V-Induced Low-Spin State Mn³⁺ Suppresses Jahn-Teller Distortion for High-Performance Aqueous Zinc Ion Batteries

The Jahn-Teller distortion caused by high-spin state Mn³⁺ (t_2g ³e_g ¹) is a major limiting factor for improving both the specific capacity and cycling stability of MnO₂ cathodes in aqueous zinc-ion batteries. Thus, an intrinsic strategy for optimizing MnO₂ involves the effective elimination of the high-spin state Mn³⁺ (t_2g ³e_g ¹) during electrochemical process. Herein, we focus on structural design that constructed NH₄V₃O₈-coated MnO₂ (Mn@V) nanorods to achieve the low-spin state of Mn³⁺ (t_2g ⁴e_g ⁰) and inhibit the Jahn-Teller distortion. The well-designed Mn@V cathode exhibits outstanding specific capacity (513.5 mAh g^-1 at 0.2 A g^-1), remarkable rate performance (205 mAh g^-1 at 2.0 A g^-1), and excellent cycling stability (201 mAh g^-1 after 2000 cycles at 1.0 A g^-1). Through a series of advanced characterization techniques, such as ex-situ X-ray absorption spectroscopy, combined with theoretical calculations, we systematically demonstrate that the NH₄V₃O₈ coating layer alters electron configuration through the V-O-Mn bridge bonds and induces the low-spin state Mn³⁺ (t_2g ⁴e_g ⁰) in MnO₂, thereby suppressing the Jahn-Teller distortion and enhancing cycling stability. This study offers profound insights into the inhibition of the Jahn-Teller distortion from an electron spin perspective, and presents a facile approach to synergistically enhance specific capacity and cycling stability.