The Lithium-ion battery is a rechargeable battery ideal for portable electronics because of it's high charge density and slow self discharge when not in use. Also, they do not have a memory effect. Lithium ions are stored on the negative electrode and move to the positive electrode through an electrolyte during discharge. The electrodes act like sponges which absorb electrons and then release them.
An anode is an electrode through which an electric current flows into a polarized electrical device. Mnemonic: ACID (Anode Current Into Device) In a device which consumes power - an iPad (Vcc) is the positive anode. In a device which provides power like a battery charger, the Anode is negative (on the battery) as the electrons are flowing back into the battery.
The electrolyte is important too. In 1996, the Lithium-ion polymer battery was released. These batteries hold their electrolyte in a solid polymer composite instead of a liquid solvent. This evolution allowed the batteries to be made in a flexible wrapping instead of a solid case which is better suited for PDA's, mobile phones and Apple's design choice of embedding the battery inside the case. The polymer electrolyte also has a higher energy density which increases the operating time of devices like the iPad.
Battery aging occurs with the cycles. When electrons flow back and forth between the anode and cathode filaments called dendrites begin to wick into the electrolyte. CAF is the term used in printed circuit board construction = Cathode to Anode Filaments. In printed circuit boards - some of the copper from the vias move into the insulating layers of the dielectric. FR-4 is one of the most commonly used board materials. It is a copper clad laminate between layers of woven glass and epoxy. The PCB and the lithium battery have a simular effect in that over time filaments grow in the insulating material. For batteries, it means that as the lithium disperses into the electrolyte, there is less space on the sponges to hold electrons. Different chemistries and battery cell manufacturers provide varying lifespans. A reasonable cycle count after which your battery will start to degrade is 200 cycles. Imagine the electrode as a parking garage with fewer places to park than it had when it was new - also known as original design capacity in milli-Amp hours.
A brief history.
Michael Faraday 1791 - 1867 was born in London and was the son of a blacksmith. He was a great experimenter and observer. He used the sunrise on the east to help his memory and naming. The Anode is the doorway where the current enters the electrolyte. The east being the Anode, the sun rising in the east traversing towards the West into the electrolyte. The positively charge cations move away from the anode to the Cathode during discharge. It was James Clerk Maxwell that put Faraday's observations to mathimatical formula demonstrating the relationship to an electrical field and a magnetic field.
There have been many different approaches to the composition of the Anode and Cathode sponges. The electrochemical properties of lithium intercalation in graphite were first discovered in 1980 by Rachid Yazam and colleagues at the Grenoble Institute of Technology and the French National Centre for Scientific Research. They demostrated the reversible intercalation of lithium into graphite in a lithium/polymer electrolyte/graphite half cell. A long sentence to say: it is the reversible nature that make batteries rechargable. Their work was published in 1982 and 1983. It covered both the thermodynamics of the staging and the kinetics of the diffusion. The electrolyte composition has also been a study of many approaches.
Around 1991 Bell labs was experimenting on using graphite as the anode and maganese spinel for the cathode.
In 1996, Goodenough, Akshaya Padhi and colleagues at the University of Texas in Austin identified lithium iron phosphate as cathode materials.
In 2002, Yet-Ming Chiang and his group at MIT found a substantial improvement in the performance of lithium batteries by boosting the material's conductivity by doping it with aluminum, niobium and zirconium.
Then in 2004, Chiang again increased performance by utilizing iron-phosphate particles of less than 100 nanometers in diameter. This decreased the particle density by almost one hundredfold while increasing the cathode's surface area which improved both capacity and performance. Commercialization led to a patent infringement battle between Chiang and Goodenough.
A123 Systems (Nasdaq: AONE) was founded in 2001 in Watertown, Mass from the work initially developed at the Massachusetts Institute of Technology. The Nanophosphate® technology is built on novel nanoscale materials and is a game changer for energy storage systems that deliver high power and energy density, long life, and excellent safety performance for the transportation, electric grid and commercial markets.
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