Angewandte Chemie International Edition ,
Coming Soon: Improved Lithium Ion Batteries?
Three-dimensional porous silicon is a highly efficient lithium-storing anode
Contact: Jaephil Cho, Hanyang University, Ansan (South Korea)
Registered journalists may download the original article here:
Three-Dimensional Porous Silicon Particles for Use in High-Performance Lithium Secondary Batteries
lithium ion batteries 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 thus
usually runs only about two hours. The reason for this is the relatively
small capacity of the graphite anode in these 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.
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
would be nice to have an anodic material that could store more lithium
ions than graphite. 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.
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.
made of this highly porous silicon have a high charge capacity for lithium
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.
first charging cycle results in an amorphous (noncrystalline) silicon
mass around residual nanocrystals
in the pore walls.
even after 100 cycles, the stress in the pore wall is not
noticeable in the material.