By their design, mobile devices, especially smartphones are always on, and with today’s need for high speed data communication via mobile base stations providing 4G data and voice services, energy consumption is significantly higher than feature phones of the previous mobile telecommunications era. Thus, battery capacity and energy consumption became primary points of consideration in smartphone design. Specifically, one approach for allowing continuous on state of the smartphone for two consecutive days with 4G connection would be increase in battery capacity beyond 2000 mAh (milli ampere hour, a unit of energy storage). Alternatively, there could also be improvement in energy efficiency in apps usage and through device design that could, hopefully, increase the battery life of the device.
But, improvement in energy efficiency and battery capacity could only lengthen the per charge usage time of the device. Charge time remains a significant problem in smartphone design and many companies have invested significant resources and time in developing improved charging software, and procured better batteries able to handle increased current flow necessary for fast charging.
In every smartphone lies a charging software which regulates the amount of current flowing into the battery. However, recent smartphone releases more commonly feature ultrafast charging capability, which allows a smartphone of battery capacity of 3000 mAh to be fully charged within 15 minutes (or at most 30 minutes). Such charge speed would necessarily require a current significantly higher than the typical 2.1 A used in charging smartphones, which may pose serious threats to the integrity and safety of the battery.
Specifically, a charge current higher than the typical 2.1 A used in charging smartphones and tablets meant that there is significant Joule heating associated with the larger current flow. Increased thermal heating could possibly reduce the integrity of the critical membrane that separates the battery’s anode and cathode, which may lead to the leakage of electrolytes. Perforation of the membrane would result in dysfunction of the battery and increased fire risk, which, in the worse case scenario, could result in explosions. All in all, a high charge current would inevitably reduce the usage life of the battery.
Additionally, electronics on the motherboard could also be significantly damaged, over many charge cycles, by the high current necessary for ultrafast charging. More importantly, damage in electronics could result in dangerous short circuits, that ultimately result in total dysregulation of the current flow and the charging process and, by extension, destruction of the mobile device.
Therefore, requirement for fast or ultrafast charging has potentiated the development of next generation high capacity, low mass charge storage device in mobile phones and tablets. Specifically, through use of material of higher strength under thermal stress conditions, as well as new battery design concepts, batteries capable of withstanding the heat and high current associated with fast charging has been developed, and deployed for use in consumer electronics smartphones and tablets. Another avenue for improving charge speed and capacity lies in finding new energy storage chemistries suited for low thermal heating charging within a reasonable fast speed. Use of new energy storage chemistries would mean a redesign of the battery architecture, that ultimately, seeks to deliver more storage capacity over a longer cycle life.
Overall, ultrafast charging has find applications in increasing number of smartphones, and have even been incorporated into mid-range phones. However, risk of excessive thermal and mechanical stress arising from extra fast charging meant that fire and explosion risk cannot be discounted from the overall safety assessment of modern smartphones, especially ones equipped with 3000 to 4000 mAh batteries. Nevertheless, improvement in design and development of new membranes and housing structures afford the opportunity for battery manufacturers to develop new generation of miniaturized batteries for mobile applications, which in enabling fast charging, provide an avenue for increasing the overall usage time of the device. Though more expensive, perceived requirement for fast charging has nevertheless driven the sales of new high capacity batteries from battery manufacturers to device developers. Incorporation of such batteries able to endure the heat and mechanical stress of ultrafast charging in even mid-range smartphones and tablets has driven the price of such devices up, which, from a consumer perspective, may be the start of an unhealthy trend in cost escalation from provision of a “want” (i.e., ultrafast charging) in a “need” device.
Category: materials, energy storage, physics, chemistry, batteries, nanotechnology,
Tags: ultrafast charging, battery membrane, electrolytes, mechanical integrity, battery housing, fire risk, short circuit,
Acknowledgement: Ng Wenfa thank Seah Kwi Shan for co-authoring this blog post.