Revealing dual capacitive mechanism of carbon cathode toward ultrafast quasi-solid-state lithium ion capacitors

High-performance lithium ion capacitors(LICs) have been seriously hindered by the very low capacity and unclear capacitive mechanism of carbon cathode.Herein,after the combination of experimental results and theoretical calculations,it is found that the critical pore size of 0.8 nm for PF_6~-ion adsorption decreases strong interactive repulsion of electrons and largely reduces adsorption energy barrier,which greatly improves the charge accommodation capacity in electrical double-layer behavior.Most importantly,the chemical-bond evolution process of C=O group has been firstly revealed by X-ray photoelectron spectroscopy(XPS),indicating that the introduction of C=O group can provide abundant redox active sites for PF_6~-ion adsorption accompanied with enhanced pseudocapacitive capacity.Attributed to the synergistic effect of dual capacitive mechanism,porous carbon sheet(PCS) cathode shows a reversible specific capacity of 53.6 mAh g^(-1) even at a high current density of 50 A g^(-1).Significantly,the quasisolid-state LIC manifests state-of-the-art electrochemical performances with an integrated maximum energy density of 163 Wh kg^(-1) and an outstanding power density of 15,000 W kg^(-1).This elaborate work promotes better fundamental understanding about capacitive mechanism of PF_6~-ion and offers a rational dual-capacitive strategy for the design of advanced carbon cathodes.

K_(x)C_(y) phase induced expanded interlayer in ultra-thin carbon toward full potassium-ion capacitors

Carbonaceous materials have been regarded as highly promising anode candidates for potassium storage with their cost-effectiveness and environmental benignity.However,low specific capacity and difficulty in large-scale synthesis largely hinder their further development.Herein,a thermal-induced potassium–carbon alloy phase(K_(x)C_(y))with the expanded interlayer spacing strategy is first put forward.Through in situ high-temperature X-ray diffraction,a K_(2)C_(2) phase is evoked by thermal energy during the in-situ carbonization process of carbon quantum dots intermediate derived from potassium-containing precursors,whereas no lithium or sodium–carbon alloy phase is observed from lithium/sodium-containing precursors.The asobtained ultra-thin carbon nanosheets achieve adjustable layer spacing,preparation in bulk,delivering reversible potassium storage of 403.4 mAh g^(−1) at 100 mA g^(−1) and 161.2 mAh g^(−1) even at 5.0 A g^(−1),which is one of the most impressive K-storage performances reported so far with great potential application.Furthermore,the assembled potassium-ion hybrid capacitor by combining the impressive CFMs-900 anode with the three-dimensional framework-activated carbon delivers a high energy-power density of 251.7 Wh kg^(−1) at 250Wkg^(−1) with long-term stability.This study opens a scalable avenue to realize the expanded interlayer spacing,which can be extended to other multicarboxyl potassium salts and can provide approach for the design of high-performance carbon anode materials for potassium storage.

Ultra-Low-Dose Pre-Metallation Strategy Served for Commercial Metal-Ion Capacitors

Sacrificial pre-metallation strategy could compensate for the irreversible consumption of metal ions and reduce the potential of anode,thereby elevating the cycle performance as well as open-circuit voltage for full metal ion capacitors(MICs).However,suffered from massive-dosage abuse,exorbitant decomposition potential,and side effects of decomposition residue,the wide application of sacrificial approach was restricted.Herein,assisted with density functional theory calculations,strongly coupled interface(M-O-C,M=Li/Na/K)and electron donating group have been put forward to regulate the band gap and highest occupied molecular orbital level of metal oxalate(M_(2)C_(2)O_(4)),reducing polarization phenomenon and Gibbs free energy required for decomposition,which eventually decrease the practical decomposition potential from 4.50 to 3.95 V.Remarkably,full sodium ion capacitors constituted of commercial materials(activated carbon//hard carbon)could deliver a prominent energy density of 118.2 Wh kg^(−1)as well as excellent cycle stability under an ultra-low dosage pre-sodiation reagent of 15-30 wt%(far less than currently 100 wt%).Noteworthily,decomposition mechanism of sacrificial compound and the relative influence on the system of MICs after pre-metallation were initially revealed by in situ differential electrochemical mass spectrometry,offering in-depth insights for comprehending the function of cathode additives.In addition,this breakthrough has been successfully utilized in high performance lithium/potassium ion capacitors with Li_(2)C_(2)O_(4)/K_(2)C_(2)O_(4) as pre-metallation reagent,which will convincingly promote the commercialization of MICs.

Interfacial/bulk synergetic effects accelerating charge transferring for advanced lithium-ion capacitors

The exploration of advanced materials through rational structure/phase design is the key to develop highperformance lithium-ion capacitors(LICs).However,high complexity of material preparation and difficulty in quantity production largely hinder the further development.Herein,Cu_(5)FeS_(4-x)/C(CFS@C)heterojunction with rich sulfur vacancies has successfully achieved from natural bornite,presenting low costeffective and bulk-production prospect.Density functional theory(DFT)calculations indicate that rich vacancies in bulk phase can decrease band gap of bornite and thus improve its intrinsic electron conductivity,as well as the heterojunction spontaneously evokes a built-in electric field between its interfacial region,largely reducing the migration barrier from 1.27 e V to 0.75 e V.Benefited from these merits,the CFS@C electrodes deliver outperformed lithium storage performance,e.g.,high reversible capacity(822.4m Ah/g at 0.1 A/g),excellent cycling stability(up to 820 cycles at 2 A/g and 540 cycles at 5 A/g with respective capacity retention of over or nearly 100%).With CFS@C as anode and porous carbon nanosheets(PCS)as cathode,the assembled CFS@C//PCS LIC full cells exhibit high energy/power density characteristics of 139.2 Wh/kg at 2500 W/kg.This work is expected to offer significant insights into structure modifications/devising toward natural minerals for advanced energy-storage systems.

缺陷辅助高阴离子S/Se/P掺杂助力高性能钠离子电容器的快速传荷动力学

设计具有快速传荷动力学的二氧化钛负极材料是进一步构建高能量功率密度混合离子电容器的关键所在.本文提出一个氧空位辅助二氧化钛高阴离子掺杂的策略,合成了高含量硫/硒/磷掺杂的二氧化钛负极材料.通过实验结果与理论计算相结合,本文系统地研究了氧空位辅助掺杂的可行性、硫掺杂对二氧化钛的影响以及二氧化钛负极材料倍率性能极大提升的深层次机理.研究发现,氧空位的引入可以使硫掺杂过程自发进行,高含量的硫掺杂在二氧化钛能带结构中引入S 2p,使得其能带间隙变小,导电率显著提升;同时,硫进入晶格后,离子的迁移能垒降低,离子迁移速率增加,传荷动力学提高.这项工作为实现阴离子的高含量掺杂和提升二氧化钛的电荷转移动力学提供了一种新的策略,为设计具有快速动力学的电极材料提供了行之有效的方法.

Methods of improving the initial Coulombic efficiency and rate performance of both anode and cathode materials for sodium-ion batteries

Sodium-ion batteries(SIBs) have gained more scientists’ interest, owing to some facts such as the natural abundance of Na, the similarities of physicochemical characteristics between Li and Na. The irreversible Na+ions consumption during the first cycle of charge/discharge process(due to the formation of the solid electrolyte interface(SEI) on the electrode surface and other irreversible reactions) is the factor that determines high performance SIBs and largely reduces the capacity of the full cell SIBs. Thus, the initial coulombic efficiency(ICE) of SIBs for both anode and cathode materials, is a key parameter for high performance SIBs, and the point is to increase the transport rate of the Na+ions. Therefore, developing SIBs with high ICE and rate performance becomes vital to boost the commercialization of SIBs. Here we provide a review on the methods to improve the ICE and the rate performance, by summarizing some methods of improving the ICE and rate performance of the anode and cathode materials for SIBs, and end by a conclusion with some perspectives and recommendations.