One major challenge in the field of lithium-ion batteries is to understand the degradation mechanism of high-energy lithium- and manganese-rich layered cathode materials. Although they can deliver 30 % excess capacity compared with today’s commercially- used cathodes, the so-called voltage decay has been restricting their practical application. In order to unravel the nature of this phenomenon, we have investigated systematically the structural and compositional dependence of manganese-rich lithium insertion compounds on the lithium content provided during synthesis. Structural, electronic and electrochemical characterizations of LixNi0.2Mn0.6Oy with a wide range of lithium contents (0.00 ≤ x ≤ 1.52, 1.07 ≤ y < 2.4) and an analysis of the complexity in the synthesis pathways of monoclinic-layered Li[Li0.2Ni0.2Mn0.6]O2 oxide provide insight into the underlying processes that cause voltage fading in these cathode materials, i.e. transformation of the lithium-rich layered phase to a lithium-poor spinel phase via an intermediate lithium-containing rock-salt phase with release of lithium/oxygen.

As promising cathode materials, the lithium‐excess 3d‐transition‐metal layered oxides can deliver much higher capacities (>250 mAh g−1 at 0.1 C) than the current commercial layered oxide materials (≈180 mAh g−1 at 0.1 C) used in lithium ion batteries. Unfortunately, the original formation mechanism of these layered oxides during synthesis is not completely elucidated, that is, how is lithium and oxygen inserted into the matrix structure of the precursor during lithiation reaction? Here, a promising and practical method, a coprecipitation route followed by a microwave heating process, for controllable synthesis of cobalt‐free lithium‐excess layered compounds is reported. A series of the consistent results unambiguously confirms that oxygen atoms are successively incorporated into the precursor obtained by a coprecipitation process to maintain electroneutrality and to provide the coordination sites for inserted Li ions and transition metal cations via a high‐temperature lithiation. It is found that the electrochemical performances of the cathode materials are strongly related to the phase composition and preparation procedure. The monoclinic layered Li[Li0.2Ni0.2Mn0.6]O2 cathode materials with state‐of‐the‐art electrochemical performance and comparably high discharge capacities of 171 mAh g−1 at 10 C are obtained by microwave annealing at 750 °C for 2 h.

A nanostructured, porous NCM cathode material is investigated regarding its behavior during electrode processing and electrochemical performance. The results are related to the densely packed NCM original material from which the nanostructure has been derived. Chemical composition and structural parameters are not affected by the nanostructuring process; changes are limited to the particle morphology in terms of primary particle size, specific surface area, and porosity. Electrodes containing a porous NCM material deliver lower adhesion strength values when adding identical amounts of PVDF binder. Increasing the binder fraction from four to six parts increases also the adhesion strength to an acceptable level without deteriorating the cell capacity. Despite initially high electrode porosities of 65−70%, electrodes with nanostructured NCM are capable of withstanding calendering to 40% porosity without destroying the porous particles. Full-cell tests with 50 mAh pouch cells and graphite anodes reveal substantially improved C-rate capabilities for the nanostructured material in relation to the commercial original NCM. The advantage increases with increasing C-rate and corresponds to shorter diffusion pathways in nanostructured NCM. Remarkably, even at low C-rates (C/20) where diffusion effects are considered secondary, porous NCM lies ahead of the original material. This can be explained by the higher surface area and thereby enlarged interface to the electrolyte, which eases delithiation. Long-term cycling up to 1100 cycles displayed further benefits for the nanostructured active material as one of the most prominent degradation factors, that is, crack formation and particle fragmentation, does not occur throughout the complete cycling procedurein contrast to the bulk particles of original NCM.