Rechargeable Battery and Electrolysis Method of Making the Same

Abstract

A block or graft copolymer coated lithium metal electrode provides the negative electrode and the solid electrolyte for a rechargeable lithium metal battery that further includes a positive electrode. Optionally, the positive electrode includes elemental sulfur in a conductive matrix. The copolymer coated lithium metal electrode may be manufactured by a process involving electroplating lithium metal through a copolymer coated conductive substrate, for which the copolymer coated conductive substrate has been prepared by coating the conductive substrate in a copolymer solution followed by evaporating the solvent. Alternatively, a lithium metal electrode may be coated directly with copolymer. Rechargeable lithium batteries according to embodiments of the invention have improved cycle life and combustion resistance compared to lithium metal batteries manufactured by conventional methods.

Claims

1. A rechargeable lithium metal battery comprising: a negative electrode, the negative electrode having a conductive substrate coated with a layer of lithium metal, the layer of lithium metal having an inner face and an outer face, the inner face contacting the conductive substrate; a positive electrode; a solid electrolyte comprising a lithium ion conductive copolymer coating the outer face of the lithium metal, the lithium ion conductive copolymer having microphase separated first domains and second domains, each domain above its respective glass transition temperature, T.sub.g, the first domains formed from lithium ion solvating segments and providing continuous conductive pathways for the transport of lithium ions and the second domains formed from second segments immiscible with the first segments, the copolymer being selected from the group consisting of a block copolymer and a graft copolymer; and a lithium salt dispersed within the solid electrolyte; wherein the solid electrolyte is disposed between the negative electrode and the positive electrode, and is in direct physical contact with both the layer of lithium metal and the cathode, wherein the lithium metal battery is configured to interact with an external circuit so that during discharge: the layer of lithium metal decreases in thickness, and the copolymer coating conforms its shape to continue to cover the thinning layer of lithium metal, and to accommodate any volume changes that may occur at the positive electrode, wherein the lithium metal battery is configured to interact with the external circuit so that during electrolytic recharging: a voltage applied across the external circuit causes the layer of lithium metal to grow in thickness, and the copolymer coating to adjust shape to continue to cover the growing layer of lithium metal, and to accommodate any volume changes that may occur at the positive electrode.

2. The rechargeable lithium metal battery of claim 1 wherein the positive electrode comprises elemental sulfur.

3. The rechargeable lithium metal battery of claim 1 wherein the lithium ion solvating segments comprise poly(oxyethylene).sub.n side chains, where n is an integer between 4 and 20.

4. The rechargeable lithium metal battery of claim 1 wherein the copolymer is a block copolymer.

5. The rechargeable lithium metal battery of claim 1 wherein the copolymer is a graft copolymer.

6. A process for manufacturing a lithium metal electrode coated with a lithium ion conductive copolymer, comprising: preparing a coating solution of a lithium salt and a block or graft copolymer in a cosolvent, the copolymer having first segments and second segments, each segment above its respective glass transition temperature, T.sub.g, the first segments formed from lithium ion solvating groups and the second segments being immiscible with the first segments, wherein each segment of the block or graft copolymer is separately soluble in the cosolvent; coating a first conductive substrate with the coating solution; evaporating the cosolvent from the coated conductive substrate so that the first conductive substrate is coated with a first layer of the lithium ion conductive copolymer, the lithium ion conductive copolymer forming microphase separated first domains and second domains, the first domains formed from the first segments and providing continuous conductive pathways for transport of lithium ions and the second domains formed from the second segments; configuring an electrolytic cell with an anode; configuring the copolymer coated first conductive substrate as a cathode in the electrolytic cell, the electrolytic cell containing a lithium salt solution interposed between the anode and the copolymer coated first conductive substrate; applying a voltage across the first conductive substrate and the anode, causing a first layer of lithium metal to deposit on the surface of the first conductive substrate, sandwiched between the first conductive substrate and the first layer of lithium ion conductive copolymer coating, the first layer of lithium ion conductive copolymer coating adjusting shape to continue to cover the growing layer of lithium metal, thereby forming the lithium metal electrode coated with the first layer of lithium ion conductive copolymer.

7. The process according to claim 6, wherein the anode is prepared by a process comprising: depositing a second layer of lithium metal on a second conductive substrate; coating the second layer of lithium metal with the coating solution; evaporating the cosolvent from the coated second layer of lithium metal so that the second layer of lithium metal is coated with a second layer of lithium ion conductive copolymer, the lithium ion conductive copolymer forming microphase separated first domains and second domains, the first domains formed from the first segments and providing continuous conductive pathways for transport of lithium ions and the second domains formed from the second segments, thereby obtaining the anode comprising the second layer of lithium metal sandwiched between the second conductive substrate and the second layer of lithium ion conductive copolymer.

8. A lithium metal electrode coated with lithium ion conductive copolymer manufactured according to the process of claim 6.

9. A lithium metal electrode coated with lithium ion conductive copolymer manufactured according to the process of claim 7.

10. The lithium metal electrode coated with lithium ion conductive copolymer according to claim 8, wherein the lithium ion conductive copolymer is a block copolymer.

11. The lithium metal electrode coated with a lithium ion conductive copolymer according to claim 8, wherein the lithium ion conductive copolymer is a graft copolymer.

12. The lithium metal electrode coated with a lithium ion conductive copolymer according to claim 8, wherein the first segments comprise poly(oxyethylene).sub.n side chains, where n is an integer between 4 and 20.

13. The lithium metal electrode coated with a lithium ion conductive copolymer according to claim 12, wherein the second segments comprise poly(alkyl methacrylate).

14. The lithium metal electrode coated with lithium ion conductive copolymer according to claim 12, wherein the second chains comprise poly(dimethyl siloxane).

15. The lithium metal electrode coated with lithium ion conductive copolymer according to claim 8, the lithium ion conductive copolymer being poly[(oxyethylene).sub.9 methacrylate]-b-poly(butyl methacrylate) (POEM-b-PBMA).

16. The lithium metal electrode coated with lithium ion conductive copolymer according to claim 8, the lithium ion conductive copolymer being poly[(oxyethylene).sub.9 methacrylate]-g-poly(dimethyl siloxane).

17. The lithium metal electrode coated with lithium ion conductive copolymer according to claim 15, wherein the ratio of POEM to PBMA is between 55:45 and 70:30 on a molar basis.

18. The lithium metal electrode coated with a lithium ion conductive copolymer according to claim 8, wherein during the manufacturing process the contents of the electrolytic cell are covered by a blanketing atmosphere, the blanketing atmosphere having no more than 10 ppm of lithium reactive components on a molar basis.

19. A process for manufacturing a lithium metal electrode comprising: inserting a first conductive substrate as a cathode in an electrolytic cell; inserting a second conductive substrate coated with lithium metal as an anode in the electrolytic cell; providing a lithium ion conducting copolymer separating and surrounding the first conductive substrate and the anode, the lithium ion conductive copolymer being a graft or block copolymer with first segments and second segments, each segment above its respective glass transition temperature, T.sub.g, the first segments formed from lithium ion solvating groups and the second segments being immiscible with the first segments; applying a voltage across the conductive substrate and the anode, causing lithium metal to deposit on the surface of the first conductive substrate, the lithium ion conductive copolymer adjusting shape to cover a growing layer of lithium metal on the first conductive substrate, and a thinning layer of lithium metal on the second conductive substrate, thereby forming the lithium metal electrode comprising the first conductive substrate and the lithium metal coating the first conductive substrate, wherein the lithium metal on the first conductive substrate is more pure than the lithium metal on the second conductive substrate.

20. A rechargeable lithium metal battery comprising: a positive electrode and a negative electrode, the negative electrode having a layer of lithium metal coated with a layer of lithium ion conductive copolymer, the negative electrode manufactured according to the process of claim 6, wherein the lithium ion conductive copolymer is disposed between the negative electrode and the positive electrode, and is in direct physical contact with both the positive electrode and the layer of lithium metal, wherein the lithium metal battery is configured so that during discharge: the layer of lithium metal decreases in thickness, and the copolymer coating conforms its shape to continue to cover the thinning layer of lithium metal, wherein the lithium metal battery is configured so that during electrolytic recharging: the layer of lithium metal grows in thickness, and the copolymer coating conforms its shape to continue to cover the growing layer of lithium metal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The foregoing features of embodiments will be more readily understood by reference to the following detailed description, taken with reference to the accompanying drawings, in which:

[0029] FIG. 1 illustrates the structural features of block and graft copolymers.

[0030] FIG. 2 shows steps in manufacturing a rechargeable lithium metal battery with a copolymer coated lithium negative electrode according to embodiments of the invention.

[0031] FIG. 3a provides a cross-sectional view of a copolymer coated conductive substrate prior to electroplating lithium metal onto the substrate according to embodiments of the invention.

[0032] FIG. 3b provides a top view of a copolymer coated conductive substrate prior to electroplating lithium metal onto the substrate according to embodiments of the invention.

[0033] FIG. 4a provides a cross-sectional view of the conductive substrate of FIGS. 3a and 3b after electroplating lithium metal onto the substrate to form a lithium metal layer sandwiched between the conductive substrate and the copolymer coating according to embodiments of the invention.

[0034] FIG. 4b provides a top view of the conductive substrate of FIG. 4a according to embodiments of the invention.

[0035] FIG. 5a provides a cross-sectional view of a lithium metal coated conductive substrate prior to coating with copolymer according to embodiments of the invention.

[0036] FIG. 5b provides a top view of a lithium metal coated conductive substrate prior to coating with copolymer according to embodiments of the invention.

[0037] FIG. 6a provides a cross-sectional view of the lithium metal coated conductive substrate of FIGS. 5a and 5b after coating with copolymer according to embodiments of the invention.

[0038] FIG. 6b provides a top view of the lithium metal coated conductive substrate of FIGS. 5a and 5b after coating with copolymer according to embodiments of the invention.

[0039] FIG. 7 shows an electrolytic cell suitable for manufacturing the copolymer coated lithium metal electrode according to embodiments of the invention, prior to electroplating of lithium onto the conductive substrate. In this cell the lithium salt solution is replenished by the flow of lithium salt solution into the cell.

[0040] FIG. 8 shows the electrolytic cell of FIG. 7 following electroplating of lithium onto the conductive substrate.

[0041] FIG. 9 shows an electrolytic cell suitable for manufacturing the copolymer coated lithium metal electrode according to embodiments of the invention, prior to electroplating of lithium onto the conductive substrate. In this cell lithium ion in the lithium salt solution is replenished by oxidation of lithium at the lithium positive electrode.

[0042] FIG. 10 shows the electrolytic cell of FIG. 9 following electroplating of lithium onto the conductive substrate.

[0043] FIG. 11 shows an electrolytic cell with a copolymer solid electrolyte suitable for electroplating lithium metal onto a conductive substrate according to embodiments of the invention.

[0044] FIG. 12 shows the electrolytic cell of FIG. 11 following electroplating of lithium metal onto the conductive substrate.

[0045] FIG. 13 shows a cross-section of a rechargeable battery constructed with the copolymer coated lithium metal electrode according to an embodiment of the invention. The battery in this embodiment includes a single positive electrode.

[0046] FIG. 14 shows a cross-section of a rechargeable battery constructed with the copolymer coated lithium metal electrode according to an embodiment of the invention. The battery in this embodiment includes two positive electrodes.

[0047] FIG. 15 shows an exterior view of the rechargeable battery embodied in FIG. 11.

[0048] FIG. 16 shows an exterior view of the rechargeable battery embodied in FIG. 12.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0049] Definitions. As used in this description and the accompanying claims, the following terms shall have the meanings indicated, unless the context otherwise requires:

[0050] A “solid electrolyte” is solid material at room temperature which allows ion transport between electrodes of an electrolytic or galvanic cell.

[0051] A “block copolymer” is a polymer with blocks made up of one monomer alternating with blocks of another monomer along a linear polymer strand.

[0052] A “graft copolymer” is a polymer which has a backbone strand made up of one type of monomer and branches of a second monomer.

[0053] A “segment” is a block for a block copolymer and a side chain or backbone for a graft copolymer.

[0054] “Microphase separation” of a block or graft copolymers occurs when polymer segments segregate into domains according to their monomeric units.

[0055] A “cosolvent” for different monomers is a solvent capable of dissolving each of the different segments of a block or graft copolymer.

[0056] A “common solvent” is identical with a “cosolvent.”

[0057] A “negative electrode” functions as an anode in a galvanic cell and as a cathode in an electrolytic cell.

[0058] A “positive electrode” functions as a cathode in a galvanic cell and as an anode in an electrolytic cell.

[0059] The tendency for lithium metal batteries to form dendrites can lead to electrical shorting. The common use of flammable organic electrolytes for such batteries exacerbates the potential of such shorts to lead to fires and explosions. Solid electrolytes have potential for eliminating these safety concerns by reducing dendrite formation and by avoiding the use of flammable organic electrolytes.

[0060] The ideal solid electrolyte has the ion transport properties of a liquid, the ability to preferentially transport desired ionic species, while blocking the transport of undesirable species. The ideal solid electrolyte has low flammability, and a resistance to dendrite formation. The ideal solid electrolyte has the mechanical properties of a solid, but can undergo molecular rearrangements to grow, to shrink, and to accommodate volume changes associated with positive and negative electrodes while still maintaining physical contact with both positive and negative electrodes.

[0061] Lithium sulfur (Li—S) batteries using sulfur as the positive electrode offer higher specific capacity than the lithium intercalation compounds that currently dominate the market. However, complex polysulfide species produced upon the reduction of elemental sulfur dissolve in the organic electrolytes typically used in lithium batteries, resulting in reduced cycle life due to the “polysulfide shuttle” effect.

[0062] Consequently, another desirable feature of a solid electrolyte for lithium metal batteries is the ability to block the “polysulfide shuttle” between the positive and negative electrodes that reduces battery performance and cycle life of Li—S batteries.

[0063] As illustrated in FIG. 1, block copolymers 5 of embodiments of the invention have alternating blocks of monomer units, here designated by type “A” and type “B” monomers. In contrast graft copolymers 15 embodiments have a backbone made up of type “A” monomers and side-chains of type “B” monomers. The block copolymer 5 of FIG. 1 is a di-block polymer (AB) with one block of A and one block of B. In other embodiments, block copolymers can be tri-block (ABA or BAB) or multi-block copolymers.

[0064] Block copolymers with blocks of immiscible groups and graft copolymers with immiscible backbone and side-chain segments as embodied in this application provide a solid electrolyte with the ion transport properties of a liquid, and with the ability to preferentially transport desired ionic species, while blocking the transport of undesirable species. The thus embodied solid electrolyte has low flammability, and a resistance to dendrite formation. The thus embodied solid electrolyte has the mechanical properties of a solid, but can undergo molecular rearrangements to grow, to shrink, and to accommodate volume changes associated with positive and negative electrodes while still maintaining physical contact with both positive and negative electrodes.

[0065] Consequently, block copolymers with blocks of immiscible groups and graft copolymers with immiscible backbone and side-chain segments as embodied in this application provide a solid electrolyte technology for lithium metal batteries in general and Li—S batteries in particular, promising improved safety and performance, longer battery life, and a solution to the “polysulfide shuttle” problem. In short, block copolymers and graft copolymers as embodied in this application provide the key features of an ideal solid electrolyte for lithium metal batteries.

[0066] A block or graft copolymer as embodied in this application has one or more “A” segments of more hydrophilic lithium salt solvating polymers interspersed with one or more “B” segments of more hydrophobic polymers. All segments are above their respective glass transition temperatures, T.sub.g. Material incorporating such a block or graft copolymer will microphase separate into locally segregated nanoscale domains of “A” and “B” segments. The resultant ordering of segments in turn confers conformational rigidity to the material even though all of the constituents are segmentally liquid. For suitable A:B ratios, the A segments form continuous lithium ion solvating channels. For lithium ion solvating segments having suitably high local chain mobility, high lithium conductivity allows the directed flow of lithium ions through the copolymer upon application of an electric field.

[0067] Dissolving the block or graft copolymer and a lithium salt in a suitable common solvent (cosolvent) that is capable of dissolving both A and B segments allows ready processing of the polymer with solvated lithium ions by conventional coating methods. For example, electrodes can be directly coated with a lithium ion conductive block or graft copolymer electrolyte by dipping the electrode in a solution of lithium salt and copolymer dissolved in cosolvent, and allowing the cosolvent to evaporate. Such an electrode can then be directly used in a battery or electrolytic cell. In this manner, as described below, lithium metal electrodes can be coated with lithium ion conducting block or graft copolymer solid electrolytes for use in solid state batteries.

[0068] Suitable copolymers can be di-block copolymers (AB), tri-block copolymers (ABA or BAB), or higher multiblock polymers with alternating A and B blocks. All blocks are above their respective glass transition temperatures, T.sub.g. Likewise suitable are graft copolymers with backbone A monomers and side-chain B monomers, or back-bone B monomers and side-chain A monomers. In some embodiments, the A segments incorporate short poly(oxyethylene).sub.n side chains, where n, the number of oxyethylene groups in the side chain ranges from 4 to 20, preferably between 7 and 11. In some embodiments n is equal to nine. In some embodiments the poly(oxyethylene).sub.n side chains are incorporated by polymerization of poly(oxyethylene).sub.n methacrylate monomers. In a preferred embodiment, the A segments are synthesized by polymerization of poly(oxyethylene).sub.9 methacrylate monomers.

[0069] In some embodiments, the B segments have alkyl side chains having from 3 to 6 carbons. In some embodiments, the B segments are synthesized from a poly(alkyl methacrylate). In some embodiments, the poly(alkyl methacrylate) is chosen from the group consisting of poly(propyl methacrylate), poly(butyl methacrylate), poly(pentyl methacrylate), and poly(hexyl methacrylate). In a preferred embodiment, the poly(alkyl methacrylate) is poly(butyl methacrylate).

[0070] In some embodiments the “A” segments incorporate a mixture of neutral and anionic groups. In some such embodiments, the anionic groups are configured in order to minimize coordination of the anionic groups with lithium cations.

[0071] In a particularly preferred embodiment, the copolymer is the di-block copolymer poly[(oxyethylene).sub.9 methacrylate]-b-poly(butyl methacrylate) (POEM-b-PBMA).

[0072] In some embodiments, the block copolymers are synthesized by living anionic polymerization. In some embodiments, the block copolymers are synthesized by atom transfer radical polymerization (ATRP).

[0073] In some embodiments, the copolymer is a graft copolymer with a hydrophilic backbone of “A” segments that are lithium salt solvating and hydrophobic side-chains of “B” segments made up of hydrophobic polymers. Each segment is above its respective glass transition temperature, T.sub.g.

[0074] In a preferred embodiment, the copolymer is a graft copolymer with backbone “A” segments incorporating short poly(oxyethylene).sub.n side chains, where n, the number of oxyethylene groups in the side chain ranges from 4 to 20, preferably between 7 and 11. In some embodiments, n is equal to nine. In some embodiments, the poly(oxyethylene).sub.n side chains are incorporated by polymerization of poly(oxyethylene).sub.n methacrylate monomers. In a preferred embodiment, the A segments are synthesized by polymerization of poly(oxyethylene).sub.9 methacrylate monomers.

[0075] In some embodiments, the polymer is a graft copolymer with side chain “B” segments incorporating poly(dimethyl siloxane) (PDMS). In a preferred embodiment, the graft copolymer is incorporated into a poly(oxyethylene).sub.n methacrylate backbone by random copolymerization of poly(dimethyl siloxane) monomethacrylate macromonomer (PDMSMA) with poly(oxyethylene).sub.n methacrylate monomers to form a graft copolymer of type POEM-g-PDMS. In preferred embodiments, poly(oxyethylene).sub.9 methacrylate monomers are reacted to form the POEM-g-PDMS copolymer.

[0076] In some embodiments, the “A” backbone includes additional monomers. In some embodiments the additional monomers are anionic. In an embodiment, poly(oxyethylene).sub.9 methacrylate monomers are copolymerized with methacrylate monomers (MAA) and with PDMSMA to form poly(oxyethylene).sub.9-ran-MAA-g-PDMS. In a preferred embodiment, the carboxylic acid groups of this polymer are reacted with BF.sub.3 to give anionic boron trifluoride esters, which have a reduced tendency to complex lithium ions when compared with MAA carboxylate groups.

[0077] As summarized by the manufacturing steps shown in FIG. 2, in some embodiments, a copolymer coated lithium metal electrode is manufactured and inserted into a cell to function as a negative electrode (the metal) and a solid electrolyte (the polymer) in a lithium metal battery.

[0078] The steps of this embodiment are as follows: First, prepare a solution of lithium ion salt and block or graft copolymer in a cosolvent capable of dissolving both A and B segments of the copolymer 2. Second, coat an electrically conductive substrate with lithium salt doped copolymer by dipping the substrate in the lithium salt and copolymer solution 4. Third, evaporate the cosolvent to leave the electrolytically conductive substrate coated with lithium ion conductive copolymer 6. Next, insert the lithium ion conductive copolymer-coated conductive substrate as a cathode in an electrolytic cell, the electrolytic cell including an anode and a lithium salt solution 8. Then, apply voltage across the anode and the substrate, acting as a cathode, causing electrons to flow from the anode through an external circuit to the conductive substrate, causing lithium ions to be pulled through the copolymer coating, to be reduced at the substrate surface, thereby electrolytically plating lithium metal onto the surface 10. As lithium metal plates, the polymer chains of the copolymer coating undergo a molecular rearrangement, allowing the copolymer coating to continue to cover the growing layer of lithium metal, resulting in a final product for which the substrate is coated with a layer of lithium metal, and the layer of lithium metal is in turn coated with a layer of copolymer solid electrolyte. In the final step, the conductive substrate layered with lithium metal and a copolymer solid electrolyte is inserted as the combined lithium metal negative electrode and solid electrolyte in a lithium metal battery 12.

[0079] FIG. 3a shows a cross-section and FIG. 3b shows a top view of a copolymer coated electrically conductive substrate 115 according to embodiments of the invention. Following the process of dipping the electrically conductive substrate 110 into a cosolvent solution of lithium salt and copolymer and drying, the centrally located electrically conductive substrate 110 is surrounded by a layer of copolymer solid electrolyte 160. FIG. 4a shows a cross-section and FIG. 4b shows a top view of the copolymer coated lithium metal electrode 116 that can be obtained following the electrolytic plating onto the electrically conductive substrate 110 of a layer of lithium metal 150 which fills the space between the conductive substrate 110 and the copolymer solid electrolyte 160.

[0080] In the embodiment shown in FIGS. 5a, 5b, 6a, and 6b, the copolymer coated lithium metal electrode 116 can be obtained by first preparing, by electroplating or by other means, a lithium plated conductive substrate 117, then dipping the lithium plated substrate in a cosolvent solution of copolymer and drying the lithium plated substrate to obtain a copolymer coated negative electrode 115. FIG. 5a shows a cross-section and FIG. 5b shows a top view of a lithium coated conductive substrate 117 prior to coating with the copolymer solid electrolyte 160. FIG. 6a shows a cross-section and FIG. 6b shows a top view of the copolymer coated lithium metal electrode 116 after coating the lithium coated conductive substrate 117 with the copolymer solid electrolyte.

[0081] In preferred embodiments, the lithium metal in the copolymer coated lithium metal electrode 116 is ultrapure, having no more than five ppm of non-metallic elements by mass. In some embodiments, the lithium metal in the copolymer coated lithium metal electrode 116 includes no more than one ppm of non-metallic elements by mass. In some embodiments the lithium coated conductive substrate 117 is manufactured by methods described in U.S. patent application Ser. Nos. 17/006,048 and 17/006,073, both of which were filed Aug. 28, 2020 and are incorporated by reference herein in their entirety.

[0082] In preferred embodiments, the conductive substrate is selected from the group consisting of copper, aluminum, graphite coated copper, and nickel. In some embodiments, the copolymer is (POEM-b-PBMA). In some embodiments, the ratio of POEM to PBMA is greater than 50:50 on a molar basis. In preferred embodiments, the ratio of POEM to PBMA is between 55:45 and 70:30 on a molar basis. In a preferred embodiment, the cosolvent is tetrahydrofuran (THF).

[0083] An embodiment of an electrolytic cell 105 for electroplating the electrically conductive substrate 110 with a layer of lithium metal 150 sandwiched between the conductive substrate 110 and the copolymer coating 160 is shown in FIG. 7 (before electroplating) and FIG. 8 (after electroplating). In manufacturing the copolymer coated lithium metal electrode 116, the copolymer coated electrically conductive substrate 115 is positioned as the cathode in the electrolytic cell 105. As shown in FIG. 7, the electrolytic cell 105 contains an anode 120 and a lithium salt solution 140 in contact with the anode 120 and with the copolymer 160 coating the conductive substrate 110.

[0084] In some embodiments, the electrolytic cell 105 is configured as a flow chamber, with an entrance port 170 and an exit port 180 allowing lithium salt solution 140 to enter the electrolytic cell 105 to provide a renewable supply of lithium ions for electroplating. In some embodiments, the electrolytic cell is completely blanketed with a blanketing atmosphere 124, the blanketing atmosphere being substantially free of lithium reactive components. In a preferred embodiment, the blanketing atmosphere includes no more than 10 ppm of lithium reactive components on a molar basis. In a preferred embodiment, the blanketing atmosphere includes no more than 5 ppm of lithium reactive components on a molar basis. In a preferred embodiment, the blanketing atmosphere includes no more than 10 ppm of nitrogen on a per molar basis. In a preferred embodiment, the blanketing atmosphere includes no more than 5 ppm of nitrogen on a per molar basis. In a preferred embodiment, the blanketing atmosphere includes no more than 1 ppm of nitrogen on a per molar basis. In a preferred environment, the blanketing atmosphere comprises argon with a purity of greater than 99.998 weight percent. In a preferred embodiment the blanketing atmosphere 124 and the electrolytic cell 105 are enclosed in a gas-impermeable container 500.

[0085] As shown in FIG. 8, in some embodiments, during electroplating a voltage is applied across the anode 120 and the conductive substrate 110 of the electrolytic cell 105, causing electrons to flow through an external circuit to the conductive substrate 110 and pulling lithium ions from the lithium salt solution 140 through the copolymer 160 to plate onto the surface of the conductive substrate, forming a layer of lithium metal 150 sandwiched between the conductive substrate 110 and the copolymer 160. As the layer of lithium metal 150 grows, the copolymer 160 undergoes molecular rearrangement, maintaining contact with the surface of the layer of lithium metal 150. In the process, a copolymer coated lithium metal electrode 116 is manufactured.

[0086] As shown in FIGS. 9 and 10, in some embodiments, the electrolytic cell 105 includes a negative electrode comprising a first conductive substrate 110 coated with copolymer 160, to be electroplated with a first layer of lithium metal 150, and a positive electrode 120 with a second conductive substrate 112 in physical contact with a second layer of lithium metal 155, the second layer of lithium metal 155 coated with copolymer 165. As voltage is applied across the electrodes, the second layer of lithium metal 155 releases lithium ions through the copolymer coating into the lithium salt solution 145, replenishing the supply of lithium ions as electroplating of lithium metal occurs on the surface of the first conductive substrate 110. Consequently, as shown in FIG. 10, as the layer of lithium metal 150 sandwiched between the first conductive substrate 110 and the copolymer 160 increases in thickness, the second layer of lithium metal 155 sandwiched between the second conductive substrate 112 and the copolymer 165 decreases in thickness.

[0087] In the embodiment of FIGS. 11 and 12, an electrolytic cell 105 includes a first conductive substrate 110 functioning as a cathode, and an anode made of a second conductive substrate 112 coated with impure lithium 155. Separating and surrounding the two electrodes is a lithium ion conducting copolymer 160. Lithium salt is dispersed in the lithium ion conducting copolymer. As voltage is applied across the electrodes, electrons flow through an external circuit from the second conductive substrate to the first conductive substrate 110, causing the second layer of lithium metal 155 to release lithium ions, which flow through the lithium ion conducting copolymer 160 to the first conductive substrate, where they are reduced, electroplating lithium metal 150 on the surface of the first conductive substrate 110. Consequently, as shown in FIG. 12, as the first layer of lithium metal 150 on the first conductive substrate 110 increases in thickness, the second layer of lithium metal on the second conductive substrate 112 decreases in thickness. As lithium metal leaves the anode and travels to the cathode, the lithium ion conducting copolymer undergoes molecular rearrangement to maintain contact with the first layer of lithium metal 150 and second layer of lithium metal 155.

[0088] An advantage of the embodiments of FIGS. 9-12 is that the electroplated first layer of lithium metal 150 will be of higher purity and will have a smoother surface than the electroplating second layer of lithium metal 155. The method thus provides a straightforward means of obtaining higher purity, microscopically smoother lithium metal electrodes to use in lithium metal batteries, starting with lower purity, microscopically rougher lithium metal.

[0089] The copolymer coated lithium metal electrode 116, prepared by electrolytic or other methods, can be inserted directly into a rechargeable lithium battery, shown in cross-section in FIGS. 13 and 14, with exterior views in FIGS. 15 and 16, respectively.

[0090] In the battery embodied in FIGS. 13 and 15, a single positive electrode 130 is directly juxtaposed against the outer layer of copolymer 160 coating the negative electrode, to form a rechargeable battery 170 with the copolymer 160 providing the solid state electrolyte.

[0091] In the battery embodied in FIGS. 14 and 16, two positive electrodes 130 are directly juxtaposed against two sides of the outer layer of copolymer 160 coating the negative electrode, to form a rechargeable battery 175 with the copolymer 160 providing the solid state electrolyte.

[0092] In preferred embodiments of the batteries of FIGS. 13-16, a lithium salt is dispersed within the copolymer. In some embodiments, the lithium salt is LiCF.sub.3SO.sub.3. In some embodiments LiCF.sub.3SO.sub.3 is dispersed within the copolymer at a molar ratio of between 50:1 and 10:1 ethylene oxide to lithium ion. In a preferred embodiment, the LiCF.sub.3SO.sub.3 is dispersed within the copolymer at a molar ratio of 20:1 ethylene oxide to lithium ion. In some embodiments, the copolymer with dispersed lithium salt coating the negative electrode is formed by solution casting directly from anhydrous THF.

[0093] In some embodiments the rechargeable batteries of FIGS. 13-16 are Li—S batteries, for which the positive electrode includes elemental sulfur. In preferred embodiments, the sulfur in the positive electrode is associated with a conductive matrix, enabling suitably high electron conductivity.

[0094] Li—S batteries constructed in the manner of FIGS. 13-16 enable Li.sup.+ transport, but block the transport of anions, including in particular polysulfide anions. Consequently, the polysulfide shuttle responsible for reducing the performance and cycle life of Li—S batteries is vitiated.

[0095] The embodiments of the invention described above are intended to be merely exemplary; numerous variations and modifications will be apparent to those skilled in the art. All such variations and modifications are intended to be within the scope of the present invention as defined in any appended claims.