How are sodium-ion cylindrical cells configured into a start-stop battery pack?

Assembling a battery pack seems simple. But one wrong connection can ruin performance and safety. We build reliable start-stop packs using precise engineering and proven configuration methods.

Sodium-ion cells are configured by connecting them in series to increase voltage and in parallel to increase capacity. This creates a pack with the required 12V power and energy for automotive start-stop systems.

A client once asked us why our battery packs were so much more consistent than his previous supplier’s. It’s not magic. It is a disciplined process of configuration, connection, and testing. Let’s walk through how we do it.

What is the optimal series-parallel configuration for 12V automotive packs?

Getting to 12 volts is a game of numbers. You need the right combination of cells in series and parallel. Here is the industry-standard approach we use for all our packs.

The optimal configuration for a 12V pack¹ using 3.0V sodium-ion cells² is 4 cells in series³ (4S). The number of cells in parallel (XP) depends on the required capacity and power output⁴.

This "4S" rule is the foundation of any 12V sodium-ion battery pack design. From there, we customize the parallel connections to meet the specific needs of our B2B clients, from e-bike distributors to EV assembly plants.

Achieving 12V: The "4S" Rule

A single sodium-ion cell has a nominal voltage of 3.0V. To get the 12V needed for a vehicle’s electrical system, we connect four cells in a chain, or "in series". The math is simple: 4 cells × 3.0V/cell = 12.0V. This is the "4S" in a pack’s name.

Increasing Capacity: The "XP" Rule

Connecting cells in parallel increases the pack’s capacity (Amp-hours) and its ability to deliver current. If a single cell has a capacity of 15Ah, connecting four of these series strings in parallel (a 4S4P configuration⁵) creates a pack with 60Ah (15Ah × 4).

Balancing Power and Energy

More cells in parallel means the pack can deliver more power for starting the engine. It also provides more total energy for running electronics when the engine is off. We help our clients choose the right balance for their specific application.

How is welding and busbar design different for sodium-ion cells?

Connecting cells is more than just making contact. The welding technique⁶ and the design of the busbars are critical for safety and efficiency. Sodium-ion cells have unique considerations.

Welding sodium-ion cells² requires precise control to avoid overheating the terminals. Busbars must be made of highly conductive materials like nickel-plated copper⁷, and sized to handle high starting currents⁸ without significant voltage loss.

The quality of a weld is invisible from the outside, but it determines the reliability of the entire pack. A single bad weld can create high resistance, leading to heat buildup and failure.

Laser vs. Spot Welding

While traditional spot welding is common, we often use laser welding for our automotive packs. Laser welding provides a very focused heat source. This creates a strong, deep weld with minimal heat spreading to the rest of the cell, which protects the sensitive internal chemistry.

Busbar Material and Thickness

Busbars are the electrical highways that connect the cells. Their material and size are critical. Pure nickel strips are acceptable for low-power packs. But for high-current start-stop applications, we use nickel-plated copper⁷. Copper has much higher conductivity, which means less heat and less wasted energy. The thickness is calculated based on the peak current draw.

Safety Fusing

For extra safety, we can integrate fusible links⁹ directly into the busbar design¹⁰. These links act like a fuse for each individual cell string. If one string has a problem, the link will safely break the connection without affecting the rest of the pack.

What role does the casing material play in vibration resistance¹¹?

Cars and e-bikes shake and vibrate constantly. The battery pack’s casing is the first line of defense. It protects the delicate cells and electrical connections inside from the harsh road environment.

The casing material¹², typically high-strength ABS plastic or metal, provides structural rigidity. It works with internal cell holders and foam padding to absorb vibrations and prevent internal connections from fatiguing and breaking.

[I will replace this later with a story about a client’s pack that failed vibration testing because of a poor casing design from a previous supplier.] This is why we treat casing design as a critical part of the engineering process, not an afterthought.

ABS vs. Metal Casings

Most of our casings are made from a tough polymer called ABS. It is lightweight, a great electrical insulator, and can be molded into complex shapes to fit tight spaces. For applications requiring extreme durability or heat dissipation, an aluminum casing is a better choice.

The Importance of Cell Holders

Inside the casing, the cells are not loose. They are snapped into custom-designed plastic cell holders, which often look like a honeycomb. These holders grip each of the dozens of cylindrical cells firmly, preventing them from moving or rubbing against each other.

Vibration Dampening

Even with cell holders, small gaps can exist. We use materials like EVA foam to fill these voids. The foam acts as a shock absorber, dampening the high-frequency vibrations that can weaken welded joints over thousands of miles of use.

How does cell matching impact the performance of the whole pack?

A battery pack is a team of cells working together. If the team members are not perfectly matched, the entire pack’s performance suffers. This is why our 100% cell matching process¹³ is non-negotiable.

Cell matching involves grouping cells with nearly identical voltage, capacity, and internal resistance. This ensures that all cells charge and discharge at the same rate, preventing weaker cells from being over-stressed and failing prematurely.

For our B2B clients who import and distribute batteries, consistent performance is key to their brand reputation. Cell matching is how we guarantee that consistency from pack to pack.

The "Weakest Link" Problem

In a string of cells connected in series, the entire string is limited by its weakest cell. If one cell has a slightly lower capacity, the whole pack will register as "empty" when that single cell is depleted. The other, stronger cells cannot be used. This leads to poor performance and frustrated customers.

Our Matching Process

Before assembly, every single cell that enters our factory is tested and graded by automated machines. We measure its exact capacity, voltage, and internal resistance. The software then sorts the cells into tightly-matched groups. Only cells from the same group are ever assembled into the same battery pack.

Impact on Cycle Life

An unmatched pack has a very short lifespan. The "weak" cells are constantly being over-discharged, while the "strong" cells are being over-charged by the BMS during balancing. This stress causes rapid degradation. A well-matched pack, however, ages evenly, delivering reliable performance for thousands of cycles.

Conclusion

A high-performance start-stop pack is built from precisely matched cells, robust connections, and a durable case. It must follow a strict series-parallel configuration method to ensure safety and reliability.