Lithium-ion secondary battery, battery module, battery pack, and electric apparatus

A lithium-ion secondary battery, comprising a positive electrode plate, a negative electrode plate, a separator, and an electrolyte, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, and the positive electrode material layer contains a positive electrode active substance, wherein

• the positive electrode active substance includes LiNixCoyNzM1-x-y-zO2, with N selected from Mn and Al, and M selected from any one of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, where 0.5≤x<1, 0≤y≤1, 0≤z≤1, and x+y+z≤1;
• and
• the electrolyte includes compounds represented by formula (1), formula (2), and formula (3):
• where R is selected from a fluorine atom and a fluorinated C1-C6 alkyl group,
• where R1 to R6 are each independently selected from a C1-C6 halogenated alkyl group, halogen, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 alkyl group containing N or P, where the halogen is fluorine, chlorine, bromine, or iodine, and a ratio of the number of halogen atoms to the number of P atoms in the compound represented by formula (2) is 1:3 to 2:1,
• where R7 and R8 are each independently selected from a C1-C3 alkyl group substituted by a fluorine atom, a hydrogen atom, a fluorine atom, and a helium atom, and
• based on a total weight of the electrolyte, a percentage by weight of the compound represented by formula (1) is W1%, wherein W1% is in a range of 1%-15%;
• a percentage by weight of the compound represented by formula (2) is W2%, wherein W2% is in a range of 1%-20%;
• and a percentage by weight of the compound represented by formula (3) is W3%, wherein W3% is in a range of 5%-20%;
• wherein W1, W2, and W3 satisfy 1≤W3/W2≤4 and 0.5≤W1/W2≤1;
• wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer contains a negative electrode active substance, and the negative electrode active substance contains graphite with OI≥8 whose percentage by weight is ≤20% based on a total weight of the negative electrode active substance,
• wherein the compound represented by formula (1) consists of fluorobenzene, the compound represented by formula (2) consists of ethoxy(pentafluoro)cyclotriphosphazene, and the compound represented by formula (3) consists of lithium bis(fluorosulfonyl)imide.