Lithium-ion batteries are rechargeable energy storage devices commonly used in portable electronics, electric vehicles, and renewable energy systems. They work by moving lithium ions between the positive and negative electrodes during charging and discharging, allowing for efficient energy transfer. These batteries are popular due to their high energy density, lightweight design, and low self-discharge rate. However, they require careful management to prevent overheating and extend their lifespan. Overall, lithium-ion batteries play a crucial role in modern technology and sustainable energy solutions.