Inductive charging threat to lithium battery performance

June 28, 2019 //By Nick Flaherty
Inductive charging could compromise lithium battery performance - comparing (a) AC mains charging (cable charging) and inductive charging when coils are (b) aligned and (c) misaligned
Inductive charging risks depleting the life of mobile phones using typical lithium-ion batteries say UK researchers.

The team at WMG at the University of Warwick found that the design of smartphones with inductive charging, especially when the coils are misaligned, led to increased heating of the batteries, reducing the lifetime of the cells. 

Inductive charging enables a power source to transmit energy across an air gap, without the use of connecting wire but one of the main issues with this mode of charging is the amount of unwanted and potentially damaging heat that can be generated. There are several sources of heat generation associated with any inductive charging system - in both the charger and the device being charged. This additional heating is made worse by the fact that the device and the charging base are in close physical contact, any heat generated in one device may be transferred to the other by simple thermal conduction and convection.

Standardisation of charging stations and inclusion of inductive charging coils in many new smartphones has led to rapidly increasing adoption of the technology. In 2017, 15 car models used the technology in consoles for inductively charging consumer electronic devices, such as smartphones.

In a smartphone, the power receiving coil is close to the back cover of the phone (which is usually electrically nonconductive) and packaging constraints necessitate placement of the phone's battery and power electronics in close proximity, with limited opportunities to dissipate heat generated in the phone, or shield the phone from heat generated by the charger. It has been well-documented that batteries age more quickly when stored at elevated temperatures and that exposure to higher temperatures can thus significantly influence the state-of-health (SoH) of batteries over their useful lifetime.

For most chemical reactions, the reaction rate doubles with each 10 °C rise in temperature. A lithium ion battery operating above 30 °C is typically considered to be at risk of a shortened useful life. Guidelines issued by battery manufacturers also specify that the upper operational temperature range of their products should not surpass the 50 to 60 °C range to avoid gas generation and catastrophic failure.

Next: The inductive charging tests

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