Why Old Lithium Ion Batteries Provide Low Power Backup In Mobile Phones And Laptops?
Lithium ion batteries are being used in almost all conventional portable electronic devices including mobile phones and laptops. While a new battery holds charge for a day, after using it repetitively for a year or two, the power backup reduces to a few hours. Scientists call this diminished performance of batteries "capacity fade." Ever wondered why this happens?
Researchers from the Argonne National Laboratory, Illinois, have elucidated the detailed chemical changes that occur inside a lithium ion battery that leads to capacity fade. The power backup or capacity of lithium ion batteries depends upon the quantity of lithium ions that are shuttled between their positive and negative terminals. The movement of these ions define the charging and discharging of the batteries.
During this process of being shuttled back and forth, the lithium ions react with many transition metal ions viz. manganese. These reactions bring about transitory changes in the oxidation states of these metals. After repetitive use of the batteries, i.e., repetitive cycling of lithium ions, some of the manganese ions move out of the cathode region of the battery and get deposited in the anode region.
According to the research article published in Journal of the Electrochemical Society, the manganese ions further react with the solid-electrolyte interphase of the battery. These interphases are formed due to the reactions between the anode and the liquid electrolyte that help in shuttling lithium ions between the two electrodes.
The reaction of manganese and the interphase leads to the decomposition of the liquid electrolyte. This process of decomposition is simultaneous with entrapment of lithium ions in the interphase. This gradually reduces the total number of available lithium ions that can mediate the process of charging and discharging of batteries.
Furthermore, some of these reactions may lead to incomplete reduction of the interphase. Due to which, they continue reacting with more number of lithium ions. This chain reaction further reduces the number of lithium ions inside the battery, thereby causing reduction in their capacity, according to Phys.org.
According to the researchers who contributed in the said study, the number of manganese ions that get transported to anode is the main factor that determines the rate and extent of capacity fade. They also proposed that the information generated from the study may be used to innovate new regulatory mechanisms that may help in controlling the number of manganese ions transported. Therefore, it reduced the impact of capacity fade on the efficiency of lithium ion batteries.