EXPLAINED: Tabless Vs. Traditional cells and the impact of cold temperatures

12 hours ago
3 min read

In brief, Tabless battery cells are lithium-ion cells engineered to eliminate the traditional single current-collector tabs used to carry power in and out of the cell. Instead of one or two discrete tabs, the electrode foils are laser-patterned or segmented and connected along its entire edge, creating parallel current paths in hundreds or thousands micro-connections.

Diagram of Tabless vs Traditional cells - Bicycle Motor Works

What are Traditional CELLs?

What are they?

Standard cylindrical cells with tabs, such as the 18650, 21700 (Example: Samsung 40T, LG M50)

How are they built?

The anode and cathode foils are wound into a jelly roll
Each foil has one metal tab (sometimes two), welded to the anode and cathode foils inside the cell
The tabs are electrical exit points for current
Current must travel: through the electrode foil, toward the single tab, out of the cell

What are the Limitations?

Current funnels into only one or two tab locations, causing localized concentration of heat at that tab
There are limited contact points for power to exit the cell, causing electrical bottlenecking under higher current stress
The concentration of heat at entry/exit points means that heat is not evenly distributed throughout the cell (jelly roll), creating a colder center
Cold, imbalanced heat distribution makes the cell to inefficiently distribute power, therefore combating a higher internal resistance (DCIR)
Cells with higher internal resistance (DCIR), especially during colder temperatures, will cause Higher Voltage Sag, reduced capacity and
premature Battery Management Systems (BMS) cut-off

How do you calculate Power LOSS?

This equation describes how much energy is lost as heat inside a battery cell or battery pack.

P𝓁ℴ𝓈𝓈 = I² × R

Pₗₒₛₛ — Power Loss

Measured in watts (W)
Represents energy that does NOT go to the motor
Instead, it becomes heat inside the cell
Higher power loss = lower efficiency, more stress on the battery

I — Current

Measured in amps (A)
The amount of electrical flow the motor is demanding
Higher power riding = higher current (hard acceleration, hills, cargo, winter riding)

Why current matters: Power loss increases with the square of the current, not linearly.

*** Double the current → 4× the heat loss

R — Resistance

Measured in ohms (Ω)
This is the battery’s internal resistance, often called DCIR
Resistance exists in:
- The cell chemistry
- The electrode foils
- Tabs or tabless connections
- Welds, busbars, and pack construction

Key cold-weather fact: As temperature drops, R increases significantly.

Drawing of Ohm's Law informative description. — Drawing is credited to: Ohm's Law, Power and Energy.

What happens to all cold lithium-ion cells (≈ 0 °C / 32 °F and below)?

When batteries get cold:

R increases (electrolyte and ion movement slow down)
Voltage drops more under load
Heat generation rises
Usable capacity shrinks

Because the equation is:

P𝓁ℴ𝓈𝓈 = I² × R

Cold weather increases R, and high-power riding increases I, so:

Losses compound rapidly

Why High-Power Systems Are Hit Harder

High-power eBikes draw more current (I).

Since current is squared in the equation:

Small increases in current cause large increases in heat loss
Cold weather multiplies the effect by increasing resistance

This is why:

Winter riding
High-power motors
Cargo and performance builds

are the most demanding scenarios for a battery.

How Tabless Cells Reduce These Losses

1. Lower Baseline Resistance (R)

Tabless architecture:

Shortens electron travel paths
Uses many parallel current exits
Reduces total internal resistance

Lower R means lower power loss at all temperatures.

2. More Even Resistance Distribution

Traditional tabbed cells:

Concentrate resistance at tab locations
Create hot spots and current bottlenecks—worse in the cold

Tabless cells:

Spread resistance evenly across the electrode edge
Prevent localized heat spikes
Improve overall efficiency

Why the Benefit Compounds

In cold, high-power conditions:

R is already higher
I is often high
Power loss scales with I² × R

Tabless cells:

Start with a lower R
Avoid uneven resistance spikes

So as current and cold stress increase: The efficiency advantage grows, not shrinks

Simple takeaway

Pₗₒₛₛ = wasted energy (heat)
I = how hard you’re riding
R = how hard the battery has to work internally

Cold weather raises R High power raises I²

Tabless cells reduce both the amount and unevenness of resistance—making them especially valuable for winter-ready, high-performance eBike batteries like those built by Bicycle Motor Works.