Lithium-ion secondary battery, battery module, battery pack, and powered device

A lithium-ion secondary battery, comprising a bare battery cell accommodating cavity in which a bare battery cell group comprising one or more bare cells A and one or more bare cells B is arranged, wherein the bare cell A comprises a first positive electrode sheet comprising a first positive-electrode active material selected from a single crystal or single crystal-like low-nickel ternary positive electrode material A1, wherein single crystal-like ternary low-nickel electrode material comprises primary particles and secondary particles and volume distribution of secondary particles formed by agglomeration is 10% to 35%, the bare cell B comprises a second positive electrode sheet comprising a second positive-electrode active material and/or a third positive-electrode active material, the second positive-electrode active material is selected from a polycrystalline high-nickel ternary positive electrode material B1, and the third positive-electrode active material is selected from a polycrystalline low-nickel ternary positive electrode material B2;

• wherein mole fraction of low-nickel is greater than 0 and less than or equal to 0.65 and mole fraction of high nickel is greater than or equal to 0.7 and less than 1, wherein 100% SOC charged unit cell volume shrinkage rate of the single crystal or single crystal-like low-nickel ternary positive electrode material A1 is ≤3%;
• and/or, the 100% SOC charged unit cell volume shrinkage rate of the polycrystalline high-nickel ternary positive electrode material B1 is ≥4%;
• and/or, the 100% SOC charged unit cell volume shrinkage rate of the polycrystalline low-nickel ternary positive electrode material B2 is ≤3%.