Function of the Cell Can or Enclosure

The function of the cell can or enclosure is to contain the chemistry over the lifetime of the battery cell and to allow the electrical, mechanical and thermal connections. It must also work in the extremes and have a controlled failure mode.

The main cell formats are: coin, cylindrical, pouch and prismatic.

The main functions mapped out and listed. Not sure which is best as there are so many links between each of these.

• Mechanical
  • Dimensional Stability
    • the dimensions of the enclosure need to be defined to a given tolerance
    • any dimensional changes to the cell during the usage and lifetime need to be defined
  • Sealing
    • the enclosure needs to be sealed to ensure no contents escape during normal use
    • the sealing also needs to ensure no external liquids or gases can enter during normal use
  • Pressure
    • the active materials including the electrolyte will exert a pressure inside the cell
    • an external pressure might need to be applied to maintain contact between the active layers
  • Weight
    • low weight
  • Weldability
    • external electrical connections will need to be made the the +ve and -ve terminals
    • the can itself might need to be welded at a number of stages during it’s manufacture and cell assembly
  • Durability
    • cell active materials expand and contract over use and lifetime
    • environmental vibration and inputs during use need to be accounted for in the can and assembly design
  • Corrosion
    • the enclosure materials must be compatible with and able to last the lifetime of the active contents of the cell
    • corrosion from materials in the cell environment need to be understood and accounted for in the material selection, materials such as: humidity, cooling fluids, cell venting materials
• Thermal
  • Conductivity
    • the thermal conductivity of the cell needs to be as high as possible
    • taking into account the heat transfer pathway from the centre of the cell to any external cooling system
• Electrical
  • Conductivity
    • if the cell enclosure is to be part of the electrical path for the cell then the electrical resistance of the material and path needs to be low compared to the electrical resistance of the cell active components
  • Corrosion
• Safety
  • Sealing
    • the sealing of the cell needs to be designed to work up to and above the point at which any pressure release vent is designed to operate
    • if the cell doesn’t have a defined vent then it will be necessary to define the failure of the seal or enclosure of the cell
  • Pressure
    • the operating pressures of the cell can be significant when the cell degrades and need to be contained and safely vented
• Manufacturable
  • Quality
    • the dimensional stability of the cell will be key parameters for end of line enclosure manufacturing process
    • manufacturing quality will also have a number of other defining features depending on the enclosure design and materials used
  • Volume
    • the design of the enclosure needs to be able to be made at high numbers whilst maintaining the quality
  • Energy
    • the energy used in processing the materials and making the cells is important in the overall LCA of the battery cell
  • Dimensional Stability
    • able to repeat manufacturer the can to a given set of dimensions and tolerances
• Recyclable
  • Disassembly
    • how easily can the enclosure be taken apart and sorted into recyclable materials
  • Material Quality
    • are the materials of a quality that is worth recycling or are they downgraded in use
• Available
  • Raw Materials
    • is there a ready supply of recycled raw materials
  • Final Parts
    • is the housing and process available from more than one supplier
• Cost
  • Capital
    • equipment costs such as forming, stamping, handling and measurement
  • Piece Cost
    • the end of line part cost needs to be optimised, but will need to consider stowage and logistics costs

Some of the cell formats may not be suitable for certain chemistries. This could be for a number of reasons.

Cell Manufacturing Process

In order to understand the function of the cell can or enclosure it is useful to understand how a battery cell is made.