About lithium iron phosphate batteries, knowing this is enough.

A lithium iron phosphate battery refers to a lithium-ion battery with lithium iron phosphate as the cathode material. The cathode materials of lithium-ion batteries mainly include lithium cobaltate, lithium manganate, lithium nickelate, ternary materials, and lithium iron phosphate. Among them, lithium cobaltate is currently the most commonly used cathode material for lithium-ion batteries. In terms of the principle of the material, lithium iron phosphate also follows the embedding and de-embedding process, which is the same principle as lithium cobaltate and lithium manganate.

1. Introduction

     Lithium iron phosphate batteries belong to lithium-ion secondary batteries, and one of the main uses is in power cells. They have significant advantages compared to NI-MH and Ni-Cd batteries.

The charge and discharge efficiency of lithium iron phosphate batteries is high. In multi-cycle discharge cases, the charge and discharge efficiency can reach 90% or more, while lead-acid batteries are around 80%.

    2. Advantages

    Improvement of safety performance

    The solid P-O bond in lithium iron phosphate crystals is difficult to decompose. Even at high temperatures or during overcharging, it will not collapse or generate strong oxidizing substances like lithium cobaltate. Therefore, it has good safety. There have been reports of a few samples burning in pinprick or short-circuit tests, but no explosions have occurred. In overcharge tests using a high voltage charge that greatly exceeded its discharge voltage several times, explosions were still observed. Nevertheless, the overcharge safety has been significantly improved compared to ordinary LiCoO2 batteries with liquid electrolytes.

   Lifespan improvement

   A lithium iron phosphate battery is a lithium-ion battery with lithium iron phosphate as the cathode material.

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Long-life lead-acid batteries have a cycle life of about 300 to 500 times, whereas lithium iron phosphate power batteries have a cycle life of over 2000 times. With standard charge (at a 5-hour rate), lithium iron phosphate batteries can reach 2000 cycles. On the other hand, lead-acid batteries of the same quality typically last around "new six months, old six months, maintenance and six months," with a maximum lifespan of 1 to 1.5 years. In contrast, lithium iron phosphate batteries used under the same conditions can theoretically last for 7 to 8 years. Taking these factors into consideration, the performance-to-price ratio of lithium-iron phosphate batteries is theoretically more than four times that of lead-acid batteries.

Lithium iron phosphate batteries can handle high-current discharge and support rapid charge and discharge at a high current of 2C. With a special charger, the battery can be fully charged at a 1.5C rate within 40 minutes. They can also provide a starting current of up to 2C, which is a performance that lead-acid batteries do not possess.

   Good performance at high temperature

   Lithium iron phosphate exhibits electric heat peaks of up to 350°C to 500°C, whereas lithium manganate and lithium cobaltate only reach approximately 200°C. It has a wide operating temperature range of -20°C to +75°C. In terms of high-temperature resistance, lithium iron phosphate can withstand peak electrical heating up to 350°C to 500°C, whereas lithium manganate and lithium cobaltate can only handle temperatures around 200°C.

   Large capacity

   Lithium iron phosphate batteries have a larger capacity compared to ordinary batteries such as lead-acid batteries. The monomer capacity ranges from 5AH to 1000AH.

   No memory effect

   Rechargeable batteries often experience a capacity decrease below their rated capacity when they are repeatedly charged without being fully discharged. This phenomenon is known as the memory effect. NiMH and NiCd batteries are prone to memory effects, whereas lithium iron phosphate batteries do not exhibit this phenomenon. Regardless of the battery's state, it can be charged and used without needing to be discharged first.

   Lightweight

   Lithium iron phosphate batteries have a volume that is two-thirds the size of lead-acid batteries with the same capacity. Additionally, they weigh only one-third of what lead-acid batteries weigh.

   Environmentally friendly

   The lithium iron phosphate battery is generally considered to be free from heavy metals and rare metals (unlike NiMH batteries that require rare metals). It is non-toxic (SGS certified) and non-polluting, adhering to the European RoHS regulations, which qualifies it for the absolute green battery certificate. The industry's preference for lithium batteries is primarily driven by environmental considerations.

   However, some experts argue that environmental pollution caused by lead-acid batteries primarily stems from non-standard production processes and inadequate recycling treatments within enterprises. Similarly, although lithium batteries belong to the new energy industry and are considered environmentally friendly, they are not entirely exempt from the issue of heavy metal pollution. The processing of metal materials may release substances such as lead, arsenic, cadmium, mercury, chromium, etc., into the surrounding environment in the form of dust and water. Moreover, as batteries themselves are chemical substances, there can be two types of pollution: pollution during the production and manufacturing processes, and pollution that arises at the end of the battery's life cycle.

   Lithium iron phosphate batteries also have their drawbacks. For example, they exhibit poor low-temperature performance. The cathode material's density is relatively low, and as a result, lithium iron phosphate batteries have a larger volume compared to lithium-ion batteries such as lithium cobaltate. Therefore, they do not possess an advantage in micro batteries. Additionally, like other types of batteries, lithium iron phosphate batteries need to address the issue of battery consistency.

    Comparison of power batteries

   Currently, the most promising cathode materials used in power lithium-ion batteries include modified lithium manganate (LiMn2O4), lithium iron phosphate (LiFePO4), and lithium nickel cobalt manganese oxide (Li(Ni, Co, Mn)O2) ternary materials. Due to the scarcity of cobalt resources and the price fluctuations of nickel and cobalt, it is generally believed that it would be challenging for them to become the mainstream choice for power lithium-ion batteries in electric vehicles. However, they can be mixed with lithium spinel manganate within a certain range.

   Industry Applications

   Carbon-coated aluminum foil brings technological innovation and industrial enhancement to the lithium-ion industry. It enhances the performance of lithium-ion products and improves their discharge efficiency. The advantage lies in the fact that when dealing with battery materials, they often exhibit good high-rate charge and discharge performance and higher specific capacity. However, they tend to suffer from poor cycle stability and more significant decay, which requires making trade-offs and compromises.

   This magical coating significantly improves battery performance and ushers in a new era.

   The conductive coating consists of well-dispersed nano-conductive graphite-coated particles, among other components. It provides excellent static conductivity and acts as a protective energy-absorbing layer. Additionally, it offers good masking protection properties. The coating is available in both aqueous and solvent-based versions and can be applied to aluminum, copper, stainless steel, and titanium bipolar plates.

   The carbon coating brings significant performance enhancements to lithium batteries, including:

1. Lowering the internal resistance of the cell and suppressing the dynamic increase in internal resistance during charge and discharge cycles.
2. Achieving a significant improvement in cell pack uniformity and reducing cell pack cost.
3. Improving the adhesive adhesion between the active material and collector fluid, thereby reducing the cost of pole piece manufacturing.
4. Reducing polarization, improving the discharge efficiency, and minimizing thermal effects.
5. Preventing corrosion of the collector by the electrolyte.
6. Acting as a comprehensive factor that extends the battery life.
7. The coating thickness typically ranges from 1 to 3 μm for conventional single-sided coatings

   Significance

   In the metal trading market, cobalt (Co) is the most expensive and typically not stored in large quantities. Nickel (Ni) and manganese (Mn) are relatively cheaper, while iron (Fe) is the least expensive. The prices of cathode materials in lithium-ion batteries align with the cost of these metals. Consequently, lithium-ion batteries made with LiFePO4 as the cathode material should be more cost-effective. Another notable characteristic of LiFePO4 batteries is their environmentally friendly nature.

   As rechargeable batteries, they need to meet several requirements, including high capacity, high output voltage, good charge and discharge cycle performance, stable output voltage, high current charge and discharge capability, electrochemical stability, safety during use (preventing combustion or explosion caused by overcharge, over-discharge, or short circuit), wide operating temperature range, non-toxicity or low toxicity, and no environmental pollution. LiFePO4, as the positive electrode material in lithium iron phosphate batteries, fulfills these performance requirements excellently. It excels particularly in large discharge rates (5 ~ 10C discharge), maintaining a stable discharge voltage, ensuring safety (no combustion or explosion), offering long cycle life, and being environmentally friendly. Therefore, LiFePO4 batteries are considered the best choice for high-current output power applications.

   Structure and working principle

   The structure of a LiFePO4 battery typically consists of a positive electrode (cathode) made of lithium iron phosphate (LiFePO4), a negative electrode (anode) made of carbon/graphite, and a separator that prevents direct contact between the two electrodes. The electrodes are immersed in an electrolyte solution, and the battery is enclosed in a protective casing.

   During operation, lithium ions (Li+) migrate from the positive electrode to the negative electrode during discharge, and vice versa during charging. This movement of lithium ions is facilitated by the flow of electrons through an external circuit, generating an electric current. The electrochemical reactions involving lithium ions between the positive and negative electrodes enable the storage and release of electrical energy.

   Main Performance

   The nominal voltage of the LiFePO4 battery is 3.2V, the termination charge voltage is 3.6V, and the termination discharge voltage is 2.0V. Due to the different quality and processes of positive and negative electrode materials and electrolyte materials used by each manufacturer, there are some differences in their performance. For example, the same model (standard battery in the same package) has a large difference (10% to 20%) in its battery capacity. 　

　It should be noted here that different factories produce lithium iron phosphate power batteries in the various performance parameters will have some differences; in addition, there are some battery performances not included, such as battery internal resistance, self-discharge rate, charge, discharge temperature, etc. 　　

Lithium iron phosphate power battery capacity has a large difference and can be divided into three categories: small zero point a few to a few mAh, medium-sized tens of mAh, and large hundreds of mAh. Different types of batteries also have some differences in similar parameters. Currently widely used a small standard cylindrical package of lithium iron phosphate power battery, its parameters outline size: 18mm in diameter, 650mm high (model 18650).

   Over-discharge to zero voltage test

   STL18650 (1100mAh) lithium iron phosphate power battery was used to do the discharge to zero voltage test. Test conditions: use a 0.5C charge rate to fill the 1100mAh STL18650 battery, and then use a 1.0C discharge rate to discharge the battery voltage to 0C. Then the battery put into 0V will be divided into two groups: one group stored for 7 days, and the other group stored for 30 days; after the expiration of storage and then use 0.5C charge rate to fill, and then use 1.0C discharge. Finally, compare the difference between the two types of zero voltage storage periods. 　　The result of the test is that after 7 days of zero voltage storage, the battery has no leakage, good performance, and 100% capacity; after 30 days of storage, no leakage, good performance, and 98% capacity; after 30 days of storage, the battery then does 3 charge and discharge cycles, and the capacity is back to 100%. 　　This test shows that even if the battery is over-discharged (even to 0V) and stored for a certain period of time, the battery will not leak or be damaged. This is a characteristic that other types of lithium-ion batteries do not have.

   Application of lithium iron phosphate power battery

   Due to the above-mentioned characteristics of lithium iron phosphate power battery, and the production of a variety of different capacities of the battery, soon to be widely used. Its main application areas are 　　

   Large electric vehicles: buses, electric cars, sightseeing vehicles, hybrid vehicles, etc.; 　　

   Light electric vehicles: electric bicycles, golf carts, small flat battery vehicles, forklifts, cleaning vehicles, electric wheelchairs, etc; 　　

   Electric tools: electric drills, chainsaws, lawnmowers, etc; 　　

   toys such as remote-controlled cars, boats, and aircraft; 　　

   Energy storage equipment for solar and wind power generation; 　　

   UPS and emergency lights, warning lights, and mining lights (best safety); 　　

   Replacement of 3V disposable lithium batteries and 9V NiCd or NiMH rechargeable batteries (identical in size) in cameras; 　　

   Small medical instruments and equipment and portable instruments, etc.