Insights on the cycling behavior of a highly-prelithiated silicon–graphite electrode in lithium-ion cells

Abstract

Nanosized silicon materials are being developed for use in the anodes of high-energy lithium-ion batteries. However, the high surface areas of these materials increase the rate of parasitic reactions in the electrode, which consume cyclable Li + and degrade battery performance. Prelithiation offers a realistic strategy to compensate for this reactivity, by injecting additional charge into the cell to counterbalance the Li + loss. Interestingly, the benefits offered by prelithiation extend beyond its more obvious purpose. Here, by using a reference electrode in NMC532//Si-Gr cells, we show how prelithiation alters the cycling potentials experienced by the Si-containing anode and how that translates into gains in cycle life. The rate of consumption of the prelithiated charge is lower than that expected from the behavior of non-prelithiated cells. Curiously, the Si particles become partially unresponsive during the C/3 cycling apparently because of kinetic constraints. Electrochemical studies on harvested electrodes in half-cells show that capacities are intact after the long-term cycling and that most of the lithium reservoir is still present in the anode. We conclude that the high capacity retention displayed by the prelithiated cells mainly results from a higher participation of graphite particles during the extended electrochemical cycling. OPEN ACCESS RECEIVED

Optimum Particle Size in Silicon Electrodes Dictated by Chemomechanical Deformation of the SEI

“…The increased surface area is strictly a geometric effect that has led to the common perception that smaller particles will inherently lead to higher capacity loss on a gravimetric basis. [54][55][56][57] The optimum particle size in Figure 7a contradicts this expectation, and follows directly from the new experiments which show that capacity loss per area increases with particle size (i.e., in Figure 3). These data show that changing the lower voltage cut-off leads to some variation in the optimum size.…”

Entropy profiling for the diagnosis of NCA/Gr-SiOx Li-ion battery health

“…A possible explanation for this is mechanical changes in the anode particles, specifically breaking and cracking, as has been reported in other studies [30,67]. This is also often mentioned as a primary cause of Si particle inactivation in Gr-Si anodes [15,68,69,70]. Entropy profiling measures (among other contributions) the configurational degrees of freedom of lithium-vacancy arrangements in the electrode materials [31,35,25,59,33].…”

Capacity and coulombic efficiency measurements underestimate the rate of SEI growth in silicon anodes

“…Very high values of 𝜆 become possible for systems that underwent extreme anode prelithiation that makes cell discharge to become limited by polarization of the cathode. 5,10 Also interestingly, varying the rate of oxidation side reactions for a fixed 𝐼 𝑟𝑒𝑑 will cause opposite changes to capacity and efficiency, as illustrated by curves with different colors in Figure 2: a lower 𝐼 𝑜𝑥 will increase CE (Figure 2a) but decrease CR (Figure 2b). Although the absolute changes in CR values portrayed in Figure 2b appear negligible, such small variation can compound into meaningful differences in performance over time.…”

“…In other words, as cells age and undergo a net loss of capacity, discharging the cell to a fixed voltage will lead both cathode and anode to experience progressively higher electrode potentials. 10 In the NMC811 electrodes like the one shown in Figure 1a, the minimum potential experienced by the cathode will be in the range of ~3.6 V vs. Li/Li + . Thus, if cells are discharged to 3 V, the anode will experience at least ~0.6 V vs. Li/Li + at the end of discharge, with this value increasing as the cell loses capacity.…”