Following the demand for increased energy density of lithium-ion batteries, the Ni content of the Nickel-Cobalt-Manganese oxide (NCM) cathode materials has been increased into the direction of LiNiO2 (LNO), which regained the attention of both industry and academia. To understand the correlations between physicochemical parameters and electrochemical performance of LNO, a calcination study was performed with variation of precursor secondary particle size, maximum calcination temperature and Li stoichiometry. The structural properties of the materials were analyzed by means of powder X-ray diffraction, magnetization measurements and half-cell voltage profiles. All three techniques yield good agreement concerning the quantification of Ni excess in the Li layer (1.6%–3.7%). This study reveals that the number of Li equivalents per Ni is the determining factor concerning the final stoichiometry rather than the calcination temperature within the used calcination parameter space. Contrary to widespread belief, the Ni excess shows no correlation to the 1st cycle capacity loss, which indicates that a formerly overlooked physical property of LNO, namely primary particle morphology, has to be considered.

A better understanding of the cathode active material (CAM) plays a crucial role in the improvement of lithium-ion batteries. We have previously reported the structural properties of the model cathode material LiNiO2 (LNO) in dependence of its calcination conditions and found that the deviation from the ideal stoichiometry in LiNiO2 (Ni excess) shows no correlation to the 1st cycle capacity loss. Rather, the morphology of LNO appears to be decisive. As CAM secondary agglomerates fracture during battery operation, the surface area in contact with the electrolyte changes during cycle life. Thus, particle morphology and especially the primary particle size become critical and are analyzed in detail in this report for LNO, using an automated SEM image segmentation method. It is shown that the accessible surface area of the pristine CAM powder measured by physisorption is close to the secondary particle geometric surface area. The interface area between CAM and electrolyte is measured by an in situ capacitance method and approaches a value proportional to the estimated primary particle surface area determined by SEM image analysis after just a few cycles. This interface area is identified to be the governing factor determining the 1st cycle capacity loss and long-term cycling behavior.

Efficient manufacturing of cathode active materials (CAMs) for Li-ion batteries is one key target on the roadmap towards cost reduction and improved sustainability. This work deals with a two-stage calcination process for the synthesis of LiNiO2 (LNO) consisting of a (partial) lithiation step at moderate temperatures and short dwell times and a subsequent high temperature crystallization to decouple the chemical reactions and crystal growth. The use of an agitated-bed lithiation using the rotational movement of a rotary kiln setup shows beneficial effects compared to its fixed-bed counterpart in a crucible as the lithiation reaction is faster under otherwise comparable conditions. The temperature profile for the agitated-bed process was further optimized to avoid the presence of needle-like LiOH residuals in the intermediate product indicative of an incomplete reaction. The partially-lithiated samples were subjected to a second calcination step at a maximum calcination temperature of 700°C and afterwards revealed comparable physico-chemical properties and electrochemical behavior compared to a reference sample made by a standard one-stage calcination. In a simplified model calculation, the proposed calcination concept leads to an increase in throughput by a factor of ~ 3 and thus could embody an important lever for the efficiency of future CAM production.

To increase the specific capacity of layered transition metal oxide based cathode active materials (CAMs) for Li-ion batteries such as NCMs (Li(NixCoyMnz)O2, with x + y + z = 1), two major strategies are pursued: (i) increasing the Ni content (beyond, e.g., NCM811 with x = 0.8 and y = z = 0.1) or (ii) using Li- and Mn-rich NCMs (LMR-NCMs) which can be represented by the formula x Li2MnO3 · (1−x) LiNixCoyMnzO2. Unfortunately, these materials strongly react with CO2 and moisture in the ambient: Ni-rich NCMs due to the high reactivity of nickel, and LMR-NCMs due to their ≈10-fold higher specific surface area. Here we present a novel surface stabilization approach via SO3 thermal treatment of LMR-NCM suitable to be implemented in CAM manufacturing. Infrared spectroscopy and X-ray photoelectron spectroscopy prove that SO3 treatment results in a sulfate surface layer, which reduces the formation of surface carbonates and hydroxides during ambient air storage. In contrast to untreated LMR-NCM, the SO3-treated material is very robust towards exposure to ambient air at high relative humidity, as demonstrated by its lower reactivity with ethylene carbonate based electrolyte (determined via on-line mass spectrometry) and by its reduced impedance build-up and improved rate capability in full-cell cycling experiments.

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