Fabrication and Characterization of Lithium-Silicon Thick-Film Electrodes for High-Energy-Density Batteries

Abstract

We have developed a method to operate lithium-silicon (Li-Si) thick-film electrodes in a manner consistent with traction applications. Key to the operating strategy is the voltage control of the electrode. It is expected that strong reducing environments, created by operating the electrode at low potentials (near that of Li), reduce battery life. We show that operating Li-Si at higher potentials is also damaging, and this is counterintuitive in that common negative electrodes (e.g., graphites and titanates) do not suffer from this limitation. Arguments based on measured Coulombic efficiencies, cycle life tests, in-situ stress measurements, and high-resolution microscopy resolve the otherwise anomalous findings. We show that promising half-cell ( Silicon film electrodes have been shown to be useful for characterization purposes insofar as one need not treat binders, various particle geometries, conductive diluents, and other complications inherent in the construction of porous electrodes. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] In this work, we focus on the potential utility of Si thick-film electrodes formed on roughened copper current collectors. If sufficient capacity can be obtained, such a geometry might simplify electrode fabrication, as the electrode host material would consist of nothing more than Si deposited on a current collector, and high specific energies (Wh/L) and energy densities (Wh/kg) could result.Four topics are examined in this endeavor. First, by controlling the potential limits over which we operate a Li-Si electrode, can we obtain sufficient stability for relatively thick-film electrodes (i.e., yielding more than 2 mAh/cm 2 )? Second, how does the electrochemical performance correlate with stress in the electrode over the potential window of operation? Third, because the electrode consists of only Li and Si, we can isolate equilibrium hysteresis behavior associated with this alloy, and we derive and implement a simple model to represent the voltage-composition data that may be useful in subsequent engineering analyses of electrodes with a significant Li-Si contribution. Last, we examine full cells (Li-Si vs. an NMC622 positive electrode, corresponding to Ni 0.6 Mn 0.2 Co 0.2 O 2 ) in the context of capacity, cycle life, cycle efficiency, microstructure, and elemental analysis. A cell modeling tool 45 is used to examine the efficacy of the Si film electrodes for actual battery electric vehicle applications based on specific energy and energy density calculations.

On the Capacity Losses Seen for Optimized Nano‐Si Composite Electrodes in Li‐Metal Half‐Cells

“…Here it should be pointed out that the lithium trapping capacity loss should be seen independent of whether the experiments are carried out using controlled current or controlled voltage methods. The latter is in excellent agreement with previous results indicating that the time available for the lithium diffusion depends on the voltage window employed in controlled voltage cycling experiments. Another important result is that the diffusion‐controlled capacity loss seen during the open circuit periods after the lithiation of the electrode discussed in Section , indicate that lithium is diffusing from the electrode surface toward the inner part of the electrode as a result of the concentration gradient formed during the lithiation step.…”

Modeling Reversible Expansion of Porous Electrodes in Si/NMC Cells within the Framework of Multi-Species, Multi-Reaction Theory

“…However, there is evidence showing that silicon expands significantly while alloying with lithium. [1][2][3][4][5][6] During discharge, the cell contracts, however, some of the expansion is retained which increases with every cycle. 5,7,8 The thickness that increases during charging (and decreases during subsequent discharge), is referred to as reversible expansion in the present work.…”

“…Additionally, the expansion/contraction of the silicon electrodes pose a challenge to the life of the cells. 1 Repeated cycling causes capacity loss through electrical isolation of active material and exposure of new surface to the growth of solid electrolyte interphase (SEI). To reduce the isolation of particles during cycling, most production level cells are operated under compression.…”

High Porosity Single-Phase Silicon Negative Electrode Made with Phase-Inversion

“…[13][14][15] Finally, (iv) the mismatch between the mechanical properties of the copper current collector and the composite electrode containing Si active material often leads to buckling, puckering, and tearing of the current collector, with eventual destruction of the electrode, particularly upon cell scale-up. 16,17 Over the past two decades, many ingenious approaches have been investigated for mitigating the issues caused by the excessive volume changes in silicon upon lithiation. They range from modifications in all components of a Si electrode (the active material particles -nanosizing, novel active material morphologies, and surface coatings, [18][19][20][21][22][23][24][25][26][27] the binders, [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] the electronically conductive fillers 43,44 and electrolyte solution, 42,[45][46][47][48][49] ), to generating novel electrode structures devoid of polymeric binders [50][51][52][53] or of copper current collectors, 54,…”