Cost-effective hard–soft carbon composite anodes with promising potassium ions storage performance

Fabrication of Soft-Hard Heterostructure Porous Carbon with Enhanced Performance for High Mass-Loading Aqueous Supercapacitors

With the increasing attention to energy and environmental issues, the high value-added utilization of biomass and pitch to functional carbon materials has become an important topic in science and technology. In this work, the soft-hard heterostructure porous carbon (NRP-HPC) is prepared by bio-template method, in which biomass and pitch are used as hard carbon and soft carbon precursors, respectively. The prepared NRP-HPC-4 shows high specific surface area (2293 m2 g-1), suitable pore size distribution, good conductivity (0.25 Ω cm-1), and strong wettability. The synergistic effect of soft carbon and hard carbon ensures the composite material exhibiting excellent electrochemical performance for high mass loading (12.0 mg cm-2) aqueous supercapacitor, i.e., high specific capacitance (304.69 F g-1 at 0.1 A g-1), high area capacitance (3.67 F cm-2 at 0.1 A g-1), high volumetric specific capacitance (202.74 F cm-3 at 0.1 A g-1), low open-circuit voltage attenuation rate (21.04 mV h-1), good voltage retention (79.12%), and excellent cyclic stability (92.04% capacitance retention and 100% coulombic efficiency after 20 000 cycles). The composite technology of soft carbon and hard carbon not only ensures the prepared porous carbon electrode materials with enhanced electrochemical performance, but also realizes the high value-added coupling utilization of biomass and pitch.

Synthesis Strategies and Applications for Pitch-Based Anode: From Industrial By-Products to Power Sources

It is significant for saving energy to manufacture superb-property batteries. Carbon is one of the most competitive anode materials in batteries, but it is hard for commercial graphite anodes to meet the increasingly higher energy-storage requirements. Moreover, the price of other better-performing carbon materials (such as graphene) is much higher than graphite, which is not conducive to massive production. Pitch, the cheap by-product in the petroleum and coal industries, has high carbon content and yield, making it possible for commercialization. Developing pitch-based anodes can not only lower raw material costs but also realize the pitch's high value-added utilization. We comprehensively reviewed the latest synthesis strategies of pitch-derived materials and then introduced their application and research progress in lithium, sodium, and potassium ion batteries (LIBs, SIBs, and PIBs). Finally, we summarize and suggest the pitch's development trend for anodes and in other fields.

Strengthen Synergistic Effect of Soft Carbon and Hard Carbon Toward High-Performance Anode for K-Ion Battery

Synergistic effect of soft carbon and hard carbon has been proven to be useful for obtaining excellent anode materials for potassium ion battery, which is determined by the mixing degree of precursors. Inspired by the formation of proteins in biology, peptide bonds are used to connect the precursors of the two sort of carbon to prepare soft-hard hybrid carbons with stronger synergistic effects. The hard carbon domain with nanometer size is so highly distributed in the soft carbon that the synergistic effect between two sorts of carbon is significantly enhanced. After the optimization, the diffusion coefficient of as-prepared hybrid carbon (CSHC_3-6-1200) is 10 times larger than that of corresponding carbon synthesized by physical method. Consequently, CSHC_3-6-1200 can maintain a specific capacity of 71.6 mAh g^-1 at a high current density of 1600 mA g^-1. It is believed that this new preparation route may bring a new perspective to the development of soft and hard composite carbon material anodes with high power density and ultralong service life.

Recent Progress of Carbon-Based Anode Materials for Potassium Ion Batteries

With the increasing demand for clean energy, rechargeable batteries with K⁺ as carriers have attracted wide attention due to their advantages of expandability and low cost. High-performance anode materials are the key to the development of potassium ion batteries (PIBs), improving their competitiveness and feasibility. Carbon materials have become promising anodes for PIBs due to their abundant resources, low cost, non-toxicity and electrochemical diversity. This article reviews the research progress of carbon based anode materials in recent years. Firstly, the unique characteristics of carbon as a competitive anode for advanced PIBs are discussed, which provides guidance for optimal design and exploration. Then, various carbon materials as the anodes towards PIBs are summarized in detail, and the involved problems and corresponding solutions are analyzed. Finally, the future development and perspective of advanced carbons for next-generation PIBs are proposed.

Ultra-Thin Wrinkled Carbon Sheet as an Anode Material of High-Power-Density Potassium-Ion Batteries

Although K⁺ is readily inserted into graphite, the volume expansion of graphite of up to 60% upon the formation of KC₈, together with its slow diffusion kinetics, prevent graphite from being used as an anode for potassium-ion batteries (PIBs). Soft carbon with low crystallinity and an incompact carbon structure can overcome these shortcomings of graphite. Here, ultra-thin two-dimensional (2D) wrinkled soft carbon sheets (USCs) are demonstrated to have high specific capacity, excellent rate capability, and outstanding reversibility. The wrinkles themselves prevent the dense stacking of micron-sized sheets and provide sufficient space to accommodate the volume change of USCs during the insertion/extraction of K⁺. The ultra-thin property reduces strain during the formation of K-C compounds, and further maintains structural stability. The wrinkles and heteroatoms also introduce abundant edge defects that can provide more active sites and shorten the K⁺ migration distance, improving reaction kinetics. The optimized USC_20-1 electrode exhibits a reversible capacity of 151 mAh g^-1 even at 6400 mA g^-1, and excellent cyclic stability up to 2500 cycles at 1000 mA g^-1. Such comprehensive electrochemical performance will accelerate the adoption of PIBs in electrical energy applications.

Modulating the Graphitic Domains of Hard Carbons Derived from Mixed Pitch and Resin to Achieve High Rate and Stable Sodium Storage

Resin derived hard carbons (HCs) generally demonstrate remarkable electrochemical performance for both sodium ion batteries (SIBs) and potassium-ion batteries (KIBs), but their practical applications are hindered by their high price and high temperature pyrolysis (≈1500 °C). Herein, low-cost pitch is coated on the resin surface to compromise the cost, and meanwhile manipulate the microstructure at a relatively low pyrolysis temperature (1000 °C). HC-0.2P-1000 has a large number of short graphitic layer structures and a relatively large interlayer spacing of 0.3743 nm, as well as ≈1 nm sized nanopores suitable for sodium storage. Consequently, the as produced material demonstrates a superior reversible capacity (349.9 mAh g^-1 for SIBs and 321.9 mAh g^-1 for KIBs) and excellent rate performance (145.1 mAh g^-1 at 20 A g^-1 for SIBs, 48.5 mAh g^-1 at 20 A g^-1 for KIBs). Furthermore, when coupled with Na₃ V₂ (PO₄ )₃ as cathode, the full cell exhibits a high energy density of 251.1 Wh kg^-1 and excellent stability with a capacity retention of 73.3% after 450 cycles at 1 A g^-1 .

Prospects of Electrode Materials and Electrolytes for Practical Potassium-Based Batteries

Potassium-ion batteries (PIBs) have attracted tremendous attention because of their high energy density and low-cost. As such, much effort has focused on developing electrode materials and electrolytes for PIBs at the material levels. This review begins with an overview of the high-performance electrode materials and electrolytes, and then evaluates their prospects and challenges for practical PIBs to penetrate the market. The current status of PIBs for safe operation, energy density, power density, cyclability, and sustainability is discussed and future studies for electrode materials, electrolytes, and electrode-electrolyte interfaces are identified. It is anticipated that this review will motivate research and development to fill existing gaps for practical potassium-based full batteries so that they may be commercialized in the near future.

Porous hard carbon spheres derived from biomass for high-performance sodium/potassium-ion batteries

Hard carbon is the most attractive anode material for electrochemical sodium/potassium-ion storage. The preparation of hard carbon spheres directly from the broad sources of biomass is of great interest but barely reported. Herein, we developed a simple two-step hydrothermal method to construct porous carbon microspheres directly from the original waste biomass of camellia shells. The porous carbon microspheres have high specific capacities of 250 mAh g^-1and 264.5 mAh g^-1at a current density of 100 mA g^-1for sodium-ion batteries and potassium-ion batteries, respectively. And it has excellent cycle stability for sodium ions and potassium ions outperforming most reported hard carbons, which is mainly attributed to the microporous structure and spherical morphology. The work paves a way to prepare porous hard carbon spheres directly from biomass for alkali metal-ion batteries.