01-11-2020 | | By Robin Mitchell
Recently, Xiaomi announced the release of its latest 80W wireless charger and its ability to charge a 4,500mAh battery from 0% to 100% in 40 minutes. What are wireless chargers, what challenges does battery technology face, and why are fast chargers becoming important?
Batteries are a crucial power technology in electronics as they allow for portable devices which do not need to be physically connected to a mains power source. Interestingly, the first source of electricity for large continual experiments came from batteries in the form of the voltaic pile (static electricity machines did exist, but the battery allow for long-term study as well as experimentation). While many battery technologies are one-use only, some allow for the ability to recharge, and one technology in particular that has taken the world by storm is Lithium-Ion due to its high energy-density.
But battery technology is only half the picture; the ability to charge that battery is equally important. Factors that are important in battery charging systems include time to charge, protection features, and the charging method. For the longest time, cables have been used to connect batteries to a charger, but recently wireless chargers have become more popular. Wireless chargers are those that use a wireless method for transmitting energy such as light and sound, but by far the most popular method is magnetic induction. The charging station has a large coil which has an AC passed through it. The receiving device has a coil inside it too, and when placed near the charging station, the magnetic flux from the charging station induces a current into the device’s coil. From there, the induced current is used to charge the battery, and thus the use of wires between the device and the charger is eliminated.
While Li-Ion batteries have high energy densities, they are not without their flaws and challenges. The first is that due to their large energy density, they are prone to react when broken or short-circuited violently. When a Li-Ion battery fails, it generally releases hydrogen, and the rapidly increasing temperature ignites the hydrogen to create streams of burning gas that can start fires. The second issue that Li-Ion batteries face is memory effect; Li-Ion batteries have a limited number of charging cycles before they deteriorate. Li-Ion batteries also face issues with over-charging, under-charging, and charging speed. If a Li-Ion battery is charged too fast, or for too long, then the battery chemistry can breakdown, thus resulting in a violent reaction.
Understanding the growing demand for fast chargers, Xiaomi has recently announced their 80W wireless charger which is stated to be able to charge a 4,000 mAh battery to 10% in 1 minute, 50% in 8 minutes, and 100% in 19 minutes. The demonstration of the wireless fast charger demonstrates how wireless charging not only provides convenience but can provide short charging times near to those provided by wired fast charging systems. While 80W fast charging smartphones are not currently in production, it is expected that the new 80W wireless charger will become commercially available soon especially considering that 50W versions of their wireless charging technology are already in production. The video demonstration of the Xiaomi 80W charger demonstrates the system being used on a modified Mi 10 Pro and considering that the Xiaomi 10 Mi has the fastest wireless charging on the market (50W). It can be expected that the next generation of Xiamoi Mi devices will integrate 80W charging.
Wireless chargers are not without their issues; they are more energy wasteful than their cable counterparts; they cannot deliver as much energy as wired systems, and can only work with devices in close proximity. However, wireless chargers do have some major advantages which may seem them replace wired systems in a wide range of different applications.
The first is that by eliminating the cable, the cable connectors can be removed, thus eliminating the possibility of mechanical damage. Cable connectors are a common source of failure, and mechanical stress on the connector can damage the PCB. It can also damage the connector itself, and this can make it impossible to charge or transfer information to and from the device (i.e. via a USB connector).
The second is that the elimination of the connector allows for an environmentally sealed design. Charging ports have to expose metal contacts for use in charging, and these can become rusted, corroded, or damaged depending on the environment that the device is exposed to. Thus, the use of wireless charging systems allow for designs to be entirely sealed, and charging is easily done by simply placing the device on the charging bed.