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Interest in developing high performance lithium-ion rechargeable batteries has motivated research in precise control over the composition, phase, and morphology during materials synthesis of battery active material particles for decades. Coprecipitation, as one of the most reported methods in the literature to produce precursors for lithium-ion battery active materials, has drawn attention due to its simplicity, scalability, homogeneous mixing at the atomic scale, and tunability over particle morphology. This highlight summarizes the advancements that have been made in producing crystalline particles of tunable and complex morphologies via coprecipitation for use as lithium-ion battery precursor materials. Comparison among different crystallization reagents, solution conditions that influence the properties of crystal particles, and the fundamental knowledge from equilibrium and/or kinetic study of the coprecipitation processes, are systematically discussed. The research reports and guiding principles summarized in this highlight are meant to improve selections made by researchers to efficiently determine synthesis conditions. In addition, it is desired that the methods applied from the study of crystallization will inspire researchers to pursue further investigation of the nucleation and growth mechanisms of these coprecipitation processes, which will be necessary to achieve truly predictive particle synthesis. 

Multicomponent transition metal oxides are among the most successful lithium-ion battery cathode materials, and many previous reports have described the sensitivity of final electrochemical performance of the active materials to the detailed composition and processing. Coprecipitation of a precursor template is a popular, scalable route to synthesize these transition metal oxide cathode materials because of the homogeneous mixing of the transition metals within the particles, and the morphology control provided by the precursors. However, the deviation of the precursor composition from feed conditions is a challenge that has generally not been reported in previous studies. Using a target final material of the high voltage spinel LiMn 1.5 Ni 0.5 O 4 as an example, we show in this study that the compositional deviation caused by coprecipitation can be significant under certain conditions, impacting the calcined final material structure and electrochemical properties. The study herein provides insights into the role of solution equilibrium and rate of precipitation of the transition metals during precipitate formation on precursor, and thus final active material, composition. Such knowledge is necessary to rationally predict and tune multicomponent battery precursor compositions synthesized via coprecipitation with high levels of accuracy. 

Switching from organic to aqueous solvents for battery electrode processing is desirable due to both safety and cost advantages. Lithium iron phosphate (LFP) is considered a cathode material for aqueous processing due to its demonstrated chemical compatibility with water, in addition to its favorable cost, safety, electrochemical performance, and environmental advantages as a battery active material. All research on LFP stability in water has been conducted in a scenario where LFP is aged in stagnant water, or surrounded by water when confined within a composite electrode. However, a much accelerated degradation in the electrochemical performance of LFP when it is in contact with water and exposed to mechanical agitation is demonstrated. Changes to LFP are probed using a combination of materials characterization methods. Although there are no significant changes to the bulk particle structure and morphology, significant particle surface damage and compositional modifications are observed. These results suggest that the systems where LFP is exposed to agitation in an aqueous environment, such as in aqueous battery electrode processing or in aqueous slurry electrodes, need to be carefully investigated for potential changes to the LFP surface environment under relevant processing conditions.