As technology advances, the demand for lithium batteries has increased significantly. These batteries are used in a wide range of applications, including electric vehicles, solar energy storage, and portable electronics. With so many options available, it is crucial to choose the right battery for your specific needs. In this article, we will discuss two types of lithium batteries: LiFePO4 and LiPo.
What is Lipo Battery?
Main Contents
Lithium polymer battery, also known as Li-Po battery, is a rechargeable battery that uses a polymer electrolyte instead of a liquid electrolyte. It is a type of lithium-ion battery that is commonly used in portable electronic devices such as smartphones, tablets, and laptops. Lithium polymer batteries are known for their high energy density, low self-discharge rate, and lightweight design. They are also safer and more stable than traditional lithium-ion batteries, as they are less prone to leakage and thermal runaway. However, they require special care and handling to prevent damage or failure.
Benefits of Lipo Batteries
1.The operating voltage of a single battery is as high as 3.6v~3.8v, which is much higher than the 1.2V voltage of nickel-metal hydride and nickel-cadmium batteries.
2.The capacity density is large, and its capacity density is 1.5 to 2.5 times that of nickel-metal hydride batteries or nickel-cadmium batteries, perhaps higher.
3.The self-discharge is small, and its capacity is also very small after being placed for a long time.
4.The life span is long, and the cycle life of normal use can reach more than 500 times.
5.There is no memory effect, and there is no need to empty the remaining power before charging, which is convenient to use.
6.The safety function is good. Lipo batteries Use aluminum-plastic flexible packaging in the structure, which is different from the metal shell of liquid batteries. Once a safety hazard occurs, the liquid batteries are easy to explode, while the polymer batteries will only bulge at most.
7.The thickness is small and can be made thinner.Ultra-thin, the battery can be assembled into a credit card.Ordinary liquid lithium batteries use the method of first customizing the shell and then plugging the positive and negative electrode data. There is a technical bottleneck in the thickness below 3.6mm. Polymer batteries do not have this problem. The thickness can be below 1mm, which is in line with the current mobile phone demand direction.
8.It is light in weight, and batteries with polymer electrolytes do not require a metal shell as a protective outer packaging.The weight of polymer batteries is 40% lighter than the standard steel-shell lithium batteries of the same capacity, and 20% lighter than aluminum-shell batteries.
9.With large capacity, polymer batteries have a capacity of 10 to 15% higher than equivalent standard steel-shell batteries and 5 to 10% higher than aluminum-shell batteries. They have become the first choice for color-screen mobile phones and MMS mobile phones. Now most of the new color-screen and MMS mobile phones on the market also use polymer batteries.
10.Small internal resistance
The internal resistance of polymer batteries is smaller than that of ordinary liquid batteries. Now the internal resistance of domestic polymer batteries can even be below 35mW, which greatly reduces the self-consumption of the battery and extends the standby time of the mobile phone. It can reach the level of international standards.This kind of polymer lithium battery, which supports large discharge currents, is an ideal choice for remote control models and has become the most promising alternative to nickel-metal hydride batteries.
11.Shape can be customized
Manufacturers do not need to be limited to standard shapes, they can be economically made into suitable sizes.Polymer lithium batteries The thickness of the battery can be added or reduced according to customer needs, and new battery types can be developed. The price is cheap and the mold opening cycle is short. Some models can be tailored according to the shape of the mobile phone to make full use of the battery shell space and increase the battery capacity.
12.Brief plan of protection board
Due to the selection of polymer batteries, the batteries do not catch fire or explode, and the batteries themselves have satisfactory safety. Therefore, the protection circuit planning of polymer batteries can consider saving PTC and fuses, and then saving battery costs.
What is LiFePO4 Battery?
The full name of LiFePO4 battery is Lithium iron phosphate lithium-ion battery, this name is too long, referred to as LiFePO4 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.”
Working Theory
Lithium iron phosphate battery refers to lithium-ion batteries that use lithium iron phosphate as the cathode material.The cathode materials of lithium-ion batteries are mainly lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, ternary materials, lithium iron phosphate and so on.Among them, lithium cobalt oxide is the cathode material used in most lithium-ion batteries.
In the metal trading market, cobalt (Co) is the most expensive and does not store much. Nickel (Ni) and manganese (Mn) are cheaper, while iron (Fe) has more storage.The price of cathode materials is also consistent with the price of these metals.Therefore, lithium-ion batteries made of LiFePO4 cathode material should be quite cheap.Another feature of it is that it is environmentally friendly and non-polluting to the environment.
Regarding the positive electrode data of LiFePO4, the source of the data is relatively extensive, the number of cycles is long, the safety index is also very high, and the environmental pollution is small. It shows a very strong inductive function in many positive electrode data.
When LiFePO4 lithium iron phosphate battery is charged, the lithium ion Li in the positive electrode is relocated to the negative electrode through the polymer diaphragm; during the discharge process, the lithium ion Li in the negative electrode is relocated to the positive electrode through the diaphragm.Lithium-ion batteries are named after the fact that lithium ions move back and forth when they are charged and discharged.
Main Performance
The nominal voltage of the LiFePO4 battery is 3.2V, the termination charging voltage is 3.6V, and the termination discharge voltage is 2.0V.Due to the different quality and technology of the positive and negative electrode materials and electrolyte materials used by various manufacturers, there will be some differences in their performance.For example, the same model (standard battery in the same package) has a large difference in battery capacity (10% to 20%).
It should be noted here that there will be some differences in the performance parameters of lithium iron phosphate power batteries produced by different factories; in addition, there are some battery properties that are not included, such as battery internal resistance, self-discharge rate, charge and discharge temperature, etc.
The capacity of lithium iron phosphate power batteries varies greatly and can be divided into three categories: small ones from a few tenths to a few milliamps, medium-sized ones with tens of milliamps, and large ones with hundreds of milliamps.There are also some differences in the same parameters of different types of batteries.
Benefits of lithium iron phosphate batteries
Improvement of safety performance
The P-O bond in the lithium iron phosphate crystal is stable and difficult to decompose. Even at high temperature or overcharge, it will not collapse and heat up like lithium cobalt oxide or form a strong oxidizing substance, so it has good safety.Some reports pointed out that in actual operation, a small number of samples were found to burn during acupuncture or short-circuit experiments, but there was no explosion. In the experiment, high-voltage charging that greatly exceeded its own discharge voltage several times was used, and it was found that there was still an explosion. Phenomenon.Nevertheless, its overcharge safety has been greatly improved compared with ordinary liquid electrolyte lithium cobalt acid batteries.
Improvement of life span
Lithium iron phosphate battery refers to lithium-ion batteries that use lithium iron phosphate as the cathode material.
The cycle life of long-life lead-acid batteries is about 300 times, the highest is 500 times, while lithium iron phosphate power batteries have a cycle life of more than 2,000 times, and standard charging (5-hour rate) can reach 2,000 times.Lead-acid batteries of the same quality are “new for half a year, old for half a year, and maintenance for half a year”, which takes up to 1 to 1.5 years, while lithium iron phosphate batteries are used under the same conditions, and the theoretical life span will reach 7 to 8 years.Taking into account the comprehensive considerations, the performance price ratio is theoretically more than 4 times that of lead-acid batteries.High-current discharge can quickly charge and discharge at a high current of 2C. Under a dedicated charger, the battery can be fully charged within 40 minutes of 1.5C charging, and the starting current can reach 2C, but the lead-acid battery does not have this performance.
Good high temperature performance
The peak electric heating of lithium iron phosphate can reach 350℃-500℃, while lithium manganese acid and lithium cobalt acid are only around 200℃.The operating temperature range is wide (-20C–75C), and the peak electric heating of lithium iron phosphate with high temperature resistance can reach 350℃-500℃, while lithium manganese acid and lithium cobalt acid are only around 200℃.
Large capacity
When the battery is often working under the condition of being fully charged and not finished, the capacity will quickly fall below the rated capacity value. This phenomenon is called the memory effect.Like nickel-metal hydride and nickel-cadmium batteries, they have memory properties, but lithium iron phosphate batteries do not have this phenomenon. No matter what state the battery is in, it can be charged and used at will, without having to be recharged first.
Light weight
The volume of lithium iron phosphate batteries of the same specification and capacity is 2/3 of the volume of lead-acid batteries and 1/3 of the weight of lead-acid batteries.
Environmental protection
Lithium iron phosphate batteries are generally considered to be free of any heavy metals and rare metals (nickel-metal hydride batteries require rare metals), non-toxic (SGS certified), pollution-free, in line with European RoHS regulations, and an absolute green battery certificate.Therefore, the reason why lithium batteries are favored by the industry is mainly due to environmental protection considerations. Therefore, the battery has been included in the “863” National High-tech Development Plan during the “Tenth Five-Year Plan” period, and has become a key national project to support and encourage development.With China’s accession to the WTO, China’s exports of electric bicycles will increase rapidly, and electric bicycles entering Europe and the United States have been required to be equipped with pollution-free batteries.
Disadvantages
- In the sintering process during the preparation of lithium iron phosphate, there is a possibility that iron oxide will be reduced to elemental iron in a high temperature reducing atmosphere.Elemental iron can cause micro-short circuits in batteries and is the most taboo substance in batteries.This is also the main reason why Japan has not used this material as the cathode material for power-type lithium-ion batteries.
- Lithium iron phosphate has some performance defects, such as the low vibration density and compaction density, which leads to the low energy density of lithium-ion batteries.The low-temperature performance is poor, even if it is nano-coated and carbon-coated, it does not solve this problem.When Dr. DonHillebrand, director of the Energy Storage System Center of the Argonne National Laboratory in the United States, talked about the low-temperature performance of lithium-iron phosphate batteries, he used terrible to describe them. Their test results of lithium iron phosphate lithium-ion batteries showed that lithium iron phosphate batteries cannot make electric vehicles travel at low temperatures (below 0℃).Although some manufacturers claim that lithium iron phosphate batteries have a good capacity retention rate at low temperatures, that is when the discharge current is small and the discharge cut-off voltage is very low.In this case, the device simply cannot start working.
- The preparation cost of materials and the manufacturing cost of batteries are higher, the battery yield is low, and the consistency is poor.Although the nanization and carbon coating of lithium iron phosphate have improved the electrochemical properties of the material, they have also brought about other problems, such as reduced energy density, increased synthesis costs, poor electrode processing performance, and harsh environmental requirements.Although the chemical elements Li, Fe and P in lithium iron phosphate are very rich and the cost is low, the cost of the prepared lithium iron phosphate product is not low. Even if the initial research and development costs are removed, the process cost of the material and the higher cost of preparing the battery will make the final unit of energy storage cost higher.
- Poor product consistency. At present, there is no lithium iron phosphate material factory in China that can solve this problem.From the point of view of material preparation, the synthesis reaction of lithium iron phosphate is a complex multi-phase reaction, with solid phase phosphates, iron oxides and lithium salts, plus carbon precursor and reducing gas phase.In this complex reaction process, it is difficult to ensure the consistency of the reaction.
