Cell Sample Maturity

Cell Sample Maturity is normally defined by the A, B, C, D sample definitions.

These stages of the cell design, production line development and material supply are key to the relationship between the cell manufacturer and cell customer. The customer needs to have confidence in the cell design, robustness and quality and this is only possible if they know the process that the manufacturer is working to.

Also, this cell development process takes a long time and so inevitably overlaps the application development process. Hence fixing the chemistry and cell design to establish the performance of the cell is crucial.

Before the cell even gets to A Sample stage there is a huge amount of time and effort spent in fundamental research.

cell sample maturity


The research into the chemistry or fundamentals of a cell design can take years or even decades. A lot of the fundamental chemistry research is initially conducted in universities, if successful this will move to material supply companies and cell manufacturers.

The work is often undertaken using coin cells or small laboratory cells designed to also allow access for instrumentation. The output from this work is fundamental to finding the next chemistry breakthrough. The cells will have capacities of a fraction of an Ah and limited rate capability.

At this stage lots of claims are made that are difficult to ratify until the cell has been scaled up in capacity and understood in terms of production processes.

Making 1g of material involves very different processes, thermodynamics and reactions, compared to making 100kg. This scaling often brings changes to the chemistry.

Coating active material onto electrodes at 100m/minute and maintaining flatness and consistency are all very different process compared to the A4 size sheet of material made in the chemistry lab.


The commercial development of the cell will often progress with small coin or pouch cells. Once the cell format, capacity and design of the active layers is complete this will then move to a cell of the correct design, size and capacity. The initial small number of cells will still be pre-A Sample and of no value to a customer.

A B C D Sample development

The first cell that will give some fundamental characteristics is the A-sample cell.

A Sample

  • Cell Design Intent
  • Prototype Tooling

The cell format and size will be fixed. Cells will be made in low sample numbers (~100 cells) for testing:

  • Performance
    • Capacity
    • OCV
    • Maximum discharge current
    • Functional charge capability
  • Lifetime
    • Capacity versus standard cycling tests eg C/3 charge / discharge 0 to 100%
  • Safety
    • Abuse testing

These cells will give a good indication of the cell performance and lifetime. However, these cells are really designed so that the manufacturer can develop the design, production line and processes.

The data from these cells are likely to be used as a directional indicator for potential customers.


B Sample

  • Cell Design Frozen
  • Process Intent
  • Production Tools
  • Prototype Line

The design of the cell is frozen, meaning there will be no changes to chemistry or physical design going forward. The prototype line using production tooling has proven that the cells can be made to all of the process parameters.

This level of cell will be made in the 1000s for part to part testing and will be used to produce A-sample module designs:

  • Performance – complete mapping versus SoC and Temperature
    • Data generated for electro-thermal modelling
  • Lifetime
    • Full mapping against application requirements
    • Data generated for ageing models
  • Safety
    • Testing to UN38.3 to qualify cell for shipping
    • Full testing at cell and cluster level
  • Control
    • Part to part variability established
    • Control features and parameters established for production line

The data from these cells will be used to establish the key parameters and behaviour of the final pack application. Hence it is important that the cell design is now fixed and that the prototype line is very close to the production line and is using production tooling.

C Sample

  • Final Design
  • Series Production Tools
  • Production Line

The cell design, sourcing of sub-components and all materials is fixed. The production line and tooling is all complete. The production line is now used to confirm the control requirements as it is brought up to run at full rate with cells made in batches.

This is a very expensive part of production where the control parameters are stabilised and proven to produce quality cells at rate. This process can take many months.

Performance, lifetime and safety testing will be re-run as an over-check against the B Sample cell data. No differences in results are to be expected.

D Sample

  • PPAP Complete
  • Line Running at Rate
  • Control Plan in Place

The production line is running in control and at rate.

Any changes to chemistry, supply, material pre-processing or production process will reset the cell back to B Sample status and require re-qualification.

WMG Smart Cell instrumentation

Smart Battery Development

A future Smart Battery will:

  • Have the ability to modulate or isolate the electrical current flowing through the terminals.
  • Have the ability to measure key internal variables such as electrode potentials, current, temperature, mechanical stress and internal pressure.
  • Be able to resolve measurements both spatially and temporally.
  • Include localised control and communication hardware to integrate the LIB with its external environment without adding complexity via wireless or powerline data-transfer.

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