HERMETIC THIN FILM ELECTROCHEMICAL CELLS HOUSED IN A CERAMIC CASING AND ACTIVATED WITH A SOLID ELECTROLYTE

Abstract

A miniature electrochemical cell having a total volume that is less than 0.5 cc is described. The cell casing is formed by joining two ceramic casing halves together. One or both casing halves are machined from ceramic to provide a recess that is sized and shaped to contain the electrode assembly. The opposite polarity terminals are metal feedthroughs, such as of gold, and are formed by brazing gold into openings machined into one or both ceramic casing halves. The two ceramic casing halves are separated from each other by a metal interlayer, such as of gold, bonded to a thin film metallization adhesion layer, such as of titanium, that contacts an edge periphery of each ceramic casing half. A solid electrolyte (Li.sub.xPO.sub.yN.sub.z) is used to activate the electrode assembly.

Claims

1. An electrochemical cell, comprising: a) a ceramic casing, comprising: i) a first ceramic substrate having a first peripheral edge extending to and meeting with opposed first substrate outer and inner major faces; ii) a first ring-shaped metallization contacting the first substrate inner major face adjacent to the first substrate peripheral edge; iii) a second ceramic substrate having a second substrate peripheral edge extending to and meeting with opposed second substrate outer and inner major faces; and iv) a second ring-shaped metallization contacting the second substrate inner major face adjacent to the second substrate peripheral edge; b) a first electrode current collector contacting the first substrate inner major face, spaced inwardly from the first ring-shaped metallization; c) a first electrode active material contacting the first electrode current collector; d) a second electrode current collector contacting the first substrate inner major face, spaced inwardly from the first ring-shaped metallization, wherein the second electrode current collector is side-by-side with the first electrode current collector; e) a solid electrolyte contacting the first electrode active material; f) a second electrode active material contacting the second electrode current collector and contacting the solid electrolyte opposite the first electrode active material; g) a first opening extending through the first ceramic substrate in alignment with the first electrode current collector, wherein a first gold body hermetically sealed to the first ceramic substrate in the first opening conductively contacts the first electrode current collector to thereby serve as a first terminal; and h) a second opening extending through the first ceramic substrate in alignment with the second electrode current collector, wherein a second gold body hermetically sealed to the first ceramic substrate in the second opening conductively contacts the second electrode current collector to thereby serve as a second, opposite polarity terminal for the electrochemical cell, i) wherein the first and second ring-shaped metallizations are in a hermetically sealed relationship with each other to thereby hermetically seal the first and second ceramic substrates together to form the casing.

2. The electrochemical cell of claim 1, wherein the first electrode is a cathode and the second electrode is an anode, or the first electrode is an anode and the second electrode is a cathode.

3. The electrochemical cell of claim 1, wherein the outer and inner major faces of the first ceramic substrate are both substantially planar.

4. The electrochemical cell of claim 1, wherein the first and second ring-shaped metallizations are of titanium or niobium.

5. The electrochemical cell of claim 1, wherein the first and second openings extending through the first ceramic substrate are each provided with a metallization of titanium or niobium, and wherein the respective first and second gold bodies are hermetically sealed to the respective first and second metallizations in the first and second openings.

6. The electrochemical cell of claim 1, wherein both the first and second ceramic substrates have an extending peripheral rim supporting the respective first and second ring-shaped metallization.

7. The electrochemical cell of claim 1, wherein the solid electrolyte contacting the first electrode active material opposite the first electrode current collector does not contact the second electrode current collector.

8. The electrochemical cell of claim 1, wherein a gold layer hermetically seals the first and second ring-shaped metallizations together to thereby hermetically seal the first and second ceramic substrates to each other.

9. The electrochemical cell of claim 1, wherein the first and second ring-shaped metallizations are hermetically sealed to each other to thereby hermetically seal the first and second ceramic substrates together to form the casing.

10. The electrochemical cell of claim 1, wherein at least one of the first and second ceramic substrates has an extending peripheral rim supporting the respective first and second ring-shaped metallization, and wherein, with the first and second ring-shaped metallizations being hermetically sealed to each other to thereby hermetically seal the first and second ceramic substrates together, a sum of a first thickness of the first electrode current collector, a second thickness of the first electrode active material, a third thickness of the solid electrolyte, a fourth thickness of the second electrode active material and a fifth thickness of the second electrode current collector is less than the distance from the first ceramic substrate inner major face to the second ceramic substrate inner major face.

11. The electrochemical cell of claim 1, wherein at least one of the first and second ceramic substrates has an extending peripheral rim supporting the respective first and second ring-shaped metallization, and wherein, with a gold layer hermetically sealing the first and second ring-shaped metallizations together to thereby hermetically seal the first and second ceramic substrates to each other, a sum of a first thickness of the first electrode current collector, a second thickness of the first electrode active material, a third thickness of the solid electrolyte, a fourth thickness of the second electrode active material and a fifth thickness of the second electrode current collector is less than the distance from the first ceramic substrate inner major face to the second ceramic substrate inner major face.

12. The electrochemical cell of claim 11, wherein the sum of the first, second, third, fourth and fifth thicknesses is less than the distance from the first ceramic substrate inner major face to the second ceramic substrate inner major face by about 1 m to 100 m.

13. The electrochemical cell of claim 1, wherein the first and second current collectors are individually selected from the group consisting of titanium, copper, stainless steel, tantalum, platinum, gold, aluminum, cobalt, molybdenum, nickel, and alloys thereof.

14. The electrochemical cell of claim 1, wherein at least the first and second inner major faces of the respective first and second ceramic substrates have a surface roughness that is greater than zero, but less than 50 nm.

15. The electrochemical cell of claim 1, wherein the solid electrolyte extends between the first and second electrode current collectors.

16. The electrochemical cell of claim 1, wherein the first and second ceramic substrates are selected from the group consisting of 3 mol % YSZ, polycrystalline alumina, and sapphire.

17. The electrochemical cell of claim 1, wherein at least one of the first and second ceramic substrates is of a substantially transparent sapphire.

18. The electrochemical cell of claim 1, wherein the anode active material is selected from the group consisting of lithium, LiSi, LiSn, LiAl, LiB and LiSiB alloys, and wherein the cathode active material is selected from the group consisting of LiCoO.sub.2, LiMnO.sub.2, LiMn.sub.2O.sub.4, LiFePO.sub.4, Ag.sub.2V.sub.4O.sub.11, V.sub.2O.sub.5, and mixtures thereof.

19. The electrochemical cell of claim 1, wherein the solid electrolyte comprises Li.sub.xPO.sub.yN.sub.z.

20. The electrochemical cell of claim 1 having a total volume that is less than 0.5 cc.

21. An electrochemical cell, comprising: a) a ceramic casing, comprising: i) a first sapphire substrate having a first peripheral edge extending to and meeting with opposed first substrate outer and inner major faces; ii) a first ring-shaped metallization contacting the first sapphire substrate inner major face adjacent to the first substrate peripheral edge; iii) a second ceramic substrate having a second substrate peripheral rim extending to and meeting with opposed second substrate outer and inner major faces; and iv) a second ring-shaped metallization contacting the second substrate peripheral rim; b) a first electrode current collector contacting the first sapphire substrate inner major face, spaced inwardly from the first ring-shaped metallization; c) a first electrode active material contacting the first electrode current collector; d) a second electrode current collector contacting the first sapphire substrate inner major face, spaced inwardly from the first ring-shaped metallization, wherein the second electrode current collector is side-by-side with the first electrode current collector; e) a solid electrolyte contacting the first electrode active material; f) a second electrode active material contacting the second electrode current collector and contacting the solid electrolyte opposite the first electrode active material; g) a first opening extending through the first sapphire substrate in alignment with the first electrode current collector, wherein a first gold body hermetically sealed to the first sapphire substrate in the first opening conductively contacts the first electrode current collector to thereby serve as a first terminal; and h) a second opening extending through the first sapphire substrate in alignment with the second electrode current collector, wherein a second gold body hermetically sealed to the first sapphire substrate in the second opening conductively contacts the second electrode current collector to thereby serve as a second, opposite polarity terminal for the electrochemical cell.

22. The electrochemical cell of claim 21, wherein the first electrode is a cathode and the second electrode is an anode, or the first electrode is an anode and the second electrode is a cathode.

23. The electrochemical cell of claim 21, wherein at least one of the first and second ceramic substrates is of a substantially transparent sapphire.

24. An electrochemical cell, comprising: a) an electrode assembly comprising: i) an anode comprising an anode active material conductively contacted to an anode current collector; and ii) a cathode comprising a cathode active material conductively contacted to a cathode current collector, iii) wherein the anode and cathode are segregated from direct physical contact with each other and activated with an electrolyte; and b) a ceramic casing housing the electrode assembly, the casing comprising: i) a first ceramic substrate having a first peripheral edge extending to and meeting with opposed first substrate outer and inner major faces; ii) a first ring-shaped metallization contacting the first substrate inner major face adjacent to the first substrate peripheral edge; iii) a second ceramic substrate having a second substrate peripheral edge extending to and meeting with opposed second substrate outer and inner major faces; and iv) a second ring-shaped metallization contacting the second substrate inner major face adjacent to the second substrate peripheral edge, v) wherein the first and second ring-shaped metallizations are in a hermetically sealed relationship with each other to thereby hermetically seal the first and second ceramic substrates together to form the casing; c) a first opening extending through the first ceramic substrate in alignment with the anode current collector, wherein a first gold body hermetically sealed to the first ceramic substrate in the first opening conductively contacts the anode current collector to thereby serve as a negative terminal; and d) a second opening extending through the first ceramic substrate in alignment with the cathode current collector, wherein a second gold body hermetically sealed to the first ceramic substrate in the second opening conductively contacts the cathode current collector to thereby serve as a positive terminal for the electrochemical cell.

25. The electrochemical cell of claim 24, wherein at least one of the first and second ceramic substrates is of a substantially transparent sapphire.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is a plan view of a ceramic cathode base substrate 12 of a casing for the electrochemical cell 10 illustrated in FIGS. 2 and 2A.

[0024] FIG. 2 is an exploded side-elevational view of an electrochemical cell 10 according to one embodiment of the present invention.

[0025] FIG. 2A is an exploded side-elevational view of the electrochemical cell 10 shown in FIG. 2, but without the gold metallization ring 50.

[0026] FIG. 3 is an exploded side-elevational view of another embodiment of an electrochemical cell 10A according to the present invention.

[0027] FIG. 3A is an exploded side-elevational view of the electrochemical cell 10A shown in FIG. 3, but without the gold metallization ring 50.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] As used herein, the term transparent is defined as a material having the property of transmitting rays of light through its substance so that bodies situated beyond or behind can be distinctly seen.

[0029] The term sapphire is defined as a variety of the mineral corundum, consisting of aluminium oxide (-Al.sub.2O.sub.3) with trace amounts of elements such as iron, titanium, chromium, copper, or magnesium. It is typically blue, but can also occur in yellow, purple, orange, and green colors (parti-sapphires show two or more colors). The only color that sapphire cannot be is redas red colored corundum is called ruby, another corundum variety. Sapphire is a remarkably hard material9 on the Mohs scale (the third hardest mineral, after diamond at 10 and moissanite at 9.5), which makes it uniquely suited for use as a casing material according to the present inventions.

[0030] Turning now to the drawings, FIGS. 1 and 2 illustrate one embodiment of an electrochemical cell 10 according to the present invention. The electrochemical cell 10 comprises a first plate-shaped ceramic substrate 12 that is preferably selected from polycrystalline alumina, 3 mol % YSZ, or a single-crystal alumina, and serves as one half of a casing for the cell. The ceramic substrate 12 is a planar structure forming the lid-side of the casing and comprises a lid substrate peripheral edge 14 meeting an outer major face 16 opposite an inner major face 18.

[0031] Since ceramic substrates are often formed with rough surfaces, which can lead to defective coatings such as interrupted interconnection traces, protrusions which may cause electric shorting between layers, uneven electrochemical reactions leading to poor cycling or dendrite formation, and the like, prior to incorporation into the cell, the lid ceramic substrate 12 is preferably lapped and polished with slurry or ceramic coated grinding paper followed by diamond polishing. This provides a surface roughness that is greater than zero, but less than 50 nm, and more preferably less than 10 nm.

[0032] In the illustrated embodiment, the peripheral edge 14 of the lid substrate 12 comprises opposed lid first and second edge portions 14A and 14B extending to and meeting with lid third and fourth edge portions 14C and 14D. The edge portions are of substantially equal lengths to thereby provide the lid substrate with a square shape in plan-view. In alternate embodiments, the lid substrate 12 has a non-square shape. In any event, the surface area of the outer major face 16 of the lid substrate 12 ranges from about 1 mm.sup.2 to about 10 cm.sup.2.

[0033] The lid substrate 12 is provided with a metallization strip 20 that is a continuous or endless strip of titanium, niobium or other metallic material having a ring-shape with an outer edge that is coincident the outer surface of the first, second, third and fourth depending edge portions 14A, 14B, 14C and 14D. The lid metallization strip 20 has a width that ranges from about 1 m to about 250 m and a thickness that ranges from about 0.1 m to 25 m to define a surrounded open area immediately adjacent to the inner major face 18 of the lid substrate.

[0034] A cathode current collector 22 is deposited as a thin-film layer that contacts the inner major face 18 of the lid substrate 12, spaced inwardly from the lid metallization strip 20. The cathode current collector is preferably a continuous layer of titanium, devoid of perforations, and has a thickness measured outwardly from the base substrate inner major face 18 that ranges from about 0.1 m to about 3 m. Stainless steel, tantalum, platinum, gold, aluminum, cobalt, molybdenum, nickel, copper, nickel, and alloys thereof are also suitable materials for the cathode current collector. A gap of at least about 1 m to about 250 m separates the cathode current collector 22 from the lid metallization strip 20.

[0035] A layer of cathode active material 24 is supported on the cathode current collector 22. The cathode active material 24 preferably extends to and is coincident with the outer peripheral edge of the current collector 22. The cathode active material 24 has a thickness that ranges from about 1 m to about 25 m. Suitable cathode active materials are selected from LiCoO.sub.2, LiMnO.sub.2, LiMn.sub.2O.sub.4, LiFePO.sub.4, Ag.sub.2V.sub.4O.sub.ii, V.sub.2O.sub.5.

[0036] FIG. 1 further shows that the lid substrate 12 is provided with spaced-apart first and second openings 26 and 28. While not shown in the drawings, the lid ceramic substrate 12 is provided with respective perimeter metallizations surrounding the openings 26 and 28. Openings 26, 28 extend completely through the thickness of the lid substrate, and the opening metallizations are of titanium, niobium or other metallic material

[0037] The first opening 26 is aligned over the cathode current collector 22 and the cathode active material 24 and receives a first gold-braze button 30. In a separate brazing step prior to the cathode active material 24 being contacted to the cathode current collector 22, the first gold-braze button 30 forms a hermetic seal with the lid ceramic substrate 12 and has an inner surface that contacts the cathode current collector. An outer surface of the first gold-braze button 30 is substantially co-planar with the lid substrate outer major face 16 or it extends outwardly about 50 m above the major face. That way, the first gold-braze button 30 serves as the positive terminal for the electrochemical cell 10.

[0038] A layer of solid electrolyte 32 (Li.sub.xPO.sub.yN.sub.z) contacts the cathode active material layer 24, opposite the cathode current collector 22 and the gold-braze button 30. The solid electrolyte layer 32 preferably extends to and curves over or around the outer peripheral edge of the cathode active material 24, but it is spaced inwardly from the lid metallization strip 20. The solid electrolyte layer 32 has a thickness that ranges from about 1 m to about 5 m with the curved peripheral edge contacting the inner major face 18 of the lid substrate 12.

[0039] Separately, a second plate-shaped base ceramic substrate 34 is selected from polycrystalline alumina, 3 mol % YSZ, and a single-crystal alumina and serves as the other half of the casing for the electrochemical cell 10. The base ceramic substrate 34 has a peripheral edge 36 meeting an outer major face 38 opposite an inner major face 40.

[0040] The peripheral edge 36 of the base substrate 34 comprises a rim that extends upwardly from the inner major face 40 to thereby provide a recess that is bounded by the opposed first and second upstanding edge portions 36A and 36B extending to and meeting with the third and fourth upstanding edge portions 36C and 36D. The edge portions 36A, 36B, 36C and 36D form a continuous upstanding edge surface 36E aligned along an imaginary plane that is parallel to the outer and inner major faces 38, 40 of the base substrate 34. The edge portions are of substantially equal lengths themselves and are also equal in length to those of the corresponding lid substrate first, second, third and fourth edge portions 14A, 14B, 14C and 14D. This provides the base substrate 34 with a square shape in plan-view that matches the square shape of the lid substrate 12. In any event, the surface area of the outer major face 38 of the base substrate 34 ranges from about 1 mm.sup.2 to about 10 cm.sup.2.

[0041] In alternate embodiments, the base substrate 34 has a non-square shape that matches that of the lid substrate 12. In that respect, those skilled in the art will readily appreciate that the lid and base substrates 12 and 34 of the electrochemical cells according to the present invention can have a myriad of different matching shapes, limited only by the device which the cell is designed to power.

[0042] The upstanding edge surface 36E of the base ceramic substrate is provided with a surrounding metallization 42. The base substrate metallization 42 is a continuous or endless strip of titanium, niobium or other metallic material having a ring-shape with an outer edge that is coincident the outer surface of the first, second, third and fourth edge portions 36A, 36B, 36C and 36D of the base substrate 34. The upstanding edge of the base ceramic substrate has a width that ranges from about 1 m to about 250 m to define a surrounded open recess immediately adjacent to the inner major face 40. The base metallization strip 42 has a width that ranges from about 1 m to 250 m and a thickness 21 that ranges from about 0.1 m to about 25 m.

[0043] FIG. 2 illustrates that the cathode current collector 22, cathode active material 24 and the solid electrolyte layer 32 are provided with respective corner cut-outs 22A, 24A and 32A. These cut-outs reside adjacent to the junction where the second and fourth edge portions 14B, 14D of the lid substrate 12 meet and where the second and fourth edge portions 36B, 36D of the base substrate 34 meet.

[0044] The respective corner cut-outs 22A, 24A and 32A of the cathode current collector 22, cathode active material 24 and the solid electrolyte layer 32 provide a space for an anode current collector 44 as a thin-film layer that contacts the inner major face 18 of the lid substrate 12, spaced from the cathode current collector 22. The anode current collector 44 is a continuous layer, preferably of titanium or copper, that is devoid of perforations, and has a thickness that is comparable to that of the cathode current collector 22. Stainless steel, tantalum, platinum, gold, cobalt, molybdenum, nickel, and alloys thereof are also suitable materials for the anode current collector 44. A gap that ranges from about 1 m to about 250 m separates the anode current collector 44 from the cathode current collector 22.

[0045] A layer of anode active material 46 contacts the solid electrolyte 32 opposite the cathode active material 24. The anode active material 46 has an extending portion 46A that laps over the solid electrolyte 32 to contact the anode current collector 44. The solid electrolyte 32 in turn has an upstanding peripheral edge 32B that physically segregates the anode active material 46 from the cathode active material 24 contacting the cathode current collector 22. The anode active material 46 has a thickness that ranges from about 1 m to about 25 m, and the combined thickness of the anode current collector 44 and the anode active material 46 is somewhat less than the thickness of the anode substrate upstanding peripheral edge 36. Suitable anode active materials include lithium and its alloys and intermetallic compounds including, for example, LiSi, LiSn, LiAl, LiB and LiSiB alloys, and mixtures and oxides thereof.

[0046] In a similar manner as with the gold-braze terminal button 30 that resides in the first opening 26 in the lid substrate 12 and contacts the cathode current collector 22 to thereby serve as the positive terminal for the electrochemical cell 10, a second gold-braze button 48 resides in the second opening 28 in the lid substrate 12. In the brazing step where the first gold-braze button 30 forms a hermetic seal with the lid ceramic substrate 12, the second gold-braze button 48 also forms a hermetic seal with the lid substrate and has an inner surface that contacts the anode current collector 44. An outer surface of the second gold-braze 48 is substantially co-planar with the outer major face 16 of the lid ceramic substrate or it extends outwardly about 50 m above the major face. That way, the second gold-braze button 48 serves as the negative terminal for the electrochemical cell 10.

[0047] During final cell assembly, with the lid substrate 12 supporting the cathode current collector 22, the cathode active material 24, the solid electrolyte 32, the anode current collector 44 and the anode active material 46, the lid and base substrates are moved into registry with each other. An endless gold pre-form 50 having a ring-shape is supported on either the lid metallization strip 20 or the base metallization strip 42. In either configuration, the cathode substrate 12 and the anode substrate 34 are moved together until the lid metallization strip 20 contacts one side of the gold pre-form 50 and the base substrate metallization strip 42 contacts the other side thereof.

[0048] The lid substrate 12 is preferably of a single-crystal alumina (sapphire), which is substantially transparent. The transparent sapphire lid substrate 12 allows that substrate and the base substrate 34 serving as the two case halves to be joined together by laser welding through the transparent ceramic 12 to melt the gold interlayer pre-form 50 into intimate hermetic contact with the opposed lid and base metallizations strips 20 and 42 to thereby hermetically seal the casing. This facilitates fabrication of electrochemical cells in multi-cell arrays/sheets to make the manufacturing process more cost-effective and practical.

[0049] FIG. 2A illustrates an alternate embodiment of the electrochemical cell 10 where the gold pre-form 50 has been eliminated. Instead, the lid and base metallization strips 20 and 42 are laser welded together without the gold pre-form 50. In still a further embodiment, gold is sputtered directly onto at least one or both metallization strips 20, 42, and a laser is preferably used to hermetically weld the lid substrate 12 to the base substrate 34 to thereby hermetically seal the casing.

[0050] In an alternate embodiment, the anode and cathode active materials can be switched with each other. In this embodiment, terminal button 30 conductively contacts the anode current collector and terminal button 48 conductively contacts the cathode current collector.

[0051] FIG. 3 illustrate another embodiment of the electrochemical cell 10A according to the present invention. Electrochemical cell 10A is similar to the electrochemical cell 10 shown in FIGS. 1, 2 and 2A with the exception that instead of being a planar structure, the lid substrate 12 has a depending rim-shaped peripheral edge 14E. The base substrate 34 has the upstanding rim-shaped peripheral edge 36E previously described with respect to FIGS. 2 and 2A. This means that the combined height of edges 14E and 36E of cell 10A in FIG. 3 is substantially equal to the height of the depending edge 14E in FIGS. 2 and 2A. In all other aspects, the cells 10, 10A are substantially similar.

[0052] In a similar manner as with the cell 10 illustrated in FIG. 2A where the lid and base metallization strips 20 and 42 are laser welded together without the gold pre-form 50, FIG. 3A illustrates a similar embodiment, but with the lid substrate 12 having a depending rim-shaped peripheral edge 14E. As before, gold is sputtered directly onto at least one or both the lid and base metallization strips 20, 42, and a laser is preferably used to hermetically weld the lid substrate 12 to the base substrate 34 to thereby hermetically seal the casing.

[0053] Thus, with the outer major faces 16 and 38 of the respective lid and base substrates 12, 34 each having a surface area ranging from about 1 mm.sup.2 to about 10 cm.sup.2, and with the height of the cell as measured from the outer major face 16 of the lid substrate 12 to the outer major face 38 of the base substrate 34 ranging from about 250 m to about 2.5 mm, the cells 10 and 10A of the present invention represent an advancement in electrochemical technology in that they can be built with a total volume that is less than 0.5 cc but, as hermetically sealed enclosures, are capable being implanted for extended periods of time.

[0054] It is appreciated that various modifications to the inventive concepts described herein may be apparent to those of ordinary skill in the art without departing from the spirit and scope of the present invention as defined by the appended claims.