In 2018, my country’s new energy vehicle sales reached 1.26 million, and the number of new energy vehicles reached 2.61 million.
In the case of new energy auto production, we have to face a large amount of powerful lithium battery retirement. Using the problem, the most effective way to use the power lithium battery is “closed use”. The so-called step utilization refers to the capacity detection after the power lithium battery is retired.
After the standard power lithium battery can be reused, the residual value of the power lithium battery can be used as the energy storage power supply.. However, many times, the decline of the lithium-ion battery is not linearly decline, but the decline rate is greatly accelerated, which seriously affects the ladder of the lithium-ion battery, then what is the life of the lithium-ion battery Does the end capacity diving? There are many factors that lead to lithium-ion batteries in the end of life, there are many factors in the end of life, and the University of Darhaus, Canada, the University of Darhaus, and JRDAHN (Corresponding author) and JRDAHN (Corresponding author), etc.
LIPF6 concentration, battery standing time, electrode thickness, graphite type, and electrolyte solvent ratio, the effect of electrolyte solvent ratio, the effect of lithium ion battery capacity diving phenomenon has been studied in detail. The authors used by the authors used a single crystal NCM523 / graphite system soft bag lithium battery as a research object, wherein according to the different positive and negative electrodes, it is divided into coating single crystal NCM523 (21.1 mg / cm2) / artificial graphite (12.
4 mg / cm2), No coated single crystal NCM 523 (21.1 mg / cm2) / artificial graphite (12.4 mg / cm2) and coating single crystal NCM 523 (21.
1 mg / cm2) / natural graphite (12.4 mg / cm2), and a coating amount is slightly low Single crystal NCM523 (14.4 mg / cm2) / artificial graphite (10.
2mg / cm2) total four batteries. The electrolyte employed is also divided into a variety of, wherein the concentration of LiPF6 is divided into 1.2m and 1.
5m, and the additives are several kinds of VC, FEC, DTD, ES and LFO.. The figure below shows the values of RCT (charge exchange impedance) after several batteries (4.
1V, 4.2V, and 4.3V three cutoff voltages), from the following picture A (coating single crystal NCM523 (21.
1mg / cm2) ) / Artificial graphite (12.4 mg / cm2)) It can see that most batteries increase with the charging cutoff voltage, RCT will become lower, only the RCT of the battery is very low only if the battery contains only LFO in different electrolytes..
At the same time, we compare the following images A and C can also find that RCT with natural graphite battery is lower than the battery of artificial graphite, while adding ES additives can also lead to higher RCT.. The figure below shows the coating NCM523 / artificial graphite battery and non-coating NCM 523 / artificial graphite, respectively, electrolyte different additives, circulatory data (1C charge / 1C) under 4.
1V, 4.2V and 4.3V, from below It is possible to see that there is no non-coating NCM523 / artificial graphite battery to be more poor in circulatory NCM523 / artificial graphite battery, and the battery internal resistance is added faster.
If 1% LFO is added in the electrolyte, it is possible to add 1% LFO in the electrolyte. Improve cycle performance of non-coated NCM523 batteries. At the same time, we can also notice from the following figure.
As the battery charging cutoff voltage is increased, all battery cycle performance will have a significant decline, and the coating NCM523 / artificial graphite battery is 4,000 thousand after 4.0 thousand times in 4.1V and 4.
2V. Decline is still very slight, and the capacity decline is very obvious after the charging deadline is increased to 4.3V.
. A 2% FEC + 1% DTD coating NCM523 battery has a phenomenon of capacity diving after the 4.3V cycle 2000, and the non-coating NCM523 battery of 1% LFO electrolyte is a phenomenon of capacity diving after the cycle of 700 times.
The coating NCM523 battery using 2% Vc + 1% DTD electrolyte occurs in a 4.3V cycle 2500, there is a capacity diving, and a coating NCM523 battery using 1% LFO electrolyte still does not have capacity diving after the cycle exceeds 4000 times. Phenomenon.
During the above battery cycle, the author tests the discharge capacity of the battery in C / 20, C / 2, 1C, 2C, and 3C magnification per cycle (the result is as shown below, each picture The capacity change of C / 20, C / 2, 1C, 2C, 3C, which can be seen from the figure, and the 3C discharge capacity decreases at the time of circulation in 4.3V, this Among them, the 3C discharge capacity of the battery of the 2% FEC + 1% DTD electrolyte is significantly faster than the battery of 2% Vc + 1% DTD, and the 3C discharge capability of the battery of the 1% LFO electrolyte is passed through There is still no very significant decline after 4,000 cycles, which also shows the importance of electrolyte additives..
The loop performance of several different batteries will be seen from the loop data of the following figure, which can be seen in all non-coating NCM523 / artificial graphite batteries, which will cause a significant deterioration in the cycle performance (compared to the above figure. The battery of the ES additive is added), wherein 2% FEC + 1% DTD + 1% ES has a large number of gases in the cycle, causing loss between the electrodes, causing battery failure while 1% LFO + 1% ES. Additives can lead to a large linear decay in the initial period of cycle.
. The following figure shows the cycle performance of using artificial graphite and natural graphite using different electrolytes. From the figure, it can be found that the coating NCM523 / natural graphite battery uses 2% Vc + 1% DTD to cause a sharp decline in battery life.
And if only the negative electrode is replaced with the artificial graphite cycle performance, it will greatly improve. At the same time, we can also pay attention to the sedation time, increase the LIPF6 concentration, and add 2% VC + 1% DTD to improve the cycle performance of the coating NCM523 / artificial graphite in 4.3V.
. The following figure shows the cycle performance of the high and low coated coating NCM523 / artificial graphite battery using different electrolytes, and the cycle performance of several batteries in 4.1V and 4.
2V is compared, at 4.3V cutoff voltage, high Applying the amount of the coated battery is faster than the low-applied amount of battery (<1000 times), but there is no significant gap between the high-low coated amount on the capacity retention ratio..
The figure below shows the change trend of the above-mentioned battery in different magnifications (C / 20, C / 2, 1C, 2C, 3C), and can be seen from the following figure, 2% Vc + 1% DTD can be seen. Or 2% FEC + 1% DTD, 1% LFO electrolyte low-applied battery When the battery is circulated in 4.3V, the 3C capacity retention ratio is significantly higher than that of the highly discharged amount, and 1% LFO + 2% FEC is used.
High and low coating battery 3C capacity retention ratio is very close. The following figure shows the circulating performance of the coating NCM523 / artificial graphite battery using different electrolytes, adding 20% of MA to the electrolyte to increase the magnification performance of the battery, but it can cause severe deterioration of the cycle performance of the battery..
The picture below shows the negative photode of the battery after a certain number of batteries. From the figure, it can see that although there is a significant capacity diving at the end of life, the negative pole does not observe the lithium lithium phenomenon, which also shows The phenomenon of the capacity of the capacity we observed above is not due to the negative electrode analysis..
The figure below shows the charge exchange impedance RCT values after several different battery cycles. It can notice that the coating protection NCM523 battery is significantly lower than the NCM523 battery without protecting the coating. This also indicates that the surface coating of the positive electrode can effectively inhibit the decomposition of electrolyte.
. XIaoweiMA’s work indicates that the surface coating of the positive electrode can effectively reduce the oxidation of the electrolyte on the surface of the positive electrode, thereby lifting the cycle performance of the battery, high cutoff voltage, unsuitable electrolyte additives can cause the electrolyte to decompose the electrolyte surface decomposition to the negative surface, thereby causing The capacity diving of the lithium ion battery, in addition to reducing the amount of coating, using artificial graphite, enhances the concentration of LiPF6 can also effectively improve the cycle performance of the battery..
The author’s work indicates that the coating NCM523 / artificial graphite battery, the battery of 2% FEC + 1% LFO electrolyte can be circulated more than 4,000 in the voltage range of 3.0-4.3V, if the charging deadline is reduced to 4.
1V Or 4.2V can also add a few thousand cycle life, with a wide range of application prospects. .