A positive-electrode plate, comprising a current collector, and a first active substance layer and a second active substance layer that are sequentially disposed on a surface of the current collector, wherein the first active substance layer comprises a first positive-electrode active material, and the first positive-electrode active material comprises at least one of a compound represented by Formula or a compound represented by Formula: Li 1+x1 Mn a1 M 1-a1 O 2-y1 A y1 Formula wherein - 0.1 ≤ x1 ≤ 0.2, 0.5 ≤ a1 ≤ 1, 0 ≤ y1 < 0.2, M comprises one or more of Ni, Fe, Cr, Co, Ti, Zn, V, Al, Zr, and Ce, and A comprises one or more of S, N, F, Cl, Br, and I; Li 1+x2 Mn a2 N 2-a2 O 4-y2 B y2 Formula in the Formula, -0.1 ≤ x2 ≤ 0.2, 1.5 ≤ a2 ≤ 2, 0 ≤ y2 < 0.5, N comprises one or more of Ni, Fe, Cr, Co, Ti, Zn, V, Al, Zr, and Ce, and B comprises one or more of S, N, F, Cl, Br, and I; and the second active substance layer comprises a second positive-electrode active material having a pH value of from 10 to 12; preferably, the second positive-electrode active material is a lithium-transition metal composite oxide or a lithium-transition metal composite phosphate having a pH value of from 10 to 12, and the pH value is measured as follows: at 25 °C, adding 5g of a purchased or self-made second positive-electrode active material into 500 ml of deionized water, stirring at a speed of 30 r/min for 2 hours by using a magnetic stirrer, placing into an ultrasonic cleaner to perform ultrasonic treatment for 2 hours, setting aside a homogeneously dispersed solution for 1 hour, and then measuring the pH value of the solution by using a pH tester; and a specific surface area BET2 of the second positive-electrode active material is not lower than a specific surface area BET1 of the first positive-electrode active material. the first active substance layer comprises a first positive-electrode active material, and the first positive-electrode active material comprises at least one of a compound represented by Formula or a compound represented by Formula: Li 1+x1 Mn a1 M 1-a1 O 2-y1 A y1 Formula wherein - 0.1 ≤ x1 ≤ 0.2, 0.5 ≤ a1 ≤ 1, 0 ≤ y1 < 0.2, M comprises one or more of Ni, Fe, Cr, Co, Ti, Zn, V, Al, Zr, and Ce, and A comprises one or more of S, N, F, Cl, Br, and I; Li 1+x2 Mn a2 N 2-a2 O 4-y2 B y2 Formula in the Formula, -0.1 ≤ x2 ≤ 0.2, 1.5 ≤ a2 ≤ 2, 0 ≤ y2 < 0.5, N comprises one or more of Ni, Fe, Cr, Co, Ti, Zn, V, Al, Zr, and Ce, and B comprises one or more of S, N, F, Cl, Br, and I; and the second active substance layer comprises a second positive-electrode active material having a pH value of from 10 to 12; preferably, the second positive-electrode active material is a lithium-transition metal composite oxide or a lithium-transition metal composite phosphate having a pH value of from 10 to 12, and the pH value is measured as follows: at 25 °C, adding 5g of a purchased or self-made second positive-electrode active material into 500 ml of deionized water, stirring at a speed of 30 r/min for 2 hours by using a magnetic stirrer, placing into an ultrasonic cleaner to perform ultrasonic treatment for 2 hours, setting aside a homogeneously dispersed solution for 1 hour, and then measuring the pH value of the solution by using a pH tester; and a specific surface area BET2 of the second positive-electrode active material is not lower than a specific surface area BET1 of the first positive-electrode active material.