Why Laptop battery reduces its efficiency? Tech Focus 9

Laptop battery is a kind of Lithium Ion ( Li-ion) battery which has features like high efficiency, slow discharge rate, best energy to weight ratio etc.Unlike other rechargeable batteries, Lithium ion battery 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 battery outperforms other types with its features like High open circuit voltage that deliver high power at low current rate, Low self discharge rate of 5-10% per month etc. But along with these advantages, lithium ion battery has demerits also. Memory effect, self discharge, over heating etc are the most important drawbacks of Laptop battery. Let us see how this happens and the solutions to prevent this.

Memory effect

 This is a term used to describe what happens when the battery is constantly recharges without it discharging fully. While batteries are not alive, this is referred to as the battery forgetting that it has unused capacity and it discharges faster each time that it is used. To avoid memory effect, recharge the battery only when it needs charging.

Self discharge

Another problems is the self discharging when the battery is not in use. Even while not in use, the battery will slowly be drained. When you finally try to turn on your laptop, the battery will be in a dead condition . The solution is charge the battery fully and remove it from the laptop and store in a cool ventilated place.

Over heating

During operation, Laptop generates very high temperature which passes out through the vent near the battery cabin. This will increase the temperature inside the battery cabin. Battery also generates heat since it is delivering high current for laptop. If this happens, the battery would be removed and allowed to cool off.

Factors reducing battery efficiency

1. Formation of an insulating deposit in the electrolyte that reduces ion transport. This reduces capacity overtime. Older batteries do not accept much charge.

2. High charge level and charging heat reduces the battery capacity

3. 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.

4. High internal resistance. This drops terminal voltage when connected to load.

5. Li-ion batteries are not durable as other rechargeable batteries. These become dangerous if mistreated. High temperature and cell rupture may cause explosions.

What is inside?

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.
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.

Charging Hints

1. Charge the battery until the voltage limit per cell is reached

2. Give maximum voltage per cell until the current drops below 3% of the rated charge current.

3. Charge time is 3-5 hours.

4. Lithium Ion cells are charged with 4.2 Volt per cell.

5. Mobile phone battery can be charged at 1C current and Laptop battery at 0.8C current.

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