New insights into electrochemical anion intercalation into carbonaceous materials for dual-ion batteries: Impact of the graphitization degree

Within the past 5 years, dual-ion batteries and in particular their all-carbon/all-graphite versions, the dual-carbon or dual-graphite batteries, have received rising interest due to the use of carbonaceous active materials for both, the positive and the negative electrode. With regard to the capacity determining reactions at the positive electrode, related to the intercalation of anions, the influence of the carbon/graphite structure has been by far not fully understood.In this work, we present a comprehensive investigation on the structure – property relationship with special focus on the preparation and characterization of carbon materials with different degree of graphitization (DoG) and their electrochemical performance study as active material for the positive electrode in dual-ion batteries. We found that an increasing DoG directly leads to an enhanced specific discharge capacity, while the crystallite height exhibits only a negligible contribution to the capacity for the carbons examined in this work. A further observation is that the staging mechanism is a major step of the overall anion storage mechanism, even for carbons possessing a low DoG. Moreover, an increased DoG leads to a decreased voltage hysteresis between the charge and discharge step and, thus, to an enhanced voltage efficiency during charge/discharge cycling

Carbons from biomass precursors as anode materials for lithium ion batteries: New insights into carbonization and graphitization behavior and into their correlation to electrochemical performance

We report a comprehensive and systematic study on the preparation and characterization of carbonaceous materials that are obtained from five different sustainable precursor materials and petroleum coke as reference material, particularly focusing on the correlation between the structural transformation of the precursors into carbons in dependence of heat treatment temperature (HTT) and their corresponding electrochemical characteristics as anode material in lithium ion batteries. The carbons were carbonized and graphitized in 200 °C steps, covering a broad temperature range from 800 °C to 2800 °C. So far, such a systematic synthesis approach has not been reported in literature. For biomass-derived carbons, we found a heterogeneous (discontinuous) graphitization process, i.e. a transformation from the amorphous to the graphitic phase via the turbostratic phase. A general trend was observed for the discharge capacity, i.e. a decrease of capacity from 800 °C to ≈1800–2000 °C, followed by an increase of capacity for temperatures >2000 °C. An increase of the 1st cyle Coulombic efficiency was found and could be directly correlated to the decrease of the “non-basal plane” surface area upon HTT. In addition, we found that the voltage efficiency and energy efficiency of the different carbons also increase with rising treatment temperatures

Understanding the effect of Nb substitution on Li-Mn-rich layered oxides

Substitution with 4d/5d-elements has been recently established as promising solution for suppressing capacity and voltage fading in Li-Mn-rich layered oxide cathodes for lithium ion batteries. This study aims at understanding of the underlying working principles of this concept through a systematic study on an Nb substituted Co-free material, i.e. Li1.2Ni0.2Mn0.6O2. Nb is confirmed by XRD to be located at the position of Li in the transition metal layer of the C/2 m phase of the composite material thereby increasing the kinetics of activation significantly. Due to substitution, the material experiences a lager extent of reversible anionic redox activity while it also gains an increased thermal stability and shows less oxygen loss than the pristine material during cycling. In addition, substitution also improves the electrochemical performance by increasing the energy efficiency of the material. This study provides insights into the effects of Nb substitution and could be a useful guide for the study of other substitution elements and the ongoing improvement of Li-Mn-rich layered oxide cathodes

Lithium-Metal Foil Surface Modification: An Effective Method to Improve the Cycling Performance of Lithium-Metal Batteries

Lithium metal as an electrode material possesses a native surface film, which leads to a rough surface and this has a negative impact on the cycling behavior. A simple, fast, and reproducible technique is shown, which makes it possible to flatten and thin the native surface film of the lithium‐metal anode. Atomic force microscopy and scanning electron microscopy images are presented to verify the success of the method and X‐ray photoelectron spectroscopy measurements reveal that the chemical composition of the lithium surface is also changed. Furthermore, galvanostatic measurements indicate superior cycling behavior of the surface modified electrodes compared to the as‐received ones. These results demonstrate that the native surface film plays a key role in the application of lithium metal as an anode material for lithium‐metal batteries and that the shown surface modification method is an excellent tool to obtain better performing Li metal electrodes

Learning from Overpotentials in Lithium Ion Batteries: A Case Study on the LiNi 1/3_{1/3} Co 1/3_{1/3} Mn 1/3_{1/3} O 2_{2} (NCM) Cathode

The practically available specific energy of Li ion batteries (LIB) is highly depending on the used specific charge/discharge current, since the respective overpotentials of each electrode affect the two vital specific energy parameters, specific capacity and voltage. Focusing on the positive composite electrode as the specific energy bottleneck, the overall nature of the overpotential is discussed for the LiNi1/3Co1/3Mn1/3O2 (NCM) active material. It is shown that the characteristic overpotentials during charge (delithiation) and discharge (lithiation) is state of charge (SOC) and depth of discharge (DOD) dependent, respectively. It was demonstrated that the discharge characteristics are intertwined with the previous charge conditions, particularly with the charging time and the specific charge capacity. Increasing both in parallel can even lead to a deterioration of the subsequent specific discharge capacity. Furthermore, Li+ transport pathways within the NCM composite electrode are discussed and their influence on the observed overpotential evaluated. Changes of the overpotential are found to be mainly associated with changes within the NCM crystal structure, which is experimentally supported by the correlation of the SOC dependent overpotential with the XRD determined c-axis lattice parameter. Consequently, the Li+ transport within the active material is mostly responsible for limiting the practically available specific energy

Effective Solid Electrolyte Interphase Formation on Lithium Metal Anodes by Mechanochemical Modification

Lithium metal batteries are gaining increasing attention due to their potential for significantly higher theoretical energy density than conventional lithium ion batteries. Here, we present a novel mechanochemical modification method for lithium metal anodes, involving roll-pressing the lithium metal foil in contact with ionic liquid-based solutions, enabling the formation of an artificial solid electrolyte interphase with favorable properties such as an improved lithium ion transport and, most importantly, the suppression of dendrite growth, allowing homogeneous electrodeposition/-dissolution using conventional and highly conductive room temperature alkyl carbonate-based electrolytes. As a result, stable cycling in symmetrical Li∥Li cells is achieved even at a high current density of 10 mA cm–2. Furthermore, the rate capability and the capacity retention in NMC∥Li cells are significantly improved

A Step toward High-Energy Silicon-Based Thin Film Lithium Ion Batteries

The next generation of lithium ion batteries (LIBs) with increased energy density for large-scale applications, such as electric mobility, and also for small electronic devices, such as microbatteries and on-chip batteries, requires advanced electrode active materials with enhanced specific and volumetric capacities. In this regard, silicon as anode material has attracted much attention due to its high specific capacity. However, the enormous volume changes during lithiation/delithiation are still a main obstacle avoiding the broad commercial use of Si-based electrodes. In this work, Si-based thin film electrodes, prepared by magnetron sputtering, are studied. Herein, we present a sophisticated surface design and electrode structure modification by amorphous carbon layers to increase the mechanical integrity and, thus, the electrochemical performance. Therefore, the influence of amorphous C thin film layers, either deposited on top (C/Si) or incorporated between the amorphous Si thin film layers (Si/C/Si), was characterized according to their physical and electrochemical properties. The thin film electrodes were thoroughly studied by means of electrochemical impedance spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. We can show that the silicon thin film electrodes with an amorphous C layer showed a remarkably improved electrochemical performance in terms of capacity retention and Coulombic efficiency. The C layer is able to mitigate the mechanical stress during lithiation of the Si thin film by buffering the volume changes and to reduce the loss of active lithium during solid electrolyte interphase formation and cycling

Surface Modification of Ni-Rich LiNi 0.8 Co 0.1 Mn 0.1 O 2 Cathode Material by Tungsten Oxide Coating for Improved Electrochemical Performance in Lithium-Ion Batteries

Ni-rich NCM-based positive electrode materials exhibit appealing properties in terms of high energy density and low cost. However, these materials suffer from different degradation effects, especially at their particle surface. Therefore, in this work, tungsten oxide is evaluated as a protective inorganic coating layer on LiNi0.8Co0.1Mn0.1O2 (NCM-811) positive electrode materials for lithium-ion battery (LIB) cells and investigated regarding rate capability and cycling stability under different operation conditions. Using electrochemical impedance spectroscopy, the interfacial resistance of uncoated and coated NCM-811 electrodes is explored to study the impact of the coating on lithium-ion diffusion. All electrochemical investigations are carried out in LIB full cells with graphite as a negative electrode to ensure better comparability with commercial cells. The coated electrodes show an excellent capacity retention for the long-term charge/discharge cycling of NCM-811-based LIB full cells, i.e., 80% state-of-health after more than 800 cycles. Furthermore, the positive influence of the tungsten oxide coating on the thermal and structural stability is demonstrated using postmortem analysis of aged electrodes. Compared to the uncoated electrodes, the surface-modified electrodes show less degradation effects, such as particle cracking on the electrode surface and improvement of the thermal stability of NCM-811 in the presence of electrolyte