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. Compared to other battery types, Lithium-ion batteries can store more energy in a smaller space, making them ideal for applications where weight and size are critical, such as in smartphones and laptops.