Demystifying EV Batteries

­The electric vehicle (EV) is widely seen as critical to the reduction of global emissions, but mass-market adoption can be hindered by concerns over the safety and performance of the battery packs which power them. This article will examine how technical advancements in battery technology are addressing these lingering concerns. Battery monitoring in particular, is a key element in ensuring battery pack safety, and the article will also describe how Dukosi’s chip-on-cell technology significantly improves control over the safety, reliability, and efficiency of the EV battery pack, while enhancing cost-efficiency.

Evolution of Modern Battery Technology

As with many new technologies, a range of high-profile issues arising from large, high voltage (HV) batteries during the early stages of the EV market have left lasting, negative impressions and concerns among the wider public. Several well-publicized cases of over-heating caused by thermal runaway, often resulting from collisions or misuse, has led to a perception that EV batteries are inherently unsafe.

Another notion, that batteries are overwhelmingly complex, stems from the raft of new components which accompanied the first batteries to be installed in EVs. This initial design complexity led to correspondingly complex manufacturing processes, which were difficult to automate, making these early batteries prohibitively expensive. Other early life issues contributing to current perceptions include concerns over shipping and recycling costs, and battery longevity.

The reality, however, is that battery development has not stood still, and current EV batteries and their associated processes are vastly different from these early versions. EV battery safety has significantly improved in recent years, owing to advancements such as smart fuses, durable casing materials, and fault-isolating internal structures, as well as stringent testing and certification requirements, which now ensure that designs meet the highest safety standards. Innovations in battery chemistry, battery architectures and manufacturing processes have also reduced their complexity and increased lifespans, with manufacturers now offering battery warranties as long as 8 to 10 years. 

New regulations, such as the EU Battery Passport, are helping to address concerns over sustainability, transport, and handling. By providing a digital record of the battery’s history and State of Health, (SoH), battery passports can help reduce insurance and shipping expenses. Battery passports also promote better recycling practices at end of life, enabling reuse and waste reduction. Engineers can use the information on battery history, and SoH to repurpose for less demanding applications, such as energy storage from the grid or renewable sources.

Battery Management Systems (BMS) play a key role in battery safety, performance and lifespans, and advancements in BMS have contributed significantly to the above improvements.

BMS Architectures

The BMS monitors key parameters such as the voltage and temperature of the battery cells and manages the connectivity to charging networks. Nevertheless, the implementation of this functionality necessitates the integration of wiring looms and sensors into confined spaces, thereby introducing extra weight, cost, and complexity to the battery. Traditional BMS architectures make trade-offs by placing temperature sensors at strategic points within the battery pack, monitoring groups of, rather than individual, cells, resulting in several limitations. Safety is compromised since detection of temperature abnormalities rely on the transmission of the temperature increase from the affected cell to neighboring cells (figure 2). This increases the risk of thermal runaway occurring, with the potential consequences of the release of combustible gasses, and, ultimately, starting a fire.

Additionally, monitoring at the battery pack or module level can mask problems occurring in individual cells, impacting the quality of SoH information, complicating reuse.

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The Dukosi approach directly monitors voltage and temperature through a Cell Monitor which is integrated on each cell. The captured data from the Cell Monitor is transmitted to a Dukosi System Hub which interfaces with the BMS main processor (Host). The System Hub manages the bidirectional communication network that connects a system of Cell Monitors using its proprietary C-SynQ communication protocol. This innovative architecture reduces the wiring and component count of EV batteries, giving a 10-fold decrease in BoM, resulting in a battery which is significantly less complex and easier to produce and maintain.

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Figure 3 – The Dukosi solution directly monitors voltage and temperature through a chip which is integrated on each cell.

The Dukosi Cell Monitoring System enhances the capabilities of the BMS in multiple ways:

●      By enabling the placement of a temperature sensor on every cell, battery safety is significantly enhanced as any cell surpassing a predefined temperature threshold can be promptly identified, eliminating the need to wait for the heat to propagate across adjacent cells.

●      The Dukosi solution uses near field communication to transmit data securely and reliably between the cell monitor chips and the System Hub via a simple single bus antenna. Near field communication combined with Dukosi C-SynQ proprietary communication protocol guarantees synchronized and deterministic data transfer, even in challenging RF environments, and are essential assets for reliable SoC and SoH calculation.

●      By limiting the cell network to only recognize known cells, and the propagation of wireless signals to just a few centimeters, the near field communication is simple and secure, removing the typical security risks that may be inherent with far field wireless battery systems.

●      By effectively eliminating the need for traditional battery modules the Dukosi cell monitoring solution enables flexible battery designs which make more efficient use of space and resources, adapting quickly and cost-effectively to different vehicle platforms and market requirements, without the need for revalidation efforts.

●      The Dukosi technology significantly impacts the total cost of ownership (TCO), particularly for industries that buy and sell energy, such as grid-scale utilities. Chip-on-cell technology cuts component count, reducing battery BoM, leading to lower manufacturing and design costs. With more accurate cell readings, SoC calculations are also more accurate, which potentially unlocks further energy for use in each cell; compounding that gain across multiple batteries provides better profitability, or, in a fixed size installation, smaller or fewer cells can be used, reducing initial costs.

●      Once a battery pack reaches the end of its first life, cell level provenance information enables individual cells to be removed from a pack and accurately assessed prior to shipping, improving safety and potentially reducing insurance costs. Cell chemistry and manufacturing information also means recycling processes can be safer and optimized to recover more material when it finally reaches end of life. Additionally, the cell’s lifetime data is stored on each Cell Monitor chip instead at the battery level in the BMS only, ensuring that the cell’s status is not lost when it is removed from the battery pack.

Conclusion

Battery safety, performance and longevity are key considerations in the selection of an EV, and a number of misperceptions in the marketplace have hindered EV adoption. Modern batteries are, however, vastly improved over the early models which suffered the widely publicized incidents behind these concerns. Battery Management Systems are key to battery performance, and ainnovations in battery system architectures and technologies, such as Dukosi’s Cell Monitoring System, have driven comprehensive improvements. 

Accurate monitoring of each individual cell ensures safer operation of the battery, while also maximizing its lifespan and performance. Battery packs integrating cell level monitoring are simpler, easier to manufacture and adapt more easily to different vehicle platforms, Additionally, cell level monitoring and stored provenance information facilitates safer shipping and reduced handling costs, contributes to reduced TCO through more efficient creation, use, re-use, and recycling of battery materials, and helps create a circular battery value chain.

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