Prismatic cell

Definition

A prismatic cell is a rechargeable electrochemical cell packaged in a flat, rectangular (rectangular-prism) enclosure. It is most commonly a lithium‑ion cell but the format can be used with other chemistries. Compared with cylindrical cells, the prismatic geometry is optimized for high volumetric packing efficiency and straightforward integration into compact modules and battery packs. Unlike pouch cells, a prismatic cell uses a rigid or semi‑rigid casing that provides mechanical protection and dimensional stability.

Construction and internal architecture

  • Rigid casing: Typically aluminum or steel cans with a welded lid; some designs use semi‑rigid multilayer laminates.
  • Electrodes and separator: Anode and cathode coated on metal current collectors (copper for anode, aluminum for cathode), separated by a porous polyolefin separator.
  • Internal layout: Stacked sheets (stacked or Z‑folded) are most common; some designs use a flattened wound “jelly‑roll.”
  • Electrolyte: Usually organic carbonate-based liquid electrolyte with lithium salt and performance/safety additives; ceramic-coated separators may be used for thermal stability.
  • Terminals: One or more tabs per polarity brought through the lid and welded to external terminals; multi‑tab or “tabless” current-collector designs are used to lower resistance and improve current distribution.
  • Safety features: Integrated safety vent in the lid; current-interrupt devices (CID) are common in many designs; PTC elements are less common than in cylindrical cells. The rigid can offers impact protection but requires careful management of internal pressure and swelling.

Key characteristics and performance

  • Geometry and size: Flat, rectangular footprint with straight sidewalls; stackable with minimal voids. Available in varied aspect ratios and thicknesses (often ~5–20+ mm); “blade” cells are long, thin prismatic variants.
  • Volumetric efficiency: High packing efficiency and high volumetric energy density at the pack level due to minimal interstitial space and fewer interconnections.
  • Capacity and power: Large individual cell capacities (tens to hundreds of ampere‑hours) reduce parts count and interconnects. Specific power can be limited by longer ionic/electronic paths in large formats, but multi‑tab layouts and optimized current collectors mitigate this.
  • Thermal behavior: Broad faces provide efficient heat transfer to cold plates or heat spreaders. Without careful tab placement and thermal design, large cells can develop internal temperature gradients.
  • Mechanical behavior: The rigid can supports handling and structural integration but concentrates stresses during gas generation or swelling. Many designs perform best under controlled external compression to maintain electrode contact and reduce lithium plating risk.
  • Safety and reliability: Robust can and integrated vents aid safety; flat geometry and large format require precise control of swelling, compression, and fast‑charge protocols to avoid delamination, gas buildup, or plating.

Relevance and applications

  • Electric vehicles (EVs): A dominant format for traction batteries across chemistries (e.g., NMC/NCA, LFP, LMFP). Their rectangular form factor enables high pack utilization, simple busbar routing, efficient cooling along broad faces, and compatibility with module, cell‑to‑pack (CTP), and cell‑to‑body (CTB) architectures. “Blade”‑type prismatic cells allow direct pack assembly with reduced parts count.
  • Other uses: Widely applied in buses, trucks, rail, marine propulsion, and stationary energy storage systems. Rigid prismatic formats are also found in some industrial and specialty portable devices.

Advantages

  • Excellent volumetric packing efficiency.
  • Mechanical robustness and dimensional stability.
  • High individual cell capacity reduces interconnect complexity.
  • Flat surfaces simplify thermal interfaces and structural integration.

Limitations

  • Heavier casing can reduce gravimetric energy density compared with pouch cells.
  • Large formats demand careful compression management and thermal/current‑distribution design to avoid gradients, swelling, or plating during fast charge.
  • Repair or replacement of individual cells can be more complex in module‑less (CTP/CTB) architectures.

Related and synonymous terms

  • Synonyms/near‑synonyms: Prismatic Li‑ion cell, rectangular cell, can‑type prismatic cell.
  • Related terms (distinct formats): Pouch cell (flexible laminate, no rigid can), cylindrical cell (e.g., 18650, 2170).
  • Subtypes/variants: Blade cell (elongated, thin prismatic cell used in CTP designs).

Materials and typical manufacturing

  • Active materials:
    • Cathodes: NMC, NCA, LFP, LMFP, high‑manganese variants; application‑specific choices balance energy, cost, power, and safety.
    • Anodes: Graphite (natural/synthetic), silicon‑graphite composites; lithium titanate (LTO) for high‑power/long‑life use cases.
    • Separator: Microporous polyolefin (PE/PP), often ceramic‑coated for thermal stability.
    • Electrolytes: LiPF6‑based carbonate electrolytes with additives (e.g., SEI formers, flame retardants); emerging localized high‑concentration or nonflammable systems.
  • Manufacturing flow (typical for Li‑ion prismatic):
    • Slurry mixing; electrode coating (slot‑die/comma‑bar), drying, and calendaring to target porosity.
    • Electrode slitting; stacking (sheet stacking or Z‑fold) or winding and flattening.
    • Insertion into the prismatic can; laser welding of tabs to terminals.
    • Vacuum electrolyte filling, wetting/soaking; sealing by laser welding/crimping/heat sealing depending on can design.
    • Formation cycling to establish SEI; aging and grading.
    • Quality control: OCV/impedance checks, mass/volume checks, leak testing (helium or pressure‑decay), X‑ray/CT for stack alignment, DCIR/EIS for performance grading.

System‑level design considerations

  • Mechanical: Use of compression frames or end plates to limit swelling and maintain interfacial contact; allowance for thermal expansion and vent paths.
  • Thermal: Cold plates, heat pipes, or heat spreaders applied to broad faces; busbar and tab placement tailored for uniform current and temperature distribution.
  • Electrical: Multi‑tab or tabless collectors to reduce ohmic losses; robust busbars; fusing and sensing strategies adapted to large cell currents.
  • End of life: Pack designs that facilitate cell access and disassembly; recycling via hydrometallurgical/pyrometallurgical routes with recovery of Ni/Co/Li and recyclable aluminum cans.