The cell to cell temperature gradient in a battery pack will limit the performance and lifetime. However, there will always be a cell temperature gradient and a cell to cell temperature gradient. It is very difficult not to have if we are rejecting or absorbing heat. The cell to cell temperature differences can be due to a number of factors, here we look at just the impact of distributed cells and a cooling system.
Thermal Conduction and Temperature Gradients
Whatever the cell format and however we cool it there will be a temperature gradient. This is described by Fourier’s Law of Conduction. An empirical law stating that the rate of heat flow is directly proportional to the temperature gradient and the area of heat transfer, and inversely proportional to the thickness of the material.
Adding in the next level of complexity, more cells and an extended cooling system.
As the coolant flows past each cell it will increase in temperature, the coolant is removing heat from the cell. This assumes the coolant is colder than the cell.
This means the coolant is getting hotter. This means the temperature delta between the coolant and the next cell is smaller, resulting in a smaller heat flow from that cell. And hence this is repeated down the line of cells.
This means the first cell (left hand side) is colder than the last cell (right hand side). The cell to cell temperature difference is determined by a number of factors, including:
- charge / discharge rate
- cell heat generation
- cell thermal conductivity
- coolant temperature
- coolant flow rate
- cooling system design
This post has been built based on the support of and sponsorship from: Resonate Testing Ltd, Quarto Technical Services, Eatron Technologies and About:Energy
The difference in temperature between cells limits the performance and lifetime of the pack.
There are ways to balance the coolant temperatures flowing past the cells.
An example, shown, is a top view where instead of a single flow front across the cell groups, you can provide a flow channel with a return loop under each cell. This gives you a better cell to cell balance since the coldest inlet temperature gets paired with the warmest outlet temperature.
The trade-off is that you now have a temperature gradient across the individual cells. This is helped somewhat by the rest of the conductive cooling element that helps heat flow across that individual cell gradient. Ian Stines
See also: Cell Temperature Sensing, Cell Temperature
Thermal gradients between cells may seem like a minor engineering detail, but as you note, they compound into real performance and lifetime constraints. Even a 2–3 °C delta across cells can accelerate imbalance, local aging, and safety risks.
That’s why next-gen approaches are looking not only at cooling architectures, but also at how charging strategies themselves can reduce thermal load distribution in the first place. With GigaPulse™ technology, current is optimized in a way that keeps cells running cooler and more uniform, lowering the burden on the cooling system.
In the long run, I think the most robust packs will come from a synergy: smarter thermal design + smarter electrochemical conditioning. Do you see OEMs beginning to integrate these two dimensions instead of treating them separately?