Improved Capacity Retention Research Articles

Pressure‐Induced Capacity Recovery and Performance Enhancements in LTO/NMC‐LCO Batteries

AbstractLithium titanate oxide (LTO) batteries are a promising technology, particularly suitable for high‐power applications, owing to their inherent cyclic stability, fast charging capability, and superior safety. However, substantial gas generation and accelerated aging driven by the cathode remain substantial challenges. This study explores the mitigation of these aging mechanisms through the application of external mechanical compression. Continuous pressure of 0.3 MPa applied to pristine cells during cycling reduces capacity loss by 42% compared to unpressurized cells cycled under identical operating conditions. Applying short‐term pressure to aged cells leads to immediate capacity recovery, reclaiming up to 57% of the lost capacity. Subsequent cycling of these aged cells under continuous pressure demonstrates improved capacity retention. In contrast, intermittently applied transient pressure causes notable capacity fluctuations. This study reveals insights into aging and healing mechanisms influenced by external pressure, benefiting both first‐ and second‐life battery applications. Understanding these mechanisms is vital for enhancing performance and lifetime in battery packs, while the findings also highlight promising opportunities for capacity recovery in reused batteries.

Electrolyte‐free solid‐state batteries demonstrated with bifunctional Li2VCl4

All‐solid‐state batteries have attracted much attention because of the expected high energy density and inherent safety stemming from their nonflammable property. While improving the energy density of the cathode poses a significant challenge, here we introduce a novel battery design strategy to enhance energy density by employing bifunctional cathode material, allowing the weight ratio of the active material to be increased without using an electrolyte for the cathode. By employing lithium‐containing vanadium halide Li2VCl4, serving as both active material and electrolyte, the all‐solid‐state battery cell with no electrolyte for the cathode with a capacity approaching the theoretical limit is demonstrated. In addition, we present a guideline for improving capacity retention from the perspective of interfacial stability. Notably, thermodynamic analysis revealed interfacial instability between Li2VCl4 and sulfide material. A double‐layer separator, incorporating halide materials for the cathode side, was implemented to enhance the interfacial stability and mitigate the capacity degradation. Furthermore, it was found that the rate capability depends on the lithium content in synthesized Li2‐xVCl4 and does not change with the state of charge significantly. This study will contribute to designing the bifunctional cathode material for an all‐solid‐state battery and describe its unique properties.

Promoting homogeneous tungsten doping in LiNiO2 through a grain boundary phase induced by excessive lithium

LiNiO2 (LNO) is one of the most promising cathode materials for lithium-ion batteries. Tungsten element in enhancing the stability of LNO has been researched extensively. However, the understanding of the specific doping process and existing form of W is still not perfect. This study proposes a lithium-induced grain boundary phase W doping mechanism. The results demonstrate that the introduced W atoms first react with the lithium source to generate a Li-W-O phase at the grain boundary of primary particles. With the increase of lithium ratio, W atoms gradually diffuse from the grain boundary phase to the interior layered structure to achieve W doping. The feasibility of grain boundary phase doping is verified by first principles calculation. Furthermore, it is found that the Li2WO4 grain boundary phase is an excellent lithium ion conductor, which can protect the cathode surface and improve the rate performance. The doped W can alleviate the harmful H2↔H3 phase transition, thereby inhibiting the generation of microcracks, and improving the electrochemical performance. Consequently, the 0.3wt% W-doped sample provides a significant improved capacity retention of 88.5% compared with the pristine LNO (80.7%) after 100 cycles at 2.8-4.3 V under 1 C.

Modality-Tunable Exfoliated N-Doped Graphene as Effective Electrolyte Additive for High-Performance Lithium-Sulfur Batteries.

While chemically doped graphene has shown great promise, the lack of cost-effective manufacturing has hindered its use. This study utilizes a facile fabrication approach for modality-tunable N-doped graphene via thermal annealing of aqueous-phase-exfoliated few-layered graphene from a Taylor-Couette reactor. This method demonstrates a high level of N-doping (27 atom % N) and offers modality tunability of the C-N bond without foregoing scalability and green chemistry principles. The resulting N-doped graphene, with varying N content and doping modality, is utilized in the lithium-sulfur battery electrolyte to address low ionic conductivity, lithium polysulfide (LiPS) shuttling, and Li anode instability. The study reveals that higher N content and pyridinic N modality graphene in the electrolyte positively influence battery performance. The results are 2-fold: higher overall N content improves capacity retention (73%) after 225 cycles at 0.2 C, and pyridinic-type nitrogen demonstrates the best performance at high C rates, exhibiting a 4-fold capacity increase relative to the reference cell at 2 C. Further, the computational study validates the adsorption affinity of LiPS to pyridinic nitrogen and improved Li+ mobility on the graphene backbone observed experimentally. This first experimental study on the impact of N-dopant concentration and modality on electrochemical performance provokes insights into tailoring N functionalization to achieve superior electrochemical performance.

Optimal charging of Li-ion batteries using sparse identification of nonlinear dynamics

Optimal charging of Li-ion batteries requires careful management of charge rates, as high rates can lead to accelerated degradation, while low rates significantly extend charging times. Traditional methods for determining charge rates often rely on rule-based approaches, which typically fail to effectively balance battery performance with charging duration. To address this, we introduce a novel optimization approach that directly integrates the dual objectives of minimizing charge time and maximizing battery lifetime into the optimization process. Unlike most existing charge optimization methods that do not directly track battery lifetime and charge time simultaneously, our method employs a data-driven model that facilitates direct and dynamic estimation of both battery lifetime and charge time at each step of the optimization process. Specifically, we utilize the Sparse Identification of Nonlinear Dynamics (SINDy) algorithm to predict battery capacity and voltage dynamics, which informs the calculations of lifetime and charge time required to solve the optimization problem. This approach provides a balanced optimization strategy that enhances the effectiveness of battery’s performance while maintaining the efficiency of the charging process. We applied this method to a novel next-generation NMC811 battery, featuring a cathode comprised of 80 % nickel, 10 % manganese, and 10 % cobalt, and a lithium metal foil anode - a combination not extensively studied previously. Experimental validation demonstrated that when optimized charge rates are applied every 10 cycles in a 100-cycle operation, the method leads to more stable cycling and improved capacity retention of approximately 7.4 % over the nominal charge rate, demonstrating the potential of the developed approach.

Synergistic Impact of Alloying with Ni on Cu Cathode Interfaces for Fluoride Batteries.

All-solid-state fluoride batteries have the potential to achieve energy densities significantly higher than those of lithium-ion batteries. A common cathode material for fluoride batteries is Cu. Cu has a low polarization, but its rapid capacity degradation due to grain growth and subsequent delamination from the solid-state electrolyte are critical issues. To enhance the performance of Cu-based cathodes in all-solid-state fluoride batteries, we explore alloying of Cu with Ni to create metastable solid solution phases (CuxNi1-x with x = 0, 0.32, 0.52, 0.72, 0.89, and 1.0). Compared to Cu, Ni has a higher polarization but exhibits superior capacity retention. The Cu0.72Ni0.28 alloy demonstrates a polarization as low as Cu, but it has a significantly improved capacity retention, which is comparable to Ni. Transmission electron microscopy observations demonstrate that the thin Ni-rich region formed near the interface inhibits Cu grain growth and delamination from the LaF3 electrolyte. By incorporating an appropriate amount of Ni into Cu, Cu-Ni alloy films combine the advantages of both metals, improving the performance of fluoride batteries.

Enhanced performance of GO and RGO/Y2SiO5: Sm3+ nanocomposites for supercapacitors and biosensors

The increasing demand for high-performance materials in energy storage and biosensing applications highlights the need for ongoing research. Traditional materials often fail to meet the required standards for specific capacitance, energy density, and selectivity. Developing advanced nanocomposites, such as reduced graphene oxide (RGO) based Y2SiO5:Sm3+ (RYSOS), seeks to overcome these limitations, providing enhanced efficiency and stability. This study synthesized RYSOS nanocomposites for supercapacitor and biosensor applications, demonstrating superior performance over graphene oxide (GO) (GYSOS). RYSOS exhibited a higher specific capacitance of 474.81 Fg−1 compared to 396.68F−1 for GYSOS, and an energy density of 55.55 Wh/kg versus 32.89 Wh/kg. Additionally, RYSOS electrodes showed improved capacity retention at 87.83 % and coulombic efficiency at 91.54 % after 5000 cycles. In biosensing, RYSOS-modified carbon paste electrodes achieved excellent dopamine detection at pH 7.4, with a limit of detection (LOD) of 0.8579 µM and a limit of quantification (LOQ) of 2.859 µM. The developed electrode also demonstrated high selectivity for dopamine over uric acid and maintained 90 % stability over 10 cycles. These findings underscore the potential of RYSOS nanocomposites in enhancing the performance of advanced energy storage systems and biosensors, highlighting their effectiveness in specific capacitance, energy density, and selective biosensing capabilities.

Surface Reconstruction Enhanced Li-Rich Cathode Materials for Durable Lithium-Ion Batteries.

Regulating the distribution of surface elements in lithium-rich cathode materials can effectively change the electrochemical performance of cathode materials. Considering that the enrichment of Mn element on the surface is the main reason for the irreversible phase transition and dissolution of its surface structure, which in turn is the main reason for performance degradation. Based on the molten salt-assisted sintering method, a lithium rich cathode material with surface rich Ni and Co is designed and prepared. The surface enrichment of Ni and Co effectively reduces the dissolution of Mn, promotes the occurrence of irreversible collapse of surface structure from layered phase to rock salt phase on the material surface, improves the stability of surface crystal phase structure, and improves the cycling stability of positive electrode materials. Notably, after 500 cycles at 1 C current density, the discharge-specific capacity attained 189.8 mAh g -1, with a capacity retention rate of 88.9%, indicating a 42.1% improvement in capacity retention. Molten salt treatment is widely used in the modification of positive electrode materials. The research work will provide new ideas for improving the stability of lithium rich materials and promoting their commercial applications.

Modulating the lattice structure via Cr3+ doping in LiFe0.4Mn0.6PO4 cathode for improved rate behavior and promoted cyclic performance

Although LiFe0.4Mn0.6PO4 cathode shows high potential in battery industry, the cyclic performance and rate behavior are still the concerns to overcome. In this paper, Cr3+ doping in the cathode is confirmed very effective to improve both the performance via increased Li migration kinetics and suppressed lattice expansion during the redox process. It is found from the XRD refinement that Li − O bond length is increased upon Cr3+ intercalation, which in turn leads to the decrease in migration energy barrier (from 48.41 KJ·mol−1 to 19.57 KJ·mol−1) and the increase in Li diffusion coefficient. GITT investigation reveals a big promotion of DLi from 7.38 × 10−11 cm2·s−1 to 4.47 × 10−10 cm2·s−1, which is regarded as the reason for the excellent rate capacity of 126.62 mAh·g−1 (80.8 % of the value at 0.1C) at 5C current density. Further study with ex-situ XRD investigation reveals that the lattice expansion during redox process is suppressed after Cr3+ doping due to the smaller radius and stronger bond energy of the substituted cations. The suppressed volume change decreases both the internal resistance and the polarization of the electrode, which therefore leads to an improved capacity retention. The initial discharge specific capacity of LFMP-2%Cr cathode material reaches 156.8 mAh·g−1 at 0.1C, and the capacity retention rate of the material is maintained as 98.4 % after 100 cycles at 0.5C. The above results reveal the effectiveness of Cr3+ in promoting the electrochemical performance and further confirm the Cr- doped LFMP cathode high potential in future application.

Enhancing the Cycling and Rate Performance of NaNi1/3Fe1/3Mn1/3O2 Cathodes by La/Al Codoping.

O3-type layered oxides hold significant promise as the material for cathodes in sodium-ion batteries for their favorable electrochemical properties, while irreversible structural degradation and harmful phase transitions during cyclic operation limit the practical application of these materials. In this work, we proposed a La3+/Al3+ codoping strategy in O3-Na(Ni1/3Mn1/3Fe1/3)O2 cathode materials and found that batteries with the Na (Ni1/3Mn1/3Fe1/3)0.998La0.001Al0.001O2 (NFM-La/Al) cathodes exhibited not only promoted capacity from 135.80 to 170.42 mAh g-1 at 0.2 C but also significantly enhanced cycling stability, with a 10% improvement in capacity retention compared with NFM cathodes after 300 cycles. Particularly, their rate performance was significantly improved as well. XRD and XPS tests indicated that La could expand the c-axis of NFM due to its larger ionic radius and thus significantly increased Na+ ion diffusion efficiency, and in addition, Al doping could effectively increase the content of Ni2+ and Mn4+ and thus greatly alleviated the negative Jahn-Teller effect caused by Mn3+. Moreover, consistent with XRD analyses, DFT calculations further substantiated the effectiveness of the La/Al codoping strategy by demonstrating the detailed atom substitution mechanism in the NFM crystal lattice. The boosted structure stability and Na+ diffusion kinetics may enhance the potential for practical applications of O3-type oxide cathodes.

A Novel 4-Fluorophenyl Isocyanate Additive Constructing Solid Cathodes-Electrolyte Interface for High-Performance Lithium-Ion Batteries.

Building a stable cathode-electrolyte interface (CEI) is crucial for achieving high-performance layered metal oxide cathode materials LiNixCoyMn1-x-yO2 (NCM). In this work, a novel 4-fluorobenzene isocyanate (4-FBC) electrolyte additive that contains isocyanate and benzene ring functional groups is proposed, which can form robust and homogeneous N-rich and benzene ring skeleton CEI film on the cathode surface, leading to significant improvement in the electrochemical performance of lithium-ion batteries. Taking LiNi0.5Co0.2Mn0.3O2 (NCM523) as an example, the NCM523/SiO@Graphite pouch full cells with electrolytes containing a mass fraction of 1% 4-FBC additives demonstrate improved capacity retention after 200 cycles, retaining capacity retention rates of 81.3%, which is much higher than that of 39.1% without additive. The improvement can be ascribed to the mitigation of electrolyte decomposition and inhibition of transition metal ions the dissolution from the cathode material due to the stable CEI film. Moreover, the electrochemical performance enhancement can also be achieved in high voltage and Ni-rich cathode materials, indicating the universality and effectiveness of this strategy for the practical applications of high energy density lithium-ion batteries.

A Na-Free Surface Enables "Three-In-One" Enhancement of Structural, Interfacial and Air Stability for Sodium-Ion Battery Cathodes.

O3-type layered oxides are regarded as one of the most promising cathode materials for sodium-ion batteries. However, the multistep phase transitions, severe electrode/electrolyte parasitic reactions, and moisture sensitivity are challenging for their practical application because of the highly active Na+. Here, a Na-free layer is built on the surface of NaNi1/3Mn1/3Fe1/3O2 (NMF111) via a leaching treatment and the subsequent surface reconstruction. Accordingly, both the structural degradation from bulk to surface and the overgrowth of the solid electrolyte interface (SEI) are greatly ameliorated, which results in the improved capacity retention of modified NMF111 from 58.3% to 89.6% after 400 cycles at 1 C. Besides, the Na-free surface with rock-salt structure prevents the H+/Na+ exchange and then enables good reversibility and low polarization of the optimal NMF111 when exposed to wet air (50% RH) for 4 days. This work opens a new avenue for the comprehensive cyclability improvement of layered oxides via surface reconstruction.

Exploring the Nb-Ti-W-O System for Use as Li-Ion Battery Anodes

While much attention in recent years has been given to high performance Li-ion batteries for electrical vehicles, other applications such as medical devices require a unique set of properties that demand a different set of material considerations such as long lifetimes and extremely high safety. Anodes for such batteries must be carefully selected to properly achieve these goals. The most commonly industrially utilized anode material, graphite, is not suitable for medical applications due to particle fracture and Li dendrite growth at high rates. Currently utilized medical device anode materials obtain this high performance by sacrificing energy density.Herein a new set of Nb based materials for use as anodes are presented that do not need to make such a sacrifice as they display high longevity along with high energy densities. The Nb-Ti-W pseudoternary features many promising single-phase compositions that could be used as anodes for such devices. These compositions derive from crystal structures that are found on both the Nb2O5-WO3 and Nb2O5-TiO2 pseudobinaries1, though they posses a more diverse range of chemical compositions. These compositions feature high performance discharge capacities of up to 300 mAh/g. Some materials also display robust capacity retentions of up to 98% after 10 cycles. The materials were also tested at 37 °C to simulate operation within the human body. At these temperatures, improvements were found in electrochemical performance for nearly all compositions, notably demonstrating a large improvement in capacity retention regardless of crystal structure. References (1) Rehman, S.; Sieffert, J. M.; Lang, C. J.; McCalla, E. NbyW1-yOz and NbxTi1-xOz pseudobinaries as anodes for Li-ion batteries. Electrochimica Acta 2023, 439. DOI: 10.1016/j.electacta.2022.141665.

Rapid in-Situ Electrochemical Formation of Partially Disordered Spinel from Mn-Rich Disordered Rocksalt Cathodes

We present the development of an electrochemical formation method that enables rapid and in-situ formation of a partially disordered spinel phase from an initially disordered rocksalt (DRX) cathode. Recent studies on Mn-rich DRX materials have demonstrated the emergence of a spinel-like phase during cycling, resulting in improved capacity retention, energy density, and rate capability compared to materials which do not transform1,2,3. However, this transformation process typically requires weeks of cycling at relatively low rates, posing significant challenges for the commercialization of such materials.To gain a deeper understanding of this transformation process, we carry-out a systematic study to determine whether the formation process of these spinel-like materials can be accelerated through a precycling formation process. By employing a novel electrochemical approach to purposefully stimulate the transformation, we successfully reduce the time required from several weeks to as little as one day for Mn-rich DRX. Extended cycling and synchrotron X-ray diffraction confirm that these materials exhibit both equivalent performance and resulting structure to those obtained through conventional cycling over a much longer duration. Further characterization of this material using HAADF and 4-D STEM reveals the complex local structure of the spinel-like partial ordering. It is hoped that such a practical electrochemical formation method will allow for an acceleration of research on these earth-abundant and energy-dense materials. Li, L.; Lun, Z.; Chen, D.; Yue, Y.; Tong, W.; Chen, G.; Ceder, G.; Wang, C. Fluorination-Enhanced Surface Stability of Cation-Disordered Rocksalt Cathodes for Li-Ion Batteries. Adv Funct Mater 2021, 31 (25), 2101888. https://doi.org/10.1002/adfm.202101888.Ahn, J.; Giovine, R.; Wu, V. C.; Koirala, K. P.; Wang, C.; Clément, R. J.; Chen, G. Ultrahigh-Capacity Rocksalt Cathodes Enabled by Cycling-Activated Structural Changes. Adv. Energy Mater. 2023. https://doi.org/10.1002/aenm.202300221. Cai, Z.; Ouyang, B.; Hau, H.-M.; Chen, T.; Giovine, R.; Koirala, K. P.; Li, L.; Ji, H.; Ha, Y.; Sun, Y.; Huang, J.; Chen, Y.; Wu, V.; Yang, W.; Wang, C.; Clément, R. J.; Lun, Z.; Ceder, G. In Situ Formed Partially Disordered Phases as Earth-Abundant Mn-Rich Cathode Materials. Nat. Energy 2023, 1–10. https://doi.org/10.1038/s41560-023-01375-9.

Understanding the Phase Evolution and Charging Mechanism in Dual Cation Cathodes

Multivalent batteries offer potential advantages over lithium-ion batteries but face challenges due to limited ionic mobility in solid-state cathodes. Recent investigations have demonstrated that incorporating multivalent cations, particularly calcium ions (Ca2+), into monovalent cathodes such as NaSICON and R-3m NaV2(PO4)3, results in improved capacity retention. This study investigates the phase evolution and charging mechanism in these dual cation cathodes by using a cluster expansion and charge-neutral Monte Carlo simulation in a Ca-Na-V2(PO4)3 system. Our results found that during the discharge with either Ca or Na ions, phase transitions occurs when the oxidation state of the transition metal changes, in particular between Na1V2(PO4)3 - Na3V2(PO4)3 and Na1V2(PO4)3 - Ca1V2(PO4)3. This behavior suggests that the charging pathway of Na/Ca ions can be altered by varying the Ca/Na chemical potential. Figure 1

Deconvoluting Effects of Lithium Morphology and SEI Stability through Interface Engineering

The widespread use of renewable energy resources and electrification is mandatory for transitioning into a fossil-fuel-free world. Currently, Li-ion battery (LIB) is the universal mode of electrochemical energy storage, but it is reaching the theoretical limit, creating the urgency of more efficient batteries for next-generation applications. Li-metal batteries (LMBs) are considered a key technology to overcome the current energy density limitations of LIBs. In the most energy-dense LMB configuration, the anode-free LMB, Li is directly plated on and stripped from the Cu current collector (CC), subjecting it to the most stringent cycling conditions and making performance regulation crucial. Therefore, engineering the Cu-electrolyte interface is both fundamentally and practically significant.The two most crucial performance modulators in LMBs are electrodeposited Li morphology and solid electrolyte interphase (SEI). The literature has shown that low surface area morphology and anion-derived SEIs are usually beneficial for improved performance. However, it is difficult to deconvolute the individual impact of low surface area morphology and anionic SEI species on performance as they coexist and are correlated. One reported approach to understand the decoupled effects of morphology and SEI is ultrafast electrodeposition of lithium outpacing SEI formation (>100 mA cm-2). Our work establishes a new approach applicable at regular plating and stripping conditions (1 mA cm-2) that uses interface engineering with atomic layer deposited (ALD) thin films to deconvolve Li morphology and SEI stability effects. First, we modify the Cu CC surface using two different thin films with distinct characteristics: resistive, acidic HfO2; and conductive, acidic ZnO.Leveraging ALD, we precisely control the thickness of the nanofilms and establish that increasing the film resistance results in improved performance due to resistance-derived Li morphology. Our approach of decoupling the impact of SEI species from morphology is to preform the SEI before cycling using a simple potential hold step for both these acidic films with opposite electrical properties at different thicknesses. We find that with increasing film thickness, generally, the preformed SEI has more anionic species due to the surface acidity of the thin films. Despite being anion-rich, the preformed SEI does not improve performance, which we attribute to its evolution into an organic-rich SEI during plating. Moreover, the impact of the preformed SEI is statistically insignificant during long-term cycling, whereas the role of resistance becomes more apparent. The effects are demonstrated through interface characterization and performance measurements in three different electrolytes, with at least a twofold increase in cycle life and improved capacity retention achieved in practical anode-free pouch cells. Our results thus indicate that morphological control is more effective for improved battery cyclability due to the inherent challenges with preformed SEI preservation, and as a result the resistance of the thin films is more important than surface acidity for CC modification.

Effect of Electrolytes on Performance of Tire Derived Carbon for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have recently become prominent in the battery ecosystem due to their low cost and use of earth abundant materials such as Sodium, Manganese, Aluminum, Iron, and Prussian blue (iron cyanide). [1] Graphite is the standard anode used for LIBs but cannot be used in SIBs due to interlayer distance being too small to accommodate Na+ ion. Hard carbons are suitable candidates for SIB due to their low cost, low working potential, high capacity, and ability to be synthesized at lower pyrolysis temperatures. In our past work we have reported a low-cost, scalable waste tire-derived carbon as an anode for SIBs [2]. In this work we test the tire derived carbon with 6 different electrolytes and understand the impact each has on the performance. The best electrolyte was found to be sodium hexafluorophosphate in ethylene carbonate (EC)–ethyl methyl carbonate (EMC) (NaPF6-EC/EMC) which showed a capacity of 108 mAh/g after 200 cycles at charge/discharge rate of C/3. The initial columbic efficiency (ICE) was found to be 52% and to mitigate this problem we tried a scalable contact pre-sodiation method. The pre-sodiation method showed high initial columbic efficiency drastically improving capacity retention of the battery.

Cracks in Polycrystalline Li(NiMnCo)O2 Particles Enable Rapid Discharging of Li-Ion Batteries

The degradation of capacity in Li-ion batteries during charging and discharging cycles has been a persistent challenge in advancing battery lifetime. Among the commonly accepted causes of capacity degradation is the formation of cracking along the grain boundaries of polycrystalline NMC particles. These cracks are known to occur from the anisotropic expansion and contraction of the crystal lattice induced by the (de)intercalation of lithium.To address this issue, single crystalline NMC particles were introduced, lacking grain boundaries and seemingly less prone to developing cracks. batteries utilizing single crystalline particles exhibited improved capacity retention. However, in terms of rapid charging and discharging, these single particle batteries experienced a sudden increase in overpotential compared to polycrystalline particle batteries. Yet, a clear explanation for this abrupt rise in overpotential during rapid charging and discharging in single crystalline particle batteries has remained elusive.In this study, we investigated the rate-capability of individual single and polycrystalline NMC particles using an innovative high-throughput single-particle electrochemistry platform. Based on our rate-capability findings, we argue that the cracks, previously identified as a factor contributing to capacity degradation, are actually a crucial element enabling rapid charging and discharging in polycrystalline particles.

Optimizing O3-Type Fe-Mn-Based Cathodes for Na-Ion Batteries: Unveiling the Synergistic Impact of Chemical Co-Substitution

Layered transition metal oxide-Na x MO2 (M = transition metal) is the most widely explored class of cathode materials in lithium and sodium-ion batteries (LIBs and SIBs).1 The replacement of expensive Co and Ni with cheaper elements like Fe and Mn is appealing, which can reduce the overall cost of the battery. Despite the higher operating voltage of Fe3+/Fe4+ and the large specific capacity of Mn3+/Mn4+, issues like irreversible Fe-migration and J. T. distortion of Mn3+/Mn4+ are yet to be overcome.2,3 To improve the electrochemical performances of layered oxide cathodes, various cationic substitutions (e.g., Li+, Cu2+, Mg2+, Zn2+, and Ti4+) are partially substituted in the place of M.4–6 Along this line, in search of better Fe/Mn-based cathodes, we selected an O3-type Na[Fe0.50Mn0.50]O2 (NFMO) material and co-substituted Li+ and Cu2+ in the transition metal layer to create a composition of Na[LixCuyFe0.50-x-yMn0.50]O2 (NCLFMO) and compared their electrochemical performances.. Both materials crystallize in a rhombohedral structure and Rietveld refinement and TEM analyses suggest an enhanced O-Na-O spacing after substitution. The NFMO and NCLFMO cathodes display a capacity of 135 and 121 mAh g-1 in the potential window of 4.0–2.0 V at 0.1 C rate, with an average voltage (Vavg) of 2.63 V and 3.31 V respectively, which leads to an increased energy density of 400 Wh kg-1 for NCLFMO.7 Following substitution, the capacity contributions of Mn and Fe become 20.2% and 79.8%, respectively, instead of 49.8% and 50.2% in NFMO. Clearly, it indicates a pronounced Fe4+/Fe3+ redox activity with a suppressed J. T. distortion for Mn4+/Mn3+ redox. Chemical co-substitution significantly improves capacity retention, with NCLFMO retaining 98% of its initial discharge capacity after 500 cycles, compared to 52% for NFMO. Better rate capability, faster diffusion coefficient of Na+ ions from GITT, and reduced cell resistance from impedance spectroscopy support the enhanced performances of NCLFMO. In-situ XRD measurement reveals a reversible O3-P3-O’3-P3-O3 phase transition and ex-situ x-ray absorption spectroscopy analysis confirms a prominent Fe4+/Fe3+ redox with a suppressed Mn4+/Mn3+ redox during charge-discharge cycling. More significantly, NCLFMO remains air-stable, retaining its structure and electrochemical properties after exposure to air for 30 days. Finally, a full cell with precycled HC is constructed, delivering a capacity of 105 mAh g-1 with a Vavg of 3.15 V in the potential window of 4.0-1.5 V at a 0.1 C rate. In conclusion, the (Li + Cu)-co-substitution strategy improves the overall performance of the Fe-Mn-based layered oxide cathode, paving the way for developing better cathodes for commercialized SIBs. References J. Y. Hwang, S. T. Myung, and Y. K. Sun, Chem. Soc. Rev., 46, 3529–3614 (2017).S. Komaba, N. Yabuuchi, T. Nakayama, A. Ogata, T. Ishikawa and I. Nakai, Inorg. Chem., 51, 6211–6220 (2012).B. Mortemard De Boisse, J. H. Cheng, D. Carlier, M. Guignard, C. J. Pan, S. Bordère, D. Filimonov, C. Drathen, E. Suard, B. J. Hwang, A. Wattiaux and C. Delmas, J. Mater. Chem. A, 3, 10976–10989 (2015).L. Yang, X. Li, J. Liu, S. Xiong, X. Ma, P. Liu, J. Bai, W. Xu, Y. Tang, Y. Y. Hu, M. Liu and H. Chen, J. Am. Chem. Soc., 141, 6680–6689 (2019).G. Singh, N. Tapia-Ruiz, J. M. Lopez Del Amo, U. Maitra, J. W. Somerville, A. R. Armstrong, J. Martinez De Ilarduya, T. Rojo and P. G. Bruce, Chem. Mater., 28, 5087–5094 (2016).L. Wang, Y. G. Sun, L. L. Hu, J. Y. Piao, J. Guo, A. Manthiram, J. Ma and A. M. Cao J. Mater. Chem. A, 5, 8752–8761 (2017).A. Ghosh, R. Hegde, K. Kumar and P. Senguttuvan, J. Am. Chem. Soc., submitted(2023).

(Invited) Innovating Sustainable, Cost-Effective, and Durable Redox Flow Battery Membranes

In the quest to integrate renewable energy sources like solar and wind into the electric grid efficiently, the development of long-duration energy storage (LDES) systems is paramount. The U.S. Department of Energy's Long Duration Storage Shot initiative is at the forefront of this endeavor, aiming to reduce the costs of grid-scale energy storage by 90% for systems with over 10 hours of operation. A key player in this mission is the non-aqueous redox flow battery (RFB), known for its use of earth-abundant materials and potential to meet these cost-reduction goals. However, the commercial viability of RFBs hinges on the development of high-performance, cost-effective membranes, which are crucial for their functionality and affordability. These membranes' ionic conductivity is vital for the power density of RFBs, while their ion selectivity and solvent uptake greatly influence the batteries' cycle life.Our team has made groundbreaking advancements in membrane technology for non-aqueous flow batteries. We've addressed the challenge of balancing ionic conductivity with mechanical strength in polymer electrolytes. Our findings reveal that enhanced solvent uptake while boosting membrane ionic conductivity, can compromise mechanical integrity. To counter this, we've employed two strategies: selective plasticization of the ion-conductive block in block copolymers and reinforcing the membrane's mechanical strength through hydrogen and ionic bonds with an inorganic scaffold. Significantly, we've also reduced the crossover of redox-active species in our membrane designs, notably decreasing polysulfide species crossover in a Na metal – polysulfide hybrid flow battery. This has led to improved capacity retention, Coulombic efficiency, and extended cycle life compared to traditional porous membranes.Our latest innovations include the development of hydrocarbon single-ion conductors, demonstrating enhanced conductivity and stability. We've also introduced crosslinking chemistry to control solvent uptake more effectively, thus improving ionic conductivity while preserving mechanical strength. Lastly, our pioneering tape casting method for producing ceramic-polymer composite membranes represents a major leap in scalable membrane production, paving the way for the practical application of non-aqueous redox flow batteries in long-duration energy storage. Acknowledgment This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and is sponsored by the U.S. Department of Energy through the Energy Storage Program in the Office of Electricity. We acknowledge Dr. Jagjit Nanda SLAC National Accelerator Laboratory for the fruitful discussions.