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.

What is claimed is: 
     
         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 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) 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 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) 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) 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) 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 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.