Lithium Iron Phosphate Cell

A battery cathode so chemically stable that the phosphorus literally locks oxygen in place — no matter how hot things get.

A lithium iron phosphate cell stores and releases electrical energy by moving lithium ions between a graphite anode and an olivine-structured LiFePO₄ cathode through a liquid electrolyte. It delivers a flat 3.2 V discharge curve — meaning the voltage barely sags as it empties — and survives thousands of deep charge-discharge cycles with remarkably little capacity loss. That combination of durability and intrinsic safety has made it the dominant chemistry for electric bus fleets, stationary grid storage, and the entry-level variants of several mass-market electric cars.

During charging, lithium ions are pulled out of the iron phosphate cathode crystal and driven through the electrolyte into the graphite anode, where they slot between carbon layers. On discharge the ions travel back. The olivine crystal structure is the key to the cell's safety: the phosphate group (PO₄³⁻) forms unusually strong covalent bonds with its oxygen atoms, so even if the cathode overheats it resists releasing that oxygen. Oxygen is the accelerant in most lithium battery fires; without it, thermal runaway becomes far harder to sustain. The iron-phosphorus framework also barely expands or contracts during cycling — only about 6–7 % volume change — which is why the electrode survives so many thousands of cycles without crumbling.

In plain terms

Imagine a toy brick that you can snap apart and put back together six thousand times and it still fits perfectly. Most batteries are like clay — squish them too many times and they fall apart. This one is the brick.

Also called: LFP cell, LiFePO4 cell, LFP battery, olivine cathode.

Why it matters

Intrinsically safer than nickel- or cobalt-based cathodes: the cathode does not release oxygen below roughly 270 °C, compared with 160–210 °C for NMC, dramatically reducing fire and thermal-runaway risk.
Cycle life of 3,000–6,000+ full cycles to 80 % retained capacity dwarfs most competing lithium chemistries at 1,000–2,000 cycles, cutting lifetime cost per kilowatt-hour.
Uses iron and phosphate — two of the most abundant and inexpensive elements — eliminating the cobalt supply-chain concerns that constrain NCA and NMC production.
The flat 3.2 V voltage plateau simplifies battery management electronics; cells can be charged to 100 % state of charge every day without accelerated degradation.

Where it lives

BYD Blade Battery (LFP prismatic, 3,000+ cycle warranty, used in BYD Han, Atto 3, and Seal)
Tesla Model 3 Standard Range (LFP variant, CATL supply, charged to 100 % daily by Tesla recommendation)
CATL prismatic LFP cells (EVE LF280K, 280 Ah, used widely in stationary storage and commercial EVs)
Grid-scale battery energy storage systems (BESS) worldwide, including many utility installations exceeding 100 MWh

Key numbers

Nominal cell voltage: 3.2 V (Flat plateau; barely sags from 20–90 % state of charge)
Theoretical cathode capacity: 170 mAh/g (Practical cells reach ~150–160 mAh/g)
Cycle life (to 80 % capacity): 3,000–6,000+ cycles (At 80 % depth of discharge; premium cells (BYD Blade, CATL) toward higher end)
Thermal runaway onset: ~270 °C (Cathode begins exothermic decomposition; NMC onset is 160–210 °C)
Cathode volume change per cycle: ~6–7 % (Low expansion preserves electrode structure over thousands of cycles)
Maximum charging voltage: 3.65 V (Per cell; exceeding this accelerates electrolyte oxidation)

Surprising facts

The theoretical specific capacity of LiFePO₄ is 170 mAh/g — a number that has barely changed since the material was first characterised in 1997, yet practical cells today reach 150–160 mAh/g, within striking distance of that theoretical ceiling.
A single LFP cell cycled once a day for 6,000 cycles would last more than 16 years before its capacity dropped to 80 % of the original — longer than most cars are owned.
The olivine crystal structure that makes LFP so stable is the same mineral family as the gemstone peridot; you could hold the same atomic framework in your hand at a jewellery counter.
Despite being rated to operate from roughly −20 °C to 60 °C, LFP cells charged at sub-zero temperatures can suffer internal lithium plating — a microscopic frost on the anode — that silently cuts cycle life even though the cell appears to function normally.

A short history

LiFePO₄ was first identified as a practical cathode material by A.K. Padhi, K.S. Nanjundaswamy, and John B. Goodenough at the University of Texas at Austin, published in the Journal of the Electrochemical Society in April 1997 (Vol. 144, p. 1188). The paper showed that lithium could be reversibly extracted from the olivine lattice at about 3.5 V versus lithium, and that the material was inexpensive, non-toxic, and thermally stable — properties no existing cathode combined. Early cells had poor rate capability because the olivine crystal conducts electrons poorly; Chiang and colleagues at MIT later solved this in 2002 by coating nanoscale LFP particles with carbon, unlocking fast charge and discharge. BYD began commercialising LFP in bulk around 2005, and the 'cell-to-pack' Blade Battery design — eliminating modules to fit prismatic LFP cells directly into the pack floor — arrived in 2020, pushing volumetric energy density high enough to make LFP competitive with NMC in electric passenger cars.

Sources

Padhi, Nanjundaswamy & Goodenough — 'Phospho-Olivines as Positive-Electrode Materials for Rechargeable Lithium Batteries', J. Electrochem. Soc. 144, 1188 (1997) (https://iopscience.iop.org/article/10.1149/1.1837571)
Goodenough Nobel Lecture slides — cathode materials timeline, UT Austin (2019) (https://www.nobelprize.org/uploads/2019/10/goodenough-lecture-slides.pdf)
Yu et al. — 'Thermal behaviors of LFP, LMO and L523 cathodes with electrolyte', J. Energy Storage (2017) — DSC data showing LFP exotherm onset ~262 °C in electrolyte (https://jbzhao.xmu.edu.cn/64.pdf)
BYD Blade Battery product page — cycle life and chemistry specifications (BYD Europe) (https://www.byd.com/eu/technology/byd-blade-battery)