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widely used in consumer electronics due to the advantages of rechargeability and high energy density. [4][5][6] Commercial LIBs are usually fabricated in fixed geometry such as cylinder, coin, and pouch with scrolled or layered planar sheets for each component. [7] Nevertheless, LIBs with customizable geometry are desired for specialized applications such as wearable electronics [8,9] and on-device power systems [10,11] for automobile and aerospace vehicles, For example, LIBs can be made into a watchband to power an electronic watch, [12] which eliminates the installation and replacement of coin cell. To meet such demands, irregular, customizable LIBs in arbitrary geometry on 3D structures along with the packaging, integrating, and manufacturing approaches need to be developed. So far, the most effective solution to fabricate freeform LIBs is additive manufacturing (AM, popularly known as 3D printing). [13][14][15][16] The on-demand and layer-by-layer manufacturing method has provided the flexibility to accommodate customizable designs of 3D LIBs.Electrodes are the most essential components of LIBs. Currently reported AM processes for electrodes are mostly based on extrusion printing, [17][18][19][20][21][22][23][24] with a few reports on other ink-based printing methods including inkjet printing [25] and aerosol printing. [10] In extrusion printing, active material laden inks are directly deposited and powered by ultra-high air pressure. The materials are extruded into semi-solidified and self-supportive filaments owing to the shear-thinning characteristics of the highly viscous inks. Main advantage of AM processes is the capability of printing electrodes in arbitrary geometry. For example, Lacey et al. and Wang et al. demonstrated 3D printing of mesh and lattice structured electrodes, which effectively introduced macroporosity and facilitated the transportation of lithium-ions under high charging/discharging rate. [18,23] The flexibility in printed geometry also enables the fabrication of electrodes with high aspect ratio and high areal capacity, which are usually not processable by conventional slurry-casting method. Sun et al. first printed high aspect ratio, multilayer, interdigitated electrodes for micro-LIBs with high energy density and power density. [21] Despite these advantages, in extrusion-printing, composition and rheological behaviors of inks are demanding due to the requirements in clogging prevention, substrate bonding and shape maintenance. [19,20] Alternatively, aerosol printing Lithium-ion batteries (LIBs) are widely used in consumer electronics due to their rechargeability and high energy density. Commercial LIBs are fabricated in fixed geometries such as cylinder, coin, and pouch. However, for specialized applications such as wearable electronics and on-device power systems, customizable LIBs with arbitrary geometry on threedimensional (3D) structures need to be developed. For this purpose, aerosol printing is uniquely suitable due to its flexible working distance, allowing deposition on nonp...

An atomic layer deposition (ALD) coating on active materials of a lithium ion battery is a more effective strategy for improving battery performance than other coating technologies. However, substantial uncertainty still remains about the underlying physics and role of the ALD coating in improving battery performance. Although improvement in the stability and capacity of CeO thin film coated particles for batteries has been reported, a detailed and accurate description of the mechanism has not been provided. We have developed a multiphysics-based model that takes into consideration stress mechanics, diffusion of lithium ion, and dissolution of transition-metal ions of spinel LiMnO cathode. The model analyzes how different coating thicknesses affect diffusion-induced stress generation and, ultimately, crack propagation. Experimentally measured diffusivity and dissolution rates were incorporated into the model to account for a trade-off between delayed transport and prevention of side reactions. Along with experimental results, density functional theory results are used to explain how a change in volume, due to dissolution of active material, can affect battery performance. The predicted behavior from the model is well-matched with experimental results obtained on coated and uncoated LiMnO-Li foil cells. The proposed approach and explanations will serve as important guidelines for thin film coating strategies for various battery materials.

The degree of metal dissolution of cathode materials is a critical parameter in determining the performance of lithium-ion batteries (LIBs). Ultra-thin coated cathode particles, fabricated via atomic layer deposition (ALD), exhibit superior battery performance over that of bare particles. Therefore, it is generally believed that a coating layer protects the particles from metal dissolution of active materials, which is a critical cathode degradation mechanism. However, it is observed that ultra-thin CeO 2 coating intensified the Mn dissolution of LiMn 2 O 4 (LMO) during cycling of LIBs, whereas ultra-thin Al 2 O 3 coating tended to inhibit Mn dissolution. A detailed density functional theory (DFT) study is carried out to explain these experimental observations by analyzing interaction of Mn atoms with neighboring electrode atoms in terms of energetic and structural aspect. All atomic and electronic analyses are consistent with the experimental observations. Several common materials are investigated as possible ALD coatings for LIBs to provide general insight, and it is found that Mn dissolution can be suppressed or accelerated depending on the material selection. This is the first report finding that depending on the coating material, metal dissolution can be accelerated, providing new insights into the impact of ALD coating materials on metal dissolution in cathode materials. potential, superior capacity, a long life cycle, and a sufficiently broad range of working temperatures. Although metal oxide cathodes satisfy the criteria, they suffer from an inevitable metal dissolution degradation process. In the dissolution degradation process, transition metal ions dissolve from cathode active materials and can deposit onto the anode, causing severe cell aging and irreversible side reactions that reduce performance. [1,2] For high performance cathode materials such as LiNi x Mn y Co z O 2 (NMC, x + y + z = 1), LiNi 0.5 Mn 1.5 O 4 (LNMO), and LiMn 2 O 4 (LMO), metal dissolution (Ni, Co, Mn, etc.) is severe, and, furthermore, it was found that in such cathode materials, which are composed of two or more transition metals, there is no preferential dissolution among the constituent metals. [3] To study the metal dissolution phenomena, manganese is an excellent candidate for intensive study of the fundamental interfacial processes and side reactions at cathode surfaces because of its low toxicity, low cost, and the high natural abundance of Mn, [4][5][6][7][8][9][10][11][12] which allows it to be used in several promising cathode materials, such as NMC, LNMO, and LMO. It has been published that Mn dissolution accounts for 23% and 34% of overall capacity degradation at room temperature and at 55°C [13] in LMO, respectively. The major reason for LMO degradation, [14][15][16][17][18] as well as for other metal oxide cathode materials, [3,[19][20][21] has been identified as structural changes in the material due to phase transformations, alternation of intrinsic properties (such as electronic and ionic conductivity), dissoluti...

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