1800mah 18650 battery have low efficiency for the first time. Which company has the best solution?

　　A lot of research work has been done to address the poor cycle life of lithium-ion batteries. Measures for electrode materials, electrolytes, and electrode structures are all relatively mature. The life of lithium-ion batteries has been greatly improved. promote. The high-voltage electrode materials and supporting electrolytes developed for low battery voltage have gradually matured and are being gradually applied.

　　There are several major problems with lithium-ion batteries: the first battery has low initial efficiency, charging 10 amps to 9 amps; the second battery has poor cycle life, and will be dead after less than 500; the third battery voltage is low, and will end at 4.2V.

　　A lot of research work has been done to address the poor cycle life of lithium-ion batteries. Measures for electrode materials, electrolytes, and electrode structures are all relatively mature. The life of lithium-ion batteries has been greatly improved. promote.

　　The high-voltage electrode materials and supporting electrolytes developed for low battery voltage have gradually matured and are being gradually applied.

　　Only the problem of low efficiency for the first time has not been solved relatively well. There is currently no mature solution. Currently, there is inert lithium powder developed by 3M Company. Although it can be used as a supplementary negative electrode lithium source, it has poor safety (there is dust explosion). risks) and high costs (high material costs and high equipment modification costs), it is difficult to achieve widespread application in the short term. Replenishing lithium in the cathode seems to be a possible option. To replenish lithium in the cathode, you only need to add lithium-containing oxide to the cathode. The cost is low, the original process is not changed, and metal lithium is not involved, so the safety is greatly improved.

　　Taking a typical LiCoO2/C full battery as an example, during the first charging process, with the embedding of Li+, the potential of graphite gradually decreases. When it is lower than the stable potential of the electrolyte, the electrolyte will be reduced on the surface of the graphite negative electrode. Decompose and consume part of the lithium, resulting in approximately 10% irreversible capacity. When the negative electrode is replaced with hard carbon, silicon and other materials with higher irreversible capacity, this capacity loss will be more obvious.

　　Li5FeO4 is an ideal cathode lithium source with a specific capacity of 867mAh/g. Theoretically, each mole of Li5FeO4 can provide 5 Li+. By mixing a certain amount of Li5FeO4 into the traditional cathode material, the lithium-ion battery can be significantly improved. First time efficiency and energy density.

　　XinSu et al. conducted relevant research on Li5FeO4 as a lithium source for the cathode. They used LiCoO2 for the cathode (Coulombic efficiency is 98%), hard carbon was used for the negative electrode (the first Coulombic efficiency was only about 80%), and Li5FeO4 was synthesized using a solid-phase method. During the first charging process, the LFO material can release at least 4 Li+, which is equivalent to a specific capacity of more than 700mAh/g, as shown in the following reaction equation:

　　During this process, most of the lithium ions are irreversibly embedded into LiFeO2 again, but these lithium ions can be used to offset the irreversible capacity loss caused by the negative electrode. Therefore, we only need to add a small amount of Li5FeO4 to the cathode material during use.

　　In the experiment, it was found that by adding only 7% LFO material to the positive electrode, the first charging capacity of the positive electrode can reach 233mAh/g, while the first discharge capacity is only 160mAh/g. The 7% content of LFO provides an additional 31% of Li+. These Lithium ions will eventually enter the negative electrode material, thus making up for the low initial efficiency of the negative electrode.

　　Therefore, when graphite materials are used as negative electrode materials (irreversible capacity is about 10%), the content of LFO in the positive electrode can be appropriately reduced.

　　Calculation shows that when the capacity ratio of the positive and negative electrodes is 1:1, due to the large irreversible capacity of hard carbon, the actual remaining capacity of the positive electrode is only 129mAh/g (charging voltage is 2.7-4.3V), and After adding LFO to the positive electrode, since the lithium of LFO replenishes the lithium lost during the first charging process, the remaining reversible capacity of the positive electrode reaches 159mAh/g, which means that the energy density of the entire battery is increased by about 10%.

　　Since 7% LFO can provide an additional 31% of lithium ions, the amount of LFO added can be appropriately reduced to just meet the irreversible capacity of the negative electrode (for example, about 10% for graphite and about 25% for Si material), so the energy of the battery Density can be further improved.

　　At the same time, the study also found that the addition of LFO not only improved the first efficiency of the battery, but also significantly improved the cycle performance of the battery because LFO provided additional Li. The 50-cycle capacity retention rate increased from 90% to 95% (LCO/hard carbon). Energy spectrum analysis and X-ray diffraction of the battery negative electrode after long-term cycling showed that the LiFeO2 material generated after the LFO material releases lithium ions will remain in the positive electrode, and there is no risk of Fe element dissolving and precipitating in the negative electrode again.

　　Li5FeO4 material is a safe, reliable and efficient lithium source for the positive electrode. Its cost is relatively low. It can release a large amount of lithium ions during the first charge. The activity of the product after releasing lithium ions is extremely low, and there will be no re-intercalation of lithium or lithium. Dissolution is therefore a very potential source of cathode lithium. With the application of high-capacity, high-irreversible-capacity anode materials such as silicon anodes, the market demand for cathode lithium supplement materials will further expand.

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