Trace amounts of zirconium (Zr) have been adopted to modify the crystal structure and surface of the Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode material. During cycling at 1.0C, the Zr-modified NCM811 shows an improved capacity retention of 92% after 100 cycles, higher than 75% for pristine NMC811. In addition, the Zr-modified NCM811 is capable of delivering a discharge capacity of 107 mA h g⁻¹ at a 10.0C rate, much higher than 28 mA h g⁻¹ delivered by pristine materials. These improved electrochemical performances are ascribed to the dual functions of Zr modification. On one hand, part of the Zr enters the crystal lattice, which is beneficial for reducing the Li/Ni cation mixing and enhancing the crystal stability of the cathode. On the other hand, the rest of the Zr forms a 1–2 nm thick coating layer on the surface of the NCM811 cathode, which effectively prevents direct contact between NCM and the electrolyte, thus suppressing the detrimental interfacial reactions. Therefore, the Zr-modified LiNi_0.8Co_0.1Mn_0.1O₂ exhibited significantly enhanced cycling stability and charge/discharge rate capability in comparison with its untreated counterpart.

Hydrated vanadium pentoxide (VOH) can deliver a gravimetric capacity as high as 400 mA h g⁻¹ owing to the variable valence states of the V cation from 5+ to 3+ in an aqueous zinc ion battery. The incorporation of divalent transition metal cations has been demonstrated to overcome the structural instability, sluggish kinetics, fast capacity degradation, and serious polarization. The current study reveals that the catalytic effects of transition metal cations are probably the key to the significantly improved electrochemical properties and battery performance because of the higher covalent character of 55% in the Cu–O bond in comparison with 32% in the Mg–O bond in the respective samples. Cu(II) pre-inserted VOH (CuVOH) possesses a significantly enhanced intercalation storage capacity, an increased discharge voltage, great transport properties, and reduced polarization, while both VOH and Mg(II) pre-inserted VOH (MgVOH) demonstrate similar electrochemical properties and performances, indicating that the incorporation of Mg cations has little or no impact. For example, CuVOH has a redox voltage gap of 0.02 V, much smaller than 0.25 V for VOH and 0.27 V for MgVOH. CuVOH shows an enhanced exchange current density of 0.23 A g⁻¹, compared to 0.20 A g⁻¹ for VOH and 0.19 A g⁻¹ for MgVOH. CuVOH delivers a zinc ion storage capacity of 379 mA h g⁻¹, higher than 349 mA h g⁻¹ for MgVOH and 337 mA h g⁻¹ for VOH at 0.5 A g⁻¹. CuVOH shows an energy efficiency of 72%, superior to 53% for VOH and 55% for MgVOH. All of the results suggest that pre-inserted Cu(II) cations played a critical role in catalyzing the zinc ion intercalation reaction, while the Mg(II) cations did not exert a detectable catalytic effect.

Interfacial oxygen vacancies were induced in V₂O₅by various conductive polymers with built-in local electric field for high-energy supercapacitors.