LITHIUM ION SECONDARY BATTERY HAVING POSITIVE ELECTRODE THAT COMPRISES THERMAL RUNAWAY SUPPRESSING LAYER ON POSITIVE ELECTRODE ACTIVE MATERIAL LAYER

摘要

To provide a lithium ion secondary battery wherein thermal runaway due to internal short circuit can be suppressed. A lithium ion secondary battery which is characterized by comprising: a positive electrode which is provided with a collector, a positive electrode active material layer that is formed on the collector and contains a lithium-containing composite oxide having a layered rock salt structure and represented by general formula LiaNibCocMndDeOf (wherein 0.2 ≤ a ≤ 1, b + c + d + e = 1, 0 ≤ e < 1, D represents at least one element selected from among Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K and Al, and 1.7 ≤ f ≤ 2.1), and a thermal runaway suppressing layer that is formed on the positive electrode active material layer and contains a lithium transition metal silicate salt; and a negative electrode which is provided with a negative electrode active material. This lithium ion secondary battery is also characterized in that the mass ratio of the lithium-containing composite oxide to the mass of the lithium transition metal silicate salt in the positive electrode is 1.5 or more.