Practical Performance Evaluation of Lithium -Lithium - Ion Battery Equipment

Practical Performance Evaluation of Lithium Batteries -Lithium - Ion Battery Equipment

In the development of many emerging applications in the future, the key technology is inseparable from rechargeable batteries. In 2018 alone, there were 11,583 battery-related academic papers. However, the conclusions and viewpoints in many papers are exaggerated. There are two reasons for this phenomenon, one is the deliberate exaggeration of the researchers, and the other is the lack of understanding of the battery test system. Therefore, the test results in many laboratories do not represent the real situation of actual battery performance. In particular, many papers are not concerned with Coulombic Efficiency (CE), knowing that if a commercial battery has a cycle life of 500 cycles, the CE per cycle should be ≥99.96%.

To this end, researcher Li Hong from the Institute of Physics, Chinese Academy of Sciences published a paper entitled "Practical Evaluation of Li-Ion Batteries" in the international journal "Joule", and specially assembled a batch of soft-pack lithium batteries to interpret the parameters and performance of the batteries. , aims to help more researchers to better identify the problem and further shorten the gap between the laboratory and the industry. The authors argue that while there cannot be a standard set of laboratory test systems, researchers must understand that the experimental design of the coin cell battery, cell fabrication, and testing methods have a significant impact on the results. Only by clarifying some concepts and parameters can we work together and seek common development in the development of next-generation lithium batteries using lithium anodes. The content of this article is concise and well-written, and it is well worth reading.(Lithium - Ion Battery Equipment)

1) When evaluating new battery anode materials in coin cells using metallic lithium as the anode of half cells, the cut-off voltage for charging is usually set at 2.0V or even 3.0V vs. Li+/Li, which will result in high initial CE and high Lithium removal ability. However, according to the authors' research, only the capacity in the voltage range of 0-0.8V is meaningful. Therefore, for most anode materials, the authors suggest that testing in the range of 0 to 0.8V is sufficient; to understand the maximum delithiation capability or to study high voltage anodes, such as Li4Ti5O12 or TiNb2O7, the voltage range can be extended to 0–3.0V.

2) High rate performance has always been very important, which has been reported in many papers, and is highly dependent on the parameters of materials and electrodes. The smaller the particle size of the material and the thinner the coating, the better the rate performance will be. However, this will result in low CE and low mass energy density, and, the areal capacity of commercial cells is around 3-4mAh/cm2, therefore, cells should measure 1C rates at 3–4mA/cm2 current densities and 9–12mA 3C rate was measured at /cm2. In many literatures, despite the obvious high-rate capability, the areal capacity is far below this value, which cannot be explained.

3) In Li-ion full cells, all active lithium is supplied by the positive electrode, and the total capacity loss determines the cycle life and actual energy density of the full cell. For graphite and Li4Ti5O12 anodes, the CE after the first cycle is close to 99.9%, while for high-capacity anode materials reported in many literatures, the CE can approach 99.5% only after 10 or more cycles. Therefore, the total irreversible capacity loss should be calculated in order to predict the cycling performance of the material in the full battery. If the CE of the battery is below 99.5% in each cycle, the authors believe that the total capacity loss should be given when publishing the article.

In the past 25 years, the average energy density of lithium batteries has increased by less than 3%, and this rate of increase will be slower and slower. From a historical point of view, due to the complex design of the battery system and high requirements for application performance, the energy density has never been increased in a sudden blowout. Just breaking the record of the energy storage performance of a material does not guarantee that the new battery can be used in a short period of time. commercialization, so researchers should be aware of the complicity of developing batteries.

After 28 years of outstanding efforts by many scientists and engineers, the energy density of power lithium batteries has now reached 300Wh/kg, and the energy density of 3C consumer batteries has also increased from 90Wh/kg to 730-750Wh/L. We often read in articles that a new energy storage device may have a 2-10 times higher energy density than current lithium batteries, which means 600-3000Wh/kg or 1460-7500Wh/L of energy density, although these values ​​are very Yes, but honestly, it's hard to achieve.



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