Since the discovery 25 years ago, many investigations have reported light-induced macroscopic mass migration of azobenzene-containing polymer films. Various mechanisms have been proposed to account for these motions. This study explores light-inert side chain liquid crystalline polymer (SCLCP) films with a photoresponsive polymer only at the free surface and reports the key effects of the topmost surface to generate surface relief gratings (SRGs) for SCLCP films. The top-coating with an azobenzene-containing SCLCP is achieved by the Langmuir-Schaefer (LS) method or surface segregation. A negligible amount of the photoresponsive skin layer can induce large SRGs upon patterned UV light irradiation. Conversely, the motion of the SRG-forming azobenzene SCLCP is impeded by the existence of a LS monolayer of the octadecyl side chain polymer on the top. These results are well understood by considering the Marangoni flow driven by the surface tension instability. This approach should pave the way toward in-situ inscription of the surface topography for light-inert materials and eliminate the strong light absorption of azobenzene, which is a drawback in optical device applications. Surface morphology generations on azobenzene(Az)-containing polymer films induced by patterned irradiation have been the active area in photofunctional material research. In 1995, Natansohn's 1 and Tripathy's 2 groups independently reported the induction of surface relief gratings (SRGs) on Az amorphous films using interference irradiation of two laser beams. Since then, photoinduced SRG processes have been reported using various photofunctional materials such as amorphous polymers 1-20 , side chain liquid crystalline polymers (SCLCPs) 21-27 , supramolecular systems 24,27-29 , amorphous molecular materials 30. Additionally, SRG formation can be realised using other photoresponsive units 31-35. Various mechanistic models for mass transfer have been proposed: isomerisation pressure due to volume change 7,8 , gradient force 9-11 , mean-field model 12 , directed softening or fluidisation 13-15 , molecular diffusion 16-18,34 , molecular orientation force 19,20 , etc. With regard to Az-containing SCLCPs 21-27 , UV light irradiation leads to a photochemical phase transition between the liquid crystal (LC) and isotropic phases. This phase change plays an important role in highly efficient SRG formation 23,25,26 , which requires an overall dose of much less than 1 J cm-2. Typically mass transport depends on the light irradiation conditions and physicochemical properties. Consequently, a universal explanation about the mechanism has yet to be provided. Recent studies have noted the importance of the surface effect on the mass transfer process. Ambrosio et al. 17,18 proposed an anisotropic light-driven molecular diffusion model for spiral morphology induction under vortexbeam illumination. Their model stressed enhanced molecular diffusion in proximity of the free surface. Ellison et al. 36-39 have proposed microfabrications via the Marangoni flow by photo...

Current standard industrial manufacturing of lithium layered transition metal oxides (LiMO2) as cathode active material (CAM) can be divided into two major process steps: The first step involves coprecipitation of mixed transition metal hydroxide (M(OH)2) particles (M consisting mainly of Ni, Co, and Mn) by mixing a transition metal sulfate solution (MSO4(aq.)) and a sodium hydroxide solution (NaOH(aq.)) in a stirred tank reactor. The resulting hierarchally structured secondary particles are composed of many primary particles which are used as precursors for CAMs (referred to as pCAM). Subsequently, the obtained pCAM is mixed with a lithium source such as Li2CO3 or LiOH and calcined at elevated temperatures to yield LiMO2.1 Recently, reports in the literature have shown clear correlations of CAM morphology with their electrochemical performance in a battery cell.2 Furthermore, it has been demonstrated that the electrochemical performance of a CAM is affected by the morphology of the associated pCAM.3, 4 However, a detailed understanding of the impact of the process parameters on the course of precipitation reaction and on the physical properties of the pCAM precipitate is still lacking. In order to gain a mechanistic understanding of the M(OH)2 pCAM particle formation, ten distinctive Ni0.8Co0.1Mn0.1(OH)2 particle lots were prepared by the coprecipitation method in a stirred tank reactor. The precipitation pH-value was systematically varied between pH = 8.6-12.7, while all other process parameters were kept constant. The S-content of the resulting pCAM powders, representing the residual sulfate (SO4 2-) content, was investigated by S-combustion and is depicted as a function of precipitation pH-value in Figure 1a. In the pH-value range between 8.57 and 10.27 (red), a slight increase in residual SO4 2- from 10.29 mol% to 12.60 mol% is observed until it decreases again to 11.10 mol%. Between pH = 10.27 and pH = 10.74, a sharp transition takes place and residual SO4 2- is reduced by a factor of 4 from 11.10 mol% to 2.60 mol%, which even decreases further with increasing pH-value, namely from 2.60 mol% at pH = 10.74 to 0.35 mol% at pH = 12.69 (green). Interestingly, the turning point in S-content between pH = 10.27 and pH = 10.74 (dashed blue line in Figure 1a) coincides with the point-of-zero-charge (pzc) of Ni(OH)2, which is reported to be at pH = 10.50-10.60.5 This result is rationalized by a pH-dependent SO4 2- adsorption equilibrium that is governing the SO4 2- uptake during the precipitation reaction, as depicted schematically in Figure 1b. For a precipitation below the pzc, positive charged surface hydroxyl-groups of Ni0.8Co0.1Mn0.1(OH)2 attract SO4 2-, resulting in high SO4 2- uptake during M(OH)2 formation and vice versa. In light of these results, it is further demonstrated by x-ray diffraction analysis that SO4 2- adsorption not only governs the crystallinity of the Ni0.8Co0.1Mn0.1(OH)2 material, but also suppresses the vertical crystal growth in the 001-direction during particle formation. This in turn seems to affect the vertical primary particle size as well as the secondary particle porosity, both observable by SEM imaging. The morphological trend is quantitatively verified by extracting the primary particle size distribution from SEM images and by measurements of the secondary particle porosity via nitrogen physisorption. As proof-of-concept for the proposed adsorption mechanism, precipitation reactions at pH = 12.0 with different metal feed sources (MX(aq.), with X = SO4 2-, (NO3 -)2, (CH3COO-)2) were conducted. The resulting clearly distinct physical properties of the Ni0.8Co0.1Mn0.1(OH)2 particles obtained from the different anion systems with different anion adsorption affinities can be well understood based on the Fajans-Paneth-Hahn law for crystallization.6 Finally, desorption experiments indicate options to reduce the residual SO4 2- amount after the Ni0.8Co0.1Mn0.1(OH)2 particle formation has been completed. Based on the results of this study, guidelines for pCAM design are formulated and discussed with respect to composition and subsequent manufacturing steps in industrial CAM production. References: M. H. Lee, Y. J. Kang, S. T. Myung, and Y. K. Sun, Electrochimica Acta, 50 (4), 939-948 (2004). F. Riewald, P. Kurzhals, M. Bianchini, H. Sommer, J. Janek, and H. A. Gasteiger, Journal of The Electrochemical Society, 169 (2), 020529 (2022). Z. Xu, L. Xiao, F. Wang, K. Wu, L. Zhao, M.-R. Li, H.-L. Zhang, Q. Wu, and J. Wang, Journal of Power Sources, 248 180-189 (2014). Y. K. Sun, S. T. Myung, B. C. Park, J. Prakash, I. Belharouak, and K. Amine, Nat Mater, 8 (4), 320-324 (2009). M. Kosmulski, Adv Colloid Interface Sci, 152 (1-2), 14-25 (2009). I. Kolthoff, The Journal of Physical Chemistry, 36 (3), 860-881 (2002). Figure 1

Over the many years of cathode active material research for lithium-ion batteries, LiNixCoyMnzO2 (NCM, x+y+z = 1) have emerged as one of the most promising chemistries for mass application.[1] The exact NCM elemental composition is directly linked to the material properties which in turn influence energy density, durability, safety and cost of the final products.[2] The individual contributions of Ni, Mn and Co have been heavy investigated in both industry and academia to find the best trade-offs between all properties, nowadays settling for materials with Ni contents > 80 %.[3] The composition of NCM materials is determined in the precipitation step of the mixed transition metal hydroxide precursors.[4] At laboratory scale, precursor precipitation is typically operated in batch mode. However, the precipitation in continuous stirred tank (CSTR) reactors is industrially favourable due to the higher space-time-yield, thus reducing the overall production cost. In comparison to batch-type precursors that exhibit a homogeneous µm-sized spherical particle morphology, CSTR-type precursors can be distinguished by their broad particle size distribution due to the intrinsic residence time distribution of particles in the reactor setup. Although rarely discussed, this phenomenon is accompanied by a particle-size dependent elemental composition of the precursor particles, consequently impacting the battery performance. Besides inductive coupled plasma-optical emission spectroscopy (ICP-OES) or mass spectrometry (ICP-MS) that both determine the bulk elemental composition of NCMs and their precursors, scanning electron microscopy (SEM) or transmission electron microscopy (TEM) energy dispersive X-ray (EDX) analysis can access local elemental inhomogeneities. However, both methods are tedious in both acquisition and data evaluation. In this work, an alternative method to determine the elemental composition of individual µm sized particles is presented using a laser ablation (LA) system coupled to an ICP-MS. By the example of a Ni0.91Co0.045Mn0.045(OH)2 CSTR precursor, particle size dependent elemental inhomogeneities are demonstrated. An enrichment of Ni in larger particles with a concomitant enrichment of Co and Mn in smaller particles is identified, which persists after thermal lithiation of the precursors. The results of the LA-ICP-MS analysis are cross-validated with both SEM-EDX and TEM-EDX. Furthermore, the impact of the process conditions during precipitation on the elemental inhomogeneity are elaborated by the comparison of a series of Ni0.83Co0.12Mn0.05(OH)2 precursors precipitated at varying pH. Finally, future applications of the method are proposed. G. E. Blomgren, Journal of The Electrochemical Society, 164, A5019 (2017). H.-J. Noh, S. Youn, C. S. Yoon and Y.-K. Sun, Journal of Power Sources, 233, 121 (2013). W. Li, E. M. Erickson and A. Manthiram, Nature Energy, 5, 26 (2020). H. Dong and G. M. Koenig, CrystEngComm, 22, 1514 (2020).