## 3 Results
Secondly, the grooves of the 3D-line-structured anodes provided more space to release stress that volume expansion brought about. As demonstrated in our in situ experiments, the stress associated with the separation of the electrode and the current collector or defect formation resulted in the failure of these batteries. Figure 4a shows the cross-section SEM image of 3D-line-structured Si/C anodes, in which the width and thickness of the lines can be easily measured. Because the maximum expansion in length of 3D-line-structured anodes is only about 1.35% (see Figure S2), which is very small in comparison with the maximum expansion in width and thickness (30% and 190%), we can evaluate the volume expansion in the lithiation process mainly based on the expansion in width and thickness. Figure 2: In situ SEM images of Si/C composites during charge and discharge processes. (**a**) The SEM images of unstructured Si/C composites were captured at the corresponding red points in (**b**) the galvanostatic charge–discharge curve (scale bar, 100 μm). (**c**) The SEM images of 3D-line-structured Si/C composites were captured at the corresponding red points in (**d**) the galvanostatic charge–discharge curve (scale bar, 50 μm). The curves were acquired at 100 mA/g in the voltage range of 0.01–1.5 V.  
Figure 4b,c show the variations in thickness and width of electrodes versus the corresponding charge capacities. In Figure 4b, the thickness of the 3D-line-structured anode exhibits a linear response to the charge capacity (lithium intercalation) before the defect formation in the contact area (see Video S2). After that, the thickness still showed a linear behavior in response to the charge capacity but with an obvious slope change due to the defect formation. The inflection point corresponded to the  
Figure 4: (**a**) The thickness and width of the selected sample were measured during the charging process. The (**b**) thickness and (**c**) width variations of 3D-line-structured Si/C composites during the charging process. (**d**) The volume change of 3D-line-structured Si/C composites during the charge process relating to the initial volume. (Measurement error: \(\pm\) 1 \(\upmu\)m). Figure 3: Schematic illustrations of morphology variation in (**a**) unstructured and (**b**) laser-structured Si/C composites caused by lithiation processes. charge capacity of 260 mAh/g. In Figure 4c, the width also increased linearly before colliding with 3D lines, which also corresponded to the charge capacity of 260 mAh/g. After this occurred, the width did not increase because of the space limitation. This limitation of width free expansion resulted from stress accumulation creating defects in the formation of electrode materials. Figure 4d shows the volume response of 3D-line-structured anodes as a function of the charge capacity. Combining the variations of both the thickness and width, the volume expansion also exhibited similar linear responses to the charge capacity with an inflection point at 260 mAh/g. The slope decrease after 260 mAh/g was due to the loss of conductive path caused by defects formation. Due to two-dimensional limitations on volume expansion, the unstructured anodes began to lift-off from the current collector in the early stage (56 min), thus resulting in a low charge capacity which for comparison is shown in Figure 4d. In the first stage of the lithiation process (0-260 mAh/g), the expansion of 3D line-structured anodes has no limitation and the channels between lines released the stress in lithiation. Thus, no apparent defects were produced during this stage. This lithiation process is favored in battery applications; this indicates that the structure could be applied to batteries.