The surface-free lithium content, which is a critical index that reflecting the quality of ternary cathode materials, usually cannot be monitored in real time due to technical restriction. To this end, soft sensor technique is applied to predict the surface-free lithium content by readily available process variables, making timely control on operation parameters. In this paper, a modeling method based on ensemble just-in-time learning (JITL) soft-sensor is developed. In the model, data feature indices are firstly designed to properly extract the real-time and short-time features between the batching and the loading procedure. Accordingly, ensemble JITL soft-sensor model is constructed with the semisupervised local weighted probability principal component regression.Moreover, considering varying working conditions, an adaptive moving window technique is adopted to improve the adaptability of the model. The validation and the flexibility of the developed modeling method are testified with the practical manufacturing data.
K E Y W O R D Sjust-in-time learning, moving window, prediction of residual lithium content, semisupervised learning
| INTRODUCTIONWith the growing demand for electric energy reliability in modern society, as well as the widespread use of intermittent new energy sources such as wind power and photovoltaics, electric energy storage technology has received extensive attention from all over the world. 1 Lithium-ion batteries, which have many merits such as portability, recyclability, high energy density, and long cycle life, are nowadays recognized as a key power storage material. In the process of manufacturing lithium-ion batteries, surface-free lithium content, namely, the content of lithium-ion on the surface of cathode materials, plays a decisive role in determining the characteristic of this material. Thus, high requirements are put forward for the real-time monitoring of surface-free lithium content. However, surface-free lithium content cannot be directly measured since the mensuration is inefficient, hysteresis, and costly. Therefore, it is a good choice to predict surface-free lithium content by using the soft-sensor model. 2,3 There are two most commonly used methods for building soft-sensor models, namely, mechanism modeling and data-driven modeling. The mechanism modeling method starts with the physical, chemical, and biological knowledge of the object process. Then, mathematical equations based on conservation laws such as mass conservation are formed to find the relationship between process variables and the key variables. The mechanism models have more application