EV battery design – innovating for longer range and battery life

This article originally appeared in the June'24 magazine issue of Electronic Specifier Design – see ES's Magazine Archives for more featured publications.

Looking forward, the automotive industry expects demand for Lithium-ion cells to grow by some 33% annually to 4,700GWh by the end of this decade.

More affordable EV batteries will help bring about the price parity between an EV and internal combustion engine car sooner than later. However, keeping a check on battery costs is a constant challenge because of rising raw materials, supply chain, and energy costs, with cell manufacturing being an energy-intensive process.

Technological innovations play a big role in contributing to the inverse relationship between plummeting prices and soaring demand for EV batteries. Cost pressures aside, battery technology must continue to evolve to support the dynamic e-mobility ecosystem.

Evolving roles of the EV battery

Figure 1. The EV battery plays a key role in the e-mobility ecosystem

Figure 1 illustrates an overview of the e-mobility ecosystem, and how the battery is impacted as the ecosystem evolves.

On the right, both automakers and battery developers have to create EV batteries that meet consumer expectations for longer ranges. On a macro level, higher capacity and longer-life batteries will support the integration of vehicle electrification into real-world applications for a circular battery economy to reduce waste and pollution.

On the left, we have an overview of the evolving smart grid, which affects how the electric vehicle battery will transform, from a one-way ‘sink’ that draws energy from charging stations to a two-way or bidirectional vehicle-to-grid (V2G) enabled power source. More on V2G later, as we dive deeper into how to make batteries better.

Designing for battery performance at cell, module, and pack levels

EV battery cells come in different form factors: cylindrical, pouch, and prismatic. Fundamentally though, the initial development phases are similar irrespective of form factors. Cell developers must characterise, select, and optimise the cell chemistries and materials in research and development.

Figure 2. Different battery cell chemical compositions yield different properties and performance

Meeting the expectations for longer range, faster charging, and future-ready V2G capabilities starts at the battery cell chemistry level. Depending on the battery performance specifications, cell developers need to analyse how each electrochemical cocktail will perform (see examples in Figure 2).

The modern battery test laboratory must handle thousands of cells under test at any one time, and accurately measure the actual performance of different cell designs to see if they meet design goals (see Figure 3).

Figure 3. Different cell characteristics must be considered when developing a new cell, as cell characteristics depend on their applications

In designing and testing batteries, the battery design manager must consider how to juggle various test parameters for different applications when the cells are eventually assembled into modules and packs to power the intended vehicles. Applications range from two-wheeler motorcycles to sedans, sports utility models, and heavy transport vehicles. The batteries for each end-user market are designed to meet different needs and will require different test set-ups. Hence, the test environment must be able to support the required voltage, channels, and safety requirements (see Figure 4).

Figure 4. Each stage of the development cycle needs test environments that can help validate the battery performance

These are some tests that need to be done to verify the battery’s performance at the cell, module, and pack levels:

• Record different temperatures to investigate the reciprocal electrical and thermal influence of the cells
• Check the mechanical connections and the performance of the module
• Communicate with the vehicles’ battery management system

Increasing role of automated management in the battery test lab

Figure 5. Data flow and management is essential in a modern battery test lab that oversees thousands of devices under test simultaneously.

Figure 5 provides a simple visualisation of the different roles and tasks in a battery test lab. With the vast number of devices under test, lab managers can no longer rely on manual tracking and spreadsheets to manage a modern battery test lab.

Automating lab operations is essential to ensure not only efficient time and resource management, but also provide tracking and traceability, as well as improving testing throughput. With vast facilities and different sites, Cloud-based lab operation management tools allow visibility and controlled accessibility on the state of battery testing operations. The test data collected from the devices under test can also be used to enhance design iterations.

Ensuring quality from blueprint to production

Once the new battery cell design is ready for mass production, it enters the mass production step, which is evolving rapidly. According to a McKinsey report, if demand for battery cells continues to increase at 30% annually, the global market will need another 90 gigafactories, as of current capacity, to support vehicle electrification over the next decade.

As the Americas and Europe catch up with China and Korea to manufacture electric vehicle batteries closer to their end-markets, billions of dollars are poured into ramping up gigafactory production, which is a complex process, as illustrated in Figure 6.

Figure 6. Cell cycling and ageing are the most time-consuming stages of the complex battery cell manufacturing process

There are many set-up challenges for a gigafactory, including location, budget, access to raw materials, manufacturing systems, and human resources. However, let’s focus on the intricacies of building better batteries from the cell-level up.

In any high-volume manufacturing environment, throughput is a vital barometer of productivity. In the Lithium-ion cell manufacturing process, the cell formation and ageing stages are the most time-consuming. During cell ageing, manufacturers must measure the cell’s self-discharge rate even when it is not connected to any device. The purpose is to sieve out errant cells that exhibit abnormal or excessive self-discharge, since such ‘bad’ cells adversely affect the performance of modules and packs.

A cell can take days, weeks, or months to exhibit its self-discharge characteristics. However, in a time and cost-sensitive manufacturing environment, the traditional way of tracking self-discharge over time is not practical.

Instead, some manufacturers now use a relatively new potentiostatic measurement method to directly measure the cell’s internal self-discharge current. This method typically takes hours or less compared with the traditional method of waiting for days or weeks to log the cell’s self-discharge performance, thereby saving time and precious floor space for holding the cells for this vital quality gate check.

New technology is creating more powerful battery cells that can charge faster. These cells need to undergo cycling, where cell samples are tested to determine the cell's cycle life and how the charge rate affects the cell's life. As cell capacity quickly increases, researchers, and manufacturers, need to source and sink larger currents.

To circumvent costly power consumption, modern cell cyclers employ regenerative power, where power regenerated during cell discharge is recycled back to the grid, thereby reducing net energy consumption to lower your operating costs. This process also generates less heat in the electronics, reducing the need to remove heat from the production facility.

Future-proofing battery test technology

As vehicle electrification continues to build momentum, battery developers and manufacturers must pre-empt new requirements in their battery testing capabilities. These include planning for equipment that can handle higher cell capacity, and source/sink larger currents, with regenerative power capabilities to lower operating costs.

Some manufacturers are also adopting modular and location-independent ‘superchambers’ to reduce their battery test investment time and costs, while allowing them the ability to scale up for rapid deployment in tandem with demand. These exciting innovations will undoubtedly help to further scale the development and production of better batteries to power the adoption of electric vehicles.