In the field of all solid state batteries, attention has been paid to the interface of an active material and a solid electrolyte material, and there have been attempts to promote an enhancement in the performance of batteries. For example, Patent Literature 1 discloses an all solid lithium battery including a lithium ion conductive solid electrolyte having a sulfide as a main component and a cathode active material having a surface coated with a lithium ion conductive oxide. Further, as an example of the lithium ion conductive oxide, LiNbO3 is disclosed. Furthermore, as an example of a method for forming a lithium ion conductive oxide, a method of using a solution containing a metal alkoxide is disclosed.
Furthermore, Patent Literature 2 discloses a lithium-transition metal oxide powder having a surface coated with a coating layer containing lithium niobate and the lithium-transition metal oxide powder having a carbon content of 0.03% by mass or less. Furthermore, as an example of a method for forming lithium niobate, a method of using a solution containing a peroxo complex of niobium acid is disclosed.