Lithium Ion (Li-ion) batteries are common in consumer electronics. It belongs to a family of rechargeable battery and uses lithium as the active material. During discharge, the lithium ions move from the negative electrode to the positive electrode. The flow of lithium ions reverse during charging. Lithium ion batteries are extensively used in portable devices due its features like best energy to weight ratio, absence of memory effect, high efficiency, slow self discharge etc.
The Li-ion battery has three components inside. These are Anode, Cathode and Electrolyte. The anode is made up of carbon and cathode is a metal oxide. The Anode is commonly made of Graphite. The metal oxide in the cathode may be Lithium cobalt oxide, lithium iron phosphate or lithium manganese oxide. The electrolyte is lithium salt dissolved in an organic solvent. It is a mixture of organic carbonates like ethylene carbonate or diethyl carbonate containing lithium ions. The sources of lithium ions are Anion salts like Lithium hexa fluorophosphates( LiPF6), Lithium hexa fluoro arsenate monohydrate(LiAsF6), Lithium perchlorate(LiClO4), Lithium tetrafluoro borate(LiBF4), Lithium triflate(LiCF3SO3) etc. Based on the anion salts used, the voltage, efficiency, life etc of lithium battery varies.
Lithium Ion Battery
Electrochemistry of Li-ion battery
Anode, Cathode and the Electrolyte in the Li-ion battery take part in the electrochemical reaction. During the intercalation process, lithium ions move from the electrolyte into the electrodes and during the de intercalation process, these ions move back into the electyrolyte.During the dis charging process, lithium ions from the anode move into the cathode and during charging reverse movement occurs. The electrolyte containing lithium ions act as the carrier between the anode and cathode when the battery discharges. The conductivity of the electrolyte varies depending on the temperature. Typically at 20-25 degree, it is around 10mS/cm.
Features of Li-ion cells
- Light weight and portable
- High open circuit voltage that deliver high power at low current rate
- Absence of Memory effect
- Low self discharge rate of 5-10% per month
Drawbacks of Li-ion cells
- Formation of an insulating deposit in the electrolyte that reduces ion transport. This reduces capacity overtime. Older batteries do not accept much charge.
- High charge level and charging heat reduces capacity
- Poor ventilation and heat reduces its efficiency. For example a Li-Ion Laptop battery losses 20% capacity in one year, if it is not properly charged.
- High internal resistance. This drops terminal voltage when connected to load.
- Li-ion batteries are not durable as other rechargeable batteries. These become dangerous if mistreated. High temperature and cell rupture may cause explosions.
- Charge the battery until the voltage limit per cell is reached
- Give maximum voltage per cell until the current drops below 3% of the rated charge current.
- Charge time is 3-5 hours.
- Lithium Ion cells are charged with 4.2 Volt per cell.
- Mobile phone battery can be charged at 1C current and Laptop battery at 0.8C current.
Lithium Air battery
This type of Lithium battery has the Lithium Anode electrochemically coupled to atmospheric oxygen through an Air Cathode. During discharge, lithium cat ions move from anode into the electrolyte and then into the cathode where it combines with oxygen. The cathode is made up of porous carbon. When the lithium ion combines with the oxygen in the cathode, Lithium oxide (Li2O) or Lithium peroxide ( Li2O2). The Lithium oxide is then coupled to the electrons from the battery and flow from Anode to Cathode through the load.
Lithium air battery has high energy density because the cathode is lighter and oxygen is freely available in the air and no storage is required. Therefore the cathode reactant is unlimited and the battery capacity is limited by the lithium anode only.
These are disposable type primary batteries using lithium metal as anode. They produce a wide range of voltage from 5.5 volts to 9.7 volts. These are widely used in portable devices. The 3 volt Lithium battery (CR Lithium / Manganese dioxide No. CR 2032) is used in computer mother board to keep the memory.
Lithium- ion Polymer battery
These are the common watch battery, or coin cell design to use in watches calculators etc. These are primary cells with voltage between 1.5 to 3 volts. Anode in the button cell is Zinc or Lithium. Cathode includes Manganese dioxide, Silver oxide, Carbon monofluoride, cupric oxide etc. The metal can of the battery is positive and the cap forms the negative. The watch batteries are usually numbered as L,S and C types.
The different forms of Button cells are.
LR = Alkaline, at 1.5V
SR = Silver Oxide, at 1.55V
CR = Lithium/manganese dioxide, at 3V
BR = Lithium carbon monofluoride, 3 V
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