EV battery design innovation: extending cruising range and extending battery life

Electric vehicle (EV) battery technology continues to innovate and has become one of the key automotive technologies supporting the rapid development of electric transportation . In 2022, the average cost of EV battery packs will be US$153/kWh, equivalent to a 90% drop in 15 years.

Looking forward, the automotive industry expects demand for lithium-ion batteries to grow at an annual rate of 33%, reaching 4,700 GWh by 2030.

More affordable EV batteries could help smooth the price gap between EVs and internal combustion engine vehicles sooner rather than later. However, controlling battery costs has always been a huge challenge as raw material, supply chain and energy costs continue to rise, and cell manufacturing is an energy-intensive process.

EV battery prices are falling rapidly, but demand is rising. How to find a balance between this and technological innovation needs to play an important role. Cost pressures aside, battery technology must continue to be upgraded to support the dynamic development of the e-mobility ecosystem.

The evolving role of EV batteries

Figure 1 provides an overview of the e-mobility ecosystem and the impact of ecosystem development on batteries.

Figure 1: EV batteries play a key role in the electric transportation ecosystem

Pictured on the right, automakers and battery developers must produce EV batteries that meet consumers’ range expectations. At a macro level, batteries with greater capacity and longer life can help integrate vehicle electrification with real-world applications, enabling battery recycling and reducing waste and pollution.

The ever-changing smart grid, pictured left, depicts how electric vehicle batteries are transforming from one-way “consumers” that draw energy from charging stations to two-way or vehicle-to-grid (V2G) power. We will further introduce V2G when we delve into how to improve battery performance.

Battery performance design at cell, module and pack levels

EV battery cells may come in different shapes such as cylindrical, pouch, and prismatic shapes. Fundamentally, the initial development stages of a cell are similar regardless of form factor. Cell developers must complete the characterization, selection and optimization of cell chemical composition and materials during the research and development process.

In order to achieve the cruising range and fast charging speed expected by users and meet future V2G functional requirements, developers need to start from the cell chemistry level. According to battery performance specifications, cell developers need to analyze the performance of various electrochemical mixtures (see Figure 2 for an example).

Lithium titanate is characterized by safety, good low-temperature performance, and long service life. Developers are currently working on improving specific energy and reducing costs. The overall performance of NMC is good, with excellent specific energy. As an EV priority, the self-heating rate of this battery is very low.

Figure 2: Different chemical compositions of battery cells have different properties and performances.

Modern battery testing laboratories must process thousands of tested cells at one time and accurately measure the actual performance of different cell designs to know whether they meet the design goals (see Figure 3).

Figure 3: Different cell characteristics must be considered when developing new cells, as the cell characteristics are determined by its application

In the process of designing and testing batteries, if the cells are ultimately assembled into modules or battery packs to power vehicles, battery design managers must consider how to take into account different test parameters for different applications. Applications for batteries range from two-wheelers, cars, sport utility vehicles and heavy transport vehicles. Batteries for different end-user markets need to meet different needs and require different test setups. Therefore, the test environment must be able to support the required voltage, channel, and safety requirements (see Figure 4).

In order to verify the performance of the battery at all levels of cells, modules and battery packs, the following tests are also required:

• Temperature values ​​are recorded in order to study the interaction between the electrical and thermal properties of the cells.

• Check mechanical connections and module performance.

• Situation in which the battery communicates with the vehicle's battery management system (BMS).

Figure 4: Each stage of the development cycle requires a test environment that helps verify battery performance

Automated management plays an increasingly important role in battery testing laboratories

Figure 5 briefly describes the different roles and their tasks in the battery testing laboratory. Lab managers can no longer manage modern battery test labs with manual tracking and spreadsheets due to the sheer volume of devices being tested.

Automating laboratory operations not only ensures efficient time and resource management, but also enables the tracking and tracing of test data and increases test throughput. If the testing facility is large and there are many test sites, laboratory managers can use cloud-based laboratory operation management tools to manage and control the status of battery testing operations. They can also use test data collected from the device under test to improve the design.

Figure 5: Modern battery test labs need to supervise thousands of devices under test simultaneously, so data flow and management in the lab are critical

Ensure consistent quality from blueprint to production stage

Once a new battery cell design can be put into mass production, it enters the rapid development stage of mass production. A McKinsey report stated that if battery cell demand continues to grow at an annual rate of 30%, then based on current production capacity, the global market will need to build another 90 gigafactories to meet the demand for vehicle electrification in the next decade.

The Americas and Europe are following the lead of China and South Korea in making EV batteries closer to the end market. These countries have invested billions of dollars to expand the production capacity of the Gigafactory. Figure 6 shows this complex manufacturing process.

Figure 6: Cell cycling and aging are the longest and most time-consuming stages in the complex process of cell manufacturing.

Many issues need to be addressed before a Gigafactory can be set up, including location, budget, raw material acquisition, manufacturing systems and human resources. However, our focus is on how to build better batteries starting from the cell level.

For high-volume manufacturing, throughput is a key indicator reflecting production efficiency. Among the lithium-ion battery cell manufacturing processes, the two processes of cell formation and aging take the most time. During the cell aging process, manufacturers must measure the self-discharge rate of the cell, even if the cell is not connected to any device. The purpose of this is to pick out bad cells with abnormal self-discharge characteristics or excessive self-discharge, because such "bad" cells will adversely affect the performance of the module and battery pack.

It may take days, weeks or even months for the cell's self-discharge characteristics to manifest. However, in the time- and cost-sensitive manufacturing environment, past methods that took a long time to track self-discharge are very impractical.

Some manufacturers now use a relatively new potentiostatic measurement method to directly measure the self-discharge current inside the cell. The past method required waiting for days or even weeks to record the self-discharge performance of the battery cells. The new method generally only takes a few hours to complete the test, thus saving time for this crucial quality inspection. This saves valuable space.

New technology brings us batteries with faster charging speed and more powerful performance. These batteries must undergo cycle testing, and the test results of the battery core samples can be used to determine the cycle life of the battery core and the impact of the charging rate on the battery life. As cell capacity increases rapidly, developers and manufacturers need to supply and consume greater current.

In order to avoid expensive power consumption, modern cell circulators use regenerative power to recycle the regenerated power during cell discharge to the grid, thereby reducing net energy consumption and operating costs. This process also reduces the heat generated by electronic devices, reducing the cooling requirements of production facilities.

Future-proof battery testing technology

As vehicle electrification continues, battery developers and manufacturers must get ahead of the curve with battery testing capabilities. They need to plan their equipment to handle larger cell capacities, higher supply/consumption currents, and be able to utilize regenerative power to reduce operating costs.

Some manufacturers use modular "super test chambers" that are not restricted by location to reduce the time and cost invested in battery testing, which also allows them to quickly deploy based on demand.

These exciting innovations will undoubtedly help further scale the development and production of batteries to power the adoption of electric vehicles.