The transition from legacy fossil fuels to low-carbon energy sources requires efficient means of storing the energy captured from intermittent renewable sources. Lithium-ion batteries currently underpin the market for portable electronics and electric vehicles, but their use for grid-scale integration remains limited. Further improvement of energy density (with respect to both mass and volume) is needed, and much attention is currently being directed to a wide range of materials for both the cathode and anode. For anodes, one material of great interest is silicon that has a theoretical capacity of 3579 mAhg -1 , based upon the formation of Li15Si4, which is almost an order of magnitude higher than that of graphite, the most commonly used anode in commercial batteries. The capacity retention of silicon, however, is poor over several hundred cycles and thus far has seen only limited deployment. The volume expansion of ~300% upon alloying silicon with lithium results in pulverization of the material and formation of freshly cleaved Si surfaces, which react with the electrolyte, resulting in the formation of new solid electrolyte interphase (SEI). Progressive fracturing and formation of SEI eventually result in disconnection of active Si, degrading the capacity. Various strategies have been employed to mitigate fracture and disconnection, such as optimizing electrolyte composition, including binders and conductive carbon additives, as well as adding protective surface layers encapsulating the silicon. Other strategies include changing the Si morphology to nanowires, reducing the particle size to less than 100 nm, and introducing porosity to better accommodate volume expansion. Targeted efforts to reduce fracture and improve capacity retention require an understanding of the alloying processes that occur as the voltage is lowered towards 0 V vs Li during lithiation and as the voltage is raised again during delithiation. In the first stages of electrochemical lithiation of crystalline Si, it is directly transformed to a highly lithiated amorphous silicon, a-LixSi, typically at around 0.1 V vs Li. The exact value of x is difficult to determine due to electrolyte decomposition taking place in conjunction with Li insertion into the Si, but the capacity associated with this transformation is >3000 mAh/g, and the value of x has been reported as 3.4-3.5. The terminal stage of lithiation that can be attained at room temperature is a metastable crystalline phase, where x = 3.75 (c-Li15Si4), typically at voltages below 50 mV vs Li. The change in x specifically associated with this transition is around 0.2 as derived from galvanostatic intermittent titration technique (GITT), and the final transition accounts for approximately 200 mAh/g of specific capacity.