Lithium titanate battery power can be high, but in order to pursue high power, it is necessary to nano-materials, and the process control requirements of processes such as nano-production and production processing are very demanding, and the cost is increased. In terms of energy storage, can we consider the requirement of reducing the high power of lithium titanate batteries, and only retain the characteristics of long life, in order to reduce the cost.
First, we studied the reconfiguration technology of lithium titanate battery
The nanometer lithium titanate material is replaced by a low-cost sub-micron lithium titanate material, and based on this, a lithium titanate battery material system for energy storage is established. Through experiments, when the material particle size is between 0.8 and 1.3 μm, it can not only ensure the long-life characteristics, but also reduce the high power requirements, reduce the harsh conditions of production process control, and thus reduce the cost. It is also possible to replace the annular structure and the cylindrical structure with a laminated flexible packaging structure having advantages in performance, manufacturing process, and cost. The above two points are to reduce the cost of the battery from the reconstruction of materials and battery structure.
Another aspect is the reconstruction of the battery production process. In the homogenization step of the electrode material, the conventional stirring process is changed into a high-viscosity stirring process; in the electrode making process, the imported pre-coating current collector is changed into a self-developed pre-coating current collector; in the environmental control section of the battery manufacturing, The ambient humidity can be relaxed from 10% to 30%; in the battery manufacturing process, the two drying processes of the roll drying before coating and the cell drying before filling can be eliminated. The above technologies are reconstructed for homogenization, pre-coating current collector, environmental control, and battery manufacturing processes to reduce battery cost.
Second, lithium titanate energy storage battery evaluation technology
As can be seen, the cycle number and capacity retention rate of lithium titanate is much better than that of lithium iron phosphate battery. According to our test experience, before the cycle number of seven or eight thousand times, the domestic battery and the international battery are not much different. After seven or eight thousand times, the consistency of the domestic battery is different. These issues have prompted us to improve our evaluation techniques.
There are two main methods for rapid evaluation of lithium titanate battery experiments: rapid evaluation technology based on accelerated aging experiments and rapid evaluation techniques based on life prediction models.
1. Research on rapid evaluation technology based on accelerated aging experiment
The key techniques for accelerated aging evaluation are: confirming the dynamic condition selection and boundary conditions of accelerated aging, and quickly evaluating the equivalent relationship between attenuation characteristics under different kinetic conditions.
In the experiment, by the regular characterization of the battery under the conditions of routine experiment and accelerated aging experiment, find the equivalent point of the battery characteristics under different conditions, and establish the functional relationship between the equivalent points (y2=f(y1)). Therefore, the data under the experimental conditions of 1C and 23°C were predicted and estimated by the data of accelerated experimental conditions.
It can be seen from the comparison of the time used in the rapid evaluation method of the equivalent experiment at different magnifications and different temperatures that the equivalent experiment can save up to half of the time, but this time is also relatively long. A quick evaluation using an accelerated method is not ideal. So we consider using the life prediction model method for rapid evaluation.
2. Research on rapid evaluation technology based on life prediction model
There are three methods for life prediction models:
(1) Linear extrapolation method: It is more common to use, and the method is simple but does not consider the electrochemical nonlinear decay characteristics of the battery.
The method uses 1000 cycles of measured data, and the capacity prediction within 3000 cycles is more accurate. The long-term cycle prediction accuracy is poor due to factors such as nonlinear decay caused by factors such as electrochemical polarization during the cycle. Obvious discrete trend.
(2) Full life cycle fitting method: It is necessary to fit the measured data of the whole life cycle, and it is often only effective for one battery.
The method uses 1000 cycles of measured data, and the fitting in the first 3000 cycles is more accurate, and the subsequent deviation rate is larger. The main reason is that the difference in performance between different batteries causes different performance degradation trends.
(3) Electrochemical model fitting method: Considering factors such as electrochemical polarization, supplemented by actual measured data revision.
The method is based on 1000 cycles of measured data, and the predicted deviation rate is small in 5000 cycles, and this method is preferable.
In general, the rapid evaluation method based on experimental equivalence has a relatively long period. For example, 5000 times as the target of cycle life prediction, it can only shorten the original time by about 50%. Since the electrochemical model fitting method requires only 1000 cycles of measured data as model reference data or correction data, if 5000 cycles are used as the cycle life prediction target, 80% of the original time can be shortened.
In the future, it is necessary to explore more detailed accelerated aging boundary conditions, and at the same time expand the rapid evaluation method to lithium titanate batteries of different manufacturers, or other types of energy storage batteries. Lithium titanate battery life time is influenced by the calendar, the next need to find a calendar time and accelerated aging of the relationship. The existing electrochemical model is optimized, combined with the more refined boundary conditions in the future, the rapid evaluation accuracy of the lithium ion energy storage battery is improved, the detection method and specification are further improved, and the standard is revised.
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