“…Thus, the interior of grains is semiconducting in nature, while the shell of the grains or grain boundaries is an insulator, as one would expect for a boundary layer capacitor (BLC) structure. Many researchers have reportedly tuned the level and types of A (e.g., Li 5,7,[9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] , Na 6,27 , K [28][29][30][31] ) and B (e.g., Sn 5 , Ti 9,11,13,17,19,24 , Si 6,10 , Sc 12 , Al 14,16 , Ta 15 , Cr 7,20,21 , V [22][23][24] , W 23 , Fe 24 , Co 25 , Cu 26 ) additives. Varying their concentration by controlling th...…”