Dual‐Gradient Structure of Component and Channel Size in Co–Ni Hydroxides Boosts Conductivity and Suppresses Self‐Discharge for High‐Performance Supercapacitors

Why It Matters

The breakthrough tackles the core limitations of nickel‑based pseudocapacitors, unlocking higher energy density and longer life for grid‑scale and portable energy storage solutions.

Key Takeaways

• Dual-gradient NiCo-LDH delivers 2200 F g⁻¹ at 1 A g⁻¹
• Retains 88% capacity after 10 000 cycles
• Voltage drop only 140 mV in 2 h open‑circuit
• Asymmetric cell reaches 146 Wh kg⁻¹ at 750 W kg⁻¹
• Gradient design boosts conductivity and curtails ion migration

Pulse Analysis

Nickel‑based hydroxides have long been prized for their pseudocapacitive behavior, yet poor electronic conductivity and rapid self‑discharge have limited commercial adoption. By engineering a dual‑gradient structure—varying metal ion ratios across the electrode while simultaneously tapering nanosheet channel dimensions—researchers create continuous pathways for electron flow and restrict ion diffusion that fuels voltage loss. This strategy leverages electrochemical co‑deposition with multi‑current steps, a scalable process that sidesteps post‑synthesis modifications, making it attractive for large‑volume manufacturing.

Performance data underscore the practical impact of the gradient design. The dual‑gradient (DG) electrode achieves a specific capacitance of 2200 F g⁻¹ at 1 A g⁻¹, outpacing its non‑gradient counterpart by 74%, and maintains 88% capacity after 10 000 charge‑discharge cycles. The reduced voltage decay—only 140 mV over two hours under open‑circuit conditions—demonstrates effective suppression of self‑discharge, a critical metric for standby power applications. Finite‑element simulations attribute these gains to enhanced intrinsic conductivity from the compositional gradient and limited ion migration due to the channel‑size gradient.

The implications extend beyond laboratory metrics. When integrated into an asymmetric supercapacitor with activated carbon, the DG electrode delivers 146 Wh kg⁻¹ at 750 W kg⁻¹, positioning it among the highest‑performing hydroxide‑based devices reported. Such energy and power densities bridge the gap between traditional capacitors and batteries, offering rapid charge‑discharge capabilities without sacrificing storage capacity. As renewable grids demand fast‑response, durable storage, the dual‑gradient approach provides a viable pathway to commercial‑grade, high‑performance supercapacitors, prompting further exploration of gradient engineering across other pseudocapacitive materials.