Chemical protection of a lithium surface

Abstract

Disclosed are compositions and methods for alleviating the problem of reaction of lithium or other alkali or alkaline earth metals with incompatible processing and operating environments by creating an ionically conductive chemical protective layer on the lithium or other reactive metal surface. Such a chemically produced surface layer can protect lithium metal from reacting with oxygen, nitrogen or moisture in ambient atmosphere thereby allowing the lithium material to be handled outside of a controlled atmosphere, such as a dry room. Production processes involving lithium are thereby very considerably simplified. One example of such a process is the processing of lithium to form negative electrodes for lithium metal batteries.

1 . A method of providing a chemical protective layer on a metal, comprising:
 introducing an alkali metal into a reaction chamber;   introducing one or more organic phosphate precursors of the protective layer into the reaction chamber and into contact with a first surface of the metal; and   conducting a reaction involving the one or more precursors to form an alkali metal phosphate chemical protective layer on the metal.   
   
   
       2 . The method of  claim 1 , wherein the metal comprises an alkali metal selected from the group consisting of lithium, sodium and potassium and alloys thereof. 
   
   
       3 . The method of  claim 2 , wherein the alkali metal layer is lithium or lithium alloy, the protective layer is lithium phosphate and the one or more precursors is anhydrous phosphoric acid in an organic solvent. 
   
   
       4 . The method of  claim 3 , wherein the solvent is selected from the group consisting of DME, mono-, di- and tri-glymes, ether, and THF. 
   
   
       5 . The method of  claim 1 , further comprising providing an ionically conductive protective inorganic glass adjacent to the chemical protective layer. 
   
   
       6 . The method of  claim 5 , wherein the ionically conductive protective inorganic glass is selected from the group consisting of phosphorus-based glass, oxide-based glass, sulfur-based glass, oxide/sulfide based glass, selenide based glass, gallium based glass, germanium based glass, and glass-ceramic active metal ion conductors, sodium beta-alumina or lithium beta-alumina. 
   
   
       7 . The method of  claim 6 , wherein the ionically conductive protective inorganic glass is selected from the group consisting of lithium phosphorus oxynitride (LiPON), Li 3 PO 4 .Li 2 S.SiS 2 , Li 2 S.GeS 2 .Ga 2 S 3  and Li 1-x-y Al x Ti 2-x Si y P 3-y O 12 , LISICON, NASICON, sodium and lithium beta-alumina. 
   
   
       8 . The method of  claim 7 , wherein the ionically conductive protective inorganic glass is lithium phosphorus oxynitride (LiPON). 
   
   
       9 . The method of  claim 1 , further comprising depositing a polymer electrolyte on the protective layer. 
   
   
       10 . The method of  claim 1 , further comprising bonding an electronically conductive backing on a second surface of said metal layer which is opposite the first surface of the alkali metal layer. 
   
   
       11 . The method of  claim 1 , wherein the metal forms at least part of a negative electrode. 
   
   
       12 . The method of  claim 1 , wherein the chemical protective layer has a thickness between about 10 nm and 1 micron. 
   
   
       13 . The method of  claim 1 , wherein the chemical protective layer has a thickness between about 50 nm and 0.1 micron. 
   
   
       14 . A method of providing a chemical protective layer on a negative metal electrode, comprising:
 forming and placing in a battery cell package an electrochemical structure comprising,
 a negative electrode comprising an alkali metal, 
 a positive electrode, 
 a separator disposed between the negative and positive electrodes, and 
 current collectors on the negative and positive electrodes; 
   introducing a liquid electrolyte or catholyte comprising one or more organic phosphate precursors of the chemical protective layer into the battery cell package and into contact with an exposed surface of the negative metal electrode; and   conducting a reaction involving the one or more chemical protective layer precursors to form the chemical protective layer on the exposed surface of the negative metal electrode.   
   
   
       15 . The method of  claim 14 , wherein the alkali metal layer is lithium or lithium alloy, the protective layer is lithium phosphate and the one or more precursors is anhydrous phosphoric acid in an organic solvent. 
   
   
       16 . The method of  claim 14 , further comprising providing an ionically conductive protective inorganic glass adjacent to the chemical protective layer. 
   
   
       17 . A battery cell, comprising:
 a negative electrode comprising an alkali metal and having a chemical protective layer coating a first surface, which protective layer comprises an alkali metal phosphate;   a physical protective layer adjacent to the chemical protective layer, the physical protective layer comprising a glass ionically conductive to ions of the alkali metal;   a positive electrode selected from the group consisting of a sulfur-based positive electrode, a metal oxide based positive electrode, and a metal sulfide based positive electrode;   a liquid electrolyte or catholyte disposed between the negative and positive electrodes, the electrolyte or catholyte comprising one or more organic phosphate precursors of the chemical protective layer; and   current collectors on the negative and positive electrodes.   
   
   
       18 . The cell of  claim 17 , wherein the alkali metal layer comprises lithium or a lithium alloy. 
   
   
       19 . The cell of  claim 17 , wherein the one or more organic phosphate precursors of the chemical protective layer comprises anhydrous phosphoric acid. 
   
   
       20 . The cell of  claim 17 , further comprising a physical protective layer adjacent to the chemical protective layer, the physical protective layer comprising a glass ionically conductive to ions of the alkali metal.