Lithium-ion batteries don't get a lot of respect these days, what with everyone talking about magical future batteries that are cheaper and won't make you Prius owners cause acid rain. They're everywhere still and they provide portable devices that require a lot of energy, such as mobile telephones, digital cameras, and notebook computers, with power. However, their capacity, and thus the running time of the devices, remain somewhat limited - a notebook computer usually runs only about two hours.
The reason is the relatively small capacity of the graphite anode in those batteries to absorb lithium ions. A team led by Jaephil Cho at Hanyang University in Korea has now developed a new material for anodes, which could clear a path for a new generation of rechargeable batteries. As reported in the journal Angewandte Chemie, their new material involves three-dimensional, highly porous silicon structures.
Lithium ion accumulator batteries produce current by moving lithium ions. The battery usually contains a cathode (positive electrode) made of a mixed metal oxide, such as lithium cobalt oxide, and an anode (negative electrode) made of graphite. While the battery is being charged, lithium ions migrate into the anode, where they are stored between the graphite layers. When the battery is being discharged, these ions migrate back to the cathode.
An anodic material that could store more lithium ions than graphite is what is needed and silicon presents an interesting alternative. The problem: silicon expands a great deal while absorbing lithium ions (charging) and shrinks when giving them up (discharging). After several cycles the required thin silicon layers are pulverized and can no longer be charged.
Cho's team has now developed a new method for the production of a porous silicon anode that can withstand this strain. They annealed silicon dioxide nanoparticles with silicon particles whose outermost silicon atoms have short hydrocarbon chains attached to them at 900 °C under an argon atmosphere. The silicon dioxide particles were removed from the resulting mass by etching. What remained were carbon-coated silicon crystals in a continuous, three-dimensional, highly porous structure.
Anodes made of this highly porous silicon have a high charge capacity for lithium ions. In addition, the lithium ions are rapidly transported and stored, making rapid charging and discharging possible. A high specific capacity is also attained with high current. The changes in volume that occur upon charging and discharging cause only a small degree of swelling and shrinking of the pore walls, which have a thickness of less than 70 nm. In addition, the first charging cycle results in an amorphous (noncrystalline) silicon mass around residual nanocrystals in the pore walls. Consequently, even after 100 cycles, the stress in the pore wall is not noticeable in the material.
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- A Dimuon Particle At 30 GeV In ALEPH ??
- Journalists - Please Fact Check Your "Doomsday" News Stories -They Terrify Young Children And Vulnerable People
- DDoS war: How zombie fridges bit the internet in the a$$ today.
- President Obama, Why Humans On Mars Right Now Are Bad For Science
- A Racist On The Jews: Let The Donald Trump!
- Biofuels Are A Climate Mistake
- EPA Again Delays Report On Safety Of Glyphosate
- "The only people who are in for a shock are the people who believe in it, when nothing happens...."
- "Oh, okay, you need to understand a bit about how solar systems form. It starts with a condensing..."
- "Are we gonna be in for a shock with this nibiru planet mr walker also if you had the chance to..."
- "The thing that gets me mr walker is planets can collide so why all of a sudden is this now impossible..."
- "Oh, I saw that comment thanks. I didn't see any point in replying. They gave no reasons, didn't..."
- Placebo: Bubbles Of Nothing Are Still Not Something
- People Who Take Drugs May Be Likelier to Commit Suicide
- Improved 'Screen Time' Guidelines Could Make Parents & Kids Happier
- Dr. Jamie Wells Named One Of America's Top Pediatricians
- Why Did EPA Delay Its Glyphosate Safety Report?
- Scientists Should Fight Postmodern Public Values