New Insight into Microstructure Engineering of Ni-Rich Layered Oxide Cathode for High Performance Lithium Ion Batteries

Ni-rich layered LiNi_xCo_yMn_1−x−yO₂ (LNCM) with Ni content over >90% is considered as a promising lithium ion battery (LIB) cathode, attributed by its low cost and high practical capacity. However, Ni-rich LNCM inevitably suffers rapid capacity fading at a high state of charge due to the mechanochemical breakdown; in particular, the microcrack formation has been regarded as one of the main culprits for Ni-rich layered cathode failure. To address these issues, Ni-rich layered cathodes with a textured microstructure are developed by phosphorous and boron doping. Attributed by the textured morphology, both phosphorous- and boron-doped cathodes suppress microcrack formation and show enhanced cycle stability compared to the undoped cathode. However, there exists a meaningful capacity retention difference between the doped cathodes. By adapting the various analysis techniques, it is shown that the boron-doped Ni-rich layered cathode displays better cycle stability not only by its ability to suppress microcracks during cycling but also by its primary particle morphology that is reluctant to oxygen evolution. The present work reveals that not only restraint of particle cracks but also suppression of oxygen release by developing the oxygen stable facets is important for further improvements in state-of-the-art Li ion battery Ni-rich layered cathode materials.     

Degradation Pathways of Cobalt-Free LiNiO2 Cathode in Lithium Batteries

Electrode-electrolyte reactivity (EER) and particle cracking (PC) are considered two main causes of capacity fade in high-nickel layered oxide cathodes in lithium-based batteries. However, whether EER or PC is more critical remains debatable. Herein, the fundamental correlation between EER and PC is systematically investigated with LiNiO₂ (LNO), the ultimate cobalt-free lithium layered oxide cathode. Specifically, EER is found more critical than secondary particle cracking (SPC) in determining the cycling stability of LNO; EER leads to primary particle cracking, but mitigates SPC due to the inhibition of H2-H3 phase transformation. Two surface degradation pathways are identified for cycled LNO under low and high EERs. A common blocking surface reconstruction layer (SRL) containing electrochemically-inactive Ni₃O₄ spinel and NiO rock-salt phases is formed on LNO in an electrolyte with a high EER; in contrast, an electrochemically-active SRL featuring regions of electron- and lithium-ion-conductive LiNi₂O₄ spinel phase is formed on LNO in an electrolyte with a low EER. These findings unveil the intrinsic degradation pathways of LNO cathode and are foreseen to provide new insights into the development of lithium-based batteries with a minimized EER and a maximized service life.     

High Cycling Rate-Induced Irreversible TMO6 Slabs Glide in Co-Free High-Ni Layered Cathode Materials

Co-free high-Ni layered transition metal oxide is a promising cost-effective cathode material for high-energy Li-ion batteries, but it suffers from undesirable rate performance and rapid capacity decay upon high-rate cycling. The underlying structural changes under fast electrochemical processes remain unclear to date. In this study, atomic scale structural evolutions of Co-free high-Ni layered cathode at different cycling rates are revealed by advanced TEM characterization. It is found that the phase transition after high-rate cycling is much different from that after low-rate cycling. The low-rate cycled sample shows a typical layer-to-rock salt transition. However, O1-type stacking faults are uncovered in the high-rate cycled sample owing to irreversible TMO₆ slabs glide, which induces severe lattice distortion and structural dislocations. These findings deepen the understanding of the rate-dependent structural degradation mechanism of Co-free high-Ni layered cathodes, and have significant implications for improving current materials to withstand high-rate applications.     

Pre-Deoxidation of Layered Ni-Rich Cathodes to Construct a Stable Interface with Electrolyte for Long Cycling Life

Ni-rich layered oxides as the cathode materials of high-energy-density lithium-ion batteries (LIBs) suffer from capacity decay and structural instability owing to oxygen loss during cycling. It is a huge challenge to prevent the oxygen loss of Ni-rich cathode materials during long cycling. Here, a pre-deoxidation of LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) single crystal materials is achieved by heat treatment at elevated temperatures in argon condition to form a stable surface with rock salt structure. The stable surface structure with oxygen vacancy defects successfully suppresses the harmful phase transitions of NCM811 and effectively improves the stability of the NCM811/electrolyte interface during cycling at a high cut-off voltage. In addition, the intragranular structural evolution and cation mixing degree is inhibited to effectively suppress the intergranular cracking and particle pulverization of cathode during long cycling. The pre-deoxidation of NCM811 exhibits 70.6% capacity retention after 1000 cycles at the current density of 0.5 C between 2.8 and 4.3 V, which is much larger than that of pristine NCM811 capacity retention of 27.3%. The strategy of pre-deoxidation of Ni-rich layered structure cathode to regulate the defect chemistry and surface structure provides a facile and effective way to achieve long cycling life high-energy density LIBs.     

Surface Structural Transition Induced by Gradient Polyanion‐Doping in Li‐Rich Layered Oxides: Implications for Enhanced Electrochemical Performance

Lithium‐rich layered oxides (LLOs) exhibit great potential as high‐capacity cathode materials for lithium‐ion batteries, but usually suffer from capacity/voltage fade during electrochemical cycling. Herein, a gradient polyanion‐doping strategy is developed to initiate surface structural transition to form a spinel‐like surface nanolayer and a polyanion‐doped layered core material in LLOs simultaneously. This strategy integrates the advantages of both bulk doping and surface modification as the oxygen close‐packed structure of LLOs is stabilized by polyanion doping, and the LLO cathodes are protected from steady corrosion induced by electrolytes. A LLO material modified with 5 at% phosphate (5%P@LLO) shows a high reversible discharge capacity of ≈300 mAh g^?1 at 0.1 C, excellent cycling stability with a capacity retention of 95% after 100 cycles, and enhanced electrode kinetics. This gradient doping strategy can be further extended to other polyanion‐doped LLO materials, such as borate and silicate polyanions.     

Tailored Redox Kinetics,Electronic Structures and Electrode/Electrolyte Interfaces for Fast and High Energy‐Density Potassium‐Organic Battery

Potassium‐organic batteries have a great potential for applications in large‐scale electricity grids and electric vehicles because of their low cost and sustainability. However, their inferior cycle stability and more importantly low energy density under fast discharge/charge process of organic cathodes limit their applications. This work introduces a simple polymerization processing which enables comprehensive tuning of redox kinetics, electronic structures, and electrode/electrolyte interfaces of the polymer cathodes. With this approach, a potassium‐organic battery with an impressive energy density of 113 Wh kg^?1 at a high power of 35.2 kW kg^?1 is shown which corresponds to a high current density of 147 C and a fully discharge within 10 s. The battery also has impressive cycling stability that a 100% Columbic efficiency is maintained and shows negligible capacity degradation after 1000 cycle at a high current density of 7.35 C. Using the polymer cathode and a dipotassium terephthalate anode, a full battery with superior energy density and cycling stability is demonstrated among all reported all‐organic full potassium ion batteries.     

Synchronous Tailoring Surface Structure and Chemical Composition of Li‐Rich–Layered Oxide for High‐Energy Lithium‐Ion Batteries

Li‐rich–layered oxide is considered to be one of the most promising cathode materials for high‐energy lithium ion batteries. However, it suffers from poor rate capability, capacity loss, and voltage decay upon cycling that limits its utilization in practical applications. Surface properties of Li‐rich–layered oxide play a critical role in the function of batteries. Herein, a novel and successful strategy for synchronous tailoring surface structure and chemical composition of Li‐rich–layered oxide is proposed. Poor nickel content on the surface of carbonate precursor is initially prepared by a facile treatment of NH₃·H₂O, which can retain at a certain low amount on the surface in the final lithiated Li‐rich–layered oxide after a solid‐phase reaction process. Moreover, a phase‐gradient outer layer with “layered‐coexisting phase‐spinel” structure toward to the outside surface is self‐induced and formed synchronously based on poor nickel surface of the precursor. Electrochemical tests reveal this unique surface enables excellent cycling stability, improved rate capability, and slight voltage decay of cathodes. The finding here sheds light on a universal principle both for masterly tailoring surface structure and chemical composition at the same time for improving electrochemical performance of electrode materials.     

Blending Layered Cathode with Olivine: An Economic Strategy for Enhancing the Structural and Thermal Stability of 4.65 V LiCoO2

The intrinsic poor structural and thermal stability of high-voltage layered cathodes are aggravated as the charging depth increases, which severely threatens the cycle life and safety of the battery. Herein, without modifying the high-voltage layered cathode itself, a simple and economic blending strategy is introduced, and an olivine-LiCoO₂ blended cathode featuring superior comprehensive performance (energy, power, cycle-life, and safety) at 4.65 V is fabricated. The strong bonding affinity at the olivine/LiCoO₂ contact interface suppresses lattice O₂ release of LiCoO₂, thus significantly improving the structural and thermal stability at high delithiation states. Meanwhile, by contacting with high-electron-conductivity LiCoO₂, the redox activity of olivine is further activated. Therefore, a stable operation of both olivine-LiCoO₂ and olivine-LiNi_0.8Co_0.1Mn_0.1O₂ blended cathode is achieved under harsh cycling conditions (high voltage or elevated temperature) and long-life pouch-cell (91.6% capacity retention after 1000 cycles) is harvested, demonstrating the feasibility and universality of this economic blending strategy on heterogenous cathode candidates.     

3D Carbonaceous Current Collectors: The Origin of Enhanced Cycling Stability for High‐Sulfur‐Loading Lithium–Sulfur Batteries

The cycling stability of high‐sulfur‐loading lithium–sulfur (Li–S) batteries remains a great challenge owing to the exaggerated shuttle problem and interface instability. Despite enormous efforts on design of advanced electrodes and electrolytes, the stability issue raised from current collectors has been rarely concerned. This study demonstrates that rationally designing a 3D carbonaceous macroporous current collector is an efficient and effective “two‐in‐one” strategy to improve the cycling stability of high‐sulfur‐loading Li–S batteries, which is highly versatile to enable various composite cathodes with sulfur loading >3.7 mAh cm^?2. The best cycling performance can be achieved upon 950 cycles with a very low decay rate of 0.029%. Moreover, the origin of such a huge enhancement in cycling stability is ascribed to (1) the inhibition of electrochemical corrosion, which severely occurs on the typical Al foil and disables its long‐term sustainability for charge transfer, and (2) the passivation of cathode surface. The role of the chemical resistivity against corrosion and favorable macroscopic porous structure is highlighted for exploiting novel current collectors toward exceptional cycling stability of high‐sulfur‐loading Li–S batteries.     

Eliminating Local Electrolyte Failure Induced by Asynchronous Reaction for High-Loading and Long-Lifespan All-Solid-State Batteries

The design of practical cathodes with high areal capacity in polymer-based all-solid-state batteries remains challenged by the absence of an effective guiding principle that prolongs battery life-span. Unlike liquid batteries, the notorious interface incompatibility between cathodes and electrolytes limited the cycling life of the all-solid-state batteries. Herein, this study proposes a dynamically stable cathode design with a fully covered surface, effectively mitigating interface failure and enabling the cyclic time of batteries with a cathode loading of 12.7 mg cm^‒2 over 10 000 h. This study unveils the importance of local state of charge in affecting the interfacial properties of particles through local oxidative-stability of electrolytes on the interface. This study shows that the phenomena can be strongly influenced by the porosity of the cathode through the perspective of discreteness of ion transport. These insights and approach provide a broader promise for solid batteries for long lifetime.     

Optimizing Both Bulk and Surface Structure of Li-Rich Layered Cathodes for Long-Life and Safe Li-Ion Batteries

Although oxygen redox in Li-rich layered cathodes can boost the available capacity over 250 mAh g⁻¹, it also brings a rapid capacity fade upon long-term cycling and serious safety issue during thermal abuse. To circumvent these problems, an integrated strategy via interlayer regulation at surface and the delocalization of Li₂MnO₃-like domain on bulk is proposed. The controllable interlayer by atomic layer deposition can maximize the coating effects on elimination of the lattice mismatch to inhibit the structural degradation during cycling. And the delocalized Li₂MnO₃-like domain through compositional control can fully prohibit lattice oxygen release from the bulk to improve the thermal stability of electrode. The optimized cathode material exhibits a capacity retention of 94.0% after 200 cycles. A 1.25 Ah multilayer pouch cell with the cathode and graphite anode delivers an outstanding cycling performance that retains 80.4% of its capacity at 0.5 C after 710 cycles. More importantly, the distinguished safety features derived from the method are verified after successfully passing practical-level thermal safety and nail penetration test.     

A Dilute Fluorinated Phosphate Electrolyte Enables 4.9 V-Class Potassium Ion Full Batteries

Potassium ion batteries using graphite anode and high-voltage cathodes are considered to be optimizing candidates for large-scale energy storage. However, the lack of suitable electrolytes significantly hinders the development of high-voltage potassium ion batteries. Herein, a dilute (0.8 m ) fluorinated phosphate electrolyte is proposed, which exhibits extraordinary compatibility with both graphite anode and high-voltage cathodes. The phosphate solvent, tris(2,2,2-trifluoroethyl) phosphate (TFP), has weak solvating ability, which not only allows the formation of robust anion-derived solid electrolyte interphase on graphite anode but also effectively suppresses the corrosion of Al current collector at high voltage. Meanwhile, the high oxidative stability of fluorinated TFP solvent enables stable ultrahigh-voltage (4.95 V) cycling of a potassium vanadium fluorophosphate (KVPO₄F) cathode. Using TFP-based electrolyte, the 4.9 V-class potassium ion full cell based on graphite anode and KVPO₄F cathode shows rather remarkable cycling performance with a high capacity retention of 87.2% after 200 cycles. This study provides a route to develop dilute electrolytes for high-voltage potassium ion batteries, by utilizing solvents with both weak solvating ability and high oxidative stability.     

In Situ Ion-Exchange Metathesis Induced Conformal LiF Surface Films on Cathode (NMC811) as a Cathode Electrolyte Interphase

High-capacity cathodes (LiNi_0.8Mn_0.1Co_0.1O₂, NMC811) are promising for vehicle electrification because of their high gravimetric energy density. However, their electrochemical performance still relies upon the stability of the cathode electrolyte interphase (CEI). A highly reactive cathode interface leads to parasitic side reactions with electrolytes, resulting in accelerated capacity fading. Well-developed LiF and LiF-like inorganic compounds are believed to be good CEI components for stabilizing such reactive electrode interfaces. However, it is challenging to form an optimal surface sub-nanolayer of LiF on the cathode surfaces because of the complexity of the electrochemical reaction during battery cycling. Herein, the formation of a conformal LiF layer on the NMC811 electrode surface via an in situ ion-exchange metathesis process is reported, demonstrating a promising electrochemical performance because of a LiF-stabilized CEI. In situ generated LiF-coated NMC811 electrodes exhibit ≈97% capacity retention up to 100 cycles at a 0.3 C rate with average coulombic efficiency of ≈99.9% and ≈80% capacity retention up to 200 cycles at a 1 C rate with average coulombic efficiency of >99.6%. This finding may pave the way for reengineering the CEI to enhance the electrochemical performances and cycling stability of the high-capacity cathodes.     

A Review on the Status and Challenges of Cathodes in Room-Temperature Na-S Batteries

The cathode materials for sodium-sulfur batteries have attracted great attention since cathode is one of the important components of the sodium-sulfur battery, and there are cathode materials that have high capacity, non-toxicity, and cost-efficiency. Nevertheless, due to their low Coulombic efficiency and proneness to cycling decay, the practical application of the sodium–sulfur battery has always been suppressed. In terms of the responsibility of these problems, the polysulfide shuttle and the sluggish kinetics are the main culprits. To address these issues, impeding the notorious reaction between polysulfide intermediates on the cathode and improve the kinetics reaction on the anode are extremely important. Herein, a comprehensive review is prepared of different approaches to increasing the electrochemical performance and strengthening the stability of cathodes. The influences of various choices and the consequent properties of the cathode in relation to the whole sodium–sulfur battery performance is investigated. Finally, the current research challenges related to cathodes for sodium–sulfur batteries and future perspectives are also discussed.     

Surface Miscible Structure Modulation of Li-Rich Cathodes by Dual Gas Surface Treatment for Super High-Temperature Electrochemical Performance

Li-rich manganese base oxides (LRNCM) are regarded as one of the most promising cathode materials among next-generation high-energy density Li-ion batteries due to the coupling effect of anion and cation redox. However, serious oxygen release, surface structure corrosion, and transformation seriously damage their electrochemical performance and restrict their commercialization process. Herein, a dual gaseous surface treatment strategy with ammonium bicarbonate is designed to reconstruct the surface chemical and structural characteristics of LRNCM. As a result, an enriched oxygen vacancies mixed-phase surface layer is achieved, which contains spinel phase and cation-disordered phase. The integration of the surface mixed phase effectively inhibits irreversible oxygen loss, prevents electrode corrosion, and promotes fast Li-ion diffusion. Accordingly, the modified cathode exhibits excellent specific capacity, high-rate capability, and superior cycle life at both 25 and 60 °C. Particularly at high temperatures, it achieves impressive performance: initial coulombic efficiency (82.0 vs 74.4%), cycling stability at 1 C after 100 cycles (92.6 vs 83.8%), and rate performance at 5 C (56.0 vs 48.7%). This reconfiguration approach introduces a novel idea for the design of cathode material interfaces.     

Combining Janus Separator and Organic Cathode for Dendrite-Free and High-Performance Na-Organic Batteries

The growth of Na-dendrites and the dissolution of organic cathodes are two major challenges that hinder the development of sodium-organic batteries (SOBs). Herein, a multifunctional Janus separator (h-BN@PP@C) by using an interfacial engineering strategy, is proposed to tackle the issues of SOBs. The carbon layer facing the organic cathode serves as a barrier to capture dissolved organic materials and enhance their utilization. Meanwhile, the h-BN layer facing the Na anode possesses high thermal conductivity and mechanical strength, which mitigates the occurrence of localized-temperature “hot spots” and promotes the formation of a NaF-enriched SEI, thereby suppressing dendrite growth. Consequently, the Janus separator enables a stable Na plating/stripping cycling for 1000 h at 3 mA cm⁻². Equipped with the Janus separator, organic cathodes including dibenzo[b,i]thianthrene-5,7,12,14-tetraone (DTT), pentacene-5,7,12,14-tetrone and Calix[4]quinone cathodes demonstrate high capacity and remarkable cycling performance. In particular, the DTT exhibits a bipolar co-reaction storage mechanism and achieves an ultrahigh capacity (≈342.6 mAh g⁻¹), long-term cycling stability (capacity decay rate of 0.15% per cycle over 550 cycles at 500 mA g⁻¹) and fast kinetics (1000 mA g⁻¹≈2.8 C). This study offers a straightforward, effective, and promising solution to address the challenges in SOBs.     

Ultrafast Charging and Stable Cycling Dual-Ion Batteries Enabled via an Artificial Cathode–Electrolyte Interface

Low-cost and environment-friendly dual-ion batteries (DIBs) with fast-charging characteristics facilitate the development of high-power energy storage devices. However, the incompatibility between the cathode and electrolyte at high voltage results in low Coulombic efficiency (CE) and short lifespan. Here, the addition of ≈ 0.5 wt% lithium difluoro(oxalate) borate salt into the electrolyte forms a robust and durable cathode–electrolyte interface (CEI) in situ on the graphite surface, which enables remarkable cycling of the graphite || Li battery with 87.5% capacity retention after 4000 cycles at 5 C and ultrafast rate capability with 88.8% capacity retention under 40 C (4 A g⁻¹), delivering high-power of 0.4–18.8 kW kg⁻¹ at energy densities of 422.7–318.8 Wh kg⁻¹. Taking advantage of this robust CEI, a graphite || graphite full battery demonstrates high reversible capacities of 97.6, 92.8, 88.7, and 85.4 mAh (g cathode)⁻¹ at current rates of 10, 20, 30, and 40 C, respectively. The full battery also shows a long cycling life of over 6500 cycles with 92.4% capacity retention and an average CE of ≈ 99.4% at 1 A g⁻¹, which is superior to other dual-graphite (carbon) batteries in the literature. This work offers an effective interface-stabilizing strategy on protecting graphite cathodes and a promising approach for developing DIBs with high-power capability.     

Comparison of facet temperature and degradation of unpumped and passivated facets of Al-free 940-nm lasers using photoluminescence

Influences of facet degradation of Al-free InGaAsP-GaAs 940-nm laser diodes were studied at power densities well below catastrophic optical mirror damage level using photoluminescence (PL) during normal operation and after a rigorous burn-in procedure. The shift in the PL peak of the cladding layer of the device is used to calculate the temperature of the facet. Devices with different facet treatments: untreated electron beam evaporation, untreated ion beam deposition, unpumped and passivated facets were compared. The results indicate that the degradation of facet is more severe for untreated and unpumped facets as compared to passivated facets. The results were also compared with power measurements, which show that the drop in the power during the first 50 h of operation is nonexistent for passivated facet devices leading to the conclusion that photo-induced oxidation is the major cause of the degradation of the facet and thus oxide removal and surface passivation are crucial to make stable laser diodes.     

A Critical Review on Functionalization of Air‐Cathodes for Nonaqueous Li–O2 Batteries

This review reports on the most updated technological aspects of Li–air battery cathode materials. It provides the reader with recent developments, alongside critical views. The requirements for air‐cathodes, as well as the classification and characterization of carbon‐based and carbon‐free air cathodes, are listed. The effects of two major substituent groups of materials, namely carbon and advanced materials (metals, metal‐oxides, metal‐carbides, and metal‐nitrides) aimed at replacing carbon, are discussed in terms of their chemical and electrochemical stability. The report covers aspects of surface chemistry and structure influence on the electrolyte and discharge products stability. The review also reports on the efforts to suppress side reactions and deterioration of the polymeric binders (if a composite electrode is being considered). This is recognized as a means to enhance Li–air battery performance. The report concludes with an outlook and perspective, providing the readers with some insight on other factors and their impact on the long road toward a viable air‐cathode suitable for Li–air battery operations.     

Lithium Phosphonate Functionalized Polymer Coating for High-Energy Li[Ni0.8Co0.1Mn0.1]O2 with Superior Performance at Ambient and Elevated Temperatures

High-energy Ni-rich lithium transition metal oxides such as Li[Ni_0.8Co_0.1Mn_0.1]O₂ (NCM₈₁₁) are appealing positive electrode materials for next-generation lithium batteries. However, the high sensitivity toward moist air during storage and the high reactivity with common organic electrolytes, especially at elevated temperatures, are hindering their commercial use. Herein, an effective strategy is reported to overcome these issues by coating the NCM₈₁₁ particles with a lithium phosphonate functionalized poly(aryl ether sulfone). The application of this coating allows for a substantial reduction of lithium-based surface impurities (e.g., LiOH, Li₂CO₃) and, generally, the suppression of detrimental side reactions upon both storage and cycling. As a result, the coated NCM₈₁₁-based cathodes reveal superior Coulombic efficiency and cycling stability at ambient and, particularly, at elevated temperatures up to 60 ° C (a temperature at which the non-coated NCM₈₁₁ electrodes rapidly fail) owing to the formation of a stable cathode electrolyte interphase with enhanced Li⁺ transport kinetics and the well-retained layered crystal structure. These results render the herein presented coating strategy generally applicable for high-performance lithium battery cathodes.