Upcycling of photovoltaic silicon (Si) waste to produce high-energy-density energy storage materials represents an effective way to achieve carbon neutrality. However, at present, photovoltaic Si waste (WSi) can only be suitable for degraded utilization because WSi recycling processes are limited by deep oxidation, entrainment of trace impurities, and structural reconstruction difficulties. Here, we propose an electrothermal shock method to convert photovoltaic WSi directly into ultrahigh areal-loaded (4.02 mg cm(-2)) silicon nanowire (SiNW) electrodes. High gradient thermal fields (similar to 10(4) K s(-1)) are produced to drive the formation and deposition of gaseous Si molecules using the easy oxidation characteristics of the WSi powder. Carbon fiber cloth is used as both a heater and an in-situ growth substrate for the SiNWs to construct SiNW-carbon cloth self-supporting electrode ([email protected]) structures. When used as a binder-free anode for lithium-ion batteries, it exhibits ultra-high areal capacity (3.2 mAh cm(-2) for 600 cycles, capacity retention rate > 83%) and long-cycle stability (1706.2 mAh g(-1) at 1 A g(-1) after 1800 cycles). A full battery assembled using a commercial LiFePO4 cathode also demonstrates stable cycling performance ( > 91.2% initial capacity maintained at 0.5 C for 250 cycles). Such an upcycling strategy will help to promote environmentally friendly, economical, and sustainable development of the photovoltaic and energy storage industries.