Industry Voices | Improving the BEV Charging Experience

The internal-combustion engine has been continuously developed for over a century, reaching impressive levels of efficiency, performance and robustness. As a result, drivers can consistently rely on their combustion-engine vehicles to perform as expected, regardless of fuel quality or environmental conditions.

In contrast, lithium-ion batteries powering electric vehicles are still relatively new. Although progressing rapidly, these batteries have inherent limitations, such as lower energy density compared to gasoline or diesel fuels. It is therefore crucial to maximize the energy stored and utilized in each battery cell, which depends not only on the cell design, but also on the charging process. Unlike refueling a combustion-engine vehicle, the BEV charging experience can significantly impact battery life and performance.

It matters little to the combustion engine whether the ambient temperature is 10°F (-12˚C) or 90°F (32˚C) as the hydrocarbons flow into the tank, and none at all on the level at the start or finish of the refueling process. But fast charging can have a marked influence on battery life, and so can temperature and state-of-charge levels when the BEV is plugged in.

OEMs and their battery suppliers know this and factor these variables into the design of the battery, its thermal management systems and control software. This gives them confidence that the battery – mandated in the U.S. with an 8-year/100,000-mile (161,000-km) warranty, and 10-year/ 150,000-mile (241,500-km) in California – will meet the needs of customers, not incur excessive warranty costs and deliver a robust service life beyond that period.

Most BEV battery-management systems rely on lookup tables, resulting in a stepped charging process that falls short of the battery’s technical limits. This conservative approach aims to prevent harmful processes like lithium plating that can degrade battery life and safety.

High currents during fast charging can result in lithium buildup on the anode, reducing energy storage capacity, range and battery life over time. This process also increases internal resistance, leading to longer charge times and reduced vehicle performance.

Severe lithium plating results in the formation of lithium dendrites; if these become large enough, they can pierce the cell separator, leading to short circuits and potentially overheating within the battery or even thermal runaway. This will remain a challenge with solid-state batteries as well, as dendrites can also pierce solid electrolytes, which effectively perform the same function as separators.

Stepped charging profiles based on lookup tables are not intelligent or adaptive, leading to a damaging feedback loop where the control strategy fails to account for the reduction in battery health over time, accelerating degradation and shortening the battery’s lifespan.

An alternative is a physics-based model that powers adaptive charging software, replacing traditional lookup tables. This real-time, closed-loop model precisely estimates the battery’s electrochemical states, actively mitigating harmful processes like lithium plating and controlling degradation by adapting the charging to the battery’s state of health.

It’s also worth noting that traditional charging slows down significantly when batteries are partially charged, for example starting at 30% or 50%. However, physics-based models maintain more consistent charging speeds regardless of the starting state of charge, which is important given that customers in real-world use don’t always plug in when the state of charge drops to 10% – the charge level typically quoted in product brochures. Also, in physics-based charging, the system performs reliably even when it’s cold or hot, unlike traditional charging strategies that are significantly impacted by temperature.

For consumers, physics-based charging provides a more consistent, reliable experience with less range degradation over time, which is essential for persuading skeptical EV buyers to switch from familiar combustion-engine vehicles. For OEMs, it can reduce warranty costs by improving battery durability. It may also enhance EV resale values as new regulations require disclosing battery state-of-health and lifetime information to consumers.

Volvo Cars has demonstrated that this system can reduce the time taken to charge from 10%-80% by as much as 30% without affecting energy density or range. Performance enhancements are also not only limited to start of life and can maintain faster charging speeds than existing charging protocols throughout the battery lifetime. With more OEMs quoting charging in miles of range gained in 15 minutes, this is an important metric – particularly as a good charging experience means more time driving and less time plugged in.

Batteries are the most expensive BEV component, so extracting maximum value before end-of-life is essential for sustainability. BEVs must also deliver the charging experience, range and durability to make the transition from combustion vehicles seamless for consumers.