LiNi_0.5Mn_1.5O₄ (LNMO) cathode active materials for lithium‐ion batteries have been investigated for over 20 years. Despite all this effort, it has not been possible to transfer their favorable properties into applicable, stable battery cells. To make further progress, the research perspective on these spinel type materials needs to be updated and a number of persisting misconceptions on LNMO have to be overcome. Therefore, the current knowledge on LNMO is summarized and controversial points are addressed by detailed considerations on the composition and crystallography of LNMO. The findings are supported by an in‐situ high temperature X‐ray diffraction study and the investigation of four different types of LNMO materials, including Mn(III) rich ordered LNMO, and disordered LNMO with low Mn(III) content. It is shown that the importance of cation order is limited to a small composition range. Furthermore, new evidence contradicting the idea of oxygen defects in LNMO is presented and an enhanced classification of LNMO based on the Ni content of the spinel phase is proposed. Moreover, a balanced chemical equation for the formation of LNMO is presented, allowing for comprehensive calculations of key properties of LNMO materials. Finally, suitable target compositions and calcination programs are suggested to obtain better LNMO materials.

Developing new electrode materials and/or electrolytes for lithium‐ion batteries requires reliable electrochemical testing thereof. For this purpose, in academic research typically hand‐made coin‐type cells are assembled. Their advantage is a rather cheap and facile assembly, and possibility to prepare full‐cells as well as half‐cells, meaning cathode‐anode or electrode‐elemental lithium configurations. Critical parameters for testing data quality and the potential and limitations of cell tests in half‐cell configuration are discussed. Further, on the basis of a round robin test, using highly homogenous commercial electrodes, where graphite is used as anode and LiNi_0.33Mn_0.33Co_0.33O₂ (NMC111) as the cathode material, it is shown that data acquired is highly influenced by assembling parameters. Besides known variables such as the amount of electrolyte or electrode positioning, the proper height of the cell stack and the steel grade of the housing material are identified as decisive variables. Finally, it is demonstrated that under proper conditions coin cells can show a great cycle stability of >2200 cycles using 1 C as dis‐/charge rate while retaining a capacity of 80 %. This performance is close to pouch‐type cells containing the same electrodes and electrolyte, which were used as a benchmark system and showed >3500 cycles of lifetime.

LiNi_0.5Mn_1.5O₄ (LNMO) based spinel cathode materials for lithium-ion batteries are promising alternatives to the widely used mixed transition-metal layered Li(Ni,Co,Mn)O₂ (NCM) oxides. LNMO is cobalt free and thus cost efficient, while providing a high operating voltage of 4.7 V (vs. Li/Li+) and remarkable energy density of ~650 Wh/kg. Commercialization and large-scale application however are still hindered, as short cycle life remains a main issue. To help overcoming this problem, we present a comprehensive investigation on Fe-Ti doped LNMO materials with the formal composition LiNi_0.5Mn_1.37Fe_0.1Ti_0.03O_3.95 (LNMFTO). Within this study, samples were calcined at temperatures between 460 °C and 940 °C and were cooled down to room temperatures fast or slowly. Small changes in the crystal structures were tracked by a high-precision powder X-ray diffraction (PXRD) setup, while changes of cation order were investigated with Raman spectroscopy. It is shown that the carefully elaborated calcination programs allow to maintain the optimized morphological features like particle size, shape and specific surface, while crystallographic properties, like the amounts of Mn(III) or (partial) cation order, can be adjusted independently. We provide experimental evidence that that calcination at high temperatures leads to nickel loss in the spinel phase, but not to the formation of additional oxygen defects. LNMFTO samples show good cycling stabilities and over 98 % capacity retention after 100 cycles with capacities larger than 90 mAh/g at discharge rates of 10 C when cycled vs. Lithium metal. These results are almost fully transferable to cathodes with high active material loadings cycled versus graphite anodes. A capacity retention > 89 % for 500 cycles and residual capacities of > 100 mAh/g are observed, which makes LNMFTO a suitable candidate for industrial applications

LiNbO₃-coated LiNi_0.5Mn_1.5O₄ spinel was fabricated by two methods: using hydrogen-peroxide as activating agent and sol-gel method. The structure of the obtained cathode materials was investigated using a scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the electrochemical properties of the prepared cathodes were probed by charge-discharge studies. The morphology of the coating material on the surface and the degree of coverage of the coated particles were investigated by SEM, which showed that the surface of LiNi_0.5Mn_1.5O₄ particles is uniformly encapsulated by lithium innovate coating. The influence of the LiNbO₃ coating layer on the spinel’s properties was explored, including its effect on the crystal structure and electrochemical performance. XRD studies of the obtained coated active materials revealed very small expansion or contraction of the unit cell. From the capacity retention tests a significant improvement of the electrochemical properties resulted when a novel chemically activated coating process was used. Poorer results, however, were obtained using the sol-gel method. The results also revealed that the coated materials by the new method exhibit enhanced reversibility and stability compared to the pristine and reference ones. It was shown that the morphology of the coating material and possible improvement of communication between the substrates play an important role.

Sodium‐ion batteries are becoming an increasingly important complement to lithium‐ion batteries. However, while extensive knowledge on the preparation of Li‐ion batteries with excellent cycling behavior exists, studies on applicable long‐lasting sodium‐ion batteries are still limited. Therefore, this study focuses on the cycling stability of batteries composed of Na₃V₂(PO₄)₃/C based cathodes and hard carbon anodes. It is shown that full‐cells with a decent stability are obtained for ethylene carbonate/propylene carbonate electrolyte and the conducting salt NaPF₆. With cathode loadings of 1.2 mAh/cm², after cell formation discharge capacities up to 92.6 mAh/g are obtained, and capacity retentions >90 % over 1000 charge/discharge cycles at 0.5 C/0.5 C are observed. It is shown that both, the additive fluoroethylene carbonate and impurities in the electrolyte, negatively affect the overall discharge capacity and cycling stability and should therefore be avoided. Remarkably, the internal resistances of well‐balanced and well‐built cells did not increase over 1500 cycles and 5 months of testing, which is a very promising result regarding the possible lifespan of the cells. The initial loss of active sodium ions in hard carbon remains a major problem, which can only be partially reduced by proper balancing.

This study addresses the improved cycling stability of Li‐ion batteries based on Fe–Ti‐doped LiNi_0.5Mn_1.5O₄ (LNMO) high‐voltage cathode active material and graphite anodes. By using 1 wt% Li₃PO₄ as cathode additive, over 90% capacity retention for 1000 charge–discharge cycles and remaining capacities of 109 mAh g⁻¹ are reached in a cell with an areal capacity of 2.3 mAh cm⁻² (potential range: 3.5–4.9 V). Cells without the additive, in contrast, suffer from accelerated capacity loss and increase polarization, resulting in capacity retention of only 78% over 1000 cycles. An electrolyte consisting of ethylene carbonate, dimethyl carbonate, and LiPF₆ is used without additional additives. The significantly improved cycling stability of the full cells is mainly due to two factors, namely, the low Mn^III content of the Fe–Ti‐doped LNMO active material and the use of the cathode‐additive Li₃PO₄. Crystalline Li₃PO₄ yields a drastic reduction of transition metal deposition on the graphite anode and prevents Li loss and the propagation of cell polarization. Li₃PO₄ is added to the cathode slurry that makes it a very simple and scalable process, first reported herein. The positive effects of crystalline Li₃PO₄ as electrode additive, however, should apply to other cell chemistries as well.