You have several unconnected questions placed together. Insulator by definition will insulate the passage of any flow of electrons. So if insulating metal oxide is applied as a coat then your material will be out of  electrochemical response . Photoluminescence  is an optical property and if your material has some   electrochemical response dependent photo-optical property then  that can influence the performance both ways.

Kindly pin-point your queries and question . Do not put vague questions as that invite similar answers

Maybe you read some reports concerning about metal oxide which is coated on the surface of LiFePO4 particles and can improve rate performance or cycling life of LiFePO4 . I am not familar with olivine type materials like LiFePO4, while I am doing a research on spinel type cathode materials such as LiNi0.5Mn1.5O4. In the case of  LiNi0.5Mn1.5O4, coating some inactive metal oxides sometimes is really  effective because these inactive coating layer can protect active materials from corrosion and decrease side reactions. 

Thanks for your ans. yes. I read some more articles regarding metal oxide modified LFPs, all the articles mentioned electrochemically inactive metal oxides and insulating metal oxide to improve the electrochemical performances, that is the reason I ask this question. In this view point I cann't understand the mechanism so that reason ask this question.