Application and research of the hottest lithium ti

Application and research of lithium titanate energy storage system

since 2006, Guodian began to pay attention to energy storage technology. At that time, there were few choices of batteries, and our key technical research projects were nano batteries and liquid sulfur batteries. At that time, lithium batteries were not considered as energy storage, because the cycle life of lithium batteries was 2000-3000 times, which was of little value in electrical applications. The cycle life of twoorthree times means that the battery should be replaced once in a few years for electricity. Lithium batteries are not suitable for electricity. By 2009, it was incredible to know that the cycle life of lithium titanate battery could reach tens of thousands of times. Later, the lithium titanate battery sample was tested, and the capacity did not decay when it was cycled for more than 1000 times. After so many years of research and development, evaluation and application of lithium titanate batteries, lithium titanate batteries do have the characteristics of long life. Of course, it also has a big disadvantage, that is, it is too expensive. As a user unit, Guodian has been trying to find ways to reduce costs

the power of lithium titanate battery can be high, but in order to pursue high power, it is necessary to nano materials. The process control requirements of production and processing after nano materials are very strict, so the cost is increased. In terms of energy storage, can we consider reducing the high-power requirements of lithium titanate batteries, only retaining the characteristics of long life, in exchange for cost reduction

first, we studied the reconstruction technology of lithium titanate battery

replace nano lithium titanate with low-cost submicron lithium titanate, and based on this, establish a lithium titanate battery material system for energy storage. Through experiments, the particle size of the material is 0.8-1.3 μ M, it can not only ensure the characteristics of long life, but also reduce the requirements of high power, reduce the harsh conditions of production process control, and thus reduce the cost. The circular structure and cylindrical structure can also be replaced by the laminated flexible packaging structure which has advantages in performance, manufacturing process and cost. The above two points are to reduce the battery cost from the reconstruction of materials and battery structure

on the other hand, it is the reconstruction of battery production process. In the homogenization of electrode materials, the conventional stirring process is changed to high viscosity stirring process; In the process of electrode manufacturing, the imported precoating fluid collector is changed into the precoating fluid collector independently developed; In the environmental control of battery production, the environmental humidity can be relaxed from 10% to 30%; In the battery manufacturing process, the two drying processes of coil drying before coating and cell drying before liquid injection can be cancelled. The above technical reconstruction is carried out for homogenization, precoating fluid collector, environmental control, battery manufacturing process and other links respectively to reduce the battery cost

second, the packaging of lithium titanate energy storage battery testing products should gradually change from the previous simple, protective and passive packaging situation to a branded, market-oriented and active packaging situation evaluation technology. It can be seen from the figure that the cycle times and capacity retention rate of lithium titanate are much better than lithium iron phosphate batteries. According to our testing experience, there is little difference between domestic batteries and international batteries before the number of cycles is sevenoreight thousand. After sevenoreight thousand, there are differences in the consistency of domestic batteries. These problems prompt us to improve the evaluation technology

there are two main methods to study the continuous expansion of downstream utilization of lithium titanate battery rapid evaluation experimental technology: rapid evaluation technology research based on accelerated aging experiment and rapid evaluation technology research based on life prediction model

1. Research on rapid evaluation technology based on accelerated aging experiment

the key technology of accelerated aging evaluation is to confirm the selection of dynamic conditions and boundary conditions of accelerated aging, and conduct rapid evaluation by establishing the equivalent relationship between attenuation characteristics under different dynamic conditions

in the experiment, through the regular characterization of the battery under the conditions of routine experiment and accelerated aging experiment, find the equivalent point with the same battery characteristics under different conditions, and establish the functional relationship between the equivalent points (y2=f (Y1)), so as to predict and estimate the data under the conditions of routine 1c and 23 ℃ experiments with the data of accelerated experimental conditions

by comparing the time spent in the rapid evaluation method of equivalent experiment at different magnification and different temperature, it can be seen that the equivalent experiment can save up to half of the time, but this time is also relatively long. It is not ideal to use the accelerated method for rapid evaluation. Therefore, we consider using the method of life prediction model for rapid evaluation

2. Research on rapid evaluation technology based on life prediction model

there are three methods for life prediction model:

(1) linear extrapolation method: it is widely used, and the method is simple, but it does not consider the electrochemical nonlinear degradation characteristics of the battery

based on the measured data of 1000 cycles, aiming at the capacity within 3000 cycles, this method predicts that the weak interface between the traditional middle layer and the rear structure will be strengthened, and the measurement is more accurate. Due to the non-linear decline caused by electrochemical polarization and other factors in the cycle process, the accuracy of long-term cycle prediction is poor, showing an obvious discrete trend

(2) whole life cycle fitting method: it requires the measured data of the whole life cycle to fit, which is often only effective for one battery

based on the measured data of 1000 cycles, the fitting of the first 3000 cycles is more accurate, and the subsequent deviation rate is larger, which is mainly due to the different performance degradation trends caused by the differences between different batteries

(3) electrochemical model fitting method: Considering electrochemical polarization and other factors, supplemented by measured data revision

this method takes 1000 cycles of measured data, and within 5000 cycles, the prediction deviation rate is small. This method is desirable

in general, the cycle of the rapid evaluation method based on experimental equivalence is longer than that of Jinan experimental machinery factory in 2017. If 5000 cycles are taken as the cycle life prediction target, it can only shorten the original time by about 50% at most. Electrochemical model fitting method only needs 1000 cycles of measured data as the model benchmark data or correction data, so if 5000 cycles are used as the cycle life prediction target, the original time can be shortened by 80%

in the future, we need to explore more detailed accelerated aging boundary conditions, and expand the rapid evaluation method to lithium titanate batteries from different manufacturers or other types of energy storage batteries. The life of lithium titanate battery is greatly affected by calendar time. Next, we need to find the relationship between calendar time and accelerated aging. Optimize the existing electrochemical model, combine it with more detailed boundary conditions in the future, improve the rapid evaluation accuracy of lithium-ion energy storage batteries, further improve the detection methods and specifications, and revise the standards