Rechargeable Li-ion Batteries Research Articles

A Novel Self-Binding Composite Separator Based on Poly(tetrafluoroethylene) Coating for Li-Ion Batteries.

In this study, a novel composite separator based on polytetrafluoroethylene (PTFE) coating layers and a commercial polyethylene (PE) separator is developed for high performance Li-ion batteries. This composite separator is prepared by immersing a PE separator directly into a commercial PTFE suspension to obtain a self-binding PTFE/PE/PTFE tri-layered structure. Then, the as-prepared composite separator is further treated with a H2O2/H2SO4 solution to enhance its electrolyte affinity. The results show that the coating layer, consisting of close-packed PTFE particles, possesses a highly ordered nano-porous structure and an excellent electrolyte wettability property, which significantly enhance the ionic conductivity of the composite separator. Due to the presence of the PTFE-based coating layer, the composite separator exhibits better thermal stability compared with the PE separator, reaching the thermal-resistant grade of commercial ceramic-coated separators. By using different separators, CR2032-type unit half-cells composed of a Li anode and a LiFePO4 cathode were assembled, and their C-rate and cycling performances were evaluated. The cell assembled with the composite separator was proven to have better C-rate capability and cycling capacity retention than the cell with the polyethylene separator. It is expected that the composite separator can be a potential candidate as a coating-type separator for high-performance rechargeable Li-ion batteries.

Carbon Coated Si-Metal Silicide Composite Anode Materials Prepared by High-Energy Milling and Carburization for Li-Ion Rechargeable Batteries

In this article, we report a novel Si-Metal silicides/Carbon composite anode material for lithium-ion rechargeable batteries. The composite powder comprised of Si, FeSi2 and CrSi2 were synthesized by high-energy mechanical milling and then a primary carbon was formed over the Si-silicide at 900°C. The prepared composite powder was agglomerated and subsequently a thin carbon layer was coated. The X-ray diffraction results revealed that the Si and silicide crystal size decrease with respect to milling time. The critical milling time to achieve the completely nano-scale powders was 5 h. The composite powder exhibits randomly distributed carbon-coated Si-silicide. The TEM microstructure revealed homogeneous distribution of nanocomposite powder consists a very fine nanoparticles of the order of ∼30 nm. The prepared Si-silicide/C composite powders exhibited good capacity retention with an average coulombic efficiency of 99.6%. The composite powders showed good cyclability, 1076 mAh g−1 at 50th cycle and 959 mAh g−1 at 100th cycle. The electrode internal microstructure revealed a shell-like carbon-coated Si-silicide phases, and a complete amorphization of nanocrystalline Si during the initial cycling, while the inactive silicide phase remains unchanged. Consequently, the size reduction of Si-silicide and carbon coating over it greatly enhanced the cycling performance of the electrode.

Swift Combustion Synthesis of PbLi2Ti6O14 Anode for Lithium-Ion Batteries: Diffusional and Electrochemical Investigation

Lead lithium titanate (PbLi2Ti6O14) was synthesized by combustion route restricting the annealing at 900°C to just 1 minute. Rietveld analysis confirmed orthorhombic (Cmca) product phase with an average particle size ∼200 nm and surface area of 2 m2/g forming secondary porous particles. From bond valence site energy (BVSE) calculations, 1 D ionic conduction was found along c axis with low activation energy (0.23 eV). AC conductivity analysis revealed a bulk conductivity of 2 × 10−7 S.cm−1 at room temperature and 1 × 10−4 S.cm−1 at 200°C with a switch from extrinsic 1D to intrinsic 2D mechanism at 150°C. Li+ diffusion coefficient was calculated to be in the order of 10−12 cm2.s−1. More than 4 lithium (per f.u.) could be reversibly (de)inserted delivering capacity over 160 mAh/g with good cycling retention over 1000 cycles. With a feasible rapid synthesis, good diffusional and electrochemical behavior especially high rate capability, PbLi2Ti6O14 can act as a safe 1.35 V anode for rechargeable Li-ion batteries.

Design and Development of a Non-volatile Counter for Metered Dose Inhaler (MDI)

In 2014, Global Asthma Report 2014 stated there were 334 million of people in the worldwide suffering of asthma and the population was increased 99 million compared in 2011. Asthma is the leading chronic childhood disease with albatross on affected children and their families. It occurs when the pulmonary airway is blocked or the airways become narrowed and result in difficult breathing. When asthma under attack, asthma patients normally use metered dose inhaler (MDI) to inhale the salbutamol to restore normal breathing. Therefore, MDI currently available in market unable to monitor the remaining amount of puffs available in the MDI canister and may lead problems for the user due to inability to monitor the amount of salbutamol in the MDI canister. Besides this, some manufacturers developed MDI with counter but it had the limitation such as unable to store memory of the last counting value if power failure occurs, uses non-rechargeable battery and are disposable. Hence, this paper is to present the development of a device consist of a non-volatile counter. It is designed using EEPROM to save the memory of the last counting value and to prevent data loss due to power failure. The MDI was installed with the limit switch for counter and the MDI press is attached to MDI canister so that when the user presses both simultaneously then it provides enough pressure to the limit switch to update the counter. The MDI cover is developed to protect the internal connection and to prevent the user from accidently pressing the limit switch. 7.4V Li-ion rechargeable battery was employed to supply power source for system operation. Arduino UNO (ATmega328P) act as microcontroller to control the system operation of this device. The device is capable of displaying the number of used salbutamol puff on the liquid crystal display (LCD). Furthermore, RGB LED is integrated into the device as visualization to indicate the level of salbutamol in the MDI canister. It consists of four levels indication which is high, medium, low and empty canister of used puff. The high level of used puffs is between 0 to 120 puffs with green colour indicator, medium level is between 121 to 160 puffs with yellow/orange colour indicator, low level is between 161 to 199 puffs with red colour indicator and empty canister without any colour of indicator when the used puffs reached to 200. This device could remind the user to prepare a new MDI canister since it had indicated of low level of salbutamol in the MDI canister. Besides this, it also could reduce the deaths from asthma due to the user would prepare a new MDI canister before attacked by asthma.

Stoichiometry and volume dependent transport in lithium ion memristive devices

LixCoO2, a thoroughly studied cathode material used extensively in Li-ion rechargeable batteries, has recently been proposed as a potential candidate for resistive random access memory and neuromorphic system applications. Memristive cells based on LixCoO2 thin films have been grown on Si substrates and two-probe current-voltage measurements were employed to investigate the origin and nature of resistive switching behavior exhibited by these cells. The results indicate that a voltage-driven metal-to-insulator transition of the active LixCoO2 layer is responsible for the resistive switching behavior, which has a homogeneous nature.

Synchronous phase transition and carbon coating on the surface of Li-rich layered oxide cathode materials for rechargeable Li-ion batteries

We describe a novel synchronous surface tailoring to form thin and uniform carbon coating layers and simultaneously induce an in-situ phase transition from a layered to spinel-like phase on the surfaces of Li-rich layered oxide (LLOs) particles by the thermal decomposition of 2,3-dihydroxynaphthalene (DN). The Li2MnO3 component in pristine LLO is not affected during carbon coating, but the coordination numbers of the Co ions and the CoO bonds in the LiTMO2 phase are diminished during carbon coating, implying that the formation of a spinel-like phase in LLO after carbon coating begins at the LiTMO2 with little variation in the Li2MnO3. As a result, the optimized DN (0.2 wt%)-coated LLO cathode material shows superb electrochemical properties owing to the formation of uniform carbon coating layers and the layered-to spinel-phase transition on the surfaces of the LLO particles, which improves the surface stability, electronic conductivity, and Li-ion kinetics in the LLO.

Influence of Zr dopant on microstructural and electrochemical properties of LiCoO2 thin film cathodes by RF sputtering

LiCoO2 thin film cathodes have been well established in Li-ion rechargeable batteries, however, its useful capacity hardly exceeds 50% of the theoretical value. Irreversible structural changes will occur upon exchange of Li ions i.e. >0.5 per unit formula limit, during intercalation/deintercalation reactions. Reportedly, lattice doping phenomenon has noticed an improvement in cyclability of LiCoO2. In this work, the influence of Zr doping on microstructural and electrochemical properties of RF magnetron sputtered LiCoO2 thin film cathodes have been presented. A series of LiZrxCo1−xO2 thin films have been deposited on Au/Ti/SiO2/Si (100) substrates using a Zr–LiCoO2 mosaic target. All the films were deposited at optimized processing conditions. XRD and Raman spectroscopy measurements confirmed the hexagonal layered structure with R3¯m symmetry for Zr doped LiCoO2 film cathodes. The AFM reveals the estimated average grain size is around 50 nm. The cyclic voltammetry studies for these cathodes exhibit narrow potential peak separation of 24 mV and resulting highest diffusion coefficient (D¯Li) of about 1.8 × 10−11 cm2 s−1, respectively. These films exhibited a highest initial discharge capacity of 64.4 μA h cm−2 μm−1 with a capacity retention of 98.5% even after 25 cycles. In non-aqueous region, the cell exhibited an initial discharge capacity of about 65 μA h cm−2 μm−1 with good cycling stability even after 80 cycles, and is observed to be the more promising cathode candidate than the pristine LiCoO2 films.

A Pair of Rare Three-Dimensional Chiral Polyoxometalate-Based Metal–Organic Framework Enantiomers Featuring Superior Performance as the Anode of Lithium-Ion Battery

Two rare three-dimensional (3D) chiral polyoxometalate-based metal–organic framework (POMOF) materials, d- [PMo8VMo4VIO37(OH)3Zn4][BPP]2·2[pyridine]·H2O (d-1) and l-[PMo8VMo4VIO37(OH)3Zn4][BPP]2·2[pyridine]·H2O (l-1) (BPP = 1,3-bis(4-pyridyl)propane) were prepared with achiral ligand under solvothermal conditions. They are the first 3D chiral POM-based frameworks based on a Zn-e-Keggin unit and achiral ligands. The CD spectra and structural analyses indicate that the two polyoxometalate-based metal–organic frameworks are enantiomers. The alternate connection of Zn-e-Keggin cluster and BPP ligands generate helical infinite chains, while each single spiral chain is further interlinked to adjacent neighboring units to produce a 3D regular ordered chiral architecture with a qtz topology. Compound 1 (mixtures of d-1 and l-1) exhibited excellent stability in both acid and base aqueous solutions. When compound 1 was used as an anode electrode material of rechargeable Li-ion batteries (LIBs), outstanding reversib...

High-Power Li-Metal Anode Enabled by Metal-Organic Framework Modified Electrolyte

Summary Although the Li-metal anode holds the key to overcoming the bottleneck of current Li-ion rechargeable batteries, the trade-off between safety and practicality, especially at high current densities, is a major barrier because of the formation of hazardous Li dendrites arising from inhomogeneous Li electrodeposition. Herein we demonstrate the feasibility of achieving homogeneous Li electrodeposition by implementing porous metal-organic framework (MOF) species in pristine liquid electrolyte. The MOF host provides considerable natural angstrom-level pores that preferentially control the migration of large-sized anions. Consequently, the “caged” electrolyte anions facilitate a homogeneous Li-ion flux, which illustrates a stable Li-metal plating/stripping at a practically high current density (10 mA cm−2). As a proof of concept, the high areal-loading Li-Li4Ti5O12 batteries (∼10 mg cm−2) with the MOF-modified electrolyte deliver excellent long-life cycling at high current densities (∼7 mA cm−2). Our results underline the great potential of MOFs in tuning the electrolyte properties to achieve desirable Li-metal battery performance.

Selective doping of Li-rich layered oxide cathode materials for high-stability rechargeable Li-ion batteries

We report the discovery of Li-rich Li1+x[(Ni0.225Co0.15Mn0.625)1−yVy]O2 as a cathode material for rechargeable lithium-ion batteries in which a small amount of tetravalent vanadium (V4+) is selectively and completely incorporated into the manganese sites in the lattice structure. The unwanted oxidation of vanadium to form a V2O5-like secondary phase during high-temperature crystallization is prevented by uniformly dispersing the vanadium ions in coprecipitated [(Ni0.225Co0.15Mn0.625)1−yVy](OH)2 particles. Upon doping with V4+ ions, the initial discharge capacity (>275mAhg−1), capacity retention, and voltage decay characteristics of the Li-rich layered oxides are improved significantly in comparison with those of the conventional undoped counterpart.

In-Situ SERS Analysis of SEI Formation at Graphite Electrode in Li Ion Battery Using Manipulated Plasmonic Sensor Element

In order to improve the performance of Li ion rechargeable batteries, solid-liquid interfacial phenomena taking place at the electrode during the operation should be well understood. For example, detailed analysis of solid electrolyte interphase (SEI) thin films formed at the electrode surface, which plays the key role to determine the battery’s properties, is a crucial issue. We have developed precise spectroscopy technique using surface enhanced Raman scattering (SERS), to realize highly selective interfacial analyses [1,2]. Here, transparent micro lens, partially covered with nano particles of plasmonic metals, such as Ag, Au, etc., is an essential component, which is called as “plasmonic sensor”. The sensor situated onto a particular sample enhances Raman signals from its surface, allowing us to get information only about the chemical state of the surface. To employ this technique for in-situ analysis of SEI film formation on the electrode surface in Li ion rechargeable battery, this study optimizes the equipment and employs it for the analyses of solvent species dependence of SEI properties. The organic solvents employed here were the mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with 1:1 (volume), and that of propylene carbonate (PC) and EMC with 1:1. The graphite and LiCoO2 films were used for anode and cathode, respectively. 1.0 mol/L of LiPF6 was contained in each solvent. The design of plasmonic sensor implemented in the measurement cell was optimized so as to be movable by magnetic manipulation, which can avoid obstruction by the sensor to the diffusion of species during the reaction, realizing highly selective interfacial analyses. This setup was shown to serve also in effective Raman signal enhancement; the greater magnetic force to properly press down the sensor provides more significant signal enhancement. The SERS measurement results suggested that SEI formation depended on the solvent species employed: Li2O3 product was detected only in the case of PC-EMC. The time-dependent behavior of SEI formation was also obtained, indicating the mechanism of SEI formation. Acknowledgements This research was partially supported by the “Development of Systems and Technology for Advanced Measurement and Analysis”, and the “Research & Development Initiative for Scientific Innovation of New Generation Batteries (RISING 2)” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

(Invited) In Operando NMR/EPR Studies of High-Performance Transition Metal Oxides for Electrochemical Energy Storage

High-voltage cathodes made of transition metal oxides have been the leading candidates for rechargeable Li and Na ion batteries. Continuous effort for further improvement in the energy density and stability of available oxides and for discovering new materials is ongoing. Understanding the Li extraction and insertion dynamics, the involved anionic redox chemistry and its coupling with transition metal redox, and the role that Li plays in stabilizing Na transition metal oxides, is important for making the effort more efficient and effective. Li in Li-rich cathodes mostly resides at octahedral sites in both Li layers (LiLi) and transition metal layers (LiTM). Extraction and insertion of LiLi and LiTM are strongly influenced by surrounding transition metals. pjMATPASS and operando Li nuclear magnetic resonance are combined to achieve both high spectral and temporal resolution for quantitative real time monitoring of lithiation and delithiation at LiLi and LiTM sites in Li2MnO3, Li1.2Ni0.2Mn0.6O2, and Li1.2Ni0.13Mn0.54Co0.13O2cathodes. The results have revealed that LiTM are preferentially extracted for the first 20% of charge and then LiLi and LiTM are removed at the same rate. No preferential insertion or extraction of LiLi and LiTM is observed beyond the first charge. Ni and Co promote faster and more complete removal of LiTM. The recovery of the removed Li is <60% for LiTM and >80% for LiLi upon first discharge. The study sheds light on the activity of LiLi and LiTM during electrochemical processes as well as their respective contributions to cathode capacity. Anionic redox chemistry offers a transformative approach for significantly increasing specific energy capacities of cathodes for rechargeable Li-ion batteries. This study employs operando electron paramagnetic resonance (EPR) to simultaneously monitor the evolution of both transition metal and oxygen redox reactions, as well as their intertwined couplings in Li2MnO3, Li1.2Ni0.2Mn0.6O2, and Li1.2Ni0.13Mn0.54Co0.13O2 cathodes. Reversible O2–/O2 n – redox takes place above 3.0 V, which is clearly distinguished from transition metal redox in the operando EPR on Li2MnO3 cathodes. O2–/O2 n – redox is also observed in Li1.2Ni0.2Mn0.6O2, and Li1.2Ni0.13Mn0.54Co0.13O2 cathodes, albeit its overlapping potential ranges with Ni redox. This study further reveals the stabilization of the reversible O redox by Mn and e– hole delocalization within the Mn–O complex. The interactions within the cation–anion pairs are essential for preventing O2 n – from recombination into gaseous O2 and prove to activate Mn for its increasing participation in redox reactions. Operando EPR helps to establish a fundamental understanding of reversible anionic redox chemistry. The gained insights will support the search for structural factors that promote desirable O redox reactions. Further efforts have been invested on monitoring the evolution of O species in Li-rich transition metal oxides using both ex and in situ 17O solid-state NMR spectroscopy. Sodium manganese oxides with different compositions and crystal structures have attracted much attention because of their high capacity and low cost. We have investigated a group of promising lithium doped sodium manganese oxide cathode materials with exceptionally high initial capacity of ∼223 mAh g−1 and excellent capacity retentions, attributed primarily to the absence of phase transformation in a wide potential range of electrochemical cycling. Solid-state 7Li and 23Na NMR characterizations have been employed to follow the evolution of these active ions, in order to understand the roles that they play in stabilizing the structures over electrochemical cycling. The systematic study of structural evolution and the correlation with the electrochemical behavior of the doped cathode materials provides new insights into rational design of high-performance intercalation compounds. Figure 1

Lithium Manganese Oxyfluoride As a New Cathode Material Exhibiting Oxygen Redox

The next generation of high performance Li-ion rechargeable batteries relies on the discovery of new positive electrode materials with a greater capacity to store charge. Generally speaking, highly ordered layered materials, such as LiCoO2 (LCO), LiNi0.85Co0.1Al0.05O2 (NCA) and LiNi0.13Mn0.54Co0.13O2 (NMC), are considered to be the best-in-class. One strategy to increase the capacity has been to explore the ordered Li-Rich materials, Li1+xM1-xO2, where x~1.2, where the greater number of Li ions increases the total theoretical capacity. However, an optimal candidate system for commercialisation within this space has yet to be identified. In contrast to ordered materials, disordered structures have been largely ignored by the scientific community as they are perceived to exhibit poor Li+ mobility. However, recent research has overturned this understanding and several disordered rock salt structures with competitive energy densities have been proposed (such as Li4Mn2O5, Li2VO2F and Li1.2Mn0.4Ti0.4O2). Could these highly disordered Li-rich materials offer better structural stability and performance than their layered counterparts? Here, we present the discovery of a new Li-rich disordered rocksalt material, lithium manganese oxyfluoride (LMOF), presented in Figure 1, whose structure appears to remain stable even over 100 charge-discharge cycles. Furthermore, LMOF exhibits a large, reversible capacity to store charge and, interestingly, this appears to be unexplained within the limits of transition metal redox capacity alone, raising the question of how such a large charge storage capacity can be achieved. In this work we fully characterise this new material and specifically we examine the role that oxygen plays in this anomalous charge compensation process. Figure 1

(Invited) Recent Advances in the DFT-Based Search of Cathode Materials for Ca Batteries

In the last years, concerns on Li availability have prompted the search for suitable alternatives to rechargeable Li-ion batteries. Batteries based on multivalent charge carriers (Mn+) can exhibit advantages in terms of energy density since for a certain amount of M carriers the capacity is doubled (n=2) or tripled (n=3) when compared to single valent carriers like Li+ or Na+. Calcium is an attractive candidate due to its low cost, natural abundance and low reduction potential. At this very early stage of the Ca-batteries technology, the quest for a high specific energy cathode material is an active field. The general goal of our work is the identification of materials able to function as positive electrode in Ca batteries. DFT is a unique tool to quickly screen a variety of structures and compositions to identify potential cathode materials for this novel technology. The general strategy is firstly to calculate average voltage and volume changes associated to the Ca insertion reaction. Further, DFT theory could be applied to gather additional information regarding electronic and ionic conductivities, crystal structure of intercalated phases and precise voltage-composition-curves at various temperatures. In this communication, we will present a survey of recent results for oxides, silicates and sulphides as cathode for Ca batteries. Special attention is given to the calculation and analysis of Ca migration pathways using the NEB method. In good agreement with parallel experimental investigations [1-3], we found that the low ionic mobility is the main handicap for the insertion/deinsertion of Ca ions in most structures. Yet, for some materials, Ca intercalation is predicted at low C rates. Acknowledgments: Authors are grateful for financial support from European Union H2020-FETOPEN funded project CARBAT-766617. References; [1]. M.E. Arroyo-de Dompablo, C. Krich, J. Nava-Avendaño, M.R. Palacin, F. Barde. Phys. Chem. Chem. Phys. 18 (2016) 19966. [2]. M.E. Arroyo-de Dompablo, C. Krich, J. Nava-Avendaño, N. Biskup, M.R. Palacin, F. Barde. Chem. Mater. 28 (2016) 6886. [3]. D. Tchitchekova, A. Ponrouch, R. Verrelli, T. Broux, C. Frontera, A. Sorrentino, F. Barde, N. Biskup, M.E. Arroyo-de Dompablo, M.R. Palacin. Chem. Mater. 30 (2018) 847.

(Invited) Deconvolution of Double-Layer, Pseudocapacitance, and Battery-like Contributions to Charge Storage in MnOx@Carbon Electrode Architectures and Interfaces

Manganese oxides (MnOx) are a well-established class of active materials for electrochemical energy-storage technologies ranging from primary alkaline cells to rechargeable Li-ion batteries. More recently, the use of manganese oxides has extended to aqueous-electrolyte electrochemical capacitors (ECs) in which nanostructured forms of MnOx exhibit pseudocapacitive charge-storage behavior that can be tapped for pulse-power applications. The ability of MnOx to alternately express battery-like and capacitor-like functionality offers intriguing prospects to design electrode materials and corresponding devices that deliver both high energy content and rapid charge/discharge response. We are exploring such opportunities with electrode architectures comprising nanoscale MnOx coatings affixed to porous carbon frameworks [1,2,3]. The battery- and capacitor-like character of these materials can be tuned by varying such factors as the oxide crystal structure (layered birnessite-MnOx vs. cubic spinel LiMn2O4) and the composition of the contacting electrolyte (mixtures of Na+, Li+, and/or Zn2+) [4]. To deconvolve the complex electrochemical response of such systems, we apply a suite of electroanalytical methods that are based on voltammetry and impedance. The 3D projection of Bode-plot parameters has proven particularly useful in mapping frequency-dependent capacitance contributions onto the potential scale, revealing mechanisms that deliver/store charge at high rates. In parallel with investigations of macroscale electrode architectures, we also examine simplified 2D MnOx//carbon interfaces where surface-sensitive characterization methods (X-ray photoelectron spectroscopy, scanning-probe microscopy) provide insights on the impact of the carbon substrate on charge-transfer kinetics, charge-storage mechanisms, and stability. E. Fischer, K.A. Pettigrew, D.R. Rolison, R.M. Stroud, and J.W. Long, Nano Letters 2007, 7, 281–286.W. Long, M.B. Sassin, A.E. Fischer, and D.R. Rolison, J. Phys. Chem. C 2009, 113, 17595–17598.B. Sassin, S.G. Greenbaum, P.E. Stallworth, A.N. Mansour, B.P. Hahn, K.A. Pettigrew, D.R. Rolison, and J.W. Long, J. Mater. Chem. A 2013, 1, 2431–2440.S. Ko, M.B. Sassin, J.F. Parker, D.R. Rolison, and J.W. Long, Sustainable Energy Fuels, 2018, 2, 626–636.

A Macroscopic Model to Describe the Composite Effects of a LiFePO4 PVDF/Csp Cell Based on Effective Transport Parameters

Li-ion batteries have been positioned like one of the best storage devices today there is a satisfactory combination of electrodes and electrolytes to be used for rechargeable Li-ion batteries in the electronic market due to their high energy densities (e.g. portable media, computers and small equipment), however, it is overriding to account for numerous problems related with transport mechanisms of charge and mass that significantly affect their capacities and power. The understanding of these mechanisms is complex due to various kinetic and transport phenomena interacting within the battery, and the difficulty of estimating local variables such as concentrations, potential, among other. Mathematical modeling based on porous electrode theory [1] has been a powerful tool to understand and optimize the functioning performance of these devices. Nevertheless, the role of each component in the porous matrix of the electrode has not been accounted for since under this perception the battery is described as a whole identity [2, 3]. In this direction, the effect of electrode composition (i.e. variation of active and inactive material) on rate capabilities cannot be explained by these models. In the present work, a macroscopic model is proposed relying on the assumption that the electrode is a porous solid matrix where active and inactive components should be separately expressed but interacting in solid and liquid phases. This enables to account for the experimental discharge of a semi cell Li °/1M LiPF6 in 1:1:1 EC:DMC:EMC/LiFePO4:PVDF-Csp considering effective transport parameters and the kinetic proposal taking in count the active material fractionin the cathode composition. Acknowledgements: I. Santos is grateful to CONACYT for the scholarship granted to pursue his doctoral studies.

Investigating LiNi1/3Mn1/3Co1/3O2 Polarization Resistances in Function of Temperature and Voltage at Different Stages of Lifetime

LiNi1-x-yMnxCoyO2 cathodes (NMCs) are currently employed or evaluated for EVs, due to their high theoretical capacities and operating voltage [1]. In view of EVs’ stringent requirements in terms of performance and lifetime, NMCs have been tested in several cycling protocols, simulating real-life applications, or moving towards more energy-dense devices (high voltage operation). In such protocols, NMCs have displayed different failure mechanisms, often consisting in an overall increased resistance towards polarization. However, hindrances towards polarization are already present in NMCs at beginning-of-life (BOL). Such resistances are voltage (x Li+)-dependent [2], while the impact of temperature is less investigated. Although some of these resistances have been recently addressed in literature (namely, the discussion over the so-called “Irreversible Capacity Loss” [3], which is actually a kinetic limitation [4]), a comprehensive explanation of NMCs’ voltage characteristics at BOL is still missing. This furthermore complicates the understanding of NMCs’ electrochemical response after prolonged cycling, which is necessary for designing optimized cycling protocols. LiNi1/3Mn1/3Co1/3O2 (NMC333) is chosen as representative of the NMCs series, as far as electrochemical [5], structural and electronic [1] properties are concerned. NMC333’s voltage characteristics at BOL and end-of-life (EOL) are investigated in terms of temperature, voltage (x Li+) and applied polarization, and compared with known structural and electronic transitions in the crystal, also x Li+-dependent. Lab-scaled pouch cells in half-cell configuration (NMC333/Li) are tested between +3.6 V and +4.6 V vs. Li. NMC333 electrodes used are either pristine, or harvested from cells cycled at high voltage (+4.6 V vs. Li upper voltage cut-off) and different temperature (10, 25 and 40 °C). Through this protocol, it is possible to decouple temperature- and voltage- related effects on NMC333’s degradation. NMC333’s electrochemistry is investigated both at steady state, by means of OCP curves, and under moderate polarization, by means of Constant Current (CC) cycling at C/10 and Slow Rate Cyclic Voltammetry (SRCV). In Figure 1, CC and SRCV of NMC333 at BOL are reported at different temperatures. Structural and electronic transitions in NMC333 are associated with a different electrochemical behavior below and above +3.8 V vs. Li. Specifically, while at higher voltages an apparent capacitive behavior is displayed, a resistance towards polarization can be identified below +3.8 V vs. Li for both CC and SRCV. Such resistance occurs during charge and discharge, although a T-dependent asymmetry emerges in SRCV between anodic and cathodic scan (namely, a shifting peak onset and an additional shoulder in the anodic peak). By the comparison between CC and SRCV, which are performed at different cycling rates, further insights into the causes of these hindrances can be gathered. A discussion on the resistances towards polarization displayed by NMC333 at different stages of lifetime will bring further insight into its thermodynamic and dynamic voltage characteristics, and their evolution in function of different cycling conditions and operation over time. These notions will be helpful for modelling NMCs, by knowing which phenomena and variables must be taken into account when fitting/predicting performance and lifetime. Additionally, such information will allow for more conscious design of cycling protocols, apt to achieve optimized performance and lifetime of NMCs-containing Li ion batteries. [1] J. Xu, F. Lin, M. M. Doeff, W. Tong, “A review on Ni-based layered oxides for rechargeable Li-ion batteries”, J. Mater. Chem. A 5 (2017), 874 – 901. [2] J. Kasnatscheew, U. Rodehorst, B. Streipert, S. Wiemer-Meyers, R. Jakelski, R. Wagner, I. Cekic Laskovic, M. Winter, “Learning from overpotentials in lithium ion batteries: a case study on the LiNi1/3Mn1/3Co1/3O2 (NMC) cathode”, Journal of the Electrochemical Society 163(14) (20016), A2943 – A2950. [3] S. Kang, W. Yoon, K. Nam, X. Yang, D. P. Abraham, ”Investigating the first-cycle irreversibility of lithium metal oxide cathodes for Li batteries”, J. Mater. Sci. 43 (2008), 4701 – 4706. [4] J. Kasnatscheew, M. Evertz, B. Streipert, R. Wagner, R. Klöpsch, B. Vortmann, H. Hahn, S. Nowak, M. Amereller, A. C. Gentschev, P. Lamp, M. Winter, ”The truth about the 1st cycle coulombic efficiency of LiNi1/3Mn1/3Co1/3O2 (NMC) cathodes”, Phys. Chem. Chem. Phys. 18 (2016), 3956 – 3965. [5] Z. Wu, S. Ji, Z. Hu, J. Zheng, S. Xiao, Y. Lin, K. Xu, K. Amine, F. Pan, “Pre-lithiation of Li(Ni1-x-yMnxCoy)O2 materials enabling enhancement of performance for Li ion battery”, ACS Appl. Mater. Interfaces 8 (2016), 15361 – 15368. Figure 1

Enhanced lithium-storage performance of Li4Ti5O12 coated with boron-doped carbon layer for rechargeable Li-ion batteries

In this study, the B-doped carbon coating has been applied to enhance the lithium-storage performance of Li4Ti5O12 anode material for Li-ion batteries. The designed B-doped carbon improved Li4Ti5O12 composite (abbreviated as Li4Ti5O12@C-B) is successfully synthesized using a sol-gel approach followed by a microwave heating route. The XRD and HRTEM results demonstrate that the well-crystallized Li4Ti5O12 particles are uniformly coated with the B-doped carbon layer with a thickness of about several nanometers. The existence of boron doping in the carbon layer is also confirmed by XPS and EDX mapping. Compared with the undoped Li4Ti5O12@C, the Li4Ti5O12@C-B anode shows superior electrochemical performances such as higher reversible capacity and better cycling stability. The enhanced lithium-storage property can be attributed to the doped boron element which could bring many amazing improvements on the carbon coating. Therefore, this novel strategy of B-doped carbon coating can be widely used to improve the electronic conductivity of other electrode materials for electrochemical energy storage.

Lithium Borocarbide LiBC as an Anode Material for Rechargeable Li-Ion Batteries

Graphite is the dominant anode material for commercial Li-ion batteries, whereas developing other graphite-like anode material has never been practically achieved to date. Here, we perform computational and experimental studies to demonstrate the feasibility of graphite-like LiBC as a high-capacity anode material for Li-ion batteries. Electrochemical measurements suggest that LiBC can deliver a reversible specific capacity of 450 mAh g–1 with an average voltage of 1.4 V vs Li+/Li. Analogous to graphite, both the discharged and charged LiBC preserve the layered structure. As far as we know, this is the first realization of a graphite-like anode material for Li-ion battery, which will shed light on the development of other graphite derivatives for energy storage.

Phase-field modeling of Li-insertion kinetics in single LiFePO4-nano-particles for rechargeable Li-ion battery application

We develop a continuum phase-field model for the simulation of diffusion limited solid-solid phase transformations during lithium insertion in LiFePO4-nano-particles. The solid-solid phase boundary between the LiFePO4 (LFP)-phase and the FePO4 (FP)-phase is modeled as a diffuse interface of finite width. The model-description explicitly resolves a single LiFePO4-particle, which is embedded in an elastically soft electrolyte-phase. Furthermore, we explicitly include anisotropic (orthorhombic) and inhomogeneous elastic effects, resulting from the coherency strain, as well as anisotropic (1D) Li-diffusion inside the nano-particle. In contrast to other related research work, we employ an Allen-Cahn-type phase-field approach for the diffuse interface modeling of the solid-solid phase boundary. The model contains an extra non-conserved order parameter field to distinguish the two different phases. The evolution of this order parameter field is controlled by an extra kinetic parameter independent from the Li-diffusion. Further, the effect of the nano-particle’s size on the kinetics of FP to LFP phase transformations is investigated by means of both model. Both models predict a substantial increase in the steady state transformation velocity as the particle-size decreases down to dimensions that are comparable with the width of the interface between the FP and the LFP-phase. However, the extra kinetic parameter of the Allen-Cahn-type description may be used to reduce the strength of the velocity-increase with the decreasing particle size. Further, we consider the influence of anisotropic and inhomogeneous elasticity on the lithiation-kinetics within a rectangularly shaped LiFePO4-particle embedded in an elastically soft electrolyte. Finally, the simulation of equilibrium shapes of LiFePO4-particles is discussed. Within a respective feasibility study, we demonstrate that also the simulation of strongly anisotropic particles with aspect ratios up to 1/5 is possible.