Battery module, battery pack, and electric apparatus

A battery module, comprising a first type of cell and a second type of cell that are cells of different chemical systems, wherein

• the first type of cell comprises n first cells, the second type of cell comprises m second cells, wherein n and m each are selected from an integer greater than 1, at least one of the first cells and at least one of the second cells are electrically connected in series, and the first cell and the second cell satisfy at least conditions (1) to (3):
• 0.08≤ΔRB/ΔRA≤3.50;
• condition (1):
• 0.10 mΩ/100 cycles≤ΔRA≤0.40 mΩ/100 cycles;
• and condition (2):
• IMPB<IMPA;
• and, condition (3):
• wherein ΔRA is a discharge resistance growth rate of the first cell,
• ΔRB is a discharge resistance growth rate of the second cell,
• IMPA is an alternating current impedance of the first cell;
• and
• IMPB is an alternating current impedance of the second cell,
• wherein the discharge resistance growth rate is measured by a difference between a discharge resistance (R) of a cell in an initial state and a discharge resistance of the cell after 100 cycles of charging/discharging, wherein the discharge resistance of the cell is calculated using formula R=(V1−V2)/I, wherein I is a constant discharge current, V1 is an initial voltage of the cell, V2 is an end voltage of the cell after discharging at I for a specified period of time, and ΔRB/ΔRA are measured under the same condition, and
• wherein the alternating current impedance is measured using a test signal with a frequency of 1000 Hz, and IMPA and IMPB are measured under the same condition.