Inhomogeneous distribution of lithium and electrolyte in aged Li-ion cylindrical cells

Abstract

Carbonate-based electrolytes in Li-ion batteries exhibit long range order in a frozen state, which enables their non-destructive analysis by diffraction methods. In the current study the spatial distribution of lithium and electrolyte inside the graphite anode was determined in cycled Li-ion cells using monochromatic spatially-resolved neutron diffraction measurements at 150 K. The results indicate a loss of lithium and electrolyte and their non-uniform distribution in the graphite anode in aged Li-ion cells. The observed lithium and electrolyte losses are directly correlated with two electrochemical performance degradation mechanisms, which are responsible for the cell capacity fade.

Heterogeneity of Graphite Lithiation in State‐of‐the‐Art Cylinder‐Type Li‐Ion Cells

“…A list of cells (Nr. 13,2,14,33,17) is yield where a uniform plateau-like behavior is dominating. Accord- ingly, evaluation of "1-η" ( Figure S6a) creates a list of cells with the most heterogeneous lithiation levels (22,23,15,8,9), where no obvious correlation to cell capacity, nominal discharge current, electrode thickness etc.…”

“…[17] Such kind of in situ neutron diffraction studies are performed on Li-ion cells of different designs, either laboratory [18][19][20][21] or commercial [22][23][24] type. In recent years a number of neutron diffraction studies dedicated to the lithiation of either positive or negative electrode materials, [25][26][27][28][29][30][31] aging behavior [32,33] and effects of temperature. [34,35] The majority of the above-mentioned reports focuses on the structure evolution obtained by integration over a large cell volume, assuming the studied cells to be uniform.…”

“…Recently, an attempt to localize and quantify the electrolyte in frozen state was made by a similar experimental approach at low temperatures. [33] The lithium distribution has been found strongly affected by the configuration of the current tabs and by the cell SOH leading to an increasingly heterogeneous character of cell fatigue. Besides neutron diffraction there is a number of neutron-based scattering and spectroscopic techniques capable to localize lithium (e. g., neutron depth profiling, [40] neutron imaging, [24] neutron reflectometry [41] and small/wide angle neutron scattering, [42] etc.…”

Heterogeneity of Graphite Lithiation in State‐of‐the‐Art Cylinder‐Type Li‐Ion Cells

“…Such kind of in situ neutron diffraction studies are performed on Li‐ion cells of different designs, either laboratory [18–21] or commercial [22–24] type. In recent years a number of neutron diffraction studies dedicated to the lithiation of either positive or negative electrode materials, [25–31] aging behavior [32,33] and effects of temperature [34,35] …”

“…The method was successfully applied to monitor the lithium distribution in four 18650‐type cells adopting different configurations of current tabs [14] and to probe the lithium distribution in variously fatigued high energy lithium cobalt oxide LCO|C [39] and high performance lithium nickel cobalt aluminum Oxide NCA|C [32] cells. Recently, an attempt to localize and quantify the electrolyte in frozen state was made by a similar experimental approach at low temperatures [33] . The lithium distribution has been found strongly affected by the configuration of the current tabs and by the cell SOH leading to an increasingly heterogeneous character of cell fatigue.…”