New battery engineering

  • 18-Jul-2011 02:30 EDT
M. Klein - CPI Portraits-011803.jpg

Martin Klein, Engineering Director, LG Chem Power Inc. (LGCPI), and member of SAE International, wrote this article for AEI’s 100th anniversary. Over the last six years, Klein’s team has been responsible for the design of battery packs for many different applications and customers.

It is hard to recall a new automotive technology that has received as much attention from nonautomotive media as vehicle electrification and, more specifically, batteries. Environmental publications debate the impact of electric vehicles (EVs) on planet Earth; business publications debate the viability and profitability of battery suppliers; investment publications analyze start-up EV and battery company IPOs; trade journals for minerals and raw materials debate supplies of lithium and rare earth metals; national news outlets cover a U.S. president’s visit to a battery plant groundbreaking; and Jay Leno holds celebrity EV races.

But for all their glamor and promise, emerging EV technologies face age-old challenges in their quest for introduction into high-volume production—namely, demonstration of safety, quality, and value. OEMs will not and cannot accept even the most promising new technologies until these fundamental attributes are demonstrated.

Large-format lithium-ion batteries are a good “new-tech” example. Consider the complexity: electrochemical reactions + embedded electronics and software + large package geometry and mass + high voltage + thermal management. Traditional engineering disciplines are more important than ever in this domain: failure mode effects and analysis, computer-aided engineering, computational fluid dynamics, and electronics circuit simulation, to name a few.

Battery-cell design alone requires optimization of chemistries for anodes, cathodes, and electrolytes; unique mechanical properties of separators; bonding techniques for electrodes, tabs, and casings; and embedded safety features. Electronic circuits measure and report voltages, currents, and temperatures while also controlling relays and thermal management components (fans, pumps, chillers). Embedded software algorithms calculate state-of-charge and power limits, perform real-time diagnostics, and make decisions on when to cool the pack, balance cells, or stop taking charge.

Systems engineering takes a lead role in tying these complex subsystems together. For instance, battery “life” (that is, the period of time over which energy storage capacity is reduced to a predetermined percentage of its beginning-of-life value) is dependent on many factors, such as cumulative time of exposure to high temperatures, number and nature of charge/discharge cycles, and mechanical integrity of the cell retention structures.

The battery systems engineer, therefore, must consider trade-offs in several areas to ensure battery life exceeds 10 years at expected levels of performance while not adding features that increase cost or mass. For example, investing in higher accuracy voltage and current measurement methods will allow cells to be operated closer to their full Vmin/Vmax range; active heating and cooling can extend cell life and range of operation but adds mass and controls complexity. How much electronics integration should occur at the module level vs. a pack-level centralized circuit topology?

The automobile—and automobile engineering—has been a remarkably complex and resilient industry over the past 100 years. More recently, vehicle electrification has attracted government grants, venture capitalism, Hollywood, and “Green Faith” to the conversation. However, commercially viable volumes will not be realized until safety, quality, and value are firmly established. And those attributes are the essence of good automotive engineering. It’s what we do.

Martin Klein, Engineering Director, LG Chem Power Inc., wrote this article for Automotive Engineering.

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