Secondary battery and preparation method thereof

A preparation method for a secondary battery, comprising a preparation method for a negative electrode plate, the preparation method for the negative electrode plate comprises:

• mixing a negative electrode active material, a conductive agent, and a binder uniformly in a solvent to form a slurry for a negative electrode active material layer;
• coating the slurry for the negative electrode active material layer on at least one surface of a negative electrode current collector to obtain a negative electrode plate to be calendered, which comprises a negative electrode film formed by the slurry for the negative electrode active material layer, wherein d represents a surface density of the negative electrode film, a value range of the d is 30 g/m2-200 g/m2;
• after calendering, forming the negative electrode plate, wherein a density of the negative electrode film after calendering is ρ, a range of ρ is 1 g/cm3-2 g/cm3;
• manufacturing a test cell using the negative electrode plate, obtaining a ratio of increase r in thickness of the negative electrode film after the test cell is fully charged, a value range of the r is 0.1%≤r≤20%;
• according to the test cell, an average voltage with a capacity of 20-90% is taken as a voltage of a lithium intercalation plate U, a value range of the U is 5 mV-1500 mV;
• the preparation method further comprises:
• manufacturing the secondary battery by combining the negative electrode plate, a positive electrode plate, a separator, and an electrolyte solution;
• the secondary battery satisfies a relational formula:
• 0.9
• ≤
• U
• ×
• (
• 1
• +
• r
• )
• /
• (
• ρ
• +
• 7.4
• )
• /
• d
• /
• (
• 1
• +
• 5.3
• ×
• ln
• ⁡
• (
• t
• )
• )
• /
• 1.335
• ≤
• 1.1
• ,
• wherein t represents a charging time of the secondary battery from 10% state of charge (SOC) to 80% SOC in min, a value range of the tis 5-100 min.