Driven by tighter CO2 regulations and more eco-conscious consumers, the pace of migration to electric vehicles continues to accelerate, with up to 10% of all vehicles sold by 2025 expected to be battery-powered, compared to less than 1% today.1 This is despite the high cost of batteries, which stubbornly remain approximately half of the overall cost of the vehicle.
While many factors go into determining the cost of the battery, one area manufacturers can make significant headway in cost reduction is during the final stages of manufacturing. Specifically, during battery formation and test, which can account for up to 20% of the cost of an EV’s battery.
Battery formation and test is a time-consuming process involving multiple charges and discharges that activate a battery’s chemistry—a process that can take up to two full days. This necessary procedure readies the battery for use and is critical to ensure its reliability and quality. Due to how slow the process is, it’s a significant bottleneck that prevents battery manufacturing from achieving greater throughput in an effort to lower overall battery-production cost.
However, partnerships between EV battery manufacturers and suppliers with formation and test systems expertise are allowing them to increase their attention to reducing the time and cost involved at this crucial stage of manufacturing. All the while, they’re still able to maintain the precision required for advanced battery chemistries.
Faster Throughput Equals Lower Battery Cost
To decrease the cost of batteries, manufacturers need to take a holistic approach that starts by leveraging suppliers’ system-level expertise to reduce the overall battery test circuit footprint while increasing the number of channels. It’s important to note that both must be done while maintaining the accuracy, precision, reliability, and speed of their battery formation and test measurements to ensure safety, performance, and reliability requirements are met.
This isn’t easy to do. For the front end, the power supplies driving the battery-charging circuits need to be tightly controlled. Going deeper, battery formation and test requires close monitoring of current and voltage profiles used during battery cycling to prevent overcharging and undercharging. This ensures safety during test, while also maximizing battery longevity, which greatly lowers overall cost of ownership for the end user.
For these critical battery measurements, very high-quality instrumentation amplifiers (in-amps) and associated shunt resistors are needed to measure battery charge/discharge current to better than ±0.05% accuracy, even under harsh factory conditions. The same level of accuracy applies to the difference amplifiers used to monitor the voltage over the entire thermal operational range.
Merging Functionality into One Chip
There are several ways to incorporate these components into a full solution, but it’s a significant challenge to maximize performance and minimize the system footprint. This is the reasoning behind Analog Devices’ development of the AD8452, which integrates the analog front end, power control, and monitoring circuits in a single IC (see figure). These ICs can include battery-reversal prevention, overvoltage-protection switches, and smart controls to prevent overcharge of batteries, and they can reduce the system footprint by 50%.
The AD8452 analog front-end, controller, and pulse-width modulator for battery test and formation systems.
This suite of capabilities allows battery manufacturers to incorporate more capabilities into test systems that will simultaneously make more efficient use of factory floor space. Moreover, they enable manufacturers to design systems with greater functionality and more robust testing procedures.
Efficient power conversion is, in turn, another opportunity to drive further system performance. By using the advanced switching architectures, test systems can minimize power consumption by enabling bidirectional energy exchange with the grid. Efficient power conversion also reduces the need for heat management equipment, which can add to the system’s overall cost and power consumption. The net result is a reduction in wasted energy and manufacturing cost. Enabling these capabilities requires an appreciation of system features, such as isolated gate drivers, which support the faster switching needs of newer silicon carbide and gallium nitride power switching technologies.
The benefits of working closely with suppliers who have system-level expertise and a broad portfolio of products goes beyond having access to more sophisticated components and building blocks. It also gives battery manufacturers access to reference designs for system architectures that can be more easily adopted, making time-to-market three to four times faster than if a battery manufacturer were to develop a formation and test system from scratch.
With the expectation that the global demand for EVs will increase at a CAGR of 21% out to 2021,2 the need for close partnerships between battery manufacturers and suppliers couldn’t be greater. Suppliers need to provide reliable, proven solutions that enable manufacturers’ systems to achieve new levels of efficiency. The best suppliers can help manufacturers bring these new capabilities to market even faster, and the results will allow battery and electric-vehicle production to flourish.
Vikas Choudhary is strategic marketing manager for battery formation and test products at Analog Devices, based in ADI’s Wilmington, Massachusetts office.
2. Electric Vehicle Market by Propulsion (BEV, PHEV, FCEV), Vehicle (PC, CV), Charging Station (Normal, Super, Inductive), Charging Infrastructure (Normal, Type-2-AC, CHAdeMO, CCS, Tesla SC), Power Output, Installation,and Region—Global Forecast to 2025.” MarketsandMarkets, June 2018.