Presented byDhruv JangdaUE115030

Nanowire Lithium ion batteries

Nanowires are microscopic wires that have a

width measured in nanometers. Typically their

width ranges from forty to fifty nanometers,

but their length is not so limited. Since they

can be lengthened by simply attaching more

wires end to end or just by growing them

longer, they can be as long as desired.

What are nanowires?

Nanowires are metal just like other, regular wires. The only real

difference in concept is their size. They also vary in complexity and uses.

While they can do many of the same things, they have many other

capabilities beyond those of regular wire.

What Are Nanowires Made of?

There are varying methods used to create nanowires. The most common involve either growing them or using DNA as a template. For the latter method, a solution containing the desired metal is mixed with DNA and then exposed to UV light. When exposed, the metal in the mixture bonds to the DNA and forms a microscopic wire, a nanowire. It’s width is dependent upon how concentrated the solution of the metal is. The more concentrated the metal solution, the wider the nanowire; likewise, the less concentrated, the thinner the wire will be.

How are nanowires made?

Recharge-ability: basically, when the direction of electron discharge (negative to positive) is reversed, restoring power.

The Memory Effect: (generally) When a battery is repeatedly recharged before it has discharged more than half of its power, it will “forget” its original power capacity.

Volume expansion of the ions while charging of the battery.

Practical factors on which a battery technology is made

• Electrochemical performance is determined by properties of the anode and cathode materials.• Currently, carbon is used as the anode material.

• Charge battery (lithiation): large volume expansion 200-400% LiM• Discharge battery (delithiation): volume contraction

xLi+ + xe- + M ↔ charge Lix+M-

Lithium Ion Battery

ElectrolyteAnode Cathode

Li Ion

Li Ion Discharge

Charge

“The storage capacity of a Li-Ion battery is limited by how much lithium can be held in the battery's anode, which is typically made of carbon. Silicon has a much higher capacity than carbon, but also has a drawback.”

“Silicon placed in a battery swells as it absorbs positively charged lithium atoms during charging, then shrinks during use as the lithium ion is drawn out of the silicon. This cycle typically causes the silicon to pulverize, degrading the performance of the battery.”

Challenges faced by Li-ion batteries

• “The lithium is stored in a forest of tiny silicon nanowires, each with a diameter one one-thousandth the thickness of a sheet of paper. The nanowires inflate to four times their normal size as they soak up lithium but, unlike other silicon shapes, they do not fracture.” Such batteries are then called Nanowire Si Li-ion batteries.

• Photos taken by a scanning electron microscope of silicon nanowires before (left) and after (right) absorbing lithium. Both photos were taken at the same magnification. The work is described in “High-performance lithium battery anodes using silicon nanowires,” published online Dec. 16 in Nature Nanotechnology.

Solution

Small NW diameter allows for better accommodation of large volume changes. All NW contribute to the capacity. Graphitized carbon (LiC6) – 372 mAh/g Silicon(Li22 Si5) – 4200 mAh/g (10x improvement!) Direct 1D electronic pathways for efficient charge transport (decrease in internal

resistance) : Due to stiff nature of Si nanowire when charged, charge transferring take place from root to end through the structure, hence a 1D motion. While for cracked particles it is not possible to maintain 1D charge transfer.

No need for binders (extra weight eliminated) : Binders are the edging materials used to bind the particles, so that they don’t get leaked away when cracked during full battery charge.

Data storage/transfer - transfer data up to 1,000 times faster, and store data for as long as 100,000 years without degradation

Advantages of Nanowire Si Li-ion Batteries

IBM has been doing research on forming U-shaped nanowires to create a “racetrack memory”.

This method would allow IBM to create a memory system with no moving parts and far greater

storage than flash memory. This U-shape is formed with closely arranged nanowires, allowing

fast transmissions and increasing storage size without adding to the overall size of the device.

Nanowires are also being developed for prototype sensors. These sensors will be used on gases

and biological molecules. They will be used to detect harmful agents by scanning each gas or

chemical on a molecular level. This is possible due to how small these wires can be. They will be

made out of materials that react to harmful agents, thus alerting to the presence of harmful

agents. For Star Trek fans, this would be a very similar device to the “Tri-Corder.”

What uses are nanowires being developed for?

Nanowires are not being heavily manufactured because they are still in the

development stage and are only produced in the laboratory. Until production has

been streamlined, made easier and faster, they will not be heavily manufactured for

commercial purposes. Furthermore, though they are 4 or 5 times more

effective than current technology, an industry-wide technology overhaul is not cost

effective at the moment.

Why Are Nanowires Not Being Implemented?

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