Lithium secondary cell and nonaqueous electrolyte

Abstract

The sudden generation of heat being frequently caused in the case of the overcharge of a lithium secondary cell which have a positive electrode comprising a composite metal oxide of lithium and cobalt or a composite metal oxide of lithium and nickel, a negative electrode comprising metallic lithium, a lithium alloy or a material capable of occluding and releasing lithium, and a nonaqueous electrolyte solution comprising a nonaqueous solvent and an electrolyte dissolved therein can be efficiently prevented by the addition, to the nonaqueous electrolyte solution, of an organic compound which, when the lithium secondary cell is overcharged, decomposes into a decomposition product capable of dissolving out the cobalt or nickel contained in the positive electrode and depositing it ion the negative electrode (for example, a tert-alkylbenzene derivative).

What is claimed is:  
     
         1 . A method of preventing sudden heat generation when a lithium secondary battery comprising a positive electrode comprising a composite metal oxide of lithium and cobalt or a composite metal oxide of lithium and nickel, a negative electrode comprising a lithium metal, a lithium alloy or a material capable occluding and releasing lithium, and a non-aqueous electrolyte solution comprising an electrolyte in a non-aqueous solvent is overcharged, which comprises dissolving an organic compound in the non-aqueous electrolyte solution, decomposing the organic compound when the overcharging takes place, to give a decomposed product, the decomposed product functioning to dissolve cobalt or nickel out of the positive electrode, and deposit the cobalt or nickel on the negative electrode.  
     
     
         2 . The method of  claim 1 , wherein the cobalt or nickel deposited on the negative electrode prevents contact between lithium in the negative electrode and the electrolyte solution, whereby preventing the heat generation.  
     
     
         3 . The method of  claim 1 , wherein the cobalt or nickel deposited on the negative electrode produces short circuit within the battery, whereby preventing the heat generation.  
     
     
         4 . A lithium secondary battery comprising a positive electrode comprising a composite metal oxide of lithium and cobalt or a composite metal oxide of lithium and nickel, a negative electrode comprising a lithium metal, a lithium alloy or a material capable occluding and releasing lithium, and a non-aqueous electrolyte solution comprising an electrolyte in a non-aqueous solvent, in which an organic compound is contained in the non-aqueous electrolyte solution, said organic compound decomposing when overcharging of the secondary battery takes place to give a decomposed product, said decomposed product functioning to dissolve cobalt or nickel out of the positive electrode and deposit the cobalt or nickel on the negative electrode.  
     
     
         5 . The lithium secondary battery of  claim 4 , wherein the organic c d has an oxidation potential in the range of +4.6 V to +5.0 V, which is determined relatively to the oxidation potential of lithium.  
     
     
         6 . The lithium secondary battery of  claim 5 , wherein the organic compound is a tert-alkylbenzene derivative.  
     
     
         7 . The lithium secondary battery of  claim 6 , wherein the tert-alkylbenzene derivative is tert-butylbenzene, 1-bromo-4-tert-butylbenzene, or tert-pentylbenzene.  
     
     
         8 . The lithium secondary battery of  claim 4 , wherein the organic compound is a combination of a tert-alkylbenzene derivative and cyclohexylbenzene.  
     
     
         9 . The lithium secondary battery of  claim 4 , wherein the organic compound is contained in the electrolyte solution in an amount of 0.1 to 10 weight %.  
     
     
         10 . A lithium secondary battery comprising a positive electrode comprising a composite metal oxide of lithium and cobalt or a composite metal oxide of lithium and nickel, a negative electrode comprising a lithium metal a lithium alloy or a material capable occluding and releasing lithium, and a non-aqueous electrolyte solution comprising an electrolyte in a non-aqueous solvent, in which the non-aqueous electrolyte solution contains an organic compound having an oxidation potential in the range of +4.6 V to +5.0 V, which is determined relatively to the oxidation potential of lithium.  
     
     
         11 . The lithium secondary battery of  claim 10 , wherein the organic compound is a tert-alkylbenzene derivative.  
     
     
         12 . The lithium secondary battery of  claim 11 , wherein the tert-alkylbenzene derivative is tert-butylbenzene, 1-bromo-4-tert-butylbenzene, or tert-pentylbenzene.  
     
     
         13 . The lithium secondary battery of  claim 10 , wherein the organic compound is a combination of a tert-alkylbenzene derivative and cyclohexylbenzene.  
     
     
         14 . The lithium secondary battery of  claim 10 , wherein the organic compound is contained in the electrolyte solution in an amount of 0.1 to 10 weight %.  
     
     
         15 . A non-aqueous electrolyte solution to be used for a lithium secondary battery comprising a positive electrode comprising a composite metal oxide of lithium and cobalt or a composite metal oxide of lithium and nickel, a negative electrode comprising a lithium metal, a lithium alloy or a material capable occluding and releasing lithium, and a non-aqueous electrolyte solution comprising an electrolyte in a non-aqueous solvent, which further contains an organic compound having an oxidation potential in the range of +4.6 V to +5.0 V, which is determined relatively to the oxidation potential of lithium.  
     
     
         16 . The non-aqueous electrolyte solution of  claim 15 , wherein the organic compound is a tert-alkylbenzene derivative.  
     
     
         17 . The non-aqueous electrolyte solution of  claim 16 , wherein the tert-alkylbenzene derivative is tert-butylbenzene, 1-bromo-4-tert-butylbenzene, or tert-pentylbenzene.  
     
     
         18 . The non-aqueous electrolyte solution of  claim 15 , wherein the organic compound is a combination of a tert-alkylbenzene derivative and cyclohexylbenzene.  
     
     
         19 . The non-aqueous electrolyte solution of  claim 15 , wherein the organic compound is contained in the electrolyte solution in an amount of 0.1 to 10 weight %.