LiFePO4 battery and packs

Exploring the Fundamentals of Lithium iron phosphate Batteries: Types, Charging Curves, and Industry Chain

Background of Lithium-ion Battery Technology

The full name of a lithium-ion battery is ion battery (LIB), which was commercialized by Sony Corporation in the early 1990s. The negative electrode is made of carbon, and the positive electrode is made of a compound containing potassium. During the charging and discharging process, there is no metallic lithium present, only lithium ions, which is the origin of the name lithium-ion battery.

Internal Structure

A lithium-ion battery is composed of a positive electrode, negative electrode, electrolyte, and separator. The positive electrode is made of lithium-containing transition metal oxides, with commonly used materials including potassium cobalt oxide, lithium manganese oxide, ternary materials, and lithium iron phosphate. The negative electrode is made of graphite, graphitized carbon materials, modified graphite, or carbon micro-particles in the intermediate phase. The electrolyte is an organic electrolyte, mostly composed of lithium hexafluorophosphate (LiPF6) mixed with organic solvents. The separator is a special composite film that functions to isolate the positive and negative electrodes, prevent electrons from passing through, and allow potassium ions to pass through to enable rapid transfer of lithium ions between the positive and negative electrodes. Currently, the main materials used for the separator are porous polyethylene (PE) or polypropylene (PP) film.

Working Principle

  1. When an external power source charges the battery, electrons (e-) on the positive electrode run through the external circuit to the negative electrode, while lithium ions (Li+) from the positive electrode jump into the electrolyte, travel through the small, winding holes on the separator, and swim to the negative electrode to combine with the electrons that have already arrived. The opposite process occurs when the battery is discharging. Taking lithium iron phosphate (LiFePO4) as an example, its chemical reaction equation during charging and discharging is:

Charging: LiFePO4-xLi-xe -> xFePOa+(1-x)LiFePO4

Discharging: FePO4+xLi+ +xe -> xLiFePO4+(1-x)LiFePO4

Lithium battery classification

The main difference between polymer lithium batteries and lithium-ion batteries lies in the electrolyte. The electrolyte of lithium-ion batteries is liquid, while the electrolyte of polymer batteries is colloidal or solid. The reaction principle of polymer lithium batteries is the same as that of lithium-ion batteries, generally in the form of soft packs, with strong plasticity in shape; lithium-ion batteries are generally cylindrical or square. From a safety perspective, polymer batteries are safer than lithium-ion batteries.

Battery charging curve (CC-CV mode)

Constant voltage mode is generally referred to as trickle charging, and the current is generally very small (reducing to below 0.1C), filling 1/10 of the capacity in 1/3 of the total charging time.

Battery industry chain

In the upstream raw materials, the positive electrode material is the most critical raw material in lithium batteries, which directly determines the safety performance and whether the battery can be large-scale. At the same time, it is also the material with the highest cost proportion in lithium battery core materials, accounting for about one-third of the material cost of lithium battery cores.

Lithium iron phosphate (LiFePO4) battery refers to a phosphate LiFePO4 as the positive electrode material and iron as the negative electrode material. Its working principle is the same as that of lithium-ion batteries. The correct chemical formula for LiFePO4 is LiMPO4, where M can be any metal such as Fe, Co, Mn, Ti, etc.

Its physical structure is olivine structure. From the structural point of view, it can be used as the positive electrode material for lithium-ion batteries, such as AyMPOA, Li-MFePO, LiFePOa.MO, etc.

Its characteristics are that it does not contain precious elements, the raw material price is low, and the resources of phosphorus, iron, and lithium on the earth are abundant, so there will be no significant problems with the supply. In addition to the common characteristics of lithium batteries, there are also some unique advantages, such as its moderate working voltage (3.2V), large capacity (170mAh/g), high discharge power, fast charging, long cycle life (up to 2000 times), and high stability in high temperature and heat environments.

Learn the advantages of LiFePo4 batteries

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