Innovations in EV Battery Technology - The Pursuit of Greater Range & Longer Battery Life

Author : Hwee Yng Yeo - Automotive Test Specialist, Keysight

06 July 2024

Figure 1: The EV battery’s role in the e-mobility ecosystem
Figure 1: The EV battery’s role in the e-mobility ecosystem

The quest for extended range in electric vehicle (EV) batteries is resulting in unprecedented engineering advances. From solid-state batteries to sodium-ion cell chemistries, battery manufacturers are pouring billions into research and development efforts.

Besides boosting travelling distances between recharges, exploring the usage of more accessible materials to lower EV battery price points is another key market driver. This article looks at the test implications.

The EV battery is a critical part of modern automotive technology, which has successfully scaled to support the current e-mobility boom. The average EV battery pack has seen a 90% price drop over the course of the last 15 years. Looking ahead, the automotive industry expects demand for lithium-ion (Li-Ion) cells to grow by some 33% annually to 4,700GWh by the end of this decade. 

More affordable batteries will help bring about price parity between EVs and internal combustion engine (ICE) cars. However, keeping a check on battery costs is a constant challenge - because of rising raw materials, supply chain and production expenses, 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 EV battery demand. Cost pressures aside, battery technology must continue to progress in order to support the dynamic e-mobility ecosystem.

Makings of a power pack on wheels
Figure 1 illustrates an overview of the whole e-mobility ecosystem, and how the battery is impacted as the ecosystem evolves. 

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

On the right, car manufacturers and battery developers both have to create EV batteries that meet consumers’ range expectations. At 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 EV battery will transform - going from a 1-way ‘sink’ that draws energy from charging stations to a 2-way vehicle-to-grid (V2G) enabled power source.

The right chemistry for the right use
Not all EV battery cells are the same - their design and specifications will depend on the vehicle use model. As an extreme comparison, let’s take the specialised battery of a Formula E race car versus that of a typical family EV. Specifications for the Formula E car’s Gen3 battery pack will include being able to absorb 4kWh of energy at a 600kW rate during a 30s pit stop. For most EV drivers though, recharging at a public station will take anywhere between 20mins and 8 hours, depending on if a DC fast charging point is used or not.

Whether the battery specifications are for a sports racer, a family car, or an electrified 18-wheeler truck, concocting the right cell chemistry to meet such specifications is paramount. EV battery cells come in different formats - cylindrical, pouch and prismatic. Fundamentally though, the initial development phases are similar, irrespective of the form factor involved. Cell developers must characterise, select and optimise the cell chemistries and materials during research phases. 

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

Figure 3. Different characteristics need to be considered when developing a new cell
Figure 3. Different characteristics need to be considered when developing a new cell

The modern battery test laboratory must handle thousands of cells at any one time. It has to accurately measure the actual performance of diverse cell designs to see if they meet the predefined goals that have been set (see Figure 3). 

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 for powering vehicles. Applications can range from 2-wheeler motorcycles through to 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, channel and safety requirements (see Figure 4).

These are some tests that need to be done to verify battery performance at the cell, module and pack levels. Namely: 
- 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 (BMS).

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

Automating the test lab for efficiency and data traceability
Figure 5 provides a simple visualisation of the different roles/tasks in a battery test lab. With the vast number of devices under test (DUTs), 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/resource management and improved testing throughput, but also provide tracking and traceability. With vast facilities and different sites to deal with, cloud-based lab operation management tools allow visibility and controlled accessibility on the state of battery testing operations. Test data collected from the DUTs can also be used to enhance design iterations. 

Ensuring quality from blueprint to production
Once the new battery cell design is ready, it will go into mass production. Production activities are 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, on top of current capacity, to support vehicle electrification over the next decade. As Europe and North America look to catch up with China and South Korea in manufacturing EV batteries closer to their end-markets, huge investments will be needed in ramping up gigafactory capacity.

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. With regard to the Li-Ion cell manufacturing process, the cell formation and aging stages are the most time-consuming. During cell aging tests, 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 these cells will adversely affect the performance of modules and packs.

A cell can take days, weeks, or months to exhibit its self-discharge characteristics. However, in time/cost-sensitive manufacturing environments, the traditional way of tracking self-discharge over time is not practical. Instead, some manufacturers now use a relatively new potentio-static 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 cycle life and the effects of charge rate. As cell capacity quickly increases, researchers need to source and sink larger currents.

Figure 5: Data flow and management is essential in a modern battery test lab that oversees thousands of DUTs simultaneously
Figure 5: Data flow and management is essential in a modern battery test lab that oversees thousands of DUTs simultaneously

To circumvent costly power consumption, modern cell cyclers employ regenerative power, where the power that is emanated during cell discharge is recycled back to the grid - thereby lowering net energy consumption and curbing operational expenses. This process also generates less heat in the electronics, reducing the need to remove heat from the production facility.

Future-ready 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, as well as the sourcing/sinking of larger currents, plus 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 to scale up for rapid deployment in alignment with demand. These exciting innovations will undoubtedly help to further scale the development and production of better batteries, in order to drive ongoing EV adoption.

Figure 6: Cell cycling and aging are the most time-consuming stages of complex battery cell manufacturing
Figure 6: Cell cycling and aging are the most time-consuming stages of complex battery cell manufacturing


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