Nonaqueous electrolyte secondary battery

Abstract

Disclosed is a nonaqueous electrolyte secondary battery which has a negative electrode containing silicon as a negative active material, a positive electrode containing a positive active material, a nonaqueous electrolyte and a separator. Characteristically, an additive which retards oxidation of silicon during operation of the battery is contained either in an interior or surface portion of the positive electrode, or in an interior or surface portion of the negative electrode, or in an interior or surface portion of the separator.

1 . A nonaqueous electrolyte secondary battery which includes a negative electrode containing silicon as a negative active material, a positive electrode containing a positive active material, a nonaqueous electrolyte and a separator;
 said battery being characterized in that an additive which retards oxidation of said silicon during battery operation is contained either in an interior or surface portion of said positive electrode, or in an interior or surface portion of said negative electrode, or in an interior or surface portion of said separator; wherein said additive is selected from the group consisting of acetic anhydride; oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid and fumaric acid, and their salts and esters; hydroxy acids; lithium carbonate; lithium nitrate; lithium sulfonate; acrylic acid and its derivatives; and methacrylic acid and its derivatives; and said nonaqueous electrolyte contains a film former which forms a film on a surface of said negative electrode, said film former comprising vinylene carbonate.   
     
     
         2 . The nonaqueous electrolyte secondary battery as recited in  claim 1 , characterized in that said additive is contained in said interior or surface portion of the positive electrode. 
     
     
         3 . The nonaqueous electrolyte secondary battery as recited in  claim 1 , characterized in that said additive is contained in said interior or surface portion of the negative electrode and a film former which forms a film on a surface of the negative electrode is contained in said nonaqueous electrolyte. 
     
     
         4 . The nonaqueous electrolyte secondary battery as recited in  claim 1 , characterized in that said additive is contained in said interior or surface portion of the separator. 
     
     
         5 . The nonaqueous electrolyte secondary battery as recited in  claim 1 , characterized in that said negative electrode is an electrode fabricated by depositing a thin film of silicon or silicon alloy on a current collector. 
     
     
         6 . The nonaqueous electrolyte secondary battery as recited in  claim 5 , characterized in that said thin film has such a columnar structure that it is divided into columns by gaps formed therein and extending in its thickness direction. 
     
     
         7 . The nonaqueous electrolyte secondary battery as recited in  claim 1 , characterized in that said negative active material comprises an alloy of silicon and other metal. 
     
     
         8 . The nonaqueous electrolyte secondary battery as recited in  claim 1 , characterized in that said additive in the nonaqueous electrolyte exists in the solid form. 
     
     
         9 . The nonaqueous electrolyte secondary battery as recited in  claim 1 , characterized in that said additive has a mean particle size within a particle size distribution of said positive or negative active material. 
     
     
         10 . The nonaqueous electrolyte secondary battery as recited in  claim 1 , characterized in that said additive is held within a support material. 
     
     
         11 . The nonaqueous electrolyte secondary battery as recited in  claim 10 , characterized in that said support material comprises solid fine particles (fillers). 
     
     
         12 . The nonaqueous electrolyte secondary battery as recited in  claim 10 , characterized in that said support material is electronically conductive.