With the spread of IoT devices in recent years, a small and thin coin-shaped lithium secondary battery with high capacity and high output which can be charged particularly at a constant voltage (CV) has been desired. Such a secondary battery which can be charged at a constant voltage does not need to be provided with a current control IC and is therefore advantageous for reducing the size and cost. Meanwhile, in order to efficiently produce IoT devices, it is desired to mount a coin-shaped lithium secondary battery on a circuit board by solder reflow, and therefore it is desired that the battery performance does not deteriorate even in a high temperature state (for example, 260° C.) during reflow soldering. In this point, the coin-shaped non-aqueous electrolyte secondary battery for reflow soldering disclosed in Patent Literature 3 (JP4392189B) exhibits some heat resistance to solder reflow but has poor constant voltage charge cycle performance, and thus a further improvement is desired. That is, a small and thin coin-shaped lithium secondary battery with high capacity and high output which can be charged at a constant voltage while having a heat resistance suitable for solder reflow has not been known so far.

The inventors have now found that a small and thin coin-shaped lithium secondary battery with high capacity and high output which can be charged at a constant voltage while having excellent heat resistance to enable reflow soldering can be provided by using a lithium complex oxide sintered plate as a positive electrode and a titanium-containing sintered plate as a negative electrode.

Accordingly, an object of the present invention is to provide a small and thin coin-shaped lithium secondary battery with high capacity and high output which can be charged at a constant voltage while having excellent heat resistance to enable reflow soldering.