Topic 4 - Types of Li-ion Cells

Section 1 · Topic 4

Types and Form Factors of Li-ion Cells

The cathode dictates the cell’s chemical behaviour; the physical casing dictates its mechanical and thermal integration. Both decisions are made before a single cell enters a pack.

Chemistry families

The industry names cell types after their cathode, because the cathode sets the voltage and the stability ceiling. The trade across families is energy density against safety, cycle life, and cost — the mechanisms behind each are taken up in Section 5.

Indicative values — exact figures are cell- and grade-specific.

Chemistry	Nominal V	Strengths	Trade-off & use
LCO LiCoO₂	3.7	High specific energy	Low thermal stability; small consumer cells
NMC Li(NiMnCo)O₂	3.6–3.7	Balanced energy & power	High-Ni grades need thermal margin; EVs, tools
LFP LiFePO₄	3.2	Thermally stable, long life, cobalt-free	Lower energy density; ESS, standard-range EVs
LTO anode swap	2.4	10,000+ cycles, fast charge	Low energy, high cost; grid, transit

Form factors

Beyond chemistry, the form factor governs mechanical and thermal integration, and each choice propagates directly into pack design (Section 6).

Fig. 1.4 — Three form factors, three trade-offs. Cylindrical wins on robustness and manufacturability but loses volume to circular packing; prismatic maximises density at the cost of cooling uniformity and swelling; pouch reaches the highest energy density but carries no rigidity of its own.

Cylindrical cells wind the electrodes into a rigid can that contains internal pressure well and mass-produces cheaply; the 46×80 mm 4680 format adds a tabless current path that shortens the electronic conduction distance along the winding, cutting internal resistance and the associated ohmic heating. Prismatic cells stack or fold electrodes into a flat rigid case, maximising packing density while becoming harder to cool uniformly and more prone to swelling. Pouch cells seal stacked electrodes in a flexible foil laminate, reaching the highest energy density but requiring external compression and framing to resist the electrode breathing and delamination that otherwise degrade them.

Engineering note

The 4680’s “tabless” design is not a capacity change — it is a resistance change. Shortening the path electrons travel along the foil drops internal resistance and I²R heating, which is what unlocks the higher charge and discharge power — not any change in the active material.

Continue the series

• Safety precautions and failure mechanisms (Section 2)
• Advanced electrochemistry and material science (Section 5)
• EV architecture — cell-to-pack and structural batteries

Section 1 · FundamentalsTopic 4 / 23