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Lithium‐ion cells encompassing LiPF6 as the lithium salt and high‐voltage (LiNi0.5Mn1.5O4, LNMO) or high‐capacity (LiNi0.8Mn0.1Co0.1O2, NMC811) cathode materials are prone to transition metal (TM) dissolution caused by HF, whose formation is catalyzed by H2O traces. TM ions can shuttle to the anodic compartment, increasing the cell degradation rate. Accordingly, specific self‐healing strategies are helpful to develop scavengers able to eliminate HF and absorb TM ions so avoiding their shuttling. In this work, the fabrication and test of a bi‐functional, autonomous scavenging agent made of Al2O3 particles decorated is reported with chitosan. The nanometric Al2O3 core is a trap for HF by chemical bonding. The chitosan coating is acid‐sensitive, and the opening of such a capping layer is triggered in the presence of even small amounts of HF, leading to an efficient TM ion‐trapping. In addition, chitosan is biocompatible, biodegradable, and abundant, which is relevant for design‐for‐recycling scopes. With ≈200 ppm of water in the electrolyte, 12 wt% of scavenger causes, after 200 cycles at 1C, an increase of capacity retention from 73% to 88% for LNMO, and, impressively, from 46% to 84% for NMC811. This autonomous self‐healing mechanism is promising for application in next‐generation smart cells without requiring any external sensing. [ABSTRACT FROM AUTHOR]

Lithium‐ion batteries (LIBs) are increasingly encouraged to enhance their environmental friendliness and safety while maintaining optimal energy density and cost‐effectiveness. Although various electrolytes using greener and safer glyme solvents have been reported, the low charge voltage (usually lower than 4.0 V vs Li/Li+) restricts the energy density of LIBs. Herein, tetraglyme, a less‐toxic, non‐volatile, and non‐flammable ether solvent, is exploited to build safer and greener LIBs. It is demonstrated that ether electrolytes, at a standard salt concentration (1 m), can be reversibly cycled to 4.5 V vs Li/Li+. Anchored with Boron‐rich cathode‐electrolyte interphase (CEI) and mitigated current collector corrosion, the LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode delivers competitive cyclability versus commercial carbonate electrolytes when charged to 4.5 V. Synchrotron spectroscopic and imaging analyses show that the tetraglyme electrolyte can sufficiently suppress the overcharge behavior associated with the high‐voltage electrolyte decomposition, which is advantageous over previously reported glyme electrolytes. The new electrolyte also enables minimal transition metal dissolution and deposition. NMC811||hard carbon full cell delivers excellent cycling stability at C/3 with a high average Coulombic efficiency of 99.77%. This work reports an oxidation‐resilient tetraglyme electrolyte with record‐high 4.5 V stability and enlightens further applications of glyme solvents for sustainable LIBs by designing Boron‐rich interphases. [ABSTRACT FROM AUTHOR]

Nickel-rich layered Li transition metal oxides are the most promising cathode materials for high-energy-density Li-ion batteries. However, they exhibit rapid capacity degradation induced by transition metal dissolution and structural reconstruction, which are associated with hydrofluoric acid (HF) generation from lithium hexafluorophosphate decomposition. The potential for thermal runaway during the working process poses another challenge. Separators are promising components to alleviate the aforementioned obstacles. Herein, an ultrathin double-layered separator with a 10 μm polyimide (PI) basement and a 2 μm polyvinylidene difluoride (PVDF) coating layer is designed and fabricated by combining a non-solvent induced phase inversion process and coating method. The PI skeleton provides good stability against potential thermal shrinkage, and the strong PI–PVDF bonding endows the composite separator with robust structural integrity; these characteristics jointly contribute to the extraordinary mechanical tolerance of the separator at elevated temperatures. Additionally, unique HF-scavenging effects are achieved with the formation of –CO···H–F hydrogen bonds for the abundant HF coordination sites provided by the imide ring; hence, the layered Ni-rich cathodes are protected from HF attack, which ultimately reduces transition metal dissolution and facilitates long-term cyclability of the Ni-rich cathodes. Li||NCM811 batteries (where “NCM” indicates LiNixCoyMn1−x−yO2) with the proposed composite separator exhibit a 90.6% capacity retention after 400 cycles at room temperature and remain sustainable at 60 °C with a 91.4% capacity retention after 200 cycles. By adopting a new perspective on separators, this study presents a feasible and promising strategy for suppressing capacity degradation and enabling the safe operation of Ni-rich cathode materials.

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. [ABSTRACT FROM AUTHOR]

Li/Mn‐rich layered oxide (LMR) offers high practical discharge capacity originating from both cationic and anionic redox, but its operation is practically challenging as full capacity utilization at high cathode potentials (> 4.6 V vs Li|Li+) is intertwined with phase transformation, oxygen release, and transition metal dissolution. Dissolved TMs in particular, can deposit and damage the anode via a process known as electrode cross‐talk that decreases Li inventory due to Li plating. Given the excess in active lithium, Li‐metal anode (LMA) is frequently paired with LMR for a systematic cathode R&D, though is believed to cause inverse cross‐talk, i.e., diffusion of LMA degradation products from the solid electrolyte interphase (SEI) toward the cathode, triggering bulid‐up of resistive cathode electrolyte interphase (CEI). Indeed, a thicker, more organic‐based, and slightly resistive CEI is proven in Li‐ compared to “SEI‐poor” Li4Ti5O12 (LTO)‐based cells via X‐ray photoelectron spectroscopy, time‐of‐flight secondary ion mass spectrometry, and electrochemical techniques, which likely even decreases metal dissolution from LMR, though their practical impact on overpotential is shown to be less relevant. The capacity recovery after transferring cycled (“old”) LMR from Li cells to fresh Li cells rather points to other meaningful contributions to capacity fading than the inverse crosstalk. [ABSTRACT FROM AUTHOR]

Na–Fe–Mn–O cathodes hold promise for environmentally benign high‐energy sodium‐ion batteries, addressing material scarcity concerns in Li‐ion batteries. To date, these materials show poor stability in the air and suffer significant Fe/Mn dissolution during use. These two detrimental surface effects have so far prevented the commercialization of these materials. Herein, high‐throughput experiments to make hundreds of substitutions into a previously optimized Na–Fe–Mn–O material are utilized. Numerous single‐phase materials are made with good electrochemical performance that shows moderate improvements over the unsubstituted. By contrast, dramatic improvements are made in suppressing decomposition in air and Fe/Mn dissolution. Machine learning algorithms are utilized to further understand the changes in air stability and to decouple the effects of various structural parameters such as lattice parameters and crystallite size. The comprehensive dataset and methodology established here lay the groundwork for future exploration and optimization of cathode materials, driving the advancement of next‐generation sodium‐ion batteries. [ABSTRACT FROM AUTHOR]

Li/Mn‐rich layered oxide (LMR) cathode active materials promise exceptionally high practical specific discharge capacity (>250 mAh g−1) as a result of both conventional cationic and anionic oxygen redox. The latter requires electrochemical activation at high cathode potential (>4.5 V vs Li|Li+), though it is accompanied by capacity and voltage fade in the course of continuous release of lattice oxygen, layered‐to‐spinel phase transformation, redox couple shift, as well as transition metal dissolution, whereas the latter is particularly detrimental for graphite‐based anodes due to electrode crosstalk. Herein, the degradation is investigated in LMR || graphite full cells by systematically varying the voltage windows, analyzing electrochemical data and changes at the anode surface. Based on this, the optimal operational voltage window, i.e., upper and lower cutoff voltage (UCV and LCV), is elaborated to finally solve the dilemma of decent cycle life (at high UCVs) and insufficient LMR activation/capacity (at low UCV) and is shown to be superior via distinguishing between formation and postformation cycles of 4.5 and 4.3 V, respectively. [ABSTRACT FROM AUTHOR]

Combining LiNixCoyMn1−x−yO2 (NCM) as cathode with bare Cu as anode will potentially lead to next‐generation batteries that are smaller, lighter, and can run for longer periods on a single charge. However, maintaining high performance and a long lifespan of NCM || Cu cells is challenging as it can be affected by various factors from both the cathode and the anode. From the cathode, it is well‐known that transition metal (TM) dissolution accelerates cell degradation. From the anode, one of the main challenges is the formation of high surface area Li deposits which later transform into "inactive Li" or "dead Li". In this study, a comprehensive assessment regarding these competing factors (i.e., TM deposits and "dead Li") is discussed. Accelerated TM dissolution is accomplished by introducing TM‐containing additives into the electrolyte. The effects of these competing factors and their degradation mechanism are studied quantitatively and qualitatively through inductively coupled plasma, i.e., optical emission spectroscopy and mass spectrometry. The "dead Li" influence is analyzed quantitatively using gas chromatography. The results demonstrate the obvious deleterious impact of dissolved TM ions on cell performance. At the same time, "dead Li" has also become a notable factor for a sudden capacity drop. [ABSTRACT FROM AUTHOR]

Na–Fe–Mn–O cathodes hold promise for environmentally benign high‐energy sodium‐ion batteries, addressing material scarcity concerns in Li‐ion batteries. To date, these materials show poor stability in the air and suffer significant Fe/Mn dissolution during use. These two detrimental surface effects have so far prevented the commercialization of these materials. Herein, high‐throughput experiments to make hundreds of substitutions into a previously optimized Na–Fe–Mn–O material are utilized. Numerous single‐phase materials are made with good electrochemical performance that shows moderate improvements over the unsubstituted. By contrast, dramatic improvements are made in suppressing decomposition in air and Fe/Mn dissolution. Machine learning algorithms are utilized to further understand the changes in air stability and to decouple the effects of various structural parameters such as lattice parameters and crystallite size. The comprehensive dataset and methodology established here lay the groundwork for future exploration and optimization of cathode materials, driving the advancement of next‐generation sodium‐ion batteries.

Li/Mn‐rich layered oxide (LMR) cathode active materials promise exceptionally high practical specific discharge capacity (>250 mAh g−1) as a result of both conventional cationic and anionic oxygen redox. The latter requires electrochemical activation at high cathode potential (>4.5 V vs Li|Li+), though it is accompanied by capacity and voltage fade in the course of continuous release of lattice oxygen, layered‐to‐spinel phase transformation, redox couple shift, as well as transition metal dissolution, whereas the latter is particularly detrimental for graphite‐based anodes due to electrode crosstalk. Herein, the degradation is investigated in LMR || graphite full cells by systematically varying the voltage windows, analyzing electrochemical data and changes at the anode surface. Based on this, the optimal operational voltage window, i.e., upper and lower cutoff voltage (UCV and LCV), is elaborated to finally solve the dilemma of decent cycle life (at high UCVs) and insufficient LMR activation/capacity (at low UCV) and is shown to be superior via distinguishing between formation and postformation cycles of 4.5 and 4.3 V, respectively.

Nickel (Ni)‐rich cathode materials use a high abundance of Ni instead of Cobalt (Co) while increasing battery voltage, making them the representative materials for developing high‐energy‐density batteries. However, Ni‐rich batteries are prone to Ni leaching and performance deterioration; stable cycling thus requires strict control of the H2O/HF content in the electrolyte. Here, the use of an emerging H2O capture metal–organic framework (MOF) is reported to realize stable cycling of Ni‐rich batteries with H2O‐containing electrolytes. The MOF‐801 separator enables NCM622 and even NCM811 batteries containing electrolyte solutions with a 300 ppm H2O content to maintain 91.4% and 81% of the initial capacities after 200 cycles at 0.2 C. Moreover, MOF‐801 is found to significantly suppress fragmentation of the cathode, Li–Ni intermixing, and Ni dissolution. Additionally, the MOF‐801@PP based separator can largely inhibit the lithium dendrite. The results reveal the pivotal role of MOF‐801 in high‐energy‐density batteries, inspiring in‐depth exploration of MOF's indispensable application in lithium batteries. [ABSTRACT FROM AUTHOR]

Lithium metal batteries (LMBs), based on high‐voltage (HV) LiNixCoyMnzO2 (NCM, x+y+z = 1) materials, exhibit great potential for next‐generation electric vehicle (EV) cells. Nevertheless, the inevitable dissolution and shuttle of transition metal (TM) ions from NCM cathodes poses a threat to the electrochemical sustainability of LMBs, especially at high voltage and high temperatures. Herein, ethylene diamine tetraacetic acid (EDTA)‐grafted MOF‐808 is proposed to serve as a multifunctional ion‐selective separator coating, in which EDTA molecules play a targeted ion sifter role in restricting active‐ion crosstalk. Judicious characterizations and theoretical calculations reveal that the separator coating effectively captures the TM‐ions in the electrolyte and thus ensures stable Li deposition without dendrites. As a result, the 4.5 V NCM622//Li cell with the ion‐selective separator achieves a high‐capacity retention over 1000 cycles with a high Coulombic efficiency of 99.68%, and its cycling stability at 55 °C is also upgraded. This crosstalk‐taming strategy offers fresh insight into constructing long‐life HV‐LMBs. [ABSTRACT FROM AUTHOR]

In our initial study on the high-voltage 5 V cobalt-free spinel LiNi0.5Mn1.5O4 (LNMO) cathode, we discovered a severe delamination issue in the laminates when cycled at a high upper cut-off voltage (UCV) of 4.95 V, especially when a large cell format was used. This delamination problem prompted us to investigate further by studying the transition metal (TM) dissolution mechanism of cobalt-free LNMO cathodes, and as a comparison, some cobalt-containing lithium nickel manganese cobalt oxides (NMC) cathodes, as the leachates from the soaking experiment might be the culprit for the delamination. Unlike other previous reports, we are interested in the intrinsic stability of the cathode in the presence of a baseline Gen2 electrolyte consisting of 1.2 M of LiPF6 in ethylene carbonate/ethyl methyl carbonate (EC/EMC), similar to a storage condition. The electrode laminates (transition metal oxides, transition metal oxides, TMOs, coated on an Al current collector with a loading level of around 2.5 mAh/cm2) or the TMO powders (pure commercial quality spinel LNMO, NMC, etc.) were stored in the baseline solution, and the transition metal dissolution was studied through nuclear magnetic resonance, such as 1H NMR, 19F NMR, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP-MS). Significant electrolyte decomposition was observed and could be the cause that leads to the TM dissolution of LNMO. To address this TM dissolution, additives were introduced into the baseline electrolyte, effectively alleviating the issue of TM dissolution. The results suggest that the observed delamination is caused by electrolyte decompositions that lead to etching, and additives such as lithium difluorooxalato borate and p-toluenesulfonyl isocyanate can alleviate this issue by forming a firm cathode electrolyte interface. This study provides a new perspective on cell degradation induced by electrode/electrolyte interactions under storage conditions. [ABSTRACT FROM AUTHOR]

Ni‐rich cathodes are the most promising candidates for realizing high‐energy‐density Li‐ion batteries. However, the high‐valence Ni4+ ions formed in highly delithiated states are prone to reduction to lower valence states, such as Ni3+ and Ni2+, which may cause lattice oxygen loss, cation mixing, and Ni ion dissolution. Further, LiPF6, a key salt in commercialized electrolytes, undergoes hydrolysis to produce acidic compounds, which accelerate Ni‐ion dissolution and the interfacial deterioration of the Ni‐rich cathode. Dissolved Ni ions migrate and deposit on the surface of the graphite anode, causing continuous electrolyte decomposition and threatening battery safety by forming Li dendrites on the anode. Herein, 1,2‐bis(diphenylphosphino)ethane (DPPE) chelates Ni ions dissolved from the Ni‐rich cathode using bidentate phosphine moieties and alleviates LiPF6 hydrolysis via complexation with PF5. Further, DPPE reduces the generation of corrosive HF and HPO2F2 substantially compared to the amounts observed using trimethyl phosphite and tris(trimethylsilyl) phosphite, which are HF‐scavenging additives. Li‐ion cells with Ni‐rich cathodes and graphite anodes containing DPPE exhibit remarkable discharge capacity retentions of 83.4%, with high Coulombic efficiencies of >99.99% after 300 cycles at 45 °C. The results of this study will promote the development of electrolyte additives. [ABSTRACT FROM AUTHOR]

In our initial study on the high-voltage 5 V cobalt-free spinel LiNi0.5Mn1.5O4 (LNMO) cathode, we discovered a severe delamination issue in the laminates when cycled at a high upper cut-off voltage (UCV) of 4.95 V, especially when a large cell format was used. This delamination problem prompted us to investigate further by studying the transition metal (TM) dissolution mechanism of cobalt-free LNMO cathodes, and as a comparison, some cobalt-containing lithium nickel manganese cobalt oxides (NMC) cathodes, as the leachates from the soaking experiment might be the culprit for the delamination. Unlike other previous reports, we are interested in the intrinsic stability of the cathode in the presence of a baseline Gen2 electrolyte consisting of 1.2 M of LiPF6 in ethylene carbonate/ethyl methyl carbonate (EC/EMC), similar to a storage condition. The electrode laminates (transition metal oxides, transition metal oxides, TMOs, coated on an Al current collector with a loading level of around 2.5 mAh/cm2) or the TMO powders (pure commercial quality spinel LNMO, NMC, etc.) were stored in the baseline solution, and the transition metal dissolution was studied through nuclear magnetic resonance, such as 1H NMR, 19F NMR, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP-MS). Significant electrolyte decomposition was observed and could be the cause that leads to the TM dissolution of LNMO. To address this TM dissolution, additives were introduced into the baseline electrolyte, effectively alleviating the issue of TM dissolution. The results suggest that the observed delamination is caused by electrolyte decompositions that lead to etching, and additives such as lithium difluorooxalato borate and p-toluenesulfonyl isocyanate can alleviate this issue by forming a firm cathode electrolyte interface. This study provides a new perspective on cell degradation induced by electrode/electrolyte interactions under storage conditions.

Increasing the upper cut-off voltage (UCV) enhances the specific energy of Li-ion batteries (LIBs), but is accompanied by higher capacity fade as a result of electrode cross-talk, i.e., transition metals (TM) dissolution from cathode and deposition on anode, finally triggering high surface area lithium (HSAL) formation due to locally enhanced resistance. Here, LiPF 6 , LiBF 4 , lithium difluoro(oxalate)borate (LiDFOB), lithium bis(oxalate)borate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in carbonate-based solvents are investigated in LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM 622) || graphite pouch cells with 4.5 V UCV. Despite the lower oxidative stabilities of LiBF 4 and LiDFOB, thus enhanced HF formation, TM dissolution, and consequently electrode cross-talk, higher capacity retention is observed compared to the case of LiPF 6 electrolyte. Counterintuitively, it is not the TM deposit amount but rather the Li plating morphology that governs capacity fade, as these salts cause more uniform and compact lithium plating, i.e., lower surface area. In contrast, the dendritic HSAL with LiPF 6 has a higher surface area, and more parasitic reactions, thus active Li ("Li inventory") losses and capacity fade. Although NCM initiates the failure cascade, the capacity losses and cycle life of high-voltage LIBs are predominantly determined by the anode, in particular the Li plating morphology and the corresponding surface area., (© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

NCM523 || graphite lithium ion cells operated at 4.5 V are prone to an early "rollover" failure, due to electrode cross‐talk, that is, transition metal (TM = Mn, Ni, and Co) dissolution from NCM523 and deposition at graphite, subsequent formation of Li metal dendrites, and, in the worst case, generation of (micro‐)short‐circuits by dendrites growing to the cathode. Here, the impact of different separators on the high‐voltage performance of NCM523 || graphite cells is elucidated focusing on the separators' structural properties (e.g., membrane vs fiber) and their reactivity toward LiPF6 (e.g., ceramic‐coated separators). First, the separator architecture has a major impact on cycle life. Fiber‐structured separators can prevent the "rollover" failure by a more homogeneous deposition of TMs and formation of Li metal dendrites, thus, hindering penetration of dendrites to the cathode. In contrast, porous membrane‐structured separators cannot prevent the cell failure due to inhomogeneous TM deposits/Li metal dendrites. Second, it is demonstrated that different types of ceramic‐coated separators (Boehmite (γ‐AlO(OH)) vs α‐Al2O3) exhibit different reactivities toward LiPF6. While α‐Al2O3 shows a minor reactivity toward LiPF6, the γ‐AlO(OH) coating leads to in situ formation of the beneficial difluorophosphate anion in high amounts due the high reactivity toward LiPF6 decomposition, which significantly improves cycle life. [ABSTRACT FROM AUTHOR]

The construction of an optimized electrolyte system compatible with layered transition metal (TM) oxides is of great importance to advanced sodium‐ion batteries (SIBs). Herein, a low‐cost iron‐containing manganese‐based layered cathode material of Na0.67Ni0.15Fe0.2Mn0.65O2 (N‐NFM) is prepared through an improved coprecipitation method. Then, the chemical properties of interfaces between the N‐NFM cathode and organic liquid electrolytes based on NaClO4 and NaPF6 are investigated, respectively. Results show that the cathode electrolyte interphase (CEI) film formed in the NaPF6‐based electrolyte is dense and uniform, which inhibits the dissolution of TM ions effectively and provides a low energy barrier for the transport of Na+. Apart from that the CEI film formed in the NaClO4‐based electrolyte contains more organic but less inorganic compounds, resulting in an increase in impedance. In addition, it is believed that the stability of the CEI film is susceptible to the perchlorate with strong oxidizing property. In this role, a small part of the CEI film falls from the cathode surface, accelerating the dissolution of TM ions and leading to the reactivation of electrolyte decomposition. [ABSTRACT FROM AUTHOR]

Nickel‐rich layered cathode materials are predominantly used for lithium‐ion batteries intended for electric vehicles owing to their high specific capacities and minimal use of high‐cost cobalt. The intrinsic drawbacks of nickel‐rich layered cathode materials with regard to cycle life and safety have largely been addressed by doping and by applying surface coatings. Here, it is reported that a highly elastic binder, namely spandex, can overcome the problems of nickel‐rich layered cathode materials and improve their electrochemical properties drastically. The high elasticity of spandex allows it to uniformly coat LiNi0.8Co0.1Mn0.1O2 particles via shear force during slurry mixing to protect the particles from undesired interfacial reactions during cycling. The uniform coating of spandex, together with its hydrogen bonding interaction with LiNi0.8Co0.1Mn0.1O2, leads to enhanced particle‐to‐particle interaction, which has multiple advantages, such as high loading capability, superior rate and cycling performance, and low binder content. This study highlights the promise of elastic binders to meet the ever‐challenging criteria with respect to nickel‐rich cathode materials in cells targeting electric vehicles. [ABSTRACT FROM AUTHOR]

Abstract P2-type Mn-based cathode materials present high reversible capacities and low cost, but still suffer the poor cycle ability. In this study, a water-stable cathode material was synthesized by simple solid-state method, and kinds of water-soluble natural biopolymers including guar gum, sodium alginate and xanthan gum were investigated as the binder for this typical P2-type cathode material. As the water-soluble binders contain a large amount of OH and COO functional groups, they could result high adhesion between the particles and conductor, thus lead to a better conductivity. Indeed, an enhanced electrochemical performance was observed on these water-soluble binder, comparing with the commercialized PVDF binder. Among them, the P2-type cathode material with xanthan gum binder delivers the most significant improvement in cycling performance with the capacity retention of 77.6% at 40 mA g−1 and 66% at 100 mA g−1 after 80 and 200 cycle. The XPS depth profiles demonstrated that the dissolution of transition metal in this cathode materials, which lead to severe structural deformation and capacity fading during the repeated cycles, can be significant suppressed by the usage of the water-soluble binders. [ABSTRACT FROM AUTHOR]

Abstract The dissolution of transition metals (TMs) from LiMO 2 (M = Ni, Co, Mn) cathodes and their subsequent side reactions on the anode and in the electrolyte result in Li-ion battery capacity and power losses. Despite the importance of this process, the lack of adequate analysis methods for tracking the subtle compositional changes at specific locations with nano-meter spatial resolution has prevented the elucidation of its microstructural origin and mechanism. Herein, we studied the dissolution of TMs from a Ni-rich layered cathode and investigated their deposition on a graphite anode and reactions with the electrolyte, with focus on the microstructural aspects. Changes in TM and oxygen contents in Ni-rich LiNi 0.87 Co 0.09 Mn 0.04 O 2 (NCM) cathode materials were two-dimensionally visualized on a micro-scale gathering by nano-scale analysis, which enabled high-resolution particle analysis, through transmission electron microscopy coupled with X-ray energy dispersive spectroscopy. Degraded (capacity retention < 80%) NCM particles featuring grain-boundary cracking caused by repeated volume expansion/contraction upon charge/discharge exhibited compositions similar to that of pristine particles, whereas sectionalized chemical composition mapping revealed that broken and pulverized NCM particles, i.e., those very heavily fractured and broken in such a way as to directly expose the particle surface to the electrolyte, exhibited decreased TM contents. Therefore, TM dissolution was concluded to occur at the cathode material–electrolyte interface and be one of the main reasons of electrode material degradation. Graphical abstract fx1 Highlights • Degradation mechanism of layered LiNi 0.87 Co 0.09 Mn 0.04 O 2 (NCM) cathode was studied. • Dissolution of TMs on the Ni-rich cathode was probed by ICP-AES, EPMA, IC, and XEDS. • TEM coupled with XEDS was used for high-precision particle compositional analysis. • TM dissolution mostly occurred for broken and pulverized particles. • TM dissolution and side reactions lead to Li-ion battery performance degradation. [ABSTRACT FROM AUTHOR]

In this work, the transition metal dissolution (TMD) from the respective ternary layered LiMO2 (M = Mn, Co, Ni, Al) cathode active material was investigated as well as the lithiation degrees of the cathodes after charge/discharge cyclic aging. Furthermore, increased nickel contents in LiNixCoyMnzO2-based (NCM) cathode materials were studied, to elucidate their influence on capacity fading and TMD. It was found, that the TMD from nickel-rich cathode materials, e.g., LiNi0.6Co0.2Mn0.2O2 or LiNi0.8Co0.1Mn0.1O2, did not differ significantly from the TMD from the stoichiometric LiNi1/3Co1/3Mn1/3O2. In detail, the TMD from the cathode did not exceed a maximum of 0.2 wt% and was uniformly distributed on all analyzed cell parts (separator, anode, and electrolyte) using total reflection X-ray fluorescence. Moreover, the investigated electrolyte solutions showed that increased Ni contents come with more nickel dissolution of the respective material. Additionally, inductively coupled plasma optical emission spectroscopy analysis on the respective charge/discharge cyclic-aged cathode active materials revealed lithium losses of 20% after 50 cycles. However, only a minimum amount of capacity loss (= 1.5 mAh g−1) can be attributed to active material loss. [ABSTRACT FROM AUTHOR]

Abstract In this work, an approach for the measurement of transition metal dissolution from the respective cathode active material LiNi 1/3 Co 1/3 Mn 1/3 O 2 is presented. Furthermore, undiluted lithium ion battery electrolyte solutions with practical (=high) salt concentration are used. It is demonstrated, that nanoliter dispensers are capable to compensate the formation of an excessive salt crust compared to conventionally prepared total reflection X-ray fluorescence (TXRF) carriers (μL droplet application), resulting in improved recovery rates. The quantification is conducted by application of an internal standard solution placed between the sample dots composed of highly concentrated salts. The application procedures are compared to inductively coupled plasma-optical emission spectroscopy. The recovery rates of the new TXRF sample preparation vary between 98% and 105%, compared to 85% to 90% obtained with the conventional application procedure. The concentration of transition metals (TMs) in real cells does not exceed a few mg L−1. To demonstrate the applicability of the nanoliter droplet approach, components from cells aged by charge/discharge cycling were analyzed. Noteworthy, though the TMs are present in the cathode material in the same amounts, the concentration of nickel in the electrolyte was three times higher than that of manganese (1.4 mg L−1 to 0.4 mg L−1). Cobalt could not even be quantified as it did not exceed the limit of quantification (LOQ > 0.3 mg L−1). This was further confirmed by the deposition of the TMs on the other cell parts (anode and separator), where nickel showed always the highest value. Graphical abstract Unlabelled Image Highlights • Development of a TXRF method for analysis of lithium ion batteries electrolytes • Determination of transition metals via nanoliter droplets • Assessment and comparison of the developed pattern with ICP-OES [ABSTRACT FROM AUTHOR]

Understanding the mechanism of the rate-dependent electrochemical performance degradation in cathodes is crucial to developing fast charging/discharging cathodes for Li-ion batteries. Here, taking Li-rich layered oxide Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 as the model cathode, the mechanisms of performance degradation at low and high rates are comparatively investigated from two aspects, the transition metal (TM) dissolution and the structure change. Quantitative analyses combining spatial-resolved synchrotron X-ray fluorescence (XRF) imaging, synchrotron X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques reveal that low-rate cycling leads to gradient TM dissolution and severe bulk structure degradation within the individual secondary particles, and especially the latter causes lots of microcracks within secondary particles, and becomes the main reason for the fast capacity and voltage decay. In contrast, high-rate cycling leads to more TM dissolution than low-rate cycling, which concentrates at the particle surface and directly induces the more severe surface structure degradation to the electrochemically inactive rock-salt phase, eventually causing a faster capacity and voltage decay than low-rate cycling. These findings highlight the protection of the surface structure for developing fast charging/discharging cathodes for Li-ion batteries., (© 2023 Wiley-VCH GmbH.)

The current study investigated the effects of active material, conductive additives, and binder in a composite electrode on battery performance. In addition, the parameters related to cell performance as well as side reactions were integrated in an electrochemical model. In order to predict the cell performance, key parameters including manganese dissolution, electronic conductivity, and resistance were first measured through experiments. Experimental results determined that a higher ratio of polymer binder to conductive additives increased the interfacial resistance, and a higher ratio of conductive additives to polymer binder in the electrode resulted in an increase in dissolved transition metal ions from the LiMn2O4 composite electrode. By performing a degradation simulation with these parameters, battery capacity was predicted with various fractions of constituents in the composite electrode. The present study shows that by using this integrated prediction method, the optimal ratio of constituents for a particular cathode composite electrode can be specified that will maximize battery performance.

In lithium-ion batteries (LIBs) comprising spinel cathode materials, the dissolution of transition metals (TMs) in the cathodes causes severe cyclic degradation. We investigate the origin and mechanism of surface TM dissolution in high-voltage spinel oxide (LiNi0.5.Mn1.5O4) nanoparticles to find a practical method for its mitigation. Atomic structures of the LiNi0.5.Mn1.5O4 surfaces are developed, and the electronic structures are investigated by first-principles calculations. The results indicate that titanium is a promising dopant for forming a more stable surface structure by reinforcing metal-oxygen bonds in LiNi0.5.Mn1.5O4. Experimentally synthesized LiNi0.5.Mn1.5O4 with titanium surface doping exhibits improved electrochemical performance by suppressing undesirable TM dissolution during cycles. The theoretical prediction and experimental validation presented here suggest a viable method to suppress TM dissolution in LiNi0.5.Mn1.5O4. [ABSTRACT FROM AUTHOR]

In this work we investigated the transition metal dissolution of the layered cathode material Li 1.04 Ni 1/3 Co 1/3 Mn 1/3 O 2 in dependence on the cycle number and cut-off cell voltage during charge by using the total reflection X-ray fluorescence technique for the elemental analysis of the specific lithium ion battery degradation products. We could show that with ongoing cycling transition metal dissolution from the cathode increased over time. However, it was less pronounced at 4.3 V compared to elevated charge cut-off voltages of 4.6 V. After a maximum of 100 cycles, we detected an overall transition metal loss of 0.2 wt‰ in relation to the whole cathode active material for cells cycled to 4.3 V. At an increased charge cut-off voltage of 4.6 V, 4.5 wt‰ transition metal loss in relation to the whole cathode active material could be detected. The corresponding transition metal dissolution induced capacity loss at the cathode could thus be attributed to 1.2 mAh g −1 . Compared to the overall capacity loss of 80 mAh g −1 of the complete cell after 100 galvanostatic charge/discharge cycles the value is quite low. Hence, the overall full cell capacity fade cannot be assigned exclusively to the transition metal dissolution induced cathode fading. [ABSTRACT FROM AUTHOR]

Crosstalk between the cathode and the anode in lithium-ion batteries has a great impact on performance, safety, and cycle lifetime. However, 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.

Lithium-ion batteries based on single-crystal LiNi 1- x - y Co x Mn y O 2 (NCM, 1-x-y ≥ 0.6) cathode materials are gaining increasing attention due to their improved structural stability resulting in superior cycle life compared to batteries based on polycrystalline NCM. However, an in-depth understanding of the less pronounced degradation mechanism of single-crystal NCM is still lacking. Here, a detailed postmortem study is presented, comparing pouch cells with single-crystal versus polycrystalline LiNi 0.60 (NCM622) cathodes after 1375 dis-/charge cycles against graphite anodes. The thickness of the cation-disordered layer forming in the near-surface region of the cathode particles does not differ significantly between single-crystal and polycrystalline particles, while cracking is pronounced for polycrystalline particles, but practically absent for single-crystal particles. Transition metal dissolution as quantified by time-of-flight mass spectrometry on the surface of the cycled graphite anode is much reduced for single-crystal NCM622. Similarly, CO 0.20 Mn 0.20 O 2 (NCM622) cathodes after 1375 dis-/charge cycles against graphite anodes. The thickness of the cation-disordered layer forming in the near-surface region of the cathode particles does not differ significantly between single-crystal and polycrystalline particles, while cracking is pronounced for polycrystalline particles, but practically absent for single-crystal particles. Transition metal dissolution as quantified by time-of-flight mass spectrometry on the surface of the cycled graphite anode is much reduced for single-crystal NCM622. Similarly, CO 2 gas evolution during the first two cycles as quantified by electrochemical mass spectrometry is much reduced for single-crystal NCM622. Benefitting from these advantages, graphite/single-crystal NMC622 pouch cells are demonstrated with a cathode areal capacity of 6 mAh cm -2 with an excellent capacity retention of 83% after 3000 cycles to 4.2 V, emphasizing the potential of single-crystalline NCM622 as cathode material for next-generation lithium-ion batteries., (© 2022 The Authors. Small published by Wiley-VCH GmbH.)

In lithium-ion batteries, dissolved transition-metal ions from the cathode deposit as a solid– electrolyte interphase (SEI) layer on the graphite electrode and degrade the battery performance. This study develops a physics-based electrochemical modeling framework with coupled side reactions to predict the cell performance of graphite/lithium half-cells, including the effect of transition-metal ions on SEI layers. The side reactions and graphite anode degradation considered in this study include 1) loss of cyclable lithium due to SEI layer formation, 2) loss of cyclable lithium and formation of additional decomposition layers due to transition metal deposition, 3) increases in film and charge-transfer resistances, and 4) decrease in the diffusion coefficient due to side reactions. This study reveals that lithium loss and capacity fading due to SEI formation were dominant initially, but side reactions and degradation induced by Mn deposition become significant as cycling progressed. Moreover, Mn ions degrade graphite mostly by increasing the electrode resistances rather than by lithium loss due to side reactions. This integrated study reveals several key mechanisms related to transition-metal deposition and SEI layer formation at the particle level and quantitatively connects the side reactions and cell-level performance. This modeling framework provides valuable guidance for battery design and management. Image 1 • Investigate the effect of transition metal ions on SEI layer of graphite electrode. • Estimate degradation parameter related to Mn deposition and SEI layer formation. • Develop and validate an improved side reaction coupled electrochemical model. • Mn ions degrade graphite mostly by increasing resistances rather than lithium loss. [ABSTRACT FROM AUTHOR]

The combination of Ni-rich layered oxide and graphite–SiO x is regarded as a high-energy-density system for the lithium-ion power batteries. It is significant to elaborate the failure mechanism of the two materials in full batteries, especially at high temperature. In this study, the failure behavior of LiNi 0 · 83 Co 0 · 12 Mn 0 · 05 O 2 /graphite–SiO x pouch batteries (≥50 Ah) cycled at 45 °C has been studied by using the non-destructive electrochemical methods and physico-chemical methods for the cathode and anode materials. Compared with the failure mechanism of lithium-ion batteries cycled at room temperature, it is more inclined to occur at high temperature that transition metal ions dissolve out from cathode and deposit on the anode, electrolyte decomposes, and solid electrolyte interphase grows. The resulting phenomena show that the cathode deterioration is slight, and the anode degradation is the main factor of pouch battery degradation. After failure analysis, the concentration-gradient NCM cathode and nitrile-containing electrolyte additive are assembled into the pouch batteries, and the capacity retention increases from 75.24% (pristine batteries at 280 cycles) to 83.44% (improved batteries at 1500 cycles). Therefore, we suggest that power batteries operating at high temperature should be with minimized transition metal dissolution of cathode materials and stable solid electrolyte interphase. Image 1 • Failure behavior of the pouch battery (≥50 Ah) cycled at 45 °C has been studied. • Both non-destructive and post-mortem methods are used. • Transition metal ion dissolving from cathode is the failure origin. • Concentration-gradient NCM and nitrile-containing additive are added. • Capacity retention increases from 75.24% (280 cycles) to 83.44% (1500 cycles). [ABSTRACT FROM AUTHOR]

A novel aminoakyldisiloxane compound, (3-(N, N -dimethylamino)diethoxypropyl) pentamethyldisiloxane (DSON), is reported as an effective electrolyte additive for improving the electrochemical performances of high energy density power batteries of nickel-rich LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622)/graphite. The NCM622/graphite cells using DSON addition in the carbonate-based reference electrolyte exhibit enhanced electrochemical performances, especially high temperature performances including long cycle life and high temperature storage. The pouch cell (1 Ah) with 0.2 wt% DSON retained a capacity of 88% as compared with 84% for that without DSON in electrolyte after 200 cycles at 45 °C. The mechanism investigation reveals that DSON acts as a film-forming additive for constructing uniform conductive cathode electrolyte interphase (CEI) layer upon NCM622 particles, which suppresses the internal cracks and prohibits the irreversible phase transformation of NCM622. DSON also serves as an effective water/acid scavenger and inhibits the hydrolysis of LiPF 6 , thus effectively blocking the occurrence of side reactions and the dissolution of transition metal ions from cathode. Therefore, NCM622 cathode sheet maintains a better integrity surface morphology after 100 cycles. This work demonstrates that aminoakyldisiloxane is promising for practical use as effective electrolyte additive for high energy density power batteries of nickel-rich NCM/graphite. • A new electrolyte additive for LiNi 0.6 Co 0.2 Mn 0.2 O 2 /graphite batteries is reported. • The additive constructs uniform cathode electrolyte interphase layer on cathode. • The additive serves as a water/acid scavenger and inhibits the hydrolysis of LiPF 6. • The additive blocks the dissolution of transition metal ions from cathode. • The batteries exhibit enhanced cycle life and high temperature storage performances. [ABSTRACT FROM AUTHOR]

A capillary electrophoresis (CE) method with ultraviolet/visible (UV-Vis) spectroscopy for iron speciation in lithium ion battery (LIB) electrolytes was developed. The complexation of Fe 2+ with 1,10-phenantroline (o-phen) and of Fe 3+ with ethylenediamine tetraacetic acid (EDTA) revealed effective stabilization of both iron species during sample preparation and CE measurements. For the investigation of small electrolyte volumes from LIB cells, a sample buffer with optimal sample pH was developed to inhibit precipitation of Fe 3+ during complexation of Fe 2+ with o-phen. However, the presence of the conducting salt lithium hexafluorophosphate (LiPF 6 ) in the electrolyte led to the precipitation of the complex [Fe(o-phen) 3 ](PF 6 ) 2 . Addition of acetonitrile (ACN) to the sample successfully re-dissolved this Fe 2+ -complex to retain the quantification of both species. Further optimization of the method successfully prevented the oxidation of dissolved Fe 2+ with ambient oxygen during sample preparation, by previously stabilizing the sample with HCl or by working under counterflow of argon. Following dissolution experiments with the positive electrode material LiFePO 4 (LFP) in LIB electrolytes under dry room conditions at 20°C and 60°C mainly revealed iron dissolution at elevated temperatures due to the formation of acidic electrolyte decomposition products. Despite the primary oxidation state of iron in LFP of +2, both iron species were detected in the electrolytes that derive from oxidation of dissolved Fe 2+ by remaining molecular oxygen in the sample vials during the dissolution experiments., (© 2020 The Authors. Electrophoresis published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel capillary electrophoresis (CE) method with ultraviolet-visible spectroscopy (UV-Vis) detection for the investigation of dissolved Cu + and Cu 2+ in lithium ion battery (LIB) electrolytes was developed. This method is of relevance, as the current collector at the anode of LIBs may dissolve under certain operation conditions. In order to preserve the actual oxidation states of dissolved copper in the electrolytes and to prevent any precipitation during sample preparation and CE measurements, neocuproine (NC) and ethylenediamine tetraacetic (EDTA) were effectively applied as complexing agents for both ionic copper species. However, precipitation and loss of the Cu + -NC-complex for quantification occurred in presence of the commonly applied conducting salt lithium hexafluorophosphate (LiPF 6 ). Therefore, acetonitrile (ACN) was added to the sample in order to suppress this precipitation. Dissolution experiments with copper-based negative electrode current collectors in a LIB electrolyte were conducted at 60°C under non-oxidizing atmosphere. First findings regarding the copper species via CE revealed dissolved Cu + and mainly Cu 2+ . However, primarily Cu + dissolved from the passivating oxide layer (Cu 2 O and CuO) of the current collector due to the formation of acidic electrolyte decomposition products. Due to the instability of Cu + in the electrolyte a further disproportionation reaction to Cu 0 and Cu 2+ occurred. The results show the high potential of this CE method for prospective investigations regarding the current collector stability in new battery electrode formulations and correlations of dissolution events with dissolution mechanisms and battery cell operation conditions., (© 2020 The Authors. Electrophoresis published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new CE method with ultraviolet-visible detection was developed in this study to investigate manganese dissolution in lithium ion battery electrolytes. The aqueous running buffer based on diphosphate showed excellent stabilization of labile Mn 3+ , even under electrophoretic conditions. The method was optimized regarding the concentration of diphosphate and modifier to obtain suitable signals for quantification. Additionally, the finally obtained method was applied on carbonate-based electrolytes samples. Dissolution experiments of the cathode material LiNi 0.5 Mn 1.5 O 4 (lithium nickel manganese oxide [LNMO]) in aqueous diphosphate buffer at defined pH were performed to investigate the effect of a transition metal-ion-scavenger on the oxidation state of dissolved manganese. Quantification of both Mn species revealed the formation of mainly Mn 3+ , which can be attributed to a comproportionation reaction of dissolved and complexed Mn 2+ with Mn 4+ at the surface of the LNMO structure. It was also shown that the formation of Mn 3+ increased with lower pH. In contrast, dissolution experiments of LNMO in carbonate-based electrolytes containing LIPF 6 showed only dissolution of Mn 2+ ., (© 2020 The Authors. Electrophoresis published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The current study investigated the effects of active material, conductive additives, and binder in a composite electrode on battery performance. In addition, the parameters related to cell performance as well as side reactions were integrated in an electrochemical model. In order to predict the cell performance, key parameters including manganese dissolution, electronic conductivity, and resistance were first measured through experiments. Experimental results determined that a higher ratio of polymer binder to conductive additives increased the interfacial resistance, and a higher ratio of conductive additives to polymer binder in the electrode resulted in an increase in dissolved transition metal ions from the LiMn2O4 composite electrode. By performing a degradation simulation with these parameters, battery capacity was predicted with various fractions of constituents in the composite electrode. The present study shows that by using this integrated prediction method, the optimal ratio of constituents for a particular cathode composite electrode can be specified that will maximize battery performance. [ABSTRACT FROM AUTHOR]

In lithium-ion batteries (LIBs) comprising spinel cathode materials, the dissolution of transition metals (TMs) in the cathodes causes severe cyclic degradation. We investigate the origin and mechanism of surface TM dissolution in high-voltage spinel oxide (LiNi 0.5 Mn 1.5 O 4 ) nanoparticles to find a practical method for its mitigation. Atomic structures of the LiNi 0.5 Mn 1.5 O 4 surfaces are developed, and the electronic structures are investigated by first-principles calculations. The results indicate that titanium is a promising dopant for forming a more stable surface structure by reinforcing metal-oxygen bonds in LiNi 0.5 Mn 1.5 O 4 . Experimentally synthesized LiNi 0.5 Mn 1.5 O 4 with titanium surface doping exhibits improved electrochemical performance by suppressing undesirable TM dissolution during cycles. The theoretical prediction and experimental validation presented here suggest a viable method to suppress TM dissolution in LiNi 0.5 Mn 1.5 O 4 ., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)