We were given a preview of new research that Ford has been doing on fast-charging solid-state batteries a month ago. At the SAE WCX earlier this month, the engineers on the project shared a few more details about just how potentially game-changing this sort of technology could be. You have to be a bit of a battery geek to understand what's going on here, but you can find said details in the paper called Fast Charging Lithium-Ion Batteries by Xiao Yang and Ted Miller, and compare them to the current state of Ford's fast charging technology, as seen above.
As previously revealed, the headline details are that Ford has figured out a way to fast charge – and we mean really, really fast charge – a full-sized li-ion battery "without undue stress." How fast? Well, Yang and Miller say that, "5 Ah prismatic Li-ion cells can be fully recharged in 3 minutes under a constant rate of 20C, or in 2 min (25.5C) from 0% to 85% state of charge (SOC) without undue stresses." The test cells were five ampere-hour (Ah) li-ion prismatic batteries made by Panasonic.
Here's how the researchers described their some of their actions:
We cycle the battery at 16C charge rate from 0 to 100%SOC and do not see any unexpected battery capacity loss in 50 cycles, where half of the cycles are charged at 1C-rate as a reference capacity check. We realize that the batteries under the fast charge tests do not experience any negative impacts related to mass transport in either solid electrodes or the electrolyte system. In the paper, we propose a new procedure to measure the ac and dc resistances of the battery under continuous operation. Electrochemical impedance analyses on the whole battery and the individual electrodes are also conducted.
The paper authors say that charging a li-ion battery, "is more difficult than discharging them because of the sluggish insertion process of lithium ions into lattices of the graphite negative electrode in common Li-ion batteries." The good news is that lithium titanate (LTO), "does not experience any phase transition and less volume expansion during charging."
While this is all promising, the issues with this paper are twofold. First, the test results come from only 50 charge/discharge cycles, which is obviously not enough to judge if this sort of rapid fast charging will work in an actual electric vehicle. Second, the authors admit that, "In the paper, we demonstrate how fast a full-sized Li-ion battery can be recharged, though the power-typed batteries (150 Wh/l) under test are not intended for pure electric vehicle uses." So, this is more a theoretical EV battery tech that needs to be explored further than something that we can guarantee will be in the new Focus Electric.
If you have access to SAE papers or want to spend $27, you can get a copy of the report yourself here.