In the evolution towards electric mobility, lithium batteries have assumed a leading role as the engine of the automotive revolution. However, beyond efficiency and performance, safety stands as the fundamental pillar underpinning confidence in electric vehicles. This article explores the safety of lithium batteries in automobiles in depth, unravelling the crucial challenges and innovative solutions that are shaping the future of safe electric driving.

The finances of some major automotive companies were affected by problems related to defective batteries in electric vehicles in 2020 and 2021. Beyond the heavy losses caused by such unforeseen events, today's post looks at the manufacturing and safety measures taken by NCPOWER and how they are keeping their 100% batteries safe and incident-free to date under strict control measures.

1. Quality

To operate safely, batteries must be produced with the utmost care and precision, from the processing of active materials to cell manufacturing and pack assembly.

Rigorous quality management, from goods receipt to final testing, is the only solution to control manufacturing defects.

In the field of electric vehicles there are two major challenges: on the one hand, many intermediate companies do not have the complete information, nor the ability to influence the quality of the cells and packs they purchase. In today's market, the simple ability to purchase batteries from a quality supplier may outweigh any quality management certification. Even the most stringent quality management measures do not guarantee 100% detection of faults.

In view of this fact, in addition to the aforementioned quality we must design systems risk prevention measures to ensure maximum safety.

2. System design

Battery systems incorporate multiple layers of protection, which serve to:

  • Maintain the battery in its intended period of operation.
  • Protect it from external damage
  • Minimise the impacts of potential individual cell failures

These measures include passive safety componentsas robust packaging to withstand knocks and bumps. hermetic sealing against fluid ingress, which act as final resources to reduce damage in critical situations. 

In turn, the Battery Management System (BMS) functions as the brain of lithium-ion battery systems, ensuring that no cell is over- or under-charged, and they bring with them basic status estimation functionalities, including state of charge (SOC) and state of health (SOH). However, BMSs also have shortcomings that need to be addressed: the BMS only sees the cells within the relevant battery pack, has little or no access to historical data or data from other battery systems, and has limited computing power. 

Therefore, NCPOWER carries out preventive analyses by monitoring the technical performance of the batteries. 

3. Cloud-based battery analysis

This approach employs more advanced methods than traditional battery management systems, allowing manufacturers and owners of electric vehicles to identify critical potential failures at an early stage. 

The implementation of cloud-based analytics represents an effective strategy to prevent critical failures and raise safety standards in lithium batteries. This approach not only empowers vehicle manufacturers, but also electric vehicle owners, enabling them to take preventive action before damage occurs. These diagnostics, based on existing field data streams, can be applied to any lithium-ion battery system without the need for product changes.

We scan sensor data for anomalies such as rapidly changing impedances or sudden voltage drops as precursors to thermal events, but the lack of baseline data and ongoing comparisons with similar systems severely limits the value of such analyses.

An example of risk detection thanks to BMS

Consider a hypothetical situation in which an electric car is equipped with an advanced Battery Management System (BMS) designed to monitor and manage the status of each cell in its battery. At a certain point, the BMS identifies an unusual temperature rise in one of the cells during the charging process. This could signal a possible risk of overheating and, ultimately, a fire hazard.

This early detection allows the BMS to take immediate action to reduce the risk. It can adjust the charging current, alert the driver or even temporarily interrupt charging until the situation is resolved. In addition, the system has the ability to store detailed data on this irregularity. This allows for continuous improvement in terms of safety and design.

Find out more about the battery design and BMS on NCPOWER here.

An example of analysis-based risk detection

There are several ways in which cloud-based analytics can identify safety-critical battery behaviour in advance. Specifically, a robust battery analytics solution should monitor at least 20 safety indicators on a daily basis.

The algorithms capture electrochemical interactions and processes, providing insights into the internal states of the battery. As an illustration, the figure below presents an analysis of lithium inventory loss, a phenomenon closely related to lithium plating. The yellow dotted line indicates a warning period identified by NCPOWER's Safety Manager battery analysis solution, while the red line indicates a critical state.

Model-based safety diagnostics monitor active lithium depletion over time. They generate automatic alerts when certain thresholds (indicated by red and yellow dotted lines) are reached.

Lithium plating is a phenomenon that occurs mainly when a battery is charged at high current rates and low temperatures. It can also occur under what are considered "normal" operating conditions. What is this phenomenon? It is the accumulation of metallic lithium on the anode surface, which has been a significant challenge in the field of lithium-ion batteries for many decades. 

This problem not only leads to a rapid degradation of battery capacity, but can also pose a safety threat. The accumulation of lithium metal can lead to the formation of metallic dendrites and trigger secondary reactions, such as outgassing. This situation results in a depletion of lithium reserves, which are no longer available to participate in the main reaction. Cloud-based safety algorithms, among other functions, must closely monitor the loss of active lithium to accurately predict safety-critical events.

Using this methodology and evaluating various safety indicators, NCPOWER's Safety Manager has successfully prevented more than 50 fire incidents.

What is the next step?

There are several challenges we must overcome to make electric vehicles significantly safer. Cloud-based battery analysis ensures that public perception of EV safety does not become another hurdle to overcome. 

In contrast, the benefits of cloud-based software that examines battery operational data go beyond providing an additional layer of security. They also lower business risks and supply chain costs. At the same time, they increase sustainability and accelerate innovation.

Today, lithium cells have become one of the most important components in the world of technology and energy. Their high energy density, long life and fast charging capability have positioned them as a leading choice in a wide range of applications, from electronic devices to electric vehicles.

However, as the demand for lithium cells increases, so does the variety of options available on the market. Understanding the differences between them and knowing how to choose the best ones for each case becomes essential.

In this article, we explore lithium cells, their differences, uses and how to choose the best ones.

Most common lithium cell types

Cells take different physical forms, which determine the structure and design, which in turn affects the electrical and mechanical characteristics of lithium batteries.

The main formats are: cylindrical, sheet or prismatic.

Cylindrical cells

Very similar to household knobs, cylindrical cells have a precisely cylindrical shape. The 18650 cell, with a diameter of 18 mm and a height of 65 mm, is one of the most common and widely used formats in the battery industry.

Advantages of cylindrical cells

Cylindrical lithium-ion cells offer several advantages, the most important of which include:

  • Durable housingCylindrical cells are designed with a rugged metal casing, usually made of stainless steel. This housing provides robust protection for the internal components of the cell, making them more durable and able to withstand adverse conditions such as shock, vibration and high temperatures. This is especially important in applications where mechanical strength and additional protection are required.
  • Flexibility in cell chemistryCylindrical cells allow the option of changing the internal chemistry of the cell while maintaining the same containment mechanism. This means that manufacturers can adjust the cell chemistry to improve performance, capacity or safety, without the need to completely redesign the case or containment system. This provides flexibility and adaptability to different requirements and advances in lithium battery technology.
  • Wide availabilityLithium-ion cylindrical cells, especially standard formats such as the 18650 cell, are widely available on the market. This makes them easy to access and purchase for use in a variety of applications, from portable electronic devices to electric vehicles. The widespread availability of these cylindrical cells contributes to their popularity and ease of integration into various systems and products.
cylindrical cells

Cylindrical cells

Disadvantages of cylindrical cells.

It is true that cylindrical lithium-ion cells also have some disadvantages. Some of these are listed here:

  • Low capacity of individual cellsCylindrical lithium-ion cells have a relatively low individual capacity compared to other lithium cell formats. For example, the most common cylindrical cells, such as the 18650, reach a maximum capacity of around 3Ah. This can limit the amount of energy stored in each cell and require the use of multiple cells in series or parallel to achieve the desired capacity.
  • Assembly by weldingIn the construction of battery packs using cylindrical cells, individual cells are assembled in series and in parallel by soldering. This involves a more complex and costly process compared to other connection methods, such as prismatic cells that can be connected by flexible connectors or laser welding. In addition, soldering makes it difficult to replace individual cells in case of failure, as replacement of the entire module is usually required.
  • Decreased security of the packageThe series and parallel nature of many cylindrical cells in a battery pack can result in a decrease in the safety of the system as a whole. If an individual cell fails, it can affect the performance and stability of the entire pack. In addition, the lack of individual cell replacement can lead to a higher safety risk, as complete module replacement is required in the event of a cell failure.

Most lithium-ion battery assemblers place several cells in parallel to achieve the desired capacity: for example, to achieve a capacity of 200 Ah using 2.5 Ah cells, 80 cells must be placed in parallel, all of these cells connected in parallel.
If an internal problem causes one of these short circuits to occur, it will not only absorb its own energy but will have to dissipate all the energy of the 80 cylindrical cells in parallel. This could result in very high heat in the module, with disastrous effects such as a fire.
To prevent this, major manufacturers such as Tesla use sophisticated production processes that allow cells to be connected in parallel by a kind of fuse. If a cell short-circuits, the "fuse" burns out and the safety of the battery pack is not compromised.

Unfortunately, none of the lithium-ion battery manufacturers in the industrial market have this type of technology. As a consequence of these negative aspects, we avoid this type of cells at NCPOWER.

Laminated cells, what are they and their advantages and disadvantages?

Laminated or pouch cells are a type of lithium cell that differs from cylindrical cells in their format and construction. Instead of having a cylindrical metal casing, these cells are composed of a flexible sheet that acts as the container and separator for the internal components.

In laminated cells, the active components, such as the cathode, anode and electrolyte, are placed between two layers of flexible material, usually laminated polymers such as polyester or polyolefin polymer. These flexible layers seal the components and prevent leakage or unwanted reactions. Additional sealing layers are used to protect the cell from moisture and external air.

Advantages of the bag cells

Laminated or pouch lithium cells offer certain positive aspects to their technology. Some of these are:

  • High energy densityBag cells have a high energy density, which means they can store a large amount of energy in a relatively small size. This is especially important in applications where long battery life or high power is required, such as in electric vehicles or portable electronic devices.
  • Low housing costCompared to cylindrical cells, pouch cells typically have a lower housing cost. This is because the manufacturing process of pouch cells is less complex and uses less expensive materials compared to the metal casings of cylindrical cells. As a result, pouch cells can offer a more economical solution for energy storage.
  • Range of available capacityIn the market, there are a variety of pouch cells available with different capacities. They range from a few hundred mAh (milliampere-hours) to around 20 Ah, although manufacturers exceeding this threshold are less common. This gives designers and manufacturers a range of options to suit different power requirements and application size.
bursal cells

Example of stock exchange cells

Disadvantages of the bag cells

Laminated or pouch lithium cells have some negative aspects associated with their fragility and limitations in terms of packaging and capacity. 

Some of these aspects are detailed below:

  • Fragility of the casingThe casing of bag cells is more susceptible to damage and breakage compared to cylindrical cells, as it is composed of flexible materials. Even slight pressure, such as the use of a fingernail, can irreversibly damage the casing. This can be problematic in environments where the battery is exposed to impacts or adverse conditions.
  • Limitations in the packaging systemPackaging of bag cells requires careful design to avoid any stress or deformation of the individual cells. Vibrations, crushing or deformation can compromise the integrity of the cells and affect their performance and lifetime. In addition, due to the flexible nature of pouch cells, it can be complicated, or even impossible, to develop customised modules for specific applications.
  • Medium-low capacity: Bag cells tend to have a medium-low capacity compared to other lithium cell formats. This means that several cells in parallel would be required to achieve sufficient capacity in industrial applications. However, this may affect the safety of the battery pack and increase the complexity of the load balancing and management system.
  • Difficulty in individual cell replacementAs with the cylindrical cells, the bag cells are also connected in series or in parallel by soldering. This makes it virtually impossible to replace an individual cell without having to replace the entire module. This can be costly and lead to downtime in the event of a cell failure.

Prismatic cells

Another common format among lithium battery cells is the prismatic type. They are mainly characterised by a solid casing and soldered terminals.

Advantages of prismatic cells

Prismatic cells offer several important advantages compared to other lithium cell formats. Some of these advantages are detailed below:

  • Durable housingPrismatic cells have a robust and durable casing, making them suitable for the production of customised battery packs. Their robustness allows them to withstand harsh conditions and minimises the need for costly and complicated mechanical stress studies and tests.
  • High capacity of individual elementsPrismatic cells can achieve high capacities in individual cells, up to 300 Ah in a single cell. This high capacity is especially valuable in the creation of large capacity batteries, such as in the industrial market, avoiding the need to use multiple cells in parallel. This not only simplifies design and assembly, but also significantly improves the safety of the entire battery pack.
  • Screw postsPrismatic cells often have screw posts on their terminals, which makes them easier to assemble and allows for more convenient element replacement, even on site. This reduces complexity and maintenance time in the event of a cell failure, as it can be replaced without having to disassemble the entire battery pack.

These advantages make prismatic cells an attractive option for a variety of applications, especially those requiring high capacity and customised assembly. However, it is also important to consider the limitations and challenges associated with this cell format.

Disadvantages of prismatic cells

One of the disadvantages of prismatic lithium cells is that their high energy density may be slightly lower compared to other cell formats, such as cylindrical cells. This is partly due to the type of containment box used in prismatic cells.

The solid and robust housing of prismatic cells, while offering advantages in terms of durability and ease of assembly, can take up additional space compared to cylindrical cells, which can affect the overall energy density of the battery. This means that a slightly larger volume is required to store the same amount of energy compared to cylindrical cells of similar dimensions.

However, it is important to note that prismatic cells are still capable of providing significant levels of energy and capacity, and are widely used in a variety of applications. The choice of the appropriate cell format will depend on the specific needs of the application, considering factors such as required capacity, available space, battery pack design and other technical and performance requirements.

prismatic cells

Example of prismatic cells

type of battery cells
CylindricalFrom stock exchangePrismatics
AdvantagesDurable housingFlexibility in cell chemistryWide availabilityHigh energy densityLow housing costAvailable capacity rangeDurable housingHigh capacity of individual elementsScrew posts
DisadvantagesLow capacity of individual cellsWelded assemblyDecreasing package securityFragility of the housingLimitations in the packaging systemMedium-low capacityDifficulty in individual cell replacementSlightly lower energy density due to containment boxSuperior battery volume and size
UsesCylindrical cells are typically used in small lithium batteries (<2kWh), e.g. electric bicycles, screwdrivers, garden tools, etc.). Only Tesla uses them in the automotive sector.Bag cells are mainly produced using NMC chemistry and are especially used in high power applications (high voltage and low capacities) or in applications where volume reduction is required, e.g. electric motorbikes or electric cars.Prismatic cells are used for lithium batteries in the industrial sector  and in the  automotive industry to produce medium and large battery packs.   

Which are the best for electric vehicles?

NCPOWER has chosen prismatic cells  for its batteries precisely because of their great advantages. These cells offer a good energy density to power density ratio, making them suitable for applications requiring high capacities and sustained energy delivery.

They enable us to achieve high quality performance in both electric vehicle applications and in the automotive industry.  leading lithium technology in Spain.

One of the important questions when it comes to electrifying a vehicle is about the best battery for it. We can differentiate between lithium and lead-acid batteries, but in reality the variants go beyond that. What is the most suitable chemistry for the electrification of electric vehicles? Let's discover the different battery types in depth.

Types of lithium batteries for vehicle electrification

We will not go into comparison here lithium vs lead as we have seen before. What we are going to look at is the difference between the different chemistries within lithium-ion batteries.

Lithium-ion (Li-ion) batteries

They are currently the most commonly used battery technology in electric vehicles due to their high energy density, which means they can store more energy in less space and weight. In addition, they are capable of delivering constant current at high discharge rates, making them ideal for applications requiring high energy demand.

Lithium-ion polymer batteries (Li-Po)

Lithium-ion polymer batteries are similar to lithium-ion batteries, but use a solid electrolyte instead of liquid. This means they are safer and less prone to leakage or fire. However, they have a slightly lower energy density and are more expensive to produce.

Lithium iron phosphate batteries (LiFePO4)

Lithium iron phosphate batteries are a variant of lithium-ion batteries that use iron phosphate as the positive electrode. They are safer than conventional lithium-ion batteries and have a longer life, but have a lower energy density and are heavier.

Impact of the choice of battery chemistry type

Choosing the right battery chemistry can have a major impact on the performance, efficiency and safety of an electric vehicle. 

Lithium-ion batteries have a higher energy density than other battery technologies, such as lead-acid or nickel-cadmium batteries.

On the other hand, the choice of battery chemistry can affect battery life and efficiency. For example, lithium-ion batteries have a longer life and better performance than lead-acid or nickel-cadmium batteries.

Finally, safety is another important factor in the choice of batteries. Nickel-cadmium batteries can be dangerous because of their tendency to overheat and their toxicity. Lithium-ion batteries, on the other hand, tend to be safer. Although they also have their own risks, such as fire or explosion, this can be prevented by choosing the right manufacturer and chemistry.

Lithium iron phosphate (LiFePO4) batteries are known for their high safety compared to other types of lithium-ion batteries. These are the ones that can be found at NCPOWER, a Spanish manufacturer of lithium-ion batteries for electric vehicles.

Conclusion

Choosing the right chemistry is critical when selecting lithium batteries. Not all solutions are the same and do not offer the same performance.

What is a fact is that any of the battery types mentioned far outperforms conventional solutions. The lead acid batteries (SLAs) have generally been the most commonly used for electric vehicles traditionally. The problem is that they have a low energy density, which means they are larger and heavier. They also have a shorter lifespan and require more maintenance than lithium-ion batteries.

In general, lithium-ion batteries and lithium-ion polymer batteries are the most suitable options for vehicle electrification due to their high energy density, efficiency and energy delivery capacity. However, the choice of the right battery will depend on the specific needs of the vehicle and the available budget.