Cobalt is considered an essential element for layered cathode active materials supporting enhanced lithium‐ion conductivity and structural stability. Herein, we investigated the influence of Co concentration on the physicochemical properties and electrochemical performance of lithium‐rich layered oxides (LRLOs) with different Co content (Li1.2Ni0.2‐x/2Mn0.6‐x/2CoxO2, x=0, 0.04, and 0.08). Though the presence of Co grants structural stability to LRLOs, superior long‐term cycling stability is achieved with the Co‐free LRLO retaining 88.1 % of the initial specific capacity (vs. 75.9 % of Li1.2Ni0.16Mn0.56Co0.08O2) after 300 galvanostatic cycles at 250 mA g−1 (1 C). The chemical stability on the surface of LRLOs containing Co declines faster, indicating a higher bulk structural stability not being the primary determinant of the LRLOs’ cycling performance. Ex‐situ investigations indicate that the superior cycling stability of Co‐free LRLO is obtained by reducing the Mn‐related redox at discharge, which contributes to the large degree of polarization and low energy efficiency. Finally, the full‐cell configured with the optimized LRLO as cathode and graphite anode delivers an energy density of 464 Wh kg−1 at C/10, and 74.4 % and 94.3 % of retention in discharge specific capacity and average voltage at the 1000th cycle, demonstrating the applicability of Co‐free LRLO for sustainable LIBs.

The reversible and irreversible cationic and anionic charge compensation mechanisms occurring along the first charge and discharge cycle of Li- and Mn-rich Li[Li0.2Ni0.16Mn0.56Co0.08]O2 cathode material at (dis)charge rates of 0.1C and 5C have been identified and quantified by X-ray absorption and emission spectroscopy. The analysis provided the oxidation states of the transition metals, the Mn local coordination, and the lattice elastic constants. Lattice softening occurs along the first charge, while a minor spinel phase forms irreversibly at the expense of the layered phase. Higher charge rate increases the spinel formation and induces an increased softening in the delithiated lattice, which is expected to correspond to a reduced reversible anionic redox. The results evidence a comparable cationic and anionic oxidation since the beginning of the charge, while only anions are contributing towards its end, equivalent to roughly 10% of structural oxygen irreversibly lost. Higher charge rates resulted in a decreased reversible anionic redox, anticipating the cationic oxidation. The reported results provide a reliable experimental approach to characterize the key parameters controlling the reversible and irreversible cationic and anionic contributions to the charge compensation mechanism.

The use of water-soluble, abundant biopolymers as binders for lithium-ion positive electrodes is explored because it represents a great step forward towards environmentally benign battery processing. However, to date, most studies that employ, for instance, carboxymethyl cellulose (CMC) as a binder have focused on rather low electrode areal loadings with limited relevance for industrial needs. This study concerns the use of natural guar gum (GG) as a binding agent for cobalt-free, high-voltage LiNi0.5Mn1.5O4 (LNMO), which realizes electrodes with substantially increased areal loadings, low binder content, and greatly enhanced cycling stability. Co-crosslinking GG through citric acid with CMC allows for an enhanced rate capability and essentially maintains the beneficial impact of using GG as a binder rather than CMC only. Lithium-ion full cells based on water-processed LNMO and graphite electrodes provide a remarkably high cycling stability with 80 % capacity retention after 1000 cycles at 1 C.

This review provides a comprehensive overview about the “hidden champion” of lithium-ion battery technology – graphite.

Lithium-ion batteries are nowadays playing a pivotal role in our everyday life thanks to their excellent rechargeability, suitable power density, and outstanding energy density. A key component that has paved the way for this success story in the past almost 30 years is graphite, which has served as a lithium-ion host structure for the negative electrode. And despite extensive research efforts to find suitable alternatives with enhanced power and/or energy density, while maintaining the excellent cycling stability, graphite is still used in the great majority of presently available commercial lithium-ion batteries. A comprehensive review article focusing on graphite as lithium-ion intercalation host, however, appeared to be missing so far. Thus, herein, we provide an overview on the relevant fundamental aspects for the de-/lithiation mechanism, the already overcome and remaining challenges (including, for instance, the potential fast charging and the recycling), as well as recent progress in the field such as the trade-off between relatively cheaper natural graphite and comparably purer synthetic graphite and the introduction of relevant amounts of silicon (oxide) to boost the energy and power density. The latter, in fact, comes with its own challenges and the different approaches to overcome these in graphite/silicon (oxide) composites are discussed herein as well.

Increasing the environmental benignity of the lithium-ion battery (LIB) technology is one of the greatest challenges associated with their continuously increasing demand. At the same time, the performance metrics in terms of energy density, power capability and reliability have to be at least maintained to meet the requirements of the rapidly growing electric vehicle market. [1] Besides introducing cobalt-free high-performance active materials, such as the high-voltage spinel LiNi 0.5 Mn 1.5 O 4 (LNMO), [2] the implementation of aqueous electrode processing strategies for lithium-ion cathodes, is a key step to realize environmentally benign battery production. To achieve this ambitious goal, the deployment of nature-derived, inexpensive polymers in combination with the use of water as dispersion agent provides the great possibility to spare energy-intensive drying procedures and costly dry-room conditions, and thus, will turn the whole battery fabrication more eco-efficient and abolish the need of harmful and rather costly N -methyl-2-pyrrolidone (NMP) as processing solvent for mutagenic and teratogenic fluorine-containing binders. [3,4] What could easily be established for graphite anodes, appears more complicated for transition metal oxide-based and imperatively cobalt-free cathode materials, which suffer from lithium leaching and transition metal dissolution when getting in contact with water, which has, so far, rendered the use of aqueous binders very challenging. [5,6] The strategies developed in our group enable the achievement of this desirable goal: The first one, i.e., the addition of phosphoric acid during electrode preparation, targets the prevention of the aluminum current collector corrosion and simultaneously stabilizes the LNMO particle surface, hence, avoiding the active material degradation in contact with water. The second one, i.e., the crosslinking of the binder by means of citric acid, provides an enhanced cycling stability of the aqueous processed electrodes. [ 6,7] Remarkably, these two complementary approaches can be easily adapted in the electrode preparation process without requiring any additional processing step. To achieve positive electrode tapes, readily available for large-scale high-energy lithium-ion batteries, a carbon-coated current collector is used. It provides functional groups to crosslink the positive electrode coating layer to the underlying aluminum foil. The resulting electrodes demonstrate significant improvements concerning the electrode to current collector adhesion and their capacity retention. [ 8] Through the further optimization of the initial formation cycles, these electrodes offer an electrochemical performance exceeding that of LNMO-based reference electrodes, comprising state-of-the-art poly(vinylidene difluoride) (PVdF) as binder. Transferring this knowledge to other modified biopolymers, such as chitosan and guar gum in combination with relations derived between structure and performance of electrodes made from these cheap, abundant and naturally available binders finally leads to the realization of entirely water-processed high-performance LIBs employing sustainable cobalt-free high-voltage LNMO cathodes and graphite anodes. [ 9,10] References D. Larcher and J. M. Tarascon, Nat. Chem. , 7 , 19–29 (2015). M. Kuenzel et al., Mater. Today , In Press (2020) https://doi.org/10.1016/j.mattod.2020.04.003. D. Bresser, D. Buchholz, A. Moretti, A. Varzi, and S. Passerini, Energy Environ. Sci. , 11 , 3096–3127 (2018). A. Kwade et al., Nat. Energy , 3 , 290–300 (2018). Michael M. Thackeray, J. Am. Ceram. Soc. , 82 , 3347–3354 (1993). N. Loeffler et al., ChemSusChem , 9 , 1112–1117 (2016). M. Kuenzel et al., ChemSusChem , 11 , 562–573 (2018). M. Kuenzel et al., ACS Appl. Energy Mater. , 3 , 218–230 (2020). M. Kuenzel et al., Batter. Supercaps , 3 , 155–164 (2020). M. Kuenzel et al., ChemSusChem , 13 (2020) https://doi.org/10.1002/cssc.201903483.

Herein we address the key challenge towards the practical use of high-voltage lithium-ion cathode materials, i.e., the insufficient stability of the electrolyte towards oxidation. The transition metals in such materials, especially nickel, catalyze the decomposition reaction of the electrolyte, ultimately leading to poor cycling stability and rapid fading of the battery. To tackle this challenge, a new combination of electrolyte additives is introduced, targeting stabilized electrode/electrolyte interfaces and interphases for both the anode and cathode. The results show that the synergistic effect of tris(trimethylsilyl) phosphite (TTSPi) and bis(2,2,2-trifluoroethyl) carbonate (TFEC) can significantly improve the performance of cathode half-cells and also of lithium-ion full-cells with a cell voltage higher than 4.5 V. Cells using both TTSPi and TFEC as additives show greatly enhanced cycling stability, increased capacity, and improved coulombic efficiency, which can be even further improved when adding also lithium bis(oxalato)borate.

In this work, we report novel room temperature ionic liquid (RTIL)-based electrolytes to be used with high-energy cathode, lithium-rich nickel manganese cobalt oxide (Li[Li0.2Mn0.56Ni0.16Co0.08]O2, LiR-NMC) in Li-ion batteries. The physical and electrochemical characteristics of the newly developed materials are thoroughly detailed, also by means of post-cycling electrochemical impedance spectroscopy (EIS) analysis of the resulting lab-scale lithium cells upon long-term, constant-current cycling (>1200 cycles). In addition, an innovative polymer electrolyte is developed encompassing the best performing RTIL-based electrolyte mixture, which is investigated in terms of its physico-chemical features, ion transport and electrochemical behaviour by EIS, cyclic voltammetry and constant-current (galvanostatic) cycling. The polymer electrolyte is obtained via facile, rapid and easily up-scalable UV-induced free radical polymerization (UV curing) technique, being a low-cost and solvent-free approach compared to other existing film formation techniques. The versatile fabrication method along with the use of appropriate materials may turn high-voltage, solid state and ageing resistant batteries into industrial reality in the coming years, as underlined by the excellent electrochemical response of the lithium polymer cell.

Layered lithium-rich nickel manganese cobalt oxide (LR-NMC) represents one of the most promising cathode materials for application in high energy density lithium-ion batteries. The extraordinary capacity delivered derives from a combination of both cationic and anionic redox processes. However, the latter ones lead to oxygen evolution which triggers structural degradation and electrode/electrolyte interface (EEI) instability that hinders the use of LR-NMC in practical application. In this work, we investigate the surface chemistry of LR-NMC and its evolution upon different conditions to give further insights into the processes occurring at the EEI. X-ray photoelectron spectroscopy studies reveal that once the organic component of the layer is formed, it remains stable independently on the higher cutoff voltage applied, while continuous growth of inorganics along with oxygen evolution occurs. The results performed on lithiated and delithiated LR-NMC surfaces indicate an instability of the EEI layer formed at high voltages, which undergoes a partial decomposition. Furthermore, the tris(pentafluorophenyl)borane electrolyte additive simultaneously prevents excess LiF formation and changes the chemical composition of the EEI layer. The latter is characterized by a higher amount of poly(ethylene oxide) oligomer species and LixPOyFz formation. In addition, the presence of boron-containing compounds in the EEI layer cannot be excluded, which may be also responsible of the increased thickness of the EEI layer. Finally, fast kinetics at elevated temperatures exacerbate the salt decomposition which results in the formation of an EEI which is thicker and richer in LiF.

The steadily rising utilization of lithium-ion batteries for large-scale applications, in particular, electric vehicles requires the development of cell chemistries that offer increased energy and power densities.1,2 Essentially, there are two options to enhance the energy density: Increasing the capacity of the employed active materials and/or elevating the full-cell voltage by switching to high-voltage cathode materials. The latter, however, face the great challenge to identify a suitable electrolyte composition, as commonly used organic carbonate-based electrolyte are not sufficiently stable towards oxidation. To avoid the resulting detrimental side reactions, the use of electrolyte additives is easily implementable into common cell manufacturing technologies and, thus, very cost-efficient.3,4 For such reason, a plethora of electrolyte additives has been reported in recent years, but frequently these additives have been proven only to enhance the performance for selected cathode materials, while particularly the evaluation with graphite-based anodes has been commonly overlooked. Herein, we report on a new electrolyte composition, incorporating functional electrolyte additives for high-voltage cathode materials like LiNi0.5Mn1.5O4 or 5V-olivines, which moreover reveal a beneficial impact also for graphite-based anodes and, consequently, also in lithium-ion full-cells. As a result, lithium-ion half- and full-cells with a cell voltage of >4.5 V show a greatly enhanced cycling stability, increased capacities, and improved efficiencies. References B. Scrosati, J. Hassoun, and Y.-K. Sun, Energy Environ. Sci., 4, 3287 (2011). D. Bresser et al., J. Power Sources, accepted manuscript (2018). S. S. Zhang, J. Power Sources, 162, 1379–1394 (2006). J. Kalhoff, G. G. Eshetu, D. Bresser, and S. Passerini, ChemSusChem, 8, 2154–2175 (2015).

Even though electrochemically inactive, the binding agent in lithium-ion electrodes substantially contributes to the performance metrics such as the achievable capacity, rate capability, and cycling stability. Herein, we present an in-depth comparative analysis of three different aqueous binding agents, allowing for the replacement of the toxic N-methyl-2-pyrrolidone as the processing solvent, for high-energy Li1.2Ni0.16Mn0.56Co0.08O2 (Li-rich NMC or LR-NMC) as a potential next-generation cathode material. The impact of the binding agents, sodium carboxymethyl cellulose, sodium alginate, and commercial TRD202A (TRD), and the related chemical reactions occurring during the electrode coating process on the electrode morphology and cycling performance is investigated. In particular, the role of phosphoric acid in avoiding the aluminum current collector corrosion and stabilizing the LR-NMC/electrolyte interface as well as its chemical interaction with the binder is investigated, providing an explanation for the observed differences in the electrochemical performance.

The recently rising awareness for a more sustainable cell manufacturing can be expected to gain even more momentum in sight of the announcements from major car manufacturers across Europe and North America to entirely electrify their fleet within the next half-decade1,2. The implementation of aqueous electrode processing strategies for lithium-ion cathodes is a key step to realize the environmentally benign battery production. To achieve this ambitious goal, most studies focus on the development of non-toxic and abundant active materials and specifically, the implementation of nature-derived, inexpensive binders in combination with the use of water as dispersion agent and solvent provides the great possibility to spare energy-intensive drying procedures and costly dry-room conditions, and thus, will turn the whole battery fabrication more eco-efficient 3,4. What could easily be established for graphite anodes – employing water-soluble natural polymers as binder, thus, abolishing the need of toxic and rather costly N-methyl-2-pyrrolidone (NMP) as processing solvent3,5 – appears more complicated for transition metal oxide-based and imperatively cobalt-free cathode materials, which suffer from lithium leaching and transition metal dissolution when getting in contact with water, which has, so far, rendered the use of aqueous binders very challenging6,7. In our group we recently demonstrated the general feasibility for the aqueous processing of several lithium-ion cathode materials, such as high-voltage LiNi0.5Mn1.5O4, by introducing a complementary approach, of suitable processing additives to stabilize the active material surface as well as the electrode/electrolyte/current collector interface8. Moreover, we extended our investigations to various binder systems and cathode materials in order to advance the aqueous electrode preparation and move from the well-established lab-scale process towards the fabrication of commercial-scale lithium-ion batteries9. References C. J. Barnhart and S. M. Benson, Energy Environ. Sci., 6, 1083 (2013). D. Larcher and J. M. Tarascon, Nat. Chem., 7, 19–29 (2015). D. Bresser, D. Buchholz, A. Moretti, A. Varzi, and S. Passerini, Energy Environ. Sci. (2018) http://xlink.rsc.org/?DOI=C8EE00640G. A. Kwade et al., Nat. Energy, 3, 290–300 (2018) http://www.nature.com/articles/s41560-018-0130-3. S. F. Lux, F. Schappacher, A. Balducci, S. Passerini, and M. Winter, J. Electrochem. Soc., 157, A320 (2010). M. M. Thackeray, J. Am. Ceram. Soc., 82, 3347–3354 (1999). N. Loeffler et al., ChemSusChem, 9, 1112–1117 (2016). M. Kuenzel et al., ChemSusChem, 11, 562–573 (2018). A. Kazzazi et al., ACS Appl. Mater. Interfaces, 10, 17214–17222 (2018).

The EU-funded collaborative MARS-EV Project (FP7, grant agreement 609201) has been targeting inter alia the realization of aqueous electrode processing technologies for high-energy lithium-ion positive electrodes with a particular focus on achieving the high recycling requirements established by the European Commission in its Battery Directive 2006/66 EG, stipulating a minimum recycling rate of 50%. Indeed, the aqueous electrode fabrication does not only allow for avoiding the use of environmentally hazardous, toxic, and expensive organic solvents as well as the need for super-dry conditions up to the cell assembly, but moreover a facilitated recycling process due to the water-soluble binding agents. Additionally, of great importance with regard to the latter is the careful selection of the cathode chemistry – not least with respect to economic aspects. Herein, we summarize the results and progresses obtained within MARS-EV, highlighting their importance for the realization of environmentally friendly lithium-ion batteries for a sustainably electrified transportation.