Durability Of Lithium-ion Batteries Research Articles

Pillaring Electronic Nano-Wires to Slice T-Nb2O5 Laminated Particles for Durable Lithium-Ion Batteries.

T-Nb2O5 characterized by the pronounced intercalation pseudocapacitance effect, is regarded as a promising and alternative anode for fast-charging Li-ion batteries. However, its electrochemical kinetics are still hindered by the absence of sufficient and homogenous conductive wiring inside active microparticles. Herein, an in situ pillaring strategy of electronic nano-wires is proposed to slice T-Nb2O5 laminated particles for the development of durable and fast-charging anodes for Li-ion batteries. A micro-level layered structure consisting of nano-carbon-inserted T-Nb2O5 composite flakes is designed and enabled by successive ion exchange, slice exfoliation, in situ polymerization, and carbonization processes. The pillared carbon interlayer (derived from polyaniline) can serve as in-built conductive wires to promote and homogenize electron transfer inside the micro-level particles. The porous structure (formed by the self-assembly of exfoliated flakes) contributes to the improved electrolyte immersion and enhanced lithium migration. Benefitting from the kinetically favorable effects, the modified T-Nb2O5 anode achieves the high-rate capability (108.4 mAhg-1 at 10 Ag-1) and ultralong cycling durability (138 mAhg-1 at 1.0 Ag-1 after 8000 cycles, with an average capacity decaying rate as small as 0.043‰). This work provides an effective strategy of electron wire pillaring with the slicing effect for laminated electrode materials with high tap density.

Intercalation Pathway in Graphite Particles Analyzed with a Multi-Layer Phase Field Model

Graphite is today the most common negative electrode material in commercial cells, alone or blended with silicon, thanks to its relatively high specific capacity of 372 mAh·g−1, its excellent cycling stability, its low thermodynamic potential, and relatively low cost compared to alternative materials. The increase in the energy densities, power capabilities, and durability of lithium-ion batteries using this conventional cost-effective active material is possible through an optimization of the electrode and material designs. Such optimization requires, however, knowledge of the fundamental mechanisms that govern both the lithium transport inside graphite particles and the electrochemical transfer at the electrolyte / active material interface.Graphite has an ideal lamellar structure made of graphene sheets. During intercalation, the lithium atoms insert between the graphene planes, with almost no lithium transport across the graphene sheets. The interactions between lithium atoms in adjacent galleries leads to the formation of structures with filled layers separated by a number of empty layers, known as stages. Given this phenomenon, graphite active material undergoes phase separation between successions of several stable phases during lithium intercalation. This staging phenomenon influences the critical properties of graphite like its equilibrium potential, lithium diffusion or lithium insertion kinetics.In the present work, we use a Cahn-Hilliard type model, adapted to multi-layered materials1 and study the influence of the parameters in the underlying free-energy models. We focus first on the intra-layer and inter-layer lithium interaction contributions. Free-energy models with increasing complexity of inter-layer interactions are introduced and discussed based on their corresponding phase diagrams. In particular, we show that occurrence of fractional 3/2 stage, observed for potassium or rubidium intercalation in graphite at high pressure, requires an interlayer interaction effective at second neighbor, while a continuous screening effect of the intercalant is necessary to predict the occurrence of stages greater than 2 without the occurrence of the fractional 3/2 stage, as observed for lithium2.The kinetics of stage formation and evolution is also greatly affected by the interaction parameters of the free-energy model. A linear stability analysis (LSA) is performed to investigate the impact of the free energy model parameters on the stage formation dynamics and growth rates. In particular, the LSA shows that stage 2 grows the fastest, even for low lithium filling fraction. In accordance with this result, simulations of spinodal decomposition from moderate homogeneous lithium filling fraction (c=0.3) shows the formation of stage 2 at early times before an evolution towards stage 3 (See figure 1). This higher growth rate of stage 2 seems to have an impact on lithium intercalation pathway. Indeed, during simulations of lithium intercalation in a graphite particle at different C-rates, stage 2 tends to form very early at the electrolyte/particle interface, even when stage 3 and dilute stage 1 dominates inside the particle. The simulation of lithium intercalation also provides access to the effective exchange current density as function of the averaged surface concentration. The presence of the stages at the surface of the particles directly affects this averaged exchange current density. It results in non-symmetric exchange current density profiles, in coherence with operando X-ray micro-diffraction measurement in thick graphite electrodes3.Figure 1: Snapshots of a spinodal decomposition at different times. The initial average filling fraction is c=0.3 and the system has six layers. For each subfigure, top: lithium content in each layer, bottom: coefficients of the Fourier transform used to track the stages Smith, R. B. et al. Intercalation Kinetics in Multiphase-Layered Materials. J. Phys. Chem. C 121, 12505–12523 (2017).Chandesris, M., et al. Thermodynamics and Related Kinetics of Staging in Intercalation Compounds. J. Phys. Chem. C 123, 23711–23720 (2019)Tardif, S. et al. Combining operando X-ray experiments and modelling to understand the heterogeneous lithiation of graphite electrodes. J. Mater. A 9, 4281–4290 (2021) Figure 1

Compositionally Partitioned Li[Ni0.9Mn0.1]O2 Cathode That Affords Fast-Charging Lithium-Ion Batteries

The development of Co-free Li[NixMn1−x]O2 cathodes for lithium-ion batteries (LIBs) that can supersede Co-containing Li[NixCoyMn1−x−y]O2 and Li[NixCoyAl1−x−y]O2 cathodes is considered a priority as Co is associated with price volatility, environmental concerns, and human rights violations.1,2 In this study, a morphology-engineering approach is used to develop a Co-free Li[Ni0.9Mn0.1]O2 cathode with a Ni-rich core–Mn-rich shell structure to overcome the limitations of Co-free Li[NixMn1−x]O2 cathodes. The engineered morphology of the Co-free Li[Ni0.9Mn0.1]O2 cathode particles effectively dissipates internal strain caused by state-of-charge heterogeneity and fracture toughening the cathode. the Co-free cathode demonstrates excellent long-term cycling stability; it retains 78.5% of its initial capacity after 2000 cycles at 1 C charge and 0.8 C discharge rates, and retains an unprecedented 79.5% after 1000 cycles under fast-charging conditions (3 C charge and 1 C discharge). The proposed Co-free layered oxide cathode represents a next-generation cathode that affords fast-charging and durable LIBs, which are more cost effective than LIBs featuring commercial Co-containing cathodes. Reference s : [1] A. Aishova, G.-T. Park, C. S. Yoon, Y.-K. Sun, Adv. Energy Mater. 10 (2019) 1903179..[2] G.-T. Park, B. Namkoong, S.-B. Kim, J. Liu, C. S. Yoon, Y.-K. Sun, Nat. Energy 7 (2022) 946.

Lyotropic Lamellar Nanostructures Enabled High-Voltage Windows, Efficient Charge Transport, and Thermally Safe Solid-State Electrolytes for Lithium-Ion Batteries.

Developing electrolytes combining solid-like instinct stability and liquid-like conducting performance will be satisfactory for efficient and durable Li-ion batteries. Herein lamellar lyotropic liquid crystals (LLCs) demonstrate high-voltage windows, efficient charge transport, and inherent thermal safety as solid-state electrolytes in lithium-ion batteries. Lamellar LLCs are simply prepared by nanosegregation of [C16Mim][BF4] and LiBF4/Propylene carbonate (PC) liquid solutions, which induce lamellar assembly of the liquids as dynamic conducting pathways. Broadened liquid conducting pathways will boost the conducting performance of the LLC electrolytes. The lyotropic lamellar nanostructures enable liquid-like ion conductivity of the LLC electrolytes at ambient temperatures, as well as provide solid-like stability for the electrolytes to resist high voltage and flammability overwhelming to LiBF4/PC liquid electrolytes. Despite minor consumption of PC solvents (34.5wt.%), the lamellar electrolytes show energy conversion efficiency comparable to the liquid electrolytes (PC wt. 92.8%) in Li/LiFePO4 batteries under ambient temperatures even at a 2C current density, and exhibit attractively robust stability after 200th cyclic charge/discharge even under 60°C. The work demonstrates LLC electrolytes have great potential to supersede traditional liquid electrolytes for efficient and durable Lithium-ion (Li-ion) batteries.

Advances in Polymer Binder Materials for Lithium-Ion Battery Electrodes and Separators.

Lithium-ion batteries (LIBs) have become indispensable energy-storage devices for various applications, ranging from portable electronics to electric vehicles and renewable energy systems. The performance and reliability of LIBs depend on several key components, including the electrodes, separators, and electrolytes. Among these, the choice of binder materials for the electrodes plays a critical role in determining the overall performance and durability of LIBs. This review introduces polymer binders that have been traditionally used in the cathode, anode, and separator materials of LIBs. Furthermore, it explores the problems identified in traditional polymer binders and examines the research trends in next-generation polymer binder materials for lithium-ion batteries as alternatives. To date, the widespread use of N-methyl-2-pyrrolidone (NMP) as a solvent in lithium battery electrode production has been a standard practice. However, recent concerns regarding its high toxicity have prompted increased environmental scrutiny and the imposition of strict chemical regulations. As a result, there is a growing urgency to explore alternatives that are both environmentally benign and safer for use in battery manufacturing. This pressing need is further underscored by the rising demand for diverse binder research within the lithium battery industry. In light of the current emphasis on sustainability and environmental responsibility, it is imperative to investigate a range of binder options that can align with the evolving landscape of green and eco-conscious battery production. In this review paper, we introduce various binder options that can align with the evolving landscape of environmentally friendly and sustainable battery production, considering the current emphasis on battery performance enhancement and environmental responsibility.

An Overview on Transport Phenomena within Solid Electrolyte Interphase and Their Impact on the Performance and Durability of Lithium-Ion Batteries

The nature of the electrode–electrolyte interface has an impact on the performance and durability of lithium-ion batteries (LIBs). The initial electrolyte’s thermodynamic instability at the anode–electrolyte interface in LIBs results in the formation of a passivation layer, called solid electrolyte interphase (SEI). The initial dense and intact layer allows Li+ transport and restricts electron tunneling, thus preventing electrolyte decomposition and ensuring the electrochemical stability of a battery. However, the growth of this layer can reduce the availability of active lithium and electrolyte, and ultimately lead to an irreversible battery capacity fade. Investigating the transport phenomena of lithium ions within SEI is crucial for understanding its formation and growth. Nonetheless, accurately describing all relevant mechanisms is challenging due to its complex and multiscale nature. An overview of current computational efforts to study Li+ transport within SEI is given in this article, ranging from electronic/atomistic scale simulations to macroscopic models. The drawbacks and advantages of the proposed numerical approaches are summarized along with the obstacles that need to be overcome to obtain accurate experimental data, identified on the basis of the most recent literature evidence. We highlight collaboration gaps between modeling and experimental approaches, as well as the urgent need for new multiscale models, to gain a better understanding of such a crucial transport phenomenon.

Challenges and Innovations of Lithium-Ion Battery Thermal Management Under Extreme Conditions: A Review

Abstract Thermal management is critical for safety, performance, and durability of lithium-ion batteries that are ubiquitous in consumer electronics, electric vehicles (EVs), aerospace, and grid-scale energy storage. Toward mass adoption of EVs globally, lithium-ion batteries are increasingly used under extreme conditions including low temperatures, high temperatures, and fast charging. Furthermore, EV fires caused by battery thermal runaway have become a major hurdle to the wide adoption of EVs. These extreme conditions pose great challenges for thermal management and require unconventional strategies. The interactions between thermal, electrochemical, materials, and structural characteristics of batteries further complicate the challenges, but they also enable opportunities for developing innovative strategies of thermal management. In this review, the challenges for thermal management under extreme conditions are analyzed. Then, the progress is highlighted in two directions. One direction is improving battery thermal management systems based on the principles of heat transfer, which are generally external to Li-ion cells. The other direction is designing novel battery structures, which are generally internal of Li-ion cells such as smart batteries with embedded sensors and actuators. The latter approach could greatly simplify or even eliminate the need for battery thermal management under extreme conditions. New research integrating these two approaches is recommended.

(In)Coherent-bond-networks in Ni-rich layered oxides for durable lithium-ion batteries

An intriguing “coherent-bond-network” effect is suggested here for mitigating anisotropic lattice variations inducing micro-cracks, for durable Ni-rich layered cathodes based on Li[Ni10/12Co1/12Mn1/12]O2 (NCM) and Li[Ni10/12Co1/12Ti1/12]O2 (NCT) oxide models in lithium-ion batteries (LIBs). Upon charging, the c and a lattice strains for NCT are lower than those for NCM, implying that mechanical failures are mitigated in the former. Considering that Ni ions are a major component in compensating for the charge imbalance caused by Li deintercalation, the Ni–O bond populations in the deeply charged state reveal a uniform bond network in NCT, relative to the conventional Ni-rich cathode with NiO6 distortion. For deeper insights, the O–O edge populations are calculated for the two oxide models, and the discretized values over the entire crystal framework are observed for NCM, whereas delocalization is shown in NCT. These results underpin the Ti-induced “coherent-bond-network” that smoothly connects the MO6 octahedral network upon charging for Ni-rich layered oxides, where M denotes a transition metal. In addition, the oxide-model-dependent (in)coherent-bond-networks are consistently identified for the Li–O bond populations of NCT and NCM, and insights into the chemical stiffness of the Ti–O bond reinforces the structural origin of the uniform octahedral environment. The structural concept based on an in-depth understanding of the Ni-rich layered models not only accounts for the fundamental origin of the Ti-doping effect on the anisotropic lattice change but also provides a local-structure-related point of view in restraining the formation of micro-cracks for durable high-energy–density LIBs.

TiFeNb10O29-δ anode for high-power and durable lithium-ion batteries.

A new Fe-substituted TiFeNb10O29-δ (TFNO) anode is proposed. TFNO possesses a defective and polycrystalline ReO3 Roth-Wadsley shear structure with a slightly larger lattice volume. Electrochemical behavior results and density functional theory (DFT) calculations show that TFNO can facilitate the kinetics of electron/Li+ transportation and demonstrates pseudocapacitive behavior. Consequently, TFNO exhibits superior high rate capacity and cycling stability compared to pristine TNO, offering 100 mA h g-1 at an ultrahigh rate of 50C and a high capacity retention of 86.7% over 1000 cycles at 10C. This work reveals that TFNO could be a promising anode material for fast-charging, stable, and safe LIBs.

Life-cycle evolution and failure mechanisms of metal-contaminant defects in lithium-ion batteries

Cathodic metal-contaminant defects are frequently introduced into lithium-ion batteries (LIBs) during production. The life-cycle evolution and influence mechanisms of cathodic metal contaminants in LIBs are the key for revealing their influence on the safety and durability of LIBs after long-term cycling, but few relevant research has been conducted. Here copper (Cu) particles are chosen and placed on the cathode of LIBs. The variation characteristics in the electrical properties of defective batteries, the evolution process of metal particles and the influence mechanisms of the metal contaminants on LIBs throughout their entire life cycle are studied. Interestingly, the short-circuit points caused by the metal contaminants continuously dissolve under cathode potential, which makes the ISC phenomenon gradually vanished with time. The metal is finally dispersed in a large area, which creates a barrier but is insufficient to cause lithium plating. In addition, the cycle performance of the defective batteries is better because a small amount of Cu ions that enter the cathode lattice retard the Li/Ni ion mixing and consequently slow down the loss of cathode. However, the excessive incorporation of Cu increases the dissolution of transition-metal ions, which accelerates the degradation of the defective batteries after cycling for a long time.

Nanostructured Co‐Free Layered Oxide Cathode that Affords Fast‐Charging Lithium‐Ion Batteries for Electric Vehicles

AbstractThe development of Co‐free Li[NixMn1−x]O2 cathodes for lithium‐ion batteries (LIBs) that can supersede Co‐containing Li[NixCoyMn1−x−y]O2 and Li[NixCoyAl1−x−y]O2 cathodes is considered a priority as Co is associated with price volatility, environmental concerns, and human rights violations. However, the complete removal of Co from cathodes for LIBs is difficult because Co‐free cathodes suffer from structural instability and inferior capacity. In this study, a morphology‐engineering approach is used to develop a Co‐free Li[Ni0.9Mn0.1]O2 cathode with a Ni‐rich core–Mn‐rich shell structure to overcome the limitations of Co‐free Li[NixMn1−x]O2 cathodes. The engineered morphology of the Co‐free Li[Ni0.9Mn0.1]O2 cathode particles effectively dissipates internal strain caused by state‐of‐charge heterogeneity and fracture toughening the cathode. Owing to the effective dissipation of internal strain and chemical protection provided by the Mn‐rich shell, the Co‐free cathode demonstrates excellent long‐term cycling stability; it retains 78.5% of its initial capacity after 2000 cycles at 1 C charge and 0.8 C discharge rates, and retains an unprecedented 79.5% after 1000 cycles under fast‐charging conditions (3 C charge and 1 C discharge). The proposed Co‐free layered oxide cathode represents a next‐generation cathode that affords fast‐charging and durable LIBs, which are more cost effective than LIBs featuring commercial Co‐containing cathodes.

Hierarchical conducting polymer coated conjugated polyimide anode towards durable lithium-ion batteries

Organic polymer materials attract lots of attention as promising anode materials for lithium ion batteries (LIBs) due to the superior lithium ion storage capability and low cost. However, the inherent insulativity of the polymer anodes results in the unsatisfactory electrochemical performance. Herein, we design and construct a hierarchical flowers-like polyaniline-coated (PANI) pyromellitic dianhydride-based polyimide (PPI) composite (PANI-PPI-9). Benefiting from the core-shell structure, the PPI presents an improved electrochemical performance, especially the remarkable cycling life (503 mAh g−1 at 1.5 A g−1 after 2400 cycles). Ex-situ characterizations and kinetics analyses also verify that the PANI shell serves as the electronic transport highway without obstructing the Li storage of PPI. This work highlights the potential application of the multifarious polymer-based composite electrodes for the lithium ion batteries.

Porous engineering of CoS2/N-doped carbon polyhedra anode for durable lithium-ion battery

In this work, the porous CoS2/N-doped carbon polyhedra (P-CoS2/CP) has been developed by employing ZIF-67 as the template for durable lithium-ion battery anode. The as-prepared P-CoS2/CP exhibits the novel dodecahedron structure filling with nanopores and CoS2 nanoparticles. As compared to CoS2/CP (122 m2 g−1), the P-CoS2/CP possesses the higher specific surface area of 367 m2 g−1, which benefits to enlarge the electrode-electrolyte contact area and promote the Li+ diffusion dynamics at high current density. On the other hand, the CoS2 nanoparticles are firmly wrapped by the carbon skeleton which can effectively suppresses the volume expansion of CoS2 during the charging/discharging process. Besides, the N-doping enable to improve the conductivity of CP. As a result, the initial discharge capacity of P-CoS2/CP at 0.1 A g−1 is 1484.7 mAh g−1 with the coulombic efficiency of 48.9%. After 100 cycles, the reversible capacity stabilized at 726.2 mAh g−1. Even the current density increases to 2.0 A g−1, a high reversible capacity of 353.7 mAh g−1 can still be achieved, realizing the good rate capability. The superior Li+ performance of P-CoS2/CP is attributed to the synergistic effect of the unique multi-space structure and the high chemical activity of CoS2. Moreover, the Li+ diffusion coefficient of P-CoS2/CP is 4.52 × 10−6 to 1.98 × 10−11 cm2 s−1, which is higher than that of CoS2/CP (1.45 × 10−9 to 5.23 × 10−11 cm2 s−1), highlighting the significance of porous engineering.

Fe2VO4 nanoparticles on rGO as anode material for high-rate and durable lithium and sodium ion batteries

Iron vanadate (FexVOy), especially Fe2VO4, is a promising anode material for lithium and sodium ion batteries due to their high capacity and abundant raw material resources. However, its capacity decays rapidly at high rates due to volume expansion and low electrical conductivity. Herein, uniform small Fe2VO4 nanoparticles (FVO) are grown on reduced graphene oxide (rGO) by solvothermal treatment and subsequent calcination, forming a conductive-network (FVO/rGO). The flexible rGO can effectively prevent FVO particles agglomerating and buffer the volume expansion during the reaction process. The high electrical conductive rGO and small FVO particles benefit from electrons’ fast transport, improving the electrical conductivity of FVO/rGO. The sheet-like structure of FVO/rGO can be fully contacted with the electrolyte to further increase electron/ion transport. The pseudocapacitive-controlled behavior is the dominating lithium/sodium storage mechanism, which facilitates a fast charge/discharge process. As a result, FVO/rGO composite displays a stable high capacity of 1013.7 mAh g-1 at 500 mA g−1 after 300 cycles when it is used for lithium-ion batteries. Moreover, it shows remarkable rate capability (228.9 mAh g-1 at 20 A g-1) and excellent long-cycle stability (223.6 mAh g-1 at 10 A g-1 after 2500 cycles). It also exhibits a high discharge capacity of 137 mAh g-1 after 1500 cycles at 1.0 A g-1 for sodium-ion batteries. The superior electrochemical performance proves it an ideal anode material for high-rate and durable lithium and sodium-ion batteries.

Pomegranate-Inspired Graphene Parcel Enables High-Performance Dendrite-Free Lithium Metal Anodes.

Uncontrolled lithium dendrites seriously hinder the commercialization of lithium metal batteries in comparison to the durable lithium‐ion batteries. Herein, inspired by squashy pomegranate structure, a novel loading strategy of metallic lithium (Li) is introduced to construct dendrite‐free Li metal anodes through porous reduced graphene oxide/Au (PRGO/Au) composite microrods (MRs) as unique storage parcels. The abundant internal voids and robust host structure are capable of achieving high mass loading of Li metal and effectively alleviating the conceivable volume change during cycling, accompanied by the preferential selective plating/stripping of Li inside the graphene‐based MRs with the embedded Au nanonuclei. As a result, the obtained PRGO/Au–Li anodes deliver a long‐lifespan stable cycling up to 600 h with a high specific capacity of ≈2140 mA h g–1 and voltage hysteresis as low as 20 mV in the absence of dendrites. The assembled full cells exhibit excellent rate capability and cycling stability. This work provides an alternative strategy to construct advanced high‐energy‐density lithium batteries via the unique 1D bioinspired graphene‐based packaging strategy.

Boosting of reversible capacity delivered at a low voltage below 0.5 V in mildly expanded graphitized needle coke anode for a high-energy lithium ion battery

The rate performance and cycle stability of graphitized needle coke (GNC) as anode are still limited by the sluggish kinetics and volume expansion during the Li ions intercalation and de-intercalation process. Especially, the output of energy density for lithium ion batteries (LIBs) is directly affected by the delithiation capacity below 0.5 V. Here, the mildly expanded graphitized needle coke (MEGNC) with the enlarged interlayer spacing from 0.346 to 0.352 nm is obtained by the two-step mild oxidation intercalation modification. The voltage plateau of MEGNC anode below 0.5 V is obviously broadened as compared to the initial GNC anode, contributing to the enhancement of Li storage below the low voltage plateau. Moreover, the coin full cell and pouch full cell configured with MEGNC anode exhibit much enhanced Li storage ability, energy density and better cycling stability than those full cells configured with GNC and commercial graphite anodes, demonstrating the practical application value of MEGNC. The superior anode behaviors of MEGNC including the increased effective capacity at low voltage and superior cyclic stability are mainly benefited from the enlarged interlayer spacing, which not only accelerates the Li ions diffusion rate, but also effectively alleviates the volume expansion and fragmentation during the Li ions intercalation process. In addition, the above result is further confirmed by the density functional theory simulation. This work provides an effective modification strategy for the NC-based graphite to enhance the delithiation capacity at a low voltage plateau, dedicated to improving the energy density and durability of LIBs.

(Invited) Understanding the Coupled Electrochemical-Mechanical Behavior of Materials for Improving the Performance and Durability of Lithium-Ion Batteries

With an increasing demand for higher energy and power density of lithium-ion batteries (LIBs), the coupled electrochemical-mechanical degradation of electrode materials becomes a more pressing problem. In particular, fracture and delamination of electrodes can occur during repeated charging and discharging of LIBs. An improved understanding of the mechanical behavior of electrode materials, which often evolves with the state-of-charge and cycle number, is therefore necessary for improving the performance and durability of LIBs and other types of batteries. In this presentation, I will provide an overview of our recent work on using four complementary measurement techniques: (1) electrochemical nanoindentation, (2) scanning probe microscopy, (3) peel adhesion and cohesion test, and (4) electrode curvature measurement to help understand several coupled effects between mechanical and electrochemical behavior of materials on the performance and durability of high capacity electrodes. Examples include silicon/polymer porous composite electrodes, polymeric binders, lithium metal electrodes, and ceramic materials for the positive electrode and solid-state electrolyte. These characterization techniques may also be used to investigate the coupled electrochemical-mechanical behavior of a wide range of materials for lithium-ion batteries and beyond.

Innovations in Post-Mortem Battery Material Characterization for Diagnosing Failure Mechanisms

An increasing demand for clean and renewable energy provides motivation for additional innovations to be sought in energy storage. Lithium-ion batteries (LIBs) have seen many advancements in terms of their cathode chemistries, including electrode coatings that are used to increase durability and capacity of cathode materials. These coatings are effective, but create additional interfaces in the battery system, that adds to complexity in characterization. To address many key issues of LIB failures, further insights are necessary that provide details on currently unknown and partially known intermediate states, side reactions, and/or mechanisms of degradation at electrode interfaces. In this work, a method is developed to enable a detailed surface analysis and additional characterization of coated cathode particles harvested from post-mortem LIBs. Procedures are outlined for the safe handling and preparation of post-mortem materials for high-quality single particle electron microscopy analyses, paired with ultramicrotome techniques for high-throughput cross-sectional imaging with elemental and structural analyses of the coatings themselves.Commonly seen in post-mortem results, the materials are kept intact as whole electrodes or large collections of particles while still held within binders and other cathode slurry components from cell fabrication. These samples are often briefly rinsed with electrolyte solvents [e.g., most commonly dimethyl carbonate (DMC)] to rinse away residual lithium salts.1 While important insights have been gained from such studies, details of surface defects are difficult to discern amidst the debris of additives and binders. To address this, we developed a non-destructive procedure for the separation of cathodes particles from their supports, followed by washing to remove binders, additives, and residual electrolyte with relatively safe and accessible solvents. This method enables high-quality single particle imaging by scanning and transmission electron microscopy (SEM and TEM) techniques. Nano-scale features on the particle surfaces can be observed with high-resolution on the post-mortem cathode particles. With this procedure, insights can be gained about the retention of coatings after battery cycling, in addition to observing visible surface defects that result from charge cycling.Typical cross-sectional analyses of interfacial systems involve expensive, time-consuming methods like focused ion beam (FIB) milling that require extensive training, and are low-throughput when FIB lift-out samples are prepared for TEM. An alternative high-throughput technique for the cross-sectional analysis of coated cathode particles by ultramicrotome was previously developed in our group.2 This technique involves embedding coated cathode particles in epoxy, from which ultra-thin slices (<100 nm) that can contain many [approx. 50-200] particles at a time are cut with a diamond knife. The resultant sheets of epoxy are deposited onto TEM grids so the cross-sections can be imaged by TEM. These sections also enable the particle coatings to be characterized separately from the bulk cathode by electron dispersive X-ray spectroscopy (EDS) and selected area electron diffraction (SAED). This technique was demonstrated on as-synthesized (pre-electrochemistry) samples but was adapted here for the prepared post-mortem samples to assess degradation of the particles and their coatings.Combining the newly developed techniques for obtaining high-quality images of single whole-particles and particle cross-sections this work provides a safe, relatively inexpensive, and high-throughput methodology for the post-mortem characterization of LIB materials. This data can be correlated to as-synthesized materials and electrochemical cycling data to create a detailed profile of cathode aging and degradation as it relates to LIB failures. We are expanding this method to a variety of standard and coated cathode systems to provide detailed information needed for the next steps towards developing new innovations in electrode designs aimed at achieving more durable LIBs.

Molybdenum-Doped Nickel Disulfide (NiS2:Mo) Microspheres as an Active Anode Material for High-Performance Durable Lithium-Ion Batteries

Molybdenum-Doped Nickel Disulfide (NiS₂:Mo) Microspheres as an Active Anode Material for High-Performance Durable Lithium-Ion Batteries

Numerical Analysis of Degradation and Capacity Loss in Graphite Active Particles of Li-Ion Battery Anodes.

It is well known that the performance and durability of lithium-ion batteries (LIBs) can be severely impaired by fracture events that originate in stresses due to Li ion diffusion in fast charge–discharge cycles. Existing models of battery damage overlook either the role of particle shape in stress concentration, the effect of material disorder and preexisting defects in crack initiation and propagation, or both. In this work we present a novel, three-dimensional, and coupled diffusive-mechanical numerical model that simultaneously accounts for all these phenomena by means of (i) a random particle generator and (ii) a stochastic description of material properties implemented within the lattice method framework. Our model displays the same complex fracture patterns that are found experimentally, including crack nucleation, growth, and branching. Interestingly, we show that irregularly shaped active particles can suffer mechanical damage up to 60% higher than that of otherwise equivalent spherical particles, while material defects can lead to damage increments of up to 110%. An evaluation of fracture effects in local Li-ion diffusivity shows that effective diffusion can be reduced up to 25% at the particle core due to lithiation, while it remains at ca. 5% below the undamaged value at the particle surface during delithiation. Using a simple estimate of capacity loss, we also show that the C-rate has a nonlinear effect on battery degradation, and the estimated capacity loss can surpass 10% at a 2C charging rate.