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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Etching-assisted upcycling of Ni-lean to Ni-rich cathode materials

Upcycling is recognized as a sustainable recycling approach for spent lithium-ion batteries. However, existing upcycling methods typically involve intricate pretreatment or post-treatment steps, complicating their practical application. Here, in this study, we propose a straightforward, etching-assisted upcycling method that effectively transforms polycrystalline Ni-lean cathodes into high-performance single crystal Ni-rich cathodes. During the etching step, nickel acetate was dissolved into acetic acid and then polycrystalline NMC111 are etched in the solution. Finally, polycrystalline NMC111 are converted into single crystal particles coated with amorphous nickel acetate. This significantly enhances elemental diffusion during subsequent sintering by minimizing both particle size and the contact distance between NMC111 and nickel acetate. As elemental diffusion is improved and acetate ions decompose completely during sintering, the process requires neither additional pretreatment nor post-treatment. The resulting cathode materials (Etched-UP622) exhibit superior structural and electrochemical properties compared to the Control622, achieving an energy density of 719.7 Wh/kg, approximately 56.7 mAh/g higher than Control622 and 125.5 Wh/kg higher than NMC111. Etched-UP622 also delivers higher discharge capacity, improved rate performance and cycling stability, surpassing Control622 and NMC111. Meanwhile, NMC811 also can be synthesized by the proposed strategy, and the discharge capacity can reach 166.9 mAh/g at 1C, similar to 14 mAh/g higher than Control811. Overall, this etching-assisted strategy simplifies the upcycling process and offers a scalable, sustainable route for producing high-quality cathode materials.

Acid etching↗
DOE OSTI2024

Slug-flow synthesis of NCMA: Effect of substitution of cobalt with aluminum on the electrochemical performance of Ni-rich cathode for lithium-ion battery

Nickle-rich Li[Ni 1-x-y Co x Mn y ]O 2 (x, y≤0.1) (NCM) layered materials are known as promising cathode materials for next-generation lithium-ion batteries and electric vehicles owing to their high-reversible capacity and operating voltage of up to 3.6 vs Li/Li + . However, issues, such as irreversible phase transition, cation mixing, microcrack formation, thermal and structural stability of the material prevent its widespread adoption. Although, cation doping is a well-known technique to enhance the electrochemical performance of the NCM-based cathode material, the performance of the material is very sensitive to the doping amount. In this study, three Al-doped quaternary Ni-rich cathode materials Li[Ni 0.85 Co (0.1-x) Mn 0.05 Al x ]O 2 (where, x=0–0.04) (NCMA) are synthesized through three-phase slug-flow based continuous manufacturing process followed by high temperature calcination to study the effect of Aldoping on the performance of the cathode material while reducing Co. The slug flow-based production platform has several advantages, like particle size uniformity, high production rate, and homogeneity in elemental distribution. It is found that with an increase in Al content, the specific capacity decreases but the cyclic stability and rate capability increases. Furthermore, optimum Al-doping not only compensates for the adverse effect of low Co by decreasing the extent of cation mixing, but it also minimizes the electrode polarization and cracking of the particles.

25 ENERGY STORAGE↗
DOE OSTI2024

Na 4 Fe 1.5 Mn 1.5 (PO 4 ) 2 (P 2 O 7 ): A low-cost and earth-abundant cathode for robust sodium storage

The mixed compounds of phosphates and pyrophosphates are attractive cathodes for sodium-ion batteries (SIBs) owing to their robust open framework structure and superior diffusion dynamics. However, most reported mixed phosphate cathodes generally suffer from low operating potential. Herein, we develop a bimetallic Na 4 Fe 1.5 Mn 1.5 (PO 4 ) 2 (P 2 O 7 )/C-rGO (NFMPP/C-rGO) cathode, which possesses two working plateaus at 2.92 and 3.95 V. The obtained NFMPP/C-rGO demonstrates a stable high capacity of over 120 mAh g −1 at 0.1 C. In-situ XRD characterization discloses a solid solution reaction for the Fe 2+/3+ redox couple and a two-phase reaction for the Mn 2+/3+ redox couple. In conclusion, first-principles calculations reveal the migration of Na + in NFMPP has low barriers. This work provides a new, low-cost, earth-abundant, and stable cathode choice for practical SIBs.

Cathode materials↗
DOE OSTI2020

Interfacial engineering for stabilizing polymer electrolytes with 4V cathodes in lithium metal batteries at elevated temperature

Poly (ethylene oxide) (PEO) polymer electrolytes are promising candidates for next-generation rechargeable lithium batteries. However, the poor interfacial stability between 4 V cathodes and PEO electrolytes impedes their applications in 4 V lithium batteries with high energy density. Here, we demonstrate a facile and effective strategy to enhance the interfacial stability by the synergy of Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) coating on the cathode surface, and salt combination in the electrolyte, even with a cut-off voltage of 4.25–4.4 V vs. Li + /Li. Nano-LAGP coated Li|PEO|LiCoO 2 cell delivers stable cycling with a capacity retention of 81.9%/400 cycles and 84.7%/200 cycles at 60 °C when charged to 4.25 and 4.3 V in pure polyether electrolyte, respectively. Steady cycling is also demonstrated at room temperature and with LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) cathode. This work offers a viable and scalable approach to improve the stability between PEO electrolytes and 4 V cathodes and open up new possibilities for practical application of 4 V lithium metal batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

A highly-stable layered Fe/Mn-based cathode with ultralow strain for advanced sodium-ion batteries

Sodium-ion batteries (SIBs) with iron- and manganese-based cathode electrodes have exhibited great promise in the grid-scale energy storage systems, on the basis of the satisfactory theoretical capacity, as well as huge abundance, low price and non-toxicity of raw materials. However, the inferior cycle life of cathode materials originating from their poor structural stability remains a formidable challenge towards practical applications. In this study, an efficient strategy of improving the structure durability is demonstrated in iron- and manganese-based cathodes by dual heteroatom doping. The as-obtained P2-type Na 0.65 Li 0.08 Cu 0.08 Fe 0.24 Mn 0.6 O 2 cathode delivers superior cyclability (88.2% capacity retention for 500 cycles at 2C), fabulous rate capability (76% capacity retention at 5C compared to 0.1C), and a useable reversible capacity of around 85 mAh g -1 at 0.1C. Through in-depth characterizations, the underlying structure-property relationship is established, revealing that the complete solid-solution reaction during cycling ensures the ultralow volume variation (as small as 0.7%) and excellent electrochemical performance. These results highlight the significance of fabricating a stable host for the design and development of advanced SIBs with long life.

25 ENERGY STORAGE↗
DOE OSTI2024

Understanding improved cycling and thermal stability of compositionally graded Ni-rich layered LiNi 0.6 Mn 0.2 Co 0.2 O 2 cathode materials

The concentration gradient is a strategic design, adjusting the distribution of Ni, typically with a higher Ni content in the core and a higher Mn content toward the surface. This design leverages the pivotal role of the Ni/Mn ratio, seeking to optimize cathode performance by balancing Ni's high capacity with Mn's stabilizing effects, particularly at the surface where degradation commonly occurs during cycling. Here, our study delves into the intricate structural and chemical transformations within concentration gradient cathode materials during electrochemical cycling. Utilizing advanced synchrotron X-ray techniques, including hard and soft X-ray absorption spectroscopy (hXAS, sXAS), and nanoscale X-ray imaging, we investigate buried changes in concentration gradient LiNi 0.6 Mn 0.2 Co 0.2 O 2 (CG NMC622). Contrary to conventional assumptions, our findings challenge the notion that cycling stability relies solely on Mn stability. Unraveling the roles of Ni and Mn, we uncover how their individual and collective contributions impact the cathode's overall performance. This investigation transcends established paradigms, shedding light on the crucial mechanisms governing the enhanced cycling stability of Nirich layered cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2020

Controlled Dy-doping to nickel-rich cathode materials in high temperature aerosol synthesis

Layered nickel-rich materials are promising next-generation cathode materials for lithium ion batteries due to their high capacity and low cost. However, the poor thermal stability and longtime cycling performance hinders the commercial applications of high nickel materials. Doping with heteroatoms has been an effective approach for improving electrochemical performance of cathode materials. Controlling doping concentration and geometrical distribution is desired for optimal electrochemical performance, but it is challenging in traditional co-precipitation methods. In this work, controlled dysprosium (Dy) doping to NCM811 was studied in an aerosol synthesis method by controlling the precursor concentrations and heating parameters. The obtained materials were characterized by SEM, XRD, and XPS, and their electrochemical properties and thermal stability were evaluated. By controlling the doping concentration (1.5%), Dy-doped NCM811 was improved simultaneously in long-term cycling and high-rate performance. Here, the thermal-chemical stability of the Dy-doped cathode materials was examined in a microflow reactor with a mass spectrometer. The results showed that Dy-doping shifted the O 2 onset temperature to a higher temperature and reduced O 2 release by 80%, thus dramatically increasing the thermal-chemical stability and improving the fire safety of cathode materials. Since high temperature aerosol synthesis is a low-cost and scalable method, the findings in this work have broad implications for commercial synthesis of novel materials with controlled doping modification to achieve high electrochemical performance and safety in lithium ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2023

Roles of Mn and Co in the Air Synthesizability of Layered Oxide Cathodes for Lithium-Based Batteries

High-nickel layered oxides (LiNi 1-x-y Mn x Co y O 2 ) are the prevailing cathode materials for high-energy-density lithium-based batteries, but they are plagued with deleterious surface air instabilities stemming from residual lithium formation. These issues severely hinder mass production as cathode calcination is limited to a flowing oxygen atmosphere, which entails high manufacturing costs as opposed to simpler and more economical air calcination. Here, while higher Ni contents are known to worsen air instabilities, the influence of Mn and Co contents on impacting these phenomena are less elucidated. We herein present the synthesis in ambient air and flowing oxygen atmospheres of three cathode variants with the same Ni contents, but varying Mn and Co contents: LiNi 0.7 Mn 0.3 O 2 , LiNi 0.7 Mn 0.15 Co 0.15 O 2 , and LiNi 0.7 Co 0.3 O 2 . It is found that the critical parameter influencing the air stability of the cathodes is the average Ni oxidation state, which is greatly dependent on the Mn and Co contents. Substitution of Mn for Ni drives down the Ni oxidation state as Mn exists as Mn4 + and reduces surface residual lithium formation, which vastly improves the overall air stability and, therefore, the synthesizability in air, but with a penalty of lowered capacity. In contrast, substitution of Co for Ni maintains Ni 3+ as Co exists as Co 3+ , offering increased initial capacity, but worsens the air stability and cyclability as the driving force for residual lithium formation and surface reactivity is increased.

25 ENERGY STORAGE↗
DOE OSTI2020

Redox Behaviors in Li-Excess Cation-Disordered Mn-Nb-O-F Rocksalt Cathode

Lithium-excess cation-disordered rocksalt oxide (DRX) is a new choice of high energy Li-ion cathode materials. DRX cathode can deliver an exceptionally high capacity of >250 mAh/g, implying the participation of cationic transition metal and anionic oxygen redox in the electrochemistry. Understanding the explicit roles of both redox reactions in the newly developed cathode is of critical importance to further development of these materials. Herein, we synthesize a representative Mn-redox-based fluorinated DRX material, Li1.2Mn0.625Nb0.175O1.95F0.05 (LMNOF). Using a comprehensive suite of electroanalytical methods, we probe the cationic and anionic redox processes and their evolution upon cycling exclusively from the electrochemical point of view. This work sheds light on understanding of cationic and anionic redox and their roles in the capacity loss for high-capacity fluorinated DRX cathode, meanwhile, showcases an explicit approach to study the electrochemistry of novel electrode materials using such non-disruptive electroanalytical methods.

Li-ion battery, high-capacity cathode, Li-excess m↗
DOE OSTI2022

Porosity Development at Li-Rich Layered Cathodes in All-Solid-State Battery during In Situ Delithiation

Structural evolutions are crucial for determining the performance of high-voltage lithium, manganese-rich layered cathodes. Moreover, interface between electrode and electrolyte plays a critical role in governing ionic transfer in all-solid-state batteries. In this work, we unveil two different types of porous structure in Li 1.2 Ni 0.2 Mn 0.6 O 2 cathode with LiPON solid-state electrolyte. Na-nopores are found near the cathode/electrolyte interface at pristine state, where cation mixing, phase transformation, oxygen loss and Mn reduction are also found. In situ Li + extraction induces the evolution of nanovoids, initially formed near the inter-face then propagated into the bulk. Despite the development of nanovoids, layered structure is conserved, suggesting the nature of nanopores and nanovoids are different and their impact would be divergent. This work demonstrates the intrinsic interfacial layer, as well as the dynamic scenario of nanovoid formation inside high-capacity layered cathode, which help understanding the performance fading in cathodes and offer insights into the all-solid-state battery design.

25 ENERGY STORAGE↗
DOE OSTI2020

Structural and Electrochemical Impacts of Mg/Mn Dual Dopants on the LiNiO 2 Cathode in Li-Metal Batteries

Doping chemistry has been regarded as an efficient strategy to overcome some fundamental challenges facing the “no-cobalt” LiNiO 2 cathode materials. By utilizing the doping chemistry, we evaluate the battery performance and structural/chemical reversibility of a new no-cobalt cathode material (Mg/Mn-LiNiO 2 ). The unique dual dopants drive Mg and Mn to occupy the Li site and Ni site, respectively. We report the Mg/Mn-LiNiO 2 cathode delivers smooth voltage profiles, enhanced structural stability, elevated self-discharge resistance, and inhibited nickel dissolution. As a result, the Mg/Mn-LiNiO 2 cathode enables improved cycling stability in lithium metal batteries with the conventional carbonate electrolyte: 80% capacity retention after 350 cycles at C /3, and 67% capacity retention after 500 cycles at 2 C (22 °C). We then take the Mg/Mn-LiNiO 2 as the platform to investigate the local structural and chemical reversibility, where we identify that the irreversibility takes place starting from the very first cycle. The highly reactive surface induces the surface oxygen loss, metal reduction reaching the subsurface, and metal dissolution. Our data demonstrate that the dual dopants can, to some degree, mitigate the irreversibility and improve the cycling stability of LiNiO 2 , but more efforts are needed to eliminate the key challenges of these materials for battery operation in the conventional carbonate electrolyte.

25 ENERGY STORAGE↗
DOE OSTI2020

LaCrO 3 -Coated La 0.6 Sr 0.4 Co 0.2 Fe0.8O3–δ Core–Shell Structured Cathode with Enhanced Cr Tolerance for Intermediate-Temperature Solid Oxide Fuel Cells

La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) is a common cathode material for intermediate temperature solid oxide fuel cells due to its excellent oxygen reduction reaction catalytic activity. However, the Cr-poisoning effect is a severe issue causing its electrochemical performance degrada-tion. To develop a LSCF-based cathode with excellent Cr-tolerance, LaCrO 3 -coated LSCF core-shell structured (LCr@LSCF) cathode was prepared via solution infiltration method. After coated by LCr shell, the long-term stability and Cr-tolerance were obviously improved, at the price of sacrificing some electrochemical performance. As a result, the development of LCr@LSCF cathode with eye-catching Cr-tolerance is of great significance to the commercialization of LSCF.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Iron-Doped Sodium Vanadium Oxyflurophosphate Cathodes for Sodium-Ion Batteries—Electrochemical Characterization and In Situ Measurements of Heat Generation

Sodium-ion batteries (NaIBs) are increasingly being envisioned for grid-scale energy-storage systems because of cost advantages. However, implementation of this vision has been challenged by the low-energy densities delivered by most NaIB cathodes. Toward addressing this challenge, the authors report the synthesis and characterization of a new iron-doped Na 3 Fe 0.3 V 1.7 O(PO 4 ) 2 F 2 cathode using a novel facile hydrothermal route. The synthesized material was characterized using scanning electron microscopy, X-ray diffraction, and Mössbauer spectroscopy techniques. The obtained discharge capacity in the half-cell configuration lies from 119 to 125 to 130 mA h/g at C/10 while tested using three different electrolyte formulations, dimethyl carbonate–ethylene carbonate (EC)–propylene carbonate (PC), diethyl carbonate–EC, and EC–PC, respectively. The synthesized cathodes were also evaluated in full-cell configurations, which delivered an initial discharge capacity of 80 mA h/g with NaTi 2 (PO 4 ) 3 MWCNT as the anode. Ionic diffusivity and interfacial charge transfer kinetics were also evaluated as a function of temperature and sodium concentration, which revealed that electrochemical rate performances in this material were limited by charge-transfer kinetics. To understand the heat generation mechanism of the Na/Na 3 Fe 0.3 V 1.7 O(PO 4 ) 2 F 2 half-cell during charge and discharge processes, an electrochemical isothermal calorimetry measurement was carried out at different current rates for two different temperatures (25 and 45 °C). The results showed that the amount of heat generated was strongly affected by the operating charge/discharge state, C-rate, and temperature. Altogether, this work provides a new synthesis route for the development of iron-doped Na 3 Fe 0.3 V 1.7 O(PO 4 ) 2 F 2 -based high-performance sodium cathode materials aimed at providing a viable pathway for the development and deployment of large-scale energy-storage based on sodium battery systems.

25 ENERGY STORAGE↗
DOE OSTI2022

Understanding the Effect of Cathode Composition on the Interface and Crosstalk in NMC/Si Full Cells

Crosstalk between the cathode and the anode in lithium-ion batteries has a great impact on performance, safety, and cycle lifetime. Still, no report exists for a systematic investigation on crosstalk behavior in silicon (Si)-based cells as a function of transition metal composition in cathodes. We studied the effect of crosstalk on degradation of Si-rich anodes in full cells with different cathodes having the same crystal structure but different transition metal compositions, such as LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NM111), LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC532), and LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811). We found that the transition metal composition in cathodes, especially Mn ion concentration, significantly affects electrolyte decomposition reactions, even from very early cycles. This change causes differences in the solid electrolyte interphase (SEI) chemistry of each aged Si sample. As a result, each of the aged Si samples has a different electrochemistry, in terms of initial Coulombic efficiency and the mechanism of capacity fade.

25 ENERGY STORAGE↗
DOE OSTI2022

Facile Dual-Protection Layer and Advanced Electrolyte Enhancing Performances of Cobalt-free/Nickel-rich Cathodes in Lithium-Ion Batteries

Despite cobalt (Co)-free/nickel (Ni)-rich layered oxides being considered as one of the promising cathode materials due to their high specific capacity, their highly reactive surface is one of the shortcomings that still hinder their practical usages in high-energy-density batteries. Herein, a polyimide/polyvinylpyrrolidone (PI/PVP, denoted as PP) coating layer is demonstrated as dual-protection for LiNi 0.96 Mg 0.02 Ti 0.02 O 2 (NMT) cathode material to suppress surface contamination against moisty air and to prevent unwanted side reactions between cathode and electrolyte during electrochemical cycling. The optimal PP-coated NMT (PP@NMT) preserves a clean surface without generation of lithium (Li) residues, structural degradation, and gas evolution after exposure to air with ~30% humidity for 2 weeks. Contrarily, the exposed bare NMT shows severe contamination, structural shrinkage due to Li loss, and increased gas release during charging. In addition, the exposed PP@NMT significantly enhances the electrochemical performance of graphite (Gr)||NMT cells by decreasing byproducts and maintaining structural stability. Moreover, the exposed PP@NMT achieves a high capacity retention of 86.7% after 500 cycles in Gr||NMT cells using an advanced localized high-concentration electrolyte. Furthermore, this work demonstrates a promising facile approach to the protection of Co-free/Ni-rich layered cathodes for their practical applications even after exposure to moisty air.

25 ENERGY STORAGE↗
DOE OSTI2023

Heuristics for Molten-Salt Synthesis of Single-Crystalline Ultrahigh-Nickel Layered Oxide Cathodes

In pursuit of Li-ion batteries with higher energy density, ultrahigh-nickel layered oxides are a leading candidate for next-generation cathode materials. Single-crystalline morphology offers a neat solution to the poor stability of ultrahigh-Ni cathodes; a lower active surface area mitigates electrolyte decomposition at high voltages, and the elimination of grain boundaries improves mechanical resilience and increases volumetric energy density. However, single-crystal cathodes possess their own challenges, several of which originate from synthesis at elevated temperatures meant to induce grain growth. Molten-salt synthesis is an alternative method for obtaining single crystals, accelerating grain growth through the presence of a molten flux without the need for increased temperature. Herein, we offer heuristic guidelines for molten-salt synthesis, discussing key factors for designing reaction mixtures and the necessary exploratory research for novel molten salt/cathode systems. Here, the influence of different salts and synthesis conditions on the morphology and properties of single-crystal LiNiO 2 is presented. It is found that oxidative salts, such as Li 2 O 2 and LiNO 3 , are crucial to supplementing dissolution of gaseous oxygen into the molten phase. Through these discussions, this work aims to provide a set of overarching principles for obtaining higher-quality single-crystal layered oxide cathodes and engender more rigorous and impactful investigation into their fundamental nature and applications.

25 ENERGY STORAGE↗
DOE OSTI2023

Enhancing the Electrode Gravimetric Capacity of Li 1.2 Mn 0.4 Ti 0.4 O 2 Cathode Using Interfacial Carbon Deposition and Carbon Nanotube-Mediated Electrical Percolation

Mn-based cation disordered rocksalt oxides (Mn-DRX) are emerging as promising cathode materials for next-generation Li-ion batteries due to their high specific capacities and cobalt and nickel free characteristic. However, to reach the theoretical capacity, solid-state method synthesized Mn-DRX materials require activation via post-synthetic ball milling, typically incorporating more than 20 wt.% conductive carbon that adversely reduces the electrode level gravimetric capacity. To solve this issue, we firstly deposit amorphous carbon on the surface of the Li 1.2 Mn 0.4 Ti 0.4 O 2 (LMTO) particles to increase the electrical conductivity by a five order of magnitude. Although the cathode material gravimetric first charge capacity reaches 180 mAh/g, its highly irreversible behavior leads to a 70 mAh/g first discharge capacity. Subsequently, to ensure a good electrical percolation network, the LMTO material is ball milled with multi-wall carbon nanotube (CNT) to obtain a 78.7 wt.% LMTO active material loading in the cathode electrode (LMTO-CNT). As a result, a 210 mAh/g cathode electrode gravimetric first charge and 165 mAh/g first discharge capacity are obtained, compared to the respective capacity values of 222 mAh/g and 155 mAh/g for the LMTO ball milled with 20 wt.% SuperP C65 electrode (LMTO-SP). After 50 cycles, the LMTO-CNT delivers a 121 mAh/g electrode gravimetric discharge capacity, largely outperforming the 44 mAh/g value of the LMTO-SP. In conclusion, our study demonstrates that while ball milling is necessary to achieve the theoretical capacity of LMTO, a careful selection of the additive, such as CNT, effectively reduces the required carbon quantity to achieve a higher electrode gravimetric discharge capacity.

25 ENERGY STORAGE↗
DOE OSTI2023

Novel Structural Motif To Promote Mg-Ion Mobility: Investigating ABO 4 Zircons as Magnesium Intercalation Cathodes

There is an increasing need for sustainable energy storage solutions as fossil fuels are replaced by renewable energy sources. Multivalent batteries, specifically Mg batteries, are one energy storage technology that researchers continue to develop with hopes to surpass the performance of Li-ion batteries. However, the limited energy density and transport properties of Mg cathodes remain critical challenges preventing the realization of high-performance multivalent batteries. In this work, ABO 4 zircon materials (A = Y, Eu and B = V, Cr) are computationally and experimentally evaluated as Mg intercalation cathodes. Remarkably good Mg-ion transport properties were predicted and Mg-ion intercalation was experimentally verified in sol-gel synthesized zircon YVO 4 , EuVO 4 , and EuCrO 4 . Among them, EuVO 4 exhibited the best electrochemical performance and demonstrated repeated reversible cycling. While we believe that the one-dimensional diffusion channels and redox-active species tetragonal coordination limit the value of many zircons as high-performance cathodes, their unique structural motif of overlapping polyhedra along the diffusion pathway appears instrumental for promoting good Mg-ion mobility. The motif results in a favorable "6-5-4" change in coordination that avoids unfavorable sites with lower coordination along the diffusion pathway and a structural design metric for future Mg cathode development.

25 ENERGY STORAGE↗