LITHIUM SECONDARY BATTERY

Provided is a lithium secondary battery including a positive electrode layer composed of a cobalt-containing lithium composite oxide sintered body, a negative electrode layer composed of a titanium-containing sintered body, a ceramic separator interposed between the positive electrode layer and the negative electrode layer, an electrolyte impregnating at least the ceramic separator, and an exterior body having a closed space and accommodating the positive electrode layer, the negative electrode layer, the ceramic separator, and the electrolyte within the closed space. The positive electrode layer, the ceramic separator, and the negative electrode layer are bonded together. The lithium composite oxide sintered body contains, as an auxiliary agent, 0.05 to 2.0 mol % of boron with respect to the content of cobalt in the lithium composite oxide sintered body or 0.05 to 1.2 mol % of strontium with respect to the aforementioned cobalt content.