Advantages and Disadvantages of LiFePO4 Batteries

1. Naming of LiFePO4 (LFP) Batteries

The full name of the LiFePO4 battery is the lithium iron phosphate lithium-ion battery. It is a type of battery that uses olivine-structured lithium iron phosphate (LiFePO4) as the cathode, carbon-based material (graphite) as the anode, with a separator in between, and transfers lithium ions through an organic electrolyte. Its theoretical specific capacity is 170mAh/g, and the actual specific capacity of currently mass-produced material is about 140-145mAh/g (1C, full cell, 2.5-3.65V). With the development of the safety and economy of LiFePO4 batteries, in order to increase energy density, the industry is now moving toward lithium iron manganese phosphate (LMFP).

After screening, cells are assembled into battery packs together with battery auxiliary materials (connector plates, protective frames, PVC, battery cases, screws, connectors, etc.) and battery protection boards (BMS boards or smart boards).

2. LFP Battery Charging Process

When a battery is charged, lithium ions migrate from the surface of the LiFePO4 crystal into the crystal, then, under the electric field force, enter the electrolyte, pass through the separator, migrate through the electrolyte to the surface of the graphite crystal, and are intercalated into the graphite lattice. At the same time, electrons flow through the conductor to the aluminum foil current collector of the cathode, then through the tab, battery terminal, external circuit, negative terminal and negative tab to the copper foil current collector of the anode, and finally through the conductor to the graphite anode, balancing the charge of the anode. After lithium ions are deintercalated from LiFePO4, the LiFePO4 is converted into iron phosphate.

3. LFP Battery Discharge Process

When a battery is discharged, lithium ions are deintercalated from the graphite crystal, enter the electrolyte, pass through the separator, migrate through the electrolyte to the surface of the LiFePO4 crystal, and are re-intercalated into the LiFePO4 lattice. At the same time, electrons flow through the conductor to the copper foil current collector of the anode, then through the tab, negative terminal, external circuit, positive terminal and positive tab to the aluminum foil current collector of the cathode, and finally through the conductor to the LiFePO4 cathode, balancing the charge of the cathode.

II. Advantages and Disadvantages of LiFePO4 Batteries

1. Advantages of LiFePO4 Batteries

1) Long service life

Under standard test conditions, the cycle life of a single LFP cell can generally reach more than 2,000 cycles, and even more than 3,500 cycles. Some specific energy storage batteries can reach 4,000-5,000 cycles. Under certain conditions, the service life can be as long as 7-8 years, which is one of the primary reasons electric vehicles choose LFP. Lead-acid batteries, even under the best conditions, have a service life of about 300 cycles and may not exceed 3 years. The assembled LFP battery pack can reach about 800-2,000 cycles.

2) Relatively high safety

Compared with ternary (NCM) and lithium cobalt oxide batteries, LFP batteries have the highest safety. This is mainly determined by the crystal structure of the LFP battery itself. Its P-O bond is relatively stable; even under overcharge or high temperature conditions, the structure will not collapse like lithium cobalt oxide, and the material will not deform or oxidize like ternary batteries under high temperature or overcharge. It can withstand a certain range of overcharge and overdischarge: after a short overdischarge to 0, it can recover more than 80%; even when overcharged to 100%, it will not catch fire or explode.

3) Good high-temperature performance

The thermal runaway temperature of LFP battery materials can reach 350-500 degrees Celsius, while lithium manganese oxide, lithium cobalt oxide and ternary batteries usually undergo violent reactions at about 200 degrees Celsius. LFP batteries can operate at temperatures up to about 75 degrees Celsius, whereas if the other three types operate at about 70 degrees Celsius for a long time, battery life will be seriously affected, and thermal accumulation may even lead to thermal runaway.

4) Light weight

For the same rated capacity, the volume of a LiFePO4 battery is 2/3 of a lead-acid battery, and its weight is 1/3 of a lead-acid battery.

5) Large single-cell capacity

As a power battery, a single LiFePO4 cell can reach a capacity of 2Ah to 1000Ah, which other batteries cannot achieve. Large-capacity cells applied in electric vehicles can easily integrate CTP and CTC technologies to improve battery energy density.

6) No memory effect

LFP batteries can be charged at any time without significantly affecting battery life or causing irreversible capacity loss. In contrast, nickel-metal hydride and lead-acid batteries have a memory effect.

7) Relatively low cost

Compared with ternary batteries, the production cost of LFP batteries is lower, mainly because raw material prices are lower than those of ternary batteries.

8) Energy saving and environmentally friendly

Compared with other types of batteries, LiFePO4 batteries contain no heavy metals. They are green, environmentally friendly, non-toxic and pollution-free.

2. Disadvantages of LiFePO4 Batteries

1) Poor low-temperature performance

The low-temperature performance of LFP batteries is poorer than that of ternary batteries. The LiFePO4 cathode itself has relatively poor electronic conductivity and slow lithium-ion diffusion, and it is prone to polarization, which reduces capacity utilization.

2) The LFP cathode material may contain metallic iron

During the sintering of LiFePO4, iron oxide may be reduced to elemental iron under a high-temperature reducing atmosphere. Elemental iron can cause micro-short circuits in the battery, which is the most dreaded substance in batteries.

3) Relatively low energy density

Compared with ternary batteries, LiFePO4 batteries have lower energy density. A single cell does not exceed 200Wh/kg at most, and after pack assembly it is generally 120-140Wh/kg. In contrast, a single ternary cell can currently reach up to 350Wh/kg, and 160-200Wh/kg after pack assembly.

4) Relatively poor consistency

From the perspective of material preparation, the synthesis reaction of LiFePO4 is a complex multiphase reaction involving solid-state phosphates, iron oxides and lithium salts, plus carbon precursors and reducing gas phases. In this complex reaction process, it is difficult to ensure reaction consistency, resulting in a single-cell life of up to 5,000 cycles but possibly only 800-2,000 cycles after pack assembly. Ternary batteries have better consistency due to their material preparation.

5) Relatively high BMS cost

Because the open-circuit voltage of LiFePO4 batteries changes very little with SOC in the range of 30%-70%, the battery management system needs to use other methods to predict the state of health of the battery, which increases the difficulty of prediction and increases the battery cost.

6) Intellectual property limitations

Currently, the basic patents for LiFePO4 are owned by the University of Texas in the United States, while the carbon coating patent was filed by a Canadian company. These two basic patents cannot be avoided. If patent royalties are included in the cost, the product cost will be further increased.

When selecting ternary or LiFePO4 batteries as the power source for electric vehicles, each has its own advantages. For owners with high range requirements, ternary battery packs are preferred; for those with higher safety requirements, LFP batteries are generally preferred. Note that LFP is not absolutely safe, as safety is also closely related to the electrical design of the battery, the BMS management system of the battery pack, the cooling system, etc. For owners in northern regions, ternary battery packs are generally recommended. For those who are price-sensitive, LFP batteries are the best choice.