In Pursuit of an Immortal Cathode: Electrical Energy Storage using MnO2 Nanowires that Never Die
Rechargeable lithium ion (Li+) batteries lose their ability to store charge over time. Whether they power your phone, your laptop, or your automobile, after 500-1000 recharge cycles they lose 20-40% of their capacity and must be replaced. Sony introduced the first commercial Li+ battery in 1990, but 27 years later our understanding of WHY they fail is still in its infancy. Li+ batteries have four parts: An anode (usually graphite), a cathode (usually a metal oxide), a separator membrane that is located between them, and a salt solution containing Li+. In our research, we have focused attention on one cathode material called ∂-MnO2. Our goals have been to increase the amount of energy we can store, to increase the rate at which we can deliver this energy, and to extend the lifetime of the cathode. Now, you might think that the worst way to make a battery cathode last longer would be to make it smaller! But we have discovered a process for preparing ∂-MnO2 nanowires - just 60 – 600 nm in diameter and up to a centimeter in length – that never fail, and rarely lose any energy storage capacity, across 100,000 charge/recharge cycles. In this talk, I’ll discuss these unusual nanomaterials and what they may mean for the future of electrical energy storage.