Full Pouch Cells Research Articles

In Situ-Constructed Multifunctional Composite Anode with Ultralong-Life Toward Advanced Lithium-Metal Batteries.

Metallic lithium is the most competitive anode material for next-generation high-energy batteries. Nevertheless, the extensive volume expansion and uncontrolled Li dendrite growth of lithium metal not only cause potential safety hazards but also lead to low Coulombic efficiency and inferior cycling lifespan for Li metal batteries. Herein, a multifunctional dendrite-free composite anode (Li/SnS2) is proposed through an in situ melt-infusion strategy. In this configuration, the 3D cross-linked porous Li2S/Li22Sn5 framework facilitates the rapid penetration of electrolytes and accommodates the volume expansion during the repeated Li-plating process. Meanwhile, the lithiophilic Li2S phases with a low Li+ transport barrier ensure preferential Li deposition, effectively avoiding uneven electron distribution. Moreover, the Li22Sn5 electron conductors with appropriate Li+ bonding ability guarantee rapid charge transport and mass transfer. Most importantly, the steady multifunctional skeleton with sufficient inner interfaces (Li2S/Li22Sn5) in the whole electrode, not only realizes the redistribution of the localized free electron, contributing to the decomposition of Li clusters, but also induces a planar deposition model, thus restraining the generation of Li dendrites. Consequently, an unprecedented cyclability of over 6500h under an ultrahigh areal capacity of 10mAhcm-2 and a current rate of 20mAcm-2 is achieved for the prepared Li2S/Li22Sn5 composite anode. Moreover, the assembled Li/SnS2||LiFePO4 (LFP) pouch full-cells also demonstrate remarkable rate capability and a convincing cycling lifespan of more than 2000 cycles at 2 C.

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.

Dendrite-free zinc metal anode for long-life zinc-ion batteries enabled by an artificial hydrophobic-zincophilic coating

Considering the desired energy density, safety and cost-effectiveness, rechargeable zinc-ion batteries (ZIBs) are regarded as one of the most promising energy storage units in next-generation energy systems. Nonetheless, the service life of the current ZIBs is significantly limited by rampant dendrite growth and severe parasitic reactions occurring on the anode side. To overcome these issues caused by poor interfacial ionic conduction and water erosion, we have developed a facile strategy to fabricate a uniform zinc borate layer at the zinc anode/electrolyte interface (ZnBO). Such protective layer integrates superhydrophobic-zincopholic properties, which can effectively eliminate the direct contact of water molecules on the anode, and homogenize the interfacial ionic transfer, thereby enhancing the cyclic stability of the zinc plating/stripping. As a result, the as-prepared ZnBO-coated anode exhibits extended lifespan of 1200 h at 1 mA cm−2 and demonstrates remarkable durability of 570 h at 20 mA cm−2 in Zn||Zn symmetric cells. Additionally, when coupled to an NH4V4O10 (NVO) cathode, it also delivers a superior cyclability (203.5 mAh/g after 2000 cycles at 5 A/g, 89.3 % capacity retention) in coin full cells and a feasible capacity of 2.5 mAh at 1 A/g after 200 cycles in pouch full cells. This work offers a unique perspective on integrating hydrophobicity and zincophilicity at the anode/electrolyte interface through an artificial layer, thereby enhancing the cycle lifespan of ZIBs.

Enabling Si‐Dominant Anodes: Influence of Neutralization Degree of Polyacrylic Acid on Low‐Cost Micron‐Sized Silicon Anode in High‐Energy Li‐Ion Full Cell

AbstractMicron‐sized silicon is a promising low‐cost, abundant material to increase the energy density of lithium‐ion batteries. Nevertheless, significant volume change and therefore excessive solid electrolyte interphase (SEI) growth lead to fast capacity fading. In this work, polyacrylic acid (PAA) with different neutralization degrees is used for the fabrication of Si anodes for practical applications. The electrochemical performance in full pouch cells reveals that the increase in neutralization degree of PAA up to 70 % enhances the overall performance by improved electrode properties, higher first cycle efficiency (FCE up to 78.1 % at C/3) and better capacity retention (85.4 % after 150 cycles at 1 C) over cycling, while with even higher neutralization degrees (such as 80 %) the performance declines. Since proper mixing of the slurry is another important factor, we optimized the mixing procedure by increasing the solid content of the slurry, which has shown positive influence on the electrochemical performance and electrode properties. To summarize, this work shows full cell 1 C cycling until capacity retention of 85 % after 150 cycles with pure Si microparticle anodes for 70 % neutralized PAA as well as increased C‐rate performance up to 5 C. Post‐mortem, less degradation on electrode and particle level is observed.

Dual Modification for Low-Strain Ni-Rich Cathodes Toward Superior Cyclability in Pouch Full Cells.

Rapid capacity fading, interfacial instability, and thermal runaway due to oxygen loss are critical obstacles hindering the practical application and commercialization of Ni-rich cathodes (LiNi0.8Co0.1Mn0.1O2, NCM811). Herein, a Sn4+/F- codoping and LiF-coated Ni-rich cathode, denoted as NCM811-SF, is structurally fabricated that demonstrates very high cyclic and thermal stabilities. The introduction of Sn4+ regulates the local electronic structure and facilitates the conversion of the layered structure into a spinel phase; F- captures lithium impurities to form LiF coatings and forms TM-F bonds to reduce Ni/Li disordering. The compositionally complex codoping strategy reduces the internal structure strain, inhibits the Li+/Ni2+ intermixing during cycling and degradation of the nanoscale structure, and further improves the thermal stability and the crystal structure. The cathodic electrode showed a little volume shift at 2.8-4.5 V, which significantly decreased lattice flaws and fractures generated by local strain, based on detailed analyses performed using COMSOL simulations, X-ray diffraction, and scanning transmission electron microscopy. Benefiting from this, after 300 cycles, our as-prepared NCM811-SF cathode maintains 85.4% of its initial capacity at 4.5 V and has an excellent reversible capacity equal to 169 mAh·g-1 at 1 C. In addition, the NCM811-SF/graphite cell in a pouch-type complete cell retained 94.8% of its starting capacity following 500 cycles. These findings underscore the effectiveness of introducing the Sn-O and TM-F bonds in improving the durability and electrochemical efficiency of the cathode material, which makes it a good choice for high-efficiency Li-ion batteries.

Evolutionary Zn ion storage mechanism of hierarchical nanotubular spinel FeV2O4 for Zinc–Metal full cells

A fundamental understanding about the evolution of energy storage mechanism by the structure reconstruction during initial cycling is crucial in establishing their correlation with the unprecedented electrochemical performance of electrodes. Herein, we demonstrate evolutionary zinc (Zn) ion storage mechanism and kinetics of the hierarchical nanotubular FeV2O4 (FeV2O4@NT) coated by turbostratic carbon layers through the anodic hydration-induced crystal reconstruction, where the smaller nanocrystalline FeV2O4 spinel phase was embedded into the newly-formed amorphous V-O-Fe phase at the heterointerface. These FeV2O4@NT cathodes achieved the synergistically combined energy storage mechanism of intercalation and pseudocapacitance for the greatly improved electrochemical performance of pouch full cells, which was not achieved by existing spinel oxides. With the polyoxometalate modified Zn metal anode at the optimized condition of 3.0 M Zn(OTf)2/(ACN/H2O-0.15) in the voltage range of [0.3–1.6 V (vs. Zn/Zn2+)], the POM-Zn||FeV2O4@NT full cells achieved a high capacity of 456.8 mAh g–1 at 200 mA g–1, high rate capacity of 222.0 mAh g−1 even at 10,000 mA g–1, and a large energy density of 337.5 Wh kg–1. Furthermore, the chemical pillar and Fe vacancies in the amorphous V-O-Fe phase allowed FeV2O4@NT electrode to achieve a low capacity decay rate of 0.0152 % per each cycle over 1,000 cycles.

Scalable Precise Nanofilm Coating and Gradient Al Doping Enable Stable Battery Cycling of LiCoO2 at 4.7 V

AbstractThe quest for smart electronics with higher energy densities has intensified the development of high‐voltage LiCoO2 (LCO). Despite their potential, LCO materials operating at 4.7 V faces critical challenges, including interface degradation and structural collapse. Herein, we propose a collective surface architecture through precise nanofilm coating and doping that combines an ultra‐thin LiAlO2 coating layer and gradient doping of Al. This architecture not only mitigates side reactions, but also improves the Li+ migration kinetics on the LCO surface. Meanwhile, gradient doping of Al inhibited the severe lattice distortion caused by the irreversible phase transition of O3−H1−3−O1, thereby enhanced the electrochemical stability of LCO during 4.7 V cycling. DFT calculations further revealed that our approach significantly boosts the electronic conductivity. As a result, the modified LCO exhibited an outstanding reversible capacity of 230 mAh g−1 at 4.7 V, which is approximately 28 % higher than the conventional capacity at 4.5 V. To demonstrate their practical application, our cathode structure shows improved stability in full pouch cell configuration under high operating voltage. LCO exhibited an excellent cycling stability, retaining 82.33 % after 1000 cycles at 4.5 V. This multifunctional surface modification strategy offers a viable pathway for the practical application of LCO materials, setting a new standard for the development of high‐energy‐density and long‐lasting electrode materials.

Scalable Precise Nanofilm Coating and Gradient Al Doping Enable Stable Battery Cycling of LiCoO2 at 4.7 V.

The quest for smart electronics with higher energy densities has intensified the development of high-voltage LiCoO2 (LCO). Despite their potential, LCO materials operating at 4.7 V faces critical challenges, including interface degradation and structural collapse. Herein, we propose a collective surface architecture through precise nanofilm coating and doping that combines an ultra-thin LiAlO2 coating layer and gradient doping of Al. This architecture not only mitigates side reactions, but also improves the Li+ migration kinetics on the LCO surface. Meanwhile, gradient doping of Al inhibited the severe lattice distortion caused by the irreversible phase transition of O3-H1-3-O1, thereby enhanced the electrochemical stability of LCO during 4.7 V cycling. DFT calculations further revealed that our approach significantly boosts the electronic conductivity. As a result, the modified LCO exhibited an outstanding reversible capacity of 230 mAh g-1 at 4.7 V, which is approximately 28 % higher than the conventional capacity at 4.5 V. To demonstrate their practical application, our cathode structure shows improved stability in full pouch cell configuration under high operating voltage. LCO exhibited an excellent cycling stability, retaining 82.33 % after 1000 cycles at 4.5 V. This multifunctional surface modification strategy offers a viable pathway for the practical application of LCO materials, setting a new standard for the development of high-energy-density and long-lasting electrode materials.

Mechanochemically Robust LiCoO2 with Ultrahigh Capacity and Prolonged Cyclability.

Pushing intercalation-type cathode materials to their theoretical capacity often suffers from fragile Li-deficient frameworks and severe lattice strain, leading to mechanical failure issues within the crystal structure and fast capacity fading. This is particularly pronounced in layered oxide cathodes because the intrinsic nature of their structures is susceptible to structural degradation with excessive Li extraction, which remains unsolved yet despite attempts involving elemental doping and surface coating strategies. Herein, a mechanochemical strengthening strategy is developed through a gradient disordering structure to address these challenges and push the LiCoO2 (LCO) layered cathode approaching the capacity limit (256mAhg-1, up to 93% of Li utilization). This innovative approach also demonstrates exceptional cyclability and rate capability, as validated in practical Ah-level pouch full cells, surpassing the current performance benchmarks. Comprehensive characterizations with multiscale X-ray, electron diffraction, and imaging techniques unveil that the gradient disordering structure notably diminishes the anisotropic lattice strain and exhibits high fatigue resistance, even under extreme delithiation states and harsh operating voltages. Consequently, this designed LCO cathode impedes the growth and propagation of particle cracks, and mitigates irreversible phase transitions. This work sheds light on promising directions toward next-generation high-energy-density battery materials through structural chemistry design.

A synergistic duo for enhanced cathode stability in high-voltage lithium-ion batteries

Lithium-ion batteries with high-nickel cathode materials are promising candidates for achieving significantly higher energy densities. However, when Ni-rich subjected to higher charging cutoff voltages accelerates both electrolyte decomposition and structural degradation, leading to compromised cycling stability and reduced lifespan. In this study, we have developed a dual-additive strategy using lithium difluoro bisoxalate phosphate (LiDFBOP), and 1,3-divinyl-1,1,3,3-tetramethyldisilazane (DTDS) to address these challenges and improve the battery's performance. Theoretical calculations and experimental results indicate that the LiDFBOP regulates Li⁺ solvation for robust CEI formation, while DTDS scavenges impurities and promotes the formation of an inorganic/organic interphase. The synergistic effect of these additives combination allows Li||NCM811 coin cell to retain a capacity retention 87.9 % at 4.6 V and Graphite||NCM811full cell achieved 90.5 % capacity retention at 4.5 V. Moreover, the 1Ah pouch full cells exhibit excellent cycling stability, with a capacity retention of 91.4 % after 610 cycles at a constant current of 500 mA and voltage of 4.5 V. This work offers guidance on designing multifunctional additives to achieve synergistic electrolyte engineering for high-energy lithium-ion batteries.

Thickness Variation of Conductive Polymer Coatings on Si Anodes for the Improved Cycling Stability in Full Pouch Cells.

Si-dominant anodes for Li-ion batteries provide very high gravimetric and volumetric capacity but suffer from low cycling stability due to an unstable solid electrolyte interphase (SEI). In this work, we improved the cycling performance of Si/NCM pouch cells by coating the Si anodes with the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) prior to cell assembly via an electropolymerization process. The thicknesses of the PEDOT coatings could be adjusted by a facile process parameter variation. Glow-discharge optical emission spectroscopy was used to determine the coating thicknesses on the electrodes prior to the cell assembly. During electrochemical testing, improvements were observed closely linked to the PEDOT coating thickness. Specifically, thinner PEDOT coatings exhibited a higher capacity retention and lower internal resistance in the corresponding pouch cells. For the thinnest coatings, the cell lifetime was 18% higher compared to that of uncoated Si anodes. Postmortem analyses via X-ray photoelectron spectroscopy and cross-sectional scanning electron microscopy revealed a better-maintained microstructure and a chemically different SEI for the PEDOT-coated anodes.

Can Layered Oxide/Hard Carbon Sodium-Ion Pouch Cells with Simple Electrolyte Additives Achieve Better Cycle Life than LFP/Graphite Cells?

This study explores the impact of simple electrolyte additives on the performance of layered oxide/hard carbon sodium-ion pouch cells. The cycle life of these cells between 2.0 and 3.8 V is assessed at various temperatures (20, 40, and 55 °C) with different solvent systems based on ethylene carbonate, diethyl carbonate, and dimethyl carbonate. A particular challenge in these cells is gas generation at high temperature. Pouch bag experiments which separate the charged electrodes to measure their gas generation from reactions with the electrolyte show that hard carbon generates no gas, but the sodium layered oxide produces large amounts of gas. Isothermal microcalorimetry corroborates these results with parasitic heat flow measurements of pouch bags and full pouch cells. A crosstalk mechanism is revealed which lowers gas generation and reduces parasitic heat flows in full cells. The electrolyte additives prop-1-ene-1,3-sultone, sodium difluorophosphate, and 1,3,2-dioxathiolane-2,2-dioxide (DTD) are effective at reducing gas generation and heat flow from the positive electrode. They also reduce self-discharge in elevated temperature storage tests. Overall, 1 M NaFSI in EC:DMC (15:85) with 2% DTD is the best electrolyte for the sodium-ion pouch cells in this work. Eventually, the performance of these cells is compared to optimized LiFePO4/graphite cells.

Towards industrial applications: Ultra-stable silicon-based pouch cell conducted via a lithiated polymer binder over a wide temperature range from −25 °C to 25 °C

Due to the large volume expansion, the multiple issue of severe pulverized Si particles, irreversible damaged electrode structure, and incompatible solid electrolyte interphase (SEI), have greatly restricted the practical application of Si-based anodes. Herein, a neutral partially lithiated binder (PVA1-g-LiPAA3) is successfully synthesized and applied in high-loaded SiOx||Li, 200 mA h and 4 A h SiOx/graphite||LiCoO2 pouch cells. The rich netural -OH and -COOLi groups show strong interaction with the Si particles during long-term cycling processes. Neutral PVA1-g-LiPAA3 binder can induce the formation of a homogenous and stable “core-shell” SEI film on the SiOx anodes, forbidding the structural evolution and volume expansion. This -CF3-rich SEI film can also improve the ionic conductivity and accelerate the electrochemical kinetics reaction. Moreover, the integrity of fluid collection and polar ears can also be protected. Thus, the manufactured 4 A h SiOx/graphite||LiCoO2 full pouch cell maintains a high 700th discharge capacity of 3.13 A h with capacity retention of 81.3% under 25 °C and 3 C, as well as 300th discharge capacity of 2.73 A h with capacity retention of 98.6% even under 0°C and 1.5 C. This work proves the industrical applications of Si-based anodes over a wide temperature range with high energy density and long cycle life.

Rational Design of Dendritic Phase‐Pure Tin Antimonide Intermetallic Film‐Based Negatrodes for Commercially‐Viable Flexible Sodium‐Ion Pouch Cell Battery

AbstractExploiting the ability to directly deposit larger‐sized, flexible, alloying‐type sodium‐ion battery electrodes without the need of additional inactive components and processing steps is a strategic way to achieve higher gravimetric capacities which will be suitable for commercial‐level sodium‐ion (SIB) pouch cell manufacturing. In this regard, a simple, template‐free electroplating protocol is reported for designing phase‐pure tin antimonide (TA)‐based negatrode. An optimum control over the potentiostatic electroplating parameters allows the preferential formation of dendritic nanostructures over an electroplated foam‐based current collector. The prepared negatrode and Mn‐based Prussian blue analog positrode in full coin cell format deliver an average nominal working voltage of 3.0 V with a discharge energy density of 342 Wh kg−1. In single‐layer full pouch cell format, an 8.01 mAh capacity (89.89 mAh g−1, 593.3 µAh cm−2) is achieved at an undeformed state and 97.12% capacity is retained at 180° bend condition. In multi‐layer full pouch cell format, a 35.86 mAh capacity (80.58 mAh g−1, 531.2 µAh cm−2) is achieved with 62.77% capacity retention after 200 cycles (0.125 C). The results of this work showcase how a simple, template free, aqueous electrolyte based electroplating protocol can be developed for the direct fabrication of large‐sized, flexible, alloying‐type negatrodes for commercial SIB pouch cells.

High voltage electrolytes for lithium-ion batteries with micro-sized silicon anodes

Micro-sized silicon anodes can significantly increase the energy density of lithium-ion batteries with low cost. However, the large silicon volume changes during cycling cause cracks for both organic-inorganic interphases and silicon particles. The liquid electrolytes further penetrate the cracked silicon particles and reform the interphases, resulting in huge electrode swelling and quick capacity decay. Here we resolve these challenges by designing a high-voltage electrolyte that forms silicon-phobic interphases with weak bonding to lithium-silicon alloys. The designed electrolyte enables micro-sized silicon anodes (5 µm, 4.1 mAh cm−2) to achieve a Coulombic efficiency of 99.8% and capacity of 2175 mAh g−1 for >250 cycles and enable 100 mAh LiNi0.8Co0.15Al0.05O2 pouch full cells to deliver a high capacity of 172 mAh g−1 for 120 cycles with Coulombic efficiency of >99.9%. The high-voltage electrolytes that are capable of forming silicon-phobic interphases pave new ways for the commercialization of lithium-ion batteries using micro-sized silicon anodes.

Lightweight Zn‐Philic 3D‐Cu Scaffold for Customizable Zinc Ion Batteries

AbstractPorous metal current collectors (CCs) serve as key component for aqueous Zn‐ion batteries (AZIBs). Herein, a lightweight 3D‐Cu architecture with customizable geometries is developed to enable reversible Zn‐metal cycling. The 3D‐Cu is prepared by 3D‐printing a crosslink‐able polymer scaffold followed by Cu‐metallization. The printed architecture is optimized to endow 3D‐Cu with electric conductivity that is on‐par with commercial Cu foam, but can reduce ≈80% of the weight and consumption of Cu. A Zn‐philic graphene (Gr) coating is adopted to promote uniform and (002)‐preferred Zn growth onto the 3D‐Cu surface, creating a 3DP‐Cu@Gr architecture that induces conformal Zn‐deposition and greatly suppressed H2‐evolution reaction. The 3DP‐Cu@Gr||Zn shows stable 700 cycles at 4 mA cm−2 and 2 mAh cm−2, with coulombic efficiency >99.6%. Zn‐loaded 3D‐electrodes enable symmetrical cells with stable 300 h cycling at 10 mA cm−2, delivering a specific accumulated capacity of 86.7 Ah g−1. This represents an unprecedented combination of cycle stability, high charge rate, and electrode lightweight. The all‐printed pantacle‐shape full pouch cells (3.6 mAh) exhibit 91.4% capacity retention after 200 cycles at 1 C. Possessing unusual design freedom, this strategy demonstrates a pathway for developing lightweight Cu CCs and customizable high‐energy AZIBs.

Anode-Free Sodium Metal Pouch Cell Using Cu3P Nanowires In Situ Grown on Current Collector.

Anode-free sodium metal battery (AFSMB) promises high energy density but suffers from the difficulty of maintaining high cycling stability. Nonuniform sodium (Na) deposition on the current collector is largely responsible for capacity decay in the cycling process of AFSMB. Here, a unique copper phosphide (Cu3P) nanowire is constructed on copper (Cu3P@Cu) as a sodium deposition substrate by an in situ growth method. Superior electrochemical performance of Cu3P@Cu anode is delivered in asymmetric cells with an average Coulombic efficiency of 99.8% for over 800 cycles at 1mA cm-2 with 1 mA h cm-2. The symmetric cell of Cu3P@Cu displayed a cycling lifespan of over 2000h at 2mA cm-2 with 1 mA h cm-2. Cryo-transmission electron microscopecharacterization and first principles calculation revealed that the low Na+ absorption energy and low Na+ diffusion energy barrier on Na3P promoted uniform Na nucleation and deposition, thus enhancing the Na surface stability. Moreover, anode-free Na3V2(PO4)3//Cu3P@Cu full pouch cell delivered a considerable cycling capacity of ≈15mA h in 170 cycles, demonstrating its practical feasibility.

Aging Mechanism For Calendar Aging of Li-Ion Cells With Si/Graphite Anodes

Calendar aging of Li-ion batteries with Si/graphite electrodes was investigated within this study. A total of 121 single-layer pouch full cells with either graphite or Si/graphite (3.0 wt−%, 5.8 wt−% and 20.8 wt−% Si) anodes and NMC622 cathodes with the same N/P ratio were built on pilot-scale. Calendar aging was studied at SoC 30%, 60%, and 100%, as well as temperature (25 °C, 45 °C, 60 °C) and time dependence. The aging data was analyzed in terms of capacity fade and a square-root behavior was observed. Differential voltage analysis (DVA) has been performed as a function of aging time. The observed temperature and time dependence is best described by time dependent, 3D Arrhenius plots. Post-Mortem analysis (SEM, EDX, GD-OES) is applied to investigate the changes on electrode and material level. Conclusions are drawn on the main aging mechanisms for calendar aging of Li-ion cells with Si/graphite anodes and differences between Si/graphite and pure graphite anodes are discussed. The Si-containing cells show a combination of lithium inventory loss and a loss of accessible Si active material, both caused by SEI growth.

(Invited) Lithium Plating as a Critical Ageing Mechanism in Lithium-Ion Batteries – Detection by Advanced Methods and Mitigation

The cycle life of Li-ion batteries is limited by aging on the material and electrode level. Prolonging the battery life helps increasing sustainability, reducing the dependency from critical raw materials, and safes costs. The first step in extending battery life is to understand the underlying degradation mechanisms. Post-Mortem analysis of commercial and pilot-line made cells showed that Lithium plating is a very relevant and severe aging mechanism which can lead to high aging rates and decrease safety properties.1 In this talk, we analyse the aging mechanism of Lithium plating on cell and electrode level.On cell level, capacity fade per time yields aging rates, which are temperature dependent. This temperature dependency is analyzed via Arrhenius plots. The Arrhenius plots for cycling aging show a typical V-shape with a low and a high temperature branch.2–4 A minimum in the Arrhenius plot corresponds to the maximum cycle life of the battery, while the low temperature branch indicates Lithium plating. Interestingly, the minimum in the Arrhenius plot shifts with the charging C-rate, the battery type,3,4 and – in case of non-linear capacity fade curves – with aging.4 In the last years, our group developed new semi-quantitative methods based on glow discharge optical emission spectroscopy (GD-OES) depth profiling for detection of Lithium plating on graphite5 and on Si/graphite composite anodes.6 Furthermore, a new in situ optical microscopy method with cross-sectioned full cells allows direct observations of the electrodes during charging and discharging.7,8 The color change of lithiated graphite in combination with simultaneous electrochemical data gives insight into the charging behavior of anodes. Under slow charging conditions (0.1C), the lithiation of the anode is observed to be homogeneously. Most interestingly, at 1C transport limitations come into play and lithiation fronts moving from the anode surface to the current collector can be directly observed and quantified by image analysis. Our results of both methods5,6,8 and in full consistence with simulations by others9 show that Lithium is mainly deposited on the anode surface, i.e. near the separator (see Figure).Finally, we show that Lithium deposition can be prevented by avoiding anode potentials < 0 V vs. Li/Li+ in commercial cells and cells from our pilot-line. Interestingly, Si/graphite anodes in pouch full cells show a lower susceptibility to Lithium plating at low temperatures with increasing Si content and the same anode areal capacity and N/P ratio. This suggests that the transport limitations in the pores of these Si/graphite anodes are reduced due to lower anode coating thickness. References T. Waldmann, B.-I. Hogg, and M. Wohlfahrt-Mehrens, J. Power Sources, 384, 107–124 (2018).T. Waldmann, M. Wilka, M. Kasper, M. Fleischhammer, and M. Wohlfahrt-Mehrens, J. Power Sources, 262, 129–135 (2014).X.-G. Yang and C.-Y. Wang, J. Power Sources, 402, 489–498 (2018).G. Kucinskis et al., J. Power Sources, 549, 232129 (2022).N. Ghanbari, T. Waldmann, M. Kasper, P. Axmann, and M. Wohlfahrt-Mehrens, J. Phys. Chem. C, 120, 22225–22234 (2016).M. Flügel, K. Richter, M. Wohlfahrt-Mehrens, and T. Waldmann, J. Electrochem. Soc., 169, 050533 (2022).C. Hogrefe et al., J. Electrochem. Soc., 169, 050519 (2022).C. Hogrefe, T. Waldmann, M. Hölzle, and M. Wohlfahrt-Mehrens, J. Power Sources, 556, 232391 (2023).S. Hein and A. Latz, Electrochimica Acta, 201, 354–365 (2016). Acknowledgement The authors would like to acknowledge the Federal Ministry for Economic Affairs and Climate Action (BMWK) for financial support of the Structur.e project (03ETE018E), the German Federal Ministry of Education and Research (BMBF) for funding of the project CharLiSiKo (03XP0333A) and the TEESMAT project (Horizon 2020 E.U. Framework Program, Grant Agreement N° 814106, http://www.teesmat.eu). Figure 1

Does Anisotropic ‘Lattice’ Collapse Always Lead to Cracking in Ni-Rich Layered Oxide Cathode Particles?

Single-crystalline Ni-rich layered oxides (LiNi x Mn y Co1−x−y O2; x ≥ 0.8) are promising high-energy-density cathodes for future Li-ion batteries as they can withstand cathode particle cracking, which is a significant contributor to electrochemical capacity loss. The absence of grain/particle boundaries substantially mitigates the build-up of bulk structural strain in these materials generated from the anisotropic structural evolution (i.e., lattice collapse) during electrochemical cycling. However, compared to their polycrystalline counterparts, rigorous evaluations of their long-term electrochemical performance and their dependence on electrode structure changes, impedance, and particle cracking, are still necessary to take it towards commercialisation. Operando X-ray diffraction (XRD) and absorption spectroscopy (XAS) are ideal probes of these bulk electrode structure properties and provide a direct temporal correlation between the battery electrochemistry and the non-equilibrium structural changes in the electrodes. However, such studies often use electrochemically compromised cells modified for X-ray transmission that are neither representative of a real-world full-cell architecture nor operable long-term under industrially relevant cycling conditions, thereby compromising the results' practicality. This is especially problematic for technologically mature cathodes like single-crystalline Ni-rich layered oxides, which require greater scrutiny of their long-term degradation modes after hundreds of cycles. In this work, using in-house operando X-ray studies and large-area post-mortem electron tomography of a (TRL-5) pilot-line-built A7 pouch full cells with industry-relevant specifications, we demonstrate how single-crystalline LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes can withstand the severe anisotropic structural evolution and show no particle cracking even when cycled under harsh conditions of 2.5–4.4 V at 40 °C for 100 cycles. The bulk structural changes in both electrodes as well as the associated electrochemical performance loss are also evaluated. Furthermore, the validity of the in-house pilot line cell results is benchmarked against a commercially sourced Li-ion cell. In addition to furthering our understanding of single-crystalline Ni-rich cathodes, this work emphasises the need for real-world-relevant reproducible fundamental investigations of academic Li-ion cells and presents a methodology for doing so. Figure 1