Do you know what is going on with low battery capacity?

Battery capacity is the first attribute of batteries, and low battery capacity is also a common problem encountered in samples and mass production. First of all, confirm whether the capacity division process is set incorrectly (for example, whether the discharge current is set large, whether the charging time is set short); if the capacity division step setting is correct, the cell must be re-division after replacing the detection point. Of course, with regard to mass production and even samples, the probability of low-volume batch caused by the error of the sub-capacitor is very low. Under normal circumstances, the battery core is really problematic. If the low-capacity is still low after the retest, then you can confirm that the low-capacity problem really exists (at the same time, it is best to keep an eye on the retest: fully charge 3pcs retest batteries for later use). After confirming the existence of low capacity of the battery, further confirm the frequency and severity of the occurrence of the low capacity, and grasp the actual situation of the low capacity as a whole. The samples are often a batch, not much to say; however, there are two situations in which the mass-produced model has always been low-capacity and the model occasionally has low-capacity. Regarding the former, the decomposition should be based on the design, material selection angle, and long-term stubborn problems encountered in mass production as the entry point and priority (for example, whether the material matching has not been verified? Is the same one on the production line often caused low capacity? For the latter, we have to give priority to production line operations and process changes (for example, is this batch of negative electrodes crushed? Has the production line shortened the aging time for production? Whether the process has been changed compared to before and this change has the risk of causing low capacity). After the frequency is confirmed, it is necessary to confirm the relatively less important severity, that is, the proportion of low-capacity cells and the proportion of the capacity lower than the required value. To a greater extent, the confirmation of the severity is for the possible relaxation of capacity specifications and the basis for determining the supply of out-of-stock quantities. Regarding the decomposition of the problem itself, the significance is not as important as the frequency of confirmation, but it is still essential. After grasping the actual situation of low capacity as a whole, it is about to start to decompose. Before disassembling the system, you can first disassemble the fully charged low-capacity battery cell that was retested before and take a look at the interface. If there is no problem, it is likely that the positive electrode coating is too light or the design margin is insufficient; if there is a problem with the interface , It may be a problem in the manufacturing process or in the design. First, at least 8pcs batteries with low capacity + 8pcs batteries with qualified capacity. The low-capacity batteries are randomly divided into two groups: low-capacity group A and low-capacity group B, and qualified-capacity batteries are randomly divided into two groups: qualified A group and qualified B group. Then discharge the two A group batteries to a static voltage of about 3.0V (Wenwu is used to discharge from 0.5C to 3.0V and then discharge to 2.5V at 0.2C; of course, the objects are lithium sulphate and ternary + graphite negative electrode); then disassemble Solve the low-capacity and qualified batteries, and bake the positive electrode sheet at a temperature above 85°C for 24h (the detailed baking parameters have not been verified by DOE, but it can be determined that the given parameters can be decomposed), and then the weighing is low The weight difference between the positive electrode sheet and the qualified positive electrode sheet; if the weight of the low-capacity electrode sheet is clearly lower than the qualified positive electrode sheet or below the process range, it can basically be judged that the low capacitance is caused by the light coating of the positive electrode. There are two points to be added about weighing the pole piece weight after baking: First, although the first irreversible lithium source of the positive electrode will cause the positive electrode to lose a little weight, the total weight of the irreversible lithium source only accounts for about 5% of the positive electrode lithium source. Less than 0.5% of the weight of the positive electrode, even if the irreversible lithium source caused by lithium evolution is added, the lightness of the positive electrode will not be less than 1% of the total weight of the electrode; the electrolyte is impossible during the baking process It is completely dried, but the weight of the actual remaining part is also very limited relative to the weight of the pole piece. In general, after baking the positive electrode, weigh the weight of the pole piece and 1% of the actual weight of the pole piece before winding; the electrolyte cannot be completely dried during the baking process, but the actual weight of the remaining part is relative to the weight of the pole piece. The language is also very limited. In general, the difference between the weight of the pole piece weighed after the positive electrode is baked and the actual weight of the pole piece before winding does not exceed 2%. Moreover, the weight of the positive electrode with qualified capacity is compared with the weight of the low-capacity pole piece. This method is still more credible (in addition, I have heard that something can be wiped through the pole piece will be more helpful to the drying of the electrolyte. The details I don’t understand the principles of civil and martial arts, I hope friends who know do not hesitate to advise). The second is that the same method is not suitable for the negative electrode. The reason is that a lot of weight will be added when the negative electrode is formed. However, the weight gain ratio of the negative electrode after the formation can be obtained through experiments, and then the weight of the negative electrode can be reversed to determine whether the low capacity is due to the excessive or insufficient negative electrode. cause. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: What are the calculation methods for UPS batteries?