Study on Cycle Life of Lithium-Ion Batteries Using in Situ ~7Li Solid-State Nuclear Magnetic Resonance

摘要

The capacity fade of lithium ion battery (LIB) was investigated using ~7Li solid-state nuclear magnetic resonance (NMR). The LIB cells composed of graphite (Gr) or hard carbon (HC) and LiCoO_2 (LCO) were used. The peak intensity for stored Li in carbon (Gr and HC) showed good proportionality to the cell capacity. The proportional constants for every after 100 cycles did not change largely, while the section of the peak intensity vs. cell capacity plot changed with cycle. This change in the section explained well the cell capacity fade, showing that 'slippage' was related to the capacity loss in lower stages due to voltage profile of carbons. The peak analysis also found 'captured' Li loss as another cause of capacity fade. The NMR measurement also found new storage peak and change in solid electrolyte interface (SEI) related peak after long cycle test.