A lithium-ion battery is a type of rechargeable battery commonly used in portable electronics, electric vehicles, and renewable energy storage. It works by moving lithium ions between the positive and negative electrodes during charging and discharging, which allows it to store and release energy efficiently. These batteries are popular due to their high energy density, lightweight design, and low self-discharge rate. They are found in devices like smartphones, laptops, and electric cars, making them essential for modern technology and sustainable energy solutions, such as solar power systems and electric grids.