Charge‐Balance Design in Complementary Electrochromic Devices Enabled by a Diffusion‐Controlled Electrochromic Anode

ABSTRACT Electrochromic devices offer a compelling platform for dynamic control of light and heat, with significant potential for energy‐efficient smart windows and adaptive optoelectronic applications. However, their widespread adoption is critically hindered by the lack of competent anodic materials capable of mitigating charge imbalance between the cathodic and anodic layers. Here, we demonstrate a full charge‐balanced electrochromic design based on a WO 3 /LiCoO 2 architecture, enabling highly stable device operation. Unlike the conventional anodic material NiO, which suffers from limited charge capacity and poor reversibility, diffusion‐controlled LiCoO 2 provides a readily tunable charge storage capability through thickness engineering. In addition, the long‐standing challenge in achieving stoichiometric LiCoO 2 via magnetron sputtering can be resolved by introducing a lithium‐supplementation strategy. The resulting WO 3 /LiCoO 2 devices exhibit both effective privacy control and thermal management, delivering high optical modulation alongside excellent cycling stability. This work establishes a viable pathway toward high‐durability, high‐performance electrochromic devices for smart windows and automotive thermal management applications.