Despite the relatively small additional capacity and expansion associated with its formation, c-Li15Si4 has been linked to an increased loss of capacity in both silicon thin films, and nanoparticles. There are several reasons to suspect that lithiation of amorphous lithium silicide to the c-Li15Si4 phase may lead to greater fracturing than lithiation ending in the amorphous phase. First, we cannot neglect that the transition from a-LixSi to c-Li3.75Si increases the theoretical capacity by around 200 mAh/g to 3579 mAh/g. We would expect additional silicon expansion due to this increased capacity regardless of crystallization to the c-Li15Si4 phase. Secondly, formation of c-Li15Si4 creates a two-phase boundary between a-LixSi and Li15Si4 during lithiation, and between c-Li15Si4 and LiySi, where y is ~2, during delithiation. Volume changes across a twophase boundary are associated with increased stress, possibly leading to fracture and capacity loss in alloyed anodes generally, and in silicon specifically. Attempts to directly observe fracture in Si by in-situ TEM have instead overwhelmingly focussed on the initial transformation of c-Si to LixSi, and approaches to mitigate fracturing during this particular transformation by reducing the particle size or using amorphous rather than crystalline Si powder. The phase transformations associated with formation of c-Li15Si4 involve a smaller change in the Li/Si ratio and hence a smaller volume change than the abrupt transformation from pristine silicon to Li-rich a-LixSi. However, the transition from c-Si to a-LixSi only happens in the first cycle and only for crystalline Si. There is a strong correlation between formation of the c-Li15Si4 phase and capacity loss during long-term cycling. For instance, Xie et al. showed that the onset or acceleration of capacity degradation in 100 nm Si films on Cu coincides with the onset of c-Li15Si4 formation. Suppression of c-Li15Si4 to improve capacity retention can be achieved by keeping the lithiation voltage above the onset of the c-Li15Si4 transition, typically above 50 mV. Higher charging rates will also prevent crystallization to c-Li15Si4, and at sufficiently high rates, c-Li15Si4 will not form even if the cell is discharged to 0 V vs. Li. The use of a constant voltage (CV) step during lithiation, which is standard in commercial cells, also plays a large role in c-Li15Si4 formation by increasing the time the electrode is exposed to low voltages. However, there is a potential limit above which c-Li15Si4 no longer forms using CCCV lithiation as well, as has been demonstrated by Sayed et al. Recent work has taken advantage of stress-voltage coupling to suppress the c-Li15Si4 phase, a process by which external stress lowers the lithiation voltage of the crystalline transition to c-Li15Si4, on the order of ~100-120 mV/GPA as measured in-situ in thin silicon films. Suppressing the transition voltage by 100 mV/GPA can be sufficient to lower the transition below 0 V vs. Li and avoid the appearance of the c-Li15Si4 phase entirely. The stress-voltage coupling effect has been effectively harnessed to suppress the c-Li15Si4 phase through the application of adhesive layers on thin films and capping layers on a variety of silicon morphologies, as well as alloying silicon with inactive transition metals. The hypothesis that alloying induces stress, thereby improving capacity retention by suppressing c-Li15Si4, has been applied to nano-and micron-sized silicon particle electrodes as well as thin films. However, most, if not all previous studies that find a correlation between the suppression of c-Li15Si4 formation and capacity retention achieve this suppression through material changes that are convoluted with other beneficial effects. For instance, a capping layer on top of a Si film can induce clamping, thereby preventing c-Li15Si4 by aforementioned stress-voltage coupling, while also minimizing reactivity with the electrolyte. Prolonged ballmilling of Si with Mo and W, for instance, increases the proportion of silicide intermetallic and allegedly induces stress, but this processing also reduces the grain size of Si, rendering its distribution more homogeneous. Rather than suppressing c-Li15Si4 formation by changing the electrode material, a test of the intrinsic effects of c-Li15Si4 on capacity retention would, ideally, involve inducing or preventing its formation by adjusting only the experimental conditions while keeping the electrode material constant.