Advancements and Prospects of Graphite Anode for Potassium-Ion Batteries

Graphitic carbon with increased interlayer spacing derived from low-temperature CO2 rapid conversion for high-performance potassium storage

Graphitic carbon has been emerged as one of the most promising anode materials for potassium-ion batteries (PIBs) due to its moderate theoretical specific capacity, high electrical conductivity, and outstanding chemical stability. However, the structure of graphitic carbon usually experiences irreversible damage during the charge and discharge process, primarily due to the large radius of potassium ion. In contrast to the traditional preparation methods, we develop a low-carbon approach to obtain graphitic carbon with larger lattice spacing via a rapid chemical conversion between CO2 and NaAlH4 at ∼62 °C. We confirm that the CO2/NaAlH4 ratio plays a crucial role in increasing the degree of graphitization and promoting the formation of a flaky morphology of carbon materials. When applied as an anode material for potassium storage, the prepared graphitic carbon exhibits outstanding cycling stability and rate performance. It maintains a reversible capacity of 210 mAh g-1 after 1000 cycles at a current density of 0.1 A g-1, with a capacity retention rate of 95.9 %. This efficient method of preparing graphitic carbon provides valuable inspiration for the development of advanced energy storage materials.

Rigid-Flexible Coupling Realized by Synergistic Engineering of the Graphitic-Amorphous Architecture for Durable and Fast Potassium Storage

Graphite anodes hold great potential for potassium-ion batteries (PIBs), yet their practical application is hindered by poor cycle performance caused by substantial interlayer expansion. Herein, a partial graphitic carbon (PGC) is elaborately engineered via the catalytic effect of ferric citrate using pitch as a carbon precursor. Systematically varying the catalyst content enables an optimal PGC design integrating a highly graphitized phase providing abundant active sites for K-ion intercalation, balanced with an amorphous carbon region that accommodates volume expansion and facilitates ion diffusion. The optimized PGC12 electrode exhibits a high reversible capacity of 281.9 mAh g-1, characterized by a prolonged low-potential plateau region, and excellent cycle stability with a capacity retention of 94.8% after 300 cycles. It also realizes an impressive rate capability with a retained capacity of 222.2 mAh g-1 at 1 C. Moreover, the assembled K-ion full-cell delivers an exceptional energy density of 148.2 Wh kg-1. In-situ XRD and DFT simulations further verify the distinct phase transition mechanisms and reaction dynamics across different carbon configurations. This work elucidates the impact of carbon configurations on K-storage performance and proposes a structural model for efficient K-ion storage, which is instrumental in the rational design and advancement of carbon anodes in PIBs.

A superatom-assembled B8N2 monolayer acting as an electronic sponge for high-capacity anode materials for Na/K-ion batteries

Rechargeable sodium/potassium-ion batteries (SIBs/PIBs) have emerged as appealing alternatives for lithium-ion batteries due to their earth-abundance and economic benefits. However, exploring high-capacity anode materials for SIBs/PIBs is still challenging. Superatoms with delocalized electronic shells possess high flexibility as electron-acceptors/donors, making them ideal candidates for anode materials. Here, a superatom-assembled boron nitride monolayer (B8N2) was theoretically predicted using first principles calculations. The B8 core is assembled with two B4 superatoms, and further linked by nitrogen atoms in a graphene-like lattice. The B8N2 monolayer has an undirected bandgap (0.82 eV/HSE06) with an ultra-high carrier mobility of 13 × 104 cm2 V-1 s-1, where Na/K ions can be effectively adsorbed on its surface. The remarkably high theoretical storage capacities (924 mA h g-1/1115 mA h g-1), and low open-circuit voltages (0.08 V/0.21 V) are also revealed for the B8N2 monolayer with Na/K ions. Intriguingly, adsorption of Na/K ions causes little geometric deformation of the B8N2 monolayer, which ensures a promising cell operating cycle during the adsorption of Na/K ions at high concentrations. This work reveals the potential of superatoms as an efficient "electronic sponge", providing impetus for the design of superatomic electrode materials for metal ion batteries.

Self-Propagating Fabrication of a 3D Graphite@rGO Film Anode for High-performance Potassium-Ion Batteries

Graphite, with abundant resources and low cost, is regarded as a promising anode material for potassium-ion batteries (PIBs). However, because of the large size of potassium ions, the intercalation/deintercalation of potassium between the interlayers of graphite results in its huge volume expansion, leading to poor cycling stability and rate performance. Herein, a self-propagating reduction strategy is adopted to fabricate a flexible, self-supporting 3D porous graphite@reduced graphene oxide (3D-G@rGO) composite film for PIBs. The 3D porous network can not only effectively mitigate the volume expansion in graphite but also provide numerous active sites for potassium storage as well as allow for electrolyte penetration and rapid ion migration. Therefore, compared to the pristine graphite anode, the flexible 3D-G@rGO film electrode exhibits greatly improved K-storage performance with a reversible capacity of 452.8 mAh g-1 at 0.1 C and a capacity retention rate of 80.4% after 100 cycles. It also presents excellent rate capability with a high specific capacity of 139.1 and 94.2 mAh g-1 maintained at 2 and 5 C, respectively. The proposed self-propagating reduction strategy to construct a three-dimensional self-supporting structure is a viable route to improve the structural stability and potassium storage performance of graphite anodes.

Revealing the Charge Storage Mechanism in Porous Carbon to Achieve Efficient K Ion Storage

Constructing a porous structure is considered an appealing strategy to improve the electrochemical properties of carbon anodes for potassium-ion batteries (PIBs). Nevertheless, the correlation between electrochemical K-storage performance and pore structure has not been well elucidated, which hinders the development of high-performance carbon anodes. Herein, various porous carbons are synthesized with porosity structures ranging from micropores to micro/mesopores and mesopores, and systematic investigations are conducted to establish a relationship between pore characteristics and K-storage performance. It is found that micropores fail to afford accessible active sites for K ion storage, whereas mesopores can provide abundant surface adsorption sites, and the enlarged interlayer spacing facilitates the intercalation process, thus resulting in significantly improved K-storage performances. Consequently, PCa electrode with a prominent mesoporous structure achieves the highest reversible capacity of 421.7 mAh g-1 and an excellent rate capability of 191.8 mAh g-1 at 5 C. Furthermore, the assembled potassium-ion hybrid capacitor realizes an impressive energy density of 151.7 Wh kg-1 at a power density of 398 W kg-1. The proposed work not only deepens the understanding of potassium storage in carbon materials with distinctive porosities but also paves a path toward developing high-performance anodes for PIBs with customized energy storage capabilities.

In Situ Chemical Modulation of Graphitization Degree of Carbon Fibers and Its Potassium Storage Mechanism

Graphite is considered to be the most auspicious anode candidate for potassium ion batteries. However, the inferior rate performances and cycling stability restrict its practical applications. Few studies have investigated the modulating the graphitization degree of graphitic materials. Herein, a nitrogen-doped carbon-coated carbon fiber composite with tunable graphitization (CNF@NC) through etching growth, in-situ oxidative polymerization, and subsequent carbonization process is reported. The prepared CNF@NC with abundant electrochemical active sites and a rapid K+/electron transfer pathway, can effectively shorten the K+ transfer distance and promote the rapid insertion/removal of K+. Amorphous domains and short-range curved graphite layers can provide ample mitigation spaces for K+ storage, alleviating the volume expansion of the highly graphitized CNF during repeated K+ insertion/de-intercalation. As expected, the CNF@NC-5 electrode presents a high initial coulombic efficiency (ICE) of 69.3%, an unprecedented reversible volumetric capacity of 510.2 mA h cm-3 at 0.1 A g-1 after 100 cycles with the mass-capacity of 294.9 mA h g-1. The K+ storage mechanism and reaction kinetic analysis are studied by combining in-situ analysis and first-principles calculation. It manifests that the K+ storage mechanism in CNF@NC-5 is an adsorption-insertion-insertion mechanism (i.e., the "1+2" model). The solid electrolyte interphase (SEI) film forming is also detected.

Fast-charging anodes for lithium ion batteries: progress and challenges

Slow charging speed has been a serious constraint to the promotion of electric vehicles (EVs), and therefore the development of advanced lithium-ion batteries (LIBs) with fast-charging capability has become an urgent task. Thanks to its low price and excellent overall electrochemical performance, graphite has dominated the anode market for the past 30 years. However, it is difficult to meet the development needs of fast-charging batteries using graphite anodes due to their fast capacity degradation and safety hazards under high-current charging processes. This feature article describes the failure mechanism of graphite anodes under fast charging, and then summarizes the basic principles, current research progress, advanced strategies and challenges of fast-charging anodes represented by graphite, lithium titanate (Li4Ti5O12) and niobium-based oxides. Moreover, we look forward to the development prospects of fast-charging anodes and provide some guidance for future research in the field of fast-charging batteries.