In Comparative Example 1 and Comparative Example 2, the positive electrode material contained only secondary particles or monocrystalline particles, and the compacted density of the prepared positive electrode plate was relatively low, which is inconducive to increasing of the volume energy density of the battery. In addition, the positive active substances in Comparative Example 1 and Comparative Example 2 were prone to particle crushing during cold pressing of the electrode plate and cycling, resulting in a severe gassing problem and a relatively high volume swelling rate of the battery. In Comparative Example 3, although a high-nickel positive electrode material with large and small particle sizes was used, the secondary particles with a small particle size had a large specific surface area and higher residual lithium content on the surface, degrading gassing performance of the lithium-ion battery. In Comparative Example 4 and Comparative Example 5, LiNi_0.5Co_0.2Mn_0.3O₂ with relatively low nickel content was included in the mixed positive electrode material. Although the gassing problem of the lithium-ion battery was mitigated by controlling the degree of crystallinity and particle size distribution of the mixed high-nickel active material, the high energy density requirements of the battery cannot be met. In Comparative Example 6, D₁₀₄×ΔPSD of the mixed high-nickel positive electrode material was excessively high, indicating that the particle size distribution of the material was excessively large and the relative content of fine powder with a small particle size was excessively high, and therefore the cycle performance was poor and the gassing problem was severe. In Comparative Example 7, the D₁₀₄×ΔPSD of the mixed high-nickel positive electrode material was relatively low, indicating that the particle size distribution of the material was relatively concentrated. However, a crystal particle size of the formed material was excessively small with a greater quantity of internal interfaces, and therefore the gassing problem of the battery was not mitigated.