Comparison between lithium iron phosphate battery and lithium manganese oxide battery

As countries around the world are leaning towards the new energy battery industry, lithium-ion power batteries, as the ideal energy source for the development of the 21st century, are attracting more and more attention. Since lithium batteries have been widely used in portable appliances such as laptops, cameras, and mobile communications, the success of the commercial production of lithium-ion power batteries by world-class lithium battery companies in the past two or three years has not only brought substantial progress to the application of UPS, mobile laser power supplies, mobile lighting power supplies, mobile communication equipment, military fields, and aerospace fields, but also brought hope to the automotive industry's desire to replace traditional energy with power supplies.

With such a broad market prospect, the commercial production of lithium-ion power batteries has become the focus of people's attention. Naturally, relevant enterprises in China's lithium battery industry will not miss this opportunity and have begun trial production or mass production of lithium-ion power batteries.

The production of lithium-ion power batteries inevitably requires the selection of positive electrode materials. Although theoretically, there are many types of positive electrode materials that can be selected, there are currently very few lithium-ion positive electrode materials that can be truly applied for commercial production purposes. In summary, there are only lithium iron phosphate, lithium manganese oxide and ternary materials. If the safety and cycle life of the battery are considered, only lithium iron phosphate and lithium manganese oxide can do the job. The reason why they can become the first choice of positive electrode materials for power lithium-ion batteries is closely related to their structure and performance. Through the unremitting efforts of material researchers from all over the world, we have the following basic understanding of the structure and performance of lithium iron phosphate and lithium manganese oxide.

Lithium iron phosphate structure

Lithium manganate structure

Lithium iron phosphate and lithium manganese oxide performance list

Based on the above research data, we can understand the advantages and disadvantages of lithium iron phosphate batteries and lithium manganese oxide batteries. The specific comparison is shown in the following table:

People who are really engaged in lithium battery work are very clear about the conclusion of the above table. As positive electrode materials for lithium-ion power batteries, there is no huge difference between lithium iron phosphate and lithium manganese oxide. However, for outsiders, it is easy to be confused by the following characteristics of lithium iron phosphate:

1) Excellent cycle performance at room temperature and higher temperature.

2) The lithium-ion power batteries prepared with it have good safety performance.

Although this is because its operating voltage platform is only 3.3V, people often overlook this point.

3) Abundant raw materials.

This easily reminds people of the simple preparation and low cost of lithium iron phosphate.

At present, some domestic lithium battery companies are relying on the vague understanding of outsiders and using various means of public opinion to exaggerate the cycle and safety performance of lithium iron phosphate and say that lithium manganese oxide is useless. If it is just individual commercial hype, it is understandable, but when this irresponsible practice is gradually accepted by the entire industry, it is incredible.

This article hopes to give a fair and objective evaluation of lithium iron phosphate and lithium manganese oxide through performance analysis.

First, let’s take a look at the situation of lithium-ion power battery production in the lithium battery industry.

The world's most successful top lithium battery companies producing lithium-ion power batteries include A123 in the United States, E-ONe Moli in Canada, Sony and Sanyo in Japan, etc. Except for A123 which uses lithium iron phosphate as the positive electrode material, the positive electrode materials used by other companies are mainly lithium manganese oxide. From the perspective of the international commercial production share of power lithium-ion batteries in 2008, lithium-ion power batteries with lithium manganese oxide as the main positive electrode material accounted for more than 90% of the entire market. It can be seen that lithium manganese oxide positive electrode material is the first choice for the world's first-class lithium battery industry to prepare lithium-ion power batteries.

At present, the companies that can achieve initial commercial mass production of lithium-ion power batteries in China's lithium battery industry include: ATL invested by Japan's TDK, BYD in Shenzhen, Lishen in Tianjin, Jiangsu Manganese in Changzhou, and Xingheng in Suzhou. Except for BYD in Shenzhen, which claims to have "iron batteries", the lithium-ion power batteries produced by other companies all use lithium manganate as the main positive electrode material.

If the above situation is still not clear to everyone, we will provide some examples for further explanation. Here we use the manganese lithium-ion power battery of Jiangsu Manganke Battery Co., Ltd. and the lithium iron phosphate lithium-ion power battery produced by a well-known lithium battery company in Hebei and a lithium battery company in Shenzhen to do some discharge tests under the same conditions. The test process and results are as follows:

1.18650 cylindrical sample pre-test parameters list:

2.18650 Cylindrical Sample Single Rate Discharge Test Procedure:

Test environment temperature: 23℃±2℃Charging current 1C*, charging cut-off voltage: manganese gram battery = 4.2V, lithium iron phosphate battery = 3.65VDischarging current is 1C*/5A/10A/15A/20A/30A respectively, discharging cut-off voltage: 2.5V*: 1CDischarging current is based on the nominal capacity of the battery sample

3.18650 cylindrical sample single rate discharge curve

MNKE-A063

A lithium battery company in Hebei A lithium battery company in Shenzhen

MNKE-A014

For power batteries, high rate discharge is a very important indicator. Through the above rate discharge test, it can be found that the power batteries of the lithium manganese oxide series of Manganese Ke Company can withstand a current discharge of up to 30A. The maximum discharge current of the lithium iron phosphate power battery of a Shenzhen company is 15A, and the product of a Hebei company is even worse, which can only withstand a discharge current of 10A. At the same time, when withstanding large current discharge, the lithium manganese oxide series batteries can still reach more than 1400mAh, while the lithium iron phosphate power batteries produced by other companies cannot reach 900mAh when the current discharge exceeds 10A. It is worth noting that none of the lithium iron phosphate power batteries have reached the nominal capacity given by the manufacturing company, that is, their actual capacity is only about 1000mAh under 1C discharge.

What does this result mean? Power tool manufacturers must be very clear. Because the normal working current of professional power tools is usually 15-20A. If it encounters a stall, the instantaneous working current will reach about 50-60A. Among the above batteries, except for the manganese lithium-ion power battery of Jiangsu Manganke Battery Co., Ltd., which can meet such working requirements, other batteries are far from meeting the basic working indicators of professional power tools.

Some people may say that the voltage and capacity of a single lithium iron phosphate battery cannot be achieved, so why not connect them in series and parallel? This is true, but the series and parallel connection greatly increases the usage, volume and weight, which brings disadvantages in terms of cost and use. From the above data, it can be seen that the capacity of MNKE batteries is 1.5 times that of other companies' lithium-ion batteries. Relatively speaking, MNKE batteries are more likely to become the first choice of power tool manufacturers.

4.18650 Cylindrical Sample Monomer Temperature Discharge Test Procedure:

Charging current 1C*, charging cut-off voltage: manganese gram battery = 4.2V, lithium iron phosphate battery = 3.65V discharge current: 1C* discharge cut-off voltage: 2.5V discharge temperature: -20℃/-15℃/-10℃/23℃*: 1C discharge current is based on the nominal capacity of the battery sample 5.18650 cylindrical sample monomer temperature discharge curve comparison shows that manganese gram lithium manganese oxide battery can be discharged normally below -20℃, while the lithium iron phosphate battery in Hebei and Shenzhen cannot be discharged at -20℃, and cannot be discharged normally at -10℃. The discharged capacity is only 30% of the nominal capacity. At the same time, the working voltage platform is unstable and cannot provide normal working efficiency.

The low temperature performance of lithium iron phosphate batteries is worrying. Although people have improved the low temperature performance of lithium iron phosphate through various methods (such as doping with lithium, iron, and even phosphoric acid to improve ion and electronic conductivity, controlling the effective reaction area by improving the particle size and morphology of primary or secondary particles, and increasing electronic conductivity by adding additional conductive agents, etc.), the inherent characteristics of lithium iron phosphate materials determine that its low temperature performance is inferior to other positive electrode materials such as lithium manganese oxide.

Power tools, electric vehicles and other equipment that use batteries as mobile energy sources must consider not only capacity but also the requirements of the working environment, among which temperature is an important indicator, especially in subarctic and arctic regions. The mobile tools used must be able to operate normally at -10℃ to -20℃. Therefore, compared with lithium iron phosphate power batteries of other companies, the superiority of MNKE brand is self-evident.

Summarize

From the above comparison, it can be seen that some domestic lithium iron phosphate power batteries are far from meeting the standards for commercial use. The main reasons are as follows:

1) The tap density and conductivity of lithium iron phosphate materials are poor. This problem has not been effectively solved in China, so the unit volume capacity of this type of product is low. Although its AC internal resistance is relatively low, because the conductivity problem has not been solved, the DC internal resistance of the product is relatively large in actual applications, and the voltage platform that can be provided during operation is tilted greatly, which has a significant adverse effect on the working efficiency of the motor in actual use.

2) Currently, lithium iron phosphate has poor working performance at low temperatures, which is one of the main reasons why it cannot become a commercial product.

3) The above reasons are not only caused by the lithium iron phosphate material itself, but also because domestic manufacturers that use lithium iron phosphate to prepare power batteries have not yet truly mastered the comprehensive manufacturing technology. Because from the world's top lithium battery companies, we can see that the lithium iron phosphate power batteries produced by A123 have basically overcome the defects of low tap density, poor conductivity and inability to work normally at low temperatures.

It can be seen that the defects of positive electrode materials can be overcome through comprehensive technologies such as optimization of process formula and improvement of process technology, and the inherent advantages of the materials can be brought into play.

4) Currently, lithium iron phosphate as a positive electrode material is still subject to two constraints. The first is the constraint of international patents, and the second is the complex process and high cost of the material itself.

In short, the commercial preparation of lithium-ion power batteries not only depends on the selection of positive electrode materials, but also requires a comprehensive balance of a series of technologies and processes such as the matching of negative electrodes, optimization of electrolytes, selection of diaphragms, selection of tabs and shell covers, etc., in order to maximize the advantages of positive electrode materials and truly prepare power batteries that meet commercial use. It is precisely because of Jiangsu Manganese Battery Co., Ltd.'s efforts in this regard that the manganese-based lithium-ion power batteries it produces have superior performance and are recognized by well-known power tool users at home and abroad.