DMF stabilized Li3N slurry for manufacturing self-prelithiatable lithium-ion capacitors

How Does Li2C4O4 Prelithiation Additive Influence the Solid Electrolyte Interphase of Dual Carbon Lithium-Ion Capacitors?

Prelithiation is a critical step in dual carbon lithium-ion capacitors (LICs) due to the lack of Li+ in the system, which needs to be incorporated externally to avoid electrolyte depletion. Several prelithiation techniques have been developed over the years, and recently, dilithium squarate (Li2C4O4) has been reported as an air-stable, easy to synthesize, safe, and cost-effective prelithiation reagent for LICs. Li2C4O4 has successfully been used in a wide range of chemistries, and its integration into positive electrodes has been scaled up to roll-to-roll processing and demonstrated in multilayer pouch cells. However, its influence in the solid electrolyte interphase (SEI) has not yet been studied. In this work, the SEI formed on the hard carbon (HC) negative electrode when using Li2C4O4 as a prelithiation agent has been studied by X-ray photoelectron spectroscopy (XPS). The electrode surface has been analyzed in the lithiated and delithiated states along the first lithiation cycle, as well as at the end of the prelithiation protocol, to gain insight into the SEI formation and evolution during the prelithiation process. In addition, an aging test has been carried out to study the long-term SEI stability. We have observed that the use of Li2C4O4 induces a chemical modification in the composition of the SEI with respect to the SEI that forms by using a standard electrochemical prelithiation process, resulting in a less soluble interface. Therefore, the chemical composition of the SEI is stable over cycling. Those findings confer to Li2C4O4 the ability to tune the SEI of the devices, enabling its use in LICs and LIBs not only as a prelithiation agent but also as a film-forming additive.

Toward High-Energy-Density Initial-Anode-Free Lithium-Metal Batteries via Ultra-Thin Protective Ion-Transport-Promoting Interface Modification and Surface Prelithiation

Anode-free lithium-metal batteries (AFLMBs) are desirable candidates for achieving high-energy-density batteries, while severe active Li+ loss and uneven Li plating/stripping behavior impede their practical application. Herein, a trilaminar LS-Cu (LiCPON + Si/C-Cu) current collector is fabricated by radio frequency magnetron sputtering, including a Si/C hybrid lithiophilic layer and a supernatant carbon-incorporated lithium phosphorus oxynitride (LiCPON) solid-state electrolyte layer. Joint experimental and computational characterizations and simulations reveal that the LiCPON solid-state electrolyte layer can decompose into an in situ stout ion-transport-promoting protective layer, which can not only regulate homogeneous Li plating/stripping behavior but also inhibit the pulverization and deactivation of Si/C hybrid lithiophilic layer. When combined with surface prelithiated Li1.2Ni0.13Co0.13Mn0.54O2 (Preli-LRM) cathode, the Preli-LRM||LS-Cu full cell delivers 896.1 Wh kg-1 initially and retains 354.1 Wh kg-1 after 50 cycles. This strategy offers an innovative design of compensating for active Li+ loss and inducing uniform Li plating/stripping behavior simultaneously for the development of AFLMBs.

Solution-Based Deep Prelithiation for Lithium-Ion Capacitors with High Energy Density

Lithium-ion capacitors (LICs) exhibit superior power density and cyclability compared to lithium-ion batteries. However, the low initial Coulombic efficiency (ICE) of amorphous carbon anodes (e.g., hard carbon (HC) and soft carbon (SC)) limits the energy density of LICs by underutilizing cathode capacity. Here, a solution-based deep prelithiation strategy for carbon anodes is applied using a contact-ion pair dominant solution, offering high energy density based on a systematic electrode balancing based on the cathode capacity increased beyond the original theoretical limit. Increasing the anode ICE to 150% over 100%, the activated carbon (AC) capacity is doubled by activating Li+ cation storage, which unleashes rocking-chair LIC operation alongside the dual-ion-storage mechanism. The increased AC capacity results in an energy density of 106.6 Wh kg-1 AC+SC, equivalent to 281% of that of LICs without prelithiation. Moreover, this process lowers the cathode-anode mass ratio, reducing the cell thickness by 67% without compromising the cell capacity. This solution-based deep chemical prelithiation promises high-energy LICs based on transition metal-free, earth-abundant active materials to meet the practical demands of power-intensive applications.

Confronting Sulfur Electrode Passivation and Li Metal Electrode Degradation in Lithium-Sulfur Batteries Using Thiocyanate Anion

Salt anions with a high donor number (DN) enable high sulfur utilization in lithium-sulfur (Li-S) batteries by inducing three-dimensional (3D) Li₂ S growth. However, their insufficient compatibility with Li metal electrodes limits their cycling stability. Herein, a new class of salt anion, thiocyanate (SCN^- ), is presented, which features a Janus character of electron donor and acceptor. Due to a strong Li⁺ coordination by SCN^- and the direct interaction of SCN^- with polysulfide anions, the LiSCN electrolyte has a remarkably high lithium polysulfide solubility. This electrolyte induces 3D Li₂ S formation and ameliorates cathode passivation, even more than Br^- , a typical high DN anion. Moreover, SCN^- forms a Li₃ N-enriched stable SEI layer at the surface of the Li metal electrode, enhancing cycling stability. A Li-S battery with the LiSCN electrolyte shows high current density operation (2.54 mA cm⁻² ) with high discharge capacity (1133 mAh g⁻¹ ) and prolonged cycle life (100 cycles). This work demonstrates that the cathode and anode performance in a Li-S battery can be simply and concurrently enhanced by the single salt anion.

Crystallization behavior of polyvinylidene fluoride (PVDF) in NMP/DMF solvents: a molecular dynamics study

In this study, the crystallization behavior of polyvinylidene fluoride (PVDF) in NMP/DMF solvent at 9 to 67 weight percent (wt%) was analyzed by molecular dynamics (MD) simulation. The PVDF phase did not gradually change with the incremental increase in PVDF wt%, but displayed rapid shifts at 34 and 50 wt% in both solvents. The solvation behavior between the two solvents was quite identical from the similar radial distribution functions. However, PVDFs in DMF solvent showed a higher ratio of β phase crystalline structures than those in NMP solvent. It was found that DMF solvents were more tightly packed near trans state PVDF fluorine compared to NMP solvents. Also, NMP oxygen atoms interacted more favorably with gauche state PVDF hydrogen atoms over DMF oxygen atoms. The evaluation of properties observed in atomic scale interactions, such as trans state inhibition and gauche state preference, can be used as indicators in future solvent research.

Opportunities and Challenges of Li2 C4 O4 as Pre-Lithiation Additive for the Positive Electrode in NMC622||Silicon/Graphite Lithium Ion Cells

Silicon (Si)-based negative electrodes have attracted much attention to increase the energy density of lithium ion batteries (LIBs) but suffer from severe volume changes, leading to continuous re-formation of the solid electrolyte interphase and consumption of active lithium. The pre-lithiation approach with the help of positive electrode additives has emerged as a highly appealing strategy to decrease the loss of active lithium in Si-based LIB full-cells and enable their practical implementation. Here, the use of lithium squarate (Li2 C4 O4 ) as low-cost and air-stable pre-lithiation additive for a LiNi0.6 Mn0.2 Co0.2 O2 (NMC622)-based positive electrode is investigated. The effect of additive oxidation on the electrode morphology and cell electrochemical properties is systematically evaluated. An increase in cycle life of NMC622||Si/graphite full-cells is reported, which grows linearly with the initial amount of Li2 C4 O4 , due to the extra Li+ ions provided by the additive in the first charge. Post mortem investigations of the cathode electrolyte interphase also reveal significant compositional changes and an increased occurrence of carbonates and oxidized carbon species. This study not only demonstrates the advantages of this pre-lithiation approach but also features potential limitations for its practical application arising from the emerging porosity and gas development during decomposition of the pre-lithiation additive.

Prelithiation Bridges the Gap for Developing Next-Generation Lithium-Ion Batteries/Capacitors

The ever-growing market of portable electronics and electric vehicles has spurred extensive research for advanced lithium-ion batteries (LIBs) with high energy density. High-capacity alloy- and conversion-type anodes are explored to replace the conventional graphite anode. However, one common issue plaguing these anodes is the large initial capacity loss caused by the solid electrolyte interface formation and other irreversible parasitic reactions, which decrease the total energy density and prevent further market integration. Prelithiation becomes indispensable to compensate for the initial capacity loss, enhance the full cell cycling performance, and bridge the gap between laboratory studies and the practical requirements of advanced LIBs. This review summarizes the various emerging anode and cathode prelithiation techniques, the key barriers, and the corresponding strategies for manufacturing-compatible and scalable prelithiation. Furthermore, prelithiation as the primary Li⁺ donor enables the safe assembly of new-configured "beyond LIBs" (e.g., Li-ion/S and Li-ion/O₂ batteries) and high power-density Li-ion capacitors (LICs). The related progress is also summarized. Finally, perspectives are suggested on the future trend of prelithiation techniques to propel the commercialization of advanced LIBs/LICs.

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

HIGHLIGHTS

Interfacial bonding strategy has been successfully applied to address the high overpotential issue of sacrificial additives, which reduced the decompositon potential of Na2C2O4 from 4.50 to 3.95 V. Ultra-low-dose technique assisted commercial sodium ion capacitor (AC//HC) could deliver a remarkable energy density of 118.2 Wh kg-1 as well as excellent cycle stability. In-depth decomposition mechanism of sacrificial compound and the relative influence after pre-metallation were revealed by advanced in situ and ex situ characterization approaches. 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 (M2C2O4), 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 Li2C2O4/K2C2O4 as pre-metallation reagent, which will convincingly promote the commercialization of MICs.

Enhancement of lithium-mediated ammonia synthesis by addition of oxygen

[Figure: see text].

Electronic Effect and Regiochemistry of Substitution in Pre-sodiation Chemistry

The low oxidation potential of a pre-sodiation cathode additive intrinsically prevents decomposition of the electrolyte. Although the introduction of electron-donating substitution reduces the oxidation potential, the additional molecular weight restricts the output capacity. Herein, as theroretically predicted, the electrochemical oxidation potential of sodium carboxylate is manipulated by the electronic effect and regiochemistry of the functionality, in which the stronger electron-donating substituent, p-π conjugation, and optimized regiochemistry can dramatically lead to the lower potential originated from the elevation of the highest occupied molecular orbital level. Thus, benefiting from the para-NH₂ unit accompanied by a conjugated aromatic architecture, molecularly engineered sodium para-aminobenzoate (PABZ-Na) presents a reduced oxidation plateau of 3.45 V. Triggered by the positive compensation merit, sodium-based electrochemical storage systems manifest excellent electrochemical performances. This breakthrough sheds light into the correlation between the electronic effect of the functional group and the oxidation potential of the organic additive, affording in-depth insights into the fundamental guidance of pre-sodiation chemistry.

Graphene-Based Cathode Materials for Lithium-Ion Capacitors: A Review

Lithium-ion capacitors (LICs) are attracting increasing attention because of their potential to bridge the electrochemical performance gap between batteries and supercapacitors. However, the commercial application of current LICs is still impeded by their inferior energy density, which is mainly due to the low capacity of the cathode. Therefore, tremendous efforts have been made in developing novel cathode materials with high capacity and excellent rate capability. Graphene-based nanomaterials have been recognized as one of the most promising cathodes for LICs due to their unique properties, and exciting progress has been achieved. Herein, in this review, the recent advances of graphene-based cathode materials for LICs are systematically summarized. Especially, the synthesis method, structure characterization and electrochemical performance of various graphene-based cathodes are comprehensively discussed and compared. Furthermore, their merits and limitations are also emphasized. Finally, a summary and outlook are presented to highlight some challenges of graphene-based cathode materials in the future applications of LICs.

Molecularly Compensated Pre-Metallation Strategy for Metal-Ion Batteries and Capacitors

The use of a sacrificial cathode additive as a pre-metallation method could ensure adequate metal sources for advanced energy storage devices. However, this pre-metallation technique suffers from the precise regulation of decomposition potential of additive. Herein, a molecularly compensated pre-metallation (Li/Na/K) strategy has been achieved through Kolbe electrolysis, in which the electrochemical oxidation potential of a metal carboxylate is manipulated by the bonding energy of the oxygen-metal (O-M) moiety. The electron-donating effect of the substituent and the low charge density of the cation can dramatically weaken the O-M bond strength, further bringing out the reduced potential. Thus, sodium acetate exhibits a superior pre-sodiation feature for sodium-ion battery accompanied with a large irreversible specific capacity of 301.8 mAh g^-1 , remarkably delivering 70.6 % enhanced capacity retention in comparison to the additive-free system after 100 cycles. This methodology has been extended to construct a high-performance lithium-ion battery and a lithium/sodium/potassium-ion capacitor.

Cationic intermediates assisted self-assembly two-dimensional Ti3C2Tx/rGO hybrid nanoflakes for advanced lithium-ion capacitors

Two-dimensional (2D) material MXenes have been intensively concerned in energy-storage field due to these unique properties of metallic-like conductivity, good hydrophilicity and high volumetric capacity. However, the self-restocking of ultra-thin 2D materials seriously hinders these performances, which significantly inhibits the full exploitation of MXenes in the field of energy storage. To solve this issue, a strategy to prepare delaminated Ti₃C₂T_x (MXene) nanoflakes/reduced graphene oxide (rGO) composites is proposed using the electrostatic self-assembly between positively charged Ti₃C₂T_x with tetrabutylammonium ion (TBA⁺) modification and negatively charged graphene. The nanoflakes of Ti₃C₂T_x/rGO are well dispersed and arranged in a face-to-face structure to effectively alleviate the self-restacking and provide more electroactive sites for accessible of electrolyte ions. The prepared delaminated Ti₃C₂T_x/rGO anode shows a high reversible capacity up to 1394 mAh g^-1 at a current density of 50 mA g^-1. Moreover, a lithium-ion capacitor (LIC) was assembled with delaminated Ti₃C₂T_x/rGO anode and activated carbon (AC) cathode which can exhibit a specific capacity of 70.7 F g^-1 at a current density of 0.1 A g^-1 and deliver an ultrahigh energy density of 114 Wh kg^-1 at a relatively high power density of 3125 W kg^-1. These good electrochemical performances demonstrate the potential of delaminated Ti₃C₂T_x/rGO as an anode material for lithium-ion capacitors.

Prelithiation: A Crucial Strategy for Boosting the Practical Application of Next-Generation Lithium Ion Battery

With the urgent market demand for high-energy-density batteries, the alloy-type or conversion-type anodes with high specific capacity have gained increasing attention to replace current low-specific-capacity graphite-based anodes. However, alloy-type and conversion-type anodes have large initial irreversible capacity compared with graphite-based anodes, which consume most of the Li⁺ in the corresponding cathode and severely reduces the energy density of full cells. Therefore, for the practical application of these high-capacity anodes, it is urgent to develop a commercially available prelithiation technique to compensate for their large initial irreversible capacity. At present, various prelithiation methods for compensating the initial irreversible capacity of the anode have been reported, but due to their respective shortcomings, large-scale commercial applications have not yet been achieved. In this review, we have systematically summarized and analyzed the advantages and challenges of various prelithiation methods, providing enlightenment for the further development of each prelithiation strategy toward commercialization and thus facilitating the practical application of high-specific-capacity anodes in the next-generation high-energy-density lithium-ion batteries.

Mechanistic implications of Li-S cell function through modification of organo-sulfur cathode architectures

Copolymeric organo-sulfur based electrodes provide a unique framework to explore and subsequently improve lithium-sulfur (Li-S) cells. There is a general difference in the way copolymers trap lithium during cell function compared to inorganic carbon-sulfur composites. Using a chain-like polyterpene copolymeric architecture involving the copolymerization of squalene monomer with sulfur (poly(S-r-squalene)), the first evidence for distinguishable differences in the entrapment of lithiated species, when using different copolymeric architectures, is provided. Investigation of poly(S-r-squalene) as an active cathode material via X-ray Absorption Near-Edge Structure (XANES) spectroscopy and high-resolution solid-state Nuclear Magnetic Resonance (NMR) reveal notable differences compared to previously studied poly(S-r-DIB) (proposed to have a less branched architecture) between the lithium environments present during electrochemistry that can be directly linked to the copolymeric structural features. Subtle but pertinent effects based on the copolymeric architecture related to the solid-electrolyte interphase (SEI) formed from the electrolytic components are also uncovered through these techniques. This work offers a comprehensive study on poly(S-r-squalene) and reveals that foundational inverse vulcanisation conditions such as choice of crosslinking monomer can dramatically impact lithium transport and SEI formation for the copolymeric electrode.

"Water in salt/ionic liquid" electrolyte for 2.8 V aqueous lithium-ion capacitor

Development of high-voltage electrolytes with non-flammability is significantly important for future energy storage devices. Aqueous electrolytes are inherently non-flammable, easy to handle, and their electrochemical stability windows (ESWs) can be considerably expanded by increasing electrolyte concentrations. However, further breakthroughs of their ESWs encounter bottlenecks because of the limited salt solubility, leading to that most of the high-energy anode materials can hardly function reversibly in aqueous electrolytes. Here, by introducing a non-flammable ionic liquid as co-solvent in a lithium salt/water system, we develop a "water in salt/ionic liquid" (WiSIL) electrolyte with extremely low water content. In such WiSIL electrolyte, commercial niobium pentoxide (Nb₂O₅) material can operate at a low potential (-1.6 V versus Ag/AgCl) and contribute its full capacity. Consequently, the resultant Nb₂O₅-based aqueous lithium-ion capacitor is able to operate at a high voltage of 2.8 V along with long cycling stability over 3000 cycles, and displays comparable energy and power performance (51.9 Wh kg^-1 at 0.37 kW kg^-1 and 16.4 Wh kg^-1 at 4.9 kW kg^-1) to those using non-aqueous electrolytes but with improved safety performance and manufacturing efficiency.

3D-metal-embroidered electrodes: dreaming for next generation flexible and personalizable energy storage devices

Flexible and Personalizable battery is a promising candidate for energy storage, but suffers from the weldablity and large-scale producibility of the electrode. To address the issues, we design a nickel foam catalyzed electroless deposition (NFED) derived 3D-metal-pattern embroidered electrodes. This is the first attempt to utilize this type of electrode in battery field. It is found that the current collector can be embroidered on any selected areas of any complex-shape electrodes, with high controllability and economical feasibility. As a result, the electronic conductivity of the flexible electrodes can be improved by nearly one order of magnitude, which can be easily and firmly weldded to the metal tab using the industry generic ultrasonic heating process. The embroidered electrodes could substantially promote the electrochemical performance under bending deformation, with both Li-S and Li-LiFePO₄ batteries as the models. This innovation is also suitable to embroider all the VIII group elements on any electrodes with personalized shapes, which is widely attractive for the development of next generation flexible and personalizable energy storage devices.