Li Trapping Research Articles

Link between anisotropic electrochemistry and surface transformations at single‐crystal silicon electrodes: Implications for lithium‐ion batteries

AbstractSilicon is a promising negative electrode material for high‐energy‐density Li‐ion batteries (LiBs) but suffers from significant degradation due to the mechanical stress induced by lithiation. Volume expansion and lithiation in Si are strongly anisotropic but associated early interfacial transformations linked to these phenomena and their implications for electrode performance remain poorly understood. Here we develop a novel correlative electrochemical multi‐microscopy approach to study local interfacial degradation at the early stages for three different surface orientations of Si single crystals: Si(1 0 0), Si(1 1 0) and Si(3 1 1), after Li‐ion electrochemical cycling. The experimental strategy combines scanning electrochemical cell microscopy (SECCM) measurements with subsequently recorded scanning transmission electron microscopy images of high‐quality cross sections of Si electrodes, extracted at selected SECCM regions, using a novel Xe+ plasma‐focused ion beam procedure. These studies reveal significant surface orientation–dependent nanoscale degradation mechanisms that strongly control electrode performance. Si(1 0 0) was immune to interfacial degradation showing the best lithiation reversibility, whereas local nanoscale delamination was observed in Si(1 1 0) leading to a lower Coulombic efficiency. Continuous electrochemical deactivation of Si(3 1 1) was associated with delamination across the whole interface, Li trapping and formation of thick (ca. 60 nm) SiO2 structures. These results demonstrate surface crystallography to be a critical factor when designing Si‐based battery materials and strongly suggest that promoting Si(1 0 0) facets could potentially provide longer cycling life and performance due to a higher resistance to degradation.

Structural and electrochemical insights into novel Wadsley Roth Nb7Ti1.5Mo1.5O25 and Ta7Ti1.5Mo1.5O25 anodes for Li-ion battery application.

Niobium based anodes are gaining increasing popularity for application in high-power lithium-ion batteries, due to their high theoretical capacities, inherent safety at high current densities, and long-term stability. Here, we report the discovery and characterisation of a new Wadsley Roth niobate system, Nb7Ti1.5Mo1.5O25, showing that it is isostructural with known systems: Nb9PO25 and Nb9VO25. To evaluate the material's electrochemical performance, including performance at high current densities (for potential high power applications), and long-term stability, Li half-coin cells were prepared. The material showed an initial capacity of 268(9) mA h g-1 at 0.01 A g-1 (voltage range of 2.5-1.0 V). However, in subsequent cycles, some of this initial capacity is lost, which is attributed to Li trapping associated with the presence of reducible MoO4 units, similar to the situation observed for isostructural Nb9VO25. After this initial irreversible capacity loss, the material showed good performance at high current density rates, such that at 2 A g-1 and 4 A g-1 respective capacities of 132(10) mA h g-1 and 115(14) mA g-1 were delivered. Moreover, the material showed respectable capacity retention (97%) after being cycled for 100 cycles at 0.2 A g-1. In order to identify the different Nb, Ti, Mo redox couples involved in this system, a Ta analogue was also synthesized (Ta7Ti1.5Mo1.5O25) and the electrochemical performance for this phase is also reported. This phase shows a lower initial capacity at 0.01 A g-1 (140(3) mA h g-1) than the Nb analogue in the same voltage range, which can be increased (225 mA h g-1) if a lower cutoff voltage (0.5 V) is applied. The capacity retention for this Ta system after 100 cycles at 0.2 A g-1 is similar to the Nb analogue (97%). Further work has explored whether the Nb-Ti-Mo contents could be varied, and these results showed that single phase Nb10-2xTixMoxO25 samples could be prepared for 1.5 ≤ x ≤ 1.75, and electrochemical testing results for the x = 1.75 endmember are also reported. Overall, this research highlights the synthesis and electrochemical characterisation of two new Wadsley Roth phases, and further highlights the challenges associated with the presence of reducible cations in tetrahedral sites in such structures with respect to minimising initial irreversible capacity loss.

Electrochemical investigation of ion-beam sputter-deposited carbon thin films for Li-ion batteries

The C-rate capability of 230 nm- and 16 nm-thin ion-beam sputter-deposited amorphous carbon films, an interesting class of carbonaceous material for lithium-ion batteries, was investigated up to Li-platting. Stepwise ascending and descending constant Li+ currents after each fifth cycle, followed by hundreds of cycles with the highest current were applied. The carbon films show similar cycling with irreversible losses during the first five cycles, followed by reversible cycling with a capacity close to that of graphite. The capacity is significantly lower at high currents; however, it is restored for subsequent cycling again at low currents. Differential charge and differential capacity curves reveal three Li+ uptake and three Li+ release peaks located between 0 and 3 V. Irreversible as well as reversible Li bonding can be associated with all these peaks. Irreversibly bonded Li can be found at the surface (solid electrolyte interphase) and in the bulk of the carbon films (Li trapping). Reversible Li bonding might be possible inside the carbon films in graphite-like nano-domains and at defects. The thinner film reveals a more pseudo-capacitive cycling behavior, pointing to enhanced Li kinetics.Graphical abstract

Exploiting the capacity merits of Si anodes in the energy-dense prototypes via a homogeneous prelithiation therapy

The practical exploitation of the high-capacity Si anodes suffers from the insufficient cation utilization degree in the energy-dense batteries, which originates from unstable interfacial dynamics, lithiation-induced mechanical stress, and irreversible Li trapping in the alloy intermediates. Herein, we develop a scalable, indirect mechanical calendaring approach to enable the homogeneous prelithiation process, specifically through interpolating an intermediate buffer layer (IBL) with tunable electronic/ionic pathways in-between the lithium foil source and the target high-capacity electrode. Upon the prototype assembly of various prelithiated Si/Graphite anodes (450–1000 mAh g−1 at the constant areal capacity of 4.6 mAh cm−2) and the LiNi0.8Co0.1Mn0.1O2 cathode (NCM811, 23 mg cm−2 for the double-sided electrode), the enhanced Li utilization degree with the highest energy density up to 362 Wh kg−1 could be achieved on the realistic cell level (1.6 Ah pouch model). More encouragingly, the reversible phasic evolution of both the cathode and anode, upon the Li+ inventory replenishment, are real-time tracked by the transmission-mode operando X-ray diffraction (XRD). This IBL-regulated approach is further extended to construct an environmental-adaptive composite film that integrates the metallic Li source, the prelithiation of which could well function even at the extreme humid conditions (long-time shelf life or relative humidity up to 85%).

Li trapping in nanolayers of cation ‘disordered’ rock salt cathodes

Cation rearrangement during cycling of a Li1.1Mn0.7Ti0.2O2 cathode with a disordered rock-salt structure forms in situ a short-range ordered superstructure changing the connectivity of Li-migration channels and the electrochemical performance.

Metallic Tin Nanoparticle-Reinforced Tin-Doped Porous Silicon Microspheres with Superior Electrochemical Lithium Storage Properties

Improving the electronic conductivity and drastic volume expansion is attractive and challenging for constructing high-performance Si-based anode materials for lithium-ion batteries. Herein, tin-doped porous silicon microspheres embedded with tin nanoparticles (Sn–PSi@Sn) are fabricated from easily available low-cost silicon–aluminum alloy precursors through a simple and scalable strategy with a chemical replacement/etching and a low-temperature annealing process. The 3D porous framework structure of Sn–PSi@Sn microspheres may buffer severe volume expansion during the electrochemical cycling and shorten the transport paths of Li+ ions. The doping of Sn atoms in the Si crystal lattice can lead to a lattice expansion in silicon, reinforce the electronic and ionic conductivities, and minimize the effect of Li trapping, which is advantageous for enhancing the rate performance and improving the initial Coulombic efficiency. The Sn nanoparticles anchoring in porous silicon microspheres may further improve the conductivity and structure stability of Sn–PSi@Sn composites. Based on the density functional theory calculation results, the effects of partial substitution of Sn into the Si lattice mentioned above have been successfully confirmed. As a consequence, the as-prepared tin-doped porous silicon microspheres embedded with tin nanoparticles show a high reversible capacity (1165.6 mA h g–1 at the 400th cycle at 1 A g–1), excellent rate properties (1433.4 mA h g–1 at a high rate of 2.5 A g–1), and superior cycling performance at an ultrahigh rate (910.9 mA h g–1 at the 500th cycle even at a high current density of 4 A g–1). This work provides a promising strategy to design high-performance anode composites.

Lithium trapping in germanium nanopores during delithiation process

Irreversible capacity loss is a critical problem in high capacity anode materials of Li-ion batteries, such as silicon, germanium, and tin. In addition to solid electrolyte interface formation and active material loss, Li trapping in high capacity anode materials during cycling has been considered a new mechanism of capacity loss but received less attention. In this study, we used single particle battery-based in situ focused ion beam-scanning electron microscopy, transmission electron microscopy (TEM), and scanning TEM to investigate the microstructure and composition of germanium nanopores formed at the end of delithiation. Our results show that a significant amount of Li accumulates inside the nanopores.

Cathode properties of FeF3–V2O5 Glass/C for lithium-ion batteries

For large storage batteries, cost performance is more important than energy density. Iron-based conversion-type cathode active materials are promising because this material group satisfies both low-cost and high-capacity requirements. In particular, iron fluoride is notable for its relatively high discharge voltage. However, the electronic conductivity of FeF3 is poor and it has large discharge-charge overvoltage. To solve these issues, xFeF3-V2O5/C (9xFeF3-9V2O5–P2O5) was investigated and the composition with x = 2 was shown to be optimal. Furthermore, the cyclability of 2FeF3–V2O5/C was improved by changing the salt from LiPF6 to LiClO4 and changing the solvent from DMC to EMC. Although the V2O5 glass component showed irreversible capacity due to Li trapping in the glass matrix at the first cycle, the irreversible capacity at the first cycle was successfully compensated by the addition of LiF as a sacrificial salt.

Incorporation of Natural Lithium‐Ion Trappers into Graphene Oxide Nanosheets

AbstractLithium consumption is estimated to face a considerable rise in the next decade; thus, finding new reproducible lithium resources such as brine deposits and seawater has become a fast‐growing research topic. However, Li+ extraction from these resources is challenging due to its low concentration and presence of other monovalent cations exhibiting identical chemical properties. Here, it is discovered that tannic acid (TA) inside graphene oxide (GO) nanochannel acts as natural ion trapper, which possesses lithiophilic elements. The lithium‐rich feed is achieved by using the potential‐driven TA‐GO membrane by excluding lithium ions from other monovalent cations. The results showed that the ion trapping capability of inexpensive TA‐GO membrane is Li+ > Na+ > K+ with Li trapping energy of −593 KJ mol−1, respectively, where its trapping efficiency goes into a top rank among their expensive synthetic counterparts. Evaluating the combined effect of three key parameters, including barrier energy, hydration energy, and binding energy illustrates that required energy to transport Li‐ion through the membrane is higher than that for other monovalent. This proof‐of‐concept work opens up an avenue of research for designing a new class of ion‐selective membranes, based on the incorporation of naturally low cost available lithiophilic guest molecules into 2D membranes.

Quantitative spatiotemporal Li profiling using nanoindentation

The rate capability and lifetime of Li-ion batteries is largely dictated by the composition dynamics of the electrodes. We set forth a nanoindentation approach to probe the spatiotemporal Li profile using the functional dependence of the mechanical properties on Li composition. This mechanics-informed material dynamics allows us to measure the composition-dependent diffusivity, assess the rate-limiting process in Li reactions, and quantitatively evaluate the stress regulation on Li transport. The experiments show that Li diffusivity in amorphous Si varies exponentially by three orders of magnitude from the pristine to the fully lithiated state. Lithiation in amorphous Si is limited by diffusion at the micron scale. We further evaluate the thermodynamic driving force for Li diffusion by including the material non-ideality and mechanical stresses. Through computational modeling, we find that the composition dependence of the Li diffusivity in general creates an asymmetry on the rate capability during lithiation versus delithiation. In Si, the exponential dependence results in a fast lithiation that proceeds via a steep concentration gradient compared to a slow and relatively smooth delithiation. This asymmetric behavior appears to be a root cause of Li trapping and loss of the deliverable capacity in Si. This work sheds light on the thermodynamics of Li transport and the lithiation kinetics of amorphous Si. It demonstrates the potential of operando nanoindentation in the mechanics-informed understanding of Li chemistry and aiding battery research beyond mechanical measurement.

Looking for the Lost Lithium: Lithium Trapping and Its Effect on Capacity Losses in Li-Ion Batteries

Rechargeable lithium batteries are well-known to exhibit progressive capacity decays upon cycling, leading to loss of cell voltage, power and energy. However, the origins of capacity losses are still not fully understood and are largely attributed to the formation of a solid electrolyte interface layer and volume expansion. Another largely overlook capacity decay mechanism is lithium trapping 1–4. Lithium trapping, caused by incomplete delithiation, is here demonstrated to be the main source of capacity losses in high energy density anodes (e.g. Si) while SEI formation and dissolution affect the accumulated capacity loss due to decreased coulombic efficiency. In the following paper we will present our findings on capacity losses in standard and optimized Si-Li half cells and how these systems affect lithium trapping inside the active electrode material. We will discuss how the cycling protocol (e.g. full capacity cycling vs coulombic limited cycling) can mask signs of Li trapping and temporarily delay capacity decay in half-cells. We will highlight the importance of lithium-trapping induced capacity or voltage decays effect in lithium-based batteries, explain the mechanism for lithium-trapping and establish diffusion-controlled lithium-trapping models. Approaches toward identifying and circumventing lithium-trapping problem will also be discussed as well as challenges and proposed future research directions within this exciting and important research field. Figure 1. Capacity evolution for an optimized nano-Silicon composite electrode in a half-cell configuration during coulombic limited cycling (i.e. 1200 mAh/g). Critical capacity decay is observed when the accumulated trapped lithium has saturated the electrode core and counteracts the deposited Li layer 1.

ALD-Modified LiNi0.33Mn0.33Co0.33O2 Paired with Macroporous Silicon for Lithium-Ion Batteries: An Investigation on Lithium Trapping, Resistance Rise, and Cycle-Life Performance

Combining high energy density electrodes, such as silicon and NMC, has the potential to meet the growing demand of high energy electric vehicles. Herein, we report a full-cell design using a macroporous silicon anode and alumina-coated NMC cathode that provides stable cyclability by means of capacity-limited charging. The proposed Si-NMC full-cell design with alumina passivation on cathode has exhibited a stable capacity of 1000 mAh/g, with 1.2 times higher energy density than the Si-NMC full-cell without cathode passivation. The role of alumina coating on the altered half-cell electrode charging mechanisms and electrochemical full-cell reactions with Si anode was investigated systematically using various structural and chemical analyses. The alumina passivated Si-NMC full-cell designed in this study elucidated an interesting electrochemical behavior of Li trapping, which shed light on a significant pathway in the efficient utilization of Si-NMC battery for high energy applications.

Boosting ionic conductivity in antiperovskite Li3OCl via defect engineering: Interstitial versus vacancy

Ion transport in solid materials is frequently facilitated by defects. It is thus attractive to increase ionic conductivity by introducing proper types of defects. In antiperovskite ${\mathrm{Li}}_{3}\mathrm{OCl}$, a promising solid-state electrolyte material, a Li interstitial is predicted to be superior to Li vacancy for Li ion transport. However, the Li interstitial is difficult to dope into ${\mathrm{Li}}_{3}\mathrm{OCl}$ and it typically comes with a charge-compensating ${\mathrm{O}}_{\mathrm{Cl}}^{\ensuremath{'}}$ substitutional defect, which is a Li trap and thus hampers Li ion transport. In this study, a protocol to enhance Li interstitial formation via S doping is proposed. With a ${\mathrm{S}}_{\mathrm{Cl}}^{\ensuremath{'}}$ charge-compensating defect, the Li interstitial becomes more stable than Li vacancy. At the same time, thanks to a cancellation of two different contributions, ${\mathrm{S}}_{\mathrm{Cl}}^{\ensuremath{'}}$ has little effect on the Li local electrostatic environment and thus ion transport. As a result, Li interstitial conductivity can be boosted from $3.822\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ to 1.286 mS/cm upon S doping, which leads to a 1-order-of-magnitude increase of the overall ionic conductivity. Such a significant performance enhancement via defect engineering opens an alternative avenue for the design of battery materials.

Minimized lithium trapping by isovalent isomorphism for high initial Coulombic efficiency of silicon anodes.

Silicon demonstrates great potential as a next-generation lithium ion battery anode because of high capacity and elemental abundance. However, the issue of low initial Coulombic efficiency needs to be addressed to enable large-scale applications. There are mainly two mechanisms for this lithium loss in the first cycle: the formation of the solid electrolyte interphase and lithium trapping in the electrode. The former has been heavily investigated while the latter has been largely neglected. Here, through both theoretical calculation and experimental study, we demonstrate that by introducing Ge substitution in Si with fine compositional control, the energy barrier of lithium diffusion will be greatly reduced because of the lattice expansion. This effect of isovalent isomorphism significantly reduces the Li trapping by ~70% and improves the initial Coulombic efficiency to over 90%. We expect that various systems of battery materials can benefit from this mechanism for fine-tuning their electrochemical behaviors.

High-Accuracy Life Estimation of Large-Size Lithium-Ion Battery Operated Under Diversified SOC Change

INTRODUCTION The use of large-size lithium-ion battery has been expanding to not only automotive but also other industrial fields such as AGV, railway, load-leveling, etc. This expansion promotes its various operation conditions and, therefore, requires the way to be able to estimate its life accurately. Many efforts have been devoted to estimate the life even in the several applications. According to the report [1], the battery capacity loss for the estimation is divided into calendar and true cycle capacity loss. The calendar capacity loss is caused by active Li trapping mainly due to SEI growth at negative electrode, of which rate is dependent on SOC level, temperature and time [1-3], whereas the true cycle capacity loss is dependent only on the amount of charge-discharge cycle number in specified DOD range [1]. However, the true cycle capacity loss and its mechanism of large-size battery has not been clarified in the diversified cycle containing high and low frequency of fluctuational SOC. In this study, the factors that affect the true cycle capacity loss with clarification of its mechanism have been investigated in detail, and then updated life estimation algorism based on the result of the investigation has been proposed to enable high-accuracy life estimation of the battery operated even under complicated condition. EXPERIMENTAL The endurance tests for large-size lithium-ion cells were conducted under various conditions of different charge-discharge route (SOC route) in order to clarify the factors that impact the capacity loss. Each amount of the Li trapping at negative electrode, and degradations of the positive and negative electrodes were investigated by discharge profile fitting analysis [4] and post-mortem analysis. RESULTS AND DISCUSSION According to results of the cells tested under various conditions, the capacity loss depends on the SOC route despite of the same accumulative amount of SOC fluctuation and test time. The relation between relative coefficient of true capacity loss and the SOC fluctuational range as controlling the designated value of center SOC at 60% is shown in Fig. 1. The coefficient of the loss drastically increases with expansion of the range, which means that the true cycle capacity loss should be estimated depending on the individual range in the diversified SOC change. Furthermore, post-mortem analysis and discharge profile fitting analysis for the tested cells prove that the total capacity loss of the cell is accelerated mainly by the factors of the range and its center value because the rates of both SEI growth at the negative electrode and degradation of positive electrode are affected by these factors. Therefore, updated model describing true cycling capacity loss has been proposed. Finally, the verification test including high and low frequency of fluctuational SOC under various operating temperature for 550 days was carried out together with estimation of capacity retention by the conventional and the updated model. As a result, the accuracy of battery life estimation even in long-term test with complex patterns is dramatically improved from 31% to within 2% of the actual capacity retention by updated model considering SOC route the cell experienced. REFERENCE H. Yoshida, N. Imamura, T. Inoue, and K. Komada, Electrochemistry, 71, 1018-1024 (2003).H. Ploehn, P. Ramadass, and R. White, J. Electrochem. Soc., 151, A456-A462 (2004).N. Shinha, T. Marks, H. Dahn, A. Smith, J. Burns, D. Coyle, J. Dahn, and J. Dahn, J. Electrochem. Soc., 159, A1672-A1681 (2012).K. Honkura, K. Takahashi, and T. Horiba, J. Power Sources, 196, 10141-10147 (2011). Fig. 1. (a) Relative coefficient of true capacity loss at the same accumulative amount of SOC fluctuation in various SOC fluctuational range. The values are normalized by true capacity loss between 30 and 90% of SOC cycle test (SOC fluctuational range = 60%). (True capacity loss [%]) = (Total capacity loss [%]) - (Calendar capacity loss [%]) (b) Cycling protocols of SOC endurance test shown in Fig. 1 (a). Charge: CC 1.0 CA 4.10 V at 25 ℃. Discharge: CC 1.0 CA 2.75 V at 25 ℃. Figure 1

Incorporation of Aluminum into High-Nickel Layered Oxide Cathodes: An Interphase and Structural Study

The rapidly growing energy market calls for advanced Li-ion batteries with high energy density and acceptable service life. Ni-rich layered oxides (LiNixM1 −xO2, x > 0.6, M = Mn, Ni, Co), especially those with ultrahigh Ni content (Ni > 0.9), are able to deliver a high capacity of > 200 mA h g−1 with a high average operating voltage of 3.8 V vs Li/Li+. They hold great promise to power a 300-mile electric vehicle and are being intensively studied in recent years. However, severe critical problems greatly hinder the widespread application of high-Ni layered oxides. First, during electrochemical cycling, the generation of monoclinic and hexagonal structures in the delithiated state induces large unit cell volume changes and anisotropic strains, which leads to microcrack formation and eventually secondary particle disintegration. Furthermore, this structural evolution process is worsened as Ni content increases due to the presence of the hexagonal 3 (H3) phase in the deeply delithiated state. Second, a high concentration of unstable Ni4+ in the highly delithiated high-nickel layered oxide tends to react aggressively with the carbonate electrolyte, resulting in the formation of cathode-electrolyte interphase (CEI). Furthermore, the unwanted reaction greatly expedites the irreversible transformation of the layered structure to a rock-salt (NiO) phase. Overall, these various degradation processes result in a high interfacial impedance and poor electrochemical performance. Herein, to tackle these issues, a trace amount of Al is substituted into a high-Ni layered oxide and the dual-function of Al cooperation is demonstrated. By substituting a small dose of Al (2 mol %) for Ni in LiNi0.92Co0.06Al0.02O2, the capacity retention of the full cells utilizing Al-doped LiNi0.92Co0.06Al0.02O2 cathode paired with graphite anode after 1000 cycles increases from 47% to 83% compared to that of Al-free LiNi0.94Co0.06O2. Through in-situ X-ray diffraction, we provide the operando evidence that Al dopant tunes the H2−H3 phase transition process from a two-phase reaction to a quasi-monophase reaction, minimizing the mechanical degradation. Furthermore, Al dopant facilities the formation of phosphate-enriched CEI on the cathode surface, which protects the cathode from severe electrolyte attack. Also, secondary-ion mass spectrometry reveals considerably suppressed transition-metal dissolution with Al doping, effectively preventing sustained parasitic reactions and active Li trapping due to chemical crossover on the graphite anodes. This work offers a viable approach for adopting high-Ni cathodes in Li-ion batteries. Figure 1

Chemical imaging and diffusion of hydrogen and lithium in lithium aluminate

Tritium (3H) must be replenished for strategic stockpile and fusion reactors. 6Li-enriched γ-LiAlO2 pellets have been used for 3H production by thermal neutron irradiation. A fundamental study of 3H and 6Li diffusion processes in irradiated γ-LiAlO2 pellets is needed to assess and predict the long-term material performance. This study focuses on identifying the trapping sites and diffusion pathways of 1H (a surrogate for 3H) and Li atoms in polycrystalline γ-LiAlO2 pellets irradiated with both 4He+ and 1H2+ ions. A combination of STEM-EELS, Nano-SIMS and APT is employed for chemical imaging at nanoscale resolution. There is direct evidence for preferred Li diffusion pathways along grain boundaries. Isolated voids are identified as possible Li trapping sites in the irradiated γ-LiAlO2 pellets. Possible lithium hydrides and/or hydrates are precipitated on the surface of the irradiated pellets. This study improves our understanding of H and Li diffusion processes and provides data for modelling and simulation to predict material performance during neutron irradiation of γ-LiAlO2 pellets.

Lithium Trapping in Microbatteries Based on Lithium‐ and Cu2O‐Coated Copper Nanorods

AbstractMicrobatteries based on three‐dimensional (3D) electrodes composed of thin films of Li and Cu2O coated on Cu nanorod current collectors by electrodeposition and spontaneous oxidation, respectively, are described and characterised electrochemically. High‐resolution scanning electron microscopy (HR‐SEM) data indicate that the Li electrodeposition resulted in a homogenous coverage of the Cu nanorods and elemental analyses were also used to determine the amount of lithium in the Li‐coated electrodes. The results show that 3D Cu2O/Cu electrodes can be cycled versus 3D Li/Cu electrodes but that the capacity decreased during the cycling due to Li trapping in the Cu current collector of the 3D Li/Cu electrode. These findings highlight the problem of using copper current collectors together with metallic lithium as the formation of a solid solution yields considerable losses of electroactive lithium and hence capacity.

(Invited) Electrode Crosstalk during Lithium-Ion Battery Aging

Lithium-ion cells containing layered-oxide based positive electrodes and graphite-based negative electrodes are being cycled at high voltages (> 4.30 V) to increase energy density. In this presentation we will detail performance changes in these cells during cycling, with a particular focus on the crosstalk between electrodes. We show that the dissolution of transition metal (TM) ions from the positive electrode, and their migration and incorporation into the solid electrolyte interphase (SEI) of the negative electrode, accelerates markedly as the upper cutoff voltage (UCV) exceeds 4.30 V. At voltages ≥ 4.40 V there is enhanced fracture of the oxide during cycling that creates new surfaces and causes increased solvent oxidation and TM dissolution. Despite this deterioration, cell capacity fade still mainly results from lithium loss in the negative electrode SEI. Among TMs, Mn content in the SEI shows a better correlation with cell capacity loss than Co and Ni contents. We estimate that each Mn ion deposited in the SEI causes trapping of ~100 additional Li+ ions thereby hastening the depletion of cyclable lithium ions. During the presentation we will highlight an electrocatalysis mechanism through which the deposited Mn ions accelerate electrolyte reduction and increase Li trapping in the negative electrode SEI. Methods to mitigate this cross-talk, through the use of coatings and additives, will also be discussed.

Investigation of the Li solubility in the intermediate phase Li17Sn4 relevant to understanding lithiation mechanisms in Sn-based anode materials

A comprehensive study of the Li-rich phase boundary of the intermediate Li17Sn4 compound is given based on thermochemical and electrochemical investigations. From the results a partial phase diagram showing the homogeneity range of this phase could be constructed. Using these results, the defect mechanism for the compound Li17Sn4 could also be clarified. Galvanostatic coulometry with potential limitation (GCPL) was performed using 2032 coin cell equipment. This allowed for the determination of the amount of Li insertion on special crystallographic sites at 25 °C, which is 0.41 ± 0.04 at.%. The respective Li loss mechanisms (solid electrolyte interface formation, Li plating, Li trapping) are discussed. Irreversible capacity according to Li trapping could be excluded due to the limited voltage window of the experiments. Moreover, differential scanning calorimetry (DSC) was carried out on two individual Tian-Calvet type calorimeters. The Li-rich boundary of the Li17Sn4 compound was determined at 81.31 ± 0.04 (C-80) and 81.28 ± 0.05 at.% Li (M-HTC) at 427 °C. In addition, the latter results were compared to the change of lattice parameters of alloys with compositions Li17+xSn4.