Working Principle of LiFePO4 Battery – SOUOP Solar Generator

The battery used by SOUOP solar generator is LiFePO4, which has more stable safety performance, is non-toxic and pollution-free, low cost, and has better stability than ordinary batteries. It is one of the most competitive materials for the cathode of next-generation lithium-ion batteries.

What is a LiFePO4 battery?

The lithium iron phosphate power battery is a lithium-ion battery using lithium iron phosphate (LiFePO4) material as the positive electrode of the battery. It is a new member of the lithium-ion battery family.

LiFePO4 battery vs general lithium-ion battery

LiFePO4 is a cathode material for lithium-ion batteries. LiFePO4 exists in the form of LiFePO4 in nature, with stable structure, abundant resources, good safety performance, and non-toxicity. Compared with traditional lithium-ion battery cathode materials LiMn2O4 and LiCoO2, LiFePO4 has a wider range of raw materials, lower prices, and no environmental pollution. Environmentally friendly and thermally stable, it is one of the most competitive materials for next-generation lithium-ion battery cathodes.

Although LiFePO4 material has many excellent electrochemical properties, it still has problems such as low diffusion coefficient. Therefore, scholars at home and abroad have launched research on improving the conductivity of LiFePO4. The use of LiFePO4 solar generators can increase its better stability and safety and is more environmentally friendly, which can reduce a small part of the pollution of the earth.

Generally, the electrolyte of lithium-ion battery is liquid. Later, solid-state and gel-type polymer electrolytes were developed. This lithium-ion battery is called a lithium polymer battery, and its performance is better than that of a liquid electrolyte lithium-ion battery. The full name of lithium iron phosphate battery should be lithium iron phosphate lithium-ion battery, this name is too long, referred to as lithium iron phosphate battery.

Because its performance is particularly suitable for power applications, the word “power” is added to the name, that is, lithium iron phosphate power battery. Some people also call it a “lithium iron (LiFe) power battery”. Relatively speaking, the general lithium-ion solar generator is more stable and safe than the LiFePO4 battery solar generator.

The working principle of an electrode in a LiFePO4 battery

(1) During discharge, the device is a primary battery. The valence of the Fe element changes from +3 to +2, and electrons are obtained to undergo a reduction reaction, so the electrode is a positive electrode, and the electrode reaction formula is FePO4+e-+Li+=LiFePO4,

(2) 100mL of a mixed solution containing 0.01mol CuSO4 and 0.01molNaCl was electrolyzed, and 0.02mol e- was transferred in the circuit,

Anode: 2Cl–2e -=Cl2↑,

0.01mol 0.01mol 0.005mol

4OH–4e-=2H2O+O2↑,

0.01mol 0.01mol 0.0025mol

Cathode: Cu2++2e-=Cu

0.01mol 0.02mol

Therefore, the volume of the gas generated on the anode under standard conditions=(0.005mol+0.0025mol)×22.4L/mol=0.168L;

(3) Iron is used as the anode, carbon is used as the cathode to electrolyze saturated brine, and Fe at the anode loses electrons to generate ferrous ions, then the electrode equation of the anode is Fe-2e-=Fe2+, and the hydrogen ions of the cathode get electrons to generate hydrogen, then the electrode equation of the cathode is: 2H++2e-=H2↑; Fe2+, H2, and OH- are generated in the solution, then the general equation of electrolysis is: Fe+2H2O electrification/.Fe(OH)2↓+H2↑;

Structure and working principle of LiFePO4 battery

The internal structure of the LiFePO4 battery The left side is LiFePO4 with an olivine structure as the positive electrode of the battery, which is connected to the positive electrode of the battery by aluminum foil, and the middle is a polymer separator, which separates the positive electrode from the negative electrode, but the lithium-ion Li+ can pass through while the electron e- cannot Pass, on the right is the negative electrode of the battery composed of carbon (graphite), which is connected to the negative electrode of the battery by a copper foil. Between the upper and lower ends of the battery is the electrolyte of the battery, and the battery is hermetically sealed by a metal casing.

The working principle of lithium iron phosphate battery

On the top is LiFePO4 of olivine structure as the positive electrode of the battery, which is connected to the positive electrode of the battery by an aluminum foil, and on the left is the polymer diaphragm (diaphragm), which separates the positive electrode from the negative electrode, but the lithium-ion Li can pass through but electron e- cannot pass through. On the right is the negative electrode of the battery composed of carbon (graphite), which is connected to the negative electrode of the battery by a copper foil. Between the upper and lower ends of the battery is the battery’s electrolyte, and the battery is hermetically sealed by a metal casing.

When LiFePO4 batteries are charged, the lithium ions Li in the positive electrode migrate to the negative electrode through the polymer separator; during the discharge process, the lithium ions Li in the negative electrode migrate to the positive electrode through the separator. Lithium-ion batteries are named after lithium ions that migrate back and forth during charging and discharging.

  1. When the battery is charged, Li migrates from the 010 surfaces of the lithium iron phosphate crystal to the crystal surface. Under the action of the electric field force, Li enters the electrolyte, passes through the diaphragm, and then migrates to the surface of the graphite crystal through the electrolyte, and then embeds the graphite crystal. in the grid. At the same time, the electrons flow to the aluminum foil collector of the positive electrode through the conductor, flow to the copper foil collector of the negative electrode through the tab, battery pole, external circuit, negative pole, and negative ear, and then flow to the graphite negative electrode through the conductor, so that The charge of the negative electrode is balanced. After lithium ions are deintercalated from lithium iron phosphate, lithium iron phosphate is converted into iron phosphate.
  2. When the battery is discharged, Li is deintercalated from the graphite crystal, enters the electrolyte, passes through the separator, migrates to the surface of the lithium iron phosphate crystal through the electrolyte, and then re-embeds into the lattice of lithium iron phosphate through the 010 surfaces. . At the same time, the battery flows to the copper foil collector of the negative electrode through the conductor, flows to the aluminum foil collector of the positive electrode of the battery through the tab, battery negative pole, an external circuit, positive pole, and positive pole, and then flows to the iron phosphate through the conductor. The lithium positive electrode balances the charge of the positive electrode.

It can be seen from the working principle of lithium iron phosphate battery that the charging and discharging process of lithium iron phosphate battery requires the joint participation of lithium ions and electrons, and the migration speed of lithium ions and the migration speed of electrons must reach a balance. This requires that the positive and negative electrodes of lithium-ion batteries must be mixed conductors of ions and electrons, and their ionic conductivity and electronic conductivity must be consistent.

However, it is well known that lithium iron phosphate has poor electrical conductivity. Although the conductivity of the graphite negative electrode is better, in order to achieve high-rate discharge, it is still necessary to improve the conductivity of the negative electrode, so that its electronic conductivity and the ability of lithium ions to be deintercalated from graphite are balanced.

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