Characterisation and modelling of potassium-ion batteries

Synergy Between Weak Solvent and Solid Electrolyte Interphase Enables High-Rate and Temperature-Resilient Potassium Ion Batteries

The rate and wide-temperature performance of graphite-based potassium-ion batteries (PIBs) are limited by slow reaction kinetics at the interphases and the solid electrolyte interphase (SEI) stability. Herein, we strategically designed weak solvating electrolytes (WSEs) to construct an efficient solvated K+ desolvation with K2SO3-rich SEI and achieve fast reaction kinetics at the electrode interface through the synergy between the SEI and the WSE. As a result of the beneficial fast reaction kinetics and stability of the electrode interface, the graphite anode shows high levels of rate performance and cycling stability, with a capacity of 249.6 mAh g-1 at 500 mA g-1 and 96.6% capacity retention after 1600 cycles. Moreover, assembled potassiated graphite (KC8)||Prussian blue nanoparticles (K-PBNPs) cells in our designed electrolyte show high-rate performance (63.1 mAh g-1 at 1500 mA g-1) and over wide operating temperature range (>99% Coulombic efficiency for over 1000 cycles and 200 cycles at -20°C and 80°C, respectively). Impressively, the pouch cell shows long-term stability for 2400 cycles at 500 mAg-1. This work bridges a longstanding gap, elucidating the synergy between the SEI components and WSEs, leading to fast-charging and temperature-resilient PIBs.

Compensating K Ions Through an Organic Salt in Electrolytes for Practical K-Ion Batteries

K-ion batteries face significant challenges due to a severe shortage of active K ions, with cathode materials typically containing less than 70% K ions and first-cycle irreversible reactions consuming up to 20% more. Conventional K-ion compensation methods fail to supply sufficient K ions without compromising cell integrity. To address this, we introduce potassium sulfocyanate (KSCN) as an electrolyte additive capable of delivering up to 100% active K ions. During initial charging, KSCN undergoes oxidative decomposition at 3.6 V, releasing active K ions and forming the cosolvent thiocyanogen ((SCN)2). This molecule, meeting diverse electrochemical properties, was identified using unsupervised machine learning and cheminformatics. The approach demonstrated full KSCN conversion and excellent compatibility with all cell components. The presence of (SCN)2 cosolvent enhanced the rate capability of anodes by promoting K-ion desolvation. In a hard carbon|K0.5Mg0.15[Mn0.8Mg0.05]O2 pouch cell, this approach tripled the capacity through supplying 58% active K ions, showcasing a practical solution for active K-ion compensation in K-ion batteries.

Ultrafast Rechargeable Aluminum-Chlorine Batteries Enabled by a Confined Chlorine Conversion Chemistry in Molten Salts

Rechargeable metal chloride batteries, with their high discharge voltage and specific capacity, are promising for next-generation sustainable energy storage. However, sluggish solid-to-gas conversion kinetics between solid metal chlorides and gaseous Cl2 cause unsatisfactory rate capability and limited cycle life, hindering their further applications. Here we present a rechargeable aluminum-chlorine (Al-Cl2) battery that relies on a confined chlorine conversion chemistry in a molten salt electrolyte, exhibiting ultrahigh rate capability and excellent cycling stability. Both experimental analysis and theoretical calculations reveal a reversible solution-to-gas conversion reaction between AlCl4- and Cl2 in the cathode. The designed nitrogen-doped porous carbon cathode enhances Cl2 adsorption, thereby improving the cycling lifespan and coulombic efficiency of the battery. The resulting Al-Cl2 battery demonstrates a high discharge plateau of 1.95 V, remarkable rate capability without capacity decay at different rates from 5 to 50 A g-1, and good cycling stability with over 1200 cycles at a rate of 10 A g-1. Additionally, we implemented a carbon nanofiber membrane on the anode side to mitigate dendrite growth, which further extends the cycle life to 3000 cycles at an ultrahigh rate of 30 A g-1. This work provides a new perspective on the advancement of high-rate metal chloride batteries.

Breaking Anionic Solvation Barrier for Safe and Durable Potassium-ion Batteries Under Ultrahigh-Voltage Operation

Ultrahigh-voltage potassium-ion batteries (PIBs) with cost competitiveness represent a viable route towards high energy battery systems. Nevertheless, rapid capacity decay with poor Coulombic efficiencies remains intractable, mainly attributed to interfacial instability from aggressive potassium metal anodes and cathodes. Additionally, high reactivity of K metal and flammable electrolytes pose severe safety hazards. Herein, a weakly solvating fluorinated electrolyte with intrinsically nonflammable feature is successfully developed to enable an ultrahigh-voltage (up to 5.5 V) operation. Through breaking the anionic solvation barrier, synergistic interfacial modulation can be achieved by the formation of robust anion-derived inorganic-rich electrode-electrolyte interfaces on both the cathode and anode. As proof of concept, a representative KVPO4F cathode can sustain 1600 cycles with 84.4 % of capacity retention at a high cutoff voltage of 4.95 V. Meanwhile, K plating/stripping process in our designed electrolyte also demonstrates optimized electrochemical reversibility and stability with effectively inhibited potassium dendrites. These findings underscore the critical impact of anion-dominated solvation configuration on synergistic interfacial modulation and electrochemical properties. This work provides new insights into rational design of ultrahigh-voltage and safe electrolyte for advanced PIBs.

Amorphous/Crystalline Heterostructured Nanomaterials: An Emerging Platform for Electrochemical Energy Storage

With the expanding adoption of large-scale energy storage systems and electrical devices, batteries and supercapacitors are encountering growing demands and challenges related to their energy storage capability. Amorphous/crystalline heterostructured nanomaterials (AC-HNMs) have emerged as promising electrode materials to address these needs. AC-HNMs leverage synergistic interactions between their amorphous and crystalline phases, along with abundant interface effects, which enhance capacity output and accelerate mass and charge transfer dynamics in electrochemical energy storage (EES) devices. Motivated by these elements, this review provides a comprehensive overview of synthesis strategies and advanced EES applications explored in current research on AC-HNMs. It begins with a summary of various synthesis strategies of AC-HNMs. Diverse EES devices of AC-HNMs, such as metal-ion batteries, metal-air batteries, lithium-sulfur batteries, and supercapacitors, are thoroughly elucidated, with particular focus on the underlying structure-activity relationship among amorphous/crystalline heterostructure, electrochemical performance, and mechanism. Finally, challenges and perspectives for AC-HNMs are proposed to offer insights that may guide their continued development and optimization.

Characterisation and modelling of potassium-ion batteries

Potassium-ion batteries (KIBs) are emerging as a promising alternative technology to lithium-ion batteries (LIBs) due to their significantly reduced dependency on critical minerals. KIBs may also present an opportunity for superior fast-charging compared to LIBs, with significantly faster K-ion electrolyte transport properties already demonstrated. In the absence of a viable K-ion electrolyte, a full-cell KIB rate model in commercial cell formats is required to determine the fast-charging potential for KIBs. However, a thorough and accurate characterisation of the critical electrode material properties determining rate performance-the solid state diffusivity and exchange current density-has not yet been conducted for the leading KIB electrode materials. Here, we accurately characterise the effective solid state diffusivities and exchange current densities of the graphite negative electrode and potassium manganese hexacyanoferrateK 2 Mn [ Fe ( CN ) 6 ] (KMF) positive electrode, through a combination of optimised material design and state-of-the-art analysis. Finally, we present a Doyle-Fuller-Newman model of a KIB full cell with realistic geometry and loadings, identifying the critical materials properties that limit their rate capability.