22Nov 2016

Qualcomm announced this week their 4th generation Quick Charge™ technology to be available in their upcoming Snapdragon 835 chipset. Quick Charge™ 4 continues to build on making fast charging an integral part of modern smartphones and consumer devices. In this latest generation, Qualcomm adds a number of key features, in particular, higher efficiency in delivering the power from the wall socket to the device, more power available for charging faster, and better thermal management. I applaud the continued evolution of Qualcomm’s QC technology.

As fast charging becomes an entrenched technology in the mobile landscape, the emphasis on battery safety itself during fast charging begins to take priority. As I highlighted in this earlier post, fast charging done improperly causes irreparable damage to the battery causing a loss of capacity (mAh) or worse yet, battery safety problems. Combining fast charging with high-energy density cells, especially the new generation that is operating at 4.4V, is a recipe for potential disasters. This post is about what can go wrong when we mix fast charging with high-energy density batteries, but neglect to implement the necessary charging intelligence and the necessary controls around the battery.

First, let me clarify a few things.

  • Fast charging includes the realm of charging the battery at rates near or above 1C . At 1C, the battery charges to half-full from empty (0 to 50%) in 30 minutes. QC 4.0 is capable to going at twice that rate, or 2C. That is very fast.
  • High-energy density batteries are those with energy densities in excess of 600 Wh/l, with the most recent ones at or near 700 Wh/l. The newest generation of these batteries are almost universally operating at 4.4V. This earlier post explains the risks and perils of operating at this voltage.
  • The last point I want to clarify is that the common charging approaches, namely CCCV and step charging do NOT provide any intelligence or controls around charging. They are open-loop methods with no mechanism to gauge the state or health of the battery in order to make the proper adjustments and avoid the risks that I will highlight below.

The mix of fast charging and high-energy batteries makes a very volatile situation. This reminds me of fancy car commercials with the fine print warning at the bottom of the screen: “Professional drivers on a closed course. Do not attempt.” Fast charging high-energy batteries is rapidly approaching this realm of cautionary warnings. The consequences of neglecting such advice can be dire especially as smartphone fires are fresh in our collective memories.

So what can go wrong?

To begin with, lithium metal plating is a huge risk when one attempts to fast charge a 4.4V cell. We see lithium plating on most if not all cells from reputable battery suppliers when charged using CCCV or step charging. This is a serious problem if not mitigated with the proper battery intelligence. Left unchecked, lithium metal plating can lead to safety hazards and potential fires. What makes lithium metal plating even more hazardous is that it is not easy to detect its presence inside your smartphone. By the time it develops into a potential electrical short inside the battery, it is often too late. Therefore it is imperative that the intelligence in the battery management seeks to avoid its forming from the very beginning of the battery’s life in your smartphone.

A second serious hazard is excess swelling of the battery. Yes, the battery will physically grow thicker as it is repeatedly charged. It is nearly impossible to measure the thickness of the battery once it is embedded inside your smartphone. Clever estimates of the thickness without physically touching the battery belong to the category of advanced intelligent algorithms that are becoming increasingly necessary. You might say: so what, let the battery swell! Excessive swelling will most certainly break your display screen.

A third hazard relates to the battery’s behavior at high temperature. The electronics inside your device consume power and cause the smartphone to get hot.  Those of you who have fast charging on your devices will attest to this fact. One misconception is that the battery itself heats up because of fast charging. That is not correct. The battery gets hot because of the heat generated by the electronics inside the smartphone. These temperatures can rise inside the smartphone to 40 °C, and in some many cases approaching 45 °C. These elevated temperatures accelerate the degradation of materials inside the battery especially at the elevated voltages. This leads to a rapid loss of charge capacity (your mAh drop very quickly) accompanied with excessive swelling of the battery. If you are an Uber driver with your smartphone fast charging on your dashboard on a hot summer day, this does not bode well for you.

These are only three examples of potential battery safety hazards associated with fast charging high-energy density cells using traditional charging methods…each one of them can lead to serious battery safety problems. That’s a good time to heed the warning in the car commercials. If you are not a professional, please do not attempt.