The electrochemical performances of lithium-ion batteries with different lattice-spacing Si negative electrodes were investigated. To achieve a homogeneous distribution of impurities in the Si anodes, single crystalline Si wafers with As-dopant were ball-milled to form irregular and agglomerated micro-flakes with an average size of ~10 μm. The structural analysis proved that the As-doped Si negative materials retain the increased lattice constant, thus, keep the existence of the residual tensile stress of around 1.7 GPa compared with undoped Si anode. Electrochemical characterization showed that the As-doped Si anodes have lower discharge capacity, but Coulombic efficiency and capacity retention were improved in contrast with those of the undoped one. This improvement of electrochemical characteristics was attributed to the increased potential barrier on the side of Si anodes, inherited from the electronic and mechanical nature of Si materials doped with As. We believe that this study will guide us the way to optimize the electrochemical performances of LIBs with Si-based anodes.

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A long-term in-situ measurement method for evolved gases in commercial 18650 cylindrical lithium ion batteries (LIBs) is proposed using Raman spectroscopy. Hydrogen, methane, carbon dioxide, and carbon monoxide were the main gases detected from cells at 4.2-4.8 V for 1800 h. Gas evolution rates were determined by the aging time and the staying potential, resulting in a nonlinear partial-pressure-dependence as a function of the aging time. Initially, the evolution of carbon dioxide and carbon monoxide was significant. After potential-dependent onset times, hydrogen and methane generation increased suddenly. At low potential ranges of 4.2-4.4 V, mostly hydrogen gas was generated, whereas at high potential ranges (>4.6 V), methane becames dominant. Even at 4.4 V, importantly, the absolute accumulative H 2 gas pressure was >3 atm, raising the requirement to monitor such gas for better safety even under nominal operating conditions. Moreover, cumulative partial pressures of the detected gases exceeded the range 5-10 atm, which was associated with the staying potential. An evolution mechanism through which the gas is converted from hydrogen to methane is proposed and discussed. The electrochemical analysis of the aged LIBs showed that the capacity fade was accelerated by the increase in the staying potential while the resistances remained similar.

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