An all-solid-state lithium secondary battery in which a solid electrolyte (e.g., a sulfide- or oxide-based solid electrolyte) is used as an electrolyte, has many advantageous such as high energy density and high power output.
For such an all-solid-state lithium secondary battery, it is known that active materials used in the electrodes are likely to be unstable and deteriorate. To avoid the problem, an electrode active material in which the surface is coated and protected with another component, is used. However, an all-solid-state lithium secondary battery using an electrode active material in which the surface is coated with lithium niobate, poses a new problem in that there is an increase in the reaction resistance.
In Patent Literature 1, a method for producing a cathode active material (a lithium-transition metal oxide powder) is disclosed, in which the surface is coated with lithium niobate by use of an aqueous solution containing a niobic acid complex and a lithium compound. According to the production method in Patent Literature 1, it is described that the content of carbon contained in the lithium-transition metal oxide powder in which the surface is coated with the lithium niobate, can be controlled to 0.03% by mass or less, so that carbon-induced lithium ion transfer inhibition can be suppressed, and the electrical resistance value (powder compact resistance) of the cathode active material can be decreased.
Patent Literature 1: Japanese Patent Application Laid-Open No. 2012-74240