member is a second multiplexor lead. 
         [0017]    In one or more embodiments the first cell stack has a first maximum thickness, the second cell stack has a second maximum thickness, and the first maximum thickness is larger than the second maximum thickness. 
         [0018]    In one or more embodiments the first side, the second side, and the third side are perpendicular to an upper surface of the first base portion. 
         [0019]    In one or more embodiments the first side, the second side, and the third side are not perpendicular to an upper surface of the first base portion. 
         [0020]    In one or more embodiments the first cell stack is connected in series with the second cell stack. 
         [0021]    In one embodiment, a method of forming a solid state battery includes providing a first cell stack including a first solid-electrolyte separator positioned between a first cathode and a first anode, positioning a first base portion of a first base layer directly beneath the first anode, the first base layer including a first lateral extension extending laterally beyond the first anode, providing a second cell stack including a second solid-electrolyte separator positioned between a second cathode and a second anode, positioning a second base portion of a second base layer directly beneath the second anode, the second base layer including a second lateral extension extending laterally beyond the second anode, such that the second base portion extends laterally beyond the first lateral extension, placing the first base portion in electrical communication with a multiplexor located above the first lateral extension through the first lateral extension, and placing the second base portion in electrical communication with the multiplexor through the second lateral extension. 
         [0022]    In one or more embodiments a method of forming a solid state battery includes positioning a first insulator above the first base portion and along a first side of the first anode, a second side of the first cathode, and a third side of the first separator, and positioning a second insulator above the second base portion and along a fourth side of the second anode, a fifth side of the second cathode, and a sixth side of the second separator. 
         [0023]    In one or more embodiments placing the first base portion in electrical communication with the multiplexor includes placing the first base portion in electrical communication with the multiplexor through a first conductive member extending between the first lateral extension and the multiplexor, placing the second base portion in electrical communication with the multiplexor includes placing the second base portion in electrical communication with the multiplexor through a second conductive member extending between the second lateral extension and the multiplexor, and positioning the second insulator includes positioning the second insulator between the first conductive member and the second conductive member. 
         [0024]    In one or more embodiments placing the first base portion in electrical communication with the multiplexor includes placing the first base portion in electrical communication with the multiplexor through an upwardly extending portion of the first base layer, and placing the second base portion in electrical communication with the multiplexor includes placing the second base portion in electrical communication with the multiplexor through an upwardly extending portion of the second base layer. 
         [0025]    In one or more embodiments providing the first cell stack includes providing the first cell stack with a first maximum thickness, providing the first cell stack includes providing the first cell stack with a first maximum thickness, and the first maximum thickness is larger than the second maximum thickness. 
         [0026]    In one or more embodiments positioning the first insulator includes positioning the first insulator along portions of the first side, the second side, and the third side which are perpendicular to an upper surface of the first base portion. 
         [0027]    In one or more embodiments positioning the first insulator includes positioning the first insulator along portions of the first side, the second side, and the third side which are not perpendicular to an upper surface of the first base portion. 
         [0028]    In one or more embodiments a method of forming a solid state battery includes connecting the first cell stack in series with the second cell stack with the multiplexor. 
         [0029]    In one or more embodiments placing the first base portion in electrical communication with the multiplexor includes placing the first base portion in electrical communication with the multiplexor through a first multiplexor lead extending between the first lateral extension and the multiplexor, and placing the second base portion in electrical communication with the multiplexor includes placing the second base portion in electrical communication with the multiplexor through a second multiplexor lead extending between the second lateral extension and the multiplexor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  depicts a plot showing the relationship between battery weight and vehicular range for various specific energies; 
           [0031]      FIG. 2  depicts a chart of the specific energy and energy density of various lithium-based cells; 
           [0032]      FIG. 3  depicts a simplified cross sectional view of a stacked battery with a bipolar design that includes offset base layers in a stepped geometry; 
           [0033]      FIG. 4  depicts a partial side perspective view of one of the cells of  FIG. 3  showing a separator with an open cell microstructured composite separator with solid-electrolyte components in the form of columns which inhibits dendrite formation while allowing flexing of the anodes; 
           [0034]      FIG. 5  depicts a simplified cross sectional view of a stacked battery with a bipolar design that includes offset base layers in an angled geometry; and 
           [0035]      FIG. 6  depicts a simplified cross sectional view of a stacked battery with a bipolar design that includes offset base layers in a stepped geometry with leads from a multiplexor that extend down to base layers. 
       
    
    
     DESCRIPTION 
       [0036]    For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written description. It is understood that no limitation to the scope of the disclosure is thereby intended. It is further understood that the present disclosure includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the disclosure as would normally occur to one of ordinary skill in the art to which this disclosure pertains. 
         [0037]      FIG. 3  depicts an electrochemical battery  100 . The electrochemical battery  100  includes a number of cells or cell stacks  102   X  within a packaging  104  or other surrounding environment that is both electrically insulating and (optionally) thermally conductive. The packaging  104  improves the safety of the electrochemical battery  100 . 
         [0038]    Each of the cells  102   X  includes an anode  106   X , a separator  108   X , and a cathode  110   X . A base layer  112   X , which is typically metal such as copper and can serve as a current collector as well as a feedthrough to an integrated circuit or multiplexor  114 , is positioned adjacent to the anode  106   X  and between the anode  106   X  and an adjacent cathode. For example, the base layer  112   1  is located between the anode  106   1  and the cathode  110   2 . 
         [0039]    While the multiplexor  114  is depicted within the packaging  104 , in some embodiments the multiplexor  114  is provided external to the packaging  104 . The multiplexer  114  may be a solid-state device with insulating material between the electronic leads. The leads of the multiplexer which contact each terminal of the cell stack may extend to the top of the cell to an electrical circuit used for monitoring and controlling the current through each of the leads. 
         [0040]    The anodes  106   X  include lithium metal or a lithium alloy metal. The anodes  106   X  are sized such that they have at least as much capacity as the associated cathode  110   X , and preferably at least 10% excess capacity and up to greater than 50% capacity in some embodiments. 
         [0041]    The cathodes  110   X  in various embodiments include a sulfur or sulfur-containing material (e.g., PAN-S composite or Li 2 S); an air electrode; Li-insertion materials such as NCM, LiNi 0.5 Mn 1.5 O 4 , Li-rich layered oxides, LiCoO 2 , LiFePO 4 , LiMn 2 O 4 ; Li-rich NCM, NCA, and other Li intercalation materials, or blends thereof or any other active material or blend of materials that react with and/or insert Li cations and/or electrolyte anions. The cathodes  110   X  may be fully dense. The cathodes  110   X  may include Li-conducting polymer, ceramic or other solid, non-polymer electrolyte. The cathode Li-insertion materials may additionally be coated (e.g., via spray coating) with a material such as LiNbO 3  in order to improve the flow of ions between the Li-insertion materials and the solid-electrolyte, as described in T. Ohtomo et al., Journal of Power Sources 233 (2013) 231-235. Solid-electrolyte materials in the cathodes  110   X  may further include lithium conducting garnets, lithium conducting sulfides (e.g., Li 2 S—P 2 S 5 ) or phosphates, Li 3 P, LIPON, Li-conducting polymer (e.g., PEO), Li-conducting metal-organic frameworks such as described by Wiers et al. “A Solid Lithium Electrolyte via Addition of Lithium Isopropoxide to a Metal-Organic Framework with Open Metal Sites,” Journal of American Chemical Society, 2011, 133 (37), pp 14522-14525, the entire contents of which are herein incorporated by reference, thio-LISiCONs, Li-conducting NaSICONs, Li 10 GeP 2 S 12 , lithium polysulfidophosphates, or other solid Li-conducting material. Other solid-electrolyte materials that may be used are described in Christensen et al., “A critical Review of Li/Air Batteries”, Journal of the Electrochemical Society 159(2) 2012, the entire contents of which are herein incorporated by reference. Other materials in the cathodes  110   X  may include Li 7−x La 3 Ta x Zr 2−x O 12 , wherein 0≦X≦2, electronically conductive additives such as carbon black, and a binder material. The cathode materials are selected to allow sufficient electrolyte-cathode interfacial area for a desired design. 
         [0042]    In some embodiments, the separators  108   X  are microstructured composite separators which conduct lithium ions between the anodes  106   X  and the cathodes  110   X  while blocking electrons. For example,  FIG. 4  depicts a partial perspective view of the cell  102   1  which includes a layer  120  adjacent to the anode  106   1  and a layer  122  adjacent to the cathode  110   1 . A current collector  124  is also shown which may be made of aluminum and is provided in some embodiments, and may be separated from an adjacent base layer  112   X  by a layer of electrically conductive but chemically inactive material such as graphite. A number of solid-electrolyte components in the form of columns  126  extend between the layer  120  and the layer  122  defining microstructure cavities  128  therebetween. 
         [0043]    The microstructured composite separator  108   X  thus consists of regularly spaced solid-electrolyte components  126  which provide sufficient ionic transport (i.e., by providing a sufficiently high volume fraction of conducing material and by limiting the thickness of the structure between the anode and cathode) and provide mechanical resistance to suppress the formation and growth of lithium dendrites in the anode  106   X . In the embodiment of  FIG. 4 , solid-electrolyte components  108   X  are flexible so as to accommodate volume change of the electrodes. 
         [0044]    While three columns  126  are shown in  FIG. 4 , there are more or fewer solid-electrolyte components in other embodiments. In other embodiments, the solid-electrolyte components may be configured in other forms. In some embodiments, the microstructure cavities  128  may be filled with different compositions to provide a desired flexibility and/or to otherwise modify mechanical properties of the microstructured composite separator. More details regarding the microstructured composite separator  108   X , and other alternative separator configurations, are provided in U.S. application Ser. No. 14/460,798, filed Aug. 15, 2014, the entire contents of which are herein incorporated by reference. 
         [0045]    By stacking the cells  102   X  in the bipolar design of  FIG. 3 , the operating voltage of the battery  100  can be modified to the desired voltage. By way of example, if each cell  102   X  has an operating voltage of ˜4 V, 100 cells  102   X  can be stacked to produce a device that has an operating voltage of ˜400 V. In this way, a given power can be achieved while passing a low current through each of the cells  102   X . Therefore, wiring of the cells  102   X  can be achieved with small-diameter electrical conductors while maintaining high energy efficiency. The battery  100  thus provides an operating voltage greater than 5 V, and in some embodiments, greater than 50 V. 
         [0046]    Returning to  FIG. 3 , the electrochemical battery  100  further includes a plurality of insulators  130   X . The insulators  130   X  insulate the cells  102   X  from the upwardly extending base layer  112   X . In order to provide sufficient space for the upwardly extending portions of the base layers  112   X  and the insulators  130   X , the cells  102   X  are “offset”. As used herein, “offset” means that the base layer  112   X  has a lateral extent (for the orientation of  FIG. 3 ) which is greater than the associated anode  106   X , separator  108   X , and cathode  110   X  on at least one side of the cell  102   X  as shown in  FIG. 3 . For example, the offset for cell  102   2  is identified as offset  140   2 . 
         [0047]    The offset  140   X  which in the embodiment of  FIG. 3  is a “step-edge” geometry, allows for independent monitoring and control of the cell sandwiches that comprise a high-voltage stack. In an offset geometry, either the positive terminal and/or negative terminal of each cell sandwich or group of cell sandwiches is exposed and can be contacted electrically by a multiplexer or multichannel circuit. In some embodiments only one terminal is exposed; in others both terminals are exposed; in still others the electronically conductive bipolar plate is exposed. Preferably, the geometry of the stack is such that the offset is greater than the thickness (t), of the respective anode  106   X , separator  108   X , and cathode  110   X . 
         [0048]    The offset  140   X  provides connection to each cell  102   X  from above rather than from the side. This type of connection is easier to achieve. For instance, a given cell  102   X  may be only 2 to 5 microns thick but the steps or offsets  140   X  may have a length of 10 microns. For a cell stack consisting of 100 cell sandwiches, the total length of the offsets  140   X  would be approximately 1 mm. Hence, if the cell area is 10 cm×10 cm, then the difference in area between the top most cell sandwich and the bottom most cell sandwich is only 1%. In some embodiments, the difference in the lengths of the individual cells  102   X  is compensated by making the electrode regions with different thicknesses such that the total capacity of each of the cells  102   X  is identical. 
         [0049]    Embodiments described herein thus provide for monitoring and control of the cells  102   X  individually or in groups of serially connected cells. This allows, for example, bypassing a defective cell as well as active and/or passive cell balancing. Active cell balancing includes charging one or more cells  102   X  or groups of cells  102   X  while discharging one or more other cells  102   X  or groups of cells  102   X , such that the energy flows from the discharged cells  102   X  to the charged cells  102   X . Passive cell balancing includes the use of a shunt such that a cell  102   X  that is deemed to be fully charged or fully discharged can be bypassed. 
         [0050]    While the offsets  140   X  are depicted in a stepped geometry, other configurations are used in other embodiments. By way of example,  FIG. 5  depicts a battery  200  which includes a packaging  204  and a number of cells  202   X , each of which is substantially the same as the cells  102   X  including anodes  206   X , separators  208   X , cathodes  210   X  and base layers  212   X . The cells  202   X  are connected to a multiplexor  214  and insulators  230   X  are provided at the ends of the cells  202   X . 
         [0051]    The main difference between the cells  102   X  and the cells  202   X  is that the ends of the anodes  206   X , separators  208   X , cathodes  210 X adjacent to the offsets  240   X  are angled thereby providing an “angled” geometry which can make connection to the cells  202   X  simpler. 
         [0052]      FIG. 6  depicts a battery  250  which includes a packaging  254  and a number of cells  252   X , each of which is substantially the same as the cells  102   X  including anodes  256   X , separators  258   X , cathodes  260   X  and base layers  262   X . The cells  252   X  are connected to a multiplexor  264  and insulators  266   X  are located at the ends of the cells  250   X . The main difference between the battery  250  and the battery  100  is that the multiplexor  264  includes leads  268  which extend downwardly to the base layers  262   X . 
         [0053]    The above described embodiments provide a solid-state battery, cell, or cell stack with high operating voltage enabled by many cell sandwiches connected in series and contained within the same package. The cell stack in some embodiments has a staircase structure on at least one edge in order to enable independent electrical contact to each cell sandwich. Hence, individual cell sandwiches can be bypassed or monitored and controlled independently, and both passive and active cell sandwich balancing can be enabled. 
         [0054]    The above described embodiments thus provide a safe energy-storage system with high voltage enabled by multiple cell sandwiches stacked in series and an electronically insulating material or medium surrounding the cell stack or incorporated into the cell packaging. 
         [0055]    The offset design in some embodiments enables independent monitoring and control of each cell sandwich, bypassing of defective cell sandwiches, active and/or passive cell balancing. 
         [0056]    While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the disclosure are desired to be protected.