Anode materials in square lithium - ion batteries are essential for the reversible insertion and extraction of lithium ions. They work in tandem with the cathode materials to enable the flow of electric current.

Graphite is the most commonly used anode material in commercial lithium - ion batteries. Graphite has a layered structure, which allows lithium ions to intercalate between the layers during charging. It offers a relatively low working potential, close to that of metallic lithium, which results in a high - voltage output for the battery. Graphite also has good cycling stability and high - rate charge - discharge capabilities. However, its theoretical capacity is limited, which restricts the overall energy density of the battery.

Silicon - based materials are emerging as promising anode candidates. Silicon has a much higher theoretical capacity compared to graphite, approximately ten times more. When lithium ions react with silicon, they form lithium - silicon alloys, which can store a large number of lithium ions. However, silicon undergoes significant volume expansion and contraction during the charge - discharge process, which can cause cracking and pulverization of the electrode, leading to a rapid decline in battery performance. To address this issue, various strategies are being explored, such as using silicon nanoparticles, composites with carbon materials, or applying special coatings.

Another type of anode material is lithium - titanate (Li₄Ti₅O₁₂). Li₄Ti₅O₁₂ has a unique spinel structure. It offers excellent cycling stability and high - rate performance. Unlike some other anode materials, Li₄Ti₅O₁₂ has a relatively high operating potential, which can enhance the safety of the battery. However, its energy density is relatively low compared to graphite - based anodes.

The development of advanced anode materials is crucial for improving the performance of square lithium - ion batteries. By increasing the capacity and cycling stability of the anode, the overall energy density, lifespan, and power capabilities of the battery can be enhanced, meeting the growing demands of modern applications.