Investigating the particle size effect on the electrochemical performance and degradation of cobalt-free lithium-rich layered oxide Li1.2Ni0.2Mn0.6O2

Lithium-rich layered oxides (LRLOs) as Li-ion battery positive electrode materials promise to deliver superior specific capacity (> 270 mAh g−1) boosting the driving range of electric vehicles (EVs). Interestingly, these materials do not strictly require cobalt in their formulation, solving the supply, environmental, and ethical issues associated to this metal. Herein the synthesis of Co-free Li1.2Ni0.2Mn0.6O2 (LRNM) via lab-scale co-precipitation and solid-state reaction is reported, employing transition metal salts with different anions. These yield to different morphological features of the resulting LRNMs, also impacting the physicochemical characteristics and electrochemical performance. The use of sulfate TMs results in a material (LRNM-S) with smaller crystallite and particle sizes, which displays very high specific capacity (more than 270 mAh g−1 at C/20) and excellent rate capability (109 mAh g−1 at 10C). However, its capacity and voltage fading are also more pronounced than for the acetate-based material (LNRM-A), which owns twice as large crystallites achieving capacity and voltage retention both higher than 97% over 100 cycles. Our investigation unveiled the prevalent trade-off between full activation and exploitation of the LRLOs high specific capacity and anion redox against structural degradation and accelerated ageing of the materials

The success story of graphite as a lithium-ion anode material – fundamentals, remaining challenges, and recent developments including silicon (oxide) composites

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

Concentrated Electrolytes Enabling Stable Aqueous Ammonium‐Ion Batteries

Rechargeable aqueous batteries are promising devices for large-scale energy-storage applications because of their low-cost, inherent safety, and environmental friendliness. Among them, aqueous ammonium-ion (NH$_4$$^+$) batteries (AAIB) are currently emerging owing to the fast diffusion kinetics of NH$_4$$^+$. Nevertheless, it is still a challenge to obtain stable AAIB with relatively high output potential, considering the instability of many electrode materials in an aqueous environment. Herein, a cell based on a concentrated (5.8 m) aqueous (NH$_4$)$_2$SO$_4$ electrolyte, ammonium copper hexacyanoferrate (N-CuHCF) as the positive electrode (cathode), and 3,4,9,10-perylene-bis(dicarboximide) (PTCDI) as the negative electrode (anode) is reported. The solvation structure, electrochemical properties, as well as the electrode–electrolyte interface and interphase are systematically investigated by the combination of theoretical and experimental methods. The results indicate a remarkable cycling performance of the low-cost rocking-chair AAIB, which offers a capacity retention of ≈72% after 1000 cycles and an average output potential of ≈1.0 V

Deriving Structure-Performance Relations of Chemically Modified Chitosan Binders for Sustainable High-Voltage LiNi0.5_{0.5}Mn1.5_{1.5}O4_{4} Cathodes

The implementation of aqueous electrode processing for lithium‐ion positive electrodes is key towards the realization of environmentally benign and cheap battery production. One of the water‐soluble binders that has attracted most attention is chitosan, the second‐most abundant natural biopolymer. Herein, the use of chitosan for high‐voltage, cobalt‐free LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ cathodes is reported for the first time. A detailed comparison of three different grades of chitosan with varying chain length and degrees of deacetylation (DD) is provided to explore the impact of these properties on the electrochemical performance. In fact, bio‐derived chitosan with a relatively lower DD outperforms synthetic chitosan‐especially after crosslinking with citric acid‐yielding about 10 % higher capacities. Higher molecular weight appears additionally advantageous for the cycling stability. Finally, guar gum is employed as slurry thickener, co‐crosslinking with chitosan. This allows for achieving 50 % higher mass loadings than for chitosan only and stable capacities above 130 and 120 mAh g$^{-1}$ at C/3 and 1 C, respectively

Deriving structure‐performance relations of chemically modified chitosan binders for sustainable high‐voltage LiNi0.5Mn1.5O4 cathodes

The implementation of aqueous electrode processing for lithium-ion positive electrodes is key towards the realization of environmentally benign and cheap battery production. One of the water-soluble binders that has attracted most attention is chitosan, the second-most abundant natural biopolymer. Herein, the use of chitosan for high-voltage, cobalt-free LiNi0.5Mn1.5O4 cathodes is reported for the first time. A detailed comparison of three different grades of chitosan with varying chain length and degrees of deacetylation (DD) is provided to explore the impact of these properties on the electrochemical performance. In fact, bio-derived chitosan with a relatively lower DD outperforms synthetic chitosan-especially after crosslinking with citric acid-yielding about 10 % higher capacities. Higher molecular weight appears additionally advantageous for the cycling stability. Finally, guar gum is employed as slurry thickener, co-crosslinking with chitosan. This allows for achieving 50 % higher mass loadings than for chitosan only and stable capacities above 130 and 120 mAh g(-1) at C/3 and 1 C, respectively

Deriving structure-performance relations of chemically modified chitosan binders for sustainable high-voltage LiNi0.5Mn1.5O4 cathode

Invited for this month's cover picture is the group of Prof. Dr. Stefano Passerini. The front cover illustrates the use of citric acid (co-)crosslinked bio-derived polymers, with chitosan and guar gum, as water-soluble binders for sustainable lithium-ion battery cathodes. Read the full text of the Article at 10.1002/batt.201900140. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei

Single-ion conducting polymer electrolyte for Li||LiNi0.6_{0.6}Mn0.2_{0.2}Co0.2_{0.2}O2_{2} batteries—impact of the anodic cutoff voltage and ambient temperature

Polymer-based electrolytes potentially enable enhanced safety and increased energy density of lithium-metal batteries employing high capacity, transition metal oxide-positive electrodes. Herein, we report the investigation of lithium-metal battery cells comprising Li[Ni$_{0.6}$Mn$_{0.2}$Co$_{0.2}$]O$_{2}$ as active material for the positive electrode and a poly(arylene ether sulfone)-based single-ion conductor as the electrolyte incorporating ethylene carbonate (EC) as selectively coordinating molecular transporter. The resulting lithium-metal battery cells provide very stable cycling for more than 300 cycles accompanied by excellent average Coulombic efficiency (99.95%) at an anodic cutoff potential of 4.2 V. To further increase the achievable energy density, the stepwise increase to 4.3 V and 4.4 V is herein investigated, highlighting that the polymer electrolyte offers comparable cycling stability, at least, as common liquid organic electrolytes. Moreover, the impact of temperature and the EC content on the rate capability is evaluated, showing that the cells with a higher EC content offer a capacity retention at 2C rate equal to 61% of the capacity recorded at 0.05 C at 60 degrees C

Elucidating the Effect of Iron Doping on the Electrochemical Performance of Cobalt‐Free Lithium‐Rich Layered Cathode Materials

The eco‐friendly and low‐cost Co‐free Li1.2Mn0.585Ni0.185Fe0.03O2 is investigated as a positive material for Li‐ion batteries. The electrochemical performance of the 3 at% Fe‐doped material exhibits an optimal performance with a capacity and voltage retention of 70 and 95%, respectively, after 200 cycles at 1C. The effect of iron doping on the electrochemical properties of lithium‐rich layered materials is investigated by means of in situ X‐ray diffraction spectroscopy and galvanostatic intermittent titration technique during the first charge–discharge cycle while high‐resolution transmission electron microscopy is used to follow the structural and chemical change of the electrode material upon long‐term cycling. By means of these characterizations it is concluded that iron doping is a suitable approach for replacing cobalt while mitigating the voltage and capacity degradation of lithium‐rich layered materials. Finally, complete lithium‐ion cells employing Li1.2Mn0.585Ni0.185Fe0.03O2 and graphite show a specific energy of 361 Wh kg−1 at 0.1C rate and very stable performance upon cycling, retaining more than 80% of their initial capacity after 200 cycles at 1C rate. These results highlight the bright prospects of this material to meet the high energy density requirements for electric vehicles

Difluorobenzene‐Based Locally Concentrated Ionic Liquid Electrolyte Enabling Stable Cycling of Lithium Metal Batteries with Nickel‐Rich Cathode

Lithium metal batteries (LMBs) with nickel-rich cathodes are promising candidates for next-generation, high-energy batteries. However, the highly reactive electrodes usually exhibit poor interfacial compatibility with conventional electrolytes, leading to limited cyclability. Herein, a locally concentrated ionic liquid electrolyte (LCILE) consisting of lithium bis(fluorosulfonyl)imide (LiFSI), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EmimFSI), and 1,2-difluorobenzene (dFBn) is designed to overcome this challenge. As a cosolvent, dFBn not only promotes the Li$^{+}$ transport with respect to the electrolyte based on the ionic liquid only, but also has beneficial effects on the electrode/electrolyte interphases (EEIs) on lithium metal anodes (LMAs) and LiNi$_{0.8}$Mn$_{0.1}$Co$_{0.1}$O$_{2}$ (NMC811) cathodes. As a result, the developed LCILE enables dendrite-free cycling of LMAs with a coulombic efficiency (CE) up to 99.57% at 0.5 mA cm$^{-2}$ and highly stable cycling of Li/NMC811 cells (4.4 V) at C/3 charge and 1 C discharge (1 C = 2 mA cm−2) for 500 cycles with a capacity retention of 93%. In contrast, the dFBn-free electrolyte achieves lithium stripping/plating CE, and the Li/NMC811 cells’ capacity retention of only 98.22% and 16%, respectively under the same conditions. The insight into the coordination structure, promoted Li$^{+}$ transport, and EEI characteristics gives fundamental information essential for further developing (IL-based) electrolytes for long-life, high-energy LMBs