0-100 Real Quick

Routes to faster EV charging.

Jun 17, 2021

Customers are demanding faster charging electric vehicles in the race to improve electric vehicles. The best electric vehicles today take roughly 15-25 minutes to charge from 20% state of charge up to 80% state of charge. On first glance this may sound like a lot given that it only takes five minutes to fill an internal combustion engine (passenger vehicle) tank from empty to full.

As Drake would say, that’s real f***ing quick.

Charging an electric vehicle is unique, because consumers don’t typically charge to 100% and deplete to 0%. Electric vehicle owners may plug into their home or employer’s Level 2 charger on a daily basis likely resulting in the battery staying in a state of charge window. In fact, maintaining a state of charge in between 20%-80% is ideal to minimize any lithium metal plating that could reduce the battery performance over time.

While the consumer can do things to improve the battery longevity on their end, researchers and engineers are developing methods to improve the charging and discharging abilities of future Li-ion batteries.

The three main routes of improving charging speed are cathode chemistry, electrical engineering of the battery pack, and battery management system/software.

LFP Chemistry

LFP (lithium iron phosphate) has garnered much more attention recently due to the number of electric vehicles being produced in China. The majority of passenger vehicles and buses contain LFP batteries due to their lower cost and higher stability.

LFP can withstand higher C-rates without the need for significant thermal management.

High nickel chemistries such as NCA and NMC are still highly regarded for their higher energy density, but the market may be hitting an inflection point. In fact, Tesla CEO Elon Musk recently announced that they will not produce the 500+ mile Plaid+ due to decreased demand from customers. Longer range may not be the answer. A Tesla Model 3 LFP has a range of 208 miles (335km) and that just may be sufficient for an electric charging infrastructure in the midst of rapid buildout.

Prismatic LFP Render by Cleantechnica

Higher Voltage packs

The higher voltage architecture is more intriguing because of the electrical engineering and design optimizations that will set manufacturers apart from one another. The earliest Tesla models S, 3, and Y were built on a 375 volt architecture.

Customer satisfaction for these models are high, but as mentioned the consumer continues to demand faster charging times. In particular, a customer would like a vehicle that could charge from 20%-80% in about 15 minutes. In order to do this battery packs have to be able to handle higher current charging.

Some of the most recent models such as the Lucid Air, Hyundai Ioniq 5, and Porsche Taycan are built on 800+ volt architectures. Based on the general power equation this would mean that a typical battery pack could run on less current.

For simplicity let’s compare a 400V versus an 800V battery pack where both output 100kWh of power. The higher voltage pack would require half of the current to generate the same amount of power. Less current could translate into thinner cables (less weight) or a battery that could accept higher current during the charging process.

In the table below I have included some important statistics regarding some of the most popular vehicles. It appears there is a trend with the newer models being built on a higher voltage architecture.

InsideEVs did a great analysis of comparing some of these vehicles.

Battery Management System

The BMS or battery controller is where the magic happens. This is the area that requires expertise and experience to optimize battery performance.

Various inputs such as battery temperature, outside temperature, state of charge, state of health, and a host of other factors are considered for writing the software that determines how a battery performs.

As shown below the C-rate of different vehicle models can vary substantially. The Tesla Model 3 has a high peak charge for about the first 30% of the charging process, and then it drops off to <2C. The Ioniq 5 is at a lower C-rate up to 30% SoC, and then it steps up to nearly 3C for the next 20% of the charging process.

What is the proper charging system for the battery? That is up to the engineers designing the vehicle. In the end, the various differences in charging result in a battery that charges from 20% to 80% in 15-25 minutes.

The debate around range will continue for years to come, but I think we can all agree that there is a clear goal of producing an electric vehicle that charges from 20% to 80% in a similar amount of time that it takes to fill a fuel tank. The Hyundai Ioniq 5 has set a high bar at 15 minutes. Batteries are improving rapidly, but I welcome the input of others on this topic. Is pushing it below 10 minutes doable?

References:

TECHtricity

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