High-energy lithium battery chemistries (e.g. silicon, lithium metal, sulfur) have the potential to facilitate our transition away from fossil fuels and towards renewable energy resources (solar, wind). In particular, silicon has more than ten times the capacity of conventional battery materials. Unfortunately, batteries using silicon cannot be recharged because the material fractures and loses electrical contact during charging and discharging, rendering the broken particles inactive. For the first time, we’ve demonstrated that by encapsulating each silicon particle within a graphene cage, the ruptured fragments continue to be electrochemically active. This graphene cage encapsulation strategy (patent submitted) allows us to achieve specific capacities more than four times that of conventional materials and enable the stabilized silicon to be recharged 300 times.
When used in lithium-ion battery anodes, silicon microparticles swell, break apart and react with the battery’s electrolyte to form a thick coating that saps the anode's performance, top. To address these problems, we built a graphene cage around each particle, bottom. The cage gives the particle room to swell during charging, holds its pieces together when it breaks apart, controls the growth of the coating and preserves electrical conductivity and performance. (Y. Li et al., Nature Energy)
This time-lapse movie from an electron microscope shows the new battery material in action: a silicon particle expanding and cracking inside a graphene cage while being charged. The cage holds the pieces of the particle together and preserves its electrical conductivity and performance. (H. Lee, Y. Li/Stanford University)
Dry eye disease is one of the most common human ocular disorders, affecting up to 60% of the world’s population and characterized by a painful burning and itching sensation. Contact lens wear and dry climates further exacerbate these symptoms. A primary cause of this disease is excessive evaporation of tears, which greatly increases the salinity in our eyes. Thus, studying rates of human tear evaporation is key to understanding and possibly alleviating dry eye disease. Previously, devices for measuring tear evaporation were flawed in their design and unable to account for several important experimental variables (i.e. air flow, temperature, and humidity). Considering the fundamental mass and energy concepts for the evaporation of water, we designed an accurate, safe, and convenient diagnostic tool for clinical evaluation of dry-eye related maladies (patent submitted).
A nanosize squeeze can significantly boost the performance of platinum catalysts that help generate energy in fuel cells, according to a new study by Stanford scientists. The team bonded a platinum catalyst to a thin material that expands and contracts as electrons move in and out, and found that squeezing the platinum a fraction of a nanometer nearly doubled its catalytic activity...Read more
Micrometre-sized silicon particles are attractive negative-electrode materials for lithium-ion batteries but are prone to mechanical failure during electrochemical cycling. Now, graphene cages grown conformally around the micro-silicon particles are shown to improve their cycling stability...Read more
Approach could remove major obstacles to increasing the capacity of lithium-ion batteries ...Read more
A network of spiky nickel nanoparticles allows electrical current to conduct through a battery, and shuts it down if the battery overheats...Read more
Hydrogen fuel cells promise clean cars that emit only water. Several major car manufacturers have recently announced their investment to increase the availability of fueling stations while others are currently rolling out new models and prototypes. However, challenges remain, including the chemistry to produce and use hydrogen and oxygen gas efficiently...Read more