2023 roadmap for potassium-ion batteries

The heavy reliance of lithium-ion batteries (LIBs) has caused rising concerns on the sustainability of lithium and transition metal and the ethic issue around mining practice. Developing alternative energy storage technologies beyond lithium has become a prominent slice of global energy research portfolio. The alternative technologies play a vital role in shaping the future landscape of energy storage, from electrified mobility to the efficient utilization of renewable energies and further to large-scale stationary energy storage. Potassium-ion batteries (PIBs) are a promising alternative given its chemical and economic benefits, making a strong competitor to LIBs and sodium-ion batteries for different applications. However, many are unknown regarding potassium storage processes in materials and how it differs from lithium and sodium and understanding of solid–liquid interfacial chemistry is massively insufficient in PIBs. Therefore, there remain outstanding issues to advance the commercial prospects of the PIB technology. This Roadmap highlights the up-to-date scientific and technological advances and the insights into solving challenging issues to accelerate the development of PIBs. We hope this Roadmap aids the wider PIB research community and provides a cross-referencing to other beyond lithium energy storage technologies in the fast-pacing research landscape

Escape of lattice water in potassium iron hexacyanoferrate for cyclic optimization in potassium‐ion batteries

Abstract Potassium iron hexacyanoferrate (Prussian blue [PB]) is a very competitive cathode for potassium‐ion batteries due to its 3D robust open framework. However, [Fe(CN)6]4− vacancies and lattice water existed in PB lattices aggravate electrochemical performances. Herein, PBs with different content of vacancies and lattice water are obtained under two synthesis temperatures of 0°C and 25°C. Although K1.36Fe[Fe(CN)6]0.74·0.48H2O (PB0) exhibits an outstanding rate capability compared with K1.43Fe[Fe(CN)6]0.94·0.42H2O (PB25), PB25 with less defects shows a lower polarization and superior stability than PB0 during the cycle. Fourier transform infrared (FTIR) spectra results show that lattice water can escape from PB lattices during the cycle, which enhances the diffusion of K+ kinetically in the PB structure. Benefited from this phenomenon, the diffusion coefficient of K+ in vacancy‐less PB25 reaches 10−8 in two reaction platforms. As potassium‐ion battery cathodes, PB25 displays higher capacity retention of 86.5% over 1000 cycles at 5 C than PB0 with 20.1% capacity retention over 600 cycles. This study provides a new understanding of [Fe(CN)6]4− vacancy and lattice water behavior in K‐containing PB structure

Ce–O Covalence in Silicate Oxyapatites and Its Influence on Luminescence Dynamics

Cerium substituting gadolinium in Ca₂Gd₈(SiO₄)₆O₂ occupies two intrinsic sites of distinct coordination. The coexistence of an ionic bonding at a 4F site and an ionic–covalent mixed bonding at a 6H site in the same crystalline compound provides an ideal system for comparative studies of ion–ligand interactions. Experimentally, the spectroscopic properties and photoluminescence dynamics of this white-phosphor are investigated. An anomalous thermal quenching of the photoluminescence of Ce³⁺ at the 6H site is analyzed. Theoretically, ab initio calculations are conducted to reveal the distinctive properties of the Ce–O coordination at the two Ce³⁺ sites. The calculated eigenstates of Ce³⁺ at the 6H site suggest a weak Ce–O covalent bond formed between Ce³⁺ and one of the coordinated oxygen ions not bonded with Si⁴⁺. The electronic energy levels and frequencies of local vibrational modes are correlated with specific Ce–O pairs to provide a comparative understanding of the site-resolved experimental results. On the basis of the calculated results, we propose a model of charge transfer and vibronic coupling for interpretation of the anomalous thermal quenching of the Ce³⁺ luminescence. The combination of experimental and theoretical studies in the present work provides a comprehensive understanding of the spectroscopy and luminescence dynamics of Ce³⁺ in crystals of ionic–covalent coordination

Oxygen-enriched carbon nanotubes as a bifunctional catalyst promote the oxygen reduction/evolution reactions in Li-O(2 )batteries

The aprotic lithium-oxygen (Li-O-2) batteries based on carbon-based oxygen cathodes usually suffer from low round-trip efficiency. Here we adopt oxygen-enriched carbon nanotubes (CNTs) by acid etching treatment as the cathode, in which a low voltage plateau at similar to 3.5 V during charge is exhibited and the initial round-trip efficiency is increased from 69.9% to 76.0%. An optimized integration of electrocatalytic property and electrical conductivity is crucial for the oxidized CNTs cathode to enhance the capacity and cycling performance. In particular, the surface oxygen groups can facilitate the electrocatalysis of O-2 with the enhanced oxygen reduction reaction activity and induce defective lithium peroxide (Li-O-2 ) formation due to their preferential adsorption of O-2 on the oxidized CNTs. Compared to the high crystalline Li-O-2 toroids, the defective Li-O-2 with poor crystallinity could be decomposed at a lower charge potential, contributing to the enhanced round-trip efficiency of Li-O(2 )batteries. (C) 2018 Elsevier Ltd. All rights reserved

Highly stable potassium metal batteries enabled by regulating surface chemistry in ether electrolyte

Rechargeable potassium (K) metal batteries (PMBs) remain deeply challenged by the lack of suitable electrolytes that are stable against both highly reactive K anodes and 4 V-class cathodes. Despite their good reductive stability with K metal, classic potassium bis(fluorosulfonyl)amide (KFSI)-based ether electrolytes are typically used only in \u3c4.0 V PMBs due to their limited oxidation stability. Herein, a potassium nitrate (KNO3)-containing ether electrolyte, at a moderate KFSI concentration (2.3 M) rather than a high concentration (normally, \u3e3 M), is reported for the first time to be used in 4 V-class PMBs. A stable N/F-rich solid electrolyte interphase (SEI) is formed, enabling dense and uniform K deposition, especially under high current density. Remarkably, the PMBs with Prussian blue cathode exhibits an unprecedented cycle life (1000 cycles, 122 days). This work provides new perspectives of electrolyte design for 4 V-class PMBs

Regulating interfacial structure enables high-voltage dilute ether electrolytes

Poor oxidation stability of ether solvents at the cathode restricts the use of dilute ether electrolytes with conventional concentrations around 1 M in high-voltage, lithium-metal batteries. Here, we report an anion-adsorption approach to altering the ether solvent environment within the electrical double layer (EDL) at the cathode by adding a small amount of nitrate so that the oxidation tolerance of nitrate-containing dilute ether electrolytes is enhanced up to 4.4 V (versus Li/Li+), leading to complete compatibility with high-voltage cathodes and exhibiting superior cycling stability. Constant potential molecular dynamics simulations reveal that ether molecules are mostly excluded from the cathode because of nitrate occupation in the inner layer of the EDL, thus suppressing ether oxidative decomposition. This work highlights that regulating the interfacial structure by adding surface adsorbates, rather than passivating the cathode-electrolyte interphase or changing ion solvation, can help to enhance the oxidation stability of ether solvents

Deciphering the Formation and Accumulation of Solid-Electrolyte Interphases in Na and K Carbonate-Based Batteries

The continuous solid-electrolyte interphase (SEI) accumulation has been blamed for the rapid capacity loss of carbon anodes in Na and K ethylene carbonate (EC)/diethyl carbonate (DEC) electrolytes, but the understanding of the SEI composition and its formation chemistry remains incomplete. Here, we explain this SEI accumulation as the continuous production of organic species in solution-phase reactions. By comparing the NMR spectra of SEIs and model compounds we synthesized, alkali metal ethyl carbonate (MEC, M = Na or K), long-chain alkali metal ethylene carbonate (LCMEC, M = Na or K), and poly(ethylene oxide) (PEO) oligomers with ethyl carbonate ending groups are identified in Na and K SEIs. These components can be continuously generated in a series of solution-phase nucleophilic reactions triggered by ethoxides. Compared with the Li SEI formation chemistry, the enhancement of the nucleophilicity of an intermediate should be the cause of continuous nucleophilic reactions in the Na and K cases

Disproportionation in Li–O₂ Batteries Based on a Large Surface Area Carbon Cathode

In this paper we report on a kinetics study of the discharge process and its relationship to the charge overpotential in a Li–O₂ cell for large surface area cathode material. The kinetics study reveals evidence for a first-order disproportionation reaction during discharge from an oxygen-rich Li₂O₂ component with superoxide-like character to a Li₂O₂ component. The oxygen-rich superoxide-like component has a much smaller potential during charge (3.2–3.5 V) than the Li₂O₂ component (∼4.2 V). The formation of the superoxide-like component is likely due to the porosity of the activated carbon used in the Li–O₂ cell cathode that provides a good environment for growth during discharge. The discharge product containing these two components is characterized by toroids, which are assemblies of nanoparticles. The morphologic growth and decomposition process of the toroids during the reversible discharge/charge process was observed by scanning electron microscopy and is consistent with the presence of the two components in the discharge product. The results of this study provide new insight into how growth conditions control the nature of discharge product, which can be used to achieve improved performance in Li–O₂ cell