Keysight Technologies: Watching the defectives

July 21, 2023


Hwee Yng Yeo, Industry & Solutions Marketing Manager at Keysight Technologies, charts the rise of the “gigafactory” in modern manufacturing and its security

The word “gigafactory” did not exist a decade ago, but gigafactories are now a cornerstone of the electric vehicle (EV) ecosystem. They have helped boost Lithium-ion (Li-ion) battery cell production from a capacity of 4-10 GWh pa to 40-80 GWh par.

Keysight Technologies has the products

Bringing cost efficiency to the forefront, high-volume battery cell production has led to a ten-year 90% plunge in EV battery prices.

Scaling up battery cell production requires high precision, automation, and quality checks at every step of a highly complex process across the gigafactory to produce the battery cell, the basic unit of battery modules which make up battery packs to power electric drivetrains.

Most EV batteries have 1,500 to 2,000 charge cycles, depending on the battery.

Keysight products, in both pre-deployment and real-world environments, enable dynamic security intelligence to help stay one step ahead.

Detecting defects

Battery cell performance can differ from its original design specifications due to electrochemical or mechanical defects during the manufacturing process.

Humidity, trace particle contaminants, and other factors adversely affect the cell, leading to faster discharge and cell failure. For example, tiny mechanical imperfections in a cell’s structure can generate significant deformities with each charge-discharge cell cycle, leading to shorter battery cell life.

Another example of defects entering the cell manufacturing process is during the tab-soldering step, where a mild tab burr can develop during tab welding. Tabs connect the anode and cathode layers to the cell’s external terminals. A burr can cause an internal short leading to thermal runaway.

A quality gate

Understanding how the cell will perform in real life versus its specifications requires each cell to pass many quality gates during manufacturing. This step checks how many times the cell can charge and discharge before it starts deteriorating faster and loses its capacity to be fully recharged.

Cell cycling is a lengthy process, taking days, weeks, or even months. Each cell must go through hundreds of cycles to characterise internal resistance and capacity retention vs the number of cycles.

In a modern gigafactory line, it is impossible to perform cell cycling quality checks on every cell. Instead, this quality gate is carried out offline on a sampling basis. 

To perform a cycle-life test, manufacturers use a cell cycler to characterize the cell’s response over time through a series of charge / discharge cycles with capacity and efficiency.

The superchamber

Innovative ways of implementing cost-saving quality gates are needed to boost efficiencies, lower operating costs, and further reduce the cost of the EV battery. This will in turn close the price parity gap between internal combustion engine cars and mid-range EVs. Figure 2 shows a typical cell cycling test setup, with each chamber capable of holding 10 -20 cells. Each chamber uses about 10kW of the energy that the cycler needs for charging and discharging the cells.

In a new way of implementing quality gates for cell manufacturing, a “superchamber” can help reduce floor space utilisation and power consumption in the gigafactory.

In the project by Keysight and Proventia, collaborators found the superchamber occupied only one-third of the floor space while providing equivalent channel capacity

If higher testing capacity is needed, additional superchamber blocks can be installed on-site more quickly to enable capacity expansion in tandem with manufacturing growth, while not compromising safety or security.

Operational efficiency savings

Another cost-saving component of using a superchamber as a cell cycling quality gate is the use of regeneration.

This is where energy from the discharging cells is recycled back to the AC power line.

These regenerative power systems can recycle 75% or more of clean power. Besides lowering the electric bill, much less heat dissipation reduces stress on the system components, increasing equipment reliability.

Less heat generation also allows for smaller system designs, further lowering floor space utilisation. A comparative study of the superchamber showed that it required only 50 kW of power versus 180 kW to run 18 traditional cell cyclers.

Software is also an indispensable tool that provides operational visibility and actionable insights for both managers and operators across the cell cycling quality gate.

Cloud-based applications provide enterprise-wide remote access at various levels for test managers and operators to monitor the test status of individual cells across thousands of channels.

Road to profitability

As vehicle electrification gains momentum, automotive manufacturers and their battery supply chain will continue to look for ways to lower battery cost.

Lower battery cost will help drive the switch from the commonplace internal combustion engine (ICE) to EVs for the mass market. Innovative ways of implementing cost-saving quality gates such as the use of superchambers, along with regenerative power and software-centric operations, can boost efficiencies, lower operating costs, and help shorten the road to profitability and accelerate EV adoption.

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