What is a Lithium Iron Phosphate (LiFePO4) Battery?

The lithium iron phosphate (LiFePO4) battery, also called the LiFePO4 lithium-ion battery, uses LiFePO4 as the positive electrode material and graphite as the negative electrode material. It has a single-cell rated voltage of 3.2V, with a charging cut-off voltage between 3.6V and 3.65V.

Among lithium batteries, LiFePO4 batteries are highly safe, environmentally friendly, long-lasting, and capable of high discharge rates, making them ideal for a wide range of applications.

Working Principle

Positive Electrode Material

Lithium Iron Phosphate (LiFePO4) serves as the positive electrode. Iron ions (Fe³⁺) are fixed within the crystal lattice. During charging, lithium ions (Li⁺) are extracted from the positive electrode and embedded into the negative electrode. During discharging, lithium ions return to the LiFePO4 structure.

Negative Electrode Material

Graphite is used as the negative electrode. Its structure can store and release lithium ions. During charging, lithium ions move from the positive electrode to the negative electrode through the electrolyte, embedding into the graphite. During discharging, the lithium ions leave the graphite and return to the positive electrode.

Electrolyte

The electrolyte, usually an organic solution or polymer film, allows lithium ions to move between electrodes during charge and discharge.

Separator

The separator prevents direct contact between positive and negative electrodes, avoiding short circuits.

Charging and Discharging Process

• Charging: An external voltage drives lithium ions from LiFePO4 through the electrolyte and separator, embedding into the graphite negative electrode for energy storage. Electrons flow through the external circuit to balance the ionic movement.
• Discharging: When connected to a load, lithium ions leave the graphite, move through the electrolyte and separator, and embed into the LiFePO4 positive electrode. Electrons flow back through the external circuit, delivering energy.

In detail, during charging, Li⁺ migrates from the (010) surface of LiFePO4 crystals, passes into the electrolyte under an electric field, traverses the separator, reaches graphene on the negative electrode, and embeds into the lattice. Electrons flow through the conductive materials to balance the charge.

During discharging, Li⁺ de-intercalates from graphite, travels through the separator to LiFePO4, while electrons move through the external circuit to the positive electrode.

Chemical Reactions

• Positive electrode: LiFePO4 → Li₁₋ₓFePO4 + xLi⁺ + xe⁻
• Negative electrode: xLi⁺ + xe⁻ + 6C → LixC6
• Overall reaction: LiFePO4 + 6xC → Li₁₋ₓFePO4 + LixC6

Key Advantages of LiFePO4 Batteries

• High working voltage and energy density
• Long cycle life
• Low self-discharge rate
• No memory effect
• Environmentally friendly
• Seamless scalability for large systems

Applications

LiFePO4 batteries are well-suited for large-scale energy storage, including:

• Renewable energy power stations
• Grid peak shaving
• Distributed power systems
• UPS power supplies
• Emergency power systems

These batteries show promising prospects due to their safety, long lifespan, and environmental benefits, making them a leading choice for modern energy storage solutions.