Thin film lithium ion batteries are similar to conventional lithium-ion batteries, but they are composed of thinner materials, some only nanometers or micrometers thick, which allow the finished battery to be just millimeters thick. They have been developed primarily within the last decade . These batteries consist of a substrate, electrolyte, current collector, anode, cathode, and a separator. There has been much research into the determination of the most effective components for this type of battery. It has been shown recently that even ordinary printer paper can be used as a charge separator and a substrate. These thin film batteries are an improvement on the common secondary, or rechargeable, lithium ion batteries in some ways. The batteries exhibit the same voltage and current as their bulky counterparts, but their dimensions allow for making electronic devices like cell phones, laptops and even implantable medical devices smaller and also reduce the weight of portable battery powered devices because of their high energy density. These batteries can be formed into any shape and can be stacked thus further reducing the space needed.