Interfacial and lattice synergy enabled by Cu/Al dual doping and carbon coating in O3-type sodium-ion battery cathodes

Nano-sized LiNi 0.4 Mn 0.4 Co 0.2 O 2 lithium-ion battery cathode materials with and without dual Mg & Al doping were synthesized by Pechini method. The powdered materials were characterized using X-ray diffraction, scanning electron microscopy and electrochemical techniques. X-ray analyses showed that 003/104 peaks intensity ratio increased from 0.95 for undoped material to 1.27 for doped material, thereby suggesting that dual doping was beneficial in terms reducing Li/Ni cation mixing. Although dual doping caused some reduction in initial discharge capacity (140 vs. 128 mAh/g) and increase in charge transfer resistance relative to the undoped material, it noticeably helped increase capacity retention during battery testing at high voltage.

Boosting sodium-ion battery performance with vanadium substituted Fe, Ni dual doped fluorophosphate cathode over a wide temperature range

Fe, N dual doped graphitic carbon derived from straw as efficient electrochemical catalysts for oxygen reduction reaction and Zn-air batteries

Carbon-based materials are usually considered as conventional electrode materials for supercapacitors (SCs), therefore it is meaningful to enhance supercapacitive capacity and cycling stability via rational surface structure design of carbon-based materials. The bio-inspired coral-like porous carbon structure has attracted much attention recently in that it can offer large surface area for ion accommodation and favor ions-diffusion, promoting its energy storage capacity. Herein, we designed a superiorly hydrophilic B, N dual doped coral-like carbon framework (BN-CCF) and studied its surface wettability via low-field nuclear magnetic resonance relaxation technique. The unique coral-like micro-nano structure and B, N dual doping in carbon framework can enhance its pseudocapacitance and improve surface wettability. Therefore, when used as electrodes of SCs, the BN-CCF displays 457.5 F g−1 at 0.5 A g−1, even when current density increases 20 folds, it still exhibits high capacitance retention of 66.1% and superior cycling stability. The symmetrical SCs assembled by BN-CCF electrodes show a high energy density of 14.92 Wh kg−1 (600 W kg−1). In this work, simple structural regulation with B, N dual doping and surface wettability should be considered as effective strategy to enhance energy storage capacity of carbon-based SCs.

High energy density at high power density is still a challenge for the current Li‐ion capacitors (LICs) due to the mismatch of charge‐storage capacity and electrode kinetics between capacitor‐type cathode and battery‐type anode. In this work, B and N dual‐doped 3D porous carbon nanofibers are prepared through a facile method as both capacitor‐type cathode and battery‐type anode for LICs. The B and N dual doping has profound effect in tuning the porosity, functional groups, and electrical conductivity for the porous carbon nanofibers. With rational design, the developed B and N dual‐doped carbon nanofibers (BNC) exhibit greatly improved electrochemical performance as both cathode and anode for LICs, which greatly alleviates the mismatch between the two electrodes. For the first time, a 4.5 V “dual carbon” BNC//BNC LIC device is constructed and demonstrated, exhibiting outstanding energy density and power capability compared to previously reported LICs with other configurations. In specific, the present BNC//BNC LIC device can deliver a large energy density of 220 W h kg−1 and a high power density of 22.5 kW kg−1 (at 104 W h kg−1) with reasonably good cycling stability (≈81% retention after 5000 cycles).

In recent years, sodium-ion batteries (SIBs) have emerged as promising alternatives to lithium-ion batteries (LIBs) due to several advantages such as low cost and high abundance of sodium precursors. However, one of the significant drawbacks of SIB cathodes is poor cycling stability at a higher current density than LIBs due to the large size of the Na+ ion. We have demonstrated a strategy to boost the cycling stability and overall performance of the SIB cathode via combined dual ion doping and nanostructuring methodologies. We synthesized a series of Na3V2–xCox(PO4)3/C (x = 0.05, 0.1, 0.5) cathode materials via a solid-state sintering process. Structural and morphological properties were analyzed by using XRD, SEM, and TEM analysis. In addition, the successful incorporation of Co was confirmed by an XPS analysis. An aqueous-based electrochemical system was utilized to check the electrochemical performance of the synthesized material. In a 1 M NaOH electrolyte, NCoVP-0.5 delivers the highest discharge time of 175.89 s at a current density of 1 A g–1. Additional K and Li dopants were utilized to further enhance the performance of NCoVP-0.5. During the initial galvanostatic charge–discharge at a current density of 1 A g–1 and a voltage window of 0.1–0.58 V, LiNCoVP delivers a discharge time of 202 s with an efficiency of 84.6%, while KNCoVP delivers the highest discharge time of 215 s with an efficiency of 86.2%. Even at a current density of 5 A g–1, KNCoVP demonstrated a Coulombic efficiency of >97% after 200 cycles. Also, KNCoVP delivers a discharge specific capacity of 116.2 mAh/g at 0.1C. Thus, the introduced material and the demonstrated strategy underscore the inherent problems of the cathode material of SIBs.

The booming development of electric vehicles (EVs) raised concerns about sustainability of Li-ion batteries (LIBs). Some of their constituents, such as Li and Co, are of scarce and highly localised resources. Furthermore, LIB’s building materials are difficult to recycle raising questions on the sustainability of the technology. These issues inspired research on chemistries based on more abundant elements, i.e. Na, Mg or Ca. Among them the most promising are sodium-ion batteries (SIBs), which are currently heavily researched as a viable and sustainable alternative to LIBs for medium to large scale energy storage applications. The mostly researched electrode materials for SIBs are hard carbons for anode and intercalation compounds for cathodes. The latter contain transition metals (including cobalt) and share the same concerns as cathode materials for LIBs. Additionally, having in mind recyclability problems of LIBs, it is necessary to take the circular economy approach when designing new technologies such as Na-ion batteries. Therefore, more sustainable and greener materials are needed. A promising solution is the use of carbon as an active electrode material. Carbonaceous materials are inexpensive, environmentally friendly and highly conductive. So called ‘dual carbon’ batteries utilise carbon for both electrodes – in case of LIBs it’s usually graphite for cathode and anode.1 Literature on this field regarding SIBs is sparse, particularly when it comes to electrochemical mechanisms and full cells performance. For instance Fan et al. reported on soft carbon-graphite Na-ion full cell with remarkable long cycle life.2 However, graphite cathode works via anion intercalation mechanism, which delivered small capacity of around 40 mAh g-1 in a full cell. Recently Ali et al. reported on electrochemical performance of reduced graphene oxide (rGO) as a suitable cathode for SIBs3. The cathode showed high specific capacity of 235 mAh g-1 and stable behaviour over 1000 cycles. Nevertheless, the exact electrochemical energy storage mechanism in rGO is unclear and its performance in a full cell wasn’t yet verified. In this work we investigated electrochemical behaviour of reduced graphene oxide based cathode for SIBs. Techniques such as in situ Raman spectroscopy and X-ray Pair Distribution Function (PDF) provided insightful look into electrochemical reactions of rGO cathodes for SIBs. It has been concluded that processes responsible for high gravimetric capacity are surface Faradaic reactions between the sodium ions and the functional groups, as well as the bipolar behaviour of rGO resulting in capacitive storage of anions from electrolyte salt (Figure 1a). Furthermore, as a proof-of-concept a full cell with the rGO cathode and hard carbon (HC) as anode was tested. It showed high energy density of 80 Wh kg-1 and outstanding stability over 1000 cycles (Figure 1b), proving that rGO is a viable SIBs cathode material candidate. Replacing expensive transition metal based oxides with carbonaceous cathodes would solve sustainability and environmental impact concerns and lead to significant reduction of overall SIBs manufacturing costs. Placke, A. Heckmann, R. Schmuch, P. Meister, K. Beltrop and M. Winter, Joule, 2018, 1–23.Fan, Q. Liu, S. Chen, Z. Xu and B. Lu, Adv. Energy Mater., 2017, 7, 1602778.G. Ali, A. Mehmood, H. Y. Ha, J. Kim and K. Y. Chung, Sci. Rep., 2017, 7, 40910. Figure 1

Bamboo-derived carbon material inherently doped with SiC and nitrogen for flexible supercapacitors

Hybrid ion capacitors (HICs) based on insertion reactions have attracted considerable attention due to their energy density being much higher than that of the electrical double-layer capacitors (EDLCs). However, the development of hybrid ion capacitors with high energy density at high power density is a big challenge due to the mismatch of charge storage capacities and electrode kinetics between the battery-type anode and capacitor-type cathode. In this work, N and O dual doped carbon nanofibers (N,O-CNFs) were combined with carbon nanotubes (CNTs) to compose a complex carbon anode. N,O dual doping effectively tuned the functional group and surface activity of the CNFs while the integration of CNTs increased the extent of graphitization and electrical conductivity. The carbon cathode with high specific surface area and high capacity was obtained by the activation of CNFs (A-CNFs). Finally, a hybrid sodium ion capacitor was constructed by the double carbon electrode, which showed a superior electrochemical capacitive performance. The as-assembled HIC device delivers a maximum energy density of 59.2 W h kg−1 at a power density of 275 W kg−1, with a high energy density of 38.7 W h kg−1 at a power density of 5500 W kg−1.

A new strategy for enhancing the oxygen reduction reaction (ORR) activity of carbon-based catalysts in acidic media is proposed and characterized; the strategy consists in modifying the ORR through dual doping of nitrogen and phosphorus into the carbon. The P, N-doped carbon is prepared via pyrolysis of a mixture composed of dicyandiamide (DCDA), phosphoric acid, cobalt chloride, and iron chloride at 900 °C under an Ar atmosphere. The P-doping induces an uneven surface with many open edged sites in the carbon morphology and increases the carbon surface area from 108.1 to 578.8 m2 g−1. The XRD, XPS-C1s, and Raman spectroscopy results reveal that the crystallinity and degree of the sp2-carbon network decrease and the number of defect sites of the carbon increase as the amount of P-doping increases. All catalysts demonstrated similar proportions of N-doping types regardless of the P-doping amount: pyridinic-N and graphitic-N were dominant phases in the carbon lattice. In the ORR, the onset potential of the prepared catalysts was 0.6 V (vs. Ag/AgCl) in 1 M HClO4. The N-doped carbon records −0.69 mA mg−1 of mass activity at 0.5 V (vs. Ag/AgCl), but additional P-doping results in an increase of activity (−2.88 mA mg−1) that is more than fourfold that produced without the additional P-doping. Moreover, additional P-doping also modifies the ORR pathway, as the N-doped carbon induces more than 10% of H2O2; however, the P, N-doped carbon produced below 4% of H2O2 during the ORR.

Doping is crucial for maintaining the long-term stability of Ni-rich layered cathodes in lithium-ion batteries. However, using a single dopant is often insufficient in achieving a stable, high-energy cathode material. In this study, we used a dual doping approach by employing Al3+ and Nb5+ ions to enhance the cycling stability of Li[Ni0.92Co0.04Mn0.04]O2 (NCM92) cathodes. Al3+ doping reinforces the crystal structure, while Nb5+ doping optimizes the morphology of primary particles. This dual doping strategy not only harnesses the advantages of both dopants simultaneously, but also showcases remarkable performance improvements through synergistic effects. The resulting Li[Ni0.905Co0.04Mn0.04Al0.005Nb0.01]O2 (AlNb-NCM92) cathode, developed via dual Al and Nb doping, demonstrates remarkable stability. These findings highlight the importance of a comprehensive doping strategy that considers both crystal structure and microstructure to maximize the long-term stability of high-energy Ni-rich cathode materials.

The synergistic effect of Na+/Al3+ dual doping is investigated to improve the structural stability and electrochemical performance of LiNi0.88Co0.08Mn0.04O2 cathodes for Li-ion batteries. Rietveld refinement and density functional theory calculations confirm that Na+/Al3+ dual doping changes the lattice parameters of LiNi0.88Co0.08Mn0.04O2. The changes in the lattice parameters and degree of cation mixing can be alleviated by maintaining the thickness of the LiO6 slab because the energy of Al-O bonds is higher than that of transition metal (TM)-O bonds. Moreover, Na is an abundant and inexpensive metal, and unlike Al3+, Na+ can be doped into the Li slab. The ionic radius of Na+ (1.02 Å) is larger than that of Li+ (0.76 Å); therefore, when Na+ is inserted into Li sites, the Li slab expands, indicating that Na+ serves as a pillar ion for the Li diffusion pathway. Upon dual doping of the Li and TM sites of Ni-rich Ni0.88Co0.08Mn0.04O2 (NCM) with Na+ and Al3+, respectively, the lattice structure of the obtained NNCMA is more ideal than those of bare NCM and Li+- and Na+-doped NCM (NNCM and NCMA, respectively). This suggests that NNCMA with an ideal lattice structure presents several advantages, namely, excellent structural stability, a low degree of cation mixing, and favorable Li-ion diffusion. Consequently, the rate capability of NNCMA (83.67%, 3 C/0.2 C), which presents favorable Li-ion diffusion because of the expanded Li sites, is higher than those of bare NCM (78.68%), NNCM (81.15%), and NCMA (83.18%). The Rietveld refinement, differential capacity analysis, and galvanostatic intermittent titration technique results indicate that NNCMA exhibits low polarization, favorable Li-ion diffusion, and a low degree of cation mixing; moreover, its phase transition is hindered. Consequently, NNCMA demonstrates a higher capacity retention (84%) than bare NCM (79%), NNCM (82%), and NCMA (82%) after 50 cycles at 1 C. This study provides insight into the fabrication of Ni-rich NCMs with excellent electrochemical performance.

Sodium-ion batteries (SIBs) have emerged as a promising alternative for large-scale energy storage due to the abundance of sodium resources. Among cathode materials, layered oxides have shown exceptional potential, yet their practical application is hindered by structural instability during electrochemical cycling. In this study, this challenge is addressed by introducing a novel strategy of Cu and F dual doping into the octahedral ligand field of oxygen-activated P2-type Na0.67Ni0.33Mn0.67O2 layered oxides. Through a comprehensive suite of advanced characterization techniques, unprecedented insights into the modulation of oxygen redox activity are uncovered. Ex situ X-ray photoelectron spectroscopy and Raman spectroscopy reveal enhanced reversibility and stability in chemical bonding, while in situ X-ray diffraction analysis indicates the suppression of detrimental phase transitions, ensuring a stable and unobstructed Na+ diffusion pathway. Density functional theory calculations further elucidate that Cu-F co-doping reduces the overlap between Ni t2 g orbitals and O 2p orbitals, thereby inhibiting oxygen redox activity. Remarkably, the co-doped material exhibits significantly improved capacity retention and rate performance. This work not only advances the fundamental understanding of octahedral ligand field engineering but also provides a transformative approach to designing high-performance and stable cathode materials for SIBs, paving the way for their widespread adoption in energy storage systems.

Ti and W dual doping combined with a two-step calcination approach promoted the formation of P2/tunnel intergrowth. This strategy produces cathodes with a capacity retention over 80% after 435 cycles at 5C for sodium ion batteries.

Suppressing the P2 − O2 phase transformation and Na+/vacancy ordering of high-voltage manganese-based P2-type cathode by cationic codoping