Electrolyte compositions for batteries using sulphur or sulphur compounds

Abstract

There are disclosed electrolytes comprising solutions of lithium salts with large anions in polar aprotic solvents with a particular concentration of background salts. The concentration of the background salts is selected to be equal or close to the concentration of a saturated solution of these salts in the aprotic solvents used. The electrolytes disclosed can be used in chemical sources of electric energy such as secondary (rechargeable) cells and batteries comprising sulphur-based positive active materials. The use of such electrolytes increases cycling efficiency and cycle life of the cells and batteries.

1 . An electrolyte composition for a sulphur-based chemical source of electric energy, the electrolyte composition comprising: a nonaqueous aprotic solvent and an alkali metal salt, wherein said electrolyte composition is chosen in a way that a concentration of the alkali metal salt is substantially equal to or close to a saturation concentration of the alkali metal salt in the solvent at operating temperature and pressure.  
   
   
       2 . An electrolyte as claimed in  claim 1 , wherein the solvent is: tetrahydrofurane, 2-methyltetrahydrofurane, dimethylcarbonate, diethylcarbonate, ethylmethylcarbonate, methylpropylcarbonate, methylpropylpropyonate, ethylpropylpropyonate, methylacetate, ethylacetate, propylacetate, dimethoxyethane, 1,3-dioxalane, diglyme (2-methoxyethyl ether), tetraglyme, ethylenecarbonate, propylenecarbonate, y-butyrolactone, sulfolane, or a sulfone.  
   
   
       3 . An electrolyte as claimed in  claim 1 , wherein the alkali metal salt is: lithium hexafluorophosphate (LiPF 6 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium perchlorate (LiClO 4 ), lithium bis(trifluoromethane sulfonyl)imide (LiN(CF 3 SO 2 ) 2 )), lithium trifluorosulfonate (LiCF 3 SO 3 ) or other lithium salts or salts of another alkali metal or a mixture thereof.  
   
   
       4 . An electrolyte as claimed in  claim 1 , wherein the concentration of alkali metal salt in the solvent is at least 90% of its saturation concentration at operating temperature and pressure.  
   
   
       5 . An electrolyte as claimed in  claim 1 , wherein the concentration of the alkali metal salt in the solvent is at least 95% of its saturation concentration at operating temperature and pressure.  
   
   
       6 . An electrolyte as claimed in  claim 1 , wherein the concentration of the at least one alkali metal salt in the at least one solvent is at least 99% of its saturation concentration at operating temperature and pressure.  
   
   
       7 . A chemical source of electrical energy comprising: a negative electrode (anode) comprising an anode active material for providing ions; a positive electrode (cathode) comprising a cathode active material comprising sulphur, organic or inorganic compounds based on sulphur; and an intermediate separator element containing a liquid or a gel electrolyte solution through which ions from the negative electrode move to the positive electrode during charge and discharge cycles of the chemical source of electrical energy, wherein the gel electrolyte solution comprises the composition of  claim 1 .  
   
   
       8 . A chemical source of electric energy as claimed in  claim 7 , wherein the cathode active material comprising sulphur is: elemental sulphur, lithium polysulphides, inorganic and organic compounds based on sulphur, or mixtures thereof.  
   
   
       9 . A chemical source of electric energy as claimed in  claim 7 , wherein the cathode active material comprising sulphur further comprises a binder and an electrically conductive material.  
   
   
       10 . A chemical source of electric energy as claimed in  claim 7 , wherein said anode active material is: metallic lithium, alloys of lithium, metallic sodium, alloys of sodium, alkali metals or alloys thereof, metal powders, alkali metal-carbon and alkali metal-graphite intercalates, compounds capable of reversibly oxidizing and reducing with an alkali metal ion, or mixtures thereof.  
   
   
       11 . A chemical source of electric energy as claimed in  claim 8 , wherein the polysulfide is represented by the general formula LiSn, where n≧1.  
   
   
       12 . A chemical source of electric energy as claimed in  claim 8 , wherein the organic compounds based on sulfur are comprised of polymeric and oligomeric compounds.