Metal-ion secondary battery

Abstract

An object of the present disclosure is to provide a secondary battery having excellent cyclability by using a sulfur-based active material as a negative-electrode active material while preventing a reaction between an elated polysulfide and a positive electrode. The metal-ion secondary battery comprises a negative electrode comprising a sulfur-containing compound as a negative-electrode active material, a positive electrode and an electrolyte, and has a polymer gel layer on a surface of the positive electrode.

What is claimed is: 
     
         1 . A metal-ion secondary battery comprising a negative electrode comprising a sulfur-containing compound as a negative-electrode active material, a positive electrode and an electrolyte, wherein the positive electrode has a polymer gel layer on a surface thereof. 
     
     
         2 . The metal-ion secondary battery of  claim 1 , wherein the electrolyte comprises sulfolane as a solvent. 
     
     
         3 . The metal-ion secondary battery of  claim 1 , wherein the positive electrode comprises a positive-electrode active material enabling lithium ion occlusion/release. 
     
     
         4 . The metal-ion secondary battery of  claim 3 , wherein the positive-electrode active material is at least one selected from the group consisting of a lithium transition metal oxide and a lithium transition metal oxide derivative. 
     
     
         5 . The metal-ion secondary battery of  claim 3 , wherein the positive-electrode active material is a lithium-manganese composite oxide. 
     
     
         6 . The metal-ion secondary battery of  claim 5 , wherein the lithium-manganese composite oxide is at least one selected from the group consisting, of LiNi 1/3 Co 1/3 Mn 1/3 O 2 , LiMn 2 O 4 , LiNi 0.5 Mn 1.5 O 4  and Li 2 MnO 3 —LiMO 2  (wherein M is one or more selected from the group consisting of Ni, Co and Mn). 
     
     
         7 . The metal-ion secondary battery of  claim 1 , wherein the negative-electrode active material is obtainable by subjecting a starting material comprising at least one polymer compound selected from the group consisting of a rubber and a polymer which consists of a monomer unit having a hetero atom-containing moiety, and sulfur to heat-treatment under a non-oxidizing atmosphere, 
       wherein the hetero atom-containing moiety is a moiety having a group selected from the group consisting of: a monovalent functional group containing at least one hetero atom selected from the group consisting of O, S, P and N; a heterocyclic group containing at least one hetero atom selected from the group consisting of O, S, P and N; and a group represented by —S a — (wherein “a” is an integer of 2 to 4). 
     
     
         8 . The metal-ion secondary battery of  claim 7 , wherein a weight-average molecular weight of the polymer compound is 2,000 to 1,500,000. 
     
     
         9 . The metal-ion secondary battery of  claim 7 , wherein the starting material to be heat-treated further comprises an electrically-conductive carbon material. 
     
     
         10 . The metal-ion secondary battery of  claim 9 , wherein the electrically-conductive carbon material is a carbon material having a graphite structure. 
     
     
         11 . The metal-ion secondary battery of  claim 1 , wherein a total sulfur amount in the negative-electrode active material is not less than 50.0% by mass.