Effect of binder on the overcharge response in LiFePO4-containing cells

• Published in: Journal of power sources Vol. 450; no. C
• Main Authors: Rago, Nancy Dietz, Li, Jianlin, Sheng, Yangping, Wood III, David L., Steele, Leigh Anna, Lamb, Joshua, Grosso, Christopher, Fenton, Kyle, Bloom, Ira
• Format: Journal Article
• Language: English
• Published: United States Elsevier 29-01-2020
• Subjects: binders; ENERGY STORAGE; LiFePO4; lithium-ion battery; overcharge
• EISSN: 1873-2755
• ISSN: 0378-7753

Two types of small pouch cells based on LiFePO4/graphite, one containing a N-methyl pyrrolidinone (NMP)-soluble binder, poly(vinylidene difluoride), and the other an aqueous-soluble binder, styrene-butadiene rubber/carboxymethylcellulose were systematically charged to 100, 120, 140, 160, 180, and 250% state of charge (SOC). The cells were then discharged to 3.0 V at room temperature before being disassembled for postmortem analysis. Microstructural changes in the anode associated with increasing SOC were more pronounced in the aqueous processed cells in comparison to the NMP-processed cells. Dendrite formation was observed on the aqueous-processed anode at 120% SOC, while the NMP-processed anode surface does not show dendrites until 250% SOC. Overall, the aqueous-processed anode surfaces displayed more evidence of microstructural degradation as a function of increasing SOC. In the NMP-processed cells, four organic compounds on the anode surface were found to show a dependence on SOC, while only two displayed a similar dependency in the aqueous-processed cells. The nature of the binder changed the number and composition of the species found at the anode.