Lithiated State Research Articles

Enabling Fast‐Charging and High Specific Capacity of Li‐Ion Batteries with Nitrogen‐Doped Bilayer Graphdiyne: A First‐Principles Study

Carbon‐based materials are the most important anode materials for Li‐ion batteries (LIBs). To improve the electrochemical performance of LIBs for high energy density and fast charging, advanced carbon allotropes are in the research focus. In this work, we applied the density functional theory to investigate the atomic and electronic structures as well as high Li‐ion specific capacity of graphdiyne (GDY). The atomic structures of monolayer graphdiyne (MGDY), bilayer AB(β1)‐stacking graphdiyne (AB(β1)BGDY) and nitrogen‐doped AB(β1)BGDY (N‐AB(β1)BGDY) at different lithiation states were thoroughly investigated. The AB(β1)BGDY and N‐AB(β1)BGDY exhibit promising characteristics in Li‐ion adsorption and intercalation, enhancing its specific capacity from 744 mAhg‐1 in the monolayer GDY to 807 mAhg‐1 in the bilayer. Besides increasing the capacity through a bilayer‐structure, it is possible to tailor its structural stability and band gap by doping. Especially shown for N‐AB(β1)BGDY (~1%), an increased structural stability and a decreased band gap of 0.24 eV is found. While this means that N doping in AB(β1)BGDY can lead to longer‐lasting and more stable operatable high‐capacity anodes in LIBs, it increases the OCV.

XCT images-based modeling for elucidating electrochemical inert phase-dependent multiscale electrode kinetic behaviors

The electrochemically inert phase (EIP) within the electrode is formed by the combination of carbon black and binder, characterized by a highly heterogeneous spatial distribution and structural morphology. This heterogeneity impairs electrode performance under varying discharge rates and temperatures. In this study, X-ray computed tomography is employed to image the original electrode. The resulting grayscale images are digitally processed to reveal the two-dimensional (2D) and three-dimensional (3D) features of the EIP morphology, thereby providing a design window to understand the influence of EIP morphology. The physical structure characterization indicates that, compared to bulk-like EIP (B-EIP), film-like EIP (F-EIP) tends to cover the active surface of the active material (AM), exacerbating the heterogeneity of the lithiation reactions within the electrode. The reduction in the AM active surface area correlates the state of lithiation (SOL) of particles with their active specific surface area (αa). At low temperatures, the temperature sensitivity of electrodes intensifies the risk of αa loss, promoting heterogeneous reaction transfer between particles. The Biot number (Bi) is used to evaluate the competing mechanisms between interfacial reactions and bulk diffusion within particles. In electrodes with a high EIP content, the reaction rate at the particle/electrolyte interface is accelerated, causing particle performance to be dominated by interfacial reactions. Finally, the electrochemistry and heat generation from the particle-level to the electrode-level in thicker electrodes are examined. It demonstrates that ion diffusion in the pore controls interfacial reactions and heat transport behavior. Aggregated high-flux reactions and localized hot spots exacerbate the heterogeneous degradation and side reactions within the electrode.

Title: Study of Structural Evolution of Silicon-Based Anodes in Lithium-Ion Batteries

The need for electrification across various sectors has led to increased demand for high-performance lithium-ion batteries (LIBs). Today’s commercial LIBs typically make use of a pure-graphite anode which offers long lifespans but a relatively meager capacity of 372 mAh/g. Silicon, by comparison, offers a theoretical capacity of 3600 mAh/g but generally suffers from short life spans due to numerous effects. Combining silicon and graphite active materials to form a composite anode can result in electrodes with improved capacities over pure-graphite systems and enhanced longevity over pure-silicon ones. However, introducing silicon to an otherwise stable graphite electrode can induce failure of the electrode partly due to the volumetric expansion/contraction that silicon experiences during lithiation/delithiation cycles. Understanding the morphological evolution of silicon particles in composite electrodes - particularly in a lithiated state - can yield a more comprehensive understanding of the interactions between the active materials which will contribute to the realization of anodes with improved capacities and lifespans. To date, characterizing lithiated silicon-containing anodes has been difficult owing to the reactivity of the lithiated materials and a lack of suitable methods to probe within an electrode’s bulk. In this work, we demonstrate recent successes in imaging lithiated silicon-composite and silicon oxide-composite electrodes via micro and nanoscale computed tomography (MicroCT, NanoCT) and electrochemical analysis to quantify (1) changes in particle size distributions over charge/discharge cycles, (2) lithium content in silicon particles as a function of depth from the electrode’s surface, (3) changes in particle morphology, and (4) electrode thickness. The development of this technique represents a significant step towards characterizing the physical behavior of silicon particles within electrodes without destroying the surrounding structures.

Elucidating the Effect of Pre-Lithiation of Silicon Dominant Anodes on the Full Cell Performance

Over the last few years, there has been a high interest in increasing the energy density of lithium-ion batteries in order to increase the driving range of battery electric vehicles. On a material level, silicon is a promising anode active material candidate due to its high theoretical capacity of 3579 mAh g-1, which is approximately ten-fold higher than that of the currently used graphite anodes with a theoretical capacity of 372 mAh g-1.[1] However, the main drawbacks of silicon are its intrinsic volume expansion of +300 % upon lithiation.[2] This leads to rupturing of the passivating solid electrolyte interphase (SEI), particle cracking, and loss of electronic contact, limiting the lifetime of batteries with silicon based anodes, thus hindering their transition into application.As a possible solution, Jantke et al. proposed the concept of partial utilization of µm-sized crystalline silicon, where only one-third of the theoretical capacity is used for (de)lithiation. Thereby, a crystalline core remains, and the volume expansion on the particle-level is reduced to approximately + 100%.[3] In addition, it was shown that irreversible losses during the formation and upon cycling can be compensated by pre-lithiation of the anode, which increases the lifetime significantly.[4,5] In this study, we investigated a promising cell chemistry for high-energy applications, containing a Si-dominant anode and a cathode based on a Co-free lithium- and manganese-rich NMC. The here used anode consists of 70 wt% silicon, 20 wt% graphite, 2 wt% conductive C65, and 8 wt% LiPAA-binder. Note that graphite mainly acts as a conductive additive within the operating voltage window, with a negligible contribution to the overall anode capacity. The electrochemical testing was conducted at 25 °C in Swagelok® T-cells containing two glass fiber separators, a 1M LiPF6 in FEC:DEC (2:8, v:v) electrolyte and a lithium metal reference.Without pre-lithiation, these full-cells suffered from rapid capacity fading, reaching the 80 % state-of-health (SOH) criterion after ~100 cycles. As will be discussed, our analysis shows that the primary mode of failure in these cells is the loss of cyclable lithium, evidenced by an increase in the end-of-discharge potential at the anode. It was found that with increasing end-of-discharge potential at the anode, the anode resistance at low state-of-charge rises significantly.Therefore, silicon anodes were lithiated in coin half-cells to 25, 50, and 75 % of the reversible cathode capacity (corresponding to 300, 600, and 900 mAh gSi -1). Then, the anodes were harvested in the lithiated state and assembled in a Swagelok® T-cell with the same cathode, separator, and electrolyte as the non-pre-lithiated reference cells. Pre-lithiation leads to similar reversible charge/discharge capacities, but generates a cyclable lithium reservoir in the anode.Successively increasing the pre-lithiation of the anode increases the lifetime from 100 to 550 cycles. The onset of the above-described aging phenomena is delayed by 150 cycles for every additional 25 % pre-lithiation. Further, the influence of aging and lithium inventory on anode and cathode resistance will be discussed, showing that the increase in anode resistance is mainly a function of (de)lithiation rather than cycle number.Acknowledgments:The authors gratefully acknowledge the funding from the BMBF (Federal Ministry of Education and Research, Germany) in the ExZellTUM III project (grant number 03XP0255). We also kindly thank Wacker Chemie AG and BASF SE for providing the anode and cathode active materials.

Mechanical Failure of Core-Shell Cathode Particles: The Effects of Concentration-Dependent Material Properties and Phase Field Fracture Modelling

The use of core-shell cathode particles in lithium-ion batteries is an attractive approach to enhancing energy density whilst retaining lifetime, through reducing undesired reactions at the electrode-electrolyte interface and limiting the volume change of the electrode particles. However, mechanical failure through the fracture and debonding of the core-shell interface is a major challenge. In this work, we employ a coupled finite-element model to predict and mitigate the mechanical failure of core-shell cathode structures, taking as example a particle of NMC811 (core) coated with NMC111 (shell). In particular, we focus on two aspects:The first one involves the assumptions of material properties as inputs of the model. The material properties are often considered constant by battery modelling researchers, yet these parameters can vary significantly during charge/discharge. For example, experiments have unveiled a three-orders-of-magnitude drop in the diffusion coefficient of NMC materials during discharge [1]. Here, we incorporate material properties obtained from experimental data, including concentration-dependent diffusion coefficient obtained from GITT measurement and partial molar volume derived from in situ X-ray diffraction data. Our results indicate that when assuming a concentration-dependent partial molar volume, the maximum values of tensile hoop stress in the shell are nearly three times lower than those predicted with constant average properties, diminishing the likelihood of fracture.When accounting for concentration-dependent diffusion coefficient, large concentration gradient is observed near the outer surface of the core due to reduced lithium mobility at high states of lithiation, hindering full electrode capacity utilisation. The significant concentration gradient and capacity underutilisation align with direct observations from experiments [2]. Notably, these phenomena cannot be captured in modelling if assuming constant diffusion coefficient. These findings offer new perspectives on the performance and design of core-shell electrode particles. Safe design maps in terms of core size and shell thickness to mitigate fracture and debonding are obtained.The second focus of this work is the utilisation of phase field fracture model in predicting cracking behaviours within the core-shell particle. Phase field modelling provides a continuous representation of cracks, enabling the tracking of complex cracking patterns [3]. We predict cracking behaviors caused by volume changes during charge/discharge, as well as inaccessible capacity and newly created active surface area caused by cracking. Our multiphyics model can hopefully act as a catalyst, accelerating the development process of the core-shell structured cathode particles and shortening the time to market of advanced batteries with extended lifetime.

Active Material Lithiation in Gr/SiOx Blend Anodes at Increased C-Rates

The energy density of lithium-ion batteries can be improved by adding silicon as a secondary active anode material alongside graphite. However, accurate state estimation of batteries with blend electrodes requires detailed knowledge of the interplay between the active materials during lithiation. Challenges arise from the current split between the active materials and the overlap of their working potentials. This study examines the lithiation behavior of blend anodes using a setup consisting of a pure graphite and a pure SiOx half-cell connected in parallel. The setup allows for current measurements of both active materials, the determination of the state of lithiation throughout the entire charging process and measurements of balancing effects between the active materials during relaxation periods. Analysis of the behavior at increased charge rates results in greater SiOx lithiation after similar charge throughput indicating better kinetics for SiOx compared to graphite. A Doyle-Fuller-Newman model of a blend anode is used to further investigate the experimental findings on the lithiation behavior and transfer them to blend electrodes. Simulation-based variations of the silicon content show that an increased SiOx content in blend anodes leads to improved rate capability.

Unveiling Electrochemical Properties of Silicon for Stable Cycling Performance of Silicon Anode Materials

Research on silicon (Si) as an anode material for Li-ion batteries has spanned two decades; however, certain electrochemical properties of Si remain unclear. Specifically, the cyclic voltammogram (CV) pattern of Li/Si cells varies from case to case, influenced not only by the material but also by the experimental conditions. In this work, slow cyclic voltammetry is employed to investigate Li/Si cells, resulting in three distinct CV patterns. It is further observed that the CV pattern, particularly during the delithiation, is contingent on the state-of-lithiation (SOL) during lithiation and correlates with the capacity fade of Li/Si cells in subsequent cycles. Additionally, it is revealed that the primary mechanism for capacity fade differs between nano-sized silicon (Si-NP) and micro-sized silicon (Si-MP). In brief, capacity fade in Li/Si-NP cells predominantly arises from parasitic reactions between the highly lithiated Li-Si alloy and electrolyte solvents, exacerbated by the large specific surface area of Si-NP materials, whereas capacity fade in Li/Si-MP cells is primarily attributed to the Li electrode rather than the Si-MP electrode due to the restricted lithiation of Si-MP materials. Finally, this work concludes that limiting the SOL of Li/Si cells offers a straightforward and effective pathway to achieving stable cycling performance.

Establishing Li-acetylide (Li2C2) as functional element in solid-electrolyte interphases in lithium-ion batteries

Previously, lithium-acetylide (Li2C2) had been identified as electrolyte degradation product on lithium-metal based electrodes using Raman spectroscopy. This raised the question, if Li2C2 is also be formed on graphitic electrodes in lithium-ion batteries without lithium metal present. In order to shed light on this research question, we performed a series of in situ Raman experiments with graphitic electrodes in half- and full-cell configuration. The recorded cell potential dependent spectra clearly prove the presence of Li2C2 in the lithiated state of the electrodes, but the according peak vanishes when delithiating. This observation indicates a somewhat reversible process involving Li2C2. Several chemical/electrochemical reactions are in question to contribute to this effect. With respect to its properties and potential role in the solid-electrolyte interphase (SEI) DFT calculations of Li2C2-nanoclusters were performed, which revealed an exceptionally low energy band gap, hence a remarkable electric conductivity. In conjunction with a relatively high ionic conductivity, Li2C2 appears to play a key role in the degradation of lithium-ion batteries, which had not yet been revealed nor taken into account in simulations of the interphase.

Unlocking iron metal as a cathode for sustainable Li-ion batteries by an anion solid solution.

Traditional cathode chemistry of Li-ion batteries relies on the transport of Li-ions within the solid structures, with the transition metal ions and anions acting as the static components. Here, we demonstrate that a solid solution of F- and PO43- facilitates the reversible conversion of a fine mixture of iron powder, LiF, and Li3PO4 into iron salts. Notably, in its fully lithiated state, we use commercial iron metal powder in this cathode, departing from electrodes that begin with iron salts, such as FeF3. Our results show that Fe-cations and anions of F- and PO43- act as charge carriers in addition to Li-ions during the conversion from iron metal to a solid solution of iron salts. This composite electrode delivers a reversible capacity of up to 368 mAh/g and a specific energy of 940 Wh/kg. Our study underscores the potential of amorphous composites comprising lithium salts as high-energy battery electrodes.

Deeply Lithiated Carbonaceous Materials for Great Lithium Metal Protection in All-Solid-State Batteries.

Protection of lithium (Li) metal electrode is a core challenge for all-solid-state Li metal batteries (ASSLMBs). Carbon materials with variant structures have shown great effect of Li protection in liquid electrolytes, however, can accelerate the solid-state electrolyte (SE) decomposition owing to the high electronic conductivity, seriously limiting their application in ASSLMBs. Here, a novel strategy is proposed to tailor the carbon materials for efficient Li protection in ASSLMBs, by in situ forming a rational niobium-based Li-rich disordered rock salt (DRS) shell on the carbon materials, providing a favorable percolating Li+ diffusion network for speeding the carbon lithiation, and enabling simultaneously improved lithiophilicity and reduced electronic conductivity of the carbon structure at deep lithiation state. Using the proposed strategy, different carbon materials, such as graphitic carbon paper and carbon nanotubes, are tailored with great ability to speed the interfacial kinetics, homogenize the Li plating/stripping processes, and suppress the SE decompositions, enabling much improved performances of ASSLMBs under various conditions approaching the practical application. This strategy is expected to create a novel roadmap of Li protection for developing reliable high-energy-density ASSLMBs.

Influence of concentration-dependent material properties on the fracture and debonding of electrode particles with core–shell structure

Core–shell electrode particle designs offer a route to improved lithium-ion battery performance. However, they are susceptible to mechanical damage such as fracture and debonding, which can significantly reduce their lifetime. Using a coupled finite element model, we explore the impacts of diffusion-induced stresses on the failure mechanisms of an exemplar system with an NMC811 core and an NMC111 shell. In particular, we systematically compare the implications of assuming constant material properties against using Li concentration-dependent diffusion coefficient and partial molar volume. With constant material properties, our results show that smaller cores with thinner shells avoid debonding and fracture regimes. When factoring in a concentration-dependent partial molar volume, the maximum values of tensile hoop stress in the shell are found to be significantly lower than those predicted with constant properties, reducing the likelihood of fracture. Furthermore, with a concentration-dependent diffusion coefficient, significant barriers to full electrode utilisation are observed due to reduced lithium mobility at high states of lithiation. This provides a possible explanation for the reduced accessible capacity observed in experiments. Shell thickness is found to be the dominant factor in precluding structural integrity once the concentration dependency is accounted for. These findings shed new light on the performance and effective design of core–shell electrode particles.

Building Interconnected Architectures with Silicon‐Based Nanospheres and TiN Ionic Fence Enables Ultrahigh Electrochemical Stability

AbstractSilicon oxide (SiOx) material is gradually developing as a promising alternative to silicon due to a better trade‐off in terms of volume expansion and theoretical capacity. However, the low conductivity and the instability of the electrode–electrolyte interface caused by the penetration of the fluorine anion (F−) severely affect the stability of the solid electrolyte interphase (SEI), ultimately leading to capacity loss and cycling instability. In this work, an “ionic fence” idea is proposed, which effectively inhibits the shuttle of F− and promotes the stability of the SEI. Based on this, a dense and orderly silicon‐based interconnected assembly covered by a TiN protective ionic fence is designed using melt‐assembly technique and nitridation strategy. After 1000 deep cycles, the capacity can be maintained at 431.7 mA h g−1, the average Coulombic efficiency can reach 99.69% throughout the cycling process, and even a steady state after 2000 cycles, showing excellent electrochemical stability. Finite element analysis reveals that the TiN fence, as a stress management layer, effectively constrains the volume expansion of materials and improves the mechanical structural stability of the particles in the fully lithiated state, thus ensuring long‐term cycling stability. Selective fence design for material interface has great universality and development potential in building stable electrode materials.

Formulating Local Environment of Oxygen Mitigates Voltage Hysteresis in Li-Rich Materials.

Li-rich cathode materials have emerged as one of the most prospective options for Li-ion batteries owing to their remarkable energy density (>900Wh kg-1). However, voltage hysteresis during charge and discharge process lowers the energy conversion efficiency, which hinders their application in practical devices. Herein, the fundamental reason for voltage hysteresis through investigating the O redox behavior under different (de)lithiation states is unveiled and it is successfully addressed by formulating the local environment of O2-. In Li-rich Mn-based materials, it is confirmed that there exists reaction activity of oxygen ions at low discharge voltage (<3.6V) in the presence of TM-TM-Li ordered arrangement, generating massive amount of voltage hysteresis and resulting in a decreased energy efficiency (80.95%). Moreover, in the case where Li 2b sites are numerously occupied by TM ions, the local environment of O2- evolves, the reactivity of oxygen ions at low voltage is significantly inhibited, thus giving rise to the large energy conversion efficiency (89.07%). This study reveals the structure-activity relationship between the local environment around O2- and voltage hysteresis, which provides guidance in designing next-generation high-performance cathode materials.

The role of oxygen in automotive grade lithium-ion battery cathodes: an atomistic survey of ageing.

The rising demand for high-performance lithium-ion batteries, pivotal to electric transportation, hinges on key materials like the Ni-rich layered oxide LiNixCoyAlzO2 (NCA) used in cathodes. The present study investigates the redox mechanisms, with particular focus on the role of oxygen in commercial NCA electrodes, both fresh and aged under various conditions (aged cells have performed >900 cycles until a cathode capacity retention of ∼80%). Our findings reveal that oxygen participates in charge compensation during NCA delithiation, both through changes in transition metal (TM)-O bond hybridization and formation of partially reversible O2, the latter occurs already below 3.8 V vs. Li/Li+. Aged NCA material undergoes more significant changes in TM-O bond hybridization when cycling above 50% SoC, while reversible O2 formation is maintained. Nickel is found to be redox active throughout the entire delithiation and shows a more classical oxidation state change during cycling with smaller changes in the Ni-O hybridization. By contrast, Co redox activity relies on a stronger change in Co-O hybridization, with only smaller Co oxidation state changes. The Ni-O bond displays an almost twice as large change in its bond length on cycling as the Co-O bond. The Ni-O6 octahedra are similar in size to the Co-O6 octahedra in the delithiated state, but are larger in the lithiated state, a size difference that increases with battery ageing. These contrasting redox activities are reflected directly in structural changes. The NCA material exhibits the formation of nanopores upon ageing, and a possible connection to oxygen redox activity is discussed. The difference in interaction of Ni and Co with oxygen provides a key understanding of the mechanism and the electrochemical instability of Ni-rich layered transition metal oxide electrodes. Our research specifically highlights the significance of the role of oxygen in the electrochemical performance of electric-vehicle-grade NCA electrodes, offering important insights for the creation of next-generation long-lived lithium-ion batteries.

Thermodynamic Stability of LixNiO2 and Polyvinylidene Difluoride Materials for Lithium+ Ion Batteries

LixNiO2 (LNO), a layered Li-ion battery cathode has been investigated for decades. LNO has been shown to proceed through multiple phase transitions at different states of lithiation as well as at different temperatures. However, in these experiments it has always been paired with additional materials typically found in the creation of cathodes, such as carbon black, aluminum foil and polyvinylidene difluoride binder. This paper investigates the thermal stability of LNO as a stand-alone material as well as a component of a traditional cathode through performing thermal gravimetric analysis (TGA), variable temperature powdered X-ray diffraction (VT-PXRD) and solid-state nuclear magnetic resonance (ss-NMR) at different states of lithiation and high temperatures. The reduction to nickel metal was found at temperatures exceeding 500 °C for the traditional cathodes at all states of charge due to the creation of lithium fluoride from hydrogen fluoride gas being released as polyvinylidene difluoride degrades. Nickel metal was also identified for the stand-alone LNO at lithium concentrations greater than x = 0.32 at temperatures of 600 °C as the system becomes depleted of oxygen and lithium due to the creation of lithium oxide. These finding indicate that the thermal stability of LNO at temperatures over 200 °C is sensitive to the presence of fluorine as well as the state of charge of the battery. Typical batteries do not reach these temperatures during cycling, but in the case of thermal runaway and recycling it is important to know the chemical reactions occurring at these temperatures and concentrations as toxic and corrosive hydrogen fluoride gas is released. An investigation into less fluorinated binder options is desirable to reduce the addressed issues.

On the Description of Electrode Materials Based on the Quantification of Ionic and Electronic Work Functions

During decharging of a lithium ion battery (LIB) electrons are transferred from the cathode material to the outer circuit and lithium ions are transferred into the electrolyte. Here, the energy required to take electrons and lithium ions out of two prototypical cathode materials, LixFePO4 and LixMn2O4 is investigated as a function of the state of lithiation, x [1]. Ionic work functions are measured by thermionic emission, electronic work functions are measured either by thermionic emission or by photoelectron spectroscopy. The work functions measured vary significantly with x for LixFePO4 with moderate, low-dimensional ionic and electronic conductivities but rather little for cubic LixMn2O4 with ca. three orders of magnitude higher ionic and electronic conductivities [2]. The experimental data are supported and rationalized by static energy-landscape calculations and molecular dynamics simulations of the Lithium migration as a function of Lithium content and electric field strength [1]. This study provides new insight into the role of ionic contributions to the energy balance in LIBs. Current efforts are aimed at a complete energetic description of LIBs as previously discussed for LiCoO2 [3].[1] J. Schepp, J. Schuch, J.P. Hofmann, S. Adams, K.-M. Weitzel, to be published[2] M. Park, X. Zhang, M. Chung, G.B. Less, A.M. Sastry, A review of conduction phenomena in Li-ion batteries, Journal of Power Sources 195 (2010) 7904–7929.[3] S. Schuld, R. Hausbrand, M. Fingerle, W. Jaegermann, K.-M. Weitzel, Experimental Studies on Work Functions of Li+ Ions and Electrons in the Battery Electrode Material LiCoO2 A Thermodynamic Cycle Combining Ionic and Electronic Structure, Adv. Energy Mater. 8 (2018) 1703411.

Characterization of Nanostructured Tin Oxide Anodes Obtained By Electrolytic Oxidation for High-Energy Lithium-Ion Batteries

In recent years, the growing electric vehicle market has increased the need for cost efficient and high energy materials for batteries drastically. Tin and tin oxide materials bear great potential as anode materials for Li-Ion batteries due to low cost and high theoretical capacity. Nevertheless, the development of commercial tin anodes has so far been hindered due to several drawbacks related to high volume expansion during operation leading to fast cell degradation. To circumvent these issues, nanostructured electrodes can be applied to mitigate volume changes. Typically, the production process of such electrodes is challenging, leading to high cost and issues in terms of scalability. Electrochemical processes, such as the electrolytic oxidation of tin, has been found a promising alternative to fabricate nanostructured electrodes. The additive-free tin oxide anodes obtained from this process exhibit high gravimetric and volumetric capacity, excellent rate capability as well as promising cycle life. The morphology and microstructure have high impact on the rate capability and cycling stability of tin oxide anodes. Since structural properties can be precisely adjusted by controlling the electrochemical oxidation process, a deeper understanding of the structure-property relationship is needed to optimize the production process and pave the way for commercialization.Herein an in-depth characterization of nanostructured tin oxide anodes formed by electrochemical oxidation is presented. The rate capability and the cycling stability are investigated by means of electrochemical measurements in battery cells. Operando electrochemical dilatometry is used to investigate the thickness change of the anodes during cycling (cell breathing). In-situ XRD measurements are applied to elucidate the reaction mechanism. The anodes are carefully analyzed by SEM/EDS at different state of lithiation to understand the impact of volume changes on the inner porosity and morphology. Finally, the cycling stability of tin oxide anodes is improved by applying an electrochemical prelithiation step. Therefore, the impact of different prelithiation regimes on the cycling stability is evaluated in full cells. The results contribute to the understanding of electrochemical behavior of nanostructured tin oxide anodes and the derivation of optimal design criteria adjusted by electrochemical surface engineering.

Visualization of Lithium Plating Morphologies on Graphite Electrode By O perando X-Ray Tomography

The plating of lithium metal on graphite electrodes in Li-ion batteries is a major factor limiting the fast charging of electric vehicles. Lithium metal plating leads to the growth of dendritic structures that can pierce through the battery’s separator resulting in an internal short circuit and catastrophic failure of the battery. Moreover, the plating of lithium metal on graphite is not reversible, manifesting in poor Coulombic efficiency, severe reduction of the battery’s life expectancy, and safety issues. Understanding how and when plating occurs in Li-ion batteries is crucial in the development of strategies to prevent plating under fast charging conditions. Thus, we have conducted an operando X-ray tomographic microscopy experiment to directly monitor the plating of lithium metal in a Li/Graphite cell when applying electrolytes with the additives vinylene carbonate (VC) and Lithium bis(fluorosulfonyl)imide (LiFSI). The experiment was performed at the ID19 beamline (ESRF, France) where tomographic scans, linked with the lithiation state of graphite, made it possible to gain a strong understanding of the mechanisms behind Li-deposition and stripping at high current rates in addition to understand the effect of the VC and LiFSI additives.

SnBi Alloy Composites Via Controlling Cooling Rate for High Performance Lithium-Ion Battery Anode

Alloying-based materials, such as tin (Sn) and bismuth (Bi), have been considered as potential anode materials for lithium-ion batteries (LIBs) due to their high theoretical volumetric capacities of 1991 and 3765 mAh cm−3, respectively. However, these materials tend to have short cycle lives due to severe volume expansion when fully lithiated, such as Li4.4Sn (300%) and Li3Bi (215%), which presents a great challenge for practical implementation. To address this issue, using two metal alloys is an effective strategy to improve electrode integrity and stability. The different working voltages of Bi (0.78−0.69V) and Sn (0.65−0.1V) hinder the extreme structural changes that occur upon cycling. At the initial discharge stage, the unreacted Sn phase acts as a buffer during the lithiation of Bi. Meanwhile, the lithiated state of Bi (LixBi) will buffer the expansion when Sn is lithiated with Li-ions. However, the definition and mechanism of the buffer effect between active-active metals are still unclear. As a result, the bismuth-tin (BiSn) alloy is designed through heat treatment by controlling the cooling rate to form micro-phase alloys (BiSnM) and nano-phase alloys (BiSnN). The BiSn nano-phase alloy anode (BiSnN) exhibits a better buffer effect and achieves a superior discharge capacity of 550 mAh g−1 at 0.1 A g−1 and 320 mAh g−1 at 2 A g−1.

Dilatometric Investigation of Si-Rich Contacting Anode Under External Pressure

Silicon with high abundance and high gravimetric capacity around 3579 mAh.g-1 at Li15Si4 fully lithiated state [1] is one of the attractive anode materials in lithium-ion batteries. Volume expansion of around 300% in the fully intercalated state is the Achilles’ heel of silicon, causing particle pulverisation, continuous formation of solid electrolyte interface (SEI), loss of electrical contact and capacity loss.[2] The use of silicon composite instead of pure silicon, [1,3] limited de/lithiation,[4] and boosting the electrical connection between particles by applying optimal external pressure[5] are practical solutions to mitigate these disadvantages. This study investigates the electrochemical performance and the dilatometric behaviour of a multilayer pouch cells (0.06 to 1.5 Ah) under the external mechanical pressure. Using 1/3 of the Si capacity in order to stabilise the electrochemical performance of a high silicon content anode (70 wt% Si). An irreversible electrode expansion of about 20% after 3 cycles of formation at 0.1C and a 75% electrode thickening after 200 cycles at 0.5C were observed.