10†µm-Level TiNb2 O7 Secondary Particles for Fast-Charging Lithium-Ion Batteries.

TiNb2 O7 with Wadsley-Roth phase delivers double theoretical specific capacity and similar working potential in comparison to spinel Li4 Ti5 O12 , the commercial high-rate anode material, and thus can enable much higher energy density of lithium-ion batteries. However, the inter-particle resistance within the high-mass-loading TiNb2 O7 electrode would impede the capacity release for practical application, especially under fast-charging conditions. Herein, 10-20 µm-size carbon-coated TiNb2 O7 secondary particle (SP-TiNb2 O7 ) consisting of initial micro-scale TiNb2 O7 particles (MP-TiNb2 O7 ) was fabricated. The high crystallinity of active material could enable fast-charge diffusion and electrochemical reaction rate within particles, and the small number of stacking layers of SP-TiNb2 O7 could reduce the large inter-particle resistance that regular particle electrode often possess and achieve high compaction density of electrodes with high mass loading. The investigation on materials structure and electrochemical reaction kinetics verified the advances of the as-fabricated SP-TiNb2 O7 in achieving superior electrochemical performance. The SP-TiNb2 O7 exhibited high reversible capacity of 292.7 mAh g-1 in the potential range of 1-3 V (Li+ /Li) at 0.1 C, delivering high-capacity release of 94.3 %, and high capacity retention of 86 % at 0.5 C for 250 cycles in half cell configuration. Particularly, the advances of such an anode were verified in practical 5 Ah-level laminated full pouch cell. The as-assembled LiFePO4 ||TiNb2 O7 full cell exhibited a high capacity of 5.08 Ah at high charging rate of 6 C (77.9 % of that at 0.2 C of 6.52 Ah), as well as an ultralow capacity decay rate of 0.0352 % for 250 cycles at 1 C, suggesting the great potential for practical fast-charging lithium-ion batteries.

Probing Hybrid LiFePO4/FePO4 Phases in a Single Olive LiFePO4 Particle and Their Recovering from Degraded Electric Vehicle Batteries.

The recycling of LiFePO4 from degraded lithium-ion batteries (LIBs) from electric vehicles (EVs) has gained significant attention due to resource, environment, and cost considerations. Through neutron diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy, we revealed continuous lithium loss during battery cycling, resulting in a Li-deficient state (Li1-xFePO4) and phase separation within individual particles, where olive-shaped FePO4 nanodomains (5-10 nm) were embedded in the LiFePO4 matrix. The preservation of the olive-shaped skeleton during Li loss and phase change enabled materials recovery. By chemical compensation for the lithium loss, we successfully restored the hybrid LiFePO4/FePO4 structure to pure LiFePO4, eliminating nanograin boundaries. The regenerated LiFePO4 (R-LiFePO4) exhibited a high crystallinity similar to the fresh counterpart. This study highlights the importance of topotactic chemical reactions in structural repair and offers insights into the potential of targeted Li compensation for energy-efficient recycling of battery electrode materials with polyanion-type skeletons.

Realizing High Utilization of High-Mass-Loading Sulfur Cathode via Electrode Nanopore Regulation.

One main challenge of realizing high-energy-density lithium-sulfur batteries is low active materials utilization, excessive use of inert components, high electrolyte intake, and mechanical instability of high-mass-loading sulfur cathodes. Herein, chunky sulfur/graphene particle electrodes were designed, where active sulfur was confined in vertically aligned nanochannels (width ∼12 nm) of chunky graphene-based particles (∼70 µm) with N, O-containing groups. The short charge transport distance and low tortuosity enabled high utilization of active materials for high-mass-loading chunky sulfur/graphene particle electrodes. The intermediate polysulfide trapping effect by capillary effect and heteroatoms-containing groups, and a mechanically robust graphene framework, helped to realize stable electrode cycling. The as-designed electrode showed high areal capacity (10.9 mAh cm-2) and high sulfur utilization (72.4%) under the rigorous conditions of low electrolyte/active material ratio (∼2.5 µL mg-1) and high sulfur loading (9.0 mg cm-2), realizing high energy densities (520 Wh kg-1, 1635 Wh L-1).

Ultrafast Metal Electrodeposition Revealed by In Situ Optical Imaging and Theoretical Modeling towards Fast-Charging Zn Battery Chemistry.

Metallic Zn is a preferred anode material for rechargeable aqueous batteries towards a smart grid and renewable energy storage. Understanding how the metal nucleates and grows at the aqueous Zn anode is a critical and challenging step to achieve full reversibility of Zn battery chemistry, especially under fast-charging conditions. Here, by combining in situ optical imaging and theoretical modeling, we uncover the critical parameters governing the electrodeposition stability of the metallic Zn electrode, that is, the competition among crystallographic thermodynamics, kinetics, and Zn2+ -ion diffusion. Moreover, steady-state Zn metal plating/stripping with Coulombic efficiency above 99 % is achieved at 10-100 mA cm-2 in a reasonably high concentration (3 M) ZnSO4 electrolyte. Significantly, a long-term cycling-stable Zn metal electrode is realized with a depth of discharge of 66.7 % under 50 mA cm-2 in both Zn||Zn symmetrical cells and MnO2 ||Zn full cells.

Engineering a Low-Strain Si@TiSi2@NC Composite for High-Performance Lithium-Ion Batteries.

The huge volume expansion/contraction of silicon (Si) during the lithium (Li) insertion/extraction process, which can lead to cracking and pulverization, poses a substantial impediment to its practical implementation in lithium-ion batteries (LIBs). The development of low-strain Si-based composite materials is imperative to address the challenges associated with Si anodes. In this study, we have engineered a TiSi2 interface on the surface of Si particles via a high-temperature calcination process, followed by the introduction of an outermost carbon (C) shell, leading to the construction of a low-strain and highly stable Si@TiSi2@NC composite. The robust TiSi2 interface not only enhances electrical and ionic transport but also, more critically, significantly mitigates particle cracking by restraining the stress/strain induced by volumetric variations, thus alleviating pulverization during the lithiation/delithiation process. As a result, the as-fabricated Si@TiSi2@NC electrode exhibits a high initial reversible capacity (2172.7 mAh g-1 at 0.2 A g-1), superior rate performance (1198.4 mAh g-1 at 2.0 A g-1), and excellent long-term cycling stability (847.0 mAh g-1 after 1000 cycles at 2.0 A g-1). Upon pairing with LiNi0.6Co0.2Mn0.2O2 (NCM622), the assembled Si@TiSi2@NC||NCM622 pouch-type full cell exhibits exceptional cycling stability, retaining 90.1% of its capacity after 160 cycles at 0.5 C.

Reaction-passivation mechanism driven materials separation for recycling of spent lithium-ion batteries.

Development of effective recycling strategies for cathode materials in spent lithium-ion batteries are highly desirable but remain significant challenges, among which facile separation of Al foil and active material layer of cathode makes up the first important step. Here, we propose a reaction-passivation driven mechanism for facile separation of Al foil and active material layer. Experimentally, >99.9% separation efficiency for Al foil and LiNi0.55Co0.15Mn0.3O2 layer is realized for a 102 Ah spent cell within 5 mins, and ultrathin, dense aluminum-phytic acid complex layer is in-situ formed on Al foil immediately after its contact with phytic acid, which suppresses continuous Al corrosion. Besides, the dissolution of transitional metal from LiNi0.55Co0.15Mn0.3O2 is negligible and good structural integrity of LiNi0.55Co0.15Mn0.3O2 is well-maintained during the processing. This work demonstrates a feasible approach for Al foil-active material layer separation of cathode and can promote the green and energy-saving battery recycling towards practical applications.

Locking Active Li Metal through Localized Redistribution of Fluoride Enabling Stable Li-Metal Batteries.

The creation of fluorinated interphase has emerged as an effective strategy for improving Li-metal anodes for rechargeable high-energy batteries. In contrast to the introduction of fluorine-containing species through widely adopted electrolyte engineering, a Li-metal composite design is reported in which LiF can locally redistribute on the Li-metal surface in liquid electrolytes via a dissolution-reprecipitation mechanism, and enable the formation of a high-fluorine-content solid electrolyte interphase (SEI). For validation, a Li/Li22 Sn5 /LiF ternary composite is investigated, where the as-formed LiF-rich SEI locks the active Li metal from corrosive electrolyte. The Li/Li22 Sn5 /LiF anode displays an impressive average Coulombic efficiency (ACE, ≈99.2%) at 1 mA cm-2 and 1 mAh cm-2 in a carbonate electrolyte and a remarkable cycling life of over 1600 h at 1 mA cm-2 and 2 mAh cm-2 . Applied to a LiCoO2 full cell with a high cathode areal capacity of 4.0 mAh cm-2 , a high capacity retention of ≈91.1% is realized for 100 cycles at 0.5 C between 2.8 to 4.5 V with a low negative/positive (N/P) ratio of 2:1. This design is conceptually different from the design employing the widely used fluorine-containing electrolyte additive and provides an alternative approach to realize reliable Li-metal batteries.

Micrometer-scale single crystalline particles of niobium titanium oxide enabling an Ah-level pouch cell with superior fast-charging capability.

Wadsley-Roth phase niobium titanium oxide (TiNb2O7) is widely regarded as a promising anode candidate for fast-charging lithium-ion batteries due to its safe working potential and doubled capacity in comparison to the commercial fast-charging anode material (lithium titanium oxide, Li4Ti5O12). Although good fast charge/discharge performance was shown for nanostructured TiNb2O7, the small size would cause the low electrode compensation density and energy density of batteries, as well as parasitic reactions. Fundamental understanding of the electrochemical lithium insertion/extraction process and the structural evolution for the micrometer-scale single crystalline TiNb2O7 (MSC-TiNb2O7) could provide insights to understand its inherent properties and possibility for fast-charging application. Here, we revealed the highly reversible structural evolution of the MSC-TiNb2O7 during the lithiation/delithiation processes. Interestingly, an ion-conductive lithium niobate interphase was in situ formed on the MSC-TiNb2O7 surface during the formation cycle, which could facilitate fast ion diffusion on the material surface and support fast electrochemical reaction kinetics. Experimentally, the MSC-TiNb2O7 delivered a high reversible capacity of 291.9 mA h g-1 at 0.5C with a high initial Coulombic efficiency (>95%), and showed superb rate capability with a reasonable capacity of 55.6 mA h g-1 under a high current density of 40C. An Ah-level pouch cell with a lithium cobalt oxide (LiCoO2) cathode exhibited 91.5% capacity retention at 3C charging rate, which revealed the significant role of high crystallinity and in situ formation of an ion conductive nano-interphase in realizing fast charging capability of practical TiNb2O7-based lithium-ion batteries.

Nanocomposite of Conducting Polymer and Li Metal for Rechargeable High Energy Density Batteries.

The structure and electrochemical performance of lithium (Li) metal degrade quickly owing to its hostless nature and high reactivity, hindering its practical application in rechargeable high energy density batteries. In order to enhance the electrochemical reversibility of metallic Li, we designed a Li/Li2S-poly(acrylonitrile) (LSPAN) composite foil via a facile mechanical kneading approach using metallic Li and sulfurized poly(acrylonitrile) as the raw materials. The uniformly dispersed Li2S-poly(acrylonitrile) (Li2S-PAN) in a metallic Li matrix buffered the volume change on cycling, and its high Li ion conductivity enabled fast Li ion diffusion behavior of the composite electrode. As expected, the LSPAN electrode showed reduced voltage polarization, enhanced rate capability, and prolonged cycle life compared with the pure Li electrode. It exhibited stable cycling for 600 h with a symmetric cell configuration at 1 mA cm-2 and 1 mA h cm-2, far outperforming the pure metallic Li counterpart (400 h). Also, the LiCoO2||LSPAN full cells with a cathode mass loading of ∼16 mg cm-2 worked stably for 100 cycles at 0.5 C with a high capacity retention of 96.5%, while the LiCoO2||Li full cells quickly failed within only 50 cycles.

Stable interphase chemistry of textured Zn anode for rechargeable aqueous batteries.

Despite the advances of aqueous zinc (Zn) batteries as sustainable energy storage systems, their practical application remains challenging due to the issues of spontaneous corrosion and dendritic deposits at the Zn metal anode. In this work, conformal growth of zinc hydroxide sulfate (ZHS) with dominating (001) facet was realized on (002) plane-dominated Zn metal foil fabricated through a facile thermal annealing process. The ZHS possessed high Zn2+ conductivity (16.9 mS cm-1) and low electronic conductivity (1.28 × 104 Ω cm), and acted as a heterogeneous and robust solid electrolyte interface (SEI) layer on metallic Zn electrode, which regulated the electrochemical Zn plating behavior and suppressed side reactions simultaneously. Moreover, low self-diffusion barrier along the (002) plane promoted the 2D diffusion and horizontal electrochemical plating of metallic Zn for (002)-textured Zn electrode. Consequently, the as-achieved Zn electrode exhibited remarkable cycling stability over 7000 cycles at 2 mA cm-2 and 0.5 mAh cm-2 with a low overpotential of 25 mV in symmetric cells. Pairing with a MnO2 cathode, the as-achieved Zn electrode achieved stable cell cycling with 92.7% capacity retention after 1000 cycles at 10 C with a remarkable average Coulombic efficiency of 99.9%.

Addressing the Low Solubility of a Solid Electrolyte Interphase Stabilizer in an Electrolyte by Composite Battery Anode Design.

Metallic sodium (Na) has been regarded as one of the most attractive anodes for Na-based rechargeable batteries due to its high specific capacity, low working potential, and high natural abundance. However, several important issues hinder the practical application of the metallic Na anode, including its high reactivity with electrolytes, uncontrolled dendrite growth, and poor processability. Metal nitrates are common electrolyte additives used to stabilize the solid electrolyte interphase (SEI) on Na anodes, though they typically suffer from poor solubility in electrolyte solvents. To address these issues, a Na/NaNO3 composite foil electrode was fabricated through a mechanical kneading approach, which featured uniform embedment of NaNO3 in a metallic Na matrix. During the battery cycling, NaNO3 was reduced by metallic Na sustainably, which addressed the issue of low solubility of an SEI stabilizer. Due to the supplemental effect of NaNO3, a stable SEI with NaNxOy and Na3N species was produced, which allowed fast ion transport. As a result, stable electrochemical performance for 600 h was achieved for Na/NaNO3||Na/NaNO3 symmetric cells at a current density of 0.5 mA cm-2 and an areal capacity of 0.5 mAh cm-2. A Na/NaNO3||Na3V2(PO4)2O2F cell with active metallic Na of ∼5 mAh cm-2 at the anode showed stable cycling for 180 cycles. In contrast, a Na||Na3V2(PO4)2O2F cell only displayed less than 80 cycles under the same conditions. Moreover, the processability of the Na/NaNO3 composite foil was also significantly improved due to the introduction of NaNO3, in contrast to the soft and sticky pure metallic Na. Mechanical kneading of soft alkali metals and their corresponding nitrates provides a new strategy for the utilization of anode stabilizers (besides direct addition into electrolytes) to improve their electrochemical performance.

A Chemically Polished Zinc Metal Electrode with a Ridge-like Structure for Cycle-Stable Aqueous Batteries.

Aqueous rechargeable zinc (Zn) metal batteries show great application prospects in grid-scale energy storage devices due to their good safety, low cost, and considerable energy density. However, the electrical and topographical inhomogeneity caused by the native passivation layer of metallic Zn foil leads to inhomogeneous electrochemical plating and stripping of metallic Zn, and the limited accessible area to the electrolyte of the regular foil electrode causes the poor rate capability, which together hinder the practical application of the Zn metal electrode in rechargeable aqueous batteries. In this work, we show that the native passivation layer on the Zn foil electrode can be removed by a simple chemical polishing strategy, associated with the formation of a three-dimensional ridge-like structure of metallic Zn (r-Zn) on the surface of the Zn foil electrode due to the selective etching of weak crystallographic planes and grain boundary of metallic Zn. The clean and uniform surface of the metallic Zn electrode enables homogeneous plating and stripping of metallic Zn, and the ridge-like structure of r-Zn increases the accessible surface area to the electrolyte and reduces the local current density, which elevates the electrochemical performance of the Zn metal anode with regard to the cycling stability and rate capability. It is demonstrated that a r-Zn anode cycles stably for over 200 h at 1 mA cm-2 and 0.5 mA h cm-2 with a low overpotential of 20 mV, which far outperforms 39 h of cycling with an overpotential of 72 mV for its pristine metallic Zn counterpart.

(001) Facet-Dominated Hierarchically Hollow Na2Ti3O7 as a High-Rate Anode Material for Sodium-Ion Capacitors.

Sodium-ion capacitors (SICs) have shown great potential to combine the merits of high-power capability of traditional capacitors and high energy capability of batteries. However, the sluggish kinetics and inferior stability of conventional sodium-ion storage anode materials are major challenges for the practical utilization of SICs. In this work, interconnected urchin-like hollow Na2Ti3O7 (Na2Ti3O7-IcUH) chains were designed and prepared by a simple one-step template-assisting method. Through a variety of controlled experiments, we explored how to effectively engineer the crystal-oriented growth and string the urchin-like spheres together. Benefiting from its urchin-like hollow structure and fully exposed (001) facet, the resulting Na2Ti3O7-IcUH exhibits a superior rate capability of 96.2 mA h g-1 at 5 A g-1. Meanwhile, the interconnected three-dimensional primary structure endows Na2Ti3O7-IcUH with excellent cyclic stability (15% capacity loss at 5 A g-1 after 2000 cycles). By coupling with commercial active carbon, the assembled SIC successfully demonstrates a energy density of 134.3 W h kg-1 at a power density of 125 W kg-1 and 38.2 W h kg-1 at a high-power density of 2500 W kg-1, as well as a superior capacity retention of 75% after 2000 cycles at 2 A g-1 within 1-4 V.

Novel CdFe Bimetallic Complex-Derived Ultrasmall Fe- and N-Codoped Carbon as a Highly Efficient Oxygen Reduction Catalyst.

During the development of oxygen reduction reaction electrocatalysts, transition-metal nanoparticles embedded in N-doped graphene have attracted increasing attention owing to their low-priced, minimal environmental impact, and satisfying performance. In this study, a new organic-cadmium (Cd) complex formed through Cd2+ coordination with p-phenylenediamine (PPD) was used to synthesize highly active Fe-embedded N-doped carbon catalysts for the first time. It is significant that with the decreasing molar ratio of Cd/Fe, an obvious microstructure evolution was observed in Cd-Fe-PPD from diamond-like blocks to thick flakes, and further bloomed into flowerlike shapes with ultrathin petals and then eventually exhibited large block starfish-like shapes. After carbonization, Cd was removed, slack and porous N-doped carbon was formed, and Fe was assembled in the N-doped carbon. Similar phenomenon was also observed in Co-PPD. The optimized Fe/NPC-2 material featuring uniform and well-dispersed 3-5 nm Fe nanoparticles embedded in two-dimensional ultrathin carbon nanosheets delivered excellent electrocatalytic performance ( Eonset: 0.96 V vs reversible hydrogen electrode (RHE), E1/2: 0.84 V vs RHE), which is very close to those of commercial platinum on carbon (Pt/C) ( Eonset: 0.95 V vs RHE, E1/2: 0.84 V vs RHE), and its methanol tolerance and durability also surpass those of Pt/C.

High-Rate and Long-Life Sodium-Ion Batteries Based on Sponge-like Three-Dimensional Porous Na-Rich Ferric Pyrophosphate Cathode Material.

Sponge-like three-dimensional porous carbon-encapsulated Na3.32Fe2.34(P2O7)2 nanoparticles (labeled to NFPO@SC) were manufactured by a sol-gel method followed by multistage calcinations and utilized as the cathode material for sodium-ion batteries. The excellent electrochemical performance of the NFPO@SC cathode can be attributed to its unique porous structure, which facilitates electrolyte penetration, reduces the diffusion path of sodium ions, and increases electronic conductivity. In addition, the full battery is assembled by NFPO@SC and hard carbon, which are employed as cathode and anode electrodes, respectively. The full battery delivers a high discharge capacity (112.2 mA h g-1 at 0.5 C) and maintains 93.9% stable capacity over 1000 cycles at 5 C.

Rechargeable K-Se batteries based on metal-organic-frameworks-derived porous carbon matrix confined selenium as cathode materials.

In this work, porous carbon matrix derived from metal-organic frameworks is synthesized by a facile carbonation process for confining element selenium. The Se/nitrogen-doped porous carbon composite is applied as the cathode for rechargeable K-Se batteries for the first time. The abundant and hierarchical porous structure is advantageous in overcoming the volume expansion problem caused by polyselenides during discharge-charge process. The in-situ nitrogen-doped porous carbon enhances electronic conductivity of the cathode composite material. The electrochemical result shows that the as-obtained Se/nitrogen-doped porous carbon composite with Se content of 53% delivers good rate capacity with coulombic efficiency of nearly ∼90% and a reversible cycling capacity of 327 mA h g-1 at 0.2 C, maintaining about 130 mA h g-1 even after 100 cycles.

Manipulating irreversible phase transition of NaCrO2 towards an effective sodium compensation additive for superior sodium-ion full cells.

During the first charge process of full cells, a solid electrolyte interphase (SEI) film is formed when the active ion from the cathode is consumed, resulting in irreversible capacity loss. This phenomenon has shown to be more serious in sodium-ion full cells than in lithium-ion full cells. Although many strategies have been employed to alleviate the loss of sodium ions, such as presodiation and construction of an artificial solid electrolyte interface, they are both cumbersome and time-consuming. For the first time, NaCrO2 was used as an effective self-sacrificing sodium compensation additive in sodium-ion full cells due to the irreversible phase transition of NaCrO2 in a high voltage region can deliver an irreversible capacity of up to 230 mAh g-1. Based on this design, sodium-ion full cells coupled with hard carbon as the anode exhibited higher capacity, less polarization, greater energy density, and superior cycle stability than those of a pristine electrode. This is mainly attributed to the removal of sodium ions from NaCrO2, which compensates for the loss of sodium ions consumed during the formation of the SEI film on the anode surface during the first charge process. Overall, this work opens up a new avenue for exploring sodium compensation strategy and contributing to practical application of sodium-ion full cells.