LITHIUM SECONDARY BATTERY

Provided is a lithium secondary battery including a positive electrode layer composed of a lithium complex oxide sintered body, a negative electrode layer composed of a titanium-containing sintered body, a ceramic separator, an electrolytic solution, and an exterior body including a closed space, the closed space accommodating the positive electrode layer, the negative electrode layer, the ceramic separator, and the electrolytic solution, wherein the positive electrode layer, the ceramic separator, and the negative electrode layer are bonded together, the ceramic separator is composed of MgO and glass, the glass has an average grain size of 0.5 to 25 μm, and a ratio of the average grain size of the glass to the average grain size of MgO is 1.5 to 85.