A positive electrode plate, comprising a positive electrode current collector, a positive electrode film layer provided on at least one surface of the positive electrode current collector, and a conductive undercoat layer between the positive electrode current collector and the positive electrode film layer, wherein the positive electrode film layer comprises a positive electrode active material with a core-shell structure; the positive electrode active material comprises an inner core and a shell coating the inner core; the inner core includes Li 1+x Mn 1-y A y P 1-z R z O 4, where x = -0.100 to 0.100, y = 0.001 to 0.500, z = 0.001 to 0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more of Fe, Ti, V, Ni, Co and Mg, and R is selected from one or more of B, Si, N and S; the shell includes a first coating layer coating the inner core and a second coating layer coating the first coating layer, wherein the first coating layer includes pyrophosphate of MP 2 O 7 and phosphate of XPO 4, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al; and the second coating layer includes carbon; and the conductive undercoat layer includes a first polymer, a first water-based binder, and a first conductive agent, wherein the first polymer comprises a first monomer unit represented by formula 1; a second monomer unit selected from at least one of a group consisting of a monomer unit represented by formula 2 and a monomer unit represented by formula 3; a third monomer unit selected from at least one of a group consisting of a monomer unit represented by formula 4 and a monomer unit represented by formula 5; and a fourth monomer unit represented by formula 6, in which R 1, R 2, and R 3 each independently represent H, a carboxyl, an ester group, and groups of substituted or unsubstituted C1-C10 alkyl, C1-C10 alkoxy, C2-C10 alkenyl, and C6-C10 aryl, and R 4 represents H, and groups of substituted or unsubstituted C1-C10 alkyl, C1-C10 alkoxy, C2-C10 alkenyl, and C6-C10 aryl; the positive electrode film layer comprises a positive electrode active material with a core-shell structure; the positive electrode active material comprises an inner core and a shell coating the inner core; the inner core includes Li 1+x Mn 1-y A y P 1-z R z O 4, where x = -0.100 to 0.100, y = 0.001 to 0.500, z = 0.001 to 0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more of Fe, Ti, V, Ni, Co and Mg, and R is selected from one or more of B, Si, N and S; the shell includes a first coating layer coating the inner core and a second coating layer coating the first coating layer, wherein the first coating layer includes pyrophosphate of MP 2 O 7 and phosphate of XPO 4, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al; and the second coating layer includes carbon; and the conductive undercoat layer includes a first polymer, a first water-based binder, and a first conductive agent, wherein the first polymer comprises a first monomer unit represented by formula 1; a second monomer unit selected from at least one of a group consisting of a monomer unit represented by formula 2 and a monomer unit represented by formula 3; a third monomer unit selected from at least one of a group consisting of a monomer unit represented by formula 4 and a monomer unit represented by formula 5; and a fourth monomer unit represented by formula 6, in which R 1, R 2, and R 3 each independently represent H, a carboxyl, an ester group, and groups of substituted or unsubstituted C1-C10 alkyl, C1-C10 alkoxy, C2-C10 alkenyl, and C6-C10 aryl, and R 4 represents H, and groups of substituted or unsubstituted C1-C10 alkyl, C1-C10 alkoxy, C2-C10 alkenyl, and C6-C10 aryl; a first monomer unit represented by formula 1; a second monomer unit selected from at least one of a group consisting of a monomer unit represented by formula 2 and a monomer unit represented by formula 3; a third monomer unit selected from at least one of a group consisting of a monomer unit represented by formula 4 and a monomer unit represented by formula 5; and a fourth monomer unit represented by formula 6, in which R 1, R 2, and R 3 each independently represent H, a carboxyl, an ester group, and groups of substituted or unsubstituted C1-C10 alkyl, C1-C10 alkoxy, C2-C10 alkenyl, and C6-C10 aryl, and R 4 represents H, and groups of substituted or unsubstituted C1-C10 alkyl, C1-C10 alkoxy, C2-C10 alkenyl, and C6-C10 aryl;