The influence of surface inhomogeneity on the overcharge and lithium plating of graphite electrodes

Abstract

We seek to clarify phenomena involved in the overcharge of a graphite electrode in a lithium ion battery, including lithium (Li) plating. In Baker and Verbrugge (2019 J. Electrochem. Soc.), we developed a set of equations that can be used to treat Li plating and subsequent electro-dissolution, and we analyzed how the equation system behaved for a particle of graphite, a fundamental unit of the negative (porous) electrode in lithium ion cells. In this work, we employ the same governing equations, but we render them in a two-dimensional setting to examine the graphite-electrolyte interface, allowing us to clarify phenomena involved in Li plating over graphitic electrode elements in the absence of complicating factors associated with the architecture of a porous electrode. For a variety of reasons described in the Introduction of this work, the surface of graphite is nonuniform in terms of reaction rates for Li insertion and plating, and we show that when the electrode is subjected to constant-current charging, as is commonly employed, such nonuniformities lead to early Li plating over the highly reactive surfaces. These observations underscore the importance of maintaining a uniform electrode surface, especially when the cell is to be subjected to high rates of charge.

Location-Dependent Cobalt Deposition in Smartphone Cells upon Long-Term Fast-Charging Visualized by Synchrotron X-ray Fluorescence

“…Combining the macroscopic observations indicates that Li deposits form primarily in edge and fold locations of the cell where compression, electrolyte, and current distributions are expected to be most heterogeneous. This is in good agreement with the literature, where it was shown that Li deposits preferentially at electrode edges due to geometric effects 40 and electrode nonuniformities, 41 heterogeneous pressure 42 and compression, 43 and higher current densities. 44 Another observation confirming this is Figure 2c, showing the depositions on the anode of cell type C after the OEM cyc protocol; here all folds and edges are fully covered in Li depositions and decomposition products of the electrolyte, while the center parts of the electrodes are not fully covered by depositions.…”

Enabling 4C Fast Charging of Lithium‐Ion Batteries by Coating Graphite with a Solid‐State Electrolyte

“…This is likely to have important implications during fast charging, because Li plating is known to occur on particles or local regions of the graphite electrode that are fully lithiated. [60,61] The fact that the SEI resistance and composition (as measured by XPS, Figure 2) do not change measurably at various states of charge are indicative of the LBCO film remaining intact and functional, despite the volume changes expected in the graphite particles during cycling. This is also consistent with the continued suppression of Li plating over more than 500 cycles, which demonstrates that the ALD coatings provide a durable a-SEI under fast-charging conditions.…”

Lithium-Ion Transport Behavior in Thin-Film Graphite Electrodes with SEI Layers Formed at Different Current Densities

“…This difference is probably related to the crystallite size of the graphite samples with the 50 nm and 23 μm particles having more exposed edges associated with their smaller graphite crystallites compared to the 790 nm and 20 μm samples. Lithium plating is known to occur on these reactive sites and edges . From this, it can be concluded that the impedance caused by the SEI formed at 0.1 C is a critical factor determining the cyclability of the electrodes at 12 C. The increased polarization due to the SEI layer formed at 0.1 C caused metal plating at 12 C.…”