The full name of a lithium iron phosphate battery is lithium-ion battery, which uses lithium iron phosphate (LiFePO4) as the positive electrode material and carbon as the negative electrode material. A single cell has a rated voltage of 3.2V and a charging cut-off voltage of 3.6V~3.65V. It is currently the most environmentally friendly, longest-lasting, safest, and highest-discharge-rate lithium battery pack available.
I. Working principle of lithium iron phosphate batteries
During charging, lithium iron phosphate batteries allow lithium ions (Li+) in the positive electrode to migrate through the polymer separator to the negative electrode; during discharging, lithium ions (Li+) in the negative electrode migrate through the separator to the positive electrode. Lithium-ion batteries are named for this back-and-forth migration of lithium ions during charging and discharging.
1. When a lithium iron phosphate battery is charged, Li+ ions migrate from the 010 facet of the lithium iron phosphate crystal to the crystal surface. Under the action of the electric field, they enter the electrolyte, pass through the separator, and then migrate to the surface of graphene through electrolysis. They are then embedded in the graphene lattice. At the same time, electrons flow through the conductor to the aluminum foil electrode of the positive electrode, through the tab, battery terminal, external circuit, negative terminal, and negative tab to the copper foil current collector of the negative electrode, and then through the conductor to the graphite negative electrode. This process brings the charge of the negative electrode to a balance. After the lithium ions are extracted from the lithium iron phosphate, the lithium iron phosphate is converted into iron phosphate.
2. During discharge, Li+ ions are extracted from the graphite crystals, enter the electrolyte, pass through the separator, and then migrate through the electrolyte to the surface of the lithium iron phosphate crystals. They are then re-inserted into the lithium iron phosphate lattice via the 010 facet. Simultaneously, the charge flows through the conductor to the copper foil current collector at the negative electrode, through the tabs, the negative terminal, the external circuit, the positive terminal, the positive tab, to the copper foil current collector at the positive electrode, and then through the conductor to the lithium iron phosphate positive electrode, thus achieving a charge balance at the positive electrode.
II. Chemical reaction equations for lithium iron phosphate battery packs
Positive electrode reaction: LiFePO4 → Li1-xFePO4 + xLi+ + xe-;
Negative electrode reaction: xLi++xe-+6C?LixC6;
Overall reaction: LiFePO4 + 6xC → Li1-xFePO4 + LixC6.
The above is an introduction to the working principle and chemical reaction equation of lithium iron phosphate batteries. Lithium iron phosphate batteries possess a series of unique advantages, including high operating voltage, high energy density, long cycle life, low self-discharge rate, no memory effect, and environmental friendliness. They also support stepless expansion, making them suitable for large-scale energy storage. They have promising application prospects in areas such as safe grid connection of renewable energy power plants, grid peak shaving, distributed power stations, UPS power supplies, and emergency power systems.
