Cathode materials play a pivotal role in the performance of square lithium - ion batteries. These materials are responsible for storing and releasing lithium ions during the charging and discharging processes.

One of the most commonly used cathode materials is lithium cobalt oxide (LiCoO₂). It has a relatively high theoretical capacity and good cycling stability. LiCoO₂ offers a high operating voltage, which contributes to the high - energy density of the battery. However, it has some drawbacks. Cobalt is a relatively expensive and scarce element, and LiCoO₂ has limited safety at high temperatures. In addition, its energy density is gradually reaching a bottleneck.

Lithium nickel - manganese - cobalt oxide (NMC) is another popular cathode material. NMC combines the advantages of nickel, manganese, and cobalt. Nickel increases the capacity, manganese improves the structural stability, and cobalt enhances the conductivity. The ratio of nickel, manganese, and cobalt can be adjusted to optimize the performance of the battery. For example, high - nickel NMC materials, such as NMC811 (80% nickel, 10% manganese, and 10% cobalt), offer a higher energy density, making them suitable for applications where long - range driving is required, like electric vehicles.

Lithium iron phosphate (LiFePO₄) is also widely used, especially in applications where safety and cost - effectiveness are crucial. LiFePO₄ has excellent thermal stability and high - rate charge - discharge capabilities. It is more environmentally friendly as iron is abundant and non - toxic. Although its energy density is lower compared to some other cathode materials, its long - cycle life and good safety make it a preferred choice for applications such as energy storage systems and electric buses.

The choice of cathode material significantly impacts the overall performance of square lithium - ion batteries. It affects the battery's energy density, power density, cycle life, and safety. As the demand for higher - performance batteries continues to grow, research is ongoing to develop new cathode materials or improve the existing ones to meet the requirements of various applications.