Final Report - Recovery Act - Development and application of processing and process control for nano-composite materials for lithium ion batteries
- ORNL
- A123 Systems, Inc.
Oak Ridge National Laboratory and A123 Systems, Inc. collaborated on this project to develop a better understanding, quality control procedures, and safety testing for A123 System s nanocomposite separator (NCS) technology which is a cell based patented technology and separator. NCS demonstrated excellent performance. x3450 prismatic cells were shown to survive >8000 cycles (1C/2C rate) at room temperature with greater than 80% capacity retention with only NCS present as an alternative to conventional polyolefin. However, for a successful commercialization, the coating conditions required to provide consistent and reliable product had not been optimized and QC techniques for being able to remove defective material before incorporation into a cell had not been developed. The work outlined in this report addresses these latter two points. First, experiments were conducted to understand temperature profiles during the different drying stages of the NCS coating when applied to both anode and cathode. One of the more interesting discoveries of this study was the observation of the large temperature decrease experienced by the wet coating between the end of the infrared (IR) drying stage and the beginning of the exposure to the convection drying oven. This is not a desirable situation as the temperature gradient could have a deleterious effect on coating quality. Based on this and other experimental data a radiative transfer model was developed for IR heating that also included a mass transfer module for drying. This will prove invaluable for battery coating optimization especially where IR drying is being employed. A stress model was also developed that predicts that under certain drying conditions tensile stresses are formed in the coating which could lead to cracking that is sometimes observed after drying is complete. Prediction of under what conditions these stresses form is vital to improving coating quality. In addition to understanding the drying process other parameters such as slurry quality and equipment optimization were examined. Removal of particles and gels by filtering, control of viscosity by %solids and mixing adjustments, removal of trapped gas in the slurry and modification of coater speed and slot die gap were all found to be important for producing uniform and flaw-free coatings. Second, an in-line Hi-Pot testing method has been developed specifically for NCS that will enable detection of coating flaws that could lead to soft or hard electrical shorts within the cell. In this way flawed material can be rejected before incorporation into the cell thus greatly reducing the amount of scrap that is generated. Improved battery safety is an extremely important benefit of NCS. Evaluation of battery safety is usually accomplished by conducting a variety of tests including nail penetration, hot box, over charge, etc. For these tests entire batteries must be built but the resultant temperature and voltage responses reveal little about the breakdown mechanism. In this report is described a pinch test which is used to evaluate NCS quality at various stages including coated anode and cathode as well as assembled cell. Coupled with post-microscopic examination of the damaged pinch point test data can assist in the coating optimization from an improved end-use standpoint. As a result of this work two invention disclosures, one for optimizing drying methodology and the other for an in-line system for flaw detection, have been filed. In addition, 2 papers are being written for submission to peer-reviewed journals.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 1095726
- Report Number(s):
- ORNL/TM-2013/259; ED1908000; RAED002; CPS 18981
- Country of Publication:
- United States
- Language:
- English
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