Enhancing the lithium extraction properties of H_1.6Mn_1.6O₄ via polypyrrole coating for capacitive deionization

With the escalating global demand for lithium, the development of efficient and sustainable lithium extraction technologies has become a critical imperative. Spinel-type lithium ion sieves have emerged as promising electrode materials owing to their favorable Li⁺ selectivity. However, their practical application is severely hampered by poor cycling stability and significant manganese dissolution. To address these challenges, this study proposes a capacitive deionization (CDI) method utilizing a polypyrrole (PPy)-coated HMO composite electrode. The PPy-HMO composite was synthesized via an in-situ polymerization method, with graphene oxide (GO) incorporated to enhance its electrical conductivity and structural integrity. This strategy preserves the spinel framework of HMO through a uniform PPy coating, thus improving the overall stability of the material. In a 50 mmol/L LiCl solution, the PPy-HMO composite exhibits a specific capacitance of 665.3 F g⁻¹, which is higher than that of the pristine HMO, along with lower polarization voltage and improved stability. Within a two-electrode CDI system, the composite achieves a lithium extraction capacity of 32.0 mg g⁻¹, which is higher than that of the unmodified HMO, with improved Li⁺ selectivity supported by electrochemical tests. Post-cycling analysis further corroborated that the PPy coating protects the internal structure of HMO and suppresses the manganese leaching. This work presents a feasible strategy for facilitating sustainable lithium resource recovery via CDI technology.