Perspectives on the Practicability of Li-Rich NMC Layered Oxide Cathodes.

Li-rich NMCs layered oxides, with the general formula of Li[LixNiyMnzCo1- x - y - z]O2, are known for their exceptionally high capacities but remain yet to be practicalized in the real world. They have attracted enormous research attention due to their complex structure and intriguing redox mechanisms, with a particular focus on anionic redox over the past decade. While fundamental understandings are fruitful, the practical considerations are emphasized here by providing perspectives on how Li-rich NMCs are limited by practical roadblocks and guidelines on how to cope with these limitations. It is also demonstrated that, via a techno-economic analysis, Li-rich NMCs have material cost ($/kg) highly dependent on the lithium price, but still preserve the dominance of lower pack cost ($/kWh) than other cathode candidates principally owing to their larger material energy densities. In addition to their pure application in electric-vehicle batteries, using them as "electrode additive" or "sacrificial agent" can further multiply their practicalities in assortment of scenarios, which is further discussed.

An entanglement association polymer electrolyte for Li-metal batteries.

To improve the interface stability between Li-rich Mn-based oxide cathodes and electrolytes, it is necessary to develop new polymer electrolytes. Here, we report an entanglement association polymer electrolyte (PVFH-PVCA) based on a poly (vinylidene fluoride-co-hexafluoropropylene) (PVFH) matrix and a copolymer stabilizer (PVCA) prepared from acrylonitrile, maleic anhydride, and vinylene carbonate. The entangled structure of the PVFH-PVCA electrolyte imparts excellent mechanical properties and eliminates the stress arising from dendrite growth during cycling and forms a stable interface layer, enabling Li//Li symmetric cells to cycle steadily for more than 4500 h at 8 mA cm-2. The PVCA acts as a stabilizer to promote the formation of an electrochemically robust cathode-electrolyte interphase. It delivers a high specific capacity and excellent cycling stability with 84.7% capacity retention after 400 cycles. Li1.2Mn0.56Ni0.16Co0.08O2/PVFH-PVCA/Li full cell achieved 125 cycles at 1 C (4.8 V cut-off) with a stable discharge capacity of ~2.5 mAh cm-2.

An Ultrasmall Ordered High-Entropy Intermetallic with Multiple Active Sites for the Oxygen Reduction Reaction.

Controlling multimetallic ensembles at the atomic level is significantly challenging, particularly for high-entropy alloys with more than five elements. Herein, we report an innovative ultrasmall (∼2 nm) PtFeCoNiCuZn high-entropy intermetallic (PFCNCZ-HEI) with a well-ordered structure synthesized by using the space-confined strategy. By exploiting these combined metals, the PFCNCZ-HEI nanoparticles achieve an ultrahigh mass activity of 2.403 A mgPt-1 at 0.90 V vs reversible hydrogen electrode for the oxygen reduction reaction, which is up to 19-fold higher than that of state-of-the-art commercial Pt/C. A proton exchange membrane fuel cell assembled with PFCNCZ-HEI as the cathode (0.03 mgPt cm-2) exhibits a power density of 1.4 W cm-2 and a high mass-normalized rated power of 45 W mgPt-1. Furthermore, theoretical calculations reveal that the outer electrons of the non-noble-metal atoms on the surface of the PFCNCZ-HEI nanoparticle are modulated to show characteristics of multiple active centers. This work offers a promising catalyst design direction for developing highly ordered HEI nanoparticles for electrocatalysis.

Unlocking the Potential of Li-Rich Mn-Based Oxides for High-Rate Rechargeable Lithium-Ion Batteries.

Lithium-rich Mn-based oxides have gained significant attention worldwide as potential cathode materials for the next generation of high-energy density lithium-ion batteries. Nonetheless, the inferior rate capability and voltage decay issues present formidable challenges. Here, a Li-rich material equipped with quasi-three-dimensional (quasi-3D) Li-ion diffusion channels is initially synthesized by introducing twin structures with high Li-ion diffusion coefficients into the crystal and constructing a "bridge" between different Li-ion diffusion tunnels. The as-prepared material exhibits monodispersed micron-sized primary particles (MP), delivering a specific capacity of 303 mAh g-1 at 0.1 C and an impressive capacity of 253 mAh g-1 at 1 C. More importantly, the twin structure also serves as a "breakwater" to inhibit the migration of Mn ions and improve the overall structural stability, leading to cycling stability with 85% capacity retention at 1 C after 200 cycles. The proposed strategy of constructing quasi-3D channels in the layered Li-rich cathodes will open up new avenues for the research and development of other layered oxide cathodes, with potential applications in industry.

Regulating the Potential of Anion Redox to Reduce the Voltage Hysteresis of Li-Rich Cathode Materials.

Layered Li-rich oxides (LROs) that exhibit anionic and cationic redox are extensively studied due to their high energy storage capacities. However, voltage hysteresis, which reduces the energy conversion efficiency of the battery, is a critical limitation in the commercial application of LROs. Herein, using two Li2RuO3 (LRO) model materials with C2/c and P21/m symmetries, we explored the relationship between voltage hysteresis and the electronic structure of Li2RuO3 by neutron diffraction, in situ X-ray powder diffraction, X-ray absorption spectroscopy, macro magnetic study, and electron paramagnetic resonance (EPR) spectroscopy. The charge-transfer band gap of the LRO cathode material with isolated eg electron filling decreases, reducing the oxidation potential of anion redox and thus displaying a reduced voltage hysteresis. We further synthesized Mn-based Li-rich cathode materials with practical significance and different electron spin states. Low-spin Li1.15Ni0.377Mn0.473O2 with isolated eg electron filling exhibited a reduced voltage hysteresis and high energy conversion efficiency. We rationalized this finding via density functional theory calculations. This discovery should provide critical guidance in designing and preparing high-energy layered Li-rich cathode materials for use in next-generation high-energy-density Li-ion batteries based on anion redox activity.

Entropy Stabilization Strategy for Enhancing the Local Structural Adaptability of Li-Rich Cathode Materials.

Layered Li-rich cathode materials with high reversible energy densities are becoming prevalent. However, owing to the activation of low-potential redox couples and the progressively irreversible structural transformation caused by the local adjustment of transition-metal ions in the intra/interlayer driven by anionic redox, continuous capacity degradation, and voltage decay emerge, thus greatly reducing the energy density and increasing the difficulty of battery system management. Herein, layered Li-rich cathode materials with higher intralayer configuration entropy have more local structural diversity and higher distortion energy, resulting in superior local structural adaptability with no drastic redox couple evolution, major local structural adjustment, or obvious layered-to-spinel phase transition. Consequently, the energy retention of the entropy-stabilization-strategy-enhanced Li-rich cathode materials is almost twice that of a typical Li-rich cathode material (Li1.20 Mn0.54 Ni0.13 Co0.13 O2 , T-LRM) after 3 months of cyclic testing. Moreover, when cycled at 1 C, the voltage degradation per cycle is less than 0.02%, that is, it results in a voltage loss of only 0.8 mV per cycle, which is excellent performance. This study paves the way for the development of Li-rich cathode materials with stabilized intralayer atomic arrangements and high local structural adaptability.

Sulfuration of Li-Rich Mn-Based Cathode Materials for Multianionic Redox and Stabilized Coordination Environment.

Lithium-rich transition metal oxides (LLOs) can deliver high specific capacity over 250 mAh g-1 , stemming from additional contribution of oxygen redox. However, the formation of O(2- n )- (0 < n < 2) species and even oxygen gas during the deep oxidation stage leads to progressive structural transformation that cause voltage decay/hysteresis, sluggish kinetics, and poor thermostability, preventing real-world application of LLOs. Therefore, the substantive key relies on enhancing the anionic redox stability in LLOs. Here, a sulfuration procedure of LLOs (S-LLOs) is proposed, in which sulfur anions are incorporated into oxygen sites in the lattice structure and form polyanions on the surface. Proved by structural characterizations and density functional theory (DFT) calculations, sulfur anions in the interior lattice can reversibly participate in the redox process and enhance the integral coordination stability by mitigating undesired oxygen redox. Moreover, S polyanions at the surface form a protecting layer for interfacial stability. The electrochemical measurements indicate that S-LLO demonstrates a high discharge capacity of 307.8 mAh g-1 , an outstanding capacity retention rate of 91.5% after 200 cycles, along with excellent voltage maintenance, rate capability, and thermostability. The sulfuration process of LLOs with multianionic redox mechanism highlights a promising strategy to design novel high-energy-density cathode materials with superior cycling performance.

Inhibition of oxygen dimerization by local symmetry tuning in Li-rich layered oxides for improved stability.

Li-rich layered oxide cathode materials show high capacities in lithium-ion batteries owing to the contribution of the oxygen redox reaction. However, structural accommodation of this reaction usually results in O-O dimerization, leading to oxygen release and poor electrochemical performance. In this study, we propose a new structural response mechanism inhibiting O-O dimerization for the oxygen redox reaction by tuning the local symmetry around the oxygen ions. Compared with regular Li2RuO3, the structural response of the as-prepared local-symmetry-tuned Li2RuO3 to the oxygen redox reaction involves the telescopic O-Ru-O configuration rather than O-O dimerization, which inhibits oxygen release, enabling significantly enhanced cycling stability and negligible voltage decay. This discovery of the new structural response mechanism for the oxygen redox reaction will provide a new scope for the strategy of enhancing the anionic redox stability, paving unexplored pathways toward further development of high capacity Li-rich layered oxides.

O2-Type Li0.78[Li0.24Mn0.76]O2 Nanowires for High-Performance Lithium-Ion Battery Cathode.

Continued improvement in the electrochemical performance of Li-Mn-O oxide cathode materials is key to achieving advanced low-cost Li-ion batteries with high energy densities. In this study, O2-type Li0.78[Li0.24Mn0.76]O2 nanowires were synthesized by a solvothermal reaction to produce P2-type Na5/6[Li1/4Mn3/4]O2 nanowires, which were then subjected to molten salt Li-ion exchange. The resulting nanowires have diameters less than 20 nm and lengths of several micrometers. The full-Mn-based nanowires cathode material delivers a reversible capacity of 275 mAh g-1 at 0.1 C and 200 mAh g-1 at a high current rate of 15 C with a capacity retention of more than 80% and the voltage decay was dramatically suppressed after 100 cycles. This excellent performance is ascribed to the highly stable oxygen redox reaction and lack of layered-to-spinel phase transition in the O2-type structure during cycling.

A High-Performance Li-Mn-O Li-rich Cathode Material with Rhombohedral Symmetry via Intralayer Li/Mn Disordering.

The search for new high-performance and low-cost cathode materials for Li-ion batteries is a challenging issue in materials research. Commonly used cobalt- or nickel-based cathodes suffer from limited resources and safety problems that greatly restrict their large-scale application, especially for electric vehicles and large-scale energy storage. Here, a novel Li-Mn-O Li-rich cathode material with R 3 ¯ m symmetry is developed via intralayer Li/Mn disordering in the Mn-layer. Due to the special atomic arrangement and higher R 3 ¯ m symmetry with respect to the C2/m symmetry, the oxygen redox activity is modulated and the Li in the Li-layer is preferentially thermodynamically extracted from the crystal structure instead of Li in the Mn-layer. The as-obtained material delivers a reversible capacity of over 300 mAh g-1 at 25 mA g-1 and rate capability of up to 260 mAh g-1 at 250 mA g-1 within 2.0-4.8 V. The excellent performance is attributed to its highly structural reversibility, mitigation of Jahn-Teller distortion, lower bandgap, and faster Li-ion 2D channels during the lithium-ion de/intercalation process. This material is not only a promising cathode material candidate but also raises new possibilities for the design of low-cost and high-performance cathode materials.

Atomically ordered non-precious Co3Ta intermetallic nanoparticles as high-performance catalysts for hydrazine electrooxidation.

Nano-ordered intermetallic compounds have generated great interest in fuel cell applications. However, the synthesis of non-preciousearly transition metal intermetallic nanoparticles remains a formidable challenge owing to the extremely oxyphilic nature and very negative reduction potentials. Here, we have successfully synthesized non-precious Co3Ta intermetallic nanoparticles, with uniform size of 5 nm. Atomic structural characterizations and X-ray absorption fine structure measurements confirm the atomically ordered intermetallic structure. As electrocatalysts for the hydrazine oxidation reaction, Co3Ta nanoparticles exhibit an onset potential of -0.086 V (vs. reversible hydrogen electrode) and two times higher specific activity relative to commercial Pt/C (+0.06 V), demonstrating the top-level performance among reported electrocatalysts. The Co-Ta bridge sites are identified as the location of the most active sites thanks to density functional theory calculations. The activation energy of the hydrogen dissociation step decreases significantly upon N2H4 adsorption on the Co-Ta bridge active sites, contributing to the significantly enhanced activity.

Suppressing Voltage Decay of a Lithium-Rich Cathode Material by Surface Enrichment with Atomic Ruthenium.

Lithium-rich layered oxides are promising cathode materials for high-energy-density lithium-ion batteries. However, the development of cathode materials based on these layered oxides has been limited by voltage fading, poor rate performance, and the low tap density of these materials. In this work, we prepared a material consisting of micrometer-scale spherical lithium-rich layered oxide particles with a three-dimensional conductivity network design and modified the surface of the primary particles with ruthenium. The as-obtained product with a maximum tap density of 2.1 g cm-3 shows a superior high reversible capacity with 280 mA h·g-1 at 0.1 C, a capacity retention of 98.1% after 100 cycles, and an outstanding rate capability. More importantly, enrichment of the primary particle surface with ruthenium can effectively suppress voltage decay. This cathode is feasible to construct high-energy and high-power lithium-ion batteries. This novel design may furthermore open the door to new material engineering applications for high-performance cathode materials.

A High-Capacity O2-Type Li-Rich Cathode Material with a Single-Layer Li2 MnO3 Superstructure.

A high capacity cathode is the key to the realization of high-energy-density lithium-ion batteries. The anionic oxygen redox induced by activation of the Li2 MnO3 domain has previously afforded an O3-type layered Li-rich material used as the cathode for lithium-ion batteries with a notably high capacity of 250-300 mAh g-1 . However, its practical application in lithium-ion batteries has been limited due to electrodes made from this material suffering severe voltage fading and capacity decay during cycling. Here, it is shown that an O2-type Li-rich material with a single-layer Li2 MnO3 superstructure can deliver an extraordinary reversible capacity of 400 mAh g-1 (energy density: ≈1360 Wh kg-1 ). The activation of a single-layer Li2 MnO3 enables stable anionic oxygen redox reactions and leads to a highly reversible charge-discharge cycle. Understanding the high performance will further the development of high-capacity cathode materials that utilize anionic oxygen redox processes.

Effects of Particle Size on Voltage Fade for Li-Rich Mn-Based Layered Oxides.

Voltage fade significantly hinders the practical use of Li-rich Mn-based layered oxides (LLOs) as cathode materials for next-generation high-energy-density Li-ion batteries. Therefore, an in-depth understanding of the factors influencing the LLO voltage fade during cycling is fundamentally important for tailoring the structure and thus improving the electrochemical performance of the corresponding electrodes. Herein, we compare the electrochemical performances of LLOs with different particle size and conduct in situ high-pressure response measurements to determine the effects of particle size on voltage fade, demonstrating that small particles can undergo a reversible layer-to-spinel phase transition that results in improved voltage stability during cycling. The above finding provides a novel paradigm for the development of high-capacity LLO electrodes and thus contributes to the establishment of a more energy-efficient and green society.

Enhanced cycle performance of lithium-sulfur batteries using a separator modified with a PVDF-C layer.

High energy density Li-S batteries are highly attractive. However, their use in practical applications has been greatly affected by their poor cycle life and low rate performance, which can be partly attributed to the dissolution of polysulfides from the S cathode and their migration to the Li anode through the separator. While much effort has been devoted to designing the structure of the S cathodes for suppressing the dissolution of polysulfides, relatively little emphasis has been placed on modifying the separator. Herein, we demonstrate a new approach for modifying the separator with a polyvinylidene fluoride-carbon (PVDF-C) layer, where the polysulfides generated in the Li-S cells can be localized on the cathode side. Li-S batteries based on the novel separator and a cathode prepared by the simple mixing of a S powder and super P have delivered discharge capacities of 918.6 mAh g(-1), 827.2 mAh g(-1), and 669.1 mAh g(-1) after 100, 200, and 500 cycles, respectively, at a discharge rate of 0.5 C. Even under current densities of up to 5 C, the cells were able to retain a discharge capacity of 393 mAh g(-1), thereby demonstrating an excellent high rate performance and stability. The exceptional electrochemical performance could be attributed to the intense adsorption capability of the micropores, presence of C-C double bonds, and conductivity of the C network in the PVDF-C layer. This economical and simple strategy to overcome the polysulfide dissolution issues provides a commercially feasible method for the construction of Li-S batteries.