Method for manufacturing composite positive electrode active material

A method for manufacturing a composite positive electrode active material being a composite of a positive electrode active material and carbon nanotubes, comprising:

• preparing an aqueous solution of a starting material of a positive electrode active material containing a starting material of the positive electrode active material, and an aqueous solution of solubilized carbon nanotubes containing the carbon nanotubes and a solubilizing material that is composed of a water-soluble polymer having a ring structure composed of carbon (C), or carbon (C) and oxygen (O), whose solubilization retention rate of carbon nanotubes does not decrease with rising temperature;
• synthesizing a positive electrode active material-carbon nanotube composite by mixing the aqueous solution of a starting material of a positive electrode active material and the aqueous solution of solubilized carbon nanotubes, and performing hydrothermal synthesis;
• and
• removing water in the positive electrode active material-carbon nanotube composite while maintaining a dispersion state of the carbon nanotubes contained in the synthesized positive electrode active material-carbon nanotube composite,
• wherein water in the positive electrode active material-carbon nanotube composite is removed by freeze-drying.