Mn-rich Layered Oxides Research Articles

Synthetic Pathway Determines the Nonequilibrium Crystallography of Li- and Mn-Rich Layered Oxide Cathode Materials

Li- and Mn-rich layered oxides show significant promise as electrode materials for future Li-ion batteries. However, an accurate description of its crystallography remains elusive, with both single...

Improved electrochemical activity of the Li2MnO3-like superstructure in high-nickel Li-rich layered oxide Li1.2Ni0.4Mn0.4O2 and its enhanced performances via tungsten doping

Voltage decay of Li- and Mn-rich layered oxides can be effectively suppressed by increasing their Ni contents, which however normally results in a sizable decrease in capacity probably due to the reduced Li2MnO3-like superlattice component. Here, we reveal that the partial replacement of Mn by W in the high-nickel Li-rich (HNLR) layered oxide Li1.2Ni0.4Mn0.4O2 leads to the increase in both Li2MnO3-like superlattice component and Ni2+ proportion due to the presence of W6+. As a result, the doping of W favors the activation of the Li2MnO3-like component with the reversible redox of more oxygen anions and the creation of a multi-cation chemical environment, accompanied by the size reduction of primary particles and the increase in lattice parameters. The reversible redox of more oxygen anions results in much higher capacity and initial Coulombic efficiency. The reduced sizes of primary particles, along with the lattice expansion significantly enhance the electrochemical kinetics, which accounts for superior rate capability and excellent high-rate cycling performance. This study opens a possibility of improving the performance of HNLR oxides by doping appropriate elements to modify and optimize the properties of the Li2MnO3-like component.

Entropy in Li- and Mn-Rich Layered Oxides Measured Via Linear Temperature Variation

For Li-ion battery development, Li- and Mn-rich layered oxide cathodes (LMRNCM, Li1+x[NiCoMn]1-xO2 with typically 0.1 < x < 0.2), are currently under development. Their exceptionally high gravimetric capacity is, however, accompanied by a significant voltage hysteresis, which complicates the SOC management and reduces the round-trip energy efficiency of the cell.1 In particular, a significant part of the voltage hysteresis is still present during open circuit conditions (OCV) being independent of the applied current and thus a material-specific property (see Figure 1a). The hysteresis is not only expressed in the voltage profile but also in other parameters, such as a path dependent cathode resistance2 and a hysteresis of the LMRNCM lattice parameters3.To investigate the OCV hysteresis, potentiometric entropy measurements were conducted to calculate the changes in the partial molar free entropy of the Li (de-)intercalation during charge and discharge, and from this, the reversible heat Qrev. The entropy is accessible via the temperature dependence of the OCV. To minimize errors from temperature history4 and relaxation5, a linear temperature variation method was established based on the work by Liebmann et al. 6 Using this method, entropy changes within the LMRNCM were measured as a function of state of charge (SOC) to reveal a path dependence between charge and discharge (see Figure 1b). This path dependence vanishes when the entropy is correlated to the OCV of the respective SOC indicating that the structural changes within the LMRNCM are rather a function of OCV than SOC, as can be seen in Figure 1c. This is in agreement with a previous study by Strehle et al.3 where a similar behavior was found for the lattice parameters of LMRNCM by diffraction methods. However, the herein conducted measurements did not reveal the entropy as a cause of the path-dependence (or hysteresis) but rather demonstrated it to be another indication of this phenomenon. Ultimately, the reversible heat Qrev will be compared to the energy loss correlating to the OCV hysteresis indicating that the latter heat term is significantly larger and independent from the entropy changes within the LMRNCM. Figure 1: (a) Voltage hysteresis and (b,c) changes in the partial molar free entropy for LMRNCM. A LMRNCM/Li Swagelok T-cell (equipped with a Li reference electrode) was cycled at C/10 at 25°C between 2.0-4.7 V. For the OCV curve, intermediate OCV phases of 1h were applied every ≈10% SOC (a). The entropy was measured in various T-cells via linear temperature variation after relaxation of the OCV at different SOCs during charge and discharge and is shown as a function of SOC (b) and OCV (c) with trendlines as guide for the eye.Acknowledgements:We want to acknowledge BASF SE for the support within the frame of its scientific network on electrochemistry.

(Invited) Exploring Sodium Layered Oxide Cathodes: Designing Tailored Materials

Interest in developing energy storage systems to meet a wide array of future challenges has driven research into a range of new battery technologies. Sodium-ion batteries (SIBs) have proven to be particularly popular due to their attractive properties and broad range of potential applications. However, before SIBs take their place in the pantheon of battery technologies, there still remain challenges to overcome - perhaps the most significant of which is the ongoing development of optimal cathode materials.Sodium Mn-rich layered oxides, i.e. NaxMn1-yMyO2 (y ≤ 0.33; M is one or more transition metals, such as Ni, Ti, Fe, etc.), have proven to be a promising family of SIB cathode materials with a low cost, highly tuneable, and environmentally friendly nature synergises well with the main advantages of SIBs.[1] Considerable research in this area, using a variety of conventional and specialised techniques, has led to an increased understanding of the nature and behaviour of these materials, and the key factors affecting their electrochemistry.[1-4]Performance of these materials is frequently governed by their structure, and in this work, we will highlight the importance of taking this into consideration. For example, while Manganese-rich layered oxides are particularly attractive due to their combination of low cost and low toxicity, their performances are often hindered by the effect of Jahn-Teller distortion (resulting from the presence of Mn3+).[5] We will not only discuss this in detail, but also highlight mitigation strategies – such as doping with electrochemically active (e.g. Fe) and inactive (e.g. Mg, Ti) elements, or synergetic P2/O3 combination effect.[5–8] This understanding has enabled the rapid investigation of not only suitable elements (selected with careful attention to electrochemical performance, cost, scarcity, etc.) but also appropriate degrees of doping and substitution.In this presentation, we will highlight some of the most significant Mn-rich materials and their properties, as well as examining and explaining the key parameters and factors which determine their performance. We will explain how this understanding has been used to develop a rational design approach, before summarising the trends in this area and areas of future exploitation.

Enhanced High-Temperature Stability of Li-Ion Battery with Li-Rich Oxide Cathode By Localized High-Concentration Electrolyte

Lithium (Li)-rich manganese (Mn)-rich oxides (LMR) have been considered as feasible cathode materials for high-energy lithium ion batteries because they possess high theoretical specific energy over 900 Wh kg−1. However, the undesirable cathode/electrolyte interfacial reaction due to the high working voltages, which results in electrolyte decomposition, transition-metal ion dissolution and surface corrosion, is considered one of the obstacles that significantly prevent their applications in electric vehicles for years.[1, 2] Although numerous efforts have been devoted to address the surface stability issues on LMR, most of them were limited to room temperature. The continuous upsurge in demand for electric vehicles requires lithium ion batteries to be operated under elevated temperatures. While, the state-of-the-art LiPF6-organocarbonate electrolytes are not compatible with LMR cathode due to the high operating voltage, which also get worse at elevated temperatures.[3] Here, an optimized localized high-concentration electrolyte (LHCEs) is studied in graphite (Gr)-based LMR full cells at 25, 45 and 60 °C. The cycling stabilities and the interfacial properties on the surfaces of both cathode and anode under different temperatures are systemically investigated. It is revealed that the LHCE enables the formation of more protective electrode/electrolyte interphases on both anode and cathode, which, in turn, lead to significantly improved cycling stability and enhanced rate capability under the selected temperatures. The electrode/electrolyte interphases formed in LHCE are found to be less susceptible towards elevated temperatures than those in conventional LiPF6-based electrolyte. The mechanistic understanding on the function of the LHCE in Gr||LMR cells under high temperatures provides valuable perspectives of electrolyte development for practical application of LMR cathodes in high energy density batteries over a wide temperature range. References C. Wang, et al., Overlooked electrolyte destabilization by manganese (II) in lithium-ion batteries. Nature Communications, 2019, 10(1), 3423.H. Pan, et al., Li- and Mn-rich layered oxide cathode materials for lithium-ion batteries: a review from fundamentals to research progress and applications, Molecular Systems Design & Engineering, 2018, 3(5), 748.M.-T.F., Rodrigues, et al., A materials perspective on Li-ion batteries at extreme temperatures, Nature Energy, 2017, 2(8), 17108.

Exploring the synthesis conditions and formation mechanisms of Li-rich layered oxides via solid-state method

Li- and Mn-rich layered oxides are receiving considerable attentions for the next-generation commercial lithium ion batteries owing to their high capacity and low cost. However, there is still some dispute about the ideal synthesis protocol to obtain the optimum electrochemical performances. Herein, we deeply explore the decomposition/lithiation mechanisms of sodium-contained Ni1/6Co1/6Mn4/6CO3 precursor (NCM-P) during calcination process, and highlight the effects of heat treatment temperature and the lithium to NCM-P molar ratio (Li/TM) on Li- and Mn-rich layered oxides. The results demonstrate that Ni1/6Co1/6Mn4/6CO3 can be initially lithiated to LiNi1/6Co1/6Mn4/6O2, then gradually lithiated/decomposed to 0.1/6Li4Mn5O12·2.5/6Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 material. The cathode crystal crystallization and the components are significantly affected by heat treatment temperature and the Li/TM ratios. The optimized synthetic conditions for Li- and Mn-rich cathode materials is in 500 °C for 4 h, 750 °C for 4 h, and 840 °C for 10 h under Li/TM = 1.4. Under this condition, the synthesized Li- and Mn-rich oxides can deliver a first discharge capacity of 259.4 mAh·g−1 at 25 mA g−1 with 84.00% coulombic efficiency, and 218.2 mAh·g−1 at 250 mA g−1 with 90.97% capacity retention after 100 cycles. This study would give some guidance for the synthesis of Li-rich layered oxides.

Unraveling Na and F coupling effects in stabilizing Li, Mn-rich layered oxide cathodes via local ordering modification

Regardless of the prevailing capacity and energy density of lithium, manganese-rich layered oxide (LMR-NMC) cathodes, continuous decay of voltage and overall energy density during cycling hinders this material from commercialization in Li-ion batteries. Although significant work focuses on single doping of Na and F, analysis in portraying the benefit of these ions in diminishing the structural distortion during activation cycle is in doubt. Herein, the effects of co-doping Na and F into the LMR-NMC structure in stabilizing the structure and mitigating oxygen loss during the first cycle are closely examined via in situ x-ray measurements. Na and F co-doping shows a 30% lower degree of Li+/Ni2+ mixing in the Li layer (C2/m structure), 50% reduced Debye-Waller factor of Mn-O bonding, increase reversible TM migration, and faster Li diffusion relative to the pristine material. Due to the utilization of Ni redox chemistry below 4.4 V, less oxygen redox is required for charge compensation at high voltage. This study offers the first instance to quantitatively evaluate the effects of co-doping Na and F in LMR-NMC cathode in order to minimize voltage degradation by altering the local ordering of O3-type structure, which may rationalize strategies to overcome the issues of the material.

Excess-Li Localization Triggers Chemical Irreversibility in Li- and Mn-Rich Layered Oxides.

Li- and Mn-rich layered oxides (LMRs) have emerged as practically feasible cathode materials for high-energy-density Li-ion batteries due to their extra anionic redox behavior and market competitiveness. However, sluggish kinetics regions (<3.5 V vs Li/Li+ ) associated with anionic redox chemistry engender LMRs with chemical irreversibility (first-cycle irreversibility, poor rate properties, voltage fading), which limits their practical use. Herein, the structural origin of this chemical irreversibility is revealed through a comparative study involving Li1.15 Mn0.51 Co0.17 Ni0.17 O2 with relatively localized and delocalized excess-Li in its lattice system. Operando fine-interval X-ray absorption spectroscopy is used to simultaneously observe the interplay between transition-metal-oxygen (TM-O) redox chemistry and TM migration behavior in real time. Density functional theory calculations show that excess-Li localization in the LMR structure attenuates TM-O covalency and stability, leading to overall chemical irreversibility. Hence, the delocalized excess-Li system is proposed as an alternative design for practically feasible LMR cathodes with restrained TM migration and sustainable O-redox chemistry.

Size‐Mediated Recurring Spinel Sub‐nanodomains in Li‐ and Mn‐Rich Layered Cathode Materials

Li- and Mn-rich layered oxides are among the most promising cathode materials for Li-ion batteries with high theoretical energy density. Its practical application is, however, hampered by the capacity and voltage fade after long cycling. Herein, a finite difference method for near-edge structure (FDMNES) code was combined with in situ X-ray absorption spectroscopy (XAS) and transmission electron microscopy/electron energy loss spectroscopy (TEM/EELS) to investigate the evolution of transition metals (TMs) in fresh and heavily cycled electrodes. Theoretical modeling reveals a recurring partially reversible LiMn2 O4 -like sub-nanodomain formation/dissolution process during each charge/discharge, which accumulates gradually and accounts for the Mn phase transition. From the modeling of spectra and maps of the valence state over large regions of the cathodes, it was found that the phase change is size-dependent. After prolonged cycling, the TMs displayed different levels of inactivity.

Entropy Measurements of Cells with Li- and Mn-Rich Layered Oxides Measured Via Linear Temperature Variation

For Li-ion battery development, Li- and Mn-rich layered oxide cathodes (HE-NCM, Li1+x[M]1-xO2 with M = Ni, Mn, Co and typically 0.1 < x < 0.2) are currently under development. Their exceptionally high gravimetric capacity is, however, accompanied by a significant voltage hysteresis which reduces the round-trip energy efficiency of the cell.1 In particular, a significant part of the voltage hysteresis is still present during measurements at open circuit voltage (OCV hysteresis, see Figure 1a) and hence leads to an energy loss, which is independent of the applied current.To investigate this OCV hysteresis, potentiometric entropy measurements were conducted in half-cells to calculate the overall entropy changes ΔS of Li (de-)intercalation during charge and discharge, and from this, the reversible heat Qrev. ΔS is accessible via the temperature dependence of the OCV. To minimize errors from temperature history2 and relaxation3, a linear temperature variation method was established based on the work by Liebmann et al. 4 Using this method, entropy changes of Li/Mn-rich NCM half-cells were measured as a function of state of charge (SOC), revealing a path dependency of ΔS between charge and discharge, which can only be ascribed to entropy changes of the cathode active material (see Figure 1b). This path dependency vanishes when the entropy is correlated to the OCV of the respective Mn-rich NCM SOC, indicating that the structural changes within the cathode are rather a function of OCV than SOC, as can be seen in Figure 1c. This is in agreement with a previous study by Strehle et al.,5 where a similar behavior was found for the hysteresis in the evolution of the Mn-rich NCM lattice parameters between the charge and the discharge direction. However, the measurements conducted in the present study did not reveal the entropy as a cause of the path-dependency (or hysteresis), but rather demonstrated it to be another indication of this phenomenon. Ultimately, the reversible heat Qrev will be compared to the energy loss correlating to the OCV hysteresis, QOCV, indicating that the latter heat term is significantly larger and independent of the entropy changes within the Mn-rich NCM.Acknowledgements:We want to acknowledge BASF SE for the support within the frame of its scientific network on electrochemistry.

Operating EC-based Electrolytes with Li- and Mn-Rich NCMs: The Role of O2-Release on the Choice of the Cyclic Carbonate

Li- and Mn-rich layered oxides are a promising class of cathode active materials (CAMs) for future lithium-ion batteries. However, they suffer from fast capacity fading in standard EC-containing electrolytes, and therefore fluorinated alternatives, such as FEC, are required to improve their full-cell performance, which unfortunately increases the cost of the electrolyte. In this study, we will analyze the reasons for the poor cycling performance of EC-containing electrolytes with CAMs that release lattice oxygen at high degrees of delithiation, i.e., either of Li- and Mn-rich NCMs (LMRNCMs) during activation or of NCMs at high cutoff voltages. By on-line electrochemical mass spectrometry (OEMS), we will show that the stability of EC towards electrochemical oxidation is sufficient up to potentials of ≈4.7 V vs Li+/Li, but that its chemical reaction with lattice oxygen released from CAMs negatively affects cycle-life. Furthermore, we will show that the use of EC-based electrolytes above the onset potential for oxygen release leads to a resistance build-up causing a rapid “rollover” fading, while FEC does not show such a dramatic impedance increase. Last, we will demonstrate that the lattice oxygen release from NCM-622 above ≈4.5 V vs Li+/Li requires the use of EC-free electrolytes for stable cycling.

Thermally Induced Structural Reordering in Li- and Mn-Rich Layered Oxide Li Ion Cathode Materials

In recent years, a considerable amount of effort has been put into a better understanding of the correlation of structure and electrochemical properties in Li- and Mn-rich NCM layered oxide Li ion ...

High-performance symmetric lithium-ion batteries constructed with a new bi-functional electrode Li- and Mn-rich layered oxide 0.3Li2MnO3·0.7LiNi1/3Co1/3Mn1/3O2

Symmetric full cells attract much attention because of various advantages including almost no cell volume expansion, simplified fabrication and reduced costs. Li- and Mn-rich layered oxide (LMROs), the traditional high-capacity cathode material, demonstrates excellent reversible capacities as anode electrode in half cell and the reaction mechanism is comprised mainly of conversion reaction. Herein, for the first time, a novel symmetric lithium-ion full battery is systemically studied constructed with bi-functional Li- and Mn-rich layered oxide 0.3Li2MnO3·0.7LiNi1/3Co1/3Mn1/3O2 (LMROs//LMROs), not involving any prelithiated/predelithiated treatments. Benefited from the high specific capacity of LMROs as cathode and anode electrodes and the potential gap between two redox couples, this symmetric battery exhibits excellent electrochemical performance, with a satisfactory capacity of 150.6 mAh g−1, average voltage of 2.01 V and energy density of 306.4 Wh kg−1 at 30 mA g−1 between 0.05 and 3.6 V. The specific capacity is superior among all the previous reported symmetric energy storage systems (including symmetric lithium/sodium/potassium ion batteries). Additionally, the lower charge cut-off voltage and higher discharge cut-off voltage facilitate the cycle performance. Collectively, the superior performance of LMROs//LMROs demonstrates a feasible and potential bi-functional electrode material for new symmetric lithium-ion battery.

In situ thermally reduced graphene oxide enhancing lithium storage of 0.3Li2MnO3•0.7LiNi1/3Co1/3Mn1/3O2 cathode material

Abstract Li- and Mn-rich layered oxides as cathode materials attract considerable academic and industrial research attention, owing to the superior specific capacity and energy density. The relatively low rate capability is one of the major problems that need to be resolved for these materials. In this work, 0.3Li2MnO3•0.7LiNi1/3Co1/3Mn1/3O2/reduced graphene oxide (LMROs/rGO) is rationally constructed via in-situ thermally reduction method in air flow. This method can reduce graphene oxide availably and meanwhile prevent the reduction of transition element including Ni, Mn and Co in LMROs through typical thermal reduction in inert atmosphere and the aggregation of graphene during chemical reduction process. LMROs/rGO shows enhanced electrical conductivity at polarization potentials of 0.2 V and 4.5 V and lower charge-transfer resistance, in comparison with LMROs, benefited from the addition of conductive rGO with promoted electron transport kinetics. Consequently, LMROs/rGO exhibits high initial capacity of 295.7 mA h−1 at 20 mA g−1 and better rate capability as high as 154.3 mA h g−1 at 500 mA g−1 under 2.0–4.8 V vs. Li/Li+, superior to those of LMROs. Considering the facility and availability of this hybrid/reduction method and needless any reducing agent and additives, it is believed that this simple and scalable in-situ thermal reduction of GO in air flow is an effective approach for the introduction of rGO to either xLi2MnO3∙(1−x)LiMO2 cathode material or other electrode materials which demand a highly oxidative environment for enhanced electrochemical performances.

Lattice Parameter Hysteresis in Li- and Mn-Rich Layered Oxides and Its Dependence on State of Charge and Open Circuit Voltage

Li- and Mn-rich layered oxides, also known as high energy NCM (HE-NCM, Li1+x[NiCoMn]1-xO2 with typically 0.1 < x < 0.2), are promising next-generation cathode active materials (CAMs) for Li-ion batteries, since they contain intrinsically more lithium ions than regular NCM materials (x < 0.05). The gain in capacity is accompanied by the drawbacks of voltage hysteresis (between charge and discharge) and voltage fade (during long-term cycling).1 The voltage hysteresis is a unique property of over-lithiated layered oxides, which does not only manifest itself in the voltage profile, but also in the cathode resistance,2 the redox activity of transition metals (TM) and oxygen,2 and the bond distances.3 Figure 1 shows our results of an in-situ X-ray diffraction (XRD) experiment during the initial cycles of a Li-rich NCM material. As seen in Figure 1a and b, the state of charge (SOC, equivalent to total xLi) dependence of the bulk lattice parameters a and c after the first activation cycle is characterized by a pronounced hysteresis between charge and discharge. Here, the hysteresis loop of the lattice parameter a is clearly different from that of c. Furthermore, the hysteresis of the lattice parameter a vanishes when it is correlated to the open circuit voltage (OCV) of the respective SOC (see Figure 1c), but c maintains the shifted maxima during charge and discharge (see Figure 1d). Based on the literature, these observations could be either explained by a path dependency of the reversible TM migration between TM and Li layer,4 the oxygen redox,2 or a combination of both.5 In addition to in-situ XRD data, we will show co-refined X-ray and neutron diffraction data of selected ex-situ samples, which have either the same SOC or OCV. By means of diffraction techniques, it is our goal to elucidate the lattice parameter variations in Li-rich CAMs and to clarify the often described contribution of TM migration to the hysteresis effects. Figure 1: In-situ XRD measurement of HE-NCM during the first 3 cycles. The pouch cell was cycled at a rate of C/10 between 2.0-4.8 V against metallic lithium with intermediate OCV steps to collect XRD patterns (at a laboratory diffractometer with Mo-Kα1 radiation). Using the trigonal model (space group R-3m), the lattice parameters a and c are shown as a function of SOC (a,b) and OCV (c,d), respectively. Acknowledgements: We want to acknowledge BASF SE for the support within the frame of its scientific network on electrochemistry and batteries and the BMBF (Federal Ministry of Education and Research, Germany) for its financial support within the ExZellTUM II project (grant number 03XP0081). We also thank the research neutron source FRM II for access to the instrument SPODI.

Structural Distribution of Redox-Active Oxygen Governing Chemical Reversibility in Li- and Mn-Rich Layered Oxides

Li- and Mn-rich layered oxides (LMR) come into the spotlight due to anomalously high capacities under O redox. However, O redox also incurs undesirable situations: voltage fade, inhomogeneous kinetics and low coulombic efficiency, limiting a practical use. Herein, through a comparative study on LMR (Li1.15Mn0.51Co0.17Ni0.17O2) having different distributions of redox-active oxygen in a structural arrangement, we reveal the origin of irreversible properties of LMR, which appear mainly at low voltage redox region (LVRR, ~3.0V). Focusing on chemical reversibility at LVRR, real-time simultaneous observations on competitive TM-O redox behavior and TM occupancies in Li sites were conducted using operando fine-interval X-ray absorption spectroscopies. First-principles calculations demonstrate that the dispersed arrangement of redox-active oxygen stabilizes TM-O coordination, leading to restrained TM migration and reversible O redox. The enlightenment of chemical reversibility which considers the real-time changes in electronic/crystalline structures provides a new perspective on a structural design for ideal future LMR.

(Invited) Development of Most Important Cathodes for Li Ion Batteries that can Promote the Electro-Mobility Revolution

Electro-mobility is the major challenge today in the field of electrochemical power sources. However, we encounter too many unsupported promises, too much noise! Examples: Many publications on ‘novel’ nano-materials, not suitable for practical battery applications. Nanomaterials may mean high surface area and pronounced side reactions. For instance - thousands of papers on conversion reactions anodes (nanomaterials), none of them show performance at elevated temperatures, why? Also nano-materials have puffy structure (difficult to process into electrodes). A lot of words (recently also conferences) on “ beyond Li-ion batteries”. Beyond… for what purposes? Hard to see what can be relevant for electrochemical propulsion beyond Li-ion batteries. In fact, the only relevant partner may be H2/O2 fuel cells, which are becoming highly relevant power sources because hydrogen can be stored in EVs at high pressure. The renaissance of Li metal based batteries is interesting, fully justified, but not for cars! Is the progress in Li-S batteries relevant to EVs? Practically, safety concerns are not being addressed well enough. The main theme of this presentation is to examine what is the true horizons for advance Li ion batteries that can promote the electro-mobility revolution. The limiting factor in Li-ion batteries in terms of energy density, cost, potential, durability and cycling efficiency are the cathode materials used. Over the years many types of cathode materials for Li-ion batteries were examined, including olivine phosphates (LiMPO4) , spinel structures (LiMn2O4,LiMn0.15Ni0.5O2) , Li and Mn rich layered oxides (Li1+x[MnNiCo]1-xO2 and layered Li[NiCoMn]O2 compounds The most promising cathode materials for advanced Li-ion batteries are lithiated transition metal oxides with a layered structure, in which the main transition metal is nickel. As the amount of Ni in lithiated transition metal cathode materials is higher, the specific capacity is higher as well, yet can be extracted at relatively low potentials (< 4.3 V vs. Li) which do not endanger the anodic stability of the electrolyte solutions used in these batteries. For instance, The specific capacity of LiNiO2 cathodes can reach 240 mAh/g upon charging to 4.3 V. However, as the content of Ni is higher, these cathode materials are less stable mechanically, thermally and electrochemically. The capacity fading mechanisms involve stresses with are formed in the particles when their full capacity is realized by charging to 4.3 V. Cracks are formed, increase the specific surface area and allow detrimental reactions of components from the electrolyte solutions with the cathode materials within their cracks. These side reactions lead to exfoliation and destruction of the active mass. Using judicious doping and/or surface coating, it is possible to fully mitigate these detrimental situation. After gaining enough experience, it is possible to develop computational routes that can suggest optimal doping and coating processes. This presentation reports about our ongoing work in the field. Accumulated results by us and by many others indicate that developing advanced Li-ion batteries, fully suitable for long range electric vehicles, is real and fruitful.

Formation Strategies for Over-Lithiated NCMs Suitable for Large-Scale Cells

As a potential next generation cathode material, Li- and Mn-rich layered oxides, also referred to as High-Energy NCM (HE-NCM), offer high reversible capacities of ≈250 mAh/g. Despite the high capacity and relatively low material cost compared to state-of-the-art cathode materials, the use of HE-NCM is still challenged by issues such as voltage fading, a relatively large charge-discharge voltage hysteresis, and high impedance. Gassing, especially oxygen and carbon dioxide release during the initial formation cycles with HE-NCM, has been studied before [1] and a recent publication by Teufl et al. [2] correlated the extent of gassing to the extent of surface degradation and impedance gain. An up to now neglected issue of the extensive gassing of HE-NCM concerns the associated difficulty during the formation of large-scale cells. The roughly one order of magnitude higher quantity of gas released from HE-NCM compared to regular NCMs results in either a large volume expansion in pouch-cells or a large pressure increase in hardcase-cells. The amount of the released gases produced by the activation of the HE-NCM during the first cycle and during cycles 2-5 depends significantly on the formation temperature, as shown by on-line electrochemical mass spectrometry (OEMS) data, given in Fig.1. For example, increasing the formation temperature from 15 to 45°C does not change the total amount of gas evolved over 5 cycles, but shifts a large fraction of the total amount of released gas into the first formation cycle. This is beneficial for industrial cell production, as degassing steps are usually placed in the first cycle. On the other hand, Erickson et. al. [3] have shown that an increased formation temperature has a negative impact on the cycling performance, leading to lower capacities. By combining OEMS analysis with operando pressure measurements, we will show the effect of different formation procedures (variation of temperature, C-rate, and number of formation cycles) on the amount of evolved gas and the long-term cycling performance. In parallel, we correlate the formation temperature with the impedance of the cell at different stages of cycling to connect the cycling performance with possible generated resistance due to the formation. Finally, the OEMS based gassing data will be used to project the behavior of 7.5 Ah pouch-cells (as done in Fig. 1) in order to evaluate the different formation procedures with regards to their feasibility for the formation of 7.5 Ah pouch-cells.

In Situ Electrochemical Zn2+-Doping for Mn-Rich Layered Oxides in Li-Ion Batteries

Mn-rich layered oxide materials have been considered as promising cathode materials for large scale Li-ion batteries because Mn is more inexpensive than Co and Ni. In this connection, a variety of doped-materials have been examined to improve the electrochemical performance of Mn-rich cathode materials. Doped-materials are conventionally synthesized using solid state synthesis at high temperatures, where most dopants are located at transition metal sites. The amount of redox-active transition metals decreases with increasing the amount of dopants in transition metals sites, resulting in the reduced reversible capacity of doped-materials. This paper demonstrates an in situ electrochemical doping of Zn2+ that is site-selective. Li+ at Li sites in Mn-rich layered oxides is selectively replaced by Zn2+ during cycling. Zn2+ ions in electrolytes are irreversibly inserted to Li sites in delithiated Mn-rich cathode materials during discharge, leading to the formation of Zn2+-doped Mn-rich layered oxides, [Li1–xZn...

Mg-doped Li1.133Ni0.2Co0.2Mn0.467O2 in Li site as high-performance cathode material for Li-ion batteries

Li- and Mn-rich layered oxides as cathode materials attract considerable attention owing to the superior capacity. However, their practical applications are still hindered by the inherent drawbacks such as the poor rate capability. Based on the structure characteristics that Li diffuses through two-dimensional lithium ion diffusion tunnel during intercalation/extraction, enlarging Li layer spacing is an effective strategy to increase Li+ diffusion coefficient and enhance rate capability. In this work, Mg-doping in Li site is employed to enhance the electrochemical performance of Li1.133Ni0.2Co0.2Mn0.467O2. With the ionic radius similar to that of Li+, Mg2+ is more suitable to occupy Li site and enlarge lattice parameter c which is critical to Li layer spacing and lithium ion diffusion coefficient. Consequently, Li1.123Mg0.010Ni0.2Co0.2Mn0.467O2 exhibits high initial capacity of 308 mAh g−1 at 25 mA g−1 and better rate capability as high as 166.1 mAh g−1 at 625 mA g−1 under 2.0–4.8 V vs. Li/Li+. Its ionic conductivity at 4.1 V during charge and 3.7 V during discharge is 4.1 ∗ 10−12 cm2·s−1 and 9.2 ∗ 10−13 cm2·s−1, 6.10 times and 6.07 times higher than that of pristine sample, indicating that magnesium doping facilitates the migration and diffusion of Li+ due to the enlargement of lithium ion diffusion channel.