The invention relates to a mixed
ion-
electron conductor with a garnet structure and application of the mixed
ion-
electron conductor in an
energy storage device. The general formula of the conductor is(LimM)xLa3(Zr<1-a>Xa)2O12, wherein m is greater than 0 and less than or equal to 1, n is greater than or equal to 0 and less than or equal to 0.5, the sum of m and n is less than or equal to 1, and xis greater than or equal to 3 and less than or equal to 7.5; M comprises at least one element selected from H, Na, K, Rb, Mg, Ca, Sr, Ba, Y, La, Ti, Zr, Zn, B, Al, Ga, In, C, Si, Ge, P, S and Se; a is greater than or equal to 0 and less than 1; and X comprises at least one element selected from Ta, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Si, Ge, Sn, Pb, As, Sb and Se. The conductor provided bythe invention has high
ionic conductivity and
electronic conductivity, and can be applied to an
electrode /
electrolyte interface layer in a battery or a
capacitor, a positive
electrode layer and a negative
electrode layer. The mixed
ion-
electron conductor can be applied to a
lithium ion battery, a rechargeable
metal lithium battery, a
lithium flow battery and a
lithium ion capacitor, and the energystorage devices have wide application.