Porous Electrode for Electrochemical Cells

Abstract

A porous electrode and methods of making the same are described. The porous electrode is comprised of a porous conductive layer and an insulating layer, where the pores inside the conductive layer function as mini-containers for the active metals for rechargeable batteries, and the insulating layer covers the top surface of the conductive layer and blocks the sites where active metal dendrites would otherwise preferentially grow. An example of such electrodes is a porous copper foil with top surface coated with polyvinylene difluoride. Electrochemical cells containing the invented electrodes, such as rechargeable lithium battery, sodium battery and aluminum battery, have good cycle life and safety performance.

Claims

1. (canceled)

2. A composition, comprising: a conductive material having a volume and defining pores having an average dimension of between 1 nm and 100 micrometers, wherein the pores have a volume that is no less than 50% of the volume of the conductive material; and an electronically and ionically non-conductive material in contact with and partially covering a surface of the conductive material without covering at least some of the pores of the conductive material.

3. The composition of claim 2, wherein the non-conductive material extends into at least some of the pores of the conductive material.

4. The composition of claim 2, wherein the conductive material has a conductivity of no less than 10.sup.-6 S/cm.

5. The composition of claim 2, wherein the surface of the conductive material is partially covered by the non-conductive material and has a total conductive surface area, and wherein the conductive material has an uncovered conductive surface area that is less than 10% of the total conductive surface area.

6. The composition of claim 5, wherein the uncovered surface area of the conductive material is less than 1% of the total surface area of the conductive material.

7. The composition of claim 2, wherein the conductive material comprises carbon.

8. The composition of claim 2, wherein the conductive material comprises one or more of copper or nickel.

9. The composition of claim 2, wherein the pores have a volume that is more than 75% of the volume of the conductive material.

10. The composition of claim 2, wherein the non-conductive material comprises a polymer.

11. The composition of claim 2, wherein the non-conductive material comprises polyethylene (PE).

12. The composition of claim 2, wherein the non-conductive material comprises one or more of polypropylene (PP), polystyrene (PS), polytetrafluoroethylene (PTFE), polyvinyldifluoride (PVDF), polyacrylic acid (including its esters) (PAA), polyamide (PA), polyester (PES), or poly(terephthalate) (PT).

13. The composition of claim 2, wherein the non-conductive material comprises a ceramic.

14. The composition of claim 2, wherein the non-conductive material comprises LiF.

15. The composition of claim 2, wherein the non-conductive material comprises one or more of Li.sub.2O, Li.sub.2S, Li.sub.2CO.sub.3, Li.sub.3PO.sub.4, LiPO.sub.2F.sub.2, Al.sub.2O.sub.3, AlF.sub.3, AlPO.sub.4, ZnF.sub.2, or Zn.sub.3(PO.sub.4).sub.2.

16. An electrochemical cell, comprising: an electrode comprising the composition of claim 2; an opposite electrode; and an electrolyte positioned between the electrode and the opposite electrode.

17. The electrochemical cell of claim 16, wherein at least some of the pores are partially or completely filled with the electrolyte.

18. The electrochemical cell of claim 16, wherein at least some of the pores contain an active metal.

19. The electrochemical cell of claim 18, wherein the active metal comprises lithium.

20. The electrochemical cell of claim 18, wherein the active metal comprises an active metal selected from the group consisting of sodium, aluminum, magnesium and zinc.

21. A composition, comprising: a conductive material having a volume and defining pores having an average dimension of between 1 nm and 100 micrometers; and an electronically and ionically non-conductive material in contact with and partially covering a surface of the conductive material without covering at least some of the pores of the conductive material, wherein the non-conductive material extends into at least some of the pores of the conductive material.

22. A composition, comprising: a conductive material having a volume and defining pores having an average dimension of between 1 nm and 100 micrometers; and an electronically and ionically non-conductive material in contact with and partially covering a surface of the conductive material without covering at least some of the pores of the conductive material, wherein the surface of the conductive material is partially covered by the non-conductive material and has a total conductive surface area, and wherein the conductive material has an uncovered conductive surface area that is less than 10% of the total conductive surface area.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 illustrates cross-sectional (left) and top (right) views of a part of the porous electrode of an embodiment of the present invention, where the insulation layer is on top of the conductive layer with random pores. 1: an uncovered top conductive material surface; 2: insulating layer; 3: a pore close to the insulating surface side of the porous conductive layer; 4: inner conductive material.

[0019] FIG. 2 illustrates cross-sectional (left) and top (right) views of a part of the porous electrode of an embodiment of the present invention, where the insulation layer extends deeper into the conductive layer with random pores. 1: an insulation material covered on top of the conductive material surface; 2: an uncovered top conductive material surface; 3: a pore close to the insulating surface side of the porous conductive layer; 4: inner conductive material without insulation coverage; Line AB: thickness of the space containing the insulation material; Line AC: thickness of the total conductive layer.

[0020] FIG. 3 illustrates cross-sectional (left) and top (right) views of a part of the porous electrode of an embodiment of the present invention, where the insulation layer is on top of the conductive layer with patterned pores. 1: an uncovered top conductive material surface; 2: insulating layer; 3: a pore close to the insulating surface side of the porous conductive layer; 4: inner conductive material.

[0021] FIG. 4 illustrates a cross-sectional view of a porous electrode of an embodiment of the present invention, where active metal is sandwiched between additional current collector and an above-mentioned structure. 1: insulating layer (uncovered top conductive surface may or may not exist); 2: porous conductive layer; 3: active metal layer (lithium, zinc, aluminum, sodium, etc.); 4: additional current collector.

[0022] FIG. 5 illustrates a cross-sectional view of a porous electrode of an embodiment of the present invention, where active metal is embedded inside the pores of an above-mentioned structure without additional current collector. 1: insulating layer (uncovered top conductive surface may or may not exist); 2: porous conductive layer; 3: Active metal (lithium, zinc, aluminum, sodium, etc.) impregnated inside the pores of the porous conductive layer. No additional current collector is needed.

[0023] FIG. 6 illustrates a cross-sectional view of a porous electrode of an embodiment of the present invention, where an above-mentioned structure and additional current collector are combined. 1: insulating layer (uncovered top conductive surface may or may not exist); 2: porous conductive layer; 3: active metal (lithium, zinc, aluminum, sodium, etc.) impregnated inside the pores of the porous conductive layer; 4: additional current collector.

[0024] FIG. 7 illustrates a cross-sectional view of a porous electrode of an embodiment of the present invention, 1: insulating layer (uncovered top conductive surface may or may not exist); 2: porous conductive layer; Active metal (lithium, zinc, aluminum, sodium, etc.) would be deposited in-situ after assembling of the electrochemical cell. 3: additional current collector.

[0025] FIG. 8 illustrates a cross-sectional view of the active material assembly of an electrochemical cell of an embodiment of the present invention. 1: insulating layer (uncovered top conductive surface may or may not exist); 2: porous conductive layer; active metal (lithium, zinc, aluminum, sodium, etc.) would be deposited in-situ after assembling of the electrochemical cell. 4: additional current collector. 5: separator layer. 6: cathode layer.

[0026] FIG. 9 illustrate a cross-sectional view of the active material assembly of an electrochemical cell of an embodiment of the present invention. 1: insulating layer, also functions as the separator layer (uncovered top conductive surface may or may not exist); 2: porous conductive layer; active metal (lithium, zinc, aluminum, sodium, etc.) would be deposited in-situ after assembling of the electrochemical cell. The pores may be partially or completely filled with gel electrolyte or solid electrolyte. 6: cathode layer.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

[0027] The performance and safety problems caused by dendrite growth of the active metal of a electrochemical cell where a metal anode is used or formed, such as rechargeable lithium metal batteries, rechargeable sodium batteries, lithium air batteries, zinc air batteries, and aluminum air batteries, may, according to the present invention, be solved by the use of a porous conductive electrode comprising an insulating surface layer.

Porous Electrodes

[0028] One aspect of the present invention pertains to a porous electrode for use in an electrochemical cell, wherein the porous electrode comprises: [0029] (i) a porous conductive layer where active materials, such as lithium, magnesium, sodium, aluminum or zinc, is present or can be incorporated; and [0030] (ii) an insulating layer made of material that is both electronically and ionically non-conductive, wherein the insulating material partially covers the conductive surface of the above porous conductive layer.

[0031] The porous electrode of embodiments of the present invention may further comprise other components, for example, additional current collector, gel electrolyte, solid electrolyte, and/or active metal.

Porous Conductive Layer

[0032] The porous conductive layer of the electrode of embodiments of the present invention functions as: (i) the current collector, where electric current can flow in and out from; (ii) the substrate, where the active metal can be deposited to or stripped from; and (iii) the container, where the active metal can be contained inside and dendrite growth can be blocked.

[0033] The porous conductive layer of the electrode of embodiments of the present invention is made of interconnected conductive material. A conductive material is defined here as any substance that has an electronic conductivity of no less than 10-.sup.6 Siem at ambient conditions, for example, copper, nickel, sodium, potassium, cesium, beryllium, magnesium, calcium, titanium, vanadium, iron, carbon, conductive polymers, such as doped polythiophenes, conductive ceramics, such as doped indium tin oxide, or any combination of conductive substance. The conductive material may be in any form of shape, such as wire, ribbon, tube, mesh or foam, and be arranged in a regular pattern, in mixed patterns, or in a random fashion. Preferably, the conductive material is selected from copper, nickel, iron, carbon or their composites, and the preferable patterns will be those economical to make, such as random, circular, triangular, and rectangular.

[0034] The pores in the porous conductive layer of embodiments of the present invention may occupy a significant volume of the porous conductive layer. Preferably, the pore volume is no less than 50% of the total volume of the porous conducive layer. More preferably, the pore volume is no less than 75% of the total volume of the porous conducive layer.

[0035] The thickness of the porous conductive layer is not particularly limited. For practical reasons, the thickness is not to be over 10 cm. For portable electronic applications, the thickness is preferably not to be over 1 cm. For various applications, the thickness can be, for example, 10 cm, 1 cm, 1 mm, 100 .Math.m, 10 .Math.m, 1 .Math.m, 0.1 .Math.m or any number in between.

Insulating Layer

[0036] The insulating layer of the electrode of embodiments of the present invention is made of material that is both electronically and ionically non-conductive. “Non-conductive” means very low conductivity, for example, less than 10-.sup.6 Siem at ambient conditions. The insulating material partially covers the surface of the conductive material of the above porous conductive layer and inhibits preferential deposition and growth of the active metal on the outside surface of the conductive layer while leaving the pores open for the flow of electrolyte and/or ions.

[0037] The insulating material that is contained in the insulating layer of the electrode of embodiments of the present invention can be any non-conductive materials, such as polymers, oxides, sulfides, fluorides, chlorides, carbonates, nitrides, silicates, borates, aluminates, sulfates, phosphates and mixed compounds. Mixed compounds are the ones with more than one cation or more than one negatively charged element in its structure, such as LiAlMgF4 and LixPOyNz, LixPOyFz, where x,y,z = ⅓, ½, 1, 1.5, 2 or 3, provided the charge is balanced for the formula. Specific examples of the non-conductive material include polyethylene (PE), polypropylene (PP), polystyrene (PS), polytetrafluoroethylene (PTFE), polyvinyldifluoride (PVDF), polyacrylic acid (including its esters) (PAA), polyamide (PA), poly(terephthalate) (PT), LiF, LizO, LizS, LizCO3, LhPO4, LiPO2F2, AhO3, AlF3,AlPO4, ZnF2, Zn3(PO4)z and any combination of the above-mentioned compounds. Material with lower conductivity, good adhesion and compatibility with other components of the electrochemical cell is preferred.

[0038] The thickness of the space containing the insulating material depends on the porous conductive layer. Generally speaking, the thickness of the space containing the insulating material is less than the thickness of the conductive layer. For practical reasons, the thickness of the space containing the insulating material is not to be over 1 cm. For portable electronic applications, the thickness is preferably not to be over 1 mm. For various applications, the thickness can be, for example, 1 cm, 1 mm, 0.1 mm, 10 .Math.m, 1 .Math.m, 0.1 .Math.m, 10 nm.

Poresoftheporouselectrode

[0039] The pores in the porous conductive layer of embodiments of the present invention are the space where an active material can be stored. The pores can be in the form of anything, for example, random-shaped space, rectangular prism, hexagonal prism, cylinder, sphere, pyramid or a combination of any form. The dimensions of the pores close to the insulating layer and the interface is of particular importance. The average dimension of a pore close to the insulating surface side of the porous conductive layer is preferably no more than 100 .Math.m; more preferably, the average dimension of the pores close to the insulating surface side of the porous conductive layer is no more than 10 .Math.m; still more preferably, the average dimension of the pores close to the insulating surface side of the porous conductive layer is no more than 5 .Math.m. On the other hand, the average dimension of the pores close to the insulating surface side of the porous conductive layer is preferably no less than 1 nm; more preferably, the average dimension of the pores close to the insulating surface side of the porous conductive layer is preferably no less than 5 nm. Still more preferably, the average dimension of the pores close to the insulating surface side of the porous conductive layer is no less than 10 nm.

[0040] The pores in the porous conductive layer of embodiments of the present invention occupy a significant volume of the porous conductive layer, so more active materials can be stored in a given electrode volume. Preferably, the pore volume is no less than 50% of the total volume of the porous conducive layer. More preferably, the pore volume is no less than 75% of the total volume of the porous conducive layer.

[0041] The pores in the porous conductive layer of embodiments of the present invention may be empty, partially filled or filled, with active materials, with liquid electrolytes, with gel electrolyte, with solid electrolyte, with composite electrolyte, or any combination of the above.

Uncovered Top Conductive Surface of the Porous Conductive Layer

[0042] The top conductive surface of the porous conductive layer broadly refers to the surface of the conductive material that is close to or in contact with the insulating layer and faces toward the direction of the insulating layer. The exact thickness of the conductive layer that is considered part of the top conductive surface may depend on the diameter of the pores of the conductive layer that borders the insulating layer. Generally, the bigger the pore diameter, the thicker the portion of the conductive layer would be considered containing the top conductive surface. For example, for a pore diameter of 2 .Math.m, the surface of the conductive material that locates within 1.5 .Math.m of the porous conductive layer bordering the insulating layer may be considered the top conductive surface; for a pore diameter of 5 .Math.m, the surface of the conductive material that locates within 2.5 .Math.m of the porous conductive layer bordering the insulating layer may be considered the top conductive surface. Any uncovered top conductive surface would provide preferential sites for dendrite growth. Ideally, the insulating material should cover the entire top conductive surface of the porous conductive layer. Practically, there may be some uncovered top conductive surface left.

[0043] The insulating material may cover only the very top of the conductive layer, whereas the uncovered top surface area of the conductive element is no more than 50% of the available top surface area of the conductive elements. Preferably, the uncovered top surface area of the conductive element is less than 10% of the available top surface area of the conductive elements. More preferably, the uncovered top surface area of the conductive element is less than 1% of the available top surface area of the conductive elements.

[0044] The insulating material coverage may extend farther to the inside of the conductive layer, wherein the thickness of the covered portion of the conductive layer is preferably less than 50% of the total conductive layer thickness. More preferably, the thickness of the covered portion of the conductive layer is less than 25% of the total conductive layer thickness.

Optional Components of the Porous Electrode

[0045] Active metal, such as lithium, sodium, zinc, magnesium or aluminum, may or may not be present in the porous electrode. When the active metal is not present, the active metal may be deposited into the electrode after assembly of the electrochemical cell. When the active metal is present, it may be either: stacked under the porous conductive layer, or impregnated inside the pores of the porous conductive layer.

[0046] Additional current collectors may or may not be present. When it is present, it can be either in the form of solid sheet, mesh or foam.

Method of Forming the Porous Electrode and Use Thereafter

[0047] Another aspect of the present invention pertains to the method of forming the porous electrode. The layers of the electrode of embodiments of the present invention may be formed by any of the methods, such as, but not limited to physical deposition methods, chemical vapor deposition methods, electrostatic spray deposition, mechanical forming methods including extrusion, winding and molding, chemical or electrochemical stripping or plating, or printing methods including 2D and 3D printing. Low cost methods are generally preferred.

[0048] One more aspect of the present invention pertains to any use of the porous electrode. In one or more embodiments of the present invention, the porous electrode is incorporated as an anode or part of the anode into an electrochemical cell that includes an anode, a cathode, a separator and an electrolyte. In an alternative embodiment of the present invention, the porous electrode is incorporated as an anode or part of the anode into an electrochemical cell that includes an anode, a cathode, and an electrolyte.

[0049] In an alternative embodiment of the present invention, lithium metal is attached to the porous electrode before being assembled into an electrochemical cell.

[0050] In alternative embodiments of the present invention, lithium or sodium metal is deposited in-situ to the porous electrode after the electrode is assembled into an electrochemical cell.

[0051] The electrode of embodiments of the present invention when incorporated into an electrochemical cell enables the active metal to be stored inside the pores and inhibit the preferential growth of active metal dendrite during charging. The electrochemical cells containing embodiments of the present invention have high energy density, good cycle life, experience little volume change during operation, and/or have improved safety.

EXAMPLES

[0052] Several embodiments of the present invention are described in the following examples, which are offered by way of illustration and not by way of limitation.

[0053] Example 1: In one embodiment, a thin copper foil is first press fixed onto a platinum foil face to face and then attached to the working terminal of a potentiostat/galvanostat. The foils are then immersed into a CuSO4/H2SO4 aqueous solution. After setting up the platinum counter electrode and Ag/AgCl reference electrode, positive current pulse is applied to the copper foil to randomly strip copper and thus a porous copper foil is obtained. The perforated copper foil is then separated from the platinum foil and one side protected with a Scotch tape and attached again to the working terminal of the potentiostat/galvanostat. Negative current pulse is then applied to the copper foil and random copper is grown onto the perforated copper foil. Thus a porous conductive layer made of copper is obtained. The porous copper foil is introduced into a physical vapor deposition chamber as the substrate together with a LiF target. After the desirable vacuum is obtained, LiF is deposited onto the copper mesh. A porous electrode as illustrated in FIG. 1 is thus prepared.

[0054] Example 2: In an alternative embodiment, a loose fine copper wire pile with thickness of 10 cm is dipped into a melted PE pan of 1 cm deep. Then the copper wire was allowed to cool slowly so that PE uniformly covers one tenth of the copper wire piles thickness. The copper wire pile was then pressed into a thickness of 1 cm. Thus a porous electrode as illustrated in FIG. 2 is prepared.

[0055] Example 3: In an alternative embodiment, a nickel mesh with average top layer pore size less than 10 .Math.m is introduced into a physical vapor deposition chamber as the substrate together with a LiF target. After the desirable vacuum is obtained, LiF is deposited onto the nickel mesh. Thus a porous electrode as illustrated in FIG. 3 is prepared.

[0056] Example 4: In an alternative embodiment, a brass alloy sheet of 50 .Math.mis immersed in a IM HCl solution until no gas bubble is generated. The sheet is then connected to the ground terminal of an electrostatic spray deposition chamber and is heated to 250° C. A 10 kV is applied on the metal needle connected to a vial of PVDF solution and the copper sheet is coated for 5 minutes. Thus a porous electrode as illustrated to FIG. 1 is prepared.

[0057] Example 5: In an alternative embodiment, a porous electrode from example 3 is stacked on top of a lithium foil and copper foil. Thus a porous electrode as illustrated in FIG. 4 is prepared.

[0058] Example 6: In an alternative embodiment, a porous electrode from example 3 is introduced into a vacuum chamber and placed upside down as the substrate. Lithium was then deposited onto the bottom surface and pores of the nickel mesh. Thus a porous electrode as illustrated in FIG. 5 is prepared.

[0059] Example 7: In an alternative embodiment, a porous electrode from example 6 stacked onto a nickel foil. Thus a porous electrode as illustrated in FIG. 6 is prepared.

[0060] Example 8: In an alternative embodiment, a porous electrode from example 3 is stacked on top of copper foil. Thus a porous electrode as illustrated in FIG. 7 is prepared.

[0061] Example 9: In an alternative embodiment, a porous electrode from example 3 is stacked on top of an aluminum foil and nickel foil. Thus a porous electrode as illustrated in FIG. 4 is prepared.

[0062] Example 10: In an alternative embodiment, a porous electrode from example 3 is stacked on top of a zinc foil and nickel foil. Thus a porous electrode as illustrated in FIG. 4 is prepared.

[0063] Example 11: In an alternative embodiment, a porous electrode from example 7 is cut into a rectangular shape with a tab, then stacked with a PP separator and an LiNio.6Coo.2Mno.2O2 based cathode sheet of the matching shape and size. Thus an active material assembly stack as illustrated in FIG. 8 is prepared. The stack is then partially sealed inside a pouch bag with attached tabs sticking out. IM LiPF6 in EC/EMC 3/7 v is then added to the pouch bag and the pouch bag is finally vacuum sealed in a dry room. An electrochemical cell of an embodiment of the present invention is thus prepared.

[0064] Example 12: In an alternative embodiment, a porous electrode from example 3 is cut into a rectangular shape with a tab, then stacked with an LiFePO4 based cathode sheet of the matching shape and size. Thus an active material assembly stack as illustrated in FIG. 9 is prepared. The stack is then partially sealed inside a pouch bag with attached tabs sticking out. 2M LiFSI in EC/PC 1/1v is then added to the pouch bag and the pouch bag is finally vacuum sealed in a dry room. An electrochemical cell of an embodiment of the present invention is thus prepared.

[0065] Example 13: In an alternative embodiment, a porous electrode from example 3 is cut into a circular shape with a tab, then stacked with an LiMn2O4 based cathode sheet of the matching shape and size. Thus an active material assembly stack as illustrated in FIG. 9 is prepared. The stack is then partially sealed inside a pouch bag with attached tabs sticking out. 1.2M LiPF6 in EC/EMC 3/7 vis then added to the pouch bag and the pouch bag is finally vacuum sealed in a dry room. An electrochemical cell of an embodiment of the present invention is thus prepared.

[0066] Example 14: In an alternative embodiment, a porous electrode from example 3 is cut into a rectangular shape with a tab, then stacked with an LiCoO2 based cathode sheet of the matching shape and size. Thus an active material assembly stack as illustrated in FIG. 9 is prepared. The stack is then partially sealed inside a pouch bag with attached tabs sticking out. 3M LiPF6 in EC/EMC 1/1 vis then added to the pouch bag and the pouch bag is finally vacuum sealed in a dry room. An electrochemical cell of an embodiment of the present invention is thus prepared.

[0067] Example 15: In an alternative embodiment, a porous electrode from example 3 is cut into a rectangular shape with a tab, then stacked with a Na2FePO4F based cathode sheet of the matching shape and size. Thus an active material assembly stack as illustrated in FIG. 9 is prepared. The stack is then partially sealed inside a pouch bag with attached tabs sticking out. 2M NaPF6 in EC/EMC 1/1 vis then added to the pouch bag and the pouch bag is finally vacuum sealed in a dry room. An electrochemical cell of an embodiment of the present invention is thus prepared.

[0068] Example 16: In an alternative embodiment, a porous electrode from example 3 is cut into a rectangular shape with a tab, then stacked with a LiCoO2 based cathode sheet of the matching shape and size. Thus an active material assembly stack as illustrated in FIG. 9 is prepared. The stack is then partially sealed inside a pouch bag with attached tabs sticking out. IM LiPF6 in EC/EMC 1/1 v solution with 6%wt (by weight) of methyl methacrylate (MMA) and 0.1%wt AIBN (initiator) is then added to the pouch bag and the pouch bag is finally vacuum sealed in a dry room. The pouch bag is then stored at 60° C. for 12 hours and so that MMA is polymerized and the electrolyte in the pores becomes solid. An electrochemical cell of an embodiment of the present invention is thus prepared.

[0069] The electrochemical cells that contain embodiments of the present invention have good cycle life, experience small volume change during operation, and/or have good safety performance.