A lithium-ion battery is a rechargeable electrochemical battery in which lithium ions move between a graphite anode and a metal-oxide or phosphate cathode during charging and discharging. In EV batteries, it is the dominant traction battery technology because it combines high energy density, long cycle life and high power at a cost that has fallen steadily for more than a decade.
The term covers a family of chemistries rather than a single design. The cathode material largely defines a cell’s energy, cost, safety and lifetime, so names such as NMC and LFP describe different lithium-ion batteries with distinctly different behavior in electric vehicles.
How a lithium-ion cell stores and releases energy
Every lithium-ion cell has four core parts: a cathode, an anode, a porous separator and a liquid electrolyte, usually a lithium salt such as LiPF6 dissolved in organic carbonates. During charging, lithium ions leave the cathode, cross the electrolyte and intercalate between the graphite layers of the anode, while electrons flow through the external circuit. Discharging reverses the process and delivers current to the motor.
On the first charges, part of the electrolyte decomposes on the anode surface and forms the solid electrolyte interphase (SEI). This thin layer is essential, because it lets ions pass while protecting the electrolyte from further reaction, but its slow growth over the battery’s life consumes lithium and is a main cause of capacity loss.
Cell voltage depends on chemistry: about 3.6 to 3.7 volts nominal for nickel-based cathodes and about 3.2 volts for lithium iron phosphate. A traction pack connects roughly 100 to 200 cells or cell groups in series to reach a system voltage of about 400 or 800 volts.
Lithium-ion chemistries used in electric vehicles
Automotive lithium-ion cells are grouped by cathode chemistry. The following values are typical cell-level ranges; pack-level figures are lower because housings, cooling and electronics add weight.
| Chemistry | Nominal voltage | Cell specific energy | Key strengths | Key weaknesses |
|---|---|---|---|---|
| NMC | About 3.6 to 3.7 V | About 200 to 300 Wh/kg | High energy density | Cost, cobalt and nickel supply |
| NCA | About 3.6 V | About 220 to 300 Wh/kg | High energy density | Thermal sensitivity |
| LFP | About 3.2 V | About 150 to 200 Wh/kg | Long life, safety, low cost | Lower energy, weaker in cold |
| LMFP | About 3.7 V | Higher than LFP | LFP-like cost with more energy | Still maturing |
Most cells use a graphite anode, increasingly blended with small amounts of silicon to raise capacity. Alternatives such as sodium-ion and solid-state batteries are separate technologies that address cost or energy density, but lithium-ion cells with liquid electrolyte remain the industry standard.
Cell formats and pack integration
Lithium-ion cells are produced in three main formats, and the choice influences cooling, packaging and manufacturing. Cells are then assembled into modules or directly into the pack, an approach known as cell-to-pack.
| Format | Construction | Advantages | Drawbacks |
|---|---|---|---|
| Cylindrical | Wound electrodes in a steel can | Mature production, robust | Many cells to connect |
| Prismatic | Stacked or wound layers in a rigid case | Good space use, large cells | Heat removal from the core |
| Pouch | Stacked layers in a flexible laminate | Light, high packing efficiency | Needs external support, swelling |
Manufacturers always hold back part of the energy as a buffer. The usable capacity shown to the driver is lower than the gross capacity, which protects cells from the most damaging extremes of very high and very low charge.
Aging, temperature and safety
A lithium-ion battery ages in two ways. Calendar aging happens even when the car is parked and accelerates at high temperature and high state of charge. Cycle aging comes from charging and discharging and grows with deep cycles, high currents and cold fast charging.
| Stress factor | Mechanism | Mitigation |
|---|---|---|
| High state of charge for long periods | Faster SEI growth, cathode stress | Daily charge limit of about 80% for nickel chemistries |
| High temperature | Accelerated side reactions | Active liquid cooling, shaded parking |
| Fast charging when cold | Lithium plating on the anode | Battery preconditioning before charging |
| Deep discharges | Mechanical strain on electrodes | Avoid regularly running near empty |
| Physical damage or internal short | Risk of thermal runaway | Robust housing, cell monitoring |
Thermal runaway is the most serious failure mode: a cell heats, its materials decompose exothermically and the heat can spread to neighboring cells. LFP cathodes release far less oxygen when overheated and are therefore more tolerant of abuse than nickel-rich chemistries. The battery management system monitors voltage, current and temperature of each cell group to keep the pack in its safe window.
Practical choices and common misconceptions
For drivers and fleet operators, chemistry matters mainly through charging habits. LFP batteries tolerate regular charging to 100% and many more cycles, while nickel-based packs last longer when kept at a moderate state of charge for daily use.
- Lithium-ion does not suffer from a memory effect; partial charging is harmless and usually beneficial.
- Capacity loss is gradual, often fastest in the first years and then slower, rather than a sudden failure.
- Cold weather reduces available energy temporarily; the capacity returns when the pack warms up.
- State of health is the right metric for battery condition, not the remaining range display alone.
End-of-life packs retain substantial value. Many can serve in second-life stationary storage, and battery recycling recovers lithium, nickel, cobalt and copper for new cells.
A non-technical view
A lithium-ion battery works like two shelves with a crowd moving between them. When the battery charges, tiny charged particles of lithium move to one shelf; when the car drives, they move back and the energy they release powers the motor.
The same basic battery sits in phones and laptops, but an electric car uses thousands of times more of it, carefully cooled and monitored. It slowly wears out over years, and heat, very full charges and cold fast charging are what wear it fastest.
A concrete example
A taxi operator runs two electric models: one with a nickel-based NMC battery of 77 kWh and one with an LFP battery of 60 kWh. Drivers cover about 250 km per shift, so both types are charged every day, mostly at DC chargers between shifts.
The operator sets an 80% daily limit on the NMC cars and lets the LFP cars charge to 100%, as recommended for each chemistry, and enables battery preconditioning before every winter fast-charging stop. After three years and well over 200,000 km per vehicle, the battery management systems report state of health above 85% on both models, and no battery has needed replacement, which confirms that charging habits matched to the chemistry protect the packs.