Compare the advantages and disadvantages of lithium iron phosphate battery

The full name of lithium iron phosphate battery is lithium iron phosphate lithium ion battery. The 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, namely lithium iron phosphate power battery. Some people call it "LiFe iron (LiFe) power battery."

The lithium iron phosphate battery refers to a lithium ion battery using lithium iron phosphate as a positive electrode material. There are many kinds of positive electrode materials for lithium ion batteries, mainly lithium cobaltate, lithium manganate, lithium nickelate, ternary materials, lithium iron phosphate and the like. Among them, lithium cobaltate is the cathode material used in most lithium ion batteries, and other cathode materials have not been mass produced in the market for various reasons. Lithium iron phosphate is also one of the lithium ion batteries. In principle, lithium iron phosphate is also an embedding/deintercalation process, which is identical to lithium cobaltate and lithium manganate.

Lithium iron phosphate battery is a lithium ion secondary battery, and one of its main uses is as a power battery, which has great advantages over NI-MH and Ni-Cd batteries.

Lithium iron phosphate battery charge and discharge efficiency is relatively high, between 85% and 90%. The lead-acid battery is about 80%.

Advantage

1. Improvement of safety performance

The PO bond in the lithium iron phosphate crystal is stable and difficult to decompose, and does not collapse or heat like a lithium cobaltate or form a strong oxidizing substance even at a high temperature or overcharge, and thus has good safety. It has been reported that in the actual operation, a small part of the sample was found to have a burning phenomenon in the acupuncture or short-circuit test, but there was no explosion event. In the overcharge experiment, a high-voltage charge that was several times higher than the self-discharge voltage was used, and it was found that there was still Explosion phenomenon. Nevertheless, its overcharge safety has been greatly improved compared to the ordinary liquid electrolyte lithium cobalt oxide battery .

2, the improvement of life

The lithium iron phosphate battery refers to a lithium ion battery using lithium iron phosphate as a positive electrode material.

The long-life lead-acid battery has a cycle life of about 300 times, and the highest is 500 times. The lithium iron phosphate power battery has a cycle life of more than 2000 times, and the standard charge (5 hour rate) can be used up to 2000 times. The same quality lead-acid battery is "new half year, old half year, maintenance and maintenance for half a year", up to 1~1.5 years, while lithium iron phosphate battery is used under the same conditions, the theoretical life will reach 7~8 years. Considering comprehensively, the performance price ratio is theoretically more than four times that of lead-acid batteries. High-current discharge can be quickly charged and discharged with high current 2C. Under the special charger, the battery can be fully charged within 1.5 minutes of 1.5C charging, and the starting current can reach 2C, but the lead-acid battery has no such performance.

3, high temperature performance

The peak temperature of lithium iron phosphate can reach 350 ° C -500 ° C while lithium manganate and lithium cobaltate are only around 200 ° C. Wide operating temperature range (-20C--75C), high temperature resistance, lithium iron phosphate electric heating peak up to 350 ° C -500 ° C and lithium manganate and lithium cobalt oxide only around 200 ° C.

4, large capacity

The rechargeable battery works under conditions that are often not fully discharged, and the capacity will quickly fall below the rated capacity. This phenomenon is called the memory effect. There are memories like nickel-metal hydride and nickel-cadmium batteries, but lithium iron phosphate batteries do not have this phenomenon. No matter what state the battery is in, it can be used with charging, no need to discharge and recharge.

6, light weight

The volume of the lithium iron phosphate battery of the same specification capacity is 2/3 of the volume of the lead-acid battery, and the weight is 1/3 of the lead-acid battery.

7, environmental protection

Lithium iron phosphate battery is generally considered to be free of any heavy metals and rare metals (Ni-MH batteries require rare metals), non-toxic (SGS certification passed), no pollution, in line with European RoHS regulations, is an absolute green battery certificate. Therefore, the reason why lithium batteries are favored by the industry is mainly environmental 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 national key support and encouragement development project. With China's accession to the WTO, the export volume of electric bicycles in China will increase rapidly, and electric bicycles entering Europe and the United States have been required to be equipped with non-polluting batteries.

However, some experts said that the environmental pollution caused by lead-acid batteries mainly occurs in the production process and recycling process of enterprises. In the same way, lithium batteries are good in the new energy industry, but it can not avoid the problem of heavy metal pollution. Lead, arsenic, cadmium, mercury, chromium, etc. in the processing of metal materials may be released into dust and water. The battery itself is a chemical substance, so there may be two kinds of pollution: one is the process waste pollution in the production process; the other is the battery pollution after the scrap.

Lithium iron phosphate batteries also have their disadvantages: for example, poor low temperature performance, low tap density of the positive electrode material, and a lithium iron phosphate battery having a capacity of more than lithium cobalt oxide, and thus have no advantage in terms of a micro battery. When used in a power battery, a lithium iron phosphate battery, like other batteries, needs to face battery consistency problems.

Advantages and disadvantages of lithium iron phosphate battery

Disadvantages and improvement measures of lithium iron phosphate battery

Lithium iron phosphate batteries also have their disadvantages. For example, lithium iron phosphate cathode materials have a lower tap density and a lower capacity such as lithium iron phosphate.

The battery has a larger volume than a lithium ion battery such as lithium cobalt oxide, so it does not have an advantage in terms of a micro battery.

The performance of lithium-ion-powered batteries mainly depends on the positive and negative materials. Lithium iron phosphate as a lithium-power battery material has only appeared in recent years. The domestic development of large-capacity lithium iron phosphate batteries was in July 2005. Its safety performance and cycle life are incomparable to other materials. These are the most important technical indicators of power batteries. 1C charge and discharge cycle life of 2000 times. Single cell battery overcharge voltage 30V does not burn, puncture does not explode. Lithium iron phosphate cathode materials make large-capacity lithium-ion batteries easier to use in series. To meet the needs of electric vehicles for frequent charging and discharging. It has the advantages of non-toxic, non-polluting, good safety performance, wide range of raw materials, low price and long life. It is an ideal cathode material for a new generation of lithium-ion batteries. This project belongs to the development of functional energy materials in high-tech projects. It is the key area supported by the national “863” plan, “973” plan and “Eleventh Five-Year” high-tech industry development plan. It has poor electrical conductivity and slow lithium ion diffusion. The problem of low specific capacity during charging and discharging at high rate is a difficulty that restricts the development of lithium iron phosphate industry. The reason why lithium iron phosphate has not been used on a large scale so late is a major problem. But poor electrical conductivity has been relatively perfect solution is to add C or other conductive agent. At present, in the actual production process, the method of adding organic carbon source and high-price metal ion doping into the precursor to improve the conductivity of materials A123 and Yantai Zhuoeng is using this method to study that the conductivity of lithium iron phosphate has been improved by 7 orders of magnitude.

The lithium iron phosphate is provided with a conductivity characteristic similar to that of lithium cobaltate. The laboratory reports that when 0.1C is charged and discharged, it can reach

The specific capacity above 165mAh/g  actually reaches 135-145mAh/g, which is close to the level of lithium cobaltate, but lithium ion expansion

The problem of slow dispersion is still not solved well. The current solution is mainly nanometerization.

The LiFePO4 grain enthalpy reduces the diffusion distance of lithium ions in the grains. In addition, the method of doping to improve the diffusion channel of lithium ions does not seem to be effective. There are more studies on nanocrystallization, but it is difficult to apply to actual industrial production. Currently, only A123 claims to have mastered the nanotechnology industry of LiFePO4.

Low tap density

Generally, the tap density of only 0.8-1.3 can be said to be a great disadvantage of lithium iron phosphate. All lithium iron phosphate cathode materials have no advantage in small batteries such as mobile phone batteries, so their use range is limited.

Fixed limit

Even if its cost is low, safety performance is good, stability is good, and the number of cycles is high, but if it is too large, it can only replace lithium cobalt oxide in a small amount. But this shortcoming does not stand out in terms of power batteries. Therefore, lithium iron phosphate is mainly used to make power batteries.

Lithium iron phosphate battery has poor low temperature performance

Although people improve ion and electron conductivity by various methods such as doping of lithium, iron, and even phosphoric acid sites, control the effective reaction area by improving the particle size and morphology of primary or secondary particles, by adding additional conductive The agent increases the electronic conductivity and the like to improve the low temperature performance of lithium iron phosphate. However, the inherent characteristics of the lithium iron phosphate material determine that its low temperature performance is inferior to other positive electrode materials such as lithium manganate.

In general,  for a single battery note that it is a single battery, not for the battery pack. For the battery pack, the measured low temperature performance may be slightly higher. This is related to the heat dissipation conditions, and its capacity retention at 0 °C. The ratio is about 6070-10°C, which is 2040 when it is 4055-20°C.

Such low temperature performance obviously cannot meet the requirements of the power source. At present, some manufacturers have improved the low-temperature performance of lithium iron phosphate by improving the electrolyte system, improving the positive electrode formula, improving the material properties and improving the design of the cell structure, but have not really met the demand.

Battery consistency problem

The life of a single lithium iron phosphate battery is currently more than 2,000 times, but the life of the battery pack will be greatly reduced. It may be 500 times. Because the battery pack is made up of a large number of single battery strings and its working state is better than a group of people tied up with ropes to run, even if everyone is a sprinter, if everyone's movement consistency is not high, the team will not run fast overall speed Even slower than the single player who runs the slowest.

Similarly, the battery pack can only reach the level of the single battery when the battery performance is highly consistent.

Under the existing conditions, due to various reasons, the poor consistency of the fabricated battery affects the battery performance and overall life, so there are certain obstacles in the application of the power car.

Advantages and disadvantages of lithium iron phosphate battery

In addition, from the experience of research and development and production of lithium-ion batteries, Japan is the first commercialized country of lithium-ion batteries, and has always occupied the high-end lithium-ion battery market. Although the United States is leading in some basic research, there is still no large-scale lithium-ion battery manufacturer. Therefore, Japan has chosen modified lithium manganate as the positive electrode material for power lithium-ion batteries. Even in the United States, lithium iron phosphate and lithium manganate are used as the cathode materials for power-based lithium-ion batteries, and the federal government also supports the development of these two systems. In view of the above problems of lithium iron phosphate, it is difficult to be widely used as a positive electrode material for a power lithium ion battery in fields such as new energy vehicles. If it can solve the problem of high temperature cycle and poor storage performance of lithium manganate, with its advantages of low cost and high rate performance, it will have great potential in the application of power lithium-ion batteries.

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