SOLID STATE BATTERY CONTAINING CONTINUOUS GLASS-CERAMIC ELECTROLYTE SEPARATOR AND PERFORATED SINTERED SOLID-STATE BATTERY CATHODE

Abstract

A solid-state battery cell is provided, which contains a sintered metal oxide cathode, in which a surface of the cathode has an array of cavities extending about 60-90% into a depth of the cathode; a glass or glass ceramic electrolyte separator forming a smooth layer on the cathode surface and extending into the depths of the cavities of the cathode; and a lithium-based anode in contact with the electrolyte on a side opposite the cathode. A method of making the solid-state battery cell is also described.

Claims

1. A solid-state battery cell comprising: a sintered metal oxide cathode, wherein a surface of the cathode has an array of cavities extending about 60-90% into a depth of the cathode; a glass or glass ceramic electrolyte separator forming a smooth layer on the cathode surface and extending into the depths of the cavities of the cathode; and a lithium-based anode, wherein the anode is in contact with the electrolyte on a side opposite the cathode.

2. The solid-state battery cell according to claim 1, wherein the cathode comprises an inorganic lithium oxide ceramic material.

3. The solid-state battery cell according to claim 2, wherein the cathode comprises lithium nickel manganese cobalt oxide (NCM), lithium titanium oxide (LTO), Lithium Nickel Oxide (LNO), lithium cobalt oxide (LCO), or lithium manganese oxide (LMO).

4. The solid-state battery cell according to claim 1, wherein the cathode has a thickness of about 10 to about 200 microns.

5. The solid-state battery cell according to claim 1, wherein the cavities have a conical, triangular, semi-circular, or rectangular shape.

6. The solid-state battery cell according to claim 1, wherein the layer of the glass or glass ceramic electrolyte separator has a thickness of about 1-50 μm.

7. The solid-state battery cell according to claim 1, wherein the glass or glass ceramic electrolyte is applied to the cathode in a molten state and flows into the cavities before solidifying.

8. The solid-state battery cell according to claim 1, wherein the glass or glass ceramic electrolyte comprises at least one of lithium metaborate, lithium metaborate doped lithium carbonate (LiBO.sub.2-Li.sub.2CO.sub.3), lithium fluoride doped lithium metaborate, lithium tetraborate, silicon doped lithium tetraborate, lithium orthoborate, lithium orthoborate doped lithium carbonate (Li.sub.3BO.sub.3-Li.sub.2CO.sub.3), lithium fluoride doped Li.sub.3BO.sub.3-Li.sub.2CO.sub.3, lithium sulfate doped Li.sub.3BO.sub.3:Li.sub.2CO.sub.3 (LCBSO), and aluminum oxide doped Li.sub.3BO.sub.3:Li.sub.2CO.sub.3:Li.sub.2SO.sub.4.

9. The solid-state battery cell according to claim 1, further comprising a lithium anode and a cathode current collector.

10. A solid-state battery cell comprising a non-homogeneous mixture of cathode active material and glass or glass ceramic electrolyte material, wherein a continuous electrolyte separator extends into cavities of a patterned cathode, providing high surface area interface.

11. The solid-state battery cell according to claim 10, wherein the cathode comprises an inorganic lithium oxide ceramic material.

12. The solid-state battery cell according to claim 11, wherein the cathode comprises lithium nickel manganese cobalt oxide (NCM), lithium titanium oxide (LTO), Lithium Nickel Oxide (LNO), lithium cobalt oxide (LCO), or lithium manganese oxide (LMO).

13. The solid-state battery cell according to claim 10, wherein the cathode has a thickness of about 10 to about 200 microns.

14. The solid-state battery cell according to claim 10, wherein the cavities have a conical, triangular, semi-circular, or rectangular shape.

15. The solid-state battery cell according to claim 10, wherein the layer of the glass or glass ceramic electrolyte separator has a thickness of about 1-50 μm.

16. The solid-state battery cell according to claim 10, wherein the glass or glass ceramic electrolyte is applied to the cathode in a molten state and flows into the cavities before solidifying.

17. The solid-state battery cell according to claim 10, wherein the glass or glass ceramic electrolyte comprises at least one of lithium metaborate, lithium metaborate doped lithium carbonate (LiBO.sub.2-Li.sub.2CO.sub.3), lithium fluoride doped lithium metaborate, lithium tetraborate, silicon doped lithium tetraborate, lithium orthoborate, lithium orthoborate doped lithium carbonate (Li.sub.3BO.sub.3-Li.sub.2CO.sub.3), lithium fluoride doped Li.sub.3BO.sub.3-Li.sub.2CO.sub.3, lithium sulfate doped Li.sub.3BO.sub.3:Li.sub.2CO.sub.3 (LCBSO), and aluminum oxide doped Li.sub.3BO.sub.3:Li.sub.2CO.sub.3:Li.sub.2SO.sub.4.

18. A method for making a solid-state battery cell comprising: (a) providing a cathode slurry comprising a cathode active material and a solvent; (b) slurry casing the cathode slurry onto a non-stick substrate to form a green ceramic cathode material; (c) printing a pattern into a surface of the cathode to produce cavities in the surface; (d) sintering the patterned cathode to form a solid ceramic cathode; (e) coating the printed surface of the cathode with a layer of molten glass or glass ceramic electrolyte; and (f) quenching the molten glass or glass ceramic electrolyte to form a dense cathode-separator composite structure comprising a continuous separator extending into the cavities of the patterned cathode.

19. The method according to claim 18, wherein the sintering step (d) comprises heating the cathode at a temperature of about 500° C. to about 900° C.

20. The method according to claim 18, wherein the cathode active material comprises an inorganic lithium oxide ceramic material.

21. The method according to claim 21, wherein the cathode active material comprises lithium nickel manganese cobalt oxide (NCM), lithium titanium oxide (LTO), Lithium Nickel Oxide (LNO), lithium cobalt oxide (LCO), or lithium manganese oxide (LMO).

22. The method according to claim 18, wherein the solid ceramic cathode has a thickness of about 10 to about 200 microns.

23. The method according to claim 18, wherein the cavities have a conical, triangular, semi-circular, or rectangular shape.

24. The method according to claim 18, wherein the layer of the glass or glass ceramic electrolyte separator has a thickness of about 1-50 μm.

25. The method according to claim 18, wherein the glass or glass ceramic electrolyte comprises at least one of lithium metaborate, lithium metaborate doped lithium carbonate (LiBO.sub.2-Li.sub.2CO.sub.3), lithium fluoride doped lithium metaborate, lithium tetraborate, silicon doped lithium tetraborate, lithium orthoborate, lithium orthoborate doped lithium carbonate (Li.sub.3BO.sub.3-Li.sub.2CO.sub.3), lithium fluoride doped Li.sub.3BO.sub.3-Li.sub.2CO.sub.3, lithium sulfate doped Li.sub.3BO.sub.3:Li.sub.2CO.sub.3 (LCBSO), and aluminum oxide doped Li.sub.3BO.sub.3:Li.sub.2CO.sub.3:Li.sub.2SO.sub.4.

26. The method according to claim 18, further comprising (g) depositing a lithium anode on the separator.

27. The method according to claim 26, further comprising (h) depositing a cathode current collector on the lithium anode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0040] Embodiments of the disclosure relate to an all inorganic solid-state battery cell having thick lithium active electrodes relative to the thickness of the inert components, and which exhibits high “C” rate capability, where “C” is defined as the Amp-hour capacity of the battery divided by discharge current. Such a solid-state battery addresses the need for improved lithium ion transport within solid-state battery electrodes by providing a non-homogenous mixture of electrode active material and electrolyte material in which a cost-effective continuous electrolyte separator material extends to a substantial depth into the surface of a patterned cathode providing high surface area interface. It addresses the need for reduced tortuous conduction paths, eliminates conduction choke points, and provides an effective voltage field gradient to promote or motivate migration of ions through the electrolyte deeper into the electrode. As described in more detail below, the desired cathode structure may be formed by slurry casting a green ceramic material followed by die or roll stamping a desired pattern into its surface. However, it may also be formed by 3D printing green ceramic cathode material or other suitable technique. The cathode structure is then sintered at high temperature and coated with a glass electrolyte using a melt quench process.

Cathode Structure and Preparation

[0041] The electrochemically active material used to form the cathode structure is preferably an inorganic lithium-based metal oxide ceramic material, such as, without limitation, lithium nickel manganese cobalt oxide (NCM), lithium titanium oxide (LTO), Lithium Nickel Oxide (LNO), lithium cobalt oxide (LCO), or lithium manganese oxide (LMO); the most preferred is NCM. Other lithium-based electrochemically active materials known in the art or to be developed are also within the scope of the disclosure. The particle size of the electrochemically active material is preferably less than about 5 μm, more preferably less than about 1 μm, depending on the application of the battery. The active material selected for inclusion in a given electrode may be selected based on the desired operating voltage and capacity.

[0042] In one embodiment, a powder of the selected electrochemically active cathode material is mixed with a polymer binder, such as polyvinyl difluoride, polyvinyl alcohol, or polyvinyl butyral, and a solvent, such as acetone, xylene, or ethanol, to form a precursor cathode tape casting material. Alternatively, a powder of the selected electrochemically active cathode material may be mixed with a solvent, such as acetone, xylene, or ethanol, to form a precursor cathode tape casting material. The resulting precursor cathode tape is doctor blade cast, extruded, or formed by other suitable means onto a non-stick substrate such as silicone coated mylar or teflon, into a planar structure of a desired thickness and allowed to dry by solvent evaporation at room or elevated temperature. The casting is subsequently calendared to densify using a press or compression rollers to yield a green cathode preform having a thickness of about 10 to 200 μm.

[0043] FIG. 3 shows substrate/mechanical support 62, a preformed green cathode casting 64 and patterning die 66 which can also serve the purpose of densifying the cathode. Die 66 may be micro-machined into a desired configuration using electrochemical etching or other suitable techniques and may be micro-machined onto the surface of the press or compression rollers used for densification of the cathode, as described above. When pressed into the green cathode material 64, protrusions 68 create cavities in the cathode material. FIG. 4 illustrates a resulting pattern of cavities 70 in material 64 after the die 66 is removed. While only one shape is illustrated, the cavities may be of any shape, such as, but not limited to conical, triangular, semi-circular, rectangular, etc. The depth of the cavities is preferably a substantial depth of the thickness of the cathode, such as about 60-95% of the thickness of the cathode. The distance between the cavities on the surface of the cathode can be about 5 μm to about 1000 μm, preferably about 5 μm to about 50 μm.

[0044] Once cathode 64b is formed, if a binder is present, it is heated to about 300° C. to 450° C. to remove the binder; in all cases it is sintered at a temperature of about 500° C. to about 900° C., preferably about 850° C., to form a solid ceramic structure.

[0045] FIG. 5 shows the application of molten glass electrolyte 72 to the surface of the sintered preformed cathode. Molten glass 72 flows into surface cavities 70 as illustrated in FIG. 6. The thickness of the coating may be controlled by a doctor blade casting processor by an extrusion die or by other suitable techniques. Roller 76 smooths and cools/quenches the coating to form the solid glass electrolyte layer. The solid glass electrolyte layer is rapidly cooled from its melting temperature to below its glass transition temperature. The molten glass electrolyte may be, for example and without limitation, lithium metaborate, lithium metaborate doped lithium carbonate (LiBO.sub.2-Li.sub.2CO.sub.3), lithium fluoride doped lithium metaborate, lithium tetraborate, silicon doped lithium tetraborate, lithium orthoborate, lithium orthoborate doped lithium carbonate (Li.sub.3BO.sub.3-Li.sub.2CO.sub.3), lithium fluoride doped Li.sub.3BO.sub.3-Li.sub.2CO.sub.3, lithium sulfate doped Li.sub.3BO.sub.3:Li.sub.2CO.sub.3 (LCBSO), aluminum oxide doped Li.sub.3BO.sub.3:Li.sub.2CO.sub.3:Li.sub.2SO.sub.4 or other similar material. The presently most preferred electrolyte material is LCBSO. The molten glass electrolyte fills the cavities and leaves a separator on the surface of the cathode having a thickness in the range of about 1-50 μm.

Solid-State Battery Cell

[0046] FIG. 7 is a cross section of a final solid-state battery cell according to embodiments of the disclosure. It includes anode layer 78 which is preferably lithium based and may be, without limitation, pure lithium, a lithium alloy or a lithium intercalation material. The anode may be deposited by evaporation or sputter deposition using methods which are known in the art. Cathode current collector 79, which may be a metal such as aluminum, nickel, etc., may also be applied by physical deposition. Alternatively, cathode material 64b may be cast upon current collector 79 as a substrate that remains with it through completion of the resulting cell. In such a scenario, the current collector may be coated with an oxidation resistive coating (such as gold cobalt, an alloy that has the desired properties) or treated by other means to maintain electronic conductivity through the high temperature sintering process.

[0047] FIG. 8 is a close-up diagram of a cavity 70 filled with electrolyte. The cavity is shown having rounded peaks and valleys, as would result from a chemical machining process for fabrication of the desired die/mold configuration. However, the dimension can be approximated using straight surfaces as represented by conical shapes 80. Test data indicates that the lithium diffusion rates within cathode materials such as those previously discussed herein is such that cathode thicknesses in the range of 7 μm to 14 μm can be accessed at useful discharge/charge rates. The dimensions shown in FIG. 8 are representative of a useful cross-sectional geometry of a full cell according to the present disclosure. The anode (preferably lithium, silicon, lithium alloy, etc.) 86 of the cell has a thickness of 17 μum. The volume of electrolyte filled conical cavity 10 that has a base diameter of 28 μm and a height of 35 μm has a volume of 7,184 μm.sup.3. The mid-radius 90 of the cathode is 7 um while the radius 92 of the base of the cathode is 14 um

[0048] FIG. 9 shows one possible arrangement pattern of the cones as a hexagonal array with hexagon unit cells 94 being concentric with cones 80. It can be shown that the length of the sides of a hexagon is 16 μm if the sides are tangent to a circle of radius 14 μm (R). For the six triangles having base length 16 μm and height 14 μm, the area is 672 μm.sup.2. Multiplying the area by the 40 μm height of the hexagonal prism yields a volume of 26,880 μm.sup.3. Referring back to FIG. 8, the volume of the active material within each hexagonal prism is 19,696 μm.sup.3, the volume of the hexagonal prism minus the volume to the electrolyte cone. The geometry meets the constraint of having a diffusion length of 14 μm or less within the active sintered metal oxide. The Am-hour capacity a high-performance cathode active material such as LiNiMnCoO.sub.2 is about 1×10.sup.−4 Ah/(μm.Math.cm.sup.2) or (1×10.sup.−12 Ah/μm.sup.3). For 19,696 μm.sup.3 of active material, the capacity is about 1.97×10.sup.−8 Ah, (1×10.sup.−12 Ah/μm.sup.3×19,696 μm.sup.3). This capacity is used to determine the anode thickness needed to accommodate lithium when the cell is in a fully charged state. The capacity of lithium is 200 μAh/μm.Math.cm.sup.2, (2×10.sup.−12 Ah/μm.sup.3). To accommodate the 1.97×10.sup.−8 Ah of capacity within the 672 μm.sup.2 area footprint, the required thickness of the anode is ˜15 μm, (1.97×10.sup.−8 Ah/(2×10.sup.−12 Ah/μm.sup.3×672 μm.sup.2)). Using a mean operating voltage of 3.9 Volts, the energy density is calculated using the total volume of within the hexagonal prism footprint, including the thicknesses of all of the component layers, cathode current collector, the active cathode material/electrolyte composite layer, the electrolyte separator layer, the thickness required for anode at full charge and the anode current collector thickness. The energy density is 1.36 Wh/cm.sup.3, [(1.97×10.sup.−8 Ah×3.9V)/(84×10.sup.−4×672×10.sup.−8) cm.sup.3]. Similarly, LiCoO.sub.2 has a capacity of 0.72×10.sup.−4 Ah/μm.Math.cm.sup.2. Its energy density for this geometry would be 0.98 Wh/cm.sup.3.

[0049] The invention will now be described in connection with the following, non-limiting examples.

EXAMPLE 1: PREPARATION AND ANALYSIS OF PERFORATED SINTERED SOLID-STATE BATTERY NCM CATHODE

[0050] A mixture was prepared by high energy milling 4 g (61%) NCM active cathode material powder (commercially obtained from BASF), 2.4 g (36 wt %) nano-sized (<0.3 μm average particle size) LLZO electrolyte (commercially obtained from MSE Supplies LLC), and 0.2 g (3 wt %) polymer binder (PVB) (commercially obtained from The Tapecasting Warehouse Inc.) with 1.5 ml of ethanol and 1.5 ml of xylene solvents. The mixture was then cast onto a metal foil and allowed to dry. The casting was calendared into a dense sheet.

[0051] A porous stainless-steel mesh of size 635 mesh was pressed into the green cathode tape and later removed, leaving a perforated cathode having the negative pattern of the mesh, as shown in the optical microscopic image in FIG. 10.

[0052] An LLZO slurry was prepared by mixing nano-LLZO powder, approximately 25 nm diameter, with 0.28 g 7 wt % polymer binder (PVB) and 1.6 ml of ethanol and 1.6 ml of xylene solvents. The resulting slurry was doctor blade cast on top of the perforated cathode and allowed to dry. The casting was calendared into a dense sheet using steel rollers. The final thickness of the cathode ranged from 20 to 30 μm.

[0053] The cathode was heated at 400° C. in a tube furnace under purging oxygen gas to remove the binder and then at 550° C. in a tube furnace under purging oxygen gas for 1 hour to obtain a porous, sintered, cathode.

[0054] Lithium ortho-borate precursor was prepared by mixing 14.7 g of lithium tetraborate with 22 g lithium peroxide powder, both commercially obtained from Sigma Aldrich. LCBSO was prepared by mixing 5 g of lithium ortho borate with 20 g of lithium sulphate, commercially obtained from Sigma Aldrich, with 13.8 g of lithium carbonate, commercially obtained from Sigma Aldrich. A slurry was formed by mixing 0.2 g Li.sub.3BO.sub.3:Li.sub.2CO.sub.3:Li.sub.2SO.sub.4 (LCBSO) with 2 g of isopropanol solvent. After sintering, a slurry of low melt temperature electrolyte was cast onto one surface of the cathode disc. Evaporation of the solvent from the casting left a dry powder coating of Li.sub.3BO.sub.3:Li.sub.2CO.sub.3:Li.sub.2SO.sub.4 on the cathode surface. Next, the cathode was placed inside an oven at 700° C. to reflow the Li.sub.3BO.sub.3:Li.sub.2CO.sub.3:Li.sub.2SO.sub.4, allowing it to migrate into the cathode under capillary force.

[0055] Subsequently, a LiPON separator material having a thickness of about 2.5 microns was reactively RF magnetron sputtered onto the surface of the cathode from a lithium phosphate target (commercially obtained from Kurt Lesker) in a nitrogen environment. Finally, a Li metal anode (commercially obtained from Alfa Aesar) was deposited on the LiPON by thermal evaporation in vacuum. The resulting cell was tested using a Maccor battery cycler to obtain the data shown in Table 1, first row.

TABLE-US-00001 TABLE 1 Properties of Perforated and Non-Perforated Cathodes Avg Discharge 1st Resistance Voltage (mAh/ cycle C- Sample Description (Ω*cm.sup.2) (V) cm.sup.2) loss (%) Rate NCM 111 perforated 1136 3.67 386 19% 10 voids filled with LLZO NCM 111 perforated 1769 3.60 461 20% 11 voids filled with LCBSO NCM 111 no 1288 3.61 500 22% 16 perforation

[0056] As shown in Table 1, the perforated cathode that is filled with LLZO has an increased c-rate compared to the cathode without any perforation. This is as a result of the reduced tortuosity of the electrolyte in the cathode, allowing continuity throughout the cathode thickness, increasing access of the cathode active material. As clearly shown in Table 1, Example 1, the perforated cathode design outperforms the non-perforated cathode when LLZO was used to infiltrate the voids.

EXAMPLE 2: PREPARATION AND ANALYSIS OF PERFORATED SINTERED SOLID-STATE BATTERY NCM CATHODE

[0057] A mixture was prepared by high energy milling 4 g (61%) NCM active cathode material powder (commercially obtained from BASF), 2.4 g (36 wt %) nano-sized (<0.3 μm average particle size) LLZO electrolyte (commercially obtained from MSE Supplies LLC), and 0.2 g (3 wt %) polymer binder (PVB) (commercially obtained from The Tapecasting Warehouse Inc) with 1.5 ml of ethanol and 1.5 ml of xylene solvents. The mixture was then cast onto a metal foil and allowed to dry. The casting was calendared into a dense sheet.

[0058] A porous stainless-steel mesh of size 635 mesh was pressed into the green cathode tape and later removed, leaving a perforated cathode having the negative pattern of the mesh, as shown in the optical microscopic image in FIG. 10.

[0059] A LCBSO slurry was prepared by mixing 4 g nano-LCBSO powder (approximately 25 nm diameter) with 0.28 g 7 wt % polymer binder (PVB) and 1.6 ml of ethanol and 1.6 ml of xylene solvents. The resulting slurry was doctor blade cast on top of the perforated cathode and allowed to dry in air. The casting was calendared into a dense sheet using steel rollers. The final thickness of the cathode ranged from 20 to 30 μm.

[0060] The cathode was heated at 400° C. in a tube furnace under purging oxygen gas to remove the binder and then at 550° C. in a tube furnace under purging oxygen gas for 1 hour to obtain a porous, sintered, cathode.

[0061] After sintering, a slurry of low melt temperature electrolyte was cast onto one surface of the cathode disc. The slurry was formed by mixing 0.2 g Li.sub.3BO.sub.3:Li.sub.2CO.sub.3:Li.sub.2SO.sub.4 (LCBSO) as described with 2 g of isopropanol solvent. Evaporation of the solvent from the casting left a dry powder coating of Li.sub.3BO.sub.3:Li.sub.2CO.sub.3:Li.sub.2SO.sub.4 on the cathode surface. Next, the cathode was placed inside an oven at 700° C. to reflow the Li.sub.3BO.sub.3:Li.sub.2CO.sub.3:Li.sub.2SO.sub.4, allowing it to migrate into the cathode under capillary force.

[0062] Subsequently, a LiPON separator material was reactively RF magnetron sputtered from lithium phosphate target (commercially obtained from Kurt Lesker) in a nitrogen environment having a thickness of about 2.5 microns was deposited onto the surface of the cathode by. Finally, a Li metal anode (commercially obtained from Alfa Aesar) was deposited on the LiPON by thermal evaporation in vacuum. The resulting cell was tested using a Maccor battery cycler to obtain the data shown in Table 1, second row.

[0063] As can be seen in Table 1, a perforated cathode that is filled with LCBSO had an increased C-rate compared to the cathode without any perforation. This is as a result of the reduced tortuosity of the electrolyte in the cathode, allowing continuity throughout the cathode thickness, increasing access of the cathode active material. It is clearly shown in Table 1 that the perforated cathode design outperforms the non-perforated cathode, regardless of the electrolyte choice for infiltrating the voids.

[0064] It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.