Ultra-thin and Mechanically Stable LiCoO2 -Electrolyte Interphase Enabled by Mg2+ Involved Electrolyte.

LiCoO2 (LCO) cathode materials have attracted significant attention for its potential to provide higher energy density in current Lithium-ion batteries (LIBs). However, the structure and performance degradation are exacerbated by increasing voltage due to the catastrophic reaction between the applied electrolyte and delithiated LCO. The present study focuses on the construction of physically and chemically robust Mg-integrated cathode-electrolyte interface (MCEI) to address this issue, by incorporating Magnesium bis(trifluoromethanesulfonyl)imide (Mg[TFSI]2 ) as an electrolyte additive. During formation cycles, the strong MCEI is formed and maintained its 2 nm thickness throughout long-term cycling. Notably, Mg is detected not only in the robust MCEI, but also imbedded in the surface of the LCO lattice. As a result, the parasitic interfacial side reactions, surface phase reconstruction, particle cracking, Co dissolution and shuttling are considerably suppressed, resulting in long-term cycling stability of LCO up to 4.5 V. Therefore, benefit from the double protection of the strong MCEI, the Li||LCO coin cell and the Ah-level Graphite||LCO pouch cell exhibit high capacity retention by using Mg-electrolyte, which are 88.13% after 200 cycles and 90.4% after 300 cycles, respectively. This work provides a novel approach for the rational design of traditional electrolyte additives.

Synergetic Dual-Additive Electrolyte Enables Highly Stable Performance in Sodium Metal Batteries.

Sodium (Na)-metal batteries (SMBs) are considered one of the most promising candidates for the large-scale energy storage market owing to their high theoretical capacity (1,166 mAh g-1) and the abundance of Na raw material. However, the limited stability of electrolytes still hindered the application of SMBs. Herein, sulfolane (Sul) and vinylene carbonate (VC) are identified as effective dual additives that can largely stabilize propylene carbonate (PC)-based electrolytes, prevent dendrite growth, and extend the cycle life of SMBs. The cycling stability of the Na/NaNi0.68Mn0.22Co0.1O2 (NaNMC) cell with this dual-additive electrolyte is remarkably enhanced, with a capacity retention of 94% and a Coulombic efficiency (CE) of 99.9% over 600 cycles at a 5 C (750 mA g-1) rate. The superior cycling performance of the cells can be attributed to the homogenous, dense, and thin hybrid solid electrolyte interphase consisting of F- and S-containing species on the surface of both the Na metal anode and the NaNMC cathode by adding dual additives. Such unique interphases can effectively facilitate Na-ion transport kinetics and avoid electrolyte depletion during repeated cycling at a very high rate of 5 C. This electrolyte design is believed to result in further improvements in the performance of SMBs.

Inorganic Polysulfide Chemistries for Better Energy Storage Systems.

ConspectusSulfur-based cathode materials have become a research hot spot as one of the most promising candidates for next-generation, high-energy lithium batteries. However, the insulating nature of elemental sulfur or organosulfides has become the biggest challenge that leads to dramatic degradation and hinders their practical application. The disadvantage is more obvious for all-solid-state battery systems, which require both high electronic and ionic migration at the same sites to realize a complete electrochemical reaction. In addition to adding conductive components into the cathode composites, another effective way to realize high-reversibility sulfur-based cathodes is by optimizing the inherent nature of sulfur-based materials to make them "conductive". Inorganic polysulfide materials including polysulfide molecules, selenium-sulfur solid solutions, and (lithium) metal polysulfides are promising, as they have different structures that can make them intrinsically conductive or becoming conductive during lithiation. They all contain at least one -S-S- bridged bond, which is the intrinsic structural characteristic and the source of the chemical properties of these polysulfide compounds. For example, by balancing the conductivity and reversible capacity, researchers in the US National Aeronautics and Space Administration (NASA) have shown that 500 Wh/kg solid-state Li-Se/S batteries can power cars and even electric aircraft.We have long been focusing on the inorganic polysulfide component, reported the selenium-sulfur solid solutions, the first sulfur-rich phosphorus polysulfide molecules, and followed the research of metal polysulfide components. The proposed Account summarizes our current knowledge of the fundamental aspects of inorganic polysulfides in energy storage systems based on state-of-the-art publications on this topic. Both fast electron and ion migrations within the electrode materials are vital to achieving high-energy batteries. We begin by illustrating effective approaches to enhance the electronic/ionic conductivity of sulfur-based electrode materials. We then present some basic observations and properties (especially the intrinsic high conductivities) of the inorganic polysulfide electrode materials. The key chemical and structural factors dictating their conductive and electrochemical behaviors will be discussed. Finally, we show the advantages and broad applications of inorganic polysulfides in energy storage areas. The proposed Account will provide an insightful perspective on the current knowledge of inorganic polysulfide materials, as well as their future research directions and development potential, serving as a keynote reference for researchers in the field of energy storage.

A Dual Anion Chemistry-Based Superionic Glass Enabling Long-Cycling All-Solid-State Sodium-Ion Batteries.

Glassy Na-ion solid-state electrolytes (GNSSEs) are an important group of amorphous SSEs. However, the insufficient ionic conductivity of state-of-the-art GNSSEs at room temperature lessens their promise in the development of all-solid-state Na-ion batteries (ASSNIBs) with high energy density and improved safety. Here we report the discovery of a new sodium superionic glass, 0.5Na2 O2 -TaCl5 (NTOC), based on dual-anion sublattice of oxychlorides. The unique local structures with abundant bridging and non-bridging oxygen atoms contributes to a highly disordered Na-ion distribution as well as low Na+ migration barrier within NTOC, enabling an ultrahigh ionic conductivity of 4.62 mS cm-1 at 25 °C (more than 20 times higher than those of previously reported GNSSEs). Moreover, the excellent formability of glassy NTOC electrolyte and its high electrochemical oxidative stability ensure a favourable electrolyte-electrode interface, contributing to superior cycling stability of ASSNIBs for over 500 cycles at room temperature. The discovery of glassy NTOC electrolyte would reignite research enthusiasm in superionic glassy SSEs based on multi-anion chemistry.

A Universal Self-Propagating Synthesis of Aluminum-Based Oxyhalide Solid-State Electrolytes.

Inorganic solid-state electrolytes (SSEs) play a vital role in high-energy all-solid-state batteries (ASSBs). However, the current method of SSE preparation usually involves high-energy mechanical ball milling and/or a high-temperature annealing process, which is not suitable for practical application. Here, a facile strategy is developed to realize the scalable synthesis of cost-effective aluminum-based oxyhalide SSEs, which involves a self-propagating method by the exothermic reaction of the raw materials. This strategy enables the synthesis of various aluminum-based oxyhalide SSEs with tunable components and high ionic conductivities (over 10-3 S cm-1 at 25 °C) for different cations (Li+, Na+, Ag+). It is elucidated that the amorphous matrix, which mainly consists of various oxidized chloroaluminate species that provide numerous sites for smooth ion migration, is actually the key factor for the achieved high conductivities. Benefit from their easy synthesis, low cost, and low weight, the aluminum-based oxyhalide SSEs synthesized by our approach could further promote practical application of high-energy-density ASSBs.

The Universal Super Cation-Conductivity in Multiple-cation Mixed Chloride Solid-State Electrolytes.

As exciting candidates for next-generation energy storage, all-solid-state lithium batteries (ASSLBs) are highly dependent on advanced solid-state electrolytes (SSEs). Here, using cost-effective LaCl3 and CeCl3 lattice (UCl3 -type structure) as the host and further combined with a multiple-cation mixed strategy, we report a series of UCl3 -type SSEs with high room-temperature ionic conductivities over 10-3  S cm-1 and good compatibility with high-voltage oxide cathodes. The intrinsic large-size hexagonal one-dimensional channels and highly disordered amorphous phase induced by multi-metal cation species are believed to trigger fast multiple ionic conductions of Li+ , Na+ , K+ , Cu+ , and Ag+ . The UCl3 -type SSEs enable a stable prototype ASSLB capable of over 3000 cycles and high reversibility at -30 °C. Further exploration of the brand-new multiple-cation mixed chlorides is likely to lead to the development of advanced halide SSEs suitable for ASSLBs with high energy density.

A glance of the layered transition metal oxide cathodes in sodium and lithium-ion batteries: difference and similarities.

The fast-growing demand for energy storage devices has prompted diverse battery techniques, while the state-of-the-art Li-ion batteries (LIBs) continue to flourish, Na-ion batteries (SIBs) have been identified to be a promising alternative to share the burden with LIBs, particularly for large-scale grid storage applications. Both LIBs and SIBs techniques work based on similar fundamental mechanisms, with a heavy focus on the intercalation chemistry of layered transition metal oxides. However, the differences between Li-ion and Na-ion in terms of their size and Lewis acidity induce many different behaviors when crystallizing or diffusing in layered cathode materials. This minireview summarizes some typical cases where Li and Na-ion differ in layered cathode materials and discusses potential approaches to leverage their similarities and dissimilarities for future developments of high-performance SIBs.

Vacancy-Enabled O3 Phase Stabilization for Manganese-Rich Layered Sodium Cathodes.

Manganese-rich layered oxide materials hold great potential as low-cost and high-capacity cathodes for Na-ion batteries. However, they usually form a P2 phase and suffer from fast capacity fade. In this work, an O3 phase sodium cathode has been developed out of a Li and Mn-rich layered material by leveraging the creation of transition metal (TM) and oxygen vacancies and the electrochemical exchange of Na and Li. The Mn-rich layered cathode material remains primarily O3 phase during sodiation/desodiation and can have a full sodiation capacity of ca. 220 mAh g-1 . It delivers ca. 160 mAh g-1 specific capacity between 2-3.8 V with >86 % retention over 250 cycles. The TM and oxygen vacancies pre-formed in the sodiated material enables a reversible migration of TMs from the TM layer to the tetrahedral sites in the Na layer upon de-sodiation and sodiation. The migration creates metastable states, leading to increased kinetic barrier that prohibits a complete O3-P3 phase transition.

Size-Mediated Recurring Spinel Sub-nanodomains in Li- and Mn-Rich Layered Cathode Materials.

Li- and Mn-rich layered oxides are among the most promising cathode materials for Li-ion batteries with high theoretical energy density. Its practical application is, however, hampered by the capacity and voltage fade after long cycling. Herein, a finite difference method for near-edge structure (FDMNES) code was combined with in situ X-ray absorption spectroscopy (XAS) and transmission electron microscopy/electron energy loss spectroscopy (TEM/EELS) to investigate the evolution of transition metals (TMs) in fresh and heavily cycled electrodes. Theoretical modeling reveals a recurring partially reversible LiMn2 O4 -like sub-nanodomain formation/dissolution process during each charge/discharge, which accumulates gradually and accounts for the Mn phase transition. From the modeling of spectra and maps of the valence state over large regions of the cathodes, it was found that the phase change is size-dependent. After prolonged cycling, the TMs displayed different levels of inactivity.

Nitrogen and Fluorine-Codoped Carbon Nanowire Aerogels as Metal-Free Electrocatalysts for Oxygen Reduction Reaction.

The development of active, durable, and low-cost catalysts to replace noble metal-based materials is highly desirable to promote the sluggish oxygen reduction reaction in fuel cells. Herein, nitrogen and fluorine-codoped three-dimensional carbon nanowire aerogels, composed of interconnected carbon nanowires, were synthesized for the first time by a hydrothermal carbonization process. Owing to their porous nanostructures and heteroatom-doping, the as-prepared carbon nanowire aerogels, with optimized composition, present excellent electrocatalytic activity that is comparable to commercial Pt/C. Remarkably, the aerogels also exhibit superior stability and methanol tolerance. This synthesis procedure paves a new way to design novel heteroatom-doped catalysts.

Protonation Stimulates the Layered to Rock Salt Phase Transition of Ni-Rich Sodium Cathodes.

Protonation of oxide cathodes triggers surface transition metal dissolution and accelerates the performance degradation of Li-ion batteries. While strategies are developed to improve cathode material surface stability, little is known about the effects of protonation on bulk phase transitions in these cathode materials or their sodium-ion battery counterparts. Here, using NaNiO2 in electrolytes with different proton-generating levels as model systems, a holistic picture of the effect of incorporated protons is presented. Protonation of lattice oxygens stimulate transition metal migration to the alkaline layer and accelerates layered-rock-salt phase transition, which leads to bulk structure disintegration and anisotropic surface reconstruction layers formation. A cathode that undergoes severe protonation reactions attains a porous architecture corresponding to its multifold performance fade. This work reveals that interactions between electrolyte and cathode that result in protonation can dominate the structural reversibility/stability of bulk cathodes, and the insight sheds light for the development of future batteries.

Challenges and approaches of single-crystal Ni-rich layered cathodes in lithium batteries.

High energy density and high safety are incompatible with each other in a lithium battery, which challenges today's energy storage and power applications. Ni-rich layered transition metal oxides (NMCs) have been identified as the primary cathode candidate for powering next-generation electric vehicles and have been extensively studied in the last two decades, leading to the fast growth of their market share, including both polycrystalline and single-crystal NMC cathodes. Single-crystal NMCs appear to be superior to polycrystalline NMCs, especially at low Ni content (≤60%). However, Ni-rich single-crystal NMC cathodes experience even faster capacity decay than polycrystalline NMC cathodes, rendering them unsuitable for practical application. Accordingly, this work will systematically review the attenuation mechanism of single-crystal NMCs and generate fresh insights into valuable research pathways. This perspective will provide a direction for the development of Ni-rich single-crystal NMC cathodes.

Uncommon Behavior of Li Doping Suppresses Oxygen Redox in P2-Type Manganese-Rich Sodium Cathodes.

Utilizing both cationic and anionic oxygen redox reactions is regarded as an important approach to exploit high-capacity layered cathode materials with earth abundant elements. It has been popular strategies to effectively elevate the oxygen redox activities by Li-doping to introduce unhybridized O 2p orbitals in Nax MnO2 -based chemistries or enabling high covalency transition metals in P2-Na0.66 Mnx TM1- x O2 (TM = Fe, Cu, Ni) materials. Here, the effect of Li doping on regulating the oxygen redox activities P2-structured Na0.66 Ni0.25 Mn0.75 O2 materials is investigated. Systematic X-ray characterizations and ab initio simulations have shown that the doped Li has uncommon behavior in modulating the density of states of the neighboring Ni, Mn, and O, leading to the suppression of the existing oxygen and Mn redox reactivities and the promotion of the Ni redox. The findings provide a complementary scenario to current oxygen redox mechanisms and shed lights on developing new routes for high-performance cathodes.

Engineering Surface Oxygenated Functionalities on Commercial Carbon toward Ultrafast Sodium Storage in Ether-Based Electrolytes.

The pursuit of a high-capacity anode material has been urgently required for commercializing sodium-ion batteries with a high energy density and an improved working safety. In the absence of thermodynamically stable sodium intercalated compounds with graphite, constructing nanostructures with expanded interlayer distances is still the mainstream option for developing high-performance carbonaceous anodes. In this regard, a surface-functionalized and pore-forming strategy through a facile CO2 thermal etching route was rationally adopted to engineer negligible oxygenated functionalities on commercial carbon for boosting the sodium storage process. Benefitted from the abundant ionic/electronic pathways and more active reaction sites in the microporous structure with noticeable pseudocapacitive behaviors, the functionalized porous carbon could achieve a highly reversible capacity of 505 mA h g-1 at 50 mA g-1, an excellent rate performance of 181 mA h g-1 at 16,000 mA g-1, and an exceptional rate cycle stability of 176 mA h g-1 at 3200 mA g-1 over 1000 cycles. These outstanding electrochemical properties should be ascribed to a synergistic mechanism, fully utilizing the graphitic and amorphous structures for synchronous intercalations of sodium ions and solvated sodium ion compounds, respectively. Additionally, the controllable generation and evolution of a robust but thin solid electrolyte interphase film with the emergence of obvious capacitive reactions on the defective surface, favoring the rapid migration of sodium ions and solvated species, also contribute to a remarkable electrochemical performance of this porous carbon black.

Enabling Ether-Based Electrolytes for Long Cycle Life of Lithium-Ion Batteries at High Charge Voltage.

Lithium-ion batteries (LIBs) with high-nickel (Ni) content LiNixMnyCozO2 (x + y + z = 1) (NMC with Ni ≥ 0.6) cathodes operated at high charge voltages have been considered as one of the most promising candidates for addressing the challenge of increasing energy density demand. Conventional LiPF6-organocarbonate electrolytes exhibit incompatibility with such cell chemistries under certain testing conditions because of the instability of electrode/electrolyte interphases. In response to this challenge, ether-based electrolytes with finely tuned structure and composition of solvation sheaths were developed and evaluated in graphite (Gr)∥NMC811 cell chemistry in 2.5-4.4 V, despite ethers being conventionally considered to be unfavorable electrolyte solvents for LIBs because of their anodic instability above 4.0 V and cointercalation into Gr electrodes. The functional ether-based electrolytes in this work enable both excellent cycle life and high rate capability of Gr∥NMC811 cells. Mechanistic studies reveal that the unique structure and composition of the solvation sheath of the functional ether electrolytes are the main reasons behind their excellent anodic stability and effective protection of the Gr electrode and, consequently, the extraordinary cell performances when operated at high charge cutoff voltages. This work also provides a feasible approach in developing highly stable functional electrolytes for high-energy density LIBs.

Hard Carbon as Sodium-Ion Battery Anodes: Progress and Challenges.

Hard carbon (HC) is the state-of-the-art anode material for sodium-ion batteries due to its excellent overall performance, wide availability, and relatively low cost. Recently, tremendous effort has been invested to elucidate the sodium storage mechanism in HC, and to explore synthetic approaches that can enhance the performance and lower the cost. However, disagreements remain in the field, particularly on the fundamental questions of ion transfer and storage and the ideal HC structure for high performance. This Minireview aims to provide an analysis and summary of the theoretical limitations of HC, discrepancies in the storage mechanism, and methods to improve the performance. Finally, future research on developing ideal structured HCs, advanced electrolytes, and optimized electrolyte-electrode interphases are proposed on the basis of recent progress.

Revealing the Atomic Origin of Heterogeneous Li-Ion Diffusion by Probing Na.

Tracing the dynamic process of Li-ion transport at the atomic scale has long been attempted in solid state ionics and is essential for battery material engineering. Approaches via phase change, strain, and valence states of redox species have been developed to circumvent the technical challenge of direct imaging Li; however, all are limited by poor spatial resolution and weak correlation with state-of-charge (SOC). An ion-exchange approach is adopted by sodiating the delithiated cathode and probing Na distribution to trace the Li deintercalation, which enables the visualization of heterogeneous Li-ion diffusion down to the atomic level. In a model LiNi1/3 Mn1/3 Co1/3 O2 cathode, dislocation-mediated ion diffusion is kinetically favorable at low SOC and planar diffusion along (003) layers dominates at high SOC. These processes work synergistically to determine the overall ion-diffusion dynamics. The heterogeneous nature of ion diffusion in battery materials is unveiled and the role of defect engineering in tailoring ion-transport kinetics is stressed.

A comparative study of pomegranate Sb@C yolk-shell microspheres as Li and Na-ion battery anodes.

Alloy-based nanostructure anodes have the privilege of alleviating the challenges of large volume expansion and improving the cycling stability and rate performance for high energy lithium- and sodium-ion batteries (LIBs and SIBs). Yet, they face the dilemma of worsening the parasitic reactions at the electrode-electrolyte interface and low packing density for the fabrication of practical electrodes. Here, pomegranate Sb@C yolk-shell microspheres were developed as a high-performance anode for LIBs and SIBs with controlled interfacial properties and enhanced packing density. Although the same yolk-shell nanostructure (primary particle size, porosity) and three-dimensional architecture alleviated the volume change induced stress and swelling in both batteries, the SIBs show 99% capacity retention over 200 cycles, much better than the 78% capacity retention of the LIBs. The comparative electrochemical study and X-ray photoelectron spectroscopy characterization revealed that the different SEIs, besides the distinct phase transition mechanism, played a critical role in the divergent cycling performance.

Formation of size-dependent and conductive phase on lithium iron phosphate during carbon coating.

Carbon coating is a commonly employed technique for improving the conductivity of active materials in lithium ion batteries. The carbon coating process involves pyrolysis of organic substance on lithium iron phosphate particles at elevated temperature to create a highly reducing atmosphere. This may trigger the formation of secondary phases in the active materials. Here, we observe a conductive phase during the carbon coating process of lithium iron phosphate and the phase content is size, temperature, and annealing atmosphere dependent. The formation of this phase is related to the reducing capability of the carbon coating process. This finding can guide us to control the phase composition of carbon-coated lithium iron phosphate and to tune its quality during the manufacturing process.

Nanoscale Manipulation of Spinel Lithium Nickel Manganese Oxide Surface by Multisite Ti Occupation as High-Performance Cathode.

A novel two-step surface modification method that includes atomic layer deposition (ALD) of TiO2 followed by post-annealing treatment on spinel LiNi0.5 Mn1.5 O4 (LNMO) cathode material is developed to optimize the performance. The performance improvement can be attributed to the formation of a TiMn2 O4 (TMO)-like spinel phase resulting from the reaction of TiO2 with the surface LNMO. The Ti incorporation into the tetrahedral sites helps to combat the impedance growth that stems from continuous irreversible structural transition. The TMO-like spinel phase also alleviates the electrolyte decomposition during electrochemical cycling. 25 ALD cycles of TiO2 growth are found to be the optimized parameter toward capacity, Coulombic efficiency, stability, and rate capability enhancement. A detailed understanding of this surface modification mechanism has been demonstrated. This work provides a new insight into the atomic-scale surface structural modification using ALD and post-treatment, which is of great importance for the future design of cathode materials.